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Nov 1981

Volume 19, Issue 4, pp. 841-1428


Ion interaction with solids: Surface texturing, some bulk effects, and their possible applications

O. Auciello

J. Vac. Sci. Technol. 19, 841 (1981); http://dx.doi.org/10.1116/1.571224 (27 pages) | Cited 23 times

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Texturing of surfaces and some bulk effects produced during ion‐solid interactions already are or have the potential to be useful and/or important in several different technologies, and/or experimental techniques, namely: (a) controlled thermonuclear fusion and vacuum technologies, (b) microelectronics, (c) surface acoustical and optical technologies, (d) solar energy conversion technology, (e) thin film technology, (f) biomedicine (implantology), (g) ion beam surface analysis, (h) field ion emission and electron microscopy, (i) surface enhanced Raman scattering spectroscopy, and (j) other technologies. In some cases texturing is desirable while the opposite is true for other situations. A review is presented on the possible technological applications of textured surfaces and some bulk effects produced when ion and electromagnetic radiations interact with solids in an attempt to bring together information which is dispersed among journals involving fields of research which are sometimes unrelated. Additionally, a critical analysis of the underlying physics of some phenomena is presented.
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81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
78.90.+t Other topics in optical properties, condensed matter spectroscopy and other interactions of particles and radiation with condensed matter (restricted to new topics in section 78)
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Prospects for high‐brightness x‐ray sources for lithography

N. P. Economou and D. C. Flanders

J. Vac. Sci. Technol. 19, 868 (1981); http://dx.doi.org/10.1116/1.571225 (4 pages) | Cited 2 times

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The x‐ray source is a critical part of any x‐ray lithography system since the source characteristics directly affect resolution, alignment, and throughput. Conventional electron bombardment sources, using either stationary or rotating anodes, are now in wide use. However their poor efficiency, low brightness, and uncollimated nature makes them doubtful candidates for high throughput lithographic systems. Several possible alternative sources have been discussed in recent years. They fall into two broad categories: accelerated charged particle beams and high temperature plasmas. The first category includes the synchrotron and related devices such as wigglers. Although these are large and costly installations, they are excellent sources of soft x‐rays and have many advantages as lithographic sources. The second category contains many different systems capable of producing dense, high temperature plasmas. Some of these have been shown to have promise as compact, efficient, high brightness x‐ray sources. Devices in each of these two categories will be discussed and the relative advantages and disadvantages of each as a source for x‐ray lithography will be outlined.
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07.85.-m X- and γ-ray instruments
52.50.Dg Plasma sources
52.75.-d Plasma devices

Organosilicon monomers for plasma‐developed x‐ray resists

G. N. Taylor, T. M. Wolf, and J. M. Moran

J. Vac. Sci. Technol. 19, 872 (1981); http://dx.doi.org/10.1116/1.571226 (9 pages) | Cited 9 times

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A variety of silicon‐containing monomers for plasma‐developed resists formulated with chlorine‐containing host polymers have been prepared and evaluated for use with x‐ray lithography. The major design problems encountered were monomer incompatibility, high volatility, and low reactivity. One class of monomers, the bis‐acryloxy‐ and and methacryloxyalkyltetramethyldisiloxanes, satisfies all requirements. A formulation with optimum properties contains 90 parts poly(2,3‐dichloro‐1‐propyl acrylate) (DCPA) and 10 parts bis‐acryloxybutyltetramethyldisiloxane (BABTDS). It is very sensitive (30–60 s exposure time), has high resolution (better than 0.5 μm), and can be developed by reactive ion etching which provides extremely uniform developed patterns.
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68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
81.65.-b Surface treatments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Submicroscopic pattern replication with visible light

U. Ch. Fischer and H. P. Zingsheim

J. Vac. Sci. Technol. 19, 881 (1981); http://dx.doi.org/10.1116/1.571227 (5 pages) | Cited 70 times

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Contact imaging with visible light is possible at submicroscopic resolution because the near field of a radiating object contains information of sufficiently high resolution. In this paper we demonstrate this principle by contact imaging of planar submicroscopic metal patterns with blue light (400 nm). Experimental details are described for two experiments: (1) The shadow of an opaque pattern was recorded on a negative photoresist and developed using permanganate staining. (2) An image of a transparent metal pattern was imprinted onto a molecular dye layer, exploiting the fact that photochemical bleaching of the dye is inhibited by contact with the metal due to energy transfer. Development was by silver decoration. The resolution obtained was 100 nm with the photoresist, and 50 to 70 nm with the dye layer.
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07.68.+m Photography, photographic instruments; xerography
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
82.50.-m Photochemistry
42.30.Sy Pattern recognition

Microstructures for high‐energy x‐ray and particle imaging applications

N. M. Ceglio, G. F. Stone, and A. M. Hawryluk

J. Vac. Sci. Technol. 19, 886 (1981); http://dx.doi.org/10.1116/1.571228 (6 pages) | Cited 1 time

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Coded imaging techniques using thick, micro‐Fresnel zone plates as coded apertures have been used to image x‐ray emission (2–20 keV) and 3.5 MeV Alpha particle emissions from laser driven micro‐implosions. Image resolution in these experiments was 3–8 μm. Extension of this coded imaging capability to higher energy x rays (∠100 KeV) and more penetrating charged particles (e.g., ∠15 MeV protons) requires the fabrication of very thick (50–200 μm), high aspect ratio (10:1), gold Fresnel zone plates with narrow linewidths (5–25 μm) for use as coded apertures. A reactive ion etch technique in oxygen has been used to produce thick zone plate patterns in polymer films. The polymer patterns serve as electroplating molds for the subsequent fabrication of the free‐standing gold zone plate structures.
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42.79.Ci Filters, zone plates, and polarizers
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
42.30.Va Image forming and processing

Application of ≊100 Å linewidth structures fabricated by shadowing techniques

D. C. Flanders and Alice E. White

J. Vac. Sci. Technol. 19, 892 (1981); http://dx.doi.org/10.1116/1.571229 (5 pages) | Cited 14 times

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A variety of shadowing techniques have been developed for fabricating simple structures with lines and spaces in the 100 Å linewidth regime. In the basic technique, a smooth vertical step with precisely determined depth is produced in a substrate by reactive ion etching. This step is shadowed at a shallow angle by evaporation in order to deposit material on the vertical wall. The substrate is then etched at normal incidence with an ion beam to remove the thin layer of material outside the step. This leaves a thin rectangular line of material at the step. By alternately evaporating different materials and by adding lithography and etching steps, more complex structures can be made. Applications of these structures in wire grating optical polarizers and the use of long thin wires for studying electron localization are described. Optical polarizers with extinction ratios of nearly 200 to 1 have been made. This demonstrates some of the unique capabilities of the shadowing technique since high quality polarizers require large areas of high aspect ratio ≊100 Å linewidth metal lines.
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42.79.Dj Gratings

Gold transmission gratings with submicrometer periods and thicknesses ≳0.5 μm

A. M. Hawryluk, N. M. Ceglio, Robert H. Price, J. Melngailis, and Henry I. Smith

J. Vac. Sci. Technol. 19, 897 (1981); http://dx.doi.org/10.1116/1.571230 (4 pages) | Cited 10 times

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Gold gratings with spatial periods of 0.3 and 0.2 μm have been fabricated in thicknesses of 0.6 and 0.25 μm, respectively, and used in x‐ray spectroscopy and spatial‐period‐division. Fabrication techniques included: holographic lithography, shadowing, x‐ray lithography, and gold microplating. Control of linewidth to tolerance of the order of 10 nm has been demonstrated for gratings of 0.2 μm period. A high resolution imaging spectrometer, composed of a 22× Wolter x‐ray microscope in conjunction with a gold transmission grating, was tested. At a wavelength of 0.69 nm, a resolving power, λ/Δλ, of 200 was demonstrated. Resolution in this case was source‐size limited. Gratings of 99.5 nm period were exposed in PMMA by x‐ray (λ = 4.5 nm) spatial‐period‐division.
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07.85.-m X- and γ-ray instruments
42.79.Dj Gratings
95.55.-n Astronomical and space-research instrumentation
42.40.My Applications

Electron‐beam fabrication of a 1.25 μm, 16‐bit I2L microprocessor

R. H. Havemann, R. L. Smith, S. A. Evans, L. A. Arledge, R.L. Love, and G. L. Varnell

J. Vac. Sci. Technol. 19, 901 (1981); http://dx.doi.org/10.1116/1.571186 (4 pages)

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E‐beam direct slice writing has been utilized to fabricate a 55% linear shrink of the SBP9989, a 16‐bit I2L microprocessor in the familiar TI SBP9900 series. The scaled device contains approximately 5 K gates and the chip area is 14.4 mm2 as compared with 37.1 mm2 for the full‐sized chip. The chip layout is maintained in a database which can be easily manipulated to change design rules, scale selected geometries (pnp base width, collector size, etc.) or vary the overall scaling factor. The design requires minimum geometries of 1.25 μm and an overall process registration of ±0.75 μm. Patterns were delineated in TI‐323A positive and TI‐309 negative electron resists using EBMIII, a vector‐scanned, laser‐controlled electron beam exposure machine with a minimum beam diameter of 0.4 μm and level‐to‐level registration accuracy of <±0.25 μm. The oxide‐separated, double‐level‐metal fabrication process used ion implantation and anisotropic plasma etching to achieve maximum control of junction depths and etch profiles, respectively. Fabricated units were fully functional from −55 °C to +125 °C and showed a speed improvement of 2× at one‐half the power of the full‐size chip.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

E‐beam fabrication of 1.25 micron 4 K static memory

P. Shah, G. Pollack, R. Miller, G. Varnell, W. Lee, R. Love, S. Wood, and R. Robbins

J. Vac. Sci. Technol. 19, 905 (1981); http://dx.doi.org/10.1116/1.571187 (6 pages)

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Fast, high density 4 K‐bit static RAM’s (SRAM’s) have been fabricated utilizing electron beam direct slice writing and dry etch processes to demonstrate 1.25 μ VLSI MOS device technology. Access times of 15 ns were obtained for these scaled memories with channel lengths of 1.0 μ on a chip size of only 6 K mil2 vs the standard production 4 K SRAM with 35–45 ns access times, a 2.5 μ channel length and a chip size of 20 K mil2. All levels were patterned using a vector‐scanned electron‐beam exposure system with a capability of 1 μ resolution, ±0.2 μ level‐to‐level registration, and automatic chip‐by‐chip alignment. High speed, high resolution positive and negative electron beam resists were used for all patterning steps. All implanted, 250 Å gate oxide, scaled MOS processes with dry etching techniques for Si, SiO2, and Si3N4 were used to realize these static memories functional over full temperature.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation
89.20.Ff Computer science and technology
41.75.Fr Electron and positron beams

Electron beam direct writing of capacitor coupled GaAs FET logic circuits

C. Dix, P. G. Flavin, P. Hendy, and M. E. Jones

J. Vac. Sci. Technol. 19, 911 (1981); http://dx.doi.org/10.1116/1.571188 (5 pages)

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Capacitor coupled logic circuits using depletion‐mode Schottky‐gate GaAs transistors are being made by direct electron beam exposure with a Cambridge Instruments EBMF‐1. Etched active mesas are defined using either a negative working polystyrene based resist or positive working PMMA. The use of PMMA is possible following the development of a tone reversal program for the PDP 11/34 EBMF‐1 control computer. The chips have 2 mm sides and each is written in a single field. Automatic registration of the FET electrodes is accomplished using topographic marks for the source/drain level and metal marks for the gate and subsequent layers. The source/drain and gate metallizations are defined by liftoff using PMMA. Software to correct the intraproximity effect within individual exposure features has been developed, and applied to the 1.5 μm gate structures. The dose given to a feature and its dimensions are simultaneously adjusted to obtain the correct feature size and resist profile for liftoff metallization. In subsequent steps a polyimide insulation layer and a metal interconnect level are defined to complete the circuit.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.77.-n Atomic, molecular, and charged-particle sources and detectors

FET fabrication using maskless ion implantation

R. L. Kubena, C. L. Anderson, R. L. Seliger, R. A. Jullens, E. H. Stevens, and I. Lagnado

J. Vac. Sci. Technol. 19, 916 (1981); http://dx.doi.org/10.1116/1.571189 (5 pages) | Cited 5 times

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Focused ion beams from Au–Si, Au–Be, and B–Pt liquid–metal–alloy ion sources have been used to implant GaAs and Si. An Al stopping layer on the wafers was used to trap the Au and Pt ions. Hall mobilities consistent with those in bulk materials have been obtained for B‐doped Si and Be‐doped GaAs. In addition, a 2000‐Å‐diam Au–Si focused ion beam was used to implant the doped regions of GaAs metal‐semiconductor gate field‐effect transistors. The 140‐keV Si++ beam component was deflected under computer control to implant 8×50 μm active channel regions and 16×50 μm contact regions. The devices were metalized using conventional lithography. DC electrical characteristics of the 1.5‐μm‐gate‐length devices are comparable to those of conventionally processed devices of identical geometry.
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85.30.Tv Field effect devices
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Ultraviolet grating polarizers

G. J. Sonek, D. K. Wagner, and J. M. Ballantyne

J. Vac. Sci. Technol. 19, 921 (1981); http://dx.doi.org/10.1116/1.571190 (3 pages) | Cited 13 times

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Wet and dry processing technologies are applied to the development of high‐aspect‐ratio gratings in SiO2. Planar gratings having nearly vertical sidewalls and periods of 3000 Å are used as the basic structure for generating ultraviolet polarizers which perform at wavelengths well below 3000 Å. Extinction ratios of 0.5 at wavelengths of 2400 Å have been obtained. With new techniques available for generating fine‐period surface gratings, it should be possible to fabricate planar polarizers with high polarization efficiencies at even shorter wavelengths.
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42.79.Dj Gratings

An electron‐beam/optical‐hybrid lithography approach to submicrometer electronic devices

J. C. Potosky, A. J. Higgins, S. T. Hoelke, R. G. Imerson, F. F. Kinoshita, R. L. Maddox, and J. P. Reekstin

J. Vac. Sci. Technol. 19, 924 (1981); http://dx.doi.org/10.1116/1.571191 (3 pages)

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Submicrometer transistor gates have been fabricated in CMOS/SOS prototype VLSI circuits and GaAs digital integrated circuits. A hybrid lithography approach was used to take advantage of the rapid throughput of optical lithography and the high resolution capabilities of electron‐beam lithography. The entire gate levels of these devices were defined with direct write electron‐beam lithography. The six remaining lithographies in the CMOS/SOS device and the five remaining levels in the GaAs device were defined with various optical lithography systems. A unique electron‐beam fiducial marker fabrication technique was required for each of the two devices. The goal of this approach was to substitute electron‐beam lithography for optical lithography in the gate level only, leaving the remaining device process unaltered. Gate lengths as small as 0.6 μm were fabricated in the Si devices and 0.9 μm gates were achieved in GaAs. The CMOS/SOS gates were patterned in PMMA resist over MoSi2 and requires an Al liftoff and ion mill. The GaAs gates were patterned in AZ2400 resist which became an etch mask for underlying SiO2 and Si3N4 films. Circuits in both devices were sucessfully operated.
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85.30.Pq Bipolar transistors
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Electron‐beam direct writing of n‐MOS devices and analysis of overlay and linewidth accuracies

S. Okazaki, F. Mulai, Y. Takeda, K. Mochiji, E. Takeda, H. Kume, and S. Asai

J. Vac. Sci. Technol. 19, 927 (1981); http://dx.doi.org/10.1116/1.571192 (5 pages)

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Electron‐beam direct writing of experimental, n‐channel MOS devices is reported. This work has been done to identify the relative potential advantages and disadvantages of e‐beam direct writing as one of the candidates for submicrometer lithography technology. The e‐beam machine used in this work is a vector‐scan system with a laser interferometry positioned stage. Both wafer registration and chip‐by‐chip registration schemes have been implemented in a simple, unified algorithm. Signal‐to‐noise ratio and process compatibility have been considered in determing the structure of alignment marks, with shallow (∠1.0 μm) grooves in the silicon wafer being adopted. Analysis of error factors, both instrumental and process related, which influence registration accuracy and linewidth control, has been carried out using a series of special experiments. It has been found that errors are rather evenly distributed over various causes. Electron beam direct writing has been found to provide excellent linewidth control and overlay accuracy, with 3 sigma limits of 0.1 and 0.5 μm, respectively.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
41.75.Fr Electron and positron beams
61.80.Fe Electron and positron radiation effects

