Thermal flow sensor based on a silicon oxide wafer and method for manufacturing

Abstract

The application discloses a thermal flow sensor prepared based on a silicon oxide wafer and a preparation method thereof. The sensor comprises a silicon substrate, a silicon dioxide layer, a back cavity, a heat insulation port, a chromium adhesion layer, a heating resistor, a temperature measuring resistor, an ambient temperature measuring resistor and a silicon nitride protective layer. The heating resistor is located at an upper middle position, and four temperature measuring resistors are symmetrically distributed on both sides of the heating resistor. The heating resistor and the temperature measuring resistor are separated by the heat insulation port, the heat insulation port is located on a suspension bridge formed by the back cavity, and the heat insulation port comprises a triangular heat insulation port and a rectangular heat insulation port. The ambient temperature measuring resistor is located outside the cavity. The chromium adhesion layer is arranged between the silicon dioxide layer and the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor. The press welding blocks are arranged on the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor. The application optimizes the suspension bridge by using a neural network, improves the mechanical strength of the thermal flow sensor, and increases the temperature difference output of the upstream and downstream temperature measuring resistors.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow sensor preparation, in particular to a thermal flow sensor prepared based on a silicon oxide wafer and a preparation method. BACKGROUND

[0002] Accurate measurement of flow can provide important information for many fields such as industrial production, scientific research and medical health. There are many types of flow sensors commonly used at present, among which thermal flow sensors based on MEMS technology are widely used due to their simple structure, small size, high precision, fast response and low power consumption.

[0003] MEMS thermal flow sensors based on the thermal temperature difference principle can be classified according to different control modes. Common control modes include constant voltage mode, constant current mode, constant power mode, constant temperature difference mode and temperature balance mode. The constant temperature difference mode is the most commonly used mode, which controls the chip temperature with a constant temperature difference higher than the ambient temperature through a feedback loop, effectively suppressing the influence of ambient temperature on the sensor measurement results. However, the disadvantage of this mode is that it requires an external ambient temperature sensor, thus increasing the complexity of the system.

[0004] In order to reduce heat loss and reduce heat transfer from the heating resistor to the substrate, thermal flow sensors are designed with an air insulation layer to improve output and achieve low power consumption. Traditional MEMS thermal flow sensors use a suspended bridge resistor structure, which is easily damaged by external factors and has a fragile structure, resulting in low reliability of the sensor. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a thermal flow sensor prepared based on a silicon oxide wafer and a preparation method, which effectively reduces heat transfer to the substrate through the back cavity and the heat insulation port, improving the performance of the product. At the same time, the presence of the triangular heat insulation port in the MEMS flow sensor improves the stability, reliability and durability of the sensor structure.

[0006] To solve the above technical problems, the present application adopts the following technical solutions:

[0007] The thermal flow sensor prepared based on a silicon oxide wafer comprises:

[0008] a silicon substrate, a silicon dioxide layer, a back cavity, a heat insulation port, a chromium adhesion layer, a heating resistor, a temperature measuring resistor, an ambient temperature measuring resistor, a pressure welding block and a silicon nitride protective layer.

[0009] The silicon dioxide layer is located on a silicon substrate; a chromium adhesion layer is arranged between the silicon dioxide layer and the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor; and a press-welding block is arranged on the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor; and a silicon nitride protective layer is located on the periphery of the silicon dioxide layer.

[0010] Further, the heat insulation opening is arranged on the suspension bridge formed by the back cavity, and includes a triangular heat insulation opening and a rectangular heat insulation opening; the rectangular heat insulation opening is located between the heating resistor and the temperature measuring resistor, and the triangular heat insulation opening is located at the edge of the suspension bridge formed by the back cavity.

[0011] Further, the silicon substrate is a semiconductor high-thermal-conductivity heat-conducting substrate compatible with a CMOS process; and the silicon dioxide layer is a dense thin film generated by thermal oxidation of the silicon substrate.

[0012] Further, the ambient temperature measuring resistor is distributed at a peripheral position above the back cavity and located at the edge of the sensor.

[0013] Further, the temperature measuring resistor includes two upstream temperature measuring resistors and two downstream temperature measuring resistors symmetrically distributed on both sides of the heating resistor, the upstream temperature measuring resistors are located on the left side of the heating resistor, and the downstream temperature measuring resistors are located on the right side of the heating resistor; the four temperature measuring resistors are located on the four arms of the Wheatstone bridge, and the ambient temperature measuring resistor is connected in series with the Wheatstone bridge.

