WO2011016381A1 - 圧電素子の製造方法 - Google Patents
圧電素子の製造方法 Download PDFInfo
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- WO2011016381A1 WO2011016381A1 PCT/JP2010/062756 JP2010062756W WO2011016381A1 WO 2011016381 A1 WO2011016381 A1 WO 2011016381A1 JP 2010062756 W JP2010062756 W JP 2010062756W WO 2011016381 A1 WO2011016381 A1 WO 2011016381A1
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- Prior art keywords
- film
- etching
- gas
- ferroelectric film
- piezoelectric element
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- 238000000034 method Methods 0.000 title claims abstract description 34
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 23
- 238000005530 etching Methods 0.000 claims abstract description 80
- 239000007789 gas Substances 0.000 claims abstract description 59
- 229910052751 metal Inorganic materials 0.000 claims abstract description 56
- 239000002184 metal Substances 0.000 claims abstract description 56
- 239000000758 substrate Substances 0.000 claims abstract description 15
- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims abstract description 10
- 229910001882 dioxygen Inorganic materials 0.000 claims abstract description 10
- 150000002500 ions Chemical class 0.000 claims abstract description 9
- 239000000126 substance Substances 0.000 claims abstract description 8
- PXGOKWXKJXAPGV-UHFFFAOYSA-N Fluorine Chemical compound FF PXGOKWXKJXAPGV-UHFFFAOYSA-N 0.000 claims abstract description 5
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 5
- 239000011737 fluorine Substances 0.000 claims abstract description 5
- 239000010408 film Substances 0.000 claims description 122
- 229910052451 lead zirconate titanate Inorganic materials 0.000 claims description 26
- 239000010409 thin film Substances 0.000 claims description 16
- 239000012495 reaction gas Substances 0.000 claims description 11
- 229910052759 nickel Inorganic materials 0.000 claims description 9
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 6
- 239000004020 conductor Substances 0.000 claims description 6
- 229910052746 lanthanum Inorganic materials 0.000 claims description 6
- HFGPZNIAWCZYJU-UHFFFAOYSA-N lead zirconate titanate Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ti+4].[Zr+4].[Pb+2] HFGPZNIAWCZYJU-UHFFFAOYSA-N 0.000 claims description 4
- 229910052726 zirconium Inorganic materials 0.000 claims description 4
- VNSWULZVUKFJHK-UHFFFAOYSA-N [Sr].[Bi] Chemical compound [Sr].[Bi] VNSWULZVUKFJHK-UHFFFAOYSA-N 0.000 claims description 3
- 229910052782 aluminium Inorganic materials 0.000 claims description 3
- 229910002113 barium titanate Inorganic materials 0.000 claims description 3
- JRPBQTZRNDNNOP-UHFFFAOYSA-N barium titanate Chemical compound [Ba+2].[Ba+2].[O-][Ti]([O-])([O-])[O-] JRPBQTZRNDNNOP-UHFFFAOYSA-N 0.000 claims description 3
- 229910052797 bismuth Inorganic materials 0.000 claims description 3
- RZEADQZDBXGRSM-UHFFFAOYSA-N bismuth lanthanum Chemical compound [La].[Bi] RZEADQZDBXGRSM-UHFFFAOYSA-N 0.000 claims description 3
- 229910052804 chromium Inorganic materials 0.000 claims description 3
- NKZSPGSOXYXWQA-UHFFFAOYSA-N dioxido(oxo)titanium;lead(2+) Chemical compound [Pb+2].[O-][Ti]([O-])=O NKZSPGSOXYXWQA-UHFFFAOYSA-N 0.000 claims description 3
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims description 3
- 238000001020 plasma etching Methods 0.000 abstract description 2
- 239000000203 mixture Substances 0.000 abstract 1
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 25
- 238000012545 processing Methods 0.000 description 19
- 238000004544 sputter deposition Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 6
- 239000000919 ceramic Substances 0.000 description 5
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 238000007772 electroless plating Methods 0.000 description 2
- 150000004820 halides Chemical class 0.000 description 2
- 238000007747 plating Methods 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 230000001133 acceleration Effects 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002309 gasification Methods 0.000 description 1
- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
- 238000009616 inductively coupled plasma Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 239000010453 quartz Substances 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 229910001925 ruthenium oxide Inorganic materials 0.000 description 1
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(iv) oxide Chemical compound O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000001771 vacuum deposition Methods 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/01—Manufacture or treatment
- H10N30/08—Shaping or machining of piezoelectric or electrostrictive bodies
- H10N30/082—Shaping or machining of piezoelectric or electrostrictive bodies by etching, e.g. lithography
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
- H02N2/00—Electric machines in general using piezoelectric effect, electrostriction or magnetostriction
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/20—Piezoelectric or electrostrictive devices with electrical input and mechanical output, e.g. functioning as actuators or vibrators
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/853—Ceramic compositions
Definitions
- the present invention relates to a method for manufacturing a piezoelectric element.
