Photoelectric detector and forming method thereof

Abstract

The invention discloses a photoelectric detector and a forming method thereof. The photoelectric detector comprises a substrate; a light absorbing layer on the substrate; the stress layer is located on the light absorption layer, at least covers part of the light absorption layer and is used for providing stress for the light absorption layer. The device comprises a stress layer located on a light absorption layer, and the stress layer at least covers part of the light absorption layer and is used for providing stress for the light absorption layer, so that the distance between atoms in the light absorption layer is changed, an energy band of the light absorption layer deflects, an indirect band gap of the light absorption layer deflects towards the top of a valence band, and therefore the light absorption effect is improved. According to the photoelectric detector provided by the invention, the energy band gap of the light absorption layer is equivalently reduced, so that electrons can still be excited from a valence band to a conduction band when photons have relatively large wavelengths, namely photon energy is relatively small, the responsivity of the light absorption layer is correspondingly improved, and the performance of the photoelectric detector is improved.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of silicon optical devices, and in particular to a photodetector and a method for forming the same. Background Art

[0002] With the development of optical communications in recent years, in pursuit of higher transmission rates, silicon photonics products have gradually extended the wavelength selection of wavelength division multiplexing from the traditional O / C band to other bands.

[0003] A photodetector is a device that converts light signals into electrical signals. Its working principle is based on the photoelectric effect, which refers to the phenomenon that when light shines on certain substances, the electrons of the substance absorb the energy of photons and produce corresponding electrical effects.

[0004] Improving the performance of silicon photonics products in other bands mainly depends on improving the performance of photodetectors in other bands. Therefore, improving the performance of photodetectors in other bands has become an urgent problem to be solved. Summary of the invention

[0005] The problem solved by the embodiments of the present invention is to provide a photodetector and a method for forming the same, so as to improve the performance of the photodetector.

[0006] To solve the above problems, an embodiment of the present invention provides a photodetector, comprising: a substrate; a light absorbing layer located on the substrate; a stress layer located on the light absorbing layer and covering at least a portion of the light absorbing layer, for providing stress to the light absorbing layer.

[0007] Correspondingly, an embodiment of the present invention also provides a method for forming a photodetector, comprising: providing a substrate; forming a light absorbing layer on the substrate; forming a stress layer on the light absorbing layer, wherein the stress layer at least covers a portion of the light absorbing layer and is used to provide stress to the light absorbing layer.

[0008] Compared with the prior art, the technical solution of the embodiment of the present invention has the following advantages:

[0009] The photodetector provided by the embodiment of the present invention includes a stress layer located on the light absorbing layer, and the stress layer covers at least a portion of the light absorbing layer, and is used to provide stress to the light absorbing layer, so that the distance between atoms inside the light absorbing layer changes, thereby causing the energy band of the light absorbing layer to deflect, and also causing the indirect band gap of the light absorbing layer to shift toward the top of the valence band, that is, the energy band gap of the light absorbing layer is equivalently reduced, and then when the wavelength of the photon is larger, that is, when the photon energy is smaller, it is still possible to excite electrons from the valence band to the conduction band, thereby correspondingly improving the responsiveness of the light absorbing layer and improving the performance of the photodetector.

[0010] In the method for forming a photodetector provided by an embodiment of the present invention, a stress layer is formed on the light absorbing layer, and the stress layer at least covers a portion of the light absorbing layer, and is used to provide stress to the light absorbing layer, so that the distance between atoms inside the light absorbing layer changes, thereby causing the energy band of the light absorbing layer to deflect, and also causing the indirect band gap of the light absorbing layer to shift toward the top of the valence band, that is, the energy band gap of the light absorbing layer is equivalently reduced, and then when the wavelength of the photon is specifically larger, that is, when the photon energy is smaller, it is still possible to excite electrons from the valence band to the conduction band, thereby correspondingly improving the responsiveness of the light absorbing layer and improving the performance of the photodetector. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the structure of a photoelectric detector;

[0012] Figure 2 is a schematic structural diagram of an embodiment of a photoelectric detector of the present invention;

[0013] Figures 3 to 7 It is a schematic structural diagram corresponding to each step in an embodiment of a method for forming a photodetector of the present invention;

[0014] Figure 8 is an energy band diagram of the light absorbing layer when no stress layer is formed on the light absorbing layer;

[0015] Fig. 9 FIG. 1 is an energy band diagram of the light absorbing layer when a stress layer is formed on the light absorbing layer. DETAILED DESCRIPTION

[0016] At present, the performance of photodetectors still needs to be improved. This paper combines a photodetector to analyze the reasons why the performance of the photodetector structure needs to be improved. Figure 1 This is a schematic diagram of the structure of a photoelectric detector.

[0017] refer to Figure 1 The photodetector includes: a substrate 1; and a light absorbing layer 2 located on the substrate 1.

[0018] Since the performance of the photodetector is related to the responsivity of the light absorbing layer 2, and the material of the light absorbing layer 2 determines that its responsivity is cut off near a certain wavelength. In order to increase the wavelength selection range of light, in the prior art, when the light absorbing layer 2 is annealed to improve the crystal quality of the light absorbing layer 2, some defects of the light absorbing layer 2 are retained, and the partial defects provide defect energy levels, that is, shorten the distance between the valence band and the conduction band, so that waves larger than the wavelength can still be absorbed by the light absorbing layer 2.

[0019] However, research has found that this method will increase the dark current of the photodetector, thereby reducing the signal-to-noise ratio of the photodetector.

[0020] In order to solve the above technical problems, an embodiment of the present invention provides a photodetector, including: a substrate; a light absorbing layer located on the substrate; a stress layer located on the light absorbing layer and covering at least part of the light absorbing layer, for providing stress to the light absorbing layer.

