Image sensor forming method capable of defining connection window structure by etching field oxide

A method for manufacturing an image sensor including a photo diode for photo sensing and a transfer transistor for transferring photo charge from the photo diode to a signal processing region, the method comprising the steps of:

• (a) forming a field oxide on a semiconductor substrate having a first dopant;
• (b) forming a first region of the photo diode by ion-injecting a second dopant selectively into the semiconductor substrate between the field oxide and the transfer transistor;
• (c) etching selectively the field oxide in contact with the photo diode to expose a portion of the semiconductor substrate between the etched field oxide and the photo diode region;
• (d) forming the second region of the photo diode by ion-injecting the first dopant into the first region of the photo diode, such that an upper surface of a top side of the second region is exposed on the semiconductor substrate and a bottom side of the second region is in contact with the first region of the photo diode;
• and
• (e) forming a connection window region connecting the second region of the photo diode to the semiconductor substrate by ion-injecting the first dopant into the exposed portion of the semiconductor substrate.