Deposition and Boron Doping of Nano-Crystalline Diamond Thin Films on Poly-crystalline Diamond Thick Films

Boron-doped nano-crystalline diamond (NCD) thin films have been successfully deposited on well-polished poly-crystalline diamond (PCD) thick films in a microwave plasma enhanced chemical vapor deposition (MPCVD) reactor for the first time. Different surface pretreatment techniques are carried out under different gas conditions (CH₄, H₂, Ar, and CH₄/H₂) to eliminate the effect of grain boundaries on the growth of a smooth NCD intrinsic layer. Well doped NCD films have been fabricated in CH4/H₂/B₂H₆ plasma by varying the atomic ratio of B/C and the substrate temperature. Atomic force microscopy (AFM) results show that pretreatment in pure CH₄ plasma at 1000 °C is most effective for NCD growth, while hydrogen containing plasma is harmful to the surface smoothness of NCD thin films. Doping research indicates that the optimum parameters for the boron-doping of high-quality NCD thin films are B/C=300 ppm (10-6) and 800 °C.