[0021] The photodetector provided by the embodiment of the present invention includes a stress layer located on the light absorbing layer, and the stress layer covers at least a portion of the light absorbing layer, and is used to provide stress to the light absorbing layer, so that the distance between atoms inside the light absorbing layer changes, thereby causing the energy band of the light absorbing layer to deflect, and also causing the indirect band gap of the light absorbing layer to shift toward the top of the valence band, that is, the energy band gap of the light absorbing layer is equivalently reduced, and then when the wavelength of the photon is larger, that is, when the photon energy is smaller, it is still possible to excite electrons from the valence band to the conduction band, thereby correspondingly improving the responsiveness of the light absorbing layer and improving the performance of the photodetector.

[0022] In order to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0023] Figure 2 is a schematic structural diagram of an embodiment of a photoelectric detector of the present invention;

[0024] In this embodiment, the photodetector includes: a substrate 100; a light absorbing layer 110 located on the substrate 100; and a stress layer 130 located on the light absorbing layer 110 and covering at least a portion of the light absorbing layer 110 for providing stress to the light absorbing layer 110.

[0025] The substrate 100 is a pixel substrate, which is used to provide a process platform for forming a photodetector.

[0026] The base 100 includes a substrate (not shown), the material of the substrate may be silicon, germanium, silicon germanium, silicon carbide, gallium arsenide, indium gallium or other materials, and the substrate may also be other types of substrates such as a silicon on insulator substrate or a germanium on insulator substrate.

[0027] In this embodiment, the substrate 100 includes, from bottom to top, a bottom semiconductor layer (not shown), an insulating material layer 101 and a top semiconductor layer 102 .

[0028] Specifically, the insulating material layer 101 is an oxide buried layer, the material of the oxide buried layer may be silicon dioxide, the material of the bottom semiconductor layer may be silicon, germanium or a mixture of germanium and silicon, the material of the top semiconductor layer 102 may be undoped silicon, doped silicon, undoped germanium or doped germanium. When the material of the top semiconductor layer 102 is undoped silicon or doped silicon, the substrate 100 is a silicon-on-insulator substrate, and when the material of the top semiconductor layer is undoped germanium or doped germanium, the substrate 100 is a germanium-on-insulator substrate.

[0029] In this embodiment, a first doping region 104 having first-type doping ions and a second doping region 105 having second-type doping ions are formed in the substrate 100. The first doping region 104 and the second doping region 105 are located on both sides of the light absorbing layer 110, and the first-type doping ions and the second-type doping ions have different conductivity types.

[0030] The substrate 100 between the first doping region 104 and the second doping region 105 is used to provide a process platform for forming the light absorption layer 110 ; and the first doping region 104 and the second doping region 105 together form a PN junction of the photodetector.

[0031] Specifically, the first doping region 104 and the second doping region 105 are respectively located in the top semiconductor layer 102 on both sides of the light absorbing layer 110 .

[0032] As an example, the first type doping ions are N type ions, and the second type doping ions are P type ions. The N type ions include B, Ga or In, and the P type ions include P, As or Sb.

[0033] It should be noted that a first isolation layer 107 is formed in the substrate 100 of the first doping region 104 and in the substrate 100 of the second doping region 105 , respectively, and the first isolation layer 107 is spaced apart from the light absorbing layer 110 .

[0034] When a conductive plug electrically connected to the first doping region 104 and the second doping region 105 is provided, the conductive plug is located on a side of the first isolation layer 107 away from the light absorbing layer 110. The first isolation layer 107 is conducive to increasing the distance between the light absorbing layer 110 and the conductive plug, thereby facilitating the reduction of parasitic capacitance. As an example, the material of the first isolation layer 107 includes silicon oxide. In other embodiments, the first isolation layer may also be other insulating materials.

[0035] In this embodiment, a second isolation layer 108 is formed on the first doping region 104 and the second doping region 105 .

[0036] Typically, the light absorbing layer 110 is formed by an epitaxial growth process, and a second isolation layer 108 is formed on the first doping region 104 and the second doping region 105 , that is, the top of the substrate 100 of the first doping region 104 and the second doping region 105 is covered by the second isolation layer 108 , thereby facilitating the formation of the light absorbing layer 110 by an epitaxial growth process.

[0037] As an example, the material of the second isolation layer 108 includes silicon oxide. In other embodiments, the second isolation layer can be other insulating materials.

[0038] The light absorbing layer 110 is used to receive an optical signal so as to convert the optical signal into an electrical signal.

[0039] It should be noted that the material of the light absorbing layer 110 includes one or more of germanium, silicon and silicon germanium. As an example, the material of the light absorbing layer 110 is germanium, and accordingly, the photodetector is a germanium photodetector. Germanium, silicon and silicon germanium are commonly used materials for the light absorbing layer 110 and are relatively easy to obtain.

[0040] It should also be noted that the thickness of the light absorbing layer 110 should not be too large or too small. If the thickness of the light absorbing layer 110 is too large, it is easy to increase the probability of carrier recombination, which is easy to affect the responsivity of the photodetector; if the thickness of the light absorbing layer 110 is too small, it is easy to make the light absorbing layer 110 have a poor coupling effect on light, and it is difficult to generate a photocurrent that meets the process requirements, which is also easy to affect the responsivity of the photodetector. Therefore, in this embodiment, along the normal direction of the top surface of the substrate 100, the thickness of the light absorbing layer 110 ranges from 10 nanometers to 10 microns.

[0041] In this embodiment, the bottom of the light absorbing layer 110 is lower than the top of the substrate 100 , and the top of the light absorbing layer 110 is higher than the top of the substrate 100 .

[0042] Specifically, a groove (not shown) is formed in the substrate 100 , and the light absorbing layer 110 is located in the groove, that is, the light absorbing layer 110 is located on the remaining substrate 100 at the bottom of the groove. In other words, the light absorbing layer 110 is embedded in the substrate 100 .

