JP2005101266A - Solid state imaging device, method for manufacturing the same and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid state imaging device and a method for manufacturing the same wherein the occurrence of a color shading in the peripheral region of an imaging area is prevented to be suited to the reduction of an emission pupil distance. <P>SOLUTION: A micro-lens 10 and color filters 8R, 8G, 8B are provided on a semiconductor substrate 1 having a plurality of light receiving parts 2 so as to correspond to each of the light receiving parts 2, and the color filter 8R of a specific color has a refractive index different from the color filters 8G, 8B of the other colors. The light receiving parts 2 corresponding to the other colors and a refractive index adjusting layer 6 for adjusting a light-gathering state are provided between the micro-lens 10 corresponding to the color filter 8R of a specific color and the light receiving parts 2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device having a microlens in each of a plurality of photoelectric conversion elements formed on a semiconductor substrate, a manufacturing method thereof, and a camera.

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 a conventional solid-state imaging device, each of the photoelectric conversion elements is provided with an optical microlens in order to improve sensitivity while reducing the chip size of the solid-state imaging device and increasing the number of pixels.

In addition, in a digital still camera, a camera-equipped mobile phone, and the like, a shorter exit pupil distance has been developed with the miniaturization of the camera. Here, the exit pupil refers to a virtual image of the lens (or diaphragm) viewed from the light receiving surface side, and the exit pupil distance refers to the distance between the light receiving surface and the lens.
FIG. 7 is a cross-sectional view of a camera portion such as a mobile phone for explaining the exit pupil distance. In the figure, a lens 110 is attached to a frame 111 of a cellular phone, and a CCD image sensor 112 is provided as a solid-state imaging device inside the cellular phone. The exit pupil distance D is a distance between the lens 110 and the CCD image sensor 112. By shortening the exit pupil distance, light enters the central portion of the light receiving surface vertically, but only oblique light enters the peripheral portion of the light receiving surface instead of vertical light.

  FIG. 8 is a cross-sectional view showing the positional relationship between a photoelectric conversion element and a microlens in a conventional solid-state imaging device. The left side of the figure shows the central part of the imaging area where the photoelectric conversion elements are arranged two-dimensionally, and the right side of the figure shows the peripheral part of the imaging area. Moreover, the arrow of the figure has shown incident light. The solid-state imaging device includes a silicon semiconductor substrate 31, a photoelectric conversion element 32 formed in the silicon semiconductor substrate 31, a transfer electrode unit 34 including a transfer electrode and a light shielding film, and a photoelectric conversion element 32 and a transfer electrode unit 34. A flattening film 37 for flattening the surface, red, green, and blue color filters 8R, 8G, and 8B, a flattening film 39, and a microlens 40 are provided. As shown by the arrow in the figure, the incident light arrives almost vertically in the central portion of the imaging area, while the shorter the exit pupil distance, the more obliquely comes in the peripheral portion.

Further, in Patent Document 1, when the color filters 8R, 8G, and 8B have different film thicknesses, the planarizing film 39 on the color filters 8R, 8G, and 8B is individually formed with different thicknesses. As a result, the sum of the thickness of the planarizing film 39 individually formed corresponding to the color filter and the thickness of the color filter are made the same, and the upper surface of the planarizing film 39 is flattened. The planarizing film 39 is for adjusting the thickness, and the microlens 40 is formed thereon. Thereby, the apparent opening area of the photoelectric conversion element with respect to the microlens is increased to improve the sensitivity.
Japanese Patent Laid-Open No. 11-289073

However, according to the prior art, there is a problem that color shading (color shading) occurs in the peripheral portion of the imaging area as the exit pupil distance is shortened. That is, the white balance is lost in the peripheral portion of the image and the color is added.
Because the refractive index of the color filter is not the same for all colors, but varies depending on the color. Due to the difference in refractive index, the optical path from the color filter to the light receiving surface varies depending on the color, resulting in a condensing state on the light receiving surface. This is because a difference occurs.

