Hi Everyone,

I have a problem with etching polysilicon by TMAH. I have 0.55um n-doped
PECVD polysilicon with silicon oxide on top as mask. I also have a layer of
oxide beneath of my poly.

I’m using 22%wt TMAH solution with 20% IPA at 70C. When I etch my poly for
about 1 min, almost my entire poly etches away but there is still some
residue on substrate and they don’t get etched anyway, even if I keep my
wafer in TMAH for several minutes. When I lower the temperature it gets
worse.

I HF dip the wafer in 50:1 solution for 1 min to get rid of the native
oxide.

I believe that these residues are byproducts from the reaction that stick to
the substrate because when I hold my wafer horizontally I end up with better
result.


I will appreciate if you colleague share your possible experience.

Regards

Kourosh khosraviani