A method for forming a MEMS sensor and the MEMS sensor itself.

Abstract

This application discloses a method for forming a MEMS sensor and a MEMS sensor. The method includes providing a first wafer and a second wafer; forming a through-hole on a first surface of the first wafer; forming a first insulating layer on the first surface and a second insulating layer on the inner wall of the through-hole; forming an initial device layer on the first insulating layer; patterning the initial device layer to form independent sensing structures and electrical connection structures, with the electrical connection structures at least partially located within the through-hole; removing a portion of the first insulating layer to create a gap between the movable part of the sensing structure and the first wafer; bonding both the sensing structure and the electrical connection structure to the second wafer; thinning the first wafer to expose the electrical connection structures on a second surface; and forming signal lead-out structures on a second surface of the first wafer, each signal lead-out structure being connected to the corresponding electrical connection structure within the through-hole. This application can improve the stability of sensor signal transmission and product consistency.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and more particularly to a method for forming a MEMS sensor and a MEMS sensor. Background Technology

[0002] As microelectromechanical systems (MEMS) and inertial sensors (such as accelerometers and gyroscopes) develop towards smaller package sizes and higher integration, in order to further reduce the size of MEMS sensors and improve integration, the substrate of traditional MEMS chips is usually replaced with an application-specific integrated circuit (ASIC) chip, thereby forming a highly integrated MEMS sensor chip.

[0003] In highly integrated MEMS sensors, through-silicon vias (TSVs) are typically used to bring up signals from ASIC chips. This involves creating vias within the chip and filling them with metal to bring internal signals to external connections. While this method avoids the complexity of traditional metal wire wiring and the problems of short circuits and leakage caused by jumpers, it is prone to incomplete filling during the process, affecting signal transmission stability and product consistency. Furthermore, due to limitations in the metal filling process, the via size is typically large to ensure filling quality, making further reduction difficult. This hinders the miniaturization and integration of MEMS sensors and results in complex fabrication processes and high manufacturing costs. Additionally, creating TSVs on ASIC chips requires thinning the ASIC chip, which can increase electrode deformation and exacerbate zero-bias issues, affecting the detection accuracy and stability of the MEMS sensor. Summary of the Invention

[0004] This application provides a method for forming a MEMS sensor and a MEMS sensor, aiming to improve the stability of signal transmission and product consistency of MEMS sensors, as well as reduce the manufacturing cost of MEMS sensors.

[0005] To achieve the above objectives, according to a first aspect of this application, a method for forming a MEMS sensor is provided, comprising: A first wafer and a second wafer are provided, the first wafer having a first surface and a second surface disposed opposite to each other along the thickness direction, and the second wafer having metal wiring laid on it; At least one through hole is formed on the first surface, the through hole extending into the interior of the first wafer along the thickness direction, but not penetrating the first wafer; A first insulating layer is formed on the first surface, and a second insulating layer is formed on the inner wall of the through hole; An initial device layer is formed on the first insulating layer, and the initial device layer fills the via. The initial device layer is patterned to form independent sensitive structures and electrical connection structures, wherein the electrical connection structures are at least partially located within the vias, and the sensitive structures include movable parts and fixed parts; Remove a portion of the first insulating layer to create a gap between the movable part and the first wafer; Both the side of the sensitive structure facing away from the first surface and the side of the electrical connection structure facing away from the first surface are bonded to the second wafer, so that the sensitive structure and the electrical connection structure are electrically connected to the second wafer respectively. A portion of the first wafer is removed from the side containing the second surface to expose the electrical connection structure located in the via on the second surface; At least one signal lead-out structure is formed on the second surface of the first wafer, and each signal lead-out structure is connected to the electrical connection structure in the corresponding via.

[0006] In some embodiments, forming a first insulating layer on the first surface and forming a second insulating layer on the inner wall of the through hole includes: After creating at least one through-hole, the first side of the first wafer is thermally oxidized to form a first insulating layer on the first surface, and a second insulating layer is formed on the inner wall of the through-hole.

