Photodetector

Abstract

To provide a photodetector that can reduce light scattered in a package.SOLUTION: A photodetector 1A includes a photodetection element 10A and a package 20, and the photodetection element 10A includes a semiconductor substrate 16 and a light absorption film 30. The light absorption film 30 is provided on at least a part of the region around a photodetection region 11 on the main surface 16a of the semiconductor substrate 16. The light absorption film 30 has a multilayer structure including a light absorption layer 31, a resonance layer 32, and a reflection layer 33. At the wavelength of the detected light, the light transmittance inside the resonance layer 32 is larger than the light transmittance inside the light absorption layer 31, and the light reflectance on the surface of the reflection layer 33 is higher than the light reflectance on the surface of the resonance layer 32.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a light detection device. [Background technology]

[0002] Patent Document 1 discloses a technology related to a silicon photomultiplier (SiPM). This SiPM includes a plurality of cells, each of which includes an avalanche photodiode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2013 / 99100 Summary of the Invention [Problem to be solved by the invention]

[0004] A photodetection device is used in which a semiconductor photodetection element, such as a photodiode, with a photodetection region formed on the surface of a semiconductor substrate is housed in a package with an optical window. In such a photodetection device, when light to be detected enters the package, part of the light strikes the periphery of the photodetection region and is scattered within the package. Then, after a certain time has elapsed since entering the package, the light enters the photodetection region.

[0005] Such behavior of the detected light causes the following problem. That is, compared with the detected light that reaches the photodetection region immediately after entering the package, the detected light that reaches the photodetection region after being scattered within the package has a delay in the timing of absorption in the photodetection region. Therefore, the waveform of the detection signal obtained by amplifying the charge output from the photodetection region spreads in time, leading to a decrease in the time resolution. Therefore, in order to increase the time resolution of the semiconductor photodetector element, it is desirable to reduce the light that scatters within the package.

[0006] The present disclosure has been made in consideration of such problems, and has an object to provide a light detection device that can reduce light scattering within a package. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a first photodetection device according to the present disclosure includes a semiconductor photodetection element and a package. The package has an optical window that allows the light to pass through and accommodates the semiconductor photodetection element. The semiconductor photodetection element includes a semiconductor substrate and a light absorbing film. The semiconductor substrate has a first surface on which the light to be detected is incident and a second surface facing away from the first surface, and has a light detection region on the first surface side that generates an amount of charge according to the light intensity of the light to be detected. The light absorbing film is provided on at least a part of the region surrounding the light detection region on the first surface. The light absorbing film has a multilayer structure including a light absorbing layer, a resonant layer provided between the light absorbing layer and the semiconductor substrate, and a reflective layer that is a metal layer provided between the resonant layer and the semiconductor substrate. At the wavelength of the light to be detected, the optical transmittance inside the resonant layer is greater than the optical transmittance inside the light absorbing layer, and the optical reflectance of the surface of the reflective layer is greater than the optical reflectance of the surface of the resonant layer.

[0008] A second photodetection device according to the present disclosure includes a semiconductor photodetection element and a package. The package has an optical window that allows the light to pass through and accommodates the semiconductor photodetection element. The semiconductor photodetection element includes a semiconductor substrate and a light absorbing film. The semiconductor substrate has a first surface and a second surface that faces the opposite direction to the first surface and receives the light to be detected, and has a photodetection region on the first surface that generates an amount of charge according to the intensity of the light to be detected. The light absorbing film is provided on at least a part of the surrounding area of ​​the area obtained by projecting the light detection region in the opposite direction to the incident direction of the light to be detected on the second surface. The light absorbing film has a multilayer structure including a light absorbing layer, a resonant layer provided between the light absorbing layer and the semiconductor substrate, and a reflective layer that is a metal layer provided between the resonant layer and the semiconductor substrate. At the wavelength of the light to be detected, the optical transmittance inside the resonant layer is greater than the optical transmittance inside the light absorbing layer, and the optical reflectance of the surface of the reflective layer is greater than the optical reflectance of the surface of the resonant layer.

[0009] In these photodetection devices, the light to be detected that has passed through the optical window is incident on the photodetection region of the semiconductor substrate. Then, an amount of charge corresponding to the light intensity of the light to be detected that has entered the photodetection region is generated in the photodetection region. This allows the amount of incident light to be electrically detected. However, a part of the light to be detected that has passed through the optical window is directed not to the photodetection region but to the region surrounding the photodetection region. This part of the light to be detected reaches a light absorbing film provided on at least a part of the region surrounding the photodetection region of the first surface (or the region of the second surface obtained by projecting the photodetection region of the first surface in the opposite direction to the incident direction of the light to be detected). The light absorbing film has a multilayer structure including a light absorbing layer, a resonant layer, and a reflecting layer. A part of the light that has entered the light absorbing film is immediately absorbed in the light absorbing layer. The light that has not been absorbed in the light absorbing layer passes through the light absorbing layer and enters the resonant layer. Then, the light that has entered the resonant layer is gradually absorbed in the light absorbing layer while being multiple-reflected between the interface between the light absorbing layer and the resonant layer and the interface between the resonant layer and the reflecting layer. Therefore, this light absorbing film can achieve extremely high absorption efficiency compared to a light absorbing film made of a single layer. Therefore, the above-mentioned light detecting device can effectively reduce reflection of the light to be detected in the area surrounding the light detection area on the first surface (or the area on the second surface obtained by projecting the light detection area on the first surface in the opposite direction to the incident direction of the light to be detected), thereby reducing light scattered inside the package and suppressing deterioration of the time resolution of the semiconductor light detecting element.

[0010] In the first light-detecting device, the semiconductor light-detecting element may further include an electrode pad for wire bonding on the first surface, the electrode pad being electrically connected to the light-detecting region, and the light-absorbing film may expose at least a part of the electrode pad. In this case, the light-absorbing film may be prevented from interfering with wire bonding to the electrode pad.

