JP2019216165A - Piezoelectric device, piezoelectric actuator, and manufacturing method of piezoelectric device - Google Patents

Abstract

To provide a piezoelectric device in which there is no defective part in a piezoelectric substance, a manufacturing method of the same, and a piezoelectric actuator.SOLUTION: A piezoelectric device 26 comprises: a lower electrode 27; an upper electrode 28; a piezoelectric substance 29 nipped between the lower electrode 27 and the upper electrode 28; and an embedded material 30 formed by an insulation material without piezoelectricity, and of which the upper electrode 28 side is blocked with the upper electrode 28 to be embedded into the piezoelectric substance 29. After the formation of a piezoelectric film 35 as the piezoelectric substance 29, a particle 37 embedded in the piezoelectric film 35 in a state where one part is exposed is replaced to the embedded material 30 before the formation of an upper electrode film 36 as the upper electrode 28.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a piezoelectric element, a piezoelectric actuator including the piezoelectric element, and a method for manufacturing the piezoelectric element.

  In recent years, in systems having a fine structure such as MEMS (Micro Electro Mechanical Systems), the need for sensors, actuators, and the like constituted by piezoelectric elements has been increasing. Among them, piezoelectric actuators have been receiving special attention because they are small, can consume low power, and can generate a large driving force.

  As a method of forming a piezoelectric film constituting a piezoelectric actuator, there are a sputtering method, an ion plating method, a metal organic chemical vapor deposition (MOCVD) method, a pulse laser deposition (PLD) method, a molecular beam epitaxy (MBE) method, a CSD ( Chemical Solution Deposition method, sol-gel method and the like are known.

  The piezoelectric films formed by these film forming methods include film defects such as voids, surface dents and protrusions, and minute cracks, although the degree is different. Since such a film defect is generated by the influence of minute dust and contamination from the film formation atmosphere, and the unevenness of the substrate, it is difficult to completely eliminate the film defect.

  Further, in order to increase the output of the piezoelectric actuator, it is necessary to increase the thickness of the piezoelectric film. However, this requires a long time to form the piezoelectric film, increases the cost, and causes peeling and cracks due to stress during the film formation. Therefore, the preferable film thickness of the piezoelectric film is 5 μm or less.

  When manufacturing a piezoelectric actuator, first, a lower electrode film is formed on an SOI (Silicon On Insulator) wafer (SOI substrate). Next, a piezoelectric film made of a piezoelectric material is formed on the lower electrode film. At this time, foreign substances such as particles embedded in the piezoelectric film and partially exposed on the surface are generated.

  Next, an upper electrode film is formed on the piezoelectric film. At this time, since it is difficult to form the upper electrode film while avoiding the foreign matter at random positions on the piezoelectric film, the upper electrode film is also formed on the foreign matter. Therefore, in the structure obtained by forming the upper electrode film, the foreign matter of the piezoelectric film is sandwiched between the upper electrode film and the lower electrode film.

  Further, an insulating film, a lead-out wiring, and the like are formed on the upper electrode film as necessary, the SOI wafer at a portion that becomes a movable portion of the piezoelectric actuator is removed, and a wiring for supplying power to the piezoelectric actuator is formed. You. Thus, a piezoelectric actuator in which the lower electrode, the piezoelectric body, and the upper electrode are respectively formed by the lower electrode film, the piezoelectric film, and the upper electrode film is formed.

  According to this method of manufacturing a piezoelectric actuator, if any measures for removing the foreign matter are not performed, the foreign matter remains even in the completed piezoelectric actuator. Then, the foreign matter forms a defective portion having a low dielectric strength in the piezoelectric body between the upper electrode and the lower electrode. For this reason, when the piezoelectric actuator is driven, a dielectric breakdown may occur in the defective portion due to a drive voltage applied to the defective portion having a low dielectric strength. This causes an increase in labor for selecting only non-defective products and a decrease in yield.

  Therefore, conventionally, various methods have been proposed to prevent the occurrence of a defective portion in a piezoelectric film or the like. For example, in Patent Document 1, after forming each layer in a piezoelectric element manufacturing process, scrub cleaning using pure water or water containing gas, a brush, or the like is performed to prevent foreign substances and the like from being included in the piezoelectric film. It has been proposed to.

