JP2023154291A - Anti-reflection film, resin lens, lens module, and camera module - Google Patents

Abstract

To prevent cracks in an oxygen permeation prevention film.SOLUTION: An anti-reflection film has at least three types of layers laminated on a resin lens, and the three types of layers comprise a low refractive index layer having the lowest refractive index among the three types of layers, a high refractive index layer having the highest refractive index among the three types of layers, and a gas barrier layer having the highest oxygen gas barrier properties among the three types of layers, and the anti-reflection film includes at least two or more layers of the gas barrier layers. At least one layer of the gas barrier layers is sandwiched by layers having a membrane stress in a direction opposite to a membrane stress of the gas barrier layers. The number of the high refractive index layers included in the anti-reflection film is equal to or more than the number of the gas barrier layers.SELECTED DRAWING: Figure 2

Description

The present invention relates to an antireflection film, a resin lens, a lens module, and a camera module.

Surveillance cameras and vehicle-mounted cameras are used in high-temperature environments such as outdoors and inside cars, and therefore are required to have high environmental resistance. In recent years, due to the desire to reduce the cost of cameras, consideration has been given to switching from glass lenses to resin lenses for lenses mounted on cameras. Patent Document 1 proposes a lens module that reduces yellowing of resin lenses that rapidly deteriorate in high-temperature environments.

Japanese Patent Application Publication No. 2013-020026

With the recent demand for higher precision in camera modules, resin lenses are also required to further suppress yellowing. Patent Document 1 proposes suppressing yellowing of a resin lens by using an oxygen permeation prevention film formed of a SiO film or a SiO ₂ film. However, when the oxygen permeation prevention film is made thicker to enhance the oxygen permeation prevention effect, the reflection characteristics may deteriorate and cracks may occur in the oxygen permeation prevention film due to the thicker film. Cracks in the oxygen permeation prevention film deteriorate the quality of images taken with a camera. Furthermore, since oxygen permeates through cracks in the oxygen permeation prevention film, the environmental resistance of the resin lens is reduced.

As described above, the present invention aims to prevent cracks in the oxygen permeation prevention film.

In order to achieve the object of the present invention, an antireflection film according to an embodiment of the present invention has the following configuration. That is, it is an antireflection film in which at least three types of layers are laminated on a resin lens, and the three types of layers include a low refractive index layer having the lowest refractive index among the three types of layers, and a low refractive index layer having the lowest refractive index among the three types of layers. The antireflection film is composed of a high refractive index layer having the highest refractive index among the layers, and a gas barrier layer having the highest oxygen gas barrier property among the three types of layers, and the antireflection film includes at least two or more layers of the gas barrier layer. , at least one layer of the gas barrier layer is sandwiched between layers having a film stress in the opposite direction to the film stress of the gas barrier layer, and the number of the high refractive index layers of the antireflection film is equal to The number of gas barrier layers is greater than or equal to the number of gas barrier layers.

According to the present invention, cracks in the oxygen permeation prevention film can be prevented.

FIG. 3 is a diagram showing the reflection characteristics of an antireflection film. FIG. 3 is a cross-sectional view of the antireflection film in the first embodiment. FIG. 3 is a cross-sectional view of an antireflection film in a second embodiment. FIG. 3 is a cross-sectional view of an antireflection film in a third embodiment. FIG. 7 is a schematic diagram showing a resin lens and an antireflection film in a third embodiment. Schematic diagram of a lens module and a camera module.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the claimed invention. Although a plurality of features are described in the embodiments, not all of these features are essential to the invention, and the plurality of features may be arbitrarily combined. Furthermore, in the accompanying drawings, the same or similar components are designated by the same reference numerals, and redundant description will be omitted.

(First embodiment)
The antireflection film consists of a low refractive index layer with the lowest refractive index among the three types of layers, a high refractive index layer with the highest refractive index among the three types of layers, and the highest oxygen gas barrier layer among the three types of layers. and a gas barrier layer with high properties. The gas barrier layer is sandwiched between layers having film stress in the opposite direction to the film stress of the gas barrier layer, and the antireflection film includes at least two or more gas barrier layers, and the antireflection film has a high refractive index layer. The number of gas barrier layers is greater than or equal to the number of gas barrier layers. Note that the antireflection film is not limited to application to camera lenses, but may be applied to other optical lenses, displays of smartphones, tablets, PCs, etc., for example.

(Anti-reflection film)
The antireflection film is a multilayer film in which at least three types of layers are laminated on a resin lens. The three types of layers include, but are not limited to, low refractive index layers, high refractive index layers, and gas barrier layers. Further, the antireflection film may be composed of four or more types of layers including other types of layers in addition to the three types of layers. The antireflection film has as a basic structural unit a laminate in which high refractive index layers and low refractive index layers are alternately laminated. The number of laminates may be two or more, and a gas barrier layer is laminated between the laminates. The term "film thickness" used below refers to physical film thickness. Film stress refers to stress caused by differences in expansion coefficients between the thin film and the substrate.

The antireflection film has good optical properties (low reflection properties over the entire target wavelength range). Further, the antireflection film has a gas barrier function that suppresses permeation of oxygen gas in order to suppress deterioration (for example, yellowing) of the resin lens in high temperature and high humidity environments. The gas barrier function is achieved by two or more gas barrier layers constituting the antireflection film.

FIG. 1 is a diagram showing the reflection characteristics of an antireflection film. The horizontal axis in FIG. 1 indicates wavelength (Wavelength [nm]), and the vertical axis indicates reflectance (Reflectance [%]). The lower the reflectance value, the more light reflection is suppressed.

The antireflection film has a reflection reducing function such that the reflectance in the visible wavelength region of 400 to 700 nm is 1% or less. Further, the antireflection film has a reflection reducing function such that the reflectance is 1% or less in the near-infrared region (wavelength of 700 nm or more) and the ultraviolet region (wavelength of 400 nm or less). Note that the antireflection films of the second and third embodiments described below have the same light reflection reduction function as the first embodiment.

