JP2007178763A - Method for manufacturing optical element, liquid crystal device, and projection-type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing the optical element of a wire grid type, capable of freely controlling the duty ratio of wire grid in simple steps and easily obtaining the desired optical characteristics. <P>SOLUTION: The method for manufacturing optical element includes a step for forming a metal layer 12a on a light-transmitting dielectric substrate 11A, a step for patterning the metal layer 12a to form a grid-like metal film 12M, and a step for performing heat processing of the grid-like metal film 12M in a gas atmosphere to modify the surface part of the metal film 12M, and to form a dielectric film 12D2 on the surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical element manufacturing method, a liquid crystal device, and a projection display device.

  A liquid crystal device is used as a light modulation device in a projection display device such as a projector. As such a liquid crystal device, one having a configuration in which a liquid crystal layer is sandwiched between a pair of opposed substrates is known, and a voltage is applied to the liquid crystal layer inside the pair of substrates. An electrode is formed. Further, an alignment film that controls the alignment of liquid crystal molecules when no voltage is applied is formed inside the electrode, and an alignment film that has been rubbed on the surface of a polyimide film is known.

On the other hand, a polarizing plate is disposed on the outside of the pair of substrates (a surface side different from the surface facing the liquid crystal layer) so that predetermined polarized light is incident on the liquid crystal layer. As a polarizing plate, a fine film made of metal is formed on a glass substrate in addition to a polarizing film manufactured by orienting iodine or a dichroic dye in a certain direction by stretching a resin film of an organic compound in one direction. For example, Patent Document 1 discloses a wire grid type polarizing element (optical element).
Special table 2003-502708 gazette

In the invention described in Patent Document 1, a dielectric layer (MgF ₂ layer) having a refractive index smaller than the refractive index of the glass substrate is formed between the glass substrate and the metal grid. This expands the usable wavelength range. However, this technique does not control the transmittance and reflectance, which are basic optical characteristics of the wire grid polarizer, and attempts to adjust the transmittance and reflectance in the wire grid polarizing element described in Patent Document 1. In this case, not only the metal grid but also the dielectric layer between the substrate and the substrate need to be adjusted in plane shape and film thickness, so that it is difficult to obtain desired optical characteristics, and there are variations in optical characteristics. It tends to occur.

  The present invention has been made in view of the above-mentioned problems of the prior art, and is capable of freely controlling the duty ratio of the wire grid in a simple process and easily obtaining desired optical characteristics. An object of the present invention is to provide a method for manufacturing the optical element.

In order to solve the above-described problems, the optical element manufacturing method of the present invention forms a metal layer on a translucent dielectric substrate, and forms a grid-like metal film by patterning the metal layer. And a step of heat-treating the grid-like metal film in a gas atmosphere to modify the surface portion of the grid-like metal film.
According to this manufacturing method, the optical characteristics (transmittance, etc.) of the optical element are adjusted after the grid-like metal film is formed by having the step of modifying the surface portion of the grid-like metal film. Is possible. In other words, since it is possible to adjust the optical characteristics without depending on the metal film forming process, which can be done only by adjusting the line width and space width of the grid-like metal film, there is a problem such as exposure accuracy. Thus, it is possible to manufacture an optical element having optical characteristics that could not be obtained conventionally by a simple process.

In the method of manufacturing an optical element of the present invention, the heat treatment causes the gas component in the gas atmosphere to react with the metal component of the grid-like metal film, and the metal component and the surface of the metal film on the grid are reacted. A dielectric film mainly comprising a compound with a gas component is formed. According to this manufacturing method, the area ratio of the metal film, which is a conductor, can be adjusted by the thickness of the dielectric film formed on the surface of the metal film by heat treatment, and thereby the optical characteristics of the optical element can be adjusted. Can be adjusted.
Therefore, it can be said that the optical element manufacturing method of the present invention is a method of adjusting the optical characteristics of the optical element by adjusting the ratio of the conductor and the dielectric in the grid-like metal film by the heat treatment. In other words, the ratio of the light reflection region (metal film) and the light transmission region (dielectric film) in the grid-like metal film is adjusted by the heat treatment, thereby adjusting the optical characteristics of the optical element. It can be said that there is.

