CH4 H2 Plasma Research Articles

Explore the growth mechanism of high-quality diamond under high average power density in the MPCVD reactor

Investigating the mechanism behind the high-efficiency deposition of high-quality diamond has always been a prominent topic in related research. This paper investigates the CH4-H2 plasma characteristics and related chemical reaction kinetics in the average power density range of 18–100 W·cm−3, which is a typical range for large-area diamond film deposition. The number densities of H, CH3 and C2H2 increase linearly with the average power density. C2H2 is the main hydrocarbon in the discharge, and CH3 is the main single-carbon hydrocarbon. The number density and radial uniformity of CH3 and C2H2 increase with the average power density, which is necessary for the high rate and uniform deposition of diamond films. The plasma's optical emission spectra indicate an acceleration in the C2 production rate at high power density. The diamond film deposition experiment demonstrates the efficacy of high average power density in achieving high-quality diamond deposition at a high growth rate.

Optical diagnostics of microwave plasma in process of micro/nanocrystalline diamond deposition on hard alloy tools

Diamond coatings on hard alloy tools produced by chemical vapor deposition (CVD) from methane-hydrogen mixtures greatly enhance the functional properties such as wear resistance and quality of the material processing. By varying the gas composition during the diamond film growth it is possible to cyclically change the film structure between microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) to produce MCD/NCD multilayers that improves the mechanical properties of the film and reduces its stress and roughness. As the diamond growth occurs with participation of radicals generated in the plasma thermo-chemical reactions it is important to control in situ the presence of those species and gas temperature Tg. Here we used optical emission spectroscopy (OES) to monitor atomic hydrogen, CN, CH and C2 dimer radicals in course of deposition of MCD/NCD coatings by microwave plasma CVD in CH4-H2 and CH4-N2-H2 mixtures. The gas temperature has been calculated from analysis of rotational components of structure of C2(Δν = 0) emission line. We found that addition of nitrogen (4%) in CH4-H2 plasma, which is needed to form NCD, significantly, by about 500 K reduces Tg (from Tg = 3910 K to Tg = 3330 K). We developed an algorithm tolerable to small shifts of the measured spectral lines which provided fast calculation of Tg, so that the spectrum record and the automatic processing of fine structure of C2(Δν = 0) line totally take the time of about 5 min.

Influence of Al content on diamond nucleation and growth on Fe-Al alloys in CH4-H2 plasma atmosphere

Fe-Al alloys with different Al contents have been exposed to a microwave plasma activated CH4-H2 gas mixture at 670 °C. An intermediate graphite layer formed on Fe-10Al substrate retarded diamond nucleation and deteriorated the interfacial adhesion, and severe metal dusting and carburization occurred. Diamond nucleation on Fe-20Al was enhanced by inhibited graphitization and cementite formation. Only Fe3AlCx-type precipitates were observed. On Fe-27Al and Fe-40Al alloys, graphitization and substrate carburization were completely prevented, producing enhanced nucleation and interfacial adhesion of diamond. The improved carburization resistance and diamond deposition with increasing Al contents is closely related to the formation of an alumina-rich layer on the alloy surface.

Metal dusting, carburization and diamond deposition on Fe–Cr alloys in CH4–H2 plasma atmospheres

Fe–Cr model alloys (with 20–80wt.% Cr) were exposed to a CH4–H2 mixture in a microwave plasma enhanced chemical vapor deposition (CVD) atmosphere. Severe metal dusting and carburization are observed on the low-Cr alloys, meanwhile, diamond cannot nucleate until a graphite intermediate layer has formed on the substrate, which takes a long incubation time. Increasing Cr concentrations in the Fe–Cr alloys promotes the formation of a Cr carbide buffer layer, which inhibits metal dusting and the formation of graphite interlayer. Consequently, diamond nucleation and growth are greatly enhanced, and continuous diamond films with enhanced adhesion are deposited on the Fe–80Cr alloys.