[0014] Further, the press-welding blocks are six pairs in total, one pair of which is arranged at the two ends of the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor, and is used for connecting with the peripheral circuit; the material of the press-welding blocks is one or several alloys of nickel, titanium, tungsten, chromium, platinum, aluminum or gold; and the material of the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor is platinum.

[0015] Further, the heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor are all processed into a back-shaped needle pattern, so that more resistors can be distributed in a smaller area.

[0016] Further, the heat insulation opening is optimized by using a neural network. The structure obtained in this way has better structural stability and higher upstream and downstream temperature difference output.

[0017] Further, the optimization of the heat insulation opening includes the following contents:

[0018] The geometric dimensions of the suspension bridge, the heating resistor, the temperature measuring resistor and the heat insulation opening are input into the neural network to obtain device indexes, the neural network is trained by using the device indexes to obtain a neural network proxy model; and based on the model, the size of the heat insulation opening is optimized by using a non-dominated sorting genetic algorithm.

[0019] Furthermore, this invention also proposes a method for fabricating a thermal flow sensor based on a silicon oxide wafer, comprising the following steps:

[0020] S1. Prepare silicon dioxide wafers: Clean the 100-axis silicon substrate and thermally oxidize it to generate a dense silicon dioxide layer.

[0021] S2. Photoresist is applied to the front side of the silicon dioxide layer by rotation, aligned with the silicon wafer, and then developed and exposed to reveal the patterns of the heating resistor, the temperature measuring resistor, and the ambient temperature measuring resistor. Chromium metal film and platinum metal film are sputtered on the front side of the chip.

[0022] S3. Use a stripping process to process the required chromium adhesive layer, heating resistor, temperature measuring resistor, and ambient temperature measuring resistor.

[0023] S4. Apply photoresist to the front of the chip for protection, align it with the silicon wafer, and then develop and expose the pattern of the leads and bonding pads. Sputter a thin metal film on the front of the chip.

[0024] S5. Use a stripping process to process the leads and solder pads.

[0025] S6. A silicon nitride protective layer is deposited on the front side of the chip using a plasma-enhanced chemical vapor deposition process.

[0026] S7. Use dry etching on the front side of the chip to etch out the silicon nitride protective layer and silicon dioxide layer, etch out the heat insulation port, and finally etch out the contact port of the bonding pad.

[0027] S8. Two methods are used to obtain the back cavity:

[0028] (1) Photoresist is applied to the front side of the chip for protection by rotation. After photolithography and development on the back side, an etching window is left. The back side is etched with BHF solution, and then TMAH wet etching is used to release the underlying silicon to obtain a back cavity.

[0029] (2) A back cavity is obtained by dry etching on the back side.

[0030] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0031] This invention incorporates a suspended bridge structure formed in the back cavity of a MEMS thermal flow sensor, along with heat insulation ports. This effectively reduces heat transfer to the substrate, improves heat utilization, and enhances the output and sensitivity of the Wheatstone bridge. The triangular heat insulation ports strengthen the sensor's strength and stability. The rectangular heat insulation ports effectively reduce lateral heat transfer across the substrate, further improving heat utilization. Four temperature-sensing resistors, located on the four arms of the Wheatstone bridge, enhance its output. The parameters of the heating and temperature-sensing resistors are optimized using COMSOL software, further improving the Wheatstone bridge's output and sensitivity. The silicon nitride protective layer resistor and the chip contribute to improved sensor stability and lifespan. Utilizing neural networks to optimize the suspended bridge structure parameters improves the structure's mechanical strength, reduces lateral heat transfer, and enhances the Wheatstone bridge's output and sensitivity. Attached Figure Description

[0032] Figure 1 This is a side view of the thermal flow sensor in Embodiment 1 of the present invention.

[0033] Figure 2 This is a three-dimensional structural schematic diagram of the thermal flow sensor in Embodiment 1 of the present invention.

[0034] Figure 3 This is a schematic diagram of the circuit structure of the thermal flow sensor in Embodiment 1 of the present invention.

[0035] Figure 4 This is a flowchart illustrating the fabrication process of the thermal flow sensor of this invention.

[0036] Figure 5 This is a three-dimensional structural schematic diagram of the thermal flow sensor in Embodiment 2 of the present invention.

[0037] Figure 6 This is a schematic diagram comparing the structural performance of Embodiment 1 and Embodiment 2 of the present invention.

