Application of reverse osmosis membranes in the electronics industry

Electronics Industry (such as semiconductor devices, integrated circuits, and cathode ray tubes ) , a large number of various levels of pure water and ultrapure water are used to clean semi-finished and finished products. The quality, qualification rate, and reliability of products in the microelectronics industry (semiconductor devices, integrated circuits, cathode ray tubes, electronic detection, computer motherboards, etc.) ) are closely related to the water quality of pure water or ultrapure water. With the development of the electronics industry, especially the rapid development of the semiconductor industry, the requirements for the water quality of pure water are also constantly improving. In the past, the practice of using resistivity as the only measure of water quality purity has been proved to be far from enough. Quantitative indicators and restrictions have been gradually introduced for the content of anions, cations, particles, organic matter, and bacteria in the water. 20 century 70 In the mid-19 80 s, the determination of the five indicators of particles, bacteria, silicon dioxide, sodium, and total organic carbon ensured the quality of integrated circuits. Entering the 20 century 90 s, due to the further improvement of integration, the requirements for the water quality of pure water, especially particles and bacteria, became stricter. On this basis, the limiting indicator of dissolved oxygen was added because the concentration of dissolved oxygen is too high. During the silicon wafer cleaning process, the release of oxygen will not only produce foam, making it impossible to completely clean the surface of the wafer, but the dissolved oxygen in the hot ultrapure water will also corrode the integrated circuit wafer. . s, integrated circuits have developed to the megabit-level submicron technology, and the processing and cleaning of wafers have stricter requirements for the water quality of pure water. In order to ensure the needs of production, major pure water treatment companies have their own set of process systems to meet the needs of production with different integration levels

(1) The pure water preparation process designed by a Japanese company in a very large-scale integrated circuit production plant in Shanghai is shown in the figure. The system consists of a pretreatment system, a primary pure water manufacturing system, a secondary pure water manufacturing system, and supporting systems such as wastewater recovery.

a. Pretreatment system. According to the raw water quality, it consists of a coagulation pressure flotation device, a double-layer filter, and a carbon dioxide degassing tower. After coagulation, the suspended matter and some dissolved organic matter in the raw water are difficult to settle due to their low density. Pressure flotation treatment can effectively remove them. The subsequent double-layer filter can intercept the fine flocculates flowing out of the flotation device, so that the raw water is further clarified. The carbon dioxide degassing tower removes the bicarbonate component to prevent the subsequent RO calcium carbonate precipitation on the concentrate side membrane surface.

b. Primary pure water system. This system consists of three-stage RO , a deoxygenation device, and an ion exchange column. RO The membrane uses a low-pressure polyamide membrane. The first stage RO mainly removes most of the anions, cations, and organic matter. ; The second stage RO mainly removes residual anions, cations, silicon, and organic matter. ; The third stage RO mainly removes trace residual cations and improves resistivity. The deoxygenation device uses a hollow fiber membrane degassing method to remove dissolved oxygen to below the required concentration, and also removes residual carbon dioxide, reducing the load on the subsequent exchange column and reducing the replacement frequency of the ion exchange resin. The ion exchange column can remove RO the very small amount of ions, heavy metals, silicon, and dissolved carbon dioxide remaining in the treated water. This exchange column is non-regenerative, and the purpose is to prevent the remaining Cl-、OH- from affecting the water quality of the treated water. According to the normal recovery rate 80% calculation, the exchange resin is replaced approximately every six months.

c. Secondary pure water system. This system consists of a heat exchanger, a UV oxidizer, a polisher, and an ultrafiltration system. The UV oxidizer uses a low-pressure 185nm UV lamp to decompose the very small amount of TOC components remaining in the primary pure water treated water. It is especially suitable for decomposing low relative molecular weight organic matter with a lower removal rate in RO membranes. The polisher uses low-leaching uniform spherical resin to remove the organic matter produced by the decomposition of the previous UV oxidizer and TOC , and simultaneously removes trace amounts of ions, silicon, and heavy metals present in the primary pure water, keeping the resistivity stable at a high level. The ultrafiltration system finally removes the ionic components at the end of the ultrapure water device to meet the process requirements. The membrane module of this system uses an external pressure ultrafiltration membrane that does not produce ions itself. CO2 d

