Micromechanical ultrasonic transducer and manufacturing method thereof

Abstract

The invention relates to the technical field of micromechanical ultrasonic transducers, in particular to a micromechanical ultrasonic transducer and a manufacturing method thereof, and the manufacturing method comprises the following steps: S1, cleaning a substrate; s2, etching a cavity structure on the front surface of the substrate by using a dry method / wet method, filling a sacrificial layer material in the cavity structure by using PEVCD, and growing a dielectric layer by using LPCVD; s3, growing a thin film on the dielectric layer by using LPCVD and annealing; s4, sequentially growing a seed layer, a lower electrode, a piezoelectric layer and an upper electrode on the thin film; s5, patterning the lower electrode, the piezoelectric layer and the upper electrode; s6, the upper electrode and the lower electrode are led out through a PAD; s7, etching the release holes, and removing the sacrificial layer material through a gaseous release / wet release process; according to the micromechanical ultrasonic transducer and the manufacturing method thereof, the integration level and the consistency are guaranteed, the acoustic performance and the physical reliability are remarkably improved, and the manufacturing cost is remarkably reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of micromechanical ultrasonic transducers, and in particular to a micromechanical ultrasonic transducer and a manufacturing method thereof. Background Art

[0002] Piezoelectric micromachined ultrasonic transducer (PMUT) is mainly a micromachined piezoelectric composite multilayer vibration membrane. The transmission and reception of ultrasonic waves are achieved through the bending vibration of the vibration membrane. Because it is easy to match the acoustic impedance of water and air and has a high degree of integration, it has great application potential in the field of sensing.

[0003] The production and manufacturing of piezoelectric micromechanical ultrasonic transducers are mainly divided into bulk silicon process and Soi process based on silicon on insulating layer: the bulk silicon process is to form a cavity structure filled with a sacrificial layer on the front side of the silicon substrate through etching and thin film process, and manufacture PMUT vibrators and arrays above the cavity structure; while the Soi process is to form the PMUT vibrators and arrays on the front side of the silicon substrate, and then use back-side processes such as deep silicon etching or wet etching to form a cavity structure on the back side of the silicon substrate.

[0004] Bulk silicon technology is widely used in high-frequency fields due to its excellent compatibility, consistency and device integration with complementary metal oxide semiconductor (CMOS). The acoustic performance and physical reliability of piezoelectric micromechanical ultrasonic transducers manufactured using bulk silicon technology are often far behind those using SOI technology, while the integration, consistency and cost of piezoelectric micromechanical ultrasonic transducers manufactured using SOI technology are at a disadvantage compared to bulk silicon technology. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a micromechanical ultrasonic transducer and a method for manufacturing the same, which has significantly enhanced acoustic performance and physical reliability and significantly reduced manufacturing cost while ensuring integration and consistency.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for manufacturing a micromechanical ultrasonic transducer, comprising the following steps:

[0007] S1. Substrate cleaning;

[0008] S2. Etching a cavity structure on the front side of the substrate by dry / wet method, filling the cavity structure with sacrificial layer material by PEVCD, and growing a dielectric layer by LPCVD;

[0009] S3. growing a thin film on the dielectric layer using LPCVD and annealing;

[0010] S4. sequentially growing a seed layer, a lower electrode, a piezoelectric layer and an upper electrode on the film;

[0011] S5. Patterning the lower electrode, the piezoelectric layer and the upper electrode;

[0012] S6. Lead out the upper electrode and the lower electrode through PAD;

[0013] S7. Etching release holes, and removing the sacrificial layer material through a gas release / wet release process.

[0014] Furthermore, the specific steps of step S2 are as follows:

[0015] S21. Etching a cavity structure on the front side of the substrate using a dry / wet method;

[0016] S22. Filling the cavity structure with a sacrificial layer material using PEVCD;

[0017] S23. After CMP planarization, stop at the front side of the substrate;

[0018] S24. Use LPCVD to grow a dielectric layer on the front side of the substrate.

