JP2018110147A - Solid state imaging device and manufacturing method thereof - Google Patents

Abstract

A solid-state imaging device having a microlens with improved light collection efficiency by reducing crosstalk. A solid-state imaging device according to the present invention includes a semiconductor substrate 1, a plurality of photoelectric conversion elements 2 arranged in a matrix on the surface of the semiconductor substrate 1, and a planarization layer formed on the photoelectric conversion element 2. 3, a plurality of color filters 4 arranged and formed on the planarizing layer 3 in the same matrix as the photoelectric conversion elements 2, and a plurality of microlenses 5 respectively formed on the plurality of color filters 4. . Edges of the plurality of microlenses 5 are connected in a valley shape next to each other, and the cross-sectional shape perpendicular to the semiconductor substrate surface of the valley portion forming the connecting portion 5a is the first cross section along the matrix row, the matrix column The second cross section along and the third cross section at 45 degrees to the row and column are V-shaped. [Selection] Figure 2

Description

  The present invention relates to a solid-state imaging device having a microlens for each pixel and a manufacturing method thereof.

  In recent years, imaging devices have been widely used with the expansion of the contents of image recording, communication, and broadcasting. Various types of image pickup devices have been proposed. An image pickup device incorporating a solid-state image pickup device that has been stably manufactured with a small size, light weight, and high performance can be used as a digital camera or digital video. It has become widespread.

  The solid-state imaging device has a plurality of photoelectric conversion elements that receive an optical image from a subject and convert incident light into an electrical signal. The types of photoelectric conversion elements are roughly classified into CCD (charge coupled device) type and CMOS (complementary metal oxide semiconductor) type. Further, two types of arrangements of the photoelectric conversion elements, a linear sensor (line sensor) in which the photoelectric conversion elements are arranged in one row and an area sensor (surface sensor) in which the photoelectric conversion elements are two-dimensionally arranged vertically and horizontally. It is divided roughly into. In any of the sensors, as the number of photoelectric conversion elements (number of pixels) increases, the captured image becomes more precise. In recent years, in particular, a method for manufacturing a solid-state imaging element having a large number of pixels at low cost has been studied.

  Color solid-state imaging as a single-plate color sensor that can obtain color information of an object by providing a color filter function that transmits light of a specific wavelength in the path of light incident on the photoelectric conversion element Elements are also widespread. The color solid-state imaging device can collect color-separated image information by patterning one pixel by a specific colored transparent pixel corresponding to one photoelectric conversion device and regularly arranging a plurality of pixels. As the color of the colored transparent pixel, three primary colors consisting of three colors of red (R), green (G), and blue (B), cyan (C), magenta (M), yellow (Y) Complementary color systems are generally used, and in particular, three primary color systems are often used.

  One of the important issues in performance required for a solid-state imaging device is to improve the sensitivity to incident light. In order to increase the amount of information of an image photographed with a miniaturized solid-state imaging device, it is necessary to miniaturize and highly integrate a photoelectric conversion device serving as a light receiving unit. However, when the photoelectric conversion elements are highly integrated, the area of each photoelectric conversion element is reduced, and the area ratio that can be used as the light receiving part is also reduced. Therefore, the amount of light that can be taken into the light receiving part of the photoelectric conversion element is reduced, which Sensitivity is reduced.

  As means for preventing the sensitivity of such a miniaturized solid-state imaging device from being lowered, in order to efficiently capture light into the light receiving portion of the photoelectric conversion device, the light incident from the object is collected for each pixel. Thus, a technique has been proposed in which a microlens led to the light receiving portion of the photoelectric conversion element is formed in a uniform shape on the photoelectric conversion element. By condensing the light with the microlens and guiding it to the light receiving portion of the photoelectric conversion element, the apparent aperture ratio of the light receiving portion can be increased, and the sensitivity of the solid-state imaging device can be improved.

  Here, as a method of forming the microlens, there are a flow lens type and a dry etching transfer type. In the flow lens type, first, a lens forming layer made of a transparent and heat-sensitive acrylic photosensitive resin that is a microlens material is formed, and the lens forming layer is divided into a plurality of pixel units (rectangular patterns). The pattern is formed by photolithography. Next, the lens forming layer is heated to form a microlens for each pixel unit.

