Effect of ion-beam assisted deposition on the film stresses of TiO_2 and SiO_2 and stress control

Based on Hartmann-Shack sensor technique, an online thin film stress measuring system was introduced to measure the film stresses of TiO2 and SiO2, and comparison was made between the film stresses prepared respectively by the conventional process and the ion-beam assisted deposition. The effect of ion-beam assisted deposition on the film stresses of TiO2 and SiO2 was investigated in details, and the stress control methodologies using on-line adjustment and film doping were put forward. The results show that the film stress value of TiO2 prepared by ion-beam assisted deposition is 40 MPa lower than that prepared by conventional process, and the stress of TiO2 film changes gradually from tensile stress into compressive stress with increasing ion energy; while the film stress of SiO2 is a tensile stress under ion-beam assisted deposition because of the ion-beam sputtering effect, and the film refractive index decreases with increasing ion energy. A dynamic film stress control can be achieved through in-situ adjustment of the processing parameters based on the online film stress measuring technique, and the intrinsic stress of film can be effectively changed through film doping.

Effects of annealing time on the structure, morphology, and stress of gold–chromium bilayer film

In this work, a 200-nm-thick gold film with a 10-nm-thick chromium layer used as an adhesive layer is fabricated on fused silica by the electron beam evaporation method. The effects of annealing time at 300℃ on the structure, morphology and stress of the film are studied. We find that chromium could diffuse to the surface of the film by formatting a solid solution with gold during annealing. Meanwhile, chromium is oxidized on the surface and diffused downward along the grain grooves in the gold film. The various operant mechanisms that change the residual stresses of gold films for different annealing times are discussed.

Stress Controlled Silicon Nitride Thin Film Deposited by Plasma Enhanced Chemical Vapour Deposition

SiN, films are deposited on silicon wafers through plasma enhanced chemical vapor deposition （PECVD）. The relationship between the film stress and deposition factors is investigated. It is found that low stress films would be obtained by adjusting the ratio of low frequency（LF） power to high frequency（HF） power pulse time or the chamber pressure. The best of the two methods to control stress in the film is changing the percentage of LF power pulse time. The low stress condition is achieved when the percentage of low frequency power pulse time in total time（LF and HF pulse time） is close to 40%, The low stress cantilever of tunable vertical cavity surface emitting laser is obtained by using this deposition condition,

Correspondence between Susceptibility to SCC of 7050 Aluminum Alloy and Passive Film-induced Stress at Various pH Values

The passive film-induced stress and the susceptibility to SCC of 7050 aluminum alloy in 3.5%sodium chloride solution at various pH values were investigated by slow strain rate testing（SSRT） and flowing stress differential method.The results showed that the passive film-induced stress and the susceptibility to SCC decreased with increasing pH values when pH≤7,while they increased with increasing pH values when pH7.However,the corrosion type was interpreted as exfoliation corrosion when pH=l and 14,and there was no film formed on the surface of the specimens.The whole variation plots of film-induced stress and the SCC susceptibility with pH values were both presented as a valley shape.The symbol and amount of the film-induced stress were related to the compositions of the passive film,which were analyzed using X-ray photoelectron spectroscopy（XPS）.

Thermoelastic stress analysis of multilayered films in a micro-thermoelectric cooling device

This paper presents an analytical solution for the thermoelastic stress in a typical in-plane＇s thin-film micro- thermoelectric cooling device under different operating con- ditions. The distributions of the permissible temperature fields in multilayered thin-films are analytically obtained, and the characteristics, including maximum temperature dif- ference and maximum refrigerating output of the thermo- electric device, are discussed for two operating conditions. Analytical expressions of the thermoelastic stresses in the layered thermoelectric thin-films induced by the tempera- ture difference are formulated based on the theory of mul- tilayer system. The results demonstrate that, the geometric dimension is a significant factor which remarkably affects the thermoelastic stresses. The stress distributions in layers of semiconductor thermoelements, insulating and support- ing membrane show distinctly different features. The present work may profitably guide the optimization design of high- efficiency micro-thermoelectric cooling devices.

