Back-thinned image sensor

Abstract

To provide a backside incident type image sensor that can improve the processing speed.SOLUTION: A backside incident type image sensor 1 includes: a semiconductor layer 30 to which the ground potential is applied; and a semiconductor substrate 10. The semiconductor layer 30 includes a light receiving part 13 that generates a signal charge according to the incident light hν from a back surface 10b side, and an analog-to-digital converter 17 that converts a signal voltage into a digital signal. A thickness of the semiconductor substrate 10 in a first direction is relatively thicker in a second region 10B of the substrate 10 corresponding to an analog-digital converter 17 in a view from the first direction than in a first region 10A of the semiconductor substrate 10 corresponding to the light receiving part 13 in the view from the first direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a back-illuminated image sensor. [Background technology]

[0002] Currently, monolithic CCD-CMOS sensors are known in which a CCD section responsible for receiving light and transferring charges and a CMOS section responsible for signal processing such as analog-to-digital conversion are formed on a single chip. Non-Patent Document 1 describes a CCD-in-CMOS sensor. This CCD-in-CMOS sensor is capable of backside illumination. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Pierre Boulenc, Jo Robbelein, Linkun Wu, Vasyl Motsnyi, Luc Haspeslagh, Stefano Guerrieri, Jonathan Borremans, Maarten Rosmeulen “High Speed ​​Backside Illuminated TDI CCD-in-CMOSSensor” [Searched on July 29, 2021], Internet<http: / / www.imagesensors.org / Past%20Workshops / 2017%20Workshop / 2017%20Papers / R50.pdf> Summary of the Invention [Problem to be solved by the invention]

[0004] Currently, there is a growing demand for higher speeds, even for the monolithic CCD-CMOS sensors described above. However, as speeds increase, the analog-to-digital conversion speed also improves, which increases the current consumption of the signal processing circuit and leads to larger fluctuations in the amount of current consumption, which can cause problems such as fluctuations in the ground potential (substrate potential). Fluctuations in the ground potential can have adverse effects, such as causing malfunctions in the signal processing circuit and superimposing noise on the output signal of the CCD section.

[0005] This problem becomes particularly apparent when a structure is adopted in which the substrate is thinned to expose the light-sensitive region and allow light to directly enter the light-sensitive region in order to increase the sensor's sensitivity in order to compensate for the decrease in the amount of light incident on the sensor as speed increases. This is because the substrate, which functions as the ground for the signal processing circuit, becomes highly resistive as it is thinned. In other words, with conventional monolithic CCD-CMOS sensors, it was difficult to improve processing speed by achieving both high sensitivity and stable ground.

[0006] An object of the present invention is to provide a back-illuminated image sensor capable of improving the processing speed. [Means for solving the problem]

[0007] A back-illuminated imaging element according to the present invention comprises a semiconductor substrate having a front surface and a back surface opposite the front surface, to which a ground potential is applied, and a semiconductor layer formed on the front surface, the semiconductor layer including a light receiving portion that generates signal charges in response to light incident from the back surface side, a first element portion that outputs a signal voltage in response to the signal charges, and a second element portion including an analog-to-digital converter that converts the signal voltage output from the first element portion into a digital signal, and the thickness of the semiconductor substrate in a first direction intersecting the front surface and the back surface is relatively thicker in a second region of the semiconductor substrate that corresponds to the analog-to-digital converter as viewed from the first direction than in a first region of the semiconductor substrate that corresponds to the light receiving portion as viewed from the first direction.

[0008] In this back-illuminated image sensor, a semiconductor layer formed on the surface of a semiconductor substrate has a first element portion and a second element portion. The first element portion includes a light-receiving portion that generates signal charges in response to light incident from the back side of the semiconductor substrate. The second element portion includes an analog-to-digital converter that converts the signal voltage into a digital signal. The thickness of the semiconductor substrate is relatively thicker in a second region corresponding to the analog-to-digital converter than in a first region corresponding to the light-receiving portion. In other words, the semiconductor substrate is thinner in the region corresponding to the light-receiving portion and thicker in the region corresponding to the analog-to-digital converter. As a result, the amount of light incident on the light-receiving portion from the first region of the semiconductor substrate is increased, and high resistance in the second region of the semiconductor substrate corresponding to the analog-to-digital converter is avoided. Therefore, this back-illuminated image sensor can improve processing speed by achieving both high sensitivity and ground stabilization.

