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 plan view of a color filter area in which color filters are arranged, the filling factor of the microlenses to the color filter area is 90% or more and 95% or less.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 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 accommodate higher definition while suppressing petal flare. [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 resin material and having a plurality of microlenses arranged corresponding to the color filters. The diameter of the microlenses is 1.2 μm or less, In a plan view of the color filter area where the color filters are arranged, the filling rate of the microlenses in the color filter area is 90% or more and 95% or less and the thickness of the microlens is 0.58 μm or more and 0.72 μm or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a solid-state imaging device that can suppress petal flare and accommodate higher definition. [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. 2 is a schematic plan view of a microlens portion of the solid-state imaging device. [Figure 4] 10 is a graph showing the results of a simulation of the relationship between the packing ratio of the microlenses in the color filter region and the light reflected in directions other than the normal direction generated on the optical surface of the microlens. [Figure 5] 10 is a graph showing the results of a simulation of the relationship between the thickness of a microlens and light reflected in directions other than the normal direction and occurring on the optical surface of the microlens. [Figure 6] 1 is a plan view photograph of a microlens according to an example. [Figure 7]10 is a photograph of petal flare occurring in a solid-state imaging device according to a comparative example. [Figure 8] 10 is a photograph of petal flare occurring in a solid-state imaging device according to an example. 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 and etch-back so that the optical surfaces of the microlenses 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 previously a problem due to the large amount of light received by the photoelectric conversion elements 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 reduce the area where the microlenses are arranged in a plan view of the microlens portion.

[0017] When the color filter has a square shape in plan view, the diameter of the microlenses is set to be roughly the same as the diagonal of the square, so that the microlenses are arranged without gaps in the color filter region as shown in Figure 2. If the diameter of the microlenses is reduced from this state, unfilled regions 22 without microlenses 21 will appear in the corners of the color filter region, as shown in Figure 3.

[0018] Figure 4 shows the results of a simulation that examines the relationship between the fill factor, which is the ratio of the microlenses to the color filter area, and the amount of light reflected in directions other than the normal. The color filter area is a square with sides of 1.1 μm. The filling rate can be calculated, for example, by the following formula (1) or formula (2), but is not limited to this and may be calculated by image processing (such as counting the number of pixels) of a planar image of the color filter region. Planar area of ​​microlens / Planar area of ​​color filter area × 100 (%)…(1) (Plane view area of ​​color filter area - Plane view area of ​​non-filled area) / Plane view area of ​​color filter area × 100 (%)... (2) As shown in Figure 4, it can be seen that as the filling rate decreases, the reflected light in directions other than the normal direction decreases. If the filling rate 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' studies have shown that if the filling rate is between 90% and 95%, 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 microlenses also affects petal flare. That is, by adjusting the thickness of the microlenses as follows while keeping the filling rate within a predetermined range, petal flare can be further suppressed. 5 shows the results of a simulation that examines the relationship between the thickness of the microlens and the amount of light reflected in directions other than the normal. The dimensions of the color filter region and other conditions were the same as those in the simulation shown in FIG. As shown in Figure 5, as the thickness of the microlens increases, the light reflected in directions other than the normal direction decreases. The inventors' investigations have shown that if the thickness is 65% or less of the length of one side of the color filter region, the light reflected in directions other than the normal direction can be reduced with almost no effect on performance such as sensitivity. In Figures 4 and 5, "Sum" refers to the sum of all diffracted light, and "Max" refers to the light that is diffracted most strongly among all diffraction orders. Both affect petal flare, but reducing the Max value is more effective in suppressing petal flare.

[0020] The solid-state imaging device of this 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 on this wafer substrate in a Bayer pattern 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 within 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 hemispherical, and then the lens pattern and the transparent layer were etched in an etching process. As a result of the above, a solid-state imaging device according to Example 1 was obtained. The dimensions of each part 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 filling rate: 99.5%

[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 microlenses was 0.52 μm (47.3% of the above-mentioned one side).

[0023] Example 2 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 lens pattern and etching process were changed to change the microlens filling rate to 94.0%. The maximum petal flare intensity for each color in Example 1 and Comparative Example is shown in Table 1. Table 1 shows relative values, with the maximum intensity in 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 relatively large unfilled areas are secured at the corners of each color filter region. Fig. 7 shows a photograph of petal flare in the comparative example, and Fig. 8 shows a photograph of petal flare in Example 2. It can be seen that the brightness of petal flare in Example 2 is suppressed compared to the comparative example.

[0027] Although the embodiments and examples of the present invention have been described above, the specific configurations are not limited to these embodiments, and modifications and combinations of the configurations may be made without departing from the spirit of the present invention.

[0028] For example, the shape of each color filter region is not limited to the square described above, but may be a rectangle or other polygon.

[0029] The solid-state imaging device 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 device in which a part of the photoelectric conversion element is used for focus adjustment, etc., 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] 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 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 In a plan view of the color filter region in which the color filters are arranged, the packing ratio of the microlenses to the color filter region is 90% or more and 95% or less, The diameter of the microlens is 1.2 μm or less, The thickness of the microlens is 0.58 μm or more and 0.72 μm or less. Solid-state imaging element.

2. the thickness of the microlens is 52.7% or more and 65% or less of the longest side of the corresponding color filter region in a plan view; The solid-state imaging device according to claim 1 .

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