JP2006147680A - Solid-state image sensor, manufacturing method thereof, and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely control the element among the smear elements where electrons generated at the surface of a semiconductor substrate with the incident light diffuse in the lateral direction along the surface of substrate and leak into a transfer channel region passing through a channel stop region. <P>SOLUTION: In a CCD solid-state image sensor of the embedded photodiode structure where a positive charge accumulating region 22 is formed in the side of the substrate surface of a photodiode based on the pn junction, the smear elements leaking into the transfer channel region 31 can be controlled by forming a getter region 23 as a gettering site within the positive charge accumulating region 22 at the surface of a sensor and then capturing, with the relevant getter region 23, the electrons generated at the front surface of the epitaxial substrate 10 with the incident light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid-state imaging device, a method for manufacturing a solid-state imaging device, and an imaging apparatus.

  One of the disadvantages unique to solid-state imaging devices, for example, CCD (Charge Coupled Device) solid-state imaging devices, is smear. Smear is a phenomenon in which when a high-luminance subject is present in a captured image, a striped bright band (vertical stripe) is formed in the vertical direction (vertical direction) of the captured image due to light leakage caused by the subject. The main component of smear in the solid-state imaging device will be described below with reference to FIG. FIG. 7 is a cross-sectional view showing the configuration of the light receiving unit and the vertical charge transfer unit in the CCD solid-state imaging device.

  In FIG. 7, the light receiving portion (photoelectric conversion portion) 101 is configured by a photodiode having a pn junction between an n-type impurity diffusion region 103 and a p-type well region 104 formed in the surface layer portion of the silicon substrate 102. The vertical charge transfer unit 105 includes an n-type impurity transfer channel region 106 formed in the surface layer portion of the silicon substrate 102 and a p-type impurity region 107 formed thereunder, and a gate insulating film 108 on the silicon substrate 102. And the transfer electrode 109 formed in this manner.

  The read gate portion 110 is configured by a part of the transfer electrode 109 serving as a gate electrode, and the gate electrode and a p-type impurity region 111 formed in the surface layer portion of the silicon substrate 102 therebelow. A p-type impurity channel stop portion 112 is formed in the surface layer portion of the silicon substrate 102 between the light receiving portion 101 and the vertical charge transfer portion 105 of the adjacent light receiving portion. A light shielding film 113 is formed so as to cover each of the vertical charge transfer portions 105.

  In the light receiving unit 101 and the vertical charge transfer unit 105 configured as described above, the general main component of smear is roughly divided into the following four components a to d. The component a is a smear component generated by electrons leaking into the transfer channel region 106 among the electrons-holes generated by photoelectric conversion in the deep part of the substrate by obliquely incident light. Component b is a smear component caused by obliquely incident light being reflected between the silicon substrate 102 and the light shielding film 113 or the transfer electrode 109 and leaking into the transfer channel region 106 to generate electrons in the transfer channel region 106. It is.

  The component c is a smear component resulting from the generation of electrons in the transfer channel region 106 by the incident light component directly transmitted through the light shielding film 113 / transfer electrode 109. The component d is a transfer channel region in which electrons generated on the surface of the silicon substrate 102 by incident light diffuse laterally along the substrate surface and pass through the p-type impurity region 111 or the channel stop portion 112 of the read gate portion 110. This is a smear component generated by leaking into 106.

  Of these four components a to d, in order to improve the component d, which is dominant as a smear component in particular, conventionally, a control unit or a separation unit positioned on the side of an n-type diffusion layer such as a transfer channel By forming the impurity concentration higher than that of the p-type well of the semiconductor substrate, the potential gradient in the vicinity of the n-type diffusion layer is almost eliminated, and the diffusion current along the surface of the semiconductor substrate is limited to reduce smear. (For example, refer to Patent Document 1).

JP 2000-77647 A

  However, in the above-described prior art, it is difficult to eliminate the potential gradient in the vicinity of the n-type diffusion layer by setting the impurity concentration of the control unit and the separation unit, so that the diffusion current along the semiconductor substrate surface can be limited to a certain extent. However, since it is difficult to eliminate this completely, it is difficult to reliably suppress smear caused by the diffusion current.

