JP2009162852A - Optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element that implements improved antireflection performance while suppressing cracks and the like at film forming. <P>SOLUTION: A surface antireflection film 43 has a region C mainly comprising an SiO<SB>2</SB>film 43a on the side of a substrate 41, and a region D mainly comprising an MgF<SB>2</SB>film 43b on an outermost surface side. A region E that is a mixed region of SiO<SB>2</SB>and MgF<SB>2</SB>is formed between the regions C and D. The region C has a decreasing SiO<SB>2</SB>component density ratio and an increasing MgF<SB>2</SB>component density ratio gradually from the region mainly of SiO<SB>2</SB>to the region mainly of MgF<SB>2</SB>, and the region D is opposite to the region C, so that there is no clear interface between the regions C and D. The structure provides a similar trend of the refractive index, which continuously varies from the region C to the region D without a junction interface, to eliminate light reflection generated at an interface of different refractive indices. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical element used in a photographing apparatus such as a camera or a video camera, an optical apparatus, or the like.

  In an optical device such as a digital camera or a video camera, when photographing when the subject has high brightness, the aperture may be small and the image may deteriorate due to diffraction. In order to prevent this, conventionally, an optical element for attenuating light such as an ND (Neutral Density) filter has been inserted on the photographing optical system.

  In recent years, with the improvement in image quality of digital cameras and video cameras, a multi-density ND filter having a plurality of density regions with different densities on a single ND filter and a continuous density gradient are provided so that more appropriate adjustment can be performed. The provided gradation ND filter is used.

  In addition, in order to avoid the difference in image quality due to the presence or absence of the ND filter in the opening, a transparent region is formed in a part of the ND filter, and the transparent region is placed in the opening even when the ND filter is not dimmed An ND filter is also used.

For example, Patent Document 1 discloses a gradation ND filter with a transparent region in which a TiO film, an Al ₂ O ₃ film, and a SiO ₂ film are formed on a transparent resin film by vacuum deposition. Patent Document 2 discloses a method for producing a gradation ND filter.

  The basic configuration of the ND filter is that an ND film made of a laminated film such as a metal film, a metal oxide film, and a dielectric film is formed on one side of a transparent substrate. A multilayer antireflection film may be formed, or an ND film may be formed on both surfaces of the transparent substrate.

FIG. 13 shows a film configuration diagram of the ND filter 1. Al ₂ O ₃ film 3a which is an antireflection layer for reducing the reflectance and TiOx film 3b as a light absorption layer for reducing the transmittance are alternately formed on the resin transparent substrate 2. Thus, the ND film 3 composed of eight layers is formed. The transmittance of the ND filter 1 varies depending on the total film thickness of the second, fourth, sixth, and eighth TiOx films 3b that are light absorption layers, and the transmittance decreases as the total film thickness increases.

The reflectance can be reduced by monitoring the reflectance at the time of vapor deposition and by controlling the film thickness of the Al ₂ O ₃ film 3a which is an antireflection layer. Further, an MgF ₂ film 4 as a low refractive material is provided on the uppermost eighth TiOx film 3b with an optical film thickness n × d (n: refractive index, d: physical film thickness) of λ / 4 (λ; Design wavelength) The antireflection effect is enhanced by forming a deposited antireflection film on the surface layer. Further, an SiO ₂ film can be used in place of the MgF ₂ film 4.

Then, after forming the ND film 3 and MgF ₂ film 4 on the transparent substrate 2, by cutting by press working or the like into a predetermined shape, it is possible to obtain the ND filter 1.

  Since an image pickup device such as a CCD easily reflects light on the surface thereof, the light reflected on the CCD surface is reflected again on the surface of the ND filter 1 and enters another pixel of the CCD, resulting in a ghost or the like. It can be a cause. Therefore, it is extremely important to suppress the surface reflection of the ND filter 1 in order to take a good quality picture or image.

FIG. 14 is a schematic cross-sectional view of a conventional gradation ND filter 11 with a transparent region. An ND film 12 having a concentration gradient is formed in the ND region A on the transparent substrate 2, and the ND region A and the transparent region B are formed. A single-layer surface antireflection film 13 is uniformly formed. In the case of the single-layer surface antireflection film 13, since the antireflection effect is higher when the refractive index is smaller and closer to the refractive index of air (n = 1), the SiO ₂ film (n = 1.46) is usually used. MgF ₂ film (n = 1.36) is used.

  Further, in the gradation ND filter 21 shown in FIG. 15, a single-layer surface antireflection film 13 is formed on the ND film 12 in the ND region A, and a multilayer surface layer is formed particularly in the transparent region B having a high reflectance. An antireflection film 22 is formed.

