JP2010272666A - Solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid-state imaging device which can image both a visible light and an infrared light sensitively. <P>SOLUTION: The solid-state imaging device includes a plurality of pixels disposed two-dimensionally on a board 52. A plurality of pixels 13 have: a first photoelectrically converting part 21; a second photoelectrically converting part 22 of which at least a part is provided right under the first photoelectrically converting part 21; and a floating diffusion 25 connected directly to the second photoelectrically converting part 22, which are formed in the board, respectively. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device capable of imaging for both visible light and invisible light.

  2. Description of the Related Art CCD (Charge Coupled Device) type and MOS (Metal Oxide Semiconductor) type solid-state imaging devices are widely used in video cameras, digital cameras, and the like as devices for acquiring video information of a subject. In a solid-state imaging device, a plurality of pixels having photoelectric conversion units are arranged in a two-dimensional array. In addition, the photoelectric conversion unit of each pixel photoelectrically converts light incident from the subject into the pixel, and the generated signal charge is output by the signal readout circuit, so that the solid-state imaging device can acquire video information. .

  In recent years, in the security field and the automotive field, there is an increasing need for a near-infrared camera that can acquire a clear image at night. The near-infrared camera uses the above-described CCD-type or MOS-type solid-state image pickup device, but these solid-state image pickup devices are mainly manufactured using a silicon substrate. In addition, it has the characteristic of being sensitive to visible light. For this reason, a solid-state imaging device provided with a color filter can also obtain a normal color image. That is, if the configuration of the color filter is devised, it is possible to acquire a color image by daytime visible light and a monochrome image by nighttime near-infrared light with one solid-state imaging device.

  In Patent Document 1, a near-infrared light cut filter provided on a solid-state imaging device is mechanically inserted and extracted, thereby enabling both visible light and non-visible light imaging using one solid-state imaging device. An imaging device is disclosed.

  Patent Document 2 discloses a signal processing method for a camera that enables imaging using both visible light and invisible light by arithmetic processing.

  Patent Document 3 discloses a solid-state imaging device that optimizes the depth of the photoelectric conversion unit of each pixel in accordance with the wavelength to be imaged.

  Patent Document 4 discloses a solid-state imaging device having a plurality of photoelectric conversion units in one pixel. A color filter that transmits light of one type of wavelength region is provided, and a plurality of photoelectric conversion units are included in one pixel.

JP 2000-59798 A JP 2008-35090 A JP 2008-91753 A Japanese Patent Laid-Open No. 2005-12007

  However, in the imaging apparatus described in Patent Document 1, since it is necessary to provide a mechanism for mechanically inserting and removing a filter, the apparatus configuration becomes complicated and the manufacturing cost increases.

  Further, in the solid-state imaging device described in Patent Document 2, since the G (green) pixel is reduced by one from the four pixels constituting the Bayer array and the IR (infrared) pixel is added, the pixels in the Bayer array The resolution of daytime imaging will be lower than that of a solid-state imaging device in which are arranged.

  In the solid-state imaging device described in Patent Document 3, in order to image near-infrared light with high sensitivity, the photoelectric conversion portion of the pixel that captures near-infrared light is enlarged to the substrate deep portion. It is difficult to completely read out the electric charges generated in. Although a potential gradient is formed in the photoelectric conversion portion by multiple ion implantations, it is difficult to form a completely smooth potential gradient, and charges are trapped in the potential well that is generated.

  In Patent Document 4, a plurality of photoelectric conversion units are provided in one pixel, and a circuit for reading out electric charges is required for each photoelectric conversion unit. Therefore, the ratio of the photoelectric conversion unit per pixel The so-called aperture ratio decreases. Further, it is not aimed at increasing the sensitivity of near-infrared light and imaging for both visible light and near-infrared light.

  As described above, with the conventional technology, it has been difficult to image infrared light without reducing the visible light resolution without increasing the manufacturing cost.

  An object of the present invention is to provide a solid-state imaging device capable of imaging both visible light and infrared light with high sensitivity.

  A solid-state imaging device according to the present invention is a solid-state imaging device including a plurality of pixels arranged two-dimensionally on a substrate, and each of the plurality of pixels is a first photoelectric element formed in the substrate. A conversion unit; a second photoelectric conversion unit at least part of which is provided directly below the first photoelectric conversion unit; and a floating diffusion directly connected to the second photoelectric conversion unit. .

