Showing papers on "Amorphous silicon published in 1994"

Semiconductor, semiconductor device, and method for fabricating the same

Abstract: Method of fabricating semiconductor devices such as thin-film transistors by annealing a substantially amorphous silicon film at a temperature either lower than normal crystallization temperature of amorphous silicon or lower than the glass transition point of the substrate so as to crystallize the silicon film. Islands, stripes, lines, or dots of nickel, iron, cobalt, or platinum, silicide, acetate, or nitrate of nickel, iron, cobalt, or platinum, film containing various salts, particles, or clusters containing at least one of nickel, iron, cobalt, and platinum are used as starting materials for crystallization. These materials are formed on or under the amorphous silicon film.

Chemical order in amorphous silicon carbide.

Abstract: While ordering in alloy crystals is well understood, short-range ordering in amorphous alloys remains controversial. Here, by studying computer-generated models of amorphous SiC, we show that there are two principal factors controlling the degree of chemical order in amorphous covalent alloys. One, the chemical preference for mixed bonds, is much the same in crystalline and amorphous materials. However, the other factor, the atomic size difference, is far less effective at driving ordering in amorphous material than in the crystal. As a result, the amorphous phase may show either strong ordering (as in GaAs), or weaker ordering (as in SiC), depending upon the relative importance of these two factors.

Method of fabricating a thin film transistor using a nickel silicide layer to promote crystallization of the amorphous silicon layer

Abstract: Method of fabricating TFTs starts with forming a nickel film selectively on a bottom layer which is formed on a substrate. An amorphous silicon film is formed on the nickel film and heated to crystallize it. The crystallized film is irradiated with infrared light to anneal it. Thus, a crystalline silicon film having excellent crystailinity is obtained. TFTs are built, using this crystalline silicon film.

Three dimensional amorphous silicon/microcrystalline silicon solar cells

Abstract: Three dimensional deep contact amorphous silicon/microcrystalline silicon (a-Si/μc-Si) solar cells which use deep (high aspect ratio) p and n contacts to create high electric fields within the carrier collection volume material of the cell. The deep contacts are fabricated using repetitive pulsed laser doping so as to create the high aspect p and n contacts. By the provision of the deep contacts which penetrate the electric field deep into the material where the high strength of the field can collect many of the carriers, thereby resulting in a high efficiency solar cell.

Method of manufacturing multiple polysilicon TFTs with varying degrees of crystallinity

Abstract: Method of fabricating a semiconductor circuit is initiated with formation of an amorphous silicon film. Then, a second layer containing at least one catalytic element is so formed as to be in intimate contact with the amorphous silicon film, or the catalytic element is introduced into the amorphous silicon film. This amorphous silicon film is selectively irradiated with laser light or other equivalent intense light to crystallize the amorphous silicon film.

Silicon nitride and oxynitride films

Abstract: The physics and chemistry of amorphous silicon oxynitride films are reviewed. Since the main applications of these materials are in the manufacture of Si-based integrated circuits (ICs), phenomena such as diffusion mechanisms, oxidation kinetics, defects and charge trapping are given special attention. Mature thin-film technologies to form oxynitride layers are in the various types of chemical vapour deposition and thermal processing in NH3 and N2O. Determined by their growth process, oxynitrides contain a certain amount of hydrogen which is shown to play a key role in the reactivity of these materials. Once this is understood, it is possible to relate the properties of a wide range of oxynitrides to their composition and the micro-chemistry involved.

Semiconductor device having improved crystal orientation

Abstract: Thin-film transistors (TFTs) of peripheral logic circuits and TFTs of an active matrix circuit (pixel circuit) are formed on a single substrate by using a crystalline silicon film. The crystalline silicon film is obtained by introducing a catalyst element, such as nickel, for accelerating crystallization into an amorphous silicon film and heating it. In doing so, the catalyst element is introduced into regions for the peripheral logic circuits in a nonselective manner, and is selectively introduced into regions for the active matrix circuit. As a result, vertical crystal growth and lateral crystal growth are effected in the former regions and the latter regions, respectively. Particularly in the latter regions, the off-current and its variation can be reduced. The vertical growth and the lateral growth have a difference in the degree of crystal orientation. In general, the vertical growth does not provide so high of a degree of crystal orientation in which orientation in the (111) plane with respect to the substrate surface is dominate to a small extent. In contrast, remarkable orientation is found in the lateral growth. For example, the ratio of a reflection intensity of the (111) plane to the sum of reflection intensities of the (111), (220) and (311) planes can amount to more than 80 or 90%.

