WO2019187577A1 - Joined body of piezoelectric material substrate and support substrate - Google Patents

Abstract

[Problem] To configure a joined body that joins a piezoelectric material substrate comprising lithium tantalite or the like to a support substrate such that the reduction of voltage resistance of an electrode is suppressed while improving heat discharge from the piezoelectric material substrate. [Solution] A joined body 8 (8A) comprises: a support substrate 3; a piezoelectric material substrate 1 (1A) comprising a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate; and an amorphous layer 7 that contacts a joining surface 6 of the support substrate 3, and a joining surface 5 of the piezoelectric material substrate 1 (1A). The thermal resistance TR from the joining surface 6 of the support substrate 3, through the amorphous layer 7, to the joining surface 5 of the piezoelectric material substrate 1 (1A) is greater than or equal to 1.0 × 10-6m2 K/W, and less than or equal to 3.0 × 10-6m2 K/W.

Description

Bonded body of piezoelectric material substrate and support substrate

The present invention relates to a joined body of a piezoelectric material substrate and a support substrate.

For the purpose of realizing a high-performance semiconductor device, an SOI substrate composed of a high resistance Si / SiO ₂ thin film / Si thin film is widely used. Plasma activation is used to realize an SOI substrate. This is because bonding can be performed at a relatively low temperature (400 ° C.). A composite substrate composed of a similar Si / SiO ₂ thin film / piezoelectric thin film has been proposed to improve the characteristics of the piezoelectric device (Patent Document 1). In Patent Document 1, a piezoelectric material substrate made of lithium niobate or lithium tantalate is bonded to a silicon substrate provided with a silicon oxide layer after activation by an ion implantation method.

In addition, a so-called FAB (Fast Atom Beam) type direct bonding method is known. In this method, a neutralized atomic beam is irradiated to each bonding surface at normal temperature to activate and bond directly (Patent Document 2).

JP 2016-225537 A JP2014-086400

The lithium tantalate and lithium niobate single crystal substrates used for acoustic wave filters have low thermal conductivity. Due to the increase in transmission power accompanying the recent increase in communication volume and the heat generation from peripheral elements due to modularization, the acoustic wave filter is in an environment where the temperature tends to increase. As a result, an elastic wave filter made of a piezoelectric single crystal single plate could not be used for a high-performance communication terminal.

On the other hand, it is also considered to improve the exhaust heat property of the acoustic wave filter by bonding a support substrate having high thermal conductivity to the back surface of the piezoelectric material substrate. However, it has been found that when the heat conduction from the piezoelectric material substrate to the support substrate is promoted to improve the exhaust heat performance, the bonding strength between the piezoelectric material substrate and the support substrate decreases. In particular, it has been found that when the piezoelectric material substrate is thinned in order to improve the performance of the acoustic wave filter, the bonding strength is significantly reduced.

An object of the present invention is to improve the heat dissipation from a piezoelectric material substrate and prevent a decrease in bonding strength in a bonded body of a type in which a piezoelectric material substrate made of lithium tantalate or the like is bonded to a support substrate. Is to be able to do it.

The present invention provides a support substrate,
A piezoelectric material substrate made of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate, and a non-contact surface that contacts the bonding surface of the support substrate and the bonding surface of the piezoelectric material substrate Crystalline layer,
A joined body comprising:
The thermal resistance from the bonding surface of the support substrate to the bonding surface of the piezoelectric material substrate through the amorphous layer is 1.0 × 10 ⁻⁶ m ² K / W or more, 3.0 × 10 ^{−. It is 6} m ² K / W or less.

