JP2023087450A - Solid-state image sensor substrate - Google Patents

Abstract

To provide a solid-state image sensor substrate excellent in alignment accuracy between a wafer and an exposure mask by increasing visibility of an alignment mark on the under layer of the wafer to improve detection accuracy of the alignment mark, even after application of a color resist in production processes of a solid-state image sensor.SOLUTION: There is provided a solid-state image sensor substrate including a substrate and a plurality of solid-state image sensors arranged in a plane on one side of the substrate. The solid-state image sensor substrate has, on the substrate, effective pixel areas, and a non-pixel area between adjacent effective pixel areas. An alignment mark is arranged in the non-pixel area, and the alignment mark is covered with a transparent film.SELECTED DRAWING: Figure 1

Description

The present invention relates to a solid-state imaging device substrate with improved alignment mark detection performance.

In recent years, solid-state imaging devices incorporating compact, high-performance solid-state imaging devices have become popular as digital cameras and digital videos.

A solid-state imaging device includes a plurality of photoelectric conversion elements that convert incident light into electrical signals. The types of photoelectric conversion elements are roughly classified into CCD type and CMOS type, and the more photoelectric conversion elements there are, the more precise the captured image becomes.

Color information of an object can be obtained by providing a color filter in which a colored transparent pattern that selectively transmits light of a specific wavelength is arranged in a plane on the path of light incident on the photoelectric conversion element. In particular, an on-chip type color solid-state imaging device, in which color filters are formed directly on an array substrate of photoelectric conversion elements, has become mainstream, aiming at making the color solid-state imaging device thinner, lighter, and higher in definition. As the colors of color filters, a three primary color system consisting of three colors of red (R), green (G), and blue (B) is often used.

A color solid-state image sensor with an on-chip color filter (OCF) is a semiconductor substrate (wafer) in which a plurality of photoelectric conversion elements are regularly provided, and a plurality of colors are repeatedly arranged via an insulating base layer. A plurality of photoelectric conversion elements are provided with color filters corresponding to each other on a one-to-one basis, and after flattening with an organic layer, microlenses are provided.

A common method for forming color filters of each color is to use a photolithographic process. A photosensitive colored resin (color resist) containing dyes such as pigments is made into droplets, and then spin-coated or the like to spread them evenly on a wafer. It is carried out by a divided exposure operation in which different positions on the same exposure wafer are successively exposed with the same pattern, and pattern development after the exposure.

In exposing the pattern, it is very important to perform the exposure without misalignment between the wafer and the exposure mask. For this purpose, the solid-state imaging devices arranged on the wafer have effective pixel areas and non-pixel areas (scribe areas) between adjacent effective pixel areas, and alignment marks are provided at regular intervals in the non-pixel areas. The alignment marks are used to align the wafer and the exposure mask.

Alignment involves the following three steps.
(1) Mechanical alignment that determines the orientation of the wafer by detecting the notch position of the wafer (2) TVPA (Televisi) that is adjusted to detect the final alignment mark
on Pre Alignment) Alignment (3) AGA (Advanced Global Alias) where alignment is finally determined
gnment) Alignment Normally, the AGA marks formed on the wafer underlayer are used for final alignment. The shape of the AGA mark may be any shape as long as the positional accuracy can be detected, but in the present application, as shown in FIG.

Alignment between each shot of the wafer and the exposure mask is performed by optically detecting the position of the alignment mark corresponding to each shot and positioning the wafer with respect to the exposure mask based on the detection result. (See Patent Document 1).

Japanese Patent No. 4794882

However, in the photolithography process, each colored resist is applied to the entire surface of the wafer, and depending on the material of the color resist, the underlying alignment marks may be difficult to see, which may reduce detection accuracy. Therefore, it may be necessary to use another alignment mark formed of green resin, which is easy to detect with a detector, for alignment with the underlying alignment mark as a reference. However, this method has the problem that the number of steps increases, leading to an increase in the production cost of the solid-state imaging device.

