Melting Temperature Of Silicon Research Articles

Утворення дефектів на поверхні Si-підкладок в процесі термічного напилення золота

Silicon photodetectors, in particular p–i–n photodiodes, are widely used as sensors of optical radiation. With technological advances, the requirements for the parameters and reliability of these elements of solid-state electronics are increasing sharply, thus improving these characteristics is an important task. During the production of silicon photosensors, parameters were observed to degrade after the stage of forming contact pads by thermal sputtering of chrome-gold. Examination of the samples in the selective etchant allowed discovering the complexes of structural defects, which contributed to the deterioration of the parameters, in particular, the growth of dark currents. When investigating the causes of the appearance of these defects, it was established that they were formed as a result of local melting of silicon when gold “drops” hit it with a temperature higher than the melting temperature of silicon due to boiling in the evaporator. It was established that the use of wire is accompanied by a more intensive appearance of gold drops than when using beads. It was also noticed that the roughness of the morphology in the case of sputtering from a wire is significantly higher than in the case of sputtering from beads. It is noted that after the metallization is formed, photolithography is performed on the front side of the substrates to form contact pads, and considering the possibility of etching due to the presence of gold thickenings, it is better to spray on the front side from crowns. Wire spraying should be used for the reverse side of substrates, where defect formation is less critical. The formation of the described defects can be minimized by using spraying from closed evaporators or by increasing the time of spraying on the shutter during gold melting.

Assessing the EDIP potential for atomic simulation of carbon diffusion, segregation and solubility in silicon melt

Molecular simulation based on empirical interatomic potential is an important tool in the study of impurity thermophysical properties, e.g. carbon diffusion, segregation and solubility in liquid silicon, which are key factors determining the carbon concentration and distribution during silicon crystal growth. The Tersoff potentials, although being very successful in describing many silicon and carbon properties, overestimate the silicon crystal melting temperature severely which incurs many criticism and restrictions when comparing the simulation results with experiments. In this study, the EDIP potential, which predicts an experimental comparable silicon melting temperature, was assessed whether it can reasonably capture the carbon diffusivity, segregation and solubility properties in silicon melt while avoiding the well-known temperature issue. We found that the EDIP potential, without requiring scaling the temperature, predicts consistent carbon and silicon diffusion coefficients with other potentials. The segregation coefficient estimated by EDIP is slightly higher than the experimental results. It fails in capturing the carbon solubility property by overestimating nearly two orders of magnitude higher than the experimental values. Based on potential energy and entropy calculation, we suggest that the problem of the EDIP potential is caused by the high entropy of the silicon melt phase. Overall, the research will provide useful information for other thermophysical studies based on EDIP potential and also be benefit to empirical potential optimization.

Research of p‐i‐n Junctions Based on 4H‐SiC Fabricated by Low‐Temperature Diffusion of Boron

Novel method of boron diffusion at low temperatures between 1150 and 1300°C is used for the formation of both p‐i SiC junction and i‐region in one technological process. As the junction formation conditions in this method are essentially different from those in the conventional diffusion (low temperatures and process of diffusion are accompanied by formation of structure defects), it is of special interest to identify advantages and disadvantages of a new method of diffusion. Developed SiC p‐i‐n junction diodes have fast switching time, and the duration of the reverse recovery current is less than 10 ns with a breakdown voltage of 120–140 V. Fabricated diodes possess capability to operate at temperatures up to 300°C. As the temperature of diffusion process is lower than the melting temperature of silicon, this new technology allows fabrication of diodes on the base of SiC/Si epitaxial structures.

Atomistic simulations of carbon diffusion and segregation in liquid silicon

The diffusivity of carbon atoms in liquid silicon and their equilibrium distribution between the silicon melt and crystal phases are key, but unfortunately not precisely known parameters for the global models of silicon solidification processes. In this study, we apply a suite of molecular simulation tools, driven by multiple empirical potential models, to compute diffusion and segregation coefficients of carbon at the silicon melting temperature. We generally find good consistency across the potential model predictions, although some exceptions are identified and discussed. We also find good agreement with the range of available experimental measurements of segregation coefficients. However, the carbon diffusion coefficients we compute are significantly lower than the values typically assumed in continuum models of impurity distribution. Overall, we show that currently available empirical potential models may be useful, at least semi-quantitatively, for studying carbon (and possibly other impurity) transport in silicon solidification, especially if a multi-model approach is taken.

