JP2009038169A - Manufacturing method of piezoelectric element, forming method of dielectric layer, and manufacturing method of actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a piezoelectric element having a dielectric layer having excellent characteristics by suppressing deviation in the composition of a dielectric in the layer. <P>SOLUTION: The manufacturing method of the piezoelectric element includes processes of forming a lower electrode 20 above a base 10; forming the dielectric layer by carrying out a pair of a first process of forming a laminar portion 311a above the lower electrode 20 and a second process of making the laminar portion 311a thin by chemical polishing once or a plurality of times; and forming an upper electrode above the dielectric layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric element manufacturing method, a dielectric layer manufacturing method, and an actuator manufacturing method.

There are piezoelectric elements and capacitive elements that make use of dielectric properties such as dielectric properties, piezoelectric properties, pyroelectric properties, and ferroelectric properties. These elements have a structure in which a layered dielectric is sandwiched between two electrode layers. As the dielectric, a sintered body of a perovskite oxide represented by the general formula ABO ₃ (A site contains Pb and B site contains Zr and Ti) is often used. In general, the dielectric in the device is formed by a vapor phase method such as chemical vapor deposition (CVD) or a liquid phase method such as sol-gel method.

When the dielectric layer is formed by a liquid phase method, it is often performed by applying a dielectric raw material composition, drying, degreasing, and crystallization annealing of the coating film. At this time, if crystallization annealing is performed in a state where the coating film is thick, volume shrinkage during crystallization increases, and the coating film may crack. Therefore, for example, Japanese Patent Application Laid-Open No. 09-223830 proposes a method of performing crystallization annealing a plurality of times.
JP 09-223830 A

  However, when crystallization annealing is performed by heating the dielectric layer, the composition of the constituent elements of the dielectric may be distributed in the layer. For example, when lead zirconate titanate is used as the dielectric material, there may be a bias in the presence of titanium and zirconium in the dielectric layer. Such a bias may worsen, for example, the piezoelectric characteristics of the dielectric layer. Therefore, a manufacturing method that does not easily cause such a bias is required.

  One of the objects according to the present invention is to provide a piezoelectric element having a dielectric layer with favorable characteristics by suppressing the deviation of the composition of the dielectric in the layer, and a method for manufacturing an actuator having the dielectric layer. .

  One of the objects according to the present invention is to provide a method for producing a dielectric layer having excellent characteristics by suppressing the deviation of the composition of the dielectric within the layer.

The method for manufacturing a piezoelectric element according to the present invention includes:
Forming a lower electrode above the substrate;
Performing a set of a first step of forming a layered portion above the lower electrode and a second step of thinning the layered portion by chemical mechanical polishing one or more times to form a dielectric layer;
Forming an upper electrode above the dielectric layer.

  In this way, it is possible to manufacture a piezoelectric element having a dielectric layer with excellent characteristics and suppressed bias in the composition of the dielectric within the layer.

  In the present invention, when a specific B member (hereinafter referred to as “B”) formed above a specific A member (hereinafter referred to as “A”), B is formed directly on A. And the case where B is formed on A via another member.

  In the method for manufacturing a piezoelectric element according to the present invention, the first step includes a step of forming a single precursor layer and a step of crystallizing the precursor layer to form the layered portion. Can do.

  In the method for manufacturing a piezoelectric element according to the present invention, the first step includes a step of laminating a plurality of precursor layers, and a step of crystallizing the plurality of precursor layers to form the layered portion. be able to.

The method for producing a dielectric layer according to the present invention includes:
A first step of forming a layered portion above the substrate;
A second step of thinning the layered portion by chemical mechanical polishing,
The set of the first step and the second step is performed one or more times.

  In this way, it is possible to manufacture a dielectric layer having excellent characteristics by suppressing the bias of the composition of the dielectric within the layer.

The manufacturing method of the actuator according to the present invention is as follows:
Forming a lower electrode above the elastic plate;
Performing a set of a first step of forming a layered portion above the lower electrode and a second step of thinning the layered portion by chemical mechanical polishing one or more times to form a dielectric layer;
Forming an upper electrode above the dielectric layer.

  In this way, it is possible to manufacture an actuator having a dielectric layer with excellent characteristics and suppressed bias in the composition of the dielectric within the layer.

  Preferred embodiments of the present invention will be described below with reference to the drawings. The following embodiment will be described as an example of the present invention.

