Method for manufacturing a composite substrate provided with a piezoelectric single crystal film

Abstract

The present application provides a method for manufacturing a composite substrate provided with a piezoelectric single crystal film having good film thickness uniformity and not affected by performance deterioration due to ion implantation. The method for manufacturing a composite substrate 10 provided with a piezoelectric single crystal film 11 includes: a step (a) of subjecting a piezoelectric single crystal substrate 1 containing lithium tantalate or lithium niobate to ion implantation to form an ion-implanted layer 11, a step (c) of bonding a surface of the piezoelectric single crystal substrate 1 on which the ion-implanted layer 11 is formed to a temporary bonding substrate 2, a step (d) of separating the piezoelectric single crystal substrate 1 into the ion-implanted layer 11 and a remaining portion of the piezoelectric single crystal substrate 1, and forming the piezoelectric single crystal film 11 on the temporary bonding substrate 2, a step (f) of bonding a support substrate 3 to a surface of the piezoelectric single crystal film 11 opposite to the bonding surface of the temporary bonding substrate, and a step (g) of separating the temporary bonding substrate from the piezoelectric single crystal film 11.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a composite substrate for a surface acoustic wave device, the composite substrate being equipped with a piezoelectric single crystal film, such as lithium tantalate single crystal. Background Technology

[0002] As a component for frequency adjustment / selection in cellular phones, etc., surface acoustic wave (SAW) devices have been used, which have interdigital transducers (IDTs) on their piezoelectric substrates for exciting surface acoustic waves.

[0003] Surface acoustic wave devices require compactness, low insertion loss, and the ability to block stray waves from passing through the device. For this purpose, piezoelectric materials such as lithium tantalate (LiTaO3; abbreviated as LT) and lithium niobate (LiNbO3; abbreviated as LN) are used.

[0004] On the other hand, according to the communication standards of fourth-generation and later cellular phones, the frequency band spacing is narrow and the transmission and reception bandwidth is wide. Under this communication standard, the piezoelectric materials used in surface acoustic wave devices are required to have the smallest possible temperature-dependent performance changes.

[0005] When manufacturing a SAW device, variations in the thickness of the piezoelectric material cause variations in the SAW speed, therefore the film thickness should be controlled with high precision.

[0006] Non-Patent Document 1 or Non-Patent Document 2 reported that a substrate obtained by bonding an LT substrate to a sapphire substrate or a silicon substrate having a linear expansion coefficient smaller than that of the LT substrate and grinding the LT substrate into a thin film suppressed the effects of thermal expansion of oxide single crystals and thus had improved temperature performance.

[0007] Patent Document 1 describes a method for manufacturing a surface acoustic wave device, comprising: injecting ions into a piezoelectric substrate from one direction, and while heating the piezoelectric substrate, separating the piezoelectric substrate into a piezoelectric film and a remaining portion of the piezoelectric substrate at a high-concentration ion-implanted portion, wherein ions are injected into the remaining piezoelectric substrate portion at the highest concentration, thereby leaving the piezoelectric film on the side of a supporting substrate. List of reference documents Patent documents

[0008] Patent Document 1: International Publication No. 2012 / 086639 Non-patent literature

[0009] Non-patent literature 1: Transactions of The Institute of Electronics, Information and Communication Engineers, Vol. J98-A, No. 9, pp. 537-544 Non-Patent Document 2: Taiyo Yuden Co., Ltd., “Temperature compensation technology for SAW-Duplexer used in RF front end of smartphone.” [Online], November 8, 2012, Dempa Shimbun High Technology, retrieved March 20, 2012, Internet<URL:http: / / www.yuden.co.jp / jp / product / tech / column / 20121108.html> Summary of the Invention The problem to be solved by the present invention

[0010] The manufacturing method of the composite substrate, which includes a milled LT substrate, described in Non-Patent Document 1 or Non-Patent Document 2 has the following problem: the uniformity of film thickness deteriorates as the piezoelectric substrate becomes thinner.

[0011] The method for obtaining piezoelectric films via ion implantation described in Patent Document 1 can provide piezoelectric films with excellent film thickness uniformity, but its drawback is that the obtained piezoelectric films have degraded performance. As a result of the inventors' research into the causes of performance degradation, it has been found that through ion implantation, H... + Ions pass through the LT substrate, thereby causing Li in the ion implantation layer to... + Ion transfer leads to piezoelectric inhomogeneities in the ion-implanted layer. It has also been found that some Li... + The upward transfer and precipitation of ions onto the ion implantation surface of the ion implantation layer causes a decrease in the Li content at the separation interface (the exposed surface of the piezoelectric film), where the hydrogen ion concentration in the ion implantation layer is particularly high.

[0012] The inventors investigated the removal of the exposed surface of a piezoelectric film by polishing, which exhibited performance degradation. However, the reduction in Li content occurred not only on the exposed surface but also in a portion of the total thickness of the piezoelectric film extending from the exposed surface, amounting to 30% or more. Therefore, this portion should be removed by polishing. However, this leads to the following problem: depending on the amount of polishing, it impairs film thickness uniformity while preventing complete recovery of piezoelectricity.

