Polycrystalline Silicon Substrates Research Articles

Evaluation of Bosch processing and C4F8 plasma deposition at cryogenic temperatures

Abstract The Bosch process was studied at a substrate temperature of −100 °C and compared to etchings performed at room temperature, as in the general case. The tests were realized using an inductively coupled plasma reactor by varying C4F8 passivating gas flow injections both at +20 °C and −100 °C. It was observed that the Bosch process is effectively temperature dependent and that the necessary C4F8 passivating gas flow can be reduced to obtain similar anisotropic profiles at −100 °C compared to the ambient temperature process. For example, in one of the studied cases, a fluorocarbon injection of 8 sccm was sufficient to obtain an anisotropic etch rate of up to 4.4 μm min−1 at −100 °C whereas the profile obtained at +20 °C using the same parameters presents lateral etching defects with a reduced etch rate of 2.4 μm min−1. At this point, the C4F8 flow must be increased to 12 sccm (50% more) to retrieve an anisotropic profile with an etch rate of 4.0 μm min−1. In the case of cryogenic Bosch (cryo-Bosch) processing, C4F8 feed dosing has a greater influence on the passivation regime which affects the subsequent etching result but it can be easily refined through the optimization of process parameters. An in-situ ellipsometry study of the deposition rate of C4F8 on both polycrystalline silicon (p-Si) and SiO2 substrates was realized by varying the gas flow at −100 °C and +20 °C. This study shows that the deposited fluorocarbon material is approximately a hundred times thicker at cryogenic temperatures using the same process parameters. Scanning electron microscopy (SEM) observation of these samples are in adequacy with the ellipsometry results. Cryo–Bosch etching also results in a slightly higher etch rate compared to room temperature processing when analyzing similar anisotropic profiles. Si:SiO2 etching selectivity is significantly increased at −100 °C although the aspect-ratio dependent etching phenomenon is more important.

Estimation of Crystal Orientation of Grains on Polycrystalline Silicon Substrate by Recurrent Neural Network

AbstractTo analyze crystal defects in polycrystalline silicon substrates, it is necessary to measure the crystal orientation at high speed. In this paper, we propose a method for simultaneous and fast estimation of the crystal orientation of an entire substrate by measuring the reflected light from a single rotation of a light source. The effectiveness of the proposed method is verified by the orientation estimation experiments. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Large-Area Polycrystalline Silicon Substrates Using Unidirectionally Solidified Metallurgical-Grade Silicon for Solar Cell Applications.(Dept.E)

Large-Area Polycrystalline Silicon Substrates Using Unidirectionally Solidified Metallurgical-Grade Silicon for Solar Cell Applications.(Dept.E)

Resolution and signal enhancement of Raman mapping by photonic nanojet of a microsphere

The field of Raman spectroscopy is constantly under improvement by development of methods of enhancement. One of the latest methods, based on photonic nanojet of a microsphere, has already been proven as simple, reliable and promising method for enhancement of single point micro Raman acquisition, but so far not for imaging. To extend the photonic nanojet method to Raman mapping, we have developed microsphere attached to two perpendicularly connected tapered optical fibers. When the sample is mapped, our two stemmed microsphere stays under the laser beam of the objective, providing enhancement on all points of the image. In addition to the demonstration of the feasibility of such enhancement, the first results reported here with 5-µm two stemmed microsphere on polycrystalline silicon substrate show ~4× signal enhancement of every point, and estimated ~3× resolution enhancement compared to the same setup without the microsphere. Detailed description of fabrication and characteristics of two stemmed microspheres is provided. Mapping images are analyzed and compared to atomic-force and scanning electron microscope images. Also, theoretical calculations of the photonic nanojet are provided. Successful implementation of two stemmed microsphere opens up a gateway and could serve as foundation for future improvements and applications in Raman imaging.

Structural and Thermodynamic Properties of Pb-Cd-Te Thin Films: Experimental Study and DFT Analysis

Vacuum evaporation technology was applied to fabricate Pb0.9Cd0.1Te:Pb (3 at.%) thin films on glass and polycrystalline silicon substrates. X-ray diffraction analysis confirms the rock salt structure with the (100) preferred growing direction for the investigated films. The formation of films on an amorphous glass substrate occurs by two consecutive growth mechanisms. The Volmer–Weber mechanism is the initial mechanism, and it gradually changes with the Frank–van der Merve mechanism. On the polycrystalline silicon substrate, the Volmer–Weber growth mechanism is dominant. Surface formations are oriented and needle-like. A complex of thermodynamic parameters: the enthalpy of formation, entropy, Gibbs free energy, and heat capacity were calculated using the estimated crystallographic data. This work brings light on the fabrication process of single-phase Pb0.9Cd0.1Te:Pb (3 at.%) thin films with a high-quality surface using the low-cost and simple vacuum evaporation method.

