Transverse bias-enhanced nucleation of diamond in hot filament chemical vapor deposition

 The nucleation density of diamond films was greatly enhanced by inserting a transverse bias into hot filament vapor deposition chamber, which differs from the conventional used longitudinal bias method. In-situ Optical Emission Spectroscopy (OES) technique was used to investigate the diamond deposition process. The relative optical emission intensities of the atomic hydrogen and CH radical to argon near the substrate were calculated. The results show that the improvement of the nucleation density is due to the product of much more atomic hydrogen and CH radicals. Received: 18 March 1998 / Accepted: 22 May 1998     

Bilayer systems of tantalum or zirconium nitrides and molybdenum for optimized diamond deposition

Thermo chemical computing validates the stability of different nitrides against Co, Mo, and methane up to 1150 K, showing the highest chemical stability against carburization for ZrN and TaN under static conditions.Single zirconium and tantalum nitrides layers have been sputtered onto WC-Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (< 500 nm). In this study, two bilayer systems have been tested: TaN-Mo and ZrN-Mo. Nano crystalline diamond has been grown under negative biased substrates.After diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. Nevertheless, a small amount of cobalt has migrated through the ZrN layer. The better efficiency of the ZrN layer to prevent diffusion of the Co element, leads to expect an increased adhesion of diamond on ZrN-Mo bilayer coating. A TEM study is done to improve understanding of phenomena occurring at the interfaces during process.     

Bias frequency, waveform and duty-cycle effects on the bias-enhanced nucleation of epitaxial diamond

In contrast to conventional DC bias-enhanced nucleation, a pre-carburization step was not needed in the processing of epitaxial diamond on (1 0 0) silicon using pulsed biasing. Otherwise, the procedure showed little frequency dependence on the epitaxial process in the range of 1 Hz–2 kHz, resulting in a constant percentage of highly oriented diamond of nearly 50%. The only variation with frequency was a linear increase in the bias current and a corresponding decrease in the biasing time required to form a quasi-continuous nucleation layer. In contrast, the variation of a 60-Hz square waveform duty cycle from 3 to 75% showed a decreasing hyperbolic relationship with the percentage of oriented diamond, with a plateau of 45% occurring at duty cycles of 17%. The bias time to film formation was also determined to be inversely proportional to the duty cycle. The collective data highlights the relevance of the waveform attributes on the epitaxial nucleation of diamond on (1 0 0) silicon.     

Diamond thin film nucleation on silicon by ultrasonication in various mixtures

Nucleation is a very important step in synthetic diamond thin film growth process and generally the incubation time for the stable diamond nuclei formation is very long. We can consider it to be a pre-treatment of the Si substrate surface before diamond film deposition.In this study we have investigated the synthetic diamond thin film nucleation mainly on Si substrates by the ultrasonication in different mixtures of isopropanol, deionized water, n-methylpyrrolidon (NMP) or sodiumdodecylsulphate (SDS) containing nanosized diamond powder (≤10 nm, Sigma-Aldrich) and micro-or nanosized metals (Nickel, Cobalt, Yttrium). Liquids NMP and SDS have a special property to separate nanoparticles.     

Chemical vapour deposition of oriented diamond nanocrystallites by a bias-enhanced nucleation method

A microwave plasma chemical vapour deposition (MPCVD) system has been used to deposit nanometre-sized single-crystalline diamonds on 1 × 1?cm(2) Si(100) substrates. The distribution of deposited diamonds has good uniformity over the whole Si substrate surface by using a dome-shaped Mo anode which allows the application of bias-enhanced nucleation. The morphology and crystallinity of the deposits on Si were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with electron diffraction and lattice images. SEM and TEM observations show that oriented diamond nuclei as single crystals with facets can form on self-formed Si cones through epitaxial SiC within a short bias period. After a longer bias time, it has been observed that polycrystalline diamonds formed as a result of secondary nucleation.     

Investigation of the nucleation and growth of SiC nanostructures on Si

Using in situ reflection high energy electron diffraction (RHEED), ex situ atomic force microscopy (AFM) and transmission electron microscopy (TEM) the early stages of SiC growth on Si during the carbonisation were investigated in a solid source molecular beam epitaxy equipment. Different mechanisms of SiC precipitate growth by SSMBE were found. The SiC growth during carbonisation of Si(111) at 600°C is controlled by diffusion and at higher temperatures by a two-dimensional nucleation process, which is mononuclear at 660°C and polynuclear above 750°C. At temperatures greater than 750°C and 850°C three-dimensional nucleation occurs at (111) and (100) surfaces, respectively.     

