Germanium photo detector having planar surface through germanium epitaxial overgrowth
A method of fabricating a germanium photo detector includes preparing a silicon substrate wafer and depositing and planarizing a silicon oxide layer on the silicon substrate. Contact holes are formed in the silicon oxide layer. An N+ epitaxial germanium layer is grown on the silicon oxide layer and in the contact holes. An N+ germanium layer is formed by ELO. The structure is smoothed and thinned. An intrinsic germanium layer is grown on the N+ epitaxial germanium layer. A P+ germanium layer is formed on the intrinsic germanium layer and a silicon oxide overcoat is deposited. A window is opened through the silicon oxide overcoat to the P+ germanium layer. A layer of conductive material is deposited on the silicon oxide overcoat and in the windows therein. The conductive material is etched to form individual sensing elements.
1. A method of fabricating a germanium photo detector comprising:
preparing a silicon substrate wafer;
depositing and planarizing a silicon oxide layer;
forming contact holes in the silicon oxide layer which communicate with the underlying silicon substrate;
selectively growing an epitaxial germanium layer of a first type on the silicon oxide layer and in the contact holes;
forming another germanium layer of the first type on the epitaxial germanium layer and the silicon oxide layer by epitaxial lateral overgrowth (ELO);
smoothing and thinning the ELO germanium layer of the first type by chemical mechanical polishing;
growing an intrinsic germanium layer on the ELO germanium layer of the first type and on any exposed silicon oxide layer;
forming a germanium layer of a second type on the intrinsic germanium layer;
depositing a silicon oxide overcoat over the wafer;
opening a window through the silicon oxide overcoat to the germanium layer of the second type;
depositing a layer of conductive material on the silicon oxide overcoat and in the windows therein; and
etching the conductive material to form individual sensing elements.
2. The method of claim 1 which includes, after said preparing a silicon substrate; performing any CMOS process steps, including, implanting ions in the silicon substrate to from a N+ layer for a bottom electrode of a photodiode; and wherein said forming contact holes in the silicon oxide layer which communicate with the underlying silicon substrate includes forming contact holes which communicate with the N+ layer.
3. The method of claim 1 which includes forming contact holes spaced apart by a distance “D” and wherein said growing an intrinsic germanium layer on the silicon oxide layer includes growing an intrinsic germanium layer to a thickness “T”, and wherein D>2 T.
4. The method of claim 1 wherein germanium of a first type is N+ germanium and germanium of a second type is P+ germanium.
5. The method of claim 1 wherein germanium of a first type is P+ germanium and germanium of a second type is N+ germanium.
6. The method of claim 1 wherein said growing an intrinsic germanium layer on the ELO germanium layer and any exposed silicon oxide layer includes growing intrinsic germanium to a thickness of between about 100 nm to 2000 nm.
7. The method of claim 1 wherein said smoothing and thinning the ELO germanium layer of the first type by chemical mechanical polishing includes, before said smoothing, depositing a layer of silicon oxide on the ELO germanium layer of the first type.
8. The method of claim 1 wherein said depositing a layer of conductive material includes depositing a layer of conductive material taken from the group of materials consisting of polysilicon and In 2 O 3 —SnO 2 (ITO).
9. The method of claim 8 wherein, for photodetector sensitive to light of a wavelength longer than 1000 nm, P+ polysilicon is deposited as the conductive material, and for photodetector sensitive to light of a wavelength shorter than 1000 nm, ITO film is deposited as the conductive material.
10. The method of claim 1 which further includes patterning and etching to remove an outer perimeter of the germanium layer of the second type and the intrinsic germanium after said forming a germanium layer of a second type on the intrinsic germanium layer.
