WO2020250490A1 - 複合基板、弾性波素子および複合基板の製造方法 - Google Patents
複合基板、弾性波素子および複合基板の製造方法 Download PDFInfo
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- 239000000758 substrate Substances 0.000 title claims abstract description 169
- 239000002131 composite material Substances 0.000 title claims abstract description 23
- 238000004519 manufacturing process Methods 0.000 title claims description 6
- 239000000463 material Substances 0.000 claims abstract description 94
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 19
- 239000010453 quartz Substances 0.000 claims abstract description 15
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 14
- 125000001153 fluoro group Chemical group F* 0.000 claims abstract description 13
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- 238000010438 heat treatment Methods 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 15
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 claims description 10
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- MYMOFIZGZYHOMD-UHFFFAOYSA-N Dioxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 8
- 239000013078 crystal Substances 0.000 claims description 8
- 229910001882 dioxygen Inorganic materials 0.000 claims description 8
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 7
- 229910001873 dinitrogen Inorganic materials 0.000 claims description 6
- 229910052731 fluorine Inorganic materials 0.000 claims description 6
- 229910052744 lithium Inorganic materials 0.000 claims description 6
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims description 6
- 238000005498 polishing Methods 0.000 claims description 6
- 230000001678 irradiating effect Effects 0.000 claims description 5
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- 230000032798 delamination Effects 0.000 abstract 1
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- 239000000203 mixture Substances 0.000 description 11
- 238000002149 energy-dispersive X-ray emission spectroscopy Methods 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 238000001994 activation Methods 0.000 description 5
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- 229910052715 tantalum Inorganic materials 0.000 description 4
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 4
- 235000012431 wafers Nutrition 0.000 description 4
- 229910000838 Al alloy Inorganic materials 0.000 description 3
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 230000008878 coupling Effects 0.000 description 3
- 238000010168 coupling process Methods 0.000 description 3
- 238000005859 coupling reaction Methods 0.000 description 3
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- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 3
- 238000009832 plasma treatment Methods 0.000 description 3
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- 238000004506 ultrasonic cleaning Methods 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 235000019687 Lamb Nutrition 0.000 description 1
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 125000005842 heteroatom Chemical group 0.000 description 1
- 238000000024 high-resolution transmission electron micrograph Methods 0.000 description 1
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Images
Classifications
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/02535—Details of surface acoustic wave devices
- H03H9/02543—Characteristics of substrate, e.g. cutting angles
- H03H9/02574—Characteristics of substrate, e.g. cutting angles of combined substrates, multilayered substrates, piezoelectrical layers on not-piezoelectrical substrate
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/08—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of resonators or networks using surface acoustic waves
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/25—Constructional features of resonators using surface acoustic waves
Definitions
- the present invention relates to a composite substrate of a piezoelectric material substrate and a support substrate, and a method for manufacturing the composite substrate.
- an SOI substrate composed of a high-resistance Si / SiO 2 thin film / Si thin film is widely used.
- Plasma activation is used to realize the SOI substrate. This is because they can be bonded at a relatively low temperature (400 ° C.).
- a composite substrate made of a similar Si / SiO 2 thin film / piezoelectric thin film has been proposed with the aim of improving the characteristics of the piezoelectric device.
- a SAW filter having a structure in which a piezoelectric material substrate is bonded to a support substrate has been reported.
- elastic wave elements using a composite substrate obtained by bonding a crystal substrate and a lithium tantalate substrate exhibit extremely excellent characteristics (Non-Patent Documents 1 and 2, Patent Documents 1 and 2). ..
- Patent Document 2 proposes a bonded body of quartz and a piezoelectric layer, but when the piezoelectric material substrate is made thin, there is a problem that peeling from the support substrate occurs, and further improvement in bonding strength is required. There is.
- An object of the present invention is to improve the bonding strength when bonding a piezoelectric material substrate to a support substrate made of quartz so that the piezoelectric material substrate will not be peeled off even if it is thinned.
- the present invention Support substrate made of crystal, Piezoelectric material substrate, It has a first amorphous layer existing between the support substrate and the piezoelectric material substrate, and a second amorphous layer existing between the support substrate and the first amorphous layer.
- the first amorphous layer contains 10 to 30 atom% of silicon atoms
- the second amorphous layer contains 1 to 10 atom% of fluorine atoms.
