Hi,

I am Pradeep Dixit, a new research student in MEMS area at NTU,
Singapore. Today, I have come to know abt MEMS exchange group and
thought to discuss my problem with you guys. I need some help with
Copper electroplating.

I am trying to achieve successful copper electroplating in deep
through and blinds hole (aspect ratio ~6-8). Presently, I have 30-40
micron wide and 200-250 micron deep trenches in silicon (produced by
DRIE) and I need to electroplate copper into the whole trench.
However, after a certain duration of plating, my trench gets closed
off and I get voids in them. Copper is plated onto the whole wafer. I
am using DC plating, Current density 15-20 mA/cm2. I have deposited Cu
seed layer of 0.5-0.6 microns thickness by sputtering.

Electrolyte and additives are from Shipley company.

I have gone through some technical papers regarding deep
electroplating techniques, but hardly get any solid conclusion about
the optimum parameters.

I have few questions about the process, I will be thankful to some one
who can help me in overcoming these doubts and this incomplete copper
filling problem.

1. Does Cu as a seed layer is a good choice, what if I use, Au as a
seed later ?  Au has higher conductivity and noble metal compared to
Cu.

2. Will Pulsed Electroplating (Forward/reverse pulse electroplating)
be a better choice than continuous Dc eletroplating ? If yes, what may
be the optimum current density and pulsed on/off time for deep
electroplating ? I have seen the values of Current density ~ 50 mA/cm2
in some papers. Will this value be a good choice ?

3. In both cases i.e through and blind holes, only the bottom portion
of the holes have Cu see layer ( by sputtering process). Side walls of
the holes have no seed layer. Will copper filling will be better if I
try to deposit Cu on the side walls too (Although Cu deposition on
side walls is difficult, as hole has high aspect ration 6-8 ??

4. Chemical composition of the hole is : CuSO4: 80 g/L,  H2SO4: 200
g/L,  PCM: .005 L/L, HCl: .5 ml/L. Its standard chemical from Shipley,
Will it be good for the case of deep holes.

 I have seen some solution to an electroplating problem by Eric
Sanjuan, Amit Panda and some more guys on this website. I will
appreciate any one if he can suggest any thing with me on this problem

Thanking you,

Pradeep Dixit
Research Student,
Micromachine Center,
NTU Singapore