  The present invention has been made in view of the above problems, and the object of the present invention is that among the smear components, electrons generated on the surface of the semiconductor substrate by incident light diffuse laterally along the substrate surface, An object of the present invention is to provide a solid-state imaging device, a manufacturing method of the solid-state imaging device, and an imaging apparatus that can reliably suppress components that pass through the channel stop portion and leak into the transfer channel region.

  In order to achieve the above object, in the present invention, a light receiving part including a photoelectric conversion element formed on a surface layer part of a semiconductor substrate and an impurity region formed on the substrate surface side of the photoelectric conversion element is arranged. The solid-state imaging device employs a configuration in which a getter region is formed in the impurity region. This solid-state imaging device is used as an imaging device in an imaging apparatus such as a digital still camera or a video camera.

  When electrons are generated on the surface of the semiconductor substrate by incident light in the solid-state imaging device having the above structure or an imaging device equipped with the imaging device, the getter region formed in the impurity region on the substrate surface side of the photoelectric conversion element is Capture electrons. Accordingly, it is possible to reliably suppress electrons caused by incident light dominant as a smear component from diffusing laterally along the substrate surface and leaking into the transfer channel region through the channel stop portion. Further, since the getter region is located in the light receiving portion, it is possible to suppress white defect and dark current component due to metal impurities mixed due to the process.

  According to the present invention, in the solid-state imaging device in which the impurity region is formed on the substrate surface side of the photoelectric conversion element, the getter region is formed in the impurity region on the sensor surface so that the getter region is incident on the semiconductor substrate by incident light. Smear characteristics can be improved because the electrons generated on the surface of the substrate can be reliably captured, and the getter region is located in the light receiving part, so that white defects and dark current components due to metal impurities mixed in due to the process can be detected. Can also be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a cross-sectional view showing the configuration of the main parts (light receiving part and vertical charge transfer part) of the CCD solid-state imaging device according to the first embodiment of the present invention.

  In FIG. 1, an epitaxial substrate 10 is formed by forming an epitaxial layer 12 on an n-type CZ substrate 11 which is a silicon substrate grown by a CZ (Czochralski) method, and further a first p-type well region 13 thereon. It is the structure which formed. In the p-type well region 13, a light receiving unit (photoelectric conversion unit) 20, a vertical charge transfer unit 40, a read gate unit 30, and a p-type channel stop unit 50 are formed.

The light receiving portion (pixel) 20 is constituted by a photodiode having a pn junction between a p-type well region 13 and an n-type impurity diffusion region 21 formed in the well region 13, and is formed on the n-type impurity diffusion region 21, that is, the substrate. An impurity region, in this example, a p-type positive charge (hole) accumulation region (p ⁺⁺ layer) 22 is provided on the surface side.

The vertical charge transfer unit 30 includes an n-type transfer channel region (p ⁺ layer) 31 formed in the p-type well region 13, and a second p-type well region 32 formed immediately below the transfer channel region 31. The transfer electrode 33 is composed of, for example, a two-layer structure made of polycrystalline silicon formed on the epitaxial substrate 10 via a gate insulating film 71 having an ONO film (SiO 2 / SiN / SiO 2) structure.

The read gate unit 40 is configured by a part of the transfer electrode 33 of the vertical charge transfer unit 30 as a gate electrode, and the gate electrode and a channel region therebelow. The channel stop unit 50 is composed of a p-type impurity (p ⁺ layer). Further, a light shielding film 73 made of aluminum (Al), tungsten (W) or the like is formed through an interlayer insulating film 72 so as to cover each of the vertical charge transfer portions 30.

  In the CCD solid-state imaging device having the above structure, that is, a CCD solid-state imaging device having an embedded photodiode structure in which a positive charge accumulation region 22 is formed on the substrate surface side of a photodiode by a pn junction, A feature is that a getter region 23 which is a gettering site is formed in the storage region 22.

  The getter region 23 captures electrons generated on the surface of the epitaxial substrate 10 by incident light, so that the electrons diffuse laterally along the substrate surface and capture components that leak into the transfer channel region 31. To act. Here, the getter region 23 needs to be inside the positive charge storage region 22 in order to reliably capture electrons generated on the substrate surface. FIG. 2 shows the potential of the cross section along the line X1-X2 in FIG.

