Depth Profiles Of Atoms Research Articles

Effects of Annealing Temperature on Bias Temperature Stress Stabilities of Bottom-Gate Coplanar In-Ga-Zn-O Thin-Film Transistors

Defect annihilation of the IGZO/SiO2 layer is of great importance to enhancing the bias stress stabilities of bottom-gate coplanar thin-film transistors (TFTs). The effects of annealing temperatures (Ta) on the structure of the IGZO/SiO2 layer and the stabilities of coplanar IGZO TFTs were investigated in this work. An atomic depth profile showed that the IGZO/SiO2 layer included an IGZO layer, an IGZO/SiO2 interfacial mixing layer, and a SiO2 layer. Higher Ta had only one effect on the IGZO layer and SiO2 layer (i.e., strengthening chemical bonds), while it had complex effects on the interfacial mixing layer—including weakening M-O bonds (M: metallic elements in IGZO), strengthening damaged Si-O bonds, and increasing O-related defects (e.g., H2O). At higher Ta, IGZO TFTs exhibited enhanced positive bias temperature stress (PBTS) stabilities but decreased negative bias temperature stress (NBTS) stabilities. The enhanced PBTS stabilities were correlated with decreased electron traps due to the stronger Si-O bonds near the interfacial layer. The decreased NBTS stabilities were related to increased electron de-trapping from donor-like defects (e.g., weak M-O bonds and H2O) in the interfacial layer. Our results suggest that although higher Ta annihilated the structural damage at the interface from ion bombardment, it introduced undesirable defects. Therefore, to comprehensively improve electrical stabilities, controlling defect generation (e.g., by using a mild sputtering condition of source/drain electrodes and oxides) was more important than enhancing defect annihilation (e.g., through increasing Ta).

Enhanced adhesion strength between electroplated Cu and ABF substrate with isothermal annealing treatment

This study aimed to enhance the adhesion strength between electroplated Cu and a low-profile Ajinomoto build-up film (ABF) substrate through isothermal annealing treatment. We examined the electroplated Cu microstructure evolution (including grain size, orientation, and texture) and elemental distribution at the Cu/ABF interface after annealing at 180 °C and 210 °C by means of electron backscatter diffraction (EBSD), X-ray diffraction (XRD), and transmission electron microscopy (TEM) in conjunction with energy dispersive X-ray spectroscopy (EDS). Furthermore, the adhesion strength of the Cu/ABF structure after isothermal annealing for different times was investigated through a peeling test based on the IPC-TM-650 test methods. The chemical bond and atomic concentration depth profiles of the fracture surface (ABF side) after the peeling test were characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). These investigations demonstrated that the adhesion strength of the Cu/ABF structure can be greatly enhanced by the electroplated Cu microstructure modification and Cu/ABF interdiffusion through appropriate isothermal annealing treatment.

Crystal Lattice Rearrangement Occurred at Au/Ag Bonded Interface in Atomic Diffusion Bonding in Vacuum

Atomic diffusion bonding (ADB) processing of wafers using thin metal films is a promising route to achieving room-temperature wafer bonding [1,2]. When two film surfaces mutually contact at room temperature during ADB, crystal lattice rearrangement occurs, thereby enhancing the bonding performance. Generally, films of the same material used for bonding are fabricated on two flat wafer surfaces. Therefore, methods for examining the crystal lattice rearrangement mechanism are few. Two representative material films used for bonding, those of the metals Au and Ag, have fcc crystal structure and show a solid solution in the whole Au–Ag composition range. Moreover, lattice mismatch of these materials is very slight: less than 0.2%. For this study, Au film and Ag film were bonded in vacuum using ADB. The crystallographic structure of Au/Ag bonded films and depth profiles of Au and Ag atoms were examined. Au and Ag films were fabricated respectively on two flat wafer surfaces using sputter deposition, followed by bonding of the two films on the wafers in vacuum. Figure 1 portrays cross-section STEM images of Au(20 nm)/Ag(20 nm) bonded films: (A) a bright field image, and (B) an HAADF image corresponding to (A). Films were deposited on Si wafers, with 5-nm-thick Ta films underneath. Figure 1(A) shows that no interface corresponding to the original Au/Ag interface is visible; no vacancy is observed. Grains were formed continuously across the original interface over the entire thickness of the bonded films, indicating that crystal lattice rearrangement occurred at room temperature when the films mutually contacted in vacuum. Although the crystallographic structures of Au and Ag layers are identical because of the crystal lattice rearrangement, the contrast between the upper and lower half areas in Figure 1(B) is expected to be attributable mainly to the different atomic weights of Au and Ag. Figure 2 presents the depth profiles of Au, Ag, and Ta evaluated using EELS analysis along line (a) in Figure 1(B). Results supported that interdiffusion at the Au/Ag bonded interface is not remarkable. This report presents discussion of the relation between crystal lattice rearrangement and interdiffusion of atoms based on results of analyses of Au/Ag bonded films with various layer structures. T. Shimatsu and M. Uomoto, J. Vac. Sci. Technol., B 28, 706 (2010).T. Shimatsu and M. Uomoto, ECS Trans., 33 (4), 61 (2010). Figure 1

