Composite Wafer and Method for Manufacturing the Same

Abstract

The present invention provides a method for producing a composite wafer, the method comprising: a step for preparing a supporting substrate which is composed of either lithium tantalate or lithium niobate, and which is not substantially polarized; a step for preparing an active substrate which is polarized and is bonded to one surface of the supporting substrate, while being composed of either lithium tantalate or lithium niobate; a step for generating an interface by implanting ions into the active substrate; a step for bonding the supporting substrate and the active substrate to each other; a step for raising the temperatures of the supporting substrate and the active substrate having been bonded to each other; and a step for separating the active substrate at the interface. The present invention also provides this composite wafer.

Description

Technical Field

[0001] The present invention relates to a composite wafer and a method for manufacturing the same.

Background Art

[0002] There is a method in which a wafer of lithium tantalate (sometimes abbreviated as LT), into which hydrogen ions have been previously implanted through a metal film, is bonded to a lithium tantalate wafer and heat-treated to avoid problems caused by the difference in thermal expansion coefficients and peel off by heat (see, for example, Non-Patent Document 1). [Prior Art Documents] [Non-Patent Documents] [Non-Patent Document 1] "3-inch single crystal LiTaO3 films onto metallic electrode using SmartCut TM technology" Tauzin et al. ELECTRIC LETTERS, 19 th June 2008, Vol.44 No.13Problems to be Solved

[0003] When lithium tantalate or lithium niobate (sometimes abbreviated as LN) is used for the support wafer, charges are also generated in the thin-film LT or LN, which is the active layer, according to the polarization of LT or LN as the support wafer, and the characteristics are adversely affected. General Disclosure

[0004] In a first aspect of the present invention, the composite wafer is either lithium tantalate or lithium niobate, and includes a support substrate that is substantially non-polarized, and an active layer that is either lithium tantalate or lithium niobate and is polarized, and is bonded to one surface side of the support substrate.

[0005] An intervening layer disposed between the support substrate and the active layer may be further provided. The intervening layer may have insulating properties. The intervening layer may include at least one of SiO2, SiON, and SiN.

[0006] In a second aspect of the present invention, there is provided a method for manufacturing a composite wafer, comprising the steps of: preparing a support substrate which is either lithium tantalate or lithium niobate and is substantially non-polarized; preparing an active substrate which is either lithium tantalate or lithium niobate and is polarized, and which is bonded to one side of the support substrate; injecting ions into the active substrate to generate an interface; bonding the support substrate and the active substrate together; heating the bonded support substrate and active substrate; and peeling the active substrate at the interface.

[0007] Before the bonding step, a step of forming an intervening layer on at least one of the surfaces of the support substrate or the active substrate that are bonded to each other may be further provided. The intervening layer may have insulating properties. The intervening layer may include at least one of SiO2, SiON, and SiN. The intervening layer may be formed by either a PVD method or a CVD method.

[0008] Before the bonding step, a step of activating at least one of the surfaces of the support substrate or the active substrate that are bonded to each other may be further provided. The activation treatment may include plasma treatment. The step of preparing the support substrate may include a step of depolarizing the polarization that the support substrate originally had.

[0009] Note that the above summary of the invention does not list all the features of the present invention. Also, sub-combinations of these feature groups may also be inventions.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution means of the invention.

[0012] FIG. 1 schematically shows a cross-sectional view of a composite wafer 10 according to the present embodiment. The composite wafer 10 includes an LT substrate 400 as a support substrate, an intervening layer 200 disposed on one surface of the LT substrate 400, and an LT layer 110 as an active layer disposed on the surface of the intervening layer 200 opposite to the LT substrate 400.

[0013] The LT layer 110 is polarized. For example, the LT layer 110 is a single crystal and is electrically polarized in the Z-axis direction of the crystal even without an external electric field. As a result, the LT layer 110 has become an active layer that exhibits functions such as the piezoelectric effect.

[0014]

[0015] On the other hand, the LT substrate 400 is substantially non-polarized. Here, being substantially non-polarized includes not only a state where there is no polarization at all when there is no external electric field, but also a state of polarization that originally occurred but was not intentionally caused, a state of polarization that remains after a process of eliminating polarization, and a state of polarization that is polarized to such an extent that it does not interfere with the LT layer 110 from functioning, and is at least weaker than the polarization of the LT layer 110. Further, for example, it is preferable that the polarization of the LT substrate 400 is 0.5 pC / N or less in absolute value of the d33 meter.