[0011] In the first and second photodetectors, the optical thickness of the resonant layer may be within a range of ±20% centered on an integral multiple of a quarter of the wavelength of the light to be detected. In this case, the phase of the light reflected at the interface between the light absorbing layer and the resonant layer and the phase of the light reflected at the interface between the resonant layer and the reflecting layer are shifted from each other by nearly π (rad), so that they cancel each other out. Therefore, the absorption efficiency (extinction efficiency) of the light absorbing film can be further increased.

[0012] In the first and second photodetection devices, the photodetection region may include an avalanche photodiode or a pn junction photodiode. In such a case, for example, an amount of charge corresponding to the intensity of the detected light can be generated in the photodetection region.

[0013] In the first and second photodetectors, the light absorption layer mainly contains tungsten silicide, and the resonant layer is SiO 2 In this case, a light absorbing film having high absorption efficiency can be realized. Effect of the Invention

[0014] According to the light detection device according to the present disclosure, the light scattered within the package can be reduced. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a light detection device according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a cross-sectional structure of a light absorbing film. [Diagram 3] FIG. 4 is a cross-sectional view of a light detection device according to a first modified example. [Figure 4] FIG. 11 is a cross-sectional view of a light detection device according to a second modified example. [Diagram 5] FIG. 11 is a cross-sectional view of a light detection device according to a third modified example. [Figure 6] FIG. 13 is a cross-sectional view of a light detection device according to a fourth modified example. [Figure 7] FIG. 13 is a cross-sectional view of a light detection device according to a fifth modified example. [Figure 8]FIG. 13 is a cross-sectional view of a photodetector according to a sixth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of a light detection device according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated description will be omitted.

[0017] (First embodiment) 1 is a cross-sectional view of a photodetector 1A according to a first embodiment of the present disclosure, showing a cross section including an optical axis AX of light to be detected. The photodetector 1A includes a semiconductor photodetector element (hereinafter simply referred to as a photodetector element) 10A that detects the intensity of light to be detected, and a package 20 that hermetically houses the photodetector element 10A. The wavelength of the light to be detected is within the range from the visible range to the near infrared range, for example, 350 nm or more and 1200 nm or less.

[0018] The package 20 has a bottom plate 21, a side wall 22, and a top plate 23. The bottom plate 21 is a plate-shaped member on which the light detection element 10A is mounted. The planar shape of the bottom plate 21 is, for example, circular. The bottom plate 21 is conductive and is mainly composed of a material such as Fe (iron). The bottom plate 21 is provided with a plurality of pins 24 penetrating the bottom plate 21. The pins 24 are made of a conductor, and the pins 24 and the bottom plate 21 are insulated from each other. The plurality of pins 24 enable electrical connection between the inside and outside of the package 20. The bottom plate 21 has a mounting surface 21a on which the light detection element 10A is mounted. In one embodiment, the mounting surface 21a is flat. The light detection element 10A and the mounting surface 21a are bonded to each other by an adhesive such as silver paste.

[0019] The side wall 22 is a cylindrical member erected on the peripheral edge of the bottom plate 21, and surrounds the light detecting element 10A. The side wall 22 is conductive and is made of the same material as the bottom plate 21, for example.

[0020] The top plate 23 is fixed to the upper end of the side wall 22 (one end opposite to the bottom plate 21) and covers the light detection element 10A. The bottom plate 21, the side wall 22, and the top plate 23 hermetically seal the internal space of the package 20. The top plate 23 includes a conductive portion 231 and an optical window 232 that passes the light to be detected. The portion 231 has an annular shape centered on the optical axis AX of the light to be detected. The portion 231 is conductive and is made of, for example, the same material as the bottom plate 21. The optical window 232 is a plate-like member that closes the opening 23a at the center of the annular portion 231. The optical window 232 is optically transparent at least to the wavelength of the light to be detected. In the present disclosure, being optically transparent means being transparent to the target wavelength, that is, having an optical transmittance of 70% or more. The optical window 232 is, for example, a glass plate. The peripheral edge of the optical window 232 and the portion 231 are air-tightly joined together with an adhesive.

[0021] The light detection element 10A is disposed on the mounting surface 21a of the bottom plate 21 at a position facing the optical window 232. The light detection element 10A includes a semiconductor substrate 16, electrode pads 51 and 52, and a light absorbing film 30.

[0022] The semiconductor substrate 16 has a rectangular shape in a plan view. The semiconductor substrate 16 includes a main surface 16a and a back surface 16b that face opposite to each other. The main surface 16a is an example of a first surface in the present disclosure, and the back surface 16b is an example of a second surface in the present disclosure. Light to be detected is incident on the main surface 16a. In one example, the semiconductor substrate 16 is a Si substrate or an InP substrate. The thickness of the semiconductor substrate 16 (the distance between the main surface 16a and the back surface 16b) is, for example, 1 μm or more and 1000 μm or less.

[0023] The photodetector element 10A includes a photodetection region 11 formed on the main surface 16a side of a semiconductor substrate 16. The photodetection region 11 generates an amount of charge corresponding to the intensity of light to be detected. A reverse bias voltage is applied to the photodetection region 11 from a power source provided outside the photodetector 1A. An output current from the photodetection region 11 is detected by a signal processing circuit provided outside the photodetector 1A.

[0024] The photodetection region 11 includes a pn junction photodiode or an avalanche photodiode. Specifically, the photodetection region 11 has a semiconductor region 14 of a first conductivity type (e.g., p type). In the illustrated example, the photodetection region 11 has a single semiconductor region 14, but the photodetection region 11 may have a plurality of semiconductor regions 14 arranged one-dimensionally or two-dimensionally. The semiconductor region 14 is formed on the main surface 16a side of the semiconductor substrate 16 (specifically, inside the semiconductor substrate 16 including the main surface 16a). The planar shape of the semiconductor region 14 is, for example, a polygon such as a rectangle. The semiconductor substrate 16 further has a semiconductor region 12 of a second conductivity type (e.g., n type) and a high-concentration semiconductor region 15 of the second conductivity type (e.g., n type). The semiconductor region 15 is formed side by side with a gap between the semiconductor region 14 on the main surface 16a side of the semiconductor substrate 16 (specifically, inside the semiconductor substrate 16 including the main surface 16a). Semiconductor region 12 occupies the area of ​​semiconductor substrate 16 excluding semiconductor regions 14 and 15 .

