JP7420922B2 - bonded substrate - Google Patents

Description

The present disclosure relates to a bonded substrate of a piezoelectric substrate and a support substrate that becomes a surface acoustic wave element.

A surface acoustic wave device (SAW device) is fabricated using a bonded substrate made by bonding a piezoelectric substrate such as lithium tantalate (LT) or lithium niobate (LN) to a supporting substrate such as silicon. be done. When bonding these substrates together, it is known that if heat treatment is applied, the difference in expansion coefficients between the two substrates will cause the substrates to warp, peel, or crack. To avoid this problem, room-temperature bonding has been proposed, which provides high bonding strength immediately after bonding.

In other words, in room temperature bonding, a high-speed argon (Ar) neutral atomic beam is irradiated onto 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 bonded. Join together. At this time, an amorphous layer containing Ar is formed near the bonding interface.

Patent Documents 1 to 3 describe that the amorphous layer at the bonding interface contains Ar, and that by regulating the content, a bonded substrate with high bonding strength can be produced.

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

The bonded substrate of the present disclosure includes a support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate, and 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 is connected to the second amorphous layer via the bonding interface. The amount of increase in oxygen content in the portion where the layer changes to an amorphous layer is 15 at % or more.

Another bonded substrate of the present disclosure includes a support substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate, which are formed between the support substrate and the piezoelectric substrate. The amorphous layer bonded through the layers includes a first amorphous layer located on the support substrate side and a second amorphous layer located on the piezoelectric substrate side, and 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 facing the piezoelectric substrate (however, when adjacent measurement points (The interval is 0.4 nm or more and 0.8 nm or less, and measurement points II and III are located closest to the bonding interface), and at least one of the changes in oxygen content with respect to the interval between each measurement point is 30%/ It is more than nm.

Still another bonded substrate of the present disclosure is an amorphous substrate formed between the supporting substrate and the piezoelectric substrate, the supporting substrate made of a silicon single crystal, and the piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate. They are joined through a stratum 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 thickness of 0.4 nm or more and 0.4 nm or more from the support substrate to the piezoelectric substrate. When analyzing the contained elements at intervals of 8 nm or less, one of the two measurement points with the largest change in oxygen content with respect to the interval between each measurement point is the second amorphous one. It is within the stratum.

FIG. 1 is a cross-sectional view schematically showing a bonded substrate of the present disclosure. 1 is a transmission electron microscope (TEM) photograph of a bonded substrate according to an embodiment of the present disclosure. It is a graph showing the analysis results by energy dispersive X-ray analysis (EDS) of a bonded substrate produced by irradiating a high-speed Ar neutral atomic beam from a Fab gun with an irradiation energy of 60 kJ. It is a graph showing the EDS analysis results of a bonded substrate produced by irradiating a high-speed Ar neutral atomic beam from a Fab gun with an irradiation energy of 30 kJ. It is a graph showing the EDS analysis results of a bonded substrate produced by irradiating a high-speed Ar neutral atomic beam from a Fab gun with a current of irradiation energy of 15 kJ.

Hereinafter, a bonded substrate according to an embodiment of the present disclosure will be described with reference to the drawings. This embodiment provides a bonded substrate that can obtain sufficient bonding strength when bonding a piezoelectric substrate and a supporting substrate. FIG. 1 is a cross-sectional view schematically showing a bonded substrate of the present disclosure. FIG. 2 is a transmission electron microscope (TEM) photograph of a bonded substrate according to an embodiment of the present disclosure.

The bonded substrate 1 of this embodiment shown in FIG. 2 and a piezoelectric substrate 3 are bonded to each other via an amorphous layer 4 formed between them.

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

Piezoelectric substrate 3 is provided on the surface of support substrate 2 . The piezoelectric substrate 3 is a thin piezoelectric material film supported by the support substrate 2. The piezoelectric substrate 3 has a thickness of several μm to several tens of μm due to grinding, polishing, etc. The piezoelectric substrate 3 is preferably single polarized.

