SEMICONDUCTOR DEVICE FOR INFRARED DETECTION, METHOD OF MANUFACTURING SEMICONDUCTOR DEVICE FOR INFRARED DETECTION AND INFRARED DETECTOR

Abstract

A semiconductor device for infrared detection comprises a stack of a first semiconductor layer, a second semiconductor layer and an optical coupling layer. The first semiconductor layer has a first type of conductivity and the second semiconductor layer has a second type of conductivity. The optical coupling layer comprises an optical coupler and at least a first lateral absorber region. The optical coupler is configured to deflect incident light towards the first lateral absorber region. The first lateral absorber region comprises an absorber material with a bandgap Eg in the infrared, IR.

Claims

1. A semiconductor device for infrared detection, comprising a stack of a first semiconductor layer, a second semiconductor layer and an optical coupling layer, wherein: the first semiconductor layer has a first type of conductivity and the second semiconductor layer has a second type of conductivity, the optical coupling layer comprises an optical coupler and at least a first lateral absorber region, the optical coupler is configured to deflect incident light towards the first lateral absorber region, and the first lateral absorber region comprises an absorber material with a bandgap E.sub.g in the infrared, IR.

2. The semiconductor device according to claim 1, wherein the absorber material has a bandgap Eg smaller in value than the bandgap for Silicon of E.sub.g=1.1 eV.

3. The semiconductor device according to claim 1, wherein the absorber material comprises a strained Silicon Germanium, Si—Ge, alloy.

4. The semiconductor device according to claim 3, wherein the Si—Ge alloy has a maximum relative amount of Si of 100% and a minimum relative amount of Si of 0%, and has a maximum relative amount of Ge of 100% and a minimum relative amount of Ge of 0%, or the Si—Ge alloy has a relative amount of Si of at least 70% and a relative amount of Ge of at most 30%.

5. The semiconductor device according to claim 1, wherein the optical coupler comprises a photonic grating integrated into the optical coupling layer, and/or the optical coupling layer is part of a Silicon Germanium-on-insulator, SGOI, or Silicon-On-Insulator, SOI, wafer.

6. The semiconductor device according to claim 5, wherein the photonic grating comprises a plurality of trenches filled with a dielectric, and the trenches are configured to form a photonic Blaze grating.

7. The semiconductor device according to claim 1, wherein the first type of conductivity is n-type conductivity and the second type of conductivity is p-type conductivity, or vice versa.

8. The semiconductor device according to claim 1, wherein the optical coupling layer comprises a second lateral absorber region made of the absorber material, and the optical coupler is configured to deflect incident light both towards the first and the second lateral absorber region.

9. The semiconductor device according to claim 8, wherein a first contact region is arranged contiguous with the first lateral absorber region to form a first electrode, and/or a second contact region is arranged contiguous with the second lateral absorber region to form a second electrode and/or wherein the grating is configured to focus deflected incident light onto the first and/or second contact region.

10. The semiconductor device according to claim 9, wherein a backend layer is arranged on the first lateral absorber region, the second lateral absorber region and/or the optical coupling layer, and the backend layer further comprises: a first metallization associated with the first lateral absorber region to form the first electrode, and/or a second metallization associated with the second contact region to form the second electrode.

11. An infrared detector, comprising: at least one semiconductor device for infrared detection according to claim 1, and a driver circuit to operate the semiconductor device, and/or a signal processor to process sensor signals to be generated by the semiconductor device.

12. A method of manufacturing semiconductor device for infrared detection, comprising: providing a first semiconductor layer with a first type of conductivity and a second semiconductor layer with a second type of conductivity, providing an optical coupling layer with an optical coupler and a first lateral absorber region, stacking the first semiconductor layer, second semiconductor layer and optical coupling layer to form the semiconductor device; wherein: the optical coupler is configured to deflect incident light towards the first lateral absorber region, and the first lateral absorber region is made of an absorber material with a bandgap E.sub.g in the infrared, IR.

13. The method according to claim 12, wherein the first lateral absorber region is formed by means of a strained Silicon Germanium, Si—Ge, alloy, and monolithically integrated into the optical coupling layer.

