A surface acoustic wave device and a method of manufacturing the same

Abstract

The present application relates to information electronic material technology, information communication, wireless radio frequency communication and the like fields, and particularly relates to a surface acoustic wave device and a preparation method thereof, the preparation method comprising: patterning and peeling the interdigital electrode layer after depositing a metal film; forming a non-closed release window when patterning and peeling the interdigital electrode layer; forming a closed release window by partially overlapping from the direction of the non-closed release window using a thickened electrode layer; etching the exposed piezoelectric film in the closed release window to form a release hole; and further releasing the substrate material through the release hole to form a suspended piezoelectric film. Through the patterning design of the resonator film structure and the optimization of the processing flow, the present application realizes the efficient peeling of the release window in the bus bar area, reduces the peeling processing difficulty of the bus bar electrode, and improves the peeling success rate of the bus bar electrode.

Description

Technical Field

[0001] This invention relates to the fields of information electronic materials technology, information communication, and wireless radio frequency communication, and specifically to a surface acoustic wave device and its preparation method. Background Technology

[0002] With the rapid development of wireless communication, the performance requirements for radio frequency (RF) filters that process RF signals have become increasingly stringent. RF filters constitute the largest proportion of components in the entire RF front-end and are also crucial components in defense, mobile communications, and automotive electronics. Their function is to filter out unwanted signals and retain useful signals during communication. Surface acoustic wave (SAW) filters are widely used in various fields due to their advantages such as small size, low insertion loss, good selectivity, low cost, and high reliability. Among them, transversely excited SAW filters (XBARs) can simultaneously achieve high frequency and large bandwidth performance, and have received significant attention and development.

[0003] The basic unit resonator of a transversely excited surface acoustic wave filter consists of a supporting substrate, a suspended piezoelectric thin film, an interdigitated electrode layer, and a thickened electrode layer, such as... Figure 1 As shown, there are two technical routes for the fabrication of resonators: front-side release and back-side etching. Front-side release requires fabricating release holes on the resonator surface to release the substrate material beneath the piezoelectric film, achieving a suspended piezoelectric film structure. Fabricating the release holes first requires patterning and peeling off the electrode material of the interdigital electrode layer of the resonator to form release windows; subsequently, the exposed piezoelectric film within the release windows is etched to form the release holes. During the peeling process to form the release windows, because the release windows are located within the busbar region, peeling off the surrounding closed pattern in the busbar can easily lead to incomplete peeling and contamination by peeling debris. While increasing the soaking time in the peeling solution can achieve sufficient peeling of the target area, it may affect the material in the non-peeled areas. Therefore, it is necessary to optimize the film structure and fabrication scheme of the laterally excited surface acoustic wave resonator to reduce the difficulty of peeling off the release windows and achieve more efficient peeling. Summary of the Invention

[0004] To effectively reduce the difficulty of single-layer release window peeling and improve the success rate and yield of release window processing, this invention proposes a method for fabricating surface acoustic wave devices. After depositing a metal thin film, the interdigital electrode layer is patterned and peeled off. The patterned peeling off of the interdigital electrode layer includes the following steps:

[0005] During patterned peeling, a non-closed release window is formed;

[0006] By partially overlapping the thickened electrode layer from the direction of the non-closed release window, a closed release window is formed.

[0007] As an optional implementation, the boundary length of the non-closed target stripping region and the thickness of the busbar between the non-closed target stripping regions are 0.1 μm to 200 μm.

[0008] Furthermore, the boundary length of the non-closed target stripping region and the thickness of the confluence strip between the non-closed target stripping regions are 2μm to 50μm.

[0009] Prioritizes a boundary length of 17 μm for the non-closed target stripping region.

[0010] Preferably, the thickness of the busbar between the non-closed target stripping regions is 13 μm.

[0011] As an optional implementation, the overlap width between the thickened electrode layer and the non-closed target stripping area is 0.1 μm to 200 μm.

[0012] Furthermore, the overlap width between the thickened electrode layer and the non-enclosed target stripping area is 1 μm to 50 μm.

[0013] Preferably, the overlap width between the thickened electrode layer and the non-enclosed target stripping area is 3 μm.

[0014] Furthermore, the electrode materials for the interdigitated electrodes and the thickened electrodes are gold, molybdenum, copper, platinum, or titanium.

[0015] The present invention also proposes a surface acoustic wave device, which is prepared by a surface acoustic wave device preparation method.

