>Dear All,
>
>I have been using a microwave asher to remove hardened resist after RIE
>etching.  I tried to remove some resist residue recently on a 6" wafer that
>had 1um of Cr deposited on it.  I used the following parameters 600ml/min
>oxygen which gives about 0.8 bar and 600W power for 60mins.  I found that
>the Cr had been etched and re-deposited all over the inside of the chamber
>as CrOx (i think it could be) ! Does anyone have any idea about how this
>might have happened ? My theory is that the microwaves have coupled into to
>the wafer and increased the surface temperature.
>
>many thanks,
>
>Iain Watson.

This is actually a well-known way to strip Cr. It is based on the presence of
oxygen and works only at elevated temperatures (I don't know the exact
temperature). What you get is an unstable chromium oxide (as you thought). I
used this process a lot on purpose. I may have to reduce either power or time
significantly in order to avoid it.

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