As described above, the antireflection film has, as a basic structural unit, a laminate in which high refractive index layers and low refractive index layers are alternately laminated. Therefore, the optical properties of the antireflection film are optimized by using the light interference effect due to the difference in refractive index between the high refractive index layer and the low refractive index layer. However, the refractive index difference of an anti-reflective film in which a gas barrier layer is inserted between the laminates is smaller than that of an anti-reflective film composed of only multiple laminates. .

Therefore, by increasing the number of high refractive index layers in the antireflection film than the number of gas barrier layers, the refractive index difference is increased. For example, when the number of gas barrier layers in the antireflection film is two, the number of high refractive index layers is two or more. Furthermore, by forming the high refractive index layer, the low refractive index layer, and the gas barrier layer using different film-forming materials, the antireflection film can efficiently exhibit its reflection reduction function and gas barrier function.

From the viewpoint of suppressing cracks in the gas barrier layer caused by film stress, layers with tensile stress and layers with compressive stress (or weak compressive stress) in the antireflection film are alternately laminated. In particular, the direction of film stress in the gas barrier layer and the direction of film stress in two layers adjacent to the gas barrier layer are made to be opposite to each other. Here, the weak compressive stress refers to a compressive stress smaller than -100 MPa when converted to a film thickness of 100 nm, for example. Further, stress expressed as a positive value (for example, 100 MPa) indicates tensile stress.

Furthermore, the value of the film stress of each layer may be adjusted so that the film stress of each layer in the antireflection film (tensile stress and compressive stress) cancels each other out. The value of film stress is adjusted, for example, by the film thickness and film density of each layer. Note that the film stress value of each layer in the antireflection film may be a small value, and this can be achieved, for example, by reducing the film thickness of each layer.

(Gas barrier layer)
The gas barrier layer has the highest gas barrier property against oxygen gas among the three types of layers. Examples of materials that can be formed as the gas barrier layer include Al ₂ O ₃ , Si ₃ N ₄ , AlN, and SiON. Note that the gas barrier layer may be a composite layer that is a combination of a plurality of thin films made of a material that can be formed as a gas barrier layer.

The refractive index of the gas barrier layer is lower than the high refractive index layer and higher than the low refractive index layer. In the gas barrier layer, the refractive index at a wavelength of 500 nm is greater than 1.6 and smaller than 1.8.

Furthermore, since the gas barrier layer has a high barrier effect against moisture, it can suppress expansion and hydrolysis of the resin lens caused by moisture under high humidity. The gas barrier layer has relatively hard film quality because of its high film density. Furthermore, in order to obtain a high gas barrier effect, it is necessary to thicken the gas barrier layer. As a result, the thickened gas barrier layer is more likely to generate cracks due to film stress or the like than other layers (low refractive index layer, high refractive index layer).

Therefore, the thickened gas barrier layer is divided into a plurality of gas barrier layers. A plurality of (for example, two or more) gas barrier layers are formed so that the physical thickness of each layer is equal to or less than a predetermined value from the viewpoint of preventing cracks in the gas barrier layer. At this time, the thickness of each gas barrier layer is, for example, 5 nm or more, or 15 nm or more, and 30 nm or less, or 20 nm or less. Furthermore, in order for the gas barrier layer to exhibit a high gas barrier effect, the total physical thickness of all the gas barrier layers in the antireflection film should be, for example, 30 nm or more, or 40 nm or more, and 100 nm or less, or 90 nm or less. be.

In addition, from the perspective of reducing film stress by reducing the film thickness of each gas barrier layer, multiple gas barrier layers are Make the layer thickness uniform. On the other hand, if the thickness (e.g., 50 nm) of the layer adjacent to the gas barrier layer (low refractive index layer or high refractive index layer) is significantly thicker than the film thickness (e.g., 20 nm) of the gas barrier layer, the gas barrier layer The film thickness (for example, 20 nm) may be larger than that of other gas barrier layers.

In each embodiment of the present invention, when the gas barrier layer is _a thin film made of SiON or _Al2O3 , the gas barrier layer has "tensile stress". From the viewpoint of preventing cracks in the gas barrier layer, the directions of film stress in the two layers adjacent to the gas barrier layer in the antireflection film are as follows. For example, when the film stress of the gas barrier layer is compressive stress, the film stress of the two layers is adjusted to be tensile stress. Further, when the film stress of the gas barrier layer is tensile stress, the film stress of the two layers adjacent to the gas barrier layer is adjusted to be compressive stress. That is, the gas barrier layer is sandwiched between two layers having a film stress in a direction opposite to that of the gas barrier layer. By employing the above laminated arrangement, it is possible to reduce local distortion due to film stress occurring in the gas barrier layer, and to suppress cracks in the gas barrier layer.

In each embodiment of the present invention, by changing the type of material constituting the gas barrier layer, the optical properties of the gas barrier layer and the direction of film stress (tensile stress or compressive stress) can be changed. The direction of film stress in the gas barrier layer can also be changed by changing the film formation method.

(High refractive index layer)
From the viewpoint of optical design, the high refractive index layer is a layer (thin film) with the highest refractive index among the three types of layers. Examples of materials that can be formed as a high refractive index layer include TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ , HfO ₂ , La ₂ Ti ₂ O ₇ (LaTiO ₃ ), Si ₃ N ₄ , etc. include. Note that the high refractive index layer may be a composite layer that is a combination of a plurality of thin films formed of a material that can be formed into a film as a high refractive index layer. Furthermore, when the high refractive index layer is made of TiO ₂ , Nb ₂ O ₅ or the like, the high refractive index layer is particularly likely to increase the refractive index difference. When the high refractive index layer is a thin film made of Ta ₂ O ₅ , HfO ₂ , La ₂ Ti ₂ O ₇ or the like, the high refractive index layer can suppress absorption of light in the ultraviolet region.

