A D-BAW air bridge structure and a method for forming the same

Abstract

The present invention proposes a D-BAW air bridge structure and a method for forming the same. The invention belongs to the technical field of bulk acoustic wave filters; the D-BAW air bridge structure comprises a substrate, a fence layer, a lower passivation layer, a lower electrode, a piezoelectric layer, an upper electrode and an upper passivation layer; the fence layer, the lower passivation layer, the lower electrode, the piezoelectric layer, the upper electrode and the upper passivation layer are sequentially deposited on the substrate, wherein an air bridge structure is arranged between the upper electrode and the piezoelectric layer.

Description

Technical Field

[0001] The invention proposes a D-BAW air bridge structure and a forming method thereof, belonging to the technical field of bulk acoustic wave filters. Background Art

[0002] BAW filter is an electronic device that uses piezoelectric body to filter acoustic wave signals. Its working principle is to use the inverse piezoelectric effect of piezoelectric body to convert electrical signal into acoustic wave signal and propagate it in acoustic wave conductor. BAW filter is usually composed of one or more acoustic waveguide devices, which are used to control the propagation path and energy distribution of acoustic waves. The main features of BAW filter are low loss, good suppression performance and temperature stability. At the same time, due to its large size and narrow bandwidth, its application is subject to certain restrictions. However, BAW filter in the prior art still has the problem of low quality factor Q value. Summary of the invention

[0003] The present invention provides a D-BAW air bridge structure and a method for forming the same, which are used to solve the problem of low Q value of bulk acoustic wave filters in the prior art. The technical solutions adopted are as follows:

[0004] A D-BAW air bridge structure comprises a substrate, a fence layer, a lower passivation layer, a lower electrode, a piezoelectric layer, an upper electrode and an upper passivation layer; the fence layer, the lower passivation layer, the lower electrode, the piezoelectric layer, the upper electrode and the upper passivation layer are sequentially deposited on the substrate, wherein an air bridge structure is arranged between the upper electrode and the piezoelectric layer.

[0005] A method for forming a D-BAW air bridge structure, the method comprising:

[0006] Step 1, depositing a thermal oxide layer 11 on a substrate 10;

[0007] Step 2, depositing an upper electrode 12 and a filling layer 13 on the thermal oxidation layer 11 in sequence;

[0008] Step 3, depositing a piezoelectric layer 14 on the filling layer 13 and the upper electrode 12, and etching to remove the substrate 10 and the thermal oxide layer 11;

[0009] Step 4, depositing a lower electrode 15 on the piezoelectric layer 14, and partially etching the lower electrode 15 to expose the piezoelectric layer 14;

[0010] Step 5, depositing a lower passivation layer 20 on the surface of the lower electrode 15;

[0011] Step 6: depositing a sacrificial layer 16 on the lower electrode 15 and the exposed piezoelectric layer 14;

[0012] Step 7, depositing a fence layer 17 on the sacrificial layer 16 to cover the sacrificial layer 16, the exposed lower passivation layer 20 and the exposed piezoelectric layer 14;

[0013] Step 8, laying a fence layer 17 on the base 18;

[0014] Step 9, partially etching and removing part of the upper electrode 12, and laying an upper passivation layer 19 on the upper electrode 12;

[0015] Step 10: etching and removing the filling layer 13 and the sacrificial layer 16.

[0016] Furthermore, the upper electrode 12 is provided with a concave structure.

[0017] Furthermore, the growth index of the thermal oxide layer 11 is: thickness 500A-5000A, uniformity <3%.

[0018] Furthermore, the etching conditions of the thermal oxide layer 11 are: an angle of 10-90 degrees, and damage to the substrate is less than 100A.

[0019] Furthermore, the thickness of the deposited upper electrode 12 is greater than the thickness of the thermal oxide layer, and the uniformity requirement is <1%. The material type of the upper electrode includes but is not limited to Mo / W and the like.

