DC Hot Cathode Glow Discharge And High Quality Diamond Film Synthesis

Hot cathode glow discharge chemical vapor deposition is a new method to deposit high quality diamond films with high deposition rate. In order to acknowledge discharge characteristics and optimize the deposition process, in this paper, the special properties of hot cathode glow discharge are studied and the effects of discharge current to hot cathode glow discharge and diamond films are studied in detail. In the first part, the characteristics of the hot cathode are studied. According to the general criterion of cathode choice and the peculiarity of PCVD system, tantalum is an ideal material for hot cathode. Tantalum has outstanding physical and chemical properties, but it also has a high activity to gases. By analyzing the action of tantalum with H2, CH4 , O2, we know that in the PCVD system, the surface of cathode is TaC, TaC has better properties than Ta, but further machining is difficult. If the ambient contains oxygen atoms over an extent, the tantalum cathode would be damaged. Therefore, the base vacuum and the gas leakage of the deposition system should be strictly controlled. Meanwhile cathode surface morphology, surface distribution, surface cleanliness, the size and place disposition between cathode and anode, cathode temperature, the base vacuum and the gas leakage of the deposition system are most important factors influencing the stability of high current glow discharge. In the second part, the effects of discharge current on the deposition process are studied. Under the conditions that other deposition parameters are immobilized, the relations between discharge current and glow discharge state, cathode temperature, discharge voltage are as following. With the increase of discharge current, the axial length of positive column plasma region is increased, the part near the Faraday dull area shows the trend of expanding and leads to the augment of the volume of the plasma sphere and the color of the plasma sphere changes from purple to light cyan then to the visible cyan, compressing the purple part to the anode fall region. Both the cathode temperature and discharge voltage increase as the discharge current increases. At last, the influences of discharge current upon the growth rate the diamond films are studied. Under our experiment conditions, as the discharge current increases, the gas dissociation rate increases, but the flux of carbon-source gas is low, the efficiency particles are few, it can not remedy the reverse effect of current increase. (as the increase of the discharge current, the anode potential fall increases, which restrains the movement of the efficiency ions toward the substrate) So the growth rate decreases as the discharge current increases. The qualities of the diamond films are characterized by the methods of SEM, Raman spectrum, XRD. Comparing the SEM pictures of the diamond films deposited under different discharge current, we can make a conclusion that the augment of discharge...