Hi all,

I am trying to electroplate gold on a seed layer (Ti/Au/Ti=500A/1500A/500A)
after removing the top layer (Ti). After gold electroplating, the gold area
electroplated was enlarged. For example, the target width of a gold signal
line was 40um, but it became 49um after electroplating. Here is the my
fabrication recipe.

Fabrication process.

Photolithography

(a) Spin Shipley 1045 photoresist on wafer at 500 rpm for 15sec, then 4500
rpm for 40 sec (4um).

(b) Soft bake the photoresist on a hot plate for 1min. 30 sec at 105˚C.

(c) Hard contact align (MA6 aligner) and expose 15sec.

(d) Develop in MF351:DI water=1:5 for 1min.

(e) Rinse the wafer in DI water.

(f) Dry with nitrogen gun.

(g) Use acetone to open small regions for the electrode contacts to the
seed layer while plating.



Au electroplating

(h) Dip in HF:H2O(=1:4) solution for 4 sec to etch exposed top Ti layer.

(i) Electroplating the Au to 3.5um thick in the electroplating solution


I tried  to figure out the causes of the enlarged gold line, and I found a
few things:

(a) After developing PR, the width of signal line was about 42um =>2um=42um-
40um.

(b) After removing the first Ti layer, there was undercut beneath the PR
layer. The width of the signal line became was about 44um => 2um=44um-42um.

(c) After gold electroplating, the width of the signal line was 49um=>
5um=49um-44um.

(Here, the width of signal line was measured by a microscope with a ruler
on  an eye piece, and these values are approximate numbers)

Based on this analysis, I believe that I have to modify the
photolithography process (exposure time and developing time). However, how
can I compensate the other problems?  Do you have any ideas?

Hosaeng Kim