The Proximity Effect which results from electron scattering can be corrected in a number of ways. The most rigorous methods use computed changes to the pattern data base and are very costly to perform on very large circuit patterns. Alternatives are presented which are more practical to implement. They are: 1) CAD corrections to the data base, 2) layout and design rules, 3) GHOSTING, 4) system set-up, 5) tri-level resist, and 6) optimum use of the resist contrast behavior.

As lithographic requirements drive minimum feature dimensions into the 0.5-micron range, the use of conventional optical tools gives way to other, less conventional methods during the pattern processing. The most serious contenders in a production environment are high-throughput, E-beam, direct-write tools. These systems can generate features as small as 0.25 μm, but cannot yet match the throughput of optical equipment. A method of achieving submicron patterning is to use E-beam direct-write lithography for critical levels of the fabrication and optical lithography for the remainder. For this strategy to work, the ability of the various tools to overlay correctly is required. AEBLE 150 is designed not only to meet such requirements but, of equal importance, to facilitate the use of such strategy. The ability of this system to modify the placement of geometries in real time is the basis by which overlay with other equipment can be achieved. This requires characterizing the previous level or levels by measuring some sort of reference marks. The challenges present in the implementation of such a scheme are the ability to match the various distortion characteristics of the optical tools being used, to acquire a variety of pre-existing alignment marks, and to acquire these marks under non-optimal conditions due to previous processing steps. Finally, for a production system, this must be accomplished using methods that will not compromise its throughput or ease of use. This paper covers the design philosophy and implementation of the system to allow interfacing to other tools; the user's perspective from the definition of alignment mark types, structure and their location in the substrate; and finally the results achieved with a test that simulates matching a distorted wafer.

A hybrid lithography technique is described in which high resolution critical mask layers are fabricated by electron-beam lithography and less critical mask layers are fabricated optically. This approach permits the high resolution imaging capability of electron-beam lithography to be exploited while still maintaining the high throughput possible with optical lithography. The lithography equipment employed for these experiments is the Hughes/Perkin-Elmer AEBLE-150 prototype and a Canon FPA-143 4:1 projection aligner. A CMOS process test chip containing 16 two-millimeter subfields in a four by four array was used for alignment evaluation. The two patterns used to evaluate overlay accuracy were the mesa and gate layers. Three cases were examined: 1) electron-beam-written gate layer aligned to electron-beam-written mesa layer, 2) optically imaged gate layer aligned to electron-beam-written mesa layer, and 3) electron beam written features overlayed to optically defined features. In the last case both the optically and electron beam defined features were aligned to the electron-beam-written reference. The resulting peak overlay error accuracies are: 1) electron-beam to electron-beam with +/- 0.05 2) optical to electron-beam with +/- 0.10 μm, and 3) optical to electron-beam referenced to second electron-beam with +/- 0.15 μm. Additionally, the critical dimension control of electron-beam-written layers was +/- 0.04 μm for 0.6 }ten feature sizes.

Hybrid utilization of e-beam direct writing and optical reduction projection is a very effective way to adopt a high accuracy advantage in e-beam direct writing without sacrificing productivity. However, alignment marks suitable for hybrid lithography have not been extensively studied. The optical system has a certain amount of lens distortion, and it is desirable to fabricate registration marks optically. Vector-scanning e-beam is superior in writing speed and registration method flexibility to raster-scanning. The vector system uses negative resist in more exposure levels than positive resist in order to minimize the exposure area. Back-scattered electron signals and detection accuracy from optical registration marks, coated with negative resist, such as CMS, were studied experimentaly with a variable-shaped vector system. Results obtained were analyzed by comparison with Monte-Carlo simulation. Studied hybrid marks are convex and concave, tapered and non-tapered, 5pm and 10pm width marks. The experiment and simulation results indicate that the key factor in achieving high accuracy within ±0.06pm (36) was easily obtained by the optimal tapered 10μm wide mark for e-beam direct writing and optical reduction projection.