- the present invention also relates to an elastic wave element, which comprises the composite substrate and electrodes on the piezoelectric single crystal substrate.
- the present invention A method for manufacturing a composite substrate having a support substrate made of quartz and a piezoelectric material substrate.
- the present inventor activates the surface of the piezoelectric material substrate and the surface of the support substrate by plasma irradiation, respectively, and prepares each activated surface.
- the present inventor further investigated the reason why the joint strength was improved, and obtained the following findings. That is, in the composite substrate with improved bonding strength, a plurality of amorphous layers existed between the support substrate and the piezoelectric material substrate. When these amorphous layers are analyzed, when they have an amorphous layer containing 10 to 30 atom% of silicon atoms and an amorphous layer containing 1 to 10 atom% of fluorine atoms, the bonding strength is particularly high and the piezoelectricity is high. We have found that the piezoelectric material substrate is difficult to peel off from the support substrate even if the material substrate is thinly processed, and the present invention has been reached.
- the amorphous layer containing 10 to 30 atom% of silicon atoms is formed by diffusing the silicon atoms from the support substrate side made of quartz to the piezoelectric material substrate side. It seems that the bonding strength is particularly high because the fluorine atoms that are generated and generated by plasma activation are adsorbed on the piezoelectric material substrate side to form an amorphous layer containing 1 to 10 atom% of fluorine atoms. It is considered that when the heat treatment temperature was low, diffusion of silicon atoms and diffusion of fluorine in the atmosphere were less likely to occur, and it was difficult to improve the bonding strength. It is considered that the fluorine atoms in the composition of the amorphous layer are derived from the fluorine-based rubber (perfluorocarbon polymer) constituting the O-ring of the plasma treatment chamber.
- the support substrate made of quartz and the piezoelectric material substrate made of lithium tantalate are bonded, but before the bonding, an amorphous silicon oxide layer or an amorphous silicon oxide layer is formed on the surface of the support substrate or the surface of the piezoelectric material substrate. It is stated that it is preferable to form an amorphous alumina layer and then heat-treat at 150 to 200 ° C.
- each surface of the support substrate made of quartz and the piezoelectric material substrate made of lithium tantalate or the like is surface-activated with plasma containing at least one of oxygen gas and nitrogen gas and directly bonded. After that, heat treatment is performed at 250 ° C. or higher, and at this time, a plurality of amorphous layers having a specific composition are formed along the bonding interface.
- (A) shows the piezoelectric material substrate 1, and (b) shows a state in which the joint surface 1a of the piezoelectric material substrate 1 is activated to generate the activated surface 1c.
- (A) shows the support substrate 4, and (b) shows the state in which the surface of the support substrate 4 is activated.
- (A) shows a bonded body 7 obtained by directly joining the piezoelectric material substrate 1 and the support substrate 4, and (b) shows a state in which the piezoelectric material substrate 1A of the bonded body is polished and thinned.
- Shown, (c) shows an elastic wave element 10. It is a graph which shows the example of the relationship between the heating temperature after direct bonding and the bonding strength. It is a high resolution transmission electron micrograph (8 million times) showing the vicinity of the interface of a composite substrate.
- a piezoelectric material substrate 1 having a pair of main surfaces 1a and 1b is prepared.
- 1a is a joint surface.
- the bonding surface 1a of the piezoelectric material substrate 1 is irradiated with plasma as shown by an arrow A to obtain a surface-activated bonding surface 1c.
- the support substrate 4 is prepared.
- the surface 4a of the support substrate 4 is surface-activated by irradiating the surface 4a with plasma as shown by an arrow B to form an activated joint surface 6.
- the activated bonding surface 1c on the piezoelectric material substrate 1 and the activated bonding surface 6 of the support substrate 4 are brought into contact with each other and directly bonded to form a bonded body.
- a joint strength sufficient to withstand the grinding process is obtained.
- the piezoelectric substrate of the bonded body is thinly processed by a grinding machine.
- the bonded body 7 can be obtained by heat-treating the bonded body at a temperature of 250 ° C. or higher and 350 ° C. or lower.
- a second amorphous layer 11 and a first amorphous layer 5 are formed between the support substrate 4 and the piezoelectric material substrate 1.
- an electrode may be provided on the piezoelectric material substrate 1.
