Patent ID: 7215431
Filing Date: 2007-05-08
Classification: G01B,G01N

Abstract:
1. An apparatus for evaluating a parameter of a sample, comprising: a radiation source generating a probe beam; an optical element focusing the probe beam substantially normal to a surface of the sample such that various rays within the focused probe beam create a spread of angles of incidence; an immersion fluid between the optical element and the sample for increasing the spread of angles of incidence; a retarding element capable of retarding a phase of one polarization state in the probe beam with respect to the phase of another polarization state in the probe beam; a polarizing element capable of creating interference between the two polarization states in the probe beam after the probe beam has been reflected from the surface of the sample; a detector for measuring the intensity of the reflected probe beam along two orthogonal axes after the probe beam has passed through the retarding and polarizing elements, the detector generating an output that integrates the intensity of various rays having different angles of incidence, the output having two components corresponding to said two orthogonal axes; and a processor for determining a parameter of the sample based on the intensity measurements, said parameter being selected from the group consisting of material composition, thickness, index of refraction, absorption, stress, feature width, critical dimension, profile dimension, and surface roughness.