Application of arch structure in MEMS hot film type flow sensor chip and preparation method of arch structure

Abstract

The invention relates to the technical field of sensors, in particular to application of an arch structure in an MEMS hot film type flow sensor chip and a preparation method of the arch structure, and the method comprises the following steps: arranging silicon nitride layers on the front and back surfaces of a silicon substrate respectively; sequentially etching the silicon nitride layer and the silicon substrate on the front surface of the substrate through photoetching and dry etching processes, and finally forming a silicon substrate bottom layer hole structure; removing the front silicon nitride layer outside the hole structure from the front through a dry / wet etching process; growing a silicon oxide filling silicon layer hole structure through a thermal oxidation method; polishing and flattening the silicon oxide surface from the front side through CMP to form a silicon oxide structure layer; sputtering a metal layer on the polished and flattened silicon oxide structure layer; depositing a passivation protection layer on the metal layer; photoetching and etching a specified area of the silicon nitride layer on the back of the silicon substrate to form a back cavity window and expose the back silicon substrate, performing wet or dry etching on the silicon substrate from the back, and stopping forming a required arched suspended film structure on the front silicon oxide structure layer; the device manufactured by the method has the advantages of high precision and high reliability, and when the device is applied to an MEMS hot film type flow sensor chip, the mechanical strength of a film area can be improved, and performance change or structural damage caused by stress can be reduced.

Description

Technical Field

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

[0002] With the development of modern industry and science and technology, MEMS (micro-electromechanical system) hot film flow sensors have been widely used in the fields of air flow detection, gas flow control, liquid flow measurement, etc. Among them, hot film flow sensor is a sensor that realizes gas or liquid flow measurement based on the principle of heat conduction. Its advantages are low cost, fast response speed, high accuracy, etc.

[0003] However, traditional MEMS thermal film flow sensors often have problems such as large pressure loss, low sensitivity, poor linearity, and easy damage to the membrane area. In order to improve the performance and accuracy of the sensor, it is necessary to optimize the design and preparation of the sensor structure. The arch structure is an arch shape formed by connecting micro-bent rods, which has good flexibility and durability. At present, there have been many studies on the application and preparation methods of arch structures in MEMS thermal film flow sensor chips, but there are still problems such as difficulty in preparation and poor consistency. The preparation method of the arched suspended membrane cannot obtain a film layer with uniform thickness by relying solely on the traditional isotropic corrosion of the oxide layer, and it is also difficult to accurately control the corrosion time to form the desired structure. Therefore, it is necessary to provide a simple, economical and efficient preparation method to solve these problems. Summary of the invention

[0004] The purpose of the present invention is to propose an application of an arch structure in a MEMS thermal film flow sensor chip and a preparation method thereof in response to the problems existing in the background technology. The application idea of ​​the arch structure provided by the present invention in a MEMS thermal mode flow sensor chip is an effective solution to the above-mentioned problems. The present invention also provides a method for preparing an arch structure. The method can use MEMS technology and related technologies to realize the formation of an arch structure during the manufacturing process of the sensor chip. Specifically, it includes depositing appropriate materials on the surface of the chip, and using process steps such as thermal oxidation, photolithography, and etching a hole structure to form the material into an arch structure. The arch structure thus formed can be used to construct functions such as thermal resistance, supporting a thin film, and reducing the flow area, thereby realizing the characteristics of the sensor such as high sensitivity, high linearity, and low pressure drop. The reliability and service life of the sensor are improved as a whole.

[0005] The technical solution of the present invention is an arched structure MEMS hot film flow sensor chip, comprising an arched suspended membrane structure, a silicon nitride layer, a silicon oxide structure layer, a metal layer and a passivation protection layer;

[0006] The arched suspended membrane structure is formed by etching a designated area on the back of the silicon base, and support ends are formed at both ends of the back cavity;

[0007] Silicon nitride layers, deposited on the front and back sides of the substrate, serve as support and dielectric isolation layers for the arched structure;

[0008] Silicon oxide structural layer: The formed arched structure is used to build thermal resistance, support the film and reduce the flow area function;

[0009] A metal layer is formed into a pattern on the silicon oxide structure layer by sputtering and etching, and is alloyed to form a corresponding resistor;

[0010] The passivation protection layer is formed on the metal layer to protect the metal layer and form a metal pad.

[0011] Preferably, the metal layer is made of a material with a positive temperature coefficient, such as platinum.

