Structural and interfacial properties of high-k HfOxNy gate dielectric films

The thermal stability and interfacial characteristics for hafnium oxynitride (HfO_xN_y) gate dielectrics formed on Si (1 0 0) by plasma oxidation of sputtered HfN films have been investigated. X-ray diffraction results show that the crystallization temperature of nitrogen-incorporated HfO₂ films increases compared to HfO₂ films. Analyses by X-ray photoelectron spectroscopy confirm the nitrogen incorporation in the as-deposited sample and nitrogen substitution by oxygen in the annealed species. Results of FTIR characterization indicate that the growth of the interfacial SiO₂ layer is suppressed in HfO_xN_y films compared to HfO₂ films annealed in N₂ ambient. The growth mechanism of the interfacial layer is discussed in detail.     

Spectroscopic ellipsometry characterization of ZrO2 thin films by nitrogen-assisted reactive magnetron sputtering

Spectroscopic ellipsometry (SE) with photon energy 0.75–6.5 eV at room temperature has been used to derive the optical properties of high-k ZrO₂ thin films on Si(1 0 0) substrates prepared by nitrogen-assisted, direct current reactive magnetron sputtering. The Tauc–Lorentz dispersion method was adopted to model the optical dispersion functions of the thin films as a function of annealing temperature. Excellent agreement has been found between the SE fitting results and X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) results, indicating that our model adequately described the measured SE data. Optical band gaps (E_g) were also obtained based on the extracted absorption edge. Our results suggest that nitrogen-assisted process can effectively limit the interfacial layer growth in high-k oxides.     

Optical characterization of as-prepared and rapid thermal oxidized partially strain compensated Si1−x−y GexCy films

The optical properties of as-prepared and rapid thermal oxidized (RTO) heteroepitaxial Si_1−x−yGe_xC_y alloys grown on Si substrate have been characterized using spectroscopic ellipsometry. The critical points E₁, E₀′, E₂ band gaps were determined by line shape fitting in the second derivative spectra of the pseudo-dielectric functions. For as-prepared films, the E₁ gap increases with C concentration and a linear dependence on C content was observed. However, the E₂ gap decreases as the C concentration increases. For the RTO samples, the amplitude of E₂ transition reduces rapidly and the E₁ transition shifts to a lower energy. The reduction in the amplitude of E₂ transitions is due to the presence of oxide layer. A high Ge content layer and the low C content in the RTO films account for the E₁ shift to lower energy and the increase of the refractive indices.     

Electrodepositing ZnxMnyOz alloys from zinc oxide to manganese oxide

Electrodeposition has emerged as a practical and simple method to synthesise semiconductor materials under different forms, thin films or nanostructured layers. This work reports on the cathodic electrodeposition of ZnMnO thin layers using both zinc and manganese chlorides as precursors. The composition of thin films can be varied from binary zinc oxide to manganese oxide varying the Mn/(Mn+Zn) ratio between 0 and 1. The composition of Zn_xMn_yO_z films was obtained by energy dispersive spectroscopy. Zn_1−xMn_xO films with Mn/Zn ratio less than 10% exhibit a crystalline wurtzite structure typical of ZnO fully oriented in the (0 0 2) direction. Higher Mn content leads to deformation of the ZnO lattice and the wurtzite structure is no longer maintained. X-ray photoelectron spectroscopy points out that Mn₃O₄ tends to be deposited when a high Mn/Zn ratio is used in the starting solution. Magnetic measurements on films with Mn/(Zn+Mn) ratio near 1 reveal magnetic characteristics similar to Mn₃O₄ compounds. The transmission spectra of Zn_xMn_yO_z show the typical absorption edge of crystalline ZnO while the wurtzite structure is maintained and it shifts to higher wavelengths when Mn content increases.     

溅射压力对制备a-GaAs1-xNx 薄膜光学常数的影响

采用反应磁控溅射法在室温条件下制备了a-GaAs_1-xN_x 薄膜。实验测定了薄膜厚度、氮含量、载流子浓度和光学透过率及并研究了其随溅射压的变化。系统研究了溅射压对所制备薄膜的光学带隙、折射率和色散参数的影响。所制备的薄膜为直接带隙材料,利用Cauchy和Wemple模型能够很好地拟合所制备薄膜的折射率色散曲线。     

