Photodetector and method for producing photodetector

Abstract

The invention relates to a photodetector for detecting electromagnetic radiation. The photoelectric detector comprises a transverse photodiode and a SiN waveguide. The lateral photodiode includes an in-situ p-doped contact region (112), an in-situ n-doped contact region (114), and an intrinsically doped photosensitive region (108) sandwiched between the p-doped contact region and the n-doped contact region in a lateral stacking direction (109). A SiN waveguide (102) comprises SiN and is configured to guide electromagnetic radiation along a propagation direction (104), the SiN waveguide being arranged on top of the lateral photodiode along a vertical stacking direction (107) perpendicular to the lateral stacking direction (109). At least a portion of the photosensitive region and at least a portion of the SiN waveguide form a common upper interface (116) at which the photosensitive region is in direct contact with the SiN waveguide. Further, the photosensitive region (108) has a lateral width (110) of 300 nm or less along the lateral stacking direction.

Description

Technical Field

[0001] The present invention relates to a photodetector for detecting electromagnetic radiation, and furthermore to a photonic integrated circuit or an electronic photonic circuit comprising the photodetector. The present invention also relates to a method for manufacturing the photodetector and to the use of the photodetector for detecting electromagnetic radiation in the wavelength range of 0.8 μm to 1.65 μm. Background Art

[0002] Optical and optoelectronic components produced with silicon-based technology are key components, for example for optical communications or for optical connections within or between microelectronic circuits. In particular, examples of such components are couplers, waveguides, modulators and photodetectors.

[0003] Modern photodetectors use, for example, germanium (Ge) as detector material due to its significantly better absorbance compared to silicon (Si) in the wavelength range used for optical communications (e.g., λ=1.3-1.6 μm). So-called PIN diodes are often used as detectors. "P" stands for p-doped region, "I" stands for intrinsic region, and "N" stands for n-doped semiconductor region. Important parameters of the diode are dark current, photocurrent, responsivity and optoelectronic bandwidth.

[0004] Germanium photodiodes with optoelectronic bandwidths of 50 GHz and higher have been demonstrated. Such germanium photodiodes are usually produced by epitaxially growing a germanium layer directly on an SOI (silicon on insulator) substrate or directly on bulk Si, which allows the detector to be coupled directly to a waveguide made, for example, of a single-crystalline Si layer of the SOI structure. Thus, the light to be detected can be supplied parallel to the waveguide-diode interface, which allows the diode to be independently optimized to a certain extent in terms of responsivity and optoelectronic bandwidth.

[0005] For example, S. Lischke et al. described such a germanium photodiode in “Silicon nitride waveguide coupled 67+GHz Gephotodiode for non-SOI PIC and ePIC platforms”, 2019 IEEE International Electron Devices Meeting (IEDM), 2019, pp. 33.2.1-33.2.4, doi: 10.1109 / IEDM19573.2019.8993651. The Ge photodiode is directly coupled to a silicon nitride waveguide and shows a bandwidth of more than 67 GHz.

[0006] Recent improvements in germanium photodiodes have been reported by S. Lischke et al. and generally include in-situ doping of p-doped and n-doped Si regions of lateral photodiodes containing intrinsically doped Ge fins. For example, S. Lischke et al. demonstrated in the article “Ultra-fast germanium photodiode with 3-dB bandwidth of 265 GHz”, Nat. Photon. 15, 925–931 (2021), a waveguide-coupled germanium photodiode with an optoelectronic 3-dB bandwidth of 265 GHz and 240 GHz at a photocurrent of 1 mA.

[0007] Accordingly, WO 2022 / 043513 A1 discloses a diode comprising a p-doped region, an n-doped region and a photosensitive intrinsic region, which is laterally sandwiched between the p-doped region and the n-doped region in a direction transverse to the direction of light propagation in the diode. The p-doped region is made of a first material doped with a first type of dopant, and the n-doped region is made of a third material doped with a second type of dopant. The first material comprises silicon or silicon germanium, and the third material comprises silicon or silicon germanium. The intrinsic region is made of a second material different from at least one of the first material and the third material, and the second material comprises germanium, germanium tin or silicon germanium. The intrinsic region has a maximum lateral extension equal to or less than 400nm between the two lateral ends of the intrinsic region. The p-doped region and the n-doped region are doped in situ so that the intrinsic region is not doped when the diode is produced.

[0008] However, it remains desirable to provide further improved photodetectors based on germanium photodiodes having high bandwidth. In particular, it remains desirable to provide manufacturing schemes for manufacturing improved photodetectors based on germanium photodiodes that can be used in commercial applications. Summary of the invention

[0009] The invention is based on the object of providing an improved photodetector for detecting electromagnetic radiation. The invention also comprises the object of providing an improved method for producing a photodetector.

[0010] According to the present invention, a photodetector for detecting electromagnetic radiation is proposed. The photodetector comprises a lateral photodiode and a SiN waveguide. The lateral photodiode comprises an in-situ p-doped contact region, an in-situ n-doped contact region, and an intrinsically doped photosensitive region sandwiched between the p-doped contact region and the n-doped contact region along a lateral stacking direction. The SiN waveguide comprises SiN and is configured to guide electromagnetic radiation along a propagation direction. The SiN waveguide is arranged on top of the lateral photodiode along a vertical stacking direction perpendicular to the lateral stacking direction. In the photodetector, at least a portion of the photosensitive region and at least a portion of the SiN waveguide form a common upper interface, at which the photosensitive region is in direct contact with the SiN waveguide. In addition, the photosensitive region has a lateral width of 300 nm or less, preferably 200 nm or less, for example 150 nm or less, along the lateral stacking direction.

[0011] The present invention includes the recognition that SiN waveguides are generally superior to SOI-based waveguides in various aspects. For example, they provide enhanced optical bandwidth, allowing low-loss waveguides in classical communication bands (e.g., C-band and O-band) widely addressed by SOI-based photonics, as well as in the visible wavelength range where Si waveguides have become opaque. In addition, due to the absence of two-photon absorption in SiN, optical power handling is generally superior compared to Si waveguides. Therefore, it is advantageous to include a SiN waveguide in a photodetector that includes a photodiode that provides a photo-3dB bandwidth of 200 GHz or more through a photosensitive region with a lateral width of 300 nm or less. In addition, in order to achieve high coupling efficiency from the SiN waveguide to the photosensitive region, direct contact between the photosensitive region and the SiN waveguide is advantageous.

[0012] However, with known device concepts, it is at least difficult (if not impossible) to realize a combination of a lateral photodiode with a SiN waveguide in a photodetector providing a photo-3dB bandwidth of 200 GHz or more for several reasons. For example, in some known device concepts as described, for example, in WO 2022 / 043513 A1, the Ge fins can be realized by double patterning and the contact regions can be realized by in-situ doping of Si regions. On the one hand, due to the in-situ doping, ion implantation can be completely abandoned, so that accidental doping into the Ge region can be prevented, which is beneficial for the photodetector performance, for example, because minority carrier diffusion can be effectively suppressed. However, this approach is rather limited to integration with SiN waveguides.

[0013] In particular, an inherent feature of this method is the protruding Si region on top of the Ge region, which defines the actual height of the photodetector. These vertical Si branches additionally cause parasitic capacitance. Moreover, for direct coupling to the SiN waveguide that must be located on top of the photodiode, these protruding Si branches prevent direct contact between the SiN waveguide and the Ge region. Thinning can be performed to a certain extent, but some material must still be left on top of the photodiode to avoid that the top damages the photodiode. In addition, depositing the SiN layer after manufacturing the photodiode will leave a fairly thick SiN spacer next to the vertical Si region, which means that the silicide is kept at a certain distance. This will be an extension of the resistance, for example, a lower fRC.

