Patent ID: 7136172

Claim:
A method of characterizing a sample utilizing a beam of electromagnetic radiation, comprising the steps of: a) providing an alignment sample, a source of electromagnetic radiation and data detector; b) orienting the alignment sample such that a beam of electromagnetic radiation produced by said source is caused to obliquely impinge thereupon, reflect therefrom and enter the data detector at a base angle-of-incidence and plane-of-incidence; c) causing a portion of the beam of electromagnetic radiation reflected from the alignment sample to enter a multi-element alignment detector, and positioning said multi-element alignment detector so that signals are developed by each of its elements; d) removing said alignment sample and placing a test sample in its place; e) obtaining data from said test sample by causing electromagnetic radiation from said source to reflect from said test sample and enter said data detector; f) characterizing said test sample by analyzing the data obtained from the data detector in step e, in combination with signals from the elements of the multi-element alignment detector which identify differences from signals determined in step c, said difference signals serving to provide information to compensate offsets in intended and actually realized angle-of-incidence and plane-of-incidence of the test sample as compared to the base angle-of-incidence and plane-of-incidence of the alignment sample in step b.