The grid, made up of 2688 3.2 micron wide and 22 mm long, transparent slits, and several auxiliary patterns has to be written on the spherical side (radius 1400 mm) of an odd-shaped quartz block. By using electron beam pattern generation in conjunction with classical chromium mask fabrication techniques, it has been possible to satisfy the tight specifications imposed on pattern registration and on critical dimension control of the individual slits. The originality of our approach lies in the fact that a dedicated wri-ting strategy is used which allows us to provide extended compensations for substrate height variations on both beam focus and beam deflection parameters. A dedicated calibration programme running on a second electron beam pattern generator has been used in order to provide a measuring tool with extended nanometer accuracy.

The Fourier and Haar transforms have been successfully employed to produce fast, efficient proximity correction calculations for electron beam lithography. The Fourier transform is used in a precompensation operation that generates a nearly exact solution to the proximity problem. The Haar transform is used to thin or reduce the size of the extremely accurate but large corrected database that results. The methodology here constitutes a signal processing or transform oriented approach to proximity correction. It has the advantage that fast digital hardware is commercially available for making accelerated computations. Detailed computer generated simulations and experimental results are presented for four different test patterns. The critical lithography features are nested gaps between large features and isolated lines and squares ranging from 0.2 to 0.5 μm. The Fourier precompensation proximity correction approach successfully preserves the fidelity of these features as well as all other features in the test patterns.

The maskless ion beam assisted etching of InP and GaAs was performed by bombarding 35 keV focused Ga+ beam in chlorine gas atmosphere at a pressure up to 80 mTorr and effect of etching parameters including substrate temperature and bombardment angle was investigated. It was observed that the enhancement of etching rate for InP is small if the bombardment is done at temperature below about 100°C. 20-30 times enhancement over physical sputter etching is achieved for bombardment at 140°C and a 6 μm deep, 0.3μm wide grooves was formed without redeposition effects. For GaAs, about 10 times enhancement was observed for bombardment at room temperature in chlorine atmosphere. The requirement of elevated temperature for InP is probably due to the lower vapor pressure for indium chlorides which is formed by the ion bombardment. Auger analysis of the etched surface was also performed.

A FIB (focused ion beam) system for the repair of clear and opaque photomask defects is described. FIB technology is uniquely capable of repairing submicron clear and opaque defects. Opaque defects are repaired by ion beam sputtering. Clear defects are repaired by the deposition of a tenaciously adherent, opaque carbon film from a hydrocarbon gas. A number of mask repair examples are shown, and the results of adhesion and chemical resistance tests of the carbon films are presented.

When Focused-Ion-Beam Milling is used for repairing opaque defects on X-ray masks, the specific sputter effects such as redeposition of the sputtered material and reflection of the primary ions influence the obtained resolution appreciably. This physical behaviour leads to edge angles 4 90° and to a shift of the milled pattern as well as to a specific kind of 'proximity effect'. That means, the repair of a defect could generate new defects due to the redeposited material which have to be corrected again. Furthermore, the achievable aspect ratio which depends on the sputter yield is limited to approximately 5 for gold under practical conditions.

MicroBeam developed a new focused-ion-beam system, the NanoFab-150, for the fabrication of submicron structures with fully integrated imaging and analysis capabilities for inspection and endpoint detection. The system can operate in a manual mode, but is fully automated to reduce operating costs and enhance application reproducibility. The ion probe for the NanoFab-150 is changeable from 50 nanometers to 500 nanometers, with voltages variable from 3 kV to 150 kV at current densities up to 5 A/cm². Elec-tronic selection of specific ion species from alloy sources is possible using the system's mass filter. An automated dual loadlock allows for rapid sample throughput. The stage has x-y travel to accommodate 6-in. wafers or masks, with the capability to use laser inter-ferometric positioning. High speed cryopumping is used for both the optical chamber (housing the ion source, lenses, mass filter and deflectors) and the target chamber (housing the x-y-theta stage, position sensors and probe monitors). The target and optical chambers are differentially pumped, allowing pressure differences of several orders of magnitude. This feature allows the use of ion-assisted chemical vapor deposition and gas-enhanced sputter etching. The differential pumping maintains a very low pressure in the optical chamber, increasing source lifetimes. In microfabrication and other applications, the NanoFab-150 functions as a scanning ion microscope in imaging and analysis of nanometer structures. The system uses a channel electron multiplier (CEM) with operating modes for collecting secondary electrons and/or secondary ions. The integral high collection efficiency SIMS optics is used for process endpoint detection and can also provide high spatial resolution maps with isotopic sensitivity in gray scale or color. The system configuration, results of early performance testing, and goals for the final performance specifications are discussed.

