When Al is exposed to Oxygen (air),  several angstroms of natural
oxide grows instantaneously. his layer acts as a diffusion barrier and
slows down further growth. I can not recall  specific references but
according to what I found at times I was interested in anodizing Al,
this thicness may reach up to sevral nanometers. I remember numbers
like 2nm and 5 nm natural oxide thicknesses. However, you should
expect higher or lower numbers depending on the deposition condition,
Al density and surface roughness.  I would suspect that most sputtered
Al films will have a lower densisty compared to eg. evaporation, hence
slightly thicker natural oxide.

Probably you may find lsome useful information or links by "Googling"
keywords like anodized Aluminum, natural oxide, air-formed oxide etc.
With regards,

MF


On Mon, 12 Jul 2004 08:48:00 +0200, Stephan Biber
 wrote:
> Hello there,
>
> What happens to a 2µm thick Aluminum layer sputtered on top of a silicon
> wafer if I do not seal the Aluminum with another material such as
> Titanium? I assume the Aluminum will react with the ambient air and a
> thin layer of Aluminum-Oxid will grow.
>
> Can anyone give me an idea of how thick this layer is going to grow
> under normal conditions (atmosphere:air, T=293K)?
> Is that 0.1nm, 1nm, 5nm, 10nm 30nm?
> Does anyone know a reference to literature where this is being discussed?
>
> Stephan
>
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