Status of Oxide etch rates in Lampoly

Jim McVittie mcvittie at cis.Stanford.EDU
Mon Apr 16 17:54:59 PDT 2001

Lam Users,

The oxide etch rate have come down a bit but they are still higher than
they should be. I now feel that the problem is that we have a carbon
source in the chamber. In CL2 and HBr processes carbon is needed for the
etching of oxide. The purpose He-O2 flow that we add to the standard poly
process is to remove carbon during the etch. Normally, 5 sccm of 20% O2 in
He is suffice to remove carbon coming from the resist mask. However, if
there is another carbon source in the chamber, 5 sccm may not be enough.
The problem with adding too much O2 is that the resist etch rate goes up
with O2 flow. Note that the oxide etch rate normally goes down faster than
the resist etch rate goes up. About a month ago when I last saw the inside
of the chamber, I noticed a black buildup on the top dielectric between
the ICP coil and the chamber. I now suscept this layer is carbon or a
carbon mixture. The etch rates below support a carbon source in the
chamber in that the ox etch is coming down as the He-O2 flow is increased.
We have several choices in what to do about this black layer which are:

1. Do nothing and live with the higher oxide etch rates. O2 plasma clean
should help but too much O2 cleaning will destory the system o-rings and
the system plasma.

2. Sand blast the layer off.

3. Turn over dielectric so that the black layer is on the outside toward
the coil. Note that this dielectric is about an inch thick and 12 inches
in diameter.

4. Get a new dielectric. We have an old style dielectric in that ours is 
made of aluminia ceramic while Lam currently uses quartz which reduced
aluminum contamination to the wafers. 

Since no one has been complaining about Al contamination in the Lam, my     
choice is to sand blast the dielectric. I would be interested in hearing
what you think about this.

Here are the results that Brian Green got today using recipe #1.

Program #1 Main Etch only (no BT or OE)
He-O2 =  0 sccm -> SiO2 etch rate = 220 A/min
He-O2 =  3 sccm -> SiO2 etch rate = 212 A/min
He-O2 =  5 sccm -> SiO2 etch rate = 184 A/min <- Normal Program #1 O2 flow
He-O2 = 10 sccm -> SiO2 etch rate = 167 A/min

Program #1 Over Etch only (no BT or ME)
He-O2 =  5 sccm -> SiO2 etch rate = 46 A/min <- Normal Program #1 O2 flow

Note: All wafers etched for 2 minutes

I will try to more data as the week goes on. 

When we initially set up the Lam, the ox etch rate during the main etch
was only 35 A/min and during the OE it was 26 A/min. However, we have been
runnig high for some time.  

	Jim McVittie

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