[0020] Furthermore, the thickness of the filling layer 13 is greater than the thickness of the thermal oxide layer. At the same time, the filling layer deposition + CMP: the material can be USG / PSG / SIN, etc., the thickness needs to be greater than the thickness of the thermal oxide layer, and the damage of CMP to the upper electrode is less than 100A. Furthermore, the thickness of the upper passivation layer is 400-4000A, and the uniformity is <3%.

[0021] Furthermore, the material of the upper passivation layer includes ALN / SIN and / or USG.

[0022] Beneficial effects of the present invention:

[0023] The D-BAW air bridge structure and the formation method thereof provided by the present invention can effectively reduce the sound wave scattering direction through the air bridge structure, thereby reducing the scattering effect and energy loss, thereby improving the quality factor Q value of the bulk acoustic wave filter. At the same time, the spatial overlap rate of the sound waves of the bulk acoustic wave filter during high-frequency vibration operation can be effectively improved through the position setting of the air bridge structure and the setting of the extension part, thereby improving the enhancement ratio of the interference effect, narrowing the resonance peak, and further improving the quality factor Q value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of the D-BAW air bridge structure of the present invention;

[0025] Figure 2 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 1 ;

[0026] Figure 3 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 2 ;

[0027] Figure 4 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 3 ;

[0028] Figure 5 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 4 ;

[0029] Figure 6 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 5 ;

[0030] Figure 7 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 6 ;

[0031] Figure 8 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 7 ;

[0032] Fig. 9 The preparation steps of the D-BAW air bridge structure of the present invention are as follows: Figure 9 ;

[0033] (10, substrate; 11, thermal oxide layer; 12, upper electrode; 13, filling layer; 14, piezoelectric layer; 15, lower electrode; 16, sacrificial layer; 17, fence layer; 18, base; 19, upper passivation layer; 20, lower passivation layer) DETAILED DESCRIPTION

[0034] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0035] The embodiment of the present invention proposes a D-BAW air bridge structure, such as Figure 1 As shown, the D-BAW air bridge structure includes a substrate, a fence layer, a lower passivation layer, a lower electrode, a piezoelectric layer, an upper electrode and an upper passivation layer; the fence layer, the lower passivation layer, the lower electrode, the piezoelectric layer, the upper electrode and the upper passivation layer are sequentially deposited on the substrate, wherein an air bridge structure is arranged between the upper electrode and the piezoelectric layer.

[0036] The working principle and technical effect of the above technical solution are as follows: the above technical solution of this embodiment provides a D-BAW air bridge structure and a method for forming the same, which can effectively reduce the scattering direction of sound waves through the air bridge structure, thereby reducing the scattering effect and energy loss, thereby improving the quality factor Q value of the bulk acoustic wave filter. At the same time, the spatial overlap rate of the sound waves of the bulk acoustic wave filter during high-frequency vibration operation can be effectively improved through the position setting of the above air bridge structure and the setting of the extension part, thereby improving the enhancement ratio of the interference effect, narrowing the resonance peak, and further improving the quality factor Q value.

[0037] The embodiment of the present invention proposes a method for forming a D-BAW air bridge structure, such as Figures 2 to 9 , the method for forming the D-BAW air bridge structure comprises:

[0038] Step 1, depositing a thermal oxide layer 11 on a substrate 10;

[0039] Step 2, depositing an upper electrode 12 and a filling layer 13 on the thermal oxidation layer 11 in sequence;

[0040] Step 3, depositing a piezoelectric layer 14 on the filling layer 13 and the upper electrode 12, and etching to remove the substrate 10 and the thermal oxide layer 11;

[0041] Step 4, depositing a lower electrode 15 on the piezoelectric layer 14, and partially etching the lower electrode 15 to expose the piezoelectric layer 14;

[0042] Step 5, depositing a lower passivation layer 20 on the surface of the lower electrode 15;

[0043] Step 6: depositing a sacrificial layer 16 on the lower electrode 15 and the exposed piezoelectric layer 14;

[0044] Step 7, depositing a fence layer 17 on the sacrificial layer 16 to cover the sacrificial layer 16, the exposed lower passivation layer 20 and the exposed piezoelectric layer 14;

[0045] Step 8, laying a fence layer 17 on the base 18;

[0046] Step 9, partially etching and removing part of the upper electrode 12, and laying an upper passivation layer 19 on the upper electrode 12;

[0047] Step 10: etching and removing the filling layer 13 and the sacrificial layer 16.

