Showing papers on "Amorphous silicon published in 2000"

Technology and Applications of Amorphous Silicon

Abstract: 1 Introduction- 2 Active-Matrix Liquid-Crystal Displays- 3 Laser Crystallization for Polycrystalline Silicon Device Applications- 4 Large Area Image Sensor Arrays- 5 Novel Processing Technology for Macroelectronics- 6 Multijunction Solar Cells and Modules- 7 Multilayer Color Detectors- 8 Thin Film Position Sensitive Detectors: From 1D to 3D Applications- Symbols and Abbreviations

Elucidation of the layer exchange mechanism in the formation of polycrystalline silicon by aluminum-induced crystallization

Abstract: Aluminum-induced crystallization of amorphous silicon is studied as a promising low-temperature alternative to solid-phase and laser crystallization. Its advantages for the formation of polycrystalline silicon on foreign substrates are the possible usage of simple techniques, such as thermal evaporation and dc magnetron sputtering deposition, and relatively short processing times in the range of 1 h. The overall process of the Al and Si layer exchange during annealing at temperatures below the eutectic temperature of 577 °C is investigated by various microscopy techniques. It is shown that the ratio of the Al and a-Si layer thicknesses is vitally important for the formation of continuous polycrystalline silicon films on glass substrates. The grain size of these films is dependent on the annealing temperature and evidence is given that grain sizes of 20 μm and more can be achieved. The poly-Si films are described as solid solutions containing 3×1019 cm−3 Al atoms as solute. Only a fraction of the solute is...

Method for producing semiconductor device

Abstract: In producing a thin film transistor, after an amorphous silicon film is formed on a substrate, a nickel silicide layer is formed by spin coating with a solution (nickel acetate solution) containing nickel as the metal element which accelerates (promotes) the crystallization of silicon and by heat treating. The nickel silicide layer is selectively patterned to form island-like nickel silicide layer. The amorphous silicon film is patterned. A laser light is irradiated while moving the laser, so that crystal growth occurs from the region in which the nickel silicide layer is formed and a region equivalent to a single crystal (a monodomain region) is obtained.

Optical modeling of a-Si:H solar cells with rough interfaces: Effect of back contact and interface roughness

Abstract: An approach to study the optical behavior of hydrogenated amorphous silicon solar cells with rough interfaces using computer modeling is presented. In this approach the descriptive haze parameters of a light scattering interface are related to the root mean square roughness of the interface. Using this approach we investigated the effect of front window contact roughness and back contact material on the optical properties of a single junction a-Si:H superstrate solar cell. The simulation results for a-Si:H solar cells with SnO2:F as a front contact and ideal Ag, ZnO/Ag, and Al/Ag as a back contact are shown. For cells with an absorber layer thickness of 150–600 nm the simulations demonstrate that the gain in photogenerated current density due to the use of a textured superstrate is around 2.3 mA cm−2 in comparison to solar cells with flat interfaces. The effect of the front and back contact roughness on the external quantum efficiency (QE) of the solar cell for different parts of the light spectrum was de...

Thin film semiconductor deposition on free-standing ZnO columns

Abstract: We report the deposition of a-Si:H on thin films of free-standing single crystalline ZnO columns. The ZnO columns have a height of several μm and a diameter between 100 and 200 nm. The ZnO films are prepared in electrodeposition and have considerable potential for use in photoelectric thin film devices. Morphology, electronic parameters, and basic optical behavior, such as reflectance and light trapping efficiency, are reported. Amorphous silicon is deposited on the columns as a continuous smooth film with conformal coverage. Some possibilities of using these films in devices are discussed.

Influence of interface and Al structure on layer exchange during aluminum-induced crystallization of amorphous silicon

Abstract: Aluminum-induced crystallization of amorphous silicon (a-Si) is studied using various microscopy techniques and x-ray photoelectron spectroscopy. During the isothermal annealing of subsequently deposited aluminum and a-Si films on glass, a layer exchange process is induced, while a continuous polycrystalline silicon film (poly-Si) on glass is formed within the initial metal layer and therefore displaces it. This crystallization process is conducted at temperatures ranging from 350 °C to 500 °C, significantly below the eutectic temperature of the Si–Al binary system of 577 °C. The results presented focus on the influences of the polycrystalline structure of the evaporated Al, the Si–Al layer sequence, and the interface layer between the Al and Si films on the overall crystallization process. They reveal that the larger the Al grain size of the initial polycrystalline Al layer, the larger the grain size of the final poly-Si film and the slower the entire layer exchange process. It is further shown that the layer sequence, although influencing the speed of the poly-Si formation, has little impact on the overall layer exchange process. Additionally, evidence is given that an Al oxide interface layer separates the continuous poly-Si layer from the Al, independent of the original layer sequence. The analyzed oxide interface layer remains at its position throughout the entire Al and Si layer exchange process. An existing phenomenological model of the diffusion-controlled crystallization during the layer exchange is extended to embrace the role of the parameters discussed in this paper.

