CN113175963B - MEMS flow sensor and preparation method thereof - Google Patents
MEMS flow sensor and preparation method thereof Download PDFInfo
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- CN113175963B CN113175963B CN202110457870.1A CN202110457870A CN113175963B CN 113175963 B CN113175963 B CN 113175963B CN 202110457870 A CN202110457870 A CN 202110457870A CN 113175963 B CN113175963 B CN 113175963B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
- G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
- G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
- G01F1/6888—Thermoelectric elements, e.g. thermocouples, thermopiles
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
- G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
- G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
- G01F1/69—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element of resistive type
- G01F1/692—Thin-film arrangements
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Abstract
The invention relates to an MEMS flow sensor and a preparation method thereof, wherein a silicon substrate of the sensor is internally provided with a closed cavity, a silicon oxide insulating layer is paved on the silicon substrate, and a thermopile, a first heating resistor and a second heating resistor are arranged on the silicon oxide insulating layer; the first heating resistor and the second heating resistor are respectively positioned at two sides of the thermopile and symmetrically arranged by taking the central line of the thermopile as a symmetry axis, the two ends of the first heating resistor are respectively provided with a first pressure welding block, the two ends of the second heating resistor are respectively provided with a second pressure welding block, and the two ends of the thermopile are respectively provided with a third pressure welding block; a silicon oxide insulating layer covers the thermopile, the first heating resistor and the second heating resistor, and a silicon nitride protective layer covers the silicon oxide insulating layer; a heat insulation groove is arranged at the periphery of the integral structure formed by the thermopile, the first heating resistor and the second heating resistor; and a silicon oxide protective layer and a silicon nitride protective layer are sequentially paved on the bottom of the heat insulation groove. The invention improves the measurement precision.
Description
Technical Field
The invention relates to the technical field of flow sensor preparation, in particular to an MEMS flow sensor and a preparation method thereof.
Background
MEMS is an industrial technology combining mechanical engineering and microelectronic technology, and the operating range of the MEMS is generally in the micro-nano level. MEMS technology is generally based on semiconductor materials, and uses surface micromachining, deep etching, bulk micromachining, and other processes as well as related processes in the field of integrated circuits to fabricate devices.
The measurement of flow is of great importance in industrial production and process control, for example in the field of consumer electronics, in the automotive field, in the medical field, etc. The flow sensors commonly used at present are various in types, and have wider development and application space under the assistance of the MEMS technology. The types of flow sensors commonly found on the market include: (1) Early flow sensors based on simple physical principles, such as positive displacement, turbine, and heat loss; (2) Based on emerging scientific technologies, such as electromagnetic, thermoelectric and differential pressure flow sensors. However, these flow sensors present their own advantages in different applications, while the disadvantages are also evident. For example, positive displacement, eddy current, and electromagnetic flow sensors typically exhibit large power consumption and volume; the differential pressure type flow sensor is complex to install, the heat loss type flow sensor is greatly influenced by the temperature of the external environment, and the precision is low; the thermoelectric flow sensor is widely researched due to simple structure, no mechanical structure, easy integration and the like, but in order to suppress the temperature drift effect, a temperature sensor is usually additionally arranged near the flow sensor for measuring the temperature of the base.
Disclosure of Invention
The invention aims to provide an MEMS flow sensor and a preparation method thereof, which improve the measurement precision.
