Boron Diffusion Mechanism Research Articles

High-efficiency TOPCon solar cell with superior P + and P++ layer via one-step processing

The boron diffusion process in the front field of N-type tunnel oxide passivated contact (TOPCon) solar cells is crucial for PN junction formation and the creation of a selective emitter. This study presents a theoretical model of boron diffusion in silicon using molecular dynamics. The research examines the mean square displacement and diffusion coefficient of boron atoms at varying temperatures, confirming their diffusion behavior. The simulations indicate predominant boron diffusion in the z-direction within the silicon matrix, with the diffusion depth being temperature dependent. The optimal temperature range for boron diffusion in silicon is identified as 950 °C to 1050 °C. Using boron-doped silicon paste and boron trichloride as dopants, thermal diffusion experiments were conducted to fabricate the front-field PN junction (p+ layer) and selective emitter (p++ layer) by one step. Subsequent processing and performance evaluation were performed on a production line. Experimental findings reveal a decrease in boron diffusion at higher temperatures, reduced sheet resistance, increased doping concentration, and deeper junction formation. The ideal boron concentration in the p+ layer is 8.68 × 1018 atom/cm3 with a depth of 0.53 μm, while the p++ layer is 2.35 × 1019 atom/cm3 and 0.82 μm. The efficiency of the optimized TOPCon + cell production line reaches up to 25.17 %, marking an improvement of 0.23 % over the standard cell production line. This research contributes to elucidating the mechanism of boron diffusion and offers insights for enhancing the efficiency of TOPCon solar cells.

Nuclear shell model for the ignition process of boron particle with binary surface oxide layer

Abstract The combustion of a single boron particle contains three continuous macroscopic processes, including ignition delay, ignition and combustion. Studies show that among these processes, the intermediate ignition process has the most complicated kinetic mechanism. On the other hand, conventional models have serious shortcomings to simulate this process. The main challenges in this regard are indeterminate initial thickness of the surface oxide layer, incomplete diffusion mechanism in the surface oxide layer, and neglected effects of the pressure and particle size on the control mechanism. In order to overcome the drawbacks of existing ignition models, a comprehensive kinetic ignition model is developed in the present study. To this end, the dual-beam focused ion beam micro/nanofabrication system is applied to etch and cut the heat-treated boron particles into slices. Then, the scanning transmission electron microscope with collateral energy dispersive spectrometer is applied for analyzing the microstructure and elementary composition of the slice. It is found that the average thickness of the surface oxide layer is higher than earlier assumed values, and the bidirectional diffusion mechanism of boron and oxygen in the liquid boron oxide is confirmed. During the model development, seven heterogeneous global reactions and two vapor-phase reactions are used in total for analyzing the kinetic mechanisms. In the present study, different indicators, including the vaporization process, O2 reactions, and H2O reactions on the internal and external surfaces of the binary oxide layer are investigated. Moreover, the conservation laws of mass and energy are used for the establishment of governing equations. Then, the accuracy of the developed model is evaluated by comparing the obtained results for the ignition time with that of the experiment, which shows a reasonable consistency between them. Then, the proposed model is applied to investigate the ignition characteristics of boron particles. Effects of different parameters, including the environment temperature, O2 concentration, and H2O concentration are studied on the ignition time. It is concluded that the established model, which is named as the nuclear shell (N-S) model is a powerful scheme to better understand the ignition mechanisms and characteristics of boron particles and can be further applied in the field of computational fluid mechanics.

Features of structure formation of surface layers with high content of boron on steel 15Х11МФ in the conditions of furnace and induction heating

