JP2017028062A - Laminate structure and piezoelectric element including the same, manufacturing method, evaluation method of laminate structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminate structure having a diameter of 100 mm or more, including a piezoelectric film where in-plane variation of the piezoelectric characteristics is suppressed, by establishing an evaluation method for determining the variation of defects in the piezoelectric film quantitatively, a manufacturing method thereof, and a piezoelectric element.SOLUTION: A laminate structure 1 includes a substrate 10 having a diameter of 100 mm or more, and a piezoelectric film 30 mainly composed of a perovskite oxide deposited on the substrate 10. On the surface 30s of the piezoelectric film 30 opposite to the substrate 10, the absolute value of the difference of refractive index, measured by ellipsometry having a wavelength of 400 nm or less in the central part 30sc and marginal part 30sp of the surface is 0.1 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multilayer structure including a piezoelectric film on a substrate, a piezoelectric element including the multilayer structure, and a method for manufacturing the multilayer structure. The present invention also relates to an evaluation method for determining in-plane composition variation on the surface of a substrate or a laminated structure.

  2. Description of the Related Art Miniaturization in combination with semiconductor process technology such as MEMS (Micro Electro Mechanical Systems) technology using a Si substrate is being advanced in piezoelectric elements such as actuators and various sensors such as liquid ejection devices. In semiconductor process technology using a piezoelectric thin film (piezoelectric film) as a piezoelectric body, high-precision processing using film formation, photolithography, etc., and batch processing on a large area wafer, Realization of miniaturization, high density and low cost of the apparatus is expected.

  As a piezoelectric material having high piezoelectric characteristics, lead zirconate titanate (PZT) perovskite oxide has been proven and widely used. In piezoelectric materials such as PZT-based perovskite oxides, as described in Non-Patent Document 1 and the like, it is considered that the piezoelectric performance of the piezoelectric body changes due to oxygen defects.

  For example, in PZT, doping a so-called donor element having an ionic valence of 5 or more into the B site of a perovskite oxide reduces oxygen defects and increases the piezoelectric performance, whereas the ionic valence is 3 or less. It is known that when so-called acceptor ions are added, oxygen defects increase and the piezoelectric performance decreases.

  However, this concept predicts the increase or decrease of oxygen vacancies based on the theory of cation valence and charge compensation, and does not directly measure oxygen vacancies. However, it is considered that there is a difference in the amount of oxygen defects, but it is difficult to determine the difference in the amount of oxygen defects.

  Similarly, Patent Document 1 describes that lead defects and oxygen defects affect the characteristics, and a positively charged region and a negatively charged region are produced by unevenly doping ions. Controlling the characteristics is disclosed. However, Patent Document 1 concludes that the positive / negative of the charge is adjusted based on the above theory due to the uneven distribution of ions, and the actual measurement results of the charged state and the measurement results of the lead defects and oxygen defects are described. Absent.

In Patent Document 2, oxygen defects affect the characteristics of the (Na _x K _y Li _z ) NbO ₃ thin film, and a film with good characteristics can be obtained by adjusting the ratio of potassium-oxygen bonds to potassium-metal atom bonds. It is stated that it can be obtained. In this composition, as with lead-based materials such as PZT, sodium, potassium, lithium, etc. are likely to volatilize in addition to oxygen vacancies and cation vacancies are thought to be present. .
As described above, although there is a hypothesis that cation deficiency or oxygen deficiency affects the characteristics, there is no example in which the characteristics can be controlled by direct measurement in the same composition.

JP 2010-199339 A JP 2013-26246 A

Yuji Noguchi, 1 other author, Monthly Display, June 2009, p. 19 Takamitsu Fujii and 6 others, “Formation of high piezoelectric constant Nb-doped PZT thin film and its MEMS application”, [online], 2014 research report, FUJIFILM Corporation, [searched on May 20, 2015] , Internet <URL: http://www.fujifilm.co.jp/rd/report/rd059/pack/pdf/ff_rd059_008.pdf>

  By the way, piezoelectric devices have been mainly used on 3 to 4 inch φ wafers in the past, but in recent years, piezoelectric films have been formed on large area wafers such as 6 inch and 8 inch φ wafers. It has become popular to make films into devices. As the diameter of the wafer increases, in-plane variation in the piezoelectric characteristics of the piezoelectric film deposited thereon becomes a problem. For example, in the case of an inkjet head, if the piezoelectric constant varies from nozzle to nozzle, the amount of discharged liquid varies, which greatly affects the image quality. If the applied voltage is changed for each nozzle, the same liquid amount can be obtained, but a circuit for changing the correction voltage for each nozzle is very complicated.

  As described above, the variation in composition and the variation in defects described above can be considered as causes of the in-plane variation in piezoelectric characteristics. However, since no quantitative measurement method has been established for the defect variation as described above, it is unclear whether the defect variation actually correlates with the piezoelectric characteristic variation. Regarding variation in composition, as described in Table 1 of Non-Patent Document 2, attempts have been made to achieve a piezoelectric film having a uniform composition by performing fluorescent X-ray analysis (XRF, x-ray-fluorescence) or the like. It is confirmed that the in-plane variation of the piezoelectric characteristics is a phenomenon seen when a wafer having a diameter of 100 mm or more is used.

