A micromechanical vent structure and method of making the same

Abstract

The present application relates to a kind of micro-mechanical deflation structure and its preparation method, the channel includes leak hole or leak hole and leak valve, connecting area, deflation passage main body and gas flow channel;Leak hole is arranged in upper structure layer, directly opposite lower structure layer above movable structure layer fixed area side, deflation passage main body is set as bending or around deflation passage, one end is connected with gas flow channel, the other end is connected with leak hole through connecting area.The preparation method is: depositing sacrificial layer on lower structure layer, forms groove by photoetching;Depositing anchor area release stop structure layer, photoetching or CMP removes part of release stop film layer;Depositing upper structure layer, photoetching forms structure layer effective area and leak hole or leak hole and leak valve;Lower structure layer back photoetching, etching stops at sacrificial layer, forms gas flow channel;Release part of sacrificial layer, forms deflation passage main body and connecting area.The present application reduces the effective sound pressure loss when device works under normal sound pressure condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of MEMS (Micro Electro Mechanical System) deflation, in particular to a micro mechanical deflation structure and a preparation method thereof. BACKGROUND

[0002] The movable structure of MEMS (Micro Electro Mechanical System) often faces the air flow impact caused by the air pressure change around the structure. When the air pressure change is large, the instantaneous air flow is too large, and the movable structure is easily damaged. As shown in FIG. 10(a), it is a schematic diagram of the cross section of the traditional structure. The cavity of the traditional structure is a whole cavity. When the air pressure change is large, the structure is easily damaged due to the too large air flow, as shown in FIG. 10(b). In order to solve this problem, the existing solutions mostly set a deflation hole or a deflation hole and a deflation valve on the movable structure. However, the current solutions are to set the deflation hole or the deflation hole and the deflation valve in the movable structure area. The performance and reliability of the device cannot be effectively guaranteed. SUMMARY

[0003] The purpose of the present application is to overcome the problem of the structure damage caused by the too large air flow during deflation in the prior art, to solve the problem of the large effective sound pressure loss when the typical silicon microphone device is used, and to provide a micro mechanical deflation structure and a preparation method thereof.

[0004] In order to solve the above technical problems, the technical scheme of the present application provides a micro mechanical deflation structure. The deflation structure comprises a deflation hole 1-1, a connecting area 1-2, a deflation channel main body 2 and a cavity 4.

[0005] The deflation hole 1-1 is arranged on the upper structure layer 7 and opposite to the movable structure layer fixed area above the lower structure layer 5. The fixed area of the movable structure layer is a sacrificial layer anchor area 8.

[0006] The connecting area 1-2 is arranged directly below the deflation hole 1-1 and is used to connect the deflation hole 1-1 and the deflation channel main body 2.

[0007] The deflation channel main body 2 is provided with a plurality of bending or winding micro deflation channels for connecting the gas flow channel 3 and the connecting area 1-2.

[0008] As one of the improvements of the above technical scheme, the deflation hole 1-1 is arranged as a flame-shaped gap to form a deflation valve 9. The deflation valve can close the deflation hole when there is no air exhaust. When air is exhausted, the deflation valve deforms due to the pressure, and the opening angle of the deflation valve can be self-adaptively adjusted according to the flow rate to realize rapid air exhaust.

[0009] As one of the improvements of the above technical scheme, the deflation channel main body 2 forms a micro deflation channel in the shape of a "bow" by means of straight angle or arc angle bending.

[0010] As one of the improvements to the above technical solution, the main body 2 of the venting channel is formed into a spiral micro-venting channel by annular bending.

[0011] As one of the improvements to the above technical solution, the cross-section of the main body 2 of the venting channel is rectangular or square, trapezoidal, inverted trapezoidal or racetrack-shaped.

[0012] As one of the improvements to the above technical solution, the height of the venting channel body 2 is the same as the height of the sacrificial layer anchor area 8.

[0013] The present invention also provides a method for preparing the micromechanical venting structure described in any one of the above, comprising the following steps:

[0014] 1) A sacrificial layer is deposited on the lower structural layer 5, and a groove is formed by photolithography etching to form the connection area 1-2, the main body of the venting channel 2, the cavity 4 and the sacrificial layer anchor area 8;

[0015] 2) Deposit the film layer of the anchor release stop structure 6, and remove part of the release stop film layer by photolithography etching or chemical mechanical polishing (CMP), while retaining the anchor release stop structure 6. At the same time, the boundaries of the connection area 1-2, the venting channel body 2, the cavity 4, and the sacrificial layer anchor area 8 are defined.

