Double-layer suspended infrared thermopile and preparation method thereof

Abstract

The present invention provides a double-layer suspended infrared thermopile and a preparation method thereof. By introducing a heat-conducting reflective layer under the absorbing part of the infrared absorption layer, the absorption rate can be improved, and the heat can be concentrated faster and more at the hot junction end, which is beneficial to increase the detection signal and improve the detection performance; further, by setting a preset sacrificial layer, an etching window with a smaller width can form a heat-insulating cavity with a larger width, which can improve the flexibility of the structural layout of the thermopile and improve the space utilization rate of the device; further, a double-layer suspended infrared thermopile can be formed at the same time in the last step, thereby effectively reducing the process complexity and improving the yield rate, which is beneficial to realize the miniaturization and high performance of the infrared thermopile. The double-layer suspended infrared thermopile of the present invention adopts a single-sided processing method, has the advantages of simple process and high yield rate, and is suitable for mass production.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon micromechanical sensors, and in particular relates to a double-layer suspended infrared thermopile and a preparation method thereof. Background Art

[0002] Infrared (IR) sensor arrays have been used in military, industrial, and consumer electronics markets, including night vision, autonomous driving, human behavior detection, non-contact temperature measurement, etc. For infrared thermal imaging, the detector needs to be assembled into a focal plane array (FPA) to capture the shape and movement of the detected object. Compared with microbolometers and pyroelectric sensors, thermopile sensors are characterized by low power consumption, no flicker noise, and compatibility with CMOS processes, so they are low cost and often used in low-cost fields such as air conditioning wind direction control and fall detection. However, the design of thermopile infrared sensor arrays faces the challenges of large size, slow response speed, and relatively low responsivity. Existing solutions mainly optimize the thermal conductivity, infrared absorptivity, etc. of the device to improve the performance of thermopile.

[0003] In terms of thermal conductivity optimization, traditional thermopile detectors usually deposit polysilicon / metal on a dielectric film to make a thermocouple pair, and then make an insulating cavity under the dielectric film to form a suspended supporting dielectric layer structure to reduce solid thermal conductivity. When making an insulating cavity, if the back release method is used, complex double-sided photolithography and other operation steps will be introduced, and the insulating cavity needs to be penetrated throughout the silicon wafer, which will greatly increase the process time and cost; while the front release method has the advantages of only front processing and the depth of the insulating cavity can be made as needed, but in the front release process, the more commonly used XeF2 dry release still has the problem of poor consistency.

[0004] In terms of infrared absorption optimization, the first method is to use porous black materials with high absorption rates, such as gold black, carbon black, and metamaterials to enhance infrared absorption. However, this method still has disadvantages in terms of process complexity, CMOS production compatibility, and cost. The second method is to increase the area of ​​the infrared absorption film, but this is not conducive to device arraying and miniaturization. Therefore, high-performance thermopile detectors often use umbrella-shaped absorption film structures. However, thermopile detectors with umbrella-shaped absorption film structures usually require multiple steps to release the structure, which not only increases the process complexity, but also the other process steps experienced in the multi-step release process will damage the fragile film and beam structure, reducing the manufacturing yield.

[0005] In addition, the radiation absorption rate of the commonly used silicon nitride umbrella-shaped absorption film needs to be improved, and the heat generated by the absorbed radiation cannot be quickly concentrated to the hot junction end of the thermocouple arm where the umbrella root contact part is located due to the low solid thermal conductivity of the umbrella-shaped absorption film, thereby causing part of the heat to dissipate into the air, resulting in energy loss and detection signal attenuation.

[0006] Therefore, it is necessary to provide a double-layer suspended infrared thermopile and a preparation method thereof. Summary of the invention

[0007] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a double-layer suspended infrared thermopile and a preparation method thereof, so as to solve the problems encountered in the prior art when preparing high-performance and high-quality infrared thermopiles.

