The influence of antenna configuration and standing wave effects on density profile in a large-area inductive plasma source

The electrical and plasma properties of a large-area inductive plasma source are investigated. The source is a 71 cm x 61 cm x 20 cm metal chamber providing a processing area of 37 cm x 47 cm for large-size wafers and glass substrates for Rat panel displays. The exciting antenna is embedded inside the processing chamber, and the rf power is inductively coupled from the antenna to the plasma through thin (1.7 mm thick) quartz tubes. A tuning network is used to launch a travelling wave or a wave with a desired standing-wave ratio. The antenna-plasma system is modelled as a lossy transmission line, and a transformer model is applied to study the electrical properties of the system. The model is used to evaluate the conditions required to launch a travelling wave, and these conditions are verified experimentally. The plasma density distributions under various operating conditions are measured with Langmuir probes and compared to a global model for inductive discharges. Our experiments show that high plasma densities are produced over a large area, and that the density profiles are strongly influenced by the antenna configuration and standing-wave effects.