[0014] Another important reason that makes the integration of SiN waveguides at least difficult, if not impossible, in the case of known device concepts, such as WO 2022 / 043513 A1, is that the SiN layer should be applied at a relatively high temperature of about 700° C., for example with low pressure chemical vapor deposition (LPCVD), in order to provide a low-loss SiN waveguide that also operates with high efficiency in the C-band wavelength region. However, applying the SiN layer after manufacturing the photodiode using LPCVD to manufacture the SiN waveguide will lead to damage of the photodiode due to the high temperatures involved and result in a significant degradation of the photodiode performance.

[0015] With the photodetector according to the invention, a low-loss SiN waveguide can be combined with a lateral photodiode which can operate at an optoelectronic -3dB bandwidth of 100 GHz or more, for example 200 GHz or more. This is possible because the deposition of the SiN layer for manufacturing the SiN waveguide can be performed before the manufacture of the in-situ p-doped and n-doped contact regions. The deposition of the SiN layer is therefore not limited by thermal budget constraints, as is the case in known device concepts. This has the following advantages: dopant diffusion and deactivation effects caused by thermal processes can be reduced or even prevented, both of which have a negative impact on the optoelectronic bandwidth of the photodetector. Therefore, a photodetector comprising a SiN waveguide with an improved optoelectronic bandwidth can be achieved. In particular, the patterning of the SiN layer to manufacture the SiN waveguide can be performed after the manufacture of the photodiode, while the application of the SiN layer can be performed before the manufacture of the photodiode. Therefore, direct contact between the photosensitive region and the SiN waveguide can be achieved, i.e. there is no gap between the two, which can lead to an improved coupling efficiency from the SiN waveguide to the photosensitive region.

[0016] Another advantage of the photodetector according to the invention is that parasitic capacitances can be prevented, which would originate from the vertically protruding branches made of n-doped and p-doped materials of the photodiode. Thus, the RC time constant of the photodetector can be reduced compared to known device concepts, resulting in an improved photoelectric bandwidth of the photodiode.

[0017] Since the photosensitive region is used to provide an optically active region, for example for detecting photons by the photoelectric effect, and is laterally sandwiched between a p-doped contact region and an n-doped contact region, preferably, one or both of the p-doped contact region and the n-doped contact region are made of another material, the generation of photocarriers in the doped region can be reduced compared to a diode in which the doped region and the intrinsic region are made of the same material as the optically active region. Photocarriers can be generated substantially in the intrinsic region, so that the photocarriers are affected by the electric field provided between the doped regions. Compared to photocarriers affected by the electric field, photocarriers in the doped region may only diffuse, i.e., they move slowly. As a result, the diode according to the present invention can provide a larger optoelectronic bandwidth, which allows a faster receiver to be provided.

[0018] A photosensitive intrinsic region laterally sandwiched between a p-doped contact region and an n-doped contact region in a direction transverse to the light propagation direction in the SiN waveguide can be obtained by sequentially providing an in-situ doped p-doped region and an in-situ doped n-doped region so that the intrinsic region has a maximum lateral extension between the two lateral ends of the intrinsic region of equal to or lower than 300 nm, preferably equal to or lower than 200 nm, more preferably equal to or lower than 150 nm, and so that the intrinsic region is substantially not unintentionally doped when producing the diode.

[0019] The photodiode may include more than one p-doped contact region and / or more than one n-doped contact region. The p-doped contact regions may be stacked on top of each other to form an overall p-doped contact region in the form of a material stack of p-doped contact regions, for example p-doped contact regions made of different materials and / or including different doping concentrations and / or different dopants. The n-doped contact regions may be stacked on top of each other to form an overall n-doped contact region in the form of a material stack of n-doped contact regions, for example p-doped contact regions made of different materials and / or including different doping concentrations and / or different dopants.

[0020] The maximum vertical extension of the photosensitive region, i.e. its vertical height along the vertical stacking direction, may be, for example, below 1000 nm, such as about 400 nm, such as 400 nm + / - 10%, or between 300 nm and 400 nm. A maximum vertical extension below 1000 nm is preferred to enable the use of contact schemes of standard back-end processing technologies. Contact schemes of standard back-end processing technologies may involve the use of tungsten or copper plugs. Preferably, the lower limit of the vertical extension of the photosensitive region is 100 nm to 150 nm to ensure sufficient crystalline quality of the photosensitive region for detecting electromagnetic radiation using a photodiode.

[0021] The p-doped contact region may be doped with, for example, boron atoms. The n-doped contact region may be doped with, for example, phosphorus atoms. Other dopants may be used to dope the n-doped contact region and / or the p-doped contact region. The doped contact region may have, for example, a carbon content greater than 5×10 19 Atom / cm 3 (For example, greater than 10 × 20 Atom / cm 3 ) doping concentration.

[0022] The photodetector may include a bottom layer or substrate arranged below the photodiode. The bottom layer may be made of, for example, Si or SiGe. The bottom layer may be, for example, a bulk wafer or a waveguide. The bottom layer may be arranged and / or embedded on top of a buried oxide (BOX) layer (e.g., a SOI BOX layer, i.e., a BOX layer of an SOI substrate). The BOX layer may be made of, for example, silicon dioxide (SiO2).

[0023] A silicide layer may be arranged on the top surface of each of the p-doped contact region and the n-doped contact region. The silicide layer may allow low-ohmic contact of the doped contact region with the electrode. The silicide layer may be a metal silicide layer. The metal silicide layer may be made of, for example, cobalt disilicide (CoSi2) or nickel silicide (NiSi). Nickel-based silicide layers may allow for a reduction in thermal budget. The silicide layers may be arranged so that they are not in direct contact with the photosensitive region. The silicide layer arranged on the top surface of the p-doped contact region may be arranged so that it is not in direct contact with the silicide layer arranged on the top surface of the n-doped contact region.

[0024] Preferably, the photosensitive region has a lateral width of 150 nm or less or even 100 nm or less. Preferably, the photosensitive region has a lateral width of at least 20 nm. A photodetector comprising a sensitive region having a lateral width of 150 nm or less and / or at least 20 nm can have an optoelectronic-3dB bandwidth far exceeding 100 GHz (e.g. 200 GHz or more). By providing in-situ p-doped and n-doped contact regions, an optoelectronic-3dB bandwidth far exceeding 100 GHz is further achieved. Thus, ion implantation can be abandoned and unintended doping of the intrinsically doped photosensitive region can be reduced or even prevented. This is particularly beneficial because minority carrier diffusion can be effectively suppressed. In addition, the performance of the photodetector is further improved by providing a direct contact between the SiN waveguide and the photosensitive region, resulting in an improved coupling efficiency from the SiN waveguide to the photosensitive region.

[0025] Preferably, the p-doped contact region and the n-doped contact region comprise Si, and the photosensitive region comprises Ge. This has the advantage that the photodetector can be manufactured using standard Si technology such as CMOS or BiCMOS lines. Furthermore, Ge is preferred for the photosensitive region because it has a better light absorption behavior than Si in the wavelength range of 0.8 μm to 1.65 μm. Therefore, preferably, the photodiode is a PIN photodiode with p-Si-i-Ge-n-Si. However, it is also possible to use a binary alloy SiGe in the p-doped and n-doped contact regions. The photosensitive region can be made of Ge, SiGe or GeSn.

[0026] Preferably, the photosensitive region comprises an optically active active material layer and a cap layer arranged on top of the active material layer along the vertical stacking direction. Therefore, it is preferred that, if present, the cap layer forms a common upper interface at which the photosensitive region is in direct contact with the SiN waveguide. Preferably, the cap layer is configured to protect the active material layer. Preferably, the cap layer has a thickness of not more than 100nm (e.g., 10nm to 100nm) along the vertical stacking direction. A thickness of not more than 100nm along the vertical stacking direction is preferred to ensure effective coupling between the SiN waveguide and the active material layer through the cap layer. In addition, a thickness of not more than 100nm along the vertical stacking direction is preferred to provide sufficient protection for the active material layer by the cap layer. For example, the active material layer is made of Ge or may include Ge, and the cap layer may be made of Si or may include Si.

