高速钢基体离子注氮对c-BN薄膜制备的影响研究

采用射频磁控溅射法在离子注氮的高速钢基体上沉积制备c-BN薄膜,主要研究离子注氮层对c-BN薄膜相结构和内应力的影响;采用各种现代分析方法对沉积的薄膜进行了表征分析,包括傅立叶红外光谱(FTIR)、X射线光电子能谱(XPS)和原子力显微镜(AFM)等分析方法;试验结果表明:高速钢基体上离子注氮有利于立方氮化硼含量的提高和薄膜内应力的降低,同时注氮处理的高速钢基体上沉积的薄膜表面形貌平整,结晶性较好.并采用X射线衍射分析(XRD)对高速钢基体的离子注氮层进行了相结构分析,探索研究了离子注氮层对c-BN薄膜生长的影响.     

New approach in depositing thick, layered cubic boron nitride coatings by oxygen addition—structural and compositional analysis

Cubic boron nitride (c-BN) can be produced by PVD and PA-CVD techniques by intensive ion bombardment leading to highly stressed films limiting its use in industrial applications. Various attempts have been undertaken to reduce the compressive stress of c-BN thin films. A significant reduction in compressive stress and a substantially improved adhesion was achieved by a new coating concept consisting of a two-step adhesion-promoting base layer, a compositional-graded nucleation layer obtained by a stepwise decrease of the oxygen content in the Ar/N₂/O₂ atmosphere and a low-stressed c-BN:O top layer with controlled oxygen addition. The four-layer c-BN:O film with a thickness of 3 μm was deposited by unbalanced radio frequency magnetron sputtering of a hot-pressed hexagonal boron nitride target on silicon substrates. The adhesion layer was deposited in a mixed Ar/O₂ atmosphere of 0.26 Pa with a stepwise increased nitrogen gas flow and a subsequent increase of the ion energy by increasing the substrate bias from 0 to − 250 V. The c-BN nucleation was gradually initiated by decreasing the O₂ gas flow. The present study was focused on the investigation of the morphology, the microstructure on the nanoscale, and the bonding structure using scanning electron microscopy (SEM), Fourier-Transmission infra-red spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) employing analytical scanning transmission electron microscopy (ASTEM). The HRTEM images revealed a four-layer coating consisting of a gradual nucleation of t-BN, on which a gradual nucleation of c-BN was achieved by decreasing the oxygen gas flow.     

用PBⅡ方法在硼膜中注入氮形成BN的结构

用电子束蒸发纯硼,在硅片上沉积不同厚度的硼膜,然后用等离子体基离子注入（ＰＢⅡ）技术在硼膜上主入氮以形成氮化硼（ＢＮ）,用ＸＰＳ分析膜的成分深度分布及化学价态;用傅里叶变换红外（ＦＴＩＲ）透射谱分析膜的结构。氮在膜中呈类似高斯分布,随着注入电压增大,膜的Ｎ／Ｂ比增大且影响氮在膜中的分布,在较高的注入电压时,膜基间产生界面混合,对ＸＰＳＢｌｓ谱进行Ｇａｕｓｓ－ｏｒｅｎｔｚ拟合表明,硼在膜中以ＢＮ及游     

PIII技术制备c-BN硬化层

采用一种新型的等离子体浸没式离子注入技术(PIII)在渗硼后的50Mn钢试样上制备出了厚度为0.15~0.2mm的立方氮化硼(c-BN)表面硬化层。经X光电子能谱(XPS)和X光衍射分析(XRD),发现硬化层中的组织有立方氮化硼(c-BN)、六方氮化硼(h-BN)、B2O3、FeB和Fe2B。在表层60nm的深度范围内,c-BN的含量较高。采用球盘式无润滑滑动摩擦试验和维氏显微硬度试验分别对渗硼+PIII复合处理以及单独渗硼的50Mn钢试样的性能进行了对比试验。结果表明,与单独渗硼的试样相比,渗硼+PIII复合处理的试样具有高得多的硬度(高达Hv0.1N44GPa)和耐磨性。该项技术在电缆压模上进行了应用试验,获得了较好的应用效果。     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 〈100〉-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal +h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

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 2 µm on silicon substrates.     

溅射气压和沉积时间对c-BN薄膜结构的影响

采用磁控反应溅射方法，在Si(100）衬底上沉积c-BN薄膜，研究了溅射气压和沉积时间对薄膜结构的影响。结果表明，随溅射气压的升高或沉积时间的增加，都是削弱荷能粒子对衬底表面的轰击效果，并导致薄膜中c-BN相含量的减小。     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 100-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal (h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Cubic BN formation by ion implantation

Boron nitride was synthesized by nitrogen ion implantation. Boron films were prepared as implantation targets on single-crystal Si(100) substrates by 13.56-MHz radio frequency sputtering. The diatomic single 30-keV nitrogen ions were chosen for implantation. The implantation dose ranged from 1×10¹⁷ ions/cm² to 2×10¹⁸ ions/cm². The films were characterized using a transmission electron microscope. Several phases of boron nitride were found at the medium implantation dose. At the high dose of 2×10¹⁸ ions/cm², the pure c-BN phase was observed. It is believed that the transition from the low ordered phases to c-BN phase occurred during implantation. The films showed good adhesion to the Si substrate.     

