Control of Plasma Parameters for High-Quality Hydrogenated Amorphous Carbon Growth

Abstract

The correlation between plasma parameters and film properties is demonstrated in the growth of device-grade hydrogenated amorphous carbon (a-C:H) from pure methane (CH4) by capacitively coupled plasma-enhanced chemical vapor deposition (CCP-CVD). The deposition rate, refractive index, film stress and film hardness are strongly correlated with the self-bias voltage, Vdc. Hard, rigid, and transparent a-C:H films can be fabricated when the self-bias voltage, Vdc, is around 160–200 V. The ion energy, which is determined by the Vdc, is used to rearrange the film structure. The Vdc of around 160–200 V corresponds to 70–80 eV of the C ion flux in the case of C2H5+ ions. According to the calculation using a modified Thomas-Fermi potential as the Coulomb screening potential, the incident C ion energy is estimated to penetrate the carbon film of 1.8 g/cm3 density to the depth of about 0.55 nm, which enables the densification of the a-C:H film.