Bias enhanced nucleation of diamond thin films in a modified HFCVD reactor

In this study we investigated the nucleation of synthetic diamond thin films on Si substrates by double bias enhanced Hot Filament Chemical Vapour Deposition (HFCVD) method. First, we investigated the influence of the bias voltage and secondly the influence of the nucleation time under different bias voltages. The bias voltage was varied from −120 V up to −220 V as well as the nucleation time was changed from 30 up to 120 min in order to obtain the optimized nucleation conditions for following growth of continuous diamond layer. Samples were analyzed by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. SEM was used for determination of cluster sizes and their distribution on the Si surface, while Raman Spectroscopy for determination and analysis of carbon phases.     

微波等离子体化学气相沉积法在硅片上同时生长碳化硅和金刚石

研究了衬底温度、核化密度、衬底表而预处理等工艺参数对微波等离子体化学气相沉积法在硅片上同时生长碳化硅和金刚石的影响.采用扫描电镜、X-射线衍射、喇曼光谱和红外光谱对样品进行了表征.结果表明:从高核化密度生长的金刚石膜中探测不到碳化硅;不论对硅衬底进行抛光预处理还是未抛光预处理,从低核化密度牛长的金刚石厚膜中总能探测到碳化硅.碳化硅生长在硅衬底上未被金刚石覆盖的地方,或者是在金刚石晶核之间的空洞处.碳化硅形成和金刚石生长是同时发生的两个竞争过程.此研究结果为制备金刚石和碳化砟复合材料提供了一种新的方法.     

Enlargement of the diamond deposition area in combustion flame method by traversing substrate

In this study, diamond deposition on traversing substrate was carried out in order to get useful information for utilizing combustion flame method. In the case of stationary substrate, diamond particles were obtained on the condition that C₂H₂/O₂ flow ratio was from 1.00 to 1.15, while no particles could be obtained in oxygen rich environment. However, in the case of traversing substrate, dense diamond belt was deposited without oxidizing of the diamond particles due to oxidative flame. From these results, it was proved that large area deposition by substrate traversing was available even in the case of combustion flame CVD.     

Electrical characterization of CVD diamond thin films grown on silicon substrates

Diamond thin films grown on high resistivity, 100 oriented silicon substrates by the hot filament chemical vapor deposition (HFCVD) method have been characterized by four-point probe and current-voltage (through film) techniques. The resistivities of the as-grown, chemically etched and annealed samples lie in the range of 10² Ω cm to 10⁸ Ω cm. The Raman measurements on these samples indicate sp³ bonding with a sharp peak at 1332 cm⁻¹. The surface morphology as determined by scanning electron microscope shows polycrystalline films with (100) or (111) faceted structures with average grain size of ≈2.5 μm. The through film current-voltage characteristics obtained via indium contacts on these diamond films showed either rectifying or ohmic behavior. The difference in Schottky and ohmic behavior is explained on the basis of the high or low sheet resistivities measured by four-point probe technique. 5% methane to hydrogen concentration during film growth resulted in poor surface morphology, absence of sp³ bonds, and low resistivity.     

Study of carbide-forming element interlayers for diamond nucleation and growth on silicon and WC-Co substrates

Diamond nucleation and growth on several typical carbide-forming elements (CFE) (Ti, Cr and W) coated Si and WC-Co substrates were studied. The ion beam sputtered CFE interlayers show an amorphous/nanocrystalline microstructure. The diamond formed on the CFE coated substrates shows higher nucleation density and rate and finer grain structure than on uncoated substrates. Consequently, nanocrystalline diamond thin films can be formed on the CFE coated substrates under conventional microcrystalline diamond growth conditions. Among the three tested CFE interlayers, diamond has the highest nucleation density and rate on W layer and the lowest on Ti layer. The diamond nucleation density and rate on CFE coated WC-Co are much higher than those on widely used metal nitride coated WC-Co.     

Comparison of mode-resolved fracture strength of silicon with mixed-mode failure of diamond crystals

Currently ab initio theory provides the ideal tensile and shear strength of the {111} cleavage plane in single-crystal silicon and diamond only for few selected planes and directions (‘geometries’). These values can be compared with the real strength of nano-, micro-, and single-crystalline devices to roughly judge their mechanical quality. A novel contact-free and notch-free optical laser method allows the measurement of the fracture strength with plane nonlinear surface acoustic waves (SAWs), providing a unique way to discriminate between tensile and shear stresses for well-defined crystallographic planes and directions in anisotropic materials. Calibration yields the critical fracture stress or strength for the geometries, which can be compared with theory. In the case of diamond mostly mechanistically unresolved mixed-mode failure has been studied for complex geometries. Nevertheless, the comparison of these critical failure stresses with the strength of the ideal lattice and the mode- and geometry-resolved fracture behavior of silicon provides new insight into the mechanical stability and failure behavior of diamond materials.     

HF CVD diamond nucleation and growth on polycrystalline copper: A kinetic study

This paper reports on the kinetics of diamond nucleation and growth on polycrystalline copper investigated by in situ Auger Electron Spectroscopy and Scanning Electron Microscopy. Copper is a reference substrate to study the diamond nucleation from graphite. The substrate is first treated with diamond paste. However the diamond seeds let on the surface by the pre-treatment are almost completely transformed into graphite. The nucleation of CVD diamond can be well described in the framework of carbon phase transformations. Diamond seeds deposited on the substrate are first transformed into graphitic layers. A process occurring on the edges site of graphite is subsequently postulated, in agreement with the Lambrecht model.     