- Piezoelectric elements are used from industrial equipment to small electronic equipment such as ink ejection drive sources for ink jet recording heads, camera shake correction mechanisms for buzzers, acceleration sensors, and digital cameras. Etc., and its application range is expanding.
- Oxide ferroelectrics such as lead zirconate titanate (Pb (Zr, Ti) O 3 , PZT) having excellent piezoelectric properties are prominent as materials that bridge the mechanical stress and electrical changes of piezoelectric elements. It has been studied.
- a ferroelectric such as PZT is called a difficult-to-etch material and has poor reactivity with a halogen gas, and the halide has a low vapor pressure, so that an etching product easily adheres to the pattern sidewall.
- Reference numeral 110 in FIG. 4 indicates an object to be processed having the ferroelectric film 113 etched by the conventional technique.
- a lower electrode film 112 is disposed below the ferroelectric film 113, and a resist 115 is disposed on the ferroelectric film 113.
- a substrate 111 is disposed under the lower electrode film 112.
- an etching product 116 made of a ferroelectric halide adheres in a fence shape. The etching product 116 cannot be removed in the resist 115 peeling process, and it is necessary to add a new removal process, or inconveniences such as disconnection or insulation failure in the process of forming a wiring in the subsequent process. It was. International Publication No. WO2007 / 129732
- the present invention was created to solve the above-mentioned disadvantages of the prior art, and an object thereof is to provide a method of manufacturing a piezoelectric element that processes a dielectric film into a good shape by plasma etching.
- the present invention has a substrate, a lower electrode film made of a conductive material, a ferroelectric film made of an oxide ferroelectric, and an upper electrode film made of a conductive material.
- the lower electrode film, the ferroelectric film, and the upper electrode film are disposed on the substrate in this order, and when a voltage is applied between the upper electrode film and the lower electrode film, the ferroelectric film.
- a metal mask comprising a patterned metal thin film on the ferroelectric film on the surface of the object, partially exposing the surface of the ferroelectric film and covering the other part; and AC voltage is applied to the electrode placed on the back side of the object to be processed.
- a plasma of an etching gas containing a mixed gas of oxygen gas and a reactive gas containing fluorine in the chemical structure is formed on the surface side of the film formation target, and the metal mask, the ferroelectric film, And an etching process in which the plasma film is brought into contact and ions in the plasma are incident to remove the ferroelectric film exposed at the bottom of the opening of the metal mask and to expose the lower electrode film. It is a manufacturing method of an element.
- the present invention relates to a method for manufacturing a piezoelectric element, wherein the ferroelectric film includes barium titanate (BaTiO 3 ), lead titanate (PbTiO 3 ), and bismuth lanthanum titanate ((Bi, La) 4 Ti 3. O 12 : BLT), lead zirconate titanate (Pb (Zr, Ti) O 3 : PZT), lead lanthanum zirconate titanate ((PbLa) (ZrTi) O 3 : PLZT), and bismuth strontium tantalate
- This is a method for manufacturing a piezoelectric element containing any one type of oxide ferroelectric selected from the group consisting of (SrBi 2 Ta 2 O 3 : SBT).
- the present invention is a method for manufacturing a piezoelectric element, wherein the mask includes any one type of metal selected from the group consisting of Ni, Al, and Cr.
- the present invention is a method for manufacturing a piezoelectric element, wherein the reaction gas is CF 4 , C 2 F 6 , C 3 F 8 , C 4 F 8 , CHF 3 , SF 6 , and C 4 F. 6 and a method of manufacturing a piezoelectric element made of any one kind of gas selected from the group consisting of C 5 F 8 , or two or more kinds of mixed gases.
- the present invention is a method of manufacturing a piezoelectric element, wherein the etching gas has a ratio of the flow rate of the reaction gas to the sum of the flow rate of oxygen gas and the flow rate of the reaction gas of 50% or more. It is a manufacturing method.
