JP2006010813A - Shape variable mirror element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape variable mirror element which is excellent in reflectivity, and also provide its manufacturing method. <P>SOLUTION: In a shape variable mirror element 1 which is equipped with; a shape variable part 3 which is equipped with a laminated thin film which consists of at least a piezoelectric film 8, a first electrode film 7 and a second electrode film 9 which supply voltage to the piezoelectric film 8 and a reflective mirror film 6 which is provided on the piezoelectric film 8; and a substrate 2 which supports the shape variable part 3 and which is used in a visible ray region, the shape variable mirror element which has little irregular reflection and has excellent reflectivity can be obtained by adjusting the shape of the reflective mirror film so that the arithmetic mean roughness Ra of the surface of the reflective mirror film 6 becomes equal to or smaller than 10nm and the mean interval of recessed parts becomes equal to or smaller than 130nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a deformable mirror element that changes its shape by applying a predetermined voltage to a piezoelectric film, and a manufacturing method thereof.

  As the deformable mirror element, an element in which a lead wire is soldered to a reflection mirror surface and an electrode on an upper surface of a ceramic piezoelectric material is disclosed (for example, see Patent Document 1).

  As a micro-sized variable shape mirror element, an element in which a piezoelectric film is attached to a reflection mirror plate is disclosed (for example, see Patent Document 2). As the reflection mirror plate, for example, a glass reflection mirror, a reflection mirror film, a silicon wafer or the like is used.

  As a deformable mirror element capable of a large shape change with a low applied voltage, there is an element in which the shape variable portion has a thin film diaphragm in an opening of a hollow portion of a substrate (for example, Japanese Patent Application No. 2003-143027 by the present applicant). In the case of a deformable mirror element using a thin film diaphragm, since the film thickness of the element can be 10 μm or less, it is possible to change the shape at a low voltage.

In this variable shape mirror element, thin films such as a piezoelectric film, an electrode film, and an elastic plate film are sequentially laminated, and finally a reflection mirror film is formed. In general, a thin film has a different crystal structure depending on conditions such as a forming method, a substrate temperature at the time of forming, and a gas pressure (see, for example, Non-Patent Document 1). For example, in the case of sputtering, the crystal grains increase as the substrate temperature increases. Further, as the film thickness increases, the crystal grows greatly.
Japanese Patent Laid-Open No. 10-10459 JP 2001-34993 A JA Thornton, J. Vac. Sci. Technol. 11, 1974, 666 (Amer. Inst. Physics)

  Since the deformable mirror element disclosed in the above (Patent Document 1) uses a bulk material for the piezoelectric material, the thickness of the piezoelectric material is very large. As a result, it is easily guessed that a very high applied voltage is required to greatly change the shape.

  Also, in the case of the deformable mirror element disclosed in (Patent Document 2), it is easily guessed that a very high applied voltage is required. That is, an element having a structure in which the piezoelectric film and the reflection mirror plate are simply bonded has a low adhesive strength, and cannot be self-supported by itself and is not suitable for practical use.

  In the variable shape mirror element according to Japanese Patent Application No. 2003-143027, the crystal structure and the size of the crystal grains are greatly reflected in the surface shape, and the surface shape is unique to the thin film. Therefore, the surface roughness of the deformable mirror element also increases gradually, and the surface roughness of the reflecting mirror film surface becomes very large. Due to this large surface roughness, the reflection mirror film has a large irregular reflection, resulting in a low reflectance. Therefore, further improvement is desired.

  SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and a first object thereof is to provide a variable shape mirror element having a high reflectance even when a reflective mirror film is formed on a laminated thin film.

  A second object of the present invention is to provide a manufacturing method capable of stably producing a deformable mirror element having a high reflectance.

  In order to achieve the first object, the deformable mirror element of the present invention is mainly defined so that the arithmetic average roughness Ra of the reflecting mirror film surface is 10 nm or less and the average interval between the recesses is 130 nm or less. Features.

  Further, in order to achieve the second object, the method of manufacturing the deformable mirror element mainly performs mechanical polishing on the surface on which the reflecting mirror film is formed as the surface shape adjusting step of the reflecting mirror film surface. Features.

