Dear Pradeep,
as a general approach, I know that the resistivity reduces with increasing
current density. However, the stress level of the electroplated copper also
increases with increasing current densitiy. So you should be careful about
problems such as "peeling off" problem of the metal from the surface.
Regards,


--
Kagan TOPALLI
Research Assistant (Ph.D Candidate)
MEMS-VLSI and EMT Group
Middle East Technical University
Dept. of Electrical & Electronics Eng.
TR-06531 Ankara Turkey
Phone: +90 312 210 44 09 or +90 312 210 23 40
Fax: +90 312 210 23 04
http://www.mems.eee.metu.edu.tr/
http://www.eee.metu.edu.tr/~emt/
--
----- Original Message -----
From: "Pradeep Dixit" 
To: "General MEMS discussion" 
Sent: Saturday, November 25, 2006 5:00 AM
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?
>