JP2012114156A - Method of manufacturing piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a piezoelectric element in which a ferroelectric layer is processed to have a taper angle of 70° or larger by dry etching, and etching products do not adhere to the sidewall.SOLUTION: A resist 15 composed of an organic matter is placed on a processed object where a lower electrode film 12, a ferroelectric layer 13 and an upper electrode film 14 are laminated, in this order, on a substrate 11. A mixed gas of a gas containing a halogen element (excluding Cl) in the chemical structure and a rare gas is plasmatized, and brought into contact with the resist 15 and a processed object 21. Furthermore, a bias voltage is applied to an electrode under the processed object 21 so as to inject ions in the plasma, and anisotropic etching is performed. The side surface is etched to have a taper angle of 70° or larger, and etching products do not adhere to the side surface.

Description

  The present invention relates to a method for manufacturing a piezoelectric element, and more particularly to a method for manufacturing a piezoelectric element whose shape is processed by dry etching.

In recent years, MEMS (Micro Electro Mechanical Systems) technology has been further developed, and its application range has been expanded to include inkjet printer heads, acceleration sensors, HDD head microactuators, and the like. Ferroelectric materials such as lead zirconate titanate (Pb (Tz, Ti) O ₃ , PZT), which have excellent piezoelectric properties, are actively studied in MEMS applications as a material that bridges mechanical stress and electrical change. Has been.

A piezoelectric element has a structure in which a ferroelectric material of several μm to several tens of μm is sandwiched between noble metal electrodes, and has been conventionally processed by wet etching using a chemical solution, argon milling, or the like. Along with miniaturization of MEMS, piezoelectric elements have become finer and more precise, and dry etching with good shape controllability has been demanded.
However, the noble metal electrodes such as Pt and Ir and the ferroelectrics such as PZT constituting the piezoelectric element are all called difficult-to-etch materials and have poor reactivity with the halogen gas, and the halide has a low vapor pressure. There is a feature.

If the ferroelectric can be processed more vertically, miniaturization can be performed. However, in the prior art, the taper angle of the ferroelectric by dry etching is limited to 60 °.
Further, the etching product easily adheres to the pattern side wall, and as a result, there is a possibility that the device in the subsequent process is contaminated, or that the disconnection or insulation failure is caused in the process of forming the wiring in the next process.

  Patent Document 2 discloses a method of increasing the reactivity between a difficult-to-etch material and an etching gas by heating the substrate to a high temperature. However, in this case, a resist made of an organic substance has a poor heat resistance, so that a hard mask material is used. There was a problem that it was necessary to use a mask.

International Publication No. 2007/129732 JP 2003-258203 A

  The present invention was created to solve the above-mentioned disadvantages of the prior art. The purpose of the present invention is to process the taper angle of the ferroelectric layer to 70 ° or more by dry etching, and an etching product is formed on the side wall. An object of the present invention is to provide a method for manufacturing a piezoelectric element that does not adhere.

