Idle… December 7, 2006
Posted by akangas in Randomness.trackback
So I’m at work as often ends up happening, and I’ve run out of work to do today. All of my projects have roadblocks so I can’t get any farther. The Yankton overetch and the “barli” planar etch “keyhole” wafers are waiting cross-section results (although I know I owned that one). The Duluth “black streets” problem can’t be worked on until the WIP backed up at the metal etchers gets taken care of. The FP34 2nd metal resist thickness test can’t go any farther (further? Drat. I’ll go with farther. Nope changed my mind. Further) further until I get the wafers cross-sectioned (at least I’m keeping Sue busy…). The edge exclusion testing…I could get started on. But I don’t want to go back into the fab today. So that one doesn’t count. I’m completely stumped on what to do with the Chicago recipe.
Maybe someone can help. It’s a deep trench silicon etch on a LAM etcher. Due to a previous experiment the etch time of the recipe was lowered to improve the results of electrical tests (it lowers the “beta”…not sure what that means). Unfortunately Mark, the head process development guy (and my dad’s lunch buddy) wants to improve the range of the betas. Which means improving the uniformity of the etch. I’ve run DOEs on just about every possible variable in this etch, and the best thing I can come up with is that lowering the power improves the uniformity a bit. From 50% to 30% nonuniform. Now you might say “But Aaron! You’re amazing! That’s almost twice as good!” But then I would raise my eyebrows at you in sort of a haughty, quizzical, amused sort of way (yes, all three of those) and point out that the generally accepted value for nonuniformity is about 5%. Yeah. That put you in your place, didn’t it.
The problem is the etch rate is too fast at the edge of the wafer, and two slow at half the radius (as etches are radially symmetric). The center of the etch I can speed up or slow down at will by varying the pressure in the chamber. But this 35-75mm area is killing me. I’ve changed the gas flows. I’ve changed the power. I’ve changed the chamber gap. Minor improvements at best. So somebody research deep silicon etching using SF6 and O2 with an inert He flow and find out how I improve my uniformity. Plz.
Shit. I’ve only wasted 15 minutes of the hours I have before I leave today.
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