  As described above, the optical element according to the present invention includes the dielectric film formed by the heat treatment on the surface of the grid-like metal film. This dielectric film is characteristic in that the film thickness is obviously larger than that of a natural oxide film formed on the surface of the metal film in the atmospheric environment. Moreover, since it is formed by heat treatment, it is characteristic in that it is formed uniformly covering the metal film and following the shape of the metal film. Furthermore, in the optical element according to the present invention, a dielectric layer containing a metal component of the metal film may be formed on the substrate side of the metal film. During the heat treatment, a gas component such as oxygen diffuses from the substrate side to the metal film, and the dielectric layer may be formed by a reaction between the gas component and the metal film. In this case, the dielectric layer is different from the dielectric film formed on the substrate prior to the formation of the metal film, and the manufacturing method according to the present invention is performed together with the dielectric film on the surface portion of the metal film. This is a characteristic of the optical element formed by using.

  In the method for producing an optical element of the present invention, the gas atmosphere is preferably formed of oxygen, nitrogen, hydrocarbon, fluorine, or a mixed gas thereof. By using these gases, it can be easily reacted with the metal component of the metal film, and the surface portion of the metal film can be modified.

  In the method for producing an optical element of the present invention, the metal layer is made of silver, gold, copper, palladium, platinum, aluminum, rhodium, silicon, nickel, cobalt, manganese, iron, chromium, titanium, ruthenium, niobium, neodymium, ytterbium. , Yttrium, molybdenum, indium, bismuth, or alloys thereof. In the manufacturing method according to the present invention, examples of the constituent material of the metal layer include these metal materials and alloys. When any metal material or alloy is used, the surface portion can be modified by heating in a gas atmosphere, and the optical characteristics of the optical element can be adjusted.

  In the method for manufacturing an optical element of the present invention, it is preferable that the heating temperature of the grid-shaped metal film in the heat treatment is 800 ° C. or less. This is to protect the substrate and the metal film.

  The liquid crystal device of the present invention is characterized in that an optical element obtained by the manufacturing method described above is provided as a polarizing element. According to this configuration, a liquid crystal device with a polarizing element whose optical characteristics are optimized according to the design can be obtained, and a liquid crystal device that can display bright, high-quality images and has excellent heat resistance and reliability is realized. can do.

  The projection display device of the present invention is characterized in that the optical element obtained by the manufacturing method described above is provided as a polarizing element. According to this configuration, a projection type display device equipped with a polarizing element whose optical characteristics are optimized according to the design is obtained, and a projection type that can display bright, high quality images and has excellent heat resistance and reliability. A display device can be realized.

  Embodiments of the present invention will be described below with reference to the drawings. In each drawing used for the following description, the scale of each member is appropriately changed to make each member a recognizable size.

(projector)
FIG. 1 is a schematic configuration diagram showing a main part of a projector which is an embodiment of a projection display device of the present invention. The projector according to the present embodiment is a liquid crystal projector using a liquid crystal device as a light modulation device.
In FIG. 1, 810 is a light source, 813 and 814 are dichroic mirrors, 815, 816 and 817 are reflection mirrors, 818 is an incident lens, 819 is a relay lens, 820 is an exit lens, and 822, 823 and 824 are liquid crystal devices. A modulation device, 825 is a cross dichroic prism, 826 is a projection lens, 831, 832, and 833 are polarization elements (optical elements) on the incident side, and 834, 835, and 836 are polarization elements (optical elements) on the emission side.

  The light source 810 includes a lamp 811 such as a metal halide and a reflector 812 that reflects the light of the lamp. As the light source 810, besides a metal halide, an ultrahigh pressure mercury lamp, a flash mercury lamp, a high pressure mercury lamp, a deep UV lamp, a xenon lamp, a xenon flash lamp, or the like can be used.

