JP2008033341A - Manufacturing method of multilayer cut filter - Google Patents

Abstract

Provided is a multilayer cut filter having characteristics as designed because the film thickness can be controlled with high accuracy.
A balance H / L or L / H ratio of optical film thicknesses of a high refractive index layer H and a low refractive index layer L in a repetitive alternating layer having a function of cutting a specific light is 1.2-2. The range is .0. Further, the width of the correction plate 16 is made wider than usual, and the tooling coefficient is set in the range of 0.6 to 0.85.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a multilayer cut filter that cuts light having a wavelength shorter than a specific wavelength and transmits light having a longer wavelength among optical filters.

  Liquid crystal projectors are becoming brighter and more compact year by year, and high-power mercury lamps that generate strong ultraviolet rays in the light source have come to be used. Since the optical system has also become smaller, the energy density of light passing through the optical system has increased. As a result, UV light and even visible light with short wavelengths cause deterioration of components that use organic materials such as liquid crystal panels, polarizing plates, and retardation plates used in internal optical systems, and display quality in a short time. The problem of falling is growing.

  In order to cut harmful ultraviolet rays generated from high-intensity mercury lamps, it is possible to use absorption glass that uses a substrate material that absorbs light, and changes to absorption wavelength and absorption-transmission depending on the composition and thickness of the material. The rising characteristic (steepness) to be adjusted can be adjusted.

  However, there is a problem that the selection of the absorption wavelength is limited by the material and the energy of the absorbed light becomes heat, so that there is a problem that the absorption glass may be broken due to a temperature rise when strong light is put. . Moreover, even with carefully selected and adjusted materials, the transmittance at a short wavelength near the wavelength to be cut cannot be so high, resulting in attenuation of transmitted light.

  On the other hand, a multilayer cut filter called an edge filter is known. This multilayer cut filter has a high refractive index layer and a low refractive index layer alternately formed on a light transmissive substrate with a predetermined optical film thickness (= refractive index n × geometric film thickness d) by a vacuum deposition method or the like. A multilayer dielectric laminated on the substrate is formed, and light having a wavelength shorter than a specific wavelength can be cut and light having a longer wavelength can be transmitted. In the multilayer film of the multilayer dielectric, the wavelength to be cut can be arbitrarily selected by adjusting the film thickness, and the transmittance at a short wavelength near the wavelength to be cut can be increased.

  For example, it can be a UV cut filter that is disposed in front of an optical component that is exposed to a light source containing strong ultraviolet rays and cuts part of the ultraviolet rays and visible light having a short wavelength.

  However, a UV cut filter formed with a multilayer dielectric is known as a filter that is extremely difficult to manufacture. That is, in order to make the rising characteristic steep, it is necessary to increase the number of film formations so that the number of times of alternately forming the high refractive index layer and the low refractive index layer is, for example, 30 or more. Further, the thickness of each layer is thin, particularly in the ultraviolet region, and the thickness of each layer must be controlled with high accuracy in order to make the rising wavelength highly accurate. For example, if the film thickness of each layer is shifted by 1%, it is said that the rising wavelength is shifted by 5 nm. With the current film forming technology, the film thickness is controlled with high accuracy to produce a UV cut filter having the characteristics as designed. Difficult to do.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a multilayer cut filter having characteristics as designed because the film thickness can be controlled with high accuracy.

  It is another object of the present invention to provide a method for manufacturing a multilayer cut filter that can easily control the film thickness with high accuracy.

  As a result of intensive studies in order to achieve the above object, the present inventor intervenes a correction plate between the vapor deposition source and the light-transmitting substrate in the film forming apparatus, and uses a correction plate having a wider width than in the past. More specifically, by increasing the ratio of the flying particles shielded by the correction plate, the tooling coefficient is the ratio between the thickness of the layer deposited on the light-transmitting substrate and the thickness of the layer deposited on the monitor substrate. In this case, the tooling coefficient is set to 0.6 to 0.85, so that the film thickness is thicker on the monitor substrate than the light transmissive substrate. And film thickness control can be facilitated.