[0008] In order to achieve the above-mentioned purpose and other related purposes, the present invention provides a double-layer suspended infrared thermopile, the double-layer suspended infrared thermopile comprising:

[0009] substrate;

[0010] A first-layer suspension structure, which is located on the substrate and includes a supporting dielectric layer, and a thermocouple material layer, an electrical insulation layer, and a metal interconnection layer located on the supporting dielectric layer;

[0011] A heat-insulating cavity, wherein the heat-insulating cavity is located below the first layer of suspension structure;

[0012] An etching window, wherein the etching window penetrates the electrical insulation layer and the supporting dielectric layer and communicates with the thermal insulation cavity;

[0013] A second-layer suspension structure, the second-layer suspension structure is located on the first-layer suspension structure, and includes an infrared absorption layer and a heat-conducting reflection layer, wherein the infrared absorption layer includes an infrared absorption layer contact portion in contact with the electrical insulation layer and an infrared absorption layer absorption portion covering the heat-conducting reflection layer, the infrared absorption layer is supported on the first-layer suspension structure through the central infrared absorption layer contact portion, and there is a gap between the heat-conducting reflection layer and the first-layer suspension structure.

[0014] Optionally, the heat conductive reflective layer is a single metal layer or a metal stack.

[0015] The present invention also provides a method for preparing a double-layer suspended infrared thermopile, comprising the following steps:

[0016] providing a substrate;

[0017] forming a thermocouple composite layer on the substrate, wherein the thermocouple composite layer comprises a supporting dielectric layer covering the substrate, and a thermocouple material layer, an electrical insulation layer and a metal interconnection layer located on the supporting dielectric layer;

[0018] Patterning the thermocouple composite layer to form an etching window exposing the substrate;

[0019] forming a sacrificial layer covering the thermocouple composite layer and the etching window;

[0020] forming a heat-conducting reflective layer covering the sacrificial layer;

[0021] Patterning the sacrificial layer and the heat-conducting reflective layer to form a groove at the hot junction end of the thermocouple to expose the electrical insulation layer;

[0022] forming an infrared absorption layer, wherein the infrared absorption layer comprises an infrared absorption layer contact portion covering the groove and contacting the electrical insulation layer and an infrared absorption layer absorption portion covering the thermal conductive reflective layer, wherein the infrared absorption layer contact portion is located at a central position of the infrared absorption layer;

[0023] The sacrificial layer is removed by wet etching to form a spacing gap, the infrared absorption layer with the heat conductive reflective layer is released to form a second suspended structure, and part of the substrate is removed from the etching window to form a heat insulating cavity, and the thermocouple composite layer is released to form a first suspended structure.

[0024] Optionally, the heat conductive reflective layer is a single metal layer or a metal stack, and has a thickness ranging from 20 nm to 1000 nm.

[0025] Optionally, the substrate is a (100) single crystal silicon substrate, and the sacrificial layer is one or a combination of an amorphous silicon sacrificial layer or a polycrystalline silicon sacrificial layer; the spacing gap and the thermal insulation cavity are formed simultaneously in the last step.

[0026] Optionally, the method further includes forming a preset sacrificial layer in contact with the substrate, and the etching window exposes the preset sacrificial layer.

[0027] Optionally, the preset sacrificial layer formed includes a silicon oxide layer or a metal layer with a thickness ranging from 0.5 μm to 5 μm, and the preset sacrificial layer formed includes a silicon oxide layer or a metal layer with a thickness ranging from 0.5 μm to 5 μm.

[0028] Optionally, the step of forming the thermocouple composite layer on the substrate includes:

[0029] forming a supporting medium layer covering the substrate on the substrate;

[0030] forming a thermocouple material layer on the supporting medium layer;

[0031] forming an electrical insulation layer covering the thermocouple material layer on the thermocouple material layer;

[0032] Patterning the electrical insulating layer to form a contact hole exposing the thermocouple material layer;

[0033] A patterned metal interconnection layer is formed on the electrical insulation layer, and the metal interconnection layer contacts the thermocouple material layer through the contact hole.

[0034] Optionally, the thermocouple material layer is one of an N-type polysilicon layer, a P-type polysilicon layer or a metal layer, or the thermocouple material layer is a stack consisting of an N-type polysilicon layer, an inter-thermocouple insulating layer and a P-type polysilicon layer; the metal interconnect layer is a single metal layer or a metal stack.

