Quartz crucible: an indispensable container for photovoltaic, semiconductor and other industries
1. Understanding the Quartz Crucible
Quartz crucibles have the advantages of high purity, strong temperature resistance, large size, high precision, and good heat preservation. Especially in the process of silicon crystal growth, the quartz crucible has become an irreplaceable key component!
Quartz crucibles can be used below 1450°C and are divided into two types: transparent and opaque. The earliest quartz crucibles were all transparent. This transparent structure easily led to uneven heat transfer conditions and increased the difficulty of ingot growth, so this kind of crucible was eliminated.
At present, translucent quartz crucible is an indispensable basic material for pulling large-diameter single crystal silicon and developing large-scale integrated circuits. Today, the developed countries of the world’s semiconductor industry have replaced the small transparent quartz crucible with this crucible. The translucent quartz crucible has the advantages of high purity, strong temperature resistance, large size and high precision, good heat preservation, energy saving and stable quality.
2. The production process of quartz crucible
According to different preparation processes and uses, quartz crucibles are divided into arc quartz crucibles and quartz ceramic crucibles. The arc quartz crucible is mainly used for Czochralski monocrystalline silicon, which is manufactured by the arc method (that is, used in the semiconductor field);
Quartz ceramic crucibles are mainly used for polycrystalline silicon ingots, using general ceramic preparation methods such as grouting or injection molding.
Large-diameter single crystal silicon (above 200mm) is basically produced by the Czochralski (CZ) method. It takes more time and more resources to grow such a large-sized silicon crystal.Therefore, it is very important to improve the success rate of silicon crystal growth per furnace.
During the growth of Czochralski silicon crystals, dislocation-free single crystal growth can fail due to various reasons, resulting in a great loss of resources and time.
There are many reasons for the failure of dislocation-free single crystal growth. Under the current conditions of stable and mature Czochralski silicon single crystal furnace and its thermal field design, the purity of the quartz crucible in direct contact with the silicon melt and the release of tiny cristobalite particles during growth are generally considered to be one of the main reasons for the failure of the growth of large-diameter dislocation-free Czochralski crystals.
In other words, the quality of the arc quartz crucible is the main factor affecting the quality of Czochralski monocrystalline silicon. Therefore, the continuous improvement of the quality requirements for large-diameter single crystal silicon has put forward higher requirements for quartz products and related materials for semiconductor materials.
Such as quartz sand inspection, quartz sand purification, initial arc melting inspection, outer wall cleaning, cutting height, chamfering, cleaning, coating, drying, final inspection, packaging, shipping, etc.
The two production processes of quartz ceramic crucibles are roughly the same. However, due to the differences in production methods, the selection of supporting equipment for the two processes is still different.
(1) Grouting production process
The general production process of the grouting method: grouting – demoulding – turning – curing – initial inspection – repairing – drying – calcining – trimming – final inspection – packaging
Since the demoulding time of injection molding is generally 8 hours, the molding efficiency is relatively low, and the output should not be too large.
(2) Production process of injection coagulation method
General production process of injection coagulation method: grouting – demoulding – turning – initial inspection – repairing – drying – calcining – trimming – final inspection – packaging
Because the grouting method relies on the water absorption of the plaster mold to dry, the demoulding time is long and the production efficiency is low.
The injection molding method uses a steel mold, but there are additives in the product ingredients. The green body can be quickly solidified and formed during the production process, improving the strength and easy to quickly demould. And the strength of the green body after demoulding is high, and it does not need to be cured by a curing furnace.
It can be seen from the above comparative analysis that the two production processes are only the injection coagulation method and do not require a curing furnace to cure the green body, and the process flow is basically the same.
3. Use and maintenance of quartz crucible
The main chemical composition of quartz crucible is silicon dioxide, which does not interact with other acids except hydrofluoric acid, and is easy to interact with caustic alkali and alkali metal carbonate;
The quartz crucible has good thermal stability and can be heated directly on the flame;
Quartz crucibles are easily broken, so be careful when using them;
Quartz crucible can use potassium hydrogen sulfate (sodium), sodium thiosulfate (drying at 212 ℃) as flux, and the melting temperature should not exceed 800 ℃.
4. The demand analysis of quartz crucible
In terms of service life, the ideal life of the quartz crucible is 400 hours+, and the worst case is about 300 hours. (Note: The service life of the quartz crucible corresponding to the N-type silicon wafer is 50-100 hours lower than that of the P-type silicon wafer, that is, the life of the quartz crucible for the P-type silicon wafer is about 400 hours, and the life of the quartz crucible for the N-type silicon wafer is 300-350 hours).
Quartz crucible consumption of a single crystal furnace: At present, a single crystal furnace of P-type silicon wafer uses an average of 2 quartz crucibles a month (720 hours) and 24 quartz crucibles a year. Quartz crucible consumption of 1GW silicon wafer: 1GW182 silicon wafer production capacity corresponds to 100 single crystal furnaces, and 1GW silicon wafer shipment corresponds to about 2400 quartz crucibles.
Quartz crucibles are mainly used in semiconductor, photovoltaic and other fields. Due to the high degree of product precision and rapid technological development in the photovoltaic industry, the requirements for the purity and precision of quartz crucibles are becoming increasingly strict.