基于V/F变换下的数字相敏检测监控光学膜厚

A digital phase sensitive detection based on V/F conversion for monitor system of optic thin film

本文采用基于电压-频率变换(V/F)的数字相敏检测技术应用于光学监控信号检测,得到的被检测信号的幅度,即光学监控信号波形。而且针对光学监控系统中被检测信号特点,从理论分析角度说明了本方案抑制被检测信号低次谐波和白噪声的性能.仿真分析中针对加入了2,3,4次谐波和零均值随机白噪声,信噪比为20dB,频率为166Hz的被检测信号,利用本方案检测出光学监控信号反射率最大误差<0.2%。分别利用本方案检测出的光学监控信号和理想监控信号读取反射率极值点对应薄膜厚度,对比可知采用本方案监控膜厚理论误差<2nm。

The amplitude of the detected signal in the optic detection system, which is also the signal of optic detection, has been obtained by a digital phase sensitive detection based on V/F conversion. The performance of restraining low - order harmonious wave and white noise is explained theoretically. Inemulational analysis, the detected signal（ SNR = 20dB） ,which mix with 2,3,4 - order harmonious wave and random white noise, and the frequency of signal is 166Hz. As a result, the most error of reflectivity of optic detective signal obtained by this scheme is less than 0.2% .The ideal optic detective signal and the one obtained by this scheme are used to distinguish the peak coordinates respectively. Finally, the calculated error of thickness in this scheme was less than 2nm.