Image sensor and method for fabricating the same
View Patent ↗The present invention provides an image sensor capable of suppressing the dark current due to crystalline defects occurring at an edge of a field oxide layer and a method for fabricating the same. The present invention provides an image sensor including: a semiconductor substrate; an active area including a photodiode area formed in a predetermined position of the substrate, a floating diffusion area having a smaller area than the photodiode area and a channel area having a bottle-neck structure connecting to the photodiode area and the floating diffusion area; a field area for isolating electrically the active area; a field stop layer being formed beneath the field area by having a wider area than the field area through an expansion towards the active area with a first width; and a gate electrode formed on the substrate by covering the channel area and having one side superposed with a second width on one entire side of the photodiode contacted to the channel area.
1. An image sensor, comprising:
a semiconductor substrate;
an active area including a photodiode area formed in a predetermined position of the substrate, a floating diffusion area having a smaller area than the photodiode area and a channel area having a bottle-neck structure connecting to the photodiode area and the floating diffusion area;
a field area for isolating electrically the active area;
a field stop layer being formed beneath the field area and being wider than the field area in a direction towards the active area; and
a gate electrode formed on the substrate by covering the channel area and a portion of the photodiode contacted to the channel area.
2. The image sensor as recited in claim 1 , wherein the photodiode area further includes:
a first diffusion layer formed in the photodiode area by being aligned to one side of the gate electrode and the field stop layer; and
a second diffusion layer formed in the first diffusion layer being aligned to the field stop layer with a predetermined distance from the one side of the gate electrode.
3. The image sensor as recited in claim 1 , wherein the gate electrode is aligned to the floating diffusion area.
4. An image sensor, comprising:
a substrate;
an active area including a photodiode area formed in a predetermined position of the substrate, a floating diffusion area having a smaller area than the photodiode area and a channel area having a bottle-neck structure connecting to the photodiode area and the floating diffusion area;
a field area for isolating electrically the active area;
a field stop layer being formed beneath the field area and being wider than the field area in a direction towards the active area; and
a gate electrode formed on the substrate by covering the channel area and a portion of the photodiode contacted to the channel area.
5. A method for fabricating an image sensor, comprising the steps of:
forming an isolation mask that exposes partially a surface of a substrate;
forming a first diffusion layer having a wider area than an area of the partially exposed substrate;
forming a field oxide layer having a smaller area than the first diffusion layer on the first diffusion layer;
forming a gate electrode on an active area of the substrate defined by the, field oxide layer;
forming a second diffusion layer being aligned to an edge of one side of the gate electrode in the substrate and to the first diffusion layer; and
forming a third diffusion layer being aligned with a predetermined distance from the edge of the one side of the gate electrode formed in the second diffusion layer.
6. The method as recited in claim 5 , wherein the step of forming the first diffusion layer is proceeded with an ion implantation that gives impurities a plurality of rotations or twists with a predetermined tilt angle.
7. The method as recited in claim 5 , wherein the active area of the substrate defined by the field oxide layer includes a photodiode area, a floating diffusion area having a smaller area than the photodiode area and a channel area having a bottle-neck structure connecting the photodiode area and the floating diffusion area,
wherein the gate electrode has one entire side of the floating diffusion area.
8. A method for forming an image sensor, comprising the steps of:
forming a first isolation mask that exposes a portion of a surface of one side of a substrate;
forming a first diffusion layer having a wider area than an exposed area of the substrate;
forming on the substrate a second isolation mask that exposes the other side of the substrate;
forming a second diffusion layer having an area identical to an exposed area of the substrate;
forming on the first diffusion layer a first field oxide layer having a smaller area than the first diffusion layer, and simultaneously forming on the second diffusion layer a second field oxide layer having an area identical to the second diffusion layer;
forming a gate electrode extending on the active area of the substrate and simultaneously on the second field oxide layer;
forming a third diffusion layer being aligned to an edge of one side of the gate electrode in the substrate and the first diffusion layer; and
forming a fourth diffusion layer being aligned with a predetermined distance from the edge of the one side of gate electrode in the third diffusion layer.
9. The method as recited in claim 8 , wherein the step of forming the first diffusion layer is proceeded with an ion implantation that gives impurities a plurality of rotations or twists with a predetermined tilt angle.
10. The method as recited in claim 8 , wherein the step of forming the second diffusion layer is proceeded with an ion implantation that implants impurities vertically.