Two-dimensional flow sensor based on silicon oxide wafer and preparation method thereof

Abstract

The application discloses a two-dimensional 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, an etching hole, an adhesion layer, a ring-shaped heating resistor, a temperature measuring resistor, an environment temperature measuring resistor and a silicon nitride protective layer. The silicon substrate and the silicon dioxide layer are generated by a silicon oxide wafer process; the center part of the ring-shaped heating resistor is located at the center position of the chip through the etching hole, and four temperature measuring resistors are symmetrically distributed around the ring-shaped heating resistor and can be divided into X-axis temperature measuring resistors and Y-axis temperature measuring resistors; the etching hole is located between the ring-shaped heating resistor and the temperature measuring resistor; and the environment temperature measuring resistor is located outside the back cavity. The application reduces the heat transmission to the substrate, effectively reduces the lateral heat transmission in the substrate through the etching hole, improves the heat utilization rate, and improves the sensitivity of the sensor output and the mechanical strength of the two-dimensional flow sensor suspended film.

Description

TECHNICAL FIELD

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

[0002] The measurement of a thermal two-dimensional flow sensor involves three energy domains of fluid, heat and electricity, and according to the testing principle, the thermal two-dimensional flow sensor can be divided into three types: heat loss type, heat temperature difference type and heat pulse type. The heat temperature difference type can measure the flow rate and flow direction simultaneously, and meets the functional requirements of the application. According to the control mode, there are mainly three types: constant power type, constant temperature difference type and constant pressure type. The application adopts the constant temperature difference type control mode, and a constant temperature difference control circuit is needed to control the heating temperature of the annular heating resistor, which effectively prevents the damage of the annular heating resistor to the sensor caused by the excessively high temperature of the annular heating resistor, and the shortcoming is that the complexity of the overall system is improved.

[0003] In order to reduce the heat transfer of the annular heating resistor to the substrate, so as to improve the output and the measurement accuracy and achieve the purpose of low power consumption, a suspended membrane structure is designed for the thermal two-dimensional flow sensor. The traditional MEMS thermal two-dimensional flow sensor generally adopts the structure of a complete suspended membrane, but the lateral transmission of heat on the suspended membrane is still a technical problem. SUMMARY

[0004] The technical problem to be solved by the application is to provide a two-dimensional flow sensor prepared based on a silicon oxide wafer and a preparation method. The existence of the back cavity and the etching hole on the suspended membrane effectively reduces the heat transfer to the substrate and improves the heat utilization rate. At the same time, the existence of the triangular etching hole improves the mechanical strength, stability and reliability of the sensor suspended membrane, and prolongs the service life of the sensor.

[0005] In order to solve the above technical problems, the application adopts the following technical scheme:

[0006] The two-dimensional flow sensor prepared based on a silicon oxide wafer comprises:

[0007] A silicon substrate, a silicon dioxide layer, a back cavity, an etching hole, an adhesion layer, an annular heating resistor, a temperature measuring resistor, an environment temperature measuring resistor, a pressure welding block and a silicon nitride protective layer.

[0008] The silicon dioxide layer is located on the silicon substrate; the etching hole is arranged on the suspended membrane formed by the back cavity; the adhesion layer is arranged between the silicon dioxide layer and the annular heating resistor, the temperature measuring resistor and the environment temperature measuring resistor, and the pressure welding block is arranged on the annular heating resistor, the temperature measuring resistor and the environment temperature measuring resistor; and the silicon nitride protective layer is located at the periphery of the silicon dioxide layer.

[0009] 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.

[0010] Further, the temperature measuring resistors include X-axis upstream temperature measuring resistors, X-axis downstream temperature measuring resistors, Y-axis upstream temperature measuring resistors and Y-axis downstream temperature measuring resistors, which are symmetrically and equidistantly located around the annular heating resistors; the X-axis temperature measuring resistors are located on the first Wheatstone bridge, and the Y-axis temperature measuring resistors are located on the second Wheatstone bridge; and the ambient temperature measuring resistors are connected in series with the Wheatstone bridges.

