The effect of oxygen and nitrogen additives on the growth of nanocrystalline diamondfilms

Abstract

Nanocrystalline diamond (NCD) films have been synthesized byusing either nitrogen addition or oxygen addition to conventionalCH4/H2 mixtures besides themost commonly used Ar/CH4 with or without H2 chemistry. However, the synthesis of NCD films using both nitrogen and oxygen addition simultaneouslyinto CH4/H2 gases has not been reported thus far. In this work, we investigate the effect of simultaneousO2 andN2 additionto CH4/H2 plasmaon the growth of nanocrystalline diamond (NCD) films, focusing particularly on the ratio between the amountof O2 andN2 additives intoconventional CH4/H2 gas mixtures on the morphology, microstructure, texture, and crystalline quality of theNCD films. The NCD samples were produced by using a high microwave power (3 kW) in amicrowave plasma-assisted chemical vapour deposition reactor with a maximum power of 5 kWon large silicon wafers, 2 inches in diameter, and characterized by high-resolution scanningelectron microscopy, x-ray diffraction and micro-Raman spectroscopy. Our work demonstratesthat, under the conditions investigated here, NCD films can be formed when the ratio ofO2/N2 addition is increasedfrom 0 through 1 up to 7/3 (at higher than 7/3, for example 4, a large-grained polycrystalline diamond film will form), and the crystallinequality is significantly enhanced with the increase of oxygen addition. The mechanism ofO2 and N2 additives on the formation of NCD films is briefly studied.