JP2019204932A - Solid-state imaging device - Google Patents

Abstract

To provide a solid-state imaging device capable of suppressing sensitivity unevenness and improving light receiving sensitivity for each pixel.SOLUTION: In a solid-state imaging device 10 in which a plurality of pixels each of which includes a semiconductor substrate 16, a photoelectric conversion element 17 formed inside the semiconductor substrate 16, a color filter 13 formed on the photoelectric conversion element 17, and a convex microlens 12 disposed above the color filter 13 in correspondence with the photoelectric conversion element 17 are two-dimensionally arranged, a microlens 12 disposed in a region other than the central portion of the solid-state imaging device 10 has a flat surface 120 formed at the top.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a solid-state imaging device, and more particularly to a microlens formed on an upper portion of a solid-state imaging device.

  In recent years, digital still cameras, digital camcorders, and the like have become mainstream using a solid-state imaging device for photographing a subject. As main solid-state imaging devices, there are a CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and the like, and in particular, CMOS image sensors have made remarkable progress by incorporating miniaturization technology.

  In general, a solid-state imaging device has a configuration in which a plurality of photoelectric conversion elements that receive an optical image from a photographing object and convert incident light into an electrical signal are arranged in a lattice pattern. As the number of photoelectric conversion elements (number of pixels) increases, the captured image becomes finer. Therefore, a method for manufacturing a solid-state imaging device having a large number of pixels at low cost has been studied.

  Further, by forming a color filter that transmits light of a specific wavelength in the path of incident light in each pixel, it is possible to obtain color information of the object. In general, color-separated image information can be obtained by forming a color filter of a specific color corresponding to one pixel and regularly arranging a plurality of color filters. As the color of the color filter, three primary colors composed of three colors of red (R), green (G), and blue (B), cyan (C), magenta (M), and yellow (Y) are used. Complementary color systems are generally used, and in particular, the three primary color systems are often used.

  In recent solid-state imaging devices in which pixels are reduced in area and highly integrated, the amount of light that can be taken into the photoelectric conversion elements decreases, and the effective sensitivity decreases. In order to prevent such a decrease in sensitivity of a miniaturized solid-state imaging device, a technology for forming a microlens with a uniform shape for each pixel that collects light incident from an object and guides it to a photoelectric conversion element Has been proposed (see Patent Document 1). By condensing the light with the microlens and guiding it to the photoelectric conversion element, the apparent aperture ratio can be increased, and the sensitivity of the solid-state imaging device can be improved.

  By the way, the light collection efficiency of the microlens decreases depending on the incident angle of light. In other words, light that is incident on the pixel perpendicularly is condensed on the light receiving portion with high efficiency, but light that is incident obliquely is directed away from the photoelectric conversion element (light receiving portion), so that photoelectric conversion is performed with high efficiency. It cannot concentrate on the element. In a normal solid-state imaging device, the incident angle of light is different between the central portion and the peripheral portion of the pixel region, and light incident on the central portion of the pixel region is incident on the pixel perpendicularly, but in the peripheral portion of the pixel region, Since the light is incident obliquely on the pixels, there is a problem that the light collection efficiency of the peripheral pixels is lowered and sensitivity unevenness occurs.

As means for solving such a problem, there are solid-state imaging devices described in Patent Documents 2 and 3. In these methods, by shifting the central axis of the microlens from the central axis of the pixel toward the center of the imaging region (pixel region) in the peripheral portion of the imaging region (pixel region), High sensitivity of the solid-state imaging device is realized by preventing a decrease in light collection efficiency.

  In addition to the above, there is a solid-state imaging device described in Patent Document 4. In this method, the light collecting efficiency to the photoelectric conversion element can be increased by flattening the top part of the microlens and refracting light incident obliquely on the flat part.

Japanese Patent Laid-Open No. 3-152972 Patent No. 2600250 Japanese Patent Laid-Open No. 10-229180 Japanese Patent No. 3399495

  However, as a result of intensive studies by the present inventors, it has been found that the structure described in Patent Document 4 has a problem that the condensing efficiency of vertically incident light becomes conspicuous as the pixel size becomes finer. In the manufacturing method described in Patent Document 4, a microlens having a flat surface is formed at the top of all the microlenses in the solid-state imaging device. Therefore, in a solid-state imaging device with a fine pixel size, the light incident angle is It is considered that the light collection efficiency at the center of the vertical imaging region is reduced, and the sensitivity of the entire imaging region is significantly reduced.