In order to achieve the purpose, the invention provides the following scheme:
a MEMS flow sensor, comprising: a silicon substrate 6, a thermopile 1, a first heating resistor 21, a second heating resistor 22, a first pressure welding block 31, a second pressure welding block 32, a third pressure welding block 33, a silicon oxide protective layer 7, a silicon nitride protective layer 8 and a silicon oxide insulating layer 9;
a closed cavity 5 is arranged in the silicon substrate 6, the silicon oxide insulating layer 9 is paved on the silicon substrate 6, and the thermopile 1, the first heating resistor 21 and the second heating resistor 22 are arranged on the silicon oxide insulating layer 9; the first heating resistor 21 and the second heating resistor 22 are respectively located at two sides of the thermopile 1 and symmetrically arranged by taking the center line of the thermopile 1 as a symmetry axis, the first pressure welding blocks 31 are respectively arranged at two ends of the first heating resistor 21, the second pressure welding blocks 32 are respectively arranged at two ends of the second heating resistor 22, and the third pressure welding blocks 33 are respectively arranged at two ends of the thermopile 1; the silicon oxide insulating layer 9 covers the thermopile 1, the first heating resistor 21 and the second heating resistor 22, and the silicon nitride protecting layer 8 covers the silicon oxide insulating layer 9; a heat insulation groove 4 is arranged on the periphery of the integral structure formed by the thermopile 1, the first heating resistor 21 and the second heating resistor 22; the silicon oxide protective layer 7 and the silicon nitride protective layer 8 are sequentially paved on the bottom of the heat insulation groove 4; one side of the first pressure welding block 31 is attached to the silicon oxide insulating layer 9, and the other side of the first pressure welding block is exposed in the air; one side of the second pressure welding block 32 is attached to the silicon oxide insulating layer 9, and the other side is exposed in the air; one side of the third pressure welding block 33 is attached to the silicon oxide insulating layer 9, and the other side is exposed in the air.
Optionally, the thermopile 1 includes a plurality of thermocouples, each of which is connected in series, the thermocouples include a semiconductor arm 12 and a metal arm 11, and one end of the semiconductor arm 12 is connected to one end of the metal arm 11 through a metal wire 13.
Optionally, the semiconductor arm 12 and the metal arm 11 are horizontally disposed on the same plane.
Optionally, the metal arm 11 is disposed above the semiconductor arm 12, and the metal arm 11 and the semiconductor arm 12 are separated by an insulating dielectric layer.
Optionally, the lower surface of the heat insulation slot 4 is a rectangular frame.
The invention also discloses a preparation method of the MEMS flow sensor, which is used for preparing the MEMS flow sensor and comprises the following steps:
etching a groove on a silicon substrate;
growing a layer of monocrystalline silicon on the groove to form a closed cavity in the groove;
growing a layer of silicon oxide on a silicon substrate with a closed cavity formed inside to form a silicon oxide insulating layer;
forming a first heating resistor, a second heating resistor and a thermopile on a silicon oxide insulating layer by photoetching, ion implantation of polycrystalline silicon and metal sputtering, wherein first pressure welding blocks are respectively formed at two ends of the first heating resistor, second pressure welding blocks are respectively formed at two ends of the second heating resistor, and third pressure welding blocks are respectively formed at two ends of the thermopile; the first heating resistor and the second heating resistor are respectively positioned at two sides of the thermopile and are symmetrically arranged by taking the center line of the thermopile as a symmetry axis;
forming a heat insulation groove on the periphery of the whole structure formed by the thermopile, the first heating resistor and the second heating resistor by adopting a body deep etching technology, wherein the bottom of the heat insulation groove extends into the silicon substrate;
depositing and photoetching silicon oxide above the heat insulation slot, the thermopile, the first heating resistor and the second heating resistor to form a silicon oxide protective layer, and exposing the upper surfaces of the first pressure welding block, the second pressure welding block and the third pressure welding block in the air;
depositing and photoetching silicon nitride above the silicon oxide protective layer to form a silicon nitride protective layer;
optionally, the etching a groove on the silicon substrate specifically includes:
etching an initial groove on the silicon substrate by adopting an anisotropic reactive ion etching method;
and continuously etching the bottom of the initial groove by adopting an isotropic etching method to form the groove.
Optionally, the thermopile comprises a plurality of thermocouples, each of which is connected in series, and the thermocouples comprise a semiconductor arm and a metal arm, and one end of the semiconductor arm is connected with one end of the metal arm through a metal wire.
