An easily-packaged thermoelectric MEMS flow sensor and a method of manufacturing the same

Abstract

The application discloses a thermoelectric pile type MEMS flow sensor easy to package and a preparation method thereof. The sensor comprises a heating resistor, an ambient temperature measuring resistor, a first temperature measuring thermoelectric pile, a second temperature measuring thermoelectric pile, a silicon dioxide layer, a mixed substrate, a conductive via, a silicon supporting layer and a back cavity. The heating resistor is distributed at a middle position of the sensor, and four groups of temperature measuring thermoelectric piles are symmetrically distributed on both sides of the heating resistor. The application effectively reduces the heat transfer through the substrate by the back cavity and the silicon dioxide heat insulation area, improves the range and sensitivity of the sensor by optimizing the arrangement mode of the thermoelectric piles, and reduces the packaging difficulty of the device by setting the back conductive via structure.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flow sensor preparation, and particularly relates to a thermoelectric pile type MEMS flow sensor easy to package and a preparation method thereof. BACKGROUND

[0002] Accurate measurement of flow can provide important information for many fields such as industrial production, scientific research and medical health. At present, there are many types of flow sensors commonly used, among which the thermoelectric flow sensor based on MEMS technology is widely used due to its simple structure, small size, high precision, fast response, low power consumption and many other advantages.

[0003] The MEMS thermal flow sensor based on the thermoelectric principle can be classified according to different control modes. Common control modes include constant voltage mode, constant current mode, constant power mode, constant temperature difference mode and temperature balance mode. Among them, the constant temperature difference mode is the most commonly used. This mode controls the chip temperature with a constant temperature difference higher than the ambient temperature through a feedback loop, effectively suppressing the influence of the ambient temperature on the sensor measurement results. However, the disadvantage of this mode is that it requires an external ambient temperature sensor, thus increasing the complexity of the system.

[0004] Factors affecting the measurement accuracy of the thermal flow sensor include the heating element, temperature measuring element and heat insulation treatment. Among them, the heating element and temperature measuring element can affect the response speed and range of the sensor, and good heat insulation treatment can improve the sensitivity of the sensor. Usually, in order to improve the heat insulation effect and reduce heat loss, the MEMS thermal flow sensor chip is usually designed as a suspended structure, such as a suspended membrane or a suspended bridge. However, due to its structural characteristics, the suspended structure is prone to uneven stress distribution, resulting in reduced device stability. At the same time, during the device packaging process, the pins leading out from the front surface of the chip will affect the flow rate measurement of the fluid, resulting in measurement errors and reducing the measurement accuracy of the chip. SUMMARY

[0005] The application aims to provide a thermoelectric pile type MEMS flow sensor easy to package and a preparation method thereof. Through the back cavity and the substrate heat insulation area, the transmission of heat through the substrate is effectively reduced, and the performance of the sensor is improved. By generating the heating resistor and the temperature measuring thermoelectric pile on a mixed substrate with certain strength, the working stability of the device is improved. By optimizing the arrangement mode of the thermoelectric pile, the number of thermoelectric piles under the same effective area is increased, and the range and sensitivity of the sensor are improved. At the same time, the back conductive via exists in the thermoelectric pile type flow sensor, which avoids the influence of the front lead on the accuracy of the sensor and reduces the packaging difficulty, so as to solve the technical problems mentioned in the background art.

[0006] To solve the above technical problems, the specific technical solutions of the present application are as follows:

[0007] An easy-to-package thermoelectric MEMS flow sensor, comprising:

[0008] A mixed substrate, a first temperature measuring thermoelectric element, a second temperature measuring thermoelectric element, a silicon support layer, a silicon dioxide layer, a heating resistor, an ambient temperature measuring resistor, a conductive via, a back cavity and a first surface of the silicon support layer.

[0009] The silicon dioxide layer is located on the first surface of the silicon support layer.

[0010] The mixed substrate is composed of the polysilicon substrate and the silicon oxide thermal isolation region; the polysilicon substrate is located on the silicon dioxide layer and is divided into several parts by the silicon oxide thermal isolation region; the silicon oxide thermal isolation region is symmetrically distributed on both sides of the center line of the flow sensor.

[0011] The heating resistor is located on the mixed substrate and is distributed at the center line of the flow sensor, and the heating resistor has a first insulating layer and a first via for leading out the heating resistor above the heating resistor, and a lead wire for connecting the heating resistor;

[0012] The ambient temperature measuring resistor is arranged on the mixed substrate and is distributed on the outside of the flow sensor, and the ambient temperature measuring resistor has the first insulating layer and the fifth via for leading out the ambient temperature measuring resistor above the ambient temperature measuring resistor, and the ambient temperature measuring resistor lead wire for connecting the ambient temperature measuring resistor and the conductive via;

[0013] The first temperature measuring thermoelectric element is formed on the surface of the mixed substrate, and the first temperature measuring thermoelectric element has two symmetrically distributed first temperature measuring thermoelectric element first temperature sensing material layers and first temperature measuring thermoelectric element second temperature sensing material layers on both sides of the heating resistor, and has a first insulating layer and a second via between the first temperature measuring thermoelectric element first temperature sensing material layer and the first temperature measuring thermoelectric element second temperature sensing material layer, and has a second insulating layer on the first temperature measuring thermoelectric element second temperature sensing material layer; the second temperature measuring thermoelectric element is formed on the surface of the mixed substrate, and the second temperature measuring thermoelectric element has two symmetrically distributed second temperature measuring thermoelectric element first temperature sensing material layers and second temperature measuring thermoelectric element second temperature sensing material layers on both sides of the heating resistor; the second temperature measuring thermoelectric element has a first insulating layer and a third via between the second temperature measuring thermoelectric element first temperature sensing material layer and the second temperature measuring thermoelectric element second temperature sensing material layer, and has a second insulating layer on the second temperature measuring thermoelectric element second temperature sensing material layer;

[0014] The conductive via penetrates the mixed substrate, the silicon oxide layer and the silicon support layer, and is sequentially connected from top to bottom by a metal conductive via, a conductive silicon column and a pressure welding block.

