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Oct 1983

Volume 1, Issue 4, pp. 865-1397


Photoemission study of GeAs(2̄01): A model for the As‐stabilized Ge surface on GaAs/Ge heterojunctions

F. Stucki, G. J. Lapeyre, Robert S. Bauer, P. Zurcher, and J. C. Mikkelsen

J. Vac. Sci. Technol. B 1, 865 (1983); http://dx.doi.org/10.1116/1.582707 (6 pages) | Cited 2 times

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We present a study of the electronic states of GeAs as a model for the ordered, anion‐stabilized surface phases which form on Ge when it is grown epitaxially on GaAs substrates using MBE. Angle‐resolved, normal emission photoelectron energy distribution curves for four different azimuthal orientations of the GeAs(2̄01) face (i.e., four different polarizations) have been measured using photon energies from hν=10 to 28 eV. The valence band structure plots (binding energy versus photon energy) show behavior typical of a layered compound. A large number of valence band states (about 12) are observed, and they show essentially no hν dispersion in normal emission and very little dispersion with polar angle. The electronic states are therefore localized both within and normal to the layer. The excitation of the Ge 3d and the As 3d core levels into conduction band states observed by measuring the core hole decay emission does not show any enhancement peaks as usually observed if empty surface states exist in the conduction band. This suggests that the GeAs(2̄01) surface may not have any surface states. Chemical bonding information was obtained by measuring the Ge 3d core level binding energy. The Ge is more tightly bound compared to the bulk Ge as indicated by a 3d core level chemical shift of 0.45±0.1 eV toward higher binding energy. 3d core threshold emission for both the Ge and the As is used together with the line shape of the valence band edge emission to determine a forbidden band gap is 0.4±0.3 eV. These results support the Bauer/Mikkelsen hypothesis that the Ge:As surface phase that floats on top of the MBE GaAs/Ge heterojunction is energetically more favorable than the corresponding clean Ge surface having unsatisfied dangling bonds. The data on GeAs(2̄01) leads to a picture of an As‐terminated surface having highly directional oribtals and very low reactivity.
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73.20.-r Electron states at surfaces and interfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic

Solid‐phase‐epitaxial growth and formation of metastable alloys in ion implanted silicon

J. Narayan, O. W. Holland, and B. R. Appleton

J. Vac. Sci. Technol. B 1, 871 (1983); http://dx.doi.org/10.1116/1.582708 (17 pages) | Cited 32 times

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Transmission electron microscopy (cross‐section and plan‐view) and ion backscattering techniques have been combined to study the details of solid‐phase‐epitaxial (SPE) growth in Sb+, In+, Bi+, Ga+, and As+ implanted silicon after furnace annealing in the temperature range 450 to 650 °C. The ion implanted amorphous layer grew ‘‘defect‐free’’ in 〈001〉 orientations and the crystalline–amorphous (c–a) interface during growth contained undulations ∼5 Å over the intervals of 200–500 Å. During SPE growth in 〈111〉 orientations, the c–a interface was atomically smooth initially, but eventually became nonplanar due to the formation of twins. From SPE growth rates at different temperatures, the activation energy associated with the growth was determined to be 2.6±0.3 eV. The dopant concentrations in defect‐free SPE grown layers were found to exceed equilibrium solid solubility limits by as much as a factor of 560 in the Si–Bi system. The absolute maximum concentrations, corresponding to the intersections of free‐energy versus composition curves of amorphous and crystalline silicon, were calculated and the results were compared with the observed concentrations. The observed concentrations, which were found to depend upon the amorphous state or free energy of as‐implanted silicon, approached the calculated limits in the case of the Si–Sb and Si–As systems. However, for the Si–In, Si–Ga, and Si–Bi systems, interfacial segregation and solute redistribution during SPE growth prevented the maximum achievable concentrations. The concentrations of dopants in excess of the solubility limits could be precipitated out completely only after annealing treatments at relatively high temperatures (≥1050 °C).
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68.55.-a Thin film structure and morphology
66.30.J- Diffusion of impurities
61.72.U- Doping and impurity implantation
61.80.Jh Ion radiation effects

The use of pulsed laser irradiation in silicon molecular beam epitaxy: A comparative low energy electron diffraction study

T. de Jong, W. A. S. Douma, L. Smit, V. V. Korablev, and F. W. Saris

J. Vac. Sci. Technol. B 1, 888 (1983); http://dx.doi.org/10.1116/1.582709 (11 pages) | Cited 7 times

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We present a low energy electron diffraction (LEED) study of the initial stages of epitaxial growth of silicon on silicon with emphasis on the growth mechanisms involved. Silicon is evaporated under ultrahigh vacuum conditions. We used pulsed laser irradiation and thermal annealing for surface preparation and show that epitaxial growth can take place on surfaces, prepared by either procedure. We determined the epitaxial temperature (defined with electron diffraction) for Si(111) and Si(100) substrates. We also used 4.0° vicinal oriented Si(111) to determine the influence of a large number of misorientation steps on the growth mechanism. The (100) epitaxial temperature equals 470 K, much lower than that of Si(111) which is found to be 870 K. The use of vicinal (111) surfaces lowers the epitaxial temperature to 770 K. Pulsed laser irradiation was not only used to prepare clean and ordered substrate surfaces, but also as a means to prepare the metastable Si(111) surface, exhibiting a (1×1) LEED pattern. The initial stages of epitaxial growth on this surface were studied. Room temperature depositions of Si on Si(100) are shown to be partly ordered. Three differently prepared (100) substrates were used to determine the influence of substrate surface preparation on the structure of the overlayer.
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68.55.-a Thin film structure and morphology
81.65.-b Surface treatments
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
79.20.Ds Laser-beam impact phenomena

Study of the stepwise oxidation and nitridation of Si(111): Electron stimulated desorption, Auger spectroscopy, and electron loss spectroscopy

M. L. Knotek and J. E. Houston

J. Vac. Sci. Technol. B 1, 899 (1983); http://dx.doi.org/10.1116/1.582710 (16 pages) | Cited 14 times

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Electron stimulated desorption, Auger line shape analysis, and electron loss spectroscopy measurements are reported for the electron activated stepwise oxidation and nitridation of the Si(111) surface. In ESD it is found that appreciable levels of surface hydrogen can be present which can lead to hydroxyl formation upon oxidation. The hydroxyl rich films are unstable in an electron beam, while surfaces oxidized with activated oxygen, where no OH is formed, are much more stable. The nitrided films are always stable in the electron beam even though there too hydrogen is always found. On the OH‐free oxide, ESD shows two chemically distinct O species, one thought to be SiO2 and the other adsorbed O2 or a chemical intermediate. The Si(L23VV) Auger spectra for both the oxide and nitride are treated by background subtraction, integration, deconvolution, and subtraction of the elemental part of the spectrum, as a function of reaction time over a well controlled series of reaction steps. The Auger spectra for both oxide and nitride films suggest that in the earliest stages of reaction, the reacted film is made up of low coordination intermediates which gradually evolve to the stoichiometric compound as the coordination increases. In loss spectroscopy, both the Si(L23) core loss and the near elastic loss were measured. The L23 core loss shows the same gradual evolution to the oxide seen in the Auger results, with an intermediate oxidation state dominating in the early stages of reaction. The near elastic loss spectra, by contrast, quickly saturate in the early stages of reaction to the final oxide spectrum which is characterized by features both of the full oxide and a suboxide. Similar results are found for the nitride.
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81.65.-b Surface treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Early stages of silicide formation on W, Ni, and Pt surfaces, an atom probe, and field ion microscope study

T. T. Tsong, S. C. Wang, F. H. Liu, H. Cheng, and M. Ahmad

J. Vac. Sci. Technol. B 1, 915 (1983); http://dx.doi.org/10.1116/1.582711 (8 pages) | Cited 6 times

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The atomic structures and composition of silicide layers grown on W, Ni, and Pt surfaces have been studied in the atom probe and the field ion microscope. Four stages of silicide growth on W surfaces have been identified. On the W{112} plane, the atomic image structure of the top surface layer in the first stage, and the first three atomic layers in the second stage of silicide formation do not correlate well with the atomic image structures of WSi2. The W{110} plane does not react with Si atoms during the first two stages. In the third stage, the growth of thin WSi2 films proceeds nearly epitaxially from the W{001} planes to cover the entire W substrate, forming mismatches of silicide lattices along the [110] zone lines of the W. In the final stage, thick layers of polycrystalline silicides are formed. Their orientations are no longer well correlated to the W substrate. Atom‐probe analyses show the stoichiometry of these atomically perfect polycrystallines to be WSi2. Identifications of crystal planes of WSi2 can be best done by comparing the image structures with the atomic arrangements of W in the silicide surface planes since the majority of Si atoms are not imaged in the field ion microscope. A pure Si atomic layer on top of the WSi2 (112) plane gives a faint image of ∼1% the regular image intensity of a W layer. FIM images show the W–WSi2 phase boundary to be very sharp. Thick layers of silicide of platinum and nickel have also been analyzed in the atom probe. The platinum silicide layers near the Pt interface have the composition of Pt2Si. Beyond the relatively sharp interface, a few Si atoms can still be found tens of atomic layers inside the platinum matrix. The composition of nickel silicide varies from one region to another. No sharp boundaries seem to exist between different phases. We also find the thick tungsten silicide films to be resistive to oxidation.
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68.60.-p Physical properties of thin films, nonelectronic
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys
68.37.Vj Field emission and field-ion microscopy

Kinetics of the ablative photodecomposition of organic polymers in the far ultraviolet (193 nm)

R. Srinivasan

J. Vac. Sci. Technol. B 1, 923 (1983); http://dx.doi.org/10.1116/1.582712 (4 pages) | Cited 29 times

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The efficiency of ablative photodecomposition of poly(methyl methacrylate) caused by pulsed radiation at 193 nm from an excimer laser (argon–fluorine fill) has been studied as a function of fluence. A threshold for the onset of the process lies at 10 mJ/cm2 per pulse of 14 ns. The efficiency of the process increases rapidly with fluence up to 250 mJ/cm2 per pulse after which it levels off sharply. The etch depth of ∼3100 Å/pulse at 250 mJ/cm2 can be compared to a depth of 4800 Å/pulse at a fluence of >20 J/cm2/pulse. A model is suggested for the ablative photodecomposition of organic materials and the photochemistry of the process at different fluences is discussed. The variation in the efficiency with the composition of the polymer is briefly considered.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
79.20.Ds Laser-beam impact phenomena
82.50.-m Photochemistry