- the metal mask is thin and adhesion of etching products to the metal mask sidewall is suppressed, the occurrence of disconnection and the like are suppressed, and the processing accuracy of the ferroelectric film is improved. Since the heat-resistant temperature range of the metal mask is wider than before, the temperature during etching can be controlled in a wider range than before. Since etching of several tens of ⁇ m is possible in the film thickness direction of the ferroelectric film, it can be applied to MEMS in fields that could not be implemented conventionally. Since chlorine gas is not used as an etching gas, it can be processed in an environment where chlorine gas cannot be used.
- FIG. 1E shows a cross-sectional view of the piezoelectric element 10e.
- the piezoelectric element 10 e has a ferroelectric film 13, an upper electrode film 14, and a lower electrode film 12.
- the ferroelectric film 13 is disposed on the lower electrode film 12, and the upper electrode film 14 is disposed on the ferroelectric film 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 10e has a piezoelectric effect, and when an external pressure is applied to the ferroelectric film 13 to deform the shape, electric polarization is induced in the ferroelectric film 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 film 13 is deformed, and when the voltage application is stopped, the shape is restored.
- the ferroelectric film 13 is made of an oxide ferroelectric, and here, lead zirconate titanate (Pb (Zr, Ti) O 3 : PZT) is used.
- PZT lead zirconate titanate
- the present invention is not limited to PZT as the material of the ferroelectric film 13, and barium titanate (BaTiO 3 ), lead titanate (PbTiO 3 ), bismuth lanthanum titanate ((Bi, La) 4 Ti 3 O 12 : Etching with gas containing fluorine in chemical structure, such as BLT), lead lanthanum zirconate titanate ((PbLa) (ZrTi) O 3 : PLZT), bismuth strontium tantalate (SrBi 2 Ta 2 O 3 : SBT)
- An oxide ferroelectric that can be used may be used.
- the upper electrode film 14 and the lower electrode film 12 are made of a conductive material, and here both use Pt films.
- the present invention is not limited to Pt as the material of the upper electrode film 14 and the lower electrode film 12, and a conductive material that does not easily react with the oxide ferroelectric such as Ir, IrO 2 , SRO (Strongium Ruthenium Oxide), respectively. It may be used.
- 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.
- Reference numeral 80 in FIG. 2 denotes an etching apparatus equipped with an inductively coupled plasma (ICP) source 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 so that the temperature of the processing object placed on the stage 86 can be controlled by flowing a temperature-controlled heat medium through a cooling pipe 98 provided in the stage 86, for example. Has been.
- the plasma generator 92 includes an RF antenna 83, a matching box 87a, and a plasma AC power source 84.
- An opening is formed above the vacuum chamber 89, and a ceramic plate 97 such as quartz is disposed in the opening.
- An RF antenna 83 is disposed on the surface of the ceramic plate 97 outside the vacuum chamber 89.
- the RF antenna 83 is electrically connected to a plasma AC power supply 84 via a matching box 87a so that the etching gas supplied into the vacuum chamber 89 can be converted into plasma.
- an electrode 96 is disposed inside the stage 86, and when the processing object is disposed on the stage 86, the electrode 96 is positioned on the back side of the processing object.
- a sputtering AC power supply 85 is electrically connected to the electrode 96 through a matching box 87b so that ions in the plasma can be accelerated and collided with the object to be processed for etching.
- Both the gas supply unit 81 and the vacuum exhaust unit 82 are disposed outside the vacuum chamber 89.
- the vacuum exhaust unit 82 is connected to the inside of the vacuum chamber 89 so that the inside of the vacuum chamber 89 can be exhausted, 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. ing.
- a reference numeral 10a in FIG. 1A indicates a processing target in a state where a lower electrode film 12 and a ferroelectric film 13 are formed on a substrate 11 in this order by a sputtering method or the like.
- a metal mask arranging step a patterned resist film is arranged on the ferroelectric film 13, and then the object to be processed is immersed in an electroless nickel plating solution, and the resist film surface and the opening bottom surface of the resist film are arranged.
- a metal mask 15 made of a patterned metal thin film (nickel thin film) is provided on the surface of the processing object 10b. The metal mask 15 is in close contact with the ferroelectric film 13, and the metal mask 15 partially exposes the surface of the ferroelectric film 13 and covers the other part.
- the object to be treated is immersed in an electroless nickel plating solution with the entire surface of the ferroelectric film 13 exposed to form a metal thin film made of nickel on the surface of the ferroelectric film 13, and then a patterned resist.
