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Electroplating onto Cr seed layer

Hi,
For one process we need to electroplate metal onto a 22 nm thick Cr seed layer. I know that Cr is typically not used as a seed layer, but we do not have another option. The Cr seed layer is on a Si substrate.
Could someone please recommend what method and plating solution we should use for this?
Thank you very much.

Dominik Bell
- Zurich, Switzerland
2005

You don't say what metal you want to add. If it is more chrome you may look into Fluoride based chrome baths. They are able to plate on top of existing chrome after a quick HCl dip. Fixturing, racking and process parameters of course, are to be engineered.

Guillermo Marrufo
Monterrey, NL, Mexico
2005

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Thank you for the reply. I do not have a specific requirement as to what metal should be plated on top of the Cr. I am happy with any metal that works. The goal is to make the resulting structure as conductive as possible.
Regards,

Dominik Bell
- Zurich, Switzerland
2005

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Gold it is then.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2005

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What is the best way to plate Au directly onto Cr please? Is Au really the best option in terms of the feasibility of plating onto such a thin Cr seed layer? Do I need anything to activate the surface or just a conventional Au plating solution?
Thank you,

Dominik Bell
- Zurich, Switzerland
2005

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Hi

I am working on the same subject as Dominik. We tried in a first step to coat the chrome with a wood's nickel strike to give a nice seed layer for further coating with copper. The problem now is, that the chrome is dissolving in the strike. Within less than 2 minutes none of the chrome is left on the Si substrate. We figured we set the Anode and Cathode the wrong way round, but even after changing the polarity the result remained the same. With a thin stripe of copper foil as substrate it works very well. Now why is the chrome dissolving in the bath? Can it be, that the chrome is completely oxidized and in that way dissolved by the acid?

Thank you for your help.

Tobias Bauert
- Zurich, Switzerland
2005

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HCl is an excellent strip for chrome. Here is one of the few places that I will recommend a sulfamate nickel strike rather than a Woods strike. It has a considerably higher pH, less chloride and more nickel so it will plate faster and cover your chrome before the acids dissolve it.

Just for grins, try going into the tank hot and hit it with twice as many amps for about 1 min and then drop the amps back to normal. This might flash the chrome enough to keep it from dissolving. You might go to formula for the Woods strike that has less acid in it. There are three fairly common formulas and they definatly are not the same. High acid -low nickel is great for some high nickel SS parts, but it is bad for your application, as you have found out.

James Watts
- Navarre, Florida
2005

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A seed layer of 22 nm is probably quite to thin to plate anything on it . Also you will probably not have a chance to get good adhesion between sputtered chrome and any metal you try to plate on it. It will be much easier to do a second sputter process with gold.

Good luck,

Marcus Hahn
- Lucerne, Switzerland
2005

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Hi

We finally managed to plate Au with an acid strike onto the Chrome layer. It worked pretty well, thanks for your support and input.
We are now working with a lower doped silicon than before as a substrate below the Chrome circuits. We worked with just the same parameters as before but now we find emormous amounts of Gold on the Silicon, which in fact should not be conductive at all compared to the Chrome. The Gold is spread out like plated metal and is thicker and more wide-spread the higher the current density is.

How could that possibly be?

We first figured there was something wrong with the doping of the Silicon, but it seems to be all right. Also the possibility of some kind of conductive "dirt" on the Au can be ruled out due to our cleaning process.

Any input is more than welcome.

Tobias Bauert
- Zurich, Switzerland
2005