JP2020077788A - Piezoelectric thin film, manufacturing method thereof, and use thereof - Google Patents

Abstract

To provide a piezoelectric thin film having a desired piezoelectric response and reducing the stress generated in the piezoelectric thin film without complicating the structure and the process, and a manufacturing method thereof.SOLUTION: In a piezoelectric thin film containing a nitride containing Al as a constituent, the mole fraction of Ar is 0.7% to 1.0% with respect to the total amount of N, O, and Ar contained in the piezoelectric thin film, and the mole fraction of O is 6.0% to 9.0%.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piezoelectric thin film, a method for manufacturing the same, and its use.

  Stress is generated in the element provided with the piezoelectric thin film due to the film formation of the piezoelectric thin film. Depending on the degree of the stress, defects such as cracking and peeling of the piezoelectric thin film or deformation of the element itself occur. In order to prevent such problems, (i) development of the material itself used as the piezoelectric body and (ii) improvement of the structure of the piezoelectric thin film are under way. As a conventional technique related to (i), an AlN crystal as a piezoelectric thin film and a piezoelectric vibrator, at least one first element replaced with Al in the AlN crystal, and an ionic radius of Al smaller than the ionic radius of the first element. There is known a piezoelectric thin film having a larger ionic radius and containing a second element added to an Al crystal (Patent Document 1). As a conventional technique related to (ii), a structure in which a stress compensation layer is provided on the back side of a semiconductor device based on gallium nitride or another nitride (Patent Document 2) and a structure in which a slit for stress relaxation is provided (Patent Document 2) 3) is disclosed.

WO2016 / 111280 Japanese Patent Publication No. 2013-513944 JP, 2013-143682, A

  However, none of the above-mentioned conventional techniques is sufficient in providing a piezoelectric thin film in which stress generated in the thin film is reduced and which has a desired piezoelectric response without complicating the structure and the process. .. In the prior art (i), it is necessary to change the proportion of main constituent elements by using different materials in order to reduce the stress at the time of forming the piezoelectric layer. Further, the conventional technique (ii) has a problem that the device structure and the process are complicated as a result of providing the stress relaxation layer and the stress compensation layer.

  An object of one embodiment of the present invention is to provide a piezoelectric thin film that reduces stress generated in the piezoelectric thin film and has a desired piezoelectric response without complicating the structure and the process, and a manufacturing method thereof. And

  In order to solve the above problems, the present invention includes the inventions described in <1> to <8> below.

<1> A piezoelectric thin film containing a nitride containing Al as a constituent,
The mole fraction of Ar is 0.7% to 1.0% and the mole fraction of O is 6.0% to 9.0% with respect to the total amount of N, O and Ar contained in the piezoelectric thin film. Is a piezoelectric thin film.

  <2> The piezoelectric thin film according to <1>, wherein a part of Al in the nitride containing Al as a constituent is replaced by another metal element.

  <3> The piezoelectric thin film according to <2>, wherein the other metal element is Sc.

  <4> Any one of <1> to <3>, in which the arithmetic average height Sa of the surface is 3.0 nm to 9.0 nm, and the developed area ratio Sdr of the interface of the surface is 0.0002 to 0.015. The piezoelectric thin film described in 1.

  <5> A piezoelectric element comprising the piezoelectric thin film according to any one of <1> to <4>.

  <6> A piezoelectric device including the piezoelectric element according to <5>.

<7> A method for manufacturing a piezoelectric thin film according to any one of <1> to <4>,
A seed layer forming step of forming a seed layer by sputtering in a mixed gas atmosphere containing Ar gas and N ₂ gas at a first sputtering gas pressure using a target containing Al;
A growth layer forming step of forming a growth layer on the seed layer by sputtering by changing the sputtering gas pressure in the seed layer forming step to a second sputtering gas pressure higher than the first sputtering gas pressure. A method of manufacturing a piezoelectric thin film, comprising:

  <8> The method for manufacturing a piezoelectric thin film according to <7>, wherein the target is made of ScAl alloy.

  According to one aspect of the present invention, it is possible to provide a piezoelectric thin film that reduces stress generated in the piezoelectric thin film and has a desired piezoelectric response, and a method for manufacturing the same.

