METHOD FOR ISOLATING ELEMENT OF SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To provide a method for isolating an element of a semiconductor device which brings about improvement in element isolation characteristics and a local flatness fault and thereby achieves overall flattening. SOLUTION: After a material film 14 is formed on a semiconductor substrate 10, a trench region A, a first active region B and a second active region C being narrower in width than the first active region B are formed by anisotropic etching of the material film 14 and the substrate 10. Subsequently, a first insulating film 18a' filling up the strength region A, a second insulating film 18b' and a third insulating film 18c' being triangular are deposited sequentially by using a plasma CVD methoed wherein deposition and etching are executed simultaneously. Next, the surface of the material film 14 is exposed by etching the first insulating film 18a', the second insulating film 18b' and the third insulating film 18c', and then the third insulating film 18c' and the second insulating film 18d' are removed by etching the material film 14 by lift-off method.