PROCESS FOR PRODUCING HIGH-PURITY LANTHANUM, HIGH-PURITY LANTHANUM, SPUTTERING TARGET COMPRISING HIGH-PURITY LANTHANUM, AND METAL GATE FILM COMPRISING HIGH-PURITY LANTHANUM AS MAIN COMPONENT

摘要

A high-purity lanthanum, characterized by having a purity of 5N or more excluding rare earth elements and gas components, and α-ray count number of 0.001 cph/cm2 or less. A method for producing the high-purity lanthanum characterized by obtaining lanthanum crystal by subjecting a crude lanthanum metal raw material having a purity of 4N or less excluding the gas component to molten salt electrolysis at a bath temperature of 450 to 700° C., subjecting the lanthanum crystal to de-salting treatment, and removing volatile substances by performing electron beam melting, wherein the high-purity lanthanum has a purity of 5N or more excluding rare earth elements and gas components, and α-ray count number of 0.001 cph/cm2 or less. The object of the present invention is providing a technique capable of efficiently and stably providing a high-purity lanthanum with low α-ray, a sputtering target made from the high-purity lanthanum, and a metal gate thin film having the high-purity lanthanum as the main component.