  Thus, when forming the surface antireflection films 13 and 22 on the transparent substrate 2 as physical vapor deposition films, the transparent substrate 2 is heated and vapor-deposited in order to improve adhesion to the transparent substrate 2. However, when the transparent substrate 2 is made of resin, there is a problem of heat resistance, and the upper limit of the substrate temperature is about 100 to 150 ° C.

In order to respond to the demand for higher sensitivity and higher resolution of the solid-state imaging device and to meet the demand for further lowering the reflectance of the ND filter, it is necessary to make the reflectance of the surface antireflection film as small as possible. However, when a surface antireflection film is formed on a resin substrate, the strength of the deposited film is weak depending on the material of the film due to the low film formation temperature, and cracks occur when processing as an optical element. There is a problem that it is easy to do. For example, when a single layer MgF ₂ film is formed as the surface antireflection film, the above-described problem occurs.

On the other hand, the SiO ₂ film that has been conventionally used as a surface antireflection film does not generate cracks even when formed at the above substrate temperature, but the SiO ₂ film is refracted compared to the MgF ₂ film. Since the rate is large, the reflectance becomes high.

In addition, as a method for solving the above-described problems of generation of cracks during film formation and reduction of reflectance on the film surface, the present applicant has proposed a method of laminating a MgF ₂ film on a SiO ₂ film. This method can suppress the generation of cracks because the SiO ₂ film is formed on the substrate, and the MgF ₂ film is formed on the outermost layer, so that reflection on the surface of the ND filter can be suppressed by the MgF ₂ film. it can.

JP 2004-205951 A Japanese Patent No. 3701931

Method of forming an MgF ₂ film on the SiO ₂ film as a surface layer antireflection film as described above, can be relatively easily suppress the surface reflection of cracks, the SiO ₂ film and the MgF ₂ film Since reflection occurs at the interface, the reflectance is higher than that of a single-layer MgF ₂ film.

  As shown in FIG. 15, when a multilayer surface antireflection film 22 is formed only in the transparent region B having a particularly high reflectance, a separate film forming process is required only for this portion. Accordingly, the manufacturing cost increases, and the thickness of the multilayer antireflection film 22 becomes too thick, usually about 300 to 400 nm, and cracks are likely to occur.

  The object of the present invention is to solve the above-mentioned problems and improve the antireflection performance at the outermost surface of the plurality of antireflection layers and the interface between the films while suppressing the occurrence of cracks and the like during film formation on the resin substrate. An optical element is provided.

  In order to achieve the above object, an optical element according to the present invention has a surface antireflection film composed of a dielectric layer formed on a resin substrate, and the dielectric layer is a component concentration ratio of a plurality of dielectric materials. It has the area | region which changes continuously.

  According to the optical element of the present invention, when forming a plurality of antireflection layers on a resin substrate, not only the generation of cracks in the antireflection layer is suppressed, but also the reflectance of the surface is reduced. The reflectance at the interface between the antireflection layers can be reduced.

  Further, when such an optical element is used in a light quantity diaphragm device, it is possible to take a good image with little ghost or the like.

  The present invention will be described in detail based on the embodiment shown in FIGS.

  FIG. 1 is a block diagram of a photographic optical system, in which a solid-state imaging device 37 including a lens 31, a light amount adjusting member 32, lenses 33 to 35, a low-pass filter 36, a CCD, and the like are sequentially arranged. In the light quantity adjusting member 32, a pair of aperture blades 39a and 39b are movably attached to an aperture blade support plate 38. An ND filter 40 is bonded to the diaphragm blade 39a for dimming the amount of transmitted light passing through an opening whose shape changes substantially in accordance with the driving amount of the diaphragm blades 39a and 39b. The ND filter 40 may be driven independently without being attached to the aperture blade 39a.

  FIG. 2 is a schematic cross-sectional view of the ND filter 40 manufactured in the present embodiment, and FIG. 3 shows a film configuration diagram in the ND region A of FIG.

  As the resin substrate 41 used for the ND filter 40, one having transparency and mechanical strength is preferable. For example, films of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), polycarbonate, polyimide resin, norbornene resin, polystyrene, polyvinyl chloride, polyarylate, polysulfone, polyethersulfone, polyetherimide, acrylic resin, etc. A shaped substrate can be used.

