Non absorbing reticle and method of making same

Abstract

A reticle or mask for use in projecting a circuit pattern on a photosensitive resist covered wafer having a transparent substrate with a reflective or dielectric layer thereon. An opaque or blocking layer, for example chrome or chromium, is placed over the reflective layer. The opaque layer then has a predetermined circuit pattern etched therein. In one embodiment, the opaque layer and the reflective layer are the same size. In another embodiment, the opaque layer has a size larger than the reflective layer. This permits the opaque layer to be adjacent the substrate which is advantageous when projection optics having a high numerical aperture are used. The reticle of the present invention has particular advantage when high throughput photolithographic tools are used having an illumination source of high energy flux with a wavelength of between 157 nanometers and 365 nanometers. Illumination in this wavelength range has considerable absorption in chrome, a common opaque material used in reticles. The reflective layer or land has a reflectance greater than chrome, and preferably greater than sixty percent. Therefore, the reflective layer greatly reduces reticle warm-up and thermal distortion. This technique is applicable not just to binary mask or reticles, but also to phase masks that may, in some embodiments, have opaque blocking areas thereon.

Dependencies are inferred from the claim text.