JP2019087977A - Solid-state imaging device and method of manufacturing the same - Google Patents

Abstract

To provide a configuration of a higher sensitivity solid-state imaging device with improved light receiving sensitivity by optimizing a shape of a microlens for each of RGB pixels.SOLUTION: The solid-state imaging device includes on a semiconductor substrate: a photoelectric conversion element; a color filter layer 4; and a plurality of microlenses 5, stacked in this order. Shapes of adjacent microlenses are different. The color filter layer 4 includes color filters of green, red, and blue. A curvature radius R1 of a top of a first microlens 7 corresponding to a green pixel is smaller than a curvature radius R2 of a top of a second microlens 8 corresponding to a red pixel.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a solid-state imaging device provided with a minute microlens array corresponding to each photoelectric conversion device, and a method of manufacturing the same.

In recent years, the resolution of imaging devices mounted on video cameras, digital cameras, and mobile phones with cameras has been advanced. With the miniaturization of pixels of solid-state imaging devices such as CCDs and CMOS sensors incorporated in imaging devices, there is a problem in that the light receiving sensitivity decreases due to the decrease in the amount of light incident per pixel.
In the solid-state imaging device, in order to suppress a decrease in sensitivity, a method of forming a microlens in one-to-one correspondence with pixels (photoelectric conversion devices) on the incident side of the light receiving device is widely used. By forming the microlens, incident light can be efficiently collected on the photodiode, and the light reception sensitivity can be improved.

In the solid-state imaging device, red (R), green (G), and blue (B) pixels are formed by providing color filters of a plurality of colors corresponding to the respective pixels. There is a problem that the light receiving sensitivity of the element is different. This is because the light reception sensitivity difference is generated due to the light transmittance difference of the color filter that performs color separation.
In order to solve these problems, Patent Document 1 describes changing the height of the microlens according to the sensitivity of the pixel for each color.

JP-A-9-148549

However, in Patent Document 1, there is no specific guideline as to which micro lens is formed in which structure with respect to the light receiving sensitivity difference to improve the light receiving sensitivity. In addition, since the manufacturing process is repeated for each height of the micro lens, there is a problem that the cost increases and the manufacturing yield decreases.
Therefore, an object of the present invention is to improve light receiving sensitivity by optimizing the shape of each microlens.

In order to solve the problems, the solid-state imaging device according to one aspect of the present invention includes a semiconductor substrate on which a plurality of photoelectric conversion devices are two-dimensionally arranged, and a plurality of photoelectric conversion devices formed on the semiconductor substrate. It has a color filter layer in which color filters of two colors are two-dimensionally arranged in a predetermined regular pattern, and a plurality of microlenses formed on the color filter layer and arranged corresponding to each color filter. The radius of curvature R1 of the top of the first microlens, which is the microlens corresponding to the green color filter, includes green, red and blue as colors of the color filter corresponds to the color filter of red color It is characterized in that it is smaller than the curvature radius R2 of the top portion of the second microlens which is the above-mentioned microlens.
In addition, when manufacturing the solid-state imaging device according to the above one aspect, which is another aspect of the present invention, the plurality of microlenses are collectively formed by photolithography using a gray tone mask.

According to an aspect of the present invention, there is an effect that the light receiving sensitivity is improved by optimizing the profile shape (hereinafter also referred to simply as a shape) of the microlens for each of the RGB pixels.
Further, according to one aspect of the present invention, since only the lens shape is optimized, it is also possible to collectively form a plurality of microlenses.

It is a conceptual diagram showing an example of a solid-state image sensing device concerning an embodiment based on the present invention. It is a part of the top view which illustrates typically arrangement | positioning of the color filter of several colors corresponding to each pixel of red, green, blue of the solid-state image sensor based on this invention. It is a figure which shows the aa 'cross section in FIG. It is a figure which shows the bb 'cross section in FIG. It is a figure for demonstrating typically the manufacturing method of the solid-state image sensor based on this invention.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
Here, the configurations shown in the respective drawings are schematic, and the relationship between the thickness and the planar dimension, the ratio of the thickness of each layer, and the like are different from the actual ones. Further, the embodiments shown below exemplify the configuration for embodying the technical idea of the present invention, and the technical idea of the present invention is that the materials, shapes, structures and the like of the components are as follows. It is not limited to things. The technical idea of the present invention can be variously modified within the technical scope defined by the claims described in the claims.