  According to the variable shape mirror element of the present invention, even in the reflective mirror film formed on the laminated thin film, the variable shape mirror element having a high reflectance equivalent to that when the reflective mirror film is formed on the mirror-polished substrate. It is possible to obtain an excellent effect that can be provided.

  Further, according to the method for manufacturing a deformable mirror element of the present invention, it is possible to stably produce a deformable mirror element having a high reflectance equivalent to that when a reflecting mirror film is formed on a mirror-polished substrate. Effect.

  An object of the present invention is to provide a variable shape mirror element having a high reflectance even when a reflecting mirror film is formed on a laminated thin film. The arithmetic average roughness Ra of the reflecting mirror film surface is 10 nm or less, and the average interval between recesses. This is realized by defining the value to be 130 nm or less.

  A first invention made to solve the above problems comprises at least a piezoelectric film, a first electrode film and a second electrode film for supplying a voltage to the piezoelectric film, and a reflection mirror film provided on the piezoelectric film. A variable shape mirror element used in a visible light region including a variable shape portion including a laminated thin film and a substrate that supports the variable shape portion, and the arithmetic average roughness Ra of the surface of the reflective mirror film is 10 nm or less In addition, a variable shape mirror element in which the average interval between the concave portions on the surface of the reflective mirror film is 130 nm or less is used. In the reflective mirror film formed on the laminated thin film, the reflective mirror film is formed on the mirror-polished substrate. A deformable mirror element having a high reflectance equivalent to that of the formed case can be obtained.

  Here, the surface shape is measured by, for example, an atomic force microscope, the measurement area is 5 μm × 5 μm, and the arithmetic average roughness Ra and the average interval between the recesses are determined by an average value at 10 arbitrary measurement locations.

Generally, a thin film has a columnar structure, and light is absorbed or irregular reflection occurs due to surface shapes such as surface undulations and fine and steep steps between grain boundaries, resulting in a decrease in reflectivity. To do. Therefore, as the thickness of the thin film and the number of layers of the laminated thin film increase, the reflectance decreases remarkably. Strictly speaking, the thin film surface is not a flat surface but has a zigzag structure with many inclinations. When a light ray enters this fine inclined surface, irregular reflection occurs. As the angle of the inclined surface is larger, the reflection angle of the light beam is greatly shifted, and the reflectance is lowered. Therefore, there are two factors of the surface shape that determine the reflectivity of the reflecting mirror film having the reflecting mirror function on the laminated thin film, the surface roughness and the average interval between the recesses. In the first invention, the arithmetic mean roughness Ra quantifying the surface roughness and the inclination angle, which are the prescribed roughness shape parameters of the JIS surface roughness (B0601), and the average interval between the recesses are specified. The arithmetic average roughness Ra is a value obtained by extracting the reference length L from the roughness curve in the direction of the average line, and summing and averaging the absolute values of deviations from the average line of the extracted portion to the measurement curve.

  As shown in FIG. 14, the average interval between the recesses is the sum of the average lines corresponding to one recess (valley) obtained by extracting only the reference length L from the roughness curve in the direction of the average line. Is what we asked for.

  The absolute value of the deviation from the average line of the sampling part to the measurement curve is summed and averaged. The measurement curve is divided horizontally at a fixed interval ΔX, and the slope of the line segment connecting the starting points of the measurement curve in each section. The absolute value of (angle) is obtained and averaged.

  When the arithmetic average roughness Ra of the reflecting mirror film surface is 10 nm or less and the average interval between the recesses is 130 nm or less, the reflectance is as high as when the reflecting mirror film is formed on the mirror-polished substrate.

  A second invention made to solve the above-described problem comprises at least a piezoelectric film, a first electrode film and a second electrode film for supplying a voltage to the piezoelectric film, and a reflection mirror film provided on the piezoelectric film. A method of manufacturing a variable shape mirror element for use in the visible light region having a variable shape portion including a laminated thin film and a substrate that supports the variable shape portion, wherein the arithmetic average roughness Ra of the surface of the reflective mirror film is 10 nm. A surface on which the reflection mirror film is formed as a surface shape adjustment step, and has a surface shape adjustment step for adjusting the surface shape so that the average distance between the concave portions on the surface of the reflection mirror film is 130 nm or less. The surface shape is adjusted by polishing the projections and projections that cause surface roughness by mechanical polishing in advance, so that the surface is mirror-polished. The variable shape mirror element having a same high reflectance in the case of forming the reflective mirror film on the plate can be stably produced.

