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Nov 1991

Volume 9, Issue 6, pp. 2733-3616


Oxidation sharpening of silicon tips

T. S. Ravi, R. B. Marcus, and D. Liu

J. Vac. Sci. Technol. B 9, 2733 (1991); http://dx.doi.org/10.1116/1.585680 (5 pages) | Cited 31 times

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Sharp microtips of silicon have potential applications as field emitters and as electrical or mechanical microsensors. This study describes a single unified etching/oxidation treatment that results in uniform tips with controlled radii of atomic dimensions or larger. Variations in the etching/oxidation treatment form multiple tips with two or four tips per etched pyramid, which offer the possibility of higher emission current density for field emitter applications, and higher sensitivity for microsensor applications.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

Desorption from oxide films made by plasma enhanced chemical vapor deposition using tetraethylorthosilicate

Harland G. Tompkins, Gordon Grivna, William G. Cowden, and Cathy Leathersich

J. Vac. Sci. Technol. B 9, 2738 (1991); http://dx.doi.org/10.1116/1.585640 (4 pages) | Cited 1 time

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The dielectric stack of multilevel metal interconnections of integrated circuits contains various forms of dielectrics separating metal conductors. Silicon dioxide deposited by plasma enhanced chemical vapor deposition (PECVD) is one such dielectric. The formation of voids in some of the metal layers stimulated a study of the thermal desorption of H2O from oxide films. The films were deposited by plasma enhanced chemical vapor deposition using a tetraethylorthosilicate precursor. The total amount of H2O desorbed was measured as a function of two deposition variables, deposition substrate temperature, and deposition plasma power. The total amount of H2O desorbed could be reduced by either increasing the deposition substrate temperature or increasing the deposition plasma power.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Influence of silicon nitride deposition conditions on the electrical properties of oxide‐nitride (ON) dielectrics on smooth and as‐deposited rugged polycrystalline silicon

Hiang C. Chan, Viju K. Mathews, Charles Turner, and Pierre C. Fazan

J. Vac. Sci. Technol. B 9, 2742 (1991); http://dx.doi.org/10.1116/1.585641 (5 pages) | Cited 1 time

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The effect of Si3N4 deposition conditions on the electrical properties of ON dielectric films on smooth and as‐deposited rugged polycrystalline silicon is investigated. The results show that the leakage current, dielectric breakdown strengths, and the charge trapping characteristics of ON dielectric films are influenced by the Si3N4 deposition conditions. Larger capacitance increases on rugged electrodes, lower leakage currents, higher breakdown fields, and lower electron trapping rates are observed for ON dielectric films fabricated with low NH3@B:SiH2Cl2 gas ratio and deposited at higher temperature. These films are also expected to have a thicker bottom oxide due to the poor oxidation resistant characteristic of the thin nitride layer deposited at high temperature.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.32.Tt Capacitors
77.55.-g Dielectric thin films

Reactive‐ion etching of tungsten silicide using NF3 gas mixtures

Ru‐Liang Lee and Fred L. Terry

J. Vac. Sci. Technol. B 9, 2747 (1991); http://dx.doi.org/10.1116/1.585637 (5 pages) | Cited 3 times

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We report in this paper the reactive‐ion etching of WSix films using gas mixtures containing NF3. A combination of NF3/H2 or NF3/He was used to anisotropically etch WSix films as thick as 4000 Å with photoresist masks. They yielded satisfactorily high etch rates and good selectivities with respect to photoresist and III–V materials. The NF3/He mixture yielded higher etch rates for both WSix and photoresist but a lower selectivity with respect to photoresist. CHF3 was used with NF3 for thicker films and/or submicron features in order to form polymer to protect the sidewalls. Metal masks have to be used in this etch since the etch rates are very low and the selectivity with respect to photoresist is no longer high. A low percentage of NF3 and a low pressure were necessary for successful etches using the NF3/CHF3 plasma. Etched lines as narrow as 0.18 μm are shown. In addition to the optimal etch conditions, data will also be presented for the effects of variations of cathode coverage, rf power, gas pressure, and gas composition.
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81.65.-b Surface treatments

Detailed measurements and simplified modeling of wafer charging in different barrel reactor configurations

Takashi Namura, Hirofumi Uchida, Yoshihiro Todokoro, and Morio Inoue

J. Vac. Sci. Technol. B 9, 2752 (1991); http://dx.doi.org/10.1116/1.585638 (7 pages) | Cited 2 times

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The detailed profiles of the wafer charging in different barrel reactor configurations have been obtained by using the electrically erasable–programmable read‐only memory devices. Charging profile in a parallel electrode system depends strongly on the wafer orientation with respect to the rf electric field, while minor changes are observed by the use of floating Al etch tunnel and by the reduction of the wafer‐to‐wafer separation. On the other hand, no wafer charging is detected in a co‐axial electrode system. A simplified equivalent circuit model, which represents the potential in 2‐dimensional rf plasma–wafer system, has been proposed. The charging profile derived from the simplified model coincides with the experimental results. This model gives an analytical explanation of the gate charging.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Thermodynamics of the homogeneous and heterogeneous decomposition of trimethylaluminum, monomethylaluminum, and dimethylaluminumhydride: Effects of scavengers and ultraviolet‐laser photolysis

J.‐O. Carlsson, S. Gorbatkin, D. Lubben, and J. E. Greene

J. Vac. Sci. Technol. B 9, 2759 (1991); http://dx.doi.org/10.1116/1.585642 (12 pages) | Cited 6 times

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Thermodynamic calculations, based upon free‐energy minimization, have been used to determine the nature and the relative amounts of equilibrium product species following thermal decomposition of the Al‐bearing metal‐alkyl donor molecules trimethylaluminum Al(CH3)3, monomethylaluminum AlCH3, and dimethylaluminumhydride Al(CH3)2H at temperatures between 0 and 1250 °C. The calculations were carried out using initial total pressures of 760, 1, and 0.1 Torr (101 kPa, 133, and 13.3 Pa) and both homogeneous and heterogeneous decomposition were considered. The calculations were repeated for mixtures containing trimethylaluminum and the reducing agents H2, arsine AsH3, and silane SiH4 in order to investigate the effectiveness of these species in scavenging C‐containing radicals. The effect of H2 on the decomposition of AlCH3 and Al(CH3)2H was also studied. The results are discussed and compared with available data from Al film growth experiments by pyrolytic chemical vapor deposition (CVD) and laser‐induced photolytic CVD. Finally, the CVD phase diagram for solid product species was computed for reactant mixtures of Al2(CH3)6+AsH3+H2.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.20.Hf Product distribution
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Characteristics of silicon strip doping sources for molecular beam epitaxy

W. D. King, G. J. Griffiths, and Stephen Giugni

J. Vac. Sci. Technol. B 9, 2771 (1991); http://dx.doi.org/10.1116/1.585639 (7 pages)

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The use of a filament doping source for Si doping of molecular beam epitaxy (MBE) grown III–V semiconductors provides many benefits in the areas of cleanliness, simplicity of construction, and source lifetime. This work details the thermal and doping characteristics associated with such sources. Expressions are developed for the flux, temperature, and power relations, and for the heating and cooling characteristics. We show that the thermal response allows the doping to be varied by at least two orders of magnitude during the time taken to grow one monolayer at normal growth rates (1 μm/h), and for most applications this obviates the need for a shutter. The source is clean (largely because it is only the strip itself which is at an elevated temperature), repeatable, reliable, has a lifetime comparable with that of the system, and can achieve doping levels of 1019 cm−3 in GaAs with mobilities of 1300 cm2 V−1 s−1 at room temperature.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Novel method for measuring and analyzing surface roughness on semiconductor laser etched facets

Robert W. Herrick, Lori G. Sabo, and Joseph L. Levy

J. Vac. Sci. Technol. B 9, 2778 (1991); http://dx.doi.org/10.1116/1.585643 (6 pages) | Cited 3 times

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We introduce a method of measuring the surface profile of etched facets on semiconductor lasers, giving direct, quantitative results. Unlike previous techniques which attempt to infer facet quality from electro‐optic performance or subjective analysis of micrographs, this technique provides the actual facet profile. We show how this information can be used for process improvement, and accurate numerical simulation of facet reflectivity.
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81.65.-b Surface treatments
42.82.-m Integrated optics
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.70.-q Methods of materials testing and analysis

Temperature measurement during implantation at elevated temperatures (300–500 °C)

Peter Vandenabeele and Karen Maex

J. Vac. Sci. Technol. B 9, 2784 (1991); http://dx.doi.org/10.1116/1.585644 (4 pages) | Cited 3 times

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Using an optical fiber thermometer, wafer temperature was measured during implantation at elevated temperatures. The wafer was mounted on a chuck which was resistively heated to 400 °C. Ar was implanted at an energy of 200 keV and a current in the range of 0–750 μA. Due to poor thermal contact between the chuck and the wafer, wafer temperature could be different from chuck temperature. The wafer temperature varied from ∼300 to 500 °C as a function of implantation current. The wafer temperature was also dependent on the optical properties of the wafer. A model was developed which took the optical properties of the wafer and the chuck into account.
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07.20.Dt Thermometers
42.81.Wg Other fiber-optical devices
61.72.uf Ge and Si

Improving projection lithography image illumination by using sources far from the optical axis

Satoru Asai, Isamu Hanyu, and Kohki Hikosaka

J. Vac. Sci. Technol. B 9, 2788 (1991); http://dx.doi.org/10.1116/1.585645 (4 pages) | Cited 2 times

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In a projection lithography system having fly‐eye elements, a virtual source is created as an array of approximately mutually incoherent point sources. This paper describes simulated results of the light amplitude and phase of the mask‐projected image for a point source and discusses the dependence on the point source location on a plane situated perpendicular to the optical axis. We showed that the projected image illuminated by point sources far from the optical axis was improved by the effect of interference between multiple apertures. Resolution of the 0.4 μm lines and spaces was improved theoretically and experimentally at a wavelength of 435.8 nm and a numerical aperture of 0.45.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Novel indices characterizing resolution power of photoresist for half‐micron feature size photolithography

Tetsuo Ito, Sadao Okano, Shigeru Takahashi, Aritoshi Sugimoto, and Kazuya Kadota

J. Vac. Sci. Technol. B 9, 2792 (1991); http://dx.doi.org/10.1116/1.585646 (6 pages)

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The photoactive and development parameters of commercially available g‐line photoresists which are TOKs OFPR800, OFPR5000, TSMR8900, and TSMR‐V3, were measured. From the simulated and experimental linewidth linearity data, it was found that the photoactive parameters have very little effect on the resolution power (linearity limit) of photoresists, while the development parameters (dissolution rate characteristics) greatly affect the resolution power. New indices, which can properly characterize the resolution power of photoresists, were extracted from the dissolution rate characteristics curves. One is Cd, which is the contrast of the dissolution rate and the other is Rd, which is the range of the dissolution rate. These indices are closely related to the resist resolution power. A larger Cd or Rd gives a higher resolution power to the photoresist. The necessary value of Cd⋅Rd for the 0.5‐μm feature size photolithography process was derived from experimental data under the present highest NA(=0.55) g‐line stepper for mass production and Cd⋅Rd must be larger than 39. Both Cd and Rd are useful parameters for estimation of the photoresist resolution power.
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85.40.Hp Lithography, masks and pattern transfer

Anisotropic etching of GaAs using a hot Cl2 molecular beam

Tetsuo Ono, Hideo Kashima, Susumu Hiraoka, Keizo Suzuki, and Andreas Jahnke

J. Vac. Sci. Technol. B 9, 2798 (1991); http://dx.doi.org/10.1116/1.585647 (4 pages) | Cited 7 times

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Anisotropic etching of GaAs(100) is performed using a hot Cl2 molecular beam produced by free expansion of gas heated in a furnace. The etch rate is 1.5 μm/min at a furnace temperature of 800 °C and a substrate temperature of 120 °C. An aspect ratio of ten and an almost smooth bottom surface are obtained under this condition.
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81.65.-b Surface treatments

Doping characteristics of Si into molecular‐beam epitaxially grown InAlAs layers

M. Higuchi, T. Ishikawa, K. Imanishi, and K. Kondo

J. Vac. Sci. Technol. B 9, 2802 (1991); http://dx.doi.org/10.1116/1.585648 (3 pages) | Cited 4 times

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We studied the doping characteristics of Si into molecular‐beam epitaxially grown InAlAs layers for various growth conditions. The growth temperature and V/III beam flux ratio proved to play different roles in Si doping. The growth temperature affects the Si doping concentration, and the V/III flux ratio does the compensation ratio. At Ts=560 °C, a rather high temperature for the growth of InAlAs layers, the Si doping concentration reached 150% as compared with growth at Ts=500 °C. With increasing V/III flux ratio, on the other hand, electron mobility and donor concentration increased, suggesting a decreased compensation ratio. We also found a considerable number of electron trapping centers at a low‐growth temperature of 400 °C.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.U- Doping and impurity implantation

Molecular beam epitaxy growth and physical characterization of precise, narrow, triangular heterostructures using an analog grading algorithm

Stephen Giugni and T. L. Tansley

J. Vac. Sci. Technol. B 9, 2805 (1991); http://dx.doi.org/10.1116/1.585649 (9 pages) | Cited 5 times

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Precise control of the compositional profile in ternary semiconductors, with the resulting spatial variation of band structure, allows electronic and/or optical properties to be tailored for specific applications. An algorithm is presented, and its implementation described, for the growth of very narrow graded compositional GaAs/AlGaAs heterostructure wells and barriers by conventional solid‐source molecular beam epitaxy. The Al source furnace temperature is controlled continuously to obtain linear analog compositional grading. Physical confirmation of the precision of the profiles has been obtained by a range of techniques including secondary ion mass spectrometry, secondary neutral mass spectroscopy, and compositional analysis from thickness fringes‐transmission electron microscopy. The results show excellent linearity and symmetry in structures with compositional changes between 0% and 30% Al over 10‐nm graded regions.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Resolution limits of optical lithography

Shinji Okazaki

J. Vac. Sci. Technol. B 9, 2829 (1991); http://dx.doi.org/10.1116/1.585650 (5 pages) | Cited 20 times

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The development of optical lithography has promoted the development of ultralarge scale integration (ULSI) devices. However, optical lithography is now facing serious obstacles due to the limitations in wavelength. Higher resolution with sufficient depth of focus is the most important requirement for ULSI engineers. To satisfy this requirement, many technologies for resolution improvement and new optical image formation technologies such as phase shifting and focus latitude enhancement exposure (FLEX) are reviewed, and a future perspective on optical lithography is also discussed in this paper.
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85.40.Hp Lithography, masks and pattern transfer

Remarkable effects in wet‐etched GaAs/GaAlAs rings

K. Y. Lee, D. P. Kern, K. Ismail, and S. Washburn

J. Vac. Sci. Technol. B 9, 2834 (1991); http://dx.doi.org/10.1116/1.585651 (4 pages) | Cited 2 times

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Coupled GaAs/GaAlAs rings have been fabricated using electron‐beam lithography and wet chemical etching. We report the first observation of conductance steps associated with e2/h in etched structures, and clear Aharonov–Bohm oscillations in multiple rings connected in parallel. The amplitude of the oscillations is found to be dependent on the number of rings indicating the possibility of phase coupling between electrons traversing different rings.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.Fz Weak or Anderson localization
85.40.Hp Lithography, masks and pattern transfer

Direct nanometer scale patterning of SiO2 with electron‐beam irradiation

D. R. Allee, C. P. Umbach, and A. N. Broers

J. Vac. Sci. Technol. B 9, 2838 (1991); http://dx.doi.org/10.1116/1.585652 (4 pages) | Cited 16 times

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Nanometer scale patterns have been fabricated in SiO2 by direct electron‐beam exposure. Two techniques have been developed to eliminate the surface contamination and enable the subsequent development of the patterns in HF based wet etches: (1) exposing the oxide through a sacrificial layer (previously reported) and (2) O2 reactive ion etching (RIE). The latter approach eliminates the need for a sacrificial layer and improves resolution by reducing the forward scattering of the beam. To determine the resolution of this process, patterns were fabricated with both 50‐ and 300‐kV electrons in thin SiO2 membrane samples and imaged in transmission. Transmission imaging avoids the resolution limit of secondary electron micrographs set by the lateral range of secondary electrons. At 300 keV with a line dose of 7.5 μC/cm, arrays of lines with a period down to 15 nm were achieved as opposed to the 21‐nm period previously reported using a sacrificial layer and secondary electron imaging of bulk substrates. A better understanding has also been obtained of the profiles of the patterns in SiO2.
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85.40.Hp Lithography, masks and pattern transfer

Facetless Bragg reflector surface‐emitting AlGaAs/GaAs lasers fabricated by electron‐beam lithography and chemically assisted ion‐beam etching

R. C. Tiberio, G. A. Porkolab, M. J. Rooks, E. D. Wolf, R. J. Lang, A. Larsson, S. Forouhar, J. Cody, G. W. Wicks, T. Erdogan, O. King, and D. G. Hall

J. Vac. Sci. Technol. B 9, 2842 (1991); http://dx.doi.org/10.1116/1.585653 (4 pages) | Cited 6 times

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We report the fabrication and characterization of facetless Bragg reflector surface‐emitting AlGaAs/GaAs lasers. Both first‐order (120‐nm period) and second‐order (240‐nm period) gratings were fabricated by electron‐beam lithography and chemically assisted ion‐beam etching (CAIBE). These grating pairs provide the optical feedback of the laser, eliminating the need for cleaved or etched mirror facets. Specifically, this work includes: the fabrication and testing of a variable pitch grating‐laser array which demonstrates optical emission peaks with 5‐Å separation for adjacent lasers; demonstration of facetless Bragg reflector lasers with 120/240‐nm grating pairs that show lower threshold currents, higher quantum efficiencies, and improved beam width compared to conventional facetless second‐order grating lasers; and a demonstration of grating surface‐emitting diode lasers with hybrid first‐order and nonresonant, 120/307‐nm, grating pairs that produced a directed beam at 45° with respect to the substrate. The fabrication technology and optical performance of these devices are presented.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
85.40.Hp Lithography, masks and pattern transfer

Free‐standing gratings and lenses for atom optics

David W. Keith, Robert J. Soave, and Michael J. Rooks

J. Vac. Sci. Technol. B 9, 2846 (1991); http://dx.doi.org/10.1116/1.585654 (5 pages) | Cited 5 times

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A fabrication process has been developed for making free‐standing gratings of silicon nitride. These structures are critical components of an atom interferometer, which uses four gratings as coherent beam splitters of atom waves. The quality of gratings necessary for an interferometer is considerably higher than is needed to demonstrate the diffraction of atoms. In particular, the gratings must be phase coherent over their entire area. This implies that the grating lines must be straight to the order of their linewidth over the full extent of the grating. In addition, the open fraction of the grating structure is more critical for an interferometer. In this paper the development of new fabrication techniques that were used to make free‐standing gratings with periods as small as 100 nm and support structure open fractions as high as 0.8 were reported on. To achieve depth‐to‐linewidth ratios greater than 4:1 with grating periods as small as 100 nm a selective, highly directional reactive ion etching (RIE) process has been developed.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
34.90.+q Other topics in atomic and molecular collision processes and interactions (restricted to new topics in section 34)

Nanofabrication techniques for 100 nm‐scale silicon metal oxide semiconductor field effect transistor

C. M. Reeves, F. J. Hohn, S. J. Wind, Y. T. Lii, T. H. Newman, J. J. Bucchignano, D. P. Klaus, and K. N. Chiong

J. Vac. Sci. Technol. B 9, 2851 (1991); http://dx.doi.org/10.1116/1.585655 (5 pages)

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In this paper we report on an exploratory metal oxide semiconductor field effect transistor (MOSFET) device which we are currently investigating which requires 100 nm lithography at all critical levels to achieve a completely fully scaled 100 nm device structure. The device also incorporates a novel trench isolation scheme whereby the isolation trenches are etched after the gate electrodes have been formed leading to a butted gate configuration. The device further incorporates fully overlapped contacts to the gate, source, and drain regions in order to provide maximum contact area. We believe that this structure will provide a good basis for exploring the density and performance limits of 100 nm‐scale devices. We describe here the structure of the proposed device and then we propose a suitable method of fabrication. This is followed by a demonstration of suitable nanofabrication techniques which are based, in each case, on high resolution electron beam lithography and precision reactive ion etching. Finally, we assess the feasibility of integrating these techniques in order to realize the proposed device.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Split‐gate electron waveguide fabrication using multilayer poly(methylmethacrylate)

M. J. Rooks, C. C. Eugster, J. A. del Alamo, G. L. Snider, and E. L. Hu

J. Vac. Sci. Technol. B 9, 2856 (1991); http://dx.doi.org/10.1116/1.585656 (5 pages) | Cited 7 times

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We report on techniques for fabricating 20‐nm scale ballistic electron devices and on techniques for imaging and characterizing these patterns in thin layers of poly(methylmethacrylate) (PMMA). A split‐gate fabrication approach with nanometer‐scale Schottky gates is used. Using a multiple layer PMMA resist technique, we have fabricated Au/Pd gates as narrow as 20 nm. In order to enhance the undercut profile a lower molecular weight PMMA is used as the bottom layer. We have also developed a resist stabilization technique which allows the viewing of 20 nm scale features in 0.1‐μm thick PMMA resist under high magnification in a scanning electron microscope. These techniques have been used to fabricate ballistic electron devices which demonstrate quantum interference effects.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Fabrication of electroplated T gates with 60 nm gate length for pseudomorphic high electron mobility transistor devices

A. Marten, H. Schneider, H. Schweizer, H. Nickel, W. Schlapp, R. Lösch, H. Dämbkes, and P. Marschall

J. Vac. Sci. Technol. B 9, 2861 (1991); http://dx.doi.org/10.1116/1.585657 (5 pages) | Cited 1 time

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We have fabricated and electrically characterized mm‐wave high electron mobility transistors (HEMTs) on pseudomorphic heterostructure GaAs/InGaAs samples. The T‐ and Γ‐shaped gates were produced using electroplating and a conventional single resist‐layer lift‐off process. High frequency measurements of the same device before and after plating demonstrate the reduction in gate resistance. Direct current and high frequency properties of the HEMTs depend strongly on gate length and gate recess depth. Characterization of parallel conducting layers, low field mobility, and sheet carrier concentration depth profiles were obtained with gated Hall measurements. Best HEMT performance was obtained at a gate length of 60 nm, giving an extrinsic (intrinsic) transconductance of 620 mS/mm (840 mS/mm) and a cutoff frequency ft of 135 GHz.
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85.30.Pq Bipolar transistors
85.40.Hp Lithography, masks and pattern transfer

First step towards application of high‐temperature superconductors for planar magnetic lenses

J. P. Adriaanse, K. D. van der Mast, and P. van Zuylen

J. Vac. Sci. Technol. B 9, 2866 (1991); http://dx.doi.org/10.1116/1.585658 (4 pages)

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The feasibility of high‐temperature superconductors for applications in particle optics is discussed. Although high Tc superconducting coils and wire are not available yet, we conclude that thin films are very promising for ironless magnetic lenses due to their high maximum current density and because they can be very accurately patterned. However, a stack of 10–100 layers will be needed to fulfil the field strength and rotational symmetry requirements. Initial experimental results obtained with a superconducting YBa2Cu3O7−x film patterned with a 50‐turn spiral‐shaped coil are presented. The maximum critical current density obtained in the 50‐turn spiral was 104 A/cm2 at 30 K. The best way to stack the films would be a multilayer fabrication process, but this is not yet available. As an intermediate step, we developed a pattern suitable for face‐to‐face stacking and we propose an alignment technique based on capacitive position sensors.
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41.75.Fr Electron and positron beams
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
74.70.-b Superconducting materials other than cuprates
74.78.-w Superconducting films and low-dimensional structures

Fabrication of sub‐100‐nm T gates with SiN passivation layer

K. Nummila, M. Tong, A. A. Ketterson, and I. Adesida

J. Vac. Sci. Technol. B 9, 2870 (1991); http://dx.doi.org/10.1116/1.585615 (5 pages) | Cited 2 times

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Low resistance T‐shaped gates as small as 60 nm have been fabricated using high resolution electron‐beam lithography (EBL). A silicon nitride (SiNx) passivation layer has been used to define the bottom of the T gate and to provide mechanical support for the top of the T gate. A two‐step etch was performed to define the gate footprint in the SiNx. First a short wet etch is used to isotropically etch the SiNx to provide a wider top opening following by reactive ion etching (RIE) to transfer the narrow resist pattern anisotropically into the bottom of the SiNx. A bilayer resist lift‐off process is then used to determine the top of the T gate and the thickness of the gate metal. End‐to‐end gate resistances of 450 Ω/mm have been measured for sub‐0.1‐μm‐long gates with a 0.5‐μm‐wide top and with 250‐nm‐thick metallization. The resistance can easily be further decreased by increasing the metal thickness and/or by widening the top of the T gate. Gate capacitances Cgs and Cgd measured on GaAs metal–semiconductor field effect transistors (MESFETs) with a SiNx layer showed a slight increase in capacitance compared to the devices without the SiNx layer. Slightly higher extrinsic transconductances gm and unity current‐gain cut‐off frequencies fT were achieved for the devices with the SiN layer. Intrinsic unity current‐gain cut‐off frequencies fT of up to 102 GHz were measured. The fabrication of GaAs MESFETs with T gates down to 60 nm is demonstrated with the SiNx passivation layer process.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Tv Field effect devices

