Hello, everyone,

Thank you all for your attention and advices. The islands problem has been
solved in my su-8 experiments. As for my case, the islands are caused by
bubble burst.
I used needle to pierce the bubbles in su-8 layer before soft-bake, and this
may introduce stress into the layer. Also, the needle may bring some
particles into su-8.
So far, the islands have gone.


2008/7/9 Oakes Garrett :

> I believe that you are in fact encountering the situation that Norbert has
> described below.  We typically use several hot plate ovens to process SU-8
> wafers on our automated systems.  In this manner each hot plate is vented
> after a few minutes of bake time.  This prevents excess solvent from
> building up inside the hot plate oven and potentially condensing and
> dripping.
>
> Each of our hotplates have greater than 5 cm of clearance to the lid and
> are greater than 200 mm in diameter.
>
> I hope this helps.
>
> - Garrett
>
> EV Group
> invent * innovate * implement
> Applications Engineer - Direct: +1 (480) 305 2443,
> Main: +1 (480) 305 2400 Fax: +1 (480) 305 2401
> Cell: +1 (480) 516 6724
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>
> -----Original Message-----
> From: 郑瑞麟(Ruilin Zheng) [mailto:[email protected]]
> Sent: Monday, July 07, 2008 5:57 PM
> To: General MEMS discussion
> Subject: Re: [mems-talk] Islands found during SU-8 soft-bake
>
> Hello, everyone
>
> the hot plate is of about 20cm in diameter, with a metal lid on top, and
> the
> lid roof is about 3cm  from the hot plate.
> Do you think it is too close for the lid to hot plate?
>
>
> On Mon, Jul 7, 2008 at 5:13 PM, Nodes Norbert  wrote:
>
> > There could be also a different reason for these islands.
> > What does the bake module look like?
> > Is the volume between wafer and bake module cover very low?
> > It can happen that the solvent condenses inside the bake module at cold
> > spots and create droplets. Then, these solvent droplets can drip down on
> the
> > wafer and cause the islands.
> > It seems the bake module can handle the solvent fume volume with 2"
> wafers.
> > But with 4" wafers, there is too much of it.
> >
> > First approach to solve this increasing the bake module's exhaust rate.
> >
> > Best regards,
> > Norbert Nodes
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--
Best Regards,

郑瑞麟

Ruilin Zheng

Address:
Pen-Tung Sah MEMS Research Center,
Xiamen University, Xiamen,361005,
P.R.China