[0016] The LT substrate 400 has a thickness of, for example, several hundred micrometers and provides mechanical strength when handling the composite wafer 10. Instead of the LT substrate 400, another substrate with a small difference in coefficient of thermal expansion from the active layer, such as an LN substrate, may be used.

[0017] The intervening layer 200 is disposed between the LT layer 110 and the LT substrate 400 in the thickness direction. The intervening layer 200 preferably has insulating properties and is preferably easy to process, such as being easy to mirror-polish. The intervening layer 200 may be at least one of SiO2, SiON, and SiN. The intervening layer 200 is not polarized in a state where no external voltage is applied.

[0018] FIG. 2 schematically shows each step of the manufacturing method of the composite wafer 10.

[0019] FIG. 2(a) shows the step of preparing the LT substrate 100. In the composite wafer 10, a part of the LT substrate 100 becomes the LT layer 110. Therefore, it can be said that the LT substrate 100 is an active substrate. The LT substrate 100 is, for example, cut out into a plate shape with a thickness of several hundred micrometers from an LT single crystal ingot formed by the pulling method. The LT substrate 100 has been subjected to a polarization treatment in which a high voltage is applied along the Z-axis of the crystal, so that polarization along the Z-axis occurs even without an external voltage.

[0020] FIG. 2(b) shows the step of implanting ions into the LT substrate 100. By implanting ions such as H + from one surface of the LT substrate 100, an ion implantation interface 300 is formed to a thickness of several hundred nanometers from the one surface. The one surface is a surface close to the side to be bonded in the bonding step.

[0021] FIG. 2(c) shows the step of forming the intervening layer 200 on the one surface of the LT substrate 100. The intervening layer 200 is formed, for example, by either the PVD method or the CVD method.

[0022] (d) of FIG. 2 shows the step of preparing the LT substrate 400 as a support substrate. The LT substrate 400, similar to the LT substrate 100, is cut out into a plate shape with a thickness of several hundred μm from an LT single crystal ingot formed, for example, by the pulling method. On the other hand, the LT substrate 400 has not been polarized like the LT substrate 100. The LT substrate 400 is not substantially polarized when no external voltage is applied.

[0023] Note that, the LT substrate 400 may be positively depolarized. For example, by heating the LT substrate 400 to a temperature above the Curie point (phase transition point), the polarization generated in the LT substrate 400 is destroyed. Note that the Curie point of LT is around 607 °C, and the Curie point of LN is around 1160 °C.

[0024] (e) of FIG. 2 shows the step of bonding the LT substrate 100 and the LT substrate 400 together. Before bonding the LT substrate 100 and the LT substrate 400 together, it is preferable to activate at least one of the surfaces to be bonded. When an interlayer 200 is provided on one surface of the LT substrate 100 as in this embodiment, the bonding surface with the LT substrate 400 is the surface of the interlayer 200 opposite to the LT substrate 100. Therefore, it is preferable to activate at least one of the bonding surfaces of the interlayer 200 and the LT substrate 400. The activation treatment includes, for example, plasma treatment.

[0025] On the above bonding surface, the LT substrate 100 and the LT substrate 400 are bonded together. In this embodiment, the LT substrate 100 and the LT substrate 400 are bonded together via the interlayer 20. When at least one of the bonding surfaces is activated, the bonding step may be performed at room temperature. Note that, instead of the activation treatment, the bonding may be performed at a high temperature of several hundred degrees (and optionally high pressure) in the bonding step.

[0026] (f) of FIG. 2 shows the step of peeling the LT substrate 100. In the step of peeling the LT substrate 100, first, the LT substrate 100, the intervening layer 200, and the LT substrate 400 bonded to each other are heated to, for example, about 200°C or higher. Further, the LT substrate 100 is physically peeled at the ion implantation interface 300. As a result, a part of the LT substrate 100 on the bonding surface side remains as the LT layer 110, and the composite wafer 10 is formed.

[0027] As described above, according to the present embodiment, by using LT substrates 100 serving as active layers and LT substrates 400 serving as support substrates having equal or nearly equal coefficients of thermal expansion, warping is less likely to occur during heat treatment, and the temperature can be raised to a temperature at which peeling can be performed. Further, since the LT substrate 400 serving as the support substrate is substantially not polarized, an adverse effect on the LT layer 110 which is the active layer can be avoided.

Example

[0028] SiO2 was deposited to a thickness of 700 nm on a 42°Y-cut LT wafer (with polarization) having a thickness of 0.35 mm and a diameter of 100 mm by PVD (sputtering) method, and polishing was performed to obtain 500 m. After subjecting the surface of this wafer to surface treatment by the plasma activation method on various support substrates, bonding was performed and the temperature was raised. FIG. 3 shows the recorded fracture temperature at that time. For those with a large difference in the coefficient of expansion, fracture occurred at a low temperature, and for those using LT or LN with no difference as the support substrate, fracture did not occur. Using LT or LN as the support substrate is considered effective from the viewpoint of preventing substrate cracking.

