EMISSION-SPECTROSCOPY DURING DIRECT-CURRENT-BIASED, MICROWAVE-PLASMA CHEMICAL-VAPOR-DEPOSITION OF DIAMOND

Optical emission spectroscopy was used to investigate dc biasing during diamond film synthesis in a microwave plasma. These measurements show that biasing produces significant changes near the substrate (i.e., close to the sheath region). Increasing the negative bias voltage (V(b)) from 0 to - 180 V in a CH4/H2/Ar (4/496/30 sccm) mixture increases the intensities of the hydrogen Balmer alpha and beta lines. The relative concentrations of neutral atomic hydrogen were estimated by using an Ar(750.4 nm) emission fine as an actinometer. At 38 Torr, increasing V(b) from 0 to - 150 V increased the concentration of atomic hydrogen by more than 20%. In addition, increasing V(b) also increased the electron temperature near the substrate. These effects are likely to play an important role in the enhanced diamond nucleation that has been observed after negative-biased pretreatment.