Suppression of platinum penetration failure in Ti/Pt/Au beam lead metal systems using a TiN diffusion barrier

In this paper we report the ability of a TiN diffusion barrier to suppress metal penetration which induces junction-shorting failure in a Ti/Pt/Au beam lead metal system on polycrystalline silicon. Practical devices, known as stepped electrode transistors, were prepared with and without the TiN layer, and the junction-shorting failure during heat treatment at 280–500 °C was investigated. Median lives at 300 °C of 2 × 10⁵ h and 1.2 × 10³ h and activation energies of 1.8 eV were and 1.8 eV were obtained with and without the TiN layer respectively. Failure analysis, carried out by Si Kβ soft X-ray spectroscopy using an electron microprobe, showed that the junction-shorting failure was dominated by platinum penetration equivalent to the localized growth of platinum silicide.     

A Study of Ta-Si-N/Ti Bilayer Diffusion Barrier for Copper/Silicon Contact Systems

Ta-Si-N (10 nm)/Ti (20 nm) bilayer film has been designed with the purpose of using as diffusion barrier in copper interconnection. Ta-Si-N/Ti bilayer diffusion barriers were deposited on the substrate of n-type (100) silicon wafer using radio-frequency (RF) magnetron sputtering, followed by in situ deposition of copper. To investigate the thermal stability of the Ta-Si-N/Ti diffusion barriers, annealing was subsequently conducted in N₂ gas for 60 min and annealing temperatures were chosen at 600°C, 650°C, 700°C, 750°C, and 800°C. X-ray diffraction (XRD) revealed that Ta-Si-N layer grown on the Ti layer exhibited an amorphous phase. The results indicated that Ta-Si-N/Ti film can prevent copper diffusion at 750°C. After annealing at 750°C, the production of Ti-Si layer can effectively decrease contact resistance between barrier and silicon.     

Nanocrystalline CuO thin films: synthesis, microstructural and optoelectronic properties

Nanocrystalline copper oxide (CuO) thin films have been synthesized by a sol–gel method using cupric acetate Cu (CH₃COO) as a precursor. The as prepared powder was sintered at various temperatures in the range of (300–700?°C) and has been deposited onto a glass substrates using spin coating technique. The structural, compositional, morphological, electrical optical and gas sensing properties of CuO thin films have been studied by X-ray diffraction, Scanning Electron Microscopy (SEM), Four Probe Resistivity measurement and UV–visible spectrophotometer. The variation in annealing temperature affected the film morphology and optoelectronic properties. X-ray diffraction patterns of CuO films show that all the films are nanocrystallized in the monoclinic structure and present a random orientation. The crystallite size increases with increasing annealing temperature (40–45?nm).The room temperature dc electrical conductivity was increased from 10^?6 to 10^?5 (Ω?cm)^?1, after annealing due to the removal of H₂O vapor which may resist conduction between CuO grain. The thermopower measurement shows that CuO films were found of n-type, apparently suggesting the existence of oxygen vacancies in the structure. The electron carrier concentration (n) and mobility (μ) of CuO films annealed at 400–700?°C were estimated to be of the order of 4.6–7.2?×?10¹⁹?cm^?3 and 3.7–5.4?×?10^?5?cm²?V^?1?s^?1?respectively. It is observed that CuO thin film annealing at 700?°C after deposition provide a smooth and flat texture suited for optoelectronic applications. The optical band gap energy decreases (1.64–1.46?eV) with increasing annealing temperature. It was observed that the crystallite size increases with increasing annealing temperature. These modifications influence the morphology, electrical and optical properties.     

Growing nanocrystalline silicon on sapphire by molecular beam epitaxy

It is established that an array of silicon nanoislands is formed on the surface of a sapphire substrate at the initial stages of molecular beam epitaxy. Silicon islands formed at low temperatures of the substrate (below 650°C) exhibit a pyramidal shape, while the islands grown at T > 650° possess a dome shape. The maximum density of islands was 2 × 10¹¹ cm^?2, their lateral dimensions were within 20 nm, and their heights did not exceed 3 nm.     

Investigation of germanium films and GeSi interface structure by transmission electron microscopy

The structure of germanium films (d≌0.3 μm) evaporated onto a silicon substrate and the GeSi interface have been investigated by transmission electron microscopy (TEM). Ge was evaporated in a vacuum of approximately 10^?6 Torr onto (111) Si. Epitaxial growth was observed at substrate temperatures T_s>500°C. The films grown at T_s = 520°–600°C (low temperature epitaxy) were characterized by a high density of stacking faults (SF), microtwin lamellae and dislocations which lay normal to the film surface. In this case the interface dislocations were regular and the dislocation density was equal to (3–4)×10¹⁰ cm^?2. At T_s = 700°–850°C (high temperature epitaxy) few stacking faults were discovered. Dislocations in the interior of the film formed three-dimensional networks as a result of interactions of different slip systems and dislocation climb. The formation of misfit dislocations was apparent at the interface. The region T_s = 630°–700°C is an intermediate region.     