  The dichroic mirror 813 transmits red light contained in white light from the light source 810 and reflects blue light and green light. The transmitted red light is reflected by the reflection mirror 817 and enters the red light liquid crystal light modulation device 822 via the polarizing element 831. The green light reflected by the dichroic mirror 813 is reflected by the dichroic mirror 814 and enters the liquid crystal light modulator 823 for green light via the polarizing element 832. Further, the blue light reflected by the dichroic mirror 813 passes through the dichroic mirror 814. For blue light, in order to prevent light loss due to a long optical path, a light guide means 821 including a relay lens system including an incident lens 818, a relay lens 819, and an exit lens 820 is provided. The blue light is incident on the blue light liquid crystal light modulation device 824 via the polarizing element 833 via the light guide unit 821.

  The three color lights modulated by the respective light modulation devices 822 to 824 are incident on the cross dichroic prism 825 via the respective color polarization elements 834 to 836. The cross dichroic prism 825 is formed by bonding four right-angle prisms. A dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are formed in an X shape at the interface. Yes. These dielectric multilayer films combine the three color lights to form light representing a color image. The synthesized light is projected onto the screen 827 by the projection lens 826 which is a projection optical system, and the image is enlarged and displayed.

  Here, in the projector according to the present embodiment, the polarizing elements 831 to 836 employ those made of an inorganic material. Since the light source 810 composed of the metal halide lamp 811 emits high energy, the organic material may be decomposed or deformed by the high energy light. Therefore, the polarizing elements 831 to 836 are made of an inorganic material (including a metal material) having high light resistance and high heat resistance.

  FIG. 2 is a perspective view showing a schematic configuration of polarizing elements 831 to 836 (hereinafter collectively referred to as polarizing element 1). FIG. 3A is a schematic plan view of the polarizing element 1. FIG. 3B is a schematic cross-sectional view of the polarizing element 1 and also shows the action when light passes through the polarizing element 1.

  The polarizing element 1 relates to the optical element of the present invention, and selects only each color light emitted from the light source 810 to transmit only linearly polarized light. Specifically, as shown in FIGS. 2 and 3, a base insulating film 15 made of silicon oxide or the like is formed on a light-transmitting substrate 11A made of a dielectric material such as glass, and stripes are formed on the base insulating film 15. And a wire grid 12 made of a plurality of metal films arranged in a shape. A protective film covering each wire grid 12 may be formed on the wire grid 12, and in this case, the surface of the protective film is preferably a flat surface.

  The pitch P of the wire grid 12 shown in FIG. 3A is a value smaller than the wavelength of the incident light on the polarizing element 1, and is set to 140 nm or less, for example. Further, the width of the wire grid 12 is set to, for example, 80 nm or less, which is convenient for manufacturing, but is preferably about 1/10 of the wavelength of incident light. Therefore, the width (space width) of the linear groove 13 formed in the gap between the wire grids 12 is about 60 nm.

  Moreover, the height of the wire grid 12 is about 100 nm to 200 nm. In addition to aluminum, the metal material constituting the wire grid 12 is silver, gold, copper, palladium, platinum, rhodium, silicon, nickel, cobalt, manganese, iron, chromium, titanium, ruthenium, niobium, neodymium, ytterbium. , Yttrium, molybdenum, indium, bismuth, or alloys thereof can be used.

  Here, FIG. 9 is a diagram showing the cross-sectional structure of the wire grid 12 according to the present embodiment in more detail. As shown in the figure, the wire grid 12 according to the present embodiment has a linear metal film 12M and a dielectric film 12D2 covering the surface thereof. The dielectric film 12D2 is a metal oxide film (aluminum oxide film) formed by oxidizing the surface of a metal film 12M formed by, for example, forming an aluminum film on the substrate 11A, and the film thickness thereof is the metal film 12M. It is thicker than the natural oxide film formed on the surface.

  Although the details will be described later, the dielectric film 12D2 is formed on the surface portion of the wire grid 12 by heat treatment when forming the wire grid 12, and is obtained by the method for manufacturing an optical element according to the present invention. It is characteristic in optical elements. In the manufacturing method according to the present invention, the optical characteristics of the wire grid 12 can be adjusted by the heat treatment, and an optical element having excellent optical characteristics that cannot be obtained by the conventional manufacturing method can be obtained.

