Single Crystal Silicon Substrates Research Articles

NITROGEN DOPING IN CAMPHORIC CARBON FILMS AND ITS APPLICATION TO PHOTOVOLTAIC CELL

Carbon films have been deposited on quartz and single-crystal silicon substrates by pulsed laser deposition technique. The soot for the target was obtained from burning camphor, a natural source. The effect of nitrogen (N) incorporation in camphoric carbon film is investigated. Optical gap for the undoped film is about 0.95 eV. The optical gap remains unchanged for low N content and decreases to about 0.7 eV. With higher N content, the optical gap increases. The resistivity of the carbon film increases with N content, initially and decreases with higher N content up till the film that is deposited at 30 mTorr. The results indicate successful doping for the film deposited at low nitrogen content. The J–V characteristics of N-incorporated carbon/silicon photovoltaic cells under illumination are observed to improve upon N-incorporation in the carbon layer.

Determination of the growth strain of LPCVD polysilicon

This work presents a semi-empirical procedure for determining the through-the-thickness variation of the eigenstrain (eigenstrain is a generic term for any inelastic strain, including plastic strain, free thermal expansion, phase transformation, etc.) that develops during the growth of thin polysilicon films formed using low-pressure chemical vapor deposition (LPCVD). This variation is assumed to depend on the polysilicon microstructure and deposition conditions, but not on the characteristics of the (single crystal silicon) substrate. The procedure involves the use of an elastic laminated plate model to determine the eigenstrain distribution that predicts the experimentally measured substrate curvatures. In comparison to the method presented by A.Ni et al., which relies on incremental etching of a single specimen, an alternative experimental procedure is followed to measure the substrate curvatures of a series of different thickness films. While being significantly more time-consuming, the alternative procedure was expected to lead to improved predictions of the eigenstrain distribution, as it avoids the nonuniform film thicknesses produced by the etching procedure. However, a comparison of the curvature histories measured using the two approaches demonstrates that, as long as sufficiently small increments are used in the shaving method, then the improvement is insignificant. This suggests that the plasma etching does not alter the polysilicon's intrinsic growth strain, and that the etch rate nonuniformities across the substrate are small. The eigenstrain distributions could be used, in conjunction with structural mechanics models, to design multilayered polysilicon devices with prescribed curvatures.

Optical parameters and absorption of copper (II)-azo complexes thin films as optical recording media

Smooth thin films of three kinds of azo dyes of 2-(5′- tert-butyl-3′-azoxylisoxazole)-1, 3-diketones and their copper (II)-azo complexes were prepared by the spin-coating method. Absorption spectra of the thin films on a glass substrate in the 300–600 nm wavelength region were measured. Optical constants (complex refractive index N= n+ ik) and thickness of the thin films prepared on single-crystal silicon substrate in the 300–600 nm wavelength region were investigated on rotating analyzer–polarizer type of scanning ellipsometer, and dielectric constants ε( ε= ε 1+ iε 2), absorption coefficients α as well as reflectance R of thin films were then calculated. In addition, one of the copper (II)-azo complex thin film prepared on glass substrate with an Ag reflective layer was also studied by atomic force microscopy (AFM) and static optical recording. AFM study shows that the copper (II)-azo complex thin film is very smooth and has a root mean square surface roughness of 1.89 nm. Static optical recording shows that the recording marks on the copper (II)-azo complex thin film are very clear and circular, and the size of the minimal recording marks can reach 200 nm.

Polarization-dependent Raman spectra of thin crystalline silicon films

Polarization-dependent Raman spectra are presented to analyze the structural properties of epitaxial, quasiepitaxial, and microcrystalline silicon films deposited on (100) single-crystal silicon substrates by electron cyclotron resonance plasma-enhanced chemical-vapor deposition. We rotate the sample with respect to the polarization direction of the incident laser light and observe the changes in Raman scattering. The measurements are very effective in differentiating between films with a preferred orientation and those that are randomly oriented or amorphous. An interesting anisotropy has been observed for quasiepitaxial films for which the spectra resemble those of single-crystal wafers under normal measurement conditions. However, at sample orientations where the scattering intensity is minimized, additional structure on the low-energy side of the main silicon TO-phonon peak becomes visible. This is tentatively attributed to scattering from crystalline and amorphouslike grain-boundary regions. Polarization-dependent Raman spectra are able to provide useful information on the structure of these films which would normally be masked by the main silicon optical-phonon peak.

