Ultrapure Water (also UPW or high purity water ) is water that has been purified to an unusual and rigorous specification. Ultrapure water is a term commonly used in the semiconductor industry to emphasize the fact that water is treated with the highest purity levels for all types of contaminants, including: organic and inorganic compounds; solute and particulate matter; volatile and non-volatile, reactive and inert; hydrophobic and hydrophobic; and dissolves the gas.
UPW and commonly used are water thermionization (DI) is not the same. In addition to the fact that the UPW has organic particles and dissolved gases removed, the typical UPW system has three stages: the pretreatment stage to produce pure water, the main stage to further purify the water, and the polishing step, the most expensive part of the treatment process.
A number of organizations and groups develop and publish standards related to UPW production. For microelectronics and power, they include the Semiconductor Equipment and the International Materials (SEMI) (microelectronics and photovoltaic), the American Society for Testing and Materials International (ASTM International) (semiconductor, electric), Electricity Research Institute (EPRI) The Society of Mechanical Engineers (ASME) (power), and the International Association for the Nature of Water and Steam (IAPWS) (power). Pharmaceutical plants follow water quality standards such as those developed by pharmacopoeia, three of which are the US Pharmacopoeia, the European Pharmacopoeia, and the Japanese Pharmacopoeia.
The most widely used requirements for UPW quality are documented by ASTM D5127 "Standard for Ultra-Pure Water Used in Electronics and Semiconductor Industries" and SEMI F63 "Guide to ultrapure water used in semiconductor processing".
Ultra pure water is also used as boiler feedwater in the AGR UK fleet.
Video Ultrapure water
Sumber dan kontrol
Bacteria, particles, sources of organic and inorganic contamination vary depending on a number of factors including feed water to make UPW as well as pipeline selection to deliver it. Bacteria are usually reported in colony-forming units (CFUs) per UPW volume. The particles use the UPW volume per volume. Total organic carbon (TOC), metal contaminants, and anionic contaminants were measured in parts without dimensions of parts per notation, such as ppm, ppb, ppt and ppq.
Bacteria have been referred to as one of the most stubborn on this list to be controlled. Techniques that help in minimizing the growth of bacterial colonies in the UPW flow include occasional chemical or vapor sanitation (commonly occurring in the pharmaceutical industry), ultrafiltration (found in some pharmaceutical industries, but mostly semiconductors), ozonization and optimization of piping system designs that promote the use of criteria Number of Reynolds for minimum flow along with minimization of dead legs. In advanced modern UPW sophisticated systems (higher than zero) the number of bacteria is usually observed in newly built facilities. This problem is effectively handled with sanitation using ozone or hydrogen peroxide. With the exact design of the polishing and distribution system there is no positive number of bacteria that is usually detected throughout the life cycle of the UPW system.
Particles at UPW are the bane of the semiconductor industry, causing defects in sensitive photolithographic processes that determine nanometer-sized features. In other industries the effect may vary from intrusive to life-threatening disturbances. Particles can be controlled using filtration and ultrafiltration. Sources can include bacterial fragments, decay of component walls in damped channels and also the cleanliness of the connecting process used to build piping systems.
Total organic carbon in ultra-pure water may contribute to the proliferation of bacteria by providing nutrients, can replace as carbides for other chemical species in sensitive thermal processes, react in undesirable ways by biochemical reactions in bioprocessing and, in severe cases, leaving a residue that undesirable in the production section. TOC can be derived from the feed water used to produce UPW, from the components used to deliver UPW (additives in manufacturing piping products or extrusion auxiliaries and mold release agents), from manufacturing and subsequent cleaning operations of piping systems or from dirty pipes, fittings and valve.
Metallic and anionic contamination in UPW systems can kill enzymatic processes in bioprocessing, corrosion equipment in the power generation industry and result in the failure of electronic components in semiconductors and photovoltaic cells in the short or long term. The source is similar to TOC. Depending on the level of purity required, the detection of these contaminants can range from simple conductivity (electrolytic) readings to advanced instrumentation such as ion chromatography (IC), atomic absorption spectroscopy (AA) and inductively coupled plasma mass spectrometry (ICP-MS).
Maps Ultrapure water
Apps
Ultrapure water is processed through several steps to meet quality standards for different users. The UPW end users include these industries: semiconductors, solar photovoltaics, pharmaceuticals, power plants (sub and super critical boilers), and specialized applications such as research laboratories. The term "ultrapure water" became more popular in the late 1970s and early 1980s as a way of describing certain water qualities used in power, pharmaceutical, or semiconductor facilities.
