A method for etching a silicon dioxide protective layer based on a sacrifice layer in the preparation of a surface acoustic wave filter

Abstract

The application relates to the field of electronic technology, and particularly discloses a silicon dioxide protective layer etching method based on a sacrifice layer in the preparation of a surface acoustic wave filter. The silicon dioxide protective layer etching method based on the sacrifice layer in the preparation of the surface acoustic wave filter comprises the following operation steps: in the preparation of the surface acoustic wave filter, an aluminum film is deposited on the input and output electrode area where a copper film has been formed through a secondary etching process before a silicon dioxide protective layer is deposited; the silicon dioxide protective layer etching method comprises the following operation steps: the wafer is vertically placed in a 15-35 DEG C phosphoric acid system solution for etching, and ultrasonic stirring is carried out under the condition of an ultrasonic power of 200-250 W and a frequency of 10-20 KHz during the etching process. The etching rate of the silicon dioxide protective layer etching method reaches 200 nm / min, and the etching rate is improved.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and more specifically, to a method for etching a silicon dioxide protective layer based on a sacrificial layer in the fabrication of a surface acoustic wave filter. Background Technology

[0002] The basic structure of a surface acoustic wave (SAW) filter consists of input and output electrodes and two interdigital transducers fabricated on a polished surface of a piezoelectric substrate. The two interdigital transducers are an input interdigital transducer and an output interdigital transducer. When a signal enters, the input interdigital transducer vibrates on the surface of the piezoelectric substrate like a drumstick, converting the electrical signal into a sound wave. This sound wave propagates laterally on the surface of the SAW filter substrate in the form of a standing wave. The output interdigital transducer converts the received sound wave into an electrical signal for output, thereby achieving filtering.

[0003] Interdigital transducers need to meet core requirements such as excellent conductivity, strong adhesion to piezoelectric substrates, resistance to plasma etching, and resistance to electromigration. They are usually made of aluminum and copper metals, which have good conductivity, resistance to electromigration, and strong adhesion. Copper films usually have a larger electromechanical coupling coefficient than aluminum films, which can be used to make wider bandwidths. However, copper films are prone to oxidation, so a silicon dioxide protective layer needs to be added to the surface of the copper film to prevent oxidation.

[0004] Since the input / output electrodes and interdigital transducers are fabricated as a single metal unit, the entire wafer needs to be placed in a silicon dioxide sputtering chamber during the fabrication of the silicon dioxide protective layer. Therefore, both the input / output electrodes and the interdigital transducers are covered with silicon dioxide. However, the input / output electrodes need to be electrically connected to the package via silicon-aluminum wires. The silicon dioxide protective layer only needs to cover the two interdigital transducers for protection, and does not need to cover the input / output electrodes. Typically, the silicon dioxide needs to be removed to ensure the normal operation of the input / output electrodes.

[0005] In related technologies, the method for removing silica involves dry etching after overlay etching. This requires additional etching equipment and etching processes, increasing equipment purchase and maintenance costs. Furthermore, the process is relatively complex and has low removal efficiency. Summary of the Invention

[0006] To reduce etching contamination and increase etching rate, this application provides a method for etching a silicon dioxide protective layer based on a sacrificial layer in the fabrication of surface acoustic wave filters.

[0007] In a first aspect, this application provides a method for etching a silicon dioxide protective layer based on a sacrificial layer in the fabrication of a surface acoustic wave filter, which adopts the following technical solution: A method for etching a silicon dioxide protective layer based on a sacrificial layer in the fabrication of a surface acoustic wave filter involves depositing an aluminum film in the input and output electrode regions where a copper film has already been formed before depositing the silicon dioxide protective layer during the fabrication of the surface acoustic wave filter. The etching method for the silicon dioxide protective layer includes the following steps: the wafer is placed vertically in a phosphoric acid solution at 15-35°C for etching, and ultrasonic stirring is performed during the etching process at an ultrasonic power of 200-250W and a frequency of 10-20KHz.

[0008] By employing the above technical solution, a layer of aluminum film of appropriate thickness is deposited in the area where copper electrodes have already been formed through a secondary overlay process. This aluminum film replaces the photoresist as a release layer, ensuring that the input and output electrode areas are completely covered by the aluminum layer. A silicon dioxide protective layer is then deposited. While the phosphoric acid solution has a low etching effect on the copper mold, it reacts violently with the aluminum film. By dissolving the aluminum film, the silicon dioxide protective layer is etched. Removing the aluminum film simultaneously allows for the physical stripping of the upper silicon dioxide protective layer, avoiding the contamination problems associated with chemical etching processes. Furthermore, this etching method does not require additional dry etching equipment, and the process flow is relatively simple.

