Compressive Stress In Films Research Articles

Structural, optical, and electrical properties of (Zn,Al)O films over a wide range of compositions

(Zn,Al)O thin films have been prepared by a dc reactive magnetron sputtering system with the Al contents in a wide range of 0–50at.%. The structural, optical, and electrical properties of (Zn,Al)O films were detailedly and systematically studied. The amount of Al in the film was nearly the same as, but often lower than, that in the sputtering target. The growth rate of films monotonically decreased as the Al content increased. In a low Al content region (<10at.%), Al-doped ZnO (AZO) thin films could be obtained at 400°C in an Ar–O2 ambient with good properties. The optimal results of n-type AZO films were obtained at an Al content of 4at.%, with low resistivity ∼10−4Ωcm, high transmittance ∼90% in the visible region, and acceptable crystal quality with a high c-axis orientation. The band gap could be widened to 3.52eV at 4at.% Al due to the Burstein-Moss shift [E. Burstein, Phys. Rev. 93, 632 (1954)] modulated by many-body effects. An appropriate Al-doping concentration served effectively to release the residual, compressive stress in film, which may be the reason for the improvement in film stability and the increment in grain size as well. In a medium Al content region (10–30at.%), however, the film quality was degraded, which was presumably due to the formation of clusters or precipitates in the grains and boundaries. Besides the (002) plane, other diffraction peaks such as (100) and (101) planes of ZnO were observed, but the (Zn,Al)O films still exhibited a single-phase wurtzite ZnO structure. An intragrain cluster scattering mechanism was proposed to interpret the reduction of carrier mobility in films with the Al contents in the 7–20at.% region. The solubility limit of Al in ZnO film was identified to be in the 20–30at.% range, much higher than the thermodynamic solubility limit of 2–3at.% in ZnO. In a high Al content region (⩾30at.%), there were distinct observations for (Zn,Al)O films. As the Al content was 30at.%, the film appeared in a two-phase nature with ZnO hexagonal and Al2O3 rhombohedral structures. At the 50at.% Al content, the matrix of the (Zn,Al)O film was Al2O3, and no evident trace of wurtzite ZnO was observed. The electrical and optical properties for both cases were also very different from those at the Al contents below 30at.%.

Structure and properties of tetrahedral amorphous carbon films implanted with Ti ion

In this paper the structures, mechanical properties and tribological characterization of the tetrahedral amorphous carbon films implanted with Ti ion with energy range from 2 keV to 12 keV using MEVVA implantation have been investigated. The structures of the Ti containing amorphous carbon film have been studied by X-ray photoelectron spectroscopes. The tetrahedral amorphous carbon transform to sp2-rich amorphous carbon during Ti ion implantation. The hardness and elastic modulus of the tetrahedral amorphous carbon films decreases with Ti ion implantation as a result of graphitization of sp3-rich amorphous carbon film. The compressive stress of tetrahedral amorphous carbon films implanted with Ti decreases with increase of ion implantation dose and energy. The friction coefficient of tetrahedral amorphous carbon film implanted with Ti increases with implantation dosage.

Effect of Ti interlayer on the residual stress and texture development of TiN thin films deposited by unbalanced magnetron sputtering

The purpose of this study is to investigate the effects of Ti interlayer on the texture and residual stress of overlaying titanium nitride (TiN) thin films at a high residual stress state. Films were deposited by unbalanced magnetron (UBM) sputtering methods on substrates with or without a Ti interlayer. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to reveal the microstructure of the thin films. Residual stresses and pole figures of the grown films including Ti interlayer and TiN were measured by X-ray diffraction (XRD) techniques. Thin films with weak fiber texture were produced. The compressive residual stresses in the TiN films of all specimens were higher than −4.5 GPa; in contrast, the stresses in the Ti-interlayers were much lower at less than 0.72 GPa and in the tensile state. Results showed that the Ti interlayer had a relatively weaker effect on the texture of the TiN films prepared by UBM sputtering compared to those deposited by ion beam assisted deposition (IBAD) in the previous study. It was found that about 50% of the residual stress in the TiN film was relieved by the introduction of a Ti interlayer with a thickness of 200 nm.