<Structure>
As shown in FIG. 1, the solid-state imaging device 6 of the present embodiment is formed on a semiconductor substrate 1 in which a plurality of photoelectric conversion devices 2 are two-dimensionally arranged, and on the semiconductor substrate 1. And a plurality of microlenses 5 formed on the color filter layer 4 and arranged corresponding to the respective color filters. And. The plurality of photoelectric conversion elements 2 are two-dimensionally arranged according to the pixel position. The code | symbol 3 is a planarization layer.

The microlens 5 of this embodiment is made of a transparent resin, and the material is usually a resin such as an acrylic resin, and is preferably transparent.
The semiconductor substrate 1 is a substrate for mounting the photoelectric conversion element 2. The photoelectric conversion element 2 is provided for each pixel, and converts light incident through the microlens 5 into a charge. The planarization layer 3 planarizes the mounting surface of the microlens 5. The color filter layers 4 composed of a plurality of color filters are respectively formed on the plurality of photoelectric conversion elements 2 via the planarization layer 3. Each color filter of a plurality of colors constituting the color filter layer 4 has 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 constituting the color filter layer 4 transmit one of the three colors of red, green and blue, and the color filters R, G and B of three colors are transmitted. Are arranged in a Bayer pattern, as shown in FIG.

As the plurality of microlenses 5, as shown in FIG. 3, microlenses of different profile shapes are arranged in the color filter layer 4 for each color of the corresponding color filters R, G, B.
Here, the microlens 5 corresponding to the green color filter G is a first microlens 7, the microlens 5 corresponding to a red color filter R is a second microlens 8, and the color filter B is blue The microlens 5 corresponding to is referred to as a third microlens. The radius of curvature of the top of the first microlens 7 is R1, the radius of curvature of the top of the second microlens 8 is R2, and the radius of curvature of the top of the third microlens 8 is R3.

Then, as shown in FIG. 3, the first microlens 7 and the second microlens are arranged such that the radius of curvature R1 of the top of the first microlens 7 is smaller than the radius of curvature R2 of the top of the second microlens 8. Design 8 shapes.
The edges of the plurality of microlenses 5 are connected by valleys 9 between adjacent microlenses.

When the cross-sectional shape of the arrangement of the plurality of micro lenses in the diagonal direction (b-b 'direction in FIG. 2) and the thickness direction of the semiconductor substrate 1 is a diagonal cross section, as shown in FIG. The valley portion 9 has a curved shape with a radius of curvature R.
Here, since the arrangement of the plurality of microlenses 5 is formed corresponding to the arrangement of the plurality of color filters constituting the color filter layer 4, the diagonal direction of the plurality of microlenses 5 and the plurality of color filters It is synonymous with the diagonal direction of. The diagonal direction is a diagonal direction if each color filter has a rectangular shape. Alternatively, a direction connecting central portions of color filters arranged diagonally is defined as a diagonal direction.

  As a result of intensive studies on the light receiving sensitivity of the microlens 5, the inventor of the present invention has a great influence on the shape of the microlens 5 arranged corresponding to each green pixel, red pixel and blue pixel in order to improve the light receiving sensitivity. I found what I was doing. Then, the light receiving sensitivity of the solid-state imaging device was successfully improved by changing the shape of the microlens 5 for each pixel. The effect was particularly large in the green pixel and the red pixel.

Specifically, it was found that the curvature radius R2 of the top of the second microlens 8 should be larger than the curvature radius R1 of the top of the first microlens 7. That is, it was confirmed that when the relationship between the first microlens 7 and the second microlens 8 satisfies R2> R1, the light reception sensitivity of each pixel can be enhanced.
As an example satisfying R2> R1, the shape of the second microlens 8 is spherical, and the shape of the first microlens 7 is parabolic with a smaller radius of curvature than the spherical shape. The shape of the second microlens 8 may be a first paraboloid shape, and the shape of the first microlens 7 may be a second paraboloid shape having a smaller radius of curvature than the first paraboloid shape. It goes without saying.

  The curvature radius R3 of the top of the third microlens (not shown) is preferably set according to the size of the curvature radius R of the valley portion 9. That is, the radius of curvature R3 of the top of the third microlens is larger than the radius of curvature R1 of the top of the first microlens 7 when the radius of curvature R of the valley 9 is 135 nm or more, and the radius of curvature R of the valley 9 is Is preferably smaller than the radius of curvature R2 of the top of the second microlens 8.