[0016] 3) Deposit the upper structural layer 7, and use photolithography to etch the effective area of ​​the structural layer and the vent holes 1-1;

[0017] 4) The back side of the lower structural layer 5 is photolithographically etched, and the etching stops at the sacrificial layer to form gas flow channel 3;

[0018] 5) Use wet or dry corrosion to release part of the sacrificial layer material to form cavity 4, connecting area 1-2 and venting channel body 2.

[0019] As one of the improvements to the above technical solution, the lower structural layer 5 is silicon; the upper structural layer 7 is a single material of silicon, polycrystalline silicon, or amorphous silicon, or a multilayer composite material formed by stacking polycrystalline silicon and silicon nitride, or a multilayer composite material formed by stacking amorphous silicon and silicon nitride; the material of the release stopping structure 6 film layer is polycrystalline silicon, amorphous silicon, or silicon nitride.

[0020] As one of the improvements to the above technical solution, the material of the sacrificial layer is silicon oxide, borosilicate glass, phosphosilicate glass, borosilicate-phosphosilicate glass, or a composite material of at least two of these randomly stacked, and its deposition method is thermal oxidation or chemical vapor deposition (CVD); the CVD includes low-pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), sub-atmospheric pressure chemical vapor deposition (SACVD), or plasma-enhanced chemical vapor deposition (PECVD).

[0021] This invention, by setting up a pressure release channel in the fixed area of ​​the movable structure layer, allows for the release of excessive airflow through the pressure release channel via a vent or vent valve when there are significant changes in air pressure around the movable structure. This protects the movable structure from impact damage and maintains normal operation. Simultaneously, by designing a long-distance micro-vent channel with various bends or detours, this invention increases flow resistance (acoustic resistance), making it less likely for sound waves to be lost through the micro-vent channel to the vent or vent valve. For acoustic applications, this effectively reduces the effective sound pressure loss, especially low-frequency attenuation, during device operation under normal sound pressure conditions.

[0022] The movable structure mentioned in this article refers to a portion of the upper structural layer 7. The sacrificial layer beneath this portion is corroded and released during processing, allowing this part to be suspended and vibrate vertically. This portion corresponds to the gas flow channel 3 and cavity 4 within the upper structural layer 7. The fixed area of ​​the movable structure is the portion of the upper structural layer 7 corresponding to the insulating layer anchor area 8 and the anchor area release and stop structure 6.

[0023] Vent holes and vent valves are located in the area outside cavity 4 of the upper structural layer; the main body of the vent channel is also located in the area outside cavity 4 of the sacrificial layer; therefore, they are all located in the area outside cavity 4, and the area outside cavity 4 corresponds to this part of the area in other layers. The area outside cavity 4 is also complementary to the movable structural area of ​​the structural layer (the movable structural area of ​​the structural layer is the part of the upper structural layer 7 corresponding to gas flow channel 3 and cavity 4, equivalent to the area inside cavity 4). This invention proposes, for acoustic applications, to set up a pressure release channel and vent hole in the fixed area of ​​the micromechanical movable structural layer, or to add a vent valve or vent valve array to the vent hole, so as to achieve rapid pressure relief when the movable structure is subjected to high sound pressure or high airflow, reducing the risk of the movable structure breaking under the impact of high sound pressure or high airflow. In addition, under normal sound pressure conditions, the long pressure release channel combined with the vent hole or vent valve can effectively reduce the effective sound pressure loss when the device is working, especially the low frequency attenuation.

[0024] The technical advantages of the micromechanical venting channel provided by this invention are as follows:

[0025] 1. By setting up an air pressure release channel in the fixed area of ​​the movable structure layer, when the air pressure around the movable structure changes significantly, the instantaneous excessive airflow is released through the air pressure release channel, protecting the movable structure from damage by airflow impact and maintaining normal operation;

[0026] 2. The air pressure release channel and vent hole, or the vent hole with a vent valve, are set in the fixed area outside the movable structure layer and above the lower structure layer to avoid the reduction of the movable structure strength caused by setting the vent hole or the vent hole with a vent valve on the movable structure layer directly above the airflow channel.

[0027] 3. When this venting channel structure is used as an acoustic device (such as a microphone), the vent or venting valve is set in the fixed area of ​​the movable structural layer above the lower structural layer, rather than directly facing the gas flow channel of the lower structural layer, which can effectively avoid the loss of effective sound pressure under normal sound pressure conditions.

