JP2016018143A - Optical filter, image capturing device and projector having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical filter whose wire grid pattern having a high aspect ratio and a wire grid protection layer that shows little deterioration in optical properties are formed simultaneously, and which offers superior performance and reliability.SOLUTION: An optical filter 205 includes a transparent substrate 20 that is transparent to light of a band in use, and a polarizing filter layer 16 that is formed on the transparent substrate 20 and has a plurality of polarizer patterns 10 having different transmission/polarization axes. Each polarizer pattern 10 contains metallic material and has a top surface covered with an oxidized layer 12 made of an oxide of the metallic material and an SiOlayer 13, in the described order, and side surfaces covered with the oxidized layer 12 made of the oxide of the metal material.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an optical filter using polarized light.

  As a polarizing element that can be used in a wide wavelength band, a wire grid element having a structure in which fine metal wires are arranged in a grating shape is used. The wire grid element has features such that it can easily function if it has a thickness corresponding to the height of the thin metal wire, and can be easily reduced in thickness, and is resistant to temperature changes because it uses an inorganic material.

  The wire grid element has been conventionally used as a polarizing element for infrared rays because the wavelength range that can be used is determined by the arrangement period of the wires. However, wire grid elements that can be used in the visible light region have been developed due to recent developments in nano-processing technology, and application to projector applications exposed to high temperatures is being studied. (For example, see Patent Documents 1 and 2.)

Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-507517) reports that, in order to prevent corrosion, a monomolecular film such as aminophosphonate is formed on the side surface of an aluminum wire grid to provide a corrosion prevention effect. However, the formation of a monomolecular film is not an easy technique, and it is not necessarily formed uniformly in a plane, and there is a concern that the yield may be reduced. Moreover, the cost of the material by newly using aminophosphonate etc. as a monomolecular film increases.
Patent Document 2 (Japanese Patent Laid-Open No. 2007-86720) discloses an imaging apparatus capable of capturing a luminance image and a polarized image. In the configuration, a patterned polarizer having a plurality of different polarization main axes is spatially arranged in an image sensor to simultaneously acquire a luminance image and a partially polarized image of a subject. As the patterned polarizer, a photonic crystal or a structural birefringent wave plate array is used.

  The visible light wire grid element requires, for example, a rectangular cross-section having an arrangement period of about 150 nm, a line width of about 70 nm, and a height of about 200 nm, and pure aluminum (Al) that provides high polarization characteristics as a metal material. As a processing means, a nanoresist pattern forming technique such as photolithography and nanoimprint lithography and an anisotropic dry etching technique are mainly used.

  However, in order to obtain a high-performance and high-reliability wire grid element, both a high aspect aluminum wire grid shape and an aluminum protective layer for obtaining high reliability are required. It was a problem.

As for the high aspect aluminum wire grid shape, there is a method of forming a wire grid by dry etching using a resist that is easy to process as a mask. However, the resist mask has a low etching selectivity (about 1), and the resist itself must be formed in a high aspect, which makes patterning difficult. In addition, etching is difficult because the aluminum under the high aspect resist pattern must be etched.
On the other hand, for the Al protective layer for obtaining high reliability, there is a method of dry etching using a hard mask (selectivity ratio of about 3) such as SiO ₂ in order to form a high aspect wire grid. When forming the aluminum protective layer after the formation, there were problems such as deterioration of optical characteristics.

  The present invention has been made in view of the above problems in the prior art, and simultaneously achieves the formation of a high aspect wire grid shape and the formation of a wire grid protective layer with little deterioration in optical properties, and has high performance. An object is to provide a highly reliable optical filter.

An optical filter according to the present invention for solving the above problems includes a transparent substrate transparent to light in a use band, a polarizing filter layer provided on the transparent substrate, and having a plurality of polarizer patterns having different transmission polarization axes, The polarizer pattern includes a metal material, and the upper surface of the polarizer pattern is sequentially covered with the oxide layer / SiO ₂ layer of the metal material, and the side surfaces are oxidized of the metal material. It is characterized by being covered with a layer.

