JP2011029526A - Method of manufacturing composite substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a composite substrate, capable of preventing hindrance derived from dielectric breakdown due to a polarization treatment of a piezoelectric substrate and suppressing an increase of the number of steps associated with the polarization treatment. <P>SOLUTION: In the method, a piezoelectric thin film 4 is laminated on a support substrate on which a conductive sacrificing layer is formed, and a meander electrode 20 turning to an open state due to over-current is formed to a wiring to form an upper surface polarizing electrode 14 on the piezoelectric thin film 4. Then, a polarizing electric field is applied between the upper surface polarizing electrode 14 and the conductive sacrificing layer, and subsequently the upper surface polarizing electrode 14, the meander electrode 20, and the conductive sacrificing layer are removed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a composite substrate having a membrane structure (hollow structure) and in which a piezoelectric substrate and a support substrate are laminated, and more particularly to a method for manufacturing a composite substrate in which a piezoelectric substrate is subjected to polarization treatment.

A piezoelectric device may be manufactured as a composite substrate having a membrane structure including a piezoelectric substrate made of quartz, LiTaO ₃ , LiNbO _{3, and the} like, and providing a space between the piezoelectric substrate and a support substrate. In the composite substrate having a membrane structure, a sacrificial layer is disposed between the support substrate and the piezoelectric substrate, the support substrate and the piezoelectric substrate are joined, and the sacrificial layer is removed to form a space portion.

  The piezoelectric substrate may be configured by depositing a piezoelectric body by a deposition method such as sputtering or CVD. (For example, refer nonpatent literature 1.). In the deposition method, not only the orientation direction of the crystal axis of the piezoelectric body is limited, but also the material is limited to AlN or ZnO. Since the orientation direction of the crystal axis and the material affect the electromechanical coupling coefficient, frequency temperature characteristics, sound speed, etc. of the piezoelectric device, the use of the deposition method suppresses the degree of freedom in designing the piezoelectric device.

  In order to arbitrarily set the crystal axis orientation direction and the material in the piezoelectric substrate, the piezoelectric substrate may be formed by cutting or polishing the piezoelectric block. However, in that case, the polarization direction of the piezoelectric substrate may be partially reversed by processing. The polarization direction can be controlled by applying an electric field to the piezoelectric substrate, and polarization processing may be performed to align the polarization direction in the piezoelectric substrate (see, for example, Patent Documents 2 and 3).

Y. Osugi et al .; "Single crystal FBAR with LiNbO3 and LiTaO3", 2007 IEEE MTT-S International Microwave Symposium, pp.873-876

Japanese Patent Laid-Open No. 5-90859 Japanese Patent Laid-Open No. 10-32454

  In order to perform the polarization treatment, it is necessary to provide polarization electrode pairs for applying an electric field on the upper and lower surfaces of the piezoelectric substrate, remove the polarization electrode pairs after the polarization treatment, and then form functional electrodes of the piezoelectric device. Therefore, the number of manufacturing steps increases with the polarization process.

In addition, for example, a piezoelectric substrate made of LiTaO ₃ or LiNbO ₃ has a high coercive electric field, and application of a high electric field of 22 kV / mm or more is necessary for the polarization treatment. In addition, when a polarization treatment is applied to a piezoelectric substrate laminated on a support substrate, it is also necessary to apply a high electric field. When applying a high electric field to a piezoelectric substrate, defects such as cracks exist in the piezoelectric substrate, causing dielectric breakdown, and the polarization electrode pair melts and short-circuits due to discharge, overcurrent flows and a voltage source failure occurs. There was sometimes.

  An object of the present invention is to provide a method of manufacturing a composite substrate that can prevent the occurrence of a failure due to dielectric breakdown during the polarization processing of a piezoelectric substrate and can suppress the number of manufacturing steps that increase accompanying the polarization processing.