Influence of growth conditions on microstructure and defects in diamond coatings grown by microwave plasma enhanced CVD

Diamond coatings were grown on SiO2/Si substrate under various process conditions by microwave plasma chemical vapour deposition (MPCVD) using CH4/H2 gas mixture. In this paper, we present a microstructural study to elucidate on the growth mechanism and evolution of defects, viz., strain, dislocations, stacking faults, twins and non-diamond impurities in diamond coatings grown under different process conditions. Transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the diamond coatings. It has been shown that our new approach of prolonged substrate pre-treatment under hydrogen plasma yielded a new growth sequence that the SiO2 layer on the Si substrate was first reduced to yield Si layer of ∼150 nm thickness before diamond was allowed to grow under CH4–H2 plasma, created subsequently. It has also been shown that Si and O as impurity from the substrate hinders the initial diamond growth to yield non-diamond phases. It is being suggested that the crystal defects like twins, stacking faults, dislocations in the diamond grains and dislocations in the intermediate Si layer are generated due to the development of non-uniform stresses during diamond growth at high temperature.

Dual-Frequency Plasma Enhanced Chemical Vapor Deposition of Diamond-Like Carbon Thin Films

Dual-frequency plasma enhanced chemical vapor deposition was used to grow diamond-like carbon thin lms from CH4, H2 gas mixture. The e ects of radio frequency, microwave power, and gas ratio were investigated. Various species have been identi ed in the CH4 H2 plasma using optical emission spectroscopy and their e ects on lm properties have been studied. Increasing the RF power to 400 W, the variation trend of refractive index and CH, C2 intensity ratios change beyond the 300 W, but the growth rate shows the continuous increasing character from 6 to 11.6 nm/min. Increasing the hydrogen content in the system, the intensity ratio of CH, C2, CH and growth rate show decreasing tendency and the refractive index rises from 1.98 to 2.63. Adding MW produced plasma to the system grows the refractive index to 2.88 and growth rate to 10.8 nm/min. The water contact angle rises from 58.95◦ to 73.74◦ as the RF power increases to 300 W but begins to reduce until 400 W. In addition, the contact angle shows a growing tendency by increasing the hydrogen ow to the chamber. In addition, the structures of the lms were investigated by the Raman spectroscopy.

Effects of applied power on hydrogenated amorphous carbon (a-C:H) film deposition by low frequency (60 Hz) plasma-enhanced chemical vapor deposition (PECVD)

Hydrogenated amorphous carbon (a-C:H) films were deposited onto glass substrates using low frequency (60Hz) plasma-enhanced chemical vapor deposition and the effects of the applied power on a-C:H films deposition were investigated. During deposition, the electron temperature and the density of CH4–H2 plasma were 2.4–3.1eV and about 108cm−3, respectively. The main optical emission peak of the carbon species observed in the CH4–H2 plasma is shown to be excited carbon CH* at 431nm. The sp3/sp2 ratio, band gap, hydrogen content, and refractive index of a-C:H films gradually increased up to a power of 25W and then saturated at higher power. This tendency is similar to the variation of plasma parameters with varying applied power, thereby indicating that a strong relationship exists between the properties of the films and the plasma discharge.

Gas temperature measurements in a microwave plasma by optical emission spectroscopy under single-wall carbon nanotube growth conditions

Plasma gas temperatures were measured via in situ optical emission spectroscopy in a microwave CH4–H2 plasma under carbon nanotube (CNT) growth conditions. Gas temperature is an important parameter in controlling and optimizing CNT growth. The temperature has a significant impact on chemical kinetic rates, species concentrations and CNT growth rates on the substrate. H2 rotational temperatures were determined from the Q-branch spectrum of the (0) transition. N2 rotational and vibrational temperatures were measured by fitting rovibrational bands from the N2 emission spectrum of the C 3Πu → B 3Πg transition. The N2 rotational temperature, which is assumed to be approximately equal to the translational gas temperature, increases with an increase in input microwave plasma power and substrate temperature. The measured H2 rotational temperatures were not in agreement with the measured N2 rotational temperatures under the CNT growth conditions in this study. The measured N2 rotational temperatures compared with the H2 rotational temperatures suggest the partial equilibration of upper excited state due to higher, 10 Torr, operating pressure. Methane addition in the hydrogen plasma increases the gas temperature slightly for methane concentrations higher than 10% in the feed gas.

