杂质磷对单晶硅微结构疲劳特性的影响——基于Paris公式的分析

硅基微机电系统中的单晶硅微结构常工作于循环加载状态，易发生疲劳失效。单晶硅微结构疲劳寿命的分散度较大，难以根据不同掺磷浓度试样的疲劳寿命测试数据对比分析出杂质磷对单晶硅微梁弯曲疲劳特性的影响规律，针对此问题进行研究。设计一种弯曲测试结构，该结构可同时对四根微梁进行疲劳测试;设计一种简易的弯曲测试装置，该装置在满足测试精度的同时有效地控制了成本。用各向异性湿法工艺制备6组不同掺磷浓度的试样，并在常温空气环境中对试样进行弯曲疲劳测试。基于Paris公式建立一种微结构疲劳寿命预测的概率模型，用模型对测试数据进行拟合计算，得到材料常数C和n。C随掺磷浓度降低近3个量级，而n增量较小，表明C的变化占主导。所以疲劳裂纹扩展速率有随掺磷浓度增高而降低，这可为硅基微机电系统的疲劳可靠性设计提供有价值的参考。

Analysis of the Effect of Phosphorus Doping on the Lifetime of the Single Crystal Silicon Micro-beam Based on Paris Formula

Single-crystal silicon structures in silicon-based micro-electro-mechanical systems are usually exposed to cyclic stresses, which, consequently, may fail easily because of mechanical fatigue. There’s a great gradient in the fatigue lifetime of the single crystal silicon micro-structures, thus rendering it hard to make out how the phosphorus impurities affect the fatigue properties by comparing the fatigue lifetime of specimens with different doping concentrations. This research aims at solving this problem. A specially designed micro-structure that can simultaneously experiment on four beams is presented. A simple bending test device is presented, which satisfies the requirement for test precision and is economically built. The bending fatigue life for six groups of specimens with different phosphorus doping concentrations is tested at room temperature. A kind of fatigue failure probability prediction model deducted from Paris formula is introduced. The C and n in Paris formula are obtained with the model. The C decreases approximately 3 orders, while the n increases only a little, indicating that C changes dominantly. Therefore, the defect propagation velocity decreases as the phosphorus doping concentration increases. Research on this topic therefore shows some practical significance for the reliability design of silicon-based micro-electro-mechanical systems.