[0027] In order to manufacture a photosensitive region including an active material layer and a cap layer, an insulating material layer having an insulating material layer window (e.g., formed as a groove) may be provided. The insulating material layer may be, for example, SiO2. The active material layer may be manufactured by filling the insulating material layer window using selective epitaxy (e.g., selective Ge epitaxy). Alternatively, a differential epitaxy method may be used for the manufacture of the active material layer.

[0028] Preferably, the insulating material layer window is not completely filled with the active material layer by means of epitaxy, but a step to the insulating material layer is created, which step preferably has a height of 10nm to 100nm. A cap layer can then be manufactured on top of the active material layer by using selective or differential epitaxy to have a thickness of 10nm to 100nm. Thus, the active material layer is covered by the cap layer along the vertical stacking direction. Alternatively, the active material layer present in the insulating material layer window can be etched to produce a step to the insulating material layer. The resulting gap can be filled with the material of the cap material.

[0029] Preferably, the capping layer is made of Si and is manufactured using selective or differential Si epitaxy. In order to restore a smooth (e.g., planar) outer surface of the photosensitive region and / or the insulating material layer, chemical mechanical polishing (CMP) may be used. In particular, in the case where differential epitaxy is used instead of selective epitaxy, CMP of the outer surface of the insulating material layer may be beneficial to expose the outer surface of the insulating material layer again before applying a SiN layer on top of the insulating material layer.

[0030] Preferably, the common upper interface between the photosensitive region and the SiN waveguide is substantially planar. Alternatively, the common upper interface between the photosensitive region and the SiN waveguide may be concavely curved along the vertical stacking direction. The concavely curved shape of the photosensitive region may include a facet form, which may originate from the crystalline properties of the material (e.g., germanium) forming the photosensitive region. A planar common upper interface may be preferred if a substantially uniform field distribution within the photosensitive region is desired. Furthermore, a planar common upper interface may result in reduced leakage current. A concavely curved common upper interface may provide improved coupling between the SiN waveguide and the photosensitive region due to a larger interface length.

[0031] Preferably, the lateral width of the SiN waveguide along the lateral stacking direction corresponds to the lateral width of the photosensitive region, or is greater than the lateral width of the photosensitive region. Preferably, the lateral width of the SiN waveguide is between 200nm and 400nm, depending on the lateral width of the photosensitive region. Such a SiN waveguide can provide effective mode confinement to effectively guide electromagnetic radiation in the wavelength range of 0.8 μm to 1.65 μm. For example, if a photosensitive region with a lateral width of 50nm to 100nm width is manufactured, with in-situ p-doped and n-doped contact regions of 50nm to 100nm on each side, and when considering a margin of about 50nm on each side of the photodiode, a lateral width of 300nm to 400nm for the SiN waveguide on top of the photosensitive region may be beneficial. Such a thickness is also compatible with optical modes in the wavelength range of 0.8 μm to 1.65 μm within the SiN waveguide.

[0032] It is particularly preferred that the lateral width of the SiN waveguide along the lateral stacking direction exceeds the lateral width of the photosensitive region by at least 20 nm, preferably at least 50 nm on both sides. In particular, it is preferred that the lateral width of the SiN waveguide is at most 50 nm greater than the lateral width of the photodiode. For some applications it may even be beneficial if the lateral width of the SiN waveguide is 100 nm greater than the lateral width of the photodiode.

[0033] For the photodetector, preferably, the p-doped contact region includes a p-doped connector region, a p-doped central region and a laterally protruding p-doped edge portion along the vertical stacking direction. The laterally protruding p-doped edge portion preferably has a larger lateral width along the lateral stacking direction than the p-doped central portion of the p-doped contact region. Additionally or alternatively, the n-doped contact region includes an n-doped connector region, an n-doped central region and a laterally protruding n-doped edge portion along the vertical stacking direction. The laterally protruding n-doped edge portion preferably has a larger lateral width along the lateral stacking direction than the n-doped central portion of the n-doped contact region. The laterally protruding p-doped and n-doped edge portions have the following advantages: the formed silicide (e.g., cobalt or nickel) maintains a certain distance from the light field in the SiN waveguide.

[0034] In particular, in a photodetector comprising a photodiode with laterally protruding p-doped and n-doped edge portions, it is preferred that the height of the laterally protruding p-doped edge portion and / or the laterally protruding n-doped edge portion along the vertical stacking direction is equal to or less than the height of the photosensitive region along the vertical stacking direction. Thus, parasitic capacitance caused by protruding vertical branches present in some known devices can be prevented, which may be beneficial for the RC time constant and thus the optoelectronic bandwidth of the photodiode. Preferably, the SiN waveguide is in contact with at least a portion of the laterally protruding p-doped edge portion and / or at least a portion of the laterally protruding n-doped edge portion.

[0035] Preferably, the photodetector comprises a Si waveguide comprising Si and arranged below the photodiode along the stacking direction, forming a common lower interface with the photodiode, at which common lower interface the Si waveguide is in direct contact with at least a portion of the photosensitive region. For example, the photodiode may have a lower coupling surface opposite to the upper coupling surface, and wherein the photodetector comprises a Si waveguide comprising Si and coupled to the photodiode on its lower coupling surface and in direct contact with at least a portion of the photosensitive region. Thereby, a dual waveguide connection may be achieved. The Si waveguide and the SiN waveguide may be arranged in different photonic planes of the photonic integrated circuit. Preferably, the Si waveguide has a width along the lateral stacking direction that is equal to or greater than the lateral width of the photodiode.

[0036] The invention also relates to a photonic integrated circuit or an electronic photonic circuit comprising a photodetector as described above.

[0037] The present invention also relates to a method for manufacturing a photodetector. The method comprises the following steps:

[0038] - manufacturing a lateral photodiode comprising an in-situ p-doped contact region, an in-situ n-doped contact region and an intrinsically doped photosensitive region sandwiched between the p-doped contact region and the n-doped contact region in a lateral stacking direction, the photosensitive region having a lateral width of 300 nm or less in the lateral stacking direction, and

[0039] - manufacturing a SiN waveguide, the SiN waveguide comprising SiN and configured to guide electromagnetic radiation along a propagation direction, the SiN waveguide being arranged on top of the lateral photodiode along a vertical stacking direction perpendicular to the lateral stacking direction, such that at least a portion of the photosensitive region and at least a portion of the SiN waveguide form a common upper interface, at which the photosensitive region is in direct contact with the SiN waveguide.

[0040] The method can be used to manufacture a photodetector as described above. The method allows direct contact between the photosensitive region and the SiN waveguide, i.e. there is no gap between them. Thereby, the coupling efficiency from the SiN waveguide to the photosensitive region can be improved. This can be achieved in the method by depositing the SiN layer before depositing the in-situ p-doped and n-doped contact regions. The deposition of the SiN layer is therefore not limited by the thermal budget. This means that the SiN layer that is subsequently patterned to be used as an optical waveguide can be deposited by an LPCVD process, which is particularly suitable for manufacturing low-loss SiN waveguides operating in the C-band wavelength region. Alternative processes such as PECVD can be used, however, LPCVD is preferred due to less hydrogen incorporation. Less hydrogen incorporation is particularly beneficial for manufacturing low-loss waveguides in multiple optical communication bands, i.e., particularly in the 1.55 μm wavelength region (C-band).