[0013] In view of the above problems, the object of the present invention is therefore to provide a method for manufacturing a composite substrate equipped with a piezoelectric single crystal film with good film thickness uniformity, and which does not suffer performance degradation even when ion implantation is performed. Problem-solving methods

[0014] To achieve the above objectives, the present invention provides a method for manufacturing a composite substrate equipped with a piezoelectric single-crystal film, the method comprising the steps of: performing ion implantation treatment on one surface of a piezoelectric single-crystal substrate composed of lithium tantalate or lithium niobate to form an ion implantation layer in the piezoelectric single-crystal substrate, wherein the ion implantation layer is formed according to the hydrogen atom ion (H + ) is calculated as 1.0 × 10 16 atoms / cm 2 Or larger and 3.0×10 17 atoms / cm 2 Or even smaller ion implantation doses using ions containing hydrogen atoms (H) + ) and hydrogen molecular ion (H 2+ The steps include: ion implantation of at least one of the ionic materials; bonding the surface of a piezoelectric single crystal substrate on which the ion implantation layer is formed and a temporary bonding substrate; separating the piezoelectric single crystal substrate into the ion implantation layer and the remaining portion of the substrate, and forming a piezoelectric single crystal film with a thickness of 2 μm or less on the temporary bonding substrate; bonding a support substrate to the surface of the piezoelectric single crystal film opposite to the bonding surface of the temporary bonding substrate; and separating part or all of the temporary bonding substrate from the piezoelectric single crystal film.

[0015] The aforementioned temporary bonding substrate can be a single-crystal silicon substrate. In this case, the method for manufacturing the composite substrate according to the present invention may further include the following steps: performing ion implantation treatment on the bonding surface of the temporary bonding substrate and the piezoelectric single-crystal substrate, thereby forming an ion-implanted layer in the temporary bonding substrate. By separating the temporary bonding substrate into the ion-implanted layer of the temporary bonding substrate and its remaining portion, a portion of the temporary bonding substrate can be separated from the piezoelectric single-crystal film, and a single-crystal silicon film with a thickness of 2 μm or less can be formed on the piezoelectric single-crystal film.

[0016] When a temporary bonding substrate undergoes ion implantation, the ionized material contains hydrogen ions (H+). + ) and hydrogen molecular ion (H 2+ At least one of ), and in the form of a hydrogen atom ion (H + The ion implantation dose is calculated to be 1.0 × 10⁻⁶. 16 atoms / cm 2 Or larger and 2.0×10 17 atoms / cm 2Or even smaller. The dose of ions implanted into the temporary bonding substrate can be adjusted to be less than the dose implanted into the piezoelectric single crystal substrate.

[0017] The temporary adhesive substrate can be separated into an ion-implanted layer of the temporary adhesive substrate and the remainder thereof by selecting at least one of the group consisting of heat treatment, mechanical impact, spraying, ultrasonic vibration and light irradiation.

[0018] The material supporting the substrate can be selected from glass, silicon, quartz, sapphire, spinel, silicon carbide, silicon nitride, and aluminum nitride.

[0019] The ion-implanted layer and the remainder of the piezoelectric single crystal substrate can be separated by at least one of heat treatment, mechanical impact, spraying, ultrasonic vibration and light irradiation.

[0020] When the entire temporary bonding substrate is separated from the piezoelectric single crystal film, it can be done by at least one of machining, spraying, ultrasonic vibration, light irradiation and immersion in a chemical solution. Invention Effects

[0021] Therefore, according to the present invention, by bonding the surface of a piezoelectric single crystal substrate having an ion-implanted layer thereon to a temporary bonding substrate, separating the piezoelectric single crystal substrate into the ion-implanted layer and the remaining portion of the substrate to form an ion-implanted layer (piezoelectric single crystal film) of predetermined thickness on the temporary bonding substrate, bonding a support substrate to the exposed surface of the resulting piezoelectric single crystal film, and separating part or all of the temporary bonding substrate from the piezoelectric single crystal film, a support substrate having a piezoelectric single crystal film thereon can be obtained without extensive polishing of the piezoelectric single crystal substrate. Therefore, a composite substrate with a piezoelectric single crystal film having improved film thickness uniformity can be manufactured. Furthermore, since the separation interface of the ion-implanted layer showing a significant reduction in Li content is bonded to the support substrate, and the ion-implanted surface of the ion-implanted layer showing no reduction in Li content is placed on the surface opposite to the support substrate, it is not affected by performance degradation. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart illustrating one embodiment of the method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to the present invention. Figure 2 This is a TEM image showing a cross-section of the composite substrate of the comparative example. Detailed Implementation

[0023] An embodiment of a method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to the present invention will now be described with reference to the accompanying drawings, but the scope of the invention is not limited to or defined thereto.