Amorphous to Polycrystalline Phase Transition in La2O3 Films Grown on a Silicon Substrate Forming Si‐Doped La2O3 Films

Herein, La2O3 films are fabricated on a Si substrate without a La–Sr intermixing layer at the La2O3/Si interface using a pulsed laser deposition method. X‐ray diffraction data shows only two discernible peaks of the La2O3 films: hexagonal La2O3 (10‐1) and cubic La2O3 (222), indicating polycrystalline character. During film growth, the reflection high‐energy electron diffraction pattern from the La2O3 surface changes from an initial column shape to a complicated distributed dot pattern with narrow lines, suggesting possible structural property changes in the La2O3 film. The occurrence of a structural transition is confirmed by high‐resolution transmission electron microscopy (HRTEM), which exhibits a clear crystalline phase change from an initial ≈10 nm thick amorphous La2O3 film to polycrystalline La2O3 film on Si. Rutherford backscattering shows a reduced La–Si intermixing between La2O3 and Si. Furthermore, the results of X‐ray photoelectron spectroscopy atomic depth profile analysis show that observation of La‐silicate over the whole La2O3 film indicates that Si diffuses through whole thick La2O3 films forming Si‐doped La2O3 films. This study of the well‐defined structural characteristics and sharp interface of La2O3/Si will enable further understanding of high dielectric constant materials grown on Si by the introduction of advanced film growth technique.

Electrohydrodynamic-Jet-Printed Cinnamate-Fluorinated Cross-Linked Polymeric Dielectrics for Flexible and Electrically Stable Operating Organic Thin-Film Transistors and Integrated Devices.

Herein, printable polymer series containing different portions of cinnamate and perfluorinated phenyl functionalities, namely, polyperfluorostyrene-co-poly(vinylbenzyl cinnamates) (PFS-co-PVBCi (x:y)) copolymers, were synthesized and applied as gate dielectrics for organic thin-film transistors (OTFTs). The polymeric dielectrics were successfully printed via electrostatic force-assisted dispensing mode of electrohydrodynamic jet printing. The dielectric characteristics of the printed polymers, such as surface energy, dielectric constant, leakage current, atomic depth profiles, and deposited semiconducting layer characteristics, were clearly identified. In particular, the difference in driving stability of OTFTs according to the type of polymer was analyzed in detail and a possible mechanism was proposed. Results suggested that PFS-co-PVBCi (3:7) led to optimized consequences, yielding an almost negligible Vth shift under continuous bias stress. Through this, we successfully implemented flexible OTFT and logic devices using printed PFS-co-PVBCi (3:7) dielectrics with stable operation properties. Therefore, we believe that this study will facilitate the printing and synthesis of polymer dielectrics to produce printed and flexible OTFTs.

