Purity Control in Dilute HF Baths Using Point-of-Use Purification
Donald C. Grant and Wayne Kelly, CT Associates, Inc.
Ven Anantharaman and Jieh-Hwa Shyu
The useful lifetime of a recirculating etch bath is often limited by the accumulation of metal ion and particulate contaminants over time. This paper describes the performance of a point-of-use purifier designed to remove multivalent ions from such baths. The purifier is a pleated filter cartridge containing a composite membrane composed of an ion removal resin embedded in an ultrahigh molecular weight polyethylene matrix. It is designed to be placed between the pump and filter in a circulating bath system.
Previous testing of the purifier indicated that it effectively removed a number of multivalent ions including copper and iron, thereby reducing the concentration of these species on the surfaces of wafers. This study was undertaken to ensure that the purifier does not add contaminants which it cannot remove and does not shed particles. In addition, the removal capacity for iron and copper at different HF concentrations, the impact of iron ions on copper ion removal, and the kinetics of ion removal were measured.
CTA Publication #28: in Proceedings of the 16th Annual Semiconductor Pure Water and Chemicals Conference, sponsored by Balazs Laboratory, Sunnyvale CA, Volume II, pp. 1-14, 1997