Hysteresis-free HfO2 film grown by atomic layer deposition at low temperature

Hysteresis-free hafnium oxide films were fabricated by atomic layer deposition at 90 °C without any post-deposition annealing, and their structures and properties were compared with films deposited at 150 °C and 250 °C. The refractivity, bandgap, dielectric constant and leakage current density all increase with deposition temperature, while the growth rate and breakdown field decrease. All films are amorphous with roughly the same composition. Although the thin films deposited at the above-mentioned temperatures all show negligible hysteresis, only the 90 °C-deposited films remain hysteresis-free when the film thickness increases. The 90 °C-deposited films remain hysteresis-free after annealing at 300 °C. The hysteresis in films deposited at high temperatures increases with deposition temperature. Evidences show such hysteresis originates in the HfO₂ film instead of the interface. Based on a careful structure analysis, middle-range order is suggested to influence the trap density in the films. HfO₂ films deposited at low temperature with negligible hysteresis and excellent electrical properties have great potential for the fabrication and integration of devices based on non-silicon channel materials and in applications as tunneling and blocking layers in memory devices.     

Electrical properties and structure of laser-spike-annealed hafnium oxide

We studied the effects of laser-spike annealing (LSA) on hafnium oxide high-k dielectrics using high power diode laser. The equivalent oxide thickness of HfO₂ gate stacks annealed using a moderate laser power decreased noticeably as compared to as-grown films due to densification and crystallization of HfO₂. Transmission electron microscope and X-ray photoelectron spectroscopy show that regrowth of interfacial oxide and silication of HfO₂ layer are suppressed in case of LSA compared with rapid thermal annealing. Capacitance voltage hysteresis revealed stronger charge trapping/de-trapping behavior for LSA gate stacks as compared to rapid thermal annealed gate stack. However, bias-stress-induced flat band voltage shifts of LSA gate stacks were within acceptable levels, ? 30 mV, showing controllable threshold voltage.     

Synthesis and characterization of HfO2 and ZrO2 thin films deposited by plasma assisted reactive pulsed laser deposition at low temperature

A plasma assisted reactive pulsed laser deposition process was demonstrated for low-temperature deposition of thin hafnia (HfO₂) and zirconia (ZrO₂) films from metallic hafnium or zirconium with assistance of an oxygen plasma generated by electron cyclotron resonance microwave discharge. The structure and the interface of the deposited films on silicon were characterized by means of Fourier transform infrared spectroscopy, which reveals the monoclinic phases of HfO₂ and ZrO₂ in the films with no interfacial SiO_x layer between the oxide film and the Si substrate. The optical properties of the deposited films were investigated by measuring the refractive indexes and extinction coefficients with the aid of spectroscopic ellipsometry technique. The films deposited on fused silica plates show excellent transparency from the ultraviolet to near infrared with sharp ultraviolet absorption edges corresponding to direct band gap.     

Atomic layer deposition of HfO2 thin films and nanolayered HfO2–Al2O3–Nb2O5 dielectrics

Smooth, 4–6-nm thick hafnium oxide films were grown by atomic layer deposition from HfI₄ or HfCl₄ and H₂O on SiO₂/Si(1 0 0) substrates at 300 °C. Non-uniform films were obtained on hydrogen-terminated Si(1 0 0). The stoichiometry of the films corresponded to that of HfO₂. The films contained small amounts of residual chlorine and iodine. The films deposited on SiO₂/Si(1 0 0) were amorphous, but crystallized upon annealing at 1000 °C. In order to decrease the conductivity, the HfO₂ films were mixed with Al₂O₃, and to increase the capacitance, the films were mixed with Nb₂O₅. The capacitance–voltage curves of the Hf–Al–O mixture films showed hysteresis. The capacitance–voltage curves of HfO₂ films and mixtures of Hf–Al–Nb–O were hysteresis free.     

