Patent Publication Number: US-2022238735-A1

Title: Light detection device, superconducting nanowire single photon detector comprising the same and method for manufacturing the same

Description:
RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0151261, filed in the Korean Intellectual Property Office on Nov. 12, 2020, the entire amounts of which are incorporated herein by reference. 
     FIELD 
     The present disclosure relates to a light detection device, superconducting nanowire single photon detector (SNSPD) including the same and a method for manufacturing the same. More particularly, it relates to a light detection device having improved self-alignment precision using a hard mask, superconducting nanowire single photon detector including the same and a method for manufacturing the same. 
     BACKGROUND 
     The single photon detector detects individual light particles even in very weak light. Among various single photon detectors, an SNSPD has advantages such as high efficiency, low dark count rate (DCR), and low jitter. Therefore, the utilization of SNSPD is increasing in the field of quantum information communication and quantum optics. 
     Among various SNSPDs, the SNSPD combined with optical fiber is the most used due to its low optical loss and high utilization. When combining SNSPD and optical fiber, it is necessary to precisely align the optical fiber core with a size of several micrometers and the detection area of the detector. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     BRIEF SUMMARY 
     A light detection device with improved self-alignment precision by using a hard mask is provided. Also, superconducting nanowire single photon detector including the light detection device is provided. A method for manufacturing such a light detection device is provided. 
     A method of manufacturing a light detection device according to an embodiment of the present disclosure includes i) providing a substrate; ii) providing a light reflecting portion on the substrate; iii) providing a light detection portion on the light reflection portion; iv) providing an anti-reflection portion provided on the light reflection portion to cover the light detection portion; v) removing each of the first outer periphery of the light reflection portion and the second outer periphery of the anti-reflection portion, and vi) providing a hard mask formed to correspond to the removed first outer periphery, positioned on the substrate, and spaced apart from the light reflecting portion to surround the light reflecting portion. 
     The providing the hard mask may include i) providing an electron beam resistance layer covering a portion except for a predetermined region formed to be spaced apart from an edge of the light reflection portion and a surface of the substrate and exposing a substrate corresponding to the predetermined region; ii) depositing a mask layer covering the predetermined region and the electron beam resistance layer; iii) removing the electron beam resistance layer and the mask layer formed on the electron beam resistance layer to provide a remaining mask layer in the predetermined region; iv) forming a photoresist layer partially covering the remaining mask layer while aligning with the remaining mask layer and exposing a third outer periphery of the remaining mask layer to the outside; v) removing a portion of the substrate exposed to the outside of the third outer periphery; and vi) removing the photoresist layer to provide the hard mask. An upper portion of the third outer periphery may be etched and then a height of the third outer periphery is smaller than an average height of the remaining mask layer in the removing a portion of the substrate exposed to the outside of the third outer periphery. 
     In the providing the substrate, the substrate may include i) a circular part and ii) a holder part connected to one side of the circular part and is longitudinally extended. The hard mask may be provided on an outer periphery of the circular part in the providing the hard mask. The removing each of the first outer periphery of the light reflection portion and the second outer periphery of the anti-reflection portion may include i) forming a photoresist layer on the anti-reflection portion; ii) removing each of the first outer periphery and the second outer periphery by wet etching, and iii) removing the photoresist layer. A shared area of the anti-reflection portion and the photoresist layer may be surrounded by a non-shared area of the anti-reflection portion and the photoresist layer, and the first outer periphery and the second outer periphery are positioned in the non-shared area. 
     A light reflection device according to an embodiment of the present disclosure includes i) a light reflecting portion positioned on the substrate; ii) a light detection portion positioned on the light reflection portion; iii) an anti-reflection portion positioned on the light reflection portion and covering the light detection portion; and iv) a hard mask positioned on the substrate and spaced apart from the light reflection portion to surround the light reflection portion. 
     The substrate may include i) a circular part and ii) a holder part connected to one side of the circular part and is longitudinally extended. The hard mask may be located on an outer periphery of the circular part. The width of the hard mask may be 10 μm to 20 μm. 