Example

[0029] SiO2 was deposited to a thickness of 700 nm on a 160°Y-cut LN wafer (with polarization) having a thickness of 0.35 mm and a diameter of 100 mm by PVD (sputtering) method, and polishing was performed to obtain 500 m. After subjecting the surface of this wafer to surface treatment by the plasma activation method on various support substrates, bonding was performed and the temperature was raised. The results were the same as in Example 1.

Example

[0030] A 42°Y-cut LT wafer with a thickness of 0.35 mm and a diameter of 100 mm (polarized) serving as the active layer was implanted with H + ions at 100 keV with a dose of 7.5e16 atoms / cm 2 . Subsequently, SiO 2 was deposited by PVD (sputtering) and polished. After the surface of this wafer was treated by plasma activation method on various support substrates, they were bonded together and heated to 180°C. Then, peeling was performed along the implant interface by the SiGen method (mechanical exfoliation method), the surface was polished, the thickness of LT was set to 500 nm, and heat treatment at 550°C was performed to obtain a composite wafer.

[0031] Resonators were fabricated on these composite wafers, and the Qmax value was measured around 2 GHz. The Q value represents the sharpness of the signal peak, and its value is an index for measuring the performance of the device. The results are shown in Figure 4. From these results, it was found that the support wafers using LT or LN without polarization had the best characteristics.

Example

[0032] Using a 160°Y-cut LN wafer with a thickness of 0.35 mm and a diameter of 100 mm (polarized) as the active layer, the same experiment as in Example 3 was conducted. The temperature increase before peeling was set to 450°C. The results showed the same tendency as in Example 3.

Example

[0033] In Example 1, even when the intermediate layer was deposited by CVD (chemical vapor deposition) method or the material of the intermediate layer was changed to SiON or SiN, the results were almost the same. It was found that the present invention does not depend on the deposition method or material of the intermediate layer.

[0034] As described above, the present invention has been described using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that the forms with such changes or improvements can also be included in the technical scope of the present invention.

[0035] In the claims, the description, and the drawings, for the operations, procedures, steps, stages, and other processes in the apparatus, system, program, and method shown, unless explicitly stated otherwise such as "earlier" or "preceding", and unless the output of a previous process is used in a subsequent process, it should be noted that they can be realized in any order. Regarding the operation flows in the claims, the description, and the drawings, even if for convenience, terms such as "first," "next," etc. are used for explanation, it does not mean that it is essential to be implemented in this order.

Description of Reference Numerals

[0036] 10 Composite wafer 100 LT substrate 110 LT layer 200 Intermediate layer 300 Ion implantation interface 400 LT substrate

Claims

1. Either lithium tantalate or lithium niobate, a substantially non-polarized support substrate, Either lithium tantalate or lithium niobate, a polarized active layer bonded to one side of the support substrate, And an intervening layer disposed on the mutually bonded surfaces of the support substrate and the active layer. The intervening layer is a composite wafer composed of at least one of SiO ２ , SiON and SiN.

2. The intervening layer is an insulating composite wafer according to claim 1.

3. Preparing a support substrate made of either lithium tantalate or lithium niobate and substantially non-polarized; Preparing an active substrate made of either lithium tantalate or lithium niobate and polarized; Injecting ions into the active substrate to generate an interface; Bonding the support substrate and the active substrate; Heating the bonded support substrate and active substrate; Peeling the active substrate at the interface; And comprising Further comprising, before the bonding step, forming an intervening layer on at least one of the mutually bonded surfaces of the support substrate or the active substrate; In the bonding step, the intervening layer is bonded to the other of the mutually bonded surfaces of the support substrate or the active substrate, The intervening layer is composed of at least one of SiO ２ , SiON and SiN, A method for manufacturing a composite wafer.

4. The intervening layer is an insulating method for manufacturing a composite wafer according to claim 3.

5. The manufacturing method of the composite wafer according to claim 3, wherein the intermediate layer is formed by either a PVD method or a CVD method.

6. The manufacturing method of the composite wafer according to any one of claims 3 to 5, further comprising a step of activating at least one of the surfaces of the support substrate or the active substrate that are to be bonded to each other before the bonding step.

7. The manufacturing method of the composite wafer according to claim 6, wherein the activation treatment includes plasma treatment.

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