Magnetic behavior of cobalt oxide films prepared by pulsed liquid injection chemical vapor deposition from a metal-organic precursor

Thin films of cobalt oxide were prepared by the pulsed liquid injection chemical vapor deposition technique from metal-organic precursor. By using a β-diketonate complex of cobalt, namely cobalt (II) acetylacetonate (Co(acac)₂) as the precursor, oxygen as the reactant and argon as the carrier gas, cobalt oxide films 100 nm in thick were deposited onto Si (100) substrates at 650 °C in about 40 min. According to the characterization by X-ray diffraction and atomic force microscopy, smooth and polycrystalline films, consisting exclusively of the Co₃O₄ phase, were deposited. Magnetic properties, such as saturation magnetization, the remanence, the coercivity, the squareness ratio and the switching field distribution, were extracted from the hysteresis loop. Cobalt oxide films with coercivities of 6.61 mT, squareness ratio of 0.2607 and saturation magnetization of 12.17 nA m², corresponding to a soft magnetic material, were achieved.     

Compositional analysis of polycrystalline hafnium oxide thin films by heavy-ion elastic recoil detection analysis

The composition of polycrystalline hafnium oxide thin films has been measured by heavy-ion elastic recoil detection analysis (HI-ERDA). The films were deposited by high-pressure reactive sputtering (HPRS) on silicon wafers using an oxygen plasma at pressures between 0.8 and 1.6 mbar and during deposition times between 0.5 and 3.0 h. Hydrogen was found to be the main impurity and its concentration increased with deposition pressure. The composition was always slightly oxygen-rich, which is attributed to the oxygen plasma. Additionally, an interfacial silicon oxide thin layer was detected and taken into account. The thickness of the hafnium oxide film was found to increase linearly with deposition time and to decrease exponentially with deposition pressure, whereas the thickness of the silicon oxide interfacial layer has a minimum as a function of pressure at around 1.2 mbar and increases slightly as a function of time. The measurements confirmed that this interfacial layer is formed mainly during the early stages of the deposition process.     

Atomic layer deposition of hafnium oxide dielectrics on silicon and germanium substrates

Hafnium oxide films have been deposited at 250 °C on silicon and germanium substrates by atomic layer deposition (ALD), using tetrakis-ethylmethylamino hafnium (TEMAH) and water vapour as precursors in a modified Oxford Instruments PECVD system. Self-limiting monolayer growth has been verified, characterised by a growth rate of 0.082 nm/cycle. Layer uniformity is approximately within ±1% of the mean value. MOS capacitors have been fabricated by evaporating aluminium electrodes. CV analysis has been used to determine the bulk and interface properties of the HfO₂, and their dependence on pre-clean schedule, deposition conditions and post-deposition annealing. The dielectric constant of the HfO₂ is typically 18. On silicon, best results are obtained when the HfO₂ is deposited on a chemically oxidised hydrophilic surface. On germanium, best results are obtained when the substrate is nitrided before HfO₂ deposition, using an in-situ nitrogen plasma treatment.     

Correlation between the structural and electrical transport properties of SnO2 films

Transparent and conducting thin films of tin oxide have been deposited by spray pyrolysis on Corning 7059 substrates. The films were investigated by X-ray diffraction and Seebeck measurements to study the structural and electrical transport properties. The films were polycrystalline and the oxide phase observed was SnO₂ in cassiterite structure. The films were preferentially oriented along [200]. Trap densities along [310] and [101] have been calculated for the first time. Assigning the traps mainly to the grain boundaries, the grain-boundary barrier height was calculated and compared with that obtained from the Seebeck measurements. A good agreement between these values was observed. The agreement was the best for films deposited under optimum deposition conditions.     