For the piezoelectric substrate 3, lithium tantalate or lithium niobate is used. 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 this embodiment includes 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 supporting substrate 2 and the piezoelectric substrate 3 are bonded together. Ar is Ar used to activate the bonded surfaces of the supporting substrate 2 and the piezoelectric substrate 3 in the bonded substrate manufacturing method 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 becomes a bonding interface 5 for bonding. The amorphous layer 4 has a total thickness of 1 nm or more and 50 nm or less.

FIG. 2 is a TEM photograph showing a cross section of the bonded substrate 1, showing the amorphous layer 4 and its vicinity. The presence of the amorphous layer 4 in the vicinity of the bonding interface 5 of the bonded substrate 1 can be confirmed from the visibility 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 shading (contrast) of a TEM image reflects the crystallinity and the type of element (difference in atomic weight), the existence of the first amorphous region 21 and the second amorphous region 31 is not obvious. , can be confirmed from the cross-sectional TEM image.

Furthermore, the amorphous layer 4 contains oxygen atoms (O) in addition to Si, Ta, and Ar. The oxygen atoms mainly originate from oxygen atoms contained in the surface oxide film of the support substrate 2 (Si) and oxygen that is a constituent element of the piezoelectric substrate 3. The Si oxide film is removed by irradiating the surface of the support substrate 2 with Ar neutral atoms, but the amorphous layer 4 formed at that time contains oxygen atoms (O) that could not be completely removed. It will be. From the viewpoint of bonding strength, it is considered preferable that the amount of oxygen derived from the Si oxide film is small. The present inventor considered that the oxygen content distribution (profile) in the amorphous layer 4 reflected the origin of oxygen and the bonding state, and verified a suitable oxygen content distribution (profile).

The amount of increase in oxygen content in the portion where the first amorphous layer 21 switches to the second amorphous layer 31 via the bonding interface 5 is preferably 15 atomic % or more, and preferably 45 atomic % or less. good. By setting the increase in oxygen content to 15 atomic % or more, it is possible to stably produce a bonded substrate 1 with high bonding strength.

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 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 are set as measurement points II and III, and the amount of oxygen (atomic %) at each measurement point II and III is measured, By taking the difference, the amount of increase in oxygen content can be obtained.

Measurement points II and III are shown in the graphs showing the EDS analysis results shown in FIGS. 3 to 5, respectively. 3 to 5 show that in Examples and Comparative Examples described later, high-speed Ar neutral atoms are irradiated onto each bonding surface of the support substrate 2 and the piezoelectric substrate 3 using a Fab (Fast atom beam) gun. The results of EDS analysis are shown for a bonded substrate 1 that is bonded at room temperature by pressurizing the bonding surfaces. Note that FIG. 5 corresponds to a comparative example of the present disclosure.

The distance between the measurement points II and III with the bonding interface 5 in between is preferably 0.4 nm or more and 0.8 nm or less. The amount of increase in the oxygen content can be determined by calculating the difference between the amounts of oxygen (atomic %) determined at measurement points II and III. According to the EDS analysis results shown in FIGS. 3 to 5, the 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. Note that 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.

If one of the measurement points II and III that sandwich the bonding interface 5 is very close to the bonding interface 5, there is a possibility that the measured information may include information about the adjacent region. Therefore, measurement points II and I were set in order in the first amorphous layer 21 toward the support substrate 2, and measurement points III and IV were set in order in the second amorphous layer 31 toward the piezoelectric substrate 3. At this time, it is preferable that at least one of the changes in oxygen content with respect to the intervals between each measurement point (ie, between I-II, II-III, and III-IV) is 30%/nm or more. Thereby, a bonded substrate 1 with high bonding strength can be stably produced.
Here, as described above, the interval between adjacent measurement points is set to 0.4 nm or more and 0.8 nm or less, and measurement points II and III are located closest to the bonding interface 5.

The amount of change in oxygen content with respect to the interval between measurement points can be determined from ΔO/L, where L is the interval between measurement points and ΔO is the amount of change in oxygen content.
According to the EDS analysis results shown in FIGS. 3 to 5, the amount of change in the oxygen content is 51 atomic %/nm between measurement points II and III shown in FIG. It is 36 atomic %/nm, and 24 atomic %/nm between 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 measurement points II and III closest to the bonding interface 5.

