The Influence of Nitrogen and Boron Implant into Silicon Substrate on the Phase and Internal Stress of c-BN Films

Cubic boron nitride(c-BN) film was deposited on a Si (100) substrate by the RF-magnetron sputtering.The mainly problems for fabrication of c-BN films are the low purity and high intrinsic compressive stress. In order to solve the two problems, the c-BN film with the buffer interlayer was deposited on the substrate which had been implanted with nitrogen and/or boron ions. The results show: the implantation of nitrogen ions can obviously increase c-BN content and reduce the internal stress slightly; while the implantation of boron shows no obvious improvement to the content of c-BN, which can reduce the internal stress in the film obviously. In addition, it is suggested that the implantation of nitrogen and boron shows the best result, which not only can increase the content of c-BN, but also reduce the internal stress in the c-BN film obviously.     

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.     

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.     

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.     

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.     

HFPECVD法沉积BN薄膜及其生长机理的研究

本文介绍了用HFPECVD(hot filament plasma enhanced chemical vapor deposition)法制备BN薄膜.通过红外吸收谱和x射线衍射图谱分析确定,射频功率和反应气体(N2)气流量显著影响薄膜中立方相BN(c-BN)的相对含量.当射频功率小于200W时,薄膜中立方相的相对含量随它的增加而增大;而当射频功率大于200W时,则随它增加而减小.当N2气流量增加时,薄膜生长速率增加,但立方相的相对含量却减少.最后通过对不同沉积时间样品的红外吸收谱的分析对BN薄膜的生长机理进行了探讨.     

Comparison of the properties of BN films synthesized by inductively coupled r.f. and microwave plasmas

Thin films of boron nitride are synthesized by two plasma-enhanced chemical vapour deposition techniques: inductively coupled r.f. plasma (13.56 MHz) and microwave plasma (2.45 GHz). We study the composition (impurity level, B/N ratio), the proportion of c-BN phase in the films and other properties of those films as a function of various process parameters. Two boron and two nitrogen precursors are compared: trimethyl borazine and diborane, dini trogen and ammonia, respectively. The advantages and disadvantages of each combinations are presented. The deposition process is followed by optical emission spectroscopy. Adhesion is one of the main problems encountered for films containing c-BN.     

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.     

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.