阅读说明：本技术 接合晶圆及其制造方法、弹性波器件的制造方法、压电材料晶圆及非压电材料晶圆 (Bonded wafer and method for manufacturing same, method for manufacturing elastic wave device, piezoelectric material wafer, and non-piezoelectric material wafer ) 是由 本山惠一郎 高桥敦哉 川内治 于 2021-03-24 设计创作，主要内容包括：本发明提供一种在由压电材料晶圆及非压电材料晶圆所接合而成的接合晶圆中,研磨后的晶圆全面的压电基板的厚度均一的接合晶圆及其制造方法、弹性波器件的制造方法、接合晶圆中使用的压电材料晶圆与非压电材料晶圆。接合晶圆由压电材料晶圆及非压电材料晶圆所接合而成。非压电材料晶圆之厚度比压电材料晶圆更厚,且非压电材料晶圆具有平边,而压电材料晶圆的外周没有平边。(The invention provides a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, wherein the whole wafer after polishing has a uniform piezoelectric substrate thickness, a manufacturing method thereof, a manufacturing method of an elastic wave device, and a piezoelectric material wafer and a non-piezoelectric material wafer used in the bonded wafer. The bonded wafer is formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer. The thickness of the non-piezoelectric material wafer is thicker than the thickness of the piezoelectric material wafer, and the non-piezoelectric material wafer has a flat edge, while the periphery of the piezoelectric material wafer has no flat edge.)

1. A bonded wafer is formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, and is characterized in that: the bonded wafers have a thickness of a non-piezoelectric material wafer that is thicker than the piezoelectric material wafer, and the non-piezoelectric material wafer has a flat edge, and the periphery of the piezoelectric material wafer has no flat edge.

2. The bonded wafer of claim 1, wherein: the area of the piezoelectric material wafer is narrower than that of the non-piezoelectric material wafer, and the periphery of the non-piezoelectric material wafer is located outside the periphery of the piezoelectric material wafer.

3. The bonded wafer of claim 1, wherein: the piezoelectric material wafer uses lithium tantalate or lithium niobate.

4. A method for manufacturing a bonded wafer obtained by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, comprising: the manufacturing method of the bonded wafer comprises the following steps: a step of manufacturing a non-piezoelectric material wafer having a flat edge on the outer periphery thereof; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and a flat edge on the outer periphery thereof; bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the flat sides provided on the wafers are aligned and arc-shaped circles on the outer peripheries of the two wafers are concentric; and polishing the arc-shaped outer periphery of the bonded piezoelectric material wafer along the arc-shaped polishing surface until the wafer is flat.

5. The method of manufacturing a bonded wafer according to claim 4, wherein: the bonded wafer is bonded to the piezoelectric material wafer and the non-piezoelectric material wafer by using a normal temperature bonding technique.

6. A method for manufacturing a bonded wafer obtained by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, comprising: the manufacturing method of the bonded wafer comprises the following steps: a step of manufacturing a non-piezoelectric material wafer having a flat edge on the outer periphery thereof; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having a mark on a surface opposite to a bonding surface with the non-piezoelectric material wafer instead of a flat edge; bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state that the relative direction of the two wafers is a preset direction and arc circles on the outer peripheries of the two wafers are concentric; and polishing the outer periphery of the bonded piezoelectric material wafer in an arc shape.

7. A method for manufacturing a bonded wafer obtained by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, comprising: the manufacturing method of the bonded wafer comprises the following steps: a step of manufacturing a non-piezoelectric material wafer having a mark on a surface of an outer periphery thereof opposite to a bonding surface of the piezoelectric material wafer instead of a flat edge; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having a mark on a surface opposite to a bonding surface with the non-piezoelectric material wafer instead of a flat edge; bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state that the relative direction of the two wafers is a preset direction and arc circles on the outer peripheries of the two wafers are concentric; and polishing the outer periphery of the bonded piezoelectric material wafer in an arc shape.

8. A method for manufacturing a bonded wafer obtained by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, comprising: the manufacturing method of the bonded wafer comprises the following steps: a step of manufacturing a non-piezoelectric material wafer having a flat edge on the outer periphery thereof; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having double recesses instead of flat edges; a step of bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the two wafers are concentric with each other, the relative direction of the two wafers being a predetermined direction; and polishing the arc-shaped outer periphery of the bonded piezoelectric material wafer until the double concave marks disappear.

9. A method for manufacturing a bonded wafer obtained by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, comprising: the manufacturing method of the bonded wafer comprises the following steps: a step of manufacturing a non-piezoelectric material wafer having a mark on a surface of an outer periphery thereof opposite to a bonding surface of the piezoelectric material wafer instead of a flat edge; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having double recesses instead of flat edges; a step of bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the two wafers are concentric with each other, the relative direction of the two wafers being a predetermined direction; and polishing the arc-shaped outer periphery of the bonded piezoelectric material wafer until the double concave marks disappear.

10. A method for manufacturing an elastic wave device, wherein a bonded wafer manufactured by the method for manufacturing a bonded wafer according to any one of claims 4 to 9 is characterized in that: the method for manufacturing an elastic wave device includes a step of forming electrodes used for a plurality of elastic wave devices on the piezoelectric material wafer of the bonded wafer; dividing the bonded wafer on which the electrodes used for the plurality of elastic wave devices are formed into individual bare chips for the elastic wave devices; mounting the bare chip on a wafer for mounting a substrate; and a step of dividing the wafer for mounting substrate on which the bare chips are mounted into individual elastic wave devices.

11. A piezoelectric material wafer used for manufacturing a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, the piezoelectric material wafer comprising: marks are provided on the surface opposite to the surface to be bonded to the non-piezoelectric material wafer, instead of the flat edge.

12. A piezoelectric material wafer used for manufacturing a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, the piezoelectric material wafer comprising: on the surface opposite to the bonding surface of the non-piezoelectric material wafer, a double concave mark is provided instead of the flat edge.

13. A non-piezoelectric material wafer used for manufacturing a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, the non-piezoelectric material wafer comprising: marks are provided on the surface opposite to the bonding surface with the piezoelectric material wafer instead of the flat edge.

Technical Field

The present invention relates to a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, a method for manufacturing the same, a method for manufacturing an elastic wave device, and a piezoelectric material wafer and a non-piezoelectric material wafer used for the bonded wafer.

