Optical and electrical properties of crystalline indium tin oxide thin film deposited by vacuum evaporation technique

Indium tin oxide (ITO) thin film was deposited on glass substrate by means of vacuum evaporation technique and annealed at 200 °C, 300 °C and 400 °C in air for 1 h. The characterization and properties of the deposited film samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-VIS-NIR spectroscopy techniques. From the XRD patterns, it was found that the deposited thin film was of crystalline at an annealing temperature of 400 °C. The crystalline phase was indexed as cubic structure with lattice constant and crystallite size of 0.511 nm and 40 nm, respectively. The SEM images showed that the films exhibited uniform surface morphology with well-defined spherical grains. The optical transmittance of ITO thin film annealed at 400 °C was improved from 44% to 84% in the wavelength range from 250 nm to 2 100 nm and an optical band gap was measured as 3.86 eV. Hall effect measurement was used to measure the resistivity and conductivity of the prepared film.     

A novel approach to silicon gate CMOS device scaling

A new approach is reported for fabricating scaled Si-gate CMOS devices using medium temperature (?900° C) LPCVD deposited SiO₂ as the dielectric interlayer. The film can be deposited from 850 to 1000°C using a graded temperature profile and optimum pressure. A maximum of 100 wafers with 8% variation of thickness per run has been achieved using the process described in this paper. The medium-temperature LPCVD SiO₂ film exhibited step-coverage as good as the conventional low temperature PSG film. Since the new film requires no high temperature treatment, the convetional Si-gate CMOS diffusion process has been used to obtain the micron and submicron junction depths that are required to fabricate scaled CMOS devices. Such a processing approach, converting a 5–6 μm geometry CMOS process to a 3 μm geometry CMOS process, is described.     

Fifteen-Nanometer Ru Diffusion Barrier on NiSi/Si for a sub-45 nm Cu Contact Plug

A ruthenium film on a NiSi/Si substrate was evaluated for barrier performance in Cu contact metallization. The films were deposited by magnetron sputtering using Ni, Ru, and Cu targets. The low-resistivity NiSi film was initially produced from an Ni/Si substrate, and Ru and Cu films were sequentially deposited on the NiSi/Si substrate so that barrier performance could be studied. Barrier properties were elucidated by four-point probe measurement, x-ray diffractometry, scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy. The stability temperatures of 600°C (Cu/NiSi/Si) and 650°C (Cu/Ru/NiSi/Si) were systematically verified and are discussed. Structural analysis indicated that the failure mechanism involved penetration of the Cu through the Ru/NiSi stacked film at a specific temperature, which induced the accelerated dissociation of the NiSi. Interposition of an Ru layer between the Cu and the NiSi/Si effectively prevented intermixing and substantially improved the thermal stability in the Cu/NiSi/Si stack films.     

Electroless CoWP as a Diffusion Barrier between Electroless Copper and Silicon

In this work, an electroless CoWP film deposited on a silicon substrate as a diffusion barrier for electroless Cu and silicon has been studied. Four different Cu 120 nm/CoWP/Si stacked samples with 30, 60, 75, and 100 nm electroless CoWP films were prepared and annealed in a rapid thermal annealing (RTA) furnace at 300°C to 800°C for 5 min. The failure behavior of the electroless CoWP film in the Cu/CoWP/Si sample and the effect of CoWP film thickness on the diffusion barrier properties have been investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and sheet resistance measurements. The composition of the electroless CoWP films was 89.4 at.% Co, 2.4 at.% W, and 8.2 at.% P, as determined by energy dispersive X-ray spectrometer (EDS). A 30 nm electroless CoWP film can prevent copper penetration up to 500°C, and a 75 nm electroless CoWP film can survive at least up to 600°C. Therefore, increasing the thickness of electroless CoWP films effectively increases the failure temperature of the Cu/CoWP/Si samples. The observations of SEM and TEM show that interdiffusion of the copper and cobalt causes the failure of the electroless CoWP diffusion barriers in Cu/CoWP/Si during thermal annealing.     