     The hard mask may include i) an inner surface portion that is spaced apart from the light reflection portion and surrounds the light reflection portion while opposing to the light reflection portion, and ii) an outer peripheral portion surrounding the outer side of the inner surface portion in contact with the inner surface portion. A height of the inner surface portion is greater than a height of the outer peripheral portion. The hard mask may include at least one metals selected from the group consisting of chromium, aluminum, or silicon oxide. 
     A distance between the hard mask and the light reflection portion may be 10 μm to 1000 μm. The side surface of the substrate and the side surface of the hard mask may be aligned with each other and vertically connected in series. 
     A superconducting nanowire single photon detector according to an embodiment of the present disclosure includes i) a holder; ii) a sleeve that is adapted to be inserted into the holder and is adapted to receive and guide an optical ferrule; and iii) a light detection device that is adapted to be inserted below the sleeve and is coupled to be inserted together with the optical ferrule. The light detection device includes i) a light reflecting portion positioned on the substrate; ii) a light detection portion positioned on the light reflection portion; iii) an anti-reflection portion positioned on the light reflection portion and covering the light detection portion; and iv) a hard mask positioned on the substrate and spaced apart from the light reflection portion to surround the light reflection portion. 
     The substrate may include i) a circular part and ii) a holder part connected to one side of the circular part and is longitudinally extended. The hard mask may be located on an outer periphery of the circular part. The hard mask may include i) an inner surface portion that is spaced apart from the light reflection portion and surrounds the light reflection portion while opposing to the light reflection portion, and ii) an outer peripheral portion surrounding the outer side of the inner surface portion in contact with the inner surface portion. The height of the inner surface portion may be greater than a height of the outer peripheral portion. The side surface of the substrate and the side surface of the hard mask may be aligned with each other and vertically connected in series. 
     The self-alignment precision of the light detection device can be improved by using a hard mask. As a result, it is possible to increase the coupling efficiency between the optical fiber and the detector, which occupies a large proportion in the detector efficiency. In addition, it can be combined with an optical fiber by minimizing the loss rate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of an SNSPD according to an embodiment of the present disclosure. 
         FIG. 2  is a schematic flowchart of a method of manufacturing a light detection device according to an embodiment of the present disclosure. 
         FIGS. 3 to 15  are schematic cross-sectional views showing each step of the method of manufacturing the light detection device of  FIG. 2 . 
         FIG. 16  is a schematic cross-sectional view of a light detecting device according to an embodiment of the present disclosure. 
         FIG. 17  is a schematic partial cross-sectional view showing a state of use of the light detection device taken along line XVII-XVII of  FIG. 1 . 
         FIGS. 18 to 20  are plan photographs of a light detection device manufactured according to an experimental example of the present disclosure. 
         FIGS. 21A and 21B  are schematic views comparing a light detection device according to an embodiment of the present disclosure and a light detection device according to a comparative example of the related art. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the present disclosure will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the disclosure are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present disclosure. Advantages and characteristics of the technical disclosure and methods for achieving them should become apparent with reference to exemplary embodiments described in detail below in addition to the accompanying drawings. However, the scope of the disclosure is not limited to the exemplary embodiments which will be described below, and may be implemented in various forms. Throughout the specification, like elements refer to like reference numerals. Detailed description of the well-known prior art is omitted. 
     It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. In addition, when a unit “comprises” an element, the unit does not exclude another element but may further include another element unless the context clearly indicates otherwise. 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present disclosure. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. 
       FIG. 1  schematically shows an SNSPD including a light detection device  100  according to an embodiment of the present disclosure. More specifically,  FIG. 1  shows a state before and after assembling of the light detection device  100  in the SNSPD. An enlarged circle of  FIG. 1  shows a schematic plan view of the light detection device  100 . The SNSPD and the light detection device  100  shown in  FIG. 1  is merely for illustrating the present disclosure, and the present disclosure is not limited thereto. Accordingly, the SNSPD and light detection device  100  of  FIG. 1  may be modified into other forms. 
