Nonalloyed ohmic contacts to N-Si using a strained Si0.5Ge0.5 buffer layer

Abstract

Nonalloyed shallow ohmic contacts to n-Si have been fabricated by using an 80 angstrom thick strained Si0.5Ge0.5 buffer layer grown by molecular beam epitaxy. X-ray photoelectron spectroscopy was employed to investigate the Si 2p and Ge 3d core level binding energies of the strained and the relaxed Si0.5Ge0.5 and to determine their relative Fermi level positions. It was found that the surfaces of strained Si0.5Ge0.5 exhibit pinning very close to the conduction band. Rutherford backscattering and Auger depth profiling were employed to determine the contact reactions using Ti, W or Pt as contact metals. In the case of Pt, a 500 angstrom W diffusion barrier can protect the ohmic behavior up to 550 °C for 30 min. The specific contact resistance of the Pt/W/Si0.5Ge0.5/n-Si contact extracted from the D-type cross-bridge Kelvin resistor was 3.5×10-5 Ω·cm2.