Methods for forming backside illuminated image sensors with front side metal redistribution layers
Methods for forming backside illuminated (BSI) image sensors having metal redistribution layers (RDL) and solder bumps for high performance connection to external circuitry are provided. In one embodiment, a BSI image sensor with RDL and solder bumps may be formed using a temporary carrier during manufacture that is removed prior to completion of the BSI image sensor. In another embodiment, a BSI image sensor with RDL and solder bumps may be formed using a permanent carrier during manufacture that partially remains in the completed BSI image sensor. A BSI image sensor may be formed before formation of a redistribution layer on the front side of the BSI image sensor. A redistribution layer may, alternatively, be formed on the front side of an image wafer before formation of BSI components such as microlenses and color filters on the back side of the image wafer.
1. A method of forming an image sensor comprising:
attaching a permanent carrier and a semiconductor substrate;
forming through-silicon vias through the permanent carrier;
thinning the semiconductor substrate that is attached to the permanent carrier in which the through-silicon vias have been formed, wherein the thinned semiconductor substrate has opposing first and second sides, wherein the permanent carrier is attached to the first side; and
forming an array of photosensitive elements and associated control circuitry on the first side and forming an array of corresponding color filter elements on the second side, wherein image light reaches the photosensitive elements by passing through the color filter elements on the second side.
2. The method defined in claim 1 further comprising:
before forming the through-silicon vias through the permanent carrier, thinning the permanent carrier.
3. The method defined in claim 2 , wherein forming the through silicon vias through the permanent carrier comprises:
forming a first dielectric layer on the permanent carrier;
forming at least one opening in the first dielectric layer and the permanent carrier, wherein the at least one opening has sidewalls;
forming a second dielectric layer on the sidewalls of the at least one opening; and
forming a metallization layer in the at least one opening, wherein the metallization layer contacts a conductive bond pad on a bottom surface of the opening, wherein the metallization layer covers the second dielectric layer on the sidewalls of the at least one opening, and wherein the metallization layer covers at least a portion of the first dielectric layer.
4. The method defined in claim 3 , wherein forming the through silicon vias through the permanent carrier further comprises:
after forming the metallization layer in the at least one opening, forming a third dielectric layer in the at least one opening, wherein the third dielectric layer covers at least a portion of the metallization layer, wherein the third dielectric layer covers at least a second portion of the first dielectric layer not covered by the metallization layer, and wherein the third dielectric layer has openings.
5. The method defined in claim 4 further comprising:
before thinning the semiconductor substrate that is attached to the permanent carrier in which the through-silicon vias have been formed, attaching a temporary carrier to the third dielectric layer.
6. The method defined in claim 5 further comprising forming solder balls in the openings in the third dielectric layer, wherein the solder balls contact the metallization layer.
7. The method defined in claim 6 further comprising:
applying a dry film adhesive to the second side of the thinned semiconductor substrate on which the color filter elements have been formed;
removing a portion of the dry film adhesive;
attaching a cover layer to a remaining portion of the dry film adhesive; and
detaching the temporary carrier from the third dielectric layer.
8. A method of forming an image sensor comprising:
attaching a permanent carrier and a semiconductor substrate, wherein the semiconductor substrate has first and second sides, wherein the first side includes a plurality of image pixels and at least one bond pad;
thinning the permanent carrier;
after thinning the permanent carrier, forming at least one opening in the permanent carrier, wherein the at least one opening in the permanent carrier is formed over the at least one bond pad;
forming a first dielectric layer on the permanent carrier, wherein the first dielectric layer has at least one opening that corresponds to the at least one opening in the permanent carrier;
forming a metal redistribution layer, wherein the metal redistribution layer contacts the at least one bond pad through the at least one opening in the permanent layer and covers at least a portion of the first dielectric layer, and wherein the metal redistribution layer contacts the at least one bond pad through the at least one opening in the permanent carrier;
forming a second dielectric layer on the metal redistribution layer;
attaching a temporary carrier to the second dielectric layer;
forming an array of color filter elements on the second side of the semiconductor substrate; and
detaching the temporary carrier from the second dielectric layer.
9. The method defined in claim 8 further comprising:
after attaching the temporary carrier to the second dielectric layer, thinning the semiconductor substrate layer.
10. The method defined in claim 8 further comprising:
before detaching the temporary carrier from the second dielectric layer, attaching a cover layer to the second side of the semiconductor substrate.
11. The method defined in claim 10 wherein the cover layer comprises a glass cover layer.
12. The method defined in claim 10 further comprising:
before attaching the cover layer to the second side of the semiconductor substrate, applying a coating of light blocking material to the second side of the semiconductor substrate, wherein the coating of light blocking material is formed adjacent to the array of color filter elements.
13. The method defined in claim 8 wherein the temporary carrier is attached to the second dielectric layer with an adhesive layer.
14. The method defined in claim 8 further comprising:
before attaching the temporary carrier to the second dielectric layer, patterning the second dielectric layer to form at least one opening.
15. The method defined in claim 14 wherein the at least one opening is laterally offset from the at least one bond pad.
16. The method defined in claim 14 further comprising:
forming a solder ball in the at least one opening in the second dielectric layer, wherein the solder ball is coupled to the metal redistribution layer through the at least one opening in the second dielectric layer.
17. A method of forming an image sensor comprising:
attaching a permanent carrier and a semiconductor substrate;
forming through-silicon vias through the permanent carrier;
forming a metal redistribution layer in the through silicon vias, wherein the metal redistribution layer contacts bond pads on the semiconductor substrate;
forming a dielectric layer over the metal redistribution layer;
attaching a temporary carrier to the dielectric layer; and
thinning the semiconductor substrate that is attached to the permanent carrier.
18. The method defined in claim 17 further comprising:
forming an array of color filter elements on the semiconductor substrate;
attaching a cover layer to the semiconductor substrate; and
detaching the temporary carrier from the dielectric layer after attaching the cover layer to the semiconductor substrate.
19. The method defined in claim 17 further comprising:
forming an array of color filter elements on the semiconductor substrate;
after forming the array of color filter elements, applying a coating of light blocking material to the semiconductor substrate, wherein the coating of light blocking material is formed adjacent to the array of color filter elements.
20. The method defined in claim 17 further comprising:
before forming the metal redistribution layer in the through-silicon vias, forming an additional dielectric layer on the permanent carrier, wherein the additional dielectric layer comprises a plurality of openings that are aligned with the through-silicon vias.