A photomask typically consists of a bulk transparent substrate and a thin metallic film with etched pattern on the surface for light absorption. Stray light reflecting off of the top surface of the photomask is especially problematic because it is focused onto the wafer surface, causing unwanted exposure of the photoresist. . Lithographic performance can be significantly improved if this reflection is reduced with an antireflective layer on the top surface of the photomask. There are commercially developed antireflective films for chrome based photomasks. These films were designed to meet certain specifications for optical density and reflectivity. The goal of this project was to develop a process to replicate these commercial films at RIT. X-ray Photoelectron Spectroscopy ~XPS) was performed on the commercial samples to obtain depth profiles of the atomic constituents of the chrome-based films. Absolute reflectivity and transmission data were obtained on these films using a Perkin-Elmer Lamba-11 UV/VIS Spectrophotometer. Finally, a sputter deposition process was developed to deposit a chrome film with bulk properties similar to those of the commercial films. The process was tuned so that the reflectivity of the RIT film closely matched the reflectivity of the commercial films. The result was an antireflective optically dense film appropriate for photomasks for optical lithography.
"A Chrome AR film for Binary Photomasks,"
Journal of the Microelectronic Engineering Conference: Vol. 10
, Article 1.
Available at: http://scholarworks.rit.edu/ritamec/vol10/iss1/1