JP5468353B2 - Solid-state image sensor - Google Patents

Description

  The present invention relates to a solid-state imaging device.

  As one of the performances of a solid-state imaging device (image sensor), there is a problem that spectral characteristics, which are sensitivity characteristics for each wavelength of incident light, are problematic. When the relationship between the wavelength of incident light and the optical response output is expressed, it is ideal that the fluctuation of the optical response output is gentle with respect to the change in wavelength, while the optical response output with respect to the change in wavelength is ideal. Spectral characteristics that fluctuate in a wave shape may be exhibited. As the cause, interference between the light directly incident on the photoelectric conversion element and the light reflected at the interface of the protective layer provided on the semiconductor substrate can be mentioned. In order to reduce such fluctuations in spectral characteristics, it is effective to suppress light interference. For example, Patent Document 1 discloses a configuration including an uneven shape formed on the surface of a silicon oxide film that is a protective layer. By providing the concavo-convex shape, the reflected light at the interface of the protective layer is dispersed, and the multiple reflection of light within the protective layer is reduced. Thereby, interference with the light directly incident on the photoelectric conversion element and the light reflected at the interface of the protective layer is suppressed.

  In general, a solid-state imaging device is provided with a pattern made of aluminum (hereinafter referred to as “aluminum wiring” as appropriate) as a light-shielding portion for reducing light leakage to adjacent pixels. Depending on the form in which the concavo-convex shape is formed on the surface of the protective layer, good spectral characteristics can be obtained, while the aluminum wiring formed inside the protective layer may be easily exposed to the outside. The exposure of the aluminum wiring to the outside reduces the reliability of the solid-state imaging device due to corrosion of the aluminum wiring or the like.

JP-A-6-125068

  An object of the present invention is to provide a solid-state imaging device having good spectral characteristics and high reliability.

  According to one aspect of the present invention, a photoelectric conversion element that is provided in a light receiving region of a semiconductor substrate and generates a charge according to an incident light amount, a light shielding unit that is formed around the light receiving region and shields light, and A protective layer that is provided on a semiconductor substrate and protects the photoelectric conversion element and the light-shielding portion, and the surface of the protective layer opposite to the semiconductor substrate side is irradiated with the photoelectric conversion element A solid-state imaging device is provided in which a step portion having a height difference in a direction perpendicular to the surface is formed, and the step portion is provided in the light receiving region.

  According to the present invention, there is an effect that high reliability can be obtained with good spectral characteristics.

FIG. 3 is a schematic diagram illustrating a planar configuration and a cross-sectional configuration of the solid-state imaging element according to the first embodiment. The figure explaining the improvement of the spectral characteristics by providing a level | step-difference part. The graph showing the relationship between the wavelength of the light which injects into a photoelectric conversion element, and the optical response output of a photoelectric conversion element. The schematic diagram which shows the plane structure and cross-sectional structure of the solid-state image sensor which concern on 2nd Embodiment. The schematic diagram which shows the planar structure and cross-sectional structure of the solid-state image sensor which concern on 3rd Embodiment. The schematic diagram which shows the planar structure and cross-sectional structure of the solid-state image sensor which concern on 4th Embodiment. The graph showing the relationship between the wavelength of the light which injects into a photoelectric conversion element, and the optical response output of a photoelectric conversion element. The schematic diagram which shows the planar structure and cross-sectional structure of the solid-state image sensor which concern on 5th Embodiment. The schematic diagram which shows the planar structure and cross-sectional structure of the solid-state image sensor which concerns on 6th Embodiment. The figure which shows the GG cross-section structure of Fig.9 (a). The graph showing the relationship between the wavelength of the light which injects into a photoelectric conversion element, and the optical response output of a photoelectric conversion element. The schematic diagram which shows the planar structure of the solid-state image sensor which concerns on a comparative example. The graph showing the spectral characteristics in the case of the comparative example shown in FIG.

