Residual Stress In Film Research Articles

Residual stress tuned magnetic properties of thick CoMnP/Cu multilayers

Electrodeposited hard magnetic thick films have vast applications in the microelectromechanical systems (MEMS). Yet the very large residual stresses (σr) built-up in monolayered thick magnetic films leads to cracks, dimensional changes and deteriorated magnetic properties. Here, we explored quantitatively magnetic properties of CoMnP/Cu multilayers tuned by σr, which in turn are varied by the inserted soft Cu interlayer and thickness of single CoMnP magnetic layers. The configuration of the multilayers is an alternating CoMnP/Cu on Cu-substrate. The thickness of Cu interlayer was 1.4 μm. We kept a sum of all magnetic layers in the multilayers at ∼20 μm to benchmark with a 19.4 μm monolayered CoMnP. The magnetic layers are 94 wt.% Co and possess highly textured (002) hexagonal close packed microstructures. We characterized the apparent crystallite stresses through sin2ψ method by X-ray diffractometer (XRD) and residual film stress by curvature method. The insertion of Cu interlayers effectively reduces σr by 23% through stacking with six single-layered CoMnP. The out-of-plane (OP) anisotropy is slightly reduced. While the maximum energy product in the in-plane (IP) direction can be significantly enhanced by 430% ∼ 690% with increasing the number of the CoMnP single layer in the multilayers. The magneto-elastic behaviors well explain the evolution of the total anisotropy energy of the mono- and multi-layers. By CoMnP/Cu configurations we successfully worked out a strategy to preserve prestigious OP performance while to enhance IP properties by 4 to 6 times to meet ever increasing challenges in MEMS applications.

Influence of Pulsed DC Sputtering Power on the Quality and Residual Stress of AlN Films on Si (100) Substrates

AbstractAluminum nitride (AlN) films are prepared on Si (100) substrates by pulsed direct current magnetron sputtering. The effect of sputtering power on the crystal quality, residual stress, surface morphology, and optical properties of AlN films is comprehensively studied using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscope, and ellipsometer. It is found that the AlN film quality is strongly impacted by the sputtering power. When the sputtering power increases to 3 kW, the full width at half maximum of the AlN (002) rocking curve decreases to 2.66°. And the film crystal quality does not change significantly when the sputtering power exceeds 3 kW. Fourier transform infrared spectrum analysis shows that with increasing sputtering power, the compressive stress of AlN films first increases and then decreases. The high sputtering power also results in smoother surface and better optical performance for the AlN films. This work can serve as an important reference for growing high‐quality AlN films on cost‐effective silicon (Si) substrates via sputtering, which can facilitate the development and commercialization of III‐nitride based photonics and electronics on AlN‐on‐Si substrates.

Crystal orientation and residual stress in TiN film by synchrotron radiation

Abstract The residual stress in a TiN film, the thickness of which is less than 1 µm, deposited by arc ion plating was measured using the SPring-8 synchrotron radiation facility installed at Japan Synchrotron Radiation Research Institute (JASRI). Films thicker than 300 nm have a {111} texture, whereas those with a thickness of 100 nm have a relatively random orientation. Instead of the conventional laboratory X-ray equipment, ultrabright synchrotron radiation can be used to precisely measure the residual stress in thin films with a thickness of 100 to 800 nm. The residual stress in thicker TiN films is about 7 GPa in compression and it is not affected by the film thickness. The slightly small compressive stress in a film of 100 nm in thickness may be due to the different crystal orientations in the film.

Estimated approach development and experimental validation of residual stress-induced warpage under the SiNx PECVD coating process

Depositing silicon nitride (SiNx) coating by utilizing the plasma-enhanced chemical vapor deposition (PECVD) procedure is currently an important approach in the semiconductor industry because SiNx coating has several excellent application functions, such as passivation layer and oxygen/vapor barrier. However, residual stress occurs in the thin film resulted from the coefficient of thermal expansion (CTE) mismatch, lattice mismatch, defects, and impurities during the PECVD process. The SiNx-coated wafer would induce harsh warpage generated by coating film's residual stress. Aforementioned issue might generate the defects in the products, thus resulting in disrupted process and reliability problems. Such warpage is also unfavorable to the high flatness requirement for subsequent fabrication with the continuous scaling of advanced-technology devices. Accordingly, this study presents a novel process-oriented simulation methodology integrated with fluid dynamics-mechanical coupling responses to estimate its induced warpage magnitude affected by the pressure and temperature distributions during PECVD process and the initial intrinsic stress of SiNx coating. Under the consideration of the abovementioned loadings, the resultant stress and warpage after force balance for depositing SiNx coatings are obtained through process-oriented layer-by-layer simulation. On the basis of the simulated results and the data of experimental measurements, an intrinsic stress surface for SiNx is established by the radio frequency power, ammonia, and silane gas flow rate. Accordingly, the warpage magnitude and intrinsic stress of PECVD SiNx thin coating prior to actual processing can be immediately and accurately judged by the simulation methodology and SiNx intrinsic stress surface presented in this investigation.

