Abstract:
A semiconductor light-receiving device includes two lenses; and a concave region, a height of the sidewall being higher than a top of the lenses, a distance between a position H and a lower edge of the sidewall vertical to a line segment C 1  being grater than following condition: {(r+L) 2 −(W/2) 2 } 1/2  where: C 1  is a line segment connecting centers of the lenses; H is a midpoint of the C 1 ; r is a radius of the lenses; W is an interval between the centers; and C 2  is a lines passing through the centers in a direction vertical to the C 1 , wherein: the lower edge of the concave portion in an outer side of a region between the C 2  is concentrically formed so as to have a distance of (r+L) from the center of the lenses; and W is following condition: W&lt;2 (r+L).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Applications No. 2012-009737, filed on Jan. 20, 2012 and No. 2012-285307, filed on Dec. 27, 2012, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to a semiconductor light-receiving device. 
     (ii) Related Art 
     Japanese Patent Application Publication No. 2011-91139 discloses a back-illuminated light-receiving element in which a lens is formed on a back face. In a chip in which a plurality of light-receiving elements are provided, it is necessary that the number of the light-receiving element is the same as that of the lens. 
     SUMMARY 
     After forming a plurality of lenses, an insulating film is formed so as to cover the lenses. In this case, a defect of the insulating film may occur. 
     It is an object to restrain a trouble such as a defect of an insulating film of a semiconductor light-receiving device having a plurality of back-illuminated light-receiving elements. 
     According to an aspect of the present invention, there is provided a semiconductor light-receiving device including two lenses provided on a semiconductor substrate; and a concave region surrounding the two lenses, a sidewall positioned along an edge of the concave region having an upper edge and a lower edge, a height of the sidewall being higher than a top of the lenses, a distance between a position H and the lower edge of the sidewall in a direction vertical to a line segment C 1  being grater than following condition (1): {(r+L) 2 −(W/2) 2 } 1/2  where: C 1  is a line segment connecting centers of the two lenses; H is a midpoint of the line segment C 1 ; r is a radius of the lenses; W is an interval between the centers of the two lenses; and C 2  is a lines passing through the centers of the lenses in a direction vertical to the line segment C 1 , wherein: the lower edge of the concave portion in an outer side of a region between the lines C 2  is concentrically formed so as to have a distance of (r+L) from the center of the lenses; and W is following condition (2): W&lt;2(r+L). 
     According to another aspect of the present invention, there is provided a semiconductor light-receiving device including two lenses provided on a side of the lower face of the substrate; and a concave region surrounding the two lenses, a sidewall positioned along an edge of the concave region having an upper edge and a lower edge, a height of the sidewall being higher than a top of the lenses, a distance between a position H and the lower edge of the sidewall in a direction vertical to a line segment C 1  being greater than following condition (1): {(r+L) 2 −(W/2) 2 } 1/2  where: C 1  is a line segment connecting centers of the two lenses; H is a midpoint of the line segment C 1 ; r is a radius of the lenses; W is an interval between the centers of the two lenses; and C 2  is a lines passing through the centers of the lenses in a direction vertical to the line segment C 1 , wherein: the lower edge of the concave portion in an outer side of a region between the lines C 2  is concentrically formed so as to have a distance of (r+L) from the center of the lenses; and W is following condition (2): W&lt;2(r+L). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a plane view of a back face side of a semiconductor light-receiving device in accordance with a first comparative example; 
         FIG. 1B  illustrates a cross sectional view taken along a line A-A of  FIG. 1A ; 
         FIG. 2A  illustrates a plane view of a back face side of a semiconductor light-receiving device in accordance with a second comparative example; 
         FIG. 2B  illustrates a cross sectional view taken along a line B-B of  FIG. 2A ; 
         FIG. 3  illustrates a case where a resist is coated so as to cover a lens of a semiconductor light-receiving device; 
         FIG. 4  illustrates a plane view of a semiconductor light-receiving device in accordance with a first embodiment; 
         FIG. 5  illustrates a cross sectional view taken along a line C-C of  FIG. 4 ; 
         FIG. 6  illustrates an enlarged cross sectional view of a light-receiving element; 
         FIG. 7  illustrates a cross sectional view taken along a line D-D of  FIG. 5 ; 
         FIG. 8A  illustrates a plane view of a back face side of a semiconductor light-receiving device; 
         FIG. 8B  illustrates another example of the back face of the semiconductor light-receiving device; 
         FIG. 9  illustrates a case where four light-receiving elements are aligned in a single row; 
         FIG. 10A  through  FIG. 10C  illustrate another example of the back face of the semiconductor device; 
         FIG. 11A  through  FIG. 11H  illustrate a forming flow of a lens and a recess; 
         FIG. 12  illustrates an optical receiver on which a semiconductor light-receiving device is mounted; and 
         FIG. 13  illustrates an enlarged view of an optical detection portion. 
