Effect Of Prior Stress-Relief On The Gliding Of Indentation Dislocations On Silicon Wafers

The mechanical strengths of silicon wafers are crucial for the manufacturing yield of integrated circuits (ICs), which have received intensive attention over the years. With reducing the feature size of ICs, the mechanical strengths of silicon wafers become more significant. Actually, the gliding of indentation dislocations on single-crystalline silicon wafers at a given temperature reflects the mechanical strengths of silicon wafers. Since the gliding of indentation dislocations is driven by the residual stress around the indentation, the investigation on the correlation between the residual stress and dislocation gliding is of significance. In this paper, we first use micro-Raman microscopy to characterize the relief of stress around the indentation due to the annealling at 300 or 500 degrees C. Then the effect of such a relief-stress on the gliding of indentation dislocations at 700-900 degrees C is investigated. In the case without the prior stress-relief, the indentation dislocations glide to the maximum distance after 2 h annealling at 700-900 degrees C. With the prior stress-relief due to the annealling at 300 or 500 degrees C, the indentation dislocations can still glide to the maximum distance after 2 h annealling at 900 degrees C, however the gliding velocity significantly decreases and the gliding distance is remarkably reduced after 2 h annealling at 700 or 800 degrees C. Such a reduction of gliding distance is most significant in the case of 700 degrees C annealling following the stress-relief with the 500 degrees C/2 h annealling. Despite the prior stress-relief, as long as the annealing time at 700 or 800 degrees C is sufficiently extended, the indentation dislocations can glide to the maximum distance. In view of the above results, it is believed that the maximum gliding distance of indentation dislocations at a given temperature is independent of the values of residual stress around the indentation provided that the residual stresses are larger than the critical stress for driving the dislocation movement. Nevertheless, the annealing time for achieving the maximum gliding distance at a given temperature should be remarkably extended as the residual stresses around the indentation are relieved.