CRACK-PROPAGATION AND MECHANICAL FRACTURE IN GAAS-ON-SI

This paper describes the study of crack propagation and mechanical fracture in GaAs-on-Si, which are closely related with the residual stress. The crack propagation is often observed as the GaAs thickness exceeds about 3-mu-m, and the upper limit of the number of cracks increases linearly as the GaAs thickness increases. The cracks propagate from the surface defects, where stress ten times larger than the original residual thermal stress in GaAs-on-Si exists. The mechanical fracture strength (zeta) of the GaAs-on-Si wafer decreases as the GaAs thickness increases, and becomes equal to that of the bulk GaAs at the thickness of about 3-mu-m due to the concentrated stress near the cracks. The back coating of SiO2 is effective for stress relaxation, and the preliminary results of about 3 x 10(8) dyn/cm2 of stress relaxation is obtained.