[0009] In the back-illuminated imaging element according to the present invention, the semiconductor substrate may include a third region located between the first region and the second region when viewed from the first direction, and the thickness of the semiconductor substrate may be made relatively thinner in the first region than in the second region by a recess provided on the back surface from the first region to the third region. In this case, in the back-illuminated imaging element according to the present invention, the inner surface of the recess is located in the third region and may include an inclined surface that is inclined so that the thickness of the semiconductor substrate gradually increases from the first region to the second region. In this way, the recess provided on the back surface of the semiconductor substrate can make the first region thin while making the second region thick.

[0010] In the back-illuminated image sensor according to the present invention, the first element portion may include an amplifier portion that converts signal charges generated in the light receiving portion into signal voltages, and the amplifier portion may be located in the third region when viewed from the first direction. In this way, the amplifier portion that is less affected by the thickness of the semiconductor substrate can be disposed in the third region.

[0011] In the back-illuminated imaging element according to the present invention, the semiconductor layer may be exposed from the semiconductor substrate at the bottom of the recess, which makes it possible to further increase the amount of light incident on the light receiving section from the first region. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a back-illuminated image sensor capable of improving the processing speed. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a back-illuminated imaging element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a detailed cross-sectional view of the back-illuminated image sensor shown in FIG. [Figure 3] FIG. 10 is a schematic diagram showing a back-illuminated imaging element according to a first modified example. [Figure 4] FIG. 10 is a schematic diagram showing a back-illuminated imaging element according to a second modified example. [Figure 5] FIG. 10 is a schematic diagram showing a back-illuminated imaging element according to a third modified example. [Figure 6] FIG. 10 is a schematic diagram showing a back-illuminated imaging element according to a fourth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment will be described in detail below with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and redundant description may be omitted.

[0015] FIG. 1 is a schematic diagram showing a back-illuminated imaging element according to this embodiment. (a) of FIG. 1 is a plan view, and (b) of FIG. 1 is a schematic cross-sectional view. FIG. 2 is a detailed cross-sectional view of the back-illuminated imaging element shown in FIG. 1. As shown in FIGS. 1 and 2, the back-illuminated imaging element 1 includes a first element section 3 and a second element section 5. The first element section 3 is, for example, a charge coupled device (CCD) section responsible for light reception and charge transfer, and the second element section 5 is, for example, a complementary metal oxide semiconductor (CMOS) section responsible for signal processing such as analog-to-digital conversion. That is, the back-illuminated imaging element 1 is, for example, a monolithic CCD-CMOS sensor. The size of the back-illuminated imaging element 1 is, for example, approximately 20 mm in the longitudinal direction and approximately 10 mm in the lateral direction in a plan view.

[0016] The back-illuminated image sensor 1 includes a semiconductor substrate 10, a semiconductor layer 30, a first insulating layer 40, and a second insulating layer 50. The semiconductor substrate 10 includes a front surface 10a and a back surface 10b opposite the front surface 10a. The semiconductor substrate 10 has, for example, P-type conductivity and is, for example, a silicon substrate. The semiconductor layer 30 is formed on the front surface 10a of the semiconductor substrate 10. The semiconductor layer 30 has, for example, P-type conductivity and is, for example, an epitaxially grown layer containing silicon. The first element portion 3 and the second element portion 5 are formed in the semiconductor layer 30. The thickness of the semiconductor layer 30 is, for example, about 10 μm.

