Method for fabricating semiconductor device

A method for fabricating a semiconductor device comprising:

• forming a field oxide layer defining an active region on a semiconductor substrate, the active region including a core device region and an input/output device region;
• forming a thin gate oxide layer on the core device region and a thick gate oxide layer on the input/output device region;
• forming gate electrodes on the gate oxide layers;
• forming a first LDD region by ion-implanting low concentration impurity ions to the core device and input/output device regions of the active region;
• forming a photoresist film pattern which is an LDD ion-implant mask for the input/output region, wherein the photoresist film exposes a portion of the semiconductor substrate at both sides of the gate electrode in the input/output device region and a portion of the semiconductor substrate adjacent to the field oxide layer at the outer rim of the core device region of the active region;
• forming a second LDD region deeper than the first LDD region by implanting low concentration impurity ions by using the photoresist film pattern as an ion implant mask;
• removing the photoresist film pattern;
• forming an insulating film spacer on side walls of the gate electrodes;
• forming a deep source/drain region and a shallow source/drain region by implanting high concentration impurity ions to the active region of the semiconductor substrate at least once, by using the insulating film spacer as an ion implant mask;
• and
• forming a silicide film on the gate electrodes and the deep and shallow source/drain regions.