The exposure characteristics of various electron resists are dependent upon the synchrotron acceleration energy (0.4-1.0 GeV). At higher acceleration energies, the exposure time necessary to develop the whole resist layer becomes shorter, and resist' -value increases. The order of resist sensitivities subjected to synchrotron X-ray (1 GeV) remains the same as that subjected to electron beam. Due to high collimation in synchrotron X-ray, high aspect-ratio (0.2-0.5 μm wide and 3 μm thick) resist patterns can easily be replicated with a larger clearance between mask and wafer. N-MOS transistors were fabricated employing a 4-level X-ray lithography process. The difference between the threshold voltages for transistors fabricated using X-ray and optical lithographies is in the error range between wafers.

Radiation imageable polysiloxanes have many outstanding properties, among which are their resistance to etching in oxygen plasmas, the ability to apply them from solution by spinning or spraying and their high thermal stability. This paper describes the use of these materials in generating high aspect ratio patterns using the polysiloxanes in two and three layer systems.

A brief account is presented on an approach for a quantitative understanding of solid state electron beam chemistry that is directed towards understanding the radiation sensitivity of electron beam resists. Results obtained by irradiating PVA with and without additives, using a 25 kV electron beam, are shown in order to investigate the possible spherical and chemical mechanisms induced by the electron beam.

Electron beam writing of fine features usually requires correction of proximity effects to achieve accurate edge placement. One scheme to reduce proximity effects is to increase the accelerating voltage (> 40 keV) [1]. We have chosen to look the other way, at low energy (< 5 keV) electron beam exposure. Retarding field electron optics enables one to form fine beams of low energy electrons. The inorganic resist system Ag₂Se/GeSe_x is well suited for low energy electron beam exposure due to its thin active region and conductive top layer. We report here on the effects of reducing the landing energy of the exposing electrons both in terms of sensitivity and proximity effects. Also we report on the absence of any edge sharpening effects for electron beam exposure and the effect of exposure rate on the required dose.

The submicron lithographic capability of several compositions of GeSe have been most conclusively shown by Tai and his co-workers.¹ Others^2,3,4 have shown that As₂S₃ and some of the other chalcogenides exhibit similar potential. In this paper we shall report on an extensive investigation of As₂S₃,.As₂Se3 and GeSe2 used in conjunction with a variety of Ag-bearing materials such as evaporated Ag, Ag₂S, Ag₂Se and Ag₂Te as well as with chemically applied Ag-bearing layers. We shall describe both wet and dry processing tech-niques used with these materials. We shall assess the submicron lithographic capabilities, processing latitudes and results obtained with the matrix combinations of these materials and show our experimental results.

The one-dimensional light intensity distributions for 10X, NA = 0.28 and 0.35 lenses with coherence of S = 0.7 at 436nm have been calculated using SAMPLE for linewidths from 2.0 to 0.4 microns. From these data, we obtain the optical contrast with varying defocus and the intensity of the light at the line edge for isolated lines, isolated spaces and equal lines and spaces. These data suggest that the presently available optical capability outstrips the capability of polymeric resist systems. It is argued that the high-gamma chalcogenide systems can better utilize this optical capability to extend lithography into the submicron regime. Some of the other advantages of the chalcogenides are the elimination of the standing wave effect, broad spectral sensitivity and the possibility of all dry processing. A simple physical model of the Ag-photodoping mechanism, useful in dealing with some of the experimental observeables, is also presented.

For over ten years IBM has been pursuing Manufacturing Electron Beam Systems in Manufacturing for direct wafer lithography exposure. These efforts have resulted in three generations of systems for wafer exposure, each with a greater capability. These systems have been configured to minimize system ailments and to maximize throughput. Their principal application has been to reduce turn around time. They have provided satisfactory service in Manufacturing and in Development applications. Having proved themselves to be beneficial and reliable Manufacturing tools, electron beams are being implemented for additional applications. Mask exposure, mask inspection and module inspection are some of the newer applications for E-Beam systems, in IBM at East Fishkill.

