And more challenges

Short delay while two of my old start-ups get exited and I launch two new ones, sorry

In the early 80`s we had replaced our barrel plasma etchers with more modern Tegal planar etchers. All of our production was converted over and soon after yields dropped drastically (especially on the 8870 DTMF tone decoder), once again everyone went into frantic overtime, weeks and months went by and our entire work-in-process was in peril. After millions of dollars in losses Stuart Boyd was able to measure definite short circuits between polysilicon lines on the wafers. He determined that there were fine 'stringers' left after etch along the edges of any 'steps' in the underlying topography. Polysilicon lines which went over a step were thicker in the vertical direction and since the reactive species in the planar etchers only travelled vertically and not anisotropically they never got completely removed.

A few months later we invited Alan Reinberg, a senior scientist at Perkin Elmer, to come and speak to us. He gave a fascinating talk on plasma etch in general and then came to he subject of the challenges of planar etchers. When he said 'obviously you have to adjust for some anisotropy in the etch to eliminate poly stringers' we all got very interested in our shoes.... if only we had invited him a few months earlier.