Large Area Ultrananocrystalline Diamond Films Deposited By Direct Current Chemical Vapor Deposition

Ultra-nanocrystalline diamond(UNCD,grain sizes less than 20 nm)is a functional carbon material with new-type structure.UNCD films possess the advantages of tiny diamond grain sizes,high hardness,high strength,outstanding physical and chemical properties as similar as single crystal diamond,which make it have broad application prospects in many fields,such as mechanical processing,marine dynamic seal,micro electron mechanical system(MEMS),field emission,optical windows,electrochemistry,acoustic devices,biomedical sciences.UNCD films were deposited on ?100 mm(100)single crystal silicon substrates by using CH4/H2/Ar or CH4/H2/N2 gas mixtures in a direct current glow discharge plasma chemical vapor deposition(CVD)system.The influence of CH4 concentration,deposition temperature,doping argon concentration,doping nitrogen concentration on the surface morphology,microstructure features of the diamond films were analyzed by scanning electron microscopy(SEM),Raman spectrometry,X-ray diffraction(XRD),atomic force microscopy(AFM)and transmission electron microscopy(TEM).The experiment results show that the diamond grain sizes decrease with the increase of CH4 concentration or the reduction of the deposition temperature.When the CH4 concentration is 12.0%,the diamond grain sizes are about 50 nm.But under high CH4 concentration,the amorphous carbon is seriously deposited on the cathode,which will make arc discharge formation.When the deposition temperature is 650?,the diamond grain sizes are about100~200 nm while the deposition rate is very low.UNCD films could be deposited by doping a certain concentration of argon or nitrogen into the methane and hydrogen mixed gas source.But too much doping argon or nitrogen cause non-diamond phase carbon to bedeposited on the surface of the cathode,which will lead to arc discharge.When the argon concentration is 25.0% or the nitrogen concentration is15.0%,the diamond grain sizes could decrease to 10~20 nm.In addition,the doping of a certain concentration of argon can decrease the temperature difference between the center and edge of the silicon wafer and is in favor of the deposition of large area UNCD films.UNCD films were deposited on ?100 mm silicon wafers under the optimized deposition process parameters: deposition temperature is 800 ?,argon concentration is 25.0%,deposition pressure is 4.0 kPa.The average diamond grain sizes and the deposition rate are 10~20 nm and 0.6 ?m/h,respectively through the characterization of SEM and TEM.