[0009] Preferably, the phosphoric acid system solution comprises the following raw materials: fluoride, organic complexing agent, and 85% by mass phosphoric acid solution.

[0010] By employing the above technical solution, adding fluoride to the phosphoric acid solution allows fluoride ions to form an ultrathin fluoride adsorption layer on the wafer surface, controlling the Si-O bond breaking rate and achieving continuously adjustable etching rate within a range of 10%-50%. Adding an organic complexing agent can complex the etching product ions, preventing their deposition at the interface and maintaining a stable etching rate. The combination of fluoride controlling the etching rate and the organic complexing agent stabilizing the rate avoids the rate drift problem caused by using only phosphoric acid solution.

[0011] Preferably, the fluoride is selected from any one of ammonium fluoride, calcium fluoride, and strontium fluoride; the organic complexing agent is selected from any one of citric acid, ethylenediaminetetraacetic acid, and aminotrimethylenephosphonic acid.

[0012] The fluoride used in this application can be any one of ammonium fluoride, calcium fluoride, or strontium fluoride, and the use of any one of these can improve the etching rate to varying degrees. The organic complexing agent used in this application can be any one of citric acid, ethylenediaminetetraacetic acid, or aminotrimethylenephosphonic acid, and the use of any one of these can improve the etching rate to varying degrees.

[0013] Preferably, the amount of fluoride added is 400 mg / L based on a phosphoric acid solution volume of 8-16 L; the amount of organic complexing agent added is 400-800 mg / L, and fluoride and organic complexing agent are added every 2-4 hours during the etching process.

[0014] By adopting the above technical solution, when the volume of the phosphoric acid solution is 8-16L, controlling the fluoride addition to 400mg / L and the organic complexing agent addition to 400-800mg / L can further improve the etching rate. Furthermore, adding fluoride and organic complexing agent every 2-4 hours during the etching process can further ensure the etching effect.

[0015] Preferably, the mass ratio of the fluoride to the organic complexing agent is 1:(1-2).

[0016] By adopting the above technical solution and controlling the mass ratio of fluoride to organic complexing agent to 1:(1-2), the etching rate can be further improved.

[0017] Preferably, plasma micro-passivation is performed before etching with the phosphoric acid solution. Specifically, the wafer is subjected to plasma micro-passivation for 30-120 seconds at 20-25°C by introducing an inert gas. The plasma power is 50-100W and the chamber pressure is 50-60mTorr. The inert gas consists of 90-95% argon and 5-10% oxygen, and the total flow rate is controlled at 50-200sccm.

[0018] By adopting the above technical solution, plasma micro-passivation is performed before etching with phosphoric acid solution. Inert gas is introduced at 20-25℃ to perform plasma micro-passivation on the wafer, forming a nanoscale passivation layer on the wafer surface. In the early stage of etching, the passivation layer is first etched by the phosphoric acid solution system, and then enters the stable etching stage. This can effectively suppress the rate fluctuation in the early stage of etching and improve the stability and uniformity of the etching rate.

[0019] Preferably, when introducing inert gas, argon gas is first introduced to purge the cavity for 3 minutes, and then oxygen is introduced to mix.

[0020] By adopting the above technical solution, when introducing inert gas, argon gas is first introduced to purge the cavity for 3 minutes to completely replace the residual process gas in the cavity, eliminate cross-contamination, and also desorb impurities on the inner wall of the cavity, wafer fixtures, and electrode surfaces, and remove residual water vapor in the cavity to ensure the density of the passivation layer. Oxygen is then introduced for mixing to prevent the passivation layer from becoming too thick or damaging the micro-nano structure of the wafer surface if oxygen is directly introduced. Purge with argon gas for 3 minutes before introducing oxygen to maintain the stability of the airflow field and pressure, thereby ensuring the process repeatability of the entire micro-passivation process.

[0021] Preferably, the thickness of the aluminum film is more than three times that of the copper film.

[0022] By adopting the above technical solution, the aluminum film needs to be thick enough to form a continuous, pinhole-free protective layer. The thickness of the aluminum film should be controlled to be more than three times that of the copper film to ensure that the input and output electrode areas are completely covered by the aluminum layer.

