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Nov 1994

Volume 12, Issue 6, pp. 3069-4054


Threading dislocations in GaAs grown with free sidewalls on Si mesas

J. Knall, L. T. Romano, B. S. Krusor, D. K. Biegelsen, and R. D. Bringans

J. Vac. Sci. Technol. B 12, 3069 (1994); http://dx.doi.org/10.1116/1.587562 (6 pages) | Cited 1 time

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We have studied the mechanisms that determine the density and structure of threading dislocations (TDs) in GaAs on Si by growing GaAs films on continuous Si substrates and on 10–34‐μm‐wide Si mesas that provided free‐sidewall growth. The effects of a soft ZnSe interlayer and of postgrowth annealing to 850 °C were also investigated. TD densities were accurately determined using large area plan‐view transmission electron microscopy. Burgers vector analysis of the TDs showed that threading segments associated with both sessile 90° misfit dislocations and glissile 60° misfit dislocations were present after growth. A difference in dislocation structure between the annealed and unannealed samples was observed. It was also found that the dislocations were unaffected by proximity to free sidewalls and by the ZnSe interlayer. The results indicate that dislocation interactions during the early stages of growth determine the structure and density of TDs in as‐grown films. It was also concluded that plastic relaxation of thermal mismatch strain during cooldown from the growth temperature does not strongly affect the TD density in the films. This is in contradiction to previous studies.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Growth of beryllium doped AlxGa1−xAs/GaAs mirrors for vertical‐cavity surface‐emitting lasers

M. G. Peters, B. J. Thibeault, D. B. Young, A. C. Gossard, and L. A. Coldren

J. Vac. Sci. Technol. B 12, 3075 (1994); http://dx.doi.org/10.1116/1.587563 (9 pages) | Cited 13 times

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We experimentally compare a variety of techniques used in the growth of p‐type Be doped AlxGa1−xAs/GaAs distributed Bragg reflector (DBR) mirrors to reduce the operating voltages of vertical‐cavity surface‐emitting lasers (VCSELs). The AlxGa1−xAs composition, average doping concentration, grading and doping profile at the interfaces, and growth temperature are all important parameters to achieve low voltage mirrors with low optical loss and high thermal conductivity. Specifically we examine band‐gap engineering techniques to flatten the voltage barrier at the DBR mirror layer interfaces. We demonstrate VCSELs with low operating voltages (1.7–3.0 V) and high continuous wave room‐temperature power‐conversion efficiencies and output powers.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Nearly ideal characteristics of GaAs metal–insulator–semiconductor diodes by atomic layer passivation

Yoshinori Wada and Kazumi Wada

J. Vac. Sci. Technol. B 12, 3084 (1994); http://dx.doi.org/10.1116/1.587564 (6 pages) | Cited 3 times

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An atomic layer passivation (ALP) structure for GaAs is studied by fabricating metal–insulator–semiconductor (MIS) diodes. An atomically thin GaP layer is grown on a (100) surface of GaAs to form the ALP structure. MIS diodes are fabricated on the GaP surface by depositing SiO2 as the insulator. Between 1 MHz and 20 Hz, the maximum capacitances are very close to the insulator capacitance without frequency dispersion. The accumulation and inversion conditions are observed in the capacitance–voltage characteristics of the diodes at room and low temperature. The capacitance–voltage characteristics of diodes with and without ALP are compared. The results show that ALP unpins the surface Fermi level which can be displaced nearly throughout the GaAs band gap by the applied gate voltage. Interface trap density is estimated to be about 5×1011 cm−2 eV−1 near the midgap. The influence of the SiO2 plasma deposition process on the interface characteristics is also described, and the mechanism of unpinning is discussed.
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85.30.Kk Junction diodes
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Surface oxidation of selenium treated GaAs(100)

T. Scimeca, Y. Watanabe, F. Maeda, R. Berrigan, and M. Oshima

J. Vac. Sci. Technol. B 12, 3090 (1994); http://dx.doi.org/10.1116/1.587483 (5 pages) | Cited 4 times

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The surface oxidation of Se treated GaAs(100) has been investigated in order to understand in greater detail the degradation of the Se passivated GaAs surface upon exposure to atmosphere. An increase in band bending is initially observed at relatively low exposure times, which corresponds to an increase in the O 2p intensity in the valence band. At this stage, oxygen is thought to weakly physisorb at the Ga vacancy sites. At intermediate exposure levels, the other unadsorbed oxygen atom of O2 attacks the nearest Ga atom. The bond between the nearest Ga atom and Se is then severed, resulting in the formation of Se, which closely resembles amorphous Se. Ultimately, both Se states are converted to this amorphouslike state and at longer exposure times are oxidized. At longer exposure times, the oxidation of Se is also accompanied by As oxidation. In contrast to S treated GaAs, Se/GaAs is relatively resistant to oxidation where only about 10% of the As is oxidized (As2O3) after 180 min of exposure versus oxidation of 35% of the As atoms for S/GaAs after only 20 min of atmosphere exposure. This relative oxidation resistance is attributed to greater penetration of Se into GaAs relative to S into GaAs.
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81.65.-b Surface treatments

Si‐indiffusion and O‐outdiffusion processes at Si/SiO2/GaAs‐oxides/GaAs structures: Implications in SiO2 formation and GaAs regrowth

I. Jiménez and J. L. Sacedón

J. Vac. Sci. Technol. B 12, 3095 (1994); http://dx.doi.org/10.1116/1.587484 (8 pages) | Cited 1 time

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The formation of SiO2/GaAs structures from reduction of substrate oxides has been studied by x‐ray photoemission spectroscopy. GaAs oxides reduction is induced by Si deposition and subsequent high‐temperature annealing. The deposition of Si on oxidized GaAs surfaces promotes the reduction of the GaAs oxides and the formation of SiO2, Si diffusion being the predominant process. This mechanism allows one to obtain SiO2 thicknesses up to 15 Å. Over this limit Si diffusion is negligible, Si nucleates on top of the Si dioxide layer, and a substantial amount of GaAs oxides can remain unreduced between the SiO2 layer and the GaAs substrate. Subsequent annealing to 870 K produces the disappearance of the GaAs oxides together with loss of Si atoms. A process based on breakage of the Ga–O bonds with Ga atoms remaining between SiO2 and the substrate, and oxygen atoms diffusing through the SiO2 to the outer surface, is consistent with the experimental results. The oxygen atoms react with the outer Si layer, showing an etchant behavior, and the Ga and As atoms supplied by their oxides recombine to form GaAs.
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68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Electroreflectance of Ag/GaAs

Dong‐Po Wang

J. Vac. Sci. Technol. B 12, 3103 (1994); http://dx.doi.org/10.1116/1.587485 (4 pages) | Cited 1 time

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The electroreflectance (ER) spectra of Schottky‐barrier Ag/GaAs have been measured at various dc bias voltages (Vbias). It is known that the surface electric field can be deduced from the period of the Franz–Keldysh oscillations (FKO) of ER. Therefore, the built‐in voltage (Vbi) and the carrier concentration in the depletion region can be calculated by the assumption of a constant charge distribution in the depletion region. In this article, we show that Vbi can also be determined from the amplitude of the FKO as a function of Vbias in the forward biased region. The Vbi determined by the above two different methods have been verified to be in good agreement.
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73.30.+y Surface double layers, Schottky barriers, and work functions
78.20.Jq Electro-optical effects

Dead‐time‐free selective dry etching of GaAs/AlGaAs using BCl3/CHF3 plasma

Hiroshi Takenaka, Yoshiro Oishi, and Daisuke Ueda

J. Vac. Sci. Technol. B 12, 3107 (1994); http://dx.doi.org/10.1116/1.587486 (5 pages) | Cited 1 time

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A dead‐time‐free selective dry etching of GaAs/AlGaAs using mixed plasma of BCl3 and CHF3 has been developed. The selectivity of the etching for GaAs/AlGaAs is strongly dependent on the flow ratio R, where R=(flow of CHF3)/(flow of CHF3+ flow of BCl3). It was also found that the angle of the sidewall can be varied from overhanging to tapered by controlling R. No undercutting was observed. Complete vertical recess structures with sub‐quarter micrometer width were obtained at R=40% where a selectivity of 30 was attained. The roughness of the etched surface was also strongly dependent on R. A smooth etched surface was obtained where R was larger than 40% even for bulk GaAs. Complete square‐shaped vertical recessed structures with sub‐quarter micrometer width were obtained in a GaAs/AlGaAs epitaxial wafer. This etching process is very applicable for the fabrication of GaAs/AlGaAs heterojunction devices such as the GaAs modulation doped field‐effect transistor and the heterojunction bipolar transistor.
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81.65.-b Surface treatments
85.30.-z Semiconductor devices

Continuous ultra‐dry process for enhancing the reliability of ultrathin silicon oxide films in metal–oxide semiconductors

Hiroshi Yamada

J. Vac. Sci. Technol. B 12, 3112 (1994); http://dx.doi.org/10.1116/1.587487 (6 pages) | Cited 17 times

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Time‐dependent dielectric breakdown lifetime of 5‐nm‐thick silicon oxide films in metal–oxide semiconductors (MOSs) fabricated by a new continuous ultra‐dry process was investigated. In this process, three fundamental stages in MOS diode fabrication—oxidation, amorphous‐Si electrode film formation, and annealing to crystallize the electrode film—are continuously performed in an ultra‐dry ambient with less than 100 ppb moisture concentration (humidity). The lifetime for the continuously ultra‐dry processed MOS diodes is considerably larger than that of conventional ones produced in an ambient with more than 100–200 ppm humidity. The stress‐induced positive charges that affect lifetime are mainly generated and trapped near both oxide interfaces. This indicates that the interface condition is probably improved by the present process.
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85.30.-z Semiconductor devices

Investigation of electron source and ion flux uniformity in high plasma density inductively coupled etching tools using two‐dimensional modeling

Peter L. G. Ventzek, Michael Grapperhaus, and Mark J. Kushner

J. Vac. Sci. Technol. B 12, 3118 (1994); http://dx.doi.org/10.1116/1.587488 (20 pages) | Cited 71 times

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Inductively coupled plasma (ICP) sources are being developed as reactors for high plasma density (1011–1012 cm−3), low‐pressure (<10–20 mTorr) etching of semiconductors and metals for microelectronics fabrication. Transformer coupled plasmas (TCPs) are one variant of ICP etching tools which use a flat spiral coil having a rectangular cross section powered at radio frequencies (rf) to produce a dense plasma in a cylindrical plasma chamber. Capacitive rf biasing of the substrate may also be used to independently control ion energies incident on the wafer. The uniformity of generating the plasma and the uniformity of the flux of reactants to the substrate are functions of the geometry and placement of the coil; and of the materials used in the construction of the chamber. In this article, we use results from a two‐dimensional model to investigate design issues in TCPs for etching. We parametrize the number of turns and locations of the coil; and material properties of the reactor. We find that at low pressure, designs which produce ionization predominantly at larger radii near the edge of the wafer produce more uniform ion fluxes to the substrate. This results from a ‘‘converging’’ ion flux which compensates for losses to lateral surfaces. Careful attention must be paid to metal structures in the vicinity of the coils which restrict the azimuthal electrical field. This situation results in reduced power deposition at large radii, which can be compensated by over sizing the coil or by using auxiliary solenoidal coils. The plasma and neutral transport, dominated by diffusion, treats the advective flow from the gas inlets and pump port as local sources and sinks which are rapidly volume averaged.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Profile simulation of electron cyclotron resonance planarization of an interlevel dielectric

A. H. Labun

J. Vac. Sci. Technol. B 12, 3138 (1994); http://dx.doi.org/10.1116/1.587489 (7 pages) | Cited 1 time

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The planarization of SiO2 interlevel dielectric layers by electron cyclotron resonance reactors has been modeled as the outcome of simultaneous sputter etching and plasma‐enhanced chemical vapor deposition. This combination of etching and deposition has been simulated by the repeated sequential execution of two third‐party topography evolution codes, one for each process. The simulations reproduced observed profiles and gap‐filling properties for etch/deposition ratios from 0.45 to 0.30 and also illustrated the origin of cracks in certain nonideal gaps. The influence of the width and separation of the metal lines over which deposition was simulated was also reproduced.  
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Morphology of anodically etched Si(111) surfaces: A structural comparison of NH4F versus HF etching

R. Houbertz, U. Memmert, and R. J. Behm

J. Vac. Sci. Technol. B 12, 3145 (1994); http://dx.doi.org/10.1116/1.587490 (4 pages) | Cited 3 times

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We present a comparative scanning tunneling microscopy (STM) study on the porous layer formation in two different fluoride containing solutions, HF/ethanol and concentrated NH4F solution. After etching in dilute HF solution the samples display a high density of micropores with typical diameters ranging from 5 to 25 nm, while NH4F treated surfaces display shallow macropores of several hundred nm in diameter. These structural differences are discussed by comparing the different activity of both solutions for chemical etching of Si in the absence of an external potential, which provides an additional reaction channel also under anodic conditions.
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.45.-h Electrochemistry and electrophoresis

Solid source diffusion from agglomerating silicide sources. II. Experimental results and analysis

J. Y. Tsai, C. M. Osburn, and C. A. Canovai

J. Vac. Sci. Technol. B 12, 3149 (1994); http://dx.doi.org/10.1116/1.587491 (11 pages) | Cited 1 time

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The interface roughness and dopant diffusion behavior of CoSi2 silicide‐as‐a‐diffusion‐source (SADS) samples annealed at different temperatures and for different periods of time were examined using secondary ion mass spectrometry, with conditions optimized to characterize the solid source diffusion profile. A convolution/deconvolution methodology was applied to derive the root‐mean‐square silicide/silicon interface roughness and to correct the dopant profiles. The model which was developed to relate the interface roughness and the sheet resistance increase of the agglomerated silicide films worked quite well over the temperature and time range of interest. The measured activation energies confirmed that silicide roughening and its resistance increase share the same kinetic mechanism. Arsenic implanted CoSi2 samples exhibited a better thermal stability than those implanted with BF2. No obvious enhancement or retardation of boron diffusion was seen, while a transient enhancement of arsenic diffusion was observed, but not as pronounced as previously reported. Furthermore, in cases where dopant is strongly segregated or exhibits a marked step at the silicide/silicon interface, even the convolution/deconvolution technique was not able to adequately determine the actual dopant diffusion.
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68.35.Fx Diffusion; interface formation
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Advanced fabrication techniques of three‐dimensional microstructures for future electronic devices

Ryuichi Ugajin, Akira Ishibashi, and Yoshifumi Mori

J. Vac. Sci. Technol. B 12, 3160 (1994); http://dx.doi.org/10.1116/1.587492 (6 pages) | Cited 2 times

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Methods to fabricate three‐dimensional microstructures for mesoscopic devices are discussed. Reactive ion etching and metalorganic chemical vapor deposition experiments were performed to obtain structures with various potential applications. For example, a structure with a pyramid shape is suitable for a field emitter, and a structure with an X‐shaped oblique groove is suitable for a vacuum microtransistor. The results are also applicable to fabrication of mesoscopic three‐dimensional structures based on GaAs/AlGaAs heterostructures.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Nanofabrication on electron beam resist using scanning tunneling microscopy

A. Archer, J. M. Hetrick, M. H. Nayfeh, and I. Adesida

J. Vac. Sci. Technol. B 12, 3166 (1994); http://dx.doi.org/10.1116/1.587493 (5 pages)

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We report the results of nanofabrication using a scanning tunneling microscope on silicon coated with SAL 601 electron beam resist. The process is found to be complex, switching over from producing structures that appear as mounds to structures that appear as grooves as the biasing voltage drops below 6 V. Mound‐like structures of width as small as 18 nm with a 2 nm corrugation, and structures like grooves as small as 15 nm in width and 0.5 nm in depth were fabricated. Somewhat narrower but shallower structures can be produced in the resist, but we believe that these results are reaching the practical limit of fabrication.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication of noble‐metal nanoconstrictions and observation of conductance fluctuations

E. Scheer, H. v. Löhneysen, and H. Hein

J. Vac. Sci. Technol. B 12, 3171 (1994); http://dx.doi.org/10.1116/1.587494 (5 pages) | Cited 2 times

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We describe the fabrication of planar metallic nanostructures with lateral dimensions down to about 80 nm and thicknesses varying from 15 to 50 nm. We use a lift‐off process with a polymethylmethacerylate bilayer resist on silicon substrate and an electron beam writer system for microfabrication. The noble‐metal layers are deposited by thermal evaporation. The geometries are point contacts, rings, and wires in two‐lead configuration. We discuss measurements of the magnetoconductance at very low temperatures and in magnetic fields up to 4 T in dependence of the width of the samples. Here the electron transport is in the diffusive regime and the width dependence of the universal conductance fluctuations is investigated.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
72.15.Gd Galvanomagnetic and other magnetotransport effects

Atomic force microscope tip radius needed for accurate imaging of thin film surfaces

K. L. Westra and D. J. Thomson

J. Vac. Sci. Technol. B 12, 3176 (1994); http://dx.doi.org/10.1116/1.587495 (6 pages) | Cited 11 times

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This article discusses the distortion of atomic force microscope (AFM) images of columnar thin films caused by the finite size of the AFM tip. The amount of distortion in an image depends on the relative sharpness of the tip and the surface features. Two‐dimensional numerical simulations were used to predict the effect of this distortion on the accuracy of AFM images. We propose that the ratio of the radius of the curvature of the features in an AFM image to the radius of the tip (RAFM/Rtip) provides an effective measure of the degree of tip induced distortion in AFM images of columnar thin films. Using simulations, we show that, for the distortion in an AFM image of columnar thin films to be undetectable by eye, the radius of the curvature of the features in the AFM image must be 10 times larger than the radius of the tip. At the other extreme, if the radius of the curvature features in the AFM image is less than twice the radius of the AFM tip, the images are severely distorted and not representative of the surface of the thin film. From a study of 23 different thin films we found that for only 6 (26%) thin films did the AFM images have distortion undetectable by eye. For 7 (30%) of the thin films, the AFM images were sufficiently distorted to be nonrepresentative of the surface of the thin film.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.55.-a Thin film structure and morphology

Microfabrication of arrays of scanning electron microscopes

A. D. Feinerman, D. A. Crewe, and A. V. Crewe

J. Vac. Sci. Technol. B 12, 3182 (1994); http://dx.doi.org/10.1116/1.587496 (5 pages) | Cited 2 times

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Arrays of miniature scanning electron microscopes (MSEMs) can conceivably solve the low throughput rates traditionally associated with direct write lithography. An inexpensive and accurate method for fabricating arrays of electron beam columns has been proposed: horizontal surface mounted electrode sectioning (slicing). This method combines the precision of semiconductor processing and fiber optic technology to fabricate macroscopic structures consisting of charged particle sources, deflecting and focusing electrodes, and detectors. Slicing can be used to miniaturize columns operating at 10–50 kV. Voltages in this range are required to produce characteristic x rays for elemental analysis. Slicing should allow the SEM to be considerably reduced in size while preserving performance and also can be adapted to produce arrays of MSEMs. The performance of the proposed sliced columns is discussed and initial results indicate that a 15 kV sliced MSEM 8.5 mm long will have 2.2 nm resolution.
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85.45.-w Vacuum microelectronics
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Reliable tip preparation for high‐resolution scanning tunneling microscopy

O. Albrektsen, H. W. M. Salemink, K. A. Mørch, and A. R. Thölen

J. Vac. Sci. Technol. B 12, 3187 (1994); http://dx.doi.org/10.1116/1.587497 (4 pages) | Cited 18 times

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We describe a method to prepare electron emitters (tips) designed to achieve routine atomic resolution in a scanning tunneling microscope. Highly reliable results were obtained with repeated sputter‐anneal processes in ultrahigh vacuum using polycrystalline tungsten wires as the base material. A tip apex radius of less than 5 nm and an atomic resolution of III–V (110) semiconductor surfaces are routinely obtained. The analysis involves scanning electron microscopy, transmission electron microscopy, scanning tunneling microscopy, and current–voltage characteristics in the field emission regime.
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85.45.-w Vacuum microelectronics
82.80.-d Chemical analysis and related physical methods of analysis

Reduced effects of laser illumination on field emission due to the finite duration of quantum tunneling

Mark J. Hagmann

J. Vac. Sci. Technol. B 12, 3191 (1994); http://dx.doi.org/10.1116/1.587498 (5 pages) | Cited 5 times

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Laser illumination of a field emitting tip modulates the barrier by superimposing the electric field of light. Numerical simulations suggest that the dependence of tunneling current on the frequency of this modulation can serve as a basis for determining the duration of barrier traversal. Modulation increases the emitted current at low frequencies, but this effect disappears at modulation frequencies much greater than the reciprocal of the traversal time.
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03.65.Sq Semiclassical theories and applications
03.65.Ta Foundations of quantum mechanics; measurement theory
79.70.+q Field emission, ionization, evaporation, and desorption

Submicron patterning of thin cobalt films for magnetic storage

R. M. H. New, R. F. W. Pease, and R. L. White

J. Vac. Sci. Technol. B 12, 3196 (1994); http://dx.doi.org/10.1116/1.587499 (6 pages) | Cited 51 times

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We are investigating the feasibility of a recording medium in which each bit of information is stored in a single‐domain magnetic particle. To this end we have developed a procedure for high‐resolution patterning of magnetic recording films using direct write electron‐beam lithography and a multistep sputter etching process. We have used this procedure to define small islands of polycrystalline magnetic thin film with feature sizes down to 0.1 μm. The patterning process is suitable for many different kinds of magnetic films, including single‐crystal epitaxially grown films, and is designed to minimize physical and chemical damage to the magnetic material being patterned. Both atomic force microscopy and x‐ray photoemission spectroscopy have been used to establish that the magnetic islands patterned using this process are physically isolated from each other.  
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Structure of Fe/δ‐Mn superlattices grown by molecular beam epitaxy

J. Pohl, E. U. Malang, B. Scheele, J. Köhler, M. Ch. Lux‐Steiner, and E. Bucher

J. Vac. Sci. Technol. B 12, 3202 (1994); http://dx.doi.org/10.1116/1.587500 (6 pages) | Cited 4 times

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We report on the successful epitaxial growth of the bcc high temperature modification δ‐manganese in Fe/Mn multilayers on Ge(001) and GaAs(001) substrates at room temperature using molecular beam epitaxy. Both structure and growth mode were observed in situ by reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy, respectively. RHEED and x‐ray measurements confirmed the superlattices to grow coherently in the [001] orientation, given by the orientation of the substrates. The obtained relationship in orientation is (001)Fe/δ‐Mn∥(001)Ge, [100]Fe/δ‐Mn∥[100]Ge. RHEED revealed a slight tetragonal distortion of the cubic lattice parameters of Mn (a=2.86 Å, c=2.79 Å). The Fe/Mn multilayers form abrupt layers; the growth mode of the individual layers could be approached by the layer‐by‐layer model. No island formation could be detected.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Reactive ion etching of RuO2 thin films using the gas mixture O2/CF3CFH2

Wei Pan and Seshu B. Desu

J. Vac. Sci. Technol. B 12, 3208 (1994); http://dx.doi.org/10.1116/1.587501 (6 pages) | Cited 11 times

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RuO2 thin films were successfully patterned by the reactive ion etching technique in O2/CF3CFH2 using SiO2 films as etch masks. The processing parameters have been optimized. The highest etch rate (1600 Å/min) was obtained by introducing a small amount (2.5%) of CF3CFH2 gas in O2. The etched surfaces were clean and shiny; the etched profiles were anisotropic and smooth. The etch rate ratios of RuO2 to SiO2, Si, and lead zirconate titanate (PZT) were studied as a function of CF3CFH2 gas concentration and the optimized ratios were obtained as 4:1 for RuO2 to SiO2, 14:1 for RuO2 to PZT, and 5:1 for RuO2 to Si. The surface chemistry of RuO2 films etched with different gas compositions was studied by x‐ray photoelectron spectroscopy. Based on these experimental data, an etching mechanism is proposed.
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81.65.-b Surface treatments
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Effects of sulfur passivation and rapid thermal annealing on the electrical properties of InP metal–insulator semiconductor Schottky diodes

G. Eftekhari

J. Vac. Sci. Technol. B 12, 3214 (1994); http://dx.doi.org/10.1116/1.587502 (4 pages) | Cited 2 times

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The effects of sulfur passivation and rapid thermal annealing on the electrical characteristics of InP metal–insulator semiconductor Schottky diodes are investigated. Passivation causes a moderate increase in barrier height and decrease in reverse current. Further reduction in the reverse current is obtained after rapid thermal annealing. The passivated diodes show a very good thermal stability. Bond formation at the interface and charge injection into the oxide are used to explain the observations.
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85.30.Kk Junction diodes
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

SiC microcomponents via reaction of C60 with silicon

M. Balooch and A. V. Hamza

J. Vac. Sci. Technol. B 12, 3218 (1994); http://dx.doi.org/10.1116/1.587503 (2 pages) | Cited 6 times

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Free silicon carbide microcomponents are produced on silicon wafers. Silicon carbide is selectively grown on silicon by reaction of C60 with the substrate at surface temperatures between 900 and 1200 K. Because of the large lattice mismatch (∼20%), the adhesion of the silicon carbide film is weak after growth of 1–1.5 μm thickness. An atomic force microscope tip can subsequently maneuver the microcomponent to a desired location on the wafer.  
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Elimination of long‐term calibration drift in molecular beam epitaxy by cooling the source flange

E. C. Larkins, H. Thaden, H. Betsche, G. Eichin, and J. D. Ralston

J. Vac. Sci. Technol. B 12, 3220 (1994); http://dx.doi.org/10.1116/1.587504 (3 pages)

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Drifts in the growth rate calibration with time constants of the order of hours are observed during molecular beam epitaxy growth, adversely influencing the calibration stability and reproducibility. The principal cause of these drifts was found to be high, time‐dependent source flange temperatures (≳40 °C) at the thermocouple feedthroughs. The installation of water‐cooled blocks on the furnace flanges eliminated this long‐term drift and improved the calibration reproducibility by a factor of 3. In addition, these cooling blocks significantly reduced the ion‐pump current in the growth chamber, presumably due to reduced outgassing of the source flange.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ultra‐large‐scale integration device scaling and reliability

Chenming Hu

J. Vac. Sci. Technol. B 12, 3237 (1994); http://dx.doi.org/10.1116/1.587505 (5 pages) | Cited 4 times

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Assuming that the requisite lithography and planarization techniques will be available, this article reviews the goals of metal–oxide semiconductor field effect transistor (MOSFET) scaling and the constraints of low leakage and adequate reliability, highlighting the impact of power‐supply voltage and oxide thickness reductions. Plasma charging damage is discussed. The first identifiable scaling limit is the direct tunneling of gate oxide at 3.5 nm, which may hinder scaling beyond 0.09 μm. From the 0.5‐μm generation onward, MOSFET current will basically cease to increase with scaling. Gate speed will double every four generations rather than two generations of technology as in the past unless technology innovations can pick up the slack.
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85.30.Tv Field effect devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Digital micromirror device and its application to projection displays