While each industry uses so-called "ultrapure water", the quality standards vary, meaning that the UPW used by pharmaceutical manufacturers is different from those used in fab semiconductors or power plants. These standards are related to the use of UPW. For example, semiconductor plants use UPW as a cleaning agent, so it is important that water does not contain any soluble contaminants that can precipitate or particles that can stick to the circuit and cause microchip failure. The electric power industry uses UPW as a source to make steam to drive steam turbines; pharmaceutical facilities will use UPW as a cleaning agent, as well as ingredients in the product, so they seek free water from endotoxins, microbes, and viruses.
Today, ion exchange (IX) and electrodeionisation (EDI) are the major deionization technologies associated with UPW production, in many cases after reverse osmosis (RO). Depending on the quality of water required, UPW plant often also features degasification, microfiltration, ultrafiltration, ultraviolet irradiation, and measurement instruments (eg, total organic carbon [TOC], resistivity/conductivity, particle, pH, and specific measurements for specific ions ).
Initially, soft water produced by technologies such as softening of zeolite â €
Ultrapure water is widely used in the semiconductor industry; this is the highest grade UPW quality. The consumption of electronic class water or molecular class by the semiconductor industry can be compared with the consumption of water from a small town; one factory can use ultra-pure water (UPW) at a rate of 2 MGD, or ~ 5500 m 3 /day. UPW usage varies; it can be used to rinse wafers after chemical applications, to melt the chemicals themselves, in an optical system for immersion of photolithography, or as a make-up of coolant in some important applications. UPW is sometimes used as a source of humidification for clean room environments.
The main and most critical UPW application is in front-end cleaning tools, when an integrated circuit foundation is created. For use as a cleaning agent and etching, impurities that may cause product contamination or collision process efficiency (eg level etching) must be removed from the water. In a chemical-mechanical polishing process, water is used in addition to reagents and abrasive particles.
Water quality standards for use in the semiconductor industry
These are used in other types of electronic manufacturing in the same way, such as displays, discrete components (such as LEDs), hard disk drives (HDD) & amp; solid-state drive (SSD), image sensor & amp; wafer-level image/optical processors (WLO), and crystalline silicon photovoltaic; Hygiene requirements in the semiconductor industry, however, are currently the most stringent.
Applications in the pharmaceutical industry
The use of typical Ultrapure water in the Pharmaceutical and Biotechnology industry is summarized in the table below:
Ultra pure water usage in the pharmaceutical and biotechnology industries
In order to be used for pharmaceutical and biotechnology applications for the production of licensed human and veterinary health care products, they must conform to the following pharmacopoeia monograph specifications:
- British Pharmacopoeia (BP): Purified Water
- Japanese Pharmacopoeia (JP): Purified Water
- Pharmacopoeia Europe (Ph Eur): Aqua purificata
- United States Pharmacopoeia (USP): Purified Water
Note: Purified water is usually a major monograph referring to other applications that use pure ultra pure water
It should be noted that Ultrapure water is often used as an essential utility for cleaning applications (as required). It is also used to produce steam cleaner for sterilization.
The following table summarizes the two main pharmacopoeia specifications for 'water for injection':
Pharmacopoeia specification for water for injection
Ultrapure water and deionized water validation
Ultrapure water validation should use a risk-based life-cycle approach. This approach consists of three stages - Design and Development, Advanced Qualification and Verification. One should take advantage of current regulatory guidelines to meet regulatory expectations. The general guidance documents to consult at the time of writing are: FDA Guidelines for High Purity Water System Inspection, High Purity Water Systems (7/93), EMEA CPMP/CVMP Notes for Water Quality Guidelines for Pharmaceutical Use (London), 2002) and USP Monograph & lt; 1231 & gt; Water For Pharmaceutical Purposes However, other jurisdictional documents may exist and it is the responsibility of practitioners who validate the water system to consult them. Currently the World Health Organization (WHO) as well as the Pharmaceutical Inspection Cooperation Scheme (PIC/S) developed a technical document outlining the validation requirements and strategies for water systems.
Analytical methods and techniques
Analytical measurements on-line
Conductivity/Resistivity
In pure water systems, electrolytic conductivity or resistivity measurements are the most common indicator of ionic contamination. The same basic measurements are read in either the microsiemens conductivity unit per centimeter (Ã,ÂμS/cm), typical of the pharmaceutical and power industries or in the megohm-centimeter (Mohmocm) resistivity unit used in the microelectronics industry. These units are reciprocal with each other. Pure pure water has a conductivity of 0.05501 μS/cm and a resistivity of 18.18 Mohmocm at 25 ° C, the most common reference temperature compensated by this measurement. An example of a sensitivity to the contamination of this measurement was 0.1 ppb sodium chloride increasing the pure water conductivity to 0.05523 μS/cm and decreasing the resistivity to 18.11 Mohmocm.