14. The method according to claim 13, wherein the Si—Ge alloy has a maximum relative amount of Si and a minimum relative amount of Si ranging between 100% and 0%, respectively, and has a maximum relative amount of Ge and a minimum relative amount of Ge ranging between 100% and 0%, or the Si—Ge alloy has a relative amount of Si of at least 70% and a relative amount of Ge of at least 30%.

15. The method according to claim 12, wherein the optical coupler is configured as a photonic grating and integrated in the optical coupling layer involving forming plurality of trenches filled with an oxide, the trenches are arranged to form a photonic Blaze grating.

16. A semiconductor device for infrared detection, comprising a stack of a first semiconductor layer, a second semiconductor layer and an optical coupling layer, wherein: a backend layer is arranged on top of the stack, the first semiconductor layer has a first type of conductivity, the second semiconductor layer is arranged on a main surface of the first semiconductor layer and has a second type of conductivity, the optical coupling layer is arranged on a main surface of the second semiconductor layer, wherein, at least in parts, the optical coupling layer is contiguous with a depletion region formed between the first and second semiconductor layers, the optical coupling layer comprises an optical coupler and two lateral absorber regions, wherein the two lateral absorber regions flank the optical coupler, the two lateral absorber regions are made of an absorber material with a characteristic bandgap E.sub.g in the infrared, IR, the optical coupler has two output sides, which are coupled to and facing the lateral absorber regions, respectively.

17. The semiconductor device according to claim 16, wherein the absorber material comprises a strained Silicon Germanium, Si—Ge, alloy and has a bandgap E.sub.g which is smaller in value than the bandgap for Silicon of E.sub.g=1.1 eV.

18. The semiconductor device according to claim 16, wherein: the optical coupler is designed as a grating coupler, or surface coupler, the grating coupler further comprises trenches, which are filled with a dielectric material, such as an oxide, and the trenches are arranged to form a photonic grating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 shows an example embodiment of semiconductor device for infrared detection,

[0035] FIG. 2 shows examples of Silicon-Germanium alloy composition,

[0036] FIG. 3 shows penetration depths of examples of Silicon-Germanium alloy compositions,

[0037] FIGS. 4A to 4C show examples of an optical coupling layer, and

[0038] FIG. 5 shows examples of prior art silicon photodiodes with silicon epilayer of different thickness.

DETAILED DESCRIPTION

[0039] FIG. 1 shows an example embodiment of a semiconductor device for infrared detection. The device comprises a stack of a first semiconductor layer 1, a second semiconductor layer 2 and an optical coupling layer 3. Furthermore, a backend layer 4 is arranged on top of the stack 1, 2, 3.

[0040] The first semiconductor layer 1 has a first type of conductivity, such as n-type or p-type. In this embodiment the first semiconductor layer 1 is of p-type conductivity. For example, the first semiconductor layer is made from p-type CMOS bulk Silicon. In other embodiments (not shown) the conductivity may be reversed and the first semiconductor layer has n-type conductivity. The second semiconductor layer 2 is arranged on a main surface of the first semiconductor layer 1. The second semiconductor layer 2 has a second type of conductivity, such as n-type or p-type. In this embodiment the second semiconductor layer 2 is of n-type conductivity. For example, the second semiconductor layer is made from n-type CMOS bulk Silicon. In other embodiments (not shown) the conductivity may be reversed and the second semiconductor layer has p-type conductivity. For example, the first and second semiconductor layers are arranged as pn-junction such that a depletion region or space charge region is formed between the layers.

