A method for manufacturing a piezoelectric oxide single crystal substrate and a SAW filter

Abstract

The present invention proposes a method for manufacturing a piezoelectric oxide single crystal substrate, including: preparing lithium-rich polycrystalline powder, mixing lithium carbonate and metal oxide, performing high-temperature solid-phase reaction, and then crushing to prepare lithium-rich polycrystalline powder, wherein the metal element in the metal oxide is the same as the metal element in the piezoelectric oxide single crystal substrate, the lithium in the lithium-rich polycrystalline powder and the metal have a first stoichiometric ratio, and the lithium in the piezoelectric oxide single crystal substrate and the metal have a second stoichiometric ratio; preparing a reduction sheet, mixing the lithium-rich polycrystalline powder and the reducing powder according to a preset ratio, and pressing the sheet to prepare a first reduction sheet and a second reduction sheet; performing a reduction treatment, placing the first reduction sheet, the piezoelectric oxide single crystal substrate, and the second reduction sheet on a bracket in sequence, and performing a high-temperature reduction treatment for a preset time to generate a piezoelectric oxide single crystal substrate with a pseudo-stoichiometric surface composition. In this way, the polarization structure of the piezoelectric oxide single crystal substrate can be maintained, and the piezoelectricity of the substrate can be improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing, and in particular to a method for manufacturing a piezoelectric oxide single crystal substrate and a SAW filter. Background Art

[0002] In the manufacturing process of surface acoustic wave devices, there are many processes that are placed at a temperature of 100 to 300°C. Therefore, if the piezoelectric oxide single crystal substrate of the surface acoustic wave device has pyroelectricity and generates charges on the substrate surface, these charges will cause spark discharges between the metal electrodes of the surface acoustic wave device, resulting in a decrease in the manufacturing yield of the surface acoustic wave device. In addition, even if the pyroelectricity of the material used for the surface acoustic wave device is weak and the charge decays over time, it can cause the electrodes of the surface acoustic wave device to short-circuit due to temperature changes, causing the surface acoustic wave device to fail.

[0003] In order to suppress the charge on the surface of the piezoelectric oxide single crystal substrate, a method of reducing the piezoelectric oxide single crystal substrate with a solid reducing agent at a temperature below the Curie temperature is usually used. However, due to the uneven distribution of the solid reducing agent on the surface of the piezoelectric oxide single crystal substrate and the difference in the degree of reduction, the color of the substrate surface is uneven. In the subsequent photolithography step of the surface acoustic wave device manufacturing process, the ultraviolet light reflection is uneven, and the interdigital transducer is difficult to be uniformly etched. The darker areas reflect the ultraviolet light weakly during the photolithography, while the lighter areas reflect the ultraviolet light strongly, resulting in secondary exposure and a low yield rate of the surface acoustic wave device. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for manufacturing a piezoelectric oxide single crystal substrate, thereby reducing the thermoelectricity generated on the substrate surface due to temperature changes, maintaining the polarization structure of the piezoelectric oxide single crystal substrate, and improving the piezoelectricity of the substrate.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] According to a first aspect of the present invention, a method for manufacturing a piezoelectric oxide single crystal substrate is provided, comprising: step 1, preparing lithium-rich polycrystalline powder, mixing lithium carbonate and metal oxide, subjecting the mixture to a high-temperature solid-phase reaction, and then crushing the mixture to prepare the lithium-rich polycrystalline powder, wherein the metal element in the metal oxide is the same as the metal element in the piezoelectric oxide single crystal substrate, the lithium in the lithium-rich polycrystalline powder has a first stoichiometric ratio to the metal, the lithium in the piezoelectric oxide single crystal substrate has a second stoichiometric ratio to the metal, and the first stoichiometric ratio is greater than the second stoichiometric ratio;

[0007] Step 2, preparing a reduction sheet, mixing the lithium-rich polycrystalline powder with a reducing powder according to a preset ratio, wherein the reducing powder is metal powder or carbon powder, and pressing the mixture into a sheet to prepare a first reduction sheet and a second reduction sheet;

[0008] Step 3, reduction treatment, placing the first reduction sheet, the piezoelectric oxide single crystal substrate, and the second reduction sheet on a bracket in sequence, burying them in the lithium-rich polycrystalline powder, and subjecting them to high-temperature reduction treatment for a preset time to generate a piezoelectric oxide single crystal substrate with a pseudo-stoichiometric surface composition.

[0009] In some embodiments, the metal oxide is tantalum pentoxide, the piezoelectric oxide single crystal substrate is lithium tantalate, and the first stoichiometric ratio is 55:45-65:35.

[0010] In some embodiments, the reducing powder is magnesium powder and / or iron powder, and the mass ratio of the reducing powder to the lithium-rich polycrystalline powder is 10:90-40:60.

[0011] In some embodiments, the metal oxide is niobium pentoxide, the piezoelectric oxide single crystal substrate is lithium niobate, and the first stoichiometric ratio is 55:45-65:35.

[0012] In some embodiments, the reducing powder is magnesium powder and / or zinc powder, and the mass ratio of the reducing powder to the lithium-rich polycrystalline powder is 10:90-40:60.

