Lateral overflow drain and channel stop regions in image sensors

A method of forming a lateral overflow drain and a channel stop associated with a pixel of an image sensor, the pixel comprising one or more shift elements for the accumulation of charge carriers in response to exposure to light, the method comprising:

• forming a first mask layer over a semiconductor layer;
• removing a portion of the first mask layer, thereby forming a first opening;
• forming a second mask layer over the first mask layer;
• removing a portion of the second mask layer to form a second opening disposed entirely within and sharing a boundary with the first opening, a width of the first opening being larger than a width of the second opening;
• introducing dopants having a first conductivity type into the semiconductor layer through the first opening, thereby forming a channel stop for preventing movement of charge carriers from the one or more shift elements into a second pixel adjacent to the pixel;
• introducing dopants having a second conductivity type opposite the first conductivity type into the semiconductor layer through only (i) the second opening and (ii) any portion of the first opening in which the second opening is disposed, thereby forming a lateral overflow drain for draining excess charge carriers from the one or more shift elements,
• wherein the lateral overflow drain is disposed within and substantially shares a boundary with the channel stop.