Profit margins on high-volume ICs, such as the 256-K DRAM, are now inadequate. U.S. and foreign manufacturers cannot fully recover the ICs' engineering costs before a new round of product competition begins. Consequently, some semiconductor manufacturers are seeking less competitive designs with healthier, longer lasting profitability. These designs must be converted quickly from CAD to functional circuits in order for irofits to be realized. For ultrahigh performance devices, customized circuits, and rapid verification of design, FIB (focused ion beam) systems provide a viable alternative to the lengthy process of producing a large mask set. Early models of FI equipment did not require sophisticated software. However, as FIB technology approaches adolescence, it must be supported by software that gives the user a friendly system, the flexibility to design a wide variety of circuits, and good growth potential for tomorrow's ICs. Presented here is an overview of IBT's MicroFocus" 150 hardware, followed by descriptions of several MicroFocus software modules. Data preparation techniques from IBCAD formats to chip layout are compared to the more conventional lithographies. The MicroFocus 150 schemes for user interfacing, error logging, calibration, and subsystem control are given. The MicroFocus's pattern generator and bit slice software are explained. IBT's FIB patterning algorithms, which allow the fabrication of unique device types, are reviewed.

A method of patterning n-type GaAs, InP, InGaAs and InGaAsP by photoelectrochemical (PEC) etching in conjunction with a submicron focused gallium ion beam (FIB) at low dose is de-scribed. The ion beam is used to produce damage in a desired pattern on the material. Subsequent PEC etching of the material reveals the ion induc5d featurs in relief. The procedure is highly sensitive, requiring a dose of only 5x10⁹ ions/cm² (about 1 ion every 1500Å) for the differential etch to become apparent. The sensitivity allows rapid pattern generation in our FIB system.

The establishment of the submicron device era brings out the problem of repairing advanced VLSI photomasks or reticles. Through recent advances in submicron focused ion beam (FIB) technology, a new method has been developed for repair of these photomasks. Using our specially designed FIB system, "opaque" repairs are performed by ion sputter etching. Repairing "clear" defects is carried out using the FIB to selectively deposit thin films using the "Ion Beam Induced Chemical Effect". Using these techniques, both "opaque" and "clear" repairs are carried out without damage to the glass substrate. "Clear" defects are repaired using carbon film deposition. The thickness of the film need only by about 200nm to have an optical density of 3 and resistance to scratch and cleaning damage equivalent to Cr. The carbon film is formed when gas molecules are continuously jetted onto the mask surface as the FIB repeat scans the defect area. Repairs to X-ray mask are carried out in the same way, using special gases containing a heavy metal. "Opaque" defects are removed by direct scanning of the FIB over the defect area. The sputter etching is automatically stopped, after the repairs are finished, by the etching monitor. Secondary ion emission is stimulated by the scanning FIB. These secondary ions are detected by a built-in mass spectrometer. The signal from the mass spectrometer can be used to image the sample surface and defect position on the CRT. This system is designed for high reliability and ease of use. Because of advanced design features, this system will smooth the transition between "micron" and "sub-micron" geometry design.

An x-ray mask suitable for use with a new x-ray step-and-repeat alignment system [1] is introduced. Design features are described which distinguish this stepper mask from the full-field x-ray mask reported earlier [2]. Processes for manufacturing such masks, patterned additively or subtractively, are described, as is the e-beam imaging technique. Finally, mask distortion results are presented and discussed with relation to mask design.

X-Ray lithography is widely believed to occupy an important future lithographic niche in the vicinity of 0.5 micron and below."] It will be technically easier to achieve resolution and depth of focus with X-Ray than with optical steppers in this lithographic regime. It will be much less expensive to print large volume runners like Dynamic RAMs, microprocessors, or CODECs with X-Ray than with electron beam direct write. However, it is also recognized that distortion in the X-Ray mask membrane may be a major obstacle to the exploitation of this niche, because of the extraordinary registration requirements of submicron design rules.