Pd/Cu(220) interdiffusion under compressive stress

This work investigates the effect of the external compressive pressure on the interdiffsuion between Pd and Cu. By analyzing ESCA atomic depth profiling without/with the external compressive pressure, two important findings were observed: (1) Pd/Cu(220) interdiffusion was found to be promoted by the external compressive pressure. (2) Under external compressive pressure, Pd atoms diffuse across the interdiffusion interface into the Cu(220) side more than the Cu atoms across the interdiffusion interface into the Pd side. Combining Matano approach and the obtained ESCA atomic profiles, the interdiffusion diffusivities and the activation enthalpy (H) of Pd/Cu(220) interdiffusion can be calculated. The activation enthalpy (0.694 eV) of Pd/Cu(220) interdiffusion is reduced to 0.625 eV and 0.604 eV with applying external pressures of 125 MPa and 250 MPa, respectively. The present calculation of the activation enthalpy implies that the applying compressive stress results in negative changes of the activation enthalpy (δH) and the free energy of activation (δG) for the Pd/Cu(220) interdiffusion. With Gibbs equation, the negative changes of δG and δH can further deduce the relation of the entropy change (δS) and the activation of enthalpy (δH) for the Pd/Cu(220) interdiffusion system under the external compressive stress, which are (1) the change of the entropy has to be positive (δS > 0) or (2) the change of the entropy (δS) has to be smaller than the term of δH/T., i.e., δS< δH/T.

Effects of hydrogen implantation on the magnetocaloric properties of amorphous FeZr films

We report on the effects of H-implantation on the magnetic and magnetocaloric properties of amorphous FeZr films. Arrott plots reveal a second order ferromagnetic to paramagnetic phase transition for the as-grown and H-implanted films, with an increase in TC from 160 to 200 K upon implantation. The maximum change in magnetic entropy (-ΔSM) increases from 0.66 to 0.77J/kgK for a field change μ0ΔH = 1.5T, as well as the relative cooling power (RCP) values were improved from 84.5 to 108.6J/kg. This improvement was attributed to the increase in magnetization and chemical inhomogeneity induced by the implantation process. The increase in the chemical inhomogeneity was supported by the determination of the local exponent n extracted from the slope of Ln(−ΔSM) as a function of Ln(μ0H), which is line with the simulated depth profile of hydrogen atoms through the FeZr film.

Glow discharge-optical emission spectroscopy for in situ analysis of surfaces in plasmas

In situ, real-time characterization of surfaces exposed to plasmas is of great interest. Common chemical analysis methods such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy cannot be used. Here, we discuss the use of glow discharge-optical emission spectroscopy for this purpose. A small coupon piece (aluminum coated with yttria in this study) was mounted on an rf-biased electrode and inserted into an opening in the reactor wall. Silicon or SiO2 substrates on a separately rf-biased electrode were etched in an inductively coupled plasma (ICP) of Cl2/Ar/O2 or C4F8/O2, respectively. Pulsed bias was applied to sputter the surface of the coupon piece in the wall at the edge of the ICP, either after etching in an Ar ICP or during etching in the Cl2/Ar/O2 ICP. Optical emission from the region above the coupon surface was collected and spectrally resolved. The difference in intensity between the coupon bias on and off conditions was used to determine what species were present on the surface. A quantification method for converting emission intensities into atomic composition depth profiles is presented.

Complementary physicochemical analysis by ellipsometry and Auger spectroscopy of nano-sized protective coating layers

Protective SiC-rich nano layer was created by ion beam mixing of Si/C multilayers. The transformation of the Si and C layers into a homogeneous SiC layer was analyzed using complementary depth profiling by spectroscopic ellipsometry (SE) and Auger electron spectroscopy (AES). The distribution of elements and their chemical states was revealed by AES, whereas SE measured the accurate thicknesses, density, crystallinity, and the distribution of different phases. The optical properties of the created SiC layer determined by SE were almost identical to that of ion implantation-amorphized SiC. Amorphous Si and void formations were revealed by SE. The void profile determined by SE correlated well with the Xe distribution measured by AES. The complementary capabilities of SE and AES for a detailed chemical investigation were pointed out, such as the atomic (AES), structural (AES and SE) and non-destructive depth profiling (SE) features. It was shown that besides the synergism that the two methods reveal, SE is capable of a quick, sensitive and non-destructive testing of such layer structures and materials.

