Surface-normal optical path structure for infrared photodetection
A SiGe surface-normal optical path photodetector structure and a method for forming the SiGe optical path normal structure are provided. The method comprises: forming a Si substrate with a surface; forming a Si feature, normal with respect to the Si substrate surface, such as a via, trench, or pillar; depositing SiGe overlying the Si normal feature to a thickness in the range of 5 to 1000 nanometers (nm); and, forming a SiGe optical path normal structure having an optical path length in the range of 0.1 to 10 microns. Typically, the SiGe has a Ge concentration in the range from 5 to 100%. The Ge concentration may be graded to increase with respect to the deposition thickness. For example, the SiGe may have a 20% concentration of Ge at the Si substrate interface, a 30% concentration of Ge at a SiGe film top surface, and a thickness of 400 nm.
1. A method for forming a silicon-germanjum (SiGe) optical path structure, normal to a silicon (Si) substrate surface, for infrared (IR) photodetection, the method comprising:
forming a Si substrate with a surface;
forming a Si feature, normal with respect to the Si substrate surface;
depositing SiGe overlying the Si normal feature;
forming a SiGe optical path normal structure;
wherein forming a Si feature, normal with respect to the Si substrate surface includes forming a pillar with two pairs of sidewalls;
wherein depositing SiGe overlying the Si normal feature includes depositing SiGe sidewalls overlying the two pairs of pillar sidewalls; and,
wherein forming a SiGe optical path normal structure includes forming an optical path array-structure adjacent the corresponding pillar sidewall pairs.
2. The method of claim 1 wherein depositing SiGe overlying the Si normal feature includes depositing SiGe to a thickness in the range of 5 to 1000 nanometers (nm).
3. The method of claim 1 wherein forming a SiGe optical path normal structure includes forming a SiGe normal structure having an optical path length in the range of 0.1 to 10 microns.
4. The method of claim 1 wherein depositing SiGe overlying the Si normal feature includes depositing SiGe with a Ge concentration in the range from 5 to 100%.
5. The method of claim 1 wherein depositing SiGe overlying the Si normal feature includes depositing SiGe with a graded Ge concentration that increases with the distance from the Si normal feature.
6. The method of claim 5 wherein the SiGe has a 20% concentration of Ge at the Si substrate interface, a 30% concentration of Ge at a SiGe film top surface, and a thickness of 400 nm.
7. The method of claim 1 further comprising:
depositing a Si layer overlying the SiGe;
depositing SiGe overlying the Si layer; and,
wherein forming a SiGe normal optical path structure includes forming a normal optical path structure with a plurality of SiGe layers.
8. The method of claim 1 further comprising:
forming an interlayer dielectric overlying the SiGe optical path normal structure; and,
forming a microlens overlying the interlayer dielectric in optical communication with the SiGe optical path normal structure.
9. A method for forming an infrared (IR) photodetector with a silicon-germanium (SiGe) optical path structure, normal to a silicon (Si) substrate surface, the method comprising:
forming a Si substrate with a surface;
forming an interconnect in electrical communication with a CMOS active region selected from the group consisting of a source, drain, gate, and a diode region;
forming a Si feature, normal with respect to the Si substrate surface;
depositing SiGe overlying the Si normal feature;
forming a SiGe optical path normal structure in electrical communication with the active region, through the interconnect;
forming an interlayer dielectric overlying the SiGe optical path normal structure; and,
forming a microlens overlying the interlayer dielectric in optical communication with the SiGe optical path normal structure.
10. A method for photodetecting infrared (IR) energy using a silicon-germanium (SiGe) surface-normal optical path structure, the method comprising:
accepting IR photons having a trajectory normal to a silicon (Si) substrate surface;
absorbing the IR photons though a SiGe surface-normal optical path structure;
generating a current in response to absorbing the IR photons; and,
conducting the current into a CMOS active region.
11. The method of claim 10 wherein accepting IR photons having a trajectory normal to a Si substrate surface includes accepting IR photons having a wavelength in the range of 0.8 to 1.6 microns.
12. The method of claim 10 wherein absorbing the IR photons through a SiGe surface-normal optical path structure includes absorbing 1.1 micron wavelength IR photons with an efficiency of approximately 7%, responsive to an optical path structure length of 10 microns.
13. The method of claim 10 wherein absorbing the IR photons through a SiGe surface-normal optical path structure includes absorbing 1.1 micron wavelength IR photons with an efficiency in the range of 0.07 to 7% efficiency, responsive to an optical path structure length in the range of 0.1 to 10 microns.
14. A silicon-germanium (SiGe) optical path structure, normal to a silicon (Si) substrate surface, for infrared (IR) photodetection, the structure comprising:
a Si substrate with a surface;
a Si feature, normal with respect to the Si substrate surface;
a surface-normal SiGe optical path overlying the Si feature;
wherein the Si feature is a pillar with two pairs of sidewalls; and,
wherein the surface-normal SiGe optical path is an optical path array-structure adjacent the corresponding pillar sidewall pairs.
15. The structure of claim 14 wherein the Si substrate surface is formed in a first plane; and,
wherein the surface-normal SiGe optical path is formed in a second plane, normal to the first plane, with a thickness in the range of 5 to 1000 nanometers (nm).
16. The structure of claim 15 wherein the surface-normal SiGe optical path has an optical path length in the range of 0.1 to 10 microns, in the second plane.
17. The structure of claim 14 wherein the surface-normal SiGe optical path includes a Ge concentration in the range from 5 to 100%.
18. The structure of claim 14 wherein the surface-normal SiGe optical path includes graded Ge concentration that increases with the distance from the Si feature.
19. The structure of claim 18 wherein the surface-normal SiGe optical path has a 20% concentration of Ge at the Si substrate interface, a 30% concentration of Ge at a SiGe film top surface, and a thickness of 400 nm.
20. The structure of claim 14 further comprising:
at least one Si layer overlying SiGe; and,
wherein the surface-normal SiGe optical path includes a plurality of SiGe layers overlying Si.
21. An infrared (IR) photodetector comprising:
a CMOS active region formed in a silicon (Si) substrate with a surface, the active region selected from the group consisting of a transistor source, drain, gate, and a diode region;
an interconnect in electrical communication with the active region
a Si feature, normal with respect to the Si substrate surface, and in electrical communication with the interconnect;
a surface-normal SiGe optical path overlying the Si feature;
an interlayer dielectric overlying the surface-normal SiGe optical path; and,
a microlens overlying the interlayer dielectric in optical communication with the surface-normal SiGe optical path.
22. A method for forming a silicon-germanium (SiGe) optical path structure, normal to a silicon (Si) substrate surface, for infrared (IR) photodetection, the method comprising:
forming a Si substrate with a surface;
forming a Si feature, normal with respect to the Si substrate surface;
depositing SiGe overlying the Si normal feature;
forming a SiGe optical path normal structure;
forming an interlayer dielectric overlying the SiGe optical path normal structure; and,
forming a microlens overlying the interlayer dielectric in optical communication with the SiGe optical path normal structure.