     
    
    
     DETAILED DESCRIPTION 
     A description will be given of comparative examples before a description of embodiments. 
     First Comparative Example 
       FIG. 1A  illustrates a plane view of a back face side (light incidence side) of a semiconductor light-receiving device  200  in accordance with a first comparative example.  FIG. 1B  illustrates a cross sectional view taken along a line A-A of  FIG. 1A . As illustrated in  FIG. 1A  and  FIG. 1B , a lens  201  for focusing on a light-receiving portion is formed on the back face of the semiconductor light-receiving device  200 . An insulating film  202  is formed on an exposed face of the lens  201 . 
     The lens  201  is formed by grinding the back face of the semiconductor light-receiving device  100  by a milling or the like. A concave region  203  is formed around the lens  201 . A sidewall  204  is formed so as to face with an outer circumference of the lens  201  when the concave region  203  is formed around the lens  201 . 
     The concave region  203  has a concentric shape with respect to the lens  201 . Thereby, when the semiconductor light-receiving device  200  is viewed from the back face side thereof, the outer circumference of the lens  201  and the sidewall  204  of the concave region  203  form a double circle as illustrated in  FIG. 1A . 
       FIG. 2A  illustrates a plane view of a back face side (light incidence side) of a semiconductor light-receiving device  200   a  in accordance with a second comparative example.  FIG. 2B  illustrates a cross sectional view taken along a line B-B of  FIG. 2A . The semiconductor light-receiving device  200   a  has two light-receiving portions on an upper face side. As illustrated in  FIG. 2A  and  FIG. 2B , two lenses  201  are formed according to the two light-receiving portions on the back face of the semiconductor light-receiving device  200   a . The insulating film  202  is formed so as to cover the two lenses  201 . 
     As illustrated in  FIG. 2A , when the two light-receiving portions are adjacent to each other, two circles formed by the sidewalls  204  of the concave regions  203  of the lenses  201  overlap with each other between the two lenses  201 . That is, there is no sidewall  204  separating the two lenses  201  between the two lenses  201 . In this case, a part where two sidewalls  204  of the concave regions  203  surrounding the lenses  201  meet with each other projects toward between the lenses  201 . That is, the sidewalls  204  of the concave regions  203  surrounding the lenses  201  projects toward between the two lenses  201  with a small angle. 
     In a step of forming the insulating film  202  after forming the lens  201  in the semiconductor light-receiving device  200   a , a resist is coated on the back face of the semiconductor light-receiving device  200   a . In this case, discontinuity of level difference may occur in a region where the sidewalls  204  of the concave regions  203  surrounding the lenses  201  meet with each other. The discontinuity of level difference means that a region on which a resist is not coated occurs. This is because the sidewalls  204  of the two concave regions  203  surrounding the two lenses  201  project toward between the two lenses  201  with a small angle. 