[0024] like Figure 1As shown, the method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to this embodiment includes the step of subjecting a piezoelectric single crystal substrate 1 to ion implantation treatment to form an ion implantation layer 11 in the piezoelectric single crystal substrate 1. Figure 1 In step (a), the preparation of temporary adhesive substrate 2 ( Figure 1 (b) of the above describes the step of bonding the temporary adhesive substrate 2 to the surface of the piezoelectric single crystal substrate 1 on the side of the ion implantation layer 11. Figure 1 (c) of the above, the step of leaving an ion implantation layer 11 on the temporary bonding substrate 2 and separating the remaining portion of the piezoelectric single crystal substrate 1. Figure 1 (d) in the middle, the step of preparing the support substrate 3 ( Figure 1 (e) in the text refers to the step of bonding the support substrate 3 to the exposed surface of the ion implantation layer 11. Figure 1 (f) in the text, and the step of separating the temporary adhesive substrate 2 from the ion implantation layer 11 to obtain a composite substrate 10 having an ion implantation layer 11 as a piezoelectric single crystal film on the support substrate 3. Figure 1 (g)). Each of these steps will be described in detail below.

[0025] The piezoelectric single crystal substrate 1 prepared in step (a) is made of lithium tantalate (LiTaO3, abbreviated as LT) or lithium niobate (LiNbO3, abbreviated as LN). The piezoelectric single crystal substrate 1 can be used in the form of a wafer. The size of the wafer is not particularly limited, and it can have, for example, a diameter of 2 to 12 inches and a thickness of 100 μm to 1000 μm. As the piezoelectric single crystal substrate 1, products obtained in the form of wafers or by processing piezoelectric single crystal ingots into wafers through slicing or the like can be used.

[0026] In step (a), the surface of the piezoelectric single crystal substrate 1 to be laminated undergoes an ion implantation treatment Y. This treatment forms an ion-implanted layer 11 on the surface of the piezoelectric single crystal substrate 1 to be laminated. Hydrogen ions (H atoms) can be used as the ionic material for the ion implantation treatment Y. + ) and hydrogen molecular ion (H 2+ One or two of them. Using hydrogen atoms (H...) + The ion implantation dose is calculated to be 1.0 × 10⁻⁶. 16 atoms / cm 2 Or larger and 3.0×10 17 atoms / cm 2 Or smaller. Less than 1.0 × 10 16 atoms / cm 2 The dosage is unlikely to cause embrittlement of the ion implantation layer in subsequent steps. When the dosage exceeds 3.0 × 10⁻⁶, 17 atoms / cm 2During ion implantation, microcavities are formed on the ion implantation surface, resulting in irregularities on the wafer surface and making it difficult to achieve the desired surface roughness. The preferred ion implantation dose is 2.5 × 10⁻⁶. 16 atoms / cm 2 Or larger and 1.5 × 10 17 atoms / cm 2 Or smaller.

[0027] The ion acceleration voltage is preferably 50 keV or greater and 200 keV or less. The ion implantation depth can be changed by adjusting the acceleration voltage. The thickness of the ion implantation layer 11 substantially corresponds to the thickness of the piezoelectric single crystal film of the composite substrate 10 thus obtained.

[0028] This ion implantation process forms an ion-implanted layer 11 on the laminated surface of the piezoelectric single-crystal substrate 1. Through ion implantation, H… + Ions pass through the piezoelectric single crystal substrate 1, thereby causing Li to be injected into the ion implantation layer 11. + Ion transfer. Therefore, although it hardly causes a decrease in Li content in the surface portion 11a of the ion-implanted surface, a decrease in Li content is observed in the deep portion 11b with a high ion concentration.

[0029] The Li concentration of a piezoelectric single-crystal substrate 1 made of LT or LN can be measured by known methods and can be evaluated, for example, by Raman spectroscopy. It is known that there is an approximately linear relationship between the half-width at the Raman shift peak of the LT substrate and the Li concentration (Li / (Li+Ta) value). The composition of the piezoelectric single-crystal substrate at any location can be evaluated using an expression representing this relationship.

[0030] By measuring the Raman half-widths (WWHMs) of several samples with known compositions and varying Li concentrations, a reasonable expression showing the relationship between the WWHM of the Raman shift peak and the Li concentration can be obtained. Under the same Raman measurement conditions, reasonable expressions already published in the literature can be used. For example, the following numerical expression 1 can be used for lithium tantalate single crystals (see 2012 IEEE International Ultrasonics Symposium Proceedings, Pages: 1252-1255). Li / (Li+Ta)=(53.15-0.5FWHM1) / 100 (Numerical Expression 1) In this expression, "FWHM1" is approximately 600cm. -1 The half-width of the Raman shift peak. For details on the measurement conditions, see the above-mentioned literature.

[0031] As the temporary bonding substrate 2 to be prepared in step (b), a monocrystalline silicon substrate, a quartz substrate, or a sapphire substrate can be used, for example. Among these, a monocrystalline silicon substrate is preferred for the following reasons: Since the temporary bonding substrate 2 is ultimately removed, a material with excellent processing properties is suitable. The monocrystalline silicon substrate can be easily thinned by ion implantation, or removed chemically or physically by polishing, etching, etc. Furthermore, the LT substrate typically has 10 10 Ω·cm or greater resistivity, while single-crystal substrates, even for high-resistivity products, exhibit relatively low resistivity of less than 2 × 10⁻⁶. 5 The resistivity is Ω·cm. The piezoelectricity of the bond between the LT substrate and the monocrystalline silicon substrate can therefore be recovered by applying a voltage (repolarization treatment). The temporary bonding substrate 2 can be used in the form of a wafer. The wafer size is preferably 2 inches to 12 inches in diameter and 100 μm to 2000 μm in thickness.

