Chemistry of Photochemical and Radiochemical Imaging Mechanisms of Positive-Tone Resists

doi:10.1117/3.2642420.ch7

Book: Chemistry and Lithography, Second Edition, Vol. 2: Chemistry in Lithography

Author(s): Uzodinma Okoroanyanwu

Published: 2023

https://doi.org/10.1117/3.2642420.ch7

Author Affiliations +

Abstract

The essential characteristic of a positive resist is that its exposed part gets dissolved away in a developer solution, while its unexposed part does not. Positive resists differ from their negative counterparts principally in their response to actinic radiation despite the fact that the essential compositions of the two resist types are similar in many ways: each contains sensitizers or appropriate radiation-sensitive compounds, resins, solvents, and additives. As in modern negative resists, the resins for positive resists are polymers, which are large molecules with repetitive sequences of monomers—groups of atoms—connected in a linear or branched fashion, as illustrated in Fig. 4.3. The physical, thermal, mechanical, and molecular weight properties of lithographic polymers are discussed in Chapter 4. Unlike some negative resists, positive resists do not swell in developer. Moreover, the use of aqueous stripping and developing solutions greatly simplifies the equipment selection for positive resists in process equipment tooling by allowing low-cost, readily available plastics to be used as containers. Problems associated with the use of flammable solvents are minimized with positive resists.