In order to solve the above problems, the present invention includes a substrate, a lower electrode film made of a conductive material, a ferroelectric layer made of a ferroelectric, and an upper electrode film made of a conductive material, The lower electrode film, the ferroelectric layer, and the upper electrode film are arranged in this order on the substrate, and when a voltage is applied between the upper electrode film and the lower electrode film, the shape of the ferroelectric layer Is a method of manufacturing a piezoelectric element in which the deformation is restored when the application of voltage is stopped, and the lower electrode film and the first film to be etched constituting the ferroelectric layer are formed on the substrate, The second etching target film that constitutes the upper electrode film is made of an organic substance that exposes a part of the second etching target film on the second etching target film of the processing target laminated in this order. Resist placement process to place resist and chemical structure The reaction gas containing a halogen element (however, Cl ₂ is excluded) and, to a plasma of a mixed gas of a rare gas, the resist and brought into contact with plasma in the processing object, an AC voltage to the electrodes under the processing object An etching step for applying ions to cause ions in plasma to be incident on the object to be processed, partially etching the first and second films to be etched, and exposing the lower electrode film. It is a manufacturing method.
The present invention is a method of manufacturing a piezoelectric element, wherein the ferroelectric layer includes PZT (Pb (Tz, Ti) O ₃ ), SBT (SrBi ₂ Ta ₂ O ₃ ), and BIO (Bi ₄ Ti ₃ O). ₁₂ ), a BLT ((Bi, La) ₄ Ti ₃ O ₁₂ ), and a piezoelectric element containing any one material selected from the group consisting of PLZT ((PbLa) (ZrTi) O ₃ ) It is a manufacturing method.
The present invention is a method for manufacturing a piezoelectric element, wherein the upper electrode film and the lower electrode film are each selected from the group consisting of Pt, Ir, IrO ₂ , and SRO (Strontium Ruthenium Oxide). This is a method of manufacturing a piezoelectric element containing one kind of material.
The present invention relates to a method for manufacturing a piezoelectric element, wherein the reaction gas includes any one gas selected from the group consisting of BCl ₃ , CHF ₃ , and C ₄ F _8. Is the method.
The present invention is a method for manufacturing a piezoelectric element, wherein the rare gas contains any one gas selected from the group consisting of He, Ne, Ar, Kr, Xe, and Rn. This is a method of manufacturing a piezoelectric element.
The present invention is a method for manufacturing a piezoelectric element, wherein the AC power density applied to the electrode in the etching step is 2.25 W / cm ² or more.

Since a gas that is polymerizable with respect to the resist is used, etching can be performed so as to keep the tapered shape of the resist vertical.
Since the taper angle can be processed at 70 ° or more and the etching residue does not adhere to the side wall, a fine piezoelectric element can be formed.
Since etching is performed at room temperature, a resist made of an organic material can be used for the mask.

(A)-(d): The figure for demonstrating the manufacturing method of the piezoelectric element which is this invention The figure for demonstrating the structure of the ICP type etching apparatus used by this invention

<Structure of piezoelectric element>
First, the structure of the piezoelectric element formed by the manufacturing method of the present invention will be described. FIG. 1D shows a cross-sectional view of the piezoelectric element 10.
The piezoelectric element 10 has a ferroelectric layer 13, an upper electrode film 14, and a lower electrode film 12.

The ferroelectric layer 13 is disposed on the lower electrode film 12, and the upper electrode film 14 is disposed on the ferroelectric layer 13. A substrate 11 is disposed under the lower electrode film 12.
The upper electrode film 14 and the lower electrode film 12 are electrically connected to a control circuit (not shown).

  Such a piezoelectric element 10 has a piezoelectric effect, and when the shape is deformed by applying pressure to the ferroelectric layer 13 from the outside, electric polarization is induced in the ferroelectric layer 13, and the upper electrode film 14 and the lower electrode A voltage is generated between the membrane 12. Conversely, when a voltage is applied between the upper electrode film 14 and the lower electrode film 12 from a control circuit (not shown), the shape of the ferroelectric layer 13 is deformed, and when the voltage application is stopped, the shape is restored.

The ferroelectric layer 13 is made of a ferroelectric, and here, PZT (Pb (Tz, Ti) O ₃ ) is used. However, the present invention is not limited to PZT as the material of the ferroelectric layer 13, but PZT, SBT (SrBi ₂ Ta ₂ O ₃ ), BIO (Bi ₄ Ti ₃ O ₁₂ ), BLT ((Bi, La) ₄ Ti ₃ O ₁₂ ) and PLZT ((PbLa) (ZrTi) O ₃ ) are also included that contain any one material selected from the group consisting of:

The upper electrode film 14 and the lower electrode film 12 are made of a conductive material, and here both use Pt films. However, the present invention is not limited to Pt as the material of the upper electrode film 14 and the lower electrode film 12, and any one material selected from the group consisting of Pt, Ir, IrO ₂ and SRO (Strongium Ruthenium Oxide), respectively. The thing containing is also included.
Here, a Si substrate with a thermal oxide film (SiO ₂ ) is used as the substrate 11, and the thermal oxide film that is an insulating layer is disposed so as to be in contact with the lower electrode film 12.

