Deposition of large area high quality diamond wafers with high growth rate by DC arc plasma jet

We have successfully developed a system for deposition of large area diamond films by a DC arc plasma jet operated in gas recycling mode. In the present paper, the influence of substrate temperature, methane concentration, flow rate of feeding gas and the input power of the jet for diamond film deposition is presented. Deposition of a large area of uniform thickness high quality diamond wafer of Φ65 mm in diameter at a growth rate of 15 μm/h is reported. The thickness of the wafer is 0.7 mm and the thermal conductivity can be 18.1 W/cm K.     

Input power dependence of growth rate and quality of diamond films deposited in a d.c. arcjet system

Using a d.c. arcjet chemical vapor deposition (CVD) system, the dependence of growth rate and quality of diamond films on input power to the plasma torch was investigated. It was found that in a remote methane feed mode, the growth rate of diamond films increases as the input power increases, confirming the benefit of using high power torches. But unexpectedly, the content of non-diamond carbon or defect density in thin diamond films was found to increase as a function of input power, and a thick diamond film deposited at a low input power was of high quality. These results were analyzed considering the kinetics of gas activation taking place in the CVD process. It is believed that high input power along with a high density of atomic hydrogen will effectively activate hydrocarbon radicals, which will bring about both a high growth rate of diamond films and a large probability of defect incorporation into the growing materials.     

NEXAFS characterization of nanocrystalline diamond thin films synthesized with high methane concentrations

Diamond thin films were deposited on silicon in gas mixtures of methane and hydrogen with different methane concentrations ranging from 1% to 100% using microwave plasma assisted chemical vapor deposition. Both Raman spectroscopy and synchrotron near edge extended X-ray absorption fine structure spectroscopy (NEXAFS) were used to characterize the electronic structure and chemical bonding of the synthesized films. The NEXAFS spectra of the nanocrystalline diamond (NCD) films exhibit clear spectral characteristics of diamond. Close observation reveals that the films (10% CH₄ or above) exhibit a slightly broadened exciton transition with a 0.25 eV blue shift. With the increase in methane concentration, the growth rate, the surface smoothness, and the sp² carbon concentration of the films increase while the grain size decreases. Well-faceted microcrystalline diamond films were synthesized with a methane concentration of 5% or lower, while NCD films were formed with a methane concentration of 10% or higher. Diamond thin films with low surface roughness and fine nanocrystalline structure have been synthesized with high methane concentrations (50% or above). It has been observed that the diamond growth rate increases with methane concentration. The growth rate at 100% methane concentration is approximately 10 times higher than at 1%.     

Growth and characterization of hillock-free high quality homoepitaxial diamond films

A suitable pre-treatment process to significantly suppress growth hillocks on homoepitaxial diamond surfaces has been successfully developed. Nanometer-scale morphologies obtained for the homoepitaxial diamond films by means of an atomic force microscope show that the mean roughness (root mean square) of the homoepitaxial diamond films with thickness of 1 μm was approximately 5 nm in the scanning region of 2×2 μm². The results from cathodoluminescence (CL) measurements indicate that the developed pre-treatment and deposition by a high power ASTeX microwave plasma chemical vapor deposition (MWP-CVD) apparatus led to growth of homoepitaxial diamond films with high crystalline quality yielding only band-edge emissions as the main peak in CL spectra at low temperatures (80 K).     

Diamond growth by hollow cathode arc chemical vapor deposition at low pressure range of 0.02–2 mbar

An attempt was made to synthesize diamond films on (001) silicon substrates by means of a graphite or tungsten hollow cathode arc chemical vapor deposition at a lower pressure range of 0.02–2 mbar. The hollow cathode arc provides the advantage of the generation of a large area, high-flux electron beam, a very high-density plasma, and the high kinetic reaction species due to relatively low pressure operation. Diamond films have been characterized by scanning electron microscopy and Raman spectroscopy. The quality of diamond films deposited using the graphite hollow cathode was better than that using the tungsten hollow cathode at 2 mbar pressure. With further decreasing the deposition pressure, the evaporation and sputtering of the graphite hollow cathode are increased and the film quality was deteriorated. The growth rate of diamond films decreased and the nucleation density increased with decreasing deposition pressure.     