1. Piezoelectric Element Manufacturing Method An example of a piezoelectric element manufacturing method according to this embodiment will be described below with reference to the drawings. 1 to 8 are cross-sectional views schematically showing a method for manufacturing the piezoelectric element 100 according to the present embodiment. FIG. 9 is a cross-sectional view schematically showing the piezoelectric element 100.

  The method for manufacturing the piezoelectric element 100 according to this embodiment includes a step of forming the lower electrode 20, a step of forming the dielectric layer 30, and a step of forming the upper electrode 40.

  As shown in FIG. 1, first, the lower electrode 20 is formed above the substrate 10. The lower electrode 20 can be provided by sputtering a metal such as platinum. The substrate 10 is not particularly limited. As the substrate 10, for example, a silicon substrate may be used, or an insulating layer or other layer may be provided on the silicon substrate. Further, the substrate 10 may be a semiconductor substrate provided with wiring, circuits, and the like.

  Next, a step of forming the dielectric layer 30 is performed. This step includes a first step of forming the layered portion 311a and a second step of forming the layered portion 311 by thinning the layered portion 311a by chemical mechanical polishing. Then, the combination of the first step and the second step is performed once or a plurality of times to form the dielectric layer 30. In the following, the case where the material of the dielectric layer 30 is lead zirconate titanate will be mainly exemplified.

  First, the first step will be described. As shown in FIG. 2, a dielectric material solution is applied over the lower electrode 20, and this is dried and degreased to form a precursor layer 301. As a raw material solution, it can comprise, for example including at least one of a metal alkoxide and an organic metal. For example, the raw material composition of lead zirconate titanate includes a composition containing lead acetate, zirconium tetrabutoxide, titanium tetraisopropoxide, alcohol and an acid. The raw material solution can be applied by spin coating or dip coating. Drying and degreasing can be performed by heating to 100 ° C. to 400 ° C., for example. In this way, the main component of the precursor layer 301 becomes amorphous lead zirconate titanate.

  In the present embodiment, as shown in FIG. 3, the above-described coating, drying and degreasing steps are repeated three times. As a result, a state in which the precursor layers 301, 302, and 303 are stacked above the lower electrode 20 is formed. Thus, if the precursor layer is laminated a plurality of times to obtain a laminate of a precursor layer having a desired thickness, each precursor layer can be formed thinly, so when drying and degreasing, When heated, it can be made difficult to crack. In this case, each precursor layer becomes a part of the layered portion 311a after the next crystallization annealing. In addition, as long as the precursor layer having a desired thickness in a single layer does not crack when being dried and degreased, it is not necessary to form the precursor layer by laminating a plurality of times in this way. When only one precursor layer 301 is formed, the precursor layer 301 becomes the entire layered portion 311a after the next crystallization annealing. The thicknesses of the precursor layers 301, 302, and 303 can be set to 100 nm, for example. The thickness of each layer may be different from each other.

  After a single-layer precursor layer or a laminate of a plurality of precursor layers is formed, crystallization annealing is performed to form a layered portion 311a (FIG. 4). Crystallization annealing is a process of changing amorphous lead zirconate titanate to crystalline lead zirconate titanate by heating. The crystallization annealing can be performed by heating to 600 ° C. to 1000 ° C., for example. In the layer of the layered portion 311a after the crystallization annealing, the distribution of the composition of titanium and zirconium occurs. Details regarding the distribution of this composition will be described later. As described above, the layered portion 311a is formed above the lower electrode 20 by the first step. The thickness of the layered portion 311a can be set to, for example, 300 nm.

  Next, the second step will be described. As schematically shown in FIG. 5, the second step is a step in which the layered portion 311 a is thinned by chemical mechanical polishing (CMP) to form the layered portion 311 (FIG. 6). See also). For CMP, a method used for polishing a semiconductor wafer can be used. In this step, a part of the layered portion 311a is removed and thinned by CMP. The thickness of the layered portion 311a to be removed is preferably 10% to 60% of the total thickness of the layered portion 311a. When the thickness to be removed is less than 10%, the effect of suppressing the compositional deviation is insufficient, and when it is more than 60%, the process throughput and the process cost are deteriorated. By the second step, for example, half of the thickness of the layered portion 311a is removed. In this case, if the thickness of the layered portion 311a is 300 nm, a layered portion 311 having a thickness of 150 nm is obtained.