A high speed electron beam lithography system

J. C. Eidson and R. K. Scudder

J. Vac. Sci. Technol. 19, 932 (1981); http://dx.doi.org/10.1116/1.571193 (4 pages) | Cited 2 times

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The Hewlett–Packard electron beam lithography system is described. The system is capable of being used either for direct writing on a wafer or for mask generation. It has been designed for high throughput production applications with data rates up to 300 MHz, using a field emitter electron source, a modified raster scan, and electrostatic deflectors. Deflection field aberrations are corrected so that patterns up to 5 in. square may be exposed with layer to layer registration better than 0.13 microns. The system architecture and design constraints will be discussed.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.77.-n Atomic, molecular, and charged-particle sources and detectors

A high‐current, high speed electron beam lithography column

J. Kelly, T. Groves, and H. P. Kuo

J. Vac. Sci. Technol. 19, 936 (1981); http://dx.doi.org/10.1116/1.571194 (5 pages) | Cited 4 times

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The design of a high speed electron‐beam lithography column is described. Designed for use with a high speed raster scan system, the column produces a beam current of 600 nA in an 0.5 μm round spot, and has a deflection field of 5 mm2. The column uses a zirconiated thermal field emission cathode, two magnetic lenses, with an intermediate cross‐over for blanking purposes, and a two‐stage electrostatic deflection system, producing both speed and precision. The column is compatible with a 300 MHz pixel exposure rate and has an accuracy of better than ±0.125 μm (2σ).
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Variably shaped electron beam lithography system, EB55: I. System design

M. Fujinami, T. Matsuda, K. Takamoto, H. Yoda, T. Ishiga, N. Saitou, and T. Komoda

J. Vac. Sci. Technol. 19, 941 (1981); http://dx.doi.org/10.1116/1.571195 (5 pages) | Cited 1 time

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The precision electron beam exposure system EB55 has been developed for direct wafer writing of submicron patterns. This paper describes the system architecture, design approach, and system specifications. The system utilizes a variably shaped beam column with a spot size ranging from 0.5 to 5.1 μm square, which is adjustable in 0.02 μm increments. Pattern data, compressed by a pattern data preparation software, is supplied to the high‐speed digital control unit, where it is expanded to provide control data at a 320 ns shot rate to an analog unit. The analog unit provides deflection current and voltage to the electrostatic deflection plates and magnetic deflection coils with 0.02 μm resolution. Pattern accuracy is maintained by deflection distortion correction and overlay techniques. The deflection error is measured within 0.02 μm accuracy over a 2.6 mm square field with a mark detector and laser position sensor and corrected by a digital correction unit. Overlay accuracy is assured by registering to fiducial marks on the wafer and measuring wafer deformation to determine field adjustments. The exposure time per wafer is about 41 min with 0.5 μm minimum linewidth and ±0.1 μm overlay accuracy (3σ) using 20 μC/cm2 resist sensitivity and 8×108 shots per wafer. In this case, the writing time, the registration time, and the stage move time are 32, 3, and 6 min, respectively.
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41.75.Fr Electron and positron beams

An e‐beam microfabrication system for nanolithography

K. L. Lee and H. Ahmed

J. Vac. Sci. Technol. 19, 946 (1981); http://dx.doi.org/10.1116/1.571196 (4 pages) | Cited 2 times

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An electron beam lithography system designed for making structures with dimensions in the range 100 to 1000 Å is described. The beam diameter is 10 Å and the maximum beam energy is 100 keV. The system is calibrated for resist exposure by measuring the beam size and current after magnifying it with projector lenses. The beam is deflected electromagnetically under computer control and vector scanning is used during lithography. The system has been used to make fine lines and grids with linewidths in the range 150 to 500 Å. Relatively dense structures with large ratios of resist thickness to linewidth have been demonstrated on both thick and thin electron‐transparent, silicon substrates with the system operated at 50 keV. Results have been obtained on both single layer crosslinked resists and double layers of crosslinked resists and PMMA. It is concluded that finer lines and more densely packed structures over larger areas can be obtained on solid substrates using 100 keV beam energy.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

EL‐3: A high throughput, high resolution e‐beam lithography tool

R. D. Moore, G. A. Caccoma, H. C. Pfeiffer, E. V. Weber, and O. C. Woodard

J. Vac. Sci. Technol. 19, 950 (1981); http://dx.doi.org/10.1116/1.571197 (3 pages) | Cited 3 times

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EL‐3 is IBM’s third generation of e‐beam lithography tools developed for the fabrication of semiconductor devices using direct write techniques. The system is designed to operate as a direct write manufacturing tool in a semiconductor factory. EL‐3 has a high throughput capability that is competitive with many optical lithography systems. The system has the capability to cover the lithography requirements at 1 μ and above. In addition, the tool can be operated as a highly effective mask maker. EL‐3 makes use of many of the state of the art techniques associated with electron beam system lithography. These techniques include (1) LEARN calibrated field scan, (2) high current, variable shaped spot, (3) dual channel deflection of large fields and of subfields, (4) high performance handling of large workpieces (6 1/2 in., 163 mm), and (5) Series/ 1 data handling, system control, and automatic operation EL‐3 can expose 30 4 in. (100 mm) wafers per hour at 1.5 μ lithography at 10 μC/cm2 current dose. Four EL‐3 tools have been completed and installed. These tools are being used for both development and manufacturing applications. The system and lithography performance achieved with these tools will be discussed, with SEM results shown for various process conditions and different resist materials.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.-z Semiconductor devices

Electron beam array lithography

D. O. Smith and K. J. Harte

J. Vac. Sci. Technol. 19, 953 (1981); http://dx.doi.org/10.1116/1.571198 (5 pages) | Cited 1 time

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Electron‐beam array lithography (EBAL) uses array optics to expose 108 to 1010 resolution elements without mechanical motion. The array optics are based on the use of a first stage of deflection (coarse deflection) which selects one of an array of lenslets. The lenslet array is followed by a second stage of deflection (fine deflection) which selects the final spot position. In order to maximize exposure rate and also minimize mechanical motion, it is proposed to use a 3×3 array of array optics channels to expose a 100 mm wafer. As a numerical example of the projected throughput of such a system consider a 20 MHz stepping rate per channel and 0.5 μm pixels. Then (3×1010 pixels)/(9×2×107 pixels per s) ≊170 s. Now if variable spot sizes and vector writing are used such that only 10% of the pattern is exposed using the smallest feature (pixel), the exposure time is reduced to ∠20 s. Consistent with these calculations, EBAL systems are presently under development with engineering goals of 0.5 μm smallest features, 100 mm wafers, and throughputs of 50 wafers/h. The electron optics of these systems are all electrostatic, and use either thermionic (e.g., LaB6) or field‐emission (e.g., W/Zr) cathodes. EBAL systems require that patterns be ’’stitched’’ across the boundaries of the lenslet fields in the array lens. This can be accomplished by the use of a standard calibration plate having fiducial marks at the corners and sides of lenslets. Measurement of the positions of these fiducials provides data from which to calculate a set of stitching constants for each lenslet of each electron‐beam channel. Overlay between different pattern levels on a wafer is accomplished by a similar process using data from fiducial marks at the corners of each chip which is being written on a wafer. By these means any pattern level on any wafer can be exposed in any EBAL exposure station.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Electron‐beam array lithography stitching experiments

E. M. Kellogg, D. C. Bono, M. J. Dalterio, G. R. Gibilaro, D. B. Greenstein, K. J. Harte, V. K. Singhal, and D. M. Walker

J. Vac. Sci. Technol. 19, 958 (1981); http://dx.doi.org/10.1116/1.571199 (5 pages)

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A series of experiments to demonstrate the feasibility of the EBAL (electron‐beam array lithography) concept is described, using a system of electron optics that deflects the electron beam in two stages: coarse and fine deflection. The field of view is divided up into a mosaic of smaller fields, called lenslets. It is required to stitch the lenslet fields into a complete, coherent field. A stitching theory is used [Singhal et al. (to be published)], together with a calibration plate. This procedure is demonstrated using two techniques: test patterns on resist are written and developed for examination by microscope; also electronic stitching is done, wherein test fiducial marks at lenslet boundaries are located with the electron beam, and data from adjacent lenslets are compared. This technique gives quantitative results more directly than writing on resist. We present results on 3×3 lenslet resist stitching to an accuracy of 0.2 μm, and 5×5 lenslet electronic stitching to 0.14 μm, which help to demonstrate the feasibility of EBAL for microcircuit lithography.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

A multibeam scheme for electron‐beam lithography

T. Sasaki

J. Vac. Sci. Technol. 19, 963 (1981); http://dx.doi.org/10.1116/1.571200 (3 pages)

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The most important requirement for the direct‐writing scheme of electron‐beam lithography is to increase the throughput. The throughput is severely impacted by the space–charge effect in the single‐beam schemes. This paper proposes a multibeam scheme in which the space–charge effect is not serious and investigates the feasibility of the scheme.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Design and performance of a 4 in. electron image projector

R. Ward, A. R. Franklin, P. Gould, and M. J. Plummer

J. Vac. Sci. Technol. 19, 966 (1981); http://dx.doi.org/10.1116/1.571201 (5 pages) | Cited 3 times

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An electron image projector has been designed and built which is currently exposing 4 in. wafers and has the capability of going to 5 in. Linewidth control of ±0.04 μm for 1 μm lines has been measured over the whole surface of 4 in. wafers. Machine alignment accuracy of ±0.03 μm has been achieved and nonrepeatable image distortion is shown to be less than 0.1 μm. Examples of resolution capability and step coverage are also shown.
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41.75.Fr Electron and positron beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors
06.60.Sx Positioning and alignment; manipulating, remote handling

Accuracy of image positioning in an electron beam proximity printer

P. Nehmiz, H. Bohlen, and J. Greschner

J. Vac. Sci. Technol. 19, 971 (1981); http://dx.doi.org/10.1116/1.571202 (4 pages) | Cited 1 time

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Electron Beam Proximity Printing is a novel method for high throughput submicron lithography. The employed method of shadow projection of a mask pattern to the wafer requires physical holes in the mask. The so‐called mask stencil problem associated with self‐supporting masks is eliminated by using complementary masks. The required accuracy of complementary mask stitching is independent of the printed linewidth. Exposures in 1 μm thick PMMA demonstrate that with a stitching accuracy of ±0.2 μm the edge roughness at the stitching positions is ?0.1 μm. Experiments show that a prototype machine equipped with a laser interferometer of λ/8 = 79 nm resolution fulfills this requirement.
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41.75.Fr Electron and positron beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling
42.62.-b Laser applications

A new type pattern generator applied to the electron‐beam exposure system

An De‐xiang, Wang Jian‐kun, and Qiu Pei‐yong

J. Vac. Sci. Technol. 19, 975 (1981); http://dx.doi.org/10.1116/1.571203 (4 pages)

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This paper describes a new type pattern generator, used in the scanning e‐beam system suitable to generate smooth skewed vector with given slope. The initial coordinate of the vector is defined by two 16 BIT DACs, each equipped with a fixed reference source, and the components of the vector are given by other two 12 BIT DACs, each equipped with a variable reference source digitally controlled by a common triangular wave generator. Digital controlled period of the triangular wave ranges from 1 μs to 10 s. A high speed dynamic zero‐correction deflection amplifier is applied to the pattern generator. The deflection amplifier and coil system are optimized to give a flat frequency response to 5 or 10 Mc, and the output current ±0.5 to ±5 A. Experimental exposure has been practiced in the 20×20 mm2 scanning field with smooth skewed vectors, location accuracy 0.03%. Scanning speed is equivalent to 100 kc to 10 Mc of the digital point–to–point scanning e‐beam system.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Control configuration for the electron beam lithographic system EL–3

J. Craft, M. Williams, G. DeFiglio, and J. Pavick

J. Vac. Sci. Technol. 19, 979 (1981); http://dx.doi.org/10.1116/1.571204 (4 pages)

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Automated electron beam lithographic tools have throughput requirements which dictate some essential control features. Data of various types flows continuously to and from the tool for deflections, field corrections, patterns, pattern registration, synchronization, and control. Data must be transferred at high speeds and in synchronization with tool writing cycles. In addition, preparation of pattern data and wafer or mask control parameters must be accommodated simultaneously. The IBM electron beam lithographic tool, EL–3, includes a control system driven by two Series 1 (S/1) minicomputers. One is the system controller; the second controls only mechanical operations, such as wafer or mask loading and X–Y stage moving. The primary S/1 controls all system activities through high‐speed memory buffers, a distributed digital control bus which interfaces to functional logic modules, and a direct connection to the S/1 mechanical controller. The buffers allow the primary S/1 to collect or transfer data at its specified rates, while tool functions are executed at high speed by the digital hardware for optimized throughput. The control system can operate stand alone or integrated into a computer‐aided manufacturing environment called Quick Turn Around Time (QTAT). In this QTAT environment, large data volume transfers are made directly into the high‐speed memory buffers at 500–600 kbyte/sec, which improves system throughput for applications requiring frequent pattern buffer reloading. This paper describes the control system configuration, data preparation, data transfer and performance features of EL–3 for both the stand‐alone and manufacturing environments.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Discontinuity reduction method in pattern connection

M. Idesawa, T. Soma, and E. Goto

J. Vac. Sci. Technol. 19, 983 (1981); http://dx.doi.org/10.1116/1.571205 (5 pages)

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A method of reducing the discontinuities which appear in the connecting boundaries of element patterns or in the stitching boundaries of sub‐scanning‐fields is proposed. Pattern elements are overlapped in the connecting region, and the beam dose in the overlapping area of each pattern element is controlled so that they are compensated by each other. Computer simulations and experiments were performed proving that the proposed method is very effective in reducing these discontinuities. For instance, by selecting an overlapping area which is several times wider than the expected positioning errors or edge definition of element pattern, discontinuities in pattern connection can be reduced remarkably without any special improvement of positioning accuracy.
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42.30.Sy Pattern recognition
41.75.Fr Electron and positron beams

Advanced pattern data processing technique for a raster scan electron beam exposure system

K. Koyama, S. Sasaki, and M. Tokita

J. Vac. Sci. Technol. 19, 988 (1981); http://dx.doi.org/10.1116/1.571206 (5 pages)

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With the increasing complexity and integration in recent LSI designs, the amount of data to be processed in EB exposure systems tends to increase steadily. This increase in data may lead to degradation in the systems’ throughputs. An overall technique associated with both software and hardware presents a realistic solution to this problem. Parallel processors combined with a simplified data format have provided efficient data manipulation. A compaction method working on smaller stripe areas is easily realized in hardware, yet can achieve significant data reduction. The data edit function, operating asynchronously with the data preparation procedure, eliminates repeated processing of identical chip patterns or chip element patterns. The feasibility of the technique thus featured has been proven on EB‐105, a raster scan electron beam exposure system.
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07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

EBCAD—Fully integrated pattern data processing for direct write electron‐beam lithography systems

O. W. Otto

J. Vac. Sci. Technol. 19, 993 (1981); http://dx.doi.org/10.1116/1.571207 (5 pages)

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EBCAD (Electron–Beam CAD) is the pattern data processing software package for Hughes direct‐write electron beam lithography systems. The purpose of EBCAD is to optimize the presentation of pattern data to the e‐beam exposure hardware for maximizing throughput and patterning fidelity, and to perform its required functions in the local hardware environment of the exposure system. The EBCAD package, which is an integral part of the e‐beam lithography systems, supports all functions associated with pattern preparation for exposure from interactive graphic data creation and manipulation to data reformating for direct use by the exposure hardware. This paper describes the EBCAD package including the major functions, the hierarchical nodal command structure and user interface, and the underlying chaining structure.
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07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Distributed control/support architecture for direct wafer write e‐beam lithography systems: Throughput considerations

P. E. Merritt and F. S. Ozdemir

J. Vac. Sci. Technol. 19, 998 (1981); http://dx.doi.org/10.1116/1.571208 (3 pages)

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An optimized implementation of the necessary control and support functions for direct wafer write e‐beam lithography systems is prerequisite to realizing the full potential of this lithography technology. This optimization must take into account both functional perfomance and cost. A real‐time process control network for the support and control of multiple direct write e‐beam lithography systems is currently operational at the Hughes Research Laboratories. This paper describes this e‐beam lithography system support and control network from the perspective of the minicomputer network.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Control of variable beam trapezoid delineator (VL–R2)

M. Sumi, F. Chiba, and H. Wada

J. Vac. Sci. Technol. 19, 1001 (1981); http://dx.doi.org/10.1116/1.571156 (6 pages)

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A new variable shaped beam system has been developed for high speed delineation of LSI patterns composed of polygons. The slant pattern data format, the pattern generating circuit, and the electron optics are presented. To test the capability, an actual 16 K RAM pattern was delineated at ×1/4∠×8 scales. The average beam size (width) was 2.44 μm for the ×1 scale. The equivalent writing speed was 780 Mbit/s.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
41.75.Fr Electron and positron beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Graphic data editor for Cambridge e beam

