Autofocus system and method

Abstract

New and useful concepts for an autofocus system and method are provided. A basic concept uses fringe projection in an autofocus system and method. A further aspect provides spatial filtering concepts for the fringe projection concept. In yet another aspect, the fringe projection autofocus system and method is provided with temporal phase shifting using no moving parts. In a still further aspect, the fringe projection autofocus system and method is provided with unambiguous height measurement concepts.

What is claimed is: 
     
         1 . A surface position detecting apparatus comprising:
 a projection system including
 a light sending system configured 
   a) to emit (i) a first light in a first direction towards a surface of a substrate, and (ii) a second light in a second direction towards the surface of the substrate, the first and second direction being different from one another at different propagation direction, each of the first and second lights being coherent, and   b) to project a fringe pattern with the first light and the second light at a two-dimensional (2D) area of the surface of the substrate, the fringe pattern including an interference fringe pattern by the first and second light at two-dimensional area on the surface of the substrate;   a light receiving system including a detection unit with a detection surface, the detection surface being optically-conjugate to the 2D area of the surface of the substrate and configured to receive an image of the interference fringe pattern formed at said 2D area and to receive light reflected by the surface of the substrate, the detection unit configured to generate an output signal in response to receiving light reflected by the surface of the substrate; and   a controller system operably cooperated with the detection unit and configured to determine a position of the surface of the substrate based on the output signal.