Jeffrey B. Sampsell

J. Vac. Sci. Technol. B 12, 3242 (1994); http://dx.doi.org/10.1116/1.587506 (5 pages) | Cited 8 times

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The digital micromirror device (DMD) is a monolithic, micromechanical spatial light modulator. The DMD has been used to implement the first truly digital projection display systems. In these systems, discrete, tilting mirror elements are fabricated from sputter deposited aluminum directly on top of arrays of complementary metal–oxide semiconductor memory cells. The mirrors are switched between two stable tilted states according to whether a ‘‘1’’ or a ‘‘0’’ is stored in the underlying memory location. An optical system illuminates the DMD and projects its image in such a way that the image of each mirror, which represents a single pixel in the projected image, is at full brightness when the mirror is tilted in the ‘‘1’’ state and full darkness when the mirror is tilted in the ‘‘0’’ state. The refresh rate of the memory and the response rate of the mirrors are high enough so that hundreds of memory frames can be displayed during one video frame, and so that each pixel can be on or off in a binary fashion for a portion of the video frame proportional to that pixel’s individual intensity. The digital‐to‐analog conversion of this intensity occurs in the eye/brain of the viewer. The mirrors are typically square, 16 μm on a side, and placed on 17 μm centers. Each mirror tilts 10° from horizontal in each of its two addressed states, so that the ‘‘1’’ state and ‘‘0’’ state are 20° apart. Arrays of mirrors ranging from resolutions of 768×576 mirrors up to 2048×1152 mirrors have been fabricated.The article will describe the fabrication process for the DMD, the optical system used to project the DMD image, and the electronic method of addressing the device. Prototype projection systems will be described and preliminary performance measurements will be presented.
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85.60.Pg Display systems
42.79.Hp Optical processors, correlators, and modulators

Evaluation of overlay accuracy for the x‐ray stepper TOXS‐1

Ryoichi Hirano, Tatsuhiko Higashiki, Hiroshi Nomura, Osamu Kuwabara, Takeshi Nishizaka, and Norio Uchida

J. Vac. Sci. Technol. B 12, 3247 (1994); http://dx.doi.org/10.1116/1.587507 (4 pages) | Cited 1 time

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This article presents the overlay accuracy for the newly developed prototype x‐ray stepper TOXS‐1. Checkerboard gratings on a mask and wafer were used for an optical‐heterodyne interferometry alignment system so that the alignment signals from the mask and wafer gratings can be detected independently without mutual interference. The alignment signal varied slightly with the mask‐to‐wafer gap due to multiple reflection of the alignment beams between the mask and wafer, which deteriorates the alignment accuracy. To reduce the multiple reflection, the mask grating and the mask alignment window were coated with opaque film and antireflecting film, respectively. A 0.025 μm (mean+3σ) overlay accuracy has been achieved for SiO2 processed wafers. The overlay accuracy was further measured for four different kinds of processed wafers, and a 0.035 μm (mean+3σ) accuracy has been obtained except for an aluminum processed wafer.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Design and test of a through‐the‐mask alignment sensor for a vertical stage x‐ray aligner

M. Nelson, J. L. Kreuzer, and G. Gallatin

J. Vac. Sci. Technol. B 12, 3251 (1994); http://dx.doi.org/10.1116/1.587508 (5 pages) | Cited 2 times

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SVG Lithography is building a production‐ready, vertical stage x‐ray proximity aligner. For aligner‐to‐itself overlays, the aligner overlay specification is a mean 3σ value of 33 nm. As part of this aligner specification, each through‐the‐mask (TTM) alignment sensor has a wafer‐to‐mask position measurement accuracy specification with a mean value of 7.1 nm and a 3σ value of 9.2 nm. This article presents a summary of the operation, design, and breadboard testing of the TTM sensor. Breadboard testing with silicon membrane x‐ray masks and process wafers confirms that the design satisfies the specification. Test data to date show position‐sensing repeatability 3σ values that range from 8 to 10 nm. Resist‐induced mean alignment offsets, measured as the separation of bare and resist‐coated wafer marks, were within the acceptable range of 5 to 8 nm.
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85.40.Hp Lithography, masks and pattern transfer

Overlay accuracy of a synchrotron radiation stepper evaluated by two‐mask double exposure

M. Fukuda, M. Suzuki, M. Kanai, H. Tsuyuzaki, A. Shibayama, and S. Ishihara

J. Vac. Sci. Technol. B 12, 3256 (1994); http://dx.doi.org/10.1116/1.587509 (5 pages) | Cited 2 times

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The overlay accuracy of a synchrotron radiation stepper has been evaluated when different masks are used as in actual exposure. Using several masks requires both high repeatability and accurate offset controllability to perform the proper alignment of the stepper. To this end, a two‐mask double‐exposure method that considers mask error has been devised. It yields a 3σ deviation of 25 nm for the overlay repeatability of our SS‐1 stepper. This is almost the same as in the one‐mask double‐exposure method, which means that the stepper effectively has an alignment repeatability of less than 25 nm. In addition, a mask stage is developed to improve the offset controllability and enlarge the stroke. The resolution and stroke of the stage are 20 nm and ±1000 μm, respectively, for x and y directions, and 0.5 and ±800 μrad, respectively, for theta. This stepper facilitates the reduction of alignment offset deviations to less than ±10 nm in the x and y directions and less than ±1.0 μrad for rotation.  
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Subnanometer alignment system for x‐ray lithography

H. Zhou, M. Feldman, and R. Bass

J. Vac. Sci. Technol. B 12, 3261 (1994); http://dx.doi.org/10.1116/1.587608 (4 pages) | Cited 2 times

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Proximity printing with soft x rays is a leading contender for very large scale integrated circuit lithography below 0.25 μm. It will require overlay accuracy far below the 100 nm (3σ) typical of today’s systems. In addition, it should use wafer marks which permit planar resist flow, so their apparent position is not distorted. We report an alignment system which uses a linear zone plate on the mask to focus laser light into a line on the wafer. The wafer mark is the boundary between two adjacent fine pitch gratings. These gratings diffract the light into photodiodes. The gratings either differ slightly in pitch or by 180° in phase. This configuration minimizes the disturbance to the resist as it flows over the alignment mark. In the case of gratings with slightly different pitch the light from each grating is detected by one‐half of a split photodiode. This arrangement has good sensitivity and a very wide capture range. The phase shift gratings have reduced capture range but enhanced sensitivity because of the improved resolution from the phase shift. We observe that the full width at half‐maximum (FWHM) of the alignment signal is 0.6 μm when the FWHM of the zone plate focus is 1.0 μm. By collecting all of the light focused by the zone plate and diffracted by the gratings we obtain strong alignment signals with signal to noise ratios of more than 1000:1. We routinely obtain a reproducibility in a bench setup equivalent to less than 1 nm (3σ). This alignment technique is currently undergoing installation in a commercially available x‐ray exposure tool.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Combined lithographies for the reduction of stitching errors in lithography

Hans W. P. Koops, Johannes Kretz, and Markus Weber

J. Vac. Sci. Technol. B 12, 3265 (1994); http://dx.doi.org/10.1116/1.587609 (5 pages)

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A new way of lithography is presented, which makes use of overlapping address fields to expose patterns by conventional or unconventional lithographies and uses the overlap area to position subsequent pattern areas with high accuracy by image processing. Dot marks are generated by beam induced deposition in the overlap areas at the end of the exposure process of each field. Then the sample is moved to the next field. The marks are searched by taking a highly magnified image scan in a reduced area. The mark position is evaluated by processing of this image to determine the new position of the sample. The position is obtained in the address scale used for exposure with an accuracy of ±1 address steps, which makes it possible to stitch the adjacent pattern in the next field with this precision. Having a ‘‘coarse’’ field or stage positioning means with 1‐μm precision is now sufficient to obtain patterns, which are stitched with an accuracy of 1 nm by using an address field of ≳14 bit for the overlapping fields and by sacrificing an area of <1% of the address area for the mark detection in the overlap region. The method is especially applicable to nanolithography with instruments and processes that allow inspection of the mark without destroying the lithography area. In this case, only the mark area of the size of a few pixels is lost for the patterning within the fields. This is especially valid for scanning probe lithographies and beam induced deposition lithography methods.    
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85.40.Hp Lithography, masks and pattern transfer

Atomic hydrogen resist process with electron beam lithography for selective Al patterning

Kazuya Masu and Kazuo Tsubouchi

J. Vac. Sci. Technol. B 12, 3270 (1994); http://dx.doi.org/10.1116/1.587610 (5 pages) | Cited 6 times

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The resolution of electron beam lithography using polymer resist is limited to be 10–20 nm because of electron scattering effects and molecular size of polymerized resist. Thinning the resist thickness is a method to improve the resolution. In this article, we discuss a new atomic hydrogen resist process for area‐selective Al patterning. The atomic resist is monolayer thick hydrogen terminated on a Si surface, i.e., the thickness of the resist is ultimately thin. The features are (1) patterning of the monolayer thick terminated H on the Si surface by focused electron beam exposure and (2) selective growth of Al on the remaining terminated H area by low pressure chemical vapor deposition using dimethylaluminum hydride [(CH3)2AlH] and H2. In the electron beam exposed area, the terminated H on Si is removed and the Si surface is activated. Then the activated Si surface is oxidized in nanometer thickness in a clean‐room environment. The Al is selectively deposited on the remaining terminated H region. We have successfully formed the area‐selective Al patterning by the atomic hydrogen resist process.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

Deep‐ultraviolet damage to fused silica

Richard Schenker, Paul Schermerhorn, and W. G. Oldham

J. Vac. Sci. Technol. B 12, 3275 (1994); http://dx.doi.org/10.1116/1.587611 (5 pages) | Cited 6 times

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Several experiments using 213‐nm radiation have been performed with the goals of characterizing and understanding better the mechanisms behind UV damage to fused silica. A novel method of monitoring compaction in real time was discovered which measures the amount which the damaged fused silica depolarizes the incident beam. Refractive index changes of less than one part in ten million were resolved. Compaction induced stress was observed to extend well beyond the irradiation site with a maximum at the edge of the irradiation site. Detection of compaction occurred much earlier than the detection of color center absorption when fused silica was irradiated. The rates of both compaction and of color center formation depend superlinearly on pulse energy density and can be fitted by a quadratic function, suggesting a two‐photon damage process. In the same energy density range, the absorption coefficient depends linearly on energy density, from which we extract a 213‐nm two‐photon absorption coefficient of 5×10−4 (cm/MW). This value is a factor of 4 smaller than the value published for 193 nm [R. S. Taylor et al., Appl. Opt. 27, 3124 (1988)].
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

Fabrication of atomic‐scale metallic microstructures by retarding‐field focused ion beams

R. G. Woodham and H. Ahmed

J. Vac. Sci. Technol. B 12, 3280 (1994); http://dx.doi.org/10.1116/1.587612 (5 pages) | Cited 6 times

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Atomic‐scale metallic microstructures have been deposited on various semiconductor substrates. A retarding‐field method is used to form a low‐energy, focused beam of Au ions from a liquid metal alloy source. The ions were deposited with landing energies down to 20 eV to form ultrathin films. The microstructure of the ultrathin films was found to be metallic islands, the smallest of which are 1 nm or less. The microstructure on a GaAs substrate displayed a high degree of size and spacing regularity. The technique was used as a method to fabricate nanometer‐scale islands in a multiple‐junction Coulomb blockade device.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

Micromechanical structures for electron‐ and ion‐beam irradiation phenomena

I. Ogo and N. C. MacDonald

J. Vac. Sci. Technol. B 12, 3285 (1994); http://dx.doi.org/10.1116/1.587613 (4 pages) | Cited 2 times

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Micromechanical structures are used to investigate the effects of electron‐ and ion‐beam irradiation on silicon dioxide. The devices are simple cantilever beams (50 μm long) fabricated from different types of silicon dioxide and integrated with two parallel driving electrodes. The electrically floating silicon dioxide beams oscillate only under electron‐beam irradiation with an ac voltage applied to the driving electrodes at resonance. Accumulated charge produced by electron‐beam irradiation in a scanning electron microscope (SEM) produces a driving force between the cantilever beam and the driving electrode. A time‐resolved SEM technique is used to determine the resonant frequencies of these micro‐cantilever beams. Electron‐ and ion‐beam damage is measured by detecting the shift in the resonant frequency as a function of the irradiation time (electron‐beam dose or sputtering time). Experimental results show that the resonant frequency of the silicon dioxide cantilever beam increases under electron‐beam irradiation; this frequency rise indicates that material hardening or mass loss or both occur when the cantilever is subjected to electron‐beam irradiation. We also observed differences in the rate of change of the frequency shift between thermally grown silicon dioxide films and plasma enhanced chemical vapor deposition silicon dioxide films. Under argon sputtering, the resonant frequency of the silicon dioxide cantilever beam decreases due to the change in the dimensions and mass of the cantilever beam caused by sputtering.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
79.20.-m Impact phenomena (including electron spectra and sputtering)

Locally focused electron‐beam deposition

Jonathan L. Shaw and Henry F. Gray

J. Vac. Sci. Technol. B 12, 3289 (1994); http://dx.doi.org/10.1116/1.587614 (5 pages)

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We describe a patterned deposition process suitable for producing three‐dimensional nanostructures. Deposition occurs when adsorbed precursor molecules are decomposed by electrons or ions. Local electrostatic focusing is used to form a pattern from a broad incoming beam. The local focusing field is produced by a set of apertures suspended above the substrate and held at about 100 V with respect to the substrate. The minimum size of the focal spot so produced is roughly 1/100 the original aperture size, hence, structures with 100‐Å features may result from 1‐μm apertures. This size is not expected to be limited by scattering effects since the impact energy is low. In contrast to scanned beam deposition methods, this process deposits material at all targeted points simultaneously. The technique may be used to fabricate large arrays of structures such as field emitter tips. We have demonstrated the basic process by depositing 0.5‐μm features starting from 25‐μm square apertures.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Three‐dimensional laser direct writing: Applications to multichip modules

N. Nassuphis, R. H. Mathews, S. T. Palmacci, and D. J. Ehrlich

J. Vac. Sci. Technol. B 12, 3294 (1994); http://dx.doi.org/10.1116/1.587615 (6 pages) | Cited 1 time

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Laser direct write deposition and etching have been developed for uses on multichip modules. Instrumentation has been demonstrated for these and other applications on substrates with significant three‐dimensional topography.
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85.40.Hp Lithography, masks and pattern transfer
42.62.Cf Industrial applications

Pulse‐time modulated electron cyclotron resonance plasma etching for highly selective, highly anisotropic, and less‐charging polycrystalline silicon patterning

Seiji Samukawa and Kazuo Terada

J. Vac. Sci. Technol. B 12, 3300 (1994); http://dx.doi.org/10.1116/1.587616 (6 pages) | Cited 17 times

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Highly selective, highly anisotropic, notch‐free and charge build‐up damage‐free polycrystalline silicon etching is achieved using an electron cyclotron resonance plasma modulated at a pulse time in the range of 10–20 μs. In this plasma, the selectivity ratio of the polycrystalline silicon etching rate to the SiO2 etching rate is increased significantly by the same etching rate as that attained using a continuous discharge. Additionally, vertical and notch‐free phosphorus‐doped polycrystalline silicon etching profiles and suppressing charge build‐up damage can be achieved. These results are attained by controlling the ion energy distribution through the duty ratio, maintaining a high ion current density, generating a collimated ion flux, and eliminating surface charge with the pulsed discharge.
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81.65.-b Surface treatments

Reflectance modeling for in situ dry etch monitoring of bulk SiO2 and III–V multilayer structures

S. E. Hicks, W. Parkes, J. A. H. Wilkinson, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 12, 3306 (1994); http://dx.doi.org/10.1116/1.587617 (5 pages) | Cited 8 times

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We investigate in situ dry etch monitoring via reflectometry. We present two approaches, the choice depending on the presence of layers (if any) deposited on the substrate. Firstly, we present a model of the normal incidence reflectance of a multilayer stack (of any number of layers) as a function of etch depth based on electrical transmission line theory. We have applied this model to the reactive ion etching of an InP/InGaAsP multilayer structure using CH4/H2/O2, and a GaAs/AlAs multilayer structure using SiCl4. In the case of the InP‐based material, use of the model enabled us to distinguish individual 10.24 nm InGaAsP quantum wells. In the case of the GaAs‐based structure, use of the model allowed us to determine the induction time for the removal of the native gallium oxide and to tell which AlAs quantum well had been reached during the etch, enabling cessation of the etch process just after the last well with no overetch. Agreement between the model and observed behavior of the reflectance was extremely good in both cases. Secondly, we have extended this approach to model the reflectance from a wafer with a suitable patterned dry etch mask and a laser beam covering both masked and etched areas, allowing the study of interference between the reflected beams from the two areas. We have compared the modeled and observed reflectance from a sample of NiCr masked bulk SiO2 and found agreement to be within 20 nm in a total etch depth of 1 μm.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Effect of superlattices on the low‐energy ion‐induced damage in GaAs/Al(Ga)As structures: Channeling or diffusion?

D. L. Green, E. L. Hu, and N. G. Stoffel

J. Vac. Sci. Technol. B 12, 3311 (1994); http://dx.doi.org/10.1116/1.587618 (6 pages) | Cited 13 times

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We have recently reported on the dramatic effect on the damage profile achieved using a ten‐period lattice‐matched AlAs/GaAs superlattice placed above a multiple quantum well probe. We sought to better understand the effect of the superlattice on the damage profile, whether due to gettering of defects or due to an actual modulation of the ion channeling. To examine the latter hypothesis, the schleich program simulating SCattering of Heavy, Low Energy Ions into CHannels, was modified to allow simulations of layered zincblende structures. We report here on simulations carried out using that modified program. Additionally, we have carried out a series of experiments to investigate effects that defect diffusion may be having on the damage profiles. Preliminary results from these experiments indicate gettering of defects by the superlattice. These results indicate that although deep channeling of ions along the 〈011〉 directions of our III–V structures most certainly defines the ion penetration depths and subsequent deeply generated damage, a second factor, that of diffusion of defects within these regions, may significantly affect the damage profile.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.80.Jh Ion radiation effects

Characterization of chemically assisted ion beam etching of InP

C. Youtsey, R. Grundbacher, R. Panepucci, I. Adesida, and C. Caneau

J. Vac. Sci. Technol. B 12, 3317 (1994); http://dx.doi.org/10.1116/1.587619 (5 pages) | Cited 22 times

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Chemically assisted ion beam etching involving an Ar ion beam and a Cl2 ambient was investigated for the etching of high quality facets in InP. Detailed investigations on how the etch anisotropy as well as surface morphology could be optimized under different etch conditions were performed. It was necessary to elevate the substrate temperature above 150 °C to obtain smooth surfaces and above 225 °C to achieve good anisotropy. At these elevated temperatures, very high etch rates in excess of 2 μm/min were obtained. The choice of mask material was found to have a strong influence on the surface quality due to micromasking effects. Hard baked photoresist and Ti masks were used to obtain surfaces free of ‘‘grasslike’’ roughness. Free standing InP wires of various widths were fabricated to estimate the extent of sidewall damage under different etch conditions.
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81.65.-b Surface treatments

Reactive ion etching‐induced damage in InAlAs/InGaAs heterostructure field‐effect transistors processed in HBr plasma

Patrick Fay, Sambhu Agarwala, Carl Scafidi, Ilesanmi Adesida, Catherine Caneau, and Rajaram Bhat

J. Vac. Sci. Technol. B 12, 3322 (1994); http://dx.doi.org/10.1116/1.587620 (5 pages) | Cited 1 time

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An investigation of the effects of HBr reactive ion etching (RIE) processing for gate recessing in lattice‐matched InAlAs/InGaAs heterostructure field‐effect transistors (HFETs) has been conducted. The effect of varying the Schottky barrier layer thickness on device performance and the susceptibility of HFETs to RIE‐induced damage are presented for barrier layer thicknesses ranging from 10 to 25 nm. The effect of plasma self‐bias voltage during gate recess etching on overall device performance for a given layer structure is also examined for voltages ranging from −100 to −200 V. Device performance is assessed through direct current (dc) characterization of transconductance, threshold voltage, reverse gate leakage current, and gate‐drain breakdown voltage, and through microwave characterization of the devices. Devices with barrier layers less than 20 nm thick are found to suffer the most degradation due to RIE‐induced damage. For devices with sufficiently thick barrier layers, dc and microwave device parameters compare well with those of corresponding devices fabricated using a selective wet‐etch process.
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85.30.Tv Field effect devices
81.65.-b Surface treatments

High aspect ratio dry etching for microchannel plates

G. L. Snider, A. M. Then, R. J. Soave, and G. W. Tasker

J. Vac. Sci. Technol. B 12, 3327 (1994); http://dx.doi.org/10.1116/1.587621 (5 pages) | Cited 1 time

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Dry etching of GaAs and fused silica for the production of microchannel plates is investigated. Etch methods used are magnetron reactive ion etching, chemically assisted ion beam etching (CAIBE), and electron cyclotron resonance etching (ECR). Extensive characterization of the ECR etcher is carried out with a designed experiment, which uses statistical methods to minimize the number of characterization runs. CAIBE gives high aspect ratio etching of GaAs, but at low etch rates. ECR provides higher etch rates of GaAs and better substrate temperature control. The effect of temperature on sidewall roughness and undercut is examined for temperatures as low as −100 °C. Features with an aspect ratio greater than 30 are presented. Etching of fused silica is difficult due to low etch rates (<0.2 μm/min), and faceting of the metal mask.
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81.65.-b Surface treatments
85.45.-w Vacuum microelectronics

Process technology for InGaAs/InAlAs modulation doped field effect transistors on InP substrates

T. Fink, B. Raynor, M. Haupt, K. Köhler, J. Braunstein, N. Grün, and J. Hornung

J. Vac. Sci. Technol. B 12, 3332 (1994); http://dx.doi.org/10.1116/1.587622 (5 pages) | Cited 2 times

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We present a process for fabricating lattice‐matched InGaAs/InAlAs modulation doped field effect transistors (MODFETs) on InP wafers including molecular beam epitaxial growth of a high electron mobility transistor structure consisting of In0.53Ga0.47As and In0.52Al0.48As layers, and electron‐beam lithography for gate definition. For selective gate recessing we investigated both wet and dry etch processes. Viable procedures have been found with a citric acid: H2O2:H2O wet etching solution and with an HBr/Ar gas mixture for reactive ion etching (RIE). The selectivities obtained for InGaAs with respect to InAlAs were 14:1 for the wet etchant and 6.7:1 for RIE. Another crucial process step is the MODFET isolation. Earlier work by other groups has shown that implant isolation is difficult on InGaAs [S. J. Pearton et al., Mater. Res. Soc. Symp. Proc. 144, 433 (1989)]. Therefore, we studied both oxygen ion implantation as well as wet‐chemical mesa etching for device isolation on the same wafer. Although the isolation sheet resistance achieved with ion implantation is inferior to that obtained in a mesa process, we found similar MODFET performance for both approaches. For devices with a 0.3‐μm gate length and 1.3‐μm source–drain distance, a transconductance of more than 600 mS/mm and threshold voltages of −1.3 and −0.6 V for wet and dry recessed transistors, respectively, were obtained. Wafer mapping measurements showed that the MODFET data are uniform over an entire 2‐in. wafer and also from wafer‐to‐wafer within a batch.  
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Investigation of modulated radio frequency plasma etching of GaAs using Langmuir probes

V. J. Law, N. St. J. Braithwaite, S. G. Ingram, D. C. Clary, and G. A. C. Jones

J. Vac. Sci. Technol. B 12, 3337 (1994); http://dx.doi.org/10.1116/1.587623 (5 pages) | Cited 2 times

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Radio frequency ClCH3/H2 plasma etching of GaAs is examined in the 10–140 mTorr pressure range using square‐wave modulation of the excitation source to control the etching. A Langmuir probe is used to measure time‐resolved electron density, characteristic temperature, and floating potential during the plasma afterglow period. The ClCH3/H2 plasma electron energy is found to be 1.2±0.3 eV. The near afterglow plasma density decay has a time constant in the order of τ=30 μs at 140 mTorr for 10%–20% ClCH3 in H2 and τ=100 μs for H2. The floating potential continues to decay into the far afterglow, with a characteristic time of the order of milliseconds. The Langmuir probe measurements indicate that in ClCH3 plasmas the near afterglow is dominated by electron attachment, whereas the far afterglow is dominated by ambipolar diffusion. The GaAs etch rate experiments show that surface reactions continue into the far afterglow, dominating the behavior of the time average etch rate.
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81.65.-b Surface treatments
52.70.Ds Electric and magnetic measurements
52.80.Pi High-frequency and RF discharges

Plasma‐immersed oxygen ion implantation of iron‐doped glass for nonmetallic magnetic hard disks

L. Zhang, J. H. Booske, R. F. Cooper, J. L. Shohet, J. R. Jacobs, F. S. B. Anderson, M. J. Goeckner, E. B. Wicksberg, and G. Was

J. Vac. Sci. Technol. B 12, 3342 (1994); http://dx.doi.org/10.1116/1.587624 (5 pages)

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The object of this work is to develop a fabrication process to produce a nonmetallic magnetic hard disk with a thin magnetic layer that features small magnetic spinel grains suspended in a host nonmetallic medium. Plasma source ion implantation (PSII) of oxygen into iron‐doped magnesium aluminosilicate (MAS) glass and simultaneous implantation of iron and oxygen into calcium aluminosilicate (CAS) glass have been investigated. The implant energy used in these experiments was 30 keV and the oxygen dose was estimated to be 1×1017 ions/cm2 for both MAS and CAS glasses. The results showed that PSII of oxygen into MAS glass increased the iron ions’ binding energy, probably due to the valence state conversion of Fe2+ to Fe3+. The post anneal yielded a thin two‐phase layer near the surface, consisting of Mg–Fe–Si–O crystals and the glass matrix. A slight segregation of Fe in the implanted region took place during the anneal, because of the out‐diffusion of Fe2+ ions from the substrate to the oxygen‐rich region. The simultaneous implantation of iron and oxygen into CAS glass resulted in the formation of an iron oxide, Fe2O3.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
61.72.up Other materials

Electron cyclotron resonance ion stream etching with high uniformity and accuracy for metal–oxide–semiconductor gate fabrication

