Measurement of lateral dopant diffusion in thin silicide layers

The lateral diffusion of dopants in silicides was studied using a sensitive Schottky-barrier test structure that relies on changes in the I-V characteristic of a silicide-polysilicon interface due to dopant diffusion from the doped silicide into the polysilicon. The process flow of the test structure makes the device readily adaptable to all deposited or reacted silicides. The test structure was used to measure the diffusivity of B, As, and P in WSi₂, TiSi ₂, and CoSi₂ at temperatures from 750 to 1000°C. No measurable lateral diffusion of B in TiSi₂ was observed. In all the other cases, diffusion was several orders of magnitude higher than in silicon. These results should aid the development of process flows to prevent device degradation due to the lateral diffusion of dopants in the silicide layer