Seeking information on polysilicon technology and management

Basic knowledge of high-purity polysilicon. The popularity of polysilicon in recent years is comparable to that of lottery tickets in the late 1980s. Given that many people are not familiar with the production processes related to polysilicon, this post provides basic information to help those who are not aware of the polysilicon industry understand it better. Polysilicon material refers to silicon material composed of two or more single-crystalline silicon grains of different sizes, and its material properties exhibit isotropy. Amorphous silicon materials are those in which silicon atoms are arranged in an orderly manner over short distances, but in a disordered manner over longer distances; such materials exhibit isotropic properties. At present, the large-scale production of high-purity polysilicon is monopolized by a few developed countries such as the United States, Japan, and Germany. Since the production of polysilicon must be on a large scale (at least several thousand tons per year) to be profitable, coupled with technical complexity, proprietary nature and confidentiality, as well as the difficulties faced by new entrants in entering the market, it is quite challenging to establish an advanced and large-scale polysilicon production facility. Metallurgical-grade silicon is the raw material used to produce semiconductor polysilicon; it is obtained by reducing quartz sand (silicon dioxide) with carbon in an electric arc furnace. Although silica ores are found everywhere in nature, only a few of them can be used to produce metallurgical-grade silicon. Generally, the silica content in the ore is required to be above 97%~98%, and there are strict limits on the levels of various impurities, especially arsenic, phosphorus, and sulfur. In the metallurgical silicon used to produce high-purity polycrystalline silicon, in addition to containing over 99% silicon (Si), it also contains elements such as iron (Fe), aluminum (Al), calcium (Ca), phosphorus (P), and boron (B); their concentrations range from several tens to one thousand parts per million (in terms of molar fraction). The impurity content in semiconductor silicon should be reduced to the level of 10~9 (mole fraction), while that in solar-grade silicon should be reduced to the level of 10~6 (mole fraction). To convert metallurgical silicon into semiconductor silicon or solar silicon, it is clearly impossible to purify it while it remains in a solid state; instead, the metallurgical silicon must first be turned into a silicon-containing gas. This gas is then purified using methods such as distillation and adsorption, after which the highly pure silicon-containing gas is converted into polycrystalline silicon through chemical vapor deposition (CVD). Currently, there are three main approaches for producing high-purity polysilicon: the use of the SIMENS method (also known as the SiHCl3 method) to produce polysilicon rods ； Producing polycrystalline silicon rods using the AsiMi method (also known as the SiH4 method) ； Granular polycrystalline silicon is produced using SiH4 as the silicon source. 1. Production of polysilicon using the SIMENS method (SiHCl3 method). This method was introduced in 1954, and it quickly replaced the SiCl4 zinc reduction method that was in use at the time, becoming the method employed to this day. Its first step is to react metallurgical silicon powder with hydrogen chloride on a fluidized bed at a temperature of 250–350 degrees ； The second step is the distillation of SiHCl3, during which chlorides with different boiling points can be separated ； The third step is the deposition of silicon. Polysilicon reaction furnaces generally adopt a bell-jar design with an open end on one side. Typically, the deposition reaction for polysilicon takes 200–300 hours, allowing the diameter of the silicon rod deposited on the silicon bridge to reach 150–200 mm. 2. Production of polycrystalline silicon by the AsiMi method (SiH4 method) At the end of the 1960s, AsiMi Company proposed using SiH4 as a raw material to produce polycrystalline silicon. To produce polycrystalline silicon rods using SiH4 as raw material, a metal bell-type furnace is generally used. At high temperatures, SiH4 decomposes to produce Si and H2; the overall production cost of this method is higher than that of the SiHCl3 method. 3. Particle polycrystalline silicon manufacturing technology: This method originated from Ethyl Company’s SiH4 process. Granular polysilicon, which was commercialized in 1987, began to be produced. This technology uses a fluidized bed reactor to decompose SiH4, and the silicon formed as a result deposits on some freely flowing fine seed particles, resulting in granular polycrystalline silicon. Due to the large surface area of the crystals, the efficiency of fluidized bed reactors is higher than that of conventional Simens reactors, resulting in lower production costs for their products. The high-purity polysilicon mentioned above is the most fundamental raw material for manufacturing crystalline silicon photovoltaic cells. It is first used to produce single-crystal or polycrystalline silicon ingots, which are then cut to yield silicon wafers used in the production of crystalline silicon photovoltaic cells. 1. Single crystal silicon ingots are the raw materials used for producing single-crystal silicon photovoltaic cells. It is produced by melting high-purity polysilicon using the Czochralski method (CZ) or the floating zone method (FZ). Its diameter is about 100–300 mm, and its length can exceed 1 m. Currently, over 80% of the total output of silicon single crystals is CZ silicon, while the remaining approximately 20% is mainly FZ silicon. The FZ method does not require the use of a crucible, and it enables the production of silicon single crystals with high resistivity and purity. However, the cost of producing such silicon single crystals is high, and as the diameter of the silicon crystals increases, the production techniques become limited. 2. Cast polycrystalline silicon (mc-Si) ingots: Photovoltaic cells made from cast polycrystalline silicon account for around 53% of the total output of photovoltaic cells, making it the most common material used in such cells. The main advantage of cast polysilicon over Czochralski-derived monocrystalline silicon is its higher material utilization rate and lower production cost ； Its disadvantages include grain boundaries, a high density of dislocations, microdefects, and a relatively high impurity concentration, which result in a significantly lower quality of the crystal compared to silicon single crystals, thereby reducing the photoelectric conversion efficiency. There are currently two main processes for producing polycrystalline silicon ingots using casting techniques: 1. The casting method involves melting high-purity polycrystalline silicon material in one crucible, and then pouring it into another preheated crucible where it cools down. By controlling the cooling rate and employing directional solidification techniques, large-grained cast polycrystalline silicon ingots can be produced. 2. Direct melting directional solidification method, abbreviated as the direct melting method, is also known as the Bridgman method. That is, high-purity polycrystalline silicon is melted directly in a crucible, and the melt is then cooled through methods such as heat exchange at the bottom of the crucible, with directional solidification technology being used to produce polycrystalline silicon ingots. The latter technology is widely used in the international industrial sector, whereas the former is currently adopted only by companies such as Solar Energy Germany and Kyocera in Japan. Essentially, there is no fundamental difference between these two technologies; both use the casting method to produce polysilicon. The main difference lies in whether one crucible or two crucibles are used. Search for more posts on related topics: High-purity polysilicon – basic knowledge