Diamond chemical vapour deposition on seeded cemented tungsten carbide substrates

Diamond particles were deposited onto seeded cemented tungsten carbide (WC-Co) substrates using conventional hot-filament chemical vapour deposition (HFCVD) and time-modulated CVD (TMCVD) processes. The substrates were pre-seeded ultrasonically with diamond particles of different grit sizes. In this investigation, we employ timed methane (CH₄) gas modulations, which are an integral part of our TMCVD process in order to enhance diamond nucleation density. During diamond deposition using the conventional HFCVD process, methane gas flow was maintained constant. The total hydrogen flow into the reactor during TMCVD process was higher than in the HFCVD process. Hydrogen etching can be expectedly more prominent in the TMCVD process than in HFCVD of diamond particles. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that a proper selection of the diamond grit size for seeding using ultrasounds can lead to enhancement in the nucleation density values of about two orders of magnitude (10⁷ to 10⁹ cm^− 2). The TMCVD process using the different seeded substrates can result in high nucleation density values of up to 10¹⁰ cm^− 2.     

Sensitivity analysis of gas-phase chemistry leading to diamond deposition

Abstract

Sensitivity analysis of gas-phase chemistry is used for improving the diamond growth model. Performed consideration shows that the more careful choice of a set of chemical reactions, both gas-phase and surface, and of their parameters is required. It is concluded that the preliminary analysis of the sensitivity of the system to key parameters is welcome.     

硅基GaN外延晶体学位相关系和生长机理研究

采用反应蒸发光地在提高缓冲层的生长温度,通过对Ｓｉ基上ＧａＮ样品缓冲层区域的高分辨透射电镜像（ＨＲＴＥＭ）和界面区域的选区电子衍射（ＳＡＥＤ）分析的基础上,提出了本系统ＧａＮ外延的晶体学位相关系和生长机理。ＧａＮ与Ｓｉ衬底之间存在着下列的晶体学位相关系：ＧａＮ〈０００１〉∥Ｓｉ〈１１１〉,ＧａＮ〈１１２０〉∥Ｓｉ〈１１０〉,ＧａＮ外延生长首先在硅衬底上形成ＧａＮ晶核,生长出ＧａＮ多晶缓冲层,ＧａＮ     

碳化钨在金刚石磨具中的应用

在金刚石磨具的金属结合剂中适当加入WC,可以提高胎体硬度耐磨性和自锐性等物理机械性能,从而取得实用效果,本文在这方面进行探讨作简单介绍。     

Stimulation of the diamond nucleation on silicon substrates with a layer of a polymeric precursor in deposition of diamond films by microwave plasma

It has been shown that layers of a certain type of polymers applied to silicon substrates at the thermal destruction form (in parallel with sp² coordinated carbon) diamond nanoparticles, which act as nucleation centers of crystallites in the subsequent chemical vapor deposition of diamond. Microcrystalline diamond films have been synthesized from methane-hydrogen mixtures by microwave plasma using poly(naphthylhydrocarbyn) and poly(hydrocarbyn) preceramic polymers.     

LiF enhanced nucleation of the low temperature microcrystalline silicon prepared by plasma enhanced chemical vapour deposition

A 15-nm lithium fluoride (LiF) thin film evaporated on glass substrate is shown to enhance the nucleation of microcrystalline Si grown by plasma enhanced chemical vapour deposition at the amorphous/microcrystalline boundary conditions. The effect is more pronounced at low substrate temperatures, nucleation density being 10 times higher at ∼ 80 °C. The effect is ascribed to the ionic chemical nature of LiF, the low work function material used in organic electronic devices, and we propose its use for micro patterning crystalline Si regions in otherwise amorphous Si film.     

Structure of diamond polycrystalline films deposited on silicon substrates

The article presents results of structural studies of polycrystalline diamond thin films deposited by hot filament CVD on silicon substrates. The films were characterized using Scanning Electron Microscopy (SEM), Raman Spectroscopy (RS), Electron Backscattered Diffraction (EBSD), Energy Dispersive Spectroscopy (EDS) and Secondary Ion Mass Spectroscopy (SIMS). Both the EBSD patterns and Raman spectra confirm that the grains visible in the electron micrographs are diamond micro-crystallites. The residual stress in the films is found to be in the range between −4.29 GPa and −0.56 GPa depending on the sample thickness. No evidence of lonsdalite and graphite has been registered in the polycrystalline material of the investigated samples. Evidence of the existence of silicon carbide at the diamond/silicon interface is presented. It is also suggested that an amorphous carbonaceous film covers the silicon surface in the regions of holes in the thin diamond layers.