According to the present invention, in a bonded body in which an amorphous layer is provided between a support substrate and a piezoelectric material substrate and bonded, the piezoelectric material is bonded via the amorphous layer from the bonding surface in contact with the amorphous layer of the support substrate. The thermal resistance to the bonding surface of the conductive material substrate was set to 1.0 × 10 ⁻⁶ m ² K / W or more and 3.0 × 10 ⁻⁶ m ² K / W or less. By setting the thermal resistance to 3.0 × 10 ⁻⁶ m ² K / W or less, heat conduction from the piezoelectric material substrate to the support substrate side can be promoted, and the exhaust heat property of the joined body can be improved. Such an effect is remarkable especially when the piezoelectric material substrate is thin.

On the other hand, theoretically, the lower the thermal resistance, the better the heat dissipation of the joined body, and the performance of the acoustic wave device should be stabilized. However, contrary to expectation, it has been found that when the thermal resistance is lowered, the bonding strength between the piezoelectric material substrate and the support substrate is significantly reduced. In particular, it has been found that when the piezoelectric material substrate is thinned in order to improve the performance of the acoustic wave filter, the bonding strength is significantly reduced.

Here, the thermal resistance from the bonding surface in contact with the amorphous layer of the support substrate to the bonding surface of the piezoelectric material substrate through the amorphous layer is set to 1.0 × 10 ⁻⁶ m ² K / W or more. As a result, it was found that the bonding strength of the piezoelectric material substrate to the support substrate was improved, and the present invention was achieved.

(A) shows the piezoelectric material substrate 1, and (b) shows a state in which the activated surface 5 is generated by irradiating the surface 1 a of the piezoelectric material substrate 1 with the neutralization beam A. (A) shows the support substrate 3, and (b) shows a state in which the neutralized beam B is applied to the surface 3 a of the support substrate 3. (A) shows the joined body 8 of the piezoelectric material substrate 1 and the support substrate 3, (b) shows a state in which the piezoelectric material substrate 1 of the joined body 8A is thinned by processing, and (c) shows elasticity. The wave element 11 is shown. It is the elements on larger scale of joined body 8 (8A).

Hereinafter, the present invention will be described in detail with appropriate reference to the drawings.
First, as shown in FIG. 1A, a piezoelectric material substrate 1 having a pair of main surfaces 1a and 1b is prepared. Next, as shown in FIG. 1B, the neutralized beam is irradiated as shown by an arrow A to the bonding surface 1a of the piezoelectric material substrate 1 to obtain the surface activated bonding surface 5.

On the other hand, as shown in FIG. 2A, a support substrate 3 having a surface 3a is prepared. Next, as shown in FIG. 2B, surface activation is performed by irradiating the surface 3a of the support substrate with a neutral beam as shown by an arrow B, thereby forming an activated bonding surface 6.

Next, the activated bonding surface 5 on the piezoelectric material substrate 1 and the activated bonding surface 6 of the support substrate 3 are brought into contact with each other and directly bonded to obtain a bonded body 8 shown in FIG. be able to. Here, an amorphous layer 7 is generated between the bonding surface 6 of the support substrate 3 and the bonding surface 5 of the piezoelectric material substrate 1.

In this state, an electrode may be provided on the piezoelectric material substrate 1. However, preferably, as shown in FIG. 3B, the main surface 1b of the piezoelectric material substrate 1 is processed to thin the substrate 1 to obtain a thinned piezoelectric material substrate 1A. 9 is a processing surface. Next, as shown in FIG. 3C, a predetermined electrode 10 is formed on the processed surface 9 of the piezoelectric material substrate 1A of the joined body 8A, and the acoustic wave element 11 can be obtained.

Here, as schematically shown in FIG. 4, the thermal resistance TR from the bonding surface 6 of the support substrate 3 to the bonding surface 5 of the piezoelectric material substrate 1 (1A) through the amorphous layer 7 is 1.0. ^{X10 −6} m ² K / W or more and 3.0 × 10 ⁻⁶ m ² K / W, so that the heat dissipation of the joined body 8 (8A) is improved and the piezoelectric material substrate 1 (1A) The bonding strength to the support substrate 3 can be improved. From this point of view, the thermal resistance TR from the bonding surface 6 of the support substrate 3 to the bonding surface 5 of the piezoelectric material substrate 1 (1A) through the amorphous layer 7 is 1.5 × 10 ⁻⁶ m ² K / More preferably, it is W or more, and more preferably 2.5 × 10 ⁻⁶ m ² K / W or less.