  The depth at which light is completely absorbed in the substrate depends on its wavelength. Therefore, an image signal of light having a different wavelength can be obtained by providing the first photoelectric conversion unit and the second photoelectric conversion unit at least partly below the first photoelectric conversion unit. For example, the first photoelectric conversion unit can be used for visible light, and the second photoelectric conversion unit can be used for infrared light. According to this configuration, for example, photoelectric conversion can be performed by the second photoelectric conversion unit without providing pixels for infrared light, and thus imaging can be performed without reducing resolution. In addition, since it is not necessary to form a special readout circuit for the second photoelectric conversion unit, the aperture ratio is not reduced.

  According to the solid-state imaging device of the present invention, at least a part of the first photoelectric conversion unit and the second photoelectric conversion unit is provided in each pixel, and the second photoelectric conversion unit is directly connected to the floating diffusion. Therefore, an image signal can be acquired without causing a decrease in resolution.

1 is a diagram illustrating a schematic configuration of a MOS type solid-state imaging device according to a first embodiment of the present invention. It is a figure which shows the circuit structural example of each unit pixel in the solid-state image sensor which concerns on 1st Embodiment. It is sectional drawing which shows typically the pixel part of the solid-state image sensor which concerns on 1st Embodiment. It is a schematic diagram which shows the example of the color filter arrangement | sequence in the pixel part of the solid-state image sensor which concerns on 1st Embodiment. It is the schematic of the imaging device which can image visible light and near-infrared light using both the solid-state image sensor which concerns on 1st Embodiment. It is sectional drawing which shows typically the pixel part of the solid-state image sensor which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows typically the pixel part of the solid-state image sensor which concerns on the 3rd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of a MOS type solid-state imaging device according to the first embodiment of the present invention.

  As shown in the figure, the solid-state imaging device of this embodiment includes a pixel unit 11 in which unit pixels 13 are two-dimensionally arranged and a peripheral circuit unit 12 arranged outside the pixel unit 11. . The peripheral circuit unit 12 has a general configuration, and includes, for example, a horizontal shift register 14, a vertical shift register 15, a noise removal circuit 16, and an amplifier circuit 17.

  FIG. 2 is a diagram illustrating a circuit configuration example of each unit pixel in the solid-state imaging device of the present embodiment. As shown in the figure, each unit pixel 13 includes a first photoelectric conversion unit 21 and a second photoelectric conversion unit 22, and signals accumulated in the first photoelectric conversion unit 21 and the second photoelectric conversion unit 22. Is read out to the signal line 29 selectively.

  The signal readout circuit 23 includes, for example, a transfer transistor 24 whose one end (source) is connected to the first photoelectric conversion unit 21, a floating diffusion 25, a reset transistor 26 for resetting the potential of the floating diffusion 25, a floating transistor It comprises an amplifying transistor 27 that amplifies the signal read to the diffusion 25 and outputs it to the signal line 29, and a selection transistor 28.

  The second photoelectric conversion unit 22 is directly connected to the floating diffusion 25. The floating diffusion 25 is preferably the drain of the transfer transistor 24 and is preferably electrically connected to the gate of the amplification transistor 27.

  The light incident on the unit pixel 13 is photoelectrically converted by the first photoelectric conversion unit 21 and the second photoelectric conversion unit 22. First, signal reading from the second photoelectric conversion unit 22 will be described. The electric charges generated by the second photoelectric conversion unit 22 are collected and accumulated in the floating diffusion 25 by the potential gradient in the second photoelectric conversion unit 22. The voltage applied to the gate of the amplification transistor 27 fluctuates due to the charge accumulated in the floating diffusion 25, and a signal converted into the voltage is output from the drain of the amplification transistor 27. Next, by using the horizontal shift register 14 and the vertical shift register 15 to turn on the selection transistor 28 of the pixel from which a signal is read by the XY address method, a signal is output from the amplification transistor 27 to the signal line 29. Further, after noise included in the signal is removed by the noise removal circuit 16, a signal (video signal) is output from the amplifier circuit 17 to the outside of the solid-state imaging device.

