JP5157436B2 - Solid-state imaging device and imaging apparatus - Google Patents

Description

  The present invention relates to a fixed imaging element and an imaging apparatus including the solid-state imaging element.

    In recent years, video cameras and electronic cameras having an AF (autofocus) function have been widely used. In these cameras, CCD type or CMOS type solid-state imaging devices are used. In these solid-state imaging devices, a plurality of pixels having a photoelectric conversion unit that generates a signal charge according to the amount of incident light is two-dimensionally arranged. On the light incident side of the photoelectric conversion unit, a microlens is arranged in an on-chip form. The microlens is provided to collect light incident on the pixel region other than the photoelectric conversion unit on the photoelectric conversion unit and increase the amount of light incident on the photoelectric conversion unit.

  In general, in a single-lens reflex electronic camera, a pupil division phase difference type focus detector is provided separately from such a solid-state imaging device for imaging so as to perform high-speed focus detection. However, since subject light does not enter the image sensor at the time of focus detection, it is not possible to confirm a live view image from a small monitor provided on the back of the camera. Conversely, during live view image display, subject light is not incident on the pupil division phase difference type focus detector. Therefore, focus detection by the focus detector cannot be performed. In such a case, contrast detection (mountain climbing) focus detection using a signal from the solid-state imaging device has been proposed, but this cannot perform focus detection at high speed. For this reason, solid-state imaging devices incorporating focus detection pixels based on the pupil division phase difference method have been proposed (see, for example, Patent Documents 1 and 2).

JP 2003-244712 A JP 2006-261929 A

  However, as described above, when a focus detection pixel based on the pupil division phase difference method is incorporated in a solid-state imaging device for imaging, there is a problem that the focus detection performance deteriorates.

According to the first aspect of the present invention, a plurality of imaging pixels each provided with a first condensing microlens and a plurality of focus detections each provided with a second concentrating microlens and used for focus detection. and use pixel, the two-dimensionally arranged solid imaging element provided between the second microlens and the focus detection pixels, a pair of light beams pupil division in the exit pupil of the optical system, whereas And a light- shielding film having an opening disposed so as to shield the other light beam , and when the optical system is in focus, the condensing position by the second microlens is the first microlens. The first and second microlenses are formed so as to be closer to the microlens and closer to the shielding film than the condensing position.
According to a second aspect of the present invention, in the solid-state imaging device according to the first aspect, the curvature of the lens surface of the second microlens is set larger than the curvature of the lens surface of the first microlens. The condensing position by the microlens is set to be closer to the microlens than the condensing position by the first microlens.
According to a third aspect of the present invention, in the solid-state imaging device according to the second aspect, by setting the lens thickness of the second microlens to be larger than the lens thickness of the first microlens, The curvature of the lens surface is larger than the curvature of the lens surface of the first microlens.
According to a fourth aspect of the present invention, in the solid-state imaging device according to the third aspect, the ratio of the lens thickness of the second microlens to the lens thickness of the first microlens when the lens aperture is the same is 1 .1 or more and less than 1.4.
According to a fifth aspect of the present invention, in the solid-state imaging device according to the second aspect, the lens diameter of the second microlens is set to be smaller than the lens diameter of the first microlens. The curvature of the surface is larger than the curvature of the lens surface of the first microlens.
According to a sixth aspect of the present invention, in the solid-state imaging device according to the fifth aspect, the ratio between the lens diameter of the second microlens and the lens diameter of the first microlens when the lens thickness is the same is set to 0. .95 or more and less than 1.0.
According to a seventh aspect of the present invention, in the solid-state imaging device according to the second aspect of the present invention, the lens planar shape of the second microlens is circular, and the lens planar shape of the first microlens is rectangular. The curvature of the lens surface of No. 2 microlens is made larger than the curvature of the lens surface of the first microlens.
According to an eighth aspect of the present invention, in the solid-state imaging device according to the second aspect, the lens plane shape of the second microlens is a polygon having eight or more angles, and the lens plane shape of the first microlens is the same. The curvature of the lens surface of the second microlens is made larger than the curvature of the lens surface of the first microlens by using a polygon having 7 or less corners.
According to a ninth aspect of the present invention, in the solid-state imaging device according to the first aspect, the refractive index of the lens material of the second microlens is set larger than the refractive index of the lens material of the lens surface of the first microlens. Thus, the condensing position by the second microlens is arranged closer to the microlens side than the condensing position by the first microlens.
According to a tenth aspect of the present invention, in the solid-state imaging device according to the first aspect, when the thickness of the microlens is L1, and the distance between the microlens and the light receiving surface of the pixel provided with the microlens is L2, The ratio L2 / L1 is set to a value different between the first microlens and the second microlens so that the condensing position by the second microlens is closer to the microlens side than the condensing position by the first microlens. It is characterized by setting.
According to an eleventh aspect of the invention, in the solid-state imaging device according to the tenth aspect, the ratio L2 / L1 of the second microlens is set to 3.72 or more and 3.98 or less.
An imaging apparatus according to a twelfth aspect of the invention includes a solid-state imaging element according to any one of claims 1 to 11, an image forming unit that forms image information based on outputs of a plurality of imaging pixels, and a plurality of imaging devices. Focus detection means for performing focus detection by a pupil division phase difference method based on the output of the focus detection pixels is provided.

