Stress In Diamond Films Research Articles

A novel method to mitigate residual stress in CVD diamond film on steel substrates with a single intermediate layer

Direct deposition of CVD diamond on steel produces useless diamond film which delaminates on cooling from deposition temperature [1–9]. The majority of current research efforts focus on single and multiple intermediate layers for CVD diamond deposition on steel substrate. There are many excellent diffusional barriers to transition metals migration from bulk to substrate surface to form graphitic sp2 bonds. However, there is no practical solution to the thermal expansion coefficient (TEC) mismatch between diamond and steels. In this work we use a vanadium carbide thermodiffused coating as the intermediate layer between diamond and AISI O1 steel substrate. It acts as a diffusional barrier and mitigates diamond residual stress after cooling from CVD temperature. Increasing vanadium carbide layer thickness creates a transition zone that attenuates diamond residual stress. Up to now, the vanadium carbide is the only single layer barrier able to inhibit graphitic phase formation and mitigate residual stress in diamond films to the level of 0.54 GPa.

Novel Surface Treatment Strategy to Improve the Binding Strength for Diamond Film on Ti Substrate

This work introduced a novel surface treatment strategy to improve the binding strength for diamond film on Ti substrate by etching the Ti substrate with alkali. The presence of diamond, titanium carbide (TiC) phase and the residual stress in diamond films (DFs) was checked by employing Raman spectrum and X-ray diffraction. It was found that the morphology of diamond grain was effected by the surface situation of Ti substrate. And the residual stress was calculated with an empirical equation. The adhesion between the diamond film and Ti substrate (Ti–DFs) was indirectly indicated by elasticity modulus calculated with Nanoindentation. The elasticity modulus was significantly increased to 13.81 GPa for the Ti surface activated by NaOH solution, compared with 1.7 GPa for the diamond film fabricated without surface activation process. As a result, the binding force between Ti–DFs was significantly increased because of the presence of the porous structure on the surface. The internal cross-linked channel structure on Ti surface can play a significant part to improve the binding force between Ti–DFs.

Sandblasting induced stress release and enhanced adhesion strength of diamond films deposited on austenite stainless steel

We firstly used sandblasting to treat austenite stainless steel and then deposited a Cr/CrN interlayer by close field unbalanced magnetron sputtering on it. After that, diamond films were prepared on the interlayer. It is found that the sandblasting process induces phase transition from austenite to martensite in the surface region of the stainless steel, which decreases thermal stress in diamond films due to lower thermal expansion coefficient of martensite phase compared with that of austenite phase. The sandblasting also makes stainless steel’s surface rough and the Cr/CrN interlayer film inherits the rough surface. This decreases the carburization extent of the interlayer, increases nucleation density and modifies the stress distribution. Due to lower residual stress and small extent of the interlayer’s carburization, the diamond film on sandblast treated austenite stainless steel shows enhanced adhesion strength.

Fabrication and Application of Si-Doped Diamond Coated Welding Dies

Si-doped diamond films are deposited on cobalt cemented tungsten carbide (WC-Co) welding dies using hot filament chemical vapor deposition (HFCVD) method, where tetraethoxysilane (C8H20O4Si) is introduced in the reactive chamber as silicon source by bubbling method. Filed emission scanning electron microscope (FESEM) and Raman spectroscopy are used to characterize the as-deposited diamond films. The results show that silicon doping can reduce the diamond crystal size and residual stress of diamond films, and also increase the FWHM of first order diamond Raman line. The polishing time of diamond coated welding dies also can be shortened by silicon doping. Si-doped diamond coated welding dies possesses comparable practical application performance with conventional diamond coated welding dies. Compared with the nylon and WC-Co welding dies, the working lifetime of diamond coated welding dies increases 200 and 10 times, respectively.

Thermo-Mechanical Coupled and Fracture in Diamond Film under High Strain Rate

According to the special case of high strain rate for diamond film produced by DC plasma jet method, a transient thermo-mechanical coupled model for the cooling process of diamond film and Mo substrate was developed. The direct coupled finite element method was used to simulate the transient thermal stresses in diamond film during the cooling period after the film deposition. The residual thermal stresses of diamond film were calculated and compared respectively under two conditions of real uneven temperature fields and unreal even temperature fields. Based on the simulated results of stresses, the moment and cause of diamond film cracking were analyzed. The conclusions are as the follows: (1) the thermal stresses in diamond film increase with the increase of cooling time, but the maximum first principal tensile stress may reach the fracture strength of common diamond film before the film cools to room temperature; (2) the excessive tensile stress at the film edge causes the film cracking; (3) in order to reduce the thermal (residual ) stresses and increase the finished product ratio of diamond film, it is essential to further improve the temperature uniformity.