Properties of Triglycine Sulfate Crystals Grown from Aqueous Solutions

A dielectric study of triglycine sulfate crystals was carried out and the phase transition temperatures were determined for samples grown at temperatures below 0°C. The influence exerted by a single-crystal silicon substrate treated by various methods on the shape of triglycine sulfate crystals was examined.

Field emission properties of polymer-converted carbon films by heat treatment

Carbon films were prepared on single crystal silicon substrates by heat-treatment of a polymer-poly(phenylcarbyne) at 800 °C in Ar atmosphere. The heat-treatment caused the change of the polymer into carbon film, which exhibited good field emission properties. Low turn-on emission field of 4.3 V/μm (at 0.1 μA/cm 2) and high emission current density of 250 μA/cm 2 (at 10 V/μm) were observed for the polymer-converted carbon films. This behavior was demonstrated to be mainly related to the microstructure of the carbon films, which consisted of fine carbon nanoparticles with high sp 2 bonding. The carbon films, which can be deposited simply with large areas, are promising for practical applications in field emission display.

The effect of the rapid thermal annealing on the interdiffusion and the reaction at the interface of the binary system Cr/Si

In order to understand the growth mechanism of the silicides and the effect of the dopant on the electrical activity, a thin layer of chromium (100 nm) is deposited on the single crystal silicon (1 0 0) substrate implanted (10 15 As + atoms/cm 2, 100 keV) and non implanted. Afterwards, we performed a rapid thermal annealing in the interval of temperature (450–600 °C) for a fixed duration of 45 s. The samples are analyzed by X ray-diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The electrical activity has been investigated by the method of the four-point probes. The analysis of the samples by XRD and RBS showed that the rapid thermal annealing (RTA) leads to a reaction at the interface Cr/Si inducing the formation and the growth of the unique silicide CrSi 2. It is also established that the kinetics growth of CrSi 2 presents a linear evolution with temperature. This fact shows that the growth is governed by a chemical reaction of the interface. Sheet resistance measurements have been performed to study the electrical behavior for these structures. It is worth to point out that the presence of the implanted arsenic in the single crystal silicon increased the resistance in a significant manner.

Design, fabrication and characterization of single crystal silicon microactuator for hard disk drives

In this paper, a single crystal silicon electrostatic microactuator for hard disk drives' (HDD) dual stage servo systems is presented. The microactuator is mounted between the slider and suspension and drives the slider on which a magnetic head element is attached. The microactuator has electrically isolated microstructures with an aspect ratio of 20:1 directly processed from a single crystal silicon substrate. It consists of a stator attached to the silicon substrate by a bus bar and a movable rotor connected to an anchored central column via spring beams. Both the stator and the rotor are suspended from the silicon substrate. Parallel plate capacitor pairs are used for the electrostatic actuation. When a voltage is applied to the microactuator, the head element will be driven to move in the tracking direction because of the rotational motion of the rotor. The microactuator prototype with overall dimensions 1.4 mm × 1.4 mm × 0.18 mm has been successfully fabricated. The techniques for integration of the microactuator with a head gimbal assembly (HGA) have been investigated. Experiments show that ±0.6 µm equivalent displacement of the head element in the tracking direction is achieved at the driving voltage 28.5 V. Dynamic frequency response testing of the microactuator bonded with the slider has been carried out. The test results demonstrate that the first in-plane resonance frequency of the electrostatic microactuator bonded with the slider is 1.9 kHz and the damping ratio is 2.8%, and the device is equivalent to a single spring mass system up to 50 kHz. The single crystal silicon electrostatic microactuator has a small mass, good thermal stability and dynamic performance, and is feasible to operate as a fine actuator in dual stage servo systems for high density HDD.

