Determination of spot size and acid diffusion length in positive chemically amplified resist for e-beam lithography at 100 and 5 kV

Abstract

An experimental method to determine the beam spot size and the acid diffusion length of a positive chemically amplified electron-beam resist (p-CAR) is proposed. This method is applied to a reference p-CAR with a Vistec VB6 electron beam at 100 kV and with a MAPPER tool at 5 kV. Beam spot size characterization is based on the width measurement of a single line exposure. This procedure is applied to two specific dose ranges. In the first one, the chemical mechanism occurring in the exposed resist is dominated by acid catalytic deprotection of a partially protected polymer (standard process). In the second dose range, the chemistry is governed by the cross-linking mechanism due to the intentional overdose of the p-CAR, leading to a polarity inversion. The authors assume that comparing the results obtained with the standard and the cross-linked p-CAR enables the determination of the acid diffusion length of the p-CAR process. This hypothesis was verified with measurements performed with a nonchemically amplified process. A relationship between the best exposure latitudes achieved at 5 and 100 kV and the minimum spot sizes determined with the present method is observed with very high resolution grating exposures. In this work, a suitable method is proposed for fine resist process characterization.