CN114577287A - Thermal flow sensor and method of making the same - Google Patents

Abstract

The application discloses hot type flow sensor and preparation method thereof, hot type flow sensor includes: an upstream thermosensitive element and a downstream thermosensitive element separately formed on a surface of the substrate; a heating resistor formed on the surface of the substrate and located between the upstream thermosensitive element and the downstream thermosensitive element, for electrically heating the upstream thermosensitive element and the downstream thermosensitive element; and the through hole is formed in the heating resistor along the direction vertical to the surface of the substrate, so that the heating resistor forms a first resistor and a second resistor, the first resistor is positioned at one end of the heating resistor facing the upstream thermosensitive element, the second resistor is positioned at one end of the heating resistor facing the downstream thermosensitive element, and the first resistor and the second resistor are symmetrical and connected in parallel. The problem that the measurement accuracy is influenced due to uneven heat diffusion of an existing thermal flow sensor can be solved, and meanwhile the sensitivity of the sensor can be improved.

Description

Thermal flow sensor and method of making the same

technical field

The application belongs to the technical field of sensing, and in particular relates to a thermal flow sensor and a manufacturing method thereof.

Background technique

With the development of society, people have higher and higher requirements for sensors. For example, sensors are required to have the characteristics of small size, fast response time, and stable performance. Thermal distributed MEMS flow sensors can meet the above requirements. The thermal flow sensor is mainly composed of one heating resistor and two temperature measuring elements. By maintaining the constant power of the heating resistor, the flow is measured according to the temperature difference of the upstream and downstream temperature measuring elements under different flow rates. In order to ensure the measurement accuracy, the thermally distributed MEMS flow sensor has high requirements on the process, but still due to process deviations and other reasons, the heat diffusion of the heating resistor is not uniform, resulting in the temperature deviation of the two temperature measuring elements, thus affecting the measurement accuracy.

SUMMARY OF THE INVENTION

The purpose of the embodiments of the present application is to provide a thermal flow sensor and a manufacturing method thereof, so as to solve the problem that the measurement accuracy of the existing thermal flow sensor is affected by uneven heat diffusion, and at the same time, the sensitivity of the sensor can be improved.

According to a first aspect of the embodiments of the present application, a thermal flow sensor is provided, including:

The upstream thermal element and the downstream thermal element are separately formed on the surface of the substrate;

a heating resistor, formed on the surface of the substrate and located between the upstream thermal element and the downstream thermal element, for electrically heating the upstream thermal element and the downstream thermal element;

A through hole, in a direction perpendicular to the surface of the substrate, is formed in the heating resistor so that the heating resistor forms a first resistance and a second resistance, the first resistance located on the heating resistor facing the upstream heat one end of the thermal element, the second resistor is located at the end of the heating resistor facing the downstream thermal element, the first resistor and the second resistor are symmetrical and connected in parallel.

Optionally, a thermally conductive layer is provided between the first resistor and the upstream thermal element and between the second resistor and the downstream thermal element.

Optionally, the material of the thermal conductive layer is silicon nitride, aluminum oxide, aluminum nitride, magnesium oxide or boron nitride.

Optionally, a cavity is provided on the back of the substrate, and the heating resistor is located at a position of the substrate corresponding to the cavity.

Optionally, the base comprises a substrate, a surface of the substrate is provided with a support layer, the upstream thermal element, the downstream thermal element and the heating resistor are located on the surface of the support layer, the The backside of the substrate is provided with the cavity and exposes the support layer.

Optionally, the surface of the substrate is further provided with an environmental resistance, which is used to generate high temperature by electrification, so as to remove the residual water vapor and gas on the surface of the thermal flow sensor.

Optionally, the ambient resistance includes an upstream serpentine resistor and a downstream serpentine resistor, the upstream serpentine resistor is located upstream of the upstream thermal element, and the downstream serpentine resistor is located downstream of the downstream thermal element .