[0041] Preferably, the method for manufacturing a photodiode includes:

[0042] a) providing a photodetector intermediate product, the photodetector intermediate product comprising an intrinsically doped photosensitive region with a lateral width of 300 nm or less, the intrinsically doped photosensitive region being embedded with its lateral side in an insulating material layer arranged on a substrate, wherein the photosensitive region is in contact with a SiN hard mask with a top side of the intrinsically doped photosensitive region facing away from the substrate in a vertical stacking direction, the SiN hard mask covering the insulating material layer with the embedded photosensitive region,

[0043] b) creating a first window in the SiN hard mask at a first predetermined distance from a first one of the lateral sides of the photosensitive region,

[0044] c) removing the insulating material layer exposed by the first window by bottom etching, so that the first lateral side of the lateral sides of the photosensitive region is exposed, and forming a first cavity beside the insulating material layer,

[0045] d) epitaxially growing an in-situ p-doped layer, the in-situ p-doped layer covering at least a portion of the SiN hard mask and the first of the lateral sides of the photosensitive region, such that a laterally protruding p-doped edge portion is formed within the first cavity and in contact with the SiN hard mask, and wherein in the laterally protruding p-doped edge portion, the p-doped contact region has a larger lateral width along the lateral stacking direction than a p-doped central portion of the in-situ p-doped layer,

[0046] e) filling the first cavity with an insulating material and exposing the upper surface of the SiN hard mask along the vertical stacking direction,

[0047] f) creating a second window at a second predetermined distance from a second one of the lateral sides of the photosensitive region such that the photosensitive region is located between the first window and the second window, wherein by creating the first window and the second window, the SiN waveguide is formed on top of the photodiode along the vertical stacking direction,

[0048] g) steps c) to f) are repeated analogously for the second window, wherein instead of epitaxially growing an in-situ p-doped layer according to step d), an in-situ n-doped layer is epitaxially grown,

[0049] h) removing those portions of the in-situ p-doped layer and the in-situ n-doped layer covering the lateral sides of the SiN waveguide, thereby forming an in-situ p-doped contact region and an in-situ n-doped contact region of the photodiode, respectively,

[0050] i) removing the insulating material in the first cavity and the second cavity to expose the in-situ p-doped contact region and the in-situ n-doped contact region of the photodiode, and

[0051] j) Performing silicide formation of in-situ p-doped contact regions and in-situ n-doped contact regions.

[0052] Additionally or alternatively, in the method, providing the photodetector intermediate product may include:

[0053] - Before applying the SiN hard mask on top of the insulating material layer with the embedded photosensitive region, chemically and / or mechanically polishing the outer surface of the insulating material layer with the embedded photosensitive region along the vertical stacking direction to provide a smooth interface between the insulating material layer with the embedded photosensitive region and the SiN hard mask.

[0054] Additionally or alternatively, in the method, providing the photodetector intermediate product may include manufacturing the photosensitive region in an insulating material layer window present in the insulating material layer.

[0055] Preferably, fabricating the photosensitive region in the insulating material layer window of the insulating material layer includes epitaxially fabricating an active material layer in the insulating material layer window, and epitaxially fabricating a cap layer on top of the active material layer, so that the active material layer is covered by the cap layer and thereby protected. In this case, the cap layer of the photosensitive region forms an upper common interface between the photosensitive region and a SiN waveguide applied on top of the photosensitive region along a vertical stacking direction. Epitaxially fabricating the active material layer may include selective Ge epitaxy. Epitaxially fabricating the cap layer on top of the active material layer may include selective or differential Si epitaxy.

[0056] Creating the first and / or second windows in the SiN hard mask at a predetermined distance from a first of the lateral sides of the photosensitive region may include a distance of 100 nm to 300 nm. The first and second windows preferably extend along the length of the photosensitive region and have a lateral width of, for example, 50 nm or more. However, lateral widths of 100 nm or more (e.g., 130 nm or more) may also be used.

[0057] Preferably, in order to remove the insulating material layer exposed by the first window by bottom etching so that the first lateral side of the lateral side of the photosensitive area is exposed, oxide wet etching is used. Preferably, creating the first and / or second windows in the SiN hard mask includes patterning of the SiN hard mask to define the area of ​​the first and / or second windows. Preferably, the insulating material used to fill the first and / or second windows is SiO2. Preferably, removing those portions of the in-situ p-doped layer and the in-situ n-doped layer covering the lateral sides of the SiN hard mask may include Si dry etching. Preferably, removing the insulating material within the first window and the second window to expose the in-situ p-doped layer and the in-situ n-doped layer may include maskless wet etching. Preferably, the SiN hard mask is manufactured to have a thickness of 200nm to 500nm.

[0058] Additionally or alternatively, in the method, fabricating the SiN waveguide comprises:

[0059] - exposing an outer surface of the SiN hard mask facing along the vertical stacking direction, and

[0060] - Patterning the SiN hard mask to define the shape of the SiN waveguide arranged on top of the photodiode. For example, CMP and dry etching (e.g. Si reactive ion etching) can be performed to expose the outer surface of the SiN hard mask facing away from the substrate. Thus, Si on the outer surface of the SiN hard mask can be removed to restore the smooth surface of the SiN hard mask, which makes patterning of the SiN hard mask possible.

[0061] The invention also relates to the use of a photodetector as described above for detecting electromagnetic radiation in the wavelength range of 0.8 μm to 1.65 μm.

[0062] It shall be understood that the photodiode of claim 1, the photonic integrated circuit or electronic photonic circuit of claim 10, the manufacturing method of claim 11 and the use of the photodetector of claim 15 have similar and / or identical preferred embodiments, in particular as defined in the dependent claims.

[0063] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims or the above embodiments with the respective independent claim.

[0064] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In the following figures:

[0066] Figure 1 A photodetector is schematically and exemplarily shown in cross-sectional view;

[0067] Figure 2 Schematically and exemplarily, a photodetector is shown, the photodetector comprising a SiN waveguide arranged on top of and coupled to a lateral photodiode;

[0068] Figure 3 A photodetector is schematically and exemplarily shown in plan view;

[0069] Figure 4 The cross-sectional view schematically and exemplarily shows Figure 3 Photodetector;

[0070] Figure 5 The longitudinal section diagram schematically and exemplarily shows Figure 3 Photodetector;

[0071] Figures 6 to 15 Several different intermediate products produced when carrying out a method for producing a photodetector comprising a Ge fin-type photodiode and a SiN waveguide are schematically and exemplarily shown; DETAILED DESCRIPTION

[0072] Figure 1 The photodetector 100 is schematically and exemplarily shown in a cross-sectional view. The photodetector 100 is configured for detecting electromagnetic radiation. In particular, the photodetector 100 can be used for detecting electromagnetic radiation in the wavelength range of 0.8 μm to 1.65 μm, which is typically used in optical communications.

[0073] The photodetector 100 includes a SiN waveguide 102 configured to extend along a direction perpendicular to the Figure 1The lateral photodiode 106 guides electromagnetic radiation in a propagation direction 104 of the cross-sectional view of FIG. The SiN waveguide 102 is arranged on top of the lateral photodiode 106 along the vertical stacking direction 107. The lateral photodiode includes a Ge fin 108 as a photosensitive region 108. The Ge fin 108 has a lateral width 110 of 200 nm along the lateral stacking direction 109. In an alternative embodiment, the photosensitive region 108 may have a lateral width of 300 nm or less and at least 20 nm. For example, the photosensitive region 108 may have a lateral width of 100 nm to 150 nm. The photosensitive region 108 is intrinsically doped. The photosensitive region 108 may also be made of a different semiconductor material such as SiGe. In a preferred embodiment, the photosensitive region 108 includes a Ge fin as an active material layer and a Si cap layer arranged on top of the Ge fin along the vertical stacking direction. In this embodiment, the Si cap layer forms a common interface between the photosensitive region and the SiN waveguide.

