Patent ID: 7723657
Filing Date: 2010-05-25
Classification: G01B,G01J,G01N,G02B

Abstract:
1. A focus sensor for providing focus detection signals that depend on the location of a workpiece surface within a focus detection range along a direction approximately parallel to the optical axis of an objective lens, the focus sensor comprising: an illumination source; a collimation lens configured to input radiation from the illumination source and output an illumination beam having a fixed degree of collimation; an objective lens configured to input the illumination beam and to focus the illumination beam at a nominal focal plane along an optical axis of the focus sensor and to receive and transmit a reflected beam reflected from a workpiece surface located along the optical axis; a focus detector arrangement positioned along the optical axis to receive light from the reflected beam that is transmitted by the objective lens; and a first beamsplitting surface positioned along the illumination beam between the objective lens and the collimation lens, and along the reflected beam between the objective lens and the dual range focus detector arrangement, wherein the focus detector arrangement is a dual range focus detector arrangement comprising: