Internal Compressive Stress Research Articles

Mechanical stresses in silicon carbonitride films obtained by PECVD from hexamethyldisilazane

Silicon carbonitride films were obtained by PECVD method from hexamethyldisilazane at different deposition temperatures. Mechanical stresses in the films were studied by laser beam deflection method. It was found that the films deposited at low temperatures (below 400°C) are in compressive internal stresses because of the volume expansion of the growing film. Meanwhile, the films deposited at high temperatures (above 400°C) have tensile stresses due to volume contraction during deposition. In addition, the dependences of coefficient of thermal expansion and Young's modulus of the films on deposition temperature are obtained. The results are discussed in the light of known features of the deposition process and also chemical and phase composition of the films.

Effect of post-sulfurization on the composition, structure and optical properties of Cu2ZnSnS4 thin films deposited by sputtering from a single quaternary target

Quaternary Cu2ZnSnS4 (CZTS) thin films were deposited on heated glass substrates directly from a non-stoichiometric quaternary CZTS target by radio-frequency (RF) magnetron sputtering process, followed by post-sulfurization in atmosphere of Ar+H2S(5%). The results of X-ray diffraction (XRD), Raman spectra, and scanning electron microscope (SEM) show that post-annealed process can improve the crystallinity of CZTS thin films. Both XRD and Raman spectra analysis indicate the internal compressive stress relaxes in post-annealed CZTS thin films. Further transmission spectra demonstrate that the band gaps of post-annealed CZTS thin films are smaller than those of as-deposited due to the relaxation of internal compressive stress and the increase of Cu content in the post-annealed CZTS films.

Effect of voltage on diamond-like carbon thin film using linear ion source

Diamond-like carbon (DLC) films were deposited by the linear ion source (LIS)-physical vapor deposition condition changing the anode voltages from 800V to 1800V and bias voltages from 0V to −200V and characteristics of the films were investigated using Nano-indentation, Micro Raman spectroscopy, Field Emission-Scanning Electron Microscope (FE-SEM), Residual stress tester, Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The residual stress and hardness increased relatively with increasing the ion energy up to anode voltage of 1400V and −100 bias voltage respectively. From the Micro Raman analysis, the content of sp3 carbon in sp3/sp2 ratio was increased with increasing the anode voltage. From these results, residual stress and hardness of DLC films are increased as increase of anode voltages due to the enhancement of 3-dimensional cross-links between carbon atoms and dangling bond. Also, the internal compressive stress is increased with increasing the voltages. Therefore, the optimum anode and bias voltage are considered to be around 1400V and −100V respectively in these experimental conditions.

Influence of Ti target current on microstructure and properties of Ti-doped graphite-like carbon films

Ti-doped graphite-like carbon (Ti-GLC) films were synthesized successfully by magnetron sputtering technique. The compositions, microstructures and properties of the Ti-doped GLC films dependent on the parameter of Ti target current were systemically investigated by Raman spectra, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation and ball-on-disk tribometer. With the increase of the Ti target current, the ratio of sp2 bond and the content of Ti as well as the film hardness and compressive internal stress increase, but the high content of the Ti would result in the loose film due to the formation of the squamose structure. Less incorporated Ti reduces the friction of the GLC film in dry-sliding condition, while pure GLC film exhibits the lowest friction coefficient in water-lubricated condition. Ti-GLC film deposited with low Ti target current shows high wear resistance in both dry-sliding and water-lubricated conditions.

Effect of Substrate Bias Voltage on the Mechanical and Tribological Properties of Low Concentration Ti-Containing Diamond Like Carbon Films

Ti containing hydrogenated diamond like carbon films (Ti-DLC) was deposited on Si substrates at room temperature by magnetron sputtering Ti-twin target in methane and argon mixture atmosphere via changing the substrate bias voltage. The Ti atomic concentration in the film is less than 0.57% and exists mainly in the form of metallic titanium rather than TiC, confirmed by XPS analysis. The internal compressive stress of the film decreases monotonically with the substrate bias voltage increase. However, the hardness values of the film keep at level (12 GPa) without almost any obvious change with the increase of the substrate bias voltage. Furthermore, Ti-containing DLC film prepared at -1600 V substrate bias voltage shows an extremely low wear rate (~10-9mm3/Nm) and low friction coefficient (0.09).