[0035] Optionally, the supporting dielectric layer is one or a combination of a silicon nitride layer and a silicon oxide layer, with a thickness ranging from 0.2μm to 2μm; the electrical insulating layer is one or a combination of a silicon nitride layer and a silicon oxide layer, with a thickness ranging from 0.05μm to 1μm; the infrared absorption layer formed is one or a combination of a silicon nitride layer and a silicon oxide layer, with a thickness of 0.5μm to 4μm.

[0036] As described above, the double-layer suspended infrared thermopile and preparation method thereof of the present invention, by introducing a thermally conductive reflective layer with "reflection + heat conduction" effect under the absorbing part of the infrared absorption layer, the reflection effect of the thermally conductive reflective layer can be used to make the infrared radiation passing through the infrared absorption layer re-enter the infrared absorption layer, so as to improve the absorption rate, and by using the good thermal conductivity of the thermally conductive reflective layer, the heat generated by the infrared absorption layer absorbing radiation can be more quickly and more concentrated to the contact part of the infrared absorption layer in contact with the electrical insulation layer, so as to be concentrated to the hot junction end of the thermocouple, both of which are conducive to increasing the detection signal and improving the detection performance; further, by setting a preset sacrificial layer, a thermally insulating cavity with a larger width can be formed through an etching window with a smaller width, which can improve the flexibility of the structural layout of the thermopile and improve the space utilization rate of the device; further, the infrared absorption layer and the thermocouple composite layer can be released simultaneously in the last wet etching step to form a double-layer suspended infrared thermopile including a first layer of suspension structure and a second layer of suspension structure, thereby effectively reducing the process complexity and improving the yield rate, which is conducive to realizing the miniaturization and high performance of the infrared thermopile. The double-layer suspended infrared thermopile of the present invention adopts a single-side processing method, has the advantages of simple process and high yield, and is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Shown is a schematic diagram of the process flow of forming a double-layer suspended infrared thermopile in an embodiment of the present invention.

[0038] Figure 2 It is a schematic diagram of the structure after a thermocouple composite layer is formed on a substrate in an embodiment of the present invention.

[0039] Figure 3 It is a schematic diagram of the structure after the etching window is formed in an embodiment of the present invention.

[0040] Figure 4 It is a schematic diagram of the structure after forming a sacrificial layer and a heat-conducting reflective layer in an embodiment of the present invention.

[0041] Figure 5a It is a schematic diagram of the structure after forming the infrared absorption layer in an embodiment of the present invention.

[0042] Figure 5b It is a schematic diagram of the structure after forming an infrared absorption layer in another embodiment of the present invention.

[0043] Figure 6a It is a schematic diagram showing the structure of a double-layer suspended infrared thermopile formed after wet etching in an embodiment of the present invention.

[0044] Figure 6b It is a schematic diagram showing the structure of a double-layer suspended infrared thermopile formed after wet etching in another embodiment of the present invention.

[0045] Component number description

[0046] 100 substrate

[0047] 200 Thermocouple Composite Layer

[0048] 201 Support medium layer

[0049] 202 thermocouple material layer

[0050] 203 electrical insulation layer

[0051] 204 metal interconnect layer

[0052] 205 Etching Window

[0053] 300 Sacrificial Layers

[0054] 301 preset sacrificial layer

[0055] 400 thermal conductive reflective layer

[0056] 500 infrared absorption layer

[0057] 501 infrared absorption layer contact part

[0058] 502 infrared absorption layer absorption part

[0059] 601 Insulated Cavity

[0060] 602 Interval Gap

[0061] 701First floor suspended structure

[0062] 702 Second-floor suspended structure

[0063] Steps S1 to S8 DETAILED DESCRIPTION

[0064] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0065] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0066] For ease of description, spatial relational terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatial relational terms 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 being "between" two layers, it can be the only layer between the two layers, or there can be one or more intervening layers. As used herein, "between..." means including the end point values.

