photoelectric conversion element

Abstract

This photoelectric conversion element 1 comprises: a photoelectric conversion unit 30 that receives light and generates an electrical charge; an electrical charge accumulation detector 70 that accumulates electric charges received from the photoelectric conversion unit 30; an optical confinement unit 50 having a back-surface-side reflection layer 50B and a front-surface-side reflection layer 50F provided on the photoelectric conversion unit 30, the optical confinement unit 50 confining light in the photoelectric conversion unit 30 so that the light reciprocates in the photoelectric conversion unit 30; and a light direction conversion unit 60 including an outer lens 10 positioned on the back-surface-side-reflection-layer 50B side, the light direction conversion unit 60 determining the direction in which the light in the photoelectric conversion unit 30 advances. The light direction conversion unit 60 is positioned on the outer side of a region sandwiched by the back-surface-side reflection layer 50B and the front-surface-side reflection layer 50F, and causes light to advance in a direction away from the optical axis Z of the outer lens 10 each time reflection of the light between the back-surface-side reflection layer 50B and the front-surface-side reflection layer 50F is repeated.

Description

[Technical Field]

[0001] The present invention relates to a photoelectric conversion element. [Background technology]

[0002] The spectrum of sunlight has a large drop in intensity around the wavelength of 940 nm due to the influence of absorption by water vapor. Imaging devices such as TOF cameras use this wavelength band to reduce the influence of sunlight. Silicon is often used as a material to construct imaging devices. The light absorption coefficient of silicon is about 1 / 10 of that of visible light in the 940 nm wavelength band. In other words, the light absorption efficiency is low. For example, if the thickness (x) of the photoelectric conversion unit of an imaging device is set to 5 × 10 -4 cm (5 μm). This thickness is that of a typical CMOS image sensor. The optical absorption coefficient (α) of silicon in the wavelength band of 940 nm is set to 250 cm -1 According to formula (1), the assumed thickness of the photoelectric conversion part (x = 5 × 10 -4 cm) and optical absorption coefficient (α = 250 cm -1 The optical absorptance (B) obtained from the

number

[0003] [Patent Document 1] Special Publication No. 2018-525837 [Patent Document 2] Japanese Patent Application Publication No. 2019-114642 Summary of the Invention [Problem to be solved by the invention]

[0004] The absorbance in silicon is proportional to the distance traveled by light inside the silicon (optical path length). Therefore, even if the optical absorption coefficient (α) is low, the amount of light absorbed by silicon can be increased by ensuring a sufficient optical path length in the photoelectric conversion unit. For example, the elements disclosed in Patent Documents 1 and 2 have a structure in which light that has passed through the photoelectric conversion unit is returned to the photoelectric conversion unit. The optical path length obtained by these structures is longer than when light passes through the photoelectric conversion unit only once. However, in this technical field, there has been a demand for even higher sensitivity in imaging devices equipped with photoelectric conversion elements.

[0005] Therefore, the present invention provides a photoelectric conversion element capable of increasing sensitivity. [Means for solving the problem]

[0006] A photoelectric conversion element according to one embodiment of the present invention comprises a photoelectric conversion unit that receives light and generates an electric charge, a charge accumulation detection unit that accumulates the electric charge received from the photoelectric conversion unit, a first reflective layer provided on the first surface side of the photoelectric conversion unit and including an opening for receiving light, and a second reflective layer provided on the second surface side of the photoelectric conversion unit opposite the first surface, a light confinement unit that confines light in the photoelectric conversion unit so that the light travels back and forth in the photoelectric conversion unit, and a light direction conversion unit that includes a first lens arranged on the first surface side and determines the direction of travel of light in the photoelectric conversion unit, wherein the light direction conversion unit is arranged outside the region sandwiched between the first surface and the second surface and causes light to travel in a direction away from the optical axis of the first lens each time the light is repeatedly reflected between the first surface and the second surface.

[0007] In this photoelectric conversion element, light is reflected multiple times between the first and second reflective layers. A photoelectric conversion section is present between the first and second reflective layers. In other words, light travels back and forth through the photoelectric conversion section multiple times. This extends the optical path length of light in the photoelectric conversion section, allowing the photoelectric conversion section to fully absorb the light. As a result, sensitivity can be increased.

[0008] In one embodiment, in a cross-sectional shape of the first lens including the optical axis, a line segment indicating the surface that accepts light may include a first curved portion and a second curved portion that is farther from the optical axis than the first curved portion, and the curvature of the second curved portion may be smaller than the curvature of the first curved portion. With this configuration, it is possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0009] In one embodiment of the photoelectric conversion element, in a cross section of the first lens including the optical axis, a line segment representing the light-receiving surface may include a portion defined as an arc. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0010] In one embodiment of the photoelectric conversion element, in a cross section of the first lens including the optical axis, a line segment representing the light-receiving surface may include a portion defined as a parabola. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0011] In one embodiment of the photoelectric conversion element, in a cross section of the first lens including the optical axis, a line segment indicating the surface that accepts light may include a first straight line portion and a second straight line portion that is farther from the optical axis than the first straight line portion, and a second inclination angle between an imaginary reference axis that is perpendicular to the optical axis and the second straight line portion may be larger than the first inclination angle between the imaginary reference axis and the first straight line portion. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0012] In one embodiment of the photoelectric conversion element, the first lens may have a shape that is rotationally symmetric about the optical axis. With this configuration, the traveling direction of light can be made radial when the photoelectric conversion unit is viewed in a plan view.

[0013] In one embodiment of the photoelectric conversion element, the first lens may have a cross-sectional shape that is elongated in a direction perpendicular to the optical axis, and this configuration allows the light traveling direction to be set to a desired direction when the photoelectric conversion unit is viewed in a plan view.

[0014] In one embodiment of the photoelectric conversion element, the light direction conversion unit may include, in addition to the first lens, a second lens disposed between the first lens and the first surface. This configuration also reduces the component of light that enters the photoelectric conversion unit through the opening in the first reflective layer and then exits the opening again. This further increases sensitivity.

[0015] In one embodiment, in a cross-sectional shape of the second lens including the optical axis, a line segment indicating the surface that accepts light may include a third curved portion and a fourth curved portion that is farther from the optical axis than the third curved portion, and the curvature of the fourth curved portion may be smaller than the curvature of the third curved portion. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0016] In one embodiment of the photoelectric conversion element, in a cross section of the second lens including the optical axis, the line segment representing the light-receiving surface may include a portion defined as an arc. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0017] In one embodiment of the photoelectric conversion element, in a cross section of the second lens including the optical axis, the line segment representing the light-receiving surface may include a portion defined as a parabola. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0018] In one embodiment, in a cross-sectional shape of the second lens including the optical axis, the line segment indicating the light-receiving surface may include a third straight line portion and a fourth straight line portion farther from the optical axis than the third straight line portion, and a fourth inclination angle between an imaginary reference axis line perpendicular to the optical axis and the fourth straight line portion may be larger than the third inclination angle between the imaginary reference axis line and the third straight line portion. This configuration also makes it possible to generate light that travels in a direction away from the optical axis of the first lens each time light is repeatedly reflected between the first surface and the second surface.

[0019] In one embodiment of the photoelectric conversion element, the light direction conversion unit may include a reflector disposed on the second surface side. This configuration also reduces the component of light that enters the photoelectric conversion unit through the opening in the first reflective layer and then exits the opening again. This further increases sensitivity.

[0020] In one embodiment of the photoelectric conversion element, the light confinement unit may further include a first partition wall surrounding the photoelectric conversion unit, one end face of the first partition wall cooperating with the first reflective layer to sandwich a part of the photoelectric conversion unit, and the other end face of the first partition wall may be flush with the second surface of the photoelectric conversion unit. This configuration can further improve the confinement of light in the photoelectric conversion unit.

[0021] In one embodiment of the photoelectric conversion element, the light confinement unit may further include a second partition wall surrounding the photoelectric conversion unit, one end face of the second partition wall being flush with the first face of the photoelectric conversion unit, and the other end face of the second partition wall cooperating with the second reflective layer to sandwich a part of the photoelectric conversion unit. This configuration can further confine light in the photoelectric conversion unit and also provide a path for extracting charges generated in the photoelectric conversion unit.

[0022] In one embodiment, the light confinement unit may further include a third partition wall surrounding the photoelectric conversion unit, one end face of the third partition wall being flush with the first face of the photoelectric conversion unit and the other end face of the third partition wall being flush with the second face of the photoelectric conversion unit. This configuration allows light to be reliably confined in the photoelectric conversion unit.

[0023] In one embodiment of the photoelectric conversion element, the photoelectric conversion unit may include a portion overlapping with the opening of the first reflective layer, and the charge accumulation detection unit may not include a portion overlapping with the opening of the first reflective layer.

[0024] In one embodiment of the photoelectric conversion element, the light confinement portion may include, in a pixel region having a photoelectric conversion region including a pn junction formed by the photoelectric conversion portion when viewed from the direction of light incidence, and a charge accumulation detection region including a charge accumulation detection portion, an outer partition portion surrounding the photoelectric conversion region and the charge accumulation detection region so as to confine light incident from the opening.

[0025] In one embodiment of the photoelectric conversion element, one end face of the outer partition wall may be in contact with the semiconductor region that forms the pn junction, and the other end face of the outer partition wall may be flush with the second surface of the photoelectric conversion body.

[0026] In one embodiment of the photoelectric conversion element, one end face of the outer partition wall may be flush with the first surface of the photoelectric conversion body, and the other end face of the outer partition wall may be in contact with a semiconductor region that forms a pn junction.

[0027] In one embodiment of the photoelectric conversion element, one end face of the outer partition wall may be flush with a first surface of the photoelectric conversion body, and the other end face of the outer partition wall may be flush with a second surface of the photoelectric conversion body.

[0028] In one embodiment of the photoelectric conversion element, the light confinement portion may include an inner partition portion that is provided between the photoelectric conversion region and the charge accumulation detection region when viewed from the direction of light incidence and optically separates the charge accumulation detection region from the photoelectric conversion region.

[0029] In one embodiment of the photoelectric conversion element, one end face of the inner partition may be in contact with the semiconductor region that forms the pn junction, and the other end face of the inner partition may be flush with the second surface of the photoelectric conversion body.

[0030] In one embodiment, one end face of the inner partition may be flush with the first surface of the photoelectric conversion body, and the other end face of the inner partition may be in contact with a semiconductor region that forms a pn junction.

[0031] In one embodiment of the photoelectric conversion element, one end face of the inner partition may be flush with the first surface of the photoelectric conversion body, and the other end face of the inner partition may be flush with the second surface of the photoelectric conversion body. [Effects of the Invention]