  Further, Patent Document 2 proposes that, when a dielectric thin film for a thin film capacitor is formed, foreign matter on the surface of the dielectric thin film that causes a short circuit or an insufficient withstand voltage is removed by brushing cleaning or the like. I have.

  Further, Patent Document 3 proposes that a film forming process is divided into, for example, two times, and a cleaning process for removing contaminating foreign matter is incorporated during the film forming process to form a piezoelectric thin film layer. In the piezoelectric thin film layer, in the region from which the foreign matter has been removed, the crystal grain boundary becomes discontinuous across the discontinuous region, so that the leak path is interrupted, and the withstand voltage characteristics are improved.

  Further, in Patent Document 4, when forming a piezoelectric film serving as a piezoelectric body of a piezoelectric element, after forming a first piezoelectric layer, holes formed in the first piezoelectric layer are buried thereon. It has been proposed to form a second piezoelectric layer made of an electrically insulating oxide. According to this, formation of a leak path in the piezoelectric film and occurrence of an electric field concentration point can be suppressed.

JP 2006-173499 A JP-A-11-154734 JP 2008-187092 A JP 2008-41921 A

  According to the methods described in Patent Documents 1 to 3, it is possible to remove foreign substances adhering to the surface of each layer of the piezoelectric element after film formation. However, although a part is exposed, it is not possible to remove a particle-like foreign matter which is mostly embedded in a piezoelectric film or a dielectric thin film.

  Further, according to the method of Patent Document 4, since the piezoelectric layer is composed of the second piezoelectric layer that fills the holes generated in the first piezoelectric layer, an interface is generated in the piezoelectric layer. In addition, pores generated in the first piezoelectric layer can be removed, but most of them are particle-like foreign matter embedded in the piezoelectric film or the dielectric thin film in the piezoelectric layer although a part is exposed. It is not possible.

  Therefore, even if the methods of Patent Documents 1 to 4 are applied to the manufacture of a piezoelectric element of a piezoelectric actuator, a defect due to the particles of the piezoelectric film occurs during the manufacture, and the defect is generated in the piezoelectric body of the manufactured piezoelectric actuator. May also remain.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric element in which the above-described defect due to particles does not exist in a piezoelectric body, a method of manufacturing the same, and a piezoelectric actuator in view of the problems of the related art.

The piezoelectric element according to the first invention includes:
A lower electrode;
An upper electrode;
A piezoelectric body sandwiched between the lower electrode and the upper electrode,
And an embedded material made of an insulator having no piezoelectricity and embedded in the piezoelectric body in a state where the upper electrode side is closed by the upper electrode.

  The piezoelectric element according to the first aspect of the invention is a particle that has appeared during the formation of the piezoelectric film serving as the piezoelectric body. The particle is partially exposed but the other portion is embedded in the piezoelectric film. By replacing the buried material with a buried material, it is possible to provide a piezoelectric element in which a defective portion having a low dielectric strength due to the particles is eliminated as much as possible.

  A piezoelectric element according to a second invention is characterized in that, in the first invention, the embedded material is unevenly distributed on the upper electrode side of the piezoelectric body.

  The above-mentioned particles are exposed to the upper electrode side when the above-described piezoelectric film is formed, and thus are unevenly distributed to the upper electrode side of the piezoelectric film. For this reason, in the piezoelectric element obtained by replacing the particles with the embedded material, the embedded material is unevenly distributed on the upper electrode side of the piezoelectric body. According to such a piezoelectric element, a defective portion having a low dielectric strength due to the particles can be eliminated as much as possible.

  A piezoelectric actuator according to a third aspect is provided with the piezoelectric element according to the first or second aspect.

  According to the third aspect of the present invention, since the defective portion due to the particles is eliminated as much as possible in the piezoelectric element, it is possible to provide a piezoelectric actuator in which dielectric breakdown due to the defective portion is prevented.

