JP2011211121A - Solid-state imaging element, imaging device, method of driving solid-state imaging element, and method of manufacturing solid-state imaging element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state imaging element that reduces smears caused by leakage of electric charge generated on a surface of a photoelectric conversion element to a charge transfer portion.SOLUTION: The solid-state imaging element 5 including a plurality of photoelectric conversion elements formed in a semiconductor substrate 56 and the charge transfer portion 53 for transferring electric charge generated by the respective photoelectric conversion elements is equipped with a charge discharge portion (n-type silicon substrate 56) provided below the respective photoelectric conversion element and discharging electric charges accumulated in charge storage portions 60 of the respective photoelectric conversion elements. The plurality of photoelectric conversion elements are divided into photoelectric conversion elements 51 and photoelectric conversion elements 52, and a height of a first potential barrier between a charge storage portion 60 of a photoelectric conversion element 51 and the charge discharge portion below the photoelectric conversion element 51 is lower than a height of a second potential barrier between a charge storage portion 60 of a photoelectric conversion element 52 and the charge discharge portion below the photoelectric conversion element 52.

Description

  The present invention relates to a solid-state imaging device, an imaging apparatus, a solid-state imaging device driving method, and a solid-state imaging device manufacturing method.

  In a CCD (Charge Coupled Device) type solid-state imaging device, a charge generated on the surface of the photoelectric conversion element is a vertical charge transfer unit from which the charge is read from the photoelectric conversion element, and an adjacent charge from which the charge is not read from the photoelectric conversion element. Smear occurs due to leakage into the vertical charge transfer section. This smear has become non-negligible due to the recent increase in the number of pixels, miniaturization, and high sensitivity of solid-state imaging devices. In particular, since this smear is caused by noise charges generated on the surface of the photoelectric conversion element, in recent years when the number of pixels (the number of photoelectric conversion elements) of 10 million pixels or more has become commonplace, how is smear suppressed? However, it is important to improve image quality.

  Consider a case in which moving image capturing and still image capturing are performed in a solid-state image sensor. At the time of moving image capturing, so-called thinning-out reading is performed in which the number of pixels from which signals are read out is reduced in order to perform high-speed processing, compared with still image capturing. For this reason, at the time of moving image capturing, the number of unnecessary pixels that output signals that are not used for moving images is significantly greater than the pixels that output signals used for moving images.

  As described above, since the surface of the photoelectric conversion element becomes a smear generation source, if the number of unnecessary pixels increases, smear generated in pixels not used in the moving image affects the signal used in the moving image. In particular, when moving images are picked up, light continues to enter the solid-state image sensor, so that smear increases and the influence on image quality is great. In addition, when the solid-state imaging device has 10 million pixels or more, the number of unnecessary pixels naturally increases, so that smear further increases. If the number of pixels is reduced, it is possible to reduce smear. However, this will go against the trend of increasing the number of pixels, and an imaging device having a function desired by the user cannot be provided.

  In Patent Document 1, the overflow drain (OFD) voltage applied to the semiconductor substrate during the charge transfer period is made larger than during the charge accumulation period to reduce noise charges that enter the vertical charge transfer unit during charge transfer. An imaging apparatus is disclosed.

  However, even with the method described in Patent Document 1, it is not possible to reduce smear that occurs in unnecessary pixels during moving image capturing.

  Patent Document 2 discloses a method for preventing excess charges from leaking to the vertical charge transfer unit by changing the OFD voltage during the charge accumulation period. It is not possible to reduce smear.

JP 2000-101060 A JP-A-4-74073

  The present invention has been made in view of the above circumstances, and is capable of reducing smear caused by leakage of charges generated on the surface of the photoelectric conversion element to the charge transfer unit. An object of the present invention is to provide a method for driving an image sensor and a method for manufacturing a solid-state image sensor.

  The solid-state imaging device of the present invention is a solid-state imaging device including a plurality of photoelectric conversion elements formed in a semiconductor substrate and a charge transfer unit that transfers charges generated in the photoelectric conversion elements. A charge discharging unit provided below the conversion element for discharging the charge stored in the charge storage unit of each photoelectric conversion element, wherein the plurality of photoelectric conversion elements include a first photoelectric conversion element and a second photoelectric conversion element; Divided into photoelectric conversion elements, the height of the first potential barrier between the charge storage part of the first photoelectric conversion element and the charge discharge part below the first photoelectric conversion element is the second The height of the second potential barrier between the charge storage part of the photoelectric conversion element and the charge discharge part below the second photoelectric conversion element is lower.

  The solid-state imaging device driving method of the present invention is the solid-state imaging device driving method, wherein the solid-state imaging device reads out signals from all the photoelectric conversion elements of the solid-state imaging device, and the solid-state imaging device has the second driving method. A driving step for performing thinning driving for reading a signal only from the photoelectric conversion element is provided.

