Hello,
I'm doing single layer SU8 2005, thickness ~6-7um. I use 60mJ/cm^-2 on sputtered
gold surface. But somehow sometimes I notice that the edges of my pattern
darkens, I suspect it's due to overexposed. But 60mJ is quite a low dose
compared to the recommended one. I would appreciate any comments given. Thank
you.
Best Regards,
Jocelyn
Sent from my iPhone
On 16 Jan, 2013, at 5:23, "Daniel Figura"
wrote:
> 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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provider of MEMS and Nanotechnology design and fabrication services.
Visit us at http://www.mems-exchange.org
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