For example, in the case of a color filter in which a pigment is dispersed in an acrylic resin, the blue and green color filters have a refractive index n = 1.55, whereas the red color filter has n = about 1.6. is there. This refractive index is determined according to the particle size of the pigment and the material of the resin, which differ depending on the color.
Due to the difference in refractive index, in the example of FIG. 8, the optical paths (arrow lines) of the blue and green passing lights passing through the color filters 8B and 8G and the optical paths (arrow lines) of the red passing light passing through the color filters 8R. And slightly different. In FIG. 8, the green and blue light passing through the color filter 8R is condensed at a position deeper than the light receiving surface, whereas the green and blue light passing through the color filter 8R is concentrated on the light receiving surface. This difference in the condensing position is not so much a problem in the central portion of the imaging area, but the condensing state differs depending on the color in the peripheral portion of the imaging area where only oblique light is incident when the exit pupil distance is short. In the example on the right side of FIG. 8, the red light collection rate is reduced.

In addition, with the recent miniaturization of cameras, it is necessary to shorten the exit pupil distance.
In view of the above problems, an object of the present invention is to provide a solid-state imaging device suitable for shortening an exit pupil distance by preventing occurrence of color unevenness (color shading) in a peripheral portion of an imaging area, and a manufacturing method thereof. .

  In order to solve the above-described problems, a solid-state imaging device according to the present invention is a solid-state imaging device having a microlens and a color filter corresponding to each light receiving unit on a semiconductor substrate having a plurality of light receiving units. The filter has a refractive index different from that of other color filters, and the solid-state imaging device has a light receiving unit corresponding to another color and a light collecting unit between the micro lens corresponding to the color filter of the specific color and the light receiving unit. A refractive index adjustment layer for adjusting the light state is provided.

  According to this configuration, since the difference in the light collection state in the light receiving unit due to the difference in refractive index due to the color of the color filter is eliminated by the refractive index adjustment layer, any color can be used even in the peripheral portion of the imaging area. Similarly, the light can be condensed on the light receiving unit. In other words, the light receiving part corresponding to any color can be in the most condensing state on the light receiving surface, not at a position deeper or shallower than the light receiving surface. As a result, it is possible to prevent the occurrence of color unevenness (color shading). Therefore, it is possible to easily shorten the exit pupil distance.

The specific color filter may have a higher refractive index than other color filters, and the refractive index adjustment layer may have a lower refractive index than the specific color filter.
Here, the refractive index adjusting layer may be formed in contact with the color filter of the specific color and may have a refractive index lower than that of a transparent film located at the same height in contact with another color filter.

According to this configuration, although the light passing through the color filter of a specific color having a high refractive index spreads compared to the color filters of other colors, the passing light is narrowed by the refractive index adjustment layer having a lower refractive index. , The same light collecting state as the light receiving units corresponding to other colors can be obtained.
The specific color filter may have a lower refractive index than other color filters, and the refractive index adjustment layer may have a higher refractive index than the specific color filter.

Here, the refractive index adjustment layer is formed in contact with the color filter of the specific color, and has a higher refractive index than a transparent film formed in contact with another color filter and at the same height as the refractive index adjustment layer. It is good also as a structure.
According to this configuration, the light passing through the color filter of a specific color having a low refractive index is narrowed compared to the color filters of other colors, but spreads by the refractive index adjustment layer having a higher refractive index. The same light collection state as the light receiving unit corresponding to the color can be obtained.

Here, the color filter may have a different film thickness depending on its color. According to this configuration, the spectral characteristics of the color filter can be adjusted by the film thickness, and the light collecting state can be adjusted in the same manner as described above.
The manufacturing method and the camera of the solid-state imaging device of the present invention are the same as described above.

  As described above, according to the solid-state imaging device of the present invention, any color can be condensed on the light receiving portion in the same manner even in the peripheral portion of the imaging area. In other words, the light receiving part corresponding to any color can be in the most condensing state on the light receiving surface, not at a position deeper or shallower than the light receiving surface. As a result, it is possible to prevent the occurrence of color unevenness (color shading). Therefore, it is possible to easily shorten the exit pupil distance.