Creep of silicon nitride-titanium nitride composites

The effect of particulate TiN additions (0–50 wt%) on creep behaviour of hot-pressed (5 wt%Y₂O₃ + 2 wt%Al₂O₃)-doped silicon nitride (HPSN)-based ceramics was studied. Creep was measured using a four-point bending fixture in air at 1100–1340 °C. At 1100 °C, very low creep rates of HPSN with 0–30 wt% TiN are observed at nominal stresses up to 160 MPa. At 1200 °C the creep rate is slightly higher, and at 1300 °C the creep rate is increased by three orders of magnitude compared to 1100 °C and rupture occurs after a few hours under creep conditions. It was established that the formation of a TiN skeleton could detrimentally affect the creep behaviour of HPSN. An increase in TiN content leads to higher creep rates and to shorter rupture times of the samples. Activation energies of 500–1000 kJ mol^?1 in the temperature range of 1100–1340 °C at 100 MPa, and stress exponentsn?4 in the stress range 100–160 MPa at 1130–1200 °C were calculated. Possible creep mechanisms and the effect of oxidation on creep are discussed.     

The chemical vapour deposition and characterization of ZrO2 films from organometallic compounds

ZrO₂ films were deposited on silicon substrates by oxygen-assisted decomposition of zirconium-β-diketonates at temperatures of 400–550°C. The deposits, fine-grained nearly stoichiometric monoclinic ZrO₂, were hard and showed strong adherence to the substrate. The films were characterized by transmission electron microscopy, X-ray diffraction and electron microprobe analysis and by measuring their dielectric and optical properties. The index of refraction was found to be 2.18, and the optical energy band gap was found to be 5.16 eV. The dielectric constant at 1 MHz was 17–18, and the dielectric strength varied between 1 × 10⁶ and 2.0 × 10⁶ V cm^?1. Capacitance-voltage measurements at 1 MHz indicated the presence of effective surface states with a concentration in the range (1.0?6.0) × 10¹¹cm^?2 for films deposited at temperatures above 500°C or for films deposited at 400–450°C and annealed at above 750°C. The flat-band voltages were between ?0.6 and + 0.2 V. The films showed satisfactory bias-temperature stability. The current-voltage characteristic followed an I ∝ V² dependence for negative bias and an I ∝ V^2.6 to I ∝ V^3.4 dependence for positive bias.     

Carrier properties of B atomic-layer-doped Si films grown by ECR Ar plasma-enhanced CVD without substrate heating

Abstract

The atomic-layer (AL) doping technique in epitaxy has attracted attention as a low-resistive ultrathin semiconductor film as well as a two-dimensional (2-D) carrier transport system. In this paper, we report carrier properties for B AL-doped Si films with suppressed thermal diffusion. B AL-doped Si films were formed on Si(100) by B AL formation followed by Si cap layer deposition in low-energy Ar plasma-enhanced chemical-vapor deposition without substrate heating. After fabrication of Hall-effect devices with the B AL-doped Si films on unstrained and 0.8%-tensile-strained Si(100)-on-insulator substrates (maximum process temperature 350°C), carrier properties were electrically measured at room temperature. Typically for the initial B amount of 2?×?10¹⁴ cm^?2 and 7?×?10¹⁴ cm^?2, B concentration depth profiles showed a clear decay slope as steep as 1.3 nm/decade. Dominant carrier was a hole and the maximum sheet carrier densities as high as 4?×?10¹³ cm^?2 and 2?×?10¹³ cm^?2 (electrical activity ratio of about 7% and 3.5%) were measured respectively for the unstrained and 0.8%-tensile-strained Si with Hall mobility around 10–13 cm² V^?1 s^?1. Moreover, mobility degradation was not observed even when sheet carrier density was increased by heat treatment at 500–700 °C. There is a possibility that the local carrier (ionized B atom) concentration around the B AL in Si reaches around 10²¹ cm^?3 and 2-D impurity-band formation with strong Coulomb interaction is expected. The behavior of carrier properties for heat treatment at 500–700 °C implies that thermal diffusion causes broadening of the B AL in Si and decrease of local B concentration.     

