JP2006113108A - Thin film element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film element used as a variable shape mirror element which is sufficiently miniaturized as an optical pickup component by integrating a variable shape thin film element whose shape is freely controllable and a mirror and simplifying the structure, the element in which a large displacement is available at low voltage, and to provide a method of manufacturing the thin film element. <P>SOLUTION: The thin film element comprises a diaphragm part having a curved face composed of at least one layer and a substrate 1 which supports the diaphragm part. The thin film element is characterized by that a cross section at an arbitrary position of the diaphragm part has no inflexion point. Further, the thin film element is characterized by that the shape of the diaphragm part is controlled by forming the thin film after the substrate 1 is machined beforehand into a desired shape. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup for an optical apparatus or an optical disk apparatus, and more particularly to a thin film element used for a wavefront aberration correction mirror and a method for manufacturing the same.

  Conventionally, various variable shape mirrors have been devised as variable focus and aberration correction means in optical devices such as microscopes and cameras, but in recent years, the demand has increased with the development of optical disc technology.

  As an information recording medium using an optical disk, there are a compact disk (CD) and a digital video disk (DVD). 2. Description of the Related Art In recent years, an optical disk device is generally configured to read and write a plurality of recording media with the same optical disk device, and a technique for further downsizing the optical disk device is required as compared with conventional products. In particular, there is an increasing need for a compact and thin optical disk device for a notebook PC. In addition, with the development of multimedia technology, the demand for storage or recording capacity on an optical disc tends to increase year by year, (1) using a blue laser with a short wavelength, (2) numerical aperture (NA) of an objective lens. ) Is increased, the recording density is improved, and (3) the recording area is increased by using a plurality of recording layers in the medium, so that the capacity is increased.

  The optical disk device is provided with a laser light source, an optical pickup, a light receiving element, and the like. The laser beam emitted from the laser light source is condensed on the data surface of the optical disk through the optical pickup, reflected, and then received by the light receiving element, and the information recorded on the optical disk is read or the information is written on the optical disk. . At this time, the wavefront of the beam is subjected to aberrations by various optical components and optical disks, so that aberration correction is indispensable for reading and writing information correctly. In particular, with respect to dynamic aberrations that occur during rotation of an optical disk or when different layers are read, fixed correction means using lenses and diffractive optical elements that constitute an optical pickup are inappropriate, and dynamic correction by an actuator is not possible. It is essential.

  Conventionally, a method for correcting the aberration as described above has been devised. For example, in the method described in Patent Document 1, spherical aberration is corrected by moving a correction lens by an actuator. However, this method has a large actuator portion, requires an extra lens, and is unsuitable for optical pickups that are required to be miniaturized, such as PC applications.

  In the method described in (Patent Document 2), a large number of minute actuators are arranged on the back surface of the reflecting surface, and the aberration is corrected by driving these actuators. However, this method is also difficult to reduce in size because of its complicated structure and wiring.

Therefore, in order to achieve downsizing to the extent that it can be used as a part of an optical pickup, it is desirable to use an element such as a unimorph type using a piezoelectric element in which a mirror and an actuator are integrated and the structure is simple. . However, since such an element has a thin film laminated structure, the influence of the internal stress of the thin film is large, and it is difficult to control the initial shape and deformation shape of the mirror and to obtain a large displacement at a low voltage. There is. In addition, it is difficult to obtain a large curvature by deformation depending on the film stress, and there is a problem that the application is limited.
JP-A-10-241201 JP-A-5-333274

  The present invention is a shape variable mirror which is sufficiently small as a component of an optical pickup by integrating a shape-variable thin film element and a mirror whose shape can be freely controlled, and simplifying the structure, and can obtain a large displacement at a low voltage. It aims at providing the thin film element used as an element, and its manufacturing method.

  In order to solve the above-described problems, the present invention provides a thin film element including a diaphragm portion having a curved surface formed of at least one layer of thin film and a substrate supporting the diaphragm portion, at an arbitrary position of the diaphragm portion. The cross-sectional shape has no inflection point. In the method of manufacturing a thin film element, the shape of the diaphragm portion is controlled by forming a thin film after processing the substrate into a desired shape in advance.

  According to the present invention, since the shape of the thin film element does not depend only on the film stress, the shape can be easily controlled, and a shape that is difficult to realize by deformation depending only on the film stress such as a spherical surface having a large curvature or an asymmetric shape. Can also be controlled. Among them, a large displacement can be obtained at a low voltage by having a shape having no inflection point in a cross section at an arbitrary position of the diaphragm portion.

