Al2O3 Interface Research Articles

Phase composition and the structure of (1–x)KNO3 + xAl2O3 nanocomposites by X-ray diffraction

The phase composition and the structural properties of potassium nitrate KNO3 and its heterogeneous composites with nanometer-sized powder of aluminum oxide Al2O3 have been studied by X-ray diffraction at various concentrations of an Al2O3 nanopowder. It is found that, in the (1–x)KNO3 + xAl2O3 nanocomposites, additional high-temperature rhombohedral phase of potassium nitrate (phase III) with lattice parameters a = 5.4644 A and c = 9.0842 A. With increasing concentration of Al2O3 nanopowder, the content of the main potassium nitrate phase (phase II) is found to significantly decrease, and the relative fraction of the phase III in the total content of the nitrate in the composite composition increases. This phase is assumed to be “frozen” in the nanocomposite at the KNO3–Al2O3 interface. The estimated size of KNO3 crystallites in the phase III is more than 20 nm.

Tailoring interfacial bonding states of highly thermal performance diamond/Al composites: Spark plasma sintering vs. vacuum hot pressing

Interfacial configurations of the diamond/Al composites fabricated by vacuum hot pressing (VHP) and spark plasma sintering (SPS) have been investigated to evaluate feasibility of both techniques for tailoring interfacial bonding states, namely non-bonded, diffusion-bonded, partially and fully reaction-bonded interfaces. Multiscale interfacial characterization reveals that the unique diffusion-bonded interface at the micrometer scale, being very favorable for enhancing global thermal conductivity (TC), has been achieved by conventional VHP technique due to its large processing window and homogenous thermal field. Comparatively, micrometer-scale and, even macroscopic (radial and axial) thermal gradients can be inevitably generated during the SPS process in rapid heating-cooling mode. As a result, the mixed interfacial bonding states have always been introduced in the SPSed samples which reduce the effectiveness of TC enhancement. The formation mechanisms of nanoscale interfacial Al2O3 and Al4C3 at the diamond/Al interface are also discussed.

Oxidizing Species Dependence of the Interface Reaction during Atomic-Layer-Deposition Process and Post-Deposition-Anneal

