Research Of Large Scale Nano-crystalline Diamond Deposition Using Novel MPCVD Apparatus

Nano-crystalline diamond film (NCD) is an ideal functional material with low surface roughness, low friction coefficient, high elastic modulus, good field emission properties and other excellent performances. At present, more researches are carried on nanocrystalline diamond films, but the use of microwave plasma chemical vapor deposition (MPCVD) of large scale of high-quality nanocrystalline diamond films are very rarely reported. This article applies a new microwave plasma chemical vapor deposition apparatus to deposited large scale high-quality nanocrystalline diamond films, and relevant studies of the deposition process are investigated.The microwave frequency of new microwave plasma chemical vapor deposition apparatus is 2.45GHz, the maximum output power is 10kW. The superposition of two different modes microwave TM01 and TM02 stimulate a plasma ball of 150mm diameter in the reaction chamber. In the process of the deposition of large scale high-quality diamond film, several factors were respectively studied, including pretreatment of the substrate, the reaction pressure, microwave power, substrate temperature and carbon concentration in the reaction gas.Via studying different pretreatment impact on the films, it shows that the film whose substrate surface was polished by pad with matte leather nano-crystalline diamond powder grinding and polished by the ultrasound process after the deposition has the smallest grain size and surface roughness. The best pretreatment parameter: the diameter of 100mm silicon mirror polished by pad in matte leather nano-crystalline diamond powder grinding for 5min, the continued use of nano-crystalline diamond powder suspension in acetone ultrasonic secondary grinding for 5min, carry out a ultrasonic cleaning with a final acetone solution for 5min, naturally dried in the air and then used for large scale deposition of high quality diamond thin films. Research on microwave power and reaction pressure shows that the increase of microwave power will increase the volume of the plasma ball, while the increase of pressure will reduce the volume of the plasma ball. The substrate deposition temperature's studies show that low temperature deposition process can increase the secondary nucleation rate, the higher temperature causes grains'growth and improves the diamond deposition rate. Generally, the deposition temperature was ultimately determined in 680℃. Research on the carbon concentration founds that as the increase of CH₄ concentration, sediment grain size decreases from thin films, surface roughness is reduced, and the high carbon concentration will increase the non diamond phase content, which will affect the quality of the film, so in the nucleation stage, the CH₄: H₂ = 15:100 is a better chose, as in the sedimentary stage CH₄: H₂ = 6:100.Through the above study, the key technologies of preparing large scale high quality diamond film in the microwave plasma chemical vapor deposition apparatus are mastered. The optimum parameters of depositing large scale high-quality nano-crystalline diamond films are obtained through systemetic researches which provides the experimental basis and theoretical guidance for nano-crystalline diamond films deposition.