Takigawa Ryo, Tomimatsu Toru, Higurashi Eiji, Asano Tanemasa
Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan.
Graduate School of Science, Tohoku University, 6-3 Aramaki Aza Aoba, Aobaku, Sendai 980-8578, Japan.
Micromachines (Basel). 2019 Feb 18;10(2):136. doi: 10.3390/mi10020136.
This paper focuses on the residual stress in a lithium niobate (LN) film layer of a LN-on-insulator (LNOI)/Si hybrid wafer. This stress originates from a large mismatch between the thermal expansion coefficients of the layers. A modified surface-activated bonding method achieved fabrication of a thin-film LNOI/Si hybrid wafer. This low-temperature bonding method at 100 °C showed a strong bond between the LN and SiO₂ layers, which is sufficient to withstand the wafer thinning to a LN thickness of approximately 5 μm using conventional mechanical polishing. Using micro-Raman spectroscopy, the residual stress in the bonded LN film in this trilayered (LN/SiO₂/Si) structure was investigated. The measured residual tensile stress in the LN film layer was approximately 155 MPa, which was similar to the value calculated by stress analysis. This study will be useful for the development of various hetero-integrated LN micro-devices, including silicon-based, LNOI-integrated photonic devices.
本文聚焦于绝缘体上铌酸锂（LNOI）/硅混合晶圆中铌酸锂（LN）薄膜层的残余应力。这种应力源于各层热膨胀系数之间的巨大差异。一种改进的表面活化键合方法实现了薄膜LNOI/硅混合晶圆的制造。这种在100°C的低温键合方法显示出LN层与SiO₂层之间有很强的键合，足以承受使用传统机械抛光将晶圆减薄至LN厚度约为5μm的过程。利用显微拉曼光谱，研究了这种三层结构（LN/SiO₂/硅）中键合的LN薄膜的残余应力。在LN薄膜层中测得的残余拉应力约为155MPa，这与通过应力分析计算得到的值相似。本研究将有助于开发各种异质集成的LN微器件，包括硅基LNOI集成光子器件。