[0025] The electrode pads 51 and 52 are electrode pads for wire bonding. The electrode pads 51 and 52 are embedded inside an insulating film 41 provided on the main surface 16a of the semiconductor substrate 16, and are arranged spaced apart from each other in a direction along the main surface 16a. When the light detection region 11 has a plurality of semiconductor regions 14, the electrode pad 51 is provided for each semiconductor region 14.

[0026] The electrode pad 51 is exposed from the insulating film 41 through an opening formed in a portion of the insulating film 41 located on the opposite side of the electrode pad 51 from the main surface 16a. One end of a bonding wire 53 is connected to the exposed portion of the electrode pad 51. The other end of the bonding wire 53 is connected to one of the multiple pins 24. That is, the electrode pad 51 can be electrically connected to an external circuit of the photodetector 1A via the bonding wire 53 and the pin 24. The electrode pad 51 is electrically connected to the semiconductor region 14 via a conductive wiring embedded inside the insulating film 41 and a first conductivity type ohmic electrode.

[0027] The electrode pad 52 is exposed from the insulating film 41 through another opening formed in a portion of the insulating film 41 located on the opposite side of the electrode pad 52 from the main surface 16a. One end of a bonding wire 54 is connected to the exposed portion of the electrode pad 52. The other end of the bonding wire 54 is connected to another one of the multiple pins 24. That is, the electrode pad 52 can be electrically connected to an external circuit of the photodetector 1A via the bonding wire 54 and the pin 24. The electrode pad 52 is electrically connected to the semiconductor region 15 via a conductive wiring embedded inside the insulating film 41 and an ohmic electrode of the second conductivity type.

[0028] The electrode pads 51, 52 and the wiring are made of metal. Examples of metals used for the electrode pads 51, 52 and the wiring include single layer films of Al, Ti, Cu, Ni, AlCu, etc., and laminated films of Al / Ni, Al / Ti / Cu, Ti / Cu, Ti / Cu / Ni, Ti / Cu / Ti, etc. The notation A / B / C means that an A layer, a B layer, and a C layer are laminated in this order from the semiconductor substrate 16 side. The electrode pads 51, 52 and the wiring can be formed by sputtering or plating.

[0029] The material of the first conductivity type (e.g., p-type) ohmic electrode is, for example, Al when the semiconductor substrate 16 is a Si substrate, and AuZn when the semiconductor substrate 16 is an InP substrate. The material of the second conductivity type (e.g., n-type) ohmic electrode is, for example, Al when the semiconductor substrate 16 is a Si substrate, and AuGe / Ni when the semiconductor substrate 16 is an InP substrate. The ohmic electrode can be formed by sputtering.

[0030] When the semiconductor substrate 16 is a Si substrate, a group 3 element such as B is used as the p-type impurity, and a group 5 element such as P or As is used as the n-type impurity. When the semiconductor substrate 16 is an InP substrate, Zn or the like is used as the p-type impurity, and S, Sn, or the like is used as the n-type impurity. The n-type and p-type semiconductor conductivity types can be substituted for each other to configure an element, and the element can still function. The impurities can be added by diffusion or ion implantation.

[0031] The material of the insulating film 41 is SiO 2 , insulating silicon compounds such as SiN or SiON, Al 2 O 3 or TiO 2 The insulating film 41 may be formed by a chemical vapor deposition (CVD) method. 2 In the case where the insulating film is made of the above-mentioned material, a thermal oxidation method may be used.

[0032] In the case of the above-mentioned structure, a pn junction is formed between the first conductive type semiconductor region 14 and the second conductive type semiconductor region 12, thereby forming a photodiode as the light detection region 11. When the light detection region 11 is an avalanche photodiode, the light detection region 11 is operated in Geiger mode. In Geiger mode, a reverse voltage (reverse bias voltage) larger than the breakdown voltage of the light detection region 11 is applied between the anode and cathode of the light detection region 11. That is, a negative potential is applied to the anode, and a positive potential is applied to the cathode. The polarities of these potentials are relative, and one of the potentials can be set to the ground potential. The anode is a p-type region of the semiconductor regions 14 and 15, and the cathode is an n-type region of the semiconductor regions 14 and 15. When a photon of the light to be detected is incident on the light detection region 11, photoelectric conversion is performed inside the semiconductor substrate 16, and photoelectrons are generated. Avalanche multiplication occurs in the region near the pn junction interface of the semiconductor region 14, and the amplified carriers flow toward the electrode pad 51 or 52. That is, when a photon is incident on the light detection region 11, electron multiplication occurs after photoelectric conversion, and a current signal is taken out from one of the pins 24.

[0033] The light absorbing film 30 is provided on the main surface 16a of the semiconductor substrate 16 (on the insulating film 41 in this embodiment). The light absorbing film 30 is provided on at least a part of the area surrounding the light detection region 11 on the main surface 16a. The area surrounding the light detection region 11 refers to the area surrounding the semiconductor region 14. The light absorbing film 30 exposes at least a part of each electrode pad 51, 52 for wire bonding. The light absorbing film 30 in the illustrated example is provided on the entire surface of the main surface 16a except for an area including the center of the semiconductor region 14 and an exposed area of ​​each electrode pad 51, 52 from the insulating film 41. That is, the light absorbing film 30 has an opening 30a on the semiconductor region 14, an opening 30b on the electrode pad 51, and an opening 30c on the electrode pad 52.

[0034] The light absorbing film 30 is provided to absorb light to be detected that travels toward the periphery of the light detection region 11. The light absorbing film 30 has a multi-layer structure including a light absorbing layer 31, a resonant layer 32, and a reflective layer 33.

[0035] The light absorbing layer 31 constitutes the surface of the light absorbing film 30. The thickness of the light absorbing layer 31 is within a range of several nm to several μm. The resonant layer 32 is provided between the light absorbing layer 31 and the semiconductor substrate 16, specifically between the light absorbing layer 31 and the reflective layer 33. The thickness of the resonant layer 32 is within a range of several nm to several hundreds μm. In one example, the optical thickness of the resonant layer 32 is an integer multiple of a quarter of the wavelength λ of the light to be detected. Alternatively, the optical thickness of the resonant layer 32 may be within a range of ±20% centered on an integer multiple of λ / 4. The reflective layer 33 is provided between the resonant layer 32 and the semiconductor substrate 16. The thickness of the reflective layer 33 is within a range of several tens of nm to several mm.