  Further, the thickness of the substrate 41 is preferably as thin as possible while maintaining the rigidity of the ND filter 40. Specifically, the thickness is preferably 300 μm or less, more preferably 50 to 100 μm. In addition, as the resin substrate 41 of a present Example, 100-micrometer-thick PET excellent in heat resistance, intensity | strength, and transparency is used.

As shown in FIG. 3, in the ND region A, a light attenuating film composed of eight alternating layers of an Al ₂ O ₃ film 42a as an antireflection layer and a TiOx film 42b as a light absorption layer on a substrate 41. A certain ND film 42 is formed.

The antireflection layer of the ND film 42 may be a dielectric layer with little light absorption. In addition to the Al ₂ O ₃ film 42a, films such as SiO ₂ , SiO, MgF ₂ , ZrO ₂ , and TiO ₂ are used. Can be used. By controlling the value of x of the TiOx film 42b, the flatness of the spectral transmittance can be adjusted, but the characteristics also change depending on the total number of multilayer films and the materials used. The light absorption layer of the ND film 42 may be any material that has a property of absorbing light in the visible region. In addition to the TiOx film 42b, a metal such as Ti, Ni, Cr, NiCr, NiFe, Nb, Alloy and oxide films can be used.

Then, on the upper layer of the TiOx film 42b of the eighth layer, as described later, a surface layer laminated so that the component concentration ratio of the SiO ₂ film 43a and the MgF ₂ film 43b of the dielectric material continuously changes in this order. An antireflection film 43 is formed.

FIG. 4 is an explanatory view of the concentration distribution of the surface antireflection film 43 in the transparent region B. The region C mainly includes the SiO ₂ film 43a on the substrate 41 side, and the region D mainly includes the MgF ₂ film 43b on the outermost layer side. Is formed.

A region E, which is a mixed region of SiO ₂ and MgF ₂ , is formed between the regions C and D. In the region C, the component concentration ratio of SiO ₂ gradually decreases from the region mainly composed of SiO ₂ to the region mainly composed of MgF ₂ , and at the same time, the component concentration ratio of MgF ₂ increases. It becomes a relationship. That is, there is no clear interface between these regions C to D.

  When the surface antireflection film 43 has such a configuration, a similar tendency appears in the refractive index. That is, since the refractive index continuously changes from the region C to the region D and there is no interface at the junction, there is no reflection of light generated at the interface having a different refractive index.

The regions C and D have a uniform component concentration distribution composed only of SiO ₂ and MgF ₂ films on the substrate 41 side and the outermost layer side, respectively, but without providing the uniform component concentration distribution, You may make it have a component concentration distribution to the side continuously.

  The surface antireflection film 43 is formed from the ND region A to the transparent region B with substantially the same film thickness in the same process.

In addition, the dielectric material forming the dielectric layer may contain other materials in addition to the two types of SiO ₂ and MgF ₂ as long as the properties such as the surface layer reflectivity are not adversely affected.

FIG. 5 shows a configuration diagram of a chamber of a vacuum evaporation machine for forming the ND film 42 of the ND filter 40. In the chamber 51, a vapor deposition source 52 and a vapor deposition material heating device for heating the vapor deposition source 52 are provided. A vapor deposition umbrella 53 that can be rotated by a driving means is provided above the vapor deposition source 52, and a substrate jig 54 as shown in FIG. An optical monitor 55 for measuring the thickness of the Al ₂ O ₃ film 42 that is an antireflection layer is disposed on the chamber 51.

  FIG. 6 shows an enlarged cross-sectional view of the substrate jig 54. The substrate jig 54 is provided with a reference pin (not shown), and the substrate 41 is fixed through a reference hole formed in the substrate 41. A vapor deposition pattern forming mask 61 is attached at intervals.

Then, after the inside of the chamber 51 is evacuated through a vacuum pump (not shown), a necessary vapor deposition material is evaporated from the vapor deposition source 52 while the vapor deposition umbrella 53 is rotated by a driving unit. In this embodiment, the vapor deposition materials are Al ₂ O ₃ and TiOx, and the Al ₂ O ₃ film 42a and the TiOx film 42b as shown in FIG. A layer of the ND film 42 is formed.

  The evaporation source 52 can set a plurality of materials on a rotary hearth, and the materials can be exchanged in a vacuum state as necessary for each film to be formed. At this time, the transmittance required for the ND film 42 is adjusted by the total film thickness of the TiOx film 42b.

  By providing the deposition pattern forming mask 61 with a predetermined distance from the substrate 41, the ND film 42 formed on the substrate 41 at a position facing the opening 61a of the mask 61 is the thickest and has a high concentration. become. Further, since the thickness of the portion shielded by the mask 61 is gradually reduced and the concentration becomes low, a concentration gradient as shown in FIG. 2 can be obtained.

