JPWO2017038806A1 - Oxide dielectric element and manufacturing method of oxide dielectric element - Google Patents

Abstract

The present invention provides an oxide dielectric that can improve the piezoelectric characteristics by reducing the restraining force by the protective film, suppress the decrease in dielectric constant, and prevent the decrease in physical characteristics due to reduction deterioration by hydrogen ions. A technology for a protective film of a body element is provided. An oxide dielectric element 15 according to the present invention includes an Si substrate 1 and an oxide having first and second electrode layers 4 and 6 provided on the Si substrate 1 and sandwiching an oxide dielectric layer 5. The oxide dielectric thin film laminate 8 is covered with a protective film 7 made of a polymer. The protective film 7 can be formed by a vapor deposition polymerization method.

Description

  The present invention relates to a protective film for an oxide dielectric element, and more particularly to a technique for providing a protective film with a polymer.

A thin film made of lead zirconate titanate (Pb (Zr, Ti) O ₃ ) or PZT, which has excellent piezoelectricity and ferroelectricity, is used for nonvolatile memory (FeRAM) applications, taking advantage of its ferroelectricity. Yes. In addition, since a thin film made of barium-strontium-titanium (BST) has a low Curie point, it is used as a variable capacitor using a high dielectric constant shown in the paraelectric phase rather than using its ferroelectricity.

  Furthermore, in recent years, MEMS piezoelectric elements are being put into practical use by fusing with MEMS technology. For example, application examples such as an inkjet head (actuator), an angular velocity sensor, and a gyro sensor are spreading as main devices.

By the way, an oxide dielectric element using an oxide dielectric such as PZT has been conventionally provided with a protective film over its entire surface in order to prevent, for example, deterioration of piezoelectric characteristics due to reduction of hydrogen gas. .
Conventionally, silicon oxide (SiO ₂ ) has been used as a material for such a protective film, and a CVD method or a sputtering method has been adopted as its manufacturing method.

  However, since the protective film made of silicon oxide has a high elastic modulus, the piezoelectric property or dielectric constant of the piezoelectric body is lowered by the restraining force, and physical properties are caused by reduction degradation due to hydrogen ions during the formation of the protective film. There exists a subject that a characteristic falls.

JP 2013-149669 A

  The present invention has been made to solve such problems of the conventional technology, and its object is to reduce physical force such as piezoelectric characteristics and dielectric constant by reducing the restraining force by the protective film. A further object is to provide a technique for a protective film for an oxide dielectric element capable of preventing a decrease in physical characteristics due to reduction deterioration due to hydrogen ions.

In order to achieve the above object, the present invention is directed to an oxide dielectric thin film stack having a base and first and second electrode layers provided on the base and sandwiching an oxide dielectric layer. And the oxide dielectric thin film laminate is covered with a protective film made of a polymer.
The present invention is also effective when the protective film is made of polyurea.
The present invention is also effective when the protective film is made of polyparaxylylene or a polyparaxylylene derivative.
The present invention is also effective when the oxide dielectric layer is made of lead zirconate titanate.
The present invention is also effective when the oxide dielectric layer is made of barium-strontium-titanium.
On the other hand, the present invention provides a method for manufacturing any one of the above-described oxide dielectric elements, the oxide dielectric having the first and second electrode layers provided with the oxide dielectric layer interposed therebetween. This is a method for manufacturing an oxide dielectric element, comprising preparing a module in which a thin film laminate is provided on the substrate and forming the protective film by vapor deposition polymerization.

  According to the present invention described above, the physical properties (for example, piezoelectric properties and dielectric constant) can be greatly improved because the elastic modulus of the protective film made of a high molecular weight polymer is considerably smaller than that of silicon oxide as a ceramic. Can do.

  In addition, according to the present invention, no by-product, particularly hydrogen, is generated during the vapor deposition polymerization, so that the physical properties due to the reduction deterioration due to hydrogen ions do not occur in the oxide dielectric layer.

  Furthermore, the vapor deposition polymerization method used in the present invention is a method in which the vapor of the raw material monomer circulates from the periphery of the film formation target and the polymerization reaction proceeds on the surface of the film formation target. A protective film can be formed with excellent step coverage with respect to the body, whereby the insulating properties of the protective film can be improved.