Optionally, a first heating resistor, a second heating resistor and a thermopile are formed on the silicon oxide insulating layer by photolithography, ion implantation of polysilicon and metal sputtering, wherein first bonding pads are formed at two ends of the first heating resistor, second bonding pads are formed at two ends of the second heating resistor, and third bonding pads are formed at two ends of the thermopile; first heating resistor with second heating resistor is located respectively the both sides of thermopile, and with the central line of thermopile sets up as symmetry axis symmetry, specifically includes:
photoetching and ion implantation are carried out on the silicon oxide insulating layer to form a semiconductor arm of the thermopile, an ohmic contact area of a metal wire of the thermopile and the semiconductor arm, the first heating resistor and the second heating resistor; the first heating resistor, the second heating resistor and the semiconductor arm of the thermopile are first polycrystalline silicon, the ohmic contact region is second polycrystalline silicon, and the concentration of the conductive metal doped with the second polycrystalline silicon is greater than that of the conductive metal doped with the first polycrystalline silicon;
and forming a metal arm, a metal lead, a first pressure welding block, a second pressure welding block and a third pressure welding block of the thermopile by sputtering metal aluminum.
Optionally, growing a layer of silicon oxide on the silicon substrate with the sealed cavity formed therein to form a silicon oxide insulating layer specifically includes:
polishing the upper surface of a silicon substrate internally forming a closed cavity;
and growing a layer of silicon oxide on the upper surface of the polished silicon substrate to form a silicon oxide insulating layer.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
according to the invention, the first heating resistor and the second heating resistor are symmetrically arranged on two sides of the thermopile in the MEMS flow sensor, so that the influence of temperature drift can be inhibited, the measurement precision and the sensitivity are improved, the closed cavity is arranged below the thermopile, the first heating resistor and the second heating resistor, and the heat insulation grooves are arranged at the peripheral edges of the surface of the silicon substrate, so that the heat loss is reduced, and the measurement precision is further improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
FIG. 1 isbase:Sub>A cross-sectional view A-A ofbase:Sub>A MEMS flow sensor of the present invention;
FIG. 2 is a side view of a MEMS flow sensor of the present invention;
FIG. 3 is a flow chart of a method of making an MEMS flow sensor according to the present invention;
description of the symbols:
1. the structure comprises a thermopile, 11, a metal arm, 12, a semiconductor arm, 13, a metal wire, 21, a first heating resistor, 22, a second heating resistor, 31, a first pressure welding block, 32, a second pressure welding block, 33, a third pressure welding block, 4, a heat insulation groove, 5, a closed cavity, 6, a silicon substrate, 7, a silicon oxide protective layer, 8, a silicon nitride protective layer, 9 and a silicon oxide insulating layer.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The invention aims to provide an MEMS flow sensor and a preparation method thereof, which improve the measurement precision.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 isbase:Sub>A cross-sectional viewbase:Sub>A-base:Sub>A ofbase:Sub>A MEMS flow sensor of the present invention, and fig. 2 isbase:Sub>A side view ofbase:Sub>A MEMS flow sensor of the present invention, as shown in fig. 1-2,base:Sub>A MEMS flow sensor comprising: a silicon substrate 6, a thermopile 1, a first heating resistor 21, a second heating resistor 22, a first pressure welding block 31, a second pressure welding block 32, and a third pressure welding block 33, a silicon oxide protective layer 7, a silicon nitride protective layer 8, and a silicon oxide insulating layer 9.
A closed cavity 5 is arranged in the silicon substrate 6, the silicon oxide insulating layer 9 is paved on the silicon substrate 6, and the thermopile 1, the first heating resistor 21 and the second heating resistor 22 are arranged on the silicon oxide insulating layer 9; the thermopile 1 is arranged in the middle of the silicon oxide insulating layer 9; the first heating resistor 21 and the second heating resistor 22 are respectively located at two sides of the thermopile 1 and symmetrically arranged by taking the center line of the thermopile 1 as a symmetry axis, the first pressure welding blocks 31 are respectively arranged at two ends of the first heating resistor 21, the second pressure welding blocks 32 are respectively arranged at two ends of the second heating resistor 22, and the third pressure welding blocks 33 are respectively arranged at two ends of the thermopile 1; the silicon oxide insulating layer 9 covers the thermopile 1, the first heating resistor 21 and the second heating resistor 22, and the silicon nitride protective layer 8 covers the silicon oxide insulating layer 9; a heat insulation groove 4 is arranged on the periphery of the integral structure formed by the thermopile 1, the first heating resistor 21 and the second heating resistor 22; the silicon oxide protective layer 7 and the silicon nitride protective layer 8 are sequentially laid on the bottom of the heat insulation groove 4; one side of the first pressure welding block 31 is attached to the silicon oxide insulating layer 9, and the other side of the first pressure welding block is exposed in the air; one side of the second pressure welding block 32 is attached to the silicon oxide insulating layer 9, and the other side is exposed in the air; one side of the third pressure welding block 33 is attached to the silicon oxide insulating layer 9, and the other side is exposed in the air.