Control of buckling in large micromembranes using engineered support structures

In this paper we describe a general method to avoid stress-induced buckling of thin and large freestanding membranes. We show that using properly designed supports, in the form of microbeams, we can reduce the out-of-plane deflection of the membrane while maintaining its stiffness. As a proof of principle, we used a silicon-on-insulator (SOI) platform to fabricate 30 µm wide, 220 nm thick, free-standing Si membranes, supported by four 15 µm long and 3 µm wide microbeams. Using our approach, we are able to achieve an out-of-plane deformation of the membrane smaller than 50 nm in spite of 39 MPa of compressive internal stress. Our method is general, and can be applied to different material systems with compressive or tensile internal stress.

Single-step preparation and characterization of Cu2ZnSn(SxSe1−x)4 thin films deposited by pulsed laser deposition method

Cu2ZnSn(S,Se)4 (CZTSSe) thin films have been firstly deposited on heating quartz substrates by pulsed laser deposition (PLD) method using one-step process. The results of energy dispersive X-ray (EDX) spectroscopy show that there are some discrepancies of the elemental composition between targets and thin films. However, structural and optical properties of CZTSSe thin films show good tolerance to the composition deviation from stoichiometry. Both X-ray diffraction (XRD) and Raman spectra analysis indicate the internal compressive stress exists in CZTSSe thin films. Further transmission spectra demonstrate that the band gaps of CZTSSe thin films are higher than those of CZTSSe bulks. The internal compressive stress and the deficiency of Cu content in the films contribute to the enlargement of the band gaps of CZTSSe thin films.

Embedded corrugated long-period fiber gratings for sensing applications

We demonstrate a method to make possible the mass production of corrugated long-period fiber gratings (C-LPFGs) by utilizing imprint lithography on polycarbonate (PC) substrates. For such C-LPFGs whose working principle is based on photoelastic effect, pretensile tension is required to be applied to inducing periodical refractive index variation. We then present an attempt to use PC as embedding material for providing internal compressive stress for C-LPFGs to have a photoelastic effect. This type of LPFG, termed embedded corrugated long-period fiber gratings (EC-LPFGs), is obtained after reimprinting the C-LPFGs into other PC substrates. Since compressive stress is retained due to the materials of different coefficients of thermal expansion (CTE), unlike C-LPFGs, EC-LPFGs can serve as strain, bending, and temperature sensors without the need of pretensile strain. The two most troublesome problems, the fragility of an etched fiber grating and the requirement of pretensile strain, can be simultaneously alleviated or solved by EC-LPFGs.

Prevention of blister formation in electrolessly deposited copper film on organic substrates

Electroless copper (Cu) plating is a key process to provide seed layers for the subsequent Cu electroplating in the printed wiring boards (PWBs). Due to the demand for lower power dissipation at higher temperatures and high signal frequencies, various kinds of organic materials have been newly introduced as substrates. However, they have come with defects such as delamination and/or blisters in the Cu layers on organic substrates, i.e., weak adhesion. Here we demonstrate the root cause and a prevention method of the blister formation. Various parameters affecting the blister formation have been investigated combined with the deposit thickness (internal stress), hydrogen gas evolution, and codeposited Ni content in the electroless Cu plating. It was not obvious that the compressive internal stress in deposits was directly related to the blister formation. Instead, the hydrogen gas evolution clearly turned out to be the key factor, and it was observed that Ni added plating solutions reduced the hydrogen gas evolution significantly and thus produced no blisters in the Cu deposits. The control of blisters would be more critical as the line and space become narrower in the production lines such as ball grid array (BGA) and high density interconnection (HDI).

About the internal pressure in cavities derived from implantation-induced blistering in semi-conductors

Silicon and germanium wafers were implanted with hydrogen at high fluence and then submitted to thermal treatment at low temperature. By means of atomic force microscopy observations and finite elements simulations, the internal pressure under the resulting blisters appearing onto the surface has been determined. It is found that the internal pressure could be strongly overestimated from calculation if the internal compressive stresses in the implanted layers are neglected and/or incorrect boundary conditions are used.

In situ measurement of the internal stress evolution during sputter deposition of ZnO:Al

Transparent and conductive ZnO:Al films were deposited by RF magnetron sputtering on opaque (Si/SiO2) or transparent (glass) substrates. The internal stress evolution has been measured in situ using a high resolution 2D curvature measurement technique. Internal tensile or compressive stresses were generated, depending on the sputtering pressure, oxygen addition level and substrate temperature. The origin of the observed stress level is correlated with factors affecting the film growth mechanism, and the relation with the electro-optical properties of the resulting transparent and conductive oxide films is highlighted.

