a method for manufacturing integrated circuit devices wherein semiconductor elements are isolated by insulation material comprising the following steps of : providing a mask pattern on a predetermined semiconductor element region of a semiconductor substrate ; introducing by first ion - implantation impurities of the same conductivity type as that of the substrate into the substrate using the mask pattern as an ion - implantation mask ; etching the substrate and forming a groove using the mask pattern as an etching mask in a manner that part of the impurities remain at least under the mask pattern in the side walls of the groove ; introducing by second ion - implantation impurities of the same conductivity type as that of the substrate through the groove into the substrate ; burying insulation material in the groove ; and forming a semiconductor element on the predetermined semiconductor element region .