The method of manufacturing a composite substrate according to the present invention includes a step of forming a conductive sacrificial layer on a support substrate, a step of providing a piezoelectric substrate overlying the conductive sacrificial layer and the support substrate, and wiring a passive element that is opened by overcurrent. Forming a top polarization electrode on the piezoelectric substrate, applying a polarization electric field between the top polarization electrode and the conductive sacrificial layer, removing the top polarization electrode and the passive element from the piezoelectric substrate, The method includes a step of forming a top-surface functional electrode that causes the piezoelectric substrate to function as a piezoelectric device, and a step of removing the conductive sacrificial layer.
In this manufacturing method, the polarization direction in the piezoelectric substrate can be aligned by applying a polarization electric field between the upper surface polarization electrode and the conductive sacrificial layer. When applying a polarization electric field to a piezoelectric substrate, even if dielectric breakdown occurs and an overcurrent occurs, the passive element provided in the wiring of the upper surface polarization electrode is opened, so that the failure caused by the overcurrent is prevented. Can do. Furthermore, since the conductive sacrificial layer serving as the space portion of the membrane structure is used as one of the polarization electrode pairs, the polarization electrode is separately formed on the lower surface of the piezoelectric substrate, or the polarization electrode on the lower surface of the piezoelectric substrate is removed. Therefore, polarization treatment can be performed and increase in the number of manufacturing steps can be suppressed. By removing the upper surface polarization electrode and the passive element after polarization, the characteristics of the finished piezoelectric device can be set without being affected by the upper surface polarization electrode and the passive element.

  The step of providing the piezoelectric substrate overlying the conductive sacrificial layer and the support substrate of the present invention includes the step of ion implantation into the block-shaped piezoelectric substrate, and the ion-implanted surface of the block-shaped piezoelectric substrate with the conductive sacrificial layer and the support substrate. And a step of peeling the thin film of the piezoelectric substrate by heating with a certain depth from the ion implantation surface of the block-shaped piezoelectric substrate as a peeling surface.

  With this manufacturing method, the thin film of the piezoelectric substrate can be formed without performing polishing or the like, and the amount of expensive piezoelectric material used can be suppressed by reusing the block-shaped piezoelectric substrate. Further, the flatness of the thin film of the piezoelectric substrate can be increased by ion implantation. In addition, although the polarization in the piezoelectric substrate may be reversed by performing ion implantation, the thin film of the piezoelectric substrate can be improved in quality by aligning the polarization direction by performing the polarization process.

The passive element of the present invention is preferably a meander-shaped electrode line.
The meander-shaped electrode line has a long line length per unit area, and when an overcurrent flows, the resistance dramatically increases due to thermal diffusion. Therefore, the electrode line is easily blown, and the response to overcurrent is increased. Moreover, by forming a passive element as an electrode line, the top surface polarization electrode and the passive element can be formed at a time, and the number of manufacturing steps can be reduced.

  The support substrate and the piezoelectric substrate of the present invention are divided into a plurality of parts, and the conductive sacrificial layer, the upper surface polarization electrode, the passive element, and the upper surface functional electrode are provided in each of a plurality of divided regions. The passive elements corresponding to each region are preferably connected in parallel to the voltage source.

  When a single substrate is divided to form a plurality of piezoelectric devices, if dielectric breakdown occurs even at one location, it may be impossible to apply a polarization electric field across the entire substrate. In that case, even if other piezoelectric devices are not directly broken down, all piezoelectric devices in the same lot are manufactured without undergoing polarization treatment, and the yield rate is reduced. In order to solve this problem, it is preferable to connect a plurality of passive elements in parallel to the voltage source. If multiple passive elements are connected in parallel to the voltage source, only the polarized electrode pair where dielectric breakdown has occurred is opened by overcurrent and separated from the voltage source, and the other polarized electrode pairs continue to be polarized. An electric field can be applied. Therefore, even when dielectric breakdown occurs, polarization processing can be performed on other piezoelectric devices in the same lot, and the yield rate can be improved.

  According to the present invention, partial inversion of the polarization direction in the piezoelectric substrate can be recovered. In addition, by providing a passive element that is opened by an overcurrent in the wiring of the upper surface polarization electrode, it is possible to prevent a failure that occurs due to a dielectric breakdown during the polarization process. Furthermore, since a conductive sacrificial layer for realizing the membrane structure is used for one of the polarization electrode pairs, polarization can be performed without forming a polarization electrode on the lower surface of the piezoelectric substrate or removing the polarization electrode on the lower surface. Processing can be performed and an increase in the number of steps can be suppressed. Since the upper surface polarization electrode and the passive element are removed after polarization, the characteristics of the finished piezoelectric device can be set without being affected by the upper surface polarization electrode and the passive element.