H. M. Zimmermann

J. Vac. Sci. Technol. 19, 1007 (1981); http://dx.doi.org/10.1116/1.571157 (3 pages)

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Circuit research with e‐beam exposure and new resist tests require a much greater data modification freedom than is possible by hand or cycling changes back through a CAD group. Developed for a Cambridge e‐beam system is a graphics editor that runs directly on the e‐beam’s computer and CRT display. The editor interactively changes rectangles, triangles, or trapezoids into any three or four sided polygon shape. Additions and deletions to the data file are easily done with a crosshair cursor of the display. Macrocommands create groups of data elements in any of the six data display levels and may be matrixed or positioned as desired. Existing data group structures may be modified as the program automatically redefines nested definitions up to ten levels deep. Particularly useful for the e‐beam is scan field boundary detection with the scan field size variable up to 4 mm. Also, a switchable reference scale may be used to examine data or input commands in microns or the Cambridge’s internal data units. Further development will include proximity corrections selective to the area displayed to save the time required to do extensive calculations on noncritical areas.
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89.20.Ff Computer science and technology
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.05.Hd Data acquisition: hardware and software
07.05.Kf Data analysis: algorithms and implementation; data management
07.05.Rm Data presentation and visualization: algorithms and implementation

Techniques for electron beam testing and restructuring integrated circuits

D. C. Shaver

J. Vac. Sci. Technol. 19, 1010 (1981); http://dx.doi.org/10.1116/1.571158 (4 pages)

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Techniques are presented for using an electron beam to control and sense logic states in integrated circuits and to control the state of nonvolatile switches. The electron beam techniques enhance testability and provide the ability to restructure circuit interconnections during testing.
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41.75.Fr Electron and positron beams
07.07.-a General equipment
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Contactless electrical testing of large area specimens using electron beams

H. C. Pfeiffer, G. O. Langner, W. Stickel, and R. A. Simpson

J. Vac. Sci. Technol. 19, 1014 (1981); http://dx.doi.org/10.1116/1.571159 (5 pages) | Cited 6 times

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An e‐beam test system has been developed to detect opens and shorts in three‐dimensional networks of conductors embedded in a dielectric matrix. The specimens, which measure up to 100×100 mm, are tested electrically without making physical contact and without mechanical stepping. The system comprise two flood beams and a focused probe beam deflected over the full specimen area at a resolution of better than 3000 lines at 1–2 kV beam energy. One flood gun is located at the rear, the other at the front of the specimen. The change in secondary emission imposed by impinging electrons charging or discharging the surface is detected as voltage contrast which allows one to discriminate between uninterrupted and interrupted as well as shorted pairs of conductors. The physical concept, the contrast mechanism, and the electron optics of the system will be presented together with experimental results.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Failure analysis of LSI using a scanning low‐energy electron probe

F. Mizuno, S. Mori, K. Satoh, K. Kanda, and H. Todokoro

J. Vac. Sci. Technol. 19, 1019 (1981); http://dx.doi.org/10.1116/1.571160 (5 pages)

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The voltage contrast mode of SEM (scanning electron microscope) operation is a powerful diagnostic tool of LSI devices which have very small geometry of metal wirings and transistors. However, a conventional SEM uses a high energy electron probe (10 to 30 keV) which gives rise to radiation damage and charging effects to the LSI devices under investigation. We developed a new SEM which uses a low energy electron probe (0.5 to 7 keV) to overcome these problems. The instrument uses a field emission gun to minimize the deterioration of spatial resolution at low beam energy, and has the facility of mounting a probe card to energize an LSI device on a silicon wafer. Power sources and input signals to energize the LSI device under investigation are controlled by a dedicated computer. The SEM has a voltage resolution of about 0.5 V and a spatial resolution of about 0.05 μm with the probe current of 0.05 nA at 1 keV. We have analyzed many failures of LSI memory and logic circuits with several hundred gates by utilizing the SEM. The instrument can easily identify disconnects and bad voltage levels in LSI devices, while other methods (optical microscope observations, mechanical probings, and higher energy electron probes) cannot identify them. Moreover, the SEM is also useful for other devices such as printed circuit boards where wide metal wirings are covered with very thick insulator films (50 μm thick).
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
07.07.-a General equipment
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

A new method for the investigation of stress in MIS devices using SEM electron channeling patterns

G. E. Davis and M. E. Taylor

J. Vac. Sci. Technol. 19, 1024 (1981); http://dx.doi.org/10.1116/1.571161 (6 pages)

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A proposed new method to measure the elastic stress in silicon induced by the presence of a thin amorphous layer is presented. The method is based on measuring the difference in the selected area channeling patterns generated by a stress‐free region of the substrate and a stressed region located under an insulating layer. The maximum thickness of the amorphous insulating layer which can be used before the backscattered signal is totally absorbed was found to be approximately 600 Å for silicon dioxide and 400 Å for silicon nitride. The strain in SiO2 and Si3N4 was found to be thickness dependent. For silicon dioxide, the stress varied between 109 to 1010 dynes/cm2. For silicon nitride, the stress was on the order of 1010 dynes/cm2.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Hemispherical retarding type energy analyzer for IC testing by electron beam

Y. Goto, A. Ito, Y. Furukawa, and T. Inagaki

J. Vac. Sci. Technol. 19, 1030 (1981); http://dx.doi.org/10.1116/1.571162 (3 pages) | Cited 2 times

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This paper describes an improved hemispherical retarding type energy analyzer for IC testing using an electron beam. A hemispherical retarding type analyzer has been proposed for IC testing but it produces a voltage measurement error of more than 10% even for an optimum slice level. The deficiencies of the analyzer and our improved arrangement are investigated by an analysis of the potential distribution using a high resistance film. A control grid and buffer grid are introduced in the new analyzer to generate a high spherical extraction field. In addition, an electron detector is arranged to give a high collection field outside the retarding grid. The improved hemispherical retarding type energy analyzer produces only a 2% voltage measurement error for a specimen voltage range of −14 to 20 V. This level of performance is ensured for a slice level margin within a 75% range of the output amplitude.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.50.-e Electrical and electronic instruments and components

A numerical and experimental study of the electric field distribution within field emission systems

H. C. Eaton

J. Vac. Sci. Technol. 19, 1033 (1981); http://dx.doi.org/10.1116/1.571163 (4 pages) | Cited 1 time

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The design of field electron and field ion sources which are useful in device fabrication systems, electron or ion microscopes requires an accurate and complete knowledge of the electric field distribution both within the gun and near the field emitter itself. Analysis has not been possible by conventional analytical methods due to the intractable nature of the equations. An analysis is presented in the present work which is obtained using the method of finite elements. The numerical approach allows the consideration of the geometric detail common to field ion and field electron microscopes. In these microscopes the ion or electron source serves as the actual specimen to be observed. It is shown that instrument features as far away as 105 tip diameters can substantially affect the electric field at the emitter. The dependence of the electric field at the apex is found to vary as k1 exp(−k2ϑ) where ϑ is the emitter shank angle. The constant k2 describes the strength of the shank angle dependence. These constants may be experimentally determined. Experiments are discussed, and ion images are shown, which demonstrate the marked effect of system geometry on ion trajectories. The ion images illustrate the large amount of trajectory bending which results from a change in the position of a microchannel plate detector. One case is shown in which a crystallographic analysis of the image confirmed that certain trajectories originate from regions on a bulb‐shaped emitter which were not within the line of sight of the detector.
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79.70.+q Field emission, ionization, evaporation, and desorption
41.75.Fr Electron and positron beams
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

A computational and experimental analysis of fifth‐order deflection aberrations

V. R. M. Rao and W. C. Nixon

J. Vac. Sci. Technol. 19, 1037 (1981); http://dx.doi.org/10.1116/1.571164 (5 pages)

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The influence of fifth‐order deflection aberrations for purely magnetic post lens single‐deflection systems has been investigated. A regrouping of the large numbers of third‐ and fifth‐order aberration coefficients has been performed to reduce the numbers of coefficients to six to the third order and seven to the fifth order. Optimization then consists of minimizing the relevant regrouped coefficients. The third‐ and fifth‐order field curvature coefficients have been measured and agree reasonably well with calculated values. It has also been found possible to obtain a change of sign between the third‐ and fifth‐order astigmatism coefficients leading to a partial cancellation of the total astigmatism. The maximum deflection angle was about 15° from the optic axis in all the deflection systems analyzed.
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41.75.Fr Electron and positron beams

A method to reduce deflection aberrations in electron‐beam lithography systems

W. Knauer

J. Vac. Sci. Technol. 19, 1042 (1981); http://dx.doi.org/10.1116/1.571165 (6 pages)

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An imaging and deflection method is described which is intended for high‐speed, submicron lithography. The basic electron‐optical approach is similar to one described by Pfeiffer, comprising a large‐bore lens and an in‐lens deflection element. A saddle coil rather than toroidal deflector is utilized in order to facilitate the simultaneous reducton of deflection aberrations and beam deflection offset due to eddy currents and skin effect. Deflection aberrations usually are minimized by varying the relative positions of lenses and deflection elements against each other. In this paper, an optimization approach is described in which the shape of the deflection coil is varied. By changing the length of the coil wires, their radial and lateral positions, and by adjusting the axial coil position in the lens, low levels of field curvature, astigmatism, and distortion are reached. To minimize eddy currents, saddle‐type deflection coils can be surrounded by secondary coils which generate the same magnetic dipole moment as the primary coils, but provide opposing polarity. This approach has been described earlier by Wardly; its extension to the correction of beam deflection offset due to skin effect is presented in this paper. Experimental tests of these concepts have been conducted. A specific result obtained is that all geometrical aberrations and all eddy current related effects are reduced to about 0.1 μm in the corners of a 2 mm scan field.
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41.75.Fr Electron and positron beams

Generation and applications of finely focused beams of low‐energy electrons

Y. W. Yau, R. F. W. Pease, A. A. Iranmanesh, and K. J. Polasko

J. Vac. Sci. Technol. 19, 1048 (1981); http://dx.doi.org/10.1116/1.571166 (5 pages) | Cited 8 times

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In electron‐beam lithography, two well‐known problems are proximity effects due to electron scattering and slow throughput because of limited exposure rate and resist sensitivity. We have investigated the generation of finely focused electron beams of low landing energy (?5 keV) and their application to materials processing. Lenses employing magnetic and retarding electric fields are found to have very low spherical and chromatic aberrations, thus facilitating the production of beams of low‐energy electrons without seriously sacrificing current density. With such beams the power dissipated per unit volume at the surface of a bulk target is higher than with high‐energy electrons, thus increasing the speed to exposure of very thin resists and dramatically reducing proximity effects. This compact volume of high‐power dissipation is also attractive for selected area annealing.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
41.75.Fr Electron and positron beams

Computerized optimization of electron‐beam lithography systems

H. C. Chu and E. Munro

J. Vac. Sci. Technol. 19, 1053 (1981); http://dx.doi.org/10.1116/1.571167 (5 pages) | Cited 1 time

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An optimization program has been developed for designing combined focusing and dual‐channel deflection systems with low aberrations for electron beam lithography. The program can handle any combination of magnetic and electrostatic lenses and deflectors, and uses the damped least squares method for minimizing a weighted sum of squares of aberrations, subject to specified physical constraints. The program has been used to optimize the design of several types of lithography system. The results show that, in many cases, the program can yield designs with extremely low aberrations. For example, a system with one magnetic lens and two deflectors has been found which, at the corners of a 5 mm scan field with 5 mrad aperture, has only 0.19 μm overall aberration before dynamic corrections; by adding an electrostatic retarding field, this can be reduced to 0.12 μm. By adjusting the strengths and positions of the deflectors, several of the aberrations can be individually eliminated, including field curvature. It is also shown that electrostatic subfield deflectors can be added without significantly increasing the aberrations, and a pure electrostatic focusing and deflection system for ion beam lithography has been designed which is limited almost entirely by axial chromatic aberration.
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41.75.Fr Electron and positron beams

Advanced deflection concept for large area, high resolution e‐beam lithography

H. C. Pfeiffer and G. O. Langner

J. Vac. Sci. Technol. 19, 1058 (1981); http://dx.doi.org/10.1116/1.571168 (6 pages) | Cited 8 times

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A novel deflection system has been developed which essentially eliminates off‐axis aberrations including the transverse chromatic aberrations by employing a variable axis lens (VAL) which shifts the electron optical axis in synchronism with the deflected beam. The system comprises two precision pole piece lenses to achieve telecentricity, two composite predeflection yokes, and two yokes positioned in the pole piece region of the final lens. The field of the latter yokes satisfies the condition for shifting the electron optical axis by the distance r. This condition is 1B(y)r(z) = 1/2 B(L) (z)r, where B(y)r denotes the deflection field of the yoke in the r direction, and B(L) the lens field on the geometrical lens axis. To successfully utilize this concept, higher order terms of the field expansions have been included in the field matching by designing yokes which satisfy first and third order conditions and dynamic focus correction coils whose field is proportional to B\\(L) (z). The theoretical analysis of the VAL concept will be discussed together with experimental results demonstrating proper shift of the electron optical axis through elimination of transverse chromatic aberrations and coma.
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41.75.Fr Electron and positron beams

Automatic measurement and correction of deflection astigmatism and defocusing in the Hewlett–Packard 605 electron beam lithography system.

G. Owen

J. Vac. Sci. Technol. 19, 1064 (1981); http://dx.doi.org/10.1116/1.571169 (5 pages) | Cited 4 times

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The specifications for the Hewlett–Packard 605 electron beam lithography system call for an angular aperture of 2.5 mrad, a main deflector field size of 5×5 mm2, and a spot diameter of 0.5 μm over the entire field. Without dynamic corrections for deflection astigmatism and defocusing, the spot diameter would increase to about 1.6 μm at the perimeter of the main deflector field, and so an aberration measurement and correction scheme is required. A scheme is described in which both measurement and correction are performed under machine control, with no operator assistance. Astigmatism and defocus corrections are first measured automatically at a number of sample points within the main deflector field of view. The measured data are then processed to express the corrections as polynomial functions of deflection, and values for the polynomial coefficients are evaluated. During exposure, the coefficients are used to evaluate the aberration corrections, which are applied as the beam is deflected. The main deflector has an octupole configuration and stigmation is achieved by adjustment of the voltages on the eight electrodes. The automatic measurement of the defocus and astigmatism aberrations at each sample point is done by taking a through local series of edge scan measurements over a specially fabricated test target. The target, the through focal series measurement technique, and the manipulation of the resulting data are described. Experimental evidence of the success of the scheme in maintaining a 0.5 μm diam spot over a 5×5 mm2 field of view is presented.
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41.75.Fr Electron and positron beams
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

The high‐performance beam deflection system of EL3

C. T. Ho, M. S. Michail, W. Stickel, and O. C. Woodard

J. Vac. Sci. Technol. 19, 1069 (1981); http://dx.doi.org/10.1116/1.571170 (5 pages)

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A new concept of beam deflection was developed and implemented to achieve the high throughput and resolution performance of EL3. It combines the advantages of raster and vector writing techniques by dividing the field into overlapping subfields which are addressed by stepped raster magnetic deflection. Within each subfield electric deflection vectorially writes the pattern elements at high speed. The advantages of dual channel deflection and yokes within the projection lens are fully exploited. The repetitive raster deflection pattern permits the use of an automatic calibration system which corrects beam positioning errors of both deflection channels for fields up to 10 mm. Automatic calibration is utilized to assure good pattern overlay between optical and e‐beam lithography tools to eliminate dedicated tool restrictions. It establishes subfield matching so that patterns are stitched together properly. In addition, overall field size and linearity are controlled to the accuracy and stability required. This paper discusses key aspects of the entire deflection system design, its components, and highlights compatibility questions and trade‐offs between them. Specific problems such as thermal stability, speed/accuracy trade‐offs, noise sources, and their solutions are presented. Calibration data are presented to illustrate the accuracy and stability achieved.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Design of an electrostatic ion optical system for microfabrication with 100 Å resolution

H. Ohiwa, R. J. Blackwell, and B. M. Siegel

J. Vac. Sci. Technol. 19, 1074 (1981); http://dx.doi.org/10.1116/1.571171 (3 pages) | Cited 1 time

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A computer‐aided design program (CAD) has been developed to provide rapid, interactive design of electron and ion optical systems. The CAD program simulates the focusing and deflection properties of systems consisting of cylinder electrodes and octupole deflectors. Ion optical systems for use with an H2+ gaseous field ion source were designed using the CAD program. The design goals were to produce a 100‐Å‐diam probe capable of scanning a 0.2‐mm‐square field with an expected energy spread in the source of ΔE/E = 1/30 000. A system of five cylindrical electrodes (6‐mm‐diam bore) with the middle electrode containing double octupole deflectors would produce a 100‐Å‐diam probe using an acceptance half‐angle of 4 mrad when dynamic correction is used. Another sytem was calculated using cylinders with bores of 8‐mm diam and somewhat larger lens elements to produce a 100‐Å‐diam probe without dynamic corrections if a 2 mrad acceptance half‐angle is used.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
41.75.Fr Electron and positron beams