[0012] A method for preparing an arched structure MEMS hot film flow sensor chip, preparing the sensor chip, comprising the following specific steps:

[0013] S1, forming a silicon nitride layer on the front and back sides of the silicon substrate by LPCVD growth;

[0014] S2, performing photolithography and etching on the front silicon nitride layer to form a hole structure and expose the front silicon substrate;

[0015] S3, the silicon substrate exposed on the front side is further etched downward by anisotropic dry etching to form a hole or groove structure in the silicon substrate layer;

[0016] S4, protecting the back silicon nitride layer, and removing the front silicon nitride layer from the front side by an etching method;

[0017] S5, growing silicon oxide to fill the silicon layer hole structure by thermal oxidation method;

[0018] S6, polishing the silicon oxide surface from the front side by CMP to form a silicon oxide structural layer;

[0019] S7, sputtering a metal layer on the polished and flattened silicon oxide structure layer to form the required upstream and downstream bridge resistors, heating resistors and environmental resistors;

[0020] S8, depositing a passivation silicon nitride protective layer on the metal layer, and forming a PAD window by photolithography and etching;

[0021] S9. Perform photolithography and etching on the designated area of ​​the silicon nitride layer on the back side of the silicon substrate to form a back cavity window and expose the back silicon substrate. Perform anisotropic wet etching or anisotropic deep reactive ion dry etching on the silicon substrate from the back side, and stop at the front silicon oxide structure layer (below the front hole structure area) to form the required arched suspended membrane structure.

[0022] Preferably, in step S4, the front silicon nitride layer is removed by phosphoric acid wet etching or dry etching.

[0023] Preferably, the layout of the openings and hole spacings of the mask in step S5 needs to satisfy the following constraints:

[0024] 1 / 2(S1+S2)=S3

[0025] Among them, S1 and S2 represent the opening sizes of two adjacent holes respectively; S3 represents the distance between two adjacent holes.

[0026] Preferably, during the process of thermal oxidation growth of silicon oxide, the top and the inside of the holes in the silicon oxide structure layer are filled to form a sealed structure.

[0027] Preferably, the thermal oxidation process parameters include rate and temperature.

[0028] Preferably, the designated area in step S9 is the area directly facing the bridge resistor, the heating resistor and the environmental resistor.

[0029] An application of an arched structure MEMS hot film flow sensor chip is prepared using the above method.

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

[0031] The preparation method of the present invention is used to improve the performance and reliability of the sensor by optimizing the membrane area structure and the preparation method of the arch structure, which specifically includes the following advantages:

[0032] The present invention forms a heat-insulating layer by arranging a silicon oxide layer arch structure connected by micro-bent rods in the membrane area, thereby effectively isolating the heat source of the sensor from the ambient temperature. This can improve the sensitivity and stability of the sensor and reduce the impact of external temperature changes on the sensor's measurement results;

[0033] The arched structure provides increased mechanical strength and stability, allowing the film to better maintain its flat shape and avoid deformation caused by stress or temperature changes, thereby improving the accuracy and reliability of the sensor.

[0034] The flow area can be effectively reduced, thereby increasing the velocity and pressure changes of the fluid. This helps to improve the sensor's sensitivity to flow changes, enabling it to more accurately measure and control the flow of the fluid.

[0035] Designers in this field should be clearly aware that the thickness of the arched structure layer produced in the above manner can be effectively adjusted according to the depth of the produced holes or grooves; while the thickness of the arched structure formed by isotropically etching the oxide layer using conventional processes is limited by the thickness of the oxide layer and the etching time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the preparation method in the embodiment of the present invention;

[0037] Figure 2 It is one of the MASK views of the top of the photomask in the embodiment of the present invention;

[0038] Figure 3 The second MASK view of the top of the photomask in the embodiment of the present invention;

[0039] Figure 4 Schematic diagram of the openings and hole spacing of the mask in an embodiment of the present invention.

[0040] Figure numerals: 1. silicon substrate; 2. silicon nitride layer; 3. hole structure of silicon nitride layer; 4. hole structure of silicon substrate layer; 5. silicon oxide structure layer; 6. metal layer; 7. passivation protection layer; 8. back cavity; 9. arched suspended membrane structure. DETAILED DESCRIPTION

[0041] Example 1

[0042] like Figure 1 As shown, the present invention proposes a method for preparing an arch structure in a MEMS thermal film flow sensor chip.