A high current gaussian E-beam system is described which exhibits superior throughput and pattern dimensional control compared to reported shaped beam systems in the resolution ranges where direct writing is economically feasible. The Waferwriter' system is an ultra-high current density multiple gaussian beam system capable of exposing popular photoresists at higher rates than any reported shaped beam system in the 0.5 to 2μm feature size range. In addition, greater pattern line width control can be achieved than with shaped beam systems due to sharper beam edge gradients. Alignment and overlay are also improved due to the higher signal-to-noise ratio obtained with the brighter electron beam source.

A comparison was made between theoretical mark position detection errors at 50 kV acceleration voltage and those at 20 kV, by analyzing mark signal wave-forms obtained through experiment and Monte Carlo simulation. The increase in acceleration voltage results in smaller detection error, mainly due to higher detector sensitivity and higher electron gun beam brightness. It is useful to coat a mark with high backscattered electron coefficient material, for the further detection error reduction. The acceleration voltage and mark shape (convex or concave) effects were also investigated for marks covered with the overlayer materials, such as multi-layer resist etc. As a result, it was found that a convex mark is satisfactorily detected with high voltage electron beam, even if it is covered with multilayer resist over a thick aluminum or silicon dioxide film.

This paper presents data comparing the radiation hardness of silicon and GaAs devices. Data presented in conjunction with this paper suggest that, when state-of-the-art electron-beam lithography is used to fabricate devices, GaAs offers a radiation-hardness advantage for certain specialty applications, including radiation-hardened spacecraft electronics.

We have developed a theoretical model for calculating the dose received by a resist behind an x-ray absorbing mask in an x-ray lithography system. The model enables the dose-depth profile due to photoelectrons entering the resist from the mask to be predicted as a function of x-ray target material, excitation voltage, mask material and thickness, and chemical composition of the resist. As an application, we have calculated the dose profile in the resist PBS next to a Au mask irradiated by x-rays from Ag and Al targets operated at 10 kilovolt beam voltage. The characteristic line and continuum spectrum from the targets are computed, the absorption by the Au mask obtained, and an approximate photoelectron and Auger electron spectrum in the gold and PBS is evaluated. The dose-depth curve next to the gold-resist interface is found using the analytic electron transport model developed by Burke and Garth (1979). The calculations show that the dose profiles obtained using bremsstrahlung-produced electrons extend deeper than profiles than are computed from characteristic photon radiation alone. At 10 kV, this effect is found to be much greater for Ag than for Al.

First-generation, full-wafer exposure, X-ray lithography equipment has been in continuous operation since 1979 in a pilot line application.(1,2,3) Second-generation, full-wafer exposure systems that incorporate the latest advancements in X-ray lithography are now being developed for early, submicron, VLSI patterning. This paper discusses recent advances in E-beam gun design and high-speed rotating anode development in terms of X-ray lithographic performances such as resolution and image contrast. In addition, the performance of a physical optics alignment technique that is compatible with submicron IC pattern overlay requirements is reported. The Perkin-Elmer X-100 full-wafer exposure system is a valuable development tool because of its flexibility. It is compatible with all X-ray masks and resists and can be used to expose either 75 mm or 100 mm diameter wafers.

The various aspects of X-ray lithography at H-P in terms of mask-fabrication, resist development, alignment systems and source development are reviewed in their present status. Masks are being developed, flat within one micron, and with very low substrate defect density. PCMS is described as an X-ray resist with moderate sensitivity, but very good physical properties. Advanced source cooling techniques are expected to allow power densities up to 60KW/cm², enhancing the source brightness. A very compact automatic exposure system is described, with alignment accuracy of .15 micron RMS.

A beamline for making X-ray lithography exposures using synchrotron radiation has been built and is now in operation at Brookhaven National Laboratory. The characteristics of synchrotron radiation and the reasons for using such a source are discussed. A description of the beamline and its control system is given, and results of early exposures are presented.

An x-ray system usable for process development and pilot line production is described, which utilizes technology based on a fixed palladium anode source. The alignment system employs three microscope objectives and optical channels to view the appropriate alignment target. The optical system has been optimized for use with circular fresnel zone plate targets. Alignment is electronically assisted using a detection system and associated electronics. The wafer stage is piezo motor driven with 6 degrees of freedom capable of placing the wafer under the mask within the allowable tolerance. The stage design incorporates a combination of flexures and air bearings to achieve the required precision. Essential features of the source, stage and alignment subsystems are described.

