Research On The Etching Of CVD Diamond Films Using DC Glow Oxygen Plasma

Chemical vapor deposition (CVD) diamond film has many excellent properties and numerous potential applications in machine, microelectronics, optics and military industry. Generally, CVD diamond films were polycrystalline wafers which have very rough surface. Therefore, they must be polished, cut and patterned to meet the different needs of particular industrial applications.At present, the focus of international researches on diamond film has transferred from the investigations on synthetic technique to the research on processing technique and application of diamond film. Improving the efficiency of conventional mechanical polishing, carrying out the basic and applied researches on plasma etching of CVD diamond and further developing the application of plasma etching are the present important issues in the industrial application of diamond films. This paper focuses on the etching of diamond film through direct current (DC) glow oxygen plasmas and mainly contains three works as below:(1) Etching of CVD diamond film using oxygen plasmas produced by self-developed DC glow discharge device was investigated. It was found that oxygen plasma etching could lead the diminishing of pyramidal crystallites and the producing of numerous etching pits. At a constant gas pressure the rise of DC power would result in the increase of deepening etch pits overspreading from the protuberant facets to the boundary of diamond crystallites with rising etching rate. And the same tendency was engendered by reducing gas pressure when the DC power remained at a constant. The numerous etch pits can be ascribed to etching with a higher rate of dislocations whose edges exist at the film surface. In accordance with an etching model, the measured results of Langmuir probe suggest that the influence mechanism was that different discharge parameters would lead different plasma densities and electron temperatures, so they would result in different ion fluxes and sheath voltages. And the increase of etching rate and the deepening etch pits can be mainly attributed to the enhanced directional etching with rising ion flux and sheath voltage.(2) The influence of oxygen plasma etching on conventional mechanical polishing was investigated. It was found that moderate plasma etching of CVD diamond can enhance the polishing efficiency of mechanical polishing. And the mechanism of etching enhanced polishing is expected to be that plasma etching can eliminate the polishing encumbrances by transforming the compact grains with sharp edges into the grains with thin faces and obtuse edges. Meanwhile it can produce a lot of etch pits and amorphous carbon which can accelerate the growing of micro cracks and thus result in faster micro-chipping of the top surface of the diamond film.(3) Deposition of carbon whistle with peculiar shape using oxygen plasma etching of diamond film was investigated. It was found that evident depositing phenomenon during etching could be observed when the diamond film temperature was above 700℃. Carbon whistle with two different shapes could be deposited through controlling etching time. And deposition of upright aligned carbon whistle could be achieved by increasing the DC voltage and etching temperature. The deposition of carbon whistle during etching could be attributed to the sputtering and re-depositing of carbon produced by enhanced etching rate of diamond film, and the deposited carbon whistle could prevent its reaction with oxygen positive ions as a consequence of the electron field emission characteristics of the micro columnar carbon tip.