As shown in FIG. 3 (b), the polarizing element 1 has a refractive index n _A of the wire grid 12 and a refractive index n _B of the groove 13 interposed between the wire grids 12. Polarization selection is performed according to the polarization direction of the light incident on. Specifically, the linearly polarized light Et having a polarization axis in a direction perpendicular to the extending direction of the wire grid 12 is transmitted, and the linearly polarized light Er having a polarization axis in a direction parallel to the extending direction of the wire grid 12 is reflected. . Therefore, the polarizing element 1 of the present embodiment has the same action as the light-reflecting polarizer, that is, has the action of transmitting polarized light parallel to the optical axis (transmission axis) and reflecting perpendicularly polarized light. .

  The linearly polarized light generated by passing through the polarizing element 1 as described above is incident on the liquid crystal devices 822 to 824 serving as light modulation means. The liquid crystal devices 822 to 824 have a configuration as shown in FIGS. 4 to 6, for example. 4A is a plan configuration diagram of the liquid crystal devices 822 to 824, and FIG. 4B is a cross-sectional configuration diagram taken along the line H-H 'in FIG. 4A. FIG. 5 is a diagram showing equivalent circuits such as various elements and wirings in a plurality of pixels formed in a matrix in the image display region of the liquid crystal devices 822 to 824. FIG. 6 is a diagram showing a schematic configuration of a side cross section of the liquid crystal devices 822 to 824.

  In the liquid crystal device 100, as shown in FIG. 4B, the TFT array substrate 10 and the counter substrate 20 are bonded together by a sealing material 52, and the liquid crystal layer 50 is sealed in a region partitioned by the sealing material 52. It has a configuration. As shown in FIG. 4A, a light-shielding film (peripheral parting) 53 made of a light-shielding material is formed in a region inside the region where the sealing material 52 is formed. A data line driving circuit 101 and an external circuit mounting terminal 102 are formed along one side of the TFT array substrate 10 in a region outside the sealing material 52, and the scanning line driving circuit is formed along two sides adjacent to the one side. 104 is formed. On the remaining side of the TFT array substrate 10, a plurality of wirings 105 are provided for connecting the scanning line driving circuits 104 provided on both sides of the image display area. In addition, an inter-substrate conductive material 106 for providing electrical continuity between the TFT array substrate 10 and the counter substrate 20 is disposed at a corner portion of the counter substrate 20.

  Instead of forming the data line driving circuit 101 and the scanning line driving circuit 104 on the TFT array substrate 10, for example, a TAB (Tape Automated Bonding) substrate on which a driving LSI is mounted and a peripheral portion of the TFT array substrate 10 The terminal group formed in the above may be electrically and mechanically connected via an anisotropic conductive film.

  In the image display region of the liquid crystal device 100 having such a structure, as shown in FIG. 5, a plurality of pixel electrodes 9 are arranged in a matrix, and each of these pixel electrodes 9 is provided for pixel switching. TFT 30 is connected. In addition, a data line 6a for supplying pixel signals S1, S2,..., Sn is electrically connected to the source of the TFT 30. Pixel signals S1, S2,..., Sn to be written to the data lines 6a may be supplied line-sequentially in this order, or may be supplied for each group to a plurality of adjacent data lines 6a. . Further, the scanning line 3a is electrically connected to the gate of the TFT 30, and the scanning signals G1, G2,..., Gm are applied to the scanning line 3a in a pulse-sequential manner in this order at a predetermined timing. It is configured. The pixel electrode 9 is electrically connected to the drain of the TFT 30, and the pixel signal S1, S2,..., Sn supplied from the data line 6a is obtained by turning on the TFT 30 as a switching element for a certain period. Write to each pixel at a predetermined timing. The pixel signals S1, S2,..., Sn written in the liquid crystal via the pixel electrode 9 in this way are held for a certain period with the counter electrode 21 of the counter substrate 20 shown in FIG. Further, in order to prevent the held pixel signals S1, S2,..., Sn from leaking, a storage capacitor 70 is added in parallel with the liquid crystal capacitor formed between the pixel electrode 9 and the counter electrode 21. Reference numeral 3 b denotes a capacitor line that constitutes the storage capacitor 70.

