新型硅基GaN外延材料的热应力模拟

The simulation of thermal stress in GaN epilayer on novel silicon-based substrates

采用有限元方法，通过ANSYS软件模拟了体硅衬底上和SOI衬底上生长的GaN外延膜从1100℃的生长温度降到20℃的热应力变化情况。模拟结果表明SOI衬底作为一种柔性衬底，能有效减少异质外延的晶格失配，但是单从热失配的角度，由于引入了热膨胀系数（CET）更小的埋层SiO2，SOI衬底会使得外延层热应力略有增大。为了降低外延层中的热应力，我们结合微机电系统（MEMS）的制造工艺，用深反应离子刻蚀（DRIE）的方法，借助于SOI材料自停止刻蚀的优势，将衬底硅和埋氧去除，使得SOI的超薄顶层硅部分悬空，形成一种新型的SOI衬底。模拟结果表明，这种新型SOI衬底可以将GaN外延层中的热应力降低20％左右。

The thermal stress in GaN epilayer on bulk silicon and silicon-on-insulator（SOI） substrates caused by the co-efficient of thermal-expansion（CET） mismatch of the GaN epilayer and silicon, was calculated by the finite element analysis method through ANSYS software. When temperature decreased from 1100～20℃ the 3-D simulation results showed that the SOI substrate can produce a little more thermal stress in GaN layer compared with bulk silicon substrate, because of the buried SiO2 layer, which would induce larger CET mismatch in the multi-layer system. A novel shape of SOI substrate with part of the substrate Si and buried SiO2 being etched using Micro electro-mechanical system（MEMS） fabrication process had been realized, and simulation result showed its advantage of reducing nearly 20% of the thermal stress in GaN epilayer effectively.