Light receiving element, light receiving device, and method for manufacturing light receiving element

Abstract

To provide a light receiving element capable of improving light receiving sensitivity, a light receiving device, and a method of manufacturing the light receiving element.SOLUTION: The light receiving element includes a substrate, a semiconductor layer, and an insulating layer located between the substrate and the semiconductor layer in a first direction. The semiconductor layer has an n-type region, a p-type region, and a mesa portion located between the n-type region and the p-type region in a second direction orthogonal to the first direction and having an upper surface and a side surface inclined with respect to the upper surface. The width of the mesa portion in the second direction decreases from the insulating layer side toward the upper surface. The mesa portion has, in a surface layer region including an upper surface and a side surface, a light absorption region capable of absorbing light having a wavelength longer than a wavelength corresponding to a bandgap energy of a material constituting the semiconductor layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a light receiving element, a light receiving device, and a method for manufacturing a light receiving element. [Background technology]

[0002] For example, Patent Document 1 discloses an infrared detector that utilizes the absorption of light in crystal defects of silicon. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-114183 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a light receiving element, a light receiving device, and a method for manufacturing a light receiving element that can improve light receiving sensitivity. [Means for solving the problem]

[0005] According to one aspect of the present disclosure, a light-receiving element includes a substrate, a semiconductor layer, and an insulating layer located between the substrate and the semiconductor layer in a first direction that is a direction from the substrate toward the semiconductor layer, the semiconductor layer having an n-type region, a p-type region, and a mesa portion located between the n-type region and the p-type region in a second direction that is perpendicular to the first direction, the mesa portion having an upper surface and a side surface inclined with respect to the upper surface, the width of the mesa portion in the second direction decreasing from the insulating layer side toward the upper surface, and the mesa portion has a light-absorbing region in a surface region including the upper surface and the side surface that can absorb light of a longer wavelength than a wavelength corresponding to the band gap energy of a material that constitutes the semiconductor layer.

[0006] According to one aspect of the present disclosure, a light receiving device includes the above-mentioned light receiving element and a lens that focuses light from outside toward an end face of the mesa portion facing a third direction perpendicular to the first direction and the second direction.

[0007] According to one aspect of the present disclosure, a method for manufacturing a light-receiving element includes preparing a structure including a substrate, a semiconductor layer, and an insulating layer located between the substrate and the semiconductor layer in a first direction that is a direction from the substrate toward the semiconductor layer, wherein the semiconductor layer has an n-type region, a p-type region, and a mesa portion located between the n-type region and the p-type region in a second direction that is perpendicular to the first direction, the mesa portion having an upper surface and side surfaces inclined relative to the upper surface, the width of the mesa portion in the second direction decreasing from the insulating layer side toward the upper surface; and, with the n-type region and the p-type region covered with a mask, implanting ions with a predetermined energy from the upper surface side into a surface region of the mesa portion including the upper surface and the side surfaces. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a light receiving element, a light receiving device, and a method for manufacturing a light receiving element that can improve light receiving sensitivity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic plan view of a light-receiving element according to the embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Figure 3] 1 is a schematic cross-sectional view of a light receiving device according to an embodiment. [Figure 4A] 5A to 5C are schematic cross-sectional views illustrating a step in a method for manufacturing a light-receiving element according to an embodiment. [Figure 4B] 5A to 5C are schematic cross-sectional views illustrating a step in a method for manufacturing a light-receiving element according to an embodiment. [Figure 4C] 5A to 5C are schematic cross-sectional views illustrating a step in a method for manufacturing a light-receiving element according to an embodiment. [Figure 4D] 5A to 5C are schematic cross-sectional views illustrating a step in a method for manufacturing a light-receiving element according to an embodiment. [Figure 4E] 5A to 5C are schematic cross-sectional views illustrating a step in a method for manufacturing a light-receiving element according to an embodiment. [Figure 4F] 5A to 5C are schematic cross-sectional views illustrating a step in a method for manufacturing a light-receiving element according to an embodiment. [Figure 5] 10 is a graph showing the results of a first experiment. [Figure 6] 10 is a graph showing the results of a second experiment. [Figure 7] 10 is a graph showing the results of a third experiment. [Figure 8] FIG. 2 is a schematic cross-sectional view of a first sample used in a first experiment. [Figure 9] FIG. 10 is a schematic cross-sectional view of a second sample used in a second experiment. [Figure 10A] FIG. 10 is a schematic cross-sectional view of Sample 3A used in the third experiment. [Figure 10B] FIG. 10 is a schematic cross-sectional view of Sample 3B used in the third experiment. [Figure 10C] FIG. 10 is a schematic cross-sectional view of a third C sample used in a third experiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings. The dimensions, materials, shapes, relative positions, and the like of components described in the embodiments are not intended to be limiting unless otherwise specified, and are merely illustrative examples. The sizes and positional relationships of components shown in each drawing may be exaggerated for clarity. In the following description, the same names and symbols indicate the same or similar components, and detailed descriptions will be omitted as appropriate. Cross-sectional views may also be shown as end views showing only the cut surface.

[0011] In the following description, terms indicating specific directions or positions (e.g., "above," "below," and other terms including these terms) may be used. However, these terms are used merely to facilitate understanding of relative directions or positions in the referenced drawings. As long as the relative direction or position relationship indicated by terms such as "above" and "below" in the referenced drawings is the same, the arrangement in drawings other than those disclosed herein, actual products, etc., does not have to be the same as in the referenced drawings. In this specification, the positional relationship expressed as "above (or below)" includes, for example, when two components are assumed to exist, a case in which the two components are in contact with each other, and a case in which the two components are not in contact and one component is located above (or below) the other component. Furthermore, in this specification, the height, thickness, and width in a specific direction represent the respective maximum values.

