Optimized HT-AttPSM blanks using $Al2O3∕TiO2$ multilayer films for the $65nm$ technology node

The optical properties of $(Al2O3)x̸(TiO2)1−x$ superlattice films have been shown to satisfy the effective medium approximation theory and, therefore, can be tunable. It is found that $(Al2O3)x∕(TiO2)1−x$ superlattice films with $x=79%–84%$ as $π$-phase shifters can be used as high-transmittance attenuated phase-shift mask (HT-AttPSM) blanks at a wavelength of $193nm$⁠. Lower transmittance at an inspection wavelength of $257nm$ is desirable for a better inspection. Due to the fact that the transmittance is less than 25% at a wavelength of $257nm$⁠, this means that these layers allow for good inspection. Lower reflectance at an exposure wavelength of $193nm$ is desirable, as this leads to better aerial images. To achieve a better aerial image, it is best to select a four-stack $(Al2O3)x̸(TiO2)1−x$ film as the HT-AttPSM blank layer because a four-stack film has the lower reflectance than others. The thickness fraction range of $Al2O3$ in the four-stack $(Al2O3)x̸(TiO2)1−x$ films used for the HT-AttPSM blanks at a wavelength of $193nm$ is found to be between about 79% and about 85%. We fabricate a four-stack $(Al2O3)x̸(TiO2)1−x$ film sample for HT-AttPSM that has the optimized optical properties, which include a transmittance of 19.9% and a lower reflectance (3.2%) at a wavelength of $193nm$ and a good inspection transmittance (less than 20%) at a wavelength of $257nm$⁠. The four-stack $(Al2O3)x̸(TiO2)1−x$ film can be used to design a desirable HT-AttPSM at the exposure wavelength of $193nm$⁠.