How can I plate Cu at very low currents

In summary, the person is working with a silicon wafer that has a layer of copper and a positive photo resist patterned with a UV laser. They want to deposit a 30µm layer of copper in a specific pattern at a slow rate, but are facing issues with low voltage and resistance. They are using a potentiostat in Chronopotentiometry mode to measure voltage at a constant current, but are considering using brief pulses of higher voltage to control the rate of deposition.
  • #1
selseg
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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?
 
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  • #2
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 .
 
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1. How does the low current affect the plating of Cu?

At low currents, the plating process can be slower and less efficient. This is because the rate of metal deposition is directly proportional to the current passing through the solution. Therefore, a lower current means a slower rate of plating.

2. What are some methods to plate Cu at low currents?

One method is to increase the surface area of the object being plated, as this can help increase the rate of plating. Another method is to use a higher concentration of Cu ions in the plating solution, which can also speed up the process. Additionally, using a higher voltage can help overcome the limitations of low current plating.

3. Can I use a different metal for the plating process?

Yes, you can use other metals for plating at low currents. However, different metals may have different deposition rates and may require different plating conditions. It is important to research and choose the appropriate metal for your specific plating needs.

4. How can I monitor the plating process at low currents?

There are a few ways to monitor the plating process at low currents. One method is to use a digital ammeter to measure the current passing through the solution. You can also visually monitor the color and texture of the plated metal as it forms. Another option is to use a coulometer to measure the amount of electricity passing through the solution.

5. What are the potential challenges of plating Cu at low currents?

Some potential challenges include slower plating rates, uneven plating, and lower quality deposits. It may also be more difficult to achieve a desired thickness or coverage at low currents. Careful monitoring and adjusting of plating conditions can help overcome these challenges.

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