Studies of high index immersion lithography

Abstract

High index immersion lithography is one of the candidates for next generation lithography technology following water immersion lithography. This technology may be most attractive for the industry since it is effective in raising resolution without seriously changing the chip making processes. This motivates us to continue to study further NA expansion although there are many challenges with respect to either high index fluid development or high index lens material development. In this paper, the current status of high index lithography development compared with the industry's requirements is discussed while considering design feasibility.

Immersion Lithography Ready for 45 nm Manufacturing and Beyond

“…However, through newly developed optimization processes, a Strehl intensity of 0.94 should be achievable. [8] Although transmission and intrinsic birefringence are significant challenges with these new lens materials, they are not perceived as "showstoppers." As shown in Fig.…”

Advances in Patterning Materials for 193 nm Immersion Lithography

“…Absorption by the fluid also increases the propensity for radiation damage and heating of the fluid. Therefore, an ideal fluid should possess a low absorption coefficient, a low thermo-optic coefficient (d n /d T ), high specific heat capacity, high thermal conductivity, and low viscosity in order to maintain stable optical properties and prevent focus errors and spherical aberrations. ,,,− For example, the optical path difference between two rays should not exceed a quarter wavelength, requiring δ n ≤ λ cos θ 4 t wherein δ n is the change in the refractive index and t is the thickness of the fluid layer . This relationship is used to define the requirements for local , and bulk temperature stability of the immersion fluid, pressure stability, and fluid thickness (i.e., the gap height between the last lens element and the imaging layer)…”

“…At the limit of water immersion lithography (∼1.3−1.35 NA), 55 nm half-pitch features can be printed at a k 1 of 0.38 (required for aggressive dual-orientation patterning) and 40 nm half-pitch features with a k 1 of 0.28 (required for aggressive single-orientation patterning) (see Table ). In order to extend 193 nm immersion lithography to 45 nm ( k 1 = 0.38) and 32 nm ( k 1 = 0.28) half-pitch, an NA of about 1.7 is required (see Table ). − , With a planar last lens element, the NA of an immersion lithography tool is limited by the lowest refractive index in the optical stack (i.e., last lens element, immersion fluid, topcoat, and photoresist). In 193 nm water immersion lithography, the immersion fluid presents the first limiting refractive index ( n water ≈ 1.44, n LLE ≈ 1.50−1.56, n topcoat ≈ 1.5−1.66, n resist ≈ 1.7) .…”

“…For commercial applications, research has focused on increasing the refractive indices of the materials in the optical stack (LLE, fluids, topcoats, and resists) to increase the NA of liquid immersion lithography tools to 1.7 and beyond. − , A 1.7 NA immersion tool would require a new high-index lens material, a high-index immersion fluid, and a high-index photoresist (see Table ). Lower NA tools (1.45 NA and 1.55 NA) using lower refractive index fluids and lens materials were proposed as development targets while research progressed on third-generation ( n > 1.8) immersion fluids and the high-index lens material.…”

Spacer double patterning technique for sub-40nm DRAM manufacturing process development

“…Due to not only the requirement of resolution but also the demands for the throughput or economical considerations, it will be a challenge to pick out the most suitable process in order to meet the generation progress. There are various limitations for these candidates, for example, the availability of hyper-NA fluid and the corresponding lens material for the immersion tool [13,14]. As referred to the EUV technology, the development for the optics including the mask or the mirrors, and the source power along with the throughput will dominate the lean-in of production.…”