Post-deposition Annealing In O2 Research Articles

Experimental investigation of dipole formation and modulation at Hf0.5Zr0.5O2/SiO2 interface

HfO2-doped ferroelectric field-effect transistors have been extensively studied since the discovery of ferroelectricity in HfO2. A metal/ferroelectric/insulator/semiconductor structure is widely used in FeFETs. The dipole at the doped-HfO2/SiO2 interface is not well understood, though it plays an important role in the flat voltage shift and band alignment which strongly affects charge trapping. This study investigates the band alignment and dipole distribution at the Hf0.5Zr0.5O2 /SiO2 interface using x-ray photoelectron spectroscopy. The band bending of the Hf0.5Zr0.5O2 /SiO2/Si structure is found to vary with Hf0.5Zr0.5O2 layer thickness. The valence band offset (VBO) at the Hf0.5Zr0.5O2 /SiO2 interface decreases with increasing Hf0.5Zr0.5O2 thickness. It is confirmed that the dipole contributes to the dependence of band bending and VBO on Hf0.5Zr0.5O2 thickness. Dipole formation is caused by the charge neutral level mismatch between Hf0.5Zr0.5O2 and the SiO2/Si stack, which induces electron transfer and band bending. O2 post deposition annealing (PDA) can modulate the dipole distribution and generate a larger dipole at the Hf0.5Zr0.5O2 /SiO2 interface than that of the sample not subjected PDA.

Charge trapping effects in nonvolatile memory cells with HfO2/Al2O3 nanolaminated trapping layer

The charge trapping effects in memory cells with HfO2/Al2O3 nanolaminated stacks with two different thicknesses (2.4 and 3.5 nm) of the tunnel SiO2 layer were investigated. The HfO2/Al2O3 stacks were fabricated by atomic layer deposition and received post deposition annealing in O2. The structures with 3.5 nm tunnel oxide were found to provide higher density of trapped charges. The obtained trapped negative charge density is -3.56×10−6 C/cm2 and the positive one is 4.03×10−6 C/cm2. It is demonstrated that the electron trapping is significantly influenced by the amount of available electrons in the inversion layer. Under illumination, pulses with duration of 1 ms could provide trapped negative charge density equal to ~60% the value obtained at 10 s duration, where a saturation of the trapped charge is found. The hole trapping is not influenced by the illumination of capacitors and it is found to be slower than the electron one. Some aspects of the trapping process as well as some of the peculiarities in the capacitance-voltage curves obtained in the course of the measurements are briefly discussed.

Effects of post deposition annealing atmosphere on interfacial and electrical properties of HfO2/Ge3N4 gate stacks

Effects of post deposition annealing (PDA) atmosphere, including oxygen (O2) gas and forming gas (FG), on interfacial and electrical properties of a HfO2 gate dielectric on nitrided Ge are analyzed. Experiments to study the dielectric morphology, interface quality, and chemical composition of HfO2/Ge3N4/Ge devices were carried out using X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) imaging, and X-ray photoelectron spectroscopy (XPS) measurements, respectively. The XPS study confirmed that O2 PDA effectively improves the HfO2 film stoichiometry, and the stability of the interface between HfO2/Ge3N4/Ge stacks is enhanced. Further, HRTEM images showed that the interface between HfO2/Ge3N4/Ge stacks for O2-annealed devices was smooth, uniform, and flat. The experimental results for devices annealed in O2 at 500 °C exhibited improved interfacial and electrical characteristics, such as a high dielectric constant of ~19.50; high capacitance, 1.24 nF, low equivalent oxide thickness, 1.74 nm; interface trap density, 2.18 × 1011 cm−2 eV−1; oxide charges, 2.50 × 1012 cm−2; and gate leakage currents in the order nA of 0.5 × 10−9 A/cm2, as compared with FG annealing devices. The Fowler−Nordheim tunneling current conduction mechanism was also verified. Therefore, these results are evidence that the O2 PDA process improves the interfacial and electrical properties of HfO2/Ge3N4/Ge metal-oxide-semiconductor (MOS) devices as compared with FG annealing, which is important for future Ge-based complementary MOS device performance and reliability.