[0017] The first element section 3 includes a light receiving section (pixel section) 13 and an amplifier section 15. The light receiving section 13 includes, for example, a plurality of pixels arranged two-dimensionally, and generates signal charges in response to incident light hν from the back surface 10b of the semiconductor substrate 10. The amplifier section 15 converts the signal charges generated by the light receiving section 13 into signal voltages. The light receiving section 13 and the amplifier section 15 are electrically connected to each other by a wiring W1. An example of the size of the light receiving section 13 is approximately 7 mm × 7 mm in a planar view. An example of the size of the amplifier section 15 is approximately 7 mm in the longitudinal direction and approximately 20 μm in the lateral direction (the direction from the light receiving section 13 toward the analog-to-digital converter 17 described later) in a planar view. Furthermore, a wiring W1 and a wiring W3 described later are provided on both sides of the amplifier section 15. An example of the length of the wiring W1 is approximately 50 μm, and the length of the wiring W3 is approximately 150 μm. The wiring W1 may be a transfer electrode. Thus, the lengths of the wiring W1 and the wiring W3 are each greater than the size of the amplifier unit 15 in the short side direction. That is, the distance between the light receiving unit 13 and the amplifier unit 15, and the distance between the amplifier unit 15 and an analog-to-digital converter 17 (described later) are each greater than the size of the amplifier unit 15 in the short side direction.

[0018] The second element unit 5 includes an analog-to-digital converter 17, a multiplexer unit 19, a driver unit 21, and an output unit 23. The analog-to-digital converter 17 converts the signal voltage output from the first element unit 3 into a digital signal. The multiplexer unit 19 combines multiple digital signals from the analog-to-digital converter 17 into a single digital signal. The driver unit 21 includes, for example, a phase-locked loop (PLL) and a timing generator, and generates a signal for driving the analog-to-digital converter 17. The output unit 23 includes, for example, an LVDS (Low Voltage Differential signaling) unit, and converts the digital signal from the multiplexer unit 19 into a differential voltage signal and outputs it to the outside.

[0019] The amplifier unit 15 and the analog-to-digital converter 17 are electrically connected to each other by a wire W3, and the analog-to-digital converter 17 and the multiplexer unit 19 are electrically connected to each other by a wire W5. Furthermore, the analog-to-digital converter 17 and the driver unit 21 are electrically connected to each other by a wire W7, and the multiplexer unit 19 and the output unit 23 are electrically connected to each other by a wire W9.

[0020] The first insulating layer 40 is formed on the surface of the semiconductor layer 30 opposite to the semiconductor substrate 10, via an insulating film 45 such as a silicon oxide film. The first insulating layer 40 is, for example, a BPSG (Boron Phospho Silicate Glass) layer. The thickness of the first insulating layer 40 is, for example, about 1 μm. The second insulating layer 50 is formed on the surface of the first insulating layer 40 opposite to the semiconductor layer 30. The second insulating layer 50 includes, for example, silicon oxide (for example, SiO2). The thickness of the second insulating layer 50 is, for example, about 1 μm.

[0021] In the back-illuminated image sensor 1 described above, when incident light hν enters the light-receiving section 13, the incident light hν is converted into signal charges in each pixel of the light-receiving section 13. The signal charges are transferred between pixels and converted into signal voltages by an amplifier section 15 provided at the end of the light-receiving section. The signal voltages are converted into digital signals by an analog-to-digital converter 17. The digital signals are combined into a single digital signal by a multiplexer section 19. This digital signal is converted into a differential voltage signal by an output section 23 and output.

[0022] Next, the structure of each layer will be described. In the semiconductor layer 30, the first element portion 3 includes an N-type channel region 31, a P-type well region 32, and a P + The N-type channel region 31 and the P-type well region 32 each have a pair of N + A part of the N-type channel region 31 is used for the light receiving section 13. The remaining part of the N-type channel region 31 and the P-type well region 32 are used for the amplifier section 15. +The P-type impurity concentration is, for example, 1×10 17 cm -3 It means that the level is high. + The type is defined as an N-type impurity concentration of, for example, 1×10 20 cm -3 It means high, such as above a certain level.

[0023] In addition, an N-type deep well region 34 is formed in the second element portion 5 of the semiconductor layer 30. In the N-type deep well region 34, a P-type well region 35 and an N-type well region 36 are formed. In the P-type well region 35, a plurality of N + The N-type well region 36 has a plurality of P + In the second element portion 5, a P type region 39 is formed outside the N type deep well region 34. + A mold region 39 is formed, and the P + The ground GND is electrically connected to the mold region 39. + A ground potential is applied to the semiconductor substrate 10 via the P-type region 39 and the P-type semiconductor layer 30 .

