JPH1168080A - Solid-state image-pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a solid-state image-pickup device which reduces the absolute vol. of smear components due to multiple reflections. SOLUTION: This device comprises plural photoelectric elements on an Si substrate, signal transfer elements 3 separated apart from the photoelectric conversion elements 2 on the surface of a substrate 1, antireflection film 10 on the surface of the substrate 1, transfer electrodes 4 on the substrate top, and a screen film 7 on these electrodes via a layer insulation film 6. The antireflection film 10 on the Si surface 1 is partly formed inside the screen film 7. A light which is incident on the film between the Si and the screen film reaches the antireflection film 10 at least once to prevent multiple reflections, and is absorbed in the substrate 1 before reaching the top of the signal transfer element 3. As the light is absorbed in the substrate 1 at the signal transfer element 3 top part, the smear components due to the multiple reflections are reduced and the smear is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid-state imaging device, and more particularly to a solid-state imaging device capable of improving smear.

[0002]

2. Description of the Related Art As a first conventional example, a sectional structure of a unit pixel of a CCD type solid-state imaging device is shown in FIG. Kono et al., 198
4th International Electronic Device Conference Proceedings, IEDM Technical Digest
Pp. 24 to 27 of "A Design Consideration on P-well Structure for Solid-State Image Sensors (A DESIGN CONSIDERATIO
N ON P-WELL STRUCTURE FOR SOLID-STATE IMAGESENSOR
S) "describes the structure of FIG. In this conventional example, a photoelectric conversion element 2 and a signal transfer element 3 are formed separately from the photoelectric conversion element 2 on a silicon substrate 1, and a channel stop 12 is provided between the photoelectric conversion element 2 and the signal transfer element 3.
Is formed, a gate insulating film 13 is formed, a light-shielding film 7 is formed via the gate insulating film 13 including the upper portion of the signal transfer element 2, and a planarization made of a transparent polymer resin is further formed thereon. Layer 8 is formed.

[0003] Other conventional examples 2 (JP-A-4-275559, JP-A-4-259256, JP-A-4-22)
Japanese Patent No. 3371) attempts to reduce flare by providing an antireflection film on the surface of a microlens formed on the surface of a solid-state imaging device or by suppressing surface reflection of the microlens.

[0004] Still another conventional example 3 (Japanese Unexamined Patent Publication No. Hei 4-22333).
No. 70) prevents multiple reflections from occurring between the light-receiving surface of a solid-state imaging chip molded with a transparent resin and the front surface of the transparent resin to eliminate disturbance of an output image and improve image clarity. And

[0005]

However, in the above-mentioned conventional example 1, the silicon substrate 1 and the upper oxide film have different refractive indexes. For this reason, as shown in FIG. 5A, the light reflected on the silicon substrate leaks below the light shielding film 7 and is multiple-reflected between the silicon substrate 1 and the light shielding film 7. The incident light after the multiple reflection reaches the inside of the signal transfer element 3,
Here, it is not possible to prevent the generation of charges that cause smear (hereinafter, referred to as smear components due to multiple reflection) due to photoelectric conversion. Further, regarding the reflectance incident on the oxide film side and reflected by silicon, in a wavelength region where the reflectance is large, the absorptance to the silicon substrate is reduced, and thus there is a problem that the sensitivity is significantly reduced.

[0006] To improve the sensitivity, a technique having a structure shown in FIG. 6 (Japanese Patent Laid-Open No. 63-14466) has been reported. In FIG. 6, 1 is a silicon substrate, 2 is a photoelectric conversion element, 3 is a signal transfer element, 4 is a transfer electrode, 10 is an antireflection film, 13 is a gate insulating film, and 14 is a gate electrode.
With this structure, the antireflection film 10 plays a role of absorbing the light incident on the oxide film by the photoelectric conversion element 2 without reflecting the light on the surface of the silicon substrate 1. Therefore, an improvement in sensitivity is realized. Normally, smear is represented by the ratio of the absolute amount of smear to the amount of signal, and it is said that the smear improves as the sensitivity increases.

However, this structure is characterized in that the antireflection film 9 is provided only on the surface of the photoelectric conversion element 2. Therefore, even if the improvement shown in FIG. No antireflection film is formed on the silicon surface. Therefore, a phenomenon similar to that in FIG. 5 occurs, and the effect of reducing the absolute amount of the smear component due to multiple reflection does not occur. The same applies to Conventional Example 2, in which the antireflection film is not formed on the silicon surface, and the effect of reducing the absolute amount of the smear component due to multiple reflection does not occur.