  As shown in FIG. 6, the liquid crystal devices 822 to 824 have a basic structure in which a liquid crystal layer 50 is sandwiched between a TFT array substrate 10 and a counter substrate 20 made of transparent glass and the like that are opposed to each other vertically. Yes. As the liquid crystal mode in the liquid crystal layer 50, in addition to the TN (Twisted Nematic) mode, an STN (Super Twisted Nematic) mode, an ECB (Electrically Controlled Birefringence) mode, a VAN (Vertical Aligned Nematic) mode, or the like can be adopted.

  The TFT array substrate 10 includes a translucent substrate body 10A made of glass, quartz, or the like, and is arranged in a matrix on the inner surface side (the side on which the liquid crystal layer 50 is provided) of the substrate body 10A. A TFT 30 provided corresponding to the pixel, a pixel electrode 9 made of a transparent conductive film such as ITO, and the like are provided. A base insulating film 31 made of silicon oxide or the like is formed on the inner surface side of the substrate body 10A, and a semiconductor layer 60 made of a silicon film or the like patterned in an island shape is formed on the base insulating film 31. A gate insulating film 42 made of silicon oxide, silicon nitride or the like is formed so as to cover the semiconductor layer 60, and a gate electrode 61 is formed at a position facing the semiconductor layer 60 with the gate insulating film 42 interposed therebetween. The gate electrode 61 is actually electrically connected to the scanning line 3a shown in FIG. A first interlayer insulating film 32 made of silicon oxide or the like is formed to cover the gate electrode 61 and the gate insulating film 42, and reaches the semiconductor layer 60 through the first interlayer insulating film 32 and the gate insulating film 42. A source electrode 62 and a drain electrode 63 formed on the first interlayer insulating film 32 are electrically connected to the semiconductor layer 60 through the contact holes. The source electrode 62 is actually electrically connected to the data line 6a shown in FIG. A second interlayer insulating film 33 made of silicon oxide or a resin material is formed so as to cover the source electrode 62, the drain electrode 63, and the first interlayer insulating film 32. The pixel electrode 9 formed on the second interlayer insulating film 33 and the drain electrode 64 are electrically connected through a contact hole that penetrates the second interlayer insulating film 33 and reaches the drain electrode 63. With this conductive connection structure, the pixel electrode 9 and the TFT 30 are electrically connected. An alignment film 16 that controls the alignment of the liquid crystal layer 50 is provided over the entire image display region so as to cover the pixel electrode 9. The alignment film 16 is an inorganic alignment film made of a silicon oxide oblique vapor deposition film or the like, and has a film thickness of 10 nm to 100 nm (for example, 25 nm).

  On the other hand, the counter substrate 20 includes a translucent substrate main body 20A such as glass or quartz, like the TFT substrate 10, and the inner surface side (the side where the liquid crystal layer 50 is provided) of the substrate main body 20A is shielded from light. A film 23 is provided. The light shielding film 23 is provided in a lattice shape along the edge of each pixel on which the TFT 30 and wirings (data line 6a, scanning line 3a, etc.) are formed. A region where the illumination light is blocked by the light shielding film 23 is a non-illumination region, and a region where the illumination light is transmitted through the opening of the light shielding film 23 is an illumination region. Only the illumination area contributes to the display. An insulating film 23a is formed on the inner surface of the substrate body 20A so as to cover the light shielding film 23, and a counter electrode 21 made of a transparent conductive film such as ITO is provided on the entire surface of the insulating film 23a. Further, an alignment film 22 for controlling the alignment of the liquid crystal layer 50 is provided over the entire image display region so as to cover the counter electrode 21. The alignment film 22 is also an inorganic alignment film made of an oblique deposition film of silicon oxide or the like, and has a film thickness of 10 nm to 100 nm (for example, 25 nm).

