Silicon Ingots Research Articles

Stress analysis and dislocation cluster generation in silicon crystal with artificial grain boundaries

We conducted a dislocation and stress analysis on various grain boundaries (GBs) using silicon ingots that contained artificial GBs to permit systematic comparison of experimental and analytical results. Through photoluminescence imaging, we found that the number of dislocation clusters generated around the 〈110〉-oriented GBs was significantly higher than those around the 〈100〉-oriented GBs. The stress analysis revealed that this difference is linked to the maximum shear stress around the GB. However, there were some GBs where dislocation cluster generation was not observed despite the presence of high shear stress. For most of these GBs, the direction of the maximum shear stress in the 12 slip system of silicon crystal was found to be oblique downward to the growth direction, which appears to inhibit dislocation propagation.

Optimizing cooling strategies in the Czochralski process for large-diameter silicon ingots

As the semiconductor industry shifts towards larger wafer sizes, such as 300 mm and 450 mm, controlling defects is crucial to ensure device performance and yield. Conversely, a high cooling rate is essential for achieving higher production rates. Therefore, finding the optimal cooling strategy is critical to maintaining high production rates while ensuring high-quality wafer production. This paper employs a simulation model to investigate the impact of various cooling strategies on point defect formation during the CZ process for 450 mm diameter silicon ingots. Using the 3D energy equation coupled with the Navier-Stokes equation and moving mesh theory, the transient CZ process is simulated, incorporating defect evaluation equations. Beside original CZ puller configuration, two cooling strategies are examined: one with a small gap and long cooling jacket (Case II) and another with a large gap and short cooling jacket (Case III), compared against a baseline setup (Case I). The simulations reveal that Case II, while enhancing the crystallization rate, increases non-uniformity. Conversely, Case III produces a flatter solid-liquid interface and lower defect concentrations, achieving a maximum Cv-Ci of 0.4 × 1014 cm−3, compared to 1.1 × 1014 cm−3 and -2.5 × 1014 cm−3 in Case I and II. These findings suggest that adjusting cooling strategies can significantly impact the quality and uniformity of large- diameter silicon ingots.

Machine Learning Methods for Structure Loss Classification in Czochralski Silicon Ingots

Machine Learning Methods for Structure Loss Classification in Czochralski Silicon Ingots

Investigation of uniformity in fused quartz crucibles for Czochralski silicon ingots

As there is an increased demand for monocrystalline silicon based solar cells, there is an increased interest in stronger and more durable fused quartz crucibles used in the Czochralski process. In this study we focused on the uniformity of hydroxyl impurities in these crucibles, and its potential influence on viscosity of the crucible by combining data from IR-microscopy and a self-made viscosity measurement setup. A half of a fused quartz crucible manufactured from two types of sands was studied, the OH groups content was mapped, and the viscosity at 1500 °C was measured. Local variations in the OH groups content of on average 26.7 ppm difference between the top and the bottom of the crucible were detected. The viscosity measurements further confirmed the crucible’s inhomogeneity as no clear trends or direct correlations to the OH groups content were observed. The correlation between the different sand types used for crucible manufacturing and the OH groups content was also investigated in four samples originating from four different crucibles. Two different trends in the OH groups distribution were found: while two of the studied crucibles showed an increased OH groups content in the boundary between the bubble free and the bubble containing layer, the other two showed an increased and maximum OH groups content in the bubble containing layer, and the link between the sand types and the OH groups content was confirmed. The source of the local inhomogeneities and the two different trends of OH groups distribution can possibly be attributed to the sand quality, the sand particle size, and the difference in the manufacturing process, such as thermal history or distribution of sand.