[0038] In the figure: silicon substrate 100, silicon dioxide layer 200, back cavity 300, heat insulation port 410, triangular heat insulation (411), rectangular heat insulation port 412, chromium adhesive layer 500, heating resistor 510, temperature measuring resistor 520, ambient temperature measuring resistor 530, pressure bonding block 540, and silicon nitride protective layer 600. Detailed Implementation

[0039] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. For ease of explanation, when detailing the embodiments of the present invention, the cross-sectional views showing the device structure are partially enlarged, not according to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. Furthermore, in actual fabrication, three-dimensional spatial dimensions of length, width, and depth should be included.

[0040] For ease of description, spatial relation terms such as "below," "below," "lower than," "below," "above," and "upper" may be used here to describe the relationship between one element or feature shown in the figures and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the figures for the device in use or operation. Furthermore, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there may be one or more layers in between. It should also be noted that, for the sake of simplicity, not all structures are labeled in the figures.

[0041] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0042] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show components related to the present invention and are not drawn according to the actual number, shape, and size of the components in the actual implementation. In the actual implementation, the form, quantity, and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex. To keep the illustrations as concise as possible, not all structures are shown in the figures.

[0043] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0044] To achieve the above objectives, this invention proposes a thermal flow sensor based on silicon oxide wafers, such as... Figure 1 , 2 As shown, it includes:

[0045] The components include a silicon substrate 100, a silicon dioxide layer 200, a back cavity 300, a heat insulation port 410, a chromium adhesion layer 500, a heating resistor 510, a temperature sensing resistor 520, an ambient temperature sensing resistor 530, a bonding pad 540, and a silicon nitride protective layer 600.

[0046] A silicon dioxide layer 200 is located on a silicon substrate 100; a chromium adhesion layer 500 is provided between the silicon dioxide layer 200 and the heating resistor 510, the temperature measuring resistor 520, and the ambient temperature measuring resistor 530, respectively; a pressure bonding block 540 is provided on the heating resistor 510, the temperature measuring resistor 520, and the ambient temperature measuring resistor 530, respectively; a silicon nitride protective layer 600 is located around the silicon dioxide layer 200, and the silicon nitride protective layer 600 is used to protect the substrate, the heating resistor, the temperature measuring resistor, and the ambient temperature measuring resistor.

[0047] The heat insulation port 410 is disposed on the suspension bridge formed by the back cavity 300, including a triangular heat insulation port 411 and a rectangular heat insulation port 412; the rectangular heat insulation port 412 is located between the heating resistor 510 and the temperature measuring resistor 520, and the triangular heat insulation port 411 is located at the edge of the suspension bridge formed by the back cavity 300.

[0048] The back cavity 300 is removed by wet etching, and the heat insulation port 410 is removed by dry etching. The back cavity 300 and the heat insulation port 410 effectively reduce the diffusion of heat generated by the heating resistor to the substrate and improve heat utilization.

[0049] The silicon substrate 100 is a semiconductor high thermal conductivity thermally conductive substrate compatible with CMOS technology; the silicon dioxide layer 200 is a dense thin film generated by thermal oxidation of the silicon substrate 100.

[0050] The heating resistor 510 is located in the center of one side of the chip.

[0051] The 530 ambient temperature sensing resistors are located on the outer periphery above the cavity on the back, at the edge of the sensor.

[0052] There are 6 pairs of pressure welding blocks 540. There is one pair at each end of the heating resistor 510, the temperature measuring resistor 520, and the ambient temperature measuring resistor 530, which are used to connect to the external circuit.

[0053] The heating resistor 510, the temperature measuring resistor 520, and the ambient temperature measuring resistor 530 are all machined into paperclip patterns.

[0054] The heating resistor 510, temperature sensing resistor 520, and ambient temperature sensing resistor 530 are made of platinum metal film, wrapped in a silicon nitride protective layer 600, and are not exposed to the environment. They have excellent chemical properties and resistive chemical characteristics.

[0055] The material of the pressure welding block 540 is one or more alloy materials selected from nickel, titanium, tungsten, chromium, platinum, aluminum or gold; the materials of the heating resistor 510, the temperature measuring resistor 520 and the ambient temperature measuring resistor 530 are all platinum.