High performance TaYOx-based MIM capacitors

TaYO_x-based metal-insulator-metal (MIM) capacitors with excellent electrical properties have been fabricated. Ultra-thin TaYO_x films in the thickness range of 15-30 nm (EOT ∼ 2.4-4.7 nm) were deposited on Au/SiO₂ (100 nm)/Si (100) structures by rf-magnetron co-sputtering of Ta₂O₅ and Y₂O₃ targets. TaYO_x layers were characterized by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) to examine the composition and crystallinity. An atomic percentage of Ta:Y = 58.32:41.67 was confirmed from the EDX analysis while XRD revealed an amorphous phase (up to 500 °C) during rapid thermal annealing. Besides, a high capacitance density of ∼3.7-5.4 fF/μm² at 10 kHz (ε_r ∼ 21), a low value of VCC (voltage coefficients of capacitance, α and β) have been achieved. Also, a highly stable temperature coefficient of capacitance, TCC has been obtained. Capacitance degradation phenomena in TaYO_x-based MIM capacitors under constant current stressing (CCS at 20 nA) have been studied. It is observed that degradation depends strongly on the dielectric thickness and a dielectric breakdown voltage of 3-5 MV/cm was found for TaYO_x films. The maximum energy storage density was estimated to be ∼5.69 J/cm³. Post deposition annealing (PDA) in O₂ ambient at 400 °C has been performed and further improvement in device reliability and electrical performances has been achieved.     

Etch damage evaluation on (Bi4−xLax)Ti3O12 thin films during the etch process using inductively coupled plasma sources

The etching mechanism of (Bi_4−xLa_x)Ti₃O₁₂ (BLT) thin films in Ar/Cl₂ inductively coupled plasma (ICP) and plasma-induced damages at the etched surfaces were investigated as a function of gas-mixing ratios. The maximum etch rate of BLT thin films was 50.8 nm/min of 80% Ar/20% Cl₂. From various experimental data, amorphous phases on the etched surface existed on both chemically and physically etched films, but the amorphous phase was thicker after the 80% Ar/20% Cl₂ process. Moreover, crystalline “breaking” appeared during the etching in Cl₂-containing plasma. Also the remnant polarization and fatigue resistances decreased more for the 80% Ar/20% Cl₂ etch than for pure Ar plasma etch.     

Influence of La substitution on the electrical properties of metal-ferroelectric (BiFeO3)-insulator (CeO2)-semiconductor nonvolatile memory structures

Metal-multiferroic (La-substituted BiFeO₃)-insulator (CeO₂)-semiconductor (MFIS) capacitors has been fabricated. The crystalline phase and amount of La³⁺ substitution at Bi-site were investigated by XRD and XPS in the postannealing temperature range from 500 to 700 °C, respectively. The microstructure and interfacial layer between CeO₂ and Si substrate were characterized by HRTEM. The memory windows as functions of insulator film thickness and DC power for La were measured. The maximum memory window is about 1.9 V under ±6 V applied voltage. The ferroelectric polarization increases with increasing substitution amount. The morphologies of La-substituted BiFeO₃ films were also studied by AFM.     

First investigation of metal–insulator–metal (MIM) capacitor using Pr2O3 dielectrics

Metal–insulator–metal (MIM) capacitors with Pr₂O₃ as high-k material have been investigated for the first time. We varied the thickness of the Pr₂O₃ layers as well as the bottom electrode material. The layers are characterised using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS). Preliminary information on the interaction of water with the films was obtained from XPS and ab initio pseudopotential calculations. The electrical characterisation shows that Pr₂O₃ MIM capacitors can provide higher capacitance densities than Si₃N₄ MIM capacitors while still maintaining comparable voltage coefficients of capacitance. The Pr₂O₃ dielectric material seems to be suitable for use in silicon RF applications.     

Annealing effect on physical and electrical characteristics of thin HfO2, HfSixOy and HfOyNz films on Si

We report the effect of annealing on electrical and physical characteristics of HfO₂, HfSi_xO_y and HfO_yN_z gate oxide films on Si. Having the largest thickness change of 0.3 nm after post deposition annealing (PDA), HfO_yN_z shows the lowest leakage current. It was found for both as-grown and annealed structures that Poole-Frenkel conduction is dominant at low field while Fowler-Nordheim tunneling in high field. Spectroscopic ellipsometry measurement revealed that the PDA process decreases the bandgap of the dielectric layers. We found that a decreasing of peak intensity in the middle HfO_yN_z layer as measured by Tof-SIMS may suggest the movement of N toward the interface region between the HfO_yN_z layer and the Si substrate during the annealing process.     