  ADVANTAGE OF THE INVENTION According to this invention, formation of a high aspect wire grid shape and formation of the wire grid protective layer with little degradation of an optical characteristic can be achieved simultaneously, and a high performance and highly reliable optical filter can be provided.

It is the schematic which shows the structure in one Embodiment of the imaging device which concerns on this invention. It is an expanded sectional view showing arrangement relation of an optical filter and an image sensor in one embodiment of an image sensor concerning the present invention. FIG. 3 is a schematic plan view illustrating an arrangement relationship between an optical filter and an image sensor (pixel sensor) in FIG. 2. It is an electron micrograph (SEM photograph) of the wire grid structure which comprises a polarizing filter layer. It is the perspective view which showed typically the structural example of the area | region division | segmentation type | mold wire grid. (Conventional example) It is a cross-sectional schematic diagram which shows the structure of the wire grid in one Embodiment of the optical filter which concerns on this invention. It is the conventional wire grid preparation flowchart using a resist mask. A conventional wire grid produced flow diagram using the SiO ₂ mask. It is the conventional wire grid preparation flowchart using a protective layer of a back attachment. It is another conventional wire grid manufacturing flowchart using a SiO ₂ mask. It is a preparation flowchart of one Embodiment of the wire grid in the optical filter which concerns on this invention. It is a graph which shows the optical characteristic of the produced wire grid. It is a graph which shows the result of the high temperature, high humidity test (85 degreeC-85% RH) of the produced wire grid. It is the schematic which shows the structure in one Embodiment of the projector which concerns on this invention. It is the schematic which shows the structure in other embodiment of the projector which concerns on this invention.

The optical filter according to the present invention includes a transparent substrate 20 that is transparent to light in a use band, and a polarizing filter layer 16 that is provided on the transparent substrate 20 and has a plurality of polarizer patterns 10 having different transmission polarization axes. In the optical filter 205, the polarizer pattern 10 includes a metal material, and the upper surface of the polarizer pattern 10 is sequentially coated with the oxide layer 12 / SiO ₂ layer 13 of the metal material (the SiO ₂ layer 13 is formed). The oxide layer 12 of the metal material is the metal material side on the surface layer or the surface layer side), and the side surface is covered with the oxide layer 12 of the metal material.
Next, the optical filter according to the present invention and the imaging apparatus and projector including the optical filter will be described in more detail.
Although the embodiments described below are preferred embodiments of the present invention, various technically preferable limitations are attached thereto, but the scope of the present invention is intended to limit the present invention in the following description. Unless otherwise described, the present invention is not limited to these embodiments.

<Imaging device>
FIG. 1 is a schematic diagram showing the configuration of an imaging apparatus according to an embodiment of the present invention.
The imaging apparatus 201 includes an imaging lens 204, an optical filter 205, an imaging element 206, a sensor substrate 601 including a PWB substrate 207 (PWB: printed wiring board), and a signal processing unit 602.
Light from the test object passes through the imaging lens 204, passes through the optical filter 205, and is converted into an electrical signal by the imaging device 206. The signal processing unit 602 receives an electrical signal output from the image sensor 206 and generates an image signal such as luminance information, spectral information, and polarization information described later. Then, the imaging device 201 outputs a digital signal indicating the brightness (luminance) for each pixel of the captured image as image data to a subsequent output device (not shown) together with the horizontal / vertical synchronization signal of the image.

  FIG. 2 is an enlarged cross-sectional view showing the positional relationship between the optical filter 205 and the image sensor 206 in an embodiment of the image sensor according to the present invention. The optical filter 205 and the image sensor 206 are orthogonal to the light transmission direction. It is the elements on larger scale when it sees from the direction to do (magnified figure of the field surrounded with a broken line).

The image sensor 206 is an image sensor using a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like, and a photodiode 217 is used as the light receiving element. The photodiodes 217 are two-dimensionally arranged for each pixel, and a microlens 216 is provided on the incident side of each photodiode 217 in order to increase the light collection efficiency of the photodiodes 217. The image sensor 206 is bonded to the PWB substrate 207 by a method such as wire bonding to form a sensor substrate 601.
An optical filter 205 is disposed close to the surface of the image sensor 206 on the microlens 216 side. The optical filter 205 and the image sensor 206 may be bonded with a UV adhesive, or UV bonding or thermocompression bonding may be performed in the four-side region outside the effective pixel while the outside of the effective pixel range used for photographing is supported by a spacer or the like. .

