A MEMS hot film flow sensor chip and its preparation method

Abstract

The present invention relates to the field of flow sensor technology, and in particular to a MEMS thermal film flow sensor chip and a preparation method thereof, comprising a substrate, a silicon nitride layer, a silicon oxide layer, a metal layer, a contact hole and a passivation protective layer, thereby forming a longitudinal multilayer structure in which the upper and lower metal layers are connected, temperature measuring resistors are arranged in the three metal layers, and the metal in the middle of the uppermost silicon nitride layer is a heating resistor; the present invention sets the structure of the temperature measuring resistor to a multilayer structure extending vertically in the longitudinal direction; by adopting a multilayer structure, the membrane area can be effectively reduced, thereby reducing the size of the sensor. In addition, the multilayer structure can provide better mechanical stability and structural strength, making the sensor more durable and reliable. In some special environments, such as high temperature, high pressure or vibration environment, this multilayer structure can better resist external influences and provide longer working and service life.

Description

Technical Field

[0001] The present invention relates to the technical field of flow sensors, and in particular to a MEMS thermal film flow sensor chip and a preparation method thereof. Background Art

[0002] Hot film air flow sensors usually contain a heating element and one or more temperature measuring resistors. The heating element generates heat by energizing it, which raises the temperature of the air around it to form a temperature field. When air flows through the sensor, the flowing air will take away some of the heat, causing the temperature to drop. The sensor that measures the temperature change can determine the air flow and convert it into an electrical signal output.

[0003] In the prior art, hot film air flow sensors have been widely used, in which the optimization of the temperature field plays a key role in the accurate measurement of the sensor. At present, traditional hot film sensors mostly use single-layer temperature measuring resistors and are arranged in the horizontal direction.

[0004] However, since the temperature measuring resistor area of ​​the single-layer structure is often relatively large during layout design, the response speed and reliability of the sensor are affected. Summary of the invention

[0005] The purpose of the present invention is to address the problems existing in the background technology and propose a MEMS thermal film flow sensor chip and a preparation method thereof. The present invention sets the structure of the temperature measuring resistor to a multi-layer structure extending vertically in the longitudinal direction, and ensures the uniform distribution of the temperature field between the layers by optimizing the resistor material and layout.

[0006] By adopting a multi-layer structure, the membrane area can be effectively reduced, thereby reducing the size of the sensor.

[0007] The technical solution of the present invention is a MEMS hot film flow sensor chip, comprising:

[0008] The substrate has a back cavity formed in the middle of the back side by etching, and two ends of the back cavity form support ends;

[0009] The silicon nitride layer is provided with two layers, which are respectively located on the front side and the back side of the substrate;

[0010] The silicon oxide layer is deposited between the three metal layers as a support layer between the metal layers, and makes the metal temperature measuring resistors of each layer not interfere with each other and connected to each other through contact holes;

[0011] The metal layer is patterned on the silicon nitride layer and the silicon oxide layer by sputtering and etching, and then alloyed to form a corresponding resistor;

[0012] A contact hole is formed on the silicon nitride layer where the upper and lower three metal layers are connected;

[0013] The passivation protection layer is formed on the third metal layer to protect the metal layer and form a metal pad.

[0014] Preferably, the substrate is photolithographed and etched starting from the middle area of ​​the silicon nitride layer on the back side, and the etching stops at the bottom of the silicon nitride layer on the front side of the substrate, thereby forming a suspended membrane structure.

[0015] Preferably, the metal layer includes a first metal layer, a second metal layer and a third metal layer;

[0016] The silicon oxide layer includes a first silicon oxide layer and a second silicon oxide layer;

[0017] A first metal layer is sputtered on the silicon nitride layer on the front side of the substrate;

[0018] A first silicon oxide layer is disposed on the first metal layer;

[0019] The second metal layer, the second silicon oxide layer and the third metal layer are sequentially stacked on the first silicon oxide layer.

[0020] Preferably, a first silicon oxide layer is formed on the first metal layer by LPCVD.

[0021] Preferably, the contact hole is formed by photolithography and etching, and the contact hole is filled with a metal for conducting electricity, preferably tungsten or platinum.

[0022] Preferably, designated positions of the first metal layer, the second metal layer and the third metal layer are aligned and connected through contact holes; and the contact holes on the third metal layer are led out to the pin windows through metal wires.

[0023] Preferably, temperature measuring resistors are arranged in the first metal layer, the second metal layer and the third metal layer; and a heating resistor is also arranged in the middle of the third metal layer.

