Patent Publication Number: US-2022223749-A1

Title: Light detector, light detection system, lidar device, and moving body

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-004297, filed on Jan. 14, 2021; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a light detector, a light detection system, a lidar device, and a moving body. 
     BACKGROUND 
     There is a light detector that detects light incident on a semiconductor region. For the light detector, it is desired that the crosstalk is small. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a light detector according to a first embodiment; 
         FIG. 2  is a plan view showing the light detector according to the first embodiment; 
         FIG. 3  is a plan view showing the light detector according to the first embodiment; 
         FIG. 4  is a cross-sectional view taken along the line A 1 -A 2  of  FIG. 1  to  FIG. 3 ; 
         FIGS. 5A and 5B  are schematic views showing a method for manufacturing the light detector according to the first embodiment; 
         FIGS. 6A and 6B  are schematic views showing a method for manufacturing the light detector according to the first embodiment; 
         FIGS. 7A and 7B  are schematic views showing a method for manufacturing the light detector according to the first embodiment; 
         FIGS. 8A and 8B  are schematic views showing a method for manufacturing the light detector according to the first embodiment; 
         FIGS. 9A and 9B  are schematic views showing a method for manufacturing the light detector according to the first embodiment; 
         FIG. 10  is an enlarged cross-sectional view of a portion of  FIG. 4 ; 
         FIG. 11  is a cross-sectional view showing a light detector according to a first variation of the first embodiment; 
         FIG. 12  is a cross-sectional view showing a light detector according to a second variation of the first embodiment; 
         FIG. 13  is a cross-sectional view showing a light detector according to a third variation of the first embodiment; 
         FIG. 14  is a plan view showing a light detector according to a fourth variation of the first embodiment; 
         FIG. 15  is a cross-sectional view taken along the line A 1 -A 2  of  FIG. 14 ; 
         FIG. 16  is an enlarged cross-sectional view of a portion of  FIG. 15 ; 
         FIGS. 17A and 17B  are schematic views showing a method for manufacturing the light detector according to the fourth variation of the first embodiment; 
         FIGS. 18A and 18B  are schematic views showing a method for manufacturing the light detector according to the fourth variation of the first embodiment; 
         FIGS. 19A and 19B  are schematic views showing a method for manufacturing the light detector according to the fourth variation of the first embodiment; 
         FIGS. 20A and 20B  are schematic views showing a method for manufacturing the light detector according to the fourth variation of the first embodiment; 
         FIG. 21  is a plan view showing a light detector according to a fifth variation of the first embodiment; 
         FIG. 22  is a plan view showing a light detector according to a fifth variation of the first embodiment; 
         FIG. 23  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 21 and 22 ; 
         FIG. 24  is an enlarged cross-sectional view of a portion of  FIG. 23 ; 
         FIG. 25  is a cross-sectional view showing another light detector according to the fifth variation of the first embodiment; 
         FIG. 26  is a plan view showing a light detector according to a sixth variation of the first embodiment; 
         FIG. 27  is a plan view showing the light detector according to the sixth variation of the first embodiment; 
         FIG. 28  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 26 and 27 ; 
         FIG. 29  is an enlarged cross-sectional view of a portion of  FIG. 28 ; 
         FIG. 30  is a plan view showing a light detector according to a seventh variation of the first embodiment; 
         FIG. 31  is a plan view showing the light detector according to the seventh variation of the first embodiment; 
         FIG. 32  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 30 and 31 ; 
         FIG. 33  is a schematic view illustrating a Laser Imaging Detection and Ranging (LIDAR) device according to a second embodiment; 
         FIG. 34  is a drawing for describing the detection of the detection object of the lidar device; and 
         FIG. 35  is a schematic top view of a moving body including the lidar device according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a light detector includes a junction region, a first insulating portion, and a quenching part. The junction region includes a first semiconductor region of a first conductivity type and a second semiconductor region of a second conductivity type. The second semiconductor region is provided on the first semiconductor region and forms a p-n junction surface with the first semiconductor region. The first insulating portion has an inclined surface inclined with respect to a first direction perpendicular to the p-n junction surface and includes void. The inclined surface is provided at a same height as at least a portion of the junction region and crosses the second direction from the junction region toward the first insulating portion. The quenching part is electrically connected to the second semiconductor region. 
     Various embodiments are described below with reference to the accompanying drawings. 
     The drawings are schematic and conceptual; and the relationships between the thickness and width of portions, the proportions of sizes among portions, etc,, are not necessarily the same as the actual values. The dimensions and proportions may be illustrated differently among drawings, even for identical portions, 
     In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with like reference numerals, and a detailed description is omitted as appropriate. 
     First Embodiment 
       FIGS. 1 to 3  are plan views showing a light detector according to a first embodiment. 
       FIG. 4  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 1 to 3 . 
     As shown in  FIGS. 1 to 4 , a light detector  100  according to the first embodiment includes a semiconductor layer  1 , a semiconductor layer  2 , a junction region  10 , a first insulating portion  21 , a second insulating portion  22 , an insulating layer  30 , a quenching part  36 , a lens  40 , and a first interconnect  41 . 
     It is noted that, in  FIG. 1 , the lens  40  is shown by a broken line, and the insulating layer  30  is omitted. In  FIG. 2 , the insulating layer  30 , the quenching part  36 , the lens  40 , and the first interconnect  41  are omitted. In  FIG. 3 , the second insulating portion  22 , the insulating layer  30 , the quenching part  36 , the lens  40 , and the first interconnect  41  are omitted, and a first semiconductor region  11  and a first opening OP 1  are shown by broken lines. 