[0012] [Photodetector] A light-receiving element 1 according to the embodiment will be described with reference to Figures 1 and 2. Note that in order to make it easier to see the configuration covered with the insulating film 50 in a plan view, the insulating film 50 is not shown in Figure 1. In addition, in cross-sectional views such as Figure 2, the n-type region 31n, the p-type region 31p, and the light absorption region 33 in the semiconductor layer 30 are represented by hatching with a dot pattern.

[0013] The light receiving element 1 according to the embodiment includes a substrate 10, a semiconductor layer 30, and an insulating layer 20. The direction from the substrate 10 toward the semiconductor layer 30 is defined as a first direction Z. Two directions perpendicular to the first direction Z are defined as a second direction X and a third direction Y. The second direction X and the third direction Y are perpendicular to each other.

[0014] The substrate 10 is, for example, a silicon substrate. The substrate 10 supports the semiconductor layer 30 via an insulating layer 20. The insulating layer 20 is located between the substrate 10 and the semiconductor layer 30 in the first direction Z. The insulating layer 20 is, for example, a silicon oxide layer. The semiconductor layer 30 is, for example, a silicon layer. The light-receiving element 1 according to the embodiment has, for example, an SOI (Silicon On Insulator) structure.

[0015] The semiconductor layer 30 has an n-type region 31n and a p-type region 31p. For example, in the semiconductor layer 30 which is a silicon layer, the n-type region 31n contains phosphorus (P), arsenic (As), antimony (Sb), or bismuth (Bi) as an n-type impurity, and the p-type region 31p contains boron (B), aluminum (Al), gallium (Ga), or indium (In) as a p-type impurity. The n-type region 31n and the p-type region 31p are located apart from each other in the second direction X. The n-type region 31n and the p-type region 31p each extend in the third direction Y.

[0016] The semiconductor layer 30 further includes a mesa portion 32. The mesa portion 32 is located between the n-type region 31n and the p-type region 31p in the second direction X and extends in the third direction Y. The mesa portion 32 has an upper surface 32A and a side surface 32B inclined relative to the upper surface 32A. The mesa portion 32 also has a lower surface 32C in contact with the insulating layer 20. The upper surface 32A is located on the opposite side of the lower surface 32C in the first direction Z. The upper surface 32A and the lower surface 32C extend in the third direction Y. The two side surfaces 32B are spaced apart in the second direction X. One of the two side surfaces 32B is located on the n-type region 31n side in the second direction X, and the other side surface 32B is located on the p-type region 31p side in the second direction X. The two side surfaces 32B extend in the third direction Y. The cross section of the mesa portion 32 parallel to the XZ plane has a trapezoidal shape. The width of the upper surface 32A in the second direction X is smaller than the width of the lower surface 32C in the second direction X. The width of the mesa portion 32 in the second direction X decreases from the lower surface 32C on the insulating layer 20 side toward the upper surface 32A.

[0017] The mesa portion 32 has a light-absorbing region 33 in a surface region including the top surface 32A and the side surface 32B. The light-absorbing region 33 can absorb light with wavelengths longer than the wavelength corresponding to the bandgap energy of the material constituting the semiconductor layer 30. In this embodiment, the light-absorbing region 33 can absorb infrared light with wavelengths longer than the wavelength corresponding to the bandgap energy of silicon constituting the semiconductor layer 30. The light-absorbing region 33 is a region containing boron, germanium, or magnesium in addition to silicon. As described below, the light-absorbing region 33 is thought to absorb light with wavelengths longer than the wavelength corresponding to the bandgap energy of silicon by utilizing defect levels. Therefore, the light-absorbing region 33 can also be specified using defect density as follows. That is, the defect density of the light-absorbing region 33 is higher than the defect density of an internal region 37 of the mesa portion 32, which is located inside the light-absorbing region 33. The internal region 37 of the mesa portion 32 is located between the light-absorbing region 33 and the insulating layer 20. The defect density can be analyzed by obtaining a cross-sectional image of the mesa portion 32, including the light absorption region 33 and the internal region 37 of the mesa portion 32, using a (scanning) transmission electron microscope ((S)TEM) and counting the number of defects per unit area.

[0018] In the light absorption region 33, the absorbed light generates electrons and holes. The electrons flow from the light absorption region 33 to the n-type region 31n to which a positive potential is applied, and the holes flow from the light absorption region 33 to the p-type region 31p to which a ground potential or a negative potential is applied. This allows current to be extracted to an external circuit connected to the n-type region 31n and the p-type region 31p.

[0019] Light can be incident on the end face of the mesa portion 32 facing the third direction Y (a surface parallel to the XZ plane). By forming the mesa portion 32 including the light absorption region 33 into a convex shape on the substrate 10 such that the height in the first direction Z is greater than the thickness in the first direction Z of the n-type region 31n and the thickness in the first direction Z of the p-type region 31p, the light incidence area can be increased when light is incident on the end face of the mesa portion 32 facing the third direction Y. This increases the light absorption efficiency in the light absorption region 33 and improves the light receiving sensitivity of the light receiving element 1.

[0020] The width of the mesa portion 32 in the third direction Y is greater than the thickness of the light absorption region 33 of the mesa portion 32 in the first direction Z. This allows the light to propagate a longer distance in the third direction Y when it is incident on the end face (a surface parallel to the XZ plane) of the mesa portion 32 facing the third direction Y, thereby enabling efficient light absorption. The width of the mesa portion 32 in the third direction Y may be 10 to 100 times the width in the first direction Z.

