CN118225306A - A MEMS high temperature pressure sensor and a method for preparing a sensor chip - Google Patents

Abstract

The invention discloses a MEMS high-temperature pressure sensor and a preparation method of a sensor chip, which belong to the field of MEMS pressure sensors, wherein in a SiC-based MEMS high-temperature pressure sensor, the packaging of the sensor chip is realized by arranging a double-layer packaging structure, and meanwhile, a cooling liquid circulating channel is arranged in the double-layer packaging structure, so that the whole sensor can be kept to operate under the condition of higher environmental temperature, and the problem that the piezoresistive pressure sensor in the prior art is not suitable for the environment higher than 250 ℃ is solved. In the preparation method of the sensor chip, the technology of the SiO2 sacrificial layer is adopted, the problems of long etching time and high cost of SiC chip preparation are solved, meanwhile, the problem of stress mismatch between Si materials and SiC materials is avoided, and the sensor precision is improved.

Description

A MEMS high temperature pressure sensor and a method for preparing a sensor chip

Technical Field

The present invention belongs to the field of MEMS pressure sensors, and in particular relates to a MEMS high-temperature pressure sensor and a method for preparing a sensor chip.

Background technique

With the development of the information age, people need different types of MEMS pressure sensors to sense external information, especially for high-temperature environments such as high-temperature oil wells in the petroleum industry, chemical reaction towers, and aircraft engine cavities. We need to use high-temperature resistant pressure sensors for pressure measurement.

At present, piezoresistive pressure sensor chips are mainly made of Si-based materials. Their manufacturing process is mature, stable and efficient. However, the semiconductor Si bandgap is narrow (1.12eV) and cannot be used in high-temperature environments. The commonly used ambient temperature is below 250°C.

As a third-generation semiconductor material, SiC has a variety of crystal structures, and the most common ones are α-SiC and β-SiC. Among them, β-SiC is mainly 3C-SiC of the cubic system, while α-SiC can be divided into 2H, 4H, and 6H types. Due to the essential properties of SiC materials, it has the advantages of wide bandgap (2.3eV for 3C-SiC), good thermal conductivity, and good chemical stability. It is an ideal material for making high-temperature pressure sensors and has broad application prospects. Therefore, when preparing high-temperature pressure sensors, SiC materials are mainly used as substrates. However, due to the good chemical stability of SiC and the difficulty in etching, dry etching is usually used to form a pressure back cavity, resulting in long etching time and high cost. Some pressure sensors use a combination of Si material substrate and SiC film layer, while taking advantage of the advantages of easy etching of Si material and high temperature resistance of SiC. However, the thermal expansion coefficients of Si substrate and SiC film layer are quite different, which easily introduces stress mismatch problems, resulting in reduced accuracy of sensor chips.

Summary of the invention

In view of the above-mentioned deficiencies in the prior art, the present invention provides a SiC-based MEMS high-temperature pressure sensor and a method for preparing a sensor chip thereof, which solves the problems in the prior art that the piezoresistive pressure sensor is not suitable for environments above 250°C and the sensor chip production time is long.

In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

A MEMS high-temperature pressure sensor is provided, which includes a double-layer packaging structure, the double-layer packaging structure is a hollow cylindrical structure, a pressure-sensitive diaphragm is arranged on the top of the double-layer packaging structure, a hollow annular diaphragm is arranged in the middle of the double-layer packaging structure, and a pressure transmission hole is arranged in the middle of the hollow annular diaphragm; a chip base is arranged at the bottom of the double-layer packaging structure, and a sensor chip is arranged on the chip base;

A coolant circulation channel is arranged in the packaging wall of the double-layer packaging structure, and the coolant circulation channel is connected with the interior of the hollow annular diaphragm; a coolant inlet and a coolant outlet are respectively arranged on the bottom end surface and the top side wall of the double-layer packaging structure, and the coolant inlet and the coolant outlet are both connected with the coolant circulation channel, and the coolant inlet and the coolant outlet are connected with an external cooling device.

