Effects of Noble Gas Dilution (Ar, Ne, He) on Hydrogenated Amorphous Carbon Films Deposited by Acetylene-Based PECVD

This study investigates the influence of noble gas (Ne and He) mixing ratio on the properties of hydrogenated amorphous carbon (a-C:H) films deposited by plasma-enhanced chemical vapor deposition (PECVD) using C 2 ​H 2 ​/Ar/Ne and C 2 ​H 2 ​/Ar/He gas mixtures. The film mass density and the Raman D and G band ratio, I D ​/I G ​ ratio remain consistent around 2.1 g/cm −3 and 0.4, respectively, across all mixing ratios for both gas mixtures. In contrast, the film compressive stress decreases with increasing the noble gas mixing ratio, dropping from 4.8 GPa to 3.7 GPa (23% decrease) for Ar+Ne and to 3.4 GPa (30% decrease) for Ar+He. Concurrently, the Full Width at Half Maximum (FWHM) of the G peak decreases slightly from 199 cm -1 to 195 cm -1 for Ar+Ne and to 193 cm -1 for Ar+ He. In other words, the addition of light noble gases brings about stress relaxation without altering the sp 3 and sp 2 bonding ratio or film density. TRIM simulations revealed that He and Ne ions penetrate deeper into the film and generate fewer vacancies and absorb less energy in carbon atoms compared to Ar ions. Among these three ions, He ions exhibited a broader energy distribution and minimal vacancy generation, indicating a milder structural impact. The observed stress reduction is attributed to the milder ion-induced structural damage by lighter noble gas ions.