Effect of Wafer Size on the Film Internal Stress Measurement by Wafer Curvature Method

Wafer curvature method has been applied to determine the internal stress in the films using Stoney＇s equation.During the film deposition,the wafer fixation on the sample holder will restrict the deformation of the rectangle-shaped wafer,which may result in the stress datum difference along length and width direction.In this paper,the effect of wafer size and the wafer fixation on the TiN film internal stress measured by wafer curvature method was discussed.The rectangle-shaped wafers with different length/width ratios（L/W=1：1,2：1,3：1 and 4：1） were fixed as a cantilever beam.After the TiN films deposition,the profiles of the film/wafer were measured using a stylus profilometer and then the internal stress was calculated using the Stoney equation in the film.The results showed that the fixed end of the wafers limited to some degree the curvature of the wafers along the width direction.For film internal stress measured by wafer curvature method,the wafer profile should be scanned along the length direction and the scan distance should be greater than or equal to half of wafer length.When the length/width ratio of the wafer reached 3：1,the wafer curvature and the calculated stress were basically the same at different positions along the length direction.For film internal stress measured by wafer curvature method,it was recommended that the length/width ratio of wafer should be considered to be greater than or equal to 3：1,and the deformed profile was scanned along the length direction.

Influences of post-annealing and internal stress on magnetoresistance properties of Ni_(80)Fe_(20) films

Ni80Fe20 films with thickness about 54 nm were deposited on K9 glass and thermally oxidized silicon substrates at ambient temperature by electron beam evaporation with deposition rate about 1.8 nm/min. The as-deposited films were annealed at 350, 450 and 570 ℃respectively for 1 h. After annealing at 570 ℃, the anisotropic magnetoresistance ratio(RAM) of the films is greatly improved. It increases to 3%3.5% nearly about three times of that of the as-deposited films. The grain size increases with the annealing temperature and the [111] crystal orientation is obviously enhanced after annealing at temperature above 450 ℃. The internal stress in the films deposited on K9 glass is compressive and the resistance measurement shows that (RM∥) is larger than (RM⊥) in these films. However, in the films deposited at the same conditions but on oxidized silicon substrates, the internal stress is tensile and (RM⊥) is larger than (RM∥). The differences of (RM∥) and (RM⊥) in two series of specimens are discussed.

Behaviour of Couple Stress Fluids in Porous Annular Squeeze Films

The laminar squeeze flow of an incompressible couple stress fluid between porous annular disks is studied using hydrodynamic lubrication theory. The modified Reynolds’ equation is derived using Stokes microcontinuum theory and is solved analytically. Analytical expressions for the squeeze film pressure and the load carrying capacity are obtained in terms of Fourier-Bessel series. Numerical results are obtained for the sinusoidal motion of the upper disk. The effect of couple stresses and that of porous facing on the squeeze film behaviour are analysed through the squeeze film pressure and the load carrying capacity. Further, the equation for the gap width between the disks is obtained from the inverse problem.

EFFECT OF RESIDUAL STRESS ON THE MARTENSITIC TRANSFORMATION OF SPUTTER-DEPOSITED SMA THIN FILMS

TiNi thin films were sputter-deposited on circular single-crystal silicon substrates un-der various sputtering parameters. The crystal structure and residual stress of the as-deposited films were determined by X-ray diffraction and substrate-curvature method. The phenomenon of stress-suppressed martensitic transformation was observed. R is considered that the residual stresses in SMA thin films based on circular substrates act as balanced biaxial tensile stresses. The status of equilibrant delays the align-ment of self-accommodated variants and the volume shrinkage during the martensitic transformation.

Temperature-dependent bias-stress-induced electrical instability of amorphous indium-gallium-zinc-oxide thin-film transistors

The time and temperature dependence of threshold voltage shift under positive-bias stress（PBS） and the following recovery process are investigated in amorphous indium-gallium-zinc-oxide（a-IGZO） thin-film transistors. It is found that the time dependence of threshold voltage shift can be well described by a stretched exponential equation in which the time constant τ is found to be temperature dependent. Based on Arrhenius plots, an average effective energy barrier Eτ stress= 0.72 eV for the PBS process and an average effective energy barrier Eτ recovery= 0.58 eV for the recovery process are extracted respectively. A charge trapping/detrapping model is used to explain the threshold voltage shift in both the PBS and the recovery process. The influence of gate bias stress on transistor performance is one of the most critical issues for practical device development.