[0007] In some embodiments, the first surface has at least one preset region, the preset region corresponding to one of the movable parts, and in the thickness direction, the preset region and the projection of the corresponding movable part onto the first surface at least partially overlap; before forming a first insulating layer on the first surface and the inner wall of the through hole, the method for forming the MEMS sensor further includes: Multiple grooves are opened at intervals in the preset area; the first surface is thermally oxidized so that the groove walls in the preset area are oxidized and filled, thereby forming a continuous oxide layer in the preset area.

[0008] In some embodiments, the first insulating layer covers the predetermined area, and the first insulating layer is made of the same material as the continuous oxide layer.

[0009] In some embodiments, the specific steps of removing a portion of the first insulating layer to create a gap between the movable portion and the first wafer include: Remove a portion of the first insulating layer and the continuous oxide layer located in the preset region, and form a first groove in the preset region that is disposed opposite to the corresponding movable part, so that a gap is formed between the movable part and the first wafer; A portion of the first insulating layer located below the fixing part is retained to form a support column connected to the fixing part.

[0010] In some embodiments, the specific steps of forming an initial device layer on the first insulating layer and filling the via with the initial device layer include: A polycrystalline silicon seed layer is formed, which covers the surface of the first insulating layer opposite to the first surface and the second insulating layer located in the through hole; Polycrystalline silicon is epitaxially grown on the polycrystalline silicon seed layer to form the initial device layer on the side of the first insulating layer opposite to the first surface, while the polycrystalline silicon fills the via.

[0011] In some embodiments, the specific steps of removing a portion of the first insulating layer to create a gap between the movable portion and the first wafer include: Remove a portion of the first insulating layer located below the movable part to create a gap between the movable part and the first wafer; A portion of the first insulating layer located below the fixing part is retained to form a support column connected to the fixing part.

[0012] In some embodiments, the fourth insulating layer is made of silicon nitride, and the initial device layer is made of polysilicon.

[0013] In some embodiments, the specific steps of forming the first insulating layer on the first surface include: Before opening at least one through hole, a third insulating layer is formed, the third insulating layer covering the first surface; A fourth insulating layer is formed on the side of the third insulating layer that is opposite to the first surface, and the fourth insulating layer is made of a different material than the third insulating layer; The first insulating layer is formed on the side of the fourth insulating layer that is opposite to the third insulating layer; The first insulating layer is etched with the fourth insulating layer as a stop layer to form at least one first notch and a second notch on the first insulating layer. The first notch corresponds to the fixing part. In the thickness direction, the projection of the first notch overlaps with the projection of the corresponding fixing part. The projection of the through hole is located within the projection range of the second notch.

[0014] In some embodiments, the through-hole extends through the first insulating layer, the fourth insulating layer, and the third insulating layer, and the specific steps of forming a second insulating layer on the inner wall of the through-hole include: After creating at least one through-hole, the first side of the first wafer is thermally oxidized to form the second insulating layer on the inner wall of the through-hole.

[0015] In some embodiments, the initial device layer further fills the first and second gaps, and the specific steps of removing a portion of the first insulating layer to form a gap between the movable portion and the first wafer include: Using the fourth insulating layer as a stop layer, the first insulating layer is removed to create a gap between the movable part and the first wafer; The initial device layer located within the first notch is retained, and the initial device layer located within the first notch forms a support column connected to the fixing part.

[0016] In some embodiments, a first bonding layer is deposited on the side of the second wafer facing the first wafer; the method for forming the MEMS sensor further includes: Before patterning the initial device layer, the side of the initial device layer opposite to the first insulating layer is etched to form a plurality of bonding bumps on the side of the initial device layer opposite to the first insulating layer. A second bonding layer is formed on the bonding protrusion; The step of bonding the side of the sensitive structure away from the first surface and the side of the electrical connection structure away from the first surface to the second wafer includes: The first bonding layer and the second bonding layer are bonded together so that the sensitive structure and the electrical connection structure are electrically connected to the second wafer, respectively.