Introduction Al2O3 film is an attractive gate dielectric material for the power devices [1] and metal-insulator-metal capacitors [2]. For Al2O3 deposition, the atomic layer deposition (ALD) is one of the most promising methods [3]. It is considered that the oxidation is one of the important processes in ALD. In the case of using radical oxidation in ALD, it is suggested by XPS evaluation that the oxidizing reaction is occurred at the Al2O3/Si interface during ALD [4]. In the former study, H2O oxidation at stage temperature of 75 °C was shown to be effective because of not oxidizing Si [4]. However the oxidation ability of H2O becomes low at such low temperature. Therefore, it is required to introduce the post-deposition-annealing (PDA) without oxidizing the interface to improve Al2O3 film quality [4, 5]. In this paper, the characteristics of Al2O3/Si interface formed during ALD and PDA are evaluated by MIS capacitor, and its interface structure was also observed by Rutherford backscattering spectroscopy (RBS) for clarifying the mechanism of its degradation. Experiment MIS capacitors were fabricated on Cz-n Si(100) wafers (8-12 ohm cm). At first, the native oxide on Si surface was removed by diluted HF (0.5%), and after that Al2O3 films (20 nm) were deposited on Si by ALD [4]. Finally, Al-electrodes were formed by the evaporation. The Al2O3 films were prepared with and without PDA. Here, PDA-I and PDA-II were carried out by O2 annealing at 400 oC [5] and Ar/O2 plasma oxidation [6], respectively. For RBS measurement, Co(10 nm)/SiN(5 nm)/Si(100)-substrate were used. SiN was formed by low-pressure thermal CVD at 725 oC on Si substrate, and after that Co was formed by sputtering. Here, Co was used because it is easy to detect the oxidizing reaction at Al2O3/Co interface. Al2O3 films were deposited on Co by 11-cycles-ALD. Here, by 11-cycles-ALD, Al2O3film (3 nm) was deposited on Si. Results and Discussion Figure 1 shows the capacitance-voltage (C-V) curves of MIS capacitors. Four samples for each were measured. In the case of Al2O3 without PDA, flat band voltage (Vfb) is negative value such as around -2.0 V. It is suggested that the positive charges (1.87×1012 cm-2 ~ 2.53×1012 cm-2) exist in Al2O3 film. After PDA-I, Vfb becomes almost same value such as 0.1 V and the negative charges (1.12×1012 cm-2 ~ 1.17×1012 cm-2) exist in Al2O3 film. In addition, Vfb variability drastically decreases. It is considered that O2 annealing at 400 oC is very effective to improve Al2O3 film quality [5]. On the other hand, after PDA-II, Vfb drastically shifts to the positive direction by the negative charges (2.96×1012 cm-2 ~ 8.61×1012 cm-2) and its variability is large. Moreover the slope of C-V curve with PDA-II is smaller than that without PDA because of increasing the interface trap. As a result, it is considered that the interfacial quality became poor by Ar/O2plasma oxidation in this experiment. Figure 2 shows the energy spectra of 450 keV He+ ions backscattered from Al2O3/Co/SiN/Si. Al2O3films without PDA, with PDA-II 20sec, 60sec and 300sec were measured. Several observed peaks indicate the energy of He ions scattered by Co, Al, Si, O and N atoms, respectively. Figure 3 (a)-(c) show the narrow spectra related to O, Al and Co, respectively. Especially, in the case of PDA-II 300 sec, each spectrum in fig. 3(a)-(c) spreads more widely. It is suggested that Al and Co interdiffuse at the interfacial layer during PDA-II 300sec. As a result, it is suggested that the intermediate oxide states consisting of Al-Co-O are formed. Conclusion We investigated the influence of PDA to the Al2O3 interface. O2 annealing at 400 oC is very effective for improving the Al2O3 film quality. However, by Ar/O2 plasma oxidation, it is considered that Al and Co interdiffuse at the interface. It is expected that a similar phenomenon is also caused with Al2O3/Si interface, then it is considered that the intermediate oxide states consisting of Al-Si-O cause the electrical characteristic degradation such as increase of fixed charge, interface trap and variability. Acknowledgments This work was carried out at fluctuation free facility of New Industry Creation Hatchery Center, Tohoku University. Reference [1] P.D. Ye et al., Appl. Phys. Lett., 86(2005) 063501 [2] A. Farcy et al., Microelectronic Eng., 85(2008) 1940-1946 [3] R. L. Puurunen, J. Appl. Phys. 97(2005) 121301 [4] H. Sugita, et al., ECS Trans, 66(2015) 305-314 [5] Y. Koda, et al., ECS Trans., to be published at 229thECS meeting [6] K. Sekine, et al., IEEE TRANS. ON ELECTRON DEVICE, 48 (8) (2001) 1550 Figure 1

Enhancing the thermoelectric properties of super-lattice Al2O3/ZnO atomic film via interface confinement

Aluminum oxide (Al2O3)/zinc oxide (ZnO) thin films deposited via atomic layer deposition (ALD) are demonstrated to enhance their thermoelectric properties by manipulating them with a nano-thick Al2O3 interface. The overall superlattice structure is tuned by varying the ZnO ALD sequence and the Al2O3 ALD sequence while maintaining the same composition. An aluminum-doped zinc oxide (AZO) thin film is deposited at 250°C, and the Al2O3 thickness in the superlattice is gradually increased from 0.13nm to 1.23nm. The total film composition is fixed at 2% AZO. We observe that an efficient superlattice structure is made with a specific Al2O3 thickness. The thermal conductivity is significantly decreased from 0.57W/mK to 0.26W/mK as the thickness of the Al2O3 layer is increased. Additionally, the absolute Seebeck coefficient is increased from 14μV/K to 65μV/K. This may be caused by the interface confinement effect and interface scattering between the ZnO layer and the Al2O3 layer. The figure of merit ZT value is 0.14 for the most efficient structure.