  Next, signal reading from the first photoelectric conversion unit 21 is performed. First, after the signal reading from the second photoelectric conversion unit 22 is completed, the reset transistor 26 is turned on while the transfer transistor 24 is turned off to reset the potential of the floating diffusion 25. After the reset operation, the transfer transistor 24 is turned on, so that all charges accumulated in the first photoelectric conversion unit 21 are transferred to the floating diffusion 25. The operation from when the electric charge is accumulated in the floating diffusion 25 until the signal is output from the amplifier circuit 17 is the same as the signal reading from the second photoelectric conversion unit 22 described above.

  As described above, in the solid-state imaging device according to the present embodiment, it is not necessary to provide an additional readout circuit in signal readout from the first photoelectric conversion unit 21 and the second photoelectric conversion unit 22, and the aperture ratio of the unit pixel. Can be maintained as it is.

  FIG. 3 is a cross-sectional view schematically showing the pixel portion 11 of the solid-state imaging device of the present embodiment. FIG. 2 shows the pixel structure of the solid-state image sensor shown in FIG.

  In each unit pixel, the first photoelectric conversion unit 21 and the second photoelectric conversion unit 22 that are both of the second conductivity type (for example, n-type) are provided above the semiconductor substrate 31. Here, the semiconductor substrate 31 is a portion of the substrate 52 that has not been introduced with impurities in the manufacturing process. The second photoelectric conversion unit 22 is located below the first photoelectric conversion unit 21, and includes a photoelectric conversion region 38 in which photoelectric conversion is actually performed and a connection region 39 directly connected to the floating diffusion 25. ing.

  A first conductivity type (for example, p-type) well 50 is provided on the semiconductor substrate 31, and the second photoelectric conversion unit 22 is provided on the well 50. A first conductivity type (for example, opposite to the photoelectric conversion unit) between the first photoelectric conversion unit 21 and the photoelectric conversion region 38 of the second photoelectric conversion unit 22 so that they are connected to each other and no color mixing occurs. A p-type first semiconductor region 34 is preferably formed.

  Each unit pixel 13 is formed with an insulating isolation region 35 for electrical isolation from adjacent pixels. Below the insulating isolation region 35, a second conductivity type opposite to each photoelectric conversion unit is formed. A semiconductor region 36 is preferably formed. Near the upper surface of the substrate 52 (the substrate portion including the semiconductor substrate 31, the well 50, the first photoelectric conversion unit 21, and the second photoelectric conversion unit 22) made of a semiconductor (on the first photoelectric conversion unit 21) ) Is preferably formed with a third semiconductor region 37 having a conductivity type opposite to that of the photoelectric conversion portion (for example, p-type) and containing a higher concentration of impurities than the photoelectric conversion portion. The third semiconductor region 37 is for reducing dark current generated at the interface between the substrate 52 and the insulating film formed thereon, and each first photoelectric conversion unit 21 is embedded in the substrate 52. Yes.

  Of the second photoelectric conversion unit 22, the impurity concentration of the photoelectric conversion region 38 located in the deep part of the substrate 52 is preferably lower than the impurity concentration of the first photoelectric conversion unit 21. Further, it is preferable that the impurity concentration of the connection region 39 gradually increases from the lower part toward the upper surface of the substrate 52. In the second photoelectric conversion unit 22, a potential gradient is formed by applying a voltage directly through the floating diffusion 25, but by providing a concentration gradient in the connection region 39 in advance as described above, The potential gradient can be made steeper and the reading of charges can be facilitated. Further, the photoelectric conversion region 38 of the second photoelectric conversion unit 22 does not need to be provided over the entire lower area of the first photoelectric conversion unit 21, and is provided below a part of the first photoelectric conversion unit 21. May be provided.

In the present embodiment, the impurity concentration of the well 50 is, for example, about 1 × 10 ¹⁵ cm ⁻³ , the impurity concentration of the first semiconductor region 34 is, for example, about 1 × 10 ¹⁶ cm ⁻³ , and the second semiconductor region The impurity concentration of 36 is, for example, about 1 × 10 ¹⁶ cm ⁻³ . The impurity concentration of the first photoelectric conversion unit 21 is, for example, about 1 × 10 ¹⁶ cm ⁻³ , and the impurity concentration of the photoelectric conversion region 38 in the second photoelectric conversion unit 22 is, for example, about 1 × 10 ¹⁵ cm ⁻³ . There, the impurity concentration of the connection region 39 is changed from a deep portion of the substrate 52 up to for example 1 × ¹⁰ 15 ^cm -3 approximately ~1 × ¹⁰ 18 ^{cm -3} toward the upper surface portion. Note that the depth of the upper end of the photoelectric conversion region 38 of the second photoelectric conversion unit 22 is, for example, about 3 μm to 5 μm from the upper surface of the substrate 52.