Transmission electron microscopy observation of deformation microstructure under spherical indentation in silicon

Abstract: Spherical indentation of crystalline silicon has been studied using cross-sectional transmission electron microscopy (XTEM). Indentation loads were chosen below and above the yield point for silicon to investigate the modes of plastic deformation. Slip planes are visible in the XTEM micrographs in both indentation loads studied. A thin layer of polycrystalline material has been identified (indexed as Si-XII from diffraction patterns) on the low-load indentation. The higher-load indentation revealed a large region of amorphous silicon. The sequence of structural deformation by indentation in silicon has been observed with the initial deformation mechanism being slip until phase transformations can take place.

Stability of low-temperature amorphous silicon thin film transistors formed on glass and transparent plastic substrates

Abstract: This article describes the formation of amorphous silicon thin film transistors (TFTs) on glass and flexible transparent plastic substrates using rf plasma enhanced chemical vapor deposition and a maximum processing temperature of 110 °C. Silane diluted with hydrogen was used for the preparation of the amorphous silicon, and SiH4/NH3/N2 or SiH4/NH3/N2/H2 mixtures were used for the deposition of the silicon nitride gate dielectric. The amorphous silicon nitride layers were characterized by transmission infrared spectroscopy and current-voltage measurements; the plastic substrates were 10 mil thick (0.25 mm) polyethylene terephthalate sheets. Transistors formed using the same process on glass and plastic showed linear mobilities ranging from 0.1 to 0.5 cm2/V s with ION/IOFF ratios⩾107. To characterize the stability of the transistors on glass, n- and p-channel transconductances were measured before and after bias stressing. Devices formed at 110 °C show evidence of charge trapping near the a-Si/SiNx interfa...

Semiconductor device and its forming method

Abstract: PROBLEM TO BE SOLVED: To realize a semiconductor device of low manufacturing cost by the use of a glass substrate the distortion spot of which is at least a specified temperature, protecting on outer peripheral surface of the high heat resistant glass substrate by using an insulating silicon film, and forming a single-crystal silicon thin film on the high heat resistant glass substrate wrapped with the insulating silicon film. SOLUTION: A glass substrate (glass substrate the distortion spot of which is at least 750 deg.C or higher), having heat resistance capable of enduring a temperature of at least 750 deg.C, is used as a substrate. An amorphous silicon film 102 is formed to crystallized glass 101. When the film 2 is formed through a low- pressure heat CVD method, the amorphous silicon film 102 can be formed on the surface, the back and the side surface of the substrate 101, which is wrapped with the film 102. By thermally oxidizing the amorphous silicon film 102, a thermal oxide film 103 is formed. A single-crystal silicon thin film 107 is formed on the crystallized glass 101 whose outer peripheral part is protected by the thermal oxide film 103.

Epitaxial oxide thin films on Si(001)

Abstract: Over the years, the development of epitaxial oxides on silicon has been a great technological challenge. Amorphous silicon oxide layer forms quickly at the interface when the Si surface is exposed to oxygen, making the intended oxide heteroepitaxy on Si substrate extremely difficult. Epitaxial oxides such as BaTiO3 (BTO) and SrTiO3 (STO) integrated with Si are highly desirable for future generation transistor gate dielectric and ferroelectric memory cell applications. In this article, we review the recent progress in the heteroepitaxy of oxide thin films on Si(001) substrate by using the molecular beam epitaxy technique at Motorola Labs. Structural, interfacial and electrical properties of the oxide thin films on Si have been characterized using in situ reflection high energy electron diffraction, x-ray diffraction, spectroscopic ellipsometry, atomic force microscopy, Auger electron spectroscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, high-resolution transmission electron energy loss spectroscopy, capacitance–voltage and current–voltage measurement. We also present the transistor results and address the impact of the epitaxial oxide films on future generation metal-oxide-semiconductor field effect transistors.