[0036] At the wavelength λ of the light to be detected, the optical transmittance inside the resonant layer 32 is greater than the optical transmittance inside the light absorbing layer 31. In other words, the extinction coefficient of the resonant layer 32 is smaller than the extinction coefficient of the light absorbing layer 31. The light absorbing layer 31 is made of, for example, a metal. The metal constituting the light absorbing layer 31 is tungsten silicide (WSi x ), Ti, TiN, and Cr. In one example, light absorbing layer 31 primarily comprises tungsten silicide, and in one embodiment consists of tungsten silicide.

[0037] The resonator layer 32 is made of, for example, SiO 2 The silicon compounds are mainly silicon compounds such as SiN, SiON, and in one embodiment, SiO 2, SiN, or SiON. At the wavelength λ of the light to be detected, the resonant layer 32 may be optically transparent. At the wavelength λ, the optical reflectance of the surface of the reflective layer 33 is greater than the optical reflectance of the surface of the resonant layer 32. In this disclosure, the "optical reflectance of the surface of the reflective layer" refers to the optical reflectance of the surface of the reflective layer on the resonant layer side, and the "optical reflectance of the surface of the resonant layer" refers to the optical reflectance of the surface of the resonant layer on the light absorption layer side. The reflective layer 33 is a metal layer. The metal constituting the reflective layer 33 may include one or more materials selected from the group consisting of Al, Al-based alloys (AlCu, AlSi, etc.), Cu, Ag, and Au. In one example, the reflective layer 33 mainly includes Al, and in one embodiment, is made of Al.

[0038] When forming the light absorbing film 30, for example, a reflective layer 33 (e.g., AlCu) is formed on the insulating film 41 by sputtering, and a resonant layer 32 (e.g., SiO 2 ) is formed by CVD, and a light absorbing layer 31 (e.g., WSi x ) may be formed by sputtering.

[0039] The effects and advantages obtained by the photodetector 1A of the present embodiment described above will be described. In the photodetector 1A, the light to be detected that has passed through the optical window 232 is incident on the light detection region 11 of the photodetector element 10A. Then, an amount of charge corresponding to the light intensity of the light to be detected that has entered the light detection region 11 is generated in the light detection region 11. This makes it possible to electrically detect the amount of incident light to be detected. However, a part of the light to be detected that has passed through the optical window 232 is directed not toward the light detection region 11 but toward the region surrounding the light detection region 11. A part of this light to be detected reaches the light absorbing film 30 provided on at least a part of the region surrounding the light detection region 11 on the main surface 16a.

[0040] The light absorbing film 30 has a multi-layer structure including a light absorbing layer 31, a resonant layer 32, and a reflecting layer 33. A part of the light incident on the light absorbing film 30 is immediately absorbed in the light absorbing layer 31. The light not absorbed in the light absorbing layer 31 passes through the light absorbing layer 31 and enters the resonant layer 32. The light that enters the resonant layer 32 is gradually absorbed in the light absorbing layer 31 while being multiple-reflected between the interface between the light absorbing layer 31 and the resonant layer 32 and the interface between the resonant layer 32 and the reflecting layer 33. Therefore, the light absorbing film 30 can achieve extremely high absorption efficiency compared to a light absorbing film (such as a black resin film) made of a single layer. Therefore, according to the light detecting device 1A of this embodiment, the reflection of the light to be detected in the area around the light detecting region 11 of the main surface 16a can be effectively reduced, so that the light scattered in the internal space of the package 20 can be reduced and the deterioration of the time resolution of the light detecting element 10A can be suppressed.

[0041] As in this embodiment, the light-detecting element 10A may include electrode pads 51, 52 for wire bonding on the main surface 16a, which are electrically connected to the light-detecting region 11. The light-absorbing film 30 may expose at least a part of each of the electrode pads 51, 52. In this case, it is possible to prevent the light-absorbing film 30 from interfering with wire bonding to the electrode pads 51, 52.

[0042] As described above, the optical thickness of the resonant layer 32 may be within a range of ±20% centered on an integral multiple of a quarter of the wavelength λ of the light to be detected (i.e., λ / 4). In this case, the phase of the light reflected at the interface between the light absorbing layer 31 and the resonant layer 32 and the phase of the light reflected at the interface between the resonant layer 32 and the reflecting layer 33 are shifted from each other by nearly π (rad), and therefore cancel each other out. Therefore, the absorption efficiency (extinction efficiency) of the light absorbing film 30 can be further improved.

[0043] As described above, the light detection region 11 may include an avalanche photodiode or a pn junction photodiode. In such a case, for example, an amount of charge corresponding to the light intensity of the detected light can be generated in the light detection region 11.

[0044] As described above, the light absorbing layer 31 mainly contains tungsten silicide, and the resonator layer 32 is made of SiO 2 In this case, it is possible to realize a light absorbing film 30 having high absorption efficiency.

[0045] Here, the function of the light absorbing film 30 of this embodiment will be described in detail. FIG. 2 is a diagram showing a schematic cross-sectional structure of the light absorbing film 30. As described above, the light absorbing film 30 has a multi-layer structure including a light absorbing layer 31, a resonant layer 32, and a reflecting layer 33. A part of the light L that reaches the light absorbing film 30 is reflected on the surface of the light absorbing layer 31, and the remaining part enters the inside of the light absorbing layer 31. At this time, if the sheet resistance of the light absorbing layer 31 is matched to the spatial impedance of the medium (e.g., air) in contact with the surface of the light absorbing layer 31, the surface reflectance becomes zero, and all the light L enters the inside of the light absorbing layer 31. The light L that enters the inside of the light absorbing layer 31 is gradually absorbed at a ratio calculated based on the extinction coefficient of the light absorbing layer 31, so if the light absorbing layer 31 is sufficiently thick, most of the light L is absorbed by the light absorbing layer 31. However, making the light absorbing layer 31 thicker leads to a smaller sheet resistance, and the surface reflectance of the light absorbing layer 31 increases. Therefore, in this embodiment, the thickness of the light absorbing layer 31 is limited to allow a part of the light L to pass through the light absorbing layer 31.

