Optimized surface structure by laser treatment for the relaxation of residual stress in bent GaN film

• Published in: Journal of physics. D, Applied physics Vol. 46; no. 6; pp. 65104 - 1-5
• Main Authors: Chen, C-H, Liao, M-H, Chang, L-C, Kao, S-C, Yang, C, Yu, M-Y, Liu, G-H
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 13.02.2013; Institute of Physics
• Subjects: Bending; Biological and medical applications; Computer simulation; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Gallium nitrides; Industrial applications; Lasers; Mathematical models; Optical materials; Optics; Other nonlinear optical materials; photorefractive and semiconductor materials; Physics; Residual stress; Sapphire; Wafers; Finite element method; Gallium Nitrides; Laser assisted processing; Thermal expansion coefficient; Theoretical study; Binary compounds; Optical materials; Residual stresses; Laser beam applications; Layer thickness; III-V semiconductors; Surface structure
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/46/6/065104

Serious wafer bending and residual stress are formed during the growth of the epi-GaN layer on a sapphire substrate due to the difference of the thermal expansion coefficients (TECs) in these two different materials. Using the theoretical analysis and a simulation model with the finite element method to describe the realistic shape for the wafer bending of epi-GaN wafers, we examine the influence of different thicknesses and TECs in the top epi-GaN layer for wafer bending reduction. Furthermore, wafer bending is also found to be worse when the process temperature and the wafer size become higher and larger. Although commercial patterned sapphire substrate can partially solve this issue, the quality of the epi-GaN layer, grown on this patterned substrate, will be impacted. In this work, the new process to reduce the wafer bending and relax the residual stress is proposed. With an additional laser treatment on the sample surface after the growth of the top epi-GaN layer on the sapphire substrate, a slight crack can provide the extra space for the relaxation of the residual stress and will not influence the GaN quality. The wafer bending can be reduced to ∼37 µm from the original ∼45 µm in the 2 inch wafer with optimized surface structure design by this treatment.