[0019] Furthermore, the specific steps of step S2 are as follows:

[0020] S21 '. The substrate front side uses LPCVD to grow a dielectric layer;

[0021] S22 'resin lithography development, forming a cavity shape;

[0022] S23' using dry / wet etching dielectric layer and the substrate below, forming a cavity structure;

[0023] S24'. The cavity structure is filled with a sacrificial layer material using PEVCD;

[0024] S25′. After CMP planarization, it stops on the upper surface of the dielectric layer.

[0025] Furthermore, the effective patterning area in step S5 is approximately 60-70% of the area of ​​the cavity structure.

[0026] Furthermore, in step S7, the release holes are etched on the back side of the substrate or on the thin film and dielectric layer.

[0027] Furthermore, in step S7, the release hole is etched on the back side of the substrate or the film.

[0028] Furthermore, the material of the dielectric layer is silicon oxide or silicon nitride.

[0029] Furthermore, the material of the thin film is polysilicon.

[0030] A micromechanical ultrasonic transducer manufactured by any of the above-mentioned micromechanical ultrasonic transducer manufacturing methods comprises a substrate, a dielectric layer, a film, a lower electrode, a piezoelectric layer, an upper electrode, a cavity structure and a release hole, wherein the dielectric layer is arranged on the front surface of the substrate, the film is arranged on the upper surface of the dielectric layer, the lower electrode, the piezoelectric layer and the upper electrode are arranged on the film in sequence, the cavity structure is formed in the middle of the front surface of the substrate, the cavity structure is filled with a sacrificial layer material, and the release hole is opened in the middle of the dielectric layer and the film.

[0031] Furthermore, the cavity structure is formed in the middle of the front surface of the substrate and in the middle of the dielectric layer, and the release hole is opened in the middle of the film.

[0032] The beneficial effects of the present invention are:

[0033] (1) The present invention utilizes bulk silicon technology to form and fill a cavity structure on the front side of the substrate, thereby reducing the manufacturing cost while ensuring integration and consistency. In addition, a dielectric layer and a thin film are formed above the cavity structure to provide mechanical support, thereby significantly enhancing the acoustic performance and physical reliability, and is suitable for large-scale production.

[0034] (2) The present invention provides a dielectric layer to play a role in transition and buffering stress, thereby preventing the wafer from warping and deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0036] Figure 1 is a flow chart of a method for manufacturing a micromechanical ultrasonic transducer in the present invention;

[0037] Figure 2 is a cross-sectional view of the micromechanical ultrasonic transducer of the present invention Figure 1 ;

[0038] Figure 3 is a cross-sectional view of the micromechanical ultrasonic transducer of the present invention Figure 2 ;

[0039] Figure 4 is a cross-sectional view of the micromechanical ultrasonic transducer of the present invention Figure 3 .

[0040] In the figure: 1. substrate; 2. dielectric layer; 3. film; 4. lower electrode; 5. piezoelectric layer; 6. upper electrode; 7. cavity structure; 8. release hole. DETAILED DESCRIPTION

[0041] The present invention will now be further described in conjunction with the accompanying drawings and preferred embodiments. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0042] Example 1

[0043] like Figure 1 As shown, a method for manufacturing a micromechanical ultrasonic transducer comprises the following steps:

[0044] S1. Substrate 1 cleaning;

[0045] S2. Etching a cavity structure 7 on the front side of the substrate 1 by dry / wet method, filling the cavity structure 7 with a sacrificial layer material by PEVCD (plasma chemical vapor deposition), and growing a dielectric layer 2 by LPCVD (low pressure chemical vapor deposition);

[0046] S3. growing a thin film 3 on the dielectric layer 2 by LPCVD and annealing;

[0047] S4. A seed layer, a lower electrode 4, a piezoelectric layer 5 and an upper electrode 6 are sequentially grown on the film 3;

[0048] S5. Patterning the lower electrode 4, the piezoelectric layer 5 and the upper electrode 6;

[0049] S6. The upper electrode 6 and the lower electrode 4 are led out through PAD (electrode);

[0050] S7. Etching the release hole 8, and removing the sacrificial layer material by a gaseous release / wet release process.