Sectional drawing which shows the structural example of the oxide dielectric element which concerns on this invention (A)-(e): Process drawing which shows an example of the manufacturing method of the oxide dielectric element concerning this invention The figure which shows the schematic structural example of the vapor deposition polymerization apparatus used for the 1st vapor deposition polymerization method The figure for demonstrating the example of the process of the 2nd vapor deposition polymerization method The graph which shows the evaluation result of an Example and a comparative example

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a configuration example of an oxide dielectric element according to the present invention.
As shown in FIG. 1, the oxide dielectric element 15 of this example includes, for example, a first electrode layer 4 and a second electrode layer 4 provided on an Si substrate (substrate) 1 with an oxide dielectric layer 5 interposed therebetween. 6 is provided.

The oxide dielectric thin film laminate 8 in this example includes a silicon oxide (SiO ₂ ) layer 2 formed on a Si substrate 1 as a semiconductor substrate, an underlayer 3 made of titanium (Ti), and platinum (Pt). A first electrode layer 4 made of, for example, lead zirconate titanate (Pb (Zr, Ti) O ₃ ), that is, an oxide dielectric layer 5 made of PZT or barium-strontium-titanium (BST), and platinum (Pt And the second electrode layer 6 formed in this order.

The oxide dielectric thin film laminate 8 is covered with a protective film 7 made of a polymer, which will be described later.
In the case of the present invention, it is preferable that the elastic modulus of the protective film 7 is as small as possible from the viewpoint of improving the piezoelectric characteristics by reducing the binding force of the oxide dielectric element 15 or suppressing the decrease in the dielectric constant.
From this viewpoint, the preferable elastic modulus of the protective film 7 is 10 GPa or less.

  Note that the oxide dielectric element 15 of the present example includes a first electrode electrically connected to the first electrode layer 4 through the metal material 11 in the first contact hole 7a provided in the protective film 7. It has an extraction electrode 13 and a second extraction electrode 14 electrically connected to the second electrode layer 6 through a metal material 12 filled in the second contact hole 7b.

  2A to 2E are process diagrams showing an example of a method for manufacturing an oxide dielectric element according to the present invention. Hereinafter, an example of a method for manufacturing an oxide dielectric device according to the present invention will be described with reference to FIGS. 2 (a) to 2 (e), FIG. 3, and FIG. 4.

In this example, first, as shown in FIG. 2A, for example, a plurality of thin film layers (a silicon oxide layer 2, a base layer 3, a first electrode layer 4, an oxide dielectric) described above on a Si substrate 1, for example. A module 10 having an oxide dielectric thin film stack 8 on which a layer 5 and a second electrode layer 6) are formed is prepared.
Next, as shown in FIG. 2B, a protective film 7 made of a polymer is formed on the oxide dielectric thin film laminate 8, and the oxide dielectric thin film laminate is formed by the protective film 7. 8 is covered entirely.

In the present invention, the method for forming the protective film 7 is not particularly limited, but the vapor deposition polymerization method described below can be suitably used.
In this specification, the vapor deposition polymerization method refers to a method in which one or a plurality of low molecular weight raw material monomers are polymerized on the substrate surface to form a polymer thin film.

  As such a vapor deposition polymerization method, a raw material monomer of a plurality of types of low molecular organic materials having high reactivity is co-evaporated, and a polymer thin film is formed by polymerizing these raw material monomers on the substrate surface (hereinafter referred to as “ A first vapor deposition polymerization method)), a dimer of a specific organic material is thermally decomposed to generate a radicalized raw material monomer, and this raw material monomer is polymerized on the substrate surface to form a polymer thin film. A forming method (hereinafter referred to as “second vapor deposition polymerization method”) is known, and any of these methods can be applied in the present invention.

FIG. 3 is a diagram illustrating a schematic configuration example of a vapor deposition polymerization apparatus used in the first vapor deposition polymerization method.
As shown in FIG. 3, the vapor deposition polymerization apparatus 20 of this example has a vacuum chamber 22 connected to an evacuation device 21, and on a stage 24 having a temperature control means 23 in the lower part of the vacuum chamber 22. The module 10 described above is placed as a film formation target.

