XBAR resonator with low temperature drift and preparation method thereof

Abstract

The invention relates to the technical field of integrated circuit manufacturing, and particularly discloses a low-temperature-drift XBAR resonator and a preparation method thereof, and the resonator comprises a first substrate, one side surface of which is covered with a bonding layer; one side surface of the first oxide layer is in contact with the surface of the bonding layer, a resonant cavity and an interdigital electrode are arranged in the first oxide layer, the resonant cavity is in contact with part of the surface of the bonding layer, and the projection of the interdigital electrode and the projection of the resonant cavity on the first substrate are overlapped; one side surface of the piezoelectric layer is in contact with the other side surface of the first oxide layer and one side surface of the interdigital electrode; and the second oxide layer covers the piezoelectric layer. According to the invention, the piezoelectric layer is covered with the second oxide layer, and temperature compensation and frequency adjustment are carried out on the resonator, so that the resonator is high in reliability, good in temperature drift performance and higher in mechanical performance; the interdigital electrode is wrapped by the first oxide layer, so that the temperature drift coefficient of the resonator is better, and the problem that the performance of a product is not constant due to the fact that a traditional XBAR changes along with the temperature is solved.

Description

Technical Field

[0001] The invention relates to the technical field of integrated circuit manufacturing, and in particular to a low-temperature drift XBAR resonator and a preparation method thereof. Background Art

[0002] The surface acoustic wave resonator (SAW) is closely related to the spacing between metal interdigitated electrodes (IDT). When SAW is used at high frequencies, the line width and spacing of IDT are small, and the process preparation is greatly restricted.

[0003] The laterally excited bulk acoustic wave resonator (XBAR) includes a piezoelectric film and an interdigitated electrode (IDT) located on the piezoelectric film. The electrode excitation of the XBAR mainly produces a horizontal electric field, which produces a resonance of a half-wavelength shear wave in the piezoelectric material. Therefore, the metallization rate of the XBAR is small, that is, the electrode spacing is large, and the preparation process is simple.

[0004] After the cavity is formed in the traditional XBAR resonator, the substrate of the piezoelectric film is released. At this time, the bow value of the piezoelectric film is large, and then the IDT is formed on the piezoelectric film. This solution will cause different degrees of warping of the piezoelectric film due to different stresses at different positions of the piezoelectric film layer, such as Figure 1 As shown, the IDT spacing and size are difficult to control, the distribution is poor, and it is difficult to ensure the structural consistency of the entire device; in addition, the difference in the thickness of the LT piezoelectric layer will affect the IDT morphology and height, causing a relatively large frequency difference, and the IDT is difficult to adjust.

[0005] Meanwhile, the traditional XBAR resonator adopts the following technical solutions:

[0006] 1. Silicon back etching: The back cavity etches away the substrate and bonding layer under the resonance area; silicon back etching removes a large area of ​​Si substrate, resulting in reduced mechanical fastness;

[0007] 2. Etching the oxide layer: The bonding layer under the resonance area is corroded by releasing the holes on the front side; it is easy to damage the film and reduce the quality of the film. In addition, corrosion residues will be formed in the cavity, affecting the performance of the device;

[0008] 3. Release the sacrificial layer: etch the groove - deposit the protective layer - fill the sacrificial layer - chemical mechanical polishing - deposit the working layer - remove the sacrificial layer - form a cavity; the process of releasing the sacrificial layer is complicated, with many steps and high cost.

[0009] Furthermore, after the IDT is formed, the frequency of the traditional XBAR resonator can only be adjusted by adjusting the thickness of the IDT. This adjustment will inevitably cause a certain amount of loss to the piezoelectric layer. The piezoelectric layer structure will not be a uniform film layer, but will have a certain pit structure between the IDTs, affecting the propagation of sound waves and device performance. In addition, the change in frequency by relying solely on adjusting the IDT is relatively weak.

[0010] In addition, after the piezoelectric thin film material is formed, the conventional XBAR resonator can only form an electrode reflection structure on a single surface where the piezoelectric thin film material is located, and the design space is small.

[0011] Based on this technical background, the present invention proposes a low-temperature drift XBAR resonator and a preparation method thereof. Summary of the invention

[0012] In view of the shortcomings of the prior art, the present invention proposes a low-temperature drift XBAR resonator and a preparation method thereof. The resonator covers a second oxide layer on the piezoelectric layer, and performs temperature compensation and frequency adjustment on the resonator, so that the resonator has high reliability, good temperature drift performance, and stronger mechanical properties; at the same time, the interdigital electrodes are wrapped by the first oxide layer, so that the temperature drift coefficient of the resonator is better, thereby solving the problem that the performance of the traditional XBAR changes with temperature and the product is not constant.