  The present invention has been made in view of the above circumstances, and provides an evaluation method for quantitatively determining variation in defects due to atomic loss in a piezoelectric film, and a piezoelectric film is formed on a substrate having a diameter of 100 mm or more. It is an object of the present invention to provide a laminated structure in which in-plane variation in piezoelectric characteristics is suppressed and a method for manufacturing the same.

The laminated structure of the present invention comprises a substrate having a diameter of 100 mm or more and a piezoelectric film mainly composed of a perovskite oxide formed on the substrate,
On the surface of the piezoelectric film opposite to the substrate, the absolute value of the difference in refractive index at a specific wavelength of less than 400 nm measured by ellipsometry between the central portion and the peripheral portion of the surface is 0.1 or less.

In this specification, the diameter of the substrate means the equivalent circle diameter of the substrate (the radius of the circumscribed circle).
In addition, the “center part of the surface” means one point in a circle having a radius of 12 mm with respect to the center of the substrate, and the “periphery part of the surface” means the endmost part when the diameter is equally divided into 10 parts. Means one point.
In this specification, unless otherwise specified, “refractive index” means a refractive index measured by ellipsometry with a wavelength of less than 400 nm.

  In the present specification, “main component” means a component having a content of 90% by mass or more.

  In the laminated structure of the present invention, the absolute value of the difference in refractive index between the central portion and the peripheral portion of the surface is preferably 0.01 or less.

In the laminated structure of the present invention, the substrate is preferably a silicon substrate, a silicon compound substrate, or a laminate substrate of silicon and a silicon compound.
The piezoelectric film has the following general formula P1.
Formula P1 (Pb _x A _ax ) B _b O _c
The main component is at least one perovskite oxide represented by:
In the general formula P1, A is an A site element containing at least one element selected from the group consisting of Pb, Ba, Sr, Bi, Li, Na, Ca, Cd, Mg, K, and a lanthanide element; Is a group consisting of Ti, Zr, V, Nb, Ta, Sb, Cr, Mo, W, Mn, Mg, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, Hf, and Al. It is a B site element containing at least one element selected from the above, and x is preferably 0 <x <a.

The piezoelectric film has the following general formula P2
Formula _{P2 Pb a (Zr y, Ti} z, M b-y-z) O c
In the general formula P2, M is V, Nb, Ta, Sb, Cr, Mo, W, Mn, Mg, Sc, Co, It is at least one B-site element selected from the group consisting of Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, Hf, and Al, y satisfies 0 <y <b, and z is It is preferable that 0 <z <b is satisfied and 0 ≦ b−z−z.

  The piezoelectric element of the present invention comprises the above-described laminated structure of the present invention and a pair of electrodes for applying a voltage to the piezoelectric film of the laminated structure.

The method for producing a laminated structure of the present invention is a method for producing a laminated structure comprising a piezoelectric film having a perovskite oxide as a main component on a substrate having a diameter of 100 mm or more,
A piezoelectric film forming step of forming a piezoelectric film on a substrate by a sputtering method;
The piezoelectric film forming step includes a first step of performing a sputtering method using a film forming gas having an oxygen concentration capable of forming a perovskite phase;
A second step of sequentially performing a sputtering method using a film-forming gas having an oxygen concentration capable of forming a pyrochlore phase,
The film formation time in the second step is less than 5% of the total film formation time in the piezoelectric film formation step.

  In the present specification, the “oxygen concentration capable of forming a perovskite phase” in the first step and the “oxygen concentration capable of forming a pyrochlore phase” in the second step in the method for producing a laminated structure refer to the surface crystal structure of the perovskite. When a piezoelectric film is formed on a film formation base having no type crystal structure, it means an oxygen concentration capable of forming each crystal phase. Therefore, when the film formation base has a perovskite crystal structure, a perovskite phase may be formed in the film formation at the oxygen concentration of the film formation gas in the second step.

  The film formation time in the second step is preferably a time during which a piezoelectric film having a film thickness of 10 nm to 100 nm can be formed.

  The evaluation method of the present invention is an evaluation method for determining variations in the in-plane composition of the surface of a laminated structure comprising a substrate or one or more films on the substrate, and a plurality of evaluation methods on the surface of the laminated structure. At the measurement point, the refractive index at a specific wavelength of less than 400 nm is measured by ellipsometry, and the variation in in-plane composition is determined by the variation in refractive index at all measurement points.