[0011] Further, the annular heating resistors are annular squares; the etching holes are arranged between the annular heating resistors, between the annular heating resistors and the temperature measuring resistors, and between the temperature measuring resistors and the substrate around the temperature measuring resistors; and the annular heating resistors, the temperature measuring resistors and the ambient temperature measuring resistors are all processed into a back-shaped needle pattern, so that more resistors can be distributed on a smaller area.

[0012] Further, the ambient temperature measuring resistors are distributed at peripheral positions above the back cavity and at edges of the sensor.

[0013] Further, the compression welding blocks have 6 pairs in total, one pair of two ends of the annular heating resistors, the temperature measuring resistors and the ambient temperature measuring resistors is used for connecting with the peripheral circuit; the material of the compression welding blocks is one or several alloy materials selected from nickel, titanium, tungsten, chromium, platinum, aluminum and gold; and the material of the annular heating resistors, the temperature measuring resistors and the ambient temperature measuring resistors is platinum.

[0014] Further, the size of the annular heating resistors and the temperature measuring resistors is obtained by using COMSOL finite element software.

[0015] Further, the etching holes are optimized by using a neural network, and the specific content is as follows:

[0016] The geometric sizes of the suspension bridge, the annular heating resistors, the temperature measuring resistors and the etching holes are input into the neural network to obtain device indexes, the neural network is trained by using the device indexes, and a neural network proxy model is obtained; based on the model, the size of the etching hole is optimized by using a non-dominated sorting genetic algorithm.

[0017] Further, the application also provides a preparation method of the two-dimensional flow sensor based on the silicon oxide wafer, which comprises the following steps:

[0018] S1, preparing a silicon oxide wafer: cleaning a 100 crystal direction silicon substrate, and generating a dense silicon dioxide layer by thermal oxidation.

[0019] S2, spin coating photoresist on the front side of the silicon dioxide layer, aligning the silicon wafer, developing and exposing the pattern of the annular heating resistor, temperature measuring resistor and environmental temperature measuring resistor, sputtering chromium and platinum thin films on the front side of the chip.

[0020] S3, using a stripping process to process the required adhesion layer, annular heating resistor, temperature measuring resistor and environmental temperature measuring resistor.

[0021] S4, spin coating photoresist on the front side of the chip, aligning the silicon wafer, developing and exposing the pattern of the lead and solder block, sputtering metal thin film on the front side of the chip.

[0022] S5, using a stripping process to process the lead and solder block.

[0023] S6, depositing a silicon nitride protective layer on the front side of the chip using a plasma-enhanced chemical vapor deposition process.

[0024] S7, dry etching the silicon nitride protective layer and the silicon dioxide layer on the front side of the chip to etch the etching hole, and finally etching the contact port of the solder block.

[0025] S8, using two methods to obtain the back cavity, which are:

[0026] (1) spin coating photoresist on the front side of the chip for protection, leaving an etching window after developing and etching on the back side, using BHF solution to etch the back side, and then using TMAH wet etching to release the bottom layer of silicon to obtain the back cavity;

[0027] (2) back dry etching to obtain the back cavity.

[0028] Compared with the prior art, the technical scheme of the present application has the following technical effects:

[0029] The present application designs a suspended membrane structure formed by a back cavity and an etching hole, which reduces the transmission of heat to the substrate and improves the heat utilization rate, thereby improving the output sensitivity and accuracy. In addition, the triangular etching hole pattern structure has better strength and stability. By using COMSOL finite element software to optimize the parameters of the annular heating resistor and the temperature measuring resistor, the output sensitivity and accuracy are further improved. In addition, the second structure of the present application uses a neural network, with the structure geometric size as the input parameter and the device performance index as the output parameter, and uses the simulation results of the finite element analysis software for network training to obtain a neural network proxy model easy to calculate, so as to optimize the structure parameters of the suspended membrane and improve the mechanical strength of the structure and reduce the lateral transmission of a small amount of heat. These design and optimization measures work together to significantly improve the performance of the MEMS thermal two-dimensional flow sensor. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1is a side structure schematic diagram of the two-dimensional flow sensor in embodiment 1 of the present application.