Relative importance of the Si–Si bond and Si–H bond for the stability of amorphous silicon thin film transistors

Abstract: We investigate the mechanism for Si dangling bond defect creation in amorphous silicon thin film transistors as a result of bias stress. We show that the rate of defect creation does not depend on the total hydrogen content or the type of hydrogen bonding in the amorphous silicon. However, the rate of defect creation does show a clear correlation with the Urbach energy and the intrinsic stress in the film. These important results support a localized model for defect creation, i.e., where a Si–Si bond breaks and a nearby H atom switches to stabilize the broken bond, as opposed to models involving the long-range diffusion of hydrogen. Our experimental results demonstrate the importance of optimizing the intrinsic stress in the films to obtain maximum stability and mobility. An important implication is that a deposition process where intrinsic stress can be independently controlled, such as an ion-energy controlled deposition should be beneficial, particularly for deposition temperatures below 300 °C.

Electrode for lithium cell and lithium secondary cell

Abstract: An electrode for a lithium cell having an active material thin film absorbing/desorbing lithium such as a microcrystalline silicon thin film or an amorphous silicon thin film provided on a current collector, characterized in that a component of the current collector is diffused into the thin film.

Recombination mechanisms in amorphous silicon/crystalline silicon heterojunction solar cells

Abstract: This article investigates limitations to the open circuit voltage of n-type amorphous silicon/p-type crystalline silicon heterojunction solar cells. The analysis of quantum efficiency and temperature dependent current/voltage characteristics identifies the dominant recombination mechanism. Depending on the electronic quality of the crystalline silicon absorber, either recombination in the neutral bulk or recombination in the space charge region prevails; recombination at the heterointerface is not relevant. Although interface recombination does not limit the open circuit voltage, recombination of photogenerated charge carriers at the heterointerface or in the amorphous silicon emitter diminishes the short circuit current of the solar cells.

Methods for producing uniform large-grained and grain boundary location manipulated polycrystalline thin film semiconductors using sequential lateral solidification

Abstract: Methods for processing an amorphous silicon thin film sample into a polycrystalline silicon thin film are disclosed. In one preferred arrangement, a method includes the steps of generating a sequence of excimer laser pulses, controllably modulating each excimer laser pulse in the sequence to a predetermined fluence, homoginizing each modulated laser pulse in the sequence in a predetermined plane, masking portions of each homoginized fluence controlled laser pulse in the sequence with a two dimensional pattern of slits to generate a sequence of fluence controlled pulses of line patterned beamlets, each slit in the pattern of slits being sufficiently narrow to prevent inducement of significant nucleation in region of a silicon thin film sample irradiated by a beamlet corresponding to the slit, irradiating an amorphous silicon thin film sample with the sequence of fluence controlled slit patterned beamlets to effect melting of portions thereof corresponding to each fluence controlled patterned beamlet pulse in the sequence of pulses of patterned beamlets, and controllably sequentially translating a relative position of the sample with respect to each of the fluence controlled pulse of slit patterned beamlets to thereby process the amorphous silicon thin film sample into a single or polycrystalline silicon thin film.

Deposition mechanism of hydrogenated amorphous silicon

Abstract: The surface and subsurface processes occurring during the growth of hydrogenated amorphous silicon (a-Si:H) are analyzed to understand how dangling bond defects and weak bonds form. It is found that the abstraction and addition of adsorbed SiH3 radicals gives a surface defect density which decreases continuously with decreasing temperature with no minimum near 250 °C. Hence it cannot be the process that defines defect densities in the bulk. Hydrogen elimination to create the bulk Si–Si network occurs because the chemical potential of hydrogen causes the expulsion of hydrogen from the bulk. Hydrogen elimination is the rate-limiting step at lower temperatures, as its diffusion is slow. The difficulty of eliminating hydrogen leads to the formation of weak bonds. Weak bonds arise at higher deposition temperatures from thermal disorder. The dangling bond defects arise from weak bonds by the defect pool process, and this process must continue at lower temperatures than normal in the growth zone. Plasma processe...

Inkjet printed copper source/drain metallization for amorphous silicon thin-film transistors

Abstract: Source/drain metallization to amorphous silicon thin-film transistors has been made by inkjet printing. Contact pads of a metal organic copper precursor were inkjet printed, and then converted to copper metal at a maximum process temperature of 200/spl deg/C. The copper contacts were used as the mask for back-channel etch. Laser printed toner was used for all other mask levels in a photoresist-free fabrication process. The inkjet printing of copper contacts represents a further step toward an all-printed thin-film transistor technology.