[0043] The bottom of the light absorbing layer 110 is lower than the top of the substrate 100, which is easy to improve the coupling efficiency of the subsequent light from the substrate 100 to the light absorbing layer 110, and is also conducive to reducing the longitudinal size of the photodetector; wherein the longitudinal direction refers to the normal direction along the top surface of the substrate 100. The top of the light absorbing layer 110 is higher than the top of the substrate 100, that is, the light absorbing layer 110 protrudes on the substrate 100, which makes it easy for the thickness of the light absorbing layer 110 to meet the process requirements, which is conducive to the light absorbing layer 110 generating a photocurrent that meets the process requirements.

[0044] Combined with reference Figure 8 and Fig. 9 , Figure 8 is an energy band diagram of the light absorbing layer when no stress layer is formed on the light absorbing layer; Fig. 9When a stress layer is formed on the light absorption layer, the energy band diagram of the light absorption layer. A stress layer 130 is formed on the light absorption layer 110, and the stress layer 130 covers at least a part of the light absorption layer 110, and is used to provide stress to the light absorption layer 110, so that the distance between atoms in the light absorption layer 110 changes, thereby causing the energy band of the light absorption layer 110 to deflect, and also causing the indirect band gap of the light absorption layer 110 to shift towards the top of the valence band, that is, the energy band gap of the light absorption layer 110 is equivalently reduced. Furthermore, when photons have a relatively large wavelength, that is, when the photon energy is small, electrons can still be excited from the valence band to the conduction band, correspondingly improving the responsivity of the light absorption layer 110 and the performance of the photodetector.

[0045] Continue to refer to Figure 8 and Fig. 9 , when no stress layer is formed on the light absorption layer, the distance between the direct conduction band Γ and the indirect conduction band L is W1 (as Figure 8 shown); when a stress layer 130 is formed on the light absorption layer 110, the distance between the direct conduction band Γ and the indirect conduction band L is W2 (as Fig. 9 shown); where, W2 < W1. Thus, it can be seen that when the light absorption layer 110 is subjected to stress, the indirect conduction band L of the light absorption layer 110 shifts towards the position of the direct conduction band Γ, making the photon energy required for electrons to transition from the valence band to the indirect conduction band L smaller. Therefore, some electrons will preferentially transition to the indirect conduction band L, thereby equivalently reducing the energy band gap.

[0046] It should be noted that the thickness of the stress layer 130 should not be too large. If the thickness of the stress layer 130 is too large, the stress provided by the stress layer 130 to the light absorption layer 110 is large, and the probability of stress mismatch between the stress layer 130 and the light absorption layer 110 is likely to increase. Therefore, in this embodiment, along the normal direction of the top surface of the substrate 100, the thickness range of the stress layer 130 is less than or equal to 10 microns.

[0047] Specifically, the material of the stress layer 130 includes one or more of silicon nitride, silicon oxide, carbon, and polysilicon. As an example, the material of the stress layer 130 is silicon nitride.

[0048] Generally, the temperature for forming the stress layer 130 is higher than room temperature. After the stress layer 130 is formed, the temperature will gradually drop back to room temperature. Since the material of the stress layer 130 is generally different from that of the light absorption layer 110, the deformation amplitudes of the stress layer 130 and the light absorption layer 110 due to temperature changes are different, so it is easy for the stress layer 130 to provide stress to the light absorption layer 110. As an example, the stress layer 130 provides tensile stress to the light absorption layer 110. However, in other embodiments, according to the material of the light absorption layer, the stress received by the light absorption layer can also be compressive stress.

[0049] Furthermore, silicon nitride, silicon nitride, silicon oxide, carbon and polysilicon are commonly used and low-cost materials in semiconductor processes and have high process compatibility, which is beneficial to reducing the process difficulty and process cost of forming the stress layer 130 .

[0050] In this embodiment, the area of ​​the light absorbing layer 110 covered by the stress layer 130 is at least 50% of the area of ​​the light absorbing layer 110 .

[0051] The area of ​​the light absorbing layer 110 covered by the stress layer 130 should not be too small. If the area of ​​the light absorbing layer 110 covered by the stress layer 130 is too small, the stress layer 130 may not provide stress to the light absorbing layer 110 well, that is, the effect of increasing the stress on the light absorbing layer 110 is not good, which may make the energy band of the light absorbing layer 110 deflect by a small amplitude, so that the distance of the indirect band gap of the light absorbing layer 110 shifting toward the top of the valence band is small, so that the effect of equivalently reducing the energy band gap of the light absorbing layer 110 is not good, and thus the effect of improving the responsiveness of the light absorbing layer 110 is not ideal. Therefore, in this embodiment, the area of ​​the light absorbing layer 110 covered by the stress layer 130 is at least 50% of the area of ​​the light absorbing layer 110.

[0052] In this embodiment, the stress layer 130 covers the entire light absorbing layer 110 exposed from the substrate 100 ; or, the stress layer 130 covers the entire light absorbing layer 110 exposed from the substrate 100 and also extends to cover a portion of the substrate 100 on the side of the light absorbing layer 110 .

[0053] The stress layer 130 completely covers the entire light absorbing layer 110 exposed from the substrate 100, which is beneficial to further enhance the effect of the stress layer 130 providing stress to the light absorbing layer 110, and it is easy to make the stress provided by the stress layer 130 to the light absorbing layer 110 more uniform, thereby helping to reduce the probability of stress mismatch between the stress layer 130 and the light absorbing layer 110.

[0054] The stress layer 130 covers the entire light absorbing layer 110 exposed from the substrate 100, and also extends to cover part of the substrate 100 on the side of the light absorbing layer 510, which helps to ensure that the stress layer 130 can completely cover the light absorbing layer 110 exposed from the substrate 100, and makes it easier for the stress layer 130 to provide a more uniform stress to the light absorbing layer 110, thereby helping to further reduce the probability of stress mismatch between the stress layer 130 and the light absorbing layer 110.

