寄生虚反射对外差干涉椭偏测量的影响

Influence of parasitic ghost reflection on measurement in a heterodyne interferometric ellipsometer

研究了一种采用横向塞曼激光器并且没有任何运动部件的外差干涉椭偏测量系统。由非理想的激光源、偏振分光镜等器件所产生的非线性误差,是影响纳米测量精度的主要因素。采用琼斯矢量法,分析并建立了光学系统寄生虚反射所引入的误差模型,讨论了虚反射对误差漂移的影响。在不考虑其它误差因素的前提下,同一光路内部产生的同频率虚反射波对测量结果没有影响;而不同频率的参考光束与测量光束之间的交叉虚反射所产生的膜厚测量误差为亚纳米量级。讨论了消除和抑制虚反射误差的方法。

A heterodyne interferometric ellipsometer using a transverse Zeeman laser, with no moving parts, is investigat ed. The nonlinear error limits t accuracy at the nanometers level, which mainly results from the imperfections of laser sources and polarization optical components used. With Jones vector method, the model of the error produced by the parasitic ghost reflection is built; the influence of ghost reflection on error drift is discussed. The ghost reflection which arises from the ,same path with the same frequency as the original light beam has no contributes to the ellipsometric parameters＇ error; however whose arises from the crass-linking between the reference arm and the measurement arm with alternative frequency really produces an error at sub-nanometers of films thickness measurement, The methods of decreasing the influence of ghost reflection are discussed.