Neutron depth profiling using the reactions 10B (n,α)7Li and 6Li(n,α)3H induced by thermal neutrons

Samples like p-type silicon and metallic glasses containing boron, were taken and used as target to induce the reaction 10B (n,α)7Li. In addition, samples containing lithium were also irradiated with thermal neutrons to induce 6Li (n,α)3H reaction. The alpha particles emitted through the reactions lose energy while traversing through the sample from point of emission to the surface and can be detected using a surface barrier detector. The out coming alpha particle spectrum can give the depth profile of boron or lithium atoms in the sample, if the energy loss of alpha particle within the matrix is known.

Architectured Cu–TNTZ Bilayered Coatings Showing Bacterial Inactivation under Indoor Light and Controllable Copper Release: Effect of the Microstructure on Copper Diffusion

A Ti–23Nb–0.7Ta–2Zr–1.2O alloy (at %), called “gum metal”, was deposited by direct-current magnetron sputtering (DCMS) on an under layer of copper. By varying the working pressure during the deposition, columnar TNTZ (Ti–Nb–Ta–Zr) nanoarchitectures were obtained. At low working pressures, the upper layer was dense with a coarse surface (Ra = 12 nm) with a maximum height of 163 nm; however, the other samples prepared at high working pressures showed columnar architectures with voids and an average roughness of 4 nm. The prepared coatings were characterized using atomic force microscopy (AFM) for surface topography, energy dispersive X-ray spectroscopy (EDX) for atomic mapping, scanning electron microscopy (SEM) for cross-section imaging, contact angle measurements for hydrophilic/hydrophobic balance of the prepared surfaces, and X-ray diffraction (XRD) for the crystallographic structures of the prepared coatings. The morphology and the density of the prepared coatings were seen to influence the hydrophilic properties of the surface. The antibacterial activity of the prepared coatings was tested in the dark and under low-intensity indoor light. Bacterial inactivation was seen to happen in the dark from samples presenting columnar nanoarchitectures. This was attributed to the diffusion of copper ions from the under layer. To verify the copper release from the prepared samples, an inductively coupled plasma mass spectrometer (ICP-MS) was used. Additionally, the atomic depth profiling of the elements was carried out by X-ray photoelectron spectroscopy (XPS) for the as-prepared samples and for the samples used for bacterial inactivation. The low amount of copper in the bulk of the TNTZ upper layer justifies its diffusion to the surface. Recycling of the antibacterial activity was also investigated and revealed a stable activity over cycles.

Sub-nanometer-scale depth profiling of nitrogen atoms in SiO2/4H-SiC structures treated with NO annealing

We developed a technique to probe, with sub-nanometer-scale resolution, depth profiles of nitrogen atoms in NO-treated SiO2/4H-SiC structures for Si- and C-face substrates. This technique revealed that preferential nitridation only at the SiO2/SiC interfaces proceeds in the initial stage of NO annealing. Then, for the Si-face, a longer NO treatment leads to a nitrogen distribution in SiO2 within a few nm of the interface. This result is in line with the mobility degradation in MOSFETs subjected to excessive NO annealing. For the C-face, a larger amount of nitrogen was introduced and the depth profile was unchanged after reaching a saturation level.

Experimental studies of thorium ion implantation from pulse laser plasma into thin silicon oxide layers

We report the results of experimental studies related to implantation of thorium ions into thin silicon dioxide by pulsed plasma flux expansion. Thorium ions were generated by laser ablation from a metal target, and the ionic component of the laser plasma was accelerated in an electric field created by the potential difference (5, 10 and 15 kV) between the ablated target and a SiO2/Si (0 0 1) sample. The laser ablation system installed inside the vacuum chamber of the electron spectrometer was equipped with a YAG:Nd3 + laser having a pulse energy of 100 mJ and time duration of 15 ns in the Q-switched regime. The depth profile of thorium atoms implanted into the 10 nm thick subsurface areas together with their chemical state as well as the band gap of the modified silicon oxide at different conditions of implantation processes were studied by means of x-ray photoelectron spectroscopy and reflected electron energy loss spectroscopy methods. Analysis of the chemical composition showed that the modified silicon oxide film contains complex thorium silicates. Depending on the local concentration of thorium atoms, the experimentally established band gaps were located in the range 6.0–9.0 eV. Theoretical studies of the optical properties of the SiO2 and ThO2 crystalline systems were performed by ab initio calculations within hybrid functional. The optical properties of the SiO2/ThO2 composite were interpreted on the basis of the Bruggeman effective medium approximation. A quantitative assessment of the yield of isomeric nuclei in ‘hot’ laser plasma at the early stages of expansion was performed. The estimates made with experimental results demonstrated that the laser implantation of thorium ions into the SiO2 matrix can be useful for further research of low-lying isomeric transitions in a 229Th isotope with energy of 7.8 0.5 eV.

