JP2014075445A - Reverse face irradiation type imaging element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of crosstalk in a backside illuminated image sensor.
A back-illuminated imaging device in which a plurality of pixels are arranged, and each of the plurality of pixels includes an on-chip microlens 101 and a plurality of layers that receive light collected by the on-chip microlens. Provided between the lens 105, the plurality of photoelectric conversion units 107 that receive the light collected by the plurality of intra-layer lenses, and the same number of photoelectric conversion units 107 as the plurality of intra-layer lenses, and between the plurality of intra-layer lenses and the plurality of photoelectric conversion units. And an optical waveguide 106 that guides light emitted from the plurality of intra-layer lenses to a plurality of photoelectric conversion units.
[Selection] Figure 1

Description

  The present invention relates to an image sensor, and more particularly to a back-illuminated image sensor.

  Conventional autofocus detection methods used for digital cameras include contrast detection methods (contrast AF) mainly used for video cameras and compact cameras, and phase difference detection methods (mainly used for single-lens reflex cameras) ( Phase difference AF).

  When a moving image is shot or recorded in a digital camera using an image sensor, contrast AF is generally used. Contrast AF performs sequential shooting while moving the focus lens included in the shooting lens in the direction of the optical axis, and the focus lens position where the contrast of the shot image peaks based on the high-frequency component of the shot image is taken as the in-focus position. To detect. In contrast AF, it is necessary to repeatedly perform shooting, contrast detection and comparison while moving the focus lens. Therefore, the time required for focus detection is long compared to phase difference AF that detects the defocus amount from the phase difference of the image signal. Is common.

  In view of this, the present applicant has proposed an image pickup device capable of detecting a phase difference type focus by providing two photoelectric conversion units for one of on-chip microlenses constituting a part of a CMOS type image pickup device. (Patent Document 1). In the imaging device disclosed in Patent Document 1, the on-chip microlens is configured so that the pupil of the photographing lens and the two photoelectric conversion units have a conjugate relationship. As a result, since light beams that have passed through different pupil regions of the photographic lens are incident on each photoelectric conversion unit, phase difference AF is possible using a signal obtained by each photoelectric conversion unit.

  On the other hand, with the increase in the density of pixels arranged in the image sensor, there has been a problem that the light receiving area per pixel becomes small. For this reason, a back-illuminated imaging device has been developed in which the electrode wiring is provided on the side opposite to the light incident side to increase the light receiving area per pixel.

JP 2001-124984 A

  However, since the back-illuminated image sensor does not have a light-shielding member such as electrode wiring on the light incident side, light rays coming from the vicinity of the periphery of the pupil of the photographing lens are likely to enter the adjacent photoelectric conversion unit, and so-called crosstalk occurs. Cheap. As a result, when the configuration in which two photoelectric conversion units are provided for one on-chip microlens is applied to a back-illuminated imaging device, the pupil separation performance of the focus detection image for realizing phase difference AF is reduced. There was a problem that the accuracy of focus detection was lowered.

  The present invention has been made in view of such a problem of the prior art, and an object of the present invention is to suppress the occurrence of crosstalk in a back-illuminated image sensor.

  In order to achieve the above object, the present invention provides a back-illuminated imaging device in which on-chip microlenses are two-dimensionally arranged, and includes a plurality of intra-layer lenses arranged in the vicinity of a predetermined imaging plane of the on-chip microlens To have a plurality of pixel parts consisting of an inner lens and a pair of photoelectric conversion parts, and to have one optical waveguide between the inner lens constituting the pixel part and the pair of photoelectric conversion parts It is characterized by comprising.

  With such a configuration, according to the present invention, it is possible to suppress the occurrence of crosstalk in the backside illumination type imaging device.

The figure which shows the structural example of the backside illumination type image pick-up element which concerns on the 1st Embodiment of this invention. The figure for demonstrating the example of the manufacturing process of the back irradiation type imaging device which concerns on the 1st Embodiment of this invention. The figure which shows the structural example of the back irradiation type imaging device which concerns on the 2nd Embodiment of this invention.

(First embodiment)
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1A is a plan view showing 2 × 2 pixels extracted from the back-illuminated image sensor according to the first embodiment of the present invention. Moreover, FIG.1 (b) and (c) are AA 'sectional drawings of Fig.1 (a).

