A semiconductor device having a P type well region formed inside a P type semiconductor substrate, on which at least three gate insulating films each having a different thickness are formed. Also, the device has the gate electrode formed extending over the three gate insulating films. The ion implantation...http://www.google.de/patents/US6613659?utm_source=gb-gplus-sharePatent US6613659 - Manufacturing method of gate insulating film of multiple thickness
