Graphite Evolution by Metal Induced Crystallization of Amorphous Carbon e on SiN_x/Si Substrate with 8 Inch Scale

Graphite is an attractive candidate for next-generation EUV pellicles due to its high emissivity (&gt;0.3) and robust mechanical properties, such as a Young's modulus of 4.1 GPa, which ensures excellent thermal and mechanical stability. A pivotal necessity for EUV pellicles is the attainment of high EUV transmission, which demands the utilization of ultra-thin films with a thickness of approximately tens of nanometers, while simultaneously ensuring uniformity across extensive areas. The most common method for synthesizing graphite is chemical vapor deposition (CVD) on thick metal catalysts, but this approach has several drawbacks, including difficulties in controlling thickness uniformity and potential damage during wet-transfer processes. To address these challenges, we propose a direct synthesis of graphite films (thickness &lt; 30 nm) on insulating substrates at a relatively low temperature of around 500°C. This process starts from amorphous carbon (a-C) deposited on a thin metal catalyst layer and is referred to as graphite-metal induced crystallization of a-C (G-MICA). Previous studies have shown that when metal and a-C layers of equal thickness are sequentially deposited and subjected to heat treatment, the a-C diffuses through the metal, forming graphite between the insulating substrate and the metal layer. Using this method, graphite can be directly grown on insulating substrates. In our study, we employed Ni as the metal catalyst, achieving uniform graphite layers with a thickness of 30 nm on 8-inch SiN_x/Si substrates.<br/>To investigate the growth kinetics of graphite from a-C through the Ni catalyst, leading to a uniform G-MICA layer, we carefully monitored the microstructural evolution of the graphite with the increasing the annealing temperatures from 400 to 800°C using X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), and double Cs-corrected transmission electron microscopy (TEM). The a-C (30 nm)/Ni (30 nm)/a-C (1 nm) layers were RF sputtered without vacuum interruption onto a 150 nm SiN_x/Si substrate. We observed that at 400°C, graphite nucleation begins at both the interface between a-C and Ni, as well as between Ni and the SiNx substrate, and all nucleation occurs in Ni layer. This agrees well with thermodynamic calculations regarding interface energies under nucleation conditions. However, further growth beyond 500°C suggests that the dominant nucleation site is the interface between a-C and Ni. The vertical growth of graphite nuclei at this interface is constrained by the thickness of the Ni layer. Interestingly, we found that the graphite thickness remained around 30 nm across all temperatures above 500°C. Furthermore, in samples with varying Ni thicknesses (10, 30, and 50 nm) while maintaining a constant a-C thickness (100 nm), and in samples with varying a-C thicknesses (30, 50, and 80 nm) with a constant Ni thickness (30 nm), the graphite thickness matched the Ni thickness in all cases. The interstitial in-diffusion of carbon into Ni is governed by the substitutional out-diffusion of Ni into a-C. Thus, it appears that the completion of Ni out-diffusion is dependent not on the thickness of the a-C layer but rather on the matching amounts of carbon and Ni. Additionally, at temperatures above 600°C, Ni begins to diffuse into the SiN_x layer, and Si and N are detected within the Ni layer. Therefore, we determined that the optimal annealing temperature should remain below 600°C to prevent unwanted diffusion. Ultimately, we demonstrate the successful formation of a uniform graphite layer, less than 30 nm thick, on an 8-inch SiN_x/Si wafer after annealing at 500°C for 1 hour.<br/>In this presentation, we will describe the detailed temperature-dependent the microstructure evolution of graphite from a-C through Ni thin film and the thickness control mechanism along the corresponding kinetic pathways.