[0024] P + Type regions 39 and N + The mold region 37 is exposed on the surface of the semiconductor layer 30 via an insulating film 45. A plurality of wiring portions 41 are formed inside the first insulating layer 40. The wiring portions 41 include, for example, polysilicon. The wiring portions 41 are formed on the semiconductor layer 30 side and are formed so as to be in contact with the semiconductor layer 30 via the insulating film 45. A plurality of metal wiring portions 51 are formed inside the second insulating layer 50. The metal wiring portions 51 include, for example, aluminum. The metal wiring portions 51 can provide, for example, the above-mentioned wirings W1 to W9.

[0025] Here, the semiconductor substrate 10 includes a first region 10A, a second region 10B, and a third region 10C. The first region 10A is a region corresponding to the light receiving portion 13. In other words, the first region 10A is a region including the light receiving portion 13 when viewed from a first direction intersecting (orthogonal to) the front surface 10a and the back surface 10b. The second region 10B is a region corresponding to the analog-to-digital converter 17. In other words, the second region 10B is a region including the analog-to-digital converter 17 when viewed from the first direction. The third region 10C is located between the first region 10A and the second region 10B.

[0026] The thickness of the semiconductor substrate 10 in the first direction (the distance between the front surface 10a and the back surface 10b) is relatively thicker in the second region 10B than in the first region 10A. This point will be explained in more detail. A recess 60 recessed toward the front surface 10a is formed in the back surface 10b of the semiconductor substrate 10 from the first region 10A to the third region 10C. As a result, the thickness of the semiconductor substrate 10 is relatively thinner in the first region 10A than in the second region 10B. On the other hand, the thickness of the semiconductor substrate 10 is maintained in the second region 10B. That is, the semiconductor substrate 10 is thinned in the region corresponding to the light receiving unit 13, while the original thickness (e.g., 300 μm) remains in the region corresponding to the analog-digital converter 17.

[0027] In particular, here, the recess 60 penetrates the semiconductor substrate 10 (i.e., the bottom surface 61 of the recess 60 becomes the surface of the semiconductor layer 30). In other words, the thickness of the semiconductor substrate 10 is zero at least in the first region 10A. In further other words, at the bottom of the recess 60, the semiconductor layer 30 is exposed from the semiconductor substrate 10.

[0028] The inner side surface of the recess 60 is located in the third region 10C and includes an inclined surface 63 that is inclined so that the thickness of the semiconductor substrate 10 gradually (continuously) increases from the first region 10A to the second region 10B. The inclined surface 63 does not reach the second region 10B when viewed from the first direction. The amplifier section 15 (and the wirings W1 and W3) are disposed on the third region 10C including the inclined surface 63. That is, the amplifier section 15 is located in the third region 10C including the inclined surface 63 when viewed from the first direction. The recess 60 can be formed by, for example, etching. The width of the third region 10C in the direction from the first region 10A to the second region 10B is the sum of the lengths of the amplifier section 15, the wiring W1, and the wiring W2, and is, for example, approximately 220 μm. By ensuring this width of the third region 10C, the inclined surface 63 does not reach the second region 10B, and it becomes possible to maintain the thickness of the semiconductor substrate 10 over the entire second region 10B.

[0029] Here, the third region 10C includes a portion whose thickness varies according to the inclination of the inclined surface 63 and a portion whose thickness is constant and equal to the thickness of the second region 10B. The semiconductor substrate 10 further includes a fourth region 10D. The fourth region 10D is located on the opposite side of the second region 10B from the first region 10A and the third region 10C. The fourth region 10D corresponds to the portion of the second element portion 5 other than the analog-digital converter 17.

[0030] Here, the fourth region 10D mainly includes the multiplexer section 19 and the output section 23 when viewed from the first direction. The thickness of the semiconductor substrate 10 in the fourth region 10D is constant and is the thickness of the second region 10B. In addition, a frame portion 10c having the same thickness as the second region 10B is formed on the outer periphery of the back-illuminated image sensor 1 (here, the outer edge of the first region 10A).

