A STUDY ON WSI2 THIN-FILMS, FORMED BY THE REACTION OF TUNGSTEN WITH SOLID OR LIQUID SILICON, BY RAPID THERMAL ANNEALING

WSi2 thin films have been grown on oxidised silicon substrates by the thermal induced reaction of a sputter-deposited poly-Si/poly-W layer. The heat treatment of the samples was performed in a rapid thermal, la rge area process, using a line electron beam as a heat source. A compl etely different growth behaviour of WSi2 is observed below and above 1 414-degrees-C, i.e. the melting point of silicon. Processing at temper atures below 1414-degrees-C leads to WSi2 formation by a solid state r eaction, leaving behind unreacted residues of the initial layers. Proc essing at temperatures above 1414-degrees-C leads to a reaction of the molten silicon with the solid tungsten. In this reaction, all tungste n is consumed. Simultaneously, excess silicon crystallises with a pref erential (111) orientation. The dependence of the WSi2 layer thickness on the process temperature can be explained by a model which takes in to account the diffusion and reaction kinetics as well as oxygen conta mination because these strongly influence the growth process and thus the thin film characteristics. The samples have been analysed using X- ray diffraction, transmission electron microscopy, secondary ion mass spectroscopy, scanning electron microscopy and electrical measurements . Tungsten silicide thin films, fabricated by the rapid thermal anneal ing process can, for example, be used as a backside contact of thin fi lm solar cells.