Pradeep,
   It seems very unlikely that you could do anything to the copper to reduce
the bulk resistivity by a factor of 10.  Electroplating is too forgiving a
process.

   I believe the problem is that the vias are not solid (there's a gap or a
bubble or a pocket of solution still trapped in there), or that somehow the
two sides did not make good contact.

   One common problem in making vias on standard silicon is that the top
corners of the holes have a higher electric field and tend to electroplate
faster, pinching the hole off before it is filled in.

  If there is liquid trapped in there, you might be able to find it by
looking at it under a microscope while heating the sample - the liquid
should heat and boil out somewhere a little above 100C.

David Nemeth
Senior Engineer
Sophia Wireless

-----Original Message-----
From: [email protected] [mailto:[email protected]]
On Behalf Of Pradeep Dixit
Sent: Friday, November 24, 2006 10:01 PM
To: General MEMS discussion
Subject: [mems-talk] Higher electrical resistivity of electroplated copper ?

Dear All,

I have fabricated through-wafer electroplated copper interconnects in 400 um
thick silicon wafer. The diameter of these copper filled vias is 50 um. Now
i am measuring the electrical properties of the electroplated interconnects.

I have used 4 point probe method to measure the electrical resistivity. A
pair of consective copper pillars interconencted at the bottom has been used
for measurement. After the measurement, the measured value of electrical
resistivity is about 10-12 times higher than the bulk electrical resistivity
(1.67 micro-ohm cm).Repeated measurement results shows the same higher value
of eletrical resistivity.

Literature shows that the sputtered copper films have lower electrical
resistivity that plated copper films so i believe this higher value of
resistivity should be related to grain size/orientation.

Can any one explain why the the electrical resistivity of electroplated
copper is so high compared to bulk copper?
What factors of electroplating specifically affect this value? how can this
resistivity can be reduced besides annealing?