Characterization of ohmic contacts to InP

The results of a study of the electrical and metallurgical properties of thin metallic layers deposited on InP for use as ohmic contacts are presented. The layers were heat treated at temperatures up to 550°C and were examined with Auger electron spectroscopy. For contact to n-type InP three thin film systems were investigated: gold, nickel and a composite Ni/Au/Ge layer. Nickel was found to produce ohmic behavior in the Ni/Au/Ge/InP system with a minimum specific contact resistance r_c of 3×10^?5 Ω cm² for a net doping of 3×10¹⁶ cm^?3. For contact to p-type InP a film consisting of Au/Mg was investigated. For heat treatment of the Au/Mg/InP system above 350°C, r_c decreased as the temperature of the heat treatment increased and the surface morphology exhibited increasing signs of alloying at higher temperatures. The smoothest surface was obtained at 446°C for 50 min with r_c≈1×10^?4Ω cm² for a net doping of 6×10¹⁷ cm^?3.     

Structure, hardness and thermal stability of nanolayered TiN/CrN multilayer coatings

Nanolayered TiN/CrN multilayer coatings were deposited on silicon substrates using a reactive DC magnetron sputtering process at various modulation wavelengths (Λ), substrate biases (V_B) and substrate temperatures (T_S). X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the coatings. The XRD confirmed the formation of superlattice structure at low modulation wavelengths. The maximum hardness of the TiN/CrN multilayers was 3800 kg/mm² at Λ=80  Å, V_B=−150 V and T_S=400°C. Thermal stability of TiN, CrN and TiN/CrN multilayer coatings was studied by heating the coatings in air in the temperature range (T_A) of 400-800°C. The XRD data revealed that TiN/CrN multilayers retained superlattice structure even up to 700°C and oxides were detected only after T_A?750°C, whereas for single layer TiN and CrN coatings oxides were detected even at 550°C and 600°C, respectively. Nanoindentation measurements showed that TiN/CrN multilayers retained a hardness of 2800 kg/mm² upon annealing at 700°C, and this decrease in the hardness was attributed to interdiffusion at the interfaces.     

Effects of water on the growth of aluminium films deposited by vacuum evaporation

Aluminium films 500 nm thick were deposited onto oxidized silicon wafers by electron gun evaporation at 250°C. The evaporation rates were 0.5 and 1.5 nm s^-1. The water partial pressure p_H2O during evaporation was varied between 1.8 × 10^-6 and 1.5 × 10^-3 Pa. It was shown that the water partial pressure has a marked effect on the growth and the morphology of the deposited aluminium films as studied by scanning electron microscopy. At low water partial pressures a faceted surface structure is obtained. With increasing p_H2O the layer becomes rougher until a maximum is reached, after which the layer becomes smooth again and a granular structure is obtained. The changes in the morphology are accompanied by changes in the structural, optical and electrical properties. The observed phenomena can be explained by the dissociative adsorption of water and the formation of oxide-hydroxide phases on the surface of the crystallites. Finally, it was shown that, under the influence of the electron gun, large changes take place in the composition of the residual gas.     

Sapphire surface preparation for the growth of silicon layers by molecular-beam epitaxy

The structural perfection and surface morphology of sapphire substrates vacuum-annealed at atomic Si flux densities from 5 × 10¹⁵ to 1 × 10¹⁶ at/(cm² s) have been studied by electron diffraction, X-ray diffraction, and atomic force microscopy. The results demonstrate that, after annealing in the range 1160–1330°C, the sapphire has a smooth, single-crystal surface, which enables the growth of twin-free silicon epilayers at 600–700°C.     

Nanospheres Containing Urea: Photothermic Properties

In the present research, nanospheres of chitosan (CS), maltodextrin, and sodium tripolyphosphate (STPP), loaded with urea, were synthesized by using an ionic gelation technique. In the nanosphere synthesis was used a central composite experimental design, obtaining nanospheres with an average size of 275?±?32 nm and 27.5 mV zeta potential. The nanospheres were characterized by their hydrodynamic diameter, polydispersity index, nitrogen content, and thermal properties such as thermal diffusivity (α), effusivity (e), and conductivity (k); also melting temperature was obtained by differential scanning calorimetry. The thermal properties of nanospheres show that the sample with the smallest size has a thermal diffusivity value of (14.4?±?0.4)?×?10^?8 m²·s^?1 and a thermal conductivity value of (6.4?±?0.1)?×?10^?1 W·m^?1·K^?1, and the obtained melting temperature was 157 °C. Higher concentrations of CS increase the values of these thermal properties, probably because chitosan interacts ionically with STPP forming a reticular network due to the opposite charges of both molecules.     