[0046] A part of the light L that has passed through is reflected at the interface between the light absorbing layer 31 and the resonant layer 32, and returns to the light absorbing layer 31. Hereinafter, this reflected light is referred to as the first reflected light. When the light absorbing layer 31 is made of a metal and the resonant layer 32 is made of a dielectric, the impedance of the resonant layer 32 is larger than the impedance of the light absorbing layer 31 (in other words, the refractive index of the resonant layer 32 is smaller than the refractive index of the light absorbing layer 31), so the first reflected light does not have a phase shift of π (rad). The remaining part of the light L passes through the interface and enters the inside of the resonant layer 32. The light L that has entered the inside of the resonant layer 32 reaches the interface between the resonant layer 32 and the reflecting layer 33 with almost no attenuation, and is totally reflected at the interface. Hereinafter, this reflected light is referred to as the second reflected light. The second reflected light again travels inside the resonant layer 32 toward the light absorbing layer 31. Since the impedance of the reflective layer 33 is close to 0Ω (in other words, the refractive index is close to infinity), the second reflected light is accompanied by a phase shift of π (rad). If the phase difference between the second reflected light and the first reflected light is π (rad) when the second reflected light reaches the light absorbing layer 31, they cancel each other out. For this purpose, the optical thickness of the resonant layer 32 (in other words, the optical distance between the light absorbing layer 31 and the reflective layer 33) is preferably close to ¼ of the wavelength of the light L. In this regard, in the above description, the optical thickness of the resonant layer 32 is set within a range of ±20% centered on ¼ of the wavelength of the light L. However, since the electric field amplitude of the first reflected light and the electric field amplitude of the second reflected light are not exactly the same, they do not cancel each other out completely, and a part of the reflected light enters the light absorbing layer 31. The reflected light that enters the light absorbing layer 31 is absorbed in the light absorbing layer 31. In addition, a part of the second reflected light remains inside the resonant layer 32 and repeats multiple reflections, but is gradually absorbed by the light absorbing layer 31. In this way, most of the light L is absorbed by the light absorbing layer 31. A design example of the light absorbing film 30 will be described. In this embodiment, the light absorbing layer 31 of the light absorbing film 30 is in contact with air. The wavelength of the light L is assumed to be 1.55 μm. The light absorbing layer 31 is made of WSi, and the resonant layer 32 is made of SiO 2 The reflecting layer 33 is made of Al. The characteristic impedance of air is 377Ω. Tungsten silicide (WSi 2 ) has a resistivity of 2.48×10 -4 Therefore, the suitable thickness t of the light absorbing layer 31 is

number

number

[0047] According to the above concept, it is easy to design the light absorbing film 30 according to the wavelength λ of the light to be detected. Table 1 below shows design examples of the light absorbing film 30 when the wavelength λ of the light to be detected is 400 nm, 800 nm, and 1000 nm. [Table 1] In the above design example, it is assumed that the light L is incident from a direction perpendicular to the surface of the light absorbing film 30 (in other words, the thickness direction of the light absorbing film 30), but when the light L is incident from a direction inclined to the surface of the light absorbing film 30, it is preferable to add the incident angle of the light L to the above design. That is, it is preferable to calculate the propagation angle of the light in each of the layers 31-33 from the refractive index of each of the layers 31-33, and to set the thickness of each of the layers 31-33 taking this propagation angle into consideration.

[0048] (First Modification) 3 is a cross-sectional view of a photodetector 1B according to a first modified example of the above embodiment, showing a cross section including the optical axis AX of the detected light. The photodetector 1B includes a photodetector element 10B that detects the intensity of the detected light, and a package 20 that hermetically houses the photodetector element 10B. The wavelength of the detected light and the configuration of the package 20 are similar to those of the first embodiment.

[0049] The photodetector 10B of this modification differs from the photodetector 10A of the first embodiment in that the semiconductor substrate 16 does not have the semiconductor region 15 (see FIG. 1) and has a back surface electrode 55.

[0050] The back electrode 55 forms an ohmic contact with the back surface 16b of the semiconductor substrate 16, and is thereby electrically connected to the semiconductor region 12. In the illustrated example, the back electrode 55 is provided on the entire surface of the back surface 16b. The light detection element 10B is bonded to the mounting surface 21a of the bottom plate 21 via the back electrode 55. The back electrode 55 is a metal film, and is made of, for example, Au. The peripheral portion of the back electrode 55 protrudes outside the back surface 16b, and one end of the bonding wire 54 is connected to the peripheral portion. Therefore, the bonding wire 54 is not connected to the electrode pad 52. In addition, the light absorbing film 30 of this modified example does not have an opening 30c for wire bonding of the electrode pad 52.

[0051] The photodetector 1B of this modified example having the above configuration can also achieve the same effects as those of the first embodiment.

[0052] (Second Modification) 4 is a cross-sectional view of a photodetector 1C according to a second modification of the above embodiment, showing a cross section including the optical axis AX of the light to be detected. The photodetector 1C includes a photodetector element 10C that detects the intensity of the light to be detected, a package 20 that hermetically houses the photodetector element 10C, and a mounting substrate 81. The wavelength of the light to be detected and the configuration of the package 20 are similar to those of the first embodiment.

[0053] The photodetector 10C of this modification is different from the photodetector 10A of the first embodiment in that the semiconductor substrate 16 has through wiring 56, through wiring 57, back surface electrode 58, back surface electrode 59, bump electrode 60, bump electrode 61, and a glass substrate 70. When the photodetection region 11 has a plurality of semiconductor regions 14, the through wiring 56, the back surface electrode 58, and the bump electrode 60 are provided for each semiconductor region 14.

