Infrared photoelasticity study of residual stresses in semiconductor structures

It is well recognized that stress and strain play an essential role in determining the structural, electrical, and optical properties of semiconductor materials, and, ultimately, the semiconductor device performance. The past four decades have witnessed the increasing effort to study the stress related problems in the microelectronics and optoelectronics technologies. This thesis is an endeavor in this subject matter and will present our research results of studying the stress problems in semiconductor materials by using infrared photoelasticity (IR PE) method.; We have studied the bonding induced stresses in silicon substrates after bonding to Mo electrodes using Al foils as the solder at high temperatures. The Si/Al/Mo structure is commonly used in the fabrication of silicon thyristors that are used for switching current in high power applications such as the generation and distribution of electricity. The experimental results are compared with the calculated results derived from a theory of interlaminar stresses in composites. The variation of the residual thermal stresses with the geometrical parameters of the structure was also studied.; The IR PE method was also employed to investigate the thin-film-edge-induced stresses problems. The stress field in silicon substrate under a silicon dioxide thin film edge, long oxide thin film stripes and long oxide window structures have been studied systematically. Dependence of the stress distribution in these structures on the geometrical parameters such as the stripe width, window width, and substrate thickness were also studied. An analytical solution for the stress distribution under a thin film edge in isotropic substrates of finite thickness and of infinite extent in the other two directions was obtained. The simulated results based on this analytical solution are consistent with IR PE experimental observation. Our analysis has revealed some new results which might lead to a better understanding of singular property of stress field under thin film edge.; In addition, the photoelastic property of GaAs crystal was also investigated. The magnitudes of the stress-optic coefficient C for (001) and (111) oriented GaAs wafers at various observation directions were determined. The anisotropic birefringence of GaAs crystal was studied.; Finally, we proposed a new PE measurement system by using a photoelastic modulator (PEM). This point-to-point modulated PE system is superior to conventional full field PE system by providing extremely higher sensitivity. The principle and theoretical analysis of this new system are described in this thesis.