FIG. 3 is a schematic diagram illustrating an example of an arrangement relationship of pixels of the optical filter 205 and the image sensor 206.
The optical filter 205 is divided into regions so as to correspond to one photodiode 217 on the image sensor 206. For example, the area indicated by 205a corresponds to the area indicated by 206a in FIG. That is, the optical filter 205 has a checkered pattern corresponding to each pixel.

Although there may be a configuration in which there is a gap between the optical filter 205 and the image sensor 206, the configuration in which the optical filter 205 is closely attached to the image sensor 206 and the boundary between the regions on the optical filter 205 and the image sensor 206. This makes it easier to match the boundaries of the regions.
Each of the divided patterns is provided with a polarization filter, a spectral filter, or a light amount adjustment filter so that the so-called three components of light of luminance information, polarization information, and spectral information are appropriately adjusted and output according to various applications described later. Formed in units.

In the present embodiment, an example of a monochrome image pickup device will be described as the image pickup device 206, but a color image pickup device may be used. When using a color image pickup device, the transmission characteristics of each pattern of the optical filter may be adjusted in accordance with the characteristics of the color filter attached to each pixel of the image pickup device 206.
Various images described later are formed from these pieces of information different in pixel units. Such image formation is performed by a signal processing unit 602 inside the camera.

<Optical filter>
Next, the configuration of the optical filter 205 will be described in more detail. The optical filter 205 includes a transparent substrate 20, and the wire grid 10 is formed on the transparent substrate 20. Further, an anti-reflective coating (ARC) layer 30 may be provided below the transparent substrate 20 as necessary.

・ Transparent substrate 20
The transparent substrate 20 is made of a material that is transparent with respect to light in the use band (visible light region in the present embodiment), such as glass, sapphire, and quartz. In this embodiment, glass, particularly quartz (refractive index: 1.46) and Tempax glass (refractive index: 1.51), which are inexpensive and durable, is used.

・ Wire grid 10
The wire grid 10 is composed of aluminum conductor wires 11 (hereinafter also referred to as “wires”) arranged in a lattice pattern at a specific pitch. If the pitch of the conductor wire 11 is considerably smaller than the incident light (for example, visible light wavelength 400 nm to 800 nm) (for example, half or less), the conductor wire 11 vibrates in parallel with the conductor wire 11. Since most of the electric field vector component light is reflected and most of the electric field vector component light perpendicular to the conductor line 11 is transmitted, it can be used as a polarizer pattern for producing a single polarized light.
In addition, as a metal material used for the conductor wire 11, what is necessary is just to show the desired effect by passivating each metal, for example, the laminated metal containing Cr, Al / Cr, Al, Al Etc. Among these metals, it is preferable to use aluminum which is excellent in optical characteristics among general metal materials.

  In addition, the polarizer pattern (hereinafter, also simply referred to as a polarizer) composed of the wire grid 10 increases the extinction ratio as the cross-sectional area of the wire 11 increases, and further, the wire 11 having a predetermined width or more with respect to the period width. Then, the transmittance decreases. Moreover, when the cross-sectional shape orthogonal to the longitudinal direction of the wire 11 is a tapered shape, the wavelength dispersion of the transmittance and the polarization degree is small in a wide band, and a high extinction ratio characteristic is exhibited.

  FIG. 4 is an electron micrograph of the cross-sectional structure of the wire grid 10 constituting the polarizing filter layer. Due to the wire grid structure, the polarizing filter layer 16 shields light when the light in the polarization direction in the direction of the groove (concave portion of the concavo-convex structure) is incident, and transmits light when the light in the direction of polarization perpendicular to the groove is incident.

The optical filter according to the present invention relates to the optical filter 205 described above, and relates to formation of a high aspect of the wire grid 10 and a protective layer of the wire grid 10. Al ₂ O ₃ is formed in advance on the upper surface of aluminum, and then has an Al ₂ O ₃ / SiO ₂ structure, and the aluminum side surface is coated with Al ₂ O ₃ .
The characteristics of the optical filter according to the present invention will be further described with reference to the drawings.