Hole and electron trapping in HfO2/Al2O3 nanolaminated stacks for emerging non-volatile flash memories

HfO2/Al2O3 nanolaminated stacks prepared by atomic layer deposition have been investigated in terms of their charge storage characteristics for possible application in charge trapping memories. It is shown that the memory window, electron and hole trapping and leakage currents depend strongly on Al2O3 thickness and post-deposition oxygen annealing. Depending on the Al2O3 thickness, post-deposition annealing in O2 creates different electrically active defects (oxide charge and traps) in the stacks. O2 annealing increases electron trapping, thus giving rise to a larger memory window and enhanced charge storage characteristics, i.e. 65% of charge is retained after ten years and the memory window decreases by 6% after 2.5 × 104 program/erase cycles.

Improved Performance of Amorphous InGaMgO Metal-Semiconductor-Metal Ultraviolet Photodetector by Post Deposition Annealing in Oxygen

In this paper, the impact of O2 postdeposition annealing treatment on the material and UV detection characteristics of amorphous InGaMgO (IGMO) thin films was intensively studied. With the replacement of Zn by Mg, amorphous InGaMgO possesses an optical bandgap larger than that of the conventional amorphous InGaZnO by over 0.5 eV. Furthermore, it was found the post-deposition annealing in O2 effectively suppressed the oxygen vacancies in the amorphous IGMO thin film, resulting in a significant reduction in its dark current. Due to strong hole trapping, all the samples except the 480-min annealed one exhibited large photocurrent and accordingly high responsivity over $1\,\times \,10^{3}\,{\rm{A/ W}}$ @ 10 V. Moreover, both photocurrent and responsivity improve with increasing annealing time up to 240 min. As a result, the Metal-Semiconductor-Metal photodetector based on the 240-min annealed amorphous InGaMgO thin film exhibited a very prominent performance, including a high responsivity of $1.6\,\times \,10^{4}\,{\rm{A/ W}}$ and a large photo-to-dark current ratio of $1.3\,\times \,10^{3}$ . We attribute such excellent properties to the improved carrier mobility as well as the reduction of recombination centers in the O2-annealed film. However, some degradations in device performance were observed when the annealing time reached 480 min, which can be explained by the suppression of localized tail states, as demonstrated by the abruptly reduced Urbach energy, and accordingly the inhibition of related extrinsic excitation. This work has provided a promising candidate for the application in transparent contact-free interactive display.

Effects of post-deposition annealing on sputtered SiO2/4H-SiC metal-oxide-semiconductor

Reactive sputtering followed by N2, NH3, O2, and NO post-deposition annealing (PDA) of SiO2 on 4H-SiC was investigated in this study. The results of ellipsometry, an etching test, and X-ray photoemission spectroscopy showed that N2 and NH3 PDA nitrified the SiO2. Devices using N2 and NH3 PDA exhibited a high gate leakage current and low breakdown field due to oxygen vacancies and incomplete oxynitride. SiO2/4H-SiC MOS capacitors were also fabricated and their electrical characteristics measured. The average breakdown fields of the devices using N2, NH3, O2, and NO PDA were 0.12, 0.17, 4.71 and 2.63 MV/cm, respectively. The shifts in the flat-band voltage after O2 and NO PDA were 0.95 and −2.56 V, respectively, compared with the theoretical value. The extracted effective oxide charge was −4.11 × 1011 cm−2 for O2 PDA and 1.11 × 1012 cm−2 for NO PDA. NO PDA for 2 h at 1200 °C shifted the capacitance–voltage curve in the negative direction. The oxygen containing PDA showed better electrical properties than non-oxygen PDA. The sputtering method described can be applied to 4H-SiC MOS fabrication.

Post Deposition Annealing Atmosphere Effect on SSI-LEDs Made of Zr-Doped HfO2 High-k Gate Dielectric

