Ultrapure Silicon Research Articles

Synthesis and Characterization of Silicon–Carbon Powder and Its Resistance to Electron Irradiation

The issue of crystallization of silicon oxide at low temperatures is a topical issue for the electronics of the future. Organosilicon oligomers and polymers are “ideal” sources for obtaining ultrapure silicon ceramics and silicon nanoparticles. This paper presents the results of the synthesis of highly dispersed silicon-carbon powder from an organohydrosiloxane oligomer and the method for increasing its crystallinity at low temperatures. The diffraction pattern of the resulting powder corresponds to the amorphous–crystalline state of the components in this material, as evidenced by two intense and broadened amorphous halos in the region of Bragg angles 2θ = 7–11° and 18–25°. The resulting silicon–carbon powder was subjected to electron irradiation (E = 10 MeV; D = 106–107 Gy). This paper presents the data on the changes in powder properties via IR-Fourier spectroscopy, X-ray phase analysis, and scanning electron microscopy. Irradiation with fast electrons with an absorbed dose of 106 Gy leads to a slight crystallization of the amorphous SiO2 phase. An increase in the absorbed dose of fast electrons from D = 106 to D = 107 Gy leads to the opposite effect. An amorphization of silica is observed. This study showed the possibility of the crystallization of a silicon–carbon powder without a significant increase in temperature, acting only with electron irradiation. It is necessary to continue further research on expanding the boundaries of the optimal doses of absorbed radiation from fast electrons in order to achieve the maximum effect of the crystallization of silicon–carbon powder.

Implementing propagating low- temperature synthesis to produce pure silicon carbide

The results of research into the formation of ultrapure silicon carbide by propagating synthesis are described in the paper. This synthesis provides a reduction of process time and energy costs. It is established that the main structural transition is caused by phase transformations and polymorphism phenomenon in silica (α-SiO 2 to β-SiO 2 transition) which is necessary to produce pure silicon carbide. It is determined that in a given time interval under the influence of imposed conditions and subsequent interaction with silicic acid and active carbon begins spontaneous transition with the formation of ultrapure silicon carbide. The implementation of the proposed technology increases the silicon carbide yield to 95‒99 % with a nanoscale product (40‒60 nm) of 99,99 % purity

Silicon wafer defect pattern detection using machine learning

A silicon integrated circuit has been created on silicon wafers by diffusing doping materials on the surface of the same. The silicon wafer is a thin disk made from semiconductor material (mostly ultrapure silicon). Silicon chip fabrication is an industrial process; hence defects occur on silicon wafers caused by unclean factory environment, production machine errors and fabrication process errors. The accurate classification of wafer defects provides information for engineers through regular patterns in the processes. Manual inspection of every chip is not economically feasible. In this study, WM-811k is used as the dataset. This is one of the most extensive wafer bin map dataset available open source on kaggle. It was created by MIRLABS. The dataset was compiled by taking the test data on 811,457 silicon wafer, in which each wafer map image was collected from real-world fabrication. A CNN and DNN model is used to classify the defect patterns.

Tackling the Challenging Determination of Trace Elements in Ultrapure Silicon Carbide by LA-ICP-MS

The goal of accurately quantifying trace elements in ultrapure silicon carbide (SiC) with a purity target of 5N (99.999% purity) was addressed. The unsuitability of microwave-assisted acid digestion followed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis was proved to depend mainly on the contamination induced by memory effects of PTFE microwave vessels and by the purity levels of acids, even if highly pure ones were used in a clean environment. A new analytical protocol for the direct analysis of the solid material by laser ablation coupled with ICP-MS (LA-ICP-MS) was then exploited. Different samples were studied; the best results were obtained by embedding SiC (powders or grains) in epoxy resin. This technique has the great advantage of avoiding any source of external contamination, as grinding, pressing and sintering pretreatments are totally unnecessary. Two different laser wavelengths (266 and 193 nm) were tested, and best results were obtained with the 266 nm laser. The optimized protocol allows the determination of elements down to the sub-mg/kg level with a good accuracy level.

Chitosan-coated ultrapure silicon nanoparticles produced by laser ablation: biomedical potential in nano-oncology as a tumor-targeting nanosystem.

