Stress Measurements in Silicon Microstructures

Raman spectroscopy is used as a noncontact probe of stress with high spatial resolution in micromachined silicon structures. The motivation for this work is that reliability or cycle life can be substantially increased by understanding the distribution of stress, including residual stress. High stresses induced by workmanship shortcomings or design constraints may be addressed by Raman measurements. In microelectronics, stress is known to play a significant role in interconnects, which limits reliability, life, and ultimately cost of many circuits. We wish to demonstrate the utility of Raman spectroscopy as a tool for the development and design of silicon microstructures. The equations for a general two-dimensional stress field are discussed. Calibration studies using macromechanical fixtures for single crystal silicon specimens under two-dimensional stress field are presented. Our measurements show good agreement with the theoretical values and thus validate the approach taken. Stress maps of conventionally fabricated test structures, laser-machined structures, and polysilicon structures are presented. --Original contains color plates: All DTIC reproductions will be in black and white.