Micro sensor chip and method for manufacturing the same

Abstract

The present application discloses a microsensor chip and a manufacturing method thereof. The microsensor chip includes a substrate, a film, a heating strip, a thermopile and a piezoresistive strip. The substrate is a silicon-based material substrate; the film is a composite film, which is arranged above the substrate; the heating strip is arranged on the upper surface of the film and located in the center of the film; two thermopiles are symmetrically arranged on both sides of the heating strip, one end of the thermopiles is arranged on the upper surface of the film, and the other end is arranged on the substrate; four piezoresistive strips are arranged on the upper surface of the film and form a Wheatstone bridge. The microsensor chip and the manufacturing method thereof disclosed in the present application integrate thermal flow sensing and piezoresistive pressure sensing on one chip, thereby solving the shortcomings of large volume and difficult packaging of traditional integrated sensor measurement modules. The microsensor chip provided by the present application has the characteristics of high integration, simple structure, small volume, and easy packaging, which reduces production costs and improves production efficiency.

Description

Technical Field

[0001] The present application relates to the field of sensor technology, and in particular to a microsensor chip and a method for manufacturing the same. Background Art

[0002] As the third revolution of the information technology industry, the Internet of Things requires the interconnection of all things through various information sensors. Traditional sensors are large in size, difficult to integrate and mass-produce, and therefore expensive, which is too costly for the Internet of Things technology, which has a huge demand for sensors. The development of micro-electromechanical technology (MEMS, Micro-Electro-Mechanical System) has promoted the commercialization of micro-sensors. This technology of manufacturing sensors on wafers can reduce the size of sensors to the micron level, so only one wafer can produce tens of thousands of sensor chips, which greatly reduces the cost of sensors. In recent years, as sensor chips have become smaller and smaller, the chip size of a single chip to achieve a single physical quantity sensing has approached the limit.

[0003] The sensitive principles of MEMS pressure sensors mainly include piezoresistive and capacitive. Although the sensitive principles of various pressure sensors are different, they all have in common that they need a sensitive element that senses changes in external pressure. The sensitive element is usually made of a film. Changes in external pressure cause the film to deform, and the external pressure can be inferred by measuring the deformation of the film.

[0004] The sensitive principles of MEMS flow sensors mainly include thermal and differential pressure. The thermal principle is usually based on the principle of anemometer or calorimeter, and the flow rate is inferred by measuring the lost heat or the temperature difference on both sides of the heat source. The differential pressure type measures the pressure at two points in the flow channel to infer the flow rate. Among them, the thermal principle usually requires a thin film structure for heat insulation in order to improve the response time, reduce thermal mass, and isolate the heat transfer between the heat source and the substrate.

[0005] In the prior art, two pressure sensors are often used to form a pressure differential type or the pressure sensor chip and the flow sensor chip are packaged in a tube shell to achieve integrated sensing measurement of pressure and flow. This has higher requirements on the packaging process, the module is larger and heavier, and the cost performance is not high. Summary of the invention

[0006] In order to solve one or more of the above problems, the present application proposes a microsensor chip and a method for manufacturing the same.

[0007] According to one aspect of the present application, a microsensor chip is provided, including a substrate, a film, a heating strip, a thermopile and a piezoresistive strip, wherein the substrate is a silicon-based material substrate; the film is a composite film, arranged above the substrate; the heating strip is arranged on the upper surface of the film and located in the center of the film; two thermopiles are symmetrically arranged on both sides of the heating strip, one end of the thermopiles is arranged on the upper surface of the film, and the other end is arranged on the substrate; four piezoresistive strips are arranged on the upper surface of the film and form a Wheatstone bridge.

[0008] In some embodiments, the substrate is a square silicon-based substrate, thereby obtaining a symmetrical stress distribution and improving the linearity of the chip.

[0009] In some embodiments, the film is a composite film of silicon dioxide and silicon nitride, so that the composite film can be used as both a pressure sensing region and a region for lateral heat transfer to the substrate.

[0010] In some embodiments, the film is a square composite film, so that the film can obtain maximum strength and symmetrical stress distribution, thereby improving the linearity of the chip.

[0011] In some embodiments, a cavity is provided on the substrate corresponding to the film, so that the cavity plays a role of heat insulation, so that heat conduction mainly occurs on the upper surface of the film.

[0012] In some embodiments, the heating strip and the piezoresistive strip are made of P-type polysilicon. Therefore, the resistivity of the heating strip made of P-type polysilicon is not sensitive to temperature, so a voltage can be applied to both sides of the resistance strip to obtain constant power to achieve temperature compensation; at the same time, P-type polysilicon has a higher Sech coefficient, which can improve chip sensitivity.