High resolution patterning of high Tc superconductors

D. P. Kern, K. Y. Lee, R. B. Laibowitz, and A. Gupta

J. Vac. Sci. Technol. B 9, 2875 (1991); http://dx.doi.org/10.1116/1.585616 (4 pages) | Cited 9 times

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A novel method for submicron patterning of high Tc superconductor thin films is presented. Specifically, we describe the patterning of the superconductor YBa2Cu3O7−x (YBCO) on single crystal SrTiO3 wafers by a selective epitaxy approach. A silicon nitride template is formed on the SrTiO3 using electron beam lithography and reactive ion etching. A thin film of YBCO is then deposited on the wafer, e.g., by laser ablation. Selective epitaxy occurs during the deposition process, the YBCO film grows epitaxially on SrTiO3, while the film depositing on the nitride forms insulating clusters. Good epitaxial films and patterns have been obtained as‐deposited without the need for further annealing or other process steps. Lines as narrow as 130 nm have been fabricated which show no significant decrease in Tc as compared with the original blanket film.
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68.55.-a Thin film structure and morphology
74.78.-w Superconducting films and low-dimensional structures

Fabrication of 0.25 μm surface acoustic wave devices by ion beam proximity printing

D. P. Stumbo, Sudipto Sen, G. A. Damm, F‐O. Fong, D. W. Engler, K‐F. Fong, J. C. Wolfe, and Frederick Cho

J. Vac. Sci. Technol. B 9, 2879 (1991); http://dx.doi.org/10.1116/1.585617 (3 pages) | Cited 5 times

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The electrodes of surface acoustic wave (SAW) devices cannot be represented in a stencil mask as cantilevered beams because the high aspect ratio makes them unstable. Therefore a complementary exposure technique has been developed. The mask pattern is formed by segmenting the electrodes into equal length open and closed areas. The wafer is then exposed twice with an offset equal to the segment length, thus forming a continuous electrode image. This approach has two advantages: (1) the high process latitude of ion beam proximity printing (IBPP) is preserved since, in contrast to the grid‐support approach, no areas are doubly exposed; and (2) only precision translation is required to register the exposures, preserving the single level nature of SAW patterns. Linewidth is shown to change by less than ±15% for ±20% changes in exposure at a 0.25 μm nominal linewidth.
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85.30.-z Semiconductor devices
85.40.Hp Lithography, masks and pattern transfer
43.38.Rh Surface acoustic wave transducers

High quantum efficiency InGaAs/GaAs quantum wires defined by selective wet etching

Ch. Gréus, A. Forchel, J. Straka, K. Pieger, and M. Emmerling

J. Vac. Sci. Technol. B 9, 2882 (1991); http://dx.doi.org/10.1116/1.585618 (4 pages) | Cited 3 times

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A technology is reported for the fabrication of buried InGaAs/GaAs quantum wires. For the pattern transfer of the nanometer structures a sensitive high resolution negative e‐beam resist is used as a direct etch mask. The essential step of the approach is a selective wet etch process by which only the top barrier layer of a quantum well structure is removed between masked regions. Due to the high energy barrier of the etched surface quantum wells compared to the masked regions a lateral potential well is formed. Investigating the width dependence of the photoluminescence efficiency a high intensity is found, even for narrow wires and a significant shift of the emission to high energies for the smallest wires with widths of 35 nm.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
84.32.Hh Inductors and coils; wiring

Full‐wafer technology for large‐scale laser processing and testing

O. Voegeli, M. K. Benedict, G. L. Bona, P. Buchmann, N. Cahoon, K. Dätwyler, H. P. Dietrich, A. Moser, G. Sasso, H. K. Seitz, P. Vettiger, D. J. Webb, and P. Wolf

J. Vac. Sci. Technol. B 9, 2886 (1991); http://dx.doi.org/10.1116/1.585619 (7 pages) | Cited 3 times

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A new approach for large‐scale semiconductor laser fabrication is presented. In this ‘‘full‐wafer processing and testing’’ concept, the mirrors are fabricated, not by cleaving the wafer but by forming them by means of a chemically assisted ion beam etching process. This allows for on‐wafer mirror passivation and testing of the finished devices. Full‐wafer technology changes the traditional way of discrete device fabrication and testing to a method more akin to today’s very large‐scale integrated (VLSI) technology. Consequently, it provides similar advantages in cost and throughput. Additionally, it allows other electrical and electro‐optical device components to be monolithically integrated on the wafer. Currently, we are routinely fabricating AlGaAs/GaAs diode lasers with a single quantum well graded index separate confinement heterostructure (SQW‐GRINSCH)‐type ridge structure using full‐wafer technology. Such lasers exhibit excellent beam properties in single mode up to at least 50 mW output power. Their functional characteristics are indistinguishable from comparable lasers with cleaved facets obtained from the same wafer for comparison purposes. This result reflects the high quality of the etched mirrors. Typically, their surface roughness is less than 200 Å, with mirror reflectivities of about 30% and losses due to mirror scattering below 2%. Having functional parts on the uncleaved wafer allows automated full‐wafer testing that encompasses wafer characterization and part screening. This not only eliminates part handling, with its associated yield loss, it also permits a much expanded scope of testing in a fraction of the time previously required.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.87.-d Optical testing techniques

Electric field coupling to quantum dot diodes

J. N. Randall, A. C. Seabaugh, Y.‐C. Kao, J. H. Luscombe, and B. L. Newell

J. Vac. Sci. Technol. B 9, 2893 (1991); http://dx.doi.org/10.1116/1.585620 (5 pages) | Cited 4 times

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We have fabricated two different structures in the GaAs/AlGaAs heterojunction system to quantify the transfer characteristics of the quantum dot subjected to external, local electric fields. The first structure is a single quantum dot diode with an annular field electrode placed adjacent to the double‐barrier structure by a self‐aligned fabrication process. A second structure consists of a pair of independently contacted quantum dot diodes separated by several hundred angstroms. The fabrication processes and transport properties for both of these structures are described. We have also attempted for the first time to form quantum dots in InGaAs/AlAs system lattice matched to InP and have observed that strong conductance fluctuations not related to lateral size quantization can occur. These fluctuations arise from the formation of rotation‐induced finite superlattices.
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85.30.Kk Junction diodes
85.40.Hp Lithography, masks and pattern transfer

0.5 μm GaAs metal semiconductor field effect transistor circuit fabrication using single layer I‐line photoresists

Andrew T. S. Pomerene, James H. Greiner, and John J. Connolly

J. Vac. Sci. Technol. B 9, 2898 (1991); http://dx.doi.org/10.1116/1.585621 (6 pages)

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This paper describes the implementation of an I‐line photoresist process which was used to build 0.5 and 0.4 μm GaAs metal semiconductor field effect transistor (MESFET) devices with good parametric test results. A new PE/Micrastep I‐line step and repeat system with enhanced air gauge focus, dark field alignment and laser stage exposed all of the photo levels. AZ 5214, AZ 5209, and KTI 895i resists were used for the liftoff wiring, gate metal, implant, and insulation levels, respectively. Thickness vs exposure and depth of focus curves are shown. The photo process effects upon the surface sensitive GaAs MESFET are discussed. Examination of alignment effects upon the device performance and the photochemistry interaction with the physical and electrical properties are shown. Final device results are shown with good results down to 0.4 μm.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Fabrication of 25 nm gold‐bridges and observation of ballistic and quantum interference effects

W. Langheinrich, H. Beneking, U. Murek, C. Braden, and D. Wohlleben

J. Vac. Sci. Technol. B 9, 2904 (1991); http://dx.doi.org/10.1116/1.585622 (4 pages)

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This paper is devoted to pure Au quantum wires with a length varied between 50 nm and 1 μm. In order to obtain extremely pure metallic nanometer structures, a liftoff process is preferred. To overcome the problem of grain size limited linewidth control and edge quality, a four‐layer resist system for electron beam lithography has been developed, which enables the reproducible fabrication of mesoscopic devices with lateral dimensions down to 25 nm. I–V characteristics and magnetoconductance measurements have been carried out. Especially in the case of short wires, where electron transport is in the quasiballistic regime, universal conductance fluctuations have been observed, which are visible even at temperatures above 30 K.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
85.40.Ls Metallization, contacts, interconnects; device isolation

Helium radio‐frequency‐plasma GaAs device isolation: Application to an in‐plane gated quantum wire transistor

S. G. Ingram, P. J. Simpson, V. J. Law, D. A. Ritchie, and G. A. C. Jones

J. Vac. Sci. Technol. B 9, 2908 (1991); http://dx.doi.org/10.1116/1.585623 (4 pages) | Cited 5 times

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Low‐energy ion bombardment has been used for isolation to define an in‐plane gated quantum wire transistor in a GaAs/AlAs heterostructure. The two‐dimensional electron gas (2DEG) was 17 nm below the GaAs/vacuum interface, with a mobility at 1.2 K of 7.97×105 and 6.3×105 cm2 V−1 s−1 at a sheet carrier concentration of 6.45×1011 and 5.98×1011 cm−2 with and without illumination, respectively. Optimum gate isolation was achieved using a 6 min exposure to a helium radio‐frequency (rf) plasma at 5.7 Pa (43 mTorr), with a dc bias of −150 V. Electrical measurements show that the application of a suitable gate bias produces conductance changes in the device, with evidence for one‐dimensional (1D) ballistic transport at 1.2 K.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.40.Hp Lithography, masks and pattern transfer

Fabrication of open and buried quantum wires using a removable mask applicable for multiple processing steps

A. Menschig, P. A. Kübler, F. E. Prins, R. Rudeloff, J. Hommel, and H. Schweizer

J. Vac. Sci. Technol. B 9, 2912 (1991); http://dx.doi.org/10.1116/1.585624 (4 pages)

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We have carried out detailed investigations on dry etch selectivity, ion penetration depths, and adhesion properties for a wide variety of materials to find a suitable combination for the fabrication of multiple process masks (MPM). A combination of Al2O3, TiO, and Pt yield the best results for the use in the In0.53Ga0.47As/InP system. Using this type of MPM for different fabrication processes, we have realized wires by deep dry etching (i.e., open wires) and also buried wires either by deep dry etching with an additional overgrowth or by ion implantation. All three kinds of wires show characteristic size effects in magnetotransport experiments.
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85.40.Hp Lithography, masks and pattern transfer
84.32.Hh Inductors and coils; wiring
81.05.Bx Metals, semimetals, and alloys
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments

Low energy off‐axis focused ion beam Ga+ implantation into Si

A. J. Steckl, H. C. Mogul, S. W. Novak, and C. W. Magee

J. Vac. Sci. Technol. B 9, 2916 (1991); http://dx.doi.org/10.1116/1.585625 (4 pages) | Cited 2 times

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Off‐axis focused ion beam (FIB) implantation of Ga+ has been performed at low energies to study the channeling effect. FIB implantations were performed at 3, 5, and 10 keV into crystalline (100) Si at tilt angles of up to 15° toward the 〈110〉 axis. The Ga atomic depth profile was measured using secondary ion mass spectrometry with a 2‐keV‐Cs+ primary beam incident at 60° from the sample normal, in order to minimize ion beam mixing effects during sputttering. The Ga depth profiles show significant reduction in channeling with implantation tilt angle. The fractions of the Ga dose found in the tail of distribution for the 5 keV implant were ∼16% and 10% for the 0° and 15° off‐axis implantation, respectively. Corresponding values reported for 5‐keV B+ implantation under the same conditions are ∼50% and 19%, respectively. Thus, low energy FIB Ga implantation is seen to not only have a much lower penetration depth than B, but also to produce more effective channeling suppression.
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61.72.uf Ge and Si
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Fabrication of sub‐50 nm finger spacing and width high‐speed metal–semiconductor–metal photodetectors using high‐resolution electron beam lithography and molecular beam epitaxy

Stephen Y. Chou, Yue Liu, and Paul B. Fischer

J. Vac. Sci. Technol. B 9, 2920 (1991); http://dx.doi.org/10.1116/1.585626 (5 pages) | Cited 8 times

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Using high‐resolution electron beam lithography, we have fabricated metal–semiconductor–metal photodetectors with sub‐50 nm finger spacing and finger width on GaAs grown by molecular beam epitaxy, which are, to our knowledge, the smallest ever reported. dc measurements showed that they have low dark current and high sensitivity. Proper scaling of the detectors to reduce the finger resistance and detector capacitance and to increase detector speed was studied. The resistances of thin metal lines with various widths were measured and compared with the value calculated from resistivity for bulk metal. Monte Carlo simulation demonstrates that for the photodetectors with 30 nm finger spacing and width, the response time is below picosecond and the cut‐off frequency is over 1 THz.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.30.Hi Surface barrier, boundary, and point contact devices
73.40.Sx Metal-semiconductor-metal structures

100 kV Schottky electron gun

J. B. McGinn, L. W. Swanson, N. A. Martin, M. A. Gesley, M. A. McCord, R. Viswanathan, F. J. Hohn, A. D. Wilson, R. Naumann, and M. Utlaut

J. Vac. Sci. Technol. B 9, 2925 (1991); http://dx.doi.org/10.1116/1.585627 (4 pages) | Cited 1 time

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We present a comparison between experimental results and computer calculations on a high current, high resolution single lens electrostatic 100 kV Schottky electron gun. One promising application for such an electron gun is for direct electron‐beam patterning of x‐ray masks. The high energy helps provide precise patterning of the thick resist, maintains vertical resist profiles, and minimizes the proximity effect. The gun was designed to operate from 25 to 100 kV, capable of focus at a distance of 145–245 mm with a magnification of 1.15. The emitter, of apex radius ∼0.6 μm operated at 1800 K in the extended Schottky regime, provides an angular intensity of 0.5 mA/sr for an extraction voltage of 5000 V and with a beam limiting aperture of 2.2 mrad, the gun delivers 7 nA of probe current. The gun consists of a replaceable high voltage optic module mounted on a precision insulator with the main acceleration occurring between the exit of the optic module and the grounded anode. A provision is made for alignment of the emitter with respect to the central optical axis of the optic module in a special alignment chamber eliminating the need for high voltage emitter alignment. Final gun alignment is achieved by X–Y motion of the grounded anode aperture. The gun is constructed to allow ease of replacement of the emitter, the beam defining aperture, and the differential pumping aperture. The beam supply has 10 ppm of ripple while lens supplies have <50 ppm of ripple. At 100 kV the power supply, cabling, connectors, insulator, and optic module draw 1 μA of ground leakage current. Pressured SF6 chambers are used for high voltage connector interfaces within the power supply and on the gun.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.Hp Lithography, masks and pattern transfer
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

High brightness limited area cathodes

Alec Broers, Shanhong Xia, Chris Maloney, Xieqing Zhu, and Eric Munro

J. Vac. Sci. Technol. B 9, 2929 (1991); http://dx.doi.org/10.1116/1.585628 (5 pages) | Cited 1 time

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In this paper the theoretical description of limited area thermionic cathodes for use in electron microscopes and related equipment is presented. With these cathodes the emitting area is set by the extent of the active cathode surface and not by a control electrode, as is the case for the conventional triode electron microscope gun. This allows the accelerating field at the cathode surface to be greatly increased and the deleterious effects of space charge eliminated. The field can also be increased to the point that the Schottky effect enhances emission without the need to use sharply pointed cathodes. For example, considerable Schottky enhancement can be realized for cathodes with tip radii around 50 μm. The overall effect is that brightness can be increased by more than an order of magnitude over the standard triode gun. Other advantages are that the total beam current can be much higher than it is with field‐emission and thermal field‐emission cathodes and that the Boersch effect is reduced because no real crossover is formed.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
79.40.+z Thermionic emission
85.80.Fi Thermoelectric devices

Aberrations of electron focusing and deflection systems in the presence of three‐dimensional perturbation fields

John Rouse, Xieqing Zhu, and Eric Munro

J. Vac. Sci. Technol. B 9, 2934 (1991); http://dx.doi.org/10.1116/1.585629 (6 pages)

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The numerical analysis of the focusing and aberration properties of electron beam columns involves two tasks: computation of the axial fields and computations of the aberrations. Some electron beam columns contain three‐dimensional (3‐D) perturbation fields that cannot be conveniently computed by two‐dimensional numerical methods. In such cases, a fully 3‐D field computation and an extension of existing aberration theories are required to compute the effects of these 3‐D fields on the primary beam optics. In this paper it is described how a software package for computing 3‐D electric and magnetic fields has been interfaced with a new optical properties package, which computes the aberrations and plots spot diagrams in electron focusing and deflection systems with additional 3‐D perturbation fields. The new aberration theory is outlined and gives several illustrative examples of the use of the new software.
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41.75.Fr Electron and positron beams

Electron optics for high throughput electron beam lithography system

Yasunari Sohda, Yoshinori Nakayama, Norio Saitou, Hiroyuki Itoh, and Hideo Todokoro

J. Vac. Sci. Technol. B 9, 2940 (1991); http://dx.doi.org/10.1116/1.585630 (4 pages) | Cited 2 times

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A new electron optical column has been designed for cell projection method involving 0.2 μm large scale integration fabrication. Assuming a resist sensitivity of 1 μC/cm2 and a deflection settling time of 100 nsec, the maximum shot length is optimized to 5 μm. The objective lens system has two magnetic lenses and one magnetic deflector, and the lens system size enlargement effect has been investigated to deflect the beam up to 5 mm square field. As a result, beam edge resolution under 0.07 μm and shaped beam distortion under 0.01 μm have been achieved. In order to reduce the practical settling time, a three stage deflection system has been adopted.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams

A microwave eight‐pole transmission line deflector for 100 keV electrons

E. H. Mulder, K. D. van der Mast, and J. L. Tauritz

J. Vac. Sci. Technol. B 9, 2944 (1991); http://dx.doi.org/10.1116/1.585631 (5 pages)

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We have studied an eight‐pole transmission line deflector, with the aim of obtaining a large bandwidth deflector with higher deflection sensitivity than an electrostatic deflector. We show that each electrode can be designed as a transmission line with a characteristic impedance that is independent of the orientation of the deflection field. In a transmission line deflector, the deflection field travels along the optical axis at the speed of light, either in the same direction as the electrons (conventional field direction, CFD) or in the opposite direction (opposite field direction, OFD). We show that at high frequencies neither CFD nor OFD improves the deflection sensitivity, due to the magnetic field in a transverse electromagnetic (TEM) wave. Therefore, this deflector is not suitable for achieving the goal of increased sensitivity. However, the OFD achieves the same sensitivity as an electrostatic deflector using a shorter axial length. Finally, the deflection sensitivity of the transmission line deflector proves to be frequency dependent in the frequency range between 100 Hz and 200 kHz, which is illustrated in the experimental results presented.
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84.40.Az Waveguides, transmission lines, striplines
85.40.Hp Lithography, masks and pattern transfer

MEBES IV thermal‐field emission tandem optics for electron beam lithography

M. Gesley

J. Vac. Sci. Technol. B 9, 2949 (1991); http://dx.doi.org/10.1116/1.585632 (6 pages) | Cited 3 times

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The MEBESR IV column design and test results are presented. A new thermal‐field emission (TFE) electron gun comprised of a Zr/O/W〈100〉 cathode and a low‐aberration, large‐aperture electrostatic lens operates as part of a variable‐magnification, four‐lens ‘‘tandem‐optics’’ column. A 10 kV beam with brightness up to 5×106 A/cm2 sr at the mask is produced. The resulting advantage in electron optical performance is divided between a maximum current density of 400 A/cm2 and a convergence angle reduced to 5 mrad at 0.1 μm beam size. System accuracy is enhanced by the improved depth of focus, reduced aberrations, and the ability to reduce address size while maintaining present throughput levels set by the writing time of the serial‐exposure, raster‐scan machine. Doubling the blanking rate to 160 MHz improves throughput and enables the use of resists having 2.5 μC/cm2 sensitivity. The use of a dual‐stigmator column setup and a 7.5 V/ns double‐deflection beam blanker maintains beam jitter below 0.01 μm. The four‐lens optics can expose masks with a continuously variable beam size over a 0.05–0.30 μm range while maintaining constant current density without adjusting the gun extraction voltage. GhostTM proximity correction of 0.25–0.50 μm features is possible with a fast defocus optic, which forms 0.50–1.0 μm beams and also reduces the exposure current to required values. A beam component analysis provides a measure of the Boersch and radial beam broadening effects.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams

Experimental evaluation of a scanning tunneling microscope‐microlens system

L. P. Muray, U. Staufer, E. Bassous, D. P. Kern, and T. H. P. Chang

J. Vac. Sci. Technol. B 9, 2955 (1991); http://dx.doi.org/10.1116/1.585633 (7 pages) | Cited 8 times

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This paper presents the results of the first successfully fabricated scanning tunneling microscope (STM) aligned field emission (SAFE) microsource. SAFE sources have been shown to produce 2–3 orders of magnitude improvement in brightness over conventional field‐emission sources. Lens electrodes were fabricated from 1‐μm thick silicon membranes by electron‐beam lithography and reactive‐ion‐beam etching. Two‐element microlenses were tested in an ultrahigh vacuum (UHV) chamber with a piezo mounted tungsten tip and a dual feedback system. The sources demonstrated stable emission for periods of hours at beam energies of up to 1 kV. Measurement of the virtual source position showed good agreement with calculated values.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.30.Tv Field effect devices

Investigation of emitter tips for scanning tunneling microscope‐based microprobe systems

U. Staufer, L. P. Muray, D. P. Kern, and T. H. P. Chang

J. Vac. Sci. Technol. B 9, 2962 (1991); http://dx.doi.org/10.1116/1.585634 (5 pages) | Cited 1 time

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This paper reports the preparation and characterization of field emitter tips for use in a scanning tunneling microscope aligned field emission (SAFE) microprobe system. With the tip being at close proximity to the extraction electrode, new demands are imposed on the emitter tips: (1) a low extraction voltage, (2) a well‐defined emission pattern, preferably a single lobe emission, and (3) a high angular emission density. A combined field ion–field electron emission microscope equipped with a special stage for mounting a small aperture in close proximity to the emitter tip, which was used to simulate the first element of the electro‐optical system of the SAFE microprobe, was used to analyze different tip preparation techniques. A low‐temperature field‐assisted thermal annealing process has been developed to routinely produce sharp W 〈111〉 tips well suited for SAFE operation. Tips having an effective tip radius of less than 500 Å, an emission half cone angle of less than 10°, and a peak angular emission density of 7 μA/sr at a total emission current of 1 μA were successfully prepared and used in the SAFE microprobe system.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
85.30.Tv Field effect devices

Development of the field emission electron gun integrated in the sputter ion pump

Y. Yamazaki, M. Miyoshi, T. Nagai, and K. Okumura

J. Vac. Sci. Technol. B 9, 2967 (1991); http://dx.doi.org/10.1116/1.585635 (5 pages)

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A field emission electron gun (FEG) integrated in a rotationally symmetric sputter ion pump (SIP) has been developed. By integrating the FEG into the SIP, a high vacuum condition at the cathode can be easily obtained. The gun chamber and its evacuation system can be very simple and small. Working pressure of 5×10−9 Torr is easily obtained in our experimental setup. Furthermore, the 15 mT axial magnetic field of SIP is superimposed on the cathode. The magnetic field forms the magnetic field immersed FEG, resulting in the reduction of the spherical aberration by one‐half. As an experimental result, a probe current of 6 nA with a 0.1 μm probe diameter at 1 kV beam voltage was successfully obtained with the two lens optical system.
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07.30.Cy Vacuum pumps
07.77.-n Atomic, molecular, and charged-particle sources and detectors

A method of beam size approximation for field emission systems

M. Sato

J. Vac. Sci. Technol. B 9, 2972 (1991); http://dx.doi.org/10.1116/1.585636 (5 pages) | Cited 2 times

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An approximate method is presented for estimating a focused beam size, based on wave optics including the effects of arbitrary spherical and chromatic aberrations, which yields the contrast performance of an optical system. In order to estimate the contrast performance of an optical system, several beam sizes which correspond to the reciprocal of the spatial frequencies resulting from different amplitudes of the optical transfer function (OTF) are defined. The focus position for estimating a beam size is found at the point where the highest quality image is obtained. This new method, which involves fitting the OTF values by means of functional approximations, can be applied with minimal computational effort.
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41.75.Fr Electron and positron beams
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

On the design and effective strength of stigmators for electron beam lithography

M. Gesley and W. DeVore

J. Vac. Sci. Technol. B 9, 2977 (1991); http://dx.doi.org/10.1116/1.585352 (4 pages) | Cited 5 times

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Past expressions for stigmator strength are applied to experimental data using three different stigmators; two having magnetic focusing with low geometric aspect ratios (bobbin length to diameter), the other using electrostatic focusing with a larger aspect ratio. While the functional dependence of the variables is confirmed, the measured effective lengths are found to be much less than predicted from heuristic formulae, which assume either the quadrupole field is defined by the physical length of the stigmator, or worse, by a longer length due to a fringe‐field effect. This fringe‐field assumption becomes progressively worse as the aspect ratio decreases or when the stigmator is placed near ferrous material. The use of a two‐stigmator column design to reduce blanker‐induced beam motion is also discussed. The stigmator located in the final lens is used to form an anastigmatic column section between the conjugate blanker and substrate. The upper stigmator independently stigmates the beam at the target.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Fr Electron and positron beams

Advanced e‐beam lithography

T. Takigawa, H. Wada, Y. Ogawa, R. Yoshikawa, I. Mori, and T. Abe

J. Vac. Sci. Technol. B 9, 2981 (1991); http://dx.doi.org/10.1116/1.585353 (5 pages)

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The acceleration voltage dependence of electron‐beam (EB) lithography was investigated. A low acceleration voltage is suitable for a mask (reticle) of several magnifications, because the proximity effect correction is not required. A reticle writing system EX‐8 with an acceleration voltage of 12.5 to 20 kV has been developed. A high acceleration voltage is preferable for the direct writing of fine patterns. A direct writing system EX‐7 with a typical acceleration voltage of 40 kV has been developed. A new shaped beam calibration method and a new astigmatism correction method have enabled the EX‐7 to write a pattern with 0.1 μm. High accuracy shaped beam calibration and alignment as required by small patterns were realized for a high acceleration voltage.
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85.40.Hp Lithography, masks and pattern transfer