[0067] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0068] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0069] like Figure 1 As shown, this embodiment provides a method for preparing a double-layer suspended infrared thermopile, comprising the following steps:

[0070] S1: providing a substrate;

[0071] S2: forming a thermocouple composite layer on the substrate, wherein the thermocouple composite layer comprises a supporting dielectric layer covering the substrate, and a thermocouple material layer, an electrical insulation layer and a metal interconnection layer located on the supporting dielectric layer;

[0072] S3: patterning the thermocouple composite layer to form an etching window exposing the substrate;

[0073] S4: forming a sacrificial layer covering the thermocouple composite layer and the etching window;

[0074] S5: forming a heat conductive reflective layer covering the sacrificial layer;

[0075] S6: patterning the sacrificial layer and the thermally conductive reflective layer to form a groove at the hot junction end of the thermocouple to expose the electrical insulating layer;

[0076] S7: forming an infrared absorption layer, wherein the infrared absorption layer includes an infrared absorption layer contact portion covering the groove and contacting the electrical insulation layer and an infrared absorption layer absorption portion covering the thermal conductive reflective layer;

[0077] S8: using wet etching to remove the sacrificial layer to form a spacing gap, releasing the infrared absorption layer with the thermal conductive reflective layer to form a second-layer suspension structure, and removing part of the substrate from the etching window to form a thermal insulation cavity, releasing the thermocouple composite layer to form a first-layer suspension structure.

[0078] The preparation method of the double-layer suspended infrared thermopile of this embodiment, by introducing the thermally conductive reflective layer with "reflection + heat conduction" function under the absorbing part of the infrared absorption layer, the reflection effect of the thermally conductive reflective layer can make the infrared radiation passing through the infrared absorption layer re-enter the infrared absorption layer, so as to improve the absorption rate, and by utilizing the good thermal conductivity of the thermally conductive reflective layer, the heat generated by the infrared absorption layer absorbing radiation can be concentrated more quickly to the contact part of the infrared absorption layer in contact with the electrical insulation layer, so as to be concentrated to the hot junction end of the thermocouple, both effects are conducive to increasing the detection signal and improving the detection performance.

[0079] The following is combined with Figure 2 to Figure 6b The double-layer suspended infrared thermopile prepared in this embodiment is introduced as follows:

[0080] First, proceed to step S1, see Figure 2 , providing a substrate 100.

[0081] Specifically, the substrate 100 may be a (100) single crystal silicon substrate, but is not limited thereto, and may also be polycrystalline silicon or amorphous silicon. No excessive restrictions are made here. In this embodiment, the more commonly used (100) single crystal silicon substrate is preferred, and the (100) single crystal silicon substrate is preferably a single-sided or double-sided polished silicon wafer to provide a flat surface to facilitate the preparation of subsequent processes.

[0082] Next, proceed to step S2, see Figure 2A thermocouple composite layer 200 is formed on the substrate 100 , and the thermocouple composite layer 200 includes a supporting dielectric layer 201 covering the substrate 100 , and a thermocouple material layer 202 , an electrical insulation layer 203 and a metal interconnection layer 204 located on the supporting dielectric layer 201 .

[0083] As an example, a vertically stacked thermocouple is provided in this embodiment, that is, the prepared thermocouple material layer 202 and the metal interconnection 204 are arranged vertically to improve space utilization, and a plurality of the thermocouples are prepared in a limited space to provide a high voltage and improve sensitivity, which is conducive to achieving high performance of the infrared thermopile.

[0084] The step of forming the thermocouple composite layer 200 on the substrate 100 may include the following steps, but is not limited thereto, and may specifically include:

[0085] Forming a supporting dielectric layer 201 covering the substrate 100 on the substrate 100;

[0086] Forming a thermocouple material layer 202 on the supporting medium layer 201;

[0087] forming an electrical insulation layer 203 on the thermocouple material layer 202 to cover the thermocouple material layer 202;

[0088] Patterning the electrical insulation layer 203 to form a contact hole exposing the thermocouple material layer 202;

[0089] A patterned metal interconnection layer 204 is formed on the electrical insulation layer 203 , and the metal interconnection 204 contacts the thermocouple material layer 202 through the contact hole.

