JP2011243749A - Solid state image pickup device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid state image pickup device capable of obtaining a sufficient reflection reduction effect with an easy manufacturing process.SOLUTION: A solid state image pickup device 100 with a plurality of pixels comprises a semiconductor substrate 101, a plurality of light receiving parts 102 formed on the semiconductor substrate 101 for each pixel, a plurality of micro-lenses 107 arranged above the light receiving parts 102 to focusing incident lights to each of the light receiving parts 102, a surface planarization layer 108 formed on the micro-lenses 107, and a low refraction index surface layer 109 formed on the surface planarization layer 108 and having a refraction index lower than that of the surface planarization layer 108.

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly, to a solid-state imaging device having a microlens formed on a light receiving portion and a surface film thereof and a manufacturing method thereof.

  In recent years, along with the reduction in the chip size of the solid-state imaging device and the increase in the number of pixels, downsizing and higher performance of digital cameras, digital movie cameras, camera-equipped mobile phones, and the like are progressing.

  In the conventional solid-state imaging device, the number of pixels is increased in order to increase the resolution of the camera, and with the miniaturization of the camera optical system, the miniaturization of the chip size is further accelerated. Therefore, the pixel size is becoming smaller and smaller. These demands are strong and further reduction is expected in the future.

  On the other hand, even though the pixel size is getting smaller and smaller, there is a strong demand from the market to capture images with high sensitivity even at low illumination. A microlens structure has been proposed.

  Furthermore, in order to increase the light collection effect, in order to play the role of the reflection reduction effect, a structure is proposed in which an antireflection film made of a fluorine-containing resin film having a predetermined thickness is formed on the microlens to further improve sensitivity. (For example, refer to Patent Document 1).

  FIG. 10 is a structural cross-sectional view of a conventional solid-state imaging device 10 described in Patent Document 1. A conventional solid-state imaging device 10 shown in FIG. 10 includes a silicon substrate 11, a photodiode 12, a polysilicon electrode 13, a silicon oxide film 14, a planarization film 15, a microlens 16, and an antireflection film 17. , Air or an inert gas layer 18.

  As shown in FIG. 10, an antireflection film 17 made of a fluorine-containing resin film having a predetermined thickness is formed on the microlens 16 to play a role of a reflection reduction effect. The antireflection film 17 is formed on the microlens 16 so that the film thickness becomes uniform along the curved surface of the microlens 16.

  With this configuration, there is an antireflection effect on the surface, and sensitivity can be improved.

Japanese Patent Laid-Open No. 4-275259

  However, the prior art has a problem that a sufficient reflection reduction effect cannot be obtained by an easy manufacturing process.

  In a conventional solid-state imaging device that does not include an antireflection film, there is a problem that reflection on the surface is approximately 4%, causing a condensing loss, and sensitivity is lowered.

  Further, in the solid-state imaging device described in Patent Document 1 shown in FIG. 10, an antireflection film for preventing reflection on the surface is formed, and the reflection reduction effect is certainly recognized. However, it is difficult to form a film uniformly on a curved surface of a microlens while maintaining a predetermined thickness by a conventional on-chip filter forming process, for example, a spin coating method. Further, the method described in Patent Document 1 has a problem that it is difficult to form a uniform film thickness when a large-diameter wafer is used.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a solid-state imaging device capable of obtaining a sufficient reflection reduction effect with an easy manufacturing process, and a manufacturing method thereof.

  In order to solve the above-described problem, a solid-state imaging device according to one embodiment of the present invention is a solid-state imaging device including a plurality of pixels, and includes a semiconductor substrate and a plurality of light receiving elements formed on the semiconductor substrate for each pixel. And a plurality of microlenses disposed above the plurality of light receiving portions so as to collect incident light on each of the plurality of light receiving portions, and a planarization layer formed on the plurality of microlenses. And a low refractive index layer having a refractive index lower than that of the planarization layer, formed on the planarization layer.

  Thereby, since the low refractive index layer is formed on the planarizing layer, a low refractive index layer having a uniform thickness can be easily formed, and a sufficient reflection reduction effect can be obtained.

  Further, the product of the film thickness and the refractive index of the low refractive index layer may be in a range of 1/4 times the wavelength of visible light.

  Thereby, since a film thickness and a refractive index are determined according to the wavelength of visible light, reflection can be sufficiently reduced.