Ultraviolet detection properties of electrodeposited n-SnO2 modified p-Si nanowires hetero-junction photodiode

Highly dense, vertically aligned silicon nanowires (SiNWs), having diameters in the range of 40–100 nm and length upto 5 µm, are grown by metal assisted chemical etching technique on p-type polycrystalline silicon (pc-Si) substrate. The hetero-junction photodiodes, for ultraviolet sensing application, are fabricated by depositing tin oxide (n-SnO2) onto pc-Si and SiNWs on pc-Si surface, using simple and low cost electrochemical deposition technique. The prepared SiNWs and n-SnO2 decorated SiNWs are examined by scanning electron microscopy and elemental dispersive analysis by X-ray. Three photodiodes with device architectures Al/Ti/SiNWs/pc-Si/Ti/Al, Al/Ti/n-SnO2/pc-Si/Ti/Al and Al/Ti/n-SnO2/SiNWs/pc-Si/Ti/Al are fabricated and their UV sensing behavior is studied by recording their V–I characteristics under dark and UV-radiation. The recorded V–I curves of the fabricated devices show diode like behavior and their rectification ratio, turn on voltage, effective barrier height and sensitivity are calculated and compared. Under UV exposure, the V–I studies under forward and reverse biasing for the device Al/Ti/n-SnO2/SiNWs/pc-Si/Ti/Al shows significantly higher rectification ratio, sensitivity, responsivity and detectivity around 172.3 at ± 9 V, 64, 0.3456 A/W at 5 V and 8.02869 × 1012 Jones respectively. Further, the photo-resistive measurements of the device also show its excellent reproducible nature. This better UV sensing behavior is also supported with proposed UV sensing mechanism under biasing conditions.

Molecular Dynamics Simulation of Nanoscale Abrasive Wear of Polycrystalline Silicon

In this work, molecular dynamics simulations of the nanoscratching of polycrystalline and singlecrystalline silicon substrates using a single-crystal diamond tool are conducted to investigate the grain size effect on the nanoscale wear process of polycrystalline silicon. We find that for a constant indentation depth, both the average normal force and friction force are much larger for single-crystalline silicon compared to polycrystalline silicon. It is also found that, for the polycrystalline substrates, both the average normal force and friction force increase with increasing grain size. However, the friction coefficient decreases with increasing grain size, and is the smallest for single-crystalline silicon. We also find that the quantity of wear atoms increases nonlinearly with the average normal load, inconsistent with Archard’s law. The quantity of wear atoms is smaller for polycrystalline substrates with a larger average grain size. The grain size effect in the nanoscale wear can be attributed to the fact that grain boundaries contribute to the plastic deformation of polycrystalline silicon.

Effect of free carbon on micro-mechanical properties of a chemically vapor deposited SiC coating

SiC coatings with different content of free carbon were deposited on polycrystalline silicon substrate by chemical vapor deposition (CVD) by using CH3SiCl3-H2-Ar reactive system. The composition, microstructure and micro-mechanical properties of coatings were investigated. The results show that, when H2/MTS is 10, there is no free carbon in coatings. However, at the ratio of H2/MTS of 8.89, 7.97 and 7.32, the content of free carbon is falling in the range of 0.025–0.065, 0.100–0.800 and 0.005–0.035 respectively. The supersaturation of [H] is a key factor to control the generation of free C and the nucleation and growth of SiC coating. As to mechanical properties of SiC coatings, there may be a critical value of the content of free carbon in the coating. When the content of carbon is less than the critical value, the free carbon can enhance the mechanical properties of the coating; otherwise, the free carbon weakens the mechanical properties.

Creation and electrical properties of p-Cu2ZnSnS4/n-Si heterojunctions

Anisotype p-Cu2ZnSnS4/n-Si heterojunctions have been manufactured for the first type by sulfidation of base-metal layers predeposited onto polycrystalline silicon substrates. Current–voltage characteristics of the heterojunctions are analyzed, and the mechanisms of current transfer are discussed. It is established that forward-biased structures are characterized by both tunneling-recombination processes and space-charge limited mobility of carriers. In reversely biased heterojunctions, space-charge limited currents predominate.

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100) and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. Finally, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.

