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Issuing time:2018-12-29 11:01

Application of SF6 gas in high voltage switchgear


Since SF6 gas monitoring has superior insulation performance, arc extinguishing performance and heat dissipation performance, since the early 1960s, SF6 gas monitoring has been applied to high-voltage equipment in power transmission and distribution systems. In the early 1980s, the first appeared. A medium voltage switchgear insulated with SF6 gas. At present, SF6 gas monitoring is mainly applied to circuit breakers, GIS combined electrical appliances and composite switches in the high-voltage field. High-voltage and ultra-high voltage are dominant in the equipment with SF6 gas as insulation. In the medium voltage field, it is mainly used in high-voltage switchgear equipment (C-GIS, inflatable ring network cabinet), circuit breakers and load switches with SF6 gas monitoring insulation. In addition to high-voltage switchgear, SF6 gas has also begun to develop in the fields of transformers, capacitors, surge arresters, fuses, gas-insulated transmission pipelines and transformers in medium and high-voltage power transmission and transformation equipment. At present, power equipment of all voltage levels from 12 to 1000 kV is widely used. Although the vacuum switch is still mainly used in the medium voltage field, the equipment for monitoring insulation with SF6 gas is increasing rapidly.


Cleaning gas in the electronics industry - fluorine-containing electron gas


The semiconductor cleaning process mainly removes particles and metal contaminants on the silicon wafer, organic matter, resist de-glue in the etching and wiring processes, removal of compounds, and cleaning after CMP (Chemical Mechanical Polishing).


     The semiconductor IC process is gradually developed based on four basic processes of ion implantation, diffusion, epitaxial growth and photolithography. Since the components and wirings in the integrated circuit are quite fine, if it is contaminated by dust particles or metal during the manufacturing process, it is easy to cause damage to the circuit function in the wafer, forming a short circuit or an open circuit, etc., resulting in failure and influence of the integrated circuit. The formation of geometric features. Therefore, in addition to external pollution sources in the production process, integrated circuit fabrication steps such as high temperature diffusion and ion implantation require cleaning.


 Fluorine-containing cleaning agents exhibit very good performance in semiconductor and electronics industry cleaning, especially in dry cleaning. The fluorine-containing cleaning agent has a low boiling point and exists in a gas phase at normal temperature, so that it is very easy to perform dry gas phase cleaning.


 Fluorine-containing cleaning agents mainly include CF4, C2F6, C3F8, c-C4F8, SF6, NF3, CF2O, F2, etc., as shown in Table 1.


Traditional fluorine-containing cleaning gases mainly include carbon tetrafluoride (CF4), hexafluoroethane (C2F6), octafluoropropane (C3F8), octafluorocyclobutane (c-C4F8), sulfur hexafluoride (SF6), and three. Nitroxide (NF3) and other varieties, in the semiconductor cleaning, mainly in situ C2F6 and CF4 and other perfluorinated nitrogen compounds (PFC) cleaning.


 As environmental requirements continue to increase, PFC emissions in the semiconductor industry are increasingly receiving global attention. The fluorocarbons used in chemical vapor deposition (CVD) chamber cleaning are the largest sources of PFCs in the semiconductor industry. Finding alternative cleaning agents is considered one of the most effective ways to reduce/eliminate PFC emissions.


 Use remote NF3 cleaning instead of the original in-situ fluorocarbons (such as C2F6, CF4). Remote NF3 cleaning refers to the plasmonization of NF3, dissociation into F ions or atoms, and then allowing F ions or atoms to enter the CVD chamber to clean the residue. Remote NF3 cleaning can achieve up to 95%-99% utilization and can reduce >95% PFC emissions. See Table 2 for comparison of remote NF3 cleaning with fluorocarbon in-situ cleaning and PFCs emissions.


 However, the remote NF3 cleaning process will generate more by-products F2, HF and NOx, which will undoubtedly increase the load and difficulty of subsequent wastewater/exhaust gas treatment, and the after-treatment system is expensive. And NF3 is explosive.


 Conventional fluorine-containing cleaning gases such as PFCs (including CF4, C2F6, C3F8, c-C4F8, etc.), SF6, and NF3 have high GWP values, and the aftertreatment system is complicated and expensive.


 The new generation of fluorine-containing cleaning gas is mainly developed in the three directions of low or even zero GWP, high cleaning efficiency and simple post-processing. A representative new generation of fluorine-containing cleaning gas is CF2O, others such as F2, CIF3 and the like.


  From 1998 to 2002, the Research Institute of Innovation Technology for the Earth (RITE) has been working on alternative cleaning agents and recommended CF2O as a new alternative cleaning agent. CF2O has a GWP of about 1, an atmospheric lifetime of approximately zero, and a very friendly environment. Compared with the traditional cleaning agents C2F6 and NF3, the environmental friendliness of CF2O is very obvious, with low GWP and MMTCE, GWP value CF2O/NF3=1/10970, CF2O/C2F6=1/9200; MMTCE value CF2O/NF3=1 /10, CF2O/C2F6 = 1/100. In addition, the CF2O explosion probability is 0, and the safety ratio range mixed with SiH4 is very wide.


 Although CF2O is a toxic substance, the exhaust gas can be easily removed by subsequent water washing, the post-treatment system is simple, and the post-treatment cost is low. The use of CF2O instead of PFCs cleaners is equivalent to a 96% reduction in PFCs emissions.


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