Ultrapure water is easily contaminated by traces of carbon dioxide from the atmosphere passing through small leaks or diffusing through thin wall polymer pipes when the sample line is used for measurement. Carbon dioxide forms conductive carbonic acids in water. For this reason, the most frequently used permanent conductivity probes are directly inserted into the ultimate ultra-pipe water to provide continuous continuous monitoring. This probe contains both conductivity and temperature sensors to allow for accurate compensation for the effects of very large temperatures on pure water conductivity. The conductivity of the probe has years of operation in pure water systems. They do not require maintenance except for periodic verification of measurements, usually annually.
Sodium
Sodium is usually the first ion to penetrate the exhausted cation exchanger. The measurement of sodium can quickly detect this condition and is widely used as an indicator for cation exchange regeneration. The effectiveness of the cation exchange effluent is always quite high due to the presence of anions and hydrogen ions and therefore conductivity measurements are useless for this purpose. Sodium is also measured in water power plants and steam samples because it is a common corrosive contaminant and can be detected at very low concentrations in the presence of higher ammonia and/or amine levels which have relatively high background conductivity.
On-line sodium measurements in ultrapure water are most common using selective glass sodium ion electrodes and reference electrodes in analyzers that measure small continuous stream flow samples. The measured voltage between the electrodes is proportional to the logarithm of the activity or the concentration of sodium ions, corresponding to the Nernst equation. Because of the logarithmic response, low concentrations in sub-parts per billion range can be measured on a regular basis. To prevent disturbance of hydrogen ions, the pH of the sample is increased by continuously adding pure amine before the measurement. Calibration at low concentrations is often done with automated analysis to save time and eliminate manual calibration variables.
Dissolved oxygen
The advanced microelectronics manufacturing process requires low soluble oxygen concentration up to 10 ppb in ultrapure wash water to prevent oxidation of layers and wafer layers. DO in water power plants and steam should be controlled to the ppb level to minimize corrosion. The copper alloy component in a power plant requires a single digit concentration of DO ppb while the iron alloy can benefit from a higher passive concentration effect in the 30 to 150 ppb range.
Dissolved oxygen is measured by two basic technologies: electrochemical cells or optical fluorescence. Traditional electrochemical measurements use sensors with gas permeable membranes. Behind the membrane, the electrode is immersed in an electrolyte developing an electric current proportional to the sample oxygen partial pressure. Signals are temperatures that are compensated for oxygen solubility in water, electrochemical cell output and the rate of oxygen diffusion through the membrane.
The DO fluorescent optical sensor uses a light source, fluorophore and optical detector. Fluorofora is immersed in the sample. Light is directed at fluorophore that absorbs energy and then re-emits light at longer wavelengths. The duration and intensity of the re-emitted light is related to the partial pressure of dissolved oxygen by the Stern-Volmer relationship. The signal is temperature compensated for oxygen solubility in water and fluorophore characteristics to obtain the DO concentration value.
Silica
Silica is a harmful contaminant of microelectronics processing and must be maintained at sub-ppb level. In silica the steam power plant can form precipitate on the heat exchange surface where it reduces thermal efficiency. In high temperature boilers, the silica will evaporate and carry with steam where it can form precipitate on the turbine blades which decrease aerodynamic efficiency. Silica deposits are very difficult to remove. Silica is the first easily measurable species to be released by anion exchange resins that are spent and is therefore used as a trigger for regenerating anion resins. Silica is non-conductive and therefore can not be detected by conductivity.
The silica was measured on a side stream sample by colorimetric analysis. Measurements of adding reagents include molybdate compounds and reducing agents to produce optically detectable blue silico-molybdate complex colors and are associated with concentrations in accordance with Beer-Lambert law. Most silica analyzers operate in semi-continuous automatic, isolating small volumes of samples, adding reagents in sequence and allowing sufficient time for reactions to occur while minimizing reagent consumption. The display and output signals are updated with each batch measurement result, usually at 10 to 20 minutes intervals.
Particle
Particles at UPW always present a major problem for semiconductor manufacturing, as any particle that lands on a silicon wafer can bridge the gap between electrical paths in a semiconductor circuit. When a short circuit the semiconductor device circuit will not work properly; Such failure is called yield loss, one of the most noteworthy parameters in the semiconductor industry. The preferred technique for detecting these single particles is to shine light (laser) through a small volume of UPW and detect light scattered by any particle (an instrument based on this technique called laser particle counters or LPCs). When semiconductor manufacturers pack more transistors into the same physical space, the width of the circuit line becomes narrow and narrow. As a result, LPC manufacturers have to use more and more powerful lasers and highly sophisticated light scattering detectors to compensate. When the line width is close to 10 nm (the human hair is about 100,000 nm in diameter), the LPC technology becomes limited by secondary optical effects, and new particle measurement techniques will be required.