  Therefore, the invention according to claim 1 repeatedly forms the particles forming the high refractive index layer flying from the vapor deposition source and the particles forming the low refractive index layer alternately on the light-transmitting substrate, and at the same time In the method of manufacturing a multilayer cut filter that forms a film on a monitor substrate and controls the film thickness while measuring the optical film thickness of the layer formed on the monitor substrate, the vapor deposition source and the light transmission property When the correction plate is interposed between the substrate and the ratio of the film thickness of the layer deposited on the light-transmitting substrate / the film thickness of the layer deposited on the monitor substrate, the tooling coefficient Is provided in the range of 0.6 to 0.85.

  In the invention described in claim 2, the multilayer cut filter is preferably a UV cut filter.

  Hereinafter, embodiments of the multilayer cut filter and the manufacturing method thereof according to the present invention will be described, but the present invention is not limited to the following embodiments.

  The multilayer cut filter of the present invention is an edge filter that cuts light having a wavelength shorter than a specific wavelength and transmits light having a long wavelength, or cuts light having a wavelength longer than a specific wavelength and transmits light having a short wavelength. Depending on the function, there are names that match the purpose of use, such as UV cut filters, IR cut filters, dichroic filters, and cold mirrors. It is used to cut unnecessary or harmful high-order frequency (short wavelength) light in various optical measurements, projection systems (projection devices), photographing devices, and laser processing devices.

  The main purpose of the multilayer cut filter of the present invention is that it is placed between an optical component exposed to a light source including a strong ultraviolet ray such as a high output mercury lamp such as a liquid crystal projector and the light source. It is a UV cut filter that protects optical components by cutting part of visible light.

In the multilayer cut filter, a dielectric multilayer film in which high refractive index layers and low refractive index layers are alternately laminated on a light transmissive substrate is formed. As a material for the high refractive index layer, TiO ₂ (n = 2.4), Ta ₂ O ₅ (n = 2.1), Nb ₂ O ₅ (n = 2.2) or the like is used. As the material, SiO ₂ (n = 1.46) or MgF ₂ (n = 1.38) is used. The refractive index varies depending on the wavelength, and the refractive index n is 500 nm.

In general, the basic design of the film thickness is (0.5H, 1L, 0.5H) as repeated alternating layers in which high refractive index layers and low refractive index layers are alternately laminated with the same optical film thickness. ^Represented as ^S. Here, the wavelength near the center of the wavelength to be cut is designated as the design wavelength λ, the film thickness of the high refractive index layer (H) is expressed as the optical film thickness nd = 1 / 4λ is 1H, and the low refractive index layer ( Similarly, L) is set to 1L. S is the number of repetitions called the number of stacks, and indicates that the configuration in parentheses is repeated periodically. The number of layers actually stacked is 2S + 1. When the value of S is increased, the rising characteristic (steepness) that changes to absorption-transmission can be made abrupt. The value of S is selected from a range of about 3 to 20. This repeated alternating layer determines the specific wavelength to be cut.

In order to increase the transmittance of the transmission band and make the unevenness of the light transmittance called ripple a flat characteristic, the optimum design is made by repeatedly changing the film thickness of the alternating layers near the substrate and several layers near the medium. I do. Therefore, the substrate | 0.5LH... HL (HL) ^s HL. In addition, when TiO ₂ or the like is used for the high refractive index layer, the design is often performed by adding SiO ₂ having better environmental resistance characteristics to the outermost layer rather than ending the outermost layer with the high refractive index layer. Since the characteristics of the layer in contact with the substrate may deteriorate when TiO ₂ reacts with the substrate, chemically stable SiO ₂ may be added to the first layer. Such a multilayer cut filter can be theoretically designed using commercially available software (reference: OPTRONICS magazine 1999 No.5 p.175-190).

