In the gas industry terminology, gases used in the semiconductor industry are collectively referred to as electronic gases. They can be categorized into three main types: pure gases, high-purity gases, and semiconductor specialty gases. Specialty gases are primarily used in epitaxy, doping, and etching processes; high-purity gases are mainly used as diluents and carrier gases. Electronic gases are an important branch of specialty gases. Based on purity levels and application scenarios, electronic gases can be classified into electronic grade, LSI (Large Scale Integration) grade, VLSI (Very Large Scale Integration) grade, and ULSI (Ultra Large Scale Integration) grade.

  In recent years, with the rapid development of industries such as ultra-large-scale integrated circuits, flat panel displays, and photovoltaic power generation in China, the market demand for electronic gases has significantly increased. The localization of electronic specialty gases has become an inevitable trend. It is reported that China has made encouraging progress in localization: domestic high-purity ammonia has changed the market monopoly by foreign gas companies, the era of "high price and no supply" for high-purity carbon tetrafluoride has ended, and high-purity hydrogen chloride has successfully entered the domestic market.

  Electronic gases (Electronic gases) are indispensable raw materials in the production of ultra-large-scale integrated circuits, flat panel display devices, compound semiconductor devices, solar cells, and optical fibers. They are widely used in processes such as thin film deposition, etching, doping, chemical vapor deposition, and diffusion. For example, in the wafer manufacturing process of advanced ultra-large-scale integrated circuit factories, there are over 450 process steps, and about 50 different types of electronic gases are used. The electronic gas delivery system is designed to meet the process requirements, ensuring the safe use of the process and products, and delivering the gases from the source to the process equipment without secondary contamination, controlling parameters such as flow rate and pressure, and ensuring stable delivery. Based on the nature of the gases and their supply packaging, electronic gases can generally be categorized into bulk ordinary gases, specialty gases, and bulk specialty gases.

  Currently, the variety of electronic consumer products is increasing, and product upgrades are becoming more frequent. Production factories and research institutions of different scales and levels coexist for the same type of products. Based on the actual requirements of different investment scales and product grades, the industry has three main types of demands for electronic gas delivery systems:

  1.1 Large-scale gas supply system

  The large-scale gas supply system mainly targets mass production of 8-12 inch (1 inch=25.4 mm) ultra-large-scale integrated circuit factories (gases include SiH4, N2O, 2, C2F6, NH3, etc.), solar cell production lines above 100MW (gases include NH3), LED epitaxy process lines (gases include NH3), 5th generation and above LCD factories (gases include 4, 3, NF3), optical fibers (gases include SiCl4), and silicon epitaxy production lines (gases include HCL). These industries have huge investment scales, use the most advanced process equipment, have large gas demands, and impose the most stringent requirements on stable and uninterrupted supply, purity control, and safe production.

  Bulk ordinary gases in the above factories are mostly supplied by on-site gas generation (On-site) or industrial park pipeline (Pipeline) centralized supply. An 8-inch ultra-large-scale integrated circuit factory with an annual output of 50,000 wafers requires over 5,000 Nm3/h of high-purity nitrogen, and the hydrogen demand for LED epitaxy process lines and silicon epitaxy production lines exceeds 100 Nm3/h.

  In addition to specialty gases packaged in ordinary cylinders (50L and below), many types of specialty gases are commonly packaged in large containers, hence they are called bulk specialty gases, including Y-cylinders (450L), T-cylinders (980L), cylinder bundles (940L), ISO tanks (22,500L), and torpedo tanks (13,400L).

  The bulk specialty gas supply system (BSGS) uses a fully automatic PLC controller with a color touch screen; the gas panel uses pneumatic valves and pressure sensors to achieve automatic switching, automatic nitrogen purging, and automatic vacuum-assisted venting; multiple safety protection measures, leak detection, remote emergency shut-off; dedicated nitrogen purging sources, etc. Specialty gases use independent gas sources, and multiple use points are supplied by VMB or VMP branch lines. VMB or VMP uses branch pneumatic valves, nitrogen purging, and vacuum-assisted venting. Due to the large total gas source of BSGS, independent gas rooms and independent exhaust systems are mostly used.

  1.2 Conventional gas supply system

  The conventional gas supply system is mainly used in 4-6 inch large-scale integrated circuit factories, solar cell production lines below 50MW, LED chip process lines, and other electronic industries with medium gas demand. Their investment scale is medium, the production lines may use second-hand equipment, the requirements for gas purity control are not stringent, and the system configuration is as simple as possible under the premise of safety to save investment.

