Hot Filament CVD System Research Articles

Structural analyses of carbon films deposited at different total mass rates in a hot-filament CVD system

XRR and XRIR analyses of the deposited carbon films showing different peaks related to the diamond and graphite state atoms.

Micro and Nano-Crystalline Diamond Coatings of Co-cemented Tungsten Carbide Tools with Their Characterization

In this study, a bias-enhanced hot filament CVD system with methane and hydrogen as reactant gasses was used to deposit microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films on Co-cemented tungsten carbide substrates. They were then characterized using FE-SEM, Optical microscopy, XRD, and Raman Spectroscopy. Nanocrystalline diamond coating displays wide carbon peaks near 1350 cm−1 and 1580 cm−1 in Raman Spectroscopy, which correspond to D band and G band of carbon, and a sharp band increase near 1140 cm−1 because of the presence of trans-polyacetylene, confirming the sample as a nanocrystalline diamond. Similarly, the microcrystalline diamond phase was observed at 1350 cm−1 as broadened carbon peaks. The average grain size of the homogenous diamond film was roughly less than 90 nm, several tens of nanometres. The average indentation depths were 45 nm and 63 nm of MCD and NCD coatings and their average hardness values were found 80GPa and 50GPa, respectively. The morphology of the samples was observed using AFM, the average root mean square roughness of the MCD sample in the scanned area was found to be 354.11 nm and of the NCD sample was found to be 142.71 nm this indicates that the nanocrystalline diamond-coated WC was much smoother and had a smaller grain size than microcrystalline diamond coated ones. The values of the coefficient of friction vary from 0.38 to 0.42 for MCD coated sample. In contrast, for the NCD samples, the variations in the coefficient of friction were 0.30–0.36. A low coefficient of friction was observed in NCD as compared to MCD due to the presence of the graphite carbon phase.

Study on the Deposition and Characterization of Nanocrystalline Diamond Composite Films

Nanocrystalline diamond composite films were fabricated on the WC-Co substrates using a bias-enhanced hot filament CVD system. Methanol solution pretreatment method for removing the Co in surface of WC-Co substrates was put forward. The composite structure was achieved by regulating the concentration of Ar in a mixture of acetone and a hydrogen gases in different stages. The surface morphologies, nucleation density, diamond films and composition of the nanocrystalline diamond composite films were observed with different techniques. The results showed that the introduction of Ar increased the second nucleation of diamond grains which made the diamond grains finer. Nanocrystallie diamond film can be successfully grown on the microcrystalline diamond films. The two-layer structure has the advantages of good adhesive strength and low surface roughness. Because of nano effects, the hardness of composite films decreases. This is prone to be polished and reduces the work load significantly. It is of great importance for the wide application of diamond films in the precision machining fields.

Diamond films grown without seeding treatment and bias by hot-filament CVD system

Diamond film growth without seeding treatment has been the subject of numerous studies. In the present study, diamond films with/without seeding treatment were grown on silicon using hot-filament chemical vapour deposition. An inexpensive and simple approach, namely, “dry ultrasonic treatment”, was introduced in which full coverage of diamond film was achieved on unseeded substrate. For comparison, one substrate was seeded with 5μm diamond particles, prior to deposition. The resulting diamond films were examined through standard characterization tools and distinct features were observed in each film. Here we present the results of uniform and high purity diamond film, free from nano-sized grains, which is grown without seeding treatment and is expected to be potential candidate for electro-optical applications, particularly as heat sinks.

Fabrication and Cutting Performance of Ultrafine Grain Composite Diamond Coated Drills

Ultrafine grain composite diamond films are deposited on the WC-Co-based drills using a bias-enhanced hot filament CVD system. During the deposition, the spiral hot filaments and novel two-step pretreatment method for complicated shape tools are adopted. The composite structure is achieved by regulating the concentration of Ar in a mixture of acetone and a hydrogen gases at different stages. The surface morphologies and composition of the first fabricated microcrystalline diamond film and the ultrafine grain diamond film grown later are observed with different techniques. The composite films have the advantages of good adhesive strength and low surface roughness. The cutting performance of the composite diamond-coated drills is investigated by drilling SiC particles reinforced aluminum matrix composites. The drilling life is improved greatly compared with those of uncoated drills and microcrystalline diamond coated drills.

