Silicon Deposition Research Articles

Do lignification and silicification of the cell wall precede silicon deposition in the silica cell of the rice (Oryza sativa L.) leaf epidermis?

Rice is a well-known silica-accumulating plant. The dumbbell-shaped silica bodies in the silica cells in rice leaf epidermis are formed via biosilicification, but the underlying mechanisms are largely unknown. Leaves at different developmental stages were collected to investigate silica cell differentiation by analyzing structures and silicon localization in the silica cells. Exogenous silicon application increased both shoot and root biomass. When silicon was supplied, silica cells in the leaf epidermis developed gradually into a dumbbell-shape and became increasingly silicified as leaves aged. Silicon deposition in the silica cells was not completed until the leaf was fully expanded. Multiple lines of evidence suggest that lignification of silica cell walls precedes silicon deposition in the lumen of silica cells. The organized needle-like silica microstructures were formed by moulding the inner cell walls and filling up the lumen of the silica cell following leaf maturation. Two processes were involved in silicon deposition: (1) the silica cell wall was lignified and silicified, and then (2) the silicon was deposited gradually in silica cells as leaves aged. Silica body formation was not completed until the leaf was fully mature.

Study on the deposition of amorphous silicon and ito thin films for heterojunction solar cell application

In the heterojunction with intrinsic thin-layer (HIT) solar cell structure studied in this work, an intrinsic amorphous silicon (a-Si) layer followed by a n-type amorphous silicon was deposited on a p-type Czochralski (CZ) monocrystalline silicon (c-Si) wafer by plasma enhanced chemical vapor deposition (PECVD) method to form an heterojunction device. Then, indium tin oxide (ITO) layer was formed by DC magnetron sputtering as the top electrode and the anti-reflection coating layer. In order to obtain the high efficiency heterojunction structure, two important aspects were focused: improving the passivation properties of a-Si/c-Si heterojunction and reducing the light absorption and the sheet resistance of ITO layers. It was found that hydrogenated amorphous silicon (a- Si:H) layers can be grown at low substrate temperature, about 200°C. High-quality ITO layers with the sheet resistance less than 15 ohm/sq and the transmittance of about 70%, can be deposited at relatively low DC power (50W).

Effect of VHF excitation frequency on localized deposition of silicon in non-equilibrium-plasma-enhanced CVD by an under-expanded supersonic jet

High rates of localized silicon deposition on a low temperature (473K) substrate impinged by an under-expanded supersonic jet in a conventional non-equilibrium-plasma chemical vapor deposition process at different excitation frequencies were observed. A single 0.3-mm internal diameter nozzle was used as one of the electrodes for the capacitively coupled plasma. A SiH4/H2 gas mixture at a pressure of 65kPa was injected through the nozzle into the vacuum chamber at a pressure of 800Pa. An under-expanded supersonic jet was generated and exhibited turbulence in the vicinity of the substrate surface. A maximum deposition rate of 4.5μm/s was obtained 10mm downstream from the nozzle with 0.8W/cm2 of 100MHz VHF power.

Chemical Vapor Deposition of Silicon by the Reaction of Bromosilanes and Hydrogen

Chemical processes occurring in the vapor deposition of silicon from a mixture of bromosilanes (SiHBr3:SiBr4 = 1:4) with hydrogen gas have been monitored by means of online gas chromatography, and the obtained deposits were characterized by XRD, SEM, and EDX techniques. The deposition of silicon occurred at 900 ºC, accompanied by the larger consumption of SiBr4 than SiHBr3. The numerous rugged rod-like deposits of poly-silicon were grown appearing the crystal diffractions of (111), (220), (311), and (331) planes. The diameter of deposits mainly ranged from 2 to 4 um and their lengths extended to about 10 um.