Wastewater recovery system. This system consists of an activated carbon filter tower and an anion exchange tower. Because the recovered water contains Cl H2O2、SO42-、F-、 − etc. NH4 Use activated carbon adsorption to remove . Use an anion exchange tower to remove H2O2 F SO42-、 to be removed later. etc. Cl-，NH4 To adapt to the development of integrated circuit production in recent years, RO major pure water manufacturers abroad have continuously researched and developed, and have made new progress. In particular, the continuous development and improvement of membrane technology, the research and practice of ozone sterilization technology, . EDI technology improvement and promotion, and the application of micro-flocculation filtration and water purification technology in the pretreatment of ultrapure water have all made the ultrapure water preparation process more perfect and stable, ensuring the yield of microelectronic products. (2)

(2) The pure water preparation process proposed by Hiroshi Shimizu of Japan is shown in the figure.

The resistivity, dissolved oxygen, and SiO2 indicators of this system basically meet the requirements, but TOC particles and bacteria counts must be treated with corresponding measures to be guaranteed. It has the following characteristics in water production technology.

a Micro-flocculation filtration is used for raw water. . That is, PAC is added to the inlet pipe PAC for coagulation, and then double-layer filtration is performed using quartz sand and anthracite coal,

b Activated carbon filtration is placed after the strong acid cation bed and degassing tower. Because the influent pH value is acidic, this can prevent microbial growth and achieve the effect of removing organic matter.

c. The reverse osmosis device is set after ion exchange, which can prevent membrane pollution and scaling from blocking the reverse osmosis components, especially for SiO2 water with high content.

d. Double degassing is used, the second being vacuum degassing, which can remove dissolved oxygen and volatile substances from the water. TOC 。

e. Two-stage ultraviolet sterilization is used, the latter stage is to prevent bacteria from growing on the membrane surface of the reverse osmosis polishing ( FRO) device.

f. Reverse osmosis device is used (FRO polishing ) instead of conventional ultrafiltration. In FRO because synthetic composite membranes are used, therefore TOC the removal rate is extremely high.

(3) An American company designed a typical high-purity water system to meet the needs of 16M in-situ device production. The system consists of a high-purity water refining circulation system and a high-purity water supplementary water system. The supplementary water volume of high-purity water is equal to the water consumption. Its water production process is shown in Figure 2 1 6 This system has the following characteristics in water production technology.

Chlorine gas is added after activated carbon filtration

a. (2~4mg/L) to minimize bacterial growth before entering reverse osmosis. Reverse osmosis device, the front stage uses cellulose acetate membrane, and the latter stage uses polyamide membrane. The combination of the two membranes can take advantage of each other's strengths.

b The latter stage reverse osmosis concentrate can be returned to the front stage reverse osmosis for reuse

c. to improve water reuse rate. . In addition to nitrogen protection, the high-purity water storage tank also needs to add

d. ozone made from pure oxygen to prevent bacterial growth. 0.2mg/L Ultraviolet lamp sterilization is used to remove residual ozone in the water. After the mixed bed, ultraviolet lamp is used again, with an equivalent of

e. times the normal retention time to further reduce 254nm Ozone lamp is added after the mixed bed 185nm (0.08~0.1mg/L) 6 1 8 to further reduce TOC

f. A catalytic deoxygenation system is used (CORS) or a two-stage vacuum degassing device can be used to remove dissolved oxygen from the water. TOC 。

g. Reverse osmosis is used instead of ultrafiltration to ensure that particles, organic matter, and suspended matter in the water are purified to the lowest level. The reverse osmosis uses a composite membrane with a relative molecular weight cutoff of and a retention rate of The pipe materials after the reverse osmosis device of the primary treatment system should use polyvinylidene fluoride pipes

h. (PVDf) 100 but the high-pressure pipes of reverse osmosis should use stainless steel pipes. 90%。

i. j. 4M High-purity water refining system for in-situ devices may not consider deoxygenation, and can use ultrafiltration devices with a relative molecular weight cutoff of for final treatment without the need for a reverse osmosis device.

 j. 4M位器件用高纯水精制系统，可不考虑除氧，并可应用截留相对分子质量1000 1 100000的超滤装置作最终处理，而不需用反渗透装置。