Hi Mario,
It is quite possible that you are unable to etch  through the polymer that
is being deposited
during the oxide etch process. You could try introducing some Argon in your
recipe. This
can help. The only problem is that too high a power in the etch recipe can
start to sputter
away your Aluminium mask also! It would be better if you donot strip the
resist mask after
patterning the Aluminum. This mask can act as a protection against Argon
sputtering.

It is also possible that there are some metal  residues after aluminum etch
which is
mico-masking during the oxide etch.

Regards
Ranga

-----Original Message-----
From: Mario Adamschik 
To: [email protected] 
Date: Tuesday, 23 March 1999 21:50


>Question for discussion Group:
>
>Subject: SiO_2 RIE
>
>We have problems regarding reactive ion etching with freon
>(CF_4) of thick (1-5um) SiO_2 layers. We use an old PLASMA
>THERM PD 2480 Plasma Etch System 1984.
>Problem: Even after very long etching times we observe high aspect
>ratio "needles" and residues at the substrate (diamond) surface.
>Our process parameters are: 400W, 45mTorr, 45 SCCM CF_4
>We use an Al mask for etching.
>
>Thanks in advance
>Mario
>
>