Kinetics of the formation of hafnium silicides on silicon

Abstract

We have investigated the composition and growth kinetics of hafnium silicides (HfSi and HfSi₂) formed from thin films of hafnium sputter deposited on silicon. Backscattering of MeV He ions was used to monitor the growth of the silicide phases and to determine the Si/Hf concentration ratios. Seemann‐Bohlin x‐ray diffraction techniques provided identification of the phases and an estimate of the crystallite size of the films. The stable‐phase HfSi forms in the temperature region 550–650 °C. The reaction initiates at the Hf/Si interface and the thickness of the HfSi increases proportional to the square root of time. The HfSi grows by diffusion of Si through the already formed phase with an interdiffusion constant D ≃ 2.4 exp(−E_A/k T) cm²/sec with E_A = 2.5 eV. Different behavior is observed for the formation of the HfSi₂. In this case the silicide forms simultaneously throughout the HfSi layer at temperatures above 750 °C. We propose that the HfSi₂ nucleates at the grain boundaries of the HfSi, rather than at the Si/HfSi interface. The transition to HfSi₂ is completed rapidly because of the large density of nucleation sites and the small grain size of the film.