Reactive ion etching of high optical quality GaN∕sapphire photonic crystal slab using CH4–H2 chemistry

Reactive ion etching (RIE) using a CH4–H2 plasma is investigated for the fabrication of a GaN one-dimensional (1D) photonic crystal (PhC) slab. The dominant control parameter for the etch rate and the sidewall profile is the dc bias. The influence of operating pressure, CH4∕H2 ratio, and total gas flow rate on the etching characteristics is also presented. An etch rate as high as 85nm∕min and an overcut angle as low as 5° obtained in this work are among the best values reported for conventional RIE technique. The CH4–H2 process is used to etch 1D PhCs with a lattice parameter ranging from 700to350nm and an air filling factor of 0.30 into a 600-nm-thick GaN∕sapphire slab. Sharp peaks corresponding to the resonant modes of the nanopatterned structures are observed in the experimental reflection spectra for all the lattice periods. Furthermore, the good optical quality of the nanostructures is evidenced by a resonantly enhanced second-harmonic generation experiment around 400nm. A second-harmonic generation enhancement factor as high as 105 is obtained, compared with the unpatterned GaN reference slab. These results demonstrate that the CH4–H2 conventional RIE technique is well adapted to the etching of GaN PhC for the fabrication of next generation photonic devices exploiting nonlinear processes.

Optical properties of bias-induced CH4–H2 plasma for diamond film deposition

Methane (CH4) and hydrogen (H2) reactive gas mixture has been in situ investigated in a hot filament diamond chemical vapor deposition reactor with a negatively variable biasing voltage applied to the hot filament with respect to the substrate using infrared absorption spectroscopy and optical emission spectroscopy. It is found that CH4 converts increasingly to C2H2 upon raising the filament temperature in a pure thermal activation state, no optical emission of species is observed. Upon bias application, both CH4 and C2H2 in infrared (IR) absorption intensity decrease with increasing bias current, even the IR absorption intensity of C2H2 decreases more rapidly than that of CH4. Meanwhile, the clear emission lines indexed to H, CH, and CH+ appear in the optical emission spectrum obtained, showing that a large amount of excited radicals are produced in the gas phase after applying bias. It is believed that the further generation of activated radicals induced by electron impact may be responsible for the increase of the growth rate of diamond films due to bias application.

Photocatalytic Property of Metal Oxide Powders Treated by CH4-H2 Plasma CVD Method.

Photocatalytic Property of Metal Oxide Powders Treated by CH4-H2 Plasma CVD Method.

Estimation of surface kinetic parameters and two-dimensional simulation of InP pattern features during CH4–H2 plasma etching

A two-dimensional simulation of reactive ion etching (RIE) of InP trench profiles is developed. The local equation of etching rate on each string is established considering the Langmuir adsorption concept. The etching rate takes into account the chemical etching on both the covered and uncovered surface fractions by the neutrals and the ion sputtering on both the covered and uncovered fraction of surface elements. Surface kinetic parameters of InP RIE process are estimated by using a minimization method to fit the experimental data of etching rate as a function of percent CH4 in the CH4–H2 plasma mixture. Such parameters are then used to simulate the etch surface profile evolution in time under the RIE process. The effect of ratio of the ion flux to the neutral flux on the anisotropy of the profiles is shown as well as the aspect ratio on the etching rate evolution in time.

Low Temperature Growth of Ultra-Nanocrystalline Diamond on Glass Substrates for Field Emission Applications

ABSTRACTRecent studies of field emission from diamond have focused on the feasibility of growing diamond films on glass substrates, which are the preferred choice for cost-effective, large area flat panel displays. However, diamond growth on glass requires temperatures < 500 °C, which is much lower than the temperature needed for growing conventional microwave plasma chemical vapor deposition (CVD) diamond films. In addition, it is desirable to minimize the deposition time for cost-effective processing. We have grown ultrananocrystalline diamond (UNCD) films using a unique microwave plasma technique that involves CH4-Ar gas mixtures, as opposed to the conventional CH4-H2 plasma CVD method. The growth species in the CH4-Ar CVD method are C2 dimers, resulting in lower activation energies and consequently the ability to grow diamond at lower temperatures than conventional CVD diamond processes. For the work discussed here, the UNCD films were grown with plasma-enhanced chemical vapor deposition (PECVD) at low temperatures on glass substrates coated with Ti thin films. The turn-on field was as low as 3 V/μm for a film grown at 500 °C with a gas chemistry of l%CH4/99%Ar at 100 Torr, and 7 V/μm for a film grown at 350 °C. UV Raman spectroscopy revealed the presence of high quality diamond in the films.

