Outlook for potential third-generation immersion fluids

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, perhydrophenanthreme (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 on the viscosity. Exhaustive purification of the fluids is a critical step in determining the real absorption of the different fluids at 193 nm. Two simple purification processes of these cycloalkanes were developed that led to low absorption fluids in the VUV region. The possibility of forming the oxygen complex in aerated fluids was reduced by purging samples with argon or nitrogen. This easy elimination of the oxygen complex shows the weak bonding nature of this complex.

Understanding Refractive Index Changes in Homologous Series of Unbranched Organic Compounds Based on Beer's Law

“…As is obvious from Figure 1, for the n-alkane series the correlation between refractive indices and density is close to being perfectly linear (R 2 = 0.994, note that branched alkanes with larger side groups do not fit, as is demonstrated for some isononanes). [10,11] In case of the 1-n-alkanols, however, this correlation is clearly worse (R 2 = 0.879), [12] in particular because of methanol and ethanol. In contrast, for the 1-carboxylic acids the correlation is somewhat better (R 2 = 0.933), [13] but the relationship obviously has a negative slope which does definitely not fit to the theories presented.…”

Advances in Patterning Materials for 193 nm Immersion Lithography

“…In general, there is a strong correlation between the degree of alicyclic unsaturation and the fluid refractive index. A related linear trend between hydrocarbon density and refractive index is shown in Figure . With these correlations in mind, the search for organic immersion fluids can simplistically be described as a search for liquid polycyclic hydrocarbons with the highest possible densities that remain transparent at 193 nm.…”

“…With these correlations in mind, the search for organic immersion fluids can simplistically be described as a search for liquid polycyclic hydrocarbons with the highest possible densities that remain transparent at 193 nm. Numerous second-order structural effects on refractive index, absorbance onset, and fluid properties have been characterized. − For example, the refractive index was found to generally increase with the number of carbon atoms and transoid-connected cyclohexane rings; however, the concomitant shifting of the absorption edge from below 190 nm to above 193 nm renders the absorbance of polycyclic compounds 97 − 101 too high to be useful immersion fluids. − On the basis of these findings, practical immersion fluid candidates can be narrowed down to bicyclic and tricyclic hydrocarbons composed of 9−12 carbon atoms, such as octahydroindene ( 91 ), ethyl norbornane ( 92 , 1,1′-bicyclohexyl ( 93 ), decahydronaphthalene (trans ( 94 ) and cis ( 95 )), and exo -tetrahydrodicyclopentadiene (tricyclo[5.2.1.0 , decane) ( 96 ). − Some of these saturated polycyclic hydrocarbons are used commercially in applications such as high-temperature process fluids (bicyclohexyl 93 ) or high-energy fuels ( exo -tetrahydrodicyclopentadiene 96 is the primary component of JP-10 missile fuel). Air Products, DuPont, ,, JSR, − and Mitsui have all produced commercial high-index immersion fluids based on saturated hydrocarbons with refractive indices ∼1.64−1.65 (listed in Table ) and transparencies sometimes exceeding that of water.…”

“…Another contribution to the absorbance of saturated alkanes in the deep ultraviolet region is the formation of contact charge transfer complexes between alkanes and oxygen in the deep UV. , The oxygen-induced absorbance of JSR HIL-203 at 193 nm was measured to be 0.018 cm −1 ppm −1 . For this reason, the measurements of fluid optical properties listed in Tables and were carried out using rigorously deoxygenated samples.…”