The result of having observed the laminated body of the piezoelectric thin film and the substrate concerning Embodiment 1 of the present invention is shown. (A) shows the result of observing the surface of the laminate on the piezoelectric thin film side by SEM. (B) shows the result of observing the surface of the laminated body on the piezoelectric thin film side with a laser microscope. (C) shows a height profile on the diagonal line (on the arrow shown in (b) of FIG. 1) of the surface of the piezoelectric thin film side. The result of having observed the layered product of the piezoelectric thin film and the substrate concerning the comparative example 1 of the present invention is shown. (A) shows the result of observing the surface of the laminate on the piezoelectric thin film side by SEM. (B) shows the result of observing the surface of the laminated body on the piezoelectric thin film side with a laser microscope. (C) shows the height profile on the diagonal line (on the arrow shown in (b) of FIG. 2) of the surface of the piezoelectric thin film side. The result of having observed the laminated body of the piezoelectric thin film and the substrate concerning the comparative example 2 of the present invention is shown. (A) shows the result of observing the surface of the laminate on the piezoelectric thin film side by SEM. (B) shows the result of observing the surface of the laminated body on the piezoelectric thin film side with a laser microscope. (C) shows the height profile on the diagonal line (on the arrow shown in (b) of FIG. 3) of the surface of the piezoelectric thin film side.

  Hereinafter, one embodiment of the present invention will be described in detail, but the present invention is not limited thereto. Unless otherwise specified in the present specification, “A to B” representing a numerical range means “A or more and B or less”.

[1. Piezoelectric thin film]
A piezoelectric thin film according to an embodiment of the present invention is a piezoelectric thin film containing a nitride containing Al as a constituent component, and the molar amount of Ar relative to the total amount of N, O and Ar contained in the piezoelectric thin film. The ratio is 0.7% to 1.0%, and the O mole fraction is 6.0% to 9.0%.

  The piezoelectric thin film is a piezoelectric thin film containing a nitride containing Al as a constituent, and more preferably a piezoelectric thin film containing a nitride containing Al as a main constituent. Here, “comprising as a main component” includes at least 50 mass% or more, preferably 80 mass% or more, more preferably 90 mass% or more, and further preferably 95 mass% or more with respect to the total amount of the piezoelectric thin film. Means that. The piezoelectric thin film may include an oxide in addition to the nitride containing Al as a constituent component.

  The piezoelectric thin film contains O and Ar in the piezoelectric thin film. O and Ar may be contained in the nitride containing Al as a constituent in the piezoelectric thin film. Here, Ar is derived from Ar gas used in manufacturing the piezoelectric thin film. Further, it is considered that O originates from the moisture adsorbed on the inner wall of the apparatus and the pipe portion, and the surface oxide film, the target and oxygen remaining in the introduced gas. In an embodiment of the present invention, the mole fraction of Ar to the total amount of N, O and Ar is 0.7% to 1.0%, and the mole fraction of O to the total amount of N, O and Ar is 6%. It is 0.0% -9.0%. By setting the mole fraction of Ar and O with respect to the total amount of N, O, and Ar within the above range, it is possible to realize a piezoelectric thin film in which the stress generated in the thin film is reduced and which has a desired piezoelectric response. ..

  In one embodiment of the present invention, the molar fraction of Ar with respect to the total amount of N, O and Ar contained in the piezoelectric thin film may be 0.7% to 1.0%, but is more preferably 0. 0.7% to 0.9%, more preferably 0.7% to 0.8%.

  Further, in one embodiment of the present invention, the molar fraction of O relative to the total amount of N, O and Ar contained in the piezoelectric thin film may be 6.0% to 9.0%, but is more preferable. Is 7.0% to 9.0%, more preferably 8.0 to 9.0%.

  In one embodiment of the present invention, a part of Al in a nitride containing Al as a constituent in the piezoelectric thin film may be replaced with another metal element. Examples of other metal elements that can replace a part of Al include Group 3 elements such as Sc (scandium) and Y (yttrium); Group 13 elements such as Ga (gallium) and In (indium); or these. A combination of two or more of the above elements can be mentioned. Substituting with the other metal element is preferable because the composition range of the wurtzite crystal structure exhibiting piezoelectricity can be expanded. Among them, the other metal element more preferably contains Sc, and more preferably Sc, from the viewpoint of improving the piezoelectric response of the piezoelectric thin film.

