JP2013084714A - Imaging element and manufacturing method of the same - Google Patents

Abstract

An object of the present invention is to improve light collection efficiency and suppress light attenuation and color mixing.
An image sensor is provided with a semiconductor substrate having a photodiode for photoelectrically converting light incident on an incident surface. The incident surface of the photodiode is formed in a lens shape. The present technology can be applied to an image sensor.
[Selection] Figure 2

Description

  The present technology relates to an image sensor and a method for manufacturing the same, and more particularly, to an image sensor and a method for manufacturing the same that can increase light collection efficiency and suppress light attenuation and color mixing.

  Conventionally, in an imaging device such as a CMOS (Complementary Metal Oxide Semiconductor) image sensor, light is collected by an on-chip lens mounted on an upper surface of a light incident surface (see, for example, Patent Document 1).

JP 2007-279380 A

  However, as the pixel size becomes finer, it becomes difficult to form an on-chip lens having a large curvature. This is because the difficulty of processing in the manufacturing process increases. The refractive index of the material of the on-chip lens is as low as about 1.4 to 2.0. Therefore, in a conventional imaging device equipped with such an on-chip lens, there is a case where a sufficient light collection efficiency cannot be realized without a sufficient lens effect.

  Furthermore, the on-chip lens is processed so as to have a sufficient thickness so that the base is not exposed in the manufacturing process. As a result, the light incident on the image sensor is attenuated while passing through the on-chip lens, which may cause a reduction in sensitivity and color mixing.

  The present technology has been made in view of such a situation, and enhances light collection efficiency so that light attenuation and color mixing can be suppressed.

  The imaging device according to the first aspect of the present technology includes a semiconductor substrate having a photodiode that photoelectrically converts light incident on the incident surface, and the incident surface of the photodiode is formed in a lens shape.

  An on-chip lens formed above the semiconductor substrate may be further provided.

  An oxide film or an organic film formed directly on the semiconductor substrate can be further provided.

  The refractive index of the oxide film or the organic film can be lower than the refractive index of the semiconductor substrate.

  The material of the semiconductor substrate can contain silicon.

  The image sensor can be provided with a light shielding film.

  The image sensor can be a CMOS image sensor or a CCD image sensor.

  The imaging element can be a backside illuminated CMOS image sensor.

  The image sensor can be provided with a light shielding film embedded in the semiconductor substrate.

  The imaging device may be a surface irradiation type CMOS image sensor.

  The manufacturing method of the imaging device according to the second aspect of the present technology includes a step of forming a photodiode on a semiconductor substrate and forming a light incident surface of the photodiode in a lens shape.

  The imaging device according to the first aspect of the present technology includes a semiconductor substrate having a photodiode that photoelectrically converts light incident on the incident surface, and the incident surface of the photodiode is formed in a lens shape.

  In the imaging device manufacturing method according to the second aspect of the present technology, a photodiode is formed on a semiconductor substrate, and a light incident surface of the photodiode is formed in a lens shape.

  As described above, according to the present technology, it is possible to increase light collection efficiency and suppress light attenuation and color mixing.

It is sectional drawing of the image sensor of a general structure. It is sectional drawing of the image sensor to which the technique of this technique was applied. It is a block diagram which shows the functional structural example of the manufacturing apparatus of an image sensor. It is a flowchart explaining the flow of the manufacturing process of an image sensor. It is a figure which shows the flow of the manufacturing process of an image sensor. It is a top view of the image sensor in steps S2 and S3.

  Hereinafter, embodiments of the present technology will be described.

[General image sensor]
The inventor first examined light collection efficiency using a general image sensor. Here, the light receiving surface of the image sensor is the upper surface, the surface opposite to the light receiving surface is the lower surface, the direction parallel to the normal of the light receiving surface is the vertical direction, and the direction parallel to the light receiving surface is the horizontal direction, explain.

  FIG. 1 is a cross-sectional view of an image sensor having a general configuration.

  In the image sensor 10, a red photodiode 21-1, a green photodiode 21-2, and a blue photodiode 21-3 formed on a semiconductor substrate are arranged adjacent to each other.

  On the red photodiode 21-1, an oxide film 22, an organic film 23, a red color filter 24-1, and an on-chip lens 25-1 are stacked in that order from below. On the green photodiode 21-2, an oxide film 22, an organic film 23, a green color filter 24-2, and an on-chip lens 25-2 are stacked in that order from below. Further, an oxide film 22, an organic film 23, a blue color filter 24-3, and an on-chip lens 25-3 are stacked in that order from below on the blue photodiode 21-3.