Advanced plasma processing combined with trench isolation technology for fabrication and fast prototyping of high aspect ratio MEMS in standard silicon wafers

A bulk micromachining technology for fabrication of micro electro mechanical systems (MEMS) in a standard silicon wafer is presented. A fabrication process, suitable for full integration with on-chip electronics, employs advanced plasma processing to etch, passivate and release micromechanical structures in a single plasma system, and vertical trench isolation to obtain electrical isolation between the released components. Distinct electrical domains can be defined even on movable parts. The sophisticated electrical isolation between high-aspect-ratio single-crystal silicon (SCS) components allows simplification of the fabrication and improvement of the performance of existing devices and design of entirely new MEMS. The presented technology is an attractive platform for both fabrication and rapid prototyping of MEMS. This is due to a short processing time, a large freedom of design, high process flexibility and low-cost of the starting SCS substrate relative to SOI substrates. Several example microstructures demonstrating the capabilities of this technology have been successfully fabricated.

A new method to evaluate the fracture toughness of thin films

A method based on microindentation is developed to determine the fracture toughness K Ic of a thin film bonded to a brittle substrate. Using an easily fabricated sample having a partially coated substrate, indentation on the uncoated portion of the substrate is used to generate a radial crack that propagates into and away from the coated region. Comparison of the lengths of the surface traces of the indentation crack into and away from the coated region is used to measure the toughening imparted by the coating. This test method avoids the complicating effects of delamination that often occur when the coating is indented directly. To extract quantitative results, a 3D finite element model of the system geometry is generated and a cohesive zone model is used to predict the complex equilibrium crack front. The model predicts the length of the crack penetration into the coating vs. the length of the crack growth away from the coating as a function of the elastic and toughness properties of the coating and the substrate, and the residual thermal stresses, which play an important contribution to the detailed crack growth. An approximate analytic model using energy balance ideas is developed to permit easy determination of the coating toughness from experimental data, and the model agrees well with full numerical results over a wide range of coating and substrate property values. The overall method is applied here to determine the toughness of a thin CVD diamond coating on a thick silicon single crystal substrate, and a coating toughness of K Ic=8.4 MPa m 1/2 is obtained using a previously measured biaxial tensile coating residual stress of 1 GPa.

29.4L: Late‐News Paper: Dual Doped High Tg White Organic Light Emitting Devices on Silicon

AbstractWe report the fabrication of efficient surface‐emitting white organic light emitting diodes (OLEDs) on single crystal silicon substrates using a high Tg blue host layer with co‐deposited blue‐green and red‐orange emitter dopant molecules. The emission layer is sandwiched between a Spiro‐TAD hole transport layer and an Alq3 electron transport layer. The devices operate near the 1931 CIE white balance point with luminous efficiencies of 2.75 lum/W and current efficiencies of 8 cd/A, representing luminance of ∼1600 cd/m2 at a current density of 20 mA/cm2. When tested under accelerated and uninterrupted 90% pulsed 20 mA/cm2 drive, our OLEDs yield luminance half‐lives of over 5000 hours, which represent normalized half life at 100 cd/m2 for color microdisplays of greater than 20,000 hours assuming a 25% duty cycle similar to that created by full motion video. These results enable us to meet commercial and military requirements for OLED color microdisplays employing passband filters for red, green and blue subpixel elements.