  In one embodiment of the present invention, the mole fraction of the other metal element relative to the total amount of Al and the other metal element is preferably 60% or less, more preferably 0.5% to 50%. When the mole fraction of the other metal element is within the above range, it is preferable from the viewpoint of piezoelectric response of the piezoelectric thin film. Further, in one embodiment of the present invention, the mole fraction of Sc with respect to the total amount of Al and other metal elements is preferably 60% or less, and more preferably 0.5% to 50%. When the mole fraction of Sc is within the above range, the piezoelectric response of the piezoelectric thin film can be further improved, which is preferable.

  The arithmetic average height Sa of the surface of the piezoelectric thin film is preferably 3.0 nm to 9.0 nm, more preferably 3.0 nm to 7.0 nm. Here, the arithmetic average height Sa is a value that represents the average of absolute values of height differences at respective points with respect to the average surface of the surface to be evaluated, which is defined in ISO 25718, and here, the piezoelectric body. It is one of the indexes for evaluating the surface roughness of the thin film. Specifically, the arithmetic average height Sa of the surface of the piezoelectric thin film is a value determined by the method described in the example.

  The developed area ratio Sdr of the interface on the surface of the piezoelectric thin film is preferably 0.0002 to 0.015, and more preferably 0.0008 to 0.010. Here, the developed area ratio Sdr of the interface is also specified in ISO 25718, and is a value that indicates how much the developed area (surface area) of the defined area increases with respect to the area of the defined area. It is one of the indicators to evaluate the quality. Specifically, the developed area ratio Sdr of the interface on the surface of the piezoelectric thin film is a value determined by the method described in the example. If it is a completely flat surface, the development area ratio Sdr of the interface will be zero.

  In one embodiment of the present invention, the film thickness of the piezoelectric thin film may be appropriately determined according to the application and the peripheral structure, and is not particularly limited, but is, for example, 0.5 μm to 10 μm, and more preferably Is 2.0 μm to 5.0 μm.

  In one embodiment of the present invention, the piezoelectric constant [pC / N] of the piezoelectric body is preferably 3 pC / N or more, and more preferably 10 pC / N or more. Here, the piezoelectric constant is an index representing the magnitude of the generated charge with respect to the applied force. It can be said that the larger the piezoelectric constant, the higher the piezoelectric response. Specifically, the piezoelectric constant is a value determined by the method described in the example. When the piezoelectric constant is within the above range, the performance expected in applications such as a high frequency filter for communication or various piezoelectric sensors can be satisfied.

  In one embodiment of the present invention, the piezoelectric thin film has a maximum height change of 10 μm or less on the surface of the piezoelectric thin film when formed on a silicon wafer of 24 mm × 24 mm × 0.5 mm. desirable. The "maximum change in height of the piezoelectric thin film surface (maximum displacement)" here is based on the straight line connecting the diagonal ends of the piezoelectric thin film formed on a 24 mm x 24 mm x 0.5 mm silicon wafer. It means the amount of change in height at the center of the diagonal line (hereinafter, referred to as “maximum displacement”). Specifically, the maximum displacement is a value determined by the method described in the example. It can be said that when a piezoelectric thin film having the same thickness is deposited, the smaller the maximum displacement is, the smaller the warp of the piezoelectric thin film is, that is, the stress generated in the piezoelectric thin film is reduced.

  The stress [MPa] generated in the piezoelectric thin film is a stress applied to the piezoelectric thin film due to a difference in physical properties between the substrate and the piezoelectric thin film. By laminating the piezoelectric thin film on the substrate, the stress generated in the thin film causes problems such as cracking and peeling of the piezoelectric thin film, and deformation of the piezoelectric element using the piezoelectric thin film. Specifically, the stress is a value determined by the method described in the examples. The stress generated in the piezoelectric thin film according to the embodiment of the present invention depends on the film thickness of the piezoelectric thin film, but is, for example, 0 MPa to 250 MPa when the thin film has a thickness of 2.5 μm. desirable.

[2. Method for manufacturing piezoelectric thin film]
The method for producing a piezoelectric thin film according to the present invention is not particularly limited as long as it is a method for producing a piezoelectric thin film as described in [1]. For example, the following method for producing a piezoelectric thin film is shown. Can be mentioned.