  Further, a light shielding film 26 is disposed above the boundary of each of the red photodiode 21-1, the green photodiode 21-2, and the blue photodiode 21-3 with an oxide film 22 interposed therebetween. .

  The light incident on the on-chip lens 25-1 passes through the red color filter 24-1, the organic film 23, and the oxide film 22 and enters the red photodiode 21-1. More precisely, in the red color filter 24-1, only the light in the wavelength band of red light out of the light emitted from the on-chip lens 25-1 is transmitted, and the organic film 23 and the oxide film 22 are further transmitted. The light passes through and enters the red photodiode 21-1. The red photodiode 21-1 generates and outputs a charge having a level corresponding to the amount of incident light, that is, the amount of received light.

  The light incident on the on-chip lenses 25-2 and 25-3 is incident on the green photodiode 21-2 and the blue photodiode 21-3, respectively, through the same path. However, in this case, among the lights emitted from the on-chip lenses 25-2 and 25-3 in the green color filter 24-2 and the blue color filter 24-3, respectively, The difference is that only light in the wavelength band is transmitted.

  As described above, in the image sensor 10, it may be difficult to form an on-chip lens having a large curvature. The refractive index of the material of the on-chip lens is as low as about 1.4 to 2.0. Therefore, in the image sensor 10 having the conventional configuration, there is a case where sufficient lens efficiency does not appear and sufficient light collection efficiency cannot be realized.

  For example, as shown in FIG. 1, the light incident from the central axis direction of the on-chip lens 25-2 is the on-chip lens 25-2, the green color filter 24-2, the organic film 23, and the oxide film 22. , And enters the green photodiode 21-2 perpendicularly.

  On the other hand, when light is incident from an oblique direction of the on-chip lens 25-2, a part of the light transmitted through the green color filter 24-2 among the light emitted from the on-chip lens 25-2. Leaks beyond the light shielding film 26 into the adjacent red photodiode 21-1. In this way, in the red photodiode 21-1, the leaked light may become a color mixture component and color mixture may occur.

  Further, as described above, the on-chip lenses 25-1 to 25-3 are processed so as to have a sufficient thickness d1 so as not to expose the base in the manufacturing process. Therefore, the light incident on the image sensor 10 having the conventional configuration may be attenuated while passing through the on-chip lenses 25-1 to 25-3 having the thickness d1, and the sensitivity may be lowered.

  Therefore, the present inventor has developed a method of forming a photodiode having a function of a convex lens by directly etching a light incident surface of a photodiode formed on a semiconductor substrate into a convex shape. By applying such a method (hereinafter, referred to as a method of the present technology), it is possible to increase light collection efficiency and suppress light attenuation and color mixing.

  In the following description, the semiconductor substrate is described as a silicon substrate, but the material of the semiconductor substrate is not particularly limited, and for example, germanium or the like can be employed.

[Image sensor to which this technology is applied]
FIG. 2 is a cross-sectional view of an image sensor to which the technique of the present technology is applied.

  In the image sensor 50, a red photodiode 61-1, a green photodiode 61-2, and a blue photodiode 61-3 formed on a silicon substrate are arranged adjacent to each other.

  On the red photodiode 61-1, an oxide film 62, an organic film 63, a red color filter 64-1, and an on-chip lens 65-1 are stacked in that order from below. On the green photodiode 61-2, an oxide film 62, an organic film 63, a green color filter 64-2, and an on-chip lens 65-2 are stacked in that order from below. Further, an oxide film 62, an organic film 63, a blue color filter 64-3, and an on-chip lens 65-3 are stacked in that order from below on the blue photodiode 61-3.

  In FIG. 2, the space in which the oxide film 62 and the organic film 63 are formed may be formed only by the oxide film 62 or may be formed only by the organic film 63.

  Further, a light shielding film 66 is disposed above the boundary of each of the red photodiode 61-1, the green photodiode 61-2, and the blue photodiode 61-3 with an oxide film 62 interposed therebetween. .

  The light incident on the on-chip lens 65-1 passes through the red color filter 64-1, the organic film 63, and the oxide film 62 and enters the red photodiode 61-1. More precisely, in the red color filter 64-1, only the light in the wavelength band of red light out of the light emitted from the on-chip lens 65-1 is transmitted, and the organic film 63 and the oxide film 62 are further passed through. The light passes through and enters the red photodiode 61-1. The red photodiode 61-1 performs photoelectric conversion for generating a charge of a level corresponding to the amount of incident light, that is, the amount of received light, and outputs the generated charge.