Ultrapure silicon nanoparticles (SiNPs) produced by femtosecond laser ablation in water have attracted great interest in the area of cancer therapy as they are efficient as photosensitizers in photodynamic therapy modality and can induce cell hyperthermia under radiofrequency radiation. Recently, we showed that these biocompatible nanoparticles were not able to reach tumors after intravenous injection in mice due to their rapid clearance from the bloodstream. In order to increase their half-life time and therefore their chances to reach and accumulate in tumors by an enhanced permeation retention (EPR) effect, a capping agent on SiNP surface acting as a colloidal stabilizer suspension is required. In this regard, this work focuses for the first time on the functionalization of SiNPs through the modification of their surface by chitosan (SiNPs-CH) in order to enhance their therapeutic properties in cancer therapy. Here, in vivo experiments were carried out during 15 days on nude mice developing a subcutaneously grafted malignant human brain tumor (glioblastoma). The characterization of SiNPs-CH showed an average hydrodynamic size of around 142 ± 65 nm as well as a relatively neutral charge (-5.2 mV) leading to a high colloidal suspension stability. The point of our work concerns the improvement of the biodistribution of SiNPs-CH with regard to tumors, the bloodstream, and organs. After the intravenous administration of 20 mg kg-1, all the studied parameters (animal behavior, organs' morphology, and histopathology) were in accord with the absence of toxicity due to SiNPs-CH, confirming their biocompatibility and even size and surface charge were modified compared to bare nanoparticles. Moreover an increased time in the bloodstream circulation of up to 7 days was observed, indicating the stealth of the nanoparticles, which could escape opsonization and premature elimination by macrophages and the reticuloendothelial system. As evidenced by silicon assessment, the interaction of the SiNPs-CH with the liver and spleen was significantly reduced compared to the bare nanoparticles. At the same time, SiNPs-CH were concentrated progressively in tumors from 12.03% after 1 day up to 39.55% after 7 days, confirming their uptake by the tumor microenvironment through the enhanced permeability retention effect. Subsequently, the silicon level declined progressively down to 33.6% after 15 days, evidencing the degradation of pH-sensitive SiNPs-CH under the acidic tumor microenvironment. Taken together, the stealthy SiNPs-CH exhibited an ideal biodistribution profile within the tumor microenvironment with a sustainable biodegradation and elimination profile, indicating their promising application in the nano-oncology field as a tumor-targeting system.

(Invited) Electrochemistry for Sustainable Solar Photovoltaics

Commercial solar photovoltaic technologies such as Si and CdTe are traditionally considered to be in a separate domain from electrochemistry. Their device operation is governed by semiconductor physics and their production involves non-electrochemical processes such as diffusion, screen printing, fractional distillation, etc. However, electrochemistry will likely play an indispensable role in sustaining the commercial solar technologies. This talk will discuss three roadblocks to sustainable solar photovoltaics and how electrochemistry can remove these roadblocks: 1) storage of intermittent solar electricity, 2) scarce Ag used in today’s Si solar cells, and 3) high energy input in producing solar Si wafers. An off-grid route is proposed for solar electricity storage based on a closed loop of Zn↔ZnO [1], in which Zn rods are produced in a solar electrolyzer from ZnO. The Zn rods are shipped to homes, offices, factories, and electric vehicles to be inserted into mechanically-recharged Zn/air batteries, for electricity on demand. The spent Zn anodes are collected for regeneration of Zn in the solar electrolyzer. This Zn↔ZnO loop is advantageous over the H2↔H2O loop in terms of theoretical performance and technical readiness. Electroplated Al on Si is proposed to replace the screen-printed Ag electrode in Si solar cells [2]. 18% efficiency has been demonstrated in a Si solar cell with an electroplated Al front electrode and a screen-printed Al back electrode, i.e., an Ag-free all-Al Si solar cell. To overcome the high resistivity of the solar Si wafer, direct Al plating on Si without any seed layer is developed through light-induced Al plating. Direct Al plating on Si drastically simplifies the metallization process for Al, resulting in a significantly-lower cost than competing technologies. Finally, electrochemical refining of metallurgical-grade Si for solar-grade Si has been unsuccessful. While metals up to 99.99% purity are readily produced by electrolysis, solar-grade Si requires a purity of at least 99.99999%. This is coupled with non-electrochemical difficulties in Si purification such as oxidation of the Si anode and crystallinity of the Si cathode. An analysis will be presented on ultrapure materials by electrolysis [3]. The reason for unsuccessful Si electrochemical refining will be discussed through an analogy between electrochemical refining and fractional distillation. A revised method for electrochemical refining of Si is proposed. [1] M. Tao, A Zn↔ZnO loop for terawatt-scale storage of solar electricity, 43rd IEEE Photovoltaic Specialist Conference (Portland, OR, 2016), p. 2011[2] 1. L. Wang, W.-H. Huang, W. J. Shin, M. Tao, B. Deng, and D. Wang, Light-induced plating of aluminum on silicon in a Lewis acidic chronoaluminate ionic liquid, Journal of the Electrochemical Society, 165, D381 (2018)[3] M. Tao, Impurity segregation in electrochemical processes and its application to electrorefining of ultrapure silicon, Electrochimica Acta, 89, 688 (2013)