Chiharu Takahashi and Seitaro Matsuo

J. Vac. Sci. Technol. B 12, 3347 (1994); http://dx.doi.org/10.1116/1.587510 (4 pages) | Cited 2 times

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A new system has been constructed for electron cyclotron resonance (ECR) ion stream etching to fabricate metal–oxide–semiconductor (MOS) gates at the quarter‐micron level. It has three features: (i) a new ECR plasma source that generates a uniform plasma; (ii) a supplementary coil that makes the ion stream perpendicular over the whole surface of a 6‐ or 8‐in. wafer; and (iii) CF4 and O2 addition to reduce the influence of SiClx by‐products formed by the reaction between silicon and the Cl2 etching gas. We have found that reducing the amount of SiClx reaction products desorbed from the chamber wall is essential for significant improvement in etching characteristics. Using this new system, we attained (i) uniformity as good as ±1.6% over a 6 in. wafer with a Si etch rate of 0.17 μm/min; (ii) uniformly vertical profiles over the whole wafer, including the edges; and (iii) stable etching conditions with a high selectivity of over 100.
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52.80.Pi High-frequency and RF discharges
81.65.-b Surface treatments
85.30.-z Semiconductor devices

Effects of etch chemistry on SF6‐based tungsten etching by electron cyclotron resonance reactive ion etching

C. R. Eddy, J. Kosakowski, L. M. Shirey, E. A. Dobisz, K. W. Rhee, W. Chu, K. W. Foster, C. R. K. Marrian, and M. C. Peckerar

J. Vac. Sci. Technol. B 12, 3351 (1994); http://dx.doi.org/10.1116/1.587511 (5 pages)

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Studies of etch chemistry effects on SF6‐based tungsten etching have been performed in an electron cyclotron resonance microwave reactive ion etching system. The etch chemistry and, therefore, reactive species concentrations were varied in several ways and the effect of these variations on etch rate and anisotropy of etched features were evaluated. Reactive species concentrations were altered by varying the residence time in a pure SF6 plasma or by introducing argon or nitrogen in the SF6 plasma under constant residence time. For pure SF6 and under conditions similar to those in a parallel plate radio frequency system, the tungsten etch rate was more than three times greater—presumably the results of higher dissociation efficiencies. As residence time was increased from 1 to 30 s the etch rate was decreased by greater than a factor of 2 and linewidth loss was reduced from better than 50 to 5%. Addition of argon to the plasma reduced the etch rate while maintaining short residence times. The addition of nitrogen to SF6 resulted in a complex behavior that provided optimum etch rate with minimum linewidth loss for a 50/50 mixture. In evaluating the behavior, sidewall passivation processes and competitive reactions in the gas phase are discussed.  
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81.05.Bx Metals, semimetals, and alloys
85.40.Hp Lithography, masks and pattern transfer
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Basis of macroscopic and microscopic surface shaping and smoothing by plasma assisted chemical etching

C. B. Zarowin

J. Vac. Sci. Technol. B 12, 3356 (1994); http://dx.doi.org/10.1116/1.587512 (7 pages)

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This is a summary of the basis of macroscopic shaping (or figuring) and microscopic pattern transfer and microsmoothing (or polishing) by plasma assisted chemical etching (PACE). The ability of PACE to precisely shape surfaces without mechanical contact stems from the reliable etch rate map of a plasma assisted chemical etch tool by programmed scanning of the etch tool’s profile over the surface to be shaped. For a given shape modification and the plasma tool removal rate map this programmed tool dwell time is obtained by deconvolution using Fourier transforms. The transforms of these quantities also yield their spatial frequency characteristics and clarify PACE’s figuring behavior, but do not explain the observed polishing. Both polishing and micropattern transfer etch profiles are governed by a differential surface evolution equation, whose behavior is reviewed here. We also show why the PACE process is able to etch directionally, produces negligible subsurface damage and vertical etch rates to 100 μm/min or volume removal rates of ∼10 mm3/min for a 1 cm diam plasma due to the atypical plasma regime employed.  
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Etched profile distortions in high density electron cyclotron resonance plasma

Masahiro Yoneda, Takahiro Maruyama, and Nobuo Fujiwara

J. Vac. Sci. Technol. B 12, 3363 (1994); http://dx.doi.org/10.1116/1.587513 (6 pages) | Cited 3 times

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Recent studies of electron cyclotron resonance plasma etching for fabricating the gate electrode of metal‐oxide‐semiconductor large‐scale integrated circuits indicate a serious problem in the etched profiles. The problem is a local pattern distortion caused by a charge buildup of the patterns. We report basic investigations of the etched profiles and propose the model for local side etch. Plasma parameters are measured by the electrostatic probes. The relationships between the local pattern distortion and the plasma properties are investigated. Lowering the electron temperature perpendicular to the surface normal is one of the most effective techniques for eliminating the local side etch. Lowering the electron temperature is enhanced by setting the wafer at the lower magnetic field. As the large space charge bends the ion trajectories, the lower ion current density is also effective to reduce the local side etch. The smoothly decreasing distribution of plasma potential which accelerates the ions can reduce the local side etch in spite of the higher current density.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Effects of cation diffusion on the monolayer control of chemical beam etching

T. H. Chiu, M. D. Williams, W. T. Tsang, and R. M. Kapre

J. Vac. Sci. Technol. B 12, 3369 (1994); http://dx.doi.org/10.1116/1.587514 (5 pages) | Cited 2 times

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There is a need to develop an etching technology for the fabrication of nanostructures which provides accurate etch rate control at the atomic level, mask pattern transfer at the nanometer scale, and a clean damage‐free surface. In addition, it is highly desirable to integrate the etch with the growth so that in regrowth the problem of contamination is eliminated. Chemical beam etching inside a chemical beam growth system has a great potential of becoming such a dry etching technology. Etching at a subnanometer scale is conveniently monitored by using in situ reflection high energy electron diffraction. Unlike other dry etching methods, the only etching parameter that is critical for etch rate control is the gas flow rate. The etch rate varies linearly with the gas flow rate, which can be adjusted easily by well established mass flow technology. However, a surface roughening mechanism due to inadequate cation diffusion may change the initially two‐dimensional (2D) process into a three dimensional (3D) etching. The effectiveness in surface impurity removal by etch cleaning also depends on the etched morphology. Using novel methods that enhance the surface cation diffusion, etching can be maintained in a 2D fashion to obtain a mirrorlike surface.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.-b Surface treatments

Reactive‐ion‐beam etching of InP in a chlorine–hydrogen mixture

G. Allen Vawter and Carol I. H. Ashby

J. Vac. Sci. Technol. B 12, 3374 (1994); http://dx.doi.org/10.1116/1.587515 (4 pages) | Cited 3 times

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We present the first application of Cl2+H2 reactive‐ion‐beam etching of InP. Specularly smooth etching is achieved using an ion beam of 53%–73% Cl2 in H2 at a 300 eV extraction potential with the substrate held at 250 °C. InP etch morphology and rate are examined as functions of Cl2+H2 mixture, sample temperature, and chamber pressure. Significant deviation from the optimum smooth‐etch conditions are seen to result in rough surfaces.
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81.65.-b Surface treatments

Radical beam ion‐beam etching of InAlAs/InP using Cl2

D. G. Yu, E. L. Hu, and G. Hasnain

J. Vac. Sci. Technol. B 12, 3378 (1994); http://dx.doi.org/10.1116/1.587516 (4 pages)

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A Cl2 radical beam ion‐beam etching (RBIBE) system was used to etch InP‐based materials. In InAlAs/InAlGaAs heterostructures, vertical sidewalls, smooth surfaces, and no delineation of the epilayers resulted from etching at elevated temperatures (≳150 °C) and low ion‐beam energies (≤300 eV). Rapid etch rates (≳1 μm/min) were also achieved under these conditions. This work demonstrates that reliable anisotropic and angled etching of InP‐based III–V compound semiconductors is possible with the RBIBE system.
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81.65.-b Surface treatments

Evaluation of surface damage on GaAs etched with an electron cyclotron resonance source

K. K. Ko, S. W. Pang, T. Brock, M. W. Cole, and L. M. Casas

J. Vac. Sci. Technol. B 12, 3382 (1994); http://dx.doi.org/10.1116/1.587517 (6 pages) | Cited 8 times

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Surface damage induced by dry etching on GaAs with an electron cyclotron resonance source has been studied using both electrical measurements and surface analysis techniques. It is found that the unalloyed contact resistance extracted from the transmission lines is very sensitive to the etch‐induced damage, and it increases significantly with ion energy and ion flux but decreases with etch temperature. Conducting wires that are 40 to 1000 nm wide have been etched down to 1.3 μm deep with vertical profile and smooth surface morphology. The extracted sidewall damage depth of these wires ranges from 2.7 to 20.4 nm and it increases with ion energy and ion flux but decreases with etch temperature. At 200 W rf power, the sidewall damage depth decreases from 13.1 to 4.0 nm after removing 10 nm of the etched surface using low‐energy reactive chlorine species. Results from cross‐sectional transmission electron microscopy show a higher defect density and a shallower defect depth for samples etched with higher rf power. A lower defect density and a deeper defect depth are found at higher etch temperature. Auger electron spectroscopy shows that after etching with the Cl2/Ar plasma, the stoichiometry is not changed even at high microwave power or high etch temperature.
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81.65.-b Surface treatments
61.80.Jh Ion radiation effects
52.40.Hf Plasma-material interactions; boundary layer effects

Magnetically confined plasma reactive ion etching of GaAs/AlGaAs/AlAs quantum nanostructures

Y. P. Song, P. D. Wang, C. M. Sotomayor Torres, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 12, 3388 (1994); http://dx.doi.org/10.1116/1.587518 (5 pages) | Cited 8 times

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An electron cyclotron resonance reactive ion etching machine has been successfully run under low magnetic field conditions. We call this the magnetically confined plasma condition. Under this condition, a new process using SiCl4 with a small amount of O2 has been developed for etching nanometer scale structures on GaAs, AlGaAs, and AlAs multilayer materials. The effects of the percentage of O2, the rf power, the microwave power, and the flow rate are described. 100 nm quantum dots have been etched on multiple quantum well materials to a depth of about 1 μm. Vertical and smooth sidewalls were obtained on these nanostructures. Poly‐methylmethacrylate (PMMA) electron beam resist can be used directly as a dry etch mask, and the selectivity between GaAs and PMMA can be as high as 28:1. Raman spectroscopic studies showed that the process induced no detectable damage to the surface for an etch depth of 130 nm and only very little damage for deeper etching.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.-b Surface treatments

Dynamic corrections in MEBES 4500

Henry Pearce‐Percy, Richard Prior, Frank Abboud, Albert Benveniste, Leonard Gasiorek, Michael Lubin, and Frederick Raymond

J. Vac. Sci. Technol. B 12, 3393 (1994); http://dx.doi.org/10.1116/1.587519 (6 pages) | Cited 4 times

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Some systematic errors of the mebes raster scan lithography system are examined and how significant accuracy improvements can be achieved is demonstrated. The accuracy improvements result from error compensation hardware and software applying corrections that are either a function of time (write scan position) or of position on the substrate. Error analysis shows the following correctable errors to be among the largest error sources in the mebes iv: electronic noise, stage z runout, deflection alignment drift, mask flatness, and clamping distortion, and scan nonlinearity. These errors contribute to placement/overlay accuracy and to butting accuracy. The dynamic corrections implemented are automatic write scan correction, which reduces deflection alignment errors, scan linearity measurement and correction, grid correction, and height detection and correction, which reduce cassette height and mask flatness errors. With these corrections implemented, system performance improves dramatically.
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85.40.Hp Lithography, masks and pattern transfer
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Electron‐beam cell projection lithography: Its accuracy and its throughput

Y. Someda, H. Satoh, Y. Sohda, Y. Nakayama, N. Saitou, H. Itoh, and M. Sasaki

J. Vac. Sci. Technol. B 12, 3399 (1994); http://dx.doi.org/10.1116/1.587520 (5 pages) | Cited 5 times

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The cell projection electron‐beam lithography system HL‐800D has been developed for 0.2 μm ultralarge scale integration circuit and application specific integrated circuit use. This system is formed by a conventional variable shaped beam and cell beams for using five apertures. To achieve high resolution and high‐stitching accuracy between the cell beams, and between variable shaped beam and cell beam, we developed the automatic tuning method for cell beams. Included in the method are: (1) rotation and magnification correction, (2) beam alignment for cell beams, (3) space‐charge effect correction, and (4) mask position alignment. This method realized a system for easy handling of cell projection tuning. As a result, stitching accuracy under 0.05 μm and resolution under 0.2 μm for cell beams have been achieved. The contact hole layer and the wiring layer of a 0.35 μm DRAM pattern have been overlaid with an accuracy of 0.04 μm (maximum value).
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85.40.Hp Lithography, masks and pattern transfer

Deflector and correction coil calibrations in an electron beam block exposure system

A. Yamada, K. Sakamoto, S. Yamazaki, K. Kobayashi, S. Sago, M. Oono, H. Watanabe, and H. Yasuda

J. Vac. Sci. Technol. B 12, 3404 (1994); http://dx.doi.org/10.1116/1.587521 (5 pages)

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Mask deflectors and correction coils in an electron beam block exposure system are calibrated to expose 48 mask patterns in a deflection area with the same current density and at the same position on a wafer. The calibration has six measurement steps. When a mask stage changes area positions on a mask, only the last step needs to be executed during exposure. This last step takes about 2 s for measurement. Calibration results show that the current density through each mask pattern differs less than 1.6% from the mean value. Exposed position errors on a wafer are below 0.04 μm for 48 mask patterns. These position errors are corrected by additional deflections with an electrostatic minor deflector. To improve stitching accuracies between exposed patterns, we discuss another routine to adjust beam sizes and rotations of spots on a wafer.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
41.85.-p Beam optics

100 kV electron beam lithography using a Schottky field emission source

B. H. Koek, T. Chisholm, J. Somers, J. Davey, J. Romijn, and A. J. v. Run

J. Vac. Sci. Technol. B 12, 3409 (1994); http://dx.doi.org/10.1116/1.587522 (4 pages) | Cited 5 times

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We have investigated the usage of high energy (100 kV) electron beam lithography for various applications. Exposures with high energy electrons are less susceptible to resist thickness variations. Additional exposures from adjacent pixels and shapes can be corrected relatively easily compared to medium energy exposures (20–50 kV). The 100 kV performance of the Leica Cambridge EBPG5‐FE system is described. A beam stability of better than 10 nm and a drift of less than 20 nm/h are combined with a Schottky field emission source for high current density. Spot sizes of 7–165 nm with corresponding currents between 0.7 and 120 nA can be selected to enable both very high resolution and accurate mask making.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

Evaluation of Zr/O/W Schottky emitters for microcolumn applications

H. S. Kim, E. Kratschmer, M. L. Yu, M. G. R. Thomson, and T. H. P. Chang

J. Vac. Sci. Technol. B 12, 3413 (1994); http://dx.doi.org/10.1116/1.587523 (5 pages) | Cited 5 times

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Schottky emission tips have been evaluated with microlenses for applications in scanning tunneling microscope aligned field emission microcolumns. Operation of Zr/O/W 〈100〉 Schottky emission tips at 1800 K with an axial separation of 50–100 μm between the tip and a microlens has been successfully tested. The microlens consists of an extraction electrode with a 5‐μm‐diam hole in a 1‐μm‐thick silicon membrane. The preliminary results of this study show that thermal field emission tips can be operated continuously in close proximity to a microlens over a long period of time, and that good emission stability of less than 1% noise fluctuation over 10 h is achieved with emission currents up to at least 100 μA.
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79.70.+q Field emission, ionization, evaporation, and desorption

Electron beam technology: The other end of the spectrum

R. Bakish

J. Vac. Sci. Technol. B 12, 3418 (1994); http://dx.doi.org/10.1116/1.587524 (7 pages)

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A brief review of high power electron guns capable of energies in terms of kilo‐ and mega‐watts is presented. Their use in industrial areas where they have and continue to make contributions will be presented. Melting and refining in the metallurgical industry, looking at its different segments, will be considered first together with a brief reference to their place in single crystal growing and zone refining. This will be followed by a review of their contributions to welding, heat treating and micro‐machining. Their role as evaporation tools: in the electronics industry (thin films), for the production of a variety of barriers, for the production of overlay coatings and for production of fiber‐reinforced materials and other materials with advanced properties will be discussed.
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81.90.+c Other topics in materials science (restricted to new topics in section 81)

High aspect ratio aligned multilayer microstructure fabrication

K. Y. Lee, S. A. Rishton, and T. H. P. Chang

J. Vac. Sci. Technol. B 12, 3425 (1994); http://dx.doi.org/10.1116/1.587525 (6 pages) | Cited 3 times

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This paper presents a technique for fabricating precisely aligned high aspect ratio multilayer microstructures based on anodic bonding of silicon and PyrexTM glass. The process involves stacking alternate silicon substrates containing patterns in two dimensions with thin Pyrex glass spacers to form tall three‐dimensional structures. The methods used for accurately aligning the layers by optical microscopy and for bonding the layers anodically are described. The application of this technique for building fully functional microlenses for electron‐beam microcolumns is presented.
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85.45.-w Vacuum microelectronics
41.85.-p Beam optics

Emission characteristics of ultrasharp cold field emitters

Ming L. Yu, Brian W. Hussey, Ho‐Seob Kim, and T. H. Philip Chang

J. Vac. Sci. Technol. B 12, 3431 (1994); http://dx.doi.org/10.1116/1.587526 (5 pages) | Cited 10 times

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We have examined the field emission characteristics of oxygen‐processed and thermal‐field buildup W 〈111〉 tips. Good emission angular confinement was found to correlate with the global geometry of the tip. Emission stability was related to the atomic arrangement at the apex. This phenomenon is described by the different driving forces for atomic surface diffusion. We also showed that tip apexes can be engineered to form flat (111) facets at the tip end for improved stability.
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79.70.+q Field emission, ionization, evaporation, and desorption

Overlay enhancement with product‐specific emulation in electron‐beam lithography tools

Denise Puisto, Maris Sturans, and Mark Lawliss

J. Vac. Sci. Technol. B 12, 3436 (1994); http://dx.doi.org/10.1116/1.587527 (4 pages) | Cited 6 times

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Electron‐beam image–placement errors, commonly expressed as registration and overlay errors, are becoming increasingly critical as the device dimensions shrink into the subhalf‐micrometer range. Contributors to image‐placement errors include: (1) system limitations, i.e., noise and minimum exposure increment or least‐significant bit (LSB); (2) column and resist charging; (3) substrate and carrier clamping; (4) resist stress; (5) thermal effects; and (6) mask‐processing effects. This article attempts to quantify the magnitude of positional errors attributable to these effects using experimental data from x‐ray membrane exposures under various conditions; when possible, a comparison to theoretical data is made. Although the image–placement errors from many of the previously mentioned contributors are typically very repeatable, they are difficult to eliminate. Methods such as discharge layers, decreased exposure time, and alternate resist systems can minimize the effects but may cause other problems such as defects due to an increased number of processing steps. A new method has been developed to address the repeatable errors. Pattern‐specific errors for a particular exposure are measured, and a calibration known as product‐specific emulation (PSE) is formed. This article explains the method used to accumulate the PSE data and demonstrates results on some dense product patterns.
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85.40.Hp Lithography, masks and pattern transfer

Application of a high‐throughput electron‐beam system for 0.3 μm large scale integration

F. Mizuno, M. Kato, H. Hayakawa, K. Sato, K. Hasegawa, Y. Sakitani, N. Saitou, F. Murai, H. Shiraishi, and S.‐i. Uchino

J. Vac. Sci. Technol. B 12, 3440 (1994); http://dx.doi.org/10.1116/1.587528 (4 pages) | Cited 1 time

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A high‐throughput electron‐beam direct writing technology has been developed. The new technology enables the manufacture of 0.3 μm large scale integration with a maximum throughput of 15 wafers/h, and the application of electron‐beam lithography for high‐volume large scale integrations. The throughput attained with this technology is 4–20 times higher than that of conventional technologies (e‐beam direct writing system: Hitachi HL‐700D; e‐beam resist: Hitachi RE‐5000P). This technology has been realized by utilizing a combination of the new e‐beam direct writing system HL‐800D and the new e‐beam resists RE‐4200N/PSR.
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85.40.Hp Lithography, masks and pattern transfer

Lithographic performance of a negative resist under scattering with angular limitation for projection electron lithography exposure at 100 keV

R. G. Tarascon, K. Bolan, M. Blakey, R. M. Camarda, R. C. Farrow, L. A. Fetter, H. A. Huggins, J. S. Kraus, J. A. Liddle, D. A. Mixon, A. E. Novembre, G. P. Watson, and S. D. Berger

J. Vac. Sci. Technol. B 12, 3444 (1994); http://dx.doi.org/10.1116/1.587529 (5 pages) | Cited 1 time

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Scattering with angular limitation for projection electron lithography (SCALPEL)TM [S. D. Berger and J. M. Gibson, Appl. Phys. Lett. 57, 153 (1990)] has been used to evaluate the lithographic performance of a negative‐acting silicon containing chloromethylstyrene resist at 100 keV [A. E. Novembre, M. J. Jurek, A. Kornblit, and E. Reichmanis, Polym. Eng. Sci. 29, 920 (1989)]. This article presents the preliminary evaluation of the resist in a small field of view SCALPEL machine using masks with a membrane area of 1 mm2. A resolution of 0.15 μm was obtained at 61 μC/cm2. Furthermore, the good electron‐beam sensitivity of this well‐characterized negative resist has allowed us to optimize the alignment, astigmatism, and focus of the experimental tool.  
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85.40.Hp Lithography, masks and pattern transfer

Interior area removal method for pyramid

Soo‐Young Lee and Brian D. Cook

J. Vac. Sci. Technol. B 12, 3449 (1994); http://dx.doi.org/10.1116/1.587530 (6 pages) | Cited 1 time

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In previous years, pyramid, a hierarchical rule‐based scheme for proximity effect correction in electron‐beam lithography was presented. pyramid has produced good experimental results for large circuit patterns (up to 80 μm × 80 μm) with a minimum feature size of 0.1 μm in 200 and 500 nm poly(methylmethacrylate) (PMMA) on silicon. Although the circuits used to test pyramid in the past have contained a rapidly varying pattern density, they did not contain very large features (e.g., 10 μm × 10 μm) next to small (0.1 μm) elements. The previous method for performing circuit correction (edge adjustment) has been found to be inadequate when correcting such occurrences. In order to overcome this problem, a new correction technique has been added to the overall pyramid hierarchy. Previously, pyramid performed its correction by adjusting only the locations of the edges of circuit elements. This new correction technique expands upon the previous edge adjustment method by allowing pyramid to remove area from circuit elements not only from the edges, but also from the interior as well. This interior area removal technique substantially improves the correction in cases when small circuit elements are placed near very large features. This article motivates the use of interior area removal both through simulation and experimental results. Experimental results indicating the usefulness of interior area removal are provided.  
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85.40.Hp Lithography, masks and pattern transfer

Spatial frequency filtering using multiple‐pass printing

Jun Ye, C. N. Berglund, and R. F. W. Pease

J. Vac. Sci. Technol. B 12, 3455 (1994); http://dx.doi.org/10.1116/1.587531 (5 pages) | Cited 2 times

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Previous work has shown that dimensional errors [critical dimension (CD) and registration] on photomasks have ‘‘nonwhite’’ spatial frequency spectra with strong peaks caused by the pattern generators [J. Ye et al. (unpublished)], and that the errors’ impact on integrated circuit performance and yield depends on their spatial frequencies [C. N. Berglund et al., J. Vac. Sci. Technol. B 10, 2633 (1992)]. In this article, we study in the spatial frequency domain the effect on these errors of multiple‐pass printing with offsets between passes, and find it equivalent to a band‐stop filter with the stopping band locations determined by the relative offset and dose between the passes. Therefore, we can systematically design multiple‐pass printing strategies that are tuned to minimize mask dimensional errors at those spatial frequencies that are particularly undesirable either due to their large magnitude or due to the fact that they have a particularly bad impact on chip performance and yield. While good designs reduce the error, bad designs may increase the error by converting errors between CD and registration through higher order effects. A good design needs to consider together the relative offset and dose, the spot and address size, and the process parameters.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Electron‐beam lithography of curved structures with an enhanced vector‐scan pattern generator supporting conic‐based primitives

F. Vasey, D. Prongúê, H. Rothuizen, and P. Vettiger

J. Vac. Sci. Technol. B 12, 3460 (1994); http://dx.doi.org/10.1116/1.587532 (5 pages) | Cited 3 times

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An IBM vector‐scan machine is adapted to the generation of curved patterns by adding a new primitive to its basic set. Quadratic polynomials characterize the curved boundaries of this new primitive, allowing the construction of any conic section in the beam‐stepping plane. The implementation is based on a digital signal processor running in tandem with the existing microcontroller and maintains full compatibility with existing hardware and software. The conic sections are approached to the best possible accuracy (better than 1/2 beam step), and the dose is uniformly distributed throughout the area of the primitive as the exposed points remain on a cartesian grid. The successful exposure of an elliptical diffractive optical element with chirped periodicity demonstrates the functionality of the upgraded machine.
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85.40.Hp Lithography, masks and pattern transfer

Address data reduction and lithography performance of graybeam writing strategies for raster scan mask generation

Andrew Muray, Frank Abboud, Frederick Raymond, and C. N. Berglund

J. Vac. Sci. Technol. B 12, 3465 (1994); http://dx.doi.org/10.1116/1.587533 (8 pages) | Cited 3 times

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Graybeam (GB) writing methods [Muray, Abboud, and Raymond, J. Vac. Sci. Technol. B 11, 2390 (1993)], including the new combination of graybeam plus per pixel deflection (GBPPD), were first investigated last year as a method for improving throughput on an e‐beam raster scan machine. These techniques were shown to produce pattern edge placement resolution equivalent to writing at a smaller address unit, thereby improving throughput. The GB and GBPPD writing techniques are further investigated to address data reduction and lithographic performance. Accurate simulations and lithography on two‐dimensional test patterns for GBPPD writing are presented.  
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85.60.-q Optoelectronic devices

Surface imaging by silylation for low voltage electron‐beam lithography

M. Böttcher, L. Bauch, and I. Stolberg

J. Vac. Sci. Technol. B 12, 3473 (1994); http://dx.doi.org/10.1116/1.587534 (5 pages) | Cited 5 times

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Electron‐beam lithography with low voltage electrons offers a number of advantages. Low voltage electrons have short penetration depths. Therefore, backscattering from the substrate which causes the proximity effect as well as radiation damage in the substrate are potentially minimized or excluded. As a consequence, a top surface imaging resist technology should be applied. The surface imaging by silylation was combined with low voltage electron exposure using 1.8‐, 3‐, and 5‐keV electrons. Resist structures down to 50 nm are shown.
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85.40.Hp Lithography, masks and pattern transfer
79.20.-m Impact phenomena (including electron spectra and sputtering)
41.85.-p Beam optics
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

