A CMOS-MEMS monolithic integrated flow and pressure sensor

Abstract

The present invention relates to a CMOS-MEMS monolithic integrated flow and pressure sensor, belonging to the field of sensors. The sensor of the present invention comprises a silicon substrate layer and a silicon dioxide structure layer. The silicon dioxide structure layer includes PAD regions arranged at both ends and a gas flow sensor region and a gas pressure sensor region arranged in the center. In the PAD regions, the silicon dioxide material and the metal material are arranged in an overlapping manner, and the metal via penetrates through the first layer of metal to the fifth layer of metal. The gas flow sensor region includes a heating resistor and a first thermistor and a second thermistor distributed on both sides of the heating resistor. The present invention adopts a Post-CMOS process that does not require mask operation, effectively reducing the complexity of the post-processing of the entire device and greatly improving the efficiency of the entire Post-CMOS post-processing. The sensing part needs to be suspended to have the characteristics of low heat dissipation and fast response speed.

Description

Technical Field

[0001] The present invention relates to a CMOS-MEMS monolithic integrated flow and pressure sensor, belonging to the field of sensors. Background Art

[0002] A ventilator can be said to be a "life-saving machine" for critically ill patients. It can effectively achieve the function of artificial replacement of spontaneous ventilation, play a role in preventing and treating respiratory failure, reduce complications, save and prolong the life of patients, and is a crucial medical device. As a special equipment related to the life of patients, a ventilator requires high-precision sensor components to ensure its normal operation, and the most important of them include flow sensors and pressure sensors. The flow sensor is the core device for monitoring respiratory flow parameters in a ventilator. The ventilator monitors the inhalation and exhalation flow data and performs closed-loop feedback control on the valve to achieve the goal of accurately delivering oxygen to the patient. The pressure sensor is the core device for monitoring pressure parameters and alarming in a ventilator. Since critically ill patients have limited breathing ability and cannot breathe normally like ordinary people, the ventilation mode of the ventilator is usually positive pressure ventilation, which will exert a certain pressure on the patient's lungs and chest. This pressure will have a certain impact on the human respiratory and circulatory systems. When the ventilation pressure setting is inappropriate and does not match the real-time needs of the patient, there will be a man-machine confrontation (it is found that the incidence of man-machine incoordination in invasive ventilation exceeds 25%), which will further cause ventilator-related lung injury, affect blood circulation (30% - 40% of ARDS patients develop acute cor pulmonale), increase the time on the ventilator, and even lead to an increase in mortality. Thus, it can be seen that achieving accurate ventilation and rapid man-machine synchronization for patients is very important. The basis for the above functions is the accurate, stable, and rapid measurement of flow and gas pressure. The performance and quality of each sensor will directly affect the reliability of the ventilator.

[0003] Thermal flow sensors have the characteristics of simple structure, low processing difficulty, good stability, strong reliability, and easy miniaturization compared with other types of flow sensors, and have been a research hotspot of flow sensors since the 1960s. In 1974, a hot-wire anemometer based on a silicon substrate was developed. Although its signal output is low, heat dissipation is large, and sensitivity is low, it is considered the beginning of micro-nano integrated flow sensors. Since then, a large number of scholars have made many attempts in substrate materials, preparation processes, structural design, etc., but the performance of the devices still cannot be optimized. In addition, the parametric analysis and performance prediction of existing thermal sensors mainly adopt numerical simulation methods, making it difficult to achieve efficient parametric analysis. At the same time, although MEMS technology can adopt relatively flexible process processing methods and a wide range of materials can be selected, it is difficult to directly interconnect with the circuit part, which limits the overall size of the test microsystem to a certain extent; due to the existence of problems such as parasitic capacitance, the performance of the devices is also reduced to a certain extent. With the rapid development of CMOS semiconductor technology, the mature CMOS processing technology has incomparable advantages in realizing device miniaturization. At the same time, it can also ensure the stability of device performance, ensure the feasibility of mass production, and shorten the product R & D cycle. Therefore, thermal flow sensors based on CMOS technology have gradually become the main research direction in the future.

