Re: Color of thin Au film is substrate dependent?

HelloWil,

I've done a lot of Ti/Au evap and sputtering work in the past, and have
encountered such abnormalities at times. In most cases, these were due to
intermixing of the substrate and dep layers due to diffusion, or similar
phenomena.

If the dep layer is not dense or thick enough, the substrate (or its oxides)
play games with the super thin metal layers.

The Ti layer can change colors (ranging from gray -- including purple --
TiOx to gold TiNx), depending on the stoichiometry of the reaction during
dep, and that can fool you too.

I bet that if you increase the thickness of the Ti layer you might eliminate
most of the above interferences and get more uniform and reliable results.

Hope this helps.

Anco Blazev

"Wil McCarthy" <wmccarth@xxxxxxx> wrote in message
news:rag8f.842$8c5.168@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Okay, I'm stumped. I put ~3 nm of Ti and ~12 nm of Au down on two Si
> chips and two GaAs chips in a single run. I *know* they got the same
> deposition, but when it was done the Si samples were purple and the GaAs
> samples were gold in color. Ellipsometer readings were also different; on
> Si the instrument saw 2.5 nm of oxide with two distinct metal layers on
> top, whereas for the GaAs samples it claimed to see an oxide layer topped
> by a single metal layer, 17 nm thick, with an index of refraction that did
> not match either Au or Ti.
>
> Why the difference? Any thoughts appreciated.
>
> --
> Wil McCarthy < http://www.wilmccarthy.com >
> Engineer, Columnist, Author, etc.
> New in Paperback: TO CRUSH THE MOON (Bantam, June 2005)
> "Nature, to be commanded, must be obeyed" -- Francis Bacon


.

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