[0056] The temperature sensing resistor 520 includes two upstream temperature sensing resistors and two downstream temperature sensing resistors symmetrically distributed on both sides of the heating resistor 510. The upstream temperature sensing resistors are located to the left of the heating resistor 510, and the downstream temperature sensing resistors are located to the right of the heating resistor 510. The four temperature sensing resistors are located on the four arms of the Wheatstone bridge, and the ambient temperature sensing resistor 530 is connected in series with the Wheatstone bridge. The specific circuit diagram is as follows. Figure 3 As shown, Ru1 and Ru2 are upstream and downstream temperature measuring resistors, and Rd1 and Rd2 are resistors in the external circuit.

[0057] This invention also provides a method for fabricating a thermal flow sensor based on a silicon oxide wafer, such as... Figure 4 As shown, the method includes the following steps:

[0058] S1. Prepare silicon dioxide wafers: After cleaning, the silicon substrate 100 with 100 crystal orientation is thermally oxidized to form a dense silicon dioxide layer 200.

[0059] S2. Photoresist is applied to the front side of the silicon dioxide layer 200 by rotation. After aligning with the silicon wafer, the pattern of heating resistor 510, temperature measuring resistor 520, and ambient temperature measuring resistor 530 is developed and exposed. Chromium metal film and platinum metal film are sputtered on the front side of the chip.

[0060] S3. Use a stripping process to process the required chromium adhesive layer 500, heating resistor 510, temperature measuring resistor 520, and ambient temperature measuring resistor 530.

[0061] S4. Spin and apply photoresist to the front side of the chip, align it with the silicon wafer, and then develop and expose the pattern of the leads and bonding pads 540. Sputter a thin metal film on the front side of the chip.

[0062] S5. Use the stripping process to process the required leads and bonding pads 540.

[0063] S6. A silicon nitride protective layer 600 is deposited on the front side of the chip using a plasma-enhanced chemical vapor deposition process.

[0064] S7. Dry etch the silicon nitride protective layer 600 and silicon dioxide layer 200 on the front side of the chip to etch out the heat insulation port 400, and finally etch out the contact port of the bonding pad 540.

[0065] S8. Two methods are used to obtain the back cavity 300, namely:

[0066] (1) Photoresist is applied to the front side of the chip for protection, and an etching window is left after photolithography and development on the back side. BHF solution is used to etch the back side, and then TMAH wet etching is used to release the underlying silicon to obtain a 300-inch back cavity.

[0067] (2) A back cavity 300 is obtained by dry etching on the back side.

[0068] To further improve the performance of this thermal flow sensor, the geometric dimensions of the suspension bridge, heating resistor 510, temperature sensing resistor 520, and heat insulation port 410 are input into a neural network to obtain device specifications. These specifications are then used to train the neural network, resulting in a neural network surrogate model. Based on this model, a non-dominated sorting genetic algorithm is used to optimize the dimensions of the heat insulation port 410. Figure 5 The figure shown is a three-dimensional structural diagram of the thermal flow sensor after the heat insulation port 410 is optimized. The size and position of the heat insulation port 410 have been changed, thereby changing the structure of the suspension bridge support beam.

[0069] like Figure 6 As shown, compared to the structure before neural network optimization, the suspended bridge structure after neural network optimization has better structural stability and the sensor has a higher upstream and downstream temperature difference.

[0070] This invention utilizes the principle of thermal difference, with four upstream and downstream temperature-sensing resistors forming a Wheatstone bridge. When there is no wind, the temperature field formed by the heating resistors is symmetrically distributed, and the Wheatstone bridge output is zero. When there is wind, the temperature field formed by the heating resistors is no longer symmetrical, and the Wheatstone bridge has an output, which is related to the wind speed; the higher the wind speed, the larger the output. Based on a silicon oxide substrate, this invention forms a suspended bridge structure through a wet etching process, significantly reducing heat transfer to the substrate. The heat insulation opening effectively reduces lateral heat transfer within the substrate, improving heat utilization while simultaneously reducing heating power.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A thermal flow sensor based on silicon oxide wafers, characterized in that, include: Silicon substrate (100), silicon dioxide layer (200), back cavity (300), heat insulation port (410), chromium adhesive layer (500), heating resistor (510), temperature sensing resistor (520), ambient temperature sensing resistor (530), bonding pad (540) and silicon nitride protective layer (600); The silicon dioxide layer (200) is located on the silicon substrate (100); a chromium adhesion layer (500) is provided between the silicon dioxide layer (200) and the heating resistor (510), the temperature measuring resistor (520), and the ambient temperature measuring resistor (530); a pressure bonding block (540) is provided on the heating resistor (510), the temperature measuring resistor (520), and the ambient temperature measuring resistor (530); a silicon nitride protective layer (600) is located around the silicon dioxide layer (200); The temperature measuring resistor (520) includes two upstream temperature measuring resistors and two downstream temperature measuring resistors symmetrically distributed on both sides of the heating resistor (510). The upstream temperature measuring resistors are located on the left side of the heating resistor (510), and the downstream temperature measuring resistors are located on the right side of the heating resistor (510). The four temperature measuring resistors are located on the four arms of the Wheatstone bridge, and the ambient temperature measuring resistor (530) is connected in series with the Wheatstone bridge.

