Brush Cleaning

3 Brush Cleaning Since the introduction of the CMP process, the most commonly used material for brush cleaning has been PVA. In order to receive thoroughly clean surfaces, the wafer is usually sandwiched between the double-sided brush scrubbers so that the front and back sides of the wafer can be cleaned simultaneously (Fig. 16.6). In addition, a lateral brush is used to clean the edges of the wafer. 

A scrubber cleaning process can be optimized by adjusting the brush and wafer rotation speed, the DI water/chemical flow rate, and the gap between the brush and the wafer surface. Because brush cleaning is based on the mechanical pressure applied to the wafer surface, the brush must be compressed to the wafer surface to have either direct or semidirect contact with the wafer to effectively remove fine particles. 

FIGURE 16.6 Cross-sectional views of post-CMP cleaning using double-sided roller brushes (a) a single brush and (b) multiple brushes (from Ref. 26). 

FIGURE 16.7 Mechanisms of brush cleaning (a) ideal, (b) fiber deformed, and (c) noncontact mode (from Ref 27). 

A tribology study [28] focusing on the coefficient of friction by varying the instrumental parameters of scrubbers suggested that the hydrodynamic drag force is a very important factor for particle removal [29]. Busnaina et al. [30] found that full contact between a brush and a particle is necessary to lift or roll particles smaller than 0.1 mm off a substrate. 

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Wasch-blau, n. bluing, laundry blue, -bottich, m. washing vat (tub, etc.), -biirste, /. washing brush, cleaning brush. -butte,/, washing tank, purifleation tub. 

Place Arcol Polyol F-3022 (100 g, 0.1 eq., 56 OH, mixed PO/EO triol from Bayer) into a suitable container. To this add distilled water (3.3 g, 0.4125 eq.), Niax Silicone L-620 (0.5 g, a silicone surfactant from OSi Specialties), and Niax C-183 (0.12 g, an amine catalyst from OSi Specialties). Thoroughly blend this mixture without incorporating air bubbles. Then add Dabco T-9 (0.25 g, stannous octoate from Air Products) and mix again. The T-9 must be added last because it is quite water sensitive, so its exposure to the water-containing polyol blend should be kept to a minimum. To this polyol blend, quickly add Mondur TD-80 (42.6 g, 0.4868 eq., a mixture of 80% 2,4-TDI and 20% 2,6-TDI isomers from Bayer) and immediately stir at 3000 rpm for 5 s. Quickly pour the reaction mixture into a suitable container such as a 1-qt paper or plastic cup and allow the foam to free-rise. The stir blade may be wiped or brushed clean. 

The old scrubber technique is in fact very attractive for post-CMP cleaning as the same mechanical effect is active for all the materials present at the surface (insulators, metal barriers). Doubled-sided scrubbers for cleaning the frontside and the backside of the wafer and lateral brushes to take care of the wafer side are now proposed on the market. Furthermore, the implementation of megasonic sprays in the scrubber can sometimes help for difficult cases. The major limitation is in terms of cost of ownership (COO) as a single-wafer process is involved. Indeed according to Witt et al. [17] who used the standard SEMATECH COO model, brush cleaning is more than three times more expensive than wet cleaning, which was confirmed by other economic studies [18]. 

Basecoats are normally cured in heated ovens with high air velocity or with infrared heaters excessive panel temperatures should be avoided to prevent drying of the particleboard. A light scuff sanding of the basecoat is used to remove high spots, followed by a brush cleaning to remove the dust and debris. 

If incoming books are found to be infected, they should be brushed clean in the open air. As soon as possible they should be sterilized, and this is vital if the temperature and the relative humidity in the library are usually high—i.e., in excess of 65°F and 60%, respectively. 

In brush cleaning, an alkaline chemistry such as NH4OH is often used to remove the particles such as particles of silica, alumina, glass, polystyrene latex (PSL), and silicon nitride from various wafers in the first brush. The basic chemistry is used mainly to increase the repulsive charge by the zeta potential between the particle and the substrate. 

Figure 16. Typical apparatus for erasure of electrostatic image and vacuum-brush cleaning. (Reproduced, with permission, from Ref. 84. Copyright 1980, Society of Photographic Scientists and Engineers.)...

For simplicity, solvent extracting soybeans, or for that matter any oilseed, has been likened to cleaning paint from a brush. To get the brush clean, the solvent must have good contact and penetration into the brush s bristles, sufficient heat to quickly do the cleaning, and enough clean solvent and time to remove all the paint. 

At the end of the filtration cycle, the dewatered filter cake must be removed from the fabric in preparation for the next cycle. It is important that the cake is effectively discharged at this point since any delays will lead to extended filtration cycle times and therefore reduced process efficiency. This is particularly apt in filter press operations, where manual intervention may be necessary to remove sticky cakes. As a consequence, in addition to longer cycle times, the cost of the operator must also be considered. To some extent this topic may be linked to the cake moisture content because, broadly speaking, wetter cakes will adhere more tenaciously to the cloth. This problem has been partly addressed by the equipment manufacturers with the incorporation of high pressure wash jets and brush cleaning devices, and the filter media producers also continue to pursue the development of fabrics that will facilitate the ultimate goal of perfect, unassisted cake release and hence the achievement of a fully automated operation. 

In preparation for installation of catalyst, the inside of the converter, the converter cover and all of the miscellaneous fittings used inside the converter should be brushed clean of scale and dirt with a wire brush and care should be taken that workmen clean their shoes before entering the converter. All interior fittings should have been assembled in the converter before beginning the installation of the catalyst, to be sure that, once begun, the installation can proceed without undue delay for the fitting of parts. 

Pointing is used to protect the joints of masonry, and is made by mixing cement and sand with a minimum of water. The joint is first cut out to the depth of from one half to one inch, carefully brushed clean, moistened with water, and fiUed with the moftar, which is well rubbed uith a steel tool. To give architectural effect, plaster of Paris (Gypsum) is sometimes used in pointing. 

The duplex or multi-basket strainer must stiU be watched to check for the need to swap baskets. Self-cleaning strainers may be used as an alternative to dual or multiple strainers where continuous operation is critical in the process system. Two methods of self-cleaning are illustrated in Figure 3.7 - one uses a brush and the other a scraper. Brush cleaning is suitable for most applications, with scraper types more specifically suited for handling high-viscosity products. 

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