[0031] Figure 2 is a front structure schematic diagram of the two-dimensional flow sensor in embodiment 1 of the present application.

[0032] Figure 3 is a circuit structure schematic diagram of the two-dimensional flow sensor in embodiment 1 of the present application.

[0033] Figure 4 is a preparation flow chart of the two-dimensional flow sensor in the present application.

[0034] Figure 5 is a front structure schematic diagram of the two-dimensional flow sensor in embodiment 2 of the present application.

[0035] Figure 6 is a structure performance comparison schematic diagram of embodiment 1 and embodiment 2 of the present application.

[0036] In the figure: silicon substrate 100, silicon dioxide layer 200, back cavity 300, etching hole 400, adhesion layer 500, annular heating resistor 510, temperature measuring resistor 520, ambient temperature measuring resistor 530, pressure welding block 540 and silicon nitride protective layer 600. DETAILED DESCRIPTION

[0037] The present application is described in detail below by specific examples. Other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the specification. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. When describing the embodiments of the present application, the cross-sectional view of the device structure is locally enlarged without the general proportion for the convenience of description, and the schematic diagram is only an example which should not limit the scope of protection of the present application. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in the actual preparation.

[0038] For the convenience of description, spatial relationship words such as "under", "below", "lower than", "under", "above", "upper" and the like can be used to describe the relationship of one element or feature with other elements or features shown in the drawings. It will be understood that these spatial relationship words are intended to include other directions of the device in use or operation in addition to the directions depicted in the drawings. In addition, when a layer is referred to as "between" two layers, it can be the only layer between the two layers, or one or more intervening layers can also be present. It should be noted that for the sake of simplicity of the drawings, not all structures are labeled in each drawing.

[0039] In the context of the present application, the structure in which the first feature is described as being "on" the second feature can include embodiments in which the first and second features are formed in direct contact, and can also include embodiments in which additional features are formed between the first and second features, such that the first and second features can not be in direct contact.

[0040] It should be noted that the diagrams provided in the embodiments of the present application only schematically illustrate the basic concepts of the present application, and thus only the components related to the present application are shown in the diagrams, rather than the number, shape and size of the components when actually implemented. The shapes, number and proportions of the components when actually implemented can be arbitrarily changed, and the layout of the components can be more complex. In order to make the diagrams as simple as possible, not all the structures are labeled in each of the accompanying drawings.

[0041] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0042] To achieve the above object, the present application proposes a two-dimensional flow sensor based on a silicon oxide wafer, as shown in Figure 1 、 Figure 2 , comprising:

[0043] a silicon substrate 100, a silicon dioxide layer 200, a back cavity 300, etching holes 400, an adhesion layer 500, a ring-shaped heating resistor 510, a temperature measuring resistor 520, an ambient temperature measuring resistor 530, a pressure welding block 540 and a silicon nitride protective layer 600.

[0044] The silicon dioxide layer 200 is located on the silicon substrate 100, the etching holes 400 include triangular etching holes and etching holes of other shapes, and are arranged on the suspended membrane formed by the back cavity 300; the adhesion layer 500 is arranged between the silicon dioxide layer 200 and the ring-shaped heating resistor 510, the temperature measuring resistor 520 and the ambient temperature measuring resistor 530, and the pressure welding block 540 is arranged on the ring-shaped heating resistor 510, the temperature measuring resistor 520 and the ambient temperature measuring resistor 530; the silicon nitride protective layer 600 is located at the periphery of the silicon dioxide layer 200, and is used to protect the substrate, the ring-shaped heating resistor, the temperature measuring resistor and the ambient temperature measuring resistor.