In the dry etching transfer type, first, a lens mother is formed using a resist material having an alkali-soluble property, photosensitivity, and heat flow property on a lens forming layer made of an acrylic transparent resin that is a microlens material and having a flat upper surface. A mold layer is formed. Next, a lens matrix is formed by performing a photolithography process and a heat flow process on the lens matrix layer. That is, this matrix layer forming step is performed by the same method as the flow lens type microlens forming method. Next, the lens forming layer is dry-etched using the lens master as a mask, whereby the shape of the lens master is transferred to the lens forming layer to form a microlens.
In recent years, various methods for manufacturing microlenses using a gray scale mask have been proposed. For example, Patent Document 1 proposes a gray scale mask design method, a gray scale mask, and a micro lens manufacturing method capable of obtaining a stable microlens shape even if the exposure amount slightly varies.

JP 2014-174456 A

In recent years, the number of pixels in solid-state image sensors has increased, and high-definition solid-state image sensors exceeding millions of pixels have been demanded. The image quality deterioration due to the increase in noise is a problem.
In order to improve the sensitivity of the solid-state imaging device, it is also required to reduce crosstalk. Crosstalk refers to a phenomenon in which light that is supposed to be incident on a certain color is incident on an adjacent color due to the influence of the refractive index difference of each color pigment. Due to the influence of crosstalk, a color with a low refractive index loses light due to the adjacent color with a high refractive index, so that the amount of light to the light receiving portion is reduced and sensitivity is lowered.
That is, the light collection efficiency of the microlens is improved by reducing the crosstalk.
An object of the present invention is to provide a solid-state imaging device having a microlens with improved light collection efficiency by reducing crosstalk, and a method for manufacturing the same.

The solid-state imaging device according to the first aspect of the present invention is a semiconductor substrate, and a plurality of photoelectric conversion elements formed on the semiconductor substrate, the photoelectric conversion elements arranged in a matrix on the surface of the semiconductor substrate, A flattening layer formed on a plurality of photoelectric conversion elements and a plurality of color filters formed on the flattening layer, arranged in the same matrix as the plurality of photoelectric conversion elements, and receiving light of each wavelength band A plurality of color filters to be transmitted, and a plurality of microlenses formed on the plurality of color filters, respectively.
The edge portions of the plurality of microlenses are connected in a valley shape next to each other, and the cross-sectional shape perpendicular to the semiconductor substrate surface of the valley portion forming the connection portion is the first cross section along the matrix row, the matrix column The second cross section along and the third cross section at 45 degrees to the row and column are V-shaped.

The method for manufacturing a solid-state imaging device according to the second aspect of the present invention includes a plurality of photoelectric conversion elements formed on a semiconductor substrate and arranged in a matrix in a plane of the semiconductor substrate, with a plurality of layers interposed between planarization layers. A color filter forming step for forming the color filters, and a microlens forming step for forming a plurality of microlenses on the plurality of color filters after the color filter forming step, respectively.
The microlens forming process includes a matrix layer forming process, a lens matrix forming process, and a heat flow process. The matrix layer forming step is a step of forming a lens matrix layer made of a transparent resin having photosensitivity and heat flow on a plurality of color filters. The lens matrix forming step is a process of forming a plurality of lens matrices on the lens matrix layer by a photolithography method using a gray tone mask, and providing a gap between the edges of adjacent lens matrices. In this step, the shape of the lens matrix is made such that the height from the color filter is higher than that of the plurality of microlenses and the spread on the color filter surface is small. The heat flow process is a process of forming a plurality of microlenses by heating a plurality of lens molds.

  According to the present invention, a solid-state imaging device having a microlens with reduced crosstalk and improved light collection efficiency and a method for manufacturing the same are provided.

It is a top view explaining the solid-state image sensing device of one embodiment of the present invention. It is a figure which shows the solid-state image sensor of one Embodiment of this invention, Comprising: It is a figure corresponding to the 1st cross section (II cross section of FIG. 1) along the row | line | column of the matrix of a color filter. It is a figure which shows the solid-state image sensor of one Embodiment of this invention, Comprising: It is a figure corresponding to the 2nd cross section (II-II cross section of FIG. 1) along the column of the matrix of a color filter. FIG. 4 is an enlarged view of a portion IV in FIG. 3. It is a figure explaining the effect | action of this invention, Comprising: It is a figure corresponding to the 3rd cross section (III-III cross section of FIG. 1) which becomes 45 degree | times with respect to the row | line | column and column of the matrix of a color filter. It is a figure explaining the method of one Embodiment of this invention.

