Device manufacturing method and vibration device
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-09-26
- Publication Date
- 2026-03-18
AI Technical Summary
Existing methods for manufacturing vibration devices result in increased variation in resonant frequency due to the removal of silicon oxide films around the vibrating part, which are used for correcting resonance frequency.
A method involving a protective film with specific openings is used to shield the electrode pad during etching, ensuring the silicon oxide film around the vibrating part remains intact, thereby maintaining resonance frequency stability.
The method reduces variations in resonance frequency by protecting the silicon oxide film, ensuring stable vibration characteristics and minimizing etching damage to the electrode pad.
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Abstract
Description
[Technical field]
[0001] The present invention relates to a method for manufacturing a device. [Background technology]
[0002] Patent Document 1 discloses a method for manufacturing a vibration device, in which wet etching is performed using a silicon oxide film formed on the vibration part and on the electrode pads as a mask to form a cavity below the vibration part, and then further wet etching is performed to remove the silicon oxide film on the electrode pads to expose the surfaces of the electrode pads. [Prior art documents] [Patent documents]
[0003] [Patent Document 1] JP 2020-36063 A Summary of the Invention [Problem to be solved by the invention]
[0004] However, with the technology described in Patent Document 1, when the silicon oxide film on the electrode pad is removed, the silicon oxide film that is arranged around the vibrating part and is used to correct the resonant frequency is also removed, resulting in a problem of large variation in the resonant frequency of the vibrating element. [Means for solving the problem]
[0005] A method for manufacturing a device includes an element substrate having an element, an element electrode for driving the element, a frame portion arranged around the element, and an electrode pad arranged on the frame portion and connected to the element electrode, and a support substrate joined to one side of the element substrate, and includes the steps of: forming a protective film on the other side of the frame portion and the other side of the element, the protective film being resistant to an etching solution and having a first opening between the outline of the element and the frame portion and a second opening on the electrode pad; and etching the support substrate through the first opening with the etching solution to form a space between the element and the support substrate. [Brief description of the drawings]
[0006] [Figure 1] FIG. 2 is a plan view showing a configuration of a vibration device. [Diagram 2] 2 is a cross-sectional view of the vibration device shown in FIG. 1 taken along line AA. [Diagram 3] 1A to 1C are cross-sectional views illustrating a method for manufacturing a vibration device. [Figure 4] 1A to 1C are cross-sectional views illustrating a method for manufacturing a vibration device. [Diagram 5] 1A to 1C are cross-sectional views illustrating a method for manufacturing a vibration device. [Figure 6] 1A to 1C are cross-sectional views illustrating a method for manufacturing a vibration device. [Figure 7] 1A to 1C are cross-sectional views illustrating a method for manufacturing a vibration device. [Figure 8] 1A to 1C are cross-sectional views illustrating a method for manufacturing a vibration device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0007] First, the configuration of a vibration device 100 will be described with reference to FIGS.
[0008] 1 and 2, the resonator device 100 includes an element substrate 10 and a support substrate 20 bonded to one surface of the element substrate 10. Specifically, the resonator device 100 includes a silicon on insulator (SOI) substrate 40 having a BOX (Buried Oxide) layer 30 between the element substrate 10 and the support substrate 20.
[0009] The SOI substrate 40 is a substrate in which a silicon layer 10a, a silicon oxide (SiO2) layer 30a, and a silicon layer 20a are laminated in this order. The silicon layer 10a is made of, for example, single crystal silicon. The element substrate 10 has a silicon layer 10a. The support substrate 20 has a silicon layer 20a.
[0010] The element substrate 10 has an element 50, element electrodes 61, 62 for driving the element 50, a frame portion 70 arranged around the element 50, and an electrode pad 80 arranged on the frame portion 70 and electrically connected to the element electrodes 61, 62.
[0011] The element 50 has a base 11 made up of a part of the silicon oxide layer 30a and a part of the silicon layer 10a. The element 50 further has, in order from the base 11 side, an element adjustment layer 12a, a piezoelectric driving unit 60, an element adjustment layer 12b, and a protective film 200. The vibration device 100 of this embodiment has three elements 50.
[0012] Between the element 50 and the supporting substrate 20, a space 90 (also called a cavity) is provided, which is a region in which the element 50 vibrates.
[0013] The element adjustment layers 12a and 12b are provided to correct the temperature characteristic of the resonant frequency of the element 50. Silicon has a resonant frequency that decreases as the temperature increases, while a silicon oxide film has a resonant frequency that increases as the temperature increases. Therefore, by providing the element adjustment layers 12a and 12b, which are silicon oxide, around the element 50, the temperature characteristic of the resonant frequency can be made closer to flat.
[0014] The piezoelectric driving section 60 includes a first element electrode 61, a piezoelectric layer 63, and a second element electrode 62. The first element electrode 61 and the second element electrode 62 are disposed so as to sandwich the piezoelectric layer 63 therebetween.