In recent months at SSRL, we have tested the feasibility of in vacuo x-ray lithographic studies using synchrotron radiation by exposing the resists PMMA and FBM-l20 to the white-light radiation in Beam Line (3°) during parasitic operation. Frequency selection was performed with Al and Ti filters, and the results of the experiment and their implications are presented in this report. A brief discussion of the advantages of synchrotron radiation for high-resolution x-ray microlithography research is also presented.

The high brightness liquid metal ion source (LMIS) is being used for ion beam lithography. Recent technological advances include a source for reactive metals and a source of ⁷Li⁺ for light ion beam lithography seems possible. Alloy sources for microfabrication by direct doping are being studied by several groups and a gold-silicon alloy source has also been used for lithography. Fundamental understanding of the LMIS is still advancing and the emission process is now generally held to be field evaporation. Recent energy spread measurements have revealed two modes of behaviour which may be linked to hydrodynamic effects.

A scanning ion beam lithography instrument for the fabrication of sub-micron structures has been constructed and evaluated. It employs a tetrode gun, which accelerates the ions to the full beam voltage, and an einzel lens objective. Both gallium and gold-silicon liquid-metal sources have been used for resist exposure, and gallium sources have been used for direct selective ion implantation and for micromachining.

Recent technology of a liquid-metal ion source makes it possible to realize maskless ion implantation with 100 nm resolution. A 100 kV implantation apparatus has been developed by using fine-focus technology of ion optics. Since alloy-metal ion sources have to be often used as the source of the apparatus, a mass filter (EXB) was equipped with for ion separation. Because the liquid-metal ion source has a large energy spread, a chromatic aberration is important to assess the optical performance of the apparatus. Particularly, the energy spread varies dependently on the emission current, so that the minimum probe size also varies with the emission current through the chromatic aberration. In order to optimize the design for such ion-optical systems, the dependency of the chromatic aberration upon the emission current must be taken into account. The optical system design was optimized under this consideration. As a result it was found that the optical system has an optimum aperture angle. Furthermore, the beam divergence in the mass filter was discussed. Ions passing through the mass filter undergo a dispersive force because of their velocity distribution. This is also a factor determining the minimum probe size. Numerical calculations of the optical property of the EXB filter showed that a weakly excited filter has a specified focal point where its velocity dispersion was apparently canceled. Therefore, if one let the focal point to be just located at a crossover point of the lens system, the effect of velocity dispersion can be reduced to the same level as the aberrations of the latter.

Focused ion beams constitute an important emerging technology that has many significant advantages for the fabrication of submicron ICs. These advantages are described vis-a-vis the currently dominant methods of pattern generation and transfer. A commercial focused ion beam system is outlined in the context of major design considerations. Probable FIB applications are also discussed.

Maskless patterning of materials using focused ion beams are important to simplify device processing and to develope full maskless processing. We have shown that a high speed maskless patterning can be done using ion beam assisted etching and ion beam modification techniques. In this paper, basic characteristics of various liquid metal alloy ion sources and a mass separatted focused ion beam system, and maskless patterning techniques for GaAs, Cr films and other materials are reported.

A finely focused ion beam system is described. Beams of Ga, In, and Au ions emitted from a liquid metal ion source are routinely focused to spot diameters of ~0.1 to 3.0 μm at a current density of ~0.5 A/cm² and a beam energy of 20 keV. Focused beams with energies of 1 to 30 keV have also been produced. Three applications are discussed: 1) scanning ion microscopy, 2) mask repair, and 3) ion beam lithography. Scanning ion images illustrating topographic and chemical contrast are presented. The repair of opaque and clear defects in optical masks, and opaque defects in X-ray masks is shown. Defects are imaged with the ion beam and removed by sputter erosion. Edge reconstruction of 0.5μm features is demonstrated. Most repairs take less than 10 sec per μm². The advantages and limitations of ion beams for lithography are discussed.

An outline is given of the range of applications and limitations of "broad beam" implantation techniques for LSI and VLSI device fabrication. Some of these limitations include dose uniformity and accuracy, resist stability and erosion, wafer heating effects during implantation, surface contamination and charging effects. The impact of these and other issues on the fabrication of fine feature (less than 0.5 micron) devices, including a comparison of the application of focused ion beams for direct implantation is discussed.