Background

An elastic wave device such as a surface acoustic wave device is configured such that comb-shaped electrodes, land electrodes, or the like are formed on a piezoelectric substrate, and a gap portion is formed between the piezoelectric substrate and a mounting substrate. In order to improve the characteristics of a piezoelectric substrate in the production of an elastic wave device, a non-piezoelectric substrate having a lower thermal expansion coefficient than the piezoelectric substrate is bonded to the piezoelectric substrate in a wafer state. And forming an excitation electrode such as a comb electrode or a pad electrode in a wafer state after bonding. One of the purposes of bonding a non-piezoelectric substrate to a piezoelectric substrate is to prevent the characteristics from changing with temperature change. In other words, if the piezoelectric substrate is deformed with temperature when the elastic wave device is configured as a filter, the pitch of the comb electrodes changes, and the frequency of filtering also changes. Therefore, in order to suppress such frequency change, a non-piezoelectric substrate having a lower thermal expansion coefficient than that of the piezoelectric substrate is bonded to the piezoelectric substrate. Thus, deformation of the piezoelectric substrate due to temperature change can be suppressed, and the frequency of filtering can be prevented from changing.

In the elastic wave device, when LT (lithium tantalate) or LN (lithium niobate) is used as the piezoelectric substrate, since the propagation characteristics of the elastic surface wave change with the crystal direction, at least the crystal direction of the piezoelectric substrate is considered when bonding the piezoelectric substrate to the non-piezoelectric substrate. Further, when the non-piezoelectric substrate is a single crystal, the crystal orientation of the non-piezoelectric substrate may be considered. Therefore, an Orientation Flat (OF) is provided on a part OF the outer periphery OF the circular wafer to indicate the position and direction OF the wafer (see, for example, patent document 1: japanese patent application laid-open No. 2010-187373).

Fig. 22 shows a bonded wafer 70 in the conventional technique shown in patent document 1. The conventional bonded wafer 70 is bonded to a non-piezoelectric material wafer 71 and a piezoelectric material wafer 72 with an adhesive 73. Flat sides 71a and 72a are provided on the outer peripheries of the non-piezoelectric material wafer 71 and the piezoelectric material wafer 72, respectively. In manufacturing such a bonded wafer 70, first, a non-piezoelectric material wafer 71 and a piezoelectric material wafer 72 each having flat sides 71a and 72a are manufactured. In the joining, the flat edge 71a and the flat edge 72a are joined in a state where their positions and directions coincide with each other. Thereafter, the surface of the piezoelectric material wafer 72 is mechanically polished by a polishing apparatus to thin the piezoelectric material wafer 72. Next, a CMP process (chemical mechanical polishing) is performed to make the piezoelectric material wafer 72 thinner and smooth the surface 72b of the piezoelectric material wafer 72 serving as the electrode formation surface.

In the conventional bonded wafer 70, it is found that after the step of thinning the piezoelectric material wafer 72 by polishing, the thickness of the piezoelectric material wafer 72 in the vicinity of the flat edge 72a is thinner than that in other regions. This results in non-uniform thickness of the piezoelectric material wafer 72. If the thickness of the piezoelectric material wafer 72 is not uniform in this manner, the frequency characteristics of the elastic wave devices will be different when the bonded wafer is divided into a plurality of elastic wave devices.

Disclosure of Invention

The present invention has been made in view of the above problems, and an object thereof is to provide a bonded wafer having a uniform thickness over the entire piezoelectric material wafer, a method for manufacturing the same, a method for manufacturing an elastic wave device, and a piezoelectric material wafer and a non-piezoelectric material wafer used for the bonded wafer.

One aspect of the bonded wafer according to the present invention is a bonded wafer in which a piezoelectric material wafer and a non-piezoelectric material wafer are bonded, the non-piezoelectric material wafer of the bonded wafer has a thickness thicker than that of the piezoelectric material wafer, the non-piezoelectric material wafer has a flat edge, and an outer periphery of the piezoelectric material wafer does not have a flat edge.

The bonded wafer of the present invention has no flat edge on the outer peripheral side of the piezoelectric material wafer. Therefore, when the surface of the piezoelectric material wafer is polished, the polishing depth in the vicinity of the flat edge does not increase due to the presence of the flat edge in the piezoelectric material wafer. As a result, the thickness of the entire area of the piezoelectric material wafer is made uniform. Therefore, when electrodes used for a plurality of elastic wave devices are formed on a piezoelectric material wafer constituting a bonded wafer, and the elastic wave devices are manufactured using an article obtained by dividing the bonded wafer, the frequency characteristics thereof are uniform.

In a specific aspect of the bonded wafer according to the present invention, in the above aspect, the area of the piezoelectric material wafer is made smaller than that of the non-piezoelectric material wafer, and the outer periphery of the non-piezoelectric material wafer is positioned outside the outer periphery of the piezoelectric material wafer.

In this way, the outer periphery of the non-piezoelectric material wafer is located outside the outer periphery of the piezoelectric material wafer, so that the piezoelectric material wafer can be supported by the non-piezoelectric material wafer more comprehensively and stably when the surface of the piezoelectric material wafer is ground. Therefore, the problem of deviation of the polishing amount in the piezoelectric material wafer can be solved, and the overall thickness uniformity of the piezoelectric material wafer can be achieved.

In a specific aspect of the bonded wafer according to the present invention, lithium tantalate or lithium niobate is used for the piezoelectric material wafer.

Thus, when lithium tantalate or lithium niobate, which is important in the characteristics of the device, is used as the piezoelectric substrate whose thickness is required to be thin, the entire thickness of the piezoelectric material wafer can be made uniform, and the present invention exerts an important effect in unifying the frequency characteristics.

A first aspect of a method for manufacturing a bonded wafer according to the present invention is a method for manufacturing a bonded wafer bonded using a piezoelectric material wafer and a non-piezoelectric material wafer, the method including: a step of manufacturing a non-piezoelectric material wafer having a flat edge on the outer periphery thereof; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and a flat edge on the outer periphery thereof; bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the flat sides provided on the wafers are aligned and arc-shaped circles on the outer peripheries of the two wafers are concentric; and polishing the arc-shaped outer periphery of the bonded piezoelectric material wafer along the arc-shaped polishing surface until the wafer is flat.

In the method for manufacturing a bonded wafer, since the piezoelectric material wafer and the non-piezoelectric material wafer have flat edges on the outer peripheral sides thereof in the stage before bonding, the flat edges can be optically detected to control the positions, and the two wafers can be bonded at predetermined relative positions. Thereafter, the outer periphery of the piezoelectric material wafer is polished until the flat edge disappears, and the piezoelectric material wafer is in a state without the flat edge. Therefore, when the surface of the piezoelectric material wafer is polished, the entire surface of the piezoelectric material wafer is stably supported by the non-piezoelectric material wafer. Thus, the polishing depth on the flat edge region side is not deeper than the other regions, and the thickness of the entire region of the piezoelectric material wafer can be made uniform. Therefore, when electrodes used for a plurality of elastic wave devices are formed on a piezoelectric material wafer constituting a bonded wafer and elastic wave devices are manufactured using an article obtained by dividing the bonded wafer, products having uniform frequency characteristics can be obtained.

