Non absorbing reticle and method of making same
A reticle or mask for use in projecting a circuit pattern, having a transparent substrate with a reflective or dielectric layer thereon. An opaque or blocking layer 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 using source wavelengths of between 157 nanometers and 365 nanometers. 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.
1. A photo lithographic reticle having reduced thermal load, comprising:
a transparent substrate, and
lands forming a pattern to be reproduced placed on the transparent substrate, wherein the same material forms both a blocking layer and a reflecting layer of the lands to electromagnetic radiation,
whereby less energy is absorbed in the photolithographic reticle and the thermal load is reduced.
2. The photolithographic reticle of claim 1 ,
wherein the transparent substrate includes first and second surfaces opposite each other, each land being placed on the first surface, and;
wherein the photolithographic reticle further comprises an antireflective coating placed on the second surface of the transparent substrate.
3. The photolithographic reticle of claim 2 , wherein the antireflective coating is antireflective at least for wavelengths ranging from approximately 157 nm to 365 nm.
4. The photolithographic reticle of claim 1 , wherein the lands are made of aluminum.
5. The photolithographic reticle of claim 1 , wherein the lands have a reflectance of greater than sixty percent for the electromagnetic radiation.
6. The photolithographic reticle of claim 1 , wherein the transparent substrate is selected from the group consisting of quartz, fluoride doped quartz, and calcium fluoride.