JP2014123584A - Method for manufacturing substrate with piezoelectric thin film and method for manufacturing piezoelectric thin film element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a substrate with a KNN piezoelectric thin film finely processed to a desired pattern and capable of lowering a manufacturing cost, and a method for manufacturing a KNN piezoelectric thin film element.SOLUTION: A method for manufacturing a substrate with a piezoelectric thin film comprises the steps of: forming a lower electrode 2 on a substrate 1; forming a piezoelectric thin film 3 composed of potassium sodium niobate on the lower electrode; forming an etching mask film 5 composed of chrome and having a desired pattern on the piezoelectric thin film (etching mask pattern forming step); diffusing an etching accelerating element composed of titanium or tantalum into a piezoelectric thin film in a region other than the region where an etching mask pattern 5' is formed; and applying fine processing of the desired pattern to the piezoelectric thin film by performing wet etching for the piezoelectric thin film in the region where the etching accelerating element is diffused using an etchant containing hydrofluoric acid (piezoelectric thin film etching step).

Description

  The present invention relates to a method for manufacturing a piezoelectric element, and more particularly to a substrate having a lead-free piezoelectric thin film and a method for manufacturing a piezoelectric thin film element.

A piezoelectric element is an element that uses the piezoelectric effect of a piezoelectric body, such as an actuator that generates displacement and vibration when a voltage is applied to the piezoelectric body, and a stress sensor that generates voltage when stress is applied to the piezoelectric body. It is widely used as a functional electronic component. Piezoelectric materials that have been used for actuators and stress sensors so far have a large piezoelectric characteristic, such as lead zirconate titanate-based ferroelectrics (composition formula: Pb (Zr _1-x Ti _x ) O ₃ , PZT ) Has been widely used.

  Although PZT is a specific hazardous substance containing lead, there is currently no suitable commercial product that can be used as a piezoelectric material. Therefore, the RoHS Directive (European Parliament on Restrictions on the Use of Specific Hazardous Substances in Electrical and Electronic Equipment) As well as exemptions from the Council Directive). However, the demand for global environmental protection is increasing worldwide, and the development of piezoelectric elements using piezoelectric materials (lead-free piezoelectric materials) that do not contain lead is strongly desired. In recent years, demands for piezoelectric thin film elements using thin film technology are increasing with the demands for reducing the size and weight of various electronic devices.

As a piezoelectric thin film element using a lead-free piezoelectric material, for example, in Patent Document 1, a piezoelectric thin film element having a lower electrode, a piezoelectric thin film, and an upper electrode on a substrate, the piezoelectric thin film is expressed by a composition formula (Na _x K _y Li _z ) NbO ₃ (0 <x <1, 0 <y <1, 0 ≦ z <1, x + y + z = 1) Dielectric thin film composed of an alkali niobium oxide perovskite compound And between the piezoelectric thin film and the lower electrode, the buffer layer has a perovskite crystal structure and has a plane orientation of (001), (100), (010), and (111) A piezoelectric thin film element characterized by providing a thin film of a material that is easily oriented with a high degree of orientation is disclosed. According to Patent Document 1, a piezoelectric thin film element using a lead-free lithium potassium sodium niobate thin film is said to provide sufficient piezoelectric characteristics.

  The piezoelectric element has a basic structure in which a piezoelectric body is sandwiched between two electrodes, and is manufactured by being finely processed into a beam shape or a tuning fork shape depending on the application. For this reason, the microfabrication process is one of the very important technologies when a piezoelectric element using a lead-free piezoelectric material is put into practical use.

For example, in Patent Document 2, a piezoelectric thin film wafer having a piezoelectric thin film (composition formula: (K _1-x Na _x ) NbO ₃ , 0.4 ≦ x ≦ 0.7) on a substrate is used using a gas containing Ar. A first processing step for performing ion etching, and a second processing step for performing reactive ion etching using a mixed etching gas in which a fluorine-based reactive gas and Ar are mixed, following the first processing step. A method for manufacturing a piezoelectric thin film wafer is disclosed. According to Patent Document 2, a piezoelectric thin film can be finely processed with high accuracy, and a highly reliable piezoelectric thin film element and an inexpensive piezoelectric thin film device are obtained.