[0024] A method for preparing a MEMS hot film flow sensor chip, the hot film flow sensor chip comprising the following specific steps:

[0025] S1, respectively providing a silicon nitride layer on the front and back sides of the substrate;

[0026] S2, sputtering a first metal layer on the silicon nitride layer on the front side of the substrate, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor;

[0027] S3, growing a first silicon oxide layer on the first metal layer by LPCVD, and forming upper and lower layer contact hole patterns by photolithography and etching processes, and filling the contact holes with metals such as platinum or tungsten to connect the upper and lower layers;

[0028] S4, sputtering a second metal layer on the first silicon oxide layer, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor;

[0029] S5, growing a second silicon oxide layer on the second metal layer by LPCVD, and forming upper and lower layer contact hole patterns by photolithography and etching processes, and filling the contact holes with metals such as platinum or tungsten to conduct the upper and lower layer resistors;

[0030] S6, sputtering a third metal layer on the second silicon oxide layer, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor;

[0031] S7, depositing a passivation protection layer on the third metal layer, and forming a pin window by photolithography and etching;

[0032] S8. Photolithography and etching are performed on the middle area of ​​the silicon nitride layer on the back side of the substrate to expose the substrate, and the substrate is corroded from the back side to form a back cavity. The etching stops at the bottom of the silicon nitride layer on the front side of the substrate to form a suspended membrane structure.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects:

[0034] The present invention sets the structure of the temperature measuring resistor as a multi-layer structure extending vertically in the longitudinal direction; by adopting the multi-layer structure, the membrane area can be effectively reduced, thereby reducing the size of the sensor. In addition, the multi-layer structure can provide better mechanical stability and structural strength, making the sensor more durable and reliable. In some special environments, such as high temperature, high pressure or vibration environment, this multi-layer structure can better resist external influences and provide longer working and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the preparation method of an embodiment of the present invention;

[0036] Figure 2 It is a schematic diagram of the process of preparing a single-layer chip in the prior art;

[0037] Figure 3 It is a schematic diagram of each layer of the upper and lower contact holes and the metal wiring method of the temperature measuring resistor formed in the method for preparing the vertical multi-layer structure of the present invention;

[0038] Figure 4 This is a schematic diagram of the metal wiring method of the temperature measuring resistor with a single-layer structure that is mostly used in traditional thermal mode sensors.

[0039] Figure numerals: 1, substrate; 2, silicon nitride layer; 3, first metal layer; 4, first silicon oxide layer; 5, first contact hole; 6, second metal layer; 7, second silicon oxide layer; 8, second contact hole; 9, third metal layer; 10, passivation protective layer; 11, back cavity. DETAILED DESCRIPTION

[0040] Example 1

[0041] like Figure 1 As shown, a method for preparing a MEMS hot film flow sensor chip proposed by the present invention comprises the following specific steps:

[0042] S1, a silicon nitride layer 2 is provided on the front and back sides of the substrate 1 respectively;

[0043] S2, sputtering a first metal layer 3 on the silicon nitride layer 2 on the front side of the substrate 1, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor;

[0044] S3, growing a first silicon oxide layer 4 on the first metal layer 3 by LPCVD, and forming upper and lower layer contact hole patterns by photolithography and etching processes, and filling the first contact hole 5 with metal such as platinum or tungsten to conduct the upper and lower layers;

[0045] S4, sputtering a second metal layer 6 on the first silicon oxide layer 4, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor;

[0046] S5, growing a second silicon oxide layer 7 on the second metal layer 6 by LPCVD, and forming upper and lower layer contact hole patterns by photolithography and etching processes, and filling the second contact hole 8 with metal such as platinum or tungsten to conduct the upper and lower layers;

[0047] S6, sputtering a third metal layer 9 on the second silicon oxide layer 7, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor and a heating resistor;

[0048] S7, depositing a passivation protection layer 10 on the third metal layer 9, and forming a pin window by photolithography and etching;

[0049] S8. Photolithography and etching are performed on the middle area of ​​the silicon nitride layer 2 on the back side of the substrate 1 to expose the substrate 1, and the substrate 1 is corroded from the back side to form a back cavity 11. The corrosion stops at the bottom of the silicon nitride layer 2 on the front side of the substrate 1 to form a suspended membrane structure.