Elaboration of nitride thin films by reactive sputtering

The aim of this paper is first a better understanding of DC reactive magnetron sputtering and its implications, such as the hysteresis effect and the process instability. In a second part, this article is devoted to an example of specific application: Aluminium Nitride. AlN thin films have been deposited by reactive triode sputtering. We have studied the effect of the nitrogen contents in the discharge and the RF bias voltage on the growth of AlN films on Si(100) deposited by triode sputtering. Stoichiometry and crystal orientation of AlN films have been characterized by means of Fourier-transform infrared spectroscopy, X-ray diffraction and secondary electron microscopy. Dense and transparent AlN layers were obtained at high deposition rates. These films have a (002) orientation whatever the nitrogen content in the discharge, but the best crystallised ones are obtained at low value (10%). A linear relationship was observed between the AlN lattice parameter "c" (perpendicular to the substrate surface) and the in-plane compressive stress. Applying an RF bias to the substrate leads to a (100) texture, and films become amorphous. Moreover, the film's compressive stress increases up to a value of 8GPa before decreasing slowly as the bias voltage increases.

Preparation of cubic boron nitride films by radio frequency sputtering

Cubic boron nitride (c-BN) thin films with approximate 100% cubic phase and lower compressive stress were prepared on n-Si(111) substrates by radio frequency sputtering. The infrared spectra showed that the negative substrate bias had important effect on the content of cubic phase and the compressive stress of films. In addition, a relatively higher substrate resistivity favored the c-BN formation and reduced the compressive stress.

An advanced method for measuring the residual stress of deposited film utilizing laser spallation technique

Residual stress of thin diamond films deposited by chemical vapor deposition (CVD) method was measured using a new method for residual stress measurement we developed. Compressive residual stresses of CVD diamond films were determined from the height and diameter of protuberance of film delaminated by pulse laser spallation technique. We produced the protuberance with different diameter and height by changing the laser energy. Compressive stresses were calculated from the momentum balance of atmospheric pressure and internal compressive force of the film. The residual stress of the well-faceted diamond film was measured as −338±22 MPa and agreed well with the stress (−348±17 MPa) measured by the X-ray diffraction method. In three other polycrystalline diamond films with different grain structure, the compressive stresses decreased from 300 to 147 MPa with decreasing the grain size from a few microns to tens of nanometers. Small compressive stresses of fine grain films are correlated with the grain boundary structure according to visible Raman spectra study conducted.

Impact of Heavy Boron Doping and Nickel Germanosilicide Contacts on Biaxial Compressive Strain in Pseudomorphic Silicon-Germanium Alloys on Silicon

AbstractIn recent years, the semiconductor industry has increasingly relied on strain as a performance enhancer for both n and p-MOSFETs. For p-MOSFETs, selectively grown SiGe alloys in recessed source/ drain regions are used to induce uniaxial compressive strain in the channel. In order to induce compressive strain effectively using this technology, a number of parameters including recess depth, SiGe thickness (junction thickness), sidewall thickness, dopant density, dislocation density, and contact materials have to be optimized. In this work, we have studied the effects of heavy boron doping and self-aligned germanosilicide formation on local strain. Raman spectroscopy has been used to study the impact of heavy boron doping on compressive stress in SiGe films. Strain energy calculations have been performed based on Vegard's law for ternary alloys and the effect of boron on strain in SiGeB alloys modeled quantitatively. It will be shown that, owing to the smaller size of a boron atom, one substitutional boron atom compensates the strain due to 6.9 germanium atoms in the SiGeB film grown pseudomorphically on silicon. The critical thickness of SiGeB has been calculated for the first time based on kinetically limited critical thickness calculations for metastable SiGe films. It will be shown that the critical thickness of the alloy increases as the boron content in the alloy is increased, making boron concentration an additional parameter for optimizing strain in the MOSFET. Based on these conclusions, boron concentration can be used to preserve the strain for thicker SiGeB films (compared to SiGe films) while keeping the dislocation density low. Furthermore, we show that NiSiGe contacts can have a profound impact on the SiGe strain. Our results indicate that NiSiGe introduces additional stress in the underlying SiGe, which further affects the strain induced in the channel

Growth mechanism and ordered structures of iron films sputter-deposited on silicone oil surfaces

