Formation of field oxide film of semiconductor element

PROBLEM TO BE SOLVED: To prevent damage to a semiconductor substrate and realize improvement in yield of process, by first forming a narrow trench and a wide trench on the surface of a nitride film and an oxide film so as to perform surface treatment under predetermined conditions, and then depositing an insulating film which causes the deposition rate to be low on the nitride film and high on the oxide film. SOLUTION: A pad oxide film 13 is formed on an upper part of a semiconductor substrate 11, and a nitride film 15 is formed on the entire surface thereof. Then, a narrow trench 17 and a wide trench 18 are formed in a cell region 100 and a peripheral circuit region 200 on the semiconductor substrate 11 in an etching process using an element isolation mask. An oxide film 19 is formed on the surface of the trench 17, and the surface of the oxide film 19 is treated to have positive charges. After that, the deposition rate is caused to be low on the nitride film 15 and high on the oxide film 19. Thus, in the process of surface treatment, damage to the semiconductor substrate 11 may be prevented and the yield of the process may be improved. COPYRIGHT: (C)1997,JPO