Investigation of the Resistivity and Emissivity of a Pellicle Membrane for EUV Lithography

Abstract

A pellicle is a thin membrane structure that protects an extreme ultraviolet (EUV) mask from contamination during the exposure process. However, its limited transmittance induces unwanted heating owing to the absorption of EUV photons. The rupture of the EUV pellicle can be avoided by improving its thermal stability, which is achieved by improving the emissivity of the film. However, the emissivity data for thin films are not easily available in the literature, and its value is very sensitive to thickness. Therefore, we investigated the dependence of emissivity on structural parameters, such as thickness, surface roughness, and grain size. We found a correlation between resistivity and emissivity using theoretical and experimental approaches. By changing the grain size of the Ru thin film, the relationship between resistivity and emissivity was experimentally verified and confirmed using the Lorentz–Drude model. Finally, we present a method to develop an EUV pellicle with better thermal stability that can withstand high-power EUV light sources.

Study on ZrSi2 as a Candidate Material for Extreme Ultraviolet Pellicles

“…In addition, the Gaussian beam profile of the UV laser was adjusted to a top-hat profile using a diffractive optics element to ensure uniform laser incidence on the pellicle. A two-channel pyrometer with a measurable temperature range of 400–1500 °C and measurement accuracy of ±2% was used to measure the temperature of the pellicle [ 9 , 18 ]. …”

“…The EUV pellicle must exhibit an EUV transmittance higher than 90% and an EUV reflectivity lower than 0.04% to minimize throughput and yield losses. In addition, it must be mechanically and chemically stable inside the EUV scanner and exhibit adequate thermal durability to withstand a high-power EUV source [ 5 , 6 , 7 , 8 , 9 ]. However, the thickness of the EUV pellicle must be in the order of several tens of nanometers to limit the high absorption of EUV light.…”

Investigating the Degradation of EUV Transmittance of an EUV Pellicle Membrane

“…The heated temperature was measured using a 2-channel pyrometer. The thermal load absorbed by the pellicle composite was calculated using the laser power, beam size, and absorbance at a wavelength of 355 nm [ 7 ]. In this study, the pellicle composite was heated for 3, 6, and 9 h under an absorbed thermal load of 0.8 W/cm 2 with an average peak temperature of 450 °C.…”

“…The mechanical, thermal, and chemical durability of the pellicle inside an EUV scanner is essential. In addition, the EUV pellicle requires a transmittance higher than 90% at a 13.5 nm wavelength to minimize the loss of throughput resulting from the absorption of EUV photons by the pellicle [ 3 , 4 , 5 , 6 , 7 ]. However, the EUV transmittance gradually decreases as the exposure time for the EUV pellicle increases.…”

Development of thermal emissivity calculation method for transmissive multilayer nanomembranes

“…To deal with this, the ε is discussed as an indicator to determine how thermally stable it is. However, it is challenging to directly measure ε of nanomembranes such as EUV pellicle, and no approach to exclude the measurement changes caused by the support membrane [2][3].…”