Electrical Characteristics and Thermal Stability of Platinum Silicide-to-Silicon Ohmic Contacts Metalized with Tungsten

The present work was undertaken in order to determine the effect of var i-ous thermal treatments up to 800 ~ and of CVD Si3N4 encapsulation on the electrical characteristics of PtSi- to-Si contacts containing an overlay of W-metalization. Ohmic PtSi contacts were made to four sets of p-type Si samples doped in the 10z~-1020 cm- ~ range and three sets of n-type Si samples doped in the 1019-102o cm-3 range. The measured contact resistivities, pc,s, contain large spreading resistance contributions, but they establish useful upper limits to effective impedance at contact areas having dimensions of the order of 20 X 20 ~m. The measured pe,s values range from 1.1 • 10-6 to 7.1 X 10-2 ohm-cm 2for p-type Si samples and from 9.4 • 10-; to 8.4>< 10-6 ohm-cm 2 for n-type Si samples. No significant degradation of contacts was observed at 600 ~ or 700 ~ or upon 680 ~ SigN4 deposition. At 800 ~ (V2-hr anneal) an excessive amount of WSi2 is formed in the contact areas. Its effects may range from no change in contact resistance to an electrical "open.&quot