[0013] In some embodiments, in step 3, a pyroelectric treatment is performed simultaneously with a high-temperature reduction treatment to remove surface static electricity of the substrate, and the pyroelectric treatment includes: the piezoelectric oxide single crystal substrate has an upper surface and a lower surface parallel to each other, the first reduction sheet is in contact with the upper surface, the second reduction sheet is in contact with the lower surface, the surface of the first reduction sheet away from the piezoelectric oxide single crystal substrate is electrically connected to the first metal electrode; the surface of the second reduction sheet away from the piezoelectric oxide single crystal substrate is electrically connected to the second metal electrode; the first metal electrode and the second metal electrode apply a reduction voltage in the z-axis direction of the piezoelectric oxide single crystal substrate.

[0014] In some embodiments, the high-temperature reduction treatment includes: performing a constant temperature heat treatment at a temperature above 400°C and below the Curie temperature for 1-2 hours in a mixed gas atmosphere of an inert gas and a reducing gas under normal pressure, applying a reduction voltage with an applied reduction current density of 0.05-0.2 mA / cm2, continuing the constant temperature for 10-50 minutes, cooling with power on, and when the temperature drops to 350°C, removing the reduction voltage and continuing to cool to room temperature.

[0015] In some embodiments, the first metal electrode and the second metal electrode apply a reduction voltage in the z-axis direction of the piezoelectric oxide single crystal substrate, including: a battery formed by a conductive coating having a silver element applies a first reduction voltage in the positive direction of the z-axis of the substrate and a second reduction voltage in the reverse direction of the z-axis of the substrate.

[0016] In some embodiments, there are multiple piezoelectric oxide single crystal substrates, and the reduction sheet, isolation sheet, piezoelectric oxide single crystal substrate, isolation sheet, and reduction sheet are sequentially placed on a bracket to achieve uniform reduction of the piezoelectric oxide single crystal substrate, and the piezoelectric oxide single crystal substrate is arranged perpendicular to the ground.

[0017] According to a second aspect of the present invention, a SAW filter is provided, comprising: a piezoelectric oxide single crystal substrate manufactured by the above-mentioned method for manufacturing a piezoelectric oxide single crystal substrate; and an IDT electrode covering the piezoelectric oxide single crystal substrate.

[0018] In some embodiments, the piezoelectric oxide single crystal substrate has a transmittance of 80% and a resistivity of less than 1010 Ω·cm when the irradiation wavelength of an ultraviolet-infrared spectrophotometer is 1500 nm or more.

[0019] In some embodiments, the piezoelectric oxide single crystal substrate is bonded to a silicon substrate;

[0020] A bonding layer is arranged between the piezoelectric oxide single crystal substrate and the silicon substrate, and the bonding layer is a silicon-containing oxide layer; and a surface of the silicon substrate away from the piezoelectric oxide single crystal substrate is mechanically roughened.

[0021] The beneficial effects achieved by the present invention are as follows:

[0022] According to the present invention, a method for manufacturing a piezoelectric oxide single crystal substrate is provided. A piezoelectric oxide single crystal substrate with uniform surface color can be prepared by a dual method of reducing gas and pyroelectricity, combined with a uniform reduction process of an isolation sheet and a reduction sheet, thereby reducing the pyroelectricity generated on the substrate surface due to temperature changes, thereby maintaining the polarization structure of the piezoelectric oxide single crystal substrate and improving the piezoelectricity of the substrate. Therefore, the piezoelectric oxide single crystal substrate prepared in this way has small warping, no cracks or damage, and good temperature characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1It is a schematic flow chart of a method for manufacturing a piezoelectric oxide single crystal substrate of the present invention;

[0025] Figure 2 It is a schematic flow chart of another method for manufacturing a piezoelectric oxide single crystal substrate of the present invention;

[0026] Figure 3 It is a schematic diagram of the structure of the SAW filter of the present invention;

[0027] Figure 4 This is another schematic diagram of the SAW filter structure of the present invention.

[0028] in, Figures 1 to 4 The corresponding relationship between the reference numerals and component names in the figure is:

[0029] 31- a piezoelectric oxide single crystal substrate, 32- an IDT electrode covering the piezoelectric oxide single crystal substrate;

[0030] 41 - piezoelectric oxide single crystal substrate, 42 - silicon substrate, 43 - bonding layer. DETAILED DESCRIPTION

[0031] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0032] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0033] Example 1

[0034] A specific embodiment of the present invention, as Figure 1 As shown, a method for manufacturing a piezoelectric oxide single crystal substrate is disclosed, the method comprising:

[0035] Step 1, prepare lithium-rich polycrystalline powder, mix lithium carbonate and metal oxide, carry out high-temperature solid-phase reaction, and then crush to prepare the lithium-rich polycrystalline powder, the metal element in the metal oxide is the same as the metal element in the piezoelectric oxide single crystal substrate, the lithium in the lithium-rich polycrystalline powder and the metal have a first stoichiometric ratio, the lithium in the piezoelectric oxide single crystal substrate and the metal have a second stoichiometric ratio, the first stoichiometric ratio is greater than the second stoichiometric ratio, wherein the piezoelectric oxide single crystal substrate is a lithium tantalate substrate.

