JP7423908B2 - solid-state imaging device - Google Patents

Description

The present invention relates to a solid-state imaging device, and particularly to a solid-state imaging device having a feature in a color filter formed on the top of the solid-state imaging device.

2. Description of the Related Art In recent years, solid-state imaging devices have become mainstream in digital still cameras, mobile phone cameras, and the like when photographing subjects. Main solid-state imaging devices include CCD (Charge Coupled Device) image sensors and CMOS (Complementary Metal Oxide Semiconductor) image sensors. In particular, CMOS image sensors have made remarkable progress by incorporating miniaturization technology.

Generally, in a solid-state imaging device, a plurality of photoelectric conversion elements that receive an optical image from an object to be photographed and convert the incident light into electrical signals are arranged two-dimensionally, for example in a lattice shape, and each photoelectric conversion element is arranged for each pixel. The greater the number of photoelectric conversion elements (the number of pixels), the finer the captured image will be.
By providing each pixel with a color filter that transmits light of a specific wavelength on the path of incident light, it is possible to obtain color information of the object. In general, by arranging a color filter of a specific color for each pixel, a large number of color filters can be arranged regularly and color-separated image information can be obtained. The colors of the color filter are three primary colors consisting of red (R), green (G), and blue (B), or complementary colors consisting of cyan (C), magenta (M), and yellow (Y). are common, and three primary colors are particularly often used.

Further, in order to efficiently condense light incident on a pixel onto a photoelectric conversion element, a configuration has been disclosed in which a microlens is arranged for each pixel on a color filter (see Patent Document 1).
Furthermore, a configuration in which a microlens and a color filter are integrated is disclosed (see Patent Document 2). The disclosed configuration is said to have the effect of alleviating color mixture by allowing the color filters of adjacent pixels to contact each other on the side surfaces without gaps.

Japanese Unexamined Patent Publication No. 59-122193 Patent No. 4710693

Since the configuration described in Patent Document 2 uses a lens-shaped color filter, the S/N characteristics and image quality characteristics deteriorate due to thinning of the color filter at the diagonal ends of the pixels. .
The present invention provides a solid-state imaging device that has a structure in which a microlens and a color filter are integrated, and is capable of improving deterioration in S/N characteristics caused by the thickness of the color filter varying depending on the position within a pixel. The purpose is to

As a result of intensive studies by the inventor, a solid-state imaging device having minute pixels has a structure in which a microlens and a color filter are integrated, and the surface of the color filter opposite to the photoelectric conversion element is in the shape of a lens. Furthermore, it has been found that by adjusting the ratio of the height of the lens-shaped portion to the height of the color filter, it is possible to realize a remarkable improvement in the S/N characteristic of the pixel.

In order to solve the problems, one embodiment of the present invention includes a semiconductor substrate on which a plurality of photoelectric conversion elements are two-dimensionally arranged, and a semiconductor substrate formed on the semiconductor substrate at a position that can face each of the photoelectric conversion elements. A plurality of color filter flat portions, and a plurality of color filter lens portions formed on each of the color filter flat portions and having a lens-shaped surface opposite to the color filter flat portions, a plurality of pixels are provided. A solid-state imaging device arranged two-dimensionally, wherein the thickness of the flat part of the color filter is defined as a flat part height, and from the surface of the color filter lens part on the side of the flat part of the color filter to the top of the lens shape. When the distance in the thickness direction is defined as the height of the lens part, the gist is that the ratio of the height of the lens part to the sum of the height of the flat part and the height of the lens part is 0.5 or more and less than 1.

According to the aspect of the present invention, even if a structure in which a microlens and a color filter are integrated is adopted, it is possible to provide a solid-state imaging device that improves the S/N characteristics of captured images.

1 is a top view schematically showing a portion of a solid-state imaging device based on an embodiment of the present invention. 2 is a cross-sectional view of the solid-state imaging device taken along the dotted line I-II in FIG. 1. FIG. 2 is a cross-sectional view of the solid-state imaging device taken along the dotted line III-IV in FIG. 1. FIG. FIG. 3 is a schematic cross-sectional view showing a difference in the propagation path of incident light depending on the presence or absence of a color filter base portion in a solid-state imaging device according to an embodiment of the present invention. 1 is a diagram schematically showing a structure in an example of a solid-state imaging device based on an embodiment of the present invention. FIG. 7 is a diagram showing characteristics of SNR10 with respect to ratio R when the sum of height A and lens portion height B is 500 nm. FIG. 7 is a diagram showing the characteristics of SNR10 with respect to ratio R when the sum of height A and lens portion height B is 600 nm. FIG. 7 is a diagram showing the characteristics of SNR10 with respect to ratio R when the sum of height A and lens portion height B is 700 nm. FIG. 7 is a diagram showing the characteristics of SNR10 with respect to ratio R when the sum of height A and lens portion height B is 800 nm.