[0043] A silicon nitride layer 2 is respectively formed on the front and back sides of the substrate 1 by LPCVD growth;

[0044] Performing photolithography and etching on the front silicon nitride layer 2 to form a silicon nitride layer hole structure 3 and expose the front silicon substrate 1;

[0045] The silicon substrate 1 exposed on the front side is further etched downward by anisotropic dry etching to form a silicon substrate layer hole structure 4;

[0046] removing the front silicon nitride layer from the front side by wet etching or dry etching with phosphoric acid;

[0047] The silicon oxide structure layer 5 is initially formed by reacting and growing silicon oxide to fill the silicon layer hole structure 4 by a thermal oxidation method;

[0048] The silicon oxide surface is polished and flattened from the front side by CMP chemical mechanical planarization to form a silicon oxide structure layer 5;

[0049] A metal layer 6 is sputtered on the polished and flat silicon oxide structure layer 5 to form the required upstream and downstream bridge resistors, heating resistors and environmental resistors;

[0050] Depositing a passivation silicon nitride protection layer 7 on the metal layer 6, and forming a PAD window by photolithography and etching;

[0051] The designated area of ​​the silicon nitride layer 2 on the back side of the silicon substrate 1 (facing the bridge resistor, heating resistor and environmental resistor area) is photolithographically processed and etched to form a back cavity 8 and expose the back silicon substrate 1, and the silicon substrate 1 is wet-etched or dry-etched from the back side thereof, and the etching stops at the back side of the silicon oxide structural layer 5 to form the desired arched suspended membrane structure 9; those skilled in the art should recognize that the etching of the back side silicon substrate mentioned above may be anisotropic wet etching, such as TMAH solution, or deep reactive ion dry etching, and may also be a method of dry etching first and then wet etching, or wet etching first and then dry etching.

[0052] The photomask is made as follows: Figure 2 The graphic design of the "MASK top view" is that the size of the square through holes on the Mask gradually decreases from the center to the periphery. When the silicon holes are etched by conventional reactive ion dry etching, the different sizes of the square through holes will form Figure 2 The more through-hole circles there are and the denser their arrangement, the smoother the arcs in the arched structure will be. It should be understood that the shapes and arrangements of through-holes are not limited to the above-mentioned ones. Any through-hole shape and arrangement that can achieve an arched arc shape are within the protection scope of this patent.

[0053] In the process of generating silicon oxide to fill the holes by thermal oxidation reaction, it is also necessary to pay attention to the layout of the openings and hole spacing of the mask. Figure 3 As shown, S1 and S2 represent the opening sizes of two adjacent holes respectively, and S3 represents the spacing between two adjacent holes. Therefore, when designing the layout size, 1 / 2(S1+S2)≤S3 must be satisfied to ensure that the top of the hole of the silicon oxide structural layer 5 is filled to form a sealed structure during the thermal oxidation growth of silicon oxide.

[0054] It should also be understood that the composition and ratio of the isotropic and anisotropic wet etching chemical solvents can be adjusted as needed, all within the scope of protection of the present invention. In addition, the size, shape, and position of the arch structure in the present invention can also be adjusted according to actual cases. Those skilled in the art should also recognize that the holes forming the arch structure can also be groove structures, such as Figure 3 The annular groove structure shown can also realize the above-mentioned arched structure.

[0055] Example 2

[0056] like Figure 1-2 As shown, this embodiment provides an arched structure MEMS hot film flow sensor chip, including an arched suspended membrane structure, a silicon nitride layer, a silicon oxide structure layer, a metal layer and a passivation protection layer;

[0057] The arched suspended membrane structure is formed by etching the middle of the back side of the silicon bottom, and supporting ends are formed at both ends of the back cavity;

[0058] Silicon nitride layers, deposited on the front and back sides of the substrate, serve as support and dielectric isolation layers for the arched structure;

[0059] Silicon oxide structural layer: The formed arched structure is used to build thermal resistance, support the film and reduce the flow area function;

[0060] A metal layer is formed into a pattern on the silicon oxide structure layer by sputtering and etching, and is alloyed to form a corresponding resistor;

[0061] The passivation protection layer is formed on the metal layer to protect the metal layer and form a metal pad.

[0062] In this embodiment, the method in embodiment 1 is used to finally prepare the hot film flow sensor chip with an arch structure as described in embodiment 2; when the arch structure is subjected to pressure, it can disperse the pressure to various parts and effectively reduce the concentrated stress. Its curved shape enables the material to better withstand pressure when bearing weight and reduce the risk of fracture.

[0063] The arched structure can effectively utilize materials and give full play to the strength of the materials. When subjected to external forces, the arched structure can absorb and disperse the forces through the bending of the materials, thus improving the overall stability and safety.

[0064] The geometric shape of the arch structure brings it natural stability. Since the arch is in the shape of an arc, when the structure is subjected to external forces, it can offset the external forces through the bending of the arc and maintain the stability of the structure.

[0065] Compared with the existing technology, the conventional process is to grow an oxide layer on the front side, then etch / dry-etch silicon on the back side, and then anisotropically etch silicon oxide on the back side to form an arch. However, this etching process cannot stop by itself and needs to be controlled by etching time. Therefore, it is impossible to control the consistency of each chip during mass production. If the etching rate is slow, the arc will be small, and if the etching rate is fast, the arc will be large, and the silicon oxide layer may even be completely corroded, so that the arch cannot be formed.

