A sealing structure of a micro-mechanical structure release window and a preparation method thereof

Abstract

This invention relates to a sealing structure for a release window of a micromechanical structure and its preparation method. The sealing structure includes a sealing body structure and a protective structure. The sealing body structure includes a cap and a sealing layer; the sealing layer fills the release window, and the cap is cylindrical and completely covers the release window. The protective structure is disposed on the outside of the sealing body structure and completely encloses it. The preparation steps of the sealing structure include: depositing sealing body structure material, sealing the release window, and removing the sealing body film material outside the release window using a dry etching process; depositing protective structure material to strengthen the protection of the outer edge of the seal, and removing the protective structure film material outside the release window using a dry etching process to form a sealed constant-pressure cavity. This invention can improve the integrity of the micromechanical structure, achieving a complete surface film; the protective structure can prevent the sealing structure from being corroded or damaged, or from leaking due to aging over time and environmental factors, affecting the constant pressure of the sealed cavity.

Description

Technical Field

[0001] This invention relates to the field of MEMS (Micro-Electro-Mechanical Systems) sealing technology, and particularly to a sealing structure for a micromechanical structure release window and its preparation method. Background Technology

[0002] In MEMS (Micro-Electro-Mechanical Systems) fabrication processes, after the sacrificial layer of many MEMS structures is released, the release window on the structure layer needs to be sealed to achieve a complete thin film on the surface and form a constant-pressure release cavity.

[0003] In existing technologies, sealing methods typically involve directly sealing a single layer of material using techniques such as PECVD or LPCVD. If a high vacuum level is required, PECVD is difficult to achieve, while LPCVD can. However, when depositing LPCVD material alone, all surfaces inside the cavity are also covered with a layer of LPCVD material during sealing, limiting the design of small-sized cavities. For example, in small cavities, the entire cavity may become completely filled with LPCVD material during the deposition of the sealing material, leading to cavity saturation and structural failure. Summary of the Invention

[0004] The purpose of this invention is to seal the release window on the structural layer, thereby solving the problem of incomplete film surface with release window or the cavity being filled, and to provide a sealing structure for the release window of a micromechanical structure and its preparation method.

[0005] To solve the above-mentioned technical problems, the present invention proposes a sealing structure for a micromechanical structure release window, characterized in that the sealing structure includes a sealing body structure and a protective structure 1;

[0006] The sealing structure includes a cap 2 and a sealing body 3; the sealing body 3 is used to fill the release window 4; the cap 2 is in the shape of a column or a platform and is used to completely cover the release window 4.

[0007] The protective structure 1 is disposed on the outside of the sealing structure and is used to completely cover the sealing structure.

[0008] As an improvement to the above technical solution, when the cap 2 is in the shape of a platform, the part away from the cap 3 is narrow and the part close to the cap 3 is wide.

[0009] As one of the improvements to the above technical solution, the sealing body 3 is in the shape of a column or a frustum; the column shape includes: cylinder and prism; the frustum shape includes: frustum of a cylinder and frustum of a prism.

[0010] As an improvement to the above technical solution, when the sealing body 3 is in the shape of a platform, the part away from the sealing cap 2 is narrow and the part close to the sealing cap 2 is wide.

[0011] As one improvement to the above technical solution, the sealing structure is a composite film layer of a single material or multiple materials. As another improvement to the above technical solution, when the sealing structure is a composite film layer of multiple materials, the material in close contact with the release window film layer is silicon oxide.

[0012] This invention proposes a method for preparing a sealing structure for a micromechanical release window as described above, comprising the following steps:

[0013] a) Deposit the thin film material of the sealing structure and remove the thin film material outside the release window using a dry etching process;

[0014] b) Deposit the thin film material to protect the structure, and use a dry etching process to remove the thin film material outside the release window.