[0045] The ring-shaped heating resistor 510 is located at the center position of the chip and is in the shape of a ring-shaped square.

[0046] The ambient temperature measuring resistor 530 is distributed at the peripheral position above the back cavity and is located at the edge of the sensor.

[0047] Etching holes 400 are arranged between the annular heating resistors 510, between the annular heating resistors 510 and the temperature measuring resistors 520, and between the temperature measuring resistors 520 and the surrounding substrate; the annular heating resistors 510, the temperature measuring resistors 520 and the ambient temperature measuring resistors 530 are all processed into a back-shaped needle pattern, and more resistors can be distributed on a smaller area.

[0048] The six pairs of pressure welding blocks 540 are respectively connected to the two ends of the annular heating resistors 510, the temperature measuring resistors 520 and the ambient temperature measuring resistors 530, and are used for connecting with the peripheral circuit.

[0049] The silicon substrate 100 is a semiconductor high-thermal-conductivity heat-conducting substrate compatible with the CMOS process; and the silicon dioxide layer 200 is a dense thin film generated by thermal oxidation of the silicon substrate 100.

[0050] The annular heating resistors 510, the temperature measuring resistors 520 and the ambient temperature measuring resistors 530 are made of platinum thin film and are wrapped by the silicon nitride protective layer 600, without being exposed to the environment, and have good chemical properties and resistance chemical properties.

[0051] The material of the pressure welding blocks 540 is one or several alloy materials selected from nickel, titanium, tungsten, chromium, platinum, aluminum and gold; and the material of the annular heating resistors 510, the temperature measuring resistors 520 and the ambient temperature measuring resistors 530 is platinum.

[0052] The temperature measuring resistors 520 include X-axis upstream temperature measuring resistors, X-axis downstream temperature measuring resistors, Y-axis upstream temperature measuring resistors and Y-axis downstream temperature measuring resistors, which are symmetrically and equidistantly arranged around the annular heating resistors 510; the X-axis temperature measuring resistors in the temperature measuring resistors 520 are located on the first Wheatstone bridge, the Y-axis temperature measuring resistors are located on the second Wheatstone bridge, and the ambient temperature measuring resistors 530 are connected in series with the Wheatstone bridge. Figure 3 As shown in the specific circuit diagram, Rx1 and Rx2 are X-axis temperature measuring resistors, and Ry1 and Ry2 are Y-axis temperature measuring resistors.

[0053] The size of the annular heating resistors 510 and the temperature measuring resistors 520 is obtained by using COMSOL.

[0054] The application further provides a preparation method of a two-dimensional flow sensor prepared based on a silicon oxide wafer, as shown in the accompanying drawings, the method comprises the following steps: Figure 4 As shown in the specific circuit diagram, Rx1 and Rx2 are X-axis temperature measuring resistors, and Ry1 and Ry2 are Y-axis temperature measuring resistors.

[0055] S1, preparing a wafer of silicon oxide wafer: after the silicon substrate 100 with a crystal direction of 100 is cleaned, a dense silicon dioxide layer 200 is generated by thermal oxidation.

[0056] S2, spin coating photoresist on the front side of the silicon dioxide layer 200, after aligning the silicon wafer, developing and exposing the pattern of the annular heating resistor 510, the temperature measuring resistor 520, and the environmental temperature measuring resistor 530, sputtering chromium and platinum thin films on the front side of the chip.

[0057] S3, using a stripping process to process the required adhesion layer 500, annular heating resistor 510, temperature measuring resistor 520, and environmental temperature measuring resistor 530.

[0058] S4, spin coating photoresist on the front side of the chip, after aligning the silicon wafer, developing and exposing the pattern of the lead and solder block 540, sputtering metal thin film on the front side of the chip.

[0059] S5, using a stripping process to process the required lead and solder block 540.

[0060] S6, depositing a silicon nitride protective layer 600 on the front side of the chip using a plasma-enhanced chemical vapor deposition process.

