矽基氮化鎵磊晶膜殘留應力的量測

Abstract

將氮化鎵薄膜磊晶於較大尺寸的矽晶圓是有效降低發光二極體(LED)生產成本的一種方法。磊晶薄膜的殘留應力來自於薄膜與基板的晶格常數不匹配生成的本質應力與熱膨脹係數不等產生的熱應力，影響LED的發光效率及產品良率。本文結合三光束量測之晶圓曲率與拉曼散射光譜量測殘留應力，分析金屬有機化學氣相沈積法(MOCVD)磊晶之薄膜殘留應力。三光束晶圓曲率量測可供線上即時量測MOCVD磊晶之晶圓曲率主值及主軸方向，修正晶圓自轉造成曲率量測值的擾動。根據量測之氮化鋁/矽、氮化鎵/氮化鋁/矽等試片之曲率主值，以層板理論計算磊晶膜的殘留應力高於拉曼散射光譜量測值。本文修正磊晶膜與晶圓的層板模型，增設本質應力影響厚度，使推算之殘留應力吻合離線量測值。本研究顯示即時量測晶圓曲率可供計算磊晶膜殘留應力的可行性。

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.