[0036] Since the existing substrate reduction method is often a method of directly using a solid reducing agent to reduce the piezoelectric oxide single crystal substrate at a temperature below the Curie temperature, the solid reducing agent is unevenly distributed on the surface of the piezoelectric oxide single crystal substrate, and the degree of reduction is different, resulting in uneven color on the substrate surface. Therefore, in order to avoid this situation, the present application places the piezoelectric oxide single crystal substrate in a lithium-rich polycrystalline powder. In this embodiment, the piezoelectric oxide single crystal substrate is mainly described as a lithium tantalate wafer, wherein the selected lithium tantalate wafer has a metal oxide of the same metal element as tantalum pentoxide, and further sets the first stoichiometric ratio of lithium in the lithium-rich polycrystalline powder to tantalum in the metal oxide to be 55:45 to 65:35. The setting of the stoichiometric ratio is because when the selected stoichiometric ratio, i.e., the lithium-tantalum ratio, is 60:40, the proportion of lithium will be too high, which is easy to cause the lithium-rich polycrystalline powder to be caking, and the particles are coarse, which is not conducive to the uniform reduction of the piezoelectric oxide single crystal substrate. When the selected stoichiometric ratio, i.e., the lithium-tantalum ratio, is too low, the Li concentration gradient between the reduction sheet and the piezoelectric oxide single crystal substrate will be too small, which is not conducive to the diffusion of Li in the lithium-rich polycrystalline powder to the single crystal substrate. Therefore, the lithium-rich polycrystalline powder under the appropriate stoichiometric lithium-tantalum ratio can be reused to reduce production costs. In this embodiment, the inventors finally selected the first stoichiometric ratio of lithium in the lithium-rich polycrystalline powder to tantalum in the metal oxide to be 55:45 to 65:35 after many studies and experiments to achieve the best effect.

[0037] In actual processing applications, it can be specifically implemented as follows: first, lithium tantalate with a high purity, such as more than 99%, and metal oxides with the same metal element are used as tantalum pentoxide. After weighing and mixing, a high-temperature solid-phase reaction is first carried out, and then the temperature is raised to melt, and after cooling and crystallization, it is taken out and crushed to prepare lithium tantalate polycrystalline particles of different particle sizes. On the other hand, for the preparation of lithium-rich polycrystalline powder, it can be placed at room temperature 800°C, then kept at a constant temperature of 1300°C for 2 hours, then heated to 1650°C and kept at a constant temperature for 8 hours, and then kept at a constant temperature for 5 hours until it cools to room temperature.

[0038] Therefore, by making the chemical composition of the wafer surface close to the stoichiometric ratio, the electromechanical coupling capability of the wafer material can be increased, thereby improving the performance of the surface acoustic wave filter.

[0039] Step 2, preparing reduction sheets, mixing lithium-rich polycrystalline powder and reducing powder according to a preset ratio, wherein the reducing powder is metal powder or carbon powder, and pressing the mixture into sheets to prepare a first reduction sheet and a second reduction sheet.

[0040] Specifically, the reducing powder can be specifically implemented as magnesium powder and / or iron powder, and the mass ratio of the reducing powder to the lithium-rich polycrystalline powder is set to 10:90-40:60. Since carbon powder only plays a simple reducing role in some cases, when the lithium tantalate single crystal substrate is photolithographic, the strong light in the ultraviolet visible light region may cause photodamage to the lithium tantalate single crystal substrate. However, in this embodiment, by doping the lithium tantalate single crystal substrate with a suitable concentration of reducing powder, i.e., magnesium powder or iron powder, it is possible to effectively avoid the occurrence of such a situation, and it is possible to overcome the problem that the chip spacing is not easy to set when the reducing gas (reducing powder) is reducing the piezoelectric oxide single crystal substrate when multiple chips are formed.

[0041] In order to ensure that the piezoelectric oxide single crystal is substantially reduced uniformly during the reduction treatment, two reduction plates, namely a first reduction plate and a second reduction plate, are provided according to the above method.

[0042] Step 3, reduction treatment, placing the first reduction sheet, the piezoelectric oxide single crystal substrate, and the second reduction sheet on the bracket in sequence, burying them in the lithium-rich polycrystalline powder, and performing high-temperature reduction treatment for a preset time to generate a piezoelectric oxide single crystal substrate with a pseudo-stoichiometric surface composition.

[0043] After the first reduction sheet, the second reduction sheet and the lithium-rich polycrystalline powder are prepared, a high-temperature reduction treatment can be performed while a pyroelectric treatment is performed to remove the surface static electricity of the substrate. Because there will be charge accumulation during the reduction treatment, the static electricity on the surface of the substrate needs to be removed by a pyroelectric method. In this embodiment, a reduction voltage is applied in the z-axis direction of the substrate as a pyroelectric treatment method, which specifically includes: first, the piezoelectric oxide single crystal substrate has an upper surface and a lower surface parallel to each other, the first reduction sheet is contacted with the upper surface, and the second reduction sheet is contacted with the lower surface. After that, the surface of the first reduction sheet away from the piezoelectric oxide single crystal substrate is electrically connected to the first metal electrode, and the surface of the second reduction sheet away from the piezoelectric oxide single crystal substrate is electrically connected to the second metal electrode, wherein the first metal electrode and the second metal electrode are preferably inert metal electrodes such as platinum Pt electrode, Ag electrode, Au gold electrode, etc. In this way, no chemical reaction occurs under high-temperature reduction, which can prevent the components of the metal electrode from contaminating the piezoelectric oxide single crystal substrate and causing the performance of the substrate to deteriorate. Finally, a reduction voltage is applied to the piezoelectric oxide single crystal substrate in the z-axis direction using the first metal electrode and the second metal electrode. For example, a battery formed by a conductive coating having a silver element is used to apply a first reduction voltage in the positive direction of the z-axis of the substrate and a second reduction voltage in the reverse direction of the z-axis of the substrate. The first reduction voltage and the second reduction voltage are mainly voltages that are applied in opposite directions along the z-axis, and are not limited to specific directions. The uniformity of reduction can be further improved by such positive and negative voltage processing.