[0051] A cavity structure 7 is formed and filled on the front side of the substrate 1 using bulk silicon technology, which reduces the manufacturing cost while ensuring the integration and consistency. The dielectric layer 2 and the thin film 3 are formed above the cavity structure 7 to play a mechanical support role, which significantly enhances the acoustic performance and physical reliability and is suitable for large-scale production.

[0052] Specifically, the material of the substrate 1 is single crystal silicon, sapphire or glass, etc.; the material of the dielectric layer 2 is silicon oxide or silicon nitride, etc.; the material of the thin film 3 is polycrystalline silicon; the seed layer is about 30nm, which is used to correct the crystal orientation of the lower electrode 4 and the piezoelectric layer 5; the lower electrode 4 and the upper electrode 6 can be a variety of metals, including but not limited to molybdenum, aluminum, tungsten, etc.; the material of the piezoelectric layer 5 is aluminum nitride, scandium-doped aluminum nitride, polycrystalline lead zirconate titanate (PZT), single crystal lead zirconate titanate (PZT), polycrystalline lithium niobate (LiNbO3) or polycrystalline lithium tantalate (TaNbO3), etc., and the above materials can also include a certain concentration of metal ion doping; the sacrificial layer material is silicon oxide or doped and modified silicon oxide, etc.

[0053] Since the bonding degree between the polysilicon film 3 and the substrate 1 is not high and there is a large stress gap, which easily leads to the warping and deformation of the wafer, the dielectric layer 2 is provided to play the role of transition and buffering stress.

[0054] The specific steps of step S2 are as follows:

[0055] S21. Etching the cavity structure 7 on the front side of the substrate 1 by dry / wet method;

[0056] S22. The cavity structure 7 is filled with a sacrificial layer material using PEVCD;

[0057] S23. CMP (chemical mechanical polishing) stops at the front side of substrate 1 after planarization;

[0058] S24. A medium layer 2 is grown on the front side of the substrate 1 using LPCVD.

[0059] The effective patterned area in step S5 is approximately 60-70% of the area of ​​the cavity structure 7, which helps to improve the maximum acoustic performance of the device.

[0060] In step S7 , the release hole 8 is etched on the back side of the substrate 1 or on the film 3 and the dielectric layer 2 .

[0061] Example 2

[0062] The difference between this embodiment and embodiment 1 mainly lies in step S2. The specific steps of step S2 are as follows:

[0063] S21 '. The front side of the substrate 1 uses LPCVD to grow a dielectric layer 2;

[0064] S22 'resin lithography development, forming a cavity shape;

[0065] S23 'using dry / wet etching dielectric layer 2 and the substrate 1 thereunder to form a cavity structure 7;

[0066] S24'. The cavity structure 7 is filled with a sacrificial layer material using PEVCD;

[0067] S25′. After CMP planarization, it stops on the upper surface of the dielectric layer 2.

[0068] Specifically, in step S7 , the release hole 8 is etched on the back side of the substrate 1 or the film 3 .

[0069] Example 3

[0070] like Figure 2 As shown, a micromechanical ultrasonic transducer manufactured by the micromechanical ultrasonic transducer manufacturing method described in Example 1 includes a substrate 1, a dielectric layer 2, a film 3, a lower electrode 4, a piezoelectric layer 5, an upper electrode 6, a cavity structure 7 and a release hole 8. The dielectric layer 2 is arranged on the front side of the substrate 1, the film 3 is arranged on the upper surface of the dielectric layer 2, the lower electrode 4, the piezoelectric layer 5 and the upper electrode 6 are arranged on the film 3 in sequence, the cavity structure 7 is formed in the middle of the front side of the substrate 1, the cavity structure 7 is filled with a sacrificial layer material, and the release hole 8 is opened in the middle of the dielectric layer 2 and the film 3.

