WO2021200861A1

WO2021200861A1 - Bonded substrate

Info

Publication number: WO2021200861A1
Application number: PCT/JP2021/013385
Authority: WO
Inventors: 賢英楢原; 光広梶原; 雅紀栗田; 陽介清水
Original assignee: 京セラ株式会社
Priority date: 2020-03-31
Filing date: 2021-03-29
Publication date: 2021-10-07
Also published as: JPWO2021200861A1; JP7420922B2

Abstract

This bonded substrate is obtained by bonding a support substrate containing silicon single crystals and a piezoelectric substrate containing lithium tantalate or lithium niobate single crystals with, interposed therebetween, an amorphous layer formed between the support substrate and the piezoelectric substrate. The amorphous layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side, and has an increase amount of contained oxygen of 15 atom% or more at a portion where layers are switched from the first amorphous layer to the second amorphous layer via a joining interface.

Description

Bonded substrate

The present disclosure relates to a bonding substrate between a piezoelectric substrate and a support substrate, which is a surface acoustic wave element.

The surface acoustic wave element (SAW element) is manufactured by using a bonded substrate in which a piezoelectric substrate such as lithium tantalate (LT) or lithium niobate (LN) is bonded to a support substrate such as silicon. Will be done. When joining these substrates, it is known that if heat treatment is applied, the substrates will warp, peel off, or crack due to the difference in expansion coefficient between the two substrates. In order to avoid this problem, room temperature bonding has been proposed in which high bond strength can be obtained immediately after bonding.

That is, in room temperature bonding, a high-speed argon (Ar) neutral atom beam is applied to the surface of the piezoelectric substrate and the surface of the support substrate to activate both surfaces, and then the surface of the piezoelectric substrate and the surface of the support substrate are attached. Join together. At that time, an amorphous layer containing Ar is formed near the bonding interface.

Patent Documents 1 to 3 describe that Ar is contained in the amorphous layer at the bonding interface, and a bonded substrate having high bonding strength can be produced by specifying the content.

Japanese Patent No. 6549054 Japanese Patent No. 5583875 Japanese Patent No. 5583876

In the bonding substrate of the present disclosure, a support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate form an amorphous layer formed between the support substrate and the piezoelectric substrate. It is joined through. The amorphous layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side, and the first amorphous layer to the second amorphous layer pass through the bonding interface. The amount of increase in oxygen contained in the portion that switches to the amorphous layer is 15 atomic% or more.

In the other bonded substrate of the present disclosure, a support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are formed between the support substrate and the piezoelectric substrate. The amorphous layer bonded via the layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side, and is said to be directed toward the support substrate. When measurement points II and I are set in order in the first amorphous layer, and measurement points III and IV are set in order in the second amorphous layer toward the piezoelectric substrate (however, of adjacent measurement points The interval shall be 0.4 nm or more and 0.8 nm or less, and measurement points II and III shall be the positions closest to the junction interface), and at least one of the changes in oxygen content with respect to the interval between each measurement point is 30% / It is nm or more.

In yet another bonding substrate of the present disclosure, a support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are formed between the support substrate and the piezoelectric substrate. It is joined via a layer. The amorphous layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side, and has a diameter of 0.4 nm or more from the support substrate to the piezoelectric substrate. When the contained elements were analyzed at intervals of 8 nm or less, one of the two measurement points with the largest change in the oxygen content with respect to the interval between the measurement points was the second amorphous. It is in the stratum.

It is sectional drawing which shows typically the bonding substrate of this disclosure. It is a transmission electron microscope (TEM) photograph of the bonding substrate which concerns on one Embodiment of this disclosure. It is a graph which shows the analysis result by the energy dispersive X-ray analysis (EDS) of the bonding substrate produced by irradiating a high-speed Ar neutral atom beam from a Fab gun with an irradiation energy of 60 kJ. It is a graph which shows the EDS analysis result of the bonding substrate produced by irradiating a high-speed Ar neutral atom beam from a Fab gun with an irradiation energy of 30 kJ. It is a graph which shows the EDS analysis result of the bonding substrate produced by irradiating a high-speed Ar neutral atom beam from a Fab gun with a current of an irradiation energy of 15 kJ.