Investigation of new stacking surface passivation structures with interfacial tuning layers on p-type crystalline silicon

We fabricated a Y2O3–ZrO2 film (YZO) on Al2O3 to achieve the field effect passivation with high negative fixed charge densities on p-type Si. The surface recombination velocity was improved down to 30 cm/s after annealing at 400 °C. This improvement can be attributed to the effective fixed charge enhancement while the interface state densities were kept almost constant. A high thermal tolerance of over 600 °C upon inserting a 2-nm-thick ZrO2 layer between the YZO and Al2O3 interface was confirmed. This result showed that the ZrO2 layer acts as a protective barrier to prevent Al and Y interdiffusions. Annealing at a higher temperature of 800 °C resulted in interface degradation and YZO crystallization, which led to the deterioration of the passivation properties.

Al2O3-TiO2 Nanolaminates for Conductive Silicon Surface Passivation

Al2O3-TiO2 nanolaminates are very attractive candidates for future conductive passivation layers because they are purely based on dielectric materials, which allow a simple integration in the state-of-the-art manufacturing process. In this study, Al2O3-TiO2 double and multilayers are grown by atomic layer deposition and systematically investigated. The nanolaminates feature good silicon surface passivation and moderate electrical conductivity. The best performance is found for a double-layer stack consisting of a 5 nm Al2O3 interface layer and a 15 nm TiO2 capping layer after postdeposition annealing in N2 or forming gas. With this stack, a surface recombination velocity of 15 cm/s and a contact resistance of 20 Ω·cm2 are achieved. In Al2O3 -TiO2 nanolaminates, the electrical transport is strongly influenced by the interaction of TiO2 and Al2O3 during layer growth. Raman measurements reveal that high conductivity correlates with a phase transition of TiO2 from amorphous to anatase.

Preferred orientation relationships at the Cu/α−Al2O3 interface: Identification and theoretical explanation

Electron backscatter diffraction studies of copper matrix composites reinforced with sapphire particles and of Cu/α−Al2O3 heterostructures obtained by the pulsed laser deposition reveal a series of misorientations with high frequencies. Two of identified orientation relationships are well known in the literature and are treated as basic ones. The other misorientations are revealed for the first time. They differ from the basic ones by small Cu crystal rotations. According to the theoretical analysis, such a behavior enables a significant reduction of the interface energy. The manufacture conditions of composites limit the possibility of Cu crystal rotations. Therefore, one of the most energetically favorable orientation relationships (−4 4 3)[1 1 0]Cu‖(0 0 0 1)[0 1 −1 0] α−Al2O3 appears with a lower frequency. The obtained results indicate the necessity of the change in present manufacture methods. The appropriately selected conditions would enable formation of composites with stronger bondings at interphase boundaries.

Nanocomposites of few-layer graphene oxide and alumina by density functional theory calculations

The atomistic and electronic structure and oxygen stoichiometry of nanocomposites between alumina and graphene oxide were investigated by density functional theory calculations. The nanocomposite was described as interfaces between α-Al2O3 (0001) surfaces and graphene oxide; the latter was defined with oxygen bound as epoxy groups and a C:O atomic ratio of 4:1. The optimized composite structure with 1–3 layers of graphene oxide in between Al2O3 contains bridging AlOC bonds at the interface. Reduction of the composite was investigated by removal of oxygen from the interface AlOC bonds, within the graphene oxide layers and in Al2O3. It was found that removal of oxygen within the graphene oxide layers is essentially independent of the Al2O3 interface, i.e., the same as in pure graphene oxide. Oxygen was, however, more strongly bound in the interface AlOC bonds by 0.80eV, and reduction of graphene oxide to graphene is accordingly preferred within the graphene oxide layers rather than at the oxide interface.

