Microwave Plasma CVD System Research Articles

Fabrication of Diamond Nanoneedle Arrays Containing High‐Brightness Silicon‐Vacancy Centers

AbstractThe optically active silicon‐vacancy (SiV) center in diamonds is an excellent candidate for quantum photonics and sensing applications. To date, optimizing the photoluminescence (PL) collection efficiency of SiV centers has proven difficult. To address this issue, the current study presents a simple two‐step method for preparing single‐crystalline diamond nanoneedle arrays. In the first step, silicon‐doped (001) textured diamond films are deposited with a mixture of microcrystalline and nanocrystalline grains in a microwave plasma CVD (MPCVD) system, using tetramethylsilane (TMS) gas as the dopant source. Subsequently, air annealing is used to selectively etch nanocrystalline diamond and sp2 amorphous carbon phases, while retaining the [001]‐oriented diamond nanoneedles with a curved top surface. In comparison to the as‐deposited films, the PL emission of SiV centers in these diamond nanoneedles is enhanced by a factor of up to 12.1. The finite‐difference time‐domain simulations further demonstrate that removing the nanocrystalline diamond and sp2 carbon from the sidewall of the diamond nanoneedles results in a remarkable increase in photoluminescence collection. Therefore, the findings have established for the first time the constraint effect of sp2 carbon on the optical collection of color centers at the sidewall rather than the top surface.

Diamond Schottky barrier diodes with floating metal rings for high breakdown voltage

Investigation of influence of floating metal rings (FMRs) edge termination technique on the breakdown voltages of diamond Schottky barrier diodes (SBDs) has been carried out. Unintentionally doped P- drift layer was grown on HPHT boron doped diamond substrate by microwave plasma CVD system and treated by ultraviolet ozone. Then, Ti/Ni/Au electrode was deposited on the back side of the substrate to form ohmic contact. Zr/Ni/Au Schottky electrodes with different FMRs parameters, such as ring spacing (RS), ring width (RW) and ring number (RN), were deposited on the P- layer. The I–V measurement results show that breakdown voltages increase firstly and then decease with increasing of RS. The increases of RW and RN are beneficial to improve breakdown voltages. Moreover, FMRs structure can effectively improve breakdown voltages without deteriorating forward current density and rectification ratio of diamond SBDs.

Lateral overgrowth of diamond film on stripes patterned Ir/HPHT-diamond substrate

Epitaxial lateral overgrowth (ELO) of diamond films on patterned Ir/(0 0 1)HPHT-diamond substrates have been carried out by microwave plasma CVD system. Ir/(0 0 1)HPHT-diamond substrates are fabricated by photolithographic and magnetron sputtering technique. The morphology of the as grown ELO diamond film is characterized by optical microscopy and scanning electronic microscopy. The quality and stress of the ELO diamond film are investigated by surface etching pit density and micro-Raman spectroscopy. Two ultraviolet photodetectors are fabricated on ELO diamond area and non-ELO diamond area prepared on same substrate, and that one on ELO diamond area indicates better photoelectric properties. All results indicate quality of ELO diamond film is improved.

Investigation of bonded hydrogen defects in nanocrystalline diamond films grown with nitrogen/methane/hydrogen plasma at high power conditions

In this work, we investigate the influence of some growth parameters such as high microwave power ranging from 3.0 to 4.0kW and N2 additive on the incorporation of bonded hydrogen defects in nanocrystalline diamond (NCD) films grown through a small amount of pure N2 addition into conventional 4% CH4/H2 plasma using a 5kW microwave plasma CVD system. Incorporation form and content of hydrogen point defects in the NCD films produced with pure N2 addition was analyzed by employing Fourier-transform infrared (FTIR) spectroscopy for the first time. A large amount of hydrogen related defects was detected in all the produced NCD films with N2 additive ranging from 29 to 87µm thick with grain size from 47nm to 31nm. Furthermore, a specific new H related sharp absorption peak appears in all the NCD films grown with pure N2/CH4/H2 plasma at high powers and becomes stronger at powers higher than 3.0kW and is even stronger than the 2920cm−1 peak, which is commonly found in CVD diamond films. Based on these experimental findings, the role of high power and pure nitrogen addition on the growth of NCD films including hydrogen defect formation is analyzed and discussed.