High-temperature oxidation of yttrium silicides

Current silicon melt-infiltrated (SMI) ceramic matrix composites (CMCs) are limited by the melting temperature of silicon (1414 °C) and the volatility of the thermally grown SiO2 scale in high-temperature water vapor environments. Replacement of the melt-infiltrated (MI) silicon with a rare-earth silicide offers the potential to address both limitations of SMI CMCs. This study focuses on the ability of yttrium silicides to form yttrium silicates (phases with greater stability in high-temperature water vapor than SiO2) in high-temperature oxidizing environments. Yttrium silicides with compositions of 41, 67 and 95 at.% Si–Y were fabricated using arc melting and oxidized in air at 1000 and 1200 °C for up to 24 h. Oxidation resulted in the rapid formation of a non-protective Y2O3 scale and rejected Si. Additional minor oxide phases of Y–Si–O, Y2SiO5, Y2Si2O7 and SiO2 were observed to form on and beneath the specimen surface. Characterization of the microstructural evolution with time and temperature helped elucidate the diffusion mechanisms that control oxide growth rates. Replacement of MI silicon with a MI yttrium silicide would significantly compromise the high-temperature performance of a CMC due to Y2O3 CTE mismatch with SiC, high oxygen permeability and the large volume change associated with its rapid subsurface formation. Results are utilized to examine the viability of other rare-earth silicides as MI materials for CMCs.

Heat-Induced Agglomeration of Amorphous Silicon Nanoparticles Toward the Formation of Silicon Thin Film.

The thermal behavior of silicon nanoparticles (Si NPs) was investigated for the preparation of silicon thin film using a solution process. TEM analysis of Si NPs, synthesized by inductively coupled plasma, revealed that the micro-structure of the Si NPs was amorphous and that the Si NPs had melted and merged at a comparatively low temperature (~750 °C) considering bulk melting temperature of silicon (1414 °C). A silicon ink solution was prepared by dispersing amorphous Si NPs in propylene glycol (PG). It was then coated onto a silicon wafer and a quartz plate to form a thin film. These films were annealed in a vacuum or in an N₂ environment to increase their film density. N2 annealing at 800 °C and 1000 °C induced the crystallization of the amorphous thin film. An elemental analysis by the SIMS depth profile showed that N₂annealing at 1000 °C for 180 min drastically reduced the concentrations of carbon and oxygen inside the silicon thin film. These results indicate that silicon ink prepared using amorphous Si NPs in PG can serve as a proper means of preparing silicon thin film via solution process.

Affect of the graphene layers on the melting temperature of silicon by molecular dynamics simulations

In the paper, molecular dynamics simulations have been used to detect the melting temperature of silicon. The two models have been considered as the graphene/silicon/graphene (GSG) sandwich and the only silicon system. Atoms in the models interact with each other via a 3-body Tersoff potential with a modified part based on a Coulomb potential and the Ziegler–Biersack–Littmark universal screening function. We find that C–Si interaction prevents the melting of the two silicon surfaces adjoining the graphene layers. The melting temperature of the silicon part in the GSG sandwich (Tm=2450K) is 1.6 times higher than that of the only silicon system (Tm,pure=1540K). Difference of these melting temperatures has original from interaction of C–Si pairs, which causes decreasing of the energy of the silicon part in the GSG sandwich during heating process leading to an increase of the melting temperature of this silicon part.

Direct Current Heating Model for the Siemens Reactor

The modified Siemens process is the primary technology of polycrystalline production at present. The Siemens reactor, which is the main equipment in the modified Siemens process, consists of a chamber where several high purity silicon slim rods are heated by an electric current flowing through them. The temperature on the rod centre must be under melting temperature of silicon (1687K) in order to avoid its breaking-down because of an uneven temperature profile of the silicon rod. Therefore the temperature profile of the silicon rod heated by direct current (DC) has been investigated by molding. The current density profile of silicon rod has also been studied to investigate the interaction of current density and temperature. The results show that the temperature is not homogeneous in the rod and the temperature in the center of the polysilicon rod is 1750K which is much higher than the melting temperature (1687K) when the temperature is 1423K on the surface of polysilicon and the radius of rod is 5cm. Therefore, the maximum growth radius of the polysilicon rod in Siemens reactor should be less than 5cm when the joule heating generated by DC. The current density increases from the center to the surface of the polysilicon rod.

