CN119437345A

CN119437345A - MEMS Thermal Flow Sensor

Info

Publication number: CN119437345A
Application number: CN202310987263.5A
Authority: CN
Inventors: 关一浩
Original assignee: CRM ICBG Wuxi Co Ltd
Current assignee: CRM ICBG Wuxi Co Ltd
Priority date: 2023-08-07
Filing date: 2023-08-07
Publication date: 2025-02-14

Abstract

The invention provides a MEMS thermal flow sensor. By arranging a beveled etching hole extending along the <100> crystal direction of a substrate in combination with a vertical etching hole, since the beveled etching hole is arranged along the <100> crystal direction of the substrate in a thermal insulation film region, when an alkaline solution is used for etching, the etching rate of the crystal surface of the substrate (100) is much greater than the etching rate of the crystal surface of the substrate (111), so that the beveled etching hole can be completely etched downward along the thickness direction of the substrate to remove the substrate, thereby improving the hill-like structure at the center of the thermal insulation film and reducing heat loss in the direction of the substrate. The vertical etching hole can also hinder heat transfer to the substrate in the horizontal direction, thereby reducing heat loss. At the same time, the beveled etching hole can hinder the lateral conduction of temperature, so that a plurality of sub-film portions obtained by dividing the sensor can be in different temperature fields. Since the distances between the hot end of the thermopile and the heating element are different, the sensitivity to different range flows is different, so that different range test requirements can be achieved through the different distances between the hot end of the thermopile and the heating element in different sub-film portions.

Description

MEMS thermal flow sensor

Technical Field

The invention belongs to the technical field of sensors, and particularly relates to an MEMS thermal flow sensor.

Background

In recent years, as human beings comprehensively enter an intelligent information age, the demands for measurement and control of information are increasing. The measurement and control of the gas flow rate are of great significance in the fields of industry, medical treatment, bioengineering and the like. The MEMS thermal flow sensor is widely applied due to the advantages of small size, high precision, low power consumption, high response speed and the like, for example, the MEMS thermal flow sensor can ensure effective combustion of fuel by controlling the flow of an air inlet of an engine in the field of automobiles, and the requirements of a traditional Chinese medical domestic breathing machine, an oxygen generator and the like on high-precision control of the flow of oxygen in the field of medical treatment and the like.

The working principle of the thermal flow sensor adopting the thermopile structure is to utilize the Seebeck effect to determine the flow rate of fluid by measuring the temperature change of the upper end and the lower end of the thermopile at the two sides of the middle heating element when the fluid passes through. The conventional MEMS thermal flow sensor at present has the problems of single measuring range, low heat exchange efficiency between a heating element and fluid and the like.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a MEMS thermal flow sensor, which is used for solving at least one technical problem of single measuring range, low heat exchange efficiency between a heating element and fluid, and the like in the MEMS thermal flow sensor in the prior art.

To achieve the above and other related objects, the present invention provides a MEMS thermal flow sensor comprising:

(100) A surface monocrystalline silicon substrate, which is provided with a groove, wherein the groove is arranged on the upper surface of the substrate;

The heat insulation film is covered above the groove and connected with the substrate, and the heat insulation film and the substrate jointly enclose a heat insulation cavity;

At least two vertical etching holes penetrating the heat insulation film and extending along the vertical direction, wherein all the vertical etching holes are sequentially arranged along the horizontal direction and sequentially divide the heat insulation film into three areas, namely an upstream film part, a central film part and a downstream film part, wherein the upstream film part and the downstream film part have the same size and are symmetrical relative to the central film part;

hypotenuse etching holes penetrating the upstream film part and the downstream film part respectively and extending along the <100> crystal direction of the substrate, wherein the hypotenuse etching holes are arranged between the hypotenuse etching holes of the upstream film part and the hypotenuse etching holes of the downstream film part in a mirror symmetry manner or a 180-degree rotation symmetry manner, and the film part where the hypotenuse etching holes are arranged is divided into a plurality of sub-film parts;

a plurality of thermopiles provided on the sub-film portion, all of the thermopiles provided on the sub-film portion of the upstream film portion being connected in series, all of the thermopiles provided on the sub-film portion of the downstream film portion being connected in series;

a heating element disposed on the central film portion and extending in a vertical direction;

Wherein the horizontal direction is the <110> crystal orientation of the substrate, and the vertical direction is the substrate And (5) crystal orientation.

