Polycycloalkanes as Potential Third-Generation Immersion Fluids for Photolithography at 193 nm

Abstract

In a search for alkane candidates for 193 nm immersion fluids, several alkanes and cycloalkanes were synthesized, purified, and screened to ascertain their absorption at 193 nm, refractive index, and temperature dispersion coefficient in the context of the actual application. In general, cycloalkanes, and more specifically polycycloalkanes, possess a higher refractive index than do linear alkanes. Decalin, cyclodecane, perhydrophenanthrene (PHP), perhydrofluorene (PHF), and perhydropyrene (PHPY) are examined as potential second- and third-generation immersion fluids. The use of perhydropyrene, which possesses a high refractive index of 1.7014 at 193 nm, may be limited as an immersion fluid because of high absorption at 193 nm. Mixtures of cycloalkanes can lead to a higher enhancement of the refractive index together with a decrease of the viscosity. Exhaustive purification of the fluids is a critical step in determining the real absorption of the different fluids at 193 nm. Even very small traces of impurities possessing a high absorption coefficient at 193 nm can lead to an unacceptably high level absorption at 193 nm, previously incorrectly attributed to the alkane instead of the absorbing impurities.

Development and evaluation of 193nm immersion generation-three fluid candidates

“…This procedure has been detailed elsewhere. 10 However, it has been highlighted by several groups that increasing the size of the organic compound while raising the RI also increases the absorbance to unacceptable levels. 10,11,16 Figure 2 shows an example of increased RI when going from decalin to perhydrofluorene and perhydropyrene.…”

“…Many possible target materials have been suggested, but in each case increases in the index have been accompanied by unacceptable levels of absorbance. [9][10][11] Part of this report illustrates the difficulty we faced in developing an acceptable transparent organic immersion fluid with an index greater that 1.7. Even more challenging is the industry goal of reaching a RI ≥ 1.80 necessary for ~ 1.7 numerical aperture imaging.…”

Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Electronic and Optical Applications

“…The equipment it requires is much less expensive (by a factor of [10][11][12][13][14][15][16][17][18][19][20] and more widely available than the e-beam or FIB writers often used to make nanostructures. Nanoskiving introduces "cutting" as a step that replicates patterns and generates nanoscale features; it is analogous to "printing" and "molding" in soft lithography, and to "exposure" in photolithography.…”

“…[11,12] This trend has become a self-fulfilling prophecy, which has motivated the development of new steppers for projection photolithography, [13] chemistry for photoresists, [14] and other technologies. [5] The state-of-the-art in photolithography produces features with an average half-pitch in memory devices of 32 nm using 193 nm light combined with immersion optics, [15] phase-shifting masks, [16] and multiple exposures. [17] Next-generation lithographic tools, including extreme ultraviolet lithography (EUVL), [18] maskless lithography (ML2, which would use thousands of electron beams to replicate patterns without the need for a physical master), [19] and step-and-flash imprint lithography (SFIL) [20] are expected to drive the average half-pitch down to 16 nm by 2019, according to the International Technical Roadmap for Semiconductors.…”

High index 193 nm immersion lithography: the beginning or the end of the road

“…[17][18][19][20][21] It was shown within eighteen months that fundamental limitations prevented the use of higher index pure organic fluids. There was also a flurry of work into alternative fluids such as organic salts and ionic liquids, but all of these systems had a least one material property and often more than one that disqualified their use as an immersion fluid.…”