[0032] The surfaces of the piezoelectric single-crystal substrate 1 to be laminated, the temporary bonding substrate 2 to be laminated, and the support substrate 3 to be laminated (which will be described in detail later) are each preferably processed to a mirror finish by grinding, polishing, or the like. The surface roughness RMS of the surfaces to be laminated is preferably 1.0 nm or less. By adjusting the RMS to 1.0 nm or less, these substrates can be laminated together. The term "RMS" is also referred to as "root mean square roughness Rq" as defined in JIS B 0601:2013.

[0033] Next, as Figure 1 As shown in step (c), the surfaces of the piezoelectric single-crystal substrate 1 to be laminated and the temporary bonding substrate 2 to be laminated are bonded together. There are no particular limitations on the bonding method in step (c); for example, direct bonding methods, such as room temperature bonding, diffusion bonding, plasma bonding, or surface-activated bonding methods, can be used, or they can be bonded using adhesives, etc. Among these bonding methods, room temperature bonding is particularly preferred to prevent peeling or defects caused by the large difference in the coefficients of thermal expansion between the piezoelectric single-crystal substrate 1 (e.g., LT substrate or LN substrate) and the temporary bonding substrate 2 (e.g., single-crystal silicon substrate). For bonding with adhesives, for example, UV-curable acrylic adhesives or adhesives mainly composed of thermosetting modified silicone can be used.

[0034] In room temperature bonding methods, one or both surfaces of the piezoelectric single-crystal substrate 1 and the temporary bonding substrate 2 to be laminated are surface activated before bonding. The surface activation treatment is not particularly limited, as long as it allows the surfaces to be laminated to bond at room temperature, and examples include beam irradiation, ozone water treatment, and UV ozone treatment. Examples of beam sources for beam irradiation include ion beams obtained by ionizing an inert gas (e.g., argon) into a beam and by using argon atoms as the beam. Beam irradiation is preferably performed in an atmosphere such as a vacuum atmosphere, and particularly preferably a high vacuum atmosphere.

[0035] Then, as Figure 1 As shown in step (d), while leaving the ion-implanted layer 11 on the temporary adhesive substrate 2, the remaining portion of the piezoelectric single-crystal substrate 1 is separated. Through this separation, a first composite material 4 having an ion-implanted layer (piezoelectric single-crystal film) 11 formed on the temporary adhesive substrate 2 can be obtained. In this first composite material 4, the surface portion 11a of the ion-implanted layer 11 showing no decrease in Li content is bonded to the temporary adhesive substrate 2, and the deeper portion 11b showing a decrease in Li content is exposed.

[0036] As a method for separating the piezoelectric single crystal substrate 1 into the ion implantation layer 11 and the remaining portion of the substrate, heat treatment, mechanical shock, spraying, ultrasonic vibration and light irradiation may be used alone, or in combination of two or more methods.

[0037] To facilitate separation via heat treatment, the first composite material 4 is preferably heated to 100°C or higher and 200°C or lower to generate microbubbles in the ion-implanted layer from the implanted hydrogen ions. The heating time is preferably 50 minutes or longer and 100 hours or less. Through this heat treatment, the piezoelectric single-crystal substrate 1 can be separated into the ion-implanted layer 11 and the remainder of the substrate.

[0038] To achieve separation by mechanical impact, a tool such as a wedge-shaped blade (not shown) can be used. Examples of materials for such tools include plastics (e.g., polyetheretherketone), metals, zirconium oxide, silicon, and diamond. The tool can have an acute-angled shape. For example, separation by mechanical impact is achieved by contacting the tool with the end of the ion-implanted layer 11 and applying an impact to it from the side surface of the first composite material 4, causing gradual dissociation towards the end on the side opposite to the aforementioned surface. Therefore, the piezoelectric single-crystal substrate 1 can be released into the ion-implanted layer 11 and the remainder of the substrate.

[0039] For separation by jetting, a fluid jet, such as an air jet or a liquid jet, can be used. As a fluid jet, such as an air jet or a liquid jet, high-pressure air or high-pressure water with a flow rate of about 10 L / min to 1000 L / min is preferably used. For example, separation by jetting is achieved by continuously or intermittently jetting fluid from the side surface of the first composite material 4 to the end of the ion implantation layer 11, thereby releasing the piezoelectric single-crystal substrate 1 into the ion implantation layer 11 and the remainder of the substrate.