Non-Patent Document 1 discloses a method for processing a ridge-type waveguide for an optical waveguide of lithium niobate (composition formula: LiNbO ₃ ) crystal, in which lithium niobate is mixed into a solution in which benzoic acid and adipic acid are mixed at a certain ratio. After mixing and exchanging atoms and protons in lithium niobate by proton exchange reaction, mixing with hydrofluoric acid (HF) and nitric acid (HNO ₃ ) using a metal mask such as tantalum (Ta) or chromium (Cr) A method of wet etching with a solution is disclosed. According to Non-Patent Document 1, when wet etching is performed by the above method, a ridge-type waveguide for an optical waveguide having a good taper shape and a smooth surface is obtained.

JP 2007-19302 A JP 2012-33693 A

Tien-Lun Ting, Liang-Yin Chen, and Way-Seen Wang: “A Novel Wet-Etching Method Using Joint Proton Source in LiNbO3” IEEE Photon. Technol. Lett., Vol. 18, No. 4, pp. 568- 570, 2006.

As a lead-free piezoelectric material, potassium sodium niobate (composition formula: (K _1-x Na _x ) NbO ₃ , sometimes referred to as KNN below) is considered to be a very promising material, but microfabrication to KNN There are only a few examples of process reports, and there are still many technical unclear points. Further, the microfabrication process by dry etching as in Patent Document 2 has a weak point that the process time is long and the manufacturing cost is likely to increase because the dry etching apparatus is expensive and the etching rate itself is low.

  In general, the wet etching process has an etching rate higher than that of the dry etching process, which is advantageous in reducing the manufacturing cost. Therefore, with reference to the purification of niobium metal from niobium ore (for example, columbite) (solvent extraction method), the present inventors performed wet etching of KNN using high-concentration hydrofluoric acid as an etching solution. Unfortunately, a sufficient etching rate could not be obtained.

  On the other hand, application of wet etching using proton exchange reaction as in Non-Patent Document 1 is concerned that protons diffuse into the piezoelectric thin film and the characteristics of the KNN piezoelectric body are degraded.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and provide a method for finely processing potassium sodium niobate (KNN), which is a lead-free piezoelectric material, into a desired pattern in a simple and short time, and use that method. It is an object of the present invention to provide a method for manufacturing a substrate having a KNN piezoelectric thin film microfabricated into a desired pattern and a method for manufacturing a KNN piezoelectric thin film element, which can reduce the manufacturing cost.

(I) One aspect of the present invention is a method for manufacturing a substrate having a piezoelectric thin film in order to achieve the above object, and a lower electrode forming step of forming a lower electrode on the substrate;
A piezoelectric thin film forming step of forming a piezoelectric thin film made of potassium sodium niobate on the lower electrode;
An etching mask pattern forming step of forming an etching mask made of chromium on the piezoelectric thin film so as to have a desired pattern;
An etching promoting element diffusion step of diffusing an etching promoting element made of titanium or tantalum into the piezoelectric thin film in a region other than the region where the etching mask pattern is formed;
Piezoelectric thin film etching that performs fine processing of a desired pattern on the piezoelectric thin film by performing wet etching using an etching solution containing hydrofluoric acid on the piezoelectric thin film in the region where the etching promoting element is diffused And a method of manufacturing a substrate having a piezoelectric thin film.

Further, the present invention can add the following improvements and changes to the method for manufacturing a substrate having the piezoelectric thin film according to the present invention.
(I) The etching promoting element diffusion step includes forming an etching promoting element layer on the piezoelectric thin film in a region other than the region where the etching mask pattern is formed;
A diffusion heat treatment step of diffusing the etching promoting element in the piezoelectric thin film by heating at a temperature of 400 ° C. to 800 ° C. in a non-oxidizing atmosphere.
(Ii) The etching solution in the piezoelectric thin film etching step is selected from hydrofluoric acid, a mixed solution of hydrofluoric acid and hydrochloric acid, a mixed solution of hydrofluoric acid and sulfuric acid, and a mixed solution of hydrofluoric acid and nitric acid. It is.
(Iii) The lower electrode is made of platinum.
(Iv) The piezoelectric thin film forming step is performed by a sputtering method so that the piezoelectric thin film has a composition formula (K _1-x Na _x ) NbO ₃ (0.4 ≦ x ≦ 0.7).
(V) The piezoelectric thin film is formed so that the crystal system is a pseudo cubic system and the main surface is preferentially oriented in the (001) plane.
(Vi) The substrate is a silicon substrate having a thermal oxide film on the surface thereof.