[0032] According to the present invention, a photoelectric conversion element capable of increasing sensitivity is provided. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is a cross-sectional view of a photoelectric conversion element according to the first embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the DTI having the first configuration shown in FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view of the DTI of the second configuration. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the DTI of the third configuration. [Figure 5] Figure 5(a) is a contour map showing the shape of the lens main surface of the outer lens, Figure 5(b) is the cross-sectional shape of the outer lens at the X-X' cross section shown in Figure 5(a), and Figure 5(c) is the cross-sectional shape of the outer lens at the Y-Y' cross section shown in Figure 5(a). [Figure 6] FIG. 6 is a cross-sectional view illustrating the confinement of light in a photoelectric conversion element. [Figure 7] FIG. 7 is a perspective view showing the shape of the outer lens and the irradiated area of ​​the shaped light. [Figure 8] FIG. 8 is a diagram illustrating the shape of the outer lens of the first modification. [Figure 9] FIG. 9 is a diagram showing a photoelectric conversion element to which the outer lens of the first modification is applied. [Figure 10] FIG. 10 is a diagram illustrating the shape of the outer lens of the second modification. [Figure 11]FIG. 11 is a diagram showing a photoelectric conversion element to which the outer lens of the second modification is applied. [Figure 12] FIG. 12 is a diagram showing a photoelectric conversion element to which the outer lens of the third modification is applied. [Figure 13] FIG. 13 is a diagram illustrating the shape of the outer lens of the fourth modification. [Figure 14] FIG. 14 is a diagram showing a photoelectric conversion element to which the outer lens of the fourth modification is applied. [Figure 15] FIG. 15 is a cross-sectional view of a photoelectric conversion element according to the second embodiment. [Figure 16] FIG. 16 is a cross-sectional view of a photoelectric conversion element according to the third embodiment. [Figure 17] FIG. 17 is a cross-sectional view of a photoelectric conversion element according to the fourth embodiment. [Figure 18] FIG. 18 is a cross-sectional view of a photoelectric conversion element according to the fifth embodiment. [Figure 19] FIG. 19 is a cross-sectional view of a photoelectric conversion element according to the sixth embodiment. [Figure 20] FIG. 20 is a perspective view showing the shape of an outer lens included in a photoelectric conversion element according to the seventh embodiment and an irradiation area of ​​shaped light. [Figure 21] Figures 21(a) and 21(c) are diagrams showing the cross-sectional shape of an outer lens of a different shape in the seventh embodiment, and Figure 21(b) is a diagram showing the light irradiation area formed by an outer lens of a different shape in the seventh embodiment. [Figure 22] Figure 22(a) is a contour map showing the shape of the lens main surface of the outer lens of the eighth embodiment, Figure 22(b) shows the cross-sectional shape of the outer lens in the X1-X1' cross section and the X2-X2' cross section, and Figure 22(c) shows the cross-sectional shape of the outer lens in the Y1-Y1' cross section and the Y2-Y2' cross section. [Figure 23] FIG. 23 is a diagram showing an irradiation area of ​​light formed by a modified example of the outer lens of the eighth embodiment. [Figure 24] FIG. 24 is a cross-sectional view of a photoelectric conversion element according to the ninth embodiment. [Figure 25]FIG. 25(a) is a cross-sectional view showing a first step for manufacturing the photoelectric conversion element of the ninth embodiment, and FIG. 25(b) is a cross-sectional view showing a second step. [Figure 26] FIG. 26(a) is a cross-sectional view showing a third step for manufacturing the photoelectric conversion element of the ninth embodiment, and FIG. 26(b) is a cross-sectional view showing a fourth step. [Figure 27] FIG. 27(a) is a cross-sectional view showing a fifth step for manufacturing the photoelectric conversion element of the ninth embodiment, and FIG. 27(b) is a cross-sectional view showing a sixth step. [Figure 28] FIG. 28(a) is a cross-sectional view showing a seventh step for manufacturing the photoelectric conversion element of the ninth embodiment, and FIG. 28(b) is a cross-sectional view showing an eighth step. [Figure 29] FIG. 29(a) is a cross-sectional view showing a first step in another method for manufacturing the photoelectric conversion element of the ninth embodiment, and FIG. 29(b) is a cross-sectional view showing a second step. [Figure 30] FIG. 30(a) is a cross-sectional view showing a third step in another method for manufacturing the photoelectric conversion element of the ninth embodiment, and FIG. 30(b) is a cross-sectional view showing a fourth step. [Figure 31] FIG. 31 is a cross-sectional view showing a fifth step in another method for manufacturing the photoelectric conversion element of the ninth embodiment. [Figure 32] FIG. 32 is a cross-sectional view of a photoelectric conversion element according to the tenth embodiment. [Figure 33] FIG. 33 is a plan view of a photoelectric conversion element according to the eleventh embodiment. [Figure 34] FIG. 34 is a plan view showing the structure of a photoelectric conversion element according to the eleventh embodiment and an irradiation area of ​​shaped light. [Figure 35] FIG. 35 is a plan view showing a first arrangement example of photoelectric conversion elements according to the eleventh embodiment. [Figure 36] FIG. 36 is a plan view showing a second arrangement example of photoelectric conversion elements according to the eleventh embodiment. [Figure 37] FIG. 37 is a plan view showing the structure of a photoelectric conversion element according to the eleventh embodiment and an irradiation area of ​​shaped light. [Figure 38]FIG. 38 is a plan view of a photoelectric conversion element according to the twelfth embodiment. [Figure 39] FIG. 39 is a plan view showing the structure of a photoelectric conversion element according to the twelfth embodiment and an irradiation area of ​​shaped light. [Figure 40] FIG. 40 is a diagram for explaining the analytical model used in calculation examples 1, 2, and 3. [Figure 41] FIG. 41 is a perspective view of the outer lens used in calculation example 1. [Figure 42] FIG. 42 is a perspective view of the outer lens used in calculation example 2. [Figure 43] FIG. 43 is a perspective view of the outer lens used in calculation example 3. [Figure 44] FIG. 44 is a first contour diagram showing the results of calculation example 1. [Figure 45] FIG. 45 is a second contour diagram showing the results of calculation example 1. [Figure 46] FIG. 46 is a first contour diagram showing the results of calculation example 2. [Figure 47] FIG. 47 is a second contour diagram showing the results of calculation example 2. [Figure 48] FIG. 48 is a diagram showing rays resulting from calculation example 2. [Figure 49] FIG. 49 is another diagram showing the light rays resulting from calculation example 2. [Figure 50] FIG. 50 is a first contour diagram showing the results of calculation example 3. [Figure 51] FIG. 51 is a diagram showing rays resulting from calculation example 3. [Figure 52] FIG. 52 is another diagram showing the light rays resulting from calculation example 3. [Figure 53] 53(a) is a second contour diagram of Calculation Example 3, and FIG. 53(b) is a third contour diagram of Calculation Example 3. [Figure 54] 54(a) is the fourth contour diagram of Calculation Example 3, and FIG. 54(b) is the fifth contour diagram of Calculation Example 3. [Figure 55]55(a) is the sixth contour diagram of Calculation Example 3, and FIG. 55(b) is the seventh contour diagram of Calculation Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0034] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0035] 1 is a so-called back-illuminated pixel. The photoelectric conversion element 1 has an outer lens 10 (first lens, light direction conversion unit 60), a main spacer 20, a photoelectric conversion unit 30, a wiring unit 40, and a light confinement unit 50.

[0036] The outer lens 10, together with the main spacer 20, determines the direction of light R incident on the photoelectric conversion unit 30. In other words, the outer lens 10, together with the main spacer 20, constitutes the light direction conversion unit 60. The outer lens 10 has a lens entrance surface 11 and a lens exit surface 12. The refractive index of the outer lens 10 is, for example, n=1.58. Details of the outer lens 10 will be described later.

[0037] The main spacer 20 determines the distance from the outer lens 10 to the photoelectric conversion unit 30. The refractive index of the main spacer 20 is, for example, n=1.58. That is, the refractive index of the main spacer 20 is the same as the refractive index of the outer lens 10. The main spacer 20 has a spacer incident surface 21 and a spacer exit surface 22.

[0038] In the photoelectric conversion element 1 of this embodiment, the incident position and incident angle of light relative to the photoelectric conversion element 30 are important for causing multiple reflections in the photoelectric conversion element 30. These incident position and incident angle are determined depending on the shape and characteristics (refractive index) of the optical components through which the light passes. In the case of the photoelectric conversion element 1, these correspond to the outer lens 10 and the main spacer 20. That is, the photoelectric conversion element 1 has a light direction conversion element 60 constituted by the outer lens 10 and the main spacer 20. That is, the light direction conversion element 60 is configured to guide light to the photoelectric conversion element 30 so as to cause multiple reflections. Since the light direction conversion element 60 is configured to guide light to the photoelectric conversion element 30, it is disposed outside the photoelectric conversion element 30.

[0039] The photoelectric conversion unit 30 absorbs light R. The photoelectric conversion unit 30 generates charges according to the absorbed light R. The photoelectric conversion unit 30 has a back surface 30B (first surface) and a front surface 30F (second surface). The photoelectric conversion unit 30 is made of silicon. For silicon, the refractive index of the photoelectric conversion unit 30 is n=3.64. That is, the refractive index of the photoelectric conversion unit 30 is greater than the refractive index of the outer lens 10. Furthermore, the refractive index of the photoelectric conversion unit 30 is greater than the refractive index of the main spacer 20.

[0040] The photoelectric conversion unit 30 includes a p+-type first semiconductor region 31, a p--type second semiconductor region 32, an n--type third semiconductor region 33, and a p+-type fourth semiconductor region 34. The first semiconductor region 31 constitutes the back surface 30B of the photoelectric conversion unit 30. The first semiconductor region 31 is in contact with the second semiconductor region 32. The second semiconductor region 32 is in contact with the first semiconductor region 31, the third semiconductor region 33, and the fourth semiconductor region 34, respectively. The third semiconductor region 33 is in contact with the second semiconductor region 32 and the fourth semiconductor region 34. The second semiconductor region 32 and the third semiconductor region 33 constitute a pn junction and function as a photodiode. In other words, the photoelectric conversion unit 30, made of silicon that absorbs light R, includes a photodiode. The photodiode preferably has a buried photodiode structure, but may also be a light-receiving element such as a photogate. The fourth semiconductor region 34 constitutes the front surface 30F of the photoelectric conversion unit 30. The fourth semiconductor region 34 is in contact with the second semiconductor region 32 and the third semiconductor region 33. The fourth semiconductor region 34 is in contact with the back surface 40B of the wiring portion 40.

[0041] The light confinement unit 50 includes a back-side reflective layer 50B (first reflective layer), a front-side reflective layer 50F (second reflective layer), an anti-reflective layer 51, and a DTI 52 (Deep Trench Isolation, first partition wall). The anti-reflective layer 51 is formed on the back surface 30B of the photoelectric conversion unit 30. The anti-reflective layer 51 is made of, for example, silicon oxide (SiO2) and silicon nitride (SiN). The anti-reflective layer 51 covers the entire pixel region defined by the DTI 52.

[0042] The back-side reflective layer 50B and the front-side reflective layer 50F are made of metal. That is, the back-side reflective layer 50B and the front-side reflective layer 50F are metal layers. The back-side reflective layer 50B and the front-side reflective layer 50F are made of, for example, aluminum (Al), copper (Cu), or tungsten (W). The back-side reflective layer 50B is formed on the antireflection layer 51. The back-side reflective layer 50B includes an incident opening 50B1 and a boundary opening 50B2. The incident opening 50B1 intersects with the optical axis Z. The position of the boundary opening 50B2 corresponds to the position of the DTI 52. The antireflection layer 51 is exposed through the incident opening 50B1 and the boundary opening 50B2. The antireflection layer 51 contacts the main spacer 20 through the incident opening 50B1 and the boundary opening 50B2. The front-side reflective layer 50F is formed inside the wiring portion 40.

[0043] The DTI 52 optically separates adjacent photoelectric conversion elements 1. The DTI 52 is formed by filling a trench formed in the silicon substrate that constitutes the photoelectric conversion unit 30 with a material having a lower refractive index than silicon (refractive index 3.64 @ 940 nm). An example of a material with a lower refractive index is SiO2 (refractive index approximately 1.45). As a result, the DTI 52 functions to reflect light R. In other words, the DTI 52 totally reflects light R that is incident obliquely.

[0044] The DTI 52 surrounds the third semiconductor region 33. The width from one DTI 52 to the other DTI 52 is greater than the width of the third semiconductor region 33. FIG. 2 is an enlarged view of one DTI 52. The DTI 52 is formed in the second semiconductor region 32 and the fourth semiconductor region 34. A front-side end face 52s of the DTI 52 contacts the wiring unit 40. The DTI 52 penetrates the fourth semiconductor region 34. An electrode 43p is provided at a portion of the wiring unit 40 where the front-side end face 52s contacts. The electrode 43p electrically connects the DTI 52 to the front-side reflective layer 50F. The DTI 52 extends from the front surface of the second semiconductor region 32 (the front surface 30F of the photoelectric conversion unit 30) toward the back surface of the second semiconductor region 32 (the back surface 30B of the photoelectric conversion unit 30). The DTI 52 having such a structure is formed by processing from the front surface 30F of the photoelectric conversion unit 30. A back surface end surface 52t of the DTI 52 is located in the second semiconductor region 32. A part of the second semiconductor region 32 exists between the back surface end surface 52t and the first semiconductor region 31. In other words, the DTI 52 does not penetrate the second semiconductor region 32.

[0045] The DTI 52 is not limited to the configuration shown in Fig. 2. The DTI 52 can adopt three configurations, including the first configuration shown in Fig. 2, regarding the relationship between the back-side end face 52t and the back surface 30B of the photoelectric conversion unit 30 and the relationship between the front-side end face 52s and the front surface 30F of the photoelectric conversion unit 30.

[0046] FIG. 3 is an enlarged view of a DTI 52A (third partition wall) having a second configuration. In the DTI 52A having the second configuration, the back-side end face 52t is flush with the back surface 30B of the photoelectric conversion unit 30, and the front-side end face 52s is flush with the front surface 30F of the photoelectric conversion unit 30. That is, the DTI 52A penetrates the photoelectric conversion unit 30. The back-side end face 52t contacts the antireflection layer 51. Furthermore, the back-side reflective layer 50B is not provided in a small region above the back-side end face 52t. That is, the back-side reflective layer 50B has a boundary opening 50B2, which is a gap. The front-side end face 52s is electrically connected to an electrode 43p exposed on the back surface 40B of the wiring unit 40. The DTI 52A optically isolates the interior of the photoelectric conversion unit 30. Therefore, the DTI 52A having the second configuration is advantageous in terms of increasing light absorption efficiency. Furthermore, the DTI 52A electrically isolates the inside of the photoelectric conversion unit 30. In other words, the DTI 52A prevents the movement of charges.

[0047] FIG. 4 is an enlarged view of a DTI 52B (second partition wall) having a third configuration. In the DTI 52B having the third configuration, the back surface end face 52t is flush with the back surface 30B of the photoelectric conversion body 30. The back surface end face 52t is in contact with the antireflection layer 51. On the other hand, the front surface end face 52s is not flush with the front surface 30F of the photoelectric conversion body 30. The front surface end face 52s is spaced from the front surface 30F of the photoelectric conversion body 30. In other words, the DTI 52B does not penetrate the photoelectric conversion body 30. Such a DTI 52B is formed by processing from the back surface 30B of the photoelectric conversion body 30. The front surface end face 52s is in contact with the second semiconductor region 32 of the photoelectric conversion body 30. As a result, the second semiconductor region 32 of the photoelectric conversion body 30 is not separated below the front surface end face 52s. This portion 32s of the second semiconductor region 32 can be used as a path for charge transfer. In other words, the region (32s) not penetrated by the DTI 52B can be used to transfer charge to the charge accumulation detector 70 (see FIG. 33) via the MOS transistor structure. Note that light R may leak from the region not penetrated by the DTI 52B. In this case, appropriate measures should be taken to prevent the leakage of light R.

[0048] Referring again to FIG. 1, the wiring unit 40 has a back surface 40B and a front surface 40F. The wiring unit 40 has a first wiring layer 41, a second wiring layer 42, electrodes 43 and 43p, and a silicon oxide region 44. The silicon oxide region 44 forms the back surface 40B and the front surface 40F of the wiring unit 40. The first wiring layer 41, the second wiring layer 42, and the electrodes 43 and 43p are embedded in the silicon oxide region 44. The front-side reflective layer 50F is also embedded in the silicon oxide region 44. The first wiring layer 41 is electrically connected to the second wiring layer 42 via the electrode 43.

[0049] The outer lens 10 will be described in more detail. The lens entrance surface 11 of the outer lens 10 has a curvature that varies depending on the location. In other words, the lens entrance surface 11 is not a curved surface with a constant curvature. For example, the curvature of the outer lens 10 can be explained as follows: in a cross-sectional shape of the outer lens 10 including the optical axis Z, a line segment representing the light-receiving surface includes a first curved portion and a second curved portion that is farther from the optical axis Z than the first curved portion, and the curvature of the second curved portion is smaller than the curvature of the first curved portion. For example, as shown in FIG. 5(a), in the lens entrance surface 11, the first region L5a corresponds to the first curved portion, and the second region L5b corresponds to the second curved portion. The curvature of the second region L5b is smaller than the curvature of the first region L5a. This configuration can be easily understood by referring to FIGS. 5(a), 5(b), and 5(c).