[0013] In order to achieve the above object, the first aspect of the present invention provides a low temperature drift XBAR resonator, comprising:

[0014] A first substrate having a bonding layer covered on one surface thereof;

[0015] a first oxide layer, one side surface of which is in contact with the surface of the bonding layer, and a resonant cavity and interdigital electrodes are arranged inside the first oxide layer, the resonant cavity is in contact with a portion of the surface of the bonding layer, and the interdigital electrodes overlap with a projection of the resonant cavity on the first substrate;

[0016] A piezoelectric layer, one side surface of which is in contact with the other side surface of the first oxide layer and one side surface of the interdigital electrode respectively;

[0017] The second oxide layer covers the piezoelectric layer and is used for temperature compensation and frequency adjustment of the resonator.

[0018] A second aspect of the present invention provides a method for preparing the above-mentioned resonator, comprising:

[0019] sequentially growing an oxide buried layer and a piezoelectric layer on a substrate;

[0020] sequentially growing interdigitated electrodes and a first oxide layer on the piezoelectric layer;

[0021] Grinding, dry etching or wet etching the first oxide layer covering the interdigital electrodes in sequence to form a groove of the resonant cavity, thereby obtaining a second wafer;

[0022] Growing a bonding layer on a first substrate to obtain a first wafer;

[0023] Flipping the first wafer over and bonding it to the second wafer to form a resonant cavity, thereby obtaining a bonded wafer;

[0024] Removing the substrate on the bonded wafer and then flipping it over, growing a second oxide layer on the buried oxide layer to obtain a resonator;

[0025] The second oxide layer is used to perform temperature compensation and frequency adjustment on the resonator.

[0026] The technical effects of the present invention include:

[0027] (1) The low-temperature drift XBAR resonator proposed in the present invention performs temperature compensation and frequency adjustment on the resonator by covering the piezoelectric layer with a second oxide layer, so that the resonator has high reliability, good temperature drift performance, and stronger mechanical properties. The interdigital electrodes are wrapped with the first oxide layer to improve the temperature drift coefficient of the resonator, thereby solving the problem that the performance of the traditional XBAR product is not constant due to temperature changes.

[0028] (2) In the method for preparing a low-temperature drift XBAR resonator proposed in the present invention, the interdigitated electrodes are formed in advance on the piezoelectric layer with a substrate, and have good uniformity. By adjusting the thickness of the piezoelectric layer, the deformation and damage of the piezoelectric film material are avoided, the morphological structure of the IDT is maintained, and there is a larger space for adjusting the frequency.

[0029] (3) Compared with the existing method of making a cavity by etching silicon on the back, the method for preparing a low-temperature drift XBAR resonator proposed in the present invention has better structural strength; compared with the existing method of etching an oxide layer to form a lower cavity, it has better temperature drift characteristics; compared with the method of releasing a sacrificial layer to form a cavity, it reduces the number of process steps and has lower cost.

[0030] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0032] Figure 1 Schematic diagram of the warping of the piezoelectric film in the XBAR resonator prepared by the traditional method.

[0033] Figure 2 This is a schematic diagram of the low-temperature drift XBAR resonator structure proposed by the present invention.

[0034] Figure 3 The figure is a schematic diagram of the overall process of a specific implementation method of the method for preparing a low-temperature drift XBAR resonator proposed by the present invention.

[0035] Figure 4 This is a schematic diagram of the process of growing interdigital electrodes in a specific implementation of the low-temperature drift XBAR resonator structure and preparation method proposed by the present invention.

[0036] Figure 5 This is a schematic diagram of the process of growing the first oxide layer in a specific implementation of the low-temperature drift XBAR resonator structure and preparation method proposed by the present invention.

[0037] Figure 6 This is a schematic diagram of the process of grinding the first oxide layer in a specific implementation of the low-temperature drift XBAR resonator structure and preparation method proposed by the present invention.

[0038] Figure 7 This is a schematic diagram of the etching process of the first oxide layer in a specific implementation of the low-temperature drift XBAR resonator structure and preparation method proposed by the present invention.

[0039] Figure 8 This is a schematic diagram of the bonding process in a specific implementation of the low-temperature drift XBAR resonator structure and preparation method proposed by the present invention.

[0040] Fig. 9 This is a schematic diagram of a substrate removal process in a specific implementation of a low-temperature drift XBAR resonator structure and a preparation method proposed in the present invention.