  The imaging apparatus of the present invention includes the solid-state imaging device, normal driving for reading signals from all the photoelectric conversion elements of the solid-state imaging device, and thinning-out for reading signals only from the second photoelectric conversion elements of the solid-state imaging device. A drive unit that performs driving is provided.

  The method for manufacturing a solid-state imaging device according to the present invention is a method for manufacturing the solid-state imaging device, wherein a conductive material opposite to the semiconductor substrate is formed in a region below the region in which the first photoelectric conversion element is to be formed in the semiconductor substrate. And implanting the opposite conductivity type impurity in a region below the region where the second photoelectric conversion element is to be formed in the semiconductor substrate from the first implantation amount. And a step of injecting with a large second injection amount.

  The method for manufacturing a solid-state imaging device according to the present invention is a method for manufacturing the solid-state imaging device, wherein the region under the region in which the first photoelectric conversion device and the second photoelectric conversion device are to be formed in the semiconductor substrate. A step of implanting an impurity having a conductivity type opposite to that of the semiconductor substrate; and after the step, an impurity having a conductivity type opposite to that of the semiconductor substrate in a region below the region where the second photoelectric conversion element is to be formed. And injecting.

  The method for manufacturing a solid-state imaging device according to the present invention is a method for manufacturing the solid-state imaging device, wherein the region under the region in which the first photoelectric conversion device and the second photoelectric conversion device are to be formed in the semiconductor substrate. A step of implanting an impurity having a conductivity type opposite to that of the semiconductor substrate; and after the step, in the region under the region where the first photoelectric conversion element is to be formed in the semiconductor substrate, the same conductivity as the semiconductor substrate is formed. Injecting a mold type impurity.

  ADVANTAGE OF THE INVENTION According to this invention, the solid-state image sensor which can reduce the smear resulting from the electric charge which generate | occur | produces on the photoelectric conversion element surface leaks to an electric charge transfer part, an imaging device, the drive method of a solid-state image sensor, and solid-state imaging An element manufacturing method can be provided.

The figure which shows schematic structure of the imaging device for describing one Embodiment of this invention FIG. 1 is a schematic plan view showing a schematic configuration of a solid-state image sensor in the digital camera shown in FIG. Sectional schematic diagram of the line 52a-52a in the solid-state imaging device shown in FIG. Cross-sectional schematic diagram of line 51a-51a in the solid-state imaging device shown in FIG. FIG. 4 is a diagram showing the potential distribution in the substrate depth direction in the section taken along the line 52b-52b ′ shown in FIG. 3 and the potential distribution in the substrate depth direction in the section taken along the line 51b-51b ′ shown in FIG. The figure which shows the potential distribution of the solid-state image sensor at the time of still image imaging mode The figure which shows the potential distribution of the solid-state image sensor at the time of animation imaging mode The figure which shows potential distribution when the voltage VOFD2 shown in FIG. The figure which shows the mask at the time of forming the photoelectric conversion element only for a normal drive, and the photoelectric conversion element for normal thinning | combining The figure which shows the mask at the time of forming the photoelectric conversion element only for a normal drive, and the photoelectric conversion element for normal thinning | combining The figure which shows the modification of the potential distribution shown in FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an imaging apparatus for explaining an embodiment of the present invention. Examples of the imaging device include an imaging device such as a digital camera and a digital video camera, an imaging module mounted on an electronic endoscope, a camera-equipped mobile phone, and the like. Here, a digital camera will be described as an example.

  The imaging system of the digital camera shown in the figure includes a photographic lens 1, a CCD type solid-state imaging device 5, a diaphragm 2 provided therebetween, an infrared cut filter 3, and an optical low-pass filter 4.

  A system control unit 11 that performs overall control of the electrical control system of the digital camera controls the flash light emitting unit 12 and the light receiving unit 13 and controls the lens driving unit 8 to adjust the position of the photographing lens 1 to the focus position and zoom. The exposure amount is adjusted by adjusting the aperture amount of the aperture 2 via the aperture drive unit 9.

  In addition, the system control unit 11 drives the solid-state imaging device 5 via the imaging device driving unit 10 and outputs a subject image captured through the photographing lens 1 as an imaging signal. An instruction signal from the user is input to the system control unit 11 through the operation unit 14.

  The electric control system of the digital camera further includes an analog signal processing unit 6 that performs analog signal processing such as correlated double sampling processing connected to the output of the solid-state imaging device 5, and RGB output from the analog signal processing unit 6. And an A / D conversion circuit 7 for converting the color signals into digital signals, which are controlled by the system control unit 11.

  Furthermore, the electric control system of this digital camera generates image data by performing main memory 16, memory control unit 15 connected to main memory 16, interpolation calculation, gamma correction calculation, RGB / YC conversion processing, and the like. A digital signal processing unit 17, a compression / decompression processing unit 18 that compresses image data generated by the digital signal processing unit 17 into a JPEG format or expands compressed image data, and a detachable recording medium 21 are connected. An external memory control unit 20 and a display control unit 22 to which a liquid crystal display unit 23 mounted on the back of the camera or the like is connected. The memory control unit 15, the digital signal processing unit 17, the compression / decompression processing unit 18, the external memory control unit 20, and the display control unit 22 are connected to each other by a control bus 24 and a data bus 25, and commands from the system control unit 11. Controlled by.