Nanotwinned medium entropy alloy CoCrFeNi thin films with ultra-high hardness: Modifying residual stress without scarifying hardness through tuning substrate bias

High entropy alloy (HEA) and highly nanotwinned (NT) material with improved ductility and high strength demonstrate promising potential compared to nanocrystalline materials and traditional metallic alloys. In this study, CoCrFeNi-based medium entropy alloy (MEA) thin films with nanotwinned structure (NT) was fabricated by sputtering technology and their corresponding properties and microstructure were investigated. The NT-MEA thin films show simple face centered cubic (FCC) structure with nearly 100% (111) texture and twin thickness in 1.8–2.8 nm. The NT-MEA thin films exhibit both low electrical resistivity (100 ± 2 μΩ-cm) and high hardness (8.0–9.15 GPa) with low roughness (Rms < 1.3 nm). By controlling the substrate bias, the residual stress of the CoCrFeNi thin film can be manipulated from compressive (−0.89 GPa) to tensile (+0.6 GPa) without scarifying the hardness.

Relationship between dielectric strength and mechanical properties of alumina films fabricated by aerosol deposition

Aerosol deposition (AD) is a promising technique for preparing insulation coatings because it allows for the room-temperature fabrication of dense films with micrometer thickness. However, films fabricated by AD are composed of tiny crystallites on the nanometer scale and contain many grain boundaries, and their insulating performance is not clear. In this study, the dielectric strength, nanoindentation hardness, and residual stress of alumina films fabricated by AD were investigated. Dielectric strengths as high as 200 kV mm−1 were achieved, which corresponds to excellent performance in the thickness range of 1–100 μm compared to other coating techniques. The dielectric strength tended to increase with increasing hardness and compressive residual stress, which was rationalized in terms of the grain size and grain boundary density.

Quantitative and nondestructive determination of residual stress for SiO2 thin film by laser-generated surface acoustic wave technique

The laser-generated surface acoustic wave (SAW) technique is a promising method to measure the mechanical properties of thin films quickly and nondestructively. Residual stress is inevitable during the processing and manufacturing of integrated circuits, which will have a major impact on the physical and mechanical properties of the thin film materials and cause deterioration to the structural strength. In this study, the SAW technique based method is proposed for quantitative and nondestructive measuring the residual stress in the nanostructured films. The method is verified by the experiment measuring the SiO2 films in the thickness range of 100–2000 nm. The experimental procedures, including signal excitation, reception and processing, are described in detail. By matching the SAW experimental dispersion curve with the calculated theoretical dispersion curve containing the residual stress, the residual stress of the SiO2 films along [110] and [100] crystallographic orientation of the Si wafer is successfully quantified. The determination results are ranged from −65.5 to 421.1 MPa and the stress value increases as the film thickness decreases, revealing the residual stress of the SiO2 film is compressive. Meanwhile, the conventional substrate curvature method as a comparison is used to verify the correctness and superiority of the proposed SAW method for the residual stress determination.

Relaxation of residual stress-controlled thermopower factor in transparent-flexible Ti-doped ZnO thin films

Transparent-flexible thermoelectric materials are attractive for future small-sized consumer electronics, the internet of things, and wearable devices. The microstructural evolution and subsequent thermoelectric properties of Ti 1%.at-doped ZnO thin films, grown on polyimide flexible substrates, are presented. The thin films were grown using radio frequency a magnetron sputtering method followed by annealing for 60 min at temperatures of 200–400 °C under vacuum atmosphere. Post-annealed films demonstrate a hexagonal Wurtize structure. It is found that the annealing helped to relax residual stresses in the thin films, subsequently leading to enhanced charge concentration, carrier mobility, mean free path, and density-of-states effective mass. The thin film, annealed at 300 °C, illustrates the highest power factor of the films measured at room temperature at 19.10 μW m−1 K−2. Further increases in the annealing temperature suggest Ti2+ diffuses into the ZnO lattice and in turn disturbs the crystalline structure; this results in a reduction of the power factor to 9.32 μW m−1 K−2 at an annealing temperature of 350 °C.

