Article Title: Direct nanoscale observations of the coupled dissolution of calcite and dolomite and the precipitation of gypsum. Etch pits developed and spread. As pH was decreased to 4. Selected squared region in a to calculate the step-retreat rate based on the variation in length with time of. Figure Lengend Snippet: AFM deflection images of reacting calcite surface: a dissolution in Millipore MQ water; b after injecting a solution in equilibrium with gypsum at pH 2.
Buy from Supplier. Structured Review. Millipore mq water Mq Water, supplied by Millipore, used in various techniques. For use as a cleaning and etching agent, impurities which can cause product contamination or impact process efficiency e. In chemical-mechanical polishing processes, water is used in addition to reagents and abrasive particles.
A typical use of ultrapure water in pharmaceutical and biotechnology industries is summarized in the table below: . In order to be used for pharmaceutical and biotechnology applications for production of licensed human and veterinary health care products it must comply with the specification of the following pharmacopeias monographs:. Note: Purified Water is typically a main monograph which references other applications that use Ultrapure water.
Ultrapure water is often used as a critical utility for cleaning applications as required. It is also used to generate clean steam for sterilization. The following table summarizes the specifications of two major pharmacopoeias for 'water for injection':.
Ultrapure water validation must utilize a risk-based lifecycle approach. One should utilize current regulatory guidance to comply with regulatory expectations. In pure water systems, electrolytic conductivity or resistivity measurement is the most common indicator of ionic contamination. These units are reciprocals of each other. Absolutely pure water has a conductivity of 0. An example of the sensitivity to contamination of these measurements is that 0.
Ultrapure water is easily contaminated by traces of carbon dioxide from the atmosphere passing through tiny leaks or diffusing through thin wall polymer tubing when sample lines are used for measurement. Carbon dioxide forms conductive carbonic acid in water.
For this reason, conductivity probes are most often permanently inserted directly into the main ultrapure water system piping to provide real-time continuous monitoring of contamination. These probes contain both conductivity and temperature sensors to enable accurate compensation for the very large temperature influence on the conductivity of pure waters.
Conductivity probes have an operating life of many years in pure water systems. They require no maintenance except for periodic verification of measurement accuracy, typically annually. Sodium is usually the first ion to break through a depleted cation exchanger. Sodium measurement can quickly detect this condition and is widely used as the indicator for cation exchange regeneration. The conductivity of cation exchange effluent is always quite high due to the presence of anions and hydrogen ion and therefore conductivity measurement is not useful for this purpose.
On-line sodium measurement in ultrapure water most commonly uses a glass membrane sodium ion-selective electrode and a reference electrode in an analyzer measuring a small continuously flowing side-stream sample. The voltage measured between the electrodes is proportional to the logarithm of the sodium ion activity or concentration, according to the Nernst equation. Because of the logarithmic response, low concentrations in sub-parts per billion ranges can be measured routinely.
To prevent interference from hydrogen ion, the sample pH is raised by the continuous addition of a pure amine before measurement. Calibration at low concentrations is often done with automated analyzers to save time and to eliminate variables of manual calibration. Advanced microelectronics manufacturing processes require low single digit to 10 ppb dissolved oxygen DO concentrations in the ultrapure rinse water to prevent oxidation of wafer films and layers.
DO in power plant water and steam must be controlled to ppb levels to minimize corrosion. Copper alloy components in power plants require single digit ppb DO concentrations whereas iron alloys can benefit from the passivation effects of higher concentrations in the 30 to ppb range. Dissolved oxygen is measured by two basic technologies: electrochemical cell or optical fluorescence.
Traditional electrochemical measurement uses a sensor with a gas-permeable membrane. Behind the membrane, electrodes immersed in an electrolyte develop an electric current directly proportional to the oxygen partial pressure of the sample. The signal is temperature compensated for the oxygen solubility in water, the electrochemical cell output and the diffusion rate of oxygen through the membrane.
Optical fluorescent DO sensors use a light source, a fluorophore and an optical detector. The fluorophore is immersed in the sample. Light is directed at the fluorophore which absorbs energy and then re-emits light at a longer wavelength. The duration and intensity of the re-emitted light is related to the dissolved oxygen partial pressure by the Stern—Volmer relationship.
The signal is temperature compensated for the solubility of oxygen in water and the fluorophore characteristics to obtain the DO concentration value. Silica is a contaminant that is detrimental to microelectronics processing and must be maintained at sub-ppb levels. In steam power generation silica can form deposits on heat-exchange surfaces where it reduces thermal efficiency. In high temperature boilers, silica will volatilize and carry over with steam where it can form deposits on turbine blades which lower aerodynamic efficiency.
Silica deposits are very difficult to remove. Silica is the first readily measurable species to be released by a spent anion exchange resin and is therefore used as the trigger for anion resin regeneration. Silica is non-conductive and therefore not detectable by conductivity. Silica is measured on side stream samples with colorimetric analyzers. The measurement adds reagents including a molybdate compound and a reducing agent to produce a blue silico-molybdate complex color which is detected optically and is related to concentration according to the Beer—Lambert law.
