Application of electronic grade trichlorosilane special gas
Electronic grade trichlorosilane is an indispensable and important electronic special gas raw material in the semiconductor industry. Currently, China mainly relies on imports. With the rapid growth of China's integrated circuit industry, the demand for electronic grade trichlorosilane is increasing. Realizing the localization of electronic grade trichlorosilane special gas is of great significance to the development of China's integrated circuit industry. This paper focuses on the role of electronic grade trichlorosilane special gas in the chip manufacturing process, and then analyzes the production and purification technology, filling points and quality control requirements.
1、 Role of electronic grade trichlorosilane in chip manufacturing process
Electronic grade trichlorosilane can be used as the silicon source of semiconductor epitaxial silicon wafer. It is mainly used to manufacture various semiconductor chips and micro integrated circuit components. It is an indispensable important material in the manufacturing process of microelectronics and optoelectronic components. Vapor phase epitaxy is the most widely used process for the growth of semiconductor silicon wafer epitaxy layer: hydrogen (H2) gas carries silicon tetrachloride (SiCl4) or trichlorosilane (SiHCl3), silane (SiH4) or silicon dichloride (SiH2Cl2) into the reaction chamber with silicon substrate, where high-temperature chemical reaction is carried out to reduce or thermally decompose the silicon containing reaction gas, and the silicon atoms generated are epitaxially grown on the silicon surface of the substrate. Trichlorosilane as silicon source has fast epitaxial growth speed and safe use. It is a relatively general silicon source. Its chemical reaction formula is: SiHCl3 + H2=Si +3 HCl
2、 Production process of electronic grade trichlorosilane special gas
（1） Synthesis of trichlorosilane
There are two main processes for the synthesis of trichlorosilane: low-pressure chlorination synthesis and hydrogenation of silicon tetrachloride. The low-pressure chlorination synthesis process uses a fluidized bed reactor. Metallurgical grade silicon powder with purity >98.5% reacts with hydrogen chloride gas raw material at about 300 ℃ and 50kPa to produce trichlorosilane and silicon tetrachloride. Controlling the reactor temperature can change the moLar ratio of trichlorosilane and silicon tetrachloride. The reaction equation is as follows:
2Si +7 HCl = SiHCl3 +sicl4 +3 H2
Trichlorosilane with a purity of about 95% can be obtained from the reaction generated gas after cyclone separation, spray condensation, and distillation crude separation. The purity of this product is far from meeting the purity requirements of trichlorosilane required for chip silicon epitaxy, and it needs to be further purified by multistage distillation. The process of synthesizing trichlorosilane by hydrogenation of silicon tetrachloride also uses a fluidized bed reactor, which uses metallurgical grade silicon powder with purity >98.5%, 99.999% hydrogen and 99.9% silicon tetrachloride as raw materials to produce trichlorosilane at about 500 ℃ and 3Mpa. The reaction equation is as follows:
Si (met) + 2H2 + 3SiCl4 = 4SiHCl3
The conversion rate of the reaction is less than 30%. After cyclone separation, spray condensation, and distillation crude separation, the reaction generated gas can obtain trichlorosilane with a purity of about 95%. The purity of the product is far from meeting the purity requirements of trichlorosilane required for chip silicon epitaxy. It needs to be further purified by multistage distillation.
（2） Trichlorosilane rectification and purification process
The crude trichlorosilane with a purity of about 95% mainly contains a small amount of silicon tetrachloride, silicon dichloride, a small amount of C, B, P and metal impurities, which can meet the requirements of trichlorosilane special gas for chip silicon after purification by multistage distillation. The trichlorosilane multistage distillation purification process mainly includes five distillation columns in series: the primary distillation column is mainly used to separate silicon tetrachloride and high boiling point substances in crude trichlorosilane from the tower kettle, the tower top effluent is sent to the secondary distillation column to separate volatile compounds and chloride and other impurities from the tower top, the trichlorosilane containing trace high boiling point impurities at the bottom of the tower is sent to the tertiary distillation column to remove from the tower kettle, and the trichlorosilane with a purity of more than 7n is obtained at the tower top, and then the remaining trace impurities are separated by distillation in the latter two columns. The purity of trichlorosilane product from the fifth distillation column can reach 11n, meeting the requirements of silicon trichlorosilane for chip silicon.