Upcycling of waste photovoltaic silicon: Co-MOF derived coating layer enhanced lithium storage

Large amounts of silicon waste (W-Si) powders or ingots from the photovoltaic (PV) industry can be recycled as the improved raw negative electrode material in Lithium-ion batteries. Herein, Co-MOFs (ZIF-67) is produced in the form of small particles which turns into the uniform coating layer on the surface of micro-sized W-Si by solvent evaporation, and then ZIF-67 is carbonized to form nitrogen-doped carbon (NC) layer and carbon nanotubes (CNTs). Finally, W-Si/NC/Co/CNTs composites are formed. The continuous and uniform NC layer and CNTs formed by the catalyzation of Co on the surface of the silicon particles can inhibit the volume expansion of silicon during the charge and discharge process, showing the reversible discharge capacity of 1039 mAh g−1 after 100 cycles. The rate performance is also improved due to the high conductivity composite structure. This work can provide a choice for the composite of MOF and micro-silicon, and the meaning guidance for the application of silicon waste from PV industry.

THERMAL SIMULATION OF THE CZOCHRALSKI PROCESS FOR SILICON CRYSTAL GROWTH USING FINITE ELEMENT MODELING APPROACH

This study investigates the thermal dynamics of the Czochralski (CZ) process for silicon crystal growth through numerical simulations. The simulation method of this study is based on finite element method (FEM) heat transfer simulation. The FEM simulation was performed using triangular mesh in half cross section of CZ system with real material properties. The analysis of heat transfer mechanisms includes conduction, convection, and radiation which reflect the impact of cooled argon convection on crystal growth. The simulations reveal that convection currents driven by cooled argon has a crucial role to promote uniform cooling which control crystal growth. This leads to enhanced mono-crystalline silicon ingot crystal quality and purity. Ultimately, insights gained from this study can inform optimization efforts in semiconductor manufacturing, facilitating advancements in electronic device fabrication.

Preparation of High-performance Multicrystalline Silicon Ingot Based on Innovative Seeding Strategy for Recycled Seeds

Preparation of High-performance Multicrystalline Silicon Ingot Based on Innovative Seeding Strategy for Recycled Seeds

Optimization of silicon ingot manufacturing for high production rates

Optimization of silicon ingot manufacturing for high production rates

Crystallization processes for photovoltaic silicon ingots: Status and perspectives

The choice of the crystallization process plays a crucial role in determining the quality and performance of the photovoltaic (PV) silicon ingots, which are subsequently used to manufacture solar cells. Silicon ingots are typically grown using either the Czochralski (Cz) process or the direction solidification (DS) method, with each technique influencing the microstructure and defects density as well as the final solar cells’ performance. In this work, we describe these two processes with a brief overview of the main challenges. For monocrystalline silicon ingots, we discuss the role of crucible and bubble development as well as structure loss. For multicrystalline silicon ingots, we briefly review some of the methods that have been developed in the past years and present results of high-performance multicrystalline (HPMC) ingots.

Effect of Silicon Nitride Coated Carbon Crucible on Multi-Crystalline Silicon Ingot during Directional Solidification Process: Numerical Simulation

Effect of Silicon Nitride Coated Carbon Crucible on Multi-Crystalline Silicon Ingot during Directional Solidification Process: Numerical Simulation

High efficiency solar-grade silicon producing by directional solidification through controlling diffusion of impurity

The precise distribution of impurity of the whole silicon ingot is investigated through a theoretical model and the experiments. This model solves the problem of inaccurate prediction of impurity distribution in the final solidification region. The model was used to calculate the distribution of iron impurity in polycrystalline silicon ingots after directional solidification and compared with experiments. The calculation accuracy was significantly improved compared to the traditional Scheil equation. This paper investigates the influence of cooling rate, silicon ingot height and solidification rate on the yield of purified products after directional solidification. For the experimental equipment and raw materials in this paper, the optimal cooling rate of silicon ingots after directional solidification is 0.33 °C/s, the optimal height of silicon ingots is 0.34 m, and the yield of silicon purification increases with the decrease of directional solidification rate. Based on the research results, a standard for removing the top skin of silicon ingots after directional solidification and a method for improving the purification yield by suppressing impurity diffusion during the cooling stage were obtained. This model can provide theoretical guidance for the development of low-cost and high-efficiency methods for removing impurities from polycrystalline silicon, and is of great significance for the development of the photovoltaic industry. In addition, the theoretical model proposed in this paper can also be applied to the directional solidification purification process of other materials, such as the preparation of high-purity aluminum and high-purity titanium, and can predict the impurity migration behavior and distribution pattern throughout the purification process.