According to a second aspect of the embodiments of the present application, a method for manufacturing a thermal flow sensor is provided, including:

provide a base;

forming a heating resistor and an upstream thermal element and a downstream thermal element on opposite sides of the heating resistor on the surface of the substrate;

A through hole is formed in the heating resistor in a direction perpendicular to the surface of the substrate, so that the heating resistor forms a first resistor and a second resistor, the first resistor is located on the heating resistor facing the upstream heat one end of the thermal element, the second resistor is located at the end of the heating resistor facing the downstream thermal element, the first resistor and the second resistor are symmetrical and connected in parallel.

Optionally, the providing a substrate includes:

provide a substrate;

forming a silicon oxide layer on the surface of the substrate;

forming a silicon nitride layer on the surface of the silicon oxide layer;

The backside of the substrate is etched to correspond to the position of the heating resistor to form a cavity.

Optionally, the forming a heating resistor on the surface of the substrate and the upstream thermal element and the downstream thermal element located on opposite sides of the heating resistor include:

depositing polysilicon on the surface of the substrate, and doping to form an N+-shaped polysilicon layer;

The N+-shaped polysilicon layer is patterned to form a heating resistor and upstream and downstream thermal elements on opposite sides of the heating resistor.

The above-mentioned technical solutions of the present application have the following beneficial technical effects:

In the thermal flow sensor of the embodiment of the present application, a through hole is formed in the heating resistor, so that the heating resistor forms a first resistor and a second resistor that are symmetrical and connected in parallel. On the one hand, the heat generated by the first resistor and the second resistor is the same and It heats the upstream thermal element and the downstream thermal element respectively, which is conducive to the uniform diffusion of heat to the thermal elements on both sides, thereby reducing the influence of process deviation and other reasons on the measurement accuracy. In the case of changing, the power of the heating resistor can be increased, and the calorific value can be increased, which is beneficial to improve the measurement sensitivity.

Description of drawings

1 is a schematic structural diagram of a thermal flow sensor in an exemplary embodiment of the present application;

2 is a cross-sectional view of a thermal flow sensor in an exemplary embodiment of the present application;

In the figure, 100, substrate; 110, substrate; 120, silicon oxide layer; 130, silicon nitride layer; 140, cavity; 200, upstream thermal element; 300, downstream thermal element; 321, N+ type polysilicon thermoelectric Couple; 322, P+ type polysilicon thermocouple; 400, heating resistor; 410, first resistor; 420, second resistor; 430, through hole; 500, thermal conductive layer; 600, first insulating layer; 700, second insulating layer 800, wire structure; 1, first electrode; 2, second electrode; 3, third electrode; 4, fourth electrode; 5, fifth electrode; 6, sixth electrode.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present application more clear, the present application will be described in further detail below in conjunction with the specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are exemplary only and are not intended to limit the scope of the application. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present application.

A schematic diagram of a layer structure according to an embodiment of the present application is shown in the accompanying drawings. The figures are not to scale, some details are exaggerated for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships are only exemplary, and in practice, there may be deviations due to manufacturing tolerances or technical limitations, and those skilled in the art should Regions/layers with different shapes, sizes, relative positions can be additionally designed as desired.

Obviously, the described embodiments are some, but not all, embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

In the description of the present application, it should be noted that the terms "first", "second" and "third" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict with each other.

FIG. 1 is a schematic structural diagram of a thermal flow sensor in an exemplary embodiment of the present application; FIG. 2 is a cross-sectional view of a thermal flow sensor in an exemplary embodiment of the present application.

As shown in FIGS. 1-2 , an embodiment of the present application provides a thermal flow sensor, including: a substrate 100 ; an upstream thermal element 200 and a downstream thermal element 300 , which are separately formed on the surface of the substrate 100 ; and a heating resistor 400 , which is formed On the surface of the substrate 100 and located between the upstream thermal element 200 and the downstream thermal element 300, for heating the upstream thermal element 200 and the downstream thermal element 300 with electricity; through holes 430, in a direction perpendicular to the surface of the substrate 100 , formed in the heating resistor 400 so that the heating resistor 400 forms a first resistor 410 and a second resistor 420, the first resistor 410 is located at the end of the heating resistor 400 facing the upstream thermistor 200, and the second resistor 420 is located at the end of the heating resistor 400 facing the upstream thermistor 200 At one end of the downstream thermal element 300, the first resistor 410 and the second resistor 420 are symmetrical and connected in parallel. In a specific application, a through hole 430 is formed in the heating resistor 400 of the thermal flow sensor, so that the heating resistor 400 forms a symmetrical and parallel first resistor 410 and a second resistor 420. On the one hand, the first resistor 410 and the second resistor 420 The heat generated by the resistors 420 is the same and each heats the upstream thermistor 200 and the downstream thermistor 300, which is beneficial for the heat to spread evenly to the thermal elements on both sides, thereby reducing the influence of process deviation and other reasons on the measurement accuracy. , the two resistors are connected in parallel, under the condition that the voltage remains unchanged, the power of the heating resistor 400 can be increased, and the calorific value can be increased, which is beneficial to improve the measurement sensitivity.