  Here, various things can be considered as the getter region 23, that is, the gettering site. As gettering technology, IG (Intrinsic Gettering) method in which oxygen in a silicon substrate is deposited only inside the substrate and this is used as a gettering site, polysilicon or high-concentration phosphorus (Phosphorus) region on the back of the substrate EG (Extrinsic Gettering) method for forming a gettering site using strain stress with silicon.

On the other hand, as a gettering region 23, a gettering site that can be locally formed in the region of the light receiving portion 20, and is electrically neutral and has low diffusion, a group 4 impurity element is ion-implanted. The gettering technique formed by this is the most desirable. Specifically, as a Group 4 impurity element, for example, carbon ions are implanted at a dose of 5 × 10 ¹³ cm ⁻² or more, preferably 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ⁻² to form a gettering site. . However, the Group 4 impurity element to be ion-implanted is not limited to carbon, but may be germanium, tin, lead, or the like.

  In forming the getter region 23, it is preferable to form the getter region 23 on the substrate surface side of the positive charge storage region 22 so as not to protrude from the positive charge storage region 22. This is because when the getter region 23 protrudes from the positive charge accumulation region 22, electrons are captured or electrons are generated due to defects and levels of the getter region 23, causing white defects and dark current components. It is because it ends.

  In order to form the getter region 23 so as not to protrude from the positive charge storage region 22, the dose amount, energy, angle, or the like at the time of ion implantation may be appropriately selected. As an example, if the positive charge storage region 22 is formed by ion implantation of boron with an energy of 20 keV or less, the getter region 23 may be formed by ion implantation of carbon with an energy of 10 keV or less. .

Further, when carbon is ion-implanted, the carbon dose is set to 5 × 10 ¹³ cm ⁻² or more, so that high-density crystal defects and stress are sufficiently generated by the carbon ion implantation. Therefore, the gettering ability for capturing electrons can be enhanced. In addition, when the carbon dose is set to 5 × 10 ¹⁵ cm ⁻² or less, deterioration of crystallinity on the surface of the epitaxial substrate 10 can be suppressed to a minimum.

  As described above, in a CCD solid-state imaging device having an embedded photodiode structure in which a positive charge accumulation region 22 is formed on the substrate surface side of a photodiode by a pn junction, a gettering site is formed in the positive charge accumulation region 22 on the sensor surface. By forming the getter region 23, the electrons generated on the surface of the epitaxial substrate 10 by the incident light are captured by the getter region 23, so that the smear component leaks into the transfer channel region 31 through the channel stop portion 50. Can be reliably suppressed.

  Since electrons captured in the getter region 23 are dominant components as smear components, the formation of the getter region 23 in the positive charge accumulation region 22 can greatly improve smear characteristics. In addition, since the getter region 23 is located in the region of the light receiving unit 20, it is possible to suppress white flaw defects and dark current components due to metal impurities mixed due to the process.

[Second Embodiment]
FIG. 3 is a cross-sectional view showing the configuration of the main part of a CCD solid-state imaging device according to the second embodiment of the present invention. In FIG. 3, the same parts as those in FIG.

The CCD solid-state imaging device according to the present embodiment is a semiconductor substrate on which the light receiving unit 20 including the getter region 23, the vertical charge transfer unit 30, the read gate unit 40, and the channel stop unit 50 are formed. An epitaxial substrate formed by forming an epitaxial layer 12 after forming a carbon implantation region 14 by implanting carbon ions at a dose of 1 × 10 ¹⁵ cm ^{−2 on} the surface of an n-type CZ substrate 11 which is a silicon substrate. The other configuration is basically the same as the configuration of the CCD solid-state imaging device according to the first embodiment.