Most silica analyzers operate on an automated semi-continuous basis, isolating a small volume of sample, adding reagents sequentially and allowing enough time for reactions to occur while minimizing consumption of reagents. The display and output signals are updated with each batch measurement result, typically at 10 to minute intervals. Particles in UPW have always presented a major problem for semiconductor manufacture, as any particle landing on a silicon wafer can bridge the gap between the electrical pathways in the semiconductor circuitry.
When a pathway is short-circuited the semiconductor device will not work properly; such a failure is called a yield loss, one of the most closely watched parameters in the semiconductor industry. The technique of choice to detect these single particles has been to shine a light beam a laser through a small volume of UPW and detect the light scattered by any particles instruments based on this technique are called laser particle counters or LPCs.
As semiconductor manufacturers pack more and more transistors into the same physical space, the circuitry line-width has become narrow and narrower. As a result, LPC manufacturers have had to use more and more powerful lasers and very sophisticated scattered light detectors to keep pace. As line-width approaches 10 nm a human hair is approximately , nm in diameter LPC technology is becoming limited by secondary optical effects, and new particle measurement techniques will be required.
Another type of contamination in UPW is dissolved inorganic material, primarily silica. Silica is one of the most abundant mineral on the planet and is found in all water supplies. Any dissolved inorganic material has the potential to remain on the wafer as the UPW dries. Once again this can lead to a significant loss in yield. To detect trace amounts of dissolved inorganic material a measurement of non-volatile residue is commonly used.
This technique involves using a nebulizer to create droplets of UPW suspended in a stream of air. These droplets are dried at a high temperature to produce an aerosol of non-volatile residue particles. A measurement device called a condensation particle counter then counts the residue particles to give a reading in parts per trillion ppt by weight.
Total organic carbon is most commonly measured by oxidizing the organics in the water to CO 2 , measuring the increase in the CO 2 concentration after the oxidation or delta CO 2 , and converting the measured delta CO 2 amount into "mass of carbon" per volume concentration units.
Organic oxidation in a combustion environment involves the creation of other energized molecular oxygen species. There are multiple methods to create sufficient concentrations of hydroxyl radicals needed to completely oxidize the organics in water to CO 2 , each method being appropriate for different water purity levels. For typical raw waters feeding into the front end of an UPW purification system the raw water can contain TOC levels between 0.
Typical equations showing persulfate generation of hydroxyl radicals follows. The wavelength of the UV light for the lower TOC waters must be less than nm and is typically nm generated by a low pressure Hg vapor lamp. The hydrogen radicals quickly react to create H 2. The equations follow:. When testing the quality of UPW, consideration is given to where that quality is required and where it is to be measured.
The point of distribution or delivery POD is the point in the system immediately after the last treatment step and before the distribution loop. It is the standard location for the majority of analytical tests. It is located at the outlet of the submain or lateral take off valve used for UPW supply to the tool. Grab sample UPW analyses are either complementary to the on-line testing or alternative, depending on the availability of the instruments and the level of the UPW quality specifications.
Grab sample analysis is typically performed for the following parameters: metals, anions, ammonium, silica both dissolved and total , particles by SEM scanning electron microscope , TOC total organic compounds and specific organic compounds. The detection level depends on the specific type of the instrument used and the method of the sample preparation and handling.
The anion analysis for seven most common inorganic anions sulfate, chloride, fluoride, phosphate, nitrite, nitrate, and bromide is performed by ion chromatography IC , reaching single digit ppt detection limits. IC is also used to analyze ammonia and other metal cations. However ICPMS is the preferred method for metals due to lower detection limits and its ability to detect both dissolved and non-dissolved metals in UPW.
IC is also used for the detection of urea in UPW down to the 0. Urea is one of the more common contaminants in UPW and probably the most difficult for treatment. Silica analysis in UPW typically includes determination of reactive and total silica. Those forms of silica that are molybdate-reactive include dissolved simple silicates, monomeric silica and silicic acid, and an undetermined fraction of polymeric silica. Total silica determination in water employs high resolution ICPMS, GFAA graphite furnace atomic absorption ,  and the photometric method combined with silica digestion.
For many natural waters, a measurement of molybdate-reactive silica by this test method provides a close approximation of total silica, and, in practice, the colorimetric method is frequently substituted for other more time-consuming techniques. However, total silica analysis becomes more critical in UPW, where the presence of colloidal silica is expected due to silica polymerization in the ion exchange columns. Colloidal silica is considered more critical than dissolved in the electronic industry due to the bigger impact of nano-particles in water on the semiconductor manufacturing process.
Sub-ppb parts per billion levels of silica make it equally complex for both reactive and total silica analysis, making the choice of total silica test often preferred. Although particles and TOC are usually measured using on-line methods, there is significant value in complementary or alternative off-line lab analysis.
The value of the lab analysis has two aspects: cost and speciation. Smaller UPW facilities that cannot afford to purchase on-line instrumentation often choose off-line testing. TOC can be measured in the grab sample at a concentration as low as 5 ppb, using the same technique employed for the on-line analysis see on-line method description.