[0040] To achieve separation via ultrasonic vibration, ultrasonic vibration tools, such as ultrasonic cutters or water tanks equipped with ultrasonic vibrators, such as ultrasonic cleaners, can be used. The ultrasonic vibration tool has a wedge-shaped blade capable of applying ultrasonic waves via the vibrator. By bringing the blade into contact with the end of the ion-implanted layer 11 from the side surface of the first composite material 4, the ion-implanted layer 11 can be made brittle, and the piezoelectric single-crystal substrate 1 can be separated into the ion-implanted layer 11 and the remaining portion of the substrate. In this case, the frequency of the ultrasonic waves is not particularly limited, but for example, 20 to 40 kHz is preferred. When using a water tank equipped with an ultrasonic vibrator, the first composite material 4 is immersed in the water tank, and ultrasonic vibration is applied to the ion-implanted layer 11 by the liquid, causing the ion-implanted layer 11 to become brittle, thereby separating the piezoelectric single-crystal substrate 1 into the ion-implanted layer 11 and the remaining portion of the substrate. In this case, the frequency of the ultrasonic waves is not particularly limited, and for example, 26 kHz to 1.6 MHz is preferred. The immersion time in the water tank is preferably, for example, 1 minute to 60 minutes.

[0041] For separation by light irradiation, for example, visible light irradiation is preferred. The ion-implanted layer can be embrittled and separated by a mechanism that allows for easy absorption of visible light and selective acceptance of energy near the ion-implantation interface formed within the amorphous piezoelectric single-crystal substrate 1. The visible light source is preferably, for example, rapid thermal annealing (RTA), a green laser, or a flash lamp.

[0042] After separating the piezoelectric single-crystal substrate 1 into the ion-implanted layer (piezoelectric single-crystal film) 11 and the remainder of the substrate as described above, the piezoelectric single-crystal film 11 on the temporary bonding substrate 2 can be repolarized if desired. The repolarization process can be performed by applying a voltage to the first composite material 4. Alternatively, known repolarization processes can be performed.

[0043] The support substrate 3 prepared in step (e) will be the support substrate for the final composite substrate 10, and is preferably made of a material selected from glass, silicon, quartz, sapphire, spinel, silicon carbide, silicon nitride, and aluminum nitride. The temporary bonding substrate 2 can be used in the form of a wafer. In terms of size, the wafer preferably has a diameter of 2 inches to 12 inches. The surface of the support substrate 3 to be laminated is preferably a mirror finish obtained by a process such as grinding and polishing as described above.

[0044] Furthermore, the exposed surface of the ion-implanted layer 11 of the first composite material 4 is preferably adjusted to have a surface roughness RMS of 1.0 nm or less by means of a process such as grinding and polishing. This polishing allows for adjustment of the thickness of the ion-implanted layer (piezoelectric single-crystal film) 11.

[0045] Then, as Figure 1 As shown in step (f), the support substrate 3 is laminated and bonded to the exposed surface of the piezoelectric single crystal film 11 of the first composite material 4 to obtain a second composite material 5 having a temporary adhesive substrate 2, a piezoelectric single crystal film 11 and a support substrate 3 stacked in the listed order.

[0046] The first composite material 4 and the supporting substrate 3 are bonded together, for example, by a direct bonding method, such as a room temperature bonding method, a diffusion bonding method, a plasma bonding method, or a surface activation bonding method, depending on the material of the supporting substrate 3. When there is a large difference in the coefficient of thermal expansion between the piezoelectric single crystal film 11 (e.g., LT or LN) and the supporting substrate 3, a room temperature bonding method is preferred to suppress peeling or defects. In the room temperature bonding method, as in step (c) above, one or both of the exposed surfaces of the piezoelectric single crystal film 11 of the first composite material 4 and the surfaces of the supporting substrate 3 to be laminated undergo surface activation treatment. Regarding the surface activation treatment, as in step (c) above, for example, beam irradiation treatment is performed.

[0047] Then, as Figure 1 As shown in step (g), the temporary adhesive substrate 2 is separated from the piezoelectric single crystal film 11 of the second composite material 5 to expose the piezoelectric single crystal film 11, thereby obtaining a composite substrate 10 having the piezoelectric single crystal film 11 on the support substrate 3. Separation methods used herein, such as mechanical processing, spraying, ultrasonic vibration, light irradiation, and immersion in a chemical solution, can be used alone or in combination of two or more.

[0048] To achieve separation by mechanical processing, one or both of grinding and polishing may be performed. For grinding, the exposed surface of the temporary bonding substrate 2 is ground, for example, with various numbers of grinding stones. For polishing, for example, the exposed surface of the temporary bonding substrate 2 is polished with a slurry containing cerium oxide particles or colloidal silica (this polishing may also be referred to as "grind polishing"). The temporary bonding substrate 2 can be removed from the piezoelectric single crystal film 11 by this process.

[0049] For separation by jetting, a fluid jet, such as an air jet or a liquid jet, can be used. As a fluid jet, such as an air jet or a liquid jet, high-pressure air or high-pressure water with a flow rate of about 10 L / min to 1000 L / min is preferably used. For example, separation by jetting is achieved by continuously or intermittently jetting fluid from the side surface of the second composite material 5 to the end of the temporary adhesive substrate 2, thereby separating the temporary adhesive substrate 2 from the piezoelectric single crystal film 11.

