Deposition Of Cubic Boron Nitride Research Articles

Lowering of the Substrate Bias Voltage for Deposition of Cubic Boron Nitride in Microwave Plasma

A moderate-pressure microwave plasma is used to deposit boron nitride (BN) films by employing boron trifluoride as a source gas. In the deposition conditions, the ion flux onto a negatively biased substrate is measured to be on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">16</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> depending upon the bias voltage. The films consisting of both hexagonal BN and cubic BN (cBN) phases are deposited on silicon substrates by applying a bias voltage ranging from -85 to -200 V. The film deposited at -85 V shows the higher crystallinity and larger roughness and grains of cBN due to a decrease in mean ion impact energy. The results suggest that the bias voltage for cBN phase formation is lowered by increasing the ion to depositing boron flux ratio even in collisional moderate-pressure conditions.

Impact of low-energy ions on plasma deposition of cubic boron nitride

Plasma deposition of cubic boron nitride (cBN) films under low-energy (a few eV to ~40eV) ion impact with the chemistry of fluorine is studied in terms of ion energy, ion flux, and ion to boron flux ratio onto the substrate. The ion energy and the ion to boron flux ratio are determined from the sheath potential and the ratio of incident ion flux to net deposited boron flux, respectively. For negative substrate biases where a mixture of turbostratic and amorphous BN phases only or no deposit is formed, both the ion energy and the ion to boron flux ratio are high. For positive substrate biases where cBN phase is formed, the ion energy and the ion to boron flux ratio are in the range of a few eV to 35eV and 100 to 130, respectively. The results indicate that the impact of positive ions with high ion to boron flux ratios makes a substantial contribution to the formation of cBN phase, while that of negative ions and electrons makes only a minor contribution.

Cubic boron nitride based metastable coatings and nanocomposites

Various PVD and plasma-assisted CVD methods presently used for the deposition of cubic boron nitride (c-BN) thin films demand adequate conditions relating to ion bombardment of growing films, growth temperature, film stoichiometry, etc. The deposition conditions, often appearing rather apparatus-dependent, can be well categorized according to the fundamental parameters of bombarding ions as well as condensing neutral particles, including their energy and flux ratio, and a few of others like ion mass and incident angle. According to these parameters, various surface kinetic processes and their consequences are discussed particularly in connection with the resulting film phases and stress. Typical c-BN films are known for their extremely high compressive stress and poor adhesion as a result of intensive ion bombardment during deposition. Individual measures attempting to relieve this detrimental stress are briefly summarized. The present paper focuses on magnetron-sputtered, c-BN-based metastable films and nanocomposite films with considerably reduced internal stress in comparison to the usual “pure” c-BN films. Two examples will be shown, namely c-BN/a-C nanocomposite and c-BN:O metastable films, including their deposition details, structure and composition characterization, and mechanical properties. Also illustrated is a growth scheme tailored for the deposition of thick, adhered, cubic-phase dominated, superhard c-BN:O films above 2µm on silicon substrates.

Binary-collision modeling of ion-induced stress relaxation in cubic BN and amorphous C thin films

It is demonstrated that ion-bombardment-induced stress release during physical vapor deposition of cubic boron nitride (cBN) and amorphous carbon (aC) films is related to collisional relocation of atoms. A model based on TRIM and molecular dynamics computer simulations is presented. Experimental results obtained using pulsed substrate bias are in good agreement with the model predictions at adequately chosen threshold energies of atomic relocation. The collisional relaxation model describes the experimental data significantly better than the widely applied thermal spike model.

Deposition of Cubic Boron Nitride in a Supersonic Plasma Jet Reactor with Secondary Discharge

We have deposited cubic boron nitride thin films with a supersonic plasma jet chemical vapor deposition system with bipolar pulsed substrate bias. Deposited films were characterized by Fourier transform infrared spectroscopy, micro-X-ray diffraction, and scanning electron microscopy. The cubic boron nitride content is observed to scale well with the degree of ion bombardment of the substrate and growing film, which is affected most drastically by the substrate bias pulse frequency, and positive and negative duty cycle. The magnitude of the negative substrate bias was also critical in depositing cubic boron nitride, with a threshold voltage of approximately 90 V necessary for cubic boron nitride deposition.