Investigations on Lithium Carbonate-alumina Composite Solid Electrolyte: Morphology and Related Conductivity

Composite solid electrolytes in the system (1-x)Li2CO3-xAl2O3 with x = 0.1 – 0.6 mole were prepared via sol-gel technique. The morphology and conductivity of the composite were investigated. Obtained materials were analysed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, Fourier transform infrared spectroscopy and chemical constituents were confirmed by energy dispersive X-ray. The ionic conductivity was measured using AC impedance spectroscopy. SEM studies of cross-section morphology clearly showed lithium carbonate crystals became radial – fluffy shaped particularly at x = 0.1 and 0.6. Morphological analysis showed homogeneous distribution between Li2CO3 and Al2O3 particles resulted in formation of amorphous phase of Li2CO3 at Li2CO3 - Al2O3 interface. Traces of α-LiAlO2, γ-LiAlO2 and LiAl5O8 were observed at x = 0.1, 0.2 and x = 0.4. Impedance spectroscopy studies showed that the conductivity is maximal at x = 0.2 and 0.4 - 0.5 with a value equal to ~10-3 Scm-1 with temperatures ranging from 130 - 180 oC.

Charge optimized many-body (COMB) potential for dynamical simulation of Ni–Al phases

An interatomic potential for the Ni–Al system is presented within the third-generation charge optimized many-body (COMB3) formalism. The potential has been optimized for Ni3Al, or the γ′ phase in Ni-based superalloys. The formation energies predicted for other Ni–Al phases are in reasonable agreement with first-principles results. The potential further predicts good mechanical properties for Ni3Al, which includes the values of the complex stacking fault (CSF) and the anti-phase boundary (APB) energies for the (1 1 1) and (1 0 0) planes. It is also used to investigate dislocation propagation across the Ni3Al (1 1 0)–Ni (1 1 0) interface, and the results are consistent with simulation results reported in the literature. The potential is further used in combination with a recent COMB3 potential for Al2O3 to investigate the Ni3Al (1 1 1)–Al2O3 (0 0 01) interface, which has not been modeled previously at the classical atomistic level due to the lack of a reactive potential to describe both Ni3Al and Al2O3 as well as interactions between them. The calculated work of adhesion for this interface is predicted to be 1.85 J m−2, which is in agreement with available experimental data. The predicted interlayer distance is further consistent with the available first-principles results for Ni (1 1 1)–Al2O3 (0 0 0 1).

Charge optimized many-body (COMB) potential for Al2O3 materials, interfaces, and nanostructures

This work presents the development and applications of a new empirical, variable charge potential for Al2O3 systems within the charge optimized many-body (COMB) potential framework. The potential can describe the fundamental physical properties of Al2O3, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of α-Al2O3 comparable to that obtained from experiments and first-principles calculations. The potential is further employed in classical molecular dynamics (MD) simulations to validate and predict the properties of the Al (1 1 1)–Al2O3 (0 0 0 1) interface, tensile properties of Al nanowires, Al2O3 nanowires, Al2O3-covered Al nanowires, and defective Al2O3 nanowires. The results demonstrate that the potential is well-suited to model heterogeneous material systems involving Al and Al2O3. Most importantly, the parameters can be seamlessly coupled with COMB3 parameters for other materials to enable MD simulations of a wide range of heterogeneous material systems.

