Solid-state imaging device

Abstract

To provide a solid-state imaging element capable of supporting high resolution while suppressing petal flare.SOLUTION: A solid-state imaging element 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 color filters arranged in correspondence with the photoelectric conversion elements, and a microlens unit 20 having a plurality of microlenses 21 arranged in correspondence with the color filters. In the plurality of microlenses, a diagonal gap, which is the shortest distance between two microlenses adjacent to each other in the diagonal direction of a color filter area in which color filters are arranged, is between 15% or more and 25% or less of the longest side in the plan view shape of the color filter area.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 elements have become widespread, which make it possible to obtain 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 a photoelectric conversion element. As solid-state imaging devices become thinner, lighter and more precise, on-chip type solid-state imaging devices in which color filters are formed directly on a substrate on which photoelectric conversion elements are arranged are becoming more common.

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

[0004] [Patent Document 1] JP 2013-8777 A 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 in size, there is a demand for on-chip solid-state imaging devices with even higher resolution. In the course of investigating ways to increase the resolution of solid-state imaging devices, the inventors 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 suppress petal flare and accommodate higher definition. [Means for solving the problem]

[0007] The present invention relates to 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, Made of resin material, and a microlens portion having a plurality of microlenses arranged corresponding to the color filters. The diameter of the microlens or the dimension of one side of the color filter is 1.2 μm or less, and in the multiple microlenses, the diagonal gap, which is the shortest distance between two adjacent microlenses in the diagonal direction of the color filter region in which the color filters are arranged, is 15% to 25% of the longest side of the color filter region in a plan view. (However, the range between 22.36% and 22.37% is excluded.) It is. Effect of the Invention

[0008] According to the present invention, it is possible to provide a solid-state imaging device capable of suppressing petal flare and supporting higher definition. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of a solid-state imaging element according to an embodiment of the present invention. [Diagram 2] 1 is a plan view photograph of a conventional microlens portion. [Diagram 3] 2 is a schematic plan view of a microlens portion of the solid-state imaging element. FIG. [Figure 4] 13 is a graph showing a simulation result of the relationship between a diagonal gap in a microlens portion and reflected light in a direction other than the normal direction that occurs on the optical surface of the microlens. [Diagram 5] 11 is a graph showing the results of a simulation of the relationship between the thickness of a microlens and light reflected in a direction other than the normal direction generated on the optical surface of the microlens. [Figure 6] 1 is a plan view photograph of a microlens according to an example. [Figure 7] 11 is a photograph of a petal flare occurring in a solid-state imaging device according to a comparative example. [Figure 8] 1 is a photograph of a petal flare occurring in a solid-state imaging device according to an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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 section 10 includes three types of color filters, 11, 12, and 13. The types, number, and distribution of colors in the filter section 10 can be determined as appropriate, and known filters can be used. For example, a Bayer array using 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 when the solid-state imaging element 100 is viewed in a plan view.

[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. In order to improve the sensitivity of a solid-state imaging element, it is necessary to guide as much light as possible to the photoelectric conversion element by the microlens. For this reason, it has been common practice to form each microlens in the microlens section using known techniques such as thermal reflow and etch-back so that the optical surfaces of the microlenses are arranged with almost no gaps when viewed 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 in 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 flare that appears in the shape of petals spaced apart around the optical axis of a microlens, and is thought to be caused by the interference of reflected light in directions other than the normal direction that occurs on the optical surface of the microlens. In principle, petal flare itself is thought to have occurred in previous microlens arrays, but it was not previously a problem due to the large amount of light received by the photoelectric conversion element and the large distance (pitch) between adjacent color filter regions.

[0016] The inventors have investigated various methods for reducing petal flare, and have found that it is effective to provide a certain amount of gap area without microlenses in a plan view of the microlens portion.

[0017] When the color filter has a square shape 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 areas without microlenses are created at the corners of the square, as shown in Figure 3.

[0018] Figure 4 shows the results of a simulation that examines the relationship between the diagonal gap of the gap region and the amount of reflected light in directions other than the normal. The color filter region is a square with each side measuring 1.1 μm. The "diagonal gap" refers to the shortest distance between a microlens arranged in a given color filter region and a microlens arranged in another color filter that is located around the color filter region and only touches the corner of the color filter region, on a line passing through the corners where the color filter regions touch, and is indicated by the symbol DG in Fig. 3. That is, the diagonal gap is the shortest distance between a given microlens and another microlens adjacent to it in the diagonal direction in a plan view. Note that in a configuration in which each color filter is separated by a partition wall and the corners of the color filters in the diagonal direction do not touch each other directly, the diagonal gap is the distance including the partition wall. As shown in Fig. 4, as the diagonal gap increases, the reflected light in directions other than the normal direction decreases. If the microlens is too small relative to the color filter region, the amount of light that can be guided to the photoelectric conversion element decreases, resulting in a decrease in sensitivity. However, the inventors' investigations have shown that if the diagonal gap is between 15% and 25% of the length of one side of the corresponding color filter region, the reflected light in directions other than the normal direction can be reduced with almost no effect on performance such as sensitivity.

