Growth Of Crystalline Silicon Research Articles

Numerical Investigation on the Effect of Thermal Gate Moving Rate on Directional Solidification Process

The temperature field distribution during the growth of crystalline silicon by the directional solidification (DS) method is an important factor affecting the growth rate, the shape of the melt-crystal (m-c) interface, and thermal stress. To solve the problem of m-c interface convexity at the early stage of crystal growth caused by supercooling at the bottom center of silicon ingot during DS. In this paper, a two dimensional (2D) global transient numerical model based on a large-size ALD-G7 (G7) crystalline silicon ingot furnace is established and experimentally verified. Based on the model, the influence of different bottom thermal gate moving process curves on the convexity of the m-c interface at the early stage was studied, with emphasis on the changes in temperature field, m-c interface, and thermal stress at the early stage of crystal growth. We have designed three cases, case 1 uses the original moving process curve of bottom thermal gate, case 2 and case 3 adjust the process curve to 0.95 and 0.9 of the original ratio, respectively. The numerical simulation results show that compared with case 1, the average heat dissipation at the bottom of the silicon ingot in case 2 and case 3 is reduced by 2.7 kW·m−2 and 4 kW·m−2, and the maximum thermal stress is also reduced by 3 MPa and 4 MPa, separately. The maximum convexity of the interface is reduced by 25 mm and 20 mm, and the convexity is reduced by 55% and 44% on average, respectively.

On-State Current Degradation Owing to Displacement Defect by Terrestrial Cosmic Rays in Nanosheet FET.

Silicon displacement defects are caused by various effects. For instance, epitaxial crystalline silicon growth and ion implantation often result in defects induced by the fabrication process, whereas displacement damage is induced by terrestrial cosmic radiation. Clustered displacement damage reportedly reduces the on-state current (Ion) in ordinary MOSFETs. In the case of an extremely scaled device such as a nanosheet field-effect transistor (NS-FET), the impact of displacement defect size was analyzed on the basis of the NS dimensions related to the device characteristics. In this study, we investigated the effect of displacement defects on NS-FETs using technology computer-aided design; the simulation model included quantum transport effects. The geometrical conditions, temperatures, trap concentrations, and scattering models were considered as the variables for on-state current reduction.

Optimization of the controlling recipe in quasi-single crystalline silicon growth using artificial neural network and genetic algorithm

The thermal field in the seeded directional solidification (DS) of quasi-single crystalline (QSC) silicon needs precise control to preserve the seed and maintain a flat solidification interface. Compared with adjusting the furnace configuration and materials properties, optimizing controlling recipe parameters of the DS process is more convenient and efficient in reality for improving the thermal field. However, controlling elements in the furnace interact with each other and the cooperation effect cannot be estimated by qualitatively deducing, which adds difficulties to the design and improvement of controlling recipe. In this study, an optimization system was built to optimize the controlling recipe during crystal growth and an industrial G6 DS furnace was taken as an application example. Flattening the solidification interface, reducing the thermal stress in the growing crystal and shortening the casting time were chosen as three optimization targets. Two independent heaters and a heat gate were the three controlling elements whose recipe parameters were the optimization variables. A 2D heat transfer model along with a thermal stress model was developed and an Artificial Neural Network (ANN) was trained to study the mapping relationship between optimization variables and targets in order to save computing resource and time. Genetic Algorithm (GA) was employed to yield the optimal recipes of the three controlling elements. The results showed that the optimal recipe achieved better crystal quality compared with the original recipe. The effectiveness and efficiency of this optimization system indicates that it can achieve the optimal result that theoretic analysis may hardly access.

Hydrogen resist lithography and electron beam lithography for fabricating silicon targets for studying donor orbital states

Recently, phosphorous structures in silicon have been of interest theoretically and experimentally due to their relevance in the field of quantum computing. Coherent control of the orbital states of shallow donors in silicon has been demonstrated in bulk doped samples. Here we discuss the fabrication techniques required to 1) obtain patterned two dimensional dilute sheets of impurities in silicon of controlled doping densities 2) get them to act as targets for a terahertz laser. Scanning tunnelling microscope hydrogen lithography enables patterning of impurity features in silicon with a resolution from 1nm to tens of nm. Molecular beam epitaxy is used for a protective thin-film crystalline silicon growth over the impurity sheet. Electron beam lithography coupled with reactive ion etching allows features from tens to hundreds of microns to be etched into the silicon with 10 to 20nm resolution. The experimental readout is achieved via illumination of the silicon target by terahertz light and subsequent electrical detection. The electrical signal comes from coherent and non-linear excitations of the impurity electrons. This detection technique enables the precision condensed matter samples to remain intact after exposure to the free electron laser pulse.