(II) Another aspect of the present invention is a method for manufacturing a piezoelectric thin film element in order to achieve the above object, wherein a desired pattern is formed by the method for manufacturing a substrate having the piezoelectric thin film according to the present invention. An upper electrode forming step of forming an upper electrode on the finely processed piezoelectric thin film;
And a dicing step of cutting out a chip-like piezoelectric thin film element from a substrate having the piezoelectric thin film on which the upper electrode is formed.

  According to the present invention, it becomes possible to finely process potassium sodium niobate (KNN), which is a lead-free piezoelectric material, into a desired pattern easily and in a short time. It is possible to provide a method for manufacturing a substrate having a KNN piezoelectric thin film finely processed into a pattern and a method for manufacturing a KNN piezoelectric thin film element.

It is an expanded sectional schematic diagram which shows the manufacturing process of the board | substrate which comprises the KNN piezoelectric material thin film which concerns on this invention. It is an expanded section schematic diagram showing a manufacturing process of a KNN piezoelectric thin film element concerning the present invention.

The present inventors have focused on KNN ((K _1-x Na _x ) NbO ₃ ) as a lead-free piezoelectric material that can be expected to have the same piezoelectric characteristics as PZT (Pb (Zr _1-x Ti _x ) O ₃ ). The present inventors have intensively studied a wet etching method for the material. As a result, it has been found that when an etching promoting element made of titanium (Ti) or tantalum (Ta) is diffused in the piezoelectric thin film, the etching property with respect to an etching solution containing hydrofluoric acid is dramatically improved. The present invention has been completed based on this finding.

  Embodiments according to the present invention will be described below with reference to the drawings. However, the present invention is not limited to the embodiments taken up here, and can be appropriately combined and improved without departing from the technical idea of the invention.

  FIG. 1 is an enlarged schematic cross-sectional view showing a manufacturing process of a substrate having a KNN piezoelectric thin film according to the present invention. In the following description, although the washing step and the drying step are omitted, it is preferable that these steps are appropriately performed as necessary.

First, the substrate 1 is prepared. The material of the substrate 1 is not particularly limited, and can be appropriately selected according to the use of the piezoelectric element. For example, silicon (Si), SOI (Silicon on Insulator), quartz glass, gallium arsenide (GaAs), sapphire (Al ₂ O ₃ ), metals such as stainless steel, magnesium oxide (MgO), strontium titanate (SrTiO ₃ ) Can be used. When the substrate 1 is made of a conductive material, it is preferable to have an electrical insulating film (for example, an oxide film) on the surface. Although there is no particular limitation on the method for forming the oxide film, for example, a thermal oxidation process or a chemical vapor deposition (CVD) method can be suitably used.

(Lower electrode formation process)
In this step, the lower electrode 2 is formed on the substrate 1 (see FIG. 1A). The material of the lower electrode 2 is not particularly limited, but it is preferable to use platinum (Pt) or an alloy containing Pt as a main component. Since Pt is inactive with respect to the etching solution used in the piezoelectric thin film etching process described later, it can function as an etching stopper. The method for forming the lower electrode 2 is not particularly limited, but for example, a sputtering method can be suitably used. The lower electrode 2 preferably has an arithmetic average surface roughness Ra of 0.86 nm or less in order that a piezoelectric thin film described later exhibits sufficient piezoelectric characteristics.

(Piezoelectric thin film formation process)
In this step, the piezoelectric thin film 3 is formed on the lower electrode 2 (see FIG. 1A). As a material of the piezoelectric body, it is preferable to use KNN ((K _1-x Na _x ) NbO ₃ , 0.4 ≦ x ≦ 0.7). As a method for forming the piezoelectric thin film 3, a sputtering method using a KNN sintered body target or an electron beam evaporation method is preferable. This is because the sputtering method and the electron beam evaporation method are excellent in terms of film reproducibility, film forming speed, and running cost, and can control the orientation of the KNN crystal. In the piezoelectric thin film 3 to be formed, it is preferable in terms of piezoelectric properties that the crystal system of the KNN crystal is a pseudo-cubic crystal and the main surface of the thin film is preferentially oriented to the (001) plane.

  The piezoelectric thin film 3 contains impurities of lithium (Li), Ta, antimony (Sb), calcium (Ca), copper (Cu), barium (Ba), and Ti within a total range of 5 atomic% or less. Also good.