Diamond overgrown InAlN/GaN HEMT

In this work the technology and characterization of nanocrystalline diamond (NCD) films directly grown on InAlN/GaN HEMTs is presented. Optimization of GaN based HEMT process steps including metallization stacks is discussed. A fully processed InAlN/GaN HEMT structure with 7 nm barrier has been overgrown in a temperature range of 750 °C to 800 °C with a 500 nm thick nanocrystalline diamond film in a Hot Filament CVD system. First results of semi-enhancement mode of DC and RF HEMT operation are reported. The grown NCD films were characterized by SEM, TEM, and Raman spectroscopy. Although no direct thermal conductivity measurements are conducted yet; the performed experiments shows the compatibility of growing high quality NCD films, several microns thick, on InAlN/GaN HEMTs as a potential material for heat extraction purposes.

Thickness controlled and smooth polycrystalline CVD diamond film deposition on SiO 2 with electrostatic self assembly seeding process

Sub micrometer thick continuous CVD diamond film was synthesized on thermally grown SiO 2 film employing the electrostatic self assembly seeding with nano-meter sized ultra dispersed diamond particles. Hot filament CVD system was used to deposit diamond film. Formation of mono-dispersed and mono-layered nano diamond seeding layer by well-known Electrostatic Self-Assembly method was effective to increase density and homogeneity of seeding particles. Because of high density of uniformed seeding particles, the nm controlled continuous CVD films with the surface roughness of less than 13 nm on silicon oxide without any mechanical damage were obtained. Linear growth rate with short incubation time was also observed. Depending on the film thickness, coloring effect was observed ranging from blue to yellow and orange. There was no visible fringe on the coated surface which affirms the good thickness uniformity.

Adhesion of nanodiamond seeded CVD diamond on ceramic substrate

Conventional structural ceramic substrates were coated with 1 μm thick polycrystalline CVD diamond layer by using the hot filament CVD system and subsequently tested. The substrates chosen were silicate, alumina, silicon nitride, and silicon carbide ceramics. To achieve a high nucleation density and to improve the adhesion between the diamond and the ceramic substrate, the newly developed Electrostatic Self-Assembly of Nano Diamond (ESAND) seeding method was used. This seeding method initiates the growth of crystalline diamond. For this seeding procedure, each negatively charged substrate surface was covered with a cationic polymer monolayer. Next, anionic polymer coated cationic nanodiamond particles were attached to the substrate by the electrostatic self-assembly process. The degree of adhesion between the diamond film and each substrate was investigated by micro-scratch testing. These tests involved the use of a Rockwell C indenter (r = 0.2 mm), which scratched the samples at a speed of 10 mm/min under a progressive normal load (from 0 to 21N). The morphology of the poly-crystalline diamond films on the various substrates was analyzed using Raman spectroscopy.

Deposition and characterization of nanocrystalline diamond films on Co-cemented tungsten carbide inserts

Nanocrystalline diamond films were deposited on Co-cemented tungsten carbides using bias-enhanced hot filament CVD system with a mixture of acetone, H 2 and Ar as the reactant gas. The effect of Ar concentration on the grain size of diamond films and diamond orientation was investigated. Nanocrystalline diamond films were characterized with field emission scan electron microscopy (FE-SEM), Atomic force microscopy (AFM), Raman spectroscopy and X-ray diffraction spectroscopy (XRD). Rockwell C indentation tests were conducted to evaluate the adhesion between diamond films and the substrates. The results demonstrated that when the Ar concentration was 90%, the diamond films exhibited rounded fine grains with an average grain size of approximately 60–80 nm. The Raman spectra showed broadened carbon peaks at 1350 cm − 1 and 1580 cm − 1 assigned to D and G bands and an intense broad Raman band near 1140 cm − 1 attributed to trans-polyacetylene, which confirmed the presence of the nanocrystalline diamond phase. The full width at half maximum of the <111> diamond peak (0.8°) was far broader than that of conventional diamond film (0.28°–0.3°). The Ra and RMS surface roughness of the nanocrystalline diamond film were measured to be approximately 202 nm and 280 nm with 4 mm scanning length, respectively. The Ar concentration in the reactant gases played an important role in the control of grain size and surface roughness of the diamond films. Nanocrystalline diamond-coated cemented tungsten carbides with very smooth surface have excellent characteristics, which made them a promising material for the development of high performance cutting tools and wear resistance components.