2. The thermal flow sensor based on silicon oxide wafers according to claim 1, characterized in that, The heat insulation port (410) is disposed on the suspension bridge formed by the back cavity (300), including a triangular heat insulation port (411) and a rectangular heat insulation port (412); the rectangular heat insulation port (412) is located between the heating resistor (510) and the temperature measuring resistor (520), and the triangular heat insulation port (411) is located at the edge of the suspension bridge formed by the back cavity (300).

3. The thermal flow sensor based on silicon oxide wafers according to claim 1, characterized in that, The silicon substrate (100) is a semiconductor high thermal conductivity thermally conductive substrate compatible with CMOS process; the silicon dioxide layer (200) is a dense thin film generated by thermal oxidation of the silicon substrate (100).

4. The thermal flow sensor based on silicon oxide wafers according to claim 1, characterized in that, The ambient temperature sensing resistor (530) is located on the outer periphery above the back cavity (300), at the edge of the sensor.

5. The thermal flow sensor based on silicon oxide wafers according to claim 1, characterized in that, The pressure welding block (540) has 6 pairs, with one pair at each end of the heating resistor (510), temperature measuring resistor (520), and ambient temperature measuring resistor (530) for connection to the external circuit; the material of the pressure welding block (500) is one or more alloys of nickel, titanium, tungsten, chromium, platinum, aluminum, or gold; the materials of the heating resistor (510), temperature measuring resistor (520), and ambient temperature measuring resistor (530) are all platinum.

6. The thermal flow sensor based on silicon oxide wafers according to claim 1, characterized in that, The heating resistor (510), the temperature measuring resistor (520), and the ambient temperature measuring resistor (530) are all processed into paperclip patterns.

7. The thermal flow sensor based on silicon oxide wafers according to claim 1, characterized in that, The heat insulation port (410) is optimized using a neural network.

8. The thermal flow sensor based on silicon oxide wafers according to claim 7, characterized in that, Optimizing the insulation opening (410) includes the following: The geometric dimensions of the levitation bridge, heating resistor (510), temperature measuring resistor (520), and heat insulation port (410) are input into the neural network to obtain device indicators. The neural network is then trained using these device indicators to obtain a neural network surrogate model. Based on this model, the dimensions of the heat insulation port (410) are optimized using a non-dominated sorting genetic algorithm.

9. The method for fabricating a thermal flow sensor based on a silicon oxide wafer as described in claim 1, characterized in that, Includes the following steps: S1. Clean the silicon substrate (100) with the 100 crystal orientation and thermally oxidize it to generate a dense silicon dioxide layer (200). S2. Photoresist is applied to the front side of the silicon dioxide layer (200) by rotation. After aligning with the silicon wafer, the pattern of heating resistor (510), temperature measuring resistor (520) and ambient temperature measuring resistor (530) is developed and exposed. Chromium metal film and platinum metal film are sputtered on the front side of the chip. S3. The required chromium adhesive layer (500), heating resistor (510), temperature measuring resistor (520) and ambient temperature measuring resistor (530) are processed using a stripping process. S4. Apply photoresist to the front side of the chip for protection, align it with the silicon wafer, and then develop and expose the pattern of the leads and bonding pads (540). Sputter a metal film on the front side of the chip. S5. Use a stripping process to process the leads and bonding pads (540); S6. A silicon nitride protective layer (600) is deposited on the front side of the chip using a plasma-enhanced chemical vapor deposition process; S7. Dry etching is used on the front side of the chip to form a silicon nitride protective layer (600) and a silicon dioxide layer (200) to form a heat insulation port (410), and finally to form the contact port of the bonding pad (540). S8. Two methods are used to obtain the back cavity (300), namely: (1) Photoresist is applied to the front side of the chip for protection, and an etching window is left after photolithography and development on the back side. BHF solution is used to etch the back side, and then TMAH wet etching is used to release the underlying silicon to obtain a back cavity (300). (2) A back cavity (300) is obtained by dry etching on the back side.

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