[0041] The optical coupling layer 3 is arranged on a main surface 21 of the second semiconductor layer 2. For example, at least in parts, the optical coupling layer 3 is contiguous with the depletion region formed between the first and second semiconductor layers. The optical coupling layer 3 comprises an optical coupler 31 and two lateral absorber regions 32, 33. The optical coupler 31 is designed as a grating coupler, or surface coupler, for vertical coupling (vertical with respect to the main surface 21 of the second semiconductor layer, for example). In other embodiments (not shown) the optical coupler can be implemented by edge couplers, inverted taper or adiabatic couplers, for instance. The grating coupler further comprises trenches 33, which are filled with a dielectric material, e.g. an oxide. The trenches are arranged to form a photonic grating (see FIGS. 4A to 4C). In this embodiment the photonic grating forms a photonic Blaze grating. The individual trenches constitute lines of the grating and are spaced apart with a line spacing according to the grating equation. For example, considering a wavelength of 1300 nm (NIR) the trenches are spaced apart by some 325 nm.

[0042] Two lateral absorber regions 32, 33 flank the optical coupler 31. The optical coupler 31 has two output sides 35 which are coupled to and facing the lateral absorber regions 32, 33, respectively. The lateral absorber regions 32, 33 are made of an absorber material with a characteristic bandgap E.sub.g in the infrared, IR. For example, the absorber material comprises a strained Silicon Germanium, Si—Ge, alloy and has a bandgap E.sub.g which is smaller in value than the bandgap for Silicon of E.sub.g=1.1 eV. In other words, in this embodiment the bandgap lies in the near infrared, NIR. The lateral absorber regions made from the Si—Ge alloy constitute layers of Silicon in which the Silicon atoms are stretched beyond their normal interatomic distance. The strain present in the layer constrains the feasible layer thickness, which lies at some 150 nm, for example. Larger layer thickness, however, may relax the Si—Ge alloy. The characteristic bandgap E.sub.g of the Si—Ge alloy can be defined during processing of the lateral absorber regions. Basically, the characteristic bandgap E.sub.g depends on relative amounts of Silicon and Germanium used to form the alloy. Further details will be discussed with respect to FIG. 2. The Si—Ge alloy can be monolithically integrated into the semiconductor device by means of epitaxial growing the alloy onto the second semiconductor layer, for example.

[0043] Furthermore, the semiconductor device comprises the backend layer 4, e.g. a CMOS backend layer, which is arranged on the second semiconductor layer 2, i.e. the backend layer 4 covers a main surface of the second semiconductor layer 2. A first contact region 41 and a second contact region 42 are arranged in the backend layer 4. In fact, the first contact region 41 is contiguous with the first lateral absorber region 32 and forms a first electrode 43. The second contact region 42 is contiguous with the second lateral absorber region 33 and forms a second electrode 44. The electrodes 43, 44 are connected to a metallization layer 45 in the backend layer 4 which allows for electrically contacting the semiconductor device. The backend layer 4 may include further contacts, insulating layers (dielectrics), metal levels, and bonding sites for chip-to-package connections etc. The backend layer 4 is made from a material which is at least partly transparent in the IR or NIR.

[0044] The semiconductor device is operated as a photodiode, for example. Light which is incident of the device traverses through the backend layer 4 and eventually strikes the optical coupling layer 3. The optical coupler receives the incident light and deflects the received light, by means of diffraction by the photonic grating, deflects towards the lateral absorber regions 32, 33. For example, light is guided into a plane defined by the semiconductor layers, e.g. parallel to said plane. This way the incident light is coupled into the depletion layer formed by the semiconductor layers. Light then traverses along the lateral absorber regions 32, 33 and eventually gets absorbed along the path.

[0045] Absorption process is largely determined by the material properties of the lateral absorber regions 32, 33. As strained Silicon-Germanium alloy is used as absorber material there is increased absorption in the infrared and especially in the near infrared. The bandgap E.sub.g is in the range of 0.66 eV, and, thus, smaller in value than the bandgap for Silicon (E.sub.g=1.1 eV). Consequently, the absorption bandgap can be extended into the IR, e.g. as for Si—Ge up to approximately 1250 nm. Depending on composition of the alloy, absorption can be extended up to some 1800 nm. Furthermore, the optical coupler, i.e. photonic grating in this embodiment, allows for deflecting incident light towards the lateral absorber regions. This effectively extends lateral absorption cross-section and depth, thus, increasing the absorption volume. Using Si—Ge alloy as material for the lateral absorption regions increases sensitivity (with respect to bare Silicon) in the IR and/or NIR up to approximately 1250 nm, or more. Ultimately this leads to much higher signal-to-noise in the IR and/or NIR when compared to conventional vertically stacked photodiode concepts.