The high refractive index layer has a refractive index of 1.8 or more at a wavelength of 500 nm, and has little light absorption in the target wavelength range.

In each embodiment of the present invention, when the high refractive index layer is a thin film made of Nb ₂ O ₅ , the film stress of the high refractive index layer has "weak compressive stress". When the high refractive index layer is a thin film made of _TiO2 , the film stress of the high refractive index layer has "tensile stress".

In each embodiment of the present invention, by changing the type of material constituting the high refractive index layer, the optical properties of the high and low refractive index layers and the direction of film stress (tensile stress or compressive stress) can be changed. The direction of film stress in the high refractive index layer can also be changed by changing the film formation method.

(Low refractive index layer)
The low refractive index layer is a layer (thin film) with the lowest refractive index among the three types of layers from the viewpoint of optical design. Materials that can be formed as the low refractive index layer include, for example, SiO ₂ and MgF ₂ .

The low refractive index layer has a refractive index of 1.6 or less at a wavelength of 500 nm, and absorbs little light in the target wavelength range.

In each embodiment of the present invention, when the low refractive index layer is a thin film made of SiO ₂ , the film stress of the low refractive index layer has "compressive stress" and is excellent in environmental resistance. On the other hand, if the low refractive index layer is made of _MgF2 , the low refractive index layer has "tensile stress" and a low refractive index.

In each embodiment of the present invention, by changing the type of material constituting the low refractive index layer, the optical properties of the low refractive index layer and the direction of film stress (tensile stress or compressive stress) can be changed. The direction of film stress in the low refractive index layer can also be changed by changing the film forming method.

(Anti-reflection film formation process)
The antireflection film is formed on a substrate (for example, on a resin lens) by a physical or chemical film forming method or a wet method such as spin coating. When forming an antireflection film on a substrate, a relatively high-energy film forming method such as a sputtering method or a vapor deposition method with some kind of assist is used from the viewpoint of film reproducibility and environmental resistance. Methods for forming the antireflection film include, for example, sputtering, IAD (Ion Assist Deposition), ion plating, IBS (Ion Beam Sputter), cluster vapor deposition, CVD (Chemical Vapor Deposition), and ALD (Atomic). This includes layer deposition methods, etc., and film forming methods that use a combination of these methods. The method is not limited to the above method as long as it is possible to accurately control the thickness of each layer constituting the antireflection film, have high film reproducibility, and form a film with high film density. Further, the optimum film forming method may be selected in consideration of the properties and productivity required for the antireflection film.

Further, when forming the antireflection film on the substrate (resin lens), it is preferable to heat the substrate (resin lens) according to its heat resistance. When forming an anti-reflection film on a resin lens that requires high environmental resistance, it is difficult to coat it at high temperatures compared to ordinary resin materials because the resin lens has a high glass transition temperature Tg (that is, it has high heat resistance). It is possible to form a film. Therefore, for example, the heating temperature during the film forming process may be 100° C. or higher. Further, when it is assumed that the film will be used in a high-temperature environment such as an on-vehicle camera, the heating temperature during the film forming process may be 110° C. or higher. On the other hand, a heating temperature during the film forming process that is close to the glass transition temperature Tg of the resin lens or a heating temperature that is higher than the glass transition temperature Tg is inappropriate as the heating temperature during the film forming process. That is, it is preferable to form the antireflection film on the resin lens at a heating temperature that is about 15° C. to 20° C. lower than the glass transition temperature Tg.

(resin lens)
The resin lens is a lens that is transparent to a target wavelength such as a visible wavelength region, and includes, for example, a camera lens. The shape of the resin lens includes, for example, a spherical shape, an aspherical shape, and a flat plate shape such as an optical filter.

The resin lens is made of a resin material with excellent mechanical properties, optical properties, and thermal properties. Examples of resin materials include polyester, polyurethane, olefin, polyether, acrylic, styrene, PET (polyethylene terephthalate), PES (polyether sulfone), polysulfone, and PEN (polyethylene naphthalate). , PC (polycarbonate), and polyimide. Further, the resin lens may be formed of an organic-inorganic hybrid material, such as a material having a silsesquioxane skeleton. The resin lens may be formed using a thermo-photocurable resin such as a polyfunctional reactive polymer having an aromatic dendrimer-like multi-branched structure.

Compared to glass, resin materials are more flexible, lighter, and easier to work with, but they are more susceptible to deformation and deterioration due to heat. Therefore, the resin material needs to have high heat resistance, and for example, it suffices if it has a glass transition temperature Tg of 120°C or higher or 140°C or higher. Further, the resin lens may be formed of an olefin-based material, particularly a cycloolefin-based material, which has a low water absorption rate when considering deformation of the substrate due to water absorption. Further, when a resin lens with a high refractive index and a small Abbe number is required, the resin lens is formed of, for example, a PC-based resin, a fluorene-containing polyester resin, or the like.

When a resin lens is mounted on, for example, an in-vehicle camera or a surveillance camera that has a wide operating temperature range, the resin lens is required to have a small change in refractive index due to temperature. For example, any resin lens may be used as long as the difference between the refractive index at 0° C. and the refractive index at 80° C. at e-line (spectral line of mercury with a wavelength of 546 nm) is 0.8% or less or 0.6% or less.

Resin lenses are required to have a low yellowing index (ΔYI), which is an index for evaluating changes in optical properties due to high-temperature environments (based on JIS K 7105). For example, if the yellowness index (ΔYI), which is the difference between the yellowness index (YI: yellow index) after being held at 110°C for 1500 hours (after exposure) and the initial yellowness index YI ₀ , is 10 or less or 3 or less. Any resin lens will suffice. The method for evaluating yellowness will be explained below.