<Configuration of solid-state imaging device>
FIG. 1 is a diagram illustrating a cross section of a solid-state imaging device according to an embodiment of the present invention. Arrows in the figure indicate incident light.
As shown in the figure, this solid-state imaging device includes a silicon semiconductor substrate 1, a photoelectric conversion element 2 formed in the silicon semiconductor substrate 1, a transfer electrode portion 4, a planarization film 5, and a refractive index adjustment layer. 6, color filters 8R, 8G, and 8B, a planarizing film 9, and a microlens 10, and by providing the refractive index adjustment layer 6, a photoelectric conversion element corresponding to the red color filter 8R as a specific color 2 and the photoelectric conversion elements 2 corresponding to other colors are configured to match the light collecting state.

The color filters 8R, 8G, and 8B are formed of a material in which a pigment is dispersed in an acrylic resin. The respective refractive indexes are determined by the material of the resin and the particle diameter of the pigment, and in this embodiment, n = 1.6, 1.55, and 1.55 in the same order.
The photoelectric conversion element 2 is formed, for example, as an n-type impurity implantation layer in the p-type silicon semiconductor substrate 1. The transfer electrode portion 4 includes two layers of transfer electrodes and a light shielding film covering the upper and side surfaces.

The flattening film 5 is formed of, for example, an acrylic resin (refractive index n = 1.5), and is a transparent film that flattens the top of the photoelectric conversion element 2 and the transfer electrode unit 4 corresponding to the color filters 8B and 8G. is there. The planarizing film 5 is formed with the refractive index adjustment layer 6 so as to be buried in the upper part of the photoelectric conversion element 2 corresponding to the color filter 8R.
The refractive index adjustment layer 6 is formed of, for example, an acrylic resin (refractive index n = 1.45). The refractive index is set lower than that of the color filter 8R of a specific color and lower than that of the planarizing film 5. In the case of an acrylic resin, the refractive indexes of the planarizing film 5 and the refractive index adjusting layer 6 are reduced by mixing impurities such as fluorine, and can be set to desired values depending on their concentrations. As shown by the arrow in FIG. 1, the light passing through the color filter 8R having a high refractive index spreads compared to the color filters 8B and 8G of other colors. However, since the light passing through the refractive index adjustment layer 6 is narrowed, it is possible to obtain a light condensing state similar to that of the photoelectric conversion elements 2 corresponding to other colors. That is, in any color filter, the passing light can be condensed on the light receiving surface of the photoelectric conversion element 2. In other words, it is possible to eliminate focusing on a position deeper or shallower than the light receiving surface due to a difference in refractive index of the color filter.

As described above, the solid-state imaging device according to the embodiment of the present invention can prevent uneven color in the peripheral portion because there is no difference in the light collection rate depending on the color in the peripheral portion of the imaging area.
In the solid-state imaging device of FIG. 1, the case where the refractive index of the red color filter 8R as the specific color is higher than that of the color filters 8B and 8G of the other colors has been described. When it is lower than the color filters of other colors, the refractive index adjustment layer 6 may have a higher refractive index than the color filter of the specific color and a higher refractive index than the planarizing film 5. In that case, the light passing through the color filter of a specific color having a low refractive index is narrower than the color filters 8B and 8G of other colors. Since the passing light is expanded by the refractive index adjustment layer 6, it is possible to obtain a light condensing state similar to that of the photoelectric conversion element 2 corresponding to another color.

