应力预释放对单晶硅片的压痕位错滑移的影响

单晶硅片的压痕位错在一定温度下的滑移距离反映了硅片的机械强度. 压痕位错的滑移是受压痕的残余应力驱动的, 因此研究残余应力与位错滑移之间的关系具有重要的意义. 本文首先采用共聚焦显微拉曼术研究了单晶硅片压痕的残余应力经过300或500 ℃ 热处理后的预释放, 然后研究了上述应力预释放对压痕位错在后续较高温度(700–900 ℃)热处理过程中滑移的影响. 在未经应力预释放的情况下, 压痕位错在700–900 ℃热处理2 h后即可滑移至最大距离. 当经过上述预应力释放后, 位错在900 ℃热处理2 h后仍能达到上述最大距离, 但位错滑移速度明显降低; 而在700和800 ℃时热处理2 h后的滑移距离变小, 其减小幅度在预热处理温度为500 ℃时更为显著. 然而, 进一步的研究表明: 即使经过预应力释放, 只要足够地延长700和800 ℃ 的热处理时间, 位错滑移的最大距离几乎与未经预应力释放情形时的一样. 根据以上结果, 可以认为在压痕的残余应力大于位错在某一温度滑移所需临界应力的前提下, 压痕位错在某一温度滑移的最大距离与应力大小无关, 不过达到最大距离所需的时间随应力的减小而显著增长.

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 ℃. Then the effect of such a relief-stress on the gliding of indentation dislocations at 700-900 ℃ 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 ℃. With the prior stress-relief due to the annealling at 300 or 500 ℃, the indentation dislocations can still glide to the maximum distance after 2 h annealling at 900 ℃, however the gliding velocity significantly decreases and the gliding distance is remarkably reduced after 2 h annealling at 700 or 800 ℃. Such a reduction of gliding distance is most significant in the case of 700 ℃ annealling following the stress-relief with the 500 ℃/2 h annealling. Despite the prior stress-relief, as long as the annealing time at 700 or 800 ℃ 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.