Hej!

It could be possible, that the chamberwalls need to be cleaned. I have
no idea why the plasma only is unstable while using mixed gases. Is
the gas flow stable? But plasma tends to get unstable when recently
hard-to-etch materials (like Ni) were etched. Those materials coat the
chamber walls with a conductive film, which causes then RF breakdowns.

/Andreas

On Sep 19, 2008, at 3:22 AM, [email protected] wrote:

> Hi, We have a STS ICP, working fine until recently.
>
> Problem is when using pure gas, such as O2 or CF4 alone, then plasma
> is
> stable. However if using mixed gas, O2+CF4, then plasma unstable.
> Lower
> top coil power helps but etch rate would be much slower compare to
> before.
>
> Can someone give a suggestion? Thanks.