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

(First embodiment)
FIG. 1 is a schematic diagram showing a planar configuration and a cross-sectional configuration of a solid-state imaging device 10 according to the first embodiment of the present invention. The solid-state image sensor 10 is a CCD area image sensor, for example, and includes a plurality of photoelectric conversion elements 5 arranged in parallel in a two-dimensional direction. FIG. 1A shows a planar configuration of one photoelectric conversion element 5 in the solid-state imaging element 10 and its peripheral portion. (B) shows the AA cross-section structure of (a). Here, the surface parallel to the irradiation surface on which light is incident in the photoelectric conversion element 5 is defined as an XY plane. It is assumed that the X direction and the Y direction are perpendicular to each other. The Z direction is a direction perpendicular to the XY plane. In the solid-state imaging element 10, the plurality of photoelectric conversion elements 5 are arranged in an array in the XY direction.

  The photoelectric conversion element 5 is configured by a part of an impurity diffusion region formed on the surface of the semiconductor substrate 1. The photoelectric conversion element 5 generates a charge corresponding to the amount of incident light. The aluminum wiring 2 is formed around the photoelectric conversion element 5 on the semiconductor substrate 1. The aluminum wiring 2 functions as a shielding part that shields light. The protective layer 6 provided on the semiconductor substrate 1 protects the photoelectric conversion element 5 and the aluminum wiring 2. The protective layer 6 is made of, for example, a silicon oxide film or a silicon nitride film.

  A light receiving region 3 indicated by a broken line in the drawing is a region of the region on the semiconductor substrate 1 whose periphery is shielded by the aluminum wiring 2, and the incident light can be effectively photoelectrically converted by the photoelectric conversion element 5. Suppose there is. In the case of this embodiment, the light receiving region 3 substantially coincides with the irradiation surface region of the photoelectric conversion element 5 and constitutes, for example, a pixel. In the planar configuration shown in (a), the light receiving region 3 and the photoelectric conversion element 5 have a rectangular shape whose longitudinal direction is the Y direction. The aluminum wiring 2 reduces light leakage to adjacent pixels by shielding light between the light receiving regions 3. The aluminum wiring 2 is not limited to the one provided only for light shielding, but may be used for charge transfer.

  The step portion 4 is provided on the surface of the protective layer 6 opposite to the semiconductor substrate 1 side. The step portion 4 has a concave shape with a difference in height in the Z direction, and has a spherical or aspherical curved surface with curvature in the X direction (first direction) and the Y direction (second direction). Prepare. The step portion 4 is formed by, for example, isotropic etching using a resist pattern as a mask.

  In the planar configuration shown in FIG. 2A, two stepped portions 4 are formed in one light receiving region 3. The two step portions 4 are arranged in the Y direction with a space therebetween. The step portion 4 is positioned at the approximate center of the light receiving region 3 in the X direction, and is positioned between the end portion and the center of the light receiving region 3 in the Y direction. The step portion 4 is arranged in the light receiving region 3 on the center position side of the boundary with the aluminum wiring 2.

  On the XY plane, the photoelectric conversion element 5 has, for example, a rectangular shape with a length m in the Y direction of 20 μm and a length in the X direction of n = 3.2 μm. Further, the stepped portion 4 has, for example, a shape close to a rectangle or a shape close to an ellipse having a length p = 2.0 μm in the Y direction and a length q = 1.0 μm in the X direction. In the entire solid-state imaging device 10, the stepped portion 4 is formed in a dot shape of 4800 dpi, for example. Note that the size, arrangement mode, and shape of the photoelectric conversion element 5 and the stepped portion 4 described here are merely examples, and may be changed as appropriate. For example, the stepped portion 4 may be further reduced in size as long as it can be formed in a desired shape.

  A part of the light incident on the irradiation surface of the photoelectric conversion element 5 is reflected by the irradiation surface and is incident on the interface between the protective layer 6 and the air layer. If the protective layer 6 is not provided with the step 4 and the surface is a flat surface, most of the light reflected at the interface of the protective layer 6 travels again toward the photoelectric conversion element 5. The more light components that are incident on the irradiation surface of the photoelectric conversion element 5 from the protective layer 6, the more easily light interference occurs due to multiple reflections within the protective layer 6.