[0004] However, there are still some technical barriers in the current thermal flow sensors based on CMOS-MEMS technology. For example, the processing process of CMOS technology is relatively fixed. At present, there is a lack of reasonable design schemes and efficient and stable Post-CMOS post-processing processes. The schemes of later mask, exposure, and etching cannot guarantee the processing accuracy, efficiency, and yield of the devices, which limits the mass processing of sensors to a certain extent.

[0005] MEMS pressure sensors originated from automotive applications. In recent years, their scope of other applications has been continuously expanding. Especially in the medical field, pressure sensors are booming. A pressure sensor is a device that can sense pressure signals and convert them into electrical signals and output them correctly according to a certain mechanism. It can be divided into piezoresistive, capacitive, fiber optic, resonant, and piezoelectric types, etc. Except for capacitive pressure sensors, other pressure sensors require specific sensing materials to achieve the sensing of pressure signals, and it is difficult to integrate piezoresistive, piezoelectric and other sensing materials in the patterned CMOS process. Capacitive pressure sensors sense pressure through the change in the distance between the capacitor plates. One or both plates are suspended in a cavity, and the cavity is sealed through a certain bonding and sealing process. Research work on capacitive pressure sensors in the academic community has been reported. For example, some scholars have proposed a new capacitive pressure sensor that integrates an on-chip interface circuit in a vacuum-sealed cavity, with a pressure sensitivity of 1100 ppm / mmHg achieved, but it has a large temperature drift and low accuracy. Other scholars have proposed a design of a double deformable diaphragm CMOS-MEMS capacitive pressure sensor to improve the sensitivity of the device (0.26 fF / kPa), but the double diaphragm design makes the structure relatively fragile and the power consumption has not been improved. Therefore, it is an urgent problem to develop a CMOS capacitive pressure sensor with stable structure and excellent performance and its post-processing technology. Summary of the Invention

[0006] The main object of the present invention is to provide a CMOS-MEMS monolithic integrated flow and pressure sensor and its preparation method; the present invention overcomes the deficiencies of the prior art to meet the needs of single-chip flow and pressure integrated sensors in the fields of intelligent medicine, health monitoring, etc. The sensor uses a Post-CMOS process that does not require mask operations, effectively reducing the complexity of the post-processing of the entire device and greatly improving the efficiency of the entire Post-CMOS post-processing. The sensing part needs to be suspended to make it have the characteristics of low heat dissipation and fast response speed.

[0007] The object of the present invention is achieved through the following technical solutions.

[0008] A CMOS-MEMS monolithic integrated flow and pressure sensor includes a silicon substrate layer (1) and a silicon dioxide structure layer (2). The silicon dioxide structure layer (2) is disposed above the silicon substrate layer (1). The silicon dioxide structure layer (2) includes PAD regions provided at both ends and a gas flow sensor region and a gas pressure sensor region provided in the center. In the PAD regions, the silicon dioxide material and the metal material are arranged in an overlapping manner, and the metal via penetrates through the first metal layer to the fifth metal layer. The gas flow sensor region includes a heating resistor (4), a first thermistor (3) and a second thermistor (5) distributed on both sides of the heating resistor (4). The heating resistor (4), the first thermistor (3) and the second thermistor (5) are placed in the silicon dioxide material, and the whole is coated with Parylene C (10), fixed on both sides, and suspended above the cavity (6). The gas pressure sensor region includes an upper capacitor plate (7), a lower capacitor plate (8) and a cavity between the upper capacitor plate (7) and the lower capacitor plate (8). The upper capacitor plate (7) and the lower capacitor plate (8) are placed in the silicon dioxide material, and the surfaces are covered with Parylene C (10). The channel between the cavity and the etched flow channel (11) is filled and covered with Parylene C (10) to form a sealed cavity (9), and at the same time, a layer of Parylene C material covers the inner wall of the cavity.