FIG. 5 shows a schematic diagram (perspective view) of a region-divided wire grid manufactured by a standard wire grid manufacturing process. The standard wire grid 10 is formed, for example, by forming an aluminum (hereinafter referred to as Al) film 200 nm to be the wire grid 10 on the transparent substrate 20 (thickness 0.6 mm) by sputtering or the like, and then forming a nanopattern ( The period is 150 nm). Next, using the formed resist pattern as a mask, anisotropic dry etching of the Al film is performed using chlorine-based gas to form the wire grid 10.
In the following description of the cross-sectional views, the AA ′ line portion in FIG. 5 is shown.

FIG. 6 is a schematic cross-sectional view showing the configuration of the wire grid in one embodiment of the optical filter according to the present invention. As shown in the drawing, in this embodiment, the upper part of the wire grid 10 is coated with aluminum oxide (hereinafter referred to as Al ₂ O ₃ ) and silicon oxide (hereinafter referred to as SiO ₂ ) and the side surfaces with Al ₂ O ₃ in order from the tongue. It is a wire grid.

Unlike the standard wire grid manufacturing process shown in FIG. 5, SiO ₂ is used instead of a resist as a mask for dry etching the Al film. By using SiO ₂ , a high aspect wire grid can be formed. Further, it is characterized in that Al ₂ O ₃ is formed in advance before forming SiO ₂ . Concerning the Al ₂ O ₃ on the Al side surface, a dense film can be formed by a simple process such as oxygen plasma before exposing the etched portion to the atmosphere continuously with the Al dry etching step.
As described above, the Al (wire 11) on the transparent substrate 20 is polarized light having the wire grid 10 having a configuration (further including the SiO ₂ film 13) whose outer periphery is protected by Al ₂ O ₃ (protective layer 12) having high moisture resistance. A filter layer 16 is formed.

(Conventional manufacturing flow)
Next, prior to explaining the production flow of the optical filter according to the present invention, the production flow of the conventional optical filter will be explained.
FIG. 7 is a manufacturing flow diagram of a conventional wire grid using a resist mask.
After depositing an Al film (which is the source of the wire 11 and indicated by reference numeral 11 in the figure for convenience of explanation) on the transparent substrate 20 by vapor deposition or sputtering, the film is formed by photolithography or imprinting. A resist pattern is formed. In the example shown in FIG. 7, a resist pattern 11a using a resin is formed.
Thereafter, anisotropic dry etching of the Al film is performed using chlorine-based gas to form the wire grid 10. Finally, a protective layer 12 such as Al ₂ O ₃ is formed by an ALD (Atomic Layer Deposition) method or the like.

  However, it is difficult to form a high aspect wire grid by this conventional method. The resist mask has a low etching selection ratio (about 1), the resist itself must be formed in a high aspect, and patterning is difficult. In addition, since Al under the high aspect resist pattern must be etched, etching becomes difficult due to the microloading effect. In addition, when the protective layer 12 is formed later, the protective layer 12 is also formed on the transparent substrate 20 between the wires 11 of the wire grid 10, so that optical characteristics are deteriorated such that the transmittance is reduced. In addition, although the deterioration of the optical characteristics derived from the protective layer 12 can be prevented by performing the retrofitting protective layer 12 by thermal oxidation or plasma oxidation of Al, the problem that the high aspect formation described above remains difficult remains. .

Further, FIG. 8 shows a conventional wire grid manufacturing flow diagram (SiO ₂ mask) different from FIG. FIG. 8 is a flowchart for manufacturing a conventional wire grid using a SiO ₂ mask (which is the basis of the SiO ₂ layer 13 and is indicated by reference numeral 13 in the figure for convenience of explanation).