Therefore, when alignment is performed using alignment marks on the underlayer of the wafer, it is necessary to improve the visibility of the alignment marks even after the color resist is applied. By increasing the visibility of the alignment marks, the detection accuracy of the marks is improved, and the alignment accuracy between the wafer and the exposure mask is improved.

The present invention has been made in view of the above problems, and its object is to improve the visibility of alignment marks on the wafer underlayer even after the color resist is applied in the production process of solid-state imaging devices. and improving the detection accuracy of the alignment mark, thereby providing a solid-state imaging device substrate with excellent alignment accuracy between a wafer and an exposure mask.

In order to solve the above problems in the present invention, a first aspect of the present invention is
A substrate and a solid-state imaging device substrate in which a plurality of solid-state imaging devices are planarly arranged on one surface side of the substrate,
having an effective pixel area on the substrate and a non-pixel area between adjacent effective pixel areas;
an alignment mark is formed in the non-pixel region;
The solid-state imaging device substrate is characterized in that the alignment mark is covered with a transparent film.

By forming a transparent film on the alignment marks, when the color resist is applied to the entire surface of the wafer, the film thickness of the color resist layer on the alignment marks on the transparent film becomes thin, and the transmittance of the alignment marks increases. Visibility can be improved. A transparent film is formed on the alignment mark by a photolithography method.

In a solid-state imaging device, the positional accuracy between the wafer and the exposure mask is one of the important factors in improving and stabilizing the sensitivity.
According to the present invention, in the production process of a solid-state imaging device, when aligning the wafer and the exposure mask using the alignment mark on the underside of the wafer, the visibility of the alignment mark can be improved even after the color resist is applied. By increasing the alignment mark detection accuracy, it is possible to provide a solid-state imaging device substrate with excellent alignment accuracy between the wafer and the exposure mask.
In addition, since it is not necessary to form a new alignment mark with a pigment whose mark is easy to detect, there is an effect of suppressing the production cost.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows the structure of the solid-state image sensor of this invention (a) Schematic sectional drawing of the code|symbol 1 (b) Schematic top view of a solid-state image sensor board|substrate. (a) Partial enlarged view of FIG. 1-reference numeral 21 (b) Schematic plan view illustrating an alignment mark. Diagrams for explaining the visibility of alignment marks after application of a color resist (a) visibility of conventional alignment marks (b) visibility of alignment marks of the present invention. 4 is a flow chart explaining the flow of transparent film and color filter formation in the production process of the solid-state imaging device of the present invention. FIG. 4 is a schematic cross-sectional view for explaining steps of forming a transparent film and a color filter in the production process of the solid-state imaging device of the present invention;

A solid-state imaging device substrate and a method for manufacturing a solid-state imaging device according to embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a schematic cross-sectional view showing the structure of the solid-state imaging device of the present invention. Since the solid-state imaging device substrate 20 of the present invention is characterized by the non-pixel region (the portion denoted by Db), a schematic cross-sectional view of only one set of non-pixel region and effective pixel region (the portion denoted by Da) 1(b) is a schematic cross-sectional view of part A surrounded by a broken line).

As shown in FIG. 1(b), the solid-state imaging devices 10 are arranged in multiple planes on a semiconductor substrate 1 such as a silicon wafer. In a dicing process, it is cut into individual pieces (chips) and separated into individual solid-state imaging devices 10 . Generally, in a camera module, in the case of a first camera attached to a mobile phone, the size of the solid-state image sensor 10 is about 10 mm square, so 300 to 400 solid-state image sensor substrates 20 with a diameter of 20 cm are used. A solid-state image pickup device with a degree of

FIG. 2A illustrates only the portion B surrounded by the broken line in FIG. Although the number of colored pixels actually reaches several thousand in one row in the horizontal direction, only a few are shown here for simplification. The array of color pixels is a Bayer array in which two pixels of G (green) are diagonally arranged and four pixels of R (red) and B (blue) are repeatedly arranged as one set of arrays. Here, the reason why the number of pixels of G (green) is doubled compared to other colors is that the apparent resolution of G, which has high luminosity of the human eye, increases the apparent resolution. If necessary, colored pixels other than RGB may be arranged, and pixels for transmitting infrared rays may be provided.