[0050] FIG. 5(a) is a contour diagram of the lens entrance surface 11 in a plan view. As shown in FIG. 5(a), the outer lens 10 has a shape that is rotationally symmetric about the optical axis Z. FIGS. 5(b) and 5(c) are cross-sectional views showing the positions of the contour lines. Cross section 10a in FIG. 5(b) corresponds to the X1-X1' cross section in FIG. 5(a). Cross section 10b in FIG. 5(b) corresponds to the X2-X2' cross section in FIG. 5(a). Cross section 10c in FIG. 5(c) corresponds to the Y1-Y1' cross section in FIG. 5(a). Cross section 10d in FIG. 5(c) corresponds to the Y2-Y2' cross section in FIG. 5(a). The axes in FIGS. 5(b) and 5(c) indicate the positions of the contour lines in FIG. 5(a). For example, the numbers on the axes in FIGS. 5(b) and 5(c) correspond to the numbers on the contour lines in FIG. 5(a). 5(a), for example, the area surrounded by contour line (11) may be defined as a first area L5a, and the area surrounded by contour lines (1) to (6) may be defined as a second area L5b. In this case, the first area L5a intersects with the optical axis Z. Furthermore, the second area L5b surrounds the first area L5a.

[0051] The outer lens 10 having such a shape can also be said to have multiple focal positions. For example, as shown in Fig. 1, the position of the focal point FP1 at the top (first region L5a) of the outer lens 10 is farther from the photoelectric conversion unit 30 than the position of the focal point F2 at the peripheral portion (second region L5b) of the outer lens 10. In other words, the focal length at the top of the outer lens 10 is shorter than the focal length at the peripheral portion of the outer lens 10.

[0052] 6 and 7, the state of light absorption in the photoelectric conversion element 1 will be described. The light R6a and R6b are assumed to be parallel light. The direction of the light R6a and R6b is parallel to the optical axis Z.

[0053] The shape of the outer lens 10, which is a microlens, can also be described as a cone with a rounded apex. With this lens shape, light R6a and R6b that pass through the outer lens 10 enters the photoelectric conversion unit 30 through the incident opening 50B1. The light then becomes a donut-shaped (ring-shaped) reflected light from the front-side reflective layer 50F. The diameter of the ring then expands near the surface, forming a thinner ring shape. Then, as the radius and diameter of the ring expand, the light repeatedly reflects between the front-side reflective layer 50F and the back-side reflective layer 50B. As a result, as long as the light R6a and R6b remain in the silicon photoelectric conversion unit 30, the light R6a and R6b continue to be absorbed by the photoelectric conversion unit 30, and photoelectric conversion continues.

[0054] Referring to FIG. 6, as a first specific example, the behavior of light R6a incident on the second region L5b on the lens incident surface 11 will be described. As light R6a passes through the lens incident surface 11, the traveling direction of light R6a changes. The change in traveling direction is based on the incident angle of light R6a with respect to the lens incident surface 11. The change in traveling direction is also based on the refractive index difference between the refractive index of air and the refractive index of the outer lens 10. Light R6a enters the main spacer 20 from the lens exit surface 12. The refractive index of the outer lens 10 is the same as the refractive index of the main spacer 20. In other words, since there is no refractive index difference between the outer lens 10 and the main spacer 20, the traveling direction of light R6a does not change. Light R6a passes through the incident opening 50B1 of the back-side reflective layer 50B and then passes through the antireflection layer 51. Light R6a then enters the photoelectric conversion unit 30. The refractive index of the first semiconductor region 31 of the photoelectric conversion unit 30 does not match the refractive index of the main spacer 20. Therefore, the traveling direction of light R6a changes when it enters the photoelectric conversion unit 30. Light R6a that enters the photoelectric conversion unit 30 passes through the first semiconductor region 31, the second semiconductor region 32, the third semiconductor region 33, and the fourth semiconductor region 34. Then, it enters the wiring unit 40. These multiple semiconductor layers do not have a significant refractive index difference. Therefore, the traveling direction of light R6a does not substantially change. In other words, light R6a travels straight in the photoelectric conversion unit 30.

[0055] The refractive index (3.64) of the photoelectric conversion unit 30 is different from the refractive index (1.45) of the silicon oxide region 44 of the wiring unit 40. Therefore, when the light R6a enters the wiring unit 40, the traveling direction of the light R6a changes depending on the difference in the refractive index. The light R6a that enters the wiring unit 40 reaches the front-side reflective layer 50F. The position at which the light R6a enters the front-side reflective layer 50F is away from the optical axis Z. The light R6a is reflected by the front-side reflective layer 50F.

[0056] The traveling direction of the reflected light R6a depends on the incident angle of the light R6a on the front-side reflective layer 50F. The reflected light R6a enters the photoelectric conversion unit 30 from the wiring unit 40. The light R6a travels straight through the photoelectric conversion unit 30. The light R6a then reaches the back-side reflective layer 50B. That is, the light R6a reflected on the front-side reflective layer 50F does not return to the incident opening 50B1. The light R6a reflected on the back-side reflective layer 50B passes through the photoelectric conversion unit 30 again before reaching the front-side reflective layer 50F. Thereafter, the light R6a travels back and forth between the back-side reflective layer 50B and the front-side reflective layer 50F, approaching the DTI 52. The light R6a that reaches the DTI 52 is then reflected by the DTI 52. Thereafter, the light R6a travels back and forth between the back-side reflective layer 50B and the front-side reflective layer 50F again, moving away from the DTI 52. Finally, the components of the light R6a that are not absorbed by the photoelectric conversion unit 30 reach the main spacer 20 from the photoelectric conversion unit 30 through the entrance opening 50B1.

[0057] In the structure shown in FIG. 6, the ratio of the thickness of the photoelectric conversion unit 30 to the pixel size (width of the light-receiving region) is 1:2. As an example, the thickness of the photoelectric conversion unit 30 is 5 μm, and the pixel size (width of the light-receiving region) is 10 μm. In this case, light R6a passes through the photoelectric conversion unit 30 eight times. In this case, the optical path length of light R6a is 40.8 μm. In the photoelectric conversion unit 30, the absorption length of light with a wavelength of 940 nm is approximately 40 μm. In other words, if there is no loss due to reflection, the quantum efficiency can be increased to approximately 64%.

[0058] Next, as a second example, the behavior of light R6b incident on the first region L5a of the lens entrance surface 11 will be described. Like light R6b incident on the first region L5a, light R6b also enters the photoelectric conversion unit 30 through the entrance opening 50B1. Light R6b then travels back and forth through the photoelectric conversion unit 30 multiple times. In the second example, the angle of incidence at which light R6b first enters the front-side reflective layer 50F after passing through the entrance opening 50B1 is smaller than in the first example. As a result, the number of times light R6b is reflected in the photoelectric conversion unit 30 is 22. In other words, the number of times light R6b travels back and forth through the photoelectric conversion unit 30 is greater than the number of times light R6a travels back and forth through the photoelectric conversion unit 30 in the first example. Therefore, the optical path length of the photoelectric conversion unit 30 in the second example is approximately 110 μm. If there is no loss due to reflection, the quantum efficiency can be increased to approximately 94%.

[0059] When viewing the photoelectric conversion element 1 as a whole, it can be assumed that the number of reflections (optical path length) lies between those in the first and second examples. In this case, the quantum efficiency of the photoelectric conversion element 1 can be increased to approximately 80%.

[0060] FIG. 7 is a perspective view illustrating the second example in a different representation. FIG. 7 illustrates a light beam of one light beam R7a. As shown in FIG. 7, the outer lens 10 has a shape symmetrical about the optical axis Z. As such, when the light beams R7a incident at the same position along the optical axis Z reach the front-side reflective layer 50F, they are incident at positions equidistant from the optical axis Z. In other words, the positions at which the light beams R7a enter the front-side reflective layer 50F are on a circle centered on the optical axis Z. Since the angles of incidence of the light beams R7a at each position are equal, the directions from the front-side reflective layer 50F toward the back-side reflective layer 50B are also equivalent. As a result, the position at which the light beams R7a again enter the front-side reflective layer 50F is also on a similar circle. In this case, the light beam R7a is approaching the DTI 52. In other words, the radius of the position at which the light beam R7a enters the front-side reflective layer 50F the second time is larger than the radius of the position at which the light beam R7a enters the front-side reflective layer 50F the first time. As a result of this repeated reflection, the positions at which the light R7a is incident on the front-side reflective layer 50F form concentric circles. In the following description, changing the traveling direction of the light R7a so that it is incident on the front-side reflective layer 50F at positions equidistant from the optical axis Z is referred to as "shaping the light."

[0061] <Action and effect> TOF cameras measure distance by illuminating an object with light and measuring the time of flight it takes for the light to reflect off the object and return. To accommodate distance measurements outdoors in the presence of sunlight, TOF cameras often use laser light in the 940 nm band, where the spectral intensity of sunlight is relatively low due to absorption by water vapor in the atmosphere. However, the absorption coefficient of silicon, a semiconductor, for light in this wavelength range is not sufficiently high. Therefore, it was not possible to achieve high quantum efficiency with the photoelectric conversion layer of conventional CMOS image sensors, which is several microns to tens of microns thick. Consequently, it could not be said that sufficient sensitivity was achieved for distance measurements outdoors.

[0062] In the photoelectric conversion element 1, light R is reflected multiple times between the back-side reflective layer 50B and the front-side reflective layer 50F. The photoelectric conversion section 30 is located between the back-side reflective layer 50B and the front-side reflective layer 50F. That is, light R travels back and forth through the photoelectric conversion section 30 multiple times. This extends the optical path length of light R in the photoelectric conversion section 30, allowing the photoelectric conversion section 30 to sufficiently absorb light R. As a result, sensitivity can be increased.

[0063] That is, the photoelectric conversion element 1 of the first embodiment reflects light R multiple times between the front-side reflective layer 50F and the back-side reflective layer 50B having the incident opening 50B1. As a result, the effective optical path length inside the silicon photoelectric conversion unit 30 can be lengthened, thereby improving near-infrared sensitivity. The outer lens 10 of the first embodiment allows the light intensity distribution in the front-side reflective layer 50F to be annular (donut-shaped). This intensity distribution allows most of the light R to be projected onto the back-side reflective layer 50B. The combination of the outer lens 10 of the first embodiment, which has a large apex curvature and a small side curvature, and the main spacer 20 disposed between the outer lens 10 and the photoelectric conversion unit 30, allows for an annular light intensity distribution. As a result, the photoelectric conversion element 1 of the present embodiment can achieve sufficient sensitivity for distance measurement outdoors.

[0064] The refraction angle from the main spacer 20 to the photoelectric conversion unit 30 and the incident position with respect to the incident opening 50B1, which cause multiple reflections inside the photoelectric conversion unit 30 made of silicon, are directly determined by the incident angle of light incident on the outer lens 10 and the inclination of the reflecting surface at the incident surface. The reflecting surface is a surface perpendicular to the normal to the surface of the outer lens 10.

[0065] In the cross-sectional shape of the outer lens 10 including the optical axis Z, the surface that receives light has conditions that cause multiple reflections even if the line segment representing the surface includes multiple straight lines. Furthermore, conditions that cause multiple reflections also exist even if the line segment representing the surface that receives light of the outer lens 10 is curved and the curvature of the curve is the same. In other words, the outer lens that constitutes the light direction conversion unit is not limited to the outer lens 10 of the first embodiment. The outer lens may have a configuration that, in cooperation with other optical components, can change the traveling direction of light so that the light travels in a direction away from the optical axis Z each time the light is repeatedly reflected between the back surface 30B of the photoelectric conversion unit 30 and the front surface 30F of the photoelectric conversion unit 30. Below, several modified examples of the outer lens are described. Even when the outer lenses of Modifications 1 to 4 are used, light that is incident on the outer lens and is parallel to the optical axis Z passes through the entrance opening 50B1, is reflected by the front-side reflective layer 50F, and is further reflected by the back-side reflective layer 50B around the entrance opening 50B1. In other words, the light redirecting portion including the outer lens is capable of causing multiple reflections. In this specification, "multiple" means at least two or more reflections.

[0066] <Variation 1> The outer lens 10S1 of Modification 1 will be described with reference to FIGS. 8 and 9. The outer lens 10S1 has a compound conical shape. In the following description, a compound conical shape refers to a multi-stage shape with inclinations at multiple angles. That is, in the cross-sectional shape of the outer lens 10S1 of Modification 1, the inclination angle increases as the distance from the optical axis Z increases. The inclination angle here refers to the angle of the contour line relative to a virtual reference axis line ZA that is perpendicular to the optical axis Z in the cross-sectional shape of the outer lens 10S1 that includes the optical axis Z. The inclination angle is more preferably a finite angle.

[0067] 8 and 9 is an example of an outer lens having a compound cone shape. Therefore, the specific numerical values ​​are not limited to the examples shown in FIGS. 8 and 9 and the specific numerical values ​​described below. The specific numerical values ​​may be set appropriately depending on the specific configuration of the photoelectric conversion element 1S1.

[0068] FIG. 8 is a schematic diagram illustrating the compound cone shape. The line segment C1 shown in FIG. 8 indicates the surface that accepts light in the cross-sectional shape of the outer lens 10S1 of Modification 1. The line segment C1 has a first straight line portion C1a, a second straight line portion C1b, and a third straight line portion C1c between the vertex C1t and the end point C1e. The first straight line portion C1a includes the vertex C1t. The third straight line portion C1c includes the end point C1e. The second straight line portion C1b is disposed between the first straight line portion C1a and the third straight line portion C1c. In other words, the second straight line portion C1b connects the first straight line portion C1a to the third straight line portion C1c.

[0069] The first straight line segment C1a has a first tilt angle A1a. The tilt angle is the angle between the first straight line segment C1a and an imaginary reference axis ZA that is perpendicular to the optical axis Z. Similarly, the second straight line segment C1b has a second tilt angle A1b, and the third straight line segment C1c has a third tilt angle A1c. The second tilt angle A1b is larger than the first tilt angle A1a. The third tilt angle A1c is larger than the second tilt angle A1b.

[0070] Fig. 9 is a cross-sectional view showing a main part of a photoelectric conversion element 1S1 including an outer lens 10S1 having a compound cone shape as described in Fig. 8. The photoelectric conversion element 1S1 includes the outer lens 10S1, a main spacer 20, and a photoelectric conversion unit 30.

