Nanometer-scale linewidth fluctuations caused by polymer aggregates in resist films

Abstract

Linewidth fluctuation in resist patterns is a serious problem in electron beam nanolithography. We have observed granular structures with a diameter of 20–30 nm in resist films, and have determined that these structures cause the linewidth fluctuations. The granules are made up of polymer aggregates. We discuss the origin of the aggregates from the result that their size depends on the polymer molecular weight. We also show that the linewidth fluctuation is reduced, though the developing rate is slow, when the pattern size is less than the aggregate size. The linewidth dependence of the fluctuation and of the developing rate can be explained by the influence of the resist polymer aggregate on the development behavior.

Surface Roughening of Polystyrene and Poly(methyl methacrylate) in Ar/O2 Plasma Etching

“…During the initial roughness formation (etch time from 0 seconds to 66 seconds), cone shaped roughness features appear and increase gradually in number on the surface [ Figure 1 (a-e)]. The roughness features show good uniformity in lateral size (~20 nm) and form, thus resembling the polymer aggregates observed in photoresist materials during development [25,[31][32][33]. Initial roughness formation is very different from the initial roughness induced by common ion bombardment or redeposition of sputtered materials from the chamber wall that normally leads to craters or clusters of random size and shape.…”

“…There are two possible causes of aggregation. It may be induced intrinsically throughout the film during polymer sample preparation [31][32][33] or induced at the surface due to plasma exposure [21]. If polymer aggregation is intrinsic, the inhomogeneity could induce etch rate non-uniformity immediately upon plasma exposure.…”

“…For example, during initial roughness formation, roughness features created by ion damage or deposition of sputtered materials are random in size and shape [29,30]. In contrast, roughness features induced by aggregation in polymer materials are more consistent in size and shape [25,[31][32][33]. Roughness amplification mechanisms may also contribute to feature characteristics during roughness evolution.…”

Suppressed Aggregate Extraction Development (SAGEX) Resists.

“…Figure 1(a) shows a schematic diagram of the LER generation process in a positive-tone resist. It has been confirmed that polymer aggregates are normally contained in resist films by observing cross-sections of resist films with a scanning electron microscope (SEM) [10] and also by observing the exposed resist surface after development with an atomic force microscope (AFM) [4,5,[10][11][12]. When such a resist film containing the polymer aggregates is developed after exposure, the developer molecules diffuse faster between aggregates and then the polymers surrounding the aggregates dissolve faster than the aggregates themselves.…”

“…This is because most LER are reported to have a magnitude of 3 nm or more [4][5][6][7][8][9] and the major cause is by polymer aggregates in resist films. The size of the polymer aggregates normally contained in resist films are 20 to 30 nm [4,10]. The polymer aggregates embedded on the pattern sidewall after development generate the LER [1 1,12].…”