  According to a first aspect of the present invention, there is provided a thin film element including a diaphragm portion having a curved surface composed of at least one thin film and a substrate that supports the diaphragm portion, and a cross-sectional shape at an arbitrary position of the diaphragm portion is It is a thin film element characterized by having no inflection point, and it can be used as an element for correcting aberrations in a wide area within the diaphragm portion by having a structure without an inflection point. Piezoelectric, thermal, electrostatic Even when the thin film element is displaced by, for example, a large displacement can be obtained as compared with a structure having an inflection point.

  Here, the inflection point is defined as Y = f (x), which represents the cross-sectional shape, and f ″ (x), which is the second derivative of f (x), is f ″ (x) = 0. It is defined by a point on Y = f (x) having a value of x as follows. In the perspective view when the thin film element according to the present invention shown in FIG. 1 is viewed from above, in the case of the shape as shown in FIG. 1A, the cross-sectional shape of the thin film element is all represented by a curve. However, in the case of the shape as shown in FIG. 1B, the cross-sectional shape of the thin film element has a portion represented by a curve and a portion represented by a straight line. In the present invention, even if such a shape having a cross section represented by a straight line exists, the diaphragm portion may have a curved surface and the cross section at an arbitrary position may be represented by a curve.

  According to a second aspect of the present invention, in the thin film element including a diaphragm portion including at least one layer of thin film and a substrate supporting the diaphragm portion, the total film thickness of the diaphragm portion is 100 μm or less. The thin film element is characterized in that at least a part of a cross section of the film is circular and the circular curvature radius is 5 mm or less. By using a thin film element having a small curvature radius, other parts such as lenses can be obtained. Without using it, it is possible to produce a variable focus mirror with space saving and low cost.

  A third invention of the present application is a thin film element according to the first or second invention of the present application, characterized in that at least a part of the diaphragm portion is movable, such as piezoelectric, heat, electrostatic force, atmospheric pressure, acceleration force, etc. By moving the diaphragm portion by applying an external force, a thin film element that can be used in various applications such as a microactuator, a pressure sensor, and an acceleration sensor can be obtained.

  According to a fourth invention of the present application, in the third invention of the present application, the diaphragm portion is constituted by a piezoelectric body and a first electrode film and a second electrode film positioned so as to sandwich the piezoelectric body. According to the above-described configuration, the thin film element can be changed in shape while saving space.

  A fifth invention of the present application is a thin film element according to any one of the first to fourth inventions of the present application, wherein a thin film having at least a function as a mirror is formed. By forming such a mirror, a thin film element that is sufficiently small as an optical pickup component can be manufactured.

  According to a sixth invention of the present application, in any one of the first to fifth inventions of the present application, the shape of the thin film element is controlled by film stress, film thickness, film thickness distribution, and film division of each film. It is a thin film element, and fine shape control of the thin film element can be performed. In particular, in the case of a variable shape element using a piezoelectric element, it is possible to finely control the shape at the time of voltage application by dividing the electrode and providing a voltage application region and a non-voltage application region.

  A seventh invention of the present application is the thin film element according to any one of the first to sixth inventions of the present application, wherein the substrate is a single layer or a multilayer structure containing at least Si, and using Si, Since an inexpensive material with stable material properties can be obtained and a processing method used in a semiconductor process can be applied, fine processing is possible.

  According to an eighth aspect of the present invention, in the method for manufacturing a thin film element according to any one of the first to seventh aspects of the present invention, the shape of the diaphragm portion is changed by forming a thin film after processing the substrate into a desired shape in advance. A method of manufacturing a thin film element characterized by controlling, and by previously processing a substrate into a desired shape, the influence of film stress, which is usually dominant as a factor determining the shape of the thin film element, can be reduced. . In addition, although it is very difficult to give a large curvature by the method of controlling the initial shape by film stress or the like, a thin film element having a large curvature can be easily manufactured according to the present invention.

  A ninth invention of the present application is a method of manufacturing a thin film element according to the eighth invention of the present application, wherein the substrate is processed using a wet etching method. By performing anisotropic etching utilizing crystal anisotropy, it can be processed into a desired shape. There is also an advantage that it can be manufactured relatively easily, such as not requiring a large-scale device.

