Imaging systems with backside isolation trenches
An image sensor such as a backside illumination image sensor may be provided with analog circuitry, digital circuitry, and an image pixel array on a semiconductor substrate. Trench isolation structures may separate the analog circuitry from the digital circuitry on the substrate. The trench isolation structures may be formed from dielectric-filled trenches in the substrate that isolate the portion of the substrate having the analog circuitry from the portion of the substrate having the digital circuitry. The trench isolation structures may prevent digital circuit operations such as switching operations from negatively affecting the performance of the analog circuitry. Additional trench isolation structures may be interposed between portions of the substrate on which bond pads are formed and other portions of the substrate to prevent capacitive coupling between the bond pad structures and the substrate, thereby enhancing the high frequency operations of the image sensor.
1. An image sensor, comprising:
a substrate having first and second portions and having first and second opposing surfaces;
an array of image pixels in the first portion of the substrate;
an intermetal dielectric stack attached to the substrate at the first surface of the substrate;
at least one trench isolation structure in the substrate that extends from the second surface of the substrate towards the first surface of the substrate and that electrically isolates the first portion of the substrate from the second portion of the substrate, wherein at least a portion of the at least one trench isolation structure is interposed between the first portion of the substrate and the second portion of the substrate; and
a conductive material in the second portion of the substrate, wherein the conductive material extends from the second surface of the substrate to the first surface of the substrate.
2. The image sensor defined in claim 1 , wherein the at least one trench isolation structure comprises dielectric material formed in a trench in the substrate.
3. The image sensor defined in claim 2 , wherein the at least one trench isolation structure comprises dielectric material formed in an additional trench in the substrate, wherein the substrate further includes a third portion interposed between the first and second portions, wherein the trench in the substrate is interposed between the first portion of the substrate and the third portion of the substrate, and wherein the additional trench is interposed between the third portion of the substrate and the second portion of the substrate.
4. The image sensor defined in claim 2 , wherein the trench in the substrate extends from the second surface of the substrate to an interface between the substrate and the intermetal dielectric stack at the first surface of the substrate.
5. The image sensor defined in claim 1 , wherein the conductive material is coupled to a metal interconnect structure in the intermetal dielectric stack.
6. The image sensor defined in claim 1 , wherein the array of image pixels comprises an array of backside-illuminated image pixels that receive light through a backside surface of the substrate and wherein the backside surface of the substrate is the second surface of the substrate.
7. A process comprising:
forming an image sensor in a substrate, the image sensor including:
a pixel array formed in or near a front surface of the substrate; and
one or more circuit blocks formed in the substrate near the pixel array;
forming an interconnect layer on the front surface of the substrate, the interconnect layer comprising a dielectric within which are embedded signal lines and vias, wherein the signal lines and vias electrically couple the pixel array to at least one circuit within one of the one or more circuit blocks; and
forming an isolation trench adjacent to at least one side of at least one circuit block of the one or more circuit blocks to isolate the pixel array from noise generated by the at least one circuit within the at least one circuit block, wherein forming the isolation trench comprises etching through the substrate to the interconnect layer.
8. The process of claim 7 , wherein forming the isolation trench comprises:
etching the isolation trench based on at least one design pattern.
9. The process of claim 7 , further comprising:
filling the isolation trench with a dielectric.
10. The process of claim 7 , further comprising:
forming one or more additional layers on a back side of the substrate.
11. The process of claim 10 , wherein at least one of the one or more additional layers is an anti-reflective coating.
12. The process of claim 7 , further comprising:
bonding a carrier wafer to the interconnect layer.
13. The process of claim 7 , wherein the isolation trench surrounds the selected circuit block to form an isolated island from a portion of the substrate.
14. The process of claim 7 , wherein the pixel array comprises a backside-illuminated pixel array that receives light through a back side of the substrate.
15. The process of claim 7 , wherein etching through the substrate to the interconnect layer comprises etching from a back surface of the substrate to the interconnect layer on the front surface of the substrate.
16. An image sensor, comprising:
a pixel array formed in a front surface of a substrate;
one or more circuit blocks formed in the substrate near the pixel array, each circuit block including at least one circuit;
an interconnect layer formed on the front surface of the substrate, the interconnect layer including a dielectric within which are embedded signal lines and vias, where the pixel array is electrically coupled to the at least one circuit by the signal lines and vias; and
an isolation trench formed in the substrate adjacent to at least one circuit block of the one or more circuit blocks to isolate the pixel array from noise created by the at least one circuit within the at least one circuit block, wherein the at least one circuit block is formed in the substrate, wherein the isolation trench is interposed between the at least one circuit block and an additional circuit block of the one or more circuit blocks, wherein the additional circuit block is formed in the substrate, and wherein the depth of the isolation trench is equal to the thickness of the substrate.
17. The image sensor defined in claim 16 , wherein the isolation trench is filled with a dielectric.
18. The image sensor defined in claim 16 , further comprising one or more additional layers formed on a back side of the substrate.
19. The image sensor defined in claim 18 , wherein at least one of the one or more additional layers is an anti-reflective coating.
20. The image sensor defined in claim 16 , further comprising a carrier wafer bonded to the interconnect layer.
21. The image sensor defined in claim 16 , wherein the isolation trench surrounds the at least one circuit block to form an isolated island from a portion of the substrate.
22. The image sensor defined in claim 16 , wherein the pixel array comprises a backside-illuminated pixel array that receives light through a back side of the substrate.