The height of each of the microlenses 5 is preferably 300 nm or more and 600 nm or less where light receiving efficiency is improved. The heights of the respective microlenses 5 may be the same or different for RGB pixels.
Here, the radius of curvature R of the valley portion 9 between the adjacent microlenses will be described in detail with reference to FIG.

  The radius of curvature R is the radius of curvature circle 10 at the deepest point of valley portion 9 between the micro-lenses, that is, lowest point 11 shown in FIG. Moreover, this curvature radius R is represented by the following formula. R is the radius of curvature of the valley 9 between the microlenses, f (a) is the shape curve of the valley 9 between the microlenses, and a is the value of the lowest point 11 of the valley 9 between the microlenses.

<Manufacturing method>
The present embodiment relates to a method of manufacturing the micro lens 5 formed on the upper part of the photoelectric conversion element, and therefore this point will be described in detail as an example below with reference to FIG.

In each of the following examples and comparative examples, a spherical shape will be described as the shape of a microlens having a large radius of curvature, and a parabolic shape will be described as a microlens shape having a small radius of curvature. In other words, the radius of curvature of the top of the spherical shape> the radius of curvature of the top of the paraboloidal shape.
Example 1
In Example 1, the photosensitive microlens material 12 that composes the microlens 5 is a photosensitive transparent resin, and is an example using a positive photosensitive resin. In the present embodiment, different micro lens shapes are controlled by the exposure method for each pixel of the micro lens 5. For this purpose, a special exposure mask called gray tone mask 13 is used.

As the semiconductor substrate 1, a silicon wafer having a thickness of 0.75 mm and a diameter of 20 cm was used. A photoelectric conversion element, a light shielding film, and a passivation film were formed on the upper surface of the silicon wafer, and a planarization layer was formed on the uppermost layer by spin coating using a thermosetting acrylic resin coating solution.
Subsequently, on the planarizing layer 3, color filters of a plurality of colors forming the color filter layer were formed respectively by the method of three times of three colors of green, blue and red (FIG. 5 (a However, in FIG.5, the photoelectric conversion element 2 and the planarization layer 3 are not shown).

Green resist is C.I. I. Pigment yellow 139, C.I. I. Pigment green 36, C.I. I. Pigment Blue 15: 6, and further, an organic solvent such as cyclohexanone and PGMEA, a polymer varnish, a monomer, and a color resist of a configuration to which an initiator was added were used.
Blue resist is C.I. I. Pigment blue 15: 6, C.I. I. Pigment Violet 23 was used, and further, a color resist having a configuration obtained by adding an organic solvent such as cyclohexanone and PGMA, a polymer varnish, a monomer, and an initiator was used.

The colorant of red resist is C.I. I. Pigment red 117, C.I. I. Pigment red 48: 1, C.I. I. Pigment yellow 139. The composition other than the coloring material was the same as that of the green resist.
The film thickness of each color filter was formed to be 0.5 to 0.8 μm. The arrangement of the plurality of color filters is a so-called Bayer arrangement in which green filters are provided every other pixel as shown in FIG. 2 and red filters and blue filters are provided every other row between green filters.

Next, on the color filter layer 4, a 1 μm thick film of a 1 μm thick alkali-soluble, photosensitive, heat-reflowable styrene resin was applied to form a photosensitive microlens material 12 (see FIG. 5B).
Thereafter, the photosensitive microlens material 12 was patterned by a process of photolithography with ultraviolet i-ray using a gray tone mask 13, and then heat treated at 250 ° C. to form the microlens 5 (FIG. 5 (e)) (D)).

The gray tone mask 13 is a mask in which the light shielding film has a gradation (darkness) on the light shielding film, in which the light transmittance is increased with respect to the lowest point of the microlens shape to be manufactured. The gradation of this gradation is achieved by the difference in the number (coarse / dense) per unit area of small diameter dots which are not resolved by light used for exposure.
In the gray tone mask 13 of the first embodiment, the radius of curvature R of the valley portion 9 between the microlenses is 225 nm in the diagonal cross section direction, and the microlenses corresponding to the green pixels correspond to the paraboloid shape and blue and red pixels. The microlens used was a photomask designed to have a spherical shape. A parabolic shape having a height of 450 nm of the microlens and a pixel configuration in which the spherical shape is mixed are obtained.

Here, in the photolithography method using the gray tone mask 13, when using the KRF laser, it is possible to control the curved surface shape of the microlens more narrowly than the ultraviolet i-line due to the wavelength limit resolution of the KRF laser. Become.
Table 1 shows the configuration of each example. In addition, in Table 1, the valley part was described as the valley.