(Evaluation method of yellowing degree)
Yellowness is the degree to which the hue departs from colorless or white in the yellow direction, and is determined by the following (Equation 1). YI=100(1.28X-1.06Z)/Y (Formula 1), where YI represents the degree of yellowness, and X, Y, and Z represent the tristimulus values of the test piece measured with a colorimeter. Yellowing index (ΔYI) is used to evaluate the deterioration of plastics exposed to environments such as light and heat, and is determined by the difference between the initial yellowness and the yellowness after exposure. The degree of yellowing (ΔYI) is calculated using the following (Equation 2). ΔYI=YI−YI ₀ (Formula 2), where ΔYI is the degree of yellowing, YI is the yellowness after exposure, and YI ₀ is the initial yellowness of the specimen. When ΔYI calculated by Equation 2 has a positive value, it indicates that the degree of yellowing has increased, and when ΔYI has a negative value, it indicates that the degree of yellowing has decreased.

Resin lenses are required to have a transmittance of 80% or more in the visible light wavelength region of 400 to 700 nm, and a transmittance of 60% or more in the visible light wavelength region mentioned above after being held at 110°C for 1500 hours. Ru.

In a lens module equipped with multiple resin lenses as described above, or a camera module in which an image sensor is incorporated into a lens module, multiple types of resin lenses with different refractive indexes and Abbe numbers are used to adjust optical characteristics such as aberrations. may be used in combination.

The resin lens is molded, for example, by an injection molding method. Specifically, a cavity including a lens portion, an outer peripheral portion, a gate portion, etc. formed by butting the fixed side mirror piece and the movable side mirror piece is filled with the resin material from the gate portion. After the resin material is solidified, the mold (fixed side mirror piece and movable side mirror piece) is opened and the substrate (resin lens) is taken out. Finally, the gate part attached to the substrate (resin lens) is cut. By injection molding, aspherical lenses and lenses with high curvature, which are difficult to realize with glass lenses, can be produced relatively easily. Note that the substrate (resin lens) is not limited to injection molding, and may be molded by, for example, injection compression molding, cast polymerization, or other methods.

Further, in order to release internal stress due to molding and remove moisture adsorbed on the substrate (resin lens), the resin lens is annealed before forming the antireflection film on the resin lens. The annealing treatment is carried out at a temperature of 80° C. to below the Tg of the substrate (resin lens) and about 15° C. lower than the Tg of the substrate (resin lens) for about 0.5 to 24 hours, 1 to 12 hours.

(lens module)
FIG. 6 is a schematic diagram of a lens module and a camera module. The lens module 54 includes a lens 50a, a lens 50b, a lens 50c, a lens 50d, a lens 50e, an aperture 53, a lens barrel (not shown), and a light shielding plate (not shown) arranged between the lenses. The aperture 53 may be omitted from the lens module 54 depending on the usage environment and the characteristics of the image sensor.

The number, shape, and material of the lenses 50a to 50e are appropriately adjusted so that the lens module 54 has predetermined optical characteristics. In FIG. 6, the lens module 54 is made up of five lenses, but the lens module 54 is not limited to this, and may be made up of an optimal number of lenses, such as four or less, six or more. An antireflection film is formed on at least one lens among the lenses 50a to 50e.

The lens module 54 may include a plurality of types of resin lenses made of different resin materials. When the lens module 54 includes one or more resin lenses, a glass lens may also be used. For example, a resin lens (cycloolefin type, PC type) and a glass lens are used together as the lens module 54. When a resin lens and a glass lens are used together in the lens module 54, it is preferable to use a glass lens as the lens 50a, which is most susceptible to the influence of heat from the outside air. In this way, by forming an antireflection film with a high gas barrier function on a resin lens, it is possible to reduce oxidative deterioration, which is a cause of yellowing of resin lenses, and realize a lens module 54 with excellent environmental resistance. can.

(The camera module)
Camera module 55 includes a lens module 54 and an image sensor 51. The image sensor 51 is a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like. Further, the camera module 55 may include an IR cut filter 52. The IR cut filter 52 is a filter that limits light in the near-infrared region. The camera module 55 may include, for example, an IR pass filter (not shown) that transmits only light in the near-infrared region, another optical filter, or a plurality of optical filters. At that time, the plurality of optical filters are inserted and removed on the optical axis of the camera module 55. In this way, by mounting the lens module 54 with reduced oxidative deterioration, which is a cause of yellowing of resin lenses, in the camera module 55, the camera module 55 with excellent environmental resistance can be realized.

FIG. 2 is a cross-sectional view of the antireflection film in the first embodiment. The antireflection film 11 on the resin lens 10 includes a gas barrier layer 12 , a high refractive index layer 13 , and a low refractive index layer 14 . The antireflection film 11 is composed of 11 layers (=2 layers + 3 layers + 6 layers) including two gas barrier layers 12 , three high refractive index layers 13 , and six low refractive index layers 14 . All layers in the antireflection film 11 are formed by sputtering. In particular, we use a post-reaction sputtering method that forms an oxide or nitride film by sputtering a metal target to form an ultra-thin metal film and then oxidizing or nitriding the metal film using a dedicated reaction source. It was used as a method.

The resin lens 10 is a lens made of a cycloolefin resin material having a glass transition temperature Tg of 150° C. or higher.

The antireflection film 11 has a structure (referred to as a laminate) in which low refractive index layers 14 and high refractive index layers 13 are alternately laminated. Although the gas barrier layer 12 is laminated as a substitute for the high refractive index layer 13 in the laminate, the gas barrier layer 12 may be laminated as a substitute for the low refractive index layer 14.

Gas barrier layer 12 is a thin film made of SiON. The film stress of the gas barrier layer 12 is tensile stress. The thickness of the gas barrier layer 12 is 20 nm (per layer) in order to obtain a good gas barrier effect against oxygen gas. The total thickness of the two gas barrier layers 12 is 40 nm (=2 layers×20 nm). By setting the thickness of the gas barrier layer 12 to about 20 nm, local distortion occurring in the gas barrier layer 12 can be reduced.