Adhesion improvement of cubic boron nitride film on high speed steel substrate by BN X implanted buffer interlayer

One of the major problems for the deposition of cubic boron nitride(c-BN) films on W6Mo5Cr4V2 high speed steels(HHS) is the poor adhesion of the film to the substrate. For the purpose of improving adhesion, the BN X implanted buffer layer was introduced between the HSS and c-BN film deposited by the RF-magnetron sputtering. The influence of the BN X buffer layer on adhesion was investigated and the results showed that when the N/B ratio of the buffer layer is about 1:1, the adhesive strength of c-BN film to the HHS substrate reached the maximum, about 28.47 N, which is sixteen times higher than that of c-BN film deposited without the buffer layer. According to the XPS analysis, the surface of buffer interlayer was mainly in BN phase, which is the main reason to reduce the internal stress and improve the adhesion strength of c-BN films.

CVD growth of cubic boron nitride: A theoretical/experimental approach

Similarities and dissimilarities in the growth of diamond vs. c-BN, in the present series of investigations, have been studied using quantum mechanical calculations. Hydrogen species have been observed to be very effective in stabilising both types of compounds. Very large similarities have also been observed when considering the adsorption of various growth species to these materials. However, it was found necessary to avoid mixtures of B- and N-containing species in the gas phase during c-BN growth, since they should most probably result in a mixture of these species also on the (111) and (110) surfaces. In addition, a careful gas phase design was found necessary in order to avoid a preferential initial growth of h-BN. These theoretical results can be used as guide lines in striving towards a thin film deposition of cubic boron nitride using gentle CVD methods like atomic layer deposition.

Growth and characterization of thick cBN coatings on silicon and tool substrates

Recently some research groups have achieved progress in the deposition of cubic boron nitride (cBN) coatings with a thickness of 2 μm and more, which is necessary for cutting tool applications. In our laboratory, thick cBN coatings were sputter deposited on silicon substrates using a boron carbide target. Following a boron carbide interlayer (few 100 nm thick), a gradient layer with continuously increasing nitrogen content was prepared. After the cBN nucleation, the process parameters were modified for the cBN film growth to a thickness of more than 2 μm. However, the transfer of this technology to technically relevant substrates, like cemented carbide cutting inserts, required some further process modifications. At first, a titanium interlayer had to be deposited followed by a more than 1-μm-thick boron carbide layer. The next steps were identical to those on silicon substrates. The total coating thickness was in the range of 3 μm with a 0.5- to nearly 1-μm-thick cBN top layer. In spite of the enormous intrinsic stress, both the coatings on silicon and on cemented carbide exhibited a good adhesion and a prolonged stability in humid air. Oxidation experiments revealed a stability of the coating system on cemented carbide up to 700 °C and higher. Coated cutting inserts were tested in turning operations with different metallic workpiece materials. The test results will be compared to those of well-established cutting materials, like polycrystalline cubic boron nitride (PCBN) and oxide ceramics, considering the wear of coated tools.

A comparative machining study of diamond-coated tools made by plasma torch, microwave, and hot filament techniques

An effective metal-cutting tool is usually a combination of a hard coating and a tough substrate. The successful deposition of diamond outside its thermodynamic stability range has stimulated the development of a new class of cutting tools: those with diamond-coated inserts of any desired style and edge geometry. The successful implementation of diamond coatings also expedited similar research in the deposition of cubic boron nitride. This paper presents superhard coating tools, with emphasis on diamond-coated WC-Co tools, the corresponding deposition of technologies and the foreseen metal-cutting applications.

