Delete comment from: Ken Shirriff's blog
Hello:
My name is Paul R. Ward, and I was a Mictolithography Process Engineer at the MMI Sunnyvale Facility from 1980 to 1985 - I worked on these parts, which were part of a series of varying sized Fuse Proms, such as the 5300, 5340, 5350, 5370, and 5390. All used Negative Photoresist technology, 5 micron lines and spaces, and were imaged on Perkin Elmer Micralign 140s. The Metalization, when I started, was done with Evaporators, but we moved to Sputtering systems as time went by, also transitioning from wet processing to Plasma Etching for certain processes.
The NiCr fuses, when I started, were done with Negative photoresist as a lift off ( scrub off ) process. You imaged the layer of photoresist with tiny bow-tie shaped windows, evaportated the NiCr metal, and then removed the photoresist with an organic stripper, after which the excess NiCr. was scrubbed off the waters using alcohol soaked Q tips on a cobilt wafer spinner. In early 1981, we converted the process to Positive photoresist, using the same masks, which meant that the metal was deposited first, then masked with the Fuse Mask, after which the unwanted metal was etched off with a dilute solution of Nitric Acid and a trace of Ceric Ammonium Nitrate. A much better process, with a much higher yield.
A major problem that was only solved when we went to sputtering systems ( P.E. 2400s and 4410s ) was the Ni to Cr ratio, which dramatically affected the Fuse Blowing Current and Temperature. Once we went to Sputtering the metal, those problems went away. Just in
time for the parts to become obsolete......
In Fab IV in Sunnyvalewe we also made some of the first Fuse PALs, using Titanium Tungsten ( TiW) fuses, which had their own problems, as they had to be etched with Hydrogen Peroxide, a tricky and troublesome process to manage.
Forty Years ago. I was about to say that it seems like a lifetime has passed, but, in fact, it has. I was a 25 year old budding Process Engineer in the summer of 1980. Now I've retired. But Silicon Valley was the place to be in the 1970s-1980s !
Paul R. Ward
Aug 3, 2020, 10:55:35 PM
Posted to Looking inside a 1970s PROM chip that stores data in microscopic fuses