- the main surface 1b of the piezoelectric material substrate 1 is processed to thin the substrate 1 to obtain a thinned piezoelectric material substrate 1A.
- 1d is a machined surface.
- a predetermined electrode 8 can be formed on the processed surface 1d of the piezoelectric material substrate 1A of the bonded body 7A to obtain an elastic wave element 10.
- the material of the support substrate 4 is quartz. Quartz is an anisotropic crystal, and the characteristics of the piezoelectric element depend on the crystal orientation. According to Non-Patent Document 1, it is shown that spurious is suppressed by paying attention to the speed of sound. Therefore, the orientation can be appropriately selected so as to obtain the desired characteristics.
- the piezoelectric material substrate 1 used in the present invention is preferably a solid solution of lithium tantalate (LT), lithium niobate (LN), or lithium niobate-lithium tantalate. Since these have a high propagation velocity of surface acoustic waves and a large electromechanical coupling coefficient, they are suitable as elastic surface wave devices for high frequencies and wideband frequencies.
- the normal directions of the main surfaces 1a and 1b of the piezoelectric material substrate 1 are not particularly limited.
- the piezoelectric material substrate 1 is made of LT
- the X-axis which is the propagation direction of surface acoustic waves, is the center.
- the direction rotated by 32 to 55 ° from the Y axis to the Z axis, and the Euler angle display (180 °, 58 to 35 °, 180 °) are preferable because the propagation loss is small.
- the piezoelectric material substrate 1 is made of LN
- 37.8 °, 0 °) is preferable because the piezoelectric coupling coefficient is large, or (a) 40 to 65 from the Y axis to the Z axis centering on the X axis, which is the propagation direction of surface acoustic waves.
- the size of the piezoelectric material substrate is not particularly limited, but is, for example, 100 to 200 mm in diameter and 0.15 to 1 ⁇ m in thickness.
- the atmosphere at the time of surface activation is an atmosphere containing oxygen.
- the atmosphere may be oxygen only, nitrogen only, or a mixed gas of oxygen with nitrogen, hydrogen, and argon.
- the ratio is not particularly limited, but the ratio may be appropriately adjusted in relation to the bonding strength.
- the atmospheric pressure at the time of surface activation is preferably 100 Pa or less, and more preferably 80 Pa or less.
- the atmospheric pressure is preferably 30 Pa or more, and more preferably 50 Pa or more.
- the temperature at the time of plasma irradiation shall be 150 ° C. or less. As a result, a bonded body 7 having high bonding strength and no deterioration of the piezoelectric material can be obtained. From this point of view, the temperature at the time of plasma irradiation is set to 150 ° C. or less. It is more preferable to keep the temperature below 100 ° C.
- the energy at the time of plasma irradiation is preferably 30 to 150 W.
- the product of the energy during plasma irradiation and the irradiation time is preferably 0.1 to 1.0 Wh.
- the surface 1a of the piezoelectric material substrate and the surface 4a of the support substrate are flattened before the plasma treatment.
- Methods for flattening the surfaces 1a and 4a include lap polishing and chemical mechanical polishing (CMP).
- the arithmetic average roughness Ra of the flat surface is preferably 1 nm or less, more preferably 0.3 nm or less.
- the activated surface of the piezoelectric material substrate and the activated surface of the support substrate are brought into contact with each other and joined.
- the bonded body is heat-treated to provide strength to withstand the polishing process of the piezoelectric material substrate.
- the heat treatment temperature is preferably 100 to 150 ° C.
- the thickness can be reduced by polishing the piezoelectric material substrate after this heat treatment.
- the bonding strength is improved by performing a heat treatment (annealing treatment) on the bonded body.
- the temperature at the time of heat treatment is 250 ° C. or higher, but more preferably 270 ° C. or higher.
- the temperature during this heat treatment is 350 ° C. or lower in order to prevent damage to the bonded body, but more preferably 300 ° C. or lower.
- the first amorphous layer contains 10 to 30 atom% of silicon atoms.
- the silicon atom content of the first amorphous layer is It is more preferably 15 atom% or more, and further preferably 25 atom% or less.
- the second amorphous layer contains 1 to 10 atom% of fluorine atoms.
- the fluorine atom content of the second amorphous layer is preferably 3 atom% or more, and the fluorine atom content of the second amorphous layer is preferably 8 atom% or less.