<Piezoelectric element manufacturing equipment>
FIG. 2 shows an inductively coupled plasma (ICP) etching apparatus 80 used in the present invention.
The etching apparatus 80 includes a vacuum chamber 89, a plasma generation unit 92, a gas supply unit 81, a vacuum exhaust unit 82, and a temperature control unit 88.

Inside the vacuum chamber 89, a stage 86 for placing a processing object is provided.
The temperature control unit 88 is connected to the stage 86, and can control the temperature of the processing object placed on the stage 86 by flowing a temperature-controlled heat medium through a cooling pipe (not shown) provided on the stage 86, for example. Has been.

  The plasma generator 92 includes an RF antenna 83, a matching box 87a, and a plasma high-frequency power source 94. The RF antenna 83 is installed above the vacuum chamber 89 and is electrically connected to the plasma high-frequency power source 94 via the matching box 87a so that the etching gas supplied into the vacuum chamber 89 can be converted into plasma. ing.

  In addition, an electrode (not shown) is arranged in the stage 86, and a high frequency power supply 85 for bias is electrically connected to the electrode via a matching box 87b. The ions in the plasma are accelerated and arranged on the stage 86. It can be etched by colliding with the processed object.

  Both the gas supply unit 81 and the vacuum exhaust unit 82 are disposed outside the vacuum chamber 89. The evacuation unit 82 is connected to the inside of the vacuum chamber 89 so that the inside of the vacuum chamber 89 can be evacuated, and the gas supply unit 81 is connected to the inside of the vacuum chamber 89 so that the etching gas can be supplied into the vacuum chamber 89. Has been.

<Method for manufacturing piezoelectric element>
Next, a method for manufacturing a piezoelectric element according to the present invention will be described with reference to FIGS.
Reference numeral 20 in FIG. 1A constitutes a lower electrode film 12, a first etched film 13a that forms a ferroelectric layer 13 after etching, and an upper electrode film 14, as will be described later. The object to be processed in a state where the second film to be etched 14a is formed in this order by the sputtering method or the like is shown.

  First, as a resist placement step, a photoresist made of an organic material is applied onto the second film to be etched 14a, exposed to a predetermined pattern, developed, and as shown by reference numeral 21 in FIG. A resist 15 that partially exposes the second film to be etched 14a is disposed.

  The resist arrangement method of the present invention is not limited to this, and an imprint resist made of an organic material is applied onto the second film to be etched 14a, softened by heating, and then cooled by pressing a mold having a predetermined pattern. Then, the mold is released, the pattern shape is transferred to the resist, and then the remaining film on the bottom surface of the pattern is removed by etching with oxygen gas. As shown by reference numeral 21 in FIG. A resist 15 that partially exposes 14a may be disposed.

The inside of the vacuum chamber 89 of the etching apparatus 80 is evacuated by the evacuation unit 82 to form a vacuum atmosphere. Thereafter, evacuation is continued to maintain the vacuum atmosphere.
Next, as an etching process, the processing object 21 after the resist placement process is carried into the vacuum chamber 89 from a loading device (not shown) while maintaining the vacuum atmosphere in the vacuum chamber 89, and the surface on which the resist 15 is formed. Is placed on the stage 86 with the opposite side facing the stage 86 and the resist 15 side exposed.

  The temperature control unit 88 controls the temperature of the processing object 21 on the stage 86. The temperature during etching is preferably in the range of 20 ° C to 80 ° C. This is because a resist made of an organic material can be used for the mask by performing etching at room temperature.

While the vacuum chamber 89 is evacuated, an etching gas is supplied from the gas supply unit 81 into the vacuum chamber 89.
As the etching gas, a mixed gas of a polymerizable reactive gas containing a halogen element in its chemical structure (excluding Cl ₂ ) and a rare gas is used.