An object of the present invention is to provide a solid-state imaging device that reduces the absolute amount of smear components due to multiple reflection.

[0009]

In order to achieve the above object, a solid-state imaging device according to the present invention comprises a plurality of photoelectric conversion elements formed on a silicon substrate and a photoelectric conversion element on a surface of the silicon substrate. Transfer element formed on the silicon substrate, an antireflection film formed on the surface of the silicon substrate, a plurality of transfer electrodes formed on the silicon substrate, and a light shielding formed on the transfer electrode via an interlayer insulating film. And the thickness of the antireflection film is 350 / (4n), where n is the refractive index.
It is characterized in that it is formed not less than nanometer and not more than 450 / (4n) nanometer.

Further, the plurality of transfer electrodes are formed via a gate insulating film composed of an oxide film or a multilayer film having the lowermost layer as an oxide film, and the antireflection film has a refractive index n smaller than that of silicon and an oxide film. Composed of a substance having a higher refractive index,
It is preferable that the end portion is formed so as to be located inside the end portion of the light shielding film and outside the end portion of the signal transfer element.

[0011]

Therefore, according to the solid-state imaging device of the present invention,
A plurality of photoelectric conversion elements are provided on the silicon substrate, a signal transfer element is separated from the photoelectric conversion element on the surface of the silicon substrate, an antireflection film is provided on the surface of the silicon substrate, and a plurality of transfer electrodes are provided on the silicon substrate. A light-shielding film is formed on the transfer electrode via an interlayer insulating film. The thickness of the formed antireflection film is 35 when the refractive index is n.
It is not less than 0 / (4n) nanometer and not more than 450 / (4n) nanometer. Therefore, the light incident on the interlayer film between the silicon and the light-shielding film is prevented from multiple reflection by the antireflection film, is absorbed by the silicon substrate before reaching the upper part of the signal transfer element, and the smear component due to the multiple reflection is further reduced. You.

Further, the plurality of transfer electrodes are formed via a gate insulating film composed of an oxide film or a multilayer film having the lowermost layer as an oxide film, and the antireflection film has a refractive index n smaller than that of silicon and a thickness of the oxide film. Due to the substance having a higher refractive index,
Since the end portion is formed so as to be located inside the end portion of the light shielding film and outside the end portion of the signal transfer element, the light shielding film
The interlayer film between the silicon substrates is hardly thick as compared with the conventional example in which the antireflection film of FIG. 5 is not formed, and the amount of light incident between the light shielding films hardly increases.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the solid-state imaging device according to the present invention will be described below in detail with reference to the accompanying drawings. 1 to 4 show an embodiment of a solid-state imaging device according to the present invention.

FIG. 1 is a schematic sectional view of the first embodiment. In FIG. 1, a solid-state imaging device according to the present embodiment includes a silicon substrate 1, a photoelectric conversion element 2, a signal transfer element 3, a transfer electrode 4, a gate insulating film 5, an interlayer insulating film 6, a light shielding film 7, a planarizing layer 8, It comprises a microlens 9 made of a transparent polymer resin and an antireflection film 10.

The gate insulating film 5 and the interlayer insulating film 6 are made of, for example, silicon dioxide (SiO ₂ ). The antireflection film 10 has a refractive index larger than silicon dioxide and smaller than silicon, for example, silicon monoxide (S
iO).

The anti-reflection film 10 is formed on the silicon surface and partly inside the light shielding film 7. With this configuration, light that has entered the interlayer film between the silicon and the light-shielding film reaches the antireflection film 10 at least once, and most of the light is absorbed inside the silicon substrate 1 via the antireflection film 10. . Since the incident light absorbed by the silicon surface above the signal transfer element 3 is reduced, the smear component due to multiple reflection is reduced and the smear is improved.

Furthermore, by limiting the thickness of the antireflection film 10 made of silicon monoxide (SiO) to 44 nm to 63 nm, the smear component due to multiple reflection is further reduced. This is for the following reason. An experimental result has been obtained in which the smear component due to multiple reflection becomes maximum at incident light near 400 nm, and decreases as the wavelength becomes longer. In order to improve smear, the antireflection film 10 used in FIG.
The antireflection film 10 for the purpose of improving the visible light region having a short wavelength of nanometer is effective. Therefore, the refractive index of silicon monoxide is about 2.0, and the thickness “λ /
By forming the antireflection film 10 of “4n”, the effect as the antireflection film 10 is maximized for the target wavelength. Therefore, when the thickness of silicon monoxide is determined, the thickness is preferably 44 nm or more and 63 nm or less. Hereinafter, such a film is referred to as a “1/4 wavelength film”.
Here, the symbol n represents the refractive index of the antireflection film 10.

