Germanium-silicon light sensing apparatus
A method for fabricating an image sensor array having a first group of photodiodes for detecting light at visible wavelengths a second group of photodiodes for detecting light at infrared or near-infrared wavelengths, the method including forming a germanium-silicon layer for the second group of photodiodes on a first semiconductor donor wafer; defining a first interconnect layer on the germanium-silicon layer; defining integrated circuitry for controlling pixels of the image sensor array on a semiconductor carrier wafer; defining a second interconnect layer on the semiconductor carrier wafer; bonding the first interconnect layer with the second interconnect layer; defining the pixels of an image sensor array on a second semiconductor donor wafer; defining a third interconnect layer on the image sensor array; and bonding the third interconnect layer with the germanium-silicon layer.
1. A method for fabricating an image sensor array having a first group of photodiodes for detecting light at visible wavelengths, and a second group of photodiodes for detecting light at infrared or near-infrared wavelengths, the method comprising:
forming the second group of photodiodes, comprising:
forming, on a first semiconductor donor wafer, one or more recesses for the second group of photodiodes; and
growing, on the one or more recesses for the second group of photodiodes, a germanium-silicon layer for the second group of photodiodes;
defining a first interconnect layer on the germanium-silicon layer, the first interconnect layer comprising a plurality of interconnects configured to be coupled to the first group of photodiodes and the second group of photodiodes;
defining, on a semiconductor carrier wafer, integrated circuitry for controlling the first group of photodiodes and the second groups of photodiodes;
after defining the integrated circuitry, defining a second interconnect layer on the semiconductor carrier wafer, the second interconnect layer comprising a plurality of interconnects coupled to the integrated circuitry;
bonding the first interconnect layer with the second interconnect layer;
forming, on a second semiconductor donor wafer, the first group of photodiodes;
defining a third interconnect layer on the second semiconductor donor wafer; and
bonding the third interconnect layer with the germanium-silicon layer, such that the first group of photodiodes and the second group of photodiodes are coupled to the integrated circuitry.
2. The method of claim 1 , further comprising:
after bonding the first interconnect layer with the second interconnect layer, removing a portion of the first semiconductor donor wafer.
3. The method of claim 2 , wherein removing the portion of the first semiconductor donor wafer comprises polishing the first semiconductor donor wafer.
4. The method of claim 1 , wherein growing, on the one or more recesses for the second group of photodiodes, the germanium-silicon layer for the second group of photodiodes further comprises:
growing the germanium-silicon layer by a selective epitaxial growth, such that the germanium-silicon layer is at least partially embedded in the one or more recesses.
5. The method of claim 4 , wherein growing, on the one or more recesses for the second group of photodiodes, the germanium-silicon layer for the second group of photodiodes further comprises:
polishing the germanium-silicon layer to planarize the germanium-silicon layer to be fully embedded in the one or more recesses.
6. The method of claim 1 , wherein forming, on the first semiconductor donor wafer, the second group of photodiodes further comprises:
forming, within the one or more recesses, one or more sidewall spacers.
7. The method of claim 6 , wherein forming the one or more sidewall spacers comprise:
depositing, on the first semiconductor donor wafer, a dielectric layer; and
performing a directional etch of the dielectric layer.
8. The method of claim 1 , further comprising:
forming lens elements over the image sensor array, wherein each of the lens elements is arranged to guide light to a respective photodiode of the image sensor array, and
forming wavelength filters over the image sensor array, wherein each of the wavelength filters is configured to filter light for a respective photodiode of the image sensor array.