This detection level covers the majority of needs of less critical electronic and all pharmaceutical applications. When speciation of the organics is required for troubleshooting or design purposes, liquid chromatography-organic carbon detection LC-OCD provides an effective analysis.
Similar to TOC, SEM particle analysis represents a lower cost alternative to the expensive online measurements and therefore it is commonly a method of choice in less critical applications. SEM analysis can provide particle counting for particle size down to 50 nm, which generally is in-line with the capability of online instruments.
The test involves installation of the SEM capture filter cartridge on the UPW sampling port for sampling on the membrane disk with the pore size equal or smaller than the target size of the UPW particles. The filter is then transferred to the SEM microscope where its surface is scanned for detection and identification of the particles.
The main disadvantage of SEM analysis is long sampling time. Depending on the pore size and the pressure in the UPW system, the sampling time can be between one week and one month. However, typical robustness and stability of the particle filtration systems allow for successful applications of the SEM method. These test methods cover both the sampling of water lines and the subsequent microbiological analysis of the sample by the culture technique.
The microorganisms recovered from the water samples and counted on the filters include both aerobes and facultative anaerobes. Longer incubation times are typically recommended for most critical applications. However 48 hrs is typically sufficient to detect water quality upsets. Some systems use direct return, reverse return or serpentine loops that return the water to a storage area, providing continuous re-circulation, while others are single-use systems that run from point of UPW production to point of use.
The constant re-circulation action in the former continuously polishes the water with every pass. The latter can be prone to contamination build up if it is left stagnant with no use. For modern UPW systems it is important to consider specific site and process requirements such as environmental constraints e. UPW systems consist of three subsystems: pretreatment, primary, and polishing.
Most systems are similar in design but may vary in the pretreatment section depending on the nature of the source water. Pretreatment: Pretreatment produces purified water. The common types of filtration are multi-media, automatic backwashable filters and ultrafiltration for suspended solids removal and turbidity reduction and Activated Carbon for the reduction of organics.
The Activated Carbon may also be used for removal of chlorine upstream of the Reverse Osmosis of Demineralization steps. If Activated Carbon is not employed then sodium bisulfite is used to de-chlorinate the feed water. Primary: Primary treatment consists of ultraviolet light UV for organic reduction, EDI and or mixed bed ion exchange for demineralization. The mixed beds may be non-regenerable following EDI , in-situ or externally regenerated.
The last step in this section may be dissolved oxygen removal utilizing the membrane degasification process or vacuum degasification. Polishing: Polishing consists of UV, heat exchange to control constant temperature in the UPW supply, non-regenerable ion exchange, membrane degasification to polish to final UPW requirements and ultrafiltration to achieve the required particle level. Some semiconductor Fabs require hot UPW for some of their processes.
In this instance polished UPW is heated in the range of 70 to 80C before being delivered to manufacturing. Most of these systems include heat recovery wherein the excess hot UPW returned from manufacturing goes to a heat recovery unit before being returned to the UPW feed tank to conserve on the use of heating water or the need to cool the hot UPW return flow.
Recirculate excess flow upstream. Consider EDI and non-regenerable primary mixed beds in lieu of in-situ or externally regenerated primary beds to assure optimum quality UPW makeup and minimize the potential for upset. Select materials that will not contribute TOC and particles to the system particularly in the primary and polishing sections. Minimize stainless steel material in the polishing loop and, if used, electropolishing is recommended.
Maintain minimum scouring velocities in the piping and distribution network to ensure turbulent flow. The recommended minimum is based on a Reynolds number of 3, Re or higher. This can range up to 10, Re depending on the comfort level of the designer. Supply UPW to manufacturing at constant flow and constant pressure to avoid system upsets such as particle bursts.
Utilize reverse return distribution loop design for hydraulic balance and to avoid backflow return to supply. Capacity plays an important role in the engineering decisions about UPW system configuration and sizing. For example, polish systems of older and smaller size electronic systems were designed for minimum flow velocity criteria of up to 2 ft per second at the end of pipe to avoid bacterial contamination.
Larger fabs required larger size UPW systems. The figure below illustrates the increasing consumption driven by the larger size of wafer manufactured in newer fabs. However, for larger pipe driven by higher consumption the 2 ft per second criteria meant extremely high consumption and an oversized polishing system. The industry responded to this issue and through extensive investigation, choice of higher purity materials, and optimized distribution design was able to reduce the design criteria for minimum flow, using Reynolds number criteria.
The figure 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 relation is known as Klaiber's law. Growing size of the piping as well as the system overall requires new approaches to space management and process optimization. As a result, newer UPW systems look rather alike, which is in contrast with smaller UPW systems that could have less optimized design due to the lower impact of inefficiency on cost and space management.
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"Milli-Q water is water that has been purified using an ion exchange cartridge. The purity of the water is monitored by measuring the. Type I/MilliQ Water has resistivity of 18 Megaohm-cm, deionized/demineralized water = Megaohm-cm, distilled water/Type II = 2 Megaohm-cm. While mQ water has been deionised/demineralised and gone through filter to remove all life forms or treated with UV-irradiation. Overall, distilled water is.