  In the CCD solid-state imaging device having such a configuration, the carbon in the carbon implantation region 14 accelerates the precipitation of oxygen to form high-density crystal defects on the CZ substrate 11, and these crystal defects serve as gettering sites. . Further, stress is generated by the difference in covalent bond radius between the element (silicon) forming the CZ substrate 11 and the carbon in the carbon implantation region 14, and this stress itself is also a gettering site. For this reason, the impurities and crystal defects originally present in the CZ substrate 11 and the impurities and crystal defects introduced when forming the epitaxial layer 12 and subsequently forming the solid-state imaging device are strongly gettered. The

  As described above, in a CCD solid-state imaging device having a buried photodiode structure, an epitaxial substrate 10 ′ having a carbon implantation region 14 is used as a semiconductor substrate, and a getter region is provided in the positive charge storage region 22 on the epitaxial substrate 10 ′. 23. By adopting the configuration in which the light receiving unit 20, the vertical charge transfer unit 30, the read gate unit 40, and the channel stop unit 50 formed by forming the channel 23, the same effect as the first embodiment, that is, the smear characteristic by the getter region 23 is obtained. In addition to the above improvement effect, impurities and crystal defects can be strongly gettered by the carbon implantation region 14, so that the effect of greatly reducing white defects and dark current components of the CCD solid-state imaging device can be obtained.

  In each of the embodiments described above, in the CCD solid-state imaging device having the embedded photodiode structure, the getter region 23 is formed in the positive charge accumulation region 22 on the sensor surface. In addition, it is possible to adopt a configuration in which a getter region is formed.

  In this way, by forming a getter region also in the channel stop portion 50, electrons generated on the substrate surface by incident light diffuse laterally along the substrate surface, and the channel stop portion 50 on the side opposite to the reading side is diffused. It is possible to capture the leakage into the adjacent transfer channel region 31 through the getter region by the getter region. Therefore, in combination with the function and effect of the getter region 23 in the positive charge accumulation region 22, smear and white defect In addition, the dark current component can be more reliably reduced.

  This getter region can basically be formed using the same gettering technique as the getter region 23 formed in the positive charge storage region 22. That is, as the gettering site that can be locally formed in the region of the channel stop portion 50 and is electrically neutral and has a small diffusion, the gettering technique in which a group 4 impurity element is ion-implanted is the best. desirable.

Specifically, as a Group 4 impurity element, for example, carbon ions are implanted at a dose of 5 × 10 ¹³ cm ⁻² or more, preferably 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ⁻² to form a gettering site. . However, the group 4 impurity element to be ion-implanted is not limited to carbon, but may be germanium, tin, lead, or the like.

In addition, when the carbon ion implantation is performed, the carbon dose is set to 5 × 10 ¹³ cm ⁻² or more, so that the formation of high-density crystal defects and the generation of stress can be sufficiently performed by the carbon ion implantation. Therefore, the gettering ability for capturing electrons can be enhanced. In addition, when the carbon dose is set to 5 × 10 ¹⁵ cm ⁻² or less, deterioration of crystallinity on the surface of the epitaxial substrate 10 can be suppressed to a minimum.

[Production method]
Next, a manufacturing method of the CCD solid-state imaging device according to the second embodiment will be described with reference to manufacturing process diagrams of FIGS. 4 and 5, the same parts as those in FIG. 3 are denoted by the same reference numerals.

First, as shown in FIG. 4A, an n-type CZ substrate 11 which is a silicon substrate grown by the CZ method is prepared. The CZ substrate 11 is a substrate having a main surface of (100) plane and having a specific resistance of 10 Ωcm and a diameter of 200 mm. A carbon implanted region 14 is formed on the surface of the CZ substrate 11 by implanting a Group 4 impurity element such as carbon at a dose of 1 × 10 ¹⁵ cm ⁻² through a thermal oxide film 81. Annealing is performed after carbon ion implantation, and then the thermal oxide film 81 is removed.

  Next, as shown in FIG. 4B, an n-type silicon epitaxial layer 2 of, eg, 8 μm is formed on one main surface of the CZ substrate 11 by using a hydrogen reduction method using SiHC 13 source gas, for example, at an epitaxial growth temperature of, eg, 1110 ° C. Grow. Next, as shown in FIG. 4C, a first p-type well region 13 is formed in the n-type silicon epitaxial layer 12.

  Next, as shown in FIG. 4D, a gate insulating film 71 having an ONO film (SiO 2 / SiN / SiO 2) structure is formed on the surface of the p-type well region 13, and the inside of the first p-type well region 13 is formed. N-type and p-type impurities are selectively ion-implanted into the n-type transfer channel region 31 and the p-type channel stop unit 50 constituting the vertical charge transfer unit 30, and the second p-type well region 32. Form each one.

