Preparation of α-alumina/polymethacrylic acid composite abrasive and its CMP performance on glass substrate

Chemical mechanic polishing (CMP) has become a widely accepted global planarization technology. Abrasive is one of key elements during CMP process. α-Alumina particles, as a kind of widely used abrasive in CMP slurries, often cause surface defects due to its high hardness and agglomeration. In order to enhance the dispersion stability and prevent agglomeration of pure alumina abrasives in CMP, α-alumina grafted with polymethacrylic acid (α-Al₂O₃-g-PMAA) composite abrasives was prepared and characterized by means of Fourier transform infrared (FTIR), Mastersizer 2000 instrument and scanning electron microscope (SEM). The results indicated that the prepared α-Al₂O₃-g-PMAA composite abrasives have better dispersion stability than pure α-Al₂O₃ abrasives. The CMP performances of the α-Al₂O₃-g-PMAA composite abrasives on glass substrate were investigated by SPEEDFAM-16B-4M CMP equipment with different process parameters. By using the optimum process parameters, the prepared abrasives exhibit better glass substrate CMP performance than pure α-Al₂O₃ abrasives. Further, the CMP mechanism of glass substrate was deduced preliminarily.     

Microwave properties of epitaxial large-area Ca-doped YBa2Cu3O7−δ thin films on r-plane sapphire

Ca doping of YBa₂Cu₃O_7−δ (YBCO) is well known to enhance the critical current density in large-angle grain boundaries for example of bicrystals. However, up to now no data are available on microwave properties of epitaxial Ca-doped YBa₂Cu₃O_7−δ thin films on r-plane sapphire with CeO₂ buffer layer.Therefore, first results are presented for large-area pulsed laser deposition (PLD) grown Ca_xY_1−xBa₂Cu₃O_7−δ films on 3-in. diameter sapphire wafers. The PLD process is optimised for undoped YBCO thin films and shows high reproducibility for YBCO. The microwave surface resistance R_s at 8.5 GHz of Ca-doped YBCO (x=0.1) thin films shows clear reduction (up to 20%) with respect to that of YBCO for temperatures from about 20–50 K. In addition, microwave surface resistance R_s of Ca-doped YBCO is lower than that of YBCO even for enhanced microwave surface magnetic field up to about 20 mT for temperatures 20 and 40 K.     

NMOSFET characteristics on a double hetero-epitaxial Si/γ-Al2O3/Si structure fabricated by a new MBE growth method

A new MBE growth method for the fabrication of a high-quality double hetero-epitaxial Si/γ-Al₂O₃/Si structure was recently developed. In the present work, characteristics of NMOSFETs fabricated on the Si/γ-Al₂O₃/Si structure were investigated, and compared with those on a Si/MgAl₂O₄/Si structure. A γ-Al₂O₃ layer was created from a MgAl₂O₄ layer by reaction with Si beams as follows: MgAl₂O₄ + Si → γ-Al₂O₃ + SiO ↑ + Mg ↑. The MBE growth of Si on the effectively restructured γ-Al₂O₃ layer was then performed at a substrate temperature of 700° C, 150° C lower than for the MBE growth of Si on a MgAl₂O₄/Si substrate. The electron field effect mobility and leakage current between source and drain for the NMOSFETs fabricated on Si/γ-Al₂O₃/Si structures were 660 cm²/V · s and 2.8 pA/μm respectively, and exhibited a higher level of performance than those on a Si/MgAl₂O₄/Si structure. In the Si/MgAl₂O₄/Si, SIMS measurements confirmed that autodoped Al and Mg atoms near the interface between the Si epi-layer and MgAl₂O₄/Si substrate diffused anomalously and accumulated at the surface during device fabrication processes. These autodoped Al and Mg atoms acted as ionized impurities during test operation. Suppression of autodoping from insulator layers during the MBE growth of Si was thus deemed essential to the improvement of NMOSFET characteristics. In the Si/γ-Al₂O₃/Si structure, autodoped atoms were scarcely detectable. It was therefore concluded that the Si/γ-Al₂O₃/Si structure under study was very promising for SOI device applications.     

