Orifice probe for plasma diagnostics: II. Multi-parameter analysis

A multi-grid orifice probe and analysis technique are presented which permit the measurement of the following plasma parameters: the electron number density n e , the electron temperature T e , the space potential V s , and an estimate of the metastable number density n m . Simultaneously, the analysis allows the quantitative determination of instrumental parameters such as the reflection coefficient for slow (<30 eV) electrons from the grids R e (G) and roughened (gold-black) collector R e (C), the secondary electron emission coefficient for fast (> 30 eV) electrons γ e (G) from the grids, and the effective transparencies of the grids for electrons τ e (G), and for metastables τ m (G). Experimental ion, electron and total current characteristics are presented for a low-pressure (1·8 × 10 −2 Torr) RF discharge in argon. The major part of the analysis method involves the use of ten `plateau values' obtained from the characteristics to determine values for most of these parameters. T e and V s are determined separately. The values obtained are: n e =2·74 × 10 9 cm −3 ±18%, kT e =1·92 eV±5%, V s =11·7±0·1 V, n m similar, equals 3·3 × 10 9 cm −3 ±50%, R e (G)=0·65±0·10, R e (C)=0·22±0·10, γ e (G)=0·935±0·010, τ e (G)=0·830±0·002, and τ m (G)=0·850±0·002. The transparencies τ e (G) and τ m (G) are within 4% of the geometrical transparency τ(G)=0·860. Approximately equal numbers of atoms (1 in 2 × 10 5 ) are in metastable and ionized states.