Silicon Carbide Ingots Research Articles

Control of the growth quality by optimizing the crucible structure for growth of large-sized SiC single crystal

Silicon carbide (SiC), as the wide bandgap semiconductor, has gradually attracted attention from investigators due to the excellent integrated performance, widely recognized as a revolution in the electronic devices. For these applications, it is crucial to prepare the high-quality SiC crystal ingot by optimizing growth parameters and crucible structures. In this study, the effect of TaC coating and graphite paper on the growth process of SiC ingot were investigated compared to the growth in conventional graphite crucible through modeling and experiment. We demonstrated that the grown crystal using TaC-coated graphite relay ring and graphite paper surrounded the inner wall of powder container shows the superior characteristics in terms of the crystalline perfection and interface shape. In addition, the new crucible structure can provide a low-cost solution to prepare SiC crystal ingot using PVT method.

Optimization of crucible and heating model for large-sized silicon carbide ingot growth in top-seeded solution growth

In this paper, a new crystal growth model for top-seeded solution growth (TSSG) was established by improving the shape of the crucible and using a heating system. The simulation results show that a relatively stable growth of large-sized (4-in.) silicon carbide ingots can be achieved by the reasonable design of the crucible dimensions, H1 and L1. This new system also has excellent potential for using TSSG to grow 6-inch crystals. Besides, more attention should be paid to the edge growth of the seed, which plays a crucial role in further improving the stability of crystal growth.

Numerical Investigation of Thermal Buoyancy, the Electromagnetic Force and Forced Convection in Conventional RF Systems for 4-Inch Sic by TSSG

In this paper, we study thermal buoyancy, the electromagnetic force and forced convection in a conventional radio frequency (RF) furnace for growing large-sized (4-inch) silicon carbide ingots using the top-seeded solution method. The thermal buoyancy and electromagnetic force are analyzed qualitatively and quantitatively under real working conditions, and a method to increase the growth stability of large-sized (4-inch) SiC is proposed through the study of forced convection.

Influence of silicon melt convection on interface instability in large-size silicon carbide solution growth

The interface instability in large-size silicon carbide solution growth has been investigated with a focus on the influence of silicon solution convection. Indications have shown that solution convection produces a substantial effect on the instability of the growth interface. As the SiC size increases, the instability becomes more evident. Therefore, improved solution convection is required for growing large-sized silicon carbide ingots by the solution method.

Thermodynamic Analysis of the Growth of Silicon Carbide Ingots in a Reducing Atmosphere

We have analyzed phase equilibria in the Si–C–H–Ar system during silicon carbide ingot growth by the modified Lely method. The results indicate that the addition of even small amounts of hydrogen to an inert carrier gas leads to a sharp increase in the rate of carbon transport through the gas phase, mediated by volatile hydrocarbons, primarily acetylene, and prevents carbon enrichment in the solid source and corrosion of the graphite equipment in the single-crystal seed region.

Control of Kerf Width in Multi-wire EDM Slicing of Semiconductors with Circular Section

Multi-wire EDM slicing method have been developed to overcome problems of conventional multi-wire saw method, and high-efficient and high-accurate slicing could be expected compared with a single-wire EDM technologies. Recently, a group power supplying method was newly proposed to satisfy both processing efficiency and simplification of slicing equipment, and it can supply sufficient discharge energy to multiple processing wire electrodes only using one conductivity piece set with one EDM power unit. Input energies were almost constant at each processing wire electrode, and electrical discharge pulses could be homogeneously distributed to each processing point without the wire breakage even by using only one conductivity piece set in the group power supplying method. This multi-wire EDM slicing method with the group power supplying can slice materials into many wafers of a certain thickness according to the pitch distance of processing wire electrode. In this method, it is important to perform the uniform kerf width in order to achieve a constant thickness of wafer. However, the cutting width of workpiece always varies in the case of silicon and silicon carbide ingots with circular cross section. Therefore, influence of cutting width of workpiece on slicing characteristics was experimentally investigated to achieve the uniform kerf width. The maximum feed rate of workpiece had a great influence on the kerf width with different cutting width of workpiece, and a larger kerf width was obtained with decreasing the cutting width of workpiece under a constant maximum feed rate condition. A uniform kerf width could be obtained by setting a half and quarter maximum feed rate of workpiece, although the cutting width of workpiece increased by twice or four times.

Heat Transfer Inside the Physical Vapor Transport Reactor

The physical vapor transport (PVT) method is widely adopted to produce semiconductor materials including silicon carbide (SiC). This work focuses on the role of thermal radiation for the heat transfer inside the PVT reactor. The radiation is characterized by two dimensionless parameters relating to the SiC charge and to the growth chamber. A simulation program is set up with the finite-volume method (FVM), considering heat generation, conduction, and radiation under the steady-state condition. Comprehensive results are obtained by tuning values of dimensionless parameters and the associated controlling variables, such as the cooling temperature and the coil current density, and illustrated in the phase diagrams. From the study, we find that the charge size has negligible influence on the temperature field, the crucible conduction determines the temperature level, and the relative strength of the chamber radiation against the crucible conduction modifies the temperature field on the SiC ingot. Finally, design guidelines are proposed with the instructive phase diagram to achieve the optimized thermal performance of the PVT reactor.

