Advanced materials for 193 nm immersion lithography

Abstract

AbstractRecently 193 nm immersion lithography is considered the most promising next generation technology which will enable a 45 nm and below node device to be manufactured. This will lead to not only depth of focus (DOF) enlargement, but immersion lithography enables the use of a hyper numerical aperture (NA) larger than 1.0 and achieve higher resolution capability. For 193 nm lithography, water is an ideal immersion fluid, providing suitable refractive index and transmission properties. Furthermore the higher refractive index fluid is expected to provide a potential extension of optical lithography to the 32 nm node. This paper describes the critical issues of the water immersion lithography process, such as photoresist component leaching into water, defectivity etc. Leaching materials were analyzed by liquid chromatography‐mass spectrometry (LC‐MS) and were found to be composed of the photoacid generator (PAG) and its decomposed chemicals. The leaching amount is in the order of 10−12 mol/cm2 with a normal 193 nm photoresist. An other issue to be studied is the water‐mark defect caused by small waters droplets left on the exposed wafer. These undesirable phenomenons could be prevented by applying a topcoat material onto the photoresist film. Material design for the topcoat material and its physical and lithographic properties are discussed in detail. Development of a high refractive index fluid is also discussed in this paper. A promising high refractive index fluid HIL‐001 was developed which has a higher refractive index (n = 1.64) than water and high transparency (98%/mm) at 193 nm wavelength. Immersion exposure experiments using high refractive index fluid with and without topcoat material was carried out and 32 nm L/S imaging capability was demonstrated by using a two‐beam interferometric exposure tool. Copyright © 2006 John Wiley & Sons, Ltd.