It is a figure which shows the board | substrate state in each process in the manufacturing process flow of the manufacturing method of the composite substrate which concerns on embodiment of this invention. It is a figure which shows the board | substrate state in each process in the manufacturing process flow of the manufacturing method of the composite substrate which concerns on embodiment of this invention. It is a top view of the composite substrate which provided the upper surface polarization electrode. It is a top view of the support substrate which provided the electroconductive sacrificial layer.

  Hereinafter, the present invention will be described by taking as an example a method of manufacturing an FBAR (Film Bulk Acoustic Resonator) device as a piezoelectric device having a membrane structure according to an embodiment of the present invention.

  FIG. 1 is a diagram showing a substrate state in each process in the manufacturing process flow according to the present embodiment. In the present embodiment, a plurality of FBAR devices are manufactured from a single substrate at a time, but only a portion constituting one FBAR device on the substrate is shown in the drawing.

First, a piezoelectric substrate 1 having a flat principal surface subjected to mirror polishing is prepared, and an ion implantation step is performed in which hydrogen ions are implanted from the principal surface (S1). As the piezoelectric substrate 1, a 42 ° Y-cut LiTaO ₃ substrate is used, the hydrogen ion implantation energy is 150 KeV, and the dose (ion implantation density) is 9 × 10 ¹⁶ atoms / cm ² . As a result, a release layer 1C is formed in which the microcavities are concentrated within a certain distance from the surface of the piezoelectric substrate 1, here, at a formation depth of about 1.0 μm. Each surface of the piezoelectric substrate 1 is charged with a positive or negative polarity. Here, hydrogen ions, which are positive ions, are implanted into the negative main surface of the piezoelectric substrate 1. Although a part of the polarization of the piezoelectric substrate 1 is reversed by the ion implantation, the occurrence of polarization reversal is suppressed by implanting ions having a polarity opposite to that of the main surface. As the piezoelectric substrate 1, in addition to the LiTaO ₃ substrate, a LiNbO ₃ substrate, a Li ₂ B ₄ O ₇ substrate, a La ₃ Ga ₅ SiO ₁₄ substrate, or the like may be used.

  Next, the electrode 11 which becomes the lower surface functional electrode of the piezoelectric device is formed on the main surface of the piezoelectric substrate 1 into which hydrogen ions are implanted (S2).

  Next, a thin insulating film 12 serving as an adhesion layer with the support substrate 2 is formed on the surface of the piezoelectric substrate 1 on which the electrode 11 is formed (S3). The main surface of the insulating film 12 is preferably smoothed by CMP. As the insulating film 12, it is preferable to select a material that can suppress the diffusion of material particles between the conductive sacrificial layer 13 and the piezoelectric substrate 1, such as SiN.

Also, a support substrate 2 having a SiO ₂ film formed on Si, glass, a piezoelectric substrate, etc. is prepared (S4). In place of the SiO ₂ film, an insulating film such as SiN, PSG (phosphosilicate glass), or ZnO may be employed.

Next, the space 2A is formed on the support substrate 2 (S5). The space 2A is formed by resist patterning on the SiO ₂ film, RIE (reactive dry etching), and resist removal.

  Next, the conductive sacrificial layer 13 is formed inside the space 2A, and the surface of the conductive sacrificial layer 13 and the surface of the support substrate 2 are planarized by CMP (S6). As the conductive sacrificial layer, it is preferable to use a material resistant to electron migration using a metal such as Cu, Al, or Ni, or a conductor such as a conductive paste. As a method for forming the conductive sacrificial layer 13, sputtering film formation, EB vapor deposition, CVD, printing, or the like may be employed. An insulating film (not shown) is further formed as an adhesion layer on the surfaces of the conductive sacrificial layer 13 and the support substrate 2. As this insulating film, it is preferable to select a material capable of suppressing the diffusion of material particles between the conductive sacrificial layer 13 and the piezoelectric substrate 1 in the same manner as the insulating film 12 described above.