[0021] The width of the mesa portion 32 in the third direction Y is preferably larger than its width in the second direction X. This allows the light to propagate a longer distance in the third direction Y when it is incident on the end face (a surface parallel to the XZ plane) of the mesa portion 32 facing the third direction Y, thereby enabling efficient light absorption. The width of the mesa portion 32 in the third direction Y may be 1 to 10 times the width in the second direction X.

[0022] The side surface 32B of the mesa portion 32 is inclined so that the width of the mesa portion 32 in the second direction X decreases from the lower surface 32C toward the upper surface 32A, and thus, by ion implantation described later, the light absorption region 33 can be formed not only in the surface region including the upper surface 32A of the mesa portion 32 but also in the surface region including the side surface 32B of the mesa portion 32. This increases the area of ​​the light absorption region 33, thereby improving the light receiving sensitivity of the light receiving element 1.

[0023] The light-receiving element 1 according to the embodiment may further include an n-side electrode 40n disposed on the n-type region 31n and a p-side electrode 40p disposed on the p-type region 31p. The n-side electrode 40n contacts the n-type region 31n and is electrically connected to the n-type region 31n. The p-side electrode 40p contacts the p-type region 31p and is electrically connected to the p-type region 31p. The n-type region 31n and the p-type region 31p can be electrically connected to an external circuit via the n-side electrode 40n and the p-side electrode 40p.

[0024] The light-receiving element 1 according to the embodiment may further include an insulating film 50 that covers at least the upper surface 32A and the side surface 32B of the mesa portion 32. The insulating film 50 protects the upper surface 32A and the side surface 32B of the mesa portion 32. This reduces leakage of current applied by the n-side electrode 40n and the p-side electrode 40p through the upper surface of the p-type region 31p, the side surface 32B of the mesa portion 32, the upper surface 32A of the mesa portion 32, and the upper surface of the n-type region 31n. Reducing the leakage current reduces dark current when no light is incident on the light absorption region 33. The insulating film 50 may be, for example, a silicon oxide film.

[0025] In this embodiment, the insulating film 50 covers the upper surface 32A and side surface 32B of the mesa portion 32, the upper surface of the n-type region 31n, the upper surface of the p-type region 31p, the n-side electrode 40n, and the p-side electrode 40p. The insulating film 50 has an n-side opening 50n that exposes a portion of the upper surface of the n-side electrode 40n and a p-side opening 50p that exposes a portion of the upper surface of the p-side electrode 40p. A wire that electrically connects an external circuit to the n-side electrode 40n can be bonded to the n-side electrode 40n through the n-side opening 50n. A wire that electrically connects an external circuit to the p-side electrode 40p can be bonded to the p-side electrode 40p through the p-side opening 50p.

[0026] The insulating film 50 may be a dielectric multilayer film. The insulating film 50 may be, for example, a dielectric multilayer film having a reflectance of 90% or more and less than 100% for the wavelength of light incident on the light receiving element 1. When light is incident on the end face (a surface parallel to the XZ plane) of the mesa portion 32 facing the third direction Y, the light is reflected by the insulating film 50, which is a dielectric multilayer film, and it is possible to reduce the loss of the light extracted to the outside of the light receiving element 1.

[0027] By making the thickness of the n-type region 31n and the p-type region 31p in the first direction Z smaller than the height of the mesa portion 32 in the first direction Z, the lower surfaces of the n-type region 31n and the p-type region 31p formed by ion implantation and annealing, which will be described later, can be more easily brought into contact with the insulating layer 20. By bringing the lower surfaces of the n-type region 31n and the p-type region 31p into contact with the insulating layer 20, it is possible to reduce leakage current that flows beneath the lower surface of the n-type region 31n and beneath the lower surface of the p-type region 31p and into the n-type region 31n and the p-type region 31p, and it is possible to reduce dark current when no light is incident on the light absorption region 33.

[0028] Preferably, the light absorbing region 33 and the n-type region 31n are spaced apart in the second direction X within the semiconductor layer 30, and the light absorbing region 33 and the p-type region 31p are spaced apart in the second direction X within the semiconductor layer 30. This reduces the dark current flowing between the light absorbing region 33 and the n-type region 31n and the dark current flowing between the light absorbing region 33 and the p-type region 31p compared to when the light absorbing region 33 is in contact with the n-type region 31n and the p-type region 31p. The light absorbing region 33 and the n-type region 31n can be spaced apart in the second direction X by, for example, 1 μm to 10 μm, and the light absorbing region 33 and the p-type region 31p can be spaced apart in the second direction X by, for example, 1 μm to 10 μm.

[0029] A boundary region 34 is located between the light absorbing region 33 and the n-type region 31n in the second direction X, and a boundary region 35 is located between the light absorbing region 33 and the p-type region 31p in the second direction X. The n-type impurity concentration of the boundary region 34 is lower than the n-type impurity concentration of the n-type region 31n, and the p-type impurity concentration of the boundary region 35 is lower than the p-type impurity concentration of the p-type region 31p. Therefore, the electrical resistivity of the boundary region 34 between the light absorbing region 33 and the n-type region 31n and the electrical resistivity of the boundary region 35 between the light absorbing region 33 and the p-type region 31p are higher than both the electrical resistivity of the n-type region 31n and the electrical resistivity of the p-type region 31p. This makes it easier to reduce dark currents flowing between the light absorbing region 33 and the n-type region 31n and between the light absorbing region 33 and the p-type region 31p. The electrical resistivity of the boundary region 34 and the electrical resistivity of the boundary region 35 can be measured by spreading resistance analysis (SRA). In addition, the impurity concentration of the boundary region 34 and the impurity concentration of the boundary region 35 can be analyzed by Non-SIMS, a type of secondary mass spectrometry (SIMS) that can measure a minute region.