Optionally, the upstream film portion and the downstream film portion are each provided with 1 bevel edge etching hole or 2 bevel edge etching holes, and when the upstream film portion and the downstream film portion are each provided with 2 bevel edge etching holes, the 2 bevel edge etching holes are vertically arranged or parallel arranged.

Optionally, the heating element metal wire and the thermopile series metal wire are also included, and pass through the vertical direction of the central film parts at two sides of the heating element.

Optionally, the heating device further comprises a radiator, wherein the radiator is arranged above the heating element and is used for radiating heat to the heating element.

Further, the heat sink is made of sheet metal, or the heat sink is made of a plurality of metal strips in the horizontal direction arranged in the vertical direction, or the heat sink is made of a plurality of inclined metal strips arranged in the vertical direction.

Optionally, the cold end of the thermopile is located on the substrate such that the cold end of the thermopile is in sufficient contact with the substrate.

Optionally, the thermoelectric module further comprises a temperature-sensitive resistor which is arranged outside the cold end of at least one thermopile.

The thermopile is arranged in at least one of a first type, the thermopile is arranged in series in a horizontal direction by a plurality of thermocouple strips in a vertical direction, a cold end of the thermopile is positioned on the substrate, a hot end of the thermopile is adjacent to the bevel corrosion hole, a second type, the thermopile is arranged in series in a horizontal direction by a plurality of thermocouple strips, the thermocouple strips are parallel to the bevel corrosion hole, a cold end of the thermopile is positioned on the substrate, a hot end of the thermopile is parallel to the heating element, a third type, the thermopile is arranged in series in a vertical direction by a plurality of thermocouple strips in a horizontal direction, a cold end of the thermopile is positioned on the substrate, a hot end of the thermopile is adjacent to the bevel corrosion hole, and all the thermopiles are arranged in at least one of the three types.

Further, the thermocouple strips in the thermopile are any two combinations of P-type doped polycrystalline silicon thermocouple strips, N-type doped polycrystalline silicon thermocouple strips and metal thermocouple strips.

Alternatively, the thermocouple strips in combination in the thermopile are vertically stacked in the thickness direction of the (100) face of the substrate or are tiled along the (100) face of the substrate.

As described above, the MEMS thermal flow sensor can achieve effective release of the heat insulation film by arranging the bevel edge corrosion holes extending along the crystal direction of the substrate <100> and combining with the vertical corrosion holes, generally when the heat insulation film is released, the substrate needs to be subjected to deep corrosion, when the substrate is corroded, the substrate is lower in corrosion rate nearer to the center, so that a hillock-like structure exists at the center, the bevel edge corrosion holes are arranged in the heat insulation film area, and are in the direction along the crystal direction of the substrate <100>, when the alkaline solution is adopted for corrosion, the corrosion rate of the crystal face of the substrate (100) is far greater than the corrosion rate of the crystal face of the substrate (111), so that the bevel edge corrosion holes can completely corrode and remove the substrate downwards along the thickness direction of the substrate, thereby improving the hillock-like structure at the center of the heat insulation film, improving the shape retention of the heat insulation cavity, reducing the heat loss towards the substrate direction, improving the measurement precision, and the vertical corrosion holes can also obstruct the transmission of the substrate in the horizontal direction, further improving the measurement precision, and meanwhile, the bevel edge corrosion holes can obstruct the transverse conduction of the temperature, can divide the obtained multiple temperature fields into different temperature fields, and heat loss fields can be positioned between the different temperature fields and the thermal power pile elements, and the thermal power element can achieve different heating range requirements, and different heating range requirements.

Drawings

FIG. 1 is a schematic cross-sectional view of a MEMS thermal flow sensor substrate of the present invention.

Fig. 2 is a schematic diagram showing a global perspective structure of the MEMS thermal flow sensor of the present invention.

Fig. 3 is a schematic cross-sectional view showing a MEMS thermal flow sensor according to the present invention.

Fig. 4 and 5 are schematic top view structures of a first example of the positional relationship of vertical etching holes, bevel etching holes, etc. in the MEMS thermal flow sensor according to the present invention.

Fig. 6 is a schematic diagram showing a second example top view structure of the vertical etching hole, the bevel etching hole, and the like in the MEMS thermal flow sensor according to the present invention.

Fig. 7 is a schematic diagram showing a third example top view structure of the vertical etching hole, the bevel etching hole, and the like in the MEMS thermal flow sensor according to the present invention.