  A tenth invention of the present application is a method of manufacturing a thin film element according to the eighth invention of the present application, wherein the substrate is processed using a dry etching method, and isotropic etching using RIE. The degree of freedom of the processing method such as anisotropic etching by the ICP method is high, and fine processing can be performed. Compared with the wet etching method, anisotropic etching is possible without using crystal anisotropy, and there is an advantage that process reproducibility is good and management is easy. In consideration of the substrate material, shape accuracy, etc., it is possible to improve the degree of shape freedom and process efficiency by using it in combination with the wet etching method.

  An eleventh invention of the present application is the method of manufacturing a thin film element according to the ninth or tenth invention of the present application, wherein the substrate is processed using a gray scale resist, and has a film thickness distribution. By using the gray scale resist and etching the resist while etching the resist, the shape of the resist can be transferred to the substrate. Depending on the etching selectivity between the resist and the substrate material, it is possible to obtain a shape that expands and contracts in the Z-axis direction (height direction) from the resist shape, and processing with high accuracy and good reproducibility is possible.

  A twelfth aspect of the present invention is a method for manufacturing a thin film element according to the ninth or tenth aspect of the present invention, wherein the processing of the substrate is performed using a doping method. In this method, the characteristics are changed, and only a selectively doped portion or, on the contrary, only an undoped portion is etched by a wet or dry etching method. There are various doping methods such as ion implantation and plasma doping, and isotropic and anisotropy can be freely controlled, so that fine processing can be performed.

  A thirteenth aspect of the present invention is a method for manufacturing a thin film element according to the eighth aspect of the present invention, wherein the substrate is processed using a laser, the processing shape is free, and the processing is accurate. It can be performed.

  A fourteenth invention of the present application is the method of manufacturing a thin film element according to the eighth invention of the present application, wherein the processing of the substrate is performed by mechanical grinding and polishing, the processing shape is free, and the processing time is Can be processed with high accuracy.

  A fifteenth invention of the present application is the method of manufacturing a thin film element according to the eighth invention of the present application, wherein the processing of the substrate is performed by press working using a mold, and the reproducibility is good with high accuracy. It is a processing method that can be processed and is extremely productive.

(Embodiment)
Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. It should be noted that the film thickness, substrate thickness, deformation amount, and other dimensions in the drawings are different from the actual dimensions in order to facilitate understanding.

  FIG. 1 is a perspective view of a thin film element according to an embodiment of the present invention as viewed from above. In this thin film element, a first electrode 2a, a piezoelectric film 3, a second electrode 2b, and a reflective film 4 are sequentially laminated on a substrate 1.

  Hereinafter, the manufacturing method of the thin film element of the present invention will be described with reference to FIG. 2 which is a cross-sectional view taken along the line AB of FIG.

  First, the substrate 1 that is flat on both sides as shown in FIG. 2A is processed to form a recess as shown in FIG. The material of the substrate 1 is not particularly limited. However, when Si or a multilayer substrate containing Si is used, processing can be performed using a semiconductor process, so that processing with high accuracy is possible. The processing shape is not limited to a circle, but a plane shape such as an ellipse, a triangle, a quadrangle, other polygons, or a star as shown in FIG. Any shape such as a shape, a triangle, a quadrangle, and other polygons may be used.

  In the processing method, a desired shape is processed using a milling machine, and polishing is performed with a grindstone with a rotating shaft in order to smooth the ground surface. There are many devices that perform such grinding and polishing, but the processing method is an example, and the processing device to be used is not particularly limited.

As another means for processing a substrate, there is a method using a series of semiconductor processes such as resist coating, resist patterning, and etching. Common etching methods include wet etching and dry etching, and isotropic or anisotropic etching is possible by selecting materials and methods. However, these combinations and free of shadow effects can be used. Can be processed into various shapes. However, this method is very difficult to process with high reproducibility in the case of a complicated curved surface and a shape that requires accuracy, and therefore it is preferable to combine it with a gray scale resist. A grayscale resist is a multiple exposure that uses a binary mask multiple times after resist coating, a grayscale lithography system that can change the exposure intensity, and the resist is exposed to grayscale. Is a resist film having a controlled film thickness distribution by exposing the resist using a gray scale mask that changes discretely or virtually continuously. If etching is performed after processing the resist shape into a desired shape in this manner, the resist shape is transferred to the substrate, and processing with good reproducibility can be performed relatively easily.

  In addition to this, the doping method is used to change only part of the material characteristics, and then etch only the part where the material characteristics have been changed by wet etching or dry etching. There is also a method in which plastic deformation is performed by a press using.

