SEMICONDUCTOR DEVICE MANUFACTURING METHOD

PROBLEM TO BE SOLVED: To form an SOI substrate composed of a perfect single crystal semiconductor layer in an easy process.SOLUTION: An SOI substrate manufacturing method comprises: forming a first single crystal semiconductor layer growth auxiliary film 3 and a second auxiliary film 4 which are formed on a semiconductor substrate 1 via an insulation film 2; forming a third auxiliary film 5 on a lateral wall of the insulation film 2 in an opening which is formed by selectively removing the auxiliary film 4, the auxiliary film 3 and the insulation film 2 by etching; forming a longitudinal (vertical) direction epitaxial Si layer 6 and a fourth auxiliary film 7 so as to fill the opening to be flattened; selectively removing the fourth auxiliary film 4 and forming at the opening formed above the auxiliary film 3, a lateral (horizontal) direction epitaxial Si layer 8 from a lateral face of the exposed Si layer 6; and filling an insulation film in the opening from which the auxiliary film 7, Si layer 6, auxiliary film 4, auxiliary film 3 just under the auxiliary film 4 and the auxiliary film 5 that hereafter become unnecessary are removed to be flattened thereby to form the SOI substrate composed of a perfect single crystal semiconductor layer which is insulatively isolated in an island shape.