  FIG. 2 is a diagram for explaining the improvement of the spectral characteristics by providing the stepped portion 4. The light reflected by the irradiation surface of the photoelectric conversion element 5 is dispersed by reflection at the step portion 4. By dispersing the light reflected at the interface of the protective layer 6 and reducing the light traveling in the direction of the photoelectric conversion element 5 again, multiple reflection in the protective layer 6 is suppressed, and light interference is reduced. In order to effectively disperse the light by reflection at the stepped portion 4, the stepped portion 4 is arranged with a certain distance in the light receiving region 3, for example, an interval of about a length p in the Y direction of the stepped portion 4 or more. It is desirable that

  FIG. 3 is a graph showing the relationship between the wavelength of light incident on the photoelectric conversion element 5 and the optical response output of the photoelectric conversion element 5. In the graph, a curve indicated by a broken line is a comparative example of the present embodiment, and represents a spectral characteristic in a case where interference of light occurs due to multiple reflection at the protective layer 6. A curve indicated by a solid line represents spectral characteristics in the case of the present embodiment. In the case of the comparative example, an interference waveform in which the optical response output fluctuates in response to a change in wavelength is confirmed. On the other hand, in the case of the present embodiment, the interference waveform is greatly reduced and spectral characteristics are improved in most of the visible light wavelength region from 400 nm to 700 nm.

  In the present embodiment, in the light receiving region 3, the step portion 4 is formed near the center position from the boundary with the aluminum wire 2, thereby suppressing the exposure of the aluminum wire 2 in the step portion 4. By suppressing the exposure of the aluminum wiring 2 from the protective layer 6 to the outside, corrosion and wear of the aluminum wiring 2 can be reduced, and the reliability of the solid-state imaging device 10 can be maintained. Thereby, the solid-state imaging device 10 can be configured to have good spectral characteristics and high reliability. Note that the number of the stepped portions 4 arranged in the light receiving region 3 is not limited to two, and may be one or three or more depending on the size of the stepped portion 4, the size of the light receiving region 3, and the like.

(Second Embodiment)
FIG. 4 is a schematic diagram illustrating a planar configuration and a cross-sectional configuration of the solid-state imaging device 20 according to the second embodiment of the present invention. FIG. 4A shows a planar configuration of one photoelectric conversion element 5 in the solid-state imaging element 20 and its peripheral portion. (B) shows the BB cross-sectional structure of (a). The solid-state imaging device 20 according to the present embodiment is characterized in that in one light receiving region 3, the stepped portions 4 are arranged in the X direction and the Y direction. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  Two stepped portions 4 are provided in a matrix for two light receiving regions 3 in the X direction and two in the Y direction. The four step portions 4 are arranged at intervals so as to be substantially symmetric with respect to the center position of the light receiving region 3. All of the stepped portions 4 are arranged in the light receiving region 3 closer to the center position than the boundary with the aluminum wiring 2.

  On the XY plane, the photoelectric conversion element 5 has, for example, a rectangular shape having a length m in the Y direction of 20 μm and a length in the X direction of n = 8.0 μm. Further, the stepped portion 4 has, for example, a shape close to a rectangle with a length p = 2.0 μm in the Y direction and a length q = 1.0 μm in the X direction. In the entire solid-state imaging device 20, the stepped portion 4 is formed in a 2400 dpi dot shape, for example. Note that the size, arrangement mode, and shape of the photoelectric conversion element 5 and the stepped portion 4 described here are merely examples, and may be changed as appropriate.

  In order to effectively disperse the light by reflection at the stepped portion 4, the stepped portion 4 has a certain distance in the light receiving region 3, for example, a length p or more in the Y direction, and a length q in the X direction, for example. It is desirable to arrange them at intervals of more than about. Also in the case of the solid-state imaging device 20 according to the present embodiment, it is possible to obtain a good spectral characteristic and to have high reliability. Note that the number of the stepped portions 4 arranged in the X direction and the Y direction in the light receiving region 3 may be appropriately changed according to the size of the stepped portion 4, the size of the light receiving region 3, and the like.

