CN115276584A

CN115276584A - Method for manufacturing interdigital electrode of surface acoustic wave device

Info

Publication number: CN115276584A
Application number: CN202210922924.1A
Authority: CN
Inventors: 翁志坤; 张溢涛; 曾沣
Original assignee: Guangdong Guangnaixin Technology Co ltd
Current assignee: Guangdong Guangnaixin Technology Co ltd
Priority date: 2022-08-02
Filing date: 2022-08-02
Publication date: 2022-11-01

Abstract

The invention provides a method for manufacturing an interdigital electrode of a surface acoustic wave device, which comprises the following steps: forming a laminate on a piezoelectric substrate, comprising: forming a buffer layer on the piezoelectric substrate; forming an alloy layer on the buffer layer; and forming a metal layer on the alloy layer; and heat-treating the laminate.

Description

Method for manufacturing interdigital electrode of surface acoustic wave device

Technical Field

The invention relates to a manufacturing method of an interdigital electrode, in particular to a method for manufacturing an interdigital electrode of a surface acoustic wave device.

Background

Surface Acoustic Wave (SAW) filters, bulk Acoustic Wave (BAW) filters, and Film Bulk Acoustic Resonators (FBAR) are three major mainstream technologies in the current filter field. At present, electronic systems are further developed in the directions of miniaturization, high reliability, strong anti-interference capability and the like, and SAW filters are favored more and more. In the fabrication of the SAW filter, the conversion of electrical signals and acoustic signals is accomplished by an Interdigital Transducer (IDT). Aluminum, copper or aluminum-copper alloy has high conductivity, low acoustic impedance and easy processing, and is commonly used as a constituent material of an interdigital transducer.

ExistingThe general technical scheme for preparing the IDT electrode is that LiTaO is used as a catalyst ₃ Or LiNiO ₃ After a thin Ti or Cr film is evaporated on the surface of the wafer, a pure Al or Al-Cu alloy metal film is plated on the thin Ti or Cr film. The AlCu alloy film is prepared by strictly controlling the growth of the Al film to obtain a strongly textured Al film or even a single-crystal Al film, or by using an AlCu alloy. For an IDT electrode applied in a high-frequency SAW device, under the action of alternating repeated stress of high-frequency sound waves, al atoms are easy to migrate along grain boundaries, and a thin film protrudes or locally forms a cavity, so that the electrode is short-circuited and fails, and therefore a film layer with higher power tolerance than a common electrode needs to be prepared. The low loss performance of the device needs to be ensured while the device has high power tolerance. Generally, the higher the Cu content of the Al, the higher the resistance, the higher the loss, but the higher the power resistance of the film. Therefore, it is difficult to satisfy both low loss and high power tolerance, based on the alloying electrode method alone.

The prior art has made many efforts to this end, and for example, chinese patent CN113346867a discloses the following manufacturing method: after a 2nm Ti electrode is plated on a piezoelectric substrate, an Al-based alloy electrode is plated on the Ti electrode, doped elements in the alloy comprise one or more of Cu, W, mo, cr, ag and the like, the bottom buffer layer and the main electrode layer are respectively provided with two layers, the content of the doped elements of the Al alloy electrode layer of each layer is different, and the obtained electrode has the limit power resistance of 35dBm at normal temperature. However, the electrode prepared by the method has higher requirements on controlling the thickness of the bottom Ti layer, has certain requirements on controlling the content of the doped alloy, and has higher difficulty in controlling the uniformity of the whole electrode layer. Mass production is not easy for mass-scale manufacturing.

In the existing technical method for improving the power durability of the electrode, the thickness of a bottom coating film is controlled by evaporating an Al alloy target material through an electron beam so as to strictly control the growth texture of Al, certain challenges exist in controlling the consistency of products, the requirement on the stability of process control is high, and batch production is difficult to realize. Therefore, in order to obtain a power-tolerant electrode with excellent performance and capable of being manufactured in batches, the consistency among product batches needs to be ensured while enough process allowance is ensured as much as possible.