The thermopile 1 comprises a plurality of thermocouples, wherein the thermocouples are mutually connected in series, the thermocouples comprise a semiconductor arm 12 and a metal arm 11, and one end of the semiconductor arm 12 is connected with one end of the metal arm 11 through a metal lead 13.
In a specific embodiment, the semiconductor arm 12 and the metal arm 11 are horizontally disposed on the same plane, or the metal arm 11 is disposed above the semiconductor arm 12, and the metal arm 11 and the semiconductor arm 12 are separated by an insulating medium layer. In fig. 1, in the case where the semiconductor arm 12 and the metal arm 11 are horizontally disposed on the same plane, when a liquid or a gas flows from left to right, the left and right ends are located upstream and downstream of the flowing liquid or gas, respectively, and when a liquid or a gas flows from right to left, the left and right ends are located downstream and upstream of the flowing liquid or gas, respectively.
The first heating resistor 21 and the second heating resistor 22 are both strip-shaped and are arranged in parallel, and the first heating resistor 21 and the second heating resistor 22 are completely the same.
The closed cavity 5 is positioned in the silicon substrate 6 below the thermopile 1, the closed cavity 5 transversely extends to the first heating resistor 21 and the second heating resistor 22, the closed cavity 5 can cover the projection of the thermopile 1, the first heating resistor 21 and the second heating resistor 22, the projection of the vertical and horizontal planes is longitudinally extended to the upper end and the lower end of the first heating resistor 21 and the second heating resistor 22, and the pressure welding blocks (the first pressure welding block 31, the second pressure welding block 32 and the third pressure welding block 33) at the upper end and the lower end of the heating resistor (the first heating resistor 21 and the second heating resistor 22) are not reached.
The silicon substrate 6 is P-type monocrystalline silicon, the metal arm 11 of the thermopile 1 can adopt metals such as Al or Ti, and the semiconductor arm 12 can adopt semiconductors such as N + polycrystalline silicon or P + polycrystalline silicon; in addition, two arms of the thermopile 1 can also adopt two semiconductor materials of N + polysilicon and P + polysilicon; in the embodiment, the metal arm 11 and the semiconductor arm 12 are selected to form the thermopile 1, and the material of the metal arm 11 is Al, and the material of the semiconductor arm 12 is N + polysilicon.
As a specific example, the doping type of the heating resistor and the semiconductor arm 12 is N-type lightly doped, and the designed doping concentration is about 10 12 ～10 15 cm -3 。
In one embodiment, the doping type of the ohmic contact region between the semiconductor arm 12 and the metal wire 13 is N-type heavy doping, and the designed doping concentration is about 10 17 ～10 19 cm -3 And good ohmic contact can be formed between the two.
The invention relates to an MEMS flow sensor, wherein a thermopile is arranged in the middle of a silicon oxide insulating layer, two heating resistors are symmetrically arranged at the left end and the right end of the thermopile, the heating resistors are electrified to generate heat, when liquid or gas flows, the heat can be brought from the upstream to the downstream, so that temperature difference is generated at the left end and the right end of the thermopile, the thermopile converts the temperature difference into output thermoelectrical potential, the flowing direction and the flowing speed of the liquid or the gas can be judged by measuring the positive, negative and magnitude of the thermoelectrical potential, and further the flow within a period of time can be obtained; the two symmetrically arranged heating resistors are used for eliminating the influence of the external temperature on the sensor, so that the temperature of the base does not need to be measured by additionally designing a temperature sensor, the measurement sensitivity and precision are improved, and the manufacturing cost is reduced; the heat insulation groove and the closed cavity are used for reducing heat loss and further improving the measurement precision, and meanwhile, the manufacturing of the flow sensor is compatible with a silicon-based circuit process; therefore, the MEMS flow sensor has the characteristics of miniaturization, low power consumption, high precision, low cost and the like.