(Invited) Gold-Induced Low-Temperature (

I NTRODUCTION Low-temperature (≤300oC) formation of quasi-single crystal SiGe, i.e., orientation-controlled large-grain crystal (≥10 μm) SiGe, on insulator is desired for realization of advanced flexible electronics, where high-speed transistors and high-efficiency optical devices are integrated on flexible plastics substrates (softening temperature: ~350°C). This is because SiGe provides higher carrier mobility and superior optical properties compared with Si. Recently, we developed gold-induced layer-exchange crystallization (GIC) using a-Ge/Au stacked structures.[1-3] This enabled selective formation of (100)- or (111)-oriented large-grain Ge (≥20 μm) through controlling nucleation during GIC by using anisotropic surface energy on substrates.[1] We have developed this technique onto plastic and realized orientation-controlled large-grain crystals on flexible plastic substrates with low concentration holes (~2×1017 cm-3), which enables high carrier mobility (~160 cm2/Vs).[2,3] However, reports of orientation-controlled growth by GIC are limited to pure Ge crystals so far. In the present study the GIC technique is developed to SiGe. Consequently, quasi-single crystal SiGe is achieved on insulating substrates at low temperatures (~300oC). EXPERIMENTAL The sample structure and experimental procedure are schematically shown in Fig. 1. In the experiment, fused-quartz chips were employed as substrates. On the substrates, a-SiGe (Ge concentration: 0-100%, thickness: 100 nm) /Au (thickness: 100 nm) stacked structures were formed. Here, amorphous Al2O3 interface-layers (thickness: 4-7 nm) were introduced between a-SiGe and Au layers as diffusion barrier to make interface-nucleation dominate over random bulk-nucleation in Au layers.[1] These samples were annealed at 250-300oC to induce crystallization. The grown layers were analyzed by Nomarski optical microscopy, electron backscattering diffraction (EBSD), and micro-probe Raman scattering spectroscopy (excitation-laser spot-diameter: ~1 μm). The Nomarski optical microscopy observations were carried out from the back sides of the samples through the transparent quartz substrates to characterize the bottom layers. RESULTS AND DISCUSSION The growth features of samples with various Ge fractions and Al2O3 interface layer thicknesses were investigated by Nomarski optical microscopy observations after annealing at 250°C for 50 h. Typical Nomarski micrographs of samples with Ge concentrations of 50% and 100% are shown in Figs. 2(a)-2(b) and 2(c)-2(d), respectively. In these micrographs, dark and bright contrast regions are observed. Micro-probe Raman measurements revealed that the dark regions dominantly observed in Figs. 2(a), 2(c), and 2(d) are crystal, while bright regions dominant in Fig. 2(b) are not crystal. These results indicate that layer exchange crystallization occurs for the samples shown in Figs. 2(a), 2(c), and 2(d), while it does not proceed for the sample shown in Fig. 2(b). EBSD measurements revealed that the grown layers for Fig. 2(d) consisted of (111)-oriented large-grains (≥10 μm). On the other hand, grown layers for Figs. 2(a) and 2(c) consisted of randomly-oriented small-grains (1-3 μm). Here, we examined the Nomarski micrographs of a no-grown Si0.5Ge0.5 sample (diffusion barrier thickness: 5 nm), shown in Fig. 2(b). It is found that nuclei are formed for the Si0.5Ge0.5 sample, though lateral growth does not proceed from the nuclei. From this finding, it is speculated that for the Si0.5Ge0.5 sample (diffusion barrier thickness: 5 nm), (111)-oriented nucleation occurs at Au/SiO2 interface. However, lateral growth does not proceed even after long time annealing. Thus, layer-exchange is not observed. It is suggested that lateral crystallization in GIC is retarded by Si introduction. This consideration triggers an idea that (111)-oriented large-grains can be obtained even for the Si0.5Ge0.5 sample by generating lateral growth from nuclei. Thus, we examine annealing at a higher temperature of 300°C. A Nomarski micrograph of Si0.5Ge0.5 sample (diffusion barrier thickness: 5 nm) after annealing at 300°C for 50 h is shown in Fig. 3(a). Micro-probe Raman measurements reveled layer-exchange crystallization in the entire area. The crystal structures of the grown layer are examined by EBSD measurements. The result is shown in Fig. 3(b), which reveals (111)-oriented large-grains (≥10 μm). As a result, quasi-single crystal SiGe is realized on insulator. This technique will facilitate realization of advanced flexible electronics. ACKNOWLEDGEMENT Part of this work was supported by JSPS Core-to-Core Program, A. Advanced Research Networks.