In some exemplary embodiments, the surface of the substrate 100 is further formed with a heating resistor 400 and electrode pads of the thermal element, which are used for electrical conduction with the outside. For example, the electrode pad includes a first electrode 1, a second electrode 2, a third electrode 3, a fourth electrode 4, a fifth electrode 5, and a sixth electrode 6, wherein the first electrode 1 and the second electrode 2 are respectively connected to Both ends of the heating resistor 400 , the third electrode 3 and the fourth electrode 4 are respectively connected to both ends of the upstream thermal element 200 , and the fifth electrode 5 and the sixth electrode 6 are respectively connected to both ends of the downstream thermal element 300 .

In some exemplary embodiments, the substrate 100 may employ a single-polish or double-polish semiconductor substrate, including but not limited to a silicon substrate, a germanium substrate, an SOI substrate, and a GeOI substrate. In the embodiment of the present application, the substrate 110 is a double-polished single crystal silicon substrate.

In some exemplary embodiments, the heating resistor 400 is a thermistor material that is sensitive to temperature, that is, its resistance is positively correlated with temperature changes. Preferably, the heating resistor 400 uses nickel (Ni), platinum (Pt), gold A combination of one or more of (Au), aluminum (Al), copper (Au), and polysilicon. In the embodiment of the present application, the heating resistor 400 can be made of N+ type polysilicon. In order to adapt to the stress changes caused by extreme temperatures, an adhesive layer may be attached to the surface of the heating resistor 400. Preferably, the adhesive layer is made of titanium (Ti), chromium (Cr), nickel (Ni), titanium oxide (TiO ₂ ) or Titanium tungsten alloy.

In some exemplary embodiments, the resistance of the upstream thermal element 200 and the downstream thermal element 300 is greater than the resistance of the heating resistor 400 , for example, the resistance of the thermal elements is 2-100 times that of the heating resistor 400 . The upstream thermal element 200 and the downstream thermal element 300 are thermistor materials that are sensitive to temperature, that is, their resistance is positively correlated with temperature changes. Preferably, the upstream thermal element 200 and the downstream thermal element 300 are made of nickel (Ni). ), platinum (Pt), gold (Au), aluminum (Al), copper (Au), and a combination of one or more of polysilicon. In the embodiment of the present application, both the upstream thermal element 200 and the downstream thermal element 300 may use N+ type polysilicon. Further, in order to adapt to the stress changes caused by extreme temperatures, an adhesive layer may be attached to the surfaces of the upstream thermal element 200 and the downstream thermal element 300. Preferably, the adhesive layer uses titanium (Ti), chromium (Cr), nickel (Ni), titanium oxide (TiO ₂ ) or titanium-tungsten alloy.

In some exemplary embodiments, the upstream thermal element 200 and the downstream thermal element 300 are thermopile. Since the thermopile is formed by N thermocouples connected in series, the output voltage is N times the output of a single thermocouple pair, Thereby, the sensitivity of the sensor is improved, thereby realizing the signal-to-noise ratio and measurement accuracy of the thermal flow sensor. Further, the thermopile includes a plurality of sets of thermocouple pairs connected in series, each set of thermocouple pairs includes an N+ type polysilicon thermocouple and a P+ type polysilicon thermocouple stacked up and down, and there is provided between the N+ type polysilicon thermocouple and the P+ type polysilicon thermocouple. The insulating layer is connected through the wire structure 800, so that the number of thermocouples is further increased under the same area, and the sensitivity of the sensor can be further improved.