Growth of free-standing diamond films of hemispheric shells

Free-standing diamond films of hemispheric shells were fabricated in a hot filament CVD system by using positive substrate bias. The graphite mold was sputtered with a stainless steel layer of 0.5 um on the surface. During the diamond growth, a thin carbon soot layer with loose structure was first formed on the iron surface and then the growth of a thick diamond film followed. The diamond film could be easily delaminated from the graphite mold due to the weak bonding between the iron-containing carbon soot layer and the graphite substrate. Without the positive substrate bias, the varied distance between the flat hot filaments and the hemispherical substrate in the hot filament CVD system resulted in low nucleation density and non-uniform diamond film. The electron bombardments induced by the positive substrate bias were shown to enhance the diamond nucleation density on the soot-covered surface and thus improved the uniformity of diamond film thickness over the non-flat graphite mold.

Analysis of the coagulation of human blood cells on diamond surfaces by atomic forcemicroscopy

Atomic force microscopy (AFM) was used to study the morphology and coagulation ofhuman blood cells in contact with solid surfaces. Blood was extracted from the veins ofhealthy adult donors and the samples were used immediately after extraction,deposited either on borosilicate glass or diamond substrates. Some blood samples wereanti-coagulated by adding heparin for single cell AFM imaging. No chemicals were used forattaching or immobilizing the cells. The diamond substrates were produced by chemicalvapour deposition (CVD diamond) using a hot-filament CVD system fed with ethanolhighly diluted in hydrogen. AFM imaging of isolated cells (anti-coagulated byheparin) was only possible on the glass substrates due to the lack of adherenceof the cells to the diamond surface. The coagulation results suggest that bloodclotting on diamond produces a less rough surface than blood clotting on glass.

Nanocrystalline diamond films for mechanical applications

Nanocrystalline diamond films have been grown in a hot filament CVD (HFCVD) system allowing BEN, textured growth and HOD growth of diamond on 4 silicon (100). The growth process of nanocrystalline diamond discussed here consists of a BEN process for diamond nucleation on silicon, with a density of more than 10 10 cm -2 across the entire wafer surface. The subsequent growth of the nanocrystalline diamond films is achieved by addition of nitrogen into the gas phase with a relative concentration to carbon of 1:1. At substrate temperatures between 680 °C and 740 °C, closed diamond films are grown with thicknesses between 1 pm and 20 pm. At low nitrogen concentrations the nanocrystalline diamond films exhibit still a columnar structure with a lateral grain size below 200 nm whereas the vertical grain size can reach several microns. Higher nitrogen concentrations lead to a nanocrystalline diamond growth mode with no columnar structure and a grain size is no longer detectable by SEM. The advantages of diamond in MEMS technology rely on its outstanding mechanical and thermal properties. Additionally, the stress distribution inside the diamond films due to thermal expansion as well as the polycrystalline nature of the film has to be taken into account. Applying different test structures we could measure fracture strength of more than 4.0 GPa and elasticity moduli of up to 1020 GPa for these nanocrystalline films. The intrinsic vertical and horizontal stress remains in most cases below the detection limit of 5 MPa, so that freestanding structures with a length of several millimeters can be fabricated without noticeable bending.

Chemical vapour deposition of diamond films onto tungsten carbide dental burs

Considerable literature is now available on the deposition of CVD diamond onto flat substrates the most common being silicon. However, very little work has been reported on the deposition of diamond onto complex three-dimensional substrates such as dental burs, micro drills and biomedical implants. Diamond is hard, wear resistant, biocompatible and corrosion resistant and therefore is an attractive candidate for uses in dental tools and for medical devices. This study focuses on the deposition of diamond, using a hot filament CVD system, on cobalt-cemented tungsten carbide (WC-Co) rotary cutting dental burs. Conventional dental burs are generally made of sintered polycrystalline diamond (PCD). These have a number of problems associated with heterogeneity of the crystallite, decreased cutting efficiency and a short life. A preferential (1 1 1) faceted diamond has been obtained after 12 h deposition at a growth rate of 1.2 μm/h. Diamond coated WC-Co dental burs and conventional sintered burs are used in turning, milling and drilling operations for machining materials made from metal alloys and borosilicate glass. After machining with excessive cutting performance, calculations can be made on flank and crater wear areas. Diamond coated WC-Co dental bur offer significantly lower erosion and higher wear resistance compared to uncoated WC-Co tools and sintered burs.

