Patent ID: 9046474
Filing Date: 2015-06-02
Classification: G01N

Abstract:
1. An ellipsometry system, comprising: a support mechanism configured for supporting a wafer; an illumination source configured for delivering an incident beam towards the wafer, wherein the incident beam reflects off the wafer thereby forming a reflected beam, the incident beam and the reflected beam define a plane of incidence; an analyzer configured for polarizing the reflected beam, the analyzer having a polarization direction rotatable between two predetermined, discrete angular positions, the two angular positions being opposite with respect to the plane of incidence, wherein a first angular position corresponds to the plane of incidence offset by an acute offset angle α and a second angular position corresponds to the plane of incidence offset by approximately −α, and wherein the second angular position is calibrated by: generating a plurality of candidate angular positions each in proximity to an angular position of the plane of incidence offset by −α, and selecting one of the plurality of candidate angular positions as the second angular position, wherein the second angular position maximizes symmetry of residual errors with respect to the first angular position; a detector configured for collecting a set of spectrum data based on the reflected beam passing through the analyzer, each spectrum data of the set of spectrum data being collected when the polarization direction of the analyzer is pointing to one of the two predetermined, discrete angular positions; and a processor module configured for performing simultaneous regression on the set of spectrum data collected.