[0074] In order to realize a lateral pin junction along the lateral stacking direction 109, the intrinsically doped photosensitive region 108 is sandwiched between an in-situ p-doped contact region 112 made of Si and an in-situ n-doped contact region 114 also made of Si. In other words, the in-situ p-doped contact region 112, the photosensitive region 108 and the in-situ n-doped contact region 114 are arranged parallel to each other along the lateral stacking direction 109 perpendicular to the vertical stacking direction 107. Since the p-doped contact region 112 and the n-doped contact region 114 are in-situ doped, the photosensitive region 108 is substantially free of unintentional doping. Therefore, in particular in combination with a relatively small lateral width of the photosensitive region 108, a high photoelectric-3dB bandwidth of 100 GHz or more (e.g., 200 GHz or more) can be achieved with the photodetector 100.

[0075] The SiN waveguide 102 is in direct contact with the photodiode 106 to form an upper common interface 116, i.e., there is no other material layer between the SiN waveguide 102 and the photodiode 106. Thus, the coupling efficiency from the SiN waveguide 102 to the Ge fin 108 can be improved. Another feature of the photodetector 100 is that both the p-doped contact region 112 and the n-doped contact region 114 terminate at the height of the upper common interface 116 between the photodiode 106 and the SiN waveguide 102 along the vertical stacking direction 107. In other words, the heights of the p-doped contact region 112 and the n-doped contact region 114 correspond to or are less than the height of the photosensitive region along the vertical stacking direction 107. With respect to the photodetectors known in the prior art having vertical branches protruding beyond the height of the photodiode itself, the photodetector 100 has the following advantages: parasitic capacitance originating from such protruding branches can be prevented, which is beneficial to the RC time constant and, therefore, is beneficial to achieving a high bandwidth of 200 GHz or more using the photodiode 106.

[0076] The p-doped contact region 112 of the photodetector 100 comprises three different parts, namely a p-doped connector region 118, a p-doped central region 120 and a laterally protruding p-doped edge portion 122. The p-doped connector region 118 is used to contact the p-doped contact region 112 with a metal electrode via a metal connector (not shown). The p-doped central region has the smallest lateral width of the p-doped contact region 112 along the lateral stacking direction 109 and follows the p-doped connection region 118 in the direction towards the SiN waveguide 102. Following the p-doped central region 112 towards the SiN waveguide 102, the p-doped contact region 118 comprises a laterally protruding p-doped edge portion 122. The laterally protruding p-doped edge portion 122 can be considered as a lateral branch that bends away laterally along the lateral stacking direction and relative to the lateral sides of the photosensitive region 108.

[0077] Similar to the p-doped contact region 112, the n-doped contact region 114 of the photodetector 100 comprises three parts, namely an n-doped connector region 124, an n-doped central region 126 and a laterally protruding n-doped edge portion 128. The n-doped connector region 124, the n-doped central region 126 and the laterally protruding n-doped edge portion 128 are configured in the same manner as described for the p-doped contact region 112, but extend laterally in the opposite direction, i.e. mirrored with respect to the photosensitive region 108.

[0078] Surfaces of the laterally protruding p-doped edge portion 122, the photosensitive region 108, and the laterally protruding n-doped edge portion 128 that face the SiN waveguide 102 form an upper coupling surface 130 of the photodiode 106. The upper coupling surface 130 includes an upper common interface 116 between the photodiode 106 and the SiN waveguide 102. Those surfaces of the p-doped connector region 118, the photosensitive region 108, and the n-doped connector region 124 that are opposite to the upper coupling surface 130 form a lower coupling surface 132. Portions of the lower coupling surface 132 form a lower common interface 134 between the photodiode 106 and a Si waveguide 136 that is coupled to the photosensitive region 108 and that is arranged on an opposite side of the photodiode 106 compared to the SiN waveguide 102. Thus, the photodetector 100 includes a dual waveguide configuration including a SiN waveguide 102 arranged on an upper coupling surface 130 of the photodiode 106 and a Si waveguide 136 arranged on a lower coupling surface 132 of the photodiode 106. Thus, the photodetector 100 is configured to detect electromagnetic radiation propagating in two different photonic planes that may be arranged parallel to each other. For example, each of the photonic planes may include or may be configured as a photonic integrated circuit or an electronic photonic integrated circuit. The Si waveguide 136 is embedded in a silicon-on-insulator (SOI) substrate material that also contacts portions of the p-doped connection region 118 and the n-doped connection region 124 of the photodetector 100. Thus, the photodetector 100 may be manufactured using standard Si technology, such as in a CMOS or BiCMOS process.

[0079] Figure 2 Schematically and exemplarily, a photodetector 200 is shown, which includes a SiN waveguide 202, which is arranged on top of and coupled to a lateral photodiode 204 along a vertical stacking direction 203 in a cross-sectional view. The SiN waveguide 202 is configured to guide electromagnetic radiation along a propagation direction 206. The electromagnetic radiation propagated through the SiN waveguide 202 can be detected by a photodiode 204, which includes a p-doped contact region 208, a photosensitive region 210, and an n-doped contact region 212, which are arranged parallel to each other along a lateral stacking direction 207 perpendicular to the vertical stacking direction 203. The photosensitive region 210 is configured as a Ge fin and has a lateral width of 100 nm along the lateral stacking direction 207. The photosensitive region 210 can alternatively be formed by a Ge fin and a cap layer (e.g., made of Si) covering the Ge fin along the stacking direction. Alternatively, the photosensitive region 210 can have a lateral width of 20 nm to 300 nm. However, it is preferred that the photosensitive region 210 has a lateral width of 150 nm or less to achieve a high optoelectronic-3 dB bandwidth of 200 GHz or more. The p-doped contact region 208 and the n-doped contact region 212 are made of Si.

[0080] As reference Figure 1 In the photodetector 100 described, the n-doped contact region 212 and the p-doped contact region 208 of the photodiode 204 each include a connector region, a central region, and a laterally protruding edge portion. The connector region is in contact with the silicon substrate 214. The p-doped laterally protruding edge portion 216 together with the photosensitive region 210 and the laterally protruding n-doped edge portion 218 form an upper coupling surface 220 of the photodiode 204, and the SiN waveguide 202 is arranged on the upper coupling surface 220. Figure 1 In contrast to the upper coupling surface 130 of the photodiode 106 described above, the interface between the photodiode 204 and the SiN waveguide 202 is not planar, but the photosensitive region 210 (i.e., the Ge fin) extends into the SiN waveguide 202. The height of the Ge fin 210 along the vertical stacking direction 203 is therefore greater than the heights of the n-doped contact region 212 and the p-doped contact region 208 of the photodiode 204.

[0081] The SiN waveguide 202 has been formed by patterning a SiN hard mask. Due to the fabrication of the SiN waveguide 202, the SiN waveguide 202 has lateral waveguide sides 230, 232 that are substantially parallel to the vertical stacking direction 203 but may also be tilted relative to the vertical stacking direction 203. In other words, the lateral waveguide sides 230, 232 of the SiN waveguide are substantially parallel relative to the interface between the p-doped or n-doped contact regions 208, 214, respectively, and the photosensitive region 210.

[0082] As part of the preparation of the SiN waveguide 202, a first window 222 and a second window 224 have been created in the SiN hard mask beside the SiN waveguide 202. Thus, these first and second windows 222, 224 are surrounded by the remaining parts 226, 228 of the SiN hard mask and the SiN waveguide 202.

[0083] The p-doped contact region 208 is covered by a first metal silicide layer 236, and the n-doped contact region 212 is covered by a second metal silicide layer 238. The first metal silicide layer 236 and the second metal silicide layer 238 may be made of AlCu or NiSi, and are used to contact the p-doped contact region 208 and the n-doped contact region 212 with a first metal connector 240 and a second metal connector 242, respectively. The first metal connector 240 and the second metal connector 242 may be made of W, and may connect the p-doped contact region 208 and the n-doped contact region 212 with a first metal electrode and a second metal electrode (not shown), respectively, which may be made of AlCu.

