PRECIPITATION AND RELAXATION IN STRAINED SI1-YCY SI HETEROSTRUCTURES/

We have studied the thermal stability of Si1-yCy/Si (y=0.007 and 0.014 ) heterostructures formed by solid phase epitaxial regrowth of C impla nted layers. The loss of substitutional C was monitored over a tempera ture range of 810-925 degrees C using Fourier transform infrared absor bance spectroscopy. Concurrent strain measurements were performed usin g rocking curve x-ray diffraction to correlate : strain relaxation wit h the loss of substitutional C from the lattice. Loss of C from the la ttice was initiated immediately without an incubation period, indicati ve of a low barrier to C clustering. The activation energy as calculat ed from a time to 50% completion analysis (3.3+/-5 eV) is near the act ivation energy for the diffusion of C in Si. Over the entire temperatu re range studied, annealing to complete loss of substitutional C resul ted in the precipitation of C into beta-SiC. The precipitates are near ly spherical with diameters of 2-4 nm. These precipitates have the sam e crystallographic orientation as the Si matrix but the interfaces bet ween the Si and beta-SiC precipitates are incoherent. During the initi al stages of precipitation, however, C-rich clusters form which mainta in coherency with the Si matrix so the biaxial strain in the heterostr ucture is partially retained.