Etch products from the reaction of XeF2 with SiO2, Si3N4, SiC, and Si in the presence of ion bombardment

Harold F. Winters

J. Vac. Sci. Technol. B 1, 927 (1983); http://dx.doi.org/10.1116/1.582713 (5 pages) | Cited 17 times

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Modulated beam mass spectrometry has been used to identify the etch products desorbed during ion bombardment of SiO2, Si3N4, SiC, and Si in the presence of XeF2. The major silicon‐containing product from all of these materials is SiF4 as judged by the intensity of the SiF+3 peak. The radicals SiF and SiF2 are observed but in much smaller quantities. N2 and O2 are major etch products from Si3N4 and SiO2, respectively. No other compounds of oxygen or nitrogen were observed. The major ‘‘carbon‐containing’’ product from SiC was not identified. The product distributions are relatively independent of XeF2 flux, ion energy, and the type of ion (i.e., Ar+ or CF+3). Rough estimates for the relative etch rates of these materials have also been obtained. The product distributions are consistent with an interpretation which suggests that ‘‘chemical sputtering’’ is the dominant (but not the only) mechanism for producing ion‐enhanced etching.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
81.65.-b Surface treatments
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Ammonium fluoride deposition during plasma etching of silicon nitride

J. A. Brewer and G. W. Miller

J. Vac. Sci. Technol. B 1, 932 (1983); http://dx.doi.org/10.1116/1.582714 (3 pages) | Cited 1 time

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During oxygen and carbon tetrafluoride plasma etching of silicon nitride, a light blue and water soluble film is deposited upon the surface of the silicon nitride layer. Depending upon the thickness, this film retards or completely inhibits the desired etching process. This film has been identified by infrared spectrophotometry as ammonium fluoride. The thickness of the ammonium fluoride layer has been determined to be a function of the ammonia to dichlorosilane mole ratio of the gas flow into the LPCVD reactor during deposition. For mole ratios greater then 4.0, the ammonium fluoride film thickness was observed to decrease to approximately one‐third of the observed value at a mole ratio of 3.0. A possible mechanism for the formation of the ammonium fluoride layer is the reaction of ammonia molecules and hydrogen atoms (which have been occluded in the silicon nitride layer during deposition) with fluorine atoms from the plasma etching process. Increasing the mole ratio during deposition improves the stoichiometry of the silicon nitride layer and reduces the number of hydrogen atoms available for subsequent formation of ammonium fluoride during etching. The etching variations caused by ammonium fluoride deposition during plasma etching of silicon nitride can be minimized by optimizing the ammonia to dichlorosilane mole ratio during the deposition of the silicon nitride layer.
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81.65.-b Surface treatments
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Plasma enhanced beam deposition of thin films at low temperatures

R. P. H. Chang, S. Darack, E. Lane, C. C. Chang, D. Allara, and E. Ong

J. Vac. Sci. Technol. B 1, 935 (1983); http://dx.doi.org/10.1116/1.582715 (8 pages) | Cited 3 times

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A plasma enhanced beam deposition technique for thin films is discussed. It is shown that thin films of tailored stoichiometry or amorphous layers can be easily deposited in the temperature range (30–250 °C). The technique uses a combination of active atomic or molecular beams generated by charged particles or photons. Films of SiO2, Al2O3, ZrO3, silicon oxynitride, NbN, etc., have been deposited on metals, semiconductors, and insulators. The interfaces between the deposited films and the substrates are extremely sharp and no native growth of oxides of nitrides occurred on the substrate surfaces during film deposition. Film thickness and composition can be precisely controlled by optical monitoring techniques. For instance, the physical properties of the deposited SiO2 at 100 °C is nearly identical to that of thermal oxides grown on Si at 1100 °C. The deposited SiO2 has an electrostatic breakdown field strength of about 5×106 V/cm, and 1 MHz C–V curves show a hysteresis of 50 mV at a sweep rate of 100 mV/s. The fixed charge density is 3.5×1011 cm−2. The advantages of this process for depositing Al2O3 on InP, GaAs, and Si are discussed. Utilizing the low temperature nature of the technique, patterns of μ‐width SiO2 features have been made using photoresist masked substrates and the lift‐off technique. Finally, it is proposed that epitaxial growth of compound films should also be possible under UHV conditions.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
52.75.-d Plasma devices

Optical monitoring for rate and uniformity control of low power plasma‐enhanced CVD

W. C. Dautremont‐Smith and J. Lopata

J. Vac. Sci. Technol. B 1, 943 (1983); http://dx.doi.org/10.1116/1.582716 (4 pages) | Cited 3 times

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Plasma‐enhanced CVD requires close control of the plasma power density for reproducibility of both deposition rate and spatial uniformity in a radial‐flow reactor. Frequently the low rf power levels needed are not adequately controlled by the output power control of the relatively high power rf generator found in most commercial multipurpose plasma etch/deposition systems. This paper describes very simple and inexpensive broadband optical monitoring of the plasma emission for improved control sensitivity. The technique has the advantage of directly monitoring the plasma intensity, avoiding effects of variable power transmission losses between the rf generator and the plasma. Application to the control of low power plasma‐enhanced CVD of ‘‘SiO2’’ from Ar:SiH4:N2O plasmas, where the monitor signal is almost entirely due to near infrared Ar emission, is described.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Molecular level fabrication techniques and molecular electronic devices

Forrest L. Carter

J. Vac. Sci. Technol. B 1, 959 (1983); http://dx.doi.org/10.1116/1.582717 (10 pages) | Cited 9 times

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In anticipation of the continued size reduction of switching elements to the molecular level, new approaches to materials, memory, and switching elements have been developed. Two of the three most promising switching phenomena include electron tunneling in short periodic arrays and soliton switching in conjugated systems. Assuming a three‐dimensional architecture, the element density can range from 1015 to 1018 per cc. In order to make the fabrication of such a molecular electronic device computer feasible, techniques for accomplishing lithography at the molecular scale must be devised. Three approaches possibly involving biological and Langmiur–Blodgett materials are described.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.-z Semiconductor devices

A review of laser–microchemical processing

D. J. Ehrlich and J. Y. Tsao

J. Vac. Sci. Technol. B 1, 969 (1983); http://dx.doi.org/10.1116/1.582718 (16 pages) | Cited 106 times

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Microfabrication processes based on focused laser‐beam activation of surface chemistry are reviewed with an emphasis on the classification of the diverse chemical processes used. Surface reactions are divided according to their method of activation and the material phase most important in the chemical kinetics. Examples of reaction mechanisms and means of confining reaction dimensions are given. New results demonstrating that linewidths for deposition and etching of Si can be <0.4 μm are described. The ultimate limits to spatial resolution are explored in terms of an effective contrast (γ∗) for laser–microchemical processes. Enhanced diffusive transport, characteristic of laser microreactions, and its effect on ultimate reaction rates are also analyzed.
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42.62.-b Laser applications
78.60.Ps Chemiluminescence
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.30.-z Semiconductor devices

Maskless etching of a nanometer structure by focused ion beams

Masanori Komuro, Hiroshi Hiroshima, Hisao Tanoue, and Toshihiko Kanayama

J. Vac. Sci. Technol. B 1, 985 (1983); http://dx.doi.org/10.1116/1.582719 (5 pages) | Cited 7 times

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Microfocused heavy ion beams obtained from liquid metal ion sources of gallium, indium, and tin are bombarded onto silicon and gallium arsenide substrates, and the amorphous regions created are selectively dissolved in suitable etchants (ion bombardment enhanced etching). The area exposure doses required to etch to the depth of the calculated projected range of the incident ions are in the region of 5×10−6∼1×10−5 C/cm2 at accelerating voltages of 30∼50 kV,and the dose dependencies of the etched depths show rapid increases in specified dose regions. Widths of etched depths obtained in line delineations depend on a line exposure dose, and the minimum linewidth clearly obtained is 20∼40 nm for all the ion beams. From measurements of the dose dependencies of linewidth, the beam diameters are evaluated for various conditions of the source operation and of a lens acceptance half‐angle. The virtual crossover diameters that are independent of the half‐angle, are found to be 40∼50 nm for the gallium source and 67 nm for the indium source at the emission current of 4∼12 μA. In the case of the tin ion beam, each line is split into two distinct lines about 100 nm apart at 50 kV. This effect is caused by the separation of singly and doubly charged atomic ions in some stray magnetic field of the order of 50 mG. From variations of the width of grooves produced by the bombardment with the doubly charged ion beam, the crossover diameter for the tin source is estimated to be 56∼67 nm.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.65.-b Surface treatments

A large angle electrostatic deflection, variable shaped, electron beam exposure system

Shigeru Moriya, Kazuhiko Komatsu, Katsuhiro Harada, and Toyoki Kitayama

J. Vac. Sci. Technol. B 1, 990 (1983); http://dx.doi.org/10.1116/1.582720 (5 pages) | Cited 2 times

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In electron beam direct writing, a capability of ‘‘one chip within one deflection field’’ can reduce time wasted in stage moving, and eliminate field stitching errors in a chip. These advantages lead to high throughput and high overlay accuracy for successful VLSI fabrications. A large angle electrostatic deflection, variable shaped, electron beam exposure system (EB57) has been developed to achieve this capability. The key EB57 technologies are a large angle electrostatic deflection and high speed deflection control. Newly developed multiple electrostatic deflectors were designed using an in‐lens, dual channel deflection method. In this method, two types of field and subfield deflectors are equipped inside a projection lens. Deflectors free of third and fifth θ components can provide a large angle of deflection with a 10 mm2 field. 18‐bit digital‐to‐analog converters, and ±800 V amplifiers effect this large field deflection. The high breakdown voltage for the amplifiers is attained by connecting vertical power MOSFETs in series. The settling time of the amplifiers is less than 10 μs at 1/64 full scale. Amplifiers for subfield scanning and beam shaping have a 250 ns settling time at full scale. To correct chip distortions, deflection distortions, and stage positioning errors, a new data correction method that takes rounding off errors into consideration has been applied to a high speed arithmetic unit. This EB57 system can write from 7 to 10 4‐in. wafers per hour with 0.5 μm lithography.
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41.75.Fr Electron and positron beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments

Design aspects of the optics of the VLS‐1000 electron‐beam direct‐write lithography system