Improved Stability of Pd/Al2O3 Prepared from Palladium Nanoparticles Protected with Carbosilane Dendrons in the Dimethyl Ether Steam Reforming Reaction

AbstractThe dimethyl ether steam reforming reaction to generate hydrogen was tested over 1 wt % Pd/Al2O3 catalysts prepared from different precursors. The conventional catalyst prepared by incipient wetness impregnation from palladium nitrate underwent strong deactivation under reforming conditions at 823 K because of metal sintering and carbon deposition. The same occurred over the catalyst prepared from preformed Pd nanoparticles protected with dodecanethiol. In contrast, catalysts prepared from Pd nanoparticles protected with carbosilane dendrons showed enhanced stability and good performance for the production of hydrogen. This was because of the formation of SiO2 at the Pd–Al2O3 interface that acted as a pinning center and prevented Pd migration under the reaction conditions as well as the accumulation of carbon.

2D AlN crystal phase formation on (0001) Al2O3 surface by ammonia MBE

AbstractKinetics of a two‐dimensional (2D) AlN layer formation on (0001) sapphire (Al2O3) surface during nitridation at different ammonia fluxes is investigated by reflection high energy electron diffraction (RHEED). The process on the surface is described in the framework of a chemical reactions kinetic model including interaction between partially reduced aluminum oxide species (AlO) and chemisorbed NH2 particles. The experimentally determined AlN formation rates as functions of both the temperature and the ammonia pressure are successfully described by a simple set of kinetic equations. Calculated maximum rate of the process well agrees with the experimental values. Precision measurement of 2D AlN lattice parameters during the nitridation process detects the value of 3.01 Å. This value coincides exactly with a characteristic structure parameter of the oxygen‐deficient Al2O3 surface. We assume this coincidence results from flexibility of the 2D AlN monolayer which provides minimization of elastic stresses at the AlN/(0001)Al2O3 interface. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectra of surface plasmon polariton enhanced electroluminescence from electroformed Al-Al2O3-Ag diodes

Narrow band-pass filters have been used to measure the spectral distribution of electroluminescent photons with energies between 1.8 eV and 3.0 eV from electroformed Al-Al2O3-Ag diodes with anodic Al2O3 thicknesses between 12 nm and 18 nm. Electroforming of metal-insulator-metal (MIM) diodes is a non-destructive dielectric breakdown that results in a conducting channel in the insulator and changes the initial high resistance of the MIM diode to a low resistance state. It is a critical step in the development of resistive-switching memories that utilize MIM diodes as the active element. Electroforming of Al-Al2O3-Ag diodes in vacuum results in voltage-controlled negative resistance (VCNR) in the current-voltage (I-V) characteristics. Electroluminescence (EL) and electron emission into vacuum (EM) develop simultaneously with the current increase that results in VCNR in the I-V characteristics. EL is due to recombination of electrons injected at the Al-Al2O3 interface with radiative defect centers in Al2O3. Measurements of EL photons between 1.8 eV and 3.0 eV using a wide band-pass filter showed that EL intensity is exponentially dependent on Al2O3 thickness for Al-Al2O3-Ag diodes between 12 nm and 20 nm thick. Enhanced El intensity in the thinnest diodes is attributed to an increase in the spontaneous emission rate of recombination centers due to high electromagnetic fields generated in Al2O3 when EL photons interact with electrons in Ag or Al to form surface plasmon polaritons at the Al2O3-Ag or Al2O3-Al interface. El intensity is a maximum at 2.0–2.2 eV for Al-Al2O3-Ag diodes with Al2O3 thicknesses between 12 nm and 18 nm. EL in diodes with 12 nm or 14 nm of Al2O3 is enhanced by factors of 8–10 over EL from a diode with 18 nm of Al2O3. The extent of EL enhancement in the thinnest diodes can vary significantly between samples. A narrow band of recombination centers was found in one Al-Al2O3-Ag diode with 12 nm of Al2O3; it had EL intensity 100 times greater at 2.15 eV than the diode with 18 nm of Al2O3. EL intensity for photons with energies greater than 2.6 eV is nearly the same for all diodes.

