Method of making a semiconductor image sensor
DCFirst Claim
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1. A method of forming an image sensor comprising:
- providing a semiconductor substrate of a first conductivity type;
forming an enhancement layer on the substrate, the enhancement layer having the first conductivity type and a first doping concentration;
forming a first well on a first portion of the enhancement layer, the first well having the first conductivity type and a second doping concentration that is greater than the first doping concentration wherein the first well has a first depth into the enhancement layer;
forming a conducting region of a second conductivity type in a second portion of the enhancement layer wherein a first portion of the conducting region forms a portion of a MOS transistor; and
forming a pinned layer of the first conductivity type in the second region of the enhancement layer by forming a first portion of the pinned layer within the conducting region and a second portion of the pinned layer extending laterally from the conducting region in a direction away from the MOS transistor.
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Abstract
An image sensor (10) has an image sensing element that includes an N-type conducting region (26) and a P-type pinned layer (37). The two regions form two P-N junctions at different depths that increase the efficiency of charge carrier collection at different frequencies of light. The conducting region (26) is formed by an angle implant that ensures that a portion of the conducting region (26) can function as a source of a MOS transistor (32).
32 Citations
34 Claims
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1. A method of forming an image sensor comprising:
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providing a semiconductor substrate of a first conductivity type;
forming an enhancement layer on the substrate, the enhancement layer having the first conductivity type and a first doping concentration;
forming a first well on a first portion of the enhancement layer, the first well having the first conductivity type and a second doping concentration that is greater than the first doping concentration wherein the first well has a first depth into the enhancement layer;
forming a conducting region of a second conductivity type in a second portion of the enhancement layer wherein a first portion of the conducting region forms a portion of a MOS transistor; and
forming a pinned layer of the first conductivity type in the second region of the enhancement layer by forming a first portion of the pinned layer within the conducting region and a second portion of the pinned layer extending laterally from the conducting region in a direction away from the MOS transistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of forming an image sensor comprising:
using an implant at a first angle to form a conducting region of the image sensor; and
forming a pinned layer at least partially within the conducting region.- View Dependent Claims (15, 16, 17, 18)
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19. A method of forming an active pixel sensor comprising:
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providing a semiconductor substrate of a first conductivity type;
forming an enhancement layer on the substrate, the enhancement layer having the first conductivity type and a first doping concentration;
forming a first well on a first portion of the enhancement layer, the first well having the first conductivity type and a second doping concentration that is greater than the first doping concentration wherein the first well has a first depth into the enhancement layer;
forming at least one MOS transistor in the first well in the first portion; and
providing a pinned photodiode in a second portion of the enhancement layer, the pinned photodiode having a first P-N junction at a first depth from the surface, a second P-N junction at a second depth that is less than the first depth, and a conducting region of the second conductivity type between the first depth and the second depth; and
forming at least one MOS transistor in the second portion of the enhancement layer, such that the pinned photodiode forms a portion of the MOS transistor in the second portion, and a gate of the MOS transistor in the second portion is within the second portion and a drain of the MOS transistor is within the first portion and the second portion. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32, 33, 34)
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30. The method of clam 19 wherein forming the conducting region includes forming the conducting region to a depth less than 0.7 microns.
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