When the MEMS flow sensor works, the same voltage is applied to the pressure welding blocks at the two ends of the two heating resistors, so that the heating resistors generate heat through current, and the two heating resistors at the two ends of the thermopile can inhibit the influence of temperature drift to a certain extent, so that a temperature sensor is not required to be additionally designed in the structure to measure the temperature of the base; if the liquid or the gas is in a static state, the temperatures of the left end and the right end of the thermopile are the same; if the liquid or the gas flows rightwards, the heat is brought to the right end from the left end of the thermopile by the liquid or the gas, so that the temperature of the right end of the thermopile is higher than that of the left end; on the contrary, if the liquid or gas flows leftwards, the heat is carried to the left end from the right end of the thermopile by the liquid or gas, so that the temperature of the left end of the thermopile is higher than that of the right end. And the temperature difference between the left end and the right end is in positive correlation with the flow velocity of the liquid or the gas. The seebeck effect shows that the output thermoelectric force of the thermopile is in a direct proportion relation with the temperature difference between the left end and the right end of the thermopile, so that the output thermoelectric force of the thermopile is in a positive correlation relation with the flow speed of liquid or gas. Therefore, by measuring the thermoelectric force between the two pressure welding blocks on the upper side and the lower side of the thermopile, the flowing direction and the flowing speed of the liquid or the gas can be judged according to the positive value, the negative value and the absolute value of the thermoelectric force, and further the volume of the liquid or the gas passing through the thermopile within a period of time can be obtained. The heat insulation grooves on the periphery of the surface of the silicon substrate and the closed cavity in the silicon substrate play a role in increasing thermal resistance, so that heat loss is reduced, and measurement accuracy is improved.
The lower surface of the heat insulation groove 4 is a rectangular frame.
The invention discloses a MEMS flow sensor which is used for measuring the flow of liquid or gas. This flow sensor adopts full passive structure to constitute, whole structure is located the silicon substrate, the silicon substrate surface is provided with the silicon oxide insulating layer, the thermopile of compriseing semiconductor arm, metal arm and metal wire has been placed to the insulating layer top, respectively be equipped with the heating device who constitutes by heating resistor at the thermopile both ends, the below of thermopile is equipped with airtight cavity in the middle of the silicon substrate, the silicon substrate surface is equipped with round heat-insulating tank all around, except that pressure welding piece on the silicon substrate surface all cover have silicon oxide protective layer and silicon nitride protective layer. When the sensor works, the two heating resistors are electrified to generate heat, the temperature distribution of the two heating resistors is symmetrically distributed relative to the thermopile, so that the temperatures of the left end and the right end of the thermopile are the same (namely the temperature difference is zero), and the output thermoelectrical potential of the thermopile is zero at the moment; when liquid or gas flows, the originally symmetrical temperature distribution can be disturbed, the temperature at the upstream in the flowing direction is lower than that at the downstream, so that the temperature difference is generated at the left end and the right end of the thermopile, the output thermal potential of the thermopile is not zero at the moment, the flowing direction and the flowing speed of the liquid or the gas can be obtained by measuring the positive value and the negative value of the thermal potential, and the volume of the liquid or the gas passing through within a period of time can be further obtained.
Fig. 3 is a flowchart of a method for manufacturing an MEMS flow sensor according to the present invention, and as shown in fig. 3, the method for manufacturing an MEMS flow sensor includes:
step 100: and etching a groove on the silicon substrate.
Wherein, step 100 specifically comprises:
etching an initial groove on the silicon substrate by adopting an anisotropic reactive ion etching method;
and continuously etching the bottom of the initial groove by adopting an isotropic etching method to form the groove.
Optionally, the thermopile comprises a plurality of thermocouples, each of which is connected in series, and the thermocouples comprise a semiconductor arm and a metal arm, and one end of the semiconductor arm is connected with one end of the metal arm through a metal wire.
Step 200: and growing a layer of monocrystalline silicon on the groove to enable the groove to form a closed cavity.