Growth Behavior of Cubic Boron Nitride Films in a Two-Step Process: Changing Bias Voltage, Gas Composition, and Substrate Temperature

In the deposition of cubic boron nitride (cBN) films by DC-bias-assisted DC jet chemical vapor deposition in an Ar–N2–BF3–H2 gas system, the balance between growth and etching and its relation to the deposition conditions were investigated. A two-step process was designed to optimize the nucleation and growth separately, and a critical bias voltage for the growth of cBN after nucleation was observed. It was found that etching occurred when the bias voltage was below this critical value. Under optimized conditions, the crystallinity and crystal size of the cBN films were improved during the second step. Furthermore, cBN films showing clear crystal facets were obtained.

Deposition of cubic boron nitride by laser ablation

Boron nitride films were obtained as a result of laser ablation of a nano-grained c-BN target. The films consist mainly of boron and nitrogen as well as some carbon and oxygen according to the results of Auger electron spectroscopy. The results of electron diffraction from the film indicate the presence of c-BN crystals in the deposit.

Molecular dynamics study of deposition mechanism of cubic boron nitride

We have performed molecular dynamics simulations of bombardment of graphitic boron nitride (gBN) by energetic boron and nitrogen particles in order to examine the roles of ion bombardment in ion/plasma-assisted deposition of cubic boron nitride (cBN) thin films. We have found that the interaction of the energetic particles with gBN creates four-fold coordinated local structures (sp3-formation) inside gBN. We have also found that clusters of sp3-formations are created as a result of successive bombardment, some of which have cBN-like structures. On the basis of these results, we propose an atomic-scale model of cBN nucleation in which successive sp3-formation converts gBN into cBN.

The mechanism of cubic boron nitride deposition in hydrogen plasmas

Deposition of cubic boron nitride in hydrogen plasma is thought to proceed as a result of selective etching of sp2-hybridized boron nitride from the surface of the growing boron nitride film, the impact of hydrogen atoms or ions leading to formation of c-BN sp3 bonds on the surface and formation of metastable BNHx species in the gas phase. The mechanism of nucleation and growth of c-BN crystals in hydrogen plasmas is proposed.

Field emission properties of BN coated Si tips by pulsed ArF laser deposition

Thin films of boron nitride (BN) were deposited by pulsed ArF laser ablation of a pyrolitic BN target in an N2 ambient with and without substrate bias and also in a nitrogen plasma. The structural property studies with infrared and reflection high-energy electron diffraction show that the films possess cubic BN and hexagonal or amorphous phase of BN. Deposition of cubic BN is enhanced by application of substrate bias whereas crystallinity is degraded by the introduction of nitrogen plasma. The field emission of electrons was tested for BN coated Si tips, and it was found that the field emission of electrons enhanced when the cubic BN was coated.

Stable anionic sites on hydrogenated (111) surfaces of cubic boron nitride resulting from hydrogen atom removal under chemical vapor deposition conditions

In plasma or hot-filament assisted chemical vapor deposition of cubic boron nitride (cBN), the formation of a surface radical site by hydrogen atom removal from a hydrogenated (111) surface was expected to be followed by the formation of an anionic vacant site (AVS) by capturing an electron, since this yields a closed shell structure of the site atom. This possibility was investigated by ab initio as well as by semiempirical molecular orbital calculations using large cluster models. The stabilization energy of the AVS on cBN(111) with a boron top layer, namely (111) B, was 1.8–2.3 eV; this value is comparable with that of diamond. On the other hand, that of cBN(111) on a nitrogen surface, namely (111) N, amounted to 5.3–5.9 eV. The nucleophilic nature of the AVS with a lone pair of electrons suggests electrophilic reagents for related reactions. This helped us to propose SN2 growth reactions for diamond growth both on diamond and cBN(111) surfaces. The difference in chemical reactivity between (111) N and (111) B could be interpreted in terms of the “hard” and “soft” acid base concept that has been renewed by the frontier orbital theory.