Recently, Kuo’s group proposed a new type of solid state incandescent light emitting device (SSI-LED) that has a simple MOS structure and emits the warm white light. This kind of device contains a high-k dielectric gate dielectric thin film, such as Zr-doped HfO2 (ZrHfO) or the HfOx [1-3]. The light emission is due to the thermal excitation of many nano-size conductive paths formed from the dielectric breakdown process when the applied gate voltage (Vg ) is above a breakdown voltage (VBD ). The post deposition annealing (PDA) step is critical to the MOS device performance because it affects the defect structures and densities in the high-k stack [4]. In this study, authors investigated the electrical and optical characteristics of the SSI-LED made of ZrHfO high-k films under different PDA atmospheres. The ZrHfO high-k films were sputter deposited on the p-type Si (100) (1015 cm-3) wafer using the one pump down process without breakdown the vacuum. The ZrHfO film was deposited from a ZrHf (12/88 wt. %) target in Ar/O2 (1:1) at 5 mTorr and 60 W for 12 min. After deposition, the sample was annealed at 800 °C in N2 or O2 for 3 min. An ITO layer was deposited on the high-k stack and etched into 300 µm dots as the gate electrodes. The backside of the wafer was sputter deposited with an aluminum layer for the ohmic contact purpose. The complete sample was annealed at 400 °C in forming gas for 5 min. The complete sample was characterized for electrical and optical properties. Figure 1 shows the I -V curves of the N2 PDA and O2 PDA devices with Vg swept from 0 to -10 V. The devices break abruptly at -5.65 V for the N2 PDA sample and -6.1 V for the O2 PDA sample. The O2 PDA sample has a larger physical thickness than that of the N2 PDA sample, e.g., the equivalent oxide thickness (EOT) of the former is 12.03 nm and that of the latter is 11.12 nm, which can explain the difference of the VBD ’s. In addition, the breakdown strength of the ZrHfO stack is related to the defect densities in the bulk high-k film and the Si/high-k interface layer [5]. The oxide trapping density (Qot ) and the interface density of states (Dit ) of the O2 PDA sample are 5.21×109 cm-2 and 1.61×1011 cm-2∙eV-1, separately, which are smaller than those of the N2 PDA sample, i.e., 7.13×109 cm-2 and 1.80×1011 cm-2∙eV-1, separately, which also favors of high VBD of the former sample. Figure 2 shows the high magnification light emission photos of the N2 PDA and O2 PDA devices stressed at Vg = -50 V. Both photos show that the light is emitted from many discrete bright dots uniformly distributed across the gate electrode. The N2 PDA sample contains a larger number of weaker dots than the O2 PDA sample does. Since the bright dots are from the thermal excitation of conductive paths in the sample, the number density of the bright dots is related to the breakdown strength of the sample. The O2 PDA sample has lower defect densities in the bulk ZrHfO and HfSiOx interface layers than the N2 PDA sample [5]. In addition, bright dots in Fig. 2(b) appear to be larger than most of those in Fig. 2(a). The bright dots at the edge of the sample appear to be larger than those in the center. The difference in the size distribution of the bright dots is related to the breakdown strength the high-k stack. Figure 3 shows the emission spectra of the N2 PDA and O2 PDA samples stressed at Vg = -50 V. Both spectra cover the same wavelength range including the visible and some of the near IR lights. The O2 PDA sample has a higher light intensity than the O2 PDA sample has, which is consistent with the result of Fig. 2. The peak wavelengths of both samples are very close, i.e., 681.5 nm for the O2 PDA sample and 682.0 nm for the N2 PDA sample. The similar composition of the conductive paths in both samples may be the cause of the spectrum shape. [1] Y. Kuo and C.-C. Lin, APL, 102, 031117 (2013). [2] Y. Kuo and C.-C. Lin, ESSL, 2, Q59 (2013). [3] Y. Kuo and C.-C. Lin, SSE, 89, 120 (2013). [4] G. D. Wilk, R. M. Wallace, and J. M. Anthony, JAP, 87, 484 (2000). [5] C.-C. Lin and Y. Kuo, E JSSST, 3,Q182 (2014). Figure 1

Mobility Enhancement and OFF Current Suppression in Atomic-Layer-Deposited ZnO Thin-Film Transistors by Post Annealing in O2

The impacts of postdeposition annealing in O2 on the electrical performance of atomic-layer-deposited ZnO thin-film transistors (TFTs) have been investigated. The TFTs are fabricated on transparent quartz substrates with Al2O3 dielectrics, ZnO active layers, and Cr/Au electrodes. The best field-effect mobility of 21.3 $\mathrm{cm}^{2}$ /Vs and a large ON/OFF current ratio of $10^{7}$ are obtained under 400 °C annealing treatment in O2. Furthermore, analysis indicates that reduction of OH bonds in both ZnO and Al2O3 layers is the key issue to achieve the excellent properties.

