With VLSI technology advancement, comes a requirement for increased density, improved resolution, higher device yield, and lower mask cost; the necessary vehicle, of course, appears to be projection or non-contact printing of mask to wafer. Several systems are presently available, including: direct step on wafer, projection alignment, and proximity (shadow projection) alignment. This paper deals with the evaluation and production use of a new proximity printing system, the Sass MjB 55 Shadow projection aligner. Image quality and resolution will be discussed, with slides demonstrating resolution. approaching the one micron limit in positive photoresist and a two micron limit in negative photoresist. Aligner environmental requirements, along with performance in production mode, and operator Hcceptability is included. Wafer requirements, specifically flatness, are shown to be much less stringent than with projection systems, the Suss having very. acceptable critical dimension stability over a range of 20 microns. Throughput figures, both for alignment and non-alignment processing, far exceeds that of all other systems previously evaluated or under consideration for upgrading and improving photolithographic processing. Comparisons of mask degradation and device yield improvement versus con ventional contact printing and projection printing shows the Suss to be equivalent to other available systems. A. unique system of calibrating mask to wafer separation (2.5 micron steps, +1 micron repeatibility), improved viewing optics, and realistic illumination intensity of 2 to 20 milliwatts at better than +2% uniformity, coupled with a new deep-UV source, certainly leads one to believe that we may indeed have found "A Better Mousetrap."

Date Published: 17 July 1979
PDF: 9 pages
Proc. SPIE 0174, Developments in Semiconductor Microlithography IV, (17 July 1979);

Published in SPIE Proceedings Vol. 0174:
Developments in Semiconductor Microlithography IV
James W. Dey, Editor(s)