The method for manufacturing a piezoelectric element according to the fourth invention is as follows.
Forming a lower electrode film, a piezoelectric film, and an upper electrode film on the substrate in this order;
After the formation of the piezoelectric film, before the formation of the upper electrode film, a replacement step of replacing particles embedded in the piezoelectric film in a partially exposed state with an embedded material made of a non-piezoelectric insulator. It is characterized by having.

  According to the fourth aspect, the particles embedded in the piezoelectric film in a partially exposed state are replaced with the above-mentioned embedded material, so that a defective portion having a low dielectric strength due to the particles is generated in the piezoelectric film of the piezoelectric element. Can be prevented.

The method for manufacturing a piezoelectric element according to the fifth invention is the method according to the fourth invention, wherein
The replacing step includes:
A particle removing step of removing the particles by polishing the piezoelectric film,
An insulating film forming step of forming an insulating film having no piezoelectricity on the piezoelectric film from which the particles have been removed,
An insulating film removing step of polishing the insulating film formed on the piezoelectric film to remove the insulating film while leaving a portion filled in a hole generated by the removal of the particles. Features.

  According to the fifth aspect, particles embedded in the piezoelectric film in a partially exposed state are reliably and easily replaced with the above-described embedded material by the particle removing step, the insulating film forming step, and the insulating film removing step. be able to. In addition, since the insulating film is removed by the insulating film removing step while leaving the portion filled in the hole where the particles are present, the upper electrode can be formed without any trouble thereafter.

  A method for manufacturing a piezoelectric element according to a sixth aspect is characterized in that, in the fifth aspect, the polishing in the particle removing step is performed by chemical mechanical polishing.

  According to the sixth aspect, particles can be removed while improving the polishing speed and quality by the synergistic effect of chemical polishing and mechanical polishing.

  A method for manufacturing a piezoelectric element according to a seventh invention is characterized in that, in any one of the fourth to sixth inventions, the insulating film having no piezoelectricity has tetraethoxysilane as a main component. .

  According to the seventh aspect, since tetraethoxysilane has a high fluidity, a hole formed by removing particles can be filled as much as possible.

It is a front view of the optical deflector concerning one embodiment of the present invention. FIG. 2 is a sectional view of a cantilever type piezoelectric actuator constituting a cantilever of the optical deflector of FIG. 1. 3A to 3E are cross-sectional views illustrating the steps of manufacturing a piezoelectric element according to an embodiment of the present invention. 4A to 4D are cross-sectional views showing a part of the manufacturing process of FIG. 3 in more detail. 5 is an oblique micrograph of an example of particles generated on a piezoelectric film during a manufacturing process. 6 is a photomicrograph showing a hole formed after the particles of FIG. 5 have been removed. 9 is a table showing results of a reliability test of an optical deflector using a piezoelectric element according to an embodiment of the present invention, in comparison with a comparative example.

(Configuration of optical deflector)
FIG. 1 shows an optical deflector configured using a piezoelectric actuator according to one embodiment of the present invention. As shown in FIG. 1, the optical deflector 1 is manufactured as a MEMS. The side of the flat optical deflector 1 on which the reflection surface of the mirror unit 2 is visible is referred to as “front”, and the opposite side is referred to as “back”.

  Hereinafter, when the light deflector 1 is referred to as up, down, left, and right, the upper, lower, left, and right in the front view of the light deflector 1 are referred to. For convenience of understanding the configuration of the optical deflector 1, three-axis orthogonal coordinates are defined in FIG. 1 and the like. The origin O is set at the center of the mirror unit 2. The Z axis corresponds to the thickness direction of the optical deflector 1. The X axis and the Y axis correspond to the horizontal direction and the vertical direction. The Z axis is directed from the back to the front. The X axis is oriented from left to right. The Y axis is oriented from bottom to top. Hereinafter, the configuration of the optical deflector 1 will be described in a state where the mirror unit 2 is stationary, that is, a state where the normal of the reflection surface of the mirror unit 2 is coincident with the Z axis.