[0030] The height of the mesa portion 32 in the first direction Z is, for example, not less than 2 μm and not more than 100 μm. The width of the upper surface 32A of the mesa portion 32 in the second direction X is, for example, not less than 10 μm and not more than 100 μm. The thickness of the light absorption region 33 on a center line C that passes through the center of the upper surface 32A of the mesa portion 32 in the second direction X and extends in the first direction Z is, for example, not more than 1.5 μm. The thickness of the n-type region 31n in the first direction Z and the thickness of the p-type region 31p in the first direction Z are, for example, not more than 1.5 μm. The thickness of the light absorption region 33 located on the side surface 32B of the mesa portion 32 in a direction perpendicular to the side surface 32B is, for example, not more than 1.5 μm.

[0031] [Light receiving device] 3 , the light-receiving device 100 according to the embodiment includes the above-described light-receiving element 1 and a lens 63. An end face 36 of the mesa portion 32 of the light-receiving element 1 facing the third direction Y is a light incident surface of the light-receiving element 1 and faces the lens 63 in the third direction Y. The lens 63 focuses external light toward the end face 36 of the mesa portion 32.

[0032] The light receiving device 100 may further include a support 61 , a cap 62 , a wiring board 66 , a wire 67 , a lead 64 , and a lead 65 .

[0033] The light-receiving element 1 is disposed on the wiring board 66 with the substrate 10 facing the wiring board 66 in the first direction Z. The n-side electrode 40n and the p-side electrode 40p of the light-receiving element 1 are each electrically connected to the wiring portion of the wiring board 66 via a wire 67 made of, for example, gold (Au). The wiring board 66 is supported on a support 61. A cap 62 is disposed on the support 61 and defines a space in which the wiring board 66, the light-receiving element 1, and the wire 67 are disposed. Leads 64 and 65 extend from the support 61 to the outside of the space within the cap 62. One of the leads 64 and 65 is electrically connected to the n-side electrode 40n via the wire 67, and the other is electrically connected to the p-side electrode 40p via the wire 67. The lens 63 is disposed in an opening 62A formed in the cap 62.

[0034] In this embodiment, the light absorption region 33 is considered to be able to absorb infrared light with wavelengths longer than the wavelength corresponding to the bandgap energy of silicon by utilizing defect levels generated in the silicon crystal by ion implantation, which will be described later. Ions are not implanted into the internal region 37 of the mesa portion 32, which is located inside the light absorption region 33, and the internal region 37 can absorb light with wavelengths shorter than the wavelength corresponding to the inherent bandgap energy of silicon (light in the visible band). If the light receiving element 1 does not need to detect visible light, the light receiving device 100 may further include a visible light cut filter 68 disposed between the lens 63 and the end face 36 (light incident surface) of the light receiving element 1. Light from which visible light has been cut by the visible light cut filter 68 enters the end face 36 of the light receiving element 1.

[0035] As shown in FIG. 3, the light-receiving element 1 of the light-receiving device 100 receives light at the end face 36 of the mesa portion 32. The lens 63 does not need to focus light only on the light-absorbing region 33; it is sufficient that the light is focused so that it strikes the light-absorbing region 33 and the internal region 37 of the mesa portion 32. This is because light incident on the light-absorbing region 33 is absorbed as it propagates in the third direction Y (the -Y direction in FIG. 3), so that the amount of absorption increases even if the area of ​​the irradiation surface of the light-absorbing region 33 is small. Furthermore, since the mesa portion 32 has a side surface 32B that is inclined with respect to the top surface 32A, the area of ​​the light-absorbing region 33 is larger than when there is no inclination, and therefore the amount of light absorption can be increased.

[0036] [Photodetector manufacturing method] A method for manufacturing the light-receiving element 1 according to this embodiment will be described with reference to FIGS. 4A to 4F.

[0037] The method for manufacturing a light-receiving element 1 according to this embodiment includes a step of preparing a structure 200 shown in FIG. 4E. The structure 200 includes a substrate 10, a semiconductor layer 30, and an insulating layer 20 located between the substrate 10 and the semiconductor layer 30 in the first direction Z. In the structure 200, the semiconductor layer 30 has an n-type region 31n, a p-type region 31p, and a mesa portion 32 located between the n-type region 31n and the p-type region 31p in the second direction X. The mesa portion 32 has an upper surface 32A and a side surface 32B inclined relative to the upper surface 32A. The width of the mesa portion 32 in the second direction X decreases from the insulating layer 20 side toward the upper surface 32A.

[0038] For example, structure 200 can be prepared by the steps shown in Figures 4A to 4E.

[0039] As shown in FIG. 4A, an SOI wafer 300 is prepared in which an insulating layer 20 is disposed on a substrate 10 and a semiconductor layer 30 is disposed on the insulating layer 20.

[0040] A portion of the semiconductor layer 30 in the SOI wafer 300 is removed to form a mesa portion 32 in the semiconductor layer 30, as shown in FIG. 4B . For example, the mesa portion 32 can be formed by removing a portion of the semiconductor layer 30 using reactive ion etching (RIE). Alternatively, the mesa portion 32 can be formed using wet etching. In this case, the angle of the side surface 32B of the mesa portion 32 depends on the plane orientation. Forming the mesa portion 32 using RIE is preferable because it is easy to select the angle of the side surface 32B of the mesa portion 32. The semiconductor layer 30 is left as a first portion 30A and a second portion 30B on the insulating layer 20 in a region adjacent to the mesa portion 32 in the second direction X. The thickness of the first portion 30A in the first direction Z and the thickness of the second portion 30B in the first direction Z are smaller than the height of the mesa portion 32 in the first direction Z.