[0016] This invention optimizes the release window in the busbar from a single-layer electrode peeling process to a process obtained by peeling and connecting two layers of electrodes, which can effectively reduce the difficulty of peeling a single-layer release window and improve the success rate and yield of release window processing. Attached Figure Description

[0017] Figure 1 A schematic diagram of a surface acoustic wave resonator structure with lateral excitation in the prior art;

[0018] Figure 2 This is a schematic diagram of the preferred processing flow of a surface acoustic wave device fabrication method according to the present invention;

[0019] Figure 3 This is a schematic diagram comparing the present invention with the prior art;

[0020] Figure 4 This is a schematic diagram showing the relevant dimensions and structure of the release window of the present invention;

[0021] Among them, 1, substrate; 2, piezoelectric thin film; 3, release hole; 4, release window; 5, thickened electrode layer; 6, interdigitated electrode layer; 7, busbar; 8, busbar connection area; a, boundary length of the non-closed target stripping area; b, busbar thickness between the non-closed target stripping areas; c, the width of overlap between the thickened electrode layer and the non-closed target stripping area. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention proposes a method for fabricating a surface acoustic wave (SAW) device, which involves patterning and peeling off the interdigitated electrode layer after depositing a metal thin film, leaving only the electrode strip region and part of the bus strip region, and also includes the following steps:

[0024] An equally spaced non-closed target stripping region is set at the edge of the busbar of the interdigitated electrode layer, and the underlying piezoelectric film is exposed during the patterned stripping process to form a non-closed release window;

[0025] The busbar region of the thickened electrode layer partially overlaps with the busbar region of the interdigitated electrode layer. The overlapping part is the busbar connection region, and the busbar region of the thickened electrode layer does not completely cover the release window in the busbar region of the interdigitated electrode layer, thus forming a closed release window.

[0026] The piezoelectric film exposed in the closed release window is etched to form a release hole; the submerged material is further released through the release hole to form a suspended piezoelectric film.

[0027] In this embodiment, the transversely excited surface acoustic wave resonator consists of a substrate material, a suspended piezoelectric thin film, an interdigitated electrode layer, and a thickened electrode layer. The processing of the interdigitated electrode layer is divided into two steps: metal thin film deposition and patterned stripping. After depositing the metal thin film, the interdigitated electrode layer is patterned and stripped so that only the electrode strip area and part of the bus strip area are retained. Before patterned stripping, release windows, i.e., the target stripping areas, are set and arranged at the edges of the busbars of the interdigital electrode layer, forming a non-closed pattern in the release window area. During the patterned stripping process, the electrode material above the non-closed release windows is stripped, exposing the piezoelectric film below the release windows. Subsequently, during the patterning design of the thickened electrodes, the busbar area of ​​the thickened electrode layer partially overlaps with the busbar area of ​​the interdigital electrode layer. The busbar area of ​​the thickened electrode layer does not completely cover the release windows in the busbar area of ​​the interdigital electrode layer, so as to achieve connection between the two busbar areas while forming a closed pattern of release windows, in which the piezoelectric film is exposed. The exposed piezoelectric film in the release windows is further etched to form release holes, through which the submerged material is further released to form a suspended piezoelectric film.

[0028] like Figure 2 As shown, this embodiment proposes a method for fabricating a surface acoustic wave device, specifically including steps (1) to (7), wherein:

[0029] (1) Obtaining a wafer, which consists of a lower substrate 1 and an upper piezoelectric thin film 2, i.e. Figure 2 (1) The blue part;

[0030] (2) Deposit interdigitated electrode layer metal material on the wafer surface, i.e. Figure 2 (2) The yellow part is the metal material used to form the interdigitated electrode layer 6 and the busbars corresponding to the interdigitated electrode layer;

[0031] (3) The patterned metal material of the interdigitated electrode layer is stripped off, and the release windows are arranged on the outside of the busbar to form a non-closed pattern. During processing, the electrode material above the non-closed release windows is stripped off, i.e. Figure 2 (3) A notch is provided at one end of the interdigitated electrode layer. The notch peels off the metal material of the electrode layer to expose the underlying wafer, forming a release window 4. That is, the release window 4 is a notch formed on the metal of the interdigitated electrode layer.

[0032] (4) Deposit thickened electrode layer metal material, i.e. Figure 2 (4) The orange part, the part of the thickened electrode layer 5 is also used as a bus bar. In this embodiment, the bus bars of the interdigitated electrode layer 6 and the thickened electrode layer 5 are collectively referred to as bus bar 7. The part where the two bus bars overlap is the bus bar connection area 8.

[0033] (5) Patterned stripping of the thickened electrode layer metal material; partial overlap between the thickened electrode layer busbars and the interdigitated electrode layer busbars to achieve electrical connection between the two electrode layers, while simultaneously forming a closed release window pattern. After stripping off the excess thickened electrode layer, the result is as follows: Figure 2 (5) The structure shown in the figure has a thickened electrode that covers part of the non-closed release window from the notch direction of the release window, so as to form a closed release window.

[0034] (6) Machining release hole 4 in the release window to obtain the following result. Figure 2 The structure shown in (6) is that the release hole 3 is a through hole on the piezoelectric film.