The gas barrier layer 12 is sandwiched between two low refractive index layers 14. Further, the two gas barrier layers 12 are stacked at positions in the antireflection film 11 that are not adjacent to each other. For example, the gas barrier layer 12 is laminated as the fourth layer and the eighth layer from the bottom of the antireflection film 11, respectively. The reason why the two gas barrier layers 12 are not arranged adjacently is to optimize the optical properties of the antireflection film 11. The antireflection film 11 shown in FIG. 2 has better optical properties (reflection properties) than an antireflection film (not shown) in which two gas barrier layers are disposed adjacent to each other. In addition, for the purpose of improving optical properties and alleviating film stress, layers made of other film-forming materials (for example, intermediate refractive index layers) different from the three types of layers (low refractive index layer, high refractive index layer, gas barrier layer) The anti-reflection film 11 may also have a coating layer (coating layer) laminated thereon. Further, the two gas barrier layers 12 may be formed using different film forming materials.

After forming an ultra-thin Si thin film on the resin lens 10 using a Si target, the ultra-thin Si film is formed by flowing a mixed gas with the blending ratio of O ₂ and N ₂ adjusted to a predetermined composition into the reaction source. A SiON thin film was formed. Thereafter, this process was repeated to form a SiON thin film on the resin lens 10 until a predetermined film thickness was achieved. Alternatively, as another film forming method, the nitriding reaction may be promoted using a reaction source using SiO or SiO ₂ as a target. A similar SiON thin film can also be formed by oxidizing the Si target using a reactive source and then nitriding it using the same reactive source or a second reactive source.

The high refractive index layer 13 is a thin film made of Nb ₂ O ₅ . The film stress of the high refractive index layer 13 is a weak compressive stress. The high refractive index layer 13 is sandwiched between two low refractive index layers 14. For example, the high refractive index layer 13 is laminated as the second layer, sixth layer, and tenth layer from the bottom of the antireflection film 11, respectively.

An extremely thin Nb thin film was formed on the resin lens 10 using an Nb target, and then oxidized with a reaction source in which oxygen gas was flowed to obtain a predetermined composition, thereby obtaining a Nb ₂ O ₅ thin film. This process was repeated to form a Nb ₂ O ₅ thin film on the resin lens 10 until a predetermined film thickness was achieved. Further, the film stress of the Nb ₂ O ₅ thin film may be changed to tensile stress by changing the sputtering conditions, oxidation conditions, heating conditions, etc. In this sputtering process, there was concern that the film density would be significantly reduced, so the film forming conditions were adjusted so that the Nb ₂ O ₅ thin film had weak compressive stress.

The low refractive index layer 14 is a thin film made of SiO ₂ . The film stress of the low refractive index layer 14 is compressive stress. The low refractive index layer 14 is laminated as the first layer, third layer, fifth layer, seventh layer, ninth layer, and eleventh layer from the bottom of the antireflection film 11, respectively. The low refractive index layer 14 laminated as the 11th layer is most exposed to outside air and light.

An extremely thin Si film was formed on the resin lens 10 using a Si target, and then oxidized to a predetermined composition using a reaction source flowing O ₂ gas to obtain a SiO ₂ thin film. This process was repeated to form a SiO ₂ thin film on the resin lens 10 until a predetermined film thickness was reached.

(Results of environmental resistance evaluation test of anti-reflection film)
In order to evaluate the environmental resistance of the plurality of resin lenses 10 having the antireflection film 11, a high temperature test (held at 110° C. for 1000 hours) was conducted. After holding at 110° C. for 1000 hours, no cracks were observed in the antireflection film 11 on any of the resin lenses 10. The ΔYI value was 2 or less. No yellowing of the resin lens 10 was observed.

By mounting the resin lens 10 having the antireflection film 11 on a lens module made up of a plurality of resin lenses 10, it is possible to obtain a lens module that suppresses yellowing in a high-temperature environment. Furthermore, by integrating the lens module and the image sensor, it is possible to obtain a camera module that suppresses yellowing in high-temperature environments.

As described above, according to the first embodiment, a layer having tensile stress and a layer having compressive stress (or weak compressive stress) are alternately arranged in consideration of the direction of film stress occurring in each layer in the antireflection film. Laminated so that Further, the gas barrier layers were laminated so that the direction of film stress in the gas barrier layer in the antireflection film was opposite to the direction of film stress in the two layers sandwiching the gas barrier layer. This makes it possible to suppress local distortion caused by film stress occurring in the gas barrier layer, thereby suppressing cracks and delamination of the gas barrier layer in a high-temperature environment.

(Second embodiment)
FIG. 3 is a cross-sectional view of the antireflection film in the second embodiment. The antireflection film 21 on the resin lens 20 includes a gas barrier layer 22 , a high refractive index layer 23 , a low refractive index layer 24 , and an adhesive layer 25 . The antireflection film 21 has 14 layers (= 3 layers + 3 layers + 7 layers) including 3 gas barrier layers 22 , 3 high refractive index layers 23 , 7 low refractive index layers 24 , and 1 adhesive layer 25 +1 layer). The antireflection film 21 of the second embodiment, unlike the antireflection film 11 of the first embodiment, further includes an adhesion layer 25.

The resin lens 20 is a lens made of a polyester resin material having a glass transition temperature Tg of 150° C. or higher.

The antireflection film 21 has a structure (referred to as a laminate) in which an adhesive layer 25 is disposed on the resin lens 20, and a low refractive index layer 24 and a high refractive index layer 23 are alternately laminated above the adhesive layer 25. Although the gas barrier layer 22 is laminated as a substitute for the high refractive index layer 23 in the laminate, the gas barrier layer 22 may be laminated as a substitute for the low refractive index layer 24.

