TWI798850B - Bonded substrate - Google Patents

Abstract

A bonded substrate according to the present disclosure includes a support substrate formed of silicon single crystal, a piezoelectric substrate formed of single crystal of lithium tantalate or single crystal of lithium niobate, and a bonding layer for bonding the support substrate and the piezoelectric substrate. The bonding layer is an amorphous bonding layer containing silicon and constituent elements of the piezoelectric substrate as main components and containing carbon.

Description

bonding substrate

The present invention relates to a bonding substrate.

A surface acoustic wave device (SAW device) is manufactured using, for example, a bonding substrate in which a piezoelectric substrate such as lithium tantalate (LT) or lithium niobate (LN) is bonded to a supporting substrate such as silicon. Such a bonded substrate uses an interlayer film on the bonded surface as described in Patent Document 1 and Patent Document 2.

If the bonding strength of the bonded substrate is low, it may be peeled off during processing, heat treatment, or other treatments. For example, if the bonded substrate is exposed to a high-temperature environment, there is a high possibility that the piezoelectric substrate and the supporting substrate will be peeled off due to the difference in thermal expansion between the piezoelectric substrate and the supporting substrate. In order to suppress peeling between the piezoelectric substrate and the support substrate, high bonding strength is required for the bonded substrate system.

[Prior Art Literature]

[Patent Document]

[Patent Document 1] Japanese Patent No. 3774782

[Patent Document 2] Japanese Patent No. 6621561

Conventional bonding substrates with low bonding strength have a high possibility of delamination between the piezoelectric substrate and the supporting substrate during processing or heat treatment as described above. Therefore, there is a need for a bonding substrate in which a piezoelectric substrate and a support substrate are firmly bonded.

The bonding substrate of the present disclosure includes: a supporting substrate formed of a silicon single crystal, a piezoelectric substrate formed of a lithium tantalate single crystal or a lithium niobate single crystal, and a substrate for bonding the supporting substrate and the piezoelectric substrate the bonding layer. The bonding layer is an amorphous bonding layer containing silicon and constituent elements of the piezoelectric substrate as main components and carbon.

The bonding layer of the bonding substrate of the present disclosure for bonding the support substrate and the piezoelectric substrate is an amorphous bonding layer containing silicon and constituent elements of the piezoelectric substrate as main components and carbon. Therefore, according to the present disclosure, it is possible to provide a bonding substrate in which a piezoelectric substrate and a supporting substrate are firmly bonded.

1: Bonding substrate

2: Support substrate

3: Piezoelectric substrate

4: Bonding layer

5: Fab gun

6: A plate with an opening (opening plate)

FIG. 1 is a schematic cross-sectional view of a bonded substrate according to an embodiment of the present disclosure.

Fig. 2 is a schematic diagram showing a high-speed atomic beam irradiation device.

3 is a graph showing the results of qualitative analysis of the bonding interface between the supporting substrate and the bonding layer by X-ray photoelectron spectroscopy (XPS) in the bonding substrate according to an embodiment of the present disclosure.

4 is a graph showing the results of analyzing the state of the bonding interface between the supporting substrate and the bonding layer by XPS in the bonding substrate according to an embodiment of the present disclosure.

Hereinafter, the bonding substrate of the present disclosure will be described based on the drawings. FIG. 1 is a schematic cross-sectional view of a bonded substrate according to an embodiment of the present disclosure.

A bonding substrate 1 of an embodiment shown in FIG. 1 has the following structure: a supporting substrate 2 formed of a single crystal of silicon, and a single crystal of lithium tantalate (LT) or a single crystal of lithium niobate (LN). The piezoelectric substrate 3 formed by crystallization is bonded via the bonding layer 4 formed between the support substrate 2 and the piezoelectric substrate 3 .

The supporting substrate 2 is formed of silicon single crystal, and is used to support the piezoelectric substrate 3 in the bonded substrate 1 . The thermal expansion coefficient of the support substrate 2 is smaller than that of the piezoelectric substrate 3 . The thickness of the supporting substrate 2 is not limited, and is, for example, 0.1 mm or more and 1.0 mm or less.

