Segregation and diffusion of impurities from doped Si1−xGex films into silicon

Abstract

The segregation and diffusion of boron from in-situ doped Si1−xGex (0.25≤x≤0.85) epitaxial films into Si at 750–850°C were investigated and compared with those properties of phosphorus diffusion from the Si1−xGex film. It was found that boron segregates in the Si1−xGex film rather than in Si, while phosphorus segregates in Si rather than in the Si1−xGex film. The segregation coefficient of boron, defined as the ratio of the active boron concentration in the Si to that in the Si1−xGex film, was about 0.4 at 850°C in the case of the Si0.75Ge0.25 film as a diffusion source, and decreased with increasing Ge fraction. It was found that the boron diffusion profiles in Si were normalized by x/t even though the segregation of boron occurred. The diffusion characteristics of boron in Si do not depend on the Ge fraction of the diffusion source, but depend on the surface boron concentration of the diffused layer, which is also the case with phosphorous diffusion from a Si1−xGex film. The high concentration diffusion characteristics of boron and phosphorus in Si were similar to those reported using conventional diffusion source.