测量薄膜厚度的数字叠栅技术

Digital Moiré Technique for Thin Film Thickness Measurement

现代干涉测试的核心是用合理的算法处理干涉图而获得所需的面形及参数。由于常见的相移法要通过移相器有规律地移动采集多幅干涉图并数字化后求取波面的相位分布,这样必然引入由于移相器的线性及非线性误差所带来的计算误差,因此需要事先对移相器进行标定。采用了数字叠栅方法,利用一幅静态干涉图与一个正弦光栅的4幅光强分布图叠加,从而实现相移式动态干涉测试的效果,借助于相移法处理干涉图原理,可获得波面相位分布,从而实现对薄膜厚度的测量。由于正弦光栅的初始相位是由计算机产生的,所给出的相位移动不含任何移相误差,因此可提高测量的精度。

The core of the modern interferometry is to obtain the necessary surface shape and parameters by processing the interferogram using the reasonable algorithm. The method of the common phase shifting interferometry is to obtain the wave surface by digitalizing the multiple interferogram which is gained by the ordered translation motion of the phase shifter, which will introduce a calculation error produced by linear and nonlinear error of phase shifter. Therefore, the phase shifter must be calibrated first. The digital Moir; technique is used, which is to separately overlay a static interferogram with four surfaces of intensity distribution of the sinusoidal grating with different light distribution, achieving the effect of dynamic test based on the phase shifting interferometry, then to obtain the phase distribution based on the principle of the phase shifting interferometry, and thus to realize the measurement of thin film thickness. The initial phase of the sinusoidal grating is generated by the computer, so this phase shift has no error on phase shift, which makes the accuracy of measurement improved.