SI/W RATIO CHANGES AND FILM PEELING DURING POLYCIDE ANNEALING

Tungsten silicide has found wide applications in VLSI device fabrications; nontheless, peeling has been a major problem in manufacturing. Adhesion of tungsten silicide films is strongly related to the film compositions, Si/W atomic ratios, which in turn can be altered by oxidation conditions. In this work, we investigated the tungsten polycide peeling mechanism and explored the causes for peeling. RBS, XRD and Auger were used to correlate the silicide adhesion to its composition changes due to oxidation. It is found that during the first oxidation of the polycide films, the silicon atoms in the silicide films are driven out of the silicide bulk toward both the surface and polysilicon-silicide interface. Bared oxidized polycide films would peel upon further oxidation. The peeling mechanism is illustrated. Solutions to the film peeling prevention will also be proposed.