Effect of additional gas on diamond deposition by DC PACVD

Abstract

The effect of the addition of Ar and nitrogen gas on the deposition of diamond using a direct current (DC) plasma of CH4-H-2 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 C-2 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 C-2 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.