Measurement Of Stress In Films Research Articles

Thin CNx overcoats deposited using various sputtering gases

This work presents systematic studies of the effect of various sputtering gases (Ar, Kr, and Xe) on the roughness, density, coverage, stress, and nanomechanical properties of CNx thin films. CNx (1–11 nm) was deposited on Si (100) substrates using dc magnetron sputtering. A three-parameter roughness analysis was carried out using atomic force microscopy. Film thickness and density were measured by x-ray reflectivity. Nanoindentation hardness and modulus were measured using a Hysitron TriboScope® nanomechanical system, while stress measurements were performed using a Flexus thin film stress measurement system. The coverage of CNx is assessed using a pinhole-decoration technique. As the mass of the sputtering gases increases, the density and hardness of CNx increases, while the deposition rate, surface roughness, and compressive stress decrease. Using Kr or Xe, a 3-nm-thick dc-sputtered CNx overcoat displaying good coverage is obtained.

Residual stress measurement in thin carbon films by Raman spectroscopy and nanoindentation

The reliability of hermetic carbon-coated optical fibers is affected by residual stresses in the coating created during the fiber draw process. Thermally induced residual stresses are caused by differences in the coefficient of thermal expansion (CTE) of the coating and the optical fiber. This mismatch creates shear stresses at the interface that can delaminate the film. This work presents and validates a surface residual-stress measurement technique using Raman spectroscopy. Since select Raman peaks for carbon films exhibit a wavenumber shift in proportion to the magnitude of residual stress, Raman spectra can be correlated to a theoretical model to obtain its residual stress. The model, validated with nanoindentation, shows an equi-biaxial stress field through the depth of the film. Nanoindentation also provides an accurate measure of residual stress in thin films with unknown material properties. The approach presented in this study is a non-destructive and non-intrusive method for measuring residual surface stress in thin films, and is ideal for small curved-surface specimens such as carbon-coated optical fibers.

Measurement of Residual Stress in ZnO Thin Films Deposited on Silicon Wafers by the Indentation Fracture Test

ABSTRCT:The indentation fracture test was used to evaluate residual stress in ZnO thin films deposited on silicon wafers. Using the calibrated constants involved in a simple semi-empirical formula, which was developed based on fracture analysis and experimental results, we estimated the residual stress in the ZnO thin films by measuring the indentation-induced crack length as a function of the indentation load.

OS4(P)-16(OS04W0240) Measurement of Residual Stress in Nano-Size Copper Thin Films by Synchrotron Radiation

OS4(P)-16(OS04W0240) Measurement of Residual Stress in Nano-Size Copper Thin Films by Synchrotron Radiation

A new dynamical diffraction-based technique of residual stress measurements in thin films

The recently discovered dynamical diffraction effect ‘neutron camel’ was used for residual stress measurements in a thick Si (111) crystal coated with a 2000 A-thick Ni film. The observed asymmetry of the back-face rocking curve corresponds to the bending radius of ∼19 km and the tension force applied to the Ni film is ∼90 N/m. Relative deformation of the Si crystallographic cells in the vicinity of diffractive surfaces is |∂uz/∂z|≈1.6×10-6.

An integrated process modeling methodology and module for sequential multilayered substrate fabrication using a coupled cure-thermal-stress analysis approach

An integrated process modeling methodology using a coupled cure-thermal-stress analysis approach has been developed to determine the evolution of warpage and stresses during the sequential fabrication of high-density electronic packaging structures. The process modeling methodology has been demonstrated, for example, with a bi-layer structure consisting of a 3 mil (76.2 /spl mu/m) thick Vialux 81 photo-definable dry film (PDDF) polymer on a silicon substrate. Extensive material characterization of the thermo-mechanical properties of the thin film polymer is presented, including the development of a viscoelastic material model. The predicted warpage values have been validated with shadow Moire experiments, while the predicted stress values have been validated with experimental data using the Flexus Thin Film Stress Measurement Apparatus. Good agreement is seen between the predicted and the experimental warpage and stress values during the entire cure cycle. Finally, the importance of incorporating viscoelastic polymer behavior and processing history is emphasized in the context of developing the multi-layered high-density wiring integrated substrate fabrication process.