The results of obtaining borated layers on 15H11MF high-alloy steel under equilibrium and non-equilibrium heating conditions are presented. Equilibrium conditions were achieved by slow furnace heating (with a heating rate of 0.1 oC/s), non-equilibrium – by induction heating (with a heating rate of 100 oC/s). The heating was controlled by measuring the thermoelectric power by a thermocouple welded to the surface of the sample by electric contact welding. The signal from the thermocouple was digitized by the ADC and transmitted to a computer where, at high speed, an array of data of temperature-time dependence of the process was formed. Furnace heating was carried out in a laboratory electric furnace at 1130 оС ± 5 оС, 1150 оС ± 5 оС and 1160 оС ± 5 оС. Induction heating was carried out to temperatures of 1180 oC ± 20oC, 1200 oC ± 20oC, 1220 oC ± 20oC. The possibility of significant reduction of the treatment process from 3 hours to 2 minutes due to the intensifying action in non-equilibrium conditions of structure formation is shown. Boron saturation came from the paste. Saturating paste consisted of 60% boron carbide, 30% NaF, 10% CaF2. The method of metallographic research shows not only the morphological differences of the obtained surface layers, but also established the predominant mechanism of boron diffusion into high-alloy martensitic steel. During furnace heating (1150оС), a solid boron with a thickness of up to 50 μm and a hardness of 15100 MPa is formed. At a depth of up to 150 μm, grain boundary diffusion is noticeable, which obviously dominates in the processes of boron saturation of high-alloy steels. At temperatures of 1160 oC and furnace heating under a solid layer of boride with a thickness of 110 μm, a two-phase zone is formed, which consists of boride and a solid solution with a thickness of 70 μm. This layer is more defective. Induction heating with boron saturation forms a thick (up to 200 μm) layer of coarse boride crystallites (18900 – 9270 MPa) with an eutectic structure (6440 MPa), which becomes coarser with increasing temperature from 1180 to 1220 оС. The ability to obtain solid hardened layers in a short treatment time makes boron saturation from pastes a more attractive alternative among other chemical-heat treatment technologies.

Investigation of the microstructure of diffusion coatings of carbon steel obtained by simultaneous diffusion saturation with boron, chromium and titanium

The mechanism of boron diffusion under conditions of simultaneous saturation of steels with boron, chromium and titanium are poorly represented in the literature. It is noted that exactly three-component saturation with boron, chromium and titanium allows to obtain diffusion coatings with unique properties. The microhardness of such coatings can achieve 5000 HV, which corresponds to the microhardness of boron carbide B4C. In addition, such coatings, depending on the saturation parameters and the saturable material, can also show high durability values. The microstructure of the diffusion coatings on carbon steels Grade C and steel 1045 has been studied. It has been shown that during the simultaneous diffusion of boron, chromium and titanium under the boride layer additional perlite volumes are formed. The perlite that existed in the steel before the diffusion processes, as a result of diffusion, is fragmented.

First principles calculation of boron diffusion in fcc-Fe

The diffusion mechanism of boron in fcc-Fe was studied by first-principles calculations. The sites where B atoms tend to occupy and the diffusion behavior were calculated. Results indicated that the main mechanism of boron diffusion in fcc-Fe was the B–monovacancy complex mechanism instead of the interstitial mechanism. The diffusion coefficient D1 of the B–monovacancy complex mechanism was calculated without considering the backward jump of the B atoms. The calculated D1 = 1.26 × 10−4 × exp(–2.01eV/kBT) m2·s−1 is consistent with the reported results from experiments.

Boron diffusion in bcc-Fe studied by first-principles calculations**Project supported by the National Natural Science Foundation of China (Grant No. 51276016) and the National Basic Research Program of China (Grant No. 2012CB720406).

The diffusion mechanism of boron in bcc-Fe has been studied by first-principles calculations. The diffusion coefficients of the interstitial mechanism, the B–monovacancy complex mechanism, and the B–divacancy complex mechanism have been calculated. The calculated diffusion coefficient of the interstitial mechanism is D0 = 1.05 × 10−7 exp (−0.75 eV/kT) m2 · s−1, while the diffusion coefficients of the B–monovacancy and the B–divacancy complex mechanisms are D1 = 1.22 × 10−6 f1 exp (−2.27 eV/kT) m2 · s−1 and D2 ≈ 8.36 × 10−6 exp (−4.81 eV/kT) m2 · s−1, respectively. The results indicate that the dominant diffusion mechanism in bcc-Fe is the interstitial mechanism through an octahedral interstitial site instead of the complex mechanism. The calculated diffusion coefficient is in accordance with the reported experiment results measured in Fe–3%Si–B alloy (bcc structure). Since the non-equilibrium segregation of boron is based on the diffusion of the complexes as suggested by the theory, our calculation reasonably explains why the non-equilibrium segregation of boron is not observed in bcc-Fe in experiments.