Residual Stress and Tribological Behavior of Hydrogen-Free Al-Dlc Films Prepared by Hipims Under Different Bias Voltages

Residual Stress and Tribological Behavior of Hydrogen-Free Al-Dlc Films Prepared by Hipims Under Different Bias Voltages

Residual Stress and Tribological Behavior of Hydrogen-Free Al-Dlc Films Prepared by Hipims Under Different Bias Voltages

Residual Stress and Tribological Behavior of Hydrogen-Free Al-Dlc Films Prepared by Hipims Under Different Bias Voltages

Optical and photoluminescence studies of precursor stabilised Aluminium-Gallium Zinc oxide thin films

A low cost, versatile, and cost-effective ultrasonic spray pyrolysis approach was used to generate aluminium and gallium doped Zinc Oxide thin films on stretchable corning glass substrates at 400 °C temperature. Ammonium acetate is employed as a stabilizing ingredient in the precursor solution. According to X-ray diffraction patterns, high quality polycrystalline films on glass substrates grew successfully. As Ga doping levels rose, photoluminescence spectra showed an increase in exciton peak emission. As time passes, photoluminescence spectra show a strong emission peak centred at 3.24 eV that is progressively pushed toward higher wavelength. When Aluminum and Gallium were added into the Zinc Oxide lattice, the crystalline size was reduced and the thin film residual stress was raised. In the visible area, all films were extremely clear, with an average transparency of 80%. The optical energy band gap increased from 3.12 eV to 3.3 eV when the doping concentration increased.

Size-tunable MoS2nanosheets for controlling the crystal morphology and residual stress in sequentially deposited perovskite solar cells with over 22.5% efficiency

MoS2nano-scaffolds are introduced into the PbI2skeleton during a sequential deposition process to realize the homogeneous growth of perovskite crystals through expanding the physical volume of the PbI2layer and reducing film residual stress.

A Novel MEMS Capacitive Microphone with Semiconstrained Diaphragm Supported with Center and Peripheral Backplate Protrusions.

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio (SNR), distortion, and dynamic range when compared to their electret condenser microphone counterparts. We present the design and modeling of a semiconstrained polysilicon diaphragm with flexible springs that are simply supported under bias voltage with a center and eight peripheral protrusions extending from the backplate. The flexible springs attached to the diaphragm reduce the residual film stress effect more effectively compared to constrained diaphragms. The center and peripheral protrusions from the backplate further increase the effective area, linearity, and sensitivity of the diaphragm when the diaphragm engages with these protrusions under an applied bias voltage. Finite element modeling approaches have been implemented to estimate deflection, compliance, and resonance. We report an 85% increase in the effective area of the diaphragm in this configuration with respect to a constrained diaphragm and a 48% increase with respect to a simply supported diaphragm without the center protrusion. Under the applied bias, the effective area further increases by an additional 15% as compared to the unbiased diaphragm effective area. A lumped element model has been also developed to predict the mechanical and electrical behavior of the microphone. With an applied bias, the microphone has a sensitivity of −38 dB (ref. 1 V/Pa at 1 kHz) and an SNR of 67 dBA measured in a 3.25 mm × 1.9 mm × 0.9 mm package including an analog ASIC.

Molecular motion activated by residual stress in a glassy polymer thin film

The activation, by residual stress, of the fast portion of rotational motion of single fluorescent probe molecules inside a polymer thin film near its glass transition temperature is studied at a single molecular level. Spin-casted poly n-butyl methacrylate thin films without thermal annealing are chosen as the model system and single molecule fluorescence defocused microscopy is adopted as the method. The rotational motion of the probes under residual stress is found to be more activated than that under mere thermal activation, and the kinetic energy exhibits a monotonic increase with the stress strength. A rough linear dependence of rotational kinetic energy at low stress is found, yielding the value of characteristic volume for the residual stress to activate the motion of the probes. The values of the volume are close to the van der Waals volume of the probes, indicating that the activation of the fast dynamics by residual stress is localized. The activation effect is weakened and vanishes at or above the glass transition temperature due to stress relaxation. The effect is also absent at temperatures far below Tg due to the frozen molecular motion with a much higher activation energy.

Modified Stoney formula for determining stress within thin films on large-deformation isotropic circular plates

The Stoney formula is widely used to obtain residual stress in films on isotropic circular plates. However, in the case of large deformations, this formula produces significant errors because of the assumption of small deformations in its derivation. In this study, a modified Stoney formula that extends its scope of application to the nonlinear domain is proposed. A one-phase exponential decay function with a single coefficient p is used to relate the curvature of the substrate to the stress in the film. The coefficient p can be expressed as a function of the thickness, the diameter, Young’s modulus, and Poisson’s ratio of the circular plate. A linear fitting technique is applied to ascertain the relationship between the coefficient p and the aforementioned parameters. The modified Stoney formula is simple, yet accurate, and can be used to calculate the residual stress in the film directly from the measured curvature of isotropic circular plates with various dimensions and materials.