[0041] Fig.10 This is a schematic diagram of the process of growing a second oxide layer and pins in a specific implementation of the low-temperature drift XBAR resonator structure and preparation method proposed by the present invention.

[0042] Fig.11 It is a schematic diagram comparing the frequency shifts of the back side OX, the reverse side OX, and the front and reverse sides OX in a specific implementation manner of the low-temperature drift XBAR resonator structure and the preparation method proposed in the present invention.

[0043] Description of reference numerals:

[0044] 101-first substrate, 102-bonding layer, 103-first oxide layer, 104-interdigitated electrodes, 105-piezoelectric layer, 106-pin, 107-second oxide layer, 108-base, 109-buried oxide layer, 110-resonant cavity;

[0045] 201-POI substrate;

[0046] SIN-silicon nitride, Oxide-oxide layer, LiNbO3-lithium niobate, PR-positive photoresist, Cu-metal copper, bonding-bonding, RDL&Pad-wiring and pins, TR wafer-TR wafer, that is, the first substrate, IDT-the abbreviation of interdigitated electrode, OX-the abbreviation of oxide layer, THK-thickness. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0048] In the present invention, unless otherwise specified, the directional words used, such as "upper and lower", generally refer to the upper and lower parts of the device in normal use, and "inside and outside" refer to the outline of the device. In addition, the terms "first, second, third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first, second, third" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0049] The present invention provides a low temperature drift XBAR resonator, such as Figure 2 As shown, including:

[0050] A first substrate 101, with a bonding layer 102 covering one surface thereof;

[0051] A first oxide layer 103, one side of which is in contact with the surface of the bonding layer 102, and a resonant cavity 110 and an interdigital electrode 104 are provided inside the first oxide layer 103, the resonant cavity 110 is in contact with a portion of the surface of the bonding layer 102, and the interdigital electrode 104 overlaps with the projection of the resonant cavity 110 on the first substrate 101;

[0052] The piezoelectric layer 105 has one side surface that is in contact with the other side surface of the first oxide layer 103 and one side surface of the interdigital electrode 104 respectively;

[0053] The second oxide layer 107 covers the piezoelectric layer 105 and is used for temperature compensation and frequency adjustment of the resonator.

[0054] In the present invention, by covering the piezoelectric layer with a second oxide layer, the resonator is temperature compensated and the frequency adjusted, so that the resonator has high reliability, good temperature drift performance, and stronger mechanical properties; by wrapping the interdigital electrodes with the first oxide layer, the resonator temperature drift coefficient is better, thereby solving the problem of traditional XBAR changing with temperature and the performance of the product being unstable.

[0055] According to the present invention, the projected area of ​​the resonant cavity 110 on the first substrate 101 is not less than the projected area of ​​the interdigital electrodes 104 on the first substrate 101 .

[0056] According to the present invention, it also includes:

[0057] The pin 106 penetrates through the piezoelectric layer 105 and serves as an electrical lead-out terminal of the interdigital electrode 104 .

[0058] According to the present invention, the first substrate 101 is a TR wafer, and the TR wafer includes a polysilicon layer for improving the Q value of the resonator;

[0059] The material of the bonding layer 102 is silicon nitride, which is used to achieve the structural strength of the resonator and improve the reliability.

[0060] According to the present invention, the interdigital electrodes 104 and the resonant cavity 110 are not in contact with each other.

[0061] The present invention also provides a method for preparing the resonator, comprising:

[0062] On the POI substrate 201 having the base 108, the buried oxide layer 109 and the piezoelectric layer 105, interdigitated electrodes 104 and a first oxide layer 103 are sequentially grown;

[0063] The first oxide layer 103 covering the interdigital electrodes 104 is sequentially ground, dry-etched or wet-etched to form a groove of the resonant cavity 110, thereby obtaining a second wafer;

[0064] Growing a bonding layer 102 on a first substrate 101 to obtain a first wafer;

[0065] The first wafer is flipped over and bonded to the second wafer to form a resonant cavity 110, thereby obtaining a bonded wafer;

[0066] The substrate 108 on the bonded wafer is removed and then turned over, and a second oxide layer 107 is grown on the buried oxide layer 109 to obtain a resonator;

[0067] The second oxide layer 107 is used to perform temperature compensation and frequency adjustment on the resonator.

[0068] According to the present invention, the projected area of ​​the resonant cavity 110 on the first substrate 101 is not less than the projected area of ​​the interdigital electrodes 104 on the first substrate 101 .

