Citric acid-modified carbon chemical filtration for cleanroom air quality control: Study on N-methyl-2-pyrrolidone and the interference of co-existing toluene

Abstract

Airborne molecular contaminants strongly affect the cleanroom air quality by severely degrading the image quality of semiconductor devices. This study aims to investigate the removal of N-methyl-2-pyrrolidone (NMP), an organic alkali compound that commonly appeared in cleanroom environment and used for photoresist stripping in integrated circuit fabrication processes, through adsorption by the citric acid (CA)-modified activated carbon chemical filters. Increase in CA concentration showed positive correlation to the quantity of CA coating but had negative influences on specific surface area. Immersion of carbon particles in solutions containing 3 M CA for 3 h yielded the most chemical modification according to the intensity of carbonyl and hydroxyl functional groups attached onto the carbon surface. NMP adsorption breakthrough studies demonstrated that NMP adsorption by virgin activated carbon was ineffective. Increase in the extent of CA modification resulted in greater adsorption capacity of NMP owing to increased quantity of carbonyl functional groups on its surface. Binary-component adsorption tests involving NMP and toluene vapours revealed that the CA-modified filters had little adsorption capability for toluene as compared to virgin filters. On the other hand, NMP was competitively favourable for adsorption on CA-modified filters, even when these filters were pre-saturated with toluene. The results of this research could be of value to cleanroom or building maintenance operators for technical and environmental improvements in future system design.