  FIG. 2 is a schematic plan view showing a schematic configuration of the solid-state imaging device 5 in the digital camera shown in FIG.

  The solid-state imaging device 5 includes a plurality of photoelectric conversion elements arranged in a two-dimensional shape (square lattice shape in the example) in a row direction X of the semiconductor substrate and in a column direction Y that intersects (orthogonally in the example in the drawing). (51, 52), a plurality of vertical charge transfer units (VCCD) 53, a horizontal charge transfer unit (HCCD) 54, and an output unit 55.

  The solid-state imaging device 5 can perform normal driving for reading signals from all the photoelectric conversion elements and thinning driving for reading signals from some of all the photoelectric conversion elements. The thinning drive is performed at the time of moving image capturing, for example, and the normal drive is performed at, for example, still image capturing. These driving operations are performed by the image sensor driving unit 10. The thinning drive is not limited to the time of moving image capturing, and may be performed, for example, when performing image capturing with reduced resolution during still image capturing.

  As described above, since the solid-state imaging device 5 can perform normal driving and thinning driving, a plurality of photoelectric conversion elements can read signals both during normal driving and during thinning driving, and only during normal driving. It can be divided into two types, that is, a signal that is not read out.

  In the example of FIG. 2, a photoelectric conversion element 52 (shaded) is used as a photoelectric conversion element from which a signal is read out during both normal driving and thinning driving, and photoelectric conversion in which a signal is read only during normal driving. The element is a photoelectric conversion element 51. Hereinafter, the photoelectric conversion element 51 is also referred to as a normal drive dedicated photoelectric conversion element 51, and the photoelectric conversion element 52 is also referred to as a normal thinning-out photoelectric conversion element 52.

  FIG. 2 shows an example in which color filters are arranged in a Bayer shape above a plurality of photoelectric conversion elements. The letter “R” is attached to the photoelectric conversion element having a color filter that transmits red light above, and the letter “G” is attached to the photoelectric conversion element having a color filter that transmits green light above. A photoelectric conversion element having a color filter that transmits blue light on the upper side is marked with a letter “B”.

  In this solid-state imaging device 5, every two photoelectric conversion element rows among the photoelectric conversion element rows composed of a plurality of photoelectric conversion elements arranged in the row direction X are usually used so that a color image can be generated with a signal obtained at the time of thinning driving. The thinning-out photoelectric conversion elements 52 are arranged, and the photoelectric conversion elements 51 dedicated for normal driving are arranged in the remaining photoelectric conversion element rows. The arrangement of the photoelectric conversion element 51 dedicated for normal driving and the photoelectric conversion element 52 for normal thinning-out is not limited to this. The optimum number of photoelectric conversion elements 52 may be arranged according to the thinning driving method.

  For example, the current digital camera has a mainstream number of photoelectric conversion elements of 10 million or more, but when capturing a moving image, when acquiring a VGA size, from 480 × 640 = a little over 300,000 photoelectric conversion elements. It is sufficient to read the signal. Even in the case of taking HD moving images, it is sufficient to read signals from 720 × 1280 = 920,000 photoelectric conversion elements. Even when a full HD moving image is taken, it is sufficient to read out signals from 1080 × 1920 = 2 million photoelectric conversion elements. In consideration of such a mode, the photoelectric conversion element 52 that is also used for normal thinning may be arranged at a position to be read out during moving image capturing.

  Note that the same color signals read from the photoelectric conversion elements may be added when capturing a moving image. Therefore, the photoelectric conversion element 52 for normal thinning is provided in consideration of this. For example, when adding two pixels, if it is VGA size, just over 600,000 photoelectric conversion elements may be used as the normal thinning-out photoelectric conversion element 52.

  A light shielding film (not shown) is provided above each of the photoelectric conversion elements 51 and 52, and openings are formed in the light shielding film above the photoelectric conversion element 51 and above the photoelectric conversion element 52. The area of the opening in plan view is the same between the photoelectric conversion element 51 and the photoelectric conversion element 52.

  The vertical charge transfer unit 53 is provided on the side (right side in the example of FIG. 2) corresponding to each photoelectric conversion element column formed of a plurality of photoelectric conversion elements arranged in the column direction Y. The vertical charge transfer unit 53 reads out charges accumulated in the respective photoelectric conversion elements of the corresponding photoelectric conversion element column and transfers them in the column direction Y. The charge transfer channel formed in the semiconductor substrate and above this It is comprised with CCD which consists of the transfer electrode provided in.

  The horizontal charge transfer unit 54 transfers charges transferred from the plurality of vertical charge transfer units 53 in the row direction X, and includes a charge transfer channel formed in the semiconductor substrate and a transfer electrode provided above the channel. It is comprised with CCD which consists of.

