Flow sensor and manufacturing method thereof

Abstract

The flow sensor comprises a first substrate, a thin film assembly and a second substrate, the first substrate is provided with a cavity penetrating in the first direction, the cavity is provided with a first cavity opening and a second cavity opening, and the thin film assembly is connected to the front side of the first substrate and comprises a first thin film area and a second thin film area. The orthographic projection of the first film area and the orthographic projection of the cavity on the projection plane perpendicular to the first direction coincide with each other, the first film area seals the first cavity opening, the orthographic projection of the second film area and the orthographic projection of the cavity on the projection plane perpendicular to the first direction are staggered with each other, and the second film area covers the front face of the first substrate. The first film free surface of the first film area is recessed inwards relative to the second film free surface of the second film area, the second substrate is connected to the back side of the first substrate, and the second substrate seals the second cavity opening. The heat loss can be effectively reduced, the device power consumption can be reduced, the device sensitivity can be improved, and the membrane rupture probability in the production process can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of flow measurement, and in particular to a flow sensor and a manufacturing method thereof. Background Art

[0002] A flow sensor is a sensor that converts flow / flow velocity signals into electrical signals. According to the technical route, it can be divided into thermal, electromagnetic, Coriolis, ultrasonic, etc. Among them, thermal flow sensors have become the most commercialized and widely used flow sensors because of their relatively easy and mature manufacturing process, wide range coverage, and low cost.

[0003] The Chinese utility model patent with publication number CN214471098U discloses a vacuum-insulated MEMS flow sensor, which includes: a substrate, provided with a vacuum-sealed cavity; a first dielectric layer, formed on the upper surface of the substrate; a heating element, a temperature-sensing element and a metal electrode, formed on the upper surface of the first dielectric layer, wherein the temperature-sensing element is symmetrically distributed on both sides of the heating element, and the heating element and the temperature-sensing element are partially located above the cavity; a second dielectric layer, covering the heating element, the temperature-sensing element, the metal electrode and the cavity, and partially etching an opening. The utility model MEMS flow sensor uses the "conformal effect" of the low-pressure chemical vapor connection method to form a vacuum-sealed cavity, which can improve the thermal insulation performance of the cavity on the one hand, and reduce the convective heat loss between the measured fluid and the cavity on the other hand, thereby reducing the power consumption of the device, increasing the temperature difference between the upstream and downstream temperature-sensing elements, and effectively improving the sensitivity of the device. However, this patent has two defects from the production perspective. First, the "conformal effect" of the low-pressure chemical vapor connection method is not a conventional semiconductor process, and requires a certain development cost and development cycle to study its process parameters (such as ventilation volume, gas ratio) and design parameters (cavity size, shape, number, arrangement); Second, after completing the cavity sealing, this patent needs to perform an etching process on the surface to form an opening to expose the metal electrode for power connection, but at this time a thin film has been formed above the cavity. During the entire etching process (including coating, photolithography, development, etching, and degumming), it is easy to cause physical damage to the thin film components, increase the probability of film breakage, reduce production yield, and increase output costs.

[0004] How to use low-cost conventional processes to form a vacuum cavity while reducing the probability of film breakage during the production process to reduce costs is a technical problem that needs to be urgently solved in this field. Summary of the invention

[0005] To this end, the present invention provides a flow sensor and a method for manufacturing the same, which uses a low-cost conventional process to form a vacuum cavity while reducing the probability of membrane breakage during the production process, thereby reducing costs.

[0006] In order to solve the above technical problems, the present invention provides a flow sensor, comprising: A first substrate, wherein the first substrate is provided with a cavity penetrating along a first direction, and the cavity has a first cavity opening and a second cavity opening respectively located on a front side and a back side of the first substrate; A thin film component, wherein the thin film component is connected to the front side of the first substrate, the thin film component includes a first thin film area and a second thin film area, the first thin film area and the orthographic projection of the cavity on the projection plane perpendicular to the first direction overlap with each other, the first thin film area includes a first insulating support layer and a sensitive layer, the first insulating support layer seals the first cavity opening, the sensitive layer is connected to the surface of the first insulating support layer facing the outside of the cavity, the second thin film area is connected to the back side of the first substrate, the second thin film area and the orthographic projection of the cavity on the projection plane perpendicular to the first direction are staggered with each other, the second thin film area includes a second insulating support layer and an electrode layer, the second insulating support layer covers the front side surface of the first substrate, the electrode layer is connected to the surface of the second insulating support layer facing away from the first substrate, and the first thin film free surface of the first thin film area facing the outside of the cavity is recessed inward relative to the second thin film free surface of the second thin film area facing away from the first substrate; A second substrate is connected to the back side of the first substrate, and the second substrate seals the second cavity.

