Chemical shrink materials and process for negative tone development (NTD) resist

Abstract

Negative tone shrink materials (NSM) suitable for resolution enhancement of negative tone development (NTD) 193nm immersion resists have been developed. While this technology is being applied to integrated circuits (IC) manufacturing, reduction of shrink differences between isolated and dense (ID) CDs also called as shrink ID bias is the challenge to meet wide-spread applications. In this paper, we present the effects of resist thermal flow, proximity effects of DUV exposure, flood exposure of after developed image (ADI) on the NSM shrink. High mixing bake (MB) temperature (example 170°C) during the shrink process resulted in increased resist thermal flow leading to worse shrink ID bias of 3.5 nm. As different pitch pattern has different proximity effect and matching with illumination condition, uneven dose is expected on them. These differences in dose required to obtain same through pitch (1:X, X-1, 1.5, 2, 3, 5) CD was assigned as the cause for shrink ID bias as the de-protection chemistry is related to dose which affects the shrink amount. This was further confirmed by flood exposure of after developed image (ADI) which reduced shrink ID bias from 3.5 nm to 1.8 nm. We concluded that the flood exposure makes the ADIs of the resist chemically uniform thereby minimizing shrink ID bias. Based on these studies, a mechanism for shrink ID bias is proposed. A modified NSM with 1.2 nm shrink ID bias has been developed without the need for the flood exposure.