Quantum lithography

Nadim I. Maluf and R. Fabian W. Pease

J. Vac. Sci. Technol. B 9, 2986 (1991); http://dx.doi.org/10.1116/1.585354 (6 pages) | Cited 3 times

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The edge definition and the interior filling of pattern features are commonly performed using the same exposing beam regardless of the feature size. Separating the two processes, as first proposed by Fulton et al. [Appl. Phys. Lett. 42, 752 (1983)], improves the efficiency of the mask making process and adds ‘‘smartness’’ to the substrate, i.e., the pattern generating tool need only provide the minimum information; the substrate and process are configured to convert the minimum information into the necessary pattern. We describe an improved level of smartness on substrates: we view the mask as a bitmapped lattice of independent pixel elements (pels), each having a given shape and carrying the relevant edge information; the desired pattern would be generated by selectively addressing a subset of the lattice and modifying the optical properties of its pels. The feature edges are effectively ‘‘quantized’’ in the sense that they can exist only in some specific places. In the edge definition step, a very fine grid whose edges are within the specifications on edge positional accuracy and precision, is inscribed on the mask blank by its manufacturer using a high resolution and high precision lithographic technique. The pitch is such that the size of the resulting tiles equals the minimum feature size of the pattern to be delineated. The limitation on the grid width is that it is not imaged by the optics upon the exposure of the mask. Once the grid is defined, the pattern can be customized by the user simply by tagging those tiles that constitute the pattern. We describe here the general principles, advantages, fabrication, and exposure of ‘‘quantum lithography’’ masks.
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85.40.Hp Lithography, masks and pattern transfer

A new approach to high fidelity e‐beam and ion‐beam lithography based on an in situ global‐fiducial grid

Henry I. Smith, Scott D. Hector, M. L. Schattenburg, and Erik H. Anderson

J. Vac. Sci. Technol. B 9, 2992 (1991); http://dx.doi.org/10.1116/1.585355 (4 pages) | Cited 19 times

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The distortion‐free scan field of an electron‐beam or ion‐beam lithography system is generally quite small (∼104×104 beam addresses) and hence to achieve pattern fidelity over large areas laser‐interferometer‐controlled stages are employed. Because the laser interferometer monitors the stage, not the electron or ion beam, beam drift of thermal, mechanical, electrostatic, magnetic, or electronic origin is not accounted for, leading to pattern placement error. To overcome this fundamental problem of ‘‘dead reckoning’’ we propose a new approach in which a global‐fiducial reference grid, which does not disturb the writing process, is put directly on the substrate. The grid is scanned with sufficiently low areal dose that the subsequent pattern development is not adversely affected. This can be achieved by ‘‘sparse sampling’’ of the grid over the entire scan field in conjunction with phase‐locking technqiues in the time domain. In this way one can spatially phase lock the two grids together and thereby ensure pattern placement accuracy. The pattern of interest is then written within the scan field. This method assumes that no drift occurs during the writing of the single field. However, it may also be feasible to do some drift monitoring during the field writing. We consider secondary electrons to be the optimal signal for ‘‘seeing’’ the grid. In addition to providing enhanced pattern integrity (and hence better overlay in 1‐to‐1 masks), lithography systems based on an in situ global‐fiducial grid may prove to be of lower cost than conventional systems since the difficult task of ensuring pattern integrity is thrust upon a computer rather than an advanced electromechanical system.
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85.40.Hp Lithography, masks and pattern transfer

Projection electron‐beam lithography: A new approach

S. D. Berger, J. M. Gibson, R. M. Camarda, R. C. Farrow, H. A. Huggins, J. S. Kraus, and J. A. Liddle

J. Vac. Sci. Technol. B 9, 2996 (1991); http://dx.doi.org/10.1116/1.585356 (4 pages) | Cited 18 times

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Projection electron‐beam lithography is potentially one of the most attractive techniques available. It offers high resolution, high throughput, and good overlay and registration characteristics. In this paper we discuss some new approaches which seem to offer solutions to problems associated with earlier systems.
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85.40.Hp Lithography, masks and pattern transfer

Mask fabrication for projection electron‐beam lithography incorporating the SCALPEL technique

J. A. Liddle, H. A. Huggins, S. D. Berger, J. M. Gibson, G. Weber, R. Kola, and C. W. Jurgensen

J. Vac. Sci. Technol. B 9, 3000 (1991); http://dx.doi.org/10.1116/1.585357 (5 pages) | Cited 17 times

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The choice of mask materials and fabrication route for a projection electron‐beam lithography system is subject to a variety of constraints. Some are encountered in most lithographic techniques, while some are unique to the scattering with regular limitation for projection electron lithography SCALPEL technique. We have developed methods for analyzing the performance of potential mask materials and constructions. These have been used to determine the composition of a prototype mask. Results from such a mask are presented.
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85.40.Hp Lithography, masks and pattern transfer

An electron‐beam inspection system for x‐ray mask production

P. Sandland, W. D. Meisburger, D. J. Clark, R. R. Simmons, D. E. A. Smith, L. H. Veneklasen, B. G. Becker, A. D. Brodie, C. H. Chadwick, Z. W. Chen, L. S. Chuu, D. G. Emge, A. A. Desai, H. J. Dohse, A. Dutta, et al.

J. Vac. Sci. Technol. B 9, 3005 (1991); http://dx.doi.org/10.1116/1.585358 (5 pages) | Cited 2 times

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SEMSpec is a scanning electron‐beam inspection system designed for high‐resolution die‐to‐die inspections of conductive x‐ray masks, wafer prints, or stencil masks in a production environment. The inspection sensitivity can be varied from 97% detection of 50‐nm defects, at a rate of 27 min cm−2, to 97% detection of 250‐nm defects at 1 min cm−2. A thermal‐field‐emission source produces a Gaussian profile electron beam that is moved by electrostatic deflectors over the continuously moving substrate that is being inspected. Secondary electrons from the substrate are collected in a high‐speed detector and the resulting digitized image data is stored in a specialized memory system. Pairs of images to be compared are continuously transferred from the memory to a high‐speed defect processor for analysis. Defect reports from the defect processor are analyzed during inspection and stored for subsequent review. We describe the overall system including the electron‐beam column with its six‐emitter field‐emission gun, the deflection system, the secondary‐electron detector, the linear‐motor drive stage, the control system, the robotic mask handler, and the image‐data flow from the high‐speed image acquisition subsystem through the analysis system. The electron‐beam column is described in detail in a companion paper [W. D. Meisburger, A. A. Desai, and A. D. Brodie, J. Vac. Sci. Technol. B 9, xxxx (1991)]. All functions of the highly automated system—including vacuum control, mask loading, electron‐beam column setup, and inspection— can be operated from the system control computer.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Requirements and performance of an electron‐beam column designed for x‐ray mask inspection

W. D. Meisburger, A. A. Desai, and A. D. Brodie

J. Vac. Sci. Technol. B 9, 3010 (1991); http://dx.doi.org/10.1116/1.585359 (5 pages) | Cited 3 times

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Production viable inspection of x‐ray masks requires the resolution of a scanning electron microscope (SEM) at an imaging rate approximately 1000 times that of commercially available systems. This article analyzes the inspection task for x‐ray masks and compares the requirements for beam‐current density and imaging efficiency necessary to achieve reasonable throughput with technologies available on current SEM and electron‐beam lithography systems. The resulting specifications have been translated into an electron‐optical column with many novel features. The gun, which contains six thermal field‐emission sources mounted on a turret, produces a Gaussian profile beam that is scanned over a continuously moving substrate. Dual electrostatic icosapole deflectors provide high speed telecentric deflection. Secondary electrons are separated from the primary beam by a Wien filter and accelerated into a semiconductor electron detector. An analog optical‐fiber link is used to transmit the signal to the image computer for defect detection. Results are presented for the performance of the electron‐optical column and imaging system and for the overall defect detection performance of SEMSpec, a dedicated production x‐ray mask inspection system.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

Performance of the EL‐3+ maskmaker

John Hartley, Timothy Groves, and Hans Pfeiffer

J. Vac. Sci. Technol. B 9, 3015 (1991); http://dx.doi.org/10.1116/1.585360 (4 pages) | Cited 1 time

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IBM’s new e‐beam maskmaker, designated EL‐3+, is installed and operating in the IBM Advanced Mask Facility in Burlington, Vermont. This tool represents a significant extension in the state of the art in the manufacture of masks, particularly in the areas of minimum feature size and overlay. The tool routinely operates with 0.35 μm ground rules at 70 nm (3σ) registration to grid. The tool has demonstrated the ability to work at 0.25 μm ground rules as well. The primary mission of the tool is the production of 1X x‐ray masks. Some of the tool parameters include a 50 keV electron beam operating at a current density of 20 A/cm2. The system uses a shaped spot with a maximum size of 2×2 μm2. Exposures are made over areas with dimensions of up to 80 by 80 mm with a 2.1 mm field size. Deflection within a field is done through a combination of magnetic and electric deflection in a variable axis immersion lens (VAIL) configuration. During exposure the pattern data is stored on‐line in a 1 G‐byte buffer. The pattern buffers are loaded directly from a host IBM 4381. The system automatically corrects for any field distortions to a level of 6.25 nm using a calibrated reference grid.
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85.40.Hp Lithography, masks and pattern transfer

A servo guided X–Y–theta stage for electron beam lithography

Rodney Kendall, Sam Doran, and Erwin Weissmann

J. Vac. Sci. Technol. B 9, 3019 (1991); http://dx.doi.org/10.1116/1.585361 (5 pages) | Cited 4 times

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This paper describes a high precision X–Y–theta stage for use inside the variable axis immersion lens of IBM’s EL3+ direct write e‐beam lithography systems. X–Y stages typically use some form of rail and bearing combination to provide guidance along the X and Y axes. The planar stage presented in this paper has no X or Y guide rails or bearings, instead both guidance and positioning are provided by the simultaneous operation of three mechanical drives controlled by closed‐loop velocity, position, and theta servos. The control requirements, architecture, and performance of the servo electronics is discussed. The design and materials constraints imposed by having to operate inside a magnetic lens are discussed and stage performance data is presented. Servo guided stages eliminate the need for precise alignment of guide rails and bearings, while the kinematic nature of the design results in low sensitivity to temperature variations and reduces the need for extreme mechanical tolerances.
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85.40.Hp Lithography, masks and pattern transfer
07.07.Tw Servo and control equipment; robots

Scanning tunneling microscope lithography: A solution to electron scattering

E. A. Dobisz and C. R. K. Marrian

J. Vac. Sci. Technol. B 9, 3024 (1991); http://dx.doi.org/10.1116/1.585362 (4 pages) | Cited 7 times

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The scanning tunneling microscope (STM) operated in the field emission mode is shown to have important lithographic applications. The technological potential of the technique is demonstrated by patterning films up to 80 nm thick of SAL‐601‐ER7, a negative resist from Shipley. With the STM, 22 nm lines of developed resist have been written on Si and 35 nm lines on GaAs. For comparison, exposures were made with a 50 kV, 17 nm 1/e diameter electron beam in identically prepared and processed resist films on a variety of substrates. The 50 kV probe produced minimum linewidths of: 60 nm on a 200 nm Si3N4 membrane; 70 nm on a 200 nm Si3N4 film on a bulk Si substrate; 95 nm on a bulk Si substrate; and 186 nm on a bulk GaAs substrate. The strong substrate dependence indicates that the resolution, at 50 kV, is determined by electron scattering rather than the post exposure processing of the resist. Low voltage lithography with an STM offers a technique which greatly reduces the effects of electron scattering with a consequent improvement in resolution. In addition, the results of the Si3N4 film suggest a novel way to reduce the effects of backscattered electrons in 50 kV lithography.
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85.40.Hp Lithography, masks and pattern transfer
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Reliability enhancements for the direct wafer exposure electron beam system EB60

Takashi Watanabe, Tetsuo Morosawa, Nobuo Shimazu, Hirofumi Morita, Hironori Yamauchi, and Atsushi Iwata

J. Vac. Sci. Technol. B 9, 3028 (1991); http://dx.doi.org/10.1116/1.585363 (5 pages)

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Based on the exposure architecture of ‘‘EB60,’’ intensive effort has been made to achieve an integrated system that is both reliable and easy to adjust. First, the central processing unit (CPU) and network structure have been modified to exploit an open system environment and to tighten communication between the e‐beam and computer aided design (CAD) systems. Exposure data are transferred over a high‐speed optical cable directly from the remotely located CAD resident host CPU. Five custom larger scale integrated circuits (LSIs) have been designed and implemented. A complimentary metal–oxide semiconductor LSI (22 Kgates) that performs general linear matrix functions in 60 ns has been applied to minor‐field‐deflector, shaping‐deflector, shot‐time, stage movement, and overlay coordinate corrections. A shot control super self‐aligned transistor (SST) LSI (2.5 Kgates), which covers all functions operating at 400 MHz, has eliminated the tedious adjustment of emitter coupled logic (ECL) circuits. Taken together, these LSIs have substantially reduced the space occupied by on‐board logic circuits. A digital calculation method has been introduced in major‐field‐deflector amplifiers. All these improvements have markedly enhanced the reliability and maintainability of EB60, while at the same time making the system more user‐friendly and comprehensive.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Preliminary analysis of electron‐beam positioning errors in Lepton EBES4

H. A. Waggener, D. W. Peters, G. Chen, C. M. Rose, D. C. Fowlis, A. Chitayat, and J. Caracci

J. Vac. Sci. Technol. B 9, 3033 (1991); http://dx.doi.org/10.1116/1.585364 (6 pages)

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A study was undertaken to quantify and minimize mechanically induced sources of electron‐beam positioning errors in Lepton EBES4. Stage performance was improved by replacing the x axis rotary motor and ball‐screw drive with a brushless, sinewave, proprietary linear motor drive. Vibrational and modal analyses indicated that the system’s present structural resonances have a negligible contribution to e‐beam positioning errors. Thermal drift of the interferometer is the major contributor to pattern placement errors. Results from a vibrational analysis performed during stage scanning indicated that the crossed roller bearing stage has low compliance with a maximum yaw value of ±0.05 μrad. MARKET analyses of arrays covering 100 mm×100 mm indicated a maximum x or y residual error of ≤50 nm with a ‖mean‖+3σ of ≤50 nm. This level of image placement accuracy is consistent with that required for an advanced e‐beam tool for reticle writing, submicron direct write applications, writing optical phase shift masks, and writing submicron 1× x‐ray masks. A ZerodurTM metrology platform is being implemented on the second EBES4 system. Use of Zerodur will further improve image placement accuracy by reducing the impact of temperature fluctuations.
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85.40.Hp Lithography, masks and pattern transfer

Charging effects on trilevel resist and metal layer in electron‐beam lithography

Hiroyuki Itoh, Kazumitsu Nakamura, and Hajime Hayakawa

J. Vac. Sci. Technol. B 9, 3039 (1991); http://dx.doi.org/10.1116/1.585365 (4 pages) | Cited 2 times

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Charging effects of trilevel resist on a W layer have been investigated with an electron beam lithography system. The tungsten layer was deposited before the resist and the charge‐induced beam deflections were measured for several thick W layers. A test pattern was employed consisting of an array 21×21 cross marks in a 3 mm field. The charging effects show different dependencies on W thickness between 20 and 30 keV because of the W backscattering. To evaluate the correlation between the charging and the backscattering process in W and trilevel resist, reflected electron signals were detected from the developed resist marks. The resist mark signal has a double sloped inverse peak characteristic due to backscattering from the W layer and absorption by the resist mark. As a result, the charge‐induced beam deflections and the intensity of backscattered electrons are increased in proportion to W thickness. The authors will discuss the electron distribution caused by the electron beam and sample material interacting using these experimental approaches and numerical simulations of electron beam scattering.
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85.40.Hp Lithography, masks and pattern transfer

Proximity correction using computer aided proximity correction (CAPROX): Evaluation and application

M. Hintermaier, U. Hofmann, B. Hübner, C. K. Kalus, E. Knapek, H. W. P. Koops, R. Schlager, E. Seebald, and M. Weber

J. Vac. Sci. Technol. B 9, 3043 (1991); http://dx.doi.org/10.1116/1.585366 (5 pages) | Cited 4 times

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Direct write electron beam lithography requires proximity effect correction to achieve high fidelity. CAPROX (computer aided proximity correction) serves this purpose. It preserves hierarchy as far as possible, thus reducing memory and CPU time. The program guides the evaluation of the correction parameters. The need for and the result of correction is judged evaluating exposures written at a reduced dose in optical white light interference contrast microscopy. If the color observed in large and small structures is equal, no poximity effect correction is necessary. We applied CAPROX to correct structures written in positive and negative resists using the Philips EBPG‐4 and the JEOL JBX‐5D11 beam writer. The proximity effect correction is indispensable for the fabrication of an ACMOS‐ASIC with 1 μm minimum features written in 1.8 μm thick negative resist.
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85.40.Hp Lithography, masks and pattern transfer

Proximity effect correction in electron‐beam lithography: A hierarchical rule‐based scheme—PYRAMID

Soo‐Young Lee, Joseph C. Jacob, Chung‐Ming Chen, Jo A. McMillan, and Noel C. MacDonald

J. Vac. Sci. Technol. B 9, 3048 (1991); http://dx.doi.org/10.1116/1.585367 (6 pages) | Cited 3 times

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PYRAMID, a hierarchical, rule‐based scheme for proximity effect correction in electron‐beam lithography is proposed. The current implementation performs solely pattern modification, and uses a single dose for the entire circuit. Based on a digital image processing model of the physical lithographic process, a hierarchical correction procedure is employed in two parts, local correction and global correction. The local correction, fully implemented, is concerned with interactions between circuit components within a small window. The local correction itself is very systematic, using two levels of correction to minimize proximity effect caused by intrashape and intershape interactions, respectively. Rule tables are used to dictate correction modes for different situations. These tables, constructed a priori, are utilized to accelerate the correction process by minimizing the numerical calculation required during circuit correction. While the local correction ignores interactions between widely separated circuit elements, the global correction takes general characteristics of the entire circuit pattern into account to make adjustments to the local correction modes. This combination of local and global corrections permits the correction of arbitrarily sized circuit patterns in a small fraction of the time required by many previous approaches that are more computationally intensive. In addition, PYRAMID produces output circuit patterns that are decomposable into rectangles, allowing efficient representation of the circuit patterns, and maintaining compatibility with shaped electron‐beam architectures. Furthermore, the hierarchical approach that has been employed permits us to develop and evaluate fast proximity correction schemes for new electron‐beam architectures such as parallel beam lithography systems. Such system architectures may place severe constraints on the allowable dosage variation, e.g., constant dose, during exposure. Test patterns with a minimum feature size of 0.1 μm are presented along with corresponding correction times.
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85.40.Hp Lithography, masks and pattern transfer

Adaptive neural network algorithms for computing proximity effect corrections

Robert C. Frye

J. Vac. Sci. Technol. B 9, 3054 (1991); http://dx.doi.org/10.1116/1.585368 (5 pages) | Cited 2 times

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Computing self‐consistent local dose corrections for images to offset proximity effects poses significant problems because the number of computations needed cannot be done in a reasonable amount of time. Recently, we have demonstrated the use of an adaptive neural network method to increase the speed of these computations by several orders of magnitude. We have now implemented these corrections in practical hardware, and have introduced improvements in the algorithm that further reduce the computational complexity and time. The challenges in computing proximity effect corrections are to find algorithms that work well for general feature shapes, and that can be efficiently implemented. This paper will discuss the iterative computation of optimal corrections for electron scattering, and the limits of image resolution that can be obtained. It will describe the neural network algorithm used to obtain equivalent results more efficiently, and the method of adaptively determining the network’s parameters. Finally, it will discuss several recent modifications that significantly improve the network’s performance.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
84.30.Bv Circuit theory

The representative figure method for the proximity effect correction [III]

Takayuki Abe, Satoshi Yamasaki, Ryoichi Yoshikawa, and Tadahiro Takigawa

J. Vac. Sci. Technol. B 9, 3059 (1991); http://dx.doi.org/10.1116/1.585369 (4 pages) | Cited 6 times

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The representative figure method for the proximity effect correction was proposed in the previous papers in order to eliminate the correction time dependence on the large‐scale integrated (LSI) pattern density. In this report, a new calculation method for the proximity effect correction is proposed. The method uses both the representative figure method and the dose formula method. When the formula of Pavkovich is adopted as a dose formula, the total correction error for the proposed method is at most 4%. The intrinsic error of the representative figure method itself is at most 0.5%. The proposed method reduces the total calculation time to (1/28) compared with the conventional method, when the minimum feature size is 0.15 μm and the acceleration voltage is 50 kV. Here, the total calculation time includes (1) preparation time for representative rectangles and (2) shorter calculation time for the correction. Furthermore, the total time is found to become less than the data format conversion time, when the minimum feature size is <0.5 μm. The calculation time for the correction is found to be <1 h for any pattern density, when the newly proposed method and the 50 MIPS engineering workstation (EWS) are used. The problem of the proximity effect correction is reduced to an easier problem; i.e., how to reduce the calculation time for obtaining the areas and the center of gravity of the LSI patterns.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Optimizing electron beam lithography writing strategy subject to electron optical, pattern, and resist constraints

Lee H. Veneklasen

J. Vac. Sci. Technol. B 9, 3063 (1991); http://dx.doi.org/10.1116/1.585370 (7 pages) | Cited 4 times

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A new model for the exposure rate of electron beam lithography is developed, accounting for electron optical, electronic, resist, and pattern statistics/quality constraints. Resist heating and beam interaction effects, as well as current density, flash size and edge resolution are included as measurable parameters that couple in rather complicated ways to determine performance for a specific task. Gaussian beam raster scan, small fixed shaped beam, and variable shaped beam vector scan machine strategies are compared using hypothetical but realistic assumptions. Address grid, minimum feature dimension, and the maximum flash area influence coverage in different ways, and pattern fracture techniques profoundly influence coverage, particularly in variable shaped beam systems. Remarkably small shapes, high current density, and high flash rates are usually favored. A constant flash area fracture is desirable because it maximizes the average beam current. The controlling resist parameter is sensitivity divided by the maximum beam current useable to achieve a given level of pattern quality. This parameter is frequently limited by heating effects. Examples of lithography guided by this model are given.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Theoretical model for scanning electron microscopy through thin film windows

E. D. Green and G. S. Kino

J. Vac. Sci. Technol. B 9, 3070 (1991); http://dx.doi.org/10.1116/1.585371 (4 pages)

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We have developed a model for electron beam scattering in a thin film window atmospheric scanning electron microscope (SEM). The model is accurate for plural scattering, which covers film thicknesses up to 100 μm and window to sample spacings to 20 μm, for energies above 20 keV. We demonstrate experimental verification of our model for energies from 20 to 50 keV and film thicknesses from 30 to 100 nm.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.75.Fr Electron and positron beams

Nanostructures processing by focused ion beam implantation

P. M. Petroff, Y. J. Li, Z. Xu, W. Beinstingl, S. Sasa, and K. Ensslin

J. Vac. Sci. Technol. B 9, 3074 (1991); http://dx.doi.org/10.1116/1.585372 (5 pages) | Cited 7 times

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We present several novel methods that use a focused ion beam (FIB) processing of quantum well structures for lateral band gap engineering and doping on a nanoscale. Antidots and electron dots have been made by FIB and some of their transport properties are presented. In situ FIB processing of buried stressor structures and localized band bending are also demonstrated as a means of achieving lateral carrier confinement.
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85.40.Hp Lithography, masks and pattern transfer
61.72.U- Doping and impurity implantation
61.80.Jh Ion radiation effects
73.20.At Surface states, band structure, electron density of states

A low magnification focused ion beam system with 8 nm spot size

R. L. Kubena, J. W. Ward, F. P. Stratton, R. J. Joyce, and G. M. Atkinson

J. Vac. Sci. Technol. B 9, 3079 (1991); http://dx.doi.org/10.1116/1.585373 (5 pages) | Cited 19 times

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A 50 keV Ga+ beam has been focused to a spot diameter of 8 nm (full width at half‐maximum) in our two‐lens microprobe system by reducing the contributions of both chromatic aberration and the virtual ion source size to the final image size. Features as small as 6 to 8 nm were distinctly visible in scanning ion images. To our knowledge, this is the smallest focused beam of ions produced to date. The limiting resolution in 30‐nm thick films of poly(methylmethacrylate) exposed with this beam was approximately 8 to 10 nm. Effects such as ion scattering, atomic recoil, and statistical dose fluctuations during exposure are believed to set inherent limits to the lithographic resolution.
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85.40.Hp Lithography, masks and pattern transfer
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
68.37.Vj Field emission and field-ion microscopy