  A transfer gate 32 is formed on the substrate 52 to transfer charges from the first photoelectric conversion unit 21 to the floating diffusion 25 with a gate insulating film interposed therebetween. An insulating film is provided on the substrate 52 and the transfer gate 32, and a color filter (filter) 33 corresponding to each pixel is provided on the insulating film. The color filter 33 provided in each unit pixel 13 has a spectral characteristic that transmits light in two different wavelength ranges.

  FIG. 4 is a schematic diagram illustrating an example of a color filter array in the pixel portion of the solid-state imaging device according to the present embodiment. Here, a color filter that transmits visible light and near-infrared light will be described as an example. However, the color filter used in the solid-state imaging device is not limited to this, and a color that transmits light in two different wavelength regions. Any filter can be used. In the embodiment described here, the pixel array is a two-dimensional array, but it may be a two-dimensional array different from a two-dimensional array array such as a honeycomb array.

  As shown in FIG. 4, in the solid-state imaging device of the present embodiment, a color filter that transmits red (R), green (G), blue (B), and green (G) light and near-infrared light. The four pixels provided with “” are set as the structural unit 41. A plurality of the structural units 41 are arranged in the pixel portion 11. Here, a pixel provided with a color filter that transmits red light and near infrared light is an R + IR pixel 42, a pixel provided with a color filter that transmits green light and near infrared light is a G + IR pixel 43, and blue light and near red light. A pixel including a color filter that transmits external light is referred to as a B + IR pixel 44.

  For example, light incident on the B + IR pixel 44 is selected only as blue light and infrared light by the color filter formed on the B + IR pixel 44. Visible light including blue light has a larger absorption coefficient in the substrate 52 than near-infrared light, and much is absorbed in a relatively shallow region of the substrate 52. In particular, almost all blue light is absorbed in the shallow region of the substrate 52. Therefore, almost all of the blue light incident on the B + IR pixel 44 is absorbed by the first photoelectric conversion unit 21, and the generated signal charge is accumulated in the first photoelectric conversion unit 21.

  On the other hand, near-infrared light is not easily absorbed by the substrate 52 and is transmitted to the deep part of the substrate 52, so that the near-infrared light entering the B + IR pixel 44 is incident on the first photoelectric conversion unit 21 and the second photoelectric conversion unit. 22 is photoelectrically converted. Therefore, signal charges generated by near-infrared light are accumulated in the first photoelectric conversion unit 21 and the floating diffusion 25 connected to the second photoelectric conversion unit 22. That is, the second photoelectric conversion unit 22 can acquire only near infrared light as a signal. Since a voltage is directly applied to the second photoelectric conversion unit 22 via the floating diffusion 25, a relatively large potential gradient is formed inside the second photoelectric conversion unit 22 formed in the deep portion of the substrate 52. Thus, the charge generated in the photoelectric conversion region 38 by near infrared light can be easily read.

  Also in the R + IR pixel 42 and the G + IR pixel 43, both the near-infrared light and the visible light are photoelectrically converted in the first photoelectric conversion unit 21 as in the B + IR pixel 44, and the near-infrared light is substantially converted in the second photoelectric conversion unit 22. Only light is photoelectrically converted, and signal charges are accumulated.

  FIG. 5 is a schematic diagram of an imaging apparatus that can capture both visible light and near infrared light using the solid-state imaging device of the present embodiment. The imaging device of the present embodiment includes a solid-state imaging device 51 and a signal processing device 55 that performs arithmetic processing on a signal output from the solid-state imaging device 51. When acquiring a color image by visible light, the signal processing device 55 generates the visible light signal and the near-infrared light signal generated by the first photoelectric conversion unit 21 of each pixel and the second photoelectric conversion unit 22. An arithmetic process is performed using the obtained near-infrared light signal, and only a visible light signal is extracted. In the calculation, the ratio of near infrared light absorbed by each photoelectric conversion unit is estimated based on the positional relationship within the substrate 52 of the first photoelectric conversion unit 21 and the second photoelectric conversion unit 22. It is also possible to correct by multiplying the obtained signal by a coefficient based on this ratio.