       FIG. 3  illustrates a case where the lens  201  is formed in the semiconductor light-receiving device  200   a . After that, the insulating film  202  (not illustrated) is formed on a whole area. In this case, a region surrounded by a broken line in  FIG. 3  projects with a small angle. Therefore, a defect may occur in the insulating film  202 . The defect of the insulating film  202  may cause a generation of a particle. Hereinafter, a description will be given of embodiments restraining the defect of the insulating film  202 . 
     First Embodiment 
       FIG. 4  illustrates a plane view of a semiconductor light-receiving device  100  in accordance with a first embodiment viewed from a front face side. A lens  11  is formed on a back face side. As illustrated in  FIG. 4 , the semiconductor light-receiving device  100  has a structure in which light-receiving elements  20   a  and  20   b  and dummy mesas  30   a  to  30   d  are provided on an upper face side (opposite to the back face) of a semiconductor substrate  10 . The light-receiving elements  20   a  and  20   b  and the dummy mesas  30   a  to  30   d  are independent of each other and have a mesa shape. The light-receiving eminent  20   a  and the light-receiving element  20   b  are adjacent to each other. The semiconductor light-receiving device  100  has a chip region and scribed regions around the chip region. An alignment mark  80  is formed on a corner of the chip region. 
     The light-receiving elements  20   a  and  20   b  have a structure in which an upper mesa  22  and an upper electrode  23  are provided on a lower mesa  21  in this order. For example, the lower mesa  21  has a circular cylinder shape. The upper mesa  22  has a circular cylinder shape having a diameter smaller than the lower mesa  21 , and is arranged on a center of the lower mesa  21 . The upper mesa  22  acts as a light-receiving region. The upper electrode  23  has a circular cylinder shape having a diameter smaller than the upper mesa  22 , and is arranged on a center of the upper mesa  22 . That is, the light-receiving elements  20   a  and  20   b  have a mesa shape whose diameter is larger at lower portion and is smaller at upper portion. Further, the light-receiving elements  20   a  and  20   b  have a lower electrode  24  on the lower mesa  21  except for the upper mesa  22 . In the first embodiment, the upper electrode  23  acts as a p-side electrode, and the lower electrode  24  acts as an n-side electrode. 
     The dummy mesas  30   a  to  30   d  have a structure in which an upper mesa  32  and an upper electrode  33  are provided on a lower mesa  31  in this order. For example, the lower mesa  31  has a circular cylinder shape. The upper mesa  32  has a circular cylinder shape having a diameter smaller than the lower mesa  31 , and is arranged on a center of the lower mesa  31 . The upper electrode  33  has a circular cylinder shape having a diameter smaller than the upper mesa  32  and is arranged on a center of the upper mesa  32 . That is, the dummy mesas  30   a  to  30   d  have a mesa shape whose diameter is larger at lower portion and is smaller at upper portion. The dummy mesas  30   a  to  30   d  do not act as a light-receiving element. 
     The upper electrode  33  of the dummy mesa  30   a  is coupled to the lower electrode  24  of the light-receiving element  20   a  by a wiring  40   a  going through a surface of the dummy mesa  30   a , an upper face of the semiconductor substrate  10 , and a surface of the light-receiving element  20   a . The upper electrode  23  of the light-receiving element  20   a  is coupled to the upper electrode  33  of the dummy mesa  30   b  by a wiring  40   b  going through the surface of the light-receiving element  20   a , the upper face of the semiconductor substrate  10 , and a surface of the dummy mesa  30   b.    
     The upper electrode  33  of the dummy mesa  30   c  is coupled to the upper electrode  23  of the light-receiving element  20   b  by a wiring  40   c  going through a surface of the dummy mesa  30   c , the upper face of the semiconductor substrate  10 , and a surface of the light-receiving element  20   b . The lower electrode  24  of the light-receiving element  20   b  is coupled to the upper electrode  33  of the dummy mesa  30   d  by a wiring  40   d  going through the surface of the light-receiving element  20   b , the upper face of the semiconductor substrate  10 , and the surface of the dummy mesa  30   c.    