Low-Temperature Silicon-to-Silicon Anodic Bonding Using Sodium-Rich Glass for MEMS Applications

In the present work, silicon-to-silicon anodic bonding has been accomplished using an intermediate sodium-rich glass layer deposited by a radiofrequency magnetron sputtering process. The bonding was carried out at low direct-current voltage of about 80 V at 365°C. The alkali ion (sodium) concentration in the deposited film, the surface roughness of the film, and the flatness of the silicon wafers were studied in detail and closely monitored to improve the bond strength of the bonded silicon wafers. The effect of chemical mechanical polishing (CMP) on the surface roughness of the deposited film was also investigated. The average roughness of the deposited film was found to be ~6 Å, being reduced to 2 Å after CMP. It was observed that the concentration of sodium ions in the deposited film varied significantly with the sputtering parameters. Scanning electron microscopy was used to obtain cross-sectional images of the bonded pair. The bonding energy of the bonded wafer pair was measured using the crack-opening method. The bonding energy was found to vary from 0.3 J/m² to 2.1 J/m² for different bonding conditions. To demonstrate the application of the process developed, a sealed cavity was created using the silicon-to-silicon anodic bonding technique, which can be used for fabrication of devices such as capacitive pressure sensors and Fabry– Perot-based pressure sensors. Also, a matrix of microwells was fabricated using this technique, which can be used in various biomicroelectromechanical system applications.     

The properties of annealed AlN films deposited by pulsed laser deposition

AlN films deposited on SiC or sapphire substrates by pulsed laser deposition were annealed at 1200°C, 1400°C, and 1600°C for 30 min in an inert atmosphere to examine how their structure, surface morphology, and substrate-film interface are altered during high temperature thermal processing. Shifts in the x-ray rocking curve peaks suggest that annealing increases the film density or relaxes the films and reduces the c-axis Poisson compression. Scanning electron micrographs show that the AlN begins to noticeably evaporate at 1600°C, and the evaporation rate is higher for the films grown on sapphire because the as-deposited film contained more pinholes. Rutherford backscattering spectroscopy shows that the interface between the film and substrate improves with annealing temperature for SiC substrates, but the interface quality for the 1600°C anneal is poorer than it is for the 1400°C anneal when the substrate is sapphire. Transmission electron micrographs show that the as-deposited films on SiC contain many stacking faults, while those annealed at 1600°C have a columnar structure with slightly misoriented grains. The as-deposited films on sapphire have an incoherent interface, and voids are formed at the interface when the samples are annealed at 1600°C. Auger electron spectroscopy shows that virtually no intermixing occurs across the interface, and that the annealed films contain less oxygen than the as-grown films.     

Microstructures and electrical properties of SrRuO3 thin films on LaAIO3 substrates

Conductive SrRuO₃ thin films have been deposited using pulsed laser deposition on LaA10₃ substrates at different substrate temperatures. Structural and microstructural properties of the SrRuO₃/LaAlO₃ system have been studied using x-ray diffraction, scanning electron microscopy, and scanning tunneling microscopy. Electrical properties of SrRuO₃ thin films have been measured. It was found that the film deposited at 250°C is amorphous, showing semiconductor-like temperature dependence of electrical conductivity. The film deposited at 425°C is crystalline with very fine grain size (100∼200?), showing both metallic and semiconductor-like temperature dependence of electrical conductivity in different temperature regions. The film deposited at 775°C shows a resistivity of 280 μΩ.cm at room temperature and a residual resistivity ratio of 8.4. Optimized deposition conditions to grow SrRuO₃ thin films on LaA10₃ substrates have been found. Possible engineering applications of SrRuO₃ thin films deposited at different temperatures are discussed. Bulk and surface electronic structures of SrRuO₃ are calculated using a semi-empirical valence electron linear combination of atomic orbitals approach. The theoretical calculation results are employed to understand the electrical properties of SrRuO₃ thin films.     

Electron microscopy and energy loss study of low temperature plasma deposited oxide on a CZ grown Si substrate

Transmission electron microscopy (TEM) and computer-controlled parallel electron energy loss spectroscopy (PEELS) are used to obtain the structure of and compositional profile across a thin oxide film deposited by remote plasma enhanced chemical vapor deposition at 300°C. The film, believed to be stoichio-metrically correct SiO₂ as determined by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS), was found to be oxygen rich with a composition non-uniformity across it. The existence of an abundance of oxygen was supported by capacitance-voltage measurements and etch rate studies. The non-uniformity was observed in TEM images. These results show what a powerful characterization technique computer-controlled PEELS can be. In addition, this is the first time that PEELS profiling was used to help interpret TEM images.     