The gas barrier layer 22 is sandwiched between two low refractive index layers 24 . Further, the three gas barrier layers 22 are stacked at positions in the antireflection film 21 that are not adjacent to each other. For example, the gas barrier layer 22 is laminated as the third layer, seventh layer, and eleventh layer from the bottom of the antireflection film 21, respectively. The reason why the three gas barrier layers 22 are not arranged adjacently is to optimize the optical properties of the antireflection film 21. The antireflection film 21 shown in FIG. 3 has better optical properties (reflection properties) than an antireflection film (not shown) in which three gas barrier layers are arranged adjacent to each other. In addition, for the purpose of improving optical properties and alleviating film stress, layers made of other film-forming materials (for example, intermediate refractive index layers) different from the three types of layers (low refractive index layer, high refractive index layer, gas barrier layer) The anti-reflection film 21 may also have a coating layer (coating layer) laminated thereon in the antireflection film 21. Further, the three gas barrier layers 22 may be formed from different film forming materials.

The gas barrier layer 22 is a thin film made of Al ₂ O ₃ . The film stress of the gas barrier layer 22 is tensile stress. Al ₂ O ₃ is used as a deposition source, and oxygen ions are irradiated from an ion source to promote oxidation so that a predetermined composition is obtained. A high-density Al ₂ O ₃ thin film was then formed on the resin lens 20 by applying energy to assist film formation.

Further, the three gas barrier layers 22 (Al ₂ O ₃ thin films) each have a thickness of about 15 nm, and are thin films that reduce local distortion. As mentioned above, the total thickness of the plurality of gas barrier layers is 40 nm or more in order to obtain a good oxygen gas barrier effect. Therefore, the film thickness of each gas barrier layer 22 is set to 15 nm so that the total film thickness of the three gas barrier layers 22 is about 45 nm, and the three gas barrier layers 22 are placed in non-contiguous positions in the antireflection film 21. Laminated.

The high refractive index layer 23 is a thin film made of TiO ₂ . The film stress of the high refractive index layer 23 is tensile stress. Ti ₃ O ₅ is used as a deposition source, and oxygen ions are irradiated from an ion source to promote oxidation so that a predetermined composition is obtained. A high-density TiO ₂ thin film was then formed on the resin lens 20 by applying energy to assist film formation. Further, the film stress of the high refractive index layer 23 (TiO ₂ thin film) may be a weak compressive stress by changing film forming conditions such as assist power and heating conditions.

The low refractive index layer 24 is a thin film made of SiO ₂ . The film stress of the low refractive index layer 24 is compressive stress. For the SiO ₂ thin film other than the SiO ₂ thin film directly above the adhesion layer 25, SiO ₂ is used as the evaporation source, and O 2 ions are irradiated from the ion source to promote oxidation and energy is given so that a predetermined composition is obtained. By assisting the film formation, it is formed as a high-density SiO ₂ thin film.

The adhesive layer 25 is a thin film made of SiO. Using SiO as the evaporation source, a SiO thin film was formed on the resin lens 20 by EB (Electron Beam evaporation) evaporation without using the assistance of an ion source. The adhesion layer 25 (SiO thin film) is formed for the purpose of increasing the adhesion between the resin lens 20 and the antireflection film 21. The adhesive layer 25 has a film thickness of 5 to 20 nm and suppresses the occurrence of light absorption. Adhesion layer 25 has small film stress. The adhesion layer 25 has a composition similar to that of the adjacent low refractive index layer 14 (SiO ₂ thin film). Since the adhesion layer 25 shares oxygen at the interface with the low refractive index layer 14, its composition is more continuous and integral than other interfaces in the antireflection film 21. That is, the adhesive layer 25 may function as a part of the low refractive index layer 14.

Immediately after forming the SiO thin film using SiO as the evaporation source, the SiO ₂ thin film was continuously formed as it is without separating the process, using the assistance of an ion source. The low refractive index layer 14 (SiO ₂ thin film) formed directly on the adhesion layer 25 can be formed by using SiO ₂ as a vapor deposition source and irradiating oxygen ions from an ion source like other SiO ₂ thin films. can be formed.

Due to the difference in coefficient of thermal expansion between the resin lens 20 and the antireflection film 21, cracks may occur starting at the interface between them. Therefore, by increasing the adhesion of the interface between the resin lens 20 and the antireflection film 21, the occurrence of cracks in the antireflection film 21 is suppressed. Layers other than the adhesive layer 25 (SiO layer) were formed by the IAD method.

(Results of environmental resistance evaluation test of anti-reflection film)
In order to evaluate the environmental resistance of the plural resin lenses 20 having the antireflection film 21, a high temperature test (held at 110° C. for 1000 hours) was conducted. No cracks were observed in the antireflection film 21 on all the resin lenses 20 that were maintained at 110° C. for 1000 hours. The ΔYI value was 2 or less. No yellowing of the resin lens 20 was observed.

By mounting the resin lens 20 having the antireflection film 21 on a lens module made up of a plurality of resin lenses 20, it is possible to obtain a lens module that suppresses yellowing in a high-temperature environment. Furthermore, by integrating the lens module and the image sensor, it is possible to obtain a camera module that suppresses yellowing in high-temperature environments.

As described above, according to the second embodiment, by providing the adhesive layer in the antireflection film, it is possible to suppress cracks in the antireflection film that occur at the interface between the resin lens and the antireflection film.

(Third embodiment)
FIG. 4 is a cross-sectional view of the antireflection film in the third embodiment. The antireflection film 31 on the resin lens 30 includes a gas barrier layer 32 , a high refractive index layer 33 , and a low refractive index layer 34 . FIG. 5 is a schematic diagram showing a resin lens and an antireflection film in the third embodiment. FIG. 5 shows that the antireflection film 31 formed by the ALD method covers the entire surface of the resin lens 30 including the side surfaces.

The antireflection film 31 is composed of eight layers (=2 layers+2 layers+4 layers) including two gas barrier layers 32, two high refractive index layers 33, and four low refractive index layers 34. All layers in the antireflection film 31 are formed by sputtering.

The resin lens 30 is a lens made of a cycloolefin resin material having a glass transition temperature Tg of 150° C. or higher. When forming the initial layer (gas barrier layer 32) directly above the resin lens 30, for example, an OH group is provided as a site on which the first precursor can be adsorbed to the resin lens 30. In order to provide OH groups on the resin lens 30, plasma treatment, UV ozone treatment, etc. may be used, or the OH groups may be adsorbed onto the resin lens 30 using water molecules as a precursor.