  The optical deflector 1 includes a mirror unit 2, inner piezoelectric actuators 3a and 3b, a movable frame 4 as a movable support, outer piezoelectric actuators 5a and 5b, and a fixed frame 6. The fixed frame 6 is a horizontally long rectangle when viewed from the front. The long side and the short side of the fixed frame 6 are parallel to the X axis and the Y axis, respectively.

  In FIG. 1, axes Lx and Ly are two axes along which the mirror unit 2 reciprocates (forward / reverse). The axes Lx and Ly are orthogonal at the center (origin O) of the mirror unit 2. The inner piezoelectric actuators 3a and 3b are supplied with a first drive voltage from a drive unit (not shown), and reciprocate the mirror unit 2 around the axis Ly at a first frequency (eg, 30 kHz). The outer piezoelectric actuators 5a and 5b are supplied with the second drive voltage from the drive unit, and reciprocate the mirror unit 2 around the axis Lx at the second frequency (eg, 60 Hz).

  The inner piezoelectric actuators 3a and 3b are constituted by cantilevers having a piezoelectric structure, and have a structure which is symmetrical with respect to the Y axis in a front view. The inner piezoelectric actuators 3a and 3b are connected to each other at both ends in the Y-axis direction, and as a whole, form a vertically long elliptical ring in the Y-axis direction surrounding the mirror unit 2. The movable frame 4 has an inner and outer periphery formed as an annular frame having an elliptical contour vertically elongated in the Y-axis direction, and surrounds an elliptical ring constituted by the inner piezoelectric actuators 3a and 3b on the inner periphery side.

  The torsion bars 21a and 21b linearly protrude vertically from the mirror portion 2 along the Y axis, are coupled to the coupling portions of the inner piezoelectric actuators 3a and 3b at an intermediate portion, and are formed on the inner periphery of the movable frame 4 at the protruding ends. Join. The axis Ly coincides with the center line of the torsion bars 21a, 21b.

  The outer piezoelectric actuators 5a and 5b are disposed on the inner peripheral side of the rectangular fixed frame 6 and symmetrically with respect to the movable frame 4 in the X-axis direction. Each of the outer piezoelectric actuators 5a and 5b includes a plurality of cantilevers 23 connected in series in a meander arrangement. The cantilever 23 also has a piezoelectric structure, like the cantilevers (no reference numeral) of the inner piezoelectric actuators 3a and 3b. Each cantilever 23 can be used alone as a piezoelectric actuator.

  Specifically, the cantilevers 23 are arranged in a line in the X-axis direction with their longitudinal directions aligned in the Y-axis direction. The plurality of cantilevers 23 are coupled to the left or right cantilever 23 in the horizontal direction (X-axis direction) at the end in the vertical direction (Y-axis direction) via a folded portion (no reference numeral).

  In each of the outer piezoelectric actuators 5a and 5b, the cantilevers 23 at both ends in the X-axis direction are half the length of the intermediate cantilevers 23, and are respectively connected to the fixed frame 6 and the movable frame 4 on the X-axis. I have. The end of the cantilever 23 connected to the fixed frame 6 forms the base end of the outer piezoelectric actuators 5a and 5b, and the end of the cantilever 23 connected to the movable frame 4 is the outer piezoelectric actuator 5a. , 5b.

  A plurality of electrode pads 16 a and 16 b are provided on the surface of each short side of the fixed frame 6. The electrode pad 16a is connected to the inner piezoelectric actuator 3a and the outer piezoelectric actuator 5a in the left half of the optical deflector 1 via the internal wiring of the optical deflector 1. The electrode pad 16b is connected to the inner piezoelectric actuator 3b and the outer piezoelectric actuator 5b in the right half of the optical deflector 1 via the internal wiring of the optical deflector 1.

(Operation of optical deflector)
The operation of the light deflector 1 will be described. Hereinafter, when there is no particular distinction between the inner piezoelectric actuators 3a and 3b, they are collectively referred to as "inner piezoelectric actuator 3". When the outer piezoelectric actuators 5a and 5b are not particularly distinguished, they are collectively referred to as "outer piezoelectric actuator 5". When the electrode pads 16a and 16b are not particularly distinguished, they are collectively referred to as "electrode pads 16".

