SU-8 2025 and 80 micron high features w/ HMDS?

Discussion:

Jose Guevarra

2008-08-01 18:46:29 UTC

Hi,

I'm trying to make some features of about 70 to 80 microns high with
SU-8 2025. I've used the recipe below. However, after the develop and
hard bake the photoresist starts to come off the wafer. So it seems it's
a bonding issue. Can anyone recommend a recipe for 70 micron high
features with SU-8 2025?

Would a layer of HMDS help the SU-8 bond to the wafer?

Thanks.

----------
1. PhotoResist
- Spin 8 sec 500 rpm
- Spread 30 sec 1250 rpm
- May Need to wipe perimeter of wafer for excess photoresist

2. Soft Bake
- 65 deg. C 2 min
- 95 deg. C 8 min
- If wrinkles form on cool down try heating up and cooling down again

3. Exposure
- 20 sec

4. PEB
- 65 deg. C 1.5 min
- 95 deg. C 6.5 min

5. Develop
- Su-8 developer for 6 min

6. Descum

7. Hard Bake
- Heat from 65 deg C to 160 deg C
- Let sit at 160 deg C for 10 min
- Cool down to room temp
----------------------------------

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Oakes Garrett

2008-08-04 18:07:05 UTC

Permalink

You should try the SU-8 adhesion promoters that are on the market. MCC
and Silicon Resources in Chandler Arizona both have products that work
well. What type of wafer are you using?

Best Regards,

Garrett Oakes

EV Group
invent * innovate * implement
Northwest Strategic Account Manager

-----Original Message-----
From: Jose Guevarra [mailto:***@gmail.com]
Sent: Friday, August 01, 2008 11:46 AM
To: General MEMS discussion
Subject: [mems-talk] SU-8 2025 and 80 micron high features w/ HMDS?

Hi,

I'm trying to make some features of about 70 to 80 microns high with
SU-8 2025. I've used the recipe below. However, after the develop and
hard bake the photoresist starts to come off the wafer. So it seems it's
a bonding issue. Can anyone recommend a recipe for 70 micron high
features with SU-8 2025?

Would a layer of HMDS help the SU-8 bond to the wafer?

Thanks.

----------
1. PhotoResist
- Spin 8 sec 500 rpm
- Spread 30 sec 1250 rpm
- May Need to wipe perimeter of wafer for excess photoresist

2. Soft Bake
- 65 deg. C 2 min
- 95 deg. C 8 min
- If wrinkles form on cool down try heating up and cooling down
again

3. Exposure
- 20 sec

4. PEB
- 65 deg. C 1.5 min
- 95 deg. C 6.5 min

5. Develop
- Su-8 developer for 6 min

6. Descum

7. Hard Bake
- Heat from 65 deg C to 160 deg C
- Let sit at 160 deg C for 10 min
- Cool down to room temp
----------------------------------

_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org

Want to advertise to this community? See http://www.memsnet.org

To unsubscribe:
http://mail.mems-exchange.org/mailman/listinfo/mems-talk

Jose Guevarra

2008-08-04 18:43:32 UTC

Permalink

I did try HMDS and that seems to work fairly well.

Thanks.

Post by Oakes Garrett
You should try the SU-8 adhesion promoters that are on the market. MCC
and Silicon Resources in Chandler Arizona both have products that work
well. What type of wafer are you using?
Best Regards,
Garrett Oakes

_______________________________________________
Hosted by the MEMS and Nanotechnology Exchange, the country's leading
provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org

Want to advertise to this community? See http://www.memsnet.org

To unsubscribe:
http://mail.mems-exchange.org/mailman/listinfo/mems-talk

Gareth Jenkins

2008-08-05 10:30:25 UTC

Permalink

I've read HMDS doesn't always work for SU-8 but baking post HMDS
spinning can improve the situation.
(see this excellent website for more details:
http://memscyclopedia.org/su8.html ).
You should consider the following in your process:
1. Increasing your exposure dose. You generally need much more that
the datasheet values for best adhesion.
2. Make sure you ramp up and down during PEB.
3. Do you really need the hard bake? This can actually increase the
likelyhood of delamination.

Post by Jose Guevarra
I did try HMDS and that seems to work fairly well.
Thanks.

Abhishek Jain

2008-08-05 14:19:34 UTC

Permalink

I have faced the problem of peeling off of very thin structures (less than
15-20um) for a long time from SU8. I figured out that I was using mylar
transparency mask for exposure and somehow, it was the cause. When I used a
soda lime chrome mask for exposure, the features turned out great and there
was no peeling.

If you have really thin structures ( or low aspect ratio ) that are peeling
off and you are using a transparency mask, I suggest trying out a glass mask
( you can play with the contact mode first ).

Best,

-Abhishek

On Tue, Aug 5, 2008 at 6:30 AM, Gareth Jenkins

Post by Gareth Jenkins
I've read HMDS doesn't always work for SU-8 but baking post HMDS
spinning can improve the situation.
http://memscyclopedia.org/su8.html ).
1. Increasing your exposure dose. You generally need much more that
the datasheet values for best adhesion.
2. Make sure you ramp up and down during PEB.
3. Do you really need the hard bake? This can actually increase the
likelyhood of delamination.

Post by Jose Guevarra
I did try HMDS and that seems to work fairly well.
Thanks.

Seena V

2008-08-05 09:11:53 UTC

Permalink

Hi,
I am facing a similar problem with SU-8 2100. The procedure and the
problem is as below :-
1. Spin coat and bake Omnicoat
2. First layer of 2 micron SU-8
Spin coat SU-8 2002
Pre bake : 68 - 2minutes
90 - 5 minutes[ramped to 90 in 10 minutes]
cooled to room temperature

. Exposure : 8 seconds
. Post bake : Same as prebake
. Develop : 2 minutes

3. Second layer of 160 micron SU-8
Pre bake : 68 - 15minutes
90 - 30 minutes[ramped to 90 in 15 minutes]
cooled to room temperature

. Exposure : 2.5 seconds
. Post bake : Same as prebake
. Develop : 20 minutes

PROBLEM :-
While developing second level, some rainbow pattern is seen [an indication
of developer solution going under the crosslinked layers] and then the
structure comes out. When I verified with microscope, the SU-82100
structure came out along with Su-8 2002 layer which is in contact. So
after development of Su-8 2100 layer, SU-8 2002 patterns which are not in
contact with Su-8 2100 were left on the wafer.

Has anyone faced a similar problem ?

Regards
Seena

Post by Jose Guevarra
Hi,
I'm trying to make some features of about 70 to 80 microns high with
SU-8 2025. I've used the recipe below. However, after the develop and
hard bake the photoresist starts to come off the wafer. So it seems it's
a bonding issue. Can anyone recommend a recipe for 70 micron high
features with SU-8 2025?
Would a layer of HMDS help the SU-8 bond to the wafer?
Thanks.
----------
1. PhotoResist
- Spin 8 sec 500 rpm
- Spread 30 sec 1250 rpm
- May Need to wipe perimeter of wafer for excess photoresist
2. Soft Bake
- 65 deg. C 2 min
- 95 deg. C 8 min
- If wrinkles form on cool down try heating up and cooling down again
3. Exposure
- 20 sec
4. PEB
- 65 deg. C 1.5 min
- 95 deg. C 6.5 min
5. Develop
- Su-8 developer for 6 min
6. Descum
7. Hard Bake
- Heat from 65 deg C to 160 deg C
- Let sit at 160 deg C for 10 min
- Cool down to room temp
----------------------------------