Post-deposition Annealing Process Research Articles

Interface chemistry and surface morphology evolution study for InAs/Al2O3 stacks upon in situ ultrahigh vacuum annealing

A systematic study of the interfacial chemistry for the HCl pretreated and native oxide InAs(100) samples upon atomic layer deposition (ALD) of Al2O3, and the post deposition annealing (PDA) process has been carried out, using in situ synchrotron radiation photoelectron spectroscopy. The “clean up” effect for the native oxide sample is detected, but it is not observed for the HCl pretreated sample. The out-diffusion and desorption of both In and As oxides have been characterized during the ALD process and the following PDA process. The surface morphology evolution during the PDA process is studied by in situ photo-emission electron microscopy. The bubbles emerged after PDA at 360 °C and grew up at 370 °C. After PDA at 400 °C and at higher temperatures, pits are seen in some areas, and the tear up of the Al2O3 film is seen in other areas with the formation of indium droplets. This study gives insight in the mechanism of elemental diffusion/desorption, which may associate the reliability of III-V semiconductor based devices.

High-sensitivity pH sensor using separative extended-gate field-effect transistors with single-walled carbon-nanotube networks

We fabricate high-sensitivity pH sensors using single-walled carbon-nanotube (SWCNT) network thin-film transistors (TFTs). The sensing and transducer parts of the pH sensor are composed of separative extended-sensing gates (ESGs) with SnO2 ion-sensitive membranes and double-gate structure TFTs with thin SWCNT network channels of ∼1 nm and AlOx top-gate insulators formed by the solution-deposition method. To prevent thermal process-induced damages on the SWCNT channel layer due to the post-deposition annealing process and improve the electrical characteristics of the SWCNT-TFTs, microwave irradiation is applied at low temperatures. As a result, a pH sensitivity of 7.6 V/pH, far beyond the Nernst limit, is obtained owing to the capacitive coupling effect between the top- and bottom-gate insulators of the SWCNT-TFTs. Therefore, double-gate structure SWCNT-TFTs with separated ESGs are expected to be highly beneficial for high-sensitivity disposable biosensor applications.

Structure and Magnetic Properties of Graded (001)-Oriented FePt Films Prepared by Magnetron Sputtering and Rapid Thermal Annealing

L10-FePt/[Fe/Pt]27 multilayer films were prepared on (100)-oriented single-crystal MgO substrates. Structural analysis indicates epitaxial growth of the L10-FePt films during high-temperature deposition. The room-temperature-deposited [Fe/Pt]27 multilayer exhibits the fcc-FePt structure grown epitaxially on the L10-FePt base layer. The degree of chemical order and thereby the anisotropy of the top layer has been controlled by varying the temperature of a post-deposition annealing process. Compared with the as-deposited films, coercivities of the films annealed below 400 ∘C are substantially decreased by introducing the formation of a graded anisotropy in the partially ordered top layer. Coercivities decrease for annealing temperatures that are greater than 400 ∘C due to improved ordering of the top layer.

Fabrication and characterization of n-Si/SiON/metal gate structure for future MOS technology

We present the fabrication and characterization of n-Si/SiON/metal (metal–oxide–semiconductor (MOS)) gate structure with silicon oxynitride (SiON) as insulating layer and different metal films such as Aluminium (Al), Titanium nitride (TiN) and Platinum (Pt) as gate electrode. Cheung’s method has been used to calculate the barrier height (ϕbo) and ideality factor (η) of these three different diodes varying in different metal electrode types. The interface state density (Dit), dielectric constant (k), effective oxide charge (Qeff) and work function (Φm) have also been extracted from the capacitance–voltage (C–V) experimental data. A gradual improvement in various parameters for n-Si/SiON/metal gate stack has been observed after annealing the SiON film under controlled conditions e.g., TiN metal gate electrode shows good electrical characteristics with improved ideality factor (1.7) and barrier height (0.69 eV) over the Al and Pt/Ti gate electrodes due to the modified interface chemistry. The extracted Φm for TiN gate electrode is ~ 5.13 eV which is in good agreement with the previous results reported in literature. The value of Dit reduces, whereas the value of k increases upon post deposition annealing (PDA) for all the metal gate electrodes. An increase in Dit causes an increase in the η for Al and Pt/Ti metal gates as compared to TiN metal gate. The influences of PDA process on the electrical characteristics of n-Si/SiON/metal MOS diodes have also been investigated for as-deposited and annealed MOS diode.