The basic principle of a MEMS high-temperature pressure sensor in this scheme is: the pressure to be measured is transmitted to the sensor chip through the pressure-sensitive diaphragm and the transmission medium, and the sensor chip detects the change in pressure according to the change in the bridge output voltage; the sensor chip is packaged by setting a double-layer packaging structure, and a coolant circulation channel is provided in the double-layer packaging structure. An external cooling device can be used to pump coolant into the coolant circulation channel, so that the entire MEMS high-temperature pressure sensor always maintains a low operating temperature inside, so that the entire MEMS high-temperature pressure sensor can be used at a higher ambient temperature, while improving the performance of the sensor in a high-temperature environment, thereby improving the monitoring accuracy of the MEMS high-temperature pressure sensor.

Further, as a specific setting mode of the double-layer packaging structure, the double-layer packaging structure includes an outer packaging layer and an inner packaging layer, both of which are hollow cylindrical structures, the inner packaging layer is sleeved inside the outer packaging layer, and the inner wall of the outer packaging layer and the outer wall of the inner packaging layer are provided with saw teeth along the axial direction of the double-layer packaging structure;

The chip base is fixedly connected to the inner wall of the inner packaging layer, the sensor chip is arranged on the upper surface of the chip base, and the sensor chip is located below the pressure transmission hole;

The signal line of the sensor chip passes through the chip base and is located outside the double-layer packaging structure.

The inner wall of the outer packaging layer and the outer wall of the inner packaging layer are provided with saw teeth, so that the coolant circulation channel is in a zigzag shape, increasing the contact area between the coolant and the side wall of the coolant circulation channel and improving the cooling effect.

Furthermore, the sensor chip includes a temperature resistor, which can monitor the temperature of the sensor chip in real time and transmit the temperature signal to an external cooling device. The external cooling device adjusts the flow rate of the coolant according to the real-time monitored temperature to keep the sensor chip in a low temperature environment, so that the sensor chip can be used in a high temperature environment of nearly 500°C while maintaining high accuracy.

Furthermore, as a specific setting method of the sensor chip, the sensor chip includes a SiC substrate, the lower end surface of the SiC substrate is fixedly connected to the upper surface of the chip base, a SiC device layer is arranged on the upper end surface of the SiC substrate, a pressure cavity is arranged between the SiC device layer and the SiC substrate, a plurality of varistors and temperature resistors are arranged on the upper end surface of the SiC device layer, and a protective layer is arranged on the SiC device layer; the plurality of varistors are connected by metal leads to form an electric bridge; the plurality of varistors and temperature resistors are electrically connected to the signal line of the sensor chip.

Since SiC has good chemical stability and high temperature resistance, the sensor chip can be used in high temperature environments of nearly 500°C while maintaining high accuracy, while Si-based materials can only be used at around 200°C.

At the same time, the SiC substrate and SiC device layer in the sensor chip are made of the same material, avoiding the stress mismatch problem between Si material and SiC material, and further improving the sensor accuracy.

The present invention also provides a method for preparing a sensor chip, which comprises the following steps:

S1. Select SiC substrate;

S2, preparing a SiO2 film layer on the upper surface of the SiC substrate;

S3, partially etching the SiO2 film layer;

S4, preparing a SiC device layer on the upper surface of the SiC substrate, wherein the SiC device layer covers the SiC substrate and the SiO2 film layer;

S5, preparing a varistor and a temperature resistor on the surface of the SiC device layer by ion implantation;

S6, preparing a Si3N4 film layer on the surface of the SiC device layer, and making an opening in the middle of the prepared Si3N4 film layer, so that the bottom of the opening is in contact with the surface of the SiC device layer, exposing the surface of the SiC device layer;

S7, opening the surface of the exposed SiC device layer until the SiO2 film layer is exposed;

S8, using HF and NH4F solution to etch the SiO2 film layer to form a pressure cavity;

S9, removing the Si3N4 film layer on the surface of the SiC device layer by a wet etching process, and redepositing the Si3N4 film layer by a chemical vapor deposition method, wherein the Si3N4 film layer seals the opening on the SiC device layer and forms a protective layer on the surface of the SiC device layer;

S10. Use a photolithography process to make an opening on the surface of the protective layer, and deposit a metal lead in the opening. The metal lead connects the varistor to form an electric bridge.