[0071] The following numerical values ​​can be given as examples of the respective components of the photoelectric conversion element 1S1. Outer lens: thickness t1 = 2.8 μm, width t4 = 10 μm, refractive index n = 1.8. Main spacer: thickness t2 = 7 μm, width t4 = 10 μm, refractive index n = 1.8. Photoelectric conversion part: thickness t3 = 20 μm, width t4 = 10 μm, refractive index n = 3.6.

[0072] 9 illustrates rays of light that are incident on the outer lens 10S1. The angles between the normal N to the lens surface at the incident position and an axis parallel to the optical axis Z are shown as angles A2a, A2b, and A2c, respectively. The following are examples of the numerical values ​​of each angle: Angle A2a=20° Angle A2b=30° Angle A2c=40°

[0073] Light incident from near the optical axis Z of the outer lens 10S1 is reflected by the front-side reflective layer 50F and then enters the back-side reflective layer 50B. That is, light incident from near the optical axis Z is not emitted to the outside of the photoelectric conversion unit 30 through the entrance opening 50B1 due to the first reflection by the front-side reflective layer 50F. Similarly, light incident from the edge of the outer lens 10S1 is also reflected by the front-side reflective layer 50F and then enters the back-side reflective layer 50B. That is, light incident from the edge of the outer lens 10S1 is not emitted to the outside of the photoelectric conversion unit 30 through the entrance opening 50B1 due to the first reflection by the front-side reflective layer 50F. Therefore, the photoelectric conversion element 1S1 including the outer lens 10S1 of Variation 1 can also effectively confine light within the photoelectric conversion unit 30.

[0074] <Variation 2> The outer lens 10S2 of Modification 2 will be described with reference to Figures 10 and 11. The portion of the cross-sectional shape showing the outline of the outer lens 10S2 that accepts light includes a curved portion. In Modification 2, the curved portion is an arc. The entire portion of the cross-sectional shape showing the outline of the outer lens 10S2 that accepts light has a shape that is a copy of the curved portion with the optical axis Z as the axis of symmetry. A portion of the curved portion does not have to include an axis of the arc that is parallel to the optical axis Z.

[0075] Line segment C2 shown in FIG. 10 indicates the surface that accepts light in the cross-sectional shape of the outer lens 10S2 of Modification 2 that includes the optical axis Z. Line segment C2 that indicates the surface that accepts light in the cross-sectional shape of the outer lens 10S2 that includes the optical axis Z includes a portion defined as an arc. More specifically, line segment C2 corresponds to a portion CA1 of arc CA. Arc CA has an imaginary reference axis ZA that is parallel to the optical axis Z. This imaginary reference axis ZA and the optical axis Z are spaced apart from each other in a direction perpendicular to the optical axis Z. Such line segment C2 has a single value of curvature, and in this respect, it differs from the outer lens 10 of the embodiment that is represented by a curve including multiple curvatures.

[0076] Fig. 11 is a cross-sectional view showing a main part of a photoelectric conversion element 1S2 including the outer lens 10S2 described in Fig. 10. The photoelectric conversion element 1S2 has the outer lens 10S2, a main spacer 20, and a photoelectric conversion unit 30.

[0077] The following numerical values ​​can be given as examples of the respective components of the photoelectric conversion element 1S2. Outer lens: thickness t1 = 2.9 μm, width t4 = 10 μm, refractive index n = 1.8. Main spacer: thickness t2 = 6 μm, width t4 = 10 μm, refractive index n = 1.8. Photoelectric conversion part: thickness t3 = 20 μm, width t4 = 10 μm, refractive index n = 3.6.

[0078] 11 also illustrates light rays representing light incident on the outer lens 10S2, similar to FIG. 9. The angles between the normal N to the lens surface at the incident position and an axis parallel to the optical axis Z are shown as angles A3a, A3b, A3c, A3d, and A3e, respectively. The following are examples of the numerical values ​​of each angle: Angle A3a=20° Angle A3b=25° Angle A3c=30° Angle A3d=35° Angle A3e=40°

[0079] Light (e.g., light Lar) incident from near the optical axis Z of the outer lens 10S2 is reflected by the front-side reflective layer 50F and then enters the back-side reflective layer 50B. That is, light incident from near the optical axis Z of the outer lens 10S2 is not emitted to the outside of the photoelectric conversion unit 30 through the incident opening 50B1. Similarly, light (e.g., light Lbr, Lbl) incident from the end of the outer lens 10S2 is also reflected by the front-side reflective layer 50F and then enters the back-side reflective layer 50B. That is, light incident from the end of the outer lens 10S2 is not emitted to the outside of the photoelectric conversion unit 30 through the incident opening 50B1. Therefore, the photoelectric conversion element 1S2 including the outer lens 10S2 of Variation 2 can also effectively confine light within the photoelectric conversion unit 30.

[0080] In the outer lens 10S2 shown in Figure 11, the right edge Er of the lens is defined on the right side of the page, and the left edge El of the lens is defined on the left side of the page. Light Lbr is incident on the right edge Er of the lens. Light Lbl is incident on the left edge El of the lens. The lights Lbr and Lbl are assumed to be parallel to the optical axis Z. Furthermore, light Lar is incident at a position slightly to the right of the optical axis Z.

[0081] Light Lbr is incident on the photoelectric conversion unit 30 at position Lbrp1. After being reflected by the front-side reflective layer 50F, the light Lbr is incident on the back-side reflective layer 50B at position Lbrp2. Light Lbl is incident on the photoelectric conversion unit 30 at position Lblp1. After being reflected by the front-side reflective layer 50F, the light Lbl is incident on the back-side reflective layer 50B at position Lblp2. Light Lar is incident on the photoelectric conversion unit 30 at position Larp1. After being reflected by the front-side reflective layer 50F, the light Lar is incident on the back-side reflective layer 50B at position Larp2.

[0082] Here, comparing the distance from the optical axis Z to the position Lblp1 with the distance from the optical axis Z to the position Lblp2, the distance from the optical axis Z to the position Lblp2 is greater than the distance from the optical axis Z to the position Lblp1. Furthermore, comparing the distance from the optical axis Z to the position Lblp1 with the distance from the optical axis Z to the position Larp2, the distance from the optical axis Z to the position Larp2 is greater than the distance from the optical axis Z to the position Lblp1. The entrance opening 50B1 is provided to pass through the positions Lbrp1 and Lblp1.

[0083] That is, in the outer lens 10S2 of the second modification, the opening end of the incident opening 50B1 is determined by the positions (positions Lbrp1, Lblp1) at which the light beams Lbr and Lbl incident at positions far from the optical axis Z enter the photoelectric conversion unit 30.

[0084] In other words, the inclination of the tangent to the lens surface of the outer lens 10S2 with respect to the light Lar and Lbr, the refractive index of the lens material of the outer lens 10S2, and the thickness of the main spacer 20 are set so that after light Lbr from the outermost periphery of the right lens and light Lar that is to the right of the optical axis Z and substantially overlaps the optical axis Z enter the silicon (photoelectric conversion unit 30), positions Lbrp2 and Larp2, where the light Lbr and Larb are reflected once by the second reflective layer (front-side reflective layer 50F) and a second time by the first reflective layer (back-side reflective layer 50B), are farther from the optical axis Z than position Lblp1, where light Lbl from the outermost periphery of the lens on the opposite side (left side) enters the photoelectric conversion unit 30. A portion of the back-side reflective layer 50B constituting the first reflective layer is provided from the left edge of the pixel to between position Lbrp2 (or position Larp2) and position Lblp1. Another portion of the back-side reflective layer 50B constituting the first reflective layer is provided on the opposite side, symmetrically with respect to the optical axis Z.

[0085] <Variation 3> 12 is a cross-sectional view showing a main part of a photoelectric conversion element 1S3 equipped with an outer lens 10S3 in which the opening edge of the incident opening 50B1 is determined by another factor. The photoelectric conversion element 1S3 has an outer lens 10S3, a main spacer 20, and a photoelectric conversion unit 30.

[0086] The following numerical values ​​can be given as examples of the respective components of the photoelectric conversion element 1S3. Outer lens: thickness t1 = 3.9 μm, width t4 = 10 μm, refractive index n = 1.56. Main spacer: thickness t2 = 12.5 μm, width t4 = 10 μm, refractive index n = 1.56. Photoelectric conversion part: thickness t3 = 5 μm, width t4 = 10 μm, refractive index n = 3.6.

[0087] 12 also illustrates light rays representing light incident on the outer lens 10S3, similar to FIG. 9. The angles between the normal N to the lens surface at the incident position and an axis parallel to the optical axis Z are shown as angles A4a and A4b, respectively. The following are examples of the numerical values ​​of each angle: Angle A4a=20° Angle A4b=55°

[0088] Furthermore, the following numerical values ​​can be additionally exemplified for each of the components included in the photoelectric conversion element 1S3. The radius of the arc defining the outer lens is t5 = 10.5 μm. The deviation t6 between the arc axis ZB and the optical axis Z is 3.7 μm. The width of the rear reflective layer t7 = 2.9 μm. The diameter of the entrance aperture t8 = 4.2 μm.

[0089] The outer lens 10S2 of Modification 2 is determined by the position where the light Lbr and Lbl, which enter the entrance opening 50B1 at a position far from the optical axis Z, enters the photoelectric conversion unit 30. In contrast, the outer lens 10S3 of Modification 3 is determined by the position where the light Lar, which enters the entrance opening 50B1 at a position close to the optical axis Z, enters the photoelectric conversion unit 30.

[0090] Specifically, light Lbr is incident on the photoelectric conversion unit 30 at position Lbrp1. Then, after being reflected by the front-side reflective layer 50F, light Lbr is incident on the back-side reflective layer 50B at position Lbrp2. Furthermore, light Lar is incident on the photoelectric conversion unit 30 at position Larp1. Then, after being reflected by the front-side reflective layer 50F, light Lar is incident on the back-side reflective layer 50B at position Larp2.

[0091] Comparing the distance from the optical axis Z to the position Larp1 with the distance from the optical axis Z to the position Lbrp2, the distance from the optical axis Z to the position Lbrp2 is greater than the distance from the optical axis Z to the position Larp1. The entrance aperture 50B1 is provided so that its end passes between the position Lbrp2 and the position Larp1.

[0092] In other words, the inclination of the tangent to the lens surface, the refractive index of the material constituting the microlens (outer lens 10S3), and the thickness of the main spacer 20 are determined so that position Lbrp2, where light Lbr from the outermost periphery (right side) of the lens enters the silicon (photoelectric conversion unit 30), is reflected once by the second reflective layer (front-side reflective layer 50F) and then reflected a second time by the first reflective layer (back-side reflective layer 50B), is farther from the optical axis Z than position Larp1, where light Lar, which is to the right of the optical axis Z and approximately overlaps with the optical axis Z, enters the silicon (photoelectric conversion unit 30). A first reflective layer (back-side reflective layer 50B) is then provided from the left edge of the pixel to a position between positions Lbrp2 and Larp1. Another first reflective layer (back-side reflective layer 50B) is also provided on the opposite side, symmetrically with respect to the optical axis Z.

[0093] <Variation 4> In Modifications 2 and 3, examples were described in which the curve was a portion of a circular arc. The curve is not limited to a circular arc. As shown in FIG. 13 , the line segment C4 indicating the portion that accepts light in the cross-sectional shape showing the outline of the outer lens 10S4 of Modification 4 may include a portion defined as a parabola CB. In other words, the cross-sectional shape showing the outline of the outer lens 10S4 may be a shape obtained by copying a portion of a parabola CB having an axis parallel to the optical axis Z with the optical axis Z as the axis of symmetry. The portion CB1 of the parabola CB does not have to include the axis ZB of the parabola CB parallel to the optical axis Z. Note that, if it is acceptable to generate a certain amount of light that does not undergo multiple reflection, the portion CB1 may include the axis ZC of the parabola CB parallel to the optical axis Z.

[0094] 14 is a cross-sectional view showing a main part of a photoelectric conversion element 1S4 equipped with an outer lens 10S4 including a line segment C4 defined as a parabola CB. The photoelectric conversion element 1S4 has the outer lens 10S4, a main spacer 20, and a photoelectric conversion unit 30.

[0095] The following numerical values ​​can be given as examples of the respective components of the photoelectric conversion element 1S4. Outer lens: thickness t1 = 3 μm, width t4 = 10 μm, refractive index n = 1.8. Main spacer: thickness t2 = 6 μm, width t4 = 10 μm, refractive index n = 1.8. Photoelectric conversion part: thickness t3 = 20 μm, width t4 = 10 μm, refractive index n = 3.6.

[0096] 14 also illustrates light rays representing light incident on the outer lens 10S4, similar to FIG. 9. The angles between the normal N to the lens surface at the incident position and an axis parallel to the optical axis Z are shown as angles A5a, A5b, A5c, A5d, and A5e, respectively. The following are examples of the numerical values ​​of each angle: Angle A5a=20° Angle A5b=25° Angle A5c=30° Angle A5d=35° Angle A5e=40°

[0097] With the outer lens 10S4 of Modification 4, neither light incident from near the optical axis Z nor light incident from a position away from the optical axis Z is emitted from the entrance opening 50B1 to the outside of the photoelectric conversion unit 30 as a result of the first reflection. Therefore, the photoelectric conversion element 1S4 equipped with the outer lens 10S4 of Modification 4 can also suitably confine light within the photoelectric conversion unit 30.

[0098] Second Embodiment In the photoelectric conversion element 1 of the first embodiment, all of the light R reflected the first time by the front-side reflective layer 50F reaches the back-side reflective layer 50B. In other words, the light R reflected the first time by the front-side reflective layer 50F does not reach the incident opening 50B1. In the first embodiment, this light R is achieved by the shape of the outer lens 10. However, a configuration that can guide the light R reflected the first time by the front-side reflective layer 50F to the back-side reflective layer 50B can also be achieved by a configuration other than the shape of the outer lens 10.