Comparison on foil EDM characteristics of single crystal SiC between in deionized water and in EDM oil

Slicing of single crystal silicon carbide (SiC) wafers by commonly used abrasive wire saw method is very time and cost consuming due to its extreme high hardness. This problem becomes more serious with the increase of SiC ingot diameter. Therefore, electrical discharge machining (EDM), which is a thermal process regardless of workpiece hardness, is developing as an alternative method for slicing SiC. In this study, EDM of SiC by a foil tool electrode was proposed for slicing SiC. Comparative experiments of foil EDM of SiC between in deionized water and in EDM oil were conducted. The tool electrode wear ratio, area cutting speed, kerf width, and surface integrity were experimentally investigated, and the reasons for the differences were discussed. It was clarified that foil EDM in deionized water can attain a higher cutting speed than that in EDM oil under the same machining conditions. However, the surface roughness and tool wear ratio were larger than in EDM oil. Short pulse duration was found to be more suitable for EDM of single crystal SiC in both dielectric liquids.

Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.

Study of EDM cutting of single crystal silicon carbide

Abstract Electrical discharge machining (EDM) is developing as a new alternative method for slicing single crystal silicon carbide (SiC) ingots into thin wafers. Aiming to improve the performance of EDM slicing of SiC wafers, the fundamental characteristics of EDM of SiC single crystal were experimentally investigated in this paper and compared to those of steel. Furthermore, EDM cutting of SiC ingot by utilizing copper foil electrodes was proposed and its performance was investigated. It is found that the EDM characteristics of SiC are very different from those of steel. The EDM machining rate of SiC is higher and the tool wear ratio is lower compared to those of steel, despite SiC having a higher thermal conductivity and melting point. Thermal cracks caused by the thermal shock of electrical discharges and the Joule heating effect due to the higher electrical resistivity are considered to be the main reasons for the higher material removal rate of SiC. It is concluded that the new EDM cutting method utilizing a foil electrode instead of a wire electrode has potential for slicing SiC wafers in the future.

Slicing of Rotating SiC Ingot by Electric Discharge Machining

A new method of electric discharge machining (EDM) is proposed for slicing a large silicon carbide (SiC) ingot in order to realize low kerf loss and fast cut. This principle is based on the rotating ingot, and it is called the rotating slicing method (RSM). It would be defecate the cutting chip effectively and one-point discharge. In this paper, we reported results of examinations of the RSM experimentally. Unstable discharge was not observed. Discharge damages on the wire surface were fewer than those of the conventional method. Net cutting speed was almost the same as the present method for the 2-inches ingot. The rotation axis of the ingot should be perpendicular to the feed direction of the wire, and it is important to fix the performance of the EDM such as the kerf loss. Roughness of the cutting surface was 3.4 µm of Ra

Fundamental Study on Multi-wire EDM Slicing of SiC by Wire Electrode with Track-shaped Section

High efficient and precise slicing method is required for the slicing of silicon carbide ingot. The newly developed multi-wire electrical discharge slicing method would decrease the kerf width and the cracks generated on machined surface. However, much higher wire tension is required in order to reduce wire vibration and to perform a smaller kerf width. Thin wire electrode with round section does not have enough cross sectional area under the high wire tension condition. Therefore, a wire electrode with track- shaped section was proposed and applied to the wire EDM slicing of silicon carbide ingot. The running control of wire electrode with track-shaped section was experimentally investigated. The side support method with fixture plates could decrease the kerf width by brass coated steel wire electrode with track-shaped section. The parallel drawing type traverser and the short distance setting points of side support fixture plates could perform the smaller vibration of w ire electrode with track-shaped section and the decrease of kerf width.

Experimental Investigations into EDM Behaviors of Single Crystal Silicon Carbide

The present study aims to investigate the fundamental electrical discharge machining (EDM) characteristics of silicon carbide (SiC) single crystal material. The EDM machining performances of SiC are experimentally studied and compared to that of steel. Die-sinking EDM of SiC by utilizing copper foil electrodes was proposed and investigated. It was found that EDM characteristics of SiC have a big difference from those of steel. The EDM speed of SiC is higher and the tool wear ratio is lower compared to that of steel material, although SiC has a higher thermal conductivity and melting point. Thermal crack caused by the thermal shock of electrical discharges was found as another main factor contributing to the removal of the material in EDM of SiC material. Also it is concluded that the new foil EDM method for slicing SiC ingot has potential for slicing SiC wafers in the future.