Nanomechanical properties of multilayered amorphous carbon structures

A possible route toward reducing the intrinsic compressive stress in as-grown amorphous carbon films on Si substrates, with a high fraction of tetrahedral bonding, is by forming multilayered $a\ensuremath{-}\mathrm{C}$ structures composed of layers dense and rich in ${\mathrm{sp}}^{3}$ sites alternated by layers rich in ${\mathrm{sp}}^{2}$ geometries, a type of an amorphous superlattice. We present here a combined theoretical and experimental effort to investigate the stability, stress, and elastic properties of this type of $a\ensuremath{-}\mathrm{C}$ material. Our theoretical approach is based on Monte Carlo simulations within an empirical potential scheme, while the experimental part consists of spectroscopic ellipsometry, x-ray reflectivity, stress, and nanoindentation measurements in films prepared by magnetron sputtering. Our central result is that the average stress in the multilayered structures is nearly eliminated through layer-by-layer stress compensation, yet the fraction of ${\mathrm{sp}}^{3}$ sites in the dense regions remains high, sustained by the overwhelmingly compressive local stresses. The ${\mathrm{sp}}^{3}$-rich layers are stable both against a moderate increase of the width of the low-density layers, as well as under thermal annealing. The elastic moduli of the multilayered films are comparable with those of single-layer films. This, in conjuction with their low stress, makes them suitable for mechanical purposes.

Influence of segregation on the measurement of stress in thin films

The force that a deposited film A exerts on its substrate B is usually written as the sum of volumetric and surface (and interface) contributions. In the simplest case (pseudomorphous film, absence of segregation), volumetric and surface contributions can be easily separated through simple force measurements. In this article, we show that, in the presence of segregation, only simultaneous in situ stress, strain, and composition measurements allow the proper analysis of stress establishment in thin films. For this purpose, we discuss how segregation influences both volumetric and surface stresses. More precisely, we show that (1) the separation between a surface and a volumetric stress can be meaningless when segregation occurs; (2) one should carefully distinguish between the true physical thickness and the deposited thickness; (3) surface strain should be accounted for in the analysis of the experimental diffraction data; and (4) when the elastic modulus misfit between film and substrate cannot be neglected the total stress depends explicitly on the shape of the concentration profile.

Stress measurements in thin zirconia films at 300°C using synchrotron radiation

Zirconium alloys used as cladding materials for nuclear fuel oxidise into zirconia during their stay in the reactor. The zirconia formed develops high compressive stresses because the molar volume of the oxide is greater than that of the metal. For a

Hydrogen Promoted Copper Migration in the High Pressure Anneal Process

To meet the requirement of lower processing temperature in the high pressure anneal process (HiPA), Cu films deposited by physical vapor deposition (PVD) with addition of hydrogen were investigated. Experimental results on the hole filling performance under high pressure, the grain growth, the micro-hardness measurement and the film stress measurement revealed that the hydrogen addition markedly changes the properties of the Cu film. It is especially effective in softening the PVD-Cu film and/or in promoting the Cu atom diffusion which also promotes grain growth. As a result the processing temperature may be lowered down to around 400°C, which is the highest temperature allowable for the interconnection structures with organic low-k dielectric layers.

A Study on the Properties of Different IMP Ta, Ta(N) and Multi-Layer Ta/Ta(N) as Diffusion Barriers for Cu Metallization

ABSTRACTWe report a study on the properties of Ionized Metal Plasma (IMP) Ta, Ta(N) and multi-layer Ta/Ta(N) based on a comparative evaluation of their performance as diffusion barriers in Cu based metallization schemes. The film structures used in this study are: IMP Cu(2000Å)/IMP Ta(250Å)/Si; IMP Cu(2000Å)/IMP Ta(N)(250Å)/Si; and IMP Cu(2000Å)/IMP multi-layer Ta/Ta(N)(250Å)/Si. The samples were annealed in N2 ambient at 500 °C, 550°C, 600°C and 650°C, respectively, for 30 minutes. The failure behavior and film properties of different barriers were investigated using MetaPULSE, Film stress measurement (FSM), Four-point probe (FPP), X-ray diffractometry (XRD), Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM). It has been observed clearly from the sheet resistance measurements that failures of Ta(N) and Ta barriers occurred at 550°C and 600°C respectively, whereas the multi-layer Ta/Ta(N) could still survive from the annealing up to 650°C. Evidence showing the formation of Cu3Si in the failed film stacks was found from XRD spectra. Based on our studies, it can be concluded that microstructures of the barriers has the major effects on preventing Cu from diffusing through them to react with Si and this makes the multi-layer Ta/Ta(N), in overall, superior to the other two Ta and Ta(N) barriers.