[0099] As shown in Fig. 15, the photoelectric conversion element 1A of the second embodiment includes an outer lens 10A, a main spacer 20A, an inner lens 61A (second lens, light direction conversion unit 60A), an inner spacer 62A, a photoelectric conversion unit 30A, and a wiring unit 40A. The photoelectric conversion element 1A of the second embodiment has a DTI 52A (see Fig. 3) which is a second configuration. The photoelectric conversion element 1A differs from the photoelectric conversion element 1 of the first embodiment in the configuration of the outer lens 10A.

[0100] Furthermore, the photoelectric conversion element 1A differs from the photoelectric conversion element 1 of the first embodiment in that it further includes an inner lens 61A and an inner spacer 62A. The photoelectric conversion element 1A includes an inner lens 61A, which is not included in the photoelectric conversion element 1 of the first embodiment. The inner lens 61A has a shape corresponding to the outer lens 10 of the first embodiment. In other words, the photoelectric conversion element 1A of the second embodiment employs a double microlens structure including an outer lens 10A and an inner lens 61A. The photoelectric conversion element 1A of the second embodiment employs a spherical microlens as the outer lens 10A for capturing light R, and a conical microlens with a rounded apex as the inner lens 61A. In other words, in the second embodiment, the components that guide light to the photoelectric conversion unit 30A are the outer lens 10A, the main spacer 20A, the inner lens 61A, and the inner spacer 62A. These optical components constitute the light direction conversion unit 60A of the second embodiment.

[0101] The photoelectric conversion element 1A guides light R that is reflected for the first time by the front-side reflective layer 50F to the back-side reflective layer 50B. The photoelectric conversion unit 30A and the wiring unit 40A are the same as the photoelectric conversion unit 30 and the wiring unit 40 of the first embodiment, so detailed description will be omitted. The outer lens 10A, the inner lens 61A, and the inner spacer 62A will be described in detail below.

[0102] The outer lens 10A of the second embodiment has a spherical lens entrance surface 11A. The focal point of this outer lens 10A is set inside the photoelectric conversion unit 30A. The positional relationship between the outer lens 10A and the inner lens 61A can be adjusted by the main spacer 20A. The inner lens 61A has an optical axis Z. For example, the optical axis of the inner lens 61A coincides with the optical axis of the outer lens 10A. Furthermore, all rays of light R passing through the outer lens 10A intersect with the light entrance surface of the inner lens 61A.

[0103] The photoelectric conversion element 1A of the second embodiment includes an outer lens 10A and an inner lens 61A. The inner lens 61A performs the same function as the outer lens 10 of the first embodiment. That is, the shape of the inner lens 61A may be the same as the shape of the outer lens 10 of the first embodiment. The shape of the inner lens 61A may also be any one of the shapes of the outer lenses 10S1 to 10S4 of Modifications 1 to 4. The inner spacer 62A adjusts the positional relationship between the inner lens 61A and the photoelectric conversion unit 30A. The refractive index (n2) of the inner lens 61A and the inner spacer 62A is greater than the refractive index (n1) of the outer lens 10A. Conversely, the refractive index of the outer lens 10A is smaller than the refractive index of the inner lens 61A. In other words, the refractive index (n2) of the inner lens 61A and the inner spacer 62A is greater than the refractive index (n1) of the main spacer 20A (n2>n1). The refractive index of the outer lens 10A ranges from approximately 1.55 to 1.6. The refractive index of the inner lens 61A is approximately 2.0. As a result, when light R enters the inner lens 61A from the main spacer 20A, refraction occurs. In other words, the traveling direction of the light R changes.

[0104] The inner lens 61A and the inner spacer 62A are disposed between the main spacer 20A and the photoelectric conversion unit 30A. The back surface of the inner spacer 62A contacts the back surface-side reflective layer 50B and the antireflection layer 51. The inner lens 61A is provided on the main surface of the inner spacer 62A. The inner lens 61A and the inner spacer 62A are integral. The main surfaces of the inner lens 61A and the inner spacer 62A contact the main spacer 20A. The main spacer 20A may be omitted.

[0105] The photoelectric conversion element 1A of the second embodiment can also enhance sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0106] Furthermore, the photoelectric conversion element 1A equipped with the inner lens 61A has a small spot diameter SD of light R at the entrance opening 50B1 of the back-side reflective layer 50B. When the camera lens is fully opened (when a small F-number is set), the angle of incidence of light R increases. Since the photoelectric conversion element 1A achieves the small spot diameter SD described above, even if the angle of incidence of light R increases, light R is not irradiated onto the back-side reflective layer 50B from the main spacer 20A side. Therefore, the photoelectric conversion element 1A of the second embodiment is advantageous in terms of increasing sensitivity because loss of light R is suppressed.

[0107] In other words, the photoelectric conversion element 1A of the second embodiment can reduce the spot diameter SD of light R at the entrance opening 50B1 compared to the photoelectric conversion element 1 of the first embodiment. According to this aspect, even if the incident angle of light R changes, light R can be reliably transmitted through the entrance opening 50B1. In other words, it is possible to prevent the light R that passes through the inner lens 61A from reaching the back-side reflective layer 50B and thus not entering the photoelectric conversion unit 30A. Therefore, all incident light R is guided to the photoelectric conversion unit 30A, thereby preventing a decrease in sensitivity due to a change in the incident angle.

[0108] Furthermore, in a case where the incident direction of light R is constant, the area of ​​the incident opening 50B1 may be reduced. This configuration can suitably prevent light R traveling back and forth inside the photoelectric conversion unit 30A from exiting through the incident opening 50B1 to the inner spacer 62A again. Therefore, light R can be more effectively confined within the photoelectric conversion unit 30A.

[0109] <Third embodiment> For example, the photoelectric conversion element 1 of the first embodiment may further include an inner lens 61B. As shown in FIG. 16, the photoelectric conversion element 1B of the third embodiment includes an outer lens 10B, a main spacer 20B, an inner lens 61B, an inner spacer 62B, a photoelectric conversion unit 30B1, and a wiring unit 40B1. Of these, the outer lens 10B, the main spacer 20B, the inner lens 61B, and the inner spacer 62B constitute the light direction conversion unit 60B. The photoelectric conversion element 1B of the third embodiment has a DTI 52 (see FIG. 2) having a first configuration. The outer lens 10B, the main spacer 20B, the photoelectric conversion unit 30B1, and the wiring unit 40B1 are the same as the outer lens 10, the main spacer 20, the photoelectric conversion unit 30, and the wiring unit 40 of the first embodiment, and therefore detailed description thereof will be omitted. Below, the inner lens 61B and the inner spacer 62B will be described in detail.

[0110] The main surface of the inner lens 61B is spherical. The photoelectric conversion element 1B includes an outer lens 10B and an inner lens 61B. The refractive index (n2) of the inner lens 61B and the inner spacer 62B is greater than the refractive index (n1) of the outer lens 10B and the main spacer 20B (n2>n1).

[0111] The photoelectric conversion element 1B of the third embodiment can also enhance sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0112] Note that the photoelectric conversion element 1A of the second embodiment included an outer lens 10A and an inner lens 61A. The photoelectric conversion element 1B of the third embodiment included an outer lens 10B and an inner lens 61B. For example, the photoelectric conversion element 1B may include the outer lens 10A and the inner lens 61B. That is, the photoelectric conversion element 1A of the third embodiment may adopt the shape of the outer lens 10 of the first embodiment as the shape of the outer lens. Also, as the shape of the outer lens, any one of the shapes of the outer lenses 10S1 to 10S4 of Modifications 1 to 4 may be adopted. Further, as the shape of the inner lens, the shape of the outer lens 10 of the first embodiment may be adopted. Also, as the shape of the inner lens, any one of the shapes of the outer lenses 10S1 to 10S4 of Modifications 1 to 4 may be adopted.

[0113] <Fourth Embodiment> In the photoelectric conversion element 1B of the third embodiment, the refractive index (n2) of the inner lens 61B is larger than the refractive index (n1) of the outer lens 10B. This refractive index relationship may be reversed. That is, as in the photoelectric conversion element 1C of the fourth embodiment shown in FIG. 17, the refractive index (n2) of the inner lens 61C may be smaller than the refractive index (n1) of the outer lens 1OC. The photoelectric conversion element 1C of the fourth embodiment is a configuration example in the case where the refractive index (n2) of the inner lens 61C is smaller than the refractive index (n1) of the outer lens 10C (n2 < n1).

[0114] The photoelectric conversion element 1C of the fourth embodiment includes an outer lens 10C, a main spacer 20C, an inner lens 61C, an inner spacer 62C, a photoelectric conversion unit 30C, and a wiring unit 40C. Of these, the outer lens 10C, the main spacer 20C, the inner lens 61C, and the inner spacer 62C constitute a light direction conversion unit 60C. The outer lens 10C, the main spacer 20C, the photoelectric conversion unit 30C, and the wiring unit 40C are the same as the outer lens 10, the main spacer 20, the photoelectric conversion unit 30, and the wiring unit 40 of the first embodiment, and therefore detailed description thereof will be omitted. In this case, the inner lens 61C is a concave lens. The photoelectric conversion element 1C of the fourth embodiment can also achieve increased sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0115] Fifth Embodiment In the first to fourth embodiments, the light R is shaped by the outer lens or the inner lens. More specifically, the light R is shaped before it reaches the front-side reflective layer 50F. In other words, the shaping of the light R is completed before it enters the photoelectric conversion unit 30, and all of the light R reflected the first time by the front-side reflective layer 50F reaches the back-side reflective layer 50B. The shaping of the light R is not limited to this configuration. Specifically, the shaping of the light R may be performed during the first reflection. Hereinafter, with reference to FIG. 18, a configuration for shaping the light R during the first reflection will be described in detail. The photoelectric conversion element 1D of the fifth embodiment includes a convex mirror 63 (reflective unit) instead of the outer lens 10.

[0116] The photoelectric conversion element 1D of the fifth embodiment includes an outer lens 10D, a main spacer 20D, a photoelectric conversion unit 30D, a wiring unit 40D, and a light confinement unit 50D. The main spacer 20D sets the distance from the outer lens 10D to the photoelectric conversion unit 30D to a predetermined value. As a result, the focal point of the outer lens 10D is located inside the photoelectric conversion unit 30D. The photoelectric conversion unit 30D and the wiring unit 40D are similar to the photoelectric conversion unit 30 and the wiring unit 40 of the first embodiment, and therefore detailed description thereof will be omitted.

[0117] The mirror 63 performs the same function as the outer lens 10 of the first embodiment. In the fifth embodiment, the outer lens 10D, the main spacer 20D, and the mirror 63 constitute a light direction conversion unit 60D. The mirror 63 is provided at a position intersecting the optical axis Z. The mirror 63 is tilted relative to a direction parallel to the optical axis Z. In other words, a slope is formed on the surface of the mirror 63, which is a reflector. For example, if the direction facing the optical axis Z is defined as inward and the opposite direction as outward, the mirror 63 faces outward. The main surface of the mirror 63 can also be considered a conical surface. The normal to the mirror 63 has a predetermined angle other than 0 degrees with respect to the optical axis Z. In this embodiment, the mirror 63 is integrated with the front-side reflective layer 50FD. The mirror 63 is embedded in the wiring portion 40D. For example, the mirror 63 can be considered a conical protrusion formed by protruding a portion of the front-side reflective layer 50FD in a conical shape.

[0118] If light R passing through the outer lens 10D is incident on a reflecting surface perpendicular to the optical axis Z, the reflected light R is focused on the optical axis Z. Then, the light R exits the photoelectric conversion unit 30D again through the entrance opening 50B1.

[0119] On the other hand, when light R that has passed through the outer lens 10D is incident on the mirror 63 that is tilted with respect to the optical axis Z, the angle of incidence of the light R differs from the angle of incidence on the reflective surface that is perpendicular to the optical axis Z. More specifically, as the angle of incidence increases, the angle of reflection also increases. In other words, the traveling direction of the light R is biased more outward. As a result, the reflected light R does not converge to a single point on the optical axis Z. Instead, the reflected light R converges on a circle centered on the optical axis Z. Then, all of the reflected light R reaches the back-side reflective layer 50B, and thereafter travels back and forth between the back-side reflective layer 50B and the front-side reflective layer 50FD.

[0120] In the photoelectric conversion element 1D of the fifth embodiment, the mirror 63 is formed by adding a dedicated process. In the process of forming the mirror 63, the mirror 63 is formed so as to have a reflection angle that increases the number of reflections. As a result, the same effects as those of the photoelectric conversion element 1 of the first embodiment that employs the outer lens 10 can be expected. In other words, the photoelectric conversion element 1D of the fifth embodiment can also increase sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0121] Sixth Embodiment The configuration for shaping light R by reflection is not limited to the mirror 63 of the fifth embodiment. Any configuration capable of converging reflected light R on a circumference centered on the optical axis Z may be appropriately adopted. For example, FIG. 19 shows a photoelectric conversion element 1E of the sixth embodiment having a different reflection structure instead of the mirror 63 of the fifth embodiment. The photoelectric conversion element 1E of the sixth embodiment realizes a pseudo-mirror 63 of the fifth embodiment using part of the wiring layer used in the image sensor and integrated circuit.

[0122] The photoelectric conversion element 1E of the sixth embodiment has an outer lens 10E, a main spacer 20E, a photoelectric conversion unit 30E, a wiring unit 40E, and a light confinement unit 50E. Of these, the outer lens 10E, the main spacer 20E, and the pseudo-mirror structure 64 constitute a light direction conversion unit 60E. The photoelectric conversion unit 30E and the wiring unit 40E are similar to the photoelectric conversion unit 30 and the wiring unit 40 of the first embodiment, and therefore detailed description thereof will be omitted.

