solid-state imaging device

Abstract

To provide a solid-state image sensor capable of suppressing petal flare and achieving high sensitivity at the same time.SOLUTION: A solid-state image sensor 100 includes a wafer substrate 101 having a plurality of photoelectric conversion elements PD, a filter unit 10 formed on the wafer substrate and having a plurality of types of color filters arranged corresponding to the photoelectric conversion elements, and a microlens unit 20 made of a non-photosensitive resin and having a plurality of microlenses 21 arranged corresponding to the color filters. The plurality of microlenses are arranged so as to have a gap between two microlenses that are adjacent in the diagonal direction of the rectangular color filter region in which the color filters are arranged, and have a gap between two microlenses that are adjacent in the direction in which the sides of the color filter region extend.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a solid-state imaging device, and more particularly to an on-chip type solid-state imaging device equipped with a color filter and a microlens array. [Background technology]

[0002] Single-plate solid-state imaging devices are becoming popular, which enable obtaining color information of an object by providing a color filter, which is a planar arrangement of multiple colored transparent patterns that selectively transmit light of specific wavelengths, in the path of light incident on the photoelectric conversion element. As solid-state imaging devices become thinner, lighter, and more highly precise, on-chip type solid-state imaging devices in which color filters are formed directly on an array substrate of photoelectric conversion elements are becoming more common.

[0003] In on-chip type solid-state imaging devices, microlenses are sometimes arranged to efficiently guide light to photoelectric conversion elements (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-8777 Summary of the Invention [Problem to be solved by the invention]

[0005] As digital imaging devices continue to improve in image quality and become smaller, there is a demand for even higher resolution in on-chip solid-state imaging devices. In addition, high sensitivity is often required. In the course of conducting research into how to deal with the increasing definition of solid-state imaging devices, the inventors have recognized and solved a new problem known as petal flare, which had not previously been considered a problem.

[0006] An object of the present invention is to provide a solid-state imaging device that can achieve both suppression of petal flare and high sensitivity. [Means for solving the problem]

[0007] The present invention is a solid-state imaging element comprising a wafer substrate having a plurality of photoelectric conversion elements, a filter section formed on the wafer substrate and having a plurality of types of color filters arranged corresponding to the photoelectric conversion elements, and a microlens section made of a non-photosensitive resin and having a plurality of microlenses arranged corresponding to the color filters. The multiple microlenses are arranged with a gap between two adjacent microlenses in the diagonal direction of the rectangular color filter region in which the color filters are arranged, and with a gap between two adjacent microlenses in the direction in which the sides of the color filter region extend. The color filter region is a square with a side length of 1.2 μm or less, and the refractive index of the microlens portion is 1.6 or more, The diagonal gap, which is the shortest distance between two diagonally adjacent microlenses, is One side and the horizontal gap, which is the shortest distance between two adjacent microlenses in the direction in which the sides of the color filter region extend, is 38% or more and 70% or less of the planar shape of the color filter region. One side is between 14% and 35%. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a solid-state imaging device that can achieve both suppression of petal flare and high sensitivity. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of a solid-state imaging device according to one embodiment of the present invention. [Figure 2] 10 is a plan view photograph of a conventional microlens portion. [Figure 3] FIG. 10 is a diagram for explaining gaps between microlenses. [Figure 4] 2A to 2C are diagrams illustrating a process during the manufacturing of the solid-state imaging device. [Figure 5]2A to 2C are diagrams illustrating a process during the manufacturing of the solid-state imaging device. [Figure 6] 2A to 2C are diagrams illustrating a process during the manufacturing of the solid-state imaging device. [Figure 7] 1 is a plan view photograph of a fabricated microlens portion. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 is a schematic cross-sectional view of a solid-state imaging device according to this embodiment. The solid-state imaging device 100 includes a wafer substrate 101 having a plurality of photoelectric conversion elements PD, and an on-chip color filter 1 formed on the wafer substrate 101.

[0011] The on-chip color filter 1 has a filter section 10 including a plurality of types of color filters, and a microlens section 20 disposed on the filter section 10. The filter unit 10 includes three types of color filters, 11, 12, and 13. The type, number, and distribution of colors in the filter unit 10 can be determined as appropriate, and known methods can be used. For example, a Bayer array using the three colors red, green, and blue can be used. In a plan view of the solid-state imaging device 100, each color filter overlaps one of the photoelectric conversion elements PD.

[0012] The microlens section 20 has a plurality of microlenses 21. The microlenses 21 are arranged in a manner generally similar to the color filters of the filter section 10, and each color filter overlaps one of the microlenses 21 in a plan view of the solid-state imaging device 100.