[0061] S7, dry etching the silicon nitride protective layer 600 and the silicon dioxide layer 200 on the front side of the chip to etch the etching hole 400, and finally etching the contact hole of the solder block 540.

[0062] S8, using two methods to obtain the back cavity 300, respectively:

[0063] (1) spin coating photoresist on the front side of the chip for protection, leaving an etching window after developing and etching on the back side, using BHF solution to etch the back side, and then using TMAH wet etching to release the bottom layer of silicon to obtain the back cavity 300;

[0064] (2) by back side dry etching, the back cavity 300 is obtained.

[0065] In order to further improve the performance of the two-dimensional flow sensor, the geometric dimensions of the suspended bridge, the annular heating resistor 510, the temperature measuring resistor 520, and the etching hole 400 are input into the neural network to obtain device indicators, and the neural network is trained using the device indicators to obtain a neural network proxy model; based on the model, the size of the etching hole 400 is optimized using a non-dominated sorting genetic algorithm. As shown in Figure 5 the front structure diagram of the two-dimensional flow sensor after optimization of the etching hole 400, the size and position of the etching hole 400 are changed, and the number of etching holes 400 is also increased, so that the two-dimensional flow sensor has better structural stability.

[0066] As shown in Figure 6 compared with the structure before the neural network optimization, the two-dimensional flow sensor after the neural network optimization has better structural stability and the sensor has higher upstream and downstream temperature difference.

[0067] The application adopts the principle of thermal temperature difference, and X-axis temperature measuring resistor and Y-axis temperature measuring resistor respectively constitute Wheatstone bridge, so as to measure flow rate and flow direction. When there is no wind, the temperature field formed by the annular heating resistor is symmetrically distributed, and the output of the Wheatstone bridge is zero; when there is wind, the temperature field formed by the annular heating resistor is no longer symmetric, the Wheatstone bridge has output, the output is related to the flow rate, the greater the flow rate, the greater the output; the measurement of the flow direction is obtained by taking the trigonometric function of the output of the X-axis and Y-axis temperature measuring resistors.

[0068] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the application, and these improvements and modifications should also be considered as the protection scope of the application.

Claims

1. A two-dimensional flow sensor prepared on the basis of a silicon oxide wafer, characterized in that, The application relates to a sensor for measuring temperature, which comprises a silicon substrate (100), a silicon dioxide layer (200), a back cavity (300), etching holes (400), an adhesive layer (500), annular heating resistors (510), temperature measuring resistors (520), ambient temperature measuring resistors (530), pressure welding blocks (540) and a silicon nitride protective layer (600). The silicon dioxide layer (200) is arranged on the silicon substrate (100); the etching holes (400) are arranged on the suspended film formed by the back cavity (300); the adhesive layer (500) is arranged between the silicon dioxide layer (200) and the annular heating resistors (510), the temperature measuring resistors (520) and the ambient temperature measuring resistors (530); the pressure welding blocks (540) are arranged on the annular heating resistors (510), the temperature measuring resistors (520) and the ambient temperature measuring resistors (530); and the silicon nitride protective layer (600) is arranged on the periphery of the silicon dioxide layer (200). The temperature measuring resistors (520) comprise X-axis upstream temperature measuring resistors, X-axis downstream temperature measuring resistors, Y-axis upstream temperature measuring resistors and Y-axis downstream temperature measuring resistors, which are symmetrically and equidistantly arranged around the annular heating resistors (510); the X-axis temperature measuring resistors are arranged on a first Wheatstone bridge, and the Y-axis temperature measuring resistors are arranged on a second Wheatstone bridge; and the ambient temperature measuring resistors (530) are connected in series with the Wheatstone bridges. The silicon substrate (100) is a semiconductor high-thermal-conductivity heat-conducting substrate compatible with a CMOS process; and the silicon dioxide layer (200) is a dense thin film generated by thermal oxidation of the silicon substrate (100).