Next, as shown in FIG. 5A, the transfer electrode 33 having a two-layer structure of the vertical charge transfer unit 30 is formed of polycrystalline silicon, and then carbon ions are selectively 5 × 10 5 in the region of the light receiving unit 20. ^The getter region 23 is formed by implantation at a dose of ¹³ cm ⁻² . In order to make the getter ability effective, ion implantation at a dose of 5 × 10 ¹³ cm ⁻² or more, preferably 5 × 10 ^{13 to} 5 × 10 ¹⁵ cm ⁻² is desirable. As for the smear reducing effect, there is an effect at a lower dose.

  As a mask at the time of ion implantation, the transfer electrode 33 may be used, or a resist formed separately by a lithographic method may be used. The energy and dose amount depend on the formation conditions of the positive charge accumulation region 22 to be formed later. In other words, it is desirable that the getter region 23 has a defect or level that does not protrude from the positive charge accumulation region 22. As an example, assuming that the positive charge accumulation region 22 is formed by ion implantation of boron with an energy of 20 keV or less, carbon is ion-implanted with an energy of 10 keV or less.

  Next, as shown in FIG. 5B, n-type and p-type impurities are selectively ion-implanted into the first p-type well region 13 using the transfer electrode 33 as a mask, and the light receiving unit 20 is formed. The n-type impurity diffusion region 21 and the p-type positive charge storage region 17 are formed. Next, as shown in FIG. 5C, after an interlayer insulating film 72 is formed over the entire surface of the element, a light shielding film 73 covering the vertical charge transfer portion 30 is formed of aluminum, tungsten, or the like. Thereafter, a well-known color filter and an on-chip lens are sequentially formed to obtain a target CCD solid-state imaging device.

  In the case of manufacturing the CCD solid-state imaging device according to the first embodiment, the step of forming the carbon implantation region 14 is omitted in FIG.

  As described above, by forming the getter region 23 in the positive charge storage region 22 of the light receiving unit 20, the getter region 23 functions to capture electrons generated on the surface of the semiconductor substrate by incident light. Therefore, it is possible to surely suppress the electrons due to the incident light dominant as a smear component from leaking into the transfer channel region 31, and the getter region 23 is located in the light receiving unit 20 and mixed due to the process. Since white scratch defects and dark current components due to metal impurities can be suppressed, a CCD solid-state imaging device having excellent smear characteristics and few white scratch defects can be manufactured.

  In the manufacturing process of FIG. 5, the getter region 23 is formed before the n-type impurity diffusion region 21 and the positive charge accumulation region 22 of the light receiving unit 20 are formed. It is also possible to form the getter region 23 after forming the positive charge accumulation region 22.

  Further, here, an n-type diffusion region 21 is formed on the surface of the p-type well region 13 formed on the n-type Si epitaxial substrate, and photon is formed by a pn junction between the p-type well 13 and the n-type diffusion region 21. The case of manufacturing a CCD solid-state image pickup device of a type that forms a diode has been described as an example. However, for a CCD solid-state image pickup device of a type that forms a photodiode by forming an n-type impurity region on a p-type Si epitaxial substrate. Can be applied similarly.

  In addition, a CCD solid-state image sensor having a plurality of intra-layer lenses, a CCD solid-state image sensor having a sensitivity to near infrared rays after forming an epitaxial layer after the formation of a vertical overflow barrier, and further being transparent to ultraviolet rays. Of course, the present invention can also be applied to a CCD solid-state imaging device in which a light receiving portion is formed only by a film having the same. Of course, the present invention is not limited to a CCD solid-state imaging device, but can be applied to a CMOS (Complementary Metal Oxide Semiconductor) solid-state imaging device (so-called CMOS sensor) or an amplification-type solid-state imaging device.

[Application example]
The solid-state imaging device according to each embodiment described above is suitable for use as an imaging device in an imaging apparatus (camera module) such as a digital still camera or a video camera.

  FIG. 6 is a block diagram showing an example of the configuration of the imaging apparatus according to the present invention. As shown in FIG. 6, the imaging apparatus according to this example includes a lens 81, an imaging device 82, a signal processing circuit 83, a device driving circuit 84, and the like.