[0031] An anti-reflection film 71 is formed on the rear surface 10b of the semiconductor substrate 10, including the inner surface of the recess 60. The anti-reflection film 71 contains, for example, silicon oxide (e.g., SiO2). The thickness of the anti-reflection film 71 is, for example, about 0.1 μm. A light-shielding film 73 is formed on the anti-reflection film 71. The light-shielding film 73 is made of, for example, aluminum. The thickness of the light-shielding film 73 is, for example, about 1 μm. An opening is formed in the light-shielding film 73 above the bottom surface 61 of the recess 60, and the light-receiving unit 13 is exposed from the opening when viewed from the first direction. The opening in the anti-reflection film 71 provides an incident portion for the incident light hν to the light-receiving unit 13. In addition, in an area of ​​the semiconductor layer 30 corresponding to the bottom surface 61 of the recess 60, P + A mold area 38 is formed.

[0032] As described above, in the back-illuminated image sensor 1, the semiconductor layer 30 formed on the front surface 10a of the semiconductor substrate 10 has the first element portion 3 and the second element portion 5. The first element portion 3 includes a light receiving portion 13 that generates signal charges in response to incident light hν from the back surface 10b side of the semiconductor substrate 10. The second element portion 5 includes an analog-to-digital converter 17 that converts a signal voltage into a digital signal. The thickness of the semiconductor substrate 10 is made relatively thicker in the second region 10B corresponding to the analog-to-digital converter 17 than in the first region 10A corresponding to the light receiving portion 13.

[0033] In other words, the semiconductor substrate 10 is thin in the region corresponding to the light receiving section 13 and thick in the region corresponding to the analog-digital converter 17. As a result, the amount of light incident on the light receiving section 13 from the first region 10A of the semiconductor substrate 10 is increased, and high resistance is avoided in the second region 10B of the semiconductor substrate 10 corresponding to the analog-digital converter 17. Therefore, the back-illuminated image sensor 1 can improve processing speed by achieving both high sensitivity and ground stabilization.

[0034] In the back-illuminated imaging element 1, the semiconductor substrate 10 includes a third region 10C located between the first region 10A and the second region 10B when viewed from the first direction. The thickness of the semiconductor substrate 10 is made relatively thinner in the first region 10A than in the second region 10B by a recess 60 provided on the back surface 10b from the first region 10A to the third region 10C. Furthermore, in the back-illuminated imaging element 1, the inner surface of the recess 60 is located in the third region 10C and includes an inclined surface 63 that is inclined so that the thickness of the semiconductor substrate 10 gradually increases from the first region 10A to the second region 10B. Thus, the recess 60 provided on the back surface 10b of the semiconductor substrate 10 can make the first region 10A thinner while making the second region 10B thicker. Furthermore, since the inner surface of the recess 60 has the inclined surface 63 (since the inclined surface 63 extends to the opening edge of the recess 60), the opening edge of the recess 60 has a blunt angle. This prevents chipping or cracking from occurring at the opening edge of the recess 60, and as a result, damage to the back-illuminated image pickup element 1 is prevented.

[0035] Furthermore, in the back-illuminated image sensor 1, the first element section 3 includes an amplifier section 15 that converts the signal charges generated in the light receiving section 13 into signal voltages. The amplifier section 15 is located in the third region 10C when viewed from the first direction. In this way, the amplifier section 15 can be disposed in the third region 10C in a manner that is less affected by the thickness of the semiconductor substrate 10.

[0036] Furthermore, in the back-illuminated imaging element 1, the semiconductor layer 30 is exposed from the semiconductor substrate 10 at the bottom of the recess 60. This makes it possible to further increase the amount of light incident on the light receiving section 13 from the first region 10A.

[0037] The above embodiment has described one aspect of the present invention. Therefore, the present invention is not limited to the back-illuminated image sensor 1 described above, and various modifications are possible. Modifications will be described below.

[0038] 3 and 4 are schematic diagrams showing back-illuminated imaging elements according to first and second modifications. As shown in FIG. 3, the back-illuminated imaging element 1A according to the first modification is identical to the back-illuminated imaging element 1 in plan view (when viewed from a first direction, the same applies below), and differs only in the cross-sectional shape of the semiconductor substrate 10. That is, in the back-illuminated imaging element 1A, the recess 60 is enlarged compared to the back-illuminated imaging element 1. More specifically, in the back-illuminated imaging element 1A, the recess 60 is formed throughout the entire third region 10C, and the third region 10C does not include a portion whose thickness is constant with the thickness of the second region 10B. As a result, the semiconductor substrate 10 is thinned throughout the entire third region 10C by the recess 60. That is, in this example, the semiconductor substrate 10 is thinned including the region corresponding to the amplifier section 15.