Pulsed Laser Ablation Induced Fragmentation, Transformation, Internal Stress, Sn2+/H+ Cosignature, and Optical Property Change of SnO2 Powders in Water

The rutile-type SnO2 powders originally ca. 25–50 nm in size were successfully size minimized by pulsed laser ablation in liquid (PLAL) under 532 nm excitation and 400 mJ per pulse at a specified water depth (5 to 20 mm) for up to 20 min in a slender vial filled with deionized water. Transmission electron microscopic observations indicated the nanoparticles via PLAL fragmentation have a minimum diameter of ca. 5 nm with a predominant rutile-type structure and an occasional high-pressure stabilized α-PbO2-type structure with 1-D 2× and 4× commensurate superstructures in accordance with a (021) shuffling derivation from a fluorite-type parental phase. Miniature size of the nanoparticles was more effective at a lower water level and a longer time of laser excitation yet limited by a coalescence process. The combined effects of nanosize, dense phase, and internal compressive stress, as well as Sn2+/H+ cosignature according to X-ray diffraction and spectroscopic results account for a lower minimum band gap down to ca. 2 eV for potential optocatalytic applications of such SnO2 nanoparticles.

Investigation of the internal stress effects on static and dynamic characteristics of an electrostatically actuated beam for MEMS and NEMS application

Internal stress is often encountered in fixed–fixed beam based devices with micron or sub-micron length scales during device fabrication or operation. In this paper, we have investigated the effects of internal stress on static and dynamic characteristics of an electrostatically actuated cylindrical beam. The beam has been modelled using Euler–Bernoulli theory including the nonlinearities due to beam stretching and electrostatic forcing. The analysis has been carried out by solving the governing differential equations using a Galerkin based multi-modal reduced order modelling technique. A standard collocation based numerical scheme has also been used to confirm the results of the reduced order method. Our study shows that internal stress significantly influences the static and dynamic characteristics of the beam. We also find that, when compressive internal stress is high, it is important to include higher modes in the reduced order model. A design technique to achieve high resonant frequency stability under temperature variation, for electrostatically actuated beam oscillators, has also been proposed as a result of this investigation.

레이저 쇼크 피닝의 마이크로 충격파 측정 및 평가

본 연구에서는 레이저 쇼크 피닝으로부터 생성되는 마이크로 충격파를 정량적으로 측정하고 그 특성을 분석하였다. 레이저 쇼크 피닝은 금속 재료에서 압축 응력을 생성시키며 그 크기가 표면에서 극대화되는 특징을 가지고 있다. 펄스 Nd:YAG 레이저를 이용하여 스틸표면에 피닝 공정을 수행하였고 이에 따른 마이크로 충격파의 정량화 및 재료의 기계적 성질 변화에 대해 평가하였다. 실험적 접근으로 피에조소자를 사용하였으며 이를 통한 실제 충격파의 정량화를 제시하였다. 또한 재료 구조 특성, 재료 강도, 인장 시험 등의 기계적 특성을 분석하였다.

Surface modification, martensitic transformation, and optical properties of hydrogenated ZrO2 nanocondensates via pulsed laser ablation in water

Pulsed laser ablation on Zr plate in water under Q-switch mode and a fluence of 700 and 800 mJ/pulse for a rather high power density of 1.5 and 1.7 × 1011 W/cm2, respectively, was employed to fabricate hydrogenated ZrO2 nanocondensates. X-ray diffraction and transmission electron microscopic observations indicated such nanocondensates are full of {111} and {100} facets and predominantly in monoclinic (m-) rather than cubic- and/or tetragonal (t-) crystal symmetry in particular when fabricated at 700 mJ/pulse. The hydrogenated ZrO2 nanocondensates underwent martensitic t → m transformation at a rather small critical size (ca. 20 nm) due to H+ signature and hence oxygen vacancy deficiency in the lattice. The resultant m-phase was free of twin and fault due to site saturation and rather limited growth of the nanosized particles. Spectroscopic characterizations indicated that the nanocondensates have a significant internal compressive stress, (H+, Zr2+, Zr3+) co-signature and hence a smaller band gap of 5.2–5.3 eV for potential applications in UV region.