A series of iron films has been successfully fabricated by deposition on silicone oil surfaces using the DC-magnetron sputtering method, and the growth mechanism and ordered surface morphologies have been systematically studied. It is found that the growth mechanism of the iron films is similar to that of nonmagnetic films on liquid substrates,in accordance with a two-stage growth model. Large disk-shaped patterns (disks) are observed in the continuous films and their growth behaviors are mainly related to the sputtering power, deposition time and growth duration in vacuum. The experiment indicates that the disks may result from the spontaneous, free organization and gathering of the iron atoms and atomic clusters driven by the internal stress. If the sputtering power and deposition time are comparatively large, wavy buckles with a nearly uniform wavelength of about 10 μm are observed in the continuous films, generally aligning parallel to the boundaries of the disks. Further analysis shows that the top surface of the silicone oil is modified to form a soft polymer layer during deposition. Subsequent cooling of the system creates compressive stress in the iron film, which is relieved by buckling to form the wavy structures.

Effect of strain on p-channel metal-oxide-semiconductor field-effect-transistor current enhancement using stress-modulated silicon nitride films

The stress in chemical-vapor-deposited silicon nitride films (∼100nm thick) is modulated by an ion implantation technique. The tensile-strained silicon nitride film is deposited on the back and front sides of a Si wafer. After implantation of P+, As+, Sb+, or BF2+ ion species, the stress of the silicon nitride film becomes compressive on the front side. It can be explained by strain relaxation of Si–N bond on the front side and highly tensile-strained Si–N bond on the back side of wafer. The compressive stress is increased with a double-implantation process because of more atomic collisions in the silicon nitride film, as well as more strain relaxation of Si–N bond on the front side of wafer. After a thermal annealing process, the compressive stress in the silicon nitride film with P+, As+, or Sb+ implantation is reduced, while compressive stress is increased for BF2+ ion implantation due to formation of the B–N bond in silicon nitride film. To justify the stress-modulated silicon nitride film by the ion implantation technique, the p-channel metal-oxide-semiconductor field-effect transistor (p-MOSFET) is fabricated. The drive current of a p-MOSFET is improved by 7–13% for implanted silicon nitride films, due to the compressive strain-induced effective mass lowering in the channel.

Comparison of structure and mechanical properties of SiO 2-like films deposited in O 2/HMDSO pulsed and continuous plasmas

In many applications (ophthalmic lenses, car headlights, etc.), silicon oxide films are used as protective coatings in order to improve the mechanical properties of polymers. The Plasma Enhanced Chemical Vapor Deposition (PECVD), which allows deposition of dense films at temperature near the ambient, is particularly relevant for this. In this work, SiO 2-like films have been deposited in a helicon reactor operated in inductive mode at low pressure with pulsed O 2/HMDSO plasmas. The influence of the plasma-off time on the structure and mechanical properties of deposited films are studied and compared to those of the film deposited with a continuously applied power. Ellipsometric measurements and infrared spectra show that all the films are SiO 2-like films, transparent from 1.5 to 5 eV and possess a refractive index ( n = 1.46 at 1.95 eV) close to the thermal oxide one. Good mechanical properties are observed from the depth sensing indentations by Fischerscope tester. The plastic hardness is found to decrease from 15.5 to 13.5 GPa when the plasma-off time increases, whereas the elastic modulus is the same (78 GPa). In continuous mode, the hardness value obtained is higher than the fused silica one (10 GPa) which is explained by a high compressive stress of 185 MPa, as determined from Newton's ring method. Plasma pulsing allows to reduce the compressive stress to 40 MPa. On the AFM micrographs, one can observe a buckling around the indentation print due to this compressive stress in films. The interfacial fracture toughness has been estimated from the radius of the delaminated area and linked to previous stress measurements. Moreover, all the films present a good resistance to delamination.

Preparation of Super-Hard Nanocomposite Films by ICP Assisted Magnetron Sputtering

Super-hard nanocomposite films were deposited on Si(100) substrates with irradiation of a high-density (~2.0 mA/cm2) low-energy (~22 eV) ion flux by an inductively coupled plasma (ICP) assistance to magnetron sputtering process. Low-stress, super-hard nanocomposite Ti-Cu-N and Ti-Si-N films could be synthesized at low deposition temperatures below 300 oC. Prepared films exhibited a pronounced TiN(200) texture and the film hardness was significantly enhanced by the addition of Cu and Si, where a maximum value of 42 GPa at approximately 2 at% Cu addition and 48 GPa at approximately 5.8 at.% Si. Ti-Cu-N films were consisting of nanocolumns of TiN crystallites with dispersion of Cu crystallites around the columnar boundaries. While Ti-Si-N films were characterized as having a nanocolumns of TiN crystallites with amorphous Si3N4 inside the columnar boundaries. The residual compressive stresses of these films were lower than 1.5 GPa and no refinement of crystallite size by the addition of Cu and /or Si was observed, from which the hardness enhancement was attributed to a nanocomposite effect.

