X-Ray Studies of Strain in Laser-Crystallized SOI Films

We have used x-ray diffraction to measure the strain perpendicular to the substrate surface in laser crystallized silicon films on oxidized silicon and fused quartz substrates. The dependence of the strain on grain orientation was determined and the influence of the scan speed, the insulating oxide thickness, and subsequent high temperature exposure was examined. Maximum strain was obtained for grains oriented with the (100) plane parallel to the substrate surface. The strain decreased with increasing angle between the surface plane and the (100) plane of the grains. The stress parallel to the surface in the variously oriented grains was calculated from the stiffness tensor, assuming an isotropic, in-plane stress, and a variation similar to the strain was found. The strain found on oxidized wafers was about half that on fused quartz. Its dependence upon the oxide thickness (0.2 µm to 1.0 µm) was not significant for scan speeds under 10 cm/sec. Similarly, the variation in strain with scan speed was very small for speeds below 10 cm/sec. Scan speeds above 50 cm/sec caused significant increases in the strain. The measured strain was reduced by high temperature anneals. A 1100°C anneal reduced the average strain by 60% and caused a clear reduction in grain imperfections (as determined by diffracted beam width). However, a 900’C anneal increased the diffracted beam widths even though the average strain was reduced by about 30%.