  The output unit 55 converts the charge transferred from the horizontal charge transfer unit 54 into a voltage signal corresponding to the charge amount, and outputs the voltage signal to the outside of the solid-state imaging device 5.

  3 is a schematic cross-sectional view taken along the line 52a-52a in the solid-state imaging device shown in FIG. FIG. 3 shows only the configuration in the semiconductor substrate.

  A P well layer 57 is formed on the surface of the n-type silicon substrate 56. Since the p well layer 57 is formed by ion implantation in the N type silicon substrate 56, it can be said that the p well layer 57 is a part of the N type silicon substrate 56.

  A charge storage portion 60 made of an N-type impurity layer is formed slightly below the surface of the P well layer 57, and the charge generated at the PN junction between the charge storage portion 60 and the P well layer 57 is this charge storage. Stored in the unit 60. The photoelectric conversion element 52 that is also used for normal thinning is formed by the charge storage unit 60 and the PN junction between the charge storage unit 60 and the P well layer 57. A surface shield region 59 made of a P-type impurity layer having a higher concentration than that of the P well layer 57 is formed on the charge storage portion 60.

  A charge readout region 61 made of a P-type impurity layer having a concentration higher than that of the P well layer 57 is formed on the right side of the charge storage unit 60.

  A charge transfer channel 62 made of an N-type impurity layer constituting the vertical charge transfer portion 53 is formed on the right side of the charge readout region 61.

  On the right side of the charge transfer channel 62 is a p-type impurity layer having a concentration higher than that of the P well layer 57 for separation from the adjacent photoelectric conversion element 52 in the row direction X not corresponding to the charge transfer channel 62. An element isolation region 63 is formed.

  Below the charge transfer channel 62, an element isolation region 64 made of a p-type impurity layer having a higher concentration than the P well layer 57 is formed. The element isolation regions 64 separate the photoelectric conversion elements 52 adjacent in the row direction X.

  4 is a schematic cross-sectional view taken along line 51a-51a in the solid-state imaging device shown in FIG. FIG. 4 shows only the configuration in the semiconductor substrate.

  The difference between the cross section shown in FIG. 4 and the cross section taken along the line 52a-52a is that a P-type impurity layer 58 having a concentration lower than that of the P-well layer 57 is formed at the end of the P-well layer 57 on the n-type silicon substrate 56 side. It is a point.

  The photoelectric conversion element 51 dedicated for normal driving is formed by the charge storage section 60 shown in FIG. 4 and a pn junction between the charge storage section 60 and the P well layer 57.

  The photoelectric conversion element 51 and the photoelectric conversion element 52 have the same formation range (size in plan view and depth in the depth direction of the substrate) and impurity concentration of the charge storage unit 60, respectively, and below the charge storage unit 60. Except for the fact that the concentration distribution of the P well layer 57 is different, the structure is exactly the same.

  3 and 4, the N-type silicon substrate 56 existing below each of the photoelectric conversion element 51 and the photoelectric conversion element 52 discharges charges accumulated in the charge accumulation unit 60. Part (overflow drain). Then, the P-type impurity layer (P well layer 57 in the example of FIG. 3, P well layer 57 and P type impurity layer 58 in the example of FIG. 4) between the charge storage unit 60 and the charge discharging unit is charged. It functions as a barrier forming part that forms a potential barrier between the storage part 60 and the charge discharging part.

  In this solid-state imaging device 5, the height of the potential barrier formed by the barrier forming unit is set to be different from that of the photoelectric conversion device 51 and the photoelectric conversion device by giving a difference in the concentration distribution of the P well layer 57 below the charge storage unit 60. Different from 52.

  5 shows the potential distribution in the substrate depth direction in the section taken along the line 52b-52b ′ shown in FIG. 3 and the potential distribution in the substrate depth direction in the section taken along the line 51b-51b ′ shown in FIG. FIG.

  In FIG. 5, the reference numeral 52b-52b ′ is the potential distribution in the substrate depth direction in the cross section of the line 52b-52b ′, and the reference numeral 51b-51b ′ is in the cross section of the line 51b-51b ′. It is a potential distribution in the substrate depth direction. FIG. 5 shows a potential distribution when a predetermined overflow drain (OFD) voltage is applied to the N-type silicon substrate 56 of the solid-state imaging device 5.

  As shown in FIG. 5, the depth of the bottom of the potential formed by the charge storage unit 60 of the photoelectric conversion element 51 dedicated to normal driving and the bottom of the potential formed by the charge storage unit 60 of the photoelectric conversion element 52 also used for normal thinning-out. The depths of these are substantially the same. On the other hand, the position of the top of the potential barrier between the charge storage unit 60 of the photoelectric conversion element 51 dedicated for normal driving and the N-type silicon substrate 56 below the photoelectric storage element 51 is the same as It is deeper than the position of the top portion of the potential barrier between the N-type silicon substrate 56 below.

