Determination of Th, U, Na and K in high-purity tantalum

Trace impurities in high-purity tantalum for ULSI were regulated severely, because they have effect on reliability of element performance. Radioactive elements and alkali metal elements which cause to trouble particularly, have been investigated by ICP-AES, fluorescence spectrometric method, and flameless-AAS after ion-exchange separation method. We examined conditions of ion-exchange separation of the object elements from matrix tantalum, influences of residual tantalum and acids for sample dissolution on measurement and the countermeasure for them, analytical conditions of ICP-AES, and correction method for fluorescence intensity of U, chiefly. The detection limits of the present methods were 2 ppb for Th, 0.5 ppb for U, and 0.01 ppb for Na and K, respectively. (author)