JP2022030762A - Solid-state imaging element - Google Patents

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

The present invention relates to a solid-state image sensor, more particularly an on-chip type solid-state image sensor to which a color filter and a microlens array are attached.

It is possible to obtain color information of an object by providing a color filter in which a colored transparent pattern of multiple colors that selectively transmits light of a specific wavelength is arranged in a plane in the path of light incident on the photoelectric conversion element. Single-panel solid-state image sensors have become widespread.
As the solid-state image sensor becomes thinner and lighter and has higher definition, the number of on-chip type solid-state image sensors that form a color filter directly on the array substrate of the photoelectric conversion element is increasing.

In the on-chip type solid-state image sensor, a microlens may be arranged in order to efficiently guide light to the photoelectric conversion element (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-8777

Higher image quality and smaller size of digital image devices are advancing, and even higher definition is required for on-chip type solid-state image sensors.
The inventor recognized and solved a new problem called petal flare, which had not been regarded as a problem in the past, in the process of proceeding with the study for dealing with such high definition of the solid-state image sensor.

An object of the present invention is to provide a solid-state image pickup device capable of high definition while suppressing petal flare.

The present invention comprises a wafer substrate having a plurality of photoelectric conversion elements, a filter unit having a plurality of types of color filters formed on the wafer substrate and arranged corresponding to the photoelectric conversion elements, and arrangement corresponding to the color filter. It is a solid-state image pickup device including a microlens unit having a plurality of microlenses.
In a plurality of microlenses, the diagonal gap, which is the shortest distance between two microlenses diagonally adjacent to each other in the color filter region in which the color filter is arranged, is 15% or more of the longest side in the plan view shape of the color filter region. It is 25% or less.

According to the present invention, it is possible to provide a solid-state image pickup device capable of high definition while suppressing petal flare.

It is a schematic cross-sectional view of the solid-state image pickup device which concerns on one Embodiment of this invention. It is a plan view photograph of a conventional microlens part. It is a schematic plan view of the microlens part which concerns on the solid-state image sensor. It is a graph of the simulation result of the relationship between the diagonal gap in a microlens part and the reflected light other than the normal direction generated in the optical surface of a microlens. It is a graph of the simulation result of the relationship between the thickness of a microlens and the reflected light other than the normal direction generated in the optical surface of a microlens. It is a plan view photograph of the microlens which concerns on Example. It is a photograph of the petal flare generated in the solid-state image sensor according to the comparative example. It is a photograph of the petal flare generated in the solid-state image sensor according to the embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 4.
FIG. 1 is a schematic cross-sectional view of a solid-state image sensor according to the present embodiment. The solid-state image sensor 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.

The on-chip color filter 1 has a filter unit 10 including a plurality of types of color filters, and a microlens unit 20 arranged on the filter unit 10.
The filter unit 10 includes three types of color filters 11, 12, and 13. The type, number, and distribution of the colors of the filter unit 10 can be appropriately determined, and known ones can be adopted. For example, a bayer arrangement using three colors of red, green, and blue can be exemplified. In the plan view of the solid-state image sensor 100, each color filter overlaps with one of the photoelectric conversion elements PD.

The microlens unit 20 has a plurality of microlenses 21. The microlens 21 has substantially the same arrangement as the color filter of the filter unit 10, and each color filter overlaps with one of the microlenses 21 in the plan view of the solid-state image pickup device 100.

In the solid-state image pickup device 100 configured as described above, the light incident on the microlens 21 is guided to the photoelectric conversion element PD through the corresponding color filter, thereby exhibiting the image pickup function.
In order to improve the sensitivity of the solid-state image sensor, it is necessary to guide as much light as possible to the photoelectric conversion element by the microlens. Therefore, each microlens of the microlens portion is formed by using known techniques such as thermal reflow and etch back so that the optical surfaces of the microlenses are arranged almost without gaps in a plan view as shown in FIG. It was common sense to be done.

However, in a solid-state image sensor in which the diameter of the microlens or the dimension of one side of the color filter in which the microlens is arranged is made high-definition to 1.2 μm or less, a phenomenon that sufficient color purity cannot be obtained is sometimes seen. became.
When the inventor examined this phenomenon, he found that petal flare caused by microlenses was a major factor.

Petal flare is flare that occurs in the shape of petals at intervals around the optical axis of the microlens, and is considered to be caused by interference of reflected light 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 conventional microlens arrays, but in the past, the amount of light received by the photoelectric conversion element was large, and the distance (pitch) from the adjacent color filter region was large. Therefore, it is probable that it did not become apparent as a problem.

The inventor has studied various methods for reducing petal flare. As a result, it has been found that it is effective to provide a certain amount of a gap region without a microlens in the plan view of the microlens portion.

When the plan-view shape of the color filter is square, the microlenses are arranged without gaps as shown in FIG. 2 by making the diameter of the microlenses substantially the same as the diagonal line of the square. When the diameter of the microlens is reduced from this state, as shown in FIG. 3, a gap region without the microlens is generated in the corner portion of the square.

FIG. 4 is a simulation result of examining the relationship between the diagonal gap in the gap region and the amount of reflected light other than the normal direction. The color filter area was a square with a side of 1.1 μm.
The "diagonal gap" is a color filter area of a microlens arranged in an arbitrary color filter area and a microlens arranged in another color filter around the color filter area and in contact with only the corners. It means the shortest distance on the line passing through the corner portion where is in contact with, and is shown by the symbol DG in FIG. That is, the diagonal gap is the shortest distance between any microlens in plan view and other microlenses adjacent in the diagonal direction thereof. When each color filter is separated by a partition wall and the corners of the diagonal color filters do not come into direct contact with each other, the diagonal gap is the distance including the partition wall.
As shown in FIG. 4, it can be seen that as the diagonal gap increases, the reflected light other than the normal direction decreases. If the microlens is too small for the color filter region, the amount of light that can be guided to the photoelectric conversion element is reduced, resulting in a decrease in sensitivity. It was found that when the length is 15% or more and 25% or less, the reflected light other than the normal direction can be reduced with almost no effect on the performance such as sensitivity.