In this embodiment, the pixel pitch is 2 μm. One on-chip microlens 101 is formed per pixel on the light incident surface of the back-illuminated image sensor 100.
Further, in this embodiment, four intra-layer lenses 105 are formed in one pixel so that, for example, a light beam incident on the on-chip microlens 101a is condensed on the intra-layer lenses 105a1, 105b1, 105a2, and 105b2. It is configured. In other words, a plurality of intra-layer lenses 105 are formed in the vicinity of the planned imaging plane of the on-chip microlens 101. One photoelectric conversion unit 107 is formed corresponding to one intralayer lens 105. That is, in this embodiment, the same number (four in this case) of photoelectric conversion units 107 as the inner lenses are formed in one pixel.

  One optical waveguide 106 is formed between the intralayer lens 105 and the photoelectric conversion unit 107 and one pixel. For example, the optical waveguide 106a is configured to guide the light beams collected by the inner lenses 105a1, 105b1, 105a2, and 105b2 to the photoelectric conversion units 107a1, 107b1, 107a2, and 107b2. Although the photoelectric conversion units 107a2 and 107b2 are not shown, they are formed corresponding to the in-layer lenses 105a2 and 105b2, similarly to the photoelectric conversion units 107a1 and 107b1 for the in-layer lenses 105a1 and 105b1.

  As will be described later, an interlayer insulating film 109, a wiring layer 108, and a substrate 110 are provided on the back side of the photoelectric conversion unit 107 when viewed from the light incident direction.

  Further, a planarizing layer 102, a color filter layer 103, and a planarizing layer 104 are formed in this order from the incident side between the on-chip microlens 101 and the in-layer lens 105. A part of the planarization layer 104 is in contact with the optical waveguide 106. The light incident on the back-illuminated image sensor 100 is collected by the on-chip microlens 101 and enters the intralayer lens 105 via the planarization layer 102, the color filter layer 103, and the planarization layer 104.

The thickness t1 and the refractive index N1 of the on-chip microlens 101 are such that the exit pupil of the imaging lens (not shown) and the individual intralayer lenses 105 formed in the same pixel as the on-chip microlens 101 have a conjugate relationship. Is set.
The light incident on each intra-layer lens 105 is condensed on the corresponding photoelectric conversion unit 107 via the optical waveguide 106.

  The optical waveguide 106 is made of a material having a refractive index N6 higher than the refractive index N4 of the planarizing layer 104 so that light reaching the interface with the planarizing layer 104 from the optical waveguide 106 is totally reflected. In addition, the thickness t6 of the optical waveguide 106 is set so that a light beam having a spread incident from the intralayer lens 105 is totally reflected as much as possible and transmitted to the photoelectric conversion unit 107. If the thickness t6 of the optical waveguide 106 is thin, the amount of light flux leaking into the photoelectric conversion unit of the adjacent pixel without being reflected by the side surface (interface) of the optical waveguide increases, and if it is thick, the light flux totally reflected by the optical waveguide 106 is the same. In addition to increasing the amount of leakage into other photoelectric conversion units in the pixel, manufacturing becomes difficult.

  Therefore, the thickness t6 of the optical waveguide 106 is such that the light beam incident on a certain intra-layer lens is not reflected on the side surface (interface) of the optical waveguide or reflected on the side surface and is not reflected on the photoelectric conversion unit that does not correspond to the intra-layer lens. Decide that the amount of leakage does not exist in the calculation or is sufficiently small. For example, the thickness t6 of the optical waveguide 106 can be determined so that the ratio of the light beam that leaks into the photoelectric conversion unit that does not correspond to the in-layer lens is equal to or less than a predetermined ratio as compared with the case where the optical waveguide is not provided. This can be realized by using, for example, an optical simulation.

  The incident angle of light incident on the in-layer lens 105 from the on-chip microlens 101 depends on the air conversion distance between the on-chip microlens 101 and the in-layer lens 105. Therefore, the thickness t6 of the optical waveguide 106 that satisfies the above-described conditions is determined as the relationship between the air equivalent distance between the on-chip microlens 101 and the in-layer lens 105 and the air equivalent distance of the thickness t6 of the optical waveguide 106. Also good.

For example, the thickness t <b> 6 of the optical waveguide 106 can be determined in a range from ¼ to ½ of the air equivalent distance between the on-chip microlens 101 and the in-layer lens 105.
Here, the thickness of the planarization layer 102 formed between the on-chip microlens 101 and the inner lens 105 is t2, the refractive index is N2, the thickness of the color filter layer 103 is t3, and the refractive index is N3. The thickness of the layer 104 is t4 and the refractive index is N4.