Non-volatile
Other types of contamination in UPW are dissolved inorganic materials, especially silica. Silica is one of the most abundant minerals on the planet and is found in all water supplies. Dissolved inorganic materials have the potential to remain on the wafer when UPW dries. Again this can cause significant yield loss. To detect trace amounts of dissolved inorganic materials measurements of non-volatile residues are typically used. This technique involves using a nebulizer to create droplets from a suspended UPW in airflow. These droplets are dried at high temperatures to produce a non-volatile residue particle aerosol. A measuring instrument called a condensing particle counter then calculates the residual particles to give a reading in parts per trillion (ppt) based on the weight.
TOC
The total organic carbon is most often measured by oxidizing the organic in water to CO 2 , measuring the increase in CO 2 concentration after oxidation or delta CO 2 , and changing the amount of delta CO measured 2 becomes "carbon mass" per unit of concentration volume. The initial CO 2 in the water sample is defined as Inorganic Carbon or IC. CO 2 produced from oxidized organic and any initial CO 2 (IC) are both defined together as Total Carbon or TC. The TOC value is then equal to the difference between TC and IC.
Organic oxidation method for TOC analysis
The organic oxidation for CO 2 is most commonly achieved in aqueous solutions by the creation of highly oxidizing chemical species, hydroxyl radicals (OHo). Organic oxidation in combustion environments involves the creation of other energetic molecular oxygen species. For typical TOC levels in the UPW system, most methods use hydroxyl radicals in the liquid phase.
There are several methods to create sufficient concentrations of hydroxyl radicals required to fully oxidize the organic in water to CO 2 , each of which is suitable for different levels of water purity. For typical feeding water to the front end UPW raw water purification system can contain TOC levels between 0.7 mg/L to 15 mg/L and requires a strong oxidation method that can ensure there is enough oxygen available to convert completely. carbon atoms in organic molecules becomes CO 2 . Strong oxidizing methods that supply sufficient oxygen include the following methods; Ultraviolet (UV) & amp; persulfate, heat persulfate, burning, and super critical oxidation. The general equations which show the persulfate of hydroxyl radical generation follow.
S 2 O 8 -2 h? (254Â nm) -> 2 SO 2 -1 o dan SO 2 -1 o H 2 O -> HSO 4 -1 OH o
When organic concentrations are less than 1 mg/L as TOC and water saturated with UV light oxygen is enough to oxidize organically into CO 2 , this is a simpler oxidation method. UV light wavelengths for lower TOC waters must be less than 200 nm and typically 184 nm produced by low pressure Hg steam lamps. The 184m UV light is energetic enough to break the water molecules into OH and H radicals. Hydrogen radicals react quickly to create H 2 . The equation follows:
Home H 2 O h? (185Ã, nm) -> OHo H or dan H or H o ​​-> H 2
Different Types of TOC UPW Analysis
IC (Inorganic Carbon) = CO 2 HCO 3 - CO 3 -2
TC (Total Karbon) = Karbon Organik IC
TOC (Total Organic Carbon) = TC - IC
H 2 O h? (185Â nm) -> OHo H o
S 2 O 8 -2 h? (254Â nm) -> 2 SO 2 -1 o
SO 2 -1 o H 2 O -> HSO 4 -1 OH o
Analisis lab offline
When testing the quality of UPW, consideration is given to where the quality is required and where it should be measured. The distribution or delivery point (POD) is the point in the system immediately after the last maintenance step and before the distribution loop. This is the standard location for most analytic tests. The connection point (POC) is another common point used to measure UPW quality. This is located in the outlet or lateral valve outlet that is used to supply the UPW to the appliance.
Take for example free UPW analysis for online or alternative testing, depending on the availability of the instrument and the level of UPW quality specifications. Grab sample analysis is usually performed for the following parameters: metal, anion, ammonium, silica (both dissolved and total), particles by SEM (scanning electron microscope), TOC (total organic compound) and specific organic compounds.
Metal analysis is usually performed by ICP-MS (Inductively coupled plasma mass spectrometry). The detection rate depends on the specific type of instrument used and the sample preparation and handling methods. The current cutting method allows achieving sub-ppt (parts per trillion) rate (& lt; 1 ppt) typically tested by ICPMS.
Anion analysis for the seven most common inorganic anions (sulfate, chloride, fluoride, phosphate, nitrite, nitrate, and bromide) was performed by ion chromatography (IC), reaching the limit of single ppt digit detection. ICs are also used to analyze ammonia and other metal cations. However ICPMS is the preferred method for metals because of its lower detection limit and its ability to detect dissolved and dissolved metals in UPW. ICs are also used to detect urea at UPW to a level of 0.5 ppb. Urea is one of the most common contaminants in UPW and probably the most difficult to treat.