  As shown in Table 1, in Examples 2 to 6 and Comparative Examples 1 to 4, the microlens height is 450 nm, and the curvature radius of the valleys between the microlenses is changed to obtain the microlens Micro-lenses of paraboloid 1 to paraboloid 5 and spherical surface 1 to spherical surface 5 different in the curvature radius at the top were respectively manufactured. The relationship of the radius of curvature of the top of the micro-lenses of the paraboloidal and spherical surfaces prepared in all cases is the radius of curvature of the top of the spherical shape> the radius of curvature of the top of the paraboloidal shape.

Example 2
The micro lens of Example 2 was formed in the same manner as Example 1 except that the radius of curvature R of the valley between adjacent micro lenses was 180 nm in the diagonal sectional direction.
Example 3
The micro lens of Example 3 was formed in the same manner as Example 1 except that the radius of curvature R of the valley between adjacent micro lenses was 135 nm in the diagonal cross sectional direction.

Example 4
In the gray tone mask 13 of the fourth embodiment, the microlenses corresponding to blue pixels have a paraboloidal shape, and the radius of curvature R of the valley between adjacent microlenses is 135 nm in the diagonal cross section direction, The microlens of Example 4 was formed in the same manner as in Example 1.
Example 5
In the gray tone mask 13 of the fifth embodiment, the microlenses corresponding to blue pixels have a paraboloidal shape, and the curvature radius R of the valley between adjacent microlenses is 90 nm in the diagonal cross section direction, The microlens of Example 5 was formed in the same manner as in Example 1.

Example 6
In the gray tone mask 13 of the sixth embodiment, the microlenses corresponding to blue pixels have a paraboloidal shape, and the radius of curvature R of the valley between adjacent microlenses is 45 nm in the diagonal cross section direction, The microlens of Example 6 was formed in the same manner as in Example 1.
Comparative Example 1
As a method of forming micro lenses of different shapes for each RGB pixel in Example 1, the gray tone mask 13 is a micro lens corresponding to a green pixel, a micro lens corresponding to a blue and a red pixel is a paraboloid. The microlens of Comparative Example 1 was formed in the same manner as in Example 1 except that a photomask designed to have a shape was used.

Comparative Example 2
As a method of forming micro lenses of different shapes for each RGB pixel in Example 2, the gray tone mask 13 is a micro lens corresponding to a green pixel, a micro lens corresponding to a blue and a red pixel is a paraboloid. The microlens of Comparative Example 2 was formed in the same manner as in Example 2 except that a photomask designed to have a shape was used.

Comparative Example 3
As a method of forming micro lenses of different shapes for each RGB pixel in Example 5, the gray tone mask 13 is a micro lens corresponding to green and blue pixels is a spherical shape, and a micro lens corresponding to red pixels is a paraboloid. The micro lens of Comparative Example 3 was formed in the same manner as in Example 5 except that a photomask designed to have a shape was used.

Comparative Example 4
As a method of forming micro lenses of different shapes for each RGB pixel in Example 6, the gray tone mask 13 is a micro lens corresponding to green and blue pixels is a spherical shape, and a micro lens corresponding to red pixels is a paraboloid. The micro lens of Comparative Example 4 was formed in the same manner as Example 6, except that a photomask designed to have a shape was used.

Table 1 also shows the results of measurement of the light receiving sensitivity for each of the RGB pixels in each example and each comparative example.
As can be seen from Table 1, the light receiving sensitivity measurement results of Example 1 having a radius of curvature R of a valley between adjacent microlenses of 225 nm and Example 2 of a radius of curvature R of a valley of 180 nm were green pixels. The light receiving sensitivity is higher than Comparative Example 1 and Comparative Example 2 by forming the corresponding microlenses into a paraboloidal shape and the microlenses corresponding to the red pixels into a spherical shape and the microlenses corresponding to the blue pixels into a spherical shape. It confirmed that it improved.

The results of light receiving sensitivity measurement in Example 3 and Example 4 confirm that the light receiving sensitivities are the same when the microlens corresponding to the blue pixel is spherical or parabolic. From this, when the curvature radius of the valley between adjacent microlenses is 135 nm, it is assumed that either a paraboloid or a spherical surface may be selected as the microlens shape corresponding to the blue pixel.
The results of measurement of light receiving sensitivity of Example 5 where the radius of curvature R of the valley between adjacent microlenses is 90 nm and Example 6 where the radius of curvature R of the valley 9 is 45 nm indicate that the microlens corresponding to the green pixel is released. The light receiving sensitivity is improved as compared with Comparative Example 3 and Comparative Example 4 by making the microlens corresponding to the object surface shape and the red pixel spherical and the microlens corresponding to the blue pixel parabolic. confirmed.

