Methods for forming backside illuminated image sensors with front side metal redistribution layers and a permanent carrier layer
View Patent ↗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. An image sensor configured to capture image light, comprising:
a semiconductor substrate having opposing first and second sides, wherein the first side includes an array of photosensitive elements and associated control circuitry and wherein the second side includes an array of corresponding color filter elements, wherein the image light reaches the photosensitive elements by passing through the color filter elements on the second side;
a light blocking layer formed adjacent to the array of color filter elements on the second side of the semiconductor substrate;
bond pads on the first side of the semiconductor substrate;
a permanent carrier mounted on the semiconductor substrate;
at least one dielectric layer that is formed on the permanent carrier, wherein openings are formed through the at least one dielectric layer and the permanent carrier; and
a patterned metallization layer that is formed on the at least one dielectric layer and that has portions in the openings and portions that form contacts with the bond pads; and
solder balls that are laterally offset from the bond pads and that contact the bond pads through the patterned metallization layer.
2. The image sensor defined in claim 1 , wherein the bond pads on the first side of the semiconductor substrate interconnect the patterned metallization layer to the control circuitry on the first side of the semiconductor substrate.
3. The image sensor defined in claim 2 further comprising a glass layer that is mounted over the second side.
4. The image sensor defined in claim 3 wherein the light blocking layer has an opening in which the array of color filter elements is located, wherein the glass layer is attached to the light blocking layer.
5. The image sensor defined in claim 4 wherein the solder balls contact the metallization layer through the openings.
6. The image sensor defined in claim 1 further comprising an array of microlenses formed over the array of color filter elements.
7. The image sensor defined in claim 1 wherein the patterned metallization layer and the at least one dielectric layer form through-silicon vias in the permanent carrier.
8. The image sensor defined in claim 7 wherein the through-silicon vias form contacts with the bond pads.
9. The image sensor defined in claim 8 , wherein the at least one dielectric layer forms sidewalls of the through-silicon vias.
10. The image sensor defined in claim 1 , further comprising:
a patterned adhesive layer interposed between the permanent carrier and the semiconductor substrate, wherein the patterned adhesive layer has openings through which the patterned metallization layer contacts the bond pads.
11. A system, comprising:
a central processing unit;
memory;
input-output circuitry; and
an imaging device, wherein the imaging device comprises:
a semiconductor substrate comprising an array of photosensitive elements that are formed in a first region on the imaging device, wherein the semiconductor substrate comprises a front side and a back side, wherein the array of photosensitive elements is formed on the front side, wherein an array of corresponding color filter elements is formed on the back side of the substrate, and wherein a coating of light blocking material is formed adjacent to the array of corresponding color filter elements on the back side of the substrate;
bond pads that contact the semiconductor substrate;
a dielectric layer having openings that are only formed in a second region on the imaging device that laterally surrounds the first region;
solder bumps that are formed over the first region; and
a pattern metallization layer that has portions in the openings that contact the bond pads and portions that are laterally offset from the openings and that directly contact the solder bumps.
12. The system defined in claim 11 wherein the coating of light blocking material has an opening in which the array of corresponding color filter elements is located, the system further comprising:
a glass layer that is mounted over the array of corresponding color filter elements and that is attached to the coating of light blocking material.