You need more bake on the 1st layer. The 1st layer is continuing to outgas when
you bake the 2nd layer, and cannot because of the 2nd layer on top of it. you
need to bake the 1st layer at a higher temp than the 2nd layer.
Robert
-----Original Message-----
From: mems-talk-bounces+r-black1=ti.com@memsnet.org [mailto:mems-talk-
bounces+r-black1=ti.com@memsnet.org] On Behalf Of Bill Chow
Sent: Sunday, January 13, 2013 9:21 AM
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
-----原始郵件-----
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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