     As shown in  FIG. 4 , the junction region  10  includes the first semiconductor region  11  and a second semiconductor region  12 . Herein, the direction from the first semiconductor region  11  toward the second semiconductor region  12  is taken as a Z-direction (first direction). The two directions perpendicular to the Z-direction and orthogonal to each other are taken as an X-direction (second direction) and a Y-direction (third direction). For the description, the direction from the first semiconductor region  11  toward the second semiconductor region  12  is referred to as an “upward direction”, and the opposite direction is referred to as a “downward direction”. These directions are based on a relative positional relationship between the first semiconductor region  11  and the second semiconductor region  12  and are independent of the direction of gravity. 
     As shown in  FIG. 4 , the semiconductor layer  2  is provided on the semiconductor layer  1 . The first semiconductor region  11  is provided on a portion of the semiconductor layer  2 . The first semiconductor region  11  is electrically connected to the semiconductor layer  1  via the semiconductor layer  2 . The second semiconductor region  12  is provided on the first semiconductor region  11 . A p-n junction surface is formed between the first semiconductor region  11  and the second semiconductor region  12 . For example, the p-n junction surface is parallel to the X-direction and Y-direction. The upper surface or the p-n junction surface of the first semiconductor region  11  is perpendicular to the Z-direction. 
     The semiconductor layer  1 , the semiconductor layer  2 , and the first semiconductor region  11  are of the first conductivity type. The second semiconductor region  12  is of a second conductivity type. The impurity concentration of the first conductivity type in the semiconductor layer  2  is lower than the impurity concentration of the first conductivity type in the semiconductor layer  1 . The impurity concentration of the first conductivity type in the first semiconductor region  11  is higher than the impurity concentration of the first conductivity type in the semiconductor layer  2 . The first conductivity type is one of the p-type and the n-type. The second conductivity type is the other of the p-type and the n-type. 
     The first insulating portion  21  is provided on another portion of the semiconductor layer  2 . The first insulating portion  21  has an inclined surface  21 S inclined with respect to the Z-direction. The inclined surface  21 S faces the junction region  10  in the second direction. That is, the inclined surface  21 S intersects the direction from the junction region  10  toward the first insulating portion  21  and faces the junction region  10 . The inclined surface  215  is provided at the same height as at least a portion of the junction region  10 . The position of the inclined surface  21 S in the Z-direction is the same as the position of at least a portion of the junction region  10  in the Z-direction. For example, a portion of the inclined surface  215  is provided at the same height as the p-n junction surface between the first semiconductor region  11  and the second semiconductor region  12 . 
     The first insulating portion  21  includes void  21   a . In the light detector  100 , the first insulating portion  21  is formed of only the void  21   a . For example, the first insulating portion  21  has a pair of the inclined surfaces  21 S facing each other. The void is located between the pair of inclined surfaces  21 S. The inclined surface  215  is an interface between the semiconductor layer  2  and the void  21   a.    
     In the portion where the inclined surface  21 S is provided, the width of a portion of the first insulating portion  21  is smaller than the width of another portion of the first insulating portion  21  located above the portion of the first insulating portion  21 . For example, the width of the lower portion of the first insulating portion  21  is smaller than the width of the upper portion of the first insulating portion  21 . The distance between the upper portion of the inclined surface  215  and the center of the junction region  10  along the X-Y plane (first plane) is shorter than the distance between the lower portion of the inclined surface  21 S and the center. The “width” is the length in the direction from the junction region  10  toward the first insulating portion  21 . For example, when the direction from the junction region  10  toward the first insulating portion  21  is parallel to the X-direction, the “width” is the length in the X-direction. 
     The first semiconductor region  11  and the second semiconductor region  12  are separated from the first insulating portion  21 . A portion of the semiconductor layer  2  is provided between the junction region  10  and the first insulating portion  21 . The inclined surface  21 S is a boundary surface between the semiconductor layer  2  and the first insulating portion  21 . 
     The second insulating portion  22  is provided on the first insulating portion  21 . The lower end of the second insulating portion  22  is provided at the same height as the second semiconductor region  12 . The second insulating portion  22  includes an insulating material. For example, the width of the second insulating portion  22  is larger than the width of the first insulating portion  21 . 
     The insulating layer  30  is a light transmissive layer and is provided on the junction region  10 , the first insulating portion  21 , and the second insulating portion  22 . The quenching part  36  is provided in the insulating layer  30  and is located on the second insulating portion  22 . 
     As shown in  FIG. 1 , one end of the quenching part  36  is electrically connected to the second semiconductor region  12  via a contact plug  36   a , an interconnect  36   b , and a contact plug  36   c . The other end of the quenching part  36  is electrically connected to the first interconnect  41  provided in the insulating layer  30  via a contact plug  36   d . The electrical resistance of the quenching part  36  is larger than the electrical resistance of each of the contact plug  36   a , the interconnect  36   b , the contact plug  36   c , and the contact plug  36   d . It is favorable that the electrical resistance of the quenching part  36  is not less than 50 kΩ and not more than 20 MΩ. 
     The lens  40  is provided on the insulating layer  30  and is located on the junction region  10 . The upper surface of the lens  40  is convex upward. The lens  40  collects the light toward the junction region  10 . The shape of the lens  40  is generally a quadrangle, a quadrangle with rounded corners, or a circle when viewed from the Z-direction. 
     As shown in  FIG. 3 , the multiple first insulating portions  21  are provided around one junction region  10  along the X-Y plane. The multiple first insulating portions  21  are separated from each other. As shown in  FIG. 2 , the one common second insulating portion  22  is provided on the multiple first insulating portions  21 . 
     As shown in  FIGS. 1 to 3 , the multiple junction regions  10  are provided in the X-direction and the Y-direction. The multiple junction regions  10  aligned in the X-direction are electrically connected to one first interconnect  41  via the multiple quenching parts  36 , respectively. One or more first insulating portions  21  are provided between the adjacent junction regions  10 . In the example shown in  FIG. 3 , one first insulating portion  21  is alternately aligned with one junction region  10  in the X-direction. In the Y-direction, the two first insulating portions  21  are alternately aligned with the one junction region  10 . 
