Image pickup element and image pickup device

Abstract

To provide an imaging element having pixels arranged in a matrix, in which when the S / N ratio of a focus detection signal differs in the row direction and the column direction, the performances of focus detection in the row direction and the column direction are brought closer to each other.SOLUTION: An imaging element has a plurality of microlenses arranged in a matrix in a first direction and in a second direction orthogonal to the first direction, and a plurality of photoelectric conversion units configured to photoelectrically convert light incident through each of the microlenses on at least a portion of each microlens of the plurality of microlenses. The plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units. When the effect of noise superimposed on a signal read out from the plurality of photoelectric conversion units is greater in the second direction than in the first direction, the charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is higher than the charge crosstalk rate in the second direction.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an imaging element in which pixel units each having a plurality of photoelectric conversion units are arranged two-dimensionally, and an imaging device incorporating the imaging element. [Background technology]

[0002] Conventionally, one of the focus detection methods used in image capture devices is the so-called image plane phase difference method, in which a pair of pupil division signals is obtained using focus detection pixels formed on an image sensor and focus detection is performed using the phase difference method.

[0003] As an example of such an imaging plane phase difference method, Patent Document 1 discloses an imaging device using a two-dimensional imaging element in which one microlens and multiple divided photoelectric conversion units are formed for each pixel. The multiple photoelectric conversion units are configured to receive light that has passed through different regions of the exit pupil of the imaging lens via one microlens, thereby performing pupil division. Phase difference focus detection can be performed by calculating the amount of image shift from the phase difference signals, which are signals from the individual photoelectric conversion units. Furthermore, a normal image signal can be obtained by adding up the signals from the individual photoelectric conversion units for each pixel. Patent Document 1 also discloses a configuration in which pixel saturation resistance is improved by arranging multiple types of pixels with different heights of separation barriers between the photoelectric conversion units in the pixels.

[0004] In such an image sensor, in a configuration in which multiple photoelectric conversion units are arranged horizontally within a pixel and the pupil division direction is horizontal, for example, if the subject has a horizontal striped pattern, parallax is less likely to appear and focus detection accuracy may decrease.

[0005] In response to this, Patent Document 2 discloses a technology for improving focus detection accuracy by providing two different arrangement directions of photoelectric conversion units relative to each microlens and two different pupil division directions. Patent Document 2 also discloses that the strength of charge leakage to adjacent photoelectric conversion units is different between a structure that separates vertically adjacent photoelectric conversion units and a structure that separates horizontally adjacent photoelectric conversion units. This structure allows oversaturated charge received in excess of the charge that a single photoelectric conversion unit can accumulate to leak to a different photoelectric conversion unit arranged in a predetermined direction, thereby enabling horizontal or vertical phase difference focus detection even when one photoelectric conversion unit is saturated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-212351 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-107835 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 2, there are two types of pupil division directions: the row direction and the column direction. Here, for example, if the number of pixels divided into the pupil in the row direction differs from the number of pixels divided into the pupil in the column direction, the S / N ratio (Signal to Noise Ratio) of the phase difference signal in the row direction and the phase difference signal in the column direction will differ. As a result, there is a possibility that the focus detection performance of the phase difference method will differ between the row direction and the column direction.

[0008] However, Patent Document 2 does not disclose anything about the case where the S / N ratio differs between the row direction and the column direction, and therefore is unable to solve the above problem.

[0009] The present invention has been made in consideration of the above-mentioned problems, and has an object to bring focus detection performance closer together in the row and column directions when the S / N ratio of focus detection signals differs between the row and column directions in an image sensor in which pixels are arranged in a matrix. [Means for solving the problem]

[0010] In order to solve the above problem, the imaging element of the present invention has a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction, and a plurality of photoelectric conversion units configured to photoelectrically convert light incident through each of at least some of the microlenses, wherein the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units, and when the influence of noise superimposed on signals read out from the plurality of photoelectric conversion units is greater in the second direction than in the first direction, the charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is made higher than the charge crosstalk rate in the second direction. [Effects of the Invention]

[0011] According to the present invention, in an image sensor in which pixels are arranged in a matrix, when the S / N ratio of focus detection signals differs between the row and column directions, it is possible to make the focus detection performance closer between the row and column directions. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing a schematic configuration of an imaging apparatus according to a first embodiment. [Figure 2] 1 is a diagram schematically showing an example of the overall configuration of an image sensor according to a first embodiment. [Figure 3] FIG. 2 is an equivalent circuit diagram of a pixel according to the first embodiment. [Figure 4] FIG. 2 is a schematic diagram showing the configuration of a pixel having a first arrangement according to the first embodiment. [Figure 5]FIG. 3 is a schematic diagram showing the configuration of a pixel having a second arrangement according to the first embodiment. [Figure 6] FIG. 4 is a diagram showing the relationship between pixels having a first arrangement and partial pupil regions according to the first embodiment. [Figure 7] FIG. 3 is a schematic diagram showing an example of a pupil intensity distribution of pixels having a first arrangement according to the first embodiment. [Figure 8] FIG. 2 is a diagram for schematically explaining the sensor entrance pupil of the image sensor according to the first embodiment. [Figure 9] 5A and 5B are diagrams showing a schematic relationship between the image shift amount between parallax images and the defocus amount according to the first embodiment. [Figure 10] FIG. 1 is a diagram illustrating a schematic relationship between pixels, an exit pupil, and a partial pupil region in the first embodiment. [Figure 11] FIG. 1 is a diagram schematically illustrating the relationship between the exit pupil and the pupil intensity distribution in the first embodiment. [Figure 12] FIG. 10 is a diagram illustrating the relationship between the charge crosstalk rate distribution and the pupil intensity distribution in the first embodiment. [Figure 13] FIG. 2 is a diagram showing an example of pixel arrangement in the first embodiment. [Figure 14] FIG. 10 is a schematic diagram showing the configuration of a pixel having a third arrangement according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0014] First Embodiment [Overall configuration] 1 is a block diagram showing a schematic configuration of an image pickup device according to a first embodiment of the present invention. The image pickup device of this embodiment includes an image pickup element 1, an overall control and calculation unit 2, an instruction unit 3, a timing generation unit 4, a photographing lens unit 5, a lens drive unit 6, a signal processing unit 7, a display unit 8, and a recording unit 9.