Magnesiothermic reduction of silica glass substrate—Chemical states of silicon in the generated layers

We applied magnesiothermic reduction to silica glass substrates at various conditions including solid state or solid-Mg liquid reaction, and solid-Mg vapor reaction. Magnesium silicide with highly oriented to the 〈110〉 direction against the substrate surface was obtained in the solid state reaction at temperatures from 600 °C to 700 °C using Mg grains while Si crystallites were obtained in the reaction with Mg film deposited on the glass substrate at 560 °C. On the other hand, in the reduction with Mg vapor at 575 °C, brown and amorphous layer was formed on the surface of the silica glass substrate. The layer was transparent in the visible and near-infrared regions, and showed an interference pattern in the transmission spectra, indicating the homogeneity of the layer. The thickness and refractive index were estimated as 770 nm and 1.94, respectively. As the reaction with Mg vapor proceeded further, Mg2Si and MgO crystallites were formed. Oxidation states and their depth profiles of silicon atoms in the layers were investigated by X-ray photoelectron spectroscopy. The silicon atoms in the brown and amorphous layer existed in intermediate oxidation states, −2 and +3. The reaction proceeding, the formal charge of the silicon atoms varied to −4 corresponding to Mg2Si and +2.

LED Die-Bonded on the Ag/Cu Substrate by a Sn-BiZn-Sn Bonding System

In this study, light emitting diode (LED) chips were die-bonded on a Ag/Cu substrate by a Sn-BixZn-Sn bonding system. A high die-bonding strength is successfully achieved by using a Sn-BixZn-Sn ternary system. At the bonding interface, there is observed a Bi-segregation phenomenon. This Bi-segregation phenomenon solves the problems of the brittle layer-type Bi at the joint interface. Our shear test results show that the bonding interface with Bi-segregation enhances the shear strength of the LED die-bonding joints. The Bi-0.3Zn and Bi-0.5Zn die-bonding cases have the best shear strength among all die-bonding systems. In addition, we investigate the atomic depth profile of the deposited Bi-xZn layer by evaporating Bi-xZn E-gun alloy sources. The initial Zn content of the deposited Bi-Zn alloy layers are much higher than the average Zn content in the deposited Bi-Zn layers.

Ceramic coatings for orthopaedic implants: preparation and characterization

Ceramic coatings are increasingly used for orthopaedic implants to improve the wear resistance and to enhance the integration into bone tissue, resulting in the long‐term stability of the implant. The innovative pulsed plasma deposition technique was used to deposit at room temperature different thin films with required mechanical parameters and good adhesion to the substrate. In this way, the films of nanostructured hydroxyapatite, magnetic hydroxyapatite, zirconia and zirconia ‐ alumina were produced and investigated by X‐ray diffraction, atomic force microscopy and XPS depth profiling techniques. Obtained results revealed the good stoichiometry, sufficient purity of chemical composition, very high uniformity in depth and thermal stability in ultra‐high vacuum of all investigated coatings. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Thermal Fields Simulation of the Refining Process for Si Wafer by Continuous-Wave Laser Irradiation

The direct removal of metal impurity from Si wafer by continuous-wave (CW) laser irradiation has been studied. The wafer was irradiated by linear (Nd:YAG) CW laser with a wavelength of 1064nm. The irradiated region of the wafer experienced melting and subsequent recrystallization process during the laser heating and cooling processes. This leads to the redistribution of the metal impurity along the depth direction. The depth profile of metal atoms in Si was measured by secondary ion mass spectrometry (SIMS). The concentration of the metal ions in the CW laser irradiated sample was dramatically decreased at the measurement range of SIMS. Thermal fields of Si wafer irradiated by CW-laser were numerically simulated to explain the SIMS results. A finite element method with a two-dimensional model was selected in the simulation process. The depth of the maximum temperature for the laser irradiated wafer in the irradiation process was related to many parameters, such as, the energy density of the laser and the velocity of the sample moving. The simulation results agree well with our experiment results.