  As a result, the height of the potential barrier (hereinafter referred to as a normal drive dedicated potential barrier) between the charge storage unit 60 of the photoelectric conversion element 51 dedicated for normal drive and the N-type silicon substrate 56 therebelow is usually used for both the thinning-out. It is lower than the height of the potential barrier between the charge storage section 60 of the photoelectric conversion element 52 and the N-type silicon substrate 56 below (hereinafter referred to as a normal thinning-out potential barrier).

  In the digital camera configured as described above, when the still image capturing mode is set, the image sensor driving unit 10 applies a predetermined overflow drain (OFD) voltage (VOFD1) to the N-type silicon substrate 56 of the solid-state image sensor 5. Apply. When there is a still image capturing instruction, normal driving for reading signals from all the photoelectric conversion elements of the solid-state image capturing element 5 is performed. Then, the digital signal processing unit 17 generates still image data from the signal obtained by this driving.

  6 is a diagram illustrating the potential distribution of the solid-state imaging device in the still image capturing mode. FIG. 6A represents the potential distribution of the line 52b-52b ′ in FIG. 3, and FIG. 6B represents the line 51b-51b ′ in FIG. Shows the potential distribution of.

  The voltage VOFD1 applied to the N-type silicon substrate 56 in the still image capturing mode is set to a value such that the photoelectric conversion element 51 dedicated for normal driving can secure the minimum saturation amount Q1 necessary for capturing a still image. Even in this case, the saturation amount of the photoelectric conversion element 52 that is also used for normal thinning is larger than that of the photoelectric conversion element 51 dedicated for normal driving. For this reason, the saturation amount Q1 can also be accumulated in the photoelectric conversion element 52 that is also used for normal thinning, and still image imaging can be performed using all the photoelectric conversion elements.

  On the other hand, when the moving image capturing mode is set, the image sensor driving unit 10 applies a voltage VOFD2 larger than the voltage VOFD1 to the N-type silicon substrate 56 of the solid-state image sensor 5. When there is a moving image imaging instruction, thinning driving is performed to read out signals only from the photoelectric conversion element 52 that is also used for normal thinning. Then, the digital signal processing unit 17 generates moving image data from the signal obtained by this driving.

  7 is a diagram showing the potential distribution of the solid-state imaging device in the moving image capturing mode. FIG. 7A shows the potential distribution of the line 52b-52b ′ in FIG. 3, and FIG. 7B shows the potential distribution of the line 51b-51b ′ in FIG. The potential distribution is shown.

  The voltage VOFD2 applied to the N-type silicon substrate 56 in the moving image capturing mode is set to such a value that the normal thinning-out photoelectric conversion element 52 can secure the minimum saturation amount Q2 necessary for moving image capturing. In this case, the saturation amount of the photoelectric conversion element 51 dedicated for normal driving is smaller than that in the still image capturing mode. As a result, the difference ΔV2 between the potential of the surface of the photoelectric conversion element 51 dedicated for normal driving and the top of the potential barrier dedicated for normal driving is equal to the potential of the surface of the photoelectric conversion unit 52 for normal thinning and the potential barrier for normal thinning. It becomes larger than the difference ΔV1 from the top.

  One of the main causes of smear is that the charges generated on the surfaces of the photoelectric conversion elements 51 and 52 (the surface of the surface shield region 59) do not move to the charge accumulation unit 60 but enter the charge transfer channel 62 of the vertical charge transfer unit 53. It can be moved. Therefore, smear can be reduced by making it easier to move this charge to the charge storage section 60.

  As shown in FIG. 7, in the solid-state imaging device 5, in the moving image imaging mode, ΔV <b> 2 is made larger than ΔV <b> 1 to move charges generated on the surface of the photoelectric conversion element 51 dedicated for normal driving to the charge storage unit 60. This makes it possible to suppress the occurrence of smear.

  As described above, the number of photoelectric conversion elements 51 dedicated to normal driving in a solid-state imaging device is often equal to or more than the number of photoelectric conversion elements 52 that are also used for normal thinning. For this reason, in the moving image capturing mode, the influence of smear caused by charges generated on the surface of the photoelectric conversion element 51 dedicated for normal driving that is not used for generating image data cannot be ignored. Since the solid-state imaging device 5 has the potential structure as shown in FIGS. 6 and 7, smear caused by charges generated on the surface of the photoelectric conversion device 51 dedicated to normal driving is not generated in the moving image imaging mode. It can be remarkably reduced, and moving image capturing with less smear becomes possible.

  Note that the voltage VOFD2 may be a value that eliminates the potential barrier dedicated to normal driving as long as the saturation amount Q2 of the photoelectric conversion element 52 that is also used for normal thinning in the moving image capturing mode can be secured.