Conformal growth and characterization of hafnium silicate thin film by MOCVD using HTB (hafnium tertra-tert-butoxide) and TDEAS (tetrakis-diethylamino silane)

Hafnium silicate (HfSi _x O _y ) films were deposited by metal-organic chemical vapor deposition (MOCVD) using hafnium tetra-tert-butoxide [HTB, Hf(OC(CH₃)₃)₄] and tetrakis-diethylamino silane [TDEAS, Si(N(C₂H₅)₂)₄]. The grown Hf-silicate films showed Hf-rich composition and impurity concentrations less than 1 atomic % (below detection limits). Uniformly deposited films with good step-coverage were obtained on hole-patterned SiO₂ substrates. Hafnium silicate films had stable amorphous crystalline structure up to 800 °C annealing and above 900 °C, a tetragonal HfO₂ crystal phase was observed. Dielectric constant (k) of the Hf-silicate films was about 15 and flat band voltage (V _fb) and hysteresis were very low.     

Characteristics of high-k dielectric ECR-ALD lanthanum hafnium oxide (LHO) films

In this study, we investigated the characteristics of various lanthanum hafnium oxide (LHO) films with different lanthanum (La) concentrations deposited by an electron cyclotron resonance plasma-enhanced atomic layer deposition (ECR-ALD). Tris(isopropyl-cyclopentadienyl)lanthanum (La(iPrCp)₃) and tetrakis(ethylmethylamino)hafnium (TEMAHf) were utilized as the La and hafnium (Hf) precursors, respectively. When the La/(La + Hf) atomic percent ratio was 49.1%, the growth rate of the LHO film was 0.5 Å/cycle, with a dielectric constant of 16.3. As the La concentration was increased, the dielectric constant decreased. In addition, we found that a La-hydrate phase (La-O-H) can be easily formed when the La/(La + Hf) is over about 50%.     

Influence of the target composition on reactively sputtered titanium oxide films

Titanium dioxide thin films have many interesting properties and are used in various applications. High refractive index of titania makes it attractive for the glass coating industry, where it is used in low-emissivity and antireflective coatings. Magnetron sputtering is the most common deposition technique for large area coatings and a high deposition rate is therefore of obvious interest. It has been shown previously that high rate can be achieved using substoichiometric targets. This work deals with reactive magnetron sputtering of titanium oxide films from TiO_x targets with different oxygen contents.The deposition rate and hysteresis behaviour are disclosed. Films were prepared at various oxygen flows and all films were deposited onto glass and silicon substrates with no external heating. The elemental compositions and structures of deposited films were evaluated by means of X-ray photoelectron spectroscopy, elastic recoil detection analysis and X-ray diffraction. All deposited films were X-ray amorphous. No significant effect of the target composition on the optical properties of coatings was observed. However, the residual atmosphere is shown to contribute to the oxidation of growing films.     

Quantitative analysis of chemical compositions in ultra-thin oxide-nitride-oxide stacked films having wet oxidized blocking layer

2nd-derivative Auger electron spectra analyses and time-of-flight secondary ion mass spectroscopy depth profiles are employed for analyzing quantitatively chemical compositions in ultra-thin oxide-nitride-oxide (ONO) stacked films. Tunnel oxide of 2.3 nm is grown on silicon substrate in nitrogen-diluted oxygen ambient. Nitride of 5.7 nm is immediately deposited on the tunnel oxide by a low-pressure chemical vapor deposition. Blocking oxide is subsequently grown by oxidizing the oxide-nitride structure in a wet O₂ ambient. Some chemical mixing occurs during the ONO formation. That is, the tunnel oxide formed on the silicon substrate changes into SiO_1.11N_0.67 by nitrogen substitution. Oxygen diffuses into the nitride layer, and converts some of the nitride layer into SiO_1.11N_0.67 during wet oxidation. We think the SiON and Si₂NO species exist near the tunnel oxide-nitride and the nitride-blocking oxide interfaces are segments of the Si₂N₂O. These are evidence of dangling bonds as unstable chemical species which may act as charge traps in the oxide-nitride interfaces.     