An improved method for numerical analysis of point electron and ion source optics

N. K. Kang, J. Orloff, L. W. Swanson, and D. Tuggle

J. Vac. Sci. Technol. 19, 1077 (1981); http://dx.doi.org/10.1116/1.571172 (5 pages) | Cited 6 times

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Numerical calculation of the potential for point source geometries such as a field emitter diode, has long proved to be a difficult problem due to the extreme difference in the magnitude of the sizes of the cathode and anode. The difference can be as large as 106 in extreme cases, and is normally in excess of 103. A number of approaches have been attempted including numerical calculations, analytical calculations, and a combination of the two. Unfortunately, no approach has had sufficient speed and accuracy to be truly versatile. The present approach makes use of a spherical coordinate system in which the radial mesh size increases with radius according to a geometrical series with a term ratio (1−hϑ)−1, where hϑ is the angular mesh size, in radians. With this method the truncation error in the finite difference formulas is small, the accuracy of the calculated potential is everywhere uniform and the form of the difference formulas is quite simple. As a result, one can achieve high accuracy with a comparatively small number of mesh points. Computations performed on several electrode structures which had a geometrical range of 10 to 103 and which could be solved analytically, showed that errors as small as 10−5 in the potential could be attained when hϑ≊0.05. The error is even smaller if hϑ is reduced. Space charge effects are easily incorporated into the analysis. Computation formulas are presented, along with results for a pointed LaB6 cathode structure and for a thermal‐field emission source.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
41.75.Fr Electron and positron beams
79.70.+q Field emission, ionization, evaporation, and desorption
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Trajectory calculations of the extraction region of a liquid‐metal ion source

J. W. Ward and R. L. Seliger

J. Vac. Sci. Technol. 19, 1082 (1981); http://dx.doi.org/10.1116/1.571173 (5 pages) | Cited 12 times

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In the ion‐extraction region of a liquid‐metal (LM) source, several phenomena occur (e.g., electrostatic‐lens action, axial and transverse space‐charge interactions) that have major effects on the performance of the source. In an effort to better understand these effects, a trajectory analysis was made of the ion‐extraction region. The trajectory calculations showed an appreciable increase in beam divergence at a Ga+ source current of only 5 μA.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
29.27.-a Beams in particle accelerators

Variably shaped electron beam lithography system, EB55: II Electron optics

Norio Saitou, Susumu Ozasa, Tsutomu Komoda, Goichi Tatsuno, and Yasumichi Uno

J. Vac. Sci. Technol. 19, 1087 (1981); http://dx.doi.org/10.1116/1.571174 (7 pages) | Cited 1 time

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A variably shaped electron beam exposure system (EB55) with a high exposure rate is developed for direct beam lithography of 0.5 μm patterns. The electron beam column consists of seven magnetic lenses. The projection lens is specially designed to minimize deflection aberations and beam landing angle deviation on the wafer. The column design facilitates a shortened distance between the object and its image plane. Accelerating voltage is 30 kV due to decreased Coulomb interaction and proximity effect. In a shaped beam system, the electron gun should have a wide emission angle, high brightness, and large crossover size. A square rod type LaB6 cathode is developed for this purpose. The shaped beam is vector scanned by electrostatic deflection plates and electromagnetic coils. The scanning area is 2.6 mm square and the maximum beam size is 5.10 μm square. The size change unit is 0.02 μm. A beam current density higher than 10 A/cm2 is obtained with a small beam covergence angle. A shape edge slope smaller than 0.2 μm is obtained. Experimental and theoretical results of the column’s optical properties are presented. Edge slope dependence on variation of the shaped beam size is also discussed. The system has been successfully used to write submicron patterns on silicon wafers.
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41.75.Fr Electron and positron beams

Monte Carlo modeling of current distribution in shaped electron beams

P. S. Dayan and G. A. C. Jones

J. Vac. Sci. Technol. 19, 1094 (1981); http://dx.doi.org/10.1116/1.571175 (4 pages)

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A Monte Carlo type simulation of electron interaction in a shaped electron beam lithography system has been developed. The simulation has been used to model a shaped beam system using Köhler illumination, and shows correct imaging when electron interaction is neglected. The loss of resolution due to interaction is demonstrated, and it is proposed that this technique may be used for the quantitive assessment of the effects on interaction in shaped beam systems.
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41.75.Fr Electron and positron beams

Current distribution in shaped e‐beams

V.R.M. Rao, G.A.C. Jones, and H. Ahmed

J. Vac. Sci. Technol. 19, 1098 (1981); http://dx.doi.org/10.1116/1.571176 (5 pages)

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The current distribution in electron beams shaped by using either Köhler or critical illumination of apertures has been determined experimentally. The experimental technique is to scan a square image across sharp edges of a Faraday cage aperture while the first and second differentials of the current are displayed on an oscilloscope. The measurements show that the type of illumination is not an important factor in determining the ultimate edge sharpness. All measurements were made with 20‐kV accelerating voltage and it was found that for a square of side 3.5 μm imaged at an angular aperture 3.7 mrad the current density edge deteriorated to about 0.7 μ at 3 μA for both types of illumination. Results of imaging a menu of variable shapes in resist are used to demonstrate uniform current density distribution in the shaped beam.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Considerations on space charge effect for high current variable shaped beam forming

M. Idesawa, T. Soma, E. Goto, and T. Sasaki

J. Vac. Sci. Technol. 19, 1103 (1981); http://dx.doi.org/10.1116/1.571177 (3 pages) | Cited 1 time

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Variable shaped beam schemes are very promising for advanced VLSI pattern generation. In such a device, beam blurring caused by the space charge effect becomes greater as the beam current increases and the focal length of the electron lens is varied as the beam current changes. In order to keep the beam blurring within a permissible amount, refocusings are required whenever beam sectional areas are changed dramatically. However, it is often difficult to complete refocusing in negligible short time in comparison with the shot time of an element pattern and total exposure time is influenced considerably. Investigating the results of computer simulations and fundamental experiments, it is found that beam blurring caused by defocusing is almost proportional to the deviation of the beam current from that at the optimum focusing point and is kept under the permissible value in certain intervals of beam current. Considering this characteristic, the defocusing problem can be improved significantly by rearranging the exposure sequence of pattern elements so that the frequency of dramatic shape change becomes minimum.
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41.75.Fr Electron and positron beams
07.77.-n Atomic, molecular, and charged-particle sources and detectors
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Mutual repulsion effects in a high throughput e‐beam lithography column

T. Groves

J. Vac. Sci. Technol. 19, 1106 (1981); http://dx.doi.org/10.1116/1.571178 (5 pages) | Cited 3 times

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A fundamental limit on the current obtainable in an electron beam writing system is set by the mutual repulsion of beam electrons. Computer Monte Carlo simulations of the electron beam take into account the essential physical properties, which are discreteness of the charge, the random nature of the problem, and the many‐body aspect. A Monte Carlo simulation has been used as a design tool for a high throughput lithography system at Hewlett‐Packard. The column, which is in successful operation, is capable of 0.6 μA of current in a 0.5 μm spot at 20 kV. This resolution is maintained over a 5 mm square deflection field. Beam broadening effects are described for both the field emission source region and the column. The energy broadening of 1.5 eV is determined mainly within the first 0.1 mm near the source, with less than 15 percent increase in the remainder of the column. The major beam broadening is caused by transverse repulsion, which acts over the entire 41.5 cm long column.
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41.75.Fr Electron and positron beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling
61.80.Fe Electron and positron radiation effects
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Novolac resins as active ingredients in positive electron resists

S. R. Fahrenholtz

J. Vac. Sci. Technol. 19, 1111 (1981); http://dx.doi.org/10.1116/1.571179 (6 pages)

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Certain pure novolac resins were found to behave as positive electron resists. Using novolacs made from phenols substituted with bulky groups, patterns with 1/2 μm resolution can be obtained with a residual film thickness of 3200 Å (1/3 of initial film thickness) at doses <5.0×10−6 C/cm2 at 20 kV. The processing conditions which favor positive tone patterns are described and a mechanism involving postexposure reaction with oxygen presented.
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07.68.+m Photography, photographic instruments; xerography
79.20.Kz Other electron-impact emission phenomena
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.65.-b Surface treatments

In situ vaporization of very low molecular weight resists using 1/2 nm diameter electron beams

M. Isaacson and A. Muray

J. Vac. Sci. Technol. 19, 1117 (1981); http://dx.doi.org/10.1116/1.571180 (4 pages) | Cited 18 times

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A technique is presented for in situ measurements of contrast curves for electron beam vaporizable resists. Using a 1/2 nm diam beam of 100 keV electrons, we have etched lines, holes and patterns in NaCl crystals at the 2 nm size scale. Troughs about 1.5 nm wide on 4.5 nm centers and 2 nm diam holes have been etched completely through NaCl crystals more than 30 nm thick.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
61.80.Fe Electron and positron radiation effects
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
79.20.-m Impact phenomena (including electron spectra and sputtering)

Molecular parameters and lithographic performance of poly(chloromethylstyrene)—a high‐performance negative electron resist

H. S. Choong and F. J. Kahn

J. Vac. Sci. Technol. 19, 1121 (1981); http://dx.doi.org/10.1116/1.571181 (6 pages) | Cited 11 times

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Poly(chloromethylstyrene) (PCMS) is shown to have a desirable combination of properties, including high sensitivity, high dry‐etch resistance, and high resolution. As a consequence, it is a very attractive candidate for high performance (throughput, resolution, process compatibility) electron beam lithography. PCMS lithographic performance is higher than that of any other previously reported, high‐sensitivity negative electron resist. Performance results are compared specifically with COP, PGMA, and CMPS, and are correlated with molecular and chemical properties. PCMS synthesis and evaluation results are reported for polymers with molecular weights (?w) between 20 000 and 450 000 and polydispersivities between 1.3 and 2.3. A typical high molecular weight (?w = 381 000) material with polydispersivity of about 1.6 has sensitivity (Dg0.5)<0.5 μC/cm2, contrast ≳1.5, and resolution <1.0 μm (equal lines and spaces). Respective values for a typical low molecular weight (?w = 22 000) material with polydispersivity of about 1.3 are sensitivity <7 μC/cm2, contrast ≳2.0, and resolution <0.5 μm.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Plasma pretreatment to improve resist properties by reduction of resist flow during postbake

J. M. Moran and G. N. Taylor

J. Vac. Sci. Technol. 19, 1127 (1981); http://dx.doi.org/10.1116/1.571182 (5 pages) | Cited 1 time

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Softening and subsequent flowing of resist during postexposure baking, used to promote resist adhesion, often results in reduced resolution and linewidth control. This is unacceptable for the fabrication of very fine feature VLSI devices since linewidth variations of 0.5–1.5 μm can be observed under certain baking conditions. Treatment of positive and negative resists with a nitrogen plasma prior to postbaking reduces resist flow significantly and enables linewidth integrity to be maintained. Minimal resist erosion occurs upon plasma treatment. In one example a series of 1.4‐μm‐diam windows were exposed and developed in 0.8‐μm‐thick HPR‐204 positive photoresist. Samples treated with a 400 W unshielded nitrogen plasma for 10 min exhibited no change in feature width whereas the untreated control, baked as above, exhibited completely closed windows due to excessive resist flow. A model is proposed to account for the improved flow characteristics.
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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.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

UV hardening of photo‐ and electron beam resist patterns

H. Hiraoka and J. Pacansky

J. Vac. Sci. Technol. 19, 1132 (1981); http://dx.doi.org/10.1116/1.571183 (4 pages) | Cited 3 times

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A simple UV‐hardening process is described that renders micron sized images in AZ resists resistant to flow when heated to temperatures above 210 °C. The UV treatment prevents the image flow problems usually encountered in reactive ion etching processes. Mechanistic studies with infrared spectroscopy and ESCA indicate that the indene carboxylic acid generated from diazo‐oxide photoactive compounds or its salt may be responsible for rendering the films resistant to flow, while the ester linkages between the photoactive compound and the host resin do not provide flow resistance.
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82.50.-m Photochemistry
42.70.Gi Light-sensitive materials
81.40.Tv Optical and dielectric properties related to treatment conditions
81.65.-b Surface treatments

Poly(vinylnaphthalene) and its derivatives as e‐beam negative resists

Y. Ohnishi

J. Vac. Sci. Technol. 19, 1136 (1981); http://dx.doi.org/10.1116/1.571184 (5 pages) | Cited 1 time

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Polymer materials, which contain vinylnaphthalene as monomer units, were developed as e‐beam negative resists. Poly(vinylnaphthalene) was found to be highly resistive to dry etching. Under Ar ion milling or CCl4 sputter etching conditions, etching rates for poly(vinylnaphthalene) were found to be about two‐thirds of those for polystyrene or AZ resist. For example, etching rates for PMMA, PMIPK, AZ1350J, polystyrene, and poly(2‐vinylnaphthalene) in a neutralized 500‐eV Ar ion beam (0.83 mA/cm2) at normal incidence, were estimated to be 400, 280, 190, 200, and 150 Å/min, respectively. The contrast (γ value) for poly(2‐vinylnaphthalene) is better than that for polystyrene, which had been considered as the highest contrast negative organic resist known. Sensitivity for poly(2‐vinylnaphthalene) is insufficient for todays’s requirements. Dig was found to be 2.5×10−4 C/cm2 for Mw = 4×104 polymer. Chloromethylation of this material improved sensitivity. For example, 38.5% chloromethylation attained Dig = 8×10−6C/cm2. Submicrometer fine pattern fabrication is presented. Preliminary results for copolymerization of vinylnaphthalene with other sensitive monomers are presented.
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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
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Postirradiation polymerization of e‐beam negative resists: Theoretical analysis and method of inhibition

Y. Ohnishi, M. Itoh, K. Mizuno, H. Gokan, and S. Fujiwara

J. Vac. Sci. Technol. 19, 1141 (1981); http://dx.doi.org/10.1116/1.571185 (4 pages) | Cited 4 times

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Many e‐beam negative resists show postirradiation polymerization, i.e., even after e‐beam irradiation termination, crosslinking reaction continues. This phenomenon shows an unfavorable effect in precise pattern fabrication; the first delineated portion of the resist undergoes a dimensional change with respect to the last‐delineated portion. A method to inhibit postirradiation polymerization is presented based on a theoretical analysis of the postpolymerization mechanism. In the model used for analysis, active radicals are not extinguished in the vacuum and polymerization proceeds at a rate proportional to the radical concentration (first order reaction). A radical loses its activity due to collision with another radical (second‐order reaction ). This model successfully explained experimental results. Postirradiation polymerization inhibition is achieved by adding a radical scavenger to resists. Active radical collision with a scavenger also extinguishes radical activity. Thus resist pattern width and thickness are freed from time dependence after irradiation. Resolution is also improved by postpolymerization inhibition as chain reactions in resists are suppressed. Although sensitivity is decreased, a highly sensitive negative resist can meet today’s requirement (around 1 μC/cm2), even after the addition of a scavenger. To demonstrate the benefit of postirradiation polymerization inhibition, a Cr mask was made with submicron features. It has 7‐μm period Y‐Y propagation patterns for a bubble memory, in which all gaps are designed as 0.5 μm. Adding a radical scavenger, 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH), and SEL‐N resist, precise pattern fabrication was achieved, irrespective of the time after exposure.
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82.35.-x Polymers: properties; reactions; polymerization
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.50.-m Photochemistry
79.20.Kz Other electron-impact emission phenomena

A 100‐kV ion probe microfabrication system with a tetrode gun

J. R. A. Cleaver and H. Ahmed

J. Vac. Sci. Technol. 19, 1145 (1981); http://dx.doi.org/10.1116/1.571231 (4 pages) | Cited 4 times

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In the design of probe‐forming systems incorporating liquid‐metal ion sources, it is necessary to maximize the current into a probe of controlled diameter and to employ a configuration that is compatible with the incorporation of a filter for the selection of ion species. A variable‐magnification two‐lens system has been adopted as the basis of a microfabrication machine for direct selective ion implantation of wafers, and a 100‐kV system has been designed. Its tetrode gun acts as the first lens and is followed by an einzel lens as the probe‐forming objective. The system has been analyzed and operating characteristics have been computed, predicting a current of 0.1 nA in a 0.1 μm diameter probe and 10 nA into 1 μm diam.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Optical column design with liquid metal ion sources