Furthermore, in step S1, the thickness of the SiC substrate is 300um-500um.

Furthermore, in step S2, a SiO2 film layer is prepared on the upper surface of the SiC substrate by using a chemical vapor deposition method, and the thickness of the SiO2 film layer is 1-10 μm.

Furthermore, in step S3, the SiO2 film layer is etched by photolithography technology; in step S4, the SiC device layer is prepared on the surface of the SiC substrate by chemical vapor deposition; in step S6, the Si3N4 film layer is prepared by photolithography and chemical vapor deposition.

The traditional method of preparing sensor chips is generally to use SiC substrates to prepare pressure sensor chips, and usually dry etching is used to form a back cavity. This method takes a long time to etch, is costly, and is not conducive to mass production. However, the method of preparing sensor chips in the present invention uses sacrificial layer technology, does not require etching of the SiC substrate, only needs to form an opening on the surface of the SiC device layer, and then etch the SiO2 sacrificial layer. This method can reduce chip preparation time and save costs.

The beneficial effects of the present invention are as follows: In the SiC-based MEMS high-temperature pressure sensor and the preparation method of the sensor chip thereof, in the SiC-based MEMS high-temperature pressure sensor, the sensor chip is packaged by setting a double-layer packaging structure, and a coolant circulation channel is set in the double-layer packaging structure, so that the entire device is kept running at a relatively high temperature, solving the problem that the piezoresistive pressure sensor in the prior art is not suitable for an environment above 250°C. In the preparation method of the sensor chip, the SiO2 sacrificial layer technology is used to solve the problems of long etching time and high cost in the preparation of the SiC chip, while avoiding the stress mismatch problem between the Si material and the SiC material, thereby improving the sensor accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the internal structure of a SiC-based MEMS high-temperature pressure sensor.

Figure 2 is a schematic diagram of the air pressure transmission and coolant circulation of the SiC-based MEMS high-temperature pressure sensor.

FIG3 is a schematic diagram of the three-dimensional structure of a sensor chip.

FIG. 4 is a schematic diagram of the preparation process of the sensor chip.

Among them, 1. double-layer packaging structure; 101. outer packaging layer; 102. inner packaging layer; 2. pressure sensitive diaphragm; 3. hollow annular diaphragm; 4. pressure transfer hole; 5. chip base; 6. sensor chip; 601. SiC substrate; 602. SiC device layer; 603. pressure cavity; 604. varistor; 605. temperature resistor; 606. Si3N4 film layer; 607. protective layer; 608. SiO2 film layer; 609. metal lead; 7. coolant circulation channel; 8. coolant inlet; 9. coolant outlet; 10. signal line.

Detailed ways

The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

As shown in Figures 1 and 2, the present invention provides a MEMS high-temperature pressure sensor, which includes a double-layer packaging structure 1, the double-layer packaging structure 1 is a hollow cylindrical structure, a pressure-sensitive diaphragm 2 is arranged on the top of the double-layer packaging structure 1, a hollow annular diaphragm 3 is arranged in the middle of the double-layer packaging structure 1, and a pressure transfer hole 4 is arranged in the middle of the hollow annular diaphragm 3; a chip base 5 is arranged at the bottom of the double-layer packaging structure 1, and a sensor chip 6 is arranged on the chip base 5.

A coolant circulation channel 7 is provided in the packaging wall of the double-layer packaging structure 1, and the coolant circulation channel 7 is connected to the interior of the hollow annular diaphragm 3; a coolant inlet 8 and a coolant outlet 9 are respectively provided on the bottom end surface and the top side wall of the double-layer packaging structure 1, and the coolant inlet 8 and the coolant outlet 9 are both connected to the coolant circulation channel 7, and the coolant inlet 8 and the coolant outlet 9 are connected to an external cooling device.

