Measurement of Residual Stress in Gallium Nitride Epitaxial Films on Silicon
|關鍵字:||矽基氮化鎵;殘留應力;曲率量測;拉曼光譜;層板理論;GaN-on-silicon;residual stress;curvature measurement;Raman spectroscopy;laminate theory|
Depositing epitaxial GaN films on large-size silicon wafers is an effective method to reduce the costs of light-emitting diode (LED) production. In the epitaxial process, residual stresses of deposited films result from the intrinsic stress and thermal stress. The former is caused by the lattice mismatch between the substrate and epitaxial layers. The latter is yielded due to a difference between the coefficients of thermal expansion. Both influence the LED luminous efficiency and product yield. This thesis analyzes residual stress in epitaxial films produced by the metal organic chemical vapor deposition (MOCVD). Both three-beam curvature measurement technology and Raman spectroscopy were applied to determine residual stresses of the GaN-on-silicon thin film structure. The principal curvatures of wafers and their directions during MOCVD process can be real-time measured by the three-beam technique. The curvature perturbation caused by wafer rotation can be reduced. For AlN/Si and GaN/AlN/Si specimens, it was found that the residual stress calculated by laminate theory is higher than that measured by Raman spectroscopy. If an influenced layer of intrinsic stress is considered in laminate theory, the calculated residual stresses in epitaxial layers are in very good agreement with the measured values. This work indicates a feasibility to determine the residual stress in epitaxial film through a real-time curvature measurement.