[0069] According to the present invention, before growing the second oxide layer 107 on the buried oxide layer 109, the method further includes:

[0070] A wiring layer is grown to form pins 106 penetrating the piezoelectric layer 105 , serving as electrical lead-out terminals of the interdigital electrodes 104 .

[0071] According to the present invention, the first substrate 101 is a TR wafer, and the TR wafer includes a polysilicon layer for improving the Q value of the resonator;

[0072] The material of the bonding layer 102 is silicon nitride, which is used to achieve the structural strength of the resonator and improve the reliability;

[0073] The base 108, the buried oxide layer 109 and the piezoelectric layer 105 together form a POI substrate 201;

[0074] During the process of forming the piezoelectric layer 105 , the thickness thereof is adjusted to avoid deformation and damage of the material of the piezoelectric layer 105 and to maintain the morphological structure of the interdigital electrodes 104 .

[0075] According to the present invention, the bottom of the groove forming the resonant cavity 110 does not contact the interdigital electrodes 104 .

[0076] In the present invention, the interdigitated electrodes are formed in advance on the piezoelectric layer with the substrate, and have good uniformity. By adjusting the thickness of the piezoelectric layer, the deformation and damage of the piezoelectric film material are avoided, the morphological structure of the IDT is maintained, and there is a larger space for adjusting the frequency.

[0077] Compared with the existing solution of etching silicon on the back to make a cavity, the present invention has better structural strength; compared with the existing solution of etching an oxide layer to form a lower cavity, the present invention has better temperature drift characteristics; compared with the solution of releasing a sacrificial layer to form a cavity, the process steps are reduced and the cost is lower.

[0078] The present invention will be described in more detail below through specific examples.

[0079] Example 1

[0080] like Figure 2 As shown, this embodiment provides a low temperature drift XBAR resonator, including:

[0081] A first substrate 101, with a bonding layer 102 covering one surface thereof;

[0082] A first oxide layer 103, one side of which is in contact with the surface of the bonding layer 102, and a resonant cavity 110 and an interdigital electrode 104 are provided inside the first oxide layer 103, the resonant cavity 110 is in contact with a portion of the surface of the bonding layer 102, and the interdigital electrode 104 overlaps with the projection of the resonant cavity 110 on the first substrate 101;

[0083] The piezoelectric layer 105 has one side surface that is in contact with the other side surface of the first oxide layer 103 and one side surface of the interdigital electrode 104 respectively;

[0084] A second oxide layer 107, covering the piezoelectric layer 105, is used for temperature compensation and frequency adjustment of the resonator;

[0085] According to the present invention, the projection area of ​​the resonant cavity 110 on the first substrate 101 is not less than the projection area of ​​the interdigital electrodes 104 on the first substrate 101;

[0086] The pin 106 penetrates the piezoelectric layer 105 and serves as an electrical lead-out terminal of the interdigital electrode 104;

[0087] In this embodiment, the first substrate 101 is a TR wafer, and the TR wafer includes a polysilicon layer, which is used to improve the Q value of the resonator;

[0088] The material of the bonding layer 102 is silicon nitride, which is used to achieve the structural strength of the resonator and improve the reliability;

[0089] In this embodiment, the interdigital electrodes 104 and the resonant cavity 110 are not in contact with each other.

[0090] This embodiment provides a method for preparing a low temperature drift XBAR resonator. Figure 3 As shown, including:

[0091] The interdigitated electrodes 104 and the first oxide layer 103 are sequentially grown on the POI substrate 201 having the base 108, the buried oxide layer 109 and the piezoelectric layer 105. Figure 4 As shown;

[0092] The first oxide layer 103 covering the interdigital electrodes 104 is sequentially ground, dry-etched or wet-etched to form a groove of the resonant cavity 110, thereby obtaining a second wafer. Figure 5 , Figure 6 and Figure 7 As shown;

[0093] Growing a bonding layer 102 on a first substrate 101 to obtain a first wafer;

[0094] The first wafer is flipped over and bonded to the second wafer to form a resonant cavity 110, so as to obtain a bonded wafer. Figure 8 As shown;

[0095] After removing the substrate 108 on the bonded wafer, the wafer is flipped over to grow a wiring layer to form a pin 106 that penetrates the piezoelectric layer 105 as an electrical lead-out end of the interdigital electrode 104. Then, a second oxide layer 107 is grown on the oxide buried layer 109 to obtain a resonator, such as Fig. 9 and Fig.10 As shown;

[0096] In this embodiment, the second oxide layer 107 is used to perform temperature compensation and frequency adjustment on the resonator;

[0097] The base 108, the buried oxide layer 109 and the piezoelectric layer 105 together form a POI substrate 201;

[0098] During the process of forming the piezoelectric layer 105 , the thickness thereof is adjusted to avoid deformation and damage of the material of the piezoelectric layer 105 and to maintain the morphological structure of the interdigital electrodes 104 ;

[0099] In this embodiment, the bottom of the groove forming the resonant cavity 110 does not contact the interdigital electrodes 104 , forming a structure in which the oxide layer wraps the interdigital electrodes.

