Abstract: Tetrakis (fluoroaryl)borate.magnesium halide (Ar4BMgX) expressed by General Formula (1): where each of R1-R10 represents a hydrogen atom, a fluorine atom, a hydrocarbon group, or an alkoxy group, provided that at least one of R1-R5 represents a fluorine atom and at least one of R6-R10 represents a fluorine atom, X represents a chlorine atom, a bromine atom, or an iodide atom, and n represents 2 or 3, is treated with alkali metal salts of carboxylic acid and/or alkali earth metal salts of carboxylic acid. Then, a tetrakis(fluoroaryl)borate derivative (Ar4BZ) is produced by reacting treated Ar4BMgX with a compound generating monovalent cation seeds (for example, N,N-dimethylaniline.hydrochloride). Consequently, it has become possible to provide a purifying process of separating/removing impurities from Ar4BMgX readily and efficiently, and a process of producing inexpensive Ar4BX efficiently.

Abstract: An etchant composition of nitrogen trifluoride and chlorine, preferably also including a passivation material such as hydrogen bromide, etches tungsten silicide-polysilicon gate layers with high selectivity to a thin underlying silicon oxide gate oxide layer to form straight wall, perpendicular profiles with low microloading and excellent profile control.