In this case, since the air conversion distance between the on-chip microlens 101 and the in-layer lens 105 is (t1 / N1 + t2 / N2 + t3 / N3 + t4 / N4), the air conversion distance of the thickness of the optical waveguide 106 (= t6 / N6)
(T1 / N1 + t2 / N2 + t3 / N3 + t4 / N4) / 4 ≦ t6 / N6 (Formula 1)
t6 / N6 ≦ (t1 / N1 + t2 / N2 + t3 / N3 + t4 / N4) / 2 (Formula 2)
It is configured to satisfy both.

  For example, the air conversion distance between the on-chip microlens 101 and the in-layer lens 105 is about 2.4 μm. In this case, if the air equivalent distance (= t6 / N6) of the thickness of the optical waveguide 106 is about 0.6 to 1.2 μm and the refractive index of the intralayer lens 105 is 2.0, the thickness is 1.2 to 2. 4 μm.

  FIG. 1B is a cross-sectional view taken along the line A-A ′ in FIG. 1A, and shows the structure in the depth direction of the backside illumination type image pickup device. FIG. 1B shows the end p of the on-chip microlens 101a out of the light incident on the on-chip microlens 101a from the pupil region in the −x direction with respect to the optical axis of the imaging lens (not shown). The optical path of the incident light to the area is shown. As shown in FIG. 1B, the incident light to the p region, which is the end portion of the on-chip microlens 101a, is incident on the intralayer lens 105b1, and most of the light is totally reflected by the optical waveguide 106a, and the photoelectric conversion unit 107b1. Condensed to That is, of the incident light flux from the pupil region in the −x direction with respect to the optical axis of the photographing lens (not shown), only one light flux is incident on the photoelectric conversion unit 107a3 adjacent to the photoelectric conversion unit 107b1 corresponding to the in-layer lens 105b1. And the occurrence of crosstalk is suppressed.

  FIG. 1C is a cross-sectional view taken along line AA ′ of FIG. 1A, and shows the light incident on the on-chip microlens 101a from the pupil region in the −x direction with respect to the optical axis of the imaging lens (not shown). Of these, the optical path of incident light to the q region, which is the end facing the p region, is shown. As shown in FIG. 1C, the incident light to the q region, which is the end of the on-chip microlens 101a, enters the intralayer lens 105b1, and is condensed on the photoelectric conversion unit 107b1 through the optical waveguide 106a. The focal length f2 of the in-layer lens 105b1 is such that light incident on the in-layer lens b1 through the on-chip microlens 101a from the pupil region in the −x direction with respect to the optical axis of the imaging lens (not shown) is adjacent to the photoelectric conversion unit 107a1. Is set so as not to enter. Note that light incident on the photoelectric conversion unit 107a1 in a deep part where the influence on the generated charge amount can be ignored may be handled as not incident.

Specifically, the focal length f2 of the in-layer lens 105 is less than or equal to ½ of the air conversion distance between the on-chip microlens 101 and the in-layer lens 105 in consideration of the imaging magnification. That is,
f2 ≦ (t1 / N1 + t2 / N2 + t3 / N3 + t4 / N4) / 2 (Formula 3)
Should be set to satisfy. For example, the focal length f2 of the in-layer lens 105 can be set to about 1.1 μm or less with respect to the air equivalent distance (about 2.3 μm) between the on-chip microlens 101 and the in-layer lens 105. When the focal length f2 exceeds 1/2 of the air-converted distance between the on-chip microlens 101 and the in-layer lens 105, the depth t7 at which the light beam incident on the on-chip microlens 101 is collected becomes the photoelectric conversion unit. Since it exceeds the thickness t8 of 107, it is not preferable.

  As described above, the light incident on the q region of the on-chip microlens 101a from the pupil region in the −x direction with respect to the optical axis of the photographing lens (not shown) is refracted by the inner lens 105b1 and passes through the optical waveguide 106a. Then, the light is condensed in the photoelectric conversion unit 107b1. Therefore, it is not necessary to provide the optical waveguide 106a with a structure that totally reflects light incident on the q region of the on-chip microlens 101a from the pupil region in the −x direction with respect to the optical axis of the photographing lens (not shown).

  Similarly, light incident on the on-chip microlens 101a from the pupil region in the + x direction with respect to the optical axis of the imaging lens (not shown) is further refracted by the in-layer lens 105a1 and collected in the photoelectric conversion unit 107a1.

  As a result, the backside illumination type imaging device 100 according to the present embodiment collects most of the light that has passed through different pupils of the photographing lens without leaking into the adjacent photoelectric conversion unit. Therefore, it is possible to accurately detect the focus state of the photographing lens based on the phase difference of the image generated from the output of each photoelectric conversion unit that receives light that has passed through different pupils of the photographing lens.