  The present invention has found a novel evaluation method for quantitatively determining the variation in defects due to atomic loss in a piezoelectric film, and based on such an evaluation method, a novel laminate capable of producing a laminated structure in which in-plane variation in piezoelectric characteristics is suppressed. A method for manufacturing a structure is provided. According to the method for manufacturing a laminated structure of the present invention, the absolute value of the difference in refractive index measured by ellipsometry with a wavelength of less than 400 nm between the central portion and the peripheral portion of the surface is 0 on a substrate having a diameter of 100 mm or more. A laminated structure of the present invention having a piezoelectric film of less than or equal to 1 can be manufactured. ADVANTAGE OF THE INVENTION According to this invention, the laminated structure provided with the piezoelectric film with which the in-plane variation | variation of the piezoelectric characteristic was suppressed, although it was a large area whose diameter is 100 mm or more can be provided.

The schematic sectional drawing and top view which show the structure of the laminated structure of one Embodiment concerning this invention. The figure which showed typically the mode of the distribution of the defect by atomic loss in the conventional laminated structure. 1 is a schematic cross-sectional view showing a configuration of a piezoelectric element according to an embodiment of the present invention. The figure which shows the ellipsometry measurement result of the piezoelectric film surface in the conventional laminated structure provided with the PZT thin film.

  The inventor has intensively studied an evaluation method for quantitatively determining the variation of defects in the piezoelectric film. The present inventor paid attention to the correlation between the film composition and the refractive index of the film, and determined the refractive index of the piezoelectric film by ellipsometry for a laminated structure including a piezoelectric film having a high piezoelectric constant manufactured by a conventional manufacturing method. It was measured by.

  Ellipsometry measures two values, Psi (Ψ) and Delta (Δ), which represent the polarization state of light that varies depending on the sample, and spectroscopic ellipsometry measures the wavelength dependence of these values, respectively. Can do. As a result of measuring the spectroscopic ellipsometry spectrum of the piezoelectric film having a high piezoelectric constant manufactured by the present inventor using the conventional manufacturing method, there is almost no difference in the spectrum having a wavelength of 400 nm or more, while the spectrum having a wavelength of less than 400 nm is clear. We have found that there may be significant differences.

  As an example, FIG. 4 shows a spectroscopic ellipsometry measurement result indicating the wavelength dependence of Psi (Ψ) on two piezoelectric film surfaces (A, B). The data shown in FIG. 4 is a spectroscopic ellipsometry measurement result when measurement light is incident on the surface of the piezoelectric film at an incident angle of 70 degrees using an ellipsometry M2000-U manufactured by woollam.

  In FIG. 4, in the spectral ellipsometry data of the piezoelectric film, the spectrum having a wavelength of 400 nm or more has almost no difference between A and B, whereas the spectrum having a wavelength of less than 400 nm has a clear difference between A and B. That is, it is shown that there is a difference in the refractive index in the vicinity of the surface obtained by the ellipsometry of less than 400 nm even with a piezoelectric film having the same refractive index in ordinary ellipsometry of 400 nm or more. Each spectral data shown in FIG. 4 is obtained by using a dielectric function model assuming absorption using a Gaussian vibrator and obtaining a refractive index at a wavelength of 300 nm by fitting. As a result, A is 2.81 and B is 3.05. Met.

  The inventor has found that the refractive index of only the air interface of the surface layer can be measured at a wavelength of less than 400 nm by ellipsometry measurement. In FIG. 4, when the wavelength is less than 400 nm, the thickness of the sample is sufficiently thick with respect to the light penetration depth (1 / α: extinction coefficient), and the optical interference effect due to reflection from the substrate interface can be ignored. Periodic intensity changes of the measurement parameters Δ and Ψ with respect to the wavelength are not observed. That is, the refractive index of the air interface surface layer can be measured from the measurement result having a wavelength of less than 400 nm.

  On the other hand, on the long wavelength side with a wavelength of 400 nm or more, since the film thickness of the measurement sample is thin with respect to the light penetration depth, periodic intensity changes of the measurement parameters Δ and Ψ with respect to the wavelength are observed. Therefore, the average refractive index of the entire measurement sample is measured.

  That is, by measuring the refractive index at a specific wavelength of less than 400 nm by ellipsometry, it is possible to measure the refractive index in the surface layer portion at a depth of 100 nm or less from the surface of the substrate or film to be measured. From the value, it is possible to estimate the composition of the measurement points and the amount of defects in the surface layer portion having a depth of 100 nm or less.

  Further, by measuring the refractive index at a specific wavelength of less than 400 nm by ellipsometry at a plurality of measurement points, the in-plane composition in the surface layer portion at a depth of 100 nm or less from the surface of the substrate or film to be measured And variations in defects can be determined.

  As long as the composition of the surface layer portion of the substrate or film and the method for evaluating defects can be measured by ellipsometry, the type of substrate to be measured, the type of film, and the laminated structure thereof are not particularly limited. can do. In particular, it can be suitably used for evaluation of a film containing an element that is easily reverse-sputtered when a film is formed by a sputtering method, and evaluation of a laminated structure that requires evaluation of the composition of only the surface layer portion with a film thickness of 100 nm or less.

  The present inventor believes that defects caused by reverse sputtering and the accompanying oxygen defects in film formation by sputtering are compensated from the upper film formed continuously, and therefore always exist in the vicinity of the surface layer of the film. ing. In that case, if the suppression of defects formed in the surface layer portion is not actively performed, the refractive index and composition of the surface layer portion do not match the refractive index and composition of the entire film. This is consistent with the results shown in FIG.