A high brightness plasma x-ray source is developed. This source can be linked to a conventional aligner by directing x-rays downwards into the atmosphere. By adopting the low pressure gas injection method, a wide discharge timing margin and strong x-ray emission are attained. X-rays having line spectra of 9-14 Å in wavelength are emitted from the Neon gas plasma. As high mask contrast can be obtained, submicron resist patterns can easily be replicated by using a 0.4 μm thick Ta absorber. The mask distortion due to mask heating is not a serious problem in He atmospheric exposure. The exposure time is about 13 seconds with a 3 Hz discharge repetition rate. Compared with a conventional source, a throughput 10 times greater is achieved.

Hybrid lithography technology, using a newly developed X-ray stepper and a conventional optical stepper, was applied to half micron CMOS device fabrication. X-ray lithography was applied to four principal mask levels in thirteen lithography steps. In order to correct the geometrical run out in X-ray lithography levels, every die on X-ray masks had been shrunk to 99.99%, in length, of the original pattern. For realizing sufficient resolution and mask alignment accuracy, X-ray mask to wafer spacing was kept at 15 ±lμm, during the mask alignment and X-ray exposure process. Several advanced technologies, such as X-ray exposure in open air, protecting the resist from oxygen, and deep UV curing for X-ray resists, were applied. As a result, a half micron 101 stage CMOS ring-oscillator, which was designed with a submicron alignment margin, has been successfully fabricated, using a single layer resist process.

Step and repeat X-ray lithography is essential for achieving the fine lines, accurate registration, and extreme density required to produce the next generation of very large scale integrated circuits. Drawing upon its own experience in developing a full-field X-ray lithography system [1], as well as upon technology developed at companies such as Thomson-CSF [2] and AT&T [3], Micronix Corporation in Los Gatos, California, is introducing such a system, called the MX-1600.

Perkin-Elmer's X-Ray Step-and-Repeat lithography system has been developed to meet the IC industry's stringent requirements for fabricating submicron VLSI chips. System performance and key equipment features will be discussed along with early subsystem and system test data. The X-ray system uses a 10-kW source to provide high-throughput exposures with a resolution of 0.17 micron. X-rays are generated by focusing a 10-KeV electron beam within a 1.5-mm spot on the rim of a rotating, water-cooled anode. Mask-to-wafer alignment is sensed and controlled during exposure in all six degrees of mechanical freedom to provide 0.1 micron alignment accuracy. The precision wafer stage has a closed-loop positioning accuracy of 0.01 micron. In-plane stage motion is accomplished using a three-axis planar motor that rides on a stiff air bearing over a patterned plate that serves as the motor's platen. A laser interferometer option can be added to the system to monitor the position of the wafer stage to an accuracy of 0.02 micron.

According to the progress of the LSI design rule, optical lithography has steadily opened its new frontier. As the dimension of the LSI design rules becomes the same as that of the resolution limit, the required image quality becomes higher and higher. Optical lithography corresponded to such requirements by the development of the lens design and simulation technique. Some of the new results are shown in this paper, and the new submicron stepper of 0.8 μm shall be introduced as the fruit of such technique. In addition, some of the new developments which correspond to the submicron lithography are introduced. As a consequence, the future of optical lithography shall be discussed in view of the recent aim of 0.5 μm.

In order to fabricate submicron pattern, total electron beam (EB) lithography system has been developed. Upper submicron pattern will be realized by optical lithography, which requires reticle with high accuracy. An EB writing system, EBM-130/40, has the performance of drawing capability of 4 M bit DRAM reticle pattern in about 40 minutes. The EB system incorporated with peripheral technologies including data compaction conversion software, reticle inspection system, APC-130R, and EBR-9 resist process can produce advanced reticles of number of about 600 per month. For lower submicron pattern formation, next generation lithography system is required. The EBM-130V is the variable shaped EB system with high acceleration voltage of 50 kV and high dosage of 50 μC/cm² for direct writing and X-ray mask fabrication for development of the high bit density VLSI pattern. This system makes possible EB/optical combined lithography. Its metrology function allows it to measure X-ray mask distortion.

Sub-100nm patterns have been fabricated in thick PMMA film on thick silicon substrates at low beam voltages using commercial e-beam machines. A higher contrast and an improved resolution are obtained by using an IPA development. 50-100nm lines are fabricated in 0.5- 1.0μm PMMA film on silicon substrates with 20-25kV e-beams. Practical aspects of sub-100nm pattern fabrication have been estimated. Pattern accuracy, field butting error, and overlay accuracy are better than ±0.1 μm 3 sigma.