  According to the present invention, since the condensing position by the second microlens is closer to the microlens side than the condensing position by the first microlens, the performance of focus detection by the pupil division phase difference method is improved. be able to.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an embodiment of an imaging apparatus according to the present invention, and is a block diagram illustrating a schematic configuration of an electronic camera 1. The electronic camera 1 is equipped with a photographic lens 2 as an optical system for imaging a subject. The photographing lens 2 is driven by the lens control unit 2a for focus and diaphragm. In the image space of the photographic lens 2, an imaging surface of a solid-state imaging device 3 that photoelectrically converts a subject image formed by the photographic lens 2 is disposed.

  The solid-state imaging device 3 is driven by a command from the imaging control unit 4 and outputs an electrical signal corresponding to the subject image. The solid-state imaging device 3 outputs an imaging signal for forming an image signal indicating a subject image and a focus detection signal for detecting the focus adjustment state of the photographing lens 2. The description is omitted because it is not related to the present invention, but other signals for exposure control may be output.

  The above-described electrical signals for imaging and focus detection signals are processed by the signal processing unit 5 and the A / D conversion unit 6 and temporarily stored in the memory 7. The memory 7 is connected to the bus 8. The bus 8 is also connected with a lens control unit 2a, an imaging control unit 4, a microprocessor 9, a focus calculation unit 10, a recording unit 11, an image compression unit 12, an image processing unit 13, and the like. An operation unit 9 a such as a release button is connected to the microprocessor 9. A recording medium 11a is detachably attached to the recording unit 11, and the recording unit 11 records data on the recording medium 11a and reproduces data from the recording medium 11a.

  The focus detection signal once stored in the memory 7 is sent to the focus calculation unit 10 via the bus 8. The focus calculation unit 10 calculates the in-focus state based on the focus detection signal, obtains the shift amount of the photographing lens 2, and sends the value to the lens control unit 2a. That is, the focus calculation unit 10 outputs a detection signal indicating the focus adjustment state to the lens control unit 2a. The lens control unit 2a performs focus adjustment by moving the photographing lens 2 to a predetermined position based on the detection signal indicating the focus adjustment state.

  FIG. 2 is a circuit diagram showing a schematic configuration of the solid-state imaging device 3 shown in FIG. The solid-state imaging device 3 includes a plurality of pixels 20 arranged two-dimensionally and a peripheral circuit for outputting a signal from the pixels 20. In FIG. 2, an effective pixel region (imaging region) in which the pixels 20 are two-dimensionally arranged is indicated by reference numeral 31. In general, the pixels 20 are two-dimensionally arranged in a perpendicular direction such as a vertical direction (column direction) and a horizontal direction (row direction). In FIG. 2, for simplification of illustration, the number of pixels 20 in which the pixels 20 are arranged in four rows and four columns vertically is set to 16, but the actual number of pixels of the solid-state imaging device 3 in the present embodiment is It is much more than shown in 2. However, in the present invention, the number of pixels is not particularly limited.

  In the present embodiment, the solid-state imaging device 3 includes an imaging pixel 20A that generates an imaging signal and a focus detection pixel (hereinafter “AF pixel”) that generates a focus detection signal (hereinafter also referred to as “AF signal”). 20B) as the pixel 20. In FIG. 2, they are shown as the pixels 20 without being distinguished. A specific circuit configuration and structure of the pixel 20 will be described later. An imaging signal or a focus detection signal is output in accordance with the drive signals of these pixels 20 and peripheral circuits.

  The peripheral circuit includes a vertical scanning circuit 21, a horizontal scanning circuit 22, driving wirings 23 and 24 connected thereto, a vertical output line 25 that receives an electrical signal from the pixel 20, and a constant current connected to the vertical output line 25. A source 26, a correlated double sampling circuit (CDS circuit) 27, a horizontal output line 28 for receiving a signal output from the CDS circuit 27, an output amplifier 29, and the like.

  The vertical scanning circuit 21 and the horizontal scanning circuit 22 output drive signals to the drive wirings 23 and 24 based on a command from the imaging control unit 4 of the electronic camera 1. Each pixel 20 is driven by receiving a driving signal output from the vertical scanning circuit 21 from a predetermined driving wiring 23, and outputs an imaging signal or a focus detection signal to the vertical output line 25. There are a plurality of drive signals output from the vertical scanning circuit 21, and accordingly, there are a plurality of drive wirings 23. Note that the driving wiring 23 connected to the vertical scanning circuit 21 is accurately connected to the gate electrode of the MOS transistor arranged in the pixel. The signal output from the pixel 20 is subjected to predetermined noise removal by the CDS circuit 27, and is output to the outside via the horizontal output line 28 and the output amplifier 29 by the drive signal of the horizontal scanning circuit 22.