100 kV ghost electron beam proximity correction on tungsten x‐ray masks

M. A. Gesley and M. A. McCord

J. Vac. Sci. Technol. B 12, 3478 (1994); http://dx.doi.org/10.1116/1.587535 (5 pages) | Cited 2 times

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100 kV electron beam exposures of tungsten x‐ray masks have been made using ghost proximity correction. 0.15 μm lithography is possible on masks having a 0.3 μm thick tungsten absorber. 0.25 μm features are resolved on masks with a 0.6 μm tungsten film thickness. The linewidth control (±5%) and dose latitude (2.5 nm edge shift per 1% dose change) are as good or better than those obtained by dose modulation, and contrast is sufficiently high to permit dry etch pattern transfer into the tungsten absorber. The process latitude makes 100 kV ghost exposures suitable for patterning 1 Gbit dynamic random access memories on 1m x‐ray masks.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Efficiency enhancement of Monte Carlo simulation of particle beam interaction by separation of stochastic and continuum contributions

T. R. Groves

J. Vac. Sci. Technol. B 12, 3483 (1994); http://dx.doi.org/10.1116/1.587536 (6 pages) | Cited 3 times

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In electron and ion beam lithography, the particle–particle interaction in the drift length of the system imposes a fundamental limitation on the useful current obtainable for a given resolution. This is a classical N‐body problem, for which Monte Carlo simulation has proven useful for predicting the size of the effect. Monte Carlo simulation is slow, however, due to the fact that N(N−1)/2 computations of the Lorentz force must be done for N particles at each step. The purpose of this study is to investigate the limitation on computational efficiency. Based on this, an efficient algorithm is proposed and demonstrated. The approach consists of separating the interaction force arising from the average charge distribution from that arising from random fluctuations in charge density. These two contributions are computed separately, and the results combined in a way which eliminates ‘‘end effects’’ arising from a finite particle sample length. The results show that a significant reduction is possible in the number of particles needed to obtain a given level of accuracy. This is expected to result in reduced computation time.  
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
02.70.Rr General statistical methods

Coulomb effects in retarding field lenses

Alan D. Brodie

J. Vac. Sci. Technol. B 12, 3489 (1994); http://dx.doi.org/10.1116/1.587456 (5 pages)

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The purpose of this article is to investigate the Coulomb interaction aberration and its impact on retarding field lens design. Discussion of Coulomb effects in electron beam systems have mainly been limited to analysis methods, accuracy of assumptions in analytical models, and optimization of computational analysis. Here, a basic column design is considered and analyzed to give some design rules. A practical system, KLA’s SEMSpec, based on these design rules is analyzed and performance given.
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41.85.Ne Electrostatic lenses, septa
41.85.Ja Particle beam transport
41.85.Gy Chromatic and geometrical aberrations
41.75.Fr Electron and positron beams

Co‐planar multiple‐ring electrostatic particle‐beam lenses

Michael J. Moran

J. Vac. Sci. Technol. B 12, 3494 (1994); http://dx.doi.org/10.1116/1.587457 (4 pages)

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Electrostatic particle‐beam lenses using a concentric co‐planar array of independently biased rings can be advantageous for some applications. Traditional electrostatic lenses often consist of axial series of biased rings, apertures, or tubes. The science of lens design has devoted much attention to finding axial arrangements that compensate for the substantial optical aberrations of the individual elements. Thus, as with multielement lenses for light, a multielement charged‐particle lens can have optical behavior that is far superior to that of the individual elements. This article discusses the possibility that transverse multiple‐concentric‐ring lenses can achieve high performance, while also having advantages in terms of compactness and optical versatility.
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41.85.Ne Electrostatic lenses, septa

Electron–electron scattering in microcolumns

M. G. R. Thomson

J. Vac. Sci. Technol. B 12, 3498 (1994); http://dx.doi.org/10.1116/1.587458 (5 pages) | Cited 7 times

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Field‐emission electron‐beam columns a few millimeters in length have been proposed as a route to gaining improved probe currents and probe sizes because of their reduced lens aberrations. The probe current and probe size in such columns will be strongly influenced by electron–electron interactions. These effects have been studied theoretically as functions of electron energy and column length to allow comparisons with instruments of conventional size. The scattering within the column has been analyzed using analytic approximations. The results show important differences in the lateral scattering effect which leads directly to broadening of the focused probe. The region close to the cathode has been treated using both Monte Carlo and analytic methods. The energy broadening from a field‐emission electron gun will be similar in all cases for equal emission angular current density, and the contribution to the final probe will depend on the chromatic aberration coefficient of the focusing lens. We conclude that small, low energy columns will have improved properties as long as the physical size and lens aberration coefficients are reduced in proportion to the beam energy, and that for low energy scanning electron microscopes, reducing the overall size is very advantageous. The scattering effects are not uniformly distributed throughout the length of the column, and design changes to reduce the lateral scattering effect for given current are discussed.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.-w Vacuum microelectronics
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Sub‐40 nm resolution 1 keV scanning tunneling microscope field‐emission microcolumn

E. Kratschmer, H. S. Kim, M. G. R. Thomson, K. Y. Lee, S. A. Rishton, M. L. Yu, and T. H. P. Chang

J. Vac. Sci. Technol. B 12, 3503 (1994); http://dx.doi.org/10.1116/1.587459 (5 pages) | Cited 5 times

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Recent advances in microcolumn design and fabrication have led to a significant improvement in the resolution obtained with a new 3.5 mm long microcolumn. At an electron energy of 1 keV and 2 mm working distance, the beam diameter, measured by the signal rise‐time while scanning over a sharp edge, is 40 nm and the resolution observed in scanning transmission electron microscope images is about 30 nm. These experimental results agree well with results of the electron‐optical modeling. All lenses and apertures in the column are made from silicon membranes and assembled using a novel ultrahigh vacuum compatible, multilayer anodic bonding technique. The scanning tunneling microscope aligned field‐emission source uses an oxygen processed, 50 nm radius, cold 〈111〉 W field‐emission tip. Good emission stability for scanning electron microscope operation has been achieved with a few percent of root‐mean‐square current fluctuation over about 30 min. With periodic tip flashes, the system has been operated reliably over several weeks. A novel in situ tip alignment technique with respect to the extractor electrode has been developed. This technique also provides information about the tip emission characteristics during column operation.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics
85.45.-w Vacuum microelectronics
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

An analytical model of stochastic interaction effects in projection systems using a nearest‐neighbor approach

M. M. Mkrtchyan, J. A. Liddle, S. D. Berger, L. R. Harriott, A. M. Schwartz, and J. M. Gibson

J. Vac. Sci. Technol. B 12, 3508 (1994); http://dx.doi.org/10.1116/1.587460 (5 pages) | Cited 9 times

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Image blurring as a result of stochastic particle interactions has been investigated for projection electron‐ and ion‐beam lithography systems. The investigation was made on the basis of a simple, nearest‐neighbor, analytical model, proposed and developed here, for stochastic particle–particle interactions. The results obtained using this model are in close agreement with those given by Jansen [Coulomb Interactions in Particle Beams (Academic, Boston, 1990)] for an extended parallel beam segment in the Holtsmark regime; at the same time they are extendable over a wide range of conditions, unlike Jansen’s results. The results obtained for a parallel beam are applied to more realistic systems by dividing the beam into nearly cylindrical, uncorrelated slices. This method is used to determine the dependence of the image blur on beam parameters for a doublet. Our results correlate well with those obtained by Monte Carlo calculations.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
42.30.Va Image forming and processing

Novel electrostatic column for ion projection lithography

A. Chalupka, G. Stengl, H. Buschbeck, G. Lammer, H. Vonach, R. Fischer, E. Hammel, H. Löschner, R. Nowak, P. Wolf, W. Finkelstein, R. W. Hill, I. L. Berry, L. R. Harriott, J. Melngailis, et al.

J. Vac. Sci. Technol. B 12, 3513 (1994); http://dx.doi.org/10.1116/1.587461 (5 pages) | Cited 13 times

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Ion projection lithography (IPL) is being considered for high volume sub‐0.25‐μm lithography. A novel ion‐optical column has been designed for exposing 20×20 mm2 fields at 3× reduction from stencil mask to wafer substrates. A diverging lens is realized by using the stencil mask as the first electrode of the ion‐optical column. The second and third electrode form an accelerating field lens. The aberrations of the first two lenses (diverging lens and field lens) are compensated by an asymmetric Einzel lens projecting an ion image of the stencil mask openings onto the wafer substrate with better than 2 mrad telecentricity. Less than 30 nm intrafield distortion was calculated within 20×20 mm2 exposure fields. The calculation uncertainty is estimated to be about 10 nm. The calculation holds for helium ions with ≊10 keV ion energy at the stencil mask and 150 keV ion energy at the wafer plane. A virtual ion source size of 10 μm has been assumed. The calculated chromatic aberrations are less than 60 nm, assuming 6 eV energy spread of the ions extracted from a duoplasmatron source. Recently a multicusp ion source has been developed for which preliminary results indicate an energy spread of less than 2 eV. Thus, with a multicusp source chromatic aberrations of less than 20 nm are to be expected. The ion energy at the crossover between the field lens and the asymmetric Einzel lens is 200 keV. Therefore, stochastic space charge induced degradations in resolution can be kept sufficiently low. The divergence of the ion image projected to the wafer plane is less than 2 mrad. Thus, the ‘‘usable’’ depth of focus for the novel ion optics is in the order of 10 μm.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.85.-p Beam optics
85.45.-w Vacuum microelectronics

Minimum feature sizes and ion beam profile for a focused ion beam system with post‐objective lens retarding and acceleration mode

A. Kieslich, J. P. Reithmaier, and A. Forchel

J. Vac. Sci. Technol. B 12, 3518 (1994); http://dx.doi.org/10.1116/1.587462 (5 pages) | Cited 11 times

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The beam characteristics of a focused Ga+‐ion beam (FIB) at ion energies between 10 and 150 keV have been investigated by using a 100 keV focused ion beam system with an additional post‐objective lens retarding and acceleration electrode. Line structures with minimum feature sizes down to 20 nm almost independent of the landing energy of the ions could be realized by sputtering line patterns in a gold‐coated GaAs substrate. The current density profile was determined over six orders of magnitude by measuring the radii of FIB‐exposed dot structures as a function of the ion dose. The beam diameters have been found to be in the range between 30 and 45 nm, nearly independent of the available ion energies. The photoluminescence signal of locally intermixed AlGaAs/GaAs quantum well structures was used to study the spatial resolution of FIB‐implanted line patterns. The results were compared with the lateral resolution, which can be calculated from the current density distribution of the beam profile.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
78.66.Fd III-V semiconductors
07.77.-n Atomic, molecular, and charged-particle sources and detectors

CoSi2 microstructures by means of a high current focused ion beam

L. Bischoff, J. Teichert, E. Hesse, D. Panknin, and W. Skorupa

J. Vac. Sci. Technol. B 12, 3523 (1994); http://dx.doi.org/10.1116/1.587463 (5 pages) | Cited 12 times

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The Rossendorf focused ion beam IMSA‐100 was constructed and used for writing implantation of cobalt to form CoSi2‐submicron structures on silicon by ion beam synthesis. Two types of cobalt containing liquid alloy ion sources were developed with Co–Nd and Co–Ge alloys. The fabrication of CoSi2 structures by stoichiometric implantation of Co+ (E=30–35 keV, Iion=1.3 nA) and Co2+ ions (E=60 keV, Iion=0.6 nA) at doses between 0.3 and 5×1017 cm−2 and a subsequent two step annealing (600 °C, 60 min; 1000 °C, 30 min in N2) is demonstrated. The dose dependence as well as the influence of the substrate temperature between room temperature and 400 °C during ion implantation on the ion beam synthesis process were studied. The quality of the silicide submicron structures was investigated by scanning electron microscopy, energy dispersive x‐ray analysis, and electrical measurements. While the room temperature implantation and subsequent annealing generate an inhomogeneous CoSi2 film, 400 °C substrate heating during implantation leads to a continuous film with a resistivity below 20 μΩ cm, comparable with broad beam implantation.
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61.72.uf Ge and Si

Stress‐induced pattern‐placement errors in thin membrane masks

J. Alexander Liddle and C. A. Volkert

J. Vac. Sci. Technol. B 12, 3528 (1994); http://dx.doi.org/10.1116/1.587464 (5 pages) | Cited 3 times

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A simple analytical model for determining stress‐induced pattern‐placement errors in a variety of thin membrane masks is described. The predicted distortions for proximity x‐ray, projection ion‐beam, and projection electron‐beam (SCALPELTM) masks, currently proposed for use with the various technologies, are compared to the maximum allowable errors for successful lithography at sub‐0.25 μm design rules. This comparison indicates that these errors may have a significant impact on mask cost and cost of ownership for x‐ray and ion‐beam lithography.
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85.40.Hp Lithography, masks and pattern transfer

Experimental investigation of stochastic space charge effects on pattern resolution in ion projection lithography systems

E. Hammel, A. Chalupka, J. Fegerl, R. Fischer, G. Lammer, H. Löschner, L. Malek, R. Nowak, G. Stengl, H. Vonach, P. Wolf, W. H. Brünger, L.‐M. Buchmann, M. Torkler, E. Cekan, et al.

J. Vac. Sci. Technol. B 12, 3533 (1994); http://dx.doi.org/10.1116/1.587465 (6 pages) | Cited 9 times

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Coulomb interactions in charged particle beams are known to blur beam profiles as the total current is increased. While this has been studied in single ion beam columns, similar studies have not been published, so far, for masked ion beam projection systems. Experiments were performed using highly transparent stencil grid masks of 40 mm×40 mm area with resolution test patterns in central and peripheral positions. Such grid test masks have been inserted into the ion projection lithography machine IPLM‐02 and into the ‘‘Alpha ion projector’’ operated at 5× ion–optical reduction (Alpha‐5×). A standard duoplasmatron ion source was used for both ion projectors. Operating the IPLM‐02 at 8.7× demagnification with He+ ions of 73 keV ion energy at the wafer plane (about 50 keV at the crossover), no significant degradation in resolution was found changing the ion beam current through the column from 300 nA to 2 μA. Using the Alpha‐5×, the total current through the column was changed either by varying the ion source emission or by blanking parts of the mask, using appropriate apertures. The special design of the Alpha ion projector with an ion energy of 5–7 keV at the crossover region between the imaging lenses is a sort of worst case scenario for space charge effects. Thus, the influence of stochastic space charge effects on resolution could be clearly identified. Using helium ions with 7 keV at the crossover the exposure latitude (change of linewidth in nm with 10% change of exposure dose) increased by 60 nm when changing the current through the column from 3 to 120 nA. Based on this experimental result with the Alpha ion projector and on well‐known scaling laws, it can be stated that a newly designed ion projector (ALG‐1000) with 200 keV ion energy at the crossover will allow sub‐0.15‐μm resolution for total ion beam currents through the column of 3 μA, as needed for future high volume production of dense patterns within ≥20 mm×20 mm exposure fields. Furthermore, improved designs of ion optical columns will allow a reduction of system length, thus reducing the influence of stochastic space charge effects. Consequently, ion projection lithography can be extended to the high volume fabrication of sub‐0.10‐μm feature patterns in large exposure fields.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Contrast of ion beam proximity printing with nonideal masks

D. P. Stumbo and J. C. Wolfe

J. Vac. Sci. Technol. B 12, 3539 (1994); http://dx.doi.org/10.1116/1.587466 (4 pages) | Cited 2 times

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In ion beam proximity printing, a broad, collimated beam of light ions is directed through a stencil mask. For this process, aerial image contrast is limited primarily by scattering near the edges of the mask openings. Previous work by Karapiperis et al. [J. Vac. Sci. Technol. 19, 1259 (1981)] considered the energy deposited in resist (and resist profiles) for ideal incident ion beams. Randall, Stern, and Donnelly [J. Vac. Sci. Technol. B 4, 201 (1986)] have calculated mask contrast as a function of pattern density and mask thickness for grid support masks with smooth vertical sidewalls, showing that contrast is a function of mask aspect ratio. We present simulations from a modified version of TRIM85 including the effects of mask wall angle, roughness and thickness, ion incident angle, resist scattering, and pattern spatial frequency for infinite line and space patterns. Contrast of the deposited energy density and estimated process sensitivity are shown, as well as a simulated resist profile derived using a string development model. A histogram of the angular dependence of ion scattering shows that the effect is a diffuse exposure at reasonable mask‐to‐wafer gaps. It is also shown that for reentrant mask profiles the contrast increases with mask thickness. Our simulations show that 0.25 μm line and space patterns in 2 μm thick masks with reasonable parameters can have a contrast of 12, a contrast of 8 is attainable for 0.125 μm line and space patterns, and the stringent linewidth control required by surface acoustic wave devices can be achieved with ±5% dose control.
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85.30.-z Semiconductor devices

Pattern distortions in stencil masks

John N. Randall

J. Vac. Sci. Technol. B 12, 3543 (1994); http://dx.doi.org/10.1116/1.587467 (4 pages) | Cited 2 times

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Stencil marks are required for some forms of projection and proximity printing with charged particles. There are several technological problems associated with the use of stencil masks such as forbidden geometries and gross pattern deformations caused by mask openings which are large even in one dimension. In this article, we will deal with the issue of mask deformation due to thermal effects and pattern‐dependent redistribution of stress. We will also discuss approaches to minimizing these pattern distortions.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Hp Lithography, masks and pattern transfer

Ion projection lithography over wafer topography

W. H. Brünger, L.‐M. Buchmann, M. A. Torkler, and W. Finkelstein

J. Vac. Sci. Technol. B 12, 3547 (1994); http://dx.doi.org/10.1116/1.587468 (3 pages) | Cited 3 times

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Ion projection lithography has been used to structure resist lines running over 0.5‐μm‐high surface steps on a wafer. Line profiles were straight and did not change at the surface step consisting of SiO2 on Si. 0.2‐μm resolution was found in 0.7‐μm‐thick positive and negative tone resist. In the list of tested resists [poly(methylmethacrylate) (PMMA), Ray PN, and AZ 5206], the novolack resist AZ 5206 showed better edge roughness compared to Ray PN due to the lower sensitivity of AZ. Exposure times range from 300 ms to 3 s. The recorded penetration depth in PMMA was 0.8 μm using H+ ions at 70 keV. A variation of ion energy gives the possibility to adjust the penetration depth to the required resist thickness and minimize radiation damage in the substrate.
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85.40.Hp Lithography, masks and pattern transfer
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

An industrial plasma process for avoiding charge effect

Philippe Romand, André Weill, Jean‐Pierre Panabière, and Alain Prola

J. Vac. Sci. Technol. B 12, 3550 (1994); http://dx.doi.org/10.1116/1.587469 (5 pages)

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Insulating materials such as photoresists retain charges during electron or ion exposure. The ultimate performances of techniques such as scanning electron microscopy (SEM), trilayer e‐beam lithography, or plasma etching can be strongly affected by this phenomenon: observations of highly resolved resist patterns and the subsequent dimensional measurements by SEM are limited by significant charge effects; resist charge during trilayer electron‐beam exposure can produce considerable pattern placement errors; surface charging is also reported to damage etching profiles and to produce microloading effects during plasma etching. Techniques such as metal deposition, use of intrinsically conducting polymers, or Ar+ or H+ high energy implantation are mentioned among others for reducing the electrical resistance of the photoresist patterns. However, due to several major drawbacks (metallic contamination, nonavailability of materials, and global cost of the process), none of these methods has been accepted today at a manufacturing level. This article reports on a new process for increasing the electrical conductance of novolak based photoresist patterns and consequently for avoiding these charge effects.
It consists in subjecting the photoresist to a nonchemically reactive plasma. The process appears to be cost‐effective, robust, and presents a wide latitude. The dependence of the electrical conductivity on the various experimental parameters is described. X‐ray photon analyses previously conducted at Centre National d’Etude des Télécommunications (CNET) have shown that argon plasma etching, under specific conditions, can create the graphitization of the surface of the photoresist, leading to a net decrease in the electrical resistivity. The results of the various physicochemical analyses reported here indicate that the composition of the materials obtained after plasma treatment is very close to that obtained by high energy ion implantation. It is shown that the argon plasma treatment yields a sufficiently high conductivity level to avoid the charge effects occurring in the three techniques mentioned above. Considering the gain in throughput (30–60 wafers per hour) and in capital cost, compared to the high energy ion implantation process, the argon plasma treatment can be considered as a real industrial process.  
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Secondary electron line scans over high resolution resist images: Theoretical and experimental investigation of induced local electrical field effects

Luca Grella, Enzo Di Fabrizio, Massimo Gentili, Marco Baciocchi, Luigi Mastrogiacomo, Romano Maggiora, and Luigi Capodicci

J. Vac. Sci. Technol. B 12, 3555 (1994); http://dx.doi.org/10.1116/1.587470 (6 pages) | Cited 2 times

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The effects of the local electric fields generated during the e‐beam inspection of high resolution resist features at low voltage are discussed. A theoretical model based on the Monte Carlo technique was developed to simulate the effect of the induced electrical fields on the primary beam and on emitted secondary electrons. It is here proved that reentering secondary electrons act as a negative feedback to the local positive retarding field when at least one of the insulating materials of the sample being inspected has a secondary electron yield bigger than one. Such a recombination mechanism is more important than primary electron absorption, as this last factor takes place far from the escape depth layer. The positive charge compensation prevents the local positive field from growing as the number of line scans increases and allows the local field to reach stability. At the top of resist features, potential values as high as 40 V were found. Although the scanning electron microscope image is highly affected by induced voltage contrast, critical dimension (CD) information is not distorted when the stability conditions are fulfilled; namely, a CD control threshold algorithm can be applied by properly choosing the threshold signal level. The modeling of secondary electron emission and absorption requires a single loop, composed of Monte Carlo simulation, local field computation, and electron ray tracing, to be iterated several times. This computation strategy is applied to feature sizes from 1 μm down to 0.25 μm and to geometries such as line arrays and isolated lines. Two different accelerating voltages are studied, namely 1.2 and 1.5 keV. Probe beam currents of 3 and 10 pA are also considered. In addition, the effect of a sample tilting of 20° is also accounted for. Computation accuracy is proved by comparing theoretical data to experimental data obtained by a cold cathode tungsten field emission microscope.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
79.20.Hx Electron impact: secondary emission

Design of an atomic force microscope with interferometric position control

J. Schneir, T. H. McWaid, J. Alexander, and B. P. Wilfley

J. Vac. Sci. Technol. B 12, 3561 (1994); http://dx.doi.org/10.1116/1.587471 (6 pages) | Cited 18 times

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Advances in the manufacture of integrated circuits, x‐ray optics, magnetic read–write heads, optical data storage media, and razor blades require advances in ultraprecision metrology. Each of these industries is currently investigating the use of atomic force microscopy (AFM) to improve the precision and accuracy of their manufacturing process control. To facilitate the use of AFMs for manufacturing we have developed an AFM capable of making accurate dimensional measurements. We call this system the calibrated AFM (C‐AFM). The C‐AFM has been constructed as much as possible out of commercially available components. We use a flexure stage driven by piezoelectric transducers for scanning, a heterodyne interferometer to measure the X and Y displacements of the sample, a capacitance sensor to measure the Z displacement of the sample, and a commercially available AFM control system. The control system has two feedback loops which read from the X and Y interferometers, respectively, and adjust the piezoelectric voltages to keep the X‐Y scan position accurate. The critical electromechanical and metrology issues involved in the construction and operation of such a system will be discussed in detail.
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07.90.+c Other topics in instruments, apparatus, and components common to several branches of physics and astronomy (restricted to new topics in section 07)

Edge position measurement with a scanning probe microscope

J. E. Griffith, H. M. Marchman, and L. C. Hopkins

J. Vac. Sci. Technol. B 12, 3567 (1994); http://dx.doi.org/10.1116/1.587472 (4 pages) | Cited 4 times

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A fundamental requirement in critical dimension measurement is determination of the edge positions. Edge position measurement can be degraded by many sources of error, the probe‐sample interaction usually being the most important of them. In most cases a sharp conical probe is adequate to locate the top of an edge, and it can scan the entire edge if the walls are not too steep. We discuss aspects of the measurement that affect the uncertainty, such as tip radius, instrument drift, and surface roughness. Measurements with a conical probe of two samples are included. The first is very thin chrome on a quartz substrate, and the second sample is photoresist on a Si wafer.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Force probe characterization using silicon three‐dimensional structures formed by focused ion beam lithography

K. M. Edenfeld, K. F. Jarausch, T. J. Stark, D. P. Griffis, and P. E. Russell

J. Vac. Sci. Technol. B 12, 3571 (1994); http://dx.doi.org/10.1116/1.587473 (5 pages) | Cited 2 times

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The creation of a localized etch stop by focused ion beam implantation of Ga+ into Si combined with selective material removal by sputtering has been used to produce submicron size three‐dimensional structures. These funnellike structures have been used to characterize probes used in atomic force microscopy.  
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Real‐time observations of extreme‐ultraviolet aerial images by fluorescence microimaging

Bruno La Fontaine, Don L. White, Obert R. Wood, Alastair A. MacDowell, Zhengquan Tan, Gary N. Taylor, Don M. Tennant, and Steven L. Hulbert

J. Vac. Sci. Technol. B 12, 3576 (1994); http://dx.doi.org/10.1116/1.587474 (4 pages)

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A new technique, fluorescence microimaging (FMI), using single‐crystal phosphors was used to look directly at aerial images produced by an extreme‐ultraviolet (EUV) camera operating at a wavelength of 139 Å. The achieved spatial resolution was estimated to be ∼0.2 μm. A comparison of this technique with the usual resist‐exposure scanning electron microscopy inspection technique as a means of focusing a 20×EUV Schwarzschild camera was performed. FMI could in principle be improved to view fluorescent images with features as small as 0.07 μm, in real time.
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42.30.Va Image forming and processing
85.40.Hp Lithography, masks and pattern transfer

Yaw compensation for an electron‐beam lithography system

Robert Innes

J. Vac. Sci. Technol. B 12, 3580 (1994); http://dx.doi.org/10.1116/1.587475 (5 pages)

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Recent experience with the wayless planar stage designed by IBM shows that accurate e‐beam lithography is possible in the Write‐on‐the‐FlyTM mode with varying stage yaw. The metrology equations necessary to compensate for yaw and axial misalignment of the interferometers with respect to the laser beam are introduced for plane mirror interferometers of the double‐beam type. Geometric equations are derived for various errors of setup of the column, lasers, and interferometers, and for relative positioning errors of the distance and yaw interferometers. The rotation of beam electron deflections and the required yaw‐induced electron‐beam offset are updated within 10 μs using digital signal processors. The offsets for each coordinate sufficient for Write‐on‐the‐Fly lithography are constants to be determined by calibration in terms of the form: const×sin(yaw), const×(interferometer reading)×sin(yaw), and (interferometer reading+const) ×[1−cos(yaw)]. The optimum choice of the definition of the zero point of yaw and the effect of this choice on both the form of the metrology equations and the calibration procedures are discussed.
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85.40.Hp Lithography, masks and pattern transfer