Normally-off Al2O3/GaN MOSFET: Role of border traps on the device transport characteristics

Based on the self-terminating gate recess technique, two different processes featuring gate-recess-first (GF) and ohmic-contact-first (OF) were proposed for E-mode Al2O3/GaN MOSFETs. Increased maximum drain current (Idmax) ∼30% (420 vs 325 mA/mm), field-effect mobility (μFEmax) ∼67% (150 vs 90 cm2/Vs) and reduced on-state resistance (Ron) ∼42% (9.7 vs 16.8 Ω·mm) were observed in the devices fabricated by GF process. Such significant performance difference of GF- and OF-devices resulted from the presence of border traps at Al2O3/GaN interface with a time constant ∼7 × 10−6 s. Experimental results indicated that: (1) the near interface border traps in Al2O3 dielectric significantly affect device channel mobility; (2) a high temperature post-deposition annealing process could effective suppress generation of border traps.

Investigation of Anomalous Hysteresis in MOS Devices With ZrO2Gate Dielectrics

Abnormal capacitance-voltage (CV) behavior is observed in metal-oxide semiconductor devices with zirconium oxide-gate dielectrics using a pulse CV technique. The relative positions of forward and reverse CV traces measured by the pulse technique are opposite those by conventional CV measurement. This unusual phenomenon is inconsistent with charge trapping and de-trapping, but may be mainly attributable to the interface dipoles at the high- ${k}$ /SiOx interface. This anomaly is sensitive to growth temperature as well as the post-deposition annealing process. Lower deposition temperature leads to more interface dipoles. However, after annealing in either nitrogen or forming gas ambient, the relative positions of forward and reverse CV curves measured by the pulse technique are consistent with those obtained by conventional CV measurement.

Interface chemistry study of InSb/Al2O3 stacks upon in situ post deposition annealing by synchrotron radiation photoemission spectroscopy

The thermal stability of InSb/Al2O3 stacks has been systematically studied upon in situ post deposition annealing (PDA) at 300°C and 400°C. Atomic layer deposition (ALD) of Al2O3 (∼3nm) has been grown on the native oxide and the HCl aqueous solution treated InSb (100) at 200°C. The interface chemistry, elemental diffusion as well as elemental desorption are characterized by synchrotron radiation photoemission spectroscopy (SRPES) with the incident photon energy of 750, 600 and 500eV. A Math model has been proposed to calculate the depth profile for In and Sb oxides based on the analysis from different incident energies. Indium atoms have re-oxidized during ALD process, and indium oxide has been observed to diffuse into the Al2O3 film upon PDA at 300°C for the HCl pretreated sample. Indium oxide has desorbed and diffused upon PDA process for the native oxide sample. Sb oxide has been observed to desorb continuously as PDA temperature increases, for all samples. The surface has been torn up upon PDA at 400°C from the morphology characterization.

Low thermal budget annealing technique for high performance amorphous In-Ga-ZnO thin film transistors

In this paper, we investigate a low thermal budget post-deposition-annealing (PDA) process for amorphous In-Ga-ZnO (a-IGZO) oxide semiconductor thin-film-transistors (TFTs). To evaluate the electrical characteristics and reliability of the TFTs after the PDA process, microwave annealing (MWA) and rapid thermal annealing (RTA) methods were applied, and the results were compared with those of the conventional annealing (CTA) method. The a-IGZO TFTs fabricated with as-deposited films exhibited poor electrical characteristics; however, their characteristics were improved by the proposed PDA process. The CTA-treated TFTs had excellent electrical properties and stability, but the CTA method required high temperatures and long processing times. In contrast, the fabricated RTA-treated TFTs benefited from the lower thermal budget due to the short process time; however, they exhibited poor stability. The MWA method uses a low temperature (100 °C) and short annealing time (2 min) because microwaves transfer energy directly to the substrate, and this method effectively removed the defects in the a-IGZO TFTs. Consequently, they had a higher mobility, higher on-off current ratio, lower hysteresis voltage, lower subthreshold swing, and higher interface trap density than TFTs treated with CTA or RTA, and exhibited excellent stability. Based on these results, low thermal budget MWA is a promising technology for use on various substrates in next generation displays.