J. Orloff and L. W. Swanson

J. Vac. Sci. Technol. 19, 1149 (1981); http://dx.doi.org/10.1116/1.571232 (4 pages) | Cited 2 times

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We have applied the results of our studies of fundamental properties of liquid metal ion (LMI) sources to the design of an optical system which exploits their unique characteristics. A gun with a beam current regulating system, a three‐element asymmetric electrostatic lens, and an einzel lens were incorporated into an optical column with a six‐pole electrostatic stigmator and post‐lens deflection. A design consideration with LMI sources is that material sputtered from apertures near the source can ’’poison’’ it, leading to source instability and short life. This problem can be avoided by large source‐lens spacing, but we have chosen to place the source close enough to the lens aperture that virtually no ion current strikes it, resulting in stable operation. While close source‐lens aperture spacing normally requires an undesirably low (∠5 kV) voltage on the source to achieve the conditions for ion emission, we have overcome the problem by surrounding the source with a grid (similar to a Wehnelt) maintained near source potential. The shielding action of the grid allows source operation at voltages in the range 15–20 kV with a 2‐mm spacing between source and lens aperture. In addition, by biasing the grid with respect to the source, the ion current can be varied while maintaining constant ion beam energy. The beam voltage can then be varied by using the variable voltage properties of the asymmetric lens. A LMI Ga source has been operated with low total current It<3 μA, corresponding to an angular intensity dI/dr≊20 A sr−1 and a beam energy spread E≊5 eV. With a beam energy of 16 keV, 2‐nA current was focused into 4000 Å at a working distance of ≊80 mm from the final lens.
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41.75.Fr Electron and positron beams

Ion source performance in a focusing column with large deflection fields

I. L. Berry

J. Vac. Sci. Technol. 19, 1153 (1981); http://dx.doi.org/10.1116/1.571233 (5 pages) | Cited 1 time

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The theoretical performance of liquid metal and field ionization ion sources in systems with large deflection fields is discussed. It is shown that simple postlens electrostatic deflection with dynamic focusing has the capability of achieving large deflection fields at reasonable beam currents. A deflection field of 3×103 spot diameters on a side is theoretically achievable for liquid gallium ion sources at beam currents of 1 nA at 100 kV and a spot size of 50 nm. Recent data from Hanson and Siegel for liquid helium cooled hydrogen field ionization indicate that even better performance may be achieved with this source.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

A mass‐separating focused‐ion‐beam system for maskless ion implantation

V. Wang, J. W. Ward, and R. L. Seliger

J. Vac. Sci. Technol. 19, 1158 (1981); http://dx.doi.org/10.1116/1.571234 (6 pages) | Cited 17 times

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The use of a focused ion beam for direct implantation of dopants into a semiconductor substrate results in appreciable simplification in the processing of semiconductor devices. We have demonstrated that liquid metal (LM) field‐ionization sources (based upon the electrostatic formation of an emitting cusp of liquid metal) offer the necessary high brightness to make focused ion beam microfabrication economically feasible. This paper reports upon two developments: (1) the development of eutectic‐alloy LM ion sources for the production of boron and arsenic for direct implantation of silicon devices, and (2) the development of a three‐lens variable‐energy focusing column that incorporates a mass‐separator of low aberration. Mass spectra of the ion emission of these sources show that the stoichiometric fraction of boron and arsenic is emitted. We have also demonstrated that the high vapor pressure of arsenic can be suppressed in the eutectic liquid metal, and that boron is predominantly emitted as a singly ionized species, while arsenic is emitted as both singly and doubly ionized species. A new focusing column has been developed that incorporates the new ion sources. It has the capability for focusing to sub‐micrometer dimensions with mass‐separation, a variable beam voltage of up to 150 kV, and a spot current of near 1 A/cm2. A high‐speed electrostatic‐deflection system with microprocessor control allows this machine to perform simple pattern exposures. Examples of the operation of this microfabrication system with eutectic alloy sources will be presented.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
07.75.+h Mass spectrometers
61.72.U- Doping and impurity implantation
85.30.-z Semiconductor devices

Ion projection microlithography for submicron device fabrication

G. Stengl, R. Kaitna, H. Löschner, R. Rieder, P. Wolf, and R. Sacher

J. Vac. Sci. Technol. 19, 1164 (1981); http://dx.doi.org/10.1116/1.571235 (2 pages) | Cited 1 time

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Ion projection microlithography is a technique employing a high‐resolution demagnifying ion‐optical imaging system in connection with a precision step‐and‐repeat stage. Design patterns are contained in a self‐supporting metal foil of 10× (or 20×) chip size, and are imaged in parallel, chip by chip. A tensile stress is induced in the mask foil such that the mask remains flat and undistorted, when heated by exposure to the ion beam. Different design layers are aligned to better than ±0.1 μm by a system that detects ions backscattered from registration marks.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Masked ion‐beam lithography: A feasibility demonstration for submicrometer device fabrication

J. L. Bartelt, C. W. Slayman, J. E. Wood, J. Y. Chen, C. M. McKenna, C. P. Minning, J. F. Coakley, R. E. Holman, and C. M. Perrygo

J. Vac. Sci. Technol. 19, 1166 (1981); http://dx.doi.org/10.1116/1.571236 (6 pages) | Cited 7 times

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Masked ion‐beam lithography (MIBL) is a high‐resolution pattern‐replication process that offers high throughput capability with submicrometer resolution. In MIBL, a collimated beam of protons is directed through a mask to expose a resist‐covered wafer in proximity to the mask. We report here on four key MIBL technology issues: (1) mask technology, (2) radiation‐damage effects, (3) resist materials, and (4) fabrication of NMOS devices using MIBL. We have established a process for fabricating thin (0.7 μm) silicon‐membrane masks with submicrometer e‐beam‐generated gold absorber patterns. We have evaluated mask‐induced beam scattering (<0.4° for channeled 175‐keV‐protons) and mask in‐plane thermal distortions (<0.1 μm over 1 cm2 for 0.1 W/cm2 beam power) which are the principle factors affecting resolution and throughput. Radiation‐damage effects were studied by simulating MIBL fabrication of MOS test chips. No statistically significant radiation effects were found after annealing at 450°C. We have demonstrated submicrometer resist patterning in both positive (PMMA) and negative (PS) resists, and have used these resists in the fabrication of submicrometer‐gate NMOS test devices using MIBL exposures on all levels.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
61.80.Jh Ion radiation effects
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Summary Abstract: High resolution ion beam lithography

N. P. Economou, D. C. Flanders, and J. P. Donnelly

J. Vac. Sci. Technol. 19, 1172 (1981); http://dx.doi.org/10.1116/1.571237 (4 pages) | Cited 3 times

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A new type of high resolution mask for ion beam lithography is described. The mask employs a thin membrane with regions of two different thicknesses to provide contrast for proton exposure of resist. A conventional ion implantation system is used to generate a collimated beam of protons for flood exposure of the sample. Beam energy is chosen so the the protons pass through the thin areas of the mask and emerge with sufficient energy to expose the resist, but are stopped in the thick areas. Experiments using polyimide membrane masks have yielded promising results. The ability to reactive ion etch structures with nearly vertical sidewalls in polyimide allows the fabrication of masks having both high contrast and high resolution. The stopping power of polyimide was determined by measuring the transmission of protons through membranes of known thickness, as a function of incident beam energy. In the energy range from 50–200 keV, the stopping power of polyimide for protons was measured to be ∠100 keV/μm. Mask fabrication procedures and exposure experiments to determine the resolution of this technique are reported. Patterns with linewidths of 〈0.1μm have been successfully replicated.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Energy spreading in the hydrogen field ionization source

G. R. Hanson and B. M. Siegel

J. Vac. Sci. Technol. 19, 1176 (1981); http://dx.doi.org/10.1116/1.571238 (6 pages) | Cited 10 times

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The application of field ionization as a tool for routine submicron fabrication will depend critically upon the characteristics of the source; the angular intensity and the energy spread of the ions. The chromatic aberration coefficient of the ion optical system, the angular aperture, and the energy spread combine to set the limit of spot size and current density for very‐high‐resolution probes with sources of energy widths even as low as 1 eV. It is known that the various molecular species produced by hydrogen field ionization are indentifiable by the energy distribution, and because the mass of the ion will determine the particle range in resists at any given energy, energy measurements carry further importance in the development of the probe‐forming system. In order to characterize the source‐energy widths and mass species as a function of beam current, angular intensity, and surface characteristics of the emitter tip, we have designed and operated a unitized, positionable intermediate image filter lens with a demonstrated resolution of 0.1 eV at 3.5 kV and acceptance half‐angles of less than 9 mrad. At angular intensities less than 10 μA/sr, 90% of the field ions from bright site emission of fields of 1.5 V/Å occur within an energy width of 1.2–1.9 eV. This narrow spread shows that only H2+ is being produced. The beam current and angular intensity from a single bright site can be increased by raising the source gas pressure and the applied field (5% increase in voltage). That energy broadening occurs at high intensities is demonstrated by the fact that at 3.5 μA/sr [0.5 nA emitted through 50 μm aperture subtending a half‐angle (ϑ1/2) of 0.0067 rad], 90% of ions appear within 1.9 eV (0.94 eV FWHM), while at 18 μA/sr (2.5 nA, ϑ1/2 of 0.0067 rad), 90% of ions appear within 2.2 eV (0.98 eV FWHM) where a tail develops on the low‐energy side causing a broadening of the energy distribution. The impact of field emitter surface configuration on source angular intensity and reliability are discussed.
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41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams

Liquid metal alloy ion sources for B, Sb, and Si

K. Gamo, T. Ukegawa, Y. Inomoto, Y. Ochiai, and S. Namba

J. Vac. Sci. Technol. 19, 1182 (1981); http://dx.doi.org/10.1116/1.571239 (4 pages) | Cited 9 times

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B, Sb, and Si ion sources using liquid metal alloys have been fabricated and basic characteristics such as current–voltage relations, angular current intensity, energy distribution, and mass spectra have been measured. Singly charged B ions which amount to 33% of the total ions and have an angular current intensity of ∠40 μA/sr at a total energy spread (FWHM) of ∠20 eV were obtained using B–Ni–Pt alloys. Singly charged Si and Sb ions with an angular current intensity of ∠11 μA/sr and ∠1.4 μA/sr at an energy spread of ∠20 eV were obtained by using Si–Au and Sb–Pb–Au alloys, respectively. These ion sources could be operated for more than 10 h without any changes in mass spectra.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
79.70.+q Field emission, ionization, evaporation, and desorption

Droplet emission in liquid metal ion sources

A. Wagner, T. Venkatesan, P. M. Petroff, and D. Barr

J. Vac. Sci. Technol. 19, 1186 (1981); http://dx.doi.org/10.1116/1.571240 (4 pages) | Cited 15 times

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Liquid indium ions sources were operated in a transmission electron microscope. The formation of a Taylor cone was directly observed during source operation. In addition, dynamic instabilities were observed on the needle shank behind the Taylor cone with the formation of liquid droplets which grew in size and left the shank. Droplets on the shank were also found in SEM observations of rapidly frozen liquid gold ion sources. The surface of silicon targets on which the ion current from a gallium ion source was allowed to impinge was studied by Rutherford backscattering spectrometry. The amount of material emitted from the ion source was measured as a function of the angle of emission and the ion current. A comparison of these emitted mass distributions with the corresponding current distributions indicated that the average mass to charge ratio of the beam decreased with angle of emission. In addition, the ratio of the amount of material to the total charge leaving the source was found to increase monotonically with the ion current with a sharp increase occurring for ion currents greater than approximately 10 μA.
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79.70.+q Field emission, ionization, evaporation, and desorption

X‐ray lithography using a pulsed plasma source

J. S Pearlman and J. C. Riordan

J. Vac. Sci. Technol. 19, 1190 (1981); http://dx.doi.org/10.1116/1.571241 (4 pages) | Cited 24 times

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An imploding gas jet plasma has been developed as a soft x‐ray source for lithographic applications. The plasma is an efficient source of krypton L radiation, which closely matches the wavelength of tungsten anode electron bombardment sources. Resist exposures have been made to evaluate the suitability of the source and determine the filtering requirements necessary to protect the resist. COP resist required 20 shots for a proper exposure; no reciprocity failure was observed with these pulsed, high‐power exposures.
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07.85.-m X- and γ-ray instruments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

High power 13.3 Å x‐ray source for submicron lithography

B. Fay

J. Vac. Sci. Technol. 19, 1194 (1981); http://dx.doi.org/10.1116/1.571242 (6 pages)

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This paper discusses the design, fabrication, and performance of a high‐power x‐ray source for submicron x‐ray lithography. The source is a conventional x‐ray source featuring a high perveance (1.0×10−6 A V−3/2) electron gun and a water cooled high‐speed rotating anode (8000 rpm). The anode material is copper and the main characteristic line radiated is the CuL line of 13.3 Å wavelength. Details are given on the geometrical design of the source, the realization of the pure Tantalum cathode indirectly heated by electron bombardment, and the high‐speed rotating anode. Results will be given on the operating conditions of the source as well as on the x‐ray exposure of high resolution x‐ray masks.
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07.85.-m X- and γ-ray instruments

Stationary anode x‐ray source for the evaluation of conventional resists

J. M. Warlaumont and J. R. Maldonado

J. Vac. Sci. Technol. 19, 1200 (1981); http://dx.doi.org/10.1116/1.571243 (4 pages) | Cited 2 times

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We have developed a high‐power stationary aluminum anode x‐ray exposure system in order to perform experiments and evaluate conventional resist processes, x‐ray mask substrates, and alignment techniques applicable to an x‐ray lithography system using an electron storage ring source. The source output energy (AlK α fine) falls within the broad energy peak from a properly filtered 700–1000 MeV storage ring spectrum. In this paper we describe the x‐ray source and also present results on sensitivity and patternability of conventional resist under x‐ray exposure.
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07.85.-m X- and γ-ray instruments
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Fabrication of polyimide masks for x‐ray lithography

B. M. Gong and Y. D. Ye

J. Vac. Sci. Technol. 19, 1204 (1981); http://dx.doi.org/10.1116/1.571244 (4 pages) | Cited 1 time

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The dimensional stability of a polyimide membrane is a key to the successful fabrication of x‐ray masks. It depends upon fractionation, purification, and the degradation prevention of polyamic acid. The polyimide membranes thus obtained have a great tensile stress so that the membrane flatness and distortion in a 30×40 mm rectangular window area are less than 1 μm and 0.2 μm, respectively. The advantages of using a polished glass plate as a substrate are good flatness, low cost, ease of fabrication, and also that the masks’ dimensions can be made large enough at will.
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81.40.Lm Deformation, plasticity, and creep
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)

Fabrication of polyimide x‐ray masks with high dimensional stability

T. Wada, S. Sakurai, and K. Kawabuchi

J. Vac. Sci. Technol. 19, 1208 (1981); http://dx.doi.org/10.1116/1.571245 (3 pages) | Cited 1 time

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A technique has been developed for fabricating polyimide x‐ray masks of high durability and excellent dimensional stability. It is found that the most serious factor causing the distortion of the polyimide membrane is the nonuniformity of the back‐etching rate. Improvements were effected to the etching apparatus and wafer holder to ensure a high uniformity of the etching rate of 3% over an 80 mm diam window. In addition, a gold layer was inserted between the polyimide membrane and the silicon wafer, and it is found that this etching stopper is very effective in reducing distortion. In addition, the distortion of the polyimide membrane is reduced, increasing the thickness of polyimide film and also decreasing the window size. As a result, polyimide x‐ray masks having a 4‐μm‐thick membrane and a 40‐mm‐diam window have been obtained with a distortion less than 0.15 μm (σ). They have shown excellent dimensional stability against a high‐level x‐ray irradiation amounting to 40 J/cm2 over one week.
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68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Fabrication of x‐ray masks using anisotropic etching of (110) Si and shadowing techniques

N. Tsumita, J. Melngailis, A. M. Hawryluk, and Henry I. Smith

J. Vac. Sci. Technol. 19, 1211 (1981); http://dx.doi.org/10.1116/1.571246 (3 pages) | Cited 7 times

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We describe a process for producing x‐ray masks of grating patterns with extremely smooth line edges. The technique developed by Flanders, in which a square‐wave profile relief grating in polyimide is obliquely shadowed with an x‐ray absorber, is followed, except that the original square‐wave structure is produced in (110) silicon by anisotropic chemical etching rather than in SiO2 by reactive ion etching. In this way, significant improvements in edge acuity are achieved because relief grating sidewalls are defined by atomic (111) planes. Holographic lithography is used to expose grating patterns in AZ 1350 over a thin Si3N4 layer on the (110) Si. The Si3N4 is patterned by reactive ion etching and serves as the mask for anisotropically etching the square‐wave‐profile grooves. At the proper crystallographic orientation the groove sidewalls are defined by (111) planes, and groove bottoms are approximately flat. The structure in Si is then transferred to polyimide which is obliquely shadowed and forms the x‐ray mask. Grating patterns replicated in PMMA using the CK x‐ray (4.5 nm) show straight lines with uniform widths and edges smooth to ∠±4 nm.
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07.85.-m X- and γ-ray instruments
07.68.+m Photography, photographic instruments; xerography
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Experimental evaluation of interferometric alignment techniques for multiple mask registration