Deposition of Cubic Boron Nitride in Hydrogen Plasma

Thin films of cubic boron nitride (c-BN) have great po-tential as hard protective coatings for wear applications orcomponents of electronic devices due to the outstandingproperties of c-BN, namely its unique combination of highhardness, high temperature oxidation and chemical stabil-ity, and excellent thermal conductivity. Only single-phasec-BN films are likely to be of practical importance sincethe difference between c-BN and hexagonal boron nitride(h-BN) is as significant as the difference between diamondand graphite. Until recently c-BN-containing films ob-tained by either physical vapor deposition (PVD) or plas-ma-assisted chemical vapor deposition (PACVD) have hadno practical significance due to their poor properties. PVDc-BN films typically have a very poor adhesion, contain aninterlayer of sp

Deposition of Cubic Boron Nitride in Hydrogen Plasma

Thin films of cubic boron nitride (c-BN) have great po-tential as hard protective coatings for wear applications orcomponents of electronic devices due to the outstandingproperties of c-BN, namely its unique combination of highhardness, high temperature oxidation and chemical stabil-ity, and excellent thermal conductivity. Only single-phasec-BN films are likely to be of practical importance sincethe difference between c-BN and hexagonal boron nitride(h-BN) is as significant as the difference between diamondand graphite. Until recently c-BN-containing films ob-tained by either physical vapor deposition (PVD) or plas-ma-assisted chemical vapor deposition (PACVD) have hadno practical significance due to their poor properties. PVDc-BN films typically have a very poor adhesion, contain aninterlayer of sp

Preparation of c-BN films by RF sputtering and the relation of BN phase formation to the substrate bias and temperature

This paper deals with the deposition of cubic boron nitride (c-BN) films by radio frequency(RF)magnetron sputtering. The nearly pure c-BN films have been prepared on Si(100)substrates using hexagonal boron nitride(h-BN)targets. Argon gas mixed with nitrogen gas was used as sputtering gas. The deposited films were characterized by Fourier transform infrared (FTIR) spectroscopy and transmission electron diffraction (TED). A ‘temperature-bias’ phase diagram has been worked out. It indicates that the c-BN phase prefers the relative high temperature and negative bias. An opinion was presented that the c-BN nuclei grow discontinuously with every time the ‘thermal spike’ coming.

Spectroscopic studies of a magnetron sputtering discharge for boron nitride deposition

Magnetron sputtering discharges for the deposition of cubic boron nitride have been investigated using optical emission spectroscopy and Langmuir double probes. Spatially resolved measurements revealed the inhomogeneous discharge structure with respect to the distribution of excited species, electron density and electron temperature. The optical emission spectra were analysed by means of the corona model. The vibrational excitation of the nitrogen molecule was examined. The ratio of selected Ar and N 2 emission intensities provided a qualitative measure of the electron temperature, which was determined by probe measurements. However, the intensity ratios of Ar and Ar + lines did not correspond to changes in electron temperature. Varying the electron density in a wide range, it could be demonstrated that the excitation mechanisms do not remain constant, mainly due to multistep excitation. The vibrational temperature of N 2 (C 3IIΠ u) has been found to be much higher in the case of r.f. sputtering than in the d.c. mode.

Deposition of c-BN films by DC magnetron sputtering

Abstract New results of the deposition of cubic boron nitride (c-BN) films by use of DC magnetron sputtering will be presented. This technique is of great interest for industrial applications, because of its high growth rates and upscaling potential. Boron carbide was used as target material with a suitable electrical conductivity for DC sputtering. The target as well as the substrate holder were connected to DC power. In the experimental set-up we used the unbalanced magnetron mode (UBM) attained with a magnetic coil surrounding the substrate table. A c-BN deposition process was developed based on a parameter transfer from a RF diode system. The c-BN content of the films will be discussed in relation to the different process parameters. Important process parameters for the formation of the cubic phase were the ion current at the substrate table and the resulting ratio of ions to neutrals. Nearly single phase c-BN films were deposited on silicon and steel substrates. The elemental film composition and the film structure were characterized by electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). Nanoindentation and friction coefficient measurements revealed excellent mechanical and tribological properties of the films.