[0044] The application of the above-mentioned reduction voltage can be specifically applied along the Z-pole axis of the substrate material by applying an external DC electric field. The voltage applied to the contacts of the substrate material is controlled to increase the bulk conductivity of the substrate, wherein the applied reduction voltage is not limited to using a constant voltage DC source, and can also be implemented as applying a time-varying reduction voltage, and connecting a constant current or controlled current source to the substrate to generate the reduction voltage. It should be noted that any DC voltage / current, including constant and time-varying DC voltage / current, falls within the scope of protection of this application.

[0045] Furthermore, since the removal method of pyroelectricity is not limited to applying a reduction voltage, in this embodiment, temperature control can also be used to achieve the removal of pyroelectricity, wherein the equipment used for temperature control treatment adopts a program-controlled vacuum reduction equipment, and the furnace body adopts a high-quality alloy resistance wire. The temperature of the furnace body is automatically adjusted by detecting the heating temperature of the substrate. In this way, through the programmable temperature increase, temperature decrease and temperature gradient control functions, the entire process can be automatically controlled by the program. It should be noted that the present invention does not limit the control method, and other methods such as artificial temperature control also belong to the protection scope of the present invention. The specific implementation is: first, the oxide single crystal substrate that has been surface diffused is placed in a crucible container, and then the crucible is placed in a heat treatment furnace, and the reduction treatment is performed under vacuum or inert or reducing flowing gas at a temperature of 400 to 600°C. Afterwards, the current heating temperature is detected, and when the heating temperature reaches the temperature threshold, the substrate is cooled to a temperature range of 20 to 28°C. Since the transmittance of piezoelectric oxide single crystal substrates with different blackening degrees is different, the darker the color of the chip, the lower the transmittance. The optical absorption of the chip is changed during the reduction process, thereby causing a change in the appearance color. In order to prevent the blackening degree from being too high or insufficient, and the phenomenon that different piezoelectric oxide single crystal substrates have different transmittances during the blackening process, a temperature threshold is set. The temperature threshold is the optimal blackening temperature of the piezoelectric oxide single crystal substrate, which can be set according to artificial experience or the characteristics of the piezoelectric oxide single crystal substrate. In this way, a substrate with the best blackening degree can be obtained, and then it is automatically cooled for 5 to 45 hours to meet the removal conditions that meet the room temperature temperature range of 20 to 28°C.

[0046] Furthermore, the high-temperature reduction treatment performed synchronously with the pyroelectric treatment can be specifically implemented as follows: a preset time treatment is performed at a temperature above 400°C and below the Curie temperature in a mixed gas atmosphere of an inert gas and a reducing gas under normal pressure. The preset time can be implemented as a constant temperature heat treatment for 1-2 hours, and then a reduction voltage is applied, and the applied reduction current density is 0.05-0.2 mA / cm 2, continue to keep the temperature constant for 10-50 minutes. This setting of small current and short constant temperature time can reduce the corrosion of metal electrodes, reuse and save costs. After that, cool down with power on. When the temperature drops to 350℃, remove the reduction voltage and continue to cool to room temperature.

[0047] Furthermore, under the above-mentioned high temperature and pyroelectric treatment method, the substrate of the lithium tantalate single crystal substrate is exposed to the vapor of lithium-rich polycrystalline powder, and the lithium element is dispersed from the surface of the substrate to the central part, so that the elemental composition of the substrate changes to a pseudo-stoichiometric composition. The realization principle of changing the elemental composition of the substrate to a pseudo-stoichiometric composition is that in a reducing environment, oxygen diffuses outward from the piezoelectric oxide single crystal, increasing the concentration of oxygen vacancies, and the oxygen vacancies obtain an electron to form F color centers (F+), which enhances the conductivity; at the same time, the color centers absorb strongly in the visible light region, making the color of the chip black. As the concentration of oxygen vacancies increases, the valence of some ions changes from +5 to +4, and the concentration of electron carriers increases accordingly. Therefore, after the reduction treatment, the concentration of carriers in the crystal increases, so that the elemental composition of the substrate changes to a pseudo-stoichiometric composition.

[0048] Furthermore, as a preferred embodiment, there can be multiple piezoelectric oxide single crystal substrates. When the reduction sheet, the isolation sheet, the piezoelectric oxide single crystal substrate, the isolation sheet, and the reduction sheet are sequentially placed on the bracket to achieve uniform reduction of the piezoelectric oxide single crystal substrate, the piezoelectric oxide single crystal substrate can be set perpendicular to the ground. Because the reduction voltage is positively correlated with the thickness of the piezoelectric single crystal substrate, the more substrates there are, the greater the reduction voltage. Therefore, setting the piezoelectric oxide single crystal substrate perpendicular to the ground can reduce cracks or uneven reduction caused by pressure between the substrates, relative to setting the substrate parallel to the ground. Moreover, multiple lithium tantalate substrates can be processed simultaneously, which improves the reduction efficiency and is conducive to mass production and processing.

