Microwave power and chamber pressure studies for single-crystalline diamond film growth using microwave plasma CVD

In this paper, the hydrogen and hydrogen-methane mixed plasma have been generated inside a 33 cm diameter quartz bell jar with a low power (9 KW) and lower frequency 915 MHz microwave plasma chemical vapor deposition system. The reactor is being used for growing polycrystalline diamond (PCD) over large area (100 mm). The generated plasma is diagnosed by in situ optical emission spectroscopy method with wave length ranging from 200 to 900 nm. The effects of microwave power, chamber pressure and gas concentration on plasma characteristics have been studied in this work. Within the optical range, Balmer H α , H β , C2swan band and CH lines have been detected at the wavelengths of 655.95, 485.7, 515.82 and 430.17 nm, respectively. It has been observed that for hydrogen plasma, the amount of transition from hydrogen atom inner shell 3 to 2 (H α ) is almost constant with increasing microwave (MW) power (from 2000 to 2800 W) and pressure (from 15 to 30 Torr) initially, after that it increases with further increase of MW power and pressure, whereas, the transition from 4 to 2 (H β ) is slowly increased with increasing MW power and pressure. For hydrogen-methane plasma, intensities of C2 swan band, i.e., the transitions from D3π g to A3π μ energy levels, are also increased with the increasing microwave power and reactor pressure. It has been observed that the radicals present in the plasma are affected by variation of different reactor parameters like pressure, MW power, CH4 concentration, etc.

Microwave Plasma Chemical Vapor Deposition (MPCVD) method can be used to grow various kinds of diamond films and carbon nanotubes at various temperatures. However, it is usually only the hand-on experience that can be relied on to obtain the nearly satisfactory plasma in the MPCVD system. Therefore, this study set up the reflected power sensor as a reference parameter and used a CCD (Charge Coupled Device) to observe the plasma image. Manufacturing parameters, such as gas flow rate, input microwave power, working distance, deposition time, chamber pressure and substrate temperature, were all fixed to grow MWCNTs. The controlled adjustments, as the independent variables, are the positions of E-H tuner along x-axis and y-axis which directly affect the conditions of the plasma. In order to grow multiwalled carbon nanotubes (MWCNTs) of better quality with a self-assembled MPCVD system, the quality indexes of MWCNTs, which are the aspect ratio of MWCNTs and the ID/IG intensity ratio of the Raman spectrum of MWCNTs, were analyzed. With the established database, it is found that there exist the optimized positions of E-H tuner along x-axis and y-axis for growing MWCNTs of high quality. Moreover, we used PCA (Principle Component Analysis) method to analysis these data, and a relationship between manufacturing parameters was found.

Deposition of large area uniform diamond films by microwave plasma CVD

This thesis focuses on the study of growth of homoepitaxial diamond film with embedded gold nanoparticles (AuNPs) by microwave plasma chemical vapor deposition (MPCVD). The first part of this thesis deals with the preparation of gold nanoparticles on diamond (111) single crystal substrate. The effect of various plasma conditions on the distribution of gold nanoparticles on diamond (111) was explored by varying power and methane concentration in plasma. In the second part, the well fabricated AuNPs/ diamond (111) was used as the substrate for further growth of oriented diamonds by MPCVD. Finally, the results of multi-step growth of epitaxial diamond film with embedded AuNPs are presented. The gold film was deposited on ~ 2 mm sized diamond (111) single crystal substrate by electron beam evaporation. The as-deposited Au on diamond was then annealed in vacuum. The higher temperature results in more uniform distribution of AuNPs on diamond substrate. The distribution of AuNPs on diamond is also affected with the thickness of the deposited gold layer and the MPCVD conditions for homoepitaxial diamond film including hydrogen/methane concentration, microwave . The morphology and roughness after the plasma treatment were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results show that the as-deposited diamond on 20nm thickness of gold layer has more uniform distribution in 0.5% methane plasma at microwave power of 800 W. In the diamond growth process, oriented diamond films were deposited on diamond substrate covered with gold by the same process parameters including mixed ratio of CH4 and H2, pressure, power, etc. Comparing with the diamond film in the various time, we can set up the growth model of diamond characterized by AFM and X-ray diffraction (XRD). At the beginning, the growth of diamond islands appears between AuNPs, followed by lateral overgrowth with coalenscence when diamond islands covers the AuNPs. From cross-sectional transmission electron microscopy (TEM) observation, a graphite layer exists at the AuNPs/diamond interface. Secondly, diamond films obtained by step direct growth on diamond seed and by multi-layer growth of gold were characterized by optical microscopy (OM) and Raman spectroscopy. The results show that cracks appear after diamond film deposition for eight hours, while the film processed with multi- layer growth of gold shows no cracks. Raman spectra show the peak in the range of 1326-1332 cm-1, suggesting that diamond films are in tensile stress. XRD and reciprocal space mapping (RSM) were used to evaluate the effect of embedded AuNPs on cracking by determination of the d-spacings of diamond and embedded gold. The results show the out-of-plane and in-plane d-spacings of diamond become larger than the bulk values, whereas gold’s d-spacings become smaller. TEM reveals the distribution of embedded AuNPs and the microstructure of epitaxial lateral growth of diamond with formation of stacking faults and threading dislocations after the coalescence of islands in the step growth. After 4 step growth, the dislocation density can be reduced to 1.41x108 cm-2. It implies the embedded gold particles may restrain the formation of the cracks on diamond.