  The optical deflector 1 is provided as a two-dimensional scanner in a video device, a vehicle headlamp, or the like. The optical deflector 1 is housed in a package, and the electrode pads 16 of the optical deflector 1 and terminals of the package are connected by bonding wires (not shown). A drive voltage is supplied to the inner piezoelectric actuator 3 and the outer piezoelectric actuator 5 from the electrode pads 16 to the piezoelectric bodies.

  Light (eg, a laser beam) from a light source (eg, a semiconductor laser light source) not shown is incident on the center (origin O of a three-axis coordinate system) of the mirror unit 2 of the optical deflector 1.

  The outer piezoelectric actuator 5 is operated by a driving voltage from the electrode pad 16 to reciprocate the movable frame 4 around the X axis at the second frequency. As a result, the mirror unit 2 reciprocates around the axis Lx at the second frequency. Note that the axis Lx does not coincide with the X axis. This is because the mirror unit 2 reciprocates around the axis Ly, as will be described later, so that the axis Lx also fluctuates with the reciprocation of the axis Ly. On the other hand, the X axis is stationary with respect to the fixed frame 6.

  The operation of the outer piezoelectric actuator 5 will be described in detail. Each outer piezoelectric actuator 5 comprises a plurality of cantilevers 23 in a meander arrangement. When the cantilevers 23 are numbered in order from the base end side (the fixed frame 6 side) to the front end side (the movable frame 4 side) of the outer piezoelectric actuator 5, the odd-numbered cantilevers 23 and the even-numbered cantilevers 23 are the same. A driving voltage having a phase opposite to that of the frequency is supplied, and the deformation is performed so that the direction of the convex side of the bending deformation is reversed.

  As a result, when the outer piezoelectric actuator 5 is operated, the cantilevers 23 constituting the meander arrangement are curved in opposite directions between adjacent ones in the X-axis direction. At this time, the accumulated amount of the relative rotation amount of the distal end portion with respect to the base end portion of each cantilever 23 is the rotation amount (torsion amount) of the inner piezoelectric actuator 3 with respect to the outer piezoelectric actuator 5 around the axis Lx.

  On the other hand, the inner piezoelectric actuator 3 causes the torsion bar 21 to reciprocate at the first frequency around the axis Ly as its central axis by the first drive voltage from the electrode pad 16. The first frequency is set to a resonance frequency of the mirror unit 2 around the axis Ly in order to secure a high frequency. The second frequency, which is the frequency of the reciprocating rotation of the mirror unit 2 around the axis Lx, is set to a non-resonant frequency.

  Thus, the mirror unit 2 reciprocates around the axis Lx at the non-resonant frequency while reciprocating around the axis Lx. As a result, the mirror section 2 swings at a resonance frequency on the left and right sides and a non-resonance frequency on the upper and lower sides in a front view.

  Note that the axis Lx matches the X axis and the axis Ly matches the Y axis only when the normal of the reflection surface of the mirror unit 2 matches the Z axis. Light from a light source (not shown) is reflected at the center of the mirror unit 2 and is emitted as scanning light in a direction corresponding to a rotation angle around the axis Lx or Ly at that time.

(Configuration of piezoelectric actuator)
FIG. 2 is a sectional view of a cantilever type piezoelectric actuator 24 constituting the cantilever 23. As shown in FIG. 2, the piezoelectric actuator 24 includes a piezoelectric element 26, one end of which is supported by a support portion 25 and the other end of which is a free end.

  However, in order to configure the outer piezoelectric actuator 5 described above, a supporting portion 25 of another piezoelectric actuator 24 is fixed to the other end of the piezoelectric element 26. When the piezoelectric actuator 24 constitutes the cantilever 23 on the distal end side (the movable frame 4 side) of the outer piezoelectric actuator 5, the other end of the piezoelectric element 26 is fixed to the movable frame 4.