Photovoltaic Manufacturing Factories and Industrial Site Environmental Impact Assessment

Life cycle inventories (LCIs) and life cycle assessments (LCAs) of photovoltaic (PV) modules and their components focus on the operations of PV factories, but the factories and industrial site product and construction stages are either not or only partially tackled. This work contributes through the bottom-up, model-based generation of LCIs and LCAs for setting up a vertically integrated 5 GWp/a PV industrial site, including the manufacturing of silicon ingots, wafers, solar cells, and PV modules, on a 50 ha greenfield location. Two comparative LCAs are performed. The first compares the annualized environmental impacts of the developed LCI sets with four existing inventories in the Ecoinvent v3.8 database. The second comparative LCA explores the environmental impact differences concerning the industrial site when using different building systems for the factories. Here, the reference system with a steel structure is compared with two alternative building systems: precast concrete and structural timber. The results show that the wafer, cell, and module factories’ annualized environmental impacts with the Ecoinvent LCIs are strongly overestimated. For the ingot factory, the opposite result is identified. The impacts of all four factories show reductions of between 11.7% and 94.3% for 14 of the 15 impact categories. High mean environmental impact shares of 79.0%, 78.2% and 79.2% for the steel, precast concrete and timber structural building systems, respectively, are generated at the product stage. The process and facilities equipment generates 54.2%, 54.4% and 58.2% of the total product and construction stages’ mean environmental impact shares. The proposed alternative timber building system reduces the environmental impacts in 14 of the 15 evaluated categories, with reductions ranging from 1.1% to 12.4%.

Role of Longitudinal Temperature Gradients in Eliminating Interleaving Inclusions in Casting of Monocrystalline Silicon Ingots

Infrared analysis reveals the presence of interwoven inclusions, primarily comprised of silicon nitride and silicon carbide, in the casting process of monocrystalline silicon ingots. This study investigates how the longitudinal temperature gradient affects the removal of inclusions during the casting of monocrystalline silicon ingots through simulations and comparative experiments. Two monocrystalline silicon ingots were cast, each using different longitudinal temperature gradients: one employing smaller gradients and the other conventional gradients. CGSim (Version Basic CGSim 23.1) simulation software was utilized to analyze the melt flow and temperature distribution during the growth process of quasi–monocrystalline silicon ingots. The findings indicate that smaller longitudinal temperature gradients lead to a more robust upward flow of molten silicon at the solid–liquid interface, effectively carrying impurities away from this interface and preventing their inclusion formation. Analysis of experimental photoluminescence and IR results reveals that although inclusions may not be observed, impurities persist but are gradually displaced to the top of the silicon melt through a stable growth process.

Efficient manufacture of high-performance electroplated diamond wires utilizing Cr-coated diamond micro-powder

