Method for making a semiconductor device having an isolated layer region on the side wall of a groove

A method for making a semiconductor device in a semiconductor substrate having a surface, the device including an isolation layer region formed on a side wall of a groove provided in a portion of the surface of the semiconductor substrate and at least two separate active regions isolated from one another by the isolation layer region, said method comprising the steps of:

• forming a pattern of photoresist on said semiconductor substrate surface such that a portion of the surface is exposed;
• forming a groove in said substrate at the exposed portion so that the groove has side walls which form an angle with the substrate surface;
• removing the photoresist, forming a thin insulation film on the substrate surface and in the groove, and depositing a silicon nitride film on the thin insulation film;
• removing the silicon nitride film from the side walls of the groove thereby leaving remaining portions of the silicon nitride film;
• forming an inversion protection layer by introducing impurities into the side walls from which the silicon nitride film has been removed;
• forming insulation films constituting isolation layer regions on the side walls from which the silicon nitride film has been removed by oxidizing said semiconductor substrate;
• removing the remaining portions of the silicon nitride film and the thin insulating film;
• and
• forming impurity diffusion regions constituting separate active regions in portions of the substrate separated by an isolation layer region.