Fig. 8 is a schematic diagram showing a fourth example top view structure of the positional relationship of vertical etching holes, bevel etching holes, and the like in the MEMS thermal flow sensor of the present invention.

Fig. 9 shows a schematic top view of a first example of a MEMS thermal flow sensor of the present invention.

Fig. 10 shows a schematic top view of a second example of a MEMS thermal flow sensor of the present invention.

Fig. 11 is an enlarged partial schematic view of the central film portion of fig. 10.

Fig. 12 shows a schematic top view of a first example of a thermopile in a MEMS thermal flow sensor of the present invention.

Fig. 13 shows a schematic top view of a second example of a thermopile in a MEMS thermal flow sensor of the present invention.

Fig. 14 shows a schematic top view of a third example of a thermopile in a MEMS thermal flow sensor of the present invention.

Fig. 15 shows a schematic top view of a fourth example of a thermopile in a MEMS thermal flow sensor of the present invention.

Fig. 16 shows a schematic top view of a third example of a MEMS thermal flow sensor of the present invention.

Fig. 17 shows a schematic top view of a fourth example of a MEMS thermal flow sensor of the present invention.

Fig. 18 shows a fifth exemplary top view structural schematic of a MEMS thermal flow sensor of the present invention.

Fig. 19 shows a schematic top view of a sixth example of a MEMS thermal flow sensor of the present invention.

Fig. 20 shows a seventh exemplary top view structural schematic of a MEMS thermal flow sensor of the present invention.

Fig. 21 shows a schematic top view of an eighth example of a MEMS thermal flow sensor of the present invention.

Fig. 22 to 28 are schematic cross-sectional structures corresponding to steps in the process of manufacturing the MEMS thermal flow sensor of the first example, wherein the schematic cross-sectional structures corresponding to the steps are cut along the AA direction in fig. 9, that is, from the <110> crystal orientation in the vertical direction to the <110> crystal orientation in the horizontal direction.

Description of element reference numerals

1. Substrate and method for manufacturing the same

11. Groove

12. Heat-insulating film

120. Upstream film section

121. Center film portion

122. Downstream film section

123. Sub-film portion

13. Heat insulation cavity

14. Vertical corrosion hole

15. Bevel edge corrosion hole

16. Thermopile

160. Cold end

161. Hot end

162. Thermocouple strip

163. Polycrystalline silicon thermocouple strip

164. Metal thermocouple strip

17. Heating element

18. Radiator

19. Metal wire

190. Heating element wire

191. Thermopile series metal wire

192. Thermopile lead-out metal wire

193. Temperature-sensitive resistor metal wire

20. Temperature-sensitive resistor

21. Lead bonding pad

22. A first insulating layer

23. Second insulating layer

24. Polysilicon layer

25. Third insulating layer

26. Ohmic contact hole

27. Metal layer

28. Passivation layer

Detailed Description

Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.

Please refer to fig. 1 to 28. It should be noted that, the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings rather than the number, shape and size of the components in actual implementation, and the form, number and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.

Example 1

As shown in fig. 1 to 8, the present invention provides a MEMS thermal flow sensor, comprising:

As shown in fig. 1, a (100) -plane monocrystalline silicon substrate 1 is provided with a groove 11, and the groove 11 is arranged on the upper surface of the substrate 1;

As shown in fig. 3, a heat insulation film 12 covers the groove 11 and is connected with the substrate 1, and the heat insulation film 12 and the substrate 1 together enclose a heat insulation cavity 13;

As shown in fig. 2 and 4 to 8, at least two vertical etching holes 14 penetrating the heat insulation film 12 and extending in a vertical direction Y, all of the vertical etching holes 14 being sequentially arranged in a horizontal direction X and dividing the heat insulation film 12 into three regions in sequence, as shown in fig. 4, 20 and 21, an upstream film portion 120, a central film portion 121 and a downstream film portion 122, wherein the upstream film portion 120 and the downstream film portion 122 are the same in size and symmetrical with respect to the central film portion 121, wherein a <110> crystal orientation of the substrate 1 is defined in the horizontal direction X, and the vertical direction Y belongs to the substrate based on the properties of silicon material

