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We discuss the nitridation of ALD-deposited hafnium silicate films by exposure to atomic nitrogen generated in a remote nitrogen plasma. Nitrogen concentration [N] as measured by X-ray photoelectron spectroscopy (XPS) is determined as a function of the nitridation temperature and other process conditions. Nitrogen concentrations up to 13.7 atomic % were achieved.
In this paper, we first propose an improved CVD-WSix metal gate suitable for use with nMOSFETs. Work function of CVD-WSi3.9 gate estimated from C-V measurements was 4.3eV. The nMOSFET using CVD-WSi3.9 gate electrode showed that Vth variation of L/W=1 μm/10μm nMOSFETs can be suppressed to be lower than 8mV in 22chip. In CVD-WSi3.9 gate MOSFETs with gate length of 50nm, a drive current of 636μA/μm was achieved for off-state leakage current of 35nA/μm at 1.0V of power supply voltage. By using CVD-WSi3.9 gate electrode, highly reliable metal gate nMOSFETs can be realized.
In this study, the investigation of crystallization behaviour of Hf-rich aluminate is presented. Different alloys were deposited by ALCVD™ with composition ranging between 16 and 47 Al2O3 mol%. Post-deposition annealings were carried out in single or sequential mode using purified N2 at atmospheric pressure. Process temperature and time were varied from 700°C to 900°C and from 1' to 30' respectively. Upon these conditions, film thermal evolution was observed without any relevant increasing of in interface layer and any change in material composition. Measurements on 20 Al2O3 mol% films evidenced that thermal treatments up to 800°C promoted initial shrinking in thickness and material densification. Above 900°C, all considered aluminates were found to crystallize in orthorhombic phase maintaining original alloy composition. The higher the alumina content, the lower the grain size, the higher the crystallites density. Stability of orthorhombic crystalline structure was demonstrated upon single prolonged annealing up to 30' and upon sequential processes. In correspondence with film crystallization, enhancement of dielectric constant was detected with an increasing trend upon hafnia content. For 20 Al2O3 mol% aluminate, change in k form 19 to 40-45 was observed together with limited degradation in conduction and breakdown characteristics.
A new method to convert 12CaO7Al2O3 (C12A7) thin films to electronic conductor by hot Ar+ ion implantation has been developed and its mechanism is discussed. It was found that hot Ar+ ion implantation extruded free O2- ions in C12A7 films by kick-out effects at fluences higher than 1×1017 cm−2, which left electrons in the cages embedded in C12A7 crystal and produced high concentration F+-like centers (∼1.4×1021 cm−3). The resulting films show coloration and persistent electronic conduction with conductivities up to ∼1 Scm−1. On the other hand, fluences less than 1×1017 cm−2 kept the films transparent and insulating.
Ferroelectric lead lanthanum titanate (Pb1−xLaxTi1−x/4O3) (PLTx) thin films (x=0.04,0.08 and 0.12) have been prepared by sol-gel spin coating process on ITO coated 7059 Corning glass substrates. Investigations have been made on the crystal structure, surface morphology, dielectric and ferroelectric properties of the thin films. For a better understanding of the crystallization mechanism, the structural investigations were carried out at various annealing temperatures (350°C, 450°C, 550°C and 650°C). Characterization of these films by X-ray diffraction shows that the films annealed at 650°C exhibit tetragonal structure with perovskite phase. Replacement of lanthanum in lead titanate results in reduction of tetragonal ratio (c/a), resulting in better mechanical stability. Microstructural analysis of the films are carried out by taking the Atomic Force Microscope (AFM) pictures. AFM images are characterized by slight surface roughness with a uniform crack free, densely packed structure. Dielectric, pyroelectric and ferroelectric studies carried out on these films have been reported. Dielectric constant and pyroelectric coefficient increase while Curie temperature decreases with increase in La content. The pyroelectric figures of merit of the films have also been calculated which suggest that 8% lanthanum is best suited material for pyroelectric detectors owing to its high pyroelectric coefficient (∼ 29nC/cm2 K), high voltage responsivity (∼420Vcm2/J), high detectivity (∼1.04×10−5Pa−1/2) and low variation of pyrocoefficient with temperature.