- the metal thin film formed on the surface of the metal thin film on which the film is formed, and the metal thin film exposed under the opening of the resist film may be removed by etching to pattern the metal thin film into a predetermined shape.
- a metal mask 15 made of a patterned metal thin film (nickel thin film) is obtained.
- the metal mask arrangement method of the present invention is not limited to the electroless plating method, and the metal mask can be formed by a sputtering method, a vacuum deposition method, or the like. In short, it is only necessary to form a thin metal thin film that is in close contact with the ferroelectric film 13 and patterned, but the electroless plating method is particularly preferable. This is because, even if the metal mask 15 is thin, it preferably has a film thickness of 4 ⁇ m or more and 10 ⁇ m or less so that it can withstand etching in an etching process to be described later. This is because it can be realized.
- the material of the metal mask 15 of the present invention is not limited to Ni metal, and is a material having an etching rate slower than the etching rate of the ferroelectric film 13 with respect to an etching gas for etching the ferroelectric film 13,
- the metal mask 15 may be formed of a metal that is difficult to be etched with oxygen gas, such as Al, Cr, Ti, or Ta, or an alloy thereof, as long as it can be patterned into a desired shape.
- the vacuum chamber 89 of the etching apparatus 80 is evacuated by the evacuation unit 82.
- the object 10b to be processed after the metal mask placement step is carried into the vacuum chamber 89 from a loading device (not shown) while maintaining the vacuum atmosphere in the vacuum chamber 89.
- the processing object 10b is placed on the stage 86 with the surface opposite to the surface on which the metal mask 15 is formed facing the stage 86 and the surface on the side on which the metal mask 15 is formed exposed.
- an etching gas is supplied from the gas supply unit 81 into the vacuum chamber 89.
- the etching gas contains a mixed gas of oxygen gas and a reaction gas containing fluorine in the chemical structure.
- the reaction gas includes CF 4 , C 2 F 6 , C 3 F 8 , C 4 F 8 , CHF 3 , SF 6 , C 4 F 6 , and C 5 F 8. It consists of any one kind of gas selected from the group which consists of, or consists of two or more types of mixed gas.
- the etching gas may contain an auxiliary gas composed of a rare gas such as Ar.
- the gas supply unit 81 is connected to a control device (not shown) and the flow rate is controlled, and the ratio of the flow rate of the reaction gas to the total of the flow rate of the oxygen gas and the flow rate of the reaction gas (hereinafter referred to as the reaction gas ratio). It is preferably 50% or more. This is because as the oxygen gas ratio increases, the etching processing speed decreases.
- the surface of the object to be deposited on which the metal mask 15 is formed faces the RF antenna 83 through the ceramic plate 97, and the plasma AC power supply 84 is activated with the vacuum chamber 89 at the ground potential.
- the radio waves pass through the ceramic plate 97 and enter the vacuum chamber 89.
- An etching gas atmosphere is formed between the ceramic plate 97 and the surface on which the metal mask 15 of the object to be processed is formed. Radio waves are irradiated to the etching gas, and etching is performed on the metal mask 15 of the object to be processed.
- a gas plasma is formed.
- the plasma may be formed by other methods.
- the plasma contains active species such as etching gas ions and radicals. Further, when plasma is generated and etched, the sputtering AC power supply 85 is activated, an AC voltage is applied to the electrode 96, and the ions of the etching gas and auxiliary gas in the plasma are not charged without charging the object to be processed. Ions are drawn into the processing object 10b side. When a portion of the ferroelectric film 13 exposed from the metal mask 15 comes into contact with the plasma, it reacts with the plasma and an etching product of the ferroelectric film 13 is generated. Among the etching products, gaseous substances are removed by evacuation, and those adhering to the object to be processed are sputtered by ions drawn into the electrode 96 and removed from the surface of the object to be processed.
- active species such as etching gas ions and radicals.
- the film thickness of the metal mask 15 is 10 ⁇ m or less, adhesion of the etching product to the side surface of the metal mask 15 is suppressed. Since the metal mask 15 made of a metal thin film has heat resistance, when the object to be processed is cooled by the temperature control unit 88, the temperature of the object to be processed 10b on the stage 86 is controlled to be room temperature or higher and etching is performed. Gasification of the product may be promoted.
- the processing object 10c after the etching process is taken out from the etching apparatus 80, and a stripping solution for selectively peeling the metal mask 15 is brought into contact with the surface of the processing object 10c.
- the metal mask 15 is dissolved in the stripping solution and removed to obtain a processing object 10d after removal of the metal mask as shown in FIG.