高功率微波等离子体环境下甲烷浓度对金刚石膜的影响

在实验室自制的10 kW微波等离子体化学气相沉积装置中,分析了高功率微波等离子体环境中甲烷浓度对金刚石膜生长的影响。利用等离子体发射光谱诊断分析高功率微波等离子体放电环境的特征,同时利用SEM及Raman光谱对不同沉积条件下获得的金刚石膜的形貌及质量进行表征,以确定高功率微波等离子体环境下金刚石膜生长的最优甲烷浓度范围。实验表明在保持微波功率为5000 W,CH₄/H₂≤1%时,金刚石膜中二次形核现象明显,晶粒尺寸较小;CH₄/H₂≥2.5%时,金刚石膜可获得较大的晶粒,但易于产生孪晶体;CH₄/H₂=1.5%～2%时,可获得晶粒完整且质量较高的金刚石膜。     

Periodic vapor-phase fluctuation influence on growth of diamond films

A computer control system was designed to work with diamond film deposition apparatus to control methane flow automatically. In experiments, the methane flow can fluctuate with a fixed period and fixed amplitude cosine curve. Diamond films were deposited by direct current arc plasma jet and their morphologies were examined by scanning electron microscopy. This proved that the reaction vapor-phase periodic fluctuation had an obvious influence upon the growth and nucleation of diamond. The phenomena of alternate growth and nucleation were observed; especially interesting are the two-dimensional fractal carbon clusters that have been observed for the first time.     

Preparation of high quality transparent chemical vapor deposition diamond films by a DC arc plasma jet method

The effects of parameters such as chamber pressure, substrate temperature and methane concentration on the growth rate and the quality of diamond films deposited by DC arc plasma jet were studied. Free standing high quality transparent diamond thick films were produced at a growth rate up to 7–10 μm h⁻¹ under the optimal conditions. Supersaturated atomic hydrogen played an important role in the process, which was produced due to the extremely high temperature of DC arc plasma jet.     

Friction force microscopy study of diamond films modified by a glow discharge treatment

A glow discharge treatment technique has been developed which enables control of the surface roughness and morphology of diamond films for applications in optical and electrical components. A conventional hot filament chemical vapour deposition (CVD) system was used to deposit the diamond films onto silicon substrates via a three-step sequential process: (i) deposition under normal conditions; (ii) exposure to either a pure hydrogen plasma or 3% methane in an excess of hydrogen using DC-bias; and (iii) diamond deposition for a further 2 h under standard conditions. The frictional characteristics and roughness of the film surfaces were investigated by atomic force microscopy (AFM) and the morphology and the growth rates determined from scanning electron microscope images. Lateral force microscopy (LFM) has revealed significant differences in frictional behaviour between the high quality diamond films and those modified by a glow discharge treatment. Friction forces on the diamond films were very low, with coefficients ∼0.01 against silicon nitride probe tips in air. However, friction forces and coefficients were significantly greater on the DC-biased films indicating the presence of a mechanically weaker material such as an amorphous carbon layer. A combination of growth rate and frictional data indicated that the exposure to the H₂ plasma etched the diamond surface whereas exposure to CH₄/H₂ plasma resulted in film growth. Re-Nucleation of diamond was possible (stage iii) after exposure to either plasma treatment. The resultant friction forces on these films were as low as on the standard diamond film.     

Experimental study of nucleation and quality of CVD diamond adopting two-step deposition approach using MPECVD

Effects of the deposition conditions on quality and nucleation density of CVD diamond were investigated using a microwave plasma enhanced chemical vapor deposition (MPECVD) method with methane-hydrogen gas mixtures. Diamond films were deposited at pressures of 665–4000 Pa, temperatures of 660–950 °C, and methane concentrations of 0.5–5 vol.%. Deposited diamond films were characterized by scanning electron microscopy, field emission scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Diamond quality and nucleation density significantly affected by the deposition pressure, substrate temperature, and methane concentration. The findings of this work were discussed in terms of the effects of deposition conditions on the plasma composition. A two-step deposition approach was applied to improve nucleation density and quality of CVD diamond films. Polycrystalline diamond films were grown using the two-step deposition process changing a combination of parameters in the two steps. Growth and quality of the deposited diamond films were improved altering the deposition pressure and substrate temperature in the two steps.     