[0041] After the mesa portion 32 is formed, as shown in FIG. 4C , a part of the first portion 30A, the mesa portion 32, and the second portion 30B are covered with a first mask 201, and p-type impurities are implanted into the first portion 30A exposed from the first mask 201 at a predetermined energy. For example, boron (B) is implanted as the p-type impurity into the first portion 30A exposed from the first mask 201 at an energy of 5 keV to 700 keV. When other ions are implanted as the p-type impurity, the energy can be adjusted appropriately depending on the desired range.

[0042] After forming the mesa portion 32, as shown in FIG. 4D, with part of the second portion 30B, the mesa portion 32, and the first portion 30A covered with the second mask 202, n-type impurities are implanted into the second portion 30B exposed from the second mask 202 at a predetermined energy. For example, phosphorus (P) is implanted as the n-type impurity into the second portion 30B exposed from the second mask 202 at an energy of 5 keV to 700 keV. When implanting other ions as the n-type impurity, the energy can be adjusted appropriately depending on the desired range.

[0043] The step of implanting p-type impurities into the first portion 30A may be followed by the step of implanting n-type impurities into the second portion 30B, or the step of implanting n-type impurities into the second portion 30B may be followed by the step of implanting p-type impurities into the first portion 30A.

[0044] After the step of implanting p-type impurities and n-type impurities into the semiconductor layer 30, the semiconductor layer 30 is annealed at a temperature of, for example, 800°C or higher. This activates the p-type impurities and n-type impurities. That is, as shown in FIG. 4E, a p-type region 31p is formed in the region implanted with the p-type impurities, and an n-type region 31n is formed in the region implanted with the n-type impurities, thereby preparing the structure 200. The annealing temperature is the temperature of the stage on which the SOI wafer 300 is held, and can be measured using a thermocouple.

[0045] By making the thickness in the first direction Z of the first portion 30A into which p-type impurities are implanted and the thickness in the first direction Z of the second portion 30B into which n-type impurities are implanted smaller than the height in the first direction Z of the mesa portion 32, the bottom surfaces of the n-type region 31n and the p-type region 31p can be brought into contact with the insulating layer 20. This allows the dark current in the light receiving element 1 to be reduced, as described above.

[0046] The method for manufacturing the light-receiving element 1 according to the embodiment includes, after the step of preparing the structure 200, a step of implanting ions at a predetermined energy into a surface region of the mesa portion 32, including the upper surface 32A and side surface 32B, from above, with the n-type region 31n and the p-type region 31p covered with a third mask 203, as shown in FIG. 4F. This forms a light absorption region 33 in the surface region of the mesa portion 32, including the upper surface 32A and side surface 32B. For example, ions of silicon (Si), boron (B), germanium (Ge), magnesium (Mg), or the like are implanted into the surface region of the mesa portion 32 at a predetermined energy. For example, an energy that can obtain a desired range is selected within the range of 5 keV to 700 keV.

[0047] Defects such as interstitial atoms and vacancies are generated in the semiconductor crystal into which ions have been implanted. Utilizing the defect levels caused by these defects enables the light absorption region 33 to absorb light with wavelengths longer than the wavelength corresponding to the bandgap energy of the material (e.g., silicon in this embodiment) constituting the semiconductor layer 30. The side surface 32B of the mesa portion 32 is inclined so that the width of the mesa portion 32 in the second direction X decreases from the insulating layer 20 side toward the top surface 32A. This allows ions to be implanted also into the surface region including the side surface 32B of the mesa portion 32 to form the light absorption region 33.

[0048] According to this embodiment, after ion implantation into the surface region of the mesa portion 32, annealing is not performed at a temperature of 800°C or higher, at which defects are repaired. This enables light absorption using the defect levels in the light absorption region 33. Annealing may be performed at a temperature lower than 800°C, for example, at a temperature between 300°C and 600°C, or between 450°C and 550°C. This can improve the absorption coefficient.

[0049] For example, resist masks can be used as the first mask 201, the second mask 202, and the third mask 203. The resist masks can be removed by, for example, oxygen plasma ashing or a commercially available resist stripper after each of the steps shown in Figures 4C, 4D, and 4F.

[0050] After forming the light absorption region 33, the third mask 203 is removed, and the insulating film 50, the n-side electrode 40n, and the p-side electrode 40p shown in Fig. 2 can be formed. The steps up to this point are performed in wafer form, and the wafer is diced to separate into individual light-receiving elements 1.

[0051] 4F , in the ion implantation step using the third mask 203, the third mask 203 further covers at least a portion 34A of the semiconductor layer 30 between the n-type region 31n and the mesa portion 32 that is adjacent to the n-type region 31n, and at least a portion 35A of the semiconductor layer 30 between the p-type region 31p and the mesa portion 32 that is adjacent to the p-type region 31p. The third mask 203 prevents ions from being implanted into the portions 34A and 35A, resulting in a configuration in which the light absorption region 33 and the n-type region 31n are spaced apart in the second direction X, and the light absorption region 33 and the p-type region 31p are spaced apart in the second direction X. This reduces the dark current in the light receiving element 1, as described above.

[0052] The results of the first to third experiments will be described below. These results led to the idea of ​​the light receiving element 1 of the embodiment.