In some exemplary embodiments, the through hole 430 may be one of a square hole, a circular hole, and an oval hole, so that the heating resistor 400 is in a "back" shape. formed at the same time.

In some exemplary embodiments, along the direction of gas flow, the centers of the first resistor 410 , the second resistor 420 , the through hole 430 , the upstream thermal element 200 and the downstream thermal element 300 are located on the same straight line.

In some exemplary embodiments, in order to further improve the sensitivity and measurement accuracy of the sensor, a thermally conductive layer 500 is provided between the first resistor 410 and the upstream thermal element 200 and between the second resistor 420 and the downstream thermal element 300 . Exemplarily, along a direction perpendicular to the surface of the substrate 100 , the thermally conductive layer 500 is deposited on the surface of the heating resistor 400 , and both ends of the thermally conductive layer 500 are in contact with the upstream thermal element 200 and the downstream thermal element 300 respectively. Specifically, the thermally conductive layer 500 acts as a medium instead of air to conduct heat to the thermal element, which can reduce the heat diffused to other elements, thereby helping to increase the temperature of the thermal element and improve the sensitivity and measurement accuracy of the sensor. Optionally, the thermally conductive layer 500 may be a whole or two independent parts. For example, the two parts are formed between the first resistor 410 and the upstream thermal element 200 and the second resistor 420 and the downstream thermal element 300 respectively. between.

In some exemplary embodiments, in order to improve the thermal conductivity, the thermally conductive layer 500 is made of a material with high thermal conductivity. For this reason, the material of the thermally conductive layer 500 can be selected from silicon nitride, aluminum oxide, aluminum nitride, magnesium oxide or boron nitride Wait.

In some exemplary embodiments, in order to ensure the thermal conductivity effect, the thermal conductive layer 500 has the same contact area and contact position with the upstream thermal element 200 and the downstream thermal element 300 .

In some exemplary embodiments, in order to improve the sensitivity and measurement accuracy of the sensor, a thermal insulation layer (marked in the figure) is provided between the thermal conductive layer 500 and the substrate 100 , and the thermal insulation layer can prevent the heating resistor 400 from energizing and generating heat. The medium heat is transferred to the substrate 100 to reduce heat loss, which is beneficial to improve the sensitivity and measurement accuracy of the sensor. Preferably, the heat insulating layer adopts insulating heat insulating materials such as silicon oxide.

In some exemplary embodiments, in order to increase the temperature difference between the hot and cold ends of the thermal element and improve the sensitivity of the sensor, both ends of the thermally conductive layer 500 cover the hot ends of the upstream thermal element 200 and the downstream thermal element 300 respectively, including the hot ends of the thermal elements 200 and 300 . Top and side. The hot end is the end of the upstream thermal element 200 and the downstream thermal element 300 close to the heating resistor 400, and has a higher temperature than the cold end.

In order to reduce heat loss, the backside of the substrate 100 is provided with a cavity 140 , and the cavity 140 is located at the position of the substrate 100 corresponding to the heating resistor 400 . When the center of the temperature field is closer to the surface of the substrate 100 , heat loss can be reduced, and the sensitivity and measurement accuracy of the sensor can be improved. In order to further reduce the heat transferred from the heating resistor 400 to the back of the substrate 100, a protective layer of the cavity 140 can be provided on the back of the substrate 100 to seal the cavity 140 on the back of the substrate 100 to form a vacuum structure. At the same time, a very low thermal conductivity can also be used. The gas or liquid fills the cavity 140 . Preferably, the protective layer of the cavity 140 is silicon (Si), quartz glass (SiO ₂ ), polyimide (Polyimide) or ceramics, and the thickness of the protective layer of the cavity 140 is 0.1-0.7 mm.

In some exemplary embodiments, in order to maintain the temperature difference between the hot and cold ends of the thermal element, the hot ends of the upstream thermal element 200 and the downstream thermal element 300 are located at the positions of the substrate 100 corresponding to the cavity 140, and the cold ends of the thermal elements It is located at a position corresponding to the surface of the substrate 100 and the non-cavity 140 . In specific applications, the cavity 140 can reduce the heat transfer from the hot end to the substrate 100 and its back surface, thereby maintaining the temperature difference between the hot and cold ends, which is beneficial to improve the sensitivity and measurement accuracy of the sensor.