介质阻挡放电常压低温等离子体转化甲烷制C2及高碳烃的研究

对介质阻挡放电(DBD)反应器用于甲烷常压低温等离子体转化过程,分别就停留时间、输入功率、内电极材料及温度、介质厚度等对反应的影响进行了研究。实验结果表明,甲烷转化率随停留时间、输入功率的增加而增加,但增加的幅度逐渐减小。内电极材料对反应积炭有很大的影响。紫铜和紫铜(镀银)材料能够有效地抑制积炭的产生,从而可以增加反应寿命,还对甲烷转化率有很大的影响。较低的内电极温度可以抑制积炭,但是甲烷转化率有所降低,同时液态高碳烃选择性增加。在甲烷流量较低时介质厚度对反应的影响很小,但随着甲烷流量的提高会逐渐增大,并且介质厚度越小,甲烷转化率越高。     

影响金刚石膜刀具涂层形貌的因素分析

采用高分辨金相显微镜对硬质合金刀生上沉各的ＣＶＤ金刚石薄膜进行了表面形貌和膜／基横截面组织形貌的观察;并利用该显微镜配备的功能测量了金刚石颗粒大小,膜厚;利用显微镜正焦／过焦观察判断了金刚石薄膜的成膜状况。初步观察结果表明：甲烷浓度和基体钴含量对金刚石薄膜的表面形貌和膜／基横截面组织形貌有显著的影响。     

Growth of microcrystalline and nanocrystalline diamond films by microwave plasmas in a gas mixture of 1% methane/5% hydrogen/94% argon

Well-faceted microcrystalline diamond (MCD) films were deposited along with nanocrystalline diamond (NCD) films on the same substrate by a microwave plasma in the gas mixture of 1% CH₄+5% H₂+94% Ar. This was achieved by forcing a microwave plasma ball generated at 170 torr gas pressure to touch a silicon substrate that was pre-seeded by nanocrystalline diamond powder resulting in a high concentration of atomic hydrogen on the surface of growing diamond. Previously reported compositional mapping of the argon–methane–hydrogen system for MCD and NCD growth was not valid in this process parameter space. The non-uniform concentrations of atomic hydrogen and carbon containing radicals such as C₂ as well as varied local substrate temperature resulted in the simultaneous deposition of well-faceted MCD films in some areas with nanograined NCD films in others. Dilution of methane/hydrogen microwave plasmas by as much as 94% of argon alone could not suppress the growth of MCD.     

Effects of nitrogen addition on morphology and mechanical property of DC arc plasma jet CVD diamond films

Nitrogen-doped diamond films have been synthesized by 100 KW DC arc plasma jet chemical vapor deposition using a CH₄/Ar/H₂ gas mixture. The effect of nitrogen addition into the feed gases on the growth and surface morphology and mechanical property of diamond film was investigated. The reactant gas composition was determined by the gas flow rates. At a constant flow rate of hydrogen (5000 sccm) and methane (100 sccm), the nitrogen to carbon ratio (N/C) were varied from 0.06 to 0.68. The films were grown under a constant pressure (4 KPa) and a constant substrate temperature (1073 K). The deposited films were characterized by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. The fracture strength of diamond films was tested by three point bending method. The results have shown that nitrogen addition to CH₄/H₂/Ar mixtures had led to a significant change of film morphology, growth rate, crystalline orientation, nucleation density and fracture strength for free-standing diamond films prepared by DC arc plasma jet.     

Synthesis of diamond films and nanotips through graphite etching

A hot filament CVD process based on hydrogen etching of graphite has been developed to synthesize diamond films and nanotips. The graphite sheet was placed close to the substrate and only hydrogen was supplied during deposition. No hydrocarbon feed gases are required for this process. High quality diamond films were synthesized with high growth rate on P-type (1 0 0)-oriented silicon wafers without discharge or bias. The diamond growth rate is approximately five times higher than that through conventional hot filament chemical vapor deposition using a gas mixture of methane and hydrogen (1 vol.% methane) under similar deposition conditions. The diamond films synthesized in this process exhibit smaller crystallites and contain smaller amount of non-diamond carbon phases. Synthesis of well-aligned diamond nanotips with various orientation angles was achieved on the CVD diamond-coated Si substrate when the substrate holder was negatively biased in a DC glow discharge. The nanotips grown at locations far enough from the sample edges are aligned vertically, while those around the sample edges are tilted and point away from the sample center. The alignment orientation of the nanotips appears to be determined by the direction of the local electric field lines on the sample surfaces.     

