Amplification of the index of refraction of aqueous immersion fluids by ionic surfactants

Abstract

In order to find new immersion liquids to improve the resolution of 193 nm immersion photolithography, we have attempted to discover aqueous system possessing an index of refraction greater than that of water using aqueous surfactant systems. The index of refraction (RI) of both cationic and anionic surfactant systems were examined in the presence of wide range of inorganic salts, and parameters such as size of surfactants, concentrations, and temperature were varied. The refractive index (RI) was found to be increased in the presence of both anionic and cationic surfactants compared to those of water and also increased as a function of surfactant concentration. However the refractive index tends to increase much more strongly as a function of salt concentration. In our study, a maximum RI enhancement was observed from 6.5 M CdCl 2 in 8.2 mM aqueous SDS solution. The effect of micellar properties such as the critical micelle concentration (cmc) and degree of ionization were systematically studied for aqueous SDS system in the presence of CdCl 2 . The correlation on index of refraction between empirical data and theoretical prediction were performed using the concept of molar refraction. Wavelength dependence of RI from theoretical prediction based on empirical equation was examined for various concentration of CdCl 2 system and the results are reported in the paper.Subject terms: index of refraction, immersion photolithography, ionic surfactants, 193 nm, SDS, CTAC, CdCl 2 IntroductionRecently, optical lithography has been incrementally marching toward dimensions less than 45 nm. The wavelength has been reduced to 193-nm and 157-nm lithography using F 2 laser was studied tentatively for the next generation of lithography. We have been studying the mechanism of the photodegradation that leads to darkening of polymer pellicles during exposure to 157 nm radiations in order to design new soft pellicle systems that possess acceptable characteristics for 157 nm photolithography.

High refractive index and high transparency HfO2 nanocomposites for next generation lithography

“…12 The push to develop materials for lithographic patterning at lower exposure wavelengths has been partially supplanted by the search for high refractive index (RI), low absorbance materials to increase the potential imaging capabilities of 193 nm immersion lithography. Initial attempts to design these materials have involved a variety of additives, including common organic materials, 13 metal salts and acids, 14,15 heavy metal cations stabilized with surfactants, 16 and nanoparticles. 17 Among these approaches, considerable progress has been made using metal oxide nanoparticles.…”

“…17 Among these approaches, considerable progress has been made using metal oxide nanoparticles. [18][19][20][21][22] Hafnium oxide (HfO 2 ) is a very promising inorganic material among many high-k and high index materials due to its relatively high dielectric constant (16)(17)(18)(19)(20)(21)(22)(23)(24)(25), large band gap (>5 eV), and good thermal and chemical stability. 7,8 There has been substantial effort to make use of HfO 2 as a dielectric layer in the semiconductor industry.…”

Second generation fluids for 193nm immersion lithography

“…In researching higher index immersion fluids, several groups have explored water with additives as second generation immersion fluid candidates. [3][4][5][6][7][8] The additives include surfactants, inorganic salts, mineral acids, and particles. To date, these water-based fluids show refractive indices of 1.55 or less at 193nm 1 -improvements over water, but not high enough for 38nm or 32nm half-pitch feature-size lithography.…”

Synthesis of high-refractive index sulfur containing polymers for 193-nm immersion lithography; a progress report

“…Advances in immersion fluid and resist design could extend 193 nm immersion lithography to the 32 nm node or below. Increases in the refractive index (RI) of the immersion fluid (the optical element currently with the lowest RI) are being sought by a number of groups, [1][2][3] with the aim of increasing the numerical aperture of a system, in turn leading to reduced the possible feature sizes. Furthermore, it is anticipated that the development of second 4 and third generation fluids over the next several years will enable the 32 nm node.…”