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Proceedings Paper

Optimization of optical properties of resist processes
Author(s): Timothy A. Brunner
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Paper Abstract

Thin film interference plays a dominant role in CD control of single layer photoresist processes, causing large changes in the effective exposure dose due to a tiny change in optical phase. Such interference effects are evident in the sinusoidal undulations of a plot of dose to clear versus resist thickness, the 'swing curve'. To quantify the interference swing, we define the swing ratio S as the ratio of the peak to valley change to the average value in the swing curve. S is a fundamental figure of merit for photoresist processes, since linewidth variations with small changes in resist thickness are proportional to S. A simple optical model of photoresist (as a Fabry-Perot etalon) leads to the following analytical expression for the swing ratio S: S approximately equals 4(root)R1R2 e-(alpha D) where R1 is the reflectivity of the resist/air interface, R2 is the reflectivity of the resist/substrate interface, and (alpha) is the resist absorption coefficient. Efforts to improve process control have lead to the invention of many cleaver resist processes including Top Surface Imaging (TSI), Anti-Reflection Coats (ARC), dyed resists, etc. Eq. 1 allows a classification of these processes according to which factor is modified. For example, TSI and dyed resist processed reduce S by increasing (alpha) . ARC processes reduce S as the square root of substrate reflectivity under the resist R2. Fundamental limits of the performance of thin absorbing ARC layers will be described. A novel approach, termed the Top Anti-Reflector (TAR) process, reduces the reflection at the top of the resist R1 and can be shown to dramatically improve process control over varying thicknesses of resist and thin film layers. The effects of multiple wavelength exposure and oblique rays from high NA optics are also briefly examined.

Paper Details

Date Published: 1 June 1991
PDF: 12 pages
Proc. SPIE 1466, Advances in Resist Technology and Processing VIII, (1 June 1991); doi: 10.1117/12.46410
Show Author Affiliations
Timothy A. Brunner, IBM/Thomas J. Watson Research Ctr. (United States)

Published in SPIE Proceedings Vol. 1466:
Advances in Resist Technology and Processing VIII
Hiroshi Ito, Editor(s)

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