Polycrystalline silicon

About: Polycrystalline silicon is a research topic. Over the lifetime, 19554 publications have been published within this topic receiving 198222 citations. The topic is also known as: polysilicon & poly-Si.

Properties of low-pressure CVD tungsten silicide for MOS VLSI interconnections

Abstract: Low-pressure chemical vapor deposition of tungsten silicide has been done and the properties of the deposited films have been studied to determine the process compatibility and suitability to form gate electrodes and interconnections in MOS VLSI applications. The silicide was deposited on single-crystal silicon and on oxidized silicon with and without a coating of polycrystalline silicon film. Auger analysis of the As-deposited films showed absence of any contaminants in it. X-ray diffraction and transmission electron microscopy showed that As-deposited films were microcrystalline with grains smaller than 30 A and upon annealing became polycrystalline WSi 2 with hexagonal structure at 500°C and tetragonal structure at or above 600°C with a corresponding decrease in resistivity from 600-900 µΩ . cm to 35-60 µΩ . cm depending upon anneal temperature and time. No appreciable change in the thickness of the silicide was found during the high-temperature anneals. Silicon-rich silicide films remained stable, smooth, and free of cracks through high-temperature anneals and oxidations, and their adherence to the wafer remained excellent. On the other hand, metal-rich films had overall inferior properties. Thermal oxidation of WSi 2 on polysilicon in dry oxygen in the temperature range of 900 to 1100°C was found to be similar to that of silicon except the linear regime of oxidation was extremely rapid and the entire process could be modeled by a parabolic equation X^{2) = Bt with an activation energy of 1.7 eV. MOS capacitors were fabricated with silicide and polycide gate electrodes. Polysilicon thickness variation from 0 to 5000 A had no adverse effect on the electrical characteristics or mechanical integrity of the devices. In all cases, low values of N f (1 × 1010-7 × 1010cm-2) and N it ( \sime 8 MV/cm) were obtained.

Mechanisms for Fatigue of Micron-Scale Silicon Structural Films†

Abstract: Although bulk silicon is not susceptible to fatigue, micron-scale silicon is. Several mechanisms have been proposed to explain this surprising behavior although the issue remains contentious. Here we review published fatigue results for micron-scale thin silicon films and find that in general they display similar trends, in that lower cyclic stresses result in larger number of cycles to failure in stress-lifetime data. We further show that one of two classes of mechanisms is invariably proposed to explain the phenomenon. The first class attributes fatigue to a surface effect caused by subcritical (stable) cracking in the silicon-oxide layer, e.g., reaction-layer fatigue; the second class proposes that subcritical cracking in the silicon itself is the cause of fatigue in Si films. It is our contention that results to date from single and polycrystalline silicon fatigue studies provide no convincing experimental evidence to support subcritical cracking in the silicon. Conversely, the reaction-layer mechanism is consistent with existing experimental results, and moreover provides a rational explanation for the marked difference between the fatigue behavior of bulk and micron-scale silicon.

High-temperature degradation of NiSi films: Agglomeration versus NiSi2 nucleation

Abstract: The thermodynamical and morphological stability of NiSi thin films has been investigated for layers of thickness ranging from 10to60nm formed on either silicon-on-insulator (SOI), polycrystalline silicon, or preannealed polycrystalline silicon substrates. The stability of the films was evaluated using in situ x-ray-diffraction, sheet resistance, and laser light-scattering measurements. For NiSi films that are thinner than 20nm, agglomeration is the main degradation mechanism. For thicker films, the agglomeration of NiSi and nucleation of NiSi2 occur simultaneously, and both degradation mechanisms influence each other. Significant differences were observed in the degradation of the NiSi formed on different substrates. Surprisingly, agglomeration is worse on SOI substrates than on poly-Si substrates, suggesting that the texture of the NiSi film plays an important role in the agglomeration process. As expected, preannealing of the polycrystalline silicon substrate prior to metal deposition results in a signi...

Green fabrication of stable lead-free bismuth based perovskite solar cells using a non-toxic solvent

Abstract: The very fast evolution in certified efficiency of lead-halide organic-inorganic perovskite solar cells to 24.2%, on par and even surpassing the record for polycrystalline silicon solar cells (22.3%), bears the promise of a new era in photovoltaics and revitalisation of thin film solar cell technologies. However, the presence of toxic lead and particularly toxic solvents during the fabrication process makes large-scale manufacturing of perovskite solar cells challenging due to legislation and environment issues. For lead-free alternatives, non-toxic tin, antimony and bismuth based solar cells still rely on up-scalable fabrication processes that employ toxic solvents. Here we employ non-toxic methyl-acetate solution processed (CH3NH3)3Bi2I9 films to fabricate lead-free, bismuth based (CH3NH3)3Bi2I9 perovskites on mesoporous TiO2 architecture using a sustainable route. Optoelectronic characterization, X-ray diffraction and electron microscopy show that the route can provide homogeneous and good quality (CH3NH3)3Bi2I9 films. Fine-tuning the perovskite/hole transport layer interface by the use of conventional 2,2′,7,7′-tetrakis (N,N′-di-p-methoxyphenylamino)−9,9′-spirbiuorene, known as Spiro-OMeTAD, and poly(3-hexylthiophene-2,5-diyl - P3HT as hole transporting materials, yields power conversion efficiencies of 1.12% and 1.62% under 1 sun illumination. Devices prepared using poly(3-hexylthiophene-2,5-diyl hole transport layer shown 300 h of stability under continuous 1 sun illumination, without the use of an ultra violet-filter. Perovskites are widely studied as components of solar cells but their synthesis often involves toxic reagents. Here lead-free bismuth-based perovskites are synthesised using a non-toxic solvent and shown to achieve power conversion efficiencies of up to 1.62 % under 1 sun illumination for up to 300 h.

Characterization of polycrystalline silicon wafers for solar cells sliced with novel fixed-abrasive wire

Abstract: For slicing crystalline silicon ingots, we have developed a novel fixed-abrasive wire where diamond grit is fixed onto a bare wire by resin bonding. The properties of the wafers sliced using a multi-wire saw with the fixed-abrasive wire have been investigated. When compared with the wafers sliced with the loose-abrasive wire, the slicing speed is improved by approximately 2.5-fold and the thicknesses of saw-damage layers are reduced by more than a factor of two. Polycrystalline silicon solar cells have been fabricated for the first time utilizing the wafers sliced with the fixed-abrasive wire, and the cells with the saw-damage etching depth of 7 µm have shown photovoltaic properties comparable to those prepared using the wafers sliced with the loose-abrasive wire and subsequently etched to remove the damage layers up to 15 µm. It has been clarified that wafer slicing using the fixed-abrasive wire is promising as a next-generation slicing technique for fabrication of solar cells, particularly thin silicon cells where the wafer thicknesses approach or become less than 150 µm. Copyright © 2010 John Wiley & Sons, Ltd.