P. F. Petric, N. J. Taylor, and M. Utlaut

J. Vac. Sci. Technol. B 1, 995 (1983); http://dx.doi.org/10.1116/1.582721 (4 pages)

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Some of the basic considerations in the design of the electron optics of a variable line scanning (VLS) system, a particular form of variable‐shape electron‐beam lithography system, are discussed. In the VLS system, the electron beam is projected on the resist‐coated wafer in the form of a narrow line whose length and position can be varied simultaneously as it is scanned. The writing is done as the stage is moved in a serpentine fashion under laser control with the pattern features placed using both raster and vectorial placement techniques. The line can be produced in either of two orthogonal directions in order to maximize the exposure rate. In general, the required source brightness is greater than that of a more conventional‐shaped‐beam system, however, this can be achieved readily with LaB6 at a desirable operating temperature. Exposed and developed patterns demonstrate the resolution capabilities of the optics.
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41.75.Fr Electron and positron beams

Dot matrix electron beam lithography

T. H. Newman, R. F. W. Pease, and W. DeVore

J. Vac. Sci. Technol. B 1, 999 (1983); http://dx.doi.org/10.1116/1.582722 (4 pages) | Cited 11 times

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Slow throughput is the major problem of scanning beam lithography. We have investigated a multiple beam approach in which an array of beams is focused and scanned by a common system but the beams are blanked independently. The individual blanking is accomplished using an assembly fabricated with silicon micromachining technology and shadow mask evaporation of blanking electrodes 50 μm wide, 400 μm deep. Analysis and experimental evaluation both indicate that blanking can be achieved with this configuration. Choosing an optimum design involves trade offs between ease of illumination, ease of fabrication, positional control, and space charge blurring. However, extension to 16 or more beams looks quite possible.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

EL‐3 application to 0.5 μm semiconductor lithography

D. E. Davis, S. J. Gillespie, S. L. Silverman, W. Stickel, and A. D. Wilson

J. Vac. Sci. Technol. B 1, 1003 (1983); http://dx.doi.org/10.1116/1.582662 (4 pages) | Cited 2 times

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The application of IBM’s 3rd generation direct write electron beam lithography tool EL‐3 has been extended into the submicron region. This was accomplished with tool modifications in conjunction with suitable process adjustments. EL‐3 is presently being used in both development and manufacturing for the exposure of wafers and masks. It was designed as a high current, high throughput tool to cover lithography requirements down to 1 μm minimum dimensions. To move into the 0.5 μm realm, no basic architecture changes were made, but the beam current, deflection speeds, and maximum spot and field sizes were reduced to make the trade‐offs against throughput that were necessary and acceptable for the system’s application to technology development. A single layer resist process was devised to demonstrate fully the performance capability of the tool. The process uses top surface imaging which allows one to analyze tool performance without excessive distortions. Spot‐to‐spot butting and illumination consistency were monitored using this process. Linewidth tolerance and overlay results obtained with the new tool/process configuration will be reported. Top surface imaging, whether in a single or multilayer resist process, represents the most viable approach for submicron electron‐beam lithography.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.65.-b Surface treatments

Edge contrast: A new definition for comparative lithography tool characterization

W. Stickel and G. O. Langner

J. Vac. Sci. Technol. B 1, 1007 (1983); http://dx.doi.org/10.1116/1.582663 (4 pages)

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A new definition called ‘‘edge contrast’’ is proposed for realistic resolution comparisons between tools of different beam technology. This new quantity does not pre‐empt the traditional intensity contrast definition, but extends it. Taken into account are both the intensity levels in areas to be exposed and not to be exposed, as well as the transition variations (edge slope) between them. As a result, it will be shown that, compared to light‐optical tools, electron beam systems have a resolving capability already superior in the range of feature dimensions well above 1 μm. A comparison on the basis of the intensity contrast definition would place the point of equivalency in the vicinity of 0.5 μm. The new definition is not only adequate to characterize the lithography tool, but also suitable to encompass the entire process chain provided the functional dependencies between the process parameters are known.
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41.75.Fr Electron and positron beams
81.65.-b Surface treatments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

A field emission e‐beam system for nanometer lithography

D. Stephani, E. Kratschmer, and H. Beneking

J. Vac. Sci. Technol. B 1, 1011 (1983); http://dx.doi.org/10.1116/1.582664 (3 pages) | Cited 3 times

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Field emitters offer a particularly high potential in e‐beam lithography when writing in the nanometer range. Using a modified VG Microscopes Ltd., model HB 501 STEM, a current of 0.1 nA can be focused into a diameter of 2.5 nm at 100 kV with a final beam aperture of 1.6 mrad. In order to fulfill the demands of microlithography, an objective lens of 15 mm nominal focal length is used. Stage travel in the system is 5 mm in the X and Y directions and the maximum scan field is 250×250 μm2. The beam is deflected electromagnetically under computer control and vector scanning is used during lithography. The 14 bit digital pattern generator has been electrically isolated by optocouplers from the host computer and is connected via analog differential buffers to the deflection amplifiers. The cold tungsten field emitter exhibits a linear decrease in current of about 20% within 20 min of continuous writing. The decrease in current is corrected during lithography by a feedback to the clock frequency of the digital pattern generator to maintain a constant exposure dose. The high current available enables the use of organic resists as well as low sensitivity inorganic resists such as NaCl or WO3. So far 10 nm resolution has been achieved by in situ vaporization of NaCl.
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41.75.Fr Electron and positron beams
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
81.65.-b Surface treatments

Performance results of an electron beam lithography machine and process by means of dc electrical test structures

Paul Rissman, En‐Den Liu, and Geraint Owen

J. Vac. Sci. Technol. B 1, 1014 (1983); http://dx.doi.org/10.1116/1.582665 (6 pages)

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Direct current electrical tests have been used to measure the performance of electron beam resists and an exposure system. Resist characterization is done by using electrical tests to measure the linewidth defined as a function of an incremental dose. The quality of different resists can be compared by means of δ, the slope of the normalized linewidth versus the logarithm of the incident dose curve. Data have been measured for three negative resists (PCMS 30, PCMS 200, and OEBR 100) and PMMA for two development conditions. Resistors fabricated from 60 nm chromium films, 300 nm polysilicon films, or 60 nm titanium films gave results within ±40 nm of one another for 500 nm lines. Without proximity effect correction, linewidth difference from design value is more than ±300 nm and the 0.5P μm lines were undefined for PMMA and the given development conditions, and 0.5P and 1.0P μm lines were undefined for PCMS 30 and the given exposure conditions. With proximity effect correction, all line sizes are within 100 nm of design value with the exception of 0.5P μm in PCMS 30. The beam diameter varies from an undeflected value of 350 nm to a maximum of 650 by 480 nm, without dynamic corrections, as calculated from measurements of 500 nm lines placed throughout the 5 mm field of view. Two‐level alignment measured electrically in the center and four corners of the 5 mm field is within 100 nm, with standard deviations typically less than 60 nm at each location for each axis. Butting of exposure subfields, measured electrically, is within 80 nm; the one sigma standard deviation of this measurement is 42 and 82 nm for the x and y axes, respectively, but is less than 15 nm at a higher exposure frequency.
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81.70.-q Methods of materials testing and analysis
07.50.-e Electrical and electronic instruments and components

The magnitude and significance of proximity effects in electron image projector defined layers

K. H. Nicholas, R. A. Ford, H. E. Brockman, and I. J. Stemp

J. Vac. Sci. Technol. B 1, 1020 (1983); http://dx.doi.org/10.1116/1.582666 (3 pages)

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Electron image projection is an attractive technique for making submicron integrated circuits (IC) but long and short range proximity effects cause some pattern distortion. Long range proximity effects have now been measured and the significance of long and short range effects to IC fabrication assessed. Long range proximity exposure effects due to re‐entrant electrons are sufficiently uniform for local corrections to be unnecessary. With automatic proximity correction IC patterns could be scaled down to below 0.5 μm (1 μm pitch) even with single level resist and 20 keV electrons.
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41.75.Fr Electron and positron beams
81.65.-b Surface treatments
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Registration mark detection in electron beam proximity printing

P. Nehmiz, U. Behringer, H. Bohlen, and M. Kallmeyer

J. Vac. Sci. Technol. B 1, 1023 (1983); http://dx.doi.org/10.1116/1.582667 (5 pages) | Cited 1 time

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Electron beam proximity printing is a lithography method for high throughput exposure of repetitive patterns with submicron structures. An electron beam shadow projects the pattern contained in a transmission mask onto the wafer. Pattern registration in this projection printer is achieved by using the electron beam current absorbed in the wafer. Two registration steps are employed: one for wafer (or global) align, the other for chip (or local) align. The achieved registration accuracy is better than 0.1 μm using 10 keV electrons and 1.1 μm thick PMMA on the wafer registration marks.
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41.75.Fr Electron and positron beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments

Chemically assisted ion beam etching for submicron structures

J. D. Chinn, I. Adesida, and E. D. Wolf

J. Vac. Sci. Technol. B 1, 1028 (1983); http://dx.doi.org/10.1116/1.582668 (5 pages) | Cited 5 times

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The flexibility of broad‐beam ion processing when used in conjunction with a chemistry assist technique is demonstrated. In this technique called chemically assisted ion beam etching (CAIBE), a chemically reactive gas is introduced into the sample chamber independent of the ion source which can be operated on inert or reactive gases. This allows for a wide range of independent control of the chemical and ionic fluxes not available in other dry etching techniques. Using a two component gas system of argon and xenon difluoride vapor under various operating conditions, the etched wall profiles of Si were found to be controllable. In the reactive ion beam etching mode of operation, overcut profiles with enhanced etch rates over ion milling rates were produced from Ar+ and XeF+x beams resulting from predominantly physical etching mechanisms. With the introduction of low vapor pressures of XeF2 into the sample chamber in conjunction with Ar+ ion bombardment, profiles resulted from line‐of‐sight ion assisted etching. Vertical walls were obtained with a collimated ion beam while profiles with directional undercutting resulted under highly divergent beam conditions. By increasing in XeF2 vapor pressure, undercut profiles from purely chemical etching were formed. Thus, by varying the partial pressure or the ion source operating conditions during an etch process, profile tailoring was accomplished.
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81.65.-b Surface treatments
85.40.Bh Computer-aided design of microcircuits; layout and modeling
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Local plasma oxidation and reactive ion etching of metal films for ultrafine line pattern inversion and transfer