Correction to: Ultra-pure silicon nanofluid by laser ablation: thermal diffusivity studies using thermal lens technique

Correction to: Ultra-pure silicon nanofluid by laser ablation: thermal diffusivity studies using thermal lens technique

Ultra-pure silicon nanofluid by laser ablation: thermal diffusivity studies using thermal lens technique

Ultra-pure silicon nanoparticles were synthesized through pulsed laser ablation (PLA) in ethanol medium using a Q-switched Nd:YAG nanosecond pulsed laser. Concentration dependence of thermal diffusivity of the silicon nanofluid was studied using dual beam thermal lens technique at room temperature. The thermal diffusivity was found to be decreased with increase in concentration of silicon nanoparticles. This property of nanofluids can be used for thermal trapping and insulating applications.

Waste Photovoltaic Panels for Ultrapure Silicon and Hydrogen through the Low-Temperature Magnesium Silicide

Circulation technology of waste photovoltaic panels for production of ultrapure silicon and energy in the form of hydrogen storage was designed and verified. Preparation of magnesium silicide from waste photovoltaic panel’s silicon and partially oxidized magnesium was thoroughly studied. Work was focused on process optimization, thus, three groups of reactors were tested, namely the continuously evacuated open reactor, pre-evacuated batch reactor and semiopened reactors. The influence of reaction temperature was evaluated in the range of 330–630 °C for various reaction atmospheres; argon and/or air at pressures of 5, 33, and 100 kPa; and vacuum in the range of 5–30 Pa. The effect of nitrogen and oxygen presence in the atmosphere on the resulted reaction and reaction rate was also thoroughly studied. The minimum reaction time guaranteeing the total conversion of silicon for two purities of used magnesium was also determined. The produced materials were analyzed by dispersive Raman spectroscopy, scanning el...

Carbon elimination from silicon kerf: Thermogravimetric analysis and mechanistic considerations

40% of ultrapure silicon is lost as kerf during slicing to produce wafers. Kerf is currently not being recycled due to engineering challenges and costs associated with removing its abundant impurities. Carbon left behind from the lubricant remains as one of the most difficult contaminants to remove in kerf without significant silicon oxidation. The present work enables to better understand the mechanism of carbon elimination in kerf which can aid the design of better processes for kef recycling and low cost photovoltaics. In this paper, we studied the kinetics of carbon elimination from silicon kerf in two atmospheres: air and N2, under a regime of no-diffusion-limitation. We report the apparent activation energy in both atmospheres using three methods: Kissinger, and two isoconversional approaches. In both atmospheres, a bimodal apparent activation energy is observed, suggesting a two stage process. A reaction mechanism is proposed in which (a) C-C and C-O bond cleavage reactions occur in parallel with polymer formation; (b) at higher temperatures, this polymer fully degrades in air but leaves a tarry residue in N2 that accounts for about 12% of the initial total carbon.

The Time and Temperature Dependence of AISI 316L Corrosion in Chlorosilane Environments

Chlorosilanes are used abundantly at high temperatures in the production of ultra-pure silicon and silicon containing materials. The presence of both chlorine and silicon presents a unique corrosion environment for the metallic materials that must handle these compounds. It is known that in chlorosilane environments, 316L can form either a protective metal silicide layer or a volatile metal chloride layer on the substrate. However, it is not known what dependence this surface reaction has on temperature, time, or gas composition. In this study, AISI 316L stainless steel was exposed to vaporized silicon tetrachloride (STC, SiCl4), pure hydrogen (H2), and anhydrous hydrogen chloride (HCl) at temperatures (>350°C), times (1-200 hours), and compositions relevant to industrial processes. Metal silicide and metal chloride formation was evaluated using surface and gravimetric analysis, with metal silicide formation causing a gain in sample mass and metal chloride formation causing a loss in sample mass. It was revealed that the transition between chloride and silicide formation depends on time of exposure, temperature, and mole fraction of HCl present in the gas stream. Lastly, some discussion is provided on the underlying mechanisms of silicide and chloride formation, and how to prevent excessive corrosion in industrial applications.

