It has been my experience with copper electroplating (35 µm tall structures, 50
µm thick resist, predominantly circles with some crosses and short lines, Cu/Ni
seed) that features with CD's below 20 µm will plate at different rates that
features with CD's above 20 µm.

I studied a case in some detail (from a litho perspective) a few years ago with
a range of feature sizes (5 - 50 µm at 5 µm increments).  As stated above, the
20 - 50 µm features plated at roughly the same rate across the entire wafer
surface.  The 15 µm features showed some decrease in plating rate and the rate
continued to drop with shrinking via dimension.  Diffusion of copper ions to the
plating surface was our suspect for the reduced plating rate.  We didn't believe
at the time that we had any wetting/trapped air issues that would lead to a
delayed start or stall in plating.

Jumping to a conclusion, the important value is most likely the aspect ratio of
thickness to lateral dimension.  This one case suggests that a ratio of roughly
5:2 is the critical plating aspect ratio for circles.

My response is a very short treatment of a complex subject.  I would like to see
responses from other people with data to see if my facts check.

Best Regards,

Garrett Oakes

EV Group
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Regional Sales Manager North America - Direct: +1 (480) 305 2443, Main: +1 (480)
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E-Mail: G.Oakes@EVGroup.com, Web: www.EVGroup.com

-----Original Message-----
From: Pradeep Dixit [mailto:pradeep.ntu@gmail.com]
Sent: Friday, July 03, 2009 2:25 AM
To: General MEMS discussion
Subject: [mems-talk] Metal electrodeposition rate

Hello All,

I would like to check some thing with you.

During through-resist electroplating, does metal deposition rate depend
upon the opening dimension of features?

I am trying to electroplating 8 um thick copper structures. resist mold is
12 um thick AZ9260. Seed layer is 30 nm TiW/ 300 nm Cu.

features are circular vias and have relatively large variation in diameter.
20 um vias are besides 100 um vias and 500 um vias.

Electroplating type: DC, 5 mA/cm2 current density

I want to know in advance:

will the electroplated thickness be same for all feautures (20 um, 100 um,
and 500 um) ?

OR

500 um diamter vias will be plated faster .

Your opinion will be appreciated.

Thanks,
Pradeep