  When the first step and the second step described above are performed, a layered portion 311 is formed as shown in FIG. 6, and a plurality of layered portions 311 can be stacked as shown in FIG. The step of laminating the layered portions can be performed by repeatedly performing a set of the first step and the second step. That is, as shown in FIG. 7, after forming the layered portion 311, a set of the first step and the second step is performed, and the layered portion 312 is stacked on the layered portion 311. A layered portion 313 can be stacked thereon. The number of times of laminating the layered portion can be arbitrarily determined according to the final design of the thickness of the dielectric layer 30. For example, if the thickness of the layered portion of one layer is 150 nm, the number of times of laminating the layered portion can be 6 to 8 times. In this case, the thickness of the dielectric layer can be set to 900 nm to 1200 nm.

  By laminating the layered portions a plurality of times, each layered portion can be formed thin in order to obtain the dielectric layer 30 having a desired thickness. Therefore, it is possible to make it difficult for cracks to occur during crystallization annealing. If the number of layers of the layered portion for obtaining the dielectric layer 30 having a desired thickness is sufficient, if this one layer does not crack during crystallization annealing, the layered portion is There is no need to form a plurality of layers. As shown in FIG. 7, in this embodiment, a dielectric layer 30 in which layered portions 311, 312, and 313 are stacked is formed.

  Next, as shown in FIG. 8, the upper electrode 40 is formed above the dielectric layer 30. The upper electrode 40 can be provided by sputtering a metal such as platinum.

  As described above, a structure in which the dielectric layer 30 is sandwiched between the lower electrode 20 and the upper electrode 40 as shown in FIG. 8 is formed. Then, for example, as shown in FIG. 9, the upper electrode 40, the dielectric layer 30 and the lower electrode 20 are patterned by a method such as photolithography, and the piezoelectric element 100 is manufactured.

2. Composition distribution The composition of each element of lead zirconate titanate is uniform in the layer before crystallization annealing, that is, in the state of the precursor layer. However, crystallization proceeds when the precursor layer is heated in the crystallization annealing step to become a layered portion. At that time, with the progress of crystallization, the composition of each element of lead zirconate titanate may be biased. This phenomenon is explained as follows.

  A perovskite oxide represented by lead zirconate titanate is a solid solution of a plurality of oxides. In the case of lead zirconate titanate, it is a solid solution of lead titanate and lead zirconate. Such oxides usually have different crystallization temperatures (temperatures when transitioning from an amorphous state to a crystalline state). In the case of lead zirconate titanate, the crystallization temperature of lead titanate is lower than that of lead zirconate. Therefore, when lead zirconate titanate is heated to change from an amorphous state to a crystalline state, lead titanate is preferentially crystallized. At this time, crystal nuclei are likely to be generated in a part in contact with a foreign substance such as an electrode, and therefore crystallization occurs in this part before the surface in contact with the gas. The same applies to the case where a solid other than the electrode, for example, already crystallized lead zirconate titanate is present. Therefore, in the case of the present embodiment, a crystal having a higher content of lead titanate is produced on the side of the layered portion 311a that is in contact with the lower electrode 20 or the lower crystallized lead zirconate titanate. In this case, the content of lead zirconate in the crystal is relatively higher toward the upper side of the layered portion 311a. This is because the average composition of the entire layered portion 311a is maintained. In general, such a phenomenon may occur in crystallization annealing of a perovskite oxide.

  10 and 11 are schematic views for further explaining the above. FIG. 10 shows a composition distribution resulting from crystallization annealing of a layered portion having a specific thickness (described as “annealed thickness” in the figure). On the other hand, FIG. 11 shows a composition distribution resulting from crystallization annealing of a layered portion having a specific thickness (denoted as “anneal thickness” in the figure) and removing only about half the thickness of the crystallized layer by CMP. It shows a state. Both FIG. 10 and FIG. 11 schematically show a state in which a plurality of crystallization annealed layers are stacked. In each figure, the vertical axis represents the composition of a constituent element, for example, titanium, with respect to the entire oxide constituting the dielectric layer 30, and the horizontal axis represents the distance from the surface of the dielectric layer 30 in the depth (thickness) direction. (The thickness direction is indicated by an arrow in FIG. 9). From these figures, the following four things are explained.

  (1) When crystallization annealing is performed, a composition distribution occurs in the thickness direction of the layered portion 311. That is, in FIGS. 10 and 11, in the thickness indicated by the annealing thickness on the horizontal axis, crystals of lead zirconate titanate having a large titanium composition are formed below, that is, in a deeper region (these compositions are respectively (Indicated by symbols C3 and C7 in the figure).

