SINGLE LASER BRIGHT FIELD AND DARK FIELD SYSTEM FOR DETECTING ANOMALIES OF A SAMPLE

摘要

A single laser (30) is used to provide light for both dark (80) and bright field (60) detection. The laser beam is split into two beams by a Wollaston prism (40) and both beams are directed towards a sample (12) to be inspected to illuminate two areas (16, 18) of the sample. The light reflected by or transmitted through the sample at the two spots is then combined by the same or a different Wollaston prism and the phase shift caused by any anomaly of a sample is detected as a phase shift between the two beams by a bright field detector. Light scattered by the sample at the two spots is detected by a dark field detector. A halfwave plate (36) is used to orient the polarization plane of light from the laser incident on the Wollaston prism so that one of the two beams (52, 54) incident on the sample has a much higher intensity than the other and so that the sensitivity and the detection operation of dark field is not altered by the presence of two illuminated spots on the sample. A transparent dielectric at a suitable angle to the incident beam and the reflected or transmitted beam may be used to enhance bright field detection.