Photoelastic study of stress field under thin oxide film edge in silicon and the validity of the concentrated force model

The experimental infrared photoelastic stress fringe patterns under a thin oxide film edge in silicon substrates were compared with the simulated patterns based on analytic solutions obtained according to a simple concentrated force model (CFM) (Hu S M 1978 Appl. Phys. Lett. 32 5) and an improved CFM (Wong S P et al 2001 Appl. Phys. Lett. 79 1628). The singular property of the stress field in the substrate at a thin film edge was shown to be associated with the concentrated force assumption. The results clearly demonstrated the limitation of the concentrated force assumption widely adopted in the study of thin film edge induced stresses in substrates and posed new fundamental questions on the nature of the singularity of the stress field under a thin film edge.