  The light incident on the on-chip lenses 65-2 and 65-3 enters the green photodiode 61-2 and the blue photodiode 61-3 through the same path. However, in this case, among the lights emitted from the on-chip lenses 65-2 and 65-3 in the green color filter 64-2 and the blue color filter 64-3, respectively, The difference is that only light in the wavelength band is transmitted.

  Hereinafter, when it is not necessary to individually distinguish the red photodiode 61-1, the green photodiode 61-2, and the blue photodiode 61-3, these are collectively referred to as the photodiode 61. Further, when it is not necessary to individually distinguish the red color filter 64-1, the green color filter 64-2, and the blue color filter 64-3, these are collectively referred to as a color filter 64. Further, when it is not necessary to individually distinguish the on-chip lenses 65-1 to 65-3, these are collectively referred to as the on-chip lens 65.

  For convenience of explanation, the color filter 64 disposed in the image sensor 50 transmits light in the wavelength bands of red light, green light, and blue light, respectively. However, the color of the color filter 64 is particularly limited. Instead, a color filter 64 that transmits light in an arbitrary wavelength band is sufficient. In this case, the photodiode 61 performs photoelectric conversion to generate a charge having a level corresponding to the amount of incident light in an arbitrary wavelength band.

  Although details will be described later, in the image sensor 50, the light incident surface of the photodiode 61 formed on the silicon substrate is etched into a convex shape, whereby the photodiode 61 having the function of a convex lens is formed. Thereby, in the photodiode 61, since light is condensed by the function of the convex lens, the light collection efficiency can be increased.

  Further, in the image sensor 50, an oxide film or an organic film having a refractive index lower than that of the silicon substrate is embedded in the upper surface of the photodiode 61 formed in a convex shape. As a result, a large refractive index difference is generated on the upper surface of the photodiode 61, so that the light collection efficiency can be increased.

  For example, as shown in FIG. 2, the light incident from the central axis direction of the on-chip lens 65-2 is the on-chip lens 65-2, the green color filter 64-2, the organic film 63, and the oxide film 62. , And enters the green photodiode 61-2 perpendicularly. At this time, the light incident on the green photodiode 61-2 is condensed by the function of the convex lens, so that the light collection efficiency can be increased.

  Further, light incident on the on-chip lens 65-2 from an oblique direction passes through the on-chip lens 65-2 and the green color filter 64-2, and the organic film 63 and the oxide film 62 (for example, wavelength) having a low refractive index. The refractive index n = 1.45 at λ = 550 is transmitted. This light is refracted by the upper surface 61-2b of the convex green photodiode 61-2 formed on the silicon substrate having a high refractive index (for example, the refractive index n = 4.08 at the wavelength λ = 550), and the green photo Incident to the diode 61-2.

  In this way, even when light is incident on the on-chip lens 65-2 from an oblique direction, the angle at which the light is refracted is large due to the difference in refractive index between the oxide film 62 and the organic film 63 and the silicon substrate. Become. Furthermore, in the green photodiode 61-2, the light is collected by the function of the convex lens, so that the light collection efficiency can be increased. As a result, the amount of light that leaks into the adjacent red photodiode 21-1 is reduced, and color mixing is suppressed.

  As described above, in the image sensor 50, the photodiode 61 having the function of a convex lens is formed, so that the light collection efficiency can be increased without increasing the curvature of the on-chip lens 65.

  This means that in the image sensor 50 to which the technique of the present technology is applied, the curvature of the on-chip lens 65 does not have to be larger than that in the case of FIG. 1, and the on-chip lens 65 has a thickness d2. It is processed to have. As is clear from a comparison between FIG. 1 and FIG. 2, the thickness of the on-chip lens 65 is suppressed to the thickness d2 (d2 <d1). Further, in the on-chip lens 65, the thickness of the on-chip lens 65 for processing margin can be suppressed. As a result, the distance between the on-chip lens 65 and the photodiode 61 formed on the silicon substrate can be shortened. Thereby, it is possible to suppress a decrease in sensitivity due to attenuation of light transmitted through the on-chip lens 65 and the occurrence of color mixing.

  Furthermore, in the image sensor 50 to which the technique of the present technology is applied, the light collection efficiency is increased only by etching the light incident surface of the photodiode 61 into a convex shape. As a result, since the structure of the image sensor 50 can be simplified, the degree of freedom in designing the upper layer is increased.

  As a matter of course, the photodiode 61 formed in a convex shape has a function of a photodiode, that is, a function of photoelectric conversion for generating a charge of a level corresponding to the amount of received light.

[Image sensor manufacturing process]
Next, the manufacturing process of the image sensor 50 will be described with reference to FIGS.

