Direct growth of highly uniform graphite on SiNx/Si through metal induced crystallization of amorphous carbon for EUV pellicle

Graphite is highly noteworthy for next-generation pellicles due to its high emissivity (>0.3), and Young's modulus (4.1 GPa) which provides high thermal and mechanical stability. The widely used graphite synthesis is chemical vapor deposition on thick metal catalyst, which involves several disadvantages such as hard to control of thickness uniformity and damage during wet-transfer processes. To overcome these problems, we propose a direct synthesis of graphite film(< 30 nm) on insulating substrate at low temperature about 500°C starting from the amorphous carbon (a-C) on catalyst metal film, which is named as graphite-metal induced crystallization of a-C (G-MICA). We finally demonstrate the formation of a graphite with uniform thickness below 30 nm on 8-inch SiN_x/Si wafer with an annealing at 500°C for 1 h. In order to reveal the origin of thickness uniformity of G-MICA, we closely observe the microstructure evolution of graphite as a function of annealing temperature (400~800°C) and time (0.25~180 min) using Cs corrected transmission electron microscopy. We believe that the nucleation of graphite starts to form at the interface between Ni and a-C and so vertical growth of graphite is limited by the thickness of Ni, which is somewhat differ from previously reports. To evaluate EUV characteristic, we removed the SiNx layer under the graphite through dry etching as thin as possible and made it in the form of a membrane. The G-MICA pellicle with thickness of 18 nm showed EUV transmittance of 88%, and emissivity of 0.3. Therefore, we confirmed the possibility of low-temperature G-MICA as a pellicle synthesis.