Filamentless neutralization of broad ion beams

D. Korzec, T. Kessler, H. M. Keller, and J. Engemann

J. Vac. Sci. Technol. B 9, 3084 (1991); http://dx.doi.org/10.1116/1.585316 (6 pages) | Cited 2 times

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A new, effective technique of broad ion beam neutralization, based on alternating ion and electron extraction via the same optic is presented and discussed. The screen and accelerator grids of a two‐grid extraction system are biased with bipolar and unipolar pulses of varying amplitude and frequency, respectively. Pulse frequencies of 500 Hz–20 kHz have been tested. In each period ions are extracted with screen pulse amplitudes of 200–800 V and accelerator voltages kept at 10%–20% of the respective screen grid potential. Similarly, electrons are extracted with screen pulse amplitudes of −50–−200 V and a grounded or slightly negatively biased accelerator grid. An electrically nonconductive target bombarded subsequently by ions and electrons will charge and discharge periodically, possibly resulting in a zero target bias. The neutralization effect has been studied in two ways: (i) measurement of a metallic target bias being electrically insulated from ground by a 220 nF capacitor; (ii) etching experiments of 1.2 μm thick polyimide layers (HPR 204) deposited on a Si3N4/Si substrate. A high positive target bias resulting from insufficient beam neutralization correlates with low etch rate and poor quality of the etched substrate surface. A negative target bias (overneutralization) increases the energy of impinging positively charged ions resulting in increased etch rates. Although unwanted in general this effect may be used intentionally in some cases. Zero target bias in all cases assures good surface quality and high etch rates. The neutralization principle presented is of prime importance in reactive ion beam processes when filamentless ion sources are used. This holds especially when interactions of chemically reactive ions with electrically insulating surfaces are considered.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
81.65.-b Surface treatments

An ion counting apparatus for studying the statistics of ion emission from liquid metal ion sources

J. W. Ward, R. L. Kubena, and R. J. Joyce

J. Vac. Sci. Technol. B 9, 3090 (1991); http://dx.doi.org/10.1116/1.585317 (5 pages)

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We have constructed a new ion counting apparatus for measuring the noise properties of liquid metal ion sources operating at low extraction currents. With this apparatus we have measured the noise properties of a gallium liquid metal ion source operating at source currents of 2, 5, and 10 μA. We have found that the spectral density of the current fluctuations corresponds to ‘‘white noise,’’ which is flat from dc out to our maximum measured frequency of 400 kHz. We also find that the variance of the current fluctuations is approximately 50% to 100% greater than would be expected for pure shot noise. These results imply that the ions do not arrive at the target at totally random times, but are partially correlated, and therefore exhibit properties of a slightly bunched beam.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
29.40.-n Radiation detectors

Control of diamond film microstructure by use of seeded focused ion beam crater arrays

A. R. Kirkpatrick and B. W. Ward

J. Vac. Sci. Technol. B 9, 3095 (1991); http://dx.doi.org/10.1116/1.585318 (4 pages) | Cited 1 time

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The nucleation densities associated with diamond growth on some nondiamond substrates are so low that it is possible to employ high resolution methods to define every site at which growth will initiate. A technique has been demonstrated on silicon substrates in which diamond growth is initiated on minute diamond seed particles introduced into patterned arrays of microscopic craters formed by focused ion beam milling. Diamond test films with controlled microstructural properties have been fabricated.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

In situ patterning of GaAs by focused ion beam

T. Kosugi, T. Yamashiro, R. Aihara, K. Gamo, and S. Namba

J. Vac. Sci. Technol. B 9, 3099 (1991); http://dx.doi.org/10.1116/1.585319 (4 pages) | Cited 1 time

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We have investigated the characteristics of ion beam induced spontaneous etching (IBISE) of GaAs by 15 keV Ga focused ion beam (FIB) irradiation and Cl2 gas. The area irradiated by the FIB showed high spontaneous etch rate to the exposure to Cl2 ambient. It was observed that the spontaneous etching depends on the residual H2O partial pressure. At H2O partial pressure less than 6×10−7 Torr, the threshold dose to observe IBISE was about 1015 ions/cm2 at a substrate temperature of 100 °C. However, at H2O partial pressure of 3×10−6 Torr, the threshold dose decreased below 1014 ions/cm2 at a substrate temperature of 90 °C. The small amount of H2O in Cl2 gas effectively decreases the threshold dose resulting in a reduction of radiation damage of the substrate and increasing the processing rate.
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81.65.-b Surface treatments

Near‐field scanning optical microscopy II

M. Isaacson, J. A. Cline, and H. Barshatzky

J. Vac. Sci. Technol. B 9, 3103 (1991); http://dx.doi.org/10.1116/1.585320 (5 pages) | Cited 12 times

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A brief survey of the principles of near‐field optical imaging will be presented. Selected examples of super resolution imaging using visible reflected light will demonstrate that lateral resolution far smaller than the illumination wavelength can be achieved and that the technique is surface sensitive. In addition, we will demonstrate that subwavelength resolution can be achieved in the near‐infrared spectral regime and that near‐field scanning optical microscopy (NSOM) can be used in diagnostic inspection of hetrojunction laser modal emission patterns.
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07.60.Pb Conventional optical microscopes
42.30.-d Imaging and optical processing

Markle–Dyson optics for 0.25 μm lithography and beyond

A. Grenville, R. L. Hsieh, R. von Bünau, Y‐H. Lee, D. A. Markle, G. Owen, and R. F. W. Pease

J. Vac. Sci. Technol. B 9, 3108 (1991); http://dx.doi.org/10.1116/1.585321 (5 pages) | Cited 3 times

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Using a modified Dyson design working at 0.7 NA with 248 nm illumination, reflective 1X masks, and conventional single‐layer resists, 0.25 μm lithographic resolution has been obtained over a semicircular field 4 mm in diameter. 0.19 μm lines and spaces have been printed using an experimental bilayer resist. To offset the small depth of focus, two precision autofocus schemes have been demonstrated and FLEX has been shown by computer simulation to triple the depth of focus for isolated features. A full size system has been designed with a 20×40 mm2 field sufficiently large for patterning 256 Mbit DRAM chips. This concept can be extended to shorter wavelengths limited only by availability of one refractive material and a suitable light source. Thus optical projection lithography appears feasible for features at least as small as 0.15 μm.
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85.40.Hp Lithography, masks and pattern transfer

Spatial filtering for depth of focus and resolution enhancement in optical lithography

Hiroshi Fukuda, Tsuneo Terasawa, and Shinji Okazaki

J. Vac. Sci. Technol. B 9, 3113 (1991); http://dx.doi.org/10.1116/1.585322 (4 pages) | Cited 14 times

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Spatial filtering at the lens pupil can achieve amplitude superposition for multiple images along the light axis and phase control between them. This enhances depth of focus while maintaining high resolution capability in optical lithography. Compared to conventional methods, three times larger depth of focus is expected for hole patterns with 20% improved resolution limit. For general pattern features, a 1.5–1.7 times larger depth of focus is expected at Rayleigh’s resolution limit.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Fabricating binary optics: Process variables critical to optical efficiency

M. B. Stern, M. Holz, S. S. Medeiros, and R. E. Knowlden

J. Vac. Sci. Technol. B 9, 3117 (1991); http://dx.doi.org/10.1116/1.585323 (5 pages) | Cited 6 times

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While conventional photolithographic and reactive ion etching techniques are employed in the manufacture of binary optical elements, the nested character of these diffractive surface relief structures, coupled with submicron linewidths and additive etch depths, puts stringent demands on process tolerances. To quantitatively assess the effects of process variables, we have utilized a mask set that incorporates ten different lenslet designs as single elements and as 10×10 arrays. All lenslets are 200 μm×200 μm with focal lengths ranging from 170 μm to 14 mm at 632.8 nm wavelength. Overlay registration accuracy is evaluated by optical microscopy of vernier‐style alignment marks, etch depths are determined by stylus profilometry, and linewidths are measured by optical and scanning electron microscopy. The optical efficiency is evaluated as a function of the focal length and compared to theoretical predictions. The eight‐phase‐level @FF/4 microlenses, measured at 96% of the expected value, exhibit the highest optical efficiency reported to date for such a lens in the visible.
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42.15.Eq Optical system design
42.79.Bh Lenses, prisms and mirrors
42.87.-d Optical testing techniques
42.82.-m Integrated optics

Recent advances in an excimer laser source for microlithography

D. J. Elliott, C. P. Pennelli, and U. K. Sengupta

J. Vac. Sci. Technol. B 9, 3122 (1991); http://dx.doi.org/10.1116/1.585324 (4 pages)

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This paper describes the advances made in a KrF excimer laser source designed specifically for the deep‐UV reduction stepper. Data is presented on key performance aspects that are required for the laser to be used in the next generation of excimer steppers. Major topics discussed will be spectral bandwidth reduction, center wavelength control, pulse‐to‐pulse energy stability, higher power performance, and the production worthiness of the system. The first generation excimer laser (CX‐2LS) for lithography operated at 200 Hz and 3 W, with a spectral bandwidth of 3 pm and a wavelength stability of ±0.5 pm. The new laser (ELS‐4000) is designed and engineered to perform at 400 Hz and 4 W with a narrower spectral bandwidth (2 pm) and a wavelength stability of better than ±0.25 pm. In addition, the pulse‐to‐pulse stability has been improved in stepper‐mode operation. The ELS‐4000 also employs a new microprocessor controlled gas injection system that permits uninterrupted operation for 10–20 h (7–10 million pulses). This level of performance assures the compatibility of the laser with the requirements of production excimer steppers being developed with higher numerical aperature lenses, larger fields, and higher wafer throughputs.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
85.40.Hp Lithography, masks and pattern transfer

Reducing coherence in a fifth‐harmonic YAG source (213 nm) for use in microlithography

William N. Partlo and William G. Oldham

J. Vac. Sci. Technol. B 9, 3126 (1991); http://dx.doi.org/10.1116/1.585325 (6 pages)

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The fifth harmonic of the YAG laser represents a possible alternative to the line‐narrowed KrF excimer laser for use in deep ultraviolet microlithography. Producing useful amounts of radiation at 213 nm, the fifth‐harmonic YAG has a spectral linewidth well within the needs of today’s nearly monochromatic microlithography lenses. This extremely narrow spectral width, combined with nearly single transverse‐mode operation, leads to challenging levels of coherence and speckle. Initial measurements of far‐field speckle patterns produced by illuminating a diffuser confirm that the speckle contrast is nearly 100%. Rotating the diffuser so that each pulse produced a different speckle pattern would require nearly 10 000 pulses to form an integrated average with 1% rms noise. We have investigated a relatively simple scheme for reducing the speckle contrast produced by a single pulse. This scheme consists of two counter rotating diffusers placed close to each other. It will be shown that for modest rotation speeds (15 K rpm for 100‐mm‐diam plates) a significant reduction in the single‐shot speckle contrast can be achieved. A relation is derived between the noise reduction capabilities of a diffuser and its scattering properties. This relation can be used to predict the maximum speckle reduction possible for a given illumination system numerical aperture.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
42.55.Mv Dye lasers

Dry etched molybdenum silicide photomasks for submicron integrated circuit fabrication

C. Pierrat, R. G. Tarascon, M. L. Peabody, L. R. Harriott, and S. Vaidya

J. Vac. Sci. Technol. B 9, 3132 (1991); http://dx.doi.org/10.1116/1.585326 (6 pages) | Cited 3 times

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The aim of this paper is to demonstrate a manufacturable molybdenum silicide mask process. Each step of the fabrication of a mask was addressed: lithography, dry etching, cleaning, inspection, and repair. SAL601 resist (Shipley) was chosen for the etch mask as dry etch resistance and almost vertical resist profiles are required [J. W. Thackeray, G. W. Orsula, E. Pavelcheck, D. Canistro, L. E. Bogan, A. K. Berry, and K. A. Graziano, Proc. SPIE 1086 (1989)]. Etching experiments of the molybdenum silicide were performed using different fluorinated gas mixtures. Two of them, CF4+O2, SF6+O2, were chosen and optimized for selectivity (ratio of molybdenum silicide etch rate versus resist etch rate) using a statistical experimental design approach. Results indicate a higher selectivity for the CF4+O2 mixture but lower loading effects for SF6+O2 leading to a better uniformity in the latter case. In both cases, the pressure was chosen low enough (below 200 mTorr to get anisotropic etching conditions even if the selectivity is reduced. Inspection has been performed using standard optical equipment from KLA Instrument Corporation. None of the defects found were related to lithography and dry etching processes. Repair feasibility has been demonstrated with both laser beam and focused ion beam (FIB). Thanks to its fine grain structure, very smooth edges have been obtained, after FIB repair, for molybdenum silicide as compared to chrome.
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85.40.Hp Lithography, masks and pattern transfer

Silicon on quartz reflective masks for 0.25‐μm microlithography

Y. H. Lee, R. L. Hsieh, A. Grenville, R. von Bünau, C. C. Tsai, D. A. Markle, G. Owen, R. Browning, and R. F. W. Pease

J. Vac. Sci. Technol. B 9, 3138 (1991); http://dx.doi.org/10.1116/1.585327 (5 pages)

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One approach to 0.25‐μm lithography currently being explored is the unity‐magnification Markle‐Dyson projection system. This system, operating at λ=248 nm, incorporates a reflective mask in its design. This utilizes the internal reflection at the quartz/film interface. To best meet the requirements of high reflectivity and quarter micron processing, amorphous silicon on quartz masks were chosen. Completed masks were used to print 0.19‐μm lines and spaces on the prototype Markle–Dyson system, demonstrating the feasibility of silicon reflective masks for lithography.
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85.40.Hp Lithography, masks and pattern transfer

Modeling and characterization of a 0.5 μm deep ultraviolet process

Chris A. Mack, Elliott Capsuto, Satyendra Sethi, and Joyce Witowski

J. Vac. Sci. Technol. B 9, 3143 (1991); http://dx.doi.org/10.1116/1.585328 (7 pages)

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A half‐micron semiconductor manufacturing process using excimer laser lithography, single‐layer chemically amplified resist on antireflective coating (ARC), and dry etch processes with in situ ARC development is discussed. Process window characterization experiments, long‐term process stability/repeatability data, and initial defect test results are presented. Results show that the complexities added to the process by the incorporation of the ARC are outweighed by the improvement in linewidth control. Additionally, modeling of the lithography process is shown to accurately predict the process window and other lithographic effects.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of phase‐shifting masks with shifter overcoat

R. L. Kostelak, J. G. Garofalo, G. Smolinsky, and S. Vaidya

J. Vac. Sci. Technol. B 9, 3150 (1991); http://dx.doi.org/10.1116/1.585329 (5 pages)

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Phase‐shifting masks have demonstrated the potential to extend the application of existing optical lithography tools by simultaneously enhancing their resolution, depth of focus, and exposure latitude. This paper identifies a processing sequence for the fabrication of phase‐shifting masks using spin‐on‐glass (SOG) as a shifter overcoat. The SOG is applied uniformly, range of 11 nm, across conventional 5‐in. mask substrates. A selective wet etch for patterning the SOG is also demonstrated. Using this processing sequence, alternate aperture, phase‐shifting masks are fabricated, and both focus and exposure latitude are evaluated. Additionally, the role of shifter wall angle and level‐to‐level alignment on the sized rim shifter are explored. It was found that a 45° shifter wall angle resulted in ∼10% degradation in the aerial image of a 0.35‐μm feature as compared with a vertical wall angle, and an alignment error of 0.25 μm on the reticle resulted in pattern placement errors of 0.06 μm. In order to circumvent second level lithography constraints several self‐aligned schemes have been proposed. Two previously published techniques are reviewed and their implications on the shifter overcoat mask are discussed. Finally, having identified several of the limitations related to the overcoat process, issues related to the fabrication of phase‐shifting masks with the shifter material beneath the chromium are defined.
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85.40.Hp Lithography, masks and pattern transfer

Fabrication of grooved glass substrates by phase mask lithography

Phillip J. Brock, Marc D. Levenson, James M. Zavislan, James R. Lyerla, John C. Cheng, and Carl V. Podlogar

J. Vac. Sci. Technol. B 9, 3155 (1991); http://dx.doi.org/10.1116/1.585308 (7 pages) | Cited 3 times

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A phase‐shifting mask without chrome opaque features can be used to print groove servo patterns for optical storage disks and provides improved contrast and resolution in printed photoresist images when used in a projection printer such as a Perkin‐Elmer MicralignTM‐500 mask aligner. Such a phase‐shifting photomask structure can be fabricated in the following way. Onto a conventional photoresist coated chrome on fused quartz photomask blank is written a pattern of concentric lines and spaces or a spiral pattern. The photoresist is developed and the exposed chrome etched in the conventional way to yield a transmission mask pattern of twice the pitch desired in the final groove pattern. The quartz is then etched, using the photoresist/chrome and/or chrome pattern as the resist, by either a wet or dry process, to a uniform depth. The chrome is then completely removed to form a ‘‘chromeless’’ phase‐shifting mask [K. K. H. Toh, G. Dao, R. Singh, H. Gaw, Proc. SPIE 1991 Symp. Microlithogr. 1463 (1991)] Phase‐shifting masks of this sort have been fabricated and used successfully to print photoresist images on glass disks yielding patterned photoresist structures of 1.5, 1.2, and 1.0 μm pitch. The resulting photoresist pattern could be transferred into the glass substrate by a wet etch process to generate the desired glass etch pattern after photoresist removal. Phase‐shifting masks of this design require careful dimensional control in three dimensions. One modification to the phase mask design described which simplifies the fabrication process is to alter the relative dimensions of the groove and land. If the land is made very small in relation to the groove, then the groove prints as though it were a clear feature in a transmission mask. Conversely, the land prints as though it were a chrome (‘‘dark’’) feature. The contrast obtained in the image is much larger than can be obtained from a conventional transmission mask of similar dimensions and the depth of focus was increased to >10 μm.
This ‘‘darker than dark’’ phase‐shifting mask phenomenon may prove valuable in the fabrication of complex patterns [K. K. H. Toh, G. Dao, R. Singh, and H. Gaw, SPIE 1991 Symp. Microlithogr. 1463 (1991) and K. Nakagawa, M. Taguchi, and T. Ema, Fabrication of 64M DRAM with i‐line Phase Shift Lithography, IEEE International Electron Devices Meeting, Dec. 9–12, 1990, San Francisco, California].
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85.40.Hp Lithography, masks and pattern transfer

Azide–novolak resin negative photoresist for i‐line phase‐shifting lithography

Shou‐ichi Uchino, Toshihiko Tanaka, Takumi Ueno, Takao Iwayanagi, and Nobuaki Hayashi

J. Vac. Sci. Technol. B 9, 3162 (1991); http://dx.doi.org/10.1116/1.585309 (4 pages) | Cited 2 times

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A negative photoresist consisting of 4,4′‐diazido‐3,3′‐dimethoxybiphenyl and a novolak resin, called micro resist for i‐line (MRI), has been prepared and evaluated for i‐line phase‐shifting lithography. MRI has a high transmittance (80%/μm) and a high resist contrast (γ) at i line (365 nm). Line‐and‐space patterns of 0.30 μm were achieved using MRI in conjunction with an i‐line phase‐shifting lithography. The insolubilization mechanism of MRI is attributed to a secondary amine formed by the reaction of nitrene with novolak resin.
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85.40.Hp Lithography, masks and pattern transfer

Phase‐shifting mask and top‐imaging resist for subhalf‐micron i‐line and deep‐ultraviolet lithography

S. Tedesco, B. Picard, M. Chevalier, and B. Dal’zotto

J. Vac. Sci. Technol. B 9, 3166 (1991); http://dx.doi.org/10.1116/1.585310 (6 pages) | Cited 1 time

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Combination of both phase‐shifting mask and single layer top‐imaging resist will allow i‐line and deep‐ultraviolet (UV) lithography to meet, respectively, 64 and 256 Mbit requirements and beyond. Using phase‐shifting mask in conjunction with DESIRE process, 0.25 μm lines and spaces have been resolved with an ASM‐L PAS 5000/50 i‐line stepper (365 nm, NA=0.48), on 1 μm thick PLASMASK 200G. With an ASM‐L PAS 5000/70 deep‐UV (248 nm, NA=0.42) 0.2 μm lines and spaces have been resolved on 0.35 μm thick PLASMASK 200 G using PRIME process. A simulation software package was developed allowing us to optimize phase shifting structures. Moreover, using existing computer aided design (CAD) tools we automatically generate ‘‘edge emphasis’’ structures on contact holes and on 0.3 μm gate level and subsequently expose this data base demonstrating the ability, using this simple technique, to process 64 Mbit DRAM with i‐line lithography.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Sub‐quarter‐micron gate pattern fabrication using a transparent phase shifting mask

Hisashi Watanabe, Hiroshi Takenaka, Yoshihiro Todokoro, and Morio Inoue

J. Vac. Sci. Technol. B 9, 3172 (1991); http://dx.doi.org/10.1116/1.585311 (4 pages) | Cited 2 times

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Phase shifting technologies with an i‐line stepper are applied for the application of defining sub‐quarter‐micron gate patterns for GaAs field‐effect transistor (FET) devices. Transparent‐type phase‐shifting masks which have no chromium layer for printing the patterns are used. Using the phase‐shifting technologies for gate delineation, it is shown that fine gate patterns with large pad areas can be defined. We have fabricated gate patterns for high‐performance GaAs FET devices with gate lengths in the 0.15–0.5 μm range.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Reflective mask technologies and imaging results in soft x‐ray projection lithography

D. M. Tennant, J. E. Bjorkholm, R. M. D’Souza, L. Eichner, R. R. Freeman, J.Z. Pastalan, L. H. Szeto, O. R. Wood, T. E. Jewell, W. M. Mansfield, W. K. Waskiewicz, D. L. White, D. L. Windt, and A. A. MacDowell

J. Vac. Sci. Technol. B 9, 3176 (1991); http://dx.doi.org/10.1116/1.585312 (8 pages) | Cited 3 times

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In this work we investigate and compare a variety of technologies for patterning high resolution Mo/Si multilayer reflective x‐ray masks for use at wavelengths near 13 nm. The patterning methods investigated include: absorbing layers deposited on top of multilayer reflectors, reflective coating removal by reactive ion etching and ion damage of multilayer regions to form a planar mask structure. Large area samples were prepared by each of the above methods and reflectivity measurements made to determine the expected mask contrast. The reflectivity data are compared with simulation for the absorber overlayer and etched multilayer measurements. Our results indicate that reflectivity changes between 5 and 300 were effected. Fine patterning tests show that mask features as fine as 0.1 μm can be achieved in each technology. The advantages, process complexity, and limits of each method are discussed. We also report the first use of an x‐ray reflectance mask to print 0.1 μm features in resist. The developed resist images obtained using reflection masks in a 20:1 Schwarzschild projection camera compare favorably with transmission mask results obtained using the same optical system.
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85.40.Hp Lithography, masks and pattern transfer

Diffraction‐limited soft x‐ray projection lithography with a laser plasma source

G. D. Kubiak, D. A. Tichenor, M. E. Malinowski, R. H. Stulen, S. J. Haney, K. W. Berger, L. A. Brown, J. E. Bjorkholm, R. R. Freeman, W. M. Mansfield, D. M. Tennant, O. R. Wood, J. Bokor, T. E. Jewell, D. L. White, et al.

J. Vac. Sci. Technol. B 9, 3184 (1991); http://dx.doi.org/10.1116/1.585313 (5 pages) | Cited 5 times

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A laser plasma source of extreme ultraviolet and soft x‐ray radiation has been used to print diffraction‐limited features using soft x‐ray projection lithography. A spherical condenser optic, a Si/Ge transmissive mask and a Mo/Si multilayer‐coated Schwarzschild objective having 20:1 reduction ratio were employed to pattern selected single‐layer and trilevel resists. At a numerical aperture of 0.12, a 0.1‐μm line and space pattern is clearly delineated and weak modulation is observed for the analogous 0.05‐μm pattern.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Two‐mirror telecentric optics for soft x‐ray reduction lithography

Kenji Kurihara, Hiroo Kinoshita, Tsutomu Mizota, Tsuneyuki Haga, and Yasuhiro Torii

J. Vac. Sci. Technol. B 9, 3189 (1991); http://dx.doi.org/10.1116/1.585314 (4 pages) | Cited 2 times

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A two‐mirror telecentric optic has been designed for soft x‐ray reduction lithography with high throughput using synchrotron radiation. A resolution of 0.1 μm is achieved at a wavelength of 130 Å with a 15‐mm ring field. In the design, aberrations, including distortion, are reduced using aspherical concave and convex mirrors with an ellipsoid surface at a numerical aperture of 0.07. Telecentric imaging is obtained by illuminating a reflection mask using focusing toroidal mirrors. The designed optics achieves a modulation transfer function (MTF) value of over 40% at a spatial frequency of 5000 lines/mm capable of resolving 0.1‐μm lines and spaces. The depth of focus is ±1 μm. The distortion is <0.01 μm in the image field. The imaging field is a 12.5‐mm radius ring field which enables a 15×15‐mm field exposure by the ring‐field scanning method. The reduction ratio is 1/5.
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85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Soft x‐ray projection lithography using a 1:1 ring field optical system

A. A. MacDowell, J. E. Bjorkholm, J. Bokor, L. Eichner, R. R. Freeman, W. M. Mansfield, J. Pastalan, L. H. Szeto, D. M. Tennant, O. R. Wood, T. E. Jewell, W. K. Waskiewicz, D. L. White, D. L. Windt, W. T. Silfvast, et al.