T. M. Lyszczarz, D. C. Flanders, N. P. Economou, and P. D. DeGraff

J. Vac. Sci. Technol. 19, 1214 (1981); http://dx.doi.org/10.1116/1.571247 (5 pages) | Cited 1 time

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An interferometric alignment technique, which is capable of achieving 200 Å overlay accuracy has been described previously. This scheme utilizes matching grating type alignment marks located on mask and sample. In this paper, an experimental evaluation of this alignment scheme is presented. A breadboard alignment system has been constructed which allows coarse and fine control of mask and substrate position in x, y, z, and ϑ. This breadboard system is used to study the alignment marks, signals, and signal processing. The alignment strategy involves an operator‐assisted coarse alignment once per wafer and automated fine alignments at each die site. The coarse alignment is based upon moiré fringe patterns, and the fine alignment is based upon the grating scheme. A vernier scheme is used to extend the capture range of the fine alignment. Experimental results are presented for the grating scheme both in transmission and in reflection. The sensitivity of the alignment signals in reflection to variations in gap is analyzed. A modified grating mark is presented as a solution to the sensitivity problem.
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06.60.Sx Positioning and alignment; manipulating, remote handling
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

A wide‐range alignment system for x‐ray lithography

D. A. Nelson, V. Dimilia, and J. M. Warlaumont

J. Vac. Sci. Technol. 19, 1219 (1981); http://dx.doi.org/10.1116/1.571248 (5 pages)

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A new wafer alignment mark is introduced which, when used in conjunction with a linear Fresnel zone plate on the mask, results in an alignment method with a wide range while retaining the high resolution implicit in the method. This new mark eliminates the need for several separate marks with different alignment ranges and/or accurate prealignment of the mask−wafer system. If a large mark is used, as is needed for the initial alignment in a step and repeat system, a unique point of alignment is determined even if the initial misalignment is as large as the mark, in this case initial misalignment as large as ±1 mm. When it is desirable to occupy less wafer area with alignment marks, the alignment signal can be attained by using a portion of this configuration with a range of ±50 μm. The optimum operating conditions which result from theoretical analysis of this alignment system are discussed, and the results of experiments using this technique are given.
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42.79.Ci Filters, zone plates, and polarizers

Application of zone plates to alignment in microlithography

M. Feldman, A. D. White, and D. L. White

J. Vac. Sci. Technol. 19, 1224 (1981); http://dx.doi.org/10.1116/1.571249 (5 pages) | Cited 1 time

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Zone plates are patterned areas with imaging properties. When printed on masks and wafers and suitably illuminated, they form high contrast images which are useful for alignment in microlithography. As with holograms, defects in the pattern arising from variations in processing and linewidth control and poor edge definition degrade the image only marginally. This paper describes the use of zone plate alignment systems for die alignment in step and repeat cameras and for x‐ray proximity printing. We find extended targets incoherently illuminated are suitable for manual alignment but better signal‐to‐noise ratios (important in automatic alignment) are obtained by using the zone plates to focus laser beams to nearly diffraction limited point sources. With zone plates approximately 100 μ in diameter and 300 μ focal length, we have obtained signal‐to‐noise ratios greater than 100 to 1 and alignment accuracy better than ±0.1 μ.
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42.79.Ci Filters, zone plates, and polarizers

A pattern recognition technique using sequences of marks for registration in electron beam lithography

D. M. Holburn, G. A. C. Jones, and H. Ahmed

J. Vac. Sci. Technol. 19, 1229 (1981); http://dx.doi.org/10.1116/1.571250 (5 pages) | Cited 4 times

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A pattern recognition technique is described for precise registration in electron beam lithography. The usual simple mark on the substrate is replaced by a symbol of carefully chosen configuration, based on a pseudorandom binary sequence. The registration symbol obtained by rapidly scanning the electron beam in the region of the symbol is then cross correlated with a stored replica of the registration symbol, either by special purpose hardware or by programmed instructions. It is shown that with this method, registration symbols may be detected accurately even when heavily contaminated with noise, the signal‐to‐noise ratio being reduced to less than 0.25. The method also allows for the presence of unrelated artefacts in the vicinity of the symbol.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

A simple technique for modifying the profile of resist exposed by holographic lithography

N. N. Efremow, N. P. Economou, K. Bezjian, S. S. Dana, and Henry I. Smith

J. Vac. Sci. Technol. 19, 1234 (1981); http://dx.doi.org/10.1116/1.571251 (4 pages) | Cited 3 times

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Holographic lithography is a rapid and convenient method of exposing low distortion periodic and quasi‐periodic patterns over large areas. Spatial periods below 0.2 μm are readily achieved using commercial He:Cd lasers. However, many substrates of interest have significant reflectivity and, because the phase change on reflection is close to π, an intensity minimum occurs at the resist–substrate interface, leading to rounded ’’overcut’’ resist profiles. Such profiles are unsuitable for liftoff and undesirable for anisotropic dry etching. Moreover, the linewidth‐to‐period ratio is difficult to control and exposure latitude is limited. If a dielectric film is placed over a reflecting substrate, the intensity at the resist–dielectric interface can be maximized by proper choice of the optical thickness of the dielectric. We have developed a simple, operational, nondestructive method for precisely determining the angles of laser incidence that correspond to the condition of maximum interface intensity. The method uses the exposure laser and consists of measuring the total reflectivity from the dielectric/substrate combination as a function of incidence angle. Knowledge of the dielectric thickness and the optical constants of the dielectic and substrate are not required. We have used this method for the case of a He:Cd laser and a Si02/Si substrate. Chemical etching of the Si02 in buffered HF allowed us to maximize interface intensity at precisely the angles corresponding to preselected grating periods of 0.2 and 1 μm. Liftoff of evaporated chromium was achieved over cm2 areas with an exposure latitude of ∠200%. This, together with SEM analysis, indicated that resist sidewalls were vertical or slightly undercut, and improved control of linewidth‐to‐period ratio was feasible.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.40.My Applications
77.55.-g Dielectric thin films

Frequency‐sweeping interferometer develops new aspects in pattern generator

J. Nishizawa, S. Kasai, Y. Aoyama, and M. Fukase

J. Vac. Sci. Technol. 19, 1238 (1981); http://dx.doi.org/10.1116/1.571252 (4 pages)

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An attempt was made to develop a new type of laser interferometer which sweeps the oscillation frequency of the laser so as to improve the position control accuracy in microfabrication process. By knowing the wave lengths at which the interference intensity takes the extreme values, the optical path difference between the reference path and the object path was obtained without moving the object. In experiment, one resonator mirror of a He–Ne laser was oscillated by a piezoelectric transducer to oscillate the laser wave length. Four‐figures resolution was obtained experimentally.
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07.60.Ly Interferometers
42.60.By Design of specific laser systems
85.30.-z Semiconductor devices

The use of bias in electron beam lithography for improved profile quality and linewidth control

M. G. Rosenfield, A. R. Neureuther, and C. H. Ting

J. Vac. Sci. Technol. 19, 1242 (1981); http://dx.doi.org/10.1116/1.571253 (6 pages)

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As in optical lithography, the use of a bias, or difference in linewidth between the exposed pattern and developed resist profile, in electron beam lithography will lead to improved resist profile shape quality and linewidth control. Simulation is used to study the key aspects of choosing the proper bias for vertical resist profiles and to illustrate the advantages of using a bias in electron beam lithography. The use of a bias is also shown to aid in proximity correction. The techniques of dose correction, bias and/or exposure position correction, and a combination of bias and dose correction are investigated by means of a comparison of developed resist profile shape quality and linewidth sensitivity.
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81.65.-b Surface treatments
07.77.-n Atomic, molecular, and charged-particle sources and detectors
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)

The effect of extra doses at the pattern edges on negative electron resist profiles

H. Nakata, T. Kato, K. Murata, Y. Hirai, and K. Nagami

J. Vac. Sci. Technol. 19, 1248 (1981); http://dx.doi.org/10.1116/1.571254 (6 pages) | Cited 1 time

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Theoretical and experimental studies have been performed to improve a quality of negative electron resist patterning of an infinite array of 1, 2, and 3 μm lines and spaces. We examined the effect of extra doses at the line pattern edges on their cross sectional profiles. Experiments were carried out using a PGMA resist with an electron beam exposure system of EBMG‐40 at 10 keV. The cross sections were observed with a scanning electron microscope. It was found that a horned shape at the edges produced by extra doses had a favorable effect on the profiles during O2 plasma treatment to remove scum. It kept the edges from rounding due to a faster etching rate. The results showed some improvement in both the linewidth and the edge slope. An analysis of experimental cross sections has also been performed based on the so‐called contrast curve. From a comparison between theory and experiment we found that the patterns seemed to shrink by 30% to 50% in the lateral direction, depending on the linewidth. A theoretical approach is useful for investigations into the characteristics of negative electron resists.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
07.77.-n Atomic, molecular, and charged-particle sources and detectors
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)

Computer simulations of resist profiles in x‐ray lithography

K. Heinrich, H. Betz, A. Heuberger, and S. Pongratz

J. Vac. Sci. Technol. 19, 1254 (1981); http://dx.doi.org/10.1116/1.571255 (5 pages) | Cited 7 times

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This paper presents a detailed study on computer simulations of resist profiles obtained in x‐ray lithography for exposures made either with synchrotron radiation or with an Al–Kα source. It is assumed, for purposes of the calculations, that the vacuum windows consist of kapton and that silicon is used as the mask material. The influence of edge shape and mask absorber thickness upon the resist structure is of special interest. The other parameters affecting resist profiles, such as Fresnel diffraction (especially in the case of semitransparent absorbers) and photoelectron range, are taken into consideration. In the case of the x‐ray tube, the penumbral blur caused by the finite dimensions of the source spot leads to an additional deterioration of the edge sharpness. For the calculations, the intensity distribution over the spot area was assumed to be uniform (with Gaussian‐shaped edges). The influence of the photoelectron range upon the resist profiles is calculated, using the simple depth‐dose relationship of Gruen. The calculated resist profiles are compared with typical experimental results.
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07.85.-m X- and γ-ray instruments
07.68.+m Photography, photographic instruments; xerography
41.60.-m Radiation by moving charges
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Ion beam exposure profiles in PMMA–computer simulation

L. Karapiperis, I. Adesida, C. A. Lee, and E. D. Wolf

J. Vac. Sci. Technol. 19, 1259 (1981); http://dx.doi.org/10.1116/1.571256 (5 pages) | Cited 14 times

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A comprehensive Monte Carlo program (piber) has been developed for the simulation of ion beam exposure of resists. piber has been used to study ion ranges, backscattering coefficients, and energy‐loss distribution data for various combinations of incident ions and multilayered targets. For lithographic applications, the spatial ion energy‐loss distribution in polymethyl methacrylate (PMMA) generated with piber for a δ‐function exposure is convoluted with realistic incident ion beam shape (Gaussian, square, etc.) to produce latent images. A string development model is then used to generate developed ion beam exposure profiles in PMMA. The developed profiles for isolated lines have been studied as a function of parameters such as ion energy, resist thickness, and exposure dosage. Closely spaced lines have also been simulated in order to study proximity effects. It is demonstrated that proximity problems are greatly reduced in comparison with electron beam exposed patterns.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
41.75.Ak Positive-ion beams
41.75.Cn Negative-ion beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Verification of a proximity effect correction program in electron‐beam lithography

E. Kratschmer

J. Vac. Sci. Technol. 19, 1264 (1981); http://dx.doi.org/10.1116/1.571257 (5 pages) | Cited 7 times

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A new method for computing proximity effect corrections for submicron electron‐beam lithography is introduced. It is based on a fast algorithm for shape partitioning to gain better control for resultant exposure intensity distribution across each shape in the pattern. By careful investigation of the intrashape and the intershape proximity effects the program supplies a means of controlling the submicron pattern delineation. Values for the parameters of the double Gaussian function used in the calculation of the dose variation factors are given for a variety of exposure conditions. Results of the application of the program to delineation of submicrometer patterns in PMMA and AZ 1350 resist on silicon substrate are presented.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Proximity effect correction using a dose compensation curve

J. S. Greeneich

J. Vac. Sci. Technol. 19, 1269 (1981); http://dx.doi.org/10.1116/1.571258 (6 pages) | Cited 7 times

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A new concept, the dose compensation curve, is described for use in a proximity effect correction algorithm. The dose compensation curve links dose compensation factors, developed resist images, and calculated values of energy density at pattern boundaries. An experimentally measured dose compensation curve agrees very well with theoretical predictions. This technique has been successfully implemented in a fast promixity‐effect correction algorithm which automatically corrects the exposure dose factor in the electron‐beam data base for vector scan machines.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
85.40.Bh Computer-aided design of microcircuits; layout and modeling
41.75.Fr Electron and positron beams

Proximity corrections in a raster scan electron lithography machine

S. K. S. Ma, M. Parikh, and W. Ward

J. Vac. Sci. Technol. 19, 1275 (1981); http://dx.doi.org/10.1116/1.571259 (4 pages) | Cited 1 time

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A method to correct proximity effects has been applied to a raster scan electron lithography machine. Since it is very difficult to vary the exposure level of a raster scan machine while it is writing, a multiple pass algorithm has been developed to achieve a maximum number of exposure levels for a given number of passes. Scanning electron micrographs of experimental patterns before and after proximity corrections are presented for comparison. The corrected results show an excellent improvement for lines and gaps at 3/4 μm, although proximity corrections may be needed for lines and gaps even at 1 1/2 μm.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling

Proximity effect correction in electron‐beam lithography

T. Kato, Y. Watakabe, and H. Nakata

J. Vac. Sci. Technol. 19, 1279 (1981); http://dx.doi.org/10.1116/1.571260 (7 pages) | Cited 1 time

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Electron‐beam fabrication offers several important advantages for lithography, including a capability of geometries smaller than one micrometer, a high adaptability to automation and the ability to write directly on a Si wafer without the need for a mask. However, for submicron patterns, a proximity effect is observed by the behavior of incident electrons in a resist. In electron‐beam lithography the exposure intensity distribution (hereafter EID) is an essential physical quantity for implementing a proximity effect correction. There are many correction methods and several methods have been tried to correct for practical devices. However, the variation of the EID along the distance into the resist from the surface is neglected, and only a two‐dimensional EID is presented in those articles. The present paper describes experimental and theoretical study on a correction method of the proximity effect which contains the consideration of the three‐dimensional profile of a resist. It has been found from a Monte Carlo simulation that a cross‐sectional profile can be controlled by an additional exposure at the vicinity of a pattern edge. With this method, for example, an undercut resist pattern, which is suitable for a lift‐off process, can be obtained, avoiding as a whole the overdose on a pattern. A 0.5 μm line and space pattern with 1 μm thickness PMMA has been easily obtained, namely, when under‐developed, the wall profile of the resist becomes rather steep, and when properly developed, the profile becomes undercut.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Proximity parameters determination for electron beam lithography using a novel technique

Ching‐Hao Shaw

J. Vac. Sci. Technol. 19, 1286 (1981); http://dx.doi.org/10.1116/1.571261 (5 pages) | Cited 2 times

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A technique of acquiring proximity parameters is presented. This technique utilizes a design pattern of line‐density exposure wedge. The pattern was written with electron‐beam line scans of line densities ranging from 500 Å to 5‐μm spacings. With small spatial scales built‐in, the proximity data are obtained through a supplemental, qualitative end point detection scheme. The end point is determined by the clearance of resist between scan lines. Since there are many scan lines in every exposure, each datum is a statistical average. Examples of using this technique are presented to determine proximity parameters for proximity corrections. In addition, they may be determined as a function of the condenser lens setting, which relates to the electron probe diameter. A variation of the technique described above indicates that the forward scattering parameter is dependent upon resist development time.
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41.75.Fr Electron and positron beams
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

An approach to correct the proximity effect in electron beam proximity printing

P. Nehmiz, H. Bohlen, J. Greschner, E. Bretscher, and P. Vettiger

J. Vac. Sci. Technol. 19, 1291 (1981); http://dx.doi.org/10.1116/1.571262 (5 pages)

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Electron beam proximity printing employs shadow projection for submicron lithography. The pattern mask has physical holes for the transmitted electrons. The mask stencil problem (ring shaped apertures would fall out of these masks) is overcome by distributing the pattern to be printed on two complementary masks. The use of two complementary masks provides means to correct the proximity effect, known to impede micron resolution in electron beam lithography. To that end, for a shape in the first complementary mask a smaller correction shape in the second is introduced. The double dose deposited in the central position of the shape modifies the development process so that the proximity effect can be corrected. Experiments are reported which demonstrate the feasibility of this proximity correction method.
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79.20.Kz Other electron-impact emission phenomena
07.68.+m Photography, photographic instruments; xerography