[0050] To separate the materials using ultrasonic vibration, an ultrasonic vibrating tool, such as an ultrasonic cutter or a water tank equipped with an ultrasonic vibrator (e.g., an ultrasonic cleaner), can be used. The ultrasonic vibrating tool has a wedge-shaped blade capable of applying ultrasonic waves via the vibrator. By bringing the blade into contact with the end of the temporary adhesive substrate 2 from the side surface of the second composite material 5, the temporary adhesive substrate 2 can be separated from the piezoelectric single-crystal film 11. In this case, the frequency of the ultrasonic waves is not particularly limited; for example, 20 kHz to 40 kHz is preferred. Alternatively, the second composite material 5 can be immersed in a water tank equipped with an ultrasonic vibrator, and ultrasonic vibration can be applied by the liquid, thus separating the temporary adhesive substrate 2 from the piezoelectric single-crystal film 11. In this case, the frequency of the ultrasonic waves is not particularly limited; for example, 26 kHz to 1.6 MHz is preferred. The immersion time in the water tank is preferably, for example, 1 minute to 60 minutes.

[0051] For separation by light irradiation, visible light irradiation is preferred, for example. This separation can be achieved by a mechanism in which visible light is readily absorbed and energy selectively accepted near the interface between the temporary bonding substrate 2 and the amorphous piezoelectric single crystal film 11. The visible light source is preferably, for example, rapid thermal annealing (RTA), a green laser, or a flash lamp.

[0052] When adhesives are used for bonding, separation can be achieved by immersion in a chemical solution. As a chemical solution, hydrocarbon solvents such as p-menthane and polar solvents such as N-methylpyrrolidone, dimethylformamide, and dimethyl sulfoxide are preferred, although this depends on the curing type of the adhesive used. The immersion time is preferably 1 to 10 minutes, more preferably 3 to 5 minutes.

[0053] After separation, if necessary, the exposed surface of the piezoelectric single crystal film 11 can undergo SC-1 cleaning (cleaning with a mixture of ammonia, hydrogen peroxide and pure water). SC-1 cleaning can oxidize, etch and remove residues of the temporary bonding substrate 2, such as silicon, remaining on the exposed surface of the piezoelectric single crystal film 11.

[0054] In the composite substrate 10 thus obtained and having a piezoelectric single crystal film 11 on the supporting substrate 3, the deep portion 11b of the piezoelectric single crystal film 11 exhibiting a reduced Li content is bonded to the supporting substrate 3, while the surface portion 11a of the piezoelectric single crystal film without a reduced Li content is exposed. Since the surface portion 11a of the piezoelectric single crystal film 11 does not exhibit a reduced Li content, even if there is a portion of the piezoelectric single crystal film 11 exhibiting a reduced Li content, it is located on the exposed surface side of the composite substrate 10, thus suppressing the degradation of the film's performance as a piezoelectric material. Furthermore, the piezoelectric single crystal film 11 is formed on the supporting substrate 3 without polishing the extensive ion-implanted layer 11 of the piezoelectric single crystal substrate 1, resulting in good film thickness uniformity.

[0055] Already referenced Figure 1 A method for manufacturing a composite substrate equipped with a piezoelectric single-crystal film according to this embodiment has been described, but the invention is not limited thereto. It may include many modifications, such as changing the order of some of the steps described above or combining another new step. For example, when using a single-crystal silicon substrate as a temporary bonding substrate 2, the surface of the temporary bonding substrate 2 is subjected to ion implantation treatment, thereby forming an ion-implanted layer before the temporary bonding substrate 2 is bonded to the piezoelectric single-crystal substrate 1. By forming an ion-implanted layer on the temporary bonding substrate 2 made of single-crystal silicon as described above, in step (g) of separating the temporary bonding substrate 2, the ion-implanted layer of the temporary bonding substrate 2 can remain on the piezoelectric single-crystal film 11 of the second composite material 5, and the remaining portion of the temporary bonding substrate 2 can be separated from the second composite material 5 by using, individually or in combination of two or more methods such as heat treatment, mechanical impact, spraying, ultrasonic vibration, and light irradiation, similar to step (d).

[0056] Hydrogen atoms (H) can be used + ) and hydrogen molecular ion (H 2+ One or two of the following are used as ionic materials to perform ion implantation on the temporary bonding substrate 2. Hydrogen ions (H+) are used as the ionic material. + The preferred ion implantation dose is 1.0 × 10⁻⁶. 16 atoms / cm 2 Or larger and 2.0×10 17 atoms / cm 2 Or smaller.

[0057] When the temporary bonding substrate 2 is separated in this manner, the ion-implanted layer of the temporary bonding substrate 2 remains on the piezoelectric single-crystal film 11. The ion-implanted layer of the temporary bonding substrate 2 can be removed from it or left on it. Removal can be achieved by performing SC-1 cleaning, thereby oxidizing, etching, and removing the ion-implanted layer from the temporary bonding substrate 2. Alternatively, the ion-implanted layer of the temporary bonding substrate 2 can remain as a single-crystal silicon film, depending on the intended use of the composite substrate 10. In this case, the composite substrate thus obtained can be a composite substrate having a support substrate, a piezoelectric single-crystal film, and a single-crystal silicon film stacked in the listed order. Example

[0058] Examples and comparative examples will be described below, but the invention is not limited to or restricted by them.