[0049] Example 2

[0050] A specific embodiment of the present invention, as Figure 2 As shown, another method for manufacturing a piezoelectric oxide single crystal substrate is disclosed, the method comprising:

[0051] Step 4, preparing lithium-rich polycrystalline powder, mixing lithium carbonate and metal oxide, performing a high-temperature solid-phase reaction, and then crushing to prepare the lithium-rich polycrystalline powder, the metal element in the metal oxide is the same as the metal element in the piezoelectric oxide single crystal substrate, the lithium in the lithium-rich polycrystalline powder has a first stoichiometric ratio to the metal, the lithium in the piezoelectric oxide single crystal substrate has a second stoichiometric ratio to the metal, the first stoichiometric ratio is greater than the second stoichiometric ratio, and the piezoelectric oxide single crystal substrate is a lithium niobate substrate.

[0052] Since the existing substrate reduction method is often a method of directly using a solid reducing agent to reduce the piezoelectric oxide single crystal substrate at a temperature below the Curie temperature, the solid reducing agent is unevenly distributed on the surface of the piezoelectric oxide single crystal substrate, and the degree of reduction is different, resulting in uneven color on the substrate surface. Therefore, in order to avoid this situation, the present application places the piezoelectric oxide single crystal substrate in a lithium-rich polycrystalline powder. In this embodiment, the piezoelectric oxide single crystal substrate is mainly described as a lithium niobate wafer, wherein the selected lithium niobate substrate has a metal oxide of the same metal element, which is niobium pentoxide, and further sets the first stoichiometric ratio of lithium in the lithium-rich polycrystalline powder to tantalum in the metal oxide to be 55:45-65:35. The setting of the stoichiometric ratio is because when the selected stoichiometric ratio, i.e., the lithium-niobium ratio, is 60:40, the proportion of lithium will be too high, which is easy to cause the lithium-rich polycrystalline powder to be caking, and the particles are coarse, which is not conducive to the uniform reduction of the piezoelectric oxide single crystal substrate. When the selected stoichiometric ratio, i.e., the lithium-tantalum ratio, is too low, the Li concentration gradient between the reduction sheet and the piezoelectric oxide single crystal substrate will be too small, which is not conducive to the diffusion of Li in the lithium-rich polycrystalline powder to the single crystal substrate. Therefore, the lithium-rich polycrystalline powder under the appropriate stoichiometric lithium-niobium ratio can be reused to reduce production costs. In this embodiment, after many studies and experiments, the inventor finally selected the first stoichiometric ratio of lithium in the lithium-rich polycrystalline powder to niobium in the metal oxide to be 55:45 to 65:35 to achieve the best effect.

[0053] In actual processing applications, it can be specifically implemented as follows: first, lithium niobate with a high purity, such as more than 99%, and metal oxides with the same metal element are used as niobium pentoxide. After weighing and mixing, a high-temperature solid phase reaction is first carried out, and then the temperature is raised to melt, and after cooling and crystallization, it is taken out and crushed to prepare lithium niobate polycrystalline particles of different particle sizes. On the other hand, for the preparation of lithium-rich polycrystalline powder, it can be placed at room temperature 800°C, then kept at a constant temperature of 1300°C for 2 hours, then heated to 1650°C and kept at a constant temperature for 8 hours, and then kept at a constant temperature for 5 hours until it cools to room temperature.

[0054] Therefore, by making the chemical composition of the wafer surface close to the stoichiometric ratio, the electromechanical coupling capability of the wafer material can be increased, thereby improving the performance of the surface acoustic wave filter.

[0055] Step 5, preparing reduction sheets, mixing lithium-rich polycrystalline powder and reducing powder according to a preset ratio, wherein the reducing powder is metal powder or carbon powder, and pressing the mixture into sheets to prepare a first reduction sheet and a second reduction sheet.

[0056] Specifically, the reducing powder can be specifically implemented as magnesium powder and / or zinc powder, and the mass ratio of the reducing powder to the lithium-rich polycrystalline powder is set to 10:90-40:60. Since carbon powder only plays a simple reducing role in some cases, when the lithium niobate single crystal substrate is photolithographic, the strong light in the ultraviolet visible light region may cause photodamage to the lithium niobate single crystal substrate. However, in this embodiment, by doping the lithium niobate single crystal substrate with a suitable concentration of reducing powder, i.e., magnesium powder or zinc powder, the occurrence of this situation can be effectively avoided, and the problem that the chip spacing is not easy to set when the reducing gas (reducing powder) is reducing the piezoelectric oxide single crystal substrate can be overcome.

[0057] In order to ensure that the piezoelectric oxide single crystal is substantially reduced uniformly during the reduction treatment, two reduction plates, namely a first reduction plate and a second reduction plate, are provided according to the above method.

[0058] Step 6, reduction treatment, placing the first reduction sheet, the piezoelectric oxide single crystal substrate, and the second reduction sheet on the bracket in sequence, burying them in the lithium-rich polycrystalline powder, and performing high-temperature reduction treatment for a preset time to generate a piezoelectric oxide single crystal substrate with a pseudo-stoichiometric surface composition.

