JP7494728B2 - Solid-state imaging device and manufacturing method - Google Patents

Description

The present invention relates to a solid-state imaging device, more specifically, to an on-chip type solid-state imaging device equipped with a microlens array. The present invention also relates to a method for manufacturing the solid-state imaging device.

As solid-state imaging elements become thinner, lighter and more precise, the number of on-chip type solid-state imaging elements in which black matrices and microlenses are formed directly on the substrate on which the photoelectric conversion elements are arranged is increasing.

In recent years, in order to improve image quality in solid-state imaging devices, a technology has been proposed in which a light-shielding film is formed in non-pixel regions. In particular, titanium-based black materials such as titanium oxide and titanium oxynitride have attracted attention as coloring materials for the light-shielding layer from the viewpoint of preventing noise caused by infrared light (see, for example, Patent Document 1).

Patent No. 5254650

In an on-chip type solid-state imaging element, if a defect occurs during the process of forming a colored layer, it is common to peel off the colored layer using a dry process such as _O2 ashing and recycle the wafer on which the imaging element circuit is formed.

However, while the titanium-based black material described above has excellent light-blocking properties, it is difficult to remove using this type of dry process. A layer made of titanium-based black material can only be removed using a heated strong alkaline solution. Using a strong alkaline solution will damage the underlying solid-state imaging element circuitry, making it difficult to reuse the wafer.

The present invention aims to provide a solid-state imaging device and a manufacturing method thereof that uses titanium-based black material and is easy to deal with defects during the manufacturing process.

The first aspect of the present invention is a solid-state imaging device comprising a wafer substrate having a plurality of photoelectric conversion elements, an organic film formed on the wafer substrate mainly composed of a resin having a carboxylic acid in its skeleton, a light-shielding layer formed on the organic film mainly composed of a titanium-based black material and having a plurality of openings, and a plurality of microlenses arranged on or within the openings.

The second aspect of the present invention is a method for manufacturing a solid-state imaging device, which comprises forming an organic film covering at least the unit sections on a silicon wafer on which a plurality of unit sections each having a plurality of photoelectric conversion elements are formed, using a resin having a carboxylic acid in its skeleton, forming a light-shielding layer on the organic film using a titanium-based black material, removing the light-shielding layer together with the organic film using an alkaline stripping solution having a pH of 11 or less, and forming a new organic film on the silicon wafer.

The solid-state imaging device of the present invention uses titanium-based black material and is easy to deal with defects during the manufacturing process.

1 is a schematic cross-sectional view of a solid-state imaging element according to one embodiment of the present invention. 3A to 3C are schematic diagrams showing a process for manufacturing the solid-state imaging device. FIG. 2 is a schematic diagram showing one process of the manufacturing method. FIG. 2 is a schematic diagram showing one process of the manufacturing method. FIG. 2 is a schematic diagram showing one process of the manufacturing method.

Hereinafter, an 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 the present embodiment. The solid-state imaging device 100 includes a wafer substrate 101 having a plurality of photoelectric conversion elements PD, an organic film 10, a light-shielding layer 20, and a microlens portion 30, which are formed in this order on the wafer substrate 101.

The organic film 10 is a transparent layer made of a resin having a carboxylic acid in its skeleton, and forms a single layer that covers the entirety of the photoelectric conversion elements PD.
From the viewpoint of ease of peeling described later, the thickness of the organic film 10 is preferably 4.0 μm or less, and from the viewpoint of the optical design of the entire solid-state imaging element 100 including the microlens portion 30, the thickness is more preferably 2.0 μm or less.

The light-shielding layer 20 is formed of a titanium-based black material whose main component is titanium oxide, titanium oxynitride, or titanium nitride. The light-shielding layer 20 is formed in a mesh shape with polygonal or pinhole-shaped openings at positions corresponding to each photoelectric conversion element PD. This allows the light-shielding layer 20 to function as a black matrix that partitions multiple photoelectric conversion elements PD as pixels.

The microlens section 30 has a plurality of microlenses 31. The microlenses 31 are arranged in a manner generally similar to the openings of the light-shielding layer 20, and each opening overlaps one of the microlenses 31 when the solid-state imaging element 100 is viewed in plan.
A microlens 31 may be disposed within the aperture.

In the solid-state imaging element 100 configured as described above, light incident on the microlens 31 passes through the opening of the light-shielding layer 20 and is guided to the photoelectric conversion element PD, thereby achieving an imaging function. This allows the solid-state imaging element 100 to function as various imagers and various sensors. By further combining a colored layer such as a color filter, the solid-state imaging element 100 can also be made compatible with color imaging. The colored layer is provided so as to overlap the opening when viewed in a plan view of the solid-state imaging element 100. The colored layer may be provided between the microlens section 30 and the light-shielding layer 20, or may be disposed within the opening.