     As shown in  FIG. 2 , the multiple first openings OP 1  are provided to the second insulating portion  22  and the insulating layer  30 . The multiple first openings OP 1  are separated from each other. One first opening OP 1  is connected to one void  21   a , As shown in  FIG. 1 , when viewed from the Z-direction, the shape of the first opening OP 1  is an I shape or a J shape. When viewed from the Z-direction, the position of the first opening OP 1  is different from the position of the junction region  10 , the position of the quenching part  36 , and the position of the first interconnect  41 . When viewed from the Z-direction, at least a portion of the position of the first opening OP 1  may be the same as a portion of the position of the lens  40 . Alternatively, the position of the first opening OP 1  may be different from the position of the lens  40 . 
     The operations of the light detector  100  will be described. 
     When the light is incident on the junction region  10  from the above, electric charges are generated in the semiconductor layer  2  or the junction region  10 . When the electric charges are generated, a current flows through the quenching part  36  and the first interconnect  41 . The incidence of the light on the junction region  10  can be detected by detecting the current flowing through the first interconnect  41 . 
     For example, a reverse voltage is applied between the first semiconductor region  11  and the second semiconductor region  12 . The junction region  10  functions as an avalanche photodiode. A reverse voltage exceeding a breakdown voltage may be applied between the first semiconductor region  11  and the second semiconductor region  12 . That is, the junction region  10  may operate in a Geiger mode. Due to the operation in the Geiger mode, a pulsed signal with a high gain and a short time constant is output. Accordingly, the light reception sensitivity of the light detector  100  can be improved. 
     When the light is incident on the junction region  10  and avalanche breakdown occurs, the quenching part  36  is provided to suppress the continuation of the avalanche breakdown. When the avalanche breakdown occurs and a current flows through the quenching part  36 , a voltage drop occurs according to the electrical resistance of the quenching part  36 . Due to the voltage drop, the potential difference between the first semiconductor region  11  and the second semiconductor region  12  is decreased, and thus, the avalanche breakdown is stopped. Accordingly, next, the light incident on the junction region  10  can be detected. 
     As described above, a resistor that causes a large voltage drop may be provided as the quenching part  36 , or a control circuit that cuts off the current instead of the resistor may be provided as the quenching part  36 . For example, the control circuit includes a comparator, a control logic unit, and two switching junction regions. A known configuration called an active quenching circuit can be applied to the control circuit. 
     An example of the material of each element will be described. 
     The semiconductor layer  1 , the semiconductor layer  2 , the first semiconductor region  11 , and the second semiconductor region  12  include silicon. For example, the semiconductor layer  1 , the semiconductor layer  2 , the first semiconductor region  11 , and the second semiconductor region  12  include silicon. Phosphorus, arsenic, or antimony is used as an n-type impurity. Boron is used as a p-type impurity. A ( 100 ) plane of a silicon single crystal included in the semiconductor layers  1  and  2  is perpendicular to the Z-direction. 
     The second insulating portion  22  and the insulating layer  30  include one selected from a group consisting of silicon, oxygen, and nitrogen. As shown in  FIG. 4 , the insulating layer  30  may include a first layer  31  to a third layer  33 . The second layer  32  is provided on the first layer  31 . The third layer  33  is provided on the second layer  32 . For example, the second insulating portion  22 , the first layer  31 , and the third layer  33  include silicon oxide. The second layer  32  includes silicon nitride. 
     The quenching part  36  as a resistor includes polysilicon. n-type impurities or p-type impurities may be added to the quenching part  36 . The contact plug and each interconnect include at least one metal selected from a group consisting of titanium, tungsten, copper, and aluminum. 
     The lens  40  includes a light-transmissive resin. It is favorable that the resin is an acrylic resin. The acrylic resin may be a resin mixed with propylene glycol monomethyl ether acetate. 
     For example, the first conductivity type is a p-type and the second conductivity type is an n-type, Boron, which is a p-type impurity, is easy to be implanted into silicon and to be diffused in silicon in comparison with n-type impurities. For this reason, when the first conductivity type is the p-type, the first semiconductor region  11  is easily formed. The sensitivity of the light detector  100  can be improved. 
     The first conductivity type may be an n-type, and the second conductivity type may be a p-type. In this case, a positive voltage is applied to the semiconductor layer  1  with respect to the second semiconductor region  12 . The electrons generated in the shallow portion of the semiconductor layer  2  can move toward the semiconductor layer  1  faster than the holes, and thus, avalanche doubling can be promoted. The electrons toward the semiconductor layer  1  are allowed to move faster, so that the time of long tail noise can be shortened. The long tail noise is a minute signal generated after the light is incident on the junction region  10  and a pulsed signal appears. 
       FIGS. 5A to 9B  are schematic views showing a method for manufacturing a light detector according to the first embodiment. 
       FIGS. 5B, 6B, 7B, 8B, and 9B  show B 1 -B 2  cross sections of  FIGS. 5A, 6A, 7A, 8A, and 9A , respectively. In  FIGS. 5A, 6A, 7A, 8A, and 9A , the insulating layer  30  is omitted. 
     As shown in  FIGS. 5A and 5B , the semiconductor layer  2 , the junction region  10 , the second insulating portion  22 , the insulating layer  30 , and the quenching part  36  are formed on the semiconductor layer  1  which is a semiconductor substrate by a known method. For example, the semiconductor layer  2  is formed by epitaxial growth of the semiconductor layer  1  on the ( 100 ) plane. The first semiconductor region  11  and the second semiconductor region  12  are formed by ion implantation into the semiconductor layer  2 . The second insulating portion  22  is formed of local oxidation of silicon (LOCOS). The insulating layer  30  and the quenching part  36  are formed by chemical vapor deposition (CVD). 