11. A method of fabricating a germanium photo detector comprising:
preparing a silicon substrate wafer;
depositing and planarizing a silicon oxide layer;
forming contact holes in the silicon oxide layer which communicate with the underlying silicon substrate;
selectively growing an N+ epitaxial germanium layer on the silicon oxide layer and in the contact holes;
forming another N+ germanium layer on the N+ epitaxial germanium layer and the silicon oxide layer by epitaxial lateral overgrowth (ELO);
smoothing and thinning the ELO N+ germanium layer by chemical mechanical polishing;
growing an intrinsic germanium layer on the ELO N+ germanium layer and on any exposed silicon oxide layer;
forming a P+ germanium layer on the intrinsic germanium layer;
patterning and etching to remove an outer perimeter of the P+ germanium layer and the intrinsic germanium;
depositing a silicon oxide overcoat over the wafer;
opening a window through the silicon oxide overcoat to the P+ germanium layer;
depositing a layer of conductive material on the silicon oxide overcoat and in the windows therein; and
etching the conductive material to form individual sensing elements.
12. The method of claim 11 which includes, after said preparing a silicon substrate; performing any CMOS process steps, including, implanting ions in the silicon substrate to from a N+ layer for a bottom electrode of a photodiode; and wherein said forming contact holes in the silicon oxide layer which communicate with the underlying silicon substrate includes forming contact holes which communicate with the N+ layer.
13. The method of claim 11 which includes forming contact holes spaced apart by a distance “D” and wherein said growing an intrinsic germanium layer on the silicon oxide layer includes growing an intrinsic germanium layer to a thickness “T”, and wherein D>2 T.
14. The method of claim 11 wherein said growing an intrinsic germanium layer on the ELO N+ germanium layer and any exposed silicon oxide layer includes growing intrinsic germanium to a thickness of between about 100 nm to 2000 nm.
15. The method of claim 11 wherein said smoothing and thinning the ELO N+ germanium layer by chemical mechanical polishing includes, before said smoothing, depositing a layer of silicon oxide on the ELO N+ germanium layer.
16. The method of claim 11 wherein said depositing a layer of conductive material includes depositing a layer of conductive material taken from the group of materials consisting of polysilicon and In 2 O 3 —SnO 2 (ITO), and wherein for photodetector sensitive to light of a wavelength longer than 1000 nm, P+ polysilicon is deposited as the conductive material, and for photodetector sensitive to light of a wavelength shorter than 1000 nm, ITO film is deposited as the conductive material.
17. A method of fabricating a germanium photo detector comprising:
preparing a silicon substrate wafer, including performing any CMOS process steps, including, implanting ions in the silicon substrate to from a N+ layer for a bottom electrode of a photodiode; and wherein said forming contact holes in the silicon oxide layer which communicate with the underlying silicon substrate includes forming contact holes which communicate with the N+ layer;
depositing and planarizing a silicon oxide layer;
forming contact holes in the silicon oxide layer which communicate with the underlying silicon substrate;
selectively growing an N+ epitaxial germanium layer on the silicon oxide layer and in the contact holes;
forming another N+ germanium layer on the N+ epitaxial germanium layer and the silicon oxide layer by epitaxial lateral overgrowth (ELO);
depositing a layer of silicon oxide on the ELO N+ germanium layer;
smoothing and thinning the ELO N+ germanium layer by chemical mechanical polishing;
growing an intrinsic germanium layer on the N+ germanium ELO layer and on any exposed silicon oxide layer;
forming a P+ germanium layer on the intrinsic germanium layer;
patterning and etching to remove an outer perimeter of the P+ germanium layer and the intrinsic germanium;
depositing a silicon oxide overcoat over the wafer; opening a window through the silicon oxide overcoat to the P+ germanium layer;
depositing a layer of conductive material on the silicon oxide overcoat and in the windows therein, including, depositing a layer of conductive material taken from the group of materials consisting of polysilicon and In 2 O 3 —SnO 2 (ITO), and wherein for a photodetector sensitive to light of a wavelength longer than 1000 nm, P+ polysilicon is deposited as the conductive material, and for photodetector sensitive to light of a wavelength shorter than 1000 nm, ITO film is deposited as the conductive material; and
etching the conductive material to form individual sensing elements.
18. The method of claim 17 which includes forming contact holes spaced apart by a distance “D” and wherein said growing an intrinsic germanium layer on the silicon oxide layer includes growing an intrinsic germanium layer to a thickness “T”, and wherein D>2 T.
19. The method of claim 17 wherein said growing an intrinsic germanium layer on the ELO N+ germanium layer and any exposed silicon oxide layer includes growing intrinsic germanium to a thickness of between about 100 nm to 2000 nm.