Carbon-based Thermal Field System

1. The Role of Carbon-Based Thermal Fields Has Evolved from Insulation Components to Process Window Regulators

The value of a carbon-based thermal field extends far beyond traditional thermal insulation. In modern crystal growth systems, it functions as a comprehensive process control platform that directly influences crystal quality, productivity, and operating costs. Its core functions can be summarized into four levels:

Functional Level	Primary Function	Key Performance Indicators
Structural Support	Supports quartz crucibles, heaters, heat shields, and insulation cylinders to ensure the mechanical stability of large-scale thermal field systems.	Furnace size, thermal field dimensions, crucible size, and charging capacity
Heat Distribution	Controls radiation, conduction, and convection pathways, regulating the thermal balance between the melt and crystal growth interface.	Temperature gradient, interface shape, pulling rate, and energy consumption
Gas Flow Management	Guides argon flow and, in SiC PVT systems, vapor-phase material transport while removing volatile species such as SiO and CO.	Flow field characteristics, oxygen and carbon impurity levels, deposit formation, and thermal field lifetime
Quality Control	Influences oxygen concentration, carbon concentration, resistivity uniformity, dislocation density, stress distribution, and crystal structure stability.	N-type silicon compatibility, SiC polytype control, and defect management

Publicly available equipment specifications indicate that photovoltaic Czochralski (CZ) crystal growth technology has entered a new stage characterized by larger furnaces, larger thermal fields, increased charging capacity, intelligent crystal pulling, and advanced low-oxygen control.

According to published specifications, some advanced crystal growth systems feature a main chamber size of Φ1700 × 2100 mm and support thermal fields up to 42 inches in diameter. Compatible crucible sizes include 33, 37, 40, and 42 inches, corresponding to charging capacities of approximately 700 kg, 1000 kg, 1200 kg, and 1300 kg, respectively.

In addition, these systems demonstrate significant improvements in operational efficiency, including:

· Constant-diameter growth power consumption as low as 42 kW

· Cooling water consumption as low as 20 m³/h

· Daily crystal output exceeding 200 kg

· Compatibility with Continuous Czochralski (CCz) technology and magnetic field-assisted crystal growth configurations

These developments indicate that thermal field design has become a critical factor in determining crystal quality, production efficiency, and overall manufacturing cost.

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2. Furnace Dimensions

2.1 Photovoltaic CZ Single Crystal Growth Furnaces

The scaling of CZ crystal growth furnaces involves far more than simply increasing furnace dimensions. Successful large-scale furnace design requires coordinated optimization of the following parameters:

· Main chamber diameter

· Auxiliary chamber height

· Throat opening dimensions

· Crucible size

· Heat shield clearance

· Feeding interfaces

· Vacuum and exhaust pathways

The typical engineering logic behind large-scale furnace design is summarized below:

Parameter	Engineering Significance	Impact on Thermal Field Performance
Main Chamber Diameter	Determines the maximum thermal field diameter, insulation thickness, and heater dimensions.	Larger chambers increase thermal inertia, resulting in slower temperature response.
Throat Opening Size	Determines the allowable dimensions of crystal rods, heat shields, guide cylinders, and upper shaft assemblies.	An excessively small throat limits thermal field and flow-guiding structure design flexibility.
Auxiliary Chamber Height	Determines crystal length capability, cooling space, and crystal extraction cycle time.	Greater height supports longer crystal growth and higher production potential.
Crucible Diameter	Determines initial charging capacity, melt depth, and oxygen dissolution area.	Larger crucibles increase productivity but make oxygen control more challenging.
External Feeding Interface	Enables OCz, CCz, or multiple recharge operations.	Extends production cycles and increases output, but also raises impurity accumulation risks.

Two different charging metrics should be distinguished:

Initial Charge Capacity

This refers to the amount of raw material loaded into the crucible at one time and is directly determined by crucible size. Publicly available equipment specifications typically indicate capacities ranging from 700 kg to 1300 kg.

Total Charge Capacity per Furnace Campaign

This includes multiple recharge cycles or continuous feeding operations during a complete production run. As a result, the total material processed during a furnace campaign can be significantly higher than the initial charge.

For example, industry comparisons disclosed in public prospectus documents indicate that:

· A 32-inch thermal field can process up to 3000 kg of material per furnace campaign.

· A 36-inch thermal field can process up to 3500 kg of material per furnace campaign.

These values represent total production during an entire operating cycle rather than the one-time loading capacity of the crucible.