As shown in Figure 2, in Figure 2, the dotted arrow indicates the flow direction of the coolant, and the solid arrow indicates the flow direction of the pressure to be measured. The pressure to be measured transmits the pressure to the sensor chip 6 through the pressure sensitive diaphragm 2 and the transmission medium, and the sensor chip 6 detects the change in pressure according to the change in the bridge output voltage; the packaging of the sensor chip 6 is achieved by setting a double-layer packaging structure 1, and a coolant circulation channel 7 is provided in the double-layer packaging structure 1. An external cooling device can be used to pump coolant into the coolant circulation channel 7, so that the entire MEMS high-temperature pressure sensor always maintains a low operating temperature inside, so that the entire MEMS high-temperature pressure sensor can be used at a higher ambient temperature while improving the performance of the sensor in a high-temperature environment, thereby improving the monitoring accuracy of the MEMS high-temperature pressure sensor.

As a specific arrangement of the double-layer packaging structure 1, the double-layer packaging structure 1 includes an outer packaging layer 101 and an inner packaging layer 102, both of which are hollow cylindrical structures. The inner packaging layer 102 is sleeved inside the outer packaging layer 101, and the inner wall of the outer packaging layer 101 and the outer wall of the inner packaging layer 102 are provided with saw teeth along the axial direction of the double-layer packaging structure 1; the chip base 5 is fixedly connected to the inner wall of the inner packaging layer 102, and the sensor chip 6 is provided on the upper surface of the chip base 5, and the sensor chip 6 is located below the pressure transmission hole 4; the signal line 10 of the sensor chip 6 passes through the chip base 5 and is located outside the double-layer packaging structure 1. The inner wall of the outer packaging layer 101 and the outer wall of the inner packaging layer 102 are provided with saw teeth, so that the coolant circulation channel 7 is in a zigzag shape, the contact area between the coolant and the side wall of the coolant circulation channel 7 is increased, and the cooling effect is improved.

As shown in Figure 3, the sensor chip 6 includes a temperature resistor 605, which can monitor the temperature of the sensor chip 6 in real time and transmit the temperature signal to an external cooling device. The external cooling device adjusts the flow rate of the coolant according to the real-time monitored temperature to keep the sensor chip 6 in a low temperature environment, so that the sensor chip 6 can be used in a high temperature environment of nearly 500°C while maintaining high accuracy.

As shown in Figures 3 and 4, as a specific setting method of the sensor chip 6, the sensor chip 6 includes a SiC substrate 601, the lower end surface of the SiC substrate 601 is fixedly connected to the upper surface of the chip base 5, the upper end surface of the SiC substrate 601 is provided with a SiC device layer 602, a pressure cavity 603 is provided between the SiC device layer 602 and the SiC substrate 601, the upper end surface of the SiC device layer 602 is provided with a plurality of varistors 604 and temperature resistors 605, and a protective layer 607 is provided on the SiC device layer 602; the plurality of varistors 604 are connected by metal leads 609 to form an electric bridge; the plurality of varistors 604 and temperature resistors 605 are electrically connected to the signal line 10 of the sensor chip 6.

Since SiC has the characteristics of good chemical stability and high temperature resistance, the sensor chip 6 can be used in a high temperature environment of nearly 500°C while maintaining high accuracy, while Si-based materials can only be used at around 200°C.

At the same time, the SiC substrate 601 and the SiC device layer 602 in the sensor chip 6 are made of the same material, which avoids the stress mismatch problem between the Si material and the SiC material and further improves the sensor accuracy.

As shown in FIG. 4 , the present solution also provides a method for preparing a sensor chip 6, which comprises the following steps:

S1. As shown in FIG. 4 a, a SiC substrate 601 is selected; the thickness of the SiC substrate 601 is 300 um to 500 um.

