John M. Warlaumont

Synchrotrom radiation X-ray lithography☆

Abstract X-ray lithography is a shadow printing technique which uses X-rays to transfer a pattern from a mask into a resist-coated wafer. Synchrotron radiation from a storage ring has advantages over the radiation from conventional X-ray sources for this purpose, since it is 2 to 4 orders of magnitude more intense and its natural collimation virtually eliminates penumbra and run-out errors. To take advantage of synchrotron radiation, we have built a beamline for X-ray lithography at the VUV storage ring of the NSLS. This beamline was designed to meet two major requirements: vacuum isolation from the UHV in the storage ring and uniform illumination over the exposure area, to achieve good linewidth control in the resist pattern. To achieve uniform illumination in the vertical direction, we use a scanning grazing-incidence mirror that sweeps the beam over the exposure area. This mirror also collimates horizontally to maximize the exposure flux. In this paper we will describe the basic design including optics, beryllium window and the calculated spectral power distribution. The performance of the beamline will be discussed in terms of experimentally achieved uniformity of illumination, mask contrast and mask substrate transmission, exposure flux and exposure flux and exposure times and resolution. With PMMA resist, features down to 0.25 μm have been copied with an aspect ratio of 16 to 1 using a 40 μm mask to wafer separation. The ultimate resolution is limited by diffraction. We have begun to study a variety of resists to evaluate their suitability for X-ray lithography.

Synchrotron Radiation X-Ray Lithography: Recent Results

A beamline for making X-ray lithography exposures using synchrotron radiation has been built and is now in routine operation at Brookhaven National Laboratory. The beamline, its optics, and its control system are described, and results are presented showing the intensity and uniformity of the radiation at the wafer. Results of exposures in a variety of resists are shown and discussed.

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.

Fabrication of 64-Mb DRAM using x-ray lithography

This paper describes results achieved from the fabrication of 64Mb DRAM chips using x-ray lithography for the gate level. Three lots were split at the gate level for exposure with either Micrascan 92 at IBMs Advanced Semiconductor Technology Center (ASTC) or x-ray at the Advanced Lithography Facility (ALF) containing a Helios super-conducting storage ring and a Suss stepper. The x-ray mask was fabricated at MMD (Microlithographic Mask Development Facility) as a two-chip mask containing one chip which had zero defects. To achieve adequate overlay performance between the x-ray exposed gate level and previous optically- printed levels, the mask was fabricated with an intentional magnification correction. The alignment scheme for both Suss and Micrascan was first order to an ASM zero level, and second order to each other. Results from the first lot show 90% of the chips tested achieved a +/- 140 nm target for the Suss to Micrascan overlay. Critical dimension control (across wafer and across chip) was measured and found to be comparable between Suss and Micrascan. Electrical performance was comparable to the optical wafers. Chips were fabricated with zero defects in many of the 1 Mb segments. There were also x-ray fabricated chips which demonstrated 63 Mb addressable bits.

X-ray lithography and storage rings

Abstract An evaluation of specification for storage rings designed for X-ray lithography has been done, based on our experience with X-ray lithography at the NSLS VUV ring at Brookhaven National Laboratory. The useful flux (from a lithography standpoint) available from a storage has been reduced to a universal curve of power as a function of critical wavelength. Similar universal curves have been generated for contrast and efficiency of use. The effect of emittance on lithographic fidelity has been analyzed for beamline optics similar to the optics we now use at the NSLS, and tolerances on emittance are given.

Status Of Microstructure Fabrication

The present capabilities of microlithography are discussed, with emphasis placed on resolution and pattern distortion. The current limits of optical reduction lithography, electron beam lithography, and optical and x-ray proximity printing are presented. It is shown that currently the major factor limiting resolution in electron beam lithography is electron scattering in the resist and substrate. Recent progress in the theoretical understanding of this scattering limit is discussed, and new techniques for reducing the resolution degradation caused by this scattering are described.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.