Engineering near-infrared single-photon emitters with optically active spins in ultrapure silicon carbide.

Vacancy-related centres in silicon carbide are attracting growing attention because of their appealing optical and spin properties. These atomic-scale defects can be created using electron or neutron irradiation; however, their precise engineering has not been demonstrated yet. Here, silicon vacancies are generated in a nuclear reactor and their density is controlled over eight orders of magnitude within an accuracy down to a single vacancy level. An isolated silicon vacancy serves as a near-infrared photostable single-photon emitter, operating even at room temperature. The vacancy spins can be manipulated using an optically detected magnetic resonance technique, and we determine the transition rates and absorption cross-section, describing the intensity-dependent photophysics of these emitters. The on-demand engineering of optically active spins in technologically friendly materials is a crucial step toward implementation of both maser amplifiers, requiring high-density spin ensembles, and qubits based on single spins.

The Time and Temperature Dependence of AISI 316L Corrosion in Chlorosilane Environments

Chlorosilanes are used abundantly at high temperatures in the production of ultra-pure silicon and silicon containing materials. The presence of both chlorine and silicon presents a unique corrosion environment for the metallic materials that must handle these compounds. It is known that in chlorosilane environments, 316L can form either a protective metal silicide layer or a volatile metal chloride layer on the substrate. However, it is not known what dependence this surface reaction has on temperature, time, or gas composition. In this study, AISI 316L stainless steel was exposed to vaporized silicon tetrachloride (STC, SiCl4), pure hydrogen (H2), and anhydrous hydrogen chloride (HCl) at temperatures (>500°C), times (1-150 hours), and compositions relevant to industrial processes. Metal silicide and metal chloride formation was evaluated using surface and gravimetric analysis, with metal silicide formation causing a gain in sample mass and metal chloride formation causing a loss in sample mass. It was revealed that the transition between chloride and silicide formation depends on time of exposure, temperature, and mole fraction of HCl present in the gas stream. Lastly, some discussion is provided on the underlying mechanisms of silicide and chloride formation, and how to prevent excessive corrosion in industrial applications.

Neutron activation analysis of the 30Si content of highly enriched 28Si: proof of concept and estimation of the achievable uncertainty

We investigated the use of neutron activation to estimate the 30Si mole fraction of the ultra-pure silicon material highly enriched in 28Si for the measurement of the Avogadro constant. Specifically, we developed a relative method based on instrumental neutron activation analysis and using a natural-Si sample as a standard. To evaluate the achievable uncertainty, we irradiated a 6 g sample of a natural-Si material and modelled experimentally the signal that would be produced by a sample of the 28Si-enriched material of similar mass and subjected to the same measurement conditions. The extrapolation of the expected uncertainty from the experimental data indicates that a measurement of the 30Si mole fraction of the 28Si-enriched material might reach a 4% relative combined standard uncertainty.

Impurity segregation in electrochemical processes and its application to electrorefining of ultrapure silicon

A theory for impurity segregation in electrochemical processes is formulated based on the Nernst equation, which forms the theoretical foundation for electrorefining. It is found that the current two-electrode configuration, while being widely used to purify metals, is incapable of producing ultrahigh purity. A three-electrode configuration is required, in which the potential applied to the anode or the cathode with respect to the reference electrode is the key to produce ultrapure materials. The theory is applied to electrorefining of metallurgical-grade silicon to produce solar-grade silicon. It is suggested that two-step electrorefining is required to remove all the impurities, in which the anode and cathode potentials are controlled in separate steps. The precise anode and cathode potentials for each step are determined from the impurity concentrations in metallurgical-grade silicon and the target impurity concentrations for solar-grade silicon. It is also found that low process temperatures promote effective electrorefining.

Nanoscale Digital Devices Based on the Photoelectrochemical Photocurrent Switching Effect: Preparation, Properties and Applications

AbstractNew materials and new phenomena which can be used for information processing always inspire great enthusiasm. On the other hand, silicon is still the main workhorse of modern electronics. Production of bulk quantities of ultrapure silicon is relatively cheap and the processing technologies are extremely sophisticated. Introduction of new materials and phenomena, on the other hand, requires an enormous amount of hard experimental and theoretical work. The photoelectrochemical photocurrent switching effect (PEPS) is one of the processes that, in principle, can evolve into new information processing technology. This review presents the effect itself, along with preparation of appropriate semiconducting materials, physical principles of semiconductor–molecule interactions, and finally some prototypical constructions of logic devices based on the PEPS effect.