  The low refractive index layer may be made of an inorganic material.

  Thereby, since the low refractive index layer is composed of an inorganic material, even when heat is applied, there is little yellowing or deformation, and weather resistance can be improved.

  Further, the difference between the refractive index of the planarizing layer and the refractive index of the low refractive index layer may be 0.04 or more.

  Thereby, reflection can be reduced more than before.

  The plurality of pixels may belong to any of a plurality of types, and the film thickness of the low refractive index layer may be different for each type of pixel.

  Thereby, the wavelength of incident light can be selected for each pixel to reduce reflection at the low refractive index layer, so that high sensitivity can be realized for each pixel and color reproducibility can be improved.

  The plurality of pixels may belong to any one of a red pixel, a green pixel, and a blue pixel, and the film thickness of the low refractive index layer may be the blue pixel, the green pixel, The thickness may be increased in the order of red pixels.

  Accordingly, when a color filter that transmits each of red light, green light, and blue light is provided, reflection can be sufficiently reduced by changing the film thickness according to the light that the color filter transmits. .

  The plurality of pixels may belong to any of a plurality of types, and a material of the low refractive index layer may be different for each type of the pixels.

  Thereby, since the material of the low refractive index layer differs for each pixel, reflection can be reduced.

  Further, the plurality of pixels belong to any one of a red pixel, a green pixel, and a blue pixel, and the product of the film thickness and the refractive index of the low refractive index layer in the red pixel is: The product of the film thickness and the refractive index of the low refractive index layer in the green pixel is 550/4 nm, and the film thickness and the refractive index of the low refractive index layer in the blue pixel are The product of may be 440/4 nm.

  Thereby, since a film thickness and a material can be changed for every pixel according to the light to permeate | transmit, high sensitivity can be implement | achieved for every pixel and color reproducibility can also be improved.

  The plurality of pixels are two-dimensionally arranged in a predetermined region, and the predetermined region includes a central region including a center and a peripheral region that is a region around the central region, and the low refraction The film thickness of the rate layer may be different between the central region and the peripheral region.

  Thereby, reflection in the central region and the peripheral region can be reduced, and sensitivity unevenness can be suppressed.

  The film thickness of the low refractive index layer in the peripheral region may be smaller than the film thickness of the low refractive index layer in the central region.

  Thereby, reflection in the central region and the peripheral region can be reduced, and sensitivity unevenness can be suppressed.

  The planarization layer may further include a convex portion having a curvature along the microlens on the upper surface.

  Thereby, since the condensing effect can be obtained not only in the microlens but also in the flattening layer, the condensing effect can be enhanced.

  The low refractive index layer may have an uneven microstructure with a pitch equal to or less than the wavelength of visible light.

  Thereby, a reflectance can be reduced significantly.

  Further, a method for manufacturing a solid-state imaging device according to one aspect of the present invention is a method for manufacturing a solid-state imaging device including a plurality of pixels, the step of forming a plurality of light receiving portions for each of the pixels on a semiconductor substrate, Forming a plurality of microlenses so as to collect incident light on each of the plurality of light receiving sections above the plurality of light receiving sections; and forming a planarizing layer on the plurality of microlenses. Forming a low refractive index layer having a refractive index lower than that of the planarizing layer on the planarizing layer.

  Thereby, since the low refractive index layer is formed on the planarizing layer, a solid imaging device capable of easily forming a low refractive index layer having a uniform film thickness and obtaining a sufficient reflection reduction effect is provided. Can be manufactured.

  In the step of forming the low refractive index layer, the low refractive index layer may be formed by applying a material having a refractive index lower than that of the planarizing layer.

  Thereby, a low refractive index layer having a uniform film thickness can be formed.

  In the step of forming the low refractive index layer, the low refractive index layer may be formed by depositing a material having a refractive index lower than that of the planarizing layer by a CVD (Chemical Vapor Deposition) method.

  Thereby, a low refractive index layer having a uniform film thickness can be formed.

  The step of forming the low refractive index layer includes a step of forming a material having a refractive index lower than that of the planarization layer and containing a photosensitive group on the planarization layer, and a mask having a gray gradation. A step of forming the deposited material and a step of forming the low refractive index layer having a different thickness for each pixel by developing the exposed material.

  As a result, the exposure amount can be adjusted for each pixel with a mask having a gray gradation, so that a low refractive index layer having a different thickness for each pixel can be easily formed.

