As-deposited Structures Research Articles

High-$\kappa$$\hbox{Al}_{2}\hbox{O}_{3}{-}\hbox{HfTiO}$ Nanolaminates With Less Than 0.8-nm Equivalent Oxide Thickness

High quality nanolaminate stacks consisting of five Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -HfTiO layers with an effective dielectric constant of about 22.5 are reported. A dielectric constant for binary HfTiO thick films of about 83 was also demonstrated. The electrical characteristics of as-deposited structures and ones which were annealed in an O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> atmosphere at up to 950 degC for 5-10 min were investigated. Two types of gate electrodes: Pt and Ti were compared. The dielectric stack which was annealed up to 500 degC exhibits a leakage current density as small as ~1times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at an electric of field 1.5 MV/cm for a quantum-mechanical corrected equivalent oxide thickness of ~0.76 nm. These values change to ~1times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 1.82 nm, respectively, after annealing at 950 degC

Characterization and optimization of a P-channel poly(o-methoxyaniline) based thin film transistor

Poly(o-methoxyaniline) based thin film organic transistors (OTFT’s) have been fabricated on a variety of dielectrics: SiO2, polyethylene, and polyvinylidene fluoride trifluoroethylene. Resulting inverted gate OTFT’s were found to be P channel with Au contacts. The mobility was measured to be around 10−3cm2V−1s−1 for as-deposited thin film OTFT structures but could be improved by an order of magnitude by doping, annealing, and decreasing the static dielectric constant of the gate dielectric.

Fabrication of Alpha-Iron and Iron Carbide Nanostructures by Electron-Beam Induced Chemical Vapor Deposition and Postdeposition Heat Treatment

We succeeded in fabricating crystalline alpha-iron nanostructures with desired shapes. Electron-beam-induced chemical vapor deposition with iron carbonyl gas, Fe(CO)5, was carried out at room temperature in a field-emission-gun scanning electron microscope to fabricate nanodots, nanorods and square frames. The as-deposited structures exhibited an amorphous phase containing iron, carbon and oxygen in their entire volumes and iron oxide nanocrystals existed near their surfaces. Postdeposition heat treatment at about 600°C resulted in the formation of crystalline alpha-iron and iron carbide phases in their structures, while maintaining their shapes. Quantitative elemental analyses using electron energy loss spectroscopy suggested that the original as-deposited iron-to-carbon compositional ratio is crucial in determining the stoichiometry of the produced structures after the heat treatment.

Investigations of the interface stability in HfO 2–metal electrodes

As the sharpness of the metal–oxide interface is of major importance to develop efficient structures, we have studied the thermal stability of interfaces in a series of thin film samples where the metallic component was either Pt, Al, Pd, Ni, Nb or Ti deposited on a thin HfO 2 film. Thermodynamic considerations have been carried out to determine the possible products of metal–oxide reaction at a temperature of 500 °C. The evolution of the as-deposited thin film structures as a function of annealing temperature has been analysed by combining various techniques and specifically using X-ray reflectometry. This particular technique allows one to detect very thin embedded interfaces, distinguish small density variations and determine accurately the thickness, the normal roughness and the density of each layer. In addition, reflectometry results have been correlated with atomic force microscopy and transmission electron microscopy observations of selected samples. Our results indicate that platinum, palladium and nickel are stable up to 500 °C on hafnium oxide. Annealed aluminium, an interfacial layer forms, whereas niobium and titanium present a diffuse interface.

Thermal domain stability of advanced digital recording (ADR) thin film heads

In this paper the thermal domain stability of electroplated Nickel–Iron flux guides is studied. During the thin film deposition process of ADR magnetic heads these magnetic structures are heated up to about 300°C on a few occasions and it is shown that this has a pronounced effect on the stress state of the deposited flux-guide layers. Domain observations are carried out on both NiFe strips of varying widths as well as on as-deposited test structures and annealed NiFe on product level of a data head.

Nucleation and growth of silicon nitride nanoneedles using microwave plasma heating

We report on needlelike silicon nitride nanowires grown on silicon using ammonia microwave plasma heating. Scanning electron microscope reveals that the nanoneedles are either straight, slightly bent, or kinked with sharp tips. Transmission electron microscope shows that the sizes of the nanowire tips are less than 5 nm and the structures are well crystallized. X-ray diffraction on the surface of the as-deposited structures indicates that both α-silicon nitride and β-silicon nitride exist. Catalyst particle splitting and merging explain observed structure derivation and bending. A vapor–liquid–solid model is employed to explain nucleation and growth mechanism.