The thermal resistance TR from the bonding surface 6 of the support substrate 3 through the amorphous layer 7 to the bonding surface 5 of the piezoelectric material substrate 1 (1A) is a total value of the following three types of thermal resistance.
(1) Contact thermal resistance TRB at the interface B between the bonding surface 6 of the support substrate 3 and the amorphous layer 7
(2) Thermal resistance TR7 in the amorphous layer 7
(3) Contact thermal resistance TRA at the interface A between the amorphous layer 7 and the bonding surface 5 of the piezoelectric material substrate 1 (1A)

Here, the thermal resistance TR referred to in the present invention is a value obtained by dividing the thickness of the material by the thermal conductivity, and is defined as a thermal resistance per unit area (m ² K / W).
In addition, the amorphous layer 7 is a single layer in this example, but may be a plurality of layers.
The thermal resistance of the entire bonded body 8 (8A) is a total value obtained by adding (4) and (5) below in addition to (1) to (3).
(4) Thermal resistance TR1 in the piezoelectric material substrate 1 (1A)
(5) Thermal resistance TR3 in the support substrate 3

The material of the support substrate 3 is not particularly limited, but it is possible to use a semiconductor with high thermal conductivity such as Si, SiC, or GaN, or ceramics such as AlN or SiC. Can be adjusted.

The piezoelectric material substrate 1 (1A) used in the present invention is a lithium tantalate (LT) single crystal, a lithium niobate (LN) single crystal, or a lithium niobate-lithium tantalate solid solution. Since these have a high propagation speed of elastic waves and a large electromechanical coupling coefficient, they are suitable as surface acoustic wave devices for high frequencies and wideband frequencies.

The normal direction of the main surface of the piezoelectric material substrate 1 (1A) is not particularly limited. For example, when the piezoelectric material substrate 1 (1A) is made of LT, the X-axis is the propagation direction of the surface acoustic wave. It is preferable to use the one rotated by 32 to 55 ° from the Y axis to the Z axis around the center and the Euler angle display (180 °, 58 to 35 °, 180 °) since the propagation loss is small. When the piezoelectric material substrate 1 (1A) is made of LN, (a) a surface rotated by 37.8 ° from the Z axis to the -Y axis around the X axis, which is the propagation direction of the surface acoustic wave. It is preferable to use (0 °, 37.8 °, 0 °) because the electromechanical coupling coefficient is large, or (b) from the Y axis to the Z axis, centering on the X axis that is the propagation direction of the surface acoustic wave. It is preferable to use (180 °, 50 to 25 °, 180 °) in the direction rotated by 40 to 65 ° and the Euler angle display because high sound speed can be obtained. Further, the size of the piezoelectric material substrate 1 (1A) is not particularly limited. For example, the diameter is 100 to 200 mm and the thickness is 0.15 to 1 mm.

The thickness T1 (see FIG. 4) of the piezoelectric material substrate 1A is preferably 20 μm or less from the viewpoint of the performance of the acoustic wave element 11, and this can reduce the thermal resistance TR1 in the piezoelectric material substrate 1A. . On the other hand, the thickness T3 of the support substrate 3 is preferably 150 μm or more and more preferably 230 μm or more from the viewpoint of easy handling of the bonded body 8 (8A). On the other hand, if the support substrate 3 is thick, the thermal resistance of the entire bonded body 8 (8A) becomes high, so that it is preferably 750 μm or less, and more preferably 675 μm or less.

The thickness T7 of the amorphous layer 7 is selected so that the thermal resistance defined in the present invention can be achieved. From this viewpoint, 5 to 15 nm is preferable, and 7 to 10 nm is more preferable.