The slicing of silicon ingots using electroplated diamond wires is a fundamental process in the creation of semiconductor devices such as chips and photovoltaic cells. Composite electroplating, a process that uses nickel (Ni) plating to fix diamond particles onto a steel wire, is a critical step in the manufacturing of these diamond wires. In this work, chromium (Cr)-coated diamond was used to achieve rapid and high-quality composite electroplating, thereby aiding the production of high-performance diamond wire saws. The Cr-coated diamond micro-powder was prepared utilizing vacuum slow evaporation technology at a temperature of 850 °C. This resulted in a uniform and firm Cr coating that was firmly bonded to the diamond surface via Cr3C2. Subsequent electrochemical tests were conducted in the composite electroplating bath. Linear scanning voltammetric curves revealed that the Cr-coated diamond was capable of inducing a more positive shift in the overpotential of Ni deposition, thus enhancing the reaction beyond that of uncoated diamond micro-powder. Additionally, the electrochemical impedance spectra indicated a decrease in charge transfer resistance during composite electroplating, attributable to the conductivity of the Cr-coated diamond. Electroplated diamond wires incorporating Cr-coated diamond demonstrated a greater abrasive density per unit length. SEM results showed that Ni was able to deposit on the Cr-coated diamond surface, resulting in the abrasives being completely covered by the Ni plating. The Cr-coated diamond wire exhibits a stronger resistance to abrasive detachment after cutting, which could increase the diamond-protrusion of the wire. The utilization of Cr-coated diamond micro-powder as an abrasive is anticipated to enhance the manufacturing efficiency of diamond wires and improve product quality, thereby promoting advancements in hard and brittle material processing technology.

Effect of horizontal magnetic field position on oxygen distribution in CZ silicon crystal growth

The horizontal magnetic field-assisted Czochralski(CZ) method is gaining significant popularity in the semiconductor industry for producing 200 mm semiconductor-grade silicon wafers. In this study, the impact of the horizontal magnetic field position on the oxygen content and radial uniformity of semiconductor-grade silicon crystals produced by the CZ method was investigated. Three-dimensional simulations were conducted using finite element software to calculate the melt convection and oxygen content before and after adjustment of the magnetic field position, respectively. The simulations results predicted a decrease in the oxygen content of the crystals following the adjustment of the magnetic field position from 0 to 75 mm below the free surface, and this was experimentally verified. The velocity distribution of the free melt surface exhibits better uniformity when lowering the magnetic field position. The influence of the magnetic field position on the temperature distribution and Marangoni flow in the melt was investigated, and the result of oxygen concentration difference identified the adjustment of the magnetic field position promoted the greater Marangoni flow below the free melt surface, which promoted the volatilization of SiO gas and thus reduced the oxygen concentration in the silicon ingot. Therefore, adjusting the position of the magnetic field is an effective way to increase the Marangoni flow and to obtain semiconductor-grade silicon crystal with lower oxygen content and better oxygen radial homogeneity.

Simulation analysis on furnace pressure for reducing the impurities concentrations distribution during the growth of mc-Si ingot by DS process: Solar cell applications

A numerical investigation is carried out for the directional solidification (DS) process with various furnace pressures such as 300 mbar, 400 mbar, 500 mbar, and 600 mbar. During the multi-crystalline silicon (mc-Si) ingot growth process, the pressure inside the furnace affects the species' transport. The oxygen and carbon concentrations for various furnace pressures have been analyzed, and the results were compared. In the gas phase, a furnace pressure of less than 500 mbar enhances the strong back diffusion of the species into the silicon melt. The furnace pressure is higher than 500 mbar, which enhances the convection transport of the species in the lab-scale furnace. The optimized furnace pressure (500 mbar) enhances the quality of multi-crystalline silicon ingot. The oxygen concentration and carbon concentration values are reduced when the furnace pressure is around 500 mbar, which reduces the light-induced degradation (LID) effects and SiC precipitation.

Reutilization of Silicon-Cutting Waste via Constructing Multilayer Si@SiO2@C Composites as Anode Materials for Li-Ion Batteries.

The rapid development of the photovoltaic industry has also brought some economic losses and environmental problems due to the waste generated during silicon ingot cutting. This study introduces an effective and facile method to reutilize silicon-cutting waste by constructing a multilayer Si@SiO2@C composite for Li-ion batteries via two-step annealing. The double-layer structure of the resultant composite alleviates the severe volume changes of silicon effectively, and the surrounding slightly graphitic carbon, known for its high conductivity and mechanical strength, tightly envelops the silicon nanoflakes, facilitates ion and electron transport and maintains electrode structural integrity throughout repeated charge/discharge cycles. With an optimization of the carbon content, the initial coulombic efficiency (ICE) was improved from 53% to 84%. The refined Si@SiO2@C anode exhibits outstanding cycling stability (711.4 mAh g-1 after 500 cycles) and rate performance (973.5 mAh g-1 at 2 C). This research presents a direct and cost-efficient strategy for transforming photovoltaic silicon-cutting waste into high-energy-density lithium-ion battery (LIB) anode materials.