Silica analysis in UPW usually includes the determination of total and reactive silica. Because of the chemical complexity of silica, the measured silica form is determined by the photometric method (colorimetry) as molybdate-reactive silica. Molybdate-reactive silica forms include soluble simple silicates, monomeric silicas and silicic acid, and undeserved silica polymer fractions. Determination of total silica in water using high-resolution ICPMS, GFAA (absorption of graphite absorption atoms), and photometric methods combined with silica digestion. For many natural waters, the measurement of molybdate-reactive silica by this test method gives approaches to total silica, and, in practice, the method of colorimetry is often superseded for other, more time-consuming techniques. However, total silica analysis becomes more important in UPW, where the presence of colloidal silica is expected due to the polymerization of silica in the ion exchange column. Colloidal silica is considered more important than dissolved in the electronics industry because of the greater impact of nanoparticles in water in semiconductor manufacturing processes. The Sub-ppb silica level (parts per billion) makes it as complex for the analysis of total and reactive silica, making the choice of the total silica assay often preferred.
Although particles and TOCs are typically measured using on-line methods, there is a significant value in free or alternative off-line lab analysis. The value of lab analysis has two aspects: cost and speciation. The smaller UPW facilities that can not afford on-line instrumentation often opt for off-line testing. TOC can be measured in grab samples at concentrations as low as 5 ppb, using the same technique used for on-line analysis (see the description of on-line method). This level of detection covers most of the less critical electronic needs and all pharmaceutical applications. When organic speciation is required for problem-solving or design purposes, organic carbon-chromatographic organic (LC-OCD) detection provides an effective analysis. This method allows for the identification of biopolymers, humics, low molecular weight and neutral acids, and more, while the characteristics of nearly 100% of the organic composition at UPW with sub-ppb levels of TOC.
Similar to TOC, SEM particle analysis is a lower cost alternative to expensive online measurement and therefore generally preferred methods in less critical applications. SEM analysis can provide particle calculations for particle sizes up to 50 nm, which are generally in line with the capabilities of online instruments. This test involves installing a SEM filter cartridge filter on the UPW sampling port for sampling on a membrane disk with pore size equal to or smaller than the target size of the UPW particle. The filter is then transferred to a SEM microscope where the surface is scanned to detect and identify particles. The main disadvantage of SEM analysis is the long sampling time. Depending on the pore size and pressure in the UPW system, the sampling time can be between one week and one month. However, the typical resilience and stability of particulate filtration systems allows the successful application of SEM methods. The application of Energy Dispersive X-ray Spectroscopy (SEM-EDS) provides particle composition analysis, making SEM also helpful for systems with on-line particle counters.
Bacterial analysis is usually performed following ASTM F1094 method. Test methods include sampling and analysis of high purity water from water purification systems and water transmission systems with direct sampling taps and filtering of samples collected in pouches. This test method includes sampling the water line and subsequent microbiological analysis of the sample by culture technique. Microorganisms recovered from water samples and calculated on filters including aerobic and facultative anaerobes. The incubation temperature is controlled at 28 Ã, Â ± 2 Ã, Â ° C, and the incubation period is 48 hours or 72 hours, if time permits. Longer incubation times are usually recommended for most important applications. But 48 hours is usually enough to detect water quality disturbances.
Purification process
UPW system design for semiconductor industry
Usually urban feedwater (containing all the previously mentioned undesirable contaminants) is taken through a series of purification steps which, depending on the quality of UPW want, include dirty filtration for large particulates, carbon filtering, water softening, reverse osmosis, ultraviolet (UV) light exposure for TOC and/or static bacterial control, polishing using ion exchange resin or electrodeionization (EDI) and ultimately filtration or ultrafiltration.
Some systems use direct returns, turning back or serpentine loops that return water to storage areas, providing continuous recirculation, while others are disposable systems that run from the UPW production point to the point of use. The constant recirculation action in the former constantly polishes the water with each pass. The latter may be susceptible to contamination if left unused.
For modern UPW systems, it is important to consider site and specific process requirements such as environmental constraints (eg, waste water discharge limits) and take back opportunities (eg, there is a minimum required amount to reclaim as needed). The UPW system consists of three subsystems: pretreatment, primary, and polishing. Most systems are similar in design but may vary in the pre-treatment section depending on the nature of the water source.
Pretreatment: Pretreatment produces pure water. Pretreatments commonly used are two pass Reverse Osmosis, Demineralization plus Reverse Osmosis or HERO (High Efficiency Reverse Osmosis). In addition, the upstream filtration rate of this process will be determined by the degree of suspended, turbidity and organic solids present in the water source. Common types of filtering are multi-media, automatic backwashable filters and ultrafiltration for suspended suspended solids and turbidity reduction and Activated Carbon for organic reduction. Activated Carbon can also be used to remove upstream chlorine from the steps of Reverse Osmosis Demineralization. If Activated Carbon is not used then sodium bisulfite is used to de-chlorinate the feed water.