As the reaction gas, a gas containing any one kind of gas selected from the group consisting of BCl ₃ , CHF ₃ , and C ₄ F ₈ is used. Further, as the rare gas, a gas containing any one kind of gas selected from the group consisting of He, Ne, Ar, Kr, Xe, and Rn is used.
The pressure of the etching gas is preferably in the range of 0.1 Pa to 10 Pa according to the etching selectivity with the resist 15.

  The plasma high frequency power supply 94 is activated, an alternating current is passed through the RF antenna 83, radio waves are emitted from the RF antenna 83 into the vacuum chamber 89, the etching gas is turned into plasma, and active species such as ions and radicals are generated, Plasma is brought into contact with the resist 15 and the processing object 21.

In addition, the bias high-frequency power source 85 is activated, and a bias voltage of 600 kHz is applied to the electrode under the processing target 21 to cause the generated ions or the like to enter the processing target 21.
Here, the AC power density applied to the electrode under the processing object 21 is preferably 2.25 W / cm ² or more.

  The exposed portion of the second etching target film 14a reacts with the plasma, and the generated etching product of the second etching target film 14a evaporates, or is sputtered by incident ions, and the gasified etching product is generated. The upper electrode film 14 is formed by being evacuated and removed, and the first film to be etched 13a is exposed.

  Next, the exposed portion of the first film to be etched 13a reacts with plasma, and the generated etching product of the first film to be etched 13a evaporates or is sputtered by incident ions to gasify the etching product. Is evacuated and removed, and the ferroelectric layer 13 is formed.

  Since a polymerizable gas is used, the resist 15 is protected from active species, is not easily side-etched, and the tapered shape is kept vertical. By the sputter etching, the taper angle of the resist 15 is transferred as the taper angle of the first and second films to be etched 13a and 14a, and the taper angle of the ferroelectric layer 13 is formed to be 70 ° or more.

The etching gas contains a rare gas, and the processing object 21 is applied with an AC power density of 2.25 W / cm ² or more, so that the etching product adheres to the side surface of the processing object, but sputters on the incident ions. As a result, the etching product does not remain on the side surface.

As a reason why the etching product does not remain on the side surface of the processing object, in addition to the above reason, the etching gas contains a rare gas, and the processing object 21 is applied with an AC power density of 2.25 W / cm ² or more. Therefore, there is a possibility that the etching product is sputtered by higher energy ions and is blown farther and does not adhere to the side surface.

When the lower electrode film 12 is exposed as in the processing object 22 shown in FIG. 1C, the operations of the plasma high-frequency power source 94 and the bias high-frequency power source 85 are stopped, and the etching gas from the gas supply unit 81 is stopped. Stop supplying.
Here, a shield 91 is provided so as to surround the stage 86, and adhesion of deposits generated by etching to the inner wall of the vacuum chamber 89 is prevented.

Next, the processed object 22 after etching is taken out from the etching apparatus 80, and a peeling solution is brought into contact with the surface of the processed object 22. The resist 15 is dissolved in the stripping solution and removed to obtain the piezoelectric element 10 as shown in FIG.
The resist removal method of the present invention is not limited to this, and the resist 15 may be chemically oxidized and volatilized to be removed by bringing oxygen radicals or the like into contact with the object 22 to be processed.

<Example 1>
A lower electrode film (Pt film), a first film to be etched (PZT film), and a second film to be etched (Pt film) are formed in this order on the substrate by sputtering or the like, and then the second film to be etched is formed. An object to be processed in a state where a resist that partially exposes the second film to be etched was disposed on the etching film was prepared.

This object to be treated was carried into a vacuum chamber of an ICP type etching apparatus. While evacuating the vacuum chamber, Ar gas and BCl ₃ gas are supplied into the vacuum chamber at a flow rate of 4.2 × 10 ⁻² Pa · m ³ / sec (25 sccm) as an etching gas, Was set to a pressure of 1.0 Pa to 0.1 Pa. Next, an AC power of 1000 W to 500 W was applied from a high frequency power source for plasma to make the etching gas into plasma, and the resist was brought into contact with the object to be processed. Further, AC power of 400 W to 100 W was applied from a high frequency power source for bias, ions in the plasma were incident on the object to be processed, and the first and second films to be etched were partially anisotropically etched.