Formation mechanism of ordered stress-relief patterns in a free sustained Cu film system

A nearly free sustained copper （Cu） film system has been successfully fabricated by thermal evaporation deposition of Cu atoms on silicone oil surfaces, and a characteristic ordered pattern has been systematically studied. The ordered pattern, namely, band, is composed of a large number of parallel key-formed domains with different width w but nearly uniform length L; its characteristic values of w and L are very susceptible to the growth period, deposition rate and nominal film thickness. The formation mechanism of the ordered patterns is well explained in terms of the relaxation of the internal stress in the films, which is related to the nearly zero adhesion of the solid-liquid interface. By using a two-time deposition method, it is confirmed that the ordered patterns really form in the vacuum chamber.

Problems in the Determination of Internal Stresses in Plasma Assisted CVD TiN Films

The measurement of internal stresses in a PACVD TiN film proved experimentally to be difficult by a conventional X-ray diffraction technique.The linear relationship between 2θ and sin^2(?) could hardly be reached in some cases.Nevertheless.a good confirmation between the variation of FWHM-sin^2(?) and 20-sin^2(?) was revealed for every nonlinear forms.It followed that the effect of nondistributed micro-strains might exist in plasma assisted vapor deposited films,which usually have a strong crystal orientation,and the method of effectively separating macro-stress and micro-strain must be applied for the precise determination of internal stresses in PACVD films.

An Analysis of the Influence of Protective Films on the Inner Surfaces of CCPP Headers and Steam Pipelines on Their Thermal Stress State

At present, the main attention of researchers is paid to the deterioration of heat transfer when heating the outer surface of the pipe with the liquid or steam, flowing inside it, in the presence of films or deposits on its inner surface. However, when pipe is heating by heat carrier medium, flowing inside it, film on the inner pipe surface serve a dual protective function, protecting the pipe from corrosion and reducing its thermal stress. The article represents the results of the computational analysis of protective films influence on the thermal stressed state of headers and steam pipelines of combined-cycle power plants (CCPP) heat-recovery steam generators at different transient operating conditions particularly at startups from different initial temperature states and thermal shock. It is shown that protective films have a significant influence on the stresses magnitude and damage accumulation mainly for great temperature disturbances (for thermal shock). Calculations were carried out at various thicknesses of films and assuming that their thermal conductivity less than thermal conductivity of the steam pipelines metal.

Effects of gradient interlayer on residual stress and cracking in TiN thin films

The influence of a gradient interlayer on the residual stress and cracking in TiN thin films was studied as a function of the thickness of gradient interlayer. Both X ray in situ tensile testing and grazing method were used to measure the residual stress in thin films. In TiN films, there exists a residual stress of 10 GPa, which can be remarkably decreased by a gradient interlayer between film and substrate. The cracking behavior of films after tension shows that the crack of film/substrate system begins at interface between film and substrate.

The model developed for stress-induced structural phase transformations of micro-crystalline silicon films

The nanoindentations were applied to island-shaped regions with metal-induced Si crystallizations. The experimental stress-strain relationship is obtained from the load-depth profile in order to investigate the critical stresses arising at various phase transitions. The stress and strain values at various indentation depths are applied to determine the Gibbs free energy at various phases. The intersections of the Gibbs free energy lines are used to determine the possible paths of phase transitions arising at various indentation depths. All the critical contact stresses corresponding to the various phase transitions at four annealing temperatures were found to be consistent with the experimental results.

Improvement in electrical properties of high-κ film on Ge substrate by an improved stress relieved pre-oxide method

High-κ /Ge gate stack has recently attracted a great deal of attention as a potential candidate to replace planar silicon transistors for sub-22 generation. However, the desorption and volatilization of GeO hamper the development of Ge-based devices. To cope with this challenge, various techniques have been proposed to improve the high-κ /Ge interface. However,these techniques have not been developed perfectly yet to control the interface. Therefore, in this paper, we propose an improved stress relieved pre-oxide（SRPO） method to improve the thermodynamic stability of the high-κ /Ge interface. The x-ray photoelectron spectroscopy（XPS） and atomic force microscopy（AFM） results indicate that the GeO volatilization of the high-κ /Ge gate stack is efficiently suppressed after 500℃ annealing, and the electrical characteristics are greatly improved.

