Martin,

This kind of problem does encounter with many polyimides. One of the reason
can be after you etch or pattern the aluminum make sure there is no
photoresist left, because many times the photoresist vapourizing temp. is
less which may form a bubble at high temperatures. Second thing is there can
be bubbles in PI 2611 bottle itself while pouring it to smaller bottle. You
might want to bring it to room temperature (if freezed or cold) before
using. And does this happen without using the VM-651 ..? It may also come
from the way you drop 2611 on the spinner.

Best of luck . I hope this works.

Aasutosh Dave




>From: "Michael D Martin" 
>Reply-To: General MEMS discussion 
>To: 
>Subject: [mems-talk] Bubbles in polyimide PI-2611 over aluminum pads
>Date: Wed, 25 Aug 2004 14:05:36 -0400
>
>All,
>The basic problem I'm having is the formation of bubbles in PI-2611
>after the hard bake. The bubbles are only forming over aluminum pads and
>appear to be within my 3micron thick polyimide, not at the metal, PI
>interface. Here are my process steps:
>
>Starting with a SiO2 and patterned aluminum substrate I prebake at 150C
>for 5min, then spin VM-651 (0.5% in DI), cure again at 150C for 5min.
>Then spin down 2611. Next the PI is soft baked from 50C to 200C on a
>hotplate at a ramp of 2C/min. Then the final cure is done in a tube
>furnace in nitrogen from 200C to 350C and we hold at 350C for 1hr.
>
>Any advice appreaciated,
>    Mike Martin
>    University of Louisville
>    502-852-1572
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