Primary: Primary treatment consists of ultraviolet (UV) light for organic reduction, EDI and or mixed ion exchange for demineralization. The mixed bed may not be updated (following EDI), in-situ or externally regenerated. The final step in this section is the removal of dissolved oxygen using the process of membrane degasification or vacuum degasification.
Polishing: Polishing consists of UV, heat exchange for constant temperature control in UPW supply, non-regenerable ion exchange, degasification membrane (to polish UPW end requirements) and ultrafiltration to achieve required particle level. Some semiconductor fabs require UPW heat for some of the process. In this case the polished UPW is heated in the range of 70 to 80C before being delivered to manufacturing. Most of these systems include heat recovery where the UPW heat back from manufacturing goes to the heat recovery unit before being returned to the UPW feed tank to conserve water heater usage or the need to cool the UPW heat backflow.
UPW key design criteria for semiconductor fabrication
Remove contaminants as far forward in the system as practical and cost-effective.
Steady state flow in makeup and main parts to avoid TOC and conductivity spikes (NOT start/stop operation). Excessive flow recirculation to the upstream.
Minimize the use of chemicals following a reverse osmosis unit.
Consider an EDI and non-regenerable primary bed instead of an in-situ or external primary bed to ensure optimal UPW quality makeup and minimize potential irritability.
Choose materials that will not contribute TOC and particle to system especially in main part and polishing. Minimize stainless steel material in polishing circle and if using electropolishing is recommended.
Minimize dead feet in piping to avoid potential bacterial propagation.
Maintain minimum scrubbing speeds in piped and distribution networks to ensure turbulent flow. The recommended minimum is based on Reynolds 3,000 Re or higher. This can reach up to 10,000 Re depending on the designer's comfort level.
Use only pure resin in mixed beds. Replace every one to two years.
Supply UPW to manufacturing at constant flow and constant pressure to avoid system breakdowns such as sprinkling of particles.
Utilize the reverse distribution backflow design for hydraulic balance and to avoid backflow (back to supply).
Capacity considerations
Capacity plays an important role in engineering decisions about the configuration and size of UPW systems. For example, the Polish system of older and smaller sized electronic systems is designed for minimum flow rate criteria of up to 2 feet per second at the end of the pipe to avoid bacterial contamination. Larger fabs require a larger size UPW system. The figure below illustrates the increase in consumption driven by larger wafer sizes produced in the new fab. However, for larger pipes (driven by higher consumption), the 2 feet per second criterion means very high consumption and large Polishing systems. The industry responds to this problem and through extensive inquiry, higher purity material options, and optimized distribution designs are able to reduce design criteria for minimum flow, using the Reynolds number criterion.
The image on the right illustrates an interesting coincidence that the largest diameter of the main supply line of UPW is equal to the size of the wafer in production (this relationship is known as Klaiber law). The growing size of piping as well as the overall system requires a new approach to space management and process optimization. As a result, newer UPW systems look somewhat similar, as opposed to smaller UPW systems that can have less optimized designs because of the lower impact of inefficiencies on cost and space management.
Other capacity considerations related to the operation of the system. Small lab scale systems (few gallons per minute) usually do not involve operators, while large-scale systems typically operate 24x7 by trained operators. As a result, smaller systems are designed without using less chemicals and water and energy efficiency than larger systems.
Critical UPW Problem
Particle control
Particles in UPW are important contaminants, which produce various forms of defects on the surface of the wafer. With the large volume of UPW, which is in contact with each wafer, the deposition of the particles on the wafer is ready to occur. Once stored, the particles are not easily removed from the surface of the wafer. With the increasing use of aqueous chemistry, the particles at UPW are a problem not only with wafer UPW wafers, but also because of particle introduction during wet and dilute wettage, where UPW is the main constituent of the chemical used.
The particle level should be controlled for the size of nm, and the current trend is close to 10 nm and smaller for particle control in UPW. While the filter is used for the main loop, the UPW system components can contribute additional particle contamination into the water, and at the point of use, additional filtering is recommended.
The filter itself must be made of ultraclean and strong material, which does not contribute organic or cation/anion to UPW, and must be tested for plant integrity to ensure reliability and performance. Common materials include nylon, polyethylene, polysulfone, and fluoropolymers. Filters will generally be constructed from a combination of polymers, and for UPW use thermally welded without the use of other contaminated adhesives or additives.