  The solid-state imaging device of the present invention is manufactured by an easy manufacturing process, and a sufficient reflection reduction effect can be obtained.

It is sectional drawing which shows an example of a structure of the solid-state imaging device which concerns on Embodiment 1 of this invention. It is a top view which shows an example of the pixel arrangement | sequence of the solid-state imaging device concerning Embodiment 1 of this invention. It is a schematic diagram which shows an example of a camera provided with the solid-state imaging device which concerns on Embodiment 1 of this invention. It is sectional drawing which shows an example of a structure of the solid-state imaging device which concerns on Embodiment 2 of this invention. It is sectional process drawing which shows an example of the manufacturing method of the solid-state imaging device which concerns on Embodiment 2 of this invention. It is sectional drawing which shows an example of a structure of the solid-state imaging device which concerns on Embodiment 3 of this invention. It is a schematic diagram which shows an example of a camera provided with the solid-state imaging device which concerns on Embodiment 3 of this invention. It is sectional drawing which shows an example of a structure of the solid-state imaging device in the modification of embodiment of this invention. It is sectional drawing which shows an example of a structure of the solid-state imaging device in the modification of embodiment of this invention. It is sectional drawing which shows the structure of the conventional solid-state imaging device.

  Hereinafter, a solid-state imaging device and a manufacturing method thereof according to embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
The solid-state imaging device according to Embodiment 1 of the present invention includes a planarization layer formed on a microlens and a low refractive index layer formed on the planarization layer and having a refractive index lower than that of the planarization layer. It is characterized by providing.

  First, the configuration of the solid-state imaging device according to Embodiment 1 of the present invention will be described. Here, a solid-state imaging device in which the color filter is a green checkered Bayer array of primary color filters will be described.

  FIG. 1 is a cross-sectional view of a solid-state imaging device 100 according to Embodiment 1 of the present invention. FIG. 2 is a plan view showing an example of a pixel array of the solid-state imaging device 100 according to Embodiment 1 of the present invention. FIG. 1 shows a part of the AA cross section shown in FIG.

  The solid-state imaging device 100 according to Embodiment 1 includes a semiconductor substrate 101, a plurality of light receiving units 102, a plurality of transfer electrodes 103, a planarization film 104, and a plurality of color filters (a red filter 105R, a green filter 105G, and the like). A blue filter 105 </ b> B), a microlens flattening film 106, a plurality of microlenses 107, a surface flattening layer 108, and a low-bending surface layer 109.

  The semiconductor substrate 101 is, for example, a silicon substrate. In the semiconductor substrate 101, a plurality of light receiving portions 102 are formed for each pixel.

  The plurality of light receiving units 102 are configured by, for example, photodiodes. Each of the plurality of light receiving units 102 generates signal charges by photoelectrically converting incident light.

  On the semiconductor substrate 101, a transfer electrode 103 is formed between the plurality of light receiving portions 102. The transfer electrode 103 is an electrode for transferring the signal charge generated by the light receiving unit 102 to the outside.

  The planarization film 104 is formed on the semiconductor substrate 101 so as to fill the concave portion generated by the transfer electrode 103. The planarization film 104 has a light-transmitting property.

  On the planarization film 104, a green filter 105G, a red filter 105R, and a blue filter 105B are formed corresponding to each pixel. Note that the blue filter 105B does not appear in the illustrated cross section.

  The green filter 105G, the red filter 105R, and the blue filter 105B are arranged corresponding to the light receiving unit 102. The green filter 105G is a color filter that transmits green light. The red filter 105R is a color filter that transmits red light. The blue filter 105B is a color filter that transmits blue light.

  The green filter 105G, the red filter 105R, and the blue filter 105B are arranged in a green checkered Bayer array as shown in FIG.

  A microlens flattening film 106 is formed on the color filters (red filter 105R, green filter 105G, and blue filter 105B). The microlens lower planarization film 106 is a planarization film for making the lower surfaces of the plurality of microlenses 107 flush with each other.

  Microlenses 107 are arranged on the planarizing film 106 under the microlenses corresponding to the light receiving unit 102 for the purpose of condensing light. That is, the microlens 107 is disposed for each pixel so as to collect incident light on each of the plurality of light receiving units 102 above the plurality of light receiving units 102.