High-κ NdTaO4 dielectrics deposited on polycrystalline silicon substrates

High-k NdTaO4 dielectrics annealed with various temperatures were first deposited on polycrystalline silicon substrates. Material and electrical characterizations were performed. To examine the crystalline structures, X-ray diffraction patterns were analyzed. Electrical measurements including current–voltage characteristics, constant current stress, and the Weibull plots show that annealing could enhance the breakdown voltages, lower the trapping rate, and strengthen the reliability. Results indicate that annealing at 900 °C may optimize the dielectric performance. This dielectric shows promise for future gate material or flash memory integrated with current NdTaO4-based optical devices.

Atmospheric pressure microplasmas in ZnO nanoforests under high voltage stress

Atmospheric pressure ZnO microplasmas have been generated by high amplitude single pulses and DC voltages applied using micrometer-separated probes on ZnO nanoforests. The high voltage stress triggers plasma breakdown and breakdown in the surrounding air followed by sublimation of ZnO resulting in strong blue and white light emission with sharp spectral lines and non-linear current-voltage characteristics. The nanoforests are made of ZnO nanorods (NRs) grown on fluorine doped tin oxide (FTO) glass, poly-crystalline silicon and bulk p-type silicon substrates. The characteristics of the microplasmas depend strongly on the substrate and voltage parameters. Plasmas can be obtained with pulse durations as short as ∼1 μs for FTO glass substrate and ∼100 ms for the silicon substrates. Besides enabling plasma generation with shorter pulses, NRs on FTO glass substrate also lead to better tunability of the operating gas temperature. Hot and cold ZnO microplasmas have been observed with these NRs on FTO glass substrate. Sputtering of nanomaterials during plasma generation in the regions surrounding the test area has also been noticed and result in interesting ZnO nanostructures (‘nano-flowers’ and ‘nano-cauliflowers’). A practical way of generating atmospheric pressure ZnO microplasmas may lead to various lighting, biomedical and material processing applications.

Preparation of nickel–silver core–shell nanoparticles by liquid-phase reduction for use in conductive paste

Nickel–silver (Ni–Ag) core–shell nanoparticles (NPs) were prepared by depositing Ag on Ni nanocores using the liquid-phase reduction technique in aqueous solution, and their properties were characterised using various experimental techniques. The core–shell NPs had good crystallinity, and the thicknesses of the Ag nanoshells could be tuned effectively. The oxidation resistance of the Ag surface and the electroconductive properties of the Ni core allowed these Ni–Ag core–shell NPs to be used in a conductive paste. Thick films composed of Ni–Ag core–shell NPs were screen-printed on a polycrystalline silicon substrate then sintered at temperatures ranging from 500 °C to 800 °C. Stable resistivity was obtained when the sintering temperature was higher than 650 °C, and the electrical properties of the Ni–Ag core–shell paste were close to those of pure Ag paste. Thus, the Ni–Ag NPs can partly replace pure Ag NPs in conductive pastes.

Material and electrical characterizations of high-k Ta2O5 dielectric material deposited on polycrystalline silicon and single crystalline substrate

Samples of high-k Ta2O5 film as a high-k gate dielectric sputtered on both a single crystalline substrate and a polycrystalline silicon substrate and annealed at different temperatures were fabricated and compared. Samples were examined using various material and electrical analyses, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force spectroscopy (AFM), equivalent oxide thickness (EOT), JE characteristics, charge-to-breakdown Weibull plots, and gate voltage shift versus stress time. The research concludes that a Ta2O5 dielectric on a single crystalline substrate had fewer structural defects than a high-k/polysilicon interface, forming a dielectric with better material properties and electrical reliability.

Fabrication of Nano-Columnar Tungsten Films and Their Deuterium and Helium Ion Irradiation Effects

We fabricate nano-columnar tungsten (W) films on polycrystalline silicon substrates by magnetron sputtering using a grazing angle deposition technique. The deposition process is performed at a base pressure of 5×10−4 Pa. The intersection angle between the direction of the incident beam and the normal direction of the substrate is set as 85°. Separate as well as synergetic irradiations of 30/50 keV deuterium ions and 60 keV helium ions are carried out for the nano-columnar W. Samples of normal structure W are also irradiated under the same conditions as a comparison. Scanning electron microscopy and x-ray diffraction are used to characterize the structure of the as-prepared as well as the irradiated samples. The experimental results show that blisters are difficult to form on the surface of nano-columnar W under the irradiation conditions in this work, which could be due to the particular structure.

Three-dimensional whispering gallery modes in InGaAs nanoneedle lasers on silicon

As-grown InGaAs nanoneedle lasers, synthesized at complementary metal–oxide–semiconductor compatible temperatures on polycrystalline and crystalline silicon substrates, were studied in photoluminescence experiments. Radiation patterns of three-dimensional whispering gallery modes were observed upon optically pumping the needles above the lasing threshold. Using the radiation patterns as well as finite-difference-time-domain simulations and polarization measurements, all modal numbers of the three-dimensional whispering gallery modes could be identified.