[0015] The photographing lens unit 5 forms an optical image of a subject on the image sensor 1. Although shown as a single lens in the figure, the photographing lens unit 5 actually includes multiple lenses, including a focus lens, a zoom lens, etc., and an aperture. The photographing lens unit 5 may be detachable from the main body of the imaging device, or may be configured as an integral part of the main body.

[0016] The image sensor 1 converts incident light through the photographing lens unit 5 into an electrical signal and outputs it. A signal is read out from each pixel of the image sensor 1 so that a pupil-divided signal (hereinafter referred to as a "phase difference signal") that can be used for phase difference focus detection and an image signal that is a signal for each pixel can be obtained.

[0017] The signal processing unit 7 performs predetermined signal processing such as correction processing on the signal output from the image sensor 1, and outputs a phase difference signal used for focus detection and an image signal used for recording.

[0018] The overall control and calculation unit 2 performs overall driving and control of the entire imaging device. It also performs calculations for focus detection using the phase difference signals processed by the signal processing unit 7, and performs calculations for exposure control on the image signals, as well as predetermined signal processing such as development and compression for generating images for recording and playback.

[0019] The lens driving section 6 drives the photographing lens unit 5 and performs focus control, zoom control, aperture control, etc. on the photographing lens unit 5 in accordance with control signals from the overall control and calculation section 2 .

[0020] The instruction unit 3 receives inputs such as instructions to perform photography, drive mode settings for the imaging device, and various other settings and selections input from the outside by operation of a user or the like, and transmits them to the overall control / calculation unit 2.

[0021] The timing generating unit 4 generates timing signals for driving the image sensor 1 and the signal processing unit 7 in accordance with control signals from the overall control and calculation unit 2 . The display unit 8 displays a preview image, a reproduced image, and information such as the drive mode setting of the imaging device.

[0022] The recording unit 9 is provided with a recording medium (not shown) in which the image signal for recording is recorded. Examples of the recording medium include semiconductor memories such as flash memories. The recording medium may be detachable from the recording unit 9 or may be built-in.

[0023] [Image sensor] Fig. 2 is a diagram schematically illustrating an example of the overall configuration of the image sensor 1 shown in Fig. 1. The image sensor 1 includes a pixel array section 201, a vertical selection circuit 202, a column circuit 203, and a horizontal selection circuit 204.

[0024] The pixel array unit 201 has a plurality of pixels 205 arranged in a matrix. The output of the vertical selection circuit 202 is input to the pixels 205 via a pixel drive wiring group 207, and pixel signals from the pixels 205 in a row selected by the vertical selection circuit 202 are read out row by row to the column circuit 203 via output signal lines 206. One output signal line 206 may be provided for each pixel column, or for multiple pixel columns, or multiple output signal lines 206 may be provided for each pixel column. The column circuit 203 receives signals read out in parallel via the multiple output signal lines 206, performs signal amplification, noise reduction, A / D conversion, and other processing, and stores the processed signals. The horizontal selection circuit 204 sequentially, randomly, or simultaneously selects signals stored in the column circuit 203, and the selected signals are output to the outside of the image sensor 1 via horizontal output lines and an output unit (not shown).

[0025] In this way, by sequentially outputting pixel signals of the row selected by the vertical selection circuit 202 to the outside of the image sensor 1 while changing the row selected by the vertical selection circuit 202, a two-dimensional image signal or phase difference signal can be read out from the image sensor 1.

[0026] [Pixel circuit / signal readout] FIG. 3 is an equivalent circuit diagram of the pixel 205 of this embodiment. Each pixel 205 has two photodiodes 301 (PDA) and 302 (PDB) that are photoelectric conversion units. The PDA 301 performs photoelectric conversion according to the amount of incident light, and the accumulated signal charge is transferred via a transfer switch (TXA) 303 to a floating diffusion (FD) 305 that constitutes a charge accumulation unit. The PDB 302 performs photoelectric conversion and accumulates the signal charge, and the transferred signal charge is transferred via a transfer switch (TXB) 304 to the FD 305. When a reset switch (RES) 306 is turned on, it resets the FD 305 to the voltage of a constant voltage source VDD. The PDA 301 and the PDB 302 can be reset by simultaneously turning on the RES 306, the TXA 303, and the TXB 304.

[0027] When a selection switch (SEL) 307 that selects a pixel is turned on, an amplification transistor (SF) 308 (charge-voltage converter) converts the signal charge accumulated in the FD 305 into a voltage, and the converted signal voltage is output from the pixel to an output signal line 206. In addition, the gates of TXA 303, TXB 304, RES 306, and SEL 307 are each connected to a pixel drive wiring group 207 and controlled by a vertical selection circuit 202.

[0028] In the following description, in this embodiment, the signal charge accumulated in the photoelectric conversion unit is assumed to be electrons, the photoelectric conversion unit is formed of an N-type semiconductor, and is separated by a P-type semiconductor, but the signal charge may also be holes, the photoelectric conversion unit may be formed of a P-type semiconductor, and is separated by an N-type semiconductor.

[0029] Next, we will explain the operation of reading out signal charges from the PDA 301 and PDB 302 after a predetermined charge accumulation time has elapsed after resetting the PDA 301 and PDB 302 in a pixel having the above-mentioned configuration. First, the SEL 307 of the row selected by the vertical selection circuit 202 is turned on, connecting the source of the SF 308 to the output signal line 206, and the output signal line 206 enters a state in which a voltage corresponding to the voltage of the FD 305 is read out. Next, the RES 306 is turned on / off, resetting the potential of the FD 305. After that, the system waits until the output signal line 206, which has been subjected to the voltage fluctuation of the FD 305, settles, and the settled voltage of the output signal line 206 is taken in by the column circuit 203 as a signal voltage N, where it is processed and held.

[0030] Thereafter, the TXA 303 is turned on / off, and the signal charge accumulated in the PDA 301 is transferred to the FD 305. The voltage of the FD 305 drops by an amount corresponding to the amount of signal charge accumulated in the PDA 301. Thereafter, the system waits until the output signal line 206, which has been subjected to the voltage fluctuation of the FD 305, settles, and the settled voltage of the output signal line 206 is taken in by the column circuit 203 as signal voltage A, where it undergoes signal processing and is held.

[0031] Thereafter, the TXB 304 is turned on / off, and the signal charge accumulated in the PDB 302 is transferred to the FD 305. The voltage of the FD 305 drops by an amount corresponding to the amount of signal charge accumulated in the PDB 302. Thereafter, the system waits until the output signal line 206, which has been subjected to the voltage fluctuation of the FD 305, settles, and the settled voltage of the output signal line 206 is taken in by the column circuit 203 as a signal voltage (A+B), which is then subjected to signal processing and held.

[0032] From the difference between the signal voltage N and the signal voltage A thus captured, a signal A corresponding to the amount of signal charge accumulated in the PDA 301 can be obtained. Furthermore, from the difference between the signal voltage A and the signal voltage (A+B), a signal B corresponding to the amount of signal charge accumulated in the PDB 302 can be obtained. This difference calculation may be performed by the column circuit 203, or may be performed after output from the image sensor 1. A phase difference signal can be obtained by using the signals A and B, and an image signal can be obtained by adding the signals A and B together. Alternatively, if the difference calculation is performed after output from the image sensor 1, the image signal may be obtained by taking the difference between the signal voltage N and the signal voltage (A+B).

[0033] Alternatively, the signal voltages N, A, and B may be read out by performing the same drive as that for reading out the signal voltages N and A on the PDB 302 instead of the PDA 301. In this case, the signals A and B obtained from the signal voltages A and B, respectively, can be used as phase difference signals as they are, and an imaging signal can be obtained by adding together the signal voltages A and B or the signals A and B.

[0034] [Photoelectric conversion area configuration] Phase difference detection pixel structure in the x direction 4A and 4B are schematic diagrams showing a first arrangement of semiconductor regions constituting a pixel 205 according to this embodiment, with FIG. 4A being a perspective schematic diagram and FIG. 4B being a plan schematic diagram showing the positional relationship in a plan view. Note that "plan view" refers to viewing from the z direction or the -z direction with respect to a plane (xy plane) parallel to the surface on which the transistor gates of the semiconductor substrate are arranged. Furthermore, the "row" direction refers to the x direction, the "column" direction refers to the y direction, and the "depth" direction refers to the z direction.

[0035] As shown in FIG. 4(a), the pixel 205 having the first arrangement includes a microlens (ML) 401, a PDA 301, a PDB 302, a TXA 303, a TXB 304, and an FD 305. In the first arrangement, the PDA 301 and the PDB 302 are aligned in the x direction and formed in a Si substrate, which is a semiconductor substrate. The side on which the ML 401 is arranged is the back side of the substrate, and the TXA 303, TXB The side on which 304 and FD 305 are arranged is the front side of the substrate.

[0036] Most of the light incident through ML401 is photoelectrically converted on the back surface of the substrate of PDA301 and PDB302. Here, a potential gradient is formed in PDA301 and PDB302 so that the potential experienced by electrons in the depth direction decreases, making it easier for charges generated in PDA301 and PDB302 to move to TXA303 and TXB304.

[0037] Furthermore, an isolation region 400 having a p-type impurity concentration higher than that of the PDA 301 and the PDB 302 is formed between the PDA 301 and the PDB 302 so that a potential barrier is formed between the PDA 301 and the PDB 302. This electrically isolates the PDA 301 and the PDB 302 so that generated charges are less likely to move between them. Therefore, in this embodiment, the separation direction of the PDA 301 and the PDB 302 in the first arrangement is the x direction (first direction).

[0038] Phase difference detection pixel structure in the y direction 5A and 5B are schematic diagrams showing a second arrangement of semiconductor regions constituting a pixel 205 according to this embodiment, with Fig. 5A being a perspective schematic diagram and Fig. 5B being a plan schematic diagram showing the positional relationship in a plan view. Note that the definitions of "plan view" and x, y, and z are the same as those in Fig. 4, and therefore will not be described here.

[0039] As shown in Fig. 5(a), the pixel 205 having the second arrangement includes ML401, PDA301, PDB302, TXA303, TXB304, and FD305. The basic configuration of the pixel 205 having the second arrangement is the same as that of the first arrangement shown in Fig. 4, but PDA301 and PDB302 are arranged side by side in the y direction, and the separation direction of the photoelectric conversion units is the y direction (second direction).

[0040] In the second arrangement as well, a potential gradient is formed in the PDA 301 and the PDB 302 such that the potential experienced by electrons decreases in the depth direction, making it easier for charges generated in the PDA 301 and the PDB 302 to move to the TXA 303 and the TXB 304. Also in the second arrangement, as in the first arrangement, an isolation region 500 is formed between the PDA 301 and the PDB 302, in which the p-type impurity concentration is higher than that of the PDA 301 and the PDB 302. This electrically separates the PDA 301 and the PDB 302 so that the generated charges are less likely to move between them.

[0041] In this embodiment, it is assumed that color filters (not shown) are arranged between the ML 401 and the PDA 301 and PDB 302. As an example, in the case of a Bayer array color filter, it is configured with an R filter that mainly transmits light of red wavelengths, a G filter that mainly transmits light of green wavelengths, and a B filter that mainly transmits light of blue wavelengths. In a 2x2 pixel unit, the R filter is arranged at the top left, the G filter at the top right, the G filter at the bottom left, and the B filter at the bottom right.

[0042] Charge crosstalk rate distribution Most of the charges generated in PDA301 and PDB302 are accumulated within each PDA301 and PDB302, but they may also migrate and accumulate from PDA301 to PDB302 or from PDB302 to PDA301. This phenomenon of charge migration from PDA301 to PDB302 or from PDB302 to PDA301 is called "charge crosstalk." The rate at which charge crosstalk occurs (hereinafter referred to as the "charge crosstalk rate") is higher the closer to the isolation regions 400 and 500 in plan view. Furthermore, in PDA301 and PDB302, a potential gradient is applied in the depth direction to facilitate charge migration toward TXA303 and TXB304. Therefore, the shorter the migration distance to TXA303 and TXB304, the smaller the charge crosstalk rate. That is, in PDA301 and PDB302, at the same x and y coordinates, the charge crosstalk rate is smaller at positions closer to TXA303 and TXB304 than at positions closer to ML401. In the following description, the distribution of crosstalk rates in PDA301 and PDB302 is referred to as the "charge crosstalk rate distribution." The steeper the potential gradient in the depth direction within PDA301 and PDB302, the smaller this charge crosstalk rate distribution becomes throughout PDA301 and PDB302.

[0043] Charge crosstalk can also occur between adjacent pixels. Charge crosstalk occurring between adjacent pixels is a cause of reduced resolution in imaging signals, etc. Therefore, it is desirable to make the charge crosstalk rate between adjacent pixels lower than the charge crosstalk rate from PDA301 to PDB302 or from PDB302 to PDA301. Specifically, for example, the charge crosstalk rate can be reduced by isolating adjacent pixels with an insulator or by increasing the height of the potential barrier.

[0044] Phase difference detection method in the x direction Next, the calculation performed by the overall control / calculation unit 2 to calculate the defocus amount from the phase difference signal will be described.

[0045] First, the focus detection using the phase difference detection method in the x direction in this embodiment will be described with reference to Figures 6 to 9. In the focus detection using the phase difference detection method in the x direction in this embodiment, the image shift amount in the x direction is calculated from the phase difference signal obtained from the pixels 205 having the first arrangement, and is converted into a defocus amount using a conversion coefficient.

[0046] 6 shows a cross-sectional view of the pixel 205 having the first arrangement taken along line A-A' shown in FIG. 4(b), and a pupil plane at a position a distance Ds away in the negative z-axis direction from the imaging plane 600 of the image sensor 1. Note that x, y, and z indicate coordinate axes on the imaging plane 600, and xp, yp, and zp indicate coordinate axes on the pupil plane.

[0047] The pupil plane and the light receiving surface of the image sensor 1 are in a substantially conjugate relationship via the ML 401. Therefore, the light beam that passes through the partial pupil region 601 is received by the PDA 301. Furthermore, the light beam that passes through the partial pupil region 602 is received by the PDB 302. In this way, when the pupil plane is divided in the x direction, the pupil division direction is the x direction. Therefore, the division direction position dependency of the pupil intensity distribution has a shape as shown in FIG. 7. In FIG. 7, the pupil intensity distribution corresponding to the PDA 301 is 701, and the pupil intensity distribution corresponding to the PDB 302 is 702.

[0048] Next, the sensor entrance pupil of the image sensor 1 will be described with reference to FIG. 8 . In the image sensor 1 of this embodiment, the ML 401 of each pixel 205 is arranged so as to be continuously shifted toward the center of the image sensor 1 according to the image height coordinate on a two-dimensional plane. That is, each ML 401 is arranged so as to be more eccentric toward the center of the image sensor 1 as the image height increases. Note that the center of the image sensor 1 and the optical axis of the imaging optical system are shifted by a mechanism that reduces the effects of blurring due to camera shake or the like by driving the imaging optical system or the image sensor 1, but they generally coincide. As a result, the first pupil intensity distribution 701 and the second pupil intensity distribution 702 of each pixel arranged at each image height coordinate of the image sensor 1 are configured to generally coincide with each other on the pupil plane located a distance Ds (entrance pupil distance) from the image sensor 1. That is, the first pupil intensity distribution 701 and the second pupil intensity distribution 702 of all pixels of the image sensor 1 are configured to generally coincide with each other on the pupil plane located a distance Ds from the image sensor 1. In this embodiment, the first pupil intensity distribution 701 and the second pupil intensity distribution 702 are called the “sensor entrance pupil” of the image sensor 1.

[0049] It is not necessary for all pixels to have a single entrance pupil distance; for example, the entrance pupil distances of pixels up to 80% of the image height may be approximately the same, or the pixels may be configured to have different entrance pupil distances for each row or each detection area.

[0050] 9 shows a schematic diagram of the relationship between the image shift amount between parallax images and the defocus amount. The image sensor 1 (not shown) of this embodiment is arranged on the imaging plane 600, and the exit pupil of the photographing lens unit 5 is divided into two, a partial pupil region 601 and a partial pupil region 602, as in FIG.

[0051] The defocus amount d is defined as the distance from the subject's imaging position to the imaging plane, with magnitude |d|, and a front-focus state where the subject's imaging position is closer to the subject than the imaging plane is negative (d<0), and a back-focus state where the subject's imaging position is on the opposite side of the subject than the imaging plane is positive (d>0). The in-focus state where the subject's imaging position is on the imaging plane is d=0. Figure 9 shows an example where the subject on object plane 901 is in-focus (d=0) and the subject on object plane 902 is in front-focus (d<0). The front-focus state (d<0) and back-focus state (d>0) are combined to form a defocus state (|d|>0).

[0052] In a front-focus state (d<0), a light beam from a subject on the object plane 902 that passes through the partial pupil region 601 (602) is first focused and then spreads to a width Γ1 (Γ2) with the center of gravity G1 (G2) of the light beam as the center, forming a blurred image on the imaging plane 600. The blurred image is received by the PDA 301 and the PDB 302, and a parallax image is generated. Therefore, in the generated parallax image, the image of the subject on the object plane 902 is blurred to a width Γ1 (Γ2) at the center of gravity G1 (G2).

[0053] The blur width Γ1 (Γ2) of the subject image increases roughly in proportion to the increase in the magnitude of the defocus amount d, |d|. Similarly, the magnitude |p| of the image shift amount p (= G2 - G1) of the subject image between the parallax images also increases roughly in proportion to the increase in the magnitude |d| of the defocus amount d. The same is true in the back-focus state (d>0), although the direction of the image shift between the subject images between the parallax images is opposite to that in the front-focus state. In the in-focus state (d=0), the center of gravity positions of the subject images between the parallax images match (p=0), and no image shift occurs.

[0054] Therefore, in the two phase difference signals obtained using the signals from the PDA 301 and the PDB 302, the image shift amount in the x direction between the two phase difference signals increases as the defocus amount of the parallax images increases. Based on this relationship, the image shift amount calculated by performing a correlation operation while shifting the parallax images in the x direction is converted into a defocus amount, thereby performing focus detection using the phase difference detection method.

[0055] Phase difference detection method in the y direction In this embodiment, the phase difference detection method in the y direction (second direction) can be the same as the phase difference detection method in the x direction (first direction) using signals from the pixels 205 having the first arrangement described above. That is, phase difference detection in the y direction (second direction) is performed using signals from the pixels 205 having the second arrangement instead of the pixels 205 having the first arrangement.

[0056] Conversion factor The coefficient used for multiplication when converting the image shift amount into the defocus amount is called the conversion coefficient. This conversion coefficient is roughly inversely proportional to the distance between the centers of gravity of pupil intensity distribution 701 and pupil intensity distribution 702. When the conversion coefficient is large, a large defocus amount is calculated from a small image shift amount compared to when the conversion coefficient is small, which means that the phase difference signal is more susceptible to the influence of noise, and there is a possibility that the phase difference detection performance will deteriorate. In other words, the longer the distance between the centers of gravity of pupil intensity distribution 701 and pupil intensity distribution 702, the less the influence of noise in the phase difference signal.

[0057] Here, the conversion coefficient when the pupil region of the photographing lens unit 5 is limited by the aperture will be described with reference to Figures 10 and 11. Figure 10 is a schematic diagram in which an exit pupil 1001 narrowed down by the aperture is superimposed on an A-A' cross section of partial pupil regions 601, 602 and pixels 205 having the first arrangement shown in Figure 6, and the exit pupil 1001 is divided by partial pupil regions 601 and 602.

[0058] 11 shows first partial pupil intensity distribution 711 and second partial pupil intensity distribution 712 of the received light beam corresponding to exit pupil 1001, out of first pupil intensity distribution 701 and second pupil intensity distribution 702 when not stopped down by the aperture stop in such a case. In this case, the conversion coefficient is determined according to the distance between the centers of gravity of first partial pupil intensity distribution 711 and second partial pupil intensity distribution 712, and therefore the greater the slope on the graph in region 713 where the pupil intensity distributions intersect, the longer the distance between the centers of gravity and the smaller the conversion coefficient. In other words, the greater the slope of the region where the pupil intensity distributions limited by exit pupil 1001 intersect, the smaller the conversion coefficient, and therefore the smaller the effect of noise on the phase difference signal.

[0059] [Charge crosstalk rate] Relationship between charge crosstalk rate distribution and conversion factor Next, the relationship between the magnitude of the charge crosstalk rate and the pupil intensity distribution will be described using Figure 12. Charge crosstalk is a phenomenon in which charge generated in PDA 301 moves to PDB 302, or charge generated in PDB 302 moves to PDA 301 and accumulates there. In other words, when the charge crosstalk rate is small, there is less mixing of signals from PDA 301 and PDB 302 compared to when the charge crosstalk rate is large. Figure 12 compares first pupil intensity distribution 701 and second pupil intensity distribution 702 when the charge crosstalk rate is large with first pupil intensity distribution 721 and second pupil intensity distribution 722 (dashed dotted lines) when the charge crosstalk rate distribution is small. When the charge crosstalk rate is small, the slope of the graph in region 713 where the pupil intensity distributions intersect becomes steeper.

[0060] Therefore, the first pupil intensity distribution 721 and the second pupil intensity distribution 722, which have a small charge crosstalk rate, have a steeper slope in the region where the pupil intensity distributions limited by the exit pupil 1001 intersect, than the first pupil intensity distribution 701 and the second pupil intensity distribution 702, which have a large charge crosstalk rate. In other words, the smaller the charge crosstalk rate, the smaller the conversion coefficient and the smaller the effect of noise on the phase difference signal.

[0061] Phase difference signal noise Noise in the phase difference signal includes optical shot noise, which is the fluctuation of the light itself, and readout circuit noise, which is superimposed on the signal in the SF308, column circuit 203, etc. In a region where a sufficient amount of charge is generated by photoelectric conversion, optical shot noise is generally equal to the square root of the number of signal charges. Furthermore, readout circuit noise is generally a constant value regardless of the amount of signal charge. Therefore, the more charge is generated by photoelectric conversion, the higher the S / N ratio and the smaller the noise in the phase difference signal.

[0062] 13 is a diagram showing an example of an 8-row, 4-column arrangement of pixels 205 having a first arrangement and pixels 205 having a second arrangement in the pixel array unit 201 of this embodiment. Here, the description will be based on a 2×2 pixel unit consisting of an R pixel covered with an R filter, two G pixels covered with a G filter, and a B pixel covered with a B filter, which constitute a Bayer arrangement. Of the 2×2 pixel unit, the R pixel, one of the G pixels, and the B pixel constitute the pixel 205 having the first arrangement that divides the pupil in the x direction, and the remaining G pixel constitutes the pixel 205 having the second arrangement that divides the pupil in the y direction.

[0063] 13, the number of pixels 205 having the first arrangement in one row is greater than the number of pixels 205 having the second arrangement in one column, so the phase difference signal in the x direction is a signal based on more light than the phase difference signal in the y direction, and therefore the S / N ratio of the phase difference signal in the x direction is higher than that of the phase difference signal in the y direction.

[0064] 3, the closer the diffusion layer constituting the FD305 and the SF308 are to each other, the shorter the wiring connecting them (hereinafter referred to as "FD wiring") and the smaller the capacitance of the FD305. When the capacitance of the FD305 is small, the charge-voltage conversion gain is large, which increases the effect of suppressing noise superimposed in the subsequent stage and results in low noise. Here, if it is difficult to align the distance between the diffusion layer constituting the FD305 and the SF308 or the size of the SF308 between the pixel 205 having the first arrangement and the pixel 205 having the second arrangement, the magnitude of the noise carried in the phase difference signal will differ.

[0065] For example, when the number of pixels 205 having the first arrangement and the number of pixels 205 having the second arrangement arranged in the image sensor 1 are different, the wiring connecting the diffusion layer constituting the FD 305 having the greater number and the SF 308 is usually made shorter first. Therefore, when the number of pixels 205 having the first arrangement is greater, the noise carried in the phase difference signal obtained from the pixels 205 having the second arrangement becomes larger. In other words, the S / N ratio of the phase difference signal is higher in the x direction than in the y direction.

[0066] Relationship between noise and charge crosstalk rate of phase difference signals and phase difference detection performance As described above, the smaller the conversion coefficient for converting the image shift amount into the defocus amount, the less susceptible to the influence of noise, and the smaller the charge crosstalk rate, the smaller the conversion coefficient can be.

[0067] Therefore, in this embodiment, the charge crosstalk rate of the pixels 205 having the second arrangement is made smaller than the charge crosstalk rate of the pixels 205 having the first arrangement. By doing so, the phase difference signal in the y direction is made relatively less susceptible to the effects of noise, improving phase difference focus detection performance and roughly matching the phase difference detection performance in the x direction.

[0068] To differentiate the charge crosstalk rates between the pixels 205 having the first arrangement and the pixels 205 having the second arrangement, an ion implantation process is performed to differentiate, for example, the p-type impurity concentrations in the isolation regions 400 and 500 of the PDA 301 and the PDB 302. This allows the image sensor 1 of this embodiment to be realized. In this embodiment, the impurity concentration in the isolation region 400 of the pixels 205 having the first arrangement is low, and the impurity concentration in the isolation region 500 of the pixels having the second arrangement is high. In other words, the magnitude relationship between the impurity concentration in the isolation region 400 of the pixels 205 having the first arrangement and the impurity concentration in the isolation region 500 of the pixels 205 having the second arrangement is set to be the same as the magnitude relationship between the noise influences.

[0069] Such adjustment of the charge crosstalk rate may be performed by varying the width of the isolation region of the photoelectric conversion unit. In this embodiment, the width of the isolation region 400 of the pixel 205 having the first arrangement is narrowed, and the width of the isolation region 500 of the pixel 205 having the second arrangement is widened. In other words, the magnitude relationship between the width of the isolation region 400 of the pixel having the first arrangement and the width of the isolation region 500 of the pixel having the second arrangement is adjusted to be the same as the magnitude relationship between the influence of noise.

[0070] Furthermore, the charge crosstalk rate between the pixels 205 having the first arrangement and the pixels 205 having the second arrangement may be adjusted by making the potential gradient for charge collection in the photoelectric conversion unit from the back side of the substrate to the front side of the substrate different between the pixels 205 having the first arrangement and the pixels 205 having the second arrangement. In this case, the potential gradient of the pixels 205 having the first arrangement is made gentler than the potential gradient of the pixels having the second arrangement, that is, the magnitude relationship of this steepness is made the same as the magnitude relationship of the noise influence.

[0071] Furthermore, the impurity concentration and width of the isolation region, as well as the electric field gradient, may be combined to adjust the charge crosstalk rate in the first direction to be higher than the charge crosstalk rate in the second direction.

[0072] In the above example, the charge crosstalk rate between the pixels 205 having the first arrangement and the pixels 205 having the second arrangement is adjusted during the manufacturing of the image sensor 1. However, the present invention is not limited to this configuration, and the charge crosstalk rate may be adjusted after manufacturing. In this case, for example, electrode units may be disposed in the isolation regions 400, 500 of the PDA 301 and the PDB 302, and the charge crosstalk rate may be adjusted by controlling the potential of the isolation regions 400, 500. In this case, the potential applied to the isolation region 400 of the pixels 205 having the first arrangement is made lower than the potential applied to the isolation region 500 of the pixels 205 having the second arrangement, i.e., the magnitude relationship between the potentials is reversed from the magnitude relationship between the width H and the height V. Note that the electrode units may be deep trench isolation (DTI) connected to control wiring.

[0073] Furthermore, in the above example, all of the pixels 205 are described as having the first arrangement or the second arrangement, but the present invention is not limited to this, and some of the pixels 205 may be discretely arranged as the first arrangement or the second arrangement.

[0074] As described above, according to the first embodiment, when image plane phase difference focus detection is performed using a signal having different amounts of noise in the x and y directions obtained from an image sensor having pixels arranged in a matrix, it is possible to make the focus detection performance in the x and y directions closer to each other.

[0075] <Second embodiment> Next, a second embodiment of the present invention will be described. Fig. 14 shows the arrangement of pixels 205 having a third arrangement of the image sensor 1 according to this embodiment.

[0076] In the third arrangement, as shown in Fig. 14, a pixel 205 is composed of four photodiodes (PD) 1101 to 1104. Hereinafter, these will be referred to as PDA1101, PDB1102, PDC1103, and PDD1104. Fig. 14(a) is a perspective view of the pixel of this embodiment, and Fig. 14(b) is a planar schematic diagram showing the positional relationship in a planar view as seen from the ML401 side (the rear surface side of the substrate); in this embodiment, transfer switches and the like are omitted. Note that the definitions of "planar view" and x, y, and z are the same as in Fig. 4, and therefore will not be described here.

[0077] In this embodiment, by defining the first direction as the x direction and the second direction as the y direction, it becomes possible to perform phase difference detection in two orthogonal directions using pixels with the same configuration.

[0078] The phase difference in the x direction is detected by using the sum of the signals of PDA1101 and PDC1103 (signal A) and the sum of the signals of PDB1102 and PDD1104 (signal B). The phase difference in the x direction is detected by using the sum of the signals of PDA1101 and PDB1102 (signal C) and the sum of the signals of PDC1103 and PDD1104 (signal D) By using this, it is possible to detect a phase difference in the y direction. That is, in this embodiment, as in the first embodiment, the pixel is configured so that the magnitude relationship between the charge crosstalk rate between the photoelectric conversion units responsible for signals A and B and the charge crosstalk rate between the photoelectric conversion units responsible for signals C and D matches the magnitude relationship between the effects of noise. As in the first embodiment, the charge crosstalk rate is adjusted by adjusting the impurity concentration and width of the isolation regions 1105 and 1106, adjusting the potential gradient in the photoelectric conversion units, and controlling the potential by electrodes.

[0079] As described above, according to the second embodiment, even when each pixel has a plurality of photoelectric conversion units divided in two directions, it is possible to obtain the same effects as in the first embodiment.

[0080] <Summary> The disclosure of this embodiment includes the following configuration.

[0081] (Configuration 1) a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction; a plurality of photoelectric conversion units configured to perform photoelectric conversion on light incident through each of at least some of the plurality of microlenses, the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units; An imaging element characterized in that, when the influence of noise superimposed on signals read out from the plurality of photoelectric conversion units is greater in the second direction than in the first direction, the charge crosstalk rate between the plurality of photoelectric conversion units in the first direction is made higher than the charge crosstalk rate in the second direction.

[0082] (Configuration 2) The imaging element according to configuration 1, wherein the plurality of photoelectric conversion units are two photoelectric conversion units arranged in the first direction or the second direction for each of the plurality of photoelectric conversion units.

[0083] (Configuration 3) 2. The imaging element according to configuration 1, wherein the plurality of photoelectric conversion units are four photoelectric conversion units arranged in the first direction and the second direction.

[0084] (Configuration 4) An imaging element described in any one of configurations 1 to 3, characterized in that the impurity concentration of an isolation region separating the plurality of photoelectric conversion units arranged in the first direction is lower than the impurity concentration of an isolation region separating the plurality of photoelectric conversion units arranged in the second direction.

[0085] (Configuration 5) An imaging element described in any one of configurations 1 to 4, characterized in that the width of an isolation region separating the plurality of photoelectric conversion units arranged in the first direction is shorter than the width of an isolation region separating the plurality of photoelectric conversion units arranged in the second direction.

[0086] (Configuration 6) An imaging element described in any one of configurations 1 to 5, characterized in that in the plurality of photoelectric conversion units arranged in the first direction, the potential gradient from the side where light is incident to the region where the charge obtained by photoelectric conversion is accumulated is made gentler than the potential gradient in the plurality of photoelectric conversion units arranged in the second direction.

[0087] (Configuration 7) further comprising an electrode for controlling the potential of an isolation region that isolates the plurality of photoelectric conversion units; An imaging element described in any one of configurations 1 to 6, characterized in that the potential of an isolation region separating the plurality of photoelectric conversion units arranged in the first direction is lower than the potential of an isolation region separating the plurality of photoelectric conversion units arranged in the second direction.

[0088] (Configuration 8) 8. The imaging device according to any one of configurations 1 to 7, further comprising output means for converting the charges photoelectrically converted by the plurality of photoelectric conversion sections into signals and outputting the signals.

[0089] (Configuration 9) a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction; a plurality of photoelectric conversion units configured to perform photoelectric conversion on light incident through each of at least some of the plurality of microlenses, the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units; An imaging element characterized in that the number of the plurality of photoelectric conversion units arranged in the first direction is greater than the number of the plurality of photoelectric conversion units arranged in the second direction, and the charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is higher than the charge crosstalk rate in the second direction.

[0090] (Configuration 10) a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction; a plurality of photoelectric conversion units configured to perform photoelectric conversion on light incident through each of at least some of the plurality of microlenses; a plurality of floating diffusion sections provided for each of the plurality of photoelectric conversion sections; a charge-voltage converter that converts the charges transferred from the plurality of photoelectric conversion units to the floating diffusion unit into voltages; and the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units; an imaging element characterized in that the length of wiring from a diffusion layer constituting the floating diffusion section corresponding to the plurality of photoelectric conversion sections arranged in the first direction to the charge-voltage conversion section is shorter than the length of wiring from a diffusion layer constituting the floating diffusion section corresponding to the plurality of photoelectric conversion sections arranged in the second direction to the charge-voltage conversion section, and the charge crosstalk rate in the first direction between the plurality of photoelectric conversion sections is higher than the charge crosstalk rate in the second direction.

[0091] (Configuration 11) the imaging element according to any one of configurations 1 to 10; a processing means for processing a signal output from the imaging element; An imaging device comprising:

[0092] (Configuration 12) 12. The imaging apparatus according to configuration 11, wherein the processing means performs focus detection using an image plane phase difference method based on the signal.

[0093] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0094] 1: image sensor, 2: overall control and calculation unit, 7: signal processing unit, 201: pixel array unit, 202: vertical selection circuit, 203: column circuit, 204: horizontal selection circuit, 205: pixel, 206: output signal line, 207: pixel drive wiring group, 301, 302: photodiode, 303, 304: transfer switch, 305: floating diffusion unit, 400, 500: separation region, 721: first pupil intensity distribution, 722: second pupil intensity distribution

Claims

1. a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction; a plurality of photoelectric conversion units configured to perform photoelectric conversion on light incident through each of at least some of the plurality of microlenses, the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units; An imaging element characterized in that, when the influence of noise superimposed on signals read out from the plurality of photoelectric conversion units is greater in the second direction than in the first direction, the charge crosstalk rate between the plurality of photoelectric conversion units in the first direction is made higher than the charge crosstalk rate in the second direction.

2. 2. The imaging element according to claim 1, wherein the plurality of photoelectric conversion units are two photoelectric conversion units arranged in the first direction or the second direction for each of the plurality of photoelectric conversion units.

3. 2. The image sensor according to claim 1, wherein the plurality of photoelectric conversion units are four photoelectric conversion units arranged in the first direction and the second direction.

4. An imaging element according to any one of claims 1 to 3, characterized in that the impurity concentration of an isolation region separating the plurality of photoelectric conversion units arranged in the first direction is lower than the impurity concentration of an isolation region separating the plurality of photoelectric conversion units arranged in the second direction.

5. An imaging element according to any one of claims 1 to 3, characterized in that the width of an isolation region separating the plurality of photoelectric conversion units arranged in the first direction is shorter than the width of an isolation region separating the plurality of photoelectric conversion units arranged in the second direction.

6. An imaging element according to any one of claims 1 to 3, characterized in that in the plurality of photoelectric conversion units arranged in the first direction, the potential gradient from the side where light is incident to the region where the charge obtained by photoelectric conversion is accumulated is made gentler than the potential gradient in the plurality of photoelectric conversion units arranged in the second direction.

7. further comprising an electrode for controlling the potential of an isolation region that isolates the plurality of photoelectric conversion units; An imaging element according to any one of claims 1 to 3, characterized in that the potential of an isolation region separating the plurality of photoelectric conversion units arranged in the first direction is lower than the potential of an isolation region separating the plurality of photoelectric conversion units arranged in the second direction.

8. 4. The image sensor according to claim 1, further comprising an output unit that converts the charges photoelectrically converted by the plurality of photoelectric conversion units into a signal and outputs the signal.

9. a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction; a plurality of photoelectric conversion units configured to perform photoelectric conversion on light incident through each of at least some of the plurality of microlenses, the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units; An imaging element characterized in that the number of the plurality of photoelectric conversion units arranged in the first direction is greater than the number of the plurality of photoelectric conversion units arranged in the second direction, and the charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is higher than the charge crosstalk rate in the second direction.

10. a plurality of microlenses arranged in a matrix in a first direction and a second direction perpendicular to the first direction; a plurality of photoelectric conversion units configured to perform photoelectric conversion on light incident through each of at least some of the plurality of microlenses; a plurality of floating diffusion sections provided for each of the plurality of photoelectric conversion sections; a charge-voltage converter that converts the charges transferred from the plurality of photoelectric conversion units to the floating diffusion unit into voltages; and the plurality of photoelectric conversion units are arranged in at least one of the first direction and the second direction for each of the plurality of photoelectric conversion units; an imaging element characterized in that the length of wiring from a diffusion layer constituting the floating diffusion section corresponding to the plurality of photoelectric conversion sections arranged in the first direction to the charge-voltage conversion section is shorter than the length of wiring from a diffusion layer constituting the floating diffusion section corresponding to the plurality of photoelectric conversion sections arranged in the second direction to the charge-voltage conversion section, and the charge crosstalk rate in the first direction between the plurality of photoelectric conversion sections is higher than the charge crosstalk rate in the second direction.

11. The imaging device according to any one of claims 1 to 3, 9 and 10; a processing means for processing a signal output from the imaging element; An imaging device comprising:

12. 12. The image pickup apparatus according to claim 11, wherein the processing means performs focus detection using an image plane phase difference method based on the signal.

Images