Study On Uniformity Of Diamond Films Prepared By MPCVD

Special crystal structure it has so that diamond has lots of excellent chemical andphysical properties, it is one of the most potential new carbon materials. The limitednumbers, high cost and granular shape of natural diamond limit its application in manyfields. Recent advances in the chemical vapor deposition of diamond films have arousedgreat interest in researchers and industry, although the performance of CVD diamondfilms is excellent, but to put it really applied to each field we must improve the preparationuniformity of the film. Microwave plasma chemical vapor deposition (MPCVD) is amethod that can effectively prepare large area、uniform、pure、high quality diamond films.In this paper, diamond thin films have been deposited onto mirror-polished (100)facets single-crystal silicon wafers using a gas mixture of hydrogen and methane by ahome-made1kW quartz bell jar MPCVD apparatus. Firstly, I have explored the impact ofchanges in process parameters on the uniformity of diamond films prepared by MPCVD,here, my experiments were main conducted from two perspectives, one is the change ofcarbon concentration, another is the change of microwave power and deposition pressure.The samples prepared by MPCVD apparatus were characterized by raman spectroscopyand scanning electron microscope(SEM). The results have showed that under the premiseof only changing the carbon concentration, plasma has provided enough energy to fullionizing the mixed gas within the chamber when carbon concentration was lower to1%,this has decreased the phenomenon of secondary nucleation, diamond grains have morespace to grow up, because of that you could see the shape of grains obviously after acertain stage’s deposition, the uniformity of the films was good. Under the premise of onlychanging the microwave power and deposition pressure, in unit time, high energy plasmahas fully ionized the rarefied gas within the chamber under the condition of microwavepower as high as800W and deposition pressure as low as7.5kPa, this has significantlyreduced the occurrence of secondary nucleation, specific facets of diamond grains wouldhave appeared obviously after a long time’s deposition, the uniformity of the films wasgood.Then, I have researched the impact of improvement in experimental devices on theuniformity of diamond films prepared by MPCVD. During the experiment, process parameters have been remained unchanged, one of the samples has added a tantalum ringof refractory metal, attempting to narrow the gap of plasma density at various positions onthe silicon wafer by the behavior of plasma was easily adsorbed on the surface of metalring, another sample has not added a tantalum ring of refractory metal, deposition time oftwo samples is24hours. After characterization I have found out that the quality ofdiamond films deposited on the centre of sample was significantly higher than diamondfilms deposited on the edge of sample, there is a big difference between sample’s filmthickness in different area: substrate centre、5mm away from substrate centre、substrateedge, the sample which has not added a tantalum metal ring; the quality of diamond filmsdeposited on the centre of sample was almost the same as diamond films deposited on theedge of sample, there is a little difference between sample’s film thickness in different area:substrate centre、5mm away from substrate centre、substrate edge, the sample which hasadded a tantalum metal ring. Finally, I have extended diamond films’ deposition time to40hours, by measurements multiple positions’ film thickness of the samples, I have drawn adiagram about thickness distribution of diamond films, through film thicknessdistribution’s comparison of the two samples I have proved that add of tantalum metal ringis a method to improve the uniformity of diamond films prepared by MPCVD.