Letter 37067

Electroplating Copper onto Nickel Seed  

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I am a chemist working in a micromachining facility. For some of our fabrication processes, we electroplate copper onto patterned wafers with an evaporated metal seed. Our Copper bath is an acid/copper solution with organic additives.

I am now experimenting with plating copper onto alternative seed layers. I am having a problem with peeling copper when it is plated over a nickel seed. I assume that this is because of a passive nickel oxide layer that I haven't been able to remove.

Here is my current process:

Evaporated nickel seed, high purity, ~3000 Angstroms
photoresist pattern applied
aggressive oxygen plasma photoresist descum process
4 minute dip into 10% HCl
DI rinse
2 minute dip into 10% H2SO4

The wafer is then placed into the plating unit with current off
Current is then applied at 8ASD for the appropriate time to deposit ~70 microns.

If I am doing something incorrectly, or if there are steps that I should take to increase adhesion prior to plating, please let me know.

I appreciate your help.

Jon McDaniels
plating shop - Blacksburg, Virginia, USA

I have never plated a chip in my life, but on other things you normally would have to use a copper strike first, normally cyanide, but possibly pyrophosphate.

James Watts
- Navarre, Florida

Just to clarify, plating for my process should be very similar to other forms of copper plating. A standard method of plating onto nickel should work except that my nickel doesn't require a cleaning step, just an oxide removal.

If at all possible, I would like to avoid an alkaline step as it starts to have detrimental effects to other parts of the fabrication. I have plenty of samples for experimentation so I'm willing to try anything though.

Jon McDaniels
- Blacksburg, Virginia, USA

I have a couple of suggestions if you have not already tried them:

1. Try plating without the last sulfuric acid dip- the hydrochloric may be enough to clean/activate.

2. If possible, go in "hot" with current to make sure that a non-adherent immersion layer is not being formed.

Teddy McCracken
Plating Shop - Blacksburg, VA

You do not need a copper strike, you need a nickel strike - a low efficient nickel chloride (Woods) strike with 2 #/gal nickel chloride and 1 quart/gal Hydrochloric Acid and Rolled Depolarized Anodes. This will activate (remove nickel oxide) the nickel and lay down a thin fresh layer of active nickel which the subsequent copper will bond to.

Robert H Probert Robert H Probert Technical Services Garner, North Carolina Editor's note:        Mr. Probert is the    author of Aluminum How-To / Aluminio El Como

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