[0015] Further, the silicon dioxide layer is a dense thin film, and the forming method is one of LPCVD, plasma enhanced chemical vapor deposition or thermal oxidation; the polysilicon substrate in the mixed substrate is obtained by epitaxial growth; the silicon oxide thermal isolation region is formed by filling the polysilicon groove array formed by etching through thermal oxidation.

[0016] Further, the hot junctions of the first temperature measuring thermocouple and the second temperature measuring thermocouple are arranged along different parallel lines parallel to the outside of the heating resistor respectively, and the distance between the hot junction of the first temperature measuring thermocouple and the heating resistor is closer than that between the hot junction of the second temperature measuring thermocouple and the heating resistor; the cold junctions of the first temperature measuring thermocouple and the second temperature measuring thermocouple are arranged along the same parallel line parallel to the outside of the heating resistor and its extension line respectively.

[0017] Further, the distribution trend of the first temperature measuring thermocouple relative to the center line of the flow sensor is an "eight" shape, the thermocouples close to the heating resistor end are arranged in parallel in a central region, and the thermocouples away from the heating resistor end are evenly distributed in two edge regions; the central region refers to the region closer to the center vertical line perpendicular to the arrangement direction of the temperature measuring thermocouple along the arrangement direction perpendicular to the temperature measuring thermocouple in the arrangement direction perpendicular to the temperature measuring thermocouple, and the edge region refers to the region farther away from the center vertical line perpendicular to the arrangement direction of the temperature measuring thermocouple along the arrangement direction perpendicular to the temperature measuring thermocouple; the thermocouples of the first temperature measuring thermocouple are arranged in one of a curved line, a straight line or a broken line in the arrangement mode close to the heating resistor end and close to the heating resistor end.

[0018] Further, the heating resistor and the ambient temperature measuring resistor are made of the same material, which is one of metal, N-type polysilicon and P-type polysilicon; the first temperature sensing material layer and the second temperature sensing material layer of the first temperature measuring thermocouple are made of a combination of two of metal, N-type polysilicon and P-type polysilicon; the first temperature sensing material layer and the second temperature sensing material layer of the second temperature measuring thermocouple are made of a combination of two of metal, N-type polysilicon and P-type polysilicon; the material of the first insulating layer is one of silicon oxide and silicon nitride, and is formed by one of PECVD and LPCVD; the material of the second insulating layer is one of silicon oxide and silicon nitride, and is formed by one of PECVD and LPCVD.

[0019] Further, the first via, the second via, the third via, the fourth via and the fifth via are formed by dry etching process such as RIE, IBE, etc.

[0020] Further, the fourth via is filled by one of metal sputtering, metal evaporation and electroplating forming; the material of the metal conductive via is one of copper, gold, titanium, chromium, aluminum, platinum and tungsten.

[0021] Further, the conductive silicon column is an independent silicon column formed by deep silicon etching; and the back cavity is formed by deep silicon etching.

[0022] Further, the number of the conductive vias is 12, which are respectively used for connecting the heating resistor, the environment temperature measuring resistor, two pairs of first temperature measuring thermocouples and two pairs of second temperature measuring thermocouples.

[0023] The preparation method of the easily packaged thermocouple MEMS flow sensor includes the following steps:

[0024] S1, providing a low-resistance silicon wafer as a silicon support layer, generating a silicon dioxide layer on a first surface of the silicon support layer;

[0025] S2, epitaxially growing polysilicon on the silicon dioxide layer to form a polysilicon substrate;

[0026] S3, etching the groove array on the polysilicon substrate;

[0027] S4, filling the groove array by thermal oxidation method to form a silicon oxide thermal isolation region;

[0028] S5, generating the heating resistor, the environment temperature measuring resistor, the first thermocouple first temperature sensing material layer and the second thermocouple first temperature sensing material layer on the surface of the mixed substrate;

[0029] S6, generating a first insulating layer on the heating resistor, the environment temperature measuring resistor, the first thermocouple first temperature sensing material layer, the second thermocouple first temperature sensing material layer and the surface of the mixed substrate, and etching a first via, a second via, a third via, a fourth via and a fifth via;

[0030] S7, filling the fourth via to form a metal conductive via;

[0031] S8, generating the first thermoelectric pile second temperature sensing material layer, the second thermoelectric pile second temperature sensing material layer, the heating resistance lead, the ambient temperature resistance lead and the thermoelectric pile lead on the first insulating layer;

[0032] S9, generating the second insulating layer on the first thermoelectric pile second temperature sensing material layer, the second thermoelectric pile second temperature sensing material layer, the heating resistance lead, the ambient temperature resistance lead and the thermoelectric pile lead;

[0033] S10, forming a back surface pressure welding block on the second surface of the silicon support layer, and performing deep silicon etching to generate a back surface cavity and a conductive silicon column.