In this paper, we report infrared absorption studies of HfO2, HfO2/Si interface and Hf(1−x)SixOy. Both HfO2 crystallization and SiO2 formation at the interface can be clearly detected in the absorption spectra in the far and middle infrared regions, respectively. By measuring the intensity change and the peak shift of infrared absorption spectra as functions of annealing temperature and time together with XRD patterns, we discuss a difference of the amorphous structure between HfO2 and SiO2, and also show an evolution of HfO2 crystallization in the monoclinic phase up to 1000 °C. On the other hand, it is shown that the interfacial SiO2 layer is qualitatively similar to the thermally grown SiO2. Furthermore, it is demonstrated that a Si incorporation into HfO2 film significantly changes the IR absorption spectra, and that the Hf(1−x)SixOy film is phase-separated with an appearance of modified monoclinic phase by higher temperature annealing.
We investigated the influence of pre-oxidation of an Ir film as a bottom electrode on the chemical composition and crystal property of the PZT film deposited on it by RF sputtering, changing the sputtering target composition ratio Zr/Ti to be 20/80, 52/48 or 80/20. The Ir film deposited on a thermally oxidized Si substrate was pre-oxidized at 600°C for 20 min in the O2 gas of 10 Pa. The XRD patterns showed a strong PbO(101) peak from the PZT film on the oxidized Ir film for Zr/Ti = 52/48, but no PbO peak from the film on a no oxidized Ir film. The RBS measurement showed that the film composition ratio of Pb/(Zr+Ti) on the pre-oxidized Ir film was much larger than that on the no oxidized Ir film. For Zr/Ti=20/80, the same tendency was observed. However, for Zr/Ti=80/20, the chemical composition of the PZT film on the pre-oxidized Ir film was almost equal to that without oxidation.
SrTa2O6 thin films with thickness between 6 and 150nm were deposited in a multi-wafer planetary MOCVD reactor combined with a TRIJET® liquid delivery system using a single source precursor, strontium-tantalum-(methoxyethoxy)-ethoxide dissolved in toluene. A rather narrow process window for the deposition of stoichiometric SrTa2O6 was found for this precursor at low pressures and a susceptor temperature around 500°C. Films were grown on Pt/TiO2/SiO2/Si, TiNx/Si, and SiO2/Si substrates. The as-deposited films were X-ray amorphous and could be crystallized by post-annealing at a temperature ≥700°C. The SrTa2O6 phase was dominating within a broad range of compositions (Sr/Ta: 0.4–0.7) and a perovskite type phase was observed for Sr/Ta > 0.7. The electrical properties have been investigated with MIM and MIS capacitors after sputter deposition of Pt top electrodes. The amorphous films had a relative permittivity, ε, in the range of 25–45, and low leakage currents. Crystallized films were investigated with Pt MIM capacitors. For stoichiometric SrTa2O6 the dielectric permittivity reached values of ε = 100–110, but the leakage currents were increased. Remarkably, the permittivity is not very sensitive to deviations from the exact stoichiometry of the SrTa2O6 phase (Sr/Ta: 0.40.7), but a decrease to values of ε = 30–40 is observed along with the phase transition at high Sr contents.
The integration of high-K materials, such as ferroelectrics in the paraelectric state, in integrated circuits presents several challenges. If high-K materials are deposited on-chip after or between Al metalization steps, then these challenges include limits on processing gas composition, deposition temperature and electrode material. Specifically, the atmosphere present during deposition and annealing must be oxygen-free; the deposition and annealing temperatures must not exceed 450°C; and the electrode material must be etchable with chemical techniques. We studied rf magnetron sputtered Ba0.96Ca0.04Ti0.84Zr0.16O3 (BCTZ) with Ni electrodes because this system meets all the above requirements. The BCTZ deposition process uses pure Ar as the sputter gas and a substrate temperature of 450°C. Subsequent anneals may be performed in a reducing (forming gas) atmosphere with little effect on either the dielectric constant or leakage current. The Ni electrodes provide a good substrate for BCTZ films and are much easier to integrate than Pt films. Observed values for the relative dielectric constant K, exceeding 100, were not as high as for BCTZ films on Pt electrodes, however these values are sufficient to provide a clear advantage over other, non-ferroelectric materials. Overall, the device characteristics observed prove that the Ni/BCTZ/Ni capacitor is a valuable technology for on-chip capacitor applications.