[0055] It should be noted that, because the area of ​​the substrate 100 where the stress layer 130 extends to cover the side of the light absorbing layer 110 is not positively correlated with the magnitude of the stress generated by the stress layer 130 on the light absorbing layer 110, when the area of ​​the substrate 100 covered by the stress layer 130 is too large, it is easy to cause the proportion of the covered area of ​​the light absorbing layer 110 to the total covered area of ​​the stress layer 130 to be too small, thereby causing the stress on the light absorbing layer 110 to become smaller. Therefore, in this embodiment, along the direction perpendicular to the end face of the stress layer 130, the lateral dimension of the portion of the stress layer 130 extending to cover the substrate 100 is less than 100 mm.

[0056] In summary, the stress layer 130 covers part of the light absorbing layer 110, or completely covers the entire light absorbing layer 110 exposed from the substrate 100 and exposes the substrate 100, or the stress layer 130 covers the entire light absorbing layer 110 exposed from the substrate 100, and also extends to cover part of the substrate 100 on the side of the light absorbing layer 110, that is, the stress layer 130 does not globally cover the entire light absorbing layer 110 and the entire substrate 100, so that the stress layer 130 can provide local stress, which is beneficial to increase the stress applied by the stress layer 130 to the light absorbing layer 110.

[0057] In this embodiment, the structure of the photodetector further includes: a buffer layer 120 located between the light absorbing layer 110 and the stress layer 130 .

[0058] The buffer layer 120 is used to provide stress buffering between the light absorbing layer 110 and the stress layer 130. The buffer layer 120 has good adhesion to both the stress layer 130 and the light absorbing layer 110, which is beneficial to reducing the probability of stress mismatch between the light absorbing layer 110 and the stress layer 130, thereby reducing the probability of delamination between the light absorbing layer 110 and the stress layer 130.

[0059] Specifically, the material of the buffer layer 120 includes one or more of silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon, and tin.

[0060] Since silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon and tin have good adhesion to various materials in semiconductor processes, when the material of the buffer layer 120 includes one or more of silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon and tin, the buffer layer 120 can be more effectively used as a stress buffer between the light absorbing layer 110 and the stress layer 130, and accordingly the probability of stress mismatch between the light absorbing layer 110 and the stress layer 130 can be better reduced, thereby making the probability of stratification between the light absorbing layer 110 and the stress layer 130 more ideal.

[0061] It should be noted that the thickness of the buffer layer 120 should not be too large. If the thickness of the buffer layer 120 is too large, that is, the distance between the light absorbing layer 110 and the stress layer 130 is too large, the light absorbing layer 110 is likely to be subjected to less stress, which may result in poor deflection of the energy band of the light absorbing layer 110, and accordingly, poor effect of shifting the indirect band gap of the light absorbing layer 110 toward the top of the valence band, that is, poor effect of equivalent reduction of the energy band gap of the light absorbing layer 110, and thus poor effect of improving the responsiveness of the light absorbing layer. Therefore, in this embodiment, the thickness of the buffer layer 120 is less than or equal to 10 microns.

[0062] In this embodiment, the structure of the photodetector further includes: conductive plugs (not shown), which are respectively located on the top of the first doping region 104 and the second doping region 105 .

[0063] Usually, before forming the conductive plug, a conductive plug hole (not shown) is first formed to expose the top of the first doping region 104 and the second doping region 105; and then a conductive plug is formed in the conductive plug hole.

[0064] Specifically, the conductive plug hole is located on the side of the first isolation layer 107 away from the light absorbing layer 110, and correspondingly, the conductive plug is also located on the side of the first isolation layer 107 away from the light absorbing layer 110, that is, the first isolation layer 107 serves to increase the distance between the conductive plug and the light absorbing layer 110.

[0065] Correspondingly, the present invention also provides a method for forming a photodetector. Figures 3 to 7 It is a schematic structural diagram corresponding to each step in an embodiment of a method for forming a photodetector of the present invention; Figure 8 is an energy band diagram of the light absorbing layer when no stress layer is formed on the light absorbing layer; Fig. 9 FIG. 1 is an energy band diagram of the light absorbing layer when a stress layer is formed on the light absorbing layer.

[0066] refer to Figure 4 , providing a substrate 500.

[0067] The substrate 500 is a pixel substrate, which is used to provide a process platform for the subsequent formation of a photodetector.

[0068] The base 500 includes a substrate (not shown), the material of the substrate may be silicon, germanium, silicon germanium, silicon carbide, gallium arsenide, indium gallium or other materials, and the substrate may also be other types of substrates such as a silicon on insulator substrate or a germanium on insulator substrate.

[0069] In this embodiment, the substrate 500 includes, from bottom to top, a bottom semiconductor layer (not shown), an insulating material layer 501 and a top semiconductor layer 502 .

[0070] Specifically, the insulating material layer 501 is an oxide buried layer, the material of the oxide buried layer may be silicon dioxide, the material of the bottom semiconductor layer may be silicon, germanium or a mixture of germanium and silicon, the material of the top semiconductor layer 502 may be undoped silicon, doped silicon, undoped germanium or doped germanium. When the material of the top semiconductor layer 502 is undoped silicon or doped silicon, the substrate 500 is a silicon-on-insulator substrate, and when the material of the top semiconductor layer is undoped germanium or doped germanium, the substrate 500 is a germanium-on-insulator substrate.

[0071] In this embodiment, in the step of providing the substrate 500 , a groove 503 is formed in the substrate 500 .

[0072] The groove 503 is used to provide a spatial position for the subsequent formation of a light absorption layer. The light absorption layer is formed in the groove 503, which is easy to improve the coupling efficiency of the subsequent light from the substrate 500 to the light absorption layer, and is also beneficial to reducing the longitudinal size of the photodetector; wherein the longitudinal direction refers to the normal direction along the top surface of the substrate 500.