[0034] The thermoelectric pile type MEMS flow sensor and the manufacturing method thereof are easy to package, and have the following advantages: the back surface cavity and the silicon oxide heat insulation region formed by the thermal oxidation method are generated, heat transfer through the substrate is effectively reduced, heat utilization rate is improved, and the performance of the sensor is improved; the heating resistance and the temperature sensing thermoelectric pile are generated on the polysilicon / silicon oxide hybrid substrate with a certain strength, the working stability of the device is improved; four groups of temperature sensing thermoelectric piles are arranged by optimizing the arrangement mode of the thermoelectric pile, the number of temperature sensing thermocouples under the same effective area is increased, the distances of different thermoelectric piles to the heating resistance are different, and then the range and the sensitivity of the sensor are improved; the back surface conductive via is generated in the thermoelectric pile type flow sensor, the influence of the front lead on the accuracy of the sensor is avoided, and the packaging difficulty of the device is effectively reduced. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a cross-sectional structure schematic view of the thermoelectric pile type MEMS flow sensor disclosed by the embodiment of the present application;

[0036] Figure 2 It is an enlarged view of the side surface structure of the heating resistance;

[0037] Figure 3 It is an enlarged view of the side surface structure of the ambient temperature resistance;

[0038] Figure 4 It is a heating resistance, an ambient temperature resistance, a temperature sensing thermoelectric pile and a front electrode pin arrangement structure schematic view of the thermoelectric pile type MEMS flow sensor disclosed by the embodiment of the present application;

[0039] Figure 5 It is a manufacturing method flow chart of the thermoelectric pile type MEMS flow sensor disclosed by the embodiment of the present application;

[0040] Figure 6 It is a cross-sectional structure schematic view of the structure prepared in step S1 in the manufacturing method disclosed by the embodiment of the present application;

[0041] Figure 7 A cross-sectional structure diagram of the structure prepared in step S2 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0042] Figure 8 A cross-sectional structure diagram of the structure prepared in step S3 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0043] Figure 9 A cross-sectional structure diagram of the structure prepared in step S4 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0044] Figure 10 A cross-sectional structure diagram of the structure prepared in step S5 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0045] Figure 11 A cross-sectional structure diagram of the structure prepared in step S6 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0046] Figure 12 A cross-sectional structure diagram of the structure prepared in step S7 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0047] Figure 13 A cross-sectional structure diagram of the structure prepared in step S8 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0048] Figure 14 A cross-sectional structure diagram of the structure prepared in step S9 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0049] Figure 15 A cross-sectional structure diagram of the structure prepared in step S10 of the manufacturing method disclosed in the embodiment of the present application is shown in the figure;

[0050] Figure 16 An enlarged view of the structure of the through-hole side of the environmental temperature measuring resistor of the present application;

[0051] Labeling in the figure: 12, hybrid substrate; 21, first temperature measurement thermocouple combination; 22, second temperature measurement thermocouple combination; 100, silicon support layer; 101, first surface of silicon support layer; 102, second surface of silicon support layer; 110, silicon dioxide layer; 120, polysilicon substrate; 130, etching groove array; 140, silicon oxide filling area; 201, heating resistor; 202, ambient temperature measurement resistor; 210, first temperature measurement thermocouple first temperature sensing material layer; 212, first temperature measurement thermocouple second temperature sensing material layer; 220, second temperature measurement thermocouple first temperature sensing material layer; 222, second temperature measurement thermocouple second temperature sensing material layer; 230, first insulating layer; 232, second insulating layer; 240, first via hole; 242, second via hole; 244, third via hole; 246, fourth via hole; 247, fifth via hole; 248, heating resistor lead; 250, ambient temperature measurement resistor lead; 300, conductive via hole; 301, metal conductive via hole; 302, thermocouple lead; 310, conductive silicon column; 320, back surface pressure welding block; 340, back surface cavity. DETAILED DESCRIPTION

[0052] In order to better understand the purpose, structure and function of the present application, the following further describes the present application in detail with reference to the accompanying drawings.

[0053] The present application is described and explained more fully with reference to the following detailed description. Other advantages of the present application will be more fully appreciated by reference to the following detailed description.

[0054] For the convenience of description, spatial relationship words such as "under", "below", "lower", "under", "upper", "upper" and the like can be used to describe the relationship between one element or feature and other elements or features shown in the drawings. It will be understood that these spatial relationship words are intended to include other directions of the device in use or operation in addition to the directions depicted in the drawings. In addition, when a layer is referred to as "between" two layers, it can be the only layer between the two layers, or one or more intervening layers can also be present. It should be noted that in order to make the drawings as simple as possible, not all structures are labeled in each drawing.

[0055] In the context of the present application, structures described as being "on" a second feature "over" a first feature can include embodiments in which the first and second features are formed in direct contact, as well as embodiments in which additional features are formed between the first and second features such that the first and second features can not be in direct contact.

[0056] Need to be explained, the embodiment provided in the figure only in a schematic way illustrates the basic idea of the present application, so the figure shows only the relevant components in the present application, not the number, shape and size of the components drawn when actually implemented, the actual implementation of each component type, quantity and ratio can be a voluntary change, and its component layout type can be more complex. In order to make the figure as simple as possible, all the structures in each drawing are not marked.

[0057] The application will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0058] In order to achieve the above object, the present application provides an easy-to-package thermoelectric pile MEMS flow sensor, comprising: a mixed substrate 12; two first temperature measuring thermoelectric piles 21, symmetrically distributed on both sides of the heating resistor; two second temperature measuring thermoelectric piles 22, symmetrically distributed on both sides of the heating resistor; a silicon support layer 100; a silicon dioxide layer 110; one heating resistor 201, distributed on the center line of the flow sensor; one ambient temperature measuring resistor 202, distributed at the edge of the flow sensor; twelve conductive vias 300, distributed on the mixed substrate 12; a back cavity 340; a first surface 101 of the silicon support layer.