That is, the method for manufacturing a piezoelectric thin film according to the embodiment of the present invention is performed by using a target containing Al and performing sputtering at a first sputtering gas pressure in a mixed gas atmosphere containing Ar gas and N ₂ gas. And a seed layer forming step of forming a seed layer by changing the sputtering gas pressure in the seed layer forming step to a second sputtering gas pressure higher than the first sputtering gas pressure, and sputtering on the seed layer. And a growth layer forming step of forming a growth layer.

  In the method for manufacturing a piezoelectric thin film according to the embodiment of the present invention, a target containing Al is used. The target only needs to contain Al. Therefore, the target may be a target made of Al or an alloy containing Al and the above-mentioned “other metal element”. Regarding “other metal elements”, [1. Piezoelectric thin film]. The target is preferably an alloy containing Sc, and more preferably a ScAl alloy from the viewpoint of improving the piezoelectric response of the piezoelectric thin film.

  In the above alloy, the mole fraction of the other metal element in the alloy is preferably 60% or less, more preferably 0.5% to 50%, although it depends on the kind of the other metal element. Further, in the above alloy, the mole fraction of Sc with respect to the alloy is preferably 60% or less, and more preferably 0.5% to 50%.

  When manufacturing a piezoelectric thin film containing the other metal element, it is more preferable to use the alloy in terms of simplification of the manufacturing process and the apparatus, but a target made of Al and a target made of the other metal element are preferable. You may perform sputtering using.

In one embodiment of the present invention, the sputtering is performed in a mixed gas atmosphere containing Ar gas and N ₂ gas. The mixed gas may include Ar gas and N ₂ gas. Therefore, the mixed gas may include gases such as O ₂ , ozone, nitrogen dioxide, water vapor, and hydrogen peroxide, in addition to Ar gas and N ₂ gas.

The nitrogen gas concentration in the mixed gas is preferably 10% by volume to 99.9999% by volume, and more preferably 20% by volume to 50% by volume from the viewpoint of improving the piezoelectric response of the piezoelectric thin film. The Ar gas concentration in the mixed gas is preferably 90% by volume or less, and more preferably 50% by volume to 80% by volume. The gas concentration of O ₂ , ozone, nitrogen dioxide, water vapor, hydrogen peroxide, etc. in the mixed gas is preferably 1% by volume or less.

  The piezoelectric thin film can be formed on a substrate. Examples of the substrate include silicon, sapphire, silicon carbide, gallium nitride, lithium niobate, tantalum niobate, crystal, glass, metal, stainless steel, nickel alloy, aluminum alloy, polyetherimide (PEI) or polyetheretherketone (PEEK). ) And other engineering plastics, polymer films and the like can be used. Examples of the polymer film include a polyimide film, a polycarbonate film, a polyethylene terephthalate (PET) film, a liquid crystal polymer (LCP) film, and the like.

  In one embodiment of the present invention, the molar fractions of Ar and O with respect to the total amount of N, O and Ar are determined by changing the sputtering gas pressure from the first sputtering gas pressure to the first sputtering gas pressure during the process of forming the piezoelectric thin film. By changing the second sputtering gas pressure higher than the sputtering gas pressure, the above range can be adjusted.

  During the film formation with the first sputtering gas pressure, the distance between the substrate and the target is shorter than the mean free path of the sputtered particles, so that the sputtered particles rarely collide with other particles. Therefore, the sputtered energy jumps to and is captured by the substrate surface without significant loss of energy, and is deposited as a nitride. At this time, sputtered particles having sufficient energy and Ar particles which are sputtered gas reversely sputter the weakly-bonded portion that is being formed on the surface, and a structure having a strong bond, that is, (0001) having a high atomic density tends to remain. .. Thus, in order to remove the unnecessary bonding portion by the reverse sputtering, it is necessary that the Ar particles, which are the sputtering gas, collide with the substrate at a proper frequency while keeping sufficient energy. When this frequency increases, naturally Ar remaining inside the piezoelectric thin film also increases, and the stress of the piezoelectric thin film increases. Therefore, when a dense piezoelectric thin film in which a wurtzite crystal exhibiting piezoelectricity is (0001) -oriented and a high-stress state is formed, the molar fraction of Ar tends to increase. ..