In the case of the wire grid manufacturing flow using the SiO ₂ mask shown in FIG. 8, after the Al film (11) and the SiO ₂ film (13) are formed on the transparent substrate 20 by vapor deposition or sputtering, photolithography or imprinting is performed. Thus, a resist pattern 11a using a resin is formed.
Thereafter, anisotropic dry etching of the SiO ₂ film (13) is performed using fluorine-based gas, the pattern is transferred, and then anisotropic dry etching of the Al film (11) is performed using chlorine-based gas. To form the wire grid 11.
Finally, a protective layer 12 such as Al ₂ O ₃ is formed by thermal oxidation or plasma oxidation. If dry etching is performed using a hard mask (selectivity ratio of about 3) such as SiO _2, a high aspect ratio with an Al thickness of 200 nm and an aspect ratio of 3 or more can be formed.

However, since only the SiO ₂ film (13) exists on the upper surface of the Al film (11), the moisture resistance of the upper surface is not good, and Al may corrode. Further, when exposed to a high temperature, the SiO ₂ film (13) has a small coefficient of thermal expansion, so that Al may expand and break or break. The thermal expansion coefficients of Al, Al ₂ O ₃ and SiO ₂ are 23, 7.2 and 0.52 (× 10 ⁻⁶ / ° C.), respectively, and the thermal expansion coefficient of SiO ₂ is small.

On the other hand, FIG. 9 is a flow chart for producing a conventional wire grid (a mask with a protective layer 12 attached later) different from FIGS. FIG. 9 is a flow chart for manufacturing a conventional wire grid using the protective layer 12 attached later.
In addition, (0) substrate acceptance and ARC to (3) SiO ₂ etching shown in FIG. 8, that is, (0) substrate acceptance, ARC, (1) film formation, (2) patterning, and (3) SiO ₂ etching Since the process is the same in the wire grid manufacturing flow shown in FIG. 9, the illustration is omitted in FIG.
In the example shown in FIG. 9, after (4) Al etching, a protective layer 12 such as Al ₂ O _{3 is} finally formed by an ALD method or the like. In the case where the protective layer 12 is formed in this way, the moisture proof property is improved, but the deterioration of the optical characteristics (transmittance) due to the influence of the protective layer 12 existing between the wires 11 and the problem of heat resistance remain.

FIG. 10 is a flowchart of manufacturing a conventional wire grid (mask SiO ₂ removal) different from those shown in FIGS. FIG. 10 is another conventional wire grid fabrication flow diagram using an SiO ₂ mask (which is the basis of the SiO ₂ layer 13 and is indicated by reference numeral 13 in the figure for convenience of explanation).
10, the process from (0) substrate reception and ARC to (3) SiO ₂ etching is the same as that in FIG.

In the conventional example shown in FIG. 10, (4) after removing the SiO ₂ mask remaining after the Al etching, a protective layer 12 such as Al ₂ O ₃ is formed over the entire surface by ALD or the like. When the protective layer 12 is formed in this way, the moisture resistance and heat resistance are improved, but the above-described problem of deterioration of optical characteristics (transmittance) remains. In particular, (5) the removal of SiO ₂ causes a depression (broken circle in the figure), and the transmittance is further lowered due to light refraction and scattering.

(Production flow of optical filter according to the present invention)
The conventional wire grid manufacturing flow has been described above. Next, an example of the wire grid manufacturing flow in the optical filter according to the present invention will be described.
FIG. 11 shows a flow chart for producing an embodiment of a wire grid in the optical filter according to the present invention. Although there is a part similar to the conventional example shown in FIG. 8, the major difference in the present embodiment is the film forming process in (1) in FIG. 11, intentionally between Al (11) and SiO ₂ (13). The point is that Al ₂ O ₃ (12) is interposed.

The sputtering apparatus or the like of the conventional multi-chamber system (i.e. the conventional method), Al, since there is no exposure to the atmosphere when the SiO ₂ are successively formed, Al, natural oxide film between SiO ₂ (Al ₂ O ₃ ) Not even interposed.
Therefore, in the present embodiment, it is desirable that the natural oxide film (Al ₂ O ₃ ) is reliably formed by exposing to the atmosphere once after the Al film formation. However, since the natural oxide film is only formed to have a thickness of about _{2 to 3} nm, it is more preferable to form an Al ₂ O ₃ layer of 5 nm or more by thermal oxidation or plasma oxidation instead of or in addition to exposure to the atmosphere. desirable. Highly moisture-proof Al ₂ O ₃ is stably provided on the entire surface, and the reliability is further improved.
Further, it is more desirable to form an Al ₂ O ₃ layer of 5 nm or more on the Al side surface. The Al side surface can also be formed by thermal oxidation or plasma oxidation.