     The surface of the light-receiving elements  20   a  and  20   b , the surface of the dummy mesas  30   a  to  30   d , and the upper face of the semiconductor substrate  10  are covered by an insulating film such as silicon nitride (SiN). The wirings  40   a  to  40   d  are provided on the insulating film. Thus, each wiring is insulated from the light-receiving elements  20   a  and  20   b , the dummy mesas  30   a  to  30   d  and the semiconductor substrate  10 . 
       FIG. 5  illustrates a cross sectional view taken along a line C-C of  FIG. 4 .  FIG. 6  illustrates an enlarged cross sectional view of the light-receiving element  20   a . As illustrated in  FIG. 5  and  FIG. 6 , the light-receiving element  20   a  has a structure in which an n-type semiconductor layer  25 , an i-type semiconductor layer  26 , a p-type semiconductor layer  27  and a contact layer  28  are provided on the semiconductor substrate  10  in this order. The n-type semiconductor layer  25  is, for example, made of n-type InP. The i-type semiconductor layer  26  is, for example, made of i-type InGaAs. The p-type semiconductor layer  27  is, for example, made of p-type InP. The thickness of the n-type semiconductor layer  25  is, for example, 1.0 μm. The thickness of the i-type semiconductor layer  26  is, for example, 1.0 μm. The thickness of the p-type semiconductor layer  27  is, for example, 1.0 μm. 
     The p-type semiconductor layer  27  has a diameter smaller than the i-type semiconductor layer  26 . An n-type semiconductor layer  29  is provided on the side face of the p-type semiconductor layer  27  on the i-type semiconductor layer  26 . The n-type semiconductor layer  29  is, for example, made of n-type InP. The semiconductor substrate  10  is made of a semi-insulated semiconductor and has resistivity of 2.2×10 7  Ωcm to 6.6×10 7  Ωcm. As an example, the semiconductor substrate  10  is made of semi-insulated InP. The contact layer  28  is, for example, made of p-type InGaAs. The lower mesa  21  of  FIG. 4  includes the n-type semiconductor layer  25 . The upper mesa  22  of  FIG. 4  includes a part of the n-type semiconductor layer  25 , the i-type semiconductor layer  26 , the p-type semiconductor layer  27 , the contact layer  28  and the n-type semiconductor layer  29 . The light-receiving element  20   b  has the same structure as the light-receiving element  20   a.    
     The lens  11  is formed at regions according to the light-receiving elements  20   a  and  20   b  on the back face of the semiconductor substrate  10 . The lens  11  focuses an incident light from the back face of the semiconductor substrate  10  on the light-receiving elements  20   a  and  20   b . The lens  11  can be formed by performing a milling on the semiconductor substrate  10 . A concave region  12  is formed during the forming of the lens  11  around the lens  11 . When the concave region  12  is formed, a sidewall  13  is formed so as to face with an outer circumference of the lens  11 . The sidewall  13  has an upper edge  13   a  and a lower edge  13   b . A top of the lens  11  is positioned at lower than the back face of the semiconductor substrate  10 . Thereby, the top of the lens  11  does not project from the back face of the semiconductor substrate  10 . Thus, a damage of the lens  11  is restrained. For example, a height of the lens  11  is 10 μm. And, a height of the sidewall  13  of the concave region  12  is 20 μm. 
     The dummy mesas  30   a  and  30   b  have a structure in which an n-type semiconductor layer  34 , an i-type semiconductor layer  35  and an n-type semiconductor layer  36  are provided on the semiconductor substrate  10  in this order. The n-type semiconductor layer  34  is, for example, made of n-type InP. The i-type semiconductor layer  35  is, for example, made of i-type InGaAs. The n-type semiconductor layer  36  is, for example, made of n-type InP. The lower mesa  31  of  FIG. 4  includes the n-type semiconductor layer  34 . The upper mesa  32  of  FIG. 4  includes a part of the n-type semiconductor layer  34 , the i-type semiconductor layer  35  and the n-type semiconductor layer  36 . The dummy mesas  30   c  and  30   d  have the same structure as the dummy mesas  30   a  and  30   b.    
