Point-of-use filtration

These large groups of particles are not desirable in CMP slurry. They will cause scratches and show an additional peak on the particle size distribution curve (see Fig. 6). To fix these problems, milling and/or slurry filters can be used. Milling is used at the point of slurry manufacture, and filtration is used at the point of use (filtration can also be used to fix the long tail problems mentioned in Fig. 2b), as discussed in the following. 

Fig. 11. Evaluation of particle post-CMP performance for commercial oxide slurries with fumed and colloidal silica with and without point-of-use filtration. The filter size is 0.3 /im. The bottom denotes that the slurry used is from the bottom of the drum.

For precision applications where the work is especially sensitive to system contamination (e.g., disk drive, optical, or electronic components), point-of-use filtration is required. Currently absolute pleated filters of 0.1 micron rating are recommended. 

Potential applications exist in industrial separations, water softening, and point-of-use filtration for high purity water in semiconductor chip manufactur-... 

Applications for NF-50 membrane potentially include industrial separations, partial water softening, removal of trihalomethane precursors from groundwaters, and point-of-use filtration of high purity water for semiconductor chip manufacturing. 

Point-of-use filtration - 0.2 micron filter pore size... 

The primary market for the disposable cartridge is sterile filtration for the pharmaceutical industry and final point-of-use polishing of ultrapure water for the microelectronics industry. Both industries require very high-quality, particle-free water. The cost of microfiltration compared to the value of the products is small so these markets have driven the microfiltration industry for the past 15 years. 

A slurry supply subsystem must be able to deliver slurry to the point of use without agglomeration and keep its CMP performance consistent. If the slurry is agglomerated or its pH has changed, the CMP outcome could be significantly altered even if the polisher and other units are kept in perfect operating conditions. There are many technical challenges in slurry supply, such as filtration, reuse, recycle, and point-of-use blending versus central supply. 

Gases. Inert gases are used to dry silicon wafers. Even high purity gases can contain more than 1,000 particles per cubic foot. In addition, particles can be generated from moving parts in compressors, valves, and piping. Point-of-use membrane filtration and central process gas filtration are recommended to minimize the particle levels in the entire system. 

Donaldson Company, Inc. 2003, Point of use (POU) filtration for optical elements in semiconductor lithography tools, http //www.donaldson.com/en/semiconductor/support/datalibrary/001802.pdf... 

Point-of-use (POU) filters have been developed as well (Gurian et ah, 2002). The replacement or regeneration frequency of the adsorbents can be nhnirnized if the filtrate is only used for drinking water purposes (Petrusevski et ah, 2002). However, the synthesis of most adsorbents, especially efficient adsorbents, are complex, and their performance of re-use is poor, and this process will produce large amounts ofAs sludge or As containing solid wastes, and other treatment methods are still much desired. 

The critical applications in the electronics industry are the production of ultra-pure water for the washing of semi-conductor material (silicon chips), and the cleaning of the chemical fluids (liquid and gaseous) used in their manufacture. The object of an ultra-pure water plant for semi-conductor manufacture is to produce water as close to the theoretical purity as possible. Users of ultra-pure water should take all steps possible to ensure that the filters selected meet the highest standards of quality and performance. Every fluid that comes into contact with integrated circuit surfaces is a potential sonrce of the contamination that will affect yields. For this reason, filtration of these fluids at the point of use is essential to obtain high yields. All chemicals that contact microcircuits should be filtered to a level of at least 0.2 pm. 

The basic central air treatment plant will have a primary filter at the plant inlet, to protect the air conditioning units, especially the heat exchanger, a humidifier and the circulating fan. There is then, finally, a second-stage filter to provide finer filtration, sited just before the outlet duct from the plant. The cost of ultra-fine filtration usually prohibits its use for a general factory scheme, it being usually restricted to point-of-use areas, especially clean rooms. 

Coalescing filters require an air velocity within specified limits if they are to operate efficiently. If the total volume of system air does not require filtration to the same level of cleanliness, it will be more economical overall (i.e. capital plus running costs) to install individual filters either at the point of use, or in branch lines downstream of a T point. Air flows through these local filters will be lower than through a central filter system, allowing the use of smaller housings and extending the service life of the elements. 

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