  As described in the “Background Art” section, etc., in Pb-containing perovskite oxides such as PZT films known as functional films having excellent piezoelectricity, Pb, which is the main component of the A-site element, is volatile. Pb-containing perovskite-type oxide film, which is a high element (low melting point) element that is easily reverse sputtered, that is, an element that easily generates defects, and causes variations in piezoelectric characteristics due to variations in Pb defects and oxygen defects that accompany it. With regard to the above, determining the variation in the refractive index of the surface layer portion by the above evaluation method determines the variation in the piezoelectric characteristics.

  In the deposition of a perovskite oxide film by a sputtering method, reverse sputtering occurs when the melting point of the metal element constituting the film is a metal that is equal to or lower than the deposition temperature. For example, Pb has a melting point as low as 327 ° C., which is lower than the deposition temperature of the PZT-based film shown in the examples described later. Similar to Pb, the A site element having a melting point lower than the film forming temperature includes Na (melting point 97 ° C.), K (melting point 63 ° C.), Bi (melting point 270 ° C.), and the like. Therefore, in the evaluation of the characteristics of the perovskite oxide film containing these elements, the characteristics and the variations thereof can be estimated by measuring the composition of the surface layer portion, the presence or absence of defects, and the variations by the above evaluation method.

  The inventor of the present invention uses the above evaluation method to determine the refractive index of the surface layer only and its variation on the surface of a conventional sputtered PZT-based perovskite oxide film (hereinafter sometimes abbreviated as PZT-based piezoelectric film). Further, the refractive index reflecting the composition and defects of the entire film thickness (hereinafter sometimes referred to as the refractive index of the entire film) and its variation were examined. As a result, in the conventional PZT-based piezoelectric film, the refractive index in the surface layer portion of the film has a large in-plane variation compared to the refractive index of the entire film, and the main factors that change the refractive index of the surface layer portion are Defects due to atomic loss (lead defects and oxygen defects in the case of lead-containing perovskite type oxides), by reducing defects near the surface layer, reducing in-plane variation in the refractive index of the film surface layer portion, and It was found that variation in in-plane characteristics can be reduced.

The inventor further includes a perovskite oxide film containing a low melting point metal (Na, K, Pb, Bi, etc.) having a melting point lower than the above-described film forming temperature, in particular, as a main component of the A site. Method for forming a novel piezoelectric film with reduced defects on the surface layer of the film and a novel piezoelectric film formed on a substrate having a diameter of mm or more with a high uniformity of in-plane characteristics with few defects on the surface layer of the film I found.
Hereinafter, a laminated structure and a piezoelectric element including the laminated structure according to an embodiment of the present invention and a method for manufacturing the laminated structure will be described with reference to the drawings. FIG. 1 is a top view and a schematic cross-sectional view of a laminated structure 1 according to this embodiment. In order to facilitate visual recognition, the scale of each part is appropriately changed in the drawings of the present specification.

As shown in FIG. 1, the laminated structure 1 includes a substrate 10 having a diameter of 100 mm or more, and a piezoelectric film 30 mainly composed of a perovskite oxide formed on the substrate 10, On the surface 30 s of the piezoelectric film 30 opposite to the substrate 10, the absolute value of the difference in refractive index at a specific wavelength of less than 400 nm measured by ellipsometry between the central portion 30 sc and the peripheral portion 30 sp of the surface | n _sc − n _sp | is 0.1 or less. The refractive index n _sc is the refractive index of the central portion 30sc of the surface, and the refractive index n _sp is the refractive index of the peripheral portion 30sp of the surface. Since the absolute value | n _sc −n _sp | of the difference in refractive index corresponds to the difference in composition including the difference in the amount of defects between the surface central part 30sc and the peripheral part 30sp of the surface, the piezoelectric film 30 This is considered to correlate with the difference in piezoelectric characteristics. Accordingly, the absolute value | n _sc −n _sp | of the difference in refractive index between the central portion 30sc and the peripheral portion 30sp of the surface is preferably smaller, and is preferably 0 or more and 0.01 or less.
In FIG. 1, as a main configuration when used as a piezoelectric element, a mode in which a piezoelectric film 30 is provided on a substrate 10 via a lower electrode 20 is shown. The lower electrode 20 will be described in the item of piezoelectric element.

  In the laminated structure 1, the substrate 10 is not particularly limited as long as the substrate has a diameter of 100 mm or more. However, a silicon substrate used as a substrate for MEMS or the like, a silicon compound substrate, or a laminate substrate of silicon and a silicon compound is preferable. .