  8 is a diagram showing the potential distribution when the voltage VOFD2 shown in FIG. 7 is further increased. FIG. 8A shows the potential distribution of the line 52b-52b ′ in FIG. 3, and FIG. 8B shows the potential distribution in FIG. The potential distribution of line 51b ′ is shown.

  As shown in FIG. 8B, if a voltage VOFD2 that can eliminate the potential barrier dedicated to normal driving is applied to the N-type silicon substrate 56, the potential of the surface of the photoelectric conversion element 51 dedicated to normal driving and the potential barrier dedicated to normal driving are applied. It is possible to make the difference from the top of ΔV3 larger than ΔV2. As a result, in the moving image capturing mode, it is possible to further reduce smear caused by the charge generated on the surface of the photoelectric conversion element 51 dedicated for normal driving, and it is possible to capture a higher quality moving image.

  Next, a method for manufacturing the solid-state imaging device 5 will be described.

  First, on the N-type silicon substrate 56, a mask having an opening in a region where the photoelectric conversion element 51 dedicated for normal driving and the photoelectric conversion element 52 for normal thinning-out are to be formed is formed. P-type impurities are implanted into the substrate 56 with a dose amount I1. At this time, the P-type impurity concentration is adjusted so that a desired impurity concentration is obtained below the region where the photoelectric conversion element 51 dedicated for normal driving is to be formed and below the region where the photoelectric conversion element 52 for normal thinning is to be formed. Make an injection. Thereby, a P well layer 57 is formed.

  Next, a mask M 1 as shown in FIG. 9 is formed on the N-type silicon substrate 56. In the plan view shown in FIG. 2, the mask M1 covers a region where the photoelectric conversion element 52 for normal thinning-out is to be formed, and has an opening K in a region where the photoelectric conversion element 51 dedicated for normal driving is to be formed. ing. Next, N-type impurities are implanted into the N-type silicon substrate 56 at a dose amount I2 through the mask M1. At this time, N-type impurities are implanted so as to obtain a desired impurity concentration below the region where the photoelectric conversion element 51 dedicated for normal driving is to be formed.

  As a result, the portion where the N-type impurity is implanted becomes the P-type impurity layer 58 having a lower concentration than the P-well layer 57.

  Thereafter, each region may be formed in the p-well layer 57 by a conventionally known method.

  As described above, the solid-state imaging device 5 can be easily manufactured by performing the impurity implantation for forming the p-well layer 57 in two steps.

  In addition, the solid-state image sensor 5 can also be manufactured as follows.

  First, on the N-type silicon substrate 56, a mask having an opening in a region where the photoelectric conversion element 51 dedicated for normal driving and the photoelectric conversion element 52 for normal thinning-out are to be formed is formed. P-type impurities are implanted into the substrate 56 with a dose amount I3. At this time, the P-type impurity concentration is adjusted so that a desired impurity concentration is obtained below the region where the photoelectric conversion element 51 dedicated for normal driving is to be formed and below the region where the photoelectric conversion element 52 for normal thinning is to be formed. Make an injection. Thereby, a P well layer 57 is formed.

  Next, a mask M 2 as shown in FIG. 10 is formed on the N-type silicon substrate 56. In the plan view shown in FIG. 2, the mask M2 covers an area where the photoelectric conversion element 51 dedicated for normal driving is to be formed, and has an opening K in an area where the photoelectric conversion element 52 for normal thinning-out is to be formed. ing.

  Next, a P-type impurity is implanted into the N-type silicon substrate 56 with a dose amount I4 through the mask M2. At this time, a P-type impurity is implanted so that a desired impurity concentration is obtained below a region where the photoelectric conversion element 52 for normal thinning-out is to be formed. Thereby, the portion where the P-type impurity is implanted becomes a P-type impurity layer having a concentration higher than that of the P well layer 57. As a result, the concentration of the P-type impurity layer between the charge storage unit 60 of the photoelectric conversion element 52 for normal thinning-out and the N-type silicon substrate 56 is set to the charge storage unit 60 of the photoelectric conversion element 51 dedicated for normal driving and the N-type. The concentration can be higher than the concentration of the P-type impurity layer between the silicon substrate 56 and the potential distribution as shown in FIG. 5 can be obtained.

  Moreover, the solid-state image sensor 5 can also be manufactured as follows.

  First, the mask M1 shown in FIG. 9 is formed on the N-type silicon substrate 56. Next, a P-type impurity is implanted into the N-type silicon substrate 56 with a dose amount I5 through the mask M1. At this time, P-type impurities are implanted so as to obtain a desired impurity concentration below the region where the photoelectric conversion element 51 dedicated for normal driving is to be formed.

  Next, the mask M <b> 2 shown in FIG. 10 is formed on the N-type silicon substrate 56. Next, a P-type impurity is implanted into the N-type silicon substrate 56 with a dose amount I6 (> I5) through the mask M2. At this time, a P-type impurity is implanted so that a desired impurity concentration is obtained below a region where the photoelectric conversion element 52 for normal thinning-out is to be formed.

