JP2006041026A - Solid-state imaging element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain incidence of light on regions other than the light receiving region from the light shielding film end which will result in smear of a solid-state imaging element. <P>SOLUTION: The solid-state imaging element comprises a light receiving region 2 formed of a diffused layer formed on a semiconductor substrate 1, a reflection preventing film 7 formed on the light receiving region 2, and a light shielding film 6 formed on the semiconductor substrate 1 so that a region of the reflection preventing film 7 becomes an aperture. The reflection preventing film 7 has the surface projected upward. Therefore, even when the light enters with inclination from the aperture of the light shielding film 6, the light can be concentrated to the center of the light receiving region 2 through refraction at the curved surface. Accordingly, the incident light does not reach a charge transfer region 3 formed adjacent to the light receiving region 2 and thereby smear can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention particularly relates to a solid-state imaging device structure including a convex antireflection film on a light-receiving portion formed on a semiconductor substrate, and a method for manufacturing the same.

  At present, a solid-state imaging device mainly uses a CCD (Charge Coupled Device) for reading signal charges generated by incident light. In order to increase the resolution of an image and reduce the size of an optical system such as a camera, as the number of pixels of a solid-state image sensor increases and downsizing, maintaining or improving sensitivity has become an issue. In the solid-state imaging device, a charge transfer gate electrode is formed on a silicon substrate on which a photodiode is formed as a light receiving portion via an insulating film, and further, an interlayer insulating film, a light shielding film having an opening above the light receiving portion, And a surface protective film are sequentially laminated. In such a solid-state imaging device, light incident from the opening of the light shielding film is photoelectrically converted by a photodiode and integrated as signal charges, and the signal charges are read by the CCD and transferred to the output amplifier unit.

  In such a solid-state imaging device, due to a difference in refractive index between an interlayer insulating film (usually a silicon oxide film) formed on the light receiving portion and silicon constituting the silicon substrate, the substrate surface is exposed from the opening of the light shielding film. Since a part of the incident light incident on the silicon substrate is reflected upward, the light reaching the photodiode is reduced, resulting in a decrease in sensitivity. As a countermeasure against this problem, for example, by providing an antireflection film made of a silicon nitride film between the silicon substrate and the interlayer insulating film, the loss of incident light is reduced by using the multiple interference effect, and the sensitivity is improved. It has been proposed to plan.

FIG. 3 shows a configuration of a conventional solid-state imaging device provided with an antireflection film. In the surface region of the silicon substrate 21, a light receiving unit 22 that is a photodiode and a diffusion layer of the transfer unit 3 are formed. 3 is provided with a charge transfer gate electrode 25 through an insulating film. An interlayer insulating film 24 is formed over the entire surface of the substrate, and a light shielding film 26 having an opening is provided on the region of the light receiving portion 22, and an antireflection film 27 is provided in the opening region of the light shielding film 26. The structure is provided. Patent Documents 1 and 2 describe examples of a solid-state imaging device having a structure in which an antireflection film is formed on a light receiving region.
JP-A-63-14466 Japanese Patent Laid-Open No. 4-152673

  However, in the conventional solid-state imaging device shown in FIG. 3, of the light incident on the silicon substrate 21 from the opening of the light shielding film 26, the incident light incident on the silicon substrate near the edge of the opening from an oblique direction. In the case of 28, the light is incident on the antireflection film 27 and refracted and enters the light receiving part 22, but a part of the light is reflected by the surface of the semiconductor substrate 21 and then reflected again by the lower surface of the upper conductive light shielding film 26. It is incident on the transfer unit 23 instead of 22. In this case, there has been a problem that a smear phenomenon in which light is converted into electric charge in the transfer unit 23 occurs.

  Therefore, in view of the above, an object of the present invention is to provide a solid-state imaging device capable of suppressing light from entering the region other than the light-receiving portion from the end of the light-shielding film that causes smear of the solid-state imaging device, and a method for manufacturing the same. Is to provide.

  In order to achieve the above object, a solid-state imaging device according to claim 1 of the present invention is a light-receiving unit comprising a diffusion layer formed on a semiconductor substrate, an antireflection film formed on the light-receiving unit, and the reflection A light-shielding film formed on the semiconductor substrate so that the region of the anti-reflection film becomes an opening, and the anti-reflection film has an upwardly convex curved surface.

  The solid-state imaging device according to claim 2 is the solid-state imaging device according to claim 1, wherein a peripheral portion of the antireflection film overlaps with an end portion of the opening of the light shielding film, and a curved surface of the antireflection film is at least the It is formed in the peripheral part including the overlapping part.

  The solid-state imaging device according to claim 3 is the solid-state imaging device according to claim 1 or 2, wherein the light shielding film is formed on the antireflection film and overlaps.

  The solid-state imaging device according to claim 4 is the solid-state imaging device according to claim 1, 2, or 3, wherein the thickness of the antireflection film is 40 to 200 nm.

