Reduction in absorption in quartz/Si,quartz/Si/SiO<Subscript>2</Subscript>, and SiC/Si/SiO<Subscript>2</Subscript> structures on laser treatment

The effect of laser radiation on the optical absorption spectra of the quartz/Si, quartz/Si/SiO₂, and SiC/Si/SiO₂ systems is studied. The effects of modification of the transparency of the structures are clarified.     

Plasma etching of poly-Si/SiO<Subscript>2</Subscript>/Si structures: Langmuir-probe and optical-emission-spectroscopy monitoring

An in-depth experimental evaluation is presented of the Langmuir probe as a tool for monitoring the etching of polysilicon-gate MOS structures with an inductively coupled high-density plasma excited in a mixture of SF₆, O₂, and Ar. It is shown that Langmuir-probe measurements made in parallel with optical actinometry offer ways of accurate end-point detection and etch-rate monitoring. It is established that the surface reactions involved lead to considerable changes in major parameters of the charged plasma species in the course of the process, affecting both the densities of electrons and ions and the electron energy distribution function (EEDF). It is found that the effective electron temperature and EEDF of the working plasma differ greatly from those of an Ar plasma under the same excitation conditions. It is concluded that wafer-surface charging could be minimized by varying the electron temperature and energy distribution. On the basis of optical-actinometry measurements, relationships are identified between the fluorine-atom density in the bulk plasma and the etch rate of the polysilicon or the oxide, taking account of the influence of ion bombardment. A conception is put forward of how the etch selectivity could be controlled.     

Traps with near-midgap energies at the bonded Si/SiO<Subscript>2</Subscript> interface in silicon-on-insulator structures

Capture centers (traps) are studied in silicon-on-insulator (SOI) structures obtained by bonding and hydrogen-induced stratification. These centers are located at the Si/SiO₂ interface and in the bulk of the split-off Si layer. The parameters of the centers were determined using charge deep-level transient spectroscopy (Q-DLTS) with scanning over the rate window at fixed temperatures. Such a method allows one to study the traps near the Si midgap at temperatures near 295 K. It is shown that the density of traps with a continuous energy spectrum, which are located at the bonded Si/SiO₂ interface, decreases by more than four orders of magnitude at the mid-gap compared with the peak density observed at the activation energy E _a ≈0.2–0.3 eV. The capture centers are also found in the split-off Si layer of the fabricated SOI structures. Their activation energy at room temperature is E _a =0.53 eV, the capture cross section is 10^?19 cm², and the concentration is (0.7–1.7)×10¹³ cm^?3. It is assumed that these capture centers are related to deep bulk levels induced by electrically active impurities (defects) in the split-off Si layer close to the Si/SiO₂ interface.     

Crystallization behavior and ferroelectric properties of PbTiO<Subscript>3</Subscript>/Ba<Subscript>0.85</Subscript>Sr<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> sandwich thin film on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrates

A PbTiO₃/Ba_0.85Sr_0.15TiO₃/PbTiO₃ (PT/BST15/PT) sandwich thin film has been prepared on Pt/Ti/SiO₂/Si substrates by an improved sol-gel technique. It is found that such films under rapid thermal annealing at 700°C crystallize more favorably with the addition of a PbTiO₃ layer. They possess a pure, perovskite-phase structure with a random orientation. The polarization-electric field (P-E) hysteresis loop and current-voltage (I-V) characteristic curves reveal that a PT/BST15/PT film exhibits good ferroelectricity at room temperature. However, no sharp peak, only a weak maximum, is observed in the curves of the dielectric constant versus temperature. The dielectric constant, loss tangent, leakage current density at 20 kV/cm, remnant polarization, and coercive field of the PT/BST15/PT film are 438, 0.025, 1.3 × 10⁻⁶ Acm⁻², 2.46 μCcm⁻², and 41 kVcm⁻¹, respectively, at 25°C and 10 kHz. The PT/BST15/PT film is a candidate material for high sensitivity elements for uncooled, infrared, focal plane arrays (UFPAs) to be used at near ambient temperature.     

