<title>Multilayer Zr/Si filters for EUV lithography and for radiation source metrology</title>

Abstract

The technique for fabrication of thin film filters with high mechanical strength, capable of withstanding the prolonged heat load of 1 W/cm 2 , has been developed. Freestanding multilayer Zr/Si filters of size 20 150 mm 2 with high transparency of 76% at wavelength = 13 nm were manufactured for EUV lithography tool. We have also developed and fabricated various designs of filters (freestanding or mesh supported) with lower transparency of 40-50% for experiments with intensive EUV sources. The tests of differential pressure withstandability and heat-resistance of filter samples were fulfilled. In order to model the influence on the filter of intensive radiation of the lithography source we have tested Zr/Si film samples by the Joule heating in vacuum at residual pressure of 10 -8 Torr. The testing consisted in continuous heating of Zr/Si films at the electrical power per area unit from 0.5 W/cm 2 to 6 W/cm 2 during long period of time (up to 2 months). The influence of the long-term heat load on the transparency of samples at = 13 nm and within wavelength region 0.3 -2 m was investigated.

Thermal stability of a freestanding EUV filter under long-term vacuum annealing at 700–1000°C

“…The first experiments modeled the effect of radia tion with a high average power on the filter by heating the sample via an electric current passing through it [2]. Heating by radiation with characteristics close to those of the EUV source for the nanolithograph must give a more precise forecast of filter operation in actual operating conditions.…”

“…Earler it was shown [2] that a filter based on a free standing multilayered structure Zr/Si, which was opti mal with respect to mechanical strength and transpar ency at λ = 13.5 nm (up to 76%), was able to withstand long term heating in a vacuum of ∼10 -8 Torr at the density q = 1 W/cm 2 of power per unit area which cor responded to the film temperature T = 420°C. At higher temperatures, there is activation of structure layer mixing, growth of crystallites, and oxidation of the materials; the latter results in a decrease in the fil ter transparency at the operating wavelength.…”

Free-standing spectral purity filters for extreme ultraviolet lithography

“…It was found, in particular for Zr/Si multilayer films, that samples are quasi-amorphous with crystallite sizes of a few nanometers. 17 Regarding the chemical composition, traces of oxygen and carbon are present, resulting in a slight drop of EUV transparency as compared to the expected value. Precise measurements of transparency at 13.5 nm are performed with a double mirror reflectometer operating in a transmission mode.…”

DLC/Si multilayer mirrors for EUV radiation

“…Hence additional spectral filters have to be introduced into the optical path. Various filter designs have been proposed for suppression of DUV and IR radiation, including thin foil filters [4], grid-type filters [5] and reflective grating-like optics [6]. For the suppression of DUV radiation, an efficient way is the addition of specific capping layers on top of standard Mo/Si multilayers.…”