  In such liquid crystal devices 822 to 824, the phase control of linearly polarized light entering through the polarizing elements 831, 832, and 833 shown in FIG. 1 is performed. That is, the drive control of the liquid crystal layer 50 is performed by the voltage applied to the electrodes 9 and 21, and the phase of the incident light is controlled. The phase-controlled light is incident on the polarizing elements 834, 835, and 836 disposed on the light exit side, and only light having a component parallel to the transmission axis of the polarizing element is transmitted through the polarizing elements 834 to 836 for display. Used.

  As described above, each color light modulated by the liquid crystal devices 822 to 824 and transmitted through the polarizing elements 831 to 836 is incident on the cross dichroic prism 825 and synthesized. The synthesized light is projected by the projection lens 826 which is a projection optical system. The image is projected on the screen 827 and the image is enlarged and displayed.

  In the present embodiment, no organic material is used for the polarizing element 1 (831 to 836). That is, the polarizing element 1 (831-836) is comprised from an inorganic material and / or a metal material, excluding the organic material which may be deteriorated by the high energy light supplied from a metal halide lamp. Moreover, since the said polarizing element 1 (831-836) is manufactured by the method as shown below, manufacturing cost is also cheap and it has become very reliable.

(Polarizing element manufacturing method)
Hereinafter, an example of the manufacturing method of the polarizing element (optical element) 1 shown in FIGS. 2 and 3 will be described with reference to FIGS. FIG. 7 is a cross-sectional process diagram for explaining the manufacturing method of the polarizing element of this embodiment. 8 and 9 are enlarged cross-sectional views showing the main part in order to explain the structure of the wire grid in the manufacturing method of this embodiment. 10 and 11 are diagrams showing optical characteristics of a polarizing element including a wire grid having the structure shown in FIGS. 8 and 9, respectively.

  First, as shown in FIG. 7A, a base insulating film 15 made of silicon oxide, which is a translucent dielectric material, is formed on a substrate 11A made of a glass substrate or the like, and on the base insulating film 15, A solid metal layer 12a made of aluminum is formed. Here, film forming means such as vapor deposition or sputtering can be used. In addition to aluminum, the metal constituting the metal layer 12a is, for example, gold, copper, palladium, platinum, rhodium, silicon, nickel, cobalt, manganese, iron, chromium, titanium, ruthenium, niobium, neodymium, ytterbium, Any of yttrium, molybdenum, indium, bismuth, or an alloy thereof can be used. The base insulating film 15 is not limited to silicon oxide, and various light-transmitting dielectric materials can be used. For example, silicon nitride or silicon oxynitride may be used.

  Next, a resist is applied onto the metal layer 12a by spin coating and baked to form a resist film. Thereafter, exposure and development processes are performed to form a linear planar resist 14a as shown in FIG. 7B. Specifically, laser irradiation is selectively performed on the resist film so that the resists 14a to be formed are arranged in stripes. As described above, since the pitch of the resist 14a to be formed is about 60 to 80 nm, an interference exposure method (here, two-beam interference exposure) capable of forming a fine striped pattern having a wavelength of visible light or less is used. Use. After such exposure, baking (PEB) is performed, and the exposed portion of the resist film is removed by etching, whereby the resist 14a having the pattern shown in FIG. 7B can be formed.

  Subsequently, the metal layer 12a is etched using the formed resist 14a as a mask, and the resist 14a is removed to form a metal film 12M as shown in FIG. 7C. Thereafter, the substrate 11A on which the metal film 12M is formed is subjected to a heat treatment (for example, 400 ° C., 60 minutes) in an oxygen atmosphere, whereby an oxide film (aluminum oxide) of the constituent material (aluminum) is formed on the surface of the metal film 12M. A dielectric film 12D2 made of is formed. Through the above steps, the polarizing element 1 including the wire grid 12 shown in FIG. 7D can be manufactured.