Charge-transport mechanisms in heterostructures based on TiO2:Cr2O3 thin films

n-TiO2:Cr2O3/p-Si anisotype heterostructures are fabricated by the deposition of a TiO2: Cr2O3 film by electron-beam evaporation onto a polished polycrystalline silicon substrate. Their electrical properties are studied and the dominant charge-transport mechanisms are determined: multistage tunneling-recombination mechanism involving surface states at the TiO2: Cr2O3/Si metallurgical interface under small forward biases and tunneling at biases exceeding 0.8 V. The reverse currents through the heterostructures under study are analyzed in terms of the single-stage tunneling mechanism of charge transport.

Nanoindentation of polysilicon and single crystal silicon: Molecular dynamics simulation and experimental validation

This paper presents novel advances in the deformation behaviour of polycrystalline and single crystal silicon using molecular dynamics (MD) simulation and validation of the same via nanoindentation experiments. In order to unravel the mechanism of deformation, four simulations were performed: indentation of a polycrystalline silicon substrate with a (i) Berkovich pyramidal and a (ii) spherical (arc) indenter, and (iii and iv) indentation of a single crystal silicon substrate with these two indenters. The simulation results reveal that high pressure phase transformation (HPPT) in silicon (Si-I to Si-II phase transformation) occurred in all cases; however, its extent and the manner in which it occurred differed significantly between polycrystalline silicon and single crystal silicon, and was the main driver of differences in the nanoindentation deformation behaviour between these two types of silicon. Interestingly, in polycrystalline silicon, the HPPT was observed to occur more preferentially along the grain boundaries than across the grain boundaries. An automated dislocation extraction algorithm (DXA) revealed no dislocations in the deformation zone, suggesting that HPPT is the primary mechanism in inducing plasticity in silicon.

Sol–gel synthesized Titania nanoparticles deposited on porous polycrystalline silicon: Improved carbon dioxide sensor properties

Titania nanoparticles (TNPs) were synthesized by a sol–gel method in our laboratory using titanium tetrachloride as the precursor and isopropanol as the solvent. The particles׳ size distribution histogram was determined using ImageJ software and the size of TNPs was obtained in the range of 7.5–10.5nm. The nanoparticle with the average size of 8.5nm was calculated using Scherrer׳s formula. Homogeneous and spherical nanoparticles were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and UV–visible spectroscopy (UV–vis). The X-ray powder diffraction analysis showed that the prepared sample (TNPs) has pure anatase phase. TNPs were deposited on porous polycrystalline silicon (PPS) substrate by electron beam evaporation. The TNPs thickness was 23±2nm at 10−5mbar pressure at room temperature. Porosity was performed by an anodization method. Since polycrystalline silicon wafers consist of different grains with different orientations, the pore size distribution in porous layer is non-uniform [1]. Therefore, the average diameter of pores can be reported in PPS layer analysis. Average diameter of pores was estimated in the range of 5μm which was characterized by FESEM. The nanostructured thin films devices (Al/Si/PPS/TNPs/Al and Al/Si/PPS/Al) were fabricated in the sandwich form by aluminum (Al) electrodes which were also deposited by electron beam evaporation. Electrical measurements (I–V curves) demonstrated the semiconducting behavior of thin film devices. The gas sensitivity was studied on exposure to 10% CO2 gas. As a result, conductivity of devices increased on exposure to CO2 gas. The device with TNPs thin film (Al/Si/PPS/TNPs/Al) was more sensitive and, had better response and reversibility in comparison with the device without TNPs thin film (Al/Si/PPS/Al).

Comparison of high-κ Nd2O3 and NdTiO3 dielectrics deposited on polycrystalline silicon substrates

High-κ Nd2O3 and NdTiO3 films deposited on polycrystalline silicon treated at various post-rapid thermal annealing temperatures were fabricated as high-κ gate dielectrics. The NdTiO3 samples demonstrated a higher effective dielectric constant, lower leakage current, higher breakdown electric field, smaller gate voltage shift, and lower electron trapping rate than the high-κ Nd2O3 polyoxide dielectric samples. Annealing effects were analyzed using electrical measurements and multiple material analysis techniques included X-ray diffraction and atomic force microscopy. Incorporating Ti content into Nd2O3 dielectrics resulted in noticeable improvements in electrical performance and material quality. Results indicate that NdTiO3 dielectrics show promise for future high-κ dielectric electronic device applications.