Instrumental neutron activation analysis of trace elements in a resist used in the LSI process

Trace elements, especially sodium, in a resist used for the fabrication process of integrated circuits were determined by instrumental neutron activation analysis (INAA). The determination of trace impurities in five resists was carried out, and the sodium contents obtained in AZ-1350 and AZ-1350J of commercial resists were higher than those of other ones. The sodium contents in the silicon dioxide layer and the silicon substrate prior to the coating of the resist were 0.02 ng and 1.2 ng, respectively. The content of sodium in AZ-1350 resist coated on the silicon substrate was 95 ng. After ashing the resist by oxygen plasma, 60 ng of sodium contaminant remained on the silicon dioxide layer and 14 ng of sodium was observed in the silicon substrate. The amounts of sodium in the silicon dioxide layer and the silicon substrate increased remarkably during the resist ashing process. (author)