JP2008021753A - Solid-state imaging element, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce shading phenomenon generated in the periphery of a solid-state imaging element. <P>SOLUTION: The solid state imaging element is provided with a plurality of photoelectric conversion elements arranged on a substrate, a transparent film which covers the surface of the substrate comprising the plurality of photoelectric conversion elements, and a plurality of color filters formed on the transparent film so as to be corresponding to the plurality of photoelectric conversion elements respectively. The plurality of color filters are respectively formed so as to have surfaces with a uniform thickness in a direction orthogonal to incident light. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid-state imaging device and a manufacturing method thereof, and more particularly, to a color filter and a microlens included in the solid-state imaging device and a method of manufacturing each.

  FIG. 5A shows a configuration of a conventional color solid-state image sensor (hereinafter simply referred to as a solid-state image sensor). A plurality of photoelectric conversion elements 102 are formed on a silicon substrate 101, an insulating film (not shown) is formed to cover the surface of the silicon substrate 101 including the photoelectric conversion elements 102, and an electrode 103 and a light shielding film 104 are flattened thereon. A transparent film 105 as a conversion layer is formed, a color filter 106 is formed on the transparent film 105, and a microlens 107 is further formed on the transparent film 105. The photoelectric conversion element 102 collects color components.

  It is desirable that the solid-state imaging device has the same output regardless of the position of the light receiving elements (that is, the photoelectric conversion elements 102) arranged on the light receiving surface when the subject to be photographed has uniform brightness. However, as shown in the figure, the principal ray incident from the light source through the photographing optical system is incident perpendicularly to the formation surface of the microlens 107 and the color filter 106 at the center of the solid-state image sensor, while the peripheral The incident light is inclined. Therefore, as shown in FIG. 5B, when the path length through which the principal ray passes through the central color filter 106 is represented by r, the path length through which the peripheral color filter 106 passes is r ′ (= r / cos θ). The path length r ′ at the peripheral portion is larger than the path length r at the center of the solid-state imaging device.

The absorption coefficient and transmission spectrum of the color filter 106 are shown in FIGS. Transmission spectroscopy is an amount (transmittance) representing the degree of light passing through a substance and is defined as shown in the following equation.
T = exp (−α · d)
Here, T is the transmittance, α is the absorption coefficient, and d is the film thickness of the substance. Since the absorption coefficient is a value specific to the substance, the transmittance decreases as the film thickness increases.

  The path lengths r and r 'correspond to the film thickness. Since the path length r 'in the peripheral portion is larger than the path length r in the central portion of the solid-state imaging device, the transmittance of light passing through the color filter is smaller in the peripheral portion. The amount of light received throughout the solid-state image sensor is not uniform, and the amount of light received by the peripheral photoelectric conversion element 102 is smaller than that of the photoelectric conversion element 102 at the center, and the output sensitivity of the image sensor at the periphery is small. As a result, the level of the image signal output from the solid-state imaging device is low in the peripheral portion of the image, and a characteristic defect called shading occurs in which the peripheral portion of the finally obtained image is darker than the central portion.

  Conventionally, various shading countermeasures have been proposed. For example, in Patent Document 1, by setting the pitch of the light collecting portions arranged on each of the plurality of light receiving portions on the light receiving surface to be smaller than the pitch of the light receiving portions, specifically, in the peripheral portion of the light receiving surface. By shifting the color filter and the micro lens toward the center of the light receiving surface, the sensitivity characteristics in the peripheral part are improved. In other words, the principal light beam that is inclined and incident on the condensing part in the peripheral part is condensed on the central part of the light receiving part, so that the invalid light that is not condensed on the light receiving part is eliminated and the shading is corrected.

  In Patent Document 2, the diameter of the microlens disposed on each of the plurality of light receiving portions on the light receiving surface is gradually increased from the central portion of the light receiving surface toward the peripheral portion, thereby receiving light at the light receiving portion in the peripheral portion. Reduced amount is prevented.

In Patent Document 3, for color filters provided on a plurality of light receiving portions of a light receiving surface, the transmittance of incident light is made different by reducing the film thickness from the central portion to the peripheral portion of the light receiving surface. The amount of received light is increased.
JP-A-1-213079 JP-A-11-150254 JP 2004-71632 A

  However, the technique of Patent Document 1 has a problem that it is possible to prevent deterioration of sensitivity characteristics due to light collection by peripheral microlenses, but it is impossible to take measures against different path lengths.

  In the technique of Patent Document 2, the diameter of the microlens disposed on each of the plurality of light receiving portions is gradually increased from the central portion of the light receiving surface toward the peripheral portion. Thus, the output sensitivity at the center is relatively lowered. For this reason, the output sensitivity at the center is lower than the level in the conventional structure shown in FIG.

