JP4853157B2 - Antireflection film, optical element, imaging device, and camera - Google Patents

Description

  The present invention relates to an antireflection film, an optical low-pass filter, a solid-state imaging device, and a digital still camera, and more particularly to an antireflection film formed on the surface of an optical component.

  The above-described anti-reflection (AR) film is used, for example, to suppress surface reflection of an optical low-pass filter (OLPF) as an optical component. As the antireflection film, for example, as described in Patent Document 1, a laminated thin film having a five-layer structure including a mixed oxide layer mainly composed of titanium (Ti) and lanthanum (La) is used. These laminated thin films are formed by using, for example, a vacuum heating vapor deposition method.

Specifically, as shown in FIG. 4, in order from the substrate 111 side, a magnesium fluoride film 112 (MgF ₂ , a refractive index n1 = 1.385, a film thickness d1 = 25.8 nm), an aluminum oxide film 113 (Al ₂ O). ₃ , refractive index n2 = 1.820, film thickness d2 = 98.0 nm), titanium and lanthanum mixed oxide film 114 (refractive index n3 = 2.100, film thickness d3 = 11.4 nm), silicon oxide film 115 ( SiO ₂ , refractive index n4 = 1.480, film thickness d4 = 17.5 nm) and magnesium fluoride film 116 (MgF ₂ , refractive index n5 = 1.385, film thickness d5 = 75.5 nm) are formed. Yes. The total film thickness of these films (antireflection film 101) is 338.2 nm. Further, the reflection characteristics indicating the relationship between the wavelength and the reflectance are as shown in the graph of FIG. The horizontal axis indicates the wavelength (nm), and the vertical axis indicates the reflectance (%).

JP 2000-227504 A

  However, when the magnesium fluoride films 112 and 116 are formed, since the melting points of the magnesium fluoride films 112 and 116 are low (for example, 1260 ° C.), it is difficult to control the heating, and the magnesium fluoride films 112 and 116 may evaporate without being completely vaporized. In some cases, it may adhere to the substrate 111 or the like in a hardened state. As a result, there is a problem that a point defect such that light does not transmit to a portion adhered in a solid state occurs, resulting in a poor appearance. In addition, since the antireflection film 101 has a five-layer structure and the number of film forming steps is relatively large, there is a high possibility that dust or the like is included in the film forming. In addition, since it has a five-layer structure and the total film thickness is relatively thick, the amount of impurities contained in the film material increases, resulting in a problem of poor appearance.

  The present invention solves the above-described problems, and an object thereof is to provide an antireflection film, an optical low-pass filter, a solid-state imaging device, and a digital still camera that can suppress appearance defects.

In order to solve the above problems, the antireflection film according to the first embodiment of the present invention has a four-layer structure in which thin films of a first layer, a second layer, a third layer, and a fourth layer are laminated from the substrate side. The first layer and the third layer are a mixed oxide film of titanium (Ti) and lanthanum (La), and the second layer and the fourth layer are silicon oxide films (SiO _2). The refractive index and film thickness of the first layer, the second layer, the third layer, and the fourth layer are n1, n2, n3, n4 and d1, d2, d3, d4, and the design dominant wavelength. Is λ0,
0.052λ0 ≦ n1d1 ≦ 0.063λ0,
0.070λ0 ≦ n2d2 ≦ 0.085λ0,
0.432λ0 ≦ n3d3 ≦ 0.528λ0,
0.200λ0 ≦ n4d4 ≦ 0.245λ0,
It is characterized by satisfying the relationship .
The antireflection film according to the second aspect of the present invention is characterized in that n1d1 = 0.058λ0, n2d2 = 0.078λ0, n3d3 = 0.480λ0, and n4d4 = 0.222λ0 .
An optical element according to a third aspect of the present invention includes the antireflection film according to the first or second aspect .
An optical element according to a fourth aspect of the present invention is characterized in that the optical element according to the third aspect is an optical low-pass filter .
An imaging device according to a fifth aspect of the present invention includes the optical element according to the third or fourth aspect and an imaging element .
A camera according to a sixth aspect of the present invention includes the imaging device according to the fifth aspect .
Application Example 1 An antireflection film according to Application Example 1 is an antireflection film in which a plurality of thin films are stacked on a substrate, and a mixed oxide film of titanium (Ti) and lanthanum (La) is a main component. It has a four-layer structure composed of a layer and a layer mainly composed of a silicon oxide film (SiO ₂ ).