Formation of dendritic crystal structures in thin silicon films on silicon dioxide by carbon ion implantation and high intensity large area flash lamp irradiation

In this paper, we use large area light pulse induced melting of deposited thin silicon films on oxidised silicon wafers to prepare coarse grained dendritic crystal structures. The results show that the addition of carbon prevents the agglomeration of the molten silicon films and largely influences the crystallisation process. The low solubility of carbon in liquid silicon and its effect on the silicon melting temperature induces a distinctive lateral dendritic grain growth. XTEM, SEM, AFM and ToF-SIMS investigations have been performed to study the crystallisation process and to characterise the resulting film structure.

Role of electronic-excitation effects in the melting and ablation of laser-excited silicon

We present a model of laser–solid interactions in silicon based on a previously-developed interatomic potential for silicon where the parameters describing the interactions depend on the temperature of the electronic subsystem Te, which is directly related to the density of electron–hole pairs and hence the number of broken covalent bonds. For 25fs pulses, a wide range of fluence values are simulated resulting in heterogeneous melting, homogeneous melting, and ablation. The results presented here demonstrate that phase transitions can usually be described by ordinary thermal processes even when the electronic temperature Te is much greater than the lattice temperature TL during the transition. However, the evolution of the system and details of the phase transitions depend strongly on Te and corresponding density of broken bonds. Homogeneous melting appears to be an ordinary thermal phase transition, but occurring over very fast time scales (1–5ps) before TL reaches the ordinary melting temperature of silicon. For high enough laser fluence, homogeneous melting is followed by rapid expansion of the superheated liquid and ablation. Rapid expansion of the superheated liquid occurs partly due to high pressures generated by a high density of broken bonds. As a result of rapid expansion of the superheated liquid, the system is readily driven into the liquid–vapor coexistence region which initiates phase explosion. These results strongly indicate that phase explosion, generally thought of as an ordinary thermal process, can occur even under strong nonequilibrium conditions when Te≫TL. Thus, the results both for melting and ablation processes suggest that for many cases there is no clear separation between thermal and nonthermal processes. Instead, ordinary thermal mechanisms are found to apply when Te≫TL, with the high density of broken bonds playing an important role in the detailed evolution of the system.

Thermal stability of silicon nanowires: atomistic simulation study

Using the Stillinger–Weber (SW) potential model, we investigate the thermal stability of pristine silicon nanowires based on classical molecular dynamics (MD) simulations. We explore the structural evolutions and the Lindemann indices of silicon nanowires at different temperatures in order to unveil atomic-level melting behaviour of silicon nanowires. The simulation results show that silicon nanowires with surface reconstructions have higher thermal stability than those without surface reconstructions, and that silicon nanowires with perpendicular dimmer rows on the two (100) surfaces have somewhat higher thermal stability than nanowires with parallel dimmer rows on the two (100) surfaces. Furthermore, the melting temperature of silicon nanowires increases as their diameter increases and reaches a saturation value close to the melting temperature of bulk silicon. The value of the Lindemann index for melting silicon nanowires is 0.037.

Controlled localised melting in silicon by high dose germanium implantation and flash lamp annealing

High intensity light pulse irradiation of monocrystalline silicon wafers is usually accompanied by inhomogeneous surface melting. The aim of the present work is to induce homogeneous buried melting in silicon by germanium implantation and subsequent flash lamp annealing. For this purpose high dose, high energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp irradiation at high energy densities leads to local melting of the germanium rich buried layer, whereby the thickness of the molten layer depends on the irradiation energy density. During the cooling down epitaxial crystallization takes place resulting in a largely defect-free layer. The combination of buried melting and dopant segregation has the potential to produce unusually buried doping profiles or to create strained silicon structures.

Buried melting in germanium implanted silicon by millisecond flash lamp annealing

Flash lamp annealing in the millisecond range has been used to induce buried melting in silicon. For this purpose high dose high-energy germanium implantation has been employed to lower the melting temperature of silicon in a predetermined depth region. Subsequent flash lamp treatment at high energy densities leads to local melting of the germanium rich layer. The thickness of the molten layer has been found to depend on the irradiation energy density. During the cool-down period, epitaxial crystallization takes place resulting in a largely defect-free layer.