An Innovative Postdeposition Annealing Approach Producing Centimeter‐Scale In2O3/In2(TeO3)3 Bulk Heterojunction Thin Film for Room‐Temperature Persistent Photoconductivity

Persistent photoconductivity holds great significance to a variety of interesting applications. However, persistent photoconductivity devices based on large‐scale thin films produced by a facile and efficient technology have rarely been achieved so far. In this work, centimeter‐scale In2O3/In2(TeO3)3 bulk heterojunction thin films are prepared via an innovative and convenient two‐step approach, an initial pulsed‐laser deposition followed by a postdeposition annealing process. A prototype optoelectronic device is fabricated and it exhibits pronounced persistent photoconductivity with positive dependence on both the source–drain voltage and incident power density. This device also shows photoresponse to incident light with wavelengths from ultraviolet to red, revealing great potential for practical device applications such as optoelectronic memory and imaging. A physical model in agreement with the observed phenomena is built to qualitatively illustrate the occurrence of the persistent photoconductivity in the bulk heterojunction system. In addition, the facile two‐step approach is further applied to flexible mica substrates and the persistent photoconductivity is maintained upon tens of bending cycles, which not only demonstrates potential for wearable device but also provides tunable and extended focus range for the photoexcitation. These findings provide an innovative and universal scenario for the development of persistent photoconductivity.

As-grown enhancement of spinodal decomposition in spinel cobalt ferrite thin films by Dynamic Aurora pulsed laser deposition

Cobalt ferrite CoxFe3−xO4 thin films with composition within the miscibility gap were grown using Dynamic Aurora pulsed laser deposition. X-ray diffraction patterns reveal as-grown phase separation to Fe-rich and Co-rich phases with no post-deposition annealing. The interconnected surface microstructure of thin film shows that this phase separation occurs through spinodal decomposition enhanced by magnetic-field-induced ion-impingement. The lattice parameter variation of the thin films with the magnetic field indicates that the composition fluctuations can be enhanced further by increasing the magnetic field. Results show that spinodal decomposition enhancement by magnetic-field-induced ion-impingement is independent of the lattice-mismatch-induced strain. This approach can promote spinodal decomposition in any thin film with no post-deposition annealing process.

Bistable Capacitance Performance-Induced Ambipolar Charge Injected Based on Ba0.6Sr0.4TiO3 by an Inlaid Zr–Hf–O Layer for Novel Nonvolatile Memory Application

In this paper, we present a distinguished hysteresis behavior by a few nanometers inlaid Zr–Hf–O (ZHO) layer between the Ba0.6Sr0.4TiO3(BST) film and the metal Pt electrode. The capacitance–voltage curve shows an insignificant change in the range of 0.3–1 MHz. The excellent retention property showing the difference of high state and low state is estimated as about 23.0% and 12.5% after one year and ten years, which might be caused by the deeper trap in an interdiffusion layer. The possible mechanism is proposed that the BST/ZHO interface exists as an interdiffusion, which could create additional defects and ambipolar charge injection causing the hysteresis behavior due to a postdeposition annealing process. The device can be employed as a promising candidate for applying in novel nonvolatile memory device.

Analysis of parasitic losses due to intermediate reflectors in silicon tandem solar cells

Intermediate reflecting layers (IRL) in multijunction solar cells improve the spectral light management and thereby increase the overall energy conversion efficiency. Nevertheless, the incorporation of an IRL can increase parasitic losses in the device mainly by three effects: (i) parasitic absorption in the IRL, (ii) increased parasitic absorption in the transparent front electrode due to the light reflection at the IRL, and (iii) reflection losses due to insufficient absorption of light in the top solar cell that is reflected at the IRL. Here, we investigate the different contributions of these three loss mechanisms on the external quantum efficiency and short-circuit current density by a combination of experiment and optical simulation. The parasitic absorption in the transparent front electrode is varied experimentally by a post-deposition laser annealing process on the front electrode layer. The experimental work is supplemented by rigorous optical simulations which allow to extract and vary the parasitic absorption losses in the IRL by a variation of the optical material properties. Furthermore, the cell reflectance is studied by experiment and simulation for different layer configurations. Our comparative study reveals that the dominating parasitic losses are absorption within the intermediate reflector and reflection out of the solar cell. From this study, we show one possible solution for advanced light management in tandem solar cells with intermediate reflectors.