[0007] Furthermore, a groove is provided on the front surface of the first substrate, the first cavity passes through the bottom of the groove, and at least a portion of the first thin film area is embedded in the groove.

[0008] Furthermore, the thickness of the portion of the first thin film region embedded in the groove is between 5nm and 5um.

[0009] Furthermore, the first film region and the second substrate seal the cavity into a vacuum cavity.

[0010] Furthermore, the first thin film region further includes a first protective layer, and the first protective layer is connected to a surface of the sensitive layer facing away from the first insulating support layer.

[0011] Furthermore, the second thin film region further includes a second protective layer, the second protective layer is connected to a surface of the electrode layer facing away from the second insulating support layer, and the second protective layer is provided with an opening exposing at least a portion of the electrode layer.

[0012] The present invention also provides a method for manufacturing the flow sensor, comprising the following steps performed in sequence: A first deposition step of depositing an insulating support material on the front surface of the first substrate to form the first insulating support layer and the second insulating support layer; A coating step, sputtering or evaporating a thermistor material on the free surface of the first insulating support layer to form the sensitive layer, and sputtering or evaporating an electrode material on the free surface of the second insulating support layer to form the electrode layer; A cavity etching step of etching the cavity on the back side of the first substrate; The substrate bonding step is to bond the second substrate to the back side of the first substrate.

[0013] Furthermore, the method further comprises the following steps before the first deposition step: A groove etching step is performed to prepare a groove of the flow sensor on the front side of the first substrate.

[0014] Furthermore, in the bonding step, the second substrate is bonded to the back side of the first substrate under a vacuum environment to form a vacuum cavity of the flow sensor.

[0015] Furthermore, the method further includes the following steps which are sequentially performed between the film coating step and the cavity etching step: A second deposition step, depositing a protective material on the free surface side of the sensitive layer and the electrode layer to form a first protective layer of the flow sensor and a second protective layer of the flow sensor; The opening etching step is to etch an opening of the flow sensor on the second protective layer.

[0016] The above technical solution of the present invention has the following advantages compared with the prior art: 1) The flow sensor and the manufacturing method thereof of the present invention can seal the cavity by providing a second substrate and adopting a low-cost conventional process, and the heat insulation performance of the cavity is further improved, which can effectively reduce heat loss, help reduce device power consumption, and improve device sensitivity; the free surface of the second film is concave inward relative to the free surface of the second film, which can avoid physical damage to the first film area during the bonding process between the first substrate and the second substrate, reduce the probability of film breakage during the production process, and thus reduce costs; 2) The flow sensor and the manufacturing method thereof of the present invention, by providing a groove on the first substrate, the first film area is embedded in the groove, on the one hand, it is convenient to form a step difference between the free surface of the first film and the free surface of the second film, on the other hand, it can reduce the thickness of the flow sensor; 3) In the flow sensor and the manufacturing method thereof of the present invention, the thickness of the portion of the first film region embedded in the groove is between 5nm and 5um, and the height difference formed by the free surface of the first film and the free surface of the second film and the thickness of the flow sensor are both suitable; 4) The flow sensor and the manufacturing method thereof described in the present invention has a vacuum cavity and has excellent heat insulation performance; 5) The flow sensor and the manufacturing method thereof according to the present invention further include a first protective layer, which can effectively protect the sensitive layer; 6) The flow sensor and the manufacturing method thereof described in the present invention further include a second protective layer, which can effectively protect the electrode layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0018] Figure 1 It is a front cross-sectional view of the flow sensor in the present invention; Figure 2 is a schematic diagram of a groove etching step in the present invention; Figure 3 is a schematic diagram of the first deposition step in the present invention; Figure 4 is a schematic diagram of the coating step in the present invention; Figure 5 is a schematic diagram of the second deposition step in the present invention; Figure 6 is a schematic diagram of an opening etching step in the present invention; Figure 7 is a schematic diagram of the cavity etching step in the present invention; Figure 8 It is a schematic diagram of the substrate bonding step in the present invention.

