How can I plate Cu at very low currents

[selseg]

Hello,

I have a silicon wafer with a 50nm layer of copper sputtered on it. I coated it with a 1µm of positive photo resist and patterned it with a UV laser stepper. Then I developed it and washed it thoroughly. The pattern has a surface area which measures appx 1300µm x 8µm. What I want to do is to deposit a 30µm homogeneous layer of Cu in the pattern at a very slow depositing rate. To do this over a long time, I need a current in the region of 10^-6A . My problem is that, at this current there is no deposition and the voltage measured is under 0.2V which is lower than the half cell potential for Cu reduction.I think that the low resistance of the electrolyte makes it impossible to get a higher voltage to allow plating . Even extremely dilute CuSO4 solutions have a a resistance of about 2k ohms which is far too low. I have tried increasing the surface area to allow larger voltages but it also doesn't work . I'm using a potentiostat using the Chronopotentiometry mode which allows me to measure voltage at a constant current. What could be the problem?

 

[Nidum]

There is a process where the plating voltage is turned on in brief pulses many times repeated . This means that the plating voltage can be as high as is needed but the rate of deposition is controlled by the pulse width and repetition frequency .