[0009] A preparation method of a CMOS-MEMS monolithic integrated flow and pressure sensor adopts a Post-CMOS method without MASK operation, and includes the following steps:

[0010] Step 1: Design a CMOS die using a 0.18um 1P6M process. Design a reasonable metal layer pattern and metal via in the PAD region, so that the silicon dioxide material fills the space between the sixth metal layer and the fifth metal layer. Therefore, when the metal is etched, a natural mask for the PAD region is formed to protect its structure. Design a reasonable polysilicon layer pattern in the gas flow sensor region to form the heating resistor, the first thermistor and the second thermistor of the flow sensor. Design a reasonable first metal layer pattern and metal via in the gas flow sensor region, so that a thin silicon dioxide material is reserved above the heating resistor, the first thermistor and the second thermistor to form a natural mask for the heating resistor, the first thermistor and the second thermistor. At the same time, the via penetrates directly to the silicon substrate to become the channel for subsequent silicon etching. Design a reasonable metal layer pattern and metal via in the gas pressure sensor region to form the upper and lower capacitor plates and the cavity between the upper and lower capacitor plates.

[0011] Step 2: The CMOS bare chip obtained in Step 1 is subjected to wet etching to remove the redundant metal layer, forming trenches and microcavities; then, silicon dioxide etching is carried out to expose the PAD and the substrate silicon; then, DRIE etching is carried out, and the above-mentioned SiO2 and PAD serve as masks for silicon to form substrate silicon trenches. Finally, XeF2 etching is carried out to form a suspended structure for the flow sensor, and a prefabricated chip is obtained.

[0012] Step 3: The prefabricated chip obtained in Step 2 is covered with a vapor deposition of Parylene C to protect the surface structure of the sensor and seal the cavity of the pressure sensor, forming the entire single-chip flow and pressure integrated sensor.

[0013] Beneficial effects:

[0014] 1. By designing the metal layer pattern, the present invention makes it a natural mask for the polysilicon layer, so that all functional components of the sensor device can be etched without a MASK and without damage.

[0015] 2. The present invention uses the CMOS process to simultaneously thin and precisely pattern the sensing structure during the wet etching of the metal, and finally adopts the DRIE anisotropic silicon etching method and the XeF2 isotropic silicon etching method to form a thermal gas flow sensor using a suspended structure without a MASK.

[0016] 3. Utilizing the multi-metal layer characteristics of the CMOS process, the present invention designs the upper and lower capacitor plates and the sealed cavity therebetween, and finally seals the cavity by vapor deposition of the high-quality sealing material Parylene C to form a capacitive gas pressure sensor without a MASK.

[0017] 4. Monolithic multi-sensor integration is achieved. The integrated and continuous process greatly reduces the cost of the sensor. Moreover, the sensor has good stability, high sensitivity, low heat dissipation, and fast response / return performance. The single-chip flow and pressure integrated sensor is small in size and high in integration, so it has the potential to be a small and multi-functional special sensor. It can effectively solve the problems of large volume and poor adaptability caused by the simple stacking of current single-function sensors, as well as the problems of high cost, large heat dissipation, relatively limited sensitivity and response speed of the single-chip flow and pressure integrated sensors available on the market. And the preparation process is simple, which is convenient for large-scale production from the perspective of industrialization. Description of the Drawings

[0018] Figure 1It is the preparation flow chart of the CMOS-MEMS monolithic integrated flow and pressure sensor of the present invention; wherein, Figure a is the designed CMOS die, Figure b shows wet etching of the CMOS die to form trenches and microcavities, Figure c shows silicon dioxide etching to expose the PAD and the silicon substrate, Figure d shows DRIE etching to form trenches on the silicon substrate, Figure e shows XeF2 etching to release the suspended thin film, and Figure f shows finally coating the device with Praylene C to seal the microcavity of the pressure sensor.

[0019] Figure 2 It is the three-dimensional structure schematic diagram of the CMOS-MEMS thermal flow sensor in the CMOS-MEMS monolithic integrated flow and pressure sensor of the present invention; wherein, Figure a is the structure schematic diagram of the CMOS-MEMS thermal flow sensor, and Figure b is the cross-sectional view and model parameters of the CMOS-MEMS thermal flow sensor (ΔT is the temperature difference between the first thermistor 1 (T1) and the second thermistor 2 (T2), that is, the temperature output of the sensor).

[0020] Figure 3 It is the structure schematic diagram of the CMOS-MEMS capacitive pressure sensor in the CMOS-MEMS monolithic integrated flow and pressure sensor of the present invention;

[0021] Figure 4 It is the cross-sectional schematic diagram of the CMOS-MEMS monolithic integrated flow and pressure sensor of the present invention;

[0022] Among them, 1 - silicon substrate layer; 2 - silicon dioxide structure layer; 3 - first thermistor; 4 - heating resistor; 5 - second thermistor; 6 - cavity; 7 - upper capacitor plate; 8 - lower capacitor plate; 9 - sealed cavity; 10 - Parylene C; 11 - etched flow channel. Detailed implementation mode

[0023] To better illustrate the purpose and advantages of the present invention, the following further describes the invention content in combination with the drawings and examples.