[0059] After the first reduction sheet, the second reduction sheet and the lithium-rich polycrystalline powder are prepared, a high-temperature reduction treatment can be performed while a pyroelectric treatment is performed to remove the surface static electricity of the substrate. Because there will be charge accumulation during the reduction treatment, the static electricity on the surface of the substrate needs to be removed by a pyroelectric method. In this embodiment, a reduction voltage is applied in the z-axis direction of the substrate as a pyroelectric treatment method, which specifically includes: first, the piezoelectric oxide single crystal substrate has an upper surface and a lower surface parallel to each other, the first reduction sheet is contacted with the upper surface, and the second reduction sheet is contacted with the lower surface. After that, the surface of the first reduction sheet away from the piezoelectric oxide single crystal substrate is electrically connected to the first metal electrode, and the surface of the second reduction sheet away from the piezoelectric oxide single crystal substrate is electrically connected to the second metal electrode, wherein the first metal electrode and the second metal electrode are preferably inert metal electrodes such as platinum Pt electrode, Ag electrode, Au gold electrode, etc. In this way, no chemical reaction occurs under high-temperature reduction, which can prevent the components of the metal electrode from contaminating the piezoelectric oxide single crystal substrate and causing the performance of the substrate to deteriorate. Finally, a reduction voltage is applied to the piezoelectric oxide single crystal substrate in the z-axis direction using the first metal electrode and the second metal electrode. For example, a battery formed by a conductive coating having a silver element is used to apply a first reduction voltage in the positive direction of the z-axis of the substrate and a second reduction voltage in the reverse direction of the z-axis of the substrate. The first reduction voltage and the second reduction voltage are mainly voltages that are applied in opposite directions along the z-axis, and are not limited to specific directions. The uniformity of reduction can be further improved by such positive and negative voltage processing.

[0060] The application of the above-mentioned reduction voltage can be specifically applied along the Z-pole axis of the substrate material by applying an external DC electric field. The voltage applied to the contacts of the substrate material is controlled to increase the bulk conductivity of the substrate, wherein the applied reduction voltage is not limited to using a constant voltage DC source, and can also be implemented as applying a time-varying reduction voltage, and connecting a constant current or controlled current source to the substrate to generate the reduction voltage. It should be noted that any DC voltage / current, including constant and time-varying DC voltage / current, falls within the scope of protection of this application.

[0061] Furthermore, since the removal method of pyroelectricity is not limited to applying a reduction voltage, in this embodiment, temperature control can also be used to achieve the removal of pyroelectricity, wherein the equipment used for temperature control treatment adopts a program-controlled vacuum reduction equipment, and the furnace body adopts a high-quality alloy resistance wire. The temperature of the furnace body is automatically adjusted by detecting the heating temperature of the substrate. In this way, through the programmable temperature increase, temperature decrease and temperature gradient control functions, the entire process can be automatically controlled by the program. It should be noted that the present invention does not limit the control method, and other methods such as artificial temperature control also belong to the protection scope of the present invention. The specific implementation is: first, the oxide single crystal substrate that has been surface diffused is placed in a crucible container, and then the crucible is placed in a heat treatment furnace, and the reduction treatment is performed under vacuum or inert or reducing flowing gas at a temperature of 400 to 600°C. Afterwards, the current heating temperature is detected, and when the heating temperature reaches the temperature threshold, the substrate is cooled to a temperature range of 20 to 28°C. Since the transmittance of piezoelectric oxide single crystal substrates with different blackening degrees is different, the darker the color of the chip, the lower the transmittance. The optical absorption of the chip is changed during the reduction process, thereby causing a change in the appearance color. In order to prevent the blackening degree from being too high or insufficient, and the phenomenon that different piezoelectric oxide single crystal substrates have different transmittances during the blackening process, a temperature threshold is set. The temperature threshold is the optimal blackening temperature of the piezoelectric oxide single crystal substrate, which can be set according to artificial experience or the characteristics of the piezoelectric oxide single crystal substrate. In this way, a substrate with the best blackening degree can be obtained, and then it is automatically cooled for 5 to 45 hours to meet the removal conditions that meet the room temperature temperature range of 20 to 28°C.

[0062] Furthermore, the high-temperature reduction treatment performed synchronously with the pyroelectric treatment can be specifically implemented as follows: a preset time treatment is performed at a temperature above 400°C and below the Curie temperature in a mixed gas atmosphere of an inert gas and a reducing gas under normal pressure. The preset time can be implemented as a constant temperature heat treatment for 1-2 hours, and then a reduction voltage is applied, and the applied reduction current density is 0.05-0.2 mA / cm 2, continue to keep the temperature constant for 10-50 minutes. This setting of small current and short constant temperature time can reduce the corrosion of metal electrodes, reuse and save costs. After that, cool down with power on. When the temperature drops to 350℃, remove the reduction voltage and continue to cool to room temperature.

[0063] Furthermore, under the above-mentioned high temperature and pyroelectric treatment method, the substrate of the lithium niobate single crystal substrate is exposed to the vapor of lithium-rich polycrystalline powder, and the lithium element is dispersed from the surface of the substrate to the central part, so that the elemental composition of the substrate changes to a pseudo-stoichiometric composition. The realization principle of changing the elemental composition of the substrate to a pseudo-stoichiometric composition is that in a reducing environment, oxygen diffuses outward from the piezoelectric oxide single crystal, increasing the concentration of oxygen vacancies, and the oxygen vacancies obtain an electron to form F color centers (F+), which enhances the conductivity; at the same time, the color centers absorb strongly in the visible light region, making the color of the chip black. As the concentration of oxygen vacancies increases, the valence of some ions changes from +5 to +4, and the concentration of electron carriers increases accordingly. Therefore, after the reduction treatment, the concentration of carriers in the crystal increases, so that the elemental composition of the substrate changes to a pseudo-stoichiometric composition.