Structure and Electrical Properties of NdBa2Cu3O y Thin Films by Laser Ablation at Low Oxygen Partial Pressure

A deposition process for NdBa2Cu3O y thin films by laser ablation at decreased deposition temperature was developed using substitution of oxygen with argon in the chamber during deposition. A low deposition rate is the crucial factor to obtain high-quality NBCO films. The Nd/Ba cation disorder in the film can be suppressed by an increase of the deposition temperature or by a decrease of the oxygen partial pressure during deposition. The presence of Nd/Ba disorder during deposition stimulates the introduction of oxygen into the growing film. A simple model is proposed for estimation of oxygen contents in the film using structural parameters measured with XRD techniques. Studies of the post-deposition annealing process showed ordering of the Nd/Ba sub-lattice and intense oxygen in- and out-diffusion. The temperature of the post-deposition annealing step should be chosen low enough (∼400 °C) to avoid oxygen diffusion out of the NBCO film.

Reduced Bimolecular Recombination in Blade-Coated, High-Efficiency, Small-Molecule Solar Cells.

To realize the full promise of solution deposited photovoltaic devices requires processes compatible with high-speed manufacturing. We report the performance and morphology of blade-coated bulk heterojunction devices based on the small molecule donor p-DTS(FBTTh2)2 when treated with a post-deposition solvent vapor annealing (SVA) process. SVA with tetrahydrofuran improves the device performance of blade-coated films more than solvent additive processing (SA) with 1,8-diiodooctane. In spin-coating, SA and SVA achieve similar device performance. Our optimized, blade coated, SVA devices achieve power conversion efficiencies over 8 % and maintain high efficiencies in films up to ≈ 250 nm thickness, providing valuable resilience to small process variations in high-speed manufacturing. Using impedance spectroscopy, we show that this advantageous behavior originates from highly suppressed bimolecular recombination in the SVA-treated films. Electron microscopy and grazing-incidence X-ray scattering experiments show that SA and SVA both produce highly crystalline donor domains, but SVA films have a radically smaller domain size compared to SA films. We attribute the different behavior to variations in initial nucleation density and relative ability of SVA and SA to control subsequent crystal growth.

Large-area MoS2 deposition via MOVPE

The direct deposition of the 2D transition metal dichalcogenide MoS2 via metal-organic vapour phase epitaxy (MOVPE) is investigated. Growth is performed in a commercial AIXTRON horizontal hot-wall reactor. Molybdenum hexacarbonyl (MCO) and Di-tert-butyl sulfide (DTBS) are used as metal-organic precursors for molybdenum and sulfur, respectively. The successful deposition of MoS2 is demonstrated via Raman spectroscopy on various substrates such as sapphire and Si as well as AlN and GaN templates. The influence of growth time on the evolution of layer morphology is investigated. Variation of carrier gas reveals that a pure nitrogen growth atmosphere and a growth temperature of 750°C improve layer quality. Additionally, a post-deposition annealing process of the grown samples is examined. It is shown that annealing in a pure nitrogen atmosphere at temperatures between 650°C and 750°C strongly increases the Raman intensities.

Near-Infrared Optical Extinction of Indium Tin Oxide Structures Prepared by Nanosphere Lithography

Indium tin oxide (ITO) has been the most widely studied conducting metal oxide and serves as the best candidate for proof-of-concept experiments in the field of surface plasmon resonance and studies of electric field confinement and manipulation. ITO is chemically stable and relatively easy to sputter. In this report, arrays of ITO nanostructures were produced using nanosphere lithography, which was originally developed for plasmonic applications involving noble metals. However, the experiments presented here show that patterned ITO with similar size and shape to noble metals has an observed extinction that corresponds to the epsilon-near-zero mode. The carrier density of ITO nanostructure can be controlled by the postdeposition annealing process. Thus, one can prove that the optical signals on the surface are those of the ITO nanostructure by reversible on/off switching of the capacitive plasmon resonance by annealing the surfaces successively in forming gas (N2/H2) and in air. Thus, using conducting metal oxides confident of the electric field is possible not only along the z-axis perpendicular to the thin film but within the plane of the film as well.