[0084] Figure 3The photodetector 300 is schematically and exemplarily shown in a plan view. The photodetector 300 comprises a SiN waveguide 302, which is arranged and configured for guiding electromagnetic radiation along a propagation direction 304. The SiN waveguide 302 extends from a SiN grating coupler 306, which is used for fiber-to-chip coupling. The electromagnetic radiation propagating through the SiN waveguide 302 can be detected by a lateral photodiode 308 arranged below and coupled to the SiN waveguide 302. The lateral photodiode 308 comprises an in-situ p-doped contact region 312, an intrinsically doped photosensitive region, which is configured here as an intrinsic Ge fin 314, followed by an in-situ n-doped contact region 316 along a lateral stacking direction 310 perpendicular to the propagation direction 304. The photodiode 308 is arranged on a Si waveguide 318. The lateral width of the Si waveguide 318 along the lateral stacking direction 310 exceeds the lateral width of the photodiode 308 and the SiN waveguide 302. On each side of the SiN waveguide 302 along the lateral direction 310 there are windows, namely first and second windows 318 , 320 produced by patterning a SiN hard mask 322 to fabricate the SiN waveguide 302 .

[0085] Figure 4 The photodetector 300 is schematically and exemplarily shown in a cross-sectional view along a cut through the photodetector 300, the cut being made by Figure 3 The first dashed line 324 shown along the transverse stacking direction 310 indicates. Figure 4 As can be seen in FIG. 3 , the SiN waveguide 302 has a lateral width 326 of 200 nm along a lateral stacking direction 310 perpendicular to the vertical stacking direction 311. Alternatively, the SiN waveguide 302 may have a lateral width 326 of 100 nm to 700 nm. The SiN waveguide 302 has a height 328 of 120 nm along the vertical stacking direction 311. Alternatively, the SiN waveguide 302 may have a height 328 of 30 nm to 500 nm. The photodiode 308 is arranged on top of the Si waveguide 318 along the vertical stacking direction 311 and embedded in the SiO2 layer 330. Thus, the SiO2 layer 330 is arranged between the Si waveguide 318 embedded in the SOI base material (not shown) and the SiN hard mask 322 and the SiN waveguide 302.

[0086] The photodiode 308, which includes a Ge fin 314 laterally sandwiched between an in-situ p-doped contact region 312 and an in-situ n-doped contact region 316 along the lateral stacking direction 310, is in direct contact with its upper coupling surface 332 to the SiN waveguide 302. The upper coupling surface 332 is formed by the Ge fin 314 and the laterally protruding p-doped edge portion 334 of the p-doped contact region 314 and the laterally protruding terminal doped edge portion 336 of the n-doped contact region 316. Figure 4339, the laterally protruding p-doped edge portion 334 protrudes away from the Ge fin 314 along the lateral stacking direction 310, i.e. perpendicular to the sides of the Ge fin 314. Likewise, the laterally protruding n-doped edge portion 336 protrudes away from the Ge fin 314 in the opposite direction, i.e. perpendicular to the sides of the Ge fin 314. In the region of the laterally protruding p-doped edge portion 334 and the laterally protruding n-doped edge portion 336, the photodiode 308 has a larger lateral width along the lateral stacking direction 310 as in the respective n-doped or p-doped central portion 338, 339. The respective n-doped or p-doped central portion 338, 339 follows the laterally protruding n-doped and p-doped edge portions 334, 336, respectively, in the direction towards the lower coupling surface 340 of the photodiode 308.

[0087] Figure 5 Schematically and exemplarily, a photodetector 300 and a longitudinal cross-sectional view along a cut through the photodetector 300 are shown, the cut being parallel to Figure 3 A second dashed line 342 extending in the direction of propagation 304 is indicated. Figure 5 In this longitudinal cross-sectional view of FIG. 3 , it can be seen that the SiN waveguide 302 is in direct contact with a coupling surface 332 of a photodiode formed in part by the Ge fin 314, thereby providing efficient coupling of electromagnetic radiation propagating through the SiN waveguide 302 along the propagation direction 304. The SiN waveguide 302 extends from the SiN grating coupler 306 to the photodiode 308 including the Ge fin 314. The photodiode 308 is embedded in the SiO2 layer 330. The photodiode 308 is in direct contact with the Si waveguide 318 via its lower coupling surface 340.

[0088] Figures 6 to 15 641 and SiN waveguide 644. Figures 1 to 5 Photodetectors 100, 200, 300 are described.

[0089] Figure 6A first intermediate product 600 of a method for manufacturing a photodetector including a Ge fin-type photodiode 641 is schematically shown. In order to manufacture the first intermediate product 600, a Ge fin 602 is manufactured as an intrinsically doped photosensitive region of the photodiode 641 by using selective Ge fin epitaxy in a SiO2 window in a SiO2 layer 604. Therefore, in order to manufacture the Ge fin 602, Ge is selectively deposited in a narrow SiO2 window of the SiO2 layer 604. It may be beneficial to manufacture the Ge fin so that it does not extend to the height of the SiO2 window in the SiO2 layer 604 but stops before (i.e., has a height smaller than the SiO2 window). Thus, a step from the Ge fin to the SiO2 layer is generated. This step can be filled with a cap layer material (e.g., Si) to form a cap layer for protecting the Ge fin. Preferably, the cap layer is manufactured to have a thickness of 10nm to 100nm. For example, the cap layer can be manufactured using selective Si epitaxy or differential Si epitaxy. In particular, in the case of differential Si epitaxy, CMP can be used to remove additional Si from the SiO2 layer to expose the outer SiO2 layer surface again. An alternative process for manufacturing a photosensitive region including an active material layer and a cap layer includes etching the active material layer toward the substrate to produce a step to the SiO2 layer. The step can then be filled with the material of the cap layer to form a cap layer on top of the active material layer along the stacking direction.

[0090] Preferably, the Ge fin 602 is manufactured to have a lateral width 610 of 300 nm or less and particularly preferably 20 nm to 150 nm along the lateral stacking direction 603. Figure 6 As can be seen in FIG. 6 , the upper surface 619 of the Ge fin 602 facing the SiN layer 606 along the vertical stacking direction 605 is not planar, but is concavely curved toward the vertical stacking direction 605, so that the interface between the Ge fin 602 and the SiN layer 606 is also concavely curved. However, CMP can also be first applied to provide a flat surface with the SiO2 layer 604 and the Ge fin 602, and the SiN layer 606 can be deposited on the flat surface. In this case, the interface between the Ge fin 602 and the SiN layer 606 is substantially planar.

[0091] After the Ge fin 602 is fabricated, a SiN layer 606 is deposited on the SiO2 layer 604 with a thickness of 200 nm to 500 nm. The SiN layer 606 can be deposited on the SiO2 layer 604 using low pressure chemical vapor deposition (LPCVD), which typically occurs at a relatively high temperature of about 700°C. The SiN layer 606 deposited by LPCVD can also be represented as a thermal nitride layer. The thermal nitride layer is preferred because it enables the fabrication of a photodetector including a lateral photodiode 641 and a SiN waveguide 644, which enables operation at an optoelectronic -3dB bandwidth of 200 GHz or more. In particular, the SiN layer 606 deposited by LPCVD can be patterned later to be used as a SiN waveguide. The correspondingly fabricated SiN waveguide can operate with relatively low losses in the C-band wavelength region (i.e., 1.5 μm).