Low temperature atomic layer deposition of highly photoactive hematite using iron(iii) chloride and water

Nanostructured hematite (α-Fe2O3) has been widely studied for use in a variety of thin film applications including solar energy conversion, water oxidation, catalysis, lithium-ion batteries, and gas sensing. Among established deposition methods, atomic layer deposition (ALD) is a leading technique for controlled synthesis of a wide range of nanostructured materials. In this work, ALD of Fe2O3 is demonstrated using FeCl3 and H2O precursors at growth temperatures between 200 and 350 °C. Self-limiting growth of Fe2O3 is demonstrated with a growth rate of ∼0.6 A per cycle. As-deposited, films are nanocrystalline with low chlorine impurities and a mixture of α- and γ-Fe2O3. Post-deposition annealing in O2 leads to phase-pure α-Fe2O3 with increased out-of-plane grain size. Photoelectrochemical measurements under simulated solar illumination reveal high photoactivity toward water oxidation in both as-deposited and post-annealed films. Planar films deposited at low temperature (235 °C) exhibit remarkably high photocurrent densities ∼0.71 mA cm−2 at 1.53 V vs. the reversible hydrogen electrode (RHE) without further processing. Films annealed in air at 500 °C show current densities of up to 0.84 mA cm−2 (1.53 V vs. RHE).

Effects of high-temperature O2 annealing on Al2O3 blocking layer and Al2O3/Si3N4 interface for MANOS structures

In this paper, we have investigated the effects of O2 post-deposition annealing (PDA) on metal/Al2O3/Si3N4/SiO2/Si (MANOS) devices. Compared with low-energy plasma oxygen pre-treatment and the N2 PDA process, the O2 PDA process can lead to a significant retention improvement. The improvement is attributed to the removal of oxygen vacancies in Al2O3 block oxide and the oxygen incorporation at the Si3N4/Al2O3 interfacial layer which is determined by x-ray photoelectron spectroscopy (XPS) depth profiling and electrical characteristics. Metal/Al2O3/SiO2/Si (MAOS) devices are also studied to confirm these effects. As a result, we consider that the O2 PDA process is a crucial process for future MANOS-type memory devices.

Annealing-temperature Dependence of Compositional Depth Profiles and Chemical Bonding States of CeOx/LaOx/Si and LaOx/CeOx/Si Structure

We have investigated the influence of post deposition annealing (PDA) on compositional depth profiles and chemical structures of CeOx/LaOx/Si(100) and LaOx/CeOx/Si(100) interfaces by angle-resolved X-ray photoemission spectroscopy. Analyses of Ce 3d and O 1s spectra show that a Ce oxidation state changes from Ce4+ to Ce3+ by PDA in N2 at and above 500{degree sign}C and changes from Ce3+ to Ce4+ by PDA in O2 at 300{degree sign}C. This implies that a Ce oxidation state can be controlled by changing the condition of PDA. The diffusion of Ce and La atom occurs at CeOx/LaOx interface by PDA above 500{degree sign}C.

Amorphous Lanthanum Lutetium Oxide Thin Films as an Alternative High-k Material

Lanthanum lutetium oxide thin films have been grown on Si substrates by three different techniques: pulsed-laser deposition, molecular beam deposition, and atomic layer deposition. Post-deposition annealing in O2 was performed to improve their electrical properties. Capacitance-voltage and current-voltage measurements reveal well-behaving C-V curves and low leakage current density levels. Most strikingly, a dielectric constant around 30 could be achieved for amorphous thin films of this material. These results are discussed in terms of the microstructural characteristics of the films before and after thermal treatment.

Effects of annealing on the electrical and interfacial properties of amorphous lanthanum scandate high-κ films prepared by molecular beam deposition

Amorphous LaScO3 thin films were grown on (100) Si by molecular beam deposition and the effects of postdeposition thermal treatments on the film properties were studied after anneals in O2 or inert Ar atmosphere at 400 or 650 °C. Rutherford backscattering spectrometry, transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy (XPS) were employed to investigate the samples. Capacitance-voltage and current-voltage measurements allowed their electrical characterization. Postdeposition annealing in O2 reduces hysteresis, flatband voltage, and also leakage current density. In contrast, films treated in Ar ambient revealed a different behavior. The observations were associated with the interface evolution as studied by XPS, which verify that an O2 atmosphere favors the formation of a SiO2-rich interface between the film and the Si substrate, while a La-Sc-silicate-like compound predominates in this region after treating the samples in Ar. Additionally, postdeposition annealing results in an improvement of the dielectric constant up to 33, which is higher than that previously determined for LaScO3 or other amorphous alternative high-κ oxide films deposited by various techniques.