[0064] Furthermore, as a preferred embodiment, there can be multiple piezoelectric oxide single crystal substrates. When the reduction sheet, the isolation sheet, the piezoelectric oxide single crystal substrate, the isolation sheet, and the reduction sheet are sequentially placed on the bracket to achieve uniform reduction of the piezoelectric oxide single crystal substrate, the piezoelectric oxide single crystal substrate can be set perpendicular to the ground. Because the reduction voltage is positively correlated with the thickness of the piezoelectric single crystal substrate, the more substrates there are, the greater the reduction voltage. Therefore, setting the piezoelectric oxide single crystal substrate perpendicular to the ground can reduce cracks or uneven reduction caused by pressure between the substrates, relative to setting the substrate parallel to the ground. Moreover, multiple lithium niobate substrates can be processed simultaneously, which improves the reduction efficiency and is conducive to mass production and processing.

[0065] Example 3

[0066] A specific embodiment of the present invention, as Figure 3 As shown, a SAW filter is disclosed, characterized in that it includes:

[0067] The piezoelectric oxide single crystal substrate 31 manufactured by the method for manufacturing a piezoelectric oxide single crystal substrate of the first or second embodiment and the IDT electrode 32 covering the piezoelectric oxide single crystal substrate 31.

[0068] The blackened piezoelectric oxide single crystal substrate 31 has a transmittance of 80% and a resistivity of less than 10 nm when the irradiation wavelength of the ultraviolet-infrared spectrophotometer is 1500 nm or more. 10Thus, according to the SAW filter of this embodiment, a filter with a low resistivity and a lithium tantalate substrate or a lithium niobate substrate can be obtained, which helps to reduce the thermal expansion coefficient and eliminate the diffraction caused by reflected light during photolithography, thereby helping to improve photolithography accuracy and device consistency, and the yield rate is also improved accordingly.

[0069] Example 4

[0070] A specific embodiment of the present invention, as Figure 4 As shown, another SAW filter is disclosed, the filter comprising:

[0071] Silicon substrate 42;

[0072] A piezoelectric oxide single crystal substrate 41 is bonded to a silicon substrate 42;

[0073] A bonding layer 43 is provided between the piezoelectric oxide single crystal substrate 41 and the silicon substrate. The bonding layer is a silicon oxide layer. The surface of the silicon substrate 42 away from the piezoelectric oxide single crystal substrate 41 is mechanically roughened, thereby reducing light transmission and increasing photolithography accuracy.

[0074] Since the material used in the piezoelectric oxide single crystal substrate will produce serious acoustic wave radiation, the out-of-band suppression at the high end of the filter frequency response is not good, and it is not conducive to the control of substrate precision due to the strong light transmittance during lithography. Therefore, in order to eliminate this influence, it is necessary to mechanically roughen the surface of the silicon substrate 42 away from the piezoelectric oxide single crystal substrate 41. The specific implementation method of this mechanical roughening can be achieved through CMP chemical mechanical polishing or grooving. For the specific implementation method using grooving, a blade can be used to scratch some fine grooves on the surface of the piezoelectric oxide single crystal substrate, so that the back of the substrate becomes rough, which cuts off the radiation path of the bulk acoustic wave to a certain extent. By comparing the out-of-band suppression of the substrate before and after grooving, the inventors obviously found that the out-of-band suppression of the device after grooving becomes higher.

[0075] Furthermore, in order to improve the device requirements of different substrates, in this embodiment, the depth, speed, density and blade thickness of the grooves can also be set differently. Among them, for the depth of the grooves, from the perspective of the effect of suppressing body waves, the deeper the grooves, the better the suppression effect, but as the groove depth increases, the reliability of the substrate material will deteriorate. In some preferred embodiments, the grooves can be staggered in a deep and shallow manner, such as an alternating groove method of deep first and shallow later, or an alternating groove method of shallow first and deep later. This can not only meet the effect of suppressing device body waves, but also ensure the reliability of the material. For the density of the grooves, as long as it refers to the layout of the grooves and the number of grooves per unit area, in this embodiment, it can be expressed as a unidirectional groove and a bidirectional groove. From the perspective of the effect of suppressing body waves, the higher the groove density, the better the suppression effect, but as the groove density increases, the reliability of the substrate material will deteriorate. Therefore, the groove density can be set based on the overall surface area of ​​the substrate, preferably covering 60% of the substrate material. The slotting speed refers to the speed at which the blade cuts the slot on the back of the substrate. The faster the slotting speed, the more obvious the slot edge collapse. The slot edge collapse will inhibit the reliability of the entire substrate material. Therefore, the slotting speed needs to be set within a safe range to ensure that the substrate material is intact after slotting and to improve productivity. For example, the slotting speed can be set to 50 mm / s. The different thicknesses of the blades used in slotting also have a significant impact on the slotting. If the blade is too thick, the surface morphology of the substrate material will be damaged. If the blade is too thin, the roughening of the substrate will not be obvious. Therefore, in this embodiment, the blade thickness is set between 0.1 mm and 0.05 mm to control the integrity of the surface morphology of the slotted substrate material.