Nitrogen and Silicon Defect Incorporation during Homoepitaxial CVD Diamond Growth on (111) Surfaces

ABSTRACTChemical Vapor Deposited (CVD) diamond growth on (111)-diamond surfaces has received increased attention lately because of the use of N-V related centers in quantum computing as well as application of these defect centers in sensing nano-Tesla strength magnetic fields. We have carried out a detailed study of homoepitaxial diamond deposition on (111)-single crystal diamond (SCD) surfaces using a 1.2 kW microwave plasma CVD (MPCVD) system employing methane/hydrogen/nitrogen/oxygen gas phase chemistry. We have utilized Type Ib (111)-oriented single crystal diamonds as seed crystals in our study. The homoepitaxially grown diamond films were analyzed by Raman spectroscopy, Photoluminescence Spectroscopy (PL), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nitrogen concentration in the plasma was carefully varied between 0 and 1500 ppm while a ppm level of silicon impurity is present in the plasma from the quartz bell jar. The concentration of N-V defect centers with PL zero phonon lines (ZPL) at 575nm and 637nm and the Si-defect center with a ZPL at 737nm were experimentally detected from a variation in CVD growth conditions and were quantitatively studied. Altering nitrogen and oxygen concentration in the plasma was observed to directly affect N-V and Si-defect incorporation into the (111)-oriented diamond lattice and these findings are presented.

나노결정질 다이아몬드가 코팅된 SiC 마모시험기 볼

Nanocrystalline diamond(NCD) coated SiC balls were applied in a ball-on-disk tribometer. After seeding in an ultrasonic bath containing nanometer diamond powders, 2.2 µm thick NCD films were deposited on sintered 3 mm diameter SiC balls at 600 o C in a 2.45 GHz microwave plasma CVD system. Bare ZrO2 and SiC balls were prepared for comparison as test balls. Tribology tests were performed in air with pairs of three different balls and mirror polished steel(SKH51) disk. The wear tracks on balls and disks were examined by optical microscope and alpha step profiler. Under the load of 3 N, the friction coefficients of steel against ZrO2, SiC and NCD-coated balls were between 0.4 and 0.8. After a few thousands sliding laps, the friction coefficient of NCD-coated balls dropped from 0.45 to below 0.1 and maintained thereafter. Under a higher load of 10 N or 20 N with a long sliding distance of 2 km, ZrO2 and SiC balls exhibited the similar friction coefficients as above. The friction coefficient of NCD-coated balls was less than 0.1 from the beginning and increased to above 0.1 steadily or with some fluctuations as sliding distance increased. NCD coating layers were found worn out after long duration and/or high load sliding test, which resulted in the friction coefficient higher than 0.1.

Growth of carbon allotropes and plasma characterization in linear antenna microwave plasma CVD system

Growth of diamond coatings with tunable morphology and concurrent substrate catalyst pretreatment and further growth of carbon nanotubes were studied. The dependence of plasma parameters on gas composition was studied by Langmuir probe measurement. Grown diamond coatings and carbon nanotubes were characterized by scanning electron microscopy and Raman spectroscopy and correlated with process parameters. Well-defined nanocrystalline, polycrystalline, and porous diamond films were prepared. Concurrent substrate catalyst pretreatment and further growth of carbon nanotubes were shown.

W 및 Ti 박막 위에서 나노결정질 다이아몬드의 성장 거동

The growth behavior of nanocrystalline diamond (NCD) film has been studied for three different substrates, i.e. bare Si wafer, 1 thick W and Ti films deposited on Si wafer by DC sputter. The surface roughness values of the substrates measured by AFM were Si ) > W () > Ti (). During deposition in the microwave plasma CVD system, NCD particles were formed and evolved to film. For the first 0.5h, the values of NCD particle density were measured as Si Si > Ti. In the case of W substrate, NCD particles were coalesced and evolved to the film in the short time of 0.5 h, which could be attributed to the fact that the diffusion of carbon species on W substrate was fast. The slower diffusion of carbon on Si substrate is believed to be the reason for slower film growth than on W substrate. The surface of Ti substrate was observed as a vertically aligned needle shape. The NCD particle formed on the top of a Ti needle should be coalesced with the particle on the nearby needle by carbon diffusion. In this case, the diffusion length is longer than that of Si or W substrate which shows a relatively flat surface. This results in a slow growth rate of NCD on Ti substrate. As deposition time is prolonged, NCD particles grow with carbon species attached from the plasma and coalesce with nearby particles, leaving many voids in NCD/Ti interface. The low adhesion of NCD films on Ti substrate is related to the void structure of NCD/Ti interface.

