Abstract: This invention relates to a process for obtaining a high purity nitrogen trifluoride gas which is used as a dry etching agent for semiconductors or a cleaning gas for CVD apparatus, etc., particularly to a process for removing oxygen difluoride. This is a process for purifying a nitrogen trifluoride gas by, after removing hydrogen fluoride from a nitrogen trifluoride crude gas, contacting with at least one aqueous solution containing one selected from the group consisting of sodium thiosulfate, hydrogen iodide and sodium sulfide.

Abstract: The present invention has as its technical theme to provide a liquefactive and condensable method that enables the reaction step of forming NF.sub.3 to be operated safely and continuously and purifying method that eliminates O.sub.2, N.sub.2, etc. in NF.sub.3.The present invention is directed to a method wherein liquefaction and condensation of NF.sub.3 is carried out with an additive gas such as He, and Ne introduced in order to prevent H.sub.2 from mixing. The present invention is also directed to a purifying method wherein deeply cooled distillation of liquefied NF.sub.3 is carried out with one or more of He, He, and Ar introduced as a third component gas.According to the present invention, a safe long-term continuous operation has been made possible. Since O.sub.2, N.sub.2, etc. in NF.sub.3 can be eliminated efficiently, highly pure NF.sub.3 can be obtained.

Abstract: The method for preparing a gaseous metallic floride is here disclosed which comprises reacting a metal or its oxide with a fluorine gas or nitrogen trifluoride gas, the aforesaid method being characterized by comprising the steps of mixing the metal or its oxide with a molding auxiliary comprising a solid metallic fluoride which does not react with fluorine and nitrogen trifluoride; molding the resulting mixture under pressure; and contacting the molded pieces with the fluorine gas or nitrogen trifluoride gas, while the molded pieces are heated.