Patent ID: 6080990
Filing Date: 2000-06-27
Classification: G03F

Abstract:
A position measuring apparatus comprising:a light source unit for emitting a coherent light to provide an illuminating beam;a frequency shifter unit for converting the beam from said light source unit into a beam having its frequency different from that of said illuminating beam and for radiating the converted beam;an illumination optical system for converting the illuminating beam from the light source unit into a first plane position measurement illuminating beam and the beam from the frequency shifter unit into a second plane position measurement illuminating beam, said illumination beam being used to irradiate a two-dimensional pattern on an object to be measured with respect to its position;a light-reception optical system for receiving a diffracted light from the two-dimensional pattern;a light receiving unit for receiving a combination of a higher-order diffracted light appearing on the object side from the zero-order diffracted light in the diffracted light received by the light-reception optical system with the zero-order diffracted light different in frequency from the higher-order diffracted light and also an interference light from a combination of higher-order diffracted lights appearing on the object side from the zero-order diffracted light, said higher-order diffracted light being different in frequency from one another, said light receiving unit being adapted to form a position measuring interference measurement signal used to perform the positional measurement in the plane of the object including the two-dimensional pattern; anda signal processing unit for determining the position of the object in the plane including the two-dimensional pattern in response of the phase of the position measuring interference measurement signal.