(Third embodiment)
FIG. 5 is a schematic diagram showing a planar configuration and a cross-sectional configuration of a solid-state imaging device 30 according to the third embodiment of the present invention. FIG. 5A shows a planar configuration of one photoelectric conversion element 5 in the solid-state imaging element 30 and its peripheral portion. (B) shows CC cross-sectional structure of (a). The solid-state imaging device 30 according to the present embodiment has a planar stepped portion obtained by extending the dot-shaped stepped portion 4 in the first and second embodiments in the Y direction which is the longitudinal direction of the light receiving region 3. 31. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The step portion 31 has a concave shape with a height difference in the Z direction and a curved surface with a curvature in the X direction. The step portion 31 has the same XZ cross-sectional shape as the step portion 4 in the first and second embodiments. With respect to the Y direction, which is the longitudinal direction, the step portion 31 is formed to have a substantially flat bottom portion except that both end portions are curved. In the planar configuration shown in FIG. 4A, the center of the step portion 31 coincides with the center position of the light receiving region 3.

  On the XY plane, the photoelectric conversion element 5 has, for example, a rectangular shape with a length m in the Y direction of 20 μm and a length in the X direction of n = 3.2 μm. The stepped portion 4 has, for example, a shape close to a rectangle having a length p = 10 μm in the Y direction and a length q = 1.0 μm in the X direction, or a shape close to an ellipse. Note that the size, arrangement mode, and shape of the photoelectric conversion element 5 and the stepped portion 31 described here are merely examples, and may be changed as appropriate.

  Also in the case of the solid-state imaging device 30 according to the present embodiment, it is possible to obtain a good spectral characteristic and to have high reliability. The single light receiving region 3 is not limited to the case where one stepped portion 31 is provided, and a plurality of stepped portions 31 may be provided. For example, in one light receiving region 3, a plurality of stepped portions 31 having the Y direction as the longitudinal direction may be provided side by side in the X direction. The number of stepped portions 31 provided in the light receiving region 3 may be changed as appropriate according to the size of the stepped portion 31, the size of the light receiving region 3, and the like.

(Fourth embodiment)
FIG. 6 is a schematic diagram showing a planar configuration and a cross-sectional configuration of a solid-state imaging device 40 according to the fourth embodiment of the present invention. FIG. 6A is a plan configuration of two photoelectric conversion elements 5 of the solid-state imaging element 40 and its peripheral portion. (B) shows DD sectional structure of (a). The solid-state imaging device 40 according to the present embodiment is characterized in that the stepped portion 4 is provided across two photoelectric conversion elements 5. The same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  In the solid-state imaging device 40 according to the present embodiment, a plurality of photoelectric conversion elements 5 are provided in the light receiving region 41. The light receiving region 41 is configured by the irradiation surfaces of the plurality of photoelectric conversion elements 5. In the planar configuration shown in (a), the photoelectric conversion element 5 has a rectangular shape whose longitudinal direction is the Y direction. In the light receiving region 41, the plurality of photoelectric conversion elements 5 are arranged in parallel in the X direction, which is a specific direction, with an interval therebetween.

  The aluminum wiring 2 is formed around the plurality of photoelectric conversion elements 5. 6A and 6B show only a part of the light receiving region 41 where the two photoelectric conversion elements 5 are provided and only the peripheral part thereof. In the solid-state imaging device 40, the entire light receiving region 41 constitutes one pixel, or the irradiation surface region of one or a plurality of photoelectric conversion elements 5 in the light receiving region 41 constitutes one pixel. good.

  In the planar configuration shown in FIG. 2A, two stepped portions 4 are formed for the two photoelectric conversion elements 5. The two step portions 4 are arranged in the Y direction with a space therebetween. The step portion 4 is located around the gap between the two photoelectric conversion elements 5 in the X direction, and is located between the end portion and the center of the light receiving region 41 in the Y direction.

  On the XY plane, the photoelectric conversion element 5 has, for example, a rectangular shape with a length m in the Y direction of 20 μm and a length in the X direction of n = 3.2 μm. The step portion 4 has, for example, a shape close to a rectangle having a length p = 2.0 μm in the Y direction and a length q = 1.0 μm in the X direction, or a shape close to an ellipse. Further, the interval between the photoelectric conversion elements 5 in the X direction is set to a length q or less of the stepped portion 4 in the X direction. The stepped portion 4 is formed so as to straddle the two photoelectric conversion elements 5 in the X direction by being formed so that the left and right portions are respectively positioned on the photoelectric conversion elements 5 in the planar configuration shown in FIG. ing. Note that the size, arrangement mode, and shape of the photoelectric conversion element 5 and the stepped portion 4 described here are merely examples, and may be changed as appropriate. For example, the stepped portion 4 may be increased in width in the X direction to ensure a wider portion located on the photoelectric conversion element 5.