[0035] (7) The substrate material below is released through the release hole to form a suspended piezoelectric film, resulting in... Figure 2 The structure shown in (7)

[0036] like Figure 3 This invention optimizes the fabrication process of the release window in the busbar of a resonator. Instead of the traditional method of forming the release window by peeling a closed pattern from the interdigitated electrode layer, it improves the process by peeling a non-closed pattern from the interdigitated electrode layer, followed by overlapping and connecting a portion of the busbar with a thickened electrode layer to form the release window. The lower interdigitated electrode layer busbar region is only a part of the complete resonator busbar, and the release area within the interdigitated electrode layer busbar is a non-closed pattern. The upper thickened electrode layer partially overlaps with the lower interdigitated electrode layer busbar region, but not completely. The purpose is to achieve electrical connection between the upper and lower busbar regions while simultaneously forming a release window within the busbar, partially exposing the piezoelectric film for further etching of the piezoelectric film within the release window to form a release hole.

[0037] like Figure 4 The interdigitated electrode layer busbar region is formed into a comb-like structure, with the area between the comb teeth serving as a non-closed release window. The spacing between the comb teeth, i.e., the boundary length 'a' of the non-closed target stripping area, can be from 0.1 μm to 200 μm, preferably from 2 μm to 50 μm. The thickness of the comb teeth, i.e., the busbar thickness 'b' between the non-closed target stripping areas, can be from 0.1 μm to 200 μm, preferably from 2 μm to 50 μm. Then, by partially overlapping the thickened electrode with the comb tooth region, a closed release window is obtained. The overlap width between the busbar region of the thickened electrode layer and the busbar region of the interdigitated electrode layer, i.e., the overlap width 'c' between the thickened electrode layer and the non-closed target stripping area, can be from 0.1 μm to 200 μm, preferably from 1 μm to 50 μm.

[0038] As an alternative implementation, the electrode materials for the interdigitated electrodes and the thickened electrodes can be one of gold, molybdenum, copper, platinum, and titanium.

[0039] This embodiment also proposes an optimal implementation method, in which a release window is provided on the outside of the bus bar region of the interdigital electrode layer. A 17μm×17μm non-closed release window is formed by a patterned peeling process. Each release window is separated by a 17μm×13μm bus bar electrode. The overlap width between the bus bar region of the thickened electrode layer and the bus bar region of the interdigital electrode layer is 3μm.

[0040] A surface acoustic wave device can be prepared according to any of the preparation methods in this embodiment. The metal deposition process and patterning lift-off process involved in this embodiment adopt any process described in the prior art, and will not be described in detail in this invention.

[0041] In the description of this invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "other end," "upper," "side," "top," "inner," "outer," "front," "center," "both ends," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0042] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a surface acoustic wave device, comprising patterning and peeling off an interdigitated electrode layer after depositing a metal thin film, characterized in that, Patterned stripping of the interdigitated electrode layer includes the following steps: During patterned stripping, a comb-like structure is formed on the busbar of the interdigital electrode layer. The area between the comb teeth is used as an unclosed release window. The unclosed release windows are arranged on the outside of the busbar. Unclosed target stripping areas are arranged at equal intervals on the edge of the busbar of the interdigital electrode layer. During the patterned stripping process, the underlying piezoelectric film is exposed to form an unclosed release window. The spacing between the comb teeth is the boundary length of the unclosed target stripping area, and the thickness of the comb teeth is the busbar thickness between the unclosed target stripping areas. By partially overlapping the thickened electrode layer from the direction of the non-closed release window, a closed release window is formed. The piezoelectric film exposed in the closed release window is etched to form a release hole. The submerged material is further released through the release hole to form a suspended piezoelectric film.

2. The preparation method according to claim 1, characterized in that, The boundary length of the non-closed target stripping region and the thickness of the confluence strip between the non-closed target stripping regions range from 0.1 μm to 200 μm.

3. The preparation method according to claim 1 or 2, characterized in that, The boundary length of the non-closed target stripping region and the thickness of the confluence strip between the non-closed target stripping regions range from 2 μm to 50 μm.

4. The preparation method according to claim 3, characterized in that, The boundary length of the non-closed target stripping region is 17 μm.

5. The preparation method according to claim 3, characterized in that, The thickness of the busbar between the non-closed target stripping regions is 13 μm.

6. The preparation method according to claim 1, characterized in that, The overlap width between the thickened electrode layer and the non-enclosed target stripping area ranges from 0.1 μm to 200 μm.

7. The preparation method according to claim 1 or 6, characterized in that, The overlap width between the thickened electrode layer and the non-enclosed target stripping area is 1 μm to 50 μm.

8. The preparation method according to claim 7, characterized in that, The overlap width between the thickened electrode layer and the non-enclosed target stripping area is 3 μm.

9. The preparation method according to claim 1, characterized in that, The electrode materials for the interdigitated electrodes and thickened electrodes are gold, molybdenum, copper, platinum, or titanium.

10. A surface acoustic wave device, characterized in that, A surface acoustic wave device prepared by the preparation method according to any one of claims 1 to 9.

Images