Low temperature growth of diamond films by microwave plasma chemical vapor deposition using CH 4 +CO 2 gas mixtures

Diamond film growth by pulse-modulated magnetoactive microwave plasma chemical vapour deposition

Research and development have been performed to investigate the effect of total pressure and microwave power on the electrical conductivity of nitrogen (N) atoms’ grain boundaries incorporated ultrananocrystalline diamond (N-UNCD) films grown by microwave plasma chemical vapor deposition (MPCVD). Insertion of N atoms into the UNCD film’s grain boundaries induces N atoms chemical reaction with C-atoms dangling bonds, resulting in release of electrons, which induce electrical conductivity. Four-point probe electrical measurements show that the highest electrically conductive N-UNCD films, produced until now, exhibit electrical resistivity of ~1 Ohm.cm, which is orders of magnitude lower than the ≥106 Ohm.cm for undoped ultrananocrystalline diamond (UNCD) films. X-ray diffraction analysis and Raman spectroscopy revealed that the growth of the N-UNCD films by MPCVD do not produce graphite phase but only crystalline nanodiamond grains. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of nitrogen (N) in the N-UNCD films and the high conductivity (no electrical charging is observed during XPS analysis) shown in electrical measurements.

Novel superhard BC10N synthesized by microwave plasma CVD

Polycrystalline diamond films have been deposited on ceramic alumina substrates by microwave plasma chemical vapor deposition method. Variation of the emission spectra in the microwave plasma with the microwave power and the vapor pressure in the reaction chamber is studied, respectively. Relationships between the hydrogen atomic spectra and the average energy of the electrons in the plasma, as well as the mechanism of diamond film deposition on ceramic alumina are discussed.

Diamond-like carbon (DLC) films have attracted great interest due to their outstanding mechanical, biocompatibility, thermal, optical and electrical properties. The DLC films can be produced by microwave plasma chemical vapor deposition (MPCVD) using Argon, methane and hydrogen mixed gases. The film properties depend strongly on the experimental parameters such as substrate temperatures; microwave power, process pressure and hydrogen concentration (H2/Ar+CH4+H2). In this study, the properties of nanomechanics of DLC films with various experimental parameters are firstly discussed which include hardness and Young’s modulus characterizing by depth-sensing nanoindentation technique. The nanoindentation is an excellent method for measuring nanomechanical properties of both bulk and thin films. The probe was conducted using a Berkovich diamond tip. To find the optimized process parameters, the statistical and mathematical response surface methodology (RSM) is used to model and analyze the effect of substrate temperature (T), microwave power (W), process pressure (P) and hydrogen concentration (H) on the properties of nanomechanics of DLC films. The central composite experimental design (CCD) is used to evaluate the interaction parametric effects of multiple experimental variables on process response (hardness and Young’s modulus). The predictive quadratic model proposed herein considering the analysis of variance (ANOVA) are proved to fit and predict values of the hardness and Young’s modulus close to those readings recorded experimentally. The most significant influential factors for maximizing the hardness and Young’s modulus have been identified from the ANOVA table. The RSM technique is demonstrated to be a powerful tool in exploration of the manufacturing parameters space of complex physical process of DLC films deposition by MPCVD.

Diamond films produced by microwave plasma chemical vapor deposition at low temperature and their characterization