[0019] Explanation of the reference numerals in the specification: 1. first substrate; 10. groove; 11. cavity; 2. thin film assembly; 21. first insulating support layer; 22. sensitive layer; 23. second insulating support layer; 24. electrode layer; 25. first thin film free surface; 26. second thin film free surface; 27. first protective layer; 28. second protective layer; 281. opening; 3. second substrate. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention. Embodiment 1

[0021] See also Figure 1 FIG. 1 is an exemplary embodiment of a flow sensor according to the present invention.

[0022] The above-mentioned flow sensor comprises: A first substrate 1, wherein the first substrate 1 is provided with a cavity 11 penetrating along a first direction, and the cavity 11 has a first cavity opening and a second cavity opening respectively located on the front side and the back side of the first substrate 1; A thin film component 2, wherein the thin film component 2 is connected to the front side of the first substrate 1, the thin film component 2 includes a first thin film region and a second thin film region, the first thin film region and the orthographic projection of the cavity 11 on the projection plane perpendicular to the first direction overlap with each other, the first thin film region includes a first insulating support layer 21 and a sensitive layer 22, the first insulating support layer 21 seals the first cavity opening, the sensitive layer 22 is connected to the surface of the first insulating support layer 21 facing the outside of the cavity 11, the second thin film region is connected to the back side of the first substrate 1, the orthographic projections of the second thin film region and the cavity 11 on the projection plane perpendicular to the first direction are staggered with each other, the second thin film region includes a second insulating support layer 23 and an electrode layer 24, the second insulating support layer 23 covers the front side surface of the first substrate 1, the electrode layer 24 is connected to the surface of the second insulating support layer 23 facing away from the first substrate 1, and a first thin film free surface 25 of the first thin film region facing the outside of the cavity is recessed inward relative to a second thin film free surface 26 of the second thin film region facing away from the first substrate; The second substrate 3 is connected to the back side of the first substrate 1 , and the second substrate 3 seals the second cavity.

[0023] The first substrate 1 is used to support the entire flow sensor. The first insulating support layer 21 is used to support the sensitive layer 22 and act as an insulator. The sensitive layer 22 is a temperature-sensitive thermistor material. The sensitive layer 22 includes a heating element and upstream and downstream temperature sensing elements (usually thermopiles / thermal resistors). The heating element provides a certain power to make the chip surface temperature higher than the ambient temperature. When there is no gas flow, the chip surface temperature is normally distributed with the heating element as the center, and the upstream and downstream temperature sensing elements have the same electrical signals; when there is gas flow, the gas molecules transfer heat to cause the temperature distribution on the chip surface to shift, and the electrical signals of the upstream and downstream temperature sensing elements will differ accordingly. The flow rate can be inferred using this difference. The second insulating support layer 23 is used to support the electrode layer 24 and act as an insulator. The electrode layer 24 is used to connect the sensitive layer 22 and the external circuit. The second substrate 3 is used to seal the cavity 11.

[0024] The first substrate 1 is a silicon substrate, the first insulating support layer 21 and the second insulating support layer 23 are silicon layers, oxide layers or nitride layers, the sensitive layer 22 is a Pt layer, a Ni layer, a polysilicon layer or an Al layer, and the electrode layer 24 is a Pt layer, a Ni layer, a polysilicon layer, an Al layer, a Cu layer or an Au layer. The second substrate 3 is a silicon substrate or a glass substrate. The thickness of the first insulating support layer 21, the sensitive layer 22, the second insulating support layer 23 and the electrode layer 24 are all between 100nm and 5um.

[0025] The heat insulation performance of the cavity 11 is further improved. The cavity 11 can effectively reduce the heat loss of the heating element, thereby generating a greater temperature difference between the upstream and downstream temperature sensing elements. Therefore, the cavity 11 is conducive to reducing the power consumption of the device and improving the sensitivity of the device. When the first substrate 1 is bonded to the second substrate 3, the first film free surface 25 and the second film free surface 26 are facing the table. Since the first film area is suspended and used to seal the cavity 11, if there is a foreign object on the table, it is easy to puncture the first film area. Therefore, the first film free surface 25 is concave inward relative to the second film free surface 26, avoiding physical damage to the film assembly during the bonding process of the first substrate 1 and the second substrate 3. The cavity is formed using a low-cost conventional process while reducing the probability of film breakage during the production process, thereby reducing costs.

