1、 Types of High Purity Gas Systems
Simple gas supply systems are mainly aimed at semiconductor chip factories with a diameter of 4 inches or less, semiconductor material research institutions, and some single process equipment. Their manufacturing process is simple, usually without the need for continuous gas supply, and the investment budget for gas supply systems is low.
2. Conventional gas supply system
Conventional gas supply systems are mainly used in 4-6 inch large-scale integrated circuit plants, solar cell production lines below 50MW, LED chip processing lines, and other medium-sized electronic industries with medium gas consumption. The requirements for gas purity control are not stringent, and the system configuration should be as simple as possible to save investment while meeting safety requirements.
3. Bulk special gas supply system
The large-scale gas supply system is mainly aimed at large-scale production of 8-12 inch (1 inch=25.4 mm) ultra large scale integrated circuit plants (gas types include SiH4, N2O, 2, C2F6, NH3, etc.), solar cell production lines (gas types include NH3) above 100 MW, LED epitaxial process lines (gas types include NH3), liquid crystal display factories (gas types include SIH4, CL2, NH3, NF3) above 5 generations, optical fiber (gas types include SiCl4) Silicon material epitaxial production lines (gas types include HCL) and other industries. They have a huge investment scale, adopt advanced process equipment, and have a large demand for gas. They have strict requirements for stable and uninterrupted supply, purity control, and safe production.
2、 Functions of high purity gas supply system
Automatic switching, automatic nitrogen purging, and automatic vacuum assisted venting can be achieved; Multiple safety protection measures, leakage detection, remote emergency shutdown; Origin of dedicated nitrogen purging, etc.
3、 Design of High Purity Gas Supply System
1. Selection of materials
Special gas pipeline systems generally use 316L stainless steel electropolishing (EP) pipes, and valves generally use high purity pressure regulating valves, diaphragm valves, filters, (<0.003 micrometers), VCR connectors, etc. The surface roughness of pipeline components in contact with gas can be controlled at 5 uin. For some highly corrosive gases such as CL2, EP pipes with strong corrosion resistance after special treatment are used.
2. Design of main pipeline system
After determining the gas room and gas consumption point, the main pipeline system generally follows the principle of short pipeline lines, fewer bends, compact and reasonable layout, giving a simple and beautiful feeling. The number of conveying systems and the size of pipe diameters are generally determined based on the number of gas consumption points and the flow rate of the machine. Basically, small pipe diameters are used for conveying (1/4-3/4), and many standby systems are designed. Due to the danger of the gas itself, many places adopt the method of laying pipes in cable trays. For places that pass through walls or through sandwiches, where there are dangerous sources and often hazardous operations around, the pipes in open air are generally arranged in fully enclosed cable trays.
For low vapor pressure gases (WF6, DCS, BCl3, C5F8, ClF3, etc.), it is necessary to consider cylinder heating, gas panel heating, pipe heat tracing, etc. In order to accurately control the flow, it is generally considered to configure high-precision pressure transmitters, electronic scales, temperature controllers, etc. at the gas source end. Mass flow meters and pressure regulating valves are also installed at the gas consumption points of the machine. For highly toxic, highly reactive, and spontaneous combustion gases, double cannulas should be used for transportation. At the same time, the design of the pipeline should adopt a zero dead zone design, that is, the entire pipeline system should be from the gas holder to the VMB, and from the VMB to the gas consumption point. The key points should be point to point, and there should be no dead corners where there is residual air during gas replacement. Therefore, the VMB completes the gas distribution in the entire pipeline system, without a tee in the middle. Then the pipeline should have a good grounding.
3. Design of auxiliary system
During the installation and transportation of the gas cabinet or control panel, due to handling and vibration, replacement of valves, connectors, filters, etc., or other reasons, it is necessary to conduct high-pressure gas tightness test and helium inspection again. The replacement of gas also requires high-pressure nitrogen or helium, so the special gas cabinet needs to be designed to be connected to high-pressure inert gas helium or nitrogen. Generally, one or more inert gas cabinets are selected to be installed in the special gas room.
4、 Construction of high purity gas supply system
The construction of high purity gas pipelines adopts fully automatic rail welding, and strict high purity construction and QA/QC assurance procedures are developed and implemented to strictly monitor and manage the construction quality and procedures. The entire system also requires helium leak detection, moisture, oxygen content, and particle size detection, as well as other required gas phase impurities testing.
Several points for attention in construction management and on-site construction
Project management personnel and construction personnel should receive training on construction safety and quality, understand the construction requirements and specifications of special pipelines, and understand the basic knowledge of high purity gas, so as to deepen the understanding of the importance of construction quality of special pipelines.
Special gas pipelines generally use small pipelines for transportation. In order to reduce costs, pipelines are directly simmered and bent with a pipe bender, which is typically 5-10 times larger but not less than 5 times larger. Therefore, pipeline construction personnel should receive training on bends from various angles, and welders must also receive training on welding procedures to familiarize themselves with the adjustment of various welding parameters. Both plumbers and welders must undergo examinations, and after being confirmed as qualified by specialized quality management personnel, they can only construct after being issued a work permit. This is also an integral part of the QA/QC assurance program. It is also the focus of personnel training in construction procedures.
3. The on-site quality management personnel should make quality inspection records of materials and daily construction quality inspection records, including the quality of plumbers' bends, whether the dimensions are accurate, whether the pipes are scratched, and whether the bends are pressed too flat; Remove the packaged pipes and prefabricated pipes, and check whether the pipe orifice is sealed properly; (Pipe sealing should be covered with a pipe cap, and then cut off a 15-20 cm long sleeve using an intact inner packaging bag of EP pipe. After the pipe orifice is folded back, wrap it with clean adhesive tape. If there is no pipe cap, use a layer of inner packaging bag to seal it with adhesive tape, and then cover it with another layer outside, and also seal it with adhesive tape.) Whether the welder's welds meet the quality requirements, each weld must be carefully inspected, and the welding operator and welding quantity records must be made.
Welders must make welding samples before welding every day, and welding construction can only be carried out after passing the inspection. At the end of each day's construction, a final sample must also be made to confirm whether there are welding hazards in today's welding operation. Each time the power supply is changed, a new sample must be made. Welding samples shall be attached with welding parameters. Daily welding samples should be properly stored. (The inspection of weld quality mainly includes the width and size of the weld, the internal and external uniformity of the weld, the concavity and convexity of the weld, whether it is oxidized, and other impermissible defects)
5. After the welding operation starts, the pipeline erected on the pipe rack should be continuously inflated, that is, the pipeline should be in a state of gas flushing protection from the beginning of construction to the end of construction, but the air pressure in the pipeline can be appropriately reduced when no welding operation is performed. However, for construction with low requirements, in order to reduce costs, after each day's welding, both ends are sealed with pipe caps and clean adhesive tape. In particular, when butt welding VM pipes with strong corrosion resistance that transport highly corrosive gases, the inflation time must reach 4-5 minutes and must be uninterrupted.