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

Next, a method for manufacturing the above-mentioned bonded substrate 1 will be explained.
First, a silicon single crystal substrate that will become the supporting 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 are preferably flattened. For example, the surface roughness of both substrates is preferably set to 1.0 nm or less in terms of arithmetic mean roughness Ra.

Next, the bonding surfaces of the silicon single crystal substrate and the lithium tantalate single crystal substrate are activated with Ar. For this purpose, for example, a Fab gun may be used to irradiate Ar neutral atoms. By using a Fab gun, it is possible to obtain an electrically highly concentrated neutralized Ar atomic beam. By using a Fab gun, Fab etching is performed under high reduced pressure, and inert films such as adsorbed molecules and oxide films on the substrate surface are removed with an inert gas beam, that is, an Ar neutral atomic beam, which is unstable and The active surface can be exposed.

At this time, in order to increase the amount of oxygen contained in the portion of the obtained bonded substrate 1 that switches from the first amorphous layer 21 to the second amorphous layer 31 via the bonding interface 5 to 15 atomic % or more, This can be achieved by particularly adjusting the current value among the Fab gun irradiation conditions for setting the irradiation energy: current value, accelerating voltage value, and irradiation time.

In addition, at least one of the changes in oxygen content with respect to the interval between each measurement point should be 30%/nm or more, and among the changes in oxygen content, the two measurement points with the largest change should be In order to set one of the measurement points within the second amorphous layer, the current value during irradiation of the Fab gun, and thus 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 a silicon single crystal substrate activated by Ar and a lithium tantalate single crystal substrate are bonded to each other. Since the surface is activated, bonding can be performed at room temperature. By this bonding, amorphous layers 4 (first amorphous region 21 and second amorphous region 31) are formed on both sides of 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 piezoelectric substrate 3. Next, heat treatment is performed as necessary to obtain the bonded substrate 1.
Note that in the above embodiments, the case where lithium tantalate is used as the piezoelectric substrate has been described, but similar effects can be obtained when lithium niobate is used instead of lithium tantalate.

Hereinafter, the bonded 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 sometimes referred to as LT substrate) and a silicon single crystal substrate (hereinafter sometimes 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 activated by irradiating Ar beams with an irradiation energy of 60 kJ using a Fab gun in a highly reduced pressure atmosphere, and then bonded. After bonding, the LT substrate was thinned to 15 μm to obtain a bonded substrate with a thickness of 245 μm. FIG. 2 is a cross-sectional TEM photograph of the bonded substrate obtained in Example 1.
EDS analysis was performed on the cross section of the obtained bonded substrate. That is, a plurality of measurements were performed at predetermined intervals on the cross section of the bonded substrate from one end of the support substrate to the other end of the piezoelectric substrate, and the concentrations of oxygen, Si, Ta, and Ar at each measurement point were measured. The results are shown in FIG.
In FIG. 3, the increase in oxygen content determined at measurement points II and III at the portion where the first amorphous layer switches to the second amorphous layer via the bonding interface was 27 at.%.
Furthermore, among the amount of change in oxygen content with respect to the interval between measurement points I and IV shown in Figure 3, the amount of change in oxygen content between measurement points II and III was 51 at%/nm. Ta.
A peel test was conducted on the obtained bonded substrate. 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 a peripheral toothed blade, and confirming peeling of the bonded portion due to cutting load by microscopic observation at 50x magnification.

(Example 2)
A bonded substrate was obtained in the same manner as in Example 1, except that Ar beam was irradiated by a Fab gun with irradiation energy of 30 kJ.
In FIG. 4, the increase in oxygen content determined at measurement points II and III at the portion where the first amorphous layer switches to the second amorphous layer via the bonding interface was 19 at.%.
Furthermore, among the amount of change in oxygen content with respect to the interval between measurement points I and IV shown in Figure 4, the amount of change in oxygen content between measurement points II and III was 36 at%/nm. Ta.
A peel test was conducted on the obtained bonded substrate 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 Ar beam was irradiated by a Fab gun with irradiation energy of 15 kJ.
In FIG. 5, the amount of increase in oxygen content determined at measurement points II and III at the portion where the first amorphous layer switches to the second amorphous layer via the bonding interface was 13 at.%.
Also, among the amount of change in oxygen content with respect to the interval between measurement points I and IV shown in Figure 5, the amount of change in oxygen content between measurement points II and III is 24 at%/nm. The amount of change in oxygen content between other measurement points I-II and III-IV also did not exceed 30 at.%/nm. The two measurement points where the amount of change in oxygen content was the largest were located in the first amorphous layer, and the amount of change was 31 atomic %/nm.
A peel test was conducted on the obtained bonded substrate 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 Bonding substrate 2 Support substrate 3 Piezoelectric substrate 4 Amorphous layer 21 First amorphous layer 31 Second amorphous layer 5 Bonding interface

