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The effects of different surface pretreatment methods on the nucleation and growth of ultra-nanocrystalline diamond (UNCD) films grown from focused microwave Ar/CH4/H2 (argon-rich) plasma were systematically studied. The surface roughness, nucleation density, microstructure, and crystallinity of the obtained UNCD films were characterized by atomic force microscope (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The results indicate that the nucleation enhancement was found to be sensitive to the different surface pretreatment methods, and a higher initial nucleation density leads to highly smooth UNCD films. When the silicon substrate was pretreated by a two-step method, i.e., plasma treatment followed by ultrasonic vibration with diamond nanopowder, the grain size of the UNCD films was greatly decreased: about 7.5 nm can be achieved. In addition, the grain size of UNCD films depends on the substrate pretreatment methods and roughness, which indicates that the surface of substrate profile has a "genetic characteristic".

In the present work, a detailed and systematic investigation of diamond films deposited on silicon is realized in an overmoded microwave plasma CVD reactor chamber. It was observed that there is a coupled effect between carbon concentration and substrate temperature on the growth of diamond films. The substrate temperature should be increased with increasing carbon concentration in order to obtain similar surface morphology. And the relative high 〈1 1 1〉 or 〈1 0 0〉 orientation diamond films can be obtained when the two parameters are both appropriate. The investigation carried out with 1.5% carbon concentrations further ascertains the rules of the coupled effect. The results indicate that there are five statuses for the surface morphology and the diamond films with 〈1 0 0〉 and 〈1 1 1〉 orientation can be deposited at the substrate temperature from around 810 °C to 870 °C and around 920 °C to 960 °C, respectively. The quality of the diamond films increases rapidly while the substrate temperature increasing from 750 °C to 870 °C and keeps relative stable at higher substrate temperature. The experimental results, in some degree, indicate that the diamond films with controllable characters can be deposited in the MPCVD apparatus.

In this work, diamond films were deposited in a 10 kW, 2450 MHz MPCVD apparatus, of which the chamber allows a multi-mode microwave electric field to be overlapped and high microwave power to be employed. The two primary modes of TM 01 and TM 02 overlap around the substrate and generate a large scale plasma ball which ensures the deposition of large area diamond films. The deposition temperature across the substrate was primarily investigated in order to deposit uniform diamond films in the multi-mode chamber. And the optical emission spectra, scanning electron microscope and Raman were used to characterize the diamond films. The results showed that higher microwave power should be selected to generate large plasma ball and obtain needed temperature uniformity for a given deposition pressure. And the temperature variation was decreased obviously when the substrate holder was improved. With the optimized parameter and the improved stage configuration, the diamond thin films deposited on Φ = 80 mm silicon wafers obtained excellent uniformity in morphology, thickness and quality. And the results of investigating growth rate further confirm that the improved substrate holder and the employment of high microwave power are useful to achieve uniform diamond films with large area and high deposition rate.

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.

Nano-crystalline diamond (NCD) films were deposited on silicon substrates by a microwave plasma enhanced chemical vapor deposition (MPCVD) reactor in C2H5OH/H2 and CH4/H2/O2 systems, respectively, with a constant ratio of carbon/hydrogen/oxygen. By means of atomic force microscopy (AFM) and X-ray diffraction (XRD), it was shown that the NCD films deposited in the C2H5OH/H2 system possesses more uniform surface than that deposited in the CH4/H2/O2 system. Results from micro-Raman spectroscopy revealed that the quality of the NCD films was different even though the plasmas in the two systems contain exactly the same proportion of elements. In order to explain this phenomenon, the bond energy of forming OH groups, energy distraction in plasma and the deposition process of NCD films were studied. The experimental results and discussion indicate that for a same ratio of carbon/hydrogen/oxygen, the C2H5OH/H2 plasma was beneficial to deposit high quality NCD films with smaller average grain size and lower surface roughness.

Plasma treatments of boron-doped nano-crystalline diamond (NCD) thin films were carried out in order to improve their electrical properties of the films. Boron-doped NCD thin films were fabricated on well polished poly-crystalline diamond (PCD) thick films in a microwave plasma enhanced chemical vapor deposition (MPCVD) reactor, then they were processed in methane, argon, hydrogen and B2H6 (0.1% diluted by H2) plasmas, respectively. Scanning electron microscopy (SEM) and atomic force microscope (AFM) results show that the surface morphology changed little during the 10 min treatment. Secondary ion mass spectroscopy (SIMS) results indicate that B2H6 plasma was efficient for increasing boron concentration in NCD films, while the carrier analyses demonstrates that CH4 plasma processing was effective to activate the dopants and resulted in good electrical properties.

Nano-crystalline diamond (NCD) films were prepared on poly-crystalline diamond (PCD) thick films by the microwave plasma enhanced chemical vapor deposition (MPCVD) method. Free standing PCD thick film (50 mm in diameter) with a thickness of 413 μm was deposited in CH4/H2 plasma. It was then abraded for 2 hours and finally cut into pieces in a size of 10 × 10 mm2 by pulse laser. NCD films were deposited on the thick film substrates by introducing a micro-crystalline diamond (MCD) interlayer. Results showed that a higher carbon concentration (5%) and a lower substrate temperature (650°C) were feasible to obtain a highly smooth interlayer, and the appropriate addition of oxygen (2%) into the gas mixture was conducive to obtaining a smooth nano-crystalline diamond film with a tiny grain size.

Thick diamond films with a thickness of up to 1.2 mm and a area of 20 cm2 have been grown in a homemade 5 kW microwave plasma chemical vapor deposition (MPCVD) reactor using CH4/H2/H2O gas mixtures. The growth rate, radial profiles of the film thickness, diamond morphology and quality were evaluated with a range of parameters such as the substrate temperature of 700 oC to 1100 oC, the fed gas composition CH4/H2 = 3.0%, H2O/H2 = 0.0%~ 2.4%. They were characterized by scanning electron microscopy and Raman spectroscopy. Translucent diamond wafers have been produced without any sign of non-diamond carbon phases, Raman peak as narrow as 4.1 cm?1. An interesting type of diamond growth instability under certain deposition conditions was observed in a form of accelerated growth of selected diamond crystallites of a very big lateral size, about 1 mm, and of a better structure compared to the rest of the film.