  In the above process, an oxygen gas atmosphere is used as the gas atmosphere during the heat treatment, but the gas atmosphere can be changed according to the material of the metal film 12M. That is, any gas that can form a dielectric film by reacting with the constituent material of the metal film 12M can be used, and in addition to oxygen, nitrogen, hydrocarbon, fluorine, or a mixed gas thereof can be used. Moreover, it is possible to change suitably also about the temperature and time of heat processing. However, from the viewpoint of protection of the metal film 12M and the substrate 11A and manufacturing efficiency, it is preferable that the heating temperature is 800 ° C. or less and the heating time is 2 hours or less.

  According to the manufacturing method of the present embodiment, the optical characteristics of the polarizing element can be adjusted by the heat treatment under the gas atmosphere. FIG. 8 is a diagram showing a cross-sectional structure of the metal film 12M before the heat treatment shown in FIG. 7C, and FIG. 9 shows the wire grid 12 after the heat treatment shown in FIG. It is a figure which shows a cross-sectional structure.

When the cross-sectional structure of the metal film 12M patterned in the process shown in FIG. 7C is viewed, the metal film 12M is formed on the surface of the metal film 12M formed on the base insulating film 15 as shown in FIG. The natural oxide film 12D1 made of aluminum is formed. Thus, the structure in which the natural oxide film is formed on the surface of the metal film is the same as the cross-sectional structure of the wire grid in the wire grid type polarizing element manufactured by a conventionally known manufacturing method.
When the transmittance and contrast of the polarizing element having the above structure shown in FIG. 8 were measured, the results shown in FIG. 10 were obtained. The line width L of the wire grid in the polarizing element subjected to the measurement is 80 nm, the space width S between the wire grids is 60 nm, and the formation height of the wire grid is 160 nm. The transmittance shown in FIG. 10 is the intensity ratio of the transmitted light to the incident light when linearly polarized light (p wave) parallel to the transmission axis of the polarizing element is incident, and the contrast is the transmittance Tp of the p wave. Is the intensity ratio Tp / Ts of the transmittance Ts of linearly polarized light (s wave) orthogonal to the transmission axis of the polarizing element.

  On the other hand, as shown in FIG. 9, the cross-sectional structure of the wire grid 12 of the polarizing element obtained by the manufacturing method of the present embodiment is formed from an aluminum oxide constituting the metal film 12M on the surface of the metal film 12M. A dielectric film 12D2 is formed. This dielectric film 12D2 is formed by heat treatment in an oxygen gas atmosphere in the step shown in FIG. 7D, and the film thickness thereof is the film thickness of the natural oxide film 12D1 shown in FIG. This structure is considerably larger than that of the wire grid and is characteristic of the wire grid obtained by using the manufacturing method according to the present invention. Further, when the manufacturing method according to the present invention is used, the metal film 12M and the base insulating film 15 (when the base insulating film is not provided) due to diffusion of the gas component accompanying the heat treatment from the base insulating film 15 and the substrate 11A side. A dielectric layer 12D3 may be formed between the substrate and the substrate. The structure in which such a dielectric layer 12D3 is formed together with the dielectric film 12D2 is also characteristic of a wire grid obtained using the manufacturing method according to the present invention.

  The film thickness of the dielectric film 12D2 varies depending on the optical characteristics of the polarizing element 1 to be manufactured, and the duty ratio of the wire grid (ratio L / S between the line width L and the space width S) is If they are the same, the film thickness of the dielectric film 12D2 increases as the transmittance increases.

  FIG. 11 shows the measurement results of the transmittance and contrast of the polarizing element 1 obtained by the manufacturing method of the present embodiment. The polarizing element subjected to the measurement is obtained by subjecting the polarizing element subjected to the measurement whose result is shown in FIG. 8 to heat treatment at 400 ° C. for 60 minutes in an oxygen gas atmosphere. Comparing FIG. 10 and FIG. 11, the transmittance in the wavelength region of 550 nm or more is almost the same, but the polarizing element 1 of this embodiment shown in FIG. 11 has improved transmittance in the range of 400 nm to 500 nm. Specifically, the transmittance at 450 nm is 60.3% in the graph shown in FIG. 10 and 68.4% in the graph shown in FIG. 11, an improvement of about 8%. .