The synergy of modeling and novel experiments for melt crystal growth research

Computational modeling and novel experiments, when performed together, can enable the identification of new, fundamental mechanisms important for the growth of bulk crystals from the melt. In this paper, we present a compelling example of this synergy via the discovery of previously unascertained physical mechanisms that govern the engulfment of silicon carbide particles during the growth of crystalline silicon.

Crystalline silicon growth on aluminum substrate for photovoltaic application

In this work, we investigate the direct formation of crystalline silicon thin films using ECR-PECVD process on aluminum substrates for solar cells applications. The aluminum substrate offers the advantages of being flexible and highly reflective in addition to serve as the back contact for the cell device. The substrates were pure aluminum or silicon rich aluminum sheets. Monocrystalline silicon substrates were used as reference substrates. Silane and hydrogen were used as precursor gases. Silicon growth was done at different substrate temperatures. The grown silicon films were characterized by Raman spectroscopy, SIMS and XRD techniques. Silicon thicknesses between 230 and 1370 nm were obtained on different types of aluminum substrates. The analyses show that the grown silicon films formed at 480 °C under SiH4: 40 sccm and H2 = 10 sccm are amorphous silicon at the initial stage and become nanocrystalline (nc-Si:H) as the deposition proceeds. The crystalline fraction of those films extracted from Raman spectra is found around 40–60% and XRD analysis shows grain silicon size between 41 and 83 A. Finally, SIMS analysis have revealed graded doping distribution profiles which is indicative of the formation of a nc-Si:H(i)/nc-Si:H (p+)/Al substrate, well suited for solar cell structures.

シリコン単結晶成長プロセスの数値シミュレーションに要求される熱物性値( バルク成長分科会特集-最先端デバイスと科学技術-)

シリコン単結晶成長プロセスの数値シミュレーションに要求される熱物性値( バルク成長分科会特集-最先端デバイスと科学技術-)

Interfacial Layer Control by Dry Cleaning Technology for Polycrystalline and Single Crystalline Silicon Growth.

Native oxide removal prior to poly-Si contact and epitaxial growth of Si is the most critical technology to ensure process and device performances of poly-Si plugs and selective epitaxial growth (SEG) layers for DRAM, flash memory, and logic device. Recently, dry cleaning process for interfacial oxide removal has attracted a world-wide attention due to its superior passivation properties to conventional wet cleaning processes. In this study, we investigated the surface states of Si substrate during and after dry cleaning process, and the role of atomic elements including fluorine and hydrogen on the properties of subsequent deposited silicon layer using SIMS, XPS, and TEM analysis. The controlling of residual fluorine on the Si surface after dry cleaning is a key factor for clean interface. The mechanism of native oxide re-growth caused by residual fluorine after dry cleaning is proposed based on analytical results.

Analysis of particle engulfment during the growth of crystalline silicon

To better understand the physical mechanisms responsible for foreign inclusions during the growth of crystalline silicon, steady-state and dynamic models are developed to simulate the engulfment of solid particles by solidification fronts. A Galerkin finite element method is developed to accurately represent forces and interfacial phenomena previously inaccessible by approaches using analytical approximations. The steady-state model is able to evaluate critical engulfment velocities, which are further validated using the dynamic model. When compared with experimental results for the SiC-Si system, our model predicts a more realistic scaling of critical velocity with particle size than that predicted by prior theories. Discrepancies between model predictions and experimental results for larger particles are posited to arise from dynamic effects, a topic worthy of future attention.

Crystalline silicon on glass by steady-state solution growth using indium as solvent

In order to grow crystalline silicon on glass at low temperatures for photovoltaic applications, a two-step process has been developed. In the first step, amorphous Si films are crystallized at temperatures around 300 °C by metal-induced crystallization, whereby liquid indium serves as a solvent for silicon. Due to the difference of chemical potentials between the amorphous and the crystalline state, an in-plane movement of the liquid metal droplets on the formerly amorphous Si film is accompanied by precipitation of crystalline Si along the droplets’ traces, a process we call amorphous–liquid–crystalline (ALC) transition. In the second step, the ALC seed layers serve as templates for the growth of crystalline silicon by steady-state solution growth. In contrast to common liquid-phase epitaxy, the supersaturation in front of the seed layer is established by a stationary temperature difference between a silicon source and the substrate. Si crystallites in the range of 20–50 µm with low impurity concentrations are grown by this technique. Essential features of steady-state solution growth are compatible with the float glass process in large-scale industrial glass production, which raises hopes for a successive production of glass and thin Si films for solar cells in a continuous production line.