Actually, by forming such an anti-reflection film 10, assuming that the refractive index of silicon is n 1 and the refractive index of the oxide film is n 2, the reflectance R 4n for vertically incident light of wavelength λ. Is represented by the following equation 1.

R4n = (n1 · n2 −n ² ) ² / (n 1 · n ² + n ² ) ² (1) In the formula 1, the reflectance of light having a wavelength λ decreases from 21% to 0.6% when the wavelength λ is 380 nm, for example. I do. Note that the material used for the antireflection film 10 of the present embodiment only needs to have a refractive index larger than that of an oxide film and smaller than that of silicon.
₃ N ₄ ) or aluminum oxide (Al ₂ O ₃ ) having a refractive index of about 1.7 may be used. The experimental results show that wavelength 3
"1/4" by silicon nitride for 80 nanometers
By forming a “wavelength film”, a vertically incident wavelength 3
80 nm light reflectivity from 21% to 0.6%
In addition, in the case of aluminum oxide, from 21% to 0.1%.
Reduced to 8%.

Further, the silicon substrate 1 and the antireflection film 10
Even if an extremely thin oxide film (thickness of 100 Å or less) is formed between the two layers for the purpose of preventing defects occurring at the interface between the two, an effect similar to that of FIG. 1 can be obtained in smear and sensitivity.

FIG. 2 is a schematic sectional view of the second embodiment. The solid-state imaging device according to the present embodiment includes a silicon substrate 1, a photoelectric conversion element 2, a signal transfer element 3, a transfer electrode 4, a light shielding film 7,
It comprises a flattening layer 8, a microlens 9, an antireflection film 10, and a gate insulating film 11 composed of a multilayer film whose lowermost layer is an oxide film. As materials used for the gate insulating film 11, silicon dioxide - silicon nitride - ONO film made of silicon dioxide _{(SiO 2 -Si 3 N 4 -SiO} 2) are considered. The material used for the gate insulating film 11 is
Even if the insulating layer is a multilayer film, if the lowermost layer is an oxide film, the effect of improving smear can be obtained.

FIG. 3 is a schematic sectional view of the third embodiment.
The solid-state imaging device according to this embodiment includes a silicon substrate 1, a photoelectric conversion element 2, a signal transfer element 3, a transfer electrode 4, a gate insulating film 5, an interlayer insulating film 6, a light shielding film 7, a flattening layer 8, a micro lens 9, The antireflection film 10 is used. Silicon-
Most of the light incident on the interlayer film between the light shielding films is transferred to the transfer electrode 4 and the silicon substrate 1 before reaching the upper part of the signal transfer element 3.
Is absorbed by However, when the anti-reflection film 10 is formed up to the upper part of the signal transfer element 3, the light remaining without being absorbed easily passes through the anti-reflection film 10 and easily enters the signal transfer element 3, causing smear. Therefore, by not forming the antireflection film 10 on the signal transfer element 3 as shown in FIG.
The smear component due to multiple reflection is further reduced, and the smear is further improved.

FIG. 4 is a schematic sectional view of the fourth embodiment. The solid-state imaging device according to this embodiment includes a silicon substrate 1, a photoelectric conversion element 2, a signal transfer element 3, a transfer electrode 4, a gate insulating film 5, an interlayer insulating film 6, a light shielding film 7, a flattening layer 8, a micro lens 9, The antireflection film 10 is used. The material used for the gate insulating film 5 in FIG. 4 may be silicon dioxide, and the material used for the antireflection film 10 may be silicon monoxide, like the antireflection film 10 in FIG.
By forming the anti-reflection film 10 such that the position of the end of the anti-reflection film 10 is inside the end of the light-shielding film 7 and outside the end of the signal transfer element 3, silicon-
Light that has entered the interlayer film between the light-shielding films reaches the anti-reflection film 10 at least once, and most of the light is absorbed inside the silicon substrate 1 via the anti-reflection film 10. Further, the thickness of the interlayer film between the light-shielding film and silicon at the end of the light-shielding film 7 is hardly increased as compared with the conventional example 1 in which the anti-reflection film 10 is not formed in FIG. The amount of light incident between the films hardly increases. Due to this, the smear component due to multiple reflection is further reduced,
Smear improves further.

Also in the fourth embodiment, the smear component due to multiple reflection is further reduced by limiting the thickness of the antireflection film 10 made of silicon monoxide to 44 nm to 63 nm. The reason is the same as the reason described in the first embodiment of FIG.