Stress stability and thermo-mechanical properties of reactively sputtered alumina films

The stability of residual stress inherent on deposition in reactively sputtered alumina films is studied during thermal cycling and annealing, simulating temperature excursions experienced by the films during device fabrication and subsequent operation. Increasing the magnitude of substrate bias applied during deposition acts to reduce the amount of argon incorporated in the films; more incorporated argon corresponds to smaller values of modulus and hardness and a larger coefficient of thermal expansion (CTE). Large, irreversible changes in film stress develop on heating, acting to decrease the compressive residual stress of films deposited on silicon substrates to a smaller, equilibrium value, whereas films deposited on Al2O3-TiC substrates behave differently. Thermal cycling and annealing have little effect on the modulus and CTE, but the hardness increases significantly and the threshold load for indentation crack initiation decreases precipitously during heat treatment. Possible mechanisms of irreversible stress development and mechanical property modifications are discussed.

Residual stresses of diamond and diamondlike carbon films

This paper evaluated the internal stresses of different diamond and diamondlike carbon (DLC) coatings. For the diamond coatings, the stresses were determined using micro-Raman spectroscopy and x-ray diffraction (XRD), while the stresses of DLC films were determined with bent plate method. The internal stress was related to the structural properties of the coatings. Direct current plasma jet, combustion flame, and microwave chemical-vapor deposition processes were used to prepare the diamond coatings on the tungsten carbide or molybdenum substrates, while the DLC films were deposited on the silicon wafers with filtered cathodic vacuum arc process. From the Raman spectra of the diamond coatings, the compressive internal stresses were determined, which were related to the microstructure of the coatings. The results from XRD were comparable with those obtained from micro-Raman spectroscopy. Higher compressive residual stresses in the DLC films were noticed, which were also related to their chemical bonding nature as well as their microstructures.

Pattern formation under residual compressive stress in free sustained aluminum films

A nearly free sustained aluminum (Al) film system has been successfully fabricated by vapor phase deposition of Al atoms on silicone oil surfaces and an unusual type of ordered patterns at the micrometer scale has been systematically studied. The ordered patterns are composed of a large number of parallel key-shaped domains and possess a sandwiched structure. The nucleation and growth of the patterns are very susceptible to the growth period, deposition rate, nominal film thickness and location of the film. The experiment shows that the ordered patterns are induced by the residual compressive stress in the film owing to contraction of the liquid surface after deposition. The appearance of these stress relief patterns generally represents the stress distribution in the nearly free sustained Al films, which mainly results from the characteristic boundary condition and the nearly zero adhesion of the solid–liquid interface.

Effect of germanium addition on the properties of reactively sputtered ZrN films

For the first time, Zr–Ge–N films were deposited on silicon and steel substrates by sputtering a Zr–Ge composite target in reactive Ar– N2 mixture. The films were characterised by electron probe microanalysis, X-ray diffraction, micro-Raman spectroscopy and depth-sensing indentation. The effects of the Ge content and substrate bias voltage on the films’ structure, internal stress, hardness and oxidation resistance were investigated. Substrate bias strongly influenced the chemical composition of the films being observed by means of a steep decrease in the Ge content for negative bias voltages higher than � 80 V. In these cases, a significant hardness improvement was registered. For � 100 V biased films, in the Ge concentrations range tested in this study, only ZrN grains were evidenced by X-ray diffraction. The film compressive stresses increased with the germanium concentration. An unexpected effect of the Ge content on the films’ hardness was observed. In spite of the increase in the compressive stresses of the films with increasing Ge content, the hardness monotonously dropped from 38 GPa for pure ZrN down to 21.5 GPa for 4.6 at.% Ge. Addition of Ge into ZrN-based coatings induced an improvement of the oxidation resistance and it favoured the tetragonal form of zirconia in oxidised Zr–Ge–N coatings. D 2005 Elsevier B.V. All rights reserved.