     As shown in  FIGS. 6A and 6B , the multiple first openings OP 1  penetrating the second insulating portion  22  and the insulating layer  30  are formed by photolithography and reactive ion etching (RIE). The multiple first openings OP 1  are formed so as to avoid the junction region  10 , the quenching part  36 , and the first interconnect  41 . The semiconductor layer  2  is exposed at the bottom of the first opening OP 1 . 
     As shown in  FIGS. 7A and 7B , a portion of the semiconductor layer  2  is removed through the first opening OP 1  by wet etching. Potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) is used as a chemical liquid. The first insulating portion  21  including the void  21   a  is formed by wet etching. As shown in  FIG. 7A , when viewed from the Z-direction, the shape of the first insulating portion  21  is a quadrangle circumscribing one first opening OP 1 . As shown in  FIG. 7B , a silicon ( 111 ) plane inclined with respect to the Z-direction appears on the side surface of the first insulating portion  21 . Accordingly, the first insulating portion  21  having the inclined surface  215  is formed. For example, the inclination of the ( 111 ) plane with respect to the X-direction is 54 degrees to 55 degrees. 
     A resin layer  40   a  is formed by applying a resin on the insulating layer  30 . As shown in  FIGS. 8A and 8B , a portion of the resin layer  40   a  located on the first opening OP 1  is removed by photolithography and RIE. Accordingly, the resin layer  40   a  is separated into multiple pieces. As a result, it is possible to prevent the resin from flowing into the first opening OP 1  and the void  21   a  in the subsequent reflow process. 
     Due to the heat treatment, the fluidity of the resin layer  40   a  is increased, so that the resin layer  40   a  is allowed to reflow. As shown in  FIGS. 9A and 9B , the upper surface of the resin layer  40   a  is curved by surface tension. The resin layer  40   a  is solidified to form the lens  40 . Through the above-described processes, the light detector  100  according to the first embodiment is manufactured. 
     In the manufacturing method described above, the formation of the first opening OP 1  and the formation of the first insulating portion  21  may be performed after the formation of the resin layer  40   a . For example, the resin layer  40   a  at the position where the first opening OP 1  is formed is removed by photolithography and RIE. The multiple first openings OP 1  penetrating the second insulating portion  22  and the insulating layer  30  through the openings formed in the resin layer  40   a  are formed. A portion of the semiconductor layer  2  is removed through the first opening OP 1  by wet etching, and thus, the first insulating portion  21  is formed. 
     The advantages of the first embodiment will be described. 
     When the light is incident on the junction region  10 , electric charges are generated. A portion of the electric charges recombine and emit light (secondary photons). When the secondary photons are incident on another junction region  10 , electric charges are generated in the other junction region  10 . That is, the crosstalk occurs. In order to improve the detection accuracy of photons by the light detector  100 , it is desirable that the crosstalk can be suppressed. 
       FIG. 10  is an enlarged cross-sectional view of a portion of  FIG. 4 , 
     The light detector  100  according to the first embodiment includes the first insulating portion  21 . The first insulating portion  21  has the inclined surface  21 S. As the secondary photons P travel toward the adjacent junction region  10 , the secondary photons P generated in the junction region  10  are reflected downward by the inclined surface  21 s. Accordingly, the crosstalk can be suppressed. 
     The first insulating portion  21  includes the void  21   a . The void  21   a  includes a gas, and the refractive index of the void  21   a  is lower than that of the semiconductor layer  2 . The void  21   a  is provided, so that the difference between the refractive index of the first insulating portion  21  and the refractive index of the semiconductor layer  2  is increased in comparison with the case where the void  21   a  is not provided. As the difference is increased, the secondary photons P are more likely to be reflected by the inclined surface  215 . According to the first embodiment, the crosstalk can be effectively suppressed, and the accuracy of photon detection by the light detector  100  can be improved, 
     The void  21   a  is provided, so that the stress generated in the light detector  100  can be relaxed in the void  21   a . For this reason, when the light detector  100  is manufactured, it is possible to reduce the occurrence of damage due to stress, the warpage of the semiconductor layers  1  and  2 , and the like, and it is possible to improve the yield of the light detector  100 . 
     As shown in  FIG. 10 , the secondary photons P are mainly generated in the vicinity of the p-n junction surface between the first semiconductor region  11  and the second semiconductor region  12 . For this reason, it is favorable that a portion of the inclined surface  215  is provided at the same height as the p-n junction surface between the first semiconductor region  11  and the second semiconductor region  12 . That is, it is favorable that the position of the portion of the inclined surface  21 S in the Z-direction is the same as the position of the p-n junction surface in the Z-direction. 
     It is favorable that the inclination θ of the inclined surface  215  with respect to the Z-direction is larger than 17 degrees. According to Snell&#39;s law, the critical angle θ m  at which the secondary photons P are totally reflected, the refractive index n of the semiconductor layer  2 , and the refractive index n o  of the first insulating portion  21  satisfy the relationship of sin θ m =n i /n o . When the semiconductor layer  2  includes silicon, the refractive index n i  is 3.6. When the first insulating portion  21  is formed of the void  21   a , the refractive index n o  is 1. The critical angle θ m  based on the refractive indexes is about 16 degrees. When the inclination θ is larger than 17 degrees, more secondary photons P can be reflected. For example, the secondary photons P that travel from the p-n junction surface along the X-Y plane are totally reflected by the inclined surface  21 S. Accordingly, the crosstalk can be effectively suppressed. 
     More favorably, the inclination θ is larger than 25 degrees. When forming the lens  40 , there is a possibility that the reflowed resin may flow into the void  21   a . In this case, a portion of the inclined surface  21 S serves as an interface between the semiconductor layer  2  and the resin. For example, the refractive index n o  of the first insulating portion  21  (resin) is 1.5. When the refractive index n i  is 3.6 and the refractive index n o  is 1.5, the critical angle θ m  is about 24 degrees. When the inclination θ is larger than 25 degrees, more secondary photons P can be reflected more reliably. 