J. Nulman and J. P. Krusius

J. Vac. Sci. Technol. B 1, 1033 (1983); http://dx.doi.org/10.1116/1.582669 (4 pages)

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A new ultrafine line pattern inversion and transfer technique based on local low temperature plasma oxidation and reactive ion etching of suitable metal films, such as aluminum, is presented. The patterned surface oxidized metal film may serve as a surface passivated interconnect or gate structure for integrated semiconductor devices, or be used as an etch mark for underlying layers. As an application a process for patterning self‐aligned two layer gate lines composed of molybdenum silicide and polycrystalline silicon is given. Linewidths as small as 1500 Å have been achieved.
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81.05.Bx Metals, semimetals, and alloys
81.65.-b Surface treatments
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Reactive ion etching for submicron structures of refractory metal silicides and polycides

M. Zhang, J. Z. Li, I. Adesida, and E. D. Wolf

J. Vac. Sci. Technol. B 1, 1037 (1983); http://dx.doi.org/10.1116/1.582670 (6 pages) | Cited 10 times

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Refractory metal silicides and n+ polysilicon/silicides are of particular interest for VLSI gate and interconnection technology. Reactive ion etching experiments have been conducted on sputter‐deposited films of MoSi2, CVD n+ polysilicon, and thermal SiO2 using admixtures of SF6 with O2. The influence of partial pressure and total pressure on profile control and etch selectivity has been determined. Highly anisotropic etching of n+ polysilicon and MoSi2 was obtained using a gas mixture of SF6 plus 50% oxygen. Examples of 0.2μ anisotropically etched structures of silicides and n+ polysilicon/silicide stacked films have been realized using electron beam lithography and one step dry etching. Mechanisms of profile control involved in the SF6/O2 system are discussed. In addition, exploratory reactive ion etching studies using SiF4/Cl2 gas mixtures for these materials and TaSi2 have been carried out.
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81.65.-b Surface treatments

Large area ion beam assisted etching of GaAs with high etch rates and controlled anisotropy

G. A. Lincoln, M. W. Geis, S. Pang, and N. N. Efremow

J. Vac. Sci. Technol. B 1, 1043 (1983); http://dx.doi.org/10.1116/1.582671 (4 pages) | Cited 16 times

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Ion beam assisted etching (IBAE) is a dry etching technique in which the sputter etching component of an argon ion beam and the chemical etching component supplied by a Cl2 gas flux are independently controlled. This technique has been used to obtain anisotropic etching of GaAs with minimal surface damage over areas of a few square millimeters. The results reported here are achieved with an improved IBAE system designed to etch considerably larger areas. The system accurately and uniformly delivers reactive gas flux to the sample giving uniform etching rates over the 2‐cm‐diam area exposed to the ion beam. When the sample is exposed to high reactive gas fluxes, equivalent to a pressure of 1×10−2 Torr, and 1 to 2 keV Ar+ ions at 1 mA cm−2, etching rates of 5 to 10 μm/min are obtained making etched through‐holes in GaAs wafers realizable. Control of the ion beam collimation and the reactive gas flux allow for accurate control of undercutting making submicrometer etched structures in GaAs with aspect ratios>35:1 easily obtainable. In addition, damage studies of the ion beam assisted etched GaAs surfaces shows a low trap density in the range of 1013 cm−3 as determined by deep level transient spectroscopy (DLTS). The improved system uses two gas jets to supply the chemically reactive flux and a liquid N2 cooled shroud to trap the unused reactive gas. The absolute reactive flux impinging on the sample is determined with a capacitance monometer and the ion beam collimation is controlled by varying the ion gun to sample distance.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.65.-b Surface treatments

Maskless etching of GaAs and InP using a scanning microplasma

Yukinori Ochiai, Kenji Gamo, and Susumu Namba

J. Vac. Sci. Technol. B 1, 1047 (1983); http://dx.doi.org/10.1116/1.582672 (3 pages) | Cited 10 times

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Etching characteristics of GaAs, InP, and other materials using a scanning microplasma have been investigated. This technique utilizes enhanced reaction between a reactive ambient gas and a target at an excited region like a microplasma which is produced by irradiating a scanning focused ion beam. It was observed that the present technique gives an enhanced etching rate over a physical sputter etching and a very smooth etched surface. Dependence of etching rate on bombarding angle and reactant gas flow rate is also measured.
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81.65.-b Surface treatments

Reactive ion etching of GaAs using CCl2F2 and the effect of Ar addition

J. Chaplart, B. Fay, and Nuyen T. Linh

J. Vac. Sci. Technol. B 1, 1050 (1983); http://dx.doi.org/10.1116/1.582673 (3 pages) | Cited 5 times

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GaAs etching rate performed by RIE in CCl2F2 gas has been shown to depend on many parameters: pressure, rf power and flow rate. Moreover addition of Ar in CCl2F2 has been found to increase the etch rate. This observation and the AES study of etched GaAs surfaces has led to the conclusion that volatile chloride species contribute to the etching mechanism, while fluoride species which are less volatile inhibit etching. Schottky diodes presenting an ideality factor of 1.02 have been fabricated on CCl2F2 etched GaAs surface.
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81.65.-b Surface treatments
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Reactive ion etching of GaAs and InP using SiCl4

M. B. Stern and P. F. Liao

J. Vac. Sci. Technol. B 1, 1053 (1983); http://dx.doi.org/10.1116/1.582674 (3 pages) | Cited 6 times

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High resolution reactive ion etching of GaAs and InP is achieved using SiCl4 as the etching gas. Etching rates and profiles are examined at pressures between 1 and 10 mTorr and power densities from 0.2 to 0.9 W/cm2. Under the proper conditions, it is possible to obtain extremely vertical etch profiles and etch ratios of GaAs relative to masking materials such as Si3N4 and NiCr which exceed 10 to 1.
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81.65.-b Surface treatments

Focused ion beam microlithography using an etch‐stop process in gallium‐doped silicon

P. H. La Marche, R. Levi‐Setti, and Y. L. Wang

J. Vac. Sci. Technol. B 1, 1056 (1983); http://dx.doi.org/10.1116/1.582675 (3 pages) | Cited 7 times

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We have found that silicon, when implanted with doses of gallium in excess of 1013 ions/cm2, experiences little or no etching in aqueous caustic solutions. By exploiting a finely focused 40–50 keV gallium ion beam (0.05–0.1 μm diameter) in our scanning ion microscope, we have shown that it is possible to fabricate structures with submicrometer (0.1 μm) features. The silicon behaves as a negative resist with a sensitivity of about 1 μC/cm2. This etch‐stop process is largely insensitive to crystallographic orientation, except for the highly insoluble (111) plane in which damage‐promoted etching occurs.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.U- Doping and impurity implantation

High resolution patterning of silicon by selective gallium doping

I. L. Berry and A. L. Caviglia

J. Vac. Sci. Technol. B 1, 1059 (1983); http://dx.doi.org/10.1116/1.582676 (3 pages) | Cited 11 times

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High resolution patterns have been fabricated in 〈100〉 silicon by doping selected areas with gallium utilizing an ion microprobe. These doped regions are used as an etch mask for subsequent anisotropic etching of silicon. The etching was performed in a KOH:IPA solution at 80–90 °C. The resulting etch rate of the doped silicon is approximately inversely proportional to the gallium impurity concentration. At high doping concentrations an etch rate difference of greater than 1000:1 has been measured between the virgin silicon and the doped regions. Using this technique features as small as 30 nm have been produced.
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81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.U- Doping and impurity implantation

Deep‐UV photolithographic applications of copolymer (methacrylonitrile–methacrylic acid)

H. Hiraoka, W. L. Welsh, and J. Bargon

J. Vac. Sci. Technol. B 1, 1062 (1983); http://dx.doi.org/10.1116/1.582677 (4 pages)

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Copolymer (methacrylonitrile–methacrylic acid), which has no significant deep UV absorption prior to prebake, starts to have a broad UV absorption with the maximum at 246 nm after prebake at 130 °C in air. Cyclized structures responsible for this absorption undergo photochemical reactions: (1) main chain scissions at deep‐UV exposure, initiated by removal of isocyanic acid, providing positive tone images; (2) hydrogen transfer reactions at mid‐UV exposures to result in conjugated structures or cross linkages, providing negative tone images. With relatively high sensitivity, 50 mJ/cm2 for positive and 100 mJ/cm2 for negative tone images, polymer patterns with vertical wall profiles are obtained. Postbake of these resist patterns increases dry etch resistance significantly.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
82.50.-m Photochemistry
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Poly(chloromethylstyrene): A high performance x‐ray resist

Hsia S. Choong and Frederic J. Kahn

J. Vac. Sci. Technol. B 1, 1066 (1983); http://dx.doi.org/10.1116/1.582678 (6 pages)

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X‐ray lithographic performance of poly(chloromethylstyrene) (PCMS), a high performance negative e‐beam resist, was investigated. Superior resolution, i.e., resist profile and linewidth control, was obtained by x‐ray exposure due to the essentially square x‐ray exposure profile and the significantly reduced amount of backscattered electrons from the substrate. Sensitivity and resolution were evaluated as a function of polymer molecular parameters. Dry etching characteristics were evaluated under polysilicon, SiO2 and Al etching conditions. Excellent resolution, sensitivity and dry process compatibility were obtained and attributed to the high absorption of chlorine to Pd Lα radiation, the high chemical reactivity of the benzyl chloride moiety and the high plasma stability of the aromatic styrene moiety. Sensitivity of 300 000 molecular weight PCMS is 25–30 mJ/cm2 (D0.5g) to Pd Lα radiation; resolution is 1 μm in 1 μm final thickness resist with vertical walls at D0.9g (70 mJ/cm2), and submicron in thinner layers. Dry etch resistance is comparable to that of AZ‐type photoresist. Postexposure deep UV hardening minimizes thermally induced flow and profile distortion even at temperatures greater than 300 °C. Lithographic performance of PCMS compares very favorably with other leading x‐ray resists including the mixture of poly(2,3‐dichloropropyl acrylate) and poly(glycidyl methacrylate‐co‐ethyl acrylate) (DCOPA), poly(allyl methacrylate‐co‐hydroxyethyl methacrylate) (EK88) and chloromethylated polystyrene (CMS).
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81.65.-b Surface treatments
78.70.-g Interactions of particles and radiation with matter