  FIG. 3 is a plan view schematically showing the solid-state imaging device 3 (particularly, its effective pixel region 31) shown in FIG. As shown in FIG. 3, in the solid-state imaging device 3 according to the present embodiment, two focus detection areas 32 and 33 having a cross shape arranged in the center and two focus detection areas 34 and 35 arranged on the left and right sides. And two focus detection areas 36 and 37 arranged above and below are provided in the effective pixel area 31. However, the present invention is not limited to this. The focus detection area may be arranged in another pattern, or the AF pixels may be arranged periodically throughout the effective pixel area 31.

  As shown in FIG. 3, an X axis, a Y axis, and a Z axis that are orthogonal to each other are defined. Of the X-axis directions, the direction of the arrow is referred to as the + X direction or + X side, and the opposite direction is referred to as the −X direction or −X side, and the same applies to the Y-axis direction. A plane parallel to the XY plane coincides with the imaging surface (light receiving surface) of the solid-state imaging device 3. The arrangement in the X-axis direction is called a row, and the arrangement in the Y-axis direction is called a column. Incident light from the photographic lens 2 is incident from the front side to the back side in FIG. These points are the same for the drawings described later.

  FIG. 4 is an enlarged view showing the vicinity of the intersection of the focus detection areas 32 and 33 shown in FIG. 3, and schematically shows the pixel arrangement. The solid-state imaging device 3 includes one type of imaging pixel 20A and four types of AF pixels 20B in which areas for receiving incident light are defined on the right, left, upper, and lower sides, respectively. In the following description, unless otherwise specified, the types of AF pixels are not distinguished.

  Each pixel 20 includes a photoelectric conversion unit 42 and a microlens 41 that guides incident light to the photoelectric conversion unit 42. A light-shielding film 43 having an opening 44 is provided on the photoelectric conversion unit (not shown in FIG. 4) of the AF pixel 20B. Depending on the position of the opening 44, the light is incident on the photoelectric conversion unit. A region where light is guided is defined.

  FIG. 5 is a circuit diagram showing 2 × 2 pixels 20 among many pixels 20 provided in the fixed imaging device 3, and shows a pixel region including a part of the focus detection region 33. is there. That is, FIG. 5 shows a circuit diagram for two AF pixels 20B and two imaging pixels 20A. In the present embodiment, all the pixels 20 (imaging pixel 20A and AF pixel 20B) have the same circuit configuration. Each pixel 20 includes a photoelectric conversion unit (photodiode) 42 that generates and accumulates charges according to incident light, a floating diffusion unit 52 that receives charges, and a pixel that outputs a signal according to the potential of the floating diffusion unit 52. An amplifier transistor 53, a transfer transistor 51 that transfers charges from the photoelectric conversion unit 42 to the floating diffusion unit 52, a reset transistor 55 that resets the voltage of the floating diffusion unit 52, and a selection transistor 54 that selects the pixel 20 are provided. ing.

  Thus, each pixel 20 is provided with a plurality of transistors for generating and outputting an electrical signal corresponding to the electric charge. The circuit configuration of the pixel 20 is general as a circuit configuration of a unit pixel of the CMOS solid-state imaging device.

  In the present embodiment, the transfer transistor 51, the pixel amplifier transistor 53, the reset transistor 55, and the selection transistor 54 are all configured by NMOS transistors. Actually, the floating diffusion portion 52 includes an n-type impurity semiconductor region (hereinafter referred to as FD) provided in a p-type silicon substrate, an internal wiring that electrically connects the FD and the gate electrode of the pixel amplifier transistor 53, And a gate electrode of the pixel amplifier transistor 53.

  2 and 5, the gate electrode of the transfer transistor 51 of each pixel 20 is connected to the driving wiring 23 in common for each pixel row, and the driving signal φTX is transmitted from the vertical scanning circuit 21 through the driving wiring 23. Is supplied. The gate electrode of the selection transistor 54 of each pixel 20 is connected to the driving wiring 23 in common for each pixel row, and a driving signal φSEL is supplied from the vertical scanning circuit 21 through the driving wiring 23. The gate electrode of the reset transistor 55 of each pixel 20 is connected to the driving wiring 23 in common for each pixel row, and the driving signal φRES is supplied from the vertical scanning circuit 21 through the driving wiring 23. The drive wirings 23 connected to the vertical scanning circuit 21 are provided so as to be parallel to each other in the row direction (X direction).

  FIG. 6 is a timing chart for explaining the operation of the solid-state imaging device 3. Here, a case where an imaging signal and a focus detection signal are output for each row is shown. However, for example, an AF signal may be selectively output from AF pixels in the focus detection area.