[0092] This is possible because, with the method for fabricating a photodetector described herein, the SiN layer 606 is deposited first, and the photodiode 641, in particular the in-situ p-doped contact region and the in-situ n-doped contact region of the photodiode, are created only afterwards. Therefore, the fabrication of the photodiode 641 does not provide a thermal budget constraint on the deposition of the SiN layer 606. That is, if the photodiode 641 is fabricated before the SiN layer 606 is deposited, a much lower temperature and a different method than LPCVD need to be employed in order not to damage the photodiode 641.

[0093] In contrast, when using plasma enhanced chemical vapor deposition (PECVD), much lower temperatures would need to be employed, but operating at much lower performance in the C-band wavelength region. Therefore, the ability to use LPCVD for deposition of the SiN layer 606 constitutes a significant advantage of the present method for fabricating photodetectors.

[0094] The SiN layer 606 is opened beside the Ge fin 602 to create a first window 608. Preferably, the first window 608 is created parallel to the Ge fin 602 at a distance of 100nm to 300nm. The SiN layer 606 serves as a hard mask for an oxide wet etch, which is applied to laterally bottom etch the SiN layer 606 in the region of the first window 608. The wet etch reaches the Ge fin 602 to expose its first sidewall 617 facing the first window 608. Thus, a first cavity 630 is formed. Since the first sidewall 617 of the Ge fin 602 is exposed, an isotropic Ge etch can be applied to further reduce the lateral width of the Ge fin 602. For example, the lateral width of the Ge fin 602 can be reduced by 10nm to 50nm to obtain a more uniform and thinner Ge fin 602.

[0095] As previously described, since the SiN layer 606 is deposited before any doping for the photodiode 641, thermal budget constraints can be alleviated, and the SiN layer 606 can be deposited before any doping using LPCVD. Accordingly, after creating the first cavity and in the presence of the SiN layer 606, differential epitaxy of in-situ p-doped Si is employed, resulting in an in-situ p-doped Si layer 612 covering the exposed first sidewall 617 of the Ge fin 602 and the free surface of the SiN layer 606 and the SiO2 layer 604. The in-situ p-doped Si layer 612 is used to form a p-doped contact region for the photodiode 641.

[0096] Figure 7 shows that by further processing reference Figure 6 The second intermediate product 700 is obtained by the first intermediate product 600 described above. To obtain the second intermediate product 700, the first intermediate product 600 is overfilled with SiO2 616. Subsequently, CMP and dry etching are used to remove the in-situ p-doped Si layer 612 outside the etched trench forming the first window 608. Thereby, the flat surface of the SiN layer 606 is restored, which enables the SiN layer 606 to be patterned on the opposite side of the Ge fin 602 for forming the n-doped contact region of the photodiode 641.

[0097] Figure 8 shows that by further processing reference Figure 7 The third intermediate product 800 is obtained by the second intermediate product 700 described above. In order to manufacture the third intermediate product 800, patterning of the SiN hard mask 606 and the wet etching oxide of the second intermediate product 700 has been performed to define the area of ​​the second window 614. For the patterning of the SiN hard mask 606 and the wet etching oxide, a resist is used because the first window 608 will remain filled with SiO2 616. Due to the wet etching in the second window 614, a second cavity 632 is created and the other sidewall 618 of the Ge fin 602 is exposed to face the second cavity 632. Again, isotropic Ge etching can be applied to further reduce the lateral width of the Ge fin 602. For example, the lateral width of the Ge fin 602 can be further reduced by 10nm to 50nm.

[0098] Fig. 9 shows that by further processing reference Figure 8The fourth intermediate product 900 is obtained by the third intermediate product 800 described above. To manufacture the fourth intermediate product 900, a first differential in-situ doped Si epitaxy is used to apply an in-situ n-doped Si layer 620, which covers the exposed second sidewall 618 of the Ge fin 602 and the free surfaces of the SiN layer 606 and the SiO2 layer 604. The in-situ n-doped Si layer 620 is used to form an n-doped contact region of the photodiode 641. Subsequently, the second cavity 632 is filled with SiO2 622 by overfilling.

[0099] Fig.10 shows that by further processing reference Fig. 9 The fifth intermediate product 1000 is obtained by converting the fourth intermediate product 900 described above into the fifth intermediate product 1000. To obtain the fifth intermediate product 1000, the fourth intermediate product 900 is further processed using SiO2 CMP and Si dry etching to remove SiO2 622 and the in-situ n-doped Si layer 620 on the SiN layer 606. Accordingly, in the fifth intermediate product 1000, SiO2 622 and the in-situ n-doped Si layer 620 exist only inside the second cavity 632. In addition, in the first window 608, portions of SiO2 612 and the in-situ p-doped Si layer 616 are exposed again.

[0100] Fig.11 shows that by further processing reference Fig.10 In order to manufacture the sixth intermediate product 1100, the fifth intermediate product 1000 has been processed by Si dry etching to remove the protruding vertical Si branches 622, 624, 626, 628 (at Fig.10608 and the first cavity 630 below, and SiO2 622 remains in the second window 614 and the second cavity 632 below. In addition, thereby, a laterally protruding p-doped edge portion 634 of the in-situ p-doped contact region 636 is formed, which extends laterally away from the Ge fin 602 along the lateral stacking direction 603. In addition, a laterally protruding n-doped region 638 of the in-situ n-doped contact region 640 is formed, which laterally extends away from the Ge fin 602, however, in the opposite direction compared to the laterally protruding p-doped edge portion 634. Thus, the in-situ p-doped contact region 636, the Ge fin 602 and the in-situ n-doped contact region 640 form a photodiode 641. The in-situ p-doped contact region 636 includes a laterally protruding p-doped edge portion 634, a p-doped central region 635 and a p-doped connector region 637. Correspondingly, the in-situ n-doped contact region 640 includes a laterally protruding p-doped edge portion 638, an n-doped central region 639 and an n-doped connector region 643. The laterally protruding p-doped edge portion 634, the laterally protruding p-doped edge portion 638 and the Ge fin 602 form an upper coupling surface 642 of the photodiode 641, on which a SiN waveguide 644 is arranged in direct contact with the Ge fin 602.

[0101] Fig.12 A seventh intermediate product 1200 is shown, which is further processed by reference Fig.11 To obtain the seventh intermediate product 1200, the SiO2 616 in the first window 608 and the first cavity 630 therebelow, as well as the SiO2 622 in the second window 614 and the first cavity 632 therebelow have been removed by wet etching (e.g., without a mask) of the sixth intermediate product 1100. Thereby, the in-situ p-doped contact region 636 and the in-situ n-doped contact region 640 are exposed, which allows subsequent silicide formation.

[0102] Fig.13 shows further processing by reference Fig.12The eighth intermediate product 1300 is obtained by obtaining the seventh intermediate product 1200 described above. The eighth intermediate product 1300 includes a resist mask 646 applied to the SiN waveguide 644, the photodiode 641, and the first cavity 630 and the second cavity 632 top that respectively accommodate the in-situ p-doped contact area 636 and the in-situ n-doped contact area 640. In order to obtain the eighth intermediate product 1300, the resist mask 646 has therefore been deposited on the seventh intermediate product 1200 in the photodiode area, and the SiN hard mask area outside the actual photodiode 641 has been removed by dry etching. The resist mask 646 can also be used for the definition and patterning of the SiN waveguide 644. For example, the resist mask 646 can be used to define the shape of the SiN waveguide 644 by dry etching. For example, the resist mask 646 can be used to reduce the lateral width 648 of the SiN waveguide 644 by dry etching. Additionally, the resist mask 646 may be used to fabricate a ridge waveguide from the SiN waveguide 644 .

