Bell Labs to study X-ray, optical lithography under $7M defense pact

Electronic News, July 27, 1992 by Peter Dunn

MURRAY HILL, N.J.--AT&T Bell Laboratories will conduct a three-year comparison of X-ray and optical lithography techniques under a $7.9 million award from the Defense Advanced Lithography Program.

Bell Labs will print test CMOS devices using its Hampshire Instruments Inc.'s Model 5000P X-ray wafer stepper and a deep-ultraviolet XLS stepper from General Signal Corp.'s GCA unit, said Larry Thompson, head of lithographic materials and chemical engineering. The devices are designed to have electrical performance related to the lithographic tolerances achieved in production, and will thus show whether X-ray's depth of focus and relative immunity to contamination translates into better device quality. As a control, devices will also be made on I-line systems.

In addition, said Dr. Thompson, the program will examine costs of ownership for the X-ray system, including the potential improvements in device performance.

"All the things that are supposed to give a more robust process, we want to quantify," he explained. "To date, most of the statements in the literature on X-ray lithography have been hand-waving."

Initial work will be done at linewidths of 0.5 micron, but Dr. Thompson noted "We'd like to get to at least 0.35 micron" before the program winds up in December, 1995. "Optical clearly can do 0.5 micron, and it's not reasonable to insert X-ray early at 0.5 micron. But if the process latitude and robustness are much, much better, people might consider it."

One of the critical elements in the program's cost-of-ownership analysis will be X-ray masks, Dr. Thompson pointed out. AT&T has its own production facility, and purchases some masks from Hampshire, but hopes to take advantage of the DALP's forthcoming mask shop program (EN, July 6). "AT&T will use masks from the shop--no question," said Martin Peckerar, Navy technical manager for the DALP.

AT&T was selected from a group of about 100 who responded to a 1991 Broad Agency Announcement soliciting proposals for work in X-ray lithography alignment and exposure, said Dr. Peckerar. "Companies proposed different types of work: studies, tool development, procurement, and so forth," he explained. "We looked to see if there would be a benefit from government funding, and if it meshed with our plans." Dr. Peckerar declined to name any of the other bidders.

Dr. Thompson said his group does not plan to purchase Hampshire's newest stepper, the Model 3500. "Our current thinking is that the 5000 is the stepper we'll use, with upgrades we'll be getting from Hampshire," he said. "Resolution-wise, it will do 0.35 micron, and we're working with Hampshire to be sure we improve the performance of the machine as we go along."