FIG. 2 is a diagram schematically illustrating a manufacturing process of the backside illumination type imaging device 100 according to the present embodiment. FIG. 2 shows a cross-sectional structure of two pixels at the center of the screen of the backside illumination type image sensor 100.
First, the photoelectric conversion unit 107 is formed on the silicon substrate. Here, four photoelectric conversion units 107a1, 107b1, 107a3, and 107b3 are formed. Then, the wiring layer 108 is provided in the interlayer insulating film 109 and bonded to the substrate 110 (FIG. 2A). The photoelectric conversion part and the wiring layer of the back-illuminated image sensor can be manufactured by an arbitrary method, for example, a method described in Japanese Patent Application Laid-Open No. 2011-119543, and thus description thereof is omitted.

  Next, after a silicon nitride film is formed on the light incident side (−z direction in the figure) of the photoelectric conversion unit 107, silicon oxide is first formed in order to form a portion of the planarizing layer 104 that contacts the side surface of the optical waveguide 106. A film is formed to a predetermined thickness. The planarizing layer 104 formed in this step has a thickness equivalent to that of the optical waveguide 106 formed in the subsequent step. Here, the thickness of the optical waveguide 106 is determined so that the spread light flux incident from the inner lens 105 is totally reflected by the optical waveguide 106 as much as possible, and the manufacturing of the optical waveguide is not difficult. (2) It is set to satisfy.

Further, in order to form the optical waveguide 106 in the planarization layer 104, a photoresist 200 having a predetermined thickness is formed, exposed and developed to create a pattern corresponding to the opening of the optical waveguide (FIG. 2). (B)). In the present embodiment, one optical waveguide 106 is formed per pixel.
Further, by performing a dry etching process using the photoresist 200 as a mask, a hole for forming the optical waveguide 106 is formed in the planarization layer 104 (FIG. 2C). Thereby, a portion in contact with the side surface of the optical waveguide 106 of the planarization layer 104 is formed.

  Next, a silicon nitride film for forming the optical waveguide 106 is formed by a high density plasma CVD method. (FIG. 2 (d)). Here, since the thickness of the silicon nitride film corresponding to the thickness of the optical waveguide 106 is equal to or less than a predetermined ratio with respect to the opening of the optical waveguide, the silicon nitride film is satisfactorily formed without generating voids. . In this embodiment, since the inner lens 105 is also formed using the same material (silicon nitride film) as the optical waveguide 106, a silicon nitride film having a thickness that combines the optical waveguide 106 and the inner lens 105 is formed. .

After the optical waveguide 106 is formed, the silicon nitride film is flattened by a dry etching process, and then a photoresist 201 is formed to form an in-layer lens (FIG. 2E). Further, the photoresist 201 is exposed and developed to form a pattern that matches the shape of the intralayer lens 105 (FIG. 2F). Next, dry etching is performed to transfer the lens shape of the photoresist 201 to the silicon nitride film, thereby manufacturing the in-layer lens 105 (FIG. 2G). In the present embodiment, four photoelectric conversion units are formed per pixel, and four intra-layer lenses 105 corresponding to individual photoelectric conversion units are formed. The shape of the in-layer lens 105 is determined so that the focal length f2 of the in-layer lens 105 satisfies the above formula (3).
When the in-layer lens 105 is formed, planarization is performed by forming a planarization layer 104 made of a silicon oxide film (FIG. 2 (h)).

  Next, the color filter layer 103 is formed. In the present embodiment, the color filter layer 103 is a primary color filter, and red, green, and blue regions are formed in a regular arrangement in units of pixels. When the color filter layer 103 is formed, the planarization layer 102 is formed of a resin material. When the planarization layer 102 is formed, the on-chip microlens 101 is formed by, for example, a known registry flow method (FIG. 2 (i)).

  As described above, according to the present embodiment, in the backside illumination type imaging device in which a plurality of photoelectric conversion units and a plurality of intralayer lenses are provided for one pixel, a plurality of layers provided in the same pixel. An optical waveguide was provided between the inner lens and the plurality of photoelectric conversion units. Therefore, it is possible to suppress the light beam incident through the inner lens from leaking to the adjacent photoelectric conversion unit, and based on the image generated from the output of each photoelectric conversion unit that receives light that has passed through different pupils of the photographing lens. It is possible to detect the focus state of the taking lens with high accuracy.

(Second Embodiment)
FIG. 3 is a view showing a configuration example of a back-illuminated image sensor according to the second embodiment of the present invention in the same manner as FIG. In the present embodiment, two intra-layer lenses are provided in one pixel. For example, a light beam incident on the on-chip microlens 101a is condensed on the intra-layer lenses 105a1 and 105b1. In addition, one photoelectric conversion unit is formed corresponding to one intralayer lens 105. That is, two photoelectric conversion units are formed per pixel.