  Hereinafter, although embodiment of this invention is described, this invention is not limited to embodiment shown below. In the embodiment described below, a technically preferable limitation is made for carrying out the present invention, but this limitation is not an essential requirement of the present invention.

<Configuration>
As shown in FIGS. 1 to 3, the solid-state imaging device 6 of this embodiment includes a photoelectric conversion element 2, a planarization layer 3, a plurality of color filters 4, and a plurality of microlenses 5 on a semiconductor substrate 1. They are stacked in this order. In FIG. 1, other components of the solid-state imaging device 6 are omitted for easy understanding of the arrangement of the plurality of photoelectric conversion elements 2 and the plurality of color filters 4.
The semiconductor substrate 1 is a substrate for mounting the photoelectric conversion element 2. The photoelectric conversion element 2 converts light incident through the microlens 5 and the color filter 4 into electric charges. The planarization layer 3 planarizes the upper surface of the semiconductor substrate 1 that is the mounting surface of the microlens 5.
The plurality of color filters 4 are respectively formed on the plurality of photoelectric conversion elements 2 via the planarization layer 3. The plurality of color filters 4 have a role of transmitting light of a specific wavelength in the path of light incident on the photoelectric conversion element 2. In the present embodiment, the plurality of color filters 4 transmit any one of the three colors of red (R), green (G), and blue (B), and the three colors are arranged in a Bayer array. It is.

The plurality of microlenses 5 are respectively formed on the plurality of color filters 4. The plurality of microlenses 5 are made of a transparent resin, and the material is usually a resin such as an acrylic resin, and is preferably transparent.
Further, the edge portions of the plurality of microlenses 5 are connected in a valley shape next to each other. Furthermore, the cross-sectional shape perpendicular to the semiconductor substrate surface of the troughs that form the connecting portions 5a of the plurality of microlenses 5 is the first cross-section along the rows of the matrix, the second cross-section along the columns of the matrix, and the rows and columns. In the third cross section at 45 degrees with respect to the angle, it is V-shaped.
The lines indicating the surface 5b excluding the connecting portions 5a of the plurality of microlenses in the first cross section, the second cross section, and the third cross section are parabolas as shown in FIGS. It may be a waveform.

  FIG. 4 is an enlarged view of a valley portion (hereinafter, also referred to as “valley”) that forms the connection portion 5 a of the plurality of microlenses 5. When the valley is arcuate, the radius of curvature R at the lowest point L of the valley is expressed by the following equation. In the formula, f (x) is a function indicating the shape curve of the valley portion forming the connecting portion 5a, and a indicates the x coordinate at the lowest point L of the valley portion.

In the first cross section, the second cross section, and the third cross section of the plurality of microlenses 5, for example, as shown in FIG. 5A, when the radius of curvature R between the plurality of microlenses 5 is large, colored transparent Light incident on a microlens near the pixel adjacent to the blue color is changed in the color filter layer to a green colored transparent pixel having a refractive index larger than that of the blue color. As a result, there is a concern that the influence of crosstalk increases.
On the other hand, for example, as shown in FIG. 5B, when the radius of curvature R between the valleys between the plurality of microlenses 5 is small, a large amount of light is incident on the adjacent microlenses on the blue side of the colored transparent pixel. Light enters the photoelectric conversion element 2 through the color filter 4 and the planarization layer 3 without changing the optical path. As a result, the influence of crosstalk is reduced and the light collection efficiency can be increased.
In the example shown in FIG. 5B, the case where the radius of curvature R is 50 nm or less is included in “the cross-sectional shape perpendicular to the semiconductor substrate surface of the valley is V-shaped”. As a matter of course, an example in which the lowest point of the valley is a contact point between straight lines (in the above formula, the lowest point L is, for example, x = 0 of f (x) = | x |)) Is also included in “the cross-sectional shape perpendicular to the semiconductor substrate surface of the valley is V-shaped”.