  Before reaching the time point t1 in FIG. 6, the drive signal φRES is set to the high level, and the reset transistor 55 is turned on. As a result, the floating diffusion unit 52 is reset to the reference level. At time t1, the drive signal φRES is set to a low level. As a result, the reset transistor 55 is turned off, but the reset level of the floating diffusion 52 is maintained off. At time t1, the drive signal φSEL of the selected row (first row in FIG. 6) is set to the high level, and the selection transistor 54 is turned on. Thereby, each pixel in the selected row is connected to the corresponding vertical output line 25, and a level (dark level) corresponding to the reference level of the floating diffusion portion 52 is supplied from the pixel amplifier transistor 53 via the vertical signal line 25 to the CDS circuit. 27 is accumulated.

  Next, the drive signal φTX is set to the high level at time t2, and the drive signal φTX is set to the low level again at time t3. As a result, the charge accumulated in the photoelectric conversion unit 42 is transferred to the floating diffusion unit 52, and the signal and the signal on which the reference level is superimposed are transmitted from the pixel amplifier transistor 53 to the CDS circuit 27 via the vertical output line 25. Accumulated. Then, the CDS circuit 27 outputs an image signal and a focus detection signal obtained by taking the difference between this signal and the previous dark level.

  At time t4, the drive signal φSEL is set to the low level, and the selection transistor 54 is turned off. Thereby, the connection between each pixel 20 of the selected row and the corresponding vertical output line 25 is cut off. Thereafter, the next row (second row) is selected, and a signal is similarly output. The read image signal or AF signal is temporarily stored in the memory 7 after predetermined processing is performed. When performing the focus detection process, the AF signal is extracted from the memory 7 and a predetermined process is performed. On the other hand, in the case of imaging, an image signal is taken out from the memory 7 and predetermined processing is performed.

  7A and 7B are diagrams schematically showing the main part of the imaging pixel 20A, where FIG. 7A is a plan view, FIG. 7B is a sectional view taken along line X1-X1 in FIG. 7A, and FIG. It is X2 sectional drawing. The imaging pixel 20 </ b> A includes a photoelectric conversion unit 42 and a microlens 41 formed on the photoelectric conversion unit 42 on-chip. Actually, various layers including a color filter are formed between the microlens 41 and the photoelectric conversion unit 42, but the illustration is omitted in FIG.

  As shown in FIG. 7, the microlens 41 has a rectangular planar shape, and the curvature of the lens curved surface S2 in the X2-X2 cross section is the curvature of the lens curved surface S1 in the X1-X1 cross section that is a diagonal cross section. Is smaller than In the case of the imaging pixel 20A, the condensing position P1 by the microlens 41 is on the light receiving surface or in the vicinity of the substrate 45 side from the light receiving surface. The center of the photoelectric conversion unit 42 and the center of the microlens 41 coincide with each other, and the photoelectric conversion unit 42 of the imaging pixel 20A is from an exit pupil region that is not substantially eccentric from the center of the exit pupil of the photographing lens 2. The light beam is received and photoelectrically converted.

  FIG. 8 is a diagram schematically showing the main part of the AF pixel 20B, where (a) is a plan view and (b) is an X3-X3 sectional view of (a). FIG. 8 shows a pixel that receives incident light on the left side of the optical axis among the AF pixels 20B arranged in the focus detection region 32 of FIG. 4, and is the same as or corresponds to the element shown in FIG. Elements are denoted by the same reference numerals, and different elements will be mainly described here.

  In the AF pixel 20 </ b> B, a light shielding film 43 is disposed between the microlens 41 and the photoelectric conversion unit 42, and the light divided by the light shielding film 43 enters the photoelectric conversion unit 42. Further, the planar shape of the microlens 41 is circular as shown in FIG. 8A, and the lens aperture is set smaller than the microlens 41 whose planar shape is rectangular as shown in FIG. Therefore, when the height (thickness) of the microlens 41 is set to be the same as that of the microlens 41 of the imaging pixel 20A shown in FIG. 7, the curvature of the lens curved surface S3 is each of the curved surfaces S1 and S2 shown in FIG. It becomes larger than the curvature. As a result, the condensing position P2 of the microlens 41 of the AF pixel 20B is closer to the microlens side than the condensing position P1 of the microlens 41 of the imaging pixel 20A. In the present embodiment, the condensing position P2 is set to be substantially the same as the position of the light shielding film 43.

  The light shielding film 43 is disposed on the side where the light of the AF pixel 20B is incident, and defines a region where the incident light is incident on the photoelectric conversion unit 42. Specifically, an opening 44 is formed in the light shielding film 43, and the opening 44 defines a region where incident light is incident on the photoelectric conversion unit 42. The opening 44 is provided on the −X side with respect to the optical axis O of the microlens 41. Therefore, the photoelectric conversion unit 42 selectively receives and photoelectrically converts the light beam from the exit pupil region that is substantially decentered to the + X side from the center of the exit pupil of the photographing lens 2.