Measurement of Residual Stress of AlN Thin Films Deposited by Two-Facing-Targets (TFT) Sputtering System

Measurement of Residual Stress of AlN Thin Films Deposited by Two-Facing-Targets (TFT) Sputtering System

Residual Film Stresses in Perovskite Solar Cells: Origins, Effects, and Mitigation Strategies.

Metal halide perovskites are an emerging class of materials that are promising for low-cost and high-quality next-generation optoelectronic devices. Despite this potential, perovskites suffer from poor thermomechanical and chemical stability that must be overcome before the technology is commercially viable. Key sources of the instabilities in perovskites are ion migration and defects that can be tied to high residual stresses accumulated in the perovskite thin films during processing. This Mini-Review serves as a general overview of residual thin-film stresses, specifically in perovskite solar cells. A brief introduction to the origin of residual stresses in thin films is followed by the effects of these stresses in perovskite films specifically. Mitigation strategies for these stresses are then highlighted, followed by potential avenues of further exploration of residual stresses in perovskite films.

Understanding residual stress in thin films: Analyzing wafer curvature measurements for Ag, Cu, Ni, Fe, Ti, and Cr with a kinetic model

An analytical model for the evolution of residual stress in polycrystalline thin films is used to analyze numerous previously reported wafer curvature measurements obtained for a variety of materials and processing conditions. The model, which has been described in previous publications, considers stress-generating mechanisms that occur at the grain boundary as it forms between adjacent grains and stress due to the subsurface grain growth in layers that have already been deposited. Current work extends the model to include different types of microstructural evolutions. A set of parameters for each dataset is obtained by non-linear least square fitting. Model parameters that are not expected to depend on the processing conditions are constrained to have a common value when fitting the multiple datasets for each material. The dependence of the fitting parameters on the material and process conditions is evaluated and compared with the physical mechanisms implemented in the model.

Simultaneous measurement of pole figure and residual stress for polycrystalline thin films: ω–φ′ compensated grazing-incidence diffraction in side-inclination mode

A new grazing-incidence diffraction (GID) measurement geometry between in plane and out of plane is proposed. It is improved from the previous ω–φ compensated GID in side-inclination mode for measurement of residual stress in polycrystalline thin films [Wang &amp; van Riessen (2017). Powder Diffr. 32, S9–S15]. Instead of keeping a constant azimuthal direction of the incident beam on the thin film sample, the current proposed variation maintains a constant azimuthal direction of the scattering vector projection on the thin film sample. The variation is named `ω–φ′ compensated GID in side-inclination mode' and enables d-spacing measurements along the same azimuthal direction. An Excel spreadsheet is included for readers to plan the measurement and to calculate the residual stress for the planned sample azimuthal direction. Anisotropic residual stresses of a polycrystalline NiFe thin film on an Si 001 substrate are measured by combining this method with phi rotations. Highly automated data analysis templates are developed using DIFFRAC.TOPAS v7 launch mode to calculate residual stress for all planned azimuthal directions sequentially. A pole figure file in simple text format is also generated from the same data set using DIFFRAC.TOPAS v7 launch mode, and can be directly imported into DIFFRAC.TEXTURE v4.1 for further texture analysis. Corrections for the incident-beam refraction have been implemented in both data analysis models.

On the PZT/Si unimorph cantilever design for the signal-to-noise ratio enhancement of piezoelectric MEMS microphone

This study presents the design, fabrication, and testing of a novel piezoelectric micro-electro-mechanical-systems microphone with the partially removed lead zirconate titanate (PZT) unimorph structure for signal-to-noise ratio (SNR) enhancement. To demonstrate the feasibility of the presented concept, the unimorph cantilever array with the patterned (triangular shape) PZT film on top of a rectangular Si layer is simulated, fabricated, and tested. In comparison, the rectangular and triangular unimorph cantilever arrays with fully covered PZT film are also investigated. The proposed and reference cantilever arrays have the same foot print for fair comparison. Simulations show the proposed design has the highest output electrical energy which indicates the proposed design could successfully enhance the SNR. Moreover, acoustic measurements in the standard anechoic box show the proposed Si cantilever with patterned PZT film design could significantlyimprove the SNR. As compared to the reference microphone with triangular PZT/Si unimorph cantilever, the proposed design shows a 9.8 dB enhancement in SNR. Finally, the influences of initial structure deflections (due to the thin film residual stresses) on the low frequency responses for proposed and reference microphone designs are also investigated.