  In the technique of Patent Document 3, the transmittance and light amount in the peripheral part are increased by decreasing the film thickness of the color filter from the central part to the peripheral part of the light receiving surface. For an optical system with a large incident angle, the sensitivity characteristic does not improve even if the transmittance of the color filter is changed in the peripheral portion. As shown in FIG. 7, when the incident angle to the light receiving surface (the surface on which the microlens and the color filter are formed) becomes ± 20 ° or more, the sensitivity characteristic of the image sensor becomes almost zero.

  In view of the above problems, an object of the present invention is to provide a solid-state imaging device and a method for manufacturing the same capable of reducing a decrease in sensitivity characteristics in a peripheral portion while ensuring sensitivity characteristics in a central portion in the same manner as in the past. .

  In order to solve the above problems, a solid-state imaging device according to the present invention includes a plurality of photoelectric conversion elements arranged on a substrate, a transparent film covering a surface of the substrate including the plurality of photoelectric conversion elements, and the plurality of the plurality of photoelectric conversion elements. A plurality of color filters formed on the transparent film corresponding to each of the photoelectric conversion elements, and each of the plurality of color filters has a surface in a direction perpendicular to the incident light and has a uniform thickness. It is formed.

The transparent film at a position where each of the plurality of color filters is formed has a surface in a direction orthogonal to incident light.
A microlens that collects incident light on each of the plurality of photoelectric conversion elements is formed on each of the plurality of color filters. The microlens has an optical axis symmetric rotation type with respect to incident light.

  The solid-state imaging device manufacturing method of the present invention includes a step (a) of forming a plurality of photoelectric conversion elements on a substrate and a step of forming a transparent film covering the surface of the substrate including the plurality of photoelectric conversion elements (b) ), A step (c) of forming a plurality of color filters corresponding to each of the plurality of photoelectric conversion elements on the transparent film, and a microlens for condensing incident light on each of the plurality of photoelectric conversion elements A step (d) of forming a solid-state image sensor on each of the plurality of color filters, wherein the transparent film is formed on each of the plurality of photoelectric conversion elements in the step (b). Each corresponding predetermined portion is formed so as to have a surface in a direction orthogonal to the incident light, and in the step (c), each of the plurality of color filters is uniformly formed on the surface of the predetermined portion of the transparent film. In the step (d), each of the plurality of microlenses is formed on each of the plurality of color filters having a uniform thickness so as to have an optical axis symmetric rotational shape with respect to incident light. It is characterized by that.

  At least one of the steps (b), (c), and (d) includes a step of forming a film made of a photosensitive material, and the film is formed for each predetermined portion corresponding to each of the plurality of photoelectric conversion elements. The method includes a step of exposing through a gray scale mask designed for an exposure amount of gray gradation, and a step of developing the exposed film to leave a film thickness corresponding to the exposure amount.

  In the solid-state imaging device of the present invention, the plurality of color filters corresponding to each of the plurality of photoelectric conversion devices have a surface in a direction orthogonal to the incident light and are formed with a uniform thickness, so that the photoelectric conversion device receives light. The same sensitivity characteristic can be ensured regardless of whether it is in the central part or the peripheral part of the surface, and the shading phenomenon can be reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing the configuration of a solid-state imaging device according to an embodiment of the present invention. In a color solid-state imaging device (hereinafter, referred to as a solid-state imaging device) 100, a plurality of photoelectric conversion elements 102 that convert incident light into charges are formed on a silicon substrate 101, and the surface of the silicon substrate 101 including the photoelectric conversion elements 102 is formed. An insulating film (not shown) is formed so as to cover, and electrodes 103 such as polycrystalline silicon that transfer charges generated by the photoelectric conversion elements 102 are formed at positions between the photoelectric conversion elements 102 on the silicon substrate 101. A light shielding film 104 that covers the electrode 103 and prevents light from entering the electrode 103 is formed, and a transparent film 105 is formed on the photoelectric conversion element 102 and the light shielding film 104. A color filter 106 is formed on the transparent film 105, and a microlens 107 is formed thereon.

  The color filter 106 includes a red color pattern 106R (hereinafter referred to as a color pattern 106R), a green color pattern 106G (hereinafter referred to as a color pattern 106G), and a blue color pattern 106B (hereinafter referred to as a color pattern 106B) 106B sequentially in the horizontal direction. One of the color patterns 106R, 106G, and 106B corresponds to each photoelectric conversion element 102. Microlenses 107 are formed on the color patterns 106R, 106G, and 106B. Each of the photoelectric conversion elements 102 has a structure in which one color pattern and one microlens 107 are provided. Each of the color patterns 106R, 106G, and 106B corresponds to the color filter referred to in claim 1.