[0076] Through this treatment, a SAW filter with a multi-layer composite substrate subjected to blackening treatment can be obtained, so that the device performance of the SAW filter is greatly improved.

[0077] In the present invention, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance; the term "plurality" means two or more. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a piezoelectric oxide single crystal substrate, characterized in that: include: Step 1, preparing lithium-rich polycrystalline powder, mixing lithium carbonate and metal oxide, performing a high-temperature solid-phase reaction, and then crushing to prepare the lithium-rich polycrystalline powder, wherein the metal element in the metal oxide is the same as the metal element in the piezoelectric oxide single crystal substrate, the lithium in the lithium-rich polycrystalline powder and the metal in the lithium-rich polycrystalline powder have a first stoichiometric ratio, the lithium in the piezoelectric oxide single crystal substrate and the metal in the piezoelectric oxide single crystal substrate have a second stoichiometric ratio, and the first stoichiometric ratio is greater than the second stoichiometric ratio; Step 2, preparing a reduction sheet, mixing the lithium-rich polycrystalline powder with a reducing powder according to a preset ratio, wherein the reducing powder is metal powder or carbon powder, and pressing the mixture into a sheet to prepare a first reduction sheet and a second reduction sheet; Step 3, reduction treatment, placing the first reduction sheet, the piezoelectric oxide single crystal substrate, and the second reduction sheet on a bracket in sequence, burying them in the lithium-rich polycrystalline powder, and subjecting them to high-temperature reduction treatment for a preset time to generate a piezoelectric oxide single crystal substrate with a pseudo-stoichiometric surface composition.

2. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 1, wherein: The metal oxide is tantalum pentoxide, the piezoelectric oxide single crystal substrate is lithium tantalate, and the first stoichiometric ratio is 55:45-65:

35.

3. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 2, wherein: The reducing powder is magnesium powder and / or iron powder, and the mass ratio of the reducing powder to the lithium-rich polycrystalline powder is 10:90-40:

60.

4. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 1, wherein: The metal oxide is niobium pentoxide, the piezoelectric oxide single crystal substrate is lithium niobate, and the first stoichiometric ratio is 55:45-65:

35.

5. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 4, wherein: The reducing powder is magnesium powder and / or zinc powder, and the mass ratio of the reducing powder to the lithium-rich polycrystalline powder is 10:90-40:

60.

6. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 1, wherein: In step 3, a pyroelectric treatment is performed simultaneously with the high-temperature reduction treatment to remove static electricity on the surface of the substrate, and the pyroelectric treatment includes: The piezoelectric oxide single crystal substrate has an upper surface and a lower surface that are parallel to each other, the first reduction sheet is in contact with the upper surface, and the second reduction sheet is in contact with the lower surface. The first reduction sheet is electrically connected to the first metal electrode away from the surface of the piezoelectric oxide single crystal substrate; The second reduction sheet is electrically connected to the second metal electrode away from the surface of the piezoelectric oxide single crystal substrate; The first metal electrode and the second metal electrode apply a reduction voltage in the z-axis direction of the piezoelectric oxide single crystal substrate.

7. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 6, wherein: The high temperature reduction treatment comprises: performing a constant temperature heat treatment at a temperature above 400° C. and below the Curie temperature for 1-2 hours in a mixed gas atmosphere of an inert gas and a reducing gas under normal pressure, and then applying a reduction voltage with a reduction current density of 0.05-0.2 mA / cm 2 , continue to maintain constant temperature for 10-50 minutes, cool down with power on, when the temperature drops to 350°C, remove the reduction voltage and continue to cool to room temperature.

8. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 6, wherein: The first metal electrode and the second metal electrode apply a reduction voltage in the z-axis direction of the piezoelectric oxide single crystal substrate, comprising: The battery formed by using the conductive coating having silver element applies a first reduction voltage to the positive direction of the z-axis of the substrate and a second reduction voltage to the reverse direction of the z-axis of the substrate.

9. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 1, wherein: There are multiple piezoelectric oxide single crystal substrates. The reduction sheet, isolation sheet, piezoelectric oxide single crystal substrate, isolation sheet, and reduction sheet are sequentially placed on a bracket to achieve uniform reduction of the piezoelectric oxide single crystal substrate. The piezoelectric oxide single crystal substrate is arranged perpendicular to the ground.

10. A SAW filter, characterized in that: include: A piezoelectric oxide single crystal substrate manufactured by the method for manufacturing a piezoelectric oxide single crystal substrate according to any one of claims 1 to 9; An IDT electrode is covered on the piezoelectric oxide single crystal substrate.

11. The SAW filter according to claim 10, characterized in that: The piezoelectric oxide single crystal substrate has a transmittance of 80% and a resistivity of less than 10 when the irradiation wavelength of the ultraviolet-infrared spectrophotometer is above 1500nm. 10 Ω·cm.

12. The SAW filter according to claim 10, characterized in that: The piezoelectric oxide single crystal substrate is bonded to a silicon substrate; A bonding layer is provided between the piezoelectric oxide single crystal substrate and the silicon substrate, and the bonding layer is a silicon-containing oxide layer; The surface of the silicon substrate away from the piezoelectric oxide single crystal substrate is mechanically roughened.

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