Method for forming semiconductor device isolating regions

DETAILED DESCRIPTION It is an object of the present invention to provide a method for forming semiconductor device isolation regions by a trench burying isolation method, in which there is needed only a single lithography step of defining device isolation regions, in order to reduce the time required to form the device isolation regions, improve the reliability of a semiconductor integrated circuit and reduce a manufacturing cost.
A method for forming semiconductor device isolation regions according to the present invention comprises steps of forming a first insulating film on a semiconductor substrate, removing the first insulating film in a portion to become a device isolation region with use of a resist pattern formed in an one-time lithography step as a mask so as to form an opening which reaches the semiconductor substrate, removing the resist pattern to deposit a second insulating film on the first insulating film and the inside of the opening and then etching the entire surface in order to make the second insulating film remain on only the periphery of the bottom of the opening and to expose the surface of the semiconductor substrate in a central portion of the bottom of the opening, forming an oxide film on the surface of the semiconductor substrate exposed in the central portion of the bottom of the opening with use of the first insulating film and the second insulating film on the periphery of the bottom of the opening as a mask by a selective oxidation method, removing the second insulating film on the periphery of the bottom of the opening and then etching the surface of the semiconductor substrate exposed on the periphery of the bottom of the opening with use of the oxide film formed in the central portion of the bottom of the opening by the selective oxidation method and the first insulating film which remains in portions other than the device isolation region as a mask so as to form a trench, and burying the trench with a third insulating film.