Preferably, the surface 1a of the piezoelectric material substrate 1 and the surface 3a of the support substrate 3 are irradiated with a neutralizing beam to activate the surfaces 1a and 3a.

When performing surface activation with a neutralized beam, it is preferable to generate and irradiate the neutralized beam using an apparatus as described in JP-A-2014-086400. That is, a saddle field type fast atomic beam source is used as the beam source. Then, an inert gas is introduced into the chamber, and a high voltage is applied to the electrodes from a DC power source. As a result, the saddle field type electric field generated between the electrode (positive electrode) and the casing (negative electrode) moves the electrons e, thereby generating atomic and ion beams by the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, so that a beam of neutral atoms is emitted from the fast atom beam source. From the viewpoint of the present invention, the atomic species constituting the neutralized beam is preferably an inert gas (argon, nitrogen, etc.). The voltage upon activation by beam irradiation is preferably 0.5 to 2.0 kV, and the current is preferably 50 to 200 mA.

Next, the activated surfaces 5 and 6 are brought into contact with each other and bonded in a vacuum atmosphere. The temperature at this time is room temperature, specifically, preferably 40 ° C. or lower, more preferably 30 ° C. or lower. The temperature at the time of joining is particularly preferably 20 ° C. or higher and 25 ° C. or lower. The pressure at the time of joining is preferably 100 to 20000 N.

In a preferred embodiment, the surface 1a of the piezoelectric material substrate 1 and the surface 3a of the support substrate 3 are planarized before irradiating the neutralized beam. Methods for flattening the surfaces 1a and 3a include lap polishing and chemical mechanical polishing (CMP). The flat surface is preferably Ra ≦ 1 nm, more preferably 0.3 nm or less.

Thereafter, it is preferable to improve the bonding strength by performing an annealing treatment. The annealing temperature is preferably 100 ° C. or higher and 300 ° C. or lower.

The joined bodies 8 and 8A of the present invention can be suitably used for the acoustic wave element 11.
As the acoustic wave element 11, a surface acoustic wave device, a Lamb wave element, a thin film resonator (FBAR), and the like are known. For example, a surface acoustic wave device has an IDT (Interdigital Transducer) electrode (also referred to as a comb-shaped electrode or a comb-shaped electrode) for exciting surface acoustic waves on the surface of a piezoelectric material substrate and an output side for receiving surface acoustic waves. IDT electrodes are provided. When a high frequency signal is applied to the IDT electrode on the input side, an electric field is generated between the electrodes, and a surface acoustic wave is excited and propagates on the piezoelectric material substrate. Then, the propagated surface acoustic wave can be taken out as an electric signal from the IDT electrode on the output side provided in the propagation direction.

The material constituting the electrode 10 on the piezoelectric material substrate 1A is preferably aluminum, aluminum alloy, copper, or gold, and more preferably aluminum or aluminum alloy. As the aluminum alloy, it is preferable to use Al mixed with 0.3 to 5% by weight of Cu. In this case, Ti, Mg, Ni, Mo, Ta may be used instead of Cu.

Example 1
According to the method described with reference to FIGS. 1 to 4, an acoustic wave device 11 shown in FIG.
Specifically, a 42Y-cut black LiTaO3 substrate (piezoelectric material substrate) 1 having a thickness of 0.25 mm and polished on both sides to a mirror surface, and a high resistance (≧ 2 kΩ · cm) Si having a thickness of 0.23 mm A substrate (support substrate) 3 was prepared. The substrate size is 100 mm for all. Next, the surface 1a of the piezoelectric material substrate 1 and the surface 3a of the support substrate 3 were cleaned, and particles were removed from the surfaces.