[0103] Fig.14 A ninth intermediate product 1400 is shown, which is further processed by reference Fig.13 The ninth intermediate product 1400 is obtained by the eighth intermediate product 1300 described in the preceding claims. The ninth intermediate product 1400 comprises a first silicide layer 650 covering the p-doped contact region 636 and a second silicide layer 652 covering the n-doped contact region 640. In contrast to the known device concepts, the laterally protruding p-doped edge portion 634 and the laterally protruding n-doped edge portion 638 are laterally deflected. Therefore, the formed silicide (e.g., cobalt or nickel) maintains a predetermined distance from the optical field in the SiN waveguide 644. This may be beneficial for achieving an optoelectronic -3dB bandwidth far exceeding 100 GHz (e.g., 200 GHz or more).

[0104] Fig.15 A tenth intermediate product 1500 is shown, which is further processed by reference Fig.14 The tenth intermediate product 1500 includes a first interlayer dielectric (ILD0) stack and a back-end of line (BEOL) contact scheme, which includes a first metal connector 654 for connecting the p-doped contact region 636 of the photodiode 641 and a second metal connector 656 for connecting the n-doped contact region 640 of the photodiode 641.

[0105] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0106] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0107] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0108] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A photodetector for detecting electromagnetic radiation, the photodetector comprising - a lateral photodiode comprising an in-situ p-doped contact region, an in-situ n-doped contact region and an intrinsically doped photosensitive region sandwiched between the p-doped contact region and the n-doped contact region in a lateral stacking direction, - a SiN waveguide comprising SiN and configured to guide electromagnetic radiation along a propagation direction, the SiN waveguide being arranged on top of the lateral photodiode along a vertical stacking direction perpendicular to the lateral stacking direction, wherein - at least a portion of the photosensitive region and at least a portion of the SiN waveguide form a common upper interface, at which the photosensitive region is in direct contact with the SiN waveguide, and - the photosensitive region has a lateral width along the lateral stacking direction of 300 nm or less.

2. The photodetector according to claim 1, wherein: The p-doped contact region and the n-doped contact region include Si, and the photosensitive region includes Ge.

3. The photodetector according to claim 1 , wherein: The common upper interface between the photosensitive region and the SiN waveguide is substantially planar or concavely curved along the vertical stacking direction.

4. The photodetector according to claim 1, wherein: The lateral width of the SiN waveguide along the lateral stacking direction corresponds to the lateral width of the photosensitive region, or is greater than the lateral width of the photosensitive region.

5. The photodetector according to claim 1, wherein: The lateral width of the SiN waveguide along the lateral stacking direction exceeds the lateral width of the photosensitive region by at least 20 nm on both sides.

6. The photodetector according to claim 1, wherein: - the p-doped contact region comprises, along the vertical stacking direction, a p-doped connector region, a p-doped central region and a laterally protruding p-doped edge portion, wherein the laterally protruding p-doped edge portion has a larger lateral width along the lateral stacking direction than the p-doped central portion of the p-doped contact region, and / or - the n-doped contact region comprises, along the vertical stacking direction, an n-doped connector region, an n-doped central region and a laterally protruding n-doped edge portion, wherein the laterally protruding n-doped edge portion has a larger lateral width along the lateral stacking direction than the n-doped central portion of the n-doped contact region.

7. The photodetector according to claim 6, wherein: A height of the laterally protruding p-doped edge portion and / or the laterally protruding n-doped edge portion along the vertical stacking direction is equal to or smaller than a height of the photosensitive region along the vertical stacking direction.

8. The photodetector according to at least one of the preceding claims, comprising a Si waveguide, which comprises Si and is arranged below the photodiode along the stacking direction so as to form a common lower interface with the photodiode, at which the Si waveguide is in direct contact with at least a portion of the photosensitive region, wherein preferably, the Si waveguide has a width along the lateral stacking direction that is equal to or greater than a lateral width of the photodiode.

9. The photodetector according to claim 1, wherein: The photosensitive region includes an optically active active material layer and a cap layer for protecting the active material layer, wherein the cap layer is arranged on top of the active material layer along the vertical stacking direction, wherein the cap layer forms the common upper interface, and at the common upper interface, the photosensitive region is in direct contact with the SiN waveguide.

10. A photonic integrated circuit or electronic photonic circuit comprising a photodetector according to at least one of the preceding claims.

11. A method for manufacturing a photodetector, the method comprising the steps of: - manufacturing a lateral photodiode comprising an in-situ p-doped contact region, an in-situ n-doped contact region and an intrinsically doped photosensitive region sandwiched between the p-doped contact region and the n-doped contact region in a lateral stacking direction, the photosensitive region having a lateral width of 300 nm or less in the lateral stacking direction, and - manufacturing a SiN waveguide, the SiN waveguide comprising SiN and configured to guide electromagnetic radiation along a propagation direction, the SiN waveguide being arranged on top of the lateral photodiode along a vertical stacking direction perpendicular to the lateral stacking direction, such that at least a portion of the photosensitive region and at least a portion of the SiN waveguide form a common upper interface, at which the photosensitive region is in direct contact with the SiN waveguide.

12. The method according to claim 11, wherein: Manufacturing the photodiode includes a) providing a photodetector intermediate product, comprising an intrinsically doped photosensitive region with a lateral width of 300 nm or less, the photosensitive region being embedded with its lateral side in an insulating material layer arranged on a substrate, wherein, through a top side of the photosensitive region facing away from the substrate in a vertical stacking direction, the photosensitive region is in contact with a SiN hard mask, the SiN hard mask covering the insulating material layer with the embedded photosensitive region, b) creating a first window in the SiN hard mask at a first predetermined distance from a first one of the lateral sides of the photosensitive region, c) removing the insulating material layer exposed by the first window by bottom etching, so that the first lateral side of the lateral sides of the photosensitive region is exposed, and a first cavity is formed adjacent to the insulating material layer, d) epitaxially growing an in-situ p-doped layer, the in-situ p-doped layer covering at least a portion of the SiN hard mask and the first of the lateral sides of the photosensitive region, such that a laterally protruding p-doped edge portion is formed in the first cavity and in contact with the SiN hard mask, and wherein, in the laterally protruding p-doped edge portion, the p-doped contact region has a larger lateral width along the lateral stacking direction than a p-doped central portion of the in-situ p-doped layer, e) filling the first cavity with an insulating material and exposing the upper surface of the SiN hard mask along the vertical stacking direction, f) creating a second window at a second predetermined distance from a second one of the lateral sides of the photosensitive region, such that the photosensitive region is located between the first window and the second window, wherein by creating the first window and the second window, the SiN waveguide is formed on top of the photodiode along the vertical stacking direction, g) analogously repeating steps c) to f) for the second window, wherein instead of epitaxially growing an in-situ p-doped layer according to step d), an in-situ n-doped layer is epitaxially grown, h) removing those portions of the in-situ p-doped layer and the in-situ n-doped layer covering lateral sides of the SiN waveguide, thereby forming the in-situ p-doped contact region and the in-situ n-doped contact region of the photodiode, respectively, i) removing the insulating material in the first cavity and the second cavity to expose the in-situ p-doped contact region and the in-situ n-doped contact region of the photodiode, and j) performing silicide formation of the in-situ p-doped contact region and the in-situ n-doped contact region.

13. The method according to claim 11 or 12, wherein: Providing the optical detector intermediate product includes: - before applying the SiN hard mask on top of the insulating material layer with the embedded photosensitive regions, chemically and / or mechanically polishing the outer surface of the insulating material layer with the embedded photosensitive regions along the vertical stacking direction to provide a smooth interface between the insulating material layer with the embedded photosensitive regions and the SiN hard mask.

14. The method according to at least one of claims 11 to 13, wherein: Fabricating the SiN waveguide includes: - exposing an outer surface of the SiN hard mask facing along the vertical stacking direction, and - Patterning a SiN hard mask to define the shape of the SiN waveguide arranged on top of the photodiode.

15. Use of the photodetector according to at least one of claims 1 to 9 for detecting electromagnetic radiation in the wavelength range of 0.8 μm to 1.65 μm.

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