Diffusion Barrier Characteristics of TaSiN for Pt/TaSiN/Poly-Si Electrode Structure of Semiconductor Memory Device

The TaSiN barrier layers for Pt/TaSiN/poly-Si structure were prepared by dc reactive magnetron sputtering. The resistivity of as-deposited films with an optimum composition of was about 1,277 μΩ cm. The TaSiN films are amorphous over a wide range of annealing temperatures up to 900°C and showed an abrupt increase of resistivity at annealing temperatures of 700 and 750°C because of the formation of amorphous phase onto TaSiN films. The characteristics of Pt/TaSiN/poly-Si structure before and after annealing at various temperatures became linear, which is indicative of Ohmic characteristics, independent of annealing temperature. The contact resistivities of Pt/TaSiN/poly-Si structures with increasing annealing temperature up to 700°C did not vary greatly compared with those of as-deposited electrode structures. The specific contact resistivities of as-deposited and annealed structures at 700°C were about and respectively. © 2001 The Electrochemical Society. All rights reserved.

Electron density fluctuations at interfaces in Nb/Si bilayer, trilayer, and multilayer films: An x-ray reflectivity study

A grazing incidence x-ray reflectivity technique has been used to determine electron density profile (EDP) as a function of depth in Nb-on-Si and Si-on-Nb bilayer, Nb–Si–Nb and Si–Nb–Si trilayer, and Nb/Si multilayer structures. In each case, films having layer thicknesses of 35 Å were deposited on float glass and Si(100) substrates under ultrahigh vacuum conditions using an electron beam evaporation technique. EDP determined in as-deposited bilayer films shows that the widths of Si-on-Nb and Nb-on-Si interfaces are 20 and 40 Å, respectively. The large difference observed in the widths is attributed to the different growth morphology of 35 Å Nb and 35 Å Si single layer films as revealed by atomic force microscopy investigations. In situ dc resistance measurements carried out on 35 Å single layer Nb films during growth show percolation at a thickness much less than the layer thickness. In case of as-deposited Nb–Si–Nb trilayer film, EDP shows a width of 21 Å at both the interfaces viz. Si-on-Nb and Nb-on-Si whereas in the case of as-deposited Si–Nb–Si trilayer films, the widths of Si-on-Nb and Nb-on-Si interfaces are 21 and 42 Å, respectively. The EDPs obtained from bilayer and trilayer films are used to determine layer-by-layer electron density variation in Nb/Si multilayer structures. The results corresponding to the as-deposited multilayer structure indicate that interdiffusion is larger in the bottom layers of the stack. To study the role of kinetic and thermodynamic factors in the interfacial reactions, the bilayer, trilayer, and multilayer samples were isochronally annealed in vacuum up to a temperature of 300 °C in steps of 50 °C for 1 h. EDP of annealed bilayer and trilayer films show an increase in interfacial width due to interdiffusion of Nb and Si and samples annealed at 250 and 300 °C show Nb-rich and Si-rich intermixed regions. In addition to this, plateau regions having an electron density of 1.8 e/Å3 are observed in the EDP of Nb–Si–Nb and Si–Nb–Si trilayer structures annealed at 300 °C which indicates the formation of a Nb3Si phase. Structural parameters obtained from EDP are extended to interpret the results in as-deposited and annealed multilayer structures. The observed contraction in a bilayer period of an annealed multilayer structure is interpreted in terms of formation of a dense Nb3Si phase confirmed by wide angle x-ray diffraction measurements. Consequently, the multilayer structure is fully destroyed between 250–300 °C.

Structural dynamics in CdS–CdTe thin films

The performance of CdS–CdTe heterojunction solar cells depends critically upon the structures formed during thin film deposition and any subsequent processing. We have undertaken a detailed examination of solar cell materials (in particular CdTe and CdS) which has enabled some correlation between their fundamental properties and structural behaviour as thin films. In particular we have determined the Vegard coefficients and phase diagram for the CdS–CdTe system. We have also examined the diffusion characteristics of both single-crystal and polycrystalline CdTe and CdS with respect to Te and S in order to define the rate at which any intermixed region may grow. Thus we have determined several fundamental properties of CdTe and CdS which were either not available or apparently anomalous. These data have been used to underpin and interpret findings from studies of the structural and electronic changes that occur during the type conversion anneal of CdTe. In particular, we have shown how an intermixed region forms during the heat treatment and that this could be mediated by the initial, as-deposited structures. We have also been able to contrast the behaviour of CdTe films produced by PVD and electrodeposition. In order to characterise the structure of these thin films it has been essential to develop novel depth profiling methods based upon our primary analytical methods, i.e. X-ray diffraction and ion-beam analysis. These techniques, when used with the fundamental material properties, are shown to provide complementary information that has allowed us to build models of the CdTe and CdS layers that may allow the formation of the intermixed region to be controlled during the fabrication process.

