Method of forming lateral overflow drain and channel stop regions in image sensors
AssigneeTruesense Imaging, Inc.
InventorsEdmund K. Banghart, Eric G. Stevens, Hung Q. Doan
Life of this patent
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Abstract
A lateral overflow drain and a channel stop are fabricated using a double mask process. Each lateral overflow drain is formed within a respective channel stop. Due to the use of two mask layers, one edge of each lateral overflow drain is aligned, or substantially aligned, with an edge of a respective channel stop.
Claims20
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 within and sharing a boundary with the first opening;
- introducing dopants having a first conductivity type into the semiconductor layer through only the second opening, thereby forming a lateral overflow drain for draining excess charge carriers from the one or more shift elements;
- removing a remaining portion of the second mask layer;
- and
- after removing the remaining portion of the second mask layer, introducing dopants having a second conductivity type opposite the 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,
- wherein the lateral overflow drain is disposed within and substantially shares a boundary with the channel stop.
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 within and sharing a boundary with the first opening;
- introducing dopants having a first conductivity type into the semiconductor layer through only the second opening, thereby forming a lateral overflow drain for draining excess charge carriers from the one or more shift elements;
- and
- introducing dopants having a second conductivity type opposite the 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,
- wherein (i) the lateral overflow drain is disposed within and substantially shares a boundary with the channel stop and (ii) the lateral overflow drain is formed before the channel stop is formed.
Dependencies are inferred from the claim text.