Stress and Curvature of Periodic Trench Structures on Sapphire Substrate with GaN Film

Due to the different thermal expansion coefficients in two materials, wafer curvature and residual stress are formed during the growth of an epi-GaN layer on Sapphire substrates. Using the finite element method to describe the realistic shape of wafer curvature on epi-GaN wafers, we examine the influence which different thickness and thermal expansion coefficients in the top epi-GaN layer have on wafer curvature reduction. In addition a new process to reduce wafer curvature and to relax residual stress is demonstrated. With an additional laser treatment on a sample surface after the growth of the top epi-GaN layer on a Sapphire substrate has taken place, the wafer curvature can be reduced from the original ∼ 45 μm to ∼ 37 μm in 2 inch wafer with an optimized surface structure design.