Preparation and characterization of amorphous SiOx nanowires

Abstract: Large-scale synthesis of amorphous silicon oxide nanowires (SiONWs) was achieved by using simple physical evaporation of the mixture of silica xerogel containing Fe nanoparticles and silicon powder. Transmission electron microscopy (TEM) observations showed that the amorphous SiONWs have a length of up to several tens of micrometers and a diameter of 10–40 nm. Energy-dispersed X-ray spectrometry (EDX) analysis revealed that the SiONWs consist of Si and O elements in atomic ratio approximately to 1:1.4. Different morphologies of nanowires such as straight, smoothly curved, braided and helical shapes were observed. The formation process of SiONWs was closely related to the VLS growth mechanism. Raman scattering spectrum of amorphous SiONWs showed that there is an asymmetric, broadened linewidth Raman peak at 502 cm −1 greatly different from that of bulk SiO 2 non-crystalline solids.

Contribution of ions to the growth of amorphous, polymorphous, and microcrystalline silicon thin films

Abstract: The growth of amorphous, microcrystalline, and polymorphous silicon has been investigated by studying the species contributing to the growth and resulting film structure. The surface reaction probability of the radicals and the contribution of ions to the growth have been determined. In a-Si:H deposition by hot wire chemical vapor deposition, the surface reaction probability (β=0.29) of the depositing radical is compatible with SiH3, whereas the surface reaction probability in microcrystalline silicon growth is higher (0.36⩽β⩽0.54). On the contrary, the deposition of amorphous silicon by plasma enhanced chemical vapor deposition indicates the contribution of more reactive radicals than SiH3. The deposition of polymorphous and microcrystalline silicon by plasma is dominated by ions, which can contribute up to 70% of the deposited film. This is attributed to efficient ionization of silane in charge exchange reactions with hydrogen ions. The surface reaction probability in the case of polymorphous silicon de...

Spin-dependent processes in amorphous and microcrystalline silicon: a survey

Abstract: Basic concepts of spin-dependent recombination and transport as well as applications in disordered Si-based semiconductors are reviewed. The magnitude of spin-dependent changes in conductivity or luminescence is outlined following the ideas developed by Lepine and Kaplan, Solomon, and Mott. Undoped a-Si:H serves as a model system for the discussion of recombination mechanisms in disordered semiconductors, in particular distant electron–hole pair recombination, recombination via excitonic pairs (spin triplets), and via dangling bond defects. Electrical detection of magnetic resonance at low magnetic fields (∼0.0155 T) can be used to study the hyperfine interaction between dangling bonds and hydrogen, and the results are discussed with respect to microscopic models for metastability phenomena in amorphous silicon. Optical detection of magnetic resonance in Si-based amorphous alloys with Ge, C, N, or O confirm the importance of dangling bonds as non-radiative recombination centers. In wide band-gap alloys, excitonic triplet states appear to be the dominant radiative recombination channel. In addition, recent results concerning spin-dependent transport in microcrystalline Si as well as new experimental approaches for the detection of magnetic resonance via noise or capacitance measurements are presented.

Determination of thickness and optical constants of amorphous silicon films from transmittance data

Abstract: This work presents the application of a recently developed numerical method to determine the thickness and the optical constants of thin films using experimental transmittance data only. This method may be applied to films not displaying a fringe pattern and is shown to work for a-Si:H (hydrogenated amorphous silicon) layers as thin as 100 nm. The performance and limitations of the method are discussed on the basis of experiments performed on a series of six a-Si:H samples grown under identical conditions, but with thickness varying from 98 nm to 1.2 μm.

Microbolometer and method for forming

Abstract: A microbolometer is provided that includes an absorber element having material properties to change temperature in response to absorbing infrared radiation. An amorphous silicon detector is thermally coupled to the absorber element and is suspended above a silicon substrate at a height of one-quarter wavelength of the infrared radiation to be detected. The amorphous silicon detector changes electrical resistance in response to the absorber element changing temperature. The microbolometer also includes electrode arms coupled to the silicon substrate to provide structural support for the amorphous silicon detector above the surface of the silicon substrate. The electrode arms further provide electrical connectivity for the microbolometer.

Handbook of semiconductor technology

Abstract: VOLUME 1 Band Theory Applied to Semiconductors Electrical and Optical Characteristics of Crystalline Semiconductors Deep Centers in Semiconductors Equilibria, Nonequilibria, Diffusion and Precipitation Dislocation Grain Boundaries Interfaces The Hall Effect in Quantum Wires Material Properties of Hydrogenated Amorphous Silicon Solubility Diffusion and Gettering of Illd Transition Elements in Silicon VOLUME 2 Silicon Processing Compound Semiconductor Processing Epitaxial Growth Photolitography Doping Etching Processes in Semiconductor Manufacturing Silicon Device Structures Compound Semicondutor Device Structures Silicon Device Processing Compound Semiconductor Device Processing Integrated Circuit Packaging Interconnect Systems