  6. The method of manufacturing a solid-state imaging device according to claim 5, wherein a step of forming a light receiving portion comprising a diffusion layer on a semiconductor substrate, a step of forming an antireflection film on the semiconductor substrate including the light receiving portion, and a portion immediately above the light receiving portion. A step of forming a mask pattern of a resin film on the portion of the antireflection film, a step of forming a cross-sectional shape of the mask pattern having a curved surface that protrudes upward, and the mask pattern and the antireflection film. Etching to make the cross-sectional shape of the antireflection film into a shape having a curved surface that protrudes upward, and the light receiving part region portion is an opening on the semiconductor substrate on which the antireflection film is formed Forming a light shielding film.

  The solid-state imaging device manufacturing method according to claim 6 is the solid-state imaging device manufacturing method according to claim 5, wherein the mask pattern is a resist, and the cross-sectional shape of the resist is convex upward by heat flow. Form.

  According to the solid-state imaging device of the first aspect of the present invention, the light receiving portion formed of the diffusion layer formed on the semiconductor substrate, the antireflection film formed on the light receiving portion, and the region of the antireflection film is the opening portion. Since the antireflection film has an upward convex curved surface, even if light enters obliquely from the opening of the light shielding film, the light is refracted on the curved surface and received. Light can be collected at the center of the section. Accordingly, the incident light does not reach the charge transfer portion formed adjacent to the light receiving portion, and smear can be reduced.

  According to the second aspect of the present invention, the peripheral portion of the antireflection film overlaps with the opening end portion of the light shielding film, and the curved surface of the antireflection film is formed in the peripheral portion including at least the overlapping portion. The peripheral portion of the antireflection film can be curved in a range including the end portions, and light can be refracted toward the center of the light receiving portion.

  According to a third aspect of the present invention, in the solid-state imaging device according to the first or second aspect, it is desirable that the light shielding film is formed on the antireflection film and overlaps. The peripheral portion of the antireflection film can be a curved surface in a range including under the end of the opening of the light shielding film.

  According to a fourth aspect of the present invention, in the solid-state imaging device according to the first, second, or third aspect, the film thickness of the antireflection film is desirably 40 to 200 nm.

  According to the method for manufacturing a solid-state imaging device according to claim 5 of the present invention, the step of forming the mask pattern of the resin film on the portion of the antireflection film directly above the light receiving portion, and the cross-sectional shape of the mask pattern is convex upward A step of forming a curved surface, a step of etching the mask pattern and the antireflection film to form a cross-sectional shape of the antireflection film having a curved surface protruding upward, and a semiconductor substrate on which the antireflection film is formed And a step of forming a light-shielding film in which the light-receiving part region portion is an opening. Therefore, the antireflection film can be shaped to have a convexly curved surface. For this reason, even if light enters obliquely from the opening of the light shielding film, the light can be refracted on the curved surface and collected at the center of the light receiving portion, and the same effect as in the first aspect can be obtained.

  According to a sixth aspect of the present invention, in the method for manufacturing a solid-state imaging device according to the fifth aspect, the mask pattern is a resist, and the cross-sectional shape of the resist can be formed to be convex upward by heat flow.

  A solid-state imaging device according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a solid-state imaging device according to an embodiment of the present invention.

  In FIG. 1, a light receiving unit 2 (for example, N type) and a transfer unit made of a diffusion layer in the surface region of a silicon substrate (semiconductor substrate) 1 (may be a well formed in the silicon substrate. For example, P type). 3 (for example, N type) is formed, a charge transfer gate electrode 5 is provided on the transfer portion 3 via an insulating film, and an interlayer insulating film 4 is provided on the entire surface of the gate electrode 5 and the light receiving portion 2. . A light shielding film 6 having an opening is provided on the light receiving portion 2 thereon. In addition, an antireflection film 7 is formed on the light receiving portion 2 via the interlayer insulating film 4.

  Here, the antireflection film 7 is provided in a state where it partially enters under the opening of the light shielding film 6, that is, its peripheral portion overlaps with the end of the opening. Unlike this, the solid-state imaging device is characterized in that the cross-sectional shape of the antireflection film is convex.

  Since the antireflection film 7 has a convex shape, the light 8 incident on the opening of the light shielding film 6 is refracted in the central direction of the light receiving part 2 and is condensed on the central part of the light receiving part 2. As in the prior art, it is possible to reduce the incidence of light on the transfer unit 3 formed adjacent to the side of the light receiving unit 2 by multiple reflection in the insulating film between the light shielding film 6 and the silicon substrate 1. Can be suppressed. The peripheral portion of the antireflection film 7 overlaps with the opening end of the light shielding film 6, and the curved surface of the antireflection film 7 only needs to be formed in the peripheral portion including at least the overlapping portion. Further, it is desirable that an antireflection film is formed under the light shielding film.