  According to this configuration, the antireflection film has a four-layer structure composed of a mixed oxide film layer of titanium and lanthanum and a silicon oxide film layer, so that magnesium fluoride is used for the antireflection film. It is possible to suppress the appearance defect including point defects due to the low melting point. Furthermore, by using a four-layer structure, the film thickness can be made relatively thin and the number of film forming steps can be reduced. Therefore, it is possible to suppress dust and impurities from being contained in the antireflection film, and it is possible to suppress appearance defects.

Application Example 2 The antireflection film according to Application Example 2 is an antireflection film having a four-layer structure in which thin films of a first layer, a second layer, a third layer, and a fourth layer are stacked from the substrate side, The first layer and the third layer are a mixed oxide film of titanium (Ti) and lanthanum (La), and the second layer and the fourth layer are silicon oxide films (SiO ₂ ). And

  According to this configuration, the antireflection film has a four-layer structure in which a mixed oxide film of titanium and lanthanum is used for the first layer and the third layer, and a silicon oxide film is used for the second layer and the fourth layer. It is possible to suppress appearance defects including point defects due to a low melting point as in the case where a magnesium fluoride film is used as the prevention film. Furthermore, by using a four-layer structure, the film thickness can be made relatively thin and the number of film forming steps can be reduced. Therefore, it is possible to suppress dust and impurities from being contained in the antireflection film, and it is possible to suppress appearance defects.

Application Example 3 In the antireflection film according to Application Example 3, the refractive index and film thickness of the first layer, the second layer, the third layer, and the fourth layer are set to n1, n2, n3, n4, and d1. , D2, d3, d4 and when the design dominant wavelength is λ0, 0.052λ0 ≦ n1d1 ≦ 0.063λ0, 0.070λ0 ≦ n2d2 ≦ 0.085λ0, 0.432λ0 ≦ n3d3 ≦ 0.528λ0, The relationship is 0.200λ0 ≦ n4d4 ≦ 0.245λ0.

  According to this configuration, since the first layer to the fourth layer have the above-described refractive index and film thickness, the reflectance is low (for example, 1.0% or less) in the visible light region (for example, 390 nm to 780 nm). Can be obtained.

Application Example 4 The optical low-pass filter according to Application Example 4 includes the antireflection film according to any one of Application Examples 1 to 3 .

  According to this configuration, since the antireflection film having a four-layer structure composed of a mixed oxide layer of titanium and lanthanum and a silicon oxide layer is formed on the optical low-pass filter, it is possible to suppress the appearance from being deteriorated. An optical low-pass filter can be provided.

Application Example 5 A solid-state imaging device according to Application Example 5 includes the optical low-pass filter according to Application Example 4 .

  According to this configuration, an optical low-pass filter formed with a four-layer antireflection film composed of a mixed oxide layer of titanium and lanthanum and a silicon oxide layer is used for a solid-state imaging device. Thus, it is possible to provide a solid-state imaging device that can be suppressed. In addition, since the quality of incident light (for example, the amount of light) generated due to the appearance defect is suppressed, incident light close to a normal state can be received by the solid-state imaging device.

Application Example 6 A digital still camera according to Application Example 6 includes the solid-state imaging device according to Application Example 5 .

  According to this configuration, since the above-described solid-state imaging device is used for a digital still camera, it is possible to provide a digital still camera that can suppress an appearance defect and can receive incident light close to a normal state. Can do.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing the configuration of the antireflection film. Hereinafter, the configuration of the antireflection film will be described with reference to FIG.

  As shown in FIG. 1, the antireflection film 10 has a four-layer structure, and the thin films of the first layer 12, the second layer 13, the third layer 14, and the fourth layer 15 are sequentially formed from the substrate 11 side. Are stacked. The substrate 11 is a low-pass filter (OLPF) made of, for example, crystal. The first layer 12 to the fourth layer 15 are formed by, for example, a vacuum heating vapor deposition method. The design dominant wavelength (λ0) is 580 nm.

  The main component of the first layer 12 is a mixed oxide of Ti (titanium) and La (lanthanum). Specifically, the first layer 12 is an oxide of a mixture of Ti and La and has a refractive index (n1) of 2.000 ± 0.200. The film thickness (d1) is 16.7 nm and the optical film thickness (nd1) is 0.058λ0 nm.

The main component of the second layer 13 is SiO ₂ (silicon oxide film). Specifically, the refractive index (n2) of the second layer 13 is 1.460 ± 0.200, and the film thickness (d2) is 30.8 nm. The optical film thickness (nd2) is 0.078λ0 nm.