[0019] Furthermore, the inventors' investigations have confirmed that the thickness of the microlens also affects petal flare. In other words, by setting the diagonal gap within a predetermined range and adjusting the thickness of the microlens as follows, it is possible to further suppress petal flare. 5 shows the results of a simulation that examines the relationship between the thickness of the microlens and the amount of reflected light in directions other than the normal direction. The dimensions of the color filter region and other conditions were the same as those in the simulation shown in FIG. As shown in Fig. 5, it can be seen that as the thickness of the microlens increases, the reflected light in directions other than the normal direction decreases. The inventors' investigations have found that if the thickness is between 50% and 65% of the length of one side of the corresponding color filter region, the reflected light in directions other than the normal direction can be reduced with almost no effect on performance such as sensitivity. Furthermore, it is more preferable for the thickness of the microlens to be in the range of between 50% and 54% of the length of one side of the color filter region, since this allows for a high level of both improvement in the light collection efficiency of the microlens and reduction in the reflected light in directions other than the normal direction. 4 and 5, "Sum" refers to the sum of all diffracted light, and "Max" refers to the strongest diffracted light among all diffraction orders. Both have an effect on petal flare, but suppressing the Max value is more effective in suppressing petal flare.

[0020] The solid-state imaging device of the present embodiment will be further described using examples and comparative examples. The technical scope of the present invention is not limited in any way by the specific contents of the examples and comparative examples.

[0021] Example 1 A wafer substrate was prepared that had multiple photoelectric conversion elements arranged in a two-dimensional matrix, metal wiring, etc. Three color filters of G (green), R (red), and B (blue) were formed in a Bayer array on this wafer substrate, corresponding to the regions of each photoelectric conversion element, and a filter section was provided on the wafer substrate. A transparent layer made of a non-photosensitive resin was formed on the filter portion using a coater, and a hard mask made of a photosensitive resin was coated on the transparent layer, exposed, and developed to form a lens pattern that was circular in plan view in each color filter region. This lens pattern was subjected to a heat flow process at 160° C. for 300 seconds to make the lens pattern into a hemispherical shape, and then the lens pattern and the transparent layer were etched by an etching process. In this manner, a solid-state imaging element according to Example 1 was obtained. The dimensions of each portion in Example 1 are as follows. Color filter area: 1.1 μm square Microlens thickness: 0.58 μm (52.7% of the above side) Microlens diagonal gap: 0.1 μm (9.09% of the above side)

[0022] (Comparative Example) A solid-state imaging device with a color filter according to the comparative example was obtained in the same manner as in Example 1, except that the etching process was changed so that the thickness of the microlens was 0.52 μm (47.3% of the above-mentioned one side).

[0023] Example 2 A solid-state imaging element with a color filter according to the comparative example was obtained in the same manner as in Example 1, except that the diagonal gap of the microlens was set to 0.27 μm (24.5% of the above-mentioned one side) by changing the lens pattern and the etching process. The maximum petal flare intensity for each color in Example 1 and the Comparative Example is shown in Table 1. In Table 1, the relative values ​​are shown with the maximum intensity in the Comparative Example taken as 100.

[0024] [Table 1]

[0025] As shown in Table 1, in Example 1, the maximum intensity of petal flare was reduced by 20% or more for all color filters.

[0026] Fig. 6 is a plan view photograph of the microlens portion according to Example 2, taken with a scanning electron microscope (SEM). Compared with Fig. 2, it can be seen that a relatively large diagonal gap is secured at the corner of each color filter region. Fig. 7 shows a photograph of the petal flare of the comparative example, and Fig. 8 shows a photograph of the petal flare of Example 2. It can be seen that the brightness of the petal flare of Example 2 is suppressed compared to the comparative example.

[0027] Although the embodiment and examples of the present invention have been described above, the specific configuration is not limited to this embodiment, and configuration changes and combinations that do not depart from the gist of the present invention are also included.

[0028] For example, the shape of each color filter region is not limited to the above-mentioned square, but may be a rectangle or other polygon. When the shape of the color filter region has a variety of 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 element of the present invention may not have a color filter disposed in a part thereof in a plan view. For example, when the present invention is applied to a solid-state imaging element in which a part of the photoelectric conversion element is used for focus adjustment or the like, a color filter may not be disposed in a region of the filter portion corresponding to the photoelectric conversion element used for focus adjustment.

[0030] A partition wall for preventing stray light may be formed between each of the color filters. The partition wall may be a light absorbing partition wall or a light reflective partition wall. [Explanation of symbols]

[0031] 1 On-chip color filter 10 Filter section 11, 12, 13 Color Filters 20 Microlens section 21 Microlens 100 Solid-state image sensor 101 Wafer Substrate DG Diagonal 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 portion made of a resin material and having a plurality of microlenses arranged corresponding to the color filters; Equipped with The diameter of the microlens or the dimension of one side of the color filter is 1.2 μm or less; a diagonal gap between two microlenses diagonally adjacent to each other in a color filter region in which the color filters are arranged is 15% to 25% (excluding a range of 22.36% to 22.37%) of a longest side of the color filter region in a plan view; Solid-state imaging element.

2. the thickness of the microlens is 50% or more and 65% or less of the longest side of the corresponding color filter region; The solid-state imaging device according to claim 1 .

Images