Negative direction of bottom 1<110> crystal orientation

As shown in fig. 4 to 8, the bevel etching holes 15 respectively penetrate through the upstream film portion 120 and the downstream film portion 122 and extend along the <100> crystal direction of the substrate 1, and are disposed between the bevel etching holes 15 of the upstream film portion 120 and the bevel etching holes 15 of the downstream film portion 122 in a mirror symmetry manner (as shown in fig. 4 to 7) or in a 180 ° rotation symmetry manner (as shown in fig. 8), the film portion where the bevel etching holes 15 are disposed is divided into a plurality of sub-film portions 123 by the bevel etching holes 15, for example, the upstream film portion 120 is divided into two sub-film portions 123 by the bevel etching holes 15 in fig. 4, and the downstream film portion 122 is divided into two sub-film portions 123 by the bevel etching holes 15 in fig. 6 to 8;

As shown in fig. 2, a plurality of thermopiles 16 are provided on the sub-film portion 123, and all the thermopiles 16 provided on the sub-film portion 123 of the upstream film portion 120 are connected in series, and all the thermopiles 16 provided on the sub-film portion 123 of the downstream film portion 122 are connected in series;

as shown in fig. 2, the heating element 17 is disposed on the central film portion 121 and extends in the vertical direction Y.

Specifically, the heating element 17 may be a heating resistor, and the material is selected from a semiconductor material, a metal material, or other materials suitable for preparing the heating element, and in addition, the structure of the heating element 17 is not particularly limited, and is set according to actual needs.

Specifically, as shown in fig. 20 and 21, two vertical etching holes 14 are provided at the center of the heat insulation film 12 so as to divide the heat insulation film 12 into three regions of an upstream film portion 120, a central film portion 121 and a downstream film portion 122, and four vertical etching holes 14 may be provided under the condition of allowable size, as shown in fig. 4, 9, 10, 16, 17, 18 and 19, two vertical etching holes 14 are provided at the center of the heat insulation film 12, and two vertical etching holes 14 are provided at both sides of the heat insulation film 12, so that the heat insulation film 12 is divided into three regions of the upstream film portion 120, the central film portion 121 and the downstream film portion 122.

The thermopiles 16 are located at two sides of the heating element 17, i.e. at the upstream and downstream positions, and are mirror symmetrical or 180 ° rotationally symmetrical, and respectively form an upstream and a downstream two independent thermopile detection circuits, when the heating element 17 is heated by electric current, a steady-state temperature curve is formed around the heating element 17. Through the symmetry of the two independent thermopile detection circuits at the upper and lower sides, when no gas (medium) passes through in the normal temperature environment, the heating element 17 applies an electric load to generate heat, the temperature fields generated by the two independent thermopiles at the upper and lower sides are symmetrical, so that the two independent thermopile detection circuits at the upper and lower sides sense the same potential difference, the two independent thermopile detection circuits at the upper and lower sides cannot sense the temperature difference of the upper and lower thermopiles, when the gas (medium) passes through, the heat at the upper side is reduced, the heat at the lower side is increased, and the corresponding thermopiles generate different potential differences, and therefore the two independent thermopile detection circuits at the upper and lower sides sense the temperature difference of the upper and lower thermopiles, and the flow sensing is performed by utilizing the temperature difference.

In this embodiment, by setting the bevel edge etching holes 15 extending along the <100> crystal direction of the substrate and combining with the vertical etching holes 14, the effective release of the heat insulation film 12 can be achieved, generally when the heat insulation film 12 is released, the substrate 1 needs to be etched back, for example, the depth of 100 μm, when the substrate 1 is corroded, the closer to the center, the smaller the corrosion rate is, so that a hill-like structure exists at the center, while in the heat insulation film area, the bevel edge etching holes 15 are set, because the direction is along the <100> crystal direction of the substrate, when the alkaline solution is adopted for corrosion, the corrosion rate of the crystal face of the substrate (100) is far greater than the corrosion rate of the crystal face of the substrate (111), so that the bevel edge etching holes 15 can be completely corroded downwards in the thickness direction of the substrate to remove the substrate, thereby improving the hill-like structure at the center of the heat insulation film, improving the shape retention of the heat insulation cavity, reducing the heat loss in the direction of the substrate, improving the measurement accuracy, and the vertical etching holes 14 can also hinder the heat from being transferred to the horizontal direction, reducing the heat loss, and further improving the measurement accuracy; meanwhile, the bevel edge corrosion hole 15 can prevent temperature from conducting transversely, so that a plurality of sub-film parts 123 obtained by dividing the bevel edge corrosion hole can be in different temperature fields, and the sensitivity to different measuring flow is different due to different distances between the hot end of the thermopile and the heating element, so that different measuring range test requirements can be realized through different distances between the hot end of the thermopile and the heating element of the different sub-film parts 123, and multi-range measurement is achieved. Taking fig. 9 as an example, one bevel etching hole 15 is respectively arranged in the upstream film portion 120 and the downstream film portion 122, the respective film portions are divided into two sub-film portions 123, and among thermopiles on the two sub-film portions 123 in the upstream film portion 120, the thermopile hot end positioned at the inner side is closer to the heating element 17, so that the fluid flow of a larger flow path can be measured, and the thermopile hot end positioned at the outer side is farther from the heating element 17, so that the fluid flow of a smaller measuring range can be measured. Specifically, the purpose of adjusting the range of the measuring range can be achieved by changing the distance from the hot end of the thermopile to the heating element according to the requirement.