[0015] As an improvement to the above technical solution, the sealing structure material in step a) is silicon nitride, polycrystalline silicon, or amorphous silicon, or a composite film layer of any combination of silicon oxide, silicon nitride, polycrystalline silicon, and amorphous silicon.

[0016] As an improvement to the above technical solution, when the sealing structure material is silicon oxide or silicon nitride, the deposition method is chemical vapor deposition (CVD); the CVD includes low-pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), or plasma-enhanced chemical vapor deposition (PECVD); when the sealing structure material is polycrystalline silicon or amorphous silicon, the deposition method is LPCVD.

[0017] As an improvement to the above technical solution, the material of the protective structure in step b) is silicon nitride, polycrystalline silicon or amorphous silicon, and its deposition method is LPCVD.

[0018] This invention proposes a method and manufacturing process for sealing a release window. This sealing structure can achieve a complete thin film on the structural surface and good sealing performance, thereby forming a relatively stable constant pressure cavity, especially a high vacuum low pressure cavity.

[0019] Technical effects of the present invention:

[0020] 1. Sealing structures can improve the integrity of micromechanical structures, resulting in a film with a complete surface.

[0021] 2. Sealing achieves constant pressure sealing of the release cavity, especially high vacuum and low pressure sealing effect, to realize the function of specific devices;

[0022] 3. The sealing film growth method and combination are flexible and diverse, achieving a constant pressure cavity while having the advantage of reliable sealing structure strength;

[0023] 4. The sealing structure is wrapped with protective material, which can prevent the sealing structure from being corroded and damaged in subsequent processing or actual use environment, thereby affecting or even destroying the constant pressure atmosphere of the cavity. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the cross-section of the sealing structure proposed in this invention;

[0025] Figure 2 This is a schematic cross-sectional view of the release window in a micromechanical structure.

[0026] Figures 3(a) and 3(b) are schematic cross-sectional views of the sealing structure of the present invention. The sealing structure in Figure 3(a) is made of a single thin film material, and the sealing structure in Figure 3(b) is made of a composite thin film material.

[0027] Figures 4(a) and 4(b) are cross-sectional schematic diagrams of the sealing body of the present invention in the form of a platform. The sealing body structure in Figure 4(a) is made of a single thin film material, and the sealing body structure in Figure 4(b) is made of a composite thin film material.

[0028] Figures 5(a) and 5(b) are schematic cross-sectional views of the seal body of the present invention in the shape of a cylinder. The seal body structure in Figure 5(a) is made of a single thin film material, and the seal body structure in Figure 5(b) is made of a composite thin film material.

[0029] Figure 6 This is a cross-sectional schematic diagram of the cap of the present invention being in the shape of a platform.

[0030] Attached Figure Labels

[0031] 1. Protective structure 2. Cap 3. Seal 4. Release window Detailed Implementation

[0032] The technical solutions provided by the present invention will be further illustrated below with reference to the embodiments.

[0033] like Figure 1 The diagram shown is a cross-sectional schematic of the sealing structure proposed in this invention. The sealing structure includes a sealing body structure and a protective structure 1. The sealing body structure includes a cap 2 and a sealing body 3. The sealing body 3 is used to fill the release window 4. The cap 2 is in the shape of a column or a platform and is used to completely cover the release window 4. The protective structure 1 is located on the outside of the sealing body structure and is used to completely wrap the sealing body structure.

[0034] The sealing body 3 is in the shape of a cylinder or a frustum; the cylinder shape includes a cylinder and a prism; the frustum shape includes a frustum of a cylinder and a frustum of a prism. When the sealing body 3 is in the shape of a frustum, its portion away from the cap is narrow, and its portion closer to the cap is wide.

[0035] Figures 5(a) and 5(b) show cross-sectional schematic diagrams of the seal body of the present invention in the shape of a cylinder. The seal body structure in Figure 5(a) is made of a single thin film material, and the seal body structure in Figure 5(b) is made of a composite thin film material.