In some exemplary embodiments, the base 100 includes a substrate 110 , the surface of the substrate 110 is provided with a supporting layer, the heating resistor 400 and the upstream thermal element 200 and the downstream thermal element 300 are located on the supporting layer, and the backside of the substrate 110 is located on the supporting layer. A cavity 140 is provided and the support layer is exposed. In a specific application, the support layer may serve as a stop layer for etching the substrate 110 during the formation of the cavity 140, and may also serve as a support layer for the heating resistor 400 and the thermal element. Specifically, the support layer may be formed by stacking the silicon oxide layer 120 and the silicon nitride layer 130. The silicon oxide layer 120 has a low thermal conductivity, which can prevent heat from being transferred to the substrate 110 and its backside. At the same time, due to the silicon oxide and nitrogen The thermal stress of silicon carbide is opposite and complementary. The use of silicon oxide and silicon nitride with different thicknesses can prepare a low-stress composite film, so that the support layer has a good supporting force.

In some exemplary embodiments, in order to prevent residues from affecting the detection accuracy, the surface of the substrate 100 is further provided with an environmental resistance (not shown in the figure), which is used to generate high temperature by energizing and heating, so as to remove the water vapor on the surface of the thermal flow sensor. and gas residues. In specific applications, the gas and the chip surface need to be kept dry and clean to ensure the accuracy of the measurement. However, in the application environment, it is inevitable that a small amount of impurity gas or water vapor will enter the pipeline, causing it to be adsorbed on the surface of the chip, resulting in accurate measurement. Therefore, after the detection is completed, a high level is applied to the environmental resistance by means of a gate switch, etc., which can make the environmental resistance generate heat and form a high temperature, and remove the water vapor and gas residues on the surface of the thermal flow sensor.

In some exemplary embodiments, in order to make the heat distribution on the chip surface uniform, the ambient resistance includes an upstream serpentine resistor and a downstream serpentine resistor, the upstream serpentine resistor is located upstream of the upstream thermal element 200, and the downstream serpentine resistor is located at the downstream thermal element 200. downstream of the sensor 300 .

In some exemplary embodiments, the upstream serpentine resistor and the downstream serpentine resistor are temperature-sensitive thermistor materials, ie, their resistances are positively related to temperature changes. Preferably, the upstream serpentine resistor and the downstream serpentine resistor use a combination of one or more of nickel (Ni), platinum (Pt), gold (Au), aluminum (Al), copper (Au) and polysilicon. In the embodiment of the present application, the upstream serpentine resistor and the downstream serpentine resistor are made of platinum alloy and deposited on the surface of the substrate 100 by magnetron sputtering. Further, in order to adapt to the stress changes caused by extreme temperatures, an adhesive layer can be attached to the surface of the upstream serpentine resistor and the downstream serpentine resistor. Preferably, the adhesive layer is made of titanium (Ti), chromium (Cr), nickel (Ni). ), titanium oxide (TiO ₂ ) or titanium-tungsten alloy.

In some exemplary embodiments, the thermal flow sensor further includes a protective layer (not shown in the figure), and the protective layer is provided on the surfaces of the heating resistor 400 , the upstream thermal element 200 , the downstream thermal element 300 and the substrate 100 . Protects components from damage and increases sensor life. Further, the protective layer is a double-layer structure, including an element protective layer and a chip protective layer. The element protective layer is formed on the surface of the heating resistor 400, the upstream thermal element 200, the downstream thermal element 300, the thermal conductive layer 500 and the substrate 100. The protective layer is formed on the element protective layer. Specifically, the element protection layer is used to protect the heating resistor 400, the upstream thermal element 200, and the downstream thermal element 300, and play an insulating role, and the element protection layer can use silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ). ), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), parylene (Parylene) or perfluoro resin (Cytop) and other materials, the thickness of the element protection layer is 0.01μm ~ 100μm; chip protection The chip protection layer is used to protect the entire sensor and improve the overall strength and mechanical properties of the sensor, which is also a key protection layer to improve the service life of the sensor. The chip protection layer can use silicon carbide (SiC), aluminum oxide (Al2O3), silicon nitride (Si3N4) ), silicon dioxide (SiO ₂ ), parylene (Parylene) or perfluoro resin (Cytop) and other materials; the thickness of the chip protection layer is 0.01 μm to 100 μm. Since the above-mentioned materials with higher mechanical properties such as hardness and wear resistance are used to form a thin film structure as a protective layer, it can effectively isolate gas and liquid to protect internal components, increase the overall strength of the sensor by 50%, and the sensor life can reach 6 years.