     An insulating film  60  is, for example, made of silicon nitride (SiN) and covers the surface of the light-receiving elements  20   a  and  20   b , the surface of the dummy mesas  30   a  to  30   d , the upper face of the semiconductor substrate  10  and the back face of the semiconductor substrate  10 . A diffusion mask  62  is provided between the upper face of the n-type semiconductor layer  29  and the insulating film  60 . The diffusion mask  62  is, for example, made of silicon nitride (SiN) and has a thickness of 0.2 μm or the like. The wirings  40   a  and  40   b  have a structure in which a Ti/Pt layer  41 , an Au sputtering layer  42 , and an Au coating layer  43  are laminated in this order from the semiconductor substrate  10  side, and is provided on the insulating film  60 . Thus, the wirings  40   a  and  40   b  are insulated from the light-receiving element  20   a , the dummy mesas  30   a  and  30   b  and the semiconductor substrate  10 . The thickness of the insulating film  60  is, for example, 0.2 μm. The thickness of the wirings  40   a  and  40   b  is, for example, 2.0 μm. The wirings  40   c  and  40   d  have the same structure as the wirings  40   a  and  40   b.    
     The insulating film  60  has an opening on the contact layer  28 . Thus, the contact layer  28  of the light-receiving element  20   a  is contact to the wiring  40   b . Similarly, the contact layer  28  of the light-receiving element  20   b  is contact to the wiring  40   d . The insulating film  60  has an opening on the lower mesa  21  except for the upper mesa  22 . A contact layer  61  is formed in the opening of the lower mesa  21 . Thus, the n-type semiconductor layer  25  of the light-receiving element  20   a  is contact to the wiring  40   a  through the contact layer  61 . Similarly, the n-type semiconductor layer  25  of the light-receiving element  20   b  is contact to the wiring  40   c  through the contact layer  61 . The contact layer  61  is, for example, made of AuGe/Au. The insulating film  60  covers the surface of the dummy mesas  30   a  to  30   c  and covers the semiconductor substrate  10  between the light-receiving elements and the dummy mesas. 
     The wiring  40   a  on the lower mesa  21  of the light-receiving element  20   a  acts as the lower electrode  24  of the light-receiving element  20   a . The wiring  40   b  on the contact layer  28  of the light-receiving element  20   a  acts as the upper electrode  23  of the light-receiving element  20   a . The wiring  40   c  on the lower mesa  21  of the light-receiving element  20   b  acts as the lower electrode  24  of the light-receiving element  20   b . The wiring  40   d  on the contact layer  28  of the light-receiving element  20   b  acts as the upper electrode  23  of the light-receiving element  20   b.    
       FIG. 7  illustrates a cross sectional view taken along a line D-D of  FIG. 4 . As illustrated in  FIG. 7 , the light-receiving elements  20   a  and  20   b  are adjacent to each other. Therefore, the lens  11  of the light-receiving element  20   a  is adjacent to another lens  11  of the light-receiving element  20   b.    
       FIG. 8A  illustrates a plane view of the back face side of the semiconductor light-receiving device  100 . The sidewall  13  and the upper edge  13   a  are omitted in this Figure. A radius of the lens  11  is expressed as a radius “r”. The radius “r” is, for example, 20 μm to 40 μm. As an example, the radius “r” is 30 μm. A distance “L” between the lens  11  and the lower edge  13   b  of the sidewall  13  of the concave region  12  is a clearance for accurately forming the lens  11  by the milling. With the clearance, a milling line with a small incidence angle is sufficiently radiated to the lens  11 . A distance between the two lenses  11  is smaller than the radius “r” and the distance “L”. Therefore, a whole circumference of the lens  11  is not surrounded by the sidewall  13 . That is, the sidewall  13  is not formed between the lenses  11 . 