- the piezoelectric material substrate is made of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalate, and the first amorphous layer is a silicon atom and said material. Contains the atoms that make up the main component.
- the atoms constituting the material of the piezoelectric material substrate are one or two atoms selected from the group consisting of niobium and tantalum, lithium, and oxygen.
- the ratio of lithium atoms cannot be directly measured by the method described in the present specification, the lithium ratio is excluded from each ratio of each atom constituting the material.
- the total ratio of one or two kinds of atoms selected from the group consisting of niobium and tantalum in the first amorphous layer and oxygen atoms is preferably 70 atom% or more, and preferably 90 atom% or less. Further, the total ratio of one or two kinds of atoms selected from the group consisting of niobium and tantalum in the first amorphous layer is more preferably 75 atom% or more, and further preferably 85 atom% or less. Further, the ratio of oxygen atoms in the second amorphous layer is more preferably 60 atom% or more, and further preferably 50 atom% or less.
- the second amorphous layer contains fluorine atoms, silicon atoms and oxygen atoms as main components.
- the ratio of silicon atoms in the second amorphous layer is more preferably 35 atom% or more, still more preferably 50 atom% or less.
- the ratio of oxygen atoms in the second amorphous layer is more preferably 45 atom% or more, and further preferably 60 atom% or less.
- the concentration of each atom is measured using the EDX method (energy dispersive X-ray analysis method).
- EDX method energy dispersive X-ray analysis method
- JEM-ARM200F manufactured by JEOL Ltd. was used as the EDX measuring device.
- the accelerating voltage was 200 kV, and the beam diameter was about 0.1 nm ⁇ .
- the thickness of the first amorphous layer is preferably 1.0 nm to 3.0 nm from the viewpoint of the present invention.
- the thickness of the second amorphous layer is preferably 4 to 10 nm, more preferably 6 to 8 nm from the viewpoint of the present invention.
- the existence and thickness of the first amorphous layer and the second amorphous layer can be confirmed by a high-resolution transmission electron microscope image (magnification of 8 million times) of the cross section of the composite substrate.
- the thickness of the piezoelectric material substrate is preferably 2.0 ⁇ m or less, more preferably 1.0 ⁇ m or less. There is no particular lower limit to the thickness of the piezoelectric material substrate, but from the viewpoint of actual processing, it can be 0.05 ⁇ m or more.
- the thickness of the piezoelectric material substrate is measured by an optical measuring machine (F20 manufactured by Filmetrix) using optical interference.
- the composite substrates 7 and 7A of the present invention can be suitably used for the elastic wave element 10.
- the surface acoustic wave element 10 an elastic surface wave device, a Lamb wave element, a thin film resonator (FBAR), and the like are known.
- a surface acoustic wave device has an IDT (Interdigital Transducer) electrode (also called a comb electrode or a surface acoustic wave) on the input side that excites a surface acoustic wave and an output side that receives the surface acoustic wave on the surface of a piezoelectric material substrate.
- IDT electrode Interdigital Transducer
- the material constituting the electrode (electrode pattern) 8 on the piezoelectric material substrate 1A is preferably aluminum, an aluminum alloy, copper, or gold, and more preferably aluminum or an aluminum alloy.
- the aluminum alloy it is preferable to use a mixture of Al and 0.3 to 5% by weight of Cu.
- Ti, Mg, Ni, Mo, and Ta may be used instead of Cu.
- Example 1 A surface acoustic wave element was manufactured as described with reference to FIGS. 1 to 3. Specifically, a 42Y-cut X-propagation LiTaO3 substrate (piezoelectric material substrate) 1 having a thickness of 250 ⁇ m and both sides polished to a mirror surface and an AT-cut crystal substrate (support substrate) 4 having a thickness of 350 ⁇ m were prepared. The substrate size is 100 mm. Next, the surface 1a of the piezoelectric material substrate 1 and the surface 4a of the support substrate 4 were cleaned and surface activated, respectively.
- ultrasonic cleaning was performed using pure water, and the substrate surface was dried by spin drying.
- the washed support substrate was introduced into the plasma activation chamber, and the joint surface was activated at 30 ° C. with oxygen gas plasma.
