Abstract: In manufacturing processes of an integrated circuit, isolation technology between adjacent active elements on a substrate plays an important role. Groove isolation filled with dielectric is known as an effective way of achieving a high integration density, however the prior art methods of forming the isolation groove have the problem of formation of BIRD'S HEAD or BIRD'S BEAK portions around the isolation region, which restricts the integration density and deteriorates a flatness of the substrate. The method of forming isolation groove according to the present invention discloses that the method comprising the steps of removing a silicon oxide layer on a specified region surrounding the isolation groove, and depositing a silicon nitride layer directly on the substrate and forming the groove self-aligned using the above silicon oxide layer removal process, eliminates the above mentioned problems achieving a higher density of integration, a flatness of the substrate and improvement of the integrated circuit.