[0046] In other embodiments (not shown) the first and second semiconductor layers may be arranged in different ways. For example, the two semiconductor layers may be embedded in an epilayer. Furthermore, the two layers may be stacked in a vertical fashion as discussed above, or horizontally, side-by-side. Instead of forming a pn-junction the semiconductor layers may form a PIN junction with an intrinsic region in-between the layers and the depletion region exists almost completely within the intrinsic region. This way the semiconductor device can be operated as a PIN photodiode. Instead of contacting the semiconductor device from the front-side, which is exposed to incident light, contacting may also be implemented from a backside of the first semiconductor layer, e.g. by means of solder balls and a redistribution layer.

[0047] FIG. 2 shows examples of Silicon-Germanium composition. The drawing depicts absorbance Abs (in units of %) as a function of wavelength A (in units of nm). Six graphs are shown which represent different relative amounts of Silicon and Germanium, respectively. Graphs g1 and g7 show pure Silicon and pure Germanium as a reference, respectively. For example, graph gl indicates the bandgap E.sub.g of Silicon as absorbance approximately reaches zero for λ>1100 nm. Pure Germanium, however, has non-zero absorbance at 1100 nm up to approximately 1850 nm. The following table gives an overview of the relative amounts represented by the graphs g1 to g7.

TABLE-US-00001 graph Si [in %] Ge [in %] g1 100 0 g2 90 10 g3 80 20 g4 70 30 g5 50 50 g6 25 75 g7 0 100

[0048] The graphs show that with increasing relative amount of Germanium, Ge, the bandgap of the Si—Ge alloy is shifted further into the IR. Absorbance has been measured in 10 μm bulk of Si(1-x)Ge(x) and Ge, wherein x represents the relative amount of Si and Ge. A relative amount of Si of 70% to 80% and a corresponding relative amount of Ge of 30% to 40% has been found suitable for a number of NIR applications.

[0049] FIG. 3 shows penetration depths of examples of Silicon-Germanium alloy compositions. The drawing depicts penetration depth (in units of μm) for various wavelength λ (in units of nm) of incident light as a function of alloy composition Si(1-x)Ge(x). Four wavelengths are depicted: λ1=800 nm, λ2=900 nm, λ3=1000 nm, and λ4=1100 nm. The dashed line in the drawing indicates the alloy composition of graph g6 with 25% relative amount of Si and 75% relative amount of Ge. It is apparent that Si—Ge alloys with higher relative amounts of Ge provide increasing penetration depth for NIR light, effectively increasing the absorption volume of the lateral absorber regions.

[0050] FIGS. 4A to 4C show examples of the optical coupling layer. The optical coupler is arranged as photonic grating having a plurality of trenches 33 which are filled with a dielectric, e.g. an oxide. The drawing shows the trenches 33 in top view. The trenches are configured to form a photonic blaze grating which obeys the grating equation. For example, the trenches are arranged in a plane with a constant line spacing. The trenches forming the grating are coupled to a tapered region 36, such as an adiabatic taper, which forms part of an output side 35 of the photonic blaze grating. The lateral absorption regions (not shown) are coupled to a respective output side 35 of the photonic blaze grating in order to receive light from the grating. The incident light (indicated by the arrows in the drawings) is deflected towards to the output side 35 by means of diffraction. Typically, the transverse mode of the incident is guided towards the output side 35. The optical coupler may be integrated into the semiconductor layers, there by forming a fully integrated semiconductor device for infrared detection. In other embodiments the optical coupler may be attached to the semiconductor layers. FIG. 4A shows an optical coupler with one output side. FIG. 4B shows an optical coupler with a dual tilted design and two output sides, respectively. FIG. 4C shows an optical coupler with curved trenches. Curvature of the trenches is configured to focus deflected incident light, e.g. onto the first and/or second contact regions.