Crystalline silicon growth in the aluminium-induced glass texturing process

Aluminium-induced texturing (AIT) is a method to texture glass surfaces by utilising the reaction between aluminium (Al) and glass at high temperature (above 500°C) and a subsequent wet-chemical treatment that removes the reaction products. In this work, we studied the solid state reaction between a sputtered Al layer and a borosilicate glass sheet during AIT annealing. Raman spectroscopy showed that crystalline silicon (c-Si) is formed during the AIT process. An optical microscope was used to visualise the evolution of the c-Si growth. Plan-view scanning electron microscopy (SEM) investigations performed on samples after completed AIT reaction showed that separate c-Si clusters formed at the glass surface. Atomic force microscopy revealed that the c-Si clusters grew upwards and were on top of the glass surface. Cross-sectional SEM examination showed that the c-Si layer is not uniform and that crater-shaped nodules are embedded into the glass. The widths and depths of the nodules are in the micrometre range. Energy-dispersive X-ray spectroscopy showed that the nodules consist mainly of aluminium oxide (Al2O3). X-ray diffraction analysis showed that the c-Si grains are preferentially (111) oriented. The activation energy of the reaction between Al and borosilicate glass is 3.0±0.2eV based on in-situ XRD analysis of the c-Si growth. Finally, a phenomenological model of the AIT process is proposed and we suggest that the topology of the glass texture strongly depends on the size, depth and lateral separation of the Al2O3 nodules embedded in the glass.

Low Temperature Plasma Synthesis of Nanocrystals and their Application to the Growth of Crystalline Silicon and Germanium Thin Films

ABSTRACTWe summarize our research studies on the synthesis of silicon and germanium nanocrystals and their application to the growth of a variety of thin films, spanning the range from fully disordered amorphous up to fully ordered crystalline. All these films are deposited in a standard radio-frequency glow discharge system at low temperature (~200 °C). We show how the plasma synthesis of silicon nanocrystals, initially a side effect of powder formation, has become over the years an exciting field of research which has opened the way to new opportunities in the field of materials deposition and their application to optoelectronic devices. Our results suggest that epitaxy requires the melting/amorphization of the nanocrystals upon impact on the substrate, the subsequent epitaxial growth being favored on (100) c-Si substrates. As a consequence, the control of the impact energy is a critical aspect of the growth which will require new strategies such as the use of tailored voltage waveforms.

Growth of Crystalline Silicon and Photovoltaic Materials(The 40th National Conference on Crystal Growth (NCCG-40) and the 16th International Conference on Crystal Growth (ICCG-16)/the 14th International Conference on Vapor Growth and Epitaxy (ICVGE-14),News of JACG)

Growth of Crystalline Silicon and Photovoltaic Materials(The 40th National Conference on Crystal Growth (NCCG-40) and the 16th International Conference on Crystal Growth (ICCG-16)/the 14th International Conference on Vapor Growth and Epitaxy (ICVGE-14),News of JACG)

PECVD growth of crystalline silicon from its tetrafluoride

AbstractThe process of plasma chemical deposition of silicon from inductively coupled plasma of the mixture of high‐purity SiF4 and H2 sustained by RF discharge at 13.56 MHz in amount sufficient for subsequent growth of crystal by Czochralski method was investigated. The structure and impurity content of the produced layers as well as of the grown crystal have been studied (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Solution growth of crystalline silicon on glass in the In–Si–Mo system

Progress in low-temperature growth of crystalline silicon from a metallic solution is presented. Growth has been performed on glass that is coated with an electrically conductive layer. Thermodynamic stability of this interlayer in contact with the saturated growth solution is an essential precondition for subsequent process steps. Therefore, materials involved in the process must be properly chosen. Molybdenum disilicide thin films are shown to withstand the solution contact. In this way, further processing, that includes the formation of seed crystals by use of the vapor–liquid–solid mechanism and subsequent outgrowth from a low-temperature metallic solution, is successful. Growth of {1 1 1} faceted silicon crystallites on glass with a size of up to 200 μ m in diameter has been shown.

Ab initiostudy of the diffusion and decomposition pathways ofSiHxspecies on Si(100)

Diffusion and decomposition of ${\text{SiH}}_{x}$ species adsorbed on the clean Si(100) surface are processes of relevance for the growth of crystalline silicon by plasma-enhanced chemical vapor deposition. In this work, we report an extensive search of diffusion and decomposition pathways for ${\text{SiH}}_{3}$, ${\text{SiH}}_{2}$, and SiH by means of combined ab initio metadynamics simulations and optimization of minimum-energy reactions paths. We find that on the clean surface ${\text{SiH}}_{3}$ undergoes stepwise decompositions into Si and H adatoms according to ${\text{SiH}}_{3}\ensuremath{\rightarrow}{\text{SiH}}_{2}+\text{H}\ensuremath{\rightarrow}\text{SiH}+2\text{H}\ensuremath{\rightarrow}\text{Si}+3\text{H}$ with an overall reaction barrier of the order of 0.8 eV, consistent with the scenario inferred from secondary ion mass spectroscopy data. The lifetime of ${\text{SiH}}_{3}$ at room temperature calculated within transition state theory in the harmonic approximation is in agreement with experiments. The lifetime of ${\text{SiH}}_{2}$ turns out to be similar to that of ${\text{SiH}}_{3}$. Possible trap states for ${\text{SiH}}_{2}$ are proposed, based on energetics and by comparing calculated scanning tunneling microscope images with experimental data.