In the method for manufacturing a bonded wafer according to the aspect of the present invention, the bonded wafer is a wafer in which the piezoelectric material wafer and the non-piezoelectric material wafer are bonded to each other by a room temperature bonding technique.

In this way, the piezoelectric material wafer and the non-piezoelectric material wafer are bonded by using a normal temperature bonding technique, and the wafer is not subjected to temperature change due to heating or other treatment during bonding, so that the wafer is not easily distorted or bent. Therefore, the problem caused by surface distortion or bending can be avoided in the process of bonding the wafer after bonding.

A second aspect of the method for manufacturing a bonded wafer according to the present invention is a method for manufacturing a bonded wafer bonded using a piezoelectric material wafer and a non-piezoelectric material wafer, the method including: a step of manufacturing a non-piezoelectric material wafer having a flat edge on the outer periphery thereof; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having a mark on a surface opposite to a bonding surface with the non-piezoelectric material wafer instead of a flat edge; bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state that the relative direction of the two wafers is a preset direction and arc circles on the outer peripheries of the two wafers are concentric; and polishing the outer periphery of the bonded piezoelectric material wafer in an arc shape.

In the method for manufacturing the bonded wafer, since the piezoelectric material wafer and the non-piezoelectric material wafer have marks in the stage before bonding, and the non-piezoelectric material wafer has a flat edge, the marks and the flat edge can be optically detected to control the positions, and the two wafers can be bonded at the preset relative positions. When the surface of the piezoelectric material wafer is polished after bonding, the piezoelectric material wafer does not have a flat edge. Therefore, when the surface of the piezoelectric material wafer is polished, the polishing depth on the flat edge region side is not deeper than the other regions, and the thickness of the entire region of the piezoelectric material wafer can be made uniform. Therefore, when electrodes used for a plurality of elastic wave devices are formed on a piezoelectric material wafer constituting a bonded wafer and elastic wave devices are manufactured using an article obtained by dividing the bonded wafer, products having uniform frequency characteristics can be obtained.

A third aspect of the method for manufacturing a bonded wafer according to the present invention is a method for manufacturing a bonded wafer bonded using a piezoelectric material wafer and a non-piezoelectric material wafer, the method including: a step of manufacturing a non-piezoelectric material wafer having a mark on a surface of an outer periphery thereof opposite to a bonding surface of the piezoelectric material wafer instead of a flat edge; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having a mark on a surface opposite to a bonding surface with the non-piezoelectric material wafer instead of a flat edge; a step of bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the two wafers are concentric with each other, the relative direction of the two wafers being a predetermined direction; and polishing the outer periphery of the bonded piezoelectric material wafer in an arc shape.

In the method of manufacturing a bonded wafer, as in the second aspect, since the piezoelectric material wafer does not have a flat edge when the surface of the piezoelectric material wafer is polished after bonding, the thickness of the entire region of the piezoelectric material wafer can be made uniform without causing the same situation as the case where the polishing depth on the flat edge region side is deeper than the other regions in the conventional art. Therefore, when electrodes used for a plurality of elastic wave devices are formed on a piezoelectric material wafer constituting a bonded wafer and elastic wave devices are manufactured using an article obtained by dividing the bonded wafer, products having uniform frequency characteristics can be obtained.

A fourth aspect of the method for manufacturing a bonded wafer according to the present invention is a method for manufacturing a bonded wafer bonded using a piezoelectric material wafer and a non-piezoelectric material wafer, the method including: a step of manufacturing a non-piezoelectric material wafer having a flat edge on the outer periphery thereof; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having double recesses instead of flat edges; a step of bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the two wafers are concentric with each other, the relative direction of the two wafers being a predetermined direction; and polishing the arc-shaped outer periphery of the bonded piezoelectric material wafer until the double concave marks disappear.

In the method for manufacturing the bonded wafer, since the piezoelectric material wafer and the non-piezoelectric material wafer have a flat edge and double dents on the outer peripheral side in the stage before bonding, for example, the positions can be optically detected and controlled, and the two wafers can be bonded at a predetermined relative position. After bonding, when the surface of the piezoelectric material wafer is polished, the piezoelectric material wafer does not have a flat edge, and therefore, the thickness of the entire region of the piezoelectric material wafer can be made uniform without the same situation as the situation where the polishing depth on the flat edge region side is deeper than the other regions in the conventional art. Therefore, when electrodes used for a plurality of elastic wave devices are formed on a piezoelectric material wafer constituting a bonded wafer and elastic wave devices are manufactured using an article obtained by dividing the bonded wafer, products having uniform frequency characteristics can be obtained.

A fifth aspect of the method for manufacturing a bonded wafer according to the present invention is a method for manufacturing a bonded wafer bonded using a piezoelectric material wafer and a non-piezoelectric material wafer, the method including: a step of manufacturing a non-piezoelectric material wafer having a mark on a surface of an outer periphery thereof opposite to a bonding surface of the piezoelectric material wafer instead of a flat edge; a step of manufacturing a piezoelectric material wafer having an area smaller than that of the non-piezoelectric material wafer and having double recesses instead of flat edges; a step of bonding the non-piezoelectric material wafer and the piezoelectric material wafer in a state in which the two wafers are concentric with each other, the relative direction of the two wafers being a predetermined direction; and polishing the arc-shaped outer periphery of the bonded piezoelectric material wafer until the double concave marks disappear.

In this method for manufacturing a bonded wafer, as in the fourth aspect, when the surface of the piezoelectric material wafer is polished after bonding, the piezoelectric material wafer does not have a flat edge, and therefore, the thickness of the entire region of the piezoelectric material wafer can be made uniform without causing the same situation as the case where the polishing depth on the flat edge region side is deeper than the other regions in the conventional art. Therefore, when electrodes used for a plurality of elastic wave devices are formed on a piezoelectric material wafer constituting a bonded wafer and elastic wave devices are manufactured using an article obtained by dividing the bonded wafer, products having uniform frequency characteristics can be obtained.