First-principles study of the bonding characteristics of TiAl(111)/Al2O3(0001) interface

First principles calculations were carried out for α-Al2O3(0001) surface and γ-TiAl(111)/α-Al2O3(0001) interface to study the adhesion properties of the interface and to clarify the mechanisms that govern the adhesion of TiAl and its oxidation product Al2O3. Two type interface models, the TiAl(111) with Al- and O-terminated α-Al2O3(0001) surfaces denoted as T(A1)-type and T(OT)-type interface, respectively, were considered. The Universal Binding Energy Relation (UBER) was used to determine the separation between TiAl and Al2O3 and the work of adhesion of the γ-TiAl(111)/α-Al2O3(0001) interface. Optimization was then performed for all interfaces considered here using the separation obtained with UBER. The lowest work of adhesion is −1.05 J/m2 for the T(A1)-type interface and is −4.04 J/m2 for the T(OT)-type interface. There exists competition between O–Ti and O–Al (on the TiAl side) interactions; however O–Al bond is stronger than O–Ti bond because the main body of the Al valences is involved in the hybriding with O p electrons, while only part of the Ti d valence is involved in the O–Ti bonding. Thus the O–Al interaction dominates the adhesion between TiAl(111) and Al2O3(0001) surfaces, and it can be inferred that an Al-rich TiAl surface will favor the adhesion between TiAl/Al2O3.

UV/O3 assisted InP/Al2O3–Al2O3/Si low temperature die to wafer bonding

Direct bonding of InP dies to Si wafer at low temperature utilizing Al2O3 high-κ dielectric as the interfacial material for homogeneous bonding is reported. The bonding technique is assisted with a UV/Ozone exposure for surface activation and the activation time is optimized for the various intermediate layer thicknesses (5, 10, 20 nm). After the pre-bonding stage, annealing is carried out at 300 °C for 3 h. A bonding interface with minimal interfacial voids is reported for low intermediate layer thickness. The bonding interfaces are examined and a homogeneously bonded interface is shown in the IR images as well as in the FIB micrographs. Additionally a heat transfer simulation is also carried out and the InP/Al2O3–Al2O3/Si bonded structure is shown to closely match the thermal characteristics of a direct bonding approach with no intermediate layer. A high quality bonding interface is revealed along with improved heat dissipation characteristic for Al2O3 interface. Therefore, Al2O3 proves to be an advantageous candidate for its use in potential Si photonic integrated circuits application.

Modulating the interface quality and electrical properties of HfTiO/InGaAs gate stack by atomic-layer-deposition-derived Al₂O₃ passivation layer.

In current work, the effect of the growth cycles of atomic-layer-deposition (ALD) derived ultrathin Al2O3 interfacial passivation layer on the interface chemistry and electrical properties of MOS capacitors based on sputtering-derived HfTiO as gate dielectric on InGaAs substrate. Significant suppression of formation of Ga-O and As-O bond from InGaAs surface after deposition of ALD Al2O3 with growth cycles of 20 has been achieved. X-ray photoelectron spectroscopy (XPS) measurements have confirmed that suppressing the formation of interfacial layer at HfTiO/InGaAs interface can be achieved by introducing the Al2O3 interface passivation layer. Meanwhile, increased conduction band offset and reduced valence band offset have been observed for HfTiO/Al2O3/InGaAs gate stack. Electrical measurements of MOS capacitor with HfTiO/Al2O3/InGaAs gate stacks with dielectric thickness of ∼4 nm indicate improved electrical performance. A low interface-state density of (∼1.9) × 10(12) eV(-1) cm(-2) with low frequency dispersion ( ∼ 3.52%), small border trap density of 2.6 × 10(12) cm(-2), and low leakage current of 1.17 × 10(-5) A/cm(2) at applied gate voltage of 1 V have been obtained. The involved leakage current conduction mechanisms for metal-oxide-semiconductor (MOS) capacitor devices with and without Al2O3 interface control layer also have been discussed in detail.

