Front side illuminated photodiode with backside bump
This invention relates to a novel optoelectronic chip with one or more optoelectronic devices, such as photodiodes, fabricated on a front side of a semiconductor wafer and contacts on a backside of the semiconductor wafer. The backside contacts can be contact bumps, which allow the optoelectronic chip to achieve the benefits of flip chip packaging without flipping the optoelectronic chip upside down with respect to a chip carrier. In an optical communication system, a photodiode chip can be backside bumped to a chip carrier or an electronic chip, allowing front side illumination of the photodiode chip. Front side illumination offers many benefits, including improved fiber alignment, reduced manufacturing time, and overall cost reduction.
1. A method of fabricating a front side illuminated photodiode with backside bump, the method comprising:
forming the photodiode on a front side of a semiconductor wafer;
forming first contacts on the front side, wherein the first contacts are respectively electrically coupled to a cathode and an anode of the photodiode; and
mounting the semiconductor wafer with the photodiode upside down on a support carrier before forming electrically conductive via holes through the semiconductor wafer and second contacts on a backside of the semiconductor wafer, wherein the second contacts are electrically coupled to the first contacts by the respective via holes.
2. The method of claim 1 , wherein the photodiode is a PIN photodiode fabricated using InP and an InGaAs layer is interposed between a P+ layer and a metal contact electrically coupled to the P+ layer.
3. The method of claim 1 , wherein the photodiode is a PIN photodiode and is formed by the following steps:
growing epitaxially N+, intrinsic and P+ layers on the front side of the semiconductor wafer;
applying one or more masks to form a desired structure for the PIN diode; and
depositing silicon nitride to exposed surfaces to reduce light reflection.
4. The method of claim 1 , wherein a metal contact on top of the photodiode has a shape with an interior area that defines an optical aperture for receiving a light signal.
5. The method of claim 4 , wherein the metal contact is a circular strip with a small opening on one side.
6. The method of claim 4 , wherein width and length dimensions of the photodiode are determined by a periphery of the metal contact on top of the photodiode.
7. The method of claim 1 , wherein the support carrier is a piece of sapphire.
8. The method of claim 1 , furthering comprising thinning the backside of the semiconductor wafer before forming the via holes.
9. The method of claim 1 , wherein infrared imaging alignment is used to align the via holes with the respective first contacts.
10. The method of claim 1 , further comprising applying a layer of dielectric material to the backside of the semiconductor wafer.
11. A method of fabricating an opto electronic device, the method comprising:
forming an optoelectronic device on a front side of a semiconductor wafer;
forming at least one electrical contact on the front side of the semiconductor wafer, wherein the electrical contact on the front side is electrically coupled to the optoelectronic device; and
mounting the semiconductor wafer with the optoelectronic device upside down on a support carrier before forming at least one electrical contact on a backside of the semiconductor wafer.
12. The method of claim 11 , wherein the optoelectronic device is a photodiode comprising at least one InP layer and an InGaAs layer is formed between the InP layer and a metal contact electrically coupled to the InP layer.
13. The method of claim 11 , further comprising a wrap-around conductor that electrically couples the electrical contact on the backside of the semiconductor wafer to the electrical contact on the front side of the semiconductor wafer.
14. The method of claim 11 , further comprising a via through the semiconductor wafer that electrically couples the electrical contact on the front side to the electrical contact on the backside of the semiconductor wafer.
15. The method of claim 11 , wherein the support carrier is a piece of sapphire.
16. A method of fabricating an array of optoelectronic devices, the method comprising:
forming an array of optoelectronic devices on a front side of a semiconductor wafer;
forming an array of first contacts on the front side of the semiconductor wafer, wherein the first contacts are electrically coupled to the respective optoelectronic devices; and
mounting the semiconductor wafer upside down on a support carrier before forming an array of vias through the semiconductor wafer and an array of second contacts on a backside of the semiconductor wafer, wherein the array of vias electrically couple the array of second contacts to the array of first contacts.
17. The method of claim 16 , wherein at least one of the optoelectronic devices is a PIN photodiode fabricated using InP material and an InGaAs layer is formed on a P+ layer of the PIN photodiode for making an ohmic contact.
18. The method of claim 16 , further comprising connecting the array of first contacts to a tester using a probe card for photonic testing at the wafer level.
19. The method of claim 16 , wherein the support carrier comprises sapphire and dual imaging alignment is used to align the array of vias with the array of first contacts.
20. The method of claim 16 , further comprising applying a layer of BCB to the backside and a layer of BCB to the first side of the semiconductor wafer with subsequent etching to expose the first contacts and the second contacts.