Letter 42037

Why Gold coating over Titanium Nitride turns reddish when touched? [India] 

August 25, 2006

We use a PVD (UBM) Machine (with Polycold) to coat Gold over Titanium Nitride. Invariably, we find the color of Gold Coating change to a Reddish Tinge when touched with bare fingers. When wiped with a good cloth, this reddish tinge disappears.

We also find this to happen on the Titanium Nitride Coating, although the TiN coating is visibly very good at a rich greenish yellow color when taken fresh. The color of TiN turns reddish brown in the areas touched.

Can some one help us to identify the actual cause of this?

Sreenivass NV
Premier Systems - Hosur, Tamil Nadu, INDIA

How thick are the films? We tried using TiN for a quartz crystal sensor coating at ~0.15 um but the surface roughness was ~0.1 um! Unless the gold is thick compared to that roughness it will not "smooth" over the spikes of the TiN surface.

Jeffrey C. Andle
- Westbrook, ME

I forgot to actually get to the point... The finger oil is absorbed in the rough surface and is optically on the order of the wavelength. The coloration we observed varied depending on roughness and what liquid...

Jeffrey C. Andle
- Westbrook, ME

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