Measurement of Resist Transmittance at Extreme Ultraviolet Wavelength Using the Extreme Ultraviolet Reflectometer

Abstract

Since the same reduction exposure as that of conventional optical lithography technology is possible and the wavelength is as short as 13 nm, extreme ultraviolet (EUV) lithography is a promising method for the fabrication of semiconductors with feature sizes of 50 nm and below. In order to resolve a fine pattern in a single-layer resist process, a resist material with a small absorption coefficient needs to be developed. We have developed a method of measuring resist transmittance at the EUV wavelength using an EUV reflectometer. The EUV light used by the EUV reflectrometer was emitted from a CO2 plasma. The resist transmittance at the EUV wavelength could be calculated based on two parameters measured by the reflectrometer, namely, the reflectivity (Rtotal) of the resist on a multilayer mirror and the reflectivity (RML) of the Mo/Si multilayer mirror surface. The resist sample measured was polymethylmethacrylate (PMMA), a typical resist polymer. We found that the measured resist transmittance is in good agreement with the calculated resist transmittance and that method developed is very effective for measuring actual resist transmittance at the EUV wavelength.