Conventional novolak resists for storage ring x‐ray lithography

J. G. Lane, J. R. Maldonado, A. N. Cleland, R. P. Haelbich, J. P. Silverman, and J. M. Warlaumont

J. Vac. Sci. Technol. B 1, 1072 (1983); http://dx.doi.org/10.1116/1.582679 (4 pages)

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This paper describes the lithographic processing of several positive novolak‐based resists exposed on the IBM x‐ray lithography system at the Brookhaven National Laboratory 750 MeV storage ring. One of the advantages of the storage ring exposure system has been the ability to use resist development processes which are the same as the corresponding optical or e‐beam processes. The exposure system and the x‐ray mask used for resist evaluation are described elsewhere in this symposium. Determining the best process conditions requires consideration of mask contrast as well as the desired linewidth and profile control, particularly in the presence of topography. Data will be presented and compared with results obtained using other lithographic systems (i.e., e‐beam and conventional source x‐ray). In particular, the relationship of mask absorber thickness to process window will be presented using a simple model of the development process. Using the process window defined by this model, we have exposed test patterns and typical device patterns in 1 to 2 μm thick conventional positive novolak resists. Linewidth control data as a function of dose and development time were determined for one resist at doses in the 100–200 mJ/cm2 range and compared with corresponding results using electron beam exposure. The x‐ray exposures compared favorably with the electron beam exposures in the dosage ranges considered.
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07.85.-m X- and γ-ray instruments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Direct engraving on positive resists by synchrotron radiation

S. Ichimura, M. Hirata, H. Tanino, N. Atoda, M. Ono, and K. Hoh

J. Vac. Sci. Technol. B 1, 1076 (1983); http://dx.doi.org/10.1116/1.582636 (4 pages) | Cited 3 times

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Direct engraving of mask patterns in a resist film was tried by exposing with synchrotron radiation. Using a stencil mask made of a Si3N4 substrate, submicron structures could be successfully replicated. Fundamental aspects of resist decomposition by synchrotron radiation were also investigated by mass and electron spectroscopy.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
78.70.-g Interactions of particles and radiation with matter

Submicrometer‐gate GaAs FET fabrication using masked ion beam/optical hybrid lithography

I. Adesida, M. Zhang, R. Sadler, R. Tiberio, and E. D. Wolf

J. Vac. Sci. Technol. B 1, 1080 (1983); http://dx.doi.org/10.1116/1.582637 (4 pages)

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A masked ion beam/optical hybrid lithography process for fabricating GaAs MESFETs is described. Techniques for eliminating the damage caused by the ions penetrating through the resist into the GaAs substrate are discussed. Submicrometer gate GaAs FET fabricated using the hybrid lithography is shown and the electrical characteristics of the depletion‐mode device presented.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.-b Surface treatments

Read‐only memory with electron‐beam programmable floating‐gate transistors

D. C. Shaver

J. Vac. Sci. Technol. B 1, 1084 (1983); http://dx.doi.org/10.1116/1.582638 (4 pages)

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Floating‐gate transistors can be used as electron‐beam programmable nonvolatile switches. These switches can provide customization, temporary test access, or fault‐avoiding interconnections for large integrated circuits. To demonstrate the feasibility of using electron‐beam programming, a 128 K bit nMOS EPROM was fabricated. It contains over 200 000 electron‐beam programmable switches which are used for the data bits, for address definition in the row and column selectors, and for deselection of defective subsystems. Such large numbers of customizing links are feasible since the programming yield is very high and a programming rate of > 1000 links/s is easily obtained. This paper discusses the design of the electron‐beam programmable ROM, design and process considerations for the individual floating‐gate devices, and results on yield, programming speed, reversibility, and nonvolatility.
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84.32.Dd Connectors, relays, and switches
85.30.-z Semiconductor devices
41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Fabrication of a high density storage medium for electron beam memory

James A. Oro and J. C. Wolfe

J. Vac. Sci. Technol. B 1, 1088 (1983); http://dx.doi.org/10.1116/1.582639 (3 pages) | Cited 1 time

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A new concept for archival electron beam memory is being investigated. The storage medium consists of a two dimensional array of columns supported by a thin, electron transparent, membrane. Information is written by melting selected columns with an electron beam. The increase in cross‐sectional area of the resulting droplets provides contrast for electron transmission readout. In this paper, we describe a fabrication process for this storage medium. Gold columns are electroplated into a resist mold defined by electron beam lithography. Proximity effects are controlled by membrane and trilevel resist techniques. Two dimensional arrays of gold columns with 50 nm diameter, 100 nm period and 3:1 aspect ratios have been fabricated on 250 nm thick polyimide membranes.
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41.75.Fr Electron and positron beams
84.60.-h Direct energy conversion and storage

Fabrication of apertures, slots, and grooves at the 8–80 nm scale in silicon and metal films

A. Muray, M. Isaacson, I. Adesida, and B. Whitehead

J. Vac. Sci. Technol. B 1, 1091 (1983); http://dx.doi.org/10.1116/1.582640 (5 pages) | Cited 5 times

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Fabrication of apertures, slots, and grooves in silicon, gold–palladium, and lithium fluoride has been demonstrated using a 100 keV electron beam. For the LiF films we have been able to etch<2 nm wide by 50 nm deep grooves on 10 nm centers. Grooves in silicon 8 nm wide by 30 nm deep have been made by reactive ion etching in SF6. Apertures as small as 8 nm in diameter have been produced in AuPd films self‐supported over larger holes in 60 nm thick Si windows.
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81.65.-b Surface treatments
41.75.Fr Electron and positron beams

Practical aspects of microfabrication in the 100 nm regime

D. P. Kern, P. J. Houzego, P. J. Coane, and T. H. P. Chang

J. Vac. Sci. Technol. B 1, 1096 (1983); http://dx.doi.org/10.1116/1.582641 (5 pages) | Cited 8 times

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The fabrication of microstructures with minimum dimensions below 100 nm introduces several additional problems not normally associated with electron‐beam lithography at the 1/2 to 1 μm level. The quality of a 100 nm resist image, when defined by an electron beam pattern generator, depends strongly upon the exposure conditions such as beam energy and dose. Another important factor is the substrate, since it greatly influences the range and amount of backscattered electrons and, hence, the exposure contrast achievable in a given resist system. There is generally a big difference in energy deposited in the resist whether the exposure is performed on a thin membrane, on bulk silicon, or on a thick layer of a heavy metal, and also whether a single thin layer of resist or thick two or three‐layer systems are used. The characteristics of the resist and the development process itself are important aspects, too. In addition to controlling the resist image, one must also consider the properties and requirements of the subsequent transfer process to the working material such as lift‐off, plating, ion milling, and reactive ion etching. The specific process is often dictated by the materials and the geometry of the particular structure to be fabricated. So, as many of the conditions interact, it is impossible to define a single process that would be suitable for the wide range of applications that structures of this size are intended for. Using examples of x‐ray zone plates and FET gate definition, we discuss the merits of some of the processes used together with the techniques and problems associated with the evaluation of process performance at these dimensions.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Electron beam lithography from 20 to 120 keV with a high quality beam

R. E. Howard, H. G. Craighead, L. D. Jackel, P. M. Mankiewich, and M. Feldman

J. Vac. Sci. Technol. B 1, 1101 (1983); http://dx.doi.org/10.1116/1.582642 (4 pages) | Cited 9 times

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We have performed electron beam lithography studies on thick substrates using beam energies of 20–120 keV and a nominal beam diameter of 2 nm in a Philips 400 electron microscope with scanning capability. Metal lines as narrow as 10 nm were fabricated on Si and GaAs substrates using liftoff of a single thin layer of resist. High resolution (approximately 10 nm) patterns could be written at all beam energies with an exposure latitude that remained approximately constant up to energies for which the range of the backscattered electrons became significantly larger than the pattern area. For large area patterns written with the small beam, the proximity effect is greatly reduced, even at 20 keV, because of the sharp edge of the exposure profile. At high beam energies, the range of backscattered electrons is large enough that they contribute only a slowly varying background dose, leading to a relatively simple proximity correction even for complex patterns.
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81.65.-b Surface treatments
41.75.Fr Electron and positron beams

Generation of <50 nm period gratings using edge defined techniques

D. C. Flanders and N. N. Efremow

J. Vac. Sci. Technol. B 1, 1105 (1983); http://dx.doi.org/10.1116/1.582643 (4 pages) | Cited 10 times

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A sequence of edge defined techniques has been developed which allows the successive multiplication of the number of lines in a grating pattern. Holographic lithography at 351.4 nm wavelength in a liquid medium has been used as the primary pattern generation technique for producing gratings with periods of ≊160 nm. A shadowing technique is then used to produce x‐ray masks with precisely controlled linewidth‐to‐period ratios. Reactive‐ion etching in CHF3 yields a square profile structure in SiO2 with precise linewidth. The basic edge defined technique consisting of CVD deposition, reactive‐ion etching, and selective isotropic etching can then be repeatedly applied given a proper choice of materials and etches. Each cycle of the edge defined technique doubles the number of lines in the pattern. Careful linewidth control at each step can result in gratings with one‐half of the initial period with minimum fundamental components. Gratings with ∼40 nm period have been fabricated by doubling the number of lines in a 160 nm period grating twice.
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42.79.Dj Gratings
81.65.-b Surface treatments
42.40.My Applications
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Applications of surface textures produced with natural lithography

H. W. Deckman and J. H. Dunsmuir

J. Vac. Sci. Technol. B 1, 1109 (1983); http://dx.doi.org/10.1116/1.582644 (4 pages) | Cited 18 times

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Surface textures with carefully controlled size, order, and morphology can be prepared by using monolayers of colloidal particles to form a lithographic mask. Microstructures produced from the mask are identical and of predetermined size because monodisperse colloidal particles can be obtained in sizes ranging from ∼200 Å–30 μm. Ordering of particles, and hence, surface texture can be either random or periodic depending upon the method used to deposit the particles. Several applications of reproducible fine structure fabricated on the surface of large area substrates are discussed.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Selective Si and Be implantation in GaAs using a 100 kV mass‐separating focused ion beam system with an Au–Si–Be liquid metal ion source

Eizo Miyauchi, Hiroshi Arimoto, Hisao Hashimoto, and Takao Utsumi

J. Vac. Sci. Technol. B 1, 1113 (1983); http://dx.doi.org/10.1116/1.582645 (4 pages) | Cited 5 times

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Submicron Si and Be ion beams have been implanted into GaAs using a 100 kV maskless ion implantation system with a liquid metal ion source which is capable of emitting double ion species (Si++ and Be++). Both ion beams are implanted at 160 keV with the dose of 1013 to 1014 cm−2. The feasibility of the focusing column was demonstrated by forming the submicron width of line patterns of alternative Si and Be doping in GaAs including a pn junction array. The linewidth of the ion implanted area has been evaluated by SEM, after selective etching of the annealed sample. It has been found that high dose implantation results in considerable lateral impurity spread of more than 1 μm even with the focused ion beams with a diameter of 0.1 μm. However, submicron width implantation turns out to be possible with relatively low doses or with shallow dopings.
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61.72.U- Doping and impurity implantation
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