On temperature coefficient of resistance of boron-doped SiGe films deposited by sputtering

Silicon–germanium films, doped with boron, were deposited on oxidised silicon substrates by RF magnetron sputtering. The post-deposition dopant activation and film crystallisation was done by annealing in the temperature range from 580 to 900 °C. The structural changes in the silicon–germanium films caused by the presence of boron and annealing were investigated by high-resolution transmission electron microscopy. The temperature coefficient of resistance (TCR) was characterised in the temperature range from room temperature to 210 °C and correlated to the nano-structure of the films. The TCR values were explained by the contribution of different scattering mechanisms and confirmed by low-frequency noise measurement. Very low values of TCR can be obtained by selecting appropriate boron content and post-deposition annealing conditions.     

Transmission electron microscope study of oxidation-induced

Boron-implanted silicon devices have been shown to be affected by the ambient conditions during implantation, anneal and drive-in diffusion. The presence of oxygen appears to be of major significance. This study was undertaken to observe directly by transmission electron microscopy defects existing in silicon implanted and annealed under varying conditions which might account for changes in device characteristics. Boron ions at doses of 10¹³ to 10¹⁶ B⁺ /cm² were implanted at 180KeV into silicon through 2000Å. thick oxide layers formed by steam at 950°C or dry oxygen at 1150°C. After implantation specimens were annealed to 950° or 1000°C for 1/2 hour periods in dry nitrogen or argon. At 950°C precipitate colonies were found in the steam-oxidized specimens and were also present in those annealed to 1000 C, whereas, to date, no such colonies were found on the specimens which had been oxidized in dry oxygen at 1150°C. Energy dispersive x-ray analysis in an electron microscope shows that the particles contain copper and are possibly a copper suicide. Precipitation occurs only along dislocations formed on annealing the ion-damaged specimens Colonies were found as deep as 0.5μm below the oxide film. Tentatively, it is proposed that precipitation of the copper is observed only in specimens implanted through the steam formed oxide because of an increase in the number of silicon oxide nuclei due to the faster rate of oxidation. These nuclei form at dislocations and become nucleation sites for copper precipitation. The source of the copper contamination has not yet been determined.     

Zinc Oxysulfide Thin Films Grown by Pulsed Laser Deposition

Pulsed laser deposition was used to produce thin films of zinc oxysulfide (ZnO _x S_1−x ) on quartz substrates. The target was a sintered pellet (ZnO_0.39S_0.61) made of a solution precipitate. The film composition obtained by electron probe microanalysis (EPMA) was ZnO_0.41S_0.59, ZnO_0.44S_0.56, and ZnO_0.37S_0.63 for substrate temperatures of 450°C, 540°C, and 630°C, respectively. X-ray diffraction (XRD) showed that samples deposited at 450°C and at 540°C had a prominent cubic sphalerite phase, whereas samples deposited at 630°C consisted of three phases, viz. hexagonal wurtzite and cubic sphalerite (ZnS), and hexagonal zincite (ZnO). With respect to the tabulated lattice spacings for sphalerite (cell constant 0.5406 nm), distinct shifts were observed for the low temperature samples, yielding cell constants around 0.533 nm. Transmission electron microscopy (TEM)–selected area electron diffraction studies support the XRD data. Patterns of films deposited at 540°C could be indexed as sphalerite, with similar lattice shifts as in XRD, resulting in a cell constant of 0.53. Locally highly resolved chemical analysis by TEM–energy dispersive x-ray analysis revealed a stoichiometry that was consistent with the EPMA results. Ultraviolet (UV)–visible transmission measurements of the films led to bandgap energies around 3.3 eV, which is well below the reported bandgap energies of ZnS.     

