Line narrowing unit with flexural grating mount

Gas discharge ultraviolet lasers used as light sources for integrated circuit lithography typically are line narrowed. A preferred prior art line narrowing technique is to use a grating based line narrowing unit along with an output coupler to form the laser resonance cavity. The gain medium within this cavity is produced by electrical discharges into a circulating laser gas such as krypton, fluorine and neon (for a KrF laser); argon, fluorine and neon (for an ArF laser); or fluorine and helium and/or neon (for an F laser). A grating based line narrowing device for line narrowing lasers producing high energy laser beams. Techniques are provided for minimizing adverse effects of heat produced by the laser beam inside the line narrowing device.A flexural grating mount is provided which virtually eliminates stress on the grating caused by differential thermal expansion between the grating and the LNP housing structure. In a preferred embodiment the grating which is comprised of a very thin lined aluminum surface on a thick ultra low expansion glass substrate is attached to an aluminum housing structure using a flexural grating mount. At least one flexure joint is provided in the grating mount which permits thermal expansion and contraction of the aluminum housing without producing undesirable mechanical stresses in the glass substrate of the grating. In some embodiments the mount comprises a metal plate and the flexure joint is a H-Flex joint which is machined into the metal plate. In another embodiment two H-Flex joints are provided. In other embodiments, the flexure joint is a dovetail joint permitting one end of the mount to slip relative to the other.In another preferred embodiments a stream of gas is directed across the face of the grating. In other embodiments the effect of a hot gas layer on the face of the grating is reduced with the use of helium as a purge gas and in other embodiments the purge gas pressure is reduced to reduce the optical effects of the hot gas layer.