Structural evolution of boron nitride films grown on diamond buffer-layers

Boron nitride films on diamond buffer layers of varying grain size, surface roughness and crystallinity are deposited by the reaction of B₂H₆ and NH₃ in a mixture of H₂ and Ar via microwave plasma-assisted chemical vapor deposition. Various forms of boron nitride, including amorphous α-BN, hexagonal h-BN, turbostratic t-BN, rhombohedral r-BN, explosion E-BN, wurzitic w-BN and cubic c-BN, are detected in the BN films grown on different diamond buffer layers at varying distances from the interface of diamond and BN layers. The c-BN content in the BN films is inversely proportional to the surface roughness of the diamond buffer layers. Cubic boron nitride can directly grow on smooth nanocrystalline diamond films, while precursor layers consisting of various sp²-bonded BN phases are formed prior to the growth of c-BN film on rough microcrystalline diamond films.     

Magnetron sputter deposition of low-stress, carbon-containing cubic boron nitride films using Ar―N2―CH4 gas mixtures

Cubic boron nitride (c-BN) films produced by PVD and plasma-assisted CVD techniques typically exhibit undesired high compressive stresses. One of the effective and feasible methods to reduce stress and hence improve film adhesion has been a controlled addition of a third element into the film during deposition. In the present study, BN films were grown on to silicon substrates using reactive magnetron sputtering with a hexagonal BN target. An auxiliary flow of methane was mixed into argon and nitrogen as the working gas. The deposition was conducted at various methane flow rates at 400 °C substrate temperature, 0.2 Pa total working pressure, and − 250 V r.f. substrate bias. The microstructure of the deposited films was then examined in dependence of the methane flow rate. With increasing methane flow rate from 0 to approx. 2.0 sccm, the fraction of the cubic BN phase in the deposited films decreased gradually down to approx. 75 vol.%, whereas the film stress was reduced much more rapidly and almost linearly in relation to the methane flow rate. At 2.1 sccm methane, the stress became approx. 3 times reduced. Owing to the significantly decreased film stress, adherent, micrometer thick, cubic-phase dominant films can be allowed to form on silicon substrate. The microstructure of the films will be illustrated through FTIR and XRR.     

立方氮化硼薄膜制备与性质研究新进展

立方氮化硼(c-BN)具有优异的物理和化学性质, 在力学、光学和电子学等方面有着广泛的应用前景. 自上世纪80年代开始, 低压沉积c-BN薄膜的研究迅速发展, 到90年代中期达到高潮, 随后进展缓慢, c-BN薄膜研究转入低潮. 近年来, c-BN薄膜研究在几方面取得了突破, 如获得与衬底粘附良好、厚度超过1μm的c-BN厚膜; 成功实现了c-BN单晶薄膜的异质外延生长; 此外, 在c-BN薄膜力学性质和过渡层微结构研究方面也取得了进展. 本文主要评述最近几年c-BN薄膜研究在以上几方面取得的最新进展.     

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.     

Facile synthesis of cubic boron nitride nanoparticles from amorphous boron by triple thermal plasma jets at atmospheric pressure

Cubic boron nitride (c-BN) is a superhard material, with hardness value comparable to that of diamond. c-BN is used in a wide range of industrial applications, including tool, abrasives, and refractory. The hardness of c-BN can be improved by decreasing the particle size to the nanoscale; however, the simultaneous application of high pressure (～8 GPa) and temperature (>2,500 K) is required to synthesize the c-BN crystal structure. In this study, we effectively synthesized c-BN nanoparticles from amorphous boron using a triple direct current (DC) thermal plasma jet system at atmospheric pressure. The injection of nitrogen as plasma forming gas generated reactive nitridation species. The average particle size of the synthesized c-BN was 22 nm, and the major crystal structure is the (1 1 1) cubic phase. We carried out a numerical simulation for a thermal fluid, to confirm the high temperature and velocity fields of the plasma jets that formed inside the reactor as the flow rate of plasma forming gas was adjusted. A high production yield of 51% was achieved using amorphous boron at a feed rate of 190 mg/min and the c-BN nanoparticles exhibited high crystallinity without requiring pre-and post-processing.     

R.F. magnetron sputtering of multilayered c-BN films on cemented carbide tool

A c-BN thin film was deposited using a B4C target in a r.f. magnetron sputtering system. The c-BN layer was coated with a TiAIN adhesion layer (approximately 2 microm), boron carbide (approximately 1 microm) and BCN (10 approximately 15 nm) nano-gradient layer system. The c-BN layers with thicknesses of more than 0.5 microm were successfully deposited onto cemented carbide substrates. The high resolution XPS spectra analysis of B1s and N1s revealed that the c-BN film was mainly composed of sp3 BN bonds.     