100 keV focused ion beam system with a E×B mass filter for maskless ion implantation

Takao Shiokawa, Pil Hyon Kim, Koichi Toyoda, Susumu Namba, Takao Matsui, and Kenji Gamo

J. Vac. Sci. Technol. B 1, 1117 (1983); http://dx.doi.org/10.1116/1.582646 (4 pages) | Cited 3 times

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Various liquid metal alloy ion sources and a 100 keV mass separated focused ion beam system have been fabricated and their basic characteristics have been measured. These are mass spectra, energy spread and angular current intensity for ion sources, and focusing characteristics of the system. It was observed that Be–Si–Au ternary alloy ion sources produce doubly charged Be and Si ions and the importance of these ion sources is demonstrated by fabricating a GaAs JFET using a maskless ion implantation technique and by PMMA resist exposure.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
61.72.U- Doping and impurity implantation

A new submicron ion probe system

T. Tsumagari, H. Ohiwa, T. Okutani, and T. Noda

J. Vac. Sci. Technol. B 1, 1121 (1983); http://dx.doi.org/10.1116/1.582647 (4 pages)

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An ion optical system for use with EHD ion sources was designed using a cad program and constructed based on the design. This system is composed of six‐cylinder electrodes of 10 mm diam where the two middle electrodes function as octopole deflectors. The design goal was to produce a submicron ion probe capable of scanning a 2×2 mm square field under the condition that ion beam energy, the energy spread and acceptance half‐angle are 30 keV, 20 eV and 2 mrad, respectively. Preliminary experiments using an electron gun showed that the optical characteristics such as focusing voltage, deflection efficiency and deflection distortion were in good agreement with the results of computer simulation. Deflection characteristics using an EHD Ga ion source showed that an undeflected probe size of 1.5 μm in diameter increased only by 0.4 μm for 0.87 mm deflection even if no dynamic correction is made.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Computer simulations of submicron FIB system optics

W. Thompson, I. Honjo, Mark Utlaut, and H. Enge

J. Vac. Sci. Technol. B 1, 1125 (1983); http://dx.doi.org/10.1116/1.582648 (4 pages)

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The design of the optical elements for a focused ion beam (FIB) system having a 50 mm spot size over a 1 mm square field requires extensive computational analysis. We discuss the mathematical techniques applied to the components of interest in this submicron FIB system; the electrostatic lenses, the mass analyzer, and the electrostatic deflectors. The results of ion trajectory calculations predicted for the whole FIB column by the computer code snow are presented. The aberration coefficients to third order and a parametric study of a stigmatic Wien filter whose design includes entrance and exit fringe field effects will be considered. We also cover our optimization algorithms for selecting lens and deflector elements which demonstrate minimal chromatic and spherical aberrations and distortions. A spot symmetry and spot location map for the final 1 mm square field and its 50 nm image constraint is shown for mixed electronic configurations of dynamic focus, dynamic distortion, and dynamic stigmation correctors. A comparison of the computer predictions to measured values of lens parameters is given for a typical liquid metal source and its extractor lens. The equipotentials in the vicinity of a representative lens is plotted with emphasis on the dielectric‐conductor interface in order to demonstrate the significance of stressed electric fields to the hardware designer.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Use of a modified paraxial formalism for particle beam dynamics: Application to liquid metal ion sources

N. M. Miskovsky, P. H. Cutler, and T. E. Feuchtwang

J. Vac. Sci. Technol. B 1, 1129 (1983); http://dx.doi.org/10.1116/1.582649 (3 pages) | Cited 1 time

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A modified paraxial formalism has been developed and used to describe two‐dimensional ion beam dynamics in liquid metal ion sources with pointed geometries. It has been shown that appreciable differences exist between first‐order and modified paraxial theory in the calculation of beam dispersion. For a singly charged ion the effects of mass and initial energies on calculated trajectories in the modified theory are demonstrated. Finally, it is argued that only the modified theory can accurately describe within the paraxial approximation the ion trajectories close to the apex of needle‐type liquid metal ion sources.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

High resolution mass spectrometry of liquid metal ion sources

B. Wilkens and T. Venkatesan

J. Vac. Sci. Technol. B 1, 1132 (1983); http://dx.doi.org/10.1116/1.582650 (5 pages) | Cited 3 times

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The mass spectra of In, Ga, and Au liquid metal ion sources (LMIS) exhibit large molecular ion clusters with the maximum observed number of atoms/cluster ranging from 6 for Ga to 12 for In. Au ion sources emit a large percentage of its ions in the form of clusters while the ratios of ion clusters to atomic ions for Ga and In sources are one part in 103 and 104, respectively. Emission characteristics (intensity, energy distributions, and deficits) of the emitted ions of different charge and mass states were measured as a function of ion source temperature, current and emission angle. The effects of these parameters on the emitted ion velocity distribution may yield information on the mechanism of ion formation and the observed energy spread. In all of the sources tested the (dI/dΩ) distribution of the molecular clusters was broad at low energy deficits and narrow at high deficits indicating different regions of formation. However, the atomic ion angular distributions for high and low ion energy deficits are nearly equal in width, but show distinct differences in shape. Models of ion formation are presented.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
07.75.+h Mass spectrometers

Improvement of electrostatic lenses for ion beam lithography

M. Szilagyi

J. Vac. Sci. Technol. B 1, 1137 (1983); http://dx.doi.org/10.1116/1.582651 (4 pages) | Cited 6 times

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A systematic investigation of a large number of practically feasible axial potential distributions was carried out with a subsequent reconstruction of the electrode systems producing such distributions. By using parametrized analytical functions and different curve‐fitting techniques we were able to find many potential distributions with both small spherical and chromatic aberrations. A cubic spline curve‐fitting algorithm proved to be especially effective. The reconstruction of the electrode systems resulted in several new electrostatic ion lenses with excellent optical properties. As an example, a four‐electrode electrostatic lens is presented with a voltage ratio of Vmax/Vmin =9, spherical aberration coefficient Cs0/f0 =0.92 and chromatic aberration coefficient Cc0/f0 =0.55 (both coefficients are referred to the object, related to the object side focal length and calculated for the case of infinite magnification). With an acceptance angle α0=5 mrad and magnification M=2.58 a 10.5 nm aberration disk diameter can be achieved. If α0=2 mrad, the disk diameter is 3 nm.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
81.65.-b Surface treatments

Space charge effects in focused ion beams

Y. W. Yau, T. R. Groves, and R. F. W. Pease

J. Vac. Sci. Technol. B 1, 1141 (1983); http://dx.doi.org/10.1116/1.582652 (4 pages) | Cited 1 time

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Focused ion beams have significant advantages (over other directed energy beams) in terms of resist response and direct materials processing. However, the low value of q/m raises questions about space charge effects—particularly the stochastic effects which limit high throughput e‐beam systems. We have modified the space charge simulation program originally set up for electrons to allow for a greater number of particles and the effect of energy spreading in the source accelerating region. Beams of 50 keV Ga ions suffer serious spreading at currents above 1 nA (α=2 mrad); 50 keV protons suffer similar spreading at currents above 50 nA.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Characteristics of an advanced electrohydrodynamic ion source with additional mode of surface ionization

T. Okutani, M. Fukuda, T. Noda, H. Tamura, H. Watanabe, and C. Shepherd

J. Vac. Sci. Technol. B 1, 1145 (1983); http://dx.doi.org/10.1116/1.582653 (3 pages) | Cited 2 times

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An electrohydrodynamic ion source composed of a reservoir with a sleeve and an emitter tip heated by electron bombardment was constructed. This ion source can produce a variety of ion species from materials including those with a high melting point or a high vapor pressure, owing to the heating method and the reservoir with the sleeve. This ion source was operated with metals such as Ga, In, Au, and Zn, and has successfully produced an intense and stable ion beam from each metal. This gun also functions in the mode of surface ionization from a point emitter when a cesium compound such as CsCl is used as a source material.
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29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors

SiO2 films deposited on Si by an ionized cluster beam

Y. Minowa, K. Yamanishi, and K. Tsukamoto

J. Vac. Sci. Technol. B 1, 1148 (1983); http://dx.doi.org/10.1116/1.582654 (4 pages) | Cited 3 times

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SiO2 films of 0.1∼1 μm thickness were deposited on Si substrates (4 in. in diameter) by the reactive ionized cluster beam (RICB) developed from the ICB. Fine powder of SiO2 is vaporized to form a jet stream, which, on being ejected from a nozzle into a high vacuum chamber, is cooled and clustered by adiabatic expansion. The clusters thus obtained are ionized in an electron shower, accelerated, and made to bombard the Si substrate. The distribution of film thickness depends on the directivity of the cluster beam and the density distribution of ion current, the latter varying with the density distribution of the electron shower and the lens effect of an accelerating electrode. The optimum design concepts to obtain uniform films are discussed in detail, focusing on the configuration of a nozzle for the cluster beam and an electron extractor and on the location of an accelerating electrode. The physical and chemical properties of SiO2 films obtained varies with ion current, accelerating voltage, substrate temperature, and oxygen partial pressure. Above all, oxygen pressure plays a very important role in the growth of SiO2 films; with approximately 4×10−3 Pa oxygen partial pressure, the SiO2 films formed by the RICB have a refractive index of 1.46, an etching rate of 540 Å/min with a solution of HF/NH4F=1/15, and the infrared spectrum peaked at 1060 cm−1, which indicates that the RICB can form almost the same quality SiO2 films as thermal oxidation but at a very low temperature of below 300 °C. When the RICB technique is applied to deposit SiO2 films as interlevel insulators for multilayer metallization, uniform step coverages are formed at a low temperature, below 300 °C, which is considered to be possible because of the migration of ionized clusters on the surface of the substrate.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Silicon nitride stencil masks for high resolution ion lithography proximity printing

