Imaging ellipsometer and method of measuring an overlay error using the same

A method of measuring an alignment error, the method comprising:

• positioning a polarizer on an optical path of incident light to be incident on a sample surface, the polarizer being rotatable by a first angle to adjusting a polarization direction of the incident light;
• positioning an analyzer on an optical path of light reflected from the sample surface, the analyzer being rotatable by a second angle to adjust a polarization direction of the reflected light;
• providing a reference wafer having a known polarization transmittance at a surface as a sample;
• obtaining an image signal from the reference wafer at set of angles including a first combination of the first angle of the polarizer and the second angle of the analyzer;
• calculating polarization transmittance of optical equipment including the polarizer and the analyzer from the image signal of the reference wafer;
• providing a measurement target wafer having a structure to be measured on a surface thereof as the sample;
• obtaining an image signal from the measurement target wafer at a set of angles including a second combination of the first angle of the polarizer and the second angle of the analyzer;
• and
• generating at least a portion of a Mueller matrix from the image signal of the measurement target wafer and the polarization transmittance of optical equipment including the polarizer and the analyzer.