[0053] [First experiment] In the first experiment, a first sample 400 shown in FIG. 8 was prepared. The first sample 400 has a light absorbing layer 133 on the surface side of the silicon substrate 110. Five first samples 400 were prepared, each having a light absorbing layer 133 formed by implanting ions of helium (He), boron (B), silicon (Si), magnesium (Mg), and germanium (Ge) into the surface side of the silicon substrate 110. The relationship between the wavelength of light and the absorption coefficient was measured for each of the five first samples 400. Light L was incident perpendicularly from the top surface of the light absorbing layer 133. The results are shown in FIG. 5. In FIG. 5, the horizontal axis represents the wavelength (nm) of the incident light, and the vertical axis represents the absorption coefficient α (cm -1 ) In addition to the first sample, a silicon substrate 110 without the light absorbing layer 133 was prepared, and the absorption coefficient α was also measured for this substrate. The absorption coefficient α of the light absorbing layer 133 was calculated by subtracting the amount of light absorption in the silicon substrate 110, which was estimated from the absorption coefficient α of the silicon substrate 110, from the light transmittance of the first sample 400 measured with a spectrophotometer.

[0054] In Figure 5, the dashed line represents the results when helium (He) was implanted. The dashed-dotted line represents the results when silicon (Si) was implanted. The solid line represents the results when germanium (Ge) was implanted. The two-dot-dash line represents the results when boron (B) was implanted. The dotted line represents the results when magnesium (Mg) was implanted. The results in Figure 5 confirm that by implanting the above ion species, it is possible to form a light absorbing layer in the silicon crystal that absorbs light in the near-infrared region of 2500 nm or less.

[0055] [Second experiment] In the second experiment, a second sample 500 shown in FIG. 9 was prepared. The second sample 500 had an SOI structure including a silicon substrate 110, a SiO2 layer 120 formed on the silicon substrate 110, and a silicon layer 130 formed on the SiO2 layer 120. The silicon layer 130 had an n-type region 131n, a p-type region 131p, and a light-absorbing region 134. The light-absorbing region 134 was located between the n-type region 131n and the p-type region 131p in the second direction X. An n-side electrode 140n was disposed on the n-type region 131n and electrically connected to the n-side electrode 140n. A p-side electrode 140p was disposed on the p-type region 131p and electrically connected to the p-side electrode 140p. The thickness of the silicon layer 130 in the first direction Z was 0.5 μm. The width of the light absorbing region 134 in the second direction X is 100 μm. The length of the light absorbing region 134 in the third direction Y is 800 μm. The n-type region 131n and the light absorbing region 134 are spaced apart by 3 μm in the second direction X, and the p-type region 131p and the light absorbing region 134 are spaced apart by 3 μm in the second direction X.

[0056] In the second experiment, the spectral sensitivity was measured. The results are shown in Figure 6. In Figure 6, the horizontal axis represents the wavelength (nm) of the incident light, and the vertical axis represents the spectral sensitivity (A / W). The spectral sensitivity is calculated by dividing the photocurrent (A) by the amount of incident light (W).

[0057] In FIG. 6, the solid line represents the spectral response when light L is perpendicularly incident on the light absorption region 134 of the second sample 500 shown in FIG. 9, which is formed by implanting boron (B). In FIG. 6, the dashed-two-dot line represents the spectral response when light L is perpendicularly incident on the light absorption region 134 of the second sample 500 shown in FIG. 9, which is formed by implanting germanium (Ge). In FIG. 6, the dashed-dotted line represents the spectral response when light L is perpendicularly incident on the light absorption region 134 of the second sample 500 shown in FIG. 9, which is formed by implanting germanium (Ge). In FIG. 6, the dashed-dotted line represents the spectral response when light L is perpendicularly incident on the light absorption region 134 of the second sample 500 shown in FIG. 9, which is not subjected to ion implantation and remains a silicon layer. In the second sample 500, photocurrent was measured using a circuit connected to the n-side electrode 140n and the p-side electrode 140p. In FIG. 6, the dashed line represents the spectral response of a commercially available silicon photodiode (Hamamatsu Photonics, model number S1337).

[0058] The results in Figure 6 show that when a light absorption region is formed by implanting B or Ge, the sensitivity to light in the near-infrared region is increased by approximately three orders of magnitude compared to a silicon photodiode. Furthermore, when a light absorption region is formed by implanting B or Ge, the sensitivity to light in the near-infrared region is increased even compared to a light absorption region (silicon region) without ion implantation.

[0059] [Third Experiment] In the third experiment, a third-order sample 600A (shown in FIG. 10A), a third-order sample 600B (shown in FIG. 10B), and a third-order sample 600C (shown in FIG. 10C) were prepared. The third-order sample 600A, the third-order sample 600B, and the third-order sample 600C all have an SOI structure including a silicon substrate 110, a silicon dioxide layer 120 formed on the silicon substrate 110, and a silicon layer 130 formed on the silicon dioxide layer 120. The silicon layer 130 in the third-order sample 600A and the third-order sample 600B is implanted with boron (B) to form a light absorption region. The third-order sample 600A and the third-order sample 600B have the same shape and dimensions as the second-order sample 500 shown in FIG. 9. FIGS. 10A and 10B are cross-sectional views of the structure shown in FIG. 9 taken along line XX. The silicon layer 130 in the third-order sample 600C is not implanted with ions.

[0060] In the third experiment, the photocurrent characteristics were measured when a laser beam with a wavelength of 1300 nm was incident. The power of the laser beam was 10 mW. Microscopic observation revealed that the spot diameter of the laser beam was approximately 100 μm at the position where the laser beam was incident on each sample. The results are shown in Figure 7. In Figure 7, the horizontal axis represents the applied voltage Vr (V), and the vertical axis represents the photocurrent (A).

[0061] In Fig. 7, 3A shows the measurement results when light L was incident from the side of the silicon layer 130 of the 3A sample 600A shown in Fig. 10A. In Fig. 7, 3B shows the measurement results when light L was incident perpendicularly from the top surface of the silicon layer 130 of the 3B sample 600B shown in Fig. 10B. In Fig. 7, 3C shows the measurement results when light L was incident perpendicularly from the top surface of the silicon layer 130 of the 3C sample 600C shown in Fig. 10C.

