Methods for forming backside illuminated image sensors with front side metal redistribution layers
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. A method of forming an image sensor comprising:
attaching a permanent carrier and a semiconductor substrate;
thinning the semiconductor substrate that is attached to the permanent carrier, wherein the thinned semiconductor substrate has opposing first and second sides, and wherein the permanent carrier is attached to the first side;
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;
forming bond pads on the first side of the semiconductor substrate;
attaching a temporary carrier to the second side of the semiconductor substrate;
thinning the permanent carrier that is attached to the semiconductor substrate; and
forming through-silicon vias through the permanent carrier that has been attached to the semiconductor substrate, wherein forming the through-silicon vias through the permanent carrier comprises:
forming a first dielectric layer on the permanent carrier such that the first dielectric layer does not contact the bond pads;
forming at least one opening in the first dielectric layer and the permanent carrier, wherein the at least one opening has sidewalls; and
forming a second dielectric layer on the sidewalls of the at least one opening such that the second dielectric layer contacts the bond pad.
2. The method defined in claim 1 further comprising:
after forming the array of corresponding color filter elements on the second side, forming an array of associated microlenses on the second side.
3. The method defined in claim 2 wherein attaching the temporary carrier to the second side of the semiconductor substrate comprises attaching the temporary carrier to the second side of the semiconductor substrate before forming the through silicon vias through the permanent carrier that has been attached to the semiconductor substrate.
4. The method defined in claim 3 further comprising:
forming a redistribution layer on the permanent carrier, wherein forming the redistribution layer comprises:
forming openings in the second dielectric layer; and
forming a metallization layer over at least a portion of the second dielectric layer, wherein the metallization layer has at least a portion in the openings in the second dielectric layer.
5. The method defined in claim 4 further comprising:
detaching the temporary carrier from the semiconductor substrate that is attached to the permanent carrier on which the redistribution layer has been formed.
6. The method defined in claim 5 further comprising forming solder balls in the openings in the at least one dielectric layer.
7. The method defined in claim 1 , further comprising:
singulating the permanent carrier and the semiconductor substrate.
8. The method defined in claim 1 wherein thinning the semiconductor substrate that is attached to the permanent carrier comprises back grinding the semiconductor substrate that is attached to the permanent carrier.
9. The method defined in claim 1 , further comprising:
forming a layer of thermosetting dielectric material on the permanent carrier.