  3rd invention made | formed in order to solve the said subject was made into the manufacturing method of the variable shape mirror element which apply | coats liquid curable resin at normal temperature with respect to the surface which forms a reflective mirror film | membrane as a surface shape adjustment process Since the surface shape adjustment process is performed by applying a thin liquid resin in advance and covering the protrusions and projections that cause the surface roughness, it is possible to stably produce variable shape mirror elements with excellent reflectivity. it can.

  According to a fourth aspect of the present invention, there is provided a variable shape mirror for forming a silicate glass containing phosphorus or boron as an impurity on a surface on which a reflecting mirror film is formed and performing a heat treatment as a surface shape adjusting step. This is an element manufacturing method, and the surface shape is adjusted by previously covering projections and projections that cause surface roughness, so that a deformable mirror element having excellent reflectivity can be stably manufactured. .

  A fifth invention made to solve the above-mentioned problem is a method for manufacturing a deformable mirror element that evaluates the surface shape adjustment step by measuring the reflectance of the reflecting mirror film surface. By obtaining the correlation between the roughness of the mirror film surface, the tilt angle, and the reflectance, the quality of the surface shape adjustment process can be judged by measuring the reflectance, so that a simple and high-quality deformable mirror element can be stably used. Can be manufactured.

(Embodiment 1)
Hereinafter, embodiments of the deformable mirror element of the present invention will be described. First, the configuration of the deformable mirror element according to the embodiment of the present invention will be described with reference to the drawings. For the purpose of facilitating understanding, the film thickness, the substrate thickness, the shape variable amount, etc. in the drawings are different from the actual dimensions. Hereinafter, the same applies to all drawings.

  FIG. 1 is a perspective view seen from the surface of a deformable mirror element according to an embodiment of the present invention. FIG. 2 is a perspective view seen from the back surface of the deformable mirror element according to the embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part of the deformable mirror element according to the embodiment of the present invention.

  The deformable mirror element 1 includes a substrate 2, a shape variable portion 3 including a diaphragm portion and a portion integrally connected to the substrate 2, and an electrode pad 4 for applying a voltage to the shape variable portion 3. The shape variable unit 3 includes a piezoelectric operating unit 5 and a reflective mirror film 6. The piezoelectric operation unit 5 includes a first electrode film 7 for applying a voltage to the piezoelectric film 8 from below, a piezoelectric film 8 for deforming the shape variable unit 3 by expansion and contraction, and a second electrode for applying a voltage to the piezoelectric film 8. It consists of a two-electrode film 9. In addition, an elastic plate film that determines a deformation direction, a deformation shape, and the like is added as necessary. However, in the variable shape mirror element 1 according to the embodiment of the present invention, the reflection mirror film 6 has a function of an elastic plate film. ing. Therefore, there is no thin film having only an elastic plate function. In addition, the shape variable part 3 and the piezoelectric action part 5 are the same members and the same structure.

  The operation of the deformable mirror element configured as described above will be described with reference to the drawings. 10 to 12 are side sectional views showing the operation of the deformable mirror element 1. When a voltage is applied to the first electrode film 7 and the second electrode film 9 of the deformable mirror element 1, for example, the cross-sectional shape shown in FIG. 11 is obtained. When voltages having opposite polarities are applied to the individual electrodes, the cross-sectional shape shown in FIG. 12 is obtained. The piezoelectric film 8 expands and contracts when a voltage is applied. Therefore, when a positive polarity voltage is applied to the first electrode film 7, the voltage application portion of the piezoelectric film expands. When a negative polarity voltage is applied, the voltage application portion of the piezoelectric film contracts. As a result, when a positive polarity voltage is applied to the first electrode film 7, the reflection mirror surface becomes convex as shown in FIG. Conversely, when a negative polarity voltage is applied to the first electrode film 7, the reflecting mirror surface becomes concave as shown in FIG.