S2. As shown in FIG. 4 b, a SiO2 film layer 608 is prepared on the upper surface of the SiC substrate 601 by chemical vapor deposition. The SiO2 film layer 608 is a sacrificial layer. The thickness of the SiO2 film layer 608 can be matched according to the pressure range, which is generally 1 to 10 μm.

S3. As shown in Figure c of Figure 4, the SiO2 film layer 608 is partially etched using photolithography technology, so that after the SiC device layer 602 is prepared, the SiC device layer 602 can be partially combined with the SiC substrate 601. This avoids the stress mismatch problem between the Si material and the SiC material, and further improves the accuracy of the sensor chip 6.

S4, as shown in FIG. 4 d, a SiC device layer 602 is prepared on the upper surface of the SiC substrate 601 by chemical vapor deposition, and the SiC device layer 602 covers the SiC substrate 601 and the SiO2 film layer 608;

S5, as shown in Figure e of FIG4 , a varistor 604 and a temperature resistor 605 are prepared on the surface of the SiC device layer 602 by ion implantation;

S6. As shown in FIG. 4 f, a Si3N4 film layer 606 is prepared on the surface of the SiC device layer 602 by photolithography and chemical vapor deposition, and an opening is made in the middle of the prepared Si3N4 film layer 606, and the bottom of the opening is in contact with the surface of the SiC device layer 602, exposing the surface of the SiC device layer 602;

S7, as shown in FIG. 4 g, opening is performed on the surface of the exposed SiC device layer 602 until the SiO2 film layer 608 is exposed;

S8, as shown in FIG. 4 h, using HF and NH4F solution to etch the SiO2 film layer 608 to form a pressure cavity 603;

S9, as shown in FIG. 4 i, the Si3N4 film layer 606 on the surface of the SiC device layer 602 is removed by a wet etching process, and the Si3N4 film layer 606 is re-deposited by chemical vapor deposition. The Si3N4 film layer 606 seals the opening on the SiC device layer 602 and forms a protective layer 607 on the surface of the SiC device layer 602;

S10, as shown in FIG. 4 j, a photolithography process is used to make an opening on the surface of the protective layer 607, and a metal lead 609 is deposited in the opening. The metal lead 609 is connected to the varistor 604 to form an electric bridge.

The conventional method for preparing the sensor chip 6 is generally to prepare the pressure sensor chip 6 using the SiC substrate 601, and usually dry etching is used to form a back cavity. This method has a long etching time and high cost, which is not conducive to mass production of products. However, the method for preparing the sensor chip 6 in the present invention uses a sacrificial layer technology, which does not require etching the SiC substrate 601, but only requires forming an opening on the surface of the SiC device layer 602, and then etching the SiO2 sacrificial layer. This method can reduce chip preparation time and save costs.

In summary, in the SiC-based MEMS high-temperature pressure sensor and the preparation method of the sensor chip 6 thereof, in the SiC-based MEMS high-temperature pressure sensor, the sensor chip 6 is packaged by setting a double-layer packaging structure 1, and a coolant circulation channel 7 is provided in the double-layer packaging structure 1, so that the entire device is kept running at a relatively high temperature, solving the problem that the piezoresistive pressure sensor in the prior art is not suitable for an environment above 250°C. In the preparation method of the sensor chip 6, the SiO2 sacrificial layer technology is used to solve the problems of long etching time and high cost in the preparation of the SiC chip, while avoiding the stress mismatch problem between the Si material and the SiC material, thereby improving the sensor accuracy.