Cathodoluminescence spectroscopy of nitrided SiO2–Si interfaces

We use cathodoluminescence spectroscopy (CLS) to investigate the electronic states of ultrathin gate dielectrics with nitrided SiO2–Si interfaces, known to improve reliability in advanced complementary metal–oxide–semiconductor devices. The 5 nm thick films investigated were: (i) as-deposited (at 300 °C) structures, (ii) 400 °C hydrogen anneal, (iii) 900 °C rapid thermal anneal (RTA), and (iv) a combination of both anneals. CLS emission energies and intensities versus excitation energy were essentially unchanged for the as-deposited interface compared to non-nitrided plasma-processed interfaces. In the near-infrared, features appear at 0.8 and 1.0 eV, with the 1.0 eV peak Si substrate intensity increasing with increasing depth. From depth variation measurements at higher photon energy, a 3.4 eV peak is also shown to arise from the Si substrate, and a 2.7 eV feature is shown to come from the interface region. After hydrogenation, the CLS is essentially the same as for non-nitrided interfaces, except for an increase in the relative intensity of a broad background luminescence ranging from 1.5 to 2.5 eV. However, the RTA and the combination of the RTA and hydrogenation do not completely suppress emission near 2.0 eV feature as for non-nitrided interfaces. From the behavior of the CLS features, we are able to clearly distinguish between interfacial defects and substrate features, which are significantly reduced by the combined RTA/hydrogen anneal, and features that are not reduced by the annealing procedures.

Al–Ta Bilayer as an Oxidation Resistant Barrier for Electrode Structures in High Dielectric Constant Capacitors

Aluminum-tantalum bilayers have been investigated for their potential to serve as conductive barriers to oxygen diffusion when annealed at conditions corresponding to crystallization of perovskite dielectrics such as lead lanthanum titanate (PLT). Ta (50 nm)/Al (15 nm) structures have been deposited on Si substrates and annealed in oxygen at 650 and 700 °C for various amounts of time. The as-deposited and annealed structures have been characterized by x-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS), and Auger electron spectroscopy (AES) analysis and by four-point probe electrical measurements. It has been found that the Al–Ta structures can withstand complete oxidation when exposed to oxygen at 650 °C for 30 min or 700 °C for 1 min and the oxide layer formed at the surface of the structure acts as a barrier to further oxygen diffusion. When a PLT film was deposited directly on the Al–Ta structures intermixing took place. It was therefore necessary to insert a Pt layer between the Al–Ta barrier and PLT layer. In such a case the PLT showed electrical properties similar to those obtained when deposited on SiO2/Pt; however, the Al–Ta structure did interact with Pt during the perovskite formation anneal. It has been found that this interaction can be prevented by preannealing the Al–Ta, in oxygen, prior to the deposition of Pt.

Low-loss polycrystalline silicon waveguides for silicon photonics

Photonic integrated circuits in silicon require waveguiding through a material compatible with silicon very large scale integrated circuit technology. Polycrystalline silicon (poly-Si), with a high index of refraction compared to SiO2 and air, is an ideal candidate for use in silicon optical interconnect technology. In spite of its advantages, the biggest hurdle to overcome in this technology is that losses of 350 dB/cm have been measured in as-deposited bulk poly-Si structures, as against 1 dB/cm losses measured in waveguides fabricated in crystalline silicon. We report methods for reducing scattering and absorption, which are the main sources of losses in this system. To reduce surface scattering losses we fabricate waveguides in smooth recrystallized amorphous silicon and chemomechanically polished poly-Si, both of which reduce losses by about 40 dB/cm. Atomic force microscopy and spectrophotometry studies are used to monitor surface roughness, which was reduced from an rms value of 19–20 nm down to about 4–6 nm. Bulk absorption/scattering losses can depend on size, structure, and quality of grains and grain boundaries which we investigate by means of transmission electron microscopy. Although the lowest temperature deposition has twice as large a grain size as the highest temperature deposition, the losses appear to not be greatly dependent on grain size in the 0.1–0.4 μm range. Additionally, absorption/scattering at dangling bonds is investigated before and after a low temperature electron-cyclotron resonance hydrogenation step. After hydrogenation, we obtain the lowest reported poly-Si loss values at λ=1.54 μm of about 15 dB/cm.

