Planarizing CVD diamond films by using hydrogen plasma etching enhanced carbon diffusion process

Polycrystalline diamond films, deposited by microwave plasma chemical vapor deposition (MPCVD), were planarized in hydrogen plasma under the graphitization of iron film obtained by reduction of iron chloride under hydrogen plasma ambient. For this process, the free-standing diamond films were dipped in a saturated iron chloride solution and dried horizontally in atmospheric ambient. Then the diamond samples were heated by hydrogen plasma in the same MPCVD reactor. Under the effect of hydrogen reduction, iron thin film was formed on the surface of diamond films. Under ca. 800 °C, the carbon diffusion process was carried out under the graphitization effect of iron thin film. Since the iron film used in this process is very thin, the diffused carbon will diffuse from the diamond side to the hydrogen plasma side and then etched away by the plasma. Therefore, the etching rate of diamond film can be kept consistent. After etching the growth surface of a free-standing diamond film, we investigated the surface morphologies and the carbon phases on the etched surfaces of diamond films. Finally, compared with the result of mechanical lapping experiments, we suggest that the hydrogen plasma etching enhanced carbon diffusion process can serve as a new planarization method for rough diamond film surface. A mechanism for this enhanced etching effect is also presented and discussed.