Tien-Syh Yang

Growth of faceted, ballas-like and nanocrystalline diamond films deposited in CH4/H2/Ar MPCVD

Abstract The influence of Ar addition to CH 4 /H 2 plasma on the crystallinity, morphology and growth rate of the diamond films deposited in MPCVD was investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. X-Ray diffraction patterns indicate that diamond films of strong (111) and weak (400) texture are produced in these samples. Faceted diamond gradually turns into ballas-like diamond with graphitic inclusions when the Ar concentration increases to above 30 vol.%, as indicated by Raman spectra. As the Ar concentration goes above 90 vol.%, nanocrystalline diamond films are formed, characterized by a 1150-cm −1 peak in the Raman spectra and morphology observation. Diamond growth by CH 3 or by C 2 mechanism is proposed to interpret the change in the growth rate of diamond films with the variation of Ar content in the plasma.

Substrate bias effect on the formation of nanocrystalline diamond films by microwave plasma-enhanced chemical vapor deposition

The influence of negative substrate bias on the crystallinity, morphology, and growth rate of the diamond films deposited using microwave plasma-enhanced chemical vapor deposition in 1% CH4/H2 plasma were investigated. The nanocrystalline diamond films were produced exclusively under the biasing at −250 V. With −50 V biasing, faceted (111) microcrystalline diamond films at higher growth rate than no-bias samples were produced. When the biasing between −100 and −200 V, faceted (100) diamond films with decreasing grain size were favored, and the growth rates were gradually reduced along with the increasing biasing. The results indicate that the etching efficiency of H+ ions is enhanced with the increasing kinetic energy obtained from the increasing bias voltage. On the other hand, CHx+ ions at −250 V biasing would have sufficient energy to perform the ion subplantation model to grow the nanocrystalline diamond films by bias-enhanced nucleation.

Synthesis and properties of boron carbon nitride (BN:C) films by pulsed-DC magnetron sputtering

Abstract The ion-assisted, high-rate, reactive and pulsed-DC magnetron sputtering technique was used to deposit boron carbon nitride (BN:C) films by sputtering a boron carbide (B4C) target in argon and nitrogen plasma. Various processing parameters were explored to grow BN:C films with high cubic boron nitride (c-BN) content. FTIR, SEM, TEM, AES, and Raman spectroscopy were used to characterize the phases, composition and surface morphology of the films. Significant influence of substrate bias voltage and temperature on phase composition of the films was found. The deposited BN:C films exhibit h-BN, wurtzite-BN (w-BN), c-BN phases and their mixed phases with the variation in substrate bias and temperature. A multi-stage deposition technique with variable substrate bias was exploited to obtain 90% c-BN film with clear grains and facets.

Combined effects of argon addition and substrate bias on the formation of nanocrystalline diamond films by chemical vapor deposition

The article reports combined effects of Ar addition and substrate bias on the grain size, microstructure, and growth rate of the diamond films prepared in microwave plasma-enhanced chemical vapor deposition. The nanocrystalline diamond (NCD) films with grain size of 50–100 nm, characterized by Raman spectra, scanning and transmission electron microscopy, were produced at 90–99 vol % Ar concentration under −50 V substrate biasing. The growth rate of the NCD films was 0.7–0.8 μm h−1, larger apparently than those grown by only Ar addition or by substrate bias effect alone. The NCD formation by various mechanisms is discussed, and a revised C2 insertion mechanism by the promotion of H+ ions is proposed to interpret the higher growth rate of the NCD films.

Deposition of carbon-containing cubic boron nitride films by pulsed-DC magnetron sputtering

Abstract An ion-assisted, high-rate, reactive and pulsed-DC magnetron sputtering technique was used to deposit boron carbon nitride (BN:C) films by sputtering a boron carbide (B 4 C) target in an argon and nitrogen plasma. Substrate bias and temperature were adjusted to grow BN:C films with a high c-BN content. FTIR, scanning and transmission electron microscopy (SEM, TEM) and Auger electron spectroscopy (AES) were used to characterize the phases, composition and surface morphology of the films. The BN:C films deposited exhibit h-BN, w-BN, c-BN and their mixed phases at various substrate bias and temperature values. The optimum conditions found to deposit BN:C films with 82% c-BN content were at a substrate bias of −250 V and a temperature of 250°C. In addition, a novel multi-step deposition technique with variable substrate bias was exploited to obtain ∼700-nm-thick, adherent films with 95% c-BN content.

Effect of diamond films as bufferlayer on formation of cubic boron nitride films by chemical vapor deposition

Boron nitride films are produced by the reaction of diborane (B2H6) and ammonia (NH3) in a mixture of hydrogen and argon using microwave plasma-assisted chemical vapor deposition. Some parameters as NH3/B2H6 ratios, hydrogen addition, substrate-bias voltage and working pressure are modulated to obtain high c-BN content in the film. The influence of diamond films with various grain sizes as bufferlayer on the formation of c-BN is investigated. As-grown BN/diamond films are characterized by Fourier transform infrared spectra, X-ray diffraction patterns and scanning electron microscopy. The results indicate that the nature of diamond film affects the amount of c-BN in the BN layer. Nanocrystalline diamond film can promote the c-BN formation, resulting in the c-BN content up to 85%. Thick c-BN/diamond multilayer up to 5.5 μm in total thickness and with nearly pure c-BN content is synthesized.

Preparation and properties of BN/AlN nanolaminates

Nanolaminates and bilayers of BN/AlN on Si were deposited using a reactive DC magnetron sputtering technique in a dual-cathode system. In the BN/AlN bilayers, there was little effect of the AlN thickness as a buffer layer on the crystallinity of the BN layer. A series of BN/AlN nanolaminates with periods (Λ) from 2.2 to 80 nm was produced by varying the rotation speed of the sample holder disc. At the periods thicker than 20 nm, the nanolaminates primarily consisted of sp3-bonded BN and w-AlN layers. For periods below 3.4 nm, the BN and AlN layers were intermixed and apparent wurtzite–AlBN phase was formed in the interfaces. Transparent and intact BN/AlN nanolaminates with thickness over 5 μm and with hardness over 33 GPa were obtained. The hardness of the nanolaminates was related to the structural characteristics obtained from XRD and FTIR results.

Diamond synthesis via CH metal precursors processed in hot filament chemical vapor deposition and microwave plasma chemical vapor deposition

Abstract The influences of various metal (Co, Ni, Cu, Ag and Mn) and carbon precursors (methane and graphite) on diamond synthesis in hot filament chemical vapor deposition (HFCVD) and microwave plasma chemical vapor deposition (MPCVD) were investigated. Diamond film is formed uniformly from 1% CH 4 /H 2 , while blocks of diamond films and particles are produced from graphite/H 2 . The promotion effects of the metals on diamond growth were observed by the variations of particle size in SEM and diamond peak intensity in XRD. Those containing Co or Ni powders exhibit the highest diamond growth rate from 1% CH 4 /H 2 , but the catalytic effects of the metals are not as significant as proposed in some of the literature. Graphite, instead of methane, can be used for diamond synthesis, but with lower growth rate and nucleation density. It is concluded that the diamond growth mechanism for the samples containing metal, using either methane or graphite as a carbon precursor, similar to that of low-pressure CVD diamond.