Effect of additional gas on diamond deposition by DC PACVD

The effect of the addition of Ar and nitrogen gas on the deposition of diamond using a direct current (DC) plasma of CH4-H2 gas mixture is investigated. The DC plasma is generated by applying a voltage between 820 and 900 V and the resulting current is between 5.5 and 6 A. The addition of Ar makes the plasma unstable and is limited to 5% owing to the plasma extinction at higher Ar concentrations. Growth rate and non-diamond carbon content in the diamond film increase with the Ar amount slightly irrespective of deposition temperature. An optical emission spectrum shows the increase of emission of C2 and CH while showing a constant average electron energy of the plasma. On the contrary, by adding nitrogen, the morphology is changed to a ball-like diamond shape as well as growth rate of diamond film is decreased abruptly. The optical emission intensities of C2 and hydrogen also show an abrupt drop with the nitrogen addition. The role of plasma species in the deposition behaviour of diamond is also discussed.