SU-8 bead-like residue along edges of metal features
Jim Beall
2006-03-06
I am patterning SU-82025 into 150 micron diameter x 20 micron tall
posts. The SU-8 is put down on a multilayer device consisting of
several patterned metal layers (100 nm Mo/ 200 nm Cu/ 500 nm Cu/ 500
nm Au).
The posts appear to develop nicely with pretty straight side walls
and no milky residue.
On some, but not all wafers, I have seen what look like tiny (couple
microns) beads of residue aligned with the edges of one of the metal
layers. There are also occasional similar sized dots of residue
scattered around on the wafer.
Has anyone seen this effect and know how to eliminate it?
We use an i-line stepper for exposure at 400 mJ/cm^2 with soda lime
masks. Pre and post bakes are 65 C for 1 min, ramp to 95 C over 2
minutes and hold at 95 C for 3 minutes. Develop in SU-8 developer 4
minutes.
Thanks in advance for any insights,
Jim