[0028] 4. When this venting channel structure is used as an acoustic device (such as a microphone), by designing a long distance and various bends or turns in the micro venting channel, the flow resistance (acoustic resistance) is increased, making it difficult for sound waves to be transmitted through the micro venting channel to the vent hole or to be lost by adding a venting valve to the vent hole. This can effectively reduce the effective sound pressure loss of the device under normal sound pressure conditions, especially the low-frequency attenuation. Attached Figure Description

[0029] Figure 1 This is a schematic cross-sectional view of the micromechanical venting channel and venting hole described in this invention.

[0030] Figures 2-5 These are top-view schematic diagrams of four typical designs of the micromechanical venting channel and connection area described in this invention;

[0031] Figure 6(a) is a top view of the vent hole, Figure 6(b) is a top view of the vent hole set as a flame-shaped slit to form a vent valve, and Figure 6(c) is a top view of multiple vent valves set according to actual needs.

[0032] Figure 7 A cross-sectional structural diagram of a structure with a vent valve installed in the middle of the vent hole;

[0033] Figure 8 A schematic diagram of the cross-sectional structure of the venting structure with a venting valve in the middle of the vent hole during venting.

[0034] Figures 9(a), (b), (c), and (d) are, respectively, cross-sectional schematic diagrams showing the different degrees of opening of the vent valve array in the micromechanical vent channel of the present invention when subjected to different sound pressures or when the gas flow is exhausting.

[0035] Figure 10(a) is a cross-sectional schematic diagram of the traditional structure; Figure 10(b) is a cross-sectional schematic diagram of the structure damaged by excessive airflow.

[0036] Figure 11 This is a schematic diagram showing the cross-sectional structure of the main body of the venting channel, which is shaped like a racetrack.

[0037] Figure Labels

[0038] 1-1, Vent Hole; 1-2, Connection Area; 2, Vent Channel Main Body

[0039] 3. Gas flow channel; 4. Cavity; 5. Lower structural layer

[0040] 6. Anchorage release and stopping structure; 7. Upper structural layer; 8. Sacrificial layer anchorage.

[0041] 9. Air relief valve Detailed Implementation

[0042] The technical solutions provided by the present invention will be further illustrated below with reference to the embodiments.

[0043] like Figure 1 The diagram shown is a cross-sectional view of the micromechanical venting channel described in this invention:

[0044] (1) A gas flow channel 3 is provided in the lower structural layer 5;

[0045] (2) The sacrificial layer is located between the lower structural layer 5 and the upper structural layer 7. The sacrificial layer is provided with an anchor release and stop structure 6. The anchor release and stop structure 6 is planarized to form a sacrificial layer anchor area 8 planar pattern, a connecting area 1-2 planar pattern, and a venting channel body 2 planar pattern. Part of the sacrificial layer is etched away to form a cavity 4, a connecting area 1-2, and a venting channel body 2. The remaining part of the sacrificial layer forms the sacrificial layer anchor area 8. The sacrificial layer anchor area 8 connects the lower structural layer 5 and the upper structural layer 7. The cavity 4 provides movement space for the upper structural layer 7.

[0046] (3) The upper structural layer 7 is located on the sacrificial layer. The upper structural layer 7 has a vent hole 1-1 in the fixed area or a vent valve 9 is set in the middle of the vent hole 1-1.

[0047] (4) One end of the venting channel body 2 is connected to the gas flow channel 3, and the other end is connected to the venting hole 1-1 through the connecting area 1-2;

[0048] (5) Other sacrificial layers and structural layers can be combined above the upper structural layer 7 to achieve more device functions;

[0049] like Figures 2-5 The diagram shows four typical designs of the micromechanical venting channel described in this invention, with the sacrificial film layer cut across it in a top plan view. Figure 2 The main body 2 of the venting channel is designed as a long strip shape, which is the most typical and easily implemented shape. Figure 3 The main body 2 of the venting channel is configured into a spiral shape by means of a circular bend. Figure 4 The main body 2 of the venting channel is bent into a "bow" shape at a right angle; Figure 5 The main body of the venting channel is bent into a bow shape by an arc angle; the main difference lies in the different bending forms and dimensions of the main body 2 of the venting channel.

