Dear All,

When I etched my wafers using buffer HF(NH4F: HF=10:1), Sio2 was etched away,
however, lots of pink pieces dropped into solution. After DI water resining and
spinning dry, more and more pink pieces appeared and stuck to the wafer. And
large areas in wafer-frontside(suppose to be PR) looked uniformly, i.e. some
area look darker than others. The backside sio2 removed compeletely.

I processed those wafers using the following step:
1) RCA clean silicon wafer and Wet-oxidize (~1 um)
2) O2 plasma etch the front side (for cleaning) [2 min, 300W, 300 mtorr]
3) Photolithagraphy (130C/1hr dehydration bake, 10 min HDMS vaper prime,
spin-coat PR[OCG825], 95C/30min softbake, exposure, develop, 130C/30min hard
bake)
4) BHF etch SiO2 for 17 min and DI risine and spin dry. (backside SiO2 has been
etched away since no protection)

Are those pink pieces PR or SiO2? Any suggestions for possible reasons or
improvements are highly apperaciate.

Lydia

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