I am having trouble posting - apologies if this appears a few times!

If it was purely insufficient soft-bake I would expect the wrinkles to
cover the whole wafer. Since they are confined to the exposed regions only,
this indicates incomplete cross-linking during the PEB.

N..B. I would not increase the temperature but rather the time when
optimising baking parameters.

On 16 January 2013 01:40, Black, Robert  wrote:

>
>
> 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: [email protected] [email protected]> [mailto:
> [email protected]] 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  [email protected]>> 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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>
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> >
>
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