Nanometer‐scale dimensional metrology for advanced lithography

H. M. Marchman, J. E. Griffith, J. Z. Y. Guo, J. Frackoviak, and G. K. Celler

J. Vac. Sci. Technol. B 12, 3585 (1994); http://dx.doi.org/10.1116/1.587476 (6 pages) | Cited 2 times

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Increased performance of lithographic process techniques has been the key enabler for the continued reduction of minimum device feature sizes down to 0.25 μm and beyond. However, this increase in performance has been accompanied by the added fabrication complexity of the various types of lithographic reticles. Theoretical simulations have revealed that metrological requirements for the fabrication of devices having subhalf micrometer dimensions are indeed on the nanometer scale. A comparison of available metrology tools is presented as well as improvements to current techniques. Direct correlations between top‐down critical dimension cleanroom scanning electron microscopy (SEM), cross‐sectional analytical SEM, and various atomic force microscopy (AFM) techniques (scanning techniques and probe shapes) are described as well as the use of AFM to nondestructively characterize features on x‐ray membrane masks is described. Finally, the use of novel optical fiber probes to image subresolution quartz features on optical phase‐shifting masks is presented.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
06.20.-f Metrology
42.87.-d Optical testing techniques

Highly accurate critical dimension measurement for sub‐0.5‐μm devices

Hiroshi Yamashita, Ken Nakajima, and Hiroshi Nozue

J. Vac. Sci. Technol. B 12, 3591 (1994); http://dx.doi.org/10.1116/1.587477 (4 pages)

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In the measurement of patterned resists, deviation of the critical dimension (CD) is frequently observed. We have found that contamination on the resist on a Si wafer can degrade the static repeatability more than the charging phenomenon at low accelerating voltage (Vacc), that is, near 1 kV. We investigate the dependence of contamination rate (Rc) and the normalized yield of secondary electrons (δ′) on Vacc and emission current (Ie) in order to clarify the influence of the contamination and charging effects. Experimental results indicate that we can minimize the Rc by optimizing Vacc and Ie. The Rc change cannot be attributed only to the contamination and charging effects, however. It seems, instead, that two competitive reactions (deposition and etching) occur simultaneously during the measurement at low voltage. The etching effect can be interpreted as a dissociation reaction at the resist surface. To reduce the CD deviation and improve the accuracy of the CD measurement, the accelerating voltage and current density must be optimized. Doing so improves the static repeatability from 0.008 to 0.003 μm (3σ).
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Inspection of optical phase‐shifting masks with an automated electron‐beam system

Alan D. Brodie, Zhong‐Wei Chen, Jack Jau, Dan Meisburger, and Brian Grenon

J. Vac. Sci. Technol. B 12, 3595 (1994); http://dx.doi.org/10.1116/1.587478 (5 pages) | Cited 1 time

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There has been great interest lately in using optical masks that contain phase‐shifting structures in order to print smaller features than is possible with a standard binary mask. Because of the many varieties under investigation and the complexity of the phase interactions, no definitive experimental work concerning the effects of various types of defects yet exists. However, it is known that, under some circumstances, defects in a phase‐shifting mask (PSM) will cause a larger deviation in the printed linewidth than a defect of equal size on a binary mask. For 0.25 μm lithography done with a 248 nm stepper using an ‘‘etched Levinson’’ or alternating PSM, it is thought that phase defects as small as 80 nm need to be detected. At present, the only inspection system capable of meeting the size requirements is based on electron optics (KLA SEMSpec). However, this type of system, which was designed to inspect x‐ray masks, requires that the defects exhibit either a topographical or material anomaly in order to be visible and that the mask be conductive. While some types of phase‐shifting masks satisfy the contrast formation requirements, none are conductive. This can be remedied by depositing a metallic layer over the surface. However, in order for inspection to proceed at high speed, the defect contrast and signal level must be high. In this article we elucidate the physics of electron‐beam image formation of conductively coated phase‐shifting masks for various types and thicknesses of coatings. Both theoretical and experimental results are presented. Since adding and removing the conductive coating must be done without damaging the mask, only certain types of coatings and processes are allowable. A list of the most promising coatings is presented along with the supporting experimental evidence. By inspecting a phase‐shifting mask that has intentionally written defects of various types, it is shown that defects as small as 0.1 μm can be reliably found.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
41.90.+e Other topics in electromagnetism; electron and ion optics (restricted to new topics in section 41)

Diffractive techniques for lithographic process monitoring and control

S. Sohail, H. Naqvi, Saleem H. Zaidi, Steven R. J. Brueck, and John R. McNeil

J. Vac. Sci. Technol. B 12, 3600 (1994); http://dx.doi.org/10.1116/1.587479 (7 pages) | Cited 6 times

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Diffraction‐based techniques have been shown to provide convenient, nondestructive, rapid metrology for lithography steps during semiconductor fabrication. Monitoring diffraction from latent images provides the capability to determine exposure tool focus to an absolute accuracy of 0.1 μm. Exposure dose and subsequently post‐exposure bake have also been monitored using diffraction from latent images. Moiré alignment and overlay measurement techniques with nm‐scale precision are demonstrated. Using 0.47‐μm pitch gratings, a 1‐nm translational sensitivity is demonstrated. A novel double‐period moiré grating is used to provide both coarse (∼10 μm) and fine (∼1 μm) capture ranges for integration with existing stage positioning systems. A new diffraction‐order interferometry technique for nm‐precision remote overlay readout is demonstrated, with potential application to latent image structures immediately after exposure. We also present diffraction‐based techniques to measure (critical dimensions) of ≥0.4‐μm linewidth photoresist gratings. The results obtained are in excellent agreement with scanning electron microscope measurements.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Nanometer‐scale patterning of high‐Tc superconductors for Josephson junction‐based digital circuits

J. R. Wendt, T. A. Plut, R. F. Corless, J. S. Martens, S. Berkowitz, K. Char, M. Johansson, S. Y. Hou, and J. M. Phillips

J. Vac. Sci. Technol. B 12, 3607 (1994); http://dx.doi.org/10.1116/1.587480 (4 pages) | Cited 3 times

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A straightforward method for nanometer‐scale patterning of high‐Tc superconductor thin films is discussed. The technique combines direct‐write electron beam lithography with well‐controlled aqueous etches and is applied to the fabrication of Josephson junction nanobridges in high‐quality, epitaxial thin‐film YBa2Cu3O7. We present the results of our studies of the dimensions, yield, uniformity, and mechanism of the junctions along with the performance of a representative digital circuit based on these junctions. Direct current junction parameter statistics measured at 77 K show critical currents of 27.5 μA±13% for a sample set of 220 junctions. The Josephson behavior of the nanobridge is believed to arise from the aggregation of oxygen vacancies in the nanometer‐scale bridge.
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85.25.Cp Josephson devices
85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Fabrication using x‐ray nanolithography and measurement of Coulomb blockade in a variable‐sized quantum dot

M. Burkhardt, Henry I. Smith, D. A. Antoniadis, T. P. Orlando, M. R. Melloch, K. W. Rhee, and M. C. Peckerar

J. Vac. Sci. Technol. B 12, 3611 (1994); http://dx.doi.org/10.1116/1.587481 (3 pages) | Cited 3 times

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We report on the fabrication and measurement of a novel type of quantum dot device in which the shape and size of the dot can be controlled. The device consists of four uniformly spaced quantum point contacts which can be biased to produce quantum dots ranging in size from 600 nm to below 200 nm. The capacitances of the gates controlling the dot are small. Measurements were made at a temperature of 0.3 K for three different dot sizes. Devices were fabricated in three lithography steps, with x‐ray nanolithography used to define the final gate layer. The device exhibits conductance maxima whose spacing depends on which quantum point contacts are used to define the quantum dot.  
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Silicon point contacts: Nanofabrication, molecular beam epitaxial growth, and transport measurements

J. W. H. Maes, J. Caro, K. Werner, S. Radelaar, V. I. Kozub, and H. W. Zandbergen

J. Vac. Sci. Technol. B 12, 3614 (1994); http://dx.doi.org/10.1116/1.587482 (5 pages) | Cited 1 time

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We describe a fabrication process for three‐dimensional Si point contacts. The process is based on molecular beam epitaxy to grow electrodes of the devices and on electron‐beam lithography and wet etching to produce holes in the insulator. From scanning electron microscopy and transmission electron microscopy analysis we find that the lower electrode has a perfect crystalline structure, while the upper electrode has a composite structure consisting of a single‐crystalline column grown out of the hole in the insulator and a poly‐crystalline environment. The smallest holes realized have a diameter of 40 nm. I–V curves of point contacts with a boron concentration of about 5×1018 cm−3 and with diameters in the range 200–2000 nm are linear at 300 K and indicate behavior according to the Maxwell resistance, as expected for diffusive transport. Below 40 K variable‐range hopping is the transport mechanism. In this temperature range quadratic I–V curves develop, which can be understood from electric field activated hopping in the point‐contact geometry.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Fabrication and characterization of single‐electron transistors and traps

L. Ji, P. D. Dresselhaus, Siyuan Han, K. Lin, W. Zheng, and J. E. Lukens

J. Vac. Sci. Technol. B 12, 3619 (1994); http://dx.doi.org/10.1116/1.587625 (4 pages) | Cited 18 times

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Al/AlOx/Al tunnel‐junction‐based prototype single‐electron devices have been fabricated using e‐beam lithography with bilayer resist, and two‐angle shadow evaporation. A single‐electron transistor is shown to operate at 4.2 K. Single‐electron traps consisting of an array of seven junctions, coupled to a cross‐type single‐electron transistor for monitoring the change of trapped charges, have been also made and demonstrated long‐term trapping of single charges. We describe the fabrication process and discuss the device characteristics, noise, yield, uniformity, and long‐term stability.  
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.40.Rw Metal-insulator-metal structures

Fabrication of nanostructures in AlGaSb/InAs using electron‐beam lithography and chemically assisted ion‐beam etching

M. Arafa, C. Youtsey, R. Grundbacher, I. Adesida, and J. Klem

J. Vac. Sci. Technol. B 12, 3623 (1994); http://dx.doi.org/10.1116/1.587626 (3 pages) | Cited 4 times

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Electron‐beam patterned wires in InAs/AlGaSb heterostructures were fabricated using chemically assisted ion‐beam etching (CAIBE) with Cl2 and an Ar ion beam. The CAIBE process yielded very vertical sidewalls and smooth wire edges. CAIBE was also used to etch deep trenches through the AlGaSb barrier layer which provided isolation for the wires and suppressed the parallel conductance of the AlGaSb barrier. The interdevice leakage current was also decreased by a final CAIBE device isolation step. Wires 1 μm long and having varying widths between 70 and 210 nm have been fabricated.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.-b Surface treatments

Writing strategies of circular gratings for surface‐emitting lasers using focused ion‐beam (x–y coordinate) and electron‐beam (polar coordinate) lithography

M. Fallahi, I. M. Templeton, F. Chatenoud, G. Champion, M. Dion, and R. Barber

J. Vac. Sci. Technol. B 12, 3626 (1994); http://dx.doi.org/10.1116/1.587627 (5 pages) | Cited 1 time

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In this article the fabrication of circular gratings by electron‐beam lithography (r‐θ coordinates) and by focused ion‐beam lithography (x‐y coordinate) is presented. The differences between the two techniques, relevant to the fabrication of circular patterns, are described. The optimum writing strategies and the quality of circular gratings are compared. Electrically pumped circular‐grating surface‐emitting distributed Bragg reflector (DBR) lasers were fabricated by the two techniques. Room temperature cw operation of a circular‐grating surface‐emitting DBR laser is demonstrated.
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42.55.Px Semiconductor lasers; laser diodes
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fifteen nanometer features by sidewall processing and pattern transfer

John N. Randall and Brian L. Newell

J. Vac. Sci. Technol. B 12, 3631 (1994); http://dx.doi.org/10.1116/1.587628 (4 pages) | Cited 2 times

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A technique which uses conformally deposited silicon oxynitride on e‐beam written polymethylmethacrylate structures to define 15 nm linewidths is described. The sidewalls can be used simply to narrow the opening in resist to produce fine metal lines with a lift‐off process. Freestanding nitride structures can be produced which may be used for pattern transfer in a variety of methods. We demonstrate the production of narrow slots in metal. Additional processing is able to produce narrow slots in resist that then can be used for pattern transfer. We demonstrate a pair of 15 nm metal lines separated by approximately 20 nm. This technique can be applied to the fabrication of quantum effect devices, and has the potential of being extended to well below 10 nm features. These techniques have the potential to be applied in manufacturing since sidewall processing is already used widely in commercial complementary metal–oxide semiconductor processes.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

High efficiency diffractive coupling lenses by three‐dimensional profiling with electron‐beam lithography and reactive ion etching

A. Stemmer, H. Zarschizky, E. Knapek, G. Lefranc, and F. Mayerhofer

J. Vac. Sci. Technol. B 12, 3635 (1994); http://dx.doi.org/10.1116/1.587629 (4 pages) | Cited 2 times

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Single diffractive lenses with submicrometer feature sizes are realized with binary, multilevel, and blazed reliefs using computer‐aided design methods, three‐dimensional (3D) profiling algorithms, direct write e‐beam lithography, reactive ion etching, antireflection coating, and wafer dicing. Depending on the relief profile, maximum diffraction efficiencies of more than 70% for lenses with a high numerical aperture of 0.5 were measured and aberration‐free imaging was observed. In order to enhance the diffraction efficiency we present a method for obtaining Fresnel grating lenses and a flexible 3D shaping of the resist mask for the dry etch process.
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42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Fabrication of single‐domain magnetic pillar array of 35 nm diameter and 65 Gbits/in.2 density

Peter R. Krauss, Paul B. Fischer, and Stephen Y. Chou

J. Vac. Sci. Technol. B 12, 3639 (1994); http://dx.doi.org/10.1116/1.587630 (4 pages) | Cited 21 times

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Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon have been fabricated. The effects of plating current and feature size on the plating rate were investigated. The pillar arrays have a period of 100 nm and the pillar diameters are uniform and as small as 35 nm. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. If each pillar were to represent one bit of information, the density of the pillar arrays would be 65 Gbits/in.2—over two orders of magnitude greater than the state‐of‐the‐art magnetic storage density. The ultrahigh density, together with the single‐domain formation, make these pillar arrays very attractive for high‐density magnetic storage devices and fundamental magnetics studies.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Multiple‐level phase gratings fabricated using focused ion‐beam milling and electron‐beam lithography

S. M. Shank, F. T. Chen, M. Skvarla, H. G. Craighead, P. Cook, R. Bussjager, F. Haas, and D. A. Honey

J. Vac. Sci. Technol. B 12, 3643 (1994); http://dx.doi.org/10.1116/1.587631 (5 pages)

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The fabrication of eight‐level reflective phase gratings in Si by electron‐beam lithography and reactive ion etching, and focused ion‐beam milling, has been investigated. Electron‐beam lithography and reactive ion etching were used to fabricate gratings with 0.5‐μm feature sizes. Alignment of successive levels was held to 50 nm by careful control of proximity effects. Focused ion‐beam milling was used to fabricate continuously blazed surface reliefs. The effects of binary and continuously blazed surface reliefs on the first‐order diffraction efficiency were determined. Eight‐level binary reliefs produced efficiencies of 75% and were limited by phase errors while continuously blazed reliefs produced efficiencies of 90%.  
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42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer

Patterning a 50‐nm period grating using soft x‐ray spatial frequency multiplication

Max Wei, David T. Attwood, T. K. Gustafson, and Erik H. Anderson

J. Vac. Sci. Technol. B 12, 3648 (1994); http://dx.doi.org/10.1116/1.587632 (5 pages) | Cited 15 times

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Soft x‐ray spatial frequency multiplication is a technique that has the capability of reducing by a factor of 2 or more the finest period grating that can be written by other methods. We describe two geometries for this technique: a single‐grating geometry that requires spatially coherent illumination, and a two‐grating geometry that can be used with incoherent illumination. Starting with a parent grating of period p and area A, gratings of period p/2, p/4, p/6 over an area A/3, A/5, A/7, respectively, can be printed in the single‐grating geometry. The two‐grating geometry produces the same final grating periods for parent gratings of period p, but the final grating area is limited only by the sizes of the parent gratings. As an initial demonstration of this technique, we have used the single‐grating geometry to pattern a 50‐nm period grating in polymethylmethacrylate over an area of 30 μm×100 μm, starting with a 100‐nm period parent grating with an area of 90 μm×100 μm. The x‐ray source was a synchrotron undulator at λ=18 Å and required a 5‐min exposure time. Recent developments in coherent radiation from x‐ray undulator sources will give shorter exposure times and permit larger areas to be patterned in the single‐grating geometry.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Low‐voltage electron beam lithography on GaAs substrates for quantum wire fabrication

R. Steffen, F. Faller, and A. Forchel

J. Vac. Sci. Technol. B 12, 3653 (1994); http://dx.doi.org/10.1116/1.587633 (5 pages) | Cited 7 times

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We have studied the benefits of low‐voltage electron beam lithography (EBL) in polymethyl methacrylate (PMMA) positive electron beam resist for the fabrication of quantum wire etch masks on GaAs substrates. In order to determine the reduction of electron scattering effects for low‐voltage EBL, we have compared point exposures in 100‐nm‐thick PMMA for energies between 2.3 and 15 keV. The exposure distribution functions were fitted by combinations of Gaussians and exponentials, showing significant energy‐dependent deviations from the widely used double‐Gaussian function. The results indicate that on GaAs substrates, backscattering at 2.3 keV is reduced by about two orders of magnitude compared to 15 keV exposures. InGaAs/GaAs quantum wires have been fabricated using low‐voltage EBL, followed by an aluminum‐liftoff step and wet‐chemical etching. In sharp contrast to wires delineated at 25 keV, the resulting structures show no width variations at the field edges caused by proximity effects. The photoluminescence spectra show a wire width dependent blue shift up to 8 meV for 18‐nm‐wide structures, caused by lateral quantization.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Luminescence spectroscopy of dry etched single dots and wires

B. Hübner, B. Jacobs, Ch. Gréus, R. Zengerle, and A. Forchel

J. Vac. Sci. Technol. B 12, 3658 (1994); http://dx.doi.org/10.1116/1.587634 (5 pages) | Cited 2 times

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Using spatially resolved luminescence spectroscopy we have measured the luminescence properties of single dry etched InP/InGaAs wires and dots. For fabrication of the test structures single quantum well samples grown by metalorganic vapor phase epitaxy were structured by e‐beam lithography and subsequent dry etched with CH4, H2, and Ar at different bias voltages. The lateral dimensions of the wires and dots ranged from 10 μm down to 70 nm. The smallest structures that could be measured at room temperature and without surface passivation were 70 nm for wires and 100 nm for dots. By spatially resolved intensity scanning of mesa structures a characteristic intensity profile could be observed. Due to the inhomogeneous excitation and diffusion effects, a significant enhancement of the luminescence on the edges and corners of the structures can be seen even for nonovergrown samples.
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78.66.Fd III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Electron beam lithography with monolayers of alkylthiols and alkylsiloxanes

M. J. Lercel, G. F. Redinbo, F. D. Pardo, M. Rooks, R. C. Tiberio, P. Simpson, H. G. Craighead, C. W. Sheen, A. N. Parikh, and D. L. Allara

J. Vac. Sci. Technol. B 12, 3663 (1994); http://dx.doi.org/10.1116/1.587635 (5 pages) | Cited 18 times

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Self‐assembled monolayers have been modified with focused electron beams of energy 1–50 keV and scanning tunneling microscopy (STM) based lithography with energies of ∼10 eV. Modifications ∼15 nm in size have been formed by STM and ∼25 nm in size by 50 keV beams. The fact that these materials work as self‐developing electron beam resists is demonstrated by both atomic force microscopy imaging and pattern transfer using conventional wet etchants. Patterns have been transferred to silicon substrates to a depth of ≳120 nm with a multistep wet etching process. The mechanism of electron beam modification has also been explored to better design future monolayer processes.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Electron‐beam lithography for the fabrication of air‐bridged, submicron Schottky collectors

R. E. Muller, S. C. Martin, R. P. Smith, S. A. Allen, M. Reddy, U. Bhattacharya, and M. J. W. Rodwell

J. Vac. Sci. Technol. B 12, 3668 (1994); http://dx.doi.org/10.1116/1.587636 (5 pages) | Cited 3 times

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T‐gate technology as is commonly used for field‐effect transistors and high electron mobility transistors has been adapted for use in Schottky‐collector resonant tunneling diodes (SRTDs) devices in which it is necessary for the footprint to be extremely small in both dimensions. By air bridging the contact, GaAs‐based RTDs with projected cutoff frequencies of nearly 1 THz have been fabricated. The process is advantageous for the fabrication of terahertz diodes because of the large periphery to area ratio associated with the small footprint (which reduces the parasitic resistance), because small areas provide better impedances, and because the air bridge both reduces parasitic capacitances and provides certain processing advantages. The process is also inherently planar in contrast with other diode implementations for use at submillimeter wave frequencies. In addition to the GaAs‐based RTDs, the process is also being used for the fabrication of GaAs Mott diodes, which have cutoff frequencies of 12.5 THz and InGaAs/AlAs RTDs, which appear to have cutoff frequencies of 2.5–3 THz.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.Hi Surface barrier, boundary, and point contact devices

Sub‐0.1‐μm T‐shaped gate fabrication technology using mixing‐layer sidewalls in a double‐layer resist system

N. Samoto, I. Miura, Y. Makino, and K. Yamanoguchi

J. Vac. Sci. Technol. B 12, 3673 (1994); http://dx.doi.org/10.1116/1.587637 (4 pages) | Cited 1 time

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In this paper, we report on a novel fabrication technique for sub‐0.1‐μm T‐shaped gates for ultrahigh frequency field effect transistors using the mixing layer generated in a double‐layer resist system. The typical resist layer structure in this work consists of a 1.1‐μm ultraviolet (UV) resist, PFI‐15A, and a 0.15‐μm electron‐beam (EB) resist, polymethylmethacrylate (PMMA). First the PMMA layer is spin‐coated, exposed by EB, and developed to define the gate footprint. Next the PFI‐15A layer is spin‐coated and exposed with i‐line stepper for the gate top, then developed using an image reversal method to obtain an undercut opening. A mixing layer is created at the interface between the resists by the method. This layer acts as a sidewall which reduces the initial PMMA pattern size by 30–40 nm. A T‐shaped gate of a 70‐nm footprint is fabricated from a 0.1‐μm initial linewidth in PMMA using a lift‐off process.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices

Progress in mask technology for ion implantation based nanofabrication

M. Burkard, U. A. Griesinger, A. Menschig, H. Schweizer, H. Klein, G. Böhm, G. Tränkle, and G. Weimann

J. Vac. Sci. Technol. B 12, 3677 (1994); http://dx.doi.org/10.1116/1.587638 (4 pages) | Cited 2 times

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Gold dot implantation masks with diameters down to 45 nm have been defined using a liftoff process and have been used to fabricate GaAs/AlGaAs quantum dots by the technique of masked‐implantation‐enhanced intermixing (MIEI). The photoluminescence of these quantum dots shows a high intensity down to the smallest diameters and a systematic blueshift due to the quantum size effect. Furthermore, a novel nanometer electroplating (NEP) technique for the fabrication of gold dot implantation masks down to 30 nm with high aspect ratios (≳1:3) is presented. It is expected that the NEP masks are superior to the liftoff masks for future application of the MIEI technique.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
61.72.uj III-V and II-VI semiconductors

Fabrication of arrays of nanometer size test structures for scanning probe microscope tips characterization@f|

A. L. Bogdanov, D. Erts, B. Nilsson, and H. Olin

J. Vac. Sci. Technol. B 12, 3681 (1994); http://dx.doi.org/10.1116/1.587639 (4 pages) | Cited 1 time

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A problem in scanning probe microscopy (SPM) is the unknown shape of the probing tip. Generally, the image is a convolution between the shape of the tip and the surface. Information of the shape of the probe may be gained by imaging very sharp tips. Here we present a method for making two‐dimensional arrays of very sharp tips. The tip arrays were made of silicon using electron beam lithography with subsequent ion‐beam etching. To achieve the best possible resolution, ultrasonic excitation was used during development of the bilayered PMMA resist. Thus, openings in the resist with size nearly equal to the spot size of the writing e‐beam have been obtained. A further decrease of the radius of the tips was obtained by the choice of appropriate thickness for the masking NiCr layer. The tips were conical with a height up to 100 nm with a radius of the tip down to 10 nm. The tips were suitable for study of the shape of AFM probe tips, under condition that the tip array samples were rinsed in water prior to the measurement. Without the rinsing procedure, strong sticking forces between the probe and the sample would have eroded both of them. The regularity of the array provided an easy way to calibrate the lateral motion of the scanner.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

High‐resolution definition of buried InGaAs/InP wires by selective thermal intermixing

K. Kerkel, J. Oshinowo, A. Forchel, J. Weber, G. Laube, I. Gyuro, and E. Zielinski

J. Vac. Sci. Technol. B 12, 3685 (1994); http://dx.doi.org/10.1116/1.587640 (4 pages) | Cited 1 time

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Buried InGaAs/InP wire structures with widths down to 30 nm by using a new and simple fabrication technique have been developed. The key point is the local removal of the InP top barrier layer of an InGaAs/InP quantum well using high‐resolution electron‐beam lithography and selective wet chemical etching. The patterned sample is then subjected to a rapid thermal annealing step. The InGaAs surface quantum wells, formed in the etched parts of the samples, display an enhanced interdiffusion compared to conventional quantum wells covered with an InP cap layer. This leads to a local increase of the band gap, which confines the carriers to the InP covered regions. The wires show sharp photoluminescence emission bands even for the smallest wire widths and a significant increase of the emission intensity due to carrier capture from the vertical and lateral barriers.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
78.66.Fd III-V semiconductors

Advances in near field holographic grating mask technology

D. M. Tennant, K. F. Dreyer, K. Feder, R. P. Gnall, T. L. Koch, U. Koren, B. I. Miller, C. Vartuli, and M. G. Young

J. Vac. Sci. Technol. B 12, 3689 (1994); http://dx.doi.org/10.1116/1.587641 (6 pages) | Cited 5 times

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We report progress on several practical issues of near field holographic (NFH) printing for optoelectronic applications. In particular, we report on the following: adaptation of the mask making process to large area holographically generated grating masks; evaluation of a commercially available UV contact aligner modified to allow routine NFH printing; use of mask copies to avoid excessive wear on original masks; options for reducing the writing time for e‐beam generated grating masks; and the application of e‐beam generated grating masks to a DFB six‐laser array with 200‐GHz frequency channel separation.
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85.60.-q Optoelectronic devices

Study of nanoscale magnetic structures fabricated using electron‐beam lithography and quantum magnetic disk

