Patent ID: 8563406

Claim:
A fabrication method of a semiconductor substrate, comprising the steps of: (i) forming a LOCOS oxide film outside a device area of a singlecrystalline Si substrate; (ia) implanting an ion for adjustment of a threshold voltage in a channel region of either N channel or P channel into the device area surrounded by the LOCOS oxide film so as to form an active layer directly adjacent to the singlecrystalline Si substrate without an intervening well, the active layer consisting of the channel region and a rest region except the channel region, the rest region interleaving the channel region and the rest region being a region which is to be changed into a source region and a drain region, the channel region, the region which is to be changed into the source region and the region which is to be changed into the drain region being all directly adjacent to the singlecrystalline Si substrate without an intervening well; (ii) forming a gate insulating film on the active layer; (iia) forming a gate electrode on the gate insulating film; (iii) implanting impurity into the rest region so as to change the rest region into the source region and the drain region; (iv) forming an insulating film with a flat upper surface over the gate electrode, the gate insulating film, and the LOCOS oxide film; and (v) implanting through the insulating film one or plural kinds of ion selected from a hydrogen ion group or an inactive element ion group so as to form an ion implantation layer with a predetermined depth in the singlecrystalline Si substrate.