  In this way, the concentration of the P-type impurity layer between the charge storage unit 60 of the photoelectric conversion element 52 for normal thinning-out and the N-type silicon substrate 56 is set to the charge storage unit of the photoelectric conversion element 51 dedicated for normal driving. It can be made higher than the concentration of the P-type impurity layer between 60 and the N-type silicon substrate 56, and a potential distribution as shown in FIG. 5 can be obtained.

  Note that the bottom of the potential of the charge storage unit 60 of the photoelectric conversion element 51 dedicated to normal driving may be at a different depth from the bottom of the potential of the charge storage unit 60 of the photoelectric conversion element 52 commonly used for thinning-out.

  For example, the potential distribution shown in FIG. 5 may be as shown in FIG. Even in this case, if the height of the potential barrier that is also used for normal thinning is higher than the height of the potential barrier dedicated for normal driving, the effect of reducing smear can be obtained. If these conditions are satisfied, for example, even if an OFD voltage that eliminates the potential barrier dedicated to normal driving is applied in the moving image capturing mode, a potential barrier that is also used for normal thinning can be left. This is because a saturation amount necessary sometimes can be secured.

  In the description so far, it is assumed that electrons generated in the photoelectric conversion element are converted into a signal and read out. However, in the case where holes are converted into a signal and read out, the p-type is used in the description so far. All n-types may be reversed. In this case, since the OFD voltage has a negative value, the relationship between OFD1 and OFD2 may be set so that the absolute value thereof is OFD <OFD2.

  Further, although FIG. 2 illustrates an example in which a plurality of photoelectric conversion elements are arranged in a square lattice pattern, the present invention is not limited to this. For example, the odd-numbered photoelectric conversion element rows may be arranged so as to be shifted in the row direction X by ½ of the row-direction arrangement pitch of each photoelectric conversion element with respect to the even-numbered photoelectric conversion element rows.

  Further, the color filter array is not limited to the primary color Bayer array, and other known arrays may be adopted. Further, a solid-state imaging device that performs monochrome imaging without providing a color filter may be used.

  As described above, the following items are disclosed in this specification.

  The disclosed solid-state imaging device is a solid-state imaging device including a plurality of photoelectric conversion elements formed in a semiconductor substrate, and a charge transfer unit that transfers charges generated in the photoelectric conversion elements. A charge discharging unit provided below the conversion element for discharging the charge stored in the charge storage unit of each photoelectric conversion element, wherein the plurality of photoelectric conversion elements include a first photoelectric conversion element and a second photoelectric conversion element; Divided into photoelectric conversion elements, the height of the first potential barrier between the charge storage part of the first photoelectric conversion element and the charge discharge part below the first photoelectric conversion element is the second The height of the second potential barrier between the charge storage part of the photoelectric conversion element and the charge discharge part below the second photoelectric conversion element is lower.

  In the disclosed solid-state imaging device, the bottom depth of the potential of the charge storage portion of the first photoelectric conversion element substantially matches the bottom depth of the potential of the charge storage portion of the second photoelectric conversion element, The top of the first potential barrier is deeper than the top of the second potential barrier.

  The disclosed imaging apparatus includes: the solid-state imaging element; normal driving for reading signals from all the photoelectric conversion elements of the solid-state imaging element; and thinning-out for reading signals only from the second photoelectric conversion element of the solid-state imaging element. A drive unit that performs driving is provided.

  In the disclosed imaging apparatus, the driving unit increases the absolute value of the voltage applied to the charge discharging unit at the time of the thinning driving than at the time of the normal driving.

  In the disclosed imaging apparatus, the driving unit applies a voltage that causes the first potential barrier to disappear during the thinning driving to the charge discharging unit.

  The disclosed solid-state imaging device driving method is a driving method of the solid-state imaging device, wherein normal driving for reading signals from all the photoelectric conversion elements of the solid-state imaging device, and the second driving of the solid-state imaging device A driving step for performing thinning driving for reading a signal only from the photoelectric conversion element is provided.

  In the driving method of the disclosed solid-state imaging device, in the driving step, the absolute value of the voltage applied to the charge discharging unit is set higher during the thinning driving than during the normal driving.

  In the driving method of the disclosed solid-state imaging device, in the driving step, a voltage for eliminating the first potential barrier is applied to the charge discharging unit during the thinning driving.

  The disclosed method for manufacturing a solid-state imaging device is a method for manufacturing the solid-state imaging device, wherein a conductive material opposite to the semiconductor substrate is formed in a region below the region in which the first photoelectric conversion element is to be formed in the semiconductor substrate. And implanting the opposite conductivity type impurity in a region below the region where the second photoelectric conversion element is to be formed in the semiconductor substrate from the first implantation amount. And a step of injecting with a large second injection amount.

