Imaging ellipsometer for areal layer thickness measurement of a sample and method using an imaging ellipsometer

An imaging ellipsometer for areal layer thickness measurement of a sample, the imaging ellipsometer comprising:

• a monochromatic light source configured to shine light onto the sample,
• a polarizer configured to linearly polarize the light emitted by the light source,
• an angle-selective lens, wherein the light reflected by the sample passes through the angle-selective lens, and
• a polarization camera, onto which the light reflected by the sample strikes,
• wherein the polarization camera having polarization filters in 0°, 45°, 90° and 135° orientations and being adapted to polarize the light emitted from the light source into linear polarization orientations and to detect and measure the light intensities thereof,
• wherein a quarter-wave plate is arranged between the sample and the polarization camera to change the polarization of the light, with a principal optical axis of the quarter-wave plate that is rotated by +/−45° with respect to a light plane, which is configured to convert certain linear polarization orientations of the light into circular polarization orientations and the ellipsometer is adapted to calculate a layer-thickness-dependent ratio of the detected light intensities using equations
• RZ
• =
• (
• IR
• -
• IL
• )
• /
• (
• IR
• +
• IL
• )
• ⁢
• and
• ⁢
• R
• ⁢
• 45
• =
• (
• I
• ⁢
• 45
• -
• I
• -
• 45
• )
• /
• (
• I
• ⁢
• 45
• +
• I
• -
• 45
• )
• ,
• where IR is an intensity of light in the right-hand circular polarization orientation, IL is an intensity of light in the left-hand circular polarization orientation, I45 is an intensity of light in the linear 45° polarization orientation, and I−45 is an intensity of light in the linear 135° polarization orientation.

A method using an imaging ellipsometer with a monochromatic light source, a polarizer, an angle-selective lens, and a polarization camera for areal layer thickness measurement of a sample, comprising the steps of:

• illuminating the sample with the aid of light emitted from the light source and subsequently linearly polarized by the polarizer;
• detecting the light reflected by the sample and imaging the sample onto a sensor plane of the polarization camera through the angle-selective lens;
• linearly polarizing the detected light in linear polarization orientations of 0°, 45°, 90° and 135° by segmented polarization filters in the polarization camera;
• converting the light polarized by the polarizer and the sample with the aid of a quarter-wave plate, whose main optical axis is rotated by +/−45° with respect to a light plane, wherein, instead of the intensities of the light in the polarization orientations 0° and 90°, an intensity of a right-hand circular polarization orientation and an intensity of a left-hand circular polarization orientation are measured by the polarization camera;
• measuring the intensities of the linearly polarized light in the respective polarization orientations by the polarization camera;
• calculating at least one layer-thickness-dependent ratio from the measured intensities of the various polarization orientations by means of equations
• RZ
• =
• (
• IR
• -
• IL
• )
• /
• (
• IR
• +
• IL
• )
• ⁢
• and
• ⁢
• R
• ⁢
• 45
• =
• (
• I
• ⁢
• 45
• -
• I
• -
• 45
• )
• /
• (
• I
• ⁢
• 45
• +
• I
• -
• 45
• )
• ,
• where IR is an intensity of light in the right-hand circular polarization orientation, IL is an intensity of light in the left-hand circular polarization orientation, I45 is an intensity of light in the linear 45° polarization orientation, and I−45 is an intensity of light in the linear 135° polarization orientation;
• and
• evaluating said at least one ratio and calculating a local layer thickness of the sample.