Engineered oxide thin films as 100% lattice match buffer layers for YBCO coated conductors

One of the most important qualities of buffer layers for RE-BCO coated conductors’ growth is close lattice match with RE-BCO. However, there is no natural material with a 100% lattice match with RE-BCO. In this study mixtures of europium oxide (Eu₂O₃) and ytterbium oxide (Yb₂O₃), (Eu_1−uYb_u)₂O₃ (0.0u1.0), were investigated as a candidate buffer layer that could have same lattice parameter as YBa₂Cu₃O_7−δ(YBCO). Because the pseudocubic lattice parameter of Eu₂O₃ is bigger, and that of Yb₂O₃ is smaller than lattice parameter of YBCO, and the mixed oxides with appropriate ratio would have same lattice parameter of YBCO. The mixtures were prepared using metal-organic precursor by sol–gel process, and it was found that all mixed samples are single phase, complete solid solutions, and have same crystal system over the whole range of “u”. Lattice parameters of mixed (Eu_1−uYb_u)₂O₃ oxide powders were changed between 10.86831 and 10.42828 Å which are lattice parameter of Eu₂O₃ and Yb₂O₃, respectively by changing the ratio of Eu/Yb in the mixture. Phase and lattice parameter analysis revealed that pseudocubic lattice parameter of (Eu_0.893Yb_0.107)₂O₃ is 3.82 Å which is same as the lattice parameter of YBCO. Textured (Eu_0.893Yb_0.107)₂O₃ buffer layers were grown on biaxially textured-Ni (1 0 0) substrates. The solution was prepared from Europium and Ytterbium 2,4-pentadioanate, and was deposited on the Ni substrates using a reel-to-reel sol–gel dip coating system. The textured films were annealed at 1150 °C for 10 min under 4% H₂–Ar gas flow. Extensive texture analysis has been done to characterize the texture of (Eu_0.893Yb_0.107)₂O₃ buffer layers. X-ray diffraction (XRD) of the buffer layer showed strong out-of-plane orientation on Ni tape. The (Eu_0.893Yb_0.107)₂O₃ (2 2 2) pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full-width-at-half-maximum (FWHM) values of omega and Phi scan of (Eu_0.893Yb_0.107)₂O₃ films were 6.45° and 7.70°, respectively. ESEM micrographs of the films revealed pinhole-free, crack-free and dense microstructures.     

Templates for LaAlO3 epitaxy on silicon

As direct epitaxy of crystalline LaAlO₃ on silicon has not been realized yet, we investigated the use of a template between the high-κ and the substrate. We performed calculations in the Density Functional Theory framework for two possible templates: a Sr_0.5O monolayer and a 0.5 nm thick γ-Al₂O₃(0 0 1) layer. We firstly found that in the Sr_0.5O monolayer case, care must be taken for the LaAlO₃ starting sequence in order to expect good band offsets with silicon. In the γ-Al₂O₃ case, a more complex engineering of the interface is needed. Nonetheless, we found stable interfaces and a surface reconstruction in agreement with experimental observations. Moreover, these interfaces exhibit insulating properties and insight calculations for a Si–γ-Al₂O₃–LaAlO₃ superstructure lead us to a 1.9 eV conduction band offset.     

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.     

Etch pits observation and etching properties of β-FeSi2

We have investigated the etching properties of p- and n-type β-FeSi₂ crystals grown from solution. Characteristic shapes of etch pits depending on the surface orientation was observed on the etched surface by using diluted hydrofluoric acid (5% of HF) and HF:HNO₃:H₂O=1:1:(2–8) solutions. However, the shapes of etch pits were independent of the conduction type and carrier density of the crystals. We also found the anisotropy of etch rates. The etch rates of the HF:HNO₃:H₂O=1:1:2 solution at 22°C were approximately 1.57, 1.43 and 1.09 μm/min on {1 1 1}, {1 0 0} and {0 0 1} faces of p-type β-FeSi₂ crystals, respectively.     

New dielectric material system of Nd(Mg1/2Ti1/2)O3–CaTiO3 at microwave frequency

The microwave dielectric properties of (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ (0.1  x  1.0) ceramics prepared by the conventional solid state method have been investigated. The system forms a solid solution throughout the entire compositional range. The dielectric constant decreases from 152 to 27 as x varies from 0.1 to 1.0. In the (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ system, the microwave dielectric properties can be effectively controlled by varying the x value. At 1400 °C, 0.1CaTiO₃–0.9Nd(Mg_1/2Ti_1/2)O₃ has a dielectric constant (ε_r) of 42, a Q × f value of 35 000 GHz and a temperature coefficient of resonant frequency (τ_f) of −10 ppm/°C. As the content of Nd(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 43 000 GHz for x = 0.9 is achieved at the sintering temperature 1500 °C.     

High temperature transport kinetics in heteroepitaxial LaFeO3 thin films

Heteroepitaxial LaFeO₃(1 1 0) thin films with a thickness of 150 nm were grown on LaAlO₃(0 0 1) by reactive sputtering in an inverted cylindrical magnetron geometry. Equilibrium conductivity was measured as a function of partial pressure of oxygen at T=1000 °C, and logσ plotted vs. logP(O₂) showed a minimum in conductivity for P(O₂)=10⁻¹¹ atm and a linear response between 10⁻¹⁰ and 1 atm. This linear response makes thin films of LaFeO₃ a promising material for oxygen sensor applications. We have also measured the time response of the film conductivity upon an abrupt change in the partial pressure of ambient oxygen from 10⁻² to 10⁻³ atm, which was determined at 60 s for T=700 °C and <3.5 s at T=1000 °C.     

