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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 2 times

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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 th