  Bulk ordinary gases in conventional gas supply systems mostly establish on-site gas stations, using on-site liquid storage tanks (LIN, LOX, LAR) or cylinder bundles (H2, He) for supply. The gas is delivered to the factory building through a pipeline system and directly branched to the use points.

  Specialty gases are supplied using ordinary cylinders (<50L). The specialty gas delivery system uses gas cylinder cabinets. It is equipped with a fully automatic PLC controller and a color touch screen; the gas panel uses pneumatic valves and pressure sensors to achieve automatic switching, automatic nitrogen purging, and automatic vacuum-assisted venting; multiple safety protection measures, leak detection, remote emergency shut-off; dedicated nitrogen purging sources, etc. VMB uses branch pneumatic valves, nitrogen purging, and vacuum-assisted venting. Inert gases mostly use semi-automatic cylinder racks, relay control, automatic switching, manual purging, and manual venting; VMB main pipe pneumatic valves, nitrogen purging; branch pneumatic valves, nitrogen purging, and vacuum-assisted venting. Gas rooms and exhaust systems are classified based on the nature of the gases.

  1.3 Simple gas supply system

  The simple gas supply system mainly targets 4-inch and below semiconductor chip factories and semiconductor material research institutions. Their processes are simple, usually do not require continuous gas supply, have low investment budgets for gas supply systems, and lack safety awareness among production and management personnel.

  Due to the small gas flow, specialty gas sources mostly use ordinary cylinders (<50L). The delivery system mostly uses semi-automatic gas cylinder cabinets or racks, equipped with relay control, automatic switching, manual purging, and manual venting, with emergency shut-off valves for hazardous gases. Inert gas cylinder racks use fully manual systems, and some even use single-cylinder systems. They share a gas room, or sometimes have no gas room, with specialty gas cylinders and delivery systems placed in return air ducts or directly next to process equipment. They share an exhaust system. The system usually has safety hazards.

  1.4 Current main electronic gases

  Currently, the main electronic gases include: silane, ammonia, carbon tetrafluoride, sulfur hexafluoride, hydrogen chloride, octafluorocyclobutane, methane, nitrous oxide, boron trichloride, hydrogen bromide, carbon monoxide, neon, krypton, etc.

  Development trends

  2.1 Increasingly stringent electronic gas pollution control requirements

  With the upgrading of electronic consumer products, the manufacturing size of products is getting larger, and the control of product yield and defects is becoming stricter. The entire electronic industry is increasingly demanding higher purity of electronic gas sources and stricter control of secondary pollution in delivery systems. Basically, the technical indicators for gaseous impurities and particle contamination in electronic gases proposed by the industry are directly related to the lowest detection limits (LDL) brought by advances in analytical instruments. For example, traditional laser particle testers can measure down to 0.1 microns, while nuclear condensation technology (CNC) can reach 0.01 microns.

  Currently, the line width of 12-inch ultra-large-scale integrated circuit manufacturing has developed to 45 nanometers, requiring bulk gas purity at the ppt level, and particle control directly points to the lower limit of CNC analytical instruments. Laboratory ultra-high-brightness LED technology indicators have reached above 200Lm/w (lumens/watt), requiring hydrogen and ammonia purity control to be less than 1ppb (one part per billion). Ammonia is produced using multi-stage distillation, reaching a technical indicator of 7N (seven nines) "white ammonia", and 5N hydrogen needs to be purified to 9N using advanced palladium membrane purifiers.

  The timely application of bulk specialty gas systems (BSGS) is beneficial for improving pollution control. Firstly, large packaging containers ensure the continuity of gas quality and reduce the risk of contamination from multiple fillings. Additionally, the reduced frequency of cylinder changes also reduces the chance of contamination. BSGS mostly uses deep purging, significantly improving the purging effect.

  The delivery pipeline system generally uses 316L stainless steel electropolished (EP) pipes, high-purity pressure regulators, diaphragm valves, high-precision filters (<0.003μm), VCR fittings, etc. The surface roughness of pipeline components in contact with gases can be controlled at 5uin, and a zero dead zone design is adopted. Construction technology uses fully automatic orbital welding, and strict ultra-high-purity construction and QA/QC assurance procedures are formulated and implemented.

  After the gas delivery system is built, it must undergo strict pressure testing, helium leak testing, particle and moisture testing, oxygen testing, and other gaseous impurity testing.

  2.2 Large flow, uninterrupted, and stable delivery

  How to meet the requirements of large-scale production factories for large flow, uninterrupted, and stable delivery of electronic gases is a challenge.