  (2) The areas of the region R1, the region R2, the region R3, and the region R4 are substantially equal to compensate for the average composition of the layered portion 311 (C2 and C5 in FIGS. 10 and 11, respectively). The titanium composition at the end of crystallization, that is, the composition on the upper portion of the layered portion 311 that is the object of crystallization annealing, has the smallest titanium composition. The minimum titanium composition is labeled C1 and C4 in the figure.

  (3) When CMP is performed (FIG. 11), since the region having a small titanium composition is removed, the minimum value and the average value of the titanium composition change. In the example of FIG. 11, since about half of the layer thickness is removed by CMP, the vicinity of the average composition before polishing becomes the minimum value (C5) of the titanium composition. In this case, the average composition (C6 in the figure) is larger than the average composition before polishing (near C5).

  (4) The fluctuation width of the composition in the thickness direction is smaller when CMP is performed (FIG. 11) (from C5 to C7) than when CMP is not performed (FIG. 10) (from C1 to C3).

  Since such a composition distribution is exhibited by at least one of the constituent elements and often decreases monotonously or increases monotonously in the thickness direction, it may be referred to as a composition gradient. Even in the case where crystallization annealing is performed on the layered portion 311a in which a plurality of precursor layers 301 are stacked, the composition distribution as described above occurs in the layered portion 311a.

  As shown in FIG. 11, when the region indicated by the polishing thickness on the horizontal axis is removed by CMP, the width of the titanium composition distribution in the dielectric layer 30 can be reduced. This is nothing but reducing the compositional deviation.

  Therefore, in this embodiment, since the second step, that is, CMP is performed, the dielectric layer 30 in which the bias of the composition of the dielectric is suppressed in the layer is obtained. In this case, the average composition in the dielectric layer 30 deviates from the average composition of the layered portion 311a. In such a case, for example, the composition of the dielectric material solution is changed to the dielectric layer 30. When it becomes, it can prepare beforehand so that it may become a target composition.

3. Experimental Example The piezoelectric element 120 and the piezoelectric element 130 of this experimental example were prepared as follows. A platinum electrode was formed on a silicon substrate by sputtering, a raw material solution of lead zirconate titanate was applied thereon by a spin coating method, and this was dried and degreased to form a precursor layer. On the obtained precursor layer, the raw material solution was further applied, dried and degreased twice. As a result, a state in which three precursor layers were stacked on the lower electrode was formed. The thickness of the precursor layer laminate was 300 nm. Next, the obtained laminate was subjected to crystallization annealing at 650 to 750 ° C. by RTA to obtain a layered portion. Next, the layered portion was thinned by CMP to be half the thickness (150 nm). By repeating such a process, eight layers were laminated. The final crystallized lead zirconate titanate layer thickness was 1200 nm. Then, the upper electrode was formed by platinum sputtering, and the lead zirconate titanate layer and the upper and lower electrodes were patterned and etched by photolithography to manufacture the piezoelectric element 120.

  The piezoelectric element 130 was manufactured in the same manner as the piezoelectric element 120, except that CMP was not performed and four layered portions having a thickness of 300 nm were stacked.

The piezoelectric constants d ₃₁ of the piezoelectric element 120 and the piezoelectric element 130 were measured and found to be 450 (pC / N) and 300 (pC / N), respectively.

  FIG. 13 shows the result of depth direction analysis of the lead zirconate titanate layer of the piezoelectric element 120 by X-ray photoelectron spectroscopy (ESCA). FIG. 14 shows the result of depth direction analysis of the lead zirconate titanate layer of the piezoelectric element 130 by ESCA. The attribution of each spectrum indicated the element name in the figure. The vertical axes in FIGS. 13 and 14 are obtained by normalizing the detection intensity of photoelectrons for each element. The intensity of the spectrum of each element in FIGS. 13 and 14 can be compared relatively. The horizontal axis of FIG. 13 and FIG. 14 shows the sputtering time of the depth direction analysis, and corresponds to the depth being analyzed, that is, the thickness direction of the layer. The horizontal axes of FIGS. 13 and 14 can be relatively compared since the sputtering conditions are aligned.

  From FIG. 13 and FIG. 14, the lead zirconate titanate layer of the piezoelectric element 120 manufactured according to the manufacturing method of this embodiment has a range of variation a and range b of titanium and zirconium without performing CMP. It was clear that the composition deviation was smaller in the lead zirconate titanate layer, which was narrower than the same range a ′ and range b ′ of the lead zirconate titanate layer of the manufactured piezoelectric element 130. .