Embodiments of the present application also provide a method for manufacturing a thermal flow sensor, including:

Step S10, providing the substrate 100;

Step S20, forming a heating resistor 400 and an upstream thermal element 200 and a downstream thermal element 300 on opposite sides of the heating resistor 400 on the surface of the substrate 100;

Step S30, along the direction perpendicular to the surface of the substrate 100, a through hole 430 is formed in the heating resistor 400, so that the heating resistor 400 forms a first resistor 410 and a second resistor 420, and the first resistor 410 is located upstream of the heating resistor 400 At one end of the thermal element 200, the second resistor 420 is located at the end of the heating resistor 400 facing the downstream thermal element 300, and the first resistor 410 and the second resistor 420 are symmetrical and connected in parallel.

According to the above steps, a through hole 430 is formed in the heating resistor 400 of the thermal flow sensor, so that the heating resistor 400 forms a symmetrical and parallel first resistor 410 and a second resistor 420. On the one hand, the first resistor 410 and the second resistor 420 The heat generated by 420 is the same, and it heats the upstream thermal element 200 and the downstream thermal element 300 respectively, which is conducive to the uniform diffusion of heat to the thermal elements on both sides, thereby reducing the influence of process deviation and other reasons on the measurement accuracy. On the other hand, Connecting the two resistors in parallel can increase the power of the heating resistor 400 and increase the calorific value under the condition that the voltage remains unchanged, thereby helping to improve the measurement sensitivity.

In step S10, the substrate 100 is provided, including:

Step S11, providing a substrate 110;

Step S12, forming a silicon oxide layer 120 on the surface of the substrate 110;

Step S13, forming a silicon nitride layer 130 on the surface of the silicon oxide layer 120;

Step S14 , etching the back surface of the substrate 110 corresponding to the position of the heating resistor 400 to form the cavity 140 .

In some exemplary embodiments, the cavity 140 is located at the position of the substrate 100 corresponding to the heating resistor 400 , so as to reduce the heat transferred from the heating resistor 400 to the substrate 100 , so that the center of the temperature field when the heating resistor 400 is heated is closer to the surface of the substrate 100 . surface, which can reduce heat loss, which is beneficial to improve the sensitivity and measurement accuracy of the sensor. In order to further reduce the heat transferred from the heating resistor 400 to the back of the substrate 100, a protective layer of the cavity 140 can be provided on the back of the substrate 100 to seal the cavity 140 on the back of the substrate 100 to form a vacuum structure. At the same time, a very low thermal conductivity can also be used. The gas or liquid fills the cavity 140 . Preferably, the protective layer of the cavity 140 is silicon (Si), quartz glass (SiO ₂ ), polyimide (Polyimide) or ceramics, and the thickness of the protective layer of the cavity 140 is 0.1-0.7 mm.

In some exemplary embodiments, in order to maintain the temperature difference between the hot and cold ends of the thermal element, the hot ends of the upstream thermal element 200 and the downstream thermal element 300 are located at the positions of the substrate 100 corresponding to the cavity 140, and the cold ends of the thermal elements It is located at a position corresponding to the surface of the substrate 100 and the non-cavity 140 . In specific applications, the cavity 140 can reduce the heat transfer from the hot end to the substrate 100 and its back surface, thereby maintaining the temperature difference between the hot and cold ends, which is beneficial to improve the sensitivity and measurement accuracy of the sensor.