Claims (10)

A supporting substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are joined via an amorphous layer formed between the supporting substrate and the piezoelectric substrate. 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 The amount of increase in oxygen content in the portion where the layer switches to the second amorphous layer is 15 atomic % or more,
The bonded substrate , wherein the ratio of silicon to tantalum or niobium at the bonding interface is 1.1 to 2.2 . The bonded substrate according to claim 1, wherein the average ratio of silicon to tantalum or niobium in the second amorphous layer is 0.5 to 0.7 . A supporting substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are joined via an amorphous layer formed between the supporting substrate and the piezoelectric substrate. 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 The amount of increase in oxygen content in the portion where the layer switches to the second amorphous layer is 15 atomic % or more,
A bonded substrate in which the average ratio of oxygen to tantalum or niobium in the second amorphous layer is 1.5 or more, and the average ratio of silicon to tantalum or niobium is 0.5 to 0.7. . The bonded substrate according to claim 1 or 3 , wherein the thickness of the amorphous layer is 1 nm or more and 50 nm or less. A supporting substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are joined via an amorphous layer formed between the supporting substrate and the piezoelectric substrate. 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 should be 0.4 nm or more and 0.8 nm or less, and measurement points II and III should be located closest to the bonding interface).
At least one of the changes in oxygen content with respect to the interval between each measurement point is 30%/nm or more,
The bonded substrate , wherein the ratio of silicon to tantalum or niobium at the bonding interface is 1.1 to 2.2 . The bonded substrate according to claim 5, wherein the average ratio of silicon to tantalum or niobium in the second amorphous layer is 0.5 to 0.7 . A supporting substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are joined via an amorphous layer formed between the supporting substrate and the piezoelectric substrate. 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 should be 0.4 nm or more and 0.8 nm or less, and measurement points II and III should be located closest to the bonding interface).
At least one of the changes in oxygen content with respect to the interval between each measurement point is 30%/nm or more,
A bonded substrate in which the average ratio of oxygen to tantalum or niobium in the second amorphous layer is 1.5 or more, and the average ratio of silicon to tantalum or niobium is 0.5 to 0.7. . A supporting substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are joined via an amorphous layer formed between the supporting substrate and the piezoelectric substrate. 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 analyzing the contained elements at intervals of 0.4 nm or more and 0.8 nm or less from the support substrate to the piezoelectric substrate,
Among the amount of change in oxygen content with respect to the interval between each measurement point, one measurement point among the two measurement points with the largest amount of change is within the second amorphous layer,
A bonded substrate , wherein the ratio of silicon to tantalum or niobium at the bonding interface between the first amorphous layer and the second amorphous layer is 1.1 to 2.2 . 9. The bonded substrate according to claim 8, wherein the average ratio of silicon to tantalum or niobium in the second amorphous layer is 0.5 to 0.7 . A supporting substrate made of a silicon single crystal and a piezoelectric substrate made of a single crystal of lithium tantalate or lithium niobate are joined via an amorphous layer formed between the supporting substrate and the piezoelectric substrate. 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 analyzing the contained elements at intervals of 0.4 nm or more and 0.8 nm or less from the support substrate to the piezoelectric substrate,
Among the amount of change in oxygen content with respect to the interval between each measurement point, one measurement point among the two measurement points with the largest amount of change is within the second amorphous layer,
A bonded substrate in which the average ratio of oxygen to tantalum or niobium in the second amorphous layer is 1.5 or more, and the average ratio of silicon to tantalum or niobium is 0.5 to 0.7. .