  According to the manufacturing method of the polarizing element as described above, it is possible to easily manufacture the polarizing element 1 that does not use an organic material, and the manufactured polarizing element 1 is extremely excellent in light resistance and heat resistance. . Further, the wire grid 12 as a conductor can be formed in a striped pattern on the substrate 11A made of a dielectric, and the pitch of the stripe is set to 140 nm (the wavelength of visible light or less). It functions as the grid-type polarizing element 1.

  Moreover, according to the said manufacturing method, the polarizing element 1 which comprises the desired transmittance | permeability can be manufactured according to the simple process of the heat processing in gas atmosphere. That is, in the conventional manufacturing method, the adjustment of the optical characteristics, which can only be realized by changing the duty ratio L / S of the wire grid, can be performed with the same formation process of the metal film 12M. It can be done. Therefore, it is possible to manufacture the polarizing element 1 having a high transmittance, which has conventionally been difficult to realize due to limitations due to the resolution of the photolithography process, by using a simple process. Specifically, when the interference exposure method is used for the exposure of the resist film, the width of the exposure region is the same as the width of the non-exposure region in order to obtain a striped exposure pattern by optically interfering two light beams ( The duty ratio L / S is usually 1), and it is extremely difficult to make the duty ratio greatly different from 1. On the other hand, according to the manufacturing method of the present invention, even when the duty ratio is 1 when the metal film 12M is formed, the polarizing element 1 can be easily changed by changing the film thickness of the dielectric film 12D2 to be formed. It is possible to control the optical characteristics.

  In the present embodiment, an example in which an optical element having a fine structure is used as a polarizing element has been described. However, it is also possible to use it as a diffraction element, a PBS (Polarized Beam Splitter), or a retardation plate. In the present embodiment, a projector is exemplified as the projector. However, the polarizing element 1 can also be used for a direct-view projector.

1 is a schematic configuration diagram of a projector according to an embodiment. FIG. 2 is a perspective configuration diagram of a polarizing element provided in the projector of FIG. 1. FIG. 2 is a plan configuration diagram and a sectional configuration diagram (operation explanatory diagram). FIG. 2 is an overall configuration diagram of a liquid crystal device provided in the projector of FIG. 1. Equivalent circuit diagram. FIG. Sectional process drawing which shows the manufacturing process of a polarizing element. The cross-sectional block diagram which expands and shows the principal part of a polarizing element. The cross-sectional block diagram which expands and shows the principal part of a polarizing element. The graph which shows the optical characteristic of the polarizing element shown in FIG. The graph which shows the optical characteristic of the polarizing element shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,831-836 ... Polarizing element (optical element), 11A ... Substrate, 12 ... Wire grid, 13 ... Groove, 822-824 Liquid crystal device (light modulation device)

Claims (7)

Forming a metal layer on a translucent dielectric substrate;
Patterning the metal layer to form a grid-like metal film;
And a step of modifying the surface portion of the metal film by heat-treating the grid-shaped metal film in a gas atmosphere.   The gas component of the gas atmosphere and the metal component of the grid-like metal film are reacted by the heat treatment, and a compound of the metal component and the gas component is a main component on the surface portion of the grid-like metal film. The method of manufacturing an optical element according to claim 1, wherein a dielectric film is formed.   3. The method of manufacturing an optical element according to claim 1, wherein the gas atmosphere is formed by oxygen, nitrogen, hydrocarbon, fluorine, or a mixed gas thereof.   The metal layer is selected from silver, gold, copper, palladium, platinum, aluminum, rhodium, silicon, nickel, cobalt, manganese, iron, chromium, titanium, ruthenium, niobium, neodymium, ytterbium, yttrium, molybdenum, indium, and bismuth. 4. The method of manufacturing an optical element according to claim 1, wherein the optical element is formed of a metal or an alloy thereof.   The method for manufacturing an optical element according to claim 1, wherein a heating temperature of the grid-like metal film in the heat treatment is 800 ° C. or less.   6. A liquid crystal device comprising an optical element obtained by the production method according to claim 1 as a polarizing element.   A projection type display device comprising an optical element obtained by the manufacturing method according to claim 1 as a polarizing element.

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