2.2 SiC PVT Crystal Growth Furnaces

Scaling silicon carbide (SiC) PVT crystal growth furnaces is considerably more challenging than enlarging conventional silicon CZ systems.

Unlike the Czochralski process, SiC crystals are not grown from a molten phase. Instead, Physical Vapor Transport (PVT) relies on the sublimation of SiC source powder at extremely high temperatures. The generated vapor species are transported along an axial temperature gradient and subsequently crystallize on a relatively cooler SiC seed crystal.

A study published by the Royal Society of Chemistry (RSC, 2026) on 150 mm SiC PVT crystal growth describes the thermal system as consisting of five primary components:

· Thermal insulation felt

· Graphite crucible

· SiC seed crystal

· SiC source material

· Resistance heater

During crystal growth, the source powder sublimates under high temperature, producing vapor-phase species that migrate upward under the temperature gradient before depositing on the lower-temperature seed crystal to form a single crystal.

Consequently, increasing the size of a SiC PVT furnace is not simply a matter of achieving higher temperatures. The primary engineering challenges include:

a. Maintaining a sufficient axial temperature gradient to continuously drive the sublimation–transport–crystallization process.

b. Minimizing radial temperature gradients to reduce thermal stress, prevent crystal cracking, and suppress polytype transformation.

c. Preserving thermal field stability throughout the growth process as the source powder is gradually consumed.

d. Maintaining a controllable crystal growth interface during the transition to 8-inch and future 12-inch SiC wafer production.

Compared with silicon crystal growth, the thermal field in SiC PVT systems must provide significantly higher temperature stability and more precise thermal control, making thermal field design one of the most critical technologies for large-diameter SiC crystal production.

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3. Critical Coupling Between Equipment Design and Thermal Field Performance

The interaction between furnace configuration, thermal field design, crystal quality, and manufacturing cost can be summarized as follows:

Equipment / Process Variable	Thermal Field Response	Crystal Quality Response	Cost Impact
Larger Furnace Size	Higher thermal inertia and longer gas flow paths	More difficult to maintain radial temperature uniformity	Higher production capacity but increased commissioning costs
Larger Thermal Field	Improved thermal insulation with reduced heat loss	More challenging oxygen and carbon impurity control	Lower depreciation cost per wafer but higher thermal field component cost
Larger Crucible	Increased melt volume and greater oxygen dissolution from crucible walls	Higher risks of oxygen concentration fluctuation and resistivity variation	Greater charging capacity and reduced production cost per kilogram
Deeper Heat Shield Position	Enhanced crystal cooling and increased axial temperature gradient (G)	Higher pulling speed potential but increased interface instability risk	Improved productivity while requiring stricter control of crystal breakage
Increased Argon Flow Rate	Stronger impurity removal and enhanced convective heat transfer	Lower oxygen and carbon concentrations but potentially greater temperature fluctuations	Increased argon consumption and higher vacuum pumping requirements
Reduced Furnace Pressure	Enhanced evaporation and volatile species removal	Modified deposition and back-diffusion mechanisms	Higher requirements for exhaust system performance and sealing reliability
Higher Pulling Speed	Increased latent heat release requiring stronger cooling capacity	Greater V/G variation and higher dislocation risk	Higher throughput with potential reduction in production yield
Multi-Zone Heater Control	Improved temperature field controllability	Better optimization of crystal interface shape and oxygen transport	Increased equipment complexity and commissioning cost
Magnetic Field / CCz Technology	More stable melt convection and continuous feeding	Improved low-oxygen control and resistivity uniformity	Higher capital investment while enabling advanced N-type silicon production
Multi-Zone SiC Thermal Field	Independent optimization of axial driving force and radial temperature uniformity	Reduced polytype transition, dislocation density, and crystal cracking	Higher crystal yield with increased control system complexity

 

The continuous evolution of crystal growth equipment demonstrates that the thermal field is no longer merely a passive structural assembly. Instead, it has become an integrated process-control system that simultaneously governs heat transfer, fluid dynamics, mass transport, impurity distribution, and crystal quality.

As wafer diameters continue to increase and semiconductor materials become more advanced, future thermal field systems will increasingly rely on digital simulation, multi-physics optimization, intelligent temperature control, and customized carbon-graphite component design to achieve higher productivity, lower defect densities, and improved manufacturing efficiency.

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Semicorex supplies a comprehensive portfolio of high-performance graphite and quartz components for advanced thermal field systems used in silicon and SiC crystal growth applications. Our products are engineered to deliver superior thermal stability, extended service life, and exceptional process consistency. For customized solutions or additional technical information, please feel free to contact our engineering team.

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