J. Vac. Sci. Technol. B 9, 3193 (1991); http://dx.doi.org/10.1116/1.585315 (5 pages) | Cited 2 times

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An iridium‐coated Offner 1:1 ring field camera has been used to carry out projection lithography using 42 nm light from an undulator in the vacuum ultra violet storage ring at Brookhaven National Laboratory. Near‐diffraction‐limited resolution has been obtained showing features as small as 0.2 μm within a 2 mm×0.25 mm image field. Images of both transmission and reflection masks have been obtained. The impact of source coherence on imagery has been investigated. Hydrocarbon contamination problems experienced in this photon energy range have been investigated and possible solutions are suggested.
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85.40.Hp Lithography, masks and pattern transfer

Preliminary evaluation of a laser‐based proximity x‐ray stepper

J. Frackoviak, G. K. Celler, R. R. Freeman, C. W. Jurgensen, R. R. Kola, A. E. Novembre, W. W. Tai, L. F. Thompson, L. E. Trimble, and D. N. Tomes

J. Vac. Sci. Technol. B 9, 3198 (1991); http://dx.doi.org/10.1116/1.585286 (4 pages)

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This paper reports on the initial lithographic evaluation of a commercial 1:1 proximity stepper that uses a laser‐based plasma x‐ray source. Our preliminary tests have shown that 0.4‐ and 0.5‐μm lines and spaces can be printed consistently on Si wafers using a positive resist, which has a sensitivity of 6–10 mJ/cm2. Features smaller than 0.4 μm can be obtained, but the overlay accuracy of this system is targeted at 0.5‐μm design rules. The 3σ spread in linewidth is greater than 0.05 μm, however, the stepper contribution must be separated from the resist processing issues, reticle critical dimension variations, and scanning electron micrograph measurement precision.
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85.40.Hp Lithography, masks and pattern transfer

A mask‐to‐wafer alignment and gap setting method for x‐ray lithography using gratings

Norio Uchida, Yoriyuki Ishibashi, and Ryoichi Hirano

J. Vac. Sci. Technol. B 9, 3202 (1991); http://dx.doi.org/10.1116/1.585287 (5 pages)

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A new optical‐heterodyne interferometry alignment and gap setting method for x‐ray lithography is developed, where the phases of beat signals are used for detection. The fact that the lateral displacement and the gap between mask and wafer can be detected independently is shown, based on the results of analysis and experiments. Two pairs of gratings are arranged as detection marks. One pair forms a window on the mask and a checkerboard grating on the wafer, while another pair forms two linear gratings at right angles to each other. Two He‐Ne laser beams with slightly different frequencies illuminate the gratings from the ±1st‐order diffraction light directions. The lateral displacement is detected by measuring the beat signal phase difference between the two (0,1)th‐order diffraction lights from two pairs of gratings. To detect the gap, the signal phase difference between the (0,1)th‐ and (1,1)th‐order diffraction lights from the pair of linear gratings is used. Better than 0.02 μm (3σ) alignment repeatability and 0.1 μm gap setting accuracy have been achieved.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Verification of partially coherent light diffraction models in x‐ray lithography

Jerry Z. Y. Guo and Franco Cerrina

J. Vac. Sci. Technol. B 9, 3207 (1991); http://dx.doi.org/10.1116/1.585288 (7 pages) | Cited 1 time

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The image formed in proximity x‐ray lithography is normally computed using a physical optics model that takes in explicit account diffraction processes. It is important to understand the assumption implicit in the various models and the effects that they have on the image formation. We concentrate, in particular, on the effect of the type of illumination on the quality of the image that can be obtained in proximity x‐ray lithography. In this paper, different methods of calculating the diffraction of partially coherent light are compared and the approximations implicit in each discussed. In a partially coherent system, the properties of the source play an intrinsic role in image formation, so they must be treated together with the imaging process. The full detailed calculations are too complex for implementation on even a supercomputer but, for some types of sources and optical systems it is possible to simplify the problem. Particularly important is the issue of the validity of the linear shift‐invariant system approximation, since it allows great improvements in computational time. We prove the validity of the approximation and verify it using a full 4D numerical integration, based on the Rayleigh–Sommerfeld theory and realized on a Cray YMP8 supercomputer. Application of the results to some physical cases of 0.25 and 0.1 μm features is presented and discussed, illustrating the wide process latitude and resolution of x‐ray lithography.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
42.30.Va Image forming and processing

High efficiency beamline for synchrotron radiation lithography

Takashi Kaneko, Yasunao Saitoh, Seiichi Itabashi, and Hideo Yoshihara

J. Vac. Sci. Technol. B 9, 3214 (1991); http://dx.doi.org/10.1116/1.585289 (4 pages) | Cited 4 times

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A highly efficient beamline for synchrotron radiation (SR) lithography has been developed for our compact storage ring (Super‐ALIS). Two toroidal mirrors are employed to increase the x‐ray intensity on the wafer and to vertically expand the exposure area. Astigmatism is intentionally introduced in these mirrors to increase their converging and collimating abilities. The first mirror converges SR beams with a divergence angle of 2°. The second mirror, which is controlled by a microcomputer, collimates the beam and oscillates to produce an exposure area of 25×25 mm2. An improved vacuum evaporation technique is used to coat the mirror surfaces with platinum, which increases the reflectivity to 50% at a wavelength of 8.34 Å. The resulting x‐ray intensity on the wafer is 5 mW/cm2/100 mA. A uniform x‐ray intensity distribution can be obtained by adjusting the scan speed of the second mirror and using an x‐ray compensation filter. The resulting nonuniformity is improved to be less than ±4%. A reliable x‐ray extraction system that consists of two Be windows and a SiN window permits exposure in an atmospheric environment.
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29.27.Eg Beam handling; beam transport
29.20.db Storage rings and colliders
85.40.Hp Lithography, masks and pattern transfer
07.85.-m X- and γ-ray instruments

Highly reliable oscillating mirror system for synchrotron radiation lithography

H. Kuroda, K. Fujii, and K. Suzuki

J. Vac. Sci. Technol. B 9, 3218 (1991); http://dx.doi.org/10.1116/1.585290 (4 pages)

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An oscillating mirror system suitable for a synchrotron radiation (SR) beamline has been developed. The system, enclosed in an ultrahigh vacuum chamber, can be used for SR lithography in subquarter micron device process due to its high reliability and high performance. Preliminary tests indicated that deviation in the driving velocity was ±3% at maximum, when a 2 cps sine wave command signal was applied. Also, vertical dose uniformity within ±3.3% was obtained, when resists were exposed by adequately modified scanning speed.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer
29.27.Eg Beam handling; beam transport

Experimental evaluation of the two‐state alignment system

G. Chen, J. Wallace, F. Cerrina, S. Palmer, B. Newell, and J. Randall

J. Vac. Sci. Technol. B 9, 3222 (1991); http://dx.doi.org/10.1116/1.585291 (5 pages)

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In previous papers we have proposed the principle of the two‐state alignment method and studied the effect of process coatings on the alignment signal. In this paper, we experimentally evaluate the performance of the two‐state alignment system. We found the alignment signal sensitivity to be larger than 3 V/μm with a noise level of <10 mV, which gives a noise equivalent error smaller than 0.003 μm. The alignment signal time response is <10 ms. In a repeatability experiment, we obtained an alignment standard deviation 3σ=0.036 μm from 500 alignment procedures. We also explored the effect of mask‐wafer gap change on alignment signals. The results show that the alignment signal is tolerant to gap changes in a range of several microns. The details of experiment and experimental data analysis are described in this paper. The possible error sources to the alignment accuracy are also discussed. On the basis of the analysis, we can expect the alignment accuracy to be much better than the 36 nm we have achieved.
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85.40.Hp Lithography, masks and pattern transfer

Effects of mirror surface roughness on exposure field uniformity in synchrotron x‐ray lithography

G. M. Wells, R. Nachman, C. Welnak, S. Singh, J. Guo, M. Khan, S. Turner, F. Cerrina, Y. Vladimirsky, and J. Maldonado

J. Vac. Sci. Technol. B 9, 3227 (1991); http://dx.doi.org/10.1116/1.585292 (5 pages) | Cited 1 time

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In this paper we discuss the surface roughness tolerances for mirrors used in synchrotron x‐ray lithography beamlines. These requirements are different for lithography beamlines than they are for traditional beamlines, which are imaging systems. For imaging optical systems it is desirable to minimize the surface roughness of the mirror in order to reduce the intensity of the scattered light. Proximity print x‐ray lithography requires nonimaging optical systems designed to deliver a uniform power distribution at the exposure field. In such applications, the scattering of x rays is less important, provided that the total flux is not too severely degraded. From this point of view it is important to notice that scattering removes power from the central, coherent, beam and redistributes it over a wider angle. The loss in reflectivity is only apparent because energy is conserved in the process. Furthermore, the presence of scattered x rays can be used to improve the uniformity of the power distribution. The requirement on the surface quality of mirrors used for scanning x‐ray illumination is thus relaxed with respect to that of typical imaging systems, providing considerable cost savings and simplifying manufacturing. The effect of the scattered light on the uniformity of illumination is dependent on intensity and angular distribution of the scattering. Experimental results will be compared to the results predicted by calculations.
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07.85.-m X- and γ-ray instruments
85.40.Hp Lithography, masks and pattern transfer

Electromagnetic calculation of soft x‐ray diffraction from 0.1‐μm scale gold structures

M. L. Schattenburg, K. Li, R. T. Shin, J. A. Kong, D. B. Olster, and Henry I. Smith

J. Vac. Sci. Technol. B 9, 3232 (1991); http://dx.doi.org/10.1116/1.585293 (5 pages) | Cited 1 time

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Because the effects of diffraction during proximity‐print x‐ray lithography are of critical importance, a number of previous researchers have attempted to calculate the diffraction patterns and minimum achievable feature sizes as a function of wavelength and gap. Work to date has assumed that scalar diffraction theory is applicable—as calculated, e.g., by the Rayleigh–Sommerfeld formulation—and that Kirchhoff boundary conditions (KBC) can be applied. KBC assume that the fields (amplitude and phase) are constant in the open regions between absorbers, and a different constant in regions just under the absorbers (i.e., that there are no fringing fields). An x‐ray absorber is, however, best described as a lossy dielectric that is tens or hundreds of wavelengths tall, and hence KBC are unsuitable. In this report we use two numerical techniques to calculate (on a Cray 2 supercomputer) accurate diffracted fields from gold absorbers for two cases: a 30‐nm‐wide line at λ=4.5 nm, and a 100‐nm‐wide line at λ=1.3 nm. We show that the use of KBC introduces unphysically high spatial frequencies into the diffracted fields. The suppression of these frequencies—which occurs naturally without the need to introduce an extended source or broad spectrum—tremendously improves exposure latitude for mask features near 0.1 μm and below. In particular, we show that KBC should not be applied to 0.1‐μm features and wavelengths near 1.3 nm for gaps below 11 μm.
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78.70.Ck X-ray scattering
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Wafer process‐induced distortion study for x‐ray technology

Dennis Schmidt and Greg Charache

J. Vac. Sci. Technol. B 9, 3237 (1991); http://dx.doi.org/10.1116/1.585294 (4 pages) | Cited 1 time

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X‐ray synchrotron radiation is a promising source for submicron lithography. For x‐ray lithography to be a useful technology, the combined overlay for the mask, stepper, and wafer processes must be less than that required by the product device specification. X‐ray lithography uses a 1× proximity printing technique. Unlike n× optical stepper lithography, a lens cannot be varied nor can a reticle be moved to correct for magnification distortions due to wafer processes. Wafer processes (such as film formation) stress the wafer, causing pattern‐magnification distortion and wafer warpage. This paper examines the process’ contribution to the overlay tolerance. Several wafer experiments have been performed using simulated 64 Mbit dynamics random access memory (DRAM) processes. Test wafers, etched with periodic ‘‘L’’ image measurement targets, were both hot processed and trench processed. The ‘‘L’’ targets on the wafers were measured using a long‐distance xy measurement system and wafer flatness system. The measurements, before and after each process, show the wafer‐induced distortion. One of the experiments discussed in this paper is a hot process used for gate oxidation. This rapid‐thermal‐oxidation‐furnace experiment generated less than 2 ppm distortion. Other examples of hot‐process distortion and trench‐process distortion data are presented.
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85.40.Hp Lithography, masks and pattern transfer
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Fabrication of a 1 Mbit dynamic random access memory with four levels using x‐ray lithography

S. Hoffman, S. Nash, R. Ritter, and W. Smith

J. Vac. Sci. Technol. B 9, 3241 (1991); http://dx.doi.org/10.1116/1.585295 (4 pages)

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A 1 Mbit dynamic random access memory (DRAM) was recently fabricated with all critical levels exposed using synchrotron x rays. Lithography for the critical levels (isolation, transfer gate, contacts, and metal) was performed at the Brookhaven National Laboratory—National Synchrotron Light Source (vacuum ultraviolet ring) on an IBM beamline using a Karl Suss XRS‐200 x‐ray stepper. The remaining levels were exposed with standard step‐and‐repeat optical tools. Most nonlithographic processing was performed in a mature 1 Mbit production line. Bit yields of up to 50% were found on several 256 K input–output (I/O) segments. An optical control lot processed through equivalent nonstandard steps produced a comparable yield. Considering the extensive off‐line processing required for this experiment, this yield exceeded expectations.
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85.30.-z Semiconductor devices
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
85.40.Hp Lithography, masks and pattern transfer

Intense pulsed plasma x‐ray source for lithography

D. H. Kalantar, D. A. Hammer, K. C. Mittal, N. Qi, J. R. Maldonado, and Y. Vladimirsky

J. Vac. Sci. Technol. B 9, 3245 (1991); http://dx.doi.org/10.1116/1.585296 (5 pages) | Cited 3 times

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The x‐pinch soft x‐ray source is described for application in submicron resolution lithography. Experiments have been performed to measure and characterize the radiation emitted from the magnesium wire x‐pinch plasma using an 80 ns, ≤500 kA pulse. Soft x‐ray yields of 14.2 J averaged over three independent calibrated diagnostics at 445 kA have been measured in magnesium K‐shell radiation (predominantly 8.4–9.4 Å or 1.5–1.3 keV) from a submillimeter source, with as little as 5–10% of the yield below the 6.74 Å silicon absorption edge. Samples of high sensitivity x‐ray resist have been exposed in as few as two pulses at a 10 cm distance. Observed scaling of the yield indicates the possibility of effectively exposing a resist at a distance of 40 cm using a<750 kA pulser.
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85.40.Hp Lithography, masks and pattern transfer
52.55.Ez Theta pinch
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Synchrotron radiation damage study of lateral pnp transistors in x‐ray lithography

L. C. Hsia and J. Aitken

J. Vac. Sci. Technol. B 9, 3250 (1991); http://dx.doi.org/10.1116/1.585297 (4 pages)

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The synchrotron radiation damage of lateral pnp transistors has been investigated using the vacuum ultraviolet (VUV) storage ring of the National Synchrotron Light Source at the Brookhaven National Laboratory. The devices under investigation were exposed to the x‐ray radiation in the range of 1–2 keV, coming out of a lithography beam line. The transistor parameters were measured before and after irradiation, and were measured again after the devices were annealed in forming gas at 400 °C for 30 min. The study shows that synchrotron x‐ray radiation reduces the current gain by one order of magnitude at small collector currents. The Gummel plot shows that x‐ray radiation adds a big recombination component to the base current. This change is primarily due to the interface traps generated at the interface between Si and SiO2 in the base region. The capacitance‐voltage (C‐V) measurements on metal‐oxide‐semiconductor (MOS) capacitors indicate that x‐ray radiation increases interface trap density from its initial order of magnitude of 1010–1012/cm2 eV. The irradiation also increases the leakage current between the collector and emitter due to the parasitic p‐channel field‐effect transistor (PFET), by a factor of 10. Upon annealing both the current gain and leakage current recover their initial values.
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85.30.Pq Bipolar transistors

SiC membranes for x‐ray masks produced by laser ablation deposition

S. Boily, M. Chaker, H. Pépin, T. Kerdja, J. Voyer, A. Jean, J. C. Kieffer, P. Leung, F. Cerrina, and G. Wells

J. Vac. Sci. Technol. B 9, 3254 (1991); http://dx.doi.org/10.1116/1.585298 (4 pages) | Cited 8 times

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Laser ablation deposition is used for the first time to fabricate SiC membranes for x‐ray lithography. The process has the unique advantage of producing in a very simple manner purely stoichiometric (1:1) SiC films free of hydrogen. The variation of deposition rate with laser energy and intensity, the uniformity and quality of the films produced as well as an estimate of the energy of the neutrals and of the ions involved in the deposition are presented. SiC membranes of 1 in. diam have been successfully fabricated after anisotropic etching of the silicon substrate in a KOH solution. They present an optical transparency of 40% at 633 nm.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Hp Lithography, masks and pattern transfer

Advanced electron cyclotron resonance chemical vapor deposition SiC coatings and x‐ray mask membranes

A. R. Shimkunas, P. E. Mauger, L. P. Bourget, R. S. Post, L. Smith, R. F. Davis, G. M. Wells, F. Cerrina, and R. B. McIntosh

J. Vac. Sci. Technol. B 9, 3258 (1991); http://dx.doi.org/10.1116/1.585299 (4 pages) | Cited 6 times

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Recent work in electron cyclotron resonance chemical vapor deposition (ECR‐CVD) SiC coating technology has demonstrated the potential for fabricating high‐quality SiC membranes for x‐ray lithography masks. Stoichiometric SiC coatings were deposited on 100‐mm‐diam silicon wafers at a susceptor temperature of 930 °C in a single‐wafer ECR‐CVD system at deposition rates of 200 Å/min with better than ±5% thickness uniformity and ±1% wafer‐to‐wafer reproducibility. The coatings were deposited under tensile stress, with a wafer‐to‐wafer stress repeatability of ±15%. The coatings were extremely smooth, and x‐ray diffraction (XRD) and transmission electron microscopy (TEM) studies showed that they were amorphous with scattered submicron crystalline inclusions. One‐ and 2‐μm‐thick membranes were made in 30 and 50 mm diameters at yields of 80%. A peak transmittance of 65% was measured at 633 nm for 1‐μm‐thick SiC membranes. The bi‐axial elastic modulus, E/(1−ν), of the SiC membranes was (4–6)×1012 dyn/cm2, about three times greater than that of (100) Si membranes. Hydrogen was undetectable in the form of either CH or SiH bonds to within the experimental detection limit of <10 ppm. Out‐of‐plane distortion could not be detected after an absorbed dose of 9.6 or 29 MJ/cm3 during exposure at the Center for X‐ray Lithography beamline at the University of Wisconsin’s Aladdin synchrotron. The membrane transmittance decreased by about 1% after the 29 MJ/cm3 dose. Plans for future work include modifications to the ECR‐CVD equipment to increase substrate temperature uniformity, temperature limit, and deposition rate, and to reduce defect density.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

A study of radiation damage in SiN and SiC mask membranes

Masamitsu Itoh, Masaru Hori, Haruki Komano, and Ichiro Mori

J. Vac. Sci. Technol. B 9, 3262 (1991); http://dx.doi.org/10.1116/1.585300 (4 pages) | Cited 4 times

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Radiation damage in SiN and SiC films prepared by low‐pressure chemical vapor deposition (LPCVD) is reported. A pattern placement error of 0.05 μm at the edge of the x‐ray radiation area was introduced for SiN membranes by a radiation dose of 12 kJ/cm2. The electron spin resonance (ESR) signals with a g value of 2.004, which was attributed to the Si–N dangling bond, were observed. Both the error and the spin density increased with increasing radiation dose up to 12 kJ/cm2 and remained constant thereafter. The error was explained as the result of Si–N bond scission caused by x‐ray radiation, leading to tensile stress relaxation in the radiated area. In the case of SiC films, a pattern placement error was less than a detection limit of 0.03 μm for a radiation dose of 10 kJ/cm2. ESR signals with a g value of 2.003, being attributed to the Si–C dangling bond, were observed. However, the spin density in this case did not change by radiation up to 20 kJ/cm2. It is inferred that the LPCVD SiC membrane is damage free to x‐ray radiation.
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61.80.Cb X-ray effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.50.Lt Crystal binding; cohesive energy

X‐ray irradiation effects on a microwave‐plasma chemical vapor deposition diamond membrane

K. Suzuki, R. Kumar, H. Windischmann, H. Sano, Y. Iimura, H. Miyashita, and N. Watanabe

J. Vac. Sci. Technol. B 9, 3266 (1991); http://dx.doi.org/10.1116/1.585301 (4 pages) | Cited 3 times

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Diamond membrane masks, fabricated using microwave‐plasma chemical vapor deposition, have been evaluated for their dimensional stability as well as other principal characteristics, during 15‐MJ/cm3 x‐ray irradiation within a vacuum. After x‐ray irradiation, intensity of the diamond Raman band at 1332 cm−1 increased to 150% of that unirradiated membrane. Spin density in the diamond increased up to 1.5×1019 spins/g; two times higher than that before irradiation. Despite these effects, in‐plane distortion due to x‐ray irradiation of the diamond membrane on a half‐area of 25‐mm square was extremely small (<0.08 μm). Optical transparency of the membrane increased by 4.5%–6.1% at 633 nm due to x‐ray irradiation.
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61.80.Cb X-ray effects
68.55.-a Thin film structure and morphology
81.40.Tv Optical and dielectric properties related to treatment conditions
81.40.Lm Deformation, plasticity, and creep

Photoelectron effects in x‐ray mask replication

V. White, L. Ocola, F. Cerrina, Y. Vladimirsky, and J. Maldonado

J. Vac. Sci. Technol. B 9, 3270 (1991); http://dx.doi.org/10.1116/1.585302 (5 pages) | Cited 2 times

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In this paper some experimental observations of the interference of photoelectrons in an x‐ray mask replicating process are reported on. High resolution low contrast (i.e., producing absorbed dose ratios of less than 2) x‐ray masks have been used to produce lines smaller than 0.1 μm in poly(methlmethacrylate) (PMMA) on a silicon substrate with an aspect ratio of about 2. When the experiment was repeated on a gold plated substrate, anomalous adhesion problems were encountered. Lines smaller than 0.2 μm, for example, had poor adhesion, and those smaller than 0.1 μm had entirely lifted off. A higher contrast mask, with a dose contrast of about 6, and with smaller features was tried on the same two substrates. Using this mask, 800 Å lines in PMMA in 0.5 μm thick resist have been demonstrated, with good adhesion. These effects are consistent with the assumption that the x rays that penetrate the mask’s absorber, and the resist, but are absorbed in the plating base, generating photoelectrons, which then propagate across the interface. These extra photoelectrons create a thin layer of increased exposure in the resist near the interface that is responsible for loss of adhesion for ultrasmall structures. A low‐Z photoelectron block layer can be used to eliminate this problem. Experimental evidence in conjuncture with computer simulation were done to investigate this assumption.
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85.40.Hp Lithography, masks and pattern transfer

Dynamic in‐plane thermal distortion analysis of an x‐ray mask membrane for synchrotron radiation lithography

Akira Chiba and Koichi Okada

J. Vac. Sci. Technol. B 9, 3275 (1991); http://dx.doi.org/10.1116/1.585303 (5 pages) | Cited 1 time

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Dynamic in‐plane thermal distortion (IPTD) in an SiN x‐ray mask membrane during repetitive scanning x‐ray exposure for synchrotron radiation (SR) lithography has been exactly calculated using a model which is close to realistic physical conditions. In order to decide the heating model, a flow regime in the mask‐to‐wafer proximity gap filled with a 760‐Torr helium gas is examined by using the value of the Knudsen number. Heat generated in the mask membrane, a helium gas, and a resist coated on a wafer during x‐ray exposure is taken into consideration for the thermal balance equations. The effects of the proximity gap, scanning frequency, and membrane window size on the dynamic IPTD are simulated. The dynamic IPTD indicates a constant value depending on a scanning frequency within the region of the 10–100‐μm gap. According to the scanning frequency dependence, the dynamic behavior of the IPTD is divided into three regions: quasistatic, transient, and saturated regions. Using >10‐Hz scanning frequencies (saturated region), the dynamic IPTD appears to converge to an equivalent value obtained by a uniform exposure. In the region of >10‐mm window size, the dynamic IPTD, not proportional to the window size, seems to be saturated.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Tungsten patterning for 1:1 x‐ray masks

C. W. Jurgensen, R. R. Kola, A. E. Novembre, W. W. Tai, J. Frackoviak, L. E. Trimble, and G. K. Celler

J. Vac. Sci. Technol. B 9, 3280 (1991); http://dx.doi.org/10.1116/1.585304 (7 pages) | Cited 7 times

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A subtractive process to form subhalf micron, vertical‐walled patterns in half‐micron thick tungsten on x‐ray masks has been developed. Electron‐beam lithography was used to form resist patterns on a structure consisting of 300 Å Cr on 5000 Å W on 200 Å Cr on an approximately 1 μm thick poly‐silicon or silicon nitride membrane. The Cr masking and etch‐stop layers above and below the W layer are required because the resist and membrane materials etch rapidly in fluorine based W etching plasmas. Chromium was chosen for these layers because it has a high selectivity in the W etch (≊40:1), is compatible with the W deposition process, and can be patterned in an O2–Cl2 plasma which does not etch W or the membrane materials. Helium backside cooling at a pressure from 1 to 5 Torr controls membrane temperature during all plasma processing steps. Pure CBrF3 or CHF3 etch W slowly while simultaneously depositing polymer which produces sloping profiles where the base of the feature is wider than the initial mask width. Pure SF6 gives high etching rates but the fluorine radicals attach the W sidewall causing undercutting. Depositing polymer on the sidewall by adding CHF3 or CBrF3 to the SF6 reduces undercutting, but produces sloping profiles. The undercutting found with pure SF6 can be eliminated with vertical profiles by etching at low temperature or by adding N2 or Cl2 to the gas mixture to form low volatility reaction products with tungsten on the sidewall.
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85.40.Hp Lithography, masks and pattern transfer
81.30.Bx Phase diagrams of metals, alloys, and oxides

Fabrication and characterization of high‐flatness mesa‐etched silicon nitride x‐ray masks

A. Moel, W. Chu, K. Early, Y.‐C. Ku, E. E. Moon, F. Tsai, Henry I. Smith, M. L. Schattenburg, C. D. Fung, F. W. Griffith, and L. E. Haas