  A surface planarization layer 108 is formed on the plurality of microlenses 107. The surface planarization layer 108 is an example of a planarization layer that has a flat upper surface and planarizes the upper surface of the microlens 107.

  On the surface flattening layer 108, a low bending surface layer 109 is formed. The refractive index of the low bending surface layer 109 is an example of a low refractive index layer and is lower than the refractive index of the surface flattening layer 108. For example, the difference between the refractive index of the low bending surface layer 109 and the refractive index of the surface flattening layer 108 is 0.04 or more.

  The surface flattening layer 108 is a layer that increases the flatness above the microlens 107, and the upper surface of the surface flattening layer 108 is flat.

Specifically, the material of the low bending surface layer 109 is an inorganic material, for example, silicon oxide (SiO ₂ ). In this case, the refractive index of the low bending surface layer 109 is about 1.46. The material of the surface flattening layer 108 is, for example, a thermosetting transparent acrylic film. In this case, the refractive index of the surface planarizing layer 108 is about 1.5.

  Hereinafter, functions of the solid-state imaging device 100 having such a structure will be described.

  As shown in FIG. 1, the reflectance on the low-bending surface layer 109 can be reduced by forming the low-bending surface layer 109 on the surface flattening layer 108. This is because the intensity reflectance R of the surface is expressed by the following formula (1).

R = (n _f ² −n ₀ n _s ) ² / (n _f ² + n ₀ n _s ) ² (1)

Here, n ₀ is the refractive index of the external medium (generally air, n ₀ ≈1), n _f is the refractive index of the low bending surface layer 109, and n _s is the refractive index of the surface flattening layer 108. Represents a rate.

  From the formula (1), the reflectance can be reduced by forming the low bending surface layer 109 using a material having a lower refractive index than the surface planarization layer 108. Specifically, when the refractive index of the surface flattening layer 108 is 1.50 and the refractive index of the low bending surface layer 109 is 1.46, the reflectance is 4 when the low bending surface layer 109 is not provided. However, it is reduced to about 3% by providing the low bending surface layer 109. From this result, it is preferable that the difference in refractive index between the surface flattening layer 108 and the low-bending surface layer 109 is approximately 0.04 or more.

  Furthermore, by configuring the low bending surface layer 109 so as to satisfy the following formula (2), the phase of the reflected light from the front surface and the back surface of the low bending surface layer 109 can be offset by half a wavelength by the interference effect. it can.

n _f d = λ / 4 (2)

  Here, d represents the thickness of the low bending surface layer 109, and λ represents the wavelength of incident light. That is, the product of the film thickness and the refractive index of the low bending surface layer 109 is 1/4 times the wavelength of the incident light. Incident light is, for example, visible light (450 nm to 650 nm). In other words, the film thickness and refraction of the low bending surface layer 109 are such that the product of the film thickness and the refractive index of the low bending surface layer 109 is in the range of 1/4 times the wavelength of visible light of 450 to 650 nm. The rate (material) is determined.

  From the formula (2), when the refractive index of the low bending surface layer 109 is 1.46, the film thickness of the low bending surface layer 109 is preferably about 94 nm when the wavelength is 550 nm. Similarly, from the viewpoint of improving sensitivity in visible light (450 nm to 650 nm), the effect can be exhibited if the thickness is about 77 nm to about 111 nm.

  In addition, that the film thickness of the low bending surface layer 109 is approximately 94 nm is substantially equal to 94 nm, for example, in a range of about 90 to 110%. Similar descriptions mean the same thing.

  As described above, the solid-state imaging device 100 according to Embodiment 1 of the present invention includes the surface flattening layer 108 formed on the microlens 107 and the surface flattening formed on the surface flattening layer 108. And a low-bending surface layer 109 having a refractive index lower than that of the layer 108.

According to this configuration, since the low-bending surface layer 109 can be formed on the flattened surface flattening layer 108, a special apparatus or process is not required, and the film thickness can be uniformly formed by a normal coating process. It is easy to stabilize the quality. Further, it can be formed by a low temperature CVD (Chemical Vapor Deposition) method. At this time, if the low-bending surface layer 109 is formed of an inorganic material such as SiO ₂ , yellowing and deformation are hardly caused even when heat is applied, and weather resistance can be improved. In the case of SiO ₂ , the refractive index is approximately 1.46, and the reflectance can be reduced by controlling the film thickness to 94 nm.