  Next, a film for forming a diaphragm is formed. There are no particular limitations on the material, shape, film thickness, etc. of the film, but here, as the variable shape thin film mirror element, the first electrode 2a, the piezoelectric film 3, the second electrode 2b, and the reflective film 4 are formed as shown in FIG. Films are formed in order. As a film forming method, a vacuum process such as vapor deposition, sputtering, or CVD, an electrochemical reaction such as electrodeposition or plating, application by dropping, spin coating, or the like is used.

  Finally, the back surface of the substrate 1 is processed as shown in FIG. The processing method is performed using wet etching, dry etching, laser processing, mechanical grinding, polishing, or the like. The machining shape is not limited to a circle, and may be any shape such as an ellipse, a triangle, a quadrangle, other polygons, and a star.

  The initial shape of the variable shape thin film mirror element thus fabricated differs greatly depending on the processed shape of the substrate, the structure of the film forming the diaphragm, etc., but here the processed shape of the substrate 1 is convex downward for easy understanding. A spherical shape and film will be described as a uniform two-layer film with reference to FIG.

  In the case of the structure as shown in FIG. 5, the diaphragm can be roughly divided into three shapes as shown in FIG. In FIG. 6, 7 is a line indicating the processed shape of the Si substrate, and 8 is a line indicating the shape of the diaphragm (at 0 V).

  In FIG. 5, when the moment generated by the film stress of the first film 5 and the second film 6 is 0 or upward, a shape very close to a spherical surface having no inflection point as shown in FIG. Become. When the moment generated by the film stress of the first film 5 and the second film 6 is in the downward direction, the shape can be made to have no inflection point, but the outer periphery as shown in FIG. It can also be made into the shape where an inflection point exists in the side. In this case, the inner peripheral side has a shape very close to a spherical surface. When the first film 5 is compressive stress and the second film 6 is tensile stress, and the difference in film stress between the first film 5 and the second film 6 is large, the first film 5 protrudes upward as shown in FIG. In addition, the shape near the inner periphery is crushed.

  FIG. 7 shows the result of analyzing the above-described shape by simulation. FIG. 7A shows the analysis results corresponding to FIG. 6A, FIG. 7B the analysis results corresponding to FIG. 6B, and FIG. 7C the analysis results corresponding to FIG. Thus, it can be seen that various shapes of diaphragms can be created by adjusting the film stress. Although only the film stress has been described here, the degree of freedom of the diaphragm shape is further increased by controlling the film thickness, film division, and film thickness distribution.

  In particular, when the diaphragm is driven using a piezoelectric element, the shape at the time of voltage application can be controlled by dividing the electrode.

FIG. 8A shows the simulation results of the diaphragm shape (at 0V) when the substrate is a plane and FIG. 8B shows the displacement shape of the diaphragm when a voltage is applied. According to this, the amount of displacement when the same voltage is applied is not less than 100 times larger when the substrate shape is spherical than when the substrate shape is flat, and not only the effect that the shape can be controlled by the present invention but also the displacement is enlarged. It can be seen that there is also an effect that it is possible.

  FIG. 9 shows a basic configuration example of the optical pickup. The light beam emitted from the laser light source 9 passes through the beam splitter 11, is reflected by the variable shape mirror element 12 that also serves as a rising mirror, passes through the objective lens 14, and forms an image on the optical disk 15. The reflected light is reflected by the variable shape mirror element 12, reflected by the beam splitter 11, and converted into an electric signal by the light receiving element 10. In this configuration, the light beam enters the deformable mirror element 12 by 45 degrees. The deformable mirror element 12 is supplied with a control voltage from the driver 13. The driver 13 determines the value of the control voltage based on a signal from at least one light receiving means such as a light receiving means (not shown) for detecting the spherical aberration and the light receiving element 10, and the variable shape mirror element. Twelve curvatures can be varied. In particular, the above configuration is particularly useful when the light emitted from the laser light source 9 is blue to blue-violet short wavelength light.

