Fundamental study of extreme UV resist line edge roughness: Characterization, experiment, and modeling

Abstract

Mitigation of line edge roughness (LER) remains a significant practical issue for extreme ultraviolet (EUV) resist performance at 22 nm dimensions and below. The authors have applied a suite of experimental characterization techniques and simulation methods to a set of model EUV resists with the aim of strengthening fundamental understanding of the nature and origins of LER. The influence of resist film composition on LER has been evaluated for positive-tone chemically amplified polymer and NORIA molecular glass resists, and has been correlated the effects with surface roughness on resist films exposed at doses comparable to those at the image line edge. The effect of developer type on LER has been characterized using two distinct developer compositions that provide aqueous base positive-tone and organic solvent negative-tone processes. The time evolution of image roughness during pattern development has been visualized using interrupted development in a flow cell configuration that halts the dissolution process at different elapsed times. A nondestructive three-dimensional atomic force microscopy technique has been used to characterize side wall roughness after sequential steps in a trilayer (resist/etch barrier/underlayer) process. Finally, a combination of analytic theory and computational modeling has been applied to examine the effect of material properties on LER. Using detailed models of polymeric and molecular glass resists, the development process was simulated on length scales (>1 μm) relevant for LER using a massively parallel supercomputer system. These simulations provide predictions of LER scaling with polymer molecular weight, and with the dimension of the zone undergoing dissolution. A comparison of modeling results indicates that LER characteristics of polymer and molecular glass resists will be similar, with the effect of molecular architecture only notable at spatial frequencies greater than 0.1 nm-1. © 2012 American Vacuum Society.