Epitaxial growth of fcc-Ag(0 0 1) nanodots on MgO(0 0 1) substrates via Ti seed layer-assisted agglomeration

We have analysed the influence of Ti seed layer (2.0 nm thick) on the agglomeration of Ag films (4.0 nm thick) grown onto MgO(0 0 1) single crystal substrates by RF magnetron sputtering. The samples were deposited at room temperature and post-annealed at 200–450 °C for 4 h while still maintaining the chamber vacuum condition. The surface profile of the sample, as analysed using atomic force microscopy, confirms that the insertion of a Ti seed layer between the MgO substrate and Ag layer promotes the agglomeration process, forming the nanodot. Furthermore, the atomic concentration depth profile of the Ag/Ti/MgO film, as estimated by using angle-resolved x-ray photoelectron spectroscopy, suggests that the nanodot surface mainly consists of Ag. Moreover, x-ray diffraction studies prove that the initial deposition of the Ti seed layer onto MgO(0 0 1) prior to the Ag deposition yields high-quality face-centred cubic (fcc)-Ag(0 0 1) oriented epitaxial nanodots. Based on these results, it can be concluded that the Ti thin film acts as a seed layer, assisting the epitaxial growth of the Ag nanodot onto the MgO substrate.

Effect of Introducing Free Gaseous Radicals of Trichlorosilane and Ammonia Precursors on Growth and Characteristics of LPCVD a-SiNx Ultra Thin Films

Preparation and characteristics of amorphous silicon nitride (a-SiNx) thin films deposited by low pressure chemical vapor deposition (LPCVD) are investigated. Free gaseous radicals of trichlorosilane (TCS) and ammonia (NH3) are produced by passing each of the precursor gases separately over Pt-Ir/Al2O3 catalyst at the temperature of 600 C. Kinetics studies of the LPCVD are carried out in different total pressures, NH3/TCS flow rate ratios and temperatures. Surface topography, chemical concentrations, growth rate and thickness are studied by Ellipsometry, x-ray photo-electron spectroscopy (XPS), atomic force microscopy (AFM) and auger depth profiling (ADP). Analysis of experiments indicates that at the temperatures between 730 C and 830 C, the growth rate of thin films follows an Arrhenius behavior with activation energy of 166.3 KJ.mol-1. The measured hydrogen contamination in a-SiNx ultra thin films is 1.05 at% which is 17 times lower than the corresponding contamination in the films produced by (PECVD) and 3.4 times lower than the contamination in the LPCVD thin films with silane (SiH4) or dichlorosilane (DCS) and Ammonia. The surface topography of the prepared films is smooth and uniform and the thickness varies between 23 and 101 nanometers.

Fluorine implantation effects on Ta2O5 dielectrics on polysilicon treated with post rapid thermal annealing

This paper investigates effects of fluorine implantation with post rapid thermal annealing on electrical characteristics and material properties of tantalum pentoxide (Ta2O5) dielectrics. The electrical behaviors of the dielectrics under various implantation doses were measured. To investigate annealing effects, secondary ion mass spectrometry (SIMS) was used to measure depth profiles of various atoms inside the dielectrics with and without annealing. In addition, atomic force microscopy measurements visualize the surface roughness and material properties of the dielectrics with different implantation doses. The dielectric performance can be significantly improved by an appropriate fluorine implantation dose of 1×1015ions/cm2 with post annealing at 800°C. The improvements in electrical characteristics were caused by the appropriate incorporation of the fluorine atoms presented in SIMS profiles and the removal of the dangling bonds and traps. The Ta2O5 dielectric incorporated with appropriate fluorine implantation and annealing treatments shows great promise for future generation of memory applications.