Enhancement in thermal stability of atomic layer deposited HfO2 films by using top Hf metal layer

A thin (∼ 0.5 nm) layer of Hf metal was deposited on an atomic layer deposited (ALD) HfO₂ film by the DC sputtering method. X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses showed that the Hf metal layer transformed into HfO₂ during the post-deposition annealing process. It appears that the HfO₂ layer formed by the oxidation of Hf metal provided the underlying ALD HfO₂ layer with the nucleation sites necessary to decrease the grain-boundary density of the crystallized HfO₂ film. The decrease in the grain-boundary density resulted in a reduction in the Hf-silicate formation and interfacial layer growth during post deposition annealing. This eventually resulted in a smaller increase in the capacitance equivalent thickness (CET) and high-k characteristics in the CET vs. leakage current density curve even after post deposition annealing at 1000 °C.     

Highly transparent and conducting zinc oxide films deposited by activated reactive evaporation

Highly transparent and conducting undoped zinc oxide films have been obtained with a best resistivity of ～1.1 × 10^-3 Ω cm, a carrier density of ～1.5 × 10²⁰ cm^?3 and a mobility of ～38 cm²V^{?1s ?1}. These were produced by activated reactive evaporation at a deposition rate of 2 to 8Å/s with a substrate temperature ≤200° C. The films deposited by this process were found to have resistivities that were thickness independent and also were relatively insensitive to deposition parameters. In terms of conductivity, it was found that films deposited at higher temperatures (T > 300°+ C) were always inferior to the films deposited below 200° C. High temperature vacuum annealing (350° C) significantly degraded the resistivity of the undoped films deposited at low temperature; this was attributable to a drop in both the electron concentration and the mobility. Aluminum doping was found to be able to stabilize the electron concentration while the drop in mobility was found to be related to the choice of substrate.     

Nanostructured ZnO Films for Room Temperature Ammonia Sensing

Zinc oxide (ZnO) thin films have been deposited by a reactive dc magnetron sputtering technique onto a thoroughly cleaned glass substrate at room temperature. X-ray diffraction revealed that the deposited film was polycrystalline in nature. The field emission scanning electron micrograph (FE-SEM) showed the uniform formation of a rugby ball-shaped ZnO nanostructure. Energy dispersive x-ray analysis (EDX) confirmed that the film was stoichiometric and the direct band gap of the film, determined using UV–Vis spectroscopy, was 3.29 eV. The ZnO nanostructured film exhibited better sensing towards ammonia (NH₃) at room temperature (～30°C). The fabricated ZnO film based sensor was capable of detecting NH₃ at as low as 5 ppm, and its parameters, such as response, selectivity, stability, and response/recovery time, were also investigated.     

Investigation into Texture,Preferential Orientation,and Optical Properties of Zinc Oxide Nanopolycrystalline Thin Films Deposited by the Sol–Gel Technique on Different Substrates

ZnO nanopolycrystalline thin films were deposited by the sol–gel technique on glass and silicon, and compared systematically via atomic force microscopy, scanning electron microscopy, x-ray diffraction, UV–Vis spectrophotometry, and fluorescence spectrophotometry. The thickness of the ZnO films was measured by ellipsometric microscopy. A higher preheating temperature was needed to obtain films with a strong preferential orientation. The optimal annealing temperatures for c-axis films on glass and silicon substrates were 525°C and 750°C, respectively. The relative intensity of the blue–green emission peak tends to increase with the annealing temperature. When the film is annealed in N₂, the transmittance of the film reduces while the intensity of the blue–green emission increases.     

Device quality MOS Gate insulators: Sputter deposition and low temperature processing

A series of n-channel, Al-gate MOS transistors were fabricated using reactively sputtered SiO2as the gate insulator. The SiO2was deposited at low temperatures and low RF powers, and during subsequent processing was not subjected to temperatures in excess of 465°C. Test results showed that for gate oxides deposited at 20 W, the measured breakdown strength was 3-4 MV/cm with interface trapped charge density of 4-8 × 10¹⁰cm^-2and that the resulting electron mobility of the transistor was 470 cm²/V.s. After annealing in nitrogen at 1000°C, the deposited oxides exhibited electrical properties which are very similar to those of thermally grown SiO2.     