  Subsequently, the vapor deposition pattern forming mask 61 is removed from the substrate jig 54 as shown in FIG. 7, and the chamber 71 of the vacuum vapor deposition machine as shown in FIG. A surface antireflection film 43 as shown is formed.

  In the chamber 71, two sets of vapor deposition sources 72 and 73 and two sets of vapor deposition material heating devices for heating the vapor deposition sources 72 and 73 are provided. Openable and closable shutters 74 and 75 are disposed above the vapor deposition sources 72 and 73, and a vapor deposition umbrella 76 that can be rotated by a driving means is provided. The vapor deposition umbrella 76 has a concentration gradient as shown in FIG. A substrate jig 54 having a substrate 41 on which an ND film 42 is formed is attached.

In the chamber 71, film thickness sensors 77 and 78 are provided for detecting the deposition rate by the deposition sources 72 and 73. An optical monitor 79 for measuring the film thickness of the surface antireflection film 43 is provided on the upper portion of the chamber 71. In this embodiment, SiO ₂ is used for the vapor deposition source 72 and MgF ₂ is used for the vapor deposition source 73.

  Using such a vacuum evaporation apparatus, the inside of the chamber 71 is evacuated by a vacuum pump, and when a predetermined degree of vacuum is reached, the evaporation sources 72 and 73 are connected to the respective evaporation material heating apparatuses while the shutters 74 and 75 are closed. Use and heat. In this embodiment, an electron beam generally used for vacuum vapor deposition is used as a vapor deposition material heating device.

When each material is stabilized at a predetermined vapor deposition rate, the shutter 74 is first opened, and SiO ₂ is allowed to fly from the vapor deposition source 72. At this time, the deposition rate of MgF ₂ of the deposition source 73 is kept very small, and the shutter 75 is closed, so that the MgF ₂ does not reach the substrate 41.

When the SiO ₂ film 43a is formed to a predetermined thickness, the shutter 75 is opened and MgF ₂ is allowed to fly from the vapor deposition source 73. At this time, since SiO ₂ is flying from the vapor deposition source 72, a region E of SiO ₂ and MgF ₂ is formed on the substrate 41.

First, since the deposition rate of MgF ₂ is kept very small, the film is formed on the substrate 41 from a mixed region having a high SiO ₂ concentration. Then, while monitoring the respective vapor deposition rates by the film thickness sensors 77 and 78, the MgF ₂ vapor deposition rate is gradually increased and the SiO ₂ vapor deposition rate is gradually decreased. The amount of change in each deposition rate is calculated in advance so that the deposition rate of SiO ₂ becomes 0 when the region E has a predetermined film thickness. When the region E reaches a predetermined film thickness, an MgF ₂ film 43b having a predetermined thickness is further formed.

In this example, the total thickness of the surface antireflection film 43 was measured using the optical monitor 79, and was formed to be λ / 4 (design wavelength 550 nm). Since the ND film 42 is formed by laminating a single material, the film is formed by evaporating a predetermined material from one evaporation source 52, but the surface antireflection film 43 in which the component ratio of SiO ₂ and MgF ₂ gradually changes. For film formation, it is necessary to evaporate SiO ₂ and MgF ₂ simultaneously from the vapor deposition sources 72 and 73.

  In addition, the mixing ratio of the region E is controlled by the above-described ratio of the deposition rate, and when the deposition rate of one of the two materials is relatively high, the mixing ratio of the material becomes high.

  In this embodiment, the ND film 42 and the surface antireflection film 43 having such a structure are formed by a vacuum deposition method, but may be formed by a film formation method such as a sputtering method or an ion plating method.

In this embodiment, the ND film 42 is formed using the chamber 51 shown in FIG. 5, but can also be formed using the chamber 71 shown in FIG. At this time, Al ₂ O ₃ can be used for the vapor deposition source 72 and TiOx can be used for the vapor deposition source 73.

  By such means, the surface antireflection film 43 is formed and the substrate 41 is taken out from the chamber 71. Then, as shown in FIG. 9, in the final step, a plurality of ND filter patterns are cut into individual ND filter shapes. At this time, the gradation ND filter 40 with a transparent region is obtained by cutting the transparent region. In this example, when the film thickness of the formed antireflection film 43 was measured with a stylus type film thickness meter, it was 96 nm.

