Applied Surface Science

Diffusion of dopants in tungsten disilicide: effects of diffusion paths

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Dopants, mostly boron, but also arsenic and antimony, implanted in unannealed WSi2 films prepared by chemical vapor deposition diffuse quite readily at temperatures as low as 600°C. Complete homogenization in layers 200 nm thick is obtained at that temperature in periods of time less than 24 h. These results can be attributed to the large density of grain boundaries in layers that are initially amorphous and crystalline during the course of the diffusion annealings. They are in sharp contrast to what is observed when the layers are annealed at high temperature to cause grain growth and stabilization of the silicide structure prior to implantation. The dopants then are largely immobile not only at 600°C, but even during prolonged oxidation procedures at 800°C. Similar low temperature diffusion of boron in WSi2 had been observed earlier in bilayers of polysilicon and WSi2, but it is only presently that one is aware of the huge difference in diffusion behaviors between annealed and unannealed silicide layers. © 1991.