J. N. Randall, D. C. Flanders, N. P. Economou, J. P. Donnelly, and E. I. Bromley

J. Vac. Sci. Technol. B 1, 1152 (1983); http://dx.doi.org/10.1116/1.582655 (4 pages) | Cited 8 times

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Masked ion beam lithography using silicon nitride stencil masks at a 25 μm mask‐to‐sample gap has been used to replicate 80 nm lines and spaces in PMMA. An improved reactive ion etching technique for the silicon‐rich silicon nitride (SiNx) mask material using CHF3 at a 500 V self‐bias potential is reported. A grid support mask is proposed as a means of exposing arbitrary patterns with a stencil mask. The principle of this technique is demonstrated in the special case of a grating.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.65.-b Surface treatments
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Application of chlorinated polymethylstyrene, CPMS, to electron beam lithography

Yoichi Kamoshida, Mitsunobu Koshiba, Hiroshi Yoshimoto, Yoshiyuki Harita, and Kunihiro Harada

J. Vac. Sci. Technol. B 1, 1156 (1983); http://dx.doi.org/10.1116/1.582656 (4 pages)

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Swelling behavior and resist performance of a series of chlorinated polymethylstyrenes, CPMS, were investigated. Measurements of swelling ratio and resolution of the CPMS resist coating in a wide variety of organic solvents disclosed that resolution depends on the swelling ratio. In addition, it was found that Cellosolve acetate or methyl isobutyl ketone was the most suitable developer, and that the critical swelling ratio might be 3.2 (=1.473) for screening of a developer. Functional testings on CPMS showed the resist had considerably high sensitivity as well as high contrast and dry etch resistance. The selectivity ratio of the resist to aluminum, when the resist was used in a dry etching process, was 1.5 times as high as that of the conventional Novolak‐type positive‐working photoresist.
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81.05.Bx Metals, semimetals, and alloys
79.20.Kz Other electron-impact emission phenomena

Copolymers of itaconic acid and methyl methacrylate as positive electron beam resists

Y. M. N. Namasté, S. K. Obendorf, C. C. Anderson, P. D. Krasicky, F. Rodriguez, and R. Tiberio

J. Vac. Sci. Technol. B 1, 1160 (1983); http://dx.doi.org/10.1116/1.582657 (6 pages) | Cited 1 time

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The copolymers of itaconic acid with methyl methacrylate P(MMA–ItA), are expected to perform as highly sensitive electron beam resists based on their high e‐beam chain scission efficiencies (Gs). The Gs for P(MMA–20% ItA) was 2.5 times that of PMMA, and the Gs for P(MMA–35% ItA) was nearly 5 times that of PMMA. The copolymers have exhibited improved thermal stability over PMMA, as indicated by a decomposition temperature for P(MMA–20% ItA) that is 30 °C higher than that of PMMA. Infrared analyses of the copolymers showed that anhydride formed during the prebake step of the lithographic evaluation. The anhydride was predominantly a five‐membered intramolecular anhydride ring which formed within single monomeric itaconic acid units. Some intermolecular anhydride was suspected because of the reduced solubility of the baked copolymers. The copolymer resists were synthesized to contain 20 and 35 mole% itaconic acid. Copolymers of each composition were evaluated with varying prebake conditions to provide varying amounts of anhydride formation. These resists were then evaluated on the basis of sensitivity, contrast, and resolution. Appropriate solvent systems for developing the lithographic patterns were chosen using a three‐dimensional solubility mapping technique based on polar, nonpolar, and hydrogen bonding solubility parameters. P(MMA–20% ItA), with a 160 °C prebake, exposed at 7.5×10−6 C/cm2 with an accelerating voltage of 20 kV, was developed using a mixture of ethyl acetate and MIBK without thinning of the unexposed resist. P(MMA–35% ItA) baked at 120 °C produced 1 μm wide images at 5 to 8 μC/cm2 with a contrast (γ) of 2.5 to 3.5. 10% thinning was observed when developing areas exposed at 8 μC/cm2. Vertical walls were obtained at about 10 μC/cm2, and undercutting was observed with higher doses.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
79.20.Kz Other electron-impact emission phenomena
82.35.-x Polymers: properties; reactions; polymerization

PMMA electron resists with narrow molecular weight distribution

H. W. Deckman and J. H. Dunsmuir

J. Vac. Sci. Technol. B 1, 1166 (1983); http://dx.doi.org/10.1116/1.582753 (5 pages) | Cited 3 times

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Narrow molecular weight distribution (mathw/mathn<1.1) poly (methyl methyacrylate) [PMMA] with low molecular weight (mathw<200 000) has been evaluated as an electron resist. It is shown that sensitivity and contrast of these narrow distribution resists can be altered by prebaking either above or below the glass transition temperature. Sensitivity of narrow distribution PMMA resists prebaked below the glass transition temperature (Tg) can be a factor of 5 greater than the same resist prebaked above Tg . Sensitivity improvement is shown to be caused by solvent trapped in the network of narrow distribution resists prebaked below Tg . Trapped solvent preswells the polymer network so that small perturbations to the molecular weight distribution of the PMMA cause it to become soluble in developer. Low molecular weight broad distribution resists similarly prepared are readily soluble in the developer and do not exhibit improved sensitivity in usable lithographic images. When narrowly fractionated PMMA is baked above Tg, the sensitivity is found to be slightly different from broad distribution material, and the contrast is significantly improved. Electron beam exposure of these narrow distribution PMMA resists baked below and above Tg has produced 2000 and 800 Å period gratings, respectively.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
79.20.Kz Other electron-impact emission phenomena

Direct pattern fabrication on silicone resin by vapor phase electron beam polymerization

Masao Morita, Saburo Imamura, Toshiaki Tamamura, Osamu Kogure, and Kei Murase

J. Vac. Sci. Technol. B 1, 1171 (1983); http://dx.doi.org/10.1116/1.582754 (3 pages) | Cited 1 time

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A new technique for high resolution lithography with a dry‐developed multilayer resist system is demonstrated. The technique involves a direct pattern fabrication by electron beam‐induced vapor phase graft polymerization. The selective pattern formation in irradiated areas was performed using PMMA or silicone resin as a base film and styrene as a grafting monomer. The base film patterns can be fabricated by dry etching with the mask of grafted patterns. However, because of isotropic behavior in the growth of grafted polymer, the base film thickness to be directly etched with the mask of graft‐polymerized film is severely limited by the resolution to be achieved. The combination of thin silicone resin as a directly etched layer using graft‐polymerized film and thick organic polymer as the bottom layer can solve the conflict between resolution and overall resist thickness, because the silicone resin has an excellent durability against oxygen RIE of organic polymers. Submicron pattern formation with a high aspect ratio was demonstrated with this dry‐developed multilayer resist system.
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81.65.-b Surface treatments
82.35.-x Polymers: properties; reactions; polymerization
41.75.Fr Electron and positron beams

High resolution patterning with Ag2S/As2S3 inorganic electron‐beam resist and reactive ion etching

B. Singh, S. P. Beaumont, A. Webb, P. G. Bower, and C. D. W. Wilkinson

J. Vac. Sci. Technol. B 1, 1174 (1983); http://dx.doi.org/10.1116/1.582755 (4 pages) | Cited 1 time

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A new two‐step development process has been devised which considerably improves edge smoothness and linewidth resolution in the Ag2S/As2S3 inorganic resist system. Using this process, smooth‐edged 30 nm wide lines have been patterned by electron‐beam lithography and transferred into an underlying polyimide film by oxygen reactive ion etching. This high resolution bilayer process exploits the exceptional etch resistance of the silver‐doped chalcogenide glass.
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81.65.-b Surface treatments
41.75.Fr Electron and positron beams

Nitrocellulose as a self‐developing resist with submicrometer resolution and processing stability

M. W. Geis, J. N. Randall, T. F. Deutsch, N. N. Efremow, J. P. Donnelly, and J. D. Woodhouse

J. Vac. Sci. Technol. B 1, 1178 (1983); http://dx.doi.org/10.1116/1.582756 (4 pages) | Cited 9 times

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Nitrocellulose films have been shown to function as self‐developing resist layers that are sensitive to both low energy ion bombardment by heavy ions such as Ar+ or Xe+ and to 193 nm UV radiation from a pulsed excimer laser. The resist develops at 0.6 μm s−1 for a beam of 2 keV Ar+ ions (1 mA cm−2), and has a sensitivity of ∼2 μm cm2 J−1 for ArF laser radiation, together with a demonstrated optical resolution of 300 nm. The decomposition products of the self‐developing resist consist primarily of water, nitrogen, carbon monoxide, nitric oxide, and carbon dioxide. When exposed to light ions, electrons, ArF laser radiation at energy densities less than 20 mJ cm−2, or heat, the resist decomposes leaving a nonvolatile residue. The formation of this residue is believed to be responsible for the comparative stability of nitrocellulose under reactive ion etching. The reactive ion etching rate in CHF3 is about twice as fast for nitrocellulose as for SiO2. The etching rate can be reduced by the addition of volatile metal salts to the nitrocellulose, but this also reduces the rate of self‐development produced by heavy ion bombardment.
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81.65.-b Surface treatments
07.68.+m Photography, photographic instruments; xerography

Resist exposure with light ions

I. Adesida, C. Anderson, and E. D. Wolf

J. Vac. Sci. Technol. B 1, 1182 (1983); http://dx.doi.org/10.1116/1.582757 (4 pages) | Cited 4 times

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Radiation yields or Gs‐values in polymethylmethacrylate (PMMA), which are the number of chain scissions per 100 eV of absorbed energy, due to irradiation with electrons, protons, and helium, lithium, beryllium, and boron ions have been measured. Gs values for protons and electrons are the same at ∼0.75, while those of helium, lithium, beryllium, and boron ions are 0.45, 0.44, 0.40, and 0.45, respectively. Initial results on sensitivities and mean pathlengths of ions in PMMA obtained from solubility studies are also presented.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.20.Kz Other electron-impact emission phenomena

Contact lithography at 157 nm with an F2 excimer laser

H. G. Craighead, J. C. White, R. E. Howard, L. D. Jackel, R. E. Behringer, J. E. Sweeney, and R. W. Epworth

J. Vac. Sci. Technol. B 1, 1186 (1983); http://dx.doi.org/10.1116/1.582758 (4 pages) | Cited 6 times

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We report the first use of an F2 excimer laser and a novel mask technology for high resolution photolithography at 157 nm. With a contact lithography technique resist lines as narrow as 0.15 μm have been made. Because of the short wavelength involved, conventional mask technology using quartz substrates could not be employed. Alkaline‐earth halide substrates (e.g., CaF2) that have high transmittance at 157 nm were used as a base for the mask production. Resolution test masks were prepared using e‐beam lithography and reactive ion etching to pattern a polyimide film on the substrates. The development of lithographic techniques at this wavelength is significant since the 157 nm radiation is currently the deepest VUV radiation available with high energy flux from a readily obtained commercial laser.
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81.65.-b Surface treatments
42.60.-v Laser optical systems: design and operation