Semiconductor device having transistors with different orientations of crystal channel growth with respect to current carrier direction

Abstract: A silicon film is crystallized in a predetermined direction by selectively adding a metal element having a catalytic action for crystallizing an amorphous silicon and annealing. In manufacturing TFT using the crystallized silicon film, TFT provided such that the crystallization direction is roughly parallel to a current-flow between a source and a drain, and TFT provided such that the crystallization direction is roughly vertical to a current-flow between a source and a drain are manufactured. Therefore, TFT capable of conducting a high speed operation and TFT having a low leak current are formed on the same substrate.

Interaction of aluminum with hydrogenated amorphous silicon at low temperatures

Abstract: Annealing effects on aluminum/hydrogenated amorphous silicon (a‐Si:H) contacts in the temperature range from 100 to 300 °C were studied. Al was evaporated on device‐quality, phosphorus‐doped (n+) a‐Si:H films deposited in a UHV plasma‐enhanced chemical‐ vapor‐deposition system. Both electrical measurements and surface morphological analyses were performed to characterize the interaction. The transmission line model technique was used to measure sheet resistance and contact resistivity. For samples where Al covered the entire a‐Si:H surface during annealing, sheet resistance and contact resistivity were found to decrease monotonically with annealing temperature; whereas, samples annealed after patterning of the Al pads exhibited a minimum in sheet resistance and contact resistivity at temperatures between 150 and 200 °C. Optical and scanning electron microscopy, surface profilometry, and Raman spectroscopy were used to study the surface morphology. Interaction of Al with a‐Si:H was observed to initiate at ...

Semiconductor device including a plurality of thin film transistors at least some of which have a crystalline silicon film crystal-grown substantially in parallel to the surface of a substrate for the transistor

Abstract: Nickel is introduced to a predetermined region of a peripheral circuit section, other than a picture element section, on an amorphous silicon film to crystallize from that region. After forming gate electrodes and others, sources, drains and channels are formed by doping impurities, and laser is irradiated to improve the crystallization. After that, electrodes/wires are formed. Thereby an active matrix type liquid crystal display whose thin film transistors (TFT) in the peripheral circuit section are composed of the crystalline silicon film whose crystal is grown in the direction parallel to the flow of carriers and whose TFTs in the picture element section are composed of the amorphous silicon film can be obtained.

Method of fabricating a semiconductor device

Abstract: Method of fabricating a semiconductor device, such as a thin-film transistor, having improved characteristics and improved reliability. The method is initiated with formation of a thin amorphous silicon film on a substrate. A metallization layer containing at least one of nickel, iron, cobalt, and platinum is selectively formed on or under the amorphous silicon film so as to be in intimate contact with the silicon film, or these metal elements are added to the amorphous silicon film. The amorphous silicon film is thermally annealed to crystallize it. The surface of the obtained crystalline silicon film is etched to a depth of 20 to 200Å, thus producing a clean surface. An insulating film is formed on the clean surface by CVD or physical vapor deposition. Gate electrodes are formed on the insulating film.

Mode of growth and microstructure of polycrystalline silicon obtained by solid‐phase crystallization of an amorphous silicon film

Abstract: The structure and the morphology of crystallized amorphous silicon (α‐Si) films which were deposited on glass and annealed in a conventional furnace or by rapid thermal process (RTP) are studied using transmission electron microscopy (TEM). The ellipsoidal shape of the grains is attributed to the fast solid‐state crystallization along the two mutually perpendicular 〈112〉 and 〈110〉 crystallographic directions. The growth is solely based on the twin formation. The stability of the microtwins was studied by RTP and in situ TEM heating experiments. The effect of the film thickness on the preferred orientation of the grains is discussed. Very thin films exhibit (111) preferred orientation due to the strongly anisotropic rate of growth of the nuclei, which imposes an orientation filtering due to a growth velocity competition. The mode of growth of these films is compared with poly‐Si films grown by low‐pressure chemical‐vapor deposition.

