As deep-UV projection system complexity increases to pursue 0.25 micron resolution, the adequacy of diffraction theory using scalar models is of concern. Approximations that are suitable for low NA reduction systems do not hold true for higher NAs. Furthermore, scalar models treat all illumination as polarized perpendicular to the plane of incidence. Feature interaction effects from the polarized radiation of an excimer laser both in a projection system and within a photoresist film cannot be accounted for. Vector diffraction theory has been utilized more appropriately for modelling in these situations, but deviations of scalar predictions from those made with vector models do not warrant abandonment. This paper will describe investigations into scalar and vector diffraction modelling for 248 nm lithography. An experimental design approach was used to study the effects and interactions of coherence, polarization, and numerical aperture on a resist feature response. An exposure latitude response to achieve 1 0% linewidth control with +1- 0.3 micron of defocus was utilized. Both vector and scalar diffraction models were used to simulate process runs. Experimental comparisons were made using a variable NA, variable coherence deep-UV projection system, adapted for control of polarization at the aperture of the mask. Exposure latitude response surfaces are presented, along with details on isolated process runs.

Date of creation, presentation, or exhibit



Copyright 1993 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.

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Document Type

Conference Paper

Department, Program, or Center

Microelectronic Engineering (KGCOE)


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