[0015] The first element electrode 61 is made of, for example, molybdenum (Mo). The piezoelectric layer 63 is made of, for example, aluminum nitride (AlN). The second element electrode 62 is made of, for example, molybdenum (Mo).
[0016] In plan view, two electrode pads 80 are arranged on the frame portion 70 on both sides of the element 50. In this embodiment, three elements 50 are arranged. In this case, the second element electrodes 62 of the two elements 50 at both ends are electrically connected to the electrode pad 80A. Also, the second element electrode 62 of the element 50 in the middle is electrically connected to the electrode pad 80B. The first element electrodes 61 (see FIG. 2) of the three elements 50 are electrically connected to the same potential.
[0017] The electrode pad 80 is formed by stacking a lower electrode pad 81 made of aluminum (Al) with a small amount of copper (Cu) added thereto, and an upper electrode pad 82 made of titanium nitride (TiN). Since the upper electrode pad 82 made of titanium nitride is exposed on the upper surface through the second opening 202, the lower electrode pad 81 can be prevented from being etched by the etching process for forming the space 90.
[0018] When a voltage is applied between the first element electrode 61 and the second element electrode 62 via the two electrode pads 80, the piezoelectric layer 63 expands and contracts, causing adjacent elements 50 to vibrate in opposite phases. The vibration is highly excited at the inherent resonant frequency, minimizing the impedance. As a result, by connecting this element 50 to an oscillation circuit, it oscillates at an oscillation frequency determined mainly by the resonant frequency of the element 50.
[0019] The protective film 200 is provided so as to cover the other surface side of the element 50 and the frame portion 70 of the resonation device 100. A first opening 201 is provided in the protective film 200 between the outline of the element 50 and the frame portion 70. A second opening 202 is provided in the protective film 200 above the electrode pad 80.
[0020] The protective film 200 is made of a material that is resistant to an etching solution. An example of the material of the protective film 200 is silicon oxide (SiO2). The etching solution is, for example, tetramethylammonium hydroxide (TMAH).
[0021] Next, a method for manufacturing the vibration device 100 will be described with reference to FIGS.
[0022] First, in the step shown in FIG. 3, an SOI substrate 40 in which a silicon layer 10a as the element substrate 10, a silicon oxide layer 30a as the BOX layer 30, and a silicon layer 20a as the support substrate 20 are stacked is prepared.
[0023] The element substrate 10 has a thickness of, for example, 5 μm. The BOX layer 30 has a thickness of, for example, 1 μm. The support substrate 20 has a thickness of, for example, 600 μm.
[0024] 4, the piezoelectric actuator 60 is formed on the SOI substrate 40. Specifically, first, the SOI substrate 40 is heat-treated to form a thermally oxidized film 12a made of silicon oxide and having a thickness of about 1 μm on the surface of the SOI substrate 40. A part of this thermally oxidized film 12a will later become the element adjustment layer 12a.
[0025] Next, a molybdenum film 61a that will become the first element electrode 61 is deposited to a thickness of 100 nm using, for example, a sputtering device. After that, an aluminum nitride film 63a that will become the piezoelectric layer 63 is deposited to a thickness of 300 nm on the molybdenum film 61a using, for example, a sputtering device. Next, a molybdenum film 62a that will become the second element electrode 62 is deposited to a thickness of 100 nm using, for example, a sputtering device.
[0026] Next, a resist is applied onto the molybdenum film 62a, and the resist is patterned by photolithography to form a resist pattern. Thereafter, the molybdenum film 62a is etched (e.g., dry etched) using the resist pattern as a mask to complete the second element electrode 62. Next, after removing the resist pattern, the piezoelectric layer 63 and the first element electrode 61 are formed by similarly carrying out photolithography and etching. Through the above steps, the piezoelectric driving unit 60 is completed.
[0027] 5, an electrode pad 80 is formed in the region of the frame portion 70. Specifically, first, a silicon oxide film 12b is formed so as to cover the piezoelectric driving portion 60 and the thermal oxide film 12a. The silicon oxide film 12b can be manufactured by, for example, a chemical vapor deposition (CVD) method. A part of this silicon oxide film 12b becomes the element adjustment layer 12b later.
[0028] Next, an aluminum alloy film 80a, which is made of aluminum (Al) to which a small amount of copper (Cu) is added, and a titanium nitride (TiN) film 80b are formed, which will become the electrode pad 80. Examples of the film formation method include a sputtering device. The aluminum alloy film 80a has a thickness of, for example, 300 nm. The titanium nitride film 80b has a thickness of, for example, 100 nm. Thereafter, photolithography and etching are performed to complete the electrode pad 80.
