Diffusion of ion-implanted elements in crystalline Si was investigated (table 18). The implantation was limited to photolithographically defined areas of the wafer, and a spreading resistance technique was used to measure the 3-dimensional concentration profiles of the metal atoms after high-temperature annealing. It was found that lateral spread under the mask was greater than vertical diffusion; especially on the side opposite to the implanted diffusion source. All of the important features of the measured profiles could be explained as being a result of a kick-out diffusion mechanism. The peculiar shape of the concentration profiles was attributed to an interplay between the incoming flux of interstitial metal atoms and the outgoing flux of Si self-interstitials that were generated by the kick-out reaction. In spite of the high lateral diffusion it was noted that, by a suitable combination of implantation fluence and annealing temperature, it was possible to limit this lateral spread to within about 200, while maintaining a high metal concentration in the region under the implanted area.

Three-Dimensional Concentration Profiles of Hybrid Diffusers in Crystalline Silicon. S.Coffa, V.Privitera, F.Frisina, F.Priolo: Journal of Applied Physics, 1993, 74[1], 195-200

Table 18

Diffusivity of Au in Dislocated and Dislocation-Free Si