Hereinafter, the bonding substrate according to the embodiment of the present disclosure will be described with reference to the drawings. The present embodiment provides a bonding substrate capable of obtaining sufficient bonding strength in bonding the piezoelectric substrate and the supporting substrate. FIG. 1 is a cross-sectional view schematically showing the bonding substrate of the present disclosure. FIG. 2 is a transmission electron microscope (TEM) photograph of the bonding substrate according to the embodiment of the present disclosure.

In the bonding substrate 1 of the present embodiment shown in FIG. 1, a support substrate 2 made of a single crystal of silicon and a piezoelectric substrate 3 made of a single crystal of lithium tantalate (LT) or lithium niobate (LN) are supported substrates. It has a structure bonded via an amorphous layer 4 formed between the 2 and the piezoelectric substrate 3.

The support substrate 2 supports the piezoelectric substrate 3 which is a thin film in the bonding substrate 1. The coefficient of thermal expansion of the support substrate 2 is smaller than the coefficient of thermal expansion of the piezoelectric substrate 3. A silicon single crystal substrate is used as the support substrate 2. In this embodiment, a silicon single crystal substrate is used as the support substrate 2.

The piezoelectric substrate 3 is provided on the surface of the support substrate 2. The piezoelectric substrate 3 is a thin-film piezoelectric material film supported by the support substrate 2. The piezoelectric substrate 3 has a thickness of several μm to several tens of μm by grinding, polishing, or the like. The piezoelectric substrate 3 is preferably unipolarized.

Lithium tantalate or lithium niobate is used for the piezoelectric substrate 3. In this embodiment, a case where lithium tantalate is used as the oxide single crystal layer 20 is taken as an example.

The amorphous layer 4 in the present embodiment contains tantalum (Ta), lithium (Li), oxygen (O), silicon (Si) and argon (Ar). The amorphous layer 4 is formed in the vicinity of the bonding interface when the support substrate 2 and the piezoelectric substrate 3 are bonded to each other. Ar is Ar used to activate the bonded surfaces of the support substrate 2 and the piezoelectric substrate 3 in the method for manufacturing a bonded substrate, which will be described later.

The amorphous layer 4 is divided into a first amorphous region 21 located on the support substrate 2 side and a second amorphous region 31 located on the piezoelectric substrate 3 side. The boundary between the first amorphous region 21 and the second amorphous region 31 is the bonding interface 5 for bonding. The amorphous layer 4 has a thickness of 1 nm or more and 50 nm or less as a whole.

FIG. 2 is a TEM photograph showing a cross section of the bonded substrate 1, showing the amorphous layer 4 and its vicinity. The existence of the amorphous layer 4 in the vicinity of the bonding interface 5 of the bonding substrate 1 can be confirmed from the appearance and shading of the crystal lattice in the cross-sectional TEM image.

In the first amorphous region 21 located on the support substrate side, the proportion of silicon (Si) is higher than the proportion of tantalum (Ta). On the other hand, in the second amorphous region 31 located on the piezoelectric substrate 3 side, the proportion of Ta is higher than the proportion of Si. Since the contrast of the TEM image reflects the crystallinity and the type of element (difference in atomic weight), it is possible that the first amorphous region 21 and the second amorphous region 31 exist. , Can be confirmed from the cross-sectional TEM image.

Further, the amorphous layer 4 contains an oxygen atom (O) in addition to Si, Ta and Ar. The oxygen atoms are mainly derived from oxygen atoms contained in the surface oxide film of the support substrate 2 (Si) and oxygen which is a constituent element of the piezoelectric substrate 3. The surface of the support substrate 2 is irradiated with Ar neutral atoms to remove the Si oxide film, but the amorphous layer 4 formed at that time contains oxygen atoms (O) that could not be completely removed. Will be. From the viewpoint of bond strength, it is considered preferable that the amount of oxygen derived from the Si oxide film is small. The present inventor considered that the distribution (profile) of the oxygen content in the amorphous layer 4 reflects the origin of oxygen and the bonding state, and verified a suitable distribution (profile) of the oxygen content.