  The third layer 14 is a mixed oxide film composed mainly of Ti (titanium) and La (lanthanum). More specifically, the third layer 14 is an oxide of a mixture of Ti and La like the first layer 12 and has a refractive index (n3) of 2.000 ± 0.200. The film thickness (d3) is 139.2 nm and the optical film thickness (nd3) is 0.480λ0 nm.

The main component of the fourth layer 15 is SiO ₂ (silicon oxide film). Specifically, the refractive index (n4) of the fourth layer 15 is 1.460 ± 0.200, and the film thickness (d4) is 88.4 nm. The optical film thickness (nd4) is 0.222λ0 nm. Here, the relationship between the film thickness d and the optical film thickness nd · λ0 at the design principal wavelength λ0 can be expressed as n · d = nd · λ0 using the refractive index n.

  FIG. 2 is a graph showing the reflection characteristics (wavelength-reflectance) of the antireflection film. Hereinafter, the reflection characteristics of the antireflection film will be described with reference to FIG.

As shown in FIG. 2, the horizontal axis indicates the wavelength (nm) and the vertical axis indicates the reflectance (%). The solid line A shown in FIG. 2 is the reflection characteristic of the antireflection film 10 of this embodiment, and the broken line B is the reflection characteristic of the conventional antireflection film. The refractive index and film thickness of the first layer 12, the second layer 13, the third layer 14, and the fourth layer 15 are n1, n2, n3, n4 and d1, d2, d3, d4, and the design dominant wavelength is λ0. If the following expressions (1) to (4) are satisfied, a low reflectance (for example, 1.0% or less) is obtained in almost the entire visible light region (for example, 390 nm to 780 nm). be able to.
(1) 0.052λ0 ≦ n1d1 ≦ 0.063λ0
(2) 0.070λ0 ≦ n2d2 ≦ 0.085λ0
(3) 0.432λ0 ≦ n3d3 ≦ 0.528λ0
(4) 0.200λ0 ≦ n4d4 ≦ 0.245λ0

  As described above, the first layer 12 (mixed oxide film of titanium and lanthanum), the second layer 13 (silicon oxide film), the third layer 14 (mixed oxide film of titanium and lanthanum), and the fourth layer 15 (silicon oxide film). By forming the antireflection film 10 with a four-layer structure of film), it is possible to prevent appearance defects such as point defects from occurring as in the case of using a magnesium fluoride film as a conventional antireflection film. it can. Furthermore, by forming the antireflection film 10 with a four-layer structure, the total film thickness can be 275.1 nm. Therefore, it can be made thinner than the conventional total film thickness, and the number of film forming steps can be reduced. As a result, it is possible to suppress the amount of dust or impurities contained in the antireflection film 10 during film formation, and it is possible to suppress the appearance failure. In addition, substantially the same reflection characteristic (see solid line A) can be obtained without degrading the conventional reflection characteristic (see broken line B).

  FIG. 3 is a schematic diagram illustrating structures of an optical low-pass filter, a solid-state imaging device, and a digital still camera. Hereinafter, the structure of the optical low-pass filter, the solid-state imaging device, and the digital still camera will be described with reference to FIG.

  As shown in FIG. 3, the digital still camera 21 includes a camera body 22 and a solid-state imaging device 23.

  The solid-state imaging device 23 includes a solid-state imaging device 32 that receives incident light 31 of an object, a package 33 that houses the solid-state imaging device 32, and the solid-state imaging device 32 that is housed in the package 33 outside (for example, dust). And an optical low-pass filter 34 that removes a spatial frequency component and an antireflection film 10 formed on the optical low-pass filter 34.

  The solid-state imaging device 32 is, for example, a CCD (Charge Coupled Device), and is configured by arranging photoelectric elements (pixels) composed of photodiodes whose storage capacities change according to the intensity of incident light 31 in a matrix. Has been. When the object is photographed using the solid-state imaging device 32, the storage capacity on the regularly arranged pixels changes, and by spatially sampling this, an electrical signal corresponding to the object is generated, This is converted to form an image. By such a solid-state imaging device 32, incident light 31 incident through the antireflection film 10 and the optical low-pass filter 34 is converted into an electrical signal.

  The package 33 accommodates the solid-state image sensor 32 as described above, and is formed in a concave shape with an opening above the accommodated solid-state image sensor 32.

  The optical low-pass filter 34 is fixed via an adhesive material 35 so as to cover the opening area of the package 33. The adhesive material 35 seals between the optical low-pass filter 34 and the package 33. Further, the optical low-pass filter 34 is formed with the antireflection film 10 for suppressing the surface reflection as described above.