[0050] like Figure 2As shown, it is a schematic diagram of the preparation process of a single-layer thermal film flow sensor in the prior art; first, a silicon nitride layer 2 is set on the front and back sides of the substrate 1 respectively; a layer of silicon oxide 3 is formed on the silicon nitride layer 2 by LPCVD, a metal layer 4 is sputtered on the silicon oxide 3, and the uppermost silicon nitride 5 is formed on the metal layer 4; the middle area of ​​the silicon nitride layer 2 on the back side of the substrate 1 is photolithographically and etched, and the substrate 1 is corroded by KOH from its back side, and the corrosion stops at the bottom of the silicon nitride layer 2 on the front side of the substrate, thereby forming a suspended membrane structure.

[0051] In this embodiment, the multilayer structure prepared by this scheme can effectively reduce the membrane area, thereby reducing the size of the sensor. In addition, the multilayer structure can provide better mechanical stability and structural strength, making the sensor more durable and reliable. In some special environments, such as high temperature, high pressure or vibration environment, this multilayer structure can better resist external influences and provide longer working and service life.

[0052] Example 2

[0053] like Figure 3 As shown, a MEMS hot film flow sensor chip proposed by the present invention comprises:

[0054] The substrate 1 has a back cavity 11 formed in the middle of the back side by etching, and two ends of the back cavity 11 form support ends;

[0055] The silicon nitride layer 2 is provided with two layers, which are respectively located on the front side and the back side of the substrate 1;

[0056] The silicon oxide layer is deposited between the three metal layers as a support layer between the metal layers, and makes the metal temperature measuring resistors of each layer not interfere with each other and connected to each other through contact holes;

[0057] The metal layer is patterned on the silicon nitride layer 2 and the silicon oxide layer by sputtering and etching, and then alloyed to form a corresponding resistor;

[0058] A contact hole is formed on the silicon nitride layer where the upper and lower three metal layers are connected;

[0059] The passivation protection layer 10 is formed on the third metal layer to protect the metal layer and form a metal pad.

[0060] In this embodiment, the substrate 1 is photolithographically and etched starting from the middle area of ​​the silicon nitride layer 2 on the back side, and the etching stops at the bottom of the silicon nitride layer 2 on the front side of the substrate 1, thereby forming a suspended membrane structure.

[0061] Wherein, the metal layer includes a first metal layer 3, a second metal layer 6 and a third metal layer 9;

[0062] The silicon oxide layer includes a first silicon oxide layer 4 and a second silicon oxide layer 7;

[0063] The first metal layer 3 is formed by sputtering on the silicon nitride layer 2 on the front side of the substrate 1;

[0064] The first silicon oxide layer 4 is formed on the first metal layer 3 by LPCVD; the second metal layer 6, the second silicon oxide layer 7 and the third metal layer 9 are sequentially stacked on the first silicon oxide layer 4;

[0065] The contact holes include a first contact hole 5 and a second contact hole 8, and are both formed by photolithography and etching, and the contact holes are filled with tungsten or platinum for conducting the upper and lower layers.

[0066] Temperature measuring resistors are arranged in the first metal layer 3 , the second metal layer 6 and the third metal layer 9 ; a heating resistor is also arranged in the middle of the third metal layer.

[0067] like Figure 4 As shown in the figure, traditional thermal mode sensors mostly use single-layer temperature measuring resistors and are arranged in the horizontal direction. This results in a relatively large membrane area, such as Figure 4 As shown in , let the total length of the membrane area be L, the total width be W3, W2 be the shortest distance from the temperature measuring resistor to the edge of the membrane area; Figure 3 and Figure 4 For comparison, when the total length L and the closest distance W2 from the temperature measuring resistor to the edge of the film area remain unchanged, Figure 3 Width ratio of middle membrane area Figure 4 The length of W1 is reduced by two times, and the membrane area is reduced from the original L*W3 to L*(W3-2W1), where W1>0 in terms of value, so L*W3>L*(W3-2W1); it can be seen that the membrane area is significantly reduced.

[0068] See also Figure 3 , from left to right are schematic diagrams of the first metal layer, the second metal layer and the third metal layer; in the figure, the three metal layers are a multilayer structure from bottom to top according to the process flow sequence, the a1 position of the first metal layer 3 is aligned and connected with the a1 position of the second metal layer 6 through the above-mentioned first contact hole 5, and then aligned and connected with the b1 of the third metal layer 9 through the second contact hole 8 through b1 in the second metal layer 6, so as to be led out to the pin window through the wire of the third metal layer 9; the c1 position of the first metal layer 3 is aligned and connected with the c1 position of the second metal layer 6 through the above-mentioned first contact hole 5, and continues to be aligned and connected with the c1 position of the third metal layer 9 through the above-mentioned second contact hole 8, so as to be led out to the pin window through the wire of the third metal layer 9; by adopting this longitudinal multilayer structure, the temperature measuring resistor is segmented and arranged in multiple longitudinal film layers without changing the area of ​​the temperature measuring resistor, which effectively reduces the area of ​​the lateral film area

[0069] Since the longitudinal area is increased, this helps to improve the sensitivity and response speed of the sensor and improve the accuracy of the measurement. In addition, the multi-layer structure provides better mechanical stability and structural strength, making the sensor more durable and reliable.