[0036] This invention proposes the following method: After the sacrificial layer release etching is completed in a MEMS structure, a sealing film material is deposited to seal the release window. A dry etching process is then used to remove the film material outside the release window. Next, a protective material for the sealing structure is deposited to strengthen the protection of the outer edges of the sealing structure. Finally, a dry etching process is used to remove the film material outside the release window. By using stepwise growth of the sealing film material, a flexible combination of different growth methods (PECVD and LPCVD), and appropriate patterning, the release window can be sealed to form a constant-pressure cavity, particularly a low-pressure, high-vacuum cavity, while simultaneously enhancing the cavity's sealing performance.

[0037] The key processes and sequence for implementing the sealing structure of the micromechanical structure release window proposed in this invention include the following steps:

[0038] a) Deposited sacrificial layer;

[0039] b) Deposit the structural layer, and etch a release window 4 on the structural layer;

[0040] c) Sacrificial layer release etching to form release cavities, such as Figure 2 As shown;

[0041] d) Deposit sealing film material to obtain sealing structure, seal the release window, and remove film material outside the release window using dry etching process, as shown in Figures 3(a) and 3(b), which are schematic cross-sectional views of the sealing structure of the present invention. The sealing structure in Figure 3(a) is made of a single film material, and the sealing structure in Figure 3(b) is made of a composite film material.

[0042] e) The protective film material of the sealing structure is deposited to obtain the protective structure 1, which strengthens the protection of the outer edge of the seal. The film material outside the release window is removed by dry etching process to form a sealed constant pressure cavity, as shown in Figures 4(a) and 4(b), which are cross-sectional schematic diagrams of the sealing body of the present invention in the shape of a platform. In Figure 4(a), the sealing body structure is a single film material, and in Figure 4(b), the sealing body structure is a composite film material.

[0043] Preferably, the sacrificial layer material is silicon oxide, phosphosilicate glass, borosilicate glass, borosilicate glass or a composite material of at least two of these materials randomly stacked;

[0044] Preferably, the structural layer is a composite layer composed of one or more of the following materials: polycrystalline silicon, monocrystalline silicon, amorphous silicon, and silicon nitride.

[0045] Preferably, the sacrificial layer release etching process in step c) is either buffer oxide etching (BOE) or vapor-phase HF etching.

[0046] Preferably, in step d), the sealing film material is one of silicon nitride, polycrystalline silicon, and amorphous silicon, or a composite layer of any combination of silicon oxide, silicon nitride, polycrystalline silicon, and amorphous silicon. Silicon oxide and silicon nitride are deposited using LPCVD, APCVD, and PECVD, while polycrystalline silicon and amorphous silicon are deposited using LPCVD. When the sealing structure is composed of multiple composite film materials, each film material is deposited in stages. If the composite layer includes an oxide layer, the oxide layer is deposited first, and the subsequent deposition order of silicon nitride, polycrystalline silicon, and amorphous silicon is not limited.

[0047] Preferably, the sealing structure protective material in step e) is a silicon nitride material, polycrystalline silicon, or amorphous silicon material, and its growth method is low-pressure chemical vapor deposition (LPCVD).

[0048] For the fabrication of cylindrical or frustum shapes, during etching, the areas to be etched are etched at right angles or bevels; for example... Figure 6 The diagram shown is a cross-sectional view of the cap of the present invention being a platform shape. Compared with a column-shaped cap, a platform-shaped cap is more conducive to the subsequent layer coverage effect, thereby enabling the protective structure to achieve a better protective effect.

[0049] In the actual preparation process, a small amount of material of the sealing structure is deposited into the cavity, but it will not pile up and cause the upper and lower layers of the cavity to stick together, so it can be ignored.

