Method of fabricating a back-illuminated image sensor
View Patent ↗A method of fabricating a back-illuminated image sensor that includes the steps of providing a first substrate of a semiconductor layer, in particular a silicon layer, forming electronic device structures over the semiconductor layer and, only then, doping the semiconductor layer. By doing so, improved dopant profiles and electrical properties of photodiodes can be achieved such that the final product, namely an image sensor, has a better quality.
1. A method of fabricating a back-illuminated image sensor which comprises:
providing a first substrate comprising a semiconductor layer having a frontside and a backside,
forming optoelectronic device structures upon or in the frontside of the semiconductor layer,
at least partially removing a rear side of the first substrate,
amorphizing at least a part of the backside of the semiconductor layer after the optoelectronic device structures are formed, and
doping the amorphized part of the semiconductor layer.
2. The method of claim 1 , wherein the semiconductor layer comprises silicon and is doped in the amorphized part of the semiconductor layer.
3. The method of claim 1 , wherein the amorphizing comprises either implanting ions of at least one of Si, Ge, Ar or Xe into the semiconductor layer or conducting a plasma treatment on the semiconductor layer.
4. The method of claim 1 , which further comprises forming a levelling layer over the optoelectronic device structures.
5. The method of claim 4 , which further comprises bonding a second substrate to the levelling layer.
6. The method of claim 5 , wherein the second substrate is one of a Si wafer, poly-Si substrate, or glass, quartz or a transparent substrate.
7. The method of claim 1 , wherein the doping occurs in the layer on a side that is opposite to the side where the optoelectronic device structures are present.
8. The method of claim 1 , which further comprises activating the dopants.
9. The method of claim 8 , wherein the activating is carried out such that a temperature of the semiconductor layer comprising the optoelectronic device structures is 450° C. or less.
10. The method of claim 8 , wherein the activating is carried out by one of conventional thermal annealing, rapid thermal annealing, laser or pulsed laser activation, or by microwave activation.
11. The method of claim 1 , wherein the first substrate is removed such that the semiconductor layer remains, or such that part of the semiconductor layer that comprises the optoelectronic device structures remains.
12. The method of claim 1 , wherein the first substrate is one of a Si wafer, a silicon on insulator wafer, a silicon germanium on insulator wafer (SiGeOI), a silicon germanium alloy (SiGe alloy), a germanium on insulator wafer (GeOI), a germanium wafer (Ge) or a gallium arsenide (GaAs) wafer.
13. The method of claim 4 , wherein the levelling layer that is formed is a dielectric layer.
14. The method of claim 13 , which further comprises planarizing the dielectric layer.
15. The method of claim 14 , wherein the dielectric layer is a TEOS or nitride layer and the planarizing is CMP planarization.
16. The method of claim 1 , wherein the doping is formed in a pattern.
17. The method of claim 16 , wherein the pattern includes non-overlapping first and second zones, and wherein the first zones are of a first doping type and second zones are of a second doping type.
18. The method of claim 1 , wherein the optoelectronic devices comprise at least one of CMOS devices, CCD devices, photodiodes, phototransistors, or pixel circuits.
19. The method of claim 1 wherein the first substrate is an SOI substrate comprising the semiconductor layer, a base substrate and a buried dielectric layer intervening between the semiconductor layer and the base substrate, and wherein the removing step further comprises removing the base substrate and the buried dielectric layer.