  In view of the above problems, an object of the present invention is to provide a solid-state imaging device capable of suppressing sensitivity unevenness and achieving improvement in sensitivity even in a solid-state imaging device having a fine pixel size. .

  In order to achieve the above object, a solid-state imaging device according to an aspect of the present invention includes a semiconductor substrate, a photoelectric conversion element formed inside the semiconductor substrate, a color filter formed on the photoelectric conversion element, A solid-state imaging device in which a plurality of pixels configured by a convex microlens arranged on the color filter in correspondence with a photoelectric conversion element are two-dimensionally arranged, and the solid-state imaging device The microlens arranged in a region other than the central portion is characterized in that a flat surface is formed at the top.

  According to the present invention, it is possible to manufacture a solid-state imaging device capable of improving sensitivity in the peripheral portion of the pixel region and suppressing sensitivity unevenness.

It is a top view which shows typically the solid-state imaging device of embodiment of this invention. It is sectional drawing of the solid-state imaging device along the dotted line X-X 'of FIG. In the solid-state imaging device according to the embodiment of the present invention, when the incident light is inclined, it is a schematic cross-sectional view showing the difference in the light propagation path due to the difference in the shape of the top of the microlens. 1 is a diagram schematically illustrating a solid-state imaging device according to a first embodiment of the present invention. It is a figure which shows schematically the solid-state imaging device of Example 2 of this invention.

  Hereinafter, a solid-state imaging device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a top view of the solid-state imaging device according to the present embodiment.

  As shown in FIG. 1, the solid-state imaging device 10 according to the present embodiment has a plurality of pixels 11 arranged in a lattice pattern in a two-dimensional plane. In FIG. 1, for easy understanding, a part of the arrangement of the pixels 11 in the pixel region of the solid-state imaging device 10 is illustrated, and the others are not illustrated by dotted lines.

FIG. 2 is a cross-sectional view of the solid-state imaging device 10 taken along the dotted line X-X ′ shown in FIG. 1.

  As shown in FIG. 2, in the solid-state imaging device 10, a plurality of photoelectric conversion elements 17 having an action of converting incident light into electric charges are formed inside the semiconductor substrate 16. The photoelectric conversion element 17 is provided for each pixel 11 illustrated in FIG. The photoelectric conversion element 17 is two-dimensionally arranged in the semiconductor substrate 16 so that the central axis thereof coincides with the central axis of each pixel 11. The semiconductor substrate 16 is made of, for example, silicon. The photoelectric conversion element 17 is formed by adding an element such as phosphorus to the semiconductor substrate 16, for example.

  As shown in FIG. 2, the planarization layer 14 and the light shielding wall 15 are formed on the semiconductor substrate 16, that is, on the photoelectric conversion element 17. The planarization layer 14 is formed of, for example, a silicon oxide film. Further, the light shielding wall 15 is formed of a metal such as aluminum, for example. The light shielding wall 15 is formed as necessary to prevent color mixture between pixels.

  A color filter 13 is formed on the planarization layer 14. The color filter 13 is made of, for example, a photosensitive organic material including a pigment or a dye that selectively transmits wavelengths corresponding to green, blue, and red. In the solid-state imaging device 10, the color filter 13 is arranged according to the Bayer array.

  A convex microlens 12 is formed on the color filter 13 so as to correspond to the photoelectric conversion element 17 inside the semiconductor substrate 16. The microlens 12 is made of, for example, a transparent resin having a photosensitivity with a refractive index of about 1.4 to 1.8.

  As shown in FIG. 2, the microlens 12A has a substantially hemispherical shape, and is arranged at a position corresponding to the pixel 11 located at the center of the solid-state imaging device 10 shown in FIG. As shown in FIG. 2, the microlenses 12B and 12C have a flat surface 120 formed at the top, and are arranged at positions corresponding to the pixels 11 located in the periphery of the solid-state imaging device 10 shown in FIG. ing. As described above, the microlenses 12 (microlenses 12A, 12B, and 12C) having different shapes are arranged in the pixel region of the solid-state imaging device 10. Here, it is desirable that the peripheral portion of the solid-state imaging device 10 is a region where the incident angle of the principal ray is 20 degrees or more with reference to the central portion of the solid-state imaging device 10. In addition, in the micro lenses 12B and 12C, the shape other than the top flat surface 120 is desirably the same structure as the micro lens 12A.

  In the solid-state imaging device 10 according to the present embodiment, the area of the flat surface 120 formed on the microlenses 12B and 12C is preferably 10% to 80% of the area of the bottom of the microlens. This is because in this range, the light receiving sensitivity of obliquely incident light is improved as compared with the case where the microlens 12 has a substantially hemispherical shape.

