Newman--
To get good profile control for most of the etch, I've done the following:
1. Etch most of the way through the wafer. You may even be able to etch all
the way through at the edges of the wafer, depending on you pattern.
2. Take the wafer out and mount it on a backing wafer using photoresist,
then complete the etch.
If you can, spin photoresist on both your product wafer and your backing
wafer.
This may require using an oxide mask so it is not damaged when it is
face-down on the chuck.
Try to get all of the air out for a better thermal contact. Having etched
all the way through the wafer will help with this.
Use as thin a photoresist layer as possible, also for better heat
conduction.
    --Kirt Williams

----- Original Message -----
From: "neo man" 
To: 
Sent: Thursday, April 22, 2004 10:08 AM
Subject: [mems-talk] STS ASE etch help


> Hello everyone,
>
> I am looking to etch THROUGH a standard thickness wafer (about 500micron).
> As a result, I am using a secondary support wafer (also 500micron
thickness)
>
> I have tried bonding the wafers prior to etch (using 7 um of SPR220-7
photoresist),
> but I am not getting good heat transfer and my resist is buring very
quickly...
> (I am using 7-10 micron SPR220-7 as a mask as well)
>
> If I am just etching one wafer (ie -- no secondary support wafer) I get
decent
> results with the same process. (but obviously I am stopping before going
all the
> way through the wafer....)
>
> I have tried reducing chiller temp, but this didn't help much. I am using
30-40W platen
> during the etch and 20W platen during the passivation. I think we have a
300W generator, so not sure how much lower I can go.
>
> I am thinking of switching to an oxide hardmask.
>
> 1 - Does anyone have an idea of how drastically this will affect the etch
results. ?
> 2 - How should I compensate ? (in order to get similar results as using PR
mask)
>
> My wafers have large features mostly and about 25-30% exposed silicon.
>
> Current process is approximately:
> etch - 450sccm SF6, 20sccm O2 ---> 2200Wsource, 40W platen (6 seconds)
> passivation - 200sccm C4F8 ----> 1600Wsource, 20W platen (3 seconds)
>
> Thanks in advance for any help.
>
> neo man
> [email protected]
>
>
>
>
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