FIG. 3 is a block diagram illustrating a functional configuration example of a manufacturing apparatus 80 that manufactures the image sensor 50.

  The manufacturing apparatus 80 includes a forming unit 91, an exposure unit 92, a reflow unit 93, an etching unit 94, a film forming unit 95, and an upper layer forming unit 96.

  The forming unit 91 forms the photodiode 61 on the silicon substrate. The exposure unit 92 patterns the resist on the silicon substrate. The reflow unit 93 reflows the patterned resist. The etching unit 94 performs anisotropic dry etching on the resist. The film forming unit 95 forms the oxide film 62, the organic film 63, and the light shielding film 66. The upper layer forming unit 96 forms the color filter 64 and the on-chip lens 65.

  FIG. 4 is a flowchart for explaining the flow of the manufacturing process of the image sensor 50. FIG. 5 is a diagram showing a flow of manufacturing processing of the image sensor 50. In the manufacturing process of the image sensor 50, the image sensor 50 may be manufactured with appropriate manual intervention or shared by a plurality of devices. In the present embodiment, in order to simplify the description, It is assumed that the manufacturing apparatus 80 executes a series of processes until the image sensor 50 is manufactured.

  In step S1, the forming unit 91 forms the photodiode 61 on the silicon substrate. At this time, the forming unit 91 performs impurity ion implantation or the like on the silicon substrate, and forms the photodiodes 61 having a pn junction and generating a level of charge corresponding to the amount of received light in an array.

  In step S2, the exposure unit 92 forms a resist 111 on the silicon substrate on which the photodiode 61 is formed, and patterns the resist 111 into a predetermined shape. That is, the exposure unit 92 patterns the resist 111 so that each of the resists partitioned by the grooves 112 becomes a convex lens-shaped base. This state is shown in FIG. 5 as states S1 and S2.

  In step S <b> 3, the reflow unit 93 reflows the patterned resist 111 so that the resist 111 has a lens shape. That is, the reflow unit 93 melts the resist 111 by performing reflow, and rounds the edge of the resist 111 into a convex lens shape. This state is shown in FIG. 5 as state S3.

  FIG. 6 is a top view of the image sensor 50 in steps S2 and S3.

  As shown on the left side of FIG. 6, in step S <b> 2, the exposure unit 92 patterns the resist 111 into a square shape that is a base of the convex lens shape. Thereafter, as shown on the right side of FIG. 6, in step S <b> 3, the reflow unit 93 reflows the resist 111 to round the edge of the resist 111 to a convex lens shape, that is, a spherical shape.

  In step S4, the etching unit 94 performs anisotropic dry etching on the resist 111 having a convex lens shape, thereby forming a convex lens shape on the silicon substrate on which the photodiode 61 is formed. This state is shown in FIG. 5 as state S4. Thereby, the photodiode 61 having the function of a convex lens is formed.

  Note that after anisotropic dry etching is performed, it is preferable to perform processing for reducing damage to the silicon substrate by wet processing, formation of a charge storage layer, or the like.

  In step S5, the film forming unit 95 forms an oxide film 62 immediately above the convex lens-shaped photodiode 61 for flattening. This state is shown in FIG. 5 as state S5. In step S5, the organic film 63 may be formed instead of the oxide film 62.

  In step S <b> 6, the film forming unit 95 forms a light shielding film 66 on the oxide film 62.

  In step S <b> 7, the film forming unit 95 forms an organic film 63 for planarization on the oxide film 62 on which the light shielding film 66 is formed. In step S7, an oxide film 62 may be formed instead of the organic film 63.

  Note that the upper surface of the oxide film 62 or the organic film 63 may be planarized by performing CMP (chemical mechanical polishing) polishing after the oxide film 62 or the organic film 63 is formed.

  In step S <b> 8, the upper layer forming unit 96 forms the color filter 64.

  In step S <b> 9, the upper layer forming unit 96 forms the on-chip lens 65. This state is shown in FIG. 5 as states S6 to S9.

  This completes the image sensor manufacturing process.

  Note that the image sensor 50 is not limited to the backside-illuminated CMOS image sensor, but can also be applied to a frontside-illuminated CMOS image sensor.

  The image sensor 50 can be applied to a CMOS image sensor or a CCD (Charge Coupled Device) image sensor.

  Thus, in the image sensor 50 to which the technique of the present technology is applied, the photodiode 61 having the function of a convex lens is formed on the silicon substrate. Thereby, as mentioned above, in the photodiode 61, since light is condensed by the function of a convex lens, the light collection efficiency can be increased.