     As shown in the state before assembling on the left side of  FIG. 1 , the light detection device  100  is coupled and inserted together with the optical ferrule  200  and the sleeve  300  in the holder  400 . The light detector  100  is guided to be inserted below the sleeve  300  and the light ferrule  200  is guided to be inserted above the sleeve  300 . Accordingly, the light detection device  100  and the optical ferrule  200  are aligned with each other by the sleeve  300  and contact each other. 
     As shown in the state after assembling on the right side of  FIG. 1 , the sleeve  300  is inserted and fixed in the holder  400 . Accordingly, the light detection device  100  and the optical ferrule  200  may be stably aligned. For this, the light detection device  100  needs to be inserted into the sleeve  300  without tolerance. In particular, since the size of the light detection device  100  is very small, precise control is required. 
     The enlarged circle of  FIG. 1  schematically shows an enlarged planar structure of the light detection device  100 . That is, the magnified circle of  FIG. 1  indicates a state in which the light detection device  100  is viewed from the XY plane direction. As shown in the enlarged circle of  FIG. 1 , the light detection device  100  includes a circular part  1001  and a holder part  1003 . The holder part  1003  is connected to one side, that is, the left side of the circular part  1001  and is longitudinally extended in the x-axis direction. The holder part  1003  is inserted into the holder  400  to stably fix the light detection device  100  to the holder  400 . 
     Meanwhile, the light detection device  100  includes a substrate  10 , a light detection device  30 , an anti-reflection portion  40 , and a hard mask  62 . In addition, the light detection device  100  may further include other components as needed. Here, since the hard mask  62  is formed at a predetermined height, the sleeve  300  may be stably guided along the outer periphery thereof. On the other hand, the holder part  1003  is inserted into the groove part  300   a  opened to one side of the sleeve  300 . Accordingly, the holder part  1003  is inserted into the groove part  300   a  and is fixed while moving stably in the z-axis direction. As a result, the light detection device  100  can be stably inserted and fixed in the sleeve  300 . 
     Here, since the hard mask  62  is guided in the sleeve  300 , it is provided only on the outer periphery of the circular part  1001 . The hard mask  62  cannot be formed at the connection part between the circular part  1001  and the holder part  1003 , and the holder part  1003  is located outside the sleeve  300 , so that the hard mask  62  is unnecessary. Therefore, the hard mask  62  is formed only on the outer periphery of the circular part  1001  except for the connection part with the holder part  1003  of the circular part  1001 . Hereinafter, a method of manufacturing the light detection device  100  will be described in more detail with reference to  FIGS. 2 to 14 . 
       FIG. 2  is a schematic flowchart of a method of manufacturing the light detection device  100  according to an embodiment of the present disclosure. The manufacturing method of the light detection device  100  of  FIG. 2  is merely to illustrate the present disclosure, and the present disclosure is not limited thereto. Accordingly, a method of manufacturing the light detection device  100  may be differently modified. 
     Meanwhile,  FIGS. 3 to 15  schematically show a cross-sectional structure of the light detection device  100  in each step of the flowchart of  FIG. 2 . Hereinafter, a method of manufacturing the light detection device  100  will be described in detail with reference to  FIGS. 3 to 15  with reference to  FIG. 2 . 
     The manufacturing method of the light detection device  100  of  FIG. 2  includes providing a substrate S 10 , providing a light reflecting portion on the substrate S 20 , providing a light detecting unit on the light reflecting portion S 30 , providing an anti-reflection portion provided on the light reflection portion to cover the light detection portion S 40 , forming a first photoresist layer on the reflection prevention portion S 50 , wet etching the first outer periphery of the light reflection portion and removing the second outer periphery of the anti-reflection portion S 60 , removing the first photoresist layer S 70 , providing an electron beam resistance layer covering the remaining portion except for the predetermined area spaced apart from the light reflection portion exposing the substrate corresponding to the predetermined region to the outside S 80 , depositing a mask layer covering the predetermined region and the electron beam resistance layer S 90 , removing the electron beam resistance layer and the mask layer formed thereon S 100 , forming a second photoresist layer partially covering the mask layer and exposing the outer periphery of the mask layer to the outside S 110 , removing a portion of the substrate exposed to the outside of the outer periphery S 120 , and removing the second photoresist layer S 130 . In addition, the method of manufacturing the light detection device  100  may further include other steps. 
