Patent ID: 6184992
Filing Date: 2001-02-06
Classification: G01N

Abstract:
An apparatus that can measure a space between a first surface and a second surface, comprising:a loader that can move the second surface adjacent to the first surface;a light source that reflects a light beam from the first and second surfaces;a birefringent element that splits the reflected light beam into an ordinary beam and an extraordinary beam which have a phase relative to each other;a mechanism which can vary the phase between the ordinary and the extraordinary beams;a photodetector which detects the interference between the ordinary and the extraordinary beams at a pixel location;a controller that is coupled to said photodetector and which can compute the space from a phase value that is determined from data collected when said mechanism varies the phase between the ordinary and extraordinary beams, and a ratio between a first modulation amplitude detected from light reflected from the first and second surfaces and a second modulation amplitude detected from light reflected from the first surface when the second surface is not adjacent to the first surface, the first modulation amplitude and the second modulation amplitude being detected at the pixel location.