     On the other hand, as the inclination θ becomes larger, the width of the upper portion of the first insulating portion  21  is increased. When the size of the light detector  100  is constant, as the width is increased, the area of the junction region  10  along the X-Y plane is decreased, so that the light reception sensitivity of the light detector  100  is lowered. Alternatively, when the area of the junction region  10  is constant, as the width is increased, the size of the light detector  100  is increased. From the viewpoint of the light reception sensitivity or the size of the light detector  100 , it is favorable that the inclination θ is smaller than 45 degrees. 
     In order to effectively reduce the crosstalk, it is favorable that the length of the first insulating portion  21  (inclined surface  21 S) in one direction is longer than the length of the junction region  10  in one direction. For example, as shown in  FIG. 3 , one first insulating portion  21  is aligned with one junction region  10  in the X-direction. A length Ly 2  of the one first insulating portion  21  in the Y-direction is longer than a length Ly 1  of the one junction region  10  in the Y-direction. Another first insulating portion  21  is aligned with the one junction region  10  in the Y-direction. A length L×2 of the other first insulating portion  21  in the X-direction is longer than a length L×1 of the one junction region  10  in the X-direction. 
     The first opening OP 1  is provided, so that the stress generated in the light detector  100  can be relieved by the first opening OP 1 . For this reason, when the light detector  100  is manufactured, it is possible to reduce the occurrence of damage due to stress, the warpage of the semiconductor layers  1  and  2 , and the like, and thus, it is possible to improve the yield of the light detector  100 . 
     [First Variation] 
       FIG. 11  is a cross-sectional view showing a light detector according to a first variation of the first embodiment. 
     In a light detector  110  according to the first variation, as shown in  FIG. 11 , an insulator  42  is provided in the first opening OP 1 . The insulator  42  is connected with the lens  40 . The insulator  42  is surrounded by the insulating layer  30  along the X-Y plane. The resin included in the insulator  42  is the same as the resin included in the lens  40 . 
     The center of the lens  40  in the X-Y plane may be deviated from the center of the junction region  10  in the X-Y plane. Due to this scaling, the difference between the sensitivity at the center of the junction region  10  and the sensitivity at the outer periphery of the junction region  10  can be reduced. When forming the scaled lens  40 , the first opening OP 1  is covered with the resin layer  40   a  during the reflowing of the resin layer  40   a . During the reflowing, the resin flows into the first opening OP 1  to form the insulator  42 . 
     Alternatively, even when scaling is not performed similarly to the light detector  100 , there is a possibility that the resin flows into the first opening OP 1  during the reflowing. In the light detector  100 , similarly to the light detector  110 , the insulator  42  may be provided in the first opening OP 1 . In this case, the insulator  42  may be connected with the lens  40  or may be separated from the lens  40 . 
     When the lens  40  and the insulator  42  include the same resin, the difference in refractive index between the lens  40  and the insulator  42  can be reduced. When the insulator  42  is connected with the lens  40 , there is no interface between the lens  40  and the insulator  42 . In comparison with the case where the resin of the lens  40  is different from the resin of the insulator  42 , the reflection of the light between the lens  40  and the insulator  42  can be suppressed. For example, when the light traveling downward passes between the lens  40  and the insulator  42 , irregular reflection of the light can be suppressed, and the light reception sensitivity of the light detector  110  can be improved. 
     [Second Variation] 
       FIG. 12  is a cross-sectional view showing a light detector according to a second variation of the first embodiment. 
     In a light detector  120  according to the second variation, as shown in  FIG. 12 , the first insulating portion  21  includes the void  21   a  and an insulating region  21   b.    
     The insulating region  21   b  is provided between the semiconductor layer  2  and the void  21   a . The inclined surface  21 S is an interface between the semiconductor layer  2  and the insulating region  21   b . The insulating region  21   b  is connected with the insulator  42 . The insulating region  21   b  includes an insulating resin. The resin included in the insulating region  21   b  is the same as the resin included in the insulator  42  and the resin included in the lens  40 . 
     According to the light detector  120 , like the light detector  100 , the secondary photons P are reflected downward by the inclined surface  21 S. Some of the secondary photons that are not reflected by the inclined surface  215  are reflected upward or downward by the interface between the void  21   a  and the insulating region  21   b . Accordingly, the crosstalk in the light detector  120  can be suppressed, 
     It is favorable that the inclination  0  of the inclined surface  215  with respect to the Z-direction is larger than 25 degrees as described above in order to reflect more secondary photons on the inclined surface  215 . 
     The insulating region  21   b  and the insulator  42  may include oxides or nitrides other than the resin. For example, the insulating region  21   b  and the insulator  42  include silicon and one selected from the group consisting of oxygen, and nitrogen. For example, after the processes shown in  FIGS. 7A and 7B  and before the formation of the resin layer  40   a , the insulating region  21   b  and the insulator  42  are formed by CVD. In this case, the insulator  42  is connected with the insulating region  21   b  and is not connected with the lens  40 . An interface is formed between the lens  40  and the insulator  42 . 
     For example, the refractive index of silicon oxide or silicon nitride is about 2.0. For this reason, when the inclination θ of the inclined surface  21 S with respect to the Z-direction is larger than 25 degrees, even in a case where the insulating region  21   b  includes any of a resin, an oxide, and a nitride, the secondary photons can be appropriately reflected by the inclined surface  215 . 
     [Third Variation] 
       FIG. 13  is a cross-sectional view showing a light detector according to a third variation of the first embodiment. 