  The solid-state imaging device 100 is different from the conventional one in that the transparent film 105 on the photoelectric conversion device 102 has an upper surface in a direction perpendicular to the principal ray of incident light and has a uniform thickness. It is a point that is formed to have. For this reason, the upper surface of the transparent film 105 on the photoelectric conversion element 102 in the peripheral portion is an inclined inclined surface, and any of the color patterns 106R, 106G, and 106B has a uniform thickness on each inclined surface. Accordingly, an inclined surface having an upper surface is formed in the same manner as the inclined surface. The microlens 107 is on the inclined surfaces of the color patterns 106R, 106G, and 106B, and has an optical axis symmetric rotation type with respect to the principal ray of incident light.

  In the solid-state imaging device 100 described above, light incident through the photographing optical system passes through the microlens 107, the color filter 106, the transparent film 105, and the insulating film (not shown) in order and enters the photoelectric conversion element 102. . At that time, incident light that has entered one microlens 107 subsequently passes through one of the color patterns 106R, 106G, and 106B below it to become light of a specific range of wavelengths, and the corresponding one. The light is condensed on one photoelectric conversion element 102.

  At that time, incident light to the central portion of the solid-state imaging device 100 is incident on the microlens 107 in a direction perpendicular to the photoelectric conversion element 102, while incident light to the peripheral portion is incident on the photoelectric conversion element 102. As described above, the upper surface of the transparent film 105 and the upper surfaces of the color patterns 106R, 106G, and 106B with respect to the incident light are incident on the microlens 107 in the inclined direction. In addition, since the microlens 107 is an optical axis symmetric rotation type with respect to the principal ray of the incident light, the individual photoelectric conversion elements 102 are condensed with high accuracy. The output sensitivity of the photoelectric conversion element 102 is improved, and the shading phenomenon can be suppressed.

  That is, since the path length r through which the principal ray passes through the color filter 106 is equal and the transmittance is equal between the central portion and the peripheral portion of the solid-state imaging device 100, the output sensitivity in the photoelectric conversion element 102 in the peripheral portion is conventional. Better than. Even in an optical system having a large incident angle to the peripheral portion, the microlens 107 in the peripheral portion is focused on the photoelectric conversion element 102 with high accuracy. Since the transparent film 105 and the color patterns 106R, 106G, and 106B have the same shape as the conventional one (see FIG. 5), the output sensitivity is not lowered at the center of the solid-state imaging device 100. This is a particularly preferable characteristic when the solid-state imaging device 100 is downsized and has a large number of pixels.

The manufacturing method of said solid-state image sensor 100 is demonstrated with reference to FIGS.
First, as shown in FIG. 2A, photoelectric conversion elements 102 are arranged and formed on a silicon substrate 101, and an insulating film (not shown) is formed so as to cover the surface of the silicon substrate 101 including each photoelectric conversion element 102. The electrode 103 is formed of polycrystalline silicon at a position between the photoelectric conversion elements 102 on the insulating film, and the light shielding film 104 covering each electrode 103 is formed. Any of these may be performed by a known method. Next, a transparent film 105 is formed using a photosensitive material by a method such as spin coating to cover the photoelectric conversion element 102, the light shielding film 104, and the like. The insulating film is a SiON film, the light shielding film is a tungsten film, the transparent film is an acrylic transparent resin, and the like.

  Next, as shown in FIG. 2B, the transparent film 105 is exposed using a gray scale mask 201. The gray scale mask 201 is designed so that a desired gray gradation is designed so that the exposure amount gradually changes, and the transparent film 105 has a gray gradation for each predetermined portion corresponding to each of the photoelectric conversion elements 102. Exposure is performed with a corresponding exposure amount. In FIG. 2B and subsequent figures, only the peripheral part of the solid-state imaging device is shown (see FIG. 1 for the central part).

  When the transparent film 105 after exposure is developed, the transparent film 105 remains with a film thickness corresponding to the exposure amount by the gray gradation of the gray scale mask 201, and as shown in FIG. Then, the upper surface of the transparent film 105 is inclined, and the inclination angle becomes larger as it approaches the outer end of the solid-state imaging device 100. The gray gradation of the gray scale mask 201 and the positive type / negative type of the photosensitive material are determined for such a desired shape.

  Next, as shown in FIG. 2D, a method such as spin coating is applied to a film 106 ′ made of a pigment-containing photosensitive material that contains a plurality of pigments on the transparent film 105 and has a desired spectral characteristic, for example, green. As shown in FIG. 2E, the film 106 ′ after exposure is exposed using an additional gray scale mask 202 (G mask pattern) with an exposure amount corresponding to the predetermined gray gradation. develop. FIG. 2F shows a color pattern 106G formed by development. The film thickness remains in accordance with the exposure amount in gray gradation, and has an upper surface that is inclined in the same manner as the upper surface of the transparent film 105 and a uniform film thickness.