FIG. 10 is a graph comparing the reflectivity of the surface antireflection film 43 according to this embodiment and the conventional single-layer antireflection layer. As described above, the reflectivity of the SiO ₂ single layer film having a high film strength is relatively high, and the MgF ₂ single layer film having a low film strength shows an extremely low reflectivity. Which was deposited SiO ₂ film on the MgF ₂ film may vary the reflectance by the respective film thicknesses, roughly fall between the reflectance of the SiO ₂ single layer and MgF ₂ monolayer film.

On the other hand, the surface antireflection film 43 according to the present embodiment is suppressed to a reflectance substantially equal to that of the MgF ₂ single layer film, and has extremely good reflectance characteristics.

  In this embodiment, the optical filter region is a gradation ND filter. However, after forming a single-concentration ND film 81 consisting of a single transmittance region on the substrate 41 as shown in FIG. A single-concentration ND filter 82 on which the prevention film 43 is formed may be used. Furthermore, the present invention can also be applied to a multi-concentration ND filter 84 having a multi-concentration ND film 83 composed of a plurality of transmittance regions as shown in FIG.

  When the ND filter 40 manufactured in this way is used for the light amount adjusting member 32 shown in FIG. 1, it is possible to realize a good light amount reduction device with little image deterioration due to ghost or the like.

  In this embodiment, two diaphragm blades 39a and 39b are used and the ND filter 40 is fixed to one diaphragm blade 39a. However, the number of diaphragm blades 39 is not particularly limited. The ND filter 40 may be driven separately from the aperture blade 39 and inserted into the photographing optical system.

  Further, such a light amount reduction device using the ND filter 40 is used as a so-called iris unit used for a video camera or the like, a shutter unit used for a digital camera or the like.

  Note that the material, the layer configuration, the number of layers, the film forming method, and the like are not limited to the present embodiment.

1 is a schematic diagram of a photographing optical system. It is sectional drawing of an ND filter. It is a film | membrane block diagram of a ND filter. It is explanatory drawing of the density distribution of the surface layer antireflection film of ND filter. It is the schematic of the vapor deposition apparatus which forms ND film | membrane. It is an expanded sectional view of a substrate jig. It is explanatory drawing for forming a surface layer antireflection film. It is the schematic of the vapor deposition apparatus which forms a surface layer antireflection film. It is explanatory drawing which cut | disconnects an ND filter from a board | substrate. It is a graph of the reflectance of ND filter. It is sectional drawing of a single concentration ND filter. It is sectional drawing of a multi-density ND filter. It is a film | membrane structural view of the conventional ND filter. It is sectional drawing of the conventional ND filter. It is sectional drawing of the conventional ND filter.

Explanation of symbols

40 ND filter 41 Resin substrate 42 ND film 42a Al ₂ O ₃ film 42b TiOx film 43 Surface antireflection film 43a SiO ₂ film 43b MgF ₂ film 51, 71 Chambers 52, 72, 73 Deposition source 53, 76 Deposition umbrella 54 Substrate healing Tool 55, 79 Optical monitor 61 Deposition pattern forming mask 74, 75 Shutter 77, 78 Film thickness sensor

Claims (7)

  An optical system comprising a surface antireflection film composed of a dielectric layer formed on a resin substrate, wherein the dielectric layer has a region in which component concentration ratios of a plurality of dielectric materials continuously change. element. The surface antireflection film is composed of at least two kinds of dielectric materials, SiO ₂ and MgF ₂ , and the component concentration ratio of the SiO ₂ is the largest on the resin substrate side, and continuously toward the surface antireflection film side. 2. The method according to claim 1, further comprising: a region that decreases, and a region in which the MgF ₂ component concentration ratio is the largest on the outermost layer side of the surface antireflection film and continuously decreases toward the resin substrate side. The optical element described.   The optical element according to claim 1, wherein an optical filter region having a light attenuating film is provided on at least a part of the resin substrate.   An optical filter region having the light attenuating film and a region not having the light attenuating film on the resin substrate, and an optical filter region having the light attenuating film and a region not having the light attenuating film. The optical element according to claim 3, wherein the surface antireflection film is continuously formed on a surface layer.   The optical element according to claim 3 or 4, wherein the optical filter region is an ND filter.   The optical filter region is either a single-density ND filter composed of a single transmittance region, a multi-density ND filter composed of a plurality of transmittance regions, or a gradation ND filter whose transmittance varies continuously. The optical element according to any one of claims 3 to 5.   6. A light amount adjusting member that adjusts an aperture of a photographing optical system and a drive unit that drives the light amount adjusting member, and the amount of light transmitted through the opening is adjusted according to a driving amount of the light amount adjusting member. A light quantity diaphragming device comprising the ND filter according to claim 6.