光电极值法结合外差干涉法监控膜厚的研究

Study on film monitoring based on the photoelectric extreme value method combined with heterodyne interferometry

光电极值法是光学薄膜厚度监测的常用方法,该方法在镀膜前引用块状材料的折射率设计膜系。而在实际镀制过程中,用于镀制光学薄膜的材料折射率会发生改变,从而给膜厚的监控带来误差。为了避免折射率变化的影响,采用外差干涉法测量折射率,将实际测得的薄膜折射率应用光电极值法监控薄膜的设计,从而减少了因材料折射率的变化引起的误差。以750nm截止滤光片的镀制为被测对象进行了实验,对制备的滤光片透射率光谱曲线进行了比较。结果表明,实际的透射率曲线与设计的透射率曲线吻合较好,两次实验曲线平均吻合度均在98%以上,系统稳定性很好,从而说明结合外差干涉法的光电极值监控法可以很好地克服折射率变化引起的误差。

Photoelectric extreme value method is a common method to monitor the optical film. The index of a bulk material is applied on the design of film before plating. However, the index of the optical film will change during the ac- tual deposition process, which leads the error to the monitoring of an optical film. In order to avoid the influence of refractive index, a heterodyne interferometry method is used to measure refractive index and then the measured refractive index is considered in the design of the film, which can reduce the error caused by the changes of refractive index. A filter with cutoff wavelength 750 nm is used as the object and the transmittance spectra are compared using photoelectric ex- treme value method and the photoelectric extreme value method combined with heterodyne interferometry. The results show that the actual transmittance curve is in good agreement with design and the agreement is more than 98% on aver- age. The stability is satisfied, which verifies that photoelectric extreme value method combined with heterodyne interfer- ometry can overcome the error of the changes of refractive index very well.