[0073] In this embodiment, the bottom of the groove 503 exposes the top of the remaining top semiconductor layer 502 .

[0074] In this embodiment, in the step of providing a substrate 500, a first doping region 504 having first-type doping ions and a second doping region 505 having second-type doping ions are formed in the substrate 500. The first doping region 504 and the second doping region 505 are arranged at intervals, and the first-type doping ions and the second-type doping ions have different conductivity types.

[0075] The substrate 500 between the first doping region 504 and the second doping region 505 is used to provide a process platform for the subsequent formation of a light absorption layer; and the first doping region 504 and the second doping region 505 together form a PN junction of the photodetector.

[0076] Specifically, the first doping region 504 and the second doping region 505 are respectively located in the top semiconductor layer 502 on both sides of the groove 503 .

[0077] As an example, the first type doping ions are N type ions, and the second type doping ions are P type ions. The N type ions include B, Ga or In, and the P type ions include P, As or Sb.

[0078] It should be noted that in the step of providing the substrate 500 , a first isolation layer 507 is formed in the substrate 500 on the side of the first doping region 504 facing away from the second doping region 505 , and a first isolation layer 507 is also formed in the substrate 500 on the side of the second doping region 505 facing away from the first doping region 504 .

[0079] The first isolation layer 507 is helpful to increase the distance between the subsequently formed light absorption layer and the conductive plug, thereby helping to reduce parasitic capacitance. As an example, the material of the first isolation layer 507 includes silicon oxide. In other embodiments, the first isolation layer can also be other insulating materials.

[0080] In this embodiment, in the step of providing the substrate 500 , a second isolation layer 508 is formed on the first doping region 504 and the second doping region 505 .

[0081] A second isolation layer 508 is formed on the first doping region 504 and the second doping region 505 , that is, the top of the substrate 500 of the first doping region 504 and the second doping region 505 is covered by the second isolation layer 508 , which is conducive to the subsequent formation of a light absorption layer by epitaxial growth.

[0082] As an example, the material of the second isolation layer 508 includes silicon oxide. In other embodiments, the second isolation layer can be other insulating materials.

[0083] refer to Figure 4 , a light absorbing layer 510 is formed on the substrate 500 .

[0084] The light absorbing layer 510 is used to receive an optical signal so as to convert the optical signal into an electrical signal.

[0085] Specifically, the process of forming the light absorbing layer 510 includes one or more of an epitaxial growth process, a chemical vapor deposition process, and a furnace process. As an example, the process of forming the light absorbing layer 510 is an epitaxial growth process, which is beneficial to improving the formation quality of the light absorbing layer 510.

[0086] It should be noted that in the step of forming the light absorbing layer 510, the material of the light absorbing layer 510 includes one or more of germanium, silicon and silicon germanium. As an example, the material of the light absorbing layer 510 is germanium, and accordingly, the photodetector is a germanium photodetector. Germanium, silicon and silicon germanium are common materials for the light absorbing layer 110 and are relatively easy to obtain.

[0087] It should also be noted that the thickness of the light absorbing layer 510 should not be too large or too small. If the thickness of the light absorbing layer 510 is too large, it is easy to increase the probability of carrier recombination, which is easy to affect the responsivity of the photodetector; if the thickness of the light absorbing layer 510 is too small, it is easy to make the light absorbing layer 510 have a poor coupling effect on light, and it is difficult to generate a photocurrent that meets the process requirements, which is also easy to affect the responsivity of the photodetector. Therefore, in the step of forming the light absorbing layer 510, in the normal direction of the top surface of the substrate 500, the thickness of the light absorbing layer 510 ranges from 10 nanometers to 10 micrometers.

[0088] In this embodiment, in the step of forming the light absorbing layer 510 , the light absorbing layer 510 is also located in the groove 503 , and the top of the light absorbing layer 510 is higher than the top of the substrate 500 .

[0089] The top of the light absorbing layer 510 is higher than the top of the substrate 500, that is, the light absorbing layer 510 protrudes on the substrate 500, which makes it easy for the thickness of the light absorbing layer 510 to meet the process requirements and is conducive to the light absorbing layer 510 generating a photocurrent that meets the process requirements.

[0090] In this embodiment, in the step of providing the substrate 500, a first doping region 504 having first-type doping ions and a second doping region 505 having second-type doping ions are formed in the substrate 500, the first doping region 504 and the second doping region 505 are arranged at intervals, and the first-type doping ions and the second-type doping ions have different conductivity types. Accordingly, in the step of forming the light absorbing layer 510, the light absorbing layer 510 is located on the substrate 500 between the first doping region 504 and the second doping region 505.

[0091] Combined with reference Figures 5 to 7 , a stress layer 530 is formed on the light absorbing layer 510 , and the stress layer 530 at least covers a portion of the light absorbing layer 510 , so as to provide stress to the light absorbing layer 510 .

[0092] Combined with reference Figure 8 and Fig. 9 , Figure 8 is an energy band diagram of the light absorbing layer when no stress layer is formed on the light absorbing layer; Fig. 9 When a stress layer is formed on the light absorbing layer, the energy band diagram of the light absorbing layer is as follows: a stress layer 530 is formed on the light absorbing layer 510, and the stress layer 530 at least covers a portion of the light absorbing layer 510, and is used to provide stress to the light absorbing layer 510, so that the distance between atoms inside the light absorbing layer 510 changes, thereby causing the energy band of the light absorbing layer 510 to deflect, and also causing the indirect band gap of the light absorbing layer 510 to shift toward the top of the valence band, that is, the energy band gap of the light absorbing layer 510 is equivalently reduced, and then when the wavelength of the photon is larger, that is, when the photon energy is smaller, it is still possible to excite electrons from the valence band to the conduction band, thereby correspondingly improving the responsiveness of the light absorbing layer 510 and improving the performance of the photodetector.