  Electronic gases are increasingly supplied in a centralized manner, with specialty gases centrally placed in gas rooms. The number of delivery systems is reasonably configured based on the flow demand of the equipment. Specialty gas delivery equipment must use fully automatic switching for gas supply, and backup equipment is often designed. For low vapor pressure gases (WF6, DCS, BCl3, C5F8, ClF3, etc.), cylinder heating, gas panel heating, and pipeline heating need to be considered. To precisely control the flow, high-precision pressure transmitters, electronic scales, and temperature controllers are generally considered at the gas source end. Mass flow meters are also configured at the equipment use points.

  For large flow BSGS, not only the pipeline pressure drop and the effect of liquefied cylinder evaporation heat absorption on flow need to be considered, but also the Joule-Thomson effect after gas pressure reduction. Generally, after gas pressure reduction, the temperature will decrease, even liquefying. This can cause unstable delivery pressure and damage to the pipeline system. Therefore, preheating the gas before pressure reduction needs to be considered. The gas monitoring system (GMS) uses computer networks to achieve real-time monitoring of the gas delivery system to ensure system stability.

  For liquefied gases (such as ammonia), the directly heated liquid vaporization delivery system (Evaporator) has been developed and will soon be promoted in BSGS applications.

  2.3 Increasingly stringent safety

  Electronic gases may have hazards such as asphyxiation, corrosiveness, toxicity, flammability, and explosiveness. Their hazards are classified in detail by different countries, regions, and industrial organizations. For a large-scale electronic production factory, the amount of electronic gases used and stored can be exaggeratedly regarded as possessing a "weapon of mass destruction" arsenal. Any safety hazards in design, construction, or daily operation can bring huge disasters to the factory, personnel, and environment.

  How to ensure the safe storage and operation of electronic gases, the intrinsic safety design of the system and products, is detailed in many international standards and norms such as SEMI, NFPA, CGA, FM, etc. Currently, China is drafting national standards and norms for electronic specialty gases. Generally, gas rooms are divided into flammable gas rooms, corrosive gas rooms, inert gas rooms, silane gas rooms, and chlorine trifluoride gas rooms based on the nature and compatibility of the gases. Gas room planning needs to consider building fire protection, explosion venting, fire and explosion protection spacing, and total hazardous material control. For silane delivery systems, especially BSGS systems, due to the large total amount, isolated buildings should be used. Gas rooms and cabinets should use automatic sprinkler systems. Chlorine trifluoride reacts with water and requires a carbon dioxide fire extinguishing system.

  The exhaust systems of factories using electronic gases are also divided into general exhaust systems (GEX), acid exhaust systems (SEX), solvent exhaust systems (VEX), and ammonia exhaust systems (AEX) based on the nature of the hazardous materials. The purging tail gas during cylinder changes is also recommended to be discharged into tail gas processors.

  Delivery pipelines generally use seamless SS316L EP pipes. Construction uses automatic orbital welding, with pressure testing, helium leak testing, and purity testing. For highly toxic, highly reactive, and self-igniting gases, double-sleeve pipelines should be used. Some highly toxic gases such as phosphine and arsine are widely using safety delivery systems (SDS). The cylinders use negative pressure adsorption and vacuum delivery, fundamentally avoiding gas leakage.

  The gas detection system (GDS) is an important part of the factory life safety system (LSS). The requirements for detectors, in addition to high accuracy and rapid response, should also include self-checking functions.

  2.4 Decreasing construction costs

  As the investment scale of the electronic industry increases, shortening the construction cycle and reducing construction costs are becoming increasingly important. For electronic gas delivery systems, how to reduce construction and operation costs without lowering system pollution control levels and sacrificing safety configurations is also a challenge.

  Reasonable system configuration and material selection can significantly reduce initial investment costs. This requires electronic gas delivery system contractors to have strong system design capabilities. Gases with matching properties can use the same purging nitrogen system, significantly saving the investment in gas cylinder cabinets. For VMB, mobile purging nitrogen panels can be used. Small pipelines (≤1/2”) can be directly bent, saving elbow costs and greatly improving construction efficiency. Strictly implementing high-purity pipeline construction standards can greatly reduce testing gas and testing time. These are effective cost control measures. Using large packaging containers for gas sources can significantly reduce logistics and labor operation costs. Therefore, BSGS is increasingly favored by more customers.

  In summary, electronic gas delivery systems face challenges in high purity, large flow, strict safety measures, and greatly reducing construction costs, and these four aspects are also future development directions.

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