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Filters for applications in etching processes are required to be capable of withstanding a broad range of aggressive chemicals, from strong acids to strong bases or strong solvents. The filters must exhibit low levels of extractables under the operating conditions of this broad range of chemicals, and must not be susceptible to releasing fibres. The filter itself should be self-wetting for easy handling.

Since the etching process is itself a source of particulate contamination, the etchant solution must be continually filtered. Such immersion processes must allow contaminantfree acids to be recirculated and employ membrane filtering at the point-of-use. Recirculation ensures continual sub-micrometre cleaning in order to minimize attachment of harmful metal-containing particles and colloids to the active wafer surfaces that are created by the etching process. The filter utilized in this process should have a cut-point of 0.2um. Traditionally, PTFE has been used for the actual filter medium,
although polypropylene material is gaining in popularity.

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