Multiferroic Bi0.7Dy0.3FeO3 thin films directly integrated on Si for integrated circuit compatible devices

Magnetoelectric multiferroic Bi_0.7Dy_0.3FeO₃ (BDFO) thin films deposited on p-type Si (100) substrate using pulsed laser deposition technique demonstrated a saturated ferroelectric and ferromagnetic hysteresis loop at room temperature. More interestingly, the observed change in electric polarization with applied magnetic field in these films indicated the presence of room temperature magnetoelectric coupling behavior. Using high-frequency capacitance-voltage measurements, the fixed oxide charge density, interface trap density and dielectric constant were estimated on Au/BDFO/Si capacitors. These results suggest the integrated circuit compatible application potential of BDFO films in the field of micro-electro-mechanical systems and non-volatile memories.     

Oligomer semiconductor/dielectric interface modification for organic thin film transistor hysteresis reduction

In this work, we investigate the hydroxyl group effect on hysteresis of the low voltage organic thin film transistor (OTFT). A high k material, hafnium oxide, is utilized as gate dielectric to reduce OTFT operational voltage. By using the hydroxyl-free polymer, polystyrene, the hydroxyl groups on hafnium oxide surface will be shielded. The modification at semiconductor/dielectric interface prevents accumulated charges from trapping in surface states. Such a polymer coverage layer reduces hysteresis and suppresses the off current as low as 10⁻¹¹ A. The interface traps resulted from ambient water absorption significantly decrease according to the hysteresis cancellation. By stacking polystyrene on hafnium oxide, the pentacene-based OTFT shows the threshold voltage of − 2.2 V, on/off current ratio of 10⁵, subthreshold swing of 0.34 V/dec, and mobility of 0.24 cm²/V s under operational voltage of 10 V.     

Effect of atomic layer deposited ultra thin HfO2 and Al2O3 interfacial layers on the performance of dye sensitized solar cells

The objective of this work was to investigate the improvement in performance of dye sensitized solar cells (DSSCs) by depositing ultra thin metal oxides (hafnium oxide (HfO₂) and aluminum oxide (Al₂O₃)) on mesoporous TiO₂ photoelectrode using atomic layer deposition (ALD) method. Different thicknesses of HfO₂ and Al₂O₃ layers (5, 10 and 20 ALD cycles) were deposited on the mesoporous TiO₂ surface prior to dye loading process used for fabrication of DSSCs. It was observed that the ALD deposition of ultrathin oxides significantly improved the performance of DSSCs and that the improvement in the DSSC performance depends on the thickness of the deposited HfO₂ and Al₂O₃ films. Compared to a reference DSSC the incorporation of a HfO₂ layer resulted in 69% improvement (from 4.2 to 7.1%) in the efficiency of the cell and incorporation of Al₂O₃ (20 cycles) resulted in 19% improvement (from 4.2 to 5.0%) in the efficiency of the cell. These results suggest that ultrathin metal oxide layers affect the density and the distribution of interface states at the TiO₂/organic dye and TiO₂/liquid electrolyte interfaces and hence can be utilized to treat these interfaces in DSSCs.     

Electrical properties and deep traps spectra of a-plane GaN films grown on r-plane sapphire

Electrical properties, deep traps spectra and luminescence spectra were studied for two undoped a-plane GaN (a-GaN) films grown on r-plane sapphire using metalorganic chemical vapor deposition and differing by structural perfection. For sample A, the a-GaN film was directly deposited on AlN buffer. A two-step growth scheme was implemented for sample B, including an initial islanding growth stage and a subsequent enhanced lateral growth. Preliminary detailed X-ray analysis showed that the stacking faults density was 8 × 10⁵ cm^?1 for sample A and 1.7 × 10⁵ cm^?1 for sample B. Electrical properties of a-GaN films were largely determined by deep traps with a level near E_c ?0.6 eV, with other prominent traps having the activation energy of 0.25 eV. The Fermi level was pinned by the E_c ?0.6 eV deep traps for sample A, but shifted to the vicinity of the shallower 0.25 eV traps for sample B, most likely due to the reduced density of the 0.6 eV traps. This decrease of deep traps density is accompanied by a very pronounced improvement in the overall luminescence intensity. A correlation of the observed improvement in deep traps spectra and luminescence efficiency with the improved crystalline quality of the films is discussed.     

