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A.ALLOUCH | 1 Mar 2010 12:02
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Re: photoresist peeled off during Ni e-beam deposition

Hi, Wei

the wafer annealing is a very hot "hard bake" (500°c for Pyrex 7740 i.e)
and it allow a very good organization for particles inside the wafer,
but the main cause of the stress is the difference in expansion between
your wafer and the deposited layer ( Ni), then to avoid the stress, it's
recommanded to deposit on the both side of your wafer.

I hope to be useful,


Alaa



Wei Tang a écrit :
> Hi, Alaa
>
> Thanks for the suggestions. I guess for my sample, the Ni film
> directly contact with the photoresist layer, and from the SEM picture
> shown in the link of my last post, the photoresist layer seems to be
> under big strain, and peeled off from the substrate (but still under
> the nickel layer). The wafer itself seems ok with nickel on it.
>
>  When referring to anneal the wafer, do you mean hard bake? I have
> tried hard bake at 130C before deposition, but the same problem
> remains. Could you specify a little bit more on wafer annealing?
>
> Thanks,
>
(Continue reading)

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Felix Lu | 1 Mar 2010 16:41
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Survivability of Cr/Au metallization in 49% HF for 30 min?

Hello,

    I was wondering if anyone has any useful tips for Chrome-Gold  
metallization on polysilicon that will survive a 20-30 min 49% HF soak.
We have Sandia's SUMMiT V die that we would like to metallize in house  
with gold (wirebond pads and reflector plates) on Poly4. The current  
design does not allow for a blanket evaporation without electrically  
shorting out devices and the TEOS sacrificial oxide they use requires  
roughly 30 min to release in 49% HF (as determined by watching the  
lateral etch rate progression under a Nomarski scope and from some  
failure analysis). We can pattern the wirebond pads and/or the  
reflector plates using e-ebeam evaporation of Cr/Au and liftoff (using  
Futurexx NR9-3000PY negative resist). The problem, as some of you may  
have surmised, is that the metal layer loses its adhesion to the  
polySi after the 30 min HF (total time) release, presumably to the HF  
attacking the chrome metal through pinholes in the gold and/or  
creeping up from the metal-polySi interface.

The process outline is as follows and seems pretty standard:

1. Remove protective photoresist from die by acetone/IPA soak and rinse.
2. "Pre-etch" some sacrificial oxide away  for 10 min  in 49%  
HF(leaving 20 min for later). We have determined that 10 min seems to  
be a good compromise between making the MEMS devices too fragile and  
leaving too much time afterwards for the final HF release. 15 min of  
"pre-etching" already leaves the devices too fragile for standard  
handling.
3. Photolithography/development using negative resist
4. 1 min oxygen ashing at 100 W to descum. (critical - without this,  
the metal pads survive visually, but not during wirebonding)
(Continue reading)

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Albert Henning | 1 Mar 2010 18:38
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Survivability of Cr/Au metallization in 49% HF for 30 min?

This problem was observed on bulk micromachined devices at Redwood
Microsystems.  Ultimately, our process was compatible with nitride, so
we ended up using nitride instead of CrAu.  Our pinholes, however, were
lithographic in nature:  the CrAu was on bare Si.

Speculating, then:  the poly has a different grain structure than bare
Si.  The grain structure of your CrAu depends not only on deposition
conditions (temperature, base pressure, Ar sputter clean [if any]), but
also on the substrate structure.  I suspect the underlying structure is
contributing to the nanoscale pinholes, which the HF then attacks.
Since you cannot work on the poly deposition (it is part of the Summit
process), your choice it seems to me is limited to the metallization.
Perhaps Ti would work better than Cr as an adhesion layer?  Cr has a lot
of stress, and I believe (but am not certain) Ti has lower stress, which
may work to your advantage in terms of grain growth in the Au.

Al

---
Albert K. Henning, PhD
Director of MEMS Technology
NanoInk, Inc.
215 E. Hacienda Avenue
Campbell, CA  95008
408-379-9069  ext 101
ahenning <at> nanoink.net

-----Original Message-----
From: Felix Lu [mailto:felix_lu <at> yahoo.com] 
Sent: Monday, March 01, 2010 7:42 AM
(Continue reading)

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Morrison, Richard H., Jr. | 1 Mar 2010 21:02

Survivability of Cr/Au metallization in 49% HF for 30 min?

Hi,

It is very difficult to get wire bonding to work with only 5000A of Au,
you really need 1um of Au. You need to be at 150c to get a good wire
bond and at those temperatures, the Cr diffuses through the gold to the
surface and it makes wire bonding very tough. So Cr/Au is not
recommended for wire bonding.

Rick Morrison
Senior Member Technical  Staff 
Draper Laboratory
555 Technology Square
Cambridge, MA  02139

617-258-3420

-----Original Message-----
From: mems-talk-bounces <at> memsnet.org
[mailto:mems-talk-bounces <at> memsnet.org] On Behalf Of Felix Lu
Sent: Monday, March 01, 2010 10:42 AM
To: General MEMS discussion
Subject: [mems-talk] Survivability of Cr/Au metallization in 49% HF for
30min?

Hello,

    I was wondering if anyone has any useful tips for Chrome-Gold  
metallization on polysilicon that will survive a 20-30 min 49% HF soak.
We have Sandia's SUMMiT V die that we would like to metallize in house  
with gold (wirebond pads and reflector plates) on Poly4. The current
(Continue reading)

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shay kaplan | 1 Mar 2010 21:11

Survivability of Cr/Au metallization in 49% HF for 30 min?