Growth of 4H silicon carbide crystals on a (11 $$ \bar 2 $$ 2) seed

The features of the defect structure of 4H silicon carbide ingots grown by the modified Lely method on (11\( \bar 2 \)2)-oriented seeds are studied. It is shown that this seed plane can be used to improve the structural quality of silicon carbide ingots. The defect structure of grown ingots features a complete lack of micropores and a decreased (by an order of magnitude) dislocation density in comparison with the seed. At the same time, growth on the (11\( \bar 2 \)2) seed results in stacking fault accumulation. The type of stacking faults corresponds to formula (5, 2) in the Zhdanov notation (internal Frank stacking fault).

Cutting Speed of Electric Discharge Machining for SiC Ingot

A new method based on electric discharge machining (EDM) was developed for cutting a silicon carbide (SiC) ingot. The EDM method is a very useful technique to cut hard materials like SiC. By cutting with the EDM method, kerf loss and roughness of sample are generally smaller than those obtained by cutting with a diamond saw. Moreover, the warpage is smaller than that by the diamond saw cutting, and the cutting speed can be 10 times faster than that of the diamond saw at the present time. We used wires of 50 mm and 100 mm diameters in the experiments, and the experimental results of the cutting speed and the kerf losses are presented. The kerf loss of the 50 mm wire is less than 100 mm, and the cutting speed is about 0.8 mm/min for the thickness of a 6 mm SiC ingot. If we can maintain the cutting speed, the slicing time of a 2 inches diameter ingot would be about seven hours.

A technique for diameter enlargement in SiC crystal growth

Abstract The availability of large high-quality silicon carbide (SiC) single crystals is a key issue in the development of the full potential of SiC-based device technology. This paper mainly discusses SiC crystal growth in the graphite crucible with several geometrical structures by using the physical vapor transport method to investigate the influence of graphite crucible structures on SiC crystal diameter enlargement. Metallographic microscopy and X-ray diffraction are applied to the obtained cross-sectional slice of SiC ingot. In a growth run with a crucible structure of cylinder platform seed-holder and additional cone-shaped inner furnace close to the seed crystal, the SiC crystal diameter increases only 4–5 mm and the growth front exhibits a smooth segment of spherical shape; but the diameter of SiC single crystal decreases when the inside diameter of the crucible is close to that of the seed crystal and the angle α between the cone-shaped platform and cylinder platform is larger than 20°. When using the crucible with a cone-shaped platform seed-holder and cone-shaped inner wall, the SiC crystal growth will proceed along the axial direction as well as the radial direction, and the diameter can be enlarged by about 12 mm in a single growth run.

Defect structure of 4H silicon carbide ingots

Defects caused by 15R polytype inclusions in 4H silicon carbide ingots have been considered. Growth rate along with curvature of the interface determines the stability of the 4H-polytype reproduction. The domain structure arising in the 4H polytype as a result of foreign polytype inclusion has been analyzed. Antiphase domains of the 4H polytype emerging at the top and lateral sides of 15R inclusion form a strictly determined set of binary and ternary joints (extended threading defects). Junctions of a higher order could generate open-core threading superdefects.

New approach to rapid characterization of single-crystalline silicon carbide

A new approach to the characterization of single-crystalline silicon carbide (SiC) ingots is proposed, which can be used for the rapid diagnostics of material quality under large-scale commercial production conditions. The proposed method can reveal various defects, such as polytype inclusions, small-angle grain boundaries, dislocations, micropipes, and inhomogeneous dopant distribution and can be used to optimize technological regimes for growing bulk SiC single crystals.

Optimization of structural perfection of 4H-polytype silicon carbide ingots

The degree of structural perfection of 4H-polytype silicon carbide ingots grown by the modified Lely method was improved using a multistage process with sequential change in the seed orientation (similar to the previously suggested RAF process). The grown ingots 20–40 mm in diameter are characterized by an almost total absence of peripheral low-angle boundaries and a significant decrease in the micropore density (two-three orders of magnitude in comparison with the starting material). Repeated shouldering of obtained seeds with (000\( \bar 1 \))C orientation up to 50–55 mm in diameter results in insignificant deterioration of the structural quality in newly formed peripheral regions of the ingot. High-quality perfect silicon carbide wafers were obtained, characterized by a micropore and basal dislocation densities of 5–40 and 103–104 cm−2, respectively.

Growth of 4H-polytype silicon carbide ingots on (10 % MathType!MTEF!2!1!+- % feaagaart1ev2aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXguY9 % gCGievaerbd9wDYLwzYbWexLMBbXgBcf2CPn2qVrwzqf2zLnharyav % P1wzZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC % 0xbbL8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yq % aqpepae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabe % qaamaaeaqbaaGcbaGafGymaeJbaebaaaa!3CDF! $$ \bar 1 $$ 0) seeds

The growth of 4 H-polytype silicon carbide ingots by the modified Lely method on (10\( \bar 1 \)0) seeds has been investigated. It is shown that this seed plane allows intense ingot outgrowth. Single-crystal ingots up to 60 mm in diameter can be obtained at growth rates below 0.6 mm/h. Investigation of the defect structure showed that the grown ingots are practically micropipe-free but contain stacking faults and carbon inclusions.