A critical examination of submicron optical lithography using simulated projection images

Alan E. Rosenbluth, Douglas Goodman, and B. J. Lin

J. Vac. Sci. Technol. B 1, 1190 (1983); http://dx.doi.org/10.1116/1.582759 (6 pages) | Cited 10 times

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It may be possible to extend optical lithography well into the submicron regime, given a multilayer resist system that confines imaging to a thin layer, and that eliminates reflection from the substrate. The necessary exposure and focus tolerances are determined by simulating the projection of partially coherent, diffraction‐limited images onto an ideal multilayer resist system. Exposure–defocus diagrams are then generated by requiring that critical dimensions satisfy a ±10% tolerance. We investigate the prospects for submicron lithography with 0.75 and 0.5 μm minimum features. Two lens systems are analyzed; a commercially available 0.28 NA lens operating at 436 nm, and an advanced 0.35 NA lens operating at 365 nm. The features studied include contact holes, rectangular lines and spaces, and equal line space gratings, and are representative of many typical IC mask patterns. Linewidth tailoring or biasing allows these features to be printed within tolerance simultaneously if the exposure can be controlled within ±6%. The corresponding depth of focus is about 3 μm for the 0.75 μm features, and 1.5 μm for the 0.5 μm features. More general shape correction may be needed to print objects of arbitrary complexity.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
42.82.-m Integrated optics

A precision wide‐range optical gap measurement technique

D. C. Flanders and T. M. Lyszczarz

J. Vac. Sci. Technol. B 1, 1196 (1983); http://dx.doi.org/10.1116/1.582760 (4 pages) | Cited 2 times

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This paper describes a new optical interferometric technique for measuring the gap between a mask and a substrate in proximity printing lithography systems. A uniform‐intensity, collimated He–Ne laser beam is focused onto the mask. Light reflected from the mask interferes with the light reflected from the substrate to form a characteristic pattern. To first order, the spatial frequency of this pattern is linearly dependent upon the mask‐to‐substrate gap. A linear array is used to observe the interference pattern. The resulting signal is processed using correlation techniques to determine the gap. Highly accurate, absolute measurements can be made using this scheme which is quite distinct from the well known interferometric methods which can only measure relative motion. The achievable accuracy and range are functions of illumination, system geometry, signal detection, and processing. An experimental measurement system has demonstrated ±0.25% accuracy over a 25 to 120 μm range.
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06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.60.Ly Interferometers
42.62.-b Laser applications
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Deep‐UV spatial‐frequency doubling by combining multilayer mirrors with diffraction gratings

A. M. Hawryluk, Henry I. Smith, and D. J. Ehrlich

J. Vac. Sci. Technol. B 1, 1200 (1983); http://dx.doi.org/10.1116/1.582745 (4 pages) | Cited 1 time

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A multilayer dielectric mirror was deposited over an aluminum grating of 198 nm period on a quartz substrate. This was then used as a parent mask to expose a grating of 99 nm period in PMMA by deep‐UV spatial‐frequency doubling with an ArF laser (λ=193 nm). The multilayer mirror suppressed the zero order permitting the doubled pattern to be exposed over a depth of field of several micrometers. Holographic lithography and spatial‐frequency doubling are compared. It is shown that the latter is preferred if λ/Δλ<105.
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42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings
42.40.My Applications

An improved technique for resist‐profile control in holographic lithography

Henri J. Lezec, Erik H. Anderson, and Henry I. Smith

J. Vac. Sci. Technol. B 1, 1204 (1983); http://dx.doi.org/10.1116/1.582746 (3 pages) | Cited 1 time

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Undercut profiles are achieved in holographically exposed resist when the maximum of the orthogonal standing wave is placed at the resist–substrate interface. We demonstrate that this condition can be achieved by tilting the substrate normal out of the plane of the interferometer. The condition of maximum interface intensity is detected by determining when there is maximum optical coupling into a test film of 10 nm‐thick photoresist. Exposure of the test film is detected by diffraction.
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42.40.My Applications
42.79.Dj Gratings
78.66.-w Optical properties of specific thin films
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures

Fabrication of submicron crossed square wave gratings by dry etching and thermoplastic replication techniques

H. W. Lehmann, R. Widmer, M. Ebnoether, A. Wokaun, M. Meier, and S. K. Miller

J. Vac. Sci. Technol. B 1, 1207 (1983); http://dx.doi.org/10.1116/1.582747 (4 pages) | Cited 9 times

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Crossed square wave grating structures with periodicities below 0.4 μm have been fabricated in SiO2 and replicated into PVC. The structure in SiO2 is made by optically contact printing a Cr mask onto a trilevel structure consisting of an amorphous quartz plate, an a‐Si film and positive photoresist and subsequent reactive sputter etching in CCl2F2 and CHF3 to pattern the a‐Si and SiO2, respectively. Up to 1 μm deep structures have been made in SiO2 and replicated into PVC by embossing with a Ni master. These PVC replicas can be used as efficient substrates for SERS (surface enhanced Raman scattering) after angle evaporation of a very thin Cu film. SERS spectra for Nile Blue are shown.
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42.79.Dj Gratings
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Electron beam fabrication of high resolution masks

J. L. Kenty, L. C. Puzio, and F. J. Schauerte

J. Vac. Sci. Technol. B 1, 1211 (1983); http://dx.doi.org/10.1116/1.582748 (4 pages)

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A mask set was fabricated with electron beam lithography using conventional and novel pattern replication techniques. Minimum feature size on the high resolution layer was 0.5 μm. The masks were later used for deep ultraviolet (UV) contact lithography to produce working MOSFET’s with submicrometer channel lengths. Two 0.5 μm level masks were fabricated on quartz plates, one each by two techniques: conventional chromium wet etching, and a new technique utilizing ion implanted polymethyl methacrylate (PMMA) as the masking medium. In this unconventional method, a PMMA coated quartz plate was exposed by an electron beam and developed to leave 0.5 μm features on a clear background. The subsequent bombardment of the patterned PMMA with 200 keV Si+ created a film which is opaque to near and deep UV, making it a suitable masking medium for conventional and deep UV photolithography. During the ion bombardment, the PMMA undergoes significant structural change, becoming harder, optically denser, and more adherent to the quartz substrate. A 0.5 μm feature size mask of the same polarity was also made using electron beam patterning of PMMA and wet etching of the underlying chromium. A mask set was also fabricated with a minimum feature size of 1.0 μm. In this level, the 1 μm clear areas were surrounded by opaque chromium areas after wet chemical etching. This mask set was used for conventional contact photolithography in the fabrication of working NMOS devices.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.Tv Field effect devices

Use of antireflective coating in bilayer resist process

Yi‐Ching Lin, Sue Jones, and Gene Fuller

J. Vac. Sci. Technol. B 1, 1215 (1983); http://dx.doi.org/10.1116/1.582749 (4 pages) | Cited 1 time

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A new multilayer resist process consisting of a thin antireflective (AR) film between the thick bottom PMMA layer and the top photoresist layer of the conventional bilayer resist process is reported in this paper. Aluminum features of micron and submicron size over topography have been achieved with this novel resist process by using a conventional 10:1 reduction GCA DSW 4800 stepper to expose the top photoresist layer. Excellent linewidth control over steps is demonstrated. Both the standing wave effect in the top resist layer and the interference from the light scattered by the substrate topography are eliminated in this AR coating approach. The mixing of the two resist layers encountered in the original bilayer resist process does not appear in this new process. The plasma etch resistance of this new multilayer resist process is improved by retaining the capping top photoresist layer, which also eliminates the delamination of the AR layer during the PMMA development. This novel resist process provides a low‐cost, reliable method for further extending the resolution capability of existing steppers to meet the needs of advanced product designs.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
75.20.Ck Nonmetals

Submicrometer contact hole delineation with a two‐layer deep‐UV portable conformable masking system

K. E. Petrillo, V. W. Chao, and B. J. Lin

J. Vac. Sci. Technol. B 1, 1219 (1983); http://dx.doi.org/10.1116/1.582750 (6 pages) | Cited 1 time

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The two‐layer deep‐UV portable conformable masking (PCM) system using a novolac resist as the imaging layer on a PMMA planarizing layer was chosen to delineate 1.0×1.25 μm contact holes with a 0.32 NA 405 nm 5× projection lens to support 1 μm MOS circuit fabrication. Measured SiO2 images, delineated with CF4+H2 reactive ion etching, exhibited insignificant biases and small size variations for critical features down to 0.87 ×0.87 μm over typical wafer topography when a near‐UV dye was incorporated in the planarizing layer. A comparison of the dyed and undyed deep‐UV PCM and a single‐layer soaked process will also be given.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Multilayer resist technique for submicron optical lithography

C. H. Ting and K. L. Liauw

J. Vac. Sci. Technol. B 1, 1225 (1983); http://dx.doi.org/10.1116/1.582751 (10 pages) | Cited 4 times

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Analysis has shown that the limiting factor in achieving 1 μ technology in optical lithography is mainly due to nonideal operating conditions such as surface topography, reflectivity, defocusing, etc. By using a multilayer resist process to eliminate these extraneous factors, we have demonstrated that optical lithography can be pushed beyond 1 μ into the submicron range. The advantages and problems encountered with the bilayer DUV flood exposure process were pointed out. One of the most serious problems, due to reflected light from surface topography, was corrected by using an antireflecting coating between the PMMA and AZ resist layers. This antireflection coating layer also eliminates the interface mixing between PMMA and AZ resists. A trilayer resist process was developed based on the highly directional RIE process. A new barrier film based on spin‐on‐glass was optimized to obtain defect free films. This spin‐on barrier layer greatly simplifies the work flow and provides significant cost savings over the conventional vacuum deposited or CVD films. Submicron resolution capability and good dimension controls over severe wafer surface topography have been demonstrated. The trilayer resist process has been demonstrated to be capable of handling dimensions beyond the resolving power of currently available optical lithographic systems.
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42.82.-m Integrated optics
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Planarization phenomena in multilayer resist processing

L. K. White

J. Vac. Sci. Technol. B 1, 1235 (1983); http://dx.doi.org/10.1116/1.582761 (6 pages)

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