[0090] As an example, the thermocouple material layer 202 may be one of an N-type polysilicon layer, a P-type polysilicon layer or a metal layer, or the thermocouple material layer 202 is a stack composed of an N-type polysilicon layer, an inter-thermocouple insulating layer and a P-type polysilicon layer; the metal interconnect layer 204 includes a single metal layer or a metal stack.

[0091] Specifically, when the thermocouple material layer 202 is made of doped polysilicon, such as an N-type polysilicon layer or a P-type polysilicon layer, or the thermocouple material layer 202 is a metal layer, the metal interconnect layer 204 serves as both a metal electrical connection layer and a thermocouple component material in the thermocouple, thereby reducing the process steps. In this embodiment, the thermocouple material layer 202 is a patterned P-type polysilicon layer with a thickness ranging from 0.2 μm to 2 μm, such as 0.2 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, etc., and the metal interconnect layer 204 is a Cr-Pt-Au composite metal laminate, but the material, structure and type of the thermocouple material layer 202 and the metal interconnect layer 204 are not limited thereto.

[0092] As an example, the supporting dielectric layer 201 may be one or a combination of a silicon nitride layer and a silicon oxide layer, and the thickness may range from 0.2μm to 2μm, such as 0.2μm, 1μm, 1.5μm, 2μm, etc.; the electrical insulating layer 203 may be one or a combination of a silicon nitride layer and a silicon oxide layer, and the thickness may range from 0.05μm to 1μm, such as 0.05μm, 0.2μm, 0.5μm, 1μm, etc.

[0093] Next, proceed to step S3, see Figure 3 , the thermocouple composite layer 200 is patterned to form an etching window 205 that exposes the substrate 100. The etching window 205 penetrates the electrical insulation layer 203 and the supporting dielectric layer 201, so as to facilitate the subsequent etching of the substrate 100 by the etching solution.

[0094] Next, proceed to step S4, see Figure 4 , forming a sacrificial layer 300 covering the thermocouple composite layer 200 and the etching window 205 .

[0095] As an example, the sacrificial layer 300 may be an amorphous silicon sacrificial layer or a polycrystalline silicon sacrificial layer, or a combination thereof.

[0096] Specifically, Figure 5a When the material of the sacrificial layer 300 and the substrate 100 are both silicon materials, the spacing gap 602 and the heat-insulating cavity 601 can be formed in the same etching step to form a double-layer suspension structure, thereby effectively reducing the process complexity and improving the yield rate, which is conducive to the miniaturization and high performance of the infrared thermopile. In this embodiment, the substrate 100 adopts a (100) single crystal silicon substrate, so that the sacrificial layer 300 adopts one or a combination of an amorphous silicon sacrificial layer or a polycrystalline silicon sacrificial layer, but the material selection of the sacrificial layer 300 is not limited thereto, and the steps of forming the spacing gap 602 and the heat-insulating cavity 601 can also be performed in steps.

[0097] As an example, the thickness of the formed sacrificial layer 300 can range from 0.5μm to 5μm, such as 0.5μm, 1.0μm, 2.0μm, 3.0μm, 4μm, 5μm, etc. The sacrificial layer 300 can be removed by wet etching to form a smaller gap while meeting device requirements, thereby reducing device size and reducing costs.

[0098] Next, step S5 is performed to form a heat-conducting reflective layer 400 covering the sacrificial layer 300 .

[0099] As an example, the thermal conductive reflective layer 400 may be a single metal layer or a metal stack, and the thickness may range from 20 nm to 1000 nm, such as 20 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1000 nm, etc.