     First, in S 10  of  FIG. 2 , the substrate  10  is provided as shown in  FIG. 3 . As a material of the substrate  10 , silicon can be used. Accordingly, a plurality of light detection devices  100  can be formed together by increasing the area of the substrate  10 . That is, since the size of the light detection device  100  is approximately 2.5 mm×5 mm, approximately 3000 light detection devices  100  can be manufactured in the case of an 8-inch wafer. In addition, the substrate  10  can be manufactured at low cost by using the substrate  10  made of a commercially available material. 
     Next, in S 20  of  FIG. 2 , an optical cavity  20  is provided on the substrate  10  as shown in  FIG. 4 . The light reflection portion  20  resonates light therein. As a result, the light incident to the light reflection portion  20  is amplified while resonating, thereby helping the light detection portion  30  to detect the light well. The light reflection portion  20  is formed on the substrate  10  through a method such as deposition. The light reflection portion  20  includes dielectrics for resonance. A diffuse Bragg reflector using a dielectric may be used as the light reflecting portion  20 . The dispersed Bragg reflector is formed into a multi-layer structure of several μm by alternately depositing two dielectric thin films with different refractive indices of several hundred nm thick. On the other hand, a metal reflection mirror may be used as the light reflection portion  20 . The metal reflection mirror is formed by coating a dielectric material and a metal having excellent reflectance. 
     In S 30  of  FIG. 2 , the light detection portion  30  is provided on the light reflection portion  20  as shown in  FIG. 5 . When a photon incident through the optical module through the light detection device  30  is absorbed, an electrical signal is generated. In SNSPD, NbN, NbTiN, WxSi1-x, MoxSi1-x, etc. may be used as a material of the light detection device  30 . The light detection device  30  is located at the center of the light detection device. That is, it is located in the center of the circular part of the light detection device and efficiently absorbs photons emitted from the corresponding optical fiber. 
     As shown in  FIG. 2 , in S 40 , the anti-reflection portion  40  covering the light detection portion  30  is provided as shown in  FIG. 6 . An anti-reflection portion  40  is provided above the light reflection portion  20 . The anti-reflection portion  40  may be manufactured through deposition in a vacuum chamber. In addition, it may be formed of titanium oxide or silicon oxide by using a sol-gel through spin coating. The anti-reflection portion  40  increases light transmittance so that light emitted from the optical fiber is easily incident on the light detection portion  30 . 
     In S 50  of  FIG. 2 , the first photoresist layer  50  is formed on the anti-reflection portion  40 . as shown in  FIG. 7 . Although not shown in  FIG. 6 , the first photoresist layer  50  is applied on the anti-reflection portion  40  to have a smaller area than the anti-reflection portion  40  using a mask. As a result, the shared area SA and the non-shared area NSA surrounding the shared area SA are formed. The shared area SA refers to an area in which the first photoresist layer  50 , the anti-reflection portion  40 , and the light reflection portion  20  overlap each other, and the non-shared area while the non-shared area NSA refers to a region in which the photoresist layer  50  is not present and only the anti-reflection portion  40  and the light reflection portion  20  are present. The outer periphery  401  of the anti-reflection portion  40  on which the first photoresist layer  50  is not formed and the outer periphery  201  of the light reflection portion  20  are exposed to the outside. The outer peripheries  201  and  401  are located in the non-shared area NSA. 