Fluid–solid interaction finite element modeling of a kinetically driven growth instability in stressed solids

The kinetically driven growth instability in stressed solids has been a subject of recent investigation as there is an increasing interest in the effects of non-hydrostatic stresses on crystal growth processes. Recent experimental and modeling work using advanced numerical methods such as boundary element and level set methods have demonstrated that the effect of stress on the solid phase epitaxy (SPE) growth of crystalline silicon from the amorphous phase is responsible for the roughening of its amorphous-crystalline interface. Although our previous model (Phan et al., in Model Simul Mater Sci Eng, 9:309-325, 2001) has been able to explain the observed interfacial instability during the crystal growth of intrinsic silicon, it has not been very successful when extended to the SPE growth process of doped silicon. In an effort to identify the sources that may improve the accuracy and robustness of the previously proposed model, we present in this paper a new approach for modeling the crystal growth in stressed Si layers. The technique is based upon the coupling of a transition-state-theory-based model, a finite element model of the sequentially weak coupling analysis for fluid-solid interaction, and the marker particle method.

Diffusion and desorption ofSiH3on hydrogenatedH:Si(100)−(2×1)from first principles

We have studied diffusion pathways of a silyl radical adsorbed on the hydrogenated $\mathrm{Si}\phantom{\rule{0.3em}{0ex}}(100)\text{\ensuremath{-}}(2\ifmmode\times\else\texttimes\fi{}1)$ surface by density-functional theory. The process is of interest for the growth of crystalline silicon by plasma-enhanced chemical vapor deposition. Preliminary searches for migration mechanisms have been performed using metadynamics simulations. Local minima and transition states have been further refined by using the nudged-elastic-band method. Barriers for diffusion from plausible adsorption sites as low as $0.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ have been found, but trap states have also been spotted, leading to a more stable configuration, with escape barriers of $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Diffusion among weakly bound physisorbed states is also possible with very low activation barriers $(l50\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$. However, desorption mechanisms (either as $\mathrm{Si}{\mathrm{H}}_{3}$ or as $\mathrm{Si}{\mathrm{H}}_{4}$) from physisorbed or more strongly bound adsorption configurations turn out to have activation energies similar to diffusion barriers. Kinetic Monte Carlo simulations based on ab initio activation energies show that the silyl radical diffuses at most by a few lattice spacing before desorbing at temperatures in the range $300--1000\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.

A sequential fluid–solid weak coupling analysis of the SPE in stressed Si layers

The kinetically driven growth instability in stressed solids has been a subject of recent investigation as there is an increasing interest in the effects of non-hydrostatic stresses on crystal growth processes. Recent experimental and modeling work have shown that the effect of stress on the solid phase epitaxy (SPE) growth of crystalline silicon from the amorphous phase is responsible for the roughening of its amorphous–crystalline interface. Although our previous model (Phan, A.-V., Kaplan, T., Gray, L.J., Adalsteinsson, D., Sethian, J.A., Barvosa-Carter, W., Aziz, M.J., 2001. Modelling a growth instability in a stressed solid. Modelling and Simulation in Materials Science and Engineering 9, 309–325.) has been able to explain the observed interfacial instability during the crystal growth of intrinsic silicon, it has not been very successful when extended to the SPE growth process of doped silicon. In an effort to identify the sources that may improve the accuracy and robustness of the previously proposed model, we present in this paper a new approach for modeling the crystal growth in stressed Si layers. The technique is based upon the coupling of finite element analysis, the sequentially weak coupling analysis for fluid–solid interaction, and the marker particle method.

Laser Doping and Recrystallization for Amorphous Silicon Films by Plasma-Enhanced Chemical Vapor Deposition

One of the most challenging problems to develop polycrystalline silicon thin-film solar cells is the growth of crystalline silicon on foreign, low-cost and low-temperature substrates. In this paper, a laser doping technique was developed for the plasma-deposited amorphous silicon film. A process combination of recrystallization and dopant diffusion (phosphorous or boron) was achieved simultaneously by the laser annealing process. The doping precursor was synthesized by a sol-gel method and was spin-coated on the sample. After laser irradiation, the grain size of the doped polycrystalline silicon was examined to be about 0.5~1.0 µm. The concentrations of 2×1019 and 5× 1018 cm-3 with Hall mobilities of 92.6 and 37.5 cm²/V-s were achieved for the laser-diffused phosphorous- and boron-type polysilicon films, respectively.