[0070] It should also be understood that the positions of the internal units of the sensor structure can be arranged and adjusted as needed, and the number of layers of the multi-layer structure is not limited and can be added or reduced according to actual conditions, all within the scope of protection of the present invention. In addition, the shape, size, position of the contact hole and the shape, depth, position of the hole in the present invention are also adjusted arbitrarily according to the actual wiring path.

[0071] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited thereto, and various changes can be made within the knowledge scope of technicians in the relevant technical field without departing from the purpose of the present invention.

Claims

1. A MEMS hot film flow sensor chip, characterized in that: include: The substrate has a back cavity formed in the middle of the back side by etching, and two ends of the back cavity form support ends; The silicon nitride layer is provided with two layers, which are respectively located on the front side and the back side of the substrate; The silicon oxide layer is deposited between the three metal layers as a support layer between the metal layers, and makes the metal temperature measuring resistors of each layer not interfere with each other and connected to each other through contact holes; The metal layer is patterned on the silicon nitride layer and the silicon oxide layer by sputtering and etching, and then alloyed to form a corresponding resistor; A contact hole is formed on the silicon nitride layer at a location where the upper and lower three metal layers are connected; the contact hole is formed by photolithography and etching, and the contact hole is filled with a metal for conducting electricity; A passivation protection layer is formed on the third metal layer to protect the metal layer and form a metal pad; The metal layer includes a first metal layer, a second metal layer and a third metal layer; The silicon oxide layer includes a first silicon oxide layer and a second silicon oxide layer; A first metal layer is sputtered on the silicon nitride layer on the front side of the substrate; A first silicon oxide layer is disposed on the first metal layer; The second metal layer, the second silicon oxide layer and the third metal layer are sequentially stacked on the first silicon oxide layer; The designated positions of the first metal layer, the second metal layer and the third metal layer are aligned and connected through contact holes; the contact holes on the third metal layer are led out to the pin windows through metal wires; temperature measuring resistors are set in the first metal layer, the second metal layer and the third metal layer; and a heating resistor is also set in the middle of the third metal layer.

2. A MEMS hot film flow sensor chip according to claim 1, characterized in that: The substrate is photolithographed and etched starting from the middle area of ​​the silicon nitride layer on the back side, and the etching stops at the bottom of the silicon nitride layer on the front side of the substrate, thereby forming a suspended membrane structure.

3. A MEMS hot film flow sensor chip according to claim 1, characterized in that: A first silicon oxide layer is formed on the first metal layer by LPCVD.

4. A method for preparing a MEMS hot film flow sensor chip, preparing the hot film flow sensor chip as described in any one of claims 1 to 3, characterized in that: The specific steps include: S1, respectively providing a silicon nitride layer on the front and back sides of the substrate; S2, sputtering a first metal layer on the silicon nitride layer on the front side of the substrate, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor; S3, growing a first silicon oxide layer on the first metal layer by LPCVD, and forming upper and lower layer contact hole patterns by photolithography and etching processes, and filling platinum or tungsten in the contact holes to connect the upper and lower layers; S4, sputtering a second metal layer on the first silicon oxide layer, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor; S5, growing a second silicon oxide layer on the second metal layer by LPCVD, and forming upper and lower layer contact hole patterns by photolithography and etching processes, and filling platinum or tungsten in the contact holes to conduct the upper and lower layers; S6, sputtering a third metal layer on the second silicon oxide layer, forming a pattern by photolithography and etching, and alloying the metal pattern to form a temperature measuring resistor and a heating resistor; S7, depositing a passivation protection layer on the third metal layer, and forming a pin window by photolithography and etching; S8. Photolithography and etching are performed on the middle area of ​​the silicon nitride layer on the back side of the substrate to expose the substrate, and the substrate is corroded from the back side to form a back cavity. The etching stops at the bottom of the silicon nitride layer on the front side of the substrate to form a suspended membrane structure.

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