Plasma-Surface Interactions and Impact on Electron Energy Distribution Function

The goal of this work is to explore the role of surface processes in influencing characteristic electron energy distribution functions (EEDF).As a model system, we use a well characterized, inductively coupled plasma system to examine Ar/H₂ (or D₂) discharges interacting with a-C:H films. The modification/erosion of a-C:H surfaces is monitored in real time by ellipsometry and the effects of gas mixtures and surface generated carbon on plasma parameters (T_e, plasma density, EEDF) are probed with Langmuir probe measurements. We find that plasma density decreased greatly (from 10¹¹ to 10⁹ per cm³) with small H₂ additions to Ar plasma (conditions: 10-30 mTorr, 300-600 W source power). The electron temperature was shown to increase with H₂ flow. At high H₂ flows, the electron energy distribution transitions from Maxwellian distribution to a two-temperature distribution. The addition of 1-20 % CH₄ into H₂ plasma shows an increase in plasma density and a change in the electron temperature. The hydrocarbon erosion products of a-C:H films in H₂ plasma are found to cause a similar effect on plasma properties as CH₄ addition. These observations indicate that prediction/control of EEDF for plasmas interacting with reactive bounding surfaces requires an understanding of the consequences of the plasma-surface interactions.