  The piezoelectric element 26 includes a lower electrode 27, an upper electrode 28, a piezoelectric body 29 interposed between the lower electrode 27 and the upper electrode 28, and a buried material 30 made of a non-piezoelectric insulator. The embedded material 30 is embedded in the piezoelectric body 29 with the upper electrode 28 side closed by the upper electrode 28.

  As described later, the embedded material 30 is a non-piezoelectric insulating film filled in a hole formed by removing particles taken in the piezoelectric film at the time of forming the piezoelectric film to be the piezoelectric body 29 of the piezoelectric element 26. Is formed by a part of.

  An insulator 31 that insulates and protects a necessary portion of the upper electrode 28 is provided on the upper electrode 28. A power supply wiring 32 is connected to one ends of the upper electrode 28 and the lower electrode 27. The support portion 25 is formed by a remaining part of a wafer which is a substrate used when forming the piezoelectric element 26.

  The piezoelectric element 26 has a fixed end supported by a support 25, functions as a cantilever-type piezoelectric actuator 24, that is, a cantilever 23, and is driven by a voltage supplied via a wiring 32. Then, as described above, the plurality of piezoelectric actuators 24 are connected in series in a meander arrangement, and the neighbors are driven by driving voltages of opposite polarities, and function as the outer piezoelectric actuator 5.

(Method of manufacturing piezoelectric element)
3A to 3E show a manufacturing process of a portion where the piezoelectric element 26 is formed when the optical deflector 1 is manufactured. 3A to 3E show cross sections of portions corresponding to the cross section of the piezoelectric element 26 in the piezoelectric actuator 24 of FIG.

  As shown in FIGS. 3A to 3E, the manufacturing process includes a step of forming a lower electrode film 34, a piezoelectric film 35, and an upper electrode film 36 on a wafer 33 in this order (FIGS. 3A and 3E). In addition, after the piezoelectric film 35 is formed and before the upper electrode film 36 is formed, the particles 37 exposed on the surface of the piezoelectric film 35 are replaced with the embedded material 30 made of a non-piezoelectric insulating material ( 3B to 3D).

4A to 4D are cross-sectional views showing a part of the manufacturing process of FIG. 3 in more detail. Specifically, in the step of forming the lower electrode film 34, as shown in FIG. 4A, a buffer layer 38 such as Ti or TiO ₂ on the wafer 33, the thickness of 10 nm (or in the range of 5~20nm thickness ).

Furthermore, Pt thereon, Ir, an electrode layer 39, such as IrO _2, is formed with a thickness of 150 nm (or thickness in the range of 80 to 200 nm). Then, a conductive oxide layer 40 such as SRO or LNO is formed thereon to a thickness of 20 nm (or a thickness in the range of 5 to 30 nm).

As the wafer 33, for example, a substrate having a surface of SiO ₂ or Si, that is, a Si substrate, an SOI substrate, or the like can be used. The thickness of the substrate is, for example, 400 μm (or a thickness in the range of 300 to 700 μm).

  The piezoelectric film 35 is formed by forming a piezoelectric layer of PZT (titanium lead zirconate) with a thickness of 5 μm (or a thickness in the range of 3 to 6 μm). The thickness of the piezoelectric layer is set so as to finally have a desired thickness in consideration of a thickness to be polished in a later step. At this time, as shown in FIG. 5, a particle 37 as a foreign substance generated by the PZT film forming process is partially exposed from the piezoelectric film 35 and the other portion is embedded in the piezoelectric film 35 in a state where the particle 37 is embedded. Occurs in large or small numbers.

  The next replacement step includes a particle removing step (FIG. 3B), an insulating film forming step (FIG. 3C), and an insulating film removing step (FIG. 3D).

  In the particle removing step, the particles 37 exposed on the surface of the piezoelectric film 35 are removed by polishing the piezoelectric film 35. FIG. 3B shows a state in which the particles 37 have been removed to form holes 41.

  That is, a flattening process is performed on the piezoelectric film 35 in which a part of the particles 37 protrudes from the surface. At this time, it is preferable to use a CMP (chemical mechanical polishing) technique for polishing. This is because particles 37 can be removed while improving the polishing speed and quality by the synergistic effect of chemical polishing and mechanical polishing. At this time, as shown in FIG. 4B, it is desirable that the piezoelectric film 35 of PZT is shaved by 0.2 to 0.4 μm.