2. The two-dimensional flow sensor prepared based on a silicon oxide wafer according to claim 1, characterized in that, The annular heating resistors (510) are annular squares; the etching holes (400) are arranged between the annular heating resistors (510), between the annular heating resistors (510) and the temperature measuring resistors (520), and between the temperature measuring resistors (520) and the periphery of the substrate; and the annular heating resistors (510), the temperature measuring resistors (520) and the ambient temperature measuring resistors (530) are all processed into a back-type needle pattern.

3. The two-dimensional flow sensor prepared based on a silicon oxide wafer according to claim 1, characterized in that, The ambient temperature measuring resistors (530) are distributed at the peripheral positions above the back cavity (300) and at the edges of the sensor.

4. The two-dimensional flow sensor prepared based on a silicon oxide wafer according to claim 1, characterized in that, The pressure welding blocks (540) are six pairs in total, one pair of which is arranged at the two ends of the annular heating resistors (510), the temperature measuring resistors (520) and the ambient temperature measuring resistors (530) and used for being connected with an external circuit; the material of the pressure welding blocks (540) is one or several alloy materials selected from nickel, titanium, tungsten, chromium, platinum, aluminum and gold; and the materials of the annular heating resistors (510), the temperature measuring resistors (520) and the ambient temperature measuring resistors (530) are all platinum.

5. The two-dimensional flow sensor prepared based on a silicon oxide wafer according to claim 1, characterized by, The sizes of the annular heating resistors (510) and the temperature measuring resistors (520) are obtained by using a finite element software.

6. The two-dimensional flow sensor prepared based on a silicon oxide wafer according to claim 1, characterized by, The etching holes (400) are optimized by using a neural network.

7. The two-dimensional flow sensor prepared based on a silicon oxide wafer according to claim 1, characterized by, The optimization of the etching holes (400) comprises the following contents:

8. The two-dimensional flow sensor prepared on the basis of a silicon oxide wafer according to claim 7, characterized in that ​ Geometrical dimensions of the suspension bridge, the annular heating resistor (510), the temperature measuring resistor (520) and the etching hole (400) are input into the neural network to obtain device indexes, the neural network is trained by using the device indexes, and a neural network proxy model is obtained; based on the model, the size of the etching hole (400) is optimized by using a non-dominated sorting genetic algorithm.

9. A method for manufacturing a two-dimensional flow sensor based on a silicon oxide wafer as claimed in claim 1, characterized in that, The method comprises the following steps: S1, cleaning a 100 crystal direction silicon substrate (100), and generating a dense silicon dioxide layer (200) by thermal oxidation; S2, rotating and coating photoresist on the front side of the silicon dioxide layer (200), developing and exposing the pattern of the annular heating resistor (510), the temperature measuring resistor (520) and the environmental temperature measuring resistor (530) after aligning the silicon wafer, and sputtering chromium and platinum thin films on the front side of the chip; S3, using a stripping process to process the required adhesion layer (500), the annular heating resistor (510), the temperature measuring resistor (520) and the environmental temperature measuring resistor (530); S4, rotating and coating photoresist on the front side of the chip, developing and exposing the pattern of the lead and the solder block (540) after aligning the silicon wafer, and sputtering metal thin films on the front side of the chip; S5, using a stripping process to process the lead and the solder block (540); S6, depositing a silicon nitride protective layer (600) on the front side of the chip by using a plasma-enhanced chemical vapor deposition process; S7, dry etching the silicon nitride protective layer (600) and the silicon dioxide layer (200) on the front side of the chip to etch the etching hole (400), and finally etching the contact opening of the solder block (540); S8, obtaining the back cavity (300) by using two methods, which are as follows: (1) rotating and coating photoresist on the front side of the chip for protection, leaving an etching window after backside lithography and development, etching the backside by using BHF solution, and then releasing the bottom layer of silicon by using TMAH wet etching to obtain the back cavity (300); (2) obtaining the back cavity (300) by backside dry etching.

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