The microporous structure of the filter is very important in providing particle control, and this structure can be isotropic or asymmetric. In the previous case the pore distribution was uniform through the filter, while on the latter the smoother surface gave the removal of the particles, with a rough structure providing physical support as well as reducing the overall differential pressure.
Filters can be a cartridge format in which UPW is flowed through a pleated structure with contaminants collected directly on the surface of the filter. Common in UPW systems are ultrafilters (UF), composed of hollow fiber membranes. In this configuration, UPW is flown across a hollow fiber, sweeping contaminants into the waste stream, known as retentate flow. The retentate stream is only a fraction of the total stream, and delivered to the trash. The product water, or permeate stream, is the UPW that passes through the hollow fiber skin and out through the hollow fiber center. UF is a very efficient filtering product for UPW, and the sweeping of particles into the retentate stream produces a very long life with only occasional cleaning required. UF use in UPW system provides excellent particle control for single digit nanometer particle size.
Point of use applications (POUs) for UPW filtration include wet and clean etching, rinse before vapor IPA or dry liquids, as well as UPW lithography dispenses following rinse develop. This application poses a special challenge for UPW POU filtering.
For wet and clean etching, most tools are a single wafer process, which requires a flow through a filter on the device request. The resulting intermittent flow, which will range from full flow through the filter after initiation of the UPW flow through the spray nozzle, and then returned to the flow of the stream. Trickle flow is usually maintained to prevent dead legs in the tool. Filters must be strong to withstand low pressure and cycles, and should continue to retain the particles captured during the life of the filter. This requires proper pleat design and geometry, as well as media designed to optimize particle capture and retention. Certain tools can use fixed filter housings with replaceable filters, while other tools can use disposable filter capsules for UPW POUs.
For lithography applications, small filter capsules are used. Similar to the challenges for wet etching and clean UPW POU applications, for UPW lithography rinse, the flow through the filter is intermittent, albeit at low flow and pressure, so that physical resistance is not so important. Another UPW POU application for lithography is submersion water used in lens/wafer interfaces for 193Ã © lithography immersion immersion patterns. UPW forms puddles between lens and wafer, increases NA, and UPW must be very pure. POU filtering is used on the UPW just before the stepper scanner.
For UPW POU applications, sub 15 nm filters are currently used for 2x and 1x advanced nodes. Filters are generally made of nylon, high-density polyethylene (HDPE), polyarylsulfone (or polysulfone), or polytetrafluoroethylene (PTFE) membranes, with hardware usually composed of HDPE or PFA.
Treatment of point of use (POU) for organic
Treatment points are often applied in important tool applications such as Immersion lithography and Mask preparation to maintain consistent ultrapure water quality. The UPW system located in the central utility building provides Fab with water quality but may not provide adequate water purification consistency for this process.
In cases where urea, THM, isopropyl alcohol (IPA) or other hard to remove (low molecular weight neutral compounds) TOC species may be present, additional treatment is required through advanced oxidation processes (AOPs) using the system. This is very important when strict TOC specifications below 1 ppb should be achieved. This difficult organic control has been shown to have an impact on the results and performance of the device, especially on the most demanding process steps. One successful example of the POU organic control up to 0.5 ppb of the TOC level is the AOP that combines ammonium persulfate and UV oxidation (see UV and persulfate oxidation chemistry in TOC measurements).
The exclusive process of exclusive POU oxidation can consistently reduce TOC to 0.5 parts per billion (ppb) in addition to maintaining consistent temperatures, oxygen and particles exceeding the SEMI F063 requirements. This is important because even the slightest variation can directly affect the manufacturing process, significantly affecting product results.
Recycle UPW in semiconductor industry
The semiconductor industry uses large amounts of ultrapure water to rinse contaminants off the surface of silicon wafers which are then converted into computer chips used in devices we use on a daily basis. Ultrapure water is by a very low definition in contamination, but after that makes contact with the surface of the wafer it brings the remaining chemicals or particles from the surface which then ends up in the industrial waste treatment system from the manufacturing facility. The level of pollution of rinse water can vary greatly depending on the step of a particular process being rinsed at that time. The first "rinsing" step can carry large amounts of residual and particulate contaminants compared to the last rinse that can carry relatively low amounts of contamination. Typical semiconductor plants have only two drain systems for all of these rinses which are also combined with acidic wastes and therefore rinsing water is not effectively reused due to the risk of contamination causing manufacturing process defects.