Semiconductor device employing crystallization catalyst

Abstract: A substance containing a catalyst element is formed so as to closely contact with an amorphous silicon film, or a catalyst element is introduced into the amorphous silicon film. The amorphous silicon film is annealed at a temperature which is lower than a crystallization temperature of usual amorphous silicon, thereby selectively crystallizing the amorphous silicon film. The crystallized region is used as a crystalline silicon TFT which can be used in a peripheral driver circuit of an active matrix circuit. The region which remains amorphous is used as an amorphous silicon TFT which can be used in a pixel circuit. A relatively small amount of a catalyst element for promoting crystallization is added to an amorphous silicon film, and an annealing process is conducted at a temperature which is lower than the distortion temperature of a substrate, thereby crystallizing the amorphous silicon film. A gate insulating film, and a gate electrode are then formed, and an impurity is implanted in a self-alignment manner. A film containing a catalyst element for promoting crystallization is closely contacted with the impurity region, or a relatively large amount of a catalyst element is introduced into the impurity region by an ion implantation or the like. Then, an annealing process is conducted at a temperature which is lower than the distortion temperature of the substrate, thereby activating the doping impurity.

Method of forming polycrystalline silicon layer on substrate by large area excimer laser irradiation

Abstract: A method of forming a polycrystalline silicon thin film improved in crystallinity and a channel of a transistor superior in electrical characteristics by the use of such a polycrystalline silicon thin film. An amorphous silicon layer of a thickness preferably of 30 nm to 50 nm is formed on a substrate. Next, substrate heating is performed to set the amorphous silicon layer to preferably 350° C. to 500° C., more preferably 350° C. to 450° C. Then, at least the amorphous silicon layer is irradiated with laser light of an excimer laser energy density of 100 mJ/cm2 to 500 mJ/cm2, preferably 280 mJ/cm2 to 330 mJ/cm2, and a pulse width of 80 ns to 200 ns, preferably 140 ns to 200 ns, so as to directly anneal the amorphous silicon layer and form a polycrystalline silicon thin film. The total energy of the laser used for the irradiation of excimer laser light is at least 5 J, preferably at least 10 J.

Method of making semiconductor device/circuit having at least partially crystallized semiconductor layer

Abstract: Amorphous silicon in impurity regions (source and drain regions or N-type or p-type regions) of TFT and TFD are crystallized and activated to lower electric resistance, by depositing film having a catalyst element such as nickel (Ni), iron (Fe), cobalt (Co) or platinum (Pt) on or beneath an amorphous silicon film, or introducing such a catalyst element into the amorphous silicon film by ion implantation and subsequently crystallizing the same by applying heat annealing at an appropriate temperature.

Numerical modeling of the optical properties of hydrogenated amorphous‐silicon‐based p‐i‐n solar cells deposited on rough transparent conducting oxide substrates

Abstract: Hydrogenated amorphous‐silicon (a‐Si:H) ‐based solar cells consist of two electrodes and a p‐i‐n structure, deposited on glass substrates. Depositing the p‐i‐n layers and the back metallic electrode on an optically rough transparent conducting oxide (TCO) electrode enhances the absorption of the incident light in the active i layer: Light is scattered at the rough front interface and is partially trapped in the high refraction index layer, as in a waveguide. In addition TCO roughness increases the front transmission coefficient, increasing the amount of light in the active layer. TCO texture yields a relative increase of the conversion efficiency up to 30%. A semiempirical model of thin‐film solar‐cell optics is presented, taking into account the interface roughness by introducing experimentally derived scattering coefficients and treating the propagation of specular light in a rigorous way. Numerically simulated spectral response and total reflectance of standard solar cells deposited on different TCO textures are compared to experimental data. The results show a better fit to measured characteristics than simulations obtained by previous semiempirical modeling. Improvements mainly come from the light propagation calculation. According to the model, the number of passes incident light may make through the active i layer reaches six for the most efficient cell. As an example of the model’s main application, the enhancement of the conversion efficiency that would be expected from an optimized TCO layer is calculated for each texture studied and for different back metallizations.

Laser dehydrogenation/crystallization of plasma‐enhanced chemical vapor deposited amorphous silicon for hybrid thin film transistors

Abstract: A low temperature process for laser dehydrogenation and crystallization of hydrogenated amorphous silicon (a‐Si:H) has been developed. This process removes hydrogen by laser irradiations at three energy steps. Studies of hydrogen out‐diffusion and microstructure show that hydrogen out‐diffusion depends strongly on film structure and the laser energy density. Both high quality and low leakage bottom gate polycrystalline silicon and a‐Si:H thin film transistors were monolithically fabricated on the same Corning 7059 glass substrate with a maximum process temperature of only 350 °C.