As shown in fig. 5, in practice, the width W1 of the center thin film portion 121 is not too wide, which tends to cause incomplete removal of the substrate under the center thin film portion 121 and increase of heat loss, or too narrow, which tends to lower mechanical stability and to break the film. Taking four vertical etching holes 14 as an example in fig. 5, the distance W1 between two vertical etching holes 14 (i.e., the width of the central film portion 121) at the middle position of the insulating film 12 and the width W2 of the two vertical etching holes 14 determine the distance relationship between the thermopile and the heating element, while the positions of all vertical etching holes 14 and the bevel etching holes 15 in the insulating film 12 and the widths W2, W3 of all vertical etching holes 14 and the width of the bevel etching holes 15 determine the size relationship of the cavity below.

The number of the bevel edge corrosion holes can be selected according to different measuring range requirements and the size of the heat insulation cavity. In practice, two ranges (wide range, small range) or three ranges (wide range, medium range, small range) are generally selected, so that more of the upstream film portion 120 and the downstream film portion 122 are each provided with 1 of the bevel-edge etching holes 15 or 2 of the bevel-edge etching holes 15, and when the upstream film portion 120 and the downstream film portion 122 are each provided with 2 of the bevel-edge etching holes 15, 2 of the bevel-edge etching holes 15 are vertically arranged as shown in fig. 6 and 7 or are arranged in parallel as shown in fig. 8. When the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with 1 bevel etching hole 15, the thin film portion where the thin film portion is located is divided into 2 sub-thin film portions 123, each sub-thin film portion 123 is provided with 2 thermopiles 16, so that two-range flow measurement can be realized, small-range measurement can be realized by ports 2 and 4, and large-range measurement can be realized by ports 3 and 4, as shown in fig. 9 to 21, and when the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with 2 bevel etching holes 15, the thin film portion where the thin film portion is located is divided into 3 sub-thin film portions 123, and each sub-thin film portion 123 is provided with 3 thermopiles 16, so that three-range flow measurement can be realized.

As shown in fig. 2 and 9, the flow sensor further includes a wire 19, which realizes the circuit extraction of each structure in the flow sensor, for example, including a heating element wire 190, a thermopile serial wire 191, a thermopile extraction wire 192, a temperature-sensitive resistor wire 193, and the like. Preferably, the heating element wires 190 and the thermopile series wires 191 may be disposed to pass through the central thin film portion 121 on both sides of the heating element 17 in the vertical direction Y, so that the uniformity of heating is ensured and the mechanical stability of the central thin film portion 121 is improved. Other metal lines may alternatively be provided on the substrate.

As a preferred example, a radiator 18 may be further provided on the heating element 17, as shown in fig. 10, to further enhance the heat exchange rate between heat and surface passing fluid and improve measurement accuracy. The specific shape of the radiator 18 is not limited, and may be any shape that can improve heat exchange efficiency, for example, sheet metal may be coated on the heating element 17, as shown in fig. 11, a plurality of metal strips in a horizontal direction may be arranged on the heating element 17 in a vertical direction, a plurality of metal strips may be arranged on the heating element 17 in an inclined direction, or the like, and the arrangement may be specifically made according to actual needs.

As a preferred example, the cold end 160 of the thermopile 16 may be disposed on the substrate 1, so that the cold end 160 of the thermopile 16 is in sufficient contact with the substrate 1 to increase the heat dissipation performance of the cold end, increase the temperature difference between the cold and hot ends, shorten the response time of the sensor, and increase the range.