[0013] In some embodiments, the thermopile is made of aluminum and P-type polysilicon. Thus, aluminum and P-type polysilicon form a thermocouple and are connected in series to form a thermopile, which can achieve higher sensitivity.

[0014] In some embodiments, four piezoresistive strips are arranged at the edge of the film. Therefore, the edge of the film is usually the location where the stress or strain is the largest, and the piezoresistive strips are arranged at the location where the stress or strain is the largest. The two positive and two negative piezoresistive strips form a differential structure, thereby obtaining the maximum sensitivity of the pressure-related bridge output.

[0015] According to another aspect of the present application, a method for manufacturing a microsensor chip is provided, comprising the following steps:

[0016] (1) Selecting a single crystal silicon wafer as the substrate;

[0017] (2) forming a silicon nitride layer on each side of the cleaned and dried single crystal silicon wafer;

[0018] (3) forming a polysilicon layer on each of the two silicon nitride layers obtained in step (2);

[0019] (4) forming a silicon dioxide layer on any one of the polysilicon layers obtained in step (3), wherein the polysilicon layer forming the silicon dioxide layer is the front polysilicon layer, and the other polysilicon layer is the back polysilicon layer;

[0020] (5) boron doping the front polysilicon layer;

[0021] (6) removing the silicon dioxide layer and excess polysilicon on the front polysilicon layer to form a heating strip, one arm of the thermopile and a piezoresistive strip;

[0022] (7) forming a silicon dioxide layer on the heating strip, one arm of the thermopile and the piezoresistive strip, and reserving a connection hole on the silicon dioxide layer by etching;

[0023] (8) sputtering aluminum on the silicon dioxide layer obtained in step (7), and etching to form another arm of the thermopile;

[0024] (9) sequentially forming a silicon dioxide layer and a silicon nitride layer on the heating strip, the thermopile and the piezoresistive strip;

[0025] (10) removing the local reverse polysilicon layer and its corresponding silicon nitride layer;

[0026] (11) Wet etching of single crystal silicon wafers forms a cavity, resulting in a suspended thin film structure.

[0027] In some embodiments, after step (11), the method further includes bonding glass or silicon outside the cavity to form a vacuum cavity. Thus, the microsensor chip with a vacuum cavity can be used for absolute pressure measurement.

[0028] The beneficial effect of the present application is that by integrating the thermal flow sensor and the piezoresistive pressure sensor on one chip, the shortcomings of the traditional integrated sensor measurement module, such as large size and difficult packaging, are solved. The micro sensor chip provided by the present application has the characteristics of high integration, simple structure, small size, and easy packaging, which reduces the production cost and improves the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structure of a microsensor chip provided in one embodiment of the present application.

[0030] Figure 2 A process flow chart of a method for manufacturing a microsensor chip provided in one embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] Embodiment 1:

[0033] In this embodiment, refer to the attached manual Figure 1 , provides a microsensor chip, including a substrate 1, a film 2, a heating strip 3, a thermopile 4 and a piezoresistive strip 5, wherein the substrate 1 is a silicon-based material substrate; the film 2 is a composite film, arranged above the substrate 1; the heating strip 3 is arranged on the upper surface of the film 2 and located in the center of the film 2; two thermopiles 4 are symmetrically arranged on both sides of the heating strip 3, one end of the thermopiles 4 is arranged on the upper surface of the film 2, and the other end is arranged on the substrate 1; four piezoresistive strips 5 are arranged on the upper surface of the film 2 and form a Wheatstone bridge.

[0034] The working principle of the present application is that the piezoresistive strips 5 form a Wheatstone bridge, and the two positive and two negative piezoresistive strips 5 form a differential structure, thereby obtaining a bridge output related to pressure and realizing pressure measurement.

[0035] The temperatures on both sides of the heating strip 3 are T h1 and T h2 Since silicon-based materials have excellent thermal conductivity, the temperature of substrate 1 tends to be equal and can be regarded as an isothermal body. Assuming that the temperature of substrate 1 is T c , then the temperature difference dT=T on both sides of the heating strip 3 is obtained h1 -T c -(T h2 -T c )=T h1 -T h2 According to the principle of thermal flowmeter, under constant heating power, the temperature difference and flow rate on both sides of the heating strip 3 have a one-to-one correspondence within a certain range. Since the film 2 is insulated to form a heat island structure, a temperature difference is formed at both ends of the thermopile 4. According to the thermoelectric effect, a temperature difference electromotive force is formed at both ends of the thermopile 4, and a voltage signal is output. If the output voltages of the two thermopiles 4 are V1 and V2 respectively, then dV=V1-V2, and dV and dT have a one-to-one correspondence. Therefore, the difference in the output voltages of the thermopiles 4 on both sides of the heating strip 3 can establish a corresponding relationship with the flow rate. When the cross-sectional area of ​​the flow channel is known and unchanged, flow measurement can be achieved.

