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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 5 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 19 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 18 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