In one aspect of the method for manufacturing an elastic wave device according to the present invention, a bonded wafer manufactured by any one of the methods for manufacturing a bonded wafer according to the first to fifth aspects includes: forming an electrode for use in a plurality of elastic wave devices on the piezoelectric material wafer of the bonded wafer; dividing the bonded wafer on which the plurality of electrodes for use in the elastic wave device are formed into individual bare chips for use in the elastic wave device; and a step of dividing the wafer for a mounting substrate on which the bare chip is mounted into individual elastic wave devices.

In this way, since the bonded wafer is an article obtained by bonding a piezoelectric material wafer and a non-piezoelectric material wafer which do not have a flat edge, an elastic wave device having uniform frequency characteristics can be obtained.

In one aspect of the piezoelectric material wafer according to the present invention, a mark is provided instead of a flat edge on a surface opposite to a bonding surface with a non-piezoelectric material wafer, the surface being used for manufacturing a bonded wafer formed by bonding the piezoelectric material wafer and the non-piezoelectric material wafer.

Thus, by printing marks on the piezoelectric material wafer instead of flat edges, the relative position and orientation of the piezoelectric material wafer with respect to the non-piezoelectric material wafer can be set when the piezoelectric material wafer is bonded to the non-piezoelectric material wafer. In addition, if the mark is provided by using laser, the positional accuracy is expected to be higher than that of the flat edge, and the positional accuracy at the time of bonding is improved.

In one aspect of the piezoelectric material wafer according to the present invention, a piezoelectric material wafer used for manufacturing a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer is provided with double concave marks instead of flat edges on a surface opposite to a bonding surface with the non-piezoelectric material wafer.

One aspect of the non-piezoelectric material wafer according to the present invention is a non-piezoelectric material wafer used for manufacturing a bonded wafer formed by bonding a piezoelectric material wafer and a non-piezoelectric material wafer, wherein a mark is provided on a surface opposite to a bonding surface with the piezoelectric material wafer instead of a flat edge.

Thus, by printing marks on the non-piezoelectric material wafer instead of flat edges, the relative position and direction of the non-piezoelectric material wafer with respect to the piezoelectric material wafer can be set when the non-piezoelectric material wafer is bonded to the piezoelectric material wafer. In addition, if the mark is provided by using laser, the positional accuracy is expected to be higher than that of the flat edge, and the positional accuracy at the time of bonding is improved.

The invention has the beneficial effects that: according to the present invention, in the bonded wafer of the piezoelectric material wafer and the non-piezoelectric material wafer, the thickness of the piezoelectric material wafer is reduced and the surface is smoothed by polishing the surface of the piezoelectric material wafer, so that a more uniform thickness can be obtained over the entire surface of the piezoelectric material wafer. Therefore, electrodes for use in a plurality of elastic wave devices are formed on the piezoelectric material wafer of the bonded wafer, so that when the elastic wave devices are obtained after the bonded wafer is divided, elastic wave devices having uniform frequency characteristics can be obtained.

Drawings

Other features and effects of the present invention will become apparent from the following detailed description of the embodiments with reference to the accompanying drawings, in which:

FIG. 1 shows a perspective view of a bonded wafer according to one embodiment of the present invention;

FIG. 2 is a plan view of the bonded wafer of FIG. 1;

FIG. 3 is a side view of the bonded wafer of FIG. 1;

FIGS. 4(a) to (d) are flowcharts showing a first embodiment of the method for manufacturing a bonded wafer according to the present invention;

FIG. 5 shows a perspective view of a grinding mechanism of the outer peripheral portion of a piezoelectric material wafer in the bonded wafer manufacturing process of FIG. 1;

fig. 6(a) to (c) are side views showing the bonded wafer of fig. 1, in which the thickness of the piezoelectric material wafer changes due to the polishing process of the surface of the piezoelectric material wafer; and

FIG. 7 shows a perspective view of the grinding mechanism of FIG. 1 engaging the surface of a wafer of piezoelectric material in the wafer;

FIG. 8(a) is a perspective view showing a CMP polishing mechanism for a piezoelectric material wafer surface; FIG. 8(b) is a side view showing a support member for supporting a wafer in the polishing mechanism;

FIG. 9 is a plan view showing a planar structure of bonded wafers when a comparative experiment comparing differences in thickness distribution of piezoelectric material wafers is conducted for the case where the piezoelectric material wafers have flat edges and do not have orientations;

FIG. 10 is a graph showing the comparison between the thickness of the piezoelectric material wafer at a plurality of measurement points in each of the prior art and the present invention in the case where the thickness of the surface of the piezoelectric material wafer after polishing is set to 1.5 μm;

fig. 11 is a graph comparing the thicknesses of the piezoelectric material wafers at several measurement points, as in fig. 10, in the case where the thickness of the surface of the piezoelectric material wafer after polishing is set to 3 μm;

fig. 12 is a graph comparing the thicknesses of the piezoelectric material wafers at several measurement points, as in fig. 10, in the case where the thickness of the surface of the piezoelectric material wafer after polishing is set to 5 μm;

fig. 13 is a graph showing an example of the relationship between the thickness of a piezoelectric substrate and the resonance frequency and antiresonance frequency in a resonator configured as an elastic surface wave device;

fig. 14 is a plan view showing an example of the electrode configuration of a filter configured as an elastic surface wave device;

FIG. 15 is a graph showing the relationship between frequency and attenuation in the filter shown in FIG. 14 and the center frequency;

FIG. 16 is a graph showing the distribution of center frequencies in the case of the filter shown in FIG. 14, using a conventional wafer having a flat edge or a wafer having no flat edge as in the present invention;

FIGS. 17(a) to (d) are flowcharts showing a second embodiment of the method for manufacturing a bonded wafer according to the present invention;

FIGS. 18(a) to (d) are flowcharts showing a third embodiment of the method for manufacturing a bonded wafer according to the present invention;

FIG. 19(a) to (d) are flowcharts showing a piezoelectric material wafer and a method for manufacturing the same according to a fourth embodiment of the method for manufacturing a bonded wafer of the present invention;

FIGS. 20(a) to (c) are flowcharts showing a part of steps in an embodiment of a method for manufacturing an elastic wave device according to the present invention;

fig. 21(a) to (b) are flowcharts showing other parts of the steps of an embodiment of the method for manufacturing an elastic wave device according to the present invention; and

fig. 22 is a perspective view showing an example of a conventional bonded wafer.

