Determination of tantalum and nitrogen for semiconductor copper metallization technology by ICP-OES and its application to XRF

The evaluation method concerning the precise composition ratio of tantalum nitride (TaN), one of the barrier metals examined for use in semiconductor copper metallization technology, was investigated by wet chemical digestion. TaN thin films could be dissolved by using a mixture of HF and HCl acids in PTFE pressure vessels at 180 C for 2 hours. In the proposed method, both tantalum and nitrogen could be measured from the same solution: tantalum by ICP-OES and nitrogen by spectrophotometry with Nessler's reagent. Moreover, several samples determined by the proposed method were successfully applied to standard materials for X-ray fluorescence analysis, indicating that both wet chemical digestion and an XRF measurement were in good agreement with each other. The results of a sample evaluation showed that the distribution of the tantalum-nitrogen composition ratio varied markedly throughout the wafer. The semiconductor process appraisal method reported herein is a reliable and rapid evaluation technique for tantalum nitride films.