  FIG. 10 shows a configuration of an optical pickup in another form. The light beam emitted from the laser light source 9 is transmitted through the polarization beam splitter 17, reflected by the rising mirror 18, and condensed on the optical disk 15 through the quarter-wave plate 16 and the objective lens 14. Thereafter, the light reflected from the optical disk changes its polarization state by 90 degrees, passes through the rising mirror 18, is reflected by the polarization beam splitter 17, passes through the other quarter-wave plate 16, and is reflected by the variable shape mirror element 12. Then, after passing through the quarter-wave plate 16 again to change the polarization state by 90 degrees, it passes through the polarizing beam splitter 17 and is converted into an electric signal in the light receiving element 10. The deformable mirror element 12 is supplied with a control voltage from the driver 13. The driver 13 determines the value of the control voltage based on a signal from at least one light receiving means such as a light receiving means (not shown) for detecting the spherical aberration and the light receiving element 10, and the variable shape mirror element. Twelve curvatures can be varied. In particular, the above configuration is particularly useful when the light emitted from the laser light source 9 is blue to blue-violet short wavelength light.

  According to the present invention, focus of an optical device such as a microscope, a camera, etc., and an optical pickup used for a CD / DVD drive recorder, decoder, CD / DVD drive, etc., in particular, an optical pickup using a blue laser and correction of aberrations can be performed. It can be used for necessary optical devices.

  In addition, according to the present invention, since a large displacement can be obtained with low energy input, it can be used as a thin film microactuator such as a printer head other than an optical device, and by incorporating a piezoelectric element and an electrode as constituent materials, It can also be used as a highly sensitive pressure sensor or acceleration sensor using the positive piezoelectric effect.

The perspective view which shows the thin film element in one embodiment of this invention Sectional drawing of the thin film element in one embodiment of this invention The top view which shows the board | substrate in one embodiment of this invention Sectional drawing of the board | substrate in one embodiment of this invention Sectional drawing of the thin film element in one embodiment of this invention The figure which shows the shape of the thin film element in one embodiment of this invention Graph of simulation showing shape of thin film element in one embodiment of the present invention Graph of simulation showing displacement shape of variable shape thin film element in one embodiment of the present invention The figure which shows the optical path of the optical pick-up by this invention The figure which shows the optical path of the optical pick-up in another form by this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2a 1st electrode 2b 2nd electrode 3 Piezoelectric film 4 Reflective film 5 1st film | membrane 6 2nd film | membrane 7 The line | wire which shows the process shape of Si substrate 8 The line | wire which shows the shape (at 0V) of a diaphragm 9 Laser light source 10 Light receiving element DESCRIPTION OF SYMBOLS 11 Beam splitter 12 Shape variable mirror element 13 Driver 14 Objective lens 15 Optical disk 16 1/4 wavelength plate 17 Polarizing beam splitter 18 Standing mirror

Claims (15)

In a thin film element composed of a diaphragm portion having a curved surface composed of at least one thin film and a substrate supporting the diaphragm portion, the cross-sectional shape at an arbitrary position of the diaphragm portion has no inflection point. A thin film element characterized. In a thin film element composed of a diaphragm portion composed of at least one thin film and a substrate supporting the diaphragm portion, the total thickness of the diaphragm portion is 100 μm or less, and at least a part of the cross section of the diaphragm portion is a circle. A thin film element having a shape and a circular radius of curvature of 5 mm or less. The thin film element according to claim 1, wherein at least a part of the diaphragm portion is movable. 4. The thin film element according to claim 3, wherein the diaphragm portion includes a piezoelectric body and a first electrode film and a second electrode film positioned so as to sandwich the piezoelectric body. 5. The thin film element according to claim 1, wherein a thin film having at least a function as a mirror is formed. 6. The thin film element according to claim 1, wherein the shape is controlled by film stress, film thickness, film thickness distribution, and film division of each film. 7. The thin film element according to claim 1, wherein the substrate has a single layer or multilayer structure containing at least Si. 8. The method of manufacturing a thin film element according to claim 1, wherein the shape of the diaphragm portion is controlled by forming the thin film after processing the substrate into a desired shape in advance. Device manufacturing method. The method of manufacturing a thin film element according to claim 8, wherein the substrate is processed using a wet etching method. The method of manufacturing a thin film element according to claim 8, wherein the substrate is processed using a dry etching method. The method of manufacturing a thin film element according to claim 9 or 10, wherein the substrate is processed using a gray scale resist. The method of manufacturing a thin film element according to claim 9 or 10, wherein the substrate is processed using a doping method. The method of manufacturing a thin film element according to claim 8, wherein the substrate is processed using a laser. 9. The method of manufacturing a thin film element according to claim 8, wherein the substrate is processed by mechanical grinding or polishing. The method of manufacturing a thin film element according to claim 8, wherein the substrate is processed by pressing using a mold.

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