Photoresists

doi:10.1117/3.2525393.ch3

Photoresists

Book: Principles of Lithography, Fourth Edition

Author(s): Harry J. Levinson

Published: 2019

https://doi.org/10.1117/3.2525393.ch3

Abstract

Resists are broadly classified as positive or negative. Unexposed positive resists normally have very low solubility in developer and become soluble by exposure to light. Negative resists behave in the opposite manner; unexposed negative resists are soluble in developer and lose their solubility upon exposure to light. Negative resists were used predominately prior to the advent of wafer steppers. Resists most widely used in the early years of the semiconductor industry, such as Kodak’s KTFR resist, were based upon the photoinduced cross-linking of low-molecularweight cyclized polyisoprene. Azide additives were used to improve their sensitivity to light and to facilitate cross-linking. Cross-linking reduced the material’s solubility in organic solvents such as xylene. After exposure, an organic solvent was used to develop the resist by removing the lowmolecular- weight unexposed resist and leaving behind cross-linked, highmolecular- weight material.