Detailed Description

< first embodiment >

Hereinafter, a first embodiment of the bonded wafer according to the present invention will be described with reference to fig. 1 to 3. The bonded wafer 1 is formed by bonding a non-piezoelectric material wafer 2 and a piezoelectric material wafer 3. In the piezoelectric material wafer 3, Lithium Tantalate (LT) or Lithium Niobate (LN) is used to form a surface acoustic wave device. The non-piezoelectric material wafer 2 is made of a material having a lower thermal expansion coefficient than the piezoelectric material wafer 3, for example, silicon, sapphire, polycrystalline alumina, polycrystalline spinel, crystal, or glass. However, in the present invention, the non-piezoelectric material wafer 2 or the piezoelectric material wafer 3 is not limited to these materials, and other materials may be used. Further, the present invention is also applicable to other elastic wave devices whose characteristics vary depending on the thickness of the piezoelectric substrate.

The non-piezoelectric material wafer 2 has a flat side 2a1 formed linearly on the outer periphery 2a thereof. The non-piezoelectric material wafer 2 has an outer periphery 2a in which a portion other than the flat side 2a1 is formed in an arc shape. The piezoelectric material wafer 3 is circular and has no flat edges. The area of the piezoelectric material wafer 3 is narrower than that of the non-piezoelectric material wafer 2. As shown in fig. 2, the outer periphery 2a of the non-piezoelectric material wafer 2 including the flat edge 2a1 is located further outside the outer periphery 3a of the piezoelectric material wafer 3. The circle drawn by the outer periphery 3a of the piezoelectric material wafer 3 is concentric with the circle drawn by the outer periphery 2a of the non-piezoelectric material wafer 2.

As shown in fig. 3, the thickness t1 of the piezoelectric material wafer 3 is thinner than the thickness t2 of the non-piezoelectric material wafer 2 (t1< t 2). For example, when the thickness t1 of the piezoelectric material wafer 3 is 0.2 μm or more and 20 μm or less, the thickness t2 of the non-piezoelectric material wafer 2 is 80 μm or more and 500 μm or less. However, the thickness of each wafer 2, 3 in the present invention is not limited to these values.

The manufacturing process of the bonded wafer 1 includes: as shown in fig. 4(a), a step of manufacturing a non-piezoelectric material wafer 2; as shown in fig. 4(b), a step of manufacturing a piezoelectric material wafer 3X; as shown in fig. 4(c), a step of bonding the wafer 2 and the wafer 3X to obtain a bonded wafer 1X; and a step of polishing the outer periphery of the piezoelectric material wafer 3X of the bonded wafer 1X to obtain a bonded wafer 1 having the piezoelectric material wafer 3 with a reduced outer diameter, as shown in fig. 4 (d).

The non-piezoelectric material wafer 2 shown in fig. 4(a) is manufactured in the same process as in the conventional case. For example: a step of cutting off both ends of the ingot from the ingot manufactured in a cylindrical shape by using a cutter; grinding the outer periphery of the ingot to unify the diameter of the ingot over the entire length thereof; cutting or grinding the side surface of the ingot having a uniform diameter to form a flat portion of the flat edge 2a1 of the wafer; cutting the ingot into a wafer shape by a cutter; and a step of polishing the wafer obtained by the cutting. However, the flat edge 2a1 may be formed by grinding or the like after the wafer is manufactured. The piezoelectric material wafer 3X shown in fig. 4(b) is also manufactured in the same process. However, the piezoelectric material wafer 3X is formed such that the diameter of the outer circumference is smaller than the diameter of the outer circumference of the non-piezoelectric material wafer 2. That is, the area of the piezoelectric material wafer 3X is narrower than the area of the non-piezoelectric material wafer 2.

The bonding of the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X is performed in a state in which the directions of the flat sides 2a1 and 3b1 provided on the respective wafers of the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X are aligned. As a result of this bonding, the outer circumferences of the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X are formed into concentric circles.

The bonding of the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X may be performed using an adhesive. However, in the present embodiment, the bonding is performed by room temperature bonding. In the case of performing this normal temperature bonding, the bonding surface of the non-piezoelectric material wafer 2 and the bonding surface of the piezoelectric material wafer 3X are irradiated with an atomic beam such as argon to activate the bonding surfaces. And bonded by interatomic force existing between atoms at the bonding surfaces of the piezoelectric material wafer 3X and the non-piezoelectric material wafer 2. Therefore, the bonded wafer is not heated and the bonded surface is free from residual stress after bonding, and the bonded wafer is prevented from being twisted or bent.

After the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X are bonded as shown in fig. 4(c), the outer periphery 3b of the piezoelectric material wafer 3X shown by the dotted line is polished to a circle reduced to the outer periphery 3a shown by the solid line as shown in fig. 4 (d). That is, the outer periphery 3b of the piezoelectric material wafer 3X is polished to have a wafer size in which the flat side 3b1 disappears along the arc-shaped polished surface, thereby obtaining the piezoelectric material wafer 3. Here, the "wafer size at which the flat side 3b1 disappears" does not strictly require that the flat side 3b1 disappear, but it is sufficient to polish the outer periphery so that the flat side 3b1 substantially disappears.

The outer periphery 3b of the piezoelectric material wafer 3X is polished in this manner, for example, by using a polishing apparatus having a mechanism shown in fig. 5. That is, the bonded wafer 1X obtained by bonding the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X is fixed to a not-shown turntable. On the other hand, the turntable is provided with a rotary grindstone 5 having a rotation axis 5X directed in the radial direction of the turntable, for example. The rotary grinding stone 5 has a grinding stone body 5a in a disk shape, and a grinding stone holder 5b holding the grinding stone body 5 a. The outer periphery 3b of the piezoelectric material wafer 3X is polished by rotating the bonded wafer 1X in the direction indicated by the arrow 6 together with the turntable, and rotating the polishing stone body 5a in the direction indicated by the arrow 7 while contacting the outer periphery 3b of the piezoelectric material wafer 3X. The turntable or the rotary grindstone 5 on which the bonded wafer 1X is disposed is moved in accordance with the progress of polishing of the outer periphery 3b of the piezoelectric material wafer 3X, and the grindstone body 5a is gradually brought closer to the rotation center of the bonded wafer 1X.

After the outer periphery 3b of the piezoelectric material wafer 3X is polished in this manner, the surface of the piezoelectric material wafer 3 is polished. That is, as shown in fig. 6(a), the front surface 3c1 of the piezoelectric material wafer 3 is mechanically polished from an unpolished state at a thickness ta to significantly reduce the thickness, and the thickness is polished to a thickness tb shown in fig. 6 (b). Next, as shown in fig. 6(b), the surface 3c2 of the piezoelectric material wafer 3 is chemically and mechanically polished to reduce the thickness to a thickness t1 shown in fig. 6(c), and the surface 3c is smoothed.