Local crystal structural modifications in pulsed laser deposited high-k dielectric thin films on silicon and germanium

The thin film growth conditions are correlated with the local structures formed in Hf_xZr_1−xO₂ (x=0.0–1.0) high-k dielectric thin films on Si and Ge substrates during deposition. Pulsed laser deposition (PLD) technique has been used in the synthesis of the thin films with systematic variations of substrate temperature, Zr content of the targets and substrate selection. The local structural information acquired from extended X-ray absorption spectroscopy (EXAFS) is correlated with the thin film growth conditions. The response of the local structure around Hf and Zr atoms to growth parameters was investigated by EXAFS experiments performed at the National Synchrotron Light Source of Brookhaven National Laboratory. The competing crystal phases of oxides of Hf were identified and the intricate relation between the stabilized phase and the parameters as: the substrate temperature; Hf to Zr ratio; have been revealed. Specifically, HfO₂ thin films on Si(1 0 0) exhibit a tetragonal to monoclinic phase transformation upon increase in the substrate temperature during deposition whereas, HfO₂ PLD films on Ge(1 0 0) substrates remain in tetragonal symmetry regardless of the substrate temperature.     

Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol-gel method and reaction-anneal treatment

Hafnium oxide (HfO₂) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl₄) source by surface sol-gel process, then ultrathin (HfO₂)_x(SiO₂)_1−x films were fabricated due to the reaction of SiO₂ layer with HfO₂ under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol-gel derived ultrathin films are Hf-Si-O alloy instead of HfO₂ and pre-grown SiO₂ layer, and the composition was Hf_0.52Si_0.48O₂ under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO₂)_x(SiO₂)_1−x composite films has been developed by means of combination of surface sol-gel and reaction-anneal treatment.     

Effect of annealing on Zn1−xCoxO thin films prepared by electrodeposition

Polycrystalline thin films of Zn_1−xCo_xO with different cobalt (Co) content were grown on indium tin oxide (ITO) substrates by cathodic electrodeposition technique and subsequently annealed in air at 400 °C. The effect of annealing in their structural, optical and chemical properties has been characterized by X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman scattering and optical spectroscopy. Our measurements indicate that moderate annealing increases the crystal quality of the films. The films are highly transparent in the visible range and evidence an increase of the band gap and of the intensity of three typical Co absorption bands in the visible with the amount of Co. Thermal annealing produces an increase of the intensity of the Co²⁺-related absorption bands revealing that higher amount of Co atoms are occupying Zn sites.     

Ballistic electron emission microscopy studies of the temperature dependence of Schottky barrier height distribution in CoSi2/n-Si(1 0 0) diodes formed by solid phase reaction

Ballistic electron emission microscopy (BEEM) and ballistic electron emission spectroscopy have been performed on polycrystalline and epitaxial CoSi₂/n-Si(1 0 0) contacts at temperatures ranging from −144°C to −20°C. The ultra-thin CoSi₂ films (10 nm) were fabricated by solid state reaction of a single layer of Co (3 nm) or a multilayer of Ti (1 nm)/Co (3 nm)/amorphous-Si(1 nm)/Ti (1 nm) with a Si substrate, respectively. The spatial distribution of barrier height over the contact area obeys a Gaussian function at each temperature. The mean barrier height increases almost linearly with decreasing temperature with a coefficient of −0.23±0.02 meV/K for polycrystalline CoSi₂/Si diodes and −0.13±0.03 meV/K for epitaxial diodes. This is approximately equal to one or one-half of the temperature coefficient of the indirect energy gap in Si, respectively. It suggests that the Fermi level is pinned to different band positions of Si. The width of the Gaussian distribution is about 30–40 meV, without clear dependence on the temperature. The results obtained from conventional current–voltage and capacitance–voltage (I–V/C–V) measurements are compared to BEEM results.     

Photoemission (XPS and XPD) study of epitaxial LaAlO3 film grown on SrTiO3(0 0 1)

This study investigates the tensile-strained growth of LaAlO₃ on SrTiO₃(0 0 1) substrate by molecular beam epitaxy (MBE). Growth was controlled in situ by reflection high energy electron diffraction (RHEED). The characterization was carried out ex situ by photoemission and atomic force microscopy (AFM). Photoelectron spectroscopy (XPS) reveals the development of a TiO_x-rich interface. Photoelectron diffraction (XPD) confirms that a 1.2-nm-thick pseudomorphic LaAlO₃ film has been grown on SrTiO₃(0 0 1) substrate with a perpendicular lattice parameter of 0.372±0.02 nm.     

Electrical properties of metal-ferroelectric-insulator-semiconductor structure using BaxSr1−xTiO3 for ferroelectric-gate field effect transistor

Perovskite ferroelectric Ba_xSr_1−xTiO₃ (x = 0.5, 0.6, 0.7 and 0.8) thin films have been fabricated as metal-ferroelectric-insulator-semiconductor (MFIS) configurations using a sol-gel technique. The C-V characteristics for different Ba-Sr ratios and different film thicknesses have been measured in order to investigate the ferroelectric memory window effect. The results show that the memory window width increases with the increase both of Ba content and film thickness. This behavior is attributed to the grain size and dipole dynamics effect. It is found also that the memory window increases as the applied voltage increases. In addition, the leakage current density for the films is measured and it is found to be of the order of 10⁻⁸ A/cm² for all tested samples, indicating that the films have good insulating characteristics.     