砷化镓上生长金刚石薄膜的研究

以CH4和H2为气源,用微波辅助等离子体装置,在10.0 mm×7.0 mm的砷化镓基底上沉积了CVD金刚石薄膜,用扫描电子显微镜观察沉积效果,拉曼光谱表征沉积质量,分析薄膜附着力与砷化镓材料性能的关系。结果表明,当基体温度为600℃,气压为5 kPa,甲烷浓度为2.0%时,在砷化镓片表面上沉积出了CVD金刚石薄膜,晶粒尺寸均匀,晶形完整、规则,晶界非常清晰。     

High rate of diamond deposition through graphite etching in a hot filament CVD reactor

Although a hot filament diamond CVD reactor has many advantages over other processes, the relatively low growth rate of the films has been a crucial drawback. We developed a new hot filament process that uses no hydrocarbon gas for diamond deposition. The graphite plate was placed below the silicon substrate and only hydrogen was supplied during the process. We could achieve the growth rate of 9 μm/h, which is approximately 9 times higher than that of conventional hot filament CVD using a gas mixture of methane and hydrogen. In spite of the high growth rate, the quality of diamond films was not degraded. Besides, the diamond films consisted of small crystallites with a smooth surface while the conventional diamond films of the same thickness tend to have a columnar structure with a rough surface.     

Processes and parameters of diamond films deposition in AC glow discharge

We report about a new PACVD reactor construction for diamond films deposition from the alternating high-current glow discharge plasma. Argon–hydrogen–methane gas mixture was used as the precursor gas. Argon percent in the gas mixture could reach 75%. The discharge was generated between two tungsten electrodes with the total area no more than 1 cm². The electrode temperature was about 2000 °C. The discharge was in the form of plasma line and could reach 20 cm lengthwise and more. The discharge voltage was varied from 90 to 700 V depending on the argon partial pressure, the discharge current and the interelectrode spacing used. The current of discharge reached 30 A. The maximum growth rate of optical grade films was about 2 μm/h. OES spectrometry showed that hydrogen activation degree decreases from the center of plasma line to its edges. X-ray diffractometry and SEM showed the high quality of diamond films. The uniformity of the films in the transverse direction was measured.     

High quality heteroepitaxial diamond films on silicon: recent progresses

This paper reports the progresses made recently on the nucleation and growth of high-quality, [001]-oriented diamond films and discusses the problems to be resolved. The interface structure of diamond on silicon has further been investigated by transmission electron microscopy (TEM). Heteroepitaxial diamond films with increased lateral grain size and reduced grain boundary density were prepared in both microwave plasma chemical vapour deposition (MW-CVD) and hot filament chemical vapour deposition (HF-CVD) processes. Using a growth process combining a bias-assisted H⁺ etching and a [001]-textured growth smooth diamond films with large lateral grain size up to 10 μm can be obtained at a film thickness of approximately 10 μm. By controlling the [001]-textured growth process thick diamond films with a lateral grain size up to 30 μm has been achieved in HF-CVD.     

Investigation of the effect of the total pressure and methane concentration on the growth rate and quality of diamond thin films grown by MPCVD

The influence of total gas pressure (50–125 Torr) and methane concentration (0.75%–10%) on diamond growth by microwave plasma chemical vapor deposition (MPCVD) was investigated. Within the regimes studied, the growth rate was proportional to the methane concentration in the source gas while it exhibited a super-linear dependence on total pressure. For a fixed methane concentration, characterization by Raman spectroscopy, scanning electron microscopy and X-ray diffraction indicated there was a minimum pressure required for the growth of large grain diamond, and conversely, for a fixed pressure, there was a maximum methane concentration that yielded diamond deposition. Higher pressures and higher carbon concentrations yielded diamond growth rates more than 10 times higher than achieved by the conventional low pressure MPCVD process.