Hi folks,

I have a trouble with some contamination after BOE wet etching.

A 30 nm thick, 300 nm wide, 10 um long Pt/Cr metal line is patterned on top
of SiO2 (100 nm)/Si substrate and I try to etch SiO2 underneath the metal
line to suspend it.
Both ends of the metal line is on top of the substrate and only middle part
of it will be suspended.
A pattern for BOE etching was done by electron beam lithography with PMMA
495 C4.
Here is my processing procedure.

1) The sample was dipped in BOE for 2 min

2) 3 x DI water rinse (5 min/ea)

3) 3 x acetone rinse (5 min/ea) (this is for removing PMMA)

4) 3 x IPA rinse (5min/ea)

5) Critical point drying.

After all the processes, I found lots of contaminant underneath and around
the metal line which is supposed to be suspended.
This contamination doesn't go away even after O2 plasma cleaning.
During the etching and rinse, the sample was faced up.

I don't know what it is and how to prevent the contamination.

Thanks

TK