[0017] In some embodiments, the specific steps of forming at least one signal lead-out structure on the second surface of the first wafer, and connecting each signal lead-out structure to the electrical connection structure in the corresponding via, include: A dielectric layer is formed, which covers the second surface. A second groove is formed on the dielectric layer, and each second groove corresponds to a through hole. The electrical connection structure corresponding to the through hole is exposed in the second groove. A redistribution layer is formed, which covers the dielectric layer and the electrical connection structure exposed in the second groove; A passivation layer is formed, which covers the redistribution layer. The passivation layer has multiple openings, and the redistribution layer is exposed in the openings. Signal lead-out structures are formed in the openings such that each signal lead-out structure is electrically connected to the corresponding electrical connection structure through the redistribution layer.

[0018] According to a second aspect of this application, a MEMS sensor is provided, comprising: A first wafer has a first surface and a second surface that are disposed opposite to each other along the thickness direction. At least one through hole is formed on the first wafer, the through hole penetrating the first surface and the second surface, and the inner wall of the through hole is covered with a second insulating layer. The second wafer has metal wiring laid on it; Independent sensing and electrical connection structures are located between the first wafer and the second wafer. The sensing structure includes a movable part and a fixed part. The movable part has a gap with the first wafer. In the thickness direction, one side of the fixed part is fixedly connected to the first wafer, and at least one side of the fixed part is fixedly connected to the second wafer. One end of the electrical connection structure extends into the through hole and is exposed on the second surface, and the other end is fixedly connected to the second wafer. A signal lead-out structure is formed on the second surface of the second wafer. Each signal lead-out structure corresponds to one of the vias and is connected to the electrical connection structure within the corresponding via.

[0019] In some embodiments, both the material of the sensitive structure and the material of the electrical connection structure include polycrystalline silicon, and the materials of the sensitive structure and the electrical connection structure are formed by the same polycrystalline silicon deposition process.

[0020] In some embodiments, a first groove is formed on the first surface, and in the thickness direction, the projection of the first groove at least partially overlaps with the projection of one of the movable parts.

[0021] In some embodiments, it also includes: A third insulating layer covers the first surface and is connected to the second insulating layer; A fourth insulating layer covers the side of the third insulating layer that faces away from the first surface; The third insulating layer and the fourth insulating layer are made of different materials. The through hole also penetrates the third insulating layer and the fourth insulating layer. The fixing part has a support column protruding on the side facing the first surface. The support column is fixedly connected to the fourth insulating layer.

[0022] This embodiment of the application creates a via on one side of a first wafer and fills the via with an initial device layer formed on the first insulating layer while simultaneously forming the sensitive structure, creating an electrical connection structure within the via for signal extraction. Subsequently, by bonding the first and second wafers, thinning the first wafer, and forming a signal extraction structure on the second side, the internal electrical signal is effectively extracted to the external connection. Since this embodiment does not use metal filling to form the electrical connection structure, there is no need to design the via as an inverted trapezoidal structure suitable for metal filling. This reduces the risk of signal transmission abnormalities caused by insufficient metal filling, voids within the via, or poor contact, thus improving the stability and consistency of MEMS sensor signal transmission. Furthermore, because this embodiment does not rely on traditional metal filling processes, the via diameter can be controlled between 5μm and 10μm, much smaller than the approximately 100μm via diameter typically required for metal filling. Therefore, it can significantly reduce the area occupied by the electrical connection structure while ensuring signal extraction, which is more conducive to the miniaturization and high integration of MEMS sensors. Meanwhile, this embodiment utilizes an initial device layer formed on the first insulating layer to fill vias simultaneously with the formation of the sensitive structure, thereby avoiding the additional process steps required for separate metal filling of vias in conventional solutions. This reduces process steps and shortens the manufacturing process; it also reduces resource consumption from additional metal filling and related processes, thus helping to control overall manufacturing costs. Furthermore, since the electrical connection structure is located on the first wafer, rather than on the second wafer, the second wafer does not need to consider the location and area occupied by the electrical connection structure when designing metal wiring. This reduces the adverse effects of thinning processing on the metal wiring and electrode structure of the second wafer, further improving the stability and consistency of MEMS sensor signal transmission and reducing manufacturing costs. Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings, wherein the same reference numerals in the following description denote the same parts.

