Growth Of Single Crystal Diamond By Microwave Plasma Chemical Vapor Deposition

Homoepitaxy of single crystal diamond on high pressure high temperature(HPHT) diamond grain, HPHT substrate and CVD substrate has been studied usingself-developed device of low power microwave plasma chemical vapor deposition(MPCVD). The main research contents are presented as follows.Firstly, homoepitaxy of single crystal diamond on HPHT diamond grain isresearched. The diamond grains loaded on the self-developed holder are pre-treatedby four steps including mechanical polishing, acid treatment, ultraphonic bath usingacetone and H plasma treatment. Then, the effects of etching pits, pressure and severalrelated parameters on the morphology and growth rate of diamond are researched. Theresults show that rectangle and triangle etching pit will expose on the etched (100)and (111) crystal surface of diamond, respectively, which may lead to formation ofrectangle and triangle morphology after growth. In a relative low pressure, the growthtrends to terrace growth composed of C-H cluster and the growth rate will increasewhen a small amount of oxygen is added into the air source. In contrary, the diamondwill grow step by step overwhelm the whole surface of diamond substrates in arelative high pressure. The growth rate of diamond will increase with the rise ofmethane concentration, pressure and the temperature of substrate. It is seen from theRaman spectra that the quality of growth layer of diamond is satisfying, while thelayer contacting with holder is graphitized seriously.Secondly, homoepitaxy of single crystal diamond on HPHT diamond substrateoffering a lager growth surface is researched. The effects of methane concentrationand H plasma etching on the mode of diamond growth, and the effects of methaneconcentration and pressure on the growth rate of diamond are studied. Thehomoepitaxy of single diamond is improving by adding H plasma etching process inthe process of growth and adding oxygen into the air source. It is shown that thegrowth mode of diamond can be divided into two main categories, includingstep-flow growth and hillock growth according the diffusion rate of C-H precursor onthe diamond substrates. A relative low methane concentration is more likely to lead to a step-flow growth and vice versa. Attributing to point and marginal charging effects,polycrystal diamond is more possible to be found on the edge of diamond substrate.After being H plasma etched, the surface of diamond substrate is covered with etchingpits, including several large size with high defect density where the hillock growthmore likely to happen. The area with polycrystal diamond grains due to hillockgrowth have more amorphous carbon and impurity than the transparent area. Thehillock growth can be suppressed effectively when H plasma etching is put into theprocess of growth, which can prolong the duration of growth. The growth rate ofdiamond will increase with the increase of pressure when methane concentration isgiven. The growth rate of diamond will rise as does as the methane concentration doesunder some pressure, however, the morphology of diamond with more amorphouscarbon will become terrible when the methane concentration is passed over more than6%. It is shown from the Raman spectra that the quality of diamond is satisfying inthe inception phase of growth, while the content of amorphous carbon become morewith the increase of thick of the growth layer. The diamond after homoepitaxy canmaintain a high quality with a methane concentration more than6%in the conceptionof addition of oxygen, what’s more, the growth rate of diamond can be furtherimproved than before. However, nanocrystalline diamond can be detected in a highmethane concentration.Thirdly, homoepitaxy of single crystal diamond on CVD diamond substrate withless impurity and defect is researched. The effect of methane concentration on thequality of diamond growth is studied. Meanwhile, the homoepitaxy on CVD andHPHT diamond substrates are compared from two perspectives including the plasmaemission spectra and the quality of growth. The results show that the growth rate ofdiamond is increasing with the rise of methane concentration, more than that, atransparent and pure epitaxial surface can be obtained when the methaneconcentration is more than8%. It is seen from plasma emission spectra in the processof growth that the Hαconcentration of CVD diamond substrate is more than that ofHPHT diamond substrate. Hαcan etch amorphous carbon and graphite effectively, sothat CVD diamond substrate can get a more ideal epitaxial surface with less amorphous than HPHT diamond substrate after growth.