[0093] Continue to refer Figure 8 and Fig. 9 When no stress layer is formed on the light absorbing layer, the distance between the direct conduction band Γ and the indirect conduction band L is W1 (e.g. Figure 8 When the stress layer 530 is formed on the light absorbing layer 510, the distance between the direct conduction band Γ and the indirect conduction band L is W2 (as shown in FIG. Fig. 9As shown in the figure; where W2 < W1. Thus, when the light absorption layer 510 is subjected to stress, the position of the indirect conduction band L of the light absorption layer 510 shifts towards the direct conduction band Γ, such that the photon energy required for electrons to transition from the valence band to the indirect conduction band L is smaller. Therefore, some electrons will preferentially transition to the indirect conduction band L, thereby equivalently reducing the band gap.

[0094] It should be noted that the thickness of the stress layer 530 should not be too large. If the thickness of the stress layer 530 is too large, the stress provided by the stress layer 530 to the light absorption layer 510 is relatively large, which easily increases the probability of stress mismatch between the stress layer 530 and the light absorption layer 510. Therefore, in this embodiment, in the step of forming the stress layer 530, along the normal direction of the top surface of the substrate 500, the thickness range of the stress layer 530 is less than or equal to 10 micrometers.

[0095] Specifically, in the step of forming the stress layer 530, the material of the stress layer 530 includes one or more of silicon nitride, silicon oxide, carbon, and polysilicon. As an example, the material of the stress layer 530 is silicon nitride.

[0096] Generally, the temperature for forming the stress layer 530 is higher than room temperature. After the stress layer 530 is formed, the temperature will gradually drop back to room temperature. Since the material of the stress layer 530 is generally different from that of the light absorption layer 510, the deformation amplitudes of the stress layer 530 and the light absorption layer 510 due to temperature changes are different, thus easily causing the stress layer 530 to provide stress to the light absorption layer 510. As an example, the stress layer 530 provides tensile stress to the light absorption layer 510. However, in other embodiments, according to the material of the light absorption layer, the stress received by the light absorption layer can also be compressive stress.

[0097] Moreover, silicon nitride, silicon nitride, silicon oxide, carbon, and polysilicon are commonly used and low-cost materials in semiconductor processes, and have high process compatibility, which is beneficial to reducing the process difficulty and process cost of forming the stress layer 530.

[0098] In this embodiment, in the step of forming the stress layer 530, the area of the stress layer 530 covering the light absorption layer 510 is at least 50% of the area of the light absorption layer 510.

[0099] The area of ​​the light absorbing layer 510 covered by the stress layer 530 should not be too small. If the area of ​​the light absorbing layer 510 covered by the stress layer 530 is too small, the stress layer 530 may not provide stress to the light absorbing layer 510 well, that is, the effect of increasing the stress on the light absorbing layer 510 is not good, which may make the energy band of the light absorbing layer 510 deflect by a small amplitude, so that the indirect band gap of the light absorbing layer 510 is offset to the top of the valence band by a small distance, so that the effect of equivalent reduction of the energy band gap of the light absorbing layer 510 is not good, and thus the effect of improving the responsiveness of the light absorbing layer 510 is not ideal. Therefore, in the step of forming the stress layer 530 in this embodiment, the area of ​​the light absorbing layer 510 covered by the stress layer 530 is at least 50% of the area of ​​the light absorbing layer 510.

[0100] In this embodiment, in the step of forming the stress layer 530 , the stress layer 530 covers the entire light absorbing layer 510 exposed from the substrate 500 ; or, the stress layer 530 covers the entire light absorbing layer 510 exposed from the substrate 500 , and also extends to cover a portion of the substrate 500 on the side of the light absorbing layer 510 .

[0101] The stress layer 530 completely covers the entire light absorbing layer 510 exposed from the substrate 500, which is beneficial to further enhance the effect of the stress layer 530 providing stress to the light absorbing layer 510, and it is easy to make the stress provided by the stress layer 530 to the light absorbing layer 510 more uniform, thereby helping to reduce the probability of stress mismatch between the stress layer 530 and the light absorbing layer 510.

[0102] The stress layer 530 covers the entire light absorbing layer 510 exposed from the substrate 500, and also extends to cover part of the substrate 500 on the side of the light absorbing layer 510, which helps to ensure that the stress layer 530 can completely cover the light absorbing layer 510 exposed from the substrate 500, and makes it easier for the stress layer 530 to provide a more uniform stress to the light absorbing layer 510, thereby helping to further reduce the probability of stress mismatch between the stress layer 530 and the light absorbing layer 510.

[0103] It should be noted that, because the area of ​​the substrate 500 where the stress layer 530 extends to cover the side of the light absorbing layer 510 is not positively correlated with the magnitude of the stress generated by the stress layer 530 on the light absorbing layer 510, when the area of ​​the substrate 500 covered by the stress layer 530 is too large, it is easy to cause the proportion of the covered area of ​​the light absorbing layer 510 to the total covered area of ​​the stress layer 530 to be too small, thereby causing the stress on the light absorbing layer 510 to become smaller. Therefore, in this embodiment, in the step of forming the stress layer 530, the lateral dimension of the portion of the stress layer 530 extending to cover the substrate 500 along the direction perpendicular to the end face of the stress layer 530 is less than 100 mm.

[0104] In summary, the stress layer 530 covers part of the light absorbing layer 510, or completely covers the entire light absorbing layer 510 exposed from the substrate 500 and exposes the substrate 500, or the stress layer 530 covers the entire light absorbing layer 510 exposed from the substrate 500, and also extends to cover part of the substrate 500 on the side of the light absorbing layer 510, that is, the stress layer 530 globally covers the entire light absorbing layer 510 and the entire substrate 500, so that the stress layer 530 can provide local stress, which is beneficial to increase the stress applied by the stress layer 530 to the light absorbing layer 510.