Step 300: and growing a layer of silicon oxide on the silicon substrate with the closed cavity formed inside to form a silicon oxide insulating layer.
Wherein, step 300 specifically includes:
polishing the upper surface of a silicon substrate with a closed cavity formed inside;
and growing a layer of silicon oxide on the upper surface of the polished silicon substrate to form a silicon oxide insulating layer.
Step 400: forming a first heating resistor, a second heating resistor and a thermopile on a silicon oxide insulating layer by photoetching, ion implantation of polycrystalline silicon and metal sputtering, wherein first pressure welding blocks are respectively formed at two ends of the first heating resistor, second pressure welding blocks are respectively formed at two ends of the second heating resistor, and third pressure welding blocks are respectively formed at two ends of the thermopile; the first heating resistor and the second heating resistor are respectively positioned at two sides of the thermopile and are symmetrically arranged by taking the center line of the thermopile as a symmetry axis.
Wherein, step 400 specifically comprises:
photoetching and ion implantation are carried out on the silicon oxide insulating layer to form a semiconductor arm of the thermopile, an ohmic contact area of a metal wire of the thermopile and the semiconductor arm, the first heating resistor and the second heating resistor; the first heating resistor, the second heating resistor and the semiconductor arm of the thermopile are first polysilicon, the ohmic contact region is second polysilicon, and the concentration of the conductive metal doped with the second polysilicon is greater than that of the conductive metal doped with the first polysilicon;
and forming a metal arm, a metal lead, a first pressure welding block, a second pressure welding block and a third pressure welding block of the thermopile by sputtering metal aluminum.
Step 500: and forming a heat insulation groove at the periphery of the whole structure formed by the thermopile, the first heating resistor and the second heating resistor by adopting a body deep etching technology, wherein the bottom of the heat insulation groove extends into the silicon substrate.
Step 600: and depositing and photoetching silicon oxide above the heat insulation slot, the thermopile, the first heating resistor and the second heating resistor to form a silicon oxide protective layer, and exposing the upper surfaces of the first pressure welding block, the second pressure welding block and the third pressure welding block in the air.
Step 700: and depositing and photoetching silicon nitride above the silicon oxide protective layer to form a silicon nitride protective layer.
The manufacturing process of the MEMS flow sensor is compatible with a silicon-based circuit process, wherein a monocrystalline silicon cavity sealing process is adopted for a closed cavity, a body etching process is adopted for a heat insulation groove, and a surface semiconductor process is adopted for structures such as a thermopile and a heating resistor in the preparation process, so that the MEMS flow sensor has the characteristics of miniaturization, low power consumption, high precision and low cost.
The following description will be made of a method for manufacturing an MEMS flow sensor according to an embodiment of the present invention, where a manufacturing process of the manufacturing method is compatible with a silicon-based circuit process, and the method includes the following steps:
a. selecting P-type monocrystalline silicon as a silicon substrate; shallow grooves (initial grooves) are etched on the silicon substrate by an anisotropic reactive ion etching process.
b. And c, protecting the side wall of the shallow groove on the silicon substrate obtained in the step a, and then carrying out isotropic corrosion on the bottom of the shallow groove of the silicon substrate, so as to form a cavity (groove) in the silicon substrate.
c. And c, epitaxially growing a layer of monocrystalline silicon on the cavity of the silicon substrate obtained in the step b to form a closed cavity.
d. And c, smoothing the upper surface of the silicon substrate obtained in the step c by utilizing a chemical mechanical polishing process, and growing a layer of silicon oxide on the silicon substrate to form a silicon oxide insulating layer.
e. And d, depositing a layer of polycrystalline silicon on the silicon substrate obtained in the step d, and carrying out photoetching and ion implantation twice to form lightly doped and heavily doped polycrystalline silicon, wherein the lightly doped polycrystalline silicon is used for forming a heating resistor and a semiconductor arm of the thermopile, and the heavily doped polycrystalline silicon is used for forming an ohmic contact region of a metal wire and the semiconductor arm in the thermopile.
f. And e, sputtering a layer of metal aluminum on the silicon substrate obtained in the step e, and carrying out photoetching to form a metal arm, a metal lead and a pressure welding block of the thermopile.
g. And f, forming a heat insulation groove on the peripheral edge of the silicon substrate by using a body deep etching technology on the silicon substrate obtained in the step f.
h. And g, depositing and photoetching silicon oxide on the silicon substrate obtained in the step g, and forming a silicon oxide protective layer at the positions of the pressure welding blocks.
i. And e, depositing and photoetching silicon nitride on the silicon substrate obtained in the step h, and forming a silicon nitride protective layer at the position of the pressure-removing welding block.
