Alignment of a rotatable polarizer with a sample

A method of calibrating a normal incidence polarized reflectance spectrometer for measuring a diffraction grating on a substrate, said normal incidence polarized reflectance spectrometer having a rotatable polarizer and a positioning stage for positioning said diffraction grating for measurement, said method comprising:

• loading a calibration substrate with a diffraction grating onto said positioning stage;
• determining the polarizer offset angle between said axis of polarization of said rotatable polarizer and an axis of orientation of a diffraction grating on said calibration substrate;
• measuring the sample offset angle between said axis of motion of said positioning stage and the axis of orientation of said diffraction grating on said calibration substrate;
• determining the system offset angle of said normal incidence polarized reflectance spectrometer by subtracting said sample offset angle from said polarizer offset angle;
• loading a second substrate with a diffraction grating to be measured onto said positioning stage;
• measuring a second sample offset angle between said axis of motion of said positioning stage and the axis of orientation of said diffraction grating on said second substrate;
• and
• rotating said rotatable polarizer to compensate for said system offset angle and said second sample offset angle.

A method of calibrating a metrology system by aligning a transmission axis of a rotatable polarizer with an axis of orientation of any diffraction grating to be measured, said system having a positioning stage with an axis of motion, said method comprising:

• determine the system offset angle between said transmission axis of said rotatable polarizer and said axis of motion of said positioning stage;
• measuring the sample offset angle between said axis of motion of said positioning stage and the axis of orientation of a first diffraction grating on a first substrate to be measured;
• and
• rotating said rotatable polarizer by said system offset angle and said sample offset angle.

A method of calibrating a metrology device to compensate for a polarizer offset angle between the transmission axis of a rotatable polarizer and an axis of orientation of any diffraction grating to be measured, said metrology device having a positioning stage for positioning a diffraction grating for measurement, said metrology device having a system offset angle between the axis of polarization of said rotatable polarizer and an axis of motion of said positioning stage, wherein said system offset angle is adjusted to be zero, said method comprising:

• loading a substrate with a diffraction grating onto said positioning stage;
• measuring the sample offset angle between said axis of motion of said positioning stage and the axis of orientation of said diffraction grating;
• and
• rotating said rotatable polarizer to compensate for said sample offset angle thereby aligning said transmission axis of said rotatable polarizer and said axis of orientation of said diffraction grating.