Solid-state camera element

Abstract

[Problem] The object of this invention is to provide a solid-state imaging element that can simultaneously suppress petal-shaped glare and achieve high sensitivity. [Solution] The solid-state imaging element 100 of this invention comprises: a wafer substrate 101 having a plurality of photoelectric conversion elements PD; a filter section 10 formed on the wafer substrate having a plurality of color filters arranged corresponding to the photoelectric conversion elements; and a microlens section 20 made of a non-photosensitive resin having a plurality of microlenses 21 arranged corresponding to the color filters. The plurality of microlenses are arranged such that: there is a gap between two adjacent microlenses along the diagonal direction of the rectangular color filter region on which the color filters are arranged, and there is a gap between two adjacent microlenses along the direction extending from the edge of the color filter region.

Description

Technical Field

[0001] This invention relates to solid-state imaging elements, and more specifically, to on-chip type solid-state imaging elements incorporating a color filter and a microlens array. Prior Technology

[0002] Single-board solid-state camera elements are very common. They are color filters formed by arranging multiple colored transparent patterns that selectively allow light of specific wavelengths to pass through on a plane in the path of light entering the photoelectric conversion element, thereby making it possible to obtain the color information of the object. With the thinning, lightening, and increasing precision of solid-state camera elements, there are more and more on-chip solid-state camera elements that directly form color filters on the substrate of photoelectric conversion elements.

[0003] In some cases, microlenses are provided in a solid-state imaging element on a substrate in order to efficiently guide light to a photoelectric conversion element (see, for example, Patent Document 1 below). [Previous Technical Documents] [Patent Literature]

[0004] Patent Document 1: Japanese Patent Application Publication No. 2013-8777 Summary of the Invention

[0005] [The problem the invention aims to solve]

[0006] As digital imaging devices continue to improve in terms of image quality and miniaturization, there is a growing demand for higher precision in on-chip solid-state camera elements. Furthermore, high sensitivity is often also required. In the process of researching high-precision solid-state camera elements as described above, the inventors recognized and solved a new problem: petal flare, which had not been considered a problem before.

[0007] The purpose of this invention is to provide a solid-state imaging element that can both suppress petal-shaped glare and achieve high sensitivity. [Methods used to solve problems]

[0008] The present invention relates to a solid-state imaging element comprising: a wafer substrate having a plurality of photoelectric conversion elements; a filter portion formed on the wafer substrate having a plurality of color filters arranged corresponding to the photoelectric conversion elements; and a microlens portion made of a non-photosensitive resin having a plurality of microlenses arranged corresponding to the color filters. A plurality of microlenses are configured such that there is a gap between two adjacent microlenses along the diagonal direction of the rectangular color filter region on which the color filter is disposed, and there is a gap between two adjacent microlenses along the direction extending from the edge of the color filter region. [Effects of the Invention]

[0009] According to the present invention, a solid-state imaging element that can both suppress petal-shaped glare and achieve high sensitivity can be provided. Simple Explanation of the Diagram

[0010] Figure 1 is a cross-sectional schematic diagram of a solid-state camera element according to an embodiment of the present invention. Figure 2 is a top view photograph of the microlens section of the conventional technology. Figure 3 is a diagram illustrating the gap between the microlenses. Figure 4 is a diagram showing a process of manufacturing a solid-state camera element according to an embodiment of the present invention. Figure 5 is a diagram showing a process of manufacturing a solid-state camera element according to an embodiment of the present invention. Figure 6 is a diagram showing a process of manufacturing a solid-state camera element according to an embodiment of the present invention. Figure 7 is a top view of the microlens section produced. Implementation

[0011] [The form in which the invention is carried out]

[0012] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 7. Figure 1 is a cross-sectional schematic diagram of the solid-state camera element of this embodiment. The solid-state camera element 100 includes: a wafer substrate 101 having a plurality of photoelectric conversion elements PD; and a chip-mounted color filter 1 formed on the wafer substrate 101.

[0013] The crystal-borne color filter 1 has: a filter section 10 containing a plurality of color filters; and a microlens section 20 disposed on the filter section 10. The filter section 10 includes three color filters: 11, 12, and 13. The type, quantity, and distribution of colors in the filter section 10 can be appropriately determined, and known techniques can be employed. For example, a Bayer array using red, green, and blue colors can be used. When viewed from above the solid-state imaging element 100, each color filter overlaps with one photoelectric conversion element (PD).

[0014] The microlens section 20 has a plurality of microlenses 21. The microlenses 21 have a configuration that is approximately the same as the color filters of the filter section 10. When viewed from above the solid-state imaging element 100, each color filter overlaps with one microlens 21.

[0015] In the solid-state imaging element 100 configured as described above, light incident on the microlens 21 is guided into the photoelectric conversion element PD after passing through the corresponding color filter, thereby performing the imaging function. To improve the sensitivity of solid-state imaging devices, microlenses must be used to guide as much light as possible into the photoelectric conversion element. Therefore, it is common practice to form each microlens in the microlens section using known techniques such as thermal reflow and etch-back in a way that makes the optical surfaces of the microlens ML almost seamlessly arranged when viewed from above, as shown in Figure 2.