Hereinafter, solid-state imaging devices according to embodiments of the present invention will be described with reference to the drawings.
In the solid-state imaging device of this embodiment, as shown in FIG. The array with 1 unit is arranged periodically. 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 plan view, the area of each color filter 12 matches the area of each pixel.

FIG. 2 is a cross-sectional view of the solid-state imaging device 10 taken along the dotted line I-II in FIG.
As shown in FIG. 2, in the solid-state imaging device 10, a plurality of photoelectric conversion elements 17 having the function of converting incident light into electric charge are provided inside the semiconductor substrate 16. The photoelectric conversion element 17 is provided for each pixel 11 shown in FIG. 1, and a plurality of photoelectric conversion elements are two-dimensionally arranged.
The semiconductor substrate 16 is made of silicon, for example. The photoelectric conversion element 17 is formed by adding an element such as phosphorus to the semiconductor substrate 16, for example.

The region of each pixel in a plan view is defined by a square having a center of gravity that coincides with the geometric center of the photoelectric conversion element 17 in a plan view and having sides in a direction connecting adjacent photoelectric conversion elements 17. Further, the length of one side of each pixel is defined as the width of the pixel.
A planarization layer 15 is formed on the semiconductor substrate 16 . The planarization layer 15 is formed of, for example, a silicon oxide film. Further, in order to reduce reflection of incident light, an antireflection film may be formed of a metal oxide at the interface between the planarization layer 15 and the semiconductor substrate.

A color filter 12 is formed on the planarization layer 15. The color filter 12 includes a color filter flat part 13 and a color filter lens part 14, which are formed in this order on the flattening layer 15. The color filter lens portion 14 has a lens-shaped surface on the opposite side from the color filter flat portion 13.
As shown in FIG. 2, the flat portion height A, which is the thickness (film thickness) of the color filter flat portion 13, is, for example, from the surface in contact with the flattening layer 15 to the surface in contact with the bottommost portion of the color filter lens portion 14. Defined as the height up to. The lens portion height B of the color filter lens portion 14 is defined, for example, as the height from the bottom surface in contact with the color filter flat portion 13 to the top of the lens shape of the color filter lens portion 14 in the thickness direction.

As shown in FIG. 3, the side height C of the color filter lens portion 14 is defined as the height from the surface in contact with the color filter flat portion 13 to the bottom of the surface opposite to the surface in contact with the color filter flat portion 13. Define. For example, the side height C is the minimum height of the color filter lens portion 14 from the color filter flat portion 13 at the boundary position between adjacent color filter lens portions 14 . The side height C of the color filter lens section 14 is lower than the lens section height B of the color filter lens section 14.
The color filter 12 is made of, for example, a photosensitive organic material containing a pigment or dye that selectively transmits wavelengths corresponding to green, blue, and red. The color filter lens portion 14 is formed by transferring the shape of the lens matrix onto the color filter 12 by dry etching using the lens matrix as a mask. Furthermore, in order to reduce reflection of incident light, an antireflection film may be formed on the top of the color filter lens section 14 using, for example, a silicon oxide film.

Next, the reason why the structure according to the embodiment of the present invention can improve image quality characteristics will be described.
FIG. 4 shows the behavior of the incident light L on the diagonal end of the pixel when light enters the solid-state imaging device 10 from a direction perpendicular to the pixel.
4A shows a configuration having a color filter flat part 13, and FIG. This is the configuration when

In the case where the color filter flat part 13 shown in FIG. 4(b) is not provided, the optical distance through which the incident light L to the diagonal end of the pixel passes through the color filter 12 is as shown in FIG. 4(a). The optical distance is shorter than the optical distance of the incident light L when the color filter has the flat portion 13 shown in FIG. Therefore, when a pixel does not have the color filter flat portion 13 and light of a wavelength other than the wavelength range to be detected is incident, the light incident on the diagonal end of the pixel will penetrate inside the color filter. Since the optical distance to be passed is short, the amount of light absorption decreases, and the detected intensity of incident light outside the wavelength range to be detected increases, resulting in increased color mixture. Therefore, the S/N ratio of the pixel deteriorates, resulting in deterioration of image quality characteristics.