[0062] 7, the photocurrent for incident light of 1300 nm was significantly increased by using a silicon layer 130 having a light absorption region formed by ion implantation, compared to when a silicon layer 130 without ion implantation was used. Furthermore, when light L was incident from the side of the silicon layer 130, the photocurrent was larger than when light L was incident perpendicularly from the top surface of the silicon layer 130. In particular, in the applied voltage range of -1 V to -5 V, the photocurrent flowing in the 3A sample 600A was about 4 to 5 times the photocurrent flowing in the 3B sample 600B.

[0063] Comparing Sample 3A 600A, in which laser light with a spot diameter of 100 μm was incident from a side surface with a thickness of 0.5 μm and a width of 100 μm, with Sample 3B 600B, in which laser light was incident from the top surface with a width of 100 μm and a depth of 800 μm, it was found that a smaller proportion of the laser light was incident on the silicon layer 130 in Sample 3A 600A. Despite this, a larger amount of photocurrent flowed in Sample 3A 600A, in which laser light was incident from the side. This is because the laser light L propagates through the silicon layer 130, as shown by the arrows in FIG. 10A. The third experiment revealed that the amount of light absorption can be improved by extending the propagation distance of light, even if the area of ​​the incident surface is relatively small.

[0064] The first to third experiments revealed the following: ion implantation creates a light absorption region capable of absorbing light with wavelengths longer than the wavelength corresponding to the bandgap energy of the material that makes up the semiconductor layer. It was also found that photocurrent can be amplified by injecting light from the side, thereby extending the propagation distance of the light.

[0065] Therefore, it is expected that a photodetector having a tapered mesa structure as described in the embodiment can increase the area of ​​the light absorption region compared to a photodetector having a non-tapered mesa structure, thereby improving the light receiving efficiency of the photodetector.

[0066] Up to this point, the configuration of the light-receiving element has been described using an example in which the semiconductor layer is made of silicon, but this embodiment is not limited to this. The semiconductor layer may be a III-V group semiconductor. Even in this case, by appropriately selecting the ion species for ion implantation, it is possible to form a light-absorbing region that can absorb light with a wavelength longer than the wavelength corresponding to the band gap energy of the material that makes up the semiconductor layer.

[0067] Embodiments of the present disclosure may include the following light receiving element, light receiving device, and method for manufacturing a light receiving element.

[0068] [Section 1] A substrate; a semiconductor layer; an insulating layer located between the substrate and the semiconductor layer in a first direction, which is a direction from the substrate toward the semiconductor layer; Equipped with The semiconductor layer is an n-type region; a p-type region; a mesa portion located between the n-type region and the p-type region in a second direction perpendicular to the first direction, the mesa portion having a top surface and a side surface inclined with respect to the top surface; and a width of the mesa portion in the second direction that decreases from the insulating layer side toward the upper surface, the mesa portion has, in a surface region including the top surface and the side surface, a light absorption region capable of absorbing light having a wavelength longer than a wavelength corresponding to the band gap energy of a material constituting the semiconductor layer. [Section 2] Item 2. The light-receiving element according to item 1, wherein the semiconductor layer is a silicon layer. [Section 3] Item 3. The light-receiving element according to item 2, wherein the light-absorbing region contains boron, germanium, or magnesium in addition to silicon. [Section 4] 4. The light-receiving element according to any one of items 1 to 3, further comprising an insulating film covering the top surface and the side surface of the mesa portion. [Section 5] 5. The light-receiving element according to any one of items 1 to 4, wherein a lower surface of the n-type region and a lower surface of the p-type region are in contact with the insulating layer. [Section 6] 6. The light-receiving element according to any one of items 1 to 5, wherein the height of the mesa portion in the first direction is 2 μm or more and 100 μm or less. [Section 7] 7. The light-receiving element according to any one of items 1 to 6, wherein the width of the upper surface of the mesa portion in the second direction is 10 μm or more and 100 μm or less. [Section 8] Item 8. The photodiode according to any one of items 1 to 7, wherein the thickness of the light absorption region on a center line passing through the center in the second direction of the upper surface of the mesa portion and extending in the first direction is 1.5 μm or less. [Section 9] Item 9. The light-receiving element according to any one of items 1 to 8, wherein the thickness of the n-type region in the first direction and the thickness of the p-type region in the first direction are 1.5 μm or less. [Section 10] Item 10. The light-receiving element according to any one of items 1 to 9, wherein the defect density of the light absorption region is higher than the defect density of an internal region of the mesa portion that is located more to the inside than the light absorption region. [Section 11] the light absorbing region and the n-type region in the semiconductor layer are spaced apart from each other in the second direction, Item 11. The light-receiving element according to any one of items 1 to 10, wherein the light absorption region and the p-type region in the semiconductor layer are spaced apart from each other in the second direction. [Section 12] Item 12. The photodiode according to item 11, wherein the electrical resistivity between the light absorption region and the n-type region and the electrical resistivity between the light absorption region and the p-type region are greater than the electrical resistivity of the n-type region and the electrical resistivity of the p-type region. [Section 13] The light receiving element according to any one of items 1 to 12, a lens that focuses light from the outside toward an end face of the mesa portion facing a third direction perpendicular to the first direction and the second direction; A light receiving device comprising: [Section 14] preparing a structure comprising: a substrate, a semiconductor layer, and an insulating layer located between the substrate and the semiconductor layer in a first direction that is a direction from the substrate toward the semiconductor layer, wherein the semiconductor layer has an n-type region, a p-type region, and a mesa portion located between the n-type region and the p-type region in a second direction that is perpendicular to the first direction, the mesa portion having an upper surface and a side surface inclined with respect to the upper surface, and wherein the width of the mesa portion in the second direction decreases from the insulating layer side toward the upper surface; ion implantation with a predetermined energy into a surface region including the top surface and the side surface of the mesa portion from the top surface side while the n-type region and the p-type region are covered with a mask; A method for manufacturing a light-receiving element, comprising: [Section 15] The mask is a portion of the semiconductor layer between the n-type region and the mesa portion that is adjacent to the n-type region; a portion of the semiconductor layer between the p-type region and the mesa portion that is adjacent to the p-type region; Item 15. The method for manufacturing a light-receiving element according to item 14, further covering [Section 16] Item 16. The method for manufacturing a light-receiving element according to item 14 or 15, wherein after the ion implantation, annealing is not performed at a temperature of 800° C. or higher.