In the embodiment of the solid-state imaging device 10 shown in FIG. 1(a), alignment marks 4 are formed on the base of the semiconductor substrate 1 in some non-pixel regions Db, and an insulating layer (inorganic layer) is formed thereon. 3. A transparent film 5 is laminated. The alignment mark 4 is covered with a transparent film 5 in plan view. A color resist used for the color filter layer 8 in the effective pixel area Da is laminated on the transparent film 5 . As for the film thickness of the transparent film 5 and the film thickness of the color resist laminated on the transparent film 5, the transparent film 5 is preferably thicker. Since the film thickness of the transparent film 5 is thicker, it is possible to further improve the reading accuracy of alignment, which will be described later.
In the effective pixel area Da, the photoelectric conversion elements 2 are regularly arranged on the semiconductor substrate 1, and the insulating layer 3, the partition layer 7, the color filter layer 8, the microlens forming layer (organic layer) 6, and the microlens are arranged thereon. Layers 9 are stacked one after the other.

Alignment marks 4 for alignment are usually provided in non-pixel regions Db between solid-state imaging elements 10, as shown in FIG. 2(a). Alignment marks 4 may be provided in all the non-pixel regions Db of the solid-state imaging device substrate 20, or may be formed only in some of the non-pixel regions Db. Forming the alignment marks 4 only in a part of the non-pixel regions Db is preferable because the alignment marks 4 are arranged at regular intervals to improve the alignment accuracy. The shape of the alignment mark 4 may be any shape as long as the position can be detected. In the following description, as shown in FIG. 2B, an alignment mark 4 composed of a square pattern S in a plan view and four square patterns s smaller than the square is taken as an example.

The transparent film 5 is made of photosensitive transparent resin and formed on the alignment mark 4 by photolithography. Acrylic resins, phenolic resins, novolac resins, and the like can be used as photosensitive transparent resins.

<Flow of transparent film and color filter formation>
Next, the flow of forming transparent films and color filters in the production process of the solid-state imaging device 10 will be described with reference to FIGS. 4 and 5. FIG. FIG. 4 is a flow chart explaining the flow of forming the transparent film and the color filter, and FIG. 5 is a schematic cross-sectional view showing the steps of forming the transparent film and the color filter.

In Step 1 of FIG. 4, a film of a photosensitive transparent resin material 5a is formed on the entire surface of the semiconductor substrate 1 (FIG. 5(a)).

In Step 2 of FIG. 4, a transparent film 5 is formed (FIG. 5(c)) through exposure and development processes (FIG. 5(b)) by photolithography. At this time, in the exposure step, exposure is performed by positioning with a transparent film mask so that the transparent film 5 is formed on the alignment marks 4 formed in the non-pixel regions Db.

In Step 3 of FIG. 4, when the color resist material 8a of the first color is formed on the entire surface of the wafer, a color resist layer thinner than the color resist layer is formed on the transparent film 5 ( FIG. 5(d)).

In Step 4 of FIG. 4, the detector 21 detects the alignment mark 4, positions the wafer and the exposure mask, and performs exposure and development to form the first color filter layer (FIG. 5(e)). , FIG. 5(f)).

In Step 5 of FIG. 4, Steps 3 and 4 are repeated to form color filter layers for the second and subsequent colors.

The reason why the thin color resist is formed on the transparent film 5 in Step 3 as described above is that the resist applied on the transparent film 5 is in a liquid state and is leveled to spread evenly over the entire surface of the wafer. A thin film is formed on the film of the transparent film 5 in order to form the height.