Understanding of post deposition annealing and substrate temperature effects on structural and electrical properties of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> MOS capacitor

The purpose of this study is to understand the effects of substrate temperature (ST) and post deposition annealing (PDA) on the structural-electrical properties of Gd₂O₃ film and to evaluate the electrical performances of the MOS based devices formed with this dielectric. The Gd₂O₃/Si structures were annealed at 500, 600, 700, and 800 °C under N₂ ambient after the films were grown on heated p-Si substrate at various temperatures ranged from 20 to 300 °C by RF magnetron sputtering. For any given ST, the crystallization/grain size increased with increasing PDA temperature. The bump in the accumulation region or continuous decrease in the capacitance values of the inversion region of the C–V curves for 800 °C PDA was not observed. The lowest effective oxide charge density (Q _eff ) value was obtained to be ??1.13?×?10¹¹ cm^?2 from the MOS capacitor with Gd₂O₃, which is grown on heated Si at 300 °C and annealed at 800 °C. The density of the interface states (D _it ) was found to be in the range of 0.84?×?10¹¹ to 1.50?×?10¹¹ eV^?1 cm^?2. The highest dielectric constant (ε) and barrier height \(({\Phi _B})\) values were found to be 14.46 and 3.68, which are obtained for 20 °C ST and 800 °C PDA. The results show that the negative charge trapping in the oxide layer is generally more than that of the positive, but, it is reverse of this situation at the interface. The leakage current density decreased after 20 °C ST, but no significant change was observed for other ST values.     

Effects of annealing process on microstructure and electrical properties of cold-drawn thin layer copper cladding steel wire

The microstructure, mechanical and electrical properties of cold-drawn thin layer copper cladding steel (CCS) wires annealed after different processes were studied by optical microscopy, electron omnipotent material experiment machine, micro hardness machine, SEM and electrical resistivity measurement system. The results indicated that the recovery and recrystallization of steel-core happened in the temperature range 550–750 °C for the holding period of 120 min. When the annealing temperature was higher than 750 °C, grains begun to grow and grain sizes increased gradually with increasing the annealing temperature. The tensile strength and micro hardness were declined with increasing annealing temperature and holding time. The distance of Cu–Fe atoms interfacial diffusion of thin layer CCS wires ranged from 4 µm of cold-drawn wire to 7.5 µm of annealed wire at 850 °C for 120 min. The higher the annealing temperature become, the larger the distance of Cu–Fe atoms interfacial diffusion is. When the annealing temperature was lower than 650 °C, the resistivity was slightly less than 71 × 10^?3 Ω mm² m^?1 which was the resistivity of cold-drawn wire. When the annealing temperature was higher than 650 °C, the resistivity increased with increasing the annealing temperature. Meanwhile, the variation of electrical property of thin layer CCS wires was analyzed and discussed based on microstructure and interfacial diffusion.     

Role of diffusion-annealing temperature on the microstructural and superconducting properties of Cu-doped MgB2 superconductors

This study deals with not only investigate the effect of the copper diffusion on the microstructural and superconducting properties of MgB₂ superconducting samples employing dc resistivity as a function of temperature, scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements but also calculate the diffusion coefficient and the activation energy of copper for the first time. Electrical-resistivity measurements indicate that both the room-temperature resistivity value and zero resistivity transition temperatures (T _c ) increase with increasing the diffusion-annealing temperature from 650 to 850?°C. SEM measurements show that not only the surface morphology and grain connectivity improve but also the grain size of the samples increases with the increase in the diffusion-annealing temperature up to 850?°C. As for the XRD results, all the samples contain the MgB₂ phase only and exhibit the polycrystalline superconducting phase with more intensity of diffraction lines, leading to the increasement in the lattice parameter a and c. Additionally, the diffusion coefficient is observed to increase from 6.81?×?10^?8 to 4.69?×?10^?7?cm²?s^?1 as the diffusion-annealing temperature increases, confirming that the Cu diffusion at lower temperatures is much less significant. Temperature dependence of the Cu diffusion coefficient is described with the aid of the Arrhenius relation D?=?3.75?×?10^?3 exp (?1.15?±?0.10?eV/k _B T) and the corresponding activation energy of copper in MgB₂ system is found to be about 1.15?eV. The possible reasons for the observed improvement in microstructural and superconducting properties of the samples due to Cu diffusion are also discussed.     

