基于高精度红外光弹法的芯片应力检测设备研制

Stress in silicon wafer will affect its electrical performance and reliability, thus semiconductor industrials need a facility for stress evaluation on their product lines. Infrared photoelasticity has potential application in this field, however, the extremely low stress-optic coefficient and thickness of silicon wafer make the measurement precision and sensitivity of infrared photoelasticity insufficient for this application. In this project, we utilize the mature technique of signal recognition and processing in electricity and improved the infrared photoelasticity. The polarization of incident beam is modulated with high frequency and serves as stress information carrier, the modulated beam was further modulated by the stress birefringence and converted to electrical signal after it pass through the specimen. Together with the modulation signal, this signal is input into lock-in amplifier and the information about the birefringence of silicon is detected with high precision. Various influence factors including the unsatisfied technical parameters of optical components in the range of infrared spectrum will be discussed and the main ones will be noted. Based on this work, an instrument with highly integration and scanning mode will be developed for stress evaluation and damage detection of silicon. .High precision stress measurement with infrared photoelasticity and corresponding facility development are not found in china at present time, thus the execution and implementation of this project will serve the semiconductor manufacturing better, which is the aim of experimental mechanics.

芯片/光伏电池板中的应力会严重影响其电性能和可靠性，半导体工业界迫切需要一种能适合生产现场使用的应力测试设备。红外光弹法具备这种潜力，但在硅材料的条纹值极低而芯片和电池板又呈薄膜化情况下，不能提供足够的测试精度和灵敏度。本项目利用电学上对电信号高精度识别和处理的成熟技术，对光弹入射光的偏振状态进行高速调制并作为载波，该光学载波经过待测试件后再被其中的应力双折射进一步调制并经光电转换后与调制电信号一起输入锁相放大器，从而将应力双折射信息高精度地检出。本项目将对该方法中的诸多影响因素，特别是红外波段光学元件的技术参数（例如偏振片较低的消光比）的影响进行分析，并在此基础上研制出一款集成化、以扫描测成像为主要工作模式的芯片应力测试和工艺缺陷检测设备。.本项目的开展将填补国内高精度红外光弹法研究和设备研制的空白，更好地服务于国内快速发展的半导体产业及相关科研需求，体现实验力学为实际工程服务的宗旨。

本项目采用光弹调制器将光的偏振状态周期性调制作为信息载体，试件的应力信息（相位差和主应力方向）附加在载体上后，再通过锁相放大器将试件的待测应力信息解调、提取，以实现高精度应力测量。本项目首先研究了调制光路不同的光学配置方式，得出了测试小应力的最佳配置，在此基础上分析了影响测试精度的关键因素。依据上述分析并借助于偏振仪搭建了测试系统的光路，采用标准波片对系统进行了标定，硅梁的纯弯曲实验证实测试误差小于4%，因此系统的可操作性和高精度测试能力得到了证实，达到了项目的预期目标。开发的测试系统除了常规的机械扫描模式（光路不动，试件动），还具备基于光学振镜的光学扫描模式（试件不动，光路动），并通过标准实验证实：在测试范围不大（15mm见方以内）的情况下，光学测试模式可以将测试效率提高4倍且不引起大的附加误差（5%）。搭建的测试系统除了应用于硅基晶圆/芯片的应力测试外，还在其它半导体材料（如InP，AsGa，AsSb）上得到了应用，证明了该系统具有较好的适应性和较广泛的应用前景。. 本项目开发的高精度应力测试系统在国内属于首创，光学扫描技术也申请了国内专利，除此以外，还发表了10篇科研论文，其中SCI论文5篇，达到了预期的考核指标。