Low temperature processed mosfet's using laser recrystallized polycrystalline silicon films

An n-channel MOS transistor was fabricated on a laser recrystallized polycrystalline silicon film at temperatures below 630°C. The gate oxide was sputter deposited at 200°C. Lasers were used for substrate recrystallization, implantation damage annealing and dopant drive-in. An electron field effect mobility higher than 100 cm²/V · sec. was observed on the finished transistors. With 10 V applied to the gate of the transistors for 2 hr, less than a 20 mV shift in threshold voltage was observed.     

Optical and microstructural characterization of the effects of rapid thermal annealing of CdTe thin films grown on Si (100) substrates

The effects of rapid thermal annealing (RTA) on CdTe/Si (100) heterostructures have been studied in order to improve the structural quality of CdTe epilayers. Samples of CdTe (111) polycrystalline thin films grown by vapor phase epitaxy (VPE) on Si (100) substrates have been investigated. The strained structures were rapidly thermally annealed at 400°C, 450°C, 500°C, 550°C, and 600°C for 10 sec. The microstructural properties of the CdTe films were characterized by carrying out scanning electron microscopy (SEM), x-ray diffraction (XRD), and atomic force microscopy (AFM). We have shown that the structural quality of the CdTe epilayers improves significantly with increasing annealing temperature. The optimum annealing temperature resulting in the highest film quality has been found to be 500°C. Additionally, we have shown that the surface nucleation characterized by the island size distribution can be correlated with the crystalline quality of the film.     

Phase transformation-dependent sensing performance of multi-walled carbon nanotube–alumina nanocomposite-based gas sensors

Alumina (Al₂O₃) exists in three different phases having different physical properties. In view of this fact, a systematic study has been carried out for the first time to investigate how its various phases influence the sensing performance of a MWCNTs–alumina nanocomposite based trace level gas sensor. A series of composite sensing film were prepared by dispersing MWCNTs in alumina solution followed by a sol–gel process, where the phase of alumina is controlled by specific temperatures set for an annealing process. The analysis revealed that porosity as well as the surface area varies from phase to phase in the composite film and it is the key factor which governs the sensing performance. Brunaur, Emmet and Teller (BET) analysis showed the significant increase in specific surface area of the composite film when boehmite (β-phase) was transformed into γ-phase. X-ray diffraction (XRD) results confirmed the presence of γ-, mixed δ- θ- and α-alumina phases when the annealing temperature of the composite film raised from room temperature to 450 °C, 800 °C and 1000 °C respectively. Field emission scanning electron microscopy (FESEM), BET and Atomic force microscopy (AFM) techniques were employed to examine the resultant porous structure and surface area of the annealed composite films in various phases. The composite having γ-alumina phase (annealed at 450 °C) was found to have maximum response, where the composite having α-alumina phase (annealed at 1000 °C) had the least.     

Facile and rapid production of conductive flexible films by deposition of polythiophene nanoparticles on transparent poly(ethyleneterephthalate): Electrical and morphological properties

In this work, polythiophene (PTh) nanoparticles were successfully deposited on poly(ethyleneterephthalate) (PET) substrate as thin film by a facile and rapid chemical oxidative deposition method using a binary organic solvent system in the presence of N-cetyl-N,N,N-trimethylammonium bromide (CTAB) as cationic surfactant. The electrical conductivity of PTh nanoparticles deposited on PET was optimized by adjusting the surfactant/oxidant/monomer molar ratio, monomer concentration and time of polymerization. Resulted film was conductive, transparent and flexible which can be used in electronic devices such as OLEDs. Electrical conductivity for the un-doped deposited PTh nanoparticles at oxidant/monomer molar ratio of 5:1 at 0 °C polymerized for 12 min was measured to be 1.18×10⁻² S/cm. The effect of oxidant and monomer concentration on polymerization yield was also investigated. The structural confirmation and transparency of the PTh nanoparticle coated PET films were characterized by FTIR and UV–vis spectroscopy, respectively. Field emission scanning electron microscopy (FESEM), laser particle size analysis and transmission electron microscopy (TEM) were employed for surface morphology and size distribution measurements of PTh nanoparticles. The results showed that the PTh nanoparticles are deposited as globular aggregates with average size of about 50 nm on PET.