Deposition and characterization of screen-printed porous multi-layer thick film structures from semiconducting and conducting nanomaterials for use in photovoltaic devices

Abstract: Three-layer structures of thick (>5 μm) films of nanosized titanium dioxide, zirconium dioxide, and carbon have been screen-printed on a semi-production level for use in photosensitized photovoltaic devices. The films have been characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and nitrogen adsorption/desorption. The rheology of the screen-printing pastes has been measured, and qualitatively matched to the quality of the resultant film. Three titanium dioxide candidates were evaluated for performance. At low light levels (<300 lux, i.e., typical indoor light levels), photosensitized photovoltaic modules made from these screen-printed structures exhibited equal or superior performance to a commercially available amorphous silicon module.

Amorphous silicon detector and thin film transistor technology for large area imaging of X-rays

Abstract: This paper will review amorphous silicon imaging technology in terms of the detector operating principles, electrical and optoelectronic characteristics, and stability. Also, issues pertinent to thin film transistor stability will be presented along with optimization of materials and processing conditions for reduced V/sub T/-shift and leakage current. Selected results are shown for X-ray and optical detectors, thin film transistors, and integrated X-ray pixel structures. Extension of the current fabrication processes to low (<100/spl deg/C) temperature, enabling fabrication of thin film electronics on flexible (polymer) substrates, will also be discussed along with preliminary results.

Process for fabricating single crystal resonant devices that are compatible with integrated circuit processing

Abstract: This invention describes fabrication procedures to construct MEMS devices, specifically band-pass filter resonators, in a manner compatible with current integrated circuit processing. The final devices are constructed of single-crystal silicon, eliminating the mechanical problems associated with using polycrystalline silicon or amorphous silicon. The final MEMS device lies below the silicon surface, allowing further processing of the integrated circuit, without any protruding structures. The MEMS device is about the size of a SRAM cell, and may be easily incorporated into existing integrated circuit chips. The natural frequency of the device may be altered with post-processing or electronically controlled using voltages and currents compatible with integrated circuits.

Method of epitaxial growth of high quality nitride layers on silicon substrates

Abstract: Aluminium nitride, A1N, layers are grown on silicon substrate (12) using molecular beam epitaxial (MBE) growth. The A1N layer is initially grown by subjecting the silicon substrate to background ammonia followed by repetitively alternating the flux of 1) Al (22) without ammonia (27) and 2) ammonia without Al. After the surface of the silicon structure is sufficiently covered with AlN, the substrate is subjected to flux of ammonia and aluminium applied simultaneously to continue the epitaxial growth process. The process minimizes the formation of amorphous silicon nitride, SiN, compounds on the surface of the substrate which form due to background nitrogen levels in the molecular beam epitaxial growth apparatus. A surface free of amorphous silicon nitirde is necessary for the formation of high quality AlN. The AlN layer may be further used as abuffer layer for AlGaN/GaN growth. After the AlN layer (30) is grown on the silicon substrate, the silicon structure may be subjected to a flux of Ga and nitrogen to form a layer of GaN (40).

Switching in coplanar amorphous hydrogenated silicon devices

Abstract: Switching has been observed in a wide variety of materials and devices. Hydrogenated amorphous silicon has become one of the most important cases because of interest in neural network applications. Although there are many reports regarding this phenomenon, not all of the physical processes involved are still determined precisely. Therefore, some more experimental information is needed in order to achieve this task. Much of the behavior of the devices has been ascribed to the existence of a filamentary region which is produced after the first switching process, called forming. We observed this filamentary region in its full extension by producing forming in amorphous silicon devices with coplanar metallic contacts placed near each other (∼5 μm). The I–V characteristics, filament optical and atomic force microscopy images and chemical etching led us to correlate changes in resistance to metal inclusion into the amorphous film. There are two stages: the first is related to contact stabilization, the second to metal transport into the film bulk. Optical images show a permanent filamentary region after forming. AFM images of these filaments showed that they are formed essentially by material accumulation between the contacts. This material tends to get some atomic arrangement, becoming a polycrystalline solid. If the device was led to breakdown, such accumulation becomes either a hillock or a thin conducting channel connecting both contacts. In the case of a switching filament, the accumulation tends to be a chain of smaller hillocks along the conduction path. Metal from the contacts remains in the conduction path after forming and chemical etching indicated that it is placed near the path core. Before forming, a tunneling transport process can be ascribed to the non-ohmic behavior of the samples during the first stage of metallic inclusion.