The production of polysilicon consists of many different steps, and it depends on which part you are responsible for. The knowledge required for each step is entirely different

Yes, the management methods for processes such as trichlorosilane, the reduction of hydrogen to polysilicon, and exhaust gas recovery are all different

I would like to know what exactly the silane method for producing polysilicon is Which domestic companies use this process?

The process is an improved version of the Siemens process, and the role involves production scheduling management. Previously, I was involved in the management of coal chemical production; I’m not sure whether there are any production scheduling roles available in polysilicon manufacturing companies. I’d like to exchange ideas on this topic

It’s not easy to manage production scheduling well; one must be familiar with the manufacturing process. I think it’s best to start by learning the operating procedures*

Bro, could you provide some simple operating procedures?

This project adopts a silane-based production process, in which **silicon compounds are used to react and produce polysilicon. Compared with the improved Siemens process that relies on reactions with trichlorosilane, the silane method used by foreign companies yields products of higher quality with lower consumption. 　　Comparison of process routes: 1. The polysilicon produced by the silane method has a lower average total metal impurity content, resulting in better quality compared to polysilicon made using trichlorosilane. 　　2. In terms of reaction temperature, the decomposition temperature for the silane method is between 850 and 1000°C, whereas the reduction temperature for producing polycrystalline silicon using the trichlorosilane method is around 1100 to 1250°C; thus, the reaction temperature for the silane method is lower. 　　3. In terms of energy consumption during the reaction, the thermal decomposition energy consumption for polysilicon production using the silane method is around 90 kWh/kg, while that for the trichlorosilane method is 120–160 kWh/kg. Thus, the energy consumption for polysilicon production via the silane method is only about 60% of that in the trichlorosilane method. Electricity consumption costs are the main expense in polysilicon production, accounting for 20 to 40% of the total production costs. Therefore, from the perspective of electricity consumption, polysilicon produced by the silane method has a clear cost advantage over that produced by the trichlorosilane method. 　　4. Highest product quality: The minimum standard is electronic grade, with N-type values ranging from 300–1000 Ω·cm or higher, and P-type values ranging from 3000, 5000–30000 Ω·cm; the quality can reach levels of N7–N9 or higher. The lifetime of minority carriers is 300–1000 μs. We possess the core technology, and through industrial production experience, we are confident in our ability to design, manufacture, and produce high-quality, first-class products as well as complete sets of equipment. 　　5. Low power consumption: The power consumption for the trichlorosilane method is 300–500 kWh/kg for high-purity polysilicon. Due to lower costs, the pyrolyzer consumes less electricity – by 200–250°C less at a lower pyrolysis temperature compared to that of trichlorosilane – resulting in one-third less power usage. Therefore, the electricity consumption of the pyrolysis furnace is 73.7 kW/h per kilogram of high-purity polysilicon. However, the electricity consumption for cryogenic processes is on par with or slightly higher than that of the trichlorosilane method. 　　6. Silanes are prone to decomposition. The decomposition rate in furnaces using trichlorosilane is only 25%, whereas it is over 95% in furnaces using silanes. The amount of unreacted material that is recycled in furnaces using silanes is less than that in furnaces using trichlorosilane. 　　7. Low equipment corrosion: The raw materials contain no chlorides, and hydrogen chloride is not produced as a by-product during the manufacturing process, resulting in low corrosion of the equipment. The main raw materials are quartz sand, liquid sodium, powdered aluminum, and hydrogen in toluene, with titanium acting as a catalyst. Synthesize **sodium aluminum hydride. The toluene is distilled off for reuse. Sodium aluminate with toluene on its surface reacts with silicon tetrafluoride in DME to produce silanes and sodium aluminum tetrafluoride. Silane is purified by distillation in 16 columns to obtain pure silane. The heat medium for distillation is heptane, and heat is transferred through heat exchange with liquid nitrogen. Pure silane is decomposed using 12 furnaces, with each furnace having a power capacity of 1000–1100 kW. 700–800°C. Bar-shaped polycrystalline silicon and hydrogen are obtained, and packaged in a 100,000-class clean environment. 　　8. The exhaust gases from the pyrolysis furnace are easy to handle. The gases produced by the pyrolysis furnace mainly consist of hydrogen and a small amount of unreacted silane; the hydrogen that is separated is filtered and reused in the production of sodium aluminum hydride, while the separated silicon powder and silane are sent back to the pyrolysis furnace. 　　The gases emerging from the pyrolysis furnace using trichlorosilane mainly consist of unreacted trichlorosilane, as well as hydrogen, hydrogen chloride, and tetrachlorosilane generated as a result of the reaction. The treatment process for these exhaust gases from the pyrolysis furnace is complex and challenging.

I wonder which process of polysilicon production the original poster is in charge of? Maybe I can help.

The real rapid development of polysilicon did not occur until 2012; currently, the application areas and development of polysilicon are relatively limited in China.