<Manufacturing method>
Next, with reference to FIG. 6, the manufacturing method of the solid-state image sensor 6 of this embodiment is demonstrated.
First, a planarization layer 3 (not shown in FIG. 6) and a color filter 4 are sequentially laminated on a semiconductor substrate 1 (not shown in FIG. 6) on which the photoelectric conversion element 2 is formed on the surface (color). Filter forming step). In the color filter forming step, three types of color filters corresponding to any of RGB are arranged and stacked in a matrix (for example, in a predetermined pattern as shown in FIG. 1) on the plurality of photoelectric conversion elements.

After the color filter forming step, a plurality of microlenses 5 are formed on the plurality of color filters 4 (microlens forming step). In the microlens forming step, first, as shown in FIG. 6A, a transparent resin having photosensitivity and heat flow property is applied on a plurality of color filters 4 with a predetermined thickness, whereby a lens matrix layer is formed. 10 is formed (matrix layer forming step).
Next, as shown in FIG. 6B, the lens matrix layer 10 is exposed to light using a gray tone mask 11 based on a photolithography method, and then developed and baked to obtain a plurality. A mother die (lens mother die) 12 of the micro lens 5 is formed (lens mother die forming step). In this step, gaps are provided between the edges of adjacent lens molds 12 so that the shape of the plurality of lens molds 12 is higher from the color filter 4 than the plurality of microlenses 5 on the color filter surface. A shape with a small spread.

Further, in this step, by using a gray tone mask that can arbitrarily change the mask transmittance gradation in accordance with the shape of the lens master 12 corresponding to the shape of the desired microlens 5, the lens master It becomes easy to control 12 shapes. The gradation of the mask transmittance gradation is achieved by a partial difference in density per unit area of small diameter dots that are not resolved by light used for exposure.
In the lens matrix 12, the gap between the edges of the adjacent lens matrices 12 is set to 50 nm or more and 250 nm or less in consideration of the heat flow amount in the heat flow process which is the next process.

  Next, the melting process by heat is performed on the matrix 12 of the microlens. That is, the microlens 5 is formed by heat-flowing the matrix 12 of the plurality of microlenses (heat flow process). By forming the microlens 5 by heat flow, the microlens 5 having a narrow valley between adjacent microlenses can be formed.

<Effect of this embodiment>
According to the solid-state imaging device of the present embodiment, in the microlens formation process, the microlens shape is formed by photolithography using a gray-tone mask, thereby facilitating control of the microlens shape and imaging each individual image. Since it becomes possible to select and form an optimal microlens shape for each element, there is an effect that the light condensing efficiency to the photoelectric conversion element can be improved.
In addition, since the valley between adjacent microlenses can be narrowed by forming the microlens by heat flow, there is an effect of increasing the light collection efficiency to the photoelectric conversion element.

Hereinafter, Example 1 will be described.
A silicon wafer having a thickness of 0.75 mm and a diameter of 20 cm was used as the semiconductor substrate. A photoelectric conversion element was formed on the upper surface of the silicon wafer, and a flattening layer was formed on the uppermost layer by spin coating using a thermosetting acrylic resin coating solution.
Next, three color filter layers were sequentially formed on the planarizing layer by photolithography using three color resists of red (R), green (G), and blue (B). The film thickness of each color filter layer was 0.5 to 0.8 μm. The arrangement of the pixels of the color filter layer is a so-called green (G) filter provided every other pixel, and a red (R) filter and a blue (B) filter provided every other row between the green (G) filters. A Bayer array was used.

Next, an acrylic transparent resin having alkali solubility and photosensitivity was applied on the color filter layer with a film thickness of 1.0 μm, and the film was cured by heating at 90 ° C. for 2 minutes.
Thereafter, a microlens matrix was formed on the acrylic transparent resin by photolithography using a gray tone mask. The gray tone mask of Example 1 was a photomask designed so that the shape of the microlens becomes a parabolic shape after heat flow.
Next, the matrix of the microlens formed by the photolithography method using a gray tone mask was heat-flowed by baking. At this time, the baking was performed in three steps of 160 ° C. → 180 ° C. → 250 ° C.