  As the surface roughness after the flattening treatment, it is preferable that the arithmetic average roughness Ra is 1 nm or less. Thereby, the surface roughness (Ra of about 10 nm or more) after the piezoelectric film 35 is formed can be simultaneously improved, and uniform film formation and processing accuracy in a subsequent process can be improved. The particles 37 fall off by the planarization processing by the CMP, and the holes 41 as shown in FIG. 3B or FIG. 4B are formed. It is assumed that the hole 41 has a maximum depth corresponding to the thickness of the piezoelectric film 35.

  In the next insulating film forming step, as shown in FIG. 3C, an insulating film 42 having no piezoelectricity is formed on the piezoelectric film 35 from which the particles 37 have been removed. As the insulating film 42, a TEOS film mainly composed of tetraethoxysilane formed by a plasma CVD method is desirable. This is because TEOS has a high fluidity and fills the holes 41 well, so that it is preferable to form the embedded material 30.

  Further, as shown in FIG. 4C, it is desirable that the insulating film 42 be formed to have a thickness equal to or greater than the thickness of the piezoelectric film 35 (= the maximum depth of the hole 41). For example, when the thickness of the piezoelectric film 35 is 5 μm, that is, when the maximum depth of the hole 41 is 5 μm, it is desirable that the insulating film 42 be formed to a thickness of about 6 μm.

  In the next insulating film removing step, as shown in FIG. 3D, the insulating film 42 formed on the piezoelectric film 35 is subjected to a planarization process by polishing, so that the insulating film 42 is formed by removing the particles 37. The hole 41 is removed while leaving the portion filled.

  At the time of polishing, it is preferable to use a CMP (chemical mechanical polishing) technique as in the case of the foreign matter removing step. At the time of polishing, as shown in FIG. 4D, it is preferable to perform over-etching for further reducing the piezoelectric film 35 by 0.2 to 0.4 μm in addition to the insulating film 42. This is because if the insulating film 42 remains in portions other than the holes 41 of the piezoelectric film 35, the piezoelectric characteristics of the piezoelectric film 35 deteriorate.

  The final thickness t of the piezoelectric film 35 is, for example, 5 μm when the deposition of the piezoelectric film 35 is completed, 0.4 μm to be removed in the particle removing step, and removed in the insulating film removing step. If the thickness is 0.4 μm, t = (5−0.4−0.4) μm = 4.2 μm.

  Thus, the replacement step of replacing the particles 37 with the embedded object 30 is completed. Thereafter, as shown in FIG. 3E, the upper electrode film 36 is formed on the piezoelectric film 35.

  During or after this, by patterning the upper electrode film 36, the piezoelectric film 35, the lower electrode film 34, and the wafer 33, the upper electrode 28 of the piezoelectric actuator 24 in the chip of each optical deflector 1 on the wafer 33, The body 29, the lower electrode 27, the wiring 32, the support 25, and the like are formed. Thus, a piezoelectric actuator 24 as shown in FIG. 2 is formed as a part of the optical deflector 1.

(Effect of embodiment)
According to the present embodiment, the particles 37 generated during the formation of the piezoelectric film 35 serving as the piezoelectric body 29 of the piezoelectric element 26 are replaced with the buried objects 30, so that the defective portions having low dielectric strength due to the particles 37 are minimized. The excluded piezoelectric element 26 can be provided. In the replacement step, the particles 37 protruding from the piezoelectric film 35 toward the upper electrode 28 are replaced with the embedded material 30, so that the piezoelectric body 29 has a structure in which the embedded material 30 is unevenly distributed on the upper electrode 28 side.

  In the piezoelectric actuator 24 having the piezoelectric element 26, the particles 37 are replaced with the buried objects 30, and therefore, the piezoelectric element 26 does not have a defect having a low dielectric strength due to the particles 37. Therefore, when the piezoelectric actuator 24 is driven, it is possible to prevent a problem from occurring due to the dielectric breakdown of the defective portion.