Investigation of the Interfaces in Ni-FUSI/Hf-Based/Si and Ni-FUSI/SiO<Subscript>2</Subscript>/Si Stacks by Physical and Electrical Characterization Techniques

The combination of full Ni silicidation (Ni-FUSI) gate electrodes and hafnium-based high-k gate dielectrics is one of the most promising replacements for poly-Si/SiO₂/Si gate stacks for the future complementary metal–oxide–semiconductor (CMOS) sub-45-nm technology node. The key challenges to successfully adopting the Ni-FUSI/high-k dielectric/Si gate stack for advanced CMOS technology are mostly due to the interfacial properties. The origins of the electrical and physical characteristics of the Ni-FUSI/dielectric oxide interface and dielectric oxide/bulk interface were studied in detail. We found that Ni-FUSI undergoes a phase transformation during silicide formation, which depends more on annealing temperature than on the underlying gate dielectric material. The correlations of Ni–Si phase transformations with their electrical and physical changes were established by sheet resistance measurements, x-ray diffraction (XRD), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS) analyses. The leakage current density–voltage (J–V) and capacitance–voltage (C–V) measurement techniques were employed to study the dielectric oxide/Si interface. The effects of the postdeposition annealing (PDA) treatment on the interface charges of dielectric oxides were studied. We found that the PDA can effectively reduce the trapping density and leakage current and eliminate hysteresis in the C–V curves. In addition, the changes in chemical bonding features at HfO₂/Si and HfSiO/Si interfaces due to PDA treatment were evaluated by XPS measurements. XPS analysis provides a better interpretation of the electrical outcomes. As a result, HfSiO films exhibited superior performance in terms of thermal stability and electrical characteristics.     

Silicon-on-insulator structures with a nitrogenated buried SiO<Subscript>2</Subscript> layer: Preparation and properties

Electrical properties of silicon-on-insulator (SOI) structures with buried SiO₂ layer implanted with nitrogen ions are studied in relation to the dose and energy of N⁺ ions. It is shown that implantation of nitrogen ions with doses >3 × 10¹⁵ cm⁻² and an energy of 40 keV brings about a decrease in the fixed positive charge in the oxide and a decrease in the density of surface stares by a factor of 2. An enhancement of the effect can be attained by lowering the energy of nitrogen ions. The obtained results are accounted for by interaction of nitrogen atoms with excess silicon atoms near the Si/SiO₂ interface; by removal of Si-Si bonds, which are traps of positive charges; and by saturation of dangling bonds at the bonding interface of the SOI structure.     

Layered structure of anodic SiO<Subscript>2</Subscript> films doped with phosphorus or boron

It is shown that anodic silicon oxide films deposited by reanodization (repeated anodic oxidation) of p- and n-type silicon in phosphate (1.5 M H₃PO₄), borate (1.5 M H₃BO₃), and nitrate (0.04 M NH₄NO₃) electrolytes based on tetrahydrofurfuryl alcohol have a three- or four-layer structure both before and after high-temperature annealing. It is assumed that this circumstance accounts for the nonuniform distribution of phosphorus and boron across the thickness of anodic SiO₂.     

SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layer formation during plasma sputtering of Si and SiO<Subscript>2</Subscript> targets

Deposition of SiO _x layers of variable composition onto silicon wafers was performed by co-sputtering of spaced Si and SiO₂ targets in argon plasma. Coordinate dependences of the thickness and refractive index of separately deposited Si and SiO₂ layers and the SiO _x layer grown during co-sputtering of targets were determined using optical techniques. It was shown that the SiO _x layer composition is not equal to a simple sum of thicknesses of separately deposited Si and SiO₂ layers. The coordinate dependences of the Si and SiO₂ layer thicknesses were calculated. To fit the calculated and experimental data, it is necessary to assume that no less than 10% of silicon is converted to dioxide during co-sputtering. A comparison of the coordinate dependences of the IR absorbance in SiO₂ and SiO _x layers with experimental ellipsometric data confirmed the presence of excess oxygen in the SiO _x layer. Taking into account such partial oxidation of sputtered silicon, composition isolines in the substrate plane were calculated. After annealing of the SiO _x layer at 1200°C, photoluminescence was observed in a wafer area predicted by calculations, which was caused by the formation of quantum-size Si nanocrystallites. The photoluminescence intensity was maximum at x = 1.78 ± 0.3, which is close to the composition optimum for ion-beam synthesis of nanocrystals.     

Gas-phase etching of SiO<Subscript>2</Subscript> layers in an HF/C<Subscript>2</Subscript>H<Subscript>5</Subscript>OH mixture

This paper describes a technique for dry etching SiO₂ layers in MEMS technologies without the moving elements sticking. Etching the sacrificial SiO₂ in anhydrous HF (hydrofluoric acid in the gas phase) allows avoiding the subsequent complex operations of cleaning and drying, which are mandatory in the case of liquid etching. Using the HF/C₂H₅OH anhydrous mixture under low pressures makes it possible to prevent water condensation, which is due to etching in HF vapor, and allows one to employ gas-phase etching in surface MEMS technologies. The mechanisms and physicochemical processes taking place when etching thermal SiO₂ are discussed. The rate of etching thermal SiO₂ films is investigated at temperatures ranging from 30 to 50°С and under chamber pressures ranging from 10 to 20 kPa.     