(Etching mask formation process)
In this step, an etching mask for wet etching described later is formed on the formed piezoelectric thin film 3. First, a photoresist pattern 4 is formed on the piezoelectric thin film 3 by a photolithography process (see FIG. 1B). Next, an etching mask film 5 is formed on the photoresist pattern 4 (see FIG. 1C). Next, an etching mask pattern 5 ′ having a desired pattern is formed by a lift-off process (see FIG. 1D). The etching mask film 5 (etching mask pattern 5 ′) is not particularly limited as long as it has sufficient resistance to the etching solution. From the viewpoint of ease of formation and cost, for example, chromium (Cr ) Film formation is preferred. Note that the etching mask pattern 5 ′ may be formed by a process other than photolithography / lift-off.

(Etching promoting element layer forming process)
In this step, an etching promoting element layer is formed in a region to be removed by wet etching in a later step. First, a photoresist pattern 6 is formed on the etching mask pattern 5 ′ by a photolithography process (see FIG. 1E). Next, an etching promoting element film is formed, and an etching promoting element layer 7 is formed on the piezoelectric thin film 3 in a region other than where the etching mask pattern 5 ′ is formed by a lift-off process (FIG. 1F). reference). As the etching promoting element, titanium (Ti) or tantalum (Ta) is preferable. The reason why Ti or Ta is preferable will be described later.

  The method for forming the etching promoting element layer 7 is not particularly limited, and a physical vapor deposition method (for example, sputtering method or electron beam evaporation method) or a coating method (for example, sol-gel method) can be used. The film thickness of the etching promoting element layer 7 is preferably 2 to 10 nm. When the film thickness is 2 nm or less, the diffusion amount of the etching promoting element (Ti or Ta) becomes insufficient in the diffusion heat treatment step described later, and a sufficient etching rate cannot be obtained. Moreover, since a sufficient etching rate can be obtained if the film thickness is 10 nm, forming a film thicker than 10 nm results in useless process costs.

(Diffusion heat treatment process)
In this step, heat treatment is performed to diffuse the etching promoting element (Ti or Ta) in a desired region of the piezoelectric thin film 3 (region to be removed by wet etching in the subsequent step) (see FIG. 1G). As heat treatment conditions, heating at a temperature of 400 ° C. or higher and 800 ° C. or lower is preferable in a non-oxidizing atmosphere. When the heat treatment temperature is less than 400 ° C., a sufficient diffusion rate cannot be obtained, and the amount of diffusion of Ti or Ta into the piezoelectric thin film 3 becomes insufficient. If the heat treatment temperature is higher than 800 ° C., the piezoelectric thin film 3 may be peeled off from the lower electrode 2. Note that the non-oxidizing atmosphere means an atmosphere substantially free of oxygen (for example, in nitrogen, argon, or a vacuum of about 1 Pa).

  The above-described etching promoting element layer forming step and diffusion heat treatment step are collectively referred to as an etching promoting element diffusion step. As an etching promoting element diffusion step, an ion implantation method using an ion source of an etching promoting element (Ti or Ta) may be used instead of the combination of the etching promoting element layer forming step and the diffusion heat treatment step described above. Is possible.

(Piezoelectric thin film etching process)
In this step, wet etching is performed on the piezoelectric thin film 3 in the region where the etching promoting element (Ti or Ta) is diffused, and fine processing is performed to a pattern defined by the etching mask pattern 5 ′. An etchant containing hydrofluoric acid as an etchant (specifically, one selected from hydrofluoric acid, a mixed liquid of hydrofluoric acid and hydrochloric acid, a mixed liquid of hydrofluoric acid and sulfuric acid, and a mixed liquid of hydrofluoric acid and nitric acid) ) Can be used to perform wet etching at room temperature (for example, 25 ° C.). Since these etching solutions are inactive with respect to the etching mask pattern 5 ′ made of Cr and the lower electrode 2 made of Pt (including a Pt alloy), the piezoelectric thin film pattern 3 ′ having a desired pattern is formed. It can be formed (see FIG. 1 (h)). As chemicals for the etching solution, commercially available chemicals for electronic industry (hydrofluoric acid (49 mass%), hydrochloric acid (36 mass%), sulfuric acid (96 mass%), nitric acid (61 mass%)) can be used. .