Claims (8)

1. A MEMS high temperature pressure sensor, characterized in that it comprises a double-layer packaging structure, the double-layer packaging structure is a hollow cylindrical structure, a pressure sensitive diaphragm is arranged on the top of the double-layer packaging structure, a hollow annular diaphragm is arranged in the middle of the double-layer packaging structure, and a pressure transmission hole is arranged in the middle of the hollow annular diaphragm; a chip base is arranged at the bottom of the double-layer packaging structure, and a sensor chip is arranged on the chip base; A coolant circulation channel is arranged in the packaging wall of the double-layer packaging structure, and the coolant circulation channel is connected to the interior of the hollow annular diaphragm; a coolant inlet and a coolant outlet are respectively arranged on the bottom end surface and the top side wall of the double-layer packaging structure, and the coolant inlet and the coolant outlet are both connected to the coolant circulation channel, and the coolant inlet and the coolant outlet are connected to an external cooling device. 2. The MEMS high temperature pressure sensor according to claim 1, characterized in that the double-layer packaging structure comprises an outer packaging layer and an inner packaging layer both of which are hollow cylindrical structures, the inner packaging layer is sleeved inside the outer packaging layer, and the inner wall of the outer packaging layer and the outer wall of the inner packaging layer are provided with saw teeth along the axial direction of the double-layer packaging structure; The chip base is fixedly connected to the inner wall of the inner packaging layer, the sensor chip is arranged on the upper surface of the chip base, and the sensor chip is located below the pressure transmission hole; The signal line of the sensor chip passes through the chip base and is located outside the double-layer packaging structure. 3 . The MEMS high temperature pressure sensor according to claim 2 , wherein the sensor chip comprises a temperature resistor. 4. The MEMS high-temperature pressure sensor according to claim 3 is characterized in that the sensor chip includes a SiC substrate, the lower end surface of the SiC substrate is fixedly connected to the upper surface of the chip base, the upper end surface of the SiC substrate is provided with a SiC device layer, a pressure cavity is provided between the SiC device layer and the SiC substrate, the upper end surface of the SiC device layer is provided with a plurality of varistors and the temperature resistor, and a protective layer is provided on the SiC device layer; the plurality of varistors are connected by metal leads to form an electric bridge; the plurality of varistors and the temperature resistor are electrically connected to the signal line of the sensor chip. 5. A method for preparing a sensor chip, characterized in that it is used to prepare the sensor chip in the MEMS high temperature pressure sensor according to claim 4, and the preparation method comprises the following steps: S1. Select SiC substrate; S2, preparing a SiO2 film layer on the upper surface of the SiC substrate; S3, partially etching the SiO2 film layer; S4, preparing a SiC device layer on the upper surface of the SiC substrate, wherein the SiC device layer covers the SiC substrate and the SiO2 film layer; S5, preparing a varistor and a temperature resistor on the surface of the SiC device layer by ion implantation; S6, preparing a Si3N4 film layer on the surface of the SiC device layer, and making an opening in the middle of the prepared Si3N4 film layer, so that the bottom of the opening is in contact with the surface of the SiC device layer, exposing the surface of the SiC device layer; S7, opening the surface of the exposed SiC device layer until the SiO2 film layer is exposed; S8, using HF and NH4F solution to etch the SiO2 film layer to form a pressure cavity; S9, removing the Si3N4 film layer on the surface of the SiC device layer by a wet etching process, and redepositing the Si3N4 film layer by a chemical vapor deposition method, wherein the Si3N4 film layer seals the opening on the SiC device layer and forms a protective layer on the surface of the SiC device layer; S10. Use a photolithography process to make an opening on the surface of the protective layer, and deposit a metal lead in the opening. The metal lead connects the varistor to form an electric bridge. 6 . The method for preparing a sensor chip according to claim 5 , wherein in step S1 , the thickness of the SiC substrate is 300 um to 500 um. 7. The method for preparing a sensor chip according to claim 5, characterized in that in step S2, a SiO2 film layer is prepared on the upper surface of the SiC substrate by using chemical vapor deposition, and the thickness of the SiO2 film layer is 1-10 μm. 8. The method for preparing a sensor chip according to claim 5 is characterized in that, in step S3, the SiO2 film layer is etched by photolithography technology; in step S4, the SiC device layer is prepared on the surface of the SiC substrate by chemical vapor deposition; in step S6, the Si3N4 film layer is prepared by photolithography and chemical vapor deposition.