Optimization techniques for proximity effect compensation

Allen M. Carroll

J. Vac. Sci. Technol. 19, 1296 (1981); http://dx.doi.org/10.1116/1.571263 (4 pages) | Cited 1 time

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The most important tool in computing proximity effect compensation for electron‐beam lithographic patterns is a powerful and general facility for correcting small subpatterns. In this paper, we propose a solution method for the subpattern correction problem which has significant advantages over the techniques currently in use. The problem is shown to be amenable to the techniques of mathematical optimization. This permits proximity effect compensation to be adapted to the needs of a particular resist, device pattern, process step, or lighographic equipment.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
02.90.+p Other topics in mathematical methods in physics (restricted to new topics in section 02)
41.75.Fr Electron and positron beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling

A model for optimizing CPU time for proximity correction

W. W. Molzen and W. D. Grobman

J. Vac. Sci. Technol. 19, 1300 (1981); http://dx.doi.org/10.1116/1.571264 (4 pages) | Cited 1 time

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Future device technologies will call for the use of very dense and pseudorandom logic patterns. Microfabrication techniques will have to cope with a large number of different designs which are essentially nonrepetitive (e.g., logic). Electron beam technology will also have to be concerned with the large amounts of CPU time it will take to process these designs, especially when considering correction for the scattering of electrons in the resist and substrate (the proximity effect). Proximity correction is divided into the partitioning of design shapes and the dose correction of the resultant shapes. For partitioning, we have evolved a scheme which separates the center from the edges of designed shapes. The centers are given a fixed dose increase of electron exposure to ensure their development and the edges are sent to the proximity correction routine. This will save CPU time for a design which has an abundance of large shape patterns. We have also investigated tradeoffs between the CPU time it takes to set up and solve the set of linear equations for dose correction, and the size of the groups of pattern shapes which are dose corrected at a given time. Since the CPU time needed to solve the matrix of linear equations goes up approximately as the cube of the number of shapes in a group, it is advantageous to know the relationship of group size to total CPU time. For too small groups, the calculations are dominated by overheads incurred in handling the large number of such groups (and their boundaries) comprising the pattern. For large groups, linear equation solution time becomes too large. We develop a polynomial model which chooses the group size for a particular design in order to minimize the total CPU time. Once this is accomplished, the CPU time will become proportional not to a power of ’’N’’ (number of shapes in a chip), but only to ’’N’’ itself.
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02.70.-c Computational techniques; simulations
41.75.Fr Electron and positron beams
85.40.Bh Computer-aided design of microcircuits; layout and modeling
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)

Twenty‐five nm features patterned with trilevel e‐beam resist

D. M. Tennant, L. D. Jackel, R. E. Howard, E. L. Hu, P. Grabbe, R. J. Capik, and B. S. Schneider

J. Vac. Sci. Technol. 19, 1304 (1981); http://dx.doi.org/10.1116/1.571265 (4 pages) | Cited 6 times

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We describe a trilevel e‐beam resist process based on the high resolution resist PMMA. This process has been used to form metal features 25 nm wide on thick Si substrates by liftoff. Ni–Cr films patterned in this way have been used as masks for reactive ion etching of Si. The resulting structures were arrays of fins ∠ 30 nm wide and 330 nm high on 95 nm centers with a total length of 3 μm. We also discuss the resolution improvement obtained in a trilevel process based on a higher speed resist, P (MMA/MAA).
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
41.75.Fr Electron and positron beams
61.80.Fe Electron and positron radiation effects
07.77.-n Atomic, molecular, and charged-particle sources and detectors

A multilayer, high resolution, ion‐bombardment‐tolerant electron resist system

B. D. Hunt and R. A. Buhrman

J. Vac. Sci. Technol. 19, 1308 (1981); http://dx.doi.org/10.1116/1.571266 (5 pages)

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A multilayer, high resolution electron resist system, which withstands ion bombardment, has been developed. This system consists of four layers which are, from top to bottom: AZ1350B, a thin metal interlayer, PMMA, and a copolymer of PMMA. The bottom two layers define the actual pattern dimensions. Two independent developers have been chosen for these two layers in order to obtain controllably undercut resist profiles ideal for liftoff applications, while maintaining high resolution in the upper PMMA layer. The top two layers of the four‐level system serve to provide a protective metal coating which prevents crosslinking of the underlying polymer layer. This allows processing involving ion bombardment, such as ion milling or reactive ion etching. Without this protective metal layer, difficulty is often encountered in liftoff processing after ion bombardment, due to the presence of a thin crosslinked polymer layer which resists solvent penetration. This resist system has been used in conjunction with reactive ion beam oxidation to fabricate high quality, small area, niobium–lead alloy tunnel junctions in an edge geometry. Using a standard Cambridge EBMF‐2 microfabricator, junctions with linewidths as small as 0.25 μm have been produced. With the edge geometry, this corresponds to junction areas smaller than 4×10−10 cm2.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
61.80.Jh Ion radiation effects
74.50.+r Tunneling phenomena; Josephson effects
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Practicing the Novolac deep‐UV portable conformable masking technique

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

J. Vac. Sci. Technol. 19, 1313 (1981); http://dx.doi.org/10.1116/1.571267 (7 pages) | Cited 3 times

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Deep‐UV portable conformable masking, a double‐layer resist patterning technique, combines the advantages of a noncontact submicron printing technique such as refractive projection imaging or scanning electron‐beam patterning with those of deep‐UV conformable printing. Feasibility studies were reported earlier.1,2 Here, the processes leading to fabrication of 1‐μm MOSFET devices by e‐beam and step‐and‐repeat optical projection printing will be presented. These include processing steps to retain or remove the top resist layer, to obtain resist image profiles suitable for liftoff or for reactive ion etching (RIE), to improve adhesion, to treat the interfacial layer between the two resists, to prevent cracking, and to monitor the development of the two resist layers. Electrical testing results on pin hole density are given, followed by uncapped and capped resist images of 1‐μm double‐poly‐Si MOSFET test sites as well as 0.8‐μm thick Al lifted‐off images.
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85.30.Tv Field effect devices

Silicon transfer layer for multilayer resist systems

J. B. Kruger, P. Rissman, and M. S. Chang

J. Vac. Sci. Technol. 19, 1320 (1981); http://dx.doi.org/10.1116/1.571268 (5 pages) | Cited 6 times

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Thin film silicon is found to be a desirable interlayer material for e‐beam lithography with multilayer resist systems. It is easily etched in CF4 plasma (Si/PMMA: 30/1) yet resists O2 reactive ion etch (Si/HPR: 1/300). It is sufficiently conductive to avoid charging effects, both during lithography and SEM inspection. High optical contrast aids in inspection. Monte Carlo calculations show that a 2.5 μm bottom layer of polymer can substantially alleviate the proximity effect, even with an 80 nm Si interlayer. Pattern transfer with less than 100 nm linewidth loss is demonstrated. Lines as narrow as 200 nm in 2 μm of Hunt positive resist were holographically produced.
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81.65.-b Surface treatments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
73.61.Cw Elemental semiconductors
73.61.Ey III-V semiconductors
73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
68.60.-p Physical properties of thin films, nonelectronic

Lift‐off of thick metal layers using multilayer resist

S. P. Lyman, J. L. Jackel, and P. L. Liu

J. Vac. Sci. Technol. 19, 1325 (1981); http://dx.doi.org/10.1116/1.571269 (4 pages) | Cited 4 times

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We have developed a modified multilayer resist technique which allows lift‐off of very thick (≳2 μm) metal layers while retaining fine resolution. The trilayer structure consists of a thick (3 μm) lower layer of AZ 2430, the top of which is plasma‐hardened in a CF4 discharge in order to render it impervious to solvents, an intermediate layer of SiO (∠1000 Å), and a thinner (1 μm) upper resist layer, typically AZ 1350 J. After standard patterning of the upper resist, the pattern is transferred to the SiO and lower resist layers by reactive ion etching in CF4 and O2 respectively. By varying the pressure of the O2 plasma, either vertical walls, or walls with controlled undercut were produced. Because the lower resist layer remains soluble in acetone, it is easily removed, making this method appropriate for lift‐off. Using this technique, we have made 2 μm thick microwave electrodes of aluminum and of gold coated copper. This procedure is potentially useful for fabricating x‐ray masks or other structures requiring thick high resolution metal patterns, as well as for these specialized electrodes.
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85.40.Ls Metallization, contacts, interconnects; device isolation

Submicron electron‐beam patterning of aluminum by a double‐layer pattern transfer technique

M. Sato, K. Kawabuchi, M. Yoshimi, and T. Yamazaki

J. Vac. Sci. Technol. 19, 1329 (1981); http://dx.doi.org/10.1116/1.571270 (4 pages)

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A double‐layer pattern transfer technique has been developed for submicron aluminum patterning. The double‐layer consists of an electron beam resist and an inorganic material ’’spacer’’ having high resistance to reactive ion etching of aluminum. When plasma‐deposited silicon dioxide is used as a spacer, severe side‐etch of aluminum occurs. On the other hand, by using plasma‐deposited silicon nitride as a spacer, submicron aluminum patterns are formed without any etch bias. On profiled surfaces, aluminum patterns with 0.75 μm lines and 0.75 μm spaces are produced without linewidth variations due to the surface topography, by applying etch‐back technique to the silicon nitride spacer before resist coating.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Deep‐UV photoresists: Poly(methyl methacrylate‐co‐indenone)

R. L. Hartless and E. A. Chandross

J. Vac. Sci. Technol. 19, 1333 (1981); http://dx.doi.org/10.1116/1.571271 (5 pages) | Cited 4 times

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Copolymers of indenone and methyl methacrylate have been evaluated as deep‐UV (200–300 nm) positive photoresists. Sensitivities of 0.02 and 0.1 J/cm2 at 248 and 280 nm were found for polymers containing 7% and 18% indenone, respectively. Exposure of a 3 in. resist‐coated silicon wafer on a Perkin Elmer 111 Projection Printer (modified for short wavelength) for 40 s resolved equal 0.75 μm lines and spaces. The materials have chemical and physical properties compatible with microfabrication processes. The resists have approximately the same plasma resistance and e‐beam sensitivity as poly(methyl methacrylate).
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42.70.Gi Light-sensitive materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.50.-m Photochemistry
85.40.Bh Computer-aided design of microcircuits; layout and modeling

A novel approach to o‐nitrobenzyl photochemistry for resists

E. Reichmanis, C. W. Wilkins, and E. A. Chandross

J. Vac. Sci. Technol. 19, 1338 (1981); http://dx.doi.org/10.1116/1.571272 (5 pages) | Cited 13 times

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We have developed a two‐component (resin‐solution inhibitor) resist system having good photosensitivity in the 230–300 nm range. The resin is an optically transparent methyl methacrylate‐methacrylic acid copolymer that is soluble in aqueous alkali. The second component is one of a family of o‐nitrobenzyl carboxylates that are initially insoluble in the alkaline developer but are cleaved to soluble components upon irradiation. A number of o‐nitrobenzyl alcohol esters have been prepared and examined for use in this two‐component system. They have proven useful in the development of sensitive high‐resolution short‐wavelength photoresists which are described.
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07.68.+m Photography, photographic instruments; xerography
42.70.Gi Light-sensitive materials
82.50.-m Photochemistry
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials

Dosimetry for lithographic applications

J.M. Shaw and M. Hatzakis

J. Vac. Sci. Technol. 19, 1343 (1981); http://dx.doi.org/10.1116/1.571273 (5 pages)

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Because of the demand for miniaturization of devices, lithographic tools are becoming more expensive and sophisticated with future emphasis being placed on x rays, e beams, and ultraviolets in the range of 2200–3200 Å. It is increasingly important to be able to easily monitor exposure dose and uniformity from tool to tool in an industrial environment. This paper investigates the use of commercially available dosimeter films for lithography applications. These films consist of radiachromic dye derivatives in various polymers. Upon exposure to ultraviolet light (<3400 Å) and other ionizing radiation, these films undergo photoionization, and change from a colorless to a deeply colored state as a direct function of the radiation exposure received. Therefore, the optical density is a means of measuring the amount of incident radiation. For e‐beam dosimetry, a measurable optical density change is observed between 0.1 and 20 μC/cm2 with saturation occurring at ∠25 μC/cm2. Maximum penetration range of the 25‐kV beam was determined to be 20–25 μ. For x‐ray application, the film is similar to e‐beam, with a linear response up to 100 mJ/cm2 using the Al–Kα line. For mid UV at 3130 Å and deep UV at 2200 Å, the dosimeter is very sensitive with a 5% change in transmission occurring for every 1 mJ/cm2 dose variation.
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97.60.-s Late stages of stellar evolution (including black holes)
42.70.Gi Light-sensitive materials

High‐sensitivity, high‐resolution, high‐thermal‐resistant negative electron x‐ray resist

Z. C. H. Tan, C. C. Petropoulos, and F. J. Rauner

J. Vac. Sci. Technol. 19, 1348 (1981); http://dx.doi.org/10.1116/1.571274 (3 pages) | Cited 1 time

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A novel negative‐working electron/x‐ray resist with high sensitivity, high resolution, and good dry etch resistance was obtained by the free radical copolymerization of an unsaturated methacrylate and a hydroxy alkyl methacrylate. Depending on the copolymer ratio, sensitivity of at least 0.2 μC/cm2 was achieved with 10 keV electrons in most cases with polymers with a ?w well below 100 000. Resolution of 1.0 μm line and space was obtained from a 0.95‐μm‐thick resist by either direct e‐beam writing or by exposure to soft x‐rays through a mask. The sensitivity to 7 Å tungsten M lines was 9 mJ/cm2 and the contrast was ∠1.3. An aspect ratio of ∠2 was obtained with isolated submicron lines 7000 Å thick. The resist had good resistance to both chemical and dry etching. The plasma etch resistance was at least twice that of PMMA.
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78.90.+t Other topics in optical properties, condensed matter spectroscopy and other interactions of particles and radiation with condensed matter (restricted to new topics in section 78)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
07.85.-m X- and γ-ray instruments
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Novel plasma developable resist compositions and performance of total dry microfabrications in submicron lithography

M. Tsuda, S. Oikawa, W. Kanai, K. Hashimoto, A. Yokota, K. Nuino, I. Hijikata, A. Uehara, and H. Nakane

J. Vac. Sci. Technol. 19, 1351 (1981); http://dx.doi.org/10.1116/1.571209 (7 pages) | Cited 3 times

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A principle for the formulation of plasma developable resists and an example of new resist compositions are described. Resist patterns with submicron resolution and excellent profile have been produced readily using new resist compositions and the dry development process which is inherently free from swelling, from which the low resolution of resist images arises. The importance of the dry developable resist in submicron fabrication technology, the characteristics of the new resist compositions in the dry development process, and the dry development mechanism are discussed. The total dry microfabrication including the development of resist, the etching of Si and SiO2 and the removal of resist, was performed in the process using the new resist compositions.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
82.50.-m Photochemistry
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Ion‐beam sensitivity of polymer resists

H. Ryssel, K. Haberger, and H. Kranz

J. Vac. Sci. Technol. 19, 1358 (1981); http://dx.doi.org/10.1116/1.571210 (5 pages) | Cited 13 times

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The ion‐beam sensitivity of polymer resists, mainly PMMA, was investigated for argon, gallium, helium, and hydrogen ions. The resists were exposed in a standard ion accelerator at energies of 40 to 120 keV. The samples were irradiated with doses varying between 5×1010 and 5×1014 cm−2. It was found that the resists are about a factor of 100 more sensitive for hydrogen ions than for electrons of 20 keV; whereas for helium, up to a factor of 150, and for argon and gallium a factor of more than 300 were found for positive resists. Using an energy of 120 keV, layers of more than 1.3 μm thickness can be exposed by hydrogen ions, 1.0 μm thickness by helium ions and 0.25 μm thickness by argon ions. The effective sensitivity is energy‐dependent, and within the region of 40 to 120 keV between a factor of 1.4 and 2.0, with the higher sensitivity at lower energies. The achievable resolution of structures using ion beams is very high. Resists with a sensitivity of 5×10−7 C/cm2 easily yield a resolution of 0.25 μm wide and 1.3 μm thick lines.
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61.80.Jh Ion radiation effects
61.80.Fe Electron and positron radiation effects