[0016] However, in solid-state imaging elements with a diameter of less than 1.2 μm for highly refined microlenses or the size of one side of the color filter containing the microlens, it is very common to fail to obtain sufficient color purity. The inventors' research into this phenomenon revealed that petal-shaped glare caused by microlenses was a significant contributing factor.

[0017] Petal-shaped glare is a type of glare generated in a petal-like pattern around the optical axis of a microlens. It is believed to be caused by the interference of reflected light outside the normal direction generated at the optical surface of the microlens. In principle, petal-shaped glare should occur in all microlens arrays to date, but it has not been a problem in the past because of the large area of ​​each pixel region receiving a large amount of light and the large distance (pitch) between it and adjacent color filter regions.

[0018] The inventors conducted various studies on methods to reduce petal-shaped glare. They discovered that, when viewed from above, setting a certain amount of gap regions without microlenses is an effective approach.

[0019] In the case where the top view of the color filter is a square or other rectangle, by setting the diameter of the microlens to be approximately the same as the diagonal of the square, the microlens are seamlessly positioned as shown in Figure 2. When the diameter of the microlens is reduced from this state, as shown in Figure 3, gap regions G without microlenses are created in the corners of the square.

[0020] Regarding the gap region, as the diameter of the microlens decreases, it first appears at the corners, and as the diameter decreases further, it appears at the edges between the corners. In the following description, the gaps appearing at the corners may be referred to as "diagonal gaps," while the gaps appearing at the edges (gap in the direction of edge extension) may be referred to as "horizontal gaps."

[0021] As the gap area increases, the top-view area of ​​the microlens decreases. This decrease in top-view area leads to a reduction in the amount of light focused, making it difficult to balance the suppression of petal-shaped glare with the maintenance of sensitivity. To overcome the aforementioned difficulties, the inventors conducted various studies and, as a result, completed this invention by focusing on the refractive index of the material forming the microlens.

[0022] An example of the manufacturing process for the solid-state camera element 100 will be described. First, a plurality of photoelectric conversion elements (PDs) arranged in a two-dimensional matrix and a wafer substrate 101 with metal wiring are prepared. 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 filter sections 10 are provided on the wafer substrate.

[0023] Next, as shown in FIG. 4, a first transparent layer 20A made of non-photosensitive resin is formed on the filter portion 10. Next, as shown in FIG. 5, a sacrificial layer 50 made of photosensitive resin is formed on the first transparent layer 20A.

[0024] Next, after exposing and developing the sacrificial layer 50 with a pattern corresponding to the position of the photoelectric conversion element PD, a thermal flow process is performed under predetermined conditions, as shown in FIG6, forming a roughly hemispherical sacrificial pattern 50A on the first transparent layer 20A at the position corresponding to the photoelectric conversion element PD. The shape of the sacrificial pattern 50A will affect the shape of the microlens formed subsequently, so it is preferable that the arranged sacrificial pattern 50A is formed in a manner that has at least both diagonal gaps and horizontal gaps.

[0025] Next, dry etching is performed on the first transparent layer 20A and the sacrificial pattern 50A. Through dry etching, the sacrificial pattern 50A disappears and its shape is transferred to the first transparent layer 20A, forming a plurality of lens-like structures on the first transparent layer 20A. At this point, the lens-like structures are not in contact with each other, and gap regions exist around the lens-like structures. In the conventional fabrication of etch-back lens arrays, dry etching continues after the shape of the sacrificial pattern is transferred to the first transparent layer until there are almost no horizontal and diagonal gaps. In this embodiment, however, dry etching is stopped immediately after the transfer is completed, or the etching is stopped after a shorter period of time than usual. In this way, the lens structure is formed with both horizontal and diagonal gaps present.

[0026] By means of the above, a microlens section 20 having a plurality of microlenses 21 is completed. Then, by dicing or the like, the wafer substrate is cut into a predetermined size, and the solid-state imaging element 100 of this embodiment is completed. Figure 7 shows a scanning electron microscope (SEM) image of the actual fabricated microlens section. It can be seen that there are both diagonal gaps DG and horizontal gaps HG between the microlenses 21.

[0027] In the microlens section 20, a diagonal gap and a horizontal gap are ensured between the microlenses 21 formed by dry etching. Therefore, even with the high precision described above, the occurrence of petal-shaped glare can still be well suppressed. In the inventors' research, it was confirmed that when the color filter area is a square with one side of 1.1 μm, by ensuring the diagonal gap is about 0.40 μm to 0.75 μm and the horizontal gap is about 0.15 μm to 0.35 μm, sufficient sensitivity can be maintained while effectively suppressing the occurrence of petal-shaped glare. Expressing the above numerical ranges as a ratio to the length of one side of the color filter area, the diagonal gap is 38% to 70% and the horizontal gap is 14% to 35%. At this point, viewed from above, the fill factor (fill ratio) of the microlens in the unit color filter area is about 65% to 75%, which is a value that is impossible to find in the typical microlens arrays used in on-chip solid-state imaging elements. In the example shown in Figure 7, the color filter area is a square with one side measuring 0.93 μm. The diagonal gap DG and the horizontal gap HG are 43% and 18% of the length of one side, respectively, satisfying the aforementioned numerical range. Furthermore, the fill factor is slightly less than 70%, also satisfying the aforementioned numerical range.