Electrical characteristics of Au/<Emphasis Type="Italic">n</Emphasis>-GaAs structures with thin and thick SiO<Subscript>2</Subscript> dielectric layer

The aim of this study, to explain effects of the SiO₂ insulator layer thickness on the electrical properties of Au/n-GaAs Shottky barrier diodes (SBDs). Thin (60 Å) and thick (250 Å) SiO₂ insulator layers were deposited on n-type GaAs substrates using the plasma enganced chemical vapour deposition technique. The current-voltage (I–V) and capacitance-voltage (C-V) characteristics have been carried out at room temperature. The main electrical parameters, such as ideality factor (n), zero-bias barrier height (? _Bo ), series resistance (R _s ), leakage current, and interface states (N _ss ) for Au/SiO₂/n-GaAs SBDs have been investigated. Surface morphologies of the SiO₂ dielectric layer was analyzed using atomic force microscopy. The results show that SiO₂ insulator layer thickness very affects the main electrical parameters. Au/n-GaAs SBDs with thick SiO₂ insulator layer have low leakage current level, small ideality factor, and low interface states. Thus, Au/n-GaAs SBDs with thick SiO₂ insulator layer shows better diode characteristics than other.     

Excitation of Er<Superscript>3+</Superscript> ions in SiO<Subscript>2</Subscript> with Si nanocrystals

Probabilities of excitation of erbium ions via Coulomb interaction with carriers localized in silicon nanocrystals embedded in SiO₂, in recombination and intraband relaxation of these carriers, have been calculated.     

Light-emitting Si nanostructures formed in SiO<Subscript>2</Subscript> on irradiation with swift heavy ions

SiO₂ layers containing implanted excess Si are irradiated with Xe ions with an energy of 130 MeV and doses of 3 × 10¹²–10¹⁴ cm⁻². In the samples irradiated with a dose of 3 × 10¹² cm⁻², ∼10¹² cm⁻² segregated clusters 3–4 nm in dimension are detected by transmission electron microscopy. With increasing dose, the dimensions and number of these clusters increase. In the photoluminescence spectrum, a 660- to 680-nm band is observed, with the intensity dependent on the dose. After passivation of the sample with hydrogen at 500°C, the band disappears, but a new ∼780-nm band typical of Si nanocrystals becomes evident. On the basis of the entire set of data, it is concluded that the 660- to 680-nm band is associated with imperfect Si nanocrystals grown in the tracks of Xe ions due to high ionization losses. The nonmonotonic dependence of the photoluminescence intensity on the dose is attributed to the difference between the diameters of tracks and the diameters of the displacements’ cascades responsible for defect formation.     

Electrical properties of InAs-SiO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript> MIS structures with a modified interface

The effect of composition of the electrolyte used in producing a thin anodic oxide layer at the surface of a semiconductor substrate on the electrical properties of the InAs-SiO₂-In₂O₃ metal-insulator-semiconductor structures is studied. It is shown that introduction of ammonium fluoride into the electrolyte results in the formation of an interface with the density of surface states below 5 × 10¹⁰ cm^?2 eV^?1, the built-in charge (4–5 × 10¹¹ cm^?2, and the maximum relaxation time of the surface potential.     

Improvement in Performance of Carbon Nanotube Field-Effect Transistors on Patterned SiO<Subscript>2</Subscript>/Si Substrates

Horizontally aligned single-walled carbon nanotubes (SWNTs) were fabricated on patterned SiO₂/Si substrates with groove-and-terrace structures, which were obtained using electron-beam lithography and reactive ion etching. Scanning electron microscopy observation revealed that SWNTs were aligned in the direction parallel to the groove-and-terrace structures and were preferentially grown along the edges of terraces. Using aligned SWNTs as multichannels, carbon nanotube field-effect transistors (CNTFETs) were fabricated on the patterned SiO₂/Si substrates. This method will be promising to control the direction of SWNTs on SiO₂/Si substrates for fabrication of high-performance CNTFETs with high current outputs.     