Method for manufacturing a semiconductor device containing a crystallization promoting material

Abstract: A method for manufacturing a semiconductor device having a crystalline silicon semiconductor layer comprises the steps of heat crystallizing an amorphous silicon semiconductor layer at a relatively low temperature because of the use of a crystallization promoting material such as Ni, Pd, Pt, Cu, Ag, Au, In, Sn, Pb, P, As, and Sb. The crystallization promoting material is introduced by mixing it within a liquid precursor material for forming silicon oxide and coating the precursor material onto the amorphous silicon film. Thus, it is possible to add the crystallization promoting material into the amorphous silicon film at a minimum density.

Method for fabricating a semiconductor device using a catalyst introduction region

Abstract: Into an amorphous silicon film, catalyst elements for accelerating the crystallization are introduced. After patterning the amorphous silicon films in which the catalyst elements have been introduced into an island pattern, a heat treatment for the crystallization is conducted. Thus, the introduced catalyst elements efficiently diffuse only inside the island-patterned amorphous silicon films. As a result, a high-quality crystalline silicon film, having the crystal growth direction aligned in one direction and having no grain boundaries, is obtained. Using the thus formed crystalline silicon film, semiconductor devices having a high performance and stable characteristics are fabricated efficiently over the entire substrate, irrespective of the size of the devices.

Erbium in crystal silicon : segregation and trapping during solid phase epitaxy of amorphous silicon

Abstract: Solid phase epitaxy of Er‐implanted amorphous Si results in segregation and trapping of the Er, incorporating up to 2×1020 Er/cm3 in single‐crystal Si. Segregation occurs despite an extremely low Er diffusivity in bulk amorphous Si of ≤10−17 cm2/s, and the narrow segregation spike (measured width ≊3 nm) suggests that kinetic trapping is responsible for the nonequilibrium concentrations of Er. The dependence of trapping on temperature, concentration, and impurities indicates instead that thermodynamics controls the segregation. We propose that Er, in analogy to transition metals, diffuses interstitially in amorphous Si, but is strongly bound at trapping centers. The binding enthalpy of these trapping sites causes the amorphous phase to be energetically favorable for Er, so that at low concentrations the Er is nearly completely segregated. Once the concentration of Er in the segregation spike exceeds the amorphous trap center concentration, though, more Er is trapped in the crystal. We also observe similar segregation and trapping behavior for another rare‐earth element, Pr.

A single chamber CVD process for thin film transistors

Abstract: A method of depositing layers (54, 56) of intrinsic amorphous silicon and doped amorphous silicon sequentially on a substrate (50) in the same CVD chamber without incurring a dopant contamination problem. The method can be carried out by first depositing an additional layer of a dielectric insulating material prior to the deposition process of the intrinsic amorphous silicon layer (54). The additional layer of insulating material deposited on the substrate should have a thickness such that residual insulating material coated on the chamber walls is sufficient to cover the residual dopants on the chamber walls left by the deposition process of the previous substrate. This provides a clean environment for the next deposition process of an intrinsic amorphous silicon layer (54) on a substrate (50) in the same CVD chamber.

Semiconductor memory device and write-once, read-only semiconductor memory array using amorphous-silicon and method therefor

Abstract: A semiconductor device used as a semiconductor memory device is disclosed which is made of an amorphous silicon material that provides either a "1" or "0" memory state when the amorphous silicon material is in a non-conduction or insulating state and a "0" or "1" memory state when the amorphous silicon material is transformed, by use of a breakdown voltage applied to electrodes coupled thereto, into a conducting state The amorphous silicon material is located adjacent to a doped semiconductor region of a semiconductor substrate separated only by a relatively thin primarily metal ohmic contact The resulting semiconductor structure for the semiconductor device or semiconductor memory device is primarily a single level metalization type structure A write-once, read-only semiconductor memory array is also disclosed which uses, as each memory cell of the array, one of the disclosed semiconductor memory devices Methods for producing the semiconductor memory device and write-once, read-only semiconductor memory array are also disclosed

