Back-illuminated imager and method for making electrical and optical connections to same
DCFirst Claim
1. A method of fabricating a backside-illuminated imaging structure, comprising:
- providing a wafer having a frontside and a backside;
forming a device layer including one or more imager structures on the frontside of the wafer;
forming a metal and dielectric stack on the device layer;
providing electrical access from the backside of the wafer to the metal and dielectric stack;
providing one or more first alignment marks or features on the frontside of the wafer in respective one or more first positions; and
providing one or more second alignment marks or features on the backside of the wafer in respective one or more second positions different from the one or more first positions by using the one or more first alignment marks or features as a positioning guide for the second one or more alignment marks or features.
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Abstract
Methods for bringing or exposing metal pads or traces to the backside of a backside-illuminated imager allow the pads or traces to reside on the illumination side for electrical connection. These methods provide a solution to a key packaging problem for backside thinned imagers. The methods also provide alignment marks for integrating color filters and microlenses to the imager pixels residing on the frontside of the wafer, enabling high performance multispectral and high sensitivity imagers, including those with extremely small pixel pitch. In addition, the methods incorporate a passivation layer for protection of devices against external contamination, and allow interface trap density reduction via thermal annealing. Backside-illuminated imagers with illumination side electrical connections are also disclosed.
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Citations
19 Claims
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1. A method of fabricating a backside-illuminated imaging structure, comprising:
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providing a wafer having a frontside and a backside; forming a device layer including one or more imager structures on the frontside of the wafer; forming a metal and dielectric stack on the device layer; providing electrical access from the backside of the wafer to the metal and dielectric stack; providing one or more first alignment marks or features on the frontside of the wafer in respective one or more first positions; and providing one or more second alignment marks or features on the backside of the wafer in respective one or more second positions different from the one or more first positions by using the one or more first alignment marks or features as a positioning guide for the second one or more alignment marks or features. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of fabricating a backside-illuminated imaging structure, comprising:
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providing a wafer having a frontside and a backside; forming a device layer including one or more imager structures on the frontside of the wafer; forming a metal and dielectric stack on the device layer; providing electrical access from the backside of the wafer to the metal and dielectric stack; and providing one or more first alignment marks or features on the frontside of the wafer, wherein providing electrical access from the metal and dielectric stack to the backside of the wafer comprises forming a at least one cavity in the wafer between the metal and dielectric stack and the backside, providing one or more alignment marks in connection with the cavity, electrically isolating the cavity from the wafer, filling the cavity with a conductive material, and adding a conductive pad on the backside of the wafer in electrical communication with the conductive material, and wherein the cavity is formed by making a larger cavity opening on the frontside of the wafer and lining the larger cavity with a dielectric liner and further comprising providing one or more microcavities projecting from the cavity adjacent the backside of the wafer, wherein the cavity and the one or more projecting microcavities are filled with the conductive material, the filled one or more microcavities form one or more second alignment marks and are visible on the backside of the wafer, wherein the one or more second alignment marks are used to align the conductive pad.
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19. A method of fabricating a backside-illuminated imaging structure, comprising:
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providing a wafer having a frontside and a backside; forming a device layer including one or more imager structures on the frontside of the wafer; forming a metal and dielectric stack on the device layer; providing electrical access from the backside of the wafer to the metal and dielectric stack; and providing one or more first alignment marks or features on the frontside of the wafer, wherein providing electrical access from the metal and dielectric stack to the backside of the wafer comprises forming a at least one cavity in the wafer between the metal and dielectric stack and the backside, providing one or more alignment marks in connection with the cavity, electrically isolating the cavity from the wafer, filling the cavity with a conductive material, and adding a conductive pad on the backside of the wafer in electrical communication with the conductive material, the method further comprising forming a larger cavity opening on the frontside of the wafer and filling the larger cavity with a dielectric and the one or more alignment marks are provided in the metal and dielectric stack, and further comprising forming the cavity in the dielectric from the backside in the dielectric and filling the second cavity with the conductive material.
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Specification