  In the prior art, since the microlens provided in the AF pixel 20B and the microlens provided in the imaging pixel 20A have the same shape, the condensing position P2 of the AF pixel 20B and the condensing of the imaging pixel 20A. It was the same position as the position P1. Therefore, in the prior art, light decentered in the opposite direction is also incident on the AF pixel 20B. However, in the solid-state imaging device 3 of the present embodiment, this reverse component is reduced (details will be described later).

  Similarly, among the AF pixels 20B shown in FIG. 4, the aperture 44 provided on the right side (+ X side) of the optical axis is from the exit pupil region decentered from the exit pupil center to the −X side. A light beam is selectively received, and an aperture 44 provided on the upper side (+ Y side) of the optical axis selectively receives a light beam from an exit pupil region decentered from the exit pupil center to the −Y side. In the case where the opening 44 is provided on the lower side (−Y side) of the optical axis, the light beam from the exit pupil region decentered to the + Y side from the exit pupil center is selectively received.

  In the focus calculation unit 10 that performs pupil division phase difference type focus detection, the AF signals of the plurality of AF pixels 20B that receive the light flux from the exit pupil region eccentric to the + X side and the exit pupil region eccentric to the -X side The correlation calculation is performed based on the AF signals of the plurality of AF pixels 20B that receive the light flux from the lens to calculate the defocus amount. In addition, AF signals of a plurality of AF pixels 20B that receive a light beam from an exit pupil region eccentric to the + Y side and AFs of a plurality of AF pixels 20B that receive a light beam from an exit pupil region eccentric to the -Y side The focus calculation based on the signal is performed in the same manner.

  In order to perform focus detection with high accuracy in such pupil division phase difference focus detection, it is important to clearly separate and detect the light flux from the exit pupil region at a symmetrical position with respect to the optical axis. On the other hand, in order to improve the imaging performance of the imaging pixel 20A, it is required to set the condensing position of the microlens 41 near the light receiving surface or its substrate side. However, this is not considered in the conventional solid-state imaging device, and both the imaging pixel 20A and the AF pixel 20B are provided with the same-shaped microlens 41 suitable for imaging. It was.

  On the other hand, in the solid-state imaging device 3 of the present embodiment, in order to satisfy the above two conditions, the condensing position of the microlens 41 is different between the imaging pixel 20A and the AF imaging device 20B. That is, in the case of the imaging pixel 20B, the condensing position P1 is set near the light receiving surface suitable for imaging (specifically, near the substrate side), and in the case of the AF pixel 20B, pupil division is performed. The condensing position P2 was set to the position of the light shielding film 43 on the microlens side of the light receiving surface so that it can be accurately performed.

  FIG. 9 is a diagram for explaining a received light beam in the AF pixel 20B. In FIG. 9, a hatched light beam indicates a light beam incident on the light receiving surface, and a non-hatched light beam indicates a light beam that does not reach the light receiving surface. The light beam on the right side of the alternate long and short dash line indicates the light beam from the exit pupil region decentered from the center of the exit pupil to the right side (+ X side). The light flux from the exit pupil region is shown. The light beam from the left exit pupil region is shielded by the shielding film 43, and only the light beam from the right exit pupil region is incident on the photoelectric conversion unit 42. Therefore, it is possible to accurately detect the focus of the pupil division phase difference method.

  FIG. 10 is a diagram showing a conventional AF pixel 20B. Conventionally, an AF pixel is provided by providing a light shielding film 43 on a pixel having the same configuration as that of the imaging pixel 20A described above. In the case of the imaging pixel 20A, the light collection position P1 is in the vicinity of the substrate side of the light receiving surface, and thus the imaging characteristics are excellent. However, in the case where the shielding film 43 is provided as shown in FIG. 10 and used for AF, since the condensing position P1 is in the vicinity of the light receiving surface, the light flux from the left exit pupil region also passes through the opening 44 and becomes a photoelectric conversion unit. 42 is incident. In addition, there is a light beam that is shielded by the shielding film 43 while being from the right exit pupil region. Therefore, the conventional case has a problem that the performance of the phase difference AF is lowered.

  However, in the solid-state imaging device 3 of the present embodiment, the condensing position of the microlens 41 is changed so as to be optimal in each of the imaging pixel 20A and the AF imaging device 20B. Both can be achieved.

  In the above-described embodiment, the planar shape of the microlens 41 of the imaging pixel 20A is the same rectangle as the pixel shape, and the microlens shape of the AF pixel 20B is a round shape. However, the shape is not limited to these shapes. That is, when the lens thickness is the same, by increasing the area of the lens planar shape, the condensing position P2 in the AF pixel 20B is smaller than the condensing position P1 in the imaging pixel 20A. Can be set on the lens side. For example, the planar shape of the macro lens 41 of the AF pixel 20B is set to be an octagon or more so as to be nearly circular, and the planar shape of the macro lens 41 of the imaging pixel 20A is smaller than the octagon. You may make it set to a polygon.