[0050] As shown in Figure 6, the membrane layer of the above structural layer is viewed from the top. Figure 6(a) is a top view of the vent hole 1-1, Figure 6(b) is a top view of the vent hole 1-1 set as a flame-shaped slit to form a vent valve 9, and Figure 6(c) is a top view of multiple flame-shaped slits of the vent hole 1-1 and corresponding vent valves 9 set according to actual needs. They are respectively connected to the vent channel body 2 of the same or different shapes. The position of these vent valves 9 on the upper structural layer and the placement and angle of the flame-shaped slit vent holes 1-1 can be adjusted according to the actual situation. The eight flame-shaped vent slits in the figure are arranged symmetrically around each other. This vent shape can achieve rapid release of gas pressure and has good structural strength. In actual preparation, the flame-shaped vent slits can be placed at any angle as needed, and the vent valves are obtained by pattern etching according to the placement arrangement.

[0051] like Figure 7 The diagram shown is a cross-sectional view of a structure with a vent valve positioned in the center of the vent hole; as shown... Figure 8 The diagram shows a cross-sectional view of a venting structure with a venting valve in the center of the vent hole during venting. By shaped like a flame to form the venting valve, the valve creates a very small venting gap on the upper structural layer, effectively closing the structure when venting. During venting, the valve deforms under the pressure of the airflow and adapts its opening angle according to the flow rate, effectively controlling the airflow velocity for uniform discharge and preventing structural damage due to improper venting.

[0052] Furthermore, depending on actual needs, multiple connection areas 1-2 and corresponding multiple vent holes 1-1 can be set in specific implementation, and simultaneously connected to a vent channel body 2. As shown in Figures 9(a)-(d), the present invention has four vent holes 1-1 with flame-shaped slits and four corresponding vent valves 9 arranged sequentially on the upper structural layer; when subjected to different sound pressures or when the gas flow is exhausted, the vent valve array can adapt to the gas flow, and each valve can be opened to full opening one by one to achieve the effect of rapid pressure relief. During exhaust, the vent valves closer to the gas flow channel open first; when the gas flow velocity is high, the vent valves closer to the gas flow channel open to a greater extent, and the vent valves farther from the gas flow channel open to a smaller extent; the opening degree of each valve can adaptively adjust with the exhaust flow rate, thereby realizing rapid gas discharge under different conditions.

[0053] The cross-section of the venting channel body 2 described in this invention can be rectangular, square, trapezoidal, inverted trapezoidal, or racetrack-shaped, such as... Figure 11 The diagram shown is a schematic of the main cross-section of the venting channel being racetrack-shaped.

[0054] Preferably, the cross-section of the venting channel body 2 of the present invention is a cuboid shape; for a cuboid-shaped airflow channel, the formula for calculating its flow resistance is:

[0055]

[0056] Where h is the channel height, w is the channel width, L is the channel length, and η is the fluid viscosity;

[0057] When the channel height and width are the same, i.e., h = w, the cross-section of the airflow channel is square. The formula for calculating the flow resistance in this case is:

[0058]

[0059] Therefore, it can be seen that, for a certain width w and thickness h, the flow resistance increases with the increase of length L;

[0060] This invention, by designing a longer venting channel, helps to increase flow resistance (acoustic resistance), making it less likely for sound waves to be transmitted through the micro-venting channel to the vent or venting valve and thus lost.

[0061] The key processes and sequence of the micromechanical venting channel described in this invention are as follows:

[0062] (1) A sacrificial layer is deposited on the lower structural layer 5, and a groove is formed by photolithography. The groove is used for subsequent deposition of the film layer of the anchor release stop structure 6, and forms the connection area 1-2, the venting channel body 2, the cavity 4 and the sacrificial layer anchor area 8.

[0063] (2) Deposit the film layer of anchor release stop structure 6, and remove part of the release stop film layer by photolithography or CMP, while retaining anchor release stop structure 6 and simultaneously defining the boundary of connection area 1-2, the boundary of venting channel body 2, the boundary of cavity 4 and the boundary of sacrificial layer anchor area 8.

[0064] (3) Deposit the upper structural layer 7, and photolithographically etch to form the effective area of ​​the structural layer and the vent hole 1-1 or the vent hole 1-1 is provided with a vent valve 9 in the middle;

[0065] (4) The back side of the lower structural layer 5 is photolithographically etched, and the etching stops at the sacrificial layer to form a gas flow channel 3;

[0066] (5) Wet corrosion is used to release part of the sacrificial layer material to form a cavity 4, which provides movement space for the upper structural layer 7, and forms the connection area 1-2 and the main body of the venting channel 2.

[0067] Preferably, the lower structural layer is silicon;

[0068] Preferably, the sacrificial layer is silicon oxide, borosilicate glass, phosphosilicate glass, borosilicate-phosphosilicate glass, or a composite material of at least two of these randomly stacked, and its deposition method is thermal oxidation or chemical vapor deposition (CVD); the CVD includes low-pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), sub-atmospheric pressure chemical vapor deposition (SACVD), or plasma-enhanced chemical vapor deposition (PECVD).

