Warren David Grobman

Application of synchrotron radiation to x‐ray lithography

Synchrotron radiation from the German electron synchrotron DESY in Hamburg has been used for x‐ray lithography. Replications of different master patterns (for magnetic bubble devices, Fresnel zone plates, etc.) were made using various wavelengths and exposures. High‐quality lines down to 500 A wide have been reproduced using very soft x rays. The sensitivities of x‐ray resists have been evaluated over a wide range of exposures. Various critical factors (heating, radiation damage, etc.) involved with x‐ray lithography using synchrotron radiation have been studied. General considerations of storage ring sources designed as radiation sources for x‐ray lithography are discussed, together with a comparison with x‐ray tube sources. The general conclusion is that x‐ray lithography using synchrotron radiation offers considerable promise as a process for forming high‐quality‐submicron images with exposure times as short as a few seconds.

X-Ray Lithography Exposures Using Synchrotron Radiation

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.

Electron beam lithography for 1 micron FET logic circuit fabrication

We describe the fabrication of 1 micron minimum linewidth FET polysilicon devices and circuits. These were designed for the tight dimensional groundrules achievable using direct wafer write scanning electron beam lithography. This paper emphasizes the vector-scan electron beam technology and processing, while other papers in this conference(1) discuss other aspects of the work. Different types of 1 micron FET chips were written on 57mm Si wafers using a totally automated electron beam system(2) which performs table stepping, registration to fiducial marks, and pattern writing in a vector scan mode (individual shape basis) with control of exposure dose for individual shapes. The pattern data were prepared by batch processing which includes proximity correction as well as sorting of shapes to achieve data compaction and minimal distance jumps between shapes. A novel two-layer positive resist system has been developed to achieve reproducible lift-off profiles over topography and better linewidth control (typically <0.1 micron). A level to level registration accuracy groundrule of 0.3 micron has been satisfied with achievement of typical alignment of 0.1-0.2 microns between any two levels.

Thermopower of Dilute Alloys of Cerium in Lanthanum

We have measured a large negative peak in the thermoelectric power S of the La–Ce Kondo system at low temperature. This result is qualitatively different than that of Sugawara. Measurements were made in the range 4.2 K≤T≤350 K for four compositions: 0.03‐, 0.5‐, 2‐, and 5‐at.% Ce. The size of the peak was in the range −1.5 to −2. μV/K and occurred at ∼20 K. The shape of the curves, and the temperature at which the peak occurred, were nearly independent of composition for T<150 K, while the curves were somewhat sample dependent at higher temperatures. While significant amounts of metallic impurities were present, they probably do not contribute a peak in the thermopower. However, on the basis of these measurements one cannot rule out the possibility that the peak is intrinsic to La.

Status of x-ray lithography

This paper will review some of the current approaches to x-ray lithography technology for device and circuit fabrication. Recent results in source, mask, process, and alignment research will be surveyed. A special emphasis will be placed on the differences in approach using full wafer, conventional source systems compared with those which are based on step and repeat and which may use a storage ring source. Systems which use a full wafer approach can compete with full wafer optical lithography at minimum circuit feature dimensions greater than about 1 1/2µm. Their resolution is also competitive with that of optical wafer steppers, but the overlay achievable with wafer steppers is potentially better. If the resolution achievable with x-rays (≪1µm) is combined with the local control over alignment obtainable with a step-and-repeat approach, then a lithographic technology compatible with dense submicron circuits is potentially obtainable. However, this case will need the increased exposure speed which is achieved most easily by use of a synchrotron radiation source.

Valence and Conduction Band- Structure of Ge Using Theoretical and Experimental Photoemission Spectra from 6.5 to 23 eV

Experimental spectra for Ge obtained using synchrotron radiation (hν ≤ 23 eV) are compared with predictions of a direct-transition theory which includes anisotropic transmission through the (111) cleaved surface. The direct transition-determined structure plot for Ge (peak binding energies as a function of photon energy), as well as other spectral features, are fit well up to hν ≳ 23 eV using a d-nonlocal pseudopotential model. We demonstrate that this model provides a proper description of conduction band topology far (~ 1 Ryd) above the gap. Our ability to obtain these results shows that features predicted by an anisotropic, direct opticaltransition model can determine one-electron energy bands over a wide energy range even in the presence of short escape depths and surface-associated emission.

Photoemission Studies of Ni‐Co Alloys Having Large Anisotropic Magnetoresistance

Photoemission measurements on ferromagnetic Ni‐Co alloys show a d‐band resonance similar to that for pure Ni but with a d‐band width narrower by ∼ 0.2 to 0.6 eV for increasing Co content. Published low temperature electronic specific heat data, which show a decrease in the density of states N(EF) at the Fermi level with increasing cobalt concentration are consistant with the photoemission. It is possible to describe the d‐bands of these alloys by a ferromagnetic rigid band “Stoner‐Wohlfarth” model which includes a compositional‐dependent exchange splitting. Using this model we find no obvious correlation between N(EF) and the anisotropic magnetoresistance of these alloys.

One-micrometer electron-beam lithography FET technology

An n-channel silicon gate technology, using electron-beam lithography with minimum dimensions of 1 µm, has been implemented for FET logic applications. The six mask process employs semi-recessed oxide isolation and makes extensive use of ion implantation, resist liftoff techniques and reactive ion etching (RIE). A description of the process is given, with particular emphasis or topographical considerations. Implementation of a field etchback after source and drain implant to eliminate a low thick-oxide parasitic device threshold is also discussed.