[0059] Example 1 As piezoelectric single-crystal substrates, temporary bonding substrates, and support substrates, LiTaO3 substrates (consistent composition: Li content 48.5%) with a thickness of 400 μm and a single-sided mirror surface, 42° rotated Y-shaped cut, were prepared, respectively; a single-crystal silicon substrate with a thickness of 400 μm and a single-sided mirror surface; and a sapphire substrate with a thickness of 400 μm and a single-sided mirror surface. It was confirmed that all three substrates had a mirror-side roughness RMS of 1.0 nm or less. Then, in the presence of hydrogen ions (H... + The dosage is 1×10 17 atoms / cm 2 Furthermore, under an accelerating voltage of 160 keV, ion implantation was performed on the mirror side of the LT substrate to form an ion implantation layer.

[0060] Next, an LT substrate and a single-crystal silicon substrate were bonded together using a room-temperature bonding method described in the non-patent literature “Takagi H et al., Room-temperature wafer bonding using argon beam activation,” from Proceedings-Electrochemical Society (2001), 99-35 (Semiconductor Wafer Bonding: Science, Technology, and Applications V), 265-274) to obtain a bonded substrate. More specifically, after the mirror surface of a clean substrate placed in a high-vacuum chamber was irradiated with a high-speed argon atomic beam (i.e., a neutralized ion beam) and subjected to activation treatment, the LT substrate and the silicon substrate were bonded together at their activated mirror surfaces. The resulting bonded substrate was heated to 120°C, and the remaining portion of the LT substrate was released from the bonded substrate while leaving the ion-implanted layer of the LT substrate on the silicon substrate side. Thus, a silicon-borne LT (LT-on-silicon) first composite material having an LT film (piezoelectric single-crystal film) thinned to a thickness of 900 nm on its silicon substrate was fabricated.

[0061] Then, after applying a voltage at 650°C and 300V to induce repolarization in the obtained first composite material, the exposed surface of the LT film was polished to remove a 30nm thick portion from the surface, and the surface roughness RMS was adjusted to 1.0nm or less. The obtained composite material was bonded to a sapphire substrate prepared as a support substrate using a room temperature bonding method to obtain a second composite material of sapphire / LT / monocrystalline silicon. The monocrystalline silicon substrate portion of the second composite material was removed by grinding and polishing, as well as SC-1 cleaning, to fabricate the LT-on-sapphire composite substrate.

[0062] The Raman shift peak of the LT composite substrate on sapphire obtained therefrom was measured at 600 cm⁻¹ using a laser Raman spectrometer (HORIBA Scientific product, LabRam HR series, He-Ne ion laser, spot size: 1 μm, room temperature). -1 The half-width (FWHM1) near the Li content is used as an index, and the Li concentration is calculated from the half-width according to the numerical expression 1 described above. Therefore, the Li content in the exposed surface of the LT film (the ion-implanted surface of the initial LT substrate) is 48.5%. It has been confirmed that the Li content in the LT substrate does not decrease from that in the initial LT substrate.

[0063] Example 2 Similar to Example 1, except that the dose is 1×1017 atoms / cm 2 Furthermore, under an accelerating voltage of 130 keV, hydrogen ion (H+) ionization was also performed on the mirror side of a single-crystal silicon substrate. + An ion implantation process was performed to prepare an LT substrate and a single-crystal silicon substrate. The LT substrate and the silicon substrate were then bonded together using a room-temperature bonding method to obtain a bonded substrate. The resulting bonded substrate was heated as in Example 1 to leave an ion-implanted layer of the LT substrate on the side of the single-crystal silicon substrate, and the remaining portion of the LT substrate was released from the bonded substrate to create a silicon-based LT first composite material with an LT film thinned to 900 nm on the single-crystal silicon substrate.

[0064] Then, after applying a voltage to the obtained silicon-based LT composite substrate at 200°C and 300V to induce repolarization, the exposed surface of the LT film was polished to remove a 30nm thick portion from the surface, and the surface roughness RMS was adjusted to 1.0nm or less. The obtained composite substrate and sapphire substrate were then bonded together using a room-temperature bonding method as described in Example 1 to obtain a second sapphire / LT / silicon composite material. The obtained second composite material was heated at 300°C to leave the ion-implanted layer of the single-crystal silicon substrate on the side of the LT film and release the remaining portion of the single-crystal silicon substrate from the second composite material. Then, a 300nm thick residual silicon film remaining on the LT film was removed by SC-1 cleaning to obtain the LT composite substrate on sapphire.

[0065] As a result of measuring the Li content of the LT film on the LT composite substrate using a laser Raman spectrometer as described in Example 1, the Li content in the exposed surface of the LT film (the ion-implanted surface of the initial LT substrate) was 48.5%, thus confirming that the Li content did not show a decrease compared to the Li content of the initial LT substrate.