Dose Dependence of Nanocrystal Formation in Helium-Implanted Silicon Layers

The possibility of nanocrystal formation in silicon layers subjected to plasma-immersion helium-ion implantation at an energy of 5 keV has been proved for the first time. The effect of the implantation dose on the microstructure of the layers has been studied by X-ray reflectometry, transmission electron microscopy and Raman scattering. It has been established that the formation of silicon nanocrystals with dimensions of 10–20 nm is accompanied by a pronounced dependence on the ion flux and occurs at a dose of 5 × 10¹⁷ cm^–2 with subsequent annealing at 700–800°C. The excessive dose has been shown to cause the destruction of the upper protective sublayer and the degradation of the optical properties of nanocrystals.     

Chemical vapor deposition and characterization of HfO2 films from organo-hafnium compounds

HfO₂ films were deposited on silicon substrates by the oxygen-assisted decomposition of hafnium β-diketonates at temperatures in the range 400–550 °C. These films were characterized by using transmission electron microscopy, X-ray diffraction, electron microprobe analysis and measurements of dielectric and optical properties. It was found that the films were fine-grained (approximately 325 Å) nearly stoichiometric monoclinic HfO₂. The films showed high resistance to most aqueous acids and bases. The deposits had a refractive index of 2.1 and an optical energy gap of 5.68 eV. The dielectric constant at 1 MHz was 22–25, and the dielectric strenght of the HfO₂ films varied between 2 × 10⁶ and 4.5 × 10⁶ V cm^?1. C-V measurements at 1 MHz indicated the presence of effective surface states which varied between 1.0 × 10¹¹ and 6 × 10¹¹ cm^t?2 for films that were deposited at temperatures higher than 500 °C or that were annealed at above 750 °C if deposited at 400–450 °C. The V_FB values were between ?0.6 and 0 V. The annealed films or films grown above 500 °C showed good bias-temperature stability. When positive bias and elevated temperatures were applied, the original C-V curve moved towards higher positive field values (0.2-0.5 V). After applying negative bias at elevated temperatures the C-V curved moved back in the direction of the original C-V curve. Measurements of the dependence of the current I on the electric field showed a dependence of I ∝ V² over a wide range.     

Author index

Films of TiC, TiN and their composite were prepared on molybdenum by a reactive sputtering method with CH₄ and N₂ as the reactive gases and argon as the sputtering gas and applying bias potentials to the substrate material.The films were characterized by X-ray photoelectron spectroscopy and Auger electron spectroscopy. The quantitative chemical composition of the TiC and TiN coatings was determined as a function of the partial pressures of CH₄ (P_CH4) and N₂ (P_N2) during the reactive sputtering. For the TiC coating the most suitable P_CH4 range which gives the stoichiometric composition (carbon-to-titanium ratio, 0.8–1.0) without impurities was found to be (2–5) × 10^?4 Torr (substrate temperature, 300 °C; bias potential, ? 300 V). For the TiN coating the structure and composition of the films prepared by reactive sputtering were observed to depend greatly on the condition of applying the bias potential. The suitable P_N2 range which gives golden films of the stoichiometric composition was higher than 1 × 10^?4 Torr (substrate temperature, 200–300 °C; bias potential from ?75 to ?200 V).On the basis of these experimental studies of TiC and TiN coatings successive coatings of TiC and TiN were deposited onto a molybdenum substrate to achieve higher thermal stability and better adhesion to the substrate. The successive coating method is a promising technique for use in fusion reactors.     

Structural investigation of silicon films chemically vapour deposited onto amorphous SiO2 substrates

The influence of substrate temperature and the silane-to-nitrogen ratio on the structure of silicon films 0.5–0.6 μm thick deposited onto amorphous SiO₂ substrates was investigated by X-ray diffraction. The investigations were carried out for silicon films deposited at various temperatures in the range 500–750 °C and with various silane-to-nitrogen ratios in the range 3.04 × 10^-4-2.84 × 10^-3 by volume. The silicon films deposited at 500 °C were amorphous while the films deposited at 550 °C were randomly oriented polycrystalline. The films deposited in the temperature range 600–700 °C were polycrystalline with a preferred orientation that changed from 〈110〉 through 〈100〉 to 〈111〉. The structure of the films deposited at 750 °C was randomly oriented polycrystalline. Investigations of the influence of the silane-to-nitrogen ratio on the silicon film structure revealed that the structure of films deposited at a substrate temperature of 500 °C was independent of the silane-to-nitrogen ratio. The structure of the films deposited at 600 °C depended on the silane-to-nitrogen ratio and changed from polycrystalline with a 〈110〉 preferred orientation to randomly oriented polycrystalline when the ratio was increased. The structure of films deposited at 700 °C also depended on the silane-to-nitrogen ratio and changed from randomly oriented polycrystalline to polycrystalline with double preferred orientation (〈100〉 and 〈111〉) when the ratio was increased.