Search

The impact of high deposition pressure on the microstructure and incorporation hydrogen impurity within nanocrystalline diamond (NCD) films have been investigated in a home-made microwave plasma chemical vapor deposition (MPCVD) apparatus when the microwave power and the substrate temperature were kept constant at 800 W and 650 °C, respectively. It is found that high deposition pressure not only influences the grain size and quality, but has conception link with the form and content of the bonded-H incorporated in NCD films. With the deposition pressure increases from 10 kPa to 30 kPa, the average grain size decreases from 33 nm to 13 nm and a large amount of hydrogen is detected in the obtained NCD films by Fourier transform infrared spectroscopy (FTIR). Particularly, the NCD films deposited at 15 kPa possesses the largest amount of the bonded H impurity. The optical emission spectroscopy (OES) from the plasma indicates that the intensity ratio between Hα and C2 decreases with the increase of the deposition pressure, which suggests the decline energy levels for the excited H atoms. Based on these experimental results the role of high deposition pressure on the growth of NCD films is discussed.

Diamond films with 70 mm in diameter were deposited on silicon substrates with Ar/CH4/H2 gas mixture, using microwave plasma chemical vapor deposition (MPCVD) technique. One designed water-cooling substrate stage was used to improve the uniformity of the surface temperature across the substrate. An uniform substrate surface temperature was obtained at the pressure of 10 kPa when the input microwave power was 5500 W. The condition of the plasma was diagnosed by optical emission spectrum (OES) and the grown diamond films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The results show that higher microwave power can further improve the uniformity of the temperature distribution across the substrate which in turn increases the uniformity of diamond film. And introducing more H2 into Ar/CH4/H2 gas mixture at high microwave power is effective on the improvement of the quality and the decrease of the stress in the deposited diamond films. The diamond films with low average intrinsic stress of 0.32 GPa were finally deposited with introducing 100 sccm H2 into Ar/CH4/H2 gas mixture at 5500 W.

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 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.

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.

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.