Modulation of interfacial and electrical properties of ALD-derived HfAlO/Al2O3/Si gate stack by annealing temperature

In current work, effects of rapid thermal annealing on the interface chemical bonding states, band alignment, and electrical properties of atomic-layer-deposition-derived HfAlO/Al2O3 gate stack on Si substrates have been studied by X-ray photoemission spectroscopy (XPS), UV–Vis transmission spectroscopy, and electrical measurements. XPS analyses have shown that HfAlO alloy and mixed silicate (Hf-Al-O-Si) increase after post-deposition annealing process. By means of UV–Vis transmission spectroscopy measurements, reduction in band gap for 400oC-annealed sample has been observed. Accordingly, reduction in the valence band offset and increase in the conduction band offset have been detected for HfAlO/Al2O3/Si gate stack annealed at 400 °C. Various current conduction mechanisms, such as Poole-Frenkel emission, Fowler-Nordheim (FN) tunneling, and space-charge-limited (SCL) conduction, have been analyzed. Detailed electrical measurements reveal that current conduct mechanisms is SCL conduction at lower field region and FN tunneling and SCL conduction are dominant conduction mechanism at higher field region.

Large-area, continuous and high electrical performances of bilayer to few layers MoS2 fabricated by RF sputtering via post-deposition annealing method.

We report a simple and mass-scalable approach for thin MoS2 films via RF sputtering combined with the post-deposition annealing process. We have prepared as-sputtered film using a MoS2 target in the sputtering system. The as-sputtered film was subjected to post-deposition annealing to improve crystalline quality at 700 °C in a sulfur and argon environment. The analysis confirmed the growth of continuous bilayer to few-layer MoS2 film. The mobility value of ~29 cm2/Vs and current on/off ratio on the order of ~104 were obtained for bilayer MoS2. The mobility increased up to ~173–181 cm2/Vs, respectively, for few-layer MoS2. The mobility of our bilayer MoS2 FETs is larger than any previously reported values of single to bilayer MoS2 grown on SiO2/Si substrate with a SiO2 gate oxide. Moreover, our few-layer MoS2 FETs exhibited the highest mobility value ever reported for any MoS2 FETs with a SiO2 gate oxide. It is presumed that the high mobility behavior of our film could be attributed to low charged impurities of our film and dielectric screening effect by an interfacial MoOxSiy layer. The combined preparation route of RF sputtering and post-deposition annealing process opens up the novel possibility of mass and batch production of MoS2 film.

Single-crystal-like GdNdOx thin films on silicon substrates by magnetron sputtering and high-temperature annealing for crystal seed layer application

Single-crystal-like rare earth oxide thin films on silicon (Si) substrates were fabricated by magnetron sputtering and high-temperature annealing processes. A 30-nm-thick high-quality GdNdOx (GNO) film was deposited using a high-temperature sputtering process at 500°C. A Gd2O3 and Nd2O3 mixture was used as the sputtering target, in which the proportions of Gd2O3 and Nd2O3 were controlled to make the GNO’s lattice parameter match that of the Si substrate. To further improve the quality of the GNO film, a post-deposition annealing process was performed at a temperature of 1000°C. The GNO films exhibited a strong preferred orientation on the Si substrate. In addition, an Al/GNO/Si capacitor was fabricated to evaluate the dielectric constant and leakage current of the GNO films. It was determined that the single-crystal-like GNO films on the Si substrates have potential for use as an insulator layer for semiconductor-on-insulator and semiconductor/insulator multilayer applications.

Breakdown field enhancement of Si-based MOS capacitor by post-deposition annealing of the reactive sputtered ZrOxNy gate oxide

Zirconium oxynitride (ZrOxNy) thin films were deposited on silicon (100) substrates by radio frequency-reactive magnetron sputtering in an argon–oxygen–nitrogen atmosphere. Post-deposition annealing (PDA) process was performed in argon ambient at various annealing temperatures (500, 600, 700 and 800 °C) for 15 min. Metal–oxide–semiconductor capacitors were then fabricated with aluminum as the gate electrode. The effects of PDA process on the thin film’s structural and electrical properties of the samples were investigated. The structural properties of the deposited films have been evaluated by atomic force microscopy, Fourier transform infrared spectroscopy and Raman spectroscopy. On the other hand, the electrical characterization of the film was conducted by current–voltage analysis. The Raman results revealed that (600–800 °C) annealed samples comprised of crystalline multiphase films (t-ZrO2, fcc-ZrN and bcc γ-Zr2ON2). Interfacial layer consisted of Zr–Si–O, Si–O–N and Si–O phase was formed for all investigated samples, and interfacial layer growth was suppressed when annealed at lower temperatures (500 °C). Electrical result revealed that the sample annealed at a relatively low temperature of 500 °C has demonstrated the highest breakdown field which was attributed to the low surface roughness, the low interface trap and the highly amorphous multiphase film.