Chemical-based cleaning processes

Recently, Contos et al. (50) and McCandless and Contos (51) have made a comprehensive assessment of the economics of the major chemical coal cleaning processes. Since pilot plant data were not available for most processes, the costs were based on preliminary conceptual designs. Taking bituminous coal from the Pittsburgh seam as a representative coal (which contained 1.93 wt% total sulfur, about 66% of which was pyritic sulfur), capital and operating costs for a feed rate of 7,200 metric ton/day plant were evaluated based on the first quarter of 1977 prices. A brief summary of their study is shown in Table 2. 

One example of the effect of such factors is UV inks used in printing, which were the snbject of a scandal early on, the positive evaluation of aqueous systems and bio paints , which were evaluated veiy positively despite their not unproblematic content of vegetable-based solvents. In addition, the comparatively speedy snbstitntion of chlorinated solvents in cleaning processes and formaldehyde separators in cooling lubricants can only in fact be explained by the pubhc-ity-effective scandals relating to chlorinated chemicals or formaldehyde. 

The substitution of chemical solvents by water in paint and coating systems and also in cleaning processes creates complex evaluation issues, as the number of the various chemical components contained in the corresponding products generally increases. In addition, the release of persistent substances into the aquatic environment tends to be favoured by this. This therefore raises the question for assessing two suitable strategies containment of known hazardous substances in closed systems or substitution of the mobile solvent by complex water-based systems that are scarcely evaluable from a toxicological aspect. 

Use and exposure Toluene is a clear, colorless liquid with an aromatic odor. It is a natural constituent of crude oil and is produced from petroleum refining and coke-oven operations. It is used in household aerosols, nail polish, paints and paint thinners, lacquers, rust inhibitors, adhesives, and solvent-based cleaning agents. Toluene is also used in printing operations, leather tanning, and chemical processes. Benzene and other PAHs are common... 

In a CMP process, a rotating polymer-based pad is pressed against the polished metal/oxide layer surface of a wafer while slurry or a combination of slurry and other chemicals is introduced into the polish platen. In a post-CMP cleaning process, residual abrasive particles and residues of polished layers are removed via flushing of the post-CMP solution and gentle mechanical... 

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. 

Cleaning methods should be able to minimize substrate damage while removing the contaminants, dust, film, and/or debris. Cleaning processes are based on two approaches chemical approach and mechanical approach. 

The successful fabrication of SiC based devices cannot be realized without reliable etching and cleaning processes for this material. The purpose of this Chapter is to review the developments and methods of etching silicon carbide for device applications. The term etching is used to describe the processes by which SiC material can be removed. It also includes chemical machining of a semiconductor as part of the fabrication process, as well as defect delineation. 

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