Development of Stress Measurement of Silicon Single Crystal by Infrared Polarized Laser

本课题研究了硅单晶光学双折射测量的理论和方法。我们研制了一种利用激光光弹方法测量应力引起的微小双折射的高灵敏度光学仪器。该装置采用He-Ne红外激光器作为光源，测量硅单晶中的应力。我们研制的测量系统可以同时定量地获得主应力差的大小和方向，并通过对多个晶体取向施加拉伸载荷来测量硅片样品的光学双折射。结果发现，光弹常数与晶体取向有关，双折射方向与主应力方向不一致。通过对硅单晶的应力应变分析，发现双折射方向与主应变方向一致，主应变差与延迟的关系与晶体取向无关。这些结果表明，布鲁斯特定律(光延迟与主应力差之间的线性关系)需要修正。

In this project, thetheory and method of the measurement of optical birefringence in silicon single crystal were investigated. We have developed the potical apparatus which possess high sensitivity to measure small birefringence typically produced by stress using the method of laser photoelasticity. The equipment adopts the He-Ne infrared laser as a light source to measure the stress in silicon single crystal. The magnitude of principal stress difference as well as the directions were obtained simultaneously and quantitatively by our developed measuring system.The optical birefringences were measured for Si-wafer specimens by applying tensile loads to several crystal orientations. Consequently, it was discovered that the photoelastic constant depended on the crystalline orientation and the birefringence direction dosen't coincide with the principal stress direction. By the stress strain analysis of silicon single crystal, it was found that the birefringence direction coincides with the principal strain direction and the relation between the principal strain difference and the retardation was independent of crystal orientation. These results show that Brewster's Law (linear relation between optical retardation and principal stress difference)should be modified.