[0024] See Figures 2 to 4As shown in the figure: A CMOS-MEMS monolithic integrated flow and pressure sensor disclosed in this embodiment includes a silicon substrate layer 1 and a silicon dioxide structure layer 2, and the silicon dioxide structure layer 2 is disposed above the silicon substrate layer 1; the silicon dioxide structure layer 2 includes PAD regions disposed at both ends and a gas flow sensor region and a gas pressure sensor region disposed in the center; in the PAD regions, the silicon dioxide material and the metal material are overlapped and arranged, and the metal via penetrates through the first layer of metal to the fifth layer of metal; the gas flow sensor region includes a heating resistor 4 and a first thermistor 3 and a second thermistor 5 distributed on both sides of the heating resistor 4. The heating resistor 4, the first thermistor 3 and the second thermistor 5 are placed in the silicon dioxide material, and are integrally coated with Parylene C 10, fixed on both sides, and integrally suspended above the cavity 6; the gas pressure sensor region includes an upper capacitor plate 7 and a lower capacitor plate 8 and a cavity between the upper capacitor plate 7 and the lower capacitor plate 8. The upper capacitor plate 7 and the lower capacitor plate 8 are placed in the silicon dioxide material, and the surfaces are covered by Parylene C 10. The channel between the cavity and the etched flow channel 11 is covered and filled with Parylene C 10 to form a sealed cavity 9, and at the same time, the inner wall of the cavity is covered with a layer of Parylene C 10 material.

[0025] The material of the substrate is a silicon wafer.

[0026] The material of the structure layer is silicon dioxide.

[0027] The materials of the flow sensor heating resistor and the first and second thermistors are polysilicon.

[0028] Parylene C is a protective polymer material, which can be vapor deposited under vacuum. The penetrating power of the molecules enables it to form a high-quality pinhole-free protective layer and sealing structure inside, at the bottom, and around the components.

[0029] The materials of the upper and lower capacitor plates of the pressure sensor are aluminum.

[0030] The materials of the polymer protective layer on the surface of the sensor structure and the sealing structure are Parylene C.

[0031] See Figure 1 As shown in the figure: The present invention also provides a preparation method for a CMOS-MEMS monolithic integrated flow and pressure sensor. Figure 1 It is a preparation flow chart of a single-chip flow and pressure integrated sensor in the implementation scheme of the present invention, including the following steps:

[0032] Step 1: Design a CMOS die using the 0.18um 1P6M process. Design a reasonable metal layer pattern and metal vias in the PAD area to fill the space between the sixth metal layer and the fifth metal layer with silicon dioxide material. Thus, when etching the metal, a natural mask for the PAD area is formed to protect its structure. Design a reasonable polysilicon layer pattern in the gas flow sensor area to form the heating resistor, the first thermistor, and the second thermistor of the flow sensor. Design a reasonable first metal layer pattern and metal vias in the gas flow sensor area to retain a thin layer of silicon dioxide material above the heating resistor, the first thermistor, and the second thermistor, forming a natural mask for them. At the same time, the via penetrates directly to the silicon substrate to become the channel for subsequent silicon etching. Design a reasonable metal layer pattern and metal vias in the gas pressure sensor area to form the upper and lower capacitor plates and the cavity between them. Using the CMOS process, sensor chips can be produced on a large scale, in multiple batches, and with a high yield, greatly reducing the production cost.

[0033] Step 2: Perform wet etching on the CMOS die obtained in Step 1 to remove the excess metal layer, forming trenches and microcavities. For example, use an etching solution with a ratio of H2SO4:H2O2 = 3:1 and etch for 10 minutes at 90°C. Then perform silicon dioxide etching to expose the PAD and the substrate silicon. For example, use reactive ion etching (RIE). Then perform DRIE etching. The SiO2 and PAD mentioned above are used as masks for silicon to form trenches in the substrate silicon. DRIE, also known as deep reactive ion etching, is a dry etching process for high aspect ratio silicon based on fluorine-based gases. Finally, perform XeF2 etching. Use XeF2 gas for dry isotropic etching, which can etch simultaneously towards both sides and the bottom, thus forming a suspended structure for the heater and the two thermistors, obtaining a prefabricated chip.

