durusmail: mems-talk: Double layer SU-8 fabrication problem
Double layer SU-8 fabrication problem
2013-01-12
Bill Chow
2013-01-13
Gareth Jenkins
2013-01-14
Bill Chow
2013-01-15
Gareth Jenkins
2013-01-15
Daniel Figura
2013-01-16
Jocelyn Ng
2013-01-16
Bill Moffat
2013-01-15
Black, Robert
2013-01-17
Gareth Jenkins
2013-01-23
Tinka Li
2013-01-23
Bill Chow
Double layer SU-8 fabrication problem
Daniel Figura
2013-01-15
Hello Bill,

I have recently done similar process (4 um + 20 um) and if I compare the
parameters I notice following differences:

> First layer 5um:
> Spin 3" Si wafer with SU-8 2002 at 500rpm for 5s, then 1000rpm for 30s.
        (similar)
> Softbake the sample  :1min@65C then 3 min@95C (hotplate)
        (I baked my 4 um layer for 1 + 4 min, so 5 um layer I would bake 1 +
5-6 min at 95)
> Expose it without waiting for 25s with a total of 125mJ/cm^-2
        (similar - I needed 200 mJ/cm2 on transparent substrate to get best
resolution so 125 mJ/cm2 on silicon sounds very real to me)
> Postbake it  without waiting for 1min@65C and 1min@95C (hotplate)
        (I would bake it much longer, 1 + 5-6 min. I bake my 4 um layer
1min/65C + 4 min 95C)


> Second layer 15um:
> Spin the second layer without waiting with SU-8 2010 at 500rpm for 5s,
> then 2000rpm for 30s.
> Softbake the sample 2min@65C then 5min@95C (hotplate)
        (I would bake 15 um layer at least 10 min at 95, I baked 20 um layer
12-15 min)
> Expose it without waiting for 45s with a total of 225mJ/cm^-2
        (Is there any need to increase the exposure dose? There is not much
light absorbed in 15 um layer of SU-8)
> Postbake it without waiting for 1min@65C and 2mailto:2min@95C (hotplate)
        (I again baked my layers much longer - same as SB)

My process was not optimized but worked fine for the goal and resolution we
needed.

Just to be sure - do you use open lid spin coater and contact exposure with
not-contaminated mask?


With best regards,

Daniel



Daniel Figura

smartfabgroupT Company

process consulting . data processing . fab software

Phone: +421 944 45 26 86

E-mail: daniel.figura@smartfabgroup.com, Web: www.smartfabgroup.com



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-----Original Message-----
From: mems-talk-bounces+daniel.figura=smartfabgroup.com@memsnet.org
[mailto:mems-talk-bounces+daniel.figura=smartfabgroup.com@memsnet.org] On
Behalf Of Bill Chow
Sent: Sunday, January 13, 2013 16:21
To: General MEMS discussion
Subject: Re: [mems-talk] Double layer SU-8 fabrication problem

Thanks for your suggestion. I will try it tomorrow.

But the wrinkles exist in between the top and bottom layer. Also, It occurs
when I soft bake the second layer. That is before the exposure of the second

layer. I doubt why it happens at that time, but not when I soft bake the
first layer?

Bill

-----????-----
From: Gareth Jenkins
Sent: Sunday, January 13, 2013 1:50 PM
To: General MEMS discussion
Subject: Re: [mems-talk] Double layer SU-8 fabrication problem

By "dry skin" effect, I assume you mean wrinkles. Since they only occur in
the exposed area, this indicates insufficient crosslinking of the exposed
resist.
Either the post-exposure bake is not enough or your exposure dose is
insufficient (probably the exposure dose is the issue in my experience).
As for expiry date - 1 month is nothing. As long as it is stored OK it
should last well beyond the stated date.


On 12 January 2013 22:36, Bill Chow  wrote:

> Hi,
>
> I am working on a double layer structure with bottom layer 5um and top
> layer at 15um. I have used SU-8 2002 and SU-8 2010, however they have
> passed the expiry date for about a month (Would it be a problem?). In the
> last month, I was successed to make a beautiful sample out without any
> problem. However, Last week I tried to fabricate one more sample (due to
> misalignment of the structure in the first sample). I found there is a
> terrible problem arise. After I fabricated the first layer and spinned the
> 2nd layer, I put the sample on the 65C hot plate for soft bake. However,
> the sample shows a "dry skin" like structure between the interface of
> the
> first and second layer of SU-8 just after a few seconds on the hotplate. I
> don't know why a previously worked process could failed after a few
> weeks.... I have try to use the same bottle of SU-8 2010 and let the
> sample
> to cool down to room temperature before the second layer softbake, however
> the problem remains. A very interest point is that, only the exposed area
> have the "dry skin" appearance, for the unexposed area it don't have
> any
> problem. I hope someone could help me in this tough situation. Thanks.
>
> First layer 5um:
> Spin 3" Si wafer with SU-8 2002 at 500rpm for 5s, then 1000rpm for 30s.
> Softbake the sample  mailto:1min@65C then 3 min@95C (hotplate)
> Expose it without waiting for 25s with a total of 125mJ/cm^-2
> Postbake it  without waiting for 1min@65C and 1min@95C (hotplate)
>
> Second layer 15um:
> Spin the second layer without waiting with SU-8 2010 at 500rpm for 5s,
> then 2000rpm for 30s.
> Softbake the sample 2min@65C then 5min@95C (hotplate)
> Expose it without waiting for 45s with a total of 225mJ/cm^-2
> Postbake it without waiting for 1min@65C and 2mailto:2min@95C (hotplate)
>
> Regards,
> Bill
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Visit us at http://www.mems-exchange.org

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To unsubscribe:
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Visit us at http://www.mems-exchange.org

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