Single crystal silicon is a crystal with a substantially complete lattice structure, that is, a crystal with substantially the same crystal lattice orientation. However, different crystal plane directions have different properties and are a good semiconductor material. The purity requirement is over 99.999%. It is currently the best material for manufacturing solar cells. It is made by drawing high-purity polysilicon in a single crystal furnace.
As shown in Figure 1-1 are various monocrystalline silicon photovoltaic panels (monocrystalline silicon cell components).
Figure 1-1 Monocrystalline silicon cell components
When molten elemental silicon is solidified, silicon atoms are arranged in a diamond lattice to form many crystal nuclei. If these crystal nuclei grow into crystal grains with the same crystal lattice orientation, they will form single crystal silicon. Single crystal silicon has the physical properties of a metalloid and has weaker conductivity. Its conductivity increases with the increase of temperature, and it has significant semiconductivity. Ultra-pure single crystal silicon is an intrinsic semiconductor. Doping a trace amount of group IIIA element (such as boron) into ultrapure single crystal silicon can improve the conductivity and form a P-type silicon semiconductor; if doping a trace amount of group VA element (such as phosphorus) can also improve its conductivity, forming N-type silicon semiconductor.
(1) The manufacturing method of single crystal silicon The manufacturing method of single crystal silicon is usually to make polycrystalline silicon or amorphous silicon first, and then use the Czochralski method or the suspension zone melting method to grow rod-shaped single crystal silicon from the melt. According to different crystal growth methods, it is divided into Czochralski method, zone melting method and epitaxy method. Czochralski method and zone melting method are used to grow monocrystalline silicon rods, and epitaxial method is used to grow monocrystalline silicon thin films. The monocrystalline silicon grown by the Czochralski method is mainly used in solar cells and other semiconductor materials, such as diodes. Due to cost and performance reasons, the Czochralski method is the most widely used in the production of monocrystalline silicon materials. At present, the diameter of monocrystalline silicon crystals can be controlled within the range of ∮3~8in (lin=2.54cm). Japan, the United States and Germany are the major silicon material producers. The production technology level of China’s silicon material industry is relatively low, and most of them are
2.5in, 3in, 4in, 5in silicon ingots. Because the silicon ingot is small, only small-diameter silicon wafers can be produced. In order to reduce production costs, solar cells used on the ground now use solar-grade monocrystalline silicon rods, and their material performance indicators have been relaxed. Some can also use the head and tail materials and waste monocrystalline silicon materials processed by semiconductor devices, and make them into monocrystalline silicon rods for solar cells after redrawing.
(2) The development trend of monocrystalline silicon materials in the world
① The monocrystalline silicon products are transitioning to 300mm, and the trend of larger diameter is obvious. According to statistics, the global consumption of 200mm silicon wafers accounts for about 60%, 150mm for about 20%, and the rest for about 20%. There are about 40 300mm silicon device production lines currently built, under construction and planned to be built in the world, mainly distributed in the United States and Taiwan, China.There are more than 20 production lines in Taiwan, China, and the rest are in Japan, South Korea, Singapore and Europe.
②The development of the silicon material industry is becoming more internationalized, grouped, and production is highly concentrated. Due to the increasing production costs of R&D and construction of solar cell factories, coupled with the advantages of existing brands and sales channels, the silicon material industry is prone to form a “bigger Hengda” situation, becoming a material monopolized by large group companies, and its market share very high
③Silicon-based materials have become an important direction for the development of the silicon material industry. This is because silicon-based materials have many excellent properties (the content has been described above). In addition, the silicon wafer manufacturing technology has been further upgraded, which has made significant progress in wafer production technology. In Japan, 50% of ∮200mm silicon wafers have been sliced by wire cutting machines, which not only improves the quality of silicon wafers, but also reduces cutting losses by 10%.