  The piezoelectric film 30 is not particularly limited in its composition and film thickness as long as it has a perovskite oxide as a main component. The perovskite oxide includes a low melting point metal (Na, K, Pb, Bi, etc.) whose melting point can be lower than the film forming temperature at the A site, and in particular, a piezoelectric having such a low melting point metal as the main component of the A site. The film 30 is easily removed from the film surface by heating conditions higher than the melting point (including the case where the temperature of the substrate on which the film is formed is higher than the melting point) or sputtering under the heating conditions. In addition, as already described, since defects due to atomic loss on the film surface are supplemented with elements from the upper layer as film formation proceeds, defects due to atomic loss mainly exist in the surface layer portion, and in the conventional surface layer portion, Since the presence and position of the defect could not be detected, a manufacturing method for suppressing a defect in the surface layer portion has not been applied. FIG. 2 schematically shows an expected distribution of defects in the surface layer of a conventional piezoelectric film, taking a Pb-containing perovskite oxide film as an example.

The piezoelectric film 30 has a piezoelectric film forming process for forming the piezoelectric film 30 on the substrate 10 having a diameter of 100 mm or more by a sputtering method. The piezoelectric film forming process has an oxygen concentration capable of forming a perovskite phase. A first step of performing a sputtering method using a deposition gas;
The second step of performing a sputtering method using a film forming gas having an oxygen concentration capable of forming a pyrochlore phase is sequentially performed. The film forming time of the second step is the total film forming time of the piezoelectric film forming step. It can be manufactured by the manufacturing method of the laminated structure of the present invention, which is less than 5%.

When a perovskite oxide film containing an A-site metal element having a melting point lower than the film-forming temperature is formed by a sputtering method, a target made of an oxide of the A-site metal element is sputtered, whereby the A-site metal element It is considered that a perovskite structure is easily formed when a part of the oxide is in a condition that a film is formed as an A-site metal. The reaction formula shown below shows the reaction in sputtering of the target metal oxide during the formation of the perovskite structure. In such a reaction, since the melting point of the A-site metal element is lower than the film-forming temperature than the film-forming temperature, the A-site metal liquid is in the formed film. Therefore, when such an A-site metal element is included, the A-site element is easily removed from the surface by reverse sputtering, and the amount of the A-site element is different depending on the ease of sputtering and the uneven substrate temperature. It is easy to become.
PbO _1−δ → δPb + (1-δ) PbO
Bi ₂ O _3−3δ → 2δBi + (1−δ) Bi ₂ O ₃
Na ₂ O _1-δ → 2δNa + (1-δ) Na ₂ O
K ₂ O _1-δ → 2δK + (1−δ) K ₂ O

  In the method for manufacturing a laminated structure of the present invention, in the piezoelectric film forming step, in the first step, film formation is performed for 95% or more of the total film formation time under the condition that the metal element at the A site is formed. The final film formation time of less than 5% is a condition that can suppress the formation of defects on the surface, that is, the metal element at the A site is difficult to form, and the oxide of the A site metal element is more easily formed. A second step of forming a film under the high oxygen concentration condition that is the condition is performed. In this second step, since the A-site metal element is difficult to form a film, the underlayer has a perovskite structure, and the regulation force from the underlayer is within a film thickness range that extends to the film formation. This is a condition capable of forming a pyrochlore phase. The film formation time in the second step is preferably a time during which a piezoelectric film having a film thickness of 10 nm to 100 nm can be formed. If the film thickness of the piezoelectric film formed in the second step is less than 10 nm, it is difficult to obtain a sufficient effect of reducing defects in the surface layer portion, and if it exceeds 100 nm, the regulation force from the ground becomes weak. The pyrochlore phase increases in the film where the film thickness of the formed piezoelectric film exceeds 100 nm, and the piezoelectric characteristics deteriorate.

  The above-described A-site elements Na, K, Bi, and Pb having a low melting point easily cause defects on the surface due to the A-site loss and the accompanying oxygen loss due to the reasons described above. Perovskite-type oxide film, especially when 40 mol% or more of the metal elements of the A site and B site are elements having a low melting point, more than 80% of the elements having a low melting point occupy the A site In this case, the method for producing a laminated structure of the present invention is suitable.

On the other hand, among the A-site elements having a low melting point, Na and K have a melting point as low as 100 ° C. or less, so it is somewhat difficult to control the content in a reducing atmosphere. Therefore, the manufacturing method of the laminated structure of the present invention is particularly suitable when the A-site metal is Pb or Bi.
In addition, it is difficult to apply the method for manufacturing a laminated structure of the present invention when the A site metal element having a melting point higher than the film forming temperature is contained in an amount of 40 mol% or more of the A site and B site metal elements.

  As will be described later in Examples, the method for producing a laminated structure of the present invention is particularly suitable when the piezoelectric film 30 is mainly composed of a Pb-containing perovskite oxide, and the Pb-containing perovskite oxide. Are preferably at least one perovskite oxide represented by the following general formula P1, and at least one perovskite oxide represented by the following general formula P2.

Formula P1 (Pb _x A _ax ) B _b O _c
In the general formula P1, A is an A site element containing at least one element selected from the group consisting of Pb, Ba, Sr, Bi, Li, Na, Ca, Cd, Mg, K, and a lanthanide element; Is a group consisting of Ti, Zr, V, Nb, Ta, Sb, Cr, Mo, W, Mn, Mg, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, Hf, and Al. A B-site element containing at least one element selected from x, and x is 0 <x <a.