Disclosure of Invention

Technical problem to be solved by the invention

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing an interdigital electrode of a surface acoustic wave device, which can improve the resistivity and mechanical properties of an alloy electrode, and can satisfy the requirement of high mechanical strength of the electrode and the requirement of low resistivity.

Technical scheme for solving technical problem

In one embodiment of the present invention for solving the above-mentioned problems, there is provided a method for manufacturing an interdigital electrode for a surface acoustic wave device, comprising: forming a laminate on a piezoelectric substrate, comprising: forming a buffer layer on the piezoelectric substrate; forming an alloy layer on the buffer layer; and forming a metal layer on the alloy layer; and heat-treating the laminate.

In an embodiment of the present invention, forming the stacked body further includes: and forming a metal protection layer on the metal layer.

In an embodiment of the invention, the metal protection layer is made of a metal that is not easily oxidized, and a material of the metal protection layer is different from that of the metal layer.

In an embodiment of the present invention, the alloy layer includes a first metal element and a second metal element, and the metal layer is composed of the first metal element or the second metal element.

In an embodiment of the present invention, the alloy layer is made of an AlCu alloy, and the metal layer is made of Cu.

In an embodiment of the invention, a ratio between a thickness of the metal layer and a thickness of the alloy layer is between 0.05 and 0.15.

In an embodiment of the present invention, the heat treatment performed on the laminate is performed under vacuum and in a protective atmosphere.

In an embodiment of the present invention, the heat treatment includes: heating the laminate from room temperature to a first temperature and holding at the first temperature for a first period of time; heating the laminate from the first temperature to a second temperature and holding at the second temperature for a second period of time; and cooling the laminate to the room temperature.

In one embodiment of the present invention which solves the above problems, there is provided a surface acoustic wave device including: a piezoelectric substrate; and an interdigital electrode formed on the piezoelectric substrate, the interdigital electrode comprising: a buffer layer formed on the piezoelectric substrate; an alloy layer formed on the buffer layer; and a metal layer formed on the alloy layer.

In an embodiment of the present invention, the interdigital electrode further includes: a metal protection layer formed on the metal layer.

Effects of the invention

According to the invention, the obtained interdigital electrode structure layer is simple, the coating is easy to control, the interdigital electrode structure layer is suitable for mass production, and the power resistance is higher.

Further, according to the present invention, the resistivity and mechanical properties of the alloy electrode can be improved, and the low resistivity can be achieved while achieving high mechanical strength of the electrode.

Drawings

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings, where like reference numerals have been used, where possible, to designate like elements that are common to the figures. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments, wherein:

fig. 1 is a flowchart of an example of a method for manufacturing an IDT electrode of a surface acoustic wave device according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of one example of an IDT electrode structure according to an embodiment of the present invention.

Fig. 3 is a schematic structural diagram of another example of an IDT electrode structure according to an embodiment of the present invention.

Fig. 4 is a temperature profile illustrating a heat treatment of the IDT electrode structure according to an embodiment of the present invention.

Fig. 5 is a graph illustrating the effect of metal layer thickness on the power resistance performance of an electrode in an example of a laminate according to an embodiment of the present invention.

Fig. 6 is a scanning electron microscope image showing a device having IDT electrodes after a power withstand test according to an embodiment of the present invention.

It is contemplated that elements of one embodiment of the present invention may be beneficially utilized on other embodiments without further recitation.

Detailed Description

Other advantages and technical effects of the present invention will be apparent to those skilled in the art from the disclosure of the present specification, which are described in the following embodiments. The present invention is not limited to the following embodiments, and various other embodiments may be implemented or applied, and various modifications and changes may be made in the details of the present description without departing from the spirit of the present invention.

This application uses specific language to describe embodiments of the application. Reference to "one embodiment," "another embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the application. Therefore, it is emphasized and should be appreciated that two or more references to "one embodiment" or "another embodiment" or "some embodiments" in various places in the specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.