  Next, the piezoelectric substrate 1 and the support substrate 2 are cleaned and bonded through the adhesion layer to form the composite substrate 5 (S7). By using the clean bonding, the bonding process at room temperature is possible.

  Next, the composite substrate 5 is placed in a 500 ° C. heating environment (S8). As a result, a microcavity is generated and grows in the release layer 1 </ b> C of the piezoelectric substrate 1, and the piezoelectric thin film 4 having a thickness of about 1 μm peels from the piezoelectric substrate 1.

  Next, the peeling surfaces of the piezoelectric substrate 1 from which the piezoelectric thin film 4 has been peeled off and the composite substrate 5 on which the piezoelectric thin film 4 remains are smoothed by CMP (s9). The piezoelectric substrate 1 from which the piezoelectric thin film 4 has peeled off is subjected to ion implantation again in order to be used for manufacturing the piezoelectric device of the next lot.

  FIG. 2 is a diagram showing a substrate state in each process in the manufacturing process flow according to the present embodiment.

  Next, in the composite substrate 5 having a flattened peel surface, the upper surface polarization electrode 14 is formed on the surface of the piezoelectric thin film 4, the upper surface polarization electrode 14 and the conductive sacrificial layer 13 are connected to a voltage source, and the upper surface polarization electrode is formed. A polarization electric field is applied between 14 and the conductive sacrificial layer 13 (S10). As a result, the polarization partially reversed at the time of ion implantation is recovered, and the polarization direction in the piezoelectric thin film 4 is made uniform.

  After the polarization treatment of the piezoelectric thin film 4, the upper surface polarization electrode 14 is removed (S11).

  Next, the upper surface functional electrode 15 for exciting the FBAR device together with the lower surface functional electrode, the electrode routing wiring (not shown), and the bump pad 16 are formed on the surface of the piezoelectric thin film 4, and the insulating film 17 is formed on the entire surface ( S12).

  Next, an opening window 18 for introducing an etchant for removing the conductive sacrificial layer 13 is formed by opening the piezoelectric thin film 4 (S13). In this step, the insulating film 17 may be patterned using a photolithography technique, and the piezoelectric thin film 4 may be etched by the RIE method.

  Next, an etching solution or etching gas is introduced into the space 2A from the opening window 18 to remove the conductive sacrificial layer 13 (S14).

  Next, the insulating film 17 used for processing the piezoelectric thin film 4 is peeled off, and cleaning and drying processes are performed, and bumps 19 for connecting the FBAR device to an external circuit are formed on the bump pads 16 (S15).

  In this embodiment, an FBAR device is manufactured by the above steps. Since the piezoelectric thin film 4 is formed by peeling from the piezoelectric substrate 1, the degree of freedom in designing the piezoelectric material, crystal orientation, etc. is higher than before, and the block-shaped piezoelectric substrate 1 can be reused and an expensive piezoelectric material is used. The amount can be suppressed. Moreover, since ion implantation is used, the flatness of the piezoelectric thin film 4 is high, and the degree of freedom in designing the thickness is also high. This makes it possible to precisely set the electromechanical coupling coefficient, frequency temperature characteristics, and sound speed in the piezoelectric thin film 4, and improve characteristics such as frequency characteristics, bandwidth, and insertion loss in the FBAR device. By performing ion implantation, the polarization in the piezoelectric substrate 1 may be reversed, but by performing the polarization step, the polarization direction is aligned, and the piezoelectric thin film 4 can be made high quality.

  FIG. 3A is a plan view of the piezoelectric thin film 4 provided with the upper surface polarization electrode 14 used for the polarization process. The plurality of upper surface polarization electrodes 14 are arranged in a matrix and are connected to the voltage application line 21 in parallel via the meander electrodes 20 and connected to the voltage source via the voltage application line 21. FIG. 3B is an enlarged plan view of the meander electrode 20. The meander electrode 20 is a line electrode folded back in a meander shape, and corresponds to a passive element of the present invention.

  FIG. 4 is a plan view of the support substrate 2 provided with the conductive sacrificial layer 13 used for the polarization step. The plurality of conductive sacrificial layers 13 are arranged in a matrix, and are electrically connected to the other conductive sacrificial layers 13 adjacent to each other in the vertical and horizontal directions through the connection line 22 and connected to the voltage source through the voltage application line 21. is doing.

