Abstract: A method of feeding pure water under germ-free conditions is provided by purifying raw water into primary water by successive passage through a defined series of purification units, temporarily storing the primary water in a primary water tank, further purifying the stored water to still higher purity by passage through a defined series of purification units; injecting HF or a salt of HF into the thus-purified water in bacteriostatic and sterilizing concentrations and then feeding it to its point of use.

Abstract: Periodical sterilization is usually needed in the ultrapure water line provided in an ultrapure water-producing system or plant to kill some occasionally occurring viable cells of microorganisms in the ultrapure water as produced or being produced and thereby keep the ultrapure water under germ-free conditions. Now, it is discovered that an aqueous solution containing 1 to 100 ppm of hydrofluoric acid is effective to sterilize the ultrapure water line and is advantageous over the conventional sterilization agents such as aqueous hydrogen peroxide and sodium hypochlorite which were employed normally for the sterilization of the ultrapure water line.

Abstract: In oxide film removing equipment for removing a SiO.sub.2 film on a semiconductor substrate by using hydrogen fluoride, a liquid mixture of hydrogen fluoride and methyl alcohol is prepared in a chemical factory beforehand. The liquid mixture of hydrogen fluoride and methyl alcohol is heated to generate azeotropic vapor at a semiconductor works and the vapor is used to remove the SiO.sub.2 film on the substrate. The liquid mixture of hydrogen fluoride and methyl alcohol previously prepared in the chemical factory increases safety during an operation at the semiconductor works.