[0025] Figure 1 This is a schematic flowchart of a method for forming a MEMS sensor disclosed in an embodiment of this application; Figure 2 This is a schematic diagram of the structure of the first wafer and the second wafer disclosed in the embodiments of this application; Figures 3 to 16 This is a schematic diagram of the process steps of a MEMS sensor disclosed in an embodiment of this application; Figures 17 to 23 This is a schematic diagram of the process steps of another MEMS sensor disclosed in the embodiments of this application; Figures 24 to 31 This is a schematic diagram of the process steps of another MEMS sensor disclosed in the embodiments of this application.

[0026] Explanation of reference numerals in the attached figures: 10. First wafer; 101. First surface; 102. Second surface; 103. Through-hole; 104. Preset area; 105. Trench; 106. First groove; 107. First notch; 110. First insulating layer; 111. Second insulating layer; 112. Third insulating layer; 113. Fourth insulating layer; 114. Continuous oxide layer; 115. Support pillar; 116. Gap; 117. Initial device layer; 118. Mask layer; 119. Polysilicon seed layer; 120. Second notch; 20. Second wafer; 201. Metal wiring; 202. First bonding layer; 203. Substrate; 301. Sensitive structure; 3011. Movable part; 3012. Fixed part; 302. Electrical connection structure; 303. Bonding boss; 304. Second bonding layer; 501, dielectric layer; 5011, second groove; 502, redistribution layer; 503, passivation layer; 5031, opening; 504, signal lead-out structure; 5041, metal layer; 5042, solder ball. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0028] As mentioned in the background technology, microelectromechanical systems (MEMS) and inertial sensors (such as accelerometers and gyroscopes) are developing towards smaller package sizes and higher integration. In order to further reduce the size of MEMS sensors and improve integration, the substrate of traditional MEMS chips is usually replaced with ASIC chips, thereby forming highly integrated MEMS sensor chips.

[0029] The existing technology discussed in the background typically involves creating vias within the chip and filling them with metal material to bring internal signals to external connections. While this method avoids the complex wiring of traditional metal leads and the problems of short circuits and leakage caused by jumpers, the metal filling process has high requirements for via size and filling conditions. Specifically, metal filling often relies on first forming a continuous seed layer, and then allowing the metal to grow gradually from the via opening into the via. When the depth-to-width ratio of the via is large, the deposition rate near the via opening is often higher than that at the depth inside the via, easily leading to accumulation at the via opening, and even forming a "narrowing" or "clamping" phenomenon. Once the via opening narrows prematurely, it becomes more difficult for the lower space inside the via to be fully filled with metal, resulting in residual gaps inside, forming voids. Therefore, when using metal filling technology to extract electrical signals, it is usually necessary to set the aperture of the via to a larger size to reduce the filling difficulty and improve the conduction reliability. However, a larger via will occupy more chip area, which is not conducive to the further miniaturization and high integration of MEMS sensors. Moreover, even if the via size is increased, there is still a risk of insufficient filling during the metal filling process, which will affect the stability of signal transmission and product consistency.

[0030] Therefore, in order to improve the stability of signal transmission and product consistency of MEMS sensors, and to reduce the manufacturing cost of MEMS sensors, [reference needed]. Figure 1 This application discloses a method for forming a MEMS sensor, which includes: S100: Provides a first wafer and a second wafer, the first wafer having a first surface and a second surface disposed opposite to each other along the thickness direction, and the second wafer having metal wiring laid on it.

[0031] S200: At least one through hole is formed on the first surface, the through hole extends into the interior of the first wafer along the thickness direction, but does not penetrate the first wafer.

[0032] S300: A first insulating layer is formed on the first surface, and a second insulating layer is formed on the inner wall of the through hole.

[0033] S400: An initial device layer is formed on the first insulating layer, and the initial device layer fills the via.

[0034] S500: The initial device layer is patterned to form independent sensing structures and electrical connection structures. The electrical connection structures are at least partially located within vias, and the sensing structures include movable and fixed parts.

[0035] S600: Remove part of the first insulating layer to create a gap between the movable part and the first wafer.