[0100] Specifically, by introducing the thermally conductive reflective layer 400 having the "reflection + heat conduction" function under the infrared absorption layer absorption part 502, the infrared radiation passing through the infrared absorption layer 500 can be re-entered into the infrared absorption layer 500 by utilizing the reflection function of the thermally conductive reflective layer 400, so that the absorption rate is improved. In addition, by utilizing the good thermal conductivity of the thermally conductive reflective layer 400, the heat generated by the infrared absorption layer 500 absorbing radiation can be concentrated more quickly to the infrared absorption layer contact part 501 in contact with the electrical insulation layer 203, so as to be concentrated to the hot junction end of the thermocouple. Both functions are conducive to increasing the detection signal and improving the detection performance.

[0101] Next, proceed to step S6, see Figure 5a , patterning the sacrificial layer 300 and the thermally conductive reflective layer 400, and forming a groove at the hot junction end of the thermocouple to expose the electrical insulation layer.

[0102] Next, step S7 is performed to form a patterned infrared absorption layer 500 covering the sacrificial layer 300 and the groove, wherein the infrared absorption layer 500 includes an infrared absorption layer contact portion 501 covering the groove and contacting the electrical insulation layer 203, and an infrared absorption layer absorption portion 502 covering the thermal conductive reflective layer 400. It is preferred that the infrared absorption layer contact portion 501 is located at the center of the infrared absorption layer 500 to increase the temperature of the hot junction, but the invention is not limited thereto.

[0103] As an example, the infrared absorption layer 500 may be one or a combination of a silicon nitride layer and a silicon oxide layer, and the thickness may be 0.5 μm to 4 μm, such as 0.5 μm, 1.0 μm, 1.5 μm, 4 μm, etc.

[0104] As an example, a plurality of the thermocouples are formed, the thermocouples are connected in series to form a thermocouple group, and the infrared absorption layer 500 is an umbrella-shaped infrared absorption layer covering the thermocouple group.

[0105] Specifically, in this embodiment, it is preferred to include a plurality of the thermocouples, and the thermocouples are connected in series to form a thermocouple group, so as to provide a sufficient number of thermocouples and provide a sufficiently high voltage, thereby improving sensitivity, and the infrared absorption layer 500 is preferably an umbrella-shaped infrared absorption layer covering the thermocouple group to increase the amount of light absorption. The number and arrangement of the thermocouples are not excessively limited here and can be set as needed.

[0106] Next, proceed to step S8, see Figure 6a and Figure 6b , wet etching is used to remove the sacrificial layer 300 to form a spacing gap 602, release the infrared absorption layer absorption part 502 with the thermal conductive reflective layer 400, form a second-layer suspension structure 702, and remove part of the substrate 100 from the etching window 205 to form a thermal insulation cavity 601, release the thermocouple composite layer 200 to form a first-layer suspension structure 701.

[0107] As an example, the wet etching solution may include tetramethylammonium hydroxide solution or potassium hydroxide solution, but is not limited thereto. In this embodiment, the sacrificial layer 300 made of silicon and part of the substrate 100 made of silicon can be removed simultaneously in the last step by the etching solution, thereby reducing the process complexity of preparing a double-layer suspended infrared thermopile, improving the yield rate, and being conducive to achieving miniaturization and high performance of the infrared thermopile.

[0108] In another embodiment, if Figure 5b , may also include a step of forming a preset sacrificial layer 301 in contact with the substrate 100 , and the etching window 205 exposes the preset sacrificial layer 301 .

[0109] As an example, the preset sacrificial layer 301 formed may include a silicon oxide layer or a metal layer, and the thickness range may be 0.5μm to 5μm, such as 0.5μm, 1μm, 2μm, 4μm, 5μm, etc.; the sacrificial layer 300 formed may include a silicon oxide layer or a metal layer, and the thickness range may be 0.5μm to 5μm, such as 0.5μm, 1μm, 2μm, 4μm, 5μm, etc.

[0110] For details, see Figure 5b and 6bBy forming the preset sacrificial layer 301, the preset sacrificial layer 301 can be effectively removed by wet etching to form the thermal insulation cavity 601 with good thermal insulation effect, thereby solving the problem that the thermal pile structure layout is limited due to the crystal orientation characteristics of the single crystal silicon substrate, which limits the performance improvement of the thermal pile detector, and can improve the flexibility of the structural layout of the thermopile and improve the space utilization of the device. In addition, by using the preset sacrificial layer 301, the thermal insulation cavity 601 with a larger width can be formed when preparing the etching window 205 with a smaller width, which can improve the flexibility of the structural layout of the thermopile and improve the space utilization of the device.