The antireflection film 31 has a structure in which low refractive index layers 34 and high refractive index layers 33 are alternately laminated (referred to as a laminate). Although the gas barrier layer 32 is laminated as a substitute for the high refractive index layer 33 in the laminate, the gas barrier layer 32 may be laminated as a substitute for the low refractive index layer 34. Here, one gas barrier layer 32 in the antireflection film 31 is placed on the resin lens 30. All layers in the antireflection film 31 are formed by ALD method.

The ALD method is a vapor phase thin film forming method similar to the CVD method. In the CVD method, two types of precursors are simultaneously introduced into a reaction chamber, and reaction products are deposited on a substrate (resin lens 30). On the other hand, in the ALD method, one type of precursor is introduced into the reaction chamber, and other than the precursor adsorbed to the substrate (resin lens 30), there is no chemical reaction with other precursors. , reaction products are formed only on the surface of the substrate. For this reason, in the ALD method, film formation progresses by adsorption of a monomolecular layer onto the film formation surface, so film formation can be performed without being affected by the shape of the substrate (resin lens 30).

The ALD method can form a conformal layer (a layer with a uniform thickness that follows the surface shape of the object to be deposited) even on substrates with complex shapes, such as lenses with high curvature and aspherical lenses. can. In the ALD method, since the layer to be formed is a monomolecular layer, precise control of the film thickness is possible. Furthermore, unlike physical vapor deposition and the like, the ALD method can reduce film defects by forming a film at a single molecule level, so it is possible to form a film with excellent gas barrier properties. Therefore, in a substrate made of a resin material having a film formed by the ALD method, yellowing caused by oxidation of the resin and swelling or hydrolysis caused by moisture are suppressed.

The gas barrier layer 32 is a thin film made of Al ₂ O ₃ . The film stress of the gas barrier layer 32 is tensile stress. The thickness of each gas barrier layer 32 is set to 20 nm in order to obtain a good gas barrier effect against oxygen. The total thickness of the two gas barrier layers 32 is 40 nm (=2 layers×20 nm). By setting the thickness of each gas barrier layer 32 to about 20 nm, local distortion occurring in the gas barrier layer 32 can be reduced.

The gas barrier layer 32 is sandwiched between two low refractive index layers 34. Further, the two gas barrier layers 32 are laminated at positions in the antireflection film 11 that are not adjacent to each other. For example, the gas barrier layer 32 is laminated as the first layer and the fifth layer from the bottom of the antireflection film 31, respectively. The reason why the two gas barrier layers 32 are not disposed adjacent to each other is to optimize the optical properties of the antireflection film 31. The antireflection film 31 shown in FIG. 4 has better optical properties (reflection properties) than an antireflection film (not shown) in which two gas barrier layers are disposed adjacent to each other. In addition, for the purpose of improving optical properties and alleviating film stress, layers made of other film-forming materials (for example, intermediate refractive index layers) different from the three types of layers (low refractive index layer, high refractive index layer, gas barrier layer) The anti-reflection film 31 may be laminated with an anti-reflection film (coating layer). Further, the two gas barrier layers 32 may be formed from different film forming materials.

The gas barrier layer 32 (Al ₂ O ₃ thin film) is formed by an ALD method using TMA (trimethylaluminum) as a first precursor and water molecules as a second precursor. Water molecules are used as the second precursor, but ozone or the like may also be used as the active oxygen. Furthermore, ammonia gas and nitrogen gas may be used as the second precursor depending on the film forming material.

In the ALD method, since there are many types of precursors used when forming the gas barrier layer 32 (Al ₂ O ₃ thin film), the film can be formed most stably. The gas barrier layer 32 (Al ₂ O ₃ thin film) was placed directly above the resin lens 30 in consideration of the adhesion state of the interface between the gas barrier layer 32 and the resin lens 30, the film composition, and homogenization of the film density.

The high refractive index layer 33 is a thin film made of TiO ₂ . The film stress of the high refractive index layer 33 is tensile stress. The high refractive index layer 33 is sandwiched between two low refractive index layers 34. For example, the high refractive index layer 33 is laminated as the third layer and seventh layer from the bottom of the antireflection film 31, respectively.

The high refractive index layer 33 (TiO ₂ thin film) is formed by an ALD method using TDMAT (tetrakis dimethylamino titanium) as a first precursor and water molecules as a second precursor. Water molecules are used as the second precursor, but ozone or the like may also be used as the active oxygen. Furthermore, ammonia gas and nitrogen gas may be used as the second precursor depending on the film forming material.

The low refractive index layer 34 is a thin film made of SiO ₂ . The film stress of the low refractive index layer 34 is compressive stress. The low refractive index layer 34 and the second, fourth, sixth, and eighth layers from the bottom of the antireflection film 31 are laminated, respectively.

The low refractive index layer 34 (SiO ₂ thin film) is formed by an ALD method using TDMAS (trisdimethylaminosilane) as a first precursor and water molecules as a second precursor. Water molecules are used as the second precursor, but ozone or the like may also be used as the active oxygen. Furthermore, ammonia gas and nitrogen gas may be used as the second precursor depending on the film forming material.

As mentioned above, it has been explained that each layer in the anti-reflection film 31 is formed using the ALD method, but each layer in the anti-reflection film 31 is formed using a film-forming process that combines the CVD method and the ALD method. A film may be used. For example, the high refractive index layer 33 (TiO ₂ thin film) and the low refractive index layer 34 (SiO ₂ thin film) may be formed by CVD, and the gas barrier layer 32 (Al ₂ O ₃ thin film) may be formed by ALD. A film may be formed.