In some exemplary embodiments, the substrate 100 may employ a single-polish or double-polish semiconductor substrate, including but not limited to silicon substrates, germanium substrates, SOI substrates, and GeOI substrates; for example, in the embodiments of the present application Among them, the substrate 110 is a double-polished single crystal silicon substrate.

In step S20, the heating resistor 400 and the upstream thermal element 200 and the downstream thermal element 300 on opposite sides of the heating resistor 400 are formed on the surface of the substrate 100, including:

Step S21, depositing polysilicon on the surface of the substrate 100, and doping to form an N+-shaped polysilicon layer;

Step S22 , the N+-shaped polysilicon layer is patterned to form the heating resistor 400 and the upstream thermal element 200 and the downstream thermal element 300 located on opposite sides of the heating resistor 400 .

In some exemplary embodiments, the heating resistor 400, the upstream thermistor element 200 and the downstream thermistor element 300 are temperature-sensitive thermistor materials, that is, their resistance is positively related to temperature changes, preferably, nickel ( A combination of one or more of Ni), platinum (Pt), gold (Au), aluminum (Al), copper (Au) and polysilicon. In the embodiment of the present application, the heating resistor 400 , the upstream thermal element 200 and the downstream thermal element 300 all use N+ type polysilicon. In order to adapt to the stress changes caused by extreme temperatures, an adhesive layer may be attached to the surface of the heating resistor 400. Preferably, the adhesive layer is made of titanium (Ti), chromium (Cr), nickel (Ni), titanium oxide (TiO ₂ ) or Titanium tungsten alloy.

In some exemplary embodiments, the resistance of the upstream thermal element 200 and the downstream thermal element 300 is greater than the resistance of the heating resistor 400 , for example, the resistance of the thermal elements is 2-100 times that of the heating resistor 400 .

In some exemplary embodiments, in step S20, the heating resistor 400 and the upstream thermal element 200 and the downstream thermal element 300 on opposite sides of the heating resistor 400 are formed on the surface of the substrate 100, including:

Polysilicon is deposited on the surface of the substrate 100 and doped to form an N+-shaped polysilicon layer;

patterning the N+-type polysilicon layer to form a heating resistor 400 and N+-type polysilicon thermocouples located on opposite sides of the heating resistor 400;

A first insulating layer 600 is formed on the surface of the heating resistor 400, the N+ type polysilicon thermocouple and the substrate 100;

Polysilicon is deposited on the surface of the insulating layer, and doped to form a P+ type polysilicon layer;

The P+ type polysilicon layer is patterned to form a P+ type polysilicon thermocouple located in the N+ type polysilicon thermocouple;

A second insulating layer 700 is formed on the surface of the P+ type polysilicon thermocouple and the first insulating layer 600;

etching in the first insulating layer 600 and the second insulating layer 700 to form contact holes exposing the N+ type polysilicon thermocouple and the P+ type polysilicon thermocouple;

depositing a metal layer on the surface of the second insulating layer 700 and in the contact hole;

The metal layer is patterned to form a wire structure 800 connecting the N+ type polysilicon thermocouple and the P+ type polysilicon thermocouple. The N+ type polysilicon thermocouple and the P+ type polysilicon thermocouple are connected by the wire structure 800 to form the upstream thermal element 200 and the downstream thermal element. 300.

Further, the electrode pads of the heating resistor 400 and the thermal element can also be formed through the contact holes and the metal layer, so as to be electrically connected to the outside. For example, the electrode pad includes a first electrode 1, a second electrode 2, a third electrode 3, a fourth electrode 4, a fifth electrode 5, and a sixth electrode 6, wherein the first electrode 1 and the second electrode 2 are respectively connected to Both ends of the heating resistor 400 , the third electrode 3 and the fourth electrode 4 are respectively connected to both ends of the upstream thermal element 200 , and the fifth electrode 5 and the sixth electrode 6 are respectively connected to both ends of the downstream thermal element 300 .

In step S30, the through hole 430 may be one of a square hole, a circular hole, and an oval hole.

In some exemplary embodiments, in order to improve the sensitivity and measurement accuracy of the sensor, the manufacturing method of the thermal flow sensor further includes:

In a direction perpendicular to the surface of the substrate 100 , a thermally conductive layer 500 is deposited on the surface and both sides of the heating resistor 400 .