The amount of increase in oxygen contained in the portion where the first amorphous layer 21 is switched to the second amorphous layer 31 via the bonding interface 5 is preferably 15 atomic% or more, and 45 atomic% or less. good. When the amount of increase in oxygen content is 15 atomic% or more, the bonding substrate 1 having high bonding strength can be stably produced.

The amount of increase in oxygen content can be determined as follows. Based on the TEM image, energy dispersive X-ray analysis (EDS) is performed on the contained elements at predetermined intervals from the support substrate 2 to the piezoelectric substrate 3. In the first amorphous layer 21 and the second amorphous layer 31, the positions closest to the bonding interface 5 were set as measurement points II and III, and the amount of oxygen (atomic%) at the respective measurement points II and III was measured. By taking the difference, the amount of increase in oxygen content can be obtained.

Measurement points II and III are shown in graphs showing the EDS analysis results shown in FIGS. 3 to 5, respectively. 3 to 5 show, in Examples and Comparative Examples described later, a Fab (Fast atom Beam) gun is used to irradiate each joint surface of the support substrate 2 and the piezoelectric substrate 3 with high-speed Ar neutral atoms. The result of EDS analysis is shown for the bonded substrate 1 in which the bonded surfaces are pressed against each other and bonded at room temperature. Note that FIG. 5 corresponds to a comparative example of the present disclosure.

The distance between measurement points II and III across the bonding interface 5 should be 0.4 nm or more and 0.8 nm or less. The amount of increase in oxygen content may be determined by the difference in the amount of oxygen (atomic%) obtained at measurement points II and III. According to the EDS analysis results shown in FIGS. 3 to 5, the amount of increase in oxygen content was 27 atomic% in FIG. 3, 19 atomic% in FIG. 4, and 13 atomic% in FIG. 5, which is a comparative example. The amount of oxygen is higher at the measurement point on the piezoelectric substrate 3 than at the measurement point on the support substrate 2.

When one of the measurement points II and III sandwiching the bonding interface 5 is in the immediate vicinity of the bonding interface 5, the measured information may include information on the adjacent region. Therefore, the measurement points II and I were set in the first amorphous layer 21 in order toward the support substrate 2, and the measurement points III and IV were set in the second amorphous layer 31 in order toward the piezoelectric substrate 3. When, at least one of the changes in oxygen content with respect to the interval between each measurement point (that is, between I-II, II-III, III-IV) is preferably 30% / nm or more. As a result, the bonding substrate 1 having high bonding strength can be stably produced.
Here, the distance between the adjacent measurement points is 0.4 nm or more and 0.8 nm or less, and the measurement points II and III are located closest to the bonding interface 5 as described above.

The amount of change in oxygen content with respect to the interval between measurement points can be obtained from ΔO / L when the interval between each measurement point is L and the amount of change in oxygen content is ΔO.
According to the EDS analysis results shown in FIGS. 3 to 5, the amount of change in the oxygen content was 51 atomic% / nm between the measurement points II and III shown in FIG. 3 and between the measurement points II and III shown in FIG. Is 36 atomic% / nm, and is 24 atomic% / nm between the measurement points II and III shown in FIG. 5, which is a comparative example. In the example, the amount of change in the oxygen content is 30 atomic% / nm or more between the measurement points II and III closest to the bonding interface 5.

As will be described later, in the embodiment, the point where the amount of change in oxygen content is maximum (the two measurement points where the amount of change in oxygen content with respect to the interval between each measurement point is the largest) is near the junction interface 5. On the other hand, in the comparative example, the two measurement points having the largest change in oxygen content are in the first amorphous layer 21. Therefore, when the contained elements are analyzed at intervals of 0.4 nm or more and 0.8 nm or less from the support substrate to the piezoelectric substrate, the change amount of the oxygen content with respect to the interval between the measurement points is the largest. It is preferable that one of the two large measurement points is in the second amorphous layer 31 in order to increase the bonding strength.

