| Chemical vapor deposition (CVD) diamond film is similar to natural diamond for their chemical and physical properties and has a wide range of applications. However, it is limited by its high surface roughness, non-uniform thickness and non-uniform grain size. And the surface roughness and the grain size increase with diamond film thickness up to a millimeter. In order to overcome these limitations, the films should be polished to a desired application specific requirement.In this paper, we propose a new method etching of diamond films by ECR plasma with an asymmetric magnetic mirror field. The plasma generates at the upstream and diffuses to the downstream. The strength of the magnetic field at the downstream is stronger than the upstream. As the magnetic field increases, parallel motion of ion is surrendered to perpendicular motion. Cyclotron ion beams with anisotropic character can be obtained and are used to etch the diamond films in this self-designed microwave ECR plasma device. This method makes great use of advantages of plasma etching, including low pollution, operating on non-planar, and low operation temperature. Meanwhile, it makes the most of the cyclotron characteristics of ions, which could be used to uniform smoothing diamond film with large area. Based on the described principle, mainly works contain as below in this paper:1. The influences of gas pressure and bias voltage of anode cylinder on the ion parameters are studied by an ion sensitive probe. The etching of CVD diamond film is accomplished under optimized gas pressure and bias voltage of anode cylinder conditions. The results showed that the diamond surface roughness is decreased from3.525μm to2.512μm and the amount of non-diamond phase dramatically increases by ion beam etching, and then the surface roughness decreases to0.517μm but the amount of non-diamond phase dramatically decreases by m(?)chanical polishing. The efficiency of m(?)hanical polishing diamond film is dramatically improved when the diamond is etched by oxygen cyclotron ion beam. The above results indicate that:The protuberant crystal edges and (111) facets suffer much more active energetic ion bombardment, while the concave grain boundary suffer less ion bombarding, resulting in the decrease of surface roughness; the amount of non-diamond phase dramatically increases with the decrease of surface roughness by ion beam etching; etching by oxygen cyclotron ion beam contributes to the the subsequent processing of diamond, and its damage to the structure of diamond only occurs on the surface of diamond film but without any effect on the performance of diamond thick slices.2. The influences of nitrogen doping on the etching characteristic of CVD diamond films are studied and the etching mechanism is explicated in detail by etching models. It is found that:The (111) facets are etched and the pyramidal crystallites of the non-nitrogen diamond film have completely sunk and only a little small protuberant wreckage of crystallites is preserved over the whole diamond surface while the crystal edges are dramatically etched for the nitrogen-doped diamond film after4h etching. And the nitrogen-doped diamond film surface roughness decreases from4.761μm to3.701μm while the surface roughness of the undoped film decreases from3.061μm to1.083μm. The results indicate that nitrogen doping has great influence on the etching characteristic of CVD diamond films. Nitrogen-doping deteriorates the film quality and increases the defect density in the crystallites. And the defect distributes in the crystal edge which leads to dramatically etching of crystal edge. Compared with nitrogen-doped diamond film, the defect density of undoped diamond film is relatively lesser and the distribution of the defect is comparatively uniform, resulting in (111) facets suffering from oxygen cyclotron ion beams bombardment and grains collapsing. The reason why the surface roughness of nitrogen-doped diamond film decreases less than undoped diamond film is that the movement of ions affects by electrons emitting from crystal edge which weaken the ion bombardment on (111) facets.3. The influence of the magnetic field configuration, work pressure, substrate temperature and the scale of substrate on the etching characteristic of CVD diamond films are investigated. The results show that:(1) With the current of coil D increasing, the strength of the magnetic field at the downstream increases and the particle dynamics totally changes that particles are constrained to gyrate about the lines of force so that they move at different rates along and across the field, resulting in the increase of ion and electron temperature, plasma density and ion flux. Meanwhile, the thicknesses of the sheath decreases while the electric field strength in the sheath increases, enhancing field emission of crystal edge. Under the above condition, the surface of diamond films suffers from the energic ion bombardment and the surface roughness dramatically decreases.(2) With the increase of work pressure, ion and electron temperature and plasma density first increases and then decreases, and ion flux changes with the changes of work pressure in response, resulting in that the surface roughness first increases and then decreases trends.(3) As the substrate temperature rises, the reactivity of diamond film is enhanced and reaction valve can be reduced. And the amounts of thermal desorption of oxygen atoms or oxygen molecules on the diamond surface increase significantly. The (111) facets and cry(?)al edge of diamond films suffers from much more energic ion bombardment, resulting in formation of larger etching pits and the dramatica(?)delecrease of surface roughness.(4) The bigger substrate significantly impedes the diffusion of particles and reduces ion flux in the diamond surface. Reducing the scale of substrate, ion and electron temperature increases causing the increase of sheath voltage, resulting in enlarge the perpendicular oxygen ion energy and intensify the perpendicular etching, which could be contributed to re-deposition. |
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