[0066] Comparative example LT substrates and silicon substrates were prepared similarly to those in Example 1. At a dosage of 1×10⁻⁶... 17 atoms / cm 2 Furthermore, under the condition of an accelerating voltage of 160 keV, hydrogen ions (H+) were used to accelerate the LT substrate on the mirror side. + The LT substrate and silicon substrate were bonded together by ion implantation of the ion implantation layer. The resulting bonded substrate was heated to 120°C and the LT substrate was separated from it along the ion implantation layer to create a silicon-based LT composite substrate with an LT film thinned to 900 nm on the silicon substrate.

[0067] The cross-section of the silicon-based LT composite substrate thus obtained was observed using transmission electron microscopy (TEM). The resulting TEM images are shown in... Figure 2In addition, as in Example 1, the Li content of the LT film on the silicon-supported LT composite substrate was measured using laser Raman spectroscopy. Reference will be made below. Figure 2 The TEM images shown illustrate the results. The Li content in the exposed surface 22 (separation interface of the ion implantation layer) of the LT film 21 on the support substrate 23 is 48.0%, indicating that, unlike Examples 1 and 2, the Li content decreases from the initial Li content of the LT substrate. In the comparative example, the ion implantation surface of the LT film 21 is bonded to the support substrate 23, and the surface portion 21a on the ion implantation side is placed on one side of the support substrate 23, with the deeper portion 21b exposed. In fact, at the distance from the exposed surface 22 of the LT film 21 (… Figure 2 In the deep layer 21b, approximately 300 nm deep, the Li content decreases, while at a distance of 23 nm from the supporting substrate... Figure 2 In the surface portion 21a) of the approximately 650 nm thick layer, the Li content did not decrease. Reference Symbol List

[0068] 1: Piezoelectric single crystal substrate 11: Ion implantation layer 11a: Surface portion 11b: Deep 2: Temporary adhesive base 3: Supporting base 4: First composite material 5: Second composite material 10: Composite substrate 20: Composite substrate (comparative example) 21: LT membrane 21a: Surface portion 21b: Deep 22: Separated Interface 23: Supporting base

Claims

1. A method for manufacturing a composite substrate equipped with a piezoelectric single-crystal film, comprising the following steps: One surface of a piezoelectric single-crystal substrate containing lithium tantalate or lithium niobate is subjected to ion implantation to form an ion implantation layer in the piezoelectric single-crystal substrate, wherein the ion implantation is performed according to the hydrogen atom ion (H + ) is calculated as 1.0 × 10 16 atoms / cm 2 Or larger and 3.0×10 17 atoms / cm 2 Or even smaller ion implantation doses using ions containing hydrogen atoms (H) + ) and hydrogen molecular ions (H2) + Ion implantation treatment is performed on at least one of the ionic substances in the group; The surface of the temporary bonding substrate to be bonded to the piezoelectric single crystal substrate is subjected to ion implantation treatment to form an ion implantation layer in the temporary bonding substrate, wherein the temporary bonding substrate is a single crystal silicon substrate; The surface of the piezoelectric single crystal substrate on which the ion implantation layer is formed is bonded to the temporary bonding substrate; The piezoelectric single crystal substrate is separated into the ion implantation layer and the remaining part of the piezoelectric single crystal substrate, and a piezoelectric single crystal film with a thickness of 2 μm or less is formed on the temporary bonding substrate; The supporting substrate is bonded to the surface of the piezoelectric single crystal film opposite to the bonding surface of the temporary bonding substrate; as well as A portion of the temporary adhesive substrate is separated from the piezoelectric single crystal film by separating the temporary adhesive substrate into the ion implanted layer of the temporary adhesive substrate and the remaining portion of the temporary adhesive substrate, so as to form a single crystal silicon film with a thickness of 2 μm or less on the piezoelectric single crystal film.

2. The method for manufacturing a composite substrate equipped with a piezoelectric single-crystal film according to claim 1, wherein hydrogen atom ions (H... + ) and hydrogen molecular ions (H2) + At least one of the following is used as an ionic substance to perform the ion implantation treatment on the temporary adhesive substrate, with hydrogen ions (H) + The ion implantation dose is calculated to be 1.0 × 10⁻⁶. 16 atoms / cm 2 Or larger and 2.0 × 10 17 atoms / cm 2 Or smaller, and the ion implantation dose implanted into the temporary bonding substrate is set to be less than the dose implanted into the piezoelectric single crystal substrate.

3. The method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to claim 1, wherein the separation of the temporary bonding substrate into an ion-implanted layer of the temporary bonding substrate and the remainder thereof is achieved by at least one selected from heat treatment, mechanical impact, spraying, ultrasonic vibration and light irradiation.

4. The method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to claim 1, wherein the material of the supporting substrate is selected from glass, silicon, sapphire, spinel, silicon carbide, silicon nitride and aluminum nitride.

5. The method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to claim 1, wherein the material of the supporting substrate is quartz.

6. The method for manufacturing a composite substrate equipped with a piezoelectric single crystal film according to claim 1, wherein the piezoelectric single crystal substrate is separated into the ion implantation layer and the remaining portion of the piezoelectric single crystal substrate by at least one selected from heat treatment, mechanical impact, spraying, ultrasonic vibration and light irradiation.

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