Reaction kinetics of tungsten thin films on silicon (100) surfaces

Abstract

The rate of reaction between Si (100) surfaces and tungsten films deposited by rf diode sputtering depends on the preparation of the silicon surface. If rf substrate bias is used to clean the silicon, then the rate of reaction in the temperature range 700–850 °C is independent of time, with an activation energy of 3 eV/mole W. The native oxide layer between the silicon and tungsten, that exists when sputter cleaning is not used, can act as a barrier to WSi₂ formation. In this case, the time‐independent region is preceded by a period when the reaction rate increases with time. The rate is then controlled by two‐dimensional spreading of discontinuous WSi₂ regions that originate at sites where the reaction barrier can be penetrated. After a continuous WSi₂ layer is formed, additional growth can produce a stage where the increased path length for silicon diffusion causes the transport step to control the over‐all rate of the reaction. Quantitative models are presented for each of the three stages in the reaction. The models explain some of the macroscopic observations made on reacted layers.