  FIG. 7 is a graph showing the relationship between the wavelength of light incident on the photoelectric conversion element 5 and the optical response output of the photoelectric conversion element 5. In the graph, a curve indicated by a broken line is a comparative example of the present embodiment, and represents a spectral characteristic in a case where interference of light occurs due to multiple reflection at the protective layer 6. A curve indicated by a solid line represents spectral characteristics in the case of the present embodiment. In the case of the present embodiment, as in the case of the first embodiment, the interference waveform is greatly reduced, and the spectral characteristics are improved.

  Also in the case of the solid-state imaging device 40 according to the present embodiment, it is possible to obtain a good spectral characteristic and to have a high reliability. Note that the number of the stepped portions 4 disposed on the two photoelectric conversion elements 5 is not limited to two, and may be one or three or more depending on the size of the stepped portion 4, the size of the light receiving region 41, and the like. .

(Fifth embodiment)
FIG. 8 is a schematic diagram showing a planar configuration and a cross-sectional configuration of a solid-state imaging device 50 according to the fifth embodiment of the present invention. FIG. 8A shows a planar configuration of two photoelectric conversion elements 5 of the solid-state imaging element 50 and its peripheral portion. (B) shows EE cross-sectional structure of (a). The solid-state imaging device 50 according to the present embodiment is characterized in that a step portion 31 similar to that of the third embodiment is provided across two photoelectric conversion elements 5. The same parts as those in the first to fourth embodiments are denoted by the same reference numerals, and redundant description is omitted.

  In the planar configuration shown in FIG. 1A, one step portion 31 is formed for the two photoelectric conversion elements 5. The step portion 31 is located around the gap portion between the two photoelectric conversion elements 5 in the X direction. With respect to the Y direction, the center of the step portion 31 coincides with the center position of the light receiving region 41.

  On the XY plane, the photoelectric conversion element 5 has, for example, a rectangular shape with a length m in the Y direction of 20 μm and a length in the X direction of n = 3.2 μm. The stepped portion 4 has, for example, a shape close to a rectangle having a length p = 10 μm in the Y direction and a length q = 1.0 μm in the X direction, or a shape close to an ellipse. Also in the case of the solid-state imaging device 50 according to the present embodiment, it is possible to obtain a good spectral characteristic and to have high reliability.

  Note that the size, arrangement mode, and shape of the photoelectric conversion element 5 and the stepped portion 31 described in this embodiment are examples, and may be changed as appropriate. For example, the stepped portion 31 may be increased in width in the X direction to ensure a wider portion located on the photoelectric conversion element 5.

(Sixth embodiment)
FIG. 9 is a schematic diagram showing a planar configuration and a cross-sectional configuration of a solid-state imaging device 60 according to the sixth embodiment of the present invention. FIG. 9A shows a planar configuration of the three photoelectric conversion elements 5 of the solid-state image sensor 60 and the peripheral portion thereof. (B) shows the FF cross-sectional structure of (a). FIG. 10 shows a GG cross-sectional configuration of FIG. The solid-state imaging device 60 according to the present embodiment includes a step portion 61 having a band shape with the X direction being a specific direction as a longitudinal direction in the XY plane. The same parts as those in the first and fourth embodiments are denoted by the same reference numerals, and redundant description is omitted.

  The step portion 61 is provided across a plurality of photoelectric conversion elements 5 arranged in parallel in one light receiving region 41. The step portion 61 is located in the entire light receiving region 41 in the X direction, and is located in the center of the light receiving region 41 in the Y direction. 9A and 9B show only a part of the light receiving region 41 where the three photoelectric conversion elements 5 are provided and only the peripheral part thereof.