[0054] The back electrodes 58 and 59 are provided on the back surface 16b with the insulating film 42 interposed therebetween. The through wirings 56 and 57 are formed penetrating between the main surface 16a and the back surface 16b of the semiconductor substrate 16. That is, the through wirings 56 and 57 are arranged in a through hole 16c penetrating the semiconductor substrate 16. The inner side surface of the through hole 16c extends in the thickness direction of the semiconductor substrate 16 (i.e., in a direction perpendicular to the main surface 16a and the back surface 16b). The insulating film 42 is also formed in the through hole 16c. The through wirings 56 and 57 are arranged on the inner side surface and bottom surface of the through hole 16c with the insulating film 42 interposed therebetween. One end of the through wiring 56 is connected to the electrode pad 51 and is electrically connected to the semiconductor region 14 of the light detection region 11 via the electrode pad 51 and the ohmic electrode. The other end of the through wiring 56 is connected to the back surface electrode 58. One end of the through wiring 57 is connected to the electrode pad 52, and is electrically connected to the semiconductor region 15 via the electrode pad 52 and the ohmic electrode. The other end of the through wiring 57 is connected to the back surface electrode 59.

[0055] The through wirings 56, 57 and the back electrodes 58, 59 are made of metal. Examples of metals used for the through wirings 56, 57 and the back electrodes 58, 59 include single layer films of Al, Ti, Cu, Ni, AlCu, etc., and laminated films of Al / Ni, Al / Ti / Cu, Ti / Cu, Ti / Cu / Ni, Ti / Cu / Ti, etc.

[0056] The mounting substrate 81 is placed on the mounting surface 21a of the bottom plate 21. The mounting substrate 81 has a flat main surface 81a. The main surface 81a faces the back surface 16b of the semiconductor substrate 16. The mounting substrate 81 includes electrodes 82, 83, 84, and 85 arranged on the main surface 81a. The electrodes 82 and 83 are arranged corresponding to the through-wires 56 and 57, respectively. Specifically, the electrodes 82 and 83 are formed on regions of the main surface 81a facing the back electrodes 58 and 59, respectively.

[0057] The back surface electrode 58 and the electrode 82 are connected by the bump electrode 60. As a result, the through wiring 56 is electrically connected to the electrode 82 via the back surface electrode 58 and the bump electrode 60. Similarly, the back surface electrode 59 and the electrode 83 are connected by the bump electrode 61. As a result, the through wiring 57 is electrically connected to the electrode 83 via the back surface electrode 59 and the bump electrode 61. The electrodes 82 and 83 are made of the same metal as the through wirings 56 and 57 and the back surface electrodes 58 and 59. The bump electrodes 60 and 61 mainly contain, for example, solder.

[0058] The mounting substrate 81 includes a signal processing circuit. That is, the mounting substrate 81 constitutes an ASIC (Application Specific Integrated Circuit). Each of the electrodes 82 and 83 is electrically connected to the signal processing circuit via wiring (not shown) formed in the mounting substrate 81. An output signal from the light detection region 11 is input to the signal processing circuit, and the signal processing circuit processes the output signal from the light detection region 11. The signal processing circuit includes a CMOS circuit that converts the output signal from the light detection region 11 into a digital pulse. In addition, when the light detection region 11 has a plurality of semiconductor regions 14, the mounting substrate 81 is configured to include a circuit that records time information corresponding to each semiconductor region 14. As the circuit that records time information, a time to digital converter (TDC) or a time to amplitude converter (TAC) is used. As a result, the difference in wiring distance in the mounting substrate 81 does not affect the time resolution.

[0059] An output signal from the signal processing circuit is output from electrodes 84, 85. One end of a bonding wire 53 is connected to the electrode 84, and one end of a bonding wire 54 is connected to the electrode 85. As a result, the output signal from the signal processing circuit is output to the outside of the photodetector 1C through the bonding wires 53, 54 and the pin 24.

[0060] An insulating protective film 43 is provided on the back surface 16b of the semiconductor substrate 16 to cover the through wirings 56, 57 and the back surface electrodes 58, 59. The insulating protective film 43 has an opening formed at a position corresponding to the bump electrode 60 and an opening formed at a position corresponding to the bump electrode 61.

[0061] An insulating film 44 in which electrodes 82 to 85 are embedded is provided on a main surface 81a of a mounting substrate 81. The insulating film 44 has an opening formed at a position on the electrode 82 corresponding to the bump electrode 60, an opening formed at a position on the electrode 83 corresponding to the bump electrode 61, an opening for the bonding wire 53 formed on the electrode 84, and an opening for the bonding wire 54 formed on the electrode 85.

[0062] The insulating protective film 43 and the insulating film 44 are made of, for example, a resin insulating film such as a polyimide-based, phenol-based, or epoxy-based film, or SiO 2 / resin insulating film, SiN / resin insulating film, SiON / resin insulating film, SiO 2 The insulating protective film 43 and the insulating film 44 are formed by a resin insulating film, a spin coating method, or a SiO 2 In the case of a film, a CVD method can be used.

[0063] The glass substrate 70 is optically transparent to the wavelength of light to be detected. The glass substrate 70 is disposed on the light absorbing film 30. The glass substrate 70 has a main surface 70a and a back surface 70b facing opposite to each other. The back surface 70b faces the main surface 16a of the semiconductor substrate 16. The main surface 70a and the back surface 70b are flat. The glass substrate 70, the light absorbing film 30, and the insulating film 41 in the opening 30a are bonded and optically connected to each other by an optical adhesive 71. The optical adhesive 71 fills the opening 30a of the light absorbing film 30.

[0064] In this modification, the light detection element 10C is electrically connected to the mounting substrate 81 via the bump electrodes 60, 61 on the rear surface 16b. Therefore, the openings 30b and 30c (see FIG. 1) in the light absorbing film 30 are not necessary in this modification.

[0065] The photodetector 1C of this modified example having the above configuration can also achieve the same effects as those of the first embodiment. However, in this modified example, the medium in contact with the light absorbing layer 31 is not air but the optical adhesive 71. Table 2 below shows examples of the refractive index of the optical adhesive 71 and the design of the light absorbing film 30 when the wavelength λ of the light to be detected is 400 nm, 800 nm, and 1000 nm. [Table 2]

[0066] (Third Modification) 5 is a cross-sectional view of a photodetector 1D according to a third modification of the above embodiment, showing a cross section including the optical axis AX of the detected light. The photodetector 1D includes a photodetector element 10D that detects the intensity of the detected light, a package 20 that hermetically houses the photodetector element 10D, and a mounting substrate 81.