As shown in fig. 6(a) to 6(b), mechanical polishing for significantly reducing the thickness of the piezoelectric material wafer 3 is performed by, for example, a polishing mechanism shown in fig. 7. The mechanical polishing mechanism has a polishing wheel 9 for polishing the upper surface 3c1 of the piezoelectric material wafer 3, which is the bonded wafer 1 mounted on a not-shown turntable. The polishing wheel 9 is disk-shaped, and a plurality of polishing heads 9a are disposed annularly on the lower surface thereof to polish the piezoelectric material wafer 3 bonded to the wafer 1. The grinding wheel 9 has a rotary drive shaft 9 b.

In this polishing mechanism, when polishing the bonded wafer 1, the polishing wheel 9 is positioned such that the polishing head 9a of the polishing wheel 9 is in contact with the bonded wafer 1 over a range from the center of rotation to the outer periphery thereof with the aggregate of the polishing heads 9 a. The bonded wafer 1 is driven to rotate in a direction indicated by an arrow 10 together with a not-shown turntable, and the polishing wheel 9 is driven to rotate in a direction indicated by an arrow 11, so as to polish the surface of the bonded wafer 1, that is, the surface 3c1 of the piezoelectric material wafer 3.

After that, in the chemical mechanical polishing shown in fig. 6(b) to 6(c), the piezoelectric material wafer 3 is polished with high precision and smooth surface, although the thickness is reduced to a low extent by the polishing. The chemical mechanical polishing is performed by a polishing mechanism shown in fig. 8(a) and 8(b), for example. The chemical mechanical polishing apparatus has a polishing pad 14 fixed on a turntable (not shown). The slurry supply device 15 supplies slurry-like abrasive 16 onto the polishing pad 14, thereby performing a chemical polishing action on the piezoelectric material wafer 3. On the other hand, the bonded wafer 1 is held by a lower surface of a circular holder 17, and the piezoelectric material wafer 3 faces downward. The surface of the piezoelectric material wafer 3 is chemically and mechanically polished by bringing the bonded wafer 1 into contact with the polishing pad 14 under pressure by the positioning mechanism of the holder 17 and driving the polishing pad 14 to rotate in the direction indicated by the arrow 18.

In this way, in order to confirm the effect of removing the flat edge of the piezoelectric material wafer 3 to make the thickness of the piezoelectric material wafer 3 uniform, a comparative experiment was performed with respect to the piezoelectric material wafer 3 having the flat edge. In a comparative experiment, as shown in fig. 9, the distribution of the thickness of the piezoelectric material wafer 3 after mechanical polishing and chemical mechanical polishing was examined for the condition where the flat side 3b1 remains as shown by the chain line and the condition where the flat side 3a does not remain as shown by the solid line. Sapphire is used for the non-piezoelectric material wafer 2, and the thickness is set to be 400 μm. The piezoelectric material wafer 3 was subjected to a comparative experiment using Lithium Tantalate (LT) with target thicknesses of 1.5 μm, 3 μm, and 5 μm, respectively.

The diameter of the arc portion of the outer periphery 2a of the non-piezoelectric material wafer 2 was set to 100 mm. In the case of having the flat side 3b1, the diameter of the circular arc portion of the outer periphery 3b of the piezoelectric material wafer 3X is determined to be 95 mm. The outer periphery 3a of the piezoelectric material wafer 3 having no flat side 3b1 is partially matched with the flat side 3b1 before the outer periphery 3b is polished.

Fig. 9 shows a measurement point 50 of the thickness of the piezoelectric material wafers 3 and 3X after polishing. The measurement points 50 are set to be spaced apart by 5mm in the direction in which the centers OF the piezoelectric material wafers 3 and 3X start to move away toward the flat side (OF)3b 1. The thickness of the piezoelectric material wafer 3 is measured by a thickness measuring device using a laser beam.

As shown in fig. 10 to 12, in any OF the cases where the target thickness is 1.5 μm, 3 μm, and 5 μm, the thickness OF the piezoelectric material wafer 3X having the flat side 3b1 becomes smaller at the measurement point on the flat side (OF)3b1 side (the measurement point OF-5 mm to-40 mm in fig. 10 to 12) than at the measurement point on the opposite side OF the flat side 3b 1. On the other hand, in the piezoelectric material wafer 3 having no flat side 3b1, the difference in thickness between the flat side 3b1 side and the opposite side before the outer periphery polishing is small. Table 1 shows the difference R (μm) between the maximum value and the minimum value of the thickness and the standard deviation σ (μm) in the thickness measurement. As can be seen from table 1, by removing the flat side 3b1, the thickness variation of the entire piezoelectric material wafer 3 can be greatly improved.

TABLE 1

Fig. 13 shows the relationship between the thickness of the piezoelectric substrate and the resonance frequency Fr and anti-resonance frequency Fa when the resonator is formed by using Lithium Tantalate (LT) for the piezoelectric substrate, but using a silicon surface acoustic wave device for the non-piezoelectric substrate. In order to examine this relationship, the resonance frequency Fr and the antiresonance frequency Fa were measured by configuring the resonator such that the electrode pitch of the comb-shaped electrodes formed on the surface of the piezoelectric material wafer 3 was 4.6 μm, and changing the thickness of the piezoelectric substrate within a range of 0.5 μm to 10 μm.

As can be understood from fig. 13, when the thickness of the piezoelectric substrate is about 3 μm or less, the thickness of the piezoelectric substrate affects the resonance frequency Fr and the antiresonance frequency Fa, and particularly, the influence thereof is very large at 2 μm or less. Therefore, if the resonator is made higher in frequency and the Q value is increased by thinning the piezoelectric substrate, it is an important subject to make the thickness of the entire piezoelectric material wafer 3 uniform.

Fig. 14 shows an example of the electrode patterns of the plurality of filters 20 formed on the surface of the piezoelectric material wafer 3. The filter 20 has a ladder structure composed of resonators 19A to 19E each having a reflector 21 arranged in parallel. A portion of the resonators 19A-19C are lines 24 interposed between the input port 22 and the output port 23. The other resonators 19D, 19E are inserted between the line 24 and the ground ports 25a, 25b, respectively. The filter is configured such that each of the resonators 19A to 19E is a basic unit of a ladder structure, and the pass band is determined by the impedance of each of the resonators 19A to 19C and the impedance of each of the resonators 19D and 19E. FIG. 15 shows the passband and center frequency F of the filter of FIG. 14_OSummary of (1).