Density of states at a gamma-irradiated Si/SiO<Subscript>2</Subscript> interface: The effect of ultrasonic treatment

An experimental study is conducted into the effect of ultrasonic treatment on the surface-state distribution function of a gamma-irradiated Si/SiO₂ interface. It is established that ultrasonic treatment reduces the density of radiation-induced states at the interface. It is shown that this effect may be linked to the ultrasound-induced transition of defects to an electrically inactive state.     

Atomic-force-microscopy visualization of Si nanocrystals in SiO<Subscript>2</Subscript> thermal oxide using selective etching

The topography and local hardness of the etched surfaces of layers of SiO₂ thermal oxide that contained Si nanocrystals in its bulk were studied using atomic-force microscopy. The Si nanocrystals were obtained by implanting Si⁺ ions into the oxide with subsequent high-temperature annealing. It is shown that the use of selective etching that removes the oxide material makes it possible to reveal Si nanocrystals that appear in the profile of etched surfaces in the form of nanohillocks with a height of up to 2–3 nm. These values are in satisfactory agreement with the average radius of Si nanocrystals in the SiO₂ oxide layer. Independent confirmation of the Si-nanocrystal observation was obtained by comparing the topography of etched surfaces with the local-hardness maps obtained for the same surfaces; in these maps, the hillocks appear as sites at the surface with a reduced hardness. The phase precipitation of implanted Si is also observed in the form of extended flat clusters oriented in the oxide bulk parallel to the oxide surface. The suggested method for revealing the Si nanocrystals and clusters incorporated into the oxide provides a convenient way to study the specific features of nucleation growth and spinodal decomposition in the Si solid solution in the SiO₂ oxide.     

Ordered arrays of Si nanocrystals in SiO<Subscript>2</Subscript>: Structural,optical, and electronic properties

It is found that irradiation of SiO₂ layers containing Si nanocrystals with high-energy heavy ions induces profound structural modifications—specifically, the formation of vertically ordered arrays of nanocrystals along the ion tracks. This effect results in substantial changes in the electrical properties (the conductivity and capacitance—voltage characteristics) and optical (photoluminescence) properties of the layers containing nanocrystals.     

On a two-layer Si<Subscript>3</Subscript>N<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> dielectric mask for low-resistance ohmic contacts to AlGaN/GaN HEMTs

The fabrication of a two-layer Si₃N₄/SiO₂ dielectric mask and features of its application in the technology of non-fired epitaxially grown ohmic contacts for high-power HEMTs on AlGaN/GaN heterostructures are described. The proposed Si₃N₄/SiO₂ mask allows the selective epitaxial growth of heavily doped ohmic contacts by nitride molecular-beam epitaxy and the fabrication of non-fired ohmic contacts with a resistance of 0.15–0.2 Ω mm and a smooth surface and edge morphology.     

Photoelectric properties of In/In<Subscript>2</Subscript>Se<Subscript>3</Subscript> structures

The hexagonal modification of In₂Se₃ single crystal is grown by planar crystallization from nearly stoichiometric melt and by the vapor-phase method. For the first time, the Schottky barriers In/n-In₂Se₃, which are photosensitive in a wide incident-photon energy range of 1–3.8 eV at 300 K, are obtained. The nature of the interband photoactive absorption is studied. The energy-barrier height and interband optical-transition energy are estimated. It is concluded that the grown crystals can be used in broadband optical-radiation converters.     

Electrical and gas-sensitive properties of nanostructured SnO<Subscript>2</Subscript>:ZrO<Subscript>2</Subscript> semiconductor films

The results of a study of the effect of atomic composition of metal-oxide semiconductor composites SnO₂:ZrO₂ on the surface morphology, polycrystal grain size, resistivity, concentration, free-carrier mobility, and gas-sensitive properties of thin films (0.5–2.5 μm) are presented. Films SnO₂ with ZrO₂ additives (the Zr content was varied from 0.5 to 4.6 at %) are grown by reactive ion-beam sputtering of metal targets of different compositions in a controlled Ar + O₂ atmosphere. Using transmission electron microscopy, atomic-force microscopy, and high-resolution transmission electron microscopy, it is experimentally shown that, as the Zr content increases in the SnO₂:ZrO₂ film composition, the polycrystal grain size decreases from 45 to 10 nm, the free-carrier concentration decreases almost by four orders of magnitude and the mobility increases by approximately nine times. As the Zr content increases in the SnO₂:ZrO₂ film from 0.5 to 4.6 at %, the temperature of maximum gas sensitivity of films to such gases as ethanol, isopropyl alcohol, and acetone decreases by 100–190°C.