The piezoelectric substrate 3 is provided on the surface of the support substrate 2 via a bonding layer 4 described later. The piezoelectric substrate 3 is a piezoelectric material film supported by the supporting substrate 2 . The piezoelectric substrate 3 is formed of a single crystal of lithium tantalate or a single crystal of lithium niobate. The piezoelectric substrate 3 is in the form of a thin film processed to a thickness of about 2 μm or more and 50 μm or less by, for example, grinding and polishing. The piezoelectric substrate 3 only needs to be formed to be single-polarized.

The bonding layer 4 bonds the support substrate 2 and the piezoelectric substrate 3 . The bonding layer 4 is an amorphous bonding layer containing silicon as a constituent element of the support substrate 2 and constituent elements (lithium, tantalum, niobium, and oxygen) of the piezoelectric substrate 3 as main components, and carbon. "Main component" means that the target element is contained in the bonding layer 4 in a ratio of 50 atm% or more (hereinafter, unless otherwise specified, the element ratio of the bonding layer 4 means an atomic ratio (atm%)). The bonding layer 4 is composed of a first bonding layer mainly composed of silicon on the support substrate 2 side, and a second bonding layer mainly composed of constituent elements of the piezoelectric substrate 3 on the piezoelectric substrate 3 side. The existence of the bonding layer 4 and the first bonding layer and the second bonding layer can be confirmed by cross-sectional TEM (transmission electron microscope) images. The composition of the main component elements can be analyzed by energy dispersive X-rays (EDS: Energy dispersive X-ray spectroscopy) to confirm. The bonding layer 4 may contain, in addition to the constituent elements of the piezoelectric substrate 3 and carbon, an element (for example, Ar) irradiated through an activation process for bonding. The silicon-based material is preferably included in the first bonding layer at a ratio of about 50% to 99%, for example. The thickness of the bonding layer 4 is not limited, for example, it is preferably about 1 nm to 50 nm.

The bonding layer 4, that is, the first bonding layer and the second bonding layer preferably contains carbon in a ratio of, for example, 1% to 10%. By including carbon in the bonding layer 4 in such a ratio, the supporting substrate 2 and the piezoelectric substrate 3 are more firmly bonded. The presence or absence of carbon can be analyzed by, for example, X-ray photoelectron spectroscopy (XPS).

Si—C bonds may also exist at the bonding interface between the supporting substrate 2 and the bonding layer 4 . The interatomic distance of the Si-C bond (1.88Å) is closer to that of the Ta-O bond of lithium tantalate (1.89Å or 2.08Å) than the interatomic distance of the Si-Si bond (2.35Å) and that of niobate The interatomic distance of the Nb-O bond of lithium (1.92Å or 2.06Å). Therefore, crystal defects are less likely to occur at the bonding interface between the piezoelectric substrate 3 and the bonding layer 4 , so that the bonding strength between the support substrate 2 and the piezoelectric substrate 3 is further improved.

Whether or not Si—C bonds exist at the bonding interface between the supporting substrate 2 and the bonding layer 4 can be analyzed, for example, by the above-mentioned XPS. By XPS, the state of the bonding interface between the supporting substrate 2 and the bonding layer 4 can be analyzed, and if a peak originating from the Si—C bond is detected, the presence of the Si—C bond can be recognized.

The method of manufacturing the bonded substrate 1 according to one embodiment of the present disclosure is not limited. A bonded substrate 1 of one embodiment can be obtained, for example, by the following method.

First, the supporting substrate 2 and the piezoelectric substrate 3 are prepared. The support substrate 2 is formed of silicon single crystal. The piezoelectric substrate 3 is formed of a single crystal of lithium tantalate or a single crystal of lithium niobate. Hereinafter, regarding the piezoelectric substrate 3, the case of using a piezoelectric substrate formed of a single crystal of lithium tantalate will be described.