Towards solar grade silicon: Challenges and benefits for low cost photovoltaics

It is well known that silicon in its various structural configurations (single crystal, multicrystalline, amorphous, micro-nanocrystalline) supplies almost 90% of the substrates used in the photovoltaic industry. It is also known, since years, that the photovoltaic (PV) industry shows a marked growth trend, which demanded and demands a continuous, huge increase of the bulk silicon supply in the order of 30%/yr. In order to fulfill their today- and future needs, many companies worldwide took the decision to start the installation of many thousand tons/year plants, most of them using the Siemens process, some of them using the MG route, to produce the so called solar grade (SG) silicon. The advantages of the Siemens process are well known, as it provides ultrapure silicon, directly usable for growing either single crystalline Czochralski ingots or multicrystalline ingots using the directional solidification (DS) technique. The disadvantages are its high energetic cost (a minimum of 120 kWH/kg) and the possible losses of chlorinated gases in the atmosphere, with possible severe environmental problems. The advantages of the MG route are still potential, as there is no commercially available production of solar silicon as yet, and rely on its reduced energetic costs (a maximum of 25–30 kWh/kg) for a feedstock directly usable for growing multicrystalline ingots using the DS technique. The drawbacks of silicon of MG origin are its larger concentration of metallic impurities, as compared with the Siemens one, the higher B and P content, and the potentially high carbon content. The aim of this paper is to deal with some of the problems encountered so far with the silicon of MG origin with respect to the metallic and non-metallic impurities content, as well as to propose technologically feasible solar grade feedstock specifications.

Recursive Operability Analysis as a decision support tool for Risk-Based Maintenance

This work was developed with the support of MEMC, one of the most important producers of ultra-pure silicon wafers for electronic applications throughout the world. The availability of ultra-pure water is of prime importance in the silicon production process. In order to maximize the availability of UP water, MEMC has developed a preventive maintenance program and a detailed record of each maintenance intervention is recorded. This has allowed a complete failure rate data bank to be developed. In order to optimize the maintenance intervention, a Recursive Operability Analysis (ROA) has been used as a decision support tool. The results of the ROA, coupled with the failure rates, have made it possible to calculate the expected number of events (ENE) of various top events (TEs). The magnitude of each TE has been estimated on the basis of the monetary losses provoked by each event. The risk then has been calculated and the events ranked on this basis. Maintenance policies have been optimized with the aim of reducing the risk of the top ranked events.

Distribution of iron in multicrystalline silicon ingots

The distribution of iron in multicrystalline silicon ingots for solar cells has been studied. A p- and a n-type multicrystalline ingot were intentionally contaminated by adding 53ppmwt (μg∕g) of iron to the silicon feedstock and compared to a reference p-type ingot produced from ultrapure silicon feedstock. The vertical total iron distribution was determined by neutron activation analysis and glow discharge mass spectrometry. For the intentionally Fe-contaminated ingots, the distribution can be described by Scheil’s equation with an effective distribution coefficient of 2×10−5. The interstitial iron concentration was measured in the p-type ingots. In the Fe-contaminated ingot, it is almost constant throughout the ingot and constitutes about 50% of the total concentration, which is in conflict with the previous studies. Gettering had a large impact on the interstitial iron levels by reducing the concentration by two orders of magnitude. Considerable trapping was observed at crystal defects on as-cut wafers from the same ingot. The trapping was suppressed by gettering. The back diffusion of iron from the ingot top after complete solidification was modeled and found to affect the iron concentration up to a distance of approximately 17mm into the ingot. The interstitial as well as the total iron concentration of the reference ingot were extremely low and difficult to measure accurately.

Quantum effects in ion implanted devices

Fabrication of nanoscale devices that exploit the rules of quantum mechanics to process information presents formidable technical challenges because of the need to control quantum states at the level of individual atoms, electrons or photons. We have used ion implantation to fabricate devices on the scale of 10nm that have allowed the development and test of nanocircuitry for the control of charge transport at the level of single electrons. This fabrication method is compatible with the construction of devices that employ counted P dopants in Si by employing the technique of ion beam induced charge (IBIC) in which single 14keV P ions can be implanted into ultra-pure silicon substrates by monitoring on-substrate detector electrodes. We have used IBIC with a MeV nuclear microprobe to map and measure the charge collection efficiency in the development of the electrode structure and show that 100% charge collection efficiency can be achieved. Prototype devices fabricated by this method have been used to investigate quantum effects in the control and transport of single electrons with potential applications to solid state quantum information processing devices.