Thermal Field System of CZ Single-Crystal Silicon Furnaces Based on Molybdenum Components

In the Czochralski (CZ) single-crystal silicon growth process, the thermal field system is one of the most critical subsystems in a crystal growth furnace. The performance of the thermal field system directly affects temperature distribution, thermal gradients, crystal growth stability, and final crystal quality—especially in large-diameter CZ furnaces (18–24 inch and above).

Modern CZ thermal field systems rely heavily on molybdenum components due to their excellent high-temperature strength, low vapor pressure, and stable performance in vacuum or inert gas environments. As crystal diameters increase, the use of molybdenum thermal field parts becomes increasingly essential.

Role of the Thermal Field in Crystal Growth

The thermal field system in a CZ furnace plays several key roles:

• Supplying stable high-temperature heat for silicon melting

• Maintaining precise axial and radial temperature gradients

• Reducing radiant heat loss through molybdenum heat shields and reflectors

• Stabilizing the solid–liquid interface during crystal pulling

• Supporting long-term continuous operation under high vacuum

Because these functions operate at temperatures exceeding 1600 °C, molybdenum materials are widely used to ensure thermal stability and mechanical reliability.

Main Components of a CZ Furnace Thermal Field System

Molybdenum Heater Assembly

The heater assembly is the core heat source of the CZ furnace thermal field system.

• Commonly manufactured from molybdenum heaters or molybdenum heating elements

• Offers excellent resistance stability and long service life

• Suitable for repeated thermal cycling under extreme temperatures

Compared with graphite heaters, molybdenum heaters provide lower contamination risk and more stable performance in advanced CZ furnace applications.

Molybdenum Heat Shields and Thermal Reflectors

Heat shields and thermal reflectors are critical for controlling heat radiation and improving thermal efficiency.

• Typically fabricated from molybdenum sheets, molybdenum plates, or molybdenum foils

• Installed in multi-layer configurations around the hot zone

• Reduce heat loss and improve temperature uniformity

Molybdenum heat shields are essential for maintaining stable thermal gradients and achieving consistent crystal diameter control.

Crucible Support and Molybdenum Structural Components

Structural components ensure stable support and precise positioning of the quartz crucible.

• Include molybdenum crucible supports, molybdenum rings, molybdenum spacers, and load-bearing frames

• Must maintain mechanical strength at high temperature

• Resist deformation during long-term furnace operation

Due to its high melting point and dimensional stability, molybdenum structural parts are widely used in large-diameter CZ furnaces.

Bottom Shields and Gas Flow Control Components

Bottom shields and gas flow guiding components regulate heat transfer beneath the crucible and control internal gas circulation.

• Commonly manufactured from molybdenum plates and molybdenum fabricated parts

• Improve vertical thermal gradient control

• Help reduce thermal stress and crystal defects

These molybdenum bottom shields contribute significantly to thermal field stability.

Why Molybdenum Is the Preferred Material for CZ Thermal Fields

Molybdenum is the preferred refractory metal for CZ furnace thermal field systems because of its unique properties:

• High melting point of 2623 °C

• Excellent high-temperature mechanical strength

• Extremely low vapor pressure in vacuum environments

• Good thermal conductivity and dimensional stability

• Low contamination risk for semiconductor-grade silicon

As CZ furnaces scale to larger diameters, the demand for high-purity molybdenum thermal field components continues to grow.

Molybdenum Thermal Field Optimization for Large-Diameter CZ Furnaces

For 18–24 inch CZ furnaces, thermal field optimization increasingly depends on molybdenum component design and quality, including:

• Optimized molybdenum heater geometry

• Multi-layer molybdenum heat shield structures

• Improved heat flow uniformity through precision-machined molybdenum parts

• Extended service life of molybdenum components under continuous operation

Advanced molybdenum thermal field systems help reduce operating costs while improving crystal yield and consistency.

Conclusion

The thermal field system is the heart of a CZ single-crystal silicon furnace, and molybdenum plays a central role in its performance. From molybdenum heaters and heat shields to molybdenum structural and support components, molybdenum materials ensure stable operation under extreme thermal and vacuum conditions.

For CZ furnace manufacturers and silicon crystal growth engineers, selecting high-quality molybdenum thermal field components is essential to achieving reliable crystal growth, high yield, and long-term process stability.