초경합금에 나노결정질 다이아몬드 코팅 시 금속 중간층의 효과

For the coating of diamond films on WC-Co tools, a buffer interlayer is needed because Co catalyzes diamond into graphite. W and Ti were chosen as candidate interlayer materials to prevent the diffusion of Co during diamond deposition. W or Ti interlayer of 1 μm thickness was deposited on WC-Co substrate under Ar in a DC magnetron sputter. After seeding treatment of the interlayer-deposited specimens in an ultrasonic bath containing nanometer diamond powders, 2 μm thick nanocrystalline diamond (NCD) films were deposited at 600oC over the metal layers in a 2.45 GHz microwave plasma CVD system. The crosssectional morphology of films was observed by FESEM. X-ray diffraction and visual Raman spectroscopy were used to confirm the NCD crystal structure. Micro hardness was measured by nano-indenter. The coefficient of friction (COF) was measured by tribology test using ball on disk method. After tribology test, wear tracks were examined by optical microscope and alpha step profiler. Rockwell C indentation test was performed to characterize the adhesion between films and substrate. Ti and W were found good interlayer materials to act as Co diffusion barriers and diamond nucleation layers. The COFs on NCD films with W or Ti interlayer were measured as less than 0.1 whereas that on bare WC-Co was 0.6~1.0. However, W interlayer exhibited better results than Ti in terms of the adhesion to WC-Co substrate and to NCD film. This result is believed to be due to smaller difference in the coefficients of thermal expansion of the related films in the case of W interlayer than Ti one. By varying the thickness of W interlayer as 1, 2, and 4 μm with a fixed 2 μm thick NCD film, no difference in COF and wear behavior but a significant change in adhesion was observed. It was shown that the thicker the interlayer, the stronger the adhesion. It is suggested that thicker W interlayer is more effective in relieving the residual stress of NCD film during cooling after deposition and results in stronger adhesion.

Growth of nanocrystalline diamond films deposited by microwave plasma CVD system at low substrate temperatures

AbstractNanocrystalline diamond (NCD) films were grown by microwave plasma CVD in hydrogen‐based gas mixture. Deposition experiments were performed at different temperatures varying from 370 to 1100 °C. Before growth step, silicon (100) oriented substrates were nucleated by bias enhanced nucleation procedure and glass substrates were pretreated in ultrasonic bath. Optical, structural and morphological properties of NCD films were systematically studied by using an optical spectroscopy, scanning electron microscopy and Raman spectroscopy. NCD films were optically transparent in wide range and had high refractive index of 2.34. All deposited samples exhibited diamond characteristic line in the Raman spectrum. The growth kinetic was attributed to the hydrogen abstraction model. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Plasma CVD reactor with two-microwave oscillators for diamond film synthesis

In this study, we present the experimental results of a new type of microwave plasma CVD system, where two of 1.5 kW microwave sources were used for enlarging the plasma discharge and the diamond film growth. One of the microwave oscillators was used to produce the microwave plasma as in the conventional microwave plasma CVD device, while the second one was used to enlarge the plasma by introducing microwave from the launcher mounted at the substrate stage. We demonstrated the enlargement of plasma discharge area from 60 mm to 100 mm in diameter by using the two-microwave oscillators system. Characteristics of diamond films deposited using H 2/CH 4 plasmas were also investigated using a scanning electron microscope (SEM) and Raman spectroscopy.

The effect of nitrogen addition during high-rate homoepitaxial growth of diamond by microwave plasma CVD

The effect of nitrogen addition on growth rate, morphology and crystallinity during high-rate microwave plasma chemical vapor deposition (MPCVD) of diamond was investigated. Epitaxial diamond was grown on type Ib diamond (100) substrates using a 5-kW, 2.45-GHz microwave plasma CVD system with nitrogen addition in the methane and hydrogen source gases. In order to obtain high growth rates, we designed the substrate holders to generate high-density plasma. The growth rates ranged from 30 to 120 μm/h. The nitrogen addition enhanced the growth rate by a factor of 2 and was beneficial to create a macroscopic smooth (100) face avoiding the growth of hillocks. However, the (100) surfaces looked microscopically rough by bunched steps as the effect of nitrogen addition. The macroscopic smoothing during the growth enabled the long-term stable deposition required to obtain large crystals. The deposited diamond was characterized by optical microscope, Raman spectroscopy, cathodoluminescence spectroscopy and X-ray diffraction.