  In order to form a high refractive index layer and a low refractive index layer alternately on a light-transmitting substrate, a physical film forming method is generally used, and a normal vacuum evaporation method is also possible. It is desirable to use ion-assisted vapor deposition, ion plating, or sputtering, which can control the rate stably and can produce a film with little spectral change over time due to changes in storage and use environment. The vacuum evaporation method is a method in which a thin film material is heated and evaporated in a high vacuum, and the evaporated particles are deposited on a substrate to form a thin film. The ion plating method is a method in which vapor deposition particles are ionized and accelerated by an electric field to adhere to a substrate. APS (Advanced Plasma Source), EBPM (Electron Beam Excited Plasma) method, RF (Radio Frequency) direct substrate application method There are methods such as (a method of performing reactive vacuum vapor deposition in a state where high-frequency gas plasma is generated in the film formation chamber). The sputtering method is a thin film forming method in which ions that are accelerated by an electric field collide with a thin film material to evaporate the thin film material by sputtering, and deposit evaporated particles on a substrate. Since the optical constant such as the refractive index of the layer to be formed varies depending on the film forming method, film forming conditions, and the like, it is necessary to accurately measure the optical constant of the layer to be formed before manufacturing.

  FIG. 1 shows an example of a physical film forming apparatus using an optical film thickness meter widely used for film thickness control. In this physical film forming apparatus, two evaporation sources 12 and 13 each having a crucible filled with a thin film material of a high-refractive index material and a low-refractive index material are provided in the lower part of a vacuum chamber 11 constituting the film forming apparatus 10. Has been placed. The evaporation sources 12 and 13 can be heated or sputtered by various methods. Above the inside of the vacuum chamber 11, a dome-shaped vapor deposition dome 14 on which a light-transmitting substrate is placed is rotatably supported. A substrate heater 15 for heating the vapor deposition dome 14 is installed above the vapor deposition dome 14. A hole for monitoring is formed in the central portion of the vapor deposition dome 14, and a monitor substrate 21 for monitoring the film thickness constituting the optical film thickness meter 20 is installed here. The monitor substrate 21 is made of a monitor glass. The light emitted from the projector 22 is incident on the film formation surface of the monitor substrate 21, the reflected light reflected by the film formation surface is received by the light receiver 23, converted into an electrical signal, and transmitted to the measurement device 24. The amount of reflected light is measured at 24, and the amount of reflected light is output to the recorder 25. A correction plate 16 for correcting the film thickness distribution is fixedly installed between the evaporation sources 12 and 13 and the vapor deposition dome 14.

  FIG. 2 shows a vertical positional relationship among the correction plate 16, the vapor deposition dome 14, the vapor deposition sources 12 and 13, and the monitor substrate 21. The two correction plates 16 are fixed above the vapor deposition sources 12 and 13, respectively, while the vapor deposition dome 14 rotates. Since the correction plate 16 prevents particles at a high concentration flying from the vapor deposition sources 12 and 13 from reaching the vapor deposition dome 14, the correction plate 16 can uniformize the distribution of particles flying to the vapor deposition dome. .

  The particles of the thin film material evaporated from the vapor deposition sources 12 and 13 are accelerated by an electric field (not shown) in the case of ion plating, or in the case of vacuum vapor deposition, fly directly to the vapor deposition dome 14 and are placed on the rotating vapor deposition dome 14. The light transmissive substrate is reached and deposited, and an optical film is formed on the light transmissive substrate. At that time, the portion where the particle density of the thin film material is large is blocked by the correction plate 16 so that a uniform film thickness distribution can be obtained. Two kinds of thin film materials can be alternately formed by switching one evaporation source 12 and the other evaporation source 13. Two types of thin film materials are alternately formed on the monitor substrate 21 at the same time as the film is formed on the light transmissive substrate.