[0036] In an optional embodiment, the substrate 1 is a square silicon-based substrate, thereby obtaining a symmetrical stress distribution and improving the linearity of the chip.

[0037] In an optional embodiment, the film 2 is a composite film of silicon dioxide and silicon nitride. Thus, the composite film can be used as both a pressure sensing region and a region for lateral heat transfer to the substrate.

[0038] In an optional embodiment, the film 2 is a square composite film, so that the film can obtain maximum strength and symmetrical stress distribution, thereby improving the linearity of the chip.

[0039] In an optional embodiment, a cavity 6 is provided on the substrate 1 corresponding to the film 2. Thus, the cavity plays a role of heat insulation, so that heat conduction mainly occurs on the upper surface of the film.

[0040] In an optional embodiment, the heating strip 3 and the piezoresistive strip 5 are made of P-type polysilicon. Therefore, the resistivity of the heating strip made of P-type polysilicon is not sensitive to temperature, so a voltage can be applied to both sides of the resistance strip to obtain constant power to achieve temperature compensation; at the same time, P-type polysilicon has a higher Sech coefficient and can improve chip sensitivity.

[0041] In an optional embodiment, the thermopile 4 is made of aluminum and P-type polysilicon. Thus, aluminum and P-type polysilicon form a thermocouple and are connected in series to form a thermopile, which can achieve higher sensitivity.

[0042] In an optional embodiment, four piezoresistive strips 5 are arranged at the edge of the film 2. Specifically, two piezoresistive strips 5 can be arranged at the area with the largest tensile stress, and the other two piezoresistive strips 5 can be arranged at the area with the largest compressive stress. Therefore, the edge of the film is usually the place with the largest stress or strain, and the piezoresistive strips are arranged at the place with the largest stress or strain. The two positive and two negative piezoresistive strips form a differential structure, thereby obtaining the maximum sensitivity of the pressure-related bridge output.

[0043] The beneficial effect of the present application is that by integrating the thermal flow sensor and the piezoresistive pressure sensor on one chip, the shortcomings of the traditional integrated sensor measurement module, such as large size and difficult packaging, are solved. The micro sensor chip provided by the present application has the characteristics of high integration, simple structure, small size, and easy packaging, which reduces the production cost and improves the production efficiency.

[0044] Embodiment 2:

[0045] In this embodiment, refer to the attached manual Figure 2 , schematically provides a method for manufacturing a microsensor chip, comprising the following steps:

[0046] (1) Selecting a single crystal silicon wafer as the substrate;

[0047] (2) forming a silicon nitride layer on each side of the cleaned and dried single crystal silicon wafer, the silicon nitride layer being both an insulating layer and a barrier layer for wet etching in step (11);

[0048] (3) forming a polysilicon layer on each of the two silicon nitride layers obtained in step (2), and specifically, the polysilicon can be grown by low pressure chemical vapor deposition;

[0049] (4) forming a silicon dioxide layer on any one of the polysilicon layers obtained in step (3), wherein the polysilicon layer forming the silicon dioxide layer is the front polysilicon layer, and the other polysilicon layer is the back polysilicon layer;

[0050] (5) boron doping the front polysilicon layer, specifically, boron doping can be performed by ion implantation;

[0051] (6) removing the silicon dioxide layer and excess polysilicon on the front polysilicon layer to form a heating strip, one arm of the thermopile and a piezoresistive strip;

[0052] (7) forming a silicon dioxide layer on the heating strip, one arm of the thermopile and the piezoresistive strip, and reserving a connection hole on the silicon dioxide layer by etching, wherein the silicon dioxide layer is used for electrical isolation;

[0053] (8) sputtering aluminum on the silicon dioxide layer obtained in step (7), and etching to form another arm of the thermopile;

[0054] (9) sequentially forming a silicon dioxide layer and a silicon nitride layer on the heating strip, the thermopile and the piezoresistive strip;

[0055] (10) removing the local reverse polysilicon layer and its corresponding silicon nitride layer;

[0056] (11) Wet etching of single crystal silicon wafers forms a cavity which is connected to the atmosphere and is used to measure relative pressure.