The effect of rapid thermal annealing on the electrical characteristics of InP MOS structures with a double oxide layer

The electrical properties of double oxide layer InP MOS structures are analyzed. The first oxide layer (next to InP) is anodized and the second oxide layer is RF magnetron sputtered SiO2. The quality of as-deposited oxide structures is not good. However, it is improved after rapid thermal annealing. The resistivity and breakdown electric field increase. The current conduction process and InP surface potential change after annealing. The oxide fixed charge density also decreases after annealing. Sputter created defects and partial removal of defects after annealing and changes in their distribution are used to explain the observations.

Polysilicon Waveguides for Silicon Photonics

AbstractPhotonic integrated circuits in silicon require waveguiding through a material compatible with silicon VLSI technology. Polysilicon (polySi), with a high index of refraction compared to SiO2 and air, is an ideal candidate for use in silicon optical interconnect technology. Inspite of its advantages, the biggest hurdle to this technology is that losses of 350dB/cm have been measured in as-deposited polySi waveguide structures, as against ldB/cm losses measured in waveguides fabricated in crystalline silicon. We report methods for reducing scattering and absorption, which are the main sources of losses in this system. To reduce surface scattering losses we fabricate waveguides in smooth recrystallized amorphous silicon and Chemo-Mechanically Polished (CMP) polySi, both of which reduce losses by about 40dB/cm to 15dB/cm. Atomic Force Microscopy (AFM) and spectrophotometry studies are used to monitor surface roughness which has been reduced from an RMS roughness value of 19–20nm down to about 4–6nm. Bulk absorption/scattering losses can depend on size, structure, and quality of grains and grain boundaries which we investigate by means of Transmission Electron Microscopy (TEM). Although the lowest temperature deposition has twice as large a grain size as the highest temperature deposition, the losses appear to not be greatly dependent on grain size in the 0.1pm to 0.4pm range. Additionally, absorption/scattering at dangling bonds is investigated before and after a low temperature Electron-Cyclotron Resonance (ECR) hydrogenation step. After hydrogenation, we obtain the lowest reported polySi loss values at λ = 1.54μm of about 15dB/cm.

Optimization of Pd/Zn/Pd/Au Ohmic Contacts to p-Type inGaAs/ InP

ABSTRACTThe electrical properties of Pd/Zn/Pd/Au based ohmic contacts to p-type In0 47Ga0 53As/ InP with an interposed superlattice of 50Å In047Gao 53As/ 50 Å InP have been investigated. In this study, several configurations of the Pd/Zn/Pd/Au metallization were fabricated with varying thicknesses of the Zn and interfacial Pd layers in the range 0 to 400 Å. The lowest values of specific contact resistance, ρc, were 1.2 x 10-5 Ω cm2 as-deposited and 7.5 x 106 Ω cm2 for samples annealed at 500 °C. In the as-deposited structures, ρc was reduced by an increase in thickness of both the Zn and Pd layers to 300 Å. For annealed samples, a critical thickness of the Zn ≥ 50 Å and Pd ≥ 100 Å layers was required in order to significantly reduce the magnitude of ρc. These results are consistent with a model of Pd/Zn contacts based on Zn doping of the interface. Studies of thermal stability of the contacts at 400 °C and 500 °C have shown that the Zn/Pd/Au and Pd/Zn/Pd/Au configurations were significanty lower in ρc at extended ageing times than the Pd/Au contacts.