Modeling of the Boron Emitter Formation Process from BCl<sub>3</sub> Diffusion for N-Type Silicon Solar Cells Processing

This work is devoted to the study of boron doping diffusion process for n-type silicon solar cells applications. Deposition temperature is an important parameter in the diffusion process. In this paper we investigate its influence using an industrial scale furnace [1] (LYDOPTM Boron), which is developed by Semco Engineering. We especially used a numerical model (Sentaurus) in order to further understand the boron diffusion mechanism mainly with respect of the diffusion temperature. The model calibration is based on boron concentration profiles obtained by SIMS (Secondary Ion Mass Spectrometry) analysis. We observed that the boron profiles could be correctly simulated by a single fitting parameter. This parameter, noted kBoron which is connected to the chemical reaction kinetics developed at the interface between the boron silicon glass (BSG) and the silicon substrate

Interstitial-based boron diffusion dynamics in amorphous silicon

Using density-functional theory calculations we identified an interstitial-based fast boron diffusion mechanism in amorphous silicon. We found that interstitial-like point defects, omnipresent in as-implanted silicon, to be very stable in an amorphous network and can form highly mobile pair with Boron atoms. The transient existence of such point defects in amorphous silicon is suggested to play an important role in boron diffusion. We found the activation energy for this pathway to be 2.73 eV, in good agreement with experimental results. In addition, this mechanism is consistent with the experimentally reported transient and concentration-dependent features of boron diffusion in amorphous silicon.

Influence of the spacer dielectric processes on PMOS junction properties

In this paper, the interaction observed in PMOS transistor between the boron lightly doped drain (LDD) extensions and the spacer oxide and nitride dielectrics have been studied, with a simple experimental methodology. Low thermal budget oxide obtained by sub-atmospheric chemical vapor deposition (SACVD) and nitride deposited by plasma process have been evaluated as spacer layers. The influence of the oxide liner hydrogen content is shown to be critical for the p type shallow junction. Indeed, during the activation anneal, hydrogen content increases the boron out diffusion from the extension into the oxide liner and yield to a significant dose loss in this area. Nitride porosity has also been studied. A lower boron dose loss is observed with a porous layer because hydrogen can degas out significantly from the oxide, during anneal, through the porous nitride film. These results confirm the model of boron out diffusion based on oxide hydrogen content proposed by Kohli. Finally, a boron diffusion mechanism driven by chemistry and enhanced by hydrogen defects is proposed.

Molecular dynamics simulation on boron diffusion in diamond

The atomic-scale diffusion mechanism of boron in diamond is investigated by molecular dynamics simulation. A substitutional boron atom diffuses to the self-interstitial site when there exists a self-interstitial carbon atom in its nearest tetrahedral center and the system temperature is high. More important, the bond between boron and the self-interstitial carbon atom is never broken during the diffusion process, indicating that B s–C i pairs diffuse in the lattice by the interstitial mechanism. The results suggest that boron diffusion is mediated by carbon self-interstitial and not by the vacancy mechanism. In addition, the estimated activation energy and the diffusion exponential prefactor of boron diffusion in diamond are found to be 0.23 eV and 1.123×10 −6cm 2/s, respectively.

Systematic Examination of Boron Diffusion Phenomenon in HfSiON High-k Gate Insulator

ABSTRACTIn this paper, boron diffusivities in HfSiON high-k gate dielectric films are systematically investigated for a wide range of the film composition. Boron diffusivities in HfSiON (1000°C) change from 3X10−17cm2/sec to 3X10−15cm2/sec according to the change in the chemical composition of the films. These diffusivity values are higher than that in SiON but lower than that in HfO2. We found that higher Hf/(Hf+Si) results in great increase of diffusivities. On the other hand, higher nitrogen concentration in the film leads to the reduction in diffusivity, in the case of the same Hf/(Hf+Si). In addition, crystallization of HfSiON with the same chemical composition gives rise to an anomalous increase in diffusivities, indicating that the micro-crystallized film structure of HfSiON critically affects the microscopic mechanism of boron diffusion in this material.