It should be noted that in order to simplify the present disclosure and thereby facilitate an understanding of one or more embodiments, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure herein. This method of disclosure, however, is not intended to require more features than are expressly recited in the claims. Indeed, embodiments may have fewer than all of the features of a single embodiment disclosed below.

Hereinafter, specific embodiments of the present invention will be described in detail based on the drawings. The drawings are for simplicity and clarity and are not intended to be drawn to scale, reflecting the actual dimensions of the structures described. To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

In this specification, the terms "interdigital transducer (IDT) electrode" and "interdigital electrode" are used interchangeably.

An example of a method for manufacturing an interdigital electrode for a surface acoustic wave device according to the present invention is described below with reference to fig. 1 to 6.

Fig. 1 is a schematic flow chart of an example of a method for manufacturing an interdigital electrode for a surface acoustic wave device to which the present invention relates.

The exemplary method 100 begins at step 101 in fig. 1. At step 101, a buffer layer 221 may be formed on a piezoelectric substrate 210. The piezoelectric substrate 210 may be formed of, for example, lithium tantalate or a lithium tantalate wafer, or the like. For example, sputtering, evaporation, chemical Vapor Deposition (CVD), physical Vapor DepositionThe buffer Layer 221 is formed by various methods such as Physical Vapor Deposition (PVD) and Atomic Layer Deposition (ALD). The buffer layer 221 is made of, for example, ti, znO/Al ₂ O ₃ And a suitable material such as a ZnO material. As an example, the thickness of the buffer layer 221 may be in a range of 2nm to 10 nm.

At step 102, an alloy layer 222 may be formed on the buffer layer 221. For example, the alloy layer 222 may be formed by various methods such as sputtering, evaporation, chemical vapor deposition, physical vapor deposition, and atomic layer deposition. The alloy layer 222 is made of, for example, alCu alloy, niCr alloy, alSi alloy, alTi alloy, or the like. As an example, the alloy layer 222 may be an AlCu alloy having a Cu content in the range of 0.5% to 4%.

At step 103, a metal layer 223 may be formed on the alloy layer 222. For example, the metal layer 223 may be formed by various methods such as sputtering, evaporation, chemical vapor deposition, physical vapor deposition, and atomic layer deposition. The metal layer 223 is made of a suitable material such as Cu, ni, cr, al, ti, or the like.

Through steps 101 to 103, the stacked body 220 in fig. 2 may be formed, the stacked body 220 including: a buffer layer 221; an alloy layer 222; and a metal layer 223. The stacked body 220 can function as an IDT electrode, and functions as an IDT electrode. The combination of the piezoelectric substrate 210 and the stack 220 may be referred to as an IDT electrode structure 200.

Optionally, further via optional step 104, a stack 220 'may be formed, which stack 220' may further comprise an optional metal protection layer 224.

At optional step 104, a metal protection layer 224 may be formed on the metal layer 223. For example, the metal protection layer 224 may be formed by various methods such as sputtering, evaporation, chemical vapor deposition, physical vapor deposition, and atomic layer deposition. The metal cap layer 224 is made of a suitable material such as Cr or Ti. The metal protection layer 224 may be composed of a metal that is not easily oxidized, and the material of the metal protection layer 224 may be different from the metal layer 223. As an example, the thickness of the metal protection layer 224 may be in the range of 5nm to 8 nm. The metal protection layer 224 may protect the metal layer 223 from oxidation of the metal layer 223. Through steps 101 to 104, through steps 101 to 103, a stacked body 220 'in fig. 2 may be formed, the stacked body 220' including a buffer layer 221, an alloy layer 222, a metal layer 223, and a metal protection layer 224. The stacked body 220' can function as an IDT electrode, and functions as an IDT electrode. The combination of the piezoelectric substrate 210 and the stack 220 'may be referred to as an IDT electrode structure 200'.