     As shown in  FIG. 2 , in S 60 , the outer peripheries  201  and  401  positioned on the substrate  10  are removed by wet etching as shown in  FIG. 8 , that is, the outer periphery  201  of the light reflection portion  20  and the outer periphery  401  of the anti-reflection portion  40  are removed. On the other hand, the central parts of the light reflection portion  20  and the anti-reflection portion  40  in contact with the outer peripheries  201  and  401  are covered with the first photoresist layer  50  to protect them from wet etching. In wet etching, an aqueous hydrofluoric acid solution or the like can be used. 
     In S 70  of  FIG. 2 , the first photoresist layer  50  is removed as shown in  FIG. 9 , and the first photoresist layer  50  is removed by cleaning or the like. Meanwhile, as a result of the wet etching in S 60 , the light reflection portion  22  and the anti-reflection portion  42  from which the outer peripheral portions  201  and  401  are removed, respectively, remain. 
     Next, in S 80  of  FIG. 2 , the electron beam resistance layer  52  covering the remaining portions except for the light reflection portion  22  and the predetermined area  625  spaced apart from the surface of the substrate  10  is provided as shown in  FIG. 9 . Although not shown in  FIG. 9 , the electron beam resistance layer  52  may be formed only on a portion except for the predetermined region  625  using an electron microscope. As a result, the predetermined area  625  is exposed to the outside. The predetermined area  625  is formed in a portion corresponding to the outer peripheral portion  201  as shown in  FIG. 7 , but is spaced apart from the light reflection portion  22 . In a subsequent process, a hard mask is formed in the predetermined region  625 . In order to uniformly coat the electron beam resistance layer  52  and the second photoresist layer  54 , it is preferable to separate the predetermined area  625  from the light reflection portion  22 . On the other hand, the electron beam resistance layer  52  is thickly coated around it due to the thickness of the light reflection portion  22  and the anti-reflection portion  42 . 
     In S 90  of  FIG. 2 , a mask layer  60  covering the predetermined region  625  and the electron beam resistance layer  52  is deposited. A mask layer  60  shown in  FIG. 11  is deposited over both the electron beam resistance layer  52  and the predetermined region  625 . As a result, the mask layer  60  directly contacts the substrate  10  in the predetermined region  625 . The mask layer  60  is formed of a material having high etch resistance in SF6 plasma, such as chromium, aluminum, silicon oxide, or the like, to form a hard mask. The mask layer  60  is formed to a sufficient height so that a portion of the edge of the substrate  10  is not completely etched while the SF6 plasma is completely etched, so that the substrate is not exposed in the predetermined region  625 . 
     Next, in S 100  of  FIG. 2 , the electron beam resistance layer  52  shown in  FIG. 11  and the mask layer  60  shown in  FIG. 11  formed thereon are removed to provide the remaining mask layer  62  as shown in  FIG. 12 . That is, since the electron beam resistance layer  52  is lifted off and cleaned, the mask layer  60  placed thereon is also removed. On the other hand, since the remaining mask layer  62  corresponding to the predetermined area  625  shown in  FIG. 11  is not provided on the electron beam resistance layer  52  but directly contact with the substrate  10  without overlying, in S 100  it is not removed by the process. Accordingly, the remaining mask layer  62  is provided directly on the substrate  10 . 
     In S 110  of  FIG. 2 , the second photoresist layer  54  partially covering the remaining mask layer  62  is formed, and the outer periphery  623  of the remaining mask layer  62  is exposed to the outside. The remaining mask layer  62  as shown in  FIG. 13  aligns the second photoresist layer  54  which is patterned using a contact aligner. Accordingly, the occurrence of an error in the pattern size of the second photoresist layer  54  may be reduced. The remaining mask layer  62  includes an inner surface portion  621  and an outer peripheral portion  623 . The inner surface portion  621  and the outer peripheral portion  623  are interconnected to the surface of the substrate  10  in the lateral direction thereof. The inner surface portion  621  is covered with the second photoresist layer  54 , and the outer peripheral portion  623  is not covered with the second photoresist layer  54 . Here, the width of the remaining mask layer  62 , that is, the sum of the length L 621  of the inner surface portion  621  and the length L 623  of the outer peripheral portion  623  is proportional to the electron beam lithography time. Accordingly, when the length of the remaining mask layer  62  increases, the process cost may increase due to an increase in the use time of the electron microscope. The width of the hard mask  63  as shown in  FIG. 16  in the finally manufactured light detection device  100  as shown in  FIG. 1  is 10 μm to 20 μm. The length L 621  of the inner surface portion  621  and the length L 623  of the outer peripheral portion  623  are preferable to be at least 5 μm in consideration of an xy-axis alignment error that may occur during pattern formation of the second photoresist layer  54  and a critical dimension CD of the pattern. 