  Next, the manufacturing process of the solid-state imaging device shown in FIG. 1 will be described with reference to FIG. FIG. 2 is a process cross-sectional view illustrating a method for manufacturing a solid-state imaging device according to an embodiment of the present invention, and illustrates a cross-section of a pixel portion.

  As shown in FIG. 2A, a light receiving portion 12 and a transfer portion 13 made of an N type diffusion layer are formed in a P type silicon substrate 11, and an insulating film 14 is formed on the surface of the silicon substrate 11. Next, after forming the gate electrode 15 on the insulating film 14 in the region of the transfer portion 13, the interlayer insulating film 14 is formed on the entire surface including the gate electrode 15 and the light receiving portion 12.

  Next, as shown in FIG. 2B, an antireflection film 17 made of a silicon nitride film is formed on the interlayer insulating film 14 by a CVD method or the like. The thickness of the antireflection film 17 is preferably 40 nm to 200 nm. In addition to the silicon nitride film, titanium oxide or tantalum oxide can be used as the antireflection film material. Next, as shown in FIG. 2C, a resist 18 that is a mask pattern of a resin film is applied on the antireflection film 17, and exposure is performed so that the resist 18 remains on the light receiving portion 12. Then, the resist 18 is heat-flowed to form an upwardly convex lens shape as shown in FIG. Next, by etching the lens-shaped resist 18 and the antireflection film 17 by using an anisotropic dry etching method, the lens shape is transferred to the antireflection film 17 and at the same time, the antireflection film material other than the region of the light receiving portion 12 is removed. Then, the shape shown in FIG. Thereafter, as shown in FIG. 2F, a light-shielding film 16 of a refractory metal such as tungsten or tungsten silicide or a compound thereof is formed, and a region of the light receiving portion 12 is opened.

  In the above manufacturing process, after the heat flow of the resist 18, the cross-sectional shape may be formed so that the peripheral region of the resist 18 having a certain width including at least the opening boundary of the light shielding film 16 has a curved surface. A convex lens shape may be formed over the entire area. Such shape control is possible by adjusting the heat treatment temperature and time of the resist 18.

  According to this embodiment, even when light is incident obliquely on the surface of the light receiving unit into the opening of the light shielding film 6, the light can be refracted and concentrated in the center direction of the light receiving unit due to the shape of the antireflection film 17. Therefore, it is possible to reduce the incidence of light on the transfer unit that causes the smear phenomenon.

  In the solid-state imaging device and the manufacturing method thereof according to the present invention, the surface of the antireflection film is curved upward so that even if light is incident obliquely from the opening of the light shielding film, it is refracted on the curved surface. Light can be collected at the center of the light receiving unit. Therefore, it is useful as one method for reducing smear in a solid-state imaging device.

It is sectional drawing of the solid-state image sensor in embodiment of this invention. It is process sectional drawing which shows the manufacturing method of the solid-state image sensor by embodiment of this invention. It is sectional drawing which shows the conventional solid-state image sensor and its problem.

Explanation of symbols

1,11,21 Silicon substrate 2,12,22 Light receiving part 3,13,23 Transfer part 4,14,24 Interlayer insulating film 5,15,25 Gate electrode 6,16,26 Light shielding film 7,27,37 Antireflection Films 8, 28 Incident light 18 Resist

Claims (6)

  A light receiving portion formed of a diffusion layer formed on the semiconductor substrate, an antireflection film formed on the light receiving portion, and a light shielding film formed on the semiconductor substrate so that a region of the antireflection film becomes an opening A solid-state imaging device, wherein the antireflection film has an upwardly convex curved surface.   2. The solid according to claim 1, wherein a peripheral portion of the antireflection film overlaps with an opening end portion of the light shielding film, and a curved surface of the antireflection film is formed in the peripheral portion including at least the overlapped portion. Image sensor.   The solid-state imaging device according to claim 1, wherein the light shielding film is formed on and overlaps the antireflection film.   The solid-state imaging device according to claim 1, wherein the antireflection film has a thickness of 40 to 200 nm.   Forming a light receiving portion comprising a diffusion layer on the semiconductor substrate; forming an antireflection film on the semiconductor substrate including the light receiving portion; and masking a resin film on a portion of the antireflection film immediately above the light receiving portion. A step of forming a pattern, a step of forming a cross-sectional shape of the mask pattern into a shape having a curved surface that protrudes upward, and etching the mask pattern and the anti-reflection film to raise the cross-sectional shape of the anti-reflection film And a step of forming a light-shielding film having an opening in the light-receiving portion region on the semiconductor substrate on which the antireflection film is formed. Manufacturing method.   6. The method of manufacturing a solid-state imaging device according to claim 5, wherein the mask pattern is a resist, and the cross-sectional shape of the resist is convex upward by heat flow.

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