The solid-state imaging device 100 can be mass-produced efficiently by forming multiple devices on a large wafer. The procedure is explained below.

First, as shown in FIG. 2, a plurality of unit sections Ua each having a plurality of photoelectric conversion elements PD and wiring are formed on a single silicon wafer Sw. Each unit section Ua functions as a wafer substrate 101.

Next, as shown in Fig. 3, an organic film 10 is formed on the front surface of the silicon wafer Sw, and the organic film 10 is patterned so as to be divided into unit sections Ua as shown in Fig. 4. Since patterning using photolithography is simple, it is preferable to form the organic film from a resin material that allows such patterning.
One example of patterning is a mode in which a part of the organic film 10 is removed along a scribe line SL when separating the unit sections Ua.

Next, as shown in FIG. 5, a light-shielding layer 20 made of a titanium-based black material is formed on each unit section Ua, and patterning is performed to form openings or pinholes. Titanium-based black material has better patterning characteristics than carbon-based black material, so the light-shielding layer 20 can be formed with greater precision.

Here, when redoing the formation of the light-shielding layer 20 due to defective formation or patterning of the light-shielding layer 20, an alkaline stripping liquid is sprayed onto the silicon wafer Sw or the silicon wafer Sw is immersed in the stripping liquid to bring the stripping liquid into contact with the organic film 10.
Since the organic film 10 is formed of a material having a carboxylic acid in its resin skeleton, it can be peeled off with a weakly alkaline stripping solution having a pH of not more than 11. In this embodiment, the stripping solution can act directly on the interface between the silicon wafer Sw and the organic film 10 from the portion where the organic film 10 has been removed by patterning, so that the organic film 10 of each unit section Ua can be quickly peeled off.

If the light-shielding layer 20 is formed directly on the silicon wafer Sw, a strong alkaline stripping solution with a pH of 14 or more is required to remove it, and significant damage to the photoelectric conversion elements PD, wiring, etc. of each unit section Ua is unavoidable. In this embodiment, since the light-shielding layer 20 is formed on the organic film 10, the light-shielding layer 20 can be removed by removing the organic film 10, and damage to each mechanism formed on the silicon wafer Sw can be almost completely eliminated.
After the organic film 10 and the light-shielding layer 20 are peeled off, a new organic film is formed on the silicon wafer Sw, and the above-mentioned steps are repeated.

Once the light-shielding layer 20 has been formed without any problems, the microlens section 30 is then formed on the light-shielding layer 20. The microlens section 30 can be formed by appropriately combining known techniques such as photolithographic patterning, thermal reflow, and back etching.

Once the microlens portion 30 has been formed without any problems, each unit section Ua is cut along the scribe line SL to complete multiple solid-state imaging elements 100.

As described above, the solid-state imaging element 100 according to this embodiment has a configuration in which the light-shielding layer 20 made of a titanium black-based material is formed on the organic film 10 formed on the wafer substrate 101. Therefore, during the manufacturing process, the light-shielding layer 20 can be easily remade without damaging the mechanisms built into the wafer substrate 101.
Therefore, the light-shielding layer has excellent light-shielding performance, and is easy to manufacture.

In the above-described manufacturing method, the patterning step of the organic film 10 may be omitted. In this case, the time required to peel off the organic film will be somewhat longer, but the organic film 10 and the light-shielding layer 20 can be peeled off at the same time.

The solid-state imaging device of this embodiment will be further described using experimental examples. The technical scope of the present invention is not limited in any way by the specific content of the experimental examples.

(Experimental Example 1)
A 1.0 μm thick organic film was formed on the entire upper surface of a silicon wafer on which multiple unit sections were formed, using a resin material having a carboxylic acid in its skeleton. The resin material used was a composition described in Japanese Patent No. 2961722. The main components were a copolymer of methacrylic acid, glycidyl methacrylate, and methyl methacrylate, 2,3,4,4'-tetrahydroxybenzophenone, and trifunctional methacrylate.
On the organic film, a plurality of light-shielding layers were formed using a titanium black material, each of which had a square shape in plan view and had approximately the same dimensions as the unit section. Each light-shielding layer had a thickness of 1.5 μm.
In this manner, a structure according to Experimental Example 1 was produced.

(Experimental Example 2)
A structure according to Experimental Example 2 was produced in the same manner as in Experimental Example 1, except that after the formation of the organic film, patterning was performed to divide the organic film into a plurality of square regions in plan view corresponding to the unit sections. The divided organic film had dimensions slightly larger than the unit sections, and was formed so that the light-shielding layer was located within the range of the organic film in plan view.