[0034] Step 3: Perform vapor deposition and coverage of Parylene C on the prefabricated chip obtained in Step 2 to seal the cavity of the pressure sensor and protect the surface of the sensor components, finally forming the entire single-chip flow and pressure integrated sensor. For example: deposit a Parylene C thin film of about 10um by chemical vapor deposition (CVD).

[0035] The present invention adopts a 0.18um 1P6M CMOS semiconductor process to form the structures required for the sensor on a silicon wafer at one time, including a silicon substrate layer 1 and a silicon dioxide structure layer 2, and the silicon dioxide structure layer 2 is disposed above the silicon substrate layer 1; the silicon dioxide structure layer 2 includes PAD regions disposed at both ends and a gas flow sensor region and a gas pressure sensor region disposed in the center; in the PAD regions, the silicon dioxide material and the metal material are overlapped and arranged, and the metal via penetrates through the first layer of metal to the fifth layer of metal; the gas flow sensor region includes a heating resistor 4 and a first thermistor 3 and a second thermistor 5 distributed on both sides of the heating resistor 4. The heating resistor 4, the first thermistor 3 and the second thermistor 5 are placed in the silicon dioxide material, and the whole is coated with Parylene C 10 material, fixed on both sides, and suspended above the cavity 6 as a whole; the gas pressure sensor region includes an upper capacitor plate 7 and a lower capacitor plate 8 and a cavity between the upper capacitor plate 7 and the lower capacitor plate 8. The upper capacitor plate 7 and the lower capacitor plate 8 are placed in the silicon dioxide material and the surfaces are covered with Parylene C 10. The channel between the cavity and the etching channel 11 is filled and covered with Parylene C 10 to form a sealed cavity 9, and at the same time, the inner wall of the cavity is covered with a layer of Parylene C 10 material.

[0036] The practical applications of the CMOS-MEMS monolithic integrated flow and pressure sensor provided by the present invention may include: attaching the sensor to a carrier, leading out wires at the ends, connecting an external signal processing module, and simultaneously detecting the gas flow and gas pressure in the environment.

[0037] There is a certain relationship between the resistance value or capacitance value in the present invention and the gas flow and gas pressure, and the signal response is determined by the change of the resistance value or capacitance value.

[0038] The present invention designs a sensor structure in one go using a 0.18um 1P6M process, including a silicon substrate layer 1 and a silicon dioxide structure layer 2, as well as various functional components contained in the silicon dioxide structure layer. Then, a CMOS-MEMS monolithic integrated flow and pressure sensor with a suspended structure and thinning treatment is obtained through a post-CMOS process without the need for a MASK. Different from the preparation methods of ordinary CMOS-MEMS integrated sensors, the present invention creatively proposes a preparation method for a CMOS-MEMS monolithic integrated flow and pressure sensor. By designing the metal layer pattern to be a natural mask for the polysilicon layer, the heater, temperature sensing area, and capacitance detection structure of the sensor device can be etched out without a MASK and without damage. Different from ordinary CMOS-MEMS integrated sensors, the present invention uses the silicon oxide region as a natural mask for the PAD, avoiding complex lithography steps, so that the PAD can be exposed without a MASK and without damage, facilitating the integration with the peripheral test circuit. Different from ordinary calorimetric flow sensors, the present invention uses the CMOS process to simultaneously thin and precisely pattern the sensing structure during the metal wet etching process. Finally, the DRIE anisotropic silicon etching method and the XeF2 isotropic silicon etching method are used to form a MASK-free thermal flow sensor using a suspended structure. Different from ordinary capacitive pressure sensors, the present invention uses the multi-metal layer characteristics of the CMOS process to design the upper and lower capacitor plates and the sealed cavity between them. Finally, the cavity is sealed by evaporating the high-quality sealing material Parylene C to form a MASK-free capacitive pressure sensor. Since the present invention manufactures the sensor with a suspended structure using an integrated CMOS processing technology and a post-processing technology without a MASK, the sensor is robust, highly sensitive, has good stability, a fast response speed, and low heat dissipation, and has the characteristics of a post-processing technology without a MASK.