  Further, due to the occurrence of a large refractive index difference between the oxide film 62 and the organic film 63 and the silicon substrate, the light collection efficiency can be increased without increasing the curvature of the on-chip lens 65, and color mixing is suppressed.

  Further, since the thickness of the on-chip lens 65 and the thickness of the processing margin on-chip lens 65 can be suppressed, it is possible to suppress a decrease in sensitivity due to attenuation of light transmitted through the on-chip lens 65 and the occurrence of color mixing.

  Furthermore, unlike the digital lens having a rectangular cross section, the photodiode 61 is etched into a convex shape, that is, a spherical shape, so that light can be incident at a wide angle. Therefore, the photodiode 61 formed in a convex shape can make it difficult for light scattering to occur.

  Further, in the image sensor 50, since the upper surface of the photodiode 61 is convex, that is, spherical, a gap exists between the light shielding film 66 and the photodiode 61. As a result, light incident directly below the light shielding film 66 can also be incident on the photodiode 61, so that sensitivity can be improved. In the backside illuminated CMOS image sensor, when it is desired to suppress color mixing rather than to improve sensitivity, it may be used in combination with a light shielding film embedded in a silicon substrate.

  The back-illuminated CMOS image sensor has no wiring layer on the light incident side surface. Therefore, in the image sensor 50 having a simplified structure, the degree of freedom in designing the upper layer is increased.

  In the front-illuminated CMOS image sensor, a wiring layer is formed above the photodiode 61 formed in a convex shape. Therefore, the photodiode 61 formed in a convex shape can be used as an inner lens.

  Embodiments of the present technology are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present technology.

In addition, this technique can also take the following structures.
(1)
A semiconductor substrate having a photodiode for photoelectrically converting light incident on the incident surface;
An imaging device in which the incident surface of the photodiode is formed in a lens shape.
(2)
The imaging device according to (1), further including an on-chip lens formed above the semiconductor substrate.
(3)
The imaging device according to (1) or (2), further including an oxide film or an organic film formed directly on the semiconductor substrate.
(4)
The imaging element according to any one of (1) to (3), wherein a refractive index of the oxide film or the organic film is lower than a refractive index of the semiconductor substrate.
(5)
The imaging device according to any one of (1) to (4), wherein the material of the semiconductor substrate contains silicon.
(6)
The imaging device according to any one of (1) to (5), wherein the imaging device includes a light shielding film.
(7)
The imaging device according to any one of (1) to (6), wherein the imaging device is a CMOS image sensor or a CCD image sensor.
(8)
The imaging device according to any one of (1) to (7), wherein the imaging device is a back-illuminated CMOS image sensor.
(9)
The imaging device according to any one of (1) to (8), wherein the imaging device includes a light shielding film embedded in the semiconductor substrate.
(10)
The imaging device according to any one of (1) to (9), wherein the imaging device is a surface irradiation type CMOS image sensor.
(11)
Forming a photodiode on a semiconductor substrate;
A method for manufacturing an imaging device, comprising: forming a light incident surface of the photodiode into a lens shape.

  The present technology can be applied to an image sensor.

  50 Image Sensor, 61 Photodiode, 62 Oxide Film, 63 Organic Film, 64 Color Filter, 65 On-Chip Lens, 66 Light-shielding Film, 80 Manufacturing Equipment, 91 Forming Section, 92 Exposure Section, 93 Reflow Section, 94 Etching Section, 95 Deposition section, 96 Upper layer formation section, 111 resist

Claims (11)

A semiconductor substrate having a photodiode for photoelectrically converting light incident on the incident surface;
An imaging device in which the incident surface of the photodiode is formed in a lens shape. The imaging device according to claim 1, further comprising an on-chip lens formed above the semiconductor substrate. The imaging device according to claim 1, further comprising an oxide film or an organic film formed directly on the semiconductor substrate. The imaging device according to claim 3, wherein a refractive index of the oxide film or the organic film is lower than a refractive index of the semiconductor substrate. The imaging device according to claim 1, wherein a material of the semiconductor substrate contains silicon. The imaging device according to claim 1, wherein the imaging device includes a light shielding film. The imaging device according to claim 1, wherein the imaging device is a CMOS image sensor or a CCD image sensor. The imaging device according to claim 7, wherein the imaging device is a backside illumination type CMOS image sensor. The imaging device according to claim 8, wherein the imaging device includes a light shielding film embedded in the semiconductor substrate. The imaging device according to claim 7, wherein the imaging device is a surface irradiation type CMOS image sensor. Forming a photodiode on a semiconductor substrate;
A method for manufacturing an imaging device, comprising: forming a light incident surface of the photodiode into a lens shape.

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