In the above steps for forming the stacked body 220, 220', the process conditions for forming each layer and the rate of forming each layer may be selected as required. As an example, each step of forming each layer may be controlled to a degree of vacuum of 5X 10 ^-5 Pa to 1X 10 ^-5 Is carried out in an environment of Pa. In addition, for example, when the alloy layer 222 and/or the metal layer 223 are formed, the Al evaporation rate is 5A/s to 10A/s, and the Cu plating rate is controlled to be 0.1A/s to 0.2A/s, and special uniformity baffles can be respectively arranged for Al plating and Cu plating, so that the thickness uniformity of the alloy film can be ensured.

As a preferred embodiment, the alloy layer 222 includes a first metal element and a second metal element, and the metal layer 223 is composed of the first metal element or the second metal element. As a further preferred embodiment, the alloy layer 222 may be an AlCu alloy, and the metal layer 223 may be a pure Cu metal.

As still another preferred embodiment, the ratio of the thickness of the metal layer 223 to the thickness of the alloy layer 222 may be controlled to be between 5% and 15%.

Alternatively, when steps 101 to 103 or steps 101 to 104 are completed, the piezoelectric substrate 210 and the formed stacked body 220 and 220' may be placed in a stripper for peeling. This process may be advantageous when using a photolithographic method to form the IDT electrodes 200, 200'.

At step 105, the laminate 220, 220' may be heat treated. The formed stacked body 220, 220' may be placed in a vacuum atmosphere protection furnace to be heat-treated. The heat treatment may be performed under vacuum and in a protective atmosphere. The protective atmosphere may be, for example, N ₂ Atmosphere, he atmosphere, ne atmosphere, or the like.

Fig. 4 depicts a temperature profile of one example of a process of heat treatment. This exemplary heat treatment process may be performed in three steps:

1) Heating the laminate 220, 220' from room temperature (e.g., the room temperature is a temperature in the range of 20 ℃ to 30 ℃) to a first temperature (e.g., the first temperature is a temperature in the range of 100 ℃ to 150 ℃) and holding at the first temperature for a first period of time (e.g., the length of the first period of time is in the range of 0.5 hours (h) to 1 h);

2) Heating the stack 220, 220' from the first temperature to a second temperature (e.g., the second temperature is a temperature in the range of 200 ℃ to 250 ℃) and holding at the second temperature for a second period of time (e.g., the length of the second period of time is in the range of 1h to 2 h); and

3) The stack 220, 220' is cooled to room temperature.

It should be clear that although some exemplary values are listed, the values of room temperature, first temperature, second temperature, first time period and second time period are arbitrarily selectable as required by the process.

With respect to this exemplary heat treatment process, for example, the sample chamber is under vacuum + N throughout the heat treatment process ₂ And (4) working modes. Wherein the furnace tube vacuum of the vacuum atmosphere protective furnace for performing heat treatment can reach 1 × 10 ^-3 Pa～2×10 ^-3 After Pa, start to feed N ₂ ,N ₂ The flow rate is controlled between 5L/min and 20L/min.

The device including the IDT electrodes 200 and 200' may be subjected to a package test after the above process is completed. The device can be selected for power endurance testing. The power withstand test temperature may be 55 ℃, i.e. the device is placed in an incubator at 55 ℃ for a power loading test.

Fig. 5 shows the effect of the thickness of the metal layer 223 on the power withstanding performance of the exemplary IDT electrode structure 200' when the alloy layer 222 is an AlCu alloy and the metal layer 223 is Cu. It can be seen that the IDT electrode structure 200' has an electrode withstand power in the range of 34dBm to 33.5dBm when the Cu thickness is in the range of 10nm to 15 nm. By adjusting the parameters of the process, higher electrode power resistance can be realized.