The high refractive index layer 33 and the low refractive index layer 34, which affect the reflection characteristics of the antireflection film 31, are formed by the CVD method, which has a faster film formation rate than the ALD method. On the other hand, the gas barrier layer 32, which is required to be dense and have few film defects in order to exhibit a high gas barrier function, is formed by the ALD method. As a result, the hybrid method that combines the CVD method and the ALD method can improve productivity more than forming all the layers in the antireflection film 31 using only the ALD method. Note that the CVD method and the ALD method may be used in combination in forming a specific layer (thin film); for example, some of the four low refractive index layers 34 may be formed by the ALD method, and the others may be formed by the ALD method. The layer may be formed by a CVD method. That is, in a plurality of layers having the same characteristics (for example, a plurality of low refractive index layers 34), the film formation method for each layer may be different from each other.

Note that the ALD method includes a thermal ALD method using heat, a plasma ALD method using plasma, etc., but each layer in the antireflection film 31 may be formed using any method. . In particular, when forming a film on a resin substrate (resin lens 30), it is preferable to use the plasma ALD method because of the advantage that the temperature during film formation can be lowered. At this time, in order to avoid damage to the resin lens 30 due to plasma, a plasma ALD method may be used in which, for example, plasma is generated outside the reaction chamber and only the excited OH radicals reach the reaction chamber. Similarly, when the substrate to be film-formed is the resin lens 30, the plasma CVD method may be used.

(Results of environmental resistance evaluation test of anti-reflection film)
In order to evaluate the environmental resistance of the plurality of resin lenses 30 having the antireflection film 31, a high temperature test (held at 110° C. for 1000 hours) was conducted. No cracks were observed in the antireflection film 31 on all the resin lenses 30 that were maintained at 110° C. for 1000 hours. The ΔYI value was 2 or less. No yellowing of the resin lens 30 was observed.

By mounting the resin lens 30 having the antireflection film 31 on a lens module made up of a plurality of resin lenses 30, it is possible to obtain a lens module that suppresses yellowing in a high-temperature environment. Furthermore, by integrating the lens module and the image sensor, it is possible to obtain a camera module that suppresses yellowing in high-temperature environments.

As described above, according to the third embodiment, an antireflection film that suppresses the occurrence of cracks can be formed on resin lenses of various shapes using a film forming method that combines ALD and CVD.

The invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the following claims are hereby appended to disclose the scope of the invention.

10, 20, 30. Resin lenses 11, 21, 31. Antireflection film 12, 22, 32. Gas barrier layers 13, 23, 33. High refractive index layers 14, 24, 34. Low refractive index layer 25. Adhesion layers 50a, 50b, 50c, 50d, 50e. Lens 51. Image sensor 52. IR cut filter 53. Aperture 54. Lens module 55. The camera module

Claims (19)

An anti-reflection film in which at least three types of layers are laminated on a resin lens,
The three types of layers are:
A low refractive index layer having the lowest refractive index among the three types of layers;
A high refractive index layer having the highest refractive index among the three types of layers;
a gas barrier layer having the highest oxygen gas barrier property among the three types of layers; the antireflection film includes at least two or more gas barrier layers;
At least one layer of the gas barrier layer is sandwiched between layers having a film stress in a direction opposite to the film stress of the gas barrier layer,
The number of the high refractive index layers included in the antireflection film is greater than or equal to the number of gas barrier layers,
An anti-reflection film characterized by: The gas barrier layer is sandwiched between the low refractive index layers,
The antireflection film according to claim 1, characterized in that: The high refractive index layer is sandwiched between the low refractive index layers,
The antireflection film according to claim 1, characterized in that: The direction of the film stress of the low refractive index layer is opposite to the direction of the film stress of the gas barrier layer and the high refractive index layer, respectively.
The antireflection film according to claim 1, characterized in that: The film stress of the low refractive index layer is compressive stress,
The film stress of the gas barrier layer is tensile stress,
The antireflection film according to claim 1, characterized in that: The film thickness of the gas barrier layer is 20 nm or less,
The antireflection film according to claim 1, characterized in that: The total thickness of all the gas barrier layers in the antireflection film is 40 nm or more,
The antireflection film according to claim 1, characterized in that: The high refractive index layer and the gas barrier layer are laminated adjacent to the low refractive index layer,
When the low refractive index layer in the antireflection film is removed, each gas barrier layer is laminated so as not to be continuous.
The antireflection film according to claim 1, characterized in that: The low refractive index layer is formed in contact with the resin lens,
The antireflection film according to claim 1, characterized in that: further comprising an adhesion layer having the highest adhesion with the resin lens,
The adhesive layer is formed in contact with the resin lens,
The low refractive index layer is formed in contact with the adhesive layer,
The antireflection film according to claim 1, characterized in that: The gas barrier layer is formed in contact with the resin lens.
The antireflection film according to claim 1, characterized in that: The low refractive index layer is a thin film made of at least one of SiO ₂ and MgF ₂ .
The antireflection film according to claim 1, characterized in that: The high refractive index layer is _a thin film made of at least _one of _TiO2 , _Nb2O5 , _ZrO2 , _Ta2O5 , _{HfO2 , La2Ti2O7} ( _LaTiO3 ), _{and Si3N4 .} ,
The antireflection film according to claim 1, characterized in that: The gas barrier layer is a thin film made of at least one of Al ₂ O ₃ , Si ₃ N ₄ , AlN, and SiON.
The antireflection film according to claim 1, characterized in that: The adhesive layer is a thin film made of SiO,
The antireflection film according to claim 10, characterized in that: A resin lens on which the antireflection film according to any one of claims 1 to 15 is formed. The resin lens according to claim 16,
Aperture and
A lens module equipped with The resin lens according to claim 16,
An image sensor and
A camera module with. An anti-reflection film with multiple layers laminated on a resin lens,
It has a structure in which two or more laminates are laminated including a low refractive index layer and a high refractive index layer having a higher refractive index than the low refractive index layer,
Further comprising a gas barrier layer having a higher oxygen gas barrier property than the low refractive index layer and the high refractive index layer between the laminates,
An anti-reflection film characterized by:

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