[0023] In summary, this application includes at least one of the following beneficial technical effects: (1) In the fabrication of surface acoustic wave filters, in the area where copper electrodes have been formed, a layer of aluminum film of appropriate thickness is deposited by a secondary overlay process. The aluminum film is used to replace the photoresist as a release layer so that the input and output electrode areas are completely covered by the aluminum layer. Then, a silicon dioxide protective layer is deposited and etched by a phosphoric acid solution system. The type and amount of each raw material in the phosphoric acid solution system are controlled to make the etching rate 150 nm / min, which improves the etching rate.

[0024] (2) This application improves the etching rate of silicon dioxide protective layer by performing plasma micro-passivation before etching with phosphoric acid solution, and controlling the purging of the cavity with argon gas for 3 minutes before mixing with oxygen gas, so that the etching rate is 200 m / min. Attached Figure Description

[0025] Figure 1 Basic structure of surface acoustic wave filter Figure 2 Flowchart of the silica protective layer etching method based on the sacrificial layer Detailed Implementation

[0026] The present application will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0027] The following raw materials used in this application are all commercially available products and are intended to fully disclose the raw materials used in this application. They should not be construed as limiting the source of the raw materials. Specifically: fluoride, ammonium fluoride is selected; organic complexing agent, citric acid is selected.

[0028] Example 1 Example 1 in preparation Figure 1 In the process of surface acoustic wave (SAW) filtering, such as Figure 2 Before depositing the silicon dioxide protective layer, an aluminum film is first deposited in the input and output electrode areas where a copper film has already been formed using a secondary overlay process. The aluminum film is four times thicker than the copper film. The etching method for the silicon dioxide protective layer based on the sacrificial layer in the fabrication of the surface acoustic wave filter includes the following steps: the wafer is vertically placed in a phosphoric acid solution at 25°C for etching, and ultrasonic stirring is performed during the etching process at an ultrasonic power of 220W and a frequency of 15kHz. The phosphoric acid solution is an 85% (w / w) phosphoric acid solution.

[0029] Example 2 The method for etching the silicon dioxide protective layer based on the sacrificial layer in the fabrication of the surface acoustic wave filter in Example 2 differs from that in Example 1 in that the phosphoric acid system solution includes the following raw materials: 4.8 g (400 mg / L) fluoride, 4.8 g (400 mg / L) organic complexing agent, and 12 L of 85% mass fraction phosphoric acid solution. The remaining steps are the same as in Example 1.

[0030] Examples 3-4 The method for etching the silicon dioxide protective layer based on the sacrificial layer in the fabrication of surface acoustic wave filters in Examples 3-4 differs from that in Example 2 in that the amount of organic complexing agent added is 7.2g (600mg / L) and 9.6g (800mg / L), respectively, while the remaining steps are the same as in Example 2.

[0031] Example 5 The difference between the etching method of the silicon dioxide protective layer based on the sacrificial layer in the fabrication of the surface acoustic wave filter in Example 5 and Example 3 is that plasma micro-passivation is performed before etching with the phosphoric acid solution. Specifically, the wafer is subjected to plasma micro-passivation for 80s at 25°C by introducing an inert gas. The plasma power is 80W and the cavity pressure is 55mTorr. The inert gas consists of 90% argon and 10% oxygen. Argon and oxygen are introduced simultaneously, and the total flow rate is controlled at 100sccm. The remaining steps are the same as in Example 3.

[0032] Example 6 The difference between the etching method of the silicon dioxide protective layer based on the sacrificial layer in the fabrication of the surface acoustic wave filter in Example 6 and Example 5 is that when the inert gas is introduced during plasma micro-passivation, argon gas is first introduced to purge the cavity for 3 minutes, and then oxygen is introduced for mixing. The remaining steps are the same as in Example 5.

[0033] Comparative Example 1 The difference between the silicon dioxide protective layer etching method based on the sacrificial layer in the fabrication of the surface acoustic wave filter in Comparative Example 1 and Example 1 is that the silicon dioxide protective layer is directly deposited after the copper film is deposited, while the remaining steps are the same as in Example 1.

[0034] Performance Testing (Part 1) The etching rate of the silicon dioxide protective layer based on the sacrificial layer in the fabrication of surface acoustic wave filters was detected by the following method. The specific detection results are shown in Table 1.

[0035] Etching rate: Table 1. Detection results of different silica protective layer etching methods

[0036] The test results in Table 1 show that in the fabrication of surface acoustic wave filters, in the area where copper electrodes have been formed, a layer of aluminum film of appropriate thickness is deposited through a secondary overlay process. The aluminum film is used to replace the photoresist as a release layer, so that the input and output electrode areas are completely covered by the aluminum layer. Then, a silicon dioxide protective layer is deposited. After adopting the silicon dioxide protective layer etching method of this application, the etching rate is as high as 200 nm / min, which improves the etching rate of the silicon dioxide protective layer.

