You should have infinite chemical selectivity to aluminum.  At 22 mtorr you're
probably sputtering the aluminum.  At higher pressure, e.g. 100 mtorr the
aluminum should last forever.

Titanium and a-si will likely etch in a fluorine based plasma at any
pressure.

>>> [email protected] 01/09/02 01:51AM >>>
Dear everybody:

I am use the unaxis-Nextral 860L equipment to etch 6-8um sio2 film now with
the recipe:O2 10sccm,CHF3 80sccm,He 10sccm,rf power 250watt, UHF power
1800watt, pressure 22mtorr.but found the selectivity is  very poor whatever
the mask material is Aluminium!"Titanium or a-si.how to etch this sample with
CHF3,can you give me some good advice.Thanking you in advance

regards.

Li-bing Zhou
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