Hi Paul,

One of the quick and dirty fix would be to have
multiple cycles with different etch:passivation
time ratio combinations. For example, start with
4s:5s -> 5s:5s -> 6s:5s. Problem of this approach
is that you may not have gradual profile transition
between cycles.

Or try to reduce passivation, i.e. reduce C4F8 flow.
You can try to change the power, but I would start
with the flow. This may cause bowing. (instead of nice
and straight negative profile) But you should be able
to have larger backside CD. This is the general
direction I would go for. I would recommend you to run
a mini DOE to find the process window before start
fine tuning the recipe.

Good luck!

ShuTing



ShuTing Hsu
Graduate Student Researcher
Integrated Photonics Laboratory
UCLA EE Department
420 Westwood Plaza, 63-128 Eng 4
Los Angeles, CA 90095
Tel:   (310) 825-7338
Fax:  (310) 794-5513
Email:  shuting@icsl.ucla.edu



-----Original Message-----
From: mems-talk-bounces+shuting=ucla.edu@memsnet.org
[mailto:mems-talk-bounces+shuting=ucla.edu@memsnet.org] On Behalf Of
Paul Elliott
Sent: Friday, April 23, 2004 11:54 AM
To: mems-talk@memsnet.org
Subject: [mems-talk] Re: Re: STS ASE etch help



Can you advise any parameters to control sidewall angle of a 500um thru
wafer etch?  I need to obtain a negative sidewall profile no greater
than 1
degree across a 4" substrate with varying diameters(~150um dia.).

Eric Miller  advised maybe the ICP power and/or
the
pressure are major contributors.

My intial posting is below.

Thanks in advance for any advice,
Paul

Sent: Tuesday, February 10, 2004 7:02 AM
Subject: [mems-talk] DRIE sidewall angle


>What is the expected tolerance for sidewall angle when DRIE 'etching a
>Si substrate 500um thick?
>
>I need to etch an arrayed die pattern consisting of two holes 125um and
>155um diameter.  The two holes are spaced 150 um apart and the die are
~1mm
>apart.  I want to etch 125 um diameter hole through the 500um thick
>wafer and obtain a negative sidewall profile no greater than 1 degree
>and a backside hole diameter of 125um +17um / -0um.  Likewise, I need
>the 155um diameter hole to have a negative sidewall profile no greater
>than 1 degree and a backside hole diameter of 155um +17um / -0um.
>
>Thank you in advance for any guidance,
>
>Paul

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