In this work, boron doped diamond (BDD) films were deposited onto a silicon substrate using the in-liquid microwave plasma chemical vapor deposition (IL-MPCVD) method. During the synthesis of BDD films, the effect of solvent, pressure, power and distance between the substrate and the microwave antenna on the growth rate of BDD films was studied. Pressure varied from 20 to 80 kPa at the interval of 20 kPa, power from 500 to 600 W at the interval of 50 W and distance from 1 to 1.5 mm. These different conditions resulted in the formation of both nanocrystalline and microcrystalline BDD films. Synthesized BDD films were characterized by Raman spectroscopy, laser microscopy, and optical emission spectroscopy. The highest growth rate of 410 μm/h is obtained as compared to the previous literature. Good synthesis parameters were used to deposit large area BDD films and the surface area expanded from 7 to 35 mm2. Along with this, the electrochemical properties of BDD films were studied in two different electrolytes. Concerning the growth rate, larger redox potential difference, IL-MPCVD is an effective method than the conventional microwave plasma chemical vapor deposition (MPCVD) method for the fabrication of high growth BDD films. Prime novelty statementIn this research, we synthesized BDD films with a B/C ratio of 1000 ppm by adjusting pressure, microwave power, and the substrate-to-electrode distance to determine the optimal synthesis conditions. This enabled us to determine the optimal synthesis conditions while examining variables like boron concentration and growth rate. By employing these optimized synthesis conditions, we successfully expanded the surface area of the BDD film from 7 to 35 mm2, which represents a fivefold increase. Most importantly, this is the first time reported the highest growth rate of 410 μm/h is achieved using this technique with to obtain highly crystalline BDD films. Additionally, we conducted an investigation into the electrochemical properties of BDD films in various electrolytes.

The internal stress and strain in boron-doped diamond films grown by microwave plasma chemical vapor deposition (MWCVD) and hot filament CVD (HFCVD) were studied as a function of boron concentration. The total stress (thermal+intrinsic) was tensile, and the stress and strain increased with boron concentration. The stress and the strain measured in HFCVD samples were greater than those of MWCVD samples at the same boron concentration. The intrinsic tensile stress, 0.84 GPa, calculated by the grain boundary relaxation model, was in good agreement with the experimental value when the boron concentration in the films was below 0.3 at.%. At boron concentrations above 0.3 at.%, the tensile stress was mainly caused by high defect density, and induced by a node-blocked sliding effect at the grain boundary.

Enhanced nucleation of diamond films assisted by positive dc bias

The objective of this work is to study the performance of the Nd:YAG laser to cut thick free standing CVD diamond films. The high flexibility of this type of laser, given by the possibility to guide the laser beam by means of an optical fibre represents a great advantage in order to automate the cutting process in the production lines. Laser cutting technology is imperative to shape non-conductive CVD diamond parts for electronic, optical and mechanical applications, namely heat sinks, infrared transparent windows and small tips to braze onto machining tool holders. Concerning diamond tool production, the rapid cutting method by laser here proposed provides an advantage to CVD diamond when compared to conventional polycrystalline diamond (PCD) blanks that are cut by the Electro-Discharge Machining (EDM), a time-consuming and very expensive technique due to the electrodes cost.Free-standing diamond films were grown on silicon wafers by microwave plasma chemical vapour deposition (MPCVD) method in a ASTeX PDS 18 unit. The diamond growth parameters were: microwave power 4.35kW; total pressure 110Torr; H2 flow 400s.c.c.m.; CH4 flow 30s.c.c.m; deposition time 70h. The final film thickness was approximately 500μm. The diamond plates were then released by chemical dissolution of the Si substrate in a nitric/hydrofluoric acids mixture. The equipment employed to perform the cutting experiments consisted of a pulsed Nd:YAG laser delivering a maximum average power of 500W at a wavelength of 1064 nm. The laser beam was coupled to an optical fibre of 400μm diameter and 10 m long. The pulsed beam coming out of the fibre was focused onto the surface of the free standing diamond coating by means of a commercial cutting head, having a lens of 80 mm focal length, in which the laser beam was coaxial to the Ar gas jet used as assist gas.In this paper we discuss the results of the work carried out to analyse the influence on cuts quality of laser processing parameters such as: cutting speed 5-20mm/s; pulse width 0.3-1ms; pulse energy 0.8-4.6J; power 80-470W. Scanning electron microscopy was used to look into film cracking events and to appraise the cut width and linearity. Micro-Raman spectroscopy allowed the evaluation of the graphitisation level on the cut surface.The objective of this work is to study the performance of the Nd:YAG laser to cut thick free standing CVD diamond films. The high flexibility of this type of laser, given by the possibility to guide the laser beam by means of an optical fibre represents a great advantage in order to automate the cutting process in the production lines. Laser cutting technology is imperative to shape non-conductive CVD diamond parts for electronic, optical and mechanical applications, namely heat sinks, infrared transparent windows and small tips to braze onto machining tool holders. Concerning diamond tool production, the rapid cutting method by laser here proposed provides an advantage to CVD diamond when compared to conventional polycrystalline diamond (PCD) blanks that are cut by the Electro-Discharge Machining (EDM), a time-consuming and very expensive technique due to the electrodes cost.Free-standing diamond films were grown on silicon wafers by microwave plasma chemical vapour deposition (MPCVD) method in a ASTeX P...