PURPOSE: To make thin a gate electrode to make small the step difference of the electrode and to facilitate the fine formation of an IC by a method wherein, after impurity ions for forming punch-through stopper layers are implanted, a heat treatment is performed to diffuse the ions, then, impurity ions for forming source and drain layers are implanted and a heat treatment is performed to activate the ions.
CONSTITUTION: A field insulating film 12 is formed on an n-type silicon substrate 11 to demarcate n-type element regions T. Then, a thermal oxidation is performed to form a gate insulating film 14 and moreover, after a gate electrode 13 is formed, P + is ion-implanted in the exposed regions T. Then, a heat treatment is performed to activate the P + and the P + is diffused to demarcate n + punch-through stopper layers 16. Then, BF + is implanted to form p - source and drain layers 18S and 18D. Then, sidewalls 15 consisting of an SiO 2 film are formed and BF + is implanted to form p + source and drain layers 17S and 17D. Then, a heat treatment is performed to activate and demarcate the source layers 18S and 17S and the drain layers 18D and 17D. After that, an electrode is formed and an insulating film is applied to complete a device.