- the piezoelectric material substrate was similarly introduced into the plasma activation chamber, and the joint surface was surface-activated with oxygen gas plasma at 30 ° C.
- the surface activation time was 40 seconds and the energy was 100 W.
- the same ultrasonic cleaning and spin drying as described above were performed again.
- a very strong joint is required. Specifically, a joint strength of 3 J / m 2 or more is required. In this example, it was found that a heating temperature of 250 ° C or higher was required. The joint strength was evaluated by the blade method shown in Non-Patent Document 3.
- the piezoelectric material substrate of the bonded body was processed by a grinding machine until the thickness became 10 ⁇ m.
- the processed substrate was heated at 250 ° C. for an additional 10 hours.
- the substrate was set on the wrapping machine, and the thickness was further reduced to 5 ⁇ m while supplying the diamond slurry.
- it was polished with a CMP processing machine to remove the work-altered layer and finally adjust the thickness.
- Colloidal silica was used as the slurry at the time of polishing.
- Example 1 When the cross section of the junction interface of Example 1 was analyzed by high-resolution TEM (device JEM-ARM200F, accelerating voltage 200 kV, magnification 8 million times), an amorphous layer was observed at the junction interface (Fig. 5). Further examination of the amorphous layer revealed that it was divided into two layers.
- region 1 is an end portion of a piezoelectric material substrate made of lithium tantalate single crystal
- region 4 is a support substrate made of silicon oxide.
- the reason why the region 1 is darker than the region 4 is that a large amount of tantalum atoms having a large atomic weight are present.
- the region 2 is the first amorphous layer
- the region 3 is the second amorphous layer.
- Example 2 In Example 1, a mixed gas plasma containing 80% nitrogen gas and 20% oxygen gas was used instead of the oxygen plasma. When changing the gas composition, the matching was changed as appropriate so that the reflected power of RF was minimized. Other than that, the joint was processed in the same manner as in Example 1. As a result, a large joint strength of 3.2 J / m 2 was measured after heating at 250 ° C. as in Example 1. Even with this substrate, peeling did not occur even when the thickness of the piezoelectric layer was set to 1 ⁇ m by CMP processing.
- Example 3 In Example 1, the heating temperature of the bonded body was changed from 250 ° C. to 270 ° C. The obtained bonded body was polished in the same manner as in Example 1, but no peeling was observed even when CMP processing was performed to a thickness of 0.3 ⁇ m.
- Example 3 When the cross section of the junction interface of Example 3 was analyzed by a high-resolution TEM in the same manner as in Example 1, a first amorphous layer and a second amorphous layer were observed at the junction interface. For the purpose of investigating the composition of each of these amorphous layers, EDX analysis was performed under the same conditions as in Example 1. The measurement results are shown in Table 3.
- the first amorphous layer and the second amorphous layer having a specific composition were formed. It is considered that the fluorine atoms in the composition are derived from the fluorine-based rubber (perfluorocarbon polymer) constituting the O-ring of the plasma treatment chamber.
- Example 1 In Example 1, the surface was activated using a neutral argon beam instead of the oxygen plasma. The activation time was 60 seconds for both the quartz and the piezoelectric material substrate. Wafers were brought into contact with each other in the vacuum chamber of the joining machine and joined by applying pressure to obtain a bonded body. The removed wafer was placed in an oven at 100 ° C. in the same manner as in Example 1 and taken out after 10 hours. I tried to process the piezoelectric material substrate with a grinder until the thickness of the piezoelectric material substrate became 10 ⁇ m, but when the thickness was about 20 ⁇ m, the grinder failed. When the wafer was taken out, the piezoelectric material was largely peeled off. From this, it was found that only a very weak bonding strength was obtained.
- Example 2 Plasma activation was performed in the same manner as in Example 1 except that the maximum heating temperature was set to a low temperature of 150 ° C. to prepare a bonded body, and when CMP processing was performed, the piezoelectric material substrate was peeled off when the thickness was less than 5 um. did.
- TEM analysis and EDX analysis were performed in the same manner as in Example 1. The measurement results are shown in Table 4. The composition was significantly different from that of the examples, probably because the heating temperature was low. It was also found that the thickness of the amorphous layer was very thin.