Evaluation of manganite films on silicon for uncooled bolometric applications

Pulsed-laser-deposited polycrystalline/amorphous films of mixed-valent manganites [La0.7Ca0.3MnO3 (LCMO), La0.5Sr0.5MnO3 (LSMO), La0.5Ba0.5MnO3 (LBMO), and (La0.6Pr0.4)0.67Ca0.33MnO3 (LPCMO)] grown at low temperature (450 °C) on single crystal (001) silicon substrate are evaluated for uncooled bolometric applications. It is shown that the temperature coefficient of resistance (TCR) and electrical noise (Sv) depend on the chemical composition. The optimum performance is found for LCMO with TCR of ∼7% K−1 and spectral noise ∼8.9×10−13 V2/Hz. In LBMO and LSMO the noise is much lower, but so is the TCR (1.5%–2% K−1). In LPCMO the TCR is high (∼10% K−1) and the noise is as well.

Complete characterization of rough polymorphous silicon films by atomic force microscopy and the combined method of spectroscopic ellipsometry and spectroscopic reflectometry

In this paper the results of the complete characterization of hydrogenated polymorphous silicon (pm-Si:H) films deposited onto silicon single crystal substrates performed by atomic force microscopy (AFM) and the combined method of spectroscopic ellipsometry and spectroscopic reflectometry are presented. This combined method is applied in the multi-sample modification. The experimental data are measured within the near-UV, visible and near-IR regions (190–1000 nm). For treating the experimental data the dispersion model recently formulated for amorphous chalcogenide films is employed. This model is based on the parameterization of the density of electronic states. Moreover, for the treatment of the experimental data the structural model containing the defects, i.e. roughness of the upper boundaries of the films, overlayers, transition layers and refractive index profile inhomogeneity is employed. The results of the characterization consist of the determination of the spectral dependences of the optical constants of the pm-Si:H films and the values of the parameters describing the defects of these films.

Microscale Laser Shock Peening of Thin Films, Part 1: Experiment, Modeling and Simulation

Microscale Laser Shock Peening (LSP), also known as Laser Shock Processing, is a technique that can be potentially applied to manipulate residual stress distributions in metal film structures and thus improve the fatigue performances of micro-devices made of such films. In this study, microscale LSP of copper films on single crystal silicon substrate is investigated. Before and after-process curvature measurement verifies that sizable compressive residual stress can be induced in copper thin films using microscale LSP. Improved modeling work of shock pressure is summarized and the computed shock pressure is used as loading in 3D stress/strain analysis of the layered film structure. Simulation shows that the stress/strain distribution in the metal film is close to equi-biaxial and is coupled into the silicon substrate.

Microscale Laser Shock Peening of Thin Films, Part 2: High Spatial Resolution Material Characterization

Microscale Laser Shock Peening (LSP) is a technique that can be potentially applied to manipulate the residual stress distributions in metal film structures and thus improve the reliability of micro-devices. This paper reports high-spatial-resolution characterization of shock treated copper thin films on single-crystal silicon substrates, where scanning x-ray microtopography is used to map the relative variation of the stress/strain field with micron spatial resolution, and instrumented nanoindentation is applied to measure the distribution of hardness and deduce the sign of the stress/strain field. The measurement results are also compared with 3-D simulation results. The general trends in simulations agree with those from experimental measurements. Simulations and experiments show that there is a near linear correlation between strain energy density at the film-substrate interface and the X-ray diffraction intensity contrast.

Formation of silica coating films from spin-on polysilazane at room temperature and their stability in hot water

Spin-coating was conducted on single-crystal silicon substrates using a xylene solution of perhydropolysilazane (PHPS) to obtain 0.14-μm-thick PHPS films. The PHPS films obtained were suspended over various acidic and basic solutions at room temperature so that they were exposed to the vapors from the solutions. PHPS-to-silica film conversion was studied by infrared absorption spectroscopy, and the stability of the exposed films in hot water was examined by soaking the films in 80 °C water. The as-deposited PHPS films were found to be dissolved in water. When the PHPS films were suspended over water, the films were partially converted into silica, but the resultant film had low stability in hot water. Higher degrees of PHPS-to-silica conversion and higher stabilities in hot water were found on exposing the PHPS films to basic or acidic vapors. Exposure to highly basic vapors from aqueous solutions of ammonia and ethylamine was significantly effective in PHPS-to-silica film conversion, which provided silica thin films with high stability in hot water.