When the shape of the microlens formed in Example 1 was measured with a scanning probe microscope, the edges of the plurality of microlenses were connected in a valley shape next to each other and perpendicular to the semiconductor substrate in the valley forming the connection. The cross-sectional shape is a V-shaped cross section (first cross section and second cross section) and 45 degree cross section (third cross section), and the line indicating the surface of the portion excluding the connecting portion is a parabola. I confirmed that there was.
In addition, when the light-receiving efficiency of the solid-state imaging device formed in Example 1 and the conventional product was measured, it was confirmed that the solid-state imaging device formed in Example 1 had a better result of about 5.3%. did. The conventional product compared in Example 1 is one in which a microlens is directly formed with the same shape design as Example 1 by a photolithography method using a gray-tone mask without going through a matrix. In this conventional product, the edges of a plurality of microlenses are connected in a valley shape next to each other, the line indicating the surface of the portion excluding the connection portion is a parabola, and the cross section perpendicular to the semiconductor substrate in the valley portion forming the connection portion The shape was arcuate, and the radius of curvature was 194 nm in the cross-sectional direction and 104 nm in the 45-degree cross-sectional direction.

Hereinafter, the second embodiment will be described.
A silicon wafer having a thickness of 0.75 mm and a diameter of 20 cm was used as the semiconductor substrate. A photoelectric conversion element was formed on the upper surface of the silicon wafer, and a flattening layer was formed on the uppermost layer by spin coating using a thermosetting acrylic resin coating solution.
Next, three color filter layers were sequentially formed on the planarizing layer by photolithography using three color resists of red (R), green (G), and blue (B). Each color filter layer was formed to have a thickness of 0.5 to 0.8 μm. The arrangement of the pixels of the color filter layer is a so-called green (G) filter provided every other pixel, and a red (R) filter and a blue (B) filter provided every other row between the green (G) filters. A Bayer array was used.

Next, an acrylic transparent resin having alkali solubility and photosensitivity was applied on the color filter layer with a film thickness of 1.0 μm, and the film was cured by heating at 90 ° C. for 2 minutes.
Thereafter, a microlens matrix was formed on the acrylic transparent resin by photolithography using a gray tone mask. As the gray tone mask of Example 2, a photo mask designed so that the shape of the microlens becomes an arc shape after heat flow was used.
Next, the matrix of the microlens formed by the photolithography method using a gray tone mask was heat-flowed by baking. At this time, the baking was performed in three steps of 160 ° C. → 180 ° C. → 250 ° C.

When the shape of the microlens formed in Example 2 was measured with a scanning probe microscope, the edges of the plurality of microlenses were connected in a valley shape next to each other and perpendicular to the semiconductor substrate in the valley forming the connection. The cross-sectional shape is a V-shaped cross section (first cross section and second cross section) and 45 degree cross section (third cross section), and the portion excluding the connecting portion is formed in a spherical shape. It was confirmed.
In addition, when the light-receiving efficiency of the solid-state imaging device formed in Example 2 and the conventional product was measured, it was confirmed that the solid-state imaging device formed in Example 2 had a better result of about 4.8%. did. The conventional product compared in Example 2 is one in which a microlens is directly formed with the same shape as in Example 2 by a photolithography method using a gray-tone mask without going through a matrix. In this conventional product, the edges of a plurality of microlenses are connected in a valley shape next to each other, the portion excluding the connection portion is spherical, and the cross-sectional shape perpendicular to the semiconductor substrate of the valley portion forming the connection portion is an arc shape The radius of curvature was 212 nm in the cross-sectional direction and 114 nm in the 45-degree cross-sectional direction.

Hereinafter, the third embodiment will be described.
A silicon wafer having a thickness of 0.75 mm and a diameter of 20 cm was used as the semiconductor substrate. A photoelectric conversion element was formed on the upper surface of the silicon wafer, and a flattening layer was formed on the uppermost layer by spin coating using a thermosetting acrylic resin coating solution.
Next, three color filter layers were sequentially formed on the planarizing layer by photolithography using three color resists of red (R), green (G), and blue (B). Each color filter layer was formed to have a thickness of 0.5 to 0.8 μm. The arrangement of the pixels of the color filter layer is a so-called green (G) filter provided every other pixel, and a red (R) filter and a blue (B) filter provided every other row between the green (G) filters. A Bayer array was used.

Next, an acrylic transparent resin having alkali solubility and photosensitivity was applied on the color filter layer with a film thickness of 1.0 μm, and the film was cured by heating at 90 ° C. for 2 minutes.
Thereafter, a microlens matrix was formed on the acrylic transparent resin by photolithography using a gray tone mask. As the gray tone mask of Example 2, a photo mask designed so that the shape of the microlens becomes a sine wave shape after heat flow was used.