Effect of rapid thermal annealing of sputtered aluminium nitride film in an oxygen ambient

Aluminium nitride (AlN) thin films were deposited by radio frequency (RF) magnetron sputtering on p-type silicon (Si) substrate of (1 0 0) orientation using only argon (Ar) gas at substrate temperature of 300 °C. In order to achieve improved electrical properties, we performed post-deposition rapid thermal annealing (RTA). Sputtered AlN films were annealed in an oxygen ambient at temperatures of 600, 700, and 800 °C using RTA for 30 min. The orientation of the AlN crystal in the film was investigated using X-ray diffraction (XRD). The characteristic spectra by functional group were analyzed by Fourier transformation infrared (FTIR) spectroscopy. The electrical properties of the AlN thin films were studied through capacitance–voltage (C–V) characteristics in metal–insulator–semiconductor (MIS) device using the films as insulating layers. The flatband voltages (V_FB) in C–V curves were found to depend on crystal orientations. Negative V_FB was found in the case when AlN (1 0 0) peak was found. Also, when AlN (1 0 3) peak was observed upon increasing the annealing temperature, the value of V_FB was positive and after annealing at 700 °C, AlN (1 0 3) peak intensity was found to be maximum and V_FB was as high as+6.5 V.     

Effects of high doping on the bandgap bowing for AlxGa1−xN

This paper gives the composition dependence of the bandgap energy for highly doped n-type Al_xGa_1−xN. We report results of the bowing parameter obtained using a random simulation. Three groups of Al_xGa_1−xN semiconductors were considered and which are distinguishable by their non degenerate or degenerate character in the doping density (10¹⁷?N_D?10²⁰ cm⁻³). A striking feature is the large discrepancy of the bandgap bowing (−2.02?b?2.94 eV), as was demonstrated from our calculations. This suggests that high doping may be a possible cause able to induce the large range of bowing parameters reported for Al_xGa_1−xN alloys.     

Structural analysis of Ge x Si1−x /Si layers by remote plasma-enhanced chemical vapor deposition on Si (100)

In this work, remote plasma-enhanced chemical vapor deposition (RPCVD) has been used to grow Ge _x Si_1−x /Si layers on Si(100) substrates at 450° C. The RPCVD technique, unlike conventional plasma CVD, uses an Ar (or He) plasma remote from the substrate to indirectly excite the reactant gases (SiH₄ and GeH₄) and drive the chemical deposition reactions. In situ reflection high energy electron diffraction, selected area diffraction, and plan-view and cross-sectional transmission electron microscopy (XTEM) were used to confirm the single crystallinity of these heterostructures, and secondary ion mass spectroscopy was used to verify abrupt transitions in the Ge profile. XTEM shows very uniform layer thicknesses in the quantum well structures, suggesting a Frank/ van der Merwe 2-D growth mechanism. The layers were found to be devoid of extended crystal defects such as misfit dislocations, dislocation loops, and stacking faults, within the TEM detection limits (∼10⁵ dislocations/cm²). Ge _x Si_1−x /Si epitaxial films with various Ge mole fractions were grown, where the Ge contentx is linearly dependent on the GeH₄ partial pressure in the gas phase for at leastx = 0 − 0.3. The incorporation rate of Ge from the gas phase was observed to be slightly higher than that of Si (1.3:1).     

Systematic optical and x-ray study of In x Ga1−x As on InP

We present a systematic study of In _x Ga_1−x As on InP grown by molecular beam epitaxy using the characterization techniques of Fourier transform photoluminescence, x-ray diffraction, micro-Raman spectroscopy, and photoreflectance spectroscopy. The four techniques were used to determine and correlate the fundamental parameters of band-gap energy, phonon frequency and composition. Comparing room temperature (293 K) PL and low temperature PL indicate the presence of a partially ionized acceptor with binding energy of about 13 meV in the unintentionally doped material. Double crystal x-ray diffraction (XRD) using a symmetric <400> and asymmetric <224> reflections was also employed. The use of two reflections gives precise lattice constants, composition, and extent of film relaxation. Micro-Raman spectroscopy was used to measure phonon frequencies in the In _x Ga_1−x As films and correlated to XRD composition. Room temperature photoreflectance (PR) was used to determine band-gap energy for both the low and intermediate field cases. Band gap energies determined at room temperature by PL and PR were in agreement within experimental error.