[0039] The design and processing method of a CMOS-MEMS monolithic integrated flow and pressure sensor provided by the present invention realizes the integration of multiple sensors on a single chip. The integrated and continuous process greatly reduces the cost of the sensor, and the sensor has good stability, high sensitivity, low heat dissipation, and fast response / reply performance. The single-chip flow and pressure integrated sensor is small in size and high in integration, so it has the potential to be a small and multi-functional dedicated sensor. It can effectively solve the problems of large volume and poor adaptability caused by the simple stacking of current single-function sensors, as well as the problems of high cost, large heat dissipation, and relatively limited sensitivity and response speed of the single-chip flow and pressure integrated sensors available on the market. Moreover, the preparation process is simple and convenient for large-scale production from an industrialization perspective.

[0040] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application. Other structures and principles are the same as those of the prior art and will not be elaborated here.

Claims

1. A CMOS-MEMS monolithic integrated flow and pressure sensor, characterized in that: It includes a silicon substrate layer (1) and a silicon dioxide structure layer (2), and the silicon dioxide structure layer (2) is disposed above the silicon substrate layer (1); the silicon dioxide structure layer (2) includes PAD regions disposed at both ends and a gas flow sensor region and a gas pressure sensor region disposed in the center; in the PAD regions, silicon dioxide materials and metal materials are arranged in an overlapping manner, and metal vias penetrate through the first metal layer to the fifth metal layer; the gas flow sensor region includes a heating resistor (4) and a first thermistor (3) and a second thermistor (5) distributed on both sides of the heating resistor (4), the heating resistor (4), the first thermistor (3) and the second thermistor (5) are placed in silicon dioxide materials, and the whole is coated with Parylene C (10), fixed on both sides, and the whole is suspended above a cavity (6); the gas pressure sensor region includes an upper capacitor plate (7) and a lower capacitor plate (8) and a cavity between the upper capacitor plate (7) and the lower capacitor plate (8), the upper capacitor plate (7) and the lower capacitor plate (8) are placed in silicon dioxide materials, and the surfaces are covered by Parylene C (10), and the channel between the cavity and the etching channel (11) is filled and covered by Parylene C (10) to form a sealed cavity (9), and at the same time, a layer of Parylene C material is covered on the inner wall of the cavity.

2. A method for preparing the sensor according to claim 1, characterized in that: Adopt a Post-CMOS method that does not require MASK operation, including the following steps: Step 1: Design a CMOS die using a 0.18um 1P6M process, and design a reasonable metal layer pattern and metal vias in the PAD regions, so that the space between the sixth metal layer and the fifth metal layer is filled with silicon dioxide materials. Therefore, when etching the metal, a natural mask for the PAD regions is formed to protect their structures; Design a reasonable polysilicon layer pattern in the gas flow sensor region to form the heating resistor, the first thermistor and the second thermistor of the flow sensor; design a reasonable first metal layer pattern and metal vias in the gas flow sensor region, so that a thin layer of silicon dioxide material is reserved above the heating resistor, the first thermistor and the second thermistor to form a natural mask for the heating resistor, the first thermistor and the second thermistor, and at the same time, the vias lead directly to the silicon substrate to become the channels for subsequent silicon etching; design a reasonable metal layer pattern and metal vias in the gas pressure sensor region to form the upper and lower capacitor plates and the cavity between the upper and lower capacitor plates; Step 2: Perform wet etching on the CMOS die obtained in Step 1 to remove the redundant metal layers to form trenches and microcavities; then perform silicon dioxide etching to expose the PAD and the base silicon; Perform DRIE etching, and the above-mentioned SiO2 and PAD are used as masks for silicon to form trenches in the base silicon. Finally, perform XeF2 etching to form a suspended structure for the flow sensor to obtain a prefabricated chip; Step 3: Perform evaporation coating of Parylene C on the prefabricated chip obtained in Step 2 to protect the surface structure of the sensor and seal the cavity of the pressure sensor to form the entire single-chip flow and pressure integrated sensor.

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