[0111] When the material of the sacrificial layer 300 is preferably the same or similar to that of the preset sacrificial layer 301, such as silicon oxide, when wet etching is performed, a silicon oxide etching solution such as BOE, HF, etc. that removes silicon oxide can be used to remove the preset sacrificial layer 301 and the sacrificial layer 300 in the same etching step to form a double-layer suspension structure. Of course, the preset sacrificial layer 301 and the sacrificial layer 300 can also be made of different materials so as to be removed in sequence by two etching solutions, which is not excessively limited here.

[0112] See also Figure 2 to Figure 6b The present embodiment further provides a double-layer suspended infrared thermopile, which can be prepared by the above-mentioned preparation process, but is not limited thereto. The above-mentioned preparation process is used to prepare the double-layer suspended infrared thermopile in the present embodiment, so the structure, material, etc. of the double-layer suspended infrared thermopile are not described in detail herein.

[0113] The double-layer suspended infrared thermopile comprises: a substrate 100, a first-layer suspended structure 701, a heat-insulating cavity 601, an etching window 205, and a second-layer suspended structure 702. The first-layer suspended structure 701 is located on the substrate 100, and comprises a supporting dielectric layer 201 and a thermocouple material layer 202, an electrical insulating layer 203, and a metal interconnect layer 204 located on the supporting dielectric layer 201. The heat-insulating cavity 601 is located below the first-layer suspended structure 701. The etching window 205 penetrates the first-layer suspended structure 701. The electric insulating layer 203 and the supporting medium layer 201 are connected with the heat insulating cavity 601. The second-layer suspension structure 702 is located on the first-layer suspension structure 701, and includes an infrared absorption layer 500 and a thermal conductive reflective layer 400, wherein the infrared absorption layer 500 includes an infrared absorption layer contact portion 501 in contact with the electric insulating layer 203 and an infrared absorption layer absorption portion 502 covering the thermal conductive reflective layer 400, and there is a spacing gap 602 between the thermal conductive reflective layer 400 and the thermocouple.

[0114] It is preferred that the infrared absorption layer contact portion 501 is located at the center of the infrared absorption layer 500 to increase the temperature of the hot junction, but the present invention is not limited thereto.

[0115] In another embodiment, if Figure 5b and 6b , and may further include the step of forming a preset sacrificial layer 301. Thus, by means of the preset sacrificial layer 301, the heat-insulating cavity 601 with a larger width can be formed when the etching window 205 with a smaller width is prepared, thereby improving the flexibility of the structural layout of the thermopile and improving the space utilization of the device.

[0116] In summary, the double-layer suspended infrared thermopile and the preparation method thereof of the present invention, by introducing a thermally conductive reflective layer with "reflection + heat conduction" effect under the absorbing part of the infrared absorption layer, the reflection effect of the thermally conductive reflective layer can be used to make the infrared radiation passing through the infrared absorption layer re-enter the infrared absorption layer, so as to improve the absorption rate, and by using the good thermal conductivity of the thermally conductive reflective layer, the heat generated by the infrared absorption layer absorbing radiation can be more quickly and more concentrated to the contact part of the infrared absorption layer in contact with the electrical insulation layer, so as to be concentrated to the hot junction end of the thermocouple, both of which are conducive to increasing the detection signal and improving the detection performance; further, by setting a preset sacrificial layer, a thermally insulating cavity with a larger width can be formed through an etching window with a smaller width, which can improve the flexibility of the structural layout of the thermopile and improve the space utilization rate of the device; further, the infrared absorption layer and the thermocouple composite layer can be released at the same time in the last step to form a double-layer suspended infrared thermopile including a first layer of suspension structure and a second layer of suspension structure, thereby effectively reducing the process complexity and improving the yield rate, which is conducive to realizing the miniaturization and high performance of the infrared thermopile. The double-layer suspended infrared thermopile of the present invention adopts a single-side processing method, has the advantages of simple process and high yield, and is suitable for mass production.

