Patent ID: 6242754
Filing Date: 2001-06-05
Classification: G03F

Abstract:
A position detecting apparatus provided with a beam applying device which applies two coherent illuminating beams to a diffraction grating-like grating pattern formed on a substrate to be position-detected at symmetrical angles of incidence, a photoelectric detector which receives interference light of two diffracted light beams travelling in the same direction, of a plurality of diffracted light beams created from said grating pattern, and a scanning device which scans said two illuminating beams and said grating pattern in a grating pitch direction relative to each other, said apparatus detecting the position of said substrate based on a photoelectric signal outputted from said photoelectric detector, comprising:(a) a first photoelectric detector for receiving a first interference light provided by interference between two diffracted light beams travelling in a first direction from said grating pattern;(b) a second photoelectric detector for receiving a second interference light provided by interference between two diffracted light beams travelling in a second direction differing from said first direction from said grating pattern;(c) a weight coefficient calculating unit which calculates a first weight coefficient conforming to the ratio between the amplitude value of a first photoelectric signal outputted from said first photoelectric detector during the relative scanning of said grating pattern by said scanning device and the substantially ideal amplitude value of said first photoelectric signal, and calculates a second weight coefficient conforming to the ratio between the amplitude value of a second photoelectric signal outputted from said second photoelectric detector during the relative scanning of said grating pattern by said scanning device and the substantially ideal amplitude value of said second photoelectric signal;(d) a position calculating system which calculates first position information specifying the position of said grating pattern based on the relation between a relative scanning position and a change in the level of said first photoelectric signal, and calculates second position information specifying the position of said grating pattern based on the relation between the relative scanning position and a change in the level of said second photoelectric signal, and(e) a weighted mean calculating unit which weighted-averages said first position information and said second position information by said first weight coefficient and said second weight coefficient, respectively, and determines the apparently most certain position of said grating pattern.