In situ measurement of mechanical stress in polycrystalline zinc-oxide thin films prepared by magnetron sputtering

The generation of stress in magnetron-sputtered undoped and aluminum-doped zinc-oxide (ZnO:Al) films has been measured by an in situ technique. Radio-frequency magnetron sputtering from ceramic targets in an argon atmosphere was used for film deposition. The stress was measured by optically detecting the deflection of a thinned silicon cantilever on which the films were deposited. This in situ stress measurement setup was tested by investigating the sputtering pressure dependence of stress in molybdenum films. For zinc-oxide films it was found that by increasing the argon-sputtering pressure during deposition the intrinsic compressive stress decreased by about a factor of 2, both for undoped and doped zinc-oxide films. The undoped films exhibit significantly higher compressive stresses (1–2.5 GPa) compared to the aluminum-doped films (0.7–1.5 GPa). This fact was ascribed to a surfactant-like effect of the dopant aluminum, which improved the crystallinity of the doped films. In contrast to magnetron-sputtered metallic films (like molybdenum) the zinc-oxide films did not show a transition from compressive to tensile stress when the argon-sputtering pressure was increased. It is assumed that this behavior of the zinc-oxide films is due to an additional incorporation of oxygen into the films. By adjusting the oxygen partial pressure during the deposition at a fixed argon pressure, a minimum of the compressive stress in ZnO: Al films was found which coincided with a minimum of the film resistivity. This observation stresses the role of even small changes in deposition parameters on the mechanical and electrical properties of zinc-oxide films. The possibilities of the in situ stress measurement are demonstrated during the deposition of zinc-oxide multilayers.

Roughness effect on the measurement of interface stress

Stimulated by a recent paper by Spaepen (Acta mater. 48 (2000) 31) we concentrate on the effect of roughness parameters on stress measurements in thin films for self-affine and mound rough interfaces. A self-affine interface is characterized by a lateral correlation length ξ, an rms roughness amplitude σ, and a roughness exponent H (0< H<1). With increasing long wavelength roughness ratio σ/ ξ, the ratio between the measured and the actual interface stress decreases. It decreases with a decreasing roughness exponent H that leads to rougher interfaces at short roughness wavelengths (< ξ). For mound roughness which is characterised besides σ by an average mound separation λ and a system correlation length ζ, the force ratio decays in an oscillatory manner as a function of σ/ λ as long as λ< ζ. It is concluded that for both cases a more precise knowledge of roughness morphology is required in order to address the influence of interface roughness on the interface stress in thin films.

An instrument for in-situ stress measurement in thin films during growth

An improved stress-measuring technique based on the cantilever bending principle is presented. Any thermal shift of the sample holder position that results in errors in the stress data is minimised by evaluating the difference in the deflection of two laser beams. The film thickness is calculated from the reflected laser intensity, or from ellipsometry data recorded simultaneously during film growth. Without using a lock-in technique or image processing, the resolution in the bending force per unit width is 0.02 N/m for a 50-μm thick cantilever. The system represents an easy, versatile and cheap technique to measure intrinsic and thermal stresses in thin films. The system has been employed to record the instantaneous stress during the ion beam-assisted deposition of BN films, and the global stress during the ion-induced amorphisation of silicon.