[0039] 4, a back-illuminated imaging element 1B according to the second modification is identical to the back-illuminated imaging elements 1 and 1A in plan view, but differs only in the cross-sectional shape of the semiconductor substrate 10. That is, the back-illuminated imaging element 1B differs from the back-illuminated imaging element 1A in that the second region 10B is relatively thicker than the fourth region 10D. More specifically, in the back-illuminated imaging element 1B, a recess 80 is provided in the back surface 10b of the semiconductor substrate 10, so that the thickness of the semiconductor substrate 10 is relatively thinner in the fourth region 10D than in the second region 10B. That is, in this example, the semiconductor substrate 10 is thickened only in the region corresponding to the analog-digital converter 17, and is thinned in regions corresponding to elements other than the analog-digital converter 17.

[0040] Here, the recess 80 penetrates the semiconductor substrate 10 (i.e., the bottom surface 81 of the recess 80 is the surface of the semiconductor layer 30). In other words, the thickness of the semiconductor substrate 10 is zero in the fourth region 10D. In other words, the semiconductor layer 30 is exposed from the semiconductor substrate 10 at the bottom of the recess 80. The inner side surface of the recess 80 is located in the fourth region 10D and includes an inclined surface 83 that is inclined so that the thickness of the semiconductor substrate 10 gradually (continuously) increases from the fourth region 10D toward the second region 10B.

[0041] As in the back-illuminated image sensors 1A and 1B described above, the semiconductor substrate 10 may be configured so that the second region 10B corresponding to (directly below) the analog-digital converter 17 is relatively thick, and any other region is relatively thin. This makes it possible to ensure the amount of light incident on the light receiving section 13 while preventing the semiconductor substrate 10 from becoming highly resistant directly below the analog-digital converter 17. In other words, by achieving both high sensitivity and ground stabilization, processing speed can be improved.

[0042] 5 is a schematic diagram showing a back-illuminated imaging element according to a third modified example. As shown in FIG. 5, the back-illuminated imaging element 1C according to the third modified example has the same structure as the back-illuminated imaging element 1. The back-illuminated imaging element 1C differs from the back-illuminated imaging element 1 in that the semiconductor substrate 10 is directly electrically connected to the ground GND. In this way, the ground potential may be applied to the semiconductor substrate 10 in any manner.

[0043] 6 is a schematic diagram showing a back-illuminated image sensor according to a fourth modification. As shown in FIG. 6, the back-illuminated image sensor 1D includes a first element portion 3 and a pair of second element portions 5 arranged on either side of the first element portion 3 so as to sandwich the first element portion 3. That is, the back-illuminated image sensor 1D has a structure in which a single CCD portion and a pair of CMOS portions are formed (integrated) on a single semiconductor substrate 10. The structures of the first element portion 3 and the pair of second element portions 5, including the cross-sectional structure of the semiconductor substrate 10, are similar to those of the back-illuminated image sensor 1.

[0044] Furthermore, the above-described embodiments and modifications may employ the structures of the respective components interchangeably. As an example, the structure of the fourth region 10D of the back-illuminated image sensor 1B according to the second modification may be employed in the back-illuminated image sensors 1, 1A, 1C, and 1D according to the embodiments and other modifications. As another example, the structure including the pair of second element portions 5 of the back-illuminated image sensor 1D according to the fourth modification may be employed in the back-illuminated image sensors 1A, 1B, and 1C according to the other modifications.

[0045] In the back-illuminated image sensors 1 to 1D according to the above-described embodiments and modifications, the image sensors are configured in an elongated shape in plan view, with the longitudinal direction being the arrangement direction of the light receiving sections 13, amplifier section 15, analog-digital converter 17, multiplexer section 19, and output section 23. However, the image sensors may be configured in an elongated shape in plan view, with the longitudinal direction being a direction (second direction) intersecting (orthogonal to) the arrangement direction of the light receiving sections 13, amplifier section 15, analog-digital converter 17, multiplexer section 19, and output section 23.