<Method for Manufacturing Solid-State Imaging Device>
2A to 2D are views showing cross sections of the method of manufacturing the solid-state imaging device according to the present embodiment in the order of the manufacturing steps. The manufacturing process will be described in the following (11) to (14).
(11) As shown in FIG. 2A, the material of the planarizing film 5 (for example, the refractive index n = 1.5) is applied to the silicon semiconductor substrate 1 on which the photoelectric conversion element 2 and the transfer electrode portion 4 are formed. (Acrylic resin) is applied flatly on the photoelectric conversion element 2 and the transfer electrode part 4, and then exposed and developed, so that the photoelectric conversion element 2 corresponding to the specific color red is transferred onto the transfer electrode part 4. Remove to height.
(12) As shown in FIG. 2B, the refractive index adjusting layer 6 is formed on the photoelectric conversion element 2 corresponding to the depressed portion of the flattening film 5, that is, the specific color red. This formation is performed on the photoelectric conversion element 2 corresponding to red by applying, exposing, and developing a material for the refractive index adjusting layer 6 (for example, an acrylic resin having a refractive index n = 1.45).
(13) As shown in FIG. 2C, the color filters 8R, 8G, and 8B are sequentially formed. These color filters are formed, for example, by applying, exposing, and developing a filter material in which a pigment is dispersed. For example, the refractive indexes of the color filters 8R, 8G, and 8B are 1.6, 1.55, and 1.55, respectively.
(14) As shown in FIG. 2D, the planarizing film 9 and the microlens 10 are formed on the color filters 8R, 8G, and 8B.

  As described above, according to the method for manufacturing the solid-state imaging device in the embodiment of the present invention, the solid-state imaging device having the refractive index adjustment layer 6 that relaxes the difference in the refractive index of the color filter that differs depending on the color is manufactured. As a result, since the light passing through any color filter is condensed on the light receiving surface in the central part and the peripheral part of the imaging area, there is no difference in the light collection rate depending on the color, and uneven color in the peripheral part can be prevented. it can.

<Modification>
The solid-state imaging device of the present invention is not limited to the configuration of the above embodiment, and various modifications can be made. Such modifications will be described below.
(1) FIG. 3 is a diagram showing a cross section of a solid-state imaging device according to a first modification of the embodiment of the present invention. The figure is different from the solid-state imaging device of FIG. 1 in that the refractive index adjustment layer 6 is formed not on the specific color filter but on the upper side.
In FIG. 3, when the refractive index of the color filter of a specific color is higher than the color filters of other colors, the refractive index adjustment layer 6 has a lower refractive index than the color filter of the specific color and is lower than the planarizing film 9. Has a refractive index. On the contrary, when the refractive index of the color filter of a specific color is lower than the color filters of other colors, the refractive index adjustment layer 6 has a higher refractive index than the color filter of the specific color and is higher than the planarizing film 9. Has a refractive index. Further, the manufacturing method of the solid-state imaging device shown in the figure may be modified so that the refractive index adjustment layer 6 is formed in (14) instead of (11).
According to this configuration, the same effect as that of the solid-state imaging device of FIG. 1 can be obtained.
(2) FIG. 4 is a diagram showing a cross section of the solid-state imaging device according to the second modification of the embodiment of the present invention. This figure is different from the solid-state imaging device of FIG. 1 in that the thickness of the color filters 8R, 8G, and 8B is different. The relationship among the refractive indexes of the color filters of specific colors, the color filters of other colors, and the planarizing film 5 may be the same as in FIG.
According to this configuration, in addition to the same effect as that of the solid-state imaging device of FIG. 1, the spectral characteristics can be easily adjusted by the thickness of the color filter.

