I have successfully used Cr layers as thin as 20A for Au adhesion to Si.
A couple of suggestions:

When depositing Cr (assuming e-beam deposition) don't open your shutter
until you have gotten rid of the oxide layer.  You can determine that
you're depositing Cr when the chamber pressure drops significantly once
you begin ejecting material from the crucible.  The bare Cr in the
chamber acts as a getter and the pressure will drop when you get through
the oxide and start depositing metal.  Only then should you expose your
substrate to the deposition.

You should deposit the Au after the Cr without breaking vacuum. Exposing
the Cr to atmosphere lowers adhesion significantly.

Substrate condition is important.  Make sure the Si is clean before you
start.

Milan Buncick PhD
The AEgis Technologies Group Inc.
631 Discovery Drive
Huntsville, Al 35806
256.922.0802
256.922.0904 Fax