[0048] Wherein, the thermal oxide layer 11 is provided with a concave structure. The growth index of the thermal oxide layer 11 is: thickness 500A-5000A, uniformity <3%. The etching conditions of the thermal oxide layer 11 are: angle 10-90 degrees, damage to the substrate <100A. The thickness of the deposited upper electrode 12 is greater than the thickness of the thermal oxide layer, and the uniformity requirement is <1%. Wherein, the material type of the upper electrode includes but is not limited to Mo / W, etc. The thickness of the filling layer 13 is greater than the thickness of the thermal oxide layer. Specifically, the thickness of the filling layer 13 is obtained by the following formula:

[0049]

[0050]

[0051] Wherein, H represents the thickness of the filling layer; H0 represents the thickness of the piezoelectric layer; A represents the parameter matrix; f represents the filter frequency of the BAW filter; λ represents the acoustic wavelength of the BAW filter; ξ represents the acoustic damping coefficient of the BAW filter; c represents the acoustic velocity of the BAW filter;

[0052] At the same time, filling layer deposition + CMP: the material can be USG / PSG / SIN, etc., the thickness needs to be greater than the thickness of the thermal oxide layer, and the damage of CMP to the upper electrode is less than 100A. The thickness of the upper passivation layer is 400-4000A, and the uniformity is <3%. The material of the upper passivation layer includes ALN / SIN and / or USG.

[0053] The working principle and technical effect of the above technical solution are as follows: the above technical solution of this embodiment provides a D-BAW air bridge structure and a method for forming the same, which can effectively reduce the scattering direction of sound waves through the air bridge structure, thereby reducing the scattering effect and energy loss, thereby improving the quality factor Q value of the bulk acoustic wave filter. At the same time, the spatial overlap rate of the sound waves of the bulk acoustic wave filter during high-frequency vibration operation can be effectively improved through the position setting of the above air bridge structure and the setting of the extension part, thereby improving the enhancement ratio of the interference effect, narrowing the resonance peak, and further improving the quality factor Q value.

[0054] On the other hand, in the above technical solution of this embodiment, in addition to the original cavity of the bulk acoustic wave filter, an air cavity can be formed by separating part of the piezoelectric layer from the electrode to reduce the energy loss of the sound wave during propagation. The propagation loss of sound waves in air media is lower than that in piezoelectric media, so this method helps to improve the Q value. By carefully designing the structure and size of the air cavity, the propagation mode and phase of the sound wave can be adjusted to more accurately control the frequency response of the filter. Enhanced frequency selectivity means that the bandwidth of the filter is narrower and the signal processing is more accurate. The introduction of the air cavity structure can reduce the impact of temperature changes on the filter performance. Since the thermal expansion coefficient of air is low, this structure can reduce the impact on the propagation of sound waves when the temperature changes, and improve the temperature stability of the filter. At the same time, by introducing the air cavity structure, the design and manufacturing process of the filter can be simplified. This structure can reduce the requirements for high-precision manufacturing and complex assembly, thereby reducing production costs.