  The disclosed method for manufacturing a solid-state imaging device is a method for manufacturing the solid-state imaging device, wherein the region under the region in which the first photoelectric conversion device and the second photoelectric conversion device are to be formed in the semiconductor substrate. A step of implanting an impurity having a conductivity type opposite to that of the semiconductor substrate; and after the step, an impurity having a conductivity type opposite to that of the semiconductor substrate in a region below the region where the second photoelectric conversion element is to be formed. And injecting.

  The disclosed method for manufacturing a solid-state imaging device is a method for manufacturing the solid-state imaging device, wherein the region under the region in which the first photoelectric conversion device and the second photoelectric conversion device are to be formed in the semiconductor substrate. A step of implanting an impurity having a conductivity type opposite to that of the semiconductor substrate; and after the step, in the region under the region where the first photoelectric conversion element is to be formed in the semiconductor substrate, the same conductivity as the semiconductor substrate is formed. Injecting a mold type impurity.

DESCRIPTION OF SYMBOLS 5 Solid-state image sensor 10 Image sensor drive part 51 Photoelectric conversion element 52 for exclusive use of normal drive Photoelectric conversion element 53 used also for normal thinning out Vertical charge transfer part 57 p well layer 58 p type impurity layer 56 n type silicon substrate 60 Charge storage part

Claims (11)

A solid-state imaging device including a plurality of photoelectric conversion elements formed in a semiconductor substrate, and a charge transfer unit that transfers charges generated in each of the photoelectric conversion elements,
Provided below each photoelectric conversion element, comprising a charge discharging unit that discharges charges accumulated in the charge storage unit of each photoelectric conversion element,
The plurality of photoelectric conversion elements are divided into a first photoelectric conversion element and a second photoelectric conversion element,
The height of the first potential barrier between the charge storage part of the first photoelectric conversion element and the charge discharge part below the first photoelectric conversion element is equal to the charge of the second photoelectric conversion element. A solid-state imaging device that is lower than a height of a second potential barrier between an accumulation unit and the charge discharging unit below the second photoelectric conversion element. The solid-state imaging device according to claim 1,
The depth of the bottom of the potential of the charge storage portion of the first photoelectric conversion element substantially matches the depth of the bottom of the potential of the charge storage portion of the second photoelectric conversion element;
A solid-state imaging device in which a top portion of the first potential barrier is deeper than a top portion of the second potential barrier. The solid-state image sensor according to claim 1 or 2,
An imaging apparatus including a drive unit that performs normal driving for reading signals from all the photoelectric conversion elements of the solid-state imaging element and thinning driving for reading signals only from the second photoelectric conversion element of the solid-state imaging element. The imaging apparatus according to claim 3,
An imaging apparatus in which the driving unit sets an absolute value of a voltage applied to the charge discharging unit to be higher during the thinning driving than during the normal driving. The imaging apparatus according to claim 4,
The image pickup apparatus that applies a voltage for eliminating the first potential barrier to the charge discharging unit when the driving unit performs the thinning driving. A method for driving a solid-state imaging device according to claim 1 or 2,
Driving of a solid-state imaging device including a driving step of performing normal driving for reading signals from all the photoelectric conversion elements of the solid-state imaging device and thinning driving for reading signals only from the second photoelectric conversion elements of the solid-state imaging device Method. A method for driving a solid-state imaging device according to claim 6,
In the driving step, the solid-state imaging device driving method wherein the absolute value of the voltage applied to the charge discharging unit is set higher during the thinning driving than during the normal driving. A method for driving a solid-state imaging device according to claim 7,
In the driving step, the solid-state imaging device driving method of applying a voltage for eliminating the first potential barrier to the charge discharging unit during the thinning driving. It is a manufacturing method of the solid-state image sensing device according to claim 1 or 2,
Injecting an impurity of a conductivity type opposite to that of the semiconductor substrate in a region below the region in which the first photoelectric conversion element is to be formed in the semiconductor substrate in a first implantation amount;
Injecting the opposite conductivity type impurity in a region below the region in which the second photoelectric conversion element is to be formed in the semiconductor substrate with a second implantation amount larger than the first implantation amount. Manufacturing method of imaging device. It is a manufacturing method of the solid-state image sensing device according to claim 1 or 2,
Injecting an impurity having a conductivity type opposite to that of the semiconductor substrate into a region below the region where the first photoelectric conversion element and the second photoelectric conversion element are to be formed in the semiconductor substrate;
After the step, a method of manufacturing a solid-state imaging device comprising the step of injecting the impurity of the opposite conductivity type into a region below the region where the second photoelectric conversion element is to be formed in the semiconductor substrate. It is a manufacturing method of the solid-state image sensing device according to claim 1 or 2,
Injecting an impurity having a conductivity type opposite to that of the semiconductor substrate into a region below the region where the first photoelectric conversion element and the second photoelectric conversion element are to be formed in the semiconductor substrate;
After the step, a method for manufacturing a solid-state imaging device comprising a step of injecting an impurity having the same conductivity type as the semiconductor substrate into a region below the region in which the first photoelectric conversion device is to be formed in the semiconductor substrate.

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