  The signal processing device 55 may be provided in the imaging device as a semiconductor chip different from the solid-state imaging device 51, but may be provided on the same substrate as the solid-state imaging device 51.

  In the prior art, when acquiring a color image by visible light, it is necessary to provide an IR pixel for acquiring a near-infrared light signal used for arithmetic processing instead of the G pixel. Moreover, since the near-infrared light signal used for the arithmetic processing is not a signal acquired by the same pixel as the visible light, the arithmetic processing is complicated. On the other hand, in the solid-state imaging device according to the present embodiment, the calculation for obtaining the visible light signal can be performed using the near-infrared light signal acquired by the same pixel as the visible light. Can be avoided. In addition, since it is not necessary to provide a dedicated pixel for IR, it is possible to prevent a decrease in resolution due to substitution of the G pixel. In particular, when the color filter 33 has a Bayer arrangement as shown in FIG. 4, the resolution of visible light can be maintained at a high level.

  Further, the photoelectric conversion region 38 for photoelectrically converting near-infrared light is disposed so as to overlap the first photoelectric conversion unit 21 when viewed from above the substrate 52, so that even compared with a conventional solid-state imaging device. The area of the pixel portion does not increase.

  Further, as described above, in the solid-state imaging device of the present embodiment, since no special readout circuit is provided for the second photoelectric conversion unit 22, the aperture ratio does not decrease, which causes a decrease in sensitivity. There is no.

  In addition, when acquiring a monochrome image using infrared light, a near-infrared light signal generated by the second photoelectric conversion unit 22 can be used. Since almost no visible light is incident on the pixel portion at night, the near-infrared light signal generated by the first photoelectric conversion unit 21 and the near-infrared light generated by the second photoelectric conversion unit 22 of each pixel. The signal can be added by the signal processing device 55. In this case, the sensitivity to infrared light can be further improved by creating a monochrome image using the added signal. Switching between using or not using the signal generated by the first photoelectric conversion unit 21 may be performed by a control circuit in the solid-state imaging device 51 or may be performed by the signal processing device 55.

  As described above, according to the solid-state imaging device of the present embodiment, it is possible to image both visible light and infrared light with high sensitivity without greatly increasing the manufacturing cost.

  In the solid-state imaging device of the present embodiment, the first photoelectric conversion unit 21 and the second photoelectric conversion unit 21 are prepared by preparing a semiconductor substrate 52 and ion-implanting p-type impurities and n-type impurities into a predetermined region of the substrate 52. Each layer such as the photoelectric conversion portion 22, the first semiconductor region 34, and the second semiconductor region 36 can be formed.

(Second Embodiment)
FIG. 6 is a cross-sectional view schematically showing a pixel portion of a solid-state imaging device according to the second embodiment of the present invention.

  The solid-state imaging device of this embodiment shown in the figure includes a plurality of pixels 61 arranged on a substrate 52, a first photoelectric conversion unit 62 corresponding to each of the plurality of pixels 61, and a second photoelectric conversion unit. 63 and a floating diffusion 64. The second photoelectric conversion unit 63 is directly connected to the floating diffusion 64 in the same pixel. A color filter 65 corresponding to each pixel is formed on each of the plurality of pixels 61, and the color filter 65 included in each of the plurality of pixels 61 has spectral characteristics that transmit light in two different wavelength ranges. have.

  In the solid-state imaging device of the present embodiment, the position of the upper end of the photoelectric conversion region 38 of the second photoelectric conversion unit 63, that is, the depth from the upper surface of the substrate 52 is the color of the color filter 65 provided in each of the plurality of pixels 61. Depending on. In addition, the position of the lower end of the first photoelectric conversion unit 62, that is, the depth from the upper surface of the substrate 52 also differs depending on the color of the color filter 65 provided in each of the plurality of pixels 61.

  Between the first photoelectric conversion unit 62 and the photoelectric conversion region 38 of the second photoelectric conversion unit 63, the opposite conductivity type (for example, p-type) of the two photoelectric conversion units is connected so as not to cause color mixing. It is preferable that the first semiconductor region 34 is formed. In addition, each of the plurality of pixels 61 is formed with an insulating isolation region 35 for electrical isolation from an adjacent pixel, and in the deep portion of the insulating isolation region 35, the opposite conductivity type of each photoelectric conversion unit. Two semiconductor regions 36 are preferably formed.