In some exemplary embodiments, the thermally conductive layer 500 is made of a material with high thermal conductivity, for example, the material of the thermally conductive layer 500 can be selected from silicon nitride, aluminum oxide, aluminum nitride, magnesium oxide, or boron nitride.

In some exemplary embodiments, in order to reduce heat loss, the manufacturing method of the thermal flow sensor further includes:

Before forming the thermally conductive layer 500 , a heat insulating layer is formed on the substrate 100 to prevent the heat from diffusing to the substrate 100 and the backside of the substrate 100 .

The embodiments of the present application have been described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific embodiments, which are merely illustrative rather than restrictive. Under the inspiration of this application, without departing from the scope of protection of the purpose of this application and the claims, many forms can be made, which all fall within the protection of this application.

Claims (10)

1. A thermal flow sensor, comprising:

an upstream thermosensitive element and a downstream thermosensitive element separately formed on a surface of the substrate;

a heating resistor formed on a surface of the substrate and located between the upstream thermosensitive element and the downstream thermosensitive element, for electrically heating the upstream thermosensitive element and the downstream thermosensitive element;

and a through hole formed in the heating resistor in a direction perpendicular to a surface of the substrate such that the heating resistor forms a first resistor and a second resistor, the first resistor being located at an end of the heating resistor facing the upstream thermistor, the second resistor being located at an end of the heating resistor facing the downstream thermistor, the first resistor and the second resistor being symmetrical and connected in parallel.

2. The thermal flow sensor according to claim 1, wherein a heat conductive layer is provided between the first resistance and the upstream thermosensitive element and between the second resistance and the downstream thermosensitive element.

3. The thermal flow sensor of claim 2, wherein the material of the thermally conductive layer is silicon nitride, aluminum oxide, aluminum nitride, magnesium oxide, or boron nitride.

4. The thermal flow sensor according to claim 1, wherein a cavity is provided on a back surface of the substrate, and the heating resistor is located at a position of the substrate corresponding to the cavity.

5. The thermal flow sensor according to claim 4, wherein the base comprises a substrate, a surface of the substrate is provided with a support layer, the upstream thermosensitive element, the downstream thermosensitive element, and the heating resistor are located on a surface of the support layer, and a back surface of the substrate is provided with the cavity and exposes the support layer.

6. The thermal flow sensor according to claim 1, wherein the surface of the substrate is further provided with an environmental resistor for generating heat by energization to form a high temperature to remove moisture and gas residue on the surface of the thermal flow sensor.

7. The thermal flow sensor of claim 6, wherein the environmental resistance comprises an upstream serpentine resistance and a downstream serpentine resistance, the upstream serpentine resistance being upstream of the upstream thermistor and the downstream serpentine resistance being downstream of the downstream thermistor.

8. A method of making a thermal flow sensor, comprising:

providing a substrate;

forming a heating resistor and an upstream thermosensitive element and a downstream thermosensitive element on opposite sides of the heating resistor on a surface of the substrate;

a through hole is formed in the heating resistor in a direction perpendicular to a surface of the substrate, so that the heating resistor forms a first resistor and a second resistor, the first resistor being located at an end of the heating resistor facing the upstream thermosensitive element, the second resistor being located at an end of the heating resistor facing the downstream thermosensitive element, the first resistor and the second resistor being symmetrical and parallel.

9. The method of claim 8, wherein the providing a substrate comprises:

providing a substrate;

forming a silicon oxide layer on the surface of the substrate;

forming a silicon nitride layer on the surface of the silicon oxide layer;

and etching the back surface of the substrate at a position corresponding to the heating resistor to form a cavity.

10. The method of claim 8, wherein forming a heating resistor and upstream and downstream thermal elements on opposite sides of the heating resistor on a surface of the substrate comprises:

depositing polycrystalline silicon on the surface of the substrate, and doping to form an N + shaped polycrystalline silicon layer;

and patterning the N + shaped polycrystalline silicon layer to form a heating resistor, and an upstream thermosensitive element and a downstream thermosensitive element which are positioned on two opposite sides of the heating resistor.

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