Microcrystalline silicon formation by silicon nanoparticles

Thin silicon films are of great importance for large-area electronic applications, for example, as the basis for switching electronics in flat-panel display devices or as the active layer of solar cells. In this paper, we show that silicon nanoparticles have the potential to be used as raw material for further processing toward a microcrystalline silicon film. This can be done by thermal treatment with a reduced thermal budget because the melting point of the nanoparticles is much lower with only 60% of the equilibrium melting temperature of silicon. Coagulation processes of liquid droplets then lead to the growth of microcrystalline silicon in agglomerated nanoparticles. We demonstrate by in situ transmission electron microscopy (TEM) and differential thermal analysis that silicon nanoparticles with a size of approximately 20nm start melting at around 1000K; furthermore, the TEM observations directly demonstrate the details of the coagulation process leading to microcrystalline silicon.

The effective viscosity of silicon melt in magnetic field

A magnetic field generated by a magic ring was applied to the space containing the silicon melt, and the effective viscosities of silicon melt were measured by the method of rotary vibration. The magic ring was constructed by permanent magnets made of NdFeB permanent-magnet material. The results showed that, at certain temperature, the effective viscosity increased with the increase of magnetic field intensity, and they are parabolically related. The magnet field had stronger effect when the silicon melt temperature increased, which was indicated by a more warped up parabola. In the range of 1490 to 1610℃, the viscosity had an extraordinary fluctuation which indicated a structure change in the silicon-melt. The value of silicon melt viscosity increased by 2—3 orders of magnitude when the magnetic field reached 0.068T. The results indicated that applying a magnetic field to the silicon melt space is an effective way to suppress thermal convection during the growth of large diameter single crystal silicon.

Homogenization of the melting depth in SiC on Si structures during flash lamp irradiation

Flash lamp annealing of heteroepitaxial silicon carbide on silicon structures involves melting the silicon below the SiC layer but the faceted nature of the liquid-solid interface leads to unacceptable surface roughness. This letter describes a method of controlling melting by using a melt stop created at a controlled depth below the Si∕SiC interface by implanting a high dose of carbon, which significantly increases the silicon melting temperature. Results confirm the effectiveness of this approach for increasing surface uniformity, making liquid phase processing compatible with standard device fabrication techniques.

Reversible scaling simulations of the melting transition in silicon

In this work we report simulations of the melting temperature of silicon at zero pressure employing a series of models, which include an empirical potential and three tight binding models. We have determined the melting temperature for each model by evaluating the free energies of the solid and liquid phases as a function of temperature, finding the temperature at which they match. We have employed the reversible scaling technique due to de Koning, Antonelli, and Yip [Phys. Rev. Lett. 83, 3973 (1999)] to obtain the free energies in a range of temperatures bracketing the melting temperature. Good agreement is found between our results and the experimental melting temperature for all models.

ESD-induced oxide breakdown on self-protecting GG-nMOSFET in 0.1-μm CMOS technology

Historically, the failure mode of the nMOS/lateral n-p-n (L/sub npn/) bipolar junction transistor (BJT) due to electrostatic discharge (ESD) is source-to-drain filamentation, as the temperature exceeds the melting temperature of silicon. However, as the gate-oxide thickness shrinks, the ESD failure changes over to oxide breakdown. In this paper, transmission line pulse (TLP) testing is combined with measurements of various leakage currents and numerical simulations of the electric field to examine the failure mode of an advanced 0.1-/spl mu/m CMOS technology, which is shown to be through gate-oxide breakdown. It is also shown by I/sub D/-V/sub G/ and I/sub G/-V/sub G/ measurements that the application of nondestructive ESD pulses causes gradual degradation of the oxide well before failure is reached, under the (leakage current) failure criteria used. Finally, the latent effects of stress-induced oxide degradation on the failure current I/sub f/ of the nMOS/L/sub npn/ are studied, and it is shown that as the device ages from an oxide perspective, its ESD protection capabilities decrease.

Effect of pressure on melting temperature of silicon

The melting temperature–pressure (Tm–P)phase diagram for both bulk and nanocrystalline silicon is predicted by using theClapeyron equation, where the pressure-dependent volume difference ismodelled by introducing the effect of surface stress induced pressure. Thepredictions are found to be consistent with other theoretical results.

Effect of pressure on melting temperature of silicon determined by Clapeyron equation

The melting temperature–pressure [ T m( P)– P] phase diagram for silicon with the diamond structure (Si-I) is predicted by Clapeyron equation where the pressure-dependent volume difference is modeled by introducing the effect of surface stress induced pressure. The result shows that the model prediction is consistent with the experimental results.