Effect of stress and density on the electrical and physical properties of MgO protecting layer for alternating current-plasma display panels

The stress state of MgO thin films, which are used as the dielectric protective layer in alternating current plasma display panels (ac-PDP), was measured by a laser scanning method, in which the bending curvature of a substrate was detected. MgO films were deposited by e-beam evaporation on glass substrates with a dielectric layer at various deposition conditions. The substrate temperatures ranged from room temperature to 300°C. The compressive stresses of the MgO films increased with increasing substrate temperature due to an increase in the intrinsic stress of MgO film. The discharge properties of the ac-PDP, specifically firing voltage (Vf), and sustaining voltage (Vs), were improved in a real panel with the strongly compressively stressed MgO film. Other properties of the MgO films were evaluated using atomic force microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and scanning electron microscopy. Strong compressive stress was caused by the dense microstructure of the film, mainly depending on the deposition temperature. The improved discharge properties of a MgO thin film were affected not by the crystallographic orientation or surface roughness of film but by the high compressive stress of film arising from its high density. In addition the more compressively stressed and denser MgO films showed better physical stability without a crack by thermal stress in the thermal budget of a manufacturing process for ac-PDPs.

Influence of stresses and magnetostriction on the soft magnetic behavior of metallic films

Nanocrystalline soft magnetic Fe–Zr–N films have been successfully deposited by DC magnetron reactive sputtering. For thick films (>200 nm), the compressive stress in the as-deposited films and the positive magnetostriction produce perpendicular anisotropy. The magnitude of this effect is smaller than the value obtained from the magnetic parameters indicating that in these films other sources of perpendicular anisotropy like columnar structure or texture play an important role. For thin films (<200 nm) with in-plane orientation of the magnetization, we have found a surprising difference between the magnitude of the induced uniaxial anisotropy in Fe–Zr–N and Fe–Co–Ta–N materials. This effect is not due to a difference in the magnitude of the magnetostriction or the strain. A possible explanation for the effect is a difference in the electronic configurations in the two materials.

Effects of Fluorine Stability and Stress in SiOF Films on Film Adhesion

Effects of fluorine stability and stress in SiOF films deposited by high-density plasma process on the generation of blisters were investigated by secondary ion mass spectrometry, thermal desorption spectroscopy (TDS), Fourier transform infrared spectroscopy (FTIR) and four point bending method using Top-SiN/TEOS/SiOF/Bottom-SiN multilayer structure. There are two kinds of fluorine in SiOF films, one is stable fluorine detected by FTIR, and the other is unstable one detected by TDS. Unstable fluorine in SiOF films is easy to diffuse and generates blisters at the interface of Top-SiN/TEOS films. Concentration of unstable fluorine is increased as the flow ratio increases and at flow ratios higher than 2.38, blisters are generated. Only the stable fluorine is related with dielectric constant of SiOF film. Hydrogen in gas phase during SiOF-film deposition plays an important role for fluorine stabilization. Compressive stress in SiOF films does not cause blisters. © 2005 The Electrochemical Society. All rights reserved.

Ordered structures and self-organized phenomena in Au films deposited on silicone oil surfaces

An optical microscopy study of ordered structures and self-organized phenomena in a continuous gold film system deposited on silicone oil surface is presented. Band-shaped ordered patterns, namely bands, are formed after deposition under certain condition. The bands are composed of a large number of parallel key-shaped domains with different width but nearly uniform length. Further experiments show that the ordered patterns result from compressive stress in films. We also study the formation mechanism of internal stress in nearly free sustained films.

X-ray diffraction study of stress relaxation in cubic boron nitride films grown with simultaneous medium-energy ion bombardment

Relaxation of the intrinsic stress of cubic boron nitride (cBN) thin films has been studied by x-ray diffraction (XRD) using synchrotron light. The stress relaxation has been attained by simultaneous medium-energy ion bombardment (2–10 keV) during magnetron sputter deposition, and was confirmed macroscopically by substrate curvature measurements. In order to investigate the stress–release mechanisms, XRD measurements were performed in in-plane and out-of-plane geometry. The analysis shows a pronounced biaxial state of compressive stress in the cBN films grown without medium-energy ion bombardment. This stress is partially released during the medium-energy ion bombardment. It is suggested that the main path for stress relaxation is the elimination of strain within the cBN grains due to annealing of interstitials.