[0059] The silicon dioxide layer 110 is formed on the first surface 101 of the silicon support layer, and the silicon dioxide layer 110 is a dense thin film, and the generation method is one of LPCVD, PECVD or thermal oxidation. In the embodiment of the present application, the silicon dioxide layer 110 is generated by LPCVD method.

[0060] The mixed substrate 12 is located on the silicon dioxide layer 110 and is composed of a polysilicon substrate 120 and a silicon oxide thermal isolation region 140; wherein the polysilicon substrate 120 is formed on the silicon dioxide layer 110 and is obtained by epitaxial growth; the silicon oxide thermal isolation region 140 is formed by filling the polysilicon groove array 130 formed by etching through thermal oxidation method, symmetrically distributed on both sides of the center line of the flow sensor, embedded in the polysilicon substrate, used for blocking the lateral transmission of heat in the substrate; in the embodiment of the present application, there are four groups of silicon oxide thermal isolation regions 140, distributed between the first temperature measuring thermoelectric pile 21 and the heating resistor 201 and the inner side of the hot end of the second temperature measuring thermoelectric pile 22, as shown in Figure 4 .

[0061] The heating resistor 201 is formed on the hybrid substrate 12 and is distributed at the center line of the flow sensor. The heating resistor 201 has a first insulating layer 230 and a first through hole 240 for leading out the heating resistor, as well as a heating resistor lead 248 for connecting the heating resistor 201 to the conductive through hole 300. The material of the heating resistor 201 is one of P-type polysilicon, N-type polysilicon, and metal. The cross-section of the connection structure of the heating resistor 201, the first insulating layer 230, the second insulating layer 232, and the heating resistor lead 248 is shown in FIG. Figure 2 As shown; in an embodiment of the present invention, the heating resistor 201 is made of metal nickel.

[0062] The ambient temperature resistor 202 is formed on the hybrid substrate 12 and is distributed at the edge of the flow sensor. The ambient temperature resistor 202 has a first insulating layer 230 and a fifth through hole 247 for leading out the ambient temperature resistor, as well as an ambient temperature resistor lead 250 for connecting the ambient temperature resistor 202 to the conductive through hole 300. The material of the ambient temperature resistor 202 is one of P-type polysilicon, N-type polysilicon, and metal; the cross-section of the connection structure of the ambient temperature resistor 202, the first insulating layer 230, the second insulating layer 232, and the ambient temperature resistor lead 250 is shown in FIG. Figure 3 As shown; the cross section of the connection structure of the ambient temperature measuring resistor 202, the first insulating layer 230 and the fifth through hole 247 is as shown Figure 16 As shown; in an embodiment of the present invention, the ambient temperature measuring resistor 202 is made of metal nickel.

[0063] The first thermopile 21 is formed on the surface of the hybrid substrate 12. Two of the first thermopile 21 are symmetrically located on either side of the heating resistor 201. These include a first thermopile first temperature-sensing material layer 210 and a second thermopile second temperature-sensing material layer 212, with a first insulating layer 230 and a second through-hole 242 located between them, and a second insulating layer 232 located thereon. The second thermopile 22 is formed on the surface of the hybrid substrate 12. Two of the second thermopile 22 are symmetrically located on either side of the centerline of the heating resistor 201. These include a first thermopile first temperature-sensing material layer 220 and a second thermopile second temperature-sensing material layer 222, with a first insulating layer 230 and a third through-hole 244 located between them, and a second insulating layer 232 located thereon.

[0064] The materials of the first temperature-sensing material layer 210 and the second temperature-sensing material layer 212 of the first temperature-sensing thermocouple 21 are a combination of two of metal, N-type polysilicon and P-type polysilicon; the materials of the first temperature-sensing material layer 220 and the second temperature-sensing material layer 222 of the second temperature-sensing thermocouple 22 are a combination of two of metal, N-type polysilicon and P-type polysilicon; in an embodiment of the present application, the materials of the first temperature-sensing material layer 210 and the second temperature-sensing material layer 212 of the first temperature-sensing thermocouple 21 are nickel and aluminum respectively; the materials of the first temperature-sensing material layer 220 and the second temperature-sensing material layer 222 of the second temperature-sensing thermocouple 22 are nickel and aluminum respectively.

[0065] The hot junctions of the first temperature-sensing thermocouple 21 and the second temperature-sensing thermocouple 22 are arranged along different parallel lines parallel to the outer side of the heating resistor 201 respectively, and the distance between the hot junction of the first temperature-sensing thermocouple 21 and the heating resistor 201 is closer than the distance between the hot junction of the second temperature-sensing thermocouple 22 and the heating resistor 201; the cold junctions of the first temperature-sensing thermocouple 21 and the second temperature-sensing thermocouple 22 are arranged along the same parallel line parallel to the outer side of the heating resistor 201 and its extension line respectively; the distribution trend of the first temperature-sensing thermocouple 21 relative to the center line of the flow sensor is in the shape of an "eight", the thermocouples close to the heating resistor end are arranged in parallel in a central region, and the thermocouples away from the heating resistor end are evenly distributed in two edge regions; the described central region refers to the region closer to the heating resistor 201 along the central vertical line perpendicular to the arrangement direction of the temperature-sensing thermocouple in the perpendicular direction to the arrangement direction of the temperature-sensing thermocouple, and the described edge region refers to the region away from the heating resistor 201 along the central vertical line perpendicular to the arrangement direction of the temperature-sensing thermocouple in the perpendicular direction to the arrangement direction of the temperature-sensing thermocouple; the arrangement mode of the thermocouples of the first temperature-sensing thermocouple 21 in the intermediate region between the region close to the heating resistor end and the region away from the heating resistor end is one of a curved line type, a straight line type or a polyline type; in an embodiment of the present application, the arrangement mode of the thermocouples of the first temperature-sensing thermocouple 21 in the intermediate region between the region close to the heating resistor end and the region away from the heating resistor end is a polyline type, and one of the arrangement modes of the first temperature-sensing thermocouple 21 and the second temperature-sensing thermocouple 22 is shown in FIG. 2. Figure 4