Experiments on GaAs polycrystal formation for isolation were made by using a combined system of a focused-ion-beam implanter with molecular-beam-epitaxy equipment. We obtained 0.7-μm-wide micropolycrystals of an aspect ratio of 3.5 above 160-keV-Be-implanted (more than lx10¹⁵ cm^-2) GaAs epilayers. Micropolycrystals exhibited almost planar form and high resistivity even with donor doping of 3.2x10^l8 cm^-3. Single crystal regions adjacent to the micropolycrystals had good crystal quality which was confirmed by microscopic Raman spectroscopy. This new technique of micropolycrystal formation is attractive for planar isolation processing of GaAs devices with novel structures.

Focused ion beam (FIB) technology has capabilities for resist exposure, maskless implantation, and other applications for semicon-ductor devices with submicron dimensions. Focused ion beam systems, the JIBL-100 and 150, are able to obtain a finely focused ion probe with a diameter less than 0.1 micron using a liquid metal ion (LMI) sources. The JIBL-100 system has been developed for fundamental experiments of FIB technology. The JIBL-150 system is a lithography system controlled by a DEC-VAX11/730 and HP9920 computers. Using these systems, some experiments for sub-half micron lithography have been demonstrated. Both single and double charge Be and Si ion beams are obtainable from an Au-Si-Be LMI source. They can be used for resist exposure with various resist thickness and resist profiles. For example, a T-shaped resist profile was fabricated using 200 keV Be and Si ion beams.

The experimental Electron Beam Inspection System (EBIS) which is used for sub-micron patterns of VLSI circuits is developed and described here. This system is designed to investigate algorithms, which extract defects, and various characteristics to use the electron beam (EB). Following will be mentioned : the configuration of EBIS, description of hardwares and softwares, considerations about pattern alignment, and algorithm extracting defects using the EB.

The Hipparcos project of the European Space Agency (ESA) is dedicated to the astrometry of 100.000 pre-selected stars with an accuracy of 2 milliarc-seconds by satellite1,2. The refocussing mechanism of the Schmidt (F/4.8; F = 1400 mm) telescope is manufactured at the TN° Institute of Applied Physics (TPD). Part of this mechanism is the grid unit, an optical block with the Hipparcos grid pattern on its convex surface (R = 1400 mm), which is positioned in the telescope focal plane. The Hipparcos mission requirements of ESA/MATRA for the grid pattern are reflected in the nanometer range. The main grid covers an area of 22.1 mm x 22.1 mm with 2688 parallel slits. The slitperiod is 8.20 micrometer and the slitwidth is 3.20 micrometer. The grid patterns for a number of units are manufactured by e-beam lithography on a chrome mask at the Centre Suisse d'Electronique et the Microtechnique (CSFM) with the use of the Philips Beamwriter. The grid pattern calibration process involves optical and e-beam methods. The e-beam metrology in the nanometer range is made possible by a dedicated Hipparcos software package on the Philips Beamwriter of the Delft Center of Submicrontechnology (CST). The main features are: - the x, y stage laser interferometer system - the marker search accuracy of 10 nm RMS - the use of an almost undeflected e-beam operation to minimize the effect of main beam deflection errors. The magtape containing the e-beam measurement data is processed on the Harris H800 super minicomputer at TPD. The resulting calibration data are used: - as a feed back to the pattern manufacturing process at CSEM - for verification with the ESA/MATRA specifications - to select the engineering and flight models and to provide the associated calibration data to ESA/MATRA.