[0117] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a double-layer suspended infrared thermopile, characterized in that: The following steps are involved: providing a substrate; forming a thermocouple composite layer on the substrate, wherein the thermocouple composite layer comprises a supporting dielectric layer covering the substrate, and a thermocouple material layer, an electrical insulation layer and a metal interconnection layer located on the supporting dielectric layer; Patterning the thermocouple composite layer to form an etching window exposing the substrate; forming a sacrificial layer covering the thermocouple composite layer and the etching window; forming a heat-conducting reflective layer covering the sacrificial layer; Patterning the sacrificial layer and the heat-conducting reflective layer to form a groove at the hot junction end of the thermocouple to expose the electrical insulation layer; forming an infrared absorption layer, wherein the infrared absorption layer comprises an infrared absorption layer contact portion covering the groove and contacting the electrical insulation layer and an infrared absorption layer absorption portion covering the thermal conductive reflective layer, wherein the infrared absorption layer contact portion is located at a central position of the infrared absorption layer; The sacrificial layer is removed by wet etching to form a spacing gap, the infrared absorption layer with the heat conductive reflective layer is released to form a second suspended structure, and part of the substrate is removed from the etching window to form a heat insulating cavity, and the thermocouple composite layer is released to form a first suspended structure.

2. The method for preparing a double-layer suspended infrared thermopile according to claim 1, characterized in that: The heat-conducting reflective layer is a single metal layer or a metal stack, and has a thickness ranging from 20nm to 1000nm.

3. The method for preparing a double-layer suspended infrared thermopile according to claim 1, characterized in that: The substrate is a (100) single crystal silicon substrate, and the sacrificial layer is an amorphous silicon sacrificial layer or a polycrystalline silicon sacrificial layer or a combination thereof; the spacing gap and the heat insulation cavity are formed simultaneously in the last step.

4. The method for preparing a double-layer suspended infrared thermopile according to claim 1, characterized in that: The method further includes forming a preset sacrificial layer in contact with the substrate, and the etching window exposes the preset sacrificial layer.

5. The method for preparing a double-layer suspended infrared thermopile according to claim 4, characterized in that: The preset sacrificial layer formed includes a silicon oxide layer or a metal layer with a thickness ranging from 0.5 μm to 5 μm. The preset sacrificial layer formed includes a silicon oxide layer or a metal layer with a thickness ranging from 0.5 μm to 5 μm.

6. The method for preparing a double-layer suspended infrared thermopile according to claim 1, characterized in that: The step of forming the thermocouple composite layer on the substrate comprises: forming a supporting medium layer covering the substrate on the substrate; forming a thermocouple material layer on the supporting medium layer; forming an electrical insulation layer covering the thermocouple material layer on the thermocouple material layer; Patterning the electrical insulating layer to form a contact hole exposing the thermocouple material layer; A patterned metal interconnection layer is formed on the electrical insulation layer, and the metal interconnection layer contacts the thermocouple material layer through the contact hole.

7. The method for preparing a double-layer suspended infrared thermopile according to claim 1, characterized in that: The thermocouple material layer is one of an N-type polysilicon layer, a P-type polysilicon layer or a metal layer, or the thermocouple material layer is a stack composed of an N-type polysilicon layer, an inter-thermocouple insulating layer and a P-type polysilicon layer; the metal interconnect layer is a single metal layer or a metal stack.

8. The method for preparing a double-layer suspended infrared thermopile according to claim 1, characterized in that: The supporting dielectric layer is one or a combination of a silicon nitride layer and a silicon oxide layer, with a thickness ranging from 0.2 μm to 2 μm; the electrical insulating layer is one or a combination of a silicon nitride layer and a silicon oxide layer, with a thickness ranging from 0.05 μm to 1 μm; the infrared absorption layer formed is one or a combination of a silicon nitride layer and a silicon oxide layer, with a thickness of 0.5 μm to 4 μm.

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