Nitrogen enhanced thermal stability of nickel monosilicide

Abstract

The effect of annealing ambient during rapid thermal processing on thermal stability of NiSi has been investigated. Nickel films deposited onto Si(100) were annealed in vacuum, Ar and N2 at pressures up to 40 Torr. Rapid thermal annealing in vacuum or in Ar at 750 °C resulted in the formation of NiSi2 with concomitant increase in sheet resistance and surface roughness. However, annealing in N2 increases the NiSi2 nucleation temperature and thus the thermal stability of NiSi. Higher the N2 pressure, higher was the annealing temperature required to initiate NiSi2 nucleation. Experimental results were analyzed using a simple thermodynamic model. It suggests dissolved nitrogen impurities lower the chemical potential and increase thermal stability of NiSi phase. Phase stability observed experimentally was in agreement with that predicted by the model. Threshold nitrogen pressure exists for stabilization of nickel monosilicide during rapid thermal annealing.