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Abstract
Description
水晶からなる支持基板、
圧電性材料基板、
前記支持基板と前記圧電性材料基板との間に存在する第一のアモルファス層、および
前記支持基板と前記第一のアモルファス層との間に存在する第二のアモルファス層を有しており、
前記第一のアモルファス層は珪素原子を10~30atom%含有し、前記第二のアモルファス層はフッ素原子を1~10atom%含有することを特徴とする。
水晶からなる支持基板と、圧電性材料基板とを有する複合基板を製造する方法であって、
前記支持基板の表面に対して酸素ガスと窒素ガスとの少なくとも一方を含有するプラズマを照射することで活性化面を生成させる工程、
前記圧電性材料基板の表面に対して酸素ガスと窒素ガスとの少なくとも一方を含有するプラズマを照射することで活性化面を生成させる工程、
前記支持基板の前記活性化面と前記圧電性材料基板の前記活性化面とを接触させることで接合体を得る工程、および
前記接合体を250℃以上、350°C以下の温度で熱処理する工程
を有することを特徴とする。
なお、アモルファス層の組成中のフッ素原子は、プラズマ処理用チャンバーのOリングを構成するフッ素系ゴム(ペルフルオロカーボン重合体)に由来するものと考えられる。
まず、図1(a)に示すように、一対の主面1a、1bを有する圧電性材料基板1を準備する。本例では1aを接合面とする。次いで、図1(b)に示すように、圧電性材料基板1の接合面1aに対して矢印Aのようにプラズマを照射し、表面活性化された接合面1cを得る。
支持基板4の材質は水晶とする。水晶は異方性を持つ結晶であり、その結晶方位により圧電素子の特性が左右される。非特許文献1によればその音速に着目することで、スプリアスを抑制することが示されている。従って所望の特性が得られるようにその方位を適宜選択することができる。
表面活性化時の雰囲気は、酸素を含有する雰囲気とする。この雰囲気は、酸素のみであってよく、窒素のみであってよく、あるいは酸素と、窒素、水素、およびアルゴンとの混合ガスであってよい。混合ガスの場合には、特に限定されるものではないが、接合強度との関係によりその比率を適宜調整してもよい。
100℃以下とすることが更に好ましい。
次いで、接合体の熱処理(アニール処理)を行うことによって、接合強度を向上させる。本発明の観点からは、熱処理時の温度は250℃以上とするが、270℃以上が更に好ましい。また、この熱処理時の温度は、接合体の破損を防止するために350℃以下とするが、300℃以下が更に好ましい。
15atom%以上が更に好ましく、25atom%以下が更に好ましい。
加速電圧: 200kV、ビーム径: 約0.1nmφとした。
弾性波素子10としては、弾性表面波デバイスやラム波素子、薄膜共振子(FBAR)などが知られている。例えば、弾性表面波デバイスは、圧電性材料基板の表面に、弾性表面波を励振する入力側のIDT(Interdigital Transducer)電極(櫛形電極、すだれ状電極ともいう)と弾性表面波を受信する出力側のIDT電極とを設けたものである。入力側のIDT電極に高周波信号を印加すると、電極間に電界が発生し、弾性表面波が励振されて圧電性材料基板上を伝搬していく。そして、伝搬方向に設けられた出力側のIDT電極から、伝搬された弾性表面波を電気信号として取り出すことができる。
図1~図3を参照しつつ説明したようにして、表面弾性波素子を作製した。
具体的には、厚さが250μmで両面が鏡面に研磨されている42YカットX伝搬LiTaO3基板(圧電性材料基板)1と、厚みが350μmのATカット水晶基板(支持基板)4を用意した。基板サイズはいずれも100mmである。次いで、圧電性材料基板1の表面1aおよび支持基板4の表面4aをそれぞれ洗浄および表面活性化した。
圧電性材料基板の厚みを光干渉を用いた光学式測定機(Filmetrix社製 F20)により測定したところ、2μmと非常に薄い層が得られた。
圧電性材料基板の厚みの限界を知る目的でさらにCMPを続けたところ、厚みが0.3μmとなっても、剥離は見られなかった。
透過電子顕微鏡: 日立ハイテクノロジーズ製 HD-2700
加速電圧: 200kV
ビーム径: 約0.2nmφ
元素分析装置: EDAX製 Genesis