Next, the manufacturing method of the above-mentioned bonding substrate 1 will be described.
First, a silicon single crystal substrate to be the support substrate 2 is prepared. Further, as the piezoelectric substrate 3, a single crystal substrate of lithium tantalate or lithium niobate is used. In this embodiment, a lithium tantalate single crystal substrate is prepared.

The surfaces of the silicon single crystal substrate and the lithium tantalate single crystal substrate should be flattened. For example, the surface roughness of both substrates is preferably 1.0 nm or less in arithmetic average roughness Ra.

Next, the bonded surface of the silicon single crystal substrate and the lithium tantalate single crystal substrate is activated by Ar. For this, for example, a Fab gun may be used to irradiate Ar neutral atoms. A Fab gun can be used to obtain an electrically high concentration neutral Ar atom beam. By using the Fab gun, Fab etching is performed under high pressure, and the inert film such as adsorbed molecules and oxide film on the substrate surface is removed with an inert gas beam, that is, an Ar neutral atom beam, which is unstable. The active surface can be exposed.

At that time, in order to increase the amount of oxygen contained in the portion switching from the first amorphous layer 21 to the second amorphous layer 31 via the bonding interface 5 of the obtained bonding substrate 1 to 15 atomic% or more, It can be achieved by adjusting the current value, the acceleration voltage value, and the irradiation time, which are the Fab gun irradiation conditions for setting the irradiation energy.

Further, at least one of the changes in oxygen content with respect to the interval between the measurement points is set to 30% / nm or more, and among the changes in oxygen content, the two measurement points having the largest change. In order to make one of the measurement points in the second amorphous layer, the current value at the time of irradiation of the Fab gun, and therefore the irradiation energy may be adjusted in the same manner as described above. The irradiation energy is not particularly limited, but is preferably 20 kJ or more and 80 kJ or less.

After activation with Ar, the silicon single crystal substrate and the lithium tantalate single crystal substrate are bonded together. That is, the surfaces of the silicon single crystal substrate activated by Ar and the lithium tantalate single crystal substrate are bonded to each other. Since the surface is activated, it is possible to join at room temperature. By this bonding, amorphous layers 4 (first amorphous region 21 and second amorphous region 31) are formed on both sides of the bonding interface 5.

Next, the lithium tantalate single crystal substrate is ground and polished to a desired thickness (for example, 50 μm or less) to form a thin-film piezoelectric substrate 3. Next, heat treatment is performed as necessary to obtain a bonded substrate 1.
In the above embodiment, the case where lithium tantalate is used as the piezoelectric substrate has been described, but the same effect can be obtained when lithium niobate is used instead of lithium tantalate.

Hereinafter, the bonding substrate 1 of the present disclosure will be described in detail with reference to examples, but the present disclosure is not limited to the above embodiments and the following examples.

(Example 1)
A lithium tantalate single crystal substrate (hereinafter, may be referred to as LT substrate) and a silicon single crystal substrate (hereinafter, may be referred to as Si substrate) having a diameter of 100 mm and a thickness of 0.20 mm are prepared. The surfaces of these substrates were irradiated with an Ar beam with a Fab gun at an irradiation energy of 60 kJ under a high decompression atmosphere to activate the surface and then bonded. After bonding, the LT substrate was thinned to 15 μm to obtain a bonded substrate having a thickness of 245 μm. FIG. 2 is a cross-sectional TEM photograph of the bonding substrate obtained in Example 1.
EDS analysis was performed on the cross section of the obtained bonded substrate. That is, with respect to the cross section of the bonded substrate, a plurality of measurements were performed at predetermined intervals from one end of the support substrate to the other multiple ends of the piezoelectric substrate, and the concentrations of oxygen, Si, Ta, and Ar at each measurement point were measured. The result is shown in FIG.
In FIG. 3, the amount of increase in oxygen contained at the measurement points B and C at the portion where the first amorphous layer is switched to the second amorphous layer via the bonding interface was 27 atomic%.
Further, among the amount of change in oxygen content with respect to the interval between the measurement points A to D shown in FIG. 3, the amount of change in oxygen content between the measurement points BC was 51 atomic% / nm.
The obtained bonded substrate was subjected to a peeling test. As a result, no peeling or the like was observed between the support substrate and the piezoelectric substrate. The peeling test was carried out by cutting the bonded substrate using the outer peripheral tooth blade and confirming the peeling of the bonded portion due to the cutting load by microscopic observation at 50 times.