3、 Quality requirements for electronic grade trichlorosilane special gas
The quality of trichlorosilane product from the fifth distillation column can reach: purity (mass fraction) /10-2: ≥ 99.999; Monochloromethane content (mass fraction) /10-6 ＜ 5; Silicon dichloride content (mass fraction) /10-6 ≤ 50; Silicon tetrachloride content (mass fraction) /10-6 ≤ 50; Iron content (mass fraction) /10-9 ≤ 30; Nickel content (mass fraction) /10-9 ≤ 2; Donor impurities (P, as) <0.100ppba; Acceptor impurities (B, Al) <0.05ppba, carbon content <0.05ppma; Each element of total metals (Fe, Cr, Ni, Cu, Na, Zn, Al) is <1.0ppbw. It far exceeds the quality index of trichlorosilane for epitaxy (gb/t30652-2014) and meets the requirements of trichlorosilane for chip silicon.
4、 Key points of electronic grade trichlorosilane special gas filling and quality control
（1） Key points of electronic grade trichlorosilane special gas filling
The electronic grade trichlorosilane special gas filling system mainly includes: gas supply pipeline and accessories, gas cylinders, gas cylinder cabinets, and particle filtration and counting. The surface finish of all pipelines and components in contact with gas is 10Ra, and the material is 316L stainless steel. Gas cylinders shall be subject to strict leakage detection. The surface area of parts in contact with gas shall be the smallest. Pipeline valves generally adopt diaphragm valves without springs and fillers, pipeline welding adopts track welding, and pipe fittings are connected with VCR joints. The instrument gas of the display instrument of the gas cylinder cabinet needs to be equipped with a purifier to filter out particulate impurities, moisture or oxygen and prevent the purge gas from being brought into the process gas system.
（2） Quality control points of electronic grade trichlorosilane special gas
1. filling cylinder cleaning
The steel cylinders filled with high-purity special gas must be clean and free of pollution. The new gas cylinders need to be strictly cleaned before use. The cleaning process mainly includes deoiling, dehydration, vacuuming, product replacement and washing. Finally, the trichlorosilane in the steel cylinders is sampled for analysis. After several product exchanges and washing, until the trichlorosilane meets the product requirements, the steel cylinders filled with qualified trichlorosilane are sampled for analysis after being placed for 3 months. Until the trichlorosilane in the steel cylinders reaches the standard, the steel cylinders can be put into normal use.
2. quality evaluation
In order to ensure that the quality of high-purity trichlorosilane meets the requirements, avoid unqualified products entering downstream users, and cause pollution to the filling system, quality evaluation must be carried out before filling each batch of products. The evaluation method is as follows: the high-purity trichlorosilane product is vaporized and passed into the test furnace, followed by ultra pure hydrogen. In the test furnace, polycrystalline silicon rods with a diameter of about 20mm are grown by chemical vapor deposition. The polycrystalline silicon rods are sent to the laboratory to be drawn into monocrystalline silicon rods by zone melting single crystal furnace. After slicing, the donor and acceptor impurity content is determined by low-temperature Fourier transform infrared spectrometer, and the metal impurity content is determined by ICP-MS. Only after confirming that the impurity index meets the requirements can it be filled into the sales link.
epilogue
With the rapid development of China's integrated circuit industry, it is imperative to realize the localization of key basic material electronic grade trichlorosilane special gas. Some domestic enterprises, especially those with electronic grade polysilicon production technology, have mastered electronic grade trichlorosilane purification technology, but it is still urgent to establish quality control standards for filling and transportation process.