[0067] This modification is different from the second modification in that the light absorbing film 30 is provided on the main surface 70a of the glass substrate 70 in the light detecting device 1D. That is, the back surface 70b of the glass substrate 70 is adhered to the insulating film 41 via an optical adhesive 71, and the reflective layer 33, the resonant layer 32, and the light absorbing layer 31 of the light absorbing film 30 are formed in this order on the main surface 70a. The light detecting device 1D of this modification having the above configuration can also achieve the same effects as those of the first embodiment.

[0068] (Fourth Modification) 6 is a cross-sectional view of a photodetector 1E according to a fourth modification of the above embodiment, showing a cross section including the optical axis AX of the light to be detected. The photodetector 1E includes a photodetector element 10E that detects the intensity of the light to be detected, a package 20 that hermetically houses the photodetector element 10E, and a mounting substrate 81. This modification differs from the first embodiment in that the light to be detected is incident on the photodetector element 10E from the rear surface 16b side of the semiconductor substrate 16, and in that the mounting substrate 81 is included.

[0069] The photodetector element 10E has a semiconductor substrate 16, an insulating film 41, and electrode pads 51 and 52, similar to the photodetector element 10A of the first embodiment. The insulating film 41 and the electrode pads 51 and 52 are provided on a main surface 16a of the semiconductor substrate 16. The semiconductor substrate 16 includes semiconductor regions 12, 14, and 15. The configurations of the semiconductor substrate 16, the insulating film 41, and the electrode pads 51 and 52 are similar to those of the first embodiment.

[0070] The configuration of the mounting substrate 81 is similar to that of the second modified example. However, the electrodes 82 and 83 of the mounting substrate 81 are arranged corresponding to the electrode pads 51 and 52, respectively. Specifically, the electrodes 82 and 83 are formed on the main surface 81a in regions facing the electrode pads 51 and 52, respectively.

[0071] The electrode pad 51 and the electrode 82 are connected by the bump electrode 62. As a result, the semiconductor region 14 is electrically connected to the electrode 82 via the electrode pad 51 and the bump electrode 62. Similarly, the electrode pad 52 and the electrode 83 are connected by the bump electrode 63. As a result, the semiconductor region 15 is electrically connected to the electrode 83 via the electrode pad 52 and the bump electrode 63. The electrodes 82 and 83 are made of the same metal as the electrode pads 51 and 52. The bump electrodes 62 and 63 mainly contain, for example, solder.

[0072] The light absorbing film 30 of this modified example is provided on the back surface 16b of the semiconductor substrate 16. The light absorbing film 30 is provided on at least a part of the surrounding area of ​​a region 16d obtained by projecting the light detection region 11 in the opposite direction to the incident direction of the light to be detected (i.e., the direction toward the optical window 232) on the back surface 16b. The light absorbing film 30 in the illustrated example is provided on the entire surface of the back surface 16b except for the area including the center of the region 16d. That is, the light absorbing film 30 has an opening 30a on the region 16d. The semiconductor substrate 16 is exposed from the light absorbing film 30 at the opening 30a.

[0073] The light absorbing film 30 is provided to absorb light to be detected that travels toward the periphery of the region 16d. As in the first embodiment, the light absorbing film 30 has a multilayer structure including a light absorbing layer 31, a resonant layer 32, and a reflective layer 33. The detailed configurations of the light absorbing layer 31, the resonant layer 32, and the reflective layer 33 are the same as in the first embodiment.

[0074] The photodetector 1E of this modified example having the above configuration can also achieve the same effects as those of the first embodiment. That is, according to the photodetector 1E, it is possible to effectively reduce reflection of the to-be-detected light in the area surrounding the area 16d obtained by projecting the photodetection area 11 on the main surface 16a in the direction opposite to the incident direction of the to-be-detected light, thereby reducing light scattered in the internal space of the package 20 and suppressing deterioration in the time resolution of the photodetector element 10E.

[0075] (Fifth Modification) 7 is a cross-sectional view of a light detection device 1F according to a fifth modification of the above embodiment, showing a cross section including the optical axis AX of the light to be detected. The light detection device 1F includes a light detection element 10F that detects the intensity of the light to be detected, a package 20 that hermetically houses the light detection element 10F, and a mounting substrate 81. This modification differs from the fourth modification in that the light detection element 10F includes a glass substrate 70.

[0076] The configuration of the glass substrate 70 is the same as that of the third modified example (see FIG. 4) described above. That is, the glass substrate 70 is optically transparent to the wavelength of light to be detected. The glass substrate 70 is disposed on the light absorbing film 30. The glass substrate 70 has a main surface 70a and a back surface 70b facing opposite to each other. The back surface 70b faces the back surface 16b of the semiconductor substrate 16. The main surface 70a and the back surface 70b are flat. The glass substrate 70, the light absorbing film 30, and the semiconductor substrate 16 in the opening 30a are bonded and optically connected to each other by an optical adhesive 71. The optical adhesive 71 fills the opening 30a of the light absorbing film 30.

[0077] The photodetector 1F of this modified example having the above configuration can also achieve the same effects as those of the first embodiment.

[0078] (Sixth Modification) 8 is a cross-sectional view of a photodetector 1G according to a sixth modified example of the embodiment, showing a cross section including the optical axis AX of the detected light. The photodetector 1G includes a photodetector element 10G that detects the intensity of the detected light, a package 20 that hermetically houses the photodetector element 10G, and a mounting substrate 81.

[0079] This modification is different from the fifth modification in that the light absorbing film 30 is provided on the main surface 70a of the glass substrate 70 in the light detecting device 1G. That is, the back surface 70b of the glass substrate 70 is bonded to the back surface 16b of the semiconductor substrate 16 via an optical adhesive 71, and the reflective layer 33, the resonant layer 32, and the light absorbing layer 31 of the light absorbing film 30 are formed in this order on the main surface 70a. The light detecting device 1G of this modification having the above configuration can also achieve the same effects as those of the first embodiment.