  When the sputtering is carried out at the second sputtering gas pressure higher than the first sputtering gas pressure, the gas pressure is increased, so that the particle density in the space is increased and the mean free path is shortened. As a result, it becomes difficult for the sputtered particles to reach the surface of the substrate without colliding with other particles. Therefore, when the sputtered particles reach the substrate, they lose energy more than when the film is formed at the first sputtering gas pressure, and N or O They combine to form diatomic bodies and fly onto the substrate. As a result, growth other than (0001) cannot be sufficiently suppressed, and preferential growth of (0001) is impeded, resulting in a decrease in the degree of (0001) orientation and piezoelectricity. When the (0001) orientation decreases and the crystal plane having a low in-plane atomic density becomes the growth surface, the stress decreases as compared with that until then. At the same time, for example, when (10-10) is formed, it is considered that Al—O bonds are easily generated with defects, instead of weak Al—N bonds in the (10-10) direction. As a result, it is considered that a piezoelectric thin film having a high O molar concentration is formed although the stress is low.

  By the film formation under the first sputtering gas pressure, a dense piezoelectric thin film in which wurtzite type crystal exhibiting piezoelectricity is (0001) oriented is formed in a high stress state. Subsequent to this, when film formation is performed at the second sputtering gas pressure, single sputtered particles that have lost energy as compared with the film formation at the first sputtering gas pressure, or diatomic bodies that combine with N or O are formed. The Al-N and Al-O particles constituting the above will fly onto the substrate. A (0001) oriented film has already been formed on the substrate, but since there are no sites on this surface that can adsorb Al-N diatomic bodies, the single sputtered particles that have lost energy will continue to exist until then. It will grow while maintaining (0001). As a result, it becomes possible to obtain a piezoelectric thin film that exhibits high piezoelectricity while suppressing an increase in the molar concentration of O and accumulation of stress in the piezoelectric thin film. Therefore, the piezoelectricity is high and the stress is low in the region lower than the Ar mole fraction required to obtain high piezoelectricity and lower than the O mole fraction required to exhibit the stress suppressing effect. It is considered that the area where the piezoelectric thin film can be formed can be found.

  In the sputtering, the alloy target material can be produced by, for example, high frequency induction heating, arc melting, or a method of compacting and sintering element powder or alloy powder.

In the sputtering, the internal pressure of the sputtering chamber is not particularly limited as long as sputtering is possible, but for example, it can be performed under 1 × 10 ⁻¹ Pa to 4 × 10 ⁰ Pa. Preferably, it is performed at 0.3 × 10 ⁻¹ Pa to 3 × 10 ⁰ Pa.

  The temperature of the substrate in the sputtering step is not particularly limited, but is preferably in the range of 400K to 650K from the viewpoint of easy control of the polarity of the piezoelectric thin film.

  In one embodiment of the present invention, the sputtering is first performed at a first sputtering gas pressure of preferably 0.1 Pa to 0.5 Pa, more preferably 0.3 Pa to 0.4 Pa to form the seed layer. Be seen. Then, in order to form a growth layer, the second sputtering gas pressure is preferably 0.5 Pa to 4.0 Pa, more preferably 1.0 Pa to 2.0 Pa. It is more preferable to continuously perform the two-step sputtering process without interruption in the middle, from the viewpoint of increasing the efficiency of the piezoelectric thin film process.

  The term "seed layer" described herein refers to the layer of the piezoelectric thin film that is first deposited on the substrate. Specifically, excellent piezoelectric characteristics obtained as a result of performing sputtering according to an embodiment of the present invention for 0.3 hours to 2 hours at a relatively low sputtering gas pressure of 0.1 Pa to 0.5 Pa. Is a layer having.

  The term "growth layer" as used herein refers to the layer formed on the seed layer. Specifically, it occurs in the piezoelectric thin film obtained as a result of performing the sputtering according to the embodiment of the present invention for 1 to 8 hours at a relatively high sputtering gas pressure of 0.5 to 4.0 Pa. A layer in which stress is relaxed more than that in the seed layer.

  Since the seed layer has high stress and is dense, crystals formed as the seed layer even under the condition that stress is less likely to be applied after the pressure is changed to the second sputtering gas pressure higher than the first sputtering gas pressure. The structure can be grown further. As a result, it is considered that the stress is relaxed and a piezoelectric thin film having excellent piezoelectricity is formed.