  After the above wet etching, the etching mask pattern 5 ′ is removed by using an etching solution for Cr film (for example, ceric ammonium nitrate, potassium ferricyanide), and the KNN piezoelectric material microfabricated into a desired pattern A substrate 10 having a thin film can be obtained (see FIG. 1 (i)).

(Upper electrode formation process)
FIG. 2 is an enlarged schematic cross-sectional view showing the manufacturing process of the KNN piezoelectric thin film element according to the present invention. In this step, the upper electrode is formed on the piezoelectric thin film (piezoelectric thin film pattern 3 ′) finely processed into the desired pattern obtained in the previous step. First, a photoresist pattern 8 is formed by leaving a space for forming an upper electrode by a photolithography process, and an upper electrode film 9 is formed on the photoresist pattern 8 (see FIG. 2A). Next, the rest of the upper electrode 9 ′ is removed by the lift-off process (see FIG. 2B). As a material of the upper electrode film 9 (upper electrode 9 ′), for example, aluminum (Al), gold (Au), nickel (Ni), Pt, or the like can be preferably used.

(Dicing process)
In this step, the chip-like piezoelectric thin film element 20 is cut out from the substrate having the piezoelectric thin film pattern 3 ′ on which the upper electrode 9 ′ is formed (see FIG. 2C). Thereby, the piezoelectric thin film element 20 including the KNN piezoelectric thin film finely processed into a desired pattern can be obtained.

  Hereinafter, the present invention will be described more specifically based on examples. However, the present invention is not limited to these examples.

(Production of Substrate (Examples 1 to 8 and Comparative Examples 1 to 10) having a KNN piezoelectric thin film finely processed into a desired pattern)
In accordance with the manufacturing process shown in FIG. 1, a substrate having a KNN piezoelectric thin film finely processed into a desired pattern was produced. As the substrate 1, a Si substrate with a thermal oxide film (4 inch wafer with (100) plane orientation, wafer thickness 0.525 mm, thermal oxide film thickness 200 nm) was used.

  First, a Ti layer having a thickness of 2.2 nm was formed on the Si substrate by sputtering as an adhesion layer for improving the adhesion between the Si substrate and the lower electrode. Subsequently, a Pt layer having a thickness of 205 nm was formed as a lower electrode 2 on the Ti layer by sputtering (see FIG. 1A). The sputter deposition conditions for the adhesion layer and the lower electrode were a substrate temperature of 250 ° C., a discharge power of 200 W, an Ar atmosphere, and a pressure of 2.5 Pa. The surface roughness of the deposited lower electrode 2 was measured, and it was confirmed that the arithmetic average surface roughness Ra was 0.86 nm or less.

Next, (K _0.35 Na _0.65 ) NbO ₃ having a thickness of 2 μm was formed as a piezoelectric thin film 3 on the lower electrode 2 by RF magnetron sputtering (see FIG. 1A). The sputtering conditions for the KNN thin film were as follows: substrate temperature 520 ° C., discharge power 700 W, mixed atmosphere of oxygen gas and argon gas (mixing ratio: O ₂ /Ar=0.005), pressure 1.3 Pa.

  Next, a photoresist (OFPR-800, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied, exposed, and developed on the piezoelectric thin film 3 to form a photoresist pattern 4 (see FIG. 1B). Subsequently, a Cr film having a thickness of 200 nm was formed as an etching mask film 5 by RF magnetron sputtering (see FIG. 1C). The film formation conditions for the Cr film were a substrate temperature of 25 ° C., a discharge power of 50 W, an Ar atmosphere, and a pressure of 0.8 Pa. Thereafter, the photoresist pattern 4 was removed by lift-off with acetone (lift-off), and an etching mask pattern 5 'was formed on the piezoelectric thin film 3 (see FIG. 1D).

  Next, a photoresist (OFPR-800, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied, exposed and developed on the etching mask pattern 5 'to form a photoresist pattern 6 (see FIG. 1 (e)). Subsequently, Ti films having various thicknesses were formed by sputtering as the etching promoting element film 7 on the piezoelectric thin film 3 on which the photoresist pattern 6 was formed (see FIG. 1F). The thickness of the Ti film is shown in Table 1 described later. In Table 1, “Ti film thickness = 0 nm” means that no Ti film was formed. The conditions for forming the Ti film were a substrate temperature of 25 ° C., a discharge power of 300 W, an Ar atmosphere, and a pressure of 7 Pa. Thereafter, the photoresist pattern 6 is removed by lift-off with acetone (lift-off), and a Ti film is formed in a region other than the region where the etching mask pattern 5 ′ is formed (region removed by wet etching in a later step) (FIG. 1F). )reference).

