etching through wafer
han-jun.kim at hp.com
Thu Apr 8 11:08:52 PDT 2004
I'd agree with Chris that holes are more difficult
than trenches. I personally didn't have any problem
in etching 40:1 AR features (0.5 um wide & 20 um deep),
with CD loss around 5%, using the current "old" STS.
But they were "trenches" with 500 um of length, not
"holes". When you etch "deep" holes, you may want to
take microloading and sidewall profile into account.
I think you will better achieve your process goal by
modifying the recipes of your current use. Let me tell
you a guideline about it briefly:
Horizontal etching may be minimized by increasing
C4F8 flow rate and decreasing power. When you add
some oxygen, the surface is also passivated with
Si(x)O(y)F(z) along with the CF(X) on it. But the
passivation is compromised with the enhanced etch rate.
If you're concerned that adding oxygen etches resist
way faster, you may introduce a hard mask. Finally,
lowering pressure helps regulate the gas density that
the resulting etch becomes more uniform. This feature
helps especially when the exposed areas are small.
But, this is at the cost of reduced etch rate.
Good luck on your process!
1501 Page Mill Rd, MS 1198
Palo Alto, CA 94304
(650) 857-8525 / 8948 FAX
hjkim at hpl.hp.com
From: Chris Kenney [mailto:kenney at slac.stanford.edu]
Sent: Thursday, April 08, 2004 10:12 AM
To: Andrew Arthur Davenport
Cc: stsetch at snf.stanford.edu
Subject: Re: etching through wafer
Our group has been etching small, high-aspect-ratio features
since the machine was installed.
When you say a 8 micrn hole, do you mean a circular cross
section or a trench?
For circular features we obtain aspect ratios of 15 to 1
after some tuning and some luck.
During the etch the diameter tends to widen.
Several years ago we etched small holes through a 300 micron thick
wafer. The holes were drawn as 15 micron diameter circles on the
mask. As I recall it took 4-5 hours to etch through and the
holes ended up around 22-23 microns in diameter after the etch.
Most papers use trenches when discussing process development
for a DRIE machine. Trenches are easier to measure and
one can obtain higher aspect ratios with trenches.
Unless a paper is very explicit in specifying that circular
holes were used I'd assume they used trenches.
On Thu, 8 Apr 2004, Andrew Arthur Davenport wrote:
> stsetch users,
> I'm trying to etch a 8um hole through a 325um wafer. I've tried the
> standard recipies (deep and fastdeep), and also 7um and 10um resist. None
> of these seem to be able to etch through within 4 hours (by that time the
> resist is burnt). Have tried bonding to another wafer with photoresist - it
> improves the resist lifetime but will still burn eventually. Just wondering
> if anyone had experience with small deep features (or aspect ratios >30).
> I'm currently trying one of the recipies in the Ayon paper listed on the SNF
> website, but am uncertain of whether it will work.
> Andrew Davenport
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