Diamond Thin Films by Microwave Plasma Chemical Vapour Deposition Process

This article reviews in brief the importance of diamond thin films for semiconductor industry. Here we report the design and development of a very high vacuum compatible microwave plasma chemical vapour deposition (MWPCVD) system. The growth of very good quality diamond thin films has been reported from the CH4—H2 plasma. The nucleation of diamond phase has been controlled by using a variety of substrate pretreatment process. The role of various deposition parameters has been investigated in brief. Optical emission spectroscopy (OES) has been used to diagnose the plasma. OES data has been correlated with microstructrue of the films. These films have been characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectrocopy and spectroscopic ellipsometry (SE).

Optical emission spectroscopy during the bias-enhanced nucleation of diamond microcrystals by microwave plasma chemical vapor deposition process

Microwave plasma chemical vapor deposition (MWPCVD) process has been used to grow diamond thin films on silicon substrates from CH4–H2 gas mixture. Bias-enhanced nucleation (BEN) pretreatment has been used to increase the density of diamond nuclei. Various species in the CH4–H2 plasma have been identified using optical emission spectroscopy (OES), and their effect on the film microstructure has been studied. During the pretreatment process the emission intensities of CH, CH+, C2, H, and H2* species have been found to increase significantly for a negative dc bias voltage |VB| > 60 V. The higher concentration of excited species and the associated effects play a significant role in the growth process. A very thin layer of a-C containing predominant sp3 bonded carbon species in the initial stages of the growth is found to be present in these films. The microstructure of the films has been found to be very sensitive to the biasing conditions.

Initial stages in the growth of carbon films produced in an Ar–CH4–H2 microwave discharge: Composition and surface layers morphology

X-ray photoelectron spectroscopy and atomic force microscopy are employed in the characterization of the first stages in the growth of carbon layers on a (001) Si substrate which is not scratched with diamond powder before placing it in an Ar–2%CH4–H2 plasma discharge. Results show that the first layers could be formed in SiC grains where the carbon diamond particles nucleate. The high nucleation density of 1.109–5.109 nuclei. cm−2 and the low aggregates density lead to a smooth surface.

Growth of diamond and nickel carbide crystals in the NiCH system

Simultaneous growth of diamond and nickel carbide on a graphite substrate was observed. Nickel carbide appeared as a nonstoichiometric interstitial solid solution possessing the NaCl-type structure. The nucleation and growth of diamond was conducted by microwave plasma chemical vapor deposition. The CH4-H2 plasma produces intensive mass transport in the separate nickel carbide crystals resulting in coalescence. A hypothesis of the formation of gaseous organometallic molecules is described and the role of atomic hydrogen which alters the NiCH equilibria is discussed.

Effect of dilution gases in methane on the deposition of diamond-like carbon in a microwave discharge II: Effect of hydrogen

The effect of hydrogen as a dilution gas on the deposition of diamond-like carbon by the decomposition of methane in a microwave discharge was studied from surface analysis of the substrate and from plasma diagnostics. When carbon deposited from a CH4-Ar plasma and consisting of large amounts of graphite and small amounts of diamond, was placed in the hydrogen plasma chemical sputtering of carbon to form hydrocarbons and adsorption of hydrogen on the carbon substrate were observed. The reaction occured only on graphite and not on diamond. The effects of hydrogen as a dilution gas on the deposition of diamond-like carbon from CH4-H2 plasma are to cause the formation of CH3 radicals in the plasma, the removal of graphite from the deposit and the adsorption of atomic hydrogen on the deposit as an active participant in the diamond crystallization process.