We have fabricated Pr-based high-k gate dielectric films by physical vapor deposition of metallic Pr on SiO2 under ultra-high vacuum (UHV) conditions at room temperature, followed by oxidation and annealing steps. The films have been analyzed by electrical measurements, X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM). Some insight into the physical processes involved has been obtained from ab initio calculations. The high-k gate stacks consist of a SiO2-based buffer with an enhanced dielectric constant and a Pr silicate barrier with a high dielectric constant. The role of the buffer is to preserve the high quality of the SiO2/Si(001) interface, and the role of the barrier is to keep the tunneling currents low by increasing its physical thickness. A Pr film deposited on a 1.8 nm SiO2 layer, oxidized at room temperature by air, and annealed in N2 atmosphere with O2 partial pressure of 10−3 mbar results in a stack with the Capacitance Equivalent Thickness of 1.5 nm and leakage of 10−4 A/cm2.
We report high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3×105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80 % in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics.
Tantalum oxide (Ta2O5) films were deposited onto p-type silicon substrates using reactive DC magnetron sputtering, and then annealed for one hour in a dry air ambient at temperatures of 730°C, 780°C, and 830°C. Annealing was shown to reduce stress from the as-deposited sample, and resulted in a compressive stress state for samples annealed at 730°C and a tensile stress state for the other samples. Hardness values were approximately 8 GPa, with the exception of the sample annealed at 780°C that demonstrated a hardness of 13 GPa. Leakage current generally decreased with annealing, especially at the lower temperatures. Electrical breakdown was observed for as-deposited and the 830°C annealed films. Resistivities of the films ranged from 6.5 × 109 to 6.1 × 1012 ω-cm, with the film annealed at 830°C being the most conductive. Annealing also led to an increase in dielectric constant. Dielectric constants varied from 9.3 for the as-deposited to greater than 30 for the 780°C and 830°C annealed sample. Annealing resulted in crystalline films that were close to stoichiometric.
The photo-induced magnetism was originally found in Pr0.65Ca0.35MnO3 powder by the ESR and x-ray diffraction studies. However, the mechanism of the photo-induce magnetism was under cover for a long time. Now, D.C. magnetization measurement under a near infrared pulsed laser irradiation (hν = 1.18 eV) reveals the mechanism. The D.C. magnetization prominently increases (approximately 6 %) under the laser irradiation, especially around 90 K near the canted antiferromagnetic (CAF) – antiferromagnetic (AF) transition. The result is consistent with the previous studies and indicates that a CAF – ferromagnetic transition is caused associating with the charge-order (CO) – charge-delocalize (CD) (insulator – metal) transition by the laser irradiation. As the second step for development, the thin films were prepared with the pellet of Pr0.65Ca0.35MnO3 in the on-axis and off-axis geometry of RF magnetron sputtering deposition. The off-axis geometry provides the Pr0.65Ca0.35MnO3 film same as powder composition and the on-axis sputtering fortunately provides the Pr0.99Ca0.01MnO3 film. Both films show photo-induced magnetism. The present photo-induced magnetism is coming from a spin-canted phase in both compounds.
The primary objective of this research is to optimize the different deposition conditions to obtain high tunability and low dielectric loss of Barium Strontium Titanate (BST) thin films at microwave frequencies. Ba0.5Sr0.5TiO3thin films were deposited on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition technique (PLD). Deposition conditions like temperature, oxygen pressure, substrate to target distance and laser energy are varied to obtain the objective. Deposition of the BST thin films on the Pt/TiO2/SiO2/Si substrates was carried out at temperatures of 450°°C, 550°°C, 650°°C and oxygen pressures of 250mTorr and 450mTorr with laser fluence of 250 mJ/cm2 and 450mJ/cm2 at 10 pulses per second. The microstructural and phase analysis of the deposited BST films at different temperatures and different oxygen pressures were performed using X-ray diffraction (XRD) method. The diffraction patterns are attributed to cubic (perovskite) crystal system. Atomic force microscopy (AFM) was used to perform the surface analysis of the films deposited at different substrate to target distances, varied laser energies and oxygen pressures. The BST capacitor was fabricated using the Coplanar Waveguide Structure and the capacitance and dielectric constant were measured using the Vector Network Analyzer (VNA). Tunability of 3.1:1 and loss tangent of 0.0121 was achieved at 0.4 – 0.8 GHz.