- the upper electrode film 14 is arranged on the surface of the processing object 10d facing the ferroelectric film 13, and the piezoelectric element 10e as shown in FIG. 1E is manufactured.
- the upper electrode film 14 may be disposed after the ferroelectric film 13 is formed.
- a PZT film made of PZT is formed on a substrate by a sputtering method or the like, and then a processing object in a state where a Ni mask made of Ni that partially exposes the PZT film is arranged on the PZT film is a vacuum chamber of an etching apparatus. Carried in. The temperature control part was started and it controlled to maintain the temperature of a process target object at 20 degreeC.
- O 2 gas was 8.4 ⁇ 10 ⁇ 3 Pa ⁇ m 3 / sec (5 sccm) and CF 4 gas was 7.6 ⁇ 10 ⁇ 2 Pa ⁇ m 3 /
- the vacuum chamber was supplied at a flow rate of sec (45 sccm), and the vacuum chamber was brought to a pressure of 0.5 Pa.
- CF 4 ratio the ratio of the flow rate of CF 4 gas to the total of the flow rate of O 2 gas and the flow rate of CF 4 gas (hereinafter referred to as CF 4 ratio) is 0.9.
- An AC power of 600 W was applied to the RF antenna 83 from the plasma AC power source to turn the etching gas into plasma and contact with the object to be processed. Further, 400 W AC power was applied to the electrode under the object to be processed from the AC power source for sputtering, so that ions in the plasma were incident on the object to be processed, and the PZT film was partially anisotropically etched. At this time, the etching rates of the PZT film and the Ni mask were measured. Next, the gas supply unit was controlled to change the CF 4 ratio of the etching gas supplied into the vacuum chamber to 0.8, and the etching rates of the PZT film and the Ni mask were measured.
- FIG. 3 shows the relationship between the CF 4 ratio and each etching rate as a measurement result.
- the relationship between the CF 4 ratio and the etching selectivity of the PZT film with respect to the Ni mask is also shown in FIG. It can be seen that when the CF 4 ratio is decreased, each etching rate is decreased, but the etching selectivity of the PZT film to the Ni mask is increased.
- a PZT film made of PZT is formed on a substrate by sputtering or the like, and then a processing object in a state where a Ni mask made of Ni that exposes a part of the PZT film is arranged on the PZT film is scanned with a scanning electron microscope ( SEM).
- SEM scanning electron microscope
- This object to be processed was carried into a vacuum chamber of an etching apparatus, a mixed gas of O 2 gas and CF 4 gas was supplied into the vacuum chamber as an etching gas, and the etching gas was turned into plasma to perform an etching process.
- the processing object was taken out of the vacuum chamber after the etching process and photographed with SEM.
- the taper angle of the etched side surface was 70 °, and no etching product adhered to this side surface.
- Example 1 In the same manner as in Example 2, an object to be processed in a state in which a resist made of an organic substance that partially exposes the PZT film was disposed on the PZT film was photographed with an SEM. This object to be processed is carried into the vacuum chamber of the etching apparatus in the same manner as in Example 2, and a mixed gas of O 2 gas and CF 4 gas is supplied into the vacuum chamber as an etching gas, thereby converting the etching gas into plasma. Then, an etching process was performed. Next, the processing object was taken out of the vacuum chamber after the etching process and photographed with SEM. Etching products adhered to the side surfaces of the resist.