[0026] In this embodiment, a groove is provided on the front surface of the first substrate 1, the first cavity passes through the bottom of the groove, and at least a portion of the first thin film region is embedded in the groove.

[0027] The groove is connected to the cavity 11 to form a through hole, and the orthographic projections of the groove and the cavity 11 on the projection plane perpendicular to the first direction may overlap or partially overlap. The first film area is embedded in the groove, which, on the one hand, facilitates the formation of a drop between the first film free surface 25 and the second film free surface 26, and on the other hand, can reduce the thickness of the flow sensor.

[0028] In this embodiment, the thickness of the portion of the first thin film region embedded in the groove is between 5nm and 5um.

[0029] The thickness of the portion of the first film region embedded in the groove is between 5nm and 5um, and the height difference formed by the first film free surface 25 and the second film free surface 26 and the thickness of the flow sensor are both suitable. Specifically, the thickness of the portion of the first film region embedded in the groove is 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1um, 2um, 3um, 4um or 5um.

[0030] In this embodiment, the first thin film region and the second substrate 3 seal the cavity 11 into a vacuum cavity.

[0031] The first film region seals the first cavity opening of the cavity 11, and the second substrate 3 seals the second cavity opening of the cavity 11. The cavity 11 is a vacuum environment. The vacuum insulation principle mainly relies on the heat transfer mechanism in a vacuum environment. In a vacuum environment, the collision frequency and intensity between gas molecules are greatly reduced, thereby preventing the occurrence of convection and contact heat transfer. The cavity 11 is a vacuum cavity with excellent thermal insulation performance.

[0032] In this embodiment, the first thin film region further includes a first protective layer 27 . The first protective layer 27 is connected to the surface of the sensitive layer 22 facing away from the first insulating support layer 21 .

[0033] The first protective layer 27 is used to protect the sensitive layer 22. The first protective layer 27 is an oxide layer or a nitride layer. The thickness of the first protective layer 27 is between 100 nm and 5 um.

[0034] In this embodiment, the second thin film region further includes a second protective layer 28 . The second protective layer 28 is connected to the surface of the electrode layer 24 facing away from the second insulating support layer 23 . The second protective layer 28 is provided with an opening exposing at least a portion of the electrode layer 24 .

[0035] The second protective layer 28 is used to protect the electrode layer 24. The second protective layer 28 is an oxide layer or a nitride layer. The thickness of the second protective layer 28 is between 100 nm and 5 um.

[0036] See also Figures 2 to 8 The present invention also provides an embodiment of a method for manufacturing the above-mentioned flow sensor.

[0037] The method for manufacturing the flow sensor comprises the following steps performed in sequence: A first deposition step is to deposit an insulating support material on the front surface of the first substrate 1 to form the first insulating support layer 21 and the second insulating support layer 23; A coating step, sputtering or evaporating a thermistor material on the free surface of the first insulating support layer 21 to form the sensitive layer 22, and sputtering or evaporating an electrode material on the free surface of the second insulating support layer 23 to form the electrode layer 24; A cavity etching step, etching the cavity 11 on the back side of the first substrate 1; In the substrate bonding step, the second substrate 3 is bonded to the back side of the first substrate 1 .

[0038] The thin film assembly 2 is formed through the first deposition step and the coating step, and the vacuum cavity is formed through the cavity etching step and the substrate bonding step.

[0039] In this embodiment, the following steps are also included before the first deposition step: In the groove etching step, the groove 10 of the flow sensor is prepared on the front surface of the first substrate 1 .

[0040] The groove etching step makes the front surface of the first substrate 1 a concave-convex surface. At this time, the first insulating support layer 21 and the second insulating support layer 23 deposited on the front surface of the first substrate 1 are also not flush, thereby forming an uneven first film free surface 25 and a second film free surface 26.

[0041] In this embodiment, in the substrate bonding step, the second substrate 3 is bonded to the back surface of the first substrate 1 under a vacuum environment to form the vacuum cavity of the flow sensor.

[0042] The bonding operation is performed between the first substrate 1 and the second substrate 3 in a vacuum environment, so the cavity 11 is in a vacuum environment after bonding.

