Dear Sir
  I'm one of Material Science student in Taiwan . Now I do have a
serious problem in etching my specimen ,so it would be great if you can
do me a fever . Here's my parameter below:
1.) 8 inch wafer ( thickness 750 micrometer )
2.) LPCVD 2000A  Silicon Rich Oxide ( SiOx  ; x<2 )
3.) After several process I have to remove back Si to form a SRO
membrane
 first :I spin PPR on my wafer , prebake... exposure .... develop
.....baking
second : sputter metal to be the mask
Third : Lift off PPR=
Fourth : Etch @ 80 oC KOH ( 20% wt )

As I know Si3N4 was the best choice to be the etching mask , but my lab
can't CVD Si3N4 . So could you tell me which metal can be the mask . I
had been sputter  Cu and Ti but they all failure during etching .
thanks
Best regards
 Eric Chang