[0066] ​The first insulating layer 230 is formed on the surface of the heating resistor 201, the ambient temperature measuring resistor 202, the first temperature sensing material layer 210 of the first temperature measuring thermocouple, the second temperature sensing material layer 220 of the second temperature measuring thermocouple and the hybrid substrate 12; the second insulating layer 232 is formed on the surface of the heating resistor lead 248, the ambient temperature measuring resistor lead 250, the thermocouple lead 302, the second temperature sensing material layer 212 of the first temperature measuring thermocouple, the second temperature sensing material layer 222 of the second temperature measuring thermocouple and the first insulating layer 230; the material of the first insulating layer 230 is one of silicon oxide and silicon nitride; the material of the second insulating layer 232 is one of silicon oxide and silicon nitride; in the embodiment of the present application, the material of the first insulating layer 230 is silicon oxide, and the material of the second insulating layer 230 is silicon nitride.

[0067] The first through hole 240 is used for leading out the heating resistor 201, the second through hole 242 is used for connecting the first temperature sensing material layer 210 of the first temperature measuring thermocouple and the second temperature sensing material layer 212 of the first temperature measuring thermocouple, the third through hole 244 is used for connecting the first temperature sensing material layer 220 of the second temperature measuring thermocouple and the second temperature sensing material layer 222 of the second temperature measuring thermocouple, the fourth through hole 246 is used for connecting the conductive silicon column 310 and the front lead, and the fifth through hole 247 is used for leading out the ambient temperature measuring resistor 202; the first through hole 240, the second through hole 242, the third through hole 244, the fourth through hole 246 and the fifth through hole 247 are formed by dry etching processes such as RIE and IBE; in the embodiment of the present application, the first through hole 240, the second through hole 242, the third through hole 244, the fourth through hole 246 and the fifth through hole 247 are formed by the RIE dry etching process.

[0068] The conductive through hole 300 penetrates the hybrid substrate 12, the silicon dioxide layer 110 and the silicon support layer 100, and includes a metal conductive through hole 301, a conductive silicon column 310 and a back welding block 320; the number of the conductive through hole 300 is 12, and the conductive through hole 300 is respectively used for electrical connection of the heating resistor 201, the ambient temperature measuring resistor 202, two pairs of first temperature measuring thermocouples 21 and two pairs of second temperature measuring thermocouples 22; in the embodiment of the present application, the arrangement of the conductive through hole 300 is as shown in the figure. Figure 4

[0069] The filling mode of the fourth through hole 246 is one of metal sputtering, metal evaporation and electroplating, and the material of the metal conductive through hole 301 is one of copper, gold, titanium, chromium, aluminum, platinum and tungsten; in the embodiment of the present application, the filling mode of the fourth through hole 246 is electroplating forming, and the material of the metal conductive through hole 301 is copper.

[0070] The conductive silicon column 310 is an independent silicon column formed by deep silicon etching; the back cavity 340 is obtained by deep silicon etching of the semiconductor high-thermal-conductivity silicon support layer 100 compatible with the CMOS process, and is used for forming back heat isolation. ​

[0071] The material of the heating resistance lead wire 248, the ambient temperature measuring resistance lead wire 250, the thermocouple lead wire 302 and the soldering block 320 is one of titanium, tungsten, chromium, platinum, aluminum or gold; in the embodiment of the application, the heating resistance lead wire 248 adopts metal aluminum, the ambient temperature measuring resistance lead wire 250 adopts metal aluminum, the thermocouple lead wire 302 adopts metal aluminum, and the back soldering block 320 adopts metal copper.

[0072] The cross-sectional structure schematic diagram of the thermocouple MEMS flow sensor easy to package provided by the application is shown as Figure 1 .

[0073] It should be noted that, compared with the design without the silicon oxide thermal isolation region, the design with the silicon oxide thermal isolation region can provide good thermal isolation between the heating resistance 201 and the temperature measuring thermocouples 21 and 22, reduce the heat conduction loss, and effectively reduce the power consumption of the device; the mixed substrate 12 composed of the polysilicon substrate 120 and the silicon oxide thermal isolation region 140 has higher stability compared with the suspended thick film structure composed of the silicon dioxide layer 110; the optimized temperature measuring thermocouple arrangement mode improves the range and sensitivity of the flow sensor by setting two groups of temperature measuring thermocouples with different distances from the heating resistance 201, i.e., the first temperature measuring thermocouple 21 and the second temperature measuring thermocouple 22; and the setting of the conductive via avoids the influence of the front lead wire on the sensor and reduces the packaging difficulty.

[0074] The application further provides a preparation method of the thermocouple MEMS flow sensor easy to package, as shown in Figure 5 , which comprises the following steps:

[0075] S1, providing a low-resistance silicon wafer as a silicon support layer 100, generating silicon dioxide on a first surface 101 of the silicon support layer to form a silicon dioxide layer 110, as shown in Figure 6 .

[0076] Specifically, the preparation method of the silicon dioxide layer is one of LPCVD, PECVD or thermal oxidation; in the application, the LPCVD method is used to generate a dense silicon dioxide layer on the surface of the silicon wafer.