(Experimental Example 3)
A structure according to Experimental Example 3 was fabricated in the same manner as in Experimental Example 1, except that no organic film was provided.

(Experimental Example 4)
A structure according to Experimental Example 4 was produced in the same manner as in Experimental Example 1, except that an organic film was formed using a resin material that did not have a carboxylic acid in its skeleton. The composition described in Japanese Patent No. 2982156 was used as the resin material. The main components were a copolymer of glycidyl methacrylate and methyl methacrylate, 2-ethyl-4-methylimidazole, and isocyanuric acid.

Two structures of each experimental example were prepared and immersed in a weakly alkaline stripping solution (pH 11 or less) heated to 50°C and a strongly alkaline stripping solution (pH 14 or more) heated to 50°C to attempt stripping of the light-shielding layer.
The results were evaluated in two areas: peeling of the light-shielding layer and damage to the structure within the unit section Ua. The evaluation criteria were as follows:
Light-shielding layer peeling: ◎ (good): the light-shielding layer was completely peeled off. ◯ (fair): some of the light-shielding layer remained. × (bad): the entire light-shielding layer remained and was not peeled off. Structural damage: ◯ (good): photoelectric conversion possible, reusable × (bad): photoelectric conversion not possible, and not reusable. Note that when light-shielding layer peeling was rated as ×, it was marked as ineligible for evaluation (-).
The results are shown in Table 1.

As shown in Table 1, in Experimental Examples 1 and 2, the organic film and the light-shielding layer could be stripped with a weakly alkaline stripping solution, and no structural damage occurred during the process.
In Experimental Example 3 in which no organic film was provided, and Experimental Example 4 in which the organic film was formed from a resin material having no carboxylic acid in the skeleton, the light-shielding layer could not be peeled off with the weak alkaline stripping solution.
In all experimental examples, the light-shielding layer could be removed using a strong alkaline stripping solution, but the damage to the silicon wafer was so great that it became impossible to reuse it.
From the above, the usefulness of the solid-state imaging device according to this embodiment was confirmed.

The above describes one embodiment of the present invention and examples, but the specific configuration is not limited to this embodiment, and includes configuration changes and combinations that do not deviate from the gist of the present invention.

For example, the composition for forming the organic film may contain other components such as a surfactant, an adhesion aid, etc. In this case, these other components may remain in the organic film.

It is preferable that the organic film be removed from all of the periphery of the effective pixel area where the photoelectric conversion elements are formed. Removal along the scribe line satisfies this condition, but by removing the organic film from the entire periphery at a position closer to the effective pixel area, the remover solution can penetrate the entire organic film in the effective pixel area from all sides, allowing the defective light-shielding layer to be removed in a shorter time.

When a colored layer is provided in the solid-state imaging element of the present invention, the colored layer does not have to be arranged in a part of the solid-state imaging element when viewed in a plane. 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, etc., it is possible to have an embodiment in which a color filter is not arranged in the area of the filter portion corresponding to the photoelectric conversion element used for focus adjustment.

10 Organic film 20 Light shielding layer 30 Microlens portion 31 Microlens 100 Solid-state imaging element 101 Wafer substrate PD Photoelectric conversion element SL Scribe line Sw Silicon wafer Ua Unit section

Claims (6)

a wafer substrate having a plurality of photoelectric conversion elements;
an organic film formed on the wafer substrate, the organic film being mainly composed of a resin having a carboxylic acid in its skeleton;
a light-shielding layer formed on the organic film and containing a titanium-based black material as a main component, the light-shielding layer having a plurality of openings;
a plurality of microlenses disposed on or within the aperture;
Equipped with
Solid-state imaging element. the organic film is removed over the entire periphery of an effective pixel region in which the plurality of photoelectric conversion elements are formed.
The solid-state imaging device according to claim 1 . The thickness of the organic film is 4.0 micrometers or less.
The solid-state imaging device according to claim 1 . Further comprising a colored layer provided at a position overlapping the opening in a plan view.
The solid-state imaging device according to claim 1 . forming an organic film, using a resin having a carboxylic acid in its skeleton, on a silicon wafer on which a plurality of unit sections each having a plurality of photoelectric conversion elements are formed, the organic film covering at least the plurality of unit sections;
forming a light-shielding layer on the organic film using a titanium black material;
removing the light-shielding layer together with the organic film using an alkaline stripping solution having a pH of 11 or less;
forming a new organic film on the silicon wafer;
A method for manufacturing a solid-state imaging device. After forming the organic film, a part of the organic film is removed along a scribe line for separating the plurality of unit sections.
The method for manufacturing the solid-state imaging device according to claim 5 .

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