Narrow band excimer laser and wavelength detecting apparatus

Abstract

A narrow band excimer laser and a wavelength detecting apparatus are suitable for use as a light source of a reduction projection aligner of a semiconductor device manufacturing apparatus. In the excimer laser, the ruling direction and the beam expanding direction of a prism beam expander are made substantially coincide with each other, and a polarizing element causing selective oscillation of a linearly polarized light wave substantially parallel with the beam spreading direction of a prism beam expander is contained in a laser cavity. A window at the front or rear side of a laser chamber is disposed such that the window make a Brewster's angle with respect to the axis of the laser beam in a plane containing the beam expanding direction of the prism expander and the laser beam axis. An anti-reflection film which selectively prevents reflection of a polarized light component substantially parallel to the direction of beam expanding of a prism beam expander is coated on one surface of a prism that constitutes the prism beam expander. The wavelength detecting apparatus is constructed to input a reference light and a light to be detected upon the etalon. The light transmitting through the etalon is condensed to focus on a light detector for detecting the wavelength of the laser beam based on interference fringe detected by the light detector.