The MEMS flow sensor and the preparation method thereof have the technical effects that:
(1) This MEMS flow sensor adopts complete passive structure to constitute, and two heating resistor at both ends all ohmic heating produced the heat about the thermopile during operation, and the flow of liquid or gas arouses to produce the difference in temperature at both ends about the thermopile, and the thermopile is changeed this difference in temperature into direct current thermoelectric force, through the output thermoelectric force of measuring the thermopile, can obtain the direction and the velocity of flow of liquid or gas, and then can obtain the volume through liquid or gas in a period.
(2) In the MEMS flow sensor, the symmetrical heating resistors are designed at the left end and the right end of the thermopile, so that the influence of temperature drift can be inhibited, and therefore, a temperature sensor does not need to be additionally designed in the structure for measuring the temperature of the base, the measurement precision and the sensitivity are improved, and the chip area and the manufacturing cost of the sensor are reduced.
(3) In the MEMS flow sensor, a closed cavity is arranged below the thermopile and the heating resistor, and a circle of heat insulation groove is arranged at the peripheral edge of the surface of the silicon substrate, so that heat loss is reduced, and the measurement precision is further improved.
(4) The manufacturing process of the MEMS flow sensor is compatible with a silicon-based circuit process, and has lower cost.
In the present specification, the embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the foregoing, the description is not to be taken in a limiting sense.
Claims (10)
1. A MEMS flow sensor, comprising: the device comprises a silicon substrate (6), a thermopile (1), a first heating resistor (21), a second heating resistor (22), a first pressure welding block (31), a second pressure welding block (32), a third pressure welding block (33), a silicon oxide protective layer (7), a silicon nitride protective layer (8) and a silicon oxide insulating layer (9);
a closed cavity (5) is formed in the silicon substrate (6), the silicon oxide insulating layer (9) is laid on the silicon substrate (6), and the thermopile (1), the first heating resistor (21) and the second heating resistor (22) are arranged on the silicon oxide insulating layer (9); the first heating resistor (21) and the second heating resistor (22) are respectively located on two sides of the thermopile (1) and symmetrically arranged by taking the center line of the thermopile (1) as a symmetry axis, the first pressure welding blocks (31) are respectively arranged at two ends of the first heating resistor (21), the second pressure welding blocks (32) are respectively arranged at two ends of the second heating resistor (22), and the third pressure welding blocks (33) are respectively arranged at two ends of the thermopile (1); the silicon oxide insulating layer (9) covers the thermopile (1), the first heating resistor (21) and the second heating resistor (22), and the silicon nitride protective layer (8) covers the silicon oxide insulating layer (9); a heat insulation groove (4) is arranged on the periphery of the whole structure formed by the thermopile (1), the first heating resistor (21) and the second heating resistor (22); the silicon oxide protective layer (7) and the silicon nitride protective layer (8) are sequentially laid on the bottom of the heat insulation groove (4); one side of the first pressure welding block (31) is attached to the silicon oxide insulating layer (9), and the other side of the first pressure welding block is exposed in the air; one side of the second pressure welding block (32) is attached to the silicon oxide insulating layer (9), and the other side of the second pressure welding block is exposed in the air; one side of the third pressure welding block (33) is attached to the silicon oxide insulating layer (9), and the other side of the third pressure welding block is exposed in the air.
2. MEMS flow sensor according to claim 1, characterised in that the thermopile (1) comprises a plurality of thermocouples, each of which is connected in series with each other, the thermocouples comprising one semiconductor arm (12) and one metal arm (11), one end of the semiconductor arm (12) being connected to one end of the metal arm (11) by means of a metal wire (13).