[0071] Example 4

[0072] like Figure 3 As shown, the main difference between this embodiment and embodiment 3 is the specific arrangement of the cavity structure 7 and the release hole 8. In this embodiment, the cavity structure 7 is formed in the middle of the front surface of the substrate 1 and the middle of the dielectric layer 2, and the release hole 8 is opened in the middle of the film 3. The micromechanical ultrasonic transducer in this embodiment is manufactured by the micromechanical ultrasonic transducer manufacturing method described in embodiment 2.

[0073] Example 5

[0074] like Figure 4 As shown, the main difference between this embodiment and embodiment 4 is the specific arrangement of the release hole 8. In this embodiment, the release hole 8 is opened in the middle of the back side of the substrate 1.

[0075] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. They cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a micromechanical ultrasonic transducer, characterized in that: The steps include: S1. Substrate (1) cleaning; S2. Etching a cavity structure (7) on the front side of the substrate (1) by dry / wet method, filling the cavity structure (7) with a sacrificial layer material by PEVCD, and growing a dielectric layer (2) by LPCVD; S3. growing a thin film (3) on the dielectric layer (2) by LPCVD and annealing; S4. sequentially growing a seed layer, a lower electrode (4), a piezoelectric layer (5) and an upper electrode (6) on the film (3); S5. Patterning the lower electrode (4), the piezoelectric layer (5) and the upper electrode (6); S6. The upper electrode (6) and the lower electrode (4) are led out through PAD; S7. Etching release holes (8) and removing the sacrificial layer material through a gas release / wet release process.

2. The method for manufacturing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The specific steps of step S2 are as follows: S21. Etching a cavity structure (7) on the front side of the substrate (1) using a dry method or a wet method; S22. The cavity structure (7) is filled with a sacrificial layer material using PEVCD; S23. After CMP planarization, the process stops at the front side of the substrate (1); S24. A medium layer (2) is grown on the front side of the substrate (1) using LPCVD.

3. The method for manufacturing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The specific steps of step S2 are as follows: S21 '. The substrate (1) is grown on the front side using LPCVD dielectric layer (2); S22 'resin lithography development, forming a cavity shape; S23' using dry / wet etching dielectric layer (2) and the substrate thereunder (1), forming a cavity structure (7); S24'. The cavity structure (7) is filled with a sacrificial layer material using PEVCD; S25′. After CMP planarization, it stops on the upper surface of the dielectric layer (2).

4. The method for manufacturing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The effective patterning area in step S5 is approximately 60-70% of the area of ​​the cavity structure (7).

5. The method for manufacturing a micromechanical ultrasonic transducer according to claim 2, characterized in that: In the step S7, the release hole (8) is etched on the back side of the substrate (1) or on the film (3) and the dielectric layer (2).

6. The method for manufacturing a micromechanical ultrasonic transducer according to claim 3, characterized in that: In the step S7, the release hole (8) is etched on the back side of the substrate (1) or the film (3).

7. The method for manufacturing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The material of the dielectric layer (2) is silicon oxide or silicon nitride.

8. The method for manufacturing a micromechanical ultrasonic transducer according to claim 1, characterized in that: The material of the thin film (3) is polycrystalline silicon.

9. A micromechanical ultrasonic transducer manufactured by the method for manufacturing a micromechanical ultrasonic transducer according to any one of claims 1, 2, 4-8, characterized in that: The invention comprises a substrate (1), a dielectric layer (2), a film (3), a lower electrode (4), a piezoelectric layer (5), an upper electrode (6), a cavity structure (7) and a release hole (8); the dielectric layer (2) is arranged on the front surface of the substrate (1); the film (3) is arranged on the upper surface of the dielectric layer (2); the lower electrode (4), the piezoelectric layer (5) and the upper electrode (6) are arranged on the film (3) in sequence; the cavity structure (7) is formed in the middle of the front surface of the substrate (1); a sacrificial layer material is filled in the cavity structure (7); and the release hole (8) is opened in the middle of the dielectric layer (2) and the film (3).

10. The micromechanical ultrasonic transducer according to claim 9, characterized in that: The cavity structure (7) is formed in the middle of the front side of the substrate (1) and in the middle of the dielectric layer (2), and the release hole (8) is opened in the middle of the film (3).

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