An optimal quasisuperlattice design to further improve thermal stability of tantalum nitride diffusion barriers

X-ray diffraction and transmission electron microscopy, along with electrical and film stress measurements, were used to evaluate the effectiveness of 40-nm-thick amorphous Ta2N and microcrystalline TaN diffusion barriers, both single and multilayered, against Cu penetration. Failure of the single-layered Ta2N diffusion barrier upon annealing is initialized by crystallization/grain growth, mainly helped by frozen-in compressive stress (3–4 GPa) to transform itself into a columnar structure with a comparable grain size to the thickness of the barrier. However, when subjected to annealing, the Ta2N/TaN alternately layered diffusion barrier with an optimum bilayer thickness (10 nm) remains almost stress-free (0–0.7 GPa) and transforms itself into an equiaxed structure with grain sizes of only ⩽3 nm. Such quasisuperlattice films can present lengthening and complex grained structures to effectively block Cu diffusion, thus acting as much more effective barriers than Ta2N (and TaN) single-layered films.

The measurement of thin film stress using phase shifting interferometry

The measurement of thin film stress using phase shifting interferometry

Dispersion of Birefringence and its Influence on On-Line Measurement of Stresses in Polymer Films

Birefringence distribution in biaxially oriented polymer films is often used to assess non-uniformities in processing and in physical properties. Off-line characterization of this property can be performed by direct measurement of anisotropy in the refractive index, a process that is slow and not suitable for on-line use. By comparison, the spectral contents analysis (SCA) method is fast and easily adaptable for on-line process monitoring and real-time process control. However, implementation of this method requires accurate knowledge of the chromatic dispersion of birefringence. This paper discusses the contribution of birefringence dispersion to the precision of birefringence measurements by the SCA method, and it describes a new spectrometric procedure for accurate measurement of this material property.

The measurement of thin film stress using phase shifting interferometry

A new technique for determining the stress of thin films is described. This technique combines digital phase shifting interferometry with image-processing software. A circular disc polished on one side is used as the coated substrate during film deposition. The average stress in thin films can be derived by comparing the deflection of the substrate before and after film deposition. The deflection of the substrate by the deposited film is obtained by the phase map. Using the Zernike polynomial fitting algorithm, a three-dimensional contour map is generated from the polynomial coefficients to visualize the deformation of the thin film and to examine the tensile or compressive stress after film deposition. Four oxide films prepared by ionbeam sputter deposition are investigated for their film stresses. The experimental results show that the stress values are concordant with measurements using other methods.

Effect of thermal stresses on temperature dependence of refractive index for Ta 2O 5 dielectric films

The effect of thermal stresses on the temperature dependence of the refractive index for tantalum pentaoxide (Ta 2O 5) dielectric films deposited on Si substrate was investigated experimentally. The thermally induced variation of refractive index of Ta 2O 5 films was characterized by measuring the index-temperature coefficient of the antiresonant reflecting optical waveguide with a Mach–Zehnder interferometry system and a film stress measurement system. The measured results with and without the thermal stresses were 7.89×10 −6 and 3.64×10 −6/°C at 632.8 nm from 25 to 55°C, respectively. A comparison of the measured results showed that the index-temperature coefficient of the Ta 2O 5 films with thermally induced stresses was about two times higher than those of films without thermal stresses. This indicates that the effect of thermally induced stresses on the temperature dependence of the refractive index for Ta 2O 5 films cannot be neglected. In particular, the optical properties of the index-temperature coefficient were characterized in the small range of 10 −6/°C.

Apparatus for the laser-optical measurement of stress in thin films: Results on CuNi

Dedicated to the investigation of the temperature dependence of mechanical stress in thin films (up to 700 °C in vacuum), a sensitive apparatus has been built up to measure the substrate curvature of a beam-shaped sample by deflection of a splitted laser beam from both ends. The measuring sensivity is about 0.1 MPa for a typical film thickness of 1000 nm. The long-term value over 24 h is about ±0.5 MPa due to ambient-temperature drifts. The determination of absolute stress magnitudes is possible by comparative measurements between the measuring bending beam and a reference one before and after film deposition or film removal. Investigations on sputtered Cu0.57Ni0.42Mn0.01 films have shown that (1) the stress relaxes above 300 °C and remains nearly constant between 430 and 550 °C during the first heating, (2) a hysteresis behavior occurs during the repeated cycles, and (3) the stress at room temperature increases a little with the cycle number.