     Meanwhile, the separation distance d 22  between the remaining mask layer  62  and the light reflection portion  22  may be 10 μm to 1000 μm. The thickness of the light reflection portion  22  using a dielectric mirror is several μm, and the thickness of the second photoresist layer  54  is at least 10 μm. Therefore, when the separation distance d 22  is too small, due to the thickness of the side surfaces of the light reflection portion  22  and the anti-reflection portion  42  and the second photoresist layer  54 , uniform coating and patterning of the second photoresist layer  54  may not be good. In addition, it is impossible for the separation distance d 22  to be too large due to the design structure of the light detection device. Therefore, the separation distance d 22  is maintained in the above-described range. 
     Next, in S 120  of  FIG. 2 , the edge of the substrate  10  is removed. as shown in  FIG. 14 , that is, the edge of the substrate  10  not covered with the second photoresist layer  54  is removed by dry etching using SF6 gas as a reactive ion etching process. That is, the area outside the dotted line in  FIG. 14  is removed. At the same time, the outer periphery  623  not covered with the second photoresist layer  54  is also partially etched to form the etched outer periphery  624 , and the height thereof is lowered. That is, the hard mask  63  including the inner surface portion  621  and the etched outer peripheral portion  624  is manufactured. 
     Finally, in S 130  of  FIG. 2 , the second photoresist layer  54  is removed as shown in  FIG. 15 . The second photoresist layer  54  is removed through cleaning. 
       FIG. 16  is a schematic cross-sectional view of the light detection device  100  manufactured by the method of manufacturing the light detection device according to an embodiment of the present disclosure described above. The cross-sectional structure of the light detection device  100  of  FIG. 16  is merely for illustrating the present disclosure, and the present disclosure is not limited thereto. Accordingly, the cross-sectional structure of the light detection device  100  may be modified into other shapes. 
     As shown in  FIG. 16 , the light detection device  100  is finally provided. The light-reflecting mirror  22  and the ring-shaped hard mask  63  are finally formed in the light detection device  100 . The hard mask  63  includes an inner surface portion  621  and an etched outer peripheral portion  624 . Here, a height h 624  of the etched outer peripheral portion  624  based on the surface of the etched substrate  11  is smaller than a height h 621  of the inner surface portion  621 . Accordingly, the average height of the hard mask  63  is smaller than the height h 624  of the etched outer peripheral portion  624 . The height h 621  of the inner surface portion  621  may be 100 nm to 200 nm, and the height h 624  of the outer peripheral portion  624  may be 10 nm to 50 nm. Meanwhile, the sleeve  300  shown in  FIG. 1  may be guided along the side surface  11   a  of the etched substrate  11 . 
     The side surface  11   a  of the substrate  11  and the side surface  63   a  of the hard mask  63  are aligned with each other and are vertically connected continuously. That is, the vertical etching is well performed so that the side surface  11   a  of the substrate  11  and the side surface  63   a  of the hard mask  63  are continuously connected by the dry etching in S 120 . As a result, the sleeve  300  shown in  FIG. 1  may be coupled to the outside of the side surface  11   a  of the substrate  11 . 
       FIG. 17  is a schematic partial cross-sectional view of the SNSPD taken along the line XVII-XVII of  FIG. 1 . The SNSPD of  FIG. 17  is only for illustrating the present disclosure, and the present disclosure is not limited thereto. Therefore, the SNSPD can be modified into other forms. 
