Abstract

Rigorous coupled-wave analysis developed by Moharram and Gaylord is used to model the diffraction from arbitrarily shaped latent image gratings. Latent image gratings are of wide interest because of their use in photolithography and, therefore, the microelectronics industry. A photomask with a grating pattern is used to expose periodic lines in the photoresist, producing a periodic index variation in the photoresist (latent image). The resultant lines after development of the photoresist are directly related to the shape of the latent image. The capability to characterize submicron gratings is of great importance as a result of the decreasing dimensions of feature sizes. Modeling of the latent image considers the effects of linewidth, sidewall angle, groove depth, and other arbitrary index profiles. The intensities diffracted into the various orders is greatly dependent upon the geometry of the grating. Utilizing the information provided by the zeroth-, first- and second-order diffracted powers, we are able to predict many characteristics of line geometries.

© 1991 Optical Society of America