  Similarly, as shown in FIGS. 3A to 3C, a color pattern 106B is formed using a gray scale mask 203 (B mask pattern), and then as shown in FIGS. 3D to 3F. In addition, the color pattern 106R is formed using the gray scale mask 204 (R mask pattern). Thereby, the color filter 106 including the color patterns 106G, 106R, and 106B is completed.

  Thereafter, as shown in FIG. 4A, a film 107 ′ of a photosensitive material made of, for example, an alkali-soluble positive phenolic resin is formed on the color filter 106 by a method such as spin coating. As shown in b), exposure is performed using a separate gray scale mask 205. The gray scale mask 205 used at this time has a gray gradation designed so that a desired curvature is formed. When the exposed film 107 ′ is developed, as shown in FIG. 4C, an optical axis symmetric rotation type microlens 107 is formed.

  As described above, each of the transparent film 105, the color filter 106, and the microlens 107 is formed with a photosensitive material and then exposed using a grayscale mask, and the grayscale mask is used in accordance with the gray gradation of the grayscale mask. It can be formed with a shape such as an inclination or unevenness.

  In the above embodiment, the case of forming a primary color filter composed of three color patterns of red, green and blue has been described. However, the present invention is not limited to this, and for example, a complementary color filter is formed. The case can be similarly implemented. The number of colors in the color pattern is not particularly limited. A part or all of the color pattern may have a laminated structure including two or more color patterns. There are no particular limitations on the types of solid-state imaging devices such as CMOS and CCD types.

  Since the solid-state imaging device and the manufacturing method thereof according to the present invention can suppress the shading phenomenon, it is particularly useful for downsizing and increasing the number of pixels.

Sectional drawing which shows the structure of the solid-state image sensor of one Embodiment of this invention typically Sectional drawing explaining the manufacturing process of the solid-state image sensor of FIG. Sectional drawing explaining the manufacturing process of the solid-state image sensor of FIG. 1 following FIG. Sectional drawing explaining the manufacturing process of the solid-state image sensor of FIG. 1 following FIG. Sectional drawing explaining the structure of the conventional solid-state image sensor, and the mechanism of the shading phenomenon Correlation diagrams showing the relationship between wavelength and absorption coefficient and the relationship between wavelength and transmission spectroscopy, which are conventionally known for solid-state imaging devices Correlation diagram showing the relationship between the incident angle and the sensitivity characteristic conventionally known for solid-state image sensors

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Silicon substrate 102 Photoelectric conversion element 103 Electrode 104 Light shielding film 105 Transparent film 106 Color filter 106R Red color pattern 106G Green color pattern 106B Blue color pattern 107 Microlens 201 Gray scale mask for transparent film 202 Gray scale mask 203 Gray scale mask 204 Grayscale mask 205 Grayscale mask for micro lens

Claims (6)

A plurality of photoelectric conversion elements arranged on a substrate;
A transparent film covering the surface of the substrate including the plurality of photoelectric conversion elements;
A plurality of color filters formed on the transparent film corresponding to each of the plurality of photoelectric conversion elements;
Each of the plurality of color filters has a surface in a direction perpendicular to incident light and is formed with a uniform thickness.   The solid-state imaging device according to claim 1, wherein the transparent film at a position where each of the plurality of color filters is formed has a surface in a direction orthogonal to incident light.   3. The solid-state imaging device according to claim 1, wherein a microlens that collects incident light on each of the plurality of photoelectric conversion elements is formed on each of the plurality of color filters.   The solid-state imaging device according to claim 3, wherein the microlens has an optical axis symmetric rotational shape with respect to incident light. A step (a) of forming a plurality of photoelectric conversion elements on a substrate;
Forming a transparent film covering the surface of the substrate including the plurality of photoelectric conversion elements (b);
A step (c) of forming a plurality of color filters corresponding to each of the plurality of photoelectric conversion elements on the transparent film;
A step (d) of forming a microlens for condensing incident light on each of the plurality of photoelectric conversion elements on each of the plurality of color filters,
In the step (b), the transparent film is formed so as to have a surface in a direction orthogonal to incident light at each predetermined location corresponding to each of the plurality of photoelectric conversion elements,
In the step (c), each of the plurality of color filters is formed with a uniform thickness on the surface of the predetermined portion of the transparent film,
In the step (d), a solid-state imaging device in which each of the plurality of microlenses is formed on each of the plurality of color filters having a uniform thickness so as to have a rotationally symmetric shape with respect to incident light. Method. At least one of the steps (b), (c) and (d) includes:
Forming a film of photosensitive material;
Exposing the film through a gray scale mask designed for an exposure amount of gray gradation for each predetermined location corresponding to each of the plurality of photoelectric conversion elements;
The method of manufacturing a solid-state imaging device according to claim 5, further comprising: developing the exposed film to leave a film thickness corresponding to an exposure amount.

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