[0077] S2, epitaxially growing polysilicon on the silicon dioxide layer 110 to form a polysilicon substrate 120, as shown in Figure 7 .

[0078] S3, etching the groove array 130 on the polysilicon substrate 120, as shown in Figure 8 .

[0079] Specifically, the RIE technology is used to etch the surface of the polysilicon substrate to form the groove array.

[0080] S4, the groove array 130 is filled by thermal oxidation method to form the silicon oxide thermal isolation region 140, and the polysilicon substrate and the silicon oxide thermal isolation region are thinned and polished, as shown in Figure 9 .

[0081] Specifically, the mixed substrate surface is processed by mechanical thinning and chemical mechanical polishing process, so that the surface is smooth and flat.

[0082] S5, the heating resistor 201, the environment temperature measuring resistor 202, the first temperature sensing material layer 210 of the first temperature measuring thermocouple and the first temperature sensing material layer 220 of the second temperature measuring thermocouple are generated on the surface of the mixed substrate 12, as shown in Figure 10 .

[0083] Specifically, the material of the heating resistor 201 is one of P-type polysilicon, N-type polysilicon and metal, in the embodiment of the present application, the heating resistor 201 adopts metal nickel, and is formed by electron beam evaporation combined with metal stripping process; the material of the environment temperature measuring resistor 202 is one of P-type polysilicon, N-type polysilicon and metal, in the embodiment of the present application, the environment temperature measuring resistor 202 adopts metal nickel, and is formed by electron beam evaporation combined with metal stripping process; the material of the first temperature sensing material layer 210 of the first temperature measuring thermocouple is one of metal, N-type polysilicon and P-type polysilicon, in the embodiment of the present application, the first temperature sensing material layer 210 of the first temperature measuring thermocouple adopts metal nickel, and is formed by electron beam evaporation combined with metal stripping process; the material of the first temperature sensing material layer 220 of the second temperature measuring thermocouple is one of metal, N-type polysilicon and P-type polysilicon, in the embodiment of the present application, the first temperature sensing material layer 220 of the second temperature measuring thermocouple adopts metal nickel, and is formed by electron beam evaporation combined with metal stripping process.

[0084] S6, the first insulating layer 230 is generated on the surface of the heating resistor 201, the environment temperature measuring resistor 202, the first temperature sensing material layer 210 of the first thermocouple, the first temperature sensing material layer 220 of the second thermocouple and the mixed substrate 12, and the first through hole 240, the second through hole 242, the third through hole 244, the fourth through hole 246 and the fifth through hole 247 are etched, as shown in Figure 11 .

[0085] Specifically, the material of the first insulating layer 230 is one of silicon oxide and silicon nitride, formed by one of PECVD and LPCVD, in the embodiment of the present application, the material of the first insulating layer 230 is silicon oxide, formed by LPCVD; the first via hole 240 is used for leading out the heating resistor 201, the second via hole 242 is used for connecting the first temperature-sensing material layer 210 of the first temperature-sensing thermocouple and the second temperature-sensing material layer 212 of the first temperature-sensing thermocouple, the third via hole 244 is used for connecting the first temperature-sensing material layer 220 of the second temperature-sensing thermocouple and the second temperature-sensing material layer 222 of the second temperature-sensing thermocouple, the fourth via hole 246 is used for connecting the conductive silicon column 310 with the front lead wire, and the fifth via hole 247 is used for leading out the ambient temperature-sensing resistor 202; the first via hole 240, the second via hole 242, the third via hole 244, the fourth via hole 246 and the fifth via hole 247 are all formed by dry etching processes such as RIE and IBE, in the embodiment of the present application, the first via hole 240, the second via hole 242, the third via hole 244, the fourth via hole 246 and the fifth via hole 247 are all formed by RIE.

[0086] S7, filling the fourth via hole 246 to form the metal conductive via hole 301, as shown in Figure 12

[0087] Specifically, the method for filling the fourth via hole 246 is one of metal evaporation, metal sputtering and electroplating, in the embodiment of the present application, the method for filling the fourth via hole 246 is electroplating; the material of the metal conductive via hole 301 is one of copper, gold, titanium, chromium, aluminum, platinum and tungsten, in the embodiment of the present application, the material of the metal conductive via hole 301 is copper.

[0088] S8, generating the second temperature-sensing material layer 212 of the first thermocouple, the second temperature-sensing material layer 222 of the second thermocouple, the heating resistor lead wire 248, the ambient temperature-sensing resistor lead wire 250 and the thermocouple lead wire 302 on the first insulating layer 230, as shown in Figure 13

[0089] ​​Specifically, the material of the first temperature measuring thermocouple second temperature sensing material layer 212 is one of metal, N-type polysilicon or P-type polysilicon, in the embodiment of the present application, the first temperature measuring thermocouple second temperature sensing material layer 212 adopts metal aluminum, and is formed by electron beam evaporation combined with metal stripping process; the material of the second temperature measuring thermocouple second temperature sensing material layer 222 is one of metal, N-type polysilicon or P-type polysilicon, in the embodiment of the present application, the second temperature measuring thermocouple second temperature sensing material layer 222 adopts metal aluminum, and is formed by electron beam evaporation combined with metal stripping process; the material of the heating resistance lead wire 248 is one of titanium, tungsten, chromium, platinum, aluminum or gold, in the embodiment of the present application, the material of the heating resistance lead wire 248 adopts metal aluminum; the material of the ambient temperature measuring resistance lead wire 250 is one of titanium, tungsten, chromium, platinum, aluminum or gold, in the embodiment of the present application, the material of the ambient temperature measuring resistance lead wire 250 adopts metal aluminum; the material of the thermocouple lead wire 302 is one of titanium, tungsten, chromium, platinum, aluminum or gold, in the embodiment of the present application, the material of the thermocouple lead wire 302 adopts metal aluminum.