Here, a pair of evaporation sources 25 and 26 for evaporating two kinds of raw material monomers are provided above the vacuum chamber 22, and the pair of evaporation sources 25 and 26 are introduced with valves 27 a and 28 a, respectively. The pipes 27 and 28 are connected to the upper part of the vacuum chamber 22 respectively.
In addition, a heater 29 for heating the vapor of the introduced raw material monomer is provided in the upper part of the vacuum chamber 22.

  Evaporation containers (not shown) are provided in the respective evaporation sources 25 and 26 of the vapor deposition polymerization apparatus 20, and the raw material monomer for forming the protective film 7 can be heated in each evaporation container. Each is infused.

In the case of the present invention, the material for forming the protective film 7 by the first vapor deposition polymerization method is not particularly limited, but suppresses the influence of the high temperature on the device during the reaction, and is an oxide by hydrogen ions. From the viewpoint of preventing reductive degradation with respect to the dielectric layer 5, it is preferable to use a material that has a low reaction temperature and that does not generate by-products, particularly hydrogen during the polymerization reaction.
From this viewpoint, it is preferable to use polyurea as the material of the protective film 7.

In order to form a polyurea film by the first vapor deposition polymerization method, a diamine monomer and an acid component monomer can be used as raw material monomers.
In the case of the present invention, examples of the diamine monomer include 4,4′-diaminodiphenylmethane (MDA), 4,4′-diaminodiphenyl ether (DDE), and 4,4′-methylenebis (cyclohexylamine) (H12MDA). An alicyclic group or an aliphatic group can be preferably used.

  On the other hand, examples of the acid component monomer include alicyclic and aliphatic diisocyanates such as 4,4'-diphenylmethane diisocyanate (MDI) and 1,3-bis (isocyanatomethyl) cyclohexane (H6XDI). Can be suitably used.

In the vapor deposition polymerization apparatus 20 described above, when the protective film 7 made of a high molecular weight polymer is formed on the oxide dielectric thin film laminate 8 of the module 10, the vacuum chamber is kept with the valves 27 a and 28 a closed. The pressure inside 22 is set to a high vacuum of about 3 × 10 ⁻³ Pa, and the raw material monomers in the respective evaporation sources 25 and 26 are heated to predetermined temperatures, respectively.

Then, after each raw material monomer reaches a predetermined temperature and a required evaporation amount is obtained, each of the raw material monomers is introduced into the vacuum chamber 22 by opening the valves 27 a and 28 a, and each raw material monomer is heated by the heater 29. Each raw material monomer is led and deposited on the oxide dielectric thin film stack 8 of the module 10 from above at a predetermined evaporation rate while heating the vapor of the above.
In this case, the temperature control means 23 controls the temperature of the module 10 on the stage 24 to a predetermined temperature.

As a result, a polymerization reaction occurs on the surface of the oxide dielectric thin film laminate 8 of the module 10, and a protective film 7 made of polyurea is formed on the entire surface. The protective film 7 covers the oxide dielectric thin film laminate 8. (See FIG. 2 (b)).
In the case of this example, no by-product, particularly hydrogen, is generated during vapor deposition polymerization.

  In the case of the present invention, the thickness of the protective film 7 made of polyurea is not particularly limited. However, from the viewpoint of securing desired insulating properties and mechanical properties (particularly elastic modulus), 0.1 μm to 2.0 μm. It is preferable that

FIG. 4 is a diagram for explaining an example of steps of the second vapor deposition polymerization method.
In this example, a case where polyparaxylylene (parylene) is used as a specific organic material will be described as an example.

In this example, first, a paraxylylene dimer is prepared.
This paraxylylene dimer is made of a solid and has a structure represented by the formula (1) in FIG.

  In this example, in the process P1, the paraxylylene dimer is vaporized by heating at a predetermined temperature.

Next, in the process P2, the vaporized paraxylylene dimer is thermally decomposed by heating at a temperature higher than that in the vaporization step (process P1).
As a result, a highly reactive radicalized paraxylylene monomer gas is generated (see equation (2) in FIG. 4).