  FIG. 7 shows an optical deflector 1 having the piezoelectric element 26 of the present embodiment in which the particles 37 are replaced by the embedded object 30 and a light having the piezoelectric element of the comparative example in which the particles 37 are left in the piezoelectric body. The results of reliability tests performed on the deflector as “Example” and “Comparative Example” are shown.

  As shown in FIG. 7, the failure rate in the case of driving for 511 hours at an AC voltage of 65 V in both the example and the comparative example was 0.01% in the example, whereas the failure rate was 61.5 in the comparative example. %Met. In addition, the failure of 0.01% in the example was not caused by the dielectric breakdown of the piezoelectric element 26, but was caused by a defect at another place.

  From these results, it is understood that the dielectric breakdown of the piezoelectric element 26 can be actually prevented by replacing the particles 37 with the embedded object 30 according to the present invention.

(Modification)
The present invention is not limited to the above-described embodiment, and can be appropriately modified and implemented. For example, when performing a flattening process in a particle removing process and an insulating film removing process, if a desired flat shape can be obtained, not only CMP (chemical mechanical polishing) but also other GCIB (gas cluster ion beam). ), RIE (reactive ion etching), and CDE (chemical dry etching).

  In addition, as an insulating film for forming the buried material 30, TEOS by plasma CVD may be used as long as it does not have piezoelectricity, has a desired withstand voltage, and can satisfactorily fill the hole after removing particles. Not limited to the film, an SiO, SIN, SiON film, SOG (spin-on-glass) film, or the like by another plasma CVD method may be used.

(Application example)
The present invention is not limited to the above-mentioned cantilever type piezoelectric actuator, but can be applied to various products such as a sensor and a speaker using a function of converting a force and a voltage of a piezoelectric element.

  DESCRIPTION OF SYMBOLS 1 ... Optical deflector, 2 ... Mirror part, 3a, 3b ... Inside piezoelectric actuator, 4 ... Movable frame, 5 (5a, 5b) ... Outside piezoelectric actuator, 6 ... Fixed frame, 16 (16a, 16b) ... Electrode Pads, 21a, 21b: torsion bar, 23: cantilever, 24: piezoelectric actuator, 25: support, 26: piezoelectric element, 27: lower electrode, 28: upper electrode, 29: piezoelectric, 30: embedded, 31 ... Insulator, 32 wiring, 33 wafer, 34 lower electrode film, 35 piezoelectric film, 36 upper electrode film, 37 particles, 38 buffer layer, 39 electrode layer, 40 conductive oxide layer, 41 ... hole.

Claims (7)

A lower electrode;
An upper electrode;
A piezoelectric body sandwiched between the lower electrode and the upper electrode,
A piezoelectric element comprising an insulator having no piezoelectricity, the embedded element being embedded in the piezoelectric body in a state where the upper electrode side is closed by the upper electrode.   The piezoelectric element according to claim 1, wherein the embedded material is unevenly distributed on the upper electrode side of the piezoelectric body.   A piezoelectric actuator comprising the piezoelectric element according to claim 1. Forming a lower electrode film, a piezoelectric film, and an upper electrode film on the substrate in this order;
After the formation of the piezoelectric film, before the formation of the upper electrode film, a replacement step of replacing particles embedded in the piezoelectric film in a partially exposed state with an embedded material made of a non-piezoelectric insulator. A method for manufacturing a piezoelectric element, comprising: The replacing step includes:
A particle removing step of removing the particles by polishing the piezoelectric film,
An insulating film forming step of forming an insulating film having no piezoelectricity on the piezoelectric film from which the particles have been removed,
An insulating film removing step of polishing the insulating film formed on the piezoelectric film to remove the insulating film while leaving a portion filled in a hole generated by the removal of the particles. The method for manufacturing a piezoelectric element according to claim 4, wherein:   The method according to claim 5, wherein the polishing in the particle removing step is performed by chemical mechanical polishing.   The method for manufacturing a piezoelectric element according to claim 4, wherein the insulating film having no piezoelectric property contains tetraethoxysilane as a main component.