     As shown in  FIG. 17 , the optical ferrule  200  is guided inside the sleeve  300  to be contact with the optical detection element  100 . The optical ferrule  200  includes an optical fiber  2001  formed in the center thereof, and the optical fiber  2001  is surrounded by the optical fiber cladding  2003 . Since the light detection device  100  is guided by the side  11   a  of the substrate  11  having a thickness of several hundred μm and is drawn into the sleeve  300 , the light detection device  30  is located exactly in the center in the sleeve  300 . As a result, the optical fiber  2001  is precisely aligned with the light detection device  30  to detect light well. That is, the optical fibers  2001  are aligned to match the detection area formed by the light detection device  30 . When the optical fiber  2001  of several tens of μm and the light detection device  30  are assembled, they are aligned in a line with each other to improve the loss rate due to assembling. 
     Hereinafter, the present disclosure will be described in more detail through experimental examples. These experimental examples are merely for illustrating the present disclosure, and the present disclosure is not limited thereto. 
     EXPERIMENTAL EXAMPLE 
     A light detection device according to an embodiment of the present disclosure and a light detection device according to the prior art were manufactured. They were compared with each other as below. 
       FIGS. 18 to 20  respectively show planar photos of the light detection devices manufactured according to the experimental examples of the present disclosure. More specifically,  FIG. 18  is a photo patterned and applied with a second photoresist before a deep reactive ion etching RIE process,  FIG. 19  is a photo of a hard mask formed around the light detection device, and  FIG. 20  shows a photograph in which a plurality of lollipop-shaped light detection devices are formed on a silicon wafer substrate. 
     The diameter of the circular part of the light detection device element manufactured in this way was 2.5 mm. In addition, the diameter of the light detection device  30  for the SNSPD was 15 μm. 
     Alignment Experiment 
       FIGS. 21A and 21B  schematically shows a comparison between the light detection device  100  according to an embodiment of the present disclosure and the light detection device  900  according to a comparative example of the prior art. More specifically,  FIG. 21A  shows the light detection device  100  having the hard mask  63  formed thereon, and  FIG. 21B  shows the light detection device  900  in which the hard mask  63  is not formed. 
     As shown in  FIG. 21A , in the experimental example of the present disclosure, a light detection device  100  was manufactured on a substrate  10  through a semiconductor manufacturing process. On the other hand, the optical fiber diameter of the optical ferrule, which is the target of the optical detection element  100 , was 9 μm. In the experimental example, the light detection device  100  was aligned with a contact aligner using the alignment key  500 . In this case, the number of position errors was several μm, and the critical dimension error of the diameter of the circular portion of the light detection device  100  was also several μm. That is, as a result of forming the inner surface portion  621 , it was possible to accurately align the error so as to be negligible. As a result, the error between the optical fiber and the light detection portion  30  was only several tens of nm. In particular, even when the light detection device  30  is not located in the center, the error is only tens of nm, and even when the diameter of the circular part of the light detection device  100  is not 2.5 mm due to tolerance, the error is in the tens of nm. it was only 
     On the other hand, as shown in  FIG. 21B , in the comparative example, the light detection device element was aligned with the contact aligner using the alignment key  500 . In this case, the number of position errors was several μm, and the critical dimension error of the diameter of the circular portion of the light detection device was also several μm. As a result of assembling the optical ferrule and the light detection device, the error between the optical fiber and the light detection device was as large as several μm. In particular, when the light detection device  30  is not located in the center, the error was several μm, and even when the diameter of the circular part of the light detection device  100  is not 2.5 mm due to tolerance, the error was very large, as many as several μm. Accordingly, the alignment accuracy between the optical fiber and the light detection portion  30  can be greatly improved by the formation of the hard mask  63 . In addition, path misalignment due to the inaccuracy of the critical dimension of the photoresist layer and the limitation of the contact aligner could be improved. 
     While this disclosure has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.