Intermediate gas phase precursors during plasma CVD of HMDSO

In plasma enhanced chemical vapor deposition (PECVD) from complex molecules like hexamethyldisiloxan (HMDSO) often not the molecules themselves but intermediate and reactive radicals or molecules are the precursors for film growth. Additionally, such PECVD processes are volume or mass flow limited under many process conditions. In these cases growth rate and film homogeneity is mainly dominated by the precursor content and its spatial distribution in the gas or plasma phase. Therefore the identification of such intermediate precursors is an important task to optimize a PECVD process and also helps us to understand the plasma chemical reactions during PECVD. A combined mass spectrometry and IR absorption study is used to identify intermediate gas phase precursors in HMDSO/O 2 PECVD remote plasmas. For this study a microwave plasma CVD system was used with HMDSO/O 2 ratios between 0.1 and 1 at typical operating pressures between 20 and 70 Pa. Three reactive intermediate species are proposed to act as a precursor for SiO x film growth from HMDSO/O 2 plasmas. All three having a mass of 148 amu. The related reactive groups are the silanon (Si=O), silanol (Si–OH) and aldehyde (C=O) groups.

Promoting secondary nucleation using methane modulations during diamond chemical vapor deposition to produce smoother, harder, and better quality films

In this paper, we present results obtained from a comparison study relating to the deposition of diamond films using two processes, namely, time-modulated chemical vapor deposition (TMCVD) and conventional CVD. Polycrystalline diamond films were deposited onto silicon substrates using both hot-filament CVD and microwave plasma CVD systems. The key feature of TMCVD is that it modulates methane (CH4) flow during diamond CVD, whereas in conventional CVD the CH4 flow is kept constant throughout the deposition process. Films grown using TMCVD were smoother, harder, and displayed better quality than similar films grown using constant CH4 flow during CVD. The advantage of using TMCVD is that it promotes secondary nucleation to occur on existing diamond crystals. Pulsing CH4, consecutively, at high and low concentrations allows the depositing film to maintain its quality in terms of diamond-carbon phase. Films grown under constant CH4 flow during diamond CVD displayed a columnar growth mode, whereas with the time modulated films the growth mode was different. The mechanism of film growth during TMCVD is presented in this paper. The growth rate of films obtained using the hot filament CVD system with constant CH4 flow was higher than the growth rate of time modulated films. However, using the microwave-plasma CVD system, the effect was the contrary and the time-modulated films were grown at a higher rate. The growth rate results are discussed in terms of substrate temperature changes during TMCVD.

大気圧以上の高圧力下でのプラズマＣＶＤによるダイヤモンドの高速形成

A new microwave plasma CVD system for generating diamond is developed and the experiments for synthesizing diamond under higher pressure than atmospheric pressure are carried out. Methane concentration in hydrogen carrier gas and substrate temperatures are optimized as the most important experimental conditions for generating diamond using the CVD system. Experiments in which diamond is synthesized under higher pressure than atmospheric pressure are also carried out, and growth rates and Raman spectra are investigated. Consequently, the growth rate of diamond using this CVD system is 100 micrometers thickness per hour, which is ten times higher than when conventional low pressure CVD systems are used. It is found that the optimal methane concentration exists, which becomes higher as pressure increases. From the experimental results obtained under conditions in which the pressure is varied from 800 hPa to 3000 hPa and the other conditions are maintained at the same values, it is also found that the growth rate of diamond reaches a maximum at 1500 hPa. This result shows that optimization of the other conditions is necessary to obtain the highest growth rate of diamond at 3000 hPa.