[0100] In this embodiment, the frequency offset comparison of the back side OX, the reverse side OX, and the front and reverse sides OX is as follows: Fig.11 As shown, from the comparison we can see: 1) Thickness of piezoelectric layer: keff2 (effective electromechanical coupling coefficient) is linearly related to it and is the main determinant of keff2 and resonant frequency fs; 2) Metallization rate of fork-finger electrode: frequency is sensitive to it, and the number of spurious modes increases with the increase of ratio; 3) Thickness of fork-finger electrode: frequency is not sensitive; 4) The material of fork-finger electrode is more sensitive to the generation of spurious modes and can be optimized using OX (oxide layer).

[0101] The low-temperature drift XBAR resonator proposed in the embodiment of the present invention performs temperature compensation and frequency adjustment on the resonator by covering the second oxide layer on the piezoelectric layer, so that the resonator has high reliability, good temperature drift performance, and stronger mechanical properties; the interdigital electrodes are wrapped by the first oxide layer, so that the temperature drift coefficient of the resonator is better, thereby solving the problem that the performance of the traditional XBAR product is not constant due to temperature changes.

[0102] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A low temperature drift XBAR resonator, characterized in that: include: A first substrate having a bonding layer covered on one surface thereof; a first oxide layer, one side surface of which is in contact with the surface of the bonding layer, and a resonant cavity and interdigital electrodes are arranged inside the first oxide layer, the resonant cavity is in contact with a portion of the surface of the bonding layer, and the interdigital electrodes overlap with a projection of the resonant cavity on the first substrate; A piezoelectric layer, one side surface of which is in contact with the other side surface of the first oxide layer and one side surface of the interdigital electrode respectively; The second oxide layer covers the piezoelectric layer and is used for temperature compensation and frequency adjustment of the resonator.

2. The resonator according to claim 1, characterized in that A projected area of ​​the resonant cavity on the first substrate is not smaller than a projected area of ​​the interdigital electrodes on the first substrate.

3. The resonator according to claim 1, characterized in that Also includes: The pins penetrate through the piezoelectric layer and serve as electrical lead-out terminals of the interdigitated electrodes.

4. The resonator according to claim 1, characterized in that The first substrate is a TR wafer; The material of the bonding layer is silicon nitride.

5. The resonator according to claim 1, characterized in that The interdigital electrodes and the resonant cavity are not in contact with each other.

6. A method for preparing a low temperature drift XBAR resonator, characterized in that: include: Growing interdigital electrodes and a first oxide layer in sequence on a POI substrate having a base, an oxide buried layer and a piezoelectric layer; Grinding, dry etching or wet etching the first oxide layer covering the interdigital electrodes in sequence to form a groove of the resonant cavity, thereby obtaining a second wafer; Growing a bonding layer on a first substrate to obtain a first wafer; Flipping the first wafer over and bonding it to the second wafer to form a resonant cavity, thereby obtaining a bonded wafer; Removing the substrate on the bonded wafer and then flipping it over, growing a second oxide layer on the buried oxide layer to obtain a resonator; The second oxide layer is used to perform temperature compensation and frequency adjustment on the resonator.

7. The preparation method according to claim 6, characterized in that: A projected area of ​​the resonant cavity on the first substrate is not smaller than a projected area of ​​the interdigital electrodes on the first substrate.

8. The preparation method according to claim 6, characterized in that: Before growing the second oxide layer on the buried oxide layer, the method further comprises: A wiring layer is grown to form pins penetrating the piezoelectric layer, which serve as electrical lead-out terminals of the interdigital electrodes.

9. The preparation method according to claim 6, characterized in that: The first substrate is a TR wafer; The material of the bonding layer is silicon nitride; The base, the buried oxide layer and the piezoelectric layer together form a POI substrate; During the process of forming the piezoelectric layer, the thickness of the piezoelectric layer is adjusted to avoid deformation and damage of the piezoelectric layer material and to maintain the morphological structure of the interdigital electrodes.

10. The preparation method according to claim 6, characterized in that: The bottom of the groove forming the resonant cavity does not contact the interdigital electrodes.

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