Formula _{P2 Pb a (Zr y, Ti} z, M b-y-z) O c
In general formula P2, M is from V, Nb, Ta, Sb, Cr, Mo, W, Mn, Mg, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, Hf, and Al. And at least one B-site element selected from the group consisting of y satisfying 0 <y <b, z satisfying 0 <z <b, and 0 ≦ b−z.
In general formulas P1 and P2, a: b: c is 1: 1: 3 as a standard, but may be deviated from the standard within a range where a perovskite type can be taken.

  The perovskite oxide represented by the general formula (P2) is a PZT-based perovskite oxide, and M in the formula means a dopant to the B site. Examples of the perovskite oxide represented by the general formula (P) include lead titanate, lead zirconate titanate (PZT), lead niobate zirconate titanate, and lead lanthanum zirconate titanate. The piezoelectric film may be a mixed crystal system of perovskite oxides represented by the above general formula (P2).

  In the general formula (P2), the ratio of Zr to Ti is not particularly limited, but a ratio of morphotropic phase boundary (MPB) composition is preferable because it has a large piezoelectric constant. The ratio of MPB composition is x: y = 52: 48.

  From the viewpoint of improving the piezoelectric characteristics, it is preferable that the dopant M contains a B-site element such as a VA group, a VB group, a VIA group, and a VIB group. As described above, when M is Nb, the piezoelectric characteristics are higher and preferable. In particular, a PZT sputtered film in which Nb is doped at a high concentration is more preferable because an effect of improving piezoelectricity by Nb doping is effectively expressed.

  In the method for manufacturing a laminated structure of the present invention, the temperature of the substrate in the piezoelectric film forming step is not particularly limited as long as a film having a perovskite crystal structure is obtained in the first step. When the main component is a Pb-containing perovskite oxide, the temperature is preferably 400 ° C. or higher and 500 ° C. or lower.

  In the piezoelectric film forming step, the oxygen concentration in the film forming gas in the first step and the oxygen concentration in the film forming gas in the second step are as described above. Is determined by the sum of oxygen supplied as oxygen gas and oxygen supplied from the target. The amount of oxygen supplied from the target has a certain range depending on the batch-to-batch difference and the film forming rate (film forming power) due to the firing variation of the target.

  In the examples described later, the oxygen concentration in the deposition gas is preferably more than 1.0% and 5.0% or less in the first step, and more preferably 1.3% or more and 2.6% or less. A favorable result was obtained. Moreover, in the 2nd process, it was preferable that it is more than 5.0%, and it is more preferable that it is 5.2% or more. In the second step, defects in the surface layer portion of the piezoelectric film 30 can be satisfactorily suppressed by using a film forming gas having such an oxygen concentration. As described above, the oxygen concentration (oxygen condition) in the film forming gas is appropriately selected and is not necessarily limited to this oxygen partial pressure.

  As described above, the method for manufacturing a laminated structure of the present invention is a method for manufacturing a novel laminated structure capable of manufacturing a laminated structure in which in-plane variation in piezoelectric characteristics is suppressed. The laminated structure 1 manufactured by the manufacturing method of FIG. 1 is obtained by measuring the absolute difference in refractive index measured by ellipsometry with a wavelength of less than 400 nm between the central portion 30sc and the peripheral portion 30sp of the surface on the substrate 10 having a diameter of 100 mm or more. The piezoelectric film 30 having a value of 0.1 or less is provided, and the piezoelectric film 30 having a large area with a diameter of 100 mm or more and suppressed in-plane variation in piezoelectric characteristics is provided.

The laminated structure 1 can also be produced by a production method other than the production method of the laminated structure of the present invention. Taking a Pb-containing perovskite oxide as an example, the film formation is determined by the balance between the amount of lead and the amount of oxygen, as shown by the formula PbO _1−δ → δPb + (1-δ) PbO 2. In the manufacturing method of the laminated structure of the present invention, the oxygen concentration in the film forming gas is higher in the second step than in the first step, that is, the oxygen gas supply amount is set in the first step and the second step. The amount of defects in the surface layer is reduced by changing the balance between the lead amount and the oxygen amount, but other conditions in the first step and the second step are changed within the range where the same effect can be obtained. You may let them.
The film formation factor that can control the balance between the lead amount and the oxygen amount other than the oxygen gas supply amount is not particularly limited, and examples thereof include plasma power, plasma potential, and substrate temperature during film formation. These factors differ from changes in the oxygen supply amount, and both lead and oxygen amounts change. Therefore, the control of the balance between the lead amount and the oxygen amount by these factors is based on the ellipsometry data described in this specification. It can be designed and performed as appropriate.

  As shown in FIG. 3, the multilayer structure 1 includes a pair of electrodes (lower electrode 20 and upper electrode 40) that sandwich the piezoelectric film 30 of the multilayer structure 1, and voltage applying means that applies a voltage to the piezoelectric film 30. By further including 50, the piezoelectric element 2 can be obtained.