(Invited) Spatial ALD, Deposition of Al2O3 Films at Throughputs Exceeding 3000 Wafers per Hour

During the last few years various types of ALD films have successfully been introduced in high-volume manufacturing in a number of industries. Particularly in the semiconductor industry the implementation is wide spread (high-k gate stacks, capacitor dielectrics, diffusion barriers, etc.).More recently a specific type of ALD film, Al2O3, was widely researched as a potential surface passivation layer for solar cell surfaces in the PV industry. Thin (< 10nm) Al2O3 films passivate p-type surfaces very effectively. On the one hand intrinsic negative charges in the dielectric film repel charge carriers, while on the other hand hydrogen that is present in the ALD films passivates dangling bonds at the Si/SiO2/ Al2O3 interface. The combination of both effects reduces the charge recombination losses considerably. The overall result is an increase in cell efficiency of 0.5-1% (absolute). Based on extensive testing of these films, it is to be expected that Implementation in PV manufacturing will take place in the near future.There is a large difference in film and process requirements of ALD films applied in the semiconductor and PV industries. Whereas uniformity and defects (particles) are very important in the IC industry this is much less so in PV. Much more important in the PV industry are cost and throughput. Typical numbers for both industries are a Cost of Ownership of 2-10 vs. 0.02-0.05$/wafer, respectively, and 10-50 vs 1500-2500 wfrs/hr..As ALD processes are notoriously slow, ways must be found to increase the throughputs considerably. This is done by either using batch furnaces loaded with 500-1000 wafers per batch, or in-line systems in which wafers are loaded, processed and unloaded in a continuous flow of 0.5-0.8 wafers/s.The latter type of system is based on the so-called spatial ALD process. An example is shown in the figure. In this system (Levitrack) wafers are loaded in a track in which zones with precursors TMA and H2O are spatially separated by zones of inert gas. While floating on a gas cushion, the wafers pass ALD ‘cells’ with fixed sequences of TMA and water, adding a thin layer of Al2O3 with each passage through a cell. The advantages of this approach are several: high throughput, atmospheric processing, no deposition on the inside walls of the track, no moving parts such as valves, pumps, etc.Typical results obtained with this system are: film uniformity 3-4%, life time of solar cell charge carriers > 3ms, efficiency enhancement 0.4-0.8%, CoO ~ 0.04$/wfr.In the paper more details will be provided on the economy of this type of system, as well as on film characteristics and efficiency enhancements realized in a variety of solar cell structures.

Effect of boron concentration on recombination at the p-Si–Al2O3 interface

We examine the surface passivation properties of Al2O3 deposited on boron-doped planar ⟨100⟩ crystalline silicon surfaces as a function of the boron concentration. Both uniformly doped and diffused surfaces are studied, with surface boron concentrations ranging from 9.2 × 1015 to 5.2 × 1019 cm−3. Atmospheric pressure chemical vapor deposition and thermal atomic layer deposition are used to deposit the Al2O3 films. The surface recombination rate of each sample is determined from photoconductance measurements together with the measured dopant profiles via numerical simulation, using the latest physical models. These values are compared with calculations based on the interface properties determined from capacitance–voltage and conductance measurements. It is found that the fundamental surface recombination velocity of electrons, Sn0, which describes the chemical passivation of the interface, is independent of the surface boron concentration Ns for Ns ≤ 3 × 1019 cm−3, and in excellent agreement with values calculated from the interface state density Dit and capture coefficients cn and cp measured on undiffused boron-doped surfaces. We conclude that the physical properties of the Si–Al2O3 interface are independent of the boron dopant concentration over this range.