J. Vac. Sci. Technol. B 9, 3287 (1991); http://dx.doi.org/10.1116/1.585305 (5 pages) | Cited 4 times

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To realize a technology for x‐ray nanolithography (<100 nm features), which is compatible with manufacturing, a number of mask design requirements must be met that are unrelated to patterning, repair, and alignment. These include high‐flatness membranes and support structures so that mask‐wafer gaps less than 10 μm can be achieved without risk of damage, and a rigid mask frame to avoid problems of distortion during handling. The membrane material should be compatible with semiconductor‐processing, possess high strength, be radiation hard, and be transparent to light for alignment purposes. Details of a mask architecture that meets these requirements will be described.
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85.40.Hp Lithography, masks and pattern transfer

Patterning tungsten films with an electron beam lithography system at 50 keV for x‐ray mask applications

K. W. Rhee, A. C. Ting, L. M. Shirey, K. W. Foster, J. M. Andrews, M. C. Peckerar, and Y.‐C. Ku

J. Vac. Sci. Technol. B 9, 3292 (1991); http://dx.doi.org/10.1116/1.585306 (5 pages) | Cited 2 times

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The application of electron beam lithography for the fabrication of x‐ray masks is essential in the development of x‐ray lithography technology. In this paper we present experimental results on the patterning of submicron (2–0.25 μm) features into a single‐layer negative e‐beam resist and then subsequent transfer of these patterns onto a 0.4 μm‐thick tungsten film by reactive ion etching. To study the dependence of the proximity effect on the substrate material, a comparison of linewidths and sidewall profiles of electron beam resist images on silicon, silicon dioxide on silicon, and tungsten on silicon wafers has been established.
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85.40.Hp Lithography, masks and pattern transfer

In situ stress monitoring and deposition of zero‐stress W for x‐ray masks

Y.‐C. Ku, Lee‐Peng Ng, Roger Carpenter, Kenneth Lu, Henry I. Smith, L. E. Haas, and I. Plotnik

J. Vac. Sci. Technol. B 9, 3297 (1991); http://dx.doi.org/10.1116/1.585307 (4 pages) | Cited 3 times

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We have developed and tested a computer‐controlled system for monitoring in situ the stress of tungsten sputter deposited onto x‐ray mask membranes. This system allows us to achieve zero stress (i.e., <5×107 dyn/cm2) tungsten. The stress is monitored via the resonant frequency of the x‐ray mask membrane which changes during deposition due to W stress, mass loading, and temperature rise. Differences in W stress give rise to differences in curvatures of the plot of resonant frequency versus W thickness. This effect can be used to ensure that a film will have stress below 1×108 dyn/cm2 and can also be the basis of an automated closed‐loop, in situ stress control system.
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85.40.Hp Lithography, masks and pattern transfer
81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties

Stable low‐stress tungsten absorber technology for sub‐half‐micron x‐ray lithography

R. R. Kola, G. K. Celler, J. Frackoviak, C. W. Jurgensen, and L. E. Trimble

J. Vac. Sci. Technol. B 9, 3301 (1991); http://dx.doi.org/10.1116/1.585330 (5 pages) | Cited 9 times

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Tungsten is attractive for very large scale integrated device metallization and as absorber for x‐ray lithographic masks. To minimize distortions in an x‐ray mask, intrinsic stresses in the absorber films have to be low and reproducible. We present the results of a systematic study of the microstructure and stress of rf sputter‐deposited W films as a function of deposition parameters, using optical interferometry, scanning electron microscopy, transmission electron microscopy, and x‐ray diffraction. Rutherford backscattering spectrometry and Auger electron spectroscopy were used for the chemical analysis of the films. By controlling the nucleating phase and mobility of the adatoms, we have produced W films with low stresses (<±50 MPa). The low‐stress films have a 〈110〉 preferred orientation and a bimodal grain size distribution with large, elongated grains surrounded by small equiaxed grains. The lattice parameter and the argon content in W films increased with decreasing argon deposition pressure. It was found that a low base pressure (<10−7 Torr) is necessary to produce stable α‐phase W and to eliminate the metastable β phase. Additional seed layers (Cr, SiO2 ) at the Si/W interface resulted in a small improvement in stress control of the W films. The W films were stable (no change in stress) on subsequent anneals at 200 °C for 50 h in vacuum and argon ambients.
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68.60.Bs Mechanical and acoustical properties
68.60.Dv Thermal stability; thermal effects
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Elastic deformation of x‐ray lithography masks under external loadings

A. C. Chen, S. N. Lalapet, and J. R. Maldonado

J. Vac. Sci. Technol. B 9, 3306 (1991); http://dx.doi.org/10.1116/1.585331 (4 pages) | Cited 1 time

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This paper describes the elastic deformation of x‐ray lithography masks due to external loadings using finite element modeling. The design of the mask support structure is critical to achieve 0.25 μm device design rules, for which the mask contribution to the total overlay budget must be kept below 50 nm. Therefore the mask deformation due to external loads should be below 10 nm. Several three‐dimensional finite element models were constructed to simulate x‐ray lithography masks under gravity loading and external in‐plane loading (an out‐of‐plane loading can be related to an equivalent in‐plane loading via the Poisson ratio of the material). A figure of merit was developed to evaluate the relative stiffness of mask support structures, and to guide future x‐ray lithography mask designs.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

X‐ray mask distortion from arbitrary integrated circuit patterns: Closed‐form and finite‐element calculation

Arnold W. Yanof

J. Vac. Sci. Technol. B 9, 3310 (1991); http://dx.doi.org/10.1116/1.585332 (5 pages)

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Distortions in x‐ray masks continue to be a critical problem for x‐ray lithographic technology because upcoming integrated circuit (IC) generations demand ever‐tightening requirements on the accuracy of pattern placement. In this work, elastic theory of plane stress is applied to calculate distortions arising from arbitrary patterned areas on an infinite mask membrane exactly. Distortions due to rectangular features of finite size are obtained in closed form. This analysis is used to model the structures in real x‐ray masks, such as interconnect level masks, where square pads, long runners, and gratings are typical. A particular issue discussed herein is the question of stress concentration at the ends of a long rectangular feature. Here the in‐plane distortion increases logarithmically with the aspect ratio of the feature. For arrays of long rectangular features, the distortion increases in accordance with the aspect ratio of the whole array. The model predictions agree with experimental data for actual x‐ray masks having arrays of rectangular features, and with numerical calculations based on finite‐element analysis. In order to treat actual complex IC masks having finite‐sized membranes, a numerical method combining both finite‐element and exact calculation is developed.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Application of e‐beam lithography and reactive ion etching to the fabrication of masks for projection x‐ray lithography

C. Khan Malek, F. R. Ladan, R. Rivoira, and T. Moreno

J. Vac. Sci. Technol. B 9, 3315 (1991); http://dx.doi.org/10.1116/1.585333 (4 pages)

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Mo/Si multilayer mirrors deposited on silicon wafers by triode sputtering were patterned by electron‐beam lithography and etched by reactive ion etching in a fluorinated plasma with an intermediate metallic mask made by the lift‐off process. The etch rate and etch profile were investigated as a function of the gas mixture, pressure, and plasma rf power. The groove depth was monitored by following the reflectivity of the structure with a helium‐neon laser during etching and comparing it with an optical model. Large structures consisting of gratings and Fresnel zone plates with potential applications to high‐resolution alignment for projection x‐ray lithography were fabricated in Mo/Si. The fabrication feasibility of finer structures such as gratings with 0.3–0.5 μm pitch and linewidths smaller than 100 nm as well as linear and circular Fresnel zone plates with a 0.4‐μm‐wide outer zones were investigated in the similar Mo/C multilayer system.
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85.40.Hp Lithography, masks and pattern transfer
81.65.-b Surface treatments
42.79.Dj Gratings
42.79.Ci Filters, zone plates, and polarizers

0.1 μm x‐ray mask replication

M. Gentili, R. Kumar, L. Luciani, L. Grella, D. Plumb, and Q. Leonard

J. Vac. Sci. Technol. B 9, 3319 (1991); http://dx.doi.org/10.1116/1.585334 (5 pages) | Cited 1 time

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In a series of experiments, we investigate issues of absorber thickness increase (contrast amplification) and resolution capabilities of an x‐ray mask copying process utilizing x‐ray lithography. Two types of high resolution master masks were patterned using e‐beam lithography and gold electroplating deposition and then replicated using x‐ray lithography. The print quality and feature linewidths of each replica were then evaluated using a scanning electron microscope. The production of ULSI masks for x‐ray lithography can be simplified if the necessary step of electron beam patterning can be performed in a thin resist layer, reducing the complexity of subsequent processing procedures and enhancing e‐beam capabilities. When working with a thin resist, however, plated absorber thicknesses are small and the resulting mask contrast is limited. For x‐ray lithography, Au absorber thicknesses on the order of 0.6 μm are required to ensure sufficient mask contrast when using synchrotron radiation (SR) sources (λ=0.1–1.2 nm). This implies than an aspect ratio of 3:1 is needed to print 0.2 μm features, and a ratio greater than 6:1 is necessary for sub‐100 nm features.
A promising approach to achieving greater absorber thickness in x‐ray masks is based on a mask replication process utilizing x‐ray lithography. The large depth of focus and wide process latitude offered by x‐ray lithography (XRL) permit exposure into thicker resist layers, and consequently, greater absorber thicknesses can be produced via direct metallization of the printed image. This technique also has the advantage of reducing e‐beam time requirements, since many x‐ray mask replicas can be produced from a single e‐beam master mask. Two types of master x‐ray masks were used in our evaluation. The first was a 2‐μm‐thick SiNx membrane with sub‐100‐nm Au features, and the second was a 2‐μm‐thick Si membrane with Au features down to 250 nm. Using the SiNx master mask, sub‐100‐nm resist features were successfully printed in 600 nm of resist on base plated wafers, using x‐ray lithography. Subsequent electroplating of these samples yielded sub‐100 nm features with Au absorber thicknesses of 450 nm. These results demonstrate successful mask contrast amplification (from 6 dB for the master to 15 dB for the copy), and show that high resolution, high contrast masks can be fabricated using this replication process.
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85.40.Hp Lithography, masks and pattern transfer

X‐ray mask process‐induced distortion study

S. C. Nash and T. B. Faure

J. Vac. Sci. Technol. B 9, 3324 (1991); http://dx.doi.org/10.1116/1.585335 (5 pages) | Cited 1 time

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X‐ray masks for fabrication of 0.25 μm ultralarge‐scale‐integration devices have to meet very tight pattern placement requirements. Because of the nature of x‐ray mask substrates, control of the distortion caused by the processing of the mask after e‐beam lithography is important. The pattern placement distortions that occur during the processing of an x‐ray mask are examined, and the effect of gold absorber electroplating, e‐beam‐resist strip, and plating‐base strip processes are studied. It has been found that x‐ray mask process‐induced distortion is very sensitive to the amount of gold coverage and the connectivity of the gold pattern.
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85.40.Hp Lithography, masks and pattern transfer

Effect of thermal treatment on the mechanical and structural properties of gold thin films

C. Khan Malek, B. Kebabi, A. Charai, and P. de la Houssaye

J. Vac. Sci. Technol. B 9, 3329 (1991); http://dx.doi.org/10.1116/1.585336 (4 pages) | Cited 2 times

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Low‐stress (<50 MPa) gold films 0.7‐ and 2‐μm thick were deposited by electroplating from a cyanide solution at 40 °C at a current density of 2.5 mA/cm2. Thin gold films under higher stress were electron‐beam evaporated at room temperature or sputtered at a power of 150 W under 2‐Pa argon gas. The stress dependence of these films on the post‐deposition annealing temperature up to 200 °C was investigated, using an interferometric method at room temperature. The stress evolution is discussed in relationship to the thermally induced changes in the structure and the microstructure of the various films investigated by transmission electron microscopy.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.60.Dv Thermal stability; thermal effects

Optimal design of an x‐ray lithography mask

D. L. Laird and R. L. Engelstad

J. Vac. Sci. Technol. B 9, 3333 (1991); http://dx.doi.org/10.1116/1.585337 (5 pages) | Cited 1 time

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The 0.25 μm 1:1, masks used in x‐ray lithography have a very tight overlay requirement: it is not just sufficient to produce a perfect mask, it is also necessary not to degrade its characteristics by incorrect mounting. This is particularly true for synchrotron‐based x‐ray lithography where the masks are patterned and used in different configurations. The computational tools necessary to model mask distortions in the nanometer range with high accuracy and reliability are developed here and used to predict an optimal mask design. The results show that the overall mask distortion resulting from gravitational loading can be accommodated within the allocated error budget.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

PTBSS: A high resolution single component aqueous base soluble chemically amplified resist

A. E. Novembre, W. W. Tai, J. M. Kometani, J. E. Hanson, O. Nalamasu, G. N. Taylor, E. Reichmanis, L. F. Thompson, and D. N. Tomes

J. Vac. Sci. Technol. B 9, 3338 (1991); http://dx.doi.org/10.1116/1.585338 (5 pages)

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Poly(4‐tert‐butoxycarbonyloxystyrene‐co‐sulfur dioxide) PTBSS has been found to act as a sensitive x‐ray (λ=1.4 nm) and weakly sensitive deep ultraviolet (λ=248 nm) chemically amplified, aqueous base soluble positive acting resist. Improvements in the lithographic sensitivity can be achieved by optimizing the post‐exposure baking (PEB) conditions. For example, increasing the PEB temperature from 115 °C to 145 °C improved the x‐ray sensitivity of a 2.6:1 4‐tert‐butoxycarbonyloxystyrene (TBS): sulfur dioxide (SO2) resist fivefold. A secondary gain in sensitivity was achieved when the PEB time was extended from the standard 2.5 min to 4.0 min. The sensitivity was also shown to be dependent on the time elapsed from exposure to post‐exposure bake. Increasing this time from 1 to 30 min increased the required x‐ray exposure energy by 60% arylmethyl model compounds of arylmethyl sulfone have provided information on how the deep‐UV sensitivity of PTBSS can be improved from a value of 1800 to 200 mJ/cm.2 Additionally, these model compounds were shown to function as effective acid generating and/or dissolution inhibitor species when added to PTBSS.
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85.40.Hp Lithography, masks and pattern transfer

Novolak resin‐based positive electron‐beam resist system utilizing acid‐sensitive polymeric dissolution inhibitor with solubility reversal reactivity

Hiroshi Shiraishi, Nobuaki Hayashi, Takumi Ueno, Toshio Sakamizu, and Fumio Murai

J. Vac. Sci. Technol. B 9, 3343 (1991); http://dx.doi.org/10.1116/1.585339 (5 pages) | Cited 3 times

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This paper deals with a novel novolak resin‐based positive resist system designed for practical direct electron‐beam fabrication. The novel positive resist system, which has a solubility reversal mechanism, consists of an acid‐sensitive polymeric dissolution inhibitor, an acid generator, and a novolak matrix resin. Various kinds of polymers, which can be converted to dissolution promoters by acid‐catalyzed reaction, are investigated as the dissolution inhibitor of the system. A tetrahydropyranyl‐protected poly(p‐vinylphenol) (THP‐M) is selected as the polymeric dissolution inhibitor. THP‐M is insoluble in aqueous base solutions and compatible with novolak resins. The acid‐catalyzed deprotection of THP‐M results in poly(p‐vinylphenol), which is soluble in aqueous base solutions and can be a dissolution promotor in the system. It is found that a methanesulfonic acid ester is the most effective acid generator for this resist system. Aryl onium salts, well‐known acid generators, are not effective because of their strong dissolution‐inhibition behavior results in negative tone patterns. High‐resolution patterns (0.4‐μm lines and spaces) are achieved with high sensitivity (2.5 μC/cm2 at 30 kV).
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization

A positive, chemically amplified, aromatic methacrylate resist employing the tetrahydropyranyl protecting group

Gary N. Taylor, Larry E. Stillwagon, Francis M. Houlihan, Thomas M. Wolf, Dotsevi Y. Sogah, and Walter R. Hertler

J. Vac. Sci. Technol. B 9, 3348 (1991); http://dx.doi.org/10.1116/1.585340 (9 pages) | Cited 2 times

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In this article we describe the synthesis, properties, and lithographic behavior of a new class of chemically‐amplified, positive‐tone, aromatic methacrylate resists incorporating the tetrahydropyranyl protecting group bound to base‐solubilizing carboxylic acid moieties. Copolymers containing equimolar amounts of benzyl methacrylate and tetrahydropyranyl methacrylate were prepared by free radical and group transfer polymerization (GTP). Photogenerated sulfonic acids formed from covalent ester or ionic salt precursors were used to remove the acid labile tetrahydropyranyl (THP) group by heating after exposure. The resulting copolymers of benzyl methacrylate (BMA) and methacrylic acid (MAA) are extremely soluble in aqueous base solutions when the MAA concentration exceeds 38 mol %, thus affording positive tone patterns. We have studied these copolymer resists and find them to have high sensitivity (<30 mJ/cm2) when formulated with aromatic sulfonate or trifluoromethyl sulfonate sensitizers. Contrast is greater than 2 and submicrometer patterns in 1 μm thick films are resolved. Resolution is significantly influenced by the sensitizer, post exposure heating and development conditions. Molecular weight distribution appears to have little effect on the lithographic properties. Resolution presently is limited by resist adhesion which remains to be optimized. Plasma etching resistance to conditions used to etch Al is 1.8 times less than for hard‐baked HPR‐206 photoresist, but can be improved to a value of 1.5 by postexposure thermolysis. Improvements are needed before this type of chemically‐amplified resist is able to meet all deep‐UV lithographic requirements. However, it appears quite promising for other lower resolution (≫1 μm), thick‐film‐imaging applications which will be the subject of future papers.
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85.40.Hp Lithography, masks and pattern transfer

High performance acrylic polymers for chemically amplified photoresist applications

Robert D. Allen, Gregory M. Wallraff, William D. Hinsberg, and Logan L. Simpson

J. Vac. Sci. Technol. B 9, 3357 (1991); http://dx.doi.org/10.1116/1.585341 (5 pages) | Cited 1 time

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Chemically amplified resists have recently achieved importance as materials useful for high density microlithographic applications requiring submicron imaging. In an effort to extend the chemical amplification concept to applications requiring thick film resists, we have developed a family of acrylic polymers which provide high performance, aqueous developing positive resists when formulated with the appropriate photo‐acid generators. The polymers were prepared from methyl methacrylate (MMA), t‐butyl methacrylate (TBMA) and methacrylic acid (MAA), each of which serves a separate function in the formed terpolymer. An unusual degree of control over the aqueous development kinetics can be achieved by manipulation of the terpolymer composition. The lithographic properties of resist formulations based on these polymers have been examined employing optical exposure at wavelengths from 248 to 514 nm, and e‐beam exposure.
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85.40.Hp Lithography, masks and pattern transfer

A statistically based model of electron‐beam exposed, chemically amplified negative resist

N. N. Tam, H. Y. Liu, C. Spanos, and A. R. Neureuther

J. Vac. Sci. Technol. B 9, 3362 (1991); http://dx.doi.org/10.1116/1.585342 (8 pages) | Cited 1 time

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A methodology based on statistically designed factorial experiments has been developed to model the dissolution rate of an electron‐beam exposed chemically amplified resist, Shipley SAL‐601‐ER7, for different post‐exposure bake (PEB) and developer concentrations. A statistical experiment of dissolution rate measurements were performed in the Perkin‐Elmer development rate monitor using a central composite design with PEB temperature, PEB time, and developer concentration as the factors. These measurements were combined with Monte Carlo simulation of electron energy deposition to generate dissolution rate data as a function of absorbed energy. These data were then fitted to a semiempirical rate equation using nonlinear regression. Statistical analysis of the effects of the three processing factors on the parameters of the rate functions yielded empirical models relating the parameters to the factors. As a result, a rate equation can be determined for any processing conditions, and thus a complete model is obtained for the simulation and optimization of the resist.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments

Electron impact reactions of triphenylsulfonium salt resist sensitizers in the solid state

Ivan Haller and Kevin J. Stewart

J. Vac. Sci. Technol. B 9, 3370 (1991); http://dx.doi.org/10.1116/1.585343 (4 pages)

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To elucidate the mechanism of electron beam exposure of triphenylsulfonium salt sensitized resists, films of triphenylsulfonium hexafluoroantimonate or triflate in various polymers and in the pure solid state were exposed to pulses of electrons. The composition of the resulting pulses of gaseous products was analyzed by Fourier transform mass spectrometry. Components of product mixtures were identified by using both electron impact and chemical ionization techniques. The main volatile products of triphenylsulfonium under electron impact are diphenyl sulfide, benzene, and biphenyl. The yield of benzene is much larger from triphenylsulfonium salts dissolved in polymer than in the pure solid state. This implies rapid hydrogen‐abstraction reactions by the intermediate phenyl radicals from matrices with available aliphatic hydrogens. The product distributions observed from several polymer solvents, and their dependence on electron energy, show few other rapid reactions between the matrix and the primary products. No volatile products arising from the anions were observed. This indicates that acidic products formed in the electron stimulated decomposition reactions of triphenylsulfonium salts are retained dissolved in the polymer under high vacuum conditions. Thus under electron beam exposure, as in deep‐UV exposure, it is the subsequent acid‐catalyzed reactions of the resin that are responsible for the high sensitivity of onium–salt resists.
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82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.-b Specific chemical reactions; reaction mechanisms

Process characteristics of an all‐organic chemically amplified deep‐ultraviolet resist

M. Cheng, O. Nalamasu, A. G. Timko, V. Pol, J. M. Kometani, E. Reichmanis, and L. F. Thompson

J. Vac. Sci. Technol. B 9, 3374 (1991); http://dx.doi.org/10.1116/1.585344 (6 pages)

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An all‐organic chemically amplified positive deep‐ultraviolet resist has been developed that demonstrates 0.35 μm resolution at a dose of ∼18 mJ/cm2 of 248 nm KrF laser radiation. Good critical dimension uniformity and process latitude were demonstrated. Additionally, use of an overcoat material applied immediately after resist coating reduces the dependence of the resist on the time delay between exposure and post‐exposure bake. Efforts relating to process optimization will be described in conjunction with current process performance capabilities and limitations. Additionally, a comparison between triphenylsulfonium hexafluoroarsenate onium salt and nitrobenzyl ester resist formulations will be discussed for select process steps.
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85.40.Hp Lithography, masks and pattern transfer

The relationship between critical dimension shift and diffusion in negative chemically amplified resist systems

Theodore H. Fedynyshyn, Michael F. Cronin, and Charles R. Szmanda

J. Vac. Sci. Technol. B 9, 3380 (1991); http://dx.doi.org/10.1116/1.585345 (7 pages) | Cited 11 times

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Reports of latent image instability in several positive acid catalyzed resists have stimulated interest in the image stability of advanced negative resists (ANR). The critical dimension stability of the chemically amplified ANR resist SAL603 with respect to delay time between the exposure and post‐exposure bake (PEB) steps was determined. Both dense and isolated 1.0 μm features were stable during a 24 h delay period and delay times from 24 h to 48 h resulted in a decrease in linewidth. The method of loss in linewidth as a function of delay time was not due to diffusion of the acid within the film. The threshold crosslink density model was introduced based on several simple assumptions concerning the effect of crosslink density (Θ) on image formation and the relationship of the crosslink density to resist acid concentrations. A method was described whereby the threshold crosslink density model can be used to determine the relative crosslink density of the resist as a function of distance along the feature edge. An analysis of the relative values of crosslink density within the resist was used to show that acid loss and not diffusion was responsible for the change in resist linewidth as a function of delay time.
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization

Metal‐free chemically amplified positive resist resolving 0.2 μm in x‐ray lithography

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

J. Vac. Sci. Technol. B 9, 3387 (1991); http://dx.doi.org/10.1116/1.585346 (5 pages) | Cited 1 time

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A chemically amplified positive resist (EXP) and its processing have been optimized for high resolution in x‐ray lithography. EXP is composed of a novolak resin, 2,2‐bis(t‐butoxycarbonyloxyphenyl)‐propane as a dissolution inhibitor, and bis(p‐t‐butylphenyl)iodonium trifluoromethanesulfonate as an acid generator. Sensitivity and resolution characteristics were greatly influenced by post‐exposure baking (PEB) conditions. Applying PEB at 65 °C for 60 s resulted in the successful fabrication of 0.2‐μm patterns in a 1.3‐μm‐thick EXP film. The pattern width remained virtually unchanged during a three‐hour holding time between x‐ray exposure and PEB. The exposure latitude for ±10% width change for 0.2 μm holes was about 10%.
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85.40.Hp Lithography, masks and pattern transfer

The influence of post‐exposure bake on linewidth control for the resist system RAY‐PN (AZ PN 100) in x‐ray mask fabrication

J. Grimm, J. Chlebek, T. Schulz, and H.‐L. Huber

J. Vac. Sci. Technol. B 9, 3392 (1991); http://dx.doi.org/10.1116/1.585347 (7 pages)

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Statistically designed experiments for optimization in processing the high sensitive negative tone Hoechst resist RAY‐PN (AZ PN 100) were used to establish robust processes for two different applications of the resist: (1) pattern replication on a wafer and (2) during the mask copy process under 40‐mbar He environment via x‐ray lithography. Minimization of linewidth change with respect to a 1:1 pattern transfer was achieved through manipulation of the following variables: exposure dose, post‐exposure bake (PEB) time and temperature, and development time. A two‐stage sequential strategy was employed. After specifying the response and the primary variables, the first stage of the sequential approach was based on a full factorial design. In the second stage, the influence of PEB parameters for wafers as well as for x‐ray mask blanks were studied using a central composite design. Finally, the response surfaces for the pattern replication on x‐ray mask blanks are demonstrated and the optimal process parameter set for a linewidth control within 50 nm for 0.5‐ to 3.0‐μm feature size values are given.
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85.40.Hp Lithography, masks and pattern transfer