  The microlens 12 can be manufactured by a photolithography method using a density distribution mask. The density distribution mask is a photomask that can control the transmitted light amount distribution during exposure by appropriately designing the density gradation of the light shielding portion. The density distribution mask has a configuration in which a density gradation pattern is formed on a substrate such as quartz or glass having good transparency with respect to exposure light. The density gradation pattern can be obtained by gradually changing the film thickness of a light-shielding metal film or the like to provide a density gradient in the region, or by dot (halftone dot) arrangement or line-and-space (line / gap is repeated). The pattern is formed by a gray scale type method or the like in which the average light shielding density of each pattern region is inclined by changing the fine pattern arrangement of the light shielding film.

  Next, the reason why the solid-state imaging device 10 according to the present embodiment employs a structure including microlenses having different shapes will be described.

  FIG. 3 is a diagram schematically illustrating the difference in the light propagation path due to the difference in the shape of the top of the microlens 12 when the light is incident on the solid-state imaging device 10 obliquely. 3A shows a light propagation path of a microlens 12 having a substantially hemispherical top (for example, the microlens 12A shown in FIG. 2), and FIG. 3B shows a flat surface 120 formed on the top. The light propagation path of the microlens 12 (for example, the microlenses 12B and 12C shown in FIG. 2) is shown.

  As shown in FIG. 3A, when the top of the microlens 12 has a substantially hemispherical shape, the obliquely incident light on the top of the microlens 12 is hardly refracted, and a certain proportion of the obliquely incident light has a certain ratio. The light is reflected by the light shielding wall 15 or is directed to an adjacent pixel. For this reason, the amount of light reaching the photoelectric conversion element 17 is reduced in the pixel 11 where the oblique incident light is incident.

  On the other hand, as shown in FIG. 3B, when the flat surface 120 is formed on the top of the microlens 12, the oblique incident light on the top of the microlens 12 is refracted. As a result, the ratio of the oblique incident light reflected by the light shielding wall 15 and the ratio toward the adjacent pixels decreases. For this reason, the rate at which the obliquely incident light reaches the photoelectric conversion element 17 in the incident pixels, that is, the amount of light reaching the photoelectric conversion element 17 increases. Therefore, as a result, when the flat surface 120 is formed on the top of the microlens 12 as shown in FIG. 3B, the top of the microlens 12 is substantially hemispherical as shown in FIG. The sensitivity of light incident obliquely is increased as compared with the case where the light is incident.

In order to further increase the sensitivity to obliquely incident light, in this embodiment, the microlens 12 (the microlenses 12B and 12C shown in FIG. 2) on which the flat surface 120 is formed is shifted toward the center of the solid-state imaging device 10. May be arranged. Here, the distance between the center of the pixel 11 located in the peripheral portion of the solid-state imaging device 10, that is, the center of the photoelectric conversion element corresponding to the pixel 11 and the center of the solid-state imaging device 10 is R, and the micro corresponding to the pixel 11. Let x be the amount by which the central axes of the lenses 12B and 12C are shifted toward the center of the solid-state imaging device 10. In the solid-state imaging device 10 according to the present embodiment, x is in the range of the following number (1). This is because if x is out of the range of the number (1), the sensitivity is lowered.
x <0.0007R Number (1)

As described above, the solid-state imaging device 10 according to the present embodiment includes the semiconductor substrate 16, the photoelectric conversion element 17 formed inside the semiconductor substrate 16, the color filter 13 formed on the photoelectric conversion element 17, A solid-state imaging device in which a plurality of pixels configured by a convex microlens 12 disposed on the color filter 13 in correspondence with the photoelectric conversion element 17 are two-dimensionally arranged. The microlens 12 disposed in a region other than the central portion 10 has a flat surface 120 formed at the top.
Here, the region other than the central portion of the solid-state imaging device 10 is, for example, a peripheral portion of the solid-state imaging device 10 and a region where the incident angle of the principal ray is 20 degrees or more with reference to the central portion of the solid-state imaging device 10. Show. That is, the microlens having the flat surface 120 formed on the top is disposed in the peripheral portion of the solid-state imaging device 10.
Thereby, the sensitivity of the obliquely incident light of the microlens 12 disposed in the peripheral portion of the solid-state imaging device 10 is increased, the sensitivity unevenness is improved, and the sensitivity of the solid-state imaging device 10 can be improved.