[0036] S700: The side of the sensitive structure facing away from the first surface and the side of the electrical connection structure facing away from the first surface are both bonded to the second wafer, so that the sensitive structure and the electrical connection structure are electrically connected to the second wafer respectively.

[0037] S800: Remove a portion of the first wafer on the side where the second surface is located to expose the electrical connection structure located in the through-hole on the second surface.

[0038] S900: At least one signal lead-out structure is formed on the second surface of the first wafer, and each signal lead-out structure is connected to an electrical connection structure in a corresponding via.

[0039] This embodiment of the application creates a through-hole 103 on one side of the first wafer 10, and fills the through-hole 103 simultaneously with the formation of the sensitive structure 301 using an initial device layer 117 formed on the first insulating layer 110, thereby forming an electrical connection structure 302 for signal extraction within the through-hole 103. Subsequently, by bonding the first wafer 10 to the second wafer 20, thinning the first wafer 10, and forming a signal extraction structure 504 on the second surface 102, the internal electrical signal is effectively extracted to the external connection terminal. Since this embodiment of the application does not use metal filling to form the electrical connection structure 302, it is not necessary to design the through-hole 103 as an inverted trapezoidal structure suitable for metal filling. This reduces the risk of signal transmission abnormalities caused by insufficient metal filling, voids in the hole, or poor contact, which is beneficial to improving the stability of MEMS sensor signal transmission and product consistency. Furthermore, since the embodiments of this application do not rely on traditional metal filling processes, the aperture of the through hole 103 can be controlled between 5μm and 10μm, which is much smaller than the aperture size of about 100μm required for metal filling. Therefore, it can significantly reduce the area occupied by the electrical connection structure 302 while ensuring signal output, which is more conducive to the development of MEMS sensors towards miniaturization and high integration.

[0040] Meanwhile, in this embodiment, the initial device layer 117 formed on the first insulating layer 110 fills the via 103 while forming the sensitive structure 301, thereby avoiding the additional process steps required for separate metal filling of vias in conventional solutions. On the one hand, this reduces process steps and shortens the manufacturing process; on the other hand, it reduces resource consumption caused by additional metal filling and related processes, which is beneficial for controlling overall manufacturing costs.

[0041] Finally, it is worth mentioning that in this embodiment, the electrical connection structure 302 is located on the first wafer 10, rather than on the second wafer 20. Therefore, the signal output path is mainly integrated on the first wafer 10 side, without the need for additional through-hole structures or a large area specifically reserved for signal output on the second wafer 20 side. Thus, when designing the metal wiring 201 on the second wafer 20, there is no need to consider the space reservation, routing avoidance, and position matching limitations caused by the electrical connection structure 302. Furthermore, there is no need for special thinning treatment to expose the electrical connection structure 302. This reduces the adverse effects of thinning on the metal wiring 201 and electrode structure of the second wafer 20, lowers the risk of deformation and misalignment of the metal wiring 201 and electrode structure, and further improves the stability and product consistency of MEMS sensor signal transmission, while reducing manufacturing costs.

[0042] Step S100: Provide a first wafer 10 and a second wafer 20. The first wafer 10 has a first surface 101 and a second surface 102 disposed opposite to each other along the thickness direction. The second wafer 20 is provided with metal wiring 201.

[0043] Reference Figure 2 In some embodiments, the first wafer 10 is made of silicon. The second wafer 20 includes a substrate 203, metal wiring 201 disposed on the substrate 203, and a first bonding layer 202 formed on the side of the substrate 203 facing the first wafer 10. The first bonding layer 202 at least partially covers the metal wiring 201 and is electrically connected to it. In some embodiments, the substrate 203 of the second wafer 20 is also made of silicon. In some embodiments, the first bonding layer 202 is made of aluminum. In some embodiments, the metal wiring 201 is made of aluminum or tungsten.

[0044] Step S200: At least one through hole 103 is formed on the first surface 101. The through hole 103 extends into the first wafer 10 along the thickness direction but does not penetrate the first wafer 10.