3. MEMS flow sensor according to claim 2, characterised in that the semiconductor arm (12) is arranged horizontally in the same plane as the metal arm (11).
4. MEMS flow sensor according to claim 2, wherein the metal arm (11) is arranged above the semiconductor arm (12), the metal arm (11) being separated from the semiconductor arm (12) by a dielectric layer.
5. MEMS flow sensor according to claim 1, wherein the lower surface of the thermal shield groove (4) is a rectangular frame.
6. A method for preparing a MEMS flow sensor, the method for preparing the MEMS flow sensor of any one of claims 1-5, comprising:
etching a groove on a silicon substrate;
growing a layer of monocrystalline silicon on the groove to enable the groove to form a closed cavity;
growing a layer of silicon oxide on a silicon substrate with a closed cavity formed inside to form a silicon oxide insulating layer;
forming a first heating resistor, a second heating resistor and a thermopile on a silicon oxide insulating layer by photoetching, ion implantation of polycrystalline silicon and metal sputtering, wherein first pressure welding blocks are respectively formed at two ends of the first heating resistor, second pressure welding blocks are respectively formed at two ends of the second heating resistor, and third pressure welding blocks are respectively formed at two ends of the thermopile; the first heating resistor and the second heating resistor are respectively positioned at two sides of the thermopile and are symmetrically arranged by taking the center line of the thermopile as a symmetry axis;
forming a heat insulation groove on the periphery of an integral structure formed by the thermopile, the first heating resistor and the second heating resistor by adopting a deep etching technology, wherein the bottom of the heat insulation groove extends into the silicon substrate;
depositing and photoetching silicon oxide above the heat insulation groove, the thermopile, the first heating resistor and the second heating resistor to form a silicon oxide protective layer, and exposing the upper surfaces of the first pressure welding block, the second pressure welding block and the third pressure welding block in the air;
and depositing and photoetching silicon nitride above the silicon oxide protective layer to form a silicon nitride protective layer.
7. The method for manufacturing an MEMS flow sensor according to claim 6, wherein the etching a groove on the silicon substrate specifically includes:
etching an initial groove on the silicon substrate by adopting an anisotropic reactive ion etching method;
and continuously etching the bottom of the initial groove by adopting an isotropic etching method to form the groove.
8. The method of making a MEMS flow sensor as recited in claim 6, wherein the thermopile includes a plurality of thermocouples, each of the thermocouples being connected in series, the thermocouples including a semiconductor arm and a metal arm, one end of the semiconductor arm being connected to one end of the metal arm by a metal wire.
9. The method for manufacturing the MEMS flow sensor according to claim 8, wherein a first heating resistor, a second heating resistor and a thermopile are formed on the silicon oxide insulating layer by photolithography, ion implantation of polysilicon and metal sputtering, wherein a first bonding pad is formed at each of two ends of the first heating resistor, a second bonding pad is formed at each of two ends of the second heating resistor, and a third bonding pad is formed at each of two ends of the thermopile; first heating resistor with second heating resistor is located respectively the both sides of thermopile, and use the central line of thermopile sets up as symmetry axis symmetry, specifically includes:
photoetching and ion implantation are carried out on the silicon oxide insulating layer to form a semiconductor arm of the thermopile, an ohmic contact area of a metal wire of the thermopile and the semiconductor arm, the first heating resistor and the second heating resistor; the first heating resistor, the second heating resistor and the semiconductor arm of the thermopile are first polycrystalline silicon, the ohmic contact region is second polycrystalline silicon, and the concentration of the conductive metal doped with the second polycrystalline silicon is greater than that of the conductive metal doped with the first polycrystalline silicon;
and forming a metal arm, a metal lead, a first pressure welding block, a second pressure welding block and a third pressure welding block of the thermopile by sputtering metal aluminum.
10. The method for preparing the MEMS flow sensor according to claim 6, wherein the step of growing a layer of silicon oxide on the silicon substrate with the closed cavity formed therein to form a silicon oxide insulating layer specifically includes:
polishing the upper surface of a silicon substrate with a closed cavity formed inside;
and growing a layer of silicon oxide on the upper surface of the polished silicon substrate to form a silicon oxide insulating layer.
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