Effect of substrate on phase transformation kinetics of WSix films

WSix films deposited by chemical vapor deposition are amorphous in nature and need to be annealed at high temperature to obtain the low resistivity required for the interconnection and metallization layer in VLSI circuits. In this paper, we focus on the annealing of WSix films. WSi2.4 films on Si and SiO2 substrates were annealed at 1000 deg. C for times ranging from 5 to 60 min. The as-deposited and annealed films were analyzed by Rutherford back-scattering spectroscopic analysis (RBS), X-ray diffraction, and four-point probe method. In our samples, we observe differences in the annealing behaviour of the films on two substrates as a function of annealing time. On Si substrate, WSi2.4 film's Si/W ratio and thickness decreased with annealing time, in contrast, there was only a small change in composition and thickness for films on SiO2 substrate. There was evidence that excess Si from WSi2.4 film segregated on the top of the silicide layer and also at the WSix/Si interface. On the Si substrate, the integrated X-ray intensity continues to increase beyond the first 15 min of anneal. On SiO2, the integrated X-ray intensity saturates beyond the first 15 min of anneal. The combined effect of compositional and structural changes is in agreement with the sheet resistance trends on two substrates