[0045] Reference Figure 3 In some embodiments, before creating the via 103, a mask layer 118 is deposited on the first surface 101. The mask layer 118 is made of silicon oxide. The mask layer 118 is formed using a deposition process with silane as a precursor or a deposition process with tetraethyl orthosilicate as a precursor. The thickness of the mask layer 118 is between 1 μm and 2 μm. Openings are formed on the mask layer 118 by dry etching, and subsequently, vias 103 are formed in the first wafer 10 using these openings as etching windows. It should be noted that the number of vias 103 can be set according to the number of electrical signals to be extracted from the second wafer 20 side.

[0046] Step S300: A first insulating layer 110 is formed on the first surface 101, and a second insulating layer 111 is formed on the inner wall of the through hole 103.

[0047] Reference Figure 4 In some embodiments, after the via 103 is formed, the mask layer 118 on the first surface 101 is first removed by wet etching; then, the side of the first surface 101 of the first wafer 10 is subjected to thermal oxidation so that the first insulating layer 110 and the second insulating layer 111 are formed simultaneously. The first insulating layer 110 and the second insulating layer 111 are both silicon oxide.

[0048] Step S400: An initial device layer 117 is formed on the first insulating layer 110, and the initial device layer 117 fills the via 103.

[0049] Reference Figure 5 and Figure 6 In some embodiments, the initial device layer 117 is made of polycrystalline silicon.

[0050] In some embodiments, step S400 specifically includes: forming a polysilicon seed layer 119, which covers the surface of the first insulating layer 110 facing away from the first surface 101 and the second insulating layer 111 located within the via 103; epitaxially growing polysilicon on the polysilicon seed layer 119 to form an initial device layer 117 on the side of the first insulating layer 110 facing away from the first surface 101, while simultaneously filling the via 103 with polysilicon. This configuration allows the initial device layer 117 to be formed inside the via 103 and on the first surface 101 in a single polysilicon epitaxial process. Compared to traditional metal plating filling methods, polysilicon deposition is less prone to preferential growth at the via opening and premature closing, leading to residual voids at the bottom of the via. Therefore, when using polysilicon to form the electrical connection structure 302 within the via 103, it is not necessary to design the via 103 as a large-sized inverted trapezoidal structure suitable for metal filling, achieving a better filling effect under smaller aperture conditions. In some embodiments, the aperture of the through hole 103 is in the range of 5μm to 10μm, which can significantly reduce the area occupied by the electrical connection structure 302 while ensuring signal output, and is more conducive to the development of MEMS sensors towards miniaturization and high integration.

[0051] Step S500: The initial device layer 117 is patterned to form a sensitive structure 301 and an electrical connection structure 302 that are independent of each other. The electrical connection structure 302 is at least partially located in the through hole 103. The sensitive structure 301 includes a movable part 3011 and a fixed part 3012.

[0052] Reference Figure 9In some embodiments, the sensing structure 301 and the electrical connection structure 302 are located on the same device layer. The sensing structure 301 includes a movable part 3011 and a fixed part 3012, used to generate a corresponding detection signal under external inertial action. The electrical connection structure 302 extends at least partially into the via 103 to form a signal extraction path. Specifically, the sensing structure 301 can be electrically connected to the second wafer 20 via subsequent bonding to transmit the detected electrical signal to the second wafer 20 for processing. The electrical connection structure 302 can also be electrically connected to the second wafer 20 via subsequent bonding and exposed on the second surface 102 after the first wafer 10 is subsequently thinned, thereby further transmitting the electrical signal from the second wafer 20 side to the outside. By designing the sensing structure 301 and the electrical connection structure 302 as independent structures, inertial detection and signal extraction functions can be realized simultaneously within the same device layer, which helps to reduce signal coupling interference and improve device integration.

[0053] In some embodiments, before patterning the initial device layer 117, the method for forming a MEMS sensor further includes: planarizing the initial device layer 117 and controlling the thickness of the initial device layer 117 to be between 20 μm and 30 μm.