  In each of the plurality of pixels 61, a third semiconductor region 37 having a conductivity type opposite to the photoelectric conversion unit (for example, p-type) and containing a higher concentration of impurities than the photoelectric conversion unit is formed near the upper surface of the substrate 52. It is preferable. The third semiconductor region 37 is for reducing dark current generated at the interface between the substrate 52 and the insulating film formed thereon, and each first photoelectric conversion unit 62 is embedded in the substrate 52. Yes.

  The impurity concentration of the photoelectric conversion region 38 located in the deep portion of the substrate 52 in the second photoelectric conversion unit 63 is preferably lower than the impurity concentration of the first photoelectric conversion unit 62. Further, it is preferable that the impurity concentration of the connection region 39 gradually increases as it approaches the upper surface of the substrate 52. In the second photoelectric conversion unit 63, a potential gradient is formed by applying a voltage directly via the floating diffusion 64. As described above, by providing a concentration gradient in the connection region 39 in advance, The potential gradient can be made steeper and the reading of charges can be facilitated. In addition, the photoelectric conversion region 38 of the second photoelectric conversion unit 63 does not need to be provided over the entire area below the first photoelectric conversion unit 62, and is located below a part of the first photoelectric conversion unit 62. May be provided.

  The B + IR pixel 67 includes a color filter 65 that transmits blue light and near infrared light, the G + IR pixel 68 includes a color filter that transmits green light and near infrared light, and the R + IR pixel 69 includes red light and near infrared light. The color filter which permeate | transmits is provided. Light has a different absorption coefficient in the substrate 52 depending on the wavelength, and the longer the wavelength, the deeper the substrate 52 is transmitted. That is, the depth at which the substrate 52 is almost completely absorbed in the order of blue light, green light, and red light increases. Therefore, in the B + IR pixel 67, the blue light is almost completely absorbed in a relatively shallow region of the substrate 52, and it is not necessary to form the first photoelectric conversion unit 62 that photoelectrically converts the blue light deep into the substrate 52. Accordingly, the area of the second photoelectric conversion unit 63B can be enlarged, and thus the sensitivity to near infrared light can be further improved.

  Here, the second photoelectric conversion unit 63 in the B + IR pixel 67 is expressed as a second photoelectric conversion unit 63B, and the second photoelectric conversion unit 63 in the G + IR pixel 68 is expressed as a second photoelectric conversion unit 63G. The second photoelectric conversion unit 63 in the R + IR pixel 69 is referred to as a second photoelectric conversion unit 63R. Further, the photoelectric conversion region 38 and the connection region 39 in the B + IR pixel 67 are expressed as a photoelectric conversion region 38B and a connection region 39B, respectively, and the photoelectric conversion region 38 and the connection region 39 in the G + IR pixel 68 are respectively connected to the photoelectric conversion region 38G and a connection. The region 39G is expressed, and the photoelectric conversion region 38 and the connection region 39 in the R + IR pixel 69 are expressed as a photoelectric conversion region 38R and a connection region 39R, respectively.

  Also in the G + IR pixel 68 and the R + IR pixel 69, the first photoelectric conversion unit 62 is formed to a depth at which light of each wavelength is almost completely absorbed, and the second photoelectric conversion unit 63 is maximized according to the depth. It has been enlarged. As described above, the use efficiency of incident light is maximized by optimizing the areas of the first photoelectric conversion unit 62 and the second photoelectric conversion unit 63 according to the color of the color filter included in each pixel. It becomes possible to raise. The upper end of the photoelectric conversion region 38B is located in a range of about 1 to 2 μm from the upper surface of the substrate 52, for example, and the upper end of the photoelectric conversion region 38G is located in a range of about 2 to 3 μm from the upper surface of the substrate 52, for example. The upper end of the photoelectric conversion region 38R may be located in a range of about 3 to 5 μm from the upper surface of the substrate 52, for example.