Stephen Y. Chou, Mark Wei, Peter R. Krauss, and Paul B. Fischer

J. Vac. Sci. Technol. B 12, 3695 (1994); http://dx.doi.org/10.1116/1.587642 (4 pages) | Cited 53 times

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Two types of nanoscale single‐domain magnetic structures were fabricated using e‐beam nanolithography and were studied using magnetic force microscopy. The first structure is the isolated and interactive arrays of Ni bars on silicon that are 35 nm thick, 1 μm long, and have widths ranging from 15 to 200 nm and spacings ranging from 200 to 600 nm. The second structure is an array of Ni pillars on silicon that have a uniform diameter of 35 nm, a height of 120 nm, and a density of 65 Gbits/in2—over two orders of magnitude greater than the state‐of‐the‐art magnetic storage density. It was found that the magnetic properties of these structures can be controlled by engineering their size and spacing. When the bar width is smaller than 150 nm, the bars become single magnetic domain. As the width of the isolated bars decreased from 200 to 55 nm, the magnetic field needed to switch the magnetization of these bars increased monotonically from 100 to 740 Oe which is the highest field reported for Ni. However, further reduction of bar width led the switching field to decrease due to thermal effect. Furthermore, it was found that as the bar spacings become smaller, the interaction between the bars will reduce the switching field. Finally, based on the artificially patterned single‐domain magnetic structures, we propose a new paradigm for ultra‐high‐density magnetic recording media: quantum magnetic disk.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

In situ GaAs/AlGaAs patterning using a thin epitaxial InGaAs layer mask as a negative‐type electron‐beam resist in Cl2 gas

S. Kohmoto, Y. Sugimoto, N. Takado, and K. Asakawa

J. Vac. Sci. Technol. B 12, 3699 (1994); http://dx.doi.org/10.1116/1.587643 (5 pages) | Cited 1 time

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A very thin (50‐Å) epitaxial In0.2Ga0.8As layer is used as a Cl2 etching mask for in situ electron‐beam (EB) induced GaAs/AlGaAs patterning. Simultaneous EB/Cl2 exposure makes the In0.2Ga0.8As mask layer resistant to Cl2 etching, while the parts of the mask only exposed to Cl2 are easily etched off, resulting in negative‐type pattern formation. The resistance of the EB/Cl2‐exposed area depends on the In content in the InGaAs mask. Possible causes of this are discussed. Using this patterning technique, a GaAs/AlGaAs quantum well is fabricated into a dot‐matrix pattern and the pattern is characterized by a cathodoluminescence measurement.  
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Luminescence enhancement of InGaAs/InP surface quantum wells by room‐temperature ion‐gun hydrogenation

Ying‐Lan Chang, I‐Hsing Tan, Casper Reaves, Evelyn Hu, James Merz, and Steve DenBaars

J. Vac. Sci. Technol. B 12, 3704 (1994); http://dx.doi.org/10.1116/1.587644 (4 pages)

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An InGaAs/InP surface quantum well has been used as a very effective probe of surface states before and after room‐temperature low‐energy ion‐gun hydrogenation. We found that the luminescence efficiency from the surface quantum well (QW) does not improve for ion exposures less than 1015 ions/cm2. Above this value, the luminescence efficiency increases monotonically, up to two orders of magnitude at the ion exposure of 1017 ions/cm2. The luminescence efficiency for samples hydrogenated with exposures of 1015 and 1016 ions/cm2 degraded slightly after two months in ambient air; however, a further enhancement of luminescence efficiency by ∼20% was observed for samples hydrogenated with an exposure of 1017 ions/cm2.
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78.66.Fd III-V semiconductors
81.65.-b Surface treatments

Electron‐beam fabrication and focused ion beam inspection of submicron structured diffractive optical elements

C. Dix, P. F. McKee, A. R. Thurlow, J. R. Towers, D. C. Wood, N. J. Dawes, and J. T. Whitney

J. Vac. Sci. Technol. B 12, 3708 (1994); http://dx.doi.org/10.1116/1.587645 (4 pages) | Cited 5 times

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Diffractive optical elements, designed by computer optimization techniques, can provide high coupling efficiencies between components in optical communications systems, and can be reproduced accurately in large numbers by the same technology employed to make microcircuits. This applications‐led development was for optimized f/0.48 Fresnel lenses to couple light from arrays of semiconductor lasers into monomode optical fibers. The lenses were fabricated as four phase level structures in fused quartz using electron‐beam lithography and reactive ion etching. The low f number needed to match between the laser and fiber numerical apertures required 0.2 μm feature sizes in the outer region of the lenses etched 2.1 μm deep. Effective use was made of focused ion beam etching and imaging to obtain cross sections of these high aspect ratio structures during process development. Differing lens designs have achieved 34% and 50% coupling efficiencies between 30° full width half peak 1.55 μm lasers and cleaved, monomode system fibers. In the former case, lens to fiber alignment tolerance was ±6 μm, making passive assembly of the lens fiber arrays feasible.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays
42.79.Bh Lenses, prisms and mirrors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Reduced electron transmission in Au/GaAs diodes damaged by focused ion beam implantation studied by ballistic electron emission microscopy

J. W. McNabb, M. Skvarla, and H. G. Craighead

J. Vac. Sci. Technol. B 12, 3712 (1994); http://dx.doi.org/10.1116/1.587646 (4 pages)

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We have used ballistic electron emission microscopy to study the technologically important area of metal contacts to III–V semiconductors. Our samples are Au/GaAs diodes selectively damaged by focused ion beam (FIB) implantation. Implanted regions display reduced interface transmission as the implantation dose is increased above 5×1012 ions/cm2 for Au+ at 30 keV energy. Localized current–voltage measurements indicate that implanted regions have Schottky barrier heights slightly different from those of unimplanted regions. However, these differences are insufficient to account for the attenuated interface transmission. We invoke increased scattering from FIB‐induced defects to explain the data. Defect sites in the Au or at the interface may scatter electrons away from the Schottky barrier, or increase inelastic scattering, both of which would lower interface transmission. The effects of several FIB related mechanisms on barrier heights and scattering are explored.  
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.Hb Impurity and defect levels; energy states of adsorbed species
73.40.Ns Metal-nonmetal contacts

Atomic desorption and readsorption of chlorine on a Si(111) 7×7 surface with a scanning tunneling microscope

Masakazu Baba and Shinji Matsui

J. Vac. Sci. Technol. B 12, 3716 (1994); http://dx.doi.org/10.1116/1.587429 (4 pages) | Cited 5 times

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This article reports on the selective atomic desorption of Cl atoms adsorbed on an Si(111) 7×7 surface by field evaporation using a scanning tunneling microscope (STM). After using the STM to study the reaction of the Cl on the surface, the STM tip is placed on the adsorbed Cl, and a positive voltage pulse is applied to the sample. This results in selective atomic desorption of Cl from the sample surface. Although both desorption and readsorption are observed at a low pulse voltage of 4–6 V, only desorption occurs at a high pulse voltage of over 6 V. When a negative pulse voltage is applied to the sample, the Cl and metallic atoms are desorbed from the tip surface by field evaporation.
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79.70.+q Field emission, ionization, evaporation, and desorption
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

25 nm chromium oxide lines by scanning tunneling lithography in air

H. J. Song, M. J. Rack, K. Abugharbieh, S. Y. Lee, V. Khan, D. K. Ferry, and D. R. Allee

J. Vac. Sci. Technol. B 12, 3720 (1994); http://dx.doi.org/10.1116/1.587430 (5 pages) | Cited 10 times

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An ambient scanning tunneling microscope is used to oxidize a thin Cr film to different oxidation states depending on the exposure conditions. These oxidation states have shown very different chemical and physical properties and can be used as positive or negative masks for lithography. Chromium oxide lines down to 25 nm have been formed.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.05.Bx Metals, semimetals, and alloys
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Proximal probe study of self‐assembled monolayer resist materials

F. Keith Perkins, Elizabeth A. Dobisz, Susan L. Brandow, Timothy S. Koloski, Jeffrey M. Calvert, Kee W. Rhee, John E. Kosakowski, and Christie R. K. Marrian

J. Vac. Sci. Technol. B 12, 3725 (1994); http://dx.doi.org/10.1116/1.587431 (6 pages) | Cited 10 times

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A scanning tunneling microscope (STM) has been used to investigate organosilane self‐assembled monolayer films (SAMs) as imaging layers for low voltage e‐beam lithography. We have studied three different SAMs [(aminoethylaminomethyl)phenethyltrimethoxysilane (PEDA), 4‐chloromethylphenyltrichlorosilane (CMPTS), and n‐octadecyltrichlorosilane (OTS)] deposited on the native oxide of Si. We have found OTS to act as a positive resist in wet etch processing upon exposure to 50 keV electrons, in agreement with Lercel [J. Vac. Sci. Technol. B 11, 2823 (1993)]. Identically processed samples patterned with low voltage (−10 to −25 V tip–sample bias) electrons in the STM exhibit a negative tone. STM biases below −10 V were insufficient to expose the film. An improved etch for STM‐generated patterns, leading to smoother surfaces, was developed. STM exposure of PEDA and CMPTS SAMs leads to a destruction of ligand functionality. An exposure threshold of −4 V bias for CMPTS and −8 V for PEDA has been established. As an example of post‐exposure processing, these latent images were metallized with an aqueous Pd(II) catalyst solution followed by an electroless Ni plating bath. The patterned, thin (25 nm) Ni layers grown in this way are shown to be excellent masks for reactive ion etching (RIE) with SF6, exhibiting at least a 1:200 etch selectivity on Si. Linewidths after metallization of 20 nm and etched (CBrF3/O2 RIE) trench widths of 25 nm are shown.
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85.40.Hp Lithography, masks and pattern transfer
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Quantitative study of metal–oxide semiconductor field effect transistor damage induced by scanning tunneling microscope lithography

Ty Fayfield and T. K. Higman

J. Vac. Sci. Technol. B 12, 3731 (1994); http://dx.doi.org/10.1116/1.587432 (4 pages)

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The channel areas of n‐channel silicon metal–oxide semiconductor field effect transistor (MOSFET) devices have been patterned with an air‐operated scanning tunneling microscope (STM) and processed to completion. Gate oxide thickness modulations greater than 80 Å have been achieved with this technique. The impact of the STM process step on the silicon/insulator interface has been characterized with two‐level charge pumping. The number of interface traps attributable to the STM lithography process is roughly 7×1010/cm2 eV. Additionally, transistor parameters from the STM FETs are compared with those from virgin FETs to assess any possible leakage current and mobility degradation induced by the STM process.  
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Nanometer scale patterning and oxidation of silicon surfaces with an ultrahigh vacuum scanning tunneling microscope

J. W. Lyding, G. C. Abeln, T.‐C. Shen, C. Wang, and J. R. Tucker

J. Vac. Sci. Technol. B 12, 3735 (1994); http://dx.doi.org/10.1116/1.587433 (6 pages) | Cited 30 times

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Nanoscale patterning of the Si(100)‐2×1 monohydride surface has been achieved by using an ultrahigh vacuum (UHV) scanning tunneling microscope (STM) to selectively desorb the hydrogen passivation. Hydrogen passivation on silicon represents one of the simplest possible resist systems for nanolithography experiments. After preparing high quality H‐passivated surfaces in the UHV chamber, patterning is achieved by operating the STM in field emission. The field emitted electrons stimulate the desorption of molecular hydrogen, restoring clean Si(100)‐2×1 in the patterned area. This depassivation mechanism seems to be related to the electron kinetic energy for patterning at higher voltages and the electron current for low voltage patterning. The patterned linewidth varies linearly with the applied tip bias achieving a minimum of <10 Å at −4.5 V. The dependence of linewidth on electron dose is also studied. For positive tip biases up to 10 V no patterning occurs. The restoration of clean Si(100)‐2×1 is suggestive of selective area chemical modifications. This possibility has been explored by exposing the patterned surface to oxygen and ammonia. For the oxygen case, initial oxidation of the patterned area is observed. Ammonia dosing, on the other hand, repassivates the surface in a manner different from that of atomic hydrogen. In both cases the pattern resolution is retained and the surrounding H‐passivated areas remain unaffected by the dosing.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.65.-b Surface treatments

Spatial‐phase‐locked electron‐beam lithography and x‐ray lithography for fabricating first‐order gratings on rib waveguides

Vincent V. Wong, Juan Ferrera, J. N. Damask, J. M. Carter, Euclid E. Moon, H. A. Haus, Henry I. Smith, and Stephen Rishton

J. Vac. Sci. Technol. B 12, 3741 (1994); http://dx.doi.org/10.1116/1.587434 (5 pages) | Cited 6 times

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The two basic structural elements of the integrated resonant channel‐dropping filter are the rib waveguides and the first‐order Bragg gratings. Spatial‐phase‐locked electron‐beam lithography is used to write the Bragg grating patterns with a coherence better than λ0/150, and x‐ray nanolithography is used to transfer the gratings onto optically patterned rib waveguides. These technologies are successfully combined to demonstrate a process by which channel‐dropping filters and related devices can be fabricated.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Laterally coupled distributed feedback laser fabricated with electron‐beam lithography and chemically assisted ion‐beam etching

R. C. Tiberio, P. F. Chapman, R. D. Martin, S. Forouhar, and R. J. Lang

J. Vac. Sci. Technol. B 12, 3746 (1994); http://dx.doi.org/10.1116/1.587435 (4 pages) | Cited 7 times

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The fabrication and optical performance of laterally coupled distributed feedback (LCDFB) lasers were investigated. This device differs from a conventional DFB laser in that the grating does not extend inside the laser ridge; rather, gratings adjacent to a single ridge are used to couple to the fringing fields of the active region. This structure allows the entire laser epilayer structure to be grown in a single step, thus eliminating any regrowth steps. A recent design with 1.5 mm cavity length and chemically assisted ion‐beam etching‐defined ridges and gratings resulted in pulsed single‐mode operation up to 36 mW at 937 nm with as‐cleaved facets. The light‐current characteristic of this device demonstrated a threshold current of 15 mA and a sidemode suppression ratio of greater than 30 dB. The spectral temperature sensitivity was 0.65 Å/ °C for this LCDFB. Fabrication processes and optical characterization are discussed.
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85.40.Hp Lithography, masks and pattern transfer
42.62.-b Laser applications
81.65.-b Surface treatments

Fabrication and characterization of InAlAs/InGaAs striped‐channel modulation‐doped field effect transistors

R. Grundbacher, P. Fay, and I. Adesida

J. Vac. Sci. Technol. B 12, 3750 (1994); http://dx.doi.org/10.1116/1.587436 (5 pages)

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Striped‐channel modulation‐doped field effect transistors (MODFETs), in which the transport of electrons from source to drain is restricted to multiple parallel channels, have been fabricated on a lattice‐matched InAlAs/InGaAs heterostructure and characterized at dc and rf frequencies. dc performance of the striped‐channel devices shows increased transconductance when normalized with the actual width of the striped channels. This may be attributed to improved control of electron concentrations in the channels since the depletion layer induced by the controlling gate is not only from above, but from below and in lateral directions as well, resulting in improved electron confinement. A reduction of output conductance of the striped‐channel device is observed when compared to a conventional MODFET. This is interpreted to be a result of an enhanced barrier between the buffer and channel layers of the striped‐channel device, which reduces the injection of hot electrons into the buffer. rf characteristics of the devices show a reduction of cutoff frequency for devices having smaller channels. dc measurements at cryogenic temperatures were performed to investigate the possibility of mobility enhancement in the striped‐channel devices.
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85.30.Tv Field effect devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Nanostructure fabrication and the science using focused ion beams

Toshimasa Fujisawa, Thomas Bever, Yoshiro Hirayama, and Seigo Tarucha

J. Vac. Sci. Technol. B 12, 3755 (1994); http://dx.doi.org/10.1116/1.587437 (5 pages)

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We describe the fabrication of nanostructures and the physics of the devices formed in InGaAs‐based modulation doped heterostructures using Ga focused ion beam implantation. The two‐dimensional electron gas in this heterostructure has a high electron density, a small effective mass, and a high mobility at high temperature, all of which are advantageous for low‐dimensional quantum devices and ballistic devices. Ballistic transport at high temperature, quantized conductance with a large spacing of one‐dimensional subbands, and a single electron transistor action with nonperiodic Coulomb oscillations are demonstrated.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

A novel technique for shifter void defect repair by a focused ion beam tool

Hideyuki Jinbo, Katsuhiro Takushima, Taro Saito, Itsuji Ashida, and Yoshio Tanaka

J. Vac. Sci. Technol. B 12, 3760 (1994); http://dx.doi.org/10.1116/1.587438 (5 pages) | Cited 2 times

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A new phase‐shifting mask repair concept, transferred image correction (TRIC), for repairing shifter void defects is proposed. TRIC repair fills shifter voids with an opaque material by focused ion beam (FIB) deposition, in which a FIB tool is used to partially remove Cr adjacent to the void. The transferred image of a TRIC‐repaired mask pattern corresponds to that of the original mask pattern with no defects.
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85.40.Hp Lithography, masks and pattern transfer

Molybdenum silicide based attenuated phase‐shift masks

Rik Jonckheere, Kurt Ronse, Ovidiu Popa, and Luc Van den hove

J. Vac. Sci. Technol. B 12, 3765 (1994); http://dx.doi.org/10.1116/1.587439 (8 pages) | Cited 2 times

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The use of phase shifting masks (PSMs) causes revolutionary improvements of the performance of existing wafer steppers. Nowadays the attenuated PSM, also referred to as halftone, is found to be most attractive, as the technique is self‐aligned. Moreover, the number of additional process steps in mask fabrication is limited to a dry etching step. Typically, both focus and exposure latitudes for contact holes of 0.35 μm are improved by a factor of 1.5–2 over a conventional mask. As linewidths on mask shrink towards 1 μm (a critical dimension of 0.25 μm, at 4× magnification) and below, the required critical dimension control becomes much tighter. It becomes more and more clear that the accuracy cannot be met anymore with wet etching of chrome. Sputtered molybdenum silicide (MoSi) is easier to dry etch than chrome and is therefore an important candidate as alternative opaque material on masks. The use of MoSi for attenuated PSMs is discussed. This approach has the advantage over the use of an SOG/Cr combination in that only a single dry etch process is required to etch the stack, since both materials can be etched using fluorine based plasmas. This is in contrast to chrome/shifter attenuated masks where chrome and shifter are etched separately, either wet/dry or both dry but in different chemistries. Recently published work describes the application of a single layer of a MoSiO or MoSiON with the required opacity and phase shift, by careful tuning of the refractive index and extinction coefficient. A comparison to these so‐called embedded PSMs is included. For the latter an important disadvantage is the lack of conductivity of the layer, such that an extra (sacrificial) layer is required for charge dissipation during electron‐beam exposure. An intermediate solution, referred to as partially embedded, is suggested as a compromise.
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85.40.Hp Lithography, masks and pattern transfer

An increased effective depth of focus at contact mask for nonvolatile memories using an enhanced planarization scheme

C. Cork and M. Bacchetta

J. Vac. Sci. Technol. B 12, 3773 (1994); http://dx.doi.org/10.1116/1.587440 (5 pages)

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Most of the work currently being published treating improvements in depth of focus (DOF) deals with expensive or complicated techniques such as phase shift masks or lower wavelength illumination. In this article we show that there is another much stronger effect that needs to be overcome before the full benefits of the I‐line lithography can be realized. A nonoptimized planarization process can have a large effect on the DOF of certain ‘‘marginal’’ contact sites. By using an enhanced planarization scheme we were able to significantly improve the DOF of these marginal sites yet retain process compatibility with the contact cleaning process and the charge retention requirements of nonvolatile memories. With this, we should be able to extend the minimum geometries printable with our current equipment from 0.7 μm down to about 0.4 μm.  
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Defocus asymmetry in projection printing

Eytan Barouch, Uwe Hollerbach, and Steven A. Orszag

J. Vac. Sci. Technol. B 12, 3778 (1994); http://dx.doi.org/10.1116/1.587441 (5 pages)

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The effect of defocus asymmetry in photolithography has been modeled by modifying FAIM to incorporate the phases of all partial fields emanating from the illuminator. Each partial field exposes the resist independently, and the integration over the illuminator takes place inside the resist, thus accounting for the correct physics of partially coherent light projection. Linewidth versus defocus is obtained as an asymmetric function around zero defocus as found experimentally.
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85.40.Hp Lithography, masks and pattern transfer
42.25.Gy Edge and boundary effects; reflection and refraction

Extending the limits of optical lithography for arbitrary mask layouts using attenuated phase‐shifting masks with optimized illumination

Kurt Ronse, Rainer Pforr, Ki‐Ho Baik, Rik Jonckheere, and Luc Van den hove

J. Vac. Sci. Technol. B 12, 3783 (1994); http://dx.doi.org/10.1116/1.587442 (10 pages) | Cited 2 times

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Optical lithography is still the technology of choice for the production of integrated circuits. The continuous need to shrink device geometry was originally made possible by reducing the wavelength and increasing the numerical aperture of the projection steppers. For the past half decade, various resolution and process latitude enhancement techniques, such as phase shifting masks (PSM) and off‐axis illumination techniques have received a lot of attention. Although very promising lithographic results have been demonstrated with each of those, their application in real device manufacturing with arbitrary mask layouts has been hampered for various reasons (PSM manufacturing, limited applicability...). World‐wide attention is directed more and more towards attenuated (embedded) PSM and annular illumination in order to overcome the limitations. In this article, both attenuated PSM design and illumination have been optimized to provide global improvements on critical random logic gate and contact levels. The optimized results, predicted by simulations, are verified experimentally using top surface imaging processes on a 0.42 NA deep‐ultraviolet stepper, focusing on quarter‐micrometer design rules. For contact levels, the best results are obtained with highly coherent conventional illumination. Gate levels require the combination of attenuated PSM with annular illumination.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Impact of lens aberrations on phase‐shifting masks

R. L. Kostelak, E. L. Raab, and S. Vaidya

J. Vac. Sci. Technol. B 12, 3793 (1994); http://dx.doi.org/10.1116/1.587443 (6 pages) | Cited 2 times

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The application of phase‐shifting mask (PSM) technology in a manufacturing environment will ultimately be decided by whether this technology provides sufficient enhancement to warrant the additional costs. Initial experimental results on flat wafers and in the center of the field have demonstrated that for select feature types and layouts there is considerable improvement in the process margin when PSM are employed. However, these studies did not include the impact of residual lens aberrations in the optical exposure system. This study examines the effect of lens aberrations on the application of attenuating PSM through both SPLAT‐generated (simulation of projection lens aberrations via TCCs) simulation and direct aerial image monitoring using latent image metrology. To benchmark the results obtained, all the work has been compared against a binary intensity mask (BIM). The simulation study concentrated on the three major Siedel aberrations detected in current i‐line steppers, namely, coma, astigmatism, and spherical aberrations. The SPLAT‐generated aerial images with these selected aberrations degrade the process latitude for both BIM and attenuated PSM; however, the initial enhancement provided by the phase‐shifting technique made the attenuated PSM more tolerant of the aberration. As the feature size increased and the incremental process latitude gained by the phase‐shifting technique decreased, the magnitude of the degradation with the two mask types became comparable. In summary, while PSM exposed on steppers will still maintain their performance superiority over BIM, the real improvement in process margin will suffer depending upon the feature type and layout.
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85.40.Hp Lithography, masks and pattern transfer
42.15.Fr Aberrations

Practical phase‐shifting mask technology for 0.3 μm large scale integrations

Fumio Mizuno, Noboru Moriuchi, Morihisa Hoga, Yasuhiro Koizumi, Osamu Suga, Hidehiko Nakaune, Kazumi Kamiyama, Norio Hasegawa, Fumio Murai, and Fumikazu Itoh

J. Vac. Sci. Technol. B 12, 3799 (1994); http://dx.doi.org/10.1116/1.587444 (5 pages)

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An i‐line phase‐shifting mask technology intended for practical use has been developed. The new technology can provide defect‐free phase‐shifting masks and can produce 0.3 μm large scale integration with large lithographic latitudes. The phase‐shifting masks manufactured here apply the following two major techniques. The first technique is to form phase‐shifting patterns on the chrome mask. This technique features single‐layer shifters using an organic spin on glass (SOG), a simple patterning process of the SOG, and a focused ion beam gas‐assisted etching repair process of shifter defects. The second technique is to create half‐micron chrome patterns using a high‐accuracy e‐beam writing system ‘‘EB‐MX’’ and high‐resolution chemically amplified e‐beam resist ‘‘PSR’’.
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85.40.Hp Lithography, masks and pattern transfer

New approach of rim phase‐shifting mask for high‐density circuit layout

G. Dao, N. Tam, R. Hainsey, Q. D. Qian, J. Neff, B. Nasre‐Esfahani, T. Deeter, H. Fujimoto, and P. Troccolo

J. Vac. Sci. Technol. B 12, 3804 (1994); http://dx.doi.org/10.1116/1.587445 (5 pages) | Cited 2 times

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The rim phase‐shifting mask (PSM) approach has been demonstrated by various researchers to provide significant improvement in performance for deep submicron optical lithography, particularly for the contact layer. The main advantage of the rim PSM approach is its relative ease of application to logic devices. The rim PSM approach, however, requires a significant allocation of reticle space due to mask biasing issues as well as the addition of rim shifters around features. A more important concern is the secondary peak intensity produced by the rim shifters when two or more features are placed in close proximity, as is commonly seen in any dense circuit layout. In this article, a new approach is proposed to make tightly packed rim contacts. Based on the basic principle of phase‐shifting, one rim feature is inverted relative to the other to eliminate the secondary peak intensity between two adjacent rim features; we dub this technique ‘‘iRim’’ for ‘‘inverted Rim.’’ Various reticle fabrication methods are available. For the iRim technique to function properly in the case where a phase error exists, it is found that the rim and iRim features need to be structurally identical. In this case, both contacts will possess the same phase error and the resulting focus shift will therefore be in the same direction, eliminating any loss in depth of focus. The iRim configuration is also proposed to be a metrology device for precise phase determination.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Quarter‐micron lithography with a gapped Markle–Dyson system

G. Owen, D. Borkholder, C. Knorr, D. A. Markle, and R. F. W. Pease

J. Vac. Sci. Technol. B 12, 3809 (1994); http://dx.doi.org/10.1116/1.587446 (5 pages)

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0.25‐μm lithography has previously been demonstrated using an ungapped prototype Markle–Dyson system, in which the wafer was held in soft contact with the mask. However, such an in‐contact scheme would be inappropriate for semiconductor fabrication, and so a second prototype has been designed and constructed, in which a gap of 25 μm is introduced between the mask and the wafer. The two major technical problems to be overcome in implementing the gap are the measurement and setting of the gap itself, and correction for the spherical aberration which it introduces. In the new prototype, the gap is set by a piezo‐electric actuator and measured using a capacitance gauge, and the spherical aberration is corrected by using a mirror which deviates slightly (by 0.33 μm) from sphericity. The system has been tested lithographically, using chromium reflective masks. It has demonstrated a resolution of 0.25 μm in Shipley XP89131 photoresist.
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85.40.Hp Lithography, masks and pattern transfer

Characterization of a 193 nm optical lithography system for 0.18 μm and below

A. Grenville, G. Owen, and R. F. W. Pease

J. Vac. Sci. Technol. B 12, 3814 (1994); http://dx.doi.org/10.1116/1.587447 (6 pages)

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A method previously employed for characterizing lithographic performance independent of resist processing has been applied to Markle–Dyson optics working at 0.7 NA and 193 nm to demonstrate diffraction limited imaging down to 0.15 μm resolution. Excellent agreement is shown between theory and experimentally measured modulation as a function of spatial frequency, defocus, and numerical aperture. We have also measured both tangential and sagittal field curvatures and found close correlation with simulation. No loss of contrast was observed inside the semicircular field of 2 mm diameter. Reflective 1× masks required for the experiment were patterned in silicon on fused silica down to 0.12 μm linewidths. To characterize the projection optics further, we have printed 0.16 μm features in resist using no resolution enhancement techniques.
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85.40.Hp Lithography, masks and pattern transfer

Characterization of an expanded‐field Schwarzschild objective for extreme ultraviolet lithography

G. D. Kubiak, D. A. Tichenor, A. K. Ray‐Chaudhuri, M. E. Malinowski, R. H. Stulen, S. J. Haney, K. W. Berger, R. P. Nissen, G. A. Wilkerson, P. H. Paul, J. E. Bjorkholm, L. A. Fetter, R. R. Freeman, M. D. Himel, A. A. MacDowell, et al.