Thermal Oxidation of Thin Cu–Ti Films

Thin Cu–Ti films are grown on single-crystal silicon substrates by magnetron sputtering, and their oxidation is studied between 420 and 670 K. A technique is proposed for producing Cu–Ti films of controlled composition using a composite target. The phase composition of the films oxidized in oxygen at atmospheric pressure is determined, and their microstructure is studied by scanning electron microscopy. The films are found to contain the intermetallic compounds Cu3Ti and CuTi2 , which form during both magnetron sputtering and subsequent oxidation.

Effect of Annealing on the Structural, Mechanical and Tribological Properties of Electroplated Cu Thin Films

AbstractThe increasing demand for faster and more reliable integrated circuits (ICs) has promoted the integration of Copper-based metallization. Electroplated Cu films demonstrate a microstructural transition at room temperature, known as self annealing. In this paper we intend to investigate the annealing behavior of electroplated Cu films grown on a seed Cu layer on top of the barrier layers over a single crystal silicon substrate. All the samples were undergone through a multistep annealing process. Grazing incident x-ray diffraction pattern shows stronger x-ray reflections from Cu (111) and (220) planes but weaker reflections from (200), (311) and (222) planes in all the electroplated Cu samples. Transmission electron microscopy was performed on the cross section of the samples and the diffraction pattern showed the crystalline behavior of both seed layer and electroplated Cu. Nanoindentation was performed on all the samples using the continuous stiffness measurement (CSM) technique and it was found that the elastic modulus varies from 110 to 130 GPa while the hardness varies from 1 to 1.6 GPa depending on the annealing conditions. The tribological properties of all the copper films were also measured using the Bench Top CMP tester. Subsequently, Nanoindentation was performed on the samples after polishing the top surface in order to investigate the work hardening and an increase in hardness and modulus was observed. Finite Element Modeling was performed in order to investigate the stress behavior during nanoindentation.

A high voltage NMOSFET fabricated by using a standard CMOS logic process as a pixel‐driving transistor for the OLED on the silicon substrate

A high voltage NMOSFET is proposed to drive top emission organic light emitting device (OLED) used in the organic electroluminescent (EL) display on the single crystal silicon substrate. The high voltage NMOSFET can be fabricated by utilizing a simple layout technique with a standard CMOS logic process. It is clearly shown that the maximum supply voltage (VDD) required for the pixel‐driving transistor could reach 45 V through analytic and experimental methods. The high voltage NMOSFET was fabricated by using a standard 1.5 μm, 5 V CMOS logic process. From the measurements, we confirmed that the high voltage NMOSFET could sustain the excellent saturation characteristic up to 50 V without breakdown phenomena.

エマルションの最前線 マイクロチャネル乳化技術の開発

Microchannel (MC) arrays with various shapes and sizes were micro-fabricated using a single-crystal silicon substrate. An emulsion is prepared by simply forcing dispersed phase fluid into continuous phase fluid through the MC. Real-time optical observations of the emulsification process can be realized with a microscope video system. The grooved type MC and module were used to characterize MC emulsification, and straight-through MC and module were developed for higher productivity. O/W-emulsions can be obtained due to its hydrophilic surface property after MC oxidation. Hydrophobic MC modified by silanization can be also applicable to W/O-emulsions. Both monodisperse O/W-and W/O-emulsions with average droplets sizes ranging 3-90 p m and coefficients of variations lower than 10% have been successfully obtained. Emulsification was significantly affected by MC sizes and structures. Analysis by high-speed camera revealed that the structure of terrace is so important for instability at the outlet, and spontaneous droplet formation caused by interfacial tension. An oblong straight-through MC was highly applicable to emulsification. MC emulsification was also applied to productions of solid-lipid and polymeric microsheres, and microcapsules, showing high availability. The MC emulsification technology has great potential for food, pharmaceutical and chemical industries.