[0055] In addition, by setting an air cavity between the electrode and the piezoelectric layer, the cross-coupling between signals of different frequencies can be effectively reduced. This structure can reduce the energy transfer of sound waves between different frequency modes, thereby improving the isolation and selectivity of the filter. The introduction of the air cavity structure can reduce the influence of factors such as temperature and mechanical stress on the filter frequency. Since the thermal expansion coefficient of air is low, this structure can reduce the influence of temperature changes on the propagation of sound waves, thereby improving the frequency stability of the filter. Under strong signal or high power conditions, the propagation of sound waves in the piezoelectric layer may cause nonlinear effects such as amplitude modulation and frequency offset. By introducing the air cavity structure, the intensity and energy density of the sound waves can be reduced, thereby reducing the occurrence of nonlinear effects and improving the purity and linearity of the signal. By rationally designing the structure and size of the air cavity, the mechanical stability of the filter can be enhanced. This structure can reduce the impact of external mechanical stress on filter performance and improve the reliability and life of the filter. The above formula can help designers and production personnel better understand and control the performance of BAW filters, thereby achieving a more efficient and stable production process. At the same time, based on the design parameters and required performance indicators, the optimal thickness of the filling layer can be accurately calculated to optimize the performance of the BAW filter; avoiding the process of determining the thickness of the filling layer by trial and error, saving time and cost, and improving production efficiency; the filling layer thickness calculated by this formula can ensure that the product has consistent performance between different batches.

[0056] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A D-BAW air bridge structure, characterized in that: The D-BAW air bridge structure comprises a substrate, a fence layer, a lower passivation layer, a lower electrode, a piezoelectric layer, an upper electrode and an upper passivation layer; the fence layer, the lower passivation layer, the lower electrode, the piezoelectric layer, the upper electrode and the upper passivation layer are sequentially deposited on the substrate, wherein an air bridge structure is provided between the upper electrode and the piezoelectric layer; The method for forming the D-BAW air bridge structure comprises: Step 1: depositing a thermal oxide layer (11) on a substrate (10), wherein the thermal oxide layer (11) does not completely cover the substrate (10), and a portion of the substrate (10) is exposed; Step 2: After the upper electrode (12) and the filling layer (13) are sequentially deposited on the thermal oxidation layer (11), the filling layer (13) is processed to form an air bridge structure region in the filling layer (13); Step 3, depositing a piezoelectric layer (14) on the filling layer (13) and the upper electrode (12), and etching to remove the substrate (10) and the thermal oxide layer (11); Step 4: depositing a lower electrode (15) on the piezoelectric layer (14), and partially etching the lower electrode (15) to expose the piezoelectric layer (14); Step 5: The surface of the lower electrode (15) is completely covered with a lower passivation layer (20); Step 6: a sacrificial layer (16) covers the exposed piezoelectric layer (14) and the lower passivation layer (20); Step 7, depositing a fence layer (17) on the sacrificial layer (16) so as to cover the sacrificial layer (16), the exposed lower passivation layer (20) and the exposed piezoelectric layer (14); Step 8: Arrange a fence layer (17) on the base (18); Step 9, partially etching and removing part of the upper electrode (12), and laying an upper passivation layer (19) on the upper electrode (12); Step 10: Etch and remove the filling layer (13) and the sacrificial layer (16).

2. The method for forming a D-BAW air bridge structure according to claim 1, characterized in that: The upper electrode (12) is provided with a concave structure.

3. The method for forming a D-BAW air bridge structure according to claim 1, characterized in that: The growth index of the thermal oxide layer (11) is: thickness 500A-5000A, uniformity <3%.

4. The method for forming a D-BAW air bridge structure according to claim 1, characterized in that: The etching conditions of the thermal oxide layer (11) are: an angle of 10-90 degrees and damage to the substrate of less than 100 Å.

5. The method for forming a D-BAW air bridge structure according to claim 1, characterized in that: The deposited thickness of the upper electrode (12) is greater than the thickness of the thermal oxide layer, and the uniformity is required to be <1%.

6. The method for forming a D-BAW air bridge structure according to claim 1, characterized in that: The thickness of the filling layer (13) is greater than the thickness of the thermal oxidation layer.

7. The method for forming a D-BAW air bridge structure according to claim 1, characterized in that: The thickness of the upper passivation layer is 400-4000A, and the uniformity is <3%.

8. The method for forming a D-BAW air bridge structure according to claim 1 or 7, characterized in that: The material of the upper passivation layer includes ALN and / or USG.

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