Effect of Diamond Film's Thickness on Thermal Residual Stress after Considering the Substrate's Plasticity

Thermal residual stress in diamond film deposited onto Mo substrate was simulated and analyzed comprehensively by using the finite element method on condition that the substrate’s plasticity was considered. The contour plots of the stresses were described. Moreover, the effect of the film’s thickness on thermal residual stress was investigated. The results show that every stress component in the film has the remarkable stress concentration at the intersection of the interface and the side of the film. The location of maximum tensile principal stress in the film is at the upward face or side face of the film or the interface. The magnitude of maximum tensile principal stress increases when the film becomes thicker. These conclusions are useful to the proper choice of the film’s thickness and the effective control of the stresses during preparation of diamond film.

Numerical Analysis of Thermal Residual Stress in Diamond Film Deposited on Molybdenum Substrate

In order to solve the problem of diamond film crack when deposited on molybdenum substrate to improve the preparation quality of diamond film and the rate of finished products , the distributions of thermal residual stress components in diamond film and at interface between the film and molybdenum substrate were simulated by finite element method in the case of whether to consider the plastic deformation of molybdenum substrate or not, moreover, the influence of thermal residual stress upon the failure of film was analyzed. Results show that thermal residual stress is more coincidental with experimental data when the plastic deformation of molybdenum substrate is considered. There are large tensile radial stress and tensile axial stress in the vicinity of upper surface of the film, which is the primary cause for the film to crack.

Anisotropic biaxial stresses in diamond films by polarized Raman spectroscopy of cubic polycrystals

The anisotropic stresses in diamond films induced by permanent deformations of titanium tensile substrates are studied by polarized Raman spectroscopy. The influence of the in-plane orientation of each grain relative to the stress directions is shown experimentally and theoretically. Considering the dynamical equations under small strains, the solutions of the secular equation permit the determination of the triply degenerate phonon frequency of polycrystalline diamond, which splits into three singlets for each crystallite. The calculation is carried out here for six growth directions, along [001], [110], [111], [112], [113], and [331], and for all in-plane orientations normal to these textures. In the case of anisotropic stresses, it is shown how the relative values of the two stresses induce different shapes in the Raman spectra. For an isotropic polycrystalline diamond film, this Raman spectroscopy of strained cubic polycrystals approximates the complete solution for all crystallite orientations relative to the anisotropic biaxial stresses. It allows calculating theoretical Raman spectra that fairly well compare to the experimental ones. The determination of the anisotropic stresses is obtained with a better accuracy when the influence of all orientations is taken into account than with the previous average procedures used for isotropic cubic polycrystalline materials. Partially or completely textured films along one of the growth directions can also be studied. If the stresses along the two directions are identical, the particular case of isotropic biaxial stresses is also studied with a better accuracy.

Investigation of biaxial stresses in diamond films deposited on a silicon substrate by the HF CVD method

The results of investigations into on composition and biaxial stress in polycrystalline diamond films deposited on silicon substrates are presented. The diamond films’ characteristics were carried out using Raman spectroscopy and Electron back-scattered diffraction. The results indicate that, apart from the dominating crystalline diamond phase inside the grains, an amount of disordered phase exists among the grains. No evidence of such diamond polymorphs as lonsdalite and graphite has been detected in the investigated films.

Analysis of residual stresses in diamond coatings deposited on cemented tungsten carbide substrates

Residual stresses in diamond films grown on WC–Co substrates have been investigated by Raman spectroscopy, x-ray diffraction (XRD), and curvature methods. Microcrystalline diamond films were deposited at 650–700 °C in a conventional hydrogen–methane environment by the microwave plasma-enhanced chemical vapor deposition technique. The film thickness, measured from cross-sectional micrographs taken by scanning electron microscopy, changed from 1.5 to 16.5 μm as the growth time increased from 1 to 12 h. The type and the magnitude of the total residual stress obtained from curvature and XRD measurements agreed very well in all of the samples and changed from tensile to compressive as film thickness increased. However, Raman spectroscopy results showed that all films exhibited compressive stress due to the domain size effect. Different methane fractions, varying from 1% to 3%, have been utilized for diamond growth, and the total residual stress increased as more methane was included.

Investigation of Technology and Analysis of Residual Stress in Large Area Diamond Films

We investigated the residual stress in diamond films grown on molybdenum substrates as a function of different places in the same large sample. The diamond film wafers of Ф60 mm diameter were deposited at 900°C by high power DC arc plasma jet CVD method using a gas mixture of methane (1.8% vol.) and hydrogen ( 90% vol.). The grain sizes, obtained from the top view scanning electron microscopy (SEM) images, were found to become larger from center to the border in the same sample, and the x-ray diffraction indicated that the intensity of characteristic spectroscopy in same diamond film was changed from (220) to (111) with the increases of (311). Profile curves presented the appreciable difference of surface texture from center to edge. The film had 4.3GPa of residual compressive stress. Examination of the Raman spectra of the film revealed that residual stress in the film of up to approximately 0.70GPa, and the Raman spectroscopy shifts from 1332.99cm-1 at the center to 1331.17cm-1 at the border, which means the stress mode changed from compressive to tensile. These demonstrated a significant inhomogeneity of stress in diamond films. The differences have been attributed partly to high temperature inhomogeneity arc jet during growth and morphological aspects of the film growth. The relationships between stress and methane concentration, and substrate temperature are discussed in detail.