  The piezoelectric constant of the seed layer is preferably 3 pC / N or more, more preferably 10 pC / N or more. In the seed layer, the mole fraction of Ar is 0.6% to 1.0%, and the mole fraction of O is 6.0% to 9.0% with respect to the total amount of N, O and Ar. Preferably.

  The thickness of the seed layer is preferably 0.05 μm to 0.7 μm, more preferably 0.2 μm to 0.5 μm.

  The thickness of the growth layer is preferably 0.4 μm to 9.95 μm, more preferably 0.5 μm to 4.0 μm, still more preferably 1.0 μm to 3.0 μm.

  In one embodiment, it is preferable that the layer-constituting material containing the nitride containing Al as a constituent of the seed layer and the growth layer is the same, and the ratios of Al and other metal elements do not change.

[3. Piezoelectric element〕
The present invention also includes a piezoelectric element including the piezoelectric thin film according to the embodiment of the present invention.

  A piezoelectric element according to an embodiment of the present invention includes the piezoelectric thin film, and two electrodes provided on both sides of the piezoelectric thin film or two electrodes provided on either one of the upper and lower sides of the piezoelectric thin film. It is more preferable to include at least. As an example of a piezoelectric element according to an embodiment of the present invention, a surface acoustic wave filter element having a regular comb-shaped electrode arranged on a piezoelectric thin film, a unimorph structure piezoelectric element used in a piezoelectric speaker or the like, a bimorph structure piezoelectric element. Examples include an element and a laminated piezoelectric element formed by stacking a large number of piezoelectric elements.

[4. Piezoelectric device]
The present invention also includes a piezoelectric device including the piezoelectric element according to the embodiment of the present invention.

  The piezoelectric device is not particularly limited as long as it is a device including the above-described piezoelectric element. Examples of the piezoelectric device according to the embodiment of the present invention include an actuator, a sensor, an oscillation circuit, a filter circuit, a piezoelectric microphone, and a vibration power generation device.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention.

  Hereinafter, the present invention will be described based on Examples and Comparative Examples, but the present invention is not limited to the Examples.

[Measurement of physical properties]
The physical properties of the piezoelectric thin films and the contents of Ar and O in Examples and Comparative Examples were measured by the following methods. In each case, a piezoelectric thin film formed on a silicon wafer (size: 24 mm × 24 mm × 0.5 mm) substrate obtained in Examples and Comparative Examples was used as an evaluation sample.

(1) Piezoelectric constant The piezoelectric constant was measured by using a piezometer system PM300 manufactured by PiezoTest, clamping the upper and lower surfaces of the sample for evaluation, and applying a load of ± 0.25 N at a frequency of 110 Hz.

(2) Molar fraction of O and Ar Elemental analysis in the piezoelectric thin film was performed by SEM-EDX analysis using FE-SEM (HITACHI S-4300) and EDX (HORIBA EX-420). From the results, the molar fractions of Ar and O with respect to the total amount of Ar, N and O were calculated.

(3) Maximum displacement and stress Using a laser microscope VK-X1100 manufactured by KEYENCE, the height was measured over the entire surface of the piezoelectric thin film. Using the result, create a height profile on the diagonal of the piezoelectric thin film surface, and increase the distance between the straight line connecting both end points and the intersection of the straight line drawn to be parallel to this and the height profile. I decided to change. Furthermore, the maximum value of this height change was defined as the maximum displacement (δ).

Assuming that this height change caused by stacking the piezoelectric thin films follows a curved surface having a specific curvature, the curvature radius R was analytically obtained from the diagonal length of the substrate and δ. This R, the Young's modulus (Y _S ), the Poisson's ratio (ν _S ), the thickness (t _S ) and the thickness (t _f ) of the substrate are applied to the following Stoney equation to calculate the stress (σ) of the thin film. ) Was calculated.

(4) Surface roughness (Sa and Sdr)
The surface roughness (Sa and Sdr) defined by ISO25178 was measured using the laser microscope VK-X1100 manufactured by KEYENCE.

[Example 1]
A silicon wafer (p-type (100) silicon manufactured by Electronics End Materials Corporation) was used as a substrate. Using an Al-43 mol% Sc alloy (manufactured by Advantech) as a target, a piezoelectric thin film was formed on the substrate by rf magnetron sputtering under a nitrogen-argon mixed gas atmosphere. The size of the substrate was 24 mm x 24 mm x 0.5 mm, and the size of the target was 76 mm x 5 mm in diameter.