  In the present embodiment, the central axis of the microlens 12 arranged in a region other than the central portion of the solid-state imaging device 10 is the center of the solid-state imaging device 10 from the central axis of the photoelectric conversion element 17 corresponding to the microlens 12. It may be shifted closer to the part. Thereby, the sensitivity to obliquely incident light can be further improved.

  Next, an embodiment of the solid-state imaging device of the present invention will be described using simulation results.

  The simulation was performed using a time domain difference method (FDTD method) which is a kind of electromagnetic field analysis method. The simulation conditions are shown below.

  FIG. 4 is a diagram schematically illustrating a part of the structure of the solid-state imaging device 10 according to the first embodiment used in the simulation. FIG. 4A is a top view of a part of the solid-state imaging device 10 according to the present embodiment. As shown in FIG. 4A, in the solid-state imaging device 10 according to the present embodiment, pixels 11 on which color filters that selectively transmit a wavelength corresponding to a specific color are formed are regularly arranged. . The red pixel 11R is a pixel that detects the intensity of red wavelength light, the green pixel 11G is a pixel that detects the intensity of green wavelength light, and the blue pixel 11B is a pixel that detects the intensity of blue wavelength light. . In FIG. 4A, the width of each of the red pixel 11R, the green pixel 11G, and the blue pixel 11B is 1.1 μm in both the X-axis direction and the Y-axis direction.

  4B is a cross-sectional view of the solid-state imaging device 10 of the present embodiment along the line AA ′ shown in FIG. 4A, and FIG. 4C is a cross-sectional view taken along the line B-- shown in FIG. It is sectional drawing of the solid-state imaging device 10 of a present Example along B 'line. In addition, the microlens 12 in this example has a substantially hemispherical shape with a bottom having a circular shape with a diameter of 1.1 μm and a height of 0.45 μm, a refractive index of 1.6, and an extinction coefficient of 0.

  The blue color filter 13B shown in FIG. 4B is a color filter that is formed at a position corresponding to the blue pixel 11B and transmits blue wavelength light. In this embodiment, the blue color filter 13B has a length in the X-axis direction and a length in the Y-axis direction of 1.1 μm, a length in the Z-axis direction of 0.7 μm, a refractive index of 1.48, and an extinction coefficient. It was set to 0.206. In the present embodiment, the blue color filter 13B is C.I. I. Pigment blue 15: 6, C.I. I. Pigment Violet 23 was used. Furthermore, after applying a photoresist composed of an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and an initiator to a thickness of 0.7 μm on the silicon substrate, and further performing exposure and heat treatment The refractive index and extinction coefficient were measured using a spectroscopic ellipsometer.

  The green color filter 13G shown in FIGS. 4B and 4C is a color filter that is formed at a position corresponding to the green pixel 11G and transmits green wavelength light. In this embodiment, the green color filter 13G has a length in the X-axis direction and a length in the Y-axis direction of 1.1 μm, a length in the Z-axis direction of 0.7 μm, a refractive index of 1.67, and an extinction coefficient. It was set to 0.00452. In the present embodiment, the green color filter 13G is C.I. I. Pigment yellow 139, C.I. I. Pigment green 36, C.I. I. Pigment Blue 15: 6 was used. Furthermore, after applying a photoresist composed of an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and an initiator to a thickness of 0.7 μm on the silicon substrate, and further performing exposure and heat treatment The refractive index and extinction coefficient were measured using a spectroscopic ellipsometer.

  The red color filter 13R shown in FIG. 4C is a color filter 13 that is formed at a position corresponding to the red pixel 11R and transmits red wavelength light. In this embodiment, the red color filter 13R has a length in the X-axis direction and a length in the Y-axis direction of 1.1 μm, a length in the Z-axis direction of 0.7 μm, a refractive index of 1.77, and an extinction coefficient. It was set to 0.281. In this embodiment, the red color filter 13R is a C.I. I. Pigment red 117, C.I. I. Pigment red 48: 1, C.I. I. Pigment yellow was used. Furthermore, after applying a photoresist composed of an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and an initiator to a thickness of 0.7 μm on the silicon substrate, and further performing exposure and heat treatment The refractive index and extinction coefficient were measured using a spectroscopic ellipsometer.

