Preparation And Properties Of High Quality Transparent Diamond Films By Microwave PCVD

Diamond is an ideal material for many applications because of itsperfect properties in mechanical, optical, thermal and electrical.However, natural diamond is rare and expensive, which limits itsextensive usage. During science and technology growth in the lastdecades, there is a great development to synthetic diamond research.High Pressure High Temperature method (HPHT) and low-pressureChemical Vapor Deposition (CVD) method are the two main methodsin fabricating diamond.Microwave PCVD method is one of the most suitable method infabricating high quality CVD diamond films. Because of its lowcontaminated and stable plasma discharge, microwave PCVD methodis considered as the best method for fabricating high qualitytransparent diamond films. There are many studies in microwavePCVD diamond films during the past years, but the research work arestill not maturity, especially lacking studies in properties and fabricateproperties of high quality diamond films. So in this thesis, the highquality transparent diamond films are fabricated by high microwavepower CVD system and the diamond films' properties are studied. Thecontent of this study comprises three parts:1. There are some factors affect the deposition of diamond films, inwhich the methane concentration, microwave power and oxygen arethe most important parameters making great effect to the quality ofdiamond films. With the increasing of the methane concentration, thediamond film growth rate increase while the diamond films' qualityget worse;at the same time, high methane concentration make thefigure of surface grains augment. The film quality is good but the filmgrowth rate is low when the methane concentration is 2%;when thegrowth rate goes to 3%, the film growth rate increase and the filmquality is as same as the film deposited in 2% methane concentration,so we conclude that 3% methane concentration is the perfect conditionin the high quality diamond film fabrication. The microwave power isanother important parameter in the diamond films deposition, moremicrowave power give more energy to the reaction. It makes someeffects to the shape and the color of the plasma and changes thecomposition and the concentration of the different radicals in thereaction. However, high microwave power is favorable to thedeposition of high quality diamond film, when the microwave powergoes to 4500W or more, the deposition is getting stable, it is notnecessary to make the power much more. A small quantity of oxygenadding in the reaction will make good effects to the deposition ofdiamond film, the quality of film with 0.4% oxygen concentration indeposition is better than the quality of film with no oxygen indeposition. Raman spectrum shows that there is Graphite peak near1550cm-1 on the curve of the film depositing with no oxygen, whilethe Graphite peak disappeared on the curve of the film depositing with0.4% oxygen concentration.2. The properties of high quality transparent diamond film bymicrowave PCVD method are studied. The transmission of transparentdiamond films by MW-PCVD in infrared region is studied, the IRspectra shows that the average transmittance of diamond films dealtwith polishing is near 60%, which is close to the theoretictransmission of diamond 71%. There is not any absorb peak on the IRspectra of films except the diamond absorb peak at 4~6μm, whichmeans the MW-PCVD diamond films is deposited with good quality.The UV(ultraviolet) spectra shows that the transmission of diamondfilm in UV region is also good, no absorb peak is found. We find thatthe diamond films by MW-PCVD have high thermal conductivity. thethermal conductivity goes to 15~16 Wcm-1K-1,which is close to thenatural IIa diamond crystal. In the research of the facture strength ofMW-PCVD diamond films, it shows that the facture strength ofdiamond film is much lower than the natural diamond;however it canbe used in many applications.3. The impurity in MW-PCVD diamond film is studied. Someresearch to the XPS of diamond films is made, the result shows thatthere are some oxygen and nitrogen impurities which existed withC-O band, O-C=O band and C-N band in diamond film. ESR testshows that there are nitrogen impurities in MW-PCVD diamond filmwith Ns0 form.