Melvin "Warren" Montgomery, principal engineer at CNSE and manager of CNSE's INVENT (International Venture for Nanolithography) program, has recently made several significant contributions in the area of photomasks and photolithography.

Montgomery recently earned three patents for his work with photomasks, and also presented on immersion lithography at an international lithography symposium. In addition, he currently serves on the steering committee for the industry's top photomask organization.

Two of Montgomery's patents deal with increasing the shelf life of photomask substrates. Patent 7,135,256, "Method of increasing the shelf life of a photomask substrate," explains how adjusting the pH level of the topcoat applied to a photoresist improves its stability. In photomask making, the environmental sensitivity of a chemically amplified photoresist is eliminated, or at least substantially reduced, by overcoating the photoresist with a thin coating (topcoat) of a protective but transmissive material. To provide improved stability during the long time period required for direct writing of a photomask pattern (typically about 20 hours), the protective topcoat material is adjusted to be as pH-neutral in pH as possible, depending on other process variable requirements. Not only is the stability of the chemically amplified photoresist better during direct writing when the protective topcoat is pH adjusted, but a photoresist-coated substrate with pH adjusted topcoat over its surface can be stored longer prior to imaging without adverse consequences.

Patent 6,998,206, "Method of increasing the shelf life of a blank photomask substrate," addresses the use of a direct write continuous wave laser in the photomask optical fabrication process. This comprises a series of steps including applying an organic antireflection coating over a surface of a photomask which includes a chrome-containing layer; applying a chemically-amplified DUV photoresist over the organic antireflection coating; post apply baking the DUV photoresist over a specific temperature range; exposing a surface of the DUV photoresist to the direct write continuous wave laser; and, post exposure baking the imaged DUV photoresist over a specific temperature range. The direct write continuous wave laser preferably operates at a wavelength of 244 nm or 257 nm. In an alternative embodiment, the organic antireflection coating may be applied over an inorganic antireflection coating which overlies the chrome containing layer.

Montgomery's third recent patent 7,067,227, "Sensitized chemically amplified photoresist for use in photomask fabrication and semiconductor processing," pertains to a photoresist composition and a method of using the photoresist in the fabrication of reticles or features on a semiconductor substrate. The photoresist composition and the method are designed to reduce the variation in critical dimension of features across a surface of a substrate, where the variation in critical dimension is a result of localized resist loading. The photoresist composition is useful when the imaging system is G-line, H-line, or I-line, and the photoresist composition includes a sensitizer which works in combination with a DUV photoresist including a PAC, to sensitize the photoresist to the G-line, H-line and I-line imaging.

In addition to his patent achievements, Montgomery co-authored a paper entitled "Immersion Lithography: Throughput Optimization for the 90 nm Node and Beyond," which was presented at the international Brewer Science Lithography Symposium.

Montgomery also currently serves on the Steering Committee of the BACUS (Photomask Technologies) Technical Group of SPIE, the International Society for Optical Engineering. BACUS is the largest and most widely known forum for the exchange of technical information among photomask manufacturers, equipment suppliers and mask users, dedicated to advancing the technology and commercial application of masks for micro- and nanolithography. Prior to serving on the BACUS Steering Committee, Montgomery chaired the organization's Photomask Equipment - Japan Session, and chaired the Photomasks Process & Materials session for several years.