  Next, a method for manufacturing the deformable mirror element according to the embodiment of the present invention will be described with reference to FIGS. 4 to 9 are cross-sectional views of the main part of the deformable mirror element showing the manufacturing process of the deformable mirror element.

  As a substrate material, a single crystal material such as Si or MgO is preferably used because the piezoelectric characteristics of the piezoelectric film 8 are likely to be good, but is not particularly limited. However, when a process for high-temperature treatment is required in the process of manufacturing the deformable mirror element 1, a substrate material having good heat resistance may be selected. Further, since the substrate is etched for forming the diaphragm, a relatively thin substrate is preferably used.

  An Ir—Ti alloy was used as the material of the first electrode film 7 and the film thickness was 0.1 μm. The material of the piezoelectric film 8 was PZT (lead zirconate titanate), and the film thickness was 3 μm. Ir—Ti alloy and PZT were both formed by sputtering, and the substrate temperature during Ir—Ti formation was 400 ° C., and the substrate temperature during PZT formation was 600 ° C. As the material of the first electrode film 7, a highly conductive metal is preferably used. In the case of using a process of performing high temperature processing in the process of manufacturing the deformable mirror element 1, a material resistant to high temperatures such as Pt, Ir, or an alloy thereof is desirable. As the material of the piezoelectric film 8, a material having a high piezoelectric constant and a large displacement such as PZT or a perovskite oxide containing Pb similar to PZT is preferably used. There are many methods for forming the electrode film and the piezoelectric film 8 such as a sputtering method, a CVD (Chemical Vapor Deposition) method, or a sol-gel method, but there are no particular limitations as long as the technology can form a film.

  After forming the piezoelectric film 8, the surface of the laminated film is mirror-finished. In the embodiment of the present invention, polishing which is machining is performed as the mirror finishing process. The surface of the piezoelectric film is polished to a thickness of about 100 nm to reduce minute irregularities to a predetermined surface roughness. Thereafter, the surface of the piezoelectric film is cleaned by ultrasonic cleaning with pure water. The slurry used for polishing was cerium oxide abrasive having a particle size of 1 μm or less, and the concentration was 15%. Further, ultrasonic cleaning after polishing was performed.

  Next, the second electrode film 9 is formed. Ti was used as a material, and Ti was formed by sputtering. The Ti film thickness was 0.1 μm, and the substrate temperature during Ti formation was room temperature. Since the Ti film thickness is 0.1 μm, the surface roughness after Ti formation is about the same as the surface roughness after PZT polishing.

Next, the reflection mirror film 6 is formed. For the reflection mirror film 6, a reflection mirror film made of SiO ₂ and Ta ₂ O ₅ was used. Since the reflection mirror film 6 of the embodiment of the present invention also has an elastic plate film, the film thickness is set to 0.8 μm in consideration of the characteristics of the reflection mirror film 6. The reflection mirror film 6 has a retardation thickness of λ / 4 and 14 layers were formed by vapor deposition. The material of the reflective mirror film 6 varies depending on the purpose of use of the mirror. For example, a metal such as Au or Ag, or a low refractive index dielectric such as SiO ₂ / Ta ₂ O ₅ / a high refractive index dielectric λ / Four multilayers are preferably used. As with the method for forming the piezoelectric film 8, there are many methods for forming the reflective mirror film 6, for example, a sputtering method or a vapor deposition method, but there is no particular limitation as long as it is a technique capable of forming a film.

  In the embodiment of the present invention, the reflection mirror film has an elastic plate film function. However, as the material of the original elastic plate film, materials such as resin, metal, and ceramic can be used. There are many elastic plate film forming methods, such as sputtering, CVD, or vapor deposition, as in the piezoelectric film 8 forming method, but there is no particular limitation as long as it is a technique capable of forming a film.

  Finally, as shown in FIG. 9, a shape variable portion made of a diaphragm is formed. In the embodiment of the present invention, the shape variable portion 3 having a diameter of 1.5 mm is formed by etching from the back surface of the Si substrate 10 to a desired thickness using a reactive ion etching technique. There are many methods for forming a diaphragm, such as a wet etching method, a dry etching method, and machining, but there is no particular limitation as long as it is a technology capable of forming a diaphragm.