[0069] Preferably, the anchor release stop structure is made of materials such as polycrystalline silicon, amorphous silicon, or silicon nitride;

[0070] Preferably, the upper structural layer is a single material such as silicon, polycrystalline silicon, or amorphous silicon, or a composite layer of polycrystalline silicon and silicon nitride, or a composite layer of amorphous silicon and silicon nitride.

[0071] As can be seen from the above detailed description of the present invention, when the micromechanical venting channel structure described in the present invention is used as an acoustic device (such as a microphone), by designing a long distance and various bends or turns in the microventing channel, the flow resistance (acoustic resistance) is increased, making it difficult for sound waves to be transmitted through the microventing channel to the vent hole or vent valve and thus lost. This can effectively reduce the effective sound pressure loss, especially low-frequency attenuation, when the device is working under normal sound pressure conditions.

[0072] 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 micromechanical venting structure, characterized in that, The venting structure includes a vent hole (1-1), a connecting area (1-2), a venting channel body (2), and a cavity (4). The vent (1-1) is located in the upper structural layer (7), directly opposite the fixed area of ​​the movable structural layer above the lower structural layer (5); the fixed area of ​​the movable structural layer is the sacrificial layer anchor area (8); The connecting area (1-2) is located directly below the vent (1-1) and is used to connect the vent (1-1) and the vent channel body (2); The main body (2) of the venting channel is provided with several bends or turns to form micro-venting channels, which are used to connect the gas flow channel (3) and the connecting area (1-2).

2. The micromechanical venting structure according to claim 1, characterized in that, The vent hole (1-1) is set as a flame-shaped slit, forming a vent valve (9).

3. The micromechanical venting structure according to claim 1, characterized in that, The main body of the venting channel (2) forms a micro-venting channel with a "bow" shaped path by bending at right angles or arc angles.

4. The micromechanical venting structure according to claim 1, characterized in that, The main body of the venting channel (2) is formed into a spiral micro-venting channel by means of annular bending.

5. The micromechanical venting structure according to claim 1, characterized in that, The cross-section of the main body (2) of the venting channel is rectangular, square, trapezoidal, inverted trapezoidal or racetrack-shaped.

6. The micromechanical venting structure according to claim 1, characterized in that, The height of the main body (2) of the venting channel is the same as the height of the sacrificial layer anchor area (8).

7. A method for preparing a micromechanical venting structure according to any one of claims 1-6, comprising the following steps: 1) A sacrificial layer is deposited on the lower structural layer (5), and a groove is formed by photolithography etching to form a connection area (1-2), a venting channel body (2), a cavity (4), and a sacrificial layer anchor area (8); 2) Deposit the film layer of the release stop structure (6) in the anchor area, and remove part of the release stop film layer by photolithography or chemical mechanical polishing (CMP) while retaining the release stop structure (6) in the anchor area. At the same time, define the boundary of the connection area (1-2), the boundary of the venting channel body (2), the boundary of the cavity (4), and the boundary of the sacrificial layer anchor area (8). 3) Deposit the upper structural layer (7), and use photolithography to etch the effective area of ​​the structural layer and the vent holes (1-1); 4) The back side of the lower structural layer (5) is photolithographically etched, and the etching stops at the sacrificial layer to form a gas flow channel (3); 5) Use wet or dry corrosion to release part of the sacrificial layer material to form a cavity (4), a connecting area (1-2), and a venting channel body (2).

8. The method for preparing the micromechanical venting structure according to claim 7, characterized in that, The lower structural layer (5) is silicon; the upper structural layer (7) is a single material of silicon, polycrystalline silicon, or amorphous silicon, or a multilayer composite material formed by stacking polycrystalline silicon and silicon nitride, or a multilayer composite material formed by stacking amorphous silicon and silicon nitride; the material of the film layer of the anchor release stop structure (6) is polycrystalline silicon, amorphous silicon, or silicon nitride.

9. The method for preparing the micromechanical venting structure according to claim 7, characterized in that, The sacrificial layer is made of silicon oxide, borosilicate glass, phosphosilicate glass, borosilicate-phosphosilicate glass, or a composite material of at least two of these randomly stacked, and is deposited by thermal oxidation or chemical vapor deposition (CVD). The CVD includes low-pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), sub-atmospheric pressure chemical vapor deposition (SACVD), or plasma-enhanced chemical vapor deposition (PECVD).

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