Effect of plasma composition on nanocrystalline diamond layers deposited by a microwave linear antenna plasma-enhanced chemical vapour deposition system

The addition of CO2 into the process gas has a significant impact on the quality and the incorporation of boron in CVD diamond layers. In this report we study the effect of CO2 addition in the gas phase on the properties of boron doped nano-crystalline diamond (BNCD) layers grown at low substrate temperatures (450-500 degrees C) using a microwave linear antenna plasma-enhanced chemical vapour deposition apparatus (MW-LA-PECVD). Experimental results show an increase in the layers' conductivity with a reduction in CO2 concentration, which is consistent with the variation in the atomic boron emission line intensity measured by optical emission spectroscopy (OES). At CO2 concentrations close to zero, we observed the formation of a smooth, transparent and highly resistive layer on unseeded substrates. This layer has been identified as silicon carbide (SiC) by transmission electron microscopy and X-ray photoelectron microscopy. The presence of silicon in the plasma is confirmed by OES and it is attributed to quartz tube etching. In this specific deposition condition, diamond growth is in competition with SiC growth, which affects the diamond layer properties. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim