Imaging element and imaging apparatus

Abstract

To bring performances of focus detection in the main scanning direction and the sub-scanning direction closer to each other in focus detection using an image surface phase detection method using a phase difference signal output from an imaging element in which pixels are arranged in a matrix.SOLUTION: An imaging element has a plurality of microlenses arranged in a matrix in a first direction and a second direction, a plurality of photoelectric conversion units configured to photoelectrically convert light incident on at least a portion of each of the microlenses of the plurality of microlenses through each microlens, and readout means for sequentially reading out signals from the plurality of photoelectric conversion units where the first direction is defined as the main scanning direction and the second direction is defined as the sub-scanning direction. The plurality of photoelectric conversion units are arranged in at least one of the first and second directions for each of the plurality of photoelectric conversion units. 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 10

Description

Technical Field

[0001] The present invention relates to an imaging device in which pixel portions each having a plurality of photoelectric conversion portions are two-dimensionally arranged, and an imaging apparatus equipped with the imaging device.

Background Art

[0002] Conventionally, as one of the focus detection methods performed by an imaging device, a so-called imaging surface phase difference method is known in which a pair of pupil division signals are acquired using focus detection pixels formed in an imaging device, and phase difference type focus detection is performed.

[0003] As an example of such an imaging surface phase difference method, an imaging device using a two-dimensional imaging device in which one pixel has one microlens and a plurality of divided photoelectric conversion portions is disclosed in Patent Document 1. The plurality of photoelectric conversion portions are configured to receive light transmitted through different regions of the exit pupil of the imaging lens via one microlens, and perform pupil division. Then, by calculating the amount of image shift from the phase difference signals that are the signals of the individual photoelectric conversion portions, phase difference type focus detection can be performed. Also, by adding together the signals of the individual photoelectric conversion portions for each pixel, a normal image signal can be acquired. Further, Patent Document 1 discloses a configuration in which the saturation resistance of pixels is enhanced by arranging a plurality of types of pixels having different heights of separation barriers between the photoelectric conversion portions in a pixel.

[0004] In such an image sensor, in a configuration where a plurality of photoelectric conversion portions are arranged horizontally within a pixel and the pupil division direction is horizontal, for example, when the subject has a horizontal stripe pattern or the like, parallax is difficult to appear and the focus detection accuracy may decrease.

[0005] In contrast, Patent Document 2 discloses a technique for improving focus detection accuracy by using two different arrangement directions for the photoelectric conversion units relative to each microlens and two different pupil division directions. Furthermore, Patent Document 2 discloses a structure that separates adjacent photoelectric conversion units in the vertical direction and a structure that separates adjacent photoelectric conversion units in the horizontal direction, thereby differentiating the intensity of charge leakage to adjacent photoelectric conversion units. This structure allows for the leakage and accumulation of supersaturated charge received in excess of the charge amount that one photoelectric conversion unit can store to different photoelectric conversion units arranged in predetermined directions, enabling phase difference focus detection in either the horizontal or vertical direction even when one photoelectric conversion unit becomes saturated. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2017-212351 [Patent Document 2] Japanese Patent Publication No. 2014-107835 [Overview of the project] [Problems that the invention aims to solve]

[0007] Many conventional image sensors prioritize reading signals in either the row or column direction, before moving on to reading the next row or column. For example, when reading rows by row and shifting the rows being read sequentially, the pixels in each row are read at the same time, but the timing of the readouts of different rows will differ as the rows are further apart.

[0008] Therefore, when pixels with multiple photoelectric conversion units arranged in rows and pixels with multiple photoelectric conversion units arranged in columns for a single microlens are mixed, the following problem arose: In other words, the focus detection accuracy decreased in the column direction (sub-scanning direction) compared to the row direction (main scanning direction), where signals can be read out from multiple photoelectric conversion units at roughly the same time intervals.

[0009] However, while Patent Documents 1 and 2 describe methods for dealing with the case where the photoelectric conversion unit is saturated, they cannot solve the problem of reduced focus detection accuracy due to the differences in readout timing mentioned above.

[0010] This invention was made in view of the above-mentioned problems, and aims to bring the focus detection performance closer in the main scanning direction and the sub-scanning direction in a focus detection method using an image plane phase difference method that utilizes a phase difference signal output from an image sensor in which pixels are arranged in a matrix. [Means for solving the problem]

[0011] To solve the above problems, the image sensor of the present invention comprises: a plurality of microlenses arranged in a matrix in a first direction and a second direction orthogonal to the first direction; a plurality of photoelectric conversion units configured to convert light incident through each of the plurality of microlenses into photoelectrics for at least some of each of the plurality of microlenses; and a readout means for sequentially reading signals from the plurality of photoelectric conversion units, with the first direction as the main scanning direction and the second direction as the sub-scanning direction, wherein each of the plurality of photoelectric conversion units is arranged in at least one of the first direction and 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. [Effects of the Invention]

[0012] According to the present invention, in focus detection using an image plane phase difference method that utilizes a phase difference signal output from an image sensor in which pixels are arranged in a matrix, the focus detection performance can be made closer in the main scanning direction and the sub-scanning direction. [Brief explanation of the drawing]

[0013] [Figure 1] A block diagram showing the schematic configuration of the imaging device according to the first embodiment. [Figure 2] A diagram schematically showing an example of the overall configuration of an image pickup device according to the first embodiment. [Figure 3] An equivalent circuit diagram of a pixel according to the first embodiment. [Figure 4] A schematic diagram showing the configuration of a pixel having the first arrangement according to the first embodiment. [Figure 5] A schematic diagram showing the configuration of a pixel having the second arrangement according to the first embodiment. [Figure 6] A diagram showing the relationship between a pixel having the first arrangement according to the first embodiment and a partial pupil region. [Figure 7] A schematic diagram showing an example of the pupil intensity distribution of a pixel having the first arrangement according to the first embodiment. [Figure 8] A diagram schematically explaining the sensor entrance pupil of the image pickup device according to the first embodiment. [Figure 9] A diagram showing the schematic relationship between the amount of image shift and the amount of defocus between parallax images according to the first embodiment. [Figure 10] A schematic diagram showing the relationship between the charge crosstalk rate and the pupil intensity distribution in the first embodiment. [Figure 11] An explanatory diagram showing an example of the readout order of pixels in the first embodiment. [Figure 12] A schematic diagram showing the configuration of a pixel having the third arrangement according to the second embodiment.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and redundant explanations are omitted.

[0015] <First Embodiment> [Overall Configuration] FIG. 1 is a block diagram showing a schematic configuration of an imaging device according to a first embodiment of the present invention. The imaging device of the present embodiment includes an imaging element 1, an overall control and arithmetic unit 2, an instruction unit 3, a timing generation unit 4, a photographing lens unit 5, a lens driving unit 6, a signal processing unit 7, a display unit 8, and a recording unit 9.

[0016] The photographing lens unit 5 forms an optical image of a subject on the imaging element 1. Although it is represented by a single lens in the figure, the photographing lens unit 5 includes a plurality of lenses including a focus lens, a zoom lens, etc., and an aperture. Further, the photographing lens unit 5 may be detachable from the main body of the imaging device or may be integrally configured with the main body.

[0017] The imaging element 1 converts the light incident through the photographing lens unit 5 into an electrical signal and outputs it. From each pixel of the imaging element 1, signals are read out so as to be able to obtain a pupil-divided pupil-divided signal (hereinafter referred to as a "phase difference signal") that can be used for phase difference method focus detection and an image signal that is a signal for each pixel.

[0018] The signal processing unit 7 performs predetermined signal processing such as correction processing on the signal output from the imaging element 1, and outputs a phase difference signal used for focus detection and an image signal used for recording.

[0019] The overall control and arithmetic unit 2 performs overall driving and control of the imaging device. Further, it performs arithmetic operations for focus detection using the phase difference signal processed by the signal processing unit 7, and performs predetermined signal processing such as arithmetic processing for exposure control and development and compression for generating an image for recording / playback on the image signal.

[0020] The lens driving unit 6 drives the photographing lens unit 5, and performs focus control, zoom control, aperture control, etc. on the photographing lens unit 5 according to a control signal from the overall control and arithmetic unit 2.

[0021] The instruction unit 3 receives inputs from the outside, such as instructions to execute shooting, settings for the drive mode of the imaging device, and various other settings and selections, via user operations, and transmits them to the overall control and calculation unit 2.

[0022] The timing generation unit 4 generates timing signals to drive the image sensor 1 and the signal processing unit 7 according to the control signals from the overall control and calculation unit 2. The display unit 8 displays information such as preview images, playback images, and the drive mode settings of the imaging device.

[0023] The recording unit 9 is equipped with a recording medium (not shown) on which recording image signals are recorded. Examples of recording media include semiconductor memory such as flash memory. The recording medium may be detachable from the recording unit 9 or may be built into it.

[0024] [Image sensor] Figure 2 is a schematic diagram showing an example of the overall configuration of the image sensor 1 shown in Figure 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.

[0025] Multiple pixels 205 are arranged in a matrix in the pixel array section 201. The output of the vertical selection circuit 202 is input to the pixels 205 via the pixel drive wiring group 207, and the pixel signals of the pixels 205 in the row selected by the vertical selection circuit 202 are read out row by row via the output signal line 206 to the column circuit 203. One output signal line 206 can be provided for each pixel column, or for multiple pixel columns, or multiple output signal lines 206 can be provided for each pixel column. Signals read out in parallel via multiple output signal lines 206 are input to the column circuit 203, where processing such as signal amplification, noise reduction, and A / D conversion is performed, and the processed signals are held. The horizontal selection circuit 204 sequentially, randomly, or simultaneously selects the signals held in the column circuit 203, and the selected signals are output outside the image sensor 1 via a horizontal output line and output section (not shown).

[0026] By sequentially performing the operation of outputting the pixel signals of the rows selected by the vertical selection circuit 202 to the outside of the image sensor 1, while changing the rows selected by the vertical selection circuit 202, it is possible to read out a two-dimensional imaging signal or a phase difference signal from the image sensor 1.

[0027] [Pixel circuit / signal readout] Figure 3 is an equivalent circuit diagram of pixel 205 in this embodiment. Each pixel 205 has two photodiodes 301 (PDA) and 302 (PDB), which are photoelectric conversion units. Depending on the amount of incident light, the signal charge is photoelectrically converted by the PDA 301 and stored, and then transferred via the transfer switch (TXA) 303 to the floating diffusion unit (FD) 305, which constitutes the charge storage unit. The signal charge is photoelectrically converted by the PDB 302 and stored, and then transferred via the transfer switch (TXB) 304 to the FD 305. When the reset switch (RES) 306 is turned on, it resets the FD 305 to the voltage of the constant voltage source VDD. Also, by turning on RES 306, TXA 303 and TXB 304 simultaneously, the PDA 301 and PDB 302 can be reset.

[0028] When the selection switch (SEL) 307 for selecting pixels is turned ON, the amplification transistor (SF) 308 converts the signal charge stored in FD305 into a voltage, and the converted signal voltage is output from the pixel to the output signal line 206. In addition, the gates of TXA303, TXB304, RES306, and SEL307 are each connected to the pixel drive wiring group 207 and controlled by the vertical selection circuit 202.

[0029] In this embodiment, the signal charge accumulated in the photoelectric conversion unit is assumed to be electrons, the photoelectric conversion unit is formed from an N-type semiconductor, and the separation is performed using a P-type semiconductor. However, the signal charge may be assumed to be holes, the photoelectric conversion unit may be formed from a P-type semiconductor, and the separation may be performed using an N-type semiconductor.

[0030] Next, we will describe the operation of reading the signal charge from PDA301 and PDB302 after resetting PDA301 and PDB302 and after a predetermined charge accumulation time has elapsed, in a pixel having the above-described configuration. First, when the SEL307 of the row selected by the vertical selection circuit 202 is turned on and the source of SF308 and the output signal line 206 are connected, the output signal line 206 enters a state where a voltage corresponding to the voltage of FD305 is read. Subsequently, RES306 is turned on / off and the potential of FD305 is reset. After that, the circuit waits until the output signal line 206, which has been affected by the voltage fluctuation of FD305, stabilizes, and the voltage of the stabilized output signal line 206 is acquired as the signal voltage N by the column circuit 203, and the signal is processed and held.

[0031] Subsequently, TXA303 is switched on / off, and the signal charge stored in PDA301 is transferred to FD305. The voltage of FD305 decreases by an amount corresponding to the amount of signal charge stored in PDA301. Then, the system waits until the output signal line 206, which has been affected by the voltage fluctuation of FD305, stabilizes. The voltage of the stabilized output signal line 206 is then taken as signal voltage A by the column circuit 203, processed, and held.

[0032] Subsequently, TXB304 is switched on / off, and the signal charge stored in PDB302 is transferred to FD305. The voltage of FD305 decreases by an amount corresponding to the amount of signal charge stored in PDB302. Then, the circuit waits until the output signal line 206, which has been affected by the voltage fluctuation of FD305, stabilizes. The voltage of the stabilized output signal line 206 is then taken as the signal voltage (A+B) by the column circuit 203, processed, and held.

[0033] In this way, the difference between the acquired signal voltage N and signal voltage A allows us to obtain signal A corresponding to the amount of signal charge stored in PDA301. Furthermore, the difference between signal voltage A and signal voltage (A+B) allows us to obtain signal B corresponding to the amount of signal charge stored in PDB302. This difference calculation may be performed in the column circuit 203 or after output from the image sensor 1. A phase difference signal can be obtained using signals A and B respectively, and the imaging signal can be obtained by adding signals A and B together. Alternatively, if the difference calculation is performed after output from the image sensor 1, the imaging signal may be obtained by taking the difference between signal voltage N and signal voltage (A+B).

[0034] Alternatively, the same drive used to read out signal voltages N and A can be applied to the PDB302 instead of the PDA301 to read out signal voltages N, A, and B, respectively. In this case, signals A and B obtained from signal voltages A and B can be used directly as phase difference signals, and the imaging signal can be obtained by adding signal voltages A and B, or A and B together.

[0035] [Configuration of the photoelectric conversion area] • x-direction phase difference detection pixel structure Figure 4 is a schematic diagram showing the first arrangement of semiconductor regions constituting the pixel 205 according to this embodiment, where Figure 4(a) is an oblique schematic diagram and Figure 4(b) is a planar schematic diagram showing the positional relationship in a planar view. "Planar view" refers to viewing from the z direction or -z direction with respect to the plane (xy plane) parallel to the side of the semiconductor substrate where the transistor gates are located. 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.

[0036] As shown in Figure 4(a), the pixel 205 having the first arrangement includes a microlens (ML) 401, PDA 301, PDB 302, TXA 303, TXB 304, and FD 305. In the first arrangement, the PDA 301 and PDB 302 are formed side by side in the x-direction within a Si substrate, which is a semiconductor substrate. The side where the ML 401 is located is the back side of the substrate, and the side where the TXA 303, 304, and FD 305 are located is the front side of the substrate.

[0037] Most of the light incident through ML401 is photoelectrically converted on the back side of the substrates of PDA301 and PDB302. Here, a potential gradient is formed within PDA301 and PDB302 such that the potential experienced by electrons decreases in the depth direction, making it easier for the charge generated in PDA301 and PDB302 to move to TXA303 and TXB304.

[0038] Furthermore, a separation region 400 is formed between PDA301 and PDB302, where the p-type impurity concentration is higher than that of PDA301 and PDB302, so as to form a potential barrier. This electrically separates the generated charge, making it difficult for it to move between PDA301 and PDB302. Therefore, in this embodiment, the separation direction of PDA301 and PDB302 in the first arrangement is the x-direction (first direction).

[0039] • Phase difference detection pixel structure in the y direction Figure 5 is a schematic diagram showing the second arrangement of semiconductor regions constituting the pixel 205 according to this embodiment, where Figure 5(a) is an oblique schematic diagram and Figure 5(b) is a plan schematic diagram showing the positional relationship in a plan view. The definitions of "plan view" and x, y, and z are the same as in Figure 4, so their explanation is omitted.

[0040] As shown in Figure 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 Figure 4, but PDA301 and PDB302 are arranged so that they are aligned in the y direction, and the separation direction of the photoelectric conversion unit is the y direction (second direction).

[0041] In the second configuration as well, a potential gradient is formed within PDA301 and PDB302 such that the potential experienced by electrons decreases in the depth direction, facilitating the transfer of charges generated within PDA301 and PDB302 to TXA303 and TXB304. Furthermore, in the second configuration as well, a separation region 500 with a higher p-type impurity concentration than PDA301 and PDB302 is formed between PDA301 and PDB302. This electrically separates the generated charges, making it difficult for them to move between PDA301 and PDB302.

[0042] • Charge crosstalk rate distribution Most of the charge generated in PDA301 and PDB302 is accumulated within each PDA301 and PDB302, but it can move from PDA301 to PDB302, or from PDB302 to PDA301, and accumulate there. This phenomenon of charge moving 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 when viewed from a planar perspective, as it is closer to the separation regions of 400 and 500. In addition, since PDA301 and PDB302 have a potential gradient in the depth direction to facilitate charge movement toward TXA303 and TXB304, the shorter the distance traveled to TXA303 and TXB304, the smaller the charge crosstalk rate. In other words, within PDA301 and PDB302, for the same x and y coordinates, the charge crosstalk rate is smaller at locations closer to TXA303 and TXB304 than at locations closer to ML401. In the following explanation, the distribution of crosstalk rate within PDA301 and PDB302 will be referred to as the "charge crosstalk rate distribution." This charge crosstalk rate distribution becomes smaller across PDA301 and PDB302 as the potential gradient in the depth direction within PDA301 and PDB302 becomes steeper.

[0043] Charge crosstalk can also occur between adjacent pixels. Charge crosstalk between adjacent pixels is a factor that reduces the resolution of the imaging signal. Therefore, it is desirable to keep 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 kept low by separating adjacent pixels with an insulator or by increasing the height of the potential barrier.

[0044] • Method for detecting phase difference in the x-direction Next, we will explain the calculation performed in the overall control and calculation unit 2 to calculate the defocus amount from the phase difference signal.

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

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

[0047] Through ML401, the pupil surface and the light-receiving surface of the image sensor 1 are approximately conjugate. Therefore, the light beam passing through partial pupil region 601 is received by PDA301. Similarly, the light beam passing through partial pupil region 602 is received by PDB302. Thus, when the pupil surface is divided in the x direction, the pupil division direction is the x direction. Therefore, the position dependence of the pupil intensity distribution on the division direction takes the shape illustrated in Figure 7. In Figure 7, the pupil intensity distribution corresponding to PDA301 is 701, and the pupil intensity distribution corresponding to PDB302 is 702.

[0048] Next, with reference to Figure 8, the sensor entrance pupil of the image sensor 1 will be described. In the image sensor 1 of this embodiment, the ML401 of each pixel 205 is continuously shifted toward the center of the image sensor 1 according to the image height coordinate on a two-dimensional plane. That is, each ML401 is positioned so as the image height increases, it is eccentric toward the center of the image sensor 1. Note that the center of the image sensor 1 and the optical axis of the imaging optical system change due to the mechanism that reduces the effects of blur caused by camera shake, etc., by driving the imaging optical system or the image sensor 1, but they are approximately the same. As a result, the first pupil intensity distribution 701 and the second pupil intensity distribution 702 of each pixel positioned at each image height coordinate of the image sensor 1 are configured to be approximately the same at the pupil plane at a distance Ds (entry pupil distance) from the image sensor 1. In other words, the first pupil intensity distribution 701 and the second pupil intensity distribution 702 of all pixels of the image sensor 1 are configured to be approximately the same at the pupil plane at 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 referred to as 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 made approximately the same, or pixels may be configured to have different entrance pupil distances for each row or detection area.

[0050] Figure 9 shows a schematic relationship between the amount of image shift and the amount of defocus between disparity images. The image sensor 1 (not shown) of this embodiment is placed on the imaging surface 600, and, as in Figure 6, the exit pupil of the imaging lens unit 5 is divided into two parts: a partial pupil region 601 and a partial pupil region 602.

[0051] The amount of defocus d is defined as the distance from the imaging plane to the subject's imaging position, with magnitude |d| being negative (d<0) for a front-focus state where the subject's imaging position is on the subject side of the imaging plane, and positive (d>0) for a back-focus state where the subject's imaging position is on the opposite side of the imaging plane. 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 front-focused (d<0). The front-focused state (d<0) and the back-focused state (d>0) together are considered a defocused state (|d|>0).

[0052] In the front-focused state (d<0), the light beam from the subject on the object surface 902 that passes through the partial pupil region 601 (602) is focused once, then spreads out with a width Γ1 (Γ2) centered on the centroid position G1 (G2) of the light beam, resulting in a blurred image on the imaging surface 600. The blurred image is received by PDA301 and PDB302, and a disparity image is generated. Therefore, the generated disparity image will have the image of the subject on the object surface 902 blurred with a width Γ1 (Γ2) at the centroid position G1 (G2).

[0053] The blur width Γ1 (Γ2) of the subject image increases roughly proportionally with increasing defocus amount d |d|. Similarly, the amount of image displacement p (=G2-G1) of the subject image between the parallax images |p| also increases roughly proportionally with increasing defocus amount d |d|. The same applies in the back-focused state (d>0), although the direction of image displacement of the subject image between the parallax images is opposite to that of the front-focused state. In the in-focus state (d=0), the centroid positions of the subject images between the parallax images coincide (p=0), and no image displacement occurs.

[0054] Therefore, in the two phase difference signals obtained using the signals from PDA301 and PDB302, as the amount of defocus in the disparity image increases, the amount of image shift in the x-direction between the two phase difference signals also increases. Based on this relationship, the amount of image shift calculated by correlation calculation while shifting the disparity image in the x-direction is converted into the amount of defocus, thereby performing focus detection using the phase difference detection method. The coefficient multiplied when converting from the amount of image shift to the amount of defocus is called the conversion coefficient. If this conversion coefficient is large, compared to the case where the conversion coefficient is small, a large amount of defocus is calculated from a small amount of image shift, making it more susceptible to noise in the phase difference signal and potentially degrading the phase difference detection performance.

[0055] • Method for detecting phase difference in the y-direction The phase difference detection method in the y-direction (second direction) in this embodiment can be the same as the phase difference detection method in the x-direction (first direction) using the signal from the pixel 205 having the first arrangement described above. That is, instead of the pixel 205 having the first arrangement, the phase difference detection in the y-direction (second direction) is performed using the signal from the pixel 205 having the second arrangement.

[0056] [Charge crosstalk rate] • Relationship between charge crosstalk rate and phase difference detection performance in pupil intensity distribution Figure 10 shows the pupil intensity distribution on the pupil plane corresponding to pixel 205 having the first arrangement. The relationship between the magnitude of the charge crosstalk rate in PDA301 and PDB302 and the phase difference detection performance will be explained below with reference to Figure 10. When the charge crosstalk rate between PDA301 and PDB302 is low (small), the pupil intensity distributions of PDA301 and PDB302 are denoted as the first pupil intensity distribution 701 and the second pupil intensity distribution 702, respectively. In contrast, when the charge crosstalk rate between PDA301 and PDB302 is high (large), the signal charge obtained in PDA301 and PDB302 increases or decreases, resulting in the pupil intensity distribution 1001 shown by the dashed line and the pupil intensity distribution 1002 shown by the dotted line.

[0057] Here, the distance between the peaks of the pupil intensity distributions corresponding to PDA301 and PDB302 is roughly related to the tolerance range of the light reception angle for light incident on the pixel, and the slope on the graph in region 1004 where the pupil intensity distributions intersect is roughly related to the basic accuracy of phase difference detection. That is, in Figure 10, when the charge crosstalk rate is low, the slope of the first pupil intensity distribution 701 and the second pupil intensity distribution 702 in region 1004 is large, resulting in high basic accuracy, and the distance 703 between the peaks of the first pupil intensity distribution 701 and the second pupil intensity distribution 702 is small, resulting in a narrow tolerance range of the light reception angle. On the other hand, when the charge crosstalk rate is high, the slope of the pupil intensity distributions 1001 and 1002 in region 1004 is small, resulting in low basic accuracy, and the distance 1003 between the peaks of pupil intensity distribution 1001 and pupil intensity distribution 1002 is large, resulting in a wide tolerance range of the light reception angle.

[0058] Furthermore, in image plane phase difference detection, since the image shift of the subject image is detected based on phase difference signals obtained from multiple PDA301 and PDB302, it is desirable to obtain the phase difference signal in the phase difference detection direction in the shortest possible time. In addition, the signal-to-noise ratio (S / N ratio) of the signal can be improved by adding the signals over several pixels in the phase difference detection direction. By improving the signal quantity and S / N ratio in this way, signal variability can be suppressed, and the shape of the pupil intensity distribution can be brought closer to an ideal shape. In other words, the accuracy of phase difference detection can be improved by speeding up the readout of pixels in the phase difference detection direction.

[0059] In Figure 11, the arrow 1200 explicitly represents the signal readout order from the image sensor 100, where the x-direction is the main scanning direction and the y-direction is the sub-scanning direction. In the main scanning direction, the time difference between reading signals from the PDA 301 and PDB 302 of the pixel 205 located at the right end of each row and reading signals from the PDA 301 and PDB 302 of the pixel 205 located at the left end is short. On the other hand, in the sub-scanning direction, the time difference between reading signals from the PDA 301 and PDB 302 of the pixel 205 located at the top end of each column and reading signals from the PDA 301 and PDB 302 of the pixel 205 located at the bottom end is longer compared to the main scanning direction. Therefore, the focus detection performance based on the phase difference signals obtained from the first arrangement of pixels 205 arranged in the main scanning direction is higher than the focus detection performance based on the phase difference signals obtained from the second arrangement of pixels 205 arranged in the sub-scanning direction.

[0060] Therefore, in the image sensor 1 of this embodiment, the charge crosstalk rate in the photoelectric conversion unit of the pixel 205 having a first arrangement in which the PDA 301 and PDB 302 are arranged in the main scanning direction, and the charge crosstalk rate of the pixel 205 having a second arrangement in which the PDA 301 and PDB 302 are arranged in the sub-scanning direction are set as follows. That is, the relationship between the magnitude of the charge crosstalk rate of the pixel 205 having the first arrangement and the charge crosstalk rate of the pixel 205 having the second arrangement is configured to be inverse to the magnitude (length) of the readout time difference in the main scanning direction and the readout time difference in the sub-scanning direction. For example, by setting the charge crosstalk rate at the peak position of the pupil intensity distribution to around 10% for the pixel 205 having the first arrangement and around 8% for the pixel 205 having the second arrangement, the phase difference detection performance in the main scanning direction and sub-scanning direction can be made more suitable as much as possible.

[0061] In order to make the charge crosstalk rates different between the pixels 205 having the first arrangement and the pixels 205 having the second arrangement, the ion implantation process is performed so that, for example, the p-type impurity concentrations in the separation regions 400 and 500 of the PDA 301 and PDB 302 are different. This makes it possible to realize the image sensor 1 of this embodiment. In this embodiment, the impurity concentration in the separation region 400 of the pixels 205 having the first arrangement is made low, and the impurity concentration in the separation region 500 of the pixels having the second arrangement is made high. In other words, the relationship between the impurity concentration in the separation region 400 of the pixels 205 having the first arrangement and the impurity concentration in the separation region 500 of the pixels 205 having the second arrangement is made to be the same as the relationship between the magnitude of the readout time difference.

[0062] Such adjustment of the charge crosstalk rate may be performed by varying the width of the separation region of the photoelectric conversion unit. In this embodiment, the width of the separation region 400 of the pixel 205 having the first arrangement is narrowed, and the width of the separation region 500 of the pixel 205 having the second arrangement is widened. In other words, the relationship between the width of the separation region 400 of the pixel having the first arrangement and the width of the separation region 500 of the pixel 205 having the second arrangement is made to be the same as the relationship between the magnitudes of the readout time difference.

[0063] Furthermore, the charge crosstalk rate between pixels 205 with the first arrangement and pixels 205 with the second arrangement can be adjusted by making the potential gradient for charge collection within the photoelectric conversion unit from the back side of the substrate to the front side different for pixels 205 with the first arrangement and pixels 205 with the second arrangement. In this case, the potential gradient of pixels 205 with the first arrangement is made gentler than the potential gradient of pixels 205 with the second arrangement, that is, the relationship between the magnitudes of these steepnesses is the same as the relationship between the magnitudes of the readout time differences.

[0064] In the example described above, the main scanning direction was the x-direction and the sub-scanning direction was the y-direction. However, if the main scanning direction is the y-direction and the sub-scanning direction is the x-direction, the relationship between the magnitude of the charge crosstalk rate between the pixel 205 with the first arrangement and the pixel 205 with the second arrangement, and the relationship between the magnitude of the readout time difference, will be reversed.

[0065] Furthermore, the impurity concentration and width of the separation region, as well as the electrolytic gradient, may be combined as described above to adjust the charge crosstalk rate in the first direction to be higher than the charge crosstalk rate in the second direction.

[0066] Furthermore, while the above example described adjusting the charge crosstalk rate between pixels 205 having the first arrangement and pixels 205 having the second arrangement during the manufacturing of the image sensor 1, the present invention is not limited to this, and a configuration that allows adjustment after manufacturing is also possible. In that case, for example, electrode sections may be placed in the separation regions 400 and 500 of PDA 301 and PDB 302, and the charge crosstalk rate may be adjusted by controlling the potential of the separation regions 400 and 500. In that case, the potential applied to the separation region 400 of pixels 205 having the first arrangement is made lower than the potential applied to the separation region 500 of pixels 205 having the second arrangement, that is, the magnitude relationship of the potentials is inverse to the magnitude relationship of the width H and height V. Deep Trench Isolation (DTI) connected to the control wiring can be used as the electrode section.

[0067] Furthermore, although the above example was described assuming that all pixels 205 have either the first or second arrangement, the present invention is not limited thereto, and some of the pixels 205 may be discretely arranged as either the first or second arrangement.

[0068] As described above, according to the first embodiment, when performing image plane phase difference focus detection using signals obtained from an image sensor in which pixels are arranged in a matrix, the focus detection performance can be made closer in the main scanning direction and the sub-scanning direction.

[0069] <Second Embodiment> Next, a second embodiment of the present invention will be described. Figure 12 shows the configuration of a pixel 205 having a third arrangement of the image sensor 1 in this embodiment.

[0070] In the third configuration, as shown in Figure 12, the pixel 205 is composed of four photodiodes (PDs) 1101 to 1104. Hereinafter, these will be referred to as PDA1101, PDB1102, PDC1103, and PDD1104. Figure 12(a) is a perspective view of the pixels in this embodiment, and Figure 12(b) is a schematic plan view showing the positional relationship in a plan view as seen from the ML401 side (back side of the substrate). In this embodiment, transfer switches and the like are omitted. Note that the definitions of "plan view" and x, y, and z are the same as in Figure 4, so the explanation is omitted.

[0071] In this embodiment, by defining the first direction as the main scanning direction and the second direction as the sub-scanning direction, it becomes possible to perform phase difference detection in two orthogonal directions using pixels with the same configuration.

[0072] When the main scanning direction is the x-direction and the sub-scanning direction is the y-direction, the x-direction phase difference can be detected using the sum of the signals from PDA1101 and PDC1103 (signal A) and the sum of the signals from PDB1102 and PDD1104 (signal B), and the y-direction phase difference can be detected using the sum of the signals from PDA1101 and PDB1102 (signal C) and the sum of the signals from PDC1103 and PDD1104. In other words, in this embodiment as well, similar to the first embodiment, the third arrangement shown in Figure 12 is used across the entire surface of the image sensor. The pixels 205 are arranged in a two-dimensional array, and when the preferred reading direction is the row direction, the pixels are configured such that the relative magnitudes of the charge crosstalk rates between the photoelectric conversion units responsible for signals A and B and between the photoelectric conversion units responsible for signals C and D are inversely related to the relative magnitudes of the readout time difference. The charge crosstalk rate is adjusted in the same way as in the first embodiment by adjusting the impurity concentration and width of the separation region 1105 and separation region 1106, adjusting the potential gradient within the photoelectric conversion unit, and controlling the potential with electrodes.

[0073] If the primary scanning direction is the y-direction and the secondary scanning direction is the x-direction, simply reverse the combinations of PDA1101 to PDD1104 as described above.

[0074] As described above, according to the second embodiment, even when each pixel has multiple photoelectric conversion units divided in two directions, the same effects as in the first embodiment can be obtained.

[0075] <Summary> This embodiment includes the following configuration.

[0076] (Composition 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 are provided for at least some of the microlenses, each of which is configured to convert light incident through each microlens into photoelectric energy. The system includes a readout means that sequentially reads signals from the plurality of photoelectric conversion units, with the first direction being the main scanning direction and the second direction being the sub-scanning direction. 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 image sensor characterized in that 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.

[0077] (Configuration 2) The image sensor according to configuration 1, characterized in that 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.

[0078] (Composition 3) The image sensor according to configuration 1, characterized in that the plurality of photoelectric conversion units are four photoelectric conversion units arranged in the first direction and the second direction.

[0079] (Composition 4) An image sensor according to any one of configurations 1 to 3, characterized in that the impurity concentration of the separation region separating the plurality of photoelectric conversion units arranged in the first direction is lower than the impurity concentration of the separation region separating the plurality of photoelectric conversion units arranged in the second direction.

[0080] (Composition 5) The image sensor according to any one of configurations 1 to 4, characterized in that the width of the separation region separating the plurality of photoelectric conversion units arranged in the first direction is shorter than the width of the separation region separating the plurality of photoelectric conversion units arranged in the second direction.

[0081] (Composition 6) An image sensor according to 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 into which light is incident to the region where the charge obtained by photoelectric conversion is stored is gentler than the potential gradient in the plurality of photoelectric conversion units arranged in the second direction.

[0082] (Composition 7) The device further includes electrodes that control the potential of the separation region separating the plurality of photoelectric conversion units, An image sensor according to any one of configurations 1 to 6, characterized in that the potential of the separation region separating the plurality of photoelectric conversion units arranged in the first direction is lower than the potential of the separation region separating the plurality of photoelectric conversion units arranged in the second direction.

[0083] (Composition 8) An image sensor according to any one of configurations 1 to 7, characterized in that the charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is approximately 10%, and the charge crosstalk rate in the second direction is approximately 8%.

[0084] (Composition 9) The image sensor according to any one of configurations 1 to 8, further comprising an output means for converting the charge photoelectrically converted by the plurality of photoelectric conversion units into a signal and outputting it.

[0085] (Composition 10) An image sensor as described in any of configurations 1 to 9, Processing means for processing the signal output from the image sensor An imaging device characterized by having the following features.

[0086] (Composition 11) The imaging apparatus according to configuration 10, characterized in that the processing means performs focus detection using an image plane phase difference method based on the signal.

[0087] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0088] 1: Image sensor, 2: Overall control / 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: Isolation region

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; a readout unit that sequentially reads out signals from the plurality of photoelectric conversion units in a main scanning direction, the first direction being a main scanning direction, and in a sub-scanning direction, the second direction being a sub-scanning direction; 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, wherein a charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is higher than a 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. An imaging element according to any one of claims 1 to 3, characterized in that the charge crosstalk rate in the first direction between the plurality of photoelectric conversion units is approximately 10%, and the charge crosstalk rate in the second direction is approximately 8%.

9. 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.

10. The imaging device according to claim 1 , a processing means for processing a signal output from the imaging element; An imaging device comprising:

11. 11. The image pickup apparatus according to claim 10, wherein the processing means performs focus detection using an image plane phase difference method based on the signal.

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