A piezoelectric material wafer 3 having a flat side 3b1 and a piezoelectric material wafer 3 having no flat side 3b1 were used to fabricate a filter having the electrode pattern of FIG. 14, respectively, to compare the center frequency F thereof_OThe difference in (a). In this production, Lithium Tantalate (LT) was used for the piezoelectric material wafer 3, and the thickness thereof was set to 3 μm. Further, sapphire was used as the non-piezoelectric material wafer 2, and the thickness thereof was set to 400 μm. The electrode pitch of the resonators 19A to 19E and the reflector 21 was set to 2.10 μm.

FIG. 16 shows the center frequency F of the filter having the structure shown in FIG. 14 when the filter is constructed using wafers having the flat side 3b1 and wafers having no flat side 3b1_OThe distribution of (2). The center frequency was measured by preparing 45 filter samples from wafers having a flat side of 3b1 and 45 filter samples from wafers not having a flat side of 3b 1. Then, the range (Rmax-Rmin) (MHz) and standard deviation σ (MHz) of the difference between the maximum value Rmax and the minimum value Rmin of the center frequency are found from the measured values. Table 2 shows the results.

TABLE 2

As can be seen from table 2, if the filter shown in fig. 14 is constructed by using the piezoelectric material wafer without the flat sides, the range of the center frequency is narrower than that of the filter made by using the piezoelectric material wafer with the flat sides, and the numerical value of the standard deviation σ is also small. That is, the flat-edged piezoelectric material wafer is removed, and a filter having more uniform frequency characteristics can be obtained.

< second embodiment >

A second embodiment of the method for manufacturing a bonded wafer according to the present invention will be described below with reference to fig. 17. In the piezoelectric material wafer 3X of this embodiment, a mark 3d is printed on the wafer surface at the same position as the flat edge 3b1 instead of the flat edge 3b 1. The mark 3d may be printed by printing using laser or coloring ink. Note that the mark 3d may not be linear, and may be configured such that a material having a color different from that of other regions is attached to the outer periphery of the linear portion indicated by the mark 3 d. The mark 3d is provided on the opposite side of the bonding surface to the non-piezoelectric material wafer 2, since it is optically detected by an imaging device when performing alignment for bonding.

When the bonded wafer is manufactured according to this second embodiment, as shown in fig. 17(a), a non-piezoelectric material wafer 2 having a flat edge 2a1 on the outer periphery is manufactured. As shown in fig. 17(b), a piezoelectric material wafer 3X having a mark 3d instead of a flat edge on the surface opposite to the bonding surface with the non-piezoelectric material wafer, which is narrower in area than the non-piezoelectric material wafer 2, is manufactured. Next, as shown in fig. 17(c), the positions of the flat side 2a1 and the mark 3d are optically detected, and based on the positional information, the relative positions of the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X are adjusted, so that the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3X are bonded so that the relative directions of the two wafers match the predetermined direction, and the outer arcs of the two wafers are concentric. In this embodiment, the flat side 2a1 and the mark 3d are joined in parallel with each other, but they are not necessarily parallel with each other, and the orientation of the crystal direction of the piezoelectric material wafer 3X with respect to the mark 3b may be a predetermined orientation. After the two wafers 2 and 3X are bonded, as shown by the solid line in fig. 17(d), the outer periphery 3b of the piezoelectric material wafer 3X having an arc shape is polished along the outer periphery 3b having an arc shape, so that the bonded piezoelectric material wafer 3X is less likely to fall off from the non-piezoelectric material wafer 2.

In the manufacturing method of the second embodiment, the piezoelectric material wafer 3X does not have the flat side 3b1 unlike the above-described embodiment. Therefore, when the surface of the piezoelectric material wafer 3 is polished, the polishing depth on the flat edge region side is not deeper than the other regions, and the thickness of the entire region of the piezoelectric material wafer 3 can be made uniform. Therefore, when an elastic wave device is manufactured using the article obtained by dividing the bonded wafer, a product having uniform frequency characteristics can be obtained.

In the manufacturing method of the second embodiment, the piezoelectric material wafer 3X does not have the flat side 3b 1. Therefore, when the surface of the piezoelectric material wafer 3 is polished, the polishing depth on the flat edge region side is not deeper than the other regions, and the thickness of the entire region of the piezoelectric material wafer 3 can be made uniform. After the surface 3c of the piezoelectric material wafer 3 is polished, the mark 3d disappears. Therefore, when an elastic wave device is manufactured using the article obtained by dividing the bonded wafer, a product having uniform frequency characteristics can be obtained.

< third embodiment >

A third embodiment of the method for manufacturing a bonded wafer according to the present invention will be described below with reference to fig. 18. In the piezoelectric material wafer 3X of this embodiment, a mark 3d is printed on the wafer surface at the same position as the flat edge 3b1 instead of the flat edge 3b1 in embodiment 1. In the same manner as in the case of the non-piezoelectric material wafer 2X, the mark 2b is provided at the same position as the flat side 2a1 on the surface opposite to the bonding surface with the piezoelectric material wafer 3X, instead of the flat side 2a 1. These marks 2b, 3d may be printed by printing using laser or colored ink. The marks 2b and 3d may not be linear, and may be configured such that a material having a color different from that of other regions is attached to the outer periphery of the linear portions shown in 2b and 3 d.

In manufacturing the bonded wafer according to the third embodiment, as shown in fig. 18(a), a non-piezoelectric material wafer 2X having a mark 2b on the outer periphery thereof instead of a flat edge is manufactured. As shown in fig. 18(b), a piezoelectric material wafer 3X having a mark 3d instead of a flat edge on the surface opposite to the bonding surface with the non-piezoelectric material wafer, which is narrower in area than the non-piezoelectric material wafer 2X, is manufactured. Next, as shown in fig. 18(c), the positions of the marks 2b and 3d are optically detected, and the relative positions of the non-piezoelectric material wafer 2X and the piezoelectric material wafer 3X are adjusted based on the positional information, so that the non-piezoelectric material wafer 2X and the piezoelectric material wafer 3X are bonded together such that the relative directions of the two wafers coincide with a predetermined direction, and the outer arcs of the two wafers are concentric. In this example, the mark 2b and the mark 3d are joined in a state parallel to each other, but they are not necessarily parallel to each other, and as a result, the orientation of the piezoelectric material wafer 3X with respect to the mark 2b, such as the crystal direction, may be a predetermined orientation.

In this embodiment, before polishing the surface of the piezoelectric material wafer 3X, as shown in fig. 18(d), the outer periphery 3b of the piezoelectric material wafer 3X is also polished, so that the bonded piezoelectric material wafer 3X is less likely to fall off.