Regarding the substrate formed of a silicon single crystal and the substrate formed of a lithium tantalate single crystal, each surface can be planarized. For example, it is preferable to set the surface roughness of the surfaces to be bonded surfaces of the two substrates so that the arithmetic mean Ra is 1.0 nm or less.

Next, the surface of the support substrate 2 and the surface of the piezoelectric substrate 3 to be joint surfaces are activated by neutral particles (atoms or molecules) or charged particles (ions, plasma or electrons). The activation treatment method is not limited, for example, a method of irradiating fast atomic beams with a fast atomic beam (Fast atom beam, hereinafter sometimes described as "Fab") gun. If a Fab gun is used, for example, electrically neutralized high-concentration Ar atomic rays can be obtained.

The Fab gun system is configured as follows, for example. The plate-shaped anode electrode and the two cathode electrodes are arranged in parallel. An inert gas (Ar in this embodiment) is injected under high reduced pressure, and a high voltage is applied to the central anode electrode to make it glow discharge. The electric field distribution in the plasma is configured such that the acceleration direction of ions is perpendicular to the cathode electrode on the exit side. The accelerated ions are combined with electrons near the cathode electrode and emitted as high-speed atomic rays.

Therefore, the Fab released from the Fab discharge hole at the exit becomes a beam with excellent straightness. Therefore, by using a Fab gun, Fab irradiation was performed under high reduced pressure. As a result, inert films such as adsorbed molecules and oxide films on the surface of the substrate can be removed by inert gas rays (that is, Ar neutral atom rays) to expose the active surface.

Fig. 2 is a schematic diagram showing a high-speed atomic beam (Fab) irradiation device. The Fab irradiation device (bonding device) used in this embodiment includes two Fab guns 5 for the support substrate 2 and for the piezoelectric substrate 3 . Plates (opening plates) 6 having openings are respectively arranged at irradiation ports on the front of the Fab gun 5 . The supporting substrate 2 and the piezoelectric substrate 3 are arranged to face each other, and each is activated by Fab irradiation. Due to the configuration of the device, the Fab irradiates the support substrate 2 and the piezoelectric substrate 3 from an oblique direction.

Here, a carbon target can be placed in the bonding apparatus, and the target can also be irradiated with Fab or the like to make the bonding layer 4 contain carbon. The method of making the bonding layer 4 contain carbon is not limited to this method.

If Fab irradiation is performed on both the support substrate 2 and the piezoelectric substrate 3, the bonding strength will be further improved. Furthermore, the temperature of the two substrates at the time of bonding can be adjusted according to the irradiation amount (irradiation energy or irradiation time) or the time from the end of irradiation to bonding to adjust the amount of thermal expansion. For example, the amount of irradiation to the piezoelectric substrate 3 (lithium tantalate) having a thermal expansion coefficient larger than that of the support substrate 2 (silicon single crystal) can be reduced to suppress temperature rise.

The adjustment of the irradiation dose by the Fab gun can also be performed by adjusting the irradiation angle of the Fab relative to the irradiation surface. For example, the closer the irradiation angle of the Fab gun is to the perpendicular to the irradiation surface, the larger the irradiation amount will be. Furthermore, the irradiation amount can also be adjusted by the irradiation energy of the Fab gun. The irradiation energy can be controlled by adjusting the current value, accelerating voltage value, irradiation time, and especially the current value belonging to the Fab irradiation conditions. The irradiation energy required for the irradiation dose is not limited, but it is preferably about 20 kJ or more and 80 kJ or less.

Next, after activation by Fab irradiation, the support substrate 2 and the piezoelectric substrate 3 are bonded together. Specifically, the surface of the support substrate 2 activated by Ar and the surface of the piezoelectric substrate 3 are brought into contact with each other, and pressure is applied to bond them. Since the surface is activated, bonding can be performed without heating (ordinary temperature bonding). By such bonding, a bonding layer 4 is formed between the support substrate 2 and the piezoelectric substrate 3 . The pressure at the time of joining is preferably about 0.5kN to 20kN.

Next, the piezoelectric substrate 3 is subjected to polishing treatment and buffing treatment to reduce the thickness to a desired thickness (for example, about 2 μm to 50 μm). Thereafter, heat treatment is applied as necessary to obtain a bonded substrate 1 .