  According to the solid-state imaging device of the present embodiment, both visible light and infrared light can be imaged with high sensitivity without greatly increasing the manufacturing cost as in the solid-state imaging device according to the first embodiment. In particular, in the B + IR pixel 67 and the like, the range of the photoelectric conversion region 38B can be expanded, so that the SN ratio (signal / noise) of infrared light can be increased, and a more accurate image can be acquired. Become.

  When obtaining a color image by visible light, based on the positional relationship between the first photoelectric conversion unit 62 and the second photoelectric conversion unit 63 in the substrate 52, the near-photographs absorbed by the respective photoelectric conversion units. Since the ratio of infrared light can be calculated, a coefficient based on this ratio can be adjusted for each pixel, and correction can be performed by performing arithmetic processing by multiplying the coefficient by the signal.

(Third embodiment)
In recent years, the pixel size of a solid-state imaging device has been rapidly miniaturized, and in order to increase the ratio of the area occupied by a photoelectric conversion unit in a unit pixel, a readout circuit is shared between adjacent pixels. Even when the readout circuit is shared, the solid-state imaging device of the present invention is effective.

  FIG. 7 is a cross-sectional view schematically showing a pixel portion of a solid-state imaging device according to the third embodiment of the present invention.

  As shown in the figure, the solid-state imaging device of the present embodiment includes a plurality of pixels 71 arranged on a substrate 52, a first photoelectric conversion unit 21 corresponding to each of the plurality of pixels 71, and a second A photoelectric conversion unit 73 and a floating diffusion 74 are provided. The second photoelectric conversion unit 73 is directly connected to the floating diffusion 74 in the corresponding pixel. The second photoelectric conversion unit 73 is formed in a deep portion of the substrate 52 and has a photoelectric conversion region 38 that actually performs photoelectric conversion and a connection region that is directly connected to the floating diffusion 74 and hardly performs photoelectric conversion. ing.

  In the solid-state imaging device of this embodiment, the second photoelectric conversion unit 73 and the floating diffusion 74 are shared between a plurality of adjacent pixels. A color filter 75 corresponding to each pixel is formed on each of the plurality of pixels 71, and the color filter 75 included in each of the plurality of pixels 71 has spectral characteristics that transmit light in two different wavelength ranges. have.

  Here, a case where the second photoelectric conversion unit 73 and the floating diffusion 74 are shared between two adjacent pixels will be described as an example. However, the present embodiment is not limited to this, and a plurality of pixels including three or more pixels are used. The second photoelectric conversion unit 73 and the floating diffusion 74 may be shared between the pixels.

  For example, when the second photoelectric conversion unit 73 and the floating diffusion 74 are shared between the pixel 76 and the pixel 77, the first photoelectric conversion unit 21 of the pixel 76 transmits the color filter 78 included in the pixel 76. Visible light and near-infrared light are photoelectrically converted, and in the first photoelectric conversion unit 21 of the pixel 77, visible light and near-infrared light transmitted through the color filter 79 provided in the pixel 77 are photoelectrically converted.

  Further, in the photoelectric conversion region 38 formed in the deep part of the substrate 52, near infrared light incident on both pixels is photoelectrically converted, and the generated charges are connected to the photoelectric conversion region 38 via the connection region 39. Accumulated in the floating diffusion 74.

  Since a voltage is directly applied to the second photoelectric conversion unit 73 formed in the deep portion of the substrate 52 through the floating diffusion 74, a relatively large potential gradient is formed in the connection region 39, and the charge is Easy to read.

The impurity concentration of the first photoelectric conversion unit 21 is, for example, about 1 × 10 ¹⁶ cm ⁻³ , and the impurity concentration of the photoelectric conversion region 38 in the second photoelectric conversion unit 73 is, for example, about 1 × 10 ¹⁵ cm ⁻³ . In addition, the impurity concentration of the connection region 39 varies from, for example, about 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ from the deep portion to the upper surface portion of the substrate 52. The depth of the upper end of the photoelectric conversion region 38 is, for example, about 3 μm to 5 μm from the upper surface of the substrate 52.

  When the solid-state imaging device of the present embodiment is used in an imaging apparatus capable of imaging both visible light and near-infrared light and a color image by visible light is acquired, it is acquired by the first photoelectric conversion unit 21 of each pixel. By performing arithmetic processing using the visible light signal, the near-infrared light signal, and the near-infrared light signal acquired by the second photoelectric conversion unit 73, it is possible to extract only the visible light signal. At this time, since the near-infrared light signal amount that can be acquired by the second photoelectric conversion unit 73 is larger than that of the solid-state imaging device according to the first embodiment, the SN ratio of the obtained color image is improved. It becomes possible. Further, as in the first embodiment, since it is not necessary to provide IR pixels instead of G pixels, it is possible to improve the resolution of a color image.