This paper describes the application of the tri-level resist system for both optical and electron beam lithographies, in order to improve the resolution.

This paper describes the application to the case of a large field X-ray exposure system of a very high accuracy registration technique developed for a small field step and repeat submicron lithography system. A major problem in large field parallel transfer lithography methods is the difficulty to achieve good overlay accuracy across the whole field as a result of distortion effects associated with both wafer and mask. A simple distortion compensating scheme based on the previously reported registration technique using Fresnel zone plates and diffraction gratings is presented. The combination of these two techniques allows to define the configuration of a possible submicron large field X-ray exposure system that will be discussed.

The influence of two kinds of electro-attractive substituents on acrylic type positive resists upon the sensitivity on electrons or soft x-rays (λ = 13.34 Å) was studied. - Fluorine atoms were incorporated into the poly(alkylmethacrylate) ester chain. - Cyano group was substituted to methyl group bonded to the polymethacrylate quaternary carbon atom. The results were interpreted on the basis of the modified relationships of KU and SCALA, SPEARS and SMITH, giving the incident dose for an electron beam and x-ray irradiation respectively.

Among various submicron lithography techniques, optical and X-rays are potentially opened for IC production in the future. The purpose of this paper is to foresee the applications of these two technics in 1990's. In the first part of this study, we define for X-rays the key points and natural limitations for various source approaches (conventional sources, gas pinch, storage ring). Then, we analyse the possibilities offered by X-ray lithography, assuming that all technological problems are solved. We suppose that every source is existing and reliable, that masks are stable and without defects, and finally that resists with good sensitivity to contrast ratio exist. Based upon experimental results, we foresee the performances of optical lithography. A second part compares the annlication of X-ray and optical lithogranhies, in terms of financial and nerformance analyses, in regard to the evolution of design rules and dimension reduction. The conclusion will try to predict the application of these two techniques.

In order to retain the simplicity of optical (400 nm) 1:1 shadow projection even in the case of sub-μm structures, the wavelength of the radiation employed has to be reduced drastically. The application of deep-UV radiation (e- 200 nm) only leads to an insignificant improvement in the Fresnel-limited resolution. Soft X-rays as well as high-energy ions are capable of replicating sub-μm features in shadow projection at reasonable proximity distances (>º 30 μm). X-ray lithography, the technique which is further developed at present, utilizes wavelengths between 0.5 and 5 nm, with structural resolution as good as 0.1 μm under certain conditions. The transition to soft X-rays requires the development of new intense sources as well as sensitive and process-stable resists, high-transmissive (optical light, X-rays) masks, and an appropriate alignment system with an accuracy below 0.1 μm. The type of X-ray source used is the most decisive parameter in determining the attainable resolution. (This is the reason why we only deal in this paper with the properties of the different X-ray sources, with strong emphasis on synchrotron sources. The use of X-ray tubes limits the minimum structure size to about 0.5 μm, even in the case of the tri-level technique.) Parallel and high-intensity synchrotron radiation makes the replication of patterns within the fresnel limit possible and provides a higher flexibility in choosing the suitable resist. Nevertheless, the two different approaches complement each other, since the first available X-ray systems will be equipped with low-cost conventional X-ray tubes which can be replaced later by compact synchrotron sources now under development. However, the technological basis, especially the mask technique, remains nearly unchanged. The technique of shadow projection using ions, as described here employs the dechanneling effect of a thin metal layer as well as the difference in energy loss between the random and the channeling directions. There are two advantageous features of ion-beam lithography in comparison to X-ray and E-beam lithography. Inexpensive ion sources with high intensities, in contrast to those for X-rays, are already available and no proximity effect occurs as in the case of electrons. Furthermore, the high energy-deposition density leads to a high sensitivity of resists. Mask problems, however, are more critical and the resolution is not as high as in the case of X-ray lithography.

The 1:1 electron image projector, with its inherent advantages of high resolution and high throughput, has the potential to perform the lithography of VLSI circuits with sub-micron dimensions at an economic price. We show here that the registration accuracy of the technique can match its high resolution capabilities. Misregistration arising from global alignment errors, mask errors, linewidth variation, wafer bowing, deflection distortion and wafer holder variations are measured using electrical techniques. The total misregistration between two levels, to be expected from a combination of all these sources amounts to a standard deviation of 0.12μm.