In the manufacturing method of the third embodiment, the piezoelectric material wafer 3X does not have a flat edge. Therefore, when the front surface 3c of the piezoelectric material wafer 3X is polished, the thickness of the entire region of the piezoelectric material wafer 3X can be made uniform without causing the same situation as the conventional case where the polishing depth on the flat edge region side is deeper than the other regions. Therefore, when an elastic wave device is manufactured using the article obtained by dividing the bonded wafer, a product having uniform frequency characteristics can be obtained.

< fourth embodiment >

A fourth embodiment of the method for manufacturing a bonded wafer according to the present invention will be described below with reference to fig. 19. In this embodiment, as shown in fig. 19(a), the outer periphery 3b of the piezoelectric material wafer 3Y is provided with V-shaped notches, that is, dimples 3f and 3f (hereinafter referred to as double dimples). The double recesses 3f, 3f are provided in place of the flat side 3b1 in embodiment 1. The double recesses 3f, 3f are provided on the outer periphery 3b of the wafer 3Y at positions substantially corresponding to both ends of the flat edge 3b1 in the circumferential direction. With respect to the non-piezoelectric material wafer 2, the flat side 2a1 is provided.

When the bonded wafer is manufactured according to this fourth embodiment, as shown in fig. 19(b), a non-piezoelectric material wafer 2 having a flat edge 2a1 on the outer periphery is manufactured. As shown in fig. 19(c), a piezoelectric material wafer 3Y having a smaller area than the non-piezoelectric material wafer 2 and having double recesses 3f and 3f instead of flat sides is manufactured. Next, as shown in fig. 19(d), the positions of the flat side 2a1 and the double concave marks 3f, 3f are optically detected, and based on the positional information, the relative positions of the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3Y are adjusted, so that the non-piezoelectric material wafer 2 and the piezoelectric material wafer 3Y are bonded so that the opposing directions of the two wafers coincide with a predetermined direction, and the outer peripheral arcs of the two wafers are concentric.

In the embodiment of fig. 19, before polishing the front surface of the piezoelectric material wafer 3Y, the outer periphery 3b of the piezoelectric material wafer 3Y is polished as shown in fig. 19 (d). At this time, the polishing depth of the outer periphery 3b in the wafer radial direction is set to a size of the wafer 3 where the double concave marks 3f and 3f of the piezoelectric material wafer 3Y disappear.

In the manufacturing method of the fourth embodiment, the piezoelectric material wafer 3Y does not have a flat edge. Therefore, when the front surface 3c1 of the piezoelectric material wafer 3Y is polished, the thickness of the entire region of the piezoelectric material wafer 3Y can be made uniform without causing the same situation as the conventional case where the polishing depth on the flat edge region side is deeper than the other regions. Therefore, when an elastic wave device is manufactured using the article obtained by dividing the bonded wafer, a product having uniform frequency characteristics can be obtained.

< fifth embodiment >

In a fifth embodiment of the method for manufacturing a bonded wafer, as shown in fig. 18(a), a mark 2b is provided on a non-piezoelectric material wafer 2 instead of a flat edge 2a1, and as shown in fig. 19, a double notch 3f, 3f is provided on a piezoelectric material wafer 3Y, and then both wafers are bonded. At this time, as described with reference to fig. 19, the outer periphery 3b of the piezoelectric material wafer 3Y is polished until the double recesses 3f disappear.

In this embodiment, since the piezoelectric material wafer 3Y does not have a flat edge, the surface 3c1 of the piezoelectric material wafer 3Y can be polished to a uniform thickness when the surface 3c1 of the piezoelectric material wafer 3Y is polished.

Next, an embodiment of a method for manufacturing an elastic wave device using the bonded wafer 1 will be described with reference to fig. 20 and 21. Fig. 20(a) conceptually shows that a plurality of electrode patterns of, for example, the filter shown in fig. 14 are formed on the bonded wafer 1 manufactured by any one of the methods of embodiment 1 to embodiment 3. That is, an electrode 31 and a pad electrode 32 used for a resonator corresponding to a surface acoustic wave are formed on the piezoelectric material wafer 3 constituting the bonded wafer 1. Here, the electrodes 31 for the resonator are referred to as comb-shaped electrodes and reflectors. The electrodes 31 and pad electrodes 32 for the resonator are formed on the surface of the piezoelectric material wafer 3 by Photolithography (Photolithography). The bonded wafer 1 having the electrodes 31, 32, etc. formed on the piezoelectric material wafer 3 is cut into individual bare chips 35 along vertical and horizontal cutting lines 33 by blade dicing (laser dicing), laser, etc., as shown in fig. 20(b), and each of the bare chips 35 has the non-piezoelectric substrate 2E and the piezoelectric substrate 3E.

On the other hand, in a step other than the step of manufacturing the bare chip 35, as shown in the lower part of fig. 20(c), a pre-dicing mounting substrate 40 made of an insulating material such as ceramic, glass, or plastic is prepared. When the mounting board 40 is provided with the conductor layer 43 for forming wiring or a component therein, a mounting board material for forming the conductor layer 43 and another mounting board material or a plurality of mounting board materials may be joined to each other in an overlapping manner. The mounting substrate 40 has pad electrodes 41 and 42 formed on the front and back surfaces thereof. The pad electrodes 41 and 42 on the front and back surfaces may be electrically connected directly via a conductive layer 43 or the like, or may be electrically connected via a component formed therein but not shown.

As shown in fig. 20(c), the bare chip 35 of the acoustic wave device is flip-chip mounted on the mounting substrate 40 on which the pad electrodes 41 and 42 configured as described above are provided. That is, the pad electrode 32 of the bare chip 35 is bonded to the pad electrode 41 of the mounting substrate 40 via the bump 44.

Next, as shown in fig. 21(a), the mounting substrate 40 on which the bare chip 35 is mounted is covered with a curable resin layer 45. The resin layer 45 may be provided by adhering a thermosetting resin or a photocurable resin film, or by applying a thermosetting resin or a photocurable resin instead of the adhesion of the film layer. Then, these resin layers 45 are heated or irradiated with light to cure the resin. Next, along the vertical and horizontal dicing lines 46, individual chips are cut out as elastic wave devices 47 by blade dicing, laser dicing, or the like, as shown in fig. 21 (b).

In this way, the elastic wave device 47 is manufactured using the bonded wafer 1 having the uniform thickness of the piezoelectric material wafer, and the elastic wave device having the uniform frequency characteristics can be obtained.

The above description is only an example of the present invention, and the scope of the present invention should not be limited thereby, and the invention is still within the scope of the present invention by simple equivalent changes and modifications made according to the claims and the contents of the specification.