Analyses of plated films by thermal desorption spectrometry (TDS)

Abstract

Thermal desorption spectrometry (TDS) is an effective method to detect gases that are trapped in films, and it has been used in the semiconductor field. In this paper, there are two main purposes. One is the detection of toxic elements such as lead, which are contained in extremely small quantities in plated films, especially for electroless Ni–P alloy films as bath stabiliser. The other is the detection of gases such as hydrogen, which is a key factor to control film properties, especially for Cu electroplating. Lead has been used for electroless Ni–P films as stabiliser; recently, bismuth has also been used as stabiliser instead of lead from the viewpoint of environment safety and restriction of hazardous substances. The TDS has detected both lead and bismuth contained in electroless Ni–P films, which have been plated from baths containing only 0·1 ppm of Pb and Bi. Copper electroplating has been used to produce printed circuit boards and recently to produce semiconductor wiring. To fill via holes, several kinds of additives, three or more, have been added into the plating bath. The TDS is effective to detect the captured materials because it detects all kinds of mass from 1 to more than 100. Moreover, this method is used for both qualitative and quantitative analyses. In this study, the kinds of additives greatly affected captured materials, kinds and quantity. Three kinds of additives were added in the bath. The film plated from the bath containing only polyethylene glycol with chloride ion showed the lowest hydrogen desorption level; the film plated from the bath containing only bis(3-sulfopropyl)disulfide (SPS) showed the highest level. However, the film plated from the bath that contained only SPS showed the lowest sulphur oxide level. On the other hand, the film plated from the bath containing only Janus green B and the plated bath without additives showed middling levels. The film plated from the bath with all additives showed the highest water desorption level and the lowest hydrogen desorption level, and its contained condition was strongly dependent on the additives.