  The lens 81 forms image light from the subject on the imaging surface of the imaging device 82. The imaging device 82 outputs, for example, a field unit of an image signal of one frame obtained by converting the image light imaged on the imaging surface by the lens 81 into an electrical signal in units of pixels under the driving of the device driving circuit 84. To do. As the imaging device 82, the CCD solid-state imaging device according to each of the above-described embodiments is used.

  The signal processing unit 83 includes a CDS (Correlated Double Sampling) circuit and an AGC (Automatic Gain Control) circuit, and an image signal output from the imaging device 82 is imaged by the CDS circuit. The fixed pattern noise included in the signal is removed, and the AGC circuit stabilizes the signal level (gain adjustment).

  Since the imaging device 82 is the CCD solid-state imaging device shown in FIG. 1 or 3, the device driving circuit 84 reads a gate pulse for reading out the signal charge photoelectrically converted by the light receiving unit 20 to the vertical charge transfer unit 30. Various timing pulses such as an n-phase vertical transfer pulse for transfer driving the vertical charge transfer unit 30 and an m-phase horizontal transfer pulse for transfer driving a horizontal charge transfer unit (not shown) are generated. The imaging device 82 is driven by the pulse.

  As described above, in an imaging apparatus such as a digital still camera or a video camera, by mounting the CCD solid-state imaging device according to each of the above-described embodiments as the imaging device, the CCD solid-state imaging device can improve smear characteristics. Since it has the feature of suppressing white defect defects and dark current components, it is possible to obtain a high-quality captured image with less smear.

It is sectional drawing which shows the structure of the principal part of the CCD solid-state image sensor which concerns on 1st Embodiment of this invention. FIG. 2 is a potential diagram of a cross section taken along line X1-X2 of FIG. It is sectional drawing which shows the structure of the principal part of the CCD solid-state image sensor concerning 2nd Embodiment of this invention. It is process drawing (the 1) which shows the procedure of the manufacturing method of the CCD solid-state image sensor which concerns on 2nd Embodiment. It is process drawing (the 2) which shows the procedure of the manufacturing method of the CCD solid-state image sensor which concerns on 2nd Embodiment. It is a block diagram which shows an example of a structure of the imaging device which concerns on this invention. It is sectional drawing which shows the structure of the principal part of the CCD solid-state image sensor concerning a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Epitaxial substrate, 11 ... CZ substrate, 12 ... N-type epitaxial layer, 13 ... First p-type well region, 14 ... Carbon implantation region, 20 ... Light receiving portion, 21 ... N-type impurity diffusion region, 22 ... Positive charge Storage region 23 ... Getter region 30 ... Vertical charge transfer portion 31 ... Transfer channel region 32 Second p-type well region 33 ... Transfer electrode 40 ... Read gate portion 50 ... Channel stop portion

Claims (7)

A solid-state imaging device in which a light receiving unit including a photoelectric conversion element formed on a surface layer portion of a semiconductor substrate and an impurity region formed on the substrate surface side of the photoelectric conversion element is disposed,
A solid-state imaging device having a getter region in the impurity region. The solid-state imaging device according to claim 1, wherein the getter region is formed of a Group 4 impurity element. The solid-state imaging device according to claim 2, wherein the Group 4 impurity element is carbon. A method for manufacturing a solid-state imaging device, in which a light receiving portion including a photoelectric conversion element formed on a surface layer portion of a semiconductor substrate and an impurity region formed on a substrate surface side of the photoelectric conversion element is disposed,
A method for manufacturing a solid-state imaging device, wherein a getter region is formed in the impurity region. The method for manufacturing a solid-state imaging device according to claim 4, wherein the getter region is formed by ion implantation of a Group 4 impurity element. The method for manufacturing a solid-state imaging device according to claim 5, wherein the Group 4 impurity element is carbon. A solid-state imaging device in which a light receiving portion including a photoelectric conversion element formed on a surface layer portion of a semiconductor substrate and an impurity region formed on the substrate surface side of the photoelectric conversion element is disposed and has a getter region in the impurity region An imaging apparatus characterized by using an element as an imaging device.

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