[0057] In an optional embodiment, when polysilicon is generated in step (3), according to different process requirements, it can be grown once, in which case the thickness of the piezoresistive strip, the heating strip and one arm of the thermopile are equal; it can also be grown multiple times, and polysilicon layers of different thicknesses are produced by etching, thereby satisfying different piezoresistive effects and thermoelectric effects.

[0058] In an optional embodiment, a silicon dioxide layer may be generated by plasma enhanced chemical vapor deposition in step (4), and the silicon dioxide layer is a buffer layer for boron doping in step (5), thereby avoiding excessively deep boron doping due to a too thin polysilicon layer, so that most of the impurity atoms are distributed under the polysilicon, affecting the doping concentration of the polysilicon. Specifically, the thickness of the silicon dioxide layer can be obtained by the distribution theory of impurity atoms in ion implantation.

[0059] In an optional embodiment, in step (5), the entire polysilicon layer may be doped to achieve a more uniform doping, or different ion concentrations may be doped in different regions to achieve better thermoelectric effect and piezoresistive effect.

[0060] In an optional embodiment, an annealing step is further included between step (5) and step (6) to repair lattice damage caused by ion implantation.

[0061] In an optional embodiment, in step (9), the silicon dioxide layer and the silicon nitride layer form a composite passivation layer structure for blocking water vapor and external impurity ions, and can also be used as a barrier layer.

[0062] In an optional embodiment, after step (11), the method further includes bonding glass or silicon outside the cavity to form a vacuum cavity. Thus, the microsensor chip with a vacuum cavity can be used for absolute pressure measurement.

[0063] The beneficial effect of the present application is that by integrating the thermal flow sensor and the piezoresistive pressure sensor on one chip, the shortcomings of the traditional integrated sensor measurement module, such as large size and difficult packaging, are solved. The micro sensor chip provided by the present application has the characteristics of high integration, simple structure, small size, and easy packaging, which reduces the production cost and improves the production efficiency.

[0064] The above is only an optional implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A micro sensor chip, characterized in that: The invention comprises a substrate (1), a film (2), a heating strip (3), a thermopile (4) and a piezoresistive strip (5), wherein the substrate (1) is a silicon-based material substrate; the film (2) is a composite film and is arranged above the substrate (1); the heating strip (3) is arranged on the upper surface of the film (2) and is located in the center of the film (2); two thermopiles (4) are symmetrically arranged on both sides of the heating strip (3), one end of the thermopiles (4) is arranged on the upper surface of the film (2), and the other end is arranged on the substrate (1); four piezoresistive strips (5) are arranged on the upper surface of the film (2) and form a Wheatstone bridge; the four piezoresistive strips (5) are arranged at the edge of the film (2), and a cavity (6) is arranged on the substrate (1) corresponding to the film (2); the heating strip (3) and the piezoresistive strip (5) are composed of P-type polysilicon, and the thermopile (4) is composed of aluminum and P-type polysilicon.

2. The microsensor chip according to claim 1, characterized in that: The substrate (1) is a square silicon-based substrate.

3. The microsensor chip according to claim 1, characterized in that: The film (2) is a composite film of silicon dioxide and silicon nitride.

4. The microsensor chip according to claim 1, characterized in that: The film (2) is a square composite film.

5. A method for manufacturing a micro sensor chip, characterized in that: The following steps are involved: (1) Selecting a single crystal silicon wafer as the substrate; (2) forming a silicon nitride layer on each side of the cleaned and dried single crystal silicon wafer; (3) forming a polysilicon layer on each of the two silicon nitride layers obtained in step (2); (4) forming a silicon dioxide layer on any one of the polysilicon layers obtained in step (3), wherein the polysilicon layer forming the silicon dioxide layer is the front polysilicon layer, and the other polysilicon layer is the back polysilicon layer; (5) boron doping the front polysilicon layer; (6) removing the silicon dioxide layer and excess polysilicon on the front polysilicon layer to form a heating strip, one arm of the thermopile and a piezoresistive strip; (7) forming a silicon dioxide layer on the heating strip, one arm of the thermopile and the piezoresistive strip, and reserving a connection hole on the silicon dioxide layer by etching; (8) sputtering aluminum on the silicon dioxide layer obtained in step (7), and etching to form another arm of the thermopile; (9) sequentially generating a silicon dioxide layer and a silicon nitride layer on the heating strip, the thermopile and the piezoresistive strip; (10) removing the local reverse polysilicon layer and its corresponding silicon nitride layer; (11) Wet etching of single crystal silicon wafers forms a cavity, resulting in a suspended thin film structure.

6. The method for manufacturing a micro sensor chip according to claim 5, characterized in that: After step (11), the method further comprises: Glass or silicon is bonded outside the cavity to form a vacuum chamber.

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