  FIG. 3 is a schematic diagram illustrating an example of a camera 120 including the solid-state imaging device 100 according to Embodiment 1 of the present invention. As shown in FIG. 3, the camera 120 includes an infrared cut filter 121, a diaphragm 122, and a lens 123.

  Due to the demand for camera miniaturization, the infrared cut filter 121 mounted on recent cameras is mainly a vapor deposition type capable of thinning. For this reason, the infrared cut filter 121 tends to reflect oblique light. Therefore, in order to suppress the occurrence of flare and ghost, it is essential to reduce reflection on the solid-state imaging device 100 side.

  According to the solid-state imaging device 100 according to Embodiment 1 of the present invention, the reflectance can be reduced as described above, so the camera 120 as shown in FIG. 3 suppresses the occurrence of flare and ghost. be able to. Therefore, the solid-state imaging device 100 according to Embodiment 1 of the present invention can generate an image signal with excellent image quality.

(Embodiment 2)
The solid-state imaging device according to Embodiment 2 of the present invention is characterized in that the plurality of pixels belong to one of a plurality of types, and the thickness of the low bending surface layer is different for each type of pixel. Specifically, the film thickness of the low bending surface layer varies depending on the wavelength of incident light incident on the light receiving portion.

  FIG. 4 is a cross-sectional view showing an example of the configuration of the solid-state imaging device 200 according to Embodiment 2 of the present invention. Note that the arrangement of the pixels is the same as that of the solid-state imaging device 100 according to Embodiment 1, and FIG. 4 shows a part of the AA cross section shown in FIG.

  As shown in FIG. 4, the solid-state imaging device 200 is different from the solid-state imaging device 100 according to the first embodiment shown in FIG. 1 in that a low-flexing surface layer 209 is provided instead of the low-flexing surface layer 109. ing. In the following, description of the same points as in the first embodiment will be omitted, and different points will be mainly described.

  The plurality of pixels included in the solid-state imaging device 200 belong to one of a plurality of types. The plurality of pixels are classified into a plurality of types depending on, for example, the wavelength of light incident on the pixel, specifically, the wavelength of light transmitted through the color filter. For example, there are three types: a blue pixel, a green pixel, and a red pixel.

  The low bending surface layer 209 is an example of a low refractive index layer, and the thickness of the low bending surface layer 209 is different for each type of pixel. That is, on each color filter, the thickness of the low bending surface layer 209 differs depending on the wavelength of light transmitted through the color filter. Specifically, the film thickness of the low bending surface layer 209 increases as the wavelength of light transmitted through the color filter increases. In visible light, the wavelength increases in the order of blue light, green light, and red light, and thus the thickness of the low-refractive-surface layer 209 increases in the order of blue pixels, green pixels, and red pixels.

  According to this structure, by selecting the wavelength that passes through each color filter and reducing the reflection at the low-bending surface layer 209, it is possible to realize high sensitivity in each pixel, thereby improving the color reproducibility. 200 can be realized.

  Specifically, from the formula (2), it is preferable that a low-bending surface layer 209B having a thickness of approximately 77 nm is formed on the blue filter 105B in order to suppress reflection at 450 nm. Similarly, in order to suppress reflection at 550 nm, it is preferable to form a low-bending surface layer 209G having a thickness of approximately 94 nm on the green filter 105G. On the red filter 105R, in order to suppress reflection at 650 nm, it is preferable to form a low-bending surface layer 209R having a thickness of approximately 111 m.

  Here, a method of manufacturing the solid-state imaging device 200 according to Embodiment 2 of the present invention will be described with reference to FIG. The structure up to the surface planarization layer 108 is the same as that of the solid-state imaging device 100 according to Embodiment 1 of the present invention, and the manufacturing method is omitted.

  First, as shown in FIG. 5A, a positive type material 211 containing a photosensitive group to be the low-bending surface layer 209 is formed on the surface planarizing layer 108 by a spin coating method. Thereafter, as shown in FIG. 5B, the formed material is exposed through a mask 210 having a gray gradation. At this time, the red filter 105R is completely shielded from light so as not to be exposed, and a gray gradation is provided on the green filter 105G and the blue filter 105B in order to adjust the irradiation amount according to the target thickness. Note that the mask 210 having a gray gradation is a mask capable of adjusting the amount of light applied to the material, that is, the exposure amount for each pixel.

