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 photolithography system comprising:
an illumination source configured to produce electromagnetic radiation; and
a reticle having reduced thermal load, said reticle comprising:
a transparent flat substrate;
dielectric lands placed on said transparent flat substrate; and
electromagnetic radiation blocking lands placed on said dielectric lands;
wherein said dielectric lands have a reflectance greater than about sixty percent,
whereby electromagnetic radiation passing through said transparent flat substrate is reflected from said dielectric lands prior to reaching said electromagnetic radiation blocking lands resulting in less energy being absorbed in the reticle and the thermal load being reduced.
2. The photolithography system of claim 1 , wherein said dielectric lands of said reticle comprise alternating layers of quarter-wave film of a higher refractive index and a lower refractive index than a refractive index of the transparent flat substrate.
3. The photolithography system of claim 1 , wherein said dielectric lands of said reticle are reflective for any predetermined wavelength of electromagnetic radiation from 157 to 365 nanometers.
4. The photolithography system of claim 1 , wherein said electromagnetic radiation blocking lands of said reticle are made of chrome.
5. The photolithography system of claim 1 , wherein said electromagnetic radiation blocking lands of said reticle are made of aluminum.
6. The photolithography system of claim 1 , wherein said transparent flat substrate of said reticle is selected from the group consisting of quartz, fluoride doped quartz, and calcium fluoride.