Fig. 6 is a Scanning Electron Microscope (SEM) photograph of an exemplary device (e.g., saw filter) including an alloy layer 222 of material AlCu and a metal layer 223 of material Cu after a 55 c limit power test. As can be seen from the figure, the finger surfaces of the electrodes are smooth, no obvious bulge or hole is seen, and only the side wall can see the bulge caused by Al atom migration, which indicates that the Al atom migration is blocked along the thickness direction of the film, almost cannot migrate, and can only migrate towards the transverse direction. In the AlCu alloy, cu atoms distributed around grain boundaries can effectively inhibit Al migration, and a Cu layer with proper thickness is plated on the AlCu alloy layer, so that an alloy transition layer can be formed at the interface of two layers of materials through atomic diffusion. Through a proper heat treatment process, an alloy transition layer between two layers of metal is more compact and uniform, al atoms are effectively prevented from migrating to the top of the electrode, and the power tolerance of the electrode is improved.

In some embodiments, the operations included in the methods in the embodiments described above may occur simultaneously, substantially simultaneously, or in a different order than shown in the figures.

According to the invention, the obtained interdigital electrode has a simple structure layer, is easy to control the coating, is suitable for mass production, and has high power resistance.

According to the invention, the resistivity and the mechanical property of the alloy electrode can be improved, and the mechanical strength of the electrode can be satisfied while the low resistivity is satisfied.

According to the invention, the multilayer alloy electrode with stronger power resistance can be formed by forming the alloy layer and the metal layer on the alloy layer and adjusting the thickness ratio of the two layers.

Alternative embodiments of the present application are described in detail above. It will be appreciated that various embodiments and modifications may be made thereto without departing from the broader spirit and scope of the application. Many modifications and variations will be apparent to those of ordinary skill in the art in light of the teachings of this application without undue experimentation. As a non-limiting example, one skilled in the art may omit one or more of the above-described components or add one or more components to the above-described system or structure, or replace some or all of the various structures or systems involved in the present embodiment with other components having the same or similar functions. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the concepts of the present application shall fall within the scope of protection defined by the claims of the present application.

Claims

1. A method for fabricating interdigital electrodes for a surface acoustic wave device, comprising:

forming a laminate on a piezoelectric substrate, comprising:

forming a buffer layer on the piezoelectric substrate;

forming an alloy layer on the buffer layer; and

forming a metal layer on the alloy layer; and

and performing heat treatment on the laminated body.

2. The method of claim 1, wherein forming the laminate further comprises: and forming a metal protection layer on the metal layer.

3. The method of claim 2, wherein the metal protection layer is composed of a metal that is not easily oxidized, and a material of the metal protection layer is different from the metal layer.

4. The method of claim 1, wherein the alloy layer comprises a first metallic element and a second metallic element, and the metallic layer consists of the first metallic element or the second metallic element.

5. The method of claim 4, wherein the alloy layer is comprised of an AlCu alloy and the metal layer is comprised of Cu.

6. The method according to claim 1, wherein the ratio between the thickness of the metal layer and the thickness of the alloy layer is between 0.05 and 0.15.

7. The method of claim 1, wherein said heat treating said laminate is performed under vacuum and in a protective atmosphere.

8. The method of claim 7, wherein the heat treating comprises:

heating the laminate from room temperature to a first temperature and holding at the first temperature for a first period of time;

heating the laminate from the first temperature to a second temperature and holding at the second temperature for a second period of time; and

cooling the laminate to the room temperature.

9. A surface acoustic wave device comprising:

a piezoelectric substrate; and

an interdigital electrode formed on the piezoelectric substrate, the interdigital electrode comprising:

a buffer layer formed on the piezoelectric substrate;

an alloy layer formed on the buffer layer; and

a metal layer formed on the alloy layer.

10. A surface acoustic wave device as set forth in claim 9, wherein said interdigital electrode further comprises: a metal protection layer formed on the metal layer.

11. A surface acoustic wave device as set forth in claim 9, wherein said alloy layer contains a first metal element and a second metal element, and said metal layer is composed of said first metal element or said second metal element.

12. A surface acoustic wave device as set forth in claim 11, wherein said alloy layer is composed of an AlCu alloy, and said metal layer is composed of Cu.

13. A surface acoustic wave device as set forth in claim 9, wherein a ratio between a thickness of said metal layer and a thickness of said alloy layer is between 0.05 and 0.15.