  The optical film thickness meter 20 continuously changes the reflected or transmitted light amount of the wavelength specified by the film attached to the monitor substrate 21 (selected from the wavelength range usable by the film thickness meter sensor) during the film formation. The film formation is terminated when a change in the light amount measured in advance and calculated in advance occurs. As shown in FIG. 3, the change in the amount of light on the monitor substrate shows a peak that repeats increasing and decreasing periodically every time the optical film thickness becomes an integral multiple of 1/4 of the measurement wavelength λ. Since the actual optical film thickness can be accurately controlled by determining the film formation amount, the optical film thickness meter 20 is widely used for film formation of optical thin films.

However, in the case of ultraviolet cut (UV cut), it is necessary to select a short wavelength as the design wavelength, and the film thickness of each layer becomes extremely thin, making it difficult to control the film thickness. Further, in the ultraviolet region, there is a problem that the measurement accuracy becomes unstable because the optical constants such as the refractive index of the substrate and the film vary greatly as shown in FIG. 4 showing the change of the refractive index of TiO ₂ with the wavelength. . Further, in the film forming apparatus using the optical film thickness meter, the light amount change is flat in the vicinity of the light amount change peak, so that it is difficult to determine the light amount change peak, and there arises a problem that the control accuracy is remarkably deteriorated. In addition, when TiO ₂ is used, the measurement of the change in the amount of light itself becomes difficult due to the absorption of TiO ₂ , so that the film forming accuracy is significantly deteriorated. Further, when the number of repetitions S increases in order to realize a steep rise characteristic, film formation becomes more difficult. Conventionally, when the stack number S is 10 or more, it is impossible to produce in large quantities.

  In the present invention, the difficulty in controlling the film thickness at the time of film formation in such a UV cut filter is overcome by repeatedly devising the balance of the film thickness of the alternating layers and the size of the correction plate, and the film thickness control with high accuracy is achieved. This enables mass production.

  That is, in the conventional design, the ratio H / L of the optical film thickness of the alternating layers is set to 1.0. When H / L is set to 1.0, it is necessary to stop film formation accurately at a peak at which the reflectance of the monitor substrate is an integral multiple of λ / 4. In this case, it is difficult to determine the light amount change peak because the light amount change is flat in the vicinity of the light amount change peak of the optical film thickness meter.

  On the other hand, in the present invention, the ratio of H / L or L / H of the alternating layers is 1.2 to 2.0, preferably 1.3 to 1.5. And one of the low refractive index layers is thickened, and the other is thinned to bias the thickness. In this case, if the bias is too large, the characteristics as a filter may be adversely affected.

  As a result, when one of the thicker films is formed, the film formation is stopped when the peak of the light intensity change of the optical film thickness meter is over, so the film formation stop time becomes clear. , Film thickness control becomes easy. In addition, since the film thickness is controlled on the thickened film in the other thin film thickness control, the film formation is stopped at the peak as usual, so that the inconvenience of thinning does not occur. In particular, by increasing the thickness of the high refractive index layer, it is possible to form a high refractive index layer having a thin geometric thickness and difficult to control the film thickness with high film thickness accuracy.

  Next, in the present invention, the width of the correction plate 16 is made wider than usual, and the ratio of the flying particles shielded by the correction plate 16 is increased. That is, when the ratio of the thickness of the film deposited on the light-transmitting substrate / the thickness of the film deposited on the monitor substrate is defined as the tooling coefficient, this tooling coefficient is in the range of 0.6 to 0.85. is there. If the tooling coefficient is too low, the amount of particles adhering to the light-transmitting substrate becomes too small, which is not preferable in terms of productivity. The normal tooling coefficient in the conventional film forming apparatus is generally in the range of 0.9 to 1.1.

  As a result, a film thicker than the light-transmitting substrate is deposited on the monitor substrate 21, and the film thickness can be measured accurately, and the optical constants such as the refractive index are unstable in the ultraviolet region. can do. Further, since the peak of the change in the light amount of the monitor substrate 21 precedes the peak of the film formation of the light-transmitting substrate and the peak of the change in the light amount has passed, the film formation can be stopped. Becomes clear and film thickness control becomes easy. As a result, the film thickness accuracy can be improved.