Physics of epitaxy and c-BN films optimized growth

The cubic zinc-blende phase of boron nitride (c-BN) affords a plethora of potential applications based on material hardness, low chemical reactivity, high thermal conductivity and also on its very large band gap. A modern growth experiments are currently carried out to elaborate monocrystalline c-BN films with a strong film-substrate adherence and up to now several substrates have been used. However, although the film concentration of c-BN is increasing, the growth optimization is still a question under debate. Optimum conditions must be found in energetic growth techniques (IBAD) as well as substrate conditions (temperature, polarization). In this field basic physics is at the very heart of any strategy which aims to elaborate high quality c-BN films. This involves the physics of heteroepitaxy, an aspect of the growth process which consists in taking advantage of complementary freedom degrees as substrate choice and introduction of buffer layers to optimize heterointerfaces. Although several substrates have been tested an optimized choice still remain to be found. On the other hand, the strategy of buffer layers to improve film quality has been less investigated. In this communication, we give the state of art of this field and we discuss the problem of the optimization of c-BN film quality and we demonstrate that the variation of c-BN content in BN films grown on different substrates can be understood on the basis of elasticity theory.     

The effect of ion implantation on r.f.-sputtered TiB2 films

Films of TiB₂ were deposited onto various substrates by r.f. sputtering in argon and in an ArBF₃ mixture. The stoichiometric composition of the films was studied by Rutherford backscattering and nuclear reaction techniques. After film deposition, the effect of ion implantation with boron and krypton ions was studied. In the last case a substantial increase in the adhesion of the film to the substrate and in the microhardness was observed.     

Boron nitride stamp for ultra-violet nanoimprinting lithography fabricated by focused ion beam lithography

Cubic boron nitride (c-BN) is one of the hardest known materials (second after diamond). It has a high level of chemical resistance and high UV transmittance. In this study, a stamp for ultra-violet nanoimprint lithography (UV-NIL) was fabricated using a bi-layered BN film deposited on a quartz substrate. Deposition of the BN was done using RF magnetron sputtering. A hexagonal boron nitride (h-BN) layer was deposited for 30?min before c-BN was deposited for 30?min. The thickness of the film was measured as 160?nm. The phase of the c-BN layer was investigated using Fourier transform infrared (FTIR) spectrometry, and it was found that the c-BN layer has a 40% cubic phase. The deposited film was patterned using focused ion beam (FIB) lithography for use as a UV-NIL stamp. Line patterns were fabricated with the line width and line distance set at 150 and 150?nm, respectively. The patterning process was performed by applying different currents to observe the effect of the current value on the pattern profile. The fabricated patterns were investigated using AFM, and it was found that the pattern fabricated by applying a current value of 50?picoamperes (pA) has a better profile with a 65?nm line depth. The UV transmittance of the 160?nm thick film was measured to be 70-86%. The hardness and modulus of the BN was measured to be 12 and 150?GPa, respectively. The water contact angle of the stamp surface was measured at 75°. The stamp was applied to UV-NIL without coating with an anti-adhesion layer. Successful imprinting was proved via scanning electron microscope (SEM) images of the imprinted resin.     

Cubic phase content and structure of BN films from an X-ray absorption study

X-ray absorption near-edge structure (XANES) was used to study the cubic boron nitride (c-BN) content in the BN films deposited on various substrates by different physical vapor deposition or plasma-enhanced chemical vapor deposition methods. By fitting the XANES curves of thin-film samples using standard spectra of pure c-BN and sp(2)-bonded BN in the films with suitable weight factors, the c-BN contents at the film's surface region and across the film's thickness have been determined quantitatively. The results agree well with the previous transmission electron microscopic observations. The method is proved to be independent of the optical properties of thin film and provides a possibility to evaluate the cubic content of BN films accurately.     

Variation of residual stress in cubic boron nitride film caused by hydrogen addition during unbalanced magnetron sputtering

The effect of hydrogen on compressive residual stress of cubic boron nitride (cBN) was investigated. The deposition was performed by unbalanced magnetron sputtering of a hexagonal boron nitride (hBN) target connected to radio-frequency electric power of 400 W. Up to 2 sccm of hydrogen was added to a gas mixture of argon and nitrogen flowing at 9 and 1 sccm, respectively. The compressive stress rapidly decreased from 10.5 GPa to 3 GPa, with increasing hydrogen flow up to 1.0 sccm. The cBN fraction in these films, however, remained over 60%, with only a trivial decrease with increasing hydrogen. This reduction was discussed in terms of the relation between the penetration probabilities of hydrogen and argon ions into the film, which was main origin of compressive residual stress of the hBN layer.