J. Vac. Sci. Technol. B 12, 3820 (1994); http://dx.doi.org/10.1116/1.587448 (6 pages)

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The performance of a new 10×‐reduction Schwarzschild system for projection imaging at 13.4 nm wavelength is reported. The optical design is optimized to achieve 0.1 μm resolution over a 0.4 mm image field of view, an increase in area of a factor of 100 over previous designs. An offset aperture, located on the convex primary, defines an unobscured 0.08 numerical aperture. The system is illuminated using extreme ultraviolet (EUV) radiation emitted from a laser plasma source and collected by an ellipsoidal condenser. A 45° turning mirror is used to relay the collected EUV radiation onto a near‐normal reflecting mask. Multiple sets of primary and secondary elements were fabricated, matched, and clocked to minimize the effects of small figure errors on imaging performance. Optical metrology indicates that the wave‐front error within the subaperture used is within a factor of 2 of the design value. Images recorded in poly(methyl methacrylate) and ZEP 520 (Nippon Zeon) resists reveal good imaging fidelity over much of the 0.4 mm field with equal line/space gratings being resolved to 0.1 μm.
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42.82.Cr Fabrication techniques; lithography, pattern transfer

Multilayer facilities required for extreme‐ultraviolet lithography

D. L. Windt and W. K. Waskiewicz

J. Vac. Sci. Technol. B 12, 3826 (1994); http://dx.doi.org/10.1116/1.587449 (7 pages) | Cited 22 times

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We have developed a magnetron sputtering system for the deposition of Mo/Si multilayer (ML) coatings onto large‐area, figured optics, as required for the imaging system in a practical, extreme‐ultraviolet (EUV) lithography tool. Coating uniformity on figured optics is adjusted by implementing contoured, shaped baffles during ML deposition. We have also developed an EUV reflectometer that is capable of measuring the reflectance versus wavelength across the surface of these optics, so that the coating uniformity can be determined with the required precision. We discuss the ML coating uniformity requirements for a practical EUV lithography tool, describe the facilities and techniques we have developed, and present some recent results wherein these facilities and techniques have been used to deposit high‐reflectance coatings onto a variety of spherical and aspherical substrates.
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81.15.Cd Deposition by sputtering
85.40.Hp Lithography, masks and pattern transfer

Imaging of extreme ultraviolet lithographic masks with programmed substrate defects

K. B. Nguyen, T. Mizota, T. Haga, H. Kinoshita, and D. T. Attwood

J. Vac. Sci. Technol. B 12, 3833 (1994); http://dx.doi.org/10.1116/1.587450 (8 pages) | Cited 2 times

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Extreme ultraviolet lithographic masks with programmed defects on the mask substrates have been imaged to study substrate defects printability. The imaging was performed with a 2‐aspherical‐mirror system operating at 14 nm wavelength. Results showed that 25 nm thick substrate defects caused observable distortions of resist patterns. Defects of sizes approximately half the minimum resolvable features resulted in 15%–20% variations in resist linewidths. However, since the imaging system was operating at a reduced resolution due to misalignments of the optics, the effect of the defects may have been partially concealed by the phase front distortions caused by mirror misalignments. The defects are difficult to observe under a scanning electron microscope.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
42.30.Va Image forming and processing

Wavelength dependence of the resist sidewall angle in extreme ultraviolet lithography

O. R. Wood, J. E. Bjorkholm, L. Fetter, M. D. Himel, D. M. Tennant, A. A. MacDowell, B. La Fontaine, J. E. Griffith, G. N. Taylor, W. K. Waskiewicz, D. L. Windt, J. B. Kortright, E. K. Gullikson, and K. Nguyen

J. Vac. Sci. Technol. B 12, 3841 (1994); http://dx.doi.org/10.1116/1.587451 (5 pages) | Cited 1 time

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We report experimental and theoretical studies of the resist sidewall angles produced using extreme ultraviolet lithography at exposure wavelengths of 37.5, 13.9, and 6.8 nm. We show that high resist absorption in this wavelength region leads to a significant degradation in pattern sidewall angle. Because steep resist profiles are needed in semiconductor manufacturing to ensure adequate linewidth control it seems unlikely that a single‐layer resist process can be used in extreme ultraviolet lithography except at the shortest wavelength.  
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of diffractive optical components for an extreme ultraviolet shearing interferometer

S. J. Spector, D. M. Tennant, Z. Tan, and J. E. Bjorkholm

J. Vac. Sci. Technol. B 12, 3846 (1994); http://dx.doi.org/10.1116/1.587452 (5 pages)

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We have constructed four optical components for use in an extreme ultraviolet shearing interferometer which will operate at a wavelength of 13.4 nm. The components that have been constructed include transmission diffractive optical components such as a Fresnel zone plate, angled gratings, and two‐frequency gratings, as well as pinhole apertures. All the components are fabricated in 110 nm of Ge, which is supported by a 0.5–0.7‐μm‐thick membrane of Si. The patterns were fabricated by first evaporating Ge and then spinning 100 nm polymethylmethacrylate (PMMA) onto the Si membranes. The desired patterns were exposed in the PMMA resist using electron beam lithography. Custom interative computer programs generated the patterns used to control the exposure. After developing the PMMA resist the Ge layer was etched using a reactive ion etching technique. Electron microscopy of the finished components show that the smallest features in our components are cleanly constructed, and the linewidths and placement of the features meet the desired accuracy.
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42.79.-e Optical elements, devices, and systems
85.40.Hp Lithography, masks and pattern transfer
07.60.Ly Interferometers

Negative‐tone deep‐ultraviolet resists containing benzylic crosslinkers: Experimental and simulation studies of the crosslinking process

A. M. Zenk, A. R. Neureuther, S. M. Lee, and J. M. J. Fréchet

J. Vac. Sci. Technol. B 12, 3851 (1994); http://dx.doi.org/10.1116/1.587453 (6 pages) | Cited 3 times

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Dissolution rate and resolution measurements are used to show that a novel acid‐hardened deep‐ultraviolet photoresist ML93, based on a benzylic crosslinker, has excellent dissolution and reasonable resolution characteristics. Experimentally, we have observed that ML93 resist is about 20 times more sensitive than Shipley SNR248. While the high sensitivity is a promising result, it has made experimental reproducibility more difficult. In addition, the effect of the crosslinker structure on dissolution is examined with three more resists, ML239, ML240, and ML241, all analogous to ML93 except for variations in the structure of the crosslinker. A kinetic model describing negative resist lithography is applied to ML93 and ML239, and some profile cross sections are simulated using sample. The kinetic model has provided a reasonable fit to the dissolution characteristics of ML93 and ML239 separately, but comparison indicates that the basic role played by the active sites in the dissolution process needs further investigation.
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82.35.-x Polymers: properties; reactions; polymerization
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Thermal and acid‐catalyzed deprotection kinetics in candidate deep ultraviolet resist materials

G. Wallraff, J. Hutchinson, W. Hinsberg, F. Houle, P. Seidel, R. Johnson, and W. Oldham

J. Vac. Sci. Technol. B 12, 3857 (1994); http://dx.doi.org/10.1116/1.587454 (6 pages) | Cited 19 times

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Deep ultraviolet (UV) chemically amplified (CA) resists are leading candidates for semiconductor lithography manufacturing in the sub‐half‐micron regime. In this article, we describe in situ, high data rate, accurate measurements of the chemical kinetics that occur in CA resists during the post‐exposure bake. The thermal and acid‐catalyzed deprotection of two candidate deep‐UV resist materials, poly(p‐t‐butoxycarbonyloxystyrene) (PTBOCST) and poly(t‐butylmethacrylate) (PTBMA), was characterized. The thermal deprotection of PTBOCST and PTBMA showed auto‐accelerated behavior as the reaction proceeds, while the acid‐catalyzed deprotection displayed inhibition as extent of conversion increased. We propose models for the thermal and acid‐catalyzed deprotection and extracted rate coefficients using a stochastic kinetics simulator. Excellent agreement between the model and experimental data was obtained.
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82.20.Wt Computational modeling; simulation
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Effect of photo acid generator concentration on the process latitude of a chemically amplified resist

Karen E. Petrillo, Andrew T. S. Pomerene, Edward D. Babich, David E. Seeger, Don Hofer, Gregory Breyta, and Hiroshi Ito

J. Vac. Sci. Technol. B 12, 3863 (1994); http://dx.doi.org/10.1116/1.587455 (5 pages) | Cited 2 times

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A positive tone chemically amplified photoresist was evaluated for use on a 0.44 NA 248 nm excimer laser stepper. The effects of various formulation changes were examined with respect to exposure latitude, depth of focus, resolution, and bias between isolated and grouped features. Of particular interest was the relationship between the percent of photo acid generator (PAG) in the resist and the process latitude. It was found that several aspects of the process window increased as the PAG content of the resist decreased. An increase in dose was expected and observed with the decrease in PAG concentration. This would reduce excimer stepper throughput by approximately 25%.
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization

Application of real time infrared spectroscopy to monitoring the kinetics of chemically amplified resists

Glenn R. Howes, Christopher J. Gamsky, and James W. Taylor

J. Vac. Sci. Technol. B 12, 3868 (1994); http://dx.doi.org/10.1116/1.587565 (6 pages) | Cited 4 times

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Currently, the major approach to improving the performance of chemically amplified resists is by means of statistical design methods. These methods do not make use of information about the underlying chemical processes, information which could be useful in expediting the optimization process. We have developed techniques and equipment to monitor changes in resist chemistry during the bake steps using in situ using real time Fourier transform infrared spectrometry (RT‐FTIR). Using the Shipley SAL 605 negative chemically amplified resist, we monitored exposed resist as it was being baked at 110 °C; we were thus able to see several peaks change, including the growth of a peak at 982 cm−1 which we associate with the formation of an ether linkage during cross‐linking. When the height of this peak is plotted over time from the start of the bake, it shows several things, among them (a) the reaction being monitored takes much longer to reach its final level of completion (≳300 s) than the statistically derived optimum (∼60 s), (b) as expected, the reaction rate is a function of dose, and (c) the results are reproducible between identically treated wafers. We speculate that the reason we see peak growth long after the resist is cross‐linked enough for processing is due to the multiple available sites on the cross‐linker molecule which allow continued bond formation after enough have formed to make the resist sufficiently insoluble. With chemically amplified resists there has been concern over residual solvent which can interfere with the catalytic mechanism of the photogenerated acid. The same RT‐FTIR techniques were also shown to be effective in monitoring the loss of solvent from the resist during the preexposure bake, giving the time at which the solvent can be assumed to have been removed—in the case of Shipley SAL 605, approx 30 s. Finally, the RT‐FTIR technique can be used to follow the individual contributions of the components of the resist formulation as their concentrations are changed to affect different resist properties. The monitoring is directly on the resist‐coated wafer, and special handling techniques, to be described in the text, are necessary to make these measurements directly applicable to resist processing.
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82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.20.-w Chemical kinetics and dynamics
82.35.-x Polymers: properties; reactions; polymerization

High‐speed single‐layer‐resist process and energy‐dependent aspect ratios for 0.2‐μm electron‐beam lithography

Fumio Murai, Jiro Yamamoto, Hidenori Yamaguchi, Shinji Okazaki, Kazuhiko Sato, Keiko Hasegawa, and Hajime Hayakawa

J. Vac. Sci. Technol. B 12, 3874 (1994); http://dx.doi.org/10.1116/1.587566 (5 pages) | Cited 1 time

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For industrial application of an electron beam direct writing a single‐layer‐resist (SLR) process is more attractive than a multilayer‐resist process, because the SLR process is less expensive and provides a precise pattern transfer for 0.2‐μm large scale integration circuit fabrication. Three key factors for SLR process are (1) high acceleration voltage for clear latent image, (2) high‐contrast resist to attain a high‐aspect‐ratio pattern, and (3) rapid dissolving resist with little effect on the substrate. With 50‐kV acceleration voltage an aspect ratio of resist pattern of about 5 is obtainable using a chemically amplified resist. However, pattern collapse limits the maximum aspect ratio for smaller resist patterns. A positive‐tone resist (PSR) and negative‐tone resist (RE‐4200N) showed excellent characteristics for a SLR process with a 0.2‐μm feature size.  
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85.40.Hp Lithography, masks and pattern transfer

Acid generation process by radiation‐induced reaction in chemically amplified resist films

T. Watanabe, Y. Yamashita, T. Kozawa, Y. Yoshida, and S. Tagawa

J. Vac. Sci. Technol. B 12, 3879 (1994); http://dx.doi.org/10.1116/1.587567 (5 pages) | Cited 2 times

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A new interpretation of the acid generation process in novolak resin systems is reported. To investigate the acid generation process in chemically amplified resist, a novolak resin system with an acid generator (PAG) was employed. In order to analyze the acid generation process, the visible absorption characteristics from a conventional spectrophotometer, and nanosecond and millisecond pulse radiolysis systems, were analyzed. For m‐cresol novolak with triphenylsulfonium triflate, it was hypothesized that acid would be generated during exposure; however, it is asserted that a protonated intermediate was generated during exposure and that acid was generated during exposure, and more acid was formed during PEB. The yield of the acid during PEB, rather than that of the protonated intermediate during exposure, was strongly influenced by the presence of triphenylamine. A comparison of the experimental result for m‐cresol novolak which contains PAG with that for p‐cresol novolak which also contains PAG indicates that the time range of acid generation may be dependent on the base resin system.
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82.50.Kx Processes caused by X-rays or γ-rays
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Photoresist channel‐constrained deposition of electroless metallization on ligating self‐assembled films

Jeffrey M. Calvert, Gary S. Calabrese, John F. Bohland, Mu‐San Chen, Walter J. Dressick, Charles S. Dulcey, Jacque H. Georger, John Kosakowski, Edward K. Pavelcheck, Kee W. Rhee, and Loretta M. Shirey

J. Vac. Sci. Technol. B 12, 3884 (1994); http://dx.doi.org/10.1116/1.587568 (4 pages) | Cited 5 times

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Patterned, selective electroless deposition has been achieved using exposed and developed photoresists, produced with UV and e‐beam exposure sources, to create channels for constrained metal growth on ligating self‐assembled film surfaces. This process is attractive for the production of high‐resolution, etching‐resistant features for semiconductor integrated circuit (IC) fabrication, as well as for the fabrication of patterned metal lines for IC‐level and (PWB)‐level interconnects. Etched metal features with linewidths of 150 nm have been demonstrated.
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Effect of acid diffusion on performance in positive deep ultraviolet resists

T. H. Fedynyshyn, J. W. Thackeray, J. H. Georger, and M. D. Denison

J. Vac. Sci. Technol. B 12, 3888 (1994); http://dx.doi.org/10.1116/1.587569 (7 pages) | Cited 31 times

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Two methods to measure acid diffusion in positive acid catalyzed resists are described. The first method employs a spectrophotometric titration to determine the acid concentration ([H+]) followed by measuring the ion conductivity (σ) of the resist film to determine the diffusion coefficient (D). This method allows the diffusion coefficient of acid in the resist to be determined at different temperatures ranging from room temperature to different post‐exposure bake (PEB) temperatures. The second method is based on the threshold acid density theory of image formation, which assumes that when a critical concentration of acid is reached, the developer solubility of the resist is changed. With this method, a constant level of acid can be followed at different PEB times and the diffusion coefficient determined. A comparison of the two methods to measure the acid diffusion coefficient will be made and the temperature dependence of diffusion for different types of organic acids will be presented. Based on a previously described reaction–diffusion model that predicts relative deblocking levels, evidence is presented for room temperature diffusion of acid to be a possible explanation for delay instability in positive deep ultraviolet resists.
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82.20.Hf Product distribution
82.30.Vy Homogeneous catalysis in solution, polymers and zeolites
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Nanometer‐scale imaging characteristics of novolak resin‐based chemical amplification negative resist systems and molecular weight distribution effects of the resin matrix

Hiroshi Shiraishi, Toshiyuki Yoshimura, Toshio Sakamizu, Takumi Ueno, and Shinji Okazaki

J. Vac. Sci. Technol. B 12, 3895 (1994); http://dx.doi.org/10.1116/1.587570 (5 pages) | Cited 11 times

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Molecular weight distribution effects of novolak resin‐based chemical amplification negative resist systems are investigated for electron‐beam lithography. The resist systems investigated consist of onium salts as an acid generator, a methoxymethyl melamine crosslinker, and a conventional/fractionated novolak resin matrix. Delineated patterns of both types of resist systems are compared to evaluate submicron‐scale resolution. The conventional novolak resin‐based system shows higher contrast than the fractionated one. High aspect ratio patterns are resolved for the conventional novolak‐based resist, whereas poor results are obtained for the fractionated resin‐based one on the submicron scale. Very thin films (30 nm) of both resist systems are delineated with a finely focused electron beam (diameter: approximately 2 nm at 5 kV) from a scanning electron microscope. Nanometer‐scale edge roughness (nanoedge roughness) is observed for the conventional novolak resin‐based resist. On the contrary, the degree of nanoedge roughness is greatly reduced for the fractionated one.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
41.90.+e Other topics in electromagnetism; electron and ion optics (restricted to new topics in section 41)

Modeling and simulations of a positive chemically amplified photoresist for x‐ray lithography

A. A. Krasnoperova, M. Khan, S. Rhyner, J. W. Taylor, Y. Zhu, and F. Cerrina

J. Vac. Sci. Technol. B 12, 3900 (1994); http://dx.doi.org/10.1116/1.587571 (5 pages) | Cited 9 times

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This article presents the results of the experimental and modeling study of a positive tone, chemically amplified photoresist, in application to x‐ray lithography. Spectrophotometric titration, Fourier transform infrared spectroscopy (FTIR), and development rate monitor data were acquired and used as inputs for the modeling of the processes and pattern simulations. The exposure model assumes monomolecular decomposition upon radiation and corresponds to Dill’s model for a nonbleaching photoactive compound. The post‐exposure bake (PEB) model is based on formal kinetic equations which include a term for photoacid loss (or side reactions) during the post‐exposure bake process in a generalized way. The effective kinetic order of the photoacid loss reaction is derived from the FTIR absorbance data obtained for different PEB times and exposure doses. For patterned exposures, a diffusion term for the local photoacid concentration is included. The photoacid and tert‐butoxycarbonyloxystyrene concentration profile changes with PEB time have been simulated for a 0.25 μm line and spaces pattern. It is shown that a nonlinear PEB photoacid reaction kinetics, rather than the photoacid diffusion, dominates the linewidth decrease during PEB for the photoresist studied.
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85.40.Hp Lithography, masks and pattern transfer

High‐speed positive x‐ray resist suitable for precise replication of sub‐0.25‐μm features

Hiroshi Ban, Jiro Nakamura, Kimiyoshi Deguchi, and Akinobu Tanaka

J. Vac. Sci. Technol. B 12, 3905 (1994); http://dx.doi.org/10.1116/1.587572 (4 pages) | Cited 1 time

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A high‐speed chemically amplified positive resist based on poly(p‐hydroxystyrene) has been developed for x‐ray lithography. This resist, CANI (meaning chemically amplified resist) by Nippon Telegraph and Telephone Corporation, has a sensitivity of 50–70 mJ/cm2 to soft x rays while maintaining sub‐0.25‐μm resolution and a rather large dose margin of 34%–40%. Another advantage of CANI is that the theoretical weight loss from the removal of t‐butyl protecting groups by chemical amplification reactions is less than 4 wt %. This leads to little volume shrinkage at uv cure and reactive ion etching processes, and thus promises good controllability of pattern feature sizes between lithography and subsequent plasma etching processes.
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85.40.Hp Lithography, masks and pattern transfer

Plasma polymerized all‐dry resist process for 0.25 μm photolithography

O. Joubert, T. Weidman, A. Joshi, R. Cirelli, S. Stein, J. T. C. Lee, and S. Vaidya

J. Vac. Sci. Technol. B 12, 3909 (1994); http://dx.doi.org/10.1116/1.587573 (5 pages) | Cited 4 times

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Plasma‐polymerized resist films (PPMS) based on methylsilane have high sensitivity to short wavelength radiation. The photoinduced oxidation of PPMS films exposed in air forms siloxane network material, allowing dry development by selective rapid etching of the unexposed regions upon treatment with chlorine based plasmas. Negative‐tone patterns of oxidized methylsilane thus formed can be transferred through an underlying organic planarizing layer (0.7 μm) with excellent selectivity (≳100) to give high resolution patterns. This provides a versatile, dry photolithographic process usable with current exposure and etching tools that can be integrated into future cluster tool technologies. This article details the process tolerances and lithographic performance of PPMS under 248 nm exposure. Structures as small as 0.2 μm were printed with exposures ranging from 50 to 200 m cm−2 on a GCA XLS DUV stepper. Promising results are also obtained over topography.
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85.40.Hp Lithography, masks and pattern transfer

Quarter‐micron lithography with a wet‐silylated and dry‐developed commercial photoresist

Evangelos Gogolides, Dimitrios Tzevelekis, Elizabeth Tsoi, Michael Hatzakis, Anne‐Marie Goethals, Ki‐Ho Baik, and Freida Van Roey

J. Vac. Sci. Technol. B 12, 3914 (1994); http://dx.doi.org/10.1116/1.587574 (5 pages) | Cited 1 time

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A positive‐tone surface imaging process using wet silylation of the commercial photoresist AZ 5214ETM is presented; it is seen as a practical method to extend optical lithography down to 0.25 μm and to increase significantly the resolution limits of available steppers, without adding appreciable process complexity and cost. A comparative study is done using H‐line, I‐line, and deep ultraviolet at 248 nm lithography on different steppers. The resolution achieved corresponds to a k factor of 0.4 [i.e., 0.4λ/(numerical aperture)]. The importance of the dry‐development step and the thermal effects associated with the heating of the wafer during etching are discussed.  
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85.40.Hp Lithography, masks and pattern transfer

Positive‐tone silylated, dry‐developed, deep ultraviolet resist with 0.2 μm resolution

R. S. Hutton, S. M. Stein, C. H. Boyce, R. A. Cirelli, G. N. Taylor, F. A. Baiocchi, J. Kovalchick, and D. R. Wheeler

J. Vac. Sci. Technol. B 12, 3919 (1994); http://dx.doi.org/10.1116/1.587575 (6 pages)

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This paper describes the development of a surface‐imaging process for a positive‐tone silylated, dry‐developed bilayer resist which has 0.2 μm resolution and an aspect ratio of 4.5 using deep‐UV (248 nm) exposure. The many processing variables such as thermal treatment parameters, silylation conditions, and etching conditions were examined to determine their effects on lithographic performance in terms of resolution, feature size linearity, focus latitude, and sensitivity. Critical to the success of the process are: the bilayer structure which restricts diffusion of the Si, the use of a disilane reagent to increase the Si content of the masking layer, limiting migration of photogenerated acid by the appropriate choice of softbake and post‐exposure bake temperatures, initial etching with an Ar/Cl2 mixture to remove the thin layer of silylated resist in the exposed areas, and employing CO2 instead of O2 as the etching gas to eliminate lateral etching of the features. With this process we have obtained good critical dimension linearity down to 0.25 μm for bright‐field and dark‐field lines and spaces as well as isolated lines and isolated spaces. The dose required is ∼75 mJ/cm2 and the dose latitude is ±6%. Focus latitude is at least ±0.4 μm. We also observe no environmental effects on sensitivity or resolution.
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85.40.Hp Lithography, masks and pattern transfer

Comparative evaluation of chemically amplified resists for electron‐beeam top surface imaging use

M. Irmscher, B. Höfflinger, and R. Springer

J. Vac. Sci. Technol. B 12, 3925 (1994); http://dx.doi.org/10.1116/1.587576 (5 pages) | Cited 3 times

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The ultimate lithographic performance of e‐beam direct writing can only be achieved if the proximity effect is reduced by a top surface imaging resist technology. The capability of some commercial and experimental chemically amplified resists for an e‐beam‐sensitive top surface imaging process were evaluated. Analogous to the resist contrast, a silicon contrast was defined, which characterizes the silylation property of the resists very well and enables a comparison of the evaluated resists. The influence of bake and silylation conditions on the silicon contrast was investigated. The patterning results prove that the proximity effect was reduced dramatically. One of the evaluated resists was applied to structuring the metal layers of a 0.8‐μm‐CMOS technology.  
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85.40.Hp Lithography, masks and pattern transfer

Updated system model for x‐ray lithography

M. Khan, L. Mohammad, J. Xiao, L. Ocola, and F. Cerrina

J. Vac. Sci. Technol. B 12, 3930 (1994); http://dx.doi.org/10.1116/1.587577 (6 pages) | Cited 20 times

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We present an updated global model for x‐ray lithography based on realistic models for image formation, demonstrating how the extendibility of x‐ray lithography is well in the nanometer range. We apply these models to define the most convenient spectral range for x‐ray lithography manufacturing and the parameters of mirrors and filters to be used in an optimized beam line.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Comparison of image shortening effects in x‐ray and optical lithography