Further, in the vapor deposition polymerization step of process P3, this radicalized paraxylylene monomer gas is applied to the oxide dielectric thin film stack 8 of the module 10 described above, which is a film formation target, in a vacuum tank (not shown). Guide and deposit.
Note that it is not necessary to heat the module 10 to a high temperature during vapor deposition.

As a result, a polymerization reaction occurs on the surface of the oxide dielectric thin film laminate 8 of the module 10, and the protective film 7 made of polyparaxylylene and a polyparaxylylene derivative represented by the formula (3) in FIG. The oxide dielectric thin film laminate 8 is covered with this protective film 7 (see FIG. 2B).
In the case of this example, no by-product, particularly hydrogen, is generated during vapor deposition polymerization.

In addition, it is preferable that the repeating unit number n in Formula (3) of FIG. 4 is 5000 or more.
In the case of the present invention, the thickness of the protective film 7 made of polyparaxylylene is not particularly limited. However, from the viewpoint of securing desired insulating properties and mechanical properties (particularly elastic modulus), the thickness is 0.1 μm to 2 μm. It is preferable that the thickness is 0.0 μm.

Thereafter, as shown in FIG. 2C, the first contact hole 7a communicating with the first electrode layer 4 and the second electrode layer 6 are communicated with the protective film 7 by a known photolithography process. A second contact hole 7b is formed.
Then, as shown in FIG. 2D, the first and second contact holes 7a and 7b are filled with metal materials 11 and 12 made of, for example, aluminum.

Further, as shown in FIG. 2 (e), it is made of, for example, aluminum electrically connected to the upper portion of the first contact hole 7a through a metal material 11 filled in the first contact hole 7a. A first lead electrode 13 is provided, and a second electrode made of, for example, copper is electrically connected to the upper portion of the second contact hole 7b through a metal material 12 filled in the second contact hole 7b. A take-out electrode 14 is provided.
Through the above steps, the target oxide dielectric element 15 can be obtained (see FIG. 2E).

  According to the present invention described above, the elastic modulus of the protective film 7 made of a high molecular polymer is considerably smaller than that of silicon oxide, which is a ceramic, so that the piezoelectric characteristics are greatly improved and the decrease in dielectric constant is suppressed. can do.

  Further, according to the present invention, no by-product, in particular, hydrogen is generated during the vapor deposition polymerization, so that the physical properties of the oxide dielectric layer 5 due to reduction deterioration due to hydrogen ions do not occur.

  Further, the vapor deposition polymerization method used in the present invention is such that the vapor of the raw material monomer circulates from the periphery of the film formation target and the polymerization reaction proceeds on the surface of the film formation target. The protective film 7 can be formed with excellent step coverage with respect to the stacked body 8, thereby improving the insulating properties of the protective film as compared with the prior art.

Examples of the present invention will be described below together with comparative examples.
[Example 1]
On a silicon substrate, a silicon oxide layer, a base layer made of titanium, a first electrode layer made of platinum, an oxide dielectric layer made of PZT which is a piezoelectric material, and a second electrode layer made of platinum Prepared a piezoelectric module having an oxide dielectric thin film stack formed in this order.
Here, the thickness of the oxide dielectric layer made of PZT was 2 μm.

A protective film made of polyurea having a thickness of 1.0 μm is formed on the oxide dielectric thin film stack of this module by the first vapor deposition polymerization method described above to produce a piezoelectric oxide dielectric element. did.
The elastic modulus of the protective film made of polyurea was 5 GPa.

  Then, this piezoelectric oxide dielectric element was formed into a cantilever shape by a known lithography technique to prepare a sample for evaluating piezoelectric characteristics.

[Example 2]
A sample for piezoelectric property evaluation was prepared in the same manner as in Example 1 except that a protective film made of polyurea having an elastic modulus of 10 GPa was formed.

[Comparative Example 1]
A sample for evaluating piezoelectric characteristics was prepared in the same manner as in Example 1 except that no protective film was provided on the oxide dielectric thin film laminate of the piezoelectric module.