  As a general method for forming the on-chip microlens 41, a reflow method (see, for example, Japanese Patent No. 2604890) or an etch back method (see, for example, Japanese Patent No. 2776810) is known. . For example, in the case of the reflow method, a microlens 41 having a convex curvature as shown in FIG. 7 is formed by heating and thermally deforming a microlens material (thermally deformable resin) patterned in a rectangular shape. be able to. If the patterning shape is a regular hexagon instead of a rectangle, the microlens 41 having a regular hexagonal planar shape can be obtained.

  On the other hand, in the case of the AF pixel 20A shown in FIG. 8, a circular microlens 41 is obtained by patterning the microlens material into a circular shape and performing reflow. In addition, since the microlens 41 is formed by thermally deforming the microlens material, the rectangular microlens 41 does not have a strictly rectangular shape but has a rounded corner portion. That is, when the planar shape of the microlens 41 is referred to as a rectangular shape, the round shape and the chamfered corner portion are included in the rectangular shape. The same applies to other polygons.

  In the above-described embodiment, different condensing positions P1 and P2 are obtained by changing the lens planar shape, but the method of changing the condensing position is not limited to such a form. For example, the condensing position is changed by changing the lens thickness by setting the lens planar shape to the same shape and the same size. The lens plane shape and the lens thickness are the same shape (for example, a circle), but the condensing position is changed by changing the aperture. Instead of changing the lens shape, the condensing position may be changed by using microlens materials having different refractive indexes. Further, examples of microlens materials having different refractive indexes include phenol-based positive resists having naphthoquinone diazide as a photosensitive group (in the case of the reflow method), silicon oxide and silicon nitride (in the case of the etch back method).

  FIG. 11 shows a list of the above-described methods for changing the condensing position. When the lens planar shape is the same, the condensing position P2 of the AF pixel 20B can be moved to the microlens side by increasing the lens thickness. When the lens thickness is constant, the lens aperture is made smaller, and when changing the refractive index of the lens material, the refractive index is made larger, so that the condensing position P of the AF pixel 20B is reduced to micro. It can be moved to the lens side.

  The pupil division is performed by the opening 44 of the light shielding film 43. In this case, a desirable condensing position is the position P2 of the light shielding film 43 as described above. And as the condensing position is shifted from the position P2, the performance of the signal output from the photoelectric conversion unit 42 as the phase difference AF signal decreases. FIG. 12 shows optical simulation results of performance as a phase difference AF signal (herein referred to as a phase difference AF signal effective coefficient) for three types of microlenses (ML) 41. The microlenses 41 were all circular (described as round in FIG. 12).

  The phase difference AF signal effective coefficient is, for example, only the light flux from the exit pupil region decentered to the right (+ X side) from the exit pupil center shown in FIG. 9, and the opening 44 has the optical axis as shown in FIG. The AF pixel 20B that detects the right light flux that is shifted to the left side and the AF pixel 20B that detects the left light beam that is shifted to the right side of the optical axis by entering the AF pixel 20B (see FIG. 4). This is an amount obtained by obtaining the intensity ratio of the detection signal. That is, the phase difference AF signal effective coefficient is an amount proportional to (output of the right beam detection pixel 20B) / (output of the left beam detection pixel 20B). As the phase difference AF signal effective coefficient is larger, the performance of the phase difference AF is improved.

  Consider the case where the value of (output of the right beam detection pixel 20B) / (output of the left beam detection pixel 20B) is the same as that of the imaging pixel 20A as shown in FIG. As described above, the hatched light beam reaches the light receiving surface, and the non-hatched light beam is shielded by the shielding film 43 and does not enter the light receiving surface. In this case, a part of the right side light beam to be detected is shielded by the shielding film 43 with respect to the right side light beam detection pixel 20B. Therefore, the numerator portion of the phase difference AF signal effective coefficient is reduced, and the phase difference AF signal is effective. It works to reduce the coefficient. Further, as can be seen from FIG. 10, a light beam (left beam) from the opposite pupil region that should not be incident is incident. This means that the right light beam enters the left light beam detection pixel 20B described above. Therefore, the denominator of the phase difference AF signal effective coefficient is increased, and in this case, the phase difference AF signal effective coefficient is also reduced. As a result, when the condensing position is the same as that of the imaging pixel 20A as shown in FIG. 10, the phase difference AF signal effective coefficient becomes small.

  In the optical simulation result shown in FIG. 12, in the microlens (ML) structure suitable for imaging shown in FIG. 10, the phase difference AF signal effective coefficient is as small as 4.3. On the other hand, if the aperture diameter of the microlens 41 is reduced by 10% without changing the lens thickness, the curvature of the lens surface increases, and the focusing position moves from P1 to the microlens side in FIG. The coefficient is improved to 10.9. Further, when the lens thickness (indicated as height in FIG. 12) is increased by 10% without changing the aperture diameter of the microlens, the phase difference AF signal effective coefficient becomes 9.7, and in this case also, the structure shown in FIG. Compared to the above, the performance of the phase difference AF is improved.