[0029] 6, a protective film 200 is formed around the element 50 and the frame 70. Specifically, first, a silicon oxide film 12c is formed so as to cover the electrode pads 80 and the silicon oxide film 12b. Next, the portion that will become the element 50 is formed up to the silicon oxide layer 30a by collective dry etching. Thereafter, a protective film 200 that is resistant to tetramethylammonium hydroxide, which is an etching solution, is formed on the entire surface of the element 50 and the other side of the frame 70.
[0030] The protective film 200 is silicon oxide (SiO2) having an etching selectivity to silicon (Si) of 1000 or more. The protective film 200 can be formed, for example, by high density plasma CVD. The protective film 200 has a thickness of, for example, 500 nm. As a result, the protective film 200 is formed on the upper surface and sidewalls of the element 50 and the upper surface and sidewalls of the frame portion 70.
[0031] 7, a first opening 201 is formed between the outer shape of the element 50 and the frame 70, and a second opening 202 is formed on the electrode pad 80. The first opening 201 and the second opening 202 in the protective film 200 are simultaneously formed by using photolithography and etching.
[0032] In this case, the first opening 201 is above the support substrate 20, and the second opening 202 is above the electrode pad 80, with a step of approximately 7 μm. Therefore, when using photolithography, it is difficult to focus the first opening 201 and the second opening 202 simultaneously.
[0033] However, since the required dimensional accuracy above the electrode pad 80 is lower than that for the formation of the space 90 that directly affects the vibration characteristics, by focusing on opening the first opening 201, it is possible to reduce the variation in the characteristics of the element 50.
[0034] During dry etching, it is necessary to adjust the etching processing conditions and overetch rate so that the etching stops at the silicon layer 20a, which is the support substrate 20, in the area of the first opening 201, and so that the etching stops at the upper electrode pad 82 made of titanium nitride in the area of the second opening 202.
[0035] 8, the support substrate 20 is etched using an etching solution through the first opening 201 to form a space 90 between the element 50 and the support substrate 20. Specifically, the etching solution is tetramethylammonium hydroxide (TMAH) with a concentration of 11%.
[0036] The space 90 needs to be etched to a depth that does not contact the bottom when the element 50 vibrates, for example, a depth of 75 μm. Both the protective film 200 made of silicon oxide and the upper electrode pad 82 made of titanium nitride have an extremely high selectivity with respect to tetramethylammonium hydroxide, so that the element 50 can be formed with almost no etching.
[0037] By applying an AC voltage at a specific frequency to the elements 50 through the two element electrodes 61, 62, the three elements 50 resonate in a walk mode and operate as a timing device that generates a stable clock.
[0038] As described above, the manufacturing method of the vibration device 100 of this embodiment is a manufacturing method of a vibration device 100 including an element substrate 10 having an element 50, element electrodes 61, 62 for driving the element 50, a frame portion 70 arranged around the element 50, and electrode pads 80 arranged on the frame portion 70 and connected to the element electrodes 61, 62, and a support substrate 20 joined to one side of the element substrate 10, and includes a step of forming a protective film 200, which is resistant to an etching solution and has a first opening 201 between the outline of the element 50 and the frame portion 70 and a second opening 202 on the electrode pad 80, on the other side of the frame portion 70 and the other side of the element 50, and a step of etching the support substrate 20 through the first opening 201 with an etching solution to form a space 90 between the element 50 and the support substrate 20.
[0039] According to this method, the protective film 200 having the first opening 201 and the second opening 202 and resistance to the etching solution is formed on the other side of the frame 70 and the other side of the element 50, and then etching is performed, so that the space 90 can be formed between the element 50 and the support substrate 20 through the first opening 201, and the surface of the electrode pad 80 can be exposed through the second opening 202. In addition, since the protective film 200 prevents the element 50 from being etched, the variation in the resonance frequency of the element 50 can be reduced.
[0040] In addition, in the manufacturing method of the resonation device 100 of this embodiment, it is preferable that the electrode pad 80 has an upper electrode pad 82 made of titanium nitride disposed on the surface exposed from the second opening 202. According to this method, since the upper electrode pad 82 having high resistance to the etching solution is exposed from the second opening 202, it is possible to suppress damage to the lower electrode pad 81 when etching is performed.
[0041] In the manufacturing method of the resonation device 100 of the present embodiment, the protective film 200 is preferably made of silicon oxide. According to this method, since the protective film 200 is made of silicon oxide, it has resistance to an etching solution and can be used as the element 50 as it is after etching.
[0042] In the manufacturing method of the resonator device 100 of the present embodiment, the support substrate 20 is preferably a silicon substrate, and the etching solution is preferably tetramethylammonium hydroxide. According to this method, since tetramethylammonium hydroxide is used as the etching solution, the space 90 can be formed in the silicon substrate according to the crystal orientation of silicon.