Next, the matrix of the microlens formed by the photolithography method using a gray tone mask was heat-flowed by baking. At this time, the baking was performed in three steps of 160 ° C. → 180 ° C. → 250 ° C.
When the shape of the microlens formed in Example 3 was measured with a scanning probe microscope, the edges of the plurality of microlenses were connected in a valley shape next to each other and perpendicular to the semiconductor substrate in the valley forming the connection. The cross-sectional shape is V-shaped for both the cross-section (first cross-section and second cross-section) and the 45-degree cross-section (third cross-section), and the line indicating the surface of the portion excluding the connecting portion is a sinusoidal waveform. It was confirmed that.

In addition, when the light-receiving efficiency of the solid-state imaging device formed in Example 3 and the conventional product was measured, it was confirmed that the solid-state imaging device formed in Example 3 had a better result of about 3.7%. did. The conventional product compared in Example 3 is one in which a microlens is directly formed with the same shape as in Example 3 by a photolithography method using a gray-tone mask without going through a matrix. In this conventional product, the edge portions of a plurality of microlenses are connected in a valley shape next to each other, and the line indicating the surface of the portion excluding the connection portion is sinusoidal and perpendicular to the semiconductor substrate in the valley portion forming the connection portion. The cross-sectional shape was an arc, and the radius of curvature was 243 nm in the cross-sectional direction and 120 nm in the 45-degree cross-sectional direction.
The results of Examples 1 to 3 are summarized in Table 1 below.

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Photoelectric conversion element 3 Flattening layer 4 Color filter 5 Microlens 5a Microlens connection part 5b Surface 6 except for microlens connection part Solid-state imaging element 10 Lens matrix layer 11 Gray tone mask 12 Lens matrix R The radius of curvature of the valley between adjacent microlenses L The lowest point of the valley between adjacent microlenses

Claims (5)

A semiconductor substrate;
A plurality of photoelectric conversion elements formed on the semiconductor substrate, wherein the photoelectric conversion elements are arranged in a matrix in the plane of the semiconductor substrate;
A planarization layer formed on the plurality of photoelectric conversion elements;
A plurality of color filters formed on the planarization layer, arranged in the same matrix as the plurality of photoelectric conversion elements, and a plurality of color filters that transmit light of each wavelength band;
A plurality of microlenses formed respectively on the plurality of color filters;
With
Edges of the plurality of microlenses are connected in a valley shape next to each other, and a cross-sectional shape perpendicular to the semiconductor substrate surface of the valley portion forming the connection portion is a first cross section along a row of the matrix, A solid-state imaging device that is V-shaped in a second cross section along a column and a third cross section that is 45 degrees to the row and the column.   The line indicating the surface excluding the connecting portion of the plurality of microlenses in the first cross section, the second cross section, and the third cross section is any one of an arc, a parabola, and a sinusoidal waveform. The solid-state imaging device described. A color filter forming step of forming a plurality of color filters on a plurality of photoelectric conversion elements formed on a semiconductor substrate and arranged in a matrix in a plane of the semiconductor substrate through a planarization layer; and A microlens forming step of forming a plurality of microlenses on the plurality of color filters after the filter forming step,
The microlens formation step includes
A matrix layer forming step of forming a lens matrix layer made of a transparent resin having photosensitivity and heat flow on the plurality of color filters;
Forming a plurality of lens dies on the lens matrix layer by a photolithography method using a gray-tone mask, wherein gaps are provided between edges of the adjacent lens dies, and the plurality of lens dies are formed. A lens matrix forming step in which the shape of the color filter is higher than the plurality of microlenses, and the spread on the color filter surface is small.
A heat flow step of heating the plurality of lens molds to form the plurality of microlenses;
A method for manufacturing a solid-state imaging device.   4. The microlens forming step controls the shape of a plurality of microlens masters by forming a plurality of microlens masters by photolithography using a gray-tone mask. The manufacturing method of the solid-state image sensor as described in 1 ..   The method for manufacturing a solid-state imaging device according to claim 3 or 4, wherein the gap is 50 nm or more and 250 nm or less.

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