As shown in fig. 2, the flow sensor may further include a temperature sensitive resistor 20 disposed outside of at least one of the thermopile cold ends 160. The ambient temperature can be directly measured and compensated by the temperature-sensitive resistor 20, so that the influence of gas temperature fluctuation on a measurement result can be eliminated, and the detection precision is improved.

The thermopile 16 may comprise various types according to the number and location of the bevel etch holes 15. For example, as shown in fig. 12 and 14, the thermopile 16 is arranged in series along the horizontal direction X with a plurality of thermocouple strips 162 in the vertical direction Y, the cold end 160 of the thermopile 16 is located on the substrate 1, the hot end 161 is adjacent to the bevel etching hole 15, as shown in fig. 13, the thermopile 16 is arranged in series along the horizontal direction with a plurality of thermocouple strips 162, the thermocouple strips 162 are parallel to the bevel etching hole 15, the cold end 160 of the thermopile 16 is located on the substrate 1, the hot end 161 is parallel to the heating element 17, as shown in fig. 15, the thermopile 16 is arranged in series along the vertical direction Y with a plurality of thermocouple strips 162 in the horizontal direction X, the cold end 160 of the thermopile 16 is located on the substrate 1, and the hot end 161 is adjacent to the bevel etching hole 15.

The thermopile 16 may be selected in at least one of the three types described above according to actual needs. When the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with 1 bevel etching hole 15, as shown in fig. 9, the four thermopiles 16 may be in the thermopile type shown in fig. 12, as shown in fig. 16, the four thermopiles 16 may be in the thermopile type shown in fig. 13, as shown in fig. 17 and 18, or the four thermopiles 16 may be a combination of the two thermopile types shown in fig. 12 and 13. When the upstream thin film portion 120 and the downstream thin film portion 122 are each provided with 2 bevel etching holes 15, as shown in fig. 19, six thermopiles may be in the form of thermopiles as shown in fig. 12 and 14, as shown in fig. 20, six thermopiles 16 may be in the form of a combination of two thermopiles as shown in fig. 12 and 15, and as shown in fig. 21, six thermopiles 16 may be in the form of a combination of two thermopiles as shown in fig. 13 and 15. Other thermopile types may be combined, and the configuration is actually set according to the shape of the sub-film portion 123, and is not limited thereto.

The material of the thermocouple strip 162 in the thermopile 16 may be selected from conventional materials suitable for use as a thermocouple, for example, a polysilicon-metal combination with a large seebeck coefficient difference is common, polysilicon may be selected from P-type doped polysilicon or N-type doped polysilicon, polysilicon-N-type doped polysilicon combination may be selected from P-type doped polysilicon, P-type doped ions may be P-type ions such as boron ions, N-type doped ions may be N-type ions such as phosphorus ions, and metal may be selected from aluminum metal or other metals. When the combination of the thermocouple strips 162 is selected to be a polysilicon-metal combination, the heating element 17 may also be selected to be a heating element of polysilicon material, and polysilicon may be selected to be P-doped or N-doped polysilicon. In this way, the polysilicon thermocouple strip 162 and the heating element 17 can be prepared simultaneously, i.e. the same doping element, dosage, concentration and other parameters are adopted, and the polysilicon thermocouple strip and the heating element are annealed and etched simultaneously to have electrical properties. Of course, doping under different conditions can be performed in batches according to actual design.

The two thermocouple strips 162 in the thermopile 16 in combination may be disposed in a conventional manner, for example, may be vertically stacked along the thickness direction of the (100) plane of the substrate 1, as shown in fig. 12 to 15, where the two thermocouple strips 162 are connected by VIA, or are disposed in a flat manner along the (100) plane of the substrate 1, that is, disposed on the same plane, but may be other manners, and specifically selected according to practical needs.

Example two

The present embodiment provides a method for preparing a MEMS thermal flow sensor, which may be used to prepare the MEMS thermal flow sensor, but the method for preparing the MEMS thermal flow sensor is not limited thereto, and other feasible methods may be used to prepare the MEMS thermal flow sensor.

The preparation method of this example is described in detail below with reference to the accompanying drawings. It should be noted that, the preparation method of the embodiment is mainly described with respect to the structure of the MEMS thermal flow sensor as shown in fig. 9, in which two thermocouple strips in a combined form in the thermopile are polysilicon-metal combinations with larger seebeck coefficient differences and are vertically stacked along the thickness direction.