     In the embodiment, the two light-receiving portions are adjacent to each other. Two circles formed by the sidewalls  13  of the concave regions  12  surrounding the lenses  11  overlap with each other between the two lenses  11 . That is, there is no sidewall  13  separating the two lenses  11  between the lenses  11 . When a line segment connecting the lens  11  and another lens  11  (a center of the lens  11  and a center of another lens  11 ) is expressed as a line segment “C 1 ”, a length “W” of the line segment “C 1 ” is set to be smaller than 2(r+L). A midpoint of the line segment “C 1 ” is expressed as “H”. A line passing a center of the lens  11  at a right angle with the line segment “C 1 ” is expressed as a line “C 2 ”. The sidewall  13  is concentrically formed at a position having a distance of “r+L” from the center of the lens  11  in the outside of the region sandwiched by the line C 2  of the lens  11  and another line C 2  of another lens  11 . Thus, the distance “L” is a distance between the lower edge  13   b  of the sidewall  13  surrounding the lens  11  and the lens  11  at the opposite side of another lens  11 . The distance “L” is, for example, 30 μm or more. As an example, the distance “L” is 40 μm. 
     In the embodiment, as illustrated in  FIG. 8A , a length of a line segment connecting a midpoint H of the line segment C 1  connecting the lens  11  and another lens  11  (the center of the lens  11  and the center of another lens  11 ) and the lower edge  13   b  surrounding each lens  11  at a right angle is expressed as “A”. The length “A” is set to be larger than {(r+L) 2 −(W/2) 2 } 1/2 . Therefore, there is no region projecting with a small angle in the concave region  12  between the two lenses  11 . Thus, the defect of the insulating film is restrained. 
       FIG. 8B  illustrates another example of the back face of the semiconductor light-receiving device  100 . As illustrated in  FIG. 8B , the lower edge  13   b  of the sidewall  13  of the concave region  12  surrounding the two lenses  11  may have a straight line shape between the two lenses  11 . 
       FIG. 9  illustrates a ease where four light-receiving elements are aligned in a single row. In this case, the length “W” of the line segment C 1  connecting the lens  11  and another lens  11  (the center of the lens  11  and the center of another lens  11 ) is set to be smaller than “r+L”. And, the length “A” of the line segment connecting the midpoint “H” of the line segment C 1  and the lower edge  13   b  of the sidewall  13  of the concave region  12  surrounding each lens  11  at a right angle is set to be larger than {(r+L) 2 −(W/2) 2 } 1/2 . Thus, the defect of the insulating film is restrained. 
       FIG. 10A  through  FIG. 10C  illustrate another example of the back face of the semiconductor light-receiving device  100 .  FIG. 10A  illustrates a plane view of the back face side of the semiconductor light-receiving device  100 .  FIG. 10B  illustrates a cross sectional view taken along a line A-A or a line B-B of  FIG. 10A .  FIG. 10C  illustrates a cross sectional view taken along a line C-C of  FIG. 10A . 
     As illustrated in  FIG. 10A  and  FIG. 10C , a recess  14   a  is formed on one side of an extended line of the line segment C 1  connecting the center of the lens  11  and the center of another lens  11 , and a recess  14   b  is formed on the other side of the extended line. The recesses  14   a  and  14   b  are exposed in the side face (a dicing line region) of the semiconductor substrate  10 . It is preferable that the recesses  14   a  and  14   b  are symmetrically with respect to the extended line of the line segment C 1 . 
