Favorite scrap event near-miss of your career
In the spirit of the post about this sub not just being career and salary advice - what's your favorite story of a fab scrap event that almost happened?
Mine was small stakes, but the circumstances are so hilarious that it's one of the most memorable stories of my career. I previously worked at a small, very manual fab that did maybe 70% production, 30% r&d of various types. "Manual" meaning still mostly cassette loaded tools, but plain old cassettes (not FOUPs or SMIF pods) and no automated material movement. People manually putting wafer cassettes into tools.
I was working with a pretty new engineer on an etch step that was unique to a specific small r&d project that I oversaw. I think we had run a lot or two together talking about the etch, doing the post-etch inspection, etc., and he was going to run the last lot himself. I walk a few bays down, come back a bit later when the etch would be done. He vents and opens the loadlock to unload the wafers, and I notice that the cassette is upside-down. I wasn't even immediately sure I understood what I was looking at, but it sure couldn't be good.
Now you are probably saying to yourself, "How is that even possible? Load ports are designed in such a way that the cassette couldn't go in the wrong way." And normally you'd be right. But this particular tool had been modified and had a custom load port that someone had machined in their garage to allow several different types of cassettes to be used interchangeably. This also had the effect of removing the poka-yoke that would prevent an upside down cassette.
So here I am thinking our wafers just got loaded in upside-down, which would have at a bare minimum scratched the shit out of the front side of the wafers, etched the backside, and probably contaminated the etch chamber. But as he unloads the cassette, the situation became even more comical. The wafers themselves were also backwards in the cassette, meaning the double negative canceled out and the wafers had been successfully processed (shockingly) without issue. I quietly vacuum wanded the wafers into another cassette (facing the right way) and we went on with our days...
For what it's worth, this engineer is now one of my best friends.