  Next, diffusion heat treatment is performed on the entire substrate in a non-oxidizing atmosphere (Ar atmosphere) at various temperatures, and Ti is applied to a predetermined region of the piezoelectric thin film 3 (region to be removed by wet etching in a later step). Diffused. The heat treatment temperature is also shown in Table 1 described later. The heat treatment time was unified for 60 minutes.

  Next, a small piece (5 × 10 mm) is cut out from the substrate subjected to the diffusion heat treatment, and the piezoelectric thin film 3 is wet-etched using various etching solutions to form the piezoelectric thin film pattern 3 ′. (See FIG. 1 (h)). The etching solution is also shown in Table 1 described later. In Table 1, "HF" is a commercially available electronic industrial chemical hydrofluoric acid (49 mass%), and "HF + HCl" is a commercial electronic industrial chemical hydrofluoric acid and hydrochloric acid (36 mass%). ). Etching was performed at room temperature (about 25 ° C.).

(Analysis / Evaluation)
(A) SIMS measurement
Secondary ion mass spectrometry (secondary ion mass spectrometry) was performed on a sample (Example 1) in which a Ti film was formed and subjected to diffusion heat treatment, and a sample (TiN 1) in which no Ti film was formed and subjected to diffusion heat treatment. The composition of the piezoelectric thin film was analyzed in the depth direction by Spectrometry (SIMS), and the presence or absence of Ti diffusion was investigated. As a result, in Comparative Example 1, a significant amount of Ti component was not detected, whereas in Example 1, Ti component was detected in the piezoelectric thin film. From this, it was confirmed that Ti formed on the piezoelectric thin film diffuses into the piezoelectric thin film by the diffusion heat treatment step described above.

(B) Evaluation of etching property In each sample, the etching rate (nm / min) was calculated from the film thickness of the piezoelectric thin film 3 and the time required for wet etching (time until the lower electrode 2 was exposed). The calculated values are also shown in Table 1. From the viewpoint of manufacturing cost reduction, an etching rate of 400 nm / min or more was judged as acceptable, and less than 400 nm / min was judged as unacceptable.

(Results and discussion)
As shown in Table 1, Examples 1 to 8 according to the present invention were all judged to be acceptable, and an etching rate clearly higher than those of Comparative Examples 1 to 10 was obtained. Specifically, when the etching solution was HF, the etching rate of the example was slightly more than 2 to 5 times higher than the etching rate of the comparative example. It was also found that the etching rate was higher when the etchant was a mixed solution of HF and HCl than when HF alone.

  Although the mechanism by which the etching rate is greatly improved in the above-described embodiments has not been completely elucidated, one of the causes is that some Nb ions (pentavalent) in the KNN crystal are tetravalent Ti ions. This is considered to be because the conductivity of the KNN crystal was improved and the reactivity with the etching solution was improved by the substitution and the Ti ion acting as an acceptor.

  On the other hand, from the results of Comparative Examples 1 to 3, the piezoelectric thin film on which the Ti film was not formed failed because a sufficient etching rate was not obtained regardless of the presence or absence of heat treatment. This is probably because the reactivity between the KNN crystal and the etching solution is not so high.

  Further, in Comparative Examples 4, 6, 7, and 10, in which the heat treatment temperature in the diffusion heat treatment step is lower than the regulation of the present invention (350 ° C.), the heat treatment temperature is too low, so Ti is sufficiently contained in the piezoelectric thin film. This is probably because it did not spread. Further, in Comparative Example 5 in which the heat treatment temperature in the diffusion heat treatment step was higher than that specified in the present invention (850 ° C.), the piezoelectric thin film was peeled off from the lower electrode. This was considered due to the difference in thermal expansion of each layer.

  In the above-described example, it was separately confirmed that even when a Ta film was formed instead of the Ti film and diffused in the piezoelectric thin film, the same effect as that of Ti was obtained. The same effect can also be obtained when a mixed solution of hydrofluoric acid and sulfuric acid (volume ratio = 15: 1) or a mixed solution of hydrofluoric acid and nitric acid (volume ratio = 15: 1) is used as the etching solution. It was confirmed separately.