  As described above, since the antireflection film 10 that suppresses the appearance defect due to point defects or the like is formed on the optical low-pass filter 34, the quality of the incident light 31 is reduced (deteriorated) when the incident light 31 is received. It is possible to provide the solid-state imaging device 23 and the digital still camera 21 that can suppress the above-described problem.

  As described above in detail, according to the present embodiment, the following effects can be obtained.

  (1) According to the present embodiment, four layers using a mixed oxide film of titanium and lanthanum for the first layer 12 and the third layer 14 and using a silicon oxide film for the second layer 13 and the fourth layer 15. Since the antireflection film 10 has a structure, it is possible to suppress appearance defects including point defects due to a low melting point as in the case of using magnesium fluoride for the antireflection film. Furthermore, by changing from the conventional five-layer structure to the four-layer structure, the total film thickness can be reduced, and the number of film forming steps can be reduced. Therefore, it is possible to prevent dust and impurities from being included in the antireflection film 10 during film formation, and it is possible to suppress appearance defects. In addition, since the first layer 12 to the fourth layer 15 have the above-described refractive index and film thickness, the reflectance is low in the visible light region (for example, 390 nm to 780 nm) without degrading the conventional reflection characteristics. (For example, 1.0% or less) can be obtained.

  (2) According to this embodiment, since the antireflection film 10 having a four-layer structure composed of a mixed oxide film of titanium and lanthanum and a silicon oxide film is formed on the optical low-pass filter 34, the appearance is poor. In addition, the quality (for example, the amount of light) of the incident light 31 can be prevented from being deteriorated (deteriorated) when passing through the optical low-pass filter 34. As a result, the solid-state imaging device 23 can receive incident light 31 that is close to a normal state.

  In addition, this embodiment is not limited above, It can also implement with the following forms.

  (Modification 1) As described above, the substrate 11 is not limited to the optical low-pass filter (OLPF) 34, and can be applied to, for example, all those requiring the antireflection film 10, for example, a heat sink, a lens, and a prism. Glass or the like may be used.

  (Modification 2) As described above, the solid-state imaging device 32 is not limited to a CCD, and may be, for example, a CMOS (Complementary Metal Oxide Semiconductor), a CPD (Charge Priming Device), or the like.

The schematic cross section which shows the structure of the anti-reflective film which concerns on embodiment of this invention. The graph which shows the reflective characteristic of an antireflection film. The schematic diagram which shows the structure of the optical low-pass filter which has an antireflection film, a solid-state imaging device, and a digital still camera. The schematic cross section which shows the structure of the conventional antireflection film. The graph which shows the reflective characteristic of the conventional antireflection film.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Antireflection film, 11 ... Board | substrate, 12 ... 1st layer which comprises an antireflection film, 13 ... 2nd layer which comprises an antireflection film, 14 ... 3rd layer which comprises an antireflection film, 15 ... Antireflection 4th layer constituting the film, 21... Digital still camera, 22... Camera body, 23... Solid-state imaging device, 31... Incident light, 32 ... solid-state imaging element constituting the solid-state imaging device, 33. Package, 34... Optical low-pass filter constituting the solid-state imaging device, 35... Adhesive material constituting the solid-state imaging device.

Claims (6)

Antireflection film having a four-layer structure in which thin films of a first layer, a second layer, a third layer, and a fourth layer are stacked from the substrate side
Because
The first layer and the third layer are a mixed oxide film of titanium (Ti) and lanthanum (La),
The second layer and the fourth layer are silicon oxide films (SiO ₂ ),
The refractive index and film thickness of the first layer, the second layer, the third layer, and the fourth layer are n1, n2, n3, n4 and d1, d2, d3, d4,
When the design dominant wavelength is λ0,
0.052λ0 ≦ n1d1 ≦ 0.063λ0,
0.070λ0 ≦ n2d2 ≦ 0.085λ0,
0.432λ0 ≦ n3d3 ≦ 0.528λ0,
0.200λ0 ≦ n4d4 ≦ 0.245λ0,
An antireflective film characterized by satisfying the above relationship . n1d1 = 0.058λ0,
n2d2 = 0.078λ0,
n3d3 = 0.480λ0,
n4d4 = 0.222λ0,
The antireflection film according to claim 1, wherein An optical element comprising the antireflection film according to claim 1 . The optical element according to claim 3 is an optical low-pass filter . An optical element according to claim 3 or 4,
An image sensor;
An imaging apparatus comprising: A camera comprising the imaging device according to claim 5 .

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