  FIG. 13 shows the relationship between the diameter ratio of the microlens 41 and the phase difference AF signal effective coefficient ratio. The value of the ratio is a value when compared with the case of the imaging pixel. When the ML diameter ratio is 0.95 or more and less than 1.0, the phase difference AF signal effective coefficient ratio is larger than 1.0, and the AF performance is improved as compared with the conventional case. FIG. 14 shows the relationship between the lens thickness ratio of the microlens 41 and the phase difference AF signal effective coefficient ratio. When the ML thickness ratio is set to 1.10 or more and less than 1.40, the phase difference AF signal effective coefficient ratio is 2 or more, and the AF performance is greatly improved as compared with the case where the diameter of the microlens 41 in FIG. 13 is changed. This is suitable for the microlens 41 of the AF pixel 20B.

  In addition to changing the aperture or lens thickness of the microlens 41, a lens material having a higher refractive index is used for the microlens 41 of the AF pixel 20B, so that the focusing position can be moved more effectively. be able to. Furthermore, it goes without saying that these may be combined.

  In the above-described embodiment, the condensing position of the AF pixel 20B is moved to the microlens side by changing the aperture, lens thickness, and refractive index of the microlens 41. However, even if the shape and material of the microlens 41 are not changed in this way, the condensing position is also moved by changing the distance L2 between the lower end of the microlens 41 and the light receiving surface of the photoelectric conversion unit 42 shown in FIG. be able to. As described above, since the condensing position varies depending on the lens thickness L1, it is possible to expect L2 / L1 that provides the microlens 41 suitable for the AF pixel 20B with respect to various values of L2 / L1.

  FIG. 16 shows a simulation result on the L2 / L1 dependence of the phase difference AF signal effective coefficient ratio. Note that the phase difference AF signal effective coefficient ratio in FIG. 16 is the phase difference AF signal effective coefficient of the microlens 41 that can obtain appropriate autofocus performance, for example, a micro that gives the phase difference AF signal effective coefficient ratio = 2 in FIG. This is calculated using the phase difference AF signal effective coefficient of the lens 41 as a reference. The simulation was performed on a lens (circular lens) having the same shape as that used for the imaging pixel 20A.

  In the calculation result shown in FIG. 16, when L2 / L1 is 3.72 or more and 3.98 or less, the phase difference AF signal effective coefficient ratio is 1 or more, and appropriate autofocus performance is obtained. That is, when the shape of the microlens 41 is the same as that of the microlens of the imaging pixel 20A, L2 / L1 may be set to be 3.72 or more and 3.98 or less. FIG. 16 shows a simulation result for a microlens having a predetermined lens shape. Even when other lens shapes are used, the same L2 / L1 dependency is obtained, and a substantially similar phase difference AF signal effective coefficient ratio is obtained. . In order to increase the AF sensitivity, it is preferable that the diameter of the microlens 41 is large, and it is preferable to arrange the microlens 41 so as to be close to the pixel size.

  As described above, in the present embodiment, for the imaging pixel 20A, the condensing position P1 of the microlens 41 is set in the vicinity of the light receiving surface as in the conventional case, and for the AF pixel 20B, the microlens 41 of the microlens 41 is set. The condensing position P2 is set closer to the microlens side by changing the planar shape and lens thickness. As a result, AF performance can be improved, and both imaging performance and AF performance can be achieved.

  In the above-described embodiment, as shown in FIG. 4, the pixels 20 </ b> B with the openings 44 on the left side and the pixels 20 </ b> B with the openings 44 to be paired with the pixels are alternately arranged in the X direction. The solid-state imaging device 3 has been described as an example. However, the present invention is not limited to such a configuration, and can be similarly applied to a configuration in which a pair of openings 44A and 44B having different pupil regions are provided in the same pixel 20B as shown in FIG. The present invention can be applied not only to an electronic camera but also to an imaging apparatus such as a video camera, that is, to an imaging apparatus that detects focus and detects a focus. In addition, the above description is an example to the last, and this invention is not limited to the said embodiment at all unless the characteristic of this invention is impaired.