     Similarly to a light detector  130  according to the third variation shown in  FIG. 13 , the insulator  42  may be provided in a portion of the first opening OP 1 . The insulator  42  is not provided in another portion of the first opening OP 1 . A portion of the first insulating portion  21  may include the insulating region  21   b . Another portion of the first insulating portion  21  includes only the insulating region  21   b  and may not include the void  21   a . Still another portion of the first insulating portion  21  does not include the insulating region  21   b  and is formed of only the void  21   a.    
     At least a portion of the multiple first insulating portions  21  includes the void  21   a , so that the crosstalk in the light detector  130  can be suppressed in comparison with the case where none of the first insulating portions  21  includes the void  21   a.    
     [Fourth Variation] 
       FIG. 14  is a plan view showing a light detector according to a fourth variation of the first embodiment.  FIG. 15  is a cross-sectional view taken along the line A 1 -A 2  of  FIG. 14 . 
     In  FIG. 14 , the lens  40  is shown by a broken line, and the first insulating portion  21  and the insulating layer  30  are omitted. As shown in  FIG. 14 , a light detector  140  according to the fourth variation further includes a third insulating portion  23 , 
     The third insulating portion  23  is provided around the junction region  10  along the X-Y plane. As shown in  FIG. 15 , the third insulating portion  23  is located between the junction region  10  and the first insulating portion  21 . For example, the first semiconductor region  11  and the second semiconductor region  12  are separated from the third insulating portion  23 . The first semiconductor region  11  and the second semiconductor region  12  may be in contact with the third insulating portion  23 . The lower end of the third insulating portion  23  is located below the inclined surface  21 S of the first insulating portion  21 . For example, the lower end of the third insulating portion  23  reaches the semiconductor layer  1 . The inclination of the interface between the third insulating portion  23  and the semiconductor layer  2  with respect to the Z-direction is smaller than the inclination of the inclined surface  21 S with respect to the Z-direction. 
     A second opening OP 2  leading to the void  21   a  may be provided under the first insulating portion  21 . The second opening OP 2  is located under the first opening OP 1 . When viewed from the Z-direction, the second opening OP 2  overlaps the first opening OP 1 . The second opening OP 2  is located between the adjacent third insulating portions  23 . For example, the lower end of the second opening OP 2  is located above the lower end of the third insulating portion  23 . The second opening OP 2  is provided, so that the stress generated in the semiconductor layer  2  can be reduced. For example, the possibility of occurrence of damage to the semiconductor layer  1  or  2  can be reduced. Alternatively, the warpage of the light detector  140  can be reduced. 
       FIG. 16  is an enlarged cross-sectional view of a portion of  FIG. 15 . 
     The insulating layer  30  includes a first layer  31  to a fourth layer  34 . The fourth layer  34  is provided on the third layer  33 . The first layer  31 , the third layer  33 , and the fourth layer  34  include silicon oxide. The second layer  32  includes silicon nitride. 
     As shown in  FIG. 16 , some of the secondary photons P generated in the junction region  10  travel the third insulating portion  23  toward the first insulating portion  21  and is reflected by the inclined surface  215 . The secondary photons P traveling below the inclined surface  215  are reflected by the interface between the semiconductor layer  2  and the third insulating portion  23 . The third insulating portion  23  is provided, so that the secondary photons P traveling below the inclined surface  215  can be reflected. According to the light detector  140  according to the fourth variation, the crosstalk can be further suppressed in comparison with the light detector  100 . 
       FIGS. 17A to 20B  are schematic views showing a method for manufacturing the light detector according to the fourth variation of the first embodiment. 
       FIGS. 17B, 18B, 19B, and 20B  show B 1 -B 2  cross sections of  FIGS. 17A, 18A, 19A, and 20A , respectively. In  FIGS. 17A, 18A, 19A, and 20A , the insulating layer  30  is omitted. 
     As shown in  FIGS. 17A and 17B , the semiconductor layer  2 , the junction region  10 , the third insulating portion  23 , the insulating layer  30 , and the quenching part  36  are formed on the semiconductor layer  1  which is a semiconductor substrate, by a known method. For example, the third insulating portion  23  is formed by forming an opening penetrating the semiconductor layer  1 , the semiconductor layer  2 , the first layer  31 , and the second layer  32  by RIE and burying the opening with an insulating material by CVD. 
     As shown in  FIGS. 18A and 18B , the multiple first openings OP 1  penetrating the insulating layer  30  are formed by photolithography and RIE. When viewed from the Z-direction, the third insulating portion  23  is located between the first opening OP 1  and the junction region  10 . 
     As shown in  FIGS. 19A and 19B , a portion of the semiconductor layer  2  is removed through the first opening OP 1  by wet etching. Accordingly, the first insulating portion  21  including the void  21   a  and having the inclined surface  21 S is formed. 
     As shown in  FIGS. 20A and 20B , a portion of the semiconductor layer  2  is further removed through the first opening OP 1  by RIE. Accordingly, the second opening OP 2  communicating with the void  21   a  is formed under the first insulating portion  21 . 
     After that, similarly to the processes shown in  FIGS. 9A and 9B , the resin layer  40   a  is formed on the insulating layer  30 , and the resin layer  40   a  is patterned. Similarly to the processes shown in  FIGS. 10A and 10B , the resin layer  40   a  is allowed to reflow to form the lens  40 . Through the above-described processes, the light detector  140  according to the fourth variation is manufactured. 
     [Fifth Variation] 
       FIGS. 21 and 22  are plan views showing a light detector according to a fifth variation of the first embodiment.  FIG. 23  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 21 and 22 . 
     In  FIG. 21 , the lens  40  is shown by a broken line, and the first insulating portion  21  and the insulating layer  30  are omitted. In  FIG. 22 , the insulating layer  30 , the quenching part  36 , the lens  40 , and the first interconnect  41  are omitted. 