  By combining the improvement of the film thickness balance with these repeated alternating layers and the improvement of the tooling coefficient by increasing the width of the correction plate, the change in the light quantity of the optical film thickness meter during the formation of the low refractive index layer can be reduced. The film thickness can be controlled more easily by adding the effect that the film formation can be stopped when the peak is exceeded.

<Example 1>
The ratio of the thicknesses of the alternating layers was set to about H / L = 1.33, so that the thickness of the H layer was increased. The first layer in contact with the outermost layer and the substrate was SiO ₂ .

BK7 (n = 1.52 white plate glass) was used as the light transmissive substrate material. A film material used is high-refractive index layer (H) is TiO _2, using the low refractive index layer (L) is SiO _2, film forming method RF ion plating apparatus (manufactured by Showa vacuum Co.). A monochromatic optical monitor type optical film thickness meter was used. A correction plate having a width wider than usual was used, and the tooling coefficient was set to 0.8.

The film thickness is λ = 360 nm and the number of layers is 33. From the substrate side, 1.08L, 0.44H, 1.04L, 0.88H, 0.80L, 1.16H, 0.76L, (1.12H, 0.84L) ¹⁰ , 1.00H, 0.92L, 1.16H, 0.60L, 1.04H, 1.80L.

  FIG. 5 shows an enlarged spectral transmittance around the wavelength of 410 nm of the obtained multilayer cut filter. Further, FIG. 6 shows the spectral transmittance in the wavelength range of 350 nm to 700 nm.

  Moreover, the change of the reflectance of the optical film thickness meter in a repeating alternating layer is shown in FIG. The solid line indicates the formation of the high refractive index layer, and the alternate long and short dash line indicates the formation of the low refractive index layer. The right end of each line indicates that film formation was stopped at that time.

<Example 2>
Under the same film forming conditions as in Example 1, the film thickness is λ = 360 nm, the number of layers is 19, and 1.08 L, 0.44 H, 1.04 L, 0.88 H, 0.80 L, 1.. 16H, 0.76L, (1.12H, 0.84L) ³ , 1.00H, 0.92L, 1.16H, 0.60L, 1.04H, 1.80L.

  FIG. 5 shows an enlarged spectral transmittance around the wavelength of 410 nm of the obtained multilayer cut filter. Further, FIG. 6 shows the spectral transmittance in the wavelength range of 350 nm to 700 nm.

  This layer structure is obtained by reducing the number of layers in consideration of productivity. Since the number of stacks of repeated alternating layers is small, the spectral characteristics are less steep.

<Comparative Example 1>
Optimization as in the conventional design was performed under the same film forming conditions as in Example 1. The film thickness is λ = 360 nm and the number of layers is 33. From the substrate side, 1L, 0.3H, 0.94L, 1.1H, 0.58L, 1.3H, 0.79L, (1H, 1L) ¹⁰ 1.02H, 0.71L, 1.74H, 0.32L, 1.35H, 1.68L.

  FIG. 5 shows an enlarged spectral transmittance around the wavelength of 410 nm of the obtained multilayer cut filter. Further, FIG. 6 shows the spectral transmittance in the wavelength range of 350 nm to 700 nm.

  Moreover, the change of the reflectance of the optical film thickness meter in a repeating alternating layer is shown in FIG. The solid line indicates the formation of the high refractive index layer, and the alternate long and short dash line indicates the formation of the low refractive index layer. The right end of each line indicates that film formation was stopped at that time.

<Comparative example 2>
Under the same film forming conditions as in Example 1, the film thickness configuration is λ = 360 nm, the number of layers is 19, and 1 L, 0.3 H, 0.94 L, 1.1 H, 0.58 L, 1.3 H, 0.79 L. , (1H, 1L) ³ , 1.02H, 0.71L, 1.74H, 0.32L, 1.35H, 1.68L.

