Immersion lithography has an advantage in the numerical aperture of optics by a factor of refractive index n of the liquid filled into the space between the bottom lens and wafer. In case of 193-nm exposure tools, water (nϭ1.44) has been found as the best liquid. It is shown, by using imaging simulations, that ArF (193-nm) immersion lithography (NAϭ1.05 to 1.23) has almost equivalent performance to F2 (157-nm) dry (NAϭ0.85 to 0.93) lithography. Issues in the ArF immersion exposure tools are discussed with fluid-dynamic and thermal simulations results. In the fundamental issues, there seems to be no showstoppers so far, however, there exist several challenges to realize viable exposure tools.
The 101–000 and 202–101 rotational transitions of HC35Cl and HC37Cl in the X̃ 1A′ ground vibronic state have been observed with a Fourier transform millimeter-wave spectrometer. The HCCl molecule is produced by discharging a gaseous sample of CH2Cl2 diluted in Ar with a pulsed discharge nozzle. The effective rotational constant (B+C)/2, the centrifugal distortion constant ΔJ, the nuclear quadrupole interaction constants, and the nuclear-spin rotation interaction constant are determined for each isotopic species. The nuclear-spin rotation interaction is found to make a significant contribution to the hyperfine structure of this molecule, which originates from the relatively low-lying electronic excited state. The nuclear quadrupole interaction tensor is highly asymmetric, indicating a significant π character of the C–Cl bond. This can be interpreted in terms of the backdonation of π electrons from the chlorine atom to the carbon atom.
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.
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