  Thereafter, as shown in FIG. 5C, the exposed material can be developed and post-baked to form a corresponding thickness on each pixel. Thus, since it can form by what is called darkroom process processes, such as a spin coat method, the equipment widely used by the process can be diverted. In addition, a film having a uniform thickness can be formed on a large-diameter wafer.

  As described above, the solid-state imaging device 200 according to Embodiment 2 of the present invention includes the low-bending surface layer 209 having a refractive index lower than that of the surface flattening layer 108 formed on the surface flattening layer 108. The thickness of the low-bending surface layer 209 is different for each pixel.

  Accordingly, by selecting the wavelength of light incident on each pixel and reducing the reflection on the low-bending surface layer 209, high sensitivity can be realized in each pixel, and thereby the solid-state imaging device 200 having good color reproducibility. Can be realized.

  Note that the refractive indexes do not have to be the same as long as the expression (2) is satisfied. For example, the low-bending surface layer 209B may be formed on the blue filter 105B so that the product of the film thickness and the refractive index is 450/4 nm. Similarly, a low bending surface layer 209G is formed on the green filter 105G so that the product of the film thickness and the refractive index is 550/4 nm, and the film thickness and the refractive index are formed on the red filter 105R. The same effect can be expected by forming the low bending surface layer 209R so that the product is 650/4 nm.

  In this embodiment, the present invention is applied to all the color filters. However, the present invention is not necessarily applied to all the color filters, and may be applied only to the color filter layer having a concern about characteristics. Thereby, the color balance can be adjusted, and a solid-state imaging device with good color reproducibility can be realized. In other words, application to all color filters is not limited.

(Embodiment 3)
In the solid-state imaging device according to Embodiment 3 of the present invention, the plurality of pixels are two-dimensionally arranged in a predetermined area, and the predetermined area includes a central area including the center and an area around the central area. Including a certain peripheral region, the thickness of the low bending surface layer is different between the central region and the peripheral region.

  FIG. 6 is a cross-sectional view showing an example of the configuration of the solid-state imaging device 300 according to Embodiment 3 of the present invention. The arrangement of the pixels is the same as that of the solid-state imaging device 100 according to Embodiment 1, and FIG. 6 shows a part of the AA cross section shown in FIG.

  As shown in FIG. 6, the solid-state imaging device 300 is different from the solid-state imaging device 100 of Embodiment 1 shown in FIG. 1 in that a low-flexion surface layer 309 is provided instead of the low-flexion surface layer 109. ing. In the following, description of the same points as in the first embodiment will be omitted, and different points will be mainly described.

  Note that the plurality of pixels included in the solid-state imaging device 300 are two-dimensionally arranged in a predetermined region. The predetermined area corresponds to, for example, an imaging area.

  The low bending surface layer 309 is an example of a low refractive index layer, and as shown in FIG. 6, the thickness of the low bending surface layer 309 is different between the central region and the peripheral region. The central region is a region including the center of the imaging region in which a plurality of pixels are arranged two-dimensionally, and corresponds to the central portion of the chip. The peripheral area is an area around the central area and corresponds to the peripheral portion of the chip.

  This shows a structure in which the thickness of the low bending surface layer 309 is different between the center portion and the peripheral portion of the chip. With this structure, when the solid-state imaging device 300 according to the present embodiment is applied to the camera 320 having a short exit pupil distance as shown in FIG. 7, both the reflection of the outermost surface of the center portion and the peripheral portion of the chip is reduced. Therefore, it is possible to realize a high-quality camera 320 with reduced sensitivity unevenness.

  More specifically, as shown in FIG. 7, in the peripheral portion of the chip, the light incident through the lens 323 and the diaphragm 322 is slanted, so that the surface is less bent than the light incident on the central portion of the chip. The optical path in the layer 309 is lengthened. In order to make the phase change in reflection uniform, it is necessary to make the peripheral part of the chip thinner than the central part of the chip. Note that if an infrared cut filter (not shown) is provided between the solid-state imaging device 300 and the diaphragm 322, infrared rays can be reduced, and noise can be reduced.

  Ideally, when the incident angle is θ, the optical path becomes longer by the optical path length divided by cos θ. In the central portion of the chip, the incident angle θ is 0 and cos θ is 1. On the other hand, if the incident angle θ is, for example, 30 degrees in the peripheral portion of the chip, cos θ is about 0.866. Therefore, in order to align the optical path, the film thickness of the low-bending surface layer 309 in the peripheral region is set to The thickness is preferably about 0.866 times the film thickness of the region.

