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I took another look and only p+ areas are showing colors, n+ seems to be unaffected. And only some of the p+ areas are colored (every single S/D on the picture above is p+). So it is not salicide.
Etching in HF for several hours would have taken care of all inconsistencies.
Whats left is either...
Colors do only appear on top of source& drain (S/D). Both n+ and p+ areas are randomly affected. Whatever gives color is in between S/D Si and M1 metal, closer to S/D Si. Must be some sort of a barrier layer right on top of S/D
Not sure if that process even used silicide, if it did, TiN would...
Thanks everyone for the input! I understand how thin films, e.g SiO2 will have different colors depending on thickness. I guess I did not phrase the question clearly, what I meant is:.
What kind of thin film could possibly be there to produce that kind of coloring? SiO2 has been etched away...
Came across an interesting picture today. Can anyone shed the light on why some diffusions on this die have different colors after a long HF etch? All of the oxide should have been etched away at this point. Note a loose poly gate at the BR corner
You are probably right, n-channel transistors should all go to GND and p-channel to Vdd, so I must have it backwards except for the photo diode which should be reverse biased
Here is what appears to be some sort of a folded cascode amplifier, but does not really match with any classic text book example. Does it make sense to you guys?
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