<title>Correcting for proximity effect widens process latitude</title>

Abstract

The optical proximity effect can be a substantial fraction ofthe CD error budget. It is insufficient to determine the proximity effect as the difference between linewidth in an equal line/gap pattern with that of an isolated line. Other geometries may have greater proximity induced line-width errors. We present here a comprehensive, four parameter, analytic process to characterize actual proximity. It is shown that when individual, geometry-dependent line bias is applied line-width uniformity can be reduced to the range. Using the criteria, individual line bias expands the range ofexposure dose and depth of focus. INTRODUCTIONThe optical proximity effect is the result that densely packed lines do not print the same as isolated features13. However, it is not sufficient to just examine the equal line/gap and isolated line patterns. VLSI circuit layouts contain many line environments including the line next to or in-between large features, line pairs, line/gap arrays, etc. Each different occurrence ofthe minimum geometry line will print with a different line-width, sidewall slope or resist loss.

Thirty years of lithography simulation

“…On the exposure tool side, modeling has become an indispensable part of the optimization of the numerical aperture and partial coherence of a stepper [43][44][45] and in the understanding of the print bias between dense and isolated lines [46]. The use of optical proximity correction software requires rules on how to perform the corrections, which are often generated with the help of lithography simulation [47], or they use lithography models directly for the corrections.…”

<title>Lithographic simulation: a review</title>

“…On the exposure tool side, modeling has become an indispensable part of the optimization of the numerical aperture and partial coherence of a stepper [50][51][52] and in the understanding ofthe print bias between dense and isolated lines [53]. The use of optical proximity correction software requires rules on how to perform the corrections, which are often generated with the help of lithography simulation [54].…”

Analysis of the impact of proximity correction algorithms on circuit performance

“…4. 2 Notice that the expansion amount is not a monotonic function of layout pattern density. This phenomenon can be explained by the standing wave effect [11].…”

“…These are the effective CD's. By linear interpolation, we obtained two mapping functions that translate optical CD's into effective CD's (1) (2) where is the effective CD and is the optical CD. Because N-and P-type devices are produced using the same mechanism, their optical CD's should be the same if they are designed with the same channel length.…”

“…One key step is the lithography process, in which optical interference and light scattering cause variations in the transistor channel length, as well as corner-rounding and reduction of the gate-overlap [1], [2]. This effect is known as the proximity effect.…”