X線検出器: Si/Li半導体検出器
エネルギー分解能: 約140eV
X線取出角: 25.7°
立体角: 0.31sr
取込時間: 30sec
実施例1において、酸素プラズマの代わりに窒素ガス80%、酸素ガス20%とした混合ガスのプラズマを用いた。ガス組成を変更するにあたり、RFの反射電力が最小となるようにマッチングは適宜変更した。
その他は実施例1と同様に接合体の加工を行った。この結果、実施例1と同様に250℃での加熱後に3.2J/m2と大きな接合強度が測定された。この基板でもCMP加工により圧電層の厚みを1μmとした場合でも剥離が発生することはなかった。
実施例1において、接合体の加熱温度を250℃から270℃に変更した。実施例1と同様にして、得られた接合体を研磨加工したが、厚さ0.3μmまでCMP加工しても、剥離は見られなかった。
実施例1において、酸素プラズマの代わりに中性アルゴンビームを用いて表面を活性化させた。活性化時間は水晶、圧電性材料基板ともに60秒とした。接合機の真空チャンバー内でウエハー同士を接触させ、圧力をかけて接合し、接合体を得た。取り出したウエハーを実施例1と同様に100℃のオーブンに投入し10時間後取り出した。研削機により圧電性材料基板の厚さが10μmになるまで加工しようとしたが、おおよそ20μm加工したところで研削機がエラーとなった。ウエハーを取り出したところ、圧電性材料が大きく剥離していた。このことから非常に弱い接合強度しか得られていないことが分かった。
最高加熱温度を150℃と低温にした以外は、実施例1と同様にしてプラズマ活性化を行い接合体を作成し、CMP加工したところ、圧電性材料基板の厚みが5umを切ったあたりで剥離した。
得られた接合体のアモルファス層の組成を調べる目的で、実施例1と同様にしてTEM分析、EDX分析を行った。測定結果を表4に示す。加熱温度が低かったためか、組成が実施例とは大きく異なっていた。
また、アモルファス層の厚みが非常に薄くなっていることがわかった。
Claims (8)
- 水晶からなる支持基板、
圧電性材料基板、
前記支持基板と前記圧電性材料基板との間に存在する第一のアモルファス層、および
前記支持基板と前記第一のアモルファス層との間に存在する第二のアモルファス層を有しており、
前記第一のアモルファス層は珪素原子を10~30atom%含有し、前記第二のアモルファス層はフッ素原子を1~10atom%含有することを特徴とする、複合基板。 - 前記圧電性材料基板が、ニオブ酸リチウム、タンタル酸リチウムおよびニオブ酸リチウム-タンタル酸リチウムからなる群より選ばれた材質からなり、前記第一のアモルファス層が前記珪素原子および前記材質を構成する原子を主成分として含むことを特徴とする、請求項1記載の複合基板。
- 前記第二のアモルファス層が、前記フッ素原子、珪素原子および酸素原子を主成分として含むことを特徴とする、請求項1または2記載の複合基板。
- 前記第一のアモルファス層の厚さが1nm~3nmであり、前記第二のアモルファス層の厚さが4~10nmであることを特徴とする、請求項1~3のいずれか一つの請求項に記載の複合基板。
- 請求項1~4のいずれか一つの請求項に記載の複合基板、および前記圧電性材料基板上の電極を備えていることを特徴とする、弾性波素子。
- 水晶からなる支持基板と、圧電性材料基板とを有する複合基板を製造する方法であって、
前記支持基板の表面に対して酸素ガスと窒素ガスとの少なくとも一方を含有するプラズマを照射することで活性化面を生成させる工程、
前記圧電性材料基板の表面に対して酸素ガスと窒素ガスとの少なくとも一方を含有するプラズマを照射することで活性化面を生成させる工程、
前記支持基板の前記活性化面と前記圧電性材料基板の前記活性化面とを接触させることで接合体を得る工程、および
前記接合体を250℃~350℃の温度で熱処理する工程
を有することを特徴とする、複合基板の製造方法。 - 前記圧電性材料基板が、ニオブ酸リチウム、タンタル酸リチウムおよびニオブ酸リチウム-タンタル酸リチウムからなる群より選ばれた材質からなることを特徴とする、請求項6記載の方法。
- 前記熱処理後に前記圧電性材料基板の厚さを研磨によって小さくすることを特徴とする、請求項6または7記載の方法。
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