Comparative study between gas‐ and liquid‐phase silylation for the diffusion‐enhanced silylated resist process

Ki‐Ho Baik, L. Van den hove, and B. Roland

J. Vac. Sci. Technol. B 9, 3399 (1991); http://dx.doi.org/10.1116/1.585348 (7 pages) | Cited 3 times

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Surface imaging in combination with dry development has been suggested as a means of overcoming the inherent limitations present in conventional wet develop lithography. The diffusion‐enhanced silylated resist process has been demonstrated as one such solution. Silylation is one of the more critical steps in the process, with hexamethyldisilazane being typically used as silylating agent. Alternative gas‐phase silylating agents, such as dimethylsilyldimethyl‐amine, 1,1,3,3‐tetramethyl disilazane and N,N‐dimethylamino trimethylsilane, have additionally been studied [Ki‐Ho Baik et al., J. Vac. Sci. Technol. B 8, 1481 (1990)]. Liquid‐phase silylation holds promise for simplifying the hardware requirements as well as improving silylation properties. Several mono‐functional and polyfunctional silylating agents have been investigated. Bis(dimethylamino)dimethylsilane has been found to be promising. N‐methyl‐2‐pyrrolidone was used as diffusion promoter and xylene as the solvent. The influence of solvent composition on the silylation kinetics has been studied. An in‐depth study of the silylation process has been performed using both Rutherford backscattering spectroscopy (RBS) and Infrared spectroscopy. Si profiles are measured for liquid‐ and gas‐phase silylation using RBS. A possible mechanism is suggested for liquid silylation. Newly formulated resists as well as the influence of a presilylation bake have been studied.
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85.40.Hp Lithography, masks and pattern transfer

X‐ray photoelectron spectroscopy and infrared study of the processing of a silylated positive photoresist

Ruud A. Haring and Kevin J. Stewart

J. Vac. Sci. Technol. B 9, 3406 (1991); http://dx.doi.org/10.1116/1.585349 (7 pages)

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Liftoff processes are being used in microelectronics technology for various metallization steps. In a typical application, a photoresist is spun on top of a soluble polymer, exposed, developed, silylated, and cured. Subsequently, the silylated resist acts as a stencil mask for O2 reactive ion etching (RIE) pattern transfer into the underlying polymer. The generation of debris, leading to etch residues (‘‘grass’’), is a major concern during this process step. The goal of this work is to follow the various process steps that the resist is subjected to, and in particular to determine the effect of ultraviolet (uv) hardening on the silylated resist. We used the complementary techniques of x‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectrophotometry (FTIR) to obtain information on the chemical composition in the surface region and in the bulk of the film. In contrast to conventional baking, uv hardening appears to induce a substantial carbon depletion in the top layer. The aromatic structure of the novolac‐type resist is diminished and the surface exhibits higher siloxane concentration. It is inferred that under O2 RIE patterning, this layer is quickly converted to an etch resistant (sub) oxide and less silicon containing debris is generated in the process than in the case of a baked silylated layer.
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85.40.Hp Lithography, masks and pattern transfer

Development of bilayer resists for deep‐ultraviolet and i‐line application

D. R. McKean, N. J. Clecak, and A. F. Renaldo

J. Vac. Sci. Technol. B 9, 3413 (1991); http://dx.doi.org/10.1116/1.585350 (5 pages) | Cited 2 times

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Bilayer photoresist schemes have the potential of satisfying the many stringent demands associated with the lithographic exposure step. Because the film thickness for this process is quite small, the aspect ratios are increased relative to single layer lithography and hence increased resolution may be obtained. The planarizing layer used in bilayer schemes can also be dyed to avoid reflectivity problems. In this paper the development of a resist for use as the imaging layer in a bilayer resist scheme incorporating oxygen reactive ion etch for image transfer is described. The resist chemistry is based on the coupling reaction(s) of cyclic polyfunctional silanols. The resist is composed of a cyclic silanol, an acid photogenerator, and a phenolic resin. The catalytic nature of the chemistry involved in the resist resulted in high sensitivity during the exposure process. The observed contrast was greater than four for several of the formulations due in part to the unique ‘‘bimodal’’ characteristics of this resist. With sufficient silanol content, high etch resistance was observed and bilayer resist methodology was carried out without loss of film thickness in the exposed regions. Submicron resolution was demonstrated.
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85.40.Hp Lithography, masks and pattern transfer

A top antireflector process for improved linewidth control and alignment

T. A. Brunner, C. F. Lyons, and S. S. Miura

J. Vac. Sci. Technol. B 9, 3418 (1991); http://dx.doi.org/10.1116/1.585351 (5 pages)

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Thin film interference plays a destructive role in optical photolithography in two regards. (1) Large linewidth variations can occur from tiny changes in the thickness of resist or underlying thin films. (2) Asymmetric flow of resist over alignment mark topography can cause optical fringes which result in poor alignment signal profiles. In this paper, a new approach is described which can address both of these issues. A thin, low index, transparent film analogous to a lens antireflector (AR) coat is placed on top of the photoresist film before exposure. The ideal top antireflector (TAR) film would have thickness T=λ/(4n′) and n′=(n)1/2 where n and n′ are the refractive indices of resist and TAR, respectively. Experimental results are presented which show how various TAR layers can improve linewidth control and reduce notching as lines are patterned over topographic steps. In addition, simulations are presented which demonstrate how a TAR layer can improve the alignment signal, for certain types of alignment systems. The TAR process has great potential for high volume, economical semiconductor manufacturing.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
78.66.-w Optical properties of specific thin films
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

In situ ellipsometric measurements of x‐ray resists

Monroe Sullivan, James W. Taylor, and Carl Babcock

J. Vac. Sci. Technol. B 9, 3423 (1991); http://dx.doi.org/10.1116/1.585815 (5 pages)

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This paper presents the results of in situ ellipsometry of x‐ray photoresists during development. PMMA was used to verify the results of previous studies and confirm the validity of the technique and the theoretical models. The technique was then applied to a negative chemically amplified photoresist Microposit XP‐90104C (Shipley). Because the chemically amplified resist uses an aqueous‐base developer (instead of the alcohol solvents such as in the PMMA system), in situ ellipsometry was employed to test the assumption that the resist does not swell during development. No appreciable swelling of exposed XP‐90104C was observed in MF‐322 developer for temperatures below 35 °C. At 40 °C, the onset of swelling was detected. The process of dissolution measured by ellipsometry departed slightly from a theoretical model of uniform film dissolution with an abrupt resist‐developer interface. Scanning electron microscopy (SEM) images of 0.3 μm lines printed with XP‐90104C indicate that surface roughening of the resist may account for the discrepancy of the experimental data from the uniform dissolution model.
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85.40.Hp Lithography, masks and pattern transfer

Lithographic applications of conducting polymers

Marie Angelopoulos, Jane M. Shaw, Kam‐Leung Lee, Wu‐Song Huang, Marie‐Annick Lecorre, and Michel Tissier

J. Vac. Sci. Technol. B 9, 3428 (1991); http://dx.doi.org/10.1116/1.585816 (4 pages) | Cited 8 times

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Electrically conducting polyaniline is found to be suitable for several lithographic applications. Because the polyaniline is not significantly soluble in the conducting state, the material has generally been processed by first applying the soluble, nonconducting version of the material, and in a second step externally doping the polymer film with aqueous acids. We have eliminated the need for this type of external doping by developing methods of inducing the doping in a dry fashion in situ in the polymer. This is accomplished by incorporating onium salts or amine triflate salts in the polyaniline which decompose upon radiation or thermal treatment, respectively, to generate the active dopant species, i.e., protonic acids. The use of these in situ dopants simplifies the processing of the conducting polyaniline and makes the material more convenient for lithographic applications. With the use of onium salts, the polyaniline is made into a high resolution negative conducting resist. 0.25 μm conducting lines have been patterned with e‐beam radiation. Polyaniline is found to be an effective discharge layer for e‐beam lithography and a removable discharge layer for the high resolution inspection and dimensional measurements of x‐ray and optical masks by scanning electron microscopy (SEM). In addition, the polyaniline can be used for both electrolytic and electroless‐type metallization processes.
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85.40.Hp Lithography, masks and pattern transfer
82.35.-x Polymers: properties; reactions; polymerization

Surface imaging of focused ion‐beam exposed resists

M. A. Hartney, D. C. Shaver, M. I. Shepard, J. Melngailis, V. Medvedev, and W. P. Robinson

J. Vac. Sci. Technol. B 9, 3432 (1991); http://dx.doi.org/10.1116/1.585817 (4 pages) | Cited 2 times

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Silylation processes have previously been applied to optical lithography to overcome deleterious substrate effects and to achieve smaller linewidths. We have applied silylation to focused ion‐beam (FIB) lithography, thereby eliminating the need for exposure throughout the entire resist thickness. This approach permits the use of Ga+ ions which have a limited range in the resist but are available from high brightness sources. Thus FIB lithography writing speed can be dramatically improved. Sensitivity of 8×1011 ions/cm2 was found with 30‐keV Ga+ using SAL 601 resist, and linewidths below 100 nm have been demonstrated.
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85.40.Hp Lithography, masks and pattern transfer

Silicon‐containing resist for phase‐shifting masks

Hisashi Watanabe, Yoshihiro Todokoro, and Morio Inoue

J. Vac. Sci. Technol. B 9, 3436 (1991); http://dx.doi.org/10.1116/1.585818 (4 pages) | Cited 1 time

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A novel silicon‐containing chemical amplified resist has been developed for a shifter layer of phase‐shifting masks. The resist is composed of an alkaline‐soluble silicone polymer and onium salt as an acid generator. The base polymer has a ladder structure and contains a methyl group as a side group and ethoxy and hydroxy groups as an end group. Shifter patterns were directly fabricated on mask substrates by electron‐beam exposure and development of the new resist. Improved resolution using an i‐line stepper can be achieved with the phase‐shifting mask having the new silicon‐containing resist shifter.
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85.40.Hp Lithography, masks and pattern transfer

Modeling of shot noise in x‐ray photoresist exposure

S. Turner, C. Babcock, and F. Cerrina

J. Vac. Sci. Technol. B 9, 3440 (1991); http://dx.doi.org/10.1116/1.585819 (7 pages) | Cited 5 times

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New photoresist technologies yielding higher resist sensitivities together with the greater photon energies inherent in x‐ray lithography put lithography systems closer and closer to the shot noise limit. Thus there is a need to address the effects of shot noise on resist exposure. We will present the description of a stochastic model, and its implementation in a simulator, which emulates the exposure process by effecting what amounts to a photon‐by‐photon treatment of the problem, thereby taking into account the effects of shot noise. The model starts with an aerial image, computed using a deterministic model based on Fresnel diffraction, interprets it as the probability density function (pdf) for the distribution of the photons. The stochasticity of the process is taken into account by randomly generating a finite number of events (photons) whose distribution follows the pdf. The penetration depths are stochastically predicted according to the appropriate distribution. At the point predicted, the incident energy is redistributed according to a point spread function or a full Monte Carlo method. The superposition of all of the photons provides us with the latent image. The dissolution process is then modeled using a stochastic cell dissolution model. We will present results of practical importance for chemically amplified resist systems and correlate the results with observations made in the laboratory.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Deep ultraviolet patterning of monolayer films for high resolution lithography

Jeffrey M. Calvert, Mu‐San Chen, Charles S. Dulcey, Jacque H. Georger, Martin C. Peckerar, Joel M. Schnur, and Paul E. Schoen

J. Vac. Sci. Technol. B 9, 3447 (1991); http://dx.doi.org/10.1116/1.585820 (4 pages) | Cited 6 times

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A new process has been developed for high resolution photolithography that employs chemisorbed monolayer films as the surface imaging layers. Organosilane treated surfaces are exposed to patterned deep UV radiation, either from excimer laser or lamp sources. The photochemical process modifies the surface wettability and reactivity of the film. Organosilane films patterned by deep UV radiation are treated with a Pd/Sn catalyst and then metallized with electroless copper and nickel baths to yield metal films several 100 Å thick. The metal is selectively deposited in the unexposed regions of the film to produce a positive tone image. The patterned metal film is then utilized as a plasma hard etch barrier in a reactive ion etch, allowing efficient pattern transfer into the underlying substrate and producing features with linewidths to 0.4 μm. Electrical testing of processed substrates demonstrates compatibility of the process with subsequent device performance, and working transistor test structures have been fabricated. Decoupling the imaging (monolayer surface imaging layer) and resist (metal film) functions of a photoresist allows separate optimization of each function in this scheme. The patterning process is very general and may be applied to a variety of substrate types. Other potential applications include patterned wettability and reactivity of surfaces for selective attachment of other species such as fluorophores or biological moieties.
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85.40.Hp Lithography, masks and pattern transfer

Structural damage induced by Ga+ focused ion beam implantation in (001) Si

C. H. Chu, Y. F. Hsieh, L. R. Harriott, and H. H. Wade

J. Vac. Sci. Technol. B 9, 3451 (1991); http://dx.doi.org/10.1116/1.585821 (5 pages) | Cited 4 times

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Ga+ focused ion beam (FIB) implantation in (001) Si was conducted in our JEOL JIBL‐104UHV FIB system. Ga+ ions with energy of 100 kV were implanted into silicon at doses from 1×1014 to 1×1016 /cm2. The current and current density of the Ga+ FIB are 20 pA and 1 A/cm2, respectively. We have made patterns consisting of single‐pixel lines with various spacings and rectangular areas of different sizes. The critical dose to form a continuous amorphous region in rectangle‐scanned samples is less than 5×1014 /cm2. The samples were annealed either in vacuum or a rapid thermal annealing furnace at 550–800 °C for 1/2 h and 60 s, respectively. Both cross‐sectional and plan‐view transmission electron microscopy were conducted to investigate the lattice disorder and residual defects in as‐implanted and post‐implantation annealed samples. After thermal annealing, dislocation lines and loops were observed along the line direction in line‐scanned samples. In rectangle‐scanned samples, dislocation lines and loops near the original amorphous/crystalline (a/c) interface, as well as edge defects along the edge of the rectangle were found.
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61.72.uf Ge and Si
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.80.Jh Ion radiation effects

Optical studies of direct modulation doping and quantum wire formation by focused Si on beam implantation

Y. J. Li, S. Sasa, W. Beinstingl, M. S. Miller, Z. Xu, G. Snider, and P. M. Petroff

J. Vac. Sci. Technol. B 9, 3456 (1991); http://dx.doi.org/10.1116/1.585822 (3 pages) | Cited 3 times

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The two‐dimensional electron gas (2DEG) produced by a Si++ focused ion beam implantation into GaAs–AlGaAs quantum well structures grown by molecular beam epitaxy (MBE) has been studied by low temperature (15 K) cathodoluminescence (CL), photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopy. Ion channeling effects were used and the Si ion activation was optimized during the rapid thermal annealing following the implantation. PL and PLE measurements were first performed in situ the electron microscope together with the CL to evaluate the 2DEG formation in a uniformly implanted pattern. The localized 2DEG created by linear modulation doping (line dose 1.5×108 ions/cm) was imaged, and a local band bending of ∼25 meV was determined from the monochromatic CL line scanning.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Fabrication of optical beamwidth transformers for guided waves on InP using wedge‐shaped taper structures

R. Zengerle, H.‐J. Brückner, H. W. P. Koops, H.‐J. Olzhausen, G. Zesch, A. Kohl, and A. Menschig

J. Vac. Sci. Technol. B 9, 3459 (1991); http://dx.doi.org/10.1116/1.585823 (5 pages) | Cited 2 times

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A waveguide device is proposed for spot‐size transformation of an optical beam from the 1 μm range to about 8 μm using a wedge‐shaped taper. The structure can be entirely integrated on an InP‐based optoelectronically integrated circuit. It is shown by numerical simulation that the width of the thin end of the wedge has a major influence on the transformation loss of such a device. By using direct writing e‐beam lithography and reactive ion etching as well as subsequent InP regrowth, we were able to produce the required structures. The beamwidth transformation capability is confirmed by optical measurements.
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42.82.-m Integrated optics
42.81.Qb Fiber waveguides, couplers, and arrays

Criterion to judge whether the resist heating effect will occur

Kenich Saito and Tomoaki Sakai

J. Vac. Sci. Technol. B 9, 3464 (1991); http://dx.doi.org/10.1116/1.585824 (6 pages)

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A specific criterion for judging whether the resist heating effect will occur under given beam and resist conditions is proposed. The criterion is directly applicable to direct‐writing variably shaped electron‐beam systems and chain‐scission type resists. After studying the relationship between resist temperature and pattern deformation, it is hypothesized then verified experimentally that pattern deformation occurs when temperature at the shot edge point is higher than the glass transition temperature of the resist. Experiments revealed that chemically amplified resists are more resistant to the resist heating effect than chain‐scission type resists. Applying the hypothesis to resist temperature calculations, a constant figure was derived that represents the criterion for high‐throughput writing systems. The figure suggests the beam and resist conditions that are required for high‐throughput pattern writing without the resist heating effect.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Thermal effects in high voltage e‐beam lithography

E. van der Drift, A. C. Enters, and S. Radelaar

J. Vac. Sci. Technol. B 9, 3470 (1991); http://dx.doi.org/10.1116/1.585825 (5 pages) | Cited 5 times

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Modeling of resist heating for 50‐ and 100‐kV e‐beam exposures of single layer resist on silicon wafers and quartz mask plates is reported. The resist heating from energy dissipation in both the thin resist layer itself and the underlying substrate has been taken into account. A variety of single spot exposure situations are considered to put forward the main features for minimization of thermal effects. Modeling results are compared with experimental results reported in literature. The future perspective for resist heating control in high throughput e‐beam writing is illustrated with a practical example.
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85.40.Hp Lithography, masks and pattern transfer

Electron beam induced metalization of palladium acetate

T. J. Stark, T. M. Mayer, D. P. Griffis, and P. E. Russell

J. Vac. Sci. Technol. B 9, 3475 (1991); http://dx.doi.org/10.1116/1.585826 (4 pages) | Cited 3 times

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Films of palladium acetate Pd(OOCH3)2 0.1 and 0.3 μm thick have been stoichiometrically altered through exposure to electron beams of 1–30 keV. The lowest required doses for alteration, 1000 and 2500 μC/cm2, were obtained using beam energies of 4 and 5 keV, respectively. These results have been related to Monte Carlo simulations of energy absorbed within a thin surface film. The minimum line widths of features produced was less than 100 nanometers with estimated Pd/C ratio of 1 and measured resistivities as low as 100 μΩ cm.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Optical properties of quantum structures fabricated by focused Ga+ ion beam implantation

W. Beinstingl, Y. J. Li, H. Weman, J. Merz, and P. M. Petroff

J. Vac. Sci. Technol. B 9, 3479 (1991); http://dx.doi.org/10.1116/1.585827 (4 pages) | Cited 3 times

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High energy focused ion beam implantation of Ga is used to interdiffuse AlGaAs/GaAs quantum wells. Results from low temperature cathodoluminescence, time‐decay photoluminescence measurements and photolumuniscence excitation spectroscopy indicate a good quality of the interdiffused quantum wells. The broadened luminescence peaks are explained by spatial inhomogeneities of the interdiffusion. Quantum boxes were fabricated and studied by cathodoluminescence line scanning. The introduction of a few monolayers of InGaAs close to the quantum well resulted in a remarkable improvement of the homogeneity of the interdiffusion.
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78.66.Fd III-V semiconductors
78.66.Hf II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers

Direct writing of iridium lines with a focused ion beam

P. Hoffmann, H. van den Bergh, J. Flicstein, G. Ben Assayag, J. Gierak, and J.‐F. Bresse

J. Vac. Sci. Technol. B 9, 3483 (1991); http://dx.doi.org/10.1116/1.585828 (4 pages) | Cited 4 times

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Direct writing of metal features narrower than 100 nm is accomplished by scanning a focused ion beam over a substrate covered with a thin solid metalorganic film. A metalorganic cluster coordination compound [Ir4(CO)11Br][N(C2H5)4] is spun on an oxidized silicon wafer from acetone solution and the resulting layer is irradiated with a focused 20 keV Ga‐ion beam. The partially decomposed irradiated film regions show a marked decrease of solubility in acetone. Developing by dissolving the nonirradiated parts of the surface hence leaves narrow lines of partially reacted metalorganic precursor. High temperature treatment of these lines, either in vacuum or in a reactive gas stream, completes the decomposition to quite pure iridium, as is confirmed by micro‐Auger analysis. In these preliminary experiments we obtained lines with room temperature electrical resistivities as low as 400 μΩ cm, at direct writing speeds of 40 μm s−1 to 0.8 mm s−1, which correspond to ion doses of 3.1×1016 ions/cm2 to 1.6×1015 ions/cm2, respectively. The width of the metal lines decreases with decreasing ion dose in this range from 180 down to 90 nm. The adhesion to the substrate increases with increasing ion dose. The thickness of the resulting iridium lines depends mainly on the thickness of the metalorganic precursor layer. The maximum possible thickness of the [Ir4(CO)11Br][N(C2H5)4] layer that can be used depends on the effective penetration depth of the ions in this layer.
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85.40.Hp Lithography, masks and pattern transfer

Plasma particulate contamination control. I. Transport and process effects

Gary S. Selwyn

J. Vac. Sci. Technol. B 9, 3487 (1991); http://dx.doi.org/10.1116/1.585829 (6 pages) | Cited 29 times

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The transport and behavior of particulates during plasma processing is imaged in real time using rastered laser light scattering combined with video detection. Results show the distribution of particles is highly ordered and predictable. Two effects have major influence on the distribution and location of particles: feed gas drag and electrostatic traps. Particle traps form from plasma disturbances and design properties of the electrode and the tooling. These results are confirmed in normal plasma conditions used in microelectronics fabrication. A strategy is presented for plasma contamination control. Complete elimination of trapping effects is not feasible. Instead, process techniques are used to minimize or defeat the attractive nature of the traps. Several examples are discussed.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
52.25.Vy Impurities in plasmas
52.25.Fi Transport properties
81.15.Cd Deposition by sputtering

Circular polarized electron cyclotron resonance source

S. Pongratz, R. Gesche, K.‐H. Kretschmer, G. Lorenz, M. Hafner, and J. Zink

J. Vac. Sci. Technol. B 9, 3493 (1991); http://dx.doi.org/10.1116/1.585830 (5 pages) | Cited 2 times

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This paper describes the first results of the new Leybold Leybold circular electron cyclotron resonance (CECR) technology which uses circular polarized microwave excitation for generating a plasma of very high density. At a pressure of 1 μbar, an ion current density of 6 mA/cm2 was measured in a pure chlorine plasma. That reveals in fact an increase of about 30% in ion density compared to the linear polarized electron cyclotron resonance (ECR) source. The appreciable improvement will be demonstrated by etching results of silicon trench with chlorine where an etch rate of 300 nm/min with a uniformity better than ±5% on 200 mm wafer size was obtained. The source has a compact design which enables multichamber processing in a cluster tool environment with the capability for processing wafers up to 200 mm diameter.
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52.50.Dg Plasma sources

Strain‐induced lateral confinement of excitons in GaAs/AlGaAs quantum well by chemical dry etching

I.‐H. Tan, D. G. Lishan, R. Mirin, V. Jayaraman, T. Yasuda, C. B. Prater, E. L. Hu, J. E. Bowers, and P. K. Hansma

J. Vac. Sci. Technol. B 9, 3498 (1991); http://dx.doi.org/10.1116/1.585831 (4 pages) | Cited 5 times

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HCl radical beam etching has been used to produce strain‐induced lateral confinement of excitons in a GaAs quantum well. This confinement was generated by etching a grating pattern into a strained layer of In0.35Ga0.65As which overlies the GaAs quantum well. Atomic force microscopy was used to examine the etched surface morphology. Photoluminescence and excitation photoluminescence spectroscopy were used to detect the optical transitions. The after‐etch photoluminescence intensity and the systematic peak shift with etch time indicate the degree of control and low‐damage nature of the etch process used.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena
81.65.-b Surface treatments

Electron cyclotron resonance plasma preparation of GaAs substrates for molecular beam epitaxy

Kent D. Choquette, M. Hong, Robert S. Freund, J. P. Mannaerts, and Robert C. Wetzel

J. Vac. Sci. Technol. B 9, 3502 (1991); http://dx.doi.org/10.1116/1.585832 (4 pages) | Cited 9 times

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We report the preparation of GaAs substrates, using only electron cyclotron resonance plasma techniques, and the subsequent growth of GaAs by molecular beam epitaxy, accomplished within an integrated processing facility. Exposure of the substrates to a hydrogen plasma with an ion current density less than 3 mA/cm2 for 1 h removes the native GaAs oxide leaving a smooth crystalline surface as revealed by streaky (1×1) reflection high energy electron diffraction patterns. At a greater ion current density a spotty diffraction pattern is obtained; a subsequent SiCl4 plasma etch restores a streaky (1×1) diffraction pattern. After plasma processing, evidence of surface reconstruction is observed at substrate temperatures greater than 400 °C in an As overpressure and during GaAs overgrowth. Impurity concentrations at the epilayer/substrate interfaces of plasma‐prepared samples are found to be comparable to those of chemically prepared wet etched substrates. This vacuum substrate preparation scheme is a first step toward realizing the benefits of integrated device processing.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Self‐aligned high electron mobility transistor gate fabrication using focused ion beams

