As a commonly used container in the semiconductor industry, the quality and stability of quartz crucibles are crucial for the growth of single crystal silicon. However, during high-temperature use, quartz crucibles often exhibit crystallization phenomena, which not only affect the strength and lifespan of the crucible, but may also lead to a series of problems during the growth process of single crystal silicon.

1. Phase transition characteristics of quartz crucible

The quartz crucible itself is amorphous, but under appropriate conditions, it undergoes a phase change from an amorphous state to a stable quartz crystal state. This phase transition includes two stages: nucleation and growth. Nucleation usually occurs at structural defects or impurities on the walls of quartz crucibles, especially at locations containing some alkaline or heavy metals. The initial quartz crystals are spherical in shape, and further growth develops in a dendritic pattern along the crucible wall, due to the suppression of vertical growth. Crystallization usually occurs on the surface of quartz crucibles. According to the Chinese quartz glass industry standard, quartz glass used in the semiconductor industry should be kept at 1400 ℃± 5 ℃ for 6 hours, and the average thickness of its crystallization layer should be<100 µ m.

2. Pollution caused by metal ions

Staining of quartz crucibles is one of the main factors leading to crystallization, especially alkali metal ions such as potassium (K), sodium (Na), lithium (Li), and alkaline earth metal ions such as calcium (Ca) and magnesium (Mg). These ions may originate from impurities in the raw materials or be introduced during the production process. The presence of these metal ions can accelerate the crystallization process of quartz crucibles, causing the crystallization layer to become thicker, and in severe cases, even penetrating the entire crucible body, resulting in serious consequences such as silicon leakage.

3. Pollution during the loading process

During the process of filling silicon materials, pollutants such as sweat, saliva, oil stains, and dust may also cause quartz crucible crystallization. These pollutants react with quartz crucibles at high temperatures, promoting the occurrence of crystallization. Therefore, the loading process needs to be strictly controlled to ensure a clean and hygienic operating environment.

4. Volatile pollution of graphite materials

The use of new graphite materials without thorough calcination or contamination is one of the main reasons for the crystallization of the outer layer of quartz crucibles. Graphite materials will evaporate some impurities at high temperatures, which react with quartz crucibles and cause outer layer crystallization. Therefore, new graphite devices need to undergo thorough high-temperature calcination before use to remove impurities and volatiles.

5. Low purity of silicon material

The raw materials used for crystal pulling have low purity, contain too many impurities, or have problems with the cleaning process, which can also cause quartz crucible crystallization. Low purity silicon materials contain a large amount of impurities, which react with quartz crucibles at high temperatures, promoting crystallization. Therefore, the purity of the raw materials used for crystal pulling must meet the production requirements, and the cleaning quality of the raw materials must also meet the process requirements to avoid residual acid and alkali on the surface of the silicon material.

6. The temperature of the melt is too high

Excessive temperature during melting can also increase the degree of crystallization. Prolonged insulation of quartz crucibles at high temperatures can accelerate the occurrence of crystallization. Therefore, it is necessary to choose an appropriate melting temperature during the melting process to reduce or decrease the degree of crystallization.

7. Quality issues with the quartz crucible itself

The geometric dimensions and appearance of quartz crucibles are determined by the production process, while the purity is determined by the raw materials. When the harmful components inside the quartz crucible are high, it will affect the melting and temperature resistance of the crucible, and even cause phenomena such as bubbles, color spots, and peeling, seriously affecting the quality of the quartz crucible. Therefore, manufacturers of quartz crucibles must ensure that their crucibles meet quality requirements at every stage of production, from raw materials to production.

8. Effects of crucible deformation

After the deformation of the quartz crucible, as the crucible position rises during the crystal pulling process, the protruding part of the deformation will collide with the guide tube, affecting or preventing normal crystal pulling. Crystallization will thin the original thickness of the quartz crucible, reduce its strength, and easily cause deformation of the quartz crucible. The deformed crucible not only affects the crystal pulling process, but may also cause the crucible to break, resulting in serious production accidents.

The reasons for crystallization in quartz crucibles are multifaceted, including the phase transition characteristics of quartz crucibles, contamination by metal ions, contamination during the loading process, volatilization contamination of graphite materials, low purity of silicon materials, high melting temperature, quality problems of quartz crucibles themselves, and the influence of crucible deformation. In order to reduce the occurrence of crystallization, strict control is needed from all aspects to ensure the quality and stability of the quartz crucible.

Luverre Quartz manufactures and sells a wide range of high quality quartz glass, including quartz tubes, quartz plates, quartz rods, quartz windows, quartz crucibles, quartz boats, quartz flanges, quartz beakers, quartz glass instruments, and more. We can meet all kinds of customized requirements for quartz glass products.