Langmuir probe diagnostics of microwave electron cyclotron resonance (ECR) plasma

A Langmuir probe diagnostics is done on the microwave ECR generated plasma in a 2.45 GHz, 1.5 kW facility set up in our laboratory (for thin film deposition) by inserting a probe in the plasma close to substrate location (640 mm away from main ECR zone). A program using Graphical User Interface (GUI) was used for data analysis of I–V probe characteristics to obtain the radial electron energy distribution function (EEDF) in plasma. Plasma parameters such as charged particle density (ne and ni), electron temperature (Te), plasma potential (Vpl) and floating potential (Vfloat) were estimated at substrate location for two incident microwave power levels at a fixed operating pressure. These parameters were estimated by different methods like orbital motion limited (OML) theory, electron energy distribution function (EEDF) and conventional method. The results obtained by the different methods are compared and observed differences are explained. The results indicate that even though the diffusion of plasma at the substrate location is mainly forced by particle collisions that lead to radial plasma uniformity, it still shows a non-Maxwellian behavior for the electrons with two groups having different energies.