1 is a diagram illustrating an embodiment of an imaging apparatus according to the present invention, and is a block diagram illustrating a schematic configuration of an electronic camera 1. 2 is a circuit diagram illustrating a schematic configuration of a solid-state imaging element 3; FIG. 2 is a plan view schematically showing a solid-state imaging element 3. FIG. It is a figure which expands and shows the intersection vicinity of the focus detection area | regions 32 and 33, and shows pixel arrangement typically. 3 is a circuit diagram showing 2 × 2 pixels 20 among a large number of pixels 20 provided in the fixed imaging element 3. FIG. 3 is a timing chart for explaining the operation of the solid-state image sensor 3. It is a figure which shows typically the principal part of 20 A of imaging pixels, (a) is a top view, (b) is X1-X1 sectional drawing, (c) is X2-X2 sectional drawing. It is a figure which shows typically the principal part of AF pixel 20B, (a) is a top view, (b) is X3-X3 sectional drawing. It is a figure explaining the received light beam in AF pixel 20B. It is a figure which shows the light received light beam in the case of AF pixel 20B of the conventional structure. It is the figure which showed and listed various methods to which a condensing position differs. It is a figure which shows the optical simulation result of the phase difference AF signal effective coefficient regarding three types of microlenses (ML) 41. It is a figure which shows the relationship between the diameter ratio of the micro lens 41, and a phase difference AF signal effective coefficient ratio. It is a figure which shows the relationship between ratio of the lens thickness of the micro lens 41, and phase difference AF signal effective coefficient ratio. It is a top view which shows a part of solid-state image sensor 3 at the time of providing a pair of opening part 44A, 44B from which a pupil area | region differs in the same pixel 20B. It is a figure which shows L2 / L1 dependence of phase difference AF signal effective coefficient ratio.

Explanation of symbols

  1: electronic camera, 2: photographing lens, 3: solid-state imaging device, 10: focus calculation unit, 13: image processing unit, 20: pixel, 20A: imaging pixel, 20B: AF pixel, 32-37: focus detection Area, 41: microlens, 42: photoelectric conversion part, 43: light shielding film, 44, 44A, 44B: opening, 45: substrate, P1, P2: condensing position, S1 to S3: lens curved surface,

Claims (12)

A plurality of imaging pixels each provided with a first condensing microlens and a plurality of focus detection pixels each provided with a second condensing microlens and used for focus detection are two-dimensional In a solid-state imaging device arranged in an
Among the pair of light beams that are provided between the second microlens and the focus detection pixel and are pupil-divided at the exit pupil of the optical system , one light beam is allowed to pass and the other light beam is shielded. Comprising a shielding film having an opening disposed in
When the optical system is in a focused state, the condensing position by the second microlens is closer to the microlens side than the condensing position by the first microlens and in the vicinity of the shielding film. A solid-state imaging device, wherein first and second microlenses are formed. The solid-state imaging device according to claim 1,
By setting the curvature of the lens surface of the second microlens to be larger than the curvature of the lens surface of the first microlens, the condensing position by the second microlens is collected by the first microlens. A solid-state imaging device characterized in that it is located closer to the microlens than the light position. The solid-state imaging device according to claim 2,
By setting the lens thickness of the second microlens to be larger than the lens thickness of the first microlens, the curvature of the lens surface of the second microlens is set to the lens surface of the first microlens. A solid-state imaging device characterized by being larger than a curvature. The solid-state imaging device according to claim 3,
Solid-state imaging characterized in that the ratio of the lens thickness of the second microlens and the lens thickness of the first microlens when the lens aperture is the same is set to 1.1 or more and less than 1.4 element. The solid-state imaging device according to claim 2,
By setting the lens diameter of the second microlens to be smaller than the lens diameter of the first microlens, the curvature of the lens surface of the second microlens is set to the curvature of the lens surface of the first microlens. A solid-state imaging device characterized by being larger than the above. The solid-state imaging device according to claim 5,
The ratio of the lens aperture of the second microlens to the lens aperture of the first microlens when the lens thickness is the same is set to 0.95 or more and less than 1.0. Image sensor. The solid-state imaging device according to claim 2,
The lens plane shape of the second microlens is circular, and the lens plane shape of the first microlens is rectangular, so that the curvature of the lens surface of the second microlens is the first microlens. A solid-state imaging device characterized by being larger than the curvature of the lens surface of the lens. The solid-state imaging device according to claim 2,
The second microlens lens planar shape is a polygon having an angle of 8 or more, and the first microlens lens planar shape is a polygon having an angle of 7 or less. A solid-state imaging device, wherein the curvature of the lens surface of the microlens is larger than the curvature of the lens surface of the first microlens. The solid-state imaging device according to claim 1,
By setting the refractive index of the lens material of the second microlens to be larger than the refractive index of the lens material of the lens surface of the first microlens, the condensing position by the second microlens is set to the first microlens. A solid-state imaging device characterized in that it is located closer to the microlens side than the condensing position by the microlens. The solid-state imaging device according to claim 1,
When the thickness of the microlens is L1, and the distance between the microlens and the light receiving surface of the pixel provided with the microlens is L2,
The ratio L2 / L1 is set so that the condensing position by the second microlens is closer to the microlens side than the condensing position by the first microlens. The solid-state imaging device is characterized in that it is set to a different value. The solid-state imaging device according to claim 10,
A solid-state imaging device, wherein the ratio L2 / L1 of the second microlens is set to 3.72 or more and 3.98 or less. A solid-state imaging device according to any one of claims 1 to 11,
Image forming means for forming image information based on outputs of the plurality of imaging pixels;
An imaging apparatus comprising: a focus detection unit that performs pupil division phase difference type focus detection based on outputs of the plurality of focus detection pixels.

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