Electrical characterization of low-pressure chemical-vapor-deposited silicon dioxide metal-oxide-silicon structures

The electrical characteristics of as-deposited and oxygen-annealed low-pressure chemical-vapor-deposited (LPCVD) silicon dioxide (SiO2) metal-oxide-silicon (MOS) structures were investigated. As-deposited LPCVD SiO2 MOS structures exhibit a high oxide fixed charge density in the mid-1011 cm−2 and an interface state density in the low-1011 cm−2 eV−1 due to the large number of oxygen and silicon dangling bonds. A low electron barrier height in these structures (1.2 eV) is presumed to be due to lowering of the barrier by excess silicon microclusters. Oxygen-annealed LPCVD SiO2 MOS structures exhibit oxide fixed charge and interface state densities in the mid-1010 cm−2 and mid-1010 cm−2 eV−1, respectively. Both the as-deposited and annealed devices exhibit turnaround in flatband voltage shift with avalanche electron injection. However, the direction of shift is opposite for the two devices with the annealed device being very similar to that of thermally grown SiO2 MOS structures. Apparently, oxygen annealing restructures and oxidizes the partial SiOx in the as-deposited LPCVD oxide into stochiometric SiO2. However, the residual nonstochiometric SiO2 microclusters in the bulk result in an electron barrier height of only 2.3 eV.

Composition/structure/property relations of multi-ion-beam reactive sputtered lead lanthanum titanate thin films: Part I. Composition and structure analysis

Material properties are greatly dependent upon the structure of the material. This paper, the first of three parts, discusses how composition influences the crystallographic structure and microstructure of lead lanthanum titanate (PLT) thin films grown by the multi-ion-beam reactive sputtering (MIBERS) technique. A transmission electron microscopy (TEM) study detailing the relationship between crystallographic texturing and microstructure development will be presented in a second paper. The dependence of the ferroelectric properties on observed crystallographic structure and microstructure is presented in the third paper of this series. As-deposited PLT microstructures coincide with the structure zone model (SZM) which has been developed to describe the microstructure of thin films deposited by physical vapor deposition. The as-deposited PLT structures are altered during post-deposition annealing as a result of crystallization and PbO evaporation. Amorphous films with more than 10 mole % excess PbO become polycrystalline with porous microstructures after annealing. When there is less PbO in the as-deposited film, 〈100〉 texture and dense structures are observed. Porosity results from PbO evaporation, and 〈100〉 texture is inhibited by excess PbO.

A15 structure formation in TiPd

Vapor phase formation of thin films in the Ti-Pd alloy system is investigated using magnetron sputter deposition. Crystalline as-deposited structures are produced with nominal compositions of 20, 25 and 30 at.%Pd. The high temperature b.c.c. phase is produced on room temperature substrates via quenching from the vapor phase. An A15 structure of Ti 3Pd is rigorously identified for the first time, in agreement with predictions from electronic structure calculations.

Annealed indium oxide transparent ohmic contacts to GaAs

The current–voltage characteristics of annealed In2O3–GaAs devices have been investigated for the purpose of fabricating transparent ohmic contacts to GaAs. A detailed study of the reverse current for as-deposited structures with degenerately doped n-type In2O3 on lightly doped n-type GaAs yields a 0.67-V high Schottky barrier. After annealing, the barrier height is only slightly modified, but the reverse current increases dramatically. This reverse current follows a voltage dependence that is consistent with a Fowler–Nordheim tunneling mechanism, for which the electric field is enhanced around localized asperities. These data suggest that an optimized annealing schedule might be used to fabricate low-resistance, transparent In2O3 ohmic contacts to GaAs-based optoelectronic devices.

PRIMARY STUDY ON THE IRRADIATION EFFECT OF HYDROGEN IONS ON DIAMOND-LIKE CARBON FILMS

Diamond-like carbon (DLC) films, prepared by dual-ion beam sputtering method on glass substrate, were irradiated by high energy hydrogen ions(H+) under different combinations of ion energy and irradiation dose. Raman spectroscopy, infra-red transmittance spectroscopy, electrical resistivity measurement and adhesive force determination were used to characterize the as-deposited and the irradiated films. The results showed that, comparing with that of as-deposited ones, the properties and structures of irradiated films were changed obviously: the infra-red transmittance in the range of 1450 to 6000 cm-1 was increased; the electrical resistivity had nearly no large change. The relative ratios of sp2 C-H bond to sp3 C-H bond and sp3 C-C bond to sp2 C-C bond were also increased, while the component of sp3 C-C bond and sp2 C-C bond was decreased because of H+ irradiation. On the basis of the above results., the relations between properties and structures for irradiation On the basis of the above results, the relations between properties and structures for irradiated films were discussed in detail between properties and structures for irradiated films were discussed in detail. It is concluded It is concluded that the H+ irradiation effect on DLC films is different from that of Cc or other heavier ions. The main role of H+ on the films is the teching effect on weaker bonds. We believe that it is possible to improve the properties of DLC films by means of high energy H+ irradiation.