Grain orientation dependence on distance to surface of CVD diamond film

Free standing chemical vapour deposition (CVD) diamond films were prepared under the gas recycling mode, where the substrate temperature ranged from 820 to 1050°C. Macro- and microtextures of the films were investigated based on the orientation distribution function (ODF) and electron backscatter diffraction (EBSD) analysis. The texture consisted of 〈001〉, 〈112〉, 〈111〉, 〈221〉 and 〈110〉 fibre components. Very high twinning frequency was observed because of the reduced purity of the deposition gas. The multi-twins appearing in series as well as in paratactic form reduced the grain size and randomised the orientation distribution. It is believed that the residual strain and stress in diamond films should relate to the fibre textures in certain extent because of the anisotropic elastic characteristics of diamond crystals.

Aspects of scaling CVD diamond reactors

Among the several techniques available for the synthesis of diamond films the hot filament CVD approach offers some unique advantages in terms of scalability for the deposition of diamond over large area substrates. In this paper some key data that supports the contention that the hot filament CVD process can be readily scaled to deposit high quality diamond films on 300 mm silicon wafers will be presented. The uniformity of wafer temperature has been characterized utilizing an instrumented 300 mm wafer with 12 individual thermocouples attached to the wafer. Temperature variations of < 20 °C across the wafer at a wafer temperature of 895 °C have been achieved. The impact of this is very uniform film quality which has been characterized by Raman spectroscopy. Control over the intrinsic stress in diamond films has been achieved to enable achieving either compressive or tensile stresses in the diamond. Modulating the process variables enables achievement of diamond coated wafers that meet the flatness requirements for the fabrication of advanced semiconductor products utilizing these wafers. This tool and process were developed to deposit thick diamond films, up to ∼40 μm, on 200 and 300 mm silicon wafers.

Residual Stress Analysis of Microwave Plasma CVD Diamond Films

The residual stress and crystallographic texture of diamond films were investigated in the present work. The diamond films were synthesized on (100) silicon wafer by Microwave Plasma Chemical Vapor deposition (MPCVD). Then the residual stresses of the films were measured by X-ray diffractometer equipped with the two-dimensional detector. The residual stresses can be classified into two categories, i.e., the intrinsic stresses and the thermal stresses. It was shown that the thermal stresses were compressive in the temperature range studied and the intrinsic stresses were tensile. The crystallographic textures of the films were measured by X-ray diffractometer with the method of pole figure and orientation distribution function (ODF). The experimental results suggest that the crystallographic textures of the films depend upon the deposition temperature and methane flow rates, and the components and intensity of crystallographic textures have effect on the residual stresses in diamond films to a certain extent.

Structural, optical and electrical properties of nanodiamond films deposited by HFCVD on borosilicate glass, fused silica and silicon at low temperature

The addition of a small amount of oxygen to the CH 4 and H 2 feed gas supports the diamond growth during hot filament assisted chemical vapor deposition (HFCVD) even at a substrate temperature below 500 °C. Here we present AFM, SEM, SIMS, X-ray diffraction, Raman scattering, optical transmittance spectra, PDS and temperature resolved resistivity measurements of thin B-doped CVD diamond layers deposited on silicon, fused silica and borosilicate glass at low substrate temperatures. The Raman peak 1332 cm -1 for diamond layers on silicon shifts towards lower (higher) values for layers deposited on fused silica (borosilicate glass) indicating a significant tensile (compressive) stress in diamond films deposited on amorphous substrates. Diamond films grown at low temperature are very smooth (the surface roughness below 10 nm) and they are optically transparent for photon energies up to 6 eV. However, they are highly resistive despite a relatively high B concentration in plasma during growth.

