Patent ID: 6400487
Filing Date: 2002-06-04
Classification: G01N,G02B

Abstract:
A focusing system for use with a substrate, comprising a discontinuous surface and a continuous surface extending in the same direction as the discontinuous surface, said system comprising:a) an objective lens through which is directed a first beam of electromagnetic radiation that is to be focused on the discontinuous surface or on an object located on the discontinuous surface; b) a second beam of electromagnetic radiation having a first wavelength, said second beam being directed through said objective lens to a focus on the discontinuous surface and reflected by said discontinuous surface back through the objective lens; c) a third beam of electromagnetic radiation having a second wavelength, said third beam being directed through said objective lens to a focus on the continuous surface and reflected by said continuous surface back through the objective lens; d) a means for separating the radiation of the first wavelength from the radiation of the second wavelength that is reflected back through the objective lens; e) a first detector for detecting the second beam reflected by the discontinuous surface back through the objective lens; f) a second detector for detecting the third beam reflected by the continuous surface back through the objective lens; g) a moving means for moving the objective lens relative to the substrate or the substrate relative to the objective lens so as to control the focus of the beams reflected back through the objective lens; and h) a controller connected to the first and second detectors and the moving means, wherein the controller operates the moving means in response to a signal from the first detector or the second detector according to the position of the second beam or the third beam on the substrate.