[0123] The pseudo-mirror structure 64 is a pseudo-reflective structure formed by the silicon oxide region 44 and wiring layers 45a, 45b, 45c, and 45d in the wiring portion 40E. The pseudo-mirror structure 64 is a stacked structure of the silicon oxide region 44 and the wiring layers 45a, 45b, 45c, and 45d. The widths of the wiring layers 45a, 45b, 45c, and 45d increase along the optical axis Z from the back surface side to the front surface side. In other words, the wiring layer 45d arranged on the front surface 40F side of the wiring portion 40E is wider than the wiring layer 45a arranged on the back surface 40B side of the wiring portion 40E. Both ends of the wiring layers 45a, 45b, 45c, and 45d contact the silicon oxide region 44. In other words, the wiring layers 45a, 45b, 45c, and 45d used as the pseudo-mirror structure 64 are physically separated from the wiring layers 41 and 42 used for electrical connection. Light R passes through silicon oxide region 44 but does not pass through wiring layers 45a, 45b, 45c, and 45d. This configuration allows light R to reach surface 40F of wiring portion 40E. The arrangement of wiring layers 45a, 45b, 45c, and 45d can be said to be stepped. If the size of one step in this stepped structure is sufficiently small compared to the wavelength of light R, it can be approximated as a reflective surface with the angle of the slope.

[0124] The photoelectric conversion element 1E of the sixth embodiment can also enhance sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0125] Seventh Embodiment The outer lenses 10 of the first embodiment all have the same cross-sectional shape including the optical axis Z. In other words, the outer lens 10 is a rotating body obtained by rotating a predetermined cross-sectional shape around the optical axis Z. The outer lens 10 is not limited to such a rotating body. Another example of the outer lens shape is a cylindrical outer lens 10F shown in FIGS. 20 and 21. When this shape is adopted, light R enters the photoelectric conversion unit 30 through the incident opening 50B1. As shown in FIG. 21, the light R reaching the front-side reflective layer 50F is irradiated onto two elongated cigar-shaped regions. The reflected light temporarily becomes thinner near the surface and is reflected by the back-side reflective layer 50B. Thereafter, the diameters of its major and minor axes increase, and the light R is repeatedly reflected between the front-side reflective layer 50F and the back-side reflective layer 50B. As a result, as long as the light R remains in the silicon photoelectric conversion unit 30, the light R is absorbed by the photoelectric conversion unit 30, and photoelectric conversion continues.

[0126] More specifically, the outer lens 10F in FIG. 20 has a shape obtained by elongating a predetermined cross-sectional shape along a sweep axis SL perpendicular to the optical axis Z. Such a three-dimensional shape can also be referred to as a cylindrical shape. In this case, the cross-sectional shape of the outer lens 10F perpendicular to the sweep axis SL is the same at every location. The cross-sectional shape perpendicular to the sweep axis SL may be the same as the cross-section of the outer lens 10 of the first embodiment, for example, or the cross-sectional shape perpendicular to the sweep axis KL may be a substantially trapezoidal shape. The outer lens 10F in FIG. 21 has a first region L14a and a second region L14b. In the outer lens 10F, the second curvature of the second region L14b is also smaller than the first curvature of the first region L14a. In the outer lens 10 of the first embodiment, the second region L5b surrounds the first region L5a in an annular shape. On the other hand, in the outer lens 10F of the seventh embodiment, the first region L14a is sandwiched between the second region L14b. More specifically, the second region L14b sandwiches the first region L14a along an axis KL that is perpendicular to both the optical axis Z and the sweep axis SL.

[0127] According to the outer lens 10F of FIG. 21, the light R is irradiated in an elliptical shape onto the front-side reflective layer 50F. The long axis direction of the elliptical irradiation region IR is aligned with the sweep axis SL. On the other hand, the short axis direction of the elliptical irradiation region IR is aligned with the axis KL. The pair of irradiation regions IR are symmetrical with respect to the sweep axis SL. That is, a pair of irradiation regions IR corresponding to each other is formed on either side of the sweep axis SL. The irradiation region IR gradually moves away from the optical axis Z while increasing the lengths of its short axis and long axis. As a result, the optical path length of the light R in the photoelectric conversion unit 30F1 can be sufficiently secured.

[0128] Eighth Embodiment A more preferred example of the outer lens will now be described. The outer lens 10G shown in Fig. 22 has a cross-sectional shape in the vertical direction (the direction of the sweep axis SL) that is approximately triangular (see Fig. 22(b)) with a smoothly changing curvature, thereby causing multiple reflections of light R. On the other hand, the outer lens 10G has a cross-sectional shape in the horizontal direction (the direction of the axis KL) that is approximately spherical (see Fig. 22(c)), thereby reducing the component of light reflected in the horizontal direction.

[0129] FIG. 22(a) is a contour map of the outer lens 10G in a plan view. FIGS. 22(b) and 22(c) are cross-sectional views showing the positions of the contour lines. A cross section 15a in FIG. 22(b) corresponds to the X1-X1' cross section in FIG. 5(a). A cross section 15b in FIG. 22(b) corresponds to the X2-X2' cross section in FIG. 22(a). A cross section 15c in FIG. 22(c) corresponds to the Y1-Y1' cross section in FIG. 22(a). A cross section 15d in FIG. 22(c) corresponds to the Y2-Y2' cross section in FIG. 22(a). The axes in FIGS. 22(b) and 22(c) indicate the positions of the contour lines in FIG. 22(a). The region surrounded by the contour lines (8) corresponds to the first region L15a. Second regions L15b are formed along the sweep axis SL, sandwiching the first region L15a.

[0130] 23 is a plan view schematically illustrating an irradiation area IR of light R shaped by the outer lens 10G. For example, when light R is irradiated onto the Y1-Y1' cross section, the first reflected light has a spot shape (see IR1). The spot-shaped light component is absorbed after one round trip inside the photoelectric conversion unit 30. Thereafter, the light R leaves the photoelectric conversion unit 30, resulting in loss. However, the light component that becomes a loss is relatively small compared to the total light that enters the photoelectric conversion unit 30.

[0131] Ninth Embodiment The photoelectric conversion element 1 of the first embodiment is a so-called back-illuminated type. The outer lens 10 employed in the photoelectric conversion element 1 of the first embodiment may also be employed in a front-illuminated type photoelectric conversion element 1H as shown in Fig. 24. In other words, even in the front-illuminated type photoelectric conversion element 1H, it is possible to increase the quantum efficiency by employing an outer lens.

[0132] 24, the photoelectric conversion element 1H of the ninth embodiment has an outer lens 10H, a main spacer 20H, a photoelectric conversion unit 30H, a wiring unit 40H, a light confinement unit 50H, and a support substrate 71H. Of these, the outer lens 10H, the main spacer 20H, and the wiring unit 40H constitute a light direction conversion unit 60H. The photoelectric conversion element 1H differs from the photoelectric conversion element 1 of the first embodiment in the arrangement of the photoelectric conversion unit 30H and the wiring unit 40H. The photoelectric conversion element 1H also differs from the photoelectric conversion element 1 of the first embodiment in that it includes a support substrate 71H.

[0133] The photoelectric conversion element 1H has a wiring portion 40H between the main spacer 20H and the photoelectric conversion portion 30H. The photoelectric conversion element 1H of the ninth embodiment has a DTI 52 (see FIG. 2) having a first configuration. The front surface 40F of the wiring portion 40H contacts the main spacer 20H. The back surface 40B of the wiring portion 40H contacts an anti-reflection layer 51 provided on the back surface 30B of the photoelectric conversion portion 30H. In the wiring portion 40H, a light-transmitting region 46H near the optical axis Z transmits light R. Therefore, the first wiring layer 41 and the second wiring layer 42, which do not transmit light R, are not formed in this light-transmitting region 46H. In other words, the light-transmitting region 46H is made of a single silicon oxide from the back surface 40B of the wiring portion 40 to the front surface 40F of the wiring portion 40. A front-side reflective layer 50F is embedded in the wiring portion 40H closest to the photoelectric conversion portion 30H. The front-side reflective layer 50F has an incident opening 50F1 provided in a portion that constitutes the light-transmitting region 46H.

[0134] The photoelectric conversion element 1H of the ninth embodiment can also enhance sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0135] Next, a method for manufacturing an imaging device 101 including a photoelectric conversion element 1H of the ninth embodiment will be described. In the method for manufacturing the imaging device 101, first, an intermediate wafer is prepared by a process for forming a standard front-illuminated imaging device. Next, the intermediate wafer is thinned, leaving only a low-concentration layer (second semiconductor region 32) for the photodiode and a p+ layer (fourth semiconductor region 34) for the electrode. Next, a back-side reflective layer 50B is formed. Next, a support substrate is bonded from the back surface. Finally, a lens unit including an outer lens 10G is formed. As a result, a photoelectric conversion element 1H having a structure in which light R is multiple-reflected inside a photoelectric conversion unit 30 made of silicon is obtained. Below, the method for manufacturing the imaging device 101 will be described in more detail.

[0136] FIG. 25(a) shows the state immediately after the step of forming the CMOS (CIS step). The example of FIG. 25(a) shows the wiring portion 40H and the second semiconductor region 32, third semiconductor region 33, and fourth semiconductor region 34 that constitute the photoelectric conversion portion 30H. First, a semiconductor layer that will later become the second semiconductor region 32 is provided on the semiconductor region 31S. The thickness of the semiconductor layer is, for example, 20 μm. Then, the third semiconductor region 33 and the fourth semiconductor region 34 are respectively provided in the semiconductor layer. Thereafter, the step of forming the DTIs 52 is performed. The DTIs 52 are respectively formed between the fourth semiconductor regions 34 that are formed adjacent to each other. As a result, the second semiconductor region 32, third semiconductor region 33, and fourth semiconductor region 34 that constitute the photoelectric conversion portion 30H are respectively formed. Next, the wiring portion 40H is formed. The thickness of the wiring portion 40H is, for example, 5 μm.

[0137] 25(b), the first support substrate 81 is adhered to the surface 40F of the wiring portion 40.

[0138] Next, as shown in FIG. 26(a), the substrate is turned over so that the first support substrate 81 is located on the bottom side. Subsequently, the semiconductor region 31S located on the top side is thinned. The semiconductor layer remaining after thinning is the first semiconductor region 31. The thickness of the first semiconductor region 31 may be 1 μm or more and 2 μm or less. Alternatively, the thickness of the first semiconductor region 31 may be 3 μm or more and 5 μm or less.

[0139] Next, as shown in FIG. 26(b), a back-side reflective layer 50B is provided. The back-side reflective layer 50B may be an aluminum layer. Next, as shown in FIG. 27(a), a second support substrate 82 is adhered. The second support substrate 82 is adhered to the back-side reflective layer 50B. Next, as shown in FIG. 27(b), the substrate is turned over so that the second support substrate 82 is positioned on the bottom. Subsequently, the first support substrate 81 is removed.

[0140] Next, as shown in FIG. 28(a), a lens unit 83 is formed on the wiring portion 40H. The lens unit 83 is formed by integrating a plurality of outer lenses 10H. Subsequently, as shown in FIG. 28(b), the wafer is housed in a package 84. At this time, the back surface of the second support substrate 82 is fixed to the bottom surface of the package 84. Next, wires 85 are bonded to electrode pads 45 provided on the periphery of the wiring portion 40H. Finally, the opening of the package 84 is closed with a plate 86 that is transparent to light R. Through the above steps, an imaging device 101 including a plurality of photoelectric conversion elements 1H is obtained.

[0141] The imaging device 101 including a plurality of photoelectric conversion elements 1H can also be manufactured by an even simpler process.

[0142] An intermediate wafer 104 shown in FIG. 29(a) is prepared. The intermediate wafer 104 includes a semiconductor substrate 87a, a semiconductor layer 87b including a second semiconductor region 32, a third semiconductor region 33, and a fourth semiconductor region 34, and a wiring portion 40H. A DTI 52 is formed in the semiconductor layer 87b. A front-side reflective layer 50F is formed in the wiring portion 40H. The manufacturing process up to this point may be referred to as, for example, a "pre-process." Next, as shown in FIG. 29(b), the semiconductor substrate 87a is thinned. Specifically, the thickness of the semiconductor substrate 87a is reduced from 750 μm to 200 μm. In other words, the entire semiconductor substrate 87a is thinned. Next, a region L22a of the semiconductor substrate 87a, in which a structure constituting the photoelectric conversion element 1H is provided, is thinned. The partial thinning of the semiconductor substrate 87a is performed by reducing the thickness of the portion corresponding to the region L22a from 200 μm to approximately 21 μm to 25 μm. The thinned portion of the semiconductor substrate 87a becomes the first semiconductor region 31.

[0143] Next, as shown in FIG. 30(a), a back-side reflective layer 50B is formed. The back-side reflective layer 50B is an aluminum film formed by sputtering. Next, as shown in FIG. 30(b), a lens unit 83H including a plurality of outer lenses 10H is formed on the front surface 40F of the wiring portion 40H. Then, as shown in FIG. 31, the lens unit 83H is mounted in a package 84. The specific procedures of the steps shown in FIG. 30(b) and FIG. 31 may be the same as those of the steps shown in FIG. 28(a) and FIG. 28(b).

[0144] Tenth Embodiment The photoelectric conversion element 1A of the second embodiment is also a so-called back-illuminated type. The inner lens 61A employed in the photoelectric conversion element 1A of the second embodiment may also be employed in a front-illuminated photoelectric conversion element 1K as shown in Fig. 32. That is, the photoelectric conversion element 1K of the tenth embodiment includes an outer lens 10K and an inner lens 61K.

[0145] The photoelectric conversion element 1K of the tenth embodiment includes an outer lens 10K, a main spacer 20K, an inner lens 61K, an inner spacer 62K, a wiring portion 40K, a photoelectric conversion portion 30K, a light confinement portion 50K, and a support substrate 71K. Of these, the outer lens 10K, the main spacer 20K, the inner lens 61K, the inner spacer 62K, and the wiring portion 40K constitute a light direction conversion portion 60K. The photoelectric conversion element 1K differs from the photoelectric conversion element 1A of the second embodiment in the arrangement of the photoelectric conversion portion 30K and the wiring portion 40K. The photoelectric conversion element 1K also differs from the photoelectric conversion element 1A of the second embodiment in that it includes a support substrate 71K.

[0146] The photoelectric conversion element 1K of the tenth embodiment can also enhance sensitivity, similar to the photoelectric conversion element 1 of the first embodiment.

[0147] Eleventh Embodiment 33 is a plan view of a photoelectric conversion element 1T according to the eleventh embodiment. In the eleventh embodiment, particular attention is paid to a DTI structure 55T.