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Abstract
Description
優れた圧電特性を有するチタン酸ジルコン酸鉛(Pb(Zr,Ti)O3、PZT)等の酸化物強誘電体は、圧電素子の機械的応力と電気的変化を橋渡しする材料として、盛んに研究されている。
またPZT等の強誘電体は難エッチング材料と呼ばれ、ハロゲンガスとの反応性に乏しく、またそのハロゲン化物は蒸気圧が低いため、エッチング生成物がパターン側壁に付着しやすい。
エッチング生成物116はレジスト115の剥離工程では除去できず、新たに除去工程を追加する必要があったり、次工程以降の配線を形成する工程において断線もしくは絶縁不良の原因となる等の不都合があった。
本発明は圧電素子の製造方法であって、前記強誘電体膜は、チタン酸バリウム(BaTiO3)と、チタン酸鉛(PbTiO3)と、チタン酸ビスマスランタン((Bi,La)4Ti3O12:BLT)と、チタン酸ジルコン酸鉛(Pb(Zr,Ti)O3:PZT)と、チタン酸ジルコン酸ランタン鉛((PbLa)(ZrTi)O3:PLZT)と、タンタル酸ビスマスストロンチウム(SrBi2Ta2O3:SBT)とからなる群より選択されるいずれか1種類の酸化物強誘電体を含有する圧電素子の製造方法である。
本発明は圧電素子の製造方法であって、前記マスクは、Niと、Alと、Crとからなる群より選択されるいずれか1種類の金属を含有する圧電素子の製造方法である。
本発明は圧電素子の製造方法であって、前記反応ガスは、CF4と、C2F6と、C3F8と、C4F8と、CHF3と、SF6と、C4F6と、C5F8とからなる群より選択されるいずれか1種類のガス、又は2種類以上の混合ガスからなる圧電素子の製造方法である。
本発明は圧電素子の製造方法であって、前記エッチングガスは、酸素ガスの流量と前記反応ガスの流量の合計に対する前記反応ガスの流量の比が50%以上であることを特徴とする圧電素子の製造方法である。
金属マスクの耐熱温度範囲が従来より広くなるので、エッチング時の温度を従来より広い範囲で制御できる。
強誘電体膜の膜厚方向に数十μmのエッチングが可能となるので、従来実施できなかった分野のMEMSへの応用が可能となる。
エッチングガスとして塩素系ガスを使用しないので、塩素系ガスを使用できない環境下で処理できる。
11……基板
12……下部電極膜
13……強誘電体膜
14……上部電極膜
15……金属マスク
96……電極
98……冷却パイプ
まず、本発明の製造方法により形成された圧電素子の構造を説明する。図1(e)は、圧電素子10eの断面図を示している。
圧電素子10eは強誘電体膜13と上部電極膜14と下部電極膜12とを有している。
強誘電体膜13は下部電極膜12上に配置され、上部電極膜14は強誘電体膜13上に配置されている。下部電極膜12下には基板11が配置されている。
上部電極膜14と下部電極膜12は不図示の制御回路と電気的に接続されている。
ただし本発明は強誘電体膜13の材料としてPZTに限定されず、チタン酸バリウム(BaTiO3)、チタン酸鉛(PbTiO3)、チタン酸ビスマスランタン((Bi,La)4Ti3O12:BLT)、チタン酸ジルコン酸ランタン鉛((PbLa)(ZrTi)O3:PLZT)、タンタル酸ビスマスストロンチウム(SrBi2Ta2O3:SBT)等の、化学構造中にフッ素を含有するガスでエッチングできる酸化物強誘電体を用いてもよい。
基板11はここでは熱酸化膜(SiO2)付きのSi基板を用いており、絶縁層である熱酸化膜が下部電極膜12と接触するように配置されている。
図2の符号80は本発明で使用する誘導結合プラズマ(ICP)源を搭載したエッチング装置を示している。
エッチング装置80は真空槽89とプラズマ生成部92とガス供給部81と真空排気部82と温度制御部88を有している。
真空槽89の内部には処理対象物を載置するためのステージ86が設けられている。
温度制御部88はステージ86に接続され、例えばステージ86に設けられた冷却パイプ98に温度制御した熱媒体を流すことにより、ステージ86上に載置される処理対象物の温度を制御できるようにされている。
真空槽89の上方には、開口が形成されており、その開口には、石英等のセラミックス板97が配置されている。セラミックス板97の真空槽89外部側の表面上には、RFアンテナ83が配置されている。このRFアンテナ83は、マッチングボックス87aを介してプラズマ用交流電源84に電気的に接続されており、真空槽89内に供給されたエッチングガスをプラズマ化できるようにされている。
またステージ86の内部には、電極96が配置されており、ステージ86上に処理対象物を配置したときには、電極96は、処理対象物の裏面側に位置するようにされている。