Growth of lanthanum oxide films for application as a gate dielectric in CMOS technology

We have investigated properties of insulating lanthanum oxide (La₂O₃) films in connection with the replacement of silicon oxide (SiO₂) gate dielectrics in new generation of CMOS devices. The La₂O₃ layers were grown using metal organic chemical vapour deposition (MOCVD) at 500 °C. X-ray diffraction analysis revealed polycrystalline character of the films grown above 500 °C. The X-ray photoemission spectroscopy detected lanthanum carbonate as a principal impurity in the films and lanthanum silicate at the interface with silicon. Density of oxide charge, interface trap density, leakage currents and dielectric constant ( κ) were extracted from the C-V and I-V measurements. Electrical properties, in particular dielectric constant of the MOCVD grown La₂O₃ are discussed with regard to the film preparation conditions. The as grown film had κ11. Electrical measurements indicate possible presence of oxygen vacancies in oxide layer. The O₂-annealed La₂O₃ film had κ17.     

Investigation of high-K gate stacks with epitaxial Gd2O3 and FUSI NiSi metal gates down to CET=0.86 nm

Novel gate stacks with epitaxial gadolinium oxide (Gd₂O₃) high-k dielectrics and fully silicided (FUSI) nickel silicide (NiSi) gate electrodes are investigated. Ultra-low leakage current densities down to 10^–7 A cm^–2 are observed at a capacitance equivalent oxide thickness of CET=1.8 nm. The influence of a titanium nitride (TiN) capping layer during silicidation is studied. Furthermore, films with an ultra-thin CET of 0.86 nm at a Gd₂O₃ thickness of 3.1 nm yield current densities down to 0.5 A cm⁻² at V_g=+1 V. The extracted dielectric constant for these gate stacks ranges from k=13 to 14. These results emphasize the potential of NiSi/Gd₂O₃ gate stacks for future material-based scaling of CMOS technology.     

电子束辐照下的石墨烯上的原子层沉积Al2O3介质层

为了研究石墨烯与高k介质的结合,使用原子层沉积氧化铝在石墨衬底上。沉积前使用电子束辐照,观测到了氧化铝明显改善的形貌。归因于电子束辐照过程中的石墨层的无定形变化过程。     

Effective formation of interface controlled Y2O3 thin film on Si(1 0 0) in a metal-(ferroelectric)-insulator-semiconductor structure

Yttrium was deposited on the chemical oxide of Si and annealed under vacuum to control the interface for the formation of Y₂O₃ as an insulating barrier to construct a metal-ferroelectric-insulator-semiconductor structure. Two different pre-annealing temperatures of 600 and 700 °C were chosen to investigate the effect of the interface state formed after the pre-annealing step on the successive formation of Y₂O₃ insulator and Nd₂Ti₂O₇ (NTO) ferroelectric layer through annealing under an oxygen atmosphere at 800 °C. Pre-anneal treatments of Y-metal/chemical-SiO₂/Si at 600 and 700 °C induced a formation of Y₂O₃ and Y-silicate, respectively. The difference in the pre-anneal temperature induced almost no change in the electrical properties of the Y₂O₃/interface/Si system, but degraded properties were observed in the NTO/Y₂O₃/interface/Si system pre-annealed at 600 °C when compared with the sample pre-annealed at 700 °C. C-V characteristics of the NTO/Y₂O₃/Si structured system showed a clockwise direction of hysteresis, and this gap could be used as a memory window for a ferroelectric-gate. A smaller hysteric gap and electrical breakdown values were observed in the NTO/Y₂O₃/Si system pre-annealed at 600 °C, and this was due to an unintentional distribution of the applied field from the presence of an interfacial layer containing Y-silicate and SiO₂ phases.     

High temperature characterization of high-κ dielectrics on SiC

We have fabricated thin catalytic metal–insulator–silicon carbide based structure with palladium (Pd) gates using TiO₂ as the dielectric. The temperature stability of the capacitor is of critical importance for use in the fabrication of electronics for deployment in extreme environments. We have evaluated the response to temperatures in excess of 450 °C in air and observed that the characteristics are stable. Results of high temperature characterization are presented here with extraction of interface state density up to 650 °C. The results show that at temperatures below 400 °C the capacitors are stable, with a density of interface traps of approximately 6×10¹¹ cm² eV⁻¹. Above this temperature the C–V and G–V characteristics show the influence of a second set of traps, with a density around 1×10¹³ cm² eV⁻¹, which is close to that observed for slow states near the conduction band edge. The study of breakdown field as a function of temperature shows two distinct regions, below 300 °C where the breakdown voltage has a strong temperature dependence and above 300, where it is weaker. We hypothesize that the oxide layer dominates the breakdown voltage at low temperature and the TiO₂ layer above 300 °C. These results at high temperatures confirms the suitability of the Pd/TiO₂/SiO₂/SiC capacitor structure for stable operation in high temperature environments.     