Characterization of photoluminescence of a-Si:H nanoball films fabricated by microwave plasma CVD

The double-tubed coaxial line-type microwave plasma CVD (MPCVD) system was developed to obtain a stable plasma with a low and high gas pressure for fabrication of electronic devices and photonic devices. The a-Si:H nanoball films were fabricated by MPCVD system. In the deposition chamber, the Ar gas was fed to the outer discharge tube and the SiH 4 gas was fed to the inner tube. The Ar gas was ionized in the cylindrical cavity region by the microwave power. The SiH 4 gas flowed into the Ar plasma at the discharge tube end through the inner tube, and then the SiH 4 was dissociated. After heat treatments for 72 h in air for as-deposited a-Si:H nanoball films, SiO 2 nanoballs included Si nanocrystal characterized from XPS spectrum of the silicon 2p region. Also, from SEM and AFM observations of the oxidized surface of a-Si:H nanoball films, the size of a-Si:H nanoball was about 20–30 nm in diameter.

Synthesis of nanocrystalline diamond films using microwave plasma CVD

Diamond is one of the most valuable materials for the industrial applications because of its excellent properties including high hardness, with good electrical insulation and thermal conductivity. Mechanical polishing processes of diamond are difficult and very costly. To limit those costs, it is reasonable to think that the surface roughness of the as-grown diamond film should be as small as possible. In this study, a nanocrystalline diamond film was synthesized on a 4-inch Si wafer at 923 K and methane concentration of 10 vol.%, (H 2/CH 4=100/10 sccm) using a microwave plasma CVD system. In order to increase the nucleation density, the substrate was pretreated by dry scratch method with diamond powder of two sizes (250 nm and 5 nm). The nucleation density was approximately 1×10 11 cm −2. The grown diamond films were analyzed by Raman spectroscopy and X-ray diffraction (XRD). The grain size was observed to be approximately 10 nm by FE-SEM observation. Surface roughness was measured as Rms=8.4 nm by atomic force microscope (AFM). The as-grown properties of those nanocrystalline diamond films were almost efficient for tribological and the optical applications.

The role of nitrogen in the deposition of polycrystalline diamond films

Abstract The role of nitrogen in the formation of polycrystalline diamond films prepared using a microwave plasma CVD system has been studied using micro-Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Although the nitrogen concentration in the films was too low to be detected by XPS, the Raman spectrum was found to be significantly affected by the nitrogen flow ratio. The intensity of the Raman peak at 1480 cm−1 significantly decreases, whereas that of 1190 cm−1 peak remains almost unchanged in comparison with the 1350 and 1550 cm−1 peaks with increasing nitrogen flow ratio. In contrast, the preferentially (111)-orientated growth and the growth rate were little influenced by the nitrogen flow ratio. These results indicate that nitrogen plays a special role in the formation and structure of the polycrystalline diamond films studied in this report.

Stabilization of Ar plasma by applying longitudinal magnetic field

This research is intended to obtain a stable plasma with a low gas pressure by applying a magnetic field parallel to the gas flow in the discharge region of a double-tubed coaxial line-type microwave plasma CVD system so that the diffusion of the plasma in the radial direction is suppressed. The stability of the plasma is studied by the width of variation and temporal change of the electron saturation current. In the case where the Ar gas flow rate is 30, 20, and 15 ml/min, the stability of the plasma is good. Improved stability is seen on application of a magnetic field. Also, in the case of Ar gas flow rate of 10 and 8 ml/min, the plasma is unstable without a magnetic field. By applying a magnetic field of more than about 500 gauss, the diffusion of electrons to the discharge tube wall is suppressed and as a result the extinction of electrons at the wall is reduced. Hence, a stable microwave plasma is obtained even at a low gas pressure (low gas flow). © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(3): 10–16, 1998

Preparation of boron nitride thin films by microwave plasma enhanced CVD, for semiconductor applications

Thin films of boron nitride (BN) have been deposited on silicon and indium phosphide (InP) substrates at low temperature (≈ 300 °C) using a microwave plasma CVD system. The source material is molten borane-dimethylamine. The vapour was decomposed in a microwave nitrogen and argon plasma. The index of refraction and the thickness of the films have been determined by ellipsometry. FTIR spectroscopy was used for a fast phase identification. The composition was analyzed by X-ray photoelectron spectroscopy (XPS). The electrical properties of the films were evaluated by capacitance-voltage ( C-V) measurements of metal/BN/semiconductor (MIS) structures. From these results a minimum interface state density of 3.5 10 11 cm −2 eV −1 and a dielectric constant of 5.2 have been deduced.