ohmic contact to Si wafer

Hi labmembers,
I would appreciate some advice.  I want to put metal vias through a 20nm oxide layer to make ohmic contact to the underlying silicon.  My wafers are degenerate n-type, resistivity < .005 ohm-cm.  I've tried evaporating titanium contacts after etching via holes through the oxide in the MRC etcher, but I see Schottky diode-like behavior, ie. an exponentially increasing IV curve.

Has anyone made ohmic contacts with a wafer of this resistivity before?  It's been suggested to me that I need to further dope the silicon to narrow the depletion region so that I have good tunneling and ohmic contact through the barrier.  I've also read that I can anneal the Ti contacts in nitrogen to form a silicide - is this something that should be done in addition to doping, or can silicide formation alone provide ohmic contact?

Thanks in advance,
Alex


Alex Neuhausen
PhD Candidate Electrical Engineering
Goldhaber-Gordon Lab
476 Lomita Mall
Stanford, CA 94305
Office: 650-725-2047
Cell: 650-776-5672