(3) FIG. 5 is a diagram showing a cross section of a solid-state imaging device according to a third modification of the embodiment of the present invention. The figure is different from the solid-state imaging device of FIG. 4 in that the color filter is flattened instead of being flattened.
Also with this configuration, the same effect as that of the solid-state imaging device of FIG. 4 can be obtained.
(4) FIG. 6 is a diagram showing a cross section of a solid-state imaging device according to a fourth modification of the embodiment of the present invention. This figure is different from the solid-state imaging device of FIG. 4 in that the refractive index adjustment layer 6 is formed not on the specific color filter but on the upper side.
Also with this configuration, the same effect as that of the solid-state imaging device of FIG. 4 can be obtained.
(5) In the above embodiment, the example in which the refractive index of the color filter 8R is different from the color filters of other colors has been shown. However, the refractive index of any one of the color filters 8G and 8B is different from the color filter 8R. The same is true.
(6) Although the refractive index adjustment layer 6 is provided for the color filter 8R in the above embodiment, the refractive index adjustment layer 6 may be provided in the color filters 8G and 8G instead of the color filter 8R. Also in that case, the light passing through the color filter of any color can be similarly condensed on the light receiving surface of the photoelectric conversion element 2.
(7) In the above-described embodiment, the case where two refractive indexes of the three color filters are the same and only one is different has been described. However, the three color filters may be different from each other. In that case, the refractive index adjustment layer may be provided in the color filters of two colors. The refractive index of the refractive index adjusting layer may be determined so as to be condensed on the light receiving surface of the photoelectric conversion element according to the refractive index of the corresponding color.

  The present invention is suitable for a solid-state imaging device having a microlens and a color filter in each of a plurality of light-receiving elements formed on a semiconductor substrate, a manufacturing method thereof, and a camera having the solid-state imaging device. It is suitable for MOS image sensors, digital still cameras, mobile phones with cameras, cameras built into notebook computers, camera units connected to information processing equipment, and the like.

It is a figure which shows the cross section of the solid-state imaging device in embodiment of this invention. (A)-(d) It is a figure which shows the cross section in order of a manufacturing process of the manufacturing method of a solid-state imaging device. It is a figure which shows the cross section of the solid-state imaging device in a 1st modification. It is a figure which shows the cross section of the solid-state imaging device in a 2nd modification. It is a figure which shows the cross section of the solid-state imaging device in a 3rd modification. It is a figure which shows the cross section of the solid-state imaging device in a 4th modification. It is sectional drawing of camera parts, such as a mobile telephone, for demonstrating exit pupil distance. It is sectional drawing which shows the positional relationship of the photoelectric conversion element and microlens in the conventional solid-state imaging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon semiconductor substrate 2 Photoelectric conversion element 4 Transfer electrode part 5 Flattening film 6 Refractive index adjustment layer 8 Color filter 9 Flattening film 10 Micro lens

Claims (8)

A solid-state imaging device having a microlens and a color filter corresponding to each light receiving part on a semiconductor substrate having a plurality of light receiving parts,
A color filter of a specific color has a refractive index different from that of other color filters,
The solid-state imaging device includes a refractive index adjustment layer for adjusting a light collecting state with a light receiving unit corresponding to another color between a micro lens corresponding to the color filter of the specific color and the light receiving unit. A solid-state imaging device. The specific color filter has a higher refractive index than other color filters,
The solid-state imaging device according to claim 1, wherein the refractive index adjustment layer has a lower refractive index than the color filter of the specific color. The refractive index adjustment layer is formed in contact with the color filter of the specific color and has a lower refractive index than a transparent film located at the same height in contact with another color filter. Solid-state imaging device. The specific color filter has a lower refractive index than other color filters,
The solid-state imaging device according to claim 1, wherein the refractive index adjustment layer has a higher refractive index than a color filter of a specific color. The refractive index adjustment layer is formed in contact with the color filter of the specific color and has a higher refractive index than a transparent film formed in contact with another color filter and at the same height as the refractive index adjustment layer. The solid-state imaging device according to claim 4. The solid-state imaging device according to claim 1, wherein the color filter has a different film thickness depending on its color. A method of manufacturing a solid-state imaging device having a microlens and a color filter corresponding to each light receiving portion on a semiconductor substrate having a plurality of light receiving portions,
Forming a refractive index adjusting layer for adjusting a light collecting state with a light receiving unit corresponding to another color above a light receiving unit corresponding to a color filter of a specific color before forming a microlens;
Forming a protective layer above a light receiving portion corresponding to a color filter other than a specific color before forming a microlens. A camera comprising the solid-state imaging device according to claim 1.

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