Electrical properties of ultrathin HfO2 gate dielectrics on partially strain compensated SiGeC/Si heterostructures

Ultrathin HfO2 gate dielectrics have been deposited on strained Si0.69Ge0.3C0.01 layers by rf magnetron sputtering. The polycrystalline HfO2 film with a physical thickness of ∼6.5 nm and an amorphous interfacial layer with a physical thickness of ∼2.5 nm have been observed by high resolution transmission electron microscopy (HRTEM). The electrical properties have been studied using metal-oxide-semiconductor (MOS) structures. The fabricated MOS capacitors on Si0.69 Ge0.3C0.01 show an equivalent oxide thickness (EOT) of 2.9 nm, with a low leakage current density of ∼4.5 × 10 − 7 A/cm2 at a gate voltage of –1.0 V. The fixed oxide charge and interface state densities are calculated to be 1.9 × 1012 cm− 2 and 3.3 × 10 11 cm− 2eV−1, respectively. The temperature dependent gate leakage characteristics has been studied to establish the current transport mechanism in high-k HfO2 gate dielectric to be Poole–Frenkel one. An improvement in electrical properties of HfO2 gate dielectrics has been observed after post deposition annealing in O2 and N2 environments.

Effects of post-deposition annealing in O2 on the electrical characteristics of LaAlO3 films on Si

LaAlO 3 films were deposited on p-type Si(100) by sputtering from a LaAlO3 target. C×V characteristics were determined in nonannealed and O2-annealed capacitors having LaAlO3 films as dielectric and RuO2 as top electrode. Thermal annealing in O2 atmosphere reduced flat band voltage to acceptable values for advanced Si-based devices. O16–O18 isotopic substitution was characterized by Rutherford backscattering spectrometry and nuclear resonant reaction profiling. Chemical analysis of the films was accomplished by x-ray photoelectron spectroscopy. The electrical improvements observed after thermal annealing in O2 were attributed to the incorporation of oxygen from the gas phase, possibly healing oxygen vacancies in the films and providing mobile oxygen to the interface.

Controlled growth of WO3 films

We have used reactive rf magnetron sputtering of a tungsten target in Ar/O2 mixtures and direct electron-beam evaporation of WO3 pellets with and without the presence of an electron cyclotron resonance (ECR) oxygen plasma to grow WO3 films on α-Al2O3(101̄2) single-crystal substrates (r-cut sapphire). The WO3 films exhibit a range of microstructures depending on deposition conditions. Using any of the deposition methods, the films are amorphous when grown at room temperature. Postdeposition annealing in O2 induces the formation of a random polycrystalline microstructure and an increased surface roughness. Growth of crystalline WO3 films can be achieved at deposition temperatures above 200 °C. During electron-beam evaporation of WO3 at 600 °C, reflection high-energy electron diffraction observations indicate that a tetragonal phase of WO3 grows epitaxially on r-cut sapphire with the (100) tetragonal plane coincident with the rectangular mesh of the r-cut sapphire substrate. Deposition of WO3 using plasma species generated by either a rf magnetron or ECR source promotes the formation of some nuclei of an orthorhombic and/or monoclinic phase coexisting with the tetragonal phase; the nearly identical lattice parameters make the orthorhombic and monoclinic phases difficult to distinguish. Compared to the polycrystalline films, the epitaxial films exhibit both a higher base-line conductivity and a larger conductivity change upon exposure to H2S gas.

Defect states responsible for leakage current in Ta2O5 films on Si due to Si contamination from the substrate

A defect state, defect B, was found in Ta2O5 after postdeposition annealing in O2 by a novel zero-bias thermally stimulated current spectroscopy technique. The activation energy ET was estimated to be about 0.3 eV. Evidence is given that defect B is a hole trap. We believe that defect B is an acceptor level in Ta2O5 due to Si substituting for Ta. The presence of Si contamination in Ta2O5 due to diffusion of Si from the Si substrate into Ta2O5 was confirmed by secondary-ion-mass spectrometry.

Nonepitaxial sputter synthesis of aligned strontium hexaferrite, SrO⋅6(Fe2O3), films

Films of strontium hexaferrite were synthesized through rf diode sputter deposition, nonepitaxially onto polycrystalline Al2O3 substrates. So far such films for the analogous Ba phase have been synthesized mostly through epitaxial growth onto suitably chosen matching substrates. Crystallization of the strontium hexaferrite phase was achieved for deposition temperatures as low as 500 °C. For nonepitaxially synthesized 2–3-μm-thick polycrystalline films, a fairly high degree of variable and controlled c-axis orientation of the crystallites has been obtained. The x-ray-diffraction traces of films with a strong c-axis in-plane alignment showed predominantly (110)-type reflections. The film coercivities were increased by postdeposition annealing in O2. The remnant to saturation flux density ratio of such in-plane anisotropy films for in-plane measurements was 0.62, with an in-plane coercivity ≊2.3 kOe.