Low temperature crystallization of amorphous silicon by gold nanoparticle

• Gold nanoparticle production. • Deposition of amorphous silicon by e-beam evaporation method. • Annealing of amorphous silicon for crystallization by gold nanoparticles. Single crystalline Si thin film fabricated on glass substrate by a process called Solid Phase Crystallization (SPC) is highly desirable for the development of high efficiency and low cost thin film solar cells. However, the use of ordinary soda lime glass requires process temperatures higher than 600 °C. Crystallization of Si film at around this temperature takes place in extremely long time exceeding 20 h in most cases. In order to reduce this long process time, new crystallization techniques such as Metal Induced Crystallization (MIC) using thin metal films as a catalyst layer is attracting much attention. Instead of using continuous metal films, the use of metal nanoparticles offers some advantages. In this work, gold thin films were deposited on aluminum doped zinc oxide (AZO) coated glass and then annealed for nanoparticle formation. Amorphous silicon was then deposited by e-beam evaporation onto metal nanoparticles. Silicon films were annealed for crystallization at different temperatures between 500 °C and 600 °C. We showed that the crystallization occurs at lower temperatures and with higher rates with the inclusion of gold nanoparticles (AuNP). Raman and XRD results indicate that the crystallization starts at temperatures as low as 500 °C and an annealing at 600 °C for a short process time provides sufficiently good crystallinity.

Back-End Deposited Silicon Photonics for Monolithic Integration on CMOS

We present the vision of back-end deposited silicon photonics (BDSP) and review works that have been done in this field. Individual aspects of BDSP platform including excimer-laser-annealed polycrystalline silicon, low-loss plasma-enhanced chemical vapor deposition silicon nitride waveguide, modulator, detector, electrical interface, back-end CMOS compatibility, and benefits of the platform are discussed in detail.

Porosity control in thin film solar cells

This work focuses on the simulation and control of a porous silicon deposition process used in the manufacture of thin film solar cell systems. Initially, a thin film deposition process is simulated via a kinetic Monte Carlo (kMC) method on a triangular lattice following the model developed in Hu et al. (2009). Then a closed-form differential equation model is introduced to predict the dynamics of the kMC model and the parameters in this model are identified by fitting to open-loop kMC simulation results. A model predictive controller (MPC) is also designed and implemented on the kMC model. Extensive closed-loop simulation results demonstrate that both film thickness and porosity can be regulated to desired values. Finally, the porosity control framework is extended into a two-stage dual porosity deposition process, with two different porosity set-points for each stage. The closed-loop results demonstrate that at the end of both stages the film porosity values can be successfully regulated at the requested set-point values.

Formation and magnetic properties of the silicon-cobalt interface

Formation of the Si/Co interface and its magnetic properties have been studied by high-resolution photoelectron spectroscopy with synchrotron radiation. The experiments have been performed in situ in superhigh vacuum (5 × 10−10 Torr) with coating thicknesses up to 2 nm. It has been found that, in the initial stage of silicon deposition on the surface of polycrystalline cobalt maintained at room temperature, ultrathin layers of the Co3Si, Co2Si, CoSi, and CoSi2 silicides are formed. The three last phases are nonmagnetic, and their formation gives rise to fast decay of magnetic linear dichroism in photoemission of Co 3p electrons. At deposition doses in excess of ∼0.4 nm Si, a film of amorphous silicon grows on the sample surface. It has been established that the Si/Co interphase boundary is stable at temperatures up to ∼250°C and that further heating of the sample brings about escape of amorphous silicon from the sample surface and initiates processes involving silicide formation.

Decorated carbon nanotubes by silicon deposition in fluidized bed for Li-ion battery anodes

Multi-walled carbon nanotubes Graphistrength® were decorated with silicon by Fluidized Bed Chemical Vapor Deposition. The ability to fluidize of these nanotubes forming ball-shaped jumbles of several hundreds of microns in diameter and that of the final CNT-Si balls was first studied. These balls reveal to fluidize with characteristics of Geldart's group A particles, i.e. without bubbles and with high bed expansion. Coating experiments from silane SiH4 were performed at 500°C in the 30–60wt.% range of silicon deposited. SEM and TEM imaging reveals that the nanotubes are coated by silicon nanoparticles uniformly distributed from the periphery to the center of the balls for the whole conditions tested. On-line acquisition of key process parameters evolution shows that the material remains fluidizable, even for large proportions of silicon deposited. The Sauter diameter and the tapped, untapped and skeleton densities of balls increase with the percentage of silicon deposited, whereas their specific surface area decreases due to the progressive filling of the pores by the deposit. This composite material is a promising candidate as anode to replace graphite in lithium-ion batteries.