[0148] The DTI structure 55T shown in FIG. 33 is intended to further enhance the absorption of light R, which contributes to the generation of charges in the photoelectric conversion unit 30. A pixel region 90T surrounded by the DTI structure 55T corresponds to one pixel. The pixel region 90T includes a photoelectric conversion region 91T and a charge accumulation detection region 92T. The planar shape of the photoelectric conversion region 91T is a regular octagon. The planar shape of the charge accumulation detection region 92T is a square. One side of the regular octagonal photoelectric conversion region 91T protrudes outward, and this protruding portion is the charge accumulation detection region 92T. The length of one side of the charge accumulation detection region 92T is equal to the length of one side of the photoelectric conversion region 91T.

[0149] The photoelectric conversion region 91T includes a photodiode formed by the second semiconductor region 32 and the third semiconductor region 33 (see FIG. 1). Furthermore, the center of the photoelectric conversion region 91T coincides with the center of the incident opening 50B1. For example, the shape of the incident opening 50B1 may be a regular octagon. In other words, the planar shape of the photoelectric conversion region 91T may be similar to the planar shape of the incident opening 50B1.

[0150] The charge accumulation detection region 92T includes a plurality of charge accumulation detection units 70. More specifically, all of the plurality of charge accumulation detection units 70 are arranged in the charge accumulation detection region 92T, and none of them are arranged in the photoelectric conversion region 91. The plurality of charge accumulation detection units 70 are connected to a photodiode formed by the second semiconductor region 32 and the third semiconductor region 33. Charges generated in the photoelectric conversion unit 30 are distributed to the charge accumulation detection units 70 at predetermined timings.

[0151] The function and effect of the photoelectric conversion element 1T of the 11th embodiment can be easily understood by referring to Figure 34. Figure 34 shows the photoelectric conversion element 1T in plan view shown in Figure 33, with the irradiation area IR of light R in the front-side reflective layer 50F shown in Figure 7 superimposed thereon. The photoelectric conversion element 1T of the 11th embodiment includes an outer lens. Note that the photoelectric conversion element 1T of the 11th embodiment may also include another light shaping component (such as an inner lens 61A) included in the photoelectric conversion element 1A, etc. In other words, the photoelectric conversion element 1T of the 11th embodiment only needs to be configured to shape light R concentrically.

[0152] As a result, the light R is irradiated onto multiple annular regions centered on the optical axis Z and gradually spreads outward. Because the photoelectric conversion region 91T is a regular octagon, the distance from the optical axis Z to the DTI structure 55T is equal in eight directions. In other words, the progression of the light R is not impeded in any particular direction. As a result, the light R, which is repeatedly reflected, can be suitably absorbed by the photoelectric conversion unit 30T.

[0153] Here, when light R is incident on the charge accumulation detection unit 70, charge may also be generated in the charge accumulation detection unit 70. The charge accumulation detection unit 70 accumulates charges that are distributed according to a predetermined rule, so charges accumulated without following the rule are noise. The charge accumulation detection region 92T is arranged adjacent to the photoelectric conversion region 91T. This arrangement places the charge accumulation detection unit 70 sufficiently far from the optical axis Z. As a result, the light R is repeatedly reflected and is sufficiently absorbed before reaching the charge accumulation detection region 92T. Therefore, the light R incident on the charge accumulation detection region 92T can be substantially ignored.

[0154] Note that in FIG. 33, the DTI structure 55T is not shown at the boundary between the photoelectric conversion region 91T and the charge accumulation detection region 92T. The charge accumulation detection region 92T must be optically isolated from the photoelectric conversion region 91T and electrically connected. Therefore, for example, a DTI 52B having a third structure as shown in FIG. 4 may be provided at the boundary between the photoelectric conversion region 91T and the charge accumulation detection region 92T. This arrangement further reduces the amount of light R that travels from the photoelectric conversion region 91T to the charge accumulation detection region 92T and confines the light R within the photoelectric conversion region 91T. In other words, the DTI 52B casts a shadow on the charge accumulation detection region 92T, making it difficult for light R to hit the PN junction that constitutes the charge accumulation detection region 92T. As a result, the parasitic sensitivity of the charge accumulation detection unit 70 can be reduced.

[0155] On the other hand, the DTI 52A having the second structure may be used as a partition wall surrounding the photoelectric conversion region 91T. Similarly, the DTI 52A having the second structure may be used as a partition wall surrounding the charge accumulation detection region 92T. The DTI 52A having the second structure can reliably separate adjacent photoelectric conversion elements 1T optically and electrically.

[0156] According to the DTI structure 55T shown in FIG. 33, an imaging device 101T can be configured in which a plurality of photoelectric conversion elements 1T are arranged in a lattice pattern as shown in FIG. 35. A lattice pattern arrangement means that a plurality of photoelectric conversion elements 1T are lined up along mutually perpendicular axes. For example, in a given photoelectric conversion element 1T, the three sides constituting the charge accumulation detection region 92T are in contact with the sides of the photoelectric conversion regions 91T of the photoelectric conversion elements 1T adjacent to the photoelectric conversion element 1T in the vertical, horizontal, and diagonal directions, respectively. The lattice pattern arrangement allows the intervals (pitch) of the photoelectric conversion elements 1T along the horizontal direction to be equal. Similarly, the intervals (pitch) of the photoelectric conversion elements 1T along the vertical direction can also be equalized.

[0157] An imaging device 101T including a photoelectric conversion element 1T according to the eleventh embodiment includes an outer lens 10T that causes multiple reflections of light in a photoelectric conversion unit 30T. The DTI structure 55T shown in FIG. 33 has the longest distance from the incident opening 50B1 of the back-side reflective layer 50B to the charge accumulation detection unit 70. The DTI structure 55T also reduces the volume through which light R is deflected. Therefore, the DTI structure 55T effectively reduces parasitic sensitivity resulting from non-demodulated component light directly entering the charge accumulation detection region 92T. As a result, the photoelectric conversion element 1T according to the eleventh embodiment can exhibit high quantum efficiency for near-infrared light.

[0158] Note that, according to the DTI structure 55T shown in FIG. 33, another arrangement as shown in FIG. 36 can also be adopted. The arrangement shown in FIG. 36 is a staggered arrangement. The arrangement shown in FIG. 36 can also be said to be a so-called honeycomb structure arrangement. When photoelectric conversion elements 1T are arranged at a certain pitch (P) in the horizontal direction, adjacent photoelectric conversion elements 1T in the vertical direction are arranged at a position half the certain pitch (P). With such an arrangement, it is possible to increase the resolution in both the horizontal and vertical directions.

[0159] The photoelectric conversion element 1T may also include an outer lens having the shape shown in FIG. 22. FIG. 37 shows the photoelectric conversion element 1T in plan view shown in FIG. 33, with the irradiation area IR of light R in the front-side reflective layer 50F shown in FIG. 23 superimposed on it. When the outer lens has the shape shown in FIG. 22, it is arranged so that the sweep axis SL of the outer lens is parallel to the axis connecting the photoelectric conversion area 91T and the charge accumulation detection area 92T. In this case, the irradiation area IR of light R does not travel from the entrance opening 50B1 toward the charge accumulation detection area 92T. This makes it possible to effectively suppress noise caused by light R entering the charge accumulation detection area 92T.

[0160] <Twelfth embodiment> In the eleventh embodiment, the DTI structure 55T forming the photoelectric conversion region 91T is illustrated as a regular octagon. The shape of the photoelectric conversion region 91T is not limited to a regular octagon. As shown in FIG. 38, the photoelectric conversion region 91R may be rectangular. FIG. 38 is a plan view of a 4-tap, 1-drain TOF photoelectric conversion element 1R. FIG. 39 shows the photoelectric conversion element 1R of FIG. 38 superimposed with the illumination region IR shown in FIG. 21(b). A shadow is created by the DTI structure 55R to reduce parasitic sensitivity to the charge accumulation detection unit 70. Furthermore, the outer lens 10F shown in the seventh embodiment causes reflected light to travel in a direction perpendicular to the direction of the charge accumulation detection unit 70. As a result, light R is confined within the photoelectric conversion unit 30, preventing light R from directly entering the charge accumulation detection region 92R.

[0161] In the photoelectric conversion element 1R of the twelfth embodiment, the pixel region 90R has a substantially rectangular shape in a plan view. The pixel region 90R has a rectangular photoelectric conversion region 91R and a rectangular charge accumulation detection region 92R. The pixel region 90R is partitioned into the photoelectric conversion region 91R and the charge accumulation detection region 92R by providing DTIs 52A. The DTIs 52A are used as four partition walls surrounding the pixel region 90R. Although not shown in FIG. 38, for example, DTIs 52B having the third structure shown in FIG. 4 may be provided between the DTIs 52A that separate the pixel region 90R.

[0162] A photodiode formed by the second semiconductor region 32 and the third semiconductor region 33 is disposed in the photoelectric conversion region 91R. Furthermore, in the example of Fig. 38, a pair of drains 72 are disposed in the photoelectric conversion region 91R. The other charge accumulation detection units 70 are disposed in the charge accumulation detection region 92R.

[0163] When such a pixel region 90R is employed, the photoelectric conversion element 1R employs the light shaping component of the seventh embodiment. As shown in FIG. 39, the shaped light repeatedly reflects along a predetermined axis KL. In the example shown in FIG. 38, the axis KL is perpendicular to the direction in which the photoelectric conversion region 91R and the charge accumulation detection region 92R are aligned. Therefore, the outer lens 10P is positioned so that the sweep axis SL coincides with the direction in which the photoelectric conversion region 91R and the charge accumulation detection region 92R are aligned. In this way, when the direction in which light diffuses is specific, it is preferable to form the photoelectric conversion region 91R into a rectangular shape.

[0164] Below, we will explain the results of several calculations (Calculation Examples 2, 3, and 4) performed to confirm the effect of the outer lens. We will also explain the results of a calculation (Calculation Example 1) performed to confirm the effect of the outer lens, which is a comparative example.

[0165] First, the analytical models used in the simulation will be described with reference to Fig. 40. As shown in Fig. 40, analytical model 103P includes outer lens 10P. Analytical model 103M includes outer lens 10M. Analytical model 103N includes outer lens 10N. Fig. 40 illustrates three outer lenses 10P, 10M, and 10N stacked together. The configurations of the main spacer 20 and the photoelectric conversion unit 30 are common to calculation examples 1 to 4.

[0166] The following parameters were set to define the shape of the outer lens 10P in calculation example 1. FIG. 41 is a perspective view of the outer lens 10P used in calculation example 1. Lens diameter: 8.4 μm Lens thickness: 5.0 μm Base thickness: 0.8 μm Offset: 1 Base: 1 Rate: 1

[0167] The following parameters were set to define the shape of the outer lens 10M of Calculation Example 2. As can be seen from a comparison with the outer lens 10P of Calculation Example 1, the outer lens 10M of Calculation Example 2 has a large curvature at the top and a small curvature at the sides. FIG. 42 is a perspective view of the outer lens 10M used in Calculation Example 2. Lens diameter: 8.4 μm Lens thickness: 5.0 μm Base thickness: 0.8 μm Offset: 1000 Base: 1 Rate: 1

[0168] The following parameters were set to define the shape of the outer lens 10N in calculation example 3. FIG. 43 is a perspective view of the outer lens 10N used in calculation example 3. The lens thickness of the outer lens 10N is different from the lens thickness of the outer lens 10M. The other parameters of the outer lens 10N are the same as the parameters of the outer lens 10M. Lens diameter: 8.4 μm Lens thickness: 3.0 μm Base thickness: 0.8 μm Offset: 1000 Base: 1 Rate: 1

[0169] The refractive index of the outer lenses 10P, 10M, and 10N was set to 1.58.

[0170] The first layer L1 corresponds to the main spacer 20. Details of the first layer L1 and the second layer L2 are as follows. First layer L1: Microlens material, refractive index (1.54 to 1.58) Second layer L2: Dielectric multilayer film (material: silicon nitride, silicon oxide), refractive index (1.46 to 1.92)

[0171] The third layer L3 corresponds to the photoelectric conversion section 30. Details of the third layer L3 are as follows. Third layer L3: Material: Silicon (Si), refractive index (automatic setting)

[0172] The conditions for the light incident on the outer lenses 10P, 10M, and 10N were set as follows. Wavelength: 870nm Direction: Normal incidence (ζ=0°, φ=0°) Light intensity: 1W / cm -2 Incidence position: Two-dimensional arrangement (60 points (X) x 60 points (Y) = 3600 points)

[0173] Using the above conditions, we performed a numerical simulation using the ray tracing method, and obtained the light intensity distribution as a contour diagram.

[0174] <Calculation Example 1 (Comparative Example)> In calculation example 1, the outer lens 10P was used. FIGS. 44 and 45 are contour diagrams of the light intensity distribution. In the contour diagram of FIG. 44, it was found that the light intensity is strongest in region A37a and decreases toward region A37b. FIG. 44 also shows that region A37a, where the light intensity is strong, appears near the surface of the photoelectric conversion unit 30 (Z=0.0 μm). FIG. 45 is a contour diagram showing a cross section of the portion of FIG. 44 where Z=15 μm. For example, the position where Z=15 μm is also considered to be the position where the front-side reflective layer 50F (see FIG. 1) is disposed. FIG. 45 shows that regions with strong light intensity occur in region A38a near the center and region A38b near the periphery. In other words, it was found that the light intensity distribution of the outer lens 10P does not have a circular shape. According to this distribution, light R irradiated onto the region A38a near the center is reflected by the front-side reflective layer 50F and then exits the photoelectric conversion unit 30 through the incident opening 50B1 (see FIG. 1). In other words, of the incident light R, a light component that does not generate electric charges is generated in the photoelectric conversion unit 30.

