Liquid immersion lithography: Why, how, and when?

Abstract

Liquid immersion lithography, especially at 193 nm, is a serious candidate for extending projection optical lithography to the 65 nm node and beyond. This article reviews the status of this technology, the potential pitfalls that it may still encounter, and also the potential to extend it to 157 nm and to higher-index liquids. At 193 nm, no fundamental obstacles have been found yet, although defect control and materials compatibility must still be worked out. At 157 nm, significant progress has been made in developing suitable liquids. The next hurdle is to increase their refractive index, in order to make the transition in wavelengths cost-effective.

Enhancement of near-field phase-shifting contact lithography by immersion technique

“…Hence, improvement in resolution by immersion unfortunately does not support any reduction in feature size. These conclusions regarding resolution enhancement appear to be validated by recent experimental studies as well [9,10].…”

“…These methods are generally called resolution enhancement techniques (RETs) [7]. One of the promising RETs that can be incorporated into NFPSCL is the immersion technique, which involves immersing the whole maskphotoresist-substrate system in a liquid medium (e.g., water) rather than air (conventional, dry environment) [8][9][10]. The refractive index of the immersion medium is certainly larger than that of air, which leads to higher spatial frequencies of light passing through the phaseshifting mask into the photoresist layer.…”

Transient evolution of multiple bubbles in laser induced breakdown in water

“…(Berns et al, 1991;Ramanathan & Molian, 2001;Kruusing, 2004;Rothschild et al, 2004;Makide et al, 1983;Schnürer et al, 2005). High power laser induced breakdown in solid, liquids, and gases leads to plasma formation with emission of shockwaves (Batani et al, 2003;Hoffmann et al, 2005), and cavitation bubbles in liquids (Nath & Khare, 2008).…”

Extreme ultraviolet lithography with table top lasers

“…Switkes and Rothschild few years later printed 60 nm period gratings using 157 nm light, proposing this technique as the way to improve the resolution of optical lithography [35,36]. The simplicity of the immersion IL approach had motivated an enormous amount of work since then, utilizing different immersion liquids and light sources [22,35,[37][38][39][40][41][42][43][44][45].…”