The influence of the electrical asymmetry effect on deposition uniformity of thin silicon film

The deposition of amorphous and microcrystalline silicon is an important step in the production of thin silicon film solar panels. Deposition rate, layer uniformity and material quality are key attributes for achieving high efficiency in such panels. Due to the multilayer structure of tandem solar cells (more than 6 thin silicon layers), it is becoming increasingly important to improve the uniformity of deposition without sacrificing deposition rate and material quality. This paper reports the results of an investigation into the influence of the electrical asymmetry effect (EAE) on the uniformity of deposited layers. 13.56MHz+27.12MHz excitation frequencies were used for thin silicon film deposition in a Gen5 reactor (1100×1400mm). To change the plasma properties, the DC self bias voltage on the RF electrode was varied by adjustment of the phase angle between the two frequencies applied. It was found that the layers deposited by EAE method have better uniformity than layers deposited in single frequency 27.12MHz discharge. The EAE provides additional opportunities for improvement of uniformity, deposition rate and material quality.

High rate deposition of nanocrystalline silicon by thermal plasma enhanced CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising alternative for crystalline silicon (c-Si) in the photovoltaic industry. We proposed an atmospheric pressure thermal plasma enhanced CVD (APTPECVD) process for high rate deposition of nc-Si:H on silicon and glass substrates using SiCl4 as the deposition precursor. The deposition rate under typical operating conditions could reach 9.78 nm s−1, and the deposited nc-Si:H film thickness could reach 17.6 μm. The grain diameter and crystalline fraction of the deposition product were characterized using SEM, TEM, Raman spectroscopy and XRD. The photoluminescence performance at room temperature was discovered.

Deposition and characterization of a dual-layer silicon- and silver-containing hydroxyapatite coating via a drop-on-demand technique

Silicon-containing hydroxyapatite (SiHA) and silver-containing hydroxyapatite (AgHA) have been shown to provide enhanced bioactivity and antibacterial properties over pure hydroxyapatite (HA), respectively. This present work is aimed at developing a dual, nano-structured HA/SiHA–AgHA coating on glass substrates via the Drop-on-Demand (DoD) micro-dispensing technique. In this study, phase-pure nano-HA, nano-SiHA containing 0.8 wt% Si, and nano-AgHA containing 0.5 wt% Ag powders were synthesized in-house, and later used to deposit onto the substrates using the DoD technique, forming the dual HA/SiHA–AgHA coatings. A uniform, phase-pure coating 34.5 ± 1.0 μm thick without any undesirable calcium phosphate phases, was achieved. In addition, several phosphate and hydroxyl bands attributed to apatite, were observed on the coatings. Energy Dispersive X-ray Spectroscopy (EDS) mapping revealed that the elements Si and Ag were observed to distribute evenly throughout the top coating layer, which confirmed the versatility of the DoD technique in the production of such a hybrid coating structure.

Электролитическое получение нановолокон кремния из расплава KCl-KF-K2SiF6-SiO2 для композиционных анодов литий-ионных аккумуляторов

Silicon nano- and microwires have been obtained by KCl-KF-K2SiF6-SiO2 melt electrolysis in air; this material is suitable as anode component for lithium ion batteries. Optimal conditions of electrolysis were determined. Morphology, phase and chemical composition of silicon deposits were established. Electrochemical behavior of silicon nanowires as anode component was evaluated using solid polymer electrolyte cells.

Analysis on steady plasma process of high-rate microcrystalline silicon by optical emission spectroscopy

The ratio of I(Hα*)/I(SiH*), obtained from the real time optical emission spectroscopy (OES) measurement in the high-rate microcrystalline silicon deposition process, as a function of time is used to analyze the cause of increasing crystallinity along the growth direction. Hydrogen dilution gradient method which means silane concentration gradient and hydrogen flow gradient method is adopted to improve vertical structure uniformity of the material. High-quality microcrystalline material around 53%-62% of Xc can be prepared through silane concentration gradient compared with 55%-75% of Xc prepared in the traditional method. In the silane depleted cases, by increasing the hydrogen flow the longitudinal uniformity of the material can be effectively improved. The vertical crystallinity around 53%-60% can be obtained. This is mainly due to the increase of the hydrogen flow that makes the collision probability increased, as a result, electron temperature of plasma reduced. Thus, the decomposition of hydrogen decreases and the reaction of hydrogen annihilation is suppressed. At the same time, the influence of back diffusion of SiH4 is suppressed. The gradually increasing trend of the ratio of I(Hα*)/I(SiH*) is controlled during the deposition of microcrystalline silicon film.

