Investigation of Photoelastic Property of Semiconductor Wafers

We developed the optical birefringence measurement by using the photoelastic modulator and the polarized laser. The equipment adopts the He-Ne infrared laser as a light source to measure the stress in semiconductor wafers. This paper explains the theory and process of the measurement of optical birefringence in wafers. The magnitude of principal stress difference as well as the directions are obtained simultaneously and quantitatively by our developed equipment. The optical birefringences of Silicon (100), (111) and Ga-As stressed specimens were measured. From the experimental results, the photoelastic constant depended on the crystalline orientation and the birefringence direction doesn’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 crystalline orientation. The preliminary result of the photoelastic property of Ga-As crystal was obtained.