     A light detector  150  according to the fifth variation is different from the light detector  100  in terms of the shape of the first opening OP 1  and the shape of the first insulating portion  21 . As shown in  FIG. 21 , in the light detector  150  according to the fifth variation, the shape of one first opening OP 1  has an U shape when viewed from the Z-direction. The shape of one first opening OP 1  may have an L shape when viewed from the Z-direction. As shown in  FIG. 22 , the shape of one first insulating portion  21  is a quadrangle circumscribing one first opening OP 1  when viewed from the Z-direction. 
     As shown in  FIGS. 22 and 23 , one first insulating portion  21  is provided around one third insulating portion  23  along the X-Y plane. When the semiconductor layer  2  is wet-etched through the first opening OP 1 , the etching toward the junction region  10  is stopped by the third insulating portion  23 . Accordingly, the first insulating portion  21  configured with the void  21   a  is formed around the third insulating portion  23 . 
       FIG. 24  is an enlarged cross-sectional view of a portion of  FIG. 23 . As shown in  FIG. 24 , the inclined surface  21 S of one first insulating portion  21  surrounds one junction region  10  along the X-Y plane. One inclined surface  21 S faces outward. The outer direction is a direction from the one junction region  10  toward one first insulating portion  21 . 
     For example, some of the secondary photons P generated in the junction region  10  pass through the first insulation portion  21  surrounding the junction region  10  and travel to another adjacent first insulation portion  21 . The secondary photons P are reflected by the inclined surface  21 S of the other first insulating portion  21 . The secondary photons P traveling below the inclined surface  21 S are reflected by the interface between the semiconductor layer  2  and the third insulating portion  23 . According to the light detector  150  according to the fifth variation, similarly to light detector  140 , the crosstalk can be suppressed. 
       FIG. 25  is a cross-sectional view showing another light detector according to the fifth variation of the first embodiment. 
     Like a light detector  151  shown in  FIG. 25 , the first opening OP 1  may be dosed by the upper portion of the insulating layer  30 . For example, the insulating layer  30  includes a first layer  31  to a fifth layer  35 . The fifth layer  35  is provided on the fourth layer  34  and includes silicon oxide. The first opening OP 1  penetrates the first layer  31  to the third layer  33  and is covered by the fourth layer  34  and the fifth layer  35 . For example, the void  21   a  is separated from the space outside the light detector  100 . 
     The light detector  151  can be manufactured by the following method. First, the semiconductor layer  2 , the junction region  10 , the third insulating portion  23 , the first layer  31 , and the second layer  32  are formed. The third layer  33  is formed on the second layer  32 . The first opening OP 1  penetrating the first layer  31  to the third layer  33  is formed by RIE. The first insulating portion  21  is formed by wet etching through the first opening OP 1 . The fourth layer  34  and the fifth layer  35  are formed and cover the first opening OP 1 . The lens  40  is formed on the insulating layer  30 . According to this manufacturing method, it is possible to prevent the resin from flowing into the void  21   a  during the forming of the lens  40 . Accordingly, the secondary photons are more easily reflected on the inclined surface  21 S. 
     [Sixth Variation] 
       FIGS. 26 and 27  are plan views showing a light detector according to a sixth variation of the first embodiment.  FIG. 28  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 26 and 27 . 
     In  FIG. 26 , the lens  40  is shown by a broken line, and the first insulating portion  21  and the insulating layer  30  are omitted. In  FIG. 27 , the insulating layer  30 , the quenching part  36 , the lens  40 , and the first interconnect  41  are omitted. 
     A light detector  160  according to the sixth variation is different from the light detector  100  in terms of the shape of the first opening OP 1  and the shape of the first insulating portion  21 . As shown in  FIG. 26 , in the light detector  160  according to the sixth variation, one continuous first opening OP 1  is provided for the multiple junction regions  10  aligned in the X-direction. The shape of the first opening OP 1  has a comb shape when viewed from the Z-direction. Alternatively, the multiple first opening OP 1  that have a T shape when viewed from the Z-direction may be aligned to be separated from each other in the X-direction, As shown in  FIGS. 27 and 28 , one first insulating portion  21  is provided around each of the multiple third insulating portions  23  aligned in the X-direction along the X-Y plane. When the semiconductor layer  2  is wet-etched through the first opening OP 1 , the etching toward the junction region  10  is stopped by the third insulating portion  23 , so that the first insulating portion  21  configured with the void  21   a  is formed. 
       FIG. 29  is an enlarged cross-sectional view of a portion of  FIG. 28 . 
     As shown in  FIG. 29 , a portion of the first insulating portion  21  is provided between the adjacent junction regions  10 . The portion of the first insulating portion  21  has a pair of the inclined surfaces  215  facing each other. 
     Some of the secondary photons P generated in the junction region  10  are reflected by the inclined surface  21 S. The secondary photons P traveling below the inclined surface  21 S are reflected by the interface between the semiconductor layer  2  and the third insulating portion  23 . According to the light detector  160  according to the sixth variation, similarly to the light detector  140 , the crosstalk can be suppressed. 
     [Seventh Variation] 
       FIGS. 30 and 31  are plan views showing a light detector according to a seventh variation of the first embodiment.  FIG. 32  is a cross-sectional view taken along the line A 1 -A 2  of  FIGS. 30 and 31 . 
     In  FIG. 30 , the lens  40  is shown by a broken line, and the first insulating portion  21  and the insulating layer  30  are omitted. In  FIG. 31 , the insulating layer  30 , the quenching part  36 , the lens  40 , and the first interconnect  41  are omitted. 
     In a light detector  170  according to the seventh variation, as shown in  FIG. 30 , the first opening OP 1  is located between the junction region  10  and the third insulating portion  23  when viewed from the Z--direction. The multiple first openings OP 1  are provided around the junction region  10 . The multiple first openings OP 1  are separated from each other. 