     As illustrated in  FIG. 10A  and  FIG. 10B , a recess  15   a  is formed on one side of an extended line of the line C 2  passing through the center of the lens  11  at a right angle with respect to the line segment C 1 , and a recess  15   b  is formed on the other side of the extended line. A recess  16   a  is formed on one side of an extended line of the line C 2  passing through the center of another lens  11  at a right angle with the line segment C 1 , and a recess  16   b  is formed on the other side of the extended line. The recesses  15   a ,  15   b ,  16   a  and  16   b  are exposed in the side face (the dicing line region) of the semiconductor substrate  10 . It is preferable that the recesses  15   a ,  15   b ,  16   a  and  16   b  are symmetrically with respect to the extended line of the line C 2 . It is preferable that the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  are formed in a region without the insulating film  60  on the back face of the semiconductor substrate  10 . 
     An angle between a bottom face and a sidewall of the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  should be determined appropriately. When the angle is close to verticality, a trouble such as a defect of crystal or a shortage of resist coverage in a subsequent process tends to occur. When the angle is small, an area of a slope region gets larger in a whole chip. The angle is appropriately determined in view of the reasons. As an example, the angles of the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  are equal to each other. 
     In the structures of  FIG. 10A  through  FIG. 10C , the center of the lens  11  is positioned at an intersection point of a line connecting the recesses  14   a  and  14   b  and a line connecting the recesses  15   a  and  15   b . The center of another lens  11  is positioned at an intersection point of a line connecting the recesses  14   a  and  14   b  and a line connecting the recesses  16   a  and  16   b . Therefore, when a positional relation between the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  is detected, it is possible to determine the positions of the lens  11  and another lens  11 . 
     When the recesses  14   a  and  14   b  are symmetrically with respect to the extended line of the line segment C 1 , a line connecting a center of the recess  14   a  in a width direction and a center of the recess  14   b  in a width direction overlaps with the line segment C 1 . When the recesses  15   a ,  15   b ,  16   a  and  16   b  are symmetrically with respect to the extended line of the line C 2 , a line connecting a center of the recess  15   a  in a width direction and a center of the recess  15   b  in a width direction overlaps with the line segment C 2 , and a line connecting a center of the recess  16   a  in a width direction and a center of the recess  16   b  in a width direction overlaps with another line C 2 . Therefore, it is possible to determine the positions of the lens  11  and another lens  11  with use of the positional relation of the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b.    
     A region between the concave region  12  and the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  is not grinded. Therefore, the region is positioned at a higher position than the lens  11  and another lens  11 . Therefore, when viewed from each recess, the lens  11  and another lens  11  are out of sight. However, it is possible to determine the positions of the lens  11  and another lens  11 , when a position of a mark for position determination and the positions of the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  are matched even if the lens  11  and another lens  11  are out of sight. 
       FIG. 11A  through  FIG. 11H  illustrate a forming flow of the lens and the recess. As illustrated in  FIG. 11A , the semiconductor substrate  10  is prepared. Next, as illustrated in  FIG. 11B , a resist  101  is formed on regions of the lens  11  and another lens  11  and the region between the concave region  12  and the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  on the back face of the semiconductor substrate  10  by performing a photo lithography process. Next, as illustrated in  FIG. 11C , the resist  101  is rounded by performing a resist cure process. 
     Next, as illustrated in  FIG. 11D , a resist  102  is formed on the resist  101  on the region between the concave region  12  and the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  by performing another photo lithography process. Next, as illustrated in  FIG. 11E , the exposed region of the resists  101  and  102  is subjected to an etching process such as an ion milling. Thus, the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  are formed. The region of the resist  101  on the lens  11  and another lens  11  are removed. And, the lens  11  and another lens  11  are formed on the back face of the semiconductor substrate  10 . On the other hand, a region of the resist  101  on the region between the concave region  12  and the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  remains. In  FIG. 11E , the recesses  14   a  and  14   b  are illustrated. 