[0069] The embodiments of the present disclosure have been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. All forms that can be implemented by a person skilled in the art through appropriate design modifications based on the above-described embodiments of the present disclosure also fall within the scope of the present disclosure, as long as they include the gist of the present disclosure. In addition, within the scope of the concept of the present disclosure, a person skilled in the art may come up with various modifications and alterations, and these modifications and alterations also fall within the scope of the present disclosure. [Explanation of symbols]

[0070] 1...photodetector, 10...substrate, 20...insulating layer, 30...semiconductor layer, 31n...n-type region, 31p...p-type region, 32...mesa portion, 32A...upper surface, 32B...side surface, 32C...lower surface, 33...light absorption region, 34, 35...boundary region, 36...end surface, 37...internal region, 40n...n-side electrode, 40p...p-side electrode, 50...insulating film, 61...support portion, 62...cap, 63...lens, 64...lead, 65...lead, 66...wiring board, 67...wire, 68...visible light cut filter, 100...photodetector, 200...structure, 201...first mask, 202...second mask, 203...third mask, 300...SOI wafer

Claims

1. A substrate; a semiconductor layer; an insulating layer located between the substrate and the semiconductor layer in a first direction, which is a direction from the substrate toward the semiconductor layer; Equipped with The semiconductor layer is an n-type region; a p-type region; a mesa portion located between the n-type region and the p-type region in a second direction perpendicular to the first direction, the mesa portion having a top surface and a side surface inclined with respect to the top surface; and a width of the mesa portion in the second direction that decreases from the insulating layer side toward the top surface, the mesa portion has, in a surface region including the top surface and the side surface, a light absorption region capable of absorbing light having a wavelength longer than a wavelength corresponding to the band gap energy of a material constituting the semiconductor layer.

2. The light-receiving element according to claim 1 , wherein the semiconductor layer is a silicon layer.

3. The light-receiving element according to claim 2 , wherein the light-absorbing region contains boron, germanium, or magnesium in addition to silicon.

4. The light-receiving element according to claim 1 , further comprising an insulating film covering the top surface and the side surfaces of the mesa portion.

5. 5. The light-receiving element according to claim 1, wherein a bottom surface of the n-type region and a bottom surface of the p-type region are in contact with the insulating layer.

6. 5. The light-receiving element according to claim 1, wherein the height of the mesa portion in the first direction is not less than 2 [mu]m and not more than 100 [mu]m.

7. 5. The light-receiving element according to claim 1, wherein the width of the top surface of the mesa portion in the second direction is not less than 10 [mu]m and not more than 100 [mu]m.

8. 5. The photodiode according to claim 1, wherein a thickness of the light absorption region on a center line passing through a center in the second direction of the upper surface of the mesa portion and extending in the first direction is 1.5 μm or less.

9. 5. The light-receiving element according to claim 1, wherein the thickness of the n-type region in the first direction and the thickness of the p-type region in the first direction are 1.5 [mu]m or less.

10. 5. The light-receiving element according to claim 1, wherein the defect density of the light absorption region is higher than the defect density of an internal region of the mesa portion that is located inside the light absorption region.

11. the light absorption region and the n-type region are spaced apart from each other in the second direction within the semiconductor layer; 5. The light-receiving element according to claim 1, wherein the light absorption region and the p-type region in the semiconductor layer are spaced apart from each other in the second direction.

12. 12. The light-receiving element according to claim 11, wherein the electrical resistivity between the light absorption region and the n-type region and the electrical resistivity between the light absorption region and the p-type region are greater than the electrical resistivity of the n-type region and the electrical resistivity of the p-type region.

13. The light receiving element according to claim 1, 2 or 4; a lens that focuses light from the outside toward an end face of the mesa portion facing a third direction perpendicular to the first direction and the second direction; A light receiving device comprising:

14. preparing a structure including a substrate, a semiconductor layer, and an insulating layer located between the substrate and the semiconductor layer in a first direction that is a direction from the substrate toward the semiconductor layer, wherein the semiconductor layer has an n-type region, a p-type region, and a mesa portion located between the n-type region and the p-type region in a second direction orthogonal to the first direction, the mesa portion having an upper surface and a side surface inclined with respect to the upper surface, and wherein the width of the mesa portion in the second direction decreases from the insulating layer side toward the upper surface; ion implantation with a predetermined energy into a surface region including the top surface and the side surface of the mesa portion from the top surface side while the n-type region and the p-type region are covered with a mask; A method for manufacturing a light-receiving element, comprising:

15. The mask is a portion of the semiconductor layer between the n-type region and the mesa portion that is adjacent to the n-type region; a portion of the semiconductor layer between the p-type region and the mesa portion that is adjacent to the p-type region; The method for manufacturing a light-receiving element according to claim 14 , further comprising covering the

16. 16. The method for manufacturing a light-receiving element according to claim 14, wherein after the ion implantation, annealing is not performed at a temperature of 800[deg.] C. or higher.

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