  Note that the above-described embodiments can be appropriately combined without departing from the scope of the present invention. For example, the position of the upper end of the photoelectric conversion region 38 may be changed according to the color of the color filter 75 while the second photoelectric conversion unit 73 is shared by a plurality of pixels.

  Moreover, the impurity concentration, the formation position of each layer, etc. mentioned in the above embodiment are merely examples, and can be changed without departing from the spirit of the present invention.

  The solid-state imaging device according to the embodiment of the present invention can be widely used for video cameras, digital cameras, and the like. In addition, an imaging apparatus (such as a camera) using a solid-state imaging element is widely used in the security field, the automotive field, and the like.

DESCRIPTION OF SYMBOLS 11 Pixel part 12 Peripheral circuit part 13 Unit pixel 14 Horizontal shift register 15 Vertical shift register 16 Noise removal circuit 17 Amplifier circuit 21, 62 1st photoelectric conversion part 22, 63, 63B, 63G, 63R, 73 2nd photoelectric conversion Unit 23 Signal readout circuit 24 Transfer transistor 25, 64, 74 Floating diffusion 26 Reset transistor 27 Amplification transistor 28 Select transistor 29 Signal line 31 Semiconductor substrate 32 Transfer gate 33, 65 Color filter 34 First semiconductor region 35 Insulation isolation region 36 Second semiconductor region 37 Third semiconductor region 38, 38B, 38G, 38R Photoelectric conversion region 39, 39B, 39G, 39R Connection region 41 Structural unit 42, 69 R + IR pixel 43, 68 G + IR pixel 44, 67 B + IR pixel 50 Well 1 solid-state imaging device 52 substrate 55 signal processing apparatus 61 and 71 a plurality of pixels 65,75,78,79 color filters 76 and 77 pixels

Claims (10)

A solid-state imaging device comprising a plurality of pixels arranged two-dimensionally on a substrate,
The plurality of pixels are each formed in the substrate, a first photoelectric conversion unit, a second photoelectric conversion unit at least part of which is provided immediately below the first photoelectric conversion unit, A solid-state imaging device having a floating diffusion directly connected to the second photoelectric conversion unit. The solid-state imaging device according to claim 1,
The second photoelectric conversion unit is located below the first photoelectric conversion unit, and includes a photoelectric conversion region that performs photoelectric conversion, and a connection region that is directly connected to the photoelectric conversion region and the floating diffusion. A solid-state imaging device. The solid-state imaging device according to claim 2,
Each of the plurality of pixels further includes a filter provided above the substrate and transmitting light in two different wavelength regions. The solid-state imaging device according to claim 3,
The solid-state imaging device, wherein the filter selectively transmits light in a visible light region and light in a non-visible light region. The solid-state imaging device according to claim 4,
The second photoelectric conversion unit photoelectrically converts only light in the invisible light region. The solid-state imaging device according to claim 5,
There are multiple types of light in the visible light region that the filter transmits,
The depth of the upper end of the photoelectric conversion region from the upper surface of the substrate is different depending on the wavelength of light that is photoelectrically converted by the first photoelectric conversion unit. The solid-state imaging device according to claim 6,
The depth of the lower end of the first photoelectric conversion unit from the upper surface of the substrate is different depending on the wavelength of light photoelectrically converted by the first photoelectric conversion unit. In the solid-state image sensor according to any one of claims 2 to 7,
The solid-state imaging device, wherein the first photoelectric conversion unit, the second photoelectric conversion unit, and the floating diffusion are provided in each of the plurality of pixels. In the solid-state image sensor according to any one of claims 2 to 7,
The solid-state imaging device, wherein the second photoelectric conversion unit and the floating diffusion are shared between at least two adjacent pixels among the plurality of pixels. The solid-state imaging device according to any one of claims 2 to 9,
The solid-state imaging device, wherein the concentration of impurities contained in the connection region is gradually increased from the lower part toward the upper surface of the substrate.

Images