MOCVD of Bi2O3 has been investigated using Bi(C6H5)3 precursor. The decomposition products obtained at various deposition temperatures were determined using in situ FT-IR analysis. Benzene was the main product formed in the heterogeneous decomposition of Bi(C6H5)3 at temperature lower than 450°C, while above 450°C typical products of the combustion of aromatic ring were observed. The effect of oxygen on the film composition and its role in the decomposition process was evaluated by XPS depth profiles. Moreover, preliminary studies on the initial step of the film deposition suggested that Bi2O3 nucleation rate depends upon precursor partial pressure.
Epitaxial La0.67Ca0.33MnO3 films have been prepared on LaAlO3 crystals by pulsed laser deposition (PLD) and by a novel all-alkoxide sol-gel technique. Different out-of-plane lattice parameters are found for the as-prepared films, and scanning electron microscopy shows a more porous structure for sol-gel films as compared to PLD films. These differences are largely removed by post-annealing at 1000 °C. Transport measurements show maximum temperature coefficient of resistivity of 8.2 % K−1 at 258 K (PLD) and 6.1 % K−1 at 241 K (sol-gel) and colossal magnetoresistance at 7 kOe of 35 % at 263 K (PLD) and 32 % at 246 K (sol-gel).
Electron traps in ALD and MOCVD HfO2 and HfSiO high-k dielectrics were investigated using both conventional DC and pulse measurements. It was found that the traps in the gate stack could be associated with defects of different activation energies and capture cross-sections. This points to potentially different origins of the electrically active defects, which can be either intrinsic or process-related. Structural non-uniformity of the high-k film, associated with grain formation and phase separation, may lead to variation of electrical properties of the gate dielectric along the transistor channel. Effects of such dielectric non-uniformity, as well as electron trapping, on the measured transistor mobility were evaluated.
Electrical properties and leakage current mechanisms of perovskite CaZrO3 dielectric thin films have been studied in this paper. CaZrO3 thin films were deposited on Pt/SiO2/n-Si substrate by the sol-gel wet chemical technology, and then annealed at temperatures ranging from 550 to 700 °C for 1h in O2. The films with platinum (Pt) top and bottom electrodes were characterized with respect to the leakage current as a function of temperature and applied voltage. The CaZrO3 film annealed at 600 °C was amorphous and showed good electrical properties with a dielectric constant of about 15 and leakage current density of 10−8 A/cm2 at high applied electrical field of 2.5 MV/cm. The data can be interpreted via a Schottky barrier model. The conduction mechanism at low electric fields is due to Ohmic conduction. On the other hand Schottky mechanism dominates at the intermediate fields. The high dielectric constant, low leakage current density and high breakdown strength suggest that the CaZrO3 thin film is a promising candidate for high-k applications.
Insulating performance of high-density SiO2 films on Si(100) wafer grown by VUV irradiation in oxygen atmosphere at low-temperatures (300 ∼ 400°C) is reported. Comparing the SiO2 films grew with various wavelength irradiation, i.e., 126, 172 and 222nm, we found a strong wavelength dependence in density and insulating performance. The results suggest that electrical characteristics are highly correlated with film density. Higher density films are formed by shorter wavelength photo-oxidation whereas higher breakdown voltage and lower leakage current are achieved by the dense films. This shows that lower density of defects, dangling bonds, existing at the Si-O interface strongly affects the insulating performance. VUV photo-oxidation is a promising silicon oxide growth technique with greater insulating performance beyond the conventional limit for thermally oxidized films.
Germanium is because of its intrinsically higher mobility than Si, currently under consideration as an alternative approach to improve transistor performance. Germanium oxide, however, is thermodynamically unstable, preventing formation of the gate dielectric by simple oxidation. At present, high-k dielectrics might be considered as an enabling technology as much progress has been made in the deposition of thin high-quality layers.
In this paper, we study the growth and physical properties of HfO2 deposited on Ge by MOCVD, using TDEAH and O2 as precursors, and compare the results to similar layers deposited on silicon substrates. Our results show that the physical properties of MOCVD-deposited HfO2 layers on Ge are very similar to what we have observed in the past for Si. Unfortunately, some of the negative aspects observed for Si, such as diffusion of substrate material in the high-k layer, a low density for thinner layers, or a rough top surface, are also observed for the case of Ge. However, careful surface pretreatments such as NH3 annealing the Ge substrate prior to deposition, can greatly improve the physical properties. An important observation is the very thin interfacial layer between HfO2 and Ge substrate, allowing a more aggressive scaling for Ge.