An improved wall shear stress measurement technique using sandwiched hot-film sensors

In this letter we present a novel wall shear stress measurement technique for a turbulent boundary layer using sandwiched hot-film sensors. Under certain conditions, satisfactory results can be obtained using only the heat generated by one of the hot-film and a calibration of the sensors is not required. Two thin Nickel films with the same size were used in this study, separated by an electrical insulating layer. The upper film served as a sensor and the bottom one served as a guard heater. The two Nickel films were operated at a same temperature, so that the Joule heat flux generated by the sensor film transferred to the air with a minimum loss or gain depending on the uncertainties in the film temperature measurements. Analytical solution of the shear stress based on the aforementioned heat flux was obtained. The preliminary results were promising and the estimated wall shear stresses agreed reasonablywell with the directly measured values （with errors less than 20%） in a fully developed turbulent pipe flow. The proposed technique can be improved to further increase precisions.

Structure and internal stress of Au films deposited on SiO_2/Si(100) and mica by dc sputtering

Au films with a thickness of about 300 nm were deposited on SiO_2/Si(100) andmica substrates by dc sputtering. X-ray diffraction spectroscopy and field emission scanningelectron microscopy were used to analyze the structure and internal stress of the Au films. Thefirms grown on SiO_2/Si(100) show a preferential orientation of [111] in the growth direction.However the films grown on mica have mixture crystalline orientations of [111], [200], [220] and[311] in the growth direction and the orientations of [200] and [311] are slightly more than thoseof [111] and [220]. An internal stress in the films grown on SiO_2/Si(100) is tensile. For Au filmsgrown on mica the internal stresses in the [111]- and [311]-orientation grains are compressive whilethose in the [200]- and [220]-orientation grains are tensile. Au films grown SiO_2/Si(100) havesome very large grains with a size of about 400 nm and have a wider grain size distribution comparedwith those grown on mica.

Negative gate bias stress effects on conduction and low frequency noise characteristics in p-type poly-Si thin-film transistors

The instability of p-channel low-temperature polycrystalline silicon thin film transistors(poly-Si TFTs)is investigated under negative gate bias stress(NBS)in this work.Firstly,a series of negative bias stress experiments is performed,the significant degradation behaviors in current-voltage characteristics are observed.As the stress voltage decreases from-25 V to-37 V,the threshold voltage and the sub-threshold swing each show a continuous shift,which is induced by gate oxide trapped charges or interface state.Furthermore,low frequency noise(LFN)values in poly-Si TFTs are measured before and after negative bias stress.The flat-band voltage spectral density is extracted,and the trap concentration located near the Si/SiO2 interface is also calculated.Finally,the degradation mechanism is discussed based on the current-voltage and LFN results in poly-Si TFTs under NBS,finding out that Si-OH bonds may be broken and form Si*and negative charge OH-under negative bias stress,which is demonstrated by the proposed negative charge generation model.

Influence of residual stress on the phase equilibrium of Ti(C_xN_y) thin films

In order to provide a theoretic basis for the research of Ti(C_xN_y) thinfilms, the thermodynamic database of Ti-C-N ternary system is established and the phase diagramsections are calculated. In addition to the assessed thermodynamic properties of Ti-C-N system, theinfluence of the residual strain energy of Ti(C_xN_y) thin films on the phase equilibria isanalyzed. The classical formula for calculating the elastic strain energy is expressed into aRedlich-Kister form in order to perform the thermodynamic and equilibrium calculations using theThermo-Calc software. Isothermal sections at 900 and 1100 K are calculated with this database andcompared with those calculated without considering the residual stress. As a result, with theaddition of strain energy delta-fcc Ti(C_xN_y) phase area shrinks. It is therefore concluded thatwith the influence of the residual stress in Ti(C_xN_y) thin solid film, the precipitation of puredelta film requires more precise control of composition.