[0037] According to the test results of Examples 1 and 2, the etching rate of the silicon dioxide protective layer using the etching method of Example 2 was 130 nm / min, which was higher than that of Example 1. This improved the etching rate of the silicon dioxide protective layer, indicating that the simultaneous addition of fluoride and organic complexing agent to the phosphoric acid system solution can further improve the etching rate of the silicon dioxide protective layer.

[0038] According to the test results of Examples 2-4, the etching rate of the silica protective layer using the etching method of Example 3 was 150 nm / min, which was higher than that of Examples 2 and 4. This indicates that a mass ratio of fluoride to organic complexing agent of 1:1.5 in the phosphoric acid system solution is more suitable, which improves the etching rate of the silica protective layer.

[0039] According to the test results of Examples 3 and 5, the etching rate of the silicon dioxide protective layer using the etching method of Example 5 was 160 nm / min, which was higher than that of Example 3. This indicates that plasma micro-passivation before etching with phosphoric acid solution can further improve the etching rate of the silicon dioxide protective layer.

[0040] According to the test results of Examples 5 and 6, the etching rate of the silicon dioxide protective layer using the etching method of Example 6 is 200 m / min, which is higher than that of Example 5. This indicates that when inert gas is introduced into the plasma micro-passivation process, argon gas is first introduced to purge the chamber for 3 minutes, and then oxygen is introduced for mixing, which can further improve the etching rate of the silicon dioxide protective layer.

[0041] According to the test results of Example 1 and Comparative Example 1, first depositing an aluminum film of appropriate thickness and using the aluminum film to replace the photoresist as the release layer, so that the input and output electrode areas are completely covered by the aluminum layer, and then depositing a silicon dioxide protective layer, and then using a phosphoric acid system solution for etching, can improve the etching rate and avoid the pollution problems caused by chemical etching processes. No additional dry etching equipment is required, and the process flow is relatively simple.

[0042] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for etching a silicon dioxide protective layer based on a sacrificial layer in the fabrication of a surface acoustic wave filter, characterized in that, In the process of fabricating surface acoustic wave filters, an aluminum film is first deposited in the input and output electrode areas where a copper film has already been formed through a secondary overlay process before depositing a silicon dioxide protective layer. The etching method for the silicon dioxide protective layer includes the following steps: the wafer is placed vertically in a phosphoric acid solution at 15-35°C for etching, and ultrasonic stirring is performed during the etching process at an ultrasonic power of 200-250W and a frequency of 10-20KHz.

2. The silicon dioxide etching method based on a sacrificial layer according to claim 1, characterized in that, The phosphoric acid system solution comprises the following raw materials: fluoride, organic complexing agent, and 85% by mass phosphoric acid solution.

3. The silicon dioxide etching method based on a sacrificial layer according to claim 2, characterized in that, The fluoride is selected from any one of ammonium fluoride, calcium fluoride, and strontium fluoride; the organic complexing agent is selected from any one of citric acid, ethylenediaminetetraacetic acid, and aminotrimethylenephosphonic acid.

4. The silicon dioxide etching method based on a sacrificial layer according to claim 2, characterized in that, Based on a phosphoric acid solution volume of 8-16L, the amount of fluoride added is 400mg / L; the amount of organic complexing agent added is 400-800mg / L, and fluoride and organic complexing agent are added every 2-4 hours during the etching process.

5. The silicon dioxide etching method based on a sacrificial layer according to claim 4, characterized in that, The mass ratio of the fluoride to the organic complexing agent is 1:1.

5.

6. The silicon dioxide etching method based on a sacrificial layer according to claim 1, characterized in that, Before etching with the phosphoric acid solution, plasma micro-passivation is performed. Specifically, the wafer is subjected to plasma micro-passivation for 30-120 seconds at 20-25°C by introducing an inert gas. The plasma power is 50-100W and the chamber pressure is 50-60mTorr. The inert gas consists of 90-95% argon and 5-10% oxygen, and the total flow rate is controlled at 50-200sccm.

7. The silicon dioxide etching method based on a sacrificial layer in the fabrication of a surface acoustic wave filter according to claim 6, characterized in that, When introducing inert gas, first purge the cavity with argon gas for 3 minutes, then introduce oxygen to mix.

8. The silicon dioxide etching method based on a sacrificial layer in the fabrication of a surface acoustic wave filter according to claim 1, characterized in that, The thickness of the aluminum film is more than three times that of the copper film.

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