  FIG. 5 shows an enlarged spectral transmittance around the wavelength of 410 nm of the obtained multilayer cut filter. Further, FIG. 6 shows the spectral transmittance in the wavelength range of 350 nm to 700 nm.

  Although the creation is somewhat easier with a smaller number of layers, the spectral characteristics are less steep and inferior.

  Example 1 and Comparative Example 1 have the same number of layers and different thickness balances of repeated alternating layers. In Example 1, the spectral characteristics are steeper. Similarly, Example 2 and Comparative Example 2 have the same number of layers and different balances of alternating alternating layer thicknesses, but Example 2 has sharper spectral characteristics.

  Further, the change in the amount of light of the optical monitor shown in FIG. 8 indicates that the film is formed at the peak apex when the high refractive index layer is formed in the conventional repeated alternating layer formation with H / L = 1.00. Since it must be stopped, it is difficult to determine when to stop the film formation, and it is difficult to control the film thickness. On the other hand, when the low refractive index layer is formed, the filming can be stopped when the peak has passed due to the effect of setting the tooling coefficient to 0.8, which indicates that film thickness control is easy. .

  On the other hand, the change in the optical monitor light quantity in the present invention in which the balance of the layer thickness of the repeated alternating layers shown in FIG. 7 is H / L = 1.33 has peaked when the high refractive index layer is formed. Since the film formation can be stopped at the time, the film thickness control is easy. In addition, the film thickness can be controlled easily because the filming can be stopped when the peak has passed due to the effect of setting the tooling coefficient to 0.8 even when the low refractive index layer is formed. Yes.

  According to the method of manufacturing a multilayer cut filter of the present invention, the tooling coefficient is reduced and the film is formed thicker on the monitor substrate, so that the film thickness can be easily controlled and the multilayer has the designed characteristics. A membrane cut filter can be manufactured.

It is a block diagram which shows the outline | summary of the physical film-forming apparatus which manufactures the multilayer film cut filter of this invention. FIG. 2 is a layout diagram illustrating a vertical positional relationship among a correction plate, a vapor deposition dome, a monitor substrate, and an evaporation source in the apparatus of FIG. 1. It is a graph which shows the relationship between the optical film thickness of the film-forming in a monitor board | substrate, and a reflectance. Is a graph showing the relationship between the wavelength and the refractive index in the deposition of the TiO _2. It is a graph which shows the spectral transmittance in 410 nm vicinity of the multilayer film cut filter obtained by the Example and the comparative example. It is a graph which shows the spectral transmittance in 350-700 nm of the multilayer film cut filter obtained by the Example and the comparative example. 5 is a graph showing a change in light amount of the optical monitor in Example 1. 5 is a graph showing a change in light amount of an optical monitor in Comparative Example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Film-forming apparatus, 11 ... Vacuum chamber, 12 ... Evaporation source, 13 ... Evaporation source, 14 ... Deposition dome, 15 ... Substrate heater, 16 ... Correction plate, 20 ... Optical film thickness meter, 21 ... Monitor substrate, 22 ... projector, 23 ... light receiver, 24 ... measuring instrument, 25 ... recorder.

Claims (2)

The particles forming the high refractive index layer and the particles forming the low refractive index layer flying from the deposition source are alternately formed on the light-transmitting substrate, and simultaneously formed on the monitor substrate. In the method of manufacturing a multilayer cut filter that controls the film thickness by measuring the optical film thickness of the layer formed on the monitor substrate,
A tooling coefficient which is a thickness of a layer deposited on the light transmissive substrate / a thickness of a layer deposited on the monitor substrate with a correction plate interposed between the vapor deposition source and the light transmissive substrate. In such a case, the tooling coefficient is in the range of 0.6 to 0.85.   The method for producing a multilayer cut filter according to claim 1, wherein the multilayer cut filter is a UV cut filter.

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