Boron Diffusion Mechanism in Silicon Oxide Using AB Initio Methods

AbstractDensity functional theory was employed to explore the diffusion mechanism of boron in amorphous silicon oxide. The oxide was modeled with clusters of various sizes, and both neutral boron atoms and cations were considered. Three stable structures were found where B (or B+) was inserted into oxide: one in which B (or B+) is divalent and two in which B (or B+) is trivalent. Boron diffusion through silicon oxide proceeds as a sequence of B hops from one inserted position to another. For neutral boron the rate limiting step is B hop from one of trivalent structures to a divalent one with activation energies (Ea) in the range of 2.0-3.1 eV, depending on the model cluster. In the case of a cation the rate-limiting step is the B+ hop over the O atom in a divalent structure Si-B+-O-Si with calculated Ea of 2.4-2.8 eV. Experimental activation energies for B diffusion in silicon oxide are in the 2.3 - 4.2 eV range. Our results suggest that both neutral and cation boron can participate in B diffusion in oxide.

POINT DEFECT REDISTRIBUTION IN SI1-XGEX ALLOYS

Using high resolution secondary ion mass spectrometry (SIMS) measurements we have studied the effects of germanium content on antimony diffusion in strained Si1−xGe x layers. Samples were molecular beam epitaxy (MBE) grown Si1−xGe x buried layers incorporating in situ doped antimony delta-layers. These were annealed for a variety of times and temperatures, following which SIMS profiles were taken and from these diffusivities were calculated. The results of a diffusivity versus germanium content study and a diffusivity versus time study are presented; equilibrium antimony diffusion coefficients in alloys of up to 30% germanium are given along with possible transient effects. Changes in antimony diffusivity with composition are attributed to changes in the vacancy population and the vacancy enthalpy of migration. Comparison with the diffusivity of boron versus germanium content in silicon-germanium alloys leads to the proposal that, in silicon-rich alloys, boron diffuses predominantly via the interstitialcy mechanism. The dependence of diffusivity on germanium content for boron is different from that of antimony and it is proposed that the boron diffusion mechanism changes from largely interstitialcy in silicon to vacancy in germanium—the change occurring at around 40% germanium.

A Monte Carlo study of the kickout mechanism of boron diffusion in silicon

In this article, the results of a study of the diffusion mechanism of boron in silicon based on the Monte Carlo method are presented. The kickout mechanism has been examined for the case of a delta function impurity profile under both inert and oxidation conditions. It is shown that the initial conditions play a significant role in obtaining the mean migration path lengths of the atoms. The kickout mechanism in the case of an initial delta function interstitial impurity profile has been analytically examined. The atomic level computational experiments carried out in this article validate Cowern’s results of ‘‘intermittent diffusion’’ of boron in silicon and yield, the values for λ0, the prefactor for the mean migration path length, which are found to lie between 0.024 and 0.035 nm.

The effect of carbon, chromium and nickel on the hardness of borided layers

The variation in hardness of the phases (Fe, M)B and (Fe, M) 2B (M ≡ Cr or Ni), which are the predominant components of the borided layer obtained on iron alloys, was defined and related to increase in chromium, nickel and carbon contents. It was found that chromium increases the hardness both of the borided layer as a whole and of the boride components, even though these values are systematically lower than those measured on pure borides. Carbon, which is insoluble in this type of phase, accumulates at the boride-matrix interface and, because of its modification of the boron diffusion mechanism, it indirectly increases the hardness of the borided surface. Nickel reduces slightly but systematically the hardness of the borides, in particular of the (Fe, Ni) 2B phase in which it has its highest concentration.

Nature of boron in α-iron

Internal friction measurements were carried out on iron-boron and iron-nickel-boron alloy specimens, in order to define the nature of the boron solid solution in α-iron. An internal friction peak corresponding to a small amount of boron in α-iron was observed. Referring to the lattice parameter measurements, and the diffusion experiment, it can be concluded that boron atoms occupy both substitutional and interstitial positions. The concept of dissociative diffusion explains well the diffusion mechanism of boron in α-iron. The relaxation time of the jump of an interstitial boron atom is shown to be 10~13 exp ( 13000/ RT) sec.