  In the above manufacturing method, variable shape mirror elements having different arithmetic average roughness Ra and arithmetic average inclination Δa were manufactured by changing the polishing time and the substrate load at the time of polishing. Table 1 shows the polishing conditions, the arithmetic average roughness Ra of the reflecting mirror film surface, the average interval between the recesses, and the reflectance. The surface shape used was an atomic force microscope SPI-3700 manufactured by Digital Instrumental. The measurement area of the surface shape is 5 μm × 5 μm, and the measurement resolution is in-plane 0.01 μm and vertical 0.1 nm. The arithmetic average roughness Ra and the average interval between the recesses are average values at 10 arbitrary measurement locations.

  The reflectance used was a spectrophotometer V-550 manufactured by JASCO Corporation. The measurement wavelength λ of the reflectance is 400 nm.

  Although not shown in (Table 1), the arithmetic average roughness Ra of the reflective mirror film formed on the borosilicate glass used as the mirror-polished optical glass substrate is 0.5 nm, and the average interval between the recesses is about 10 nm. Yes, the reflectivity was 99%.

  From the results of (Table 1), when the arithmetic average roughness Ra is 10 nm or more or the average interval between the recesses exceeds 130 nm, the reflectivity is about 80%, which is considerably lower than that of the mirror mirror polished optical glass substrate. I understood. At the same time, when the arithmetic average roughness Ra is 10 nm or less and the average interval between the recesses is 130 nm or less, the reflectivity is 98%, and the reflectivity is equivalent to that of the reflection mirror film of the mirror-polished optical glass substrate. I understood.

  Further, even in the measurement of wavelengths in the visible light region exceeding 400 nm, if the arithmetic average roughness Ra is 10 nm or less and the average interval between the recesses is 130 nm or less, the optical glass substrate is mirror-polished with a reflectance of 98%. It was confirmed to have a reflectance equivalent to that of the reflective mirror film.

  The following can be considered as the reason for the above results.

  FIG. 13 shows the surface shape of the reflection mirror film obtained by an atomic force microscope when the arithmetic average roughness Ra is 8 nm and the average interval between the recesses is 100 nm. In FIG. 13, even if the surface is polished, the surface is still very rough when viewed strictly. The arithmetic average roughness Ra is 10 times or more that of the optical glass substrate, but the reflectance is the same as that of the optical glass substrate. The reason for this is that although the surface shape of the reflective mirror film 6 is an uneven shape reflecting the columnar structure peculiar to the thin film, the unevenness interval is smaller than the wavelength λ (400 to 800 nm) of light in the visible light region. It is conceivable that the light is totally reflected without entering the uneven gap due to the diffraction limit. When the reflectance is compared with the reflection mirror film 6 of the mirror-polished optical glass substrate, the arithmetic average roughness Ra of the surface shape of the reflection mirror film 6 formed on the laminated thin film is 10 nm or less and the average interval between the recesses Is 130 nm or less, it is conceivable that the reflectance is equivalent to that of the reflection mirror film 6 of the mirror-polished optical glass substrate.

  According to the variable shape mirror element 1 of the embodiment of the present invention, the reflection mirror film 6 formed on the laminated thin film also has a high reflection equivalent to the case where the reflection mirror film 6 is formed on the mirror-polished substrate. It has been clarified that the deformable mirror element 1 having a ratio can be realized. Moreover, according to the manufacturing method of the deformable mirror element 1 of the embodiment of the present invention, the deformable mirror element 1 having a high reflectance equivalent to that when the reflecting mirror film 6 is formed on the mirror-polished substrate is provided. It became clear that it could be produced stably.

  On the other hand, when there is a surface shape adjustment step, a surface inspection step is also required. Measurement of the surface shape with an atomic force microscope takes time and requires skill, so it is not suitable for the inspection process. The correlation between the surface shape of the thin film and the measured value of the reflectance is obtained in advance, and the result is fed back to the film forming process of the reflecting mirror film 6, whereby the simple variable shape mirror element 1 can be manufactured stably.