  When the film was taken out from the vacuum chamber after etching and photographed with an SEM (scanning electron microscope), the taper angle of the etched side surface was formed at 72 °, and it was confirmed that the etching product did not adhere to this side surface.

<Comparative Example 1>
In the same manner as in Example 1, an object to be processed in which a resist that partially exposes the second film to be etched was placed on the second film to be etched was carried into a vacuum chamber of an ICP type etching apparatus. While evacuating the inside of the vacuum chamber, BCl ₃ gas as an etching gas is supplied into the vacuum chamber at a flow rate of 8.4 × 10 ⁻² Pa · m ³ / sec (50 sccm). The pressure was 0.1 Pa. Next, an AC power of 1000 W to 500 W was applied from a high frequency power source for plasma to make the etching gas into plasma, and the resist was brought into contact with the object to be processed. Further, AC power of 400 W to 100 W was applied from a high frequency power source for bias, ions in the plasma were incident on the object to be processed, and the first and second films to be etched were partially anisotropically etched.

  When the film was taken out from the vacuum chamber after etching and photographed with SEM, the taper angle of the etched side surface was formed to be 60 ° or less, and it was confirmed that the etching product adhered to this side surface. Moreover, when it image | photographed by SEM after mask removal, it was confirmed that the etching product adhering to the side surface was not removed but remained in the shape of a fence.

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric element 11 ... Substrate 12 ... Lower electrode film 13 ... Ferroelectric layer 13a ... First to-be-etched film 14 ... Upper electrode film 14a ... Second to-be-etched film 15 ... Resist 20 …… Processing object before resist placement process 21 …… Processing object after resist placement process

Claims (6)

A substrate,
A lower electrode film made of a conductive material;
A ferroelectric layer made of a ferroelectric;
An upper electrode film made of a conductive material,
The lower electrode film, the ferroelectric layer, and the upper electrode film are disposed on the substrate in this order,
When a voltage is applied between the upper electrode film and the lower electrode film, the shape of the ferroelectric layer is deformed, and when the voltage application is stopped, the deformation is restored.
A processing object in which the lower electrode film, the first etching target film constituting the ferroelectric layer, and the second etching target film constituting the upper electrode film are laminated in this order on the substrate. A resist disposing step of disposing a resist made of an organic substance that partially exposes the second etching target film on the second etching target film;
A reaction gas containing a halogen element in the chemical structure (however, except for Cl ₂ ) and a rare gas are turned into plasma, plasma is brought into contact with the resist and the object to be processed, and an electrode under the object to be processed An etching step in which an alternating voltage is applied to the substrate, ions in plasma are incident on the object to be processed, the first and second etching target films are partially etched, and the lower electrode film is exposed;
A method of manufacturing a piezoelectric element having The ferroelectric layer includes PZT (Pb (Tz, Ti) O ₃ ), SBT (SrBi ₂ Ta ₂ O ₃ ), BIO (Bi ₄ Ti ₃ O ₁₂ ), and BLT ((Bi, La) _4. The method for manufacturing a piezoelectric element according to claim 1, comprising any one material selected from the group consisting of Ti ₃ O ₁₂ ) and PLZT ((PbLa) (ZrTi) O ₃ ). The upper electrode film and the lower electrode film each contain any one material selected from the group consisting of Pt, Ir, IrO ₂ , and SRO (Strongium Ruthenium Oxide). Item 3. A method for manufacturing a piezoelectric element according to any one of Items 2 to 3. 4. The piezoelectric element according to claim 1, wherein the reaction gas contains any one kind of gas selected from the group consisting of BCl ₃ , CHF ₃ , and C ₄ F _8. Manufacturing method.   The said rare gas contains any one kind of gas selected from the group which consists of He, Ne, Ar, Kr, Xe, and Rn. The manufacturing method of the piezoelectric element of description. 6. The method of manufacturing a piezoelectric element according to claim 1, wherein an AC power density applied to the electrode in the etching step is 2.25 W / cm ² or more.

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