Precipitation and relaxation in strained Si1−yCy/Si heterostructures

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Abstract
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 implanted layers. The loss of substitutional C was monitored over a temperature range of 810–925 °C using Fourier transform infrared absorbance spectroscopy. Concurrent strain measurements were performed using rocking curve x‐ray diffraction to correlate strain relaxation with the loss of substitutional C from the lattice. Loss of C from the lattice was initiated immediately without an incubation period, indicative of a low barrier to C clustering. The activation energy as calculated from a time to 50% completion analysis (3.3±5 eV) is near the activation energy for the diffusion of C in Si. Over the entire temperature range studied, annealing to complete loss of substitutional C resulted in the precipitation of C into β‐SiC. The precipitates are nearly spherical with diameters of 2–4 nm. These precipitates have the same crystallographic orientation as the Si matrix but the interfaces between the Si and β‐SiC precipitates are incoherent. During the initial stages of precipitation, however, C‐rich clusters form which maintain coherency with the Si matrix so the biaxial strain in the heterostructure is partially retained.