Design, manufacture and function of graphite thermal field

Design, manufacture and function of graphite thermal field

The thermal system of the Czochralski single crystal furnace is the so-called thermal field. The function of the graphite thermal field system refers to the entire system for melting the silicon material and keeping the single crystal growth at a certain temperature.
Graphite thermal field generally includes (graphite material) pressure ring, insulation cover, upper, middle and lower insulation cover, graphite crucible (three-petal crucible), crucible support rod, crucible tray, electrode, heater, guide tube, graphite bolt. In order to prevent silicon leakage, the furnace bottom, metal electrodes, and supporting rods are all equipped with protective plates and protective sleeves.
The graphite thermal field of the single crystal furnace is simply a complete graphite heating system for pulling single crystal silicon. The common ones are 18-inch, 22-inch and 24-inch graphite thermal fields. A popular industry standard design solution for graphite thermal fields is to use graphite materials to make thermal field insulation components. Standard graphite insulation materials are composed of plate-like or multi-layer blanket-like graphitized carbon fiber materials. The inner surface near the center of the thermal field often needs to be covered with a layer of graphite paper or carbon-carbon composite material sheet to improve heat reflectivity and prevent high pressure air wash.
Due to the porosity and permeability of the isostatic graphite heat field material itself, there is no need to reserve additional space between layers of heat insulation materials. Graphite materials have excellent thermal insulation properties, are generally less expensive than metal screens, and are very easy to use. In terms of manufacturing cost, durability and maintainability, graphite insulation soft felt has certain advantages over graphite insulation rigid felt. Through production practice, metal heat shields are often not suitable for vacuum brazing processes with harsh environments.
Graphite thermal field manufacturers use graphite materials to make thermal insulation parts of graphite thermal field. Practice has proved that although Although there will be a lot of solder deposited on the surface of the graphite insulation material during the brazing process, the fusion of the molten solder and the graphite insulation material will not occur. Although some people may question that graphite materials are more likely to absorb moisture than metal materials, and moisture is very harmful to the brazing process, but practice has proved that the repeated heating and cooling of the thermal field will well eliminate the moisture in graphite insulation materials.

The characteristics of the graphite thermal field are as follows:

1. The thermal field of single crystal silicon graphite is a comprehensive theory of physics, chemistry and geometry, which has been repeatedly verified by specialized researchers for many years. Formulated based on years of experience.
2. The thermal field adopts fine-structure medium-coarse graphite as the furnace bottom protection plate, heat preservation cover, and upper and lower covers. Imported isostatic graphite is used as the heater, crucible, guide tube, support rod, pot holder, etc., which ensures the strength and purity of the graphite crucible.
3. The thermal field is one of the important conditions for the crystallization of single crystal silicon. The gradient distribution of the thermal field directly affects whether the single crystal can be pulled out, as well as the quality of the pulled single crystal. The quality of the material directly affects the life of the thermal field .