  As described above, according to the present invention, potassium sodium niobate (KNN), which is a lead-free piezoelectric material, can be finely processed into a desired pattern easily and in a short time using a wet etching method. Proven. As a result, it is possible to provide a method of manufacturing a substrate and a method of manufacturing a KNN piezoelectric thin film element that include a KNN piezoelectric thin film that has been finely processed into a desired pattern while reducing the manufacturing cost.

  Note that the above-described embodiments and examples have been specifically described in order to help understanding of the present invention, and the present invention is not limited to having all the configurations described. For example, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, replaced with another configuration, or added with another configuration.

1 ... Substrate, 2 ... Lower electrode, 3 ... Piezoelectric thin film, 3 '... Piezoelectric thin film pattern,
4, 6, 8 ... photoresist pattern, 5 ... etching mask film,
5 '... etching mask pattern, 7 ... etching promoting element layer,
9 ... Upper electrode film, 9 '... Upper electrode,
10 ... Substrate having a piezoelectric thin film, 20 ... Piezoelectric thin film element.

Claims (8)

A method of manufacturing a substrate comprising a piezoelectric thin film,
A lower electrode forming step of forming a lower electrode on the substrate;
A piezoelectric thin film forming step of forming a piezoelectric thin film made of potassium sodium niobate on the lower electrode;
An etching mask pattern forming step of forming an etching mask made of chromium on the piezoelectric thin film so as to have a desired pattern;
An etching promoting element diffusion step of diffusing an etching promoting element made of titanium or tantalum into the piezoelectric thin film in a region other than the region where the etching mask pattern is formed;
Piezoelectric thin film etching that performs fine processing of a desired pattern on the piezoelectric thin film by performing wet etching using an etching solution containing hydrofluoric acid on the piezoelectric thin film in the region where the etching promoting element is diffused And a process for producing a substrate having a piezoelectric thin film. In the manufacturing method of the board | substrate which comprises the piezoelectric material thin film of Claim 1,
The etching promoting element diffusion step includes an etching promoting element layer forming step of forming a layer of the etching promoting element on the piezoelectric thin film in a region other than the region where the etching mask pattern is formed,
And a diffusion heat treatment step of diffusing the etching promoting element in the piezoelectric thin film by heating at a temperature of 400 ° C. to 800 ° C. in a non-oxidizing atmosphere. Method. In the manufacturing method of the board | substrate which comprises the piezoelectric material thin film of Claim 1 or Claim 2,
The etching solution in the piezoelectric thin film etching step is one selected from hydrofluoric acid, a mixed solution of hydrofluoric acid and hydrochloric acid, a mixed solution of hydrofluoric acid and sulfuric acid, and a mixed solution of hydrofluoric acid and nitric acid. A method of manufacturing a substrate comprising a piezoelectric thin film characterized by the above. In the manufacturing method of the board | substrate which comprises the piezoelectric material thin film of Claim 1 thru | or 3,
The method for manufacturing a substrate having a piezoelectric thin film, wherein the lower electrode is made of platinum. In the manufacturing method of the board | substrate which comprises the piezoelectric material thin film of Claim 1 thru | or 4,
The piezoelectric thin film forming step is performed by sputtering so that the piezoelectric thin film has a composition formula (K _1-x Na _x ) NbO ₃ (0.4 ≦ x ≦ 0.7). The manufacturing method of the board | substrate which comprises this. In the manufacturing method of the board | substrate which comprises the piezoelectric material thin film of Claim 5,
The method for manufacturing a substrate having a piezoelectric thin film, wherein the piezoelectric thin film is formed so that a crystal system is a pseudo-cubic crystal and a main surface is preferentially oriented in a (001) plane. In the manufacturing method of the board | substrate which comprises the piezoelectric material thin film of Claims 1 thru | or 6,
The method of manufacturing a substrate having a piezoelectric thin film, wherein the substrate is a silicon substrate having a thermal oxide film on a surface thereof. A method for manufacturing a piezoelectric thin film element, comprising:
An upper electrode forming step of forming an upper electrode on the piezoelectric thin film finely processed into a desired pattern by the manufacturing method according to claim 1;
And a dicing step of cutting a chip-like piezoelectric thin film element from a substrate having the piezoelectric thin film on which the upper electrode is formed.

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