Dear Jamie,

STS maintains a team of process engineers to answer your questions and
provide support with development of new processes. Please feel free to
contact them, they should always be your first port of call.

Due to the wide range of structure size you are seeing RIE lag (ARDE) and
that can be minimised by setting up a specific process to counter this. I do
not know the configuration for the tool you have but it sounds as though you
may want to upgrade to the SOI option that removes notching when stopping on
an oxide layer, if it is not fitted.

I am not sure where you are located, therefore please contact
[email protected] or [email protected] and they will assist
you with your process development for your specific application.

Best Regards
Andrew Tucker
ST Systems USA

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Message: 8
Date: Tue, 26 Aug 2003 14:03:05 -0700
From: "Zhimin J Yao" 
Subject: [mems-talk] Bosch etch Si/SiO2 selectivity
To: [email protected]
Message-ID: 
Content-Type: text/plain; charset=us-ascii

Hello,

I need to etch 200 um deep cavities in Si and stop at 1 um thick of thermal
oxide (grown on the backside).  The cavities have diameters in the range of
300 um to 1 mm.  Bosch process etch condition: ETCH
750 watts coil power
10 watts platen power
105sccms SF6
some O2
pressure 30

PASSIVATION
600 watts coil power
6 watts platen power
40sccms C4F8

The oxide was etched through in some cavities, while Si is not etched
through in other cavities (mostly in the center of the wafer).  The STS
system we have etches center of the wafer slower.  However, I did not
expect the oxide to be etched so quickly.  Is it true that the etch
selectivity between thermal oxide and Si is about 150:1?

I thought may be the oxide was sputtered away since the power we used was
pretty high.  I want to try lower power toward the end of etching. But I do
not know how low to go.  Does anyone have suggestions on how to solve the
problem?

Thanks,

Jamie Yao
Research Scientist
RSC
750 watts coil power
10 watts platen power




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