Introduction

doi:10.1117/3.2581446.ch1

Introduction

Book: Extreme Ultraviolet Lithography

Author(s): Harry J. Levinson

Published: 2020

https://doi.org/10.1117/3.2581446.ch1

Abstract

For several decades, the resolution capability of optical lithography was extended by a succession of transitions to shorter imaging wavelengths. The first commercially available wafer stepper operated at a visible wavelength (436 nm), while later generations of exposure tools imaged at mid-ultraviolet and deep-ultraviolet wavelengths. During efforts to continue this process of improving resolution by using a wavelength of 157 nm, with F₂ excimer lasers as the light sources, a number of difficulties were encountered, and optical lithography was eventually extended not by using light with a wavelength of 157 nm but by adapting ArF lithography to an immersion configuration that enabled the numerical aperture (NA) to be increased to 1.35. There were some additional efforts to increase the numerical aperture of ArF immersion lithography further, but development activities were eventually suspended because progress was slow. The shortest wavelength used in optical lithography continues to be 193 nm.