As described above, the thickness of the Al ₂ O ₃ layer on the upper surface of the wires 11 of the wire grid 10 is preferably 2 nm or more, more preferably 5 nm or more, and preferably 15 nm or less. If it is too thick, Al etching in a later process may cause an etching inhibition factor.
Further, the thickness of the Al ₂ O ₃ layer on the side surface of the wire 11 of the wire grid 10 is preferably 2 nm or more, more preferably 5 nm or more, and preferably 15 nm or less, like the upper surface of the wire 11. If it is too thick, the volume of Al may decrease and the polarization characteristics may deteriorate.

  The wire grid produced by the method as described above has a structure that can achieve both a high aspect shape and high reliability.

  FIG. 12 shows the optical characteristics of the wire grid produced in the above embodiment. By manufacturing in this embodiment, a wire grid having TM transmittance of 88.0%, extinction ratio (TM / TE) 2481, and high transmittance and high contrast (extinction ratio) at a wavelength of 550 nm is obtained. Can do.

FIG. 13 shows the results of the high-temperature and high-humidity test (85 ° C.-85% RH) of the wire grid produced in the above embodiment. Before the high-temperature and high-humidity test and after 1000 hours, the TM transmittance fluctuated about 1% (at a wavelength of 550 nm) with almost no deterioration. Since the high-temperature and high-humidity test (85 ° C.-85% RH, 1000 h), which is an in-vehicle standard, can be cleared, a high-performance and highly reliable imaging device that can be used for in-vehicle applications with a large market can be obtained.
In addition, regarding heat resistance, rupture and breakage at high temperatures (200 ° C. or higher) can be suppressed, and high heat resistance does not cause any problem up to 250 ° C.

  The optical filter described above can also be used in a projector, and has heat resistance that does not cause a problem even if it is provided in the vicinity of a light source such as a projector. As the configuration of the projector excluding the optical filter, a well-known and conventional one can be used, and the above-described optical filter of the present invention may be applied thereto.

The projector will be described below with specific examples, but the present invention is not limited to this.
As shown in FIG. 14, an illumination light source 1101 for the image forming element 1107 is used in a projector (projection apparatus) including the optical filter of the present invention.
As the illumination light source 1101, a halogen lamp, a xenon lamp, a metal halide lamp, an ultrahigh pressure mercury lamp, an LED, or the like is used. Usually, an illumination optical system is mounted so that high illumination efficiency can be obtained.

Specific examples of the illumination optical system include a reflector 1102 disposed in the vicinity of the light source 1101 (integrated with the light source 1101), and a luminous flux reflected by the reflector 1102 and having directivity as an integrator optical system. An optical system that can obtain a uniform illumination distribution on the surface of the image forming element 1107 by the uniformizing means 1105 (comprising the polarization conversion element 1104) may be mounted, or the illumination light is emitted using the color wheel 1106. A color image may be projected by colorizing and controlling the image of the image forming element 1107 in synchronization therewith.
In the projector according to the present invention, the above-described optical filter according to the present invention is used for the polarization conversion element 1104.

When a reflection type liquid crystal image forming element is used, more efficient illumination can be achieved by using a polarization separation means 1108 of an illumination optical path combined with PBS and a projection optical path. When a DMD panel is mounted, optical path separation using a total reflection prism is employed.
Thus, an appropriate optical system may be employed according to the type of light valve.

  As shown in FIG. 15, a plurality of image forming elements 1207 such as red, green, and blue are used, and the illumination light is applied to the illumination light of each color separated by the color separation unit 1206 and synthesized by the color synthesis unit 1209. It goes without saying that a color image can be projected on the screen 1211 by making the emitted light incident on the projection optical system 1210.