Specifically, a substrate (diameter: 100 mm) formed of a silicon single crystal and a substrate (diameter: 100 mm) formed of a lithium tantalate single crystal were used to obtain a bonding substrate 1 of an embodiment in the following steps.

First, the arithmetic average roughness Ra of the surface of the substrate (support substrate 2) formed of silicon single crystal and the surface of the substrate (piezoelectric substrate 3) formed of lithium tantalate single crystal is 1.0 nm or less. Apply planarization. Next, as shown in FIG. 2, two Fab guns 5 and a carbon-containing opening plate 6 are used to activate the surface of the substrate formed of silicon single crystals and the surface of the substrate formed of lithium tantalate single crystals. deal with. The irradiation energy of the Fab gun 5 was set to about 30 kJ.

Next, the activation-treated surfaces of the respective substrates are brought into contact with each other and pressed with a force of about 5 kN to form a joint between the substrate formed of a silicon single crystal and the substrate formed of a lithium tantalate single crystal. Layer 4 (thickness about 5nm). Thereafter, polishing and buffing treatments are performed and heat treatment is performed so that the thickness of the substrate formed of the lithium tantalate single crystal becomes about 15 μm. In this way, a bonded substrate 1 having a thickness of 245 μm in one embodiment was obtained.

For the obtained bonding substrate 1 of one embodiment, the first bonding layer was analyzed by XPS. The qualitative analysis results are shown in Figure 3, and the status analysis results are shown in Figure 4.

From the qualitative analysis results shown in Fig. 3, it can be known that the peak (C1s) originating from carbon exists. It is believed that this carbon system originates from the carbon of the opening plate 6 . In this qualitative analysis, the detection limit of carbon is around 1%. Therefore, it can be seen from the existence of the peak of carbon that the carbon system is included in the bonding interface between the supporting substrate 2 and the bonding layer 4 at a ratio of 1% or more. "Fab not irradiated" described in the graph of FIG. 3 and the graph of FIG. 4 described later represents the qualitative analysis results of the surface of the silicon single crystal substrate that was not subjected to activation treatment by Fab irradiation.

Furthermore, by Rutherford Backscattering Spectrometry (RBS: Rutherford Backscattering Spectrometry) with a detection limit of about 10% of carbon and nuclear reaction analysis (NRA: Nuclear Reaction Analysis) to analyze the bonding interface between the supporting substrate 2 and the bonding layer 4, no carbon was detected. Therefore, it can be seen that in the bonding substrate 1 of one embodiment, the ratio of carbon contained in the bonding layer 4 is about 1% to 10%.

Next, from the state analysis results shown in FIG. 4 , it can be known that the peak originating from the Si—C bond exists. Therefore, it can be seen that Si—C bonds exist at the bonding interface between the supporting substrate 2 and the bonding layer 4 .

A bonding substrate using lithium niobate as the piezoelectric substrate 3 instead of a substrate formed of a lithium tantalate single crystal, although not specifically shown, exhibits the same characteristics.

1: Bonding substrate

2: Support substrate

3: Piezoelectric substrate

4: Bonding layer

Claims (3)

A bonding substrate, comprising: a supporting substrate formed of a silicon single crystal, a piezoelectric substrate formed of a lithium tantalate single crystal or a lithium niobate single crystal, and a substrate for bonding the aforementioned supporting substrate and the aforementioned piezoelectric substrate and the aforementioned bonding layer is an amorphous layer containing silicon and the constituent elements of the aforementioned piezoelectric substrate as main components and carbon; the aforementioned carbon is contained in the aforementioned bonding layer at a ratio of 1 atm% to 10 atm%. The bonding substrate according to claim 1, wherein the bonding layer includes a first bonding layer, the first bonding layer is located on the support substrate side, and contains silicon as a main component and carbon. The bonding substrate according to claim 1 or 2, wherein a Si-C bond exists at a bonding interface between the supporting substrate and the bonding layer.

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