As described above, according to the solid-state imaging device of the present invention, the antireflection film 10 is formed on the upper surface of the silicon substrate, and the end of the antireflection film is located inside the end of the light shielding film 7. In addition, since the light is incident on the interlayer film between the silicon and the light-shielding film, the light is absorbed by the silicon substrate 1 before reaching the upper part of the signal transfer element 3 by being formed outside the end of the signal transfer element. Is done. Thereby, the smear component can be reduced. Furthermore, by forming the position of the end of the antireflection film inside the end of the light shielding film 7 and outside the end of the signal transfer element 3, the interlayer between the light shielding film and the silicon substrate is formed. The film is hardly thick as compared with the conventional example in which the antireflection film of FIG. 5 is not formed, and the amount of light incident between the light shielding films hardly increases. The amount of smear due to multiple reflection is reduced, and the smear is further improved. The largest number of smear components due to multiple reflection is 350 nm or more and 450 nm or less.
By forming the wavelength film, the smear component due to multiple reflection can be significantly reduced and reduced, and the smear can be further improved.

The above embodiment is a preferred embodiment of the present invention, but the present invention is not limited to this embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0027]

As is clear from the above description, in the solid-state imaging device of the present invention, a plurality of photoelectric conversion elements are provided on a silicon substrate, and a signal transfer element is provided on a surface portion of the silicon substrate so as to be separated from the photoelectric conversion elements. An anti-reflection film is formed on the surface of the silicon substrate, a plurality of transfer electrodes are formed on the silicon substrate, and a light-shielding film is formed on the transfer electrode with an interlayer insulating film interposed therebetween. If n, the thickness is 350 /
It is not less than (4n) nanometer and not more than 450 / (4n) nanometer. Therefore, the light that has entered the interlayer film between the silicon and the light-shielding film in a wavelength range where smear components are easily generated is prevented from multiple reflection by the antireflection film, and is absorbed by the silicon substrate before reaching the upper part of the signal transfer element, and is multiplexed. The smear component due to reflection is further reduced. The prevention of multiple reflection reduces the generation of smear components and can improve smear.

Further, the plurality of transfer electrodes are formed via a gate insulating film composed of an oxide film or a multilayer film having the lowermost layer as an oxide film, and the antireflection film has a refractive index n smaller than that of silicon and is smaller than that of silicon. Because it is composed of a substance having a higher refractive index, the smear component is further reduced by multiple reflection,
Smear is improved. Further, by forming the end portion inside the end portion of the light shielding film and outside the end portion of the signal transfer element, the thickness between the silicon and the light shielding film and the light incident between the light shielding films are formed. Smears are further improved because the amount of

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a first embodiment of a solid-state imaging device according to the present invention.

FIG. 2 is a schematic sectional view showing a second embodiment of the solid-state imaging device according to the present invention.

FIG. 3 is a schematic cross-sectional view showing a third embodiment of the solid-state imaging device according to the present invention.

FIG. 4 is a schematic cross-sectional view showing a fourth embodiment of the solid-state imaging device according to the present invention.

FIG. 5 is a schematic sectional view showing a conventional solid-state imaging device.

FIG. 6 is a cross-sectional view showing a conventional solid-state imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Photoelectric conversion element 3 Signal transfer element 4 Transfer electrode 5 Gate insulating film 6 Interlayer insulating film 7 Light-shielding film 8 Flattening layer 9 Microlens 10 Antireflection film 11 Gate insulation consisting of a multilayer film whose lowermost layer is an oxide film Film 12 channel stop 13 insulating film 14 gate electrode

Claims (4)

[Claims] A plurality of photoelectric conversion elements formed on a silicon substrate; a signal transfer element formed on a surface of the silicon substrate at a distance from the photoelectric conversion elements; and a plurality of photoelectric conversion elements formed on a surface of the silicon substrate. An anti-reflection film, a plurality of transfer electrodes formed on the silicon substrate, and a light-shielding film formed on the transfer electrode via an interlayer insulating film, wherein the anti-reflection film has a refractive index of If n, the thickness is 350 /
(4n) The solid-state imaging device characterized by being formed in more than nanometer and below 450 / (4n) nanometer. 2. The solid-state imaging device according to claim 1, wherein said plurality of transfer electrodes are formed via a gate insulating film made of an oxide film or a multilayer film having a lowermost layer as an oxide film. 3. The solid-state imaging device according to claim 1, wherein said antireflection film is made of a substance having a refractive index n smaller than that of silicon and larger than that of said oxide film. 4. The anti-reflection film is formed such that an end is located inside an end of the light-shielding film and outside an end of the signal transfer element. The solid-state imaging device according to claim 1.