電極96にはマッチングボックス87bを介してスパッタ用交流電源85が電気的に接続されており、プラズマ中のイオンを加速して処理対象物に衝突させてエッチングできるようにされている。
次に、本発明である圧電素子の製造方法を、図1(a)~(e)を参照して説明する。
図1(a)の符号10aは、基板11上に、下部電極膜12と、強誘電体膜13とを、この順にスパッタ法等により成膜した状態の処理対象物を示している。
先ず、金属マスク配置工程として、強誘電体膜13上に、パターニングされたレジスト膜を配置した後、処理対象物を無電解ニッケルめっき液に浸漬し、レジスト膜の表面と、レジスト膜の開口底面に露出する強誘電体膜13の表面とにニッケルを析出させ、ニッケルの金属薄膜を形成した後、レジストを除去すると、レジスト上の金属薄膜はレジストと共に除去され、強誘電体膜13上の金属薄膜は残され、図1(b)の処理対象物10bが得られる。
この処理対象物10bの表面には、パターニングされた金属薄膜(ニッケル薄膜)から成る金属マスク15が設けられている。この金属マスク15は強誘電体膜13に密着しており、金属マスク15により、強誘電体膜13の表面は、一部は露出され、他の部分は覆われている。
なお、強誘電体膜13の表面を全部露出させた状態で処理対象物を無電解ニッケルめっき液に浸漬し、強誘電体膜13の表面にニッケルから成る金属薄膜を形成した後、パターニングしたレジスト膜を形成した金属薄膜表面に形成し、レジスト膜の開口下に露出する金属薄膜をエッチング除去して金属薄膜を所定形状にパターニングしてもよい。レジストを除去するとパターニングされた金属薄膜(ニッケル薄膜)から成る金属マスク15が得られる。
要するに、強誘電体膜13と密着し、パターニングされた厚みの薄い金属薄膜が形成されればよいが、特に無電解めっき法が好ましい。なぜなら、金属マスク15は薄くても、後述するエッチング工程でのエッチングに耐えられるように4μm以上10μm以下の膜厚を有することが好ましく、無電解めっき法は他の方法より容易にこの膜厚を実現できるからである。
本発明の金属マスク15の材料はNi金属に限定されず、強誘電体膜13をエッチングするエッチングガスに対して、強誘電体膜13のエッチング速度よりも遅いエッチング速度を有する材料であって、所望形状にパターニングできるものであればよく、Niの他、Al、Cr、Ti、Ta等の、酸素ガスでエッチングされにくい金属や、それらの合金によって金属マスク15を形成してもよい。
金属マスク配置工程後の処理対象物10bを、不図示の搬入装置から真空槽89内の真空雰囲気を維持しながら、真空槽89内に搬入する。
処理対象物10bは、金属マスク15が形成された面とは逆の面をステージ86に向け、金属マスク15が形成された側の面を露出させてステージ86上に載置する。
真空槽89内を真空排気しながら、ガス供給部81から真空槽89内にエッチングガスを供給する。
エッチングガスはAr等の希ガスから成る補助ガスを含有してもよい。
セラミックス板97と、処理対象物の金属マスク15が形成された面との間には、エッチングガス雰囲気になっており、電波はエッチングガスに照射され、処理対象物の金属マスク15の上にエッチングガスのプラズマが形成される。プラズマは他の方法によって形成してもよい。
プラズマ中には、エッチングガスのイオンやラジカル等の活性種が含まれている。
また、プラズマを生成してエッチングする際には、スパッタ用交流電源85を起動し電極96に交流電圧を印加し、処理対象物を帯電させずに、プラズマ中のエッチングガスのイオンや補助ガスのイオンを処理対象物10b側に引き込むようにしておく。
強誘電体膜13の金属マスク15から露出した部分がプラズマと接触するとプラズマと反応して強誘電体膜13のエッチング生成物が生成される。
エッチング生成物のうち、気体状のものは、真空排気によって除去され、処理対象物に付着するものは、電極96に引き込まれたイオンによってスパッタリングされ、処理対象物の表面から除去される。
金属薄膜からなる金属マスク15は耐熱性を有するため、温度制御部88により処理対象物を冷却する際に、ステージ86上の処理対象物10bの温度を室温以上になるように制御して、エッチング生成物のガス化を促進させてもよい。
ここでは、ステージ86を囲むようにシールド91が設けられており、エッチングで生じる付着物の真空槽89の内壁への付着が防止されている。
次いで、処理対象物10dの強誘電体膜13の上を向いた面に上部電極膜14を配置し、図1(e)に示すような圧電素子10eが製造される。
上部電極膜14は強誘電体膜13を成膜後に配置することも可能である。
