Study Of Diamond Films Preparation And Microstructure By DC Hot Cathode PCVD Method

Diamond films with high quality were synthesized by DC glow discharge plasma chemical vapor deposition. Diamond films with this method have high growth rate. There are great differences between DC glow discharge at high gas pressure and at low gas pressure. The characteristics of DC glow discharge at high pressure were researched in this thesis. The technics of DC glow discharge at high pressure were optimized. Growth characteristics of diamond films were studied. Growth techniques of diamond films with high thermal conductivity and high abrasiveness ratio were set up. The followings are the main contents of this these:1. Characteristics of dischargeCharacteristics of DC glow discharge at high gas pressure were researched. There are four parts in the region of discharge: cathode-glow, Faraday dull area, sphere of plasma and anode-glow. The situation of different discharge parts was studied: original electrons come from thermal electron emission andγprocess. A lot of electrons appear when original electrons and gas particles collide, and at the same time gas was ionized. Cathode-glow covers cathode, and its area increases with discharge current increasing or gas pressure decreasing. Energy of electrons in the Faraday dull area is low. Most collisions between electrons and other particles are elastic, and energy of electrons increases gradually in the course of moving to the anode. Thickness of Faraday dull area is correlative with the category of discharge gas. Sphere of plasma is main region of gas excitation and ionization. Its color, size and shape depend on gas category, gas density, gas pressure and discharge current, size proportion and space between cathode and anode. We have acquired the relations of various discharge parameters that discharge voltage increases with gas pressure increasing as well as space between cathode and anode. Voltage saturation appears in the course of electric current increasing. Resistance between two electrodes decreases with the current increasing. It indicates that the number of the electrification particles increases as current increases.2. The growth characteristics of thick diamond filmsGrowth rate of diamond films, surface figure, crystal boundary, quality, distribution of thickness, micro-crack and split have been researched in this paper.Discharge current and gas flux have a great impact on growth rate of diamond films. Diamond films were deposited by employing methane, acetone, ethanol as well as the compounds of methane and methanol, and growth rate of diamond films was studied. The growth rate of diamond films increases when carbon-source gas increases. Diamond phase is restrained because of graphite phase being deposited heavily on the diamond surface when carbon-source gas reached to a curtain amount. Meanwhile, graphite is etched rapidly, leading to the decreasing of the growth rate of diamond films. And growth rate maximum, which depends on the categories of carbon-source gas, appears with flow rate increasing. The maximum of growth rate will increase if we have appended oxygenous carbon-source gas properly, but the growth rate will decrease obviously when oxygen flow rate excess. The maximum of growth rate appears with discharge current increasing as well as carbonaceous gas flow rate increasing. The growth rate will increase with gas pressure increasing. Substrate temperature influences the growth rate evidently. It is beneficial to increase the growth rate of diamond films that stabilize the substrate temperature at about 1000℃.Diamond films were deposited with compounds of methane and ethanol. We have investigated the surface figure of diamond films. The figure varies gradually from mix-faces of (111) and (110) to (110) and then from (110) to (100) with the gas flow rate increasing. The most (110) and (100) faces appear when carbon-source gas is the compounds of methane and methanol. Crystal grain edges and corners are etched obviously when methanol flow rate increases. (100) appears when substrate temperature is low. (111) and (110) faces appear gradually with the increasing of the temperature. Integrity of crystal shape is destroyed at 1100℃.Boundaries of diamond films have been studied. They can be shown clearly on the diamond films section that are etched and polished by hydrogen microwave plasma. Grains that are fabricated with low carbon-gas flow rate are long and big at growth direction, and hypo-nucleation is rare. The hypo-nucleation appears when carbonaceous gas flow rate increases. Boundary density increases at the growth direction. The quality of diamond films gets worse, for example, the grains become small and the boundary becomes dense and roughness, with the carbonaceous gas flow rate increasing,. It is shown that non-diamond carbon concentration is high in the boundary.The study of micro Raman spectroscopy shows that the quality of diamond films gets worse with carbonaceous gas flow rate increasing and its quality improves with current increasing. The quality decreases radially gradually, the primary cause is no-uniformity of plasma at the radial direction.3. Thermal conductivity and mechanical properties of diamond films and Micro- crack and splitThermal conductivity of diamond films increases with current increasing. It decreases as ethanol flux increases. Characteristics of diamond films with thermal conductivity higher than 8W/K.cm are as follows: amorphous carbon and graphite are not seen in Raman spectroscopy. Morphology of diamond films shows (111) and (110). Diamond films with high thermal conductivity are transparent. We get optimal technics in our experiment conditions, and diamond films with high growth rate and high thermal conductivity (16W/K.cm) are synthesized.We have researched anti-abrasiveness of diamond films. Abrasiveness ratio decreases rapidly as discharge current decreases or flux increases when carbonous gas flux is high or discharge current is low. Abrasiveness ration is high (200,000-400,000) when carbonous gas flux is low and discharge current is high. We get optimal technics to synthesize diamond films with high abrasiveness ratio. Micro- crack and split often happen when diamond films are synthesized. We research micro-crack and split according to tension of diamond films. The predominant factors are the substrate temperature and its variety. Micro-crack and split can be avoided when substrate temperature is stabilized at about 1000℃.