Adjustment of oxygen transport phenomena for Czochralski silicon crystal growth

During silicon crystal growth, oxygen, a well-known major impurity, affects the final silicon wafer's mechanical and electrical properties. This study focused on regulation of discharge of different concentrations of oxygen from the quartz crucible into the silicon melt while considering the crucible angular speed and the friction at the melt–crucible interface. The three-dimensional transient governing equations for heat transfer, fluid flow, and impurity transportation in the Czochralski (CZ) puller were solved numerically. The oxygen solvation equation representing the crucible to silicon melt was modified to evaluate the accuracy of oxygen concentration calculations during the CZ process. Experimental measurements using the Fourier-transform infrared (FTIR) technique were used to confirm the simulation results. The results demonstrate that the crucible angular speed affects the oxygen concentration near the crucible wall and therefore in the silicon ingot. The proposed modifications for evaluating oxygen concentration offer a more comprehensive understanding of the oxygen dynamics during the CZ crystal growth.

Surface Examination of Structure Loss in N-Type Czochralski Silicon Ingots

In principle, growing a dislocation-free Czochralski silicon ingot is possible if the growth process is kept stable and below the critical resolved shear stress value. However, in practice, a considerable proportion of the Si ingots are remelted due to the generation of dislocations or the so-called structure loss. The assessment of the failed ingots is a crucial step toward higher yield. However, the characterization of Si ingots is challenging due to their high brittleness and the high concentration of dislocations related to slip. In this work, we develop a non-destructive method to investigate the ingots that have experienced structure loss and reveal the root causes of this failure. Many characteristic features have been found on the surface of Czochralski silicon ingots. Based on these features, the ingots are classified into seven major groups that could be related to the main causes of the structure loss. Furthermore, the temperature gradient of several ingots is revealed by careful measurements of the growth ridges’ widths of these ingots. The results show that most of the failed ingots experience low-temperature gradients before the dislocation generation which agrees with the previous results. Three ingots have a clear particle hit on the surface, which caused an immediate transition to a multi-crystalline silicon structure. Particles are found on atomically smooth and rough interfaces, growth ridges, and surfaces in between. The surface examination method is a promising, fast, low-cost, and non-destructive technique that can be used to identify the most critical factors of structure loss in industrial ingots.

Silicon Solar Cells: Trends, Manufacturing Challenges, and AI Perspectives

Photovoltaic (PV) installations have experienced significant growth in the past 20 years. During this period, the solar industry has witnessed technological advances, cost reductions, and increased awareness of renewable energy’s benefits. As more than 90% of the commercial solar cells in the market are made from silicon, in this work we will focus on silicon-based solar cells. As PV research is a very dynamic field, we believe that there is a need to present an overview of the status of silicon solar cell manufacturing (from feedstock production to ingot processing to solar cell fabrication), including recycling and the use of artificial intelligence. Therefore, this work introduces the silicon solar cell value chain with cost and sustainability aspects. It provides an overview of the main manufacturing techniques for silicon ingots, specifically Czochralski and directional solidification, with a focus on highlighting their key characteristics. We discuss the major challenges in silicon ingot production for solar applications, particularly optimizing production yield, reducing costs, and improving efficiency to meet the continued high demand for solar cells. We review solar cell technology developments in recent years and the new trends. We briefly discuss the recycling aspects, and finally, we present how digitalization and artificial intelligence can aid in solving some of the current PV industry challenges.