<Alignment method>
Alignment images the alignment marks 4 formed on the underlying layer of the substrate 1 from one side of the semiconductor substrate 1 using a detector 21 installed in an exposure device (not shown). After that, the position is detected based on the captured image, and the exposure mask is moved to the exposure shot position registered in advance based on the detection result. In order to perform alignment with high accuracy, it is necessary to detect the position of the alignment mark 4 with high accuracy. For that purpose, a clear captured image of the alignment mark is required. Then, using this captured image, position detection is performed by a method such as image processing.

A known technique can be used as the image processing method, but it is necessary, for example, to be able to identify the outer edge, which is the boundary of the alignment mark 4, in the captured image. When an image of the alignment mark 4 is imaged, a difference in contrast occurs between the alignment mark side and the side where the alignment mark is not provided with the outer edge as a boundary. Mark position information can be acquired. The exposure mask can be moved to the exposure shot position with respect to the semiconductor substrate 1 according to this position information. However, if the shape of the alignment mark cannot be detected with high accuracy, an error occurs in the position information obtained by image processing, and the exposure position shifts from the required exposure shot position.

<Improved visibility by forming a transparent film>
As described above, the color filter 8 is generally formed by a photolithography process, in which a color resist containing dyes such as pigments is dropped, and the wafer substrate is rotated to spread the color resist uniformly. (spin coating) is performed, and then, using an exposure mask having a pattern forming portion as a light transmission portion, the color resist is repeatedly exposed and developed for each color.

In such a color filter layer forming process, when a color resist is applied to the entire surface of the wafer and a uniform coating surface is formed by spin coating, the effective pixel area of the solid-state image sensor and the non-pixel area formed between the effective pixel areas are formed. A color resist layer having a constant thickness is formed on the substrate. Therefore, conventionally, as shown in FIG. 3A, a color resist layer is formed on the alignment marks formed in the non-pixel region Db. Since the color resist layer with low brightness is on the alignment mark, the alignment mark cannot be detected accurately by the detector, and the exposure position may be shifted from the required exposure shot position.

In the embodiment of the present invention, a transparent film 5 is formed on alignment marks 4 formed in non-pixel regions. Therefore, as shown in FIG. 3B, the color resist on the alignment mark 4 is formed with a thin film thickness by subtracting the height of the transparent film from the height of the color resist layer by leveling after coating. As a result, the reflected light from the alignment mark increases, making it possible to detect the alignment mark with high accuracy. Therefore, it is possible to perform exposure without deviation between the wafer and the exposure shot position.

DESCRIPTION OF SYMBOLS 1... Semiconductor substrate 2... Photoelectric conversion element 3... Insulating layer (inorganic layer)
4 Alignment mark 5 Transparent film 5a Photosensitive transparent resist film 6 Microlens forming layer (organic layer)
7... Partition (light shielding film)
8 Color filter 8a Color resist film 9 Microlens 10 Solid-state imaging element 11 Notch 20 Solid-state imaging element substrate 21 Detector 22 Transparent Film exposure mask 23 Color filter exposure mask S, s Alignment mark rectangular shape

Claims (3)

A substrate and a solid-state imaging device substrate in which a plurality of solid-state imaging devices are planarly arranged on one surface side of the substrate,
having an effective pixel area on the substrate and a non-pixel area between adjacent effective pixel areas;
Alignment marks are arranged in the non-pixel regions,
A solid-state imaging device substrate, wherein the alignment mark is covered with a transparent film. colored pixels are formed in the effective pixel area;
2. The solid-state imaging device substrate according to claim 1, wherein a colored layer made of one color of said colored pixels is provided on a surface of said transparent film opposite to said alignment mark. 3. A solid-state imaging device substrate according to claim 2, wherein the film thickness of said transparent film is thicker than the film thickness of said colored layer.

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