On the other hand, the ratio of the lens portion height B of the color filter lens portion 14 to the sum of the lens portion height B of the color filter lens portion 14 and the flat portion height A of the color filter flat portion 13 is lower than a certain value. In this case, sufficient light is not collected by the color filter lens portion, so that the light receiving sensitivity decreases, and the S/N ratio of the pixel deteriorates, resulting in deterioration of image quality characteristics.
For the above-mentioned reasons, by adopting a configuration having the color filter flat portion 13, it is possible to improve image quality characteristics.

In this embodiment, the ratio (B/(A+B)) of the lens portion height B to the sum of the flat portion height A and the lens portion height B is 0.5 or more and less than 1.
If the above ratio is lower than 0.5, the color filter lens section does not collect enough light, and the light receiving sensitivity decreases, causing the S/N ratio of the pixel to deteriorate, resulting in poor image quality. (See examples below). The sum of the flat part height A and the lens part height B is preferably 500 nm or more and 800 nm or less.

The reason for this is that if the sum of the flat part height A and the lens part height B is lower than the above range, the transmittance of incident light having a wavelength outside the selected wavelength range of each color filter increases, and each color filter This is because the wavelength selectivity of the pixel deteriorates, and the S/N ratio of the pixel deteriorates. In addition, each color filter has the property of slightly absorbing light in the selected wavelength range, so if the sum of the flat part height A and the lens part height B is higher than the above range, the selected wavelength range of each color filter This causes a decrease in the transmittance of each color filter for incident light having a specific wavelength, and the amount of light reaching the photoelectric conversion element of each pixel decreases, resulting in a decrease in the light receiving sensitivity of the pixel and a deterioration of the S/N ratio of the pixel. This is to do so.

Further, it is preferable that the width of each pixel in the horizontal direction is 0.6 μm or more and 3.0 μm or less.
The reason is that when the width of each pixel becomes narrower than 0.6 μm, the proportion of light that goes to adjacent pixels increases compared to the light incident on a certain pixel, and the deterioration of the S/N ratio of the pixel becomes noticeable. It's for a reason. In addition, if the width of each pixel is wider than 3.0 μm, the light receiving sensitivity will decrease because the color filter lens section will not be able to collect enough light, and the deterioration of the S/N ratio of the pixel will become noticeable. It is.

Next, an example of the solid-state imaging device of the present invention will be described using simulation results.
The simulation was performed using the finite difference time domain method (FDTD method), which is a type of electromagnetic field analysis method. The simulation conditions are shown below.
FIG. 5 shows the structure of the solid-state imaging device 10 used in the simulation.
In FIG. 5A, which is a top view, the widths of each of the red pixel 11R, the green pixel 11G, and the blue pixel 11B were set to 0.9 μm in both the X-axis direction and the Y-axis direction. The red color filter flat portion 13R and the red color filter lens portion 14R are both color filters 12 that transmit red wavelength light, and have a length in the X-axis direction and a length in the Y-axis direction of 0.9 μm. The green color filter flat portion 13G and the green color filter lens portion 14G are both color filters 12 that transmit green wavelength light, and have a length in the X-axis direction and a length in the Y-axis direction of 0.9 μm. The color filter flat portion 13B and the color filter lens portion 14B are both color filters 12 that transmit blue wavelength light, and have a length in the X-axis direction and a length in the Y-axis direction of 0.9 μm. The flattening layer 15 had a height in the Z-axis direction of 0.1 μm, a refractive index of 1.6, and an extinction coefficient of 0. The semiconductor substrate 16 had a length in the X direction and a Y direction of 1.8 μm, and a height in the Z axis direction of 3 μm. The incident light was parallel light, and the vibration direction of the electric field was the X-axis direction.

The refractive index and extinction coefficient of the color filter 13R are based on C. I. Pigment Red 117, C. I. Pigment Red 48:1, C.I. I. pigment yellow, an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and an initiator. A photoresist is coated on a silicon substrate to a thickness of 0.6 μm, and then exposed and heated. After the treatment, the values measured using a spectroscopic ellipsometer were used.

The refractive index and extinction coefficient of the color filter 13G are based on C. I. Pigment Yellow 139, C. I. Pigment Green 36, C. I. Pigment Blue 15:6, an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and an initiator were applied to the silicon substrate to a thickness of 0.6 μm. After exposure and heat treatment, the values measured using a spectroscopic ellipsometer were used.
The refractive index and extinction coefficient of the color filter 13B are based on C. I. Pigment Blue 15:6, C. I. Pigment Violet 23, an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and an initiator were applied to a silicon substrate to a thickness of 0.6 μm, and then exposed and After the heat treatment, the values measured using a spectroscopic ellipsometer were used.