[0043] In this embodiment, the following steps are also performed in sequence between the above-mentioned coating step and the cavity etching step: A second deposition step, depositing a protective material on the free surface side of the sensitive layer 22 and the electrode layer 24 to form the first protective layer 27 of the flow sensor and the second protective layer 28 of the flow sensor; The opening etching step is to etch the opening 281 of the flow sensor on the second protection layer 28 .

[0044] The first protection layer 27 and the second protection layer 28 are formed through the second deposition step and the opening etching step, and the electrode layer 24 can be electrically connected to the outside through the opening 281 .

[0045] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A flow sensor, characterized in that: include: A substrate assembly, comprising a first substrate, wherein the first substrate is provided with a cavity penetrating along a first direction, wherein the cavity has a first cavity opening and a second cavity opening respectively located on a front side and a back side of the first substrate; A thin film component, wherein the thin film component is connected to the front side of the first substrate, the thin film component includes a first thin film area and a second thin film area, the first thin film area and the orthographic projection of the cavity on the projection plane perpendicular to the first direction overlap with each other, the first thin film area includes a first insulating support layer and a sensitive layer, the first insulating support layer seals the first cavity opening, the sensitive layer is connected to the surface of the first insulating support layer facing the outside of the cavity, the second thin film area is connected to the back side of the first substrate, the second thin film area and the orthographic projection of the cavity on the projection plane perpendicular to the first direction are staggered with each other, the second thin film area includes a second insulating support layer and an electrode layer, the second insulating support layer covers the front side surface of the first substrate, the electrode layer is connected to the surface of the second insulating support layer facing away from the first substrate, and the first thin film free surface of the first thin film area facing the outside of the cavity is recessed inward relative to the second thin film free surface of the second thin film area facing away from the first substrate; A second substrate is connected to the back side of the first substrate, and the second substrate seals the second cavity.

2. The flow sensor according to claim 1, characterized in that: A groove is provided on the front side of the first substrate, the first cavity passes through the bottom of the groove, and at least a part of the first thin film area is embedded in the groove.

3. The flow sensor according to claim 2, characterized in that: The thickness of the portion of the first thin film region embedded in the groove is between 5nm and 5um.

4. The flow sensor according to claim 1, characterized in that: The first thin film region and the second substrate seal the cavity into a vacuum cavity.

5. The flow sensor according to claim 1, characterized in that: The first thin film region further includes a first protective layer, which is connected to a surface of the sensitive layer facing away from the first insulating support layer.

6. The flow sensor according to claim 1, characterized in that: The second thin film region further comprises a second protective layer, the second protective layer is connected to the surface of the electrode layer facing away from the second insulating support layer, and the second protective layer is provided with an opening exposing at least a portion of the electrode layer.

7. The method for manufacturing a flow sensor according to any one of claims 1 to 6, characterized in that: The method comprises the following steps in sequence: A first deposition step of depositing an insulating support material on the front surface of the first substrate to form the first insulating support layer and the second insulating support layer; A coating step, sputtering or evaporating a thermistor material on the free surface of the first insulating support layer to form the sensitive layer, and sputtering or evaporating an electrode material on the free surface of the second insulating support layer to form the electrode layer; A cavity etching step of etching the cavity on the back side of the first substrate; The substrate bonding step is to bond the second substrate to the back side of the first substrate.

8. The method for manufacturing a flow sensor according to claim 7, characterized in that: The method further comprises the following steps before the first deposition step: A groove etching step is performed to prepare a groove of the flow sensor according to claim 2 or 3 on the front side of the first substrate.

9. The method for manufacturing a flow sensor according to claim 7, characterized in that: In the bonding step, the second substrate is bonded to the back surface of the first substrate in a vacuum environment to form the vacuum chamber of the flow sensor according to claim 4.

10. The method for manufacturing a flow sensor according to claim 7, characterized in that: The invention also includes the following steps which are sequentially performed between the coating step and the cavity etching step: A second deposition step of depositing a protective material on the free surface side of the sensitive layer and the electrode layer to form a first protective layer of the flow sensor of claim 5 and a second protective layer of the flow sensor of claim 6; An opening etching step is to etch an opening of the flow sensor according to claim 6 on the second protective layer.

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