[0175] <Calculation example 2> In Calculation Example 2, the outer lens 10M was used. FIGS. 46 and 47 are contour diagrams of the light intensity distribution. In the contour diagram of FIG. 46, the intensity is strongest in region A39a, and decreases toward region A39b. FIG. 46 also shows that region A39a, where the light intensity is high, appears near the surface of the photoelectric conversion unit 30 (Z=0.0 μm). FIG. 47 is a contour diagram showing a cross section of the portion of FIG. 46 where Z=15 μm. In Calculation Example 2, the light intensity is weak in region A40a near the center, gradually increases toward the outside, reaches a maximum in region A40b, and then decreases. In other words, the outer lens 10M exhibits a circular light intensity distribution. According to this distribution, for example, when light irradiated onto region A40b is reflected by the front-side reflective layer 50F, it travels toward the back-side reflective layer 50B without exiting the photoelectric conversion unit 30 through the incident opening 50B1. Therefore, it was found that the outer lens 10M can change the traveling direction of the light R so as to suitably confine the light R within the photoelectric conversion unit 30.

[0176] Now, let us refer again to the contour diagram of FIG. 46. Looking at the distribution of light intensity in the third layer L3 in the contour diagram of FIG. 46, it can be seen that light R spreads in the third layer L3 (photoelectric conversion section 30) (see arrow S39). The spread of light R in the third layer L3 can be better understood by looking at the ray diagram of FIG. 48. We have considered the cause of this spread of light R. FIG. 49 illustrates only one of the rays shown in FIG. 48. Ray L41a represents incident light. Ray L41c represents refracted light. As shown in FIG. 49, it is believed that the spread of light R is caused by the fact that the intersection L41p of the optical axis Z of the outer lens 10M and the rays L41a and L41c is located on the surface of the third layer L3.

[0177] <Calculation example 3> Therefore, we investigated factors that suppress the spread of light R. We focused on lens thickness as a factor that suppresses the spread of light R. In calculation example 3, the thickness of the outer lens 10N was set to 3 μm.

[0178] According to the contour diagram shown in FIG. 50, it can be seen that the light intensity distribution in the third layer L3 does not spread in the range L43a from Z=0 μm to 10.0 μm, but rather is narrowed. This can also be clearly understood from the region L44a in the ray diagram of FIG. 51. The cause of this distribution of light R was considered. FIG. 52 illustrates only one of the rays shown in FIG. 51. Ray L45a represents incident light. Ray L45c represents refracted light. As shown in FIG. 52, it is believed that the cause of the distribution of light R is that the intersection L45p of the optical axis Z of the outer lens 10N and ray L45c is located inside the third layer L3.

[0179] We also confirmed the shape of the light intensity distribution in the third layer L3. Figures 53, 54, and 55 are contour diagrams of light intensity at different cross-sectional positions. Figure 53(a) corresponds to Z=0 μm, and Figure 53(b) corresponds to Z=5 μm. Figure 54(a) corresponds to Z=10 μm, and Figure 54(b) corresponds to Z=15 μm. Figure 55(a) corresponds to Z=20 μm, and Figure 55(b) corresponds to Z=25 μm. As shown in each diagram, it was found that the light intensity distribution was circular in shape at all cross-sections. [Explanation of symbols]

[0180] 1, 1A, 1B, 1C, 1D, 1E, 1H, 1K, 1R, 1T... Photoelectric conversion element, 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10K, 10M, 10N, 10P, 10T... Outer lens, 30, 30A, 30B1, 30C, 30D, 30E, 30F1, 30H, 30K, 30T... Photoelectric conversion unit, 30B... Optical Back surface (first surface) of the electrical conversion unit, 30F... surface (second surface) of the photoelectric conversion unit, 50, 50D, 50E, 50H, 50K... light confinement unit, 61A, 61B, 61C, 61K... inner lens, 63... mirror (reflecting unit), L5a, L14a, L15a... first region, L5b, L14b, L15b... second region, R, R6a, R6b, R7a... light, Z... optical axis.

Claims

1. A photoelectric conversion unit including a rear surface of a photoelectric conversion unit and a front surface of a photoelectric conversion unit opposite to the rear surface of the photoelectric conversion unit, the photoelectric conversion unit generating charges based on light received from the rear surface of the photoelectric conversion unit; a charge accumulation detection unit that accumulates the charge received from the photoelectric conversion unit; a wiring section including a rear surface of the wiring section facing the front surface of the photoelectric conversion section, the charge accumulation detection section being provided on the rear surface of the wiring section; a light confinement section that confines the light in the photoelectric conversion section so that the light travels back and forth between a rear surface of the photoelectric conversion section and a front surface of the photoelectric conversion section; a first lens disposed on the rear surface of the photoelectric conversion unit; and a light exit surface that provides the light that has passed through the first lens to the photoelectric conversion unit, and a light direction change unit that is disposed on the rear surface of the photoelectric conversion unit outside an area sandwiched between the rear surface of the photoelectric conversion unit and the front surface of the photoelectric conversion unit and determines the traveling direction of the light in the photoelectric conversion unit, the photoelectric conversion unit includes a first conductivity type semiconductor layer disposed on a rear surface side of the photoelectric conversion unit, and a second conductivity type semiconductor layer disposed on a front surface side of the photoelectric conversion unit and constituting a pn junction in cooperation with the first conductivity type semiconductor layer, The optical confinement portion is a first reflective layer provided between a rear surface of the photoelectric conversion unit of the photoelectric conversion unit and the light exit surface of the light direction conversion unit, the first reflective layer including an opening for receiving the light; a second reflective layer embedded in the wiring portion so as to be disposed on a surface side of the photoelectric conversion portion of the photoelectric conversion portion; an inner partition wall portion extending in a direction from the rear surface of the photoelectric conversion unit toward the front surface of the photoelectric conversion unit and optically separating the charge accumulation detection unit from the photoelectric conversion unit; an end portion of the inner partition wall on the surface side of the photoelectric conversion unit is spaced from the wiring unit and is in contact with the semiconductor layer of the first conductivity type; the light direction conversion unit guides the light incident on the photoelectric conversion unit through the opening so as to be condensed at a position on the second reflective layer away from a position where an optical axis of the first lens and the second reflective layer intersect, A photoelectric conversion element in which the light guided to a position away from the position where the optical axis and the second reflective layer intersect travels in a direction away from the optical axis of the first lens each time the light is repeatedly reflected between the back surface of the photoelectric conversion unit and the front surface of the photoelectric conversion unit.

2. In a cross-sectional shape of the first lens including the optical axis, a line segment indicating the surface that receives the light includes a first curved portion and a second curved portion that is farther from the optical axis than the first curved portion, The photoelectric conversion element according to claim 1 , wherein the curvature of the second curved portion is smaller than the curvature of the first curved portion.

3. The photoelectric conversion element according to claim 1 , wherein in a cross section of the first lens that includes the optical axis, a line segment that indicates the surface that receives the light includes a portion that is defined as an arc.

4. The photoelectric conversion element according to claim 1 , wherein in a cross-sectional shape of the first lens including the optical axis, a line segment representing the surface that receives the light includes a portion defined as a parabola.

5. In a cross-sectional shape of the first lens including the optical axis, a line segment indicating the surface that receives the light includes a first straight line portion and a second straight line portion that is farther from the optical axis than the first straight line portion, 2. The photoelectric conversion element according to claim 1, wherein a second tilt angle between a virtual reference axis perpendicular to the optical axis and the second straight portion is larger than a first tilt angle between the virtual reference axis and the first straight portion.

6. 6. The photoelectric conversion element according to claim 2, wherein the first lens has a shape that is rotationally symmetric about the optical axis.

7. 6. The photoelectric conversion element according to claim 2, wherein the first lens has a shape obtained by elongating the cross-sectional shape in a direction perpendicular to the optical axis.

8. The photoelectric conversion element according to any one of claims 1 to 7, wherein the light direction conversion unit further includes, in addition to the first lens, a second lens arranged between the first lens and the back surface of the photoelectric conversion unit.

9. In a cross-sectional shape of the second lens including the optical axis, a line segment indicating the surface that accepts the light includes a third curved portion and a fourth curved portion that is farther from the optical axis than the third curved portion, The photoelectric conversion element according to claim 8 , wherein the curvature of the fourth curved portion is smaller than the curvature of the third curved portion.

10. The photoelectric conversion element according to claim 8 , wherein in a cross-sectional shape of the second lens that includes the optical axis, a line segment that indicates the surface that receives the light includes a portion that is defined as an arc.

11. The photoelectric conversion element according to claim 8 , wherein in a cross-sectional shape of the second lens that includes the optical axis, a line segment that indicates the surface that receives the light includes a portion that is defined as a parabola.

12. In a cross-sectional shape of the second lens including the optical axis, a line segment indicating the surface that accepts the light includes a third straight line portion and a fourth straight line portion that is farther from the optical axis than the third straight line portion, 9. The photoelectric conversion element according to claim 8, wherein a fourth tilt angle between a virtual reference axis perpendicular to the optical axis and the fourth straight line portion is larger than a third tilt angle between the virtual reference axis and the third straight line portion.

13. The photoelectric conversion element according to any one of claims 1 to 12, wherein the light direction conversion section includes a reflecting section disposed on a surface side of the photoelectric conversion section.

14. the photoelectric conversion unit includes a portion that overlaps with the opening of the first reflective layer, 14. The photoelectric conversion element according to claim 1, wherein the charge accumulation detection section does not include a portion that overlaps with the opening of the first reflective layer.

15. A photoelectric conversion element according to any one of claims 1 to 14, wherein the portion of the first conductivity type semiconductor layer sandwiched between the end of the inner partition portion on the surface side of the photoelectric conversion portion and the back surface of the wiring portion is a path for moving charges from the photoelectric conversion portion to the charge accumulation detection portion.

16. the light confinement portion further includes an antireflection layer provided between the semiconductor layer of the first conductivity type and the first reflective layer, The photoelectric conversion element according to any one of claims 1 to 15, wherein the end of the inner partition wall on the back surface side of the photoelectric conversion unit penetrates the semiconductor layer of the first conductivity type and contacts the anti-reflection layer.

17. 17. The photoelectric conversion element according to claim 1, wherein the first reflective layer includes an opening formed on an end of the inner partition wall on a rear surface side of the photoelectric conversion unit.

18. The photoelectric conversion element according to any one of claims 1 to 17, wherein the light confinement section further has an outer partition wall section extending in a direction from the back surface of the photoelectric conversion section toward the surface of the photoelectric conversion section and surrounding the photoelectric conversion section and the charge accumulation detection section.

19. A photoelectric conversion element as described in claim 1, wherein the light guided to a position away from the position where the optical axis and the second reflective layer intersect forms a ring-shaped reflected light on the second reflective layer.

20. A photoelectric conversion element as described in claim 1, wherein the light incident at the same position along the optical axis on the light-incident surface of the first lens is incident at a position equidistant from the optical axis when it reaches the second reflective layer.

21. A photoelectric conversion unit including a rear surface of a photoelectric conversion unit and a front surface of a photoelectric conversion unit opposite to the rear surface of the photoelectric conversion unit, the photoelectric conversion unit generating charges based on light received from the rear surface of the photoelectric conversion unit; a charge accumulation detection unit that accumulates the charge received from the photoelectric conversion unit; a light confinement unit that confines the light in the photoelectric conversion unit so that the light travels back and forth within the photoelectric conversion unit; a light direction conversion unit that includes a first lens arranged on the back surface side of the photoelectric conversion unit and a reflecting unit arranged on the front surface side of the photoelectric conversion unit so as to overlap with the optical axis of the first lens, and that determines the traveling direction of the light in the photoelectric conversion unit; a wiring portion having a back surface on which the photoelectric conversion portion and the charge accumulation detection portion are provided, the light direction changer is a region sandwiched between the rear surface of the photoelectric conversion unit and the front surface of the photoelectric conversion unit, and is disposed on the rear surface side of the photoelectric conversion unit, and causes the light to travel in a direction away from the optical axis of the first lens each time the light is repeatedly reflected between the rear surface of the photoelectric conversion unit and the front surface of the photoelectric conversion unit, the wiring portion includes the reflective portion having a layered structure in which a plurality of insulating regions formed of an insulating material and a plurality of metal regions formed of a metal material are alternately layered, the plurality of metal regions are arranged in a stepped pattern such that a width thereof in a direction intersecting with the optical axis increases from a back surface of the wiring portion facing the front surface of the photoelectric conversion portion toward a front surface of the wiring portion opposite to the back surface of the wiring portion, the reflective portion is a pseudo-reflective structure that functions as a pseudo-reflective surface by having a step of the laminated structure including the plurality of metal regions arranged in a stepped pattern that is smaller than the wavelength of the light, A photoelectric conversion element, wherein the light confinement section has a first reflective layer on the back surface side of the photoelectric conversion section, between the photoelectric conversion section and the first lens, and including an opening for receiving the light, and a second reflective layer on the front surface side of the photoelectric conversion section of the photoelectric conversion section, opposite the back surface of the photoelectric conversion section, embedded in the wiring section, and arranged so as not to overlap with the optical axis of the first lens.

22. The photoelectric conversion element according to claim 21 , wherein the reflecting portion reflects the light so that the light is collected on a circumference of a circle centered on the optical axis in the first reflecting layer.

23. A photoelectric conversion unit including a rear surface of a photoelectric conversion unit and a front surface of a photoelectric conversion unit opposite to the rear surface of the photoelectric conversion unit, the photoelectric conversion unit receiving light from the rear surface of the photoelectric conversion unit and generating electric charges; a charge accumulation detection unit that accumulates the charge generated by the photoelectric conversion unit; a light direction conversion unit including a first lens arranged on the rear surface side of the photoelectric conversion unit and a light exit surface that provides the light that has passed through the first lens to the photoelectric conversion unit, and that determines the traveling direction of the light in the photoelectric conversion unit; a first reflective layer provided between the rear surface of the photoelectric conversion unit and the light exit surface of the light direction conversion unit and including an opening for receiving the light, and a second reflective layer provided on the front surface side of the photoelectric conversion unit, and a light confinement unit that confines the light incident from the opening in the photoelectric conversion unit so that the light goes back and forth in the photoelectric conversion unit, the light direction conversion unit guides the light incident on the photoelectric conversion unit through the opening so as to be condensed at a position on the second reflective layer away from a position where an optical axis of the first lens and the second reflective layer intersect, A photoelectric conversion element in which the light guided to a position away from the position where the optical axis and the second reflective layer intersect travels in a direction away from the optical axis of the first lens each time the light is repeatedly reflected between the back surface of the photoelectric conversion unit and the front surface of the photoelectric conversion unit.

Images