SOI thickness measurement by Nanospec?

[Hatice Altug]

Hi all,

I wonder if anybody currently using nanospec (or ellipsometer if possible)
to measure thin silicon thickness on SOI wafer.
My SOI wafer has 1um oxide and silicon with thickness ranging from
300nm-1500nm. I have used three programs written by labmembers but it could
not measure my chips.

Could you reply me if you know how to measure it?

thank you,

-hatice