(Example 2)
A bonded substrate was obtained in the same manner as in Example 1 except that the Ar beam was irradiated with the Fab gun at an irradiation energy of 30 kJ.
In FIG. 4, the amount of increase in oxygen contained at the measurement points B and C at the portion where the first amorphous layer is switched to the second amorphous layer via the bonding interface was 19 atomic%.
Further, among the amount of change in oxygen content with respect to the interval between the measurement points A to D shown in FIG. 4, the amount of change in oxygen content between measurement points BC was 36 atomic% / nm.
The obtained bonded substrate was subjected to a peeling test in the same manner as in Example 1. As a result, no peeling or the like was observed between the support substrate and the piezoelectric substrate.

(Comparative Example 1)
A bonded substrate was obtained in the same manner as in Example 1 except that the Ar beam was irradiated with the Fab gun at an irradiation energy of 15 kJ.
In FIG. 5, the amount of increase in oxygen contained at the measurement points B and C at the portion where the first amorphous layer is switched to the second amorphous layer via the bonding interface was 13 atomic%.
Further, among the amount of change in the oxygen content with respect to the interval between the measurement points A to D shown in FIG. 5, the amount of change in the oxygen content between the measurement points BC is 24 atomic% / nm, and the like. The amount of change in oxygen content between the measurement points AB and CD did not exceed 30 atomic% / nm. The two measurement points with the largest change in oxygen content were in the first amorphous layer, and the change was 31 atomic% / nm.
The obtained bonded substrate was subjected to a peeling test in the same manner as in Example 1. As a result, some peeling was observed at the bonding interface between the support substrate and the piezoelectric substrate.

1 Bonded substrate 2 Support substrate 3 Piezoelectric substrate 4 Amorphous layer 21 First amorphous layer 31 Second amorphous layer 5 Bonded interface

Claims

A support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are bonded via an amorphous layer formed between the support substrate and the piezoelectric substrate. It is a bonded substrate
The amorphous layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side, and the first amorphous layer is interposed through a bonding interface. A bonded substrate in which the amount of increase in oxygen contained in the portion switching from the layer to the second amorphous layer is 15 atomic% or more.
The bonded substrate according to claim 1, wherein the thickness of the amorphous layer is 1 nm or more and 50 nm or less.
A support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are bonded via an amorphous layer formed between the support substrate and the piezoelectric substrate. It is a bonded substrate
The amorphous layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side.
When measurement points II and I are set in order in the first amorphous layer toward the support substrate, and measurement points III and IV are set in order in the second amorphous layer toward the piezoelectric substrate ( However, the distance between adjacent measurement points shall be 0.4 nm or more and 0.8 nm or less, and measurement points II and III shall be the positions closest to the junction interface).
A bonded substrate in which at least one of the changes in oxygen content with respect to the interval between measurement points is 30% / nm or more.
A support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are bonded via an amorphous layer formed between the support substrate and the piezoelectric substrate. It is a bonded substrate
The amorphous layer includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side.
When the contained elements were analyzed at intervals of 0.4 nm or more and 0.8 nm or less from the support substrate to the piezoelectric substrate,
A bonding substrate in which one of the two measurement points having the largest change in the oxygen content with respect to the interval between the measurement points is in the second amorphous layer.