R. Dellaguardia, J. R. Maldonado, F. Prein, T. Zell, A. Kluwe, and H. K. Oertel

J. Vac. Sci. Technol. B 12, 3936 (1994); http://dx.doi.org/10.1116/1.587578 (7 pages) | Cited 2 times

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Data on image shortening effects with patterns replicated with x‐ray and optical lithography are presented. The x‐ray exposures were performed at the IBM Advanced Lithography Facility using the Helios superconducting storage ring and a SUSS stepper. The optical exposures were performed using SVGL Micrascan 1 and 2 tools and biased optical masks. The results indicate that the image shortening effects using x‐ray lithography (XRL) are considerably less pronounced than the effects observed with the optical tools. In addition, modeling of the image shortening effects for XRL using the xmas three‐dimensional program for resist patterns is presented and compared with experimental results.
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85.40.Hp Lithography, masks and pattern transfer
42.30.Va Image forming and processing

Application of proximity synchrotron orbital radiation lithography and deep ultraviolet phase‐shifted‐mask lithography to sub‐quarter‐micron complimentary metal oxide semiconductor devices

L. Liebmann, R. Ferguson, A. Molless, and A. Lamberti

J. Vac. Sci. Technol. B 12, 3943 (1994); http://dx.doi.org/10.1116/1.587579 (6 pages)

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Sub‐quarter‐micron gate‐level device development and process integration of a complimentary metal oxide semiconductor (CMOS) program are being supported at IBM Microelectronics’ Advanced Semiconductor Technology Center with both synchrotron orbital radiation lithography (proximity x‐ray) and phase‐edge deep ultraviolet phase‐shifted‐mask lithography. Data highlighting the feasibility of these two advanced techniques for the lithography support of very aggressive CMOS technologies are presented. Issues of design complexity, design rule impact, and mask engineering are discussed, the exposure process is described, and current process latitude data are presented. Both lithography techniques show feasibility for 200 nm lithography, each with its unique set of challenges and trade‐offs.  
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85.40.Hp Lithography, masks and pattern transfer
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Applicability test for synchrotron radiation x‐ray lithography in 64‐Mb dynamic random access memory fabrication processes

Kiyoshi Fujii, Takuya Yoshihara, Yuusuke Tanaka, Katsumi Suzuki, Takashi Nakajima, Tsutomu Miyatake, Eisaku Orita, and Kazuhiro Ito

J. Vac. Sci. Technol. B 12, 3949 (1994); http://dx.doi.org/10.1116/1.587580 (5 pages) | Cited 4 times

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To evaluate the applicability of synchrotron radiation x‐ray lithography (SRXL) in ultra‐large‐scale integration manufacturing processes, we simulate a part of a dynamic random access memory process using SRXL. Four levels of x‐ray masks (field, gate, bit contact, and bit line), including fiducial patterns for coordinate/overlay measurement, alignment marks, and 0.4‐μm‐rule memory cells were fabricated using an i‐line stepper. The maximum overlay error between the different level masks was 60–100 nm. In SRXL processes alignment errors of the x‐ray stepper were 60–100 nm (3σ), and the overlay errors over a 20‐mm‐exposure field were 130–160 nm (‖mean‖+3σ) in most of alignment levels. Critical dimension control of 27–47 nm was obtained for gate length and contact hole diameter.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Fabrication of controlled slope attenuated phase‐shift x‐ray masks for 250 nm synchrotron lithography

M. Gentili, E. Di Fabrizio, L. Grella, M. Baciocchi, L. Mastrogiacomo, R. Maggiora, J. Xiao, and F. Cerrina

J. Vac. Sci. Technol. B 12, 3954 (1994); http://dx.doi.org/10.1116/1.587409 (5 pages) | Cited 3 times

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This article reports the manufacturing process of 250 nm resolution x‐ray masks featuring gold absorbers optimized for synchrotron radiation lithography in both thickness and absorber slope. X‐ray optics modeling predicts that nonvertical absorber flanks may provide better linewidth control by suppressing higher spatial frequencies. To test these conclusions, masks were patterned by electron beam lithography at accelerating voltages of 30 kV with the final goal of developing various slopes and feature sizes. Monte Carlo simulation is used to predict the best exposure conditions. An intelligent usage of the resist thickness and exposure conditions allow us to exploit forward scattering of electrons to provide the required resist profile in a well controlled way. By adjusting exposure dose and development time, the slope profile can be altered from 90° to about 82°. We demonstrate that lines and spaces of 250 nm with controlled and repeatable profile slope of 87° are achievable in 400‐nm‐thick gold with good exposure latitude. Under such optimized process conditions a dose variation of 10% leads to a 10% linewidth change for 250 nm features. Exposure latitude for all the writing conditions was also determined. Finally, we performed x‐ray exposure using a mask including both sloped and nonsloped absorbers using Suss XRS 200/2M aligner at the Centre for X‐Ray Lithography of the University of Wisconsin (CXrL). The results confirmed the theoretical model used in image calculations, providing experimental evidence that the exposure latitude is not degraded, but actually improves in case of sloped patterns.
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85.40.Hp Lithography, masks and pattern transfer

50‐nm x‐ray lithography using synchrotron radiation

Y. Chen, R. K. Kupka, F. Rousseaux, F. Carcenac, D. Decanini, M. F. Ravet, and H. Launois

J. Vac. Sci. Technol. B 12, 3959 (1994); http://dx.doi.org/10.1116/1.587410 (6 pages) | Cited 25 times

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A technology of proximity x‐ray lithography has been developed to replicate patterns of sub‐100‐nm feature size using synchrotron radiation. Process modeling has been done in advance in order to optimize the mask absorber thickness. It is shown that with tungsten absorber, a 0.3 μm thickness is the most desirable for 50 nm linewidth processing. Masks compatible with a Karl Suss stepper have been fabricated using 50 keV electron‐beam lithography and reactive ion etching techniques. As a result, well‐defined 50‐nm‐wide isolated W lines and small gratings of period down to 100 nm have been fabricated. Then they have been replicated under proximity condition using Super ACO synchrotron radiation. We present details of a replication procedure with gap settings down to 5 μm and show how sub‐100 nm structures can be 1:1 printed into both poly (methylmethacrylate) (PMMA) and (8.5%) MAA/PMMA resists. Finally, the results are analyzed in terms of a scaling rule to evaluate the resolution limit as a function of proximity gap using a synchrotron source.
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85.40.Hp Lithography, masks and pattern transfer

Printability of sub‐150 nm features in x‐ray lithography: Theory and experiments

Scott D. Hector, Vincent V. Wong, Henry I. Smith, M. A. McCord, and K. W. Rhee

J. Vac. Sci. Technol. B 12, 3965 (1994); http://dx.doi.org/10.1116/1.587411 (5 pages) | Cited 4 times

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Image formation in x‐ray lithography has been studied extensively. A previous theoretical study predicted that 0.1 μm features can be printed at large gaps (≳10 μm) with absorbers attenuating less than 10 dB. This study seeks to verify rigorous electromagnetic simulations of image formation by directly measuring the aerial image. Exposures of features with linewidths ranging from 0.15 to 0.075 μm were performed on the Helios synchrotron. Pedestal‐style x‐ray masks, consisting of SiNx membranes and a Au absorber, were patterned with e‐beam lithography at 100 and 50 kV. By careful dose control and inspection of the resulting features, one can directly determine the aerial image (the image at the resist surface). This is verified using a string model of the resist development. Aerial image measurements correlate reasonably well with modeling results.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Fabrication of 150‐nm gate‐length high electron mobility transistors using x‐ray lithography

A. M. Haghiri‐Gosnet, H. Lafontaine, Y. Jin, F. Rousseaux, M. Chaker, H. Pépin, and H. Launois

J. Vac. Sci. Technol. B 12, 3970 (1994); http://dx.doi.org/10.1116/1.587412 (5 pages)

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Functional 150‐nm gate‐length high electron mobility transistors (HEMTs) have been successfully fabricated using storage ring x‐ray lithography (XRL) for all process levels. This article describes the L2M XRL exposure system including x‐ray masks, the planar‐doped GaAlAs/GaAs HEMT fabrication process, and the characteristics of the resulting devices. The gate length, a key device performance parameter, was minimized down to 150 nm using an optimized chemically amplified SAL601 negative resist process at small proximity gap (≤20 μm). This optimization process indicates that process latitude and resolution are primarily limited by the post‐exposure bake (PEB) step which has been adjusted to 95 °C. The fabricated HEMTs have excellent dc characteristics with a peak extrinsic transconductance as high as 400 mS/mm.
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85.40.Hp Lithography, masks and pattern transfer
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Novel technique for the separation of mechanical properties and intrinsic stress of pre‐ and post‐irradiated membranes

H. T. H. Chen, R. L. Engelstad, and F. Cerrina

J. Vac. Sci. Technol. B 12, 3975 (1994); http://dx.doi.org/10.1116/1.587413 (4 pages)

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The focus of this paper is to introduce and describe a new technique for the determination of x‐ray lithography mask distortions for pre‐ and post‐irradiated membranes using a combination of numerical, analytical, and experimental methods. At the heart of this technique is a new test structure and fixture that allow for the accurate determination of material properties so that changes due to radiation exposure can then be incorporated into a finite element model to predict distortions. In addition, due to the size of the membranes used for the test structure, larger accumulated doses can be delivered in shorter periods of time. Once the material property and stress changes have been incorporated into numerical models, calculations can then be performed to simulate the effect of radiation on various membrane pattern areas and geometries.  
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85.40.Hp Lithography, masks and pattern transfer
81.40.Lm Deformation, plasticity, and creep

High‐performance multilevel blazed x‐ray microscopy Fresnel zone plates: Fabricated using x‐ray lithography

E. Di Fabrizio, M. Gentili, L. Grella, M. Baciocchi, A. Krasnoperova, F. Cerrina, W. Yun, B. Lai, and E. Gluskin

J. Vac. Sci. Technol. B 12, 3979 (1994); http://dx.doi.org/10.1116/1.587414 (7 pages) | Cited 8 times

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Diffractive lenses are becoming the optical elements of choice for many applications. One type of diffractive lens, the binary zone plate, has already demonstrated high‐resolution performance experimentally. However, in order to increase the diffraction efficiency of these zone plates, a blazed grating profile must be used. This can best be approximated by a staircase grating profile, created by multilevel exposures. Using x‐ray lithograph, we fabricated for the first time circular, linear bi‐ and trilevel zone plates, with gold structures 0.75 μm thick (per level), on silicon nitride substrates. The zone plates were designed for use at a wavelength of 1.54 Å, and had a theoretical efficiency of 68.5% for bilevel and 81.5% for trilevel zone plates. Due to the large depth of focus and high resolution inherent to x‐ray lithography, the finished zone plate exhibits very steep sidewall profiles, with linewidth resolution down to 0.25 μm. Such vertical sidewalls are essential for achieving high lens efficiency. Fabrication errors, such as thickness variation in the electroplated gold and misalignment, were considered, and their effect on the optical efficiency of the zone plate was estimated. Alignment errors between levels were minimized, achieving a best result of 25 nm (3σ). In fabricating the zone plates, we employed standard integrated device tools, such as a Leica Cambridge Electron Beam microfabricator (EBMF) 10cs/120 electron‐beam writer for the x‐ray mask fabrication, and a Suss 200 x‐ray stepper for the multilevel exposures. Thus, we have shown that it will be possible to fabricate many lenses, with a variety of optical characteristics, in one wafer.  
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42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Parametric modeling at resist–substrate interfaces

L. E. Ocola and F. Cerrina

J. Vac. Sci. Technol. B 12, 3986 (1994); http://dx.doi.org/10.1116/1.587415 (4 pages) | Cited 7 times

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In the energy range of interest for x‐ray lithography, absorption of x rays by atoms results in the emission of photoelectrons and Auger secondary electrons, as well as a shower of low energy electrons. The development of accurate image formation models in x‐ray lithography requires that these mechanisms be included. The photoelectron processes produce a redistribution of the x‐ray energy over a finite volume. The interaction of the electrons with the medium is complex and can be treated in the framework of a response theory (dielectric function). A simulation code, based on the Monte Carlo method (lesis), has been developed to study the photon energy redistribution in resists, in the vicinity of resist–substrate interfaces and overlayers. The low computational efficiency of the Monte Carlo method motivates the need to parametrize the energy redistribution results of the simulation. This parametrization was performed for a polymethyl‐methacrylate/Si interface, as a function of the photon energy. The parametrization can be interpreted as the weighted sum of individual electron responses. The effects on the resist of photoelectrons generated in the substrate are discussed. These effects have been incorporated in an effective dose model that can be used to compute complex interface geometries. The results are particularly relevant for the nanolithography domain (< 100 nm).
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
79.60.Fr Polymers; organic compounds

Effect of brightener concentration on the thermal distortion of gold plated x‐ray masks

W. J. Dauksher, D. J. Resnick, P. A. Seese, K. D. Cummings, A. W. Yanof, and W. A. Johnson

J. Vac. Sci. Technol. B 12, 3990 (1994); http://dx.doi.org/10.1116/1.587416 (5 pages)

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In‐plane distortion of a fiducial array was used as a metric to compare the relative responses to heat treatments of x‐ray masks doped with different brightener levels. Samples plated from gold‐sulfite baths containing 0, 2, and 75 ppm Tl all distorted by more than 50 nm after annealing at 100 °C. Quenching in liquid nitrogen fully relieved the stress of the undoped sample only. Room temperature stress relaxation behavior after storage of the gold samples for 2.5 years is detailed. Gold samples doped to any level with a thallium‐based brightener gradually relax, if initially stressed, and remain at a zero stress state. Behavior is explained in terms of room temperature grain growth and plastic deformation.
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81.40.Lm Deformation, plasticity, and creep
85.40.Hp Lithography, masks and pattern transfer

Accelerated radiation damage studies of antireflection materials on SiC x‐ray mask membrane

T. Shoki, R. Ohkubo, H. Kosuga, Y. Yamaguchi, N. Annaka, G. M. Wells, K. Yamazaki, and F. Cerrina

J. Vac. Sci. Technol. B 12, 3995 (1994); http://dx.doi.org/10.1116/1.587417 (6 pages)

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The effect of antireflection (AR) coating on optical transparency for SiC membrane and the accelerated radiation damage of thicker AR film of 0.4 μm in thickness on a 2‐μm‐thick SiC membrane have been investigated in detail using SiO2, Al2O3, and ITO (indium tin oxide) films. SiO2, Al2O3, and ITO films were suitable for obtaining higher optical transparency and reducing the amplitude of interference fringes. The transmittance above 80% at 633 nm was achieved for 1‐μm‐thick as‐deposited SiC membrane with these AR films on both sides. AR films showed film stress change toward the compressive direction by synchrotron radiation (SR) irradiation. ITO film was found to have the strongest durability against SR irradiation among the AR films studied. The measured maximum and 3σ values for X and Y coordinates of the SR‐induced displacement of the SiC membrane with 0.4‐μm‐thick ITO film on one side were 30 nm and X=11 and Y=39 nm, respectively, after irradiation of 191 kJ/cm2. Optical transparency of the mask membrane with ITO film was not changed after SR irradiation.
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85.40.Hp Lithography, masks and pattern transfer
61.80.Cb X-ray effects
42.79.Bh Lenses, prisms and mirrors

Sputtering of fibrous‐structured low‐stress Ta films for x‐ray masks

Takuya Yoshihara and Katsumi Suzuki

J. Vac. Sci. Technol. B 12, 4001 (1994); http://dx.doi.org/10.1116/1.587418 (4 pages) | Cited 7 times

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In order to achieve precise control for the internal stress of x‐ray absorber films, we have controlled the sputtering‐gas (Xe) pressure within ±0.002 Pa (at 0.5 Pa) using a newly developed ultrahigh‐vacuum sputtering system, but we found that it was difficult to reproducibly obtain sufficiently low‐stress Ta films over the long term. We therefore investigated the relationship between the internal stress and substrate temperature at a low deposition pressure (0.45 Pa). It was found that internal stress changes basically toward tensile with increasing substrate temperature because of the bimetal effect, but at substrate temperature from 205 to 220 °C, the internal stress changes toward compressive with increasing temperature. We characterized Ta films deposited at various temperatures using x‐ray diffraction and secondary electron microscopy and found that a film deposited at 205 °C was columnar‐structure β‐Ta and that one deposited at 240 °C was fibrous‐structured β‐Ta. Films deposited at temperatures higher than 270 °C were rough‐surfaced α‐Ta. For films deposited at pressures lower than 0.8 Pa and at a substrate temperature of 240 °C, the internal stress was almost constant regardless of gas pressure fluctuation. Thus, at 240 °C and 0.45 Pa, we can deposit low‐stress (<5×107 N/m2) Ta films with excellent long‐term reproducibility.
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85.40.Hp Lithography, masks and pattern transfer

Experimental determination of the effective lithographic contrast for x‐ray masks

Juan R. Maldonado

J. Vac. Sci. Technol. B 12, 4005 (1994); http://dx.doi.org/10.1116/1.587419 (4 pages)

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A new technique for measuring effective lithographic contrast based on its definition is presented. Results obtained at the IBM Advanced Lithography Facility using the Helios storage ring are compared with conventional ways of determining mask contrast. In addition, a method to decrease the effects of multiple exposures in adjacent fields during the step and repeat operation of an x‐ray lithography stepper is presented.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
42.30.Va Image forming and processing

Deep etch x‐ray lithography at the advanced light source: First results

Chantal Khan Malek, Keith Jackson, Reid A. Brennen, Michael H. Hecht, William D. Bonivert, and Jill Hruby

J. Vac. Sci. Technol. B 12, 4009 (1994); http://dx.doi.org/10.1116/1.587420 (4 pages)

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Deep etch x‐ray lithography permits the manufacture of very accurate high‐aspect‐ratio microstructures, which can be used as master templates for subsequent replication by electroforming and/or molding processes. This allows for mass production of three‐dimensional microstructures in a variety of materials. In this article we report on the first results using x rays from the Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory, as well as on the processing and technology developed to produce high‐aspect‐ratio microstructures. The first masks used were simple stencil masks chemically or laser etched in thick metal sheets. For resist, we used commercial acrylic cast sheets. Microstructures 840 μm thick were fabricated by deep x‐ray lithography and used as templates for copper electroforming. A technology for the high contrast masks required to work at these short wavelengths is being developed and a deep etch x‐ray lithography facility is under construction at the ALS.
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85.40.Hp Lithography, masks and pattern transfer

Synchrotron radiation x‐ray lithography beamline optics alignment using the Hartmann method

G. Chen, K. Yamazaki, W. Waldo, J. Welnak, G. M. Wells, and F. Cerrina

J. Vac. Sci. Technol. B 12, 4013 (1994); http://dx.doi.org/10.1116/1.587421 (5 pages)

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This article studies the effect of mirror misalignment on run‐out overlay errors in a synchrotron radiation based x‐ray lithography system. Using the ES‐5 beam‐line installation at the CXrL as an example, we found that the current beamline mirror alignment method, which relies on the final beam shape and orientation at the mask‐wafer plane, is insensitive to the mirror grazing incident angle alignment. Simulations using the ray‐tracing program shadow indicate that a smaller than ±0.5‐mrad mirror grazing angle misalignment consumes the required run‐out overlay error budget of the beamline. A direct beamline run‐out overlay measurement technique based on the Hartmann method was developed for the beamline mirror alignment. This measurement technique was applied to our ES‐5 beamline mirror alignment procedure. The measurement results show that the beamline induced run‐out error of the installed ES‐5 beamline is less than 0.014 μm in both horizontal and vertical direction for a 25‐mm exposure field with a mask‐wafer gap of 40 μm. The across field run‐out error distribution is also compared with shadow simulation results. The good agreement between measurement and simulation data indicates that our measurement technique provides a sensitive, practical, and accurate method for x‐ray lithography beamline mirror alignment and evaluation.
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85.40.Hp Lithography, masks and pattern transfer
41.50.+h X-ray beams and x-ray optics

Novel single mirror condenser for x‐ray lithography beam lines

Jiabei Xiao, Franco Cerrina, and Robert P. Rippstein

J. Vac. Sci. Technol. B 12, 4018 (1994); http://dx.doi.org/10.1116/1.587422 (6 pages) | Cited 4 times

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In proximity x‐ray lithography (XRL), two types of illumination are used: full field and scanning. We describe a single mirror condenser for XRL beam lines which provides a high flux of soft x rays. The surface is generally aspheric, designed using numerical methods, and described by polynomials. The flexible design approach can be used to find a result with specific imaging characteristics according to the various requirements of the beam line, and thus is of more general application. The performance of the designed condenser is verified with ray tracing. For advanced submicron applications, mirror scanning is preferred because of its higher scanning speed. However, with figured mirrors, a small change of grazing angle may cause a large variation of image shape, so that to provide a uniform beam, the scanning of the mirror is compensated by a lateral shift. A uniform exposure of 50×50 mm2 field can be achieved.
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42.79.Bh Lenses, prisms and mirrors
85.40.Hp Lithography, masks and pattern transfer

Uniform‐stress tungsten on x‐ray mask membranes via He–backside temperature homogenization

Mark Mondol, Huiying Li, Gabrielle Owen, and Henry I. Smith

J. Vac. Sci. Technol. B 12, 4024 (1994); http://dx.doi.org/10.1116/1.587423 (4 pages) | Cited 1 time

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When x‐ray absorbers such as W are sputtered directly onto x‐ray mask membranes a large temperature gradient is set up due to the power input from the plasma, and the very inefficient thermal conduction in the plane of the thin membrane. To obtain absorber stresses sufficiently low that pattern distortion is negligible, the temperature gradient across the membrane must be no greater than a few degrees. To achieve this we introduce He at about 665 Pa (5 Torr) between the back surface of the membrane and an Al heat sink heated to 200 °C, separated by 1 mm. Uniform stress is easily achieved. The He gas also allows one to implement an in situ stress control feedback system based on an array of optically based gap sensors which can determine stress of the deposited film from the change in the pressure‐induced bulge of the membrane.
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85.40.Hp Lithography, masks and pattern transfer
81.40.Lm Deformation, plasticity, and creep

Evaluation of temperature rise and thermal distortions of x‐ray mask for synchrotron radiation lithography

K. Yamazaki, F. Satoh, K. Fujii, Y. Tanaka, and T. Yoshihara

J. Vac. Sci. Technol. B 12, 4028 (1994); http://dx.doi.org/10.1116/1.587424 (5 pages) | Cited 1 time

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This article presents experimental results on the temperature rise in x‐ray masks and the temperature‐induced distortions printed on wafers during scanning synchrotron radiation exposure. It also presents theoretical analyses confirming the validity of the experiments. The temperature rise was measured with an infrared camera and the resultant thermal distortions were quantified by measuring the displacements of patterns printed on wafers. The theoretical simulations were performed using the finite element method. Results of experiments and simulations agree and indicate that even for exposures in air the temperature‐induced distortions are rather small.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Temperature uniformity across an x‐ray mask membrane during resist baking

D. J. Resnick, K. D. Cummings, W. A. Johnson, H. T. H. Chen, B. Choi, and R. L. Engelstad

J. Vac. Sci. Technol. B 12, 4033 (1994); http://dx.doi.org/10.1116/1.587425 (5 pages) | Cited 2 times

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We have studied temperature uniformity during the post‐exposure bake process across a 40 mm diameter of an x‐ray mask membrane. Membrane temperature was determined by measuring line size as a function of position across the membrane. A two‐dimensional finite element model (FEM) was used to analyze the results and optimize the design of a new bake chuck. The 3σ variation across the diameter of the mask was reduced to 27 nm. The FEM was also used to examine issues associated with resist baking on the ARPA‐NIST X‐ray Mask Standard and the initial results are discussed.
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85.40.Hp Lithography, masks and pattern transfer

Modeling image formation: Application to mask optimization

Jiabei Xiao, Mumit Khan, Ramez Nachman, John Wallace, Zheng Chen, and Franco Cerrina

J. Vac. Sci. Technol. B 12, 4038 (1994); http://dx.doi.org/10.1116/1.587426 (6 pages) | Cited 4 times

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From an image formation point of view, the design of x‐ray masks has been optimized for realistic exposure systems using synchrotron radiation. The analysis has then been carried forward to study the effect of environmental factors such as vibrations. We conclude that the ideal x‐ray mask is based on thin absorbers (0.3–0.4 μm) for Au and W, that the existence of a sidewall slope improves the exposure latitude, and that vibrations (amplitude less than 1/2 critical dimension) do not represent a source of concern. All in all, the x‐ray lithography mask emerges with more relaxed specifications and with a simpler manufacturing process.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
42.30.Va Image forming and processing

Wavelength dependence of exposure window and resist profile in x‐ray lithography

Jerry Z. Y. Guo, George K. Celler, Juan R. Maldonado, and Scott D. Hector

J. Vac. Sci. Technol. B 12, 4044 (1994); http://dx.doi.org/10.1116/1.587427 (7 pages) | Cited 1 time

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In proximity x‐ray lithography, wavelengths in the range of 4–20 Å are used. The choice of wavelength is a complicated system issue, which depends on many lithographic aspects. Shorter wavelength x rays offer aerial image diffraction advantages. However, they may also give rise to spurious photoelectron effects. Longer wavelength x rays make mask patterning easier since the absorber can have a smaller aspect ratio for the required contrast, but a thinner, less robust membrane is needed to give the same x‐ray transmission. Softer x rays are also better absorbed in resist, reducing the exposure time, but higher absorption can have an adverse effect on the resist sidewall profile. A study is conducted to address the wavelength issue in x‐ray lithography using the exposure window, resist profiles, power efficiency, and the mask contrast as merit/cost functions. Results show that a compromise among these factors is needed to achieve best performance.
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85.40.Hp Lithography, masks and pattern transfer

High performance self‐aligned sub‐100 nm metal–oxide‐semiconductor field‐effect transistors using x‐ray lithography

Isabel Y. Yang, Hang Hu, Lisa T. Su, Vincent V. Wong, M. Burkhardt, Euclid E. Moon, J. M. Carter, D. A. Antoniadis, Henry I. Smith, Kee W. Rhee, and W. Chu

J. Vac. Sci. Technol. B 12, 4051 (1994); http://dx.doi.org/10.1116/1.587428 (4 pages) | Cited 1 time

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Recent studies have shown that high performance 0.1 μm complementary metal–oxide semiconductor (CMOS) can be achieved with proper channel and source/drain engineering. Specifically, retrograde channel doping and shallow source/drain junctions with counterdoping implant (halo) allow the threshold voltage to be kept low while maintaining acceptable short‐channel behavior. These studies have certainly demonstrated the feasibility of CMOS technology scaled down to 0.1 μm from a device design point‐of‐view. However, the main challenge to the lithography technology is to fabricate 0.1 μm metal‐oxide‐semiconductor field‐effect transistor (MOSFET) devices with high yield and high throughput, as required in manufacturing. X‐ray lithography is a technology that can potentially meet this challenge. This work shows the results of integrating a low cost x‐ray technology with standard IC processing to fabricate high performance 100 nm and even sub‐100 nm MOSFETs.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
85.30.Tv Field effect devices
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