Focused beam spectroscopic ellipsometry method and system

Abstract

A method and system for spectroscopic ellipsometry employing reflective optics to measure a small region of a sample by reflecting radiation (preferably broadband UV, visible, and near infrared radiation) from the region. The system preferably has an autofocus assembly and a processor programmed to determine from the measurements the thickness and/or complex refractive index of a thin film on the sample. Preferably, only reflective optics are employed along the optical path between the polarizer and analyzer, a sample beam reflects with low incidence angle from each component of the reflective optics, the beam is reflectively focused to a small, compact spot on the sample at a range of high incidence angles, and an incidence angle selection element is provided for selecting for measurement only radiation reflected from the sample at a single, selected angle (or narrow range of angles). The focusing mirror preferably has an elliptical shape to reduce off-axis aberrations in the focused beam. Some embodiments include both a spectrophotometer and an ellipsometer integrated together as a single instrument. In such instrument, the spectrophotometer and ellipsometer share a radiation source, and radiation from the source can be focused by either the spectrophotometer or the ellipsometer to the same focal point on a sample. Preferred embodiments of the ellipsometer employ a rotating, minimal-length Rochon prism as a polarizer, and include a spectrometer with an intensified photodiode array to measure reflected radiation from the sample, and a reference channel (in addition to a sample channel which detects radiation reflected from the sample).

1 . A spectroscopic ellipsometer for measuring a sample, including: 
 a source which emits broadband radiation;    a polarizer for polarizing the broadband radiation, thereby producing a sample beam;    an analyzer positioned for receiving radiation of the sample beam that has reflected from the sample, wherein the analyzer produces an output beam in response to said radiation;    detector means for detecting the output beam; and    all-reflective optics between the polarizer and the analyzer, wherein the sample beam reflects with low incidence angle from each component of the all-reflective optics, and wherein the all-reflective optics reflectively focuses the sample beam to a small spot on the sample.    
   
   
       2 - 52 . (canceled)