[0013] In the solid-state imaging device 100 configured as above, light incident on the microlenses 21 passes through the corresponding color filters and is guided to the photoelectric conversion elements PD, thereby achieving an imaging function. To improve the sensitivity of a solid-state imaging device, it is necessary to guide as much light as possible to the photoelectric conversion element using the microlenses. For this reason, it has been common practice to form each microlens in the microlens section using known techniques such as thermal reflow or etch-back so that the optical surfaces of the microlenses ML are arranged with almost no gaps in a plan view, as shown in Figure 2.

[0014] However, in solid-state imaging devices in which the diameter of a microlens or the dimension of one side of a color filter on which a microlens is arranged has been increased to 1.2 μm or less, a phenomenon has been observed in which sufficient color purity cannot be obtained. The inventors have investigated this phenomenon and found that petal flare caused by microlenses is a major factor.

[0015] Petal flare is a petal-shaped flare that appears at intervals around the optical axis of a microlens, and is thought to be caused by the interference of light reflected off the optical surface of the microlens in a direction other than the normal. In principle, petal flare itself is thought to have occurred in previous microlens arrays, but it was not a significant problem due to the large area of ​​the unit pixel region, the large amount of light received, and the large distance (pitch) between adjacent color filter regions.

[0016] The inventors have studied various methods for reducing petal flare, and as a result have found that it is effective to provide a certain amount of gap area where no microlenses are present in a plan view of the microlens portion.

[0017] When the color filter has a rectangular shape such as a square in plan view, the microlenses are arranged without gaps by making the diameter of the microlenses roughly the same as the diagonal of the square, as shown in Figure 2. If the diameter of the microlenses is reduced from this state, gap regions G without microlenses are created at the corners of the square, as shown in Figure 3.

[0018] As the diameter of the microlens decreases, gap regions first appear in the corners, and as the diameter decreases further, gap regions appear in the side portions between the corners. In the following explanation, gaps that appear in the corners may be referred to as "diagonal gaps," and gaps that appear in the side portions (gaps in the direction in which the sides extend) may be referred to as "horizontal gaps."

[0019] As the gap area increases, the planar area of ​​the microlens decreases, which leads to a decrease in the amount of collected light, making it difficult to suppress petal flare while maintaining sensitivity. The inventors have conducted various studies to solve this problem, and as a result have focused on the refractive index of the material forming the microlenses, thereby completing the present invention.

[0020] An example of a manufacturing procedure for the solid-state imaging device 100 will be described. First, a wafer substrate 101 is prepared, which has a plurality of photoelectric conversion elements PD arranged in a two-dimensional matrix and metal wiring, etc. Next, color filters are formed on the wafer substrate 101 in a desired arrangement corresponding to the regions of each photoelectric conversion element PD, and a filter unit 10 is provided on the wafer substrate.

[0021] Next, a first transparent layer 20A made of a non-photosensitive resin is formed on the filter portion 10 as shown in Fig. 4. Furthermore, a sacrificial layer 50 made of a photosensitive resin is formed on the first transparent layer 20A as shown in Fig. 5.

[0022] Next, the sacrificial layer 50 is exposed and developed with a pattern corresponding to the position of the photoelectric conversion element PD, and then a thermal flow process is performed under specified conditions, whereby an approximately hemispherical sacrificial pattern 50A is formed on the first transparent layer 20A at a position corresponding to the photoelectric conversion element PD, as shown in Figure 6. Since the shape of the sacrificial patterns 50A affects the shape of the microlenses to be formed later, it is preferable that the arranged sacrificial patterns 50A be formed so as to have at least both diagonal gaps and horizontal gaps.

[0023] Next, dry etching is performed on the first transparent layer 20A and the sacrificial pattern 50A. By dry etching, the sacrificial pattern 50A disappears, and the shape of the sacrificial pattern 50A is transferred to the first transparent layer 20A, forming a plurality of lens-shaped structures in the first transparent layer 20A. At this point, the lens-shaped structures are not in contact with each other, and gap regions exist around the lens-shaped structures. In the manufacture of a typical etch-back lens array, dry etching continues even after the shape of the sacrificial pattern is transferred to the first transparent layer until the horizontal and diagonal gaps are almost completely eliminated. However, in this embodiment, the dry etching is terminated immediately after the transfer is completed, or after continuing for a shorter period of time than usual, thereby completing the formation of the lens-shaped structure while both the horizontal and diagonal gaps remain.

[0024] This completes the microlens section 20 having a plurality of microlenses 21. Thereafter, the wafer substrate is cut into pieces of a predetermined size by dicing or the like, thereby completing the solid-state imaging device 100 of this embodiment. A scanning electron microscope (SEM) image of the microlens portion that was actually fabricated is shown in Figure 7. It can be seen that both a diagonal gap DG and a horizontal gap HG are secured between the microlenses 21.