[0090] S9, a second insulating layer 232 is formed on the first thermocouple second temperature sensing material layer 212, the second thermocouple second temperature sensing material layer 222, the heating resistance lead wire 248, the ambient temperature measuring resistance lead wire 250 and the thermocouple lead wire 302, as shown in Figure 14 .

[0091] Specifically, the material of the second insulating layer 232 is one of silicon oxide and silicon nitride, and is formed by one of PECVD and LPCVD, in the embodiment of the present application, the material of the second insulating layer 232 is silicon nitride, and is formed by LPCVD deposition.

[0092] S10, a press welding block 320 is formed on the second surface 102 of the silicon support layer, and deep silicon etching is performed to form a back cavity 340 and a conductive silicon column 310, as shown in Figure 15 .

[0093] Specifically, the DRIE technology is used to etch the second surface 102 of the silicon support layer to obtain the isolation cavity 340, and 12 independent conductive silicon columns 310 are formed; the material of the press welding block 320 is one of titanium, tungsten, chromium, platinum, aluminum or gold, in the embodiment of the present application, the material of the press welding block 320 adopts metal copper.

[0094] It is to be understood that the present application is described by way of example only, and that modifications or alterations can be made to the features and embodiments described without departing from the spirit and scope of the application. In addition, modifications can be made to the features and embodiments described to accommodate specific situations and materials without departing from the spirit and scope of the application. Accordingly, the application is not limited to the specific embodiments disclosed herein, but rather, the scope of the application includes all embodiments falling within the scope of the claims.

Claims

1. A thermopile MEMS flow sensor that is easy to package, characterized in that: include: A hybrid substrate (12), a first temperature measuring thermopile (21), a second temperature measuring thermopile (22), a silicon support layer (100), a silicon dioxide layer (110), a heating resistor (201), an ambient temperature measuring resistor (202), a conductive through hole (300), a back cavity (340), and a first surface (101) of the silicon support layer; The silicon dioxide layer (110) is located on the first surface (101) of the silicon support layer; The hybrid substrate (12) is composed of a polycrystalline silicon substrate (120) and a silicon oxide thermal isolation region (140); the polycrystalline silicon substrate (120) is located on the silicon dioxide layer (110) and is divided into several parts by the silicon oxide thermal isolation region (140); the silicon oxide thermal isolation region (140) is symmetrically distributed on both sides of the center line of the flow sensor; The heating resistor (201) is located on the hybrid substrate (12) and distributed at the center line of the flow sensor. The heating resistor (201) has a first insulating layer (230) and a first through hole (240) for leading out the heating resistor (201), and a heating resistor lead (248) for connecting the heating resistor (201) and the conductive through hole (300). The environmental temperature measuring resistor (202) is arranged on the hybrid substrate (12) and distributed outside the flow sensor, and the environmental temperature measuring resistor (202) has the first insulating layer (230) and a fifth through hole (247) for leading out the environmental temperature measuring resistor (202), and an environmental temperature measuring resistor lead (250) for connecting the environmental temperature measuring resistor (202) and the conductive through hole (300); The first temperature measuring thermopile (21) is formed on the surface of the hybrid substrate (12), and the first temperature measuring thermopile (21) has two symmetrically distributed on both sides of the heating resistor (201); the first temperature measuring thermopile (21) comprises a first temperature measuring thermopile first temperature sensing material layer (210) and a first temperature measuring thermopile second temperature sensing material layer (212); a first insulating layer (230) and a second through hole (242) are provided between the first temperature measuring thermopile first temperature sensing material layer (210) and the first temperature measuring thermopile second temperature sensing material layer (212); and a second insulating layer (230) and a second through hole (242) are provided on the first temperature measuring thermopile second temperature sensing material layer (212). (232); the second temperature measuring thermopile (22) is formed on the surface of the hybrid substrate (12); the second temperature measuring thermopile (22) has two symmetrically distributed on both sides of the heating resistor (201), including a first temperature sensing material layer (220) of the second temperature measuring thermopile and a second temperature sensing material layer (222) of the second temperature measuring thermopile; a first insulating layer (230) and a third through hole (244) are provided between the first temperature sensing material layer (220) of the second temperature measuring thermopile and the second temperature sensing material layer (222); and a second insulating layer (232) is provided on the second temperature sensing material layer (222) of the second temperature measuring thermopile; The conductive through hole (300) penetrates the hybrid substrate (12), the silicon dioxide layer (110) and the silicon support layer (100), and is formed by sequentially connecting the metal conductive through hole (301), the conductive silicon column (310) and the pressure welding block (320) from top to bottom; the metal conductive through hole (301) is formed by filling the fourth through hole (246), and the fourth through hole (246) penetrates the hybrid substrate (12) and the silicon dioxide layer (110); the center of the back cavity (340) is at the same position as the heating resistor (201) in the horizontal direction; the back cavity (340) penetrates the silicon support layer (100) in the vertical direction, extending from the first surface (101) of the silicon support layer to the second surface (102) of the silicon support layer, and the depth is equal to the thickness of the silicon support layer (100).

2. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The silicon dioxide layer (110) is a dense thin film, and is generated by one of LPCVD, plasma enhanced chemical vapor deposition, or thermal oxidation; the polysilicon substrate (120) in the hybrid substrate (12) is obtained by epitaxial growth; and the silicon oxide thermal isolation region (140) is formed by filling a polysilicon groove array (130) formed by etching with a thermal oxidation method.

3. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The hot junctions of the first temperature measuring thermopile (21) and the second temperature measuring thermopile (22) are respectively arranged along different parallel lines parallel to the outside of the heating resistor (201), and the distance between the hot junction of the first temperature measuring thermopile (21) and the heating resistor (201) is closer than the distance between the second temperature measuring thermopile (22) and the heating resistor (201); the cold junctions of the first temperature measuring thermopile (21) and the second temperature measuring thermopile (22) are respectively arranged along the same parallel line parallel to the outside of the heating resistor (201) and its extension line.

4. The easily packaged thermopile MEMS flow sensor according to claim 3, characterized in that: The distribution trend of the first temperature measuring thermopile (21) relative to the center line of the flow sensor is in the shape of an "eight", the thermocouples close to the end of the heating resistor (201) are concentrated in a central area and arranged in parallel, and the thermocouples far from the end of the heating resistor are evenly distributed in two edge areas; the central area refers to an area closer to the heating resistor (201) along the central vertical line perpendicular to the arrangement direction of the temperature measuring thermopile, and the edge area refers to an area farther away from the heating resistor (201) along the central vertical line perpendicular to the arrangement direction of the temperature measuring thermopile; the shape arrangement mode of the thermocouples of the first temperature measuring thermopile (21) in the area close to the heating resistor end and the area between the area close to the heating resistor end is one of a curve type, a straight line type or a broken line type.

5. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The heating resistor (201) and the environmental temperature measuring resistor (202) are made of the same material, which is one of metal, N-type polysilicon or P-type polysilicon; the first temperature-sensing material layer (210) and the second temperature-sensing material layer (212) of the first temperature-measuring thermopile (21) are made of a combination of two of metal, N-type polysilicon or P-type polysilicon; the first temperature-sensing material layer (220) and the second temperature-sensing material layer (222) of the second temperature-measuring thermopile (22) are made of a combination of two of metal, N-type polysilicon or P-type polysilicon; the first insulating layer (230) is made of a material of silicon oxide or silicon nitride, and is formed by a technique selected from the group consisting of PECVD and LPCVD; and the second insulating layer (232) is made of a material of silicon oxide or silicon nitride, and is formed by a technique selected from the group consisting of PECVD and LPCVD.

6. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The first through hole (240), the second through hole (242), the third through hole (244), the fourth through hole (246) and the fifth through hole (247) are all formed by RIE and IBE dry etching processes; the fourth through hole (246) is filled by metal sputtering, metal evaporation or electroplating; the material of the metal conductive through hole (301) is one of copper, gold, titanium, chromium, aluminum, platinum or tungsten; the material of the heating resistor lead (248), the environmental temperature measuring resistor lead (250), the thermopile lead (302) and the pressure welding block (320) is one of titanium, tungsten, chromium, platinum, aluminum or gold; and the conductive silicon column (310) is an independent silicon column generated by deep silicon etching.

7. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The fourth through hole (246) is filled by metal sputtering, metal evaporation or electroplating; the material of the metal conductive through hole (301) is one of copper, gold, titanium, chromium, aluminum, platinum or tungsten.

8. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The conductive silicon pillar (310) is an independent silicon pillar generated by deep silicon etching; and the back cavity (340) is formed by deep silicon etching.

9. The easily packaged thermopile MEMS flow sensor according to claim 1, characterized in that: The number of the conductive through holes (300) is 12, which are respectively used for connecting the heating resistor (201), the environmental temperature measuring resistor (202), two pairs of first temperature measuring thermopiles (21), and two pairs of second temperature measuring thermopiles (22).

10. A method for preparing an easily packaged thermopile MEMS flow sensor, used for the easily packaged thermopile MEMS flow sensor according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1, providing a low-resistance silicon wafer as a silicon support layer (100), generating silicon dioxide on a first surface (101) of the silicon support layer (100), to form a silicon dioxide layer (110); S2, epitaxially growing polysilicon on the silicon dioxide layer (110) to form a polysilicon substrate (120); S3, etching a groove array (130) on the polysilicon substrate (120); S4, performing oxidation filling on the groove array (130) by a thermal oxidation method to form a silicon oxide thermal isolation region (140); S5, generating a heating resistor (201), an environmental temperature measuring resistor (202), a first thermopile first temperature-sensitive material layer (210), and a second thermopile first temperature-sensitive material layer (220) on the surface of the hybrid substrate (12); S6, forming a first insulating layer (230) on the surface of the heating resistor (201), the environmental temperature measuring resistor (202), the first thermopile first temperature-sensitive material layer (210), the second thermopile first temperature-sensitive material layer (220), and the mixed substrate (12), and etching a first through hole (240), a second through hole (242), a third through hole (244), a fourth through hole (246), and a fifth through hole (247); S7, filling the fourth through hole (246) to form a metal conductive through hole (301); S8, forming a first thermopile second temperature-sensing material layer (212), a second thermopile second temperature-sensing material layer (222), a heating resistor lead (248), an environmental temperature-measuring resistor lead (250), and a thermopile lead (302) on the first insulating layer (230); S9, forming a second insulating layer (232) on the first thermopile second temperature-sensitive material layer (212), the second thermopile second temperature-sensitive material layer (222), the heating resistor lead (248), the environmental temperature-measuring resistor lead (250), and the thermopile lead (302); S10, forming a pressure welding block (320) on the second surface (102) of the silicon support layer, and performing deep silicon etching to generate a backside cavity (340) and a conductive silicon column (310).

Images