[0046] In this case, the light receiving section 13, the amplifier section 15, the analog-to-digital converter 17, the multiplexer section 19, and the output section 23 can also be formed elongated in the second direction. In this case, the output section 23 may be divided into a plurality of sections arranged in the second direction.

[0047] In the above example, a CCD is used as the first element portion 3. However, the first element portion 3 may be an active pixel sensor having an amplifier portion for each pixel. In this case, the amplifier portion 15 located in the third region 10C is unnecessary. However, even in this case, the light receiving portion 13 and the analog-to-digital converter 17, which are affected by the change in the thickness of the semiconductor substrate 10, may not be disposed on the third region 10C including the inclined surface 63 (i.e., where the thickness of the semiconductor substrate 10 changes), and wiring W1 and W3 that electrically connect the light receiving portion 13 and the analog-to-digital converter 17 to each other may be disposed.

[0048] In the above example, the thickness of the semiconductor substrate 10 is zero in the first region 10A corresponding to the light receiving portion 13 of the semiconductor substrate 10. However, the thickness of the semiconductor substrate 10 does not have to be zero in the first region 10A, as long as the transmittance of incident light hν to the semiconductor layer 30 (the amount of light incident on the light receiving portion 13) in the first region 10A is greater than that in the second region 10B. [Explanation of symbols]

[0049] 1, 1A, 1B, 1C, 1D... back-illuminated imaging element, 3... first element portion, 5... second element portion, 10... semiconductor substrate, 10a... front surface, 10b... back surface, 10A... first region, 10B... second region, 10C... third region, 13... light receiving portion, 15... amplifier portion, 17... analog-to-digital converter, 30... semiconductor layer, 60... recess, 63... inclined surface.

Claims

1. a semiconductor substrate having a front surface and a back surface opposite to the front surface, the back surface being applied with a ground potential; a semiconductor layer formed on the surface, The semiconductor layer is a first element portion including a light receiving portion that generates a signal charge in response to light incident from the rear surface side and outputs a signal voltage in response to the signal charge; a second element unit including an analog-to-digital converter that converts the signal voltage output from the first element unit into a digital signal; and a thickness of the semiconductor substrate in a first direction intersecting the front surface and the back surface is relatively thicker in a second region of the semiconductor substrate corresponding to the analog-to-digital converter as viewed from the first direction than in a first region of the semiconductor substrate corresponding to the light receiving unit as viewed from the first direction; the semiconductor substrate includes a third region located between the first region and the second region when viewed from the first direction, the first element portion includes an amplifier portion that converts the signal charge generated in the light receiving portion into the signal voltage; the amplifier section is located in the third region when viewed from the first direction, the distance between the amplifier unit and the analog-to-digital converter is greater than the size of the amplifier unit in the short side direction; The short-side direction is a direction from the light receiving unit toward the analog-to-digital converter. Back-thinned image sensor.

2. the thickness of the semiconductor substrate is made relatively thinner in the first region than in the second region by a recess provided on the back surface from the first region to the third region; The back-illuminated imaging device according to claim 1 .

3. an inner side surface of the recessed portion is located in the third region and includes an inclined surface that is inclined such that the thickness of the semiconductor substrate gradually increases from the first region toward the second region; The back-illuminated imaging device according to claim 2 .

4. the semiconductor layer is exposed from the semiconductor substrate at a bottom of the recess; The back-illuminated imaging device according to claim 3 .

5. a light-shielding film formed on the rear surface of the semiconductor substrate including the inner surface of the recess, the light-shielding film extends on the inclined surface and has an opening on a bottom surface of the recess; 5. The back-illuminated imaging device according to claim 4.

6. the semiconductor substrate has a first conductivity type; the semiconductor layer includes a well region of the first conductivity type in the amplifier section, and a well region of a second conductivity type different from the first conductivity type in the second element section; 6. The back-illuminated imaging device according to claim 1.

7. the semiconductor layer includes another region of the first conductivity type between the amplifier section and the analog-to-digital converter, the region having an impurity concentration higher than that of the well region of the first conductivity type in the amplifier section; 7. The back-illuminated imaging device according to claim 6.

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