As shown in fig. 22, first, step S1 is performed, a (100) -plane single crystal silicon wafer is selected as the substrate 1, and a first insulating layer 22 and a second insulating layer 23 are sequentially formed on the surface of the substrate 1.

The first insulating layer 22 is selected to be a silicon oxide film, and is formed by a thermal oxidation process, and the second insulating layer 23 is selected to be a silicon nitride film, and is prepared by an LPCVD process. The first insulating layer 22 and the second insulating layer 23 serve as support film structures for the device.

As shown in fig. 23, step S2 is then performed to deposit polysilicon on the support film structure and perform P-type ion implantation, such as B-ion implantation, and anneal and repair the lattice damage to obtain a P-type ion doped polysilicon layer 24.

Of course, an N-type ion implantation, such as a phosphorus ion implantation, may also be performed, and the lattice damage repaired by annealing to obtain the N-type ion doped polysilicon layer 24. In addition, in order to reduce the contact resistance, ohmic contact is easier to form later, and secondary heavy doping can be performed at the position where the subsequent heavy doping is needed to be connected with metal, so that a heavy doped region is formed.

As shown in fig. 24, step S3 is performed to pattern the polysilicon layer 24 by photolithography and etching processes, so as to obtain the polysilicon thermocouple strips 163 and the heating elements 17.

As shown in fig. 25, step S4 is performed, using a third insulating layer 25, such as a silicon oxide insulating layer, filling up the patterned polysilicon layer 24 and covering the polysilicon layer 24 by a predetermined thickness, and forming an ohmic contact hole 26 penetrating the third insulating layer 25 at a predetermined position of the third insulating layer 25, where the ohmic contact hole 26 is formed at the cold end and the hot end to realize the subsequent electrical connection with the metal thermocouple strip 164.

As shown in fig. 25, next, step S5 is performed, a metal layer 27 is formed on the third insulating layer 25, and the metal layer 27 is filled with the ohmic contact hole 26, for example, an aluminum metal layer, and then the metal layer 27 is patterned to obtain structures such as a metal thermocouple strip 164, a metal wire 19, a heat spreader 18, and a lead pad 21, and ohmic contact annealing is performed to form ohmic contact between the polysilicon thermocouple strip 163 and the metal thermocouple strip 164.

As shown in fig. 26, step S6 is performed, and a passivation layer 28 is formed on the surface of the above structure to protect the whole structure, wherein the passivation layer 28 may be a stacked structure of silicon oxide and silicon nitride, and the wire bonding pad 21 is sequentially exposed, and the vertical etching holes 14 and the bevel etching holes 15 are prepared.

As shown in fig. 27 and 28, finally, step S7 is performed, in which the substrate 1 is etched by using an alkaline etching solution, such as TMAH, KOH, etc., based on the vertical etching holes 14 and the bevel etching holes 15 to obtain the insulating cavity 13, and then the first insulating layer 22 and the second insulating layer 23 on the back surface of the device are removed. And finally obtaining the MEMS thermal flow sensor.

In summary, the invention provides the MEMS thermal flow sensor, through setting up the hypotenuse corrosion hole that extends along the <100> crystal direction of the substrate and combining with the vertical corrosion hole, can achieve the effective release of the heat insulation film, generally, when releasing the heat insulation film, the substrate needs to be corroded in depth, when corroding the substrate, the closer to the center the corrosion rate is smaller, so there is a hillock-like structure in the center, and the hypotenuse corrosion hole is set in the heat insulation film area, because the direction is along the <100> crystal direction of the substrate, when corroding by alkaline solution, the corrosion rate of the crystal face of the substrate (100) is far greater than the corrosion rate of the crystal face of the substrate (111), so the hypotenuse corrosion hole can completely corrode and remove the substrate downwards along the thickness direction of the substrate, thereby improving the hillock-like structure in the center of the heat insulation film, improving the shape retention of the heat insulation cavity, reducing the hypotenuse towards the substrate direction, improving the measurement accuracy, the vertical corrosion hole can also obstruct the heat transfer towards the substrate in the horizontal direction, further improving the measurement accuracy, meanwhile, the corrosion hole can obstruct the transverse temperature, and can divide the heat loss, and the obtained by the heat loss, and the temperature can reach the different thermal-pile temperature, and the different thermal-resistance, the thermal-electric element, and the thermal-electric element can reach the thermal-electric element, and the thermal element can reach the requirements, and the thermal-flow and the thermal element. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.