     As shown in  FIGS. 31 and 32 , the first insulating portion  21  is provided between the junction region  10  and the third insulating portion  23 . The multiple first insulating portions  21  are provided around the junction region  10  along the X-Y plane. The multiple first insulating portions  21  are separated from each other. 
     According to the light detector  170 , similarly to the light detector  140 , some of the secondary photons generated in the junction region  10  are reflected by the inclined surface  21 S. The secondary photons traveling below the inclined surface  21 S are reflected by the interface between the semiconductor layer  2  and the third insulating portion  23 . Accordingly, the crosstalk in the light detector  170  can be suppressed, 
     The structures according to the above-described variations can be appropriately combined. For example, in any of the light detectors  140 ,  150 ,  160 , and  170 , similarly to the light detector  110 , the insulator  42  may be provided. In any of the light detectors  140 ,  150 ,  160 , and  170 , similarly to the light detector  120 , the insulating region  21   b  and the insulator  42  may be provided. In any of the light detectors  150 ,  151 ,  160 , and  170 , similarly to light detector  140 , the second opening OP 2  communicating with the void  21   a  may be provided. 
     Second Embodiment 
       FIG. 33  is a schematic view illustrating a Laser Imaging Detection and Ranging (LIDAR) device according to a second embodiment. 
     The embodiment is applicable to a long-distance subject detection system (LIDAR) or the like including a line light source and a lens. The lidar device  5001  includes a light projecting unit T projecting laser light toward an object  411 , and a light receiving unit R (also called a light detection system) receiving the laser light from the object  411 , measuring the time of the round trip of the laser light to and from the object  411 , and converting the time into a distance. 
     In the light projecting unit T, a laser light oscillator (also called a light source)  404  produces laser light. A drive circuit  403  drives the laser light oscillator  404 . An optical system  405  extracts a portion of the laser light as reference light, and irradiates the rest of the laser light on the object  411  via a mirror  406 . A mirror controller  402  projects the laser light onto the object  411  by controlling the mirror  406 . Herein, “project” means to cause the light to strike. 
     In the light receiving unit R, a reference light detector  409  detects the reference light extracted by the optical system  405 . A light detector  410  receives the reflected light from the object  411 . A distance measuring circuit  408  measures the distance to the object  411  based on the reference light detected by the reference light detector  409  and the reflected light detected by the light detector  410 . An image recognition system  407  recognizes the object  411  based on the measurement results of the distance measuring circuit  408 . 
     The lidar device  5001  employs light time-of-flight ranging (Time of Flight) in which the time of the round trip of the laser light to and from the object  411  is measured and converted into a distance. The lidar device  5001  is applied to an automotive drive-assist system, remote sensing, etc. Good sensitivity is obtained particularly in the near-infrared region when the light detectors of the embodiments described above are used as the light detector  410 . Therefore, the lidar device  5001  is applicable to a light source of a wavelength band that is invisible to humans. For example, the lidar device  5001  can be used for obstacle detection in a moving body. 
       FIG. 34  is a drawing for describing the detection of the detection object of the lidar device. 
     A light source  3000  emits light  412  toward an object  600  that is the detection object. A light detector  3001  detects light  413  that passes through the object  600 , is reflected by the object  600 , or is diffused by the object  600 . 
     For example, the light detector  3001  can realize highly-sensitive detection when the light detector according to the embodiment described above is used. It is favorable to provide multiple sets of the light detector  410  and the light source  404  and to preset the arrangement relationship in the software (which is replaceable with a circuit). For example, it is favorable for the arrangement relationship of the sets of the light detector  410  and the light source  404  to be provided at uniform spacing. Thereby, an accurate three-dimensional image can be generated by the output signals of each light detector  410  complementing each other. 
       FIG. 35  is a schematic top view of a moving body including the lidar device according to the second embodiment. 
     A moving body according to the embodiment may be a vehicle as illustrated in  FIG. 35 . The vehicle  700  according to the embodiment includes the lidar devices  5001  at four corners of a vehicle body  710 . Because the vehicle according to the embodiment includes the lidar devices at the four corners of the vehicle body, the environment in all directions of the vehicle can be detected by the lidar devices. 
     The moving body may be a drone, a robot, or the like, other than the vehicle shown in  FIG. 35 . The robot is, for example, an automatic guided vehicle (AGV). By providing the lidar devices at the four corners of these moving bodies, the environment of the moving body in all directions can be detected by the lidar devices. 
     According to the embodiment described above, it is possible to reduce crosstalk in a light detector. 
     In the specification of the application, “perpendicular” and “parallel” refer to not only strictly perpendicular and strictly parallel but also include, for example, the fluctuation due to manufacturing processes, etc. It is sufficient to be substantially perpendicular and substantially parallel, 
     Hereinabove, exemplary embodiments of the invention are described with reference to specific examples. However, the embodiments of the invention are not limited to these specific examples. For example, one skilled in the art may similarly practice the invention by appropriately selecting specific configurations of components included in light detectors such as semiconductor layers, first semiconductor regions, second semiconductor regions, first insulating portions, second insulating portions, third insulating portions, insulating layers, quenching parts, lenses, first interconnects, insulators, etc., from known art. Such practice is included in the scope of the invention to the extent that similar effects thereto are obtained. 
     Further, any two or more components of the specific examples may be combined within the extent of technical feasibility and are included in the scope of the invention to the extent that the purport of the invention is included. 
     Moreover, all light detectors, light detection systems, lidar devices, and moving bodies practicable by an appropriate design modification by one skilled in the art based on the light detectors, the light detection systems, the lidar devices, and the moving bodies described above as embodiments of the invention also are within the scope of the invention to the extent that the purport of the invention is included. 
     Various other variations and modifications can be conceived by those skilled in the art within the spirit of the invention, and it is understood that such variations and modifications are also encompassed within the scope of the invention. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.