If you are plating from a cyanide bath, you can improve the uniformity by pulse
plating. You can
use something with < 50% duty cycle (4ms on, 10 ms off). I do pulseplating on a
4" * 4" wafer with
a current density less than 1.5 mA/cm2 and I get pretty good uniformity.(3.2 um
center and 3 on
the edge). You will notice that the thickness trend gets reversed with pulse
plating because the
polarization increases in the high current density areas thus counteracting
deposition rate
variation.
Lakshmi Namburi.
Process Engineer.
Teravicta Technologies Inc.,
Austin, TX-78758
[email protected]



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