Magnetic-field-driven reversal phase transition in highly textured and self-accommodated martensites of Ni–Co–Mn–In composite

In this paper, in-situ high-energy X-ray diffraction was employed to trace the phase transition via the change in the lattice strains under multiple (stress and magnetic) fields for a polymer-bonded Ni–Co–Mn–In composite. Under uniaxial compressive deformation, the parent phase in the Ni–Co–Mn–In alloy endured a compressive internal stress along the loading direction and a tensile internal stress in the transverse direction, leading to the formation of a highly textured martensite. This paper is intended to examine the effect of the external magnetic field on the phase transition in two types of martensite, i.e. highly textured martensite and temperature-induced self-accommodated martensite. For the highly textured martensite, a compressive or tensile internal stress can be observed for the parent phase parallel or perpendicular respectively to the preloading direction under an applied magnetic field. This is due to the magnetic-field-induced transformation from the highly textured martensite to the parent phase. For the self-accommodated martensite accompanied by the random distribution of martensitic variants, no obvious internal stresses are generated in the parent phase under an applied magnetic field of up to 6 T. The insight into the stress state of the alloy phase reinforces the in-depth understanding of the role of external fields in affecting the functional performance of the polymer-bonded Ni–Co–Mn–In composite.

Characterizations of CrN/a-CN x nanolayered coatings deposited by DC reactive magnetron sputtering of Cr and graphite targets

CrN/a-CN x nanolayered coatings have been deposited by DC reactive magnetron sputtering of pure Cr and graphite targets. The total thickness is 1 μm and that of a-CN x layers is kept constant at 3.5 nm. The period (bilayer thickness) is in the range 8–16 nm. CrN and a-CN x layers are crystalline and amorphous respectively. The decrease of CrN layers’ thickness (decrease of period) in the stack leads to refinement of CrN microstructure associated with (200) preferred orientation. The hardness of nanolayered films is independent of the period’s thickness, while internal compressive stress, which remains between that of each elementary layer, follows an evolution close to that of the law of mixtures. The best tribological behaviours are reached for a periods’ thickness of 8 nm.

Stress-affected and stress-affecting instabilities during the growth of anodic oxide films

The objective of the current paper is to (re-)address the question whether internal stress is a fundamental parameter driving some generic cases of growth instabilities commonly encountered during the growth of anodic oxide films, namely breakdown and pore initiation. This has been done by unraveling possible correlations between a key electrochemical characteristic of the instability event and the internal stress evolution, the latter being measured in situ during the very same anodising experiment. As such, we have been able to make more conclusive statements as compared to the merely speculative arguments in the literature whether these instabilities have a mechanical origin or not. In the case of breakdown, the two well-documented types of breakdown events encountered during galvanostatic Zr anodising were both found to be stress-affected: instantaneous compressive internal stresses were identified as the driving force for both the densifying phase transformation responsible for type-I breakdown, as well as for the buckling-induced delamination events observed during type-II breakdown. Pore initiation in anodic Al 2O 3 on the other hand was found not be stress-affected. Instead, pore formation is rather believed to induce itself a modification in the mechanical behaviour, and was therefore classified as stress-affecting.

Effect of Ag on oxidation of Cu-base leadframe

It was found that trace Ag on surface has great effect on the oxidation failure of Cu-base lead frame. Trace Ag on the surface increases its peeling resistance in dry condition, while decreases that under hygrothermal aging treatment. The oxide thickness, morphology and compositions were examined to understand the key factor of peeling of oxide film. It becomes evident that Ag has ability to block the diffusion of copper atoms, and so hold back the oxidation of copper. But adhesive strength between copper and oxide layer has little relation with oxide thickness but more important influence comes from internal compressive stress which has great relations with initial structure of the copper lead frame.

Internal Stress and Grain Size Effect on the Phase Stabilization of ZrO<sub>2</sub> Deposited by MOCVD

Zirconia (ZrO2) films were deposited by metal-organic chemical vapor deposition (MOCVD) on {1 0 0} Si single crystal using Zr(thd)4 precursors. The thickness of obtained films is typically of 3.5 μm. The samples have been characterized by Field-Emission-Gun Scanning Electron Microscopy (FEG-SEM) for morphologic and microstructure study, and by X-ray Diffraction (XRD) for crystalline structure. The microstructure analysis showed that unexpected stable single tetragonal phase preferentially grew in low temperature area. According to the literature, the tetragonal phase stabilization is related to the crystalline size and the internal compressive stress. To analyze the effect of grain size and internal stress on the phase transformation, the thermal annealing were carried out in different temperatures and internal stress was measured by XRD method.