Next, the surface 1a of the piezoelectric material substrate 1 and the surface 3a of the support substrate 3 were surface activated, respectively. Specifically, both substrates were introduced into an ultrahigh vacuum chamber, and each surface was surface activated with an Ar atom beam for 50 seconds. Next, the activated bonding surfaces 5 and 6 of both substrates were brought into contact with each other at room temperature. A load of 200 kgf was applied by contacting the piezoelectric material substrate 1 side up. Next, the joined body 8 was taken out of the chamber, put in an oven in a nitrogen atmosphere for the purpose of increasing the joining strength, and held at 120 ° C. for 10 hours to obtain the joined body 8.

The thermal resistance of the obtained bonded body 8 was measured and calculated using a laser flash method.
The apparatus used for the measurement was LFA-502 manufactured by Kyoto Electronics Industry Co., Ltd. The sample surface was heated using an Nd-YAG laser with a wavelength of 1.06 μm, and the temperature change on the back surface was measured with an infrared sensor.
First, when only the LiTaO3 substrate (piezoelectric material substrate) 1 having a thickness of 0.25 mm was measured, the thermal resistance TR1 was 65.8 × 10 ⁻⁶ m ² K / W. The thermal resistance TR3 of the Si substrate (support substrate) 3 was 1.9 × 10 ⁻⁶ m ² K / W.

Next, the piezoelectric material substrate 1 of the obtained bonded body 8 was ground and polished, and finally the thickness of the piezoelectric material substrate 1A was 20 μm. The thermal resistance TR of the bonded body 8A thus polished was measured and found to be 9.8 × 10 ⁻⁶ m ² K / W. Further, when only the piezoelectric material substrate 1A having a thickness of 20 μm was measured, the thermal resistance TR1 of the piezoelectric material substrate 1A was 5.8 × 10 ⁻⁶ m ² K / W. From the measurement results of the piezoelectric material substrate 1A and the Si substrate (support substrate) 3, the thermal resistance from the bonding surface 6 of the support substrate 3 to the bonding surface 5 of the piezoelectric material substrate 1A through the amorphous layer 7 is measured. TR (calculated value): 2.1 × 10 ⁻⁶ m ² K / W (= 9.8 m ² K / W− (5.8 × 10 ⁻⁶ m ² K / W + 1.9 × 10 ⁻⁶ m ² K) / W)).

The IDT electrode 10 was provided on the piezoelectric material substrate 1A of the obtained bonded body 8A using photolithography. The material of the IDT electrode 10 is aluminum metal, the thickness is 4200 angstroms, the width of the electrode 10 is 0.5 μm, and 200 resonators are formed as a single resonator. The period λ of the electrode 10 was 4 μm so that the oscillation frequency was about 1000 MHz. 80 pairs of reflectors were provided on both sides of 200 pairs of IDT electrodes 10 to produce a 1-port acoustic wave element (SAW resonator) 11.

The bottom surface of the support substrate 3 of the acoustic wave element 11 was bonded to a copper heat dissipation jig having a thickness of 1 cm using silicon grease, a high frequency oscillator was connected, and the frequency characteristics were measured with a network analyzer. When the characteristics of the acoustic wave element 11 were observed by gradually increasing the input power of the oscillator, the resonance characteristics were not observed at all when the input power of 3.8 W was applied. Thereafter, the acoustic wave element 11 was taken out and the surface 9 of the piezoelectric material substrate 1A was observed. As a result, it was found that the IDT electrode 10 flew away as if it exploded.

Furthermore, the bonding strength between the piezoelectric material substrate 1A and the support substrate 3 was measured by a crack opening method, and the results are shown in Table 1.