G. M. Atkinson, R. L. Kubena, L. E. Larson, L. D. Nguyen, F. P. Stratton, L. M. Jelloian, M. V. Le, and H. McNulty

J. Vac. Sci. Technol. B 9, 3506 (1991); http://dx.doi.org/10.1116/1.585833 (5 pages) | Cited 1 time

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A new gate fabrication technique has been developed based on focused ion beam exposure and reactive ion etching of a polymethylmethacrylate (PMMA)/Ge/PMMA multilevel resist structure. The focused ion beam exposes the thin PMMA imaging layer that is transferred directly to the germanium layer using reactive ion etching (RIE). The underlying resist is etched first in oxygen at high pressure, providing an undercut, bowl‐shaped profile, followed by an extremely low pressure, anisotropic oxygen process, which etches a narrow stem down to the base of the resist, resulting in a chalice‐shaped profile. Removing the germanium layer allows the profile to be used to lift off the Ti/Pt/Au gate. This process is compatible with our self‐aligned gate high electron mobility transistor (HEMT) process and provides an alternative technique for gate fabrication below 75 nm. Focused ion beam gate structures have been fabricated with 60 nm gate length and 0.15 μm2 cross section using this technique and shown that the resulting gate profile can be used to shadow a 200 nm thick Ohmic contact evaporation to form the self‐aligned structure with a source/drain spacing of 225 nm. It has also been determined that ion bombardment damage to the HEMT channel during RIE can be eliminated by limiting the plasma potential to less than 45 V.
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85.40.Hp Lithography, masks and pattern transfer
85.30.Pq Bipolar transistors

Superconducting‐normal metal interfaces produced by reactive ion etching

K. Lin, Y. K. Kwong, M. Park, J. M. Parpia, and M. S. Isaacson

J. Vac. Sci. Technol. B 9, 3511 (1991); http://dx.doi.org/10.1116/1.585834 (5 pages)

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We have used CHF3/O2 reactive ion etching to reliably change the superconducting transition temperature (Tc) of aluminum thin films by 10–50 mK. Microanalyses using scanning Auger and scanning electron microscopy (SEM) indicate that the etching process results in a surface layer of high fluorine and low oxygen contents. The analyses show that photolithography and etching can produce very sharp interfaces between etched (lowered Tc) and unetched (higher Tc) regions. This technique is applied to study two specific configurations. First, long strips of aluminum thin films are patterned with a periodic structure of alternating regions of high and low Tc. The resistive transition of these films shows a surprisingly long proximity effect with a length scale of more than 50 μm, nearly two orders of magnitude greater than expected from established theory. Second, an aluminum strip with a single S–N–S (high–low–high Tc ) structure possesses a resistive anomaly just above the lower Tc. This anomaly depends on the position of the measurement voltage probes relative to the interfaces and appears to have a length scale of several μm.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
81.05.Bx Metals, semimetals, and alloys
81.40.Rs Electrical and magnetic properties related to treatment conditions

Investigation of radical‐beam ion‐beam etching‐induced damage in GaAs/AlGaAs quantum‐well structures

J. A. Skidmore, D. L. Green, D. B. Young, J. A. Olsen, E. L. Hu, L. A. Coldren, and P. M. Petroff

J. Vac. Sci. Technol. B 9, 3516 (1991); http://dx.doi.org/10.1116/1.585835 (5 pages) | Cited 3 times

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Dry etching‐induced damage is investigated using radical‐beam ion‐beam etching. This technique allows the systematic study of process‐induced damage over a wide range of etching rates and with varying components of physical and chemical etching. Induced damage is characterized by I‐V measurements from Schottky diodes on etched surfaces and from luminescence from quantum wells situated in close proximity to etched surfaces. We have designed a novel multiple‐quantum‐well probe structure that also includes a 4000 Å‐thick quarter‐wavelength mirror stack layer to allow in situ monitoring of etch rate and etched depth. Our work examines damage as a function of ion beam voltage and beam current density, microwave power, and with and without a reactive gas. We have found that damage increases with increased ion energy and decreases with etch yield.
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81.65.-b Surface treatments
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Anisotropic etching of submicron silicon features in a 23 cm diameter microwave multicusp electron‐cyclotron‐resonance plasma reactor

B. D. Musson, F. C. Sze, D. K. Reinhard, and J. Asmussen

J. Vac. Sci. Technol. B 9, 3521 (1991); http://dx.doi.org/10.1116/1.585836 (5 pages) | Cited 2 times

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The performance of a large diameter, 2.45 GHz multicusp electron‐cyclotron‐resonance (ECR) plasma etching system with regard to etch rate uniformity and submicron pattern definition in silicon is described. Results are compared to earlier work on a similar system operated at 915 MHz. The plasma source utilizes a 23 cm diam discharge and a 12‐pole static magnetic field geometry to create multicusp ECR zones in the plasma excitation region. Microwave excitation at 2.45 GHz with power levels up to 600 W is used to excite discharges for etching of single 125 mm diam wafers and multiple 75 mm diam wafers. For single 125 mm wafers with oxide masks the 3σ variation of silicon etch rate uniformity was 2.3% and for multiple 75 mm wafers with aluminum masks the 3σ variation was 8.1% over a 150 mm diam. Vertical anisotropic etching was obtained both at the center of the wafers and the peripheries. Etch profiles were evaluated as a function of position on the substrate and no substantial positional or orientation effects were observed. Microloading effects appear small for both oxide and aluminum masks. Submicron (0.6 μm) trenches and holes were anisotropically etched in silicon and show approximately a 5% lower etch rate than large (>5 μm) features. For the relatively low microwave input power densities used, etch rates ranged from 40 to 140 nm/min as the SF6 ratio ranged from 5% to 15%.
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81.65.-b Surface treatments
52.40.Hf Plasma-material interactions; boundary layer effects

Investigations of dry etching in AlGaInP/GaInP using CCl2F2/Ar reactive ion etching and Ar ion beam etching

J. Hommel, M. Moser, M. Geiger, F. Scholz, and H. Schweizer

J. Vac. Sci. Technol. B 9, 3526 (1991); http://dx.doi.org/10.1116/1.585837 (4 pages) | Cited 1 time

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We report on investigations of dry etching in GaInP/AlGaInP. As a method of dry etching we used CCl2F2/Ar reactive ion etching (RIE) and Ar ion beam etching (IBE). The suitability of these two methods for microstructure technology with respect to etch rates in investigated. First data on damage resulting from application of these two dry etching techniques in GaInP/AlGaInP are presented. The degree of damage was detected by performing photoluminescence measurement.
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81.65.-b Surface treatments

Etching of GaAs and InP using a hybrid microwave and radio‐frequency system

S. W. Pang, Y. Liu, and K. T. Sung

J. Vac. Sci. Technol. B 9, 3530 (1991); http://dx.doi.org/10.1116/1.585838 (5 pages) | Cited 4 times

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A hybrid system consisting of a multipolar electron cyclotron resonance source driven by a microwave power supply at 2.45 GHz and a radio‐frequency (rf) powered electrode at 13.56 MHz is used for the etching of GaAs and InP. Both CCl2F2 and Cl2 are used as the gas sources, and the effect of rf and microwave power, pressure, as well as flow rate on etch rate and surface morphology are evaluated. Fast etch rate up to 3.4 μm/min is obtained for GaAs. Etch rate increases with rf power and decreases with microwave power when CCl2F2 is used. Optical emission and x‐ray photoelectron measurements indicate that more C‐related compounds are generated when microwave power is on. With Cl2 addition, etch rate increases with microwave power and smoother morphology is obtained. Etching for InP yields smooth morphology at a typical rate of 50 nm/min.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer

Anisotropic reactive ion etching of InP in methane/hydrogen based plasmas

J. W. McNabb, H. G. Craighead, H. Temkin, and R. A. Logan

J. Vac. Sci. Technol. B 9, 3535 (1991); http://dx.doi.org/10.1116/1.585839 (3 pages) | Cited 14 times

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Reactive ion etching of InP in CH4/H2 has been studied to assess anisotropy and surface morphology. Empirical models have been developed for etch and polymer deposition rates. Highly anisotropic features characterized by high ratios of etch to polymer formation rates are obtained at low methane concentration and relatively high power density. The inclusion of oxygen in the gas composition reduces polymer deposition but increases surface roughness.
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81.65.-b Surface treatments

Selective reactive ion etching of GaAs/AlGaAs metal‐semiconductor field effect transistors

N. I. Cameron, G. Hopkins, I. G. Thayne, S. P. Beaumont, C. D. W. Wilkinson, M. Holland, A. H. Kean, and C. R. Stanley

J. Vac. Sci. Technol. B 9, 3538 (1991); http://dx.doi.org/10.1116/1.585840 (4 pages) | Cited 2 times

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The high selectivity between the etch rates of GaAs and AlxGa1−xAs or AlAs obtained in plasmas containing both chlorine and fluorine is widely used to obtain accurate and uniform etching of molecular beam epitaxy grown high electron mobility transistor and (less commonly) metal‐semiconductor field‐effect transistor (MESFET) layers. The influence of gas residence time on the selectivity of GaAs to Al0.3Ga0.7As in CCl2F2 reactive ion etching (RIE) at 50 V dc bias is investigated, finding that maximum selectivity (>4000 to 1) and maximum GaAs etch rate (1.75 μm/min) are achieved with a residence time for CCl2F2 of between two and four seconds. No evidence of any significant damage to MESFET layers when overetching a 50 Å Al0.3Ga0.7As etch stop was observed at these RIE conditions by either Hall measurements or by CV and IV characterization of Schottky diodes. MESFETs with 0.2 μm gates recessed in CCl2F2 show good dc and microwave performance.
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85.30.Tv Field effect devices
81.65.-b Surface treatments

In situ device electrical parameter adjustment and monitoring during remote plasma dry etching

David G. Lishan, Gregory L. Snider, and Evelyn L. Hu

J. Vac. Sci. Technol. B 9, 3542 (1991); http://dx.doi.org/10.1116/1.585841 (4 pages)

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By monitoring device electrical parameters during remote plasma dry etching, we have demonstrated a novel method for in situ adjustment of saturation currents. Time‐elapsed I‐V curves and current‐versus‐time plots illustrate the low damage, controllable gate recess etching of a metal‐semiconductor field‐effect transistor device structure and two different high electron mobility transistors. Using a one‐dimensional Poisson solver, simulations of conduction versus depth are made and discussed in relation to experimental results.
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85.30.Tv Field effect devices
81.65.-b Surface treatments

Optical studies of dry etched GaAs

O. J. Glembocki, B. E. Taylor, and E. A. Dobisz

J. Vac. Sci. Technol. B 9, 3546 (1991); http://dx.doi.org/10.1116/1.585842 (5 pages) | Cited 3 times

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Reactive‐ion etching (RIE) and chemically assisted ion‐beam etching are routinely used in the fabrication of submicrometer features. Both techniques are known to produce electrical damage. We have used a combination of Raman spectroscopy and photoreflectance to study the effects of dry etching on the depletion layer width and built‐in electric field of heavily doped GaAs. We find that RIE reduces the built‐in electric field and at the same time increases the depletion layer width. These results can be understood in terms of the formation of a more insulating layer near the surface. Our analysis shows that even though the Fermi‐level pinning position can change, the predominant effect of dry etching is to change the carrier density of the near‐surface region. We also observe that the use of chlorine‐based species in the etch reduces the electrical damage.
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81.65.-b Surface treatments
85.40.Hp Lithography, masks and pattern transfer
61.80.Jh Ion radiation effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Etching of indium tin oxide in methane/hydrogen plasmas

I. Adesida, D. G. Ballegeer, J. W. Seo, A. Ketterson, H. Chang, K. Y. Cheng, and T. Gessert

J. Vac. Sci. Technol. B 9, 3551 (1991); http://dx.doi.org/10.1116/1.585843 (4 pages) | Cited 5 times

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The reactive ion etching of the transparent conductor, indium tin oxide (ITO), in methane/hydrogen plasmas has been characterized. It is shown that ITO can be selectively etched on GaAs and AlGaAs. Anisotropic structures and gratings with submicrometer dimensions in ITO are presented. Application of the etching process to the fabrication of highly sensitive metal–semiconductor–metal (MSM) photodetectors with interdigitated ITO fingers is demonstrated.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
85.60.Gz Photodetectors (including infrared and CCD detectors)

Statistics of pattern placement errors in lithography

T. R. Groves

J. Vac. Sci. Technol. B 9, 3555 (1991); http://dx.doi.org/10.1116/1.585844 (7 pages)

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The placement of pattern features in lithography must be accurate to within some small fraction of the minimum feature size or critical dimension (CD). As CDs decrease over the years, driven by the demand for high density memory, the requirements on pattern placement become accordingly more stringent. A practical problem exists: after a wafer or mask is written, a binary decision must be made, based on a set of measurements, whether the pattern placement is deemed acceptably accurate. Based on this decision, the substrate will either be retained for further processing, or discarded. The large number of pattern features, together with the slowness of present‐day metrology, cause the acceptance decision to be based on measurement of a tiny fraction of all features in the pattern. It is a classic problem in sampling statistics. A proper analysis relies on the probability that any feature, were it to be measured, would have a placement error exceeding some predetermined limit. In practice errors contain both systematic and random components. Systematic errors include magnification, orthogonality, and distortion, to name a few. Random errors arise from noise and jitter in the lithography or metrology tool, for example. The purpose of this paper is to derive a criterion for the binary acceptance decision, which is useful in the presence of combined systematic and random errors. The distribution of systematic errors is shown to be proportional to the area between the lines of a contour map of the error. The method is applied to an e‐beam written mask for x‐ray lithography. It is shown that conventional variance analysis is inadequate for predicting the error rate.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
06.20.Dk Measurement and error theory
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Submicron Si trench profiling with an electron‐beam fabricated atomic force microscope tip

Kam L. Lee, David W. Abraham, F. Secord, and L. Landstein

J. Vac. Sci. Technol. B 9, 3562 (1991); http://dx.doi.org/10.1116/1.585845 (7 pages) | Cited 18 times

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The atomic force microscope (AFM) has the potential for profiling on a nanometer scale. However, for the AFM to be useful as a reliable and accurate metrology tool, the atomic force sensor used (i.e., cantilever and sensor tip) should be highly reproducible in the fabrication process and the tip shape used should be known with high accuracy. Moreover, for profiling and critical dimension measurement of device trenches with submicron openings and trench depth of 1 μm or more, nanometer‐scale tip shapes with high aspect ratio will be required. In order to meet the above requirement, a novel high‐resolution direct electron‐beam deposition process has been developed in which a sharp tip is grown onto an existing Si cantilever structure. In the example to be discussed, sharp tips have been grown directly on the integrated tip of a micromachined Si cantilever by decomposition of a dimethyl‐gold organometallic complex. The direct e‐beam deposition process provides a unique capability for the controllable fabrication of high aspect ratio, nanometer‐scale tip structures. Typical dimensions of the AFM tips achieved are 0.1 μm in column diameter, 1–4 μm high, and 15 nm in tip radius. Recent feasibility experiments of using these e‐beam tips in the laser force microscope have demonstrated for the first time that this nano‐scale tip can be used for mapping 1‐μm‐deep Si trenches. Submicron trenches with openings as small as 0.36 μm have been successfully profiled. In this paper, various issues on tip fabrication, deep trench profiling and comparision of AFM and corresponding scanning electron microscopy measurements will be discussed.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Scanning probe tip geometry optimized for metrology by focused ion beam ion milling

M. J. Vasile, D. Grigg, J. E. Griffith, E. Fitzgerald, and P. E. Russell

J. Vac. Sci. Technol. B 9, 3569 (1991); http://dx.doi.org/10.1116/1.585846 (4 pages) | Cited 24 times

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We have developed a novel technique for producing tips for scanning probe microscopy. The shape of the tip is optimized for applications where high aspect ratio surface topography is the norm, as with integrated circuit structures. The technique involves focused ion beam (FIB) milling of a tip which was previously shaped to a nominal geometry by electrochemical etching. The ion milling pattern is annular, and the ion beam is collinear with the axis of the tip. The process allows control of the ion milling dose using 20 keV Ga+ with submicron control of the annular patterns. The result is a narrow, tapered structure approximately 20 μm in length which ends in a point with a radius of curvature between 30 and 50 nm when grains dominate the sputter process, and radii of about 3–4 nm when there is no evidence of grain structure effects. This microstructure is 3 μm in diameter at the base and it protrudes from a portion of the shank of the macrostructure where the diameter is about 15 μm. We have sufficient control over the sputter process to yield the final tip length, taper, and radius. Cone angles between 12° and 15° over the first two microns from the apex can be achieved routinely, by the correct choice of annulus and ion dose. Sputter simulations predict the correct shape of the final tip profile, and show the effect of varying the ion beam focus, dose, and inner and outer annulus radii. Tips with the desired geometry have been produced in polycrystalline tungsten, iridium, and platinum‐iridium. Significant improvements in scanning tip microscopy (STM) images have been consistently observed with these FIB milled tips.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

A new high‐speed simulation method for electron‐beam critical dimension metrology profile modeling

Xinlei Wang and David C. Joy

J. Vac. Sci. Technol. B 9, 3573 (1991); http://dx.doi.org/10.1116/1.585847 (5 pages)

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Critical dimension metrology relies on the analysis of electron‐beam signal profiles from structures of arbitrary size and shape. Conventional modeling techniques for simulating such profiles use Monte Carlo techniques which, while very accurate, require considerable computing time since any change in any parameter necessitates a complete new calculation. This paper describes an alternative approach in which a Monte Carlo simulation is used to derive the coefficients of a diffusion matrix. From this matrix the backscattering and secondary electron profiles from a surface of given geometry can be found by simple summation, and the results of a change in the geometry can be determined immediately without the need for further computation. The predictions of this method are in excellent agreement with those of the conventional approach.
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68.35.B- Structure of clean surfaces (and surface reconstruction)

An elastic cross section model for use with Monte Carlo simulations of low energy electron scattering from high atomic number targets

R. Browning, T. Eimori, E. P. Traut, B. Chui, and R. F. W. Pease

J. Vac. Sci. Technol. B 9, 3578 (1991); http://dx.doi.org/10.1116/1.585848 (4 pages) | Cited 14 times

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The form of the screened Rutherford elastic scattering cross section has been modified to approximate the Mott scattering cross section for low energy electrons interacting with high atomic number targets, both for the total and the differential elastic cross section. A modified form of the total scattering cross section has been found that fits the Mott scattering cross section derived using a partial wave expansion. The fit is from atomic number 6–92 over the energy range 1–100 keV. The differential elastic cross section has been modeled using a screened Rutherford distribution plus an isotropic distribution. The ratio of forward to backscattering found from the Mott cross section was used as a fitting criteria. The screened Rutherford distribution is fitted to the forward scattering half‐angle of the Mott distribution and the size of the isotopic distribution is then adjusted to give the correct forward to backscattering ratio. This differential form has been used in a Monte Carlo simulation of the backscattering from Au. Both the total and the differential cross sections are straightforward to implement in a Monte Carlo simulation of electron/target scattering.
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34.80.Bm Elastic scattering

Alignment and registration schemes for projection electron lithography

R. C. Farrow, S. D. Berger, J. M. Gibson, J. A. Liddle, J. S. Kraus, R. M. Camarda, and H. A. Huggins

J. Vac. Sci. Technol. B 9, 3582 (1991); http://dx.doi.org/10.1116/1.585849 (4 pages) | Cited 1 time

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Techniques for doing alignment and registration in projection electron lithography are reviewed. The issues associated with extending these techniques to the case of high incident electron energy exposure are discussed. Measurements of backscatter electron emission contrast from W markers on Si wafers at 200 kV show that mark detection within the expected range of voltages is feasible.
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85.40.Hp Lithography, masks and pattern transfer

Characterization of scanning probe microscope tips for linewidth measurement

J. E. Griffith, D. A. Grigg, M. J. Vasile, P. E. Russell, and E. A. Fitzgerald

J. Vac. Sci. Technol. B 9, 3586 (1991); http://dx.doi.org/10.1116/1.585850 (4 pages) | Cited 13 times

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For accurate linewidth measurement in scanning probe metrology the shape and size of the probe tip must be known. Since the probe can be degraded during a scan, quick in situ characterization is desirable. A technique is described employing an array of known structures that allows tip characterization with the probe microscope itself. This technique can be used to measure either the shape of a probe tip or the flexing caused by attractive forces near a sidewall. The results suggest that the sharpest probes may experience significant bending in the vicinity of a wall.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Low voltage backscattered electron collection for package substrates and integrated circuit inspection

K. L. Lee and M. Ward

J. Vac. Sci. Technol. B 9, 3590 (1991); http://dx.doi.org/10.1116/1.585851 (7 pages)

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A low voltage backscattered electron collection technique has been developed. This technique collects low energy backscattered electrons in a sequential retarding field environment. This collection approach provides most of the desirable features for insulating package substrates and passivated integrated circuit (IC) devices inspection. These features are (1) high current and resolution, (2) high detector gain at low voltage, (3) good signal immunity from sample surface charging, and (4) on‐line topographical and compositional information at low voltage. In this paper, various details of the technique; such as detector arrangement, signal collection efficiency, sample charging immunity, beam current and resolution, image distortion and its comparison with conventional low voltage scanning electron microscopy inspection for insulating package substrate, and passivated IC inspection will be discussed.
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85.40.Qx Microcircuit quality, noise, performance, and failure analysis
85.40.Bh Computer-aided design of microcircuits; layout and modeling

High‐precision motion and alignment in an ion‐beam proximity printing system

D. P. Stumbo, G. A. Damm, S. Sen, D. W. Engler, F‐O. Fong, J. C. Wolfe, and James A. Oro

J. Vac. Sci. Technol. B 9, 3597 (1991); http://dx.doi.org/10.1116/1.585852 (4 pages) | Cited 7 times

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We measure the fluorescent alignment generated by ion bombardment of an SiO2 wafer mark scanned behind a corresponding window pattern in a silicon stencil mask. We conclude that an optimized system can align to 50 nm (mean+3σ) in less than 300 ms. Throughput is shown to be limited not by the alignment system, but by thermal loading of the mask during exposure.
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85.40.Hp Lithography, masks and pattern transfer

A lower bound on alignment accuracy and subpixel resolution in lithography

Alan Gatherer and Teresa H.‐Y. Meng

J. Vac. Sci. Technol. B 9, 3601 (1991); http://dx.doi.org/10.1116/1.585853 (5 pages)

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In wafer alignment, subpixel resolution methods have been used in an attempt to increase the accuracy of the wafer positioning algorithm. These methods produce line positions that are between the pixels of the rasterized image of the alignment pattern. In this paper we provide a lower bound on the error variance of any alignment algorithm for a given alignment system and develop a method of ranking alignment patterns for their suitability for the task. We show that the use of a nonsymmetric alignment pattern will cause a decrease in accuracy unless information about the amplitude of the alignment pattern is known. An expression for the maximum useful subpixel resolution of any alignment system is derived and it is shown that with pixel resolution higher than this maximum value the subpixel methods produce no significant increase in accuracy. Examples of the use of the bound will be given.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Metrology of electron‐beam lithography systems using holographically produced reference samples

Erik H. Anderson, Volker Boegli, Mark L. Schattenburg, Dieter Kern, and Henry I. Smith

J. Vac. Sci. Technol. B 9, 3606 (1991); http://dx.doi.org/10.1116/1.585854 (6 pages) | Cited 6 times

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Metrology in an electron‐beam lithography system is typically carried out by a combination of beam scan and laser‐interferometer‐controlled sample motion. The high‐resolution technique presented in this paper avoids the stage motion by using a holographically produced grid, which is essentially a permanently recorded interference pattern. This grid can be at least as accurate as the interferometer, and no stage motion, with the potential for additional error sources, is required to map out the distortion in the deflection field. The quality of the grid is critical since it is the reference to which the distortion is compared. With careful control of the holographic exposure system, high‐quality low‐distortion orthogonal grids were fabricated. We have produced grids with a period of 200 nm and orthogonality of a few arc seconds using an UV laser holographic system. Once the grid is processed to produce a high‐contrast signal for either back‐scattered or transmitted electrons, both scanning and signal‐processing techniques are needed to measure the distortion. If the errors are larger or similar in size to the grating period a moiré technique can be used. Unfortunately, when the distortion is much less than the period this technique does not have the required resolution. Therefore, two new techniques have been developed. The first uses a lock‐in amplifier to measure the phase difference between the expected signal and the actual measured signal. The second uses digital image processing to compare the expected and measured images. With both of these techniques resolution of about one beam step (≊6 nm) has been achieved.
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85.40.Hp Lithography, masks and pattern transfer

Two‐dimensional atomic force microprobe trench metrology system

D. Nyyssonen, L. Landstein, and E. Coombs

J. Vac. Sci. Technol. B 9, 3612 (1991); http://dx.doi.org/10.1116/1.585855 (5 pages) | Cited 12 times

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This article describes the extension of atomic force microprobe (AFM) technology to two dimensions (2D) for accurate measurement of submicron critical dimensions (CDs). The system utilizes a vibrating tip with heterodyne‐interferometer sensor similar to that introduced by Martin, Williams, and Wickramasinghe. [Y. Martin, C. C. Williams, and H. K. Wickramasinghe, J. Appl. Phys. 61, 4723 (1987)]. However, the tip vibrates in 2D with dual heterodyne detection. The sample is moved relative to the tip by means of coarse‐ and fine‐motion stages whose position is monitored with 3D interferometry. The system does not scan the sample, but operates like a nanorobot sensing the approach of the tip to the surface by means of the vibration damping. A special three‐point tip has been fabricated by Lee [K. L. Lee, D. W. Abraham, F. Serord, and L. Landstein, Proceedings of the 35th ISEIPB Conference, Seattle, WA, May 28–31, 1991 (unpublished), paper K1] with 0.1 μm shank diameter which allows measurement of submicrometer trench widths up to 2 μm in depth with accuracy and repeatability at the nanometer level. Measurements are made under computer control. The system design and operating characteristics are discussed.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
06.60.Sx Positioning and alignment; manipulating, remote handling
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