Ti will fly of within seconds in HF. Cr/Au is the best combination. However,
usually with this thin coating, there are pinholes in the surface. If you
can add some gold using electroplating, most of the pinholes will be sealed
off

shay

-----Original Message-----
From: mems-talk-bounces <at> memsnet.org [mailto:mems-talk-bounces <at> memsnet.org]
On Behalf Of Albert Henning
Sent: Monday, March 01, 2010 7:39 PM
To: General MEMS discussion
Subject: [mems-talk] Survivability of Cr/Au metallization in 49% HF for 30
min?

This problem was observed on bulk micromachined devices at Redwood
Microsystems.  Ultimately, our process was compatible with nitride, so
we ended up using nitride instead of CrAu.  Our pinholes, however, were
lithographic in nature:  the CrAu was on bare Si.

Speculating, then:  the poly has a different grain structure than bare
Si.  The grain structure of your CrAu depends not only on deposition
conditions (temperature, base pressure, Ar sputter clean [if any]), but
also on the substrate structure.  I suspect the underlying structure is
contributing to the nanoscale pinholes, which the HF then attacks.
Since you cannot work on the poly deposition (it is part of the Summit
process), your choice it seems to me is limited to the metallization.
Perhaps Ti would work better than Cr as an adhesion layer?  Cr has a lot
of stress, and I believe (but am not certain) Ti has lower stress, which
may work to your advantage in terms of grain growth in the Au.
(Continue reading)

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Johnson, Stafford | 1 Mar 2010 22:57

Survivability of Cr/Au metallization in 49% HF for 30 min?

Chrome is not readily attacked by HF, so pinholes in the gold are not likely the cause of your issue.  As you
know, Cr/Au is the standard metal in PolyMUMPs and it has been shown to hold up in >20min HF release.  Cr is
also used as a hardmask or adhesion layer for a hardmask for HF etching glass wafers.  In this case I have seen
Cr hold up for >1 hour in HF. If it were attacked in HF, there would be a path on the edges of pads, so you would
always see the edges lifting after release.    I recommend you look into your process.  In order to maintain
good adhesion, it is critical that you have a clean, oxide free surface prior to metal.  If your process
works on bare silicon, but not your chips, you may need to increase your cleaning process for the chips. 
Check the manufacturer's recommenda
 tion on the plasma cleaning process for the photoresist.  With some resists, forming gas instead of O2
plasma is recommended.

Another possibility is galvanic attack of the polysilicon that is attached to gold.  This is design and
process dependant, so you may be able to find some clues if you have different designs on the die.  Check the
pads that survive and ones that fail to see if there are similarities/differences in how they are
connected to the substrate and other layers.

Stafford Johnson
MEMSCAP, Inc.

-----Original Message-----
From: mems-talk-bounces <at> memsnet.org [mailto:mems-talk-bounces <at> memsnet.org] On Behalf Of Felix Lu
Sent: Monday, March 01, 2010 10:42 AM
To: General MEMS discussion
Subject: [mems-talk] Survivability of Cr/Au metallization in 49% HF for 30 min?

Hello,

    I was wondering if anyone has any useful tips for Chrome-Gold
metallization on polysilicon that will survive a 20-30 min 49% HF soak.
We have Sandia's SUMMiT V die that we would like to metallize in house
(Continue reading)

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Paul Nguyen | 2 Mar 2010 05:45
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BPR100 Developer

Hello all:

Has anyone experienced BPR100 developer? if mixed with water, what is its
shelf life?

Thanks in advance,

Paul
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Wei Tang | 2 Mar 2010 06:35
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Re: photoresist peeled off during Ni e-beam deposition

Hi, Alaa

Thanks for the specification. I guess my wafer cannot survive very
high temperature annealing, since there is photoresist coating. I
think coating both side of the wafer is a good idea, if the stress in
wafer is of concern. However, in my case, nickel film applies the
stress to the photoresist coating directly, I am looking for methods
to prevent photoresist peeling off from the wafer, by the nickel film.

Wei


>
>
> ---------- 已转发邮件 ----------
> From: "A.ALLOUCH" <aedallou <at> laas.fr>
> To: General MEMS discussion <mems-talk <at> memsnet.org>
> Date: Mon, 01 Mar 2010 12:02:08 +0100
> Subject: Re: [mems-talk] photoresist peeled off during Ni e-beam deposition
> Hi, Wei
>
> the wafer annealing is a very hot "hard bake" (500°c for Pyrex 7740 i.e)
> and it allow a very good organization for particles inside the wafer,
> but the main cause of the stress is the difference in expansion between
> your wafer and the deposited layer ( Ni), then to avoid the stress, it's
> recommanded to deposit on the both side of your wafer.
>
> I hope to be useful,
>
>
(Continue reading)

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Reza Rashidi | 2 Mar 2010 07:57
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PEEK coatings

Hi everyone,

I am looking for a company to coat PEEK on si wafers. Please let me know if you know any facility especially in
north america.

Thanks,
Reza

      
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Kumar, Parshant | 2 Mar 2010 15:50

Re: Survivability of Cr/Au metallization in 49% HF for 30 min?

Hi Lu, 

You can adopt two way approach. One is to avoid HF sieve in through Au
film  pin holes and attack the Cr-Si interface by protecting the pads
using shadow masking with resist for HF release and second one to
thicken up the Au film (at least 1 um)  so that you can have good wire
bonding.

Best regards,

Parshant Kumar (Ph D)
Draper Inc- Cambridge
617-258-4417
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Gmane