Hey Jeffrey,

>From my experiences, two methods may be helpful:

1. The dimples may form after spin coating. You can level the SU-8 for
30mins after spin coating. This can make the su-8 "smooth out".

2. Another way which is always beneficial is that you can prewet the wafer
with a thinner su-8, e.g 2002. This can homogenize your surface.

These all work perfectly for me. Hope this may help.

Peng Li

> Hi,
> I am trying to coat 2-3 layers of SU-8 2050.  My process is aas follows:
>
> 1.  Dehydration bake SiO2 wfr at 120'C for 2mins
> 2.  Spin coat SU-8 2050 at 500rpm and ramp up to 3000rpm for 30sec.
> 3.  Soft bake the first layer at 65'C for 3mins (ramped from 50'C to 65'C
> and hold for 3mins)
> 4.  Return wafer to spin coat another layer at the same conditions stated
> in 2.
> 5.  Soft bake wafer at 65'C for 5mins and ramp to 95'C for 20mins, since
> the layers now have a nominal thickness of 100 microns.
>
> I noticed that while baking at 95'C the SU-8 film developed dimples.
> These may or may not be an issue for my process, but they are cosmetically
> ugly.  Can anyone tell me how do I solve this dimple issue?
>