Specifically, using a parallel plate type sputtering device (L-332S-FH manufactured by Canon Anelva Co.), a high frequency applied voltage is 400 W (target power density 9.1 W / cm ² ), argon (Ar) gas (purity : 99.99995%), the flow rate of nitrogen (N ₂ ) gas (purity: 99.99995%) was 4 sccm, the substrate temperature was 480 K, and the substrate-target distance was 70 mm. The background pressure was less than 5 × 10 ⁻⁵ Pa. Then, sputtering was performed for 1 hour at a sputtering gas pressure of 0.4 Pa (film thickness of about 0.5 μm, seed layer forming step). Then, without interrupting the sputtering, the sputtering gas pressure was changed to 1.0 Pa, and sputtering was further performed for 4 hours (growth layer forming step).

  In this way, a piezoelectric thin film made of ScAl nitride was produced on the silicon wafer substrate. The thickness of the obtained piezoelectric thin film was 2.3 μm. When the molar fraction of Ar and O with respect to the total amount of N, O and Ar contained in this piezoelectric thin film was analyzed, the molar fraction of Ar was 0.77% and the molar fraction of O was 8.3. %Met.

  The result of observing the obtained laminated body of the piezoelectric thin film and the substrate is shown in FIG. In FIG. 1, (a) shows the result of observing the surface of the laminated body on the piezoelectric thin film side by SEM, and (b) shows the result of observing the surface of the laminated body on the piezoelectric thin film side by a laser microscope. , (C) show the height profile on the diagonal (on the arrow shown in (b) of FIG. 1) of the surface of the piezoelectric thin film side.

[Example 2]
A piezoelectric thin film was produced under the same conditions as in Example 1 except that the sputtering time in the growth layer forming step was changed from 4 hours to 1 hour. The thickness of the obtained piezoelectric thin film was 1 μm. When the mole fraction of Ar and O with respect to the total amount of N, O and Ar contained in this piezoelectric thin film was analyzed, the mole fraction of Ar was 0.88% and the mole fraction of O was 8.3. %Met.

[Comparative Example 1]
Under the same conditions as in Example 1, only the seed layer forming step was performed to produce a piezoelectric thin film. However, the sputtering time in the seed layer forming step was changed from 1 hour to 4 hours. The thickness of the obtained piezoelectric thin film was 2.3 μm. When the molar fraction of Ar and O with respect to the total amount of N, O and Ar contained in this piezoelectric thin film was analyzed, the molar fraction of Ar was 1.1% and the molar fraction of O was 9.4. %Met.

  The result of observing the obtained laminated body of the piezoelectric thin film and the substrate is shown in FIG. Since (a) to (c) in FIG. 2 are the same as those in the first embodiment, the description thereof is omitted here.

[Comparative Example 2]
Under the same conditions as in Example 1, only the growth layer forming step was performed to produce a piezoelectric thin film. However, the sputtering time in the growth layer forming step was changed from 4 hours to 6 hours. The thickness of the obtained piezoelectric thin film was 2.6 μm. Analysis of the mole fraction of Ar and O relative to the total amount of N, O and Ar contained in this piezoelectric thin film revealed that the mole fraction of Ar was 0.24% and the mole fraction of O was 18%. there were.

  The result of observing the obtained laminated body of the piezoelectric thin film and the substrate is shown in FIG. Since (a) to (c) in FIG. 3 are the same as those in the first embodiment, the description thereof is omitted here.

[Comparative Example 3]
Only the seed layer forming step was performed under the same conditions as in Example 1. The thickness of the obtained piezoelectric thin film was 0.5 μm. When the molar fraction of Ar and O with respect to the total amount of N, O and Ar contained in this piezoelectric thin film was analyzed, the molar fraction of Ar was 0.64% and the molar fraction of O was 6.8. %Met.

  The sputtering conditions of Examples 1 and 2 and Comparative Examples 1 to 3 are summarized in Table 1. Table 2 shows the results of measuring the piezoelectric constant, the stress, the Ar and O content, the maximum displacement, and the surface roughness of the piezoelectric thin films obtained in the respective examples and comparative examples.