  As described above, the solid-state imaging device 300 according to Embodiment 3 of the present invention can be formed by using a mask provided with a gray gradation.

  As described above, in the solid-state imaging device 300 according to Embodiment 3 of the present invention, the plurality of pixels are two-dimensionally arranged in the central region and the peripheral region that is the peripheral region of the central region, so that low bending is achieved. The thickness of the surface layer 309 is different between the central region and the peripheral region. Specifically, the film thickness of the low bending surface layer 309 in the peripheral region is smaller than the film thickness of the low bending surface layer 309 in the central region. More specifically, it is preferable that the thickness of the low bending surface layer 309 decreases stepwise or smoothly from the center toward the end. At this time, the low bending surface layer 309 having a film thickness corresponding to the incident angle θ may be provided for each pixel.

  Thereby, reflection in the central region and the peripheral region can be reduced, and sensitivity unevenness can be suppressed.

  As described above, the solid-state imaging device and the manufacturing method thereof according to the present invention have been described based on the embodiments. However, the present invention is not limited to these embodiments. Unless it deviates from the meaning of this invention, the form which carried out the various deformation | transformation which those skilled in the art can think to the said embodiment, and the form constructed | assembled combining the component in a different embodiment is also contained in the scope of the present invention. .

For example, like the solid-state imaging device 400 illustrated in FIG. 8, as an example of the low refractive index layer, a low-bending surface layer 409 having an uneven microstructure with a pitch equal to or less than the wavelength of visible light may be provided. Further, by increasing the occupation ratio of the shape from the outermost surface toward the surface planarization layer 108, for example, in the case of a SiO ₂ film, the effective refractive index also increases continuously from 1.0 to 1.46. Thus, the reflectance can be greatly reduced. Also in this case, since it can be formed on the surface flattening layer 108, it is possible to form the film with good uniformity. The height of the fine structure is preferably 200 nm or more.

  Further, like the solid-state imaging device 500 illustrated in FIG. 9, a surface planarization layer 508 having a convex portion with a curvature along the microlens 107 on the upper surface may be provided. Thereby, the surface planarization layer 508 can have a light condensing effect. The surface flattening layer 508 is an example of a flattening layer according to the present invention, and is a layer for increasing the flatness above the microlens 107. The convex portion included in the surface planarization layer 508 has a curvature smaller than the curvature of the microlens 107. That is, the planarization layer may be any layer that improves the flatness, and the surface does not necessarily have to be completely flat.

  Furthermore, by providing the low bending surface layer 509 on the surface flattening layer 508, the surface reflection can be reduced. In this example, the low-bending surface layer 509 is formed with the same thickness in all pixels as in the first embodiment.

  On the other hand, the thickness may be changed for each color as in the second embodiment, or the thickness may be changed between the central portion and the peripheral portion of the chip as in the third embodiment. Furthermore, it may have a surface irregularity as in the modification of the embodiment (FIG. 8).

  In the first to third embodiments described above and the modifications thereof, the primary color filter (red, green, and blue) is used as the color filter, but the complementary color filter (yellow, cyan, magenta, and green) is used. ) May be used. In addition, various filters are also effective.

  It is also effective for a solid-state imaging device without a color filter used for black and white or three-plate type.

  In the present embodiment, the solid-state imaging device is configured as a CCD (Charge Coupled Device) image sensor. However, the solid-state imaging device may be used as a MOS (Metal Oxide Semiconductor) image sensor. is there. Further, it can also be used in the case of a back-illuminated image sensor.

  In addition, by using the solid-state imaging device according to this embodiment for digital still cameras and digital movie cameras, a camera with high sensitivity, high S / N ratio, high color reproducibility, and reduced flare and ghosting is realized. can do.

  The above-described embodiment is merely an example, and the solid-state imaging device according to the present invention is not limited to the configuration shown in the above-described embodiment.

  The present invention has an effect that a sufficient reflection reduction effect can be obtained with an easy manufacturing process, and can be used in the fields of CCD sensors, MOS sensors, digital still cameras, and the like.