  In the embodiment of the present invention, polishing which is machining is used as the mirroring process, but the means capable of mirroring is not limited. For example, even if spin coating is applied to a thickness of about 0.01 to 1 μm with a thermosetting polyimide resin that is liquid at room temperature after forming the second electrode, it can be mirror-finished. That is, if a liquid is applied to a very uneven surface, a liquid resin enters the recess, the surface is smoothed, and the surface is flattened to achieve a mirror surface. Further, similar curing can be obtained even when an ultraviolet curable resin is used.

  In addition, as a surface shape adjusting step, a silicate glass containing phosphorus or boron as an impurity is formed to have a surface roughness thickness, for example, a thickness of about 50 nm, by a vapor phase growth method such as a CVD method, and then heat treatment is performed. Thus, even if the flattening process is performed, mirroring is achieved.

  According to the deformable mirror element of the present invention, it is possible to provide a deformable mirror element having a large shape variable amount at a low voltage. Therefore, for example, a video projector, a digital camera, or an optical disc apparatus having an optical system including the variable optical element. It can also be applied to applications such as pickup parts.

The perspective view seen from the surface of the form variable mirror element of an embodiment of the invention The perspective view seen from the back surface of the form variable mirror element of embodiment of this invention Sectional drawing of the principal part of the variable shape mirror element of embodiment of this invention Sectional drawing of a variable shape mirror element which shows the manufacturing process of the variable shape mirror element of embodiment of this invention Sectional drawing of a variable shape mirror element which shows the manufacturing process of the variable shape mirror element of embodiment of this invention Sectional drawing of a variable shape mirror element which shows the manufacturing process of the variable shape mirror element of embodiment of this invention Sectional drawing of a variable shape mirror element which shows the manufacturing process of the variable shape mirror element of embodiment of this invention Sectional drawing of a variable shape mirror element which shows the manufacturing process of the variable shape mirror element of embodiment of this invention Sectional drawing of a variable shape mirror element which shows the manufacturing process of the variable shape mirror element of embodiment of this invention The figure which shows operation | movement of the variable shape mirror element of embodiment of this invention The figure which shows operation | movement of the variable shape mirror element of embodiment of this invention The figure which shows operation | movement of the variable shape mirror element of embodiment of this invention The figure which shows the surface shape of the reflective mirror film | membrane of embodiment of this invention by atomic force microscope The figure which shows the average space | interval of the recessed part of embodiment of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shape variable mirror element 2 Substrate 3 Shape variable part 4 Electrode pad 5 Piezoelectric action part 6 Reflection mirror film 7 1st electrode film 8 Piezoelectric film 9 2nd electrode film 10 Si substrate

Claims (5)

A shape variable section including at least a piezoelectric film, a first electrode film and a second electrode film for supplying a voltage to the piezoelectric film, a laminated thin film made of a reflective mirror film provided on the piezoelectric film, and the shape variable A variable shape mirror element used in a visible light region having a substrate for supporting a portion, wherein the arithmetic mean roughness Ra of the surface of the reflecting mirror film is 10 nm or less, and the average of the recesses on the surface of the reflecting mirror film A variable shape mirror element characterized in that the interval is 130 nm or less. A shape variable section including at least a piezoelectric film, a first electrode film and a second electrode film for supplying a voltage to the piezoelectric film, a laminated thin film made of a reflective mirror film provided on the piezoelectric film, and the shape variable A variable shape mirror element for use in a visible light region provided with a substrate for supporting a portion, wherein the reflective mirror film surface has an arithmetic average roughness Ra of 10 nm or less, and the reflective mirror film A surface shape adjusting step for adjusting the surface shape so that an average interval between the concave portions on the surface is 130 nm or less, and mechanical polishing is performed on the surface on which the reflection mirror film is formed as the surface shape adjusting step. A method for manufacturing a deformable mirror element, characterized in that: 3. The method of manufacturing a deformable mirror element according to claim 2, wherein as the surface shape adjustment step, a liquid curable resin is applied to a surface on which the reflection mirror film is formed at room temperature. 3. The variable shape mirror element according to claim 2, wherein, as the surface shape adjusting step, a silicate glass containing phosphorus or boron as an impurity is formed on the surface on which the reflection mirror film is formed and heat treatment is performed. Method. 5. The method for manufacturing a variable shape mirror element according to claim 2, wherein the surface shape adjustment step is evaluated by measuring a reflectance of the reflecting mirror film surface. 6.

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