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

Abstract

The present work was undertaken in order to determine the effect of various thermal treatments up to 800°C and of CVD encapsulation on the electrical characteristics of contacts containing an overlay of W‐metalization. Ohmic contacts were made to four sets of p‐type Si samples doped in the range and three sets of n‐type Si samples doped in the range. The measured contact resistivities, , contain large spreading resistance contributions, but they establish useful upper limits to effective impedance at contact areas having dimensions of the order of . The measured values range from for p‐type Si samples and from for n‐type Si samples. No significant degradation of contacts was observed at 600° or 700°C, or upon 680°C deposition. At 800°C (½‐hr anneal) an excessive amount of is formed in the contact areas. Its effects may range from no change in contact resistance to an electrical “open.” A large disagreement exists between the measured contact resistivities and those predicted by calculations based on one‐dimensional electron tunneling through a potential barrier at the metal‐semiconductor interface. A major part of the discrepancy results from extending the theory to very small (<150Aå) depletion widths for alloyed interfaces that are physically not sharp. A three‐dimensional micromodel that includes effects of nonuniform current flow and mobility differences between n‐ and p‐type Si may be more appropriate.