  Further, in Table 1, when the micro-lenses (ie, the first micro-lenses) disposed corresponding to the green pixels and the micro-lenses (ie, the second micro-lenses) disposed corresponding to the red pixels are compared, Since the relationship of the radius of curvature> the radius of curvature of the top of the paraboloid shape is established, the radius of curvature R of the valley is affected when the relationship between the first microlens 7 and the second microlens is R1 <R2. It can be confirmed that the light receiving sensitivity is improved.

Further, the curvature radius R3 of the top of the third micro lens is the curvature of the top of the first micro lens 7 when the curvature radius R of the valley is 135 nm or more, when the curvature radius R of the valley is 135 nm. By making it larger than the radius R1, the light receiving sensitivity is improved, and when the curvature radius R of the valley is less than 135 nm, the light receiving sensitivity can be confirmed by making it smaller than the curvature radius R2 of the top of the second microlens. .
The curvature radius of the top of the parabolic microlens corresponding to the green and blue pixels in each embodiment is the same, but may be different. In addition, while the same curvature radius of the top of the spherical shaped microlens corresponding to the red and blue pixels is used, it may be different.

1, semiconductor substrate 2, photoelectric conversion element 3, flattening layer 4, color filter layer 5, micro lens 6, solid-state imaging element 7, first micro lens 8, second micro lens 9, valley portion 10, adjacent micro lens Curvature circle 11 between valleys, lowest point 12 of valleys between adjacent microlenses, photosensitive microlens material 13, gray tone mask

Claims (6)

A semiconductor substrate on which a plurality of photoelectric conversion elements are two-dimensionally arranged;
A color filter layer formed on the semiconductor substrate and two-dimensionally arranged in a regular pattern having a plurality of color filters set in advance corresponding to each photoelectric conversion element;
And a plurality of microlenses formed on the color filter layer and disposed corresponding to each color filter,
Green, red and blue as colors of the color filter
The radius of curvature R1 of the top of the first microlens, which is the microlens corresponding to the color filter of green, is the radius of curvature R2 of the top of the second microlens, which is the microlens corresponding to the color filter of red. A solid-state imaging device characterized by being smaller than the above. The plurality of microlenses are connected at valleys between adjacent ones of the microlenses at the edges of the microlenses,
When the cross-sectional shape in the diagonal direction of the arrangement of the plurality of microlenses and the thickness direction of the semiconductor substrate is defined as a diagonal cross section, the radius of curvature of the valley in the diagonal cross section is 135 nm or more.
The solid-state imaging device according to claim 1, wherein a curvature radius R3 of a top portion of the third microlens which is the microlens corresponding to the blue color filter is larger than the curvature radius R1. The plurality of microlenses are connected at valleys between adjacent ones of the microlenses at the edges of the microlenses,
When the cross-sectional shape in the diagonal direction of the disposition of the plurality of microlenses and the thickness direction of the semiconductor substrate is defined as a diagonal cross section, the radius of curvature of the valley in the diagonal cross section is less than 135 nm,
The solid-state imaging device according to claim 1, wherein a curvature radius R3 of a top portion of the third microlens, which is the microlens corresponding to the blue color filter, is smaller than the curvature radius R2. The profile shape of the first microlens is a paraboloid shape,
The profile shape of the second microlens is a spherical shape,
The plurality of microlenses are connected at valleys between adjacent ones of the microlenses at the edges of the microlenses,
When the cross-sectional shape in the diagonal direction of the arrangement of the plurality of microlenses and in the thickness direction of the semiconductor substrate is defined as a diagonal cross section,
The profile shape of the third microlens, which is the microlens corresponding to the blue color filter, is spherical when the radius of curvature of the valley in the diagonal cross section is 135 nm or more, and the diagonal cross section The solid-state imaging device according to any one of claims 1 to 3, wherein when the radius of curvature of the valley portion is less than 135 nm, the valley has a parabolic shape. It is a manufacturing method of the solid-state imaging device according to any one of claims 1 to 4.
A method of manufacturing a solid-state imaging device, wherein the plurality of microlenses are collectively formed by photolithography using a gray tone mask.   The method for manufacturing a solid-state imaging device according to claim 5, wherein an ultraviolet i-ray or a KRF laser is used for the photolithography method.

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