[0105] In this embodiment, the step of forming the stress layer 530 on the light absorbing layer 510 includes: forming a stress material layer 531 (eg, Figure 6 ); removing the stress material layer 531 in a part of the area, so that the remaining stress material layer at least covers part of the light absorbing layer, and the remaining stress layer material layer 531 serves as a stress layer (as shown); Figure 7 shown).

[0106] First forming the stress material layer 531 covering the substrate 500 and the light absorbing layer 510 and then removing the stress material layer 531 in a partial area is beneficial to reducing the process difficulty of forming the stress layer 530 and improving the formation quality of the stress layer 530 .

[0107] Specifically, the process of removing the stress material layer 531 in a part of the region includes a dry etching process, which has the advantages of high etching rate, good etching directionality, strong process controllability, etc., and is conducive to forming a stress layer 530 with high morphology quality.

[0108] In this embodiment, in the step of forming the stress layer 530 , the process of forming the stress layer 530 includes a plasma enhanced vapor deposition process.

[0109] The plasma enhanced vapor deposition process has the advantages of fast deposition rate and good film quality. The stress layer 530 formed by the plasma enhanced vapor deposition process can easily provide a large stress value to the light absorption layer 510, which can easily cause the distance between atoms inside the light absorption layer 510 to change more obviously, thereby causing the energy band of the light absorption layer 510 to deflect more obviously, and also causing the indirect band gap of the light absorption layer 510 to shift toward the top of the valence band by a larger distance, that is, the effect of equivalently reducing the energy band gap of the light absorption layer 510 is more obvious.

[0110] Specifically, the process parameters of the plasma enhanced vapor deposition process include: the reaction gas includes a silicon source gas and a nitrogen source gas, the gas flow ratio of the silicon source gas to the nitrogen source gas is 1:2 to 100:1, and the pressure of the reaction chamber is 1 to 100 Torr.

[0111] As an example, in order to make the stress layer 530 provide a better stress value to the light absorbing layer 510, the gas flow ratio of the silicon source gas to the nitrogen source gas is 1:2 to 100:1.

[0112] As an example, the silicon source gas includes SiH4 gas, and the nitrogen source gas includes one or two of NH3 gas and N2O gas. SiH4 gas is a commonly used silicon source gas in semiconductor processes, and NH3 gas and N2O gas are commonly used nitrogen source gases in semiconductor processes. They are easy to obtain, have high process compatibility, and low process risk. In a specific embodiment, a plasma enhanced vapor deposition process can be performed in a nitrogen atmosphere with nitrogen as a catalytic gas to accelerate the reaction speed, thereby facilitating the acceleration of the deposition to form the stress layer 530.

[0113] It should also be noted that the pressure of the reaction chamber should not be too high or too low. If the pressure of the reaction chamber is too high, the effect of increasing the stress value provided by the stress layer 530 to the light absorbing layer 510 is not good when the thickness of the stress layer 530 is the same; if the pressure of the reaction chamber is too low, the deposition rate of forming the stress layer 530 is low. Therefore, in this embodiment, the pressure of the reaction chamber is 1 to 100 torr.

[0114] Continue to refer Figures 5 to 7 In this embodiment, after forming the light absorbing layer 510 and before forming the stress layer 530 , the forming method further includes: forming a buffer layer 520 on the light absorbing layer 510 .

[0115] The buffer layer 520 is used to provide stress buffering between the light absorbing layer 510 and the stress layer 530. The buffer layer 520 has good adhesion to both the stress layer 530 and the light absorbing layer 510, which is beneficial to reducing the probability of stress mismatch between the light absorbing layer 510 and the stress layer 530, thereby reducing the probability of delamination between the light absorbing layer 510 and the stress layer 530.

[0116] Specifically, in the step of forming the buffer layer 520 , the material of the buffer layer 520 includes one or more of silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon, and tin.

[0117] Since silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon and tin have good adhesion to various materials in semiconductor processes, when the material of the buffer layer 520 includes one or more of silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon and tin, the buffer layer 520 can be more effectively used as a stress buffer between the light absorption layer 510 and the stress layer 530, which correspondingly makes it easier to reduce the probability of stress mismatch between the light absorption layer 510 and the stress layer 530, thereby making it more ideal to reduce the probability of stratification between the light absorption layer 510 and the stress layer 530.

[0118] It should be noted that the process of forming the buffer layer 520 includes one or both of a chemical vapor deposition process and a furnace process.

[0119] It should also be noted that the thickness of the buffer layer 520 should not be too large. If the thickness of the buffer layer 520 is too large, that is, the distance between the light absorbing layer 510 and the stress layer 530 is too large, the light absorbing layer 510 is likely to be subjected to less stress, which may result in poor deflection of the energy band of the light absorbing layer 510, and accordingly, poor effect of shifting the indirect band gap of the light absorbing layer 510 toward the top of the valence band, that is, poor effect of equivalent reduction of the energy band gap of the light absorbing layer 510, and thus poor effect of improving the responsiveness of the light absorbing layer. Therefore, in the present embodiment, in the step of forming the buffer layer 520, the thickness of the buffer layer 520 is less than or equal to 10 microns.

[0120] Accordingly, in this embodiment, in the step of forming the stress layer 530 , the stress layer 530 is formed on the buffer layer 520 .

[0121] Specifically, the steps of forming the buffer layer 520 and the stress layer 530 include: Figure 5 and Figure 6 As shown, a buffer material layer 521 and a stress material layer 531 are stacked on the substrate 500 and the light absorbing layer 510; Figure 7 As shown, the stress material layer 531 and the buffer material layer 521 are patterned in sequence using the same photomask to form a stress layer 530 and a buffer layer 520 located between the stress layer 530 and the light absorbing layer 510 .