  The main component of the lower electrode 20 is not particularly limited, but platinum group elements such as Pt and Ir, metal elements generally used in semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof include Can be mentioned. The thickness of the lower electrode 20 is not particularly limited, but is preferably 50 to 500 nm.

  The film thickness of the piezoelectric film 30 is not particularly limited and is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 to 5 μm. By using the piezoelectric film having such a film thickness range, the piezoelectric performance can be sufficiently exhibited, and the problem that the substrate is warped greatly due to excessive stress is less likely to occur.

  The main component of the upper electrode 40 is not particularly limited, and the same material as that exemplified for the lower electrode 30 is exemplified.

The piezoelectric element 2 has the laminated structure 1 of the above embodiment. Therefore, the same effect as the laminated structure 1 is produced. Moreover, since the laminated structure 1 can reduce the in-plane variation of the piezoelectric film 30, a piezoelectric device can be easily manufactured. For example, in the case of an ink jet head, the piezoelectric characteristics are almost the same in each head, so that it is not necessary to specify an applied voltage for each nozzle, and the same amount can be obtained if the same voltage is applied all at once. Therefore, IC design and wiring are simplified, and cost reduction can be realized. In the case of other piezoelectric thin film devices, variation in characteristics can be similarly suppressed, and similarly, the cost can be reduced by suppressing the redundancy of the driving IC and simplifying the inspection process.
(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate without departing from the spirit of the present invention.

Examples and comparative examples according to the present invention will be described.
Example 1
A Si wafer having a thickness of 625 μm and a diameter of 150 mm was prepared as a substrate.
Using a sputtering apparatus, a 20 nm-thick TiW layer and a 150 nm-thick (111) Ir lower electrode are sequentially formed on substantially the entire surface of the substrate under the conditions of an Ar atmosphere with a substrate temperature of 200 ° C. and a degree of vacuum of 0.1 Pa. did. At this time, the distance between the substrate and the target was 6 cm, and the target power density was 4 W / cm ² .

Subsequently, Pb _1.3 (Zr _0.52 Ti _0.48 ) is assumed with a substrate temperature of 450 ° C., a vacuum degree of 0.5 Pa, and a deposition gas of Ar / O ₂ mixed gas (O ₂ volume fraction of 2.6%). ) The Nb-doped PZT film (Nb-PZT) was formed using a _0.88 Nb _0.12 O ₃ target. A layered structure including an Nb-PZT film having a film thickness of about 3 μm is used as a film formation gas corresponding to the last 50 nm of film formation, which is an Ar / O ₂ mixed gas (O ₂ volume fraction 5.2%). Obtained.

(Example 2)
A laminated structure including an Nb—PZT film having a thickness of about 3 μm was obtained in the same manner as in Example 1 except that the substrate temperature was changed to 425 ° C.

(Example 3)
An Nb-PZT film having a film thickness of about 3 μm is formed in the same manner as in Example 2 except that the film thickness of the Nb-PZT film formed by Ar / O ₂ mixed gas (O ₂ volume fraction 5.2%) is set to 100 nm. A laminated structure provided with a film was obtained.

Example 4
A laminated structure including an Nb-PZT film having a thickness of about 3 μm in the same manner as in Example 1 except that a Pb _1.3 (Zr _0.52 Ti _0.48 ) O ₃ target was used as the Nb-PZT target. Got the body.

(Comparative Example 1)
A laminated structure including an Nb—PZT film having a film thickness of about 3 μm was obtained in the same manner as in Example 1 except that the oxygen concentration of the film forming gas for the time corresponding to the last 50 nm of the film formation was not changed.

(Comparative Example 2)
A laminated structure including an Nb—PZT film having a thickness of about 3 μm was obtained in the same manner as in Example 2 except that the oxygen concentration of the film forming gas for the time corresponding to the last 50 nm of the film formation was not changed.

(Comparative Example 3)
A laminated structure having a PZT film having a film thickness of about 3 μm was obtained in the same manner as in Example 3 except that the oxygen concentration of the film forming gas for the time corresponding to the last 50 nm of film formation was not changed.

(Evaluation)
<Composition analysis>
For the piezoelectric film (Nb-PZT film or PZT film) of each example, composition analysis by XRF (fluorescence X-ray Axios manufactured by Panallytical) at the center and periphery of the surface (a point from the periphery of 50 mm from the measurement point of the center), And the spectroscopic ellipsometry measurement (incident angle 70 degree | times) by ellipsometry (M2000-U made from woollam) was implemented.

As a result of measuring the spectroscopic ellipsometry, as in A and B shown in FIG. 4, there is almost no difference in the measurement result at the wavelength of 400 nm or more between the central portion and the peripheral portion of the surface. The result was that there was a difference.
For the refractive index n _{sc at the} central portion and the refractive index n _{sp at the} peripheral portion, fitting is performed using data at a wavelength of 300 nm of the spectroscopic ellipsometry spectrum using a dielectric function model assuming absorption using a Gaussian vibrator. Asked.