Characteristics of thin nitrided oxides prepared by an in-situ process

In this paper a new method of depositing silicon nitrided oxide by an in-situ process is introduced. Thin nitrided-oxide (NO) films were deposited on silicon by rapid thermal oxidation and rapid thermal chemical vapour deposition (RTCVD). Thin oxide films, 10.0 nm, were rapidly thermally grown in a dry oxygen ambient at 1000 °C and the silicon-nitride films were deposited on the oxide at 700–900 °C using an NH₃ and SiH₄ gaseous mixture. The effect of the NH₃/SiH₄ input ratio and the deposition temperature on the deposition rate and the electrical properties was studied. The experimental results show that the deposition rate increased with increasing deposition temperature and decreasing NH₃/SiH₄ input ratio. From the data for the Fourier-transform infrared spectroscopy (FTIR) and the C-V curves of the NO films, it was observed that the flat-band voltage is directly related to the N-H-bond peak intensity. The flat-band voltage shifts to the positive with increasing deposition temperature and to the negative with increasing NH₃/SiH₄ input ratio, and the breakdown field of NO films is higher than that of the RTP oxidation (RTO) films.     

Indium sulfide buffer layers deposited by dry and wet methods

Indium sulfide (In₂S₃) thin films have been deposited on amorphous glass, glass coated by tin oxide (TCO) and crystalline silicon substrates by two different methods: modulated flux deposition (MFD) and chemical bath deposition (CBD). Composition, morphology and optical characterization have been carried out with Scanning Electron Microscopy (SEM), IR-visible-UV Spectrophotometry, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectrometer. Different properties of the films have been obtained depending on the preparation techniques. With MFD, In₂S₃ films present more compact and homogeneous surface than with CBD. Films deposited by CBD present also indium oxide in their composition and higher absorption edge values when deposited on glass.     

Dosimetry aspects of hafnium oxide metal-oxide-semiconductor (MOS) capacitor

This paper reports the investigation of hafnium oxide based metal-oxide-semiconductor capacitor for the detection of gamma radiation. The fabrication of the device involved deposition of hafnium oxide thin film on n-type Si wafer by electron beam evaporation technique followed by deposition of aluminum metal layer by thermal evaporation process. The device was irradiated incrementally to the cumulative dose of 480 Gy by gamma rays of 1.25 MeV (Co-60). The change in accumulation capacitance, effective oxide charge and interface trap density with cumulative gamma dose was examined at room temperature. As the creation of oxide charge and change in oxide capacitance are well correlated with radiation dose, the device can be useful for radiation dosimetry.     

Properties of aluminum oxide thin films deposited by pulsed laser deposition and plasma enhanced chemical vapor deposition

The chemical, structural, mechanical and optical properties of thin aluminum oxide films deposited at room temperature (RT) and 800 °C on (100) Si and Si-SiO₂ substrates by pulsed laser deposition and plasma enhanced chemical vapor deposition are investigated and compared. All films are smooth and near stoichiometric aluminum oxide. RT films are amorphous, whereas γ type nano-crystallized structures are pointed out for films deposited at 800 °C. A dielectric constant of ∼ 9 is obtained for films deposited at room temperature and 11-13 for films deposited at 800 °C. Young modulus and hardness are in the range 116-254 GPa and 6.4-28.8 GPa respectively. In both cases, the results show that the deposited films have very interesting properties opening applications in mechanical, dielectric and optical fields.