Thus, in the lead zirconate titanate layer, by reducing the deviation of the composition was higher piezoelectric constant d _31. This can be explained as follows. The relationship between the composition of lead zirconate titanate and the piezoelectric constant is described, for example, in the literature Applied Phisics Letter, Vol. 72, no. 19, 2421-2423. This document describes that the value of the piezoelectric constant changes greatly even with a slight change in the composition of lead zirconate titanate. The result of the piezoelectric element 120 of the experimental example described above was caused by removing the low piezoelectric constant portion of the lead zirconate titanate layer, so that the average composition of the entire layer became a composition showing a high piezoelectric constant. It is considered a thing. Conversely, the result of the piezoelectric element 130 of this experimental example is that the low piezoelectric constant portion of the lead zirconate titanate layer was not removed, and this region was generated because the piezoelectric constant of the entire layer was lowered. it is conceivable that.

4). Manufacturing Method of Actuator 200 FIG. 12 is a cross-sectional view schematically showing the actuator 200 of the present embodiment.

  The actuator 200 includes the above-described piezoelectric element 100 and at least the elastic plate 3. The elastic plate 3 can vibrate by the operation of the piezoelectric element 100. Such an actuator 200 includes, for example, the above-described piezoelectric element 100 in which the base 10 is a laminate of the silicon substrate 1, the silicon oxide layer 2, and the elastic plate 3, and the silicon substrate 1 below the piezoelectric element 100 is etched. Then, it can be manufactured by removing.

  The silicon oxide layer 2 can be formed, for example, by thermally oxidizing the silicon substrate 1. The elastic plate 3 can be formed by depositing zirconium oxide by, for example, a CVD (Chemical Vapor Deposition) method. Patterning of the silicon substrate 1 can be performed using a photolithography method, a dry etching method, or the like, using the silicon oxide layer 2 as a stopper layer.

5). As described above, according to the manufacturing method of the present embodiment, it is possible to provide the piezoelectric element 100 having the dielectric layer 30 in which the bias of the composition of the dielectric is suppressed in the layer and the characteristics are good. According to the manufacturing method of the present embodiment, it is possible to provide the dielectric layer 30 having excellent characteristics by suppressing the deviation of the composition of the dielectric in the layer. According to the manufacturing method of the present embodiment, it is possible to provide the actuator 200 having the dielectric layer 30 having excellent characteristics in which the bias of the composition of the dielectric is suppressed in the layer.

  As described above, the embodiments of the present invention have been described in detail. However, those skilled in the art can easily understand that many modifications can be made without departing from the novel matters and effects of the present invention. . Accordingly, all such modifications are intended to be included in the scope of the present invention.

Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. Sectional drawing which shows typically the manufacturing method of the piezoelectric element 100 concerning this embodiment. 1 is a cross-sectional view schematically showing a piezoelectric element 100 according to an embodiment. The schematic diagram explaining an example of a composition distribution of a prior art example. The schematic diagram explaining an example of the composition distribution of this embodiment. A sectional view showing actuator 200 concerning this embodiment typically. The depth direction analysis result of the lead zirconate titanate layer concerning this embodiment. The depth direction analysis result of the lead zirconate titanate layer concerning an experiment example.

Explanation of symbols

1 silicon substrate, 2 silicon oxide layer, 3 elastic plate, 10 substrate, 20 lower electrode,
30 dielectric layer, 40 upper electrode, 100 piezoelectric element, 200 actuator,
301, 302, 303 Precursor layer, 311, 311a Layered part,
312,313 Layered part

Claims (5)

Forming a lower electrode above the substrate;
Performing a set of a first step of forming a layered portion above the lower electrode and a second step of thinning the layered portion by chemical mechanical polishing one or more times to form a dielectric layer;
Forming an upper electrode above the dielectric layer. In claim 1,
The first step includes
Forming one precursor layer;
And crystallization of the precursor layer to form the layered portion. In claim 1,
The first step includes
Laminating a plurality of precursor layers;
And a step of crystallizing the plurality of precursor layers to form the layered portion. A first step of forming a layered portion above the substrate;
A second step of thinning the layered portion by chemical mechanical polishing,
A method for manufacturing a dielectric layer, wherein the combination of the first step and the second step is performed one or more times. Forming a lower electrode above the elastic plate;
Performing a set of a first step of forming a layered portion above the lower electrode and a second step of thinning the layered portion by chemical mechanical polishing one or more times to form a dielectric layer;
Forming an upper electrode above the dielectric layer;
A method for manufacturing an actuator, comprising:

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