[0043] Moreover, in the manufacturing method of the vibration device 100 of this embodiment, it is preferable to have a step of simultaneously forming the first opening 201 and the second opening 202 after the step of forming the protective film 200. According to this method, since the first opening 201 and the second opening 202 are formed simultaneously, it is possible to reduce the number of manufacturing steps, and the number of man-hours involved can be reduced.
[0044] Modifications of the above embodiment will now be described.
[0045] As described above, the configuration of the vibration device 100 having three elements 50 has been described as a MEMS device, but the present invention is not limited to this. The MEMS device can also be applied to a tuning fork type vibration element having two elements 50, an angular velocity sensor element, an acceleration sensor element, a pressure sensor element, etc. Other examples include ultrasonic sensors using a piezoelectric film and resonators used in timing devices. [Explanation of symbols]
[0046] 10...element substrate, 10a...silicon layer, 11...base, 12a...thermal oxide film (element adjustment layer), 12b...silicon oxide film (element adjustment layer), 12c...silicon oxide film, 20...support substrate, 20a...silicon layer, 30...BOX layer, 30a...silicon oxide layer, 40...SOI substrate, 50...element, 60...piezoelectric driving portion, 61...first element electrode, 61a...molybdenum film, 62...second element electrode, 62a...molybdenum film, 63...piezoelectric layer, 63a...aluminum nitride film, 70...frame, 80...electrode pad, 80a...aluminum alloy film, 80b...titanium nitride film, 81...lower electrode pad, 82...upper electrode pad, 90...space, 100...vibration device, 200...protective film, 201...first opening, 202...second opening.
Claims
1. An element substrate including an element, an element electrode for driving the element, a frame portion arranged around the element, and an electrode pad arranged in the frame portion and connected to the element electrode, A support substrate bonded to one side of the element substrate, A method for manufacturing a device including, A step of forming a protective film on the other side of the frame and on the other side of the element such that a first opening is formed between the outer shape of the element and the frame, and a second opening is formed on the electrode pad, A step of forming a space between the element and the support substrate by etching the support substrate through the first opening using an etching solution, Includes, A method for manufacturing a device, wherein the protective film is resistant to the etching solution.
2. In claim 1, The electrode pad has titanium nitride disposed on the surface exposed from the second opening. A method for manufacturing a device.
3. In claim 1 or 2, A method for manufacturing a device, wherein the protective film is silicon oxide.
4. In claim 1 or 2, The support substrate is a silicon substrate, A method for manufacturing a device, wherein the etching solution is tetramethylammonium hydroxide.
5. In claim 1 or 2, After the step of forming the protective film, the first opening and the second opening are formed simultaneously. A method for manufacturing a device, comprising the steps of [details omitted].
6. An SOI substrate in which a support substrate, a BOX layer, and an element substrate are stacked in order, A protective film disposed on the element substrate side of the SOI substrate, Includes, The aforementioned element substrate is Element and, A frame portion arranged around the element, Includes, The element includes an element electrode that drives the element, The frame portion includes electrode pads that are electrically connected to the element electrodes. The electrode pad is Lower electrode pad and The upper electrode pad is stacked on the upper surface of the lower electrode pad, Includes, The aforementioned protective film is The first protective film covering the element, The second protective film covering the frame portion, Includes, In a plan view, a first opening is provided between the outer shape of the element and the frame portion. In a plan view, the second protective film is provided with a second opening. In a plan view, the upper electrode pad is exposed from the second opening. A vibration device wherein the protective film and the upper electrode pad are made of a material resistant to etching solutions.
7. In claim 6, The aforementioned device, On the surface of the BOX layer, The first element adjustment layer, Piezoelectric drive unit, The second element adjustment layer, The first protective film and, A vibration device composed of a series of stacked elements.
8. In claim 7, The aforementioned device electrode is First element electrode and The second element electrode, Includes, The piezoelectric drive unit is The first element electrode and, The preceding two-element electrode, A piezoelectric layer disposed between the first element electrode and the second element electrode, A vibration device composed of the following.
9. In claim 8, The aforementioned frame portion is The first frame section and, The second frame section, Includes, The element is a vibration device located between the first frame and the second frame in a plan view.
10. In claim 9, The electrode pad is First electrode pad and The second electrode pad and Includes, The first electrode pad is positioned in the first frame portion, The second electrode pad is a vibration device located in the second frame.
11. In claim 10, The element consists of three vibrating arms arranged in a row, The three vibrating arms described above are, A vibration device that resonates in walk mode by applying an AC voltage through the first element electrode and the second element electrode.
12. In claim 11, The material of the protective film is silicon oxide, in the vibrating device.
13. In claim 12, The lower electrode pad is made of a material mainly composed of aluminum. The upper electrode pad is made of titanium nitride, and the device is a vibrating device.