Furthermore, in the inventor's study, it was confirmed that the thickness of the microlens also affects petal flare. That is, petal flare can be further suppressed by adjusting the thickness of the microlens as follows while setting the diagonal gap within a predetermined range.
FIG. 5 is a simulation result of examining the relationship between the thickness of the microlens and the amount of reflected light other than the normal direction. The conditions such as the dimensions of the color filter area were the same as in the simulation according to FIG.
As shown in FIG. 5, it can be seen that as the thickness of the microlens increases, the reflected light other than the normal direction decreases. According to the study of the inventor, if the thickness is 50% or more and 65% or less of the length of one side of the corresponding color filter region, the reflected light other than the normal direction can be reduced with almost no effect on the performance such as sensitivity. I understood. Furthermore, if the thickness of the microlens is in the range of 50% or more and 54% or less of the length of one side of the color filter region, it is possible to improve the light collection efficiency of the microlens and reduce the reflected light other than the normal direction at a high level. Therefore, it can be said that it is more preferable.
In FIGS. 4 and 5, "Sum" refers to the sum of all diffracted light, and "Max" refers to the light most strongly diffracted in all diffraction orders. Both affect petal flare, but in order to suppress petal flare, it is more effective to suppress the Max value.

The solid-state image sensor of this embodiment will be further described with reference to Examples and Comparative Examples. The technical scope of the present invention is not limited to the specific contents of Examples and Comparative Examples.

(Example 1)
A wafer substrate having a plurality of photoelectric conversion elements arranged in a two-dimensional matrix and metal wiring and the like was prepared. Three color filters of G (green), R (red), and B (blue) are formed on this wafer substrate in a bayer arrangement while corresponding to the regions of each photoelectric conversion element, and the filters are formed on the wafer substrate. A part was provided.
A transparent layer made of a non-photosensitive resin is formed on the filter portion by a coater, a hard mask made of a photosensitive resin is coated on the transparent layer and exposure-developed, and a circular lens pattern in a plan view is formed in each color filter region. Formed.
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 by an etching process.
From the above, the solid-state image sensor according to Example 1 was obtained. The dimensions of each part in Example 1 are as follows.
Color filter area: Square microlens with a side of 1.1 μm Thickness: 0.58 μm (52.7% of the above side)
Microlens diagonal gap: 0.1 μm (9.09% of the above side)

(Comparative example)
A solid-state image sensor with a color filter according to a comparative example was obtained by the same procedure as in Example 1 except that the thickness of the microlens was set to 0.52 μm (47.3% of the above side) by changing the etching process.

(Example 2)
Solid-state imaging with a color filter according to the comparative example in the same procedure as in Example 1 except that the diagonal gap of the microlens was set to 0.27 μm (24.5% of the above side) by changing the lens pattern and etching process. Obtained the element.
Table 1 shows the maximum intensity of petal flare in each color of Example 1 and Comparative Example. Table 1 shows relative values with the maximum intensity of the comparative example as 100.

As shown in Table 1, in Example 1, the maximum intensity of petal flare was reduced by 20% or more in any of the color filters.

FIG. 6 is a plan view photograph of the microlens portion according to the second embodiment, which was obtained by 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 the second embodiment. In Example 2, it can be seen that the brightness of the petal flare is suppressed as compared with the comparative example.

Although the embodiments and examples of the present invention have been described above, the specific configuration is not limited to this embodiment, and includes changes and combinations of configurations within a range that does not deviate from the gist of the present invention.

For example, the shape of each color filter region is not limited to the square described above, and may be a rectangle or another polygon. When the shape of the color filter area has a plurality of types of side lengths such as a rectangle, the thickness, diagonal gap, etc. may be set based on the length of the longest side.

In the solid-state image pickup device of the present invention, the color filter may not be arranged in a part in the plan view. For example, when the present invention is applied to a solid-state image pickup device or the like in which a part of a photoelectric conversion element is used for focus adjustment or the like, there is also an embodiment in which a color filter is not arranged in a region corresponding to the photoelectric conversion element used for focus adjustment in the filter unit. sell.

A partition wall may be formed between the color filters to prevent stray light. The partition wall may be a light-absorbing partition wall or a light-reflecting partition wall.

1 On-chip color filter 10 Filter unit 11, 12, 13 Color filter 20 Micro lens unit 21 Micro lens 100 Solid-state image sensor 101 Wafer substrate DG Diagonal gap PD Photoelectric conversion element

Claims (2)

A wafer substrate with multiple photoelectric conversion elements and
A filter unit having a plurality of types of color filters formed on the wafer substrate and arranged corresponding to the photoelectric conversion element, and
A microlens unit having a plurality of microlenses arranged corresponding to the color filter,
Equipped with
In the plurality of microlenses, the diagonal gap, which is the shortest distance between two microlenses diagonally adjacent to each other in the color filter region in which the color filter is arranged, is the longest side in the plan view shape of the color filter region. 15% or more and 25% or less,
Solid-state image sensor. The thickness of the microlens is 50% or more and 65% or less of the longest side in the corresponding color filter region.
The solid-state image sensor according to claim 1.

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