  The step portion 61 has a concave shape with a height difference in the Z direction and a curved surface with a curvature in the Y direction. The step portion 61 has a bottom that is substantially flat in the X direction, which is the longitudinal direction, except that both end portions are curved. In the XZ cross section shown in FIG. 9B, one end of the stepped portion 61 in the X direction is represented by a curve, and a part of the bottom following the end is represented by a straight line. Further, as shown in FIG. 10, the YZ cross-sectional shape of the stepped portion 61 is the same shape as the XZ cross-sectional shape of the stepped portion 4 in the first embodiment.

  On the XY plane, the photoelectric conversion element 5 has, for example, a rectangular shape with a length m in the Y direction of 20 μm and a length in the X direction of n = 3.2 μm. The step portion 61 has, for example, a band shape having a width r = 2.0 μm in the Y direction.

  FIG. 11 is a graph showing the relationship between the wavelength of light incident on the photoelectric conversion element 5 and the optical response output of the photoelectric conversion element 5. In the graph, a curve indicated by a broken line is a comparative example of the present embodiment, and represents a spectral characteristic in a case where interference of light occurs due to multiple reflection at the protective layer 6. A curve indicated by a solid line represents spectral characteristics in the case of the present embodiment. Also in this embodiment, the interference waveform is reduced from 400 nm to 700 nm in most of the visible light wavelength region, and the spectral characteristics are improved. In the case of the solid-state imaging device 60 according to the present embodiment, it is possible to obtain a good spectral characteristic and to have a high reliability.

  FIG. 12 is a schematic diagram illustrating a planar configuration of a solid-state imaging device 70 according to a comparative example of the present embodiment. FIG. 13 is a graph showing the spectral characteristics in the case of the comparative example shown in FIG. The solid-state imaging device 70 according to this comparative example includes a stepped portion 71 having a band shape with a width r = 10 μm in the Y direction. The spectral characteristic in the case of this comparative example is represented by a solid curve in the graph of FIG.

  As shown by the dotted lines in both graphs of FIGS. 11 and 13, particularly in the wavelength region from 450 nm to 520 nm, the interference waveform is greatly reduced in the case of the present embodiment than in the comparative example. ing. Therefore, the interference waveform can be effectively reduced by reducing the width of the band shape of the stepped portion and increasing the curvature of the concave shape.

  Note that the size, arrangement mode, and shape of the photoelectric conversion element 5 and the stepped portion 61 described in this embodiment are merely examples, and may be changed as appropriate. For example, the stepped portion 61 is not limited to the case where one step is provided for one light receiving region 41, and a plurality of stepped portions 61 may be provided. Further, the stepped portion 61 is not limited to being formed in the entire X direction of one light receiving region 41, and may be formed by being divided into a plurality of portions in the X direction, for example.

  DESCRIPTION OF SYMBOLS 1 Semiconductor substrate, 2 Aluminum wiring, 3, 41 Light reception area | region, 4, 31, 61 Step part, 5 Photoelectric conversion element, 6 Protective layer 10, 20, 30, 40, 50, 60 Solid-state image sensor.

Claims (5)

A photoelectric conversion element that is provided in a light receiving region of the semiconductor substrate and generates a charge corresponding to the amount of incident light;
A light shielding portion that is formed around the light receiving region and shields light;
A protective layer provided on the semiconductor substrate and protecting the photoelectric conversion element and the light shielding part;
On the surface opposite to the semiconductor substrate side of the protective layer, a plurality of step portions having a height difference in the direction perpendicular to the irradiation surface of the photoelectric conversion element are formed,
The plurality of stepped portions are provided in the light receiving region and are arranged symmetrically with respect to the center position of the light receiving region .   2. The solid-state imaging device according to claim 1, wherein the plurality of stepped portions are arranged to be symmetric in a first direction or a second direction perpendicular to the first direction. Wherein the plurality of stepped portions, a first direction, and according to claim 1 or 2, characterized in that forming said first direction perpendicular to a second direction having a shape to have a least one for curvature Solid-state image sensor. The step portion is a solid-state imaging device according to any one of claims 1 to 3, characterized in that provided by reluctant extend over at least two of the photoelectric conversion element. The plurality of photoelectric conversion elements are juxtaposed in a specific direction in the light receiving region,
5. The solid-state imaging device according to claim 4, wherein the stepped portion has a band shape whose longitudinal direction is the specific direction in a plane parallel to the irradiation surface.

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