Fluoroscopic x-ray imaging with amorphous silicon thin-film arrays

Abstract: The dream of an all-solid state large area x-ray image sensor with digital readout and full dynamic performance will most probably find a first realization in 2D thin-film amorphous silicon arrays. In this paper we address in particular the evaluation of the limits of the signal/noise ratio in this concept. Using small prototype detectors measurements of MTF and noise power spectra have been made as a function of x-ray dose. The results are given in terms of the detective quantum efficiency as a function of dose and spatial frequency. We further present an analysis of the different noise sources and their dependence on the detector parameters, and we provide estimates on the maximum signals that may be achieved per unit dose. The intrinsic lag of the amorphous silicon photodiodes causes a second problem area with this type of x-ray detectors. Especially in radiography/fluoroscopy mixed applications, memory effects may not be negligible.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method for processing silicon solar cells

Abstract: The instant invention teaches a novel method for fabricating silicon solar cells utilizing concentrated solar radiation. The solar radiation is concentrated by use of a solar furnace which is used to form a front surface junction and back-surface field in one processing step. The present invention also provides a method of making multicrystallline silicon from amorphous silicon. The invention also teaches a method of texturing the surface of a wafer by forming a porous silicon layer on the surface of a silicon substrate and a method of gettering impurities. Also contemplated by the invention are methods of surface passivation, forming novel solar cell structures, and hydrogen passivation.

Semiconductor device and method for its preparation

Abstract: A semiconductor device is disclosed. The semiconductor device has a crystalline silicon film as an active layer region. The crystalline silicon film has needle-like or columnar crystals oriented parallel to the substrate and having a crystal growth direction of (111) axis. A method for preparing the semiconductor device comprises steps of adding a catalytic element to an amorphous silicon film; and heating the amorphous silicon film containing the catalytic element at a low temperature to crystallize the silicon film.

Method of manufacturing a polysilicon thin film transistor

Abstract: An amorphous silicon hydride thin film is deposited on an insulating body by a plasma CVD method, and is then heated for dehydrogenating the amorphous silicon thin film so that a dehydrogenated amorphous silicon thin film containing hydrogen of 3 atomic % or less is formed. The insulating body may be an insulating substrate (such as a glass substrate) alone, or a combination of an insulating substrate with an intermediate insulating base layer thereon. Impurity ions are injected into the dehydrogenated amorphous silicon hydride thin film to form source and drain regions. Excimer laser beams are applied to the dehydrogenated amorphous silicon thin film, thereby polycrystallizing the amorphous silicon thin film into a polysilicon thin film and activating the injected impurity ions.

Synthesis and Characterization of Amorphous Si2N2O

Abstract: Amorphous silicon oxynitride powder was synthesized by nitridation of high-purity silica in ammonia at 1120°C. The resulting material was X-ray amorphous, and its chemical characteristics were determined by X-ray photoelectron spectroscopy (XPS) and 29Si nuclear magnetic resonance (NMR). The XPS analysis showed a shift to lower binding energies for the Si2p peak with increasing nitrogen content. Upon initial nitridation, the full width at half maximum (FWHM) of the Si2p peak increased, but decreased again at higher nitrogen contents, thus showing the formation of a silicon oxynitride phase with a single or small range of composition. The 29Si NMR analysis showed the formation of (amorphous) Si3N4 (Si–N4) and possibly two oxynitride phases (Si–N3O, Si–N2O2). It is concluded that while XPS, FT-IR, and nitrogen analysis may show the formation of an homogeneous, amorphous silicon oxynitride (Si2N2O) phase, the formation of phase–pure, amorphous Si2N2O is extremely difficult via this route.

Emission of blue light from hydrogenated amorphous silicon carbide

Abstract: THE development of new electroluminescent materials is of current technological interest for use in flat-screen full-colour displays1. For such applications, amorphous inorganic semiconductors appear particularly promising, in view of the ease with which uniform films with good mechanical and electronic properties can be deposited over large areas2. Luminescence has been reported1 in the red-green part of the spectrum from amorphous silicon carbide prepared from gas-phase mixtures of silane and a carbon-containing species (usually methane or ethylene). But it is not possible to achieve blue luminescence by this approach. Here we show that the use of an aromatic species—xylene—as the source of carbon during deposition results in a form of amorphous silicon carbide that exhibits strong blue luminescence. The underlying structure of this material seems to be an unusual combination of an inorganic silicon carbide lattice with a substantial 'organic' π-conjugated carbon system, the latter dominating the emission properties. Moreover, the material can be readily doped with an electron acceptor in a manner similar to organic semiconductors3, and might therefore find applications as a conductivity- or colour-based chemical sensor.