[Comparative Example 2]
A sample for evaluating piezoelectric characteristics was prepared by the same method as in Example 1 except that a protective film made of silicon oxide was formed by chemical vapor deposition (CVD) instead of polyurea.
The elastic modulus of the protective film made of silicon oxide was 72 GPa.

<Evaluation of piezoelectric characteristics of oxide dielectric element>
The piezoelectric constant was measured by applying an AC driving voltage of 250 Hz to the samples of Examples 1 and 2 and Comparative Examples 1 and 2 and measuring the displacement of the cantilever using a laser Doppler vibrometer. . The result is shown in FIG.

<Evaluation results>
As can be seen from FIG. 5, Example 1 in which a protective film made of polyurea having a thickness of 1.0 μm and an elastic modulus of 5 GPa provided a piezoelectric constant equivalent to that of Comparative Example 1 in which no protective film was provided. .
On the other hand, in Example 2, which has a modulus of elasticity of 10 GPa, which is larger than that of Example 1, the piezoelectric constant was slightly reduced (about 5%), but it was at a sufficiently practical level.

On the other hand, in Comparative Example 2 in which the protective film made of silicon oxide was formed, the piezoelectric constant was considerably reduced as compared with Examples 1 and 2.
Specifically, a decrease in piezoelectric constant of about 20% was observed with respect to Comparative Example 1 in which no protective film was provided.
From the above, the effect of the present invention could be verified.

1 ... Si substrate (base)
DESCRIPTION OF SYMBOLS 2 ... Silicon oxide layer 3 ... Underlayer 4 ... 1st electrode layer 5 ... Oxide dielectric layer 6 ... 2nd electrode layer 7 ... Protective film 8 ... Oxide dielectric thin film laminated body 10 ... Module 15 ... Oxide Dielectric element

In order to achieve the above object, the present invention is directed to an oxide dielectric thin film stack having a base and first and second electrode layers provided on the base and sandwiching an oxide dielectric layer. And the oxide dielectric thin film laminate is covered with a protective film made of a polymer.
The present invention is also effective when the protective film is made of polyurea.
The present invention is also effective when the protective film is made of polyparaxylylene or a polyparaxylylene derivative.
The present invention is also effective when the oxide dielectric layer is made of lead zirconate titanate.
The present invention is also effective when the oxide dielectric layer is made of barium-strontium-titanium.
The present invention is also effective when the protective film has an elastic modulus of 5 GPa or less.
On the other hand, the present invention provides a method for manufacturing any one of the above-described oxide dielectric elements, the oxide dielectric having the first and second electrode layers provided with the oxide dielectric layer interposed therebetween. This is a method for manufacturing an oxide dielectric element, comprising preparing a module in which a thin film laminate is provided on the substrate and forming the protective film by vapor deposition polymerization.

Next, the process P2, the vaporized para-xylylene dimer over, by heating at a temperature higher than the vaporization step (process P1), to thermally decompose.
As a result, a highly reactive radicalized paraxylylene monomer gas is generated (see equation (2) in FIG. 4).

Claims (6)

A substrate;
An oxide dielectric thin film laminate having first and second electrode layers provided on the substrate and sandwiching an oxide dielectric layer;
An oxide dielectric element in which the oxide dielectric thin film laminate is covered with a protective film made of a polymer.   The oxide dielectric element according to claim 1, wherein the protective film is made of polyurea.   The oxide dielectric element according to claim 1, wherein the protective film is made of polyparaxylylene or a derivative of polyparaxylylene.   The oxide dielectric element according to any one of claims 1 to 3, wherein the oxide dielectric layer is made of lead zirconate titanate.   4. The oxide dielectric element according to claim 1, wherein the oxide dielectric layer is made of barium-strontium-titanium. A substrate, and an oxide dielectric thin film stack including first and second electrode layers provided on the substrate and sandwiching the oxide dielectric layer, the oxide dielectric thin film stack Is a method of manufacturing an oxide dielectric element covered with a protective film made of a polymer,
Preparing a module in which an oxide dielectric thin film stack having the first and second electrode layers provided on both sides of the oxide dielectric layer is provided on the substrate;
A method for manufacturing an oxide dielectric element, comprising a step of forming the protective film by vapor deposition polymerization.

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