10, 100, 200, 300, 400, 500 Solid-state imaging device 11 Silicon substrate 12 Photo diode 13 Polysilicon electrode 14 Silicon oxide film 15, 104 Planarizing film 16 Micro lens 17 Antireflection film 18 Air or inert gas layer 101 Semiconductor Substrate 102 Light receiving portion 103 Transfer electrode 105G Green filter 105R Red filter 105B Blue filter 106 Microlens lower planarization film 107 Microlens 108, 508 Surface planarization layer 109, 209, 209G, 209R, 209B, 309, 409, 509 Low bending Surface layer 120, 320 Camera 121 Infrared cut filter 122, 322 Aperture 123, 323 Lens 210 Mask 211 Positive material

Claims (16)

A solid-state imaging device including a plurality of pixels,
A semiconductor substrate;
A plurality of light receiving portions formed for each of the pixels on the semiconductor substrate;
A plurality of microlenses arranged above each of the plurality of light receiving units to collect incident light on each of the plurality of light receiving units;
A planarization layer formed on the plurality of microlenses;
A solid-state imaging device comprising: a low refractive index layer formed on the planarization layer and having a refractive index lower than that of the planarization layer. The solid-state imaging device according to claim 1, wherein a product of the film thickness and the refractive index of the low refractive index layer is in a range of ¼ times the wavelength of visible light. The solid-state imaging device according to claim 1, wherein the low refractive index layer is made of an inorganic material. The solid-state imaging device according to claim 1, wherein a difference between a refractive index of the planarization layer and a refractive index of the low refractive index layer is 0.04 or more. The plurality of pixels belong to any of a plurality of types,
The solid-state imaging device according to claim 1, wherein a film thickness of the low refractive index layer is different for each type of the pixel. The plurality of pixels belong to any one of a red pixel, a green pixel, and a blue pixel,
The solid-state imaging device according to claim 5, wherein a film thickness of the low refractive index layer increases in the order of the blue pixel, the green pixel, and the red pixel. The plurality of pixels belong to any of a plurality of types,
The solid-state imaging device according to claim 1, wherein a material of the low refractive index layer is different for each type of the pixel. The plurality of pixels belong to any one of a red pixel, a green pixel, and a blue pixel,
The product of the film thickness and the refractive index of the low refractive index layer in the red pixel is 650/4 nm,
The product of the film thickness and refractive index of the low refractive index layer in the green pixel is 550/4 nm,
The solid-state imaging device according to claim 7, wherein a product of a film thickness and a refractive index of the low refractive index layer in the blue pixel is 440/4 nm. The plurality of pixels are two-dimensionally arranged in a predetermined region,
The predetermined region includes a central region including a center, and a peripheral region that is a region around the central region,
The solid-state imaging device according to claim 1, wherein a film thickness of the low refractive index layer is different between the central region and the peripheral region. The solid-state imaging device according to claim 9, wherein a film thickness of the low refractive index layer in the peripheral region is smaller than a film thickness of the low refractive index layer in the central region. The solid-state imaging device according to claim 1, wherein the planarization layer further includes a convex portion having a curvature along the microlens on an upper surface. The solid-state imaging device according to any one of claims 1 to 11, wherein the low refractive index layer has an uneven microstructure with a pitch equal to or less than a wavelength of visible light. A method of manufacturing a solid-state imaging device including a plurality of pixels,
Forming a plurality of light receiving portions for each pixel on a semiconductor substrate;
Forming a plurality of microlenses above the plurality of light receiving units so as to collect incident light on each of the plurality of light receiving units;
Forming a planarization layer on the plurality of microlenses;
Forming a low refractive index layer having a refractive index lower than that of the planarization layer on the planarization layer. The method for manufacturing a solid-state imaging device according to claim 13, wherein in the step of forming the low refractive index layer, the low refractive index layer is formed by applying a material having a refractive index lower than that of the planarizing layer. The solid-state imaging according to claim 13, wherein in the step of forming the low refractive index layer, the low refractive index layer is formed by depositing a material having a refractive index lower than that of the planarizing layer by a CVD (Chemical Vapor Deposition) method. Device manufacturing method. The step of forming the low refractive index layer includes:
Forming a material having a refractive index lower than that of the planarization layer and containing a photosensitive group on the planarization layer;
Forming the deposited material through a mask having a gray gradation;
The manufacturing method of the solid-state imaging device of any one of Claims 13-15 including developing the said exposed material, and forming the said low refractive index layer from which a film thickness differs for every said pixel. .

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