[0080] Although the preferred embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-mentioned embodiment, and various modifications are possible within the scope of the gist of the present invention. For example, the light detection region 11 is not limited to a photodiode, and may include, for example, a charge coupled device (CCD). Even in this case, the effect of suppressing the deterioration of the time resolution can be achieved. [Explanation of symbols]

[0081] 1A to 1G... photodetector, 10A to 10G... photodetector element, 11... photodetection region, 12, 14, 15... semiconductor region, 16a... main surface, 16b... back surface, 16c... through hole, 16d... region, 20... package, 21... bottom plate, 21a... mounting surface, 22... side wall, 23... top plate, 23a... opening, 24... pin, 30... light absorbing film, 30a, 30b, 30c... opening, 31... light absorbing layer, 32... resonance layer, 33... reflection layer, 41, 42, 44...insulating film, 43...insulating protective film, 51, 52...electrode pad, 53, 54...bonding wire, 55...rear electrode, 56, 57...through wiring, 58, 59...rear electrode, 60 to 63...bump electrodes, 70...glass substrate, 70a...main surface, 70b...rear surface, 71...optical adhesive, 81...mounting substrate, 81a...main surface, 82 to 85...electrodes, 231...portion, 232...optical window, AX...optical axis, L...light.

Claims

1. a semiconductor photodetector element including: a semiconductor substrate having a first surface on which light to be detected is incident and a second surface facing away from the first surface, the semiconductor substrate having a photodetection region on the first surface side that generates an amount of charge corresponding to the intensity of the light to be detected; and a light absorbing film provided on at least a part of a region around the photodetection region on the first surface; a package having an optical window through which the light to be detected passes and housing the semiconductor light detecting element; Equipped with The light absorbing film is a light absorbing layer mainly containing tungsten silicide; a resonator layer provided between the light absorption layer and the semiconductor substrate, the resonator layer mainly containing a silicon compound; a reflective layer which is a metal layer provided between the resonant layer and the semiconductor substrate; A multilayer structure comprising: A photodetection device, wherein, at the wavelength of the light to be detected, the optical transmittance inside the resonant layer is greater than the optical transmittance inside the light absorption layer, and the optical reflectance of the surface of the reflective layer is greater than the optical reflectance of the surface of the resonant layer.

2. the semiconductor light-detecting element further includes an electrode pad for wire bonding on the first surface, the electrode pad being electrically connected to the light-detecting region; The light detection device according to claim 1 , wherein the light absorbing film exposes at least a portion of the electrode pad.

3. a semiconductor photodetector element including: a semiconductor substrate having a first surface and a second surface facing away from the first surface and on which the light to be detected is incident, the semiconductor substrate having a photodetection region on the first surface that generates an amount of charge corresponding to the intensity of the light to be detected; and a light absorbing film provided on at least a part of a surrounding region on the second surface that is obtained by projecting the photodetection region in a direction opposite to the incident direction of the light to be detected; a package having an optical window through which the light to be detected passes and housing the semiconductor light detecting element; Equipped with The light absorbing film is a light absorbing layer mainly containing tungsten silicide; a resonator layer provided between the light absorption layer and the semiconductor substrate, the resonator layer mainly containing a silicon compound; a reflective layer which is a metal layer provided between the resonant layer and the semiconductor substrate; A multilayer structure comprising: A photodetection device, wherein, at the wavelength of the light to be detected, the optical transmittance inside the resonant layer is greater than the optical transmittance inside the light absorption layer, and the optical reflectance of the surface of the reflective layer is greater than the optical reflectance of the surface of the resonant layer.

4. 4. The light detection device according to claim 1, wherein the optical thickness of the resonant layer is within a range of ±20% centered on an integral multiple of a quarter of the wavelength of the light to be detected.

5. 5. The photodetection device according to claim 1, wherein the photodetection region includes an avalanche photodiode or a pn junction photodiode.

6. a semiconductor photodetector element including: a semiconductor substrate having a first surface on which light to be detected is incident and a second surface facing away from the first surface, the semiconductor substrate having a photodetection region on the first surface side that generates an amount of charge corresponding to the intensity of the light to be detected; and a light absorbing film provided on at least a part of a region around the photodetection region on the first surface; a package having an optical window through which the light to be detected passes and housing the semiconductor light detecting element; Equipped with The light absorbing film is A light absorbing layer; a resonance layer provided between the light absorption layer and the semiconductor substrate; a reflective layer which is a metal layer provided between the resonant layer and the semiconductor substrate; A multilayer structure including At the wavelength of the detected light, the optical transmittance inside the resonant layer is greater than the optical transmittance inside the light absorbing layer, and the optical reflectance of the surface of the reflective layer is greater than the optical reflectance of the surface of the resonant layer; The light absorbing layer mainly contains tungsten silicide, and the resonant layer is made of SiO. ２ A light detection device, mainly comprising:

7. a semiconductor photodetector element including: a semiconductor substrate having a first surface and a second surface facing away from the first surface and on which the light to be detected is incident, the semiconductor substrate having a photodetection region on the first surface that generates an amount of charge corresponding to the intensity of the light to be detected; and a light absorbing film provided on at least a part of a surrounding region on the second surface that is obtained by projecting the photodetection region in a direction opposite to the incident direction of the light to be detected; a package having an optical window through which the light to be detected passes and housing the semiconductor light detecting element; Equipped with The light absorbing film is A light absorbing layer; a resonance layer provided between the light absorption layer and the semiconductor substrate; a reflective layer which is a metal layer provided between the resonant layer and the semiconductor substrate; A multilayer structure including At the wavelength of the detected light, the optical transmittance inside the resonant layer is greater than the optical transmittance inside the light absorbing layer, and the optical reflectance of the surface of the reflective layer is greater than the optical reflectance of the surface of the resonant layer; The light absorbing layer mainly contains tungsten silicide, and the resonant layer is made of SiO. ２ A light detection device, mainly comprising:

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