Claims

1. A MEMS thermal flow sensor, characterized in that the MEMS thermal flow sensor comprises:

(100) a single crystal silicon substrate having a groove, wherein the groove is opened on the upper surface of the substrate;

A heat-insulating film, covering the groove and connected to the substrate, wherein the heat-insulating film and the substrate together form a heat-insulating cavity;

At least two vertical corrosion holes penetrating the thermal insulation film and extending in the vertical direction, all of the vertical corrosion holes are arranged in sequence in the horizontal direction and divide the thermal insulation film into three regions: an upstream film portion, a central film portion, and a downstream film portion, wherein the upstream film portion and the downstream film portion have the same size and are symmetrical about the central film portion;

Beveled etching holes respectively penetrating the upstream thin film portion and the downstream thin film portion and extending along the <100> crystal direction of the substrate, wherein the beveled etching holes arranged in the upstream thin film portion and the beveled etching holes arranged in the downstream thin film portion are arranged mirror-symmetrically or 180° rotationally symmetrically, and the beveled etching holes divide the thin film portion where they are located into a plurality of sub-thin film portions;

A plurality of thermopiles are arranged on the sub-thin film portion, and all the thermopiles arranged on the sub-thin film portion of the upstream thin film portion are connected in series, and all the thermopiles arranged on the sub-thin film portion of the downstream thin film portion are connected in series;

A heating element is disposed on the central film portion and extends in a vertical direction;

Wherein, the horizontal direction is the <110> crystal direction of the substrate, and the vertical direction is the Crystal direction.

2. The MEMS thermal flow sensor according to claim 1 is characterized in that: the upstream thin film portion and the downstream thin film portion are each provided with one of the beveled edge corrosion holes or two of the beveled edge corrosion holes, and when the upstream thin film portion and the downstream thin film portion are each provided with two of the beveled edge corrosion holes, the two beveled edge corrosion holes are vertically arranged or parallel arranged.

3. The MEMS thermal flow sensor according to claim 1, further comprising a heating element metal wire and a thermopile series metal wire, both of which pass through the central thin film portion on both sides of the heating element in a vertical direction.

4 . The MEMS thermal flow sensor according to claim 1 , further comprising a heat sink, wherein the heat sink is disposed above the heating element and is used to dissipate heat from the heating element.

5. The MEMS thermal flow sensor according to claim 4 is characterized in that: the heat sink is a sheet of metal, or the heat sink is composed of a plurality of horizontal metal strips arranged in a vertical direction, or the heat sink is composed of a plurality of inclined metal strips arranged in a vertical direction.

6 . The MEMS thermal flow sensor according to claim 1 , wherein the cold end of the thermopile is located on the substrate so that the cold end of the thermopile is in full contact with the substrate.

7 . The MEMS thermal flow sensor according to claim 1 , further comprising a temperature-sensitive resistor disposed outside of at least one of the cold ends of the thermopile.

8. The MEMS thermal flow sensor according to claim 1, wherein the thermopile is configured as at least one of the following three types:

In the first type, the thermopile is composed of a plurality of vertical thermocouple strips arranged in series in a horizontal direction, the cold end of the thermopile is located on the substrate, and the hot end is adjacent to the bevel etched hole;

In the second form, the thermopile is arranged in series with a plurality of thermocouple strips in a horizontal direction, the thermocouple strips are parallel to the beveled etched holes, the cold end of the thermopile is located on the substrate, and the hot end is parallel to the heating element;

In the third type, the thermopile is arranged in series in a vertical direction with a plurality of horizontal thermocouple strips, the cold end of the thermopile is located on the substrate, and the hot end is adjacent to the bevel corrosion hole; all the thermopiles are arranged in at least one of the three types.

9. The MEMS thermal flow sensor according to claim 1 or 8, characterized in that the thermocouple strips in the thermopile are a combination of any two of P-type doped polysilicon thermocouple strips, N-type doped polysilicon thermocouple strips and metal thermocouple strips.

10. The MEMS thermal flow sensor according to claim 9, characterized in that the thermocouple strips in the combined form in the thermopile are vertically stacked along the thickness direction of the (100) surface of the substrate or are laid flat along the (100) surface of the substrate.