Bias enhanced nucleation of diamond on silicon (100) in a HFCVD system

A setup for bias enhanced nucleation inside a hot filament CVD system is described. It consists of a combination of two separate voltages for independent generation of ions in the gas phase as well as the acceleration of the ions toward the substrate surface. Using the bias current as a monitor for the dynamics of diamond nucleation, the pretreatment can be terminated at a definite condition and the diamond growth process can be continued under normal deposition conditions. With suitable deposition parameters we are able to obtain diamond nucleation on an entire 4″ Si (100) substrate with a density of more than 10 9 cm −2 as confirmed by secondary electron microscopy. Furthermore, the area of oriented diamond nucleation on a 4″ Si wafer was investigated. Terminating the pretreatment at the threshold of the bias current rise leads to oriented nucleation of diamond. With the present homogeneity of the filament-substrate distance we are able to extend the area of oriented diamonds up to 50 cm 2.

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.

A simple method to grow textured (1 1 1) diamond thin films in a hot-filament CVD system

A simple and new method for synthesizing (1 1 1)-textured diamond films in a hot-filament CVD reactor has been developed by adopting a lower-than-normal filament temperature pretreatment. The (1 1 1) facets are always dominant in the resulting diamond films using a low filament temperature range of 1300–1600 °C. This growth habit is insensitive to the change in deposition parameters, such as substrate temperature, methane concentration, and even addition of a small amount of nitrogen. High-quality and high-textured (1 1 1) diamond films can be easily achieved by a subsequent growth at a normal filament temperature of 2000 °C.

Lower filament temperature limit of diamond growth in a hot-filament CVD system

The effect of decreasing filament temperature on growth of diamond films is reported. Well-faceted diamond crystals can be synthesized at a low filament temperature in the range 1500–1700 °C by low-pressure hot-filament chemical vapor deposition with use of a CH 4–H 2 gas mixture. At a lower filament temperature of 1300 °C, although the morphology of the grains is ball-like in the films deposited, their structure still displays diamond characteristics when assessed by X-ray diffraction and Raman spectroscopy. Under low filament temperature, hot filaments can be used repeatedly many times, have a very long operating life and hold their shape well, which is of special interest for uniform diamond deposition over a large area. The low growth rate and relatively low quality of diamond films due to the low filament temperature can be enhanced to a certain extent by introducing an inert gas.

High nitrogen amounts incorporated diamond films deposited by the addition of nitrogen in a hot-filament CVD system

Abstract Nitrogen-doped diamond films have been synthesized by hot-filament chemical vapor deposition using a CH 4 /N 2 /H 2 gas mixture. The influence of the addition of a large amount of nitrogen in the gas phase on the nucleation and the growth of diamond films and on the binding structure and the content of the nitrogen species in the deposited thin films has been investigated. The deposited films were characterized by scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The results have shown that the crystal size decreased and the nucleation density increased with increasing nitrogen concentration in the mixture gas. With the addition of a large amount of nitrogen, the crystal structure of the grown films transformed from micrographite to amorphous, and then to microcrystalline diamond with an increase in methane concentration in the range of 1–4 vol.%. From the X-ray photoelectron spectroscopy analysis, nitrogen was chemically bonded into diamond films to a maximum content of about 3.3 at.%.

High quality textured growth of oriented diamond thin films on Si (100) in a hot filament-CVD system

Abstract High quality textured and oriented diamond (100) films were grown in a two step process on Si (100). Bias-enhanced nucleation and textured growth by microwave CVD was followed by hot filament deposition without the addition of nitrogen to yield a smooth (100) oriented surface with defect free (as judged by SEM) areas of up to 200×200 μm2 and no detectable (111) facets. Low energy electron diffraction confirmed the high degree of lateral ordering which is much improved compared with oriented textured diamond grown by conventional methods on Si (100). Raman measurements confirm the excellent quality of these films with no detectable graphitic or amorphous carbon phase and a vanishing background due to nitrogen related photoluminescence.

Pressure effect on diamond nucleation in a hot-filament CVD system

Using extraordinarily low pressure (0.1-1 Torr) we obtained high-density nucleation of diamond on mirror-polished silicon in a hot-filament chemical vapor deposition (HF-CVD) system. A diamond nuclei density as high as 10(10)-10(11) cm(-2) was achieved, which was comparable to the largest nuclei density obtained in a microwave-plasma chemical vapor deposition system. The low-pressure nucleation technique and the pressure effect on diamond nucleation were discussed in detail based on molecular dynamics. The enhanced nucleation at low pressure was attributed to an increased mean free path, which gave rise to an increased concentration of nucleating species at the substrate and other beneficial nucleating factors. The present work suggests that very low pressure may be an effective approach to nucleate and grow diamond films on untreated substrates via HF-CVD.