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Pollutants which are said to affect LSI yields include not only particles, but also gaseous chemicals. As semiconductor devices are recently miniaturized and highly integrated, great importance is placed on the control and elimination of chemicals, such as a trace of ions and organic substances, that arise from clean rooms, manufacturing equipment components, agents, gases, people, and whatever exists in manufacturing environments. As an example, let us consider the NH3 component in clean rooms. Since this component raises problems with the use of chemically amplified resists (hereinafter referred to as CA resists) and could cause the generation of post-process particles in some film forming equipment, the NH3 concentration in the process environment must be reduced. The use of chemical filters is of help as a means for removing such gaseous chemicals. However, since the clean room environment is in a wide range of variety, it is necessary to understand various characteristics of chemical filters as used in various conditions (including the pollutant concentration, humidity, and other factors in the clean room). It is expected that local measures, including a means for satisfying cost reduction requirements, will be necessary for cleaning process environments. This means that greater importance will be placed on atmospheric pollution control technology that is aimed to assure stable operation of manufacturing equipment. This paper discusses our efforts for evaluating NH3 eliminating filters and controlling ion pollution using these filters.