[0066] The conventional process in MEMS technology can also realize the arch, but the realization method has the problem that the uniformity of mass production is difficult to control. In this solution, after the arched oxide layer is formed on the front, the silicon is first etched through the bottom, and then it stops at the bottom of the arched oxide layer, thus forming an arched suspended oxide film.

[0067] The present invention forms a heat insulation layer by arranging a silicon oxide layer arch structure connected by micro-bent rods in the membrane area, thereby effectively isolating the heat source of the sensor from the ambient temperature. In this way, the sensitivity and stability of the sensor can be improved, and the influence of external temperature changes on the sensor measurement results can be reduced; the mechanical strength and stability can be increased through the supporting effect of the arch structure. The film can better maintain a flat shape and avoid deformation of the film caused by stress or temperature changes, thereby improving the accuracy and reliability of the sensor. The circulation area can be effectively reduced, thereby increasing the velocity and pressure changes of the fluid. This helps to improve the sensitivity of the sensor to flow changes, so that it can more accurately measure and control the flow of the fluid.

[0068] Obviously, the above embodiments are merely examples for the purpose of 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 therefrom are still within the scope of protection created by this application.

Claims

1. An arched structure MEMS hot film flow sensor chip, characterized in that: It includes an arched suspended membrane structure, a silicon nitride layer, a silicon oxide structure layer, a metal layer and a passivation protection layer; The arched suspended membrane structure is formed by etching the middle of the back side of the silicon bottom, and support ends are formed at both ends of the back cavity; Silicon nitride layers, deposited on the front and back sides of the substrate, serve as support and dielectric isolation layers for the arched structure; Silicon oxide structural layer: The formed arched structure is used to build thermal resistance, support the film and reduce the flow area function; A metal layer is formed into a pattern on the silicon oxide structure layer by sputtering and etching, and is alloyed to form a corresponding resistor; The passivation protection layer is formed on the metal layer to protect the metal layer and form a metal pad.

2. The arched structure MEMS hot film flow sensor chip according to claim 1, characterized in that: The metal layer is made of a material with a positive temperature coefficient.

3. A method for preparing an arched structure MEMS hot film flow sensor chip, preparing the sensor chip as claimed in claim 1 or 2, characterized in that: The specific steps include: S1, forming a silicon nitride layer on the front and back sides of the silicon substrate by LPCVD growth; S2, performing photolithography and etching on the front silicon nitride layer to form a hole structure, and exposing the front silicon substrate; S3, the silicon substrate leaking out from the front side is further etched downward by anisotropic dry etching to form a hole structure of the silicon substrate layer; S4, protecting the back silicon nitride layer, and removing the front silicon nitride layer from the front by an etching method; S5, growing silicon oxide to fill the silicon layer hole structure by thermal oxidation method; S6, polishing the silicon oxide surface from the front side by CMP to form a silicon oxide structural layer; S7, sputtering a metal layer on the flat silicon oxide structure layer to form the required upstream and downstream bridge resistors, heating resistors and environmental resistors; S8, depositing a passivation silicon nitride protective layer on the metal layer, and forming a PAD window by photolithography and etching; S9, photolithography and etching of a designated area of ​​the silicon nitride layer on the back side of the silicon substrate to form a back cavity window and expose the back silicon substrate, wet or dry etching of the silicon substrate from the back side, and stopping at the front silicon oxide structure layer to form the desired arched suspended membrane structure.

4. The method for preparing the arched structure MEMS hot film flow sensor chip according to claim 3, characterized in that: In step S4, the front silicon nitride layer is removed by phosphoric acid wet etching or dry etching.

5. The method for preparing the arched structure MEMS hot film flow sensor chip according to claim 3, characterized in that: The layout of the openings and hole spacing of the mask in step S5 needs to meet the following constraints: 1 / 2(S1+S2)=S3 Among them, S1 and S2 represent the opening sizes of two adjacent holes respectively; S3 represents the distance between two adjacent holes.

6. The method for preparing the arched structure MEMS hot film flow sensor chip according to claim 5, characterized in that: During the thermal oxidation growth of silicon oxide, the inside and top of the hole are filled to form a sealed structure by controlling the thermal oxidation process parameters.

7. The method for preparing the arched structure MEMS hot film flow sensor chip according to claim 6, characterized in that: Thermal oxidation process parameters include rate and temperature.

8. The method for preparing the arched structure MEMS hot film flow sensor chip according to claim 3, characterized in that: The designated area in step S9 is the area directly facing the bridge resistance, the heating resistance and the environmental resistance.

9. An application of an arched structure MEMS thermal film flow sensor chip, characterized in that: Prepared by the method described in any one of claims 3 to 8.

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