According to the present invention described above, the following effects (1) to (5) are obtained.
(1) A polarizer having high performance (high contrast while suppressing a reduction in transmittance) and high reliability (high temperature, high temperature and high humidity) can be obtained. In other words, SiO ₂ is provided as an Al etching mask on the upper surface, a high aspect polarizer can be formed, and high performance (high contrast while suppressing a decrease in transmittance) can be obtained. This is because Al ₂ O ₃ is previously provided between the upper surface of Al and SiO ₂ , so that it is not necessary to finally remove SiO ₂ that is an etching mask, so that deterioration of optical characteristics can be suppressed. Further, by providing Al ₂ O ₃ on the upper surface and side surfaces, a highly reliable polarizer (with respect to high temperature, high temperature and high humidity) can be obtained.

(2) The reliability is further improved by forming Al ₂ O ₃ on the Al to be thicker than the natural oxide film thickness ( _{2 to 3} nm). That is, Al ₂ O ₃ on the upper surface of Al is intentionally formed to be thicker than the natural oxide film thickness ( _{2 to 3} nm), so that Al ₂ O ₃ with high moisture resistance can be stably provided on the entire surface and more reliable. Will improve.

(3) Since Al ₂ O ₃ on the Al side surface can be selectively formed only on the side surface, there is little deterioration in optical characteristics. Moreover, since a dense Al ₂ O ₃ film can be formed, the reliability is further improved. That is, Al ₂ O _{3 on} the side surface of Al can be selectively formed only on the side surface by being formed by plasma oxidation, so that there is little deterioration in optical characteristics. In addition, since plasma oxidation is performed using Al of the polarizer as a material, a dense Al ₂ O ₃ film can be formed, so that reliability is further improved.

(4) A high-performance and highly reliable imaging device can be obtained. That is, since the high-temperature and high-humidity test (85 ° C.-85% RH, 1000 h), which is a vehicle-mounted standard, can be cleared, it is possible to obtain a high-performance and highly reliable imaging device that can be used for a large vehicle-mounted application.

(5) It has heat resistance with no problem even if it is provided near the light source such as a projector. That is, since not only SiO ₂ but also Al ₂ O ₃ is interposed on the upper surface of Al, the coefficient of thermal expansion with Al becomes close, rupture and breakage at high temperatures can be suppressed, and high heat resistance is achieved.

10 Wire Grid 11 Conductor Wire (Wire)
11a resist pattern 12 protective layer (Al ₂ O ₃ layer)
13 SiO ₂ layer 20 Transparent substrate 30 Antireflection (ARC) layer 204 Imaging lens 205 Optical filter 206 Imaging element 601 Sensor substrate 602 Signal processing unit 1101 Light source 1102 Reflector 1103 Relay lens 1104 Polarization conversion element 1105 Illumination uniformizing means 1106 Color wheel 1107 Image forming element 1108 Polarization separating means 1109 Projection optical system 1110 Screen 1201 Light source 1202 Reflector 1203 Relay lens 1204 Polarization converting element 1205 Illumination uniformizing means 1206 Color separating means 1207 Image forming element 1208 Polarization separating means 1209 Color combining means 1210 Projecting optical system 1211 screen

JP 2006-507517 A JP 2007-86720 A

Claims (6)

An optical filter comprising a transparent substrate transparent to light in a use band, and a polarizing filter layer provided on the transparent substrate and having a plurality of polarizer patterns having different transmission polarization axes,
The polarizer pattern includes a metal material, and an upper surface of the polarizer pattern is sequentially covered with an oxide layer / SiO ₂ layer of the metal material, and a side surface is covered with an oxide layer of the metal material. An optical filter.   The optical filter according to claim 1, wherein the metal material is aluminum.   The optical filter according to claim 1 or 2, wherein a thickness of the oxide layer of the metal material on the upper surface is 5 nm or more.   The optical filter according to claim 1, wherein the oxide layer of the metal material on the side surface is formed by plasma oxidation. In an imaging apparatus comprising an imaging lens, an imaging element, and an optical filter provided between the imaging lens and the imaging element,
The image pickup apparatus according to claim 1, wherein the optical filter is an optical filter according to claim 1.   A projector comprising the optical filter according to claim 1.