Germanium selenide: A resist for low‐energy ion beam lithography

A. Wagner, D. Barr, T. Venkatesan, W. S. Crane, V. E. Lamberti, K. L. Tai, and R. G. Vadimsky

J. Vac. Sci. Technol. 19, 1363 (1981); http://dx.doi.org/10.1116/1.571211 (5 pages) | Cited 13 times

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A negative resist consisting of a layer of germanium selenide ∠1800 Å thick with a surface layer of silver selenide ∠100 Å thick was irradiated with 10 to 38 keV He, N, Ar, and Xe ions. While polymer resists require an incident ion to pass through the entire thickness of the resist film for exposure, germanium selenide films can be exposed with ions which penetrate only the ∠100 Å thick silver selenide surface layer. Thus, germanium selenide is an attractive resist system for low energy focused ion beam lithography. Resist sensitivities of ∠1013 to 1015 ions/cm2 were measured. Both nuclear and electronic stopping contribute to exposing the resist. Submicron lines have been produced in germanium selenide with a 20 keV finely focused ion beam.
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07.68.+m Photography, photographic instruments; xerography
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.-b Surface treatments

The chemical reactivity and lithographic sensitivity of obliquely deposited germanium selenide films used as low energy ion beam resists

T. Venkatesan

J. Vac. Sci. Technol. 19, 1368 (1981); http://dx.doi.org/10.1116/1.571212 (6 pages) | Cited 7 times

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Silver sensitized obliquely deposited germanium selenide films exposed to 25 keV N+ ion beam exposure exhibit an increasing sensitivity with increasing deposition angle with respect to the substrate surface normal. Films deposited at 75° are 20 times more sensitive than the films deposited normally (0°). The film density was found to decrease with increasing deposition angle with a reduction as high as 25% for the films deposited at 75°. The obliquely deposited films are chemically very reactive both in terms of silver adsorption in a sensitizer and their dissolution rate in a developer. Rutherford back scattering spectra of the adsorbed Ag indicate penetration of Ag through more than half the thickness of the film deposited at 60° and 75° indicative of deep voids in these films, a consequence of the oblique deposition. The 45° film shows a photodoping efficiency 3 times that of a 0° film. This enhanced silver doping efficiency may be primarily responsible for the increased sensitivity of the oblique films. Using a bilevel scheme involving a GeSe2 film deposited at 45° on a poly (vinyl formal) PVF layer submicron patterns were written on the GeSe2 film with a 20 keV vector scanned, In+ ion beam focussed to a spot size of 2500 Å. The developed patterns on the GeSe2 were successfully transferred to the underlying PVF by an oxygen reactive ion etch, producing 0.3 μm wide polymer patterns.
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61.80.Jh Ion radiation effects
07.68.+m Photography, photographic instruments; xerography
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Oblique deposition enhanced sensitivity in electron beam exposed g‐GexSe1−x inorganic resist

K. Balasubramanyam and Arthur L. Ruoff

J. Vac. Sci. Technol. 19, 1374 (1981); http://dx.doi.org/10.1116/1.571213 (5 pages) | Cited 3 times

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The enhancement of the electron beam sensitivity by a factor of ten has been achieved in silver adsorbed g−Ge0.25Se0.75 inorganic resist by oblique deposition of the amorphous chalcogenide films. The electron beam induced chemical and structural changes in obliquely deposited films, the lithographic performance, and the resolution limits are reported.
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07.68.+m Photography, photographic instruments; xerography
68.90.+g Other topics in structure, and nonelectronic properties of surfaces and interfaces; thin films and low-dimensional structures (restricted to new topics in section 68)
79.20.Kz Other electron-impact emission phenomena
81.65.-b Surface treatments

Plasma‐developed ion‐implanted resists with submicron resolution

T. Venkatesan, G. N. Taylor, A. Wagner, B. Wilkens, and D. Barr

J. Vac. Sci. Technol. 19, 1379 (1981); http://dx.doi.org/10.1116/1.571214 (6 pages) | Cited 2 times

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Resist materials and processes are described for use with low energy ion beam lithographic tools. Ion implanted regions on polymer and (SiO2) resists serve as in situ etch masks during reactive ion etch development of unexposed regions. Presumably, nonvolatile inorganic compounds formed from the implanted ions act as the in situ masks. Two classes of resist have been employed (1) an inorganic SiO2 layer exposed by In+ ions and developed in a fluorocarbon plasma and (2) a thick organic polymer exposed by In+ and developed in an oxygen plasma. For the latter, Rutherford backscattering spectroscopy was used to analyze the amount and depth distribution of the implanted ions before and after the reactive ion etching process (RIE). Between 5% and 15% of the implanted species are lost during the RIE development. Ionic organic resists exhibited deeper In+ distributions after a 3 keV implant and subsequent reactive ion etching than insulating organic materials. Conducting resists are required for finely focussed ion beam writing because of charging which occurs on insulating materials and causes beam broadening. Using a finely focussed In+ ion beam at 20 keV, and RIE, it was possible to fabricate 2500 Å wide lines, about O.8 μm high at an exposure dose of 2×1016 ions/cm2 in a 2:1 mixture of the semiconducting poly (vinyl carbazole) ‐trinitrofluorenone complex. Regions of the stepped beam as small as 500 Å were also reproduced.
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61.72.U- Doping and impurity implantation
81.65.-b Surface treatments
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
61.80.Jh Ion radiation effects

A new conformal dry‐etch technique for submicrometer structuresa)

Ma Jun‐Ru, Shen Kuo‐Hsiung, E. D. Wolf, and T. E. Everhart

J. Vac. Sci. Technol. 19, 1385 (1981); http://dx.doi.org/10.1116/1.571215 (5 pages) | Cited 4 times

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A new microlithographic pattern transfer technique that does not require resist development has been studied. The technique involves the diffusion of gaseous HF and water vapor through the exposed resist and the selective etching of the underlying SiO2. Etching is found to proceed only when the resist is in contact with the SiO2 underneath. The ratio of the etch rate of SiO2 beneath exposed and unexposed resist can be essentially infinity and this very high selectivity was used for etching high resolution SiO2 patterns without development. Variations of etch rate with substrate temperature (100° to 250°C), exposure dose (0−54 J/cm2 for UV, and 0−3.2 mC/cm2 for e‐beam at 20 keV) HF vapor flow and resist thickness (1600 to 4000 Å) are presented. This new microlithographic etch process for patterning SiO2 does not require resist development and therefore reduces the three key steps in microlithography—exposure, development, and etching to two. As a result it eliminates the problems introduced during the development stage such as pinholes and loss of pattern fidelity. The process is capable of resolution down to at least 0.7 μm linewidths in silicon dioxide and in principle can be applied to other materials with volatile reaction products.
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66.30.Ny Chemical interdiffusion; diffusion barriers
85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments

A novel anisotropic dry etching technique

M. W. Geis, G. A. Lincoln, N. Efremow, and W. J. Piacentini

J. Vac. Sci. Technol. 19, 1390 (1981); http://dx.doi.org/10.1116/1.571216 (4 pages) | Cited 36 times

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We have developed a dry etching technique in which the chemically reactive species and the energetic ions are independently controlled. This technique, which we call ion beam assisted etching (IBAE), is accomplished by impinging a chemically reactive gas from a jet and an ion beam from a Kaufman ion source upon the sample. It is based upon the work of Coburn et al., 1 and differs fundamentally from reactive ion etching (RIE), which relies upon a plasma to produce both the chemically active species and the energic ions. In IBAE the partial pressure of the reactive gas can be as high as several Pa (tens of microns) at the sample surface while the chamber pressure can easily be maintained at about 1×10−2 Pa (10−4 Torr). Although a variety of reactive gases and sample materials have been characterized, the presentation will concentrate on using Cl2 as a reactive gas and an argon ion beam. The anisotropic character of this etching technique has been found to depend on the angles that the gas jet and the ion beam make with the surface of the sample. Etching rates as high as a few micrometers per minute have been obtained with GaAs and Al samples and anisotropic etching aspect ratios as large as 50 were easily obtained with GaAs. The etched surface of the GaAs was also electrically characterized in two ways: first, by fabricating Schottky diodes on it and measuring the ideality factor, and secondly, by growing VPE GaAs on the etched surface and profiling the traps at the interface between the etched surface and the VPE GaAs using deep level transient spectroscopy (DLTS). The quality of the etched surface was found to improve as the reactive gas flux varied from about 1×1017 to 5×1018 atoms cm−2 s−1. Measured ideality factors of the Schottky diodes fabricated on GaAs etched under high reactive gas flux conditions were equivalent to diodes fabricated on virgin GaAs. The density of traps at the interface between the etched GaAs and the VPE GaAs was less than 1×1015 cm−3 which is low enough for many GaAs device applications. The independent parameter control afforded by this technique has enabled us to achieve desirable anisotropic etching characteristics while producing etched GaAs surfaces with acceptable electrical quality.
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81.65.-b Surface treatments
07.77.-n Atomic, molecular, and charged-particle sources and detectors
79.20.Kz Other electron-impact emission phenomena

Reactive ion etching of niobium

T. T. Foxe, B. D. Hunt, C. Rogers, A. W. Kleinsasser, and R. A. Buhrman

J. Vac. Sci. Technol. 19, 1394 (1981); http://dx.doi.org/10.1116/1.571217 (4 pages) | Cited 4 times

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The reactive gases CBrF3 and CF4 have both been found to be effective in the reactive ion etching of niobium. At relatively high pressures, 100 mTorr, rapid etching with a small degree of undercutting occurs at moderate rf power levels. At lower pressures, higher rf power levels, ≳1 W/ cm2, are required but vertical edge profiles result. The RIE process can be useful in producing electrodes for Josephson circuits and superconducting microbridges.
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81.05.Bx Metals, semimetals, and alloys

Reactive ion beam etching of silicon compounds with a saddle–field ion source

P. J. Revell and G. F. Goldspink

J. Vac. Sci. Technol. 19, 1398 (1981); http://dx.doi.org/10.1116/1.571218 (5 pages) | Cited 1 time

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Previous work using cold cathode ion sources of the saddle‐field type has indicated that they are suitable for the reactive ion beam etching of many materials. Using a B93 source with a nominal beam current density of 0.16 mA cm−5 (neutral beam ion equivalent for argon), targets of Si, SiO2, and Si3N4 have been etched with a beam produced by injecting the source with Ar, CF4, and CHF3. Data are presented which show the etch rate dependence on beam current density for various combinations of etchant and target material. There is evidence to indicate that silicon was etched by free radical species which were produced at low beam energy (0.6 kV anode potential). Test patterns etched in SiO2 and Si3N4 by ’’CF4 and CHF3 beams’’, which have been examined by Scanning Electron Microscopy, reveal no evidence of redeposition, trenching, or lateral etching. Lines and troughs etched in SiO2 with a ’’CHF3 beam’’ to a depth of approximately 1 μm are shown to be vertical and free of undercutting.
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81.65.-b Surface treatments
07.77.-n Atomic, molecular, and charged-particle sources and detectors

Anisotropic and selective reactive ion etching of polysilicon using SF6

P. Parrens

J. Vac. Sci. Technol. 19, 1403 (1981); http://dx.doi.org/10.1116/1.571219 (5 pages) | Cited 4 times

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Experiments performed in a reactive ion etching system are discussed with the purpose of displaying the influence of reactive gas nature, ion energy, and the nature of the cathode on etching anisotropy and selectivity. Using SF6 etching, isotropy or anisotropy is believed to be related to the enthalpy of product formation reaction. Cathodes consisting of elements that form volatile fluorides lead to perfect anisotropic etching and low selective etching of polysilicon over Si02; whereas cathode material which does not react leads to higher selectivity but undercutting appears with an overetch. The possibility of achieving anisotropic and selective etching of polysilicon over thermal Si02 (etch rate ratio = 10:1) is demonstrated for NMOS technology. Examples of polysilicon gates of submicron (0.6 μ) MOST are given.
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81.65.-b Surface treatments
82.60.Cx Enthalpies of combustion, reaction, and formation
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology

Reactive sputter etching of Si, SiO2, Cr, Al, and other materials with gas mixtures based on CF4 and Cl2 

C. M. Horwitz and J. Melngailis

J. Vac. Sci. Technol. 19, 1408 (1981); http://dx.doi.org/10.1116/1.571220 (4 pages) | Cited 1 time

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All etching processes require control of the relative etch rates of the mask and substrate materials. This is especially important in vacuum‐etching processes where directional etching is often obtained at the expense of increased mask etch rate. Etch rate control requires good control of the etching parameters, and here at a constant gas flow of 2×10−2 Pa m3/s we use target voltage (peak‐to‐peak) and partial pressure of reactant species as controlled variables rather than power density and total pressure, as is common practice. SiO2 and Si etch rates in CF4 with a Si target were found to vary as P1/2V2 where V is the peak‐to‐peak target voltage (varied between 0.6 kV and 2.9 kV) and P is the reactant gas pressure varied between 0.35 Pa (2.7 μm) and 14.3 Pa (110 μm). Cr and Al rates varied as V3, but were almost independent of pressure. These differences enable accurate selection of relative etch rates and appropriate masks. For instance, SiO2/Cr etch rate ratios as high as 50:1 may be achieved for 3.7 Pa of CF4 at 0.8 kV peak‐to‐peak target voltage. Chlorine mixed with CF4 enables the properties of the two gases to be combined. Thus, by adjusting only the gas mixture from pure CF4 to pure Cl2, the Si/SiO2 etch rate ratio can be continuously varied between 0.33 and 6, respectively, at 1.3 kV peak‐to‐peak target voltage, 3.7 Pa pressure, and with substrates on a Si target.
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81.65.-b Surface treatments

Comparison of CF4/O2 and CF2Cl2/O2 plasmas used for the reactive ion etching of single crystal silicon

J. Paraszczak and M. Hatzakis

J. Vac. Sci. Technol. 19, 1412 (1981); http://dx.doi.org/10.1116/1.571221 (6 pages) | Cited 4 times

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The etching of single crystal silicon in CF4/O2 and CF2Cl2/O2 gas mixtures in a 13.56 MHz plasma generated in a radial flow reactor at 0.4 W/cm2 and 30 mTorr total pressure has been studied. It was found that for an unloaded reactor, the addition of oxygen to a CF4 plasma increased the lateral and vertical etch rate of single crystal silicon. The maximum lateral etch rate coincided with the maximum vertical etch rate of silicon which occured at 30% of added oxygen (by flow). Simultaneously, the sputtering of gold, used to define the silicon pattern, increased with the proportion of added oxygen. The effect of reactor loading with silicon was also studied, and found to affect the etching anisotropy in a CF4/O2 plasma. Under similar conditions of flow, pressure and power, the CF2Cl2/O2 plasma was found to produce a reduced self bias voltage at the cathode. The etch rate of the gold mask was found to vary with added oxygen in this plasma, as did the silicon etch rate. In general, the anisotropy of etching silicon in the CF2Cl2/O2 plasma was found to be much higher than that in the CF4/O2 plasma at the same oxygen concentration. Possible mechanisms accounting for this difference in anisotropy will be explored.
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81.65.-b Surface treatments
52.40.Hf Plasma-material interactions; boundary layer effects

Reactive ion etching for submicron structures

J. D. Chinn, I. Adesida, E. D. Wolf, and R. C. Tiberio

J. Vac. Sci. Technol. 19, 1418 (1981); http://dx.doi.org/10.1116/1.571222 (5 pages) | Cited 2 times

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The etch resistance of PMMA was measured under various reactive ion etching conditions and compared with that of silicon dioxide, silicon and Shipley AZ 1350 resist. The resulting profiles transferred into the substrates masked with PMMA were also studied under various reactive ion etching conditions. This study showed that PMMA can be used as a masking resist for etching silicon dioxide using fluorine‐deficient etch gases. Linewidths with dimensions of 0.1 μm have been obtained in silicon dioxide with usable selectivity between PMMA and silicon dioxide.
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85.40.Bh Computer-aided design of microcircuits; layout and modeling
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Recent developments in two‐level resist technology

B. F. Griffing

J. Vac. Sci. Technol. 19, 1423 (1981); http://dx.doi.org/10.1116/1.571223 (6 pages) | Cited 1 time

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High resolution optical lithography requires a sophisticated photoresist technology. In the micron and submicron linewidth regime, the shallow depth of focus characteristic of optical systems gives rise to the need for multilevel resists. Recent work in this area has concentrated on both two‐and three‐level systems. An example is a two‐layer resist (TLR) technique 1 which uses a thin top layer of positive resist over a thick layer of PMMA. The pattern formed in the thin top layer serves as a mask for a deep UV blanket exposure of the thick PMMA bottom layer. Recently a new deep UV source 2 was described for use with this technology. This paper will describe the exposure/development characteristics of the thick PMMA layer for the combination of this novel UV source and a new development chemistry. The paper will compare the complexity of several multilevel resist processes to point up the advantages of simplicity that the TLR technique provides. A comparison of the step coverage ability of this particular TLR technology with that of conventional positive resists is also made. Using the new development chemistry and lamp, (PMMA) structures of 0.4 μ width having 3.5:1 vertical: horizontal aspect ratios have been fabricated.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.40.Tv Optical and dielectric properties related to treatment conditions
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