The color filter flat portion 13R, the color filter flat portion 13G, and the color filter flat portion 13B all had the same height A. The color filter lens portion 14R, the color filter lens portion 14G, and the color filter lens portion 14B all had the same lens portion height B.
The incident light was parallel light, and the vibration direction of the electric field was the X-axis direction. The wavelength of the incident light was a single wavelength, and 31 conditions were performed for each level from 400 nm to 700 nm in 10 nm increments.

A simulation was performed under the above conditions, and the light intensity absorbed in each pixel from the surface of the semiconductor substrate 16 to a depth of 3 μm was calculated. The light receiving sensitivity was calculated as the ratio of the intensity of the optical power absorbed in each pixel up to a depth of 3 μm from the surface of the semiconductor substrate 16 to the intensity of the optical power incident on one pixel.
SNR10 was used as a performance index of image quality. This is used as an index of image quality after color correction processing and the like in solid-state imaging devices for mobile phone cameras.
In this example, when the F value is set to 1.8, the light receiving sensitivity of each pixel is regarded as the quantum efficiency, and the SNR10 is calculated from the spectral sensitivity characteristics calculated from the simulation results of each level. The SNR10 value has a unit of illuminance (lux), and is preferably a low value.

FIG. 6 shows the characteristics of the SNR10 with respect to the ratio R when the sum of the height A and the lens height B is 500 nm.
FIG. 7 shows the characteristics of the SNR10 with respect to the ratio R when the sum of the height A and the lens height B is 600 nm.
FIG. 8 shows the characteristics of the SNR10 with respect to the ratio R when the sum of the height A and the lens height B is 700 nm.
FIG. 9 shows the characteristics of the SNR10 with respect to the ratio R when the sum of the height A and the lens portion height B is 800 nm.

As can be seen from the results in FIGS. 7 to 9, the ratio R of the color filter lens portion 14B to the sum of the height A of the color filter flat portion 13 and the lens portion height B of the color filter lens portion 14 is 0.5. It can be seen that in the above range of less than 1, the value of SNR10 is lower than when the ratio R is 1, which is the same configuration as the configuration without the color filter flat portion 13.
From the results of the above examples, the ratio R of the color filter lens portion 14B to the sum of the height A of the color filter flat portion 13 and the lens portion height B of the color filter lens portion 14 is 0.5 or more and less than 1. It has been confirmed that a configuration within this range is more effective in improving image quality characteristics than a configuration without the color filter flat portion 13.

10 Solid-state imaging device 11 Pixel 11B Blue pixel 11G Green pixel 11R Red pixel 12 Color filter 13 Color filter flat portion 13B Blue color filter flat portion 13G Green color filter flat portion 13R Red color filter flat portion 14 Color filter lens portion 14B Blue color filter Lens portion 14G Green color filter lens portion 14R Red color filter lens portion 15 Flattening layer 16 Semiconductor substrate 17 Photoelectric conversion element A Height of color filter flat portion B Height of color filter lens portion C Side height of color filter lens portion

Claims (4)

A semiconductor substrate on which a plurality of photoelectric conversion elements are two-dimensionally arranged, a plurality of color filter flat portions formed on the semiconductor substrate at positions that can face each of the photoelectric conversion elements, and each of the color filter flat portions. A solid-state imaging device in which a plurality of pixels are two-dimensionally arranged, comprising: a plurality of color filter lens portions formed on the top of the color filter lens portion, the surface of which is opposite to the color filter flat portion, has a lens shape;
When the thickness of the flat part of the color filter is defined as the flat part height, and the distance in the thickness direction of the color filter lens part from the surface on the color filter flat part side to the top of the lens shape is defined as the lens part height,
The sum of the flat part height and the lens part height is 500 nm or more and 800 nm or less, and the ratio of the lens part height to the sum of the flat part height and the lens part height is 0.6 or more and less than 1. A solid-state imaging device characterized by the following. The sum of the flat part height and the lens part height is 500 nm or more and 700 nm or less, and the ratio of the lens part height to the sum of the flat part height and the lens part height is 0.6 or more and 0.8 The solid-state imaging device according to claim 1, characterized in that : The solid-state imaging device according to claim 1 , wherein each pixel has a width of 0.6 μm or more and less than 2.2 μm . The solid-state imaging device according to claim 1, wherein each pixel has a width of 0.6 μm or more and 0.9 μm or less.

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