Hi Lihua,

In general, you don't want to purge a wafer with N2 during exposure with a
positive Novalac photoresist.  The chemistry of the photo-reaction depends on
moisture in the air, so using dry N2 would actually create conditions that would
not favor proper exposure.  This is why the humidity is very tightly controlled
in fabs.

Have you established whether the mouse bites are due to physical contact with
the mask?  In other words, have you inspected the mask for bits of photoresist
immediately after exposure?  Perhaps you can post a photo.

Brad Cantos
[email protected]
http://holage.com




On Jan 12, 2010, at 10:41 PM, Lihua Li wrote:

> I have a recipe setup for 17um resist with AZ4620. The process worked fine on
Aluminum coated wafers. When I used same recipe on LTO coated wafers, I can see
mouse bites right after exposure.
>
> Here is my current recipe setup:
>
> 1, Vapor prime
> 2, 1st resist spin @ 2000rpm
> 3, Soft bake at hot plate, 90 sec at 105C
> 4, 2nd resist spin  @ 2000rpm
> 5, Soft bake on tho plate, 120 sec at 110C
> 6, Wait for 2hr to rehydrate the resist
> 7, Expose with MA150, total exposure time is 30sec (5 sec exposure and wait
for 60sec before next exposure)
> 8, Develop
>
> I changed soft bake temperature (up and down), tried pre-bake with convection
oven, tried dehydration bake before vapor prime, but the mouse bites is still on
the wafers. Is this related to the thermal conduction of LTO films? How can I
improve my process? Unfortunately my MA150 does not have the option of purging
N2 during exposure.
>
> Thanks!