[0050] The most typical example of this invention is the deposition of two layers of material: one layer is silicon oxide deposited by PECVD, and the other layer is silicon nitride deposited by LPCVD. The silicon oxide deposited by PECVD should be as large and the film should be as thick as possible, but care should be taken not to seal the opening. The complete sealing is achieved by LPCVD. When using LPCVD for sealing, a lower cavity vacuum can be achieved.

[0051] The key highlight of this invention is the combination of PECVD and LPCVD. First, PECVD seals part of the opening, and the remaining small opening is sealed with LPCVD. LPCVD can achieve a lower cavity vacuum. When sealing the small hole after PECVD with LPCVD, only a very thin layer of LPCVD material needs to be deposited. In this way, the LPCVD on the inner wall of the cavity will also be very thin, which takes into account the small-size cavity design.

[0052] As can be seen from the above detailed description of the present invention, the sealing structure provided by the present invention can improve the integrity of the micromechanical structure and achieve a complete thin film on the surface; the sealing structure is wrapped with a protective material, which can prevent the sealing structure from being corroded and damaged or the sealing material from aging over time and under environmental influences, thereby affecting or even destroying the constant pressure atmosphere of the cavity.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A sealing structure for a micromechanical release window, characterized in that, The sealing structure includes a sealing body structure and a protective structure (1); The sealing structure includes a cap (2) and a sealing body (3); the sealing body (3) is used to fill the release window (4); the cap (2) is in the shape of a column or a platform and is used to completely cover the release window (4); The protective structure (1) is disposed on the outside of the sealing structure to completely cover the sealing structure; The sealing structure is a composite film layer, in which one layer is deposited by PECVD and the other layer is deposited by LPCVD when fully sealed.

2. The sealing structure of the micromechanical structure release window according to claim 1, characterized in that, When the cap (2) is in the shape of a platform, the part away from the cap (3) is narrow and the part close to the cap (3) is wide.

3. The sealing structure of the micromechanical structure release window according to claim 1, characterized in that, The sealing body (3) is in the shape of a column or a platform; The column shape includes: cylinder and prism; the frustum shape includes: frustum of a cylinder and frustum of a prism.

4. The sealing structure of the micromechanical structure release window according to claim 3, characterized in that, When the sealing body (3) is in the shape of a platform, the part away from the cap (2) is narrow and the part close to the cap (2) is wide.

5. The sealing structure of the micromechanical structure release window according to claim 1, characterized in that, The sealing structure is a single material or a composite membrane layer of multiple materials.

6. The sealing structure of the micromechanical structure release window according to claim 5, characterized in that, When the sealing structure is a composite film layer of multiple materials, the material in close contact with the release window film layer is silicon oxide.

7. A method for preparing the sealing structure of the micromechanical structure release window according to claim 1, comprising the following steps: a) Deposit the thin film material of the sealing structure and remove the thin film material outside the release window using a dry etching process; b) Deposit the thin film material of the protective structure and remove the thin film material outside the release window using a dry etching process; the sealing structure is a composite film layer, wherein one layer is deposited by PECVD and the other layer is deposited by LPCVD when fully sealed.

8. The method for preparing the sealing structure of the micromechanical structure release window according to claim 7, characterized in that, The material of the sealing structure in step a) is silicon nitride, polycrystalline silicon, or amorphous silicon, or a composite film of any combination of silicon oxide, silicon nitride, polycrystalline silicon, and amorphous silicon.

9. The method for preparing the sealing structure of the micromechanical structure release window according to claim 8, characterized in that, When the encapsulation structure material is silicon oxide or silicon nitride, the deposition method is chemical vapor deposition (CVD); the CVD includes: low-pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), or plasma-enhanced chemical vapor deposition (PECVD); when the encapsulation structure material is polycrystalline silicon or amorphous silicon, the deposition method is LPCVD.

10. The method for preparing the sealing structure of the micromechanical structure release window according to claim 7, characterized in that, In step b), the material of the protective structure is silicon nitride, polycrystalline silicon, or amorphous silicon, and its deposition method is LPCVD.

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