DEPENDENCE OF THE OPTICAL AND ELECTRICAL PROPERTIES OF CHEMICALLY ANNEALED VACUUM-DEPOSITED a-Si:H FILMS ON THE DEPOSITION RATE

The influence of the deposition rate of chemically annealed vacuum-deposited a-Si : H films on its optical and electrical properties was studied. The optical parameters were studied using spectrophotometric measurements of the film transmittance in the wavelength range 200–3000 nm. It was found that with increasing the silicon deposition rate from 0.09 to 0.23 nm/s, the refractive index, n, decreases from 3.78 to 3.45 at 1.5 μm, and the optical energy gap, Eg, decreases from 1.74 to 1.66 eV, while the Urbach parameter, ΔE, increases from 77 to 99 meV. The dark conductivity was measured at temperatures descending from 480 to 170 K. It was found that the room temperature dark conductivity values decreased from 1.11 × 10-6 (Ω⋅ cm )-1 to 2.08 × 10-10 (Ω⋅ cm )-1 with increasing the deposition rate from 0.09 to 0.23 nm/s respectively, while the activation energy Ea increased from 0.53 to 0.84 eV with increasing deposition rate. As a result, a good quality a-Si : H film with optical energy gap of 1.74 eV, Urbach parameter of 77 meV, dark conductivity of 1.11 × 10-6 (Ω⋅ cm )-1, and activation energy of 0.53 eV was successfully prepared at a low deposition rate of 0.09 nm/s.

Purification of metallurgical grade silicon by electrorefining in molten salts

Electrochemical studies on silicon deposition were performed in molten salt electrolytes. Purification of metallurgical grade silicon by electrorefining was carried out in molten Si–chloride salts at temperatures from 973 K to 1223 K. It was found that the use of a liquid alloy anode of silicon and copper was beneficial in molten CaCl2 with NaCl, CaO and dissolved Si. ICP-AES analysis results showed efficient removal of metal impurities, such as titanium, aluminum and iron, which are present in significant quantities in the feedstock. The contents of boron and phosphorus in the silicon after electrorefining were reduced from 36×10−6 and 25×10−6 to 4.6×10−6 and 2.8 ×10−6, respectively. The energy consumption of electrorefining was estimated to be about 9.3 kW·h/kg.

Laser-Induced Breakdown Spectroscopy and Phytolith Analysis: An Approach to Study the Deposition and Distribution Pattern of Silicon in Different Parts of Wheat (Triticum aestivum L.) Plant

The distribution/deposition pattern of silicon and minerals in different parts of wheat (Triticum aestivum) plants was determined using laser-induced breakdown spectroscopy (LIBS) and phytolith analysis. The LIBS spectra of different parts of wheat plants gave spectral signature of Ca, Mg, Si, Fe, Na, K, C, H, O and N. Phytolith analysis showed that the leaves of wheat plants are the highest silicon accumulator followed by the awn, leaf sheath, lemma, rachilla and stem. The results of LIBS analysis and the phytolith analysis were in close agreement. The multivariate statistical analysis, principal component analysis (PCA), was applied to the data set of the LIBS spectra of the different parts of the wheat plants. PCA on LIBS data matrix gives PC1 (99 %) and PC2 (1 %) which explains the 100 % variance in the data set. The PCA plots discriminate the vegetative and fertile parts of the wheat plant. Furthermore, the appearance of silicon in each part of the wheat plants also demonstrates its significance in biocement production.