In the example shown in FIG. 3, the thickness t6 of the optical waveguide 106 is larger than that of the first embodiment shown in FIG. Therefore, unlike FIG. 1B, in the present embodiment, among the light beams from the pupil region in the −x direction with respect to the optical axis of the photographing lens (not shown), the photoelectric conversion unit that is incident on the inner lens 105 b 1 and is adjacent thereto. There is no light beam incident on 107a3 and there is no influence of crosstalk.
Further, the focal length f2 of the in-layer lens 105 is changed so that the depth t7 at which the light beam incident on the on-chip microlens 101 is condensed in the photoelectric conversion unit 107 is slightly shallower. In addition, although it injects into the photoelectric conversion part 107a1 adjacent in the position deeper than t7, the leak in this depth can be disregarded substantially.

  The reason why the thickness of the optical waveguide 106 and the focal length f2 of the in-layer lens 105 are slightly changed from those in the first embodiment is to show changes in the optical path when these values are changed. It should be noted that this is an independent event from the fact that the number of per photoelectric conversion units is two.

  Thus, even if the number of pixels per pixel is two, the present invention can be implemented, and the same effect as in the first embodiment in which four pixels are formed per pixel can be obtained.

  In the embodiment described above, the cross-sectional structure of the pixel located in the vicinity of the center of the screen of the back-illuminated image sensor has been described in order to facilitate understanding of the present invention. However, it is said that on-chip microlenses, color filter layers, in-layer lenses, optical waveguides, and photoelectric conversion portions are relatively displaced in pixels at the periphery of the screen away from the optical axis of the photographing lens. Not too long.

  In addition, signals obtained from a plurality of photoelectric conversion units provided in the pixels of the back-illuminated image sensor described above can be suitably used for an imaging apparatus and an electronic apparatus that perform phase difference detection type automatic focus detection. . Therefore, the present invention also includes an imaging apparatus and an electronic apparatus having an automatic focus detection circuit that performs automatic focus detection by a phase difference detection method using the backside illumination type imaging device of the present invention.

Claims (8)

A back-illuminated image sensor in which a plurality of pixels are arranged,
Each of the plurality of pixels is
With on-chip microlenses,
A plurality of in-layer lenses that receive the light collected by the on-chip microlens;
A plurality of photoelectric conversion units having the same number as the plurality of intra-layer lenses, receiving light collected by the plurality of intra-layer lenses;
An optical waveguide provided between the plurality of intra-layer lenses and the plurality of photoelectric conversion units, and guiding light beams collected by the plurality of intra-layer lenses to the plurality of photoelectric conversion units. A back-illuminated image sensor.   The thickness of the optical waveguide corresponds to any of the plurality of intra-layer lenses when a light beam incident on one of the plurality of intra-layer lenses is not reflected on the side surface of the optical waveguide or reflected on the side surface. 2. The backside illumination type imaging apparatus according to claim 1, wherein a ratio of leaking into the photoelectric conversion unit that is not determined is determined to be equal to or less than a predetermined ratio as compared with a case where the optical waveguide is not provided.   The air conversion distance of the thickness of the optical waveguide is determined so as to be ¼ or more and ½ or less of the air conversion distance between the plurality of intra-layer lenses and the on-chip microlens. The back-illuminated image sensor according to claim 1 or 2.   The focal lengths of the plurality of intra-layer lenses are set so that light incident on the intra-layer lens from an on-chip microlens does not enter a photoelectric conversion unit adjacent to the photoelectric conversion unit corresponding to the intra-layer lens. The backside illumination type image pickup device according to any one of claims 1 to 3, wherein   The focal length of the plurality of intra-layer lenses is determined to be equal to or less than ½ of an air-converted distance between the plurality of intra-layer lenses and the on-chip microlens. 5. The backside illumination type image pickup device according to any one of 4 above.   The back-illuminated image pickup device according to claim 1, wherein the optical waveguide and the on-chip microlens are formed of the same material.   The back surface according to any one of claims 1 to 6, wherein a space between adjacent optical waveguides is formed of a material having a refractive index lower than a refractive index of a material forming the optical waveguide. Irradiation type image sensor. The backside illumination type imaging device according to any one of claims 1 to 7,
A focus detection unit that performs phase difference detection type automatic focus detection using a signal obtained from a photoelectric conversion unit that receives light incident from different exit pupils of the photographing lens among the plurality of photoelectric conversion units. An imaging apparatus characterized by the above.

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