Patent Number: 6,166,808

Title: Optical height meter, surface-inspection device provided with such a height meter, and lithographic apparatus provided with the inspection device

Abstract: A height meter for measuring the height of a first surface of a transparent object is described, which height meter comprises a radiation source for supplying a converging measuring beam whose chief ray extends at an angle to the normal on the surface, and a radiation-sensitive detection unit for detecting a radiation beam reflected by the surface to be measured. Since a diaphragm is arranged in the path of this beam, it is prevented that radiation reflected by a second surface situated opposite the first surface can reach the detection unit. The height meter is notably suitable for an inspection device for a lithographic mask.

Inventors: Greve; Peter F. (Eindhoven, NL)

Assignee: U.S. Philips Corporation

International Classification: G01B 11/06 (20060101); G03F 7/20 (20060101); G01B 011/14 (); G01N 021/00 ()

Expiration Date: 12/26/2017