[0122] First, a stacked buffer material layer 521 and a stress material layer 531 are formed on the substrate 500 and the light absorption layer 510, and then the stress material layer 531 and the buffer material layer 521 are patterned in sequence using the same mask. That is, no additional mask is needed to pattern the buffer material layer 521, which is beneficial to saving the number of masks and reducing process costs.

[0123] In this embodiment, after forming the stress layer 530 , the method further includes: forming conductive plugs (not shown) on top of the first doping region 504 and the second doping region 505 , wherein the conductive plugs are electrically connected to the first doping region 504 and the second doping region 505 , respectively.

[0124] Specifically, the step of forming a conductive plug on the top of the first doping region 504 and the second doping region 505 includes: forming a dielectric layer (not shown) covering the first doping region 504 and the second doping region 505 on the substrate 500; forming a conductive plug hole (not shown) exposing the top of the first doping region 504 and the second doping region 505 in the dielectric layer, and the conductive plug hole is located on the side of the first isolation layer 107 away from the light absorption layer 110; forming a conductive plug in the conductive plug hole. As an example, the dielectric layer also covers the stress layer 530.

[0125] The conductive plug hole is located on the side of the first isolation layer 507 away from the light absorbing layer 510 . Correspondingly, the conductive plug is also located on the side of the first isolation layer 507 away from the light absorbing layer 510 . That is, the first isolation layer 507 serves to increase the distance between the conductive plug and the light absorbing layer 510 .

[0126] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A photoelectric detector, characterized in that: include: substrate; a light absorbing layer, located on the substrate; The stress layer is located on the light absorbing layer and covers at least a portion of the light absorbing layer, and is used to provide stress to the light absorbing layer.

2. The photodetector according to claim 1, wherein: The bottom of the light absorbing layer is lower than the top of the substrate, and the top of the light absorbing layer is higher than the top of the substrate.

3. The photodetector according to claim 1, wherein: The structure of the photodetector further includes a buffer layer located between the light absorption layer and the stress layer.

4. The photodetector according to claim 3, wherein: The thickness of the buffer layer is less than or equal to 10 micrometers.

5. The photodetector according to claim 3, characterized in that The material of the buffer layer includes one or more of silicon oxide, silicon nitride, silicon oxynitride, polycrystalline silicon, single crystal silicon, carbon and tin.

6. The photodetector according to claim 1, wherein: The material of the light absorbing layer includes one or more of germanium, silicon and silicon germanium.

7. The photodetector according to claim 1, wherein: The area covered by the stress layer on the light absorbing layer is at least 50% of the area of ​​the light absorbing layer.

8. The photodetector according to claim 1, wherein: The stress layer covers the entire light absorbing layer exposed from the substrate; Alternatively, the stress layer covers the entire light absorbing layer exposed from the substrate, and further extends to cover a portion of the substrate at a side portion of the light absorbing layer.

9. The photodetector according to claim 8, wherein: Along a direction perpendicular to an end surface of the stress layer, a lateral dimension of a portion of the stress layer extending to cover the substrate is less than 100 mm.

10. The photodetector according to claim 1, wherein: The material of the stress layer includes one or more of silicon nitride, silicon oxide, carbon and polysilicon.

11. The photodetector according to claim 1, wherein: Along the normal direction of the top surface of the substrate, the thickness of the stress layer is less than or equal to 10 microns.

12. A method for forming a photodetector, characterized in that: include: providing a substrate; forming a light absorbing layer on the substrate; A stress layer is formed on the light absorbing layer, wherein the stress layer at least covers a portion of the light absorbing layer and is used to provide stress to the light absorbing layer.

13. The method for forming a photodetector according to claim 12, wherein: In the step of providing a substrate, a groove is formed in the substrate; In the step of forming the light absorbing layer, the light absorbing layer is located in the groove, and a top of the light absorbing layer is higher than a top of the substrate.

14. The method for forming a photodetector according to claim 12, wherein: After forming the light absorbing layer and before forming the stress layer, the forming method further comprises: forming a buffer layer on the light absorbing layer; In the step of forming the stress layer, the stress layer is formed on the buffer layer.

15. The method for forming a photodetector according to claim 14, wherein: The step of forming the buffer layer and the stress layer includes: forming a stacked buffer material layer and a stress material layer on the substrate and the light absorbing layer; The stress material layer and the buffer material layer are patterned in sequence by using the same photomask to form a stress layer and a buffer layer located between the stress layer and the light absorbing layer.

16. The method for forming a photodetector according to claim 12, wherein: In the step of forming the stress layer, the process of forming the stress layer includes a plasma enhanced vapor deposition process.

17. The method for forming a photodetector according to claim 16, wherein: The process parameters of the plasma enhanced vapor deposition process include: the reaction gas includes a silicon source gas and a nitrogen source gas, the gas flow ratio of the silicon source gas to the nitrogen source gas is 1:2 to 100:1, and the pressure of the reaction chamber is 1 to 100 torr.

18. The method for forming a photodetector according to claim 17, wherein: The silicon source gas includes SiH 4 gas, and the nitrogen source gas includes one or both of NH 3 gas and N 2 O gas.

19. The method for forming a photodetector according to any one of claims 12 to 15, wherein: In the step of forming the stress layer, the stress layer covers the entire light absorbing layer exposed from the substrate; Alternatively, the stress layer covers the entire light absorbing layer exposed from the substrate, and further extends to cover a portion of the substrate at a side portion of the light absorbing layer.

20. The method for forming a photodetector according to claim 12, wherein: The step of forming a stress layer on the light absorbing layer comprises: forming a stress material layer covering the substrate and the light absorbing layer; The stress material layer in a partial area is removed so that the remaining stress material layer at least covers a portion of the light absorbing layer, and the remaining stress material layer serves as a stress layer.

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