<Piezoelectric properties>
The piezoelectric constant is measured by sputtering to form a piezoelectric element by forming Pt as a 100 nm upper electrode, and then cutting it into a 2 mm × 25 mm strip so that the center and peripheral parts of the surface are centered. A cantilever was prepared and performed. The measurement was performed according to the method described in “I. Kanno et. Al. Sensor and Actuator A 107 (2003) 68.” with an applied voltage of a sine wave of −10 V ± 10 V.

Table 1 shows each evaluation result.

As shown in Table 1, in Comparative Examples 1 to 3, even in a piezoelectric film in which almost no difference is detected between the central portion and the peripheral portion of the surface in the measurement of the refractive index by XRF or ellipsometry at a wavelength of 600 nm, at a wavelength of 300 nm. In the measurement of the refractive index by ellipsometry, a clear difference was detected between the central portion and the peripheral portion of the surface, and a result correlated with the rate of decrease in piezoelectric characteristics was obtained.
Thus, it was confirmed that the variation in the in-plane characteristics of the piezoelectric film can be estimated based on the refractive index measurement result by ellipsometry at a wavelength of 300 nm.

  Further, as in Examples 1 to 3, by increasing the oxygen concentration of the film forming gas and forming the last 5% of the film formation, the surface has few defects and good in-plane uniformity of piezoelectric characteristics. It was confirmed that a piezoelectric film can be formed.

  The laminated structure and piezoelectric element of the present invention can be preferably used for a vibration gyro sensor, an energy harvest (power generation element), a MEMS (Micro Electro-Mechanical Systems) device, and the like.

1 the refractive index of the refractive index n _sp periphery of the laminated structure 2 a piezoelectric element 10 substrate 20 lower electrode 30 piezoelectric film 30s surface 30sc central portion 30sp periphery 40 upper electrode n _sc central portion

Claims (9)

A substrate having a diameter of 100 mm or more, and a piezoelectric film mainly composed of a perovskite oxide formed on the substrate,
On the surface of the piezoelectric film opposite to the substrate, the absolute value of the difference in refractive index at a specific wavelength of less than 400 nm measured by ellipsometry between the central portion and the peripheral portion of the surface is 0.1 or less. A laminated structure.   The laminated structure according to claim 1, wherein an absolute value of the difference in refractive index is 0.01 or less.   The laminated structure according to claim 1 or 2, wherein the substrate is a silicon substrate, a silicon compound substrate, or a laminate substrate of silicon and a silicon compound. The piezoelectric film has the following general formula P1
Formula P1 (Pb _x A _ax ) B _b O _c
The main component is at least one perovskite-type oxide perovskite-type oxide represented by:
In the general formula P1, A is an A site element containing at least one element selected from the group consisting of Pb, Ba, Sr, Bi, Li, Na, Ca, Cd, Mg, K, and a lanthanide element, B is made of Ti, Zr, V, Nb, Ta, Sb, Cr, Mo, W, Mn, Mg, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, Hf, and Al. The laminated structure according to any one of claims 1 to 3, which is an element of a B site containing at least one element selected from the group, and x is 0 <x <a. The piezoelectric film has the following general formula P2
Formula _{P2 Pb a (Zr y, Ti} z, M b-y-z) O c
The main component is at least one perovskite-type oxide perovskite-type oxide represented by:
In the general formula P2, M is V, Nb, Ta, Sb, Cr, Mo, W, Mn, Mg, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni, Hf, and Al. At least one B-site element selected from the group consisting of: y satisfying 0 <y <b, z satisfying 0 <z <b, and 0 ≦ b−z. The laminated structure according to any one of 1 to 3. The laminated structure according to any one of claims 1 to 5,
A piezoelectric element comprising a pair of electrodes for applying a voltage to the piezoelectric film of the laminated structure. A method for producing a laminated structure comprising a piezoelectric film having a perovskite oxide as a main component on a substrate having a diameter of 100 mm or more,
A piezoelectric film forming step of forming the piezoelectric film on the substrate by a sputtering method;
The piezoelectric film forming step includes a first step of performing the sputtering method using a film forming gas having an oxygen concentration capable of forming a perovskite phase;
And sequentially performing the second step of performing the sputtering method using a film-forming gas having an oxygen concentration capable of forming a pyrochlore phase,
The method for producing a laminated structure, wherein the film formation time in the second step is less than 5% of the total film formation time in the piezoelectric film formation step.   The method for manufacturing a laminated structure according to claim 7, wherein the film formation time in the second step is a time during which the piezoelectric film having a film thickness of 10 nm to 100 nm can be formed. An evaluation method for determining variation in in-plane composition of a surface of a substrate or a laminated structure including one or more layers on the substrate,
An evaluation method in which at a plurality of measurement points on the surface, a refractive index at a specific wavelength of less than 400 nm is measured by ellipsometry, and the variation is determined by variation in the refractive index at all the measurement points.