  The upper surface polarization electrode 14 and the conductive sacrificial layer 13 are opposed to each other in a shape that coincides with each other in plan view, and are polarized on the piezoelectric thin film 4 by a voltage applied from a voltage source via the voltage application line 21. Give an electric field. This polarization electric field restores the partially reversed polarization direction in the piezoelectric thin film 4.

When a LiTaO ₃ substrate or a LiNbO ₃ substrate having a high coercive electric field is used as a piezoelectric substrate, a high electric field of 22 kV / mm or more is required for polarization treatment at room temperature, and there are fine cracks in the piezoelectric thin film 4. A discharge may occur between the upper surface polarization electrode 14 and the conductive sacrificial layer 13 due to dielectric breakdown. When discharge occurs in this way, the top-polarized electrode 14 and the conductive sacrificial layer 13 may melt and short-circuit with each other, resulting in dielectric breakdown.

  In the conventional configuration, when dielectric breakdown occurs even at one location, it becomes impossible to apply a polarization electric field to the entire substrate thereafter, and all piezoelectric devices of the same lot will be manufactured without completing the polarization process, The yield rate will decrease.

  On the other hand, in this configuration, since the meander electrode 20 is individually inserted between each upper surface polarization electrode 14 and the voltage source, an excess occurs at a short portion of the specific upper surface polarization electrode 14 due to dielectric breakdown of the piezoelectric thin film 4. When a current flows, the meander electrode 20 connected to the upper surface polarization electrode 14 is thermally diffused to increase the resistance. As a result, the meander electrode 20 is blown, the voltage application line 21 is opened, and the upper surface polarization electrode 14 at the short portion is separated from the voltage application line 21. Therefore, it is possible to prevent the influence of the overcurrent from reaching other upper surface polarization electrodes 14, meander electrodes 20, voltage sources, and the like.

  As the meander electrode, it is preferable to select a material such as Cu or Ti that is easily thermally diffused, because the resistance of the meander electrode can be increased by the thermal diffusion. Since the meander electrode can increase the line length per unit area, it is effective in increasing the resistance.

  Although the present invention can be implemented as shown in the above embodiments, the present invention can be suitably implemented even with plate wave devices, gyros, RF switches, pyroelectric devices, etc. in addition to FBAR devices.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 1C ... Release layer 2 ... Supporting substrate 2A ... Space part 4 ... Piezoelectric thin film 5 ... Composite substrate 13 ... Conductive sacrificial layer 14 ... Upper surface polarization electrode 15 ... Upper surface functional electrode 18 ... Opening window 20 ... Meander electrode 21 ... Voltage application line

Claims (4)

Forming a conductive sacrificial layer on the support substrate;
Providing a piezoelectric substrate overlying the conductive sacrificial layer and the support substrate;
Providing a passive element that is opened by an overcurrent in the wiring to form a top surface polarization electrode on the piezoelectric substrate;
Applying a polarization electric field between the upper surface polarization electrode and the conductive sacrificial layer;
Removing the top polarized electrode and the passive element from the piezoelectric substrate;
Forming a top functional electrode that causes the piezoelectric substrate to function as a piezoelectric device;
A step of removing the conductive sacrificial layer. The step of providing a piezoelectric substrate overlying the conductive sacrificial layer and the support substrate includes:
Ion implantation into a block-shaped piezoelectric substrate;
Bonding the ion-implanted surface of the block-shaped piezoelectric substrate to the conductive sacrificial layer and the support substrate;
2. The method of manufacturing a composite substrate according to claim 1, further comprising a step of peeling the thin film of the piezoelectric substrate by heating with a predetermined depth from the ion implantation surface of the block-shaped piezoelectric substrate as a peeling surface.   The method for manufacturing a composite substrate according to claim 1, wherein the passive element is a meander-shaped electrode line. The support substrate and the piezoelectric substrate are divided into a plurality of parts,
The conductive sacrificial layer, the upper surface polarization electrode, the passive element, and the upper surface functional electrode are provided in each of a plurality of divided regions,
The said passive element corresponding to each area | region is a manufacturing method of the composite substrate in any one of Claims 1-3 connected in parallel with respect to a voltage source.

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