Define:
The following definitions are used by ITRS:
- UPW Recycle - Reuse of the same in-app water after treatment
- Air Reuse - Use it in the secondary app
- Water Reclaim - Extracts water from wastewater
Water retrieval and recycling:
Some semiconductor manufacturing plants have used reclaimed water for non-process applications such as chemical aspirators in which waste water is shipped to industrial waste. Water reclamation is also a typical application in which rinse water spent from manufacturing facilities can be used in the supply of cooling towers, scrubber cleaning supplies, or point-of-use reduction systems. UPW recycling is not as usual and involves collecting rinsed water, treating it and reusing it in the wafer rinsing process. Some additional water treatment may be required for these cases depending on the quality of rinse water spent and the reclamation water application. This is a fairly common practice in many semiconductor facilities around the world, but there are limits to how much water can be reclaimed and recycled if it does not consider reuse in the manufacturing process.
UP UP UPDATE:
The recycling of rinse water from the semiconductor manufacturing process has been underestimated by many manufacturing engineers for decades because of the risk that contamination from residues and chemical particles can end up back in UPW feedwater and result in product defects. The Modern Ultrapure Water System is very effective at removing ionic contamination down to the trillions per trillion (ppt) level while organic contamination of ultrapure water systems is still in parts per billion level (ppb). However, the process of recycling the process of rinse water for UPW makeup has always been a big concern and to date this is not a common practice. Increased water and wastewater costs in parts of the US and Asia have encouraged some semiconductor companies to investigate the recycling of rinse water-making processes in the UPW dressing system. Some companies have incorporated approaches that use complex, large-scale maintenance designed for the worst conditions of combined waste water discharges. Recently a new approach has been developed to incorporate detailed water management plans to try to minimize the cost and complexity of the maintenance system.
Water management plan:
The key to maximizing water retrieval, recycling, and reuse is to have a well thought-out water management plan. Successful water management plans include a full understanding of how rinse water is used in manufacturing processes including the chemicals used and their products. With the development of this important component, the disposal collection system can be designed to separate concentrated chemicals from contaminated rinse water, and contaminated rinse water. Once separated into a separate collection system, the chemical waste streams once considered to be altered or sold as a product stream, and rinse water can be reclaimed.
The water management plan will also require large amounts of data and sample analysis to determine proper channel separation, the adoption of online analytic measurements, transfer controls and final processing technologies. Collecting these samples and conducting laboratory analysis can help characterize the various waste streams and determine their potential reuse. In the case of the UPW process, rinse the lab analysis data then can be used for the typical and non-typical contamination profile profiles which can then be used to design the rinse water treatment system. In general, the most cost effective way to design a system to treat typical pollution levels that may occur is 80-90% of the time, then incorporating on-line sensors and controls to divert rinse water to industrial waste or to non-critical use such as cooling towers when the level of contamination exceeds the ability of the treatment system. By incorporating all aspects of the water management plan at semiconductor manufacturing sites, the water usage rate can be reduced by 90%.
Transport
Stainless steel remains the preferred piping material for the pharmaceutical industry. Due to its metal contribution, most of the steel was removed from the microelectronic UPW system in 1980 and replaced with high performance polymer polyvinylidene fluoride (PVDF), perfluoroalkoxy (PFA), ethylene chlorotrifluoroethylene (ECTFE) and polytetrafluoroethylene (PTFE) in the US and Europe.. In Asia, polyvinyl chloride (PVC), polyvinyl chloride (CPVC) and polypropylene (PP) chlorinated are very popular, along with high performance polymers.
The join method with thermoplastics used for the UPW transport
Thermoplastics can be combined with different thermofusion techniques.
- Socket fusion (SF) is a process in which the outer diameter of the pipe uses a "fit" fit with the inner diameter of the fittings. Both pipes and fittings are heated on the bushing (outside and inside, respectively) for a specified time period. Then the pipe is pressed into the fittings. After cooling the welded part is removed from the clamp.
- Conventional fusion pedestal (CBF) is a process in which two components to be connected have the same inner and outer diameters. The tip is heated by pressing it to the opposite side of the heating plate for a specified time period. Then the two components are put together. After cooling the welded part is removed from the clamp.
- Bead and crevice free (BCF), using the process of placement of two thermoplastic components having the same inner and outer diameters. Furthermore, the bladder bladder is introduced inside the component and placed in two components. The head of the heater clamps the joint components and the bladder increases. After a specified period of time, the head of the heater starts to cool and the bladder deflates. After completely cooled the bladder is removed and the joining component is taken from the clamp station. The benefit of the BCF system is that there is no weld bead, which means that the surface of the weld zone is routinely as smooth as the inner wall of the pipe.
- Infrared (IR) fusion is a process similar to CBF except that its component ends never touch the heater head. In contrast, the energy to thaw the thermoplastic is transferred by radiant heat. IRs come in two variations; one uses overlap distances when carrying two components together while others use pressure. The use of overlap on the first reduces the visible variation in bead size, which means that the proper dimensional tolerances required for industrial installation can be maintained better.
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Source of the article : Wikipedia
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