  As shown in Table 2, in the piezoelectric thin films obtained in Examples 1 and 2, the molar fraction of Ar was 0.7% to the total amount of N, O and Ar contained in the piezoelectric thin film. It is in the range of 1.0% and the O mole fraction is in the range of 6.0% to 9.0%. On the other hand, in the piezoelectric thin films obtained in Comparative Examples 1 to 3, at least one of the mole fractions of Ar and O with respect to the total amount of N, O and Ar contained in the piezoelectric thin film is outside the above range. ..

  The surface of the piezoelectric thin film obtained in Comparative Example 1 is smooth as shown in FIG. 2 (a) and the surface roughness of Table 2, and the piezoelectric constant is sufficiently high at 19.2 pC / N. On the other hand, however, the maximum displacement reaches 26 μm, and the stress in the piezoelectric thin film having a thickness of 2.3 μm is 841 MPa, which is a high value. From the measurement result shown in FIG. 2C and the maximum displacement in Table 2, it can be seen that the substrate has a large upward warp.

  The piezoelectric thin film obtained in Comparative Example 2 has no stress, but has a piezoelectric constant of 9.8 pC / N, which is about half that of Comparative Example 1. Further, as shown in FIG. 3A, the surface of the piezoelectric thin film is covered only with coarse particles, and the surface roughness is large as shown in Table 2.

  The piezoelectric thin film obtained in Comparative Example 3 has a thin film thickness of 0.5 μm due to a short film forming time, but has a high stress of 1273 MPa and a maximum displacement of 9.9 μm. On the other hand, the piezoelectric constant shows a sufficiently high value of 17.1 pC / N. If the film formation is continued as it is, the stress gradually decreases while the maximum displacement increases, and the piezoelectric thin film shown in Comparative Example 1 grows. Therefore, if a maximum displacement of 10 μm is allowed, a piezoelectric thin film having excellent piezoelectricity up to a film thickness of 0.5 μm can be obtained, but if the film thickness is further increased, the maximum displacement exceeds 10 μm. It becomes unsuitable for use as a device.

  On the other hand, the piezoelectric thin film obtained in Example 1 has a piezoelectric constant of 20.1 pC / N, which is higher than that of Comparative Example 1, which has excellent piezoelectric characteristics. Further, the stress is 220 MPa, which is 70% or more lower than the value of Comparative Example 1. The surface of the piezoelectric thin film obtained in Example 1 was the same as the result observed in Comparative Example 1 as shown in FIG. It is found that the generated rough particles are scattered here and there, and as shown in Table 2, the surface roughness is sufficiently small.

  The piezoelectric thin film obtained in Example 2 also has a sufficient piezoelectric constant as shown in Table 2, and both the maximum displacement and the stress are reduced as compared with the piezoelectric thin film obtained in Comparative Example 1. You can see that it is done.

  The present invention contributes to the production of a piezoelectric thin film having good piezoelectric properties at a relatively low cost.

Claims (8)

A piezoelectric thin film containing a nitride containing Al as a constituent component,
The mole fraction of Ar is 0.7% to 1.0% and the mole fraction of O is 6.0% to 9.0% with respect to the total amount of N, O and Ar contained in the piezoelectric thin film. Is a piezoelectric thin film.   The piezoelectric thin film according to claim 1, wherein a part of Al in the nitride containing Al as a constituent component is replaced by another metal element.   The piezoelectric thin film according to claim 2, wherein the other metal element is Sc.   The piezoelectric according to any one of claims 1 to 3, wherein the arithmetic average height Sa of the surface is 3.0 nm to 9.0 nm, and the developed area ratio Sdr of the interface of the surface is 0.0002 to 0.015. Body thin film.   A piezoelectric element comprising the piezoelectric thin film according to claim 1.   A piezoelectric device comprising the piezoelectric element according to claim 5. It is a manufacturing method of the piezoelectric thin film according to any one of claims 1 to 4,
A seed layer forming step of forming a seed layer by sputtering in a mixed gas atmosphere containing Ar gas and N ₂ gas at a first sputtering gas pressure using a target containing Al;
A growth layer forming step of forming a growth layer on the seed layer by sputtering by changing the sputtering gas pressure in the seed layer forming step to a second sputtering gas pressure higher than the first sputtering gas pressure. A method of manufacturing a piezoelectric thin film, comprising:   The method for manufacturing a piezoelectric thin film according to claim 7, wherein the target is made of a ScAl alloy.