Requirements for measurement of very small integrated circuit (IC) device structures have become increasingly more demanding with the advent of electron beam, x-ray and advanced optical lithographic processes. High throughput, highly accurate and repeatable measurement tools are needed to guarantee dimensional control for device performance. This paper describes a dimensional measurement tool based on a Scanning Electron Microscope (SEM) which uses a fixed beam and scanning stage technique for gathering measurement data. This measurement tool is designed to make dimensional measurements of IC devices from 0.1 μm to 15 μm. Superior accuracies and precision are realized by eliminating dependence on calibration of the beam deflection as is required in digital scanning type tools. The deflection of the stage is measured by a laser interferometer which provides accurate traceability. Deflection versus secondary electron intensity profiles are gathered as scan lines. The scan lines are analyzed by the computer with an algorithm designed to detect the edges of the line according to particular sets of criteria set up uniquely for each line type. An important application of this tool is the capability to use the SEM electron beam to expose precisely spaced lines in photoresist with line widths as small as 0.1 μm and a pitch as small as 0.3 μm. These lines are excellent for use as calibration standards for other measurement operations.

A software closed loop technique was devised for quantitative voltage measurement in electron beam testing for LSIs. A retarding voltage of an energy analyzer is controlled iteratively by a computer to reduce difference between a slice level and a secondary electron signal to zero. The voltage is determined by the retarding voltage at the cross point of the slice level and the energy distribution curve. Using this technique, the waveform of 256 sampling phases with more than 5 V amplitude can be measured in about 30 s with 200 mV voltage resolution and 100 ps time resolution.

A variable shaped beam type, high accuracy high throughput EB system Model HL-600 was developed a few years ago. It has been investigated how to apply this system to higher throughput and submicron fabrication. In order to increase throughput, some modifications have been done for controlling two sets of EB units by single computer system. According to some experiments, it has been made clear that this system is applicable to a quarter micron fabrication.

The proximity effect in electron-beam lithography can be corrected by the "GHOST" method, in which an additional field exposure with defocused beam at lower dose is used to compensate proximity effect. This technique was applied to CMS-EX(R) and RD-2000N negative resist successfully. Excellent linewidth control was confirmed by an electrical test method. A parameter of development rate ratio was used to characterize the performance of nonswelling negative resist.

We describe a method of metal deposition by electron beam exposure and pyrolysis of a gold containing organometallic polymer. We have demonstrated the formation of metal patterns on Si, GaAs, and multilayer resist systems with line widths as small as 0.25 μm. There has been considerable work on direct deposition of materials by laser driven processes. These methods usually involve depositions of films by pyrolysis or photolysis of gas phase precursors. The handling of these reactive gases, which can be a problem, was eliminated in a recently described technique of laser pyrolysis of solid organometallic films. In this technique, heat from a focused laser beam decomposes an organometallic polymer removing the organic component and leaving a metal film. Organometallic polymers are commercially available with a wide range of metals and have been used for optical, electrical and decorative coatings. The advantage of the organometallic films is that no vacuum film deposition is required and the handling is similar to standard photoresist processing. The laser thermal process provides a way of forming patterns in this material, but the spatial resolution is limited by both the diffraction of light and thermal diffusion making submicrometer dimensions difficult to obtain.

A simple, compact, high brightness x-ray source has recently been built. This source utilizes a commercially available, cylindrical geometry electron beam evaporator, which has been modified to enhance the thermal cooling to the anode. Cooling is accomplished by using standard, low-conductivity laboratory water, with an inlet pressure of less than 50 psi, and a flow rate of approximately 0.3 gal./min. The anode is an inverted cone geometry for efficient cooling. The x-ray source has a measured sub-millimeter spot size (FWHM). The anode has been operated at 1 KW e-beam power (10 KV, 100 ma). Higher operating levels will be investigated. A variety of different x-ray lines can be obtained by the simple interchange of anodes of different materials. Typical anodes are made from easily machined metals, or materials which are vacuum deposited onto a copper anode. Typically, a few microns of material are sufficient to stop 10 KV electrons without significantly decreasing the thermal conductivity through the anode. The small size and high brightness of this source make it useful for step and repeat exposures over several square centimeter areas, especially in a research laboratory environment. For an aluminum anode, the estimated Al-K x-ray flux at 10 cms. from the source is 70 μW/cm².

A study of Fresnel diffraction effects is presented for structures of interest for X-Ray Microlithography. This analysis uses the full optical constants of the mask absorber pattern. Therefore, our calculations take into account the fact that the photons experience a phase shift as they go through the mask's absorbing layer in addition to simple absorption. Results are presented which show the consequences of adding the phase effects to the Fresnel analysis. These results show that phase effects cannot be disregarded in modeling Fresnel intensity profiles on resists.