     Next, as illustrated in  FIG. 11F , the remaining resist  101  is removed. Next, as illustrated in  FIG. 11G , the insulating film  60  is formed on the exposed region of the back face of the semiconductor substrate  10 . Next, as illustrated in  FIG. 11H , the region of the insulating film  60  on the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  are removed by performing a resist coating process, a patterning process and an etching process. Thus, a dicing line region is formed. 
     Next, a description will be given of a mounting of the semiconductor light-receiving device  100 .  FIG. 12  illustrates an optical receiver  300  on which the semiconductor light-receiving device  100  is mounted. As illustrated in  FIG. 12 , a first optical fiber  210  for inputting a signal light (S) and a second optical fiber  212  for inputting a local oscillation light (LO) are connected to the optical receiver  300 . The optical fibers may be a polarization maintaining optical fiber. 
     In an optical system connected to the first optical fiber  210 , a first lens  220 , a VOA  222 , a second lens  224 , and a PBS  226  are arranged in this order from the first optical fiber  210  side. The first lens  220  and the second lens  224  are a collecting lens. The VOA (Variable Optical Attenuator)  222  is an example of an optical attenuator that is capable of changing a pass amount of a light, and adjusts a light amount of a signal light reaching the second lens  224  from the first lens  220 . The PBS (Polarizing Beam Splitter)  226  disperses the signal light (S) into a polarized wave (SX) in an X-direction and a polarized wave (SY) in a Y-direction. The dispersed signal light is input into an optical hybrid  240 . 
     In an optical system connected to the second optical fiber  212 , a third lens  230 , a fourth lens  232  and a BS  234  are arranged in this order from the second optical fiber  212  side. The BS (Beam Splitter)  234  disperses the oscillation light (LO) having passed through the third lens  230  and the fourth lens  232  into a polarized wave (LO_X) and a polarized wave (LO_Y). The dispersed oscillation light is input into the optical hybrid  240 . 
     The optical hybrid  240  is an optical circuit for delaying, dispersing and combining an input light, and is structured with a quartz-based PLC (Planar Lightwave Circuit) or the like. The signal light SX is combined with the oscillation lights LO_X and LO_Y by the optical hybrid  240 . After that, the signal light SX is divided into an In-Phase component I and a Quadrature component Q, and is output as an optical signal X-Ip, an optical signal X-In, an optical signal X-Qp and an optical signal X-Qn. The signal light SY is combined with the oscillation lights LO_X and LO_Y by the optical hybrid  240 . After that, the signal light SY is divided into an In-phase component I and a Quadrature component Q, and is output as an optical signal Y-Ip, an optical signal Y-In, an optical signal Y-Qp and an optical signal Y-Qn. The “p” and “n” respectively means positive and negative. For example, The X-Ip means an output signal light of a positive component of the In-Phase component of the signal light SX. 
     Optical detection portions  242   a  to  242   d  including a photodiode and a trans-impedance amplifier are provided across the first lens  220  and the second lens  224  from the optical hybrid  240 . Interconnection substrates  244  and  246  are provided around the optical hybrid  240 . 
       FIG. 13  illustrates an enlarged view of the optical detection portions  242   a  to  242   d . As illustrated in  FIG. 13 , the optical detection portions  242   a  to  242   d  have a TIA  50  and the semiconductor light-receiving device  100 . A recess  240   a  is formed as a mark at a position where the optical hybrid  240  faces with the back face of the semiconductor light-receiving device  100 . It is possible to match the position of a waveguide of the optical hybrid  240  and the position of the light-receiving element  20  of the semiconductor light-receiving device  100 , when the position of the recesses  14   a ,  14   b ,  15   a ,  15   b ,  16   a  and  16   b  are determined with use of the recess  240   a  as a mark. When the lens  11  is located between the optical hybrid  240  and the light-receiving element  20 , an active alignment can be achieved. 
     The present invention is not limited to the specifically disclosed embodiments and variations but may include other embodiments and variations without departing from the scope of the present invention.