[0028] A microlens array system with both diagonal and horizontal gaps can be formed through development, exposure, and heat flow of the sacrificial layer 50. However, in the inventors' research, it was learned that because the photosensitive resin used in the sacrificial layer has an upper limit on its refractive index, it is not easy to maintain or improve sensitivity while ensuring both diagonal and horizontal gaps. In contrast, the non-photosensitive resin used in the first transparent layer has a sufficient refractive index exceeding the upper limit of photosensitive resins, for example, a non-photosensitive resin with a refractive index n of 1.6 or higher. Examples of non-photosensitive resins with high refractive index, such as those described above, include polyamide, polyamideimide, polyetherimide, norbornene resins, methacrylic resins, isobutylene maleic anhydride copolymer resins, cyclic olefin resins, polyvinyl alcohol, 3-methoxybutyl acetate, cyclopentanone, γ-butyrolactone, propylene glycol monomethyl ether acetate, and acrylic resins. Based on the above findings, this invention uses a high-refractive-index material to form the first transparent layer and employs back etching to form a lens array. This increases the refractive index of the microlens portion 20 and enhances the light-gathering efficiency. As a result, both suppression of petal-shaped glare and high sensitivity can be achieved.

[0029] The above description pertains to one embodiment of the present invention, but the specific configuration is not limited to this embodiment. The present invention also includes modifications and combinations of configurations that do not depart from the scope of the present invention. Some modifications are illustrated below, but these modifications are not exhaustive, and modifications other than those described below are also possible. Two or more suitable combinations of these modifications are also possible.

[0030] The shape of each color filter area is not limited to the aforementioned square; it can also be a rectangle or other polygons. In the case of a color filter area with multiple side lengths, such as a rectangle, the thickness and diagonal gap can be set based on the length of the longest side.

[0031] The solid-state imaging element of the present invention may also omit a color filter in a portion when viewed from above. For example, when applying the present invention to solid-state imaging elements that use a portion of the photoelectric conversion element for focus adjustment, there may be a situation where a color filter is not provided in the area of ​​the filter section corresponding to the photoelectric conversion element used for focus adjustment.

[0032] It can also form a partition between color filters to prevent stray light. The partition can be a light-absorbing partition or a light-reflecting partition.

[0033] 10: Filter Section 11, 12, 13: Color Filters 20: Microlens section 21: Microlenses 100: Solid-state camera element 101: Wafer substrate DG: Diagonal gap HG: Horizontal clearance PD: Photoelectric conversion element

Claims

1. A solid-state imaging element comprising: a wafer substrate having a plurality of photoelectric conversion elements; a filter portion formed on the wafer substrate having a plurality of color filters disposed corresponding to the photoelectric conversion elements; and a microlens portion made of a non-photosensitive resin having a plurality of microlenses disposed corresponding to the color filters; wherein the plurality of microlenses are configured such that: there is a gap between two adjacent microlenses along the diagonal direction of a rectangular color filter region on which the color filters are disposed, and there is a gap between two adjacent microlenses along the direction extending from the edge of the color filter region, wherein the shortest distance between two adjacent microlenses along the diagonal direction, i.e., the diagonal gap, is 38% to 70% of the longest side of the top view shape of the color filter region, and the shortest distance between two adjacent microlenses along the direction extending from the edge of the color filter region, i.e., the horizontal gap, is 14% to 35% of the longest side of the top view shape of the color filter region.

2. A solid-state imaging element comprising: a wafer substrate having a plurality of photoelectric conversion elements; a filter portion formed on the wafer substrate having a plurality of color filters disposed corresponding to the photoelectric conversion elements; and a microlens portion made of a non-photosensitive resin having a plurality of microlenses disposed corresponding to the color filters; wherein the fill factor of the microlens is the ratio of the top view area of ​​the microlens to the area of ​​the rectangular color filter region on which the color filters are disposed, i.e., 65% to 75%; wherein the shortest distance between two adjacent microlenses along the diagonal direction, i.e., the diagonal gap, is 38% to 70% of the longest side of the top view shape of the color filter region; and the shortest distance between two adjacent microlenses along the direction extending from the edge of the color filter region, i.e., the horizontal gap, is 14% to 35% of the longest side of the top view shape of the color filter region.

3. The solid-state imaging element of claim 1 or 2, wherein the refractive index of the aforementioned microlens portion is 1.6 or higher.

4. The solid-state imaging element of claim 1 or 2, wherein the aforementioned color filter area is a square with one side less than 1.2 μm.

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