[0025] In the microlens section 20, diagonal and horizontal gaps are secured between the microlenses 21 formed by dry etching, so the occurrence of petal flare can be suitably suppressed even with the high resolution described above. The inventors' investigations have confirmed that, when the color filter region is a square with sides of 1.1 μm, ensuring a diagonal gap of approximately 0.40 to 0.75 μm and a horizontal gap of approximately 0.15 to 0.35 μm can adequately suppress the occurrence of petal flare while maintaining sufficient sensitivity. Expressed as a ratio to the length of one side of the color filter region, the diagonal gap is 38% to 70% and the horizontal gap is 14% to 35%. In this case, the fill factor, which is the ratio of the microlenses to the unit color filter area in a planar view, is approximately 65% ​​to 75%, a value that is completely impossible for a typical microlens array used in an on-chip solid-state imaging device. 7, the color filter region is a square with sides of 0.93 μm, and the diagonal gap DG and horizontal gap HG are 43% and 18% of the length of one side, respectively, which satisfy the above numerical range. The fill factor is also just under 70%, which also satisfies the above numerical range.

[0026] A microlens array with diagonal and horizontal gaps can also be formed by developing, exposing, and thermally flowing a sacrificial layer 50. However, the inventors' investigations revealed that the photosensitive resin used in the sacrificial layer has an upper limit on its refractive index, making it difficult to maintain or improve sensitivity while maintaining diagonal and horizontal gaps. On the other hand, some non-photosensitive resins used in the first transparent layer have a refractive index that exceeds the upper limit of the photosensitive resin, for example, a refractive index n of 1.6 or higher. Examples of non-photosensitive resins with such high refractive indices include polyamide, polyamideimide, polyetherimide, norbornene-based resins, methacrylic resins, isobutylene-maleic anhydride copolymer resins, cyclic olefin-based resins, polyvinyl alcohol, 3-methoxybutyl acetate, cyclopentanone, γ-butyrolactone, propylene glycol monomethyl ether acetate, and acrylic resins. In the present invention, based on the above findings, the first transparent layer is formed using such a material with a high refractive index, and the lens array is formed by etching back, thereby increasing the refractive index of the microlens portion 20 and improving the light collection efficiency. As a result, it is possible to achieve both suppression of petal flare and high sensitivity.

[0027] Although one embodiment of the present invention has been described above, the specific configuration is not limited to this embodiment, and configuration changes and combinations within the scope of the gist of the present invention are also included. Some examples of changes are shown below, but these are not all inclusive, and other changes are also possible. Two or more of these changes may be combined as appropriate.

[0028] The shape of each color filter region is not limited to the square described above, but may be a rectangle or other polygon. When the shape of a color filter region has multiple side lengths, such as a rectangle, the thickness, diagonal gap, etc. may be set based on the length of the longest side.

[0029] The solid-state imaging device of the present invention may not have a color filter disposed in a portion thereof in plan view. For example, when the present invention is applied to a solid-state imaging device in which a portion of the photoelectric conversion elements is used for focus adjustment, a color filter may not be disposed in the region of the filter portion corresponding to the photoelectric conversion element used for focus adjustment.

[0030] A partition wall may be formed between each color filter to prevent stray light. The partition wall may be a light-absorbing partition wall or a light-reflective partition wall. [Explanation of symbols]

[0031] 10 Filter section 11, 12, 13 color filters 20 Microlens section 21 Microlens 100 solid-state image sensor 101 wafer substrate DG Diagonal Gap HG Horizontal Gap PD photoelectric conversion element

Claims

1. a wafer substrate having a plurality of photoelectric conversion elements; a filter section formed on the wafer substrate and having a plurality of types of color filters arranged corresponding to the photoelectric conversion elements; a microlens section made of a non-photosensitive resin and having a plurality of microlenses arranged corresponding to the color filters; Equipped with the plurality of microlenses are arranged with a gap between two adjacent microlenses in a diagonal direction of a rectangular color filter region in which the color filters are arranged, and with a gap between two adjacent microlenses in a direction in which a side of the color filter region extends; the color filter region has a square shape in plan view, each side of which has a length of 1.2 μm or less; The refractive index of the microlens portion is 1.6 or more, a diagonal gap, which is the shortest distance between two diagonally adjacent microlenses, is 38% to 70% of one side of the shape of the color filter region in a planar view, and a horizontal gap, which is the shortest distance between two adjacent microlenses in a direction in which the side of the color filter region extends, is 14% to 35% of one side of the shape of the color filter region in a planar view. Solid-state imaging element.

2. In the microlens, a fill factor, which is a ratio of a planar view area of ​​the microlens to an area of ​​a rectangular color filter region in which the color filters are arranged, is 65% or more and 75% or less. The solid-state imaging device according to claim 1 .

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