JP7729026B2 - solid-state imaging device - Google Patents

Description

The present invention relates to a solid-state imaging device, and more specifically to an on-chip type solid-state imaging device equipped with a color filter and a microlens array.

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.

On-chip solid-state imaging devices may be equipped with microlenses to efficiently guide light to the photoelectric conversion elements (see, for example, Patent Document 1).

JP 2013-8777 A

As digital imaging devices continue to improve in image quality and become smaller in size, there is a demand for even higher definition 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.

The present invention aims to provide a solid-state imaging device that can accommodate higher resolution while suppressing petal flare.

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 microlens is 1.2 μm or less,
In a plan view of a color filter region where color filters are arranged, the packing ratio of the microlenses to the color filter region is 90% to 95%, and the thickness of the microlenses is 0.58 μm to 0.72 μm.

The present invention provides a solid-state imaging device that can accommodate higher resolution while suppressing petal flare.

1 is a schematic cross-sectional view of a solid-state imaging device according to one embodiment of the present invention. 10 is a plan view photograph of a conventional microlens portion. FIG. 2 is a schematic plan view of a microlens portion of the solid-state imaging device. 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. 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 from the optical surface of the microlens. 1 is a plan view photograph of a microlens according to an example. 10 is a photograph of petal flare occurring in a solid-state imaging device according to a comparative example. 10 is a photograph of petal flare occurring in a solid-state imaging device according to an example.

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 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.

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, namely, 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 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.

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

In the solid-state imaging device 100 configured as described 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 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.

However, in high-definition 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 is 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.

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 normal direction from 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 significant problem due to the large amount of light received by the photoelectric conversion elements and the large distance (pitch) between adjacent color filter regions.

The inventors have investigated various methods for reducing petal flare. As a result, they have found that reducing the area in which the microlenses are arranged when viewed from above is effective.

When the color filter has a square shape in plan view, the microlenses are arranged without gaps in the color filter region as shown in Figure 2 by making the diameter of the microlenses roughly the same as the diagonal of the square. If the diameter of the microlenses is reduced from this state, unfilled regions 22 without microlenses 21 are created in the corners of the color filter region as shown in Figure 3.

4 shows the results of a simulation that examines the relationship between the fill factor, which is the ratio of the area of the color filter region occupied by microlenses, and the amount of light reflected in directions other than the normal. The color filter region 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.
Plan view area of microlens/Plan view area of color filter region×100(%) (1)
(area in plan view of color filter region−area in plan view of non-filled region)/area in plan view of color filter region×100(%) (2)
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.

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 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.
5, it can be seen that 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.
4 and 5, "Sum" indicates the sum of all diffracted light, and "Max" indicates the most strongly diffracted light among all diffraction orders. Both affect petal flare, but reducing the value of Max is more effective in suppressing petal flare.

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 content of the examples and comparative examples.

Example 1
A wafer substrate was prepared having a plurality of 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 array 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: square with one side of 1.1 μm Microlens thickness: 0.58 μm (52.7% of the above one side)
Microlens filling rate: 99.5%

(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).

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. In Table 1, the maximum intensity in Comparative Example is shown as a relative value, with the maximum intensity being 100.

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

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 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.

The above describes embodiments and examples of the present invention, but the specific configuration is not limited to these embodiments, and includes modifications and combinations of configurations that do 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, but may be rectangular or another polygonal shape.

The solid-state imaging device of the present invention may not have a color filter disposed in a portion thereof in a planar 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, etc., a color filter may not be disposed in the area of the filter portion corresponding to the photoelectric conversion element used for focus adjustment.

Partitions may be formed between each color filter to prevent stray light. The partitions may be light-absorbing or light-reflective.

1 On-chip color filter 10 Filter section 11, 12, 13 Color filter 20 Microlens section 21 Microlens 100 Solid-state imaging element 101 Wafer substrate PD Photoelectric conversion element

Claims (2)

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. 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 .