Electrodeposition of silicon from fluoride melts

Electrochemical studies, mainly cyclic voltammetry, square wave voltammetry and chronoamperometry, were carried out to study the behavior of dissolved silicon species in molten LiF-KF with additions of K2SiF6 at temperatures from 550 to 800°C. Electrolysis experiments were run at constant current to deposit pure silicon. Working electrodes of silver, tungsten and glassy carbon and cathodes of silver and silicon were used.The cathodic reduction of dissolved Si (IV) species to silicon was found to be diffusion controlled. Some influence of nucleation phenomena was observed on silver cathode substrates. High purity and good quality silicon deposits were obtained during galvanostatic electrolysis. One challenge is to reduce the inclusions of solidified electrolyte. Current efficiencies for silicon deposition were found to be in the range from 85 to 95%.

Generation of Charged Nanoparticles and Their Deposition Behavior under Alternating Electric Bias during Chemical Vapor Deposition of Silicon

The generation of charged nanoparticles was confirmed under typical conditions of the thin film deposition during the silicon chemical vapor deposition (CVD) process. To exert the electric force on these charged nanoparticles, the alternating current (ac) bias was applied to the stainless substrate holder during CVD. The bias frequency and voltage significantly affected the microstructure evolution and the growth rate. As the frequency at ±100 V was increased from 0.2 to 0.5, 1, and 5 Hz, the mass of the film became respectively 1.1, 2.2, 3.0, and 3.5 times compared with that of the film deposited under the zero bias. As the bias voltage at 1 Hz was increased from 0 to ±50, ±100, ±150, and ±200 V, the mass was increased respectively by 1.8, 3, 4.5, and 8.5 times.

실리콘 슬러지로부터 실리콘의 전해회수(電解回收)

실리콘 웨이퍼공정에서 발생하는 실리콘 슬러지로부터 실리콘 및 탄화규소를 분리한 다음, 전해법으로 원소형태의 실리콘을 회수하는 연구를 수행하였다. 실리콘 슬러지의 주요 불순물은 절삭유, 금속불순물, 실리콘 및 실리콘 카바이드를 들 수 있다. 기계적 선별법으로 분리한 실리콘, 탄화실리콘 복합물을 <TEX>$1000^{\circ}C$</TEX>에 1시간동안 염화 배소하여 응축하고 회수한 사염화실리콘을 이온성액체인 <TEX>$[Bmpy]Tf_2N$</TEX>에 용해하여 전해액으로 사용하였다. 순환전위법으로부터 <TEX>$[Bmpy]Tf_2N$</TEX>의 안정한 전압구간과 사염화실리콘을 용해한 <TEX>$[Bmpy]Tf_2N$</TEX> 전해액에서 실리콘의 환원으로 추정되는 환원피크를 얻을 수 있었다. 정전위법(-1.9 V vs. Pt-QRE)에서 1시간동안 금 전극 상에 전해한 다음, 전극표면을 XRD, SEM-EDS 및 XPS 분석을 통하여 실리콘이 원소형태로 전착되었음을 확인하였으며, 미량의 산소가 검출되는 것은 분석과정에서 시편이 공기 중에 노출되었기 때문으로 판단된다. As a recovery of elemental silicon from the sludge of Si wafer process, a process of mechanical separation-chlorine roasting-electrolysis has been suggested. The silicon sludge consisted of Si, SiC, machine oil, and metallic impurities. The oil and metal impurities was removed by mechanical separation. The Si-SiC mixture was converted to silicon chloride by chlorine roasting at <TEX>$1000^{\circ}C$</TEX> for 1 hr and the silicon chloride was dissolved into an ionic liquid of <TEX>$[Bmpy]Tf_2N$</TEX> as an electrolyte. Cyclic voltammetry results showed an wide voltage window of pure <TEX>$[Bmpy]Tf_2N$</TEX> and a reduction peak of elemental Si from <TEX>$[Bmpy]Tf_2N$</TEX> dissolved <TEX>$SiCl_4$</TEX> on Au electrode, respectively. The silicon deposits could be prepared on the Au electrode by the potentiostatic electrolysis of -1.9 V vs. Pt-QRE. The elemental silicon uniformly electrodeposited was confirmed by various analytical techniques including XRD, FE-SEM with EDS, and XPS. Any impurity was not detected except trace oxygen contaminated during handling for analysis.