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.     

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.     

The properties of high-k gate dielectric films deposited on HRSOI

In this paper, HfO₂ dielectric films with blocking layers (BL) of Al₂O₃ were deposited on high resistivity silicon-on-insulator (HRSOI), and the interfacial and electrical properties are reported. High-resolution transmission electron microscopy (HRTEM) indicated that BL could thin the interfacial layer, keep the interface smooth, and retain HfO₂ amorphous after annealing. Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) confirmed that BL weaken Si diffusion and suppressed the further growth of HfSiO. Electrical measurements indicated that there was no hysteresis was observed in capacitance–voltage curves, and Flatband shift and interface state density is 0.05 V and −1.3 × 10¹² cm⁻², respectively.     

Infrared spectroscopy and X-ray diffraction studies on the crystallographic evolution of La2O3 films upon annealing

Rare earth oxides (REOs) have lately received extensive attention in relation to the continuous scaling down of non-volatile memories (NVMs). In particular, La₂O₃ films are promising for integration into future NVMs because they are expected to crystallize above 400 °C in the hexagonal phase (h-La₂O₃) which has a higher κ value than the cubic phase (c-La₂O₃) in which most of REOs crystallize. In this work, La₂O₃ films are grown on Si by atomic layer deposition using La(C₅H₅)₃ and H₂O. Within the framework of the h-La₂O₃ formation, we systematically study the crystallographic evolution of La₂O₃ films versus annealing temperature (200-600 °C) by Fourier transform infrared spectroscopy (FTIR) and grazing incidence X-ray diffraction (GIXRD). As-grown films are chemically unstable in air since a rapid transformation into monoclinic LaO(OH) and hexagonal La(OH)₃ occurs. Vacuum annealing of sufficiently thick (>100 nm) La(OH)₃ layers induces clear changes in FTIR and GIXRD spectra: c-La₂O₃ gradually forms in the 300-500 °C range while annealing at 600 °C generates h-La₂O₃ which exhibits, as inferred from our electrical data, a desirable κ ∼ 27. A quick transformation from h-La₂O₃ into La(OH)₃ occurs due to H₂O absorption, indicating that the annealed films are chemically unstable. This study extends our recent work on the h-La₂O₃ formation.     

A comparison of liquid and gas phase surface preparation of III-V compound semiconductors for atomic layer deposition

Native oxide removal and surface termination of InAs(1 0 0) and InSb(1 0 0) using liquid and gas phase HF chemistries were studied using X-ray photoelectron spectroscopy. Aqueous HF etching removed the native oxides on InAs and produced elemental As, which reoxidized when exposed to air. On InSb the native oxides were not completely removed due to F-termination, which passivated the surface. Gas phase HF etching of InSb native oxide completely removed Sb₂O₅ producing a stoichiometric semiconductor surface terminated by F atoms on primarily In surface sites. On InAs gas phase HF completely removed As₂O₃ producing two surface stoichiometries. For the majority of HF to water molar ratios studied, a stoichiometric bulk metal and an As-rich overlayer were produced. For a lean HF composition, an As-rich bulk metal and In-rich overlayer were produced. Deposition of Al₂O₃ by atomic layer deposition (ALD) at 170 °C directly onto F-terminated InSb produced a chemically sharp Al₂O₃/InSb interface. ALD of Al₂O₃ on an In-rich overlayer on InAs resulted in an interfacial layer containing As-oxide.     

Selective etching of (Ba,Sr)TiO3 thin films over silicon in an inductively coupled plasma

In this work, we investigated etching characteristics of BST thin films and higher selectivity of BST over Si using inductive coupled O₂/Cl₂/Ar plasma (ICP) system. The maximum etch rate of BST thin films and selectivity of BST over Si were 61.5 nm/min at a O₂ addition of 1 sccm, 9.52 at a O₂ addition of 4 sccm into the Cl₂(30%)/Ar(70%) plasma, respectively. Plasma diagnostics was performed by Langmuir probe (LP), optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). These results confirm that the increased etch rates at O₂ addition of 1 sccm is the result of the enhanced chemical reaction between BST and Cl radicals and an ion bombardment effect.