Analysis of residual stress in diamond films by x-ray diffraction and micro-Raman spectroscopy

We investigate the residual stress in diamond films grown on (001) silicon substrates as a function of film thickness. The diamond films were deposited at 1070 K by the conventional hot filament technique using a gas mixture of methane (1.0% vol) and hydrogen (99.0% vol). The film thickness, obtained from cross section scanning electron micrographs, varied from 3.0 to 42 μm as the growth time increased from 1 to 10 h. These images evidenced that the columnar growth is already established for films thicker than 10 μm. Top view micrographs revealed predominantly faceted pyramidal grains for the films at all growth stages. The grain size, obtained from these images, was found to vary linearly with film thickness. Using a high resolution x-ray diffractometer, the residual stress was determined by measuring, for each sample, the (331) diamond Bragg diffraction peak for Ψ values ranging from −60° to +60°, and applying the sin2 ψ method. For the micro-Raman spectroscopy, we used the summation method, which consists in recording and adding a large number of spectra in different places of a selected area of the sample. All Raman spectra were fitted with Lorentzian lines to separate the contribution of the pure diamond and the other nondiamond (graphite) phases. This spectral analysis performed in each sample allowed the determination of the residual stress, from the diamond Raman peak shifts, and also the diamond purity, which increases from 70% to 90% as the thickness goes from 3 to 42 μm. The type and magnitude of the residual stress obtained from x-ray and micro-Raman measurements agreed well for films thicker than 10 μm. For films thinner than this value, an opposite behavior between both results was observed. We attributed this discrepancy to the domain size characteristic of each technique.

Intrinsic stress in chemical vapor deposited diamond films: An analytical model for the plastic deformation of the Si substrate

The intrinsic stress in diamond film deposited on a Si substrate is difficult to measure because high-temperature deposition induces plastic deformation in the Si and so renders useless an elastic solution. In this study, an analytical model is proposed to estimate intrinsic stress using a substrate-curvature technique and considering the plastic deformation of substrate. The stress distribution of the as-deposited film is affected not only by the intrinsic stress of the film but also by the bending and plastic deformation of the substrate. In this model, the distribution is formulated, based on elastic/plastic plate-bending theory, in terms of substrate curvatures, intrinsic stress in the film, and yield stress of the substrate. The intrinsic stress of the film together with the yield stress of the substrate can be obtained from experimentally measured substrate curvatures by solving two equilibrium equations and a moment-relaxation equation describing the film removal. Diamond films were deposited by microwave plasma chemical vapor deposition at varying film thicknesses and deposition temperatures. For the application of the model, the curvature of the film-removed substrate was measured as well as that of as-deposited substrate. The results show that overestimated intrinsic stress can be corrected successfully through this new model. The validity of the results was confirmed by stress measurement using a Raman-peak-shift method. In addition, the generation mechanism of intrinsic stress is analyzed as reflecting a competition between a grain-size effect and nondiamond carbon effect.

Residual stresses in chemical vapour deposited diamond films

Abstract In this paper we report the determination of residual stresses in diamond films grown on Si(100) using a plate bending theory and a bi-metal theory combined with micro-Raman spectroscopy. Raman spectra show that with an increase in the film thickness, the characteristic diamond line shifts from higher wave numbers (>1332 cm −1 ) to lower ( −1 ), indicating a change of compressive to tensile bi-axial stress with increase in the film thickness. A plate bending theory and a bi-metal theory are used to determine the distribution of the stress induced by the thermal mismatch. The modelled results show that the bi-axial stress decreases linearly along the film growth direction and the stress at the film/substrate interface decreases when the film becomes thicker. The difference from the Raman results is attributed to intrinsic stress.

Intrinsic stress evolution in diamond films prepared in a CH4H2NH3 hot filament chemical vapor deposition system

Abstract The intrinsic stress in diamond films prepared in a CH 4 H 2 NH 3 hot filament chemical vapor deposition system has been investigated by the substrate curvature technique as a function of film thickness (2.2–50 μm) and ammonia concentration (0–1.4%). Our results indicated that the film stress changed from compressive to tensile with the increase of film thickness and diamond quality at a constant ammonia concentration of 0.5%. The existence of a non-diamond phase was found to be beneficial to the relaxation of intrinsic tensile stress in the films. The intrinsic stress in diamond films was tensile at an ammonia concentration from 0 to 1.4%, while the maximum tensile stress existed at 0.75% NH 3 . The possible origin of intrinsic tensile stress was discussed.

Evaluation of residual stresses in chemical-vapor-deposited diamond films

In this article we report the determination of residual stresses in diamond films grown on Si (100) by using a plate bending theory and a bimetal theory combined with micro-Raman spectroscopy. Raman spectra show that with increase in the film thickness the characteristic diamond line shifts from higher wave numbers (&amp;gt;1332 cm−1) to lower (&amp;lt;1332 cm−1), indicating a change in the nature of residual stress with the film growth. A plate bending theory and a bimetal theory are used to determine the distribution of residual stress induced by thermal mismatch. The modeled results show that the thermal stress decreases linearly along the film growth direction and the stress at the film/substrate interface decreases once the film becomes thicker. The difference from the Raman results is attributed to intrinsic stress, originating from lattice mismatch between the diamond and Si at the growth temperature and from a variation in microstructure of the film with its growth evolution.