In this embodiment, the planarizing layer 14 has a thickness of 0.55 μm, a refractive index of 1.6, and an extinction coefficient of 0.
Further, the light shielding wall 15 is arranged in a grid pattern at the boundary between the pixels, the length in the width direction (X-axis direction and Y-axis direction) is 0.1 μm, the thickness in the Z-axis direction is 0.2 μm, and the light is refracted. The rate was 0.982 and the extinction coefficient was 6.45. The light shielding wall 15 is located at the center of the length in the width direction (X-axis direction and Y-axis direction) at the boundary between the pixels, is in contact with the surface of the semiconductor substrate 16, and is included in the planarization layer 14. Arranged to be.
In this embodiment, the semiconductor substrate 16 has a length in the X-axis direction and a length in the Y-axis direction of 2.2 μm, a thickness in the Z-axis direction of 2.5 μm, a refractive index of 4.24, and an extinction coefficient. Was set to 0.0303.
In this example, the wavelength of incident light was 0.55 μm. The incident light was parallel light, the XZ plane was the incident surface, and the incident angles were 0 degrees, 10 degrees, and 20 degrees. The vibration direction of the electric field was the X-axis direction.

FIG. 5 is a diagram schematically illustrating a part of the structure of the solid-state imaging device 10 according to the second embodiment used in the simulation. FIG. 5A is a top view of a part of the solid-state imaging device 10 according to this embodiment, and FIG. 5B is a solid-state imaging according to this embodiment along the line AA ′ shown in FIG. It is sectional drawing of the apparatus 10, FIG.5 (c) is sectional drawing of the solid-state imaging device 10 by a present Example along the BB 'line shown to Fig.5 (a).
As shown in FIGS. 5B and 5C, the microlens 12 of this example has a structure in which a flat surface 120 is formed on the top. Further, the microlens 12 in the present example has a height of 0.35 μm, and the height up to 0.35 μm is the same as the microlens 12 of Example 1 shown in FIG. Further, in the solid-state imaging device 10 according to the present embodiment shown in FIG. 5, the other simulation conditions are the same as those of the solid-state imaging device 10 according to the first embodiment shown in FIG.

  Simulations were performed on the solid-state imaging devices of Example 1 and Example 2 under the above conditions, and the light intensity absorbed at a depth of 2.5 μm from the surface of the semiconductor substrate 16 in each pixel was calculated.

  After calculating the light intensity, the light receiving sensitivity was calculated as the ratio of the incident light intensity absorbed from the surface of the semiconductor substrate 16 to the depth of 2.5 μm in each pixel with respect to the light intensity incident on one pixel. .

  The light receiving sensitivity of the green pixel 11G under each condition is shown in Table 1 below.

  From Table 1, in the structure of Example 2 (see FIGS. 5A to 5C) in which the top of the microlens 12 is a flat surface, the microlens 12 is substantially hemispherical in Example 1 (FIG. 4A). ) To (c)), the sensitivity at the incident angles of 0 degrees and 10 degrees decreases, but the sensitivity at the incident angle of 20 degrees increases.

  From the above embodiment, the microlens 12 has a substantially hemispherical shape at the center of the solid-state imaging device 10 where light enters vertically, and the light is incident obliquely (for example, the incident angle is 20 degrees or more). It was confirmed that making the top part of the microlens 12 flat in the peripheral part is effective in improving sensitivity unevenness and improving sensitivity in the solid-state imaging device.

  The scope of the present invention is not limited to the illustrated and described exemplary embodiments, but also includes all embodiments that provide equivalent effects to those intended by the present invention. Furthermore, the scope of the invention is not limited to the combinations of features of the invention defined by the claims, but may be defined by any desired combination of particular features among all the disclosed features.

DESCRIPTION OF SYMBOLS 10 Solid-state imaging device 11 Pixel 11B Blue pixel 11G Green pixel 11R Red pixel 12, 12A, 12B, 12C Micro lens 13 Color filter 13B Blue color filter 13G Green color filter 13R Red color filter 14 Flattening layer 15 Light shielding wall 16 Semiconductor substrate 17 Photoelectric conversion element 120 Flat surface

Claims (3)

A semiconductor substrate; a photoelectric conversion element formed inside the semiconductor substrate; a color filter formed on the photoelectric conversion element; and a convex type disposed on the color filter in correspondence with the photoelectric conversion element. A solid-state imaging device in which a plurality of pixels configured with a microlens are two-dimensionally arranged,
The microlens arranged in a region other than the central portion of the solid-state imaging device has a flat surface formed at the top. The center axis of the microlens arranged in a region other than the central portion of the solid-state imaging device is shifted from the central axis of the corresponding photoelectric conversion element toward the central portion of the solid-state imaging device. The solid-state imaging device according to claim 1. The microlens having a flat surface formed on the top is disposed in a region where an incident angle of a principal ray is 20 degrees or more with respect to a central portion of the solid-state imaging device. Item 3. The solid-state imaging device according to Item 2.

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