Wavefront engineering issues for deep-UV lithography
Tittel, Frank K.
Doctor of Philosophy thesis
The principal objective of this work is the investigation and development of wavefront engineering or optical resolution enhancement techniques using deep-UV lithography. Current technologies used in optical microlithography allow the manufacture of microelectronic circuit features that are larger or about equal to about 2/3 of the wavelength of the exposure tools. In order to extend the capabilities of optical lithography, new optical resolution enhancement techniques are needed and the existing methods have to be analyzed and improved. The study of limitations of tolerances and the overall performance of diverse wavefront engineering techniques is critically important to the microelectronics industry. Techniques such as phase-shift masks, optical proximity correction, and off-axis illumination are being studied in order to obtain a clear understanding of their impact on critical dimension uniformity, resolution and depth of focus. Proximity effects, feature offset and pattern displacement issues, as well as sensitivity to lens aberrations and coherence of the light source are being investigated. Tolerances of these techniques and their performance when used with 248 nm and 193 nm deep-UV lithography are also of concern. In addition, a new resolution enhancement technique is being developed. This technique is based on coherent image superposition which is expected to improve both the resolution and depth of focus of integrated circuit features.
Engineering, Electronics and Electrical; Physics, Optics; Engineering, Materials Science