基板上にPZTからなるPZT膜をスパッタ法等により成膜し、次いで、PZT膜上に、PZT膜を一部露出させるNiからなるNiマスクを配置した状態の処理対象物をエッチング装置の真空槽内に搬入した。温度制御部を起動し、処理対象物の温度を20℃を維持するように制御した。
真空槽内を真空排気しながら、エッチングガスとして、O2ガスを8.4×10-3Pa・m3/sec(5sccm)、CF4ガスを7.6×10-2Pa・m3/sec(45sccm)の流量で真空槽内に供給し、真空槽内を0.5Paの圧力にした。このとき、O2ガスの流量とCF4ガスの流量の合計に対するCF4ガスの流量の比(以下、CF4比と呼ぶ)は0.9である。
次いで、ガス供給部を制御して、真空槽内に供給するエッチングガスのCF4比を0.8へ変化させ、PZT膜とNiマスクの各エッチング速度を測定した。
CF4比を減少させると、各エッチング速度がそれぞれ減少するが、Niマスクに対するPZT膜のエッチング選択比は増加したことがわかる。
基板上にPZTからなるPZT膜をスパッタ法等により成膜し、次いでPZT膜上に、PZT膜を一部露出させるNiからなるNiマスクを配置した状態の処理対象物を、走査型電子顕微鏡(SEM)で撮影した。
この処理対象物をエッチング装置の真空槽内に搬入し、エッチングガスとしてO2ガスとCF4ガスとの混合ガスを真空槽内に供給し、エッチングガスをプラズマ化して、エッチング処理を行った。
次に、処理対象物をエッチング処理後に真空槽から取り出して、SEMで撮影した。
エッチングされた側面のテーパー角度は70°に形成され、この側面にエッチング生成物は付着しなかった。
実施例2と同様にしてPZT膜上に、PZT膜を一部露出させる有機物から成るレジストを配置した状態の処理対象物をSEMで撮影した。
この処理対象物を実施例2と同様にして、エッチング装置の真空槽内に搬入し、エッチングガスとしてO2ガスとCF4ガスとの混合ガスを真空槽内に供給し、エッチングガスをプラズマ化して、エッチング処理を行った。
次に、処理対象物をエッチング処理後に真空槽から取り出して、SEMで撮影した。
レジストの側面にエッチング生成物が付着していた。
Claims (5)
- 基板と、
導電性材料からなる下部電極膜と、
酸化物強誘電体からなる強誘電体膜と、
導電性材料からなる上部電極膜と、を有し、
前記下部電極膜と、前記強誘電体膜と、前記上部電極膜はこの順に前記基板上に配置され、
前記上部電極膜と前記下部電極膜との間に電圧を印加すると前記強誘電体膜の形状が変形し、電圧の印加を停止すると変形が復元する圧電素子の製造方法であって、
前記基板上に、前記上部電極膜と、前記強誘電体膜とがこの順に積層された処理対象物の表面の前記強誘電体膜上にパターニングされた金属薄膜から成る金属マスクを形成し、前記強誘電体膜の表面を部分的に露出させ、他の部分を覆う金属マスク配置工程と、
前記処理対象物の裏面側に配置された電極に交流電圧を印加しながら、酸素ガスと、化学構造中にフッ素を含む反応ガスとの混合ガスを含有するエッチングガスのプラズマを前記成膜対象物の表面側に形成し、
前記金属マスクと前記強誘電体膜とに、前記プラズマを接触させると共に前記プラズマ中のイオンを入射させて、前記金属マスクの開口底面に露出する前記強誘電体膜を除去し、前記下部電極膜を露出させるエッチング工程と、
を有する圧電素子の製造方法。 - 前記強誘電体膜は、チタン酸バリウム(BaTiO3)と、チタン酸鉛(PbTiO3)と、チタン酸ビスマスランタン((Bi,La)4Ti3O12:BLT)と、チタン酸ジルコン酸鉛(Pb(Zr,Ti)O3:PZT)と、チタン酸ジルコン酸ランタン鉛((PbLa)(ZrTi)O3:PLZT)と、タンタル酸ビスマスストロンチウム(SrBi2Ta2O3:SBT)とからなる群より選択されるいずれか1種類の酸化物強誘電体を含有する請求項1記載の圧電素子の製造方法。
- 前記金属マスクは、Niと、Alと、Crとからなる群より選択されるいずれか1種類の金属を含有する請求項1又は請求項2のいずれか1項記載の圧電素子の製造方法。
- 前記反応ガスは、CF4と、C2F6と、C3F8と、C4F8と、CHF3と、SF6と、C4F6と、C5F8とからなる群より選択されるいずれか1種類のガス、又は2種類以上の混合ガスからなる請求項1乃至請求項3のいずれか1項記載の圧電素子の製造方法。
- 前記エッチングガスは、酸素ガスの流量と前記反応ガスの流量の合計に対する前記反応ガスの流量の比が50%以上であることを特徴とする請求項1乃至請求項4のいずれか1項記載の圧電素子の製造方法。
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