(Example 2)
A joined body 8A and an acoustic wave device 11 were produced in the same manner as in Example 1. However, in Example 1, the final thermal resistance TR was adjusted as follows by setting the irradiation time with the Ar beam to 30 seconds instead of 50 seconds.
Thermal resistance TR of the entire joined body 8A: 8.7 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR1 of piezoelectric material substrate 1A: 5.8 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR3 of the support substrate 3: 1.9 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR (calculated value) from the bonding surface 6 of the support substrate 3 to the bonding surface 5 of the piezoelectric material substrate 1A through the amorphous layer 7: 1.0 × 10 ⁻⁶ m ² K / W

Regarding the obtained acoustic wave element 11, the input power of the oscillator was gradually increased, and the characteristics of the acoustic wave element 11 were observed. When 5.0 W input power was applied, no resonance characteristics were observed. It was. Thereafter, the acoustic wave element 11 was taken out and the surface 9 of the piezoelectric material substrate 1A was observed, and it was found that the IDT electrode 10 was broken. Table 1 shows the bonding strength.

Example 3
A joined body 8A and an acoustic wave device 11 were produced in the same manner as in Example 1. However, in Example 1, the final thermal resistance was adjusted as follows by setting the irradiation time with the Ar beam to 100 seconds.
Thermal resistance TR of the entire joined body 8A: 10.7 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR1 of piezoelectric material substrate 1A: 5.8 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR3 of the support substrate 3: 1.9 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR (calculated value) from the bonding surface 6 of the support substrate 3 to the bonding surface 5 of the piezoelectric material substrate 1A through the amorphous layer 7: 3.0 × 10 ⁻⁶ m ² K / W

Regarding the obtained acoustic wave element 11, the input power of the oscillator was gradually increased and the characteristics of the acoustic wave element 11 were observed. When 3.3 W input power was applied, no resonance characteristics were observed. It was. Thereafter, the acoustic wave element 11 was taken out and the surface 9 of the piezoelectric material substrate 1A was observed, and it was found that the IDT electrode 10 was broken. Table 1 shows the bonding strength.

(Comparative Example 1)
An IDT electrode 10 was formed on the piezoelectric material substrate 1 made of a lithium tantalate single crystal having a thickness of 0.25 mm in the same manner as in Example 1 to obtain an acoustic wave element 11. The obtained acoustic wave device 11 was measured for power resistance in the same manner as in Examples 1 to 3. As a result, the IDT electrode 10 was damaged at an input power of 1.6 W. Table 1 shows the bonding strength.

(Comparative Example 2)
A joined body 8A and an acoustic wave device 11 were produced in the same manner as in Example 1. However, in Example 1, the final thermal resistance TR was adjusted as follows by setting the irradiation time with the Ar beam to 20 seconds.
Thermal resistance TR of the entire joined body 8A: 8.5 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR1 of piezoelectric material substrate 1A: 5.8 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR3 of the support substrate 3: 1.9 × 10 ⁻⁶ m ² K / W,
Thermal resistance TR (calculated value) from the bonding surface 6 of the supporting substrate 3 to the bonding surface 5 of the piezoelectric material substrate 1A through the amorphous layer 7: 0.8 × 10 ⁻⁶ m ² K / W

Regarding the obtained acoustic wave element 11, the input power of the oscillator was gradually increased and the characteristics of the acoustic wave element 11 were observed. When 5.1W input power was applied, no resonance characteristics were observed. It was. Then, when the resonator was taken out and the surface 9 of the piezoelectric material substrate 1A was observed, it was found that the IDT electrode 10 was damaged. Table 1 shows the bonding strength.

 

 

Claims (1)

Support substrate,
A piezoelectric material substrate made of a material selected from the group consisting of lithium niobate, lithium tantalate, and lithium niobate-lithium tantalate, and a non-contact surface that contacts the bonding surface of the support substrate and the bonding surface of the piezoelectric material substrate Crystalline layer,
A joined body comprising:
The thermal resistance from the bonding surface of the support substrate to the bonding surface of the piezoelectric material substrate through the amorphous layer is 1.0 × 10 ⁻⁶ m ² K / W or more, 3.0 × 10 ^{−. It is 6} m < ² > K / W or less, The joined body characterized by the above-mentioned.

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