Crayton,

A question and a suggestion.  When you do a hard bake of the first
layer, are you seeing rounding of the photoresist?  This is desirable
in order to get metal coverage with an evaporated metal, but you may
need to adjust the CDs of the bottom layer to get the desired
linewidths.

My suggestion is that you flood expose the first PR layer after
patterning but before the hard bake.  Make sure you use an exposure
level 2-3x that of your imagewise exposure.  This will destroy the
remaining PAC and assist in the removal of the resist.  It should also
help with minimizing bubbles.

Brad Cantos
brad.cantos@holage.com
http://holage.com

LinkedIn: http://www.linkedin.com/in/bradcantos

On Mar 29, 2009, at 10:39 PM, Yang Fu wrote:

> Hi All,
> I am having some troubles with fabrication air-bridges on Si. The
> dimensions
> of the air-bridges are: height 1.6um, length 90um, width 20um. I use
> double
> layer AZ5214 and electroplated gold. My process is as follows:
> patten first
> PR layer--> evaporate Ti/Au seed layer--> patten second PR layer-->
> electroplating gold (~1.8um thick)--> AZ300T or NMP to strip PR.
>
> The problem is that bubbles appear after the second PR layer
> baking(90deg,
> 2min). I have to do a long hard bake(120deg, 30min) for the first PR
> layer
> to prevent these bubbles. But it would be very difficult to remove
> the first
> hard baked PR layer in the last step. The air-bridges won't release.
> Is it
> because the first PR layer has been baked too long? Or the AZ300T
> just could
> not squeeze through the 1.6um slit to touch the PR? Thank you for
> the input!
>
> Crayon Fu
> University of Virginia