[0054] In some embodiments, before patterning the initial device layer 117, the method for forming a MEMS sensor further includes: etching the side of the initial device layer 117 away from the first insulating layer 110 to form a plurality of bonding protrusions 303 on the side of the initial device layer 117 away from the first insulating layer 110; and forming a second bonding layer 304 on the bonding protrusions 303.

[0055] Reference Figure 7 and Figure 8 Multiple bonding bosses 303 are arranged at intervals. After subsequent patterning, at least one fixing portion 3012 has a bonding boss 303 formed on the side opposite to the first insulating layer 110. Each electrical connection structure 302 has at least one bonding boss 303 formed on the side opposite to the first insulating layer 110. Each bonding boss 303 is covered by a second bonding layer 304 on the side opposite to the first insulating layer 110. In some embodiments, the material of the second bonding layer 304 includes doped germanium.

[0056] Step S600: Remove part of the first insulating layer 110 to form a gap 116 between the movable part 3011 and the first wafer 10.

[0057] Reference Figure 10After the sensitive structure 301 and the electrical connection structure 302 are formed, multiple gaps are formed in the device layer containing the sensitive structure 301 and the electrical connection structure 302, thereby allowing the first insulating layer 110 located below the sensitive structure 301 to communicate with the external etching medium through the gaps. Therefore, when releasing the sensitive structure 301 in the future, a wet etching process, such as a diluted hydrofluoric acid wet etching process or a vapor phase hydrofluoric acid etching process, can be used to selectively remove the first insulating layer 110 located below the sensitive structure 301.

[0058] In some embodiments, step S600 includes the following specific steps: Remove a portion of the first insulating layer 110 located below the movable part 3011 to form a gap 116 between the movable part 3011 and the first wafer 10; A portion of the first insulating layer 110 located below the fixing part 3012 is retained to form a support column 115 connected to the fixing part 3012.

[0059] Thus, the movable part 3011 in the sensitive structure 301 can move relative to the first wafer 10 (e.g., move along a direction parallel to the first surface 101), while the fixed part 3012 is maintained connected to the first wafer 10 via the support pillar 115. In this embodiment, the release of the sensitive structure 301 and the formation of the support pillar 115 can be completed simultaneously in a single wet etching process, reducing process steps and thus shortening the process time.

[0060] Step S700: Bond the side of the sensitive structure 301 away from the first surface 101 and the side of the electrical connection structure 302 away from the first surface 101 to the second wafer 20, so that the sensitive structure 301 and the electrical connection structure 302 are electrically connected to the second wafer 20 respectively.

[0061] Reference Figure 11 A bonding protrusion 303 is formed on the fixing portion 3012 of the sensitive structure 301, and a bonding protrusion 303 is formed on the electrical connection structure 302. A second bonding layer 304 is formed on each bonding protrusion 303. Step S700 specifically includes: bonding the first bonding layer 202 and the corresponding second bonding layer 304 of the fixing portion 3012 of the sensitive structure 301 together to electrically connect the sensitive structure 301 and the second wafer 20; and bonding the second bonding layer 304 of the electrical connection structure 302 together with the corresponding second bonding layer 304 to electrically connect the electrical connection structure 302 to the second wafer 20.

[0062] It should be noted that in some embodiments, the first bonding layer 202 is made of aluminum, and the second bonding layer 304 is made of doped germanium. The first bonding layer 202 and the second bonding layer 304 are connected by aluminum-germanium eutectic bonding. This method can achieve reliable bonding between the first wafer 10 and the second wafer 20 while forming an electrical connection path, thereby simultaneously realizing inter-wafer signal interconnection and wafer-level packaging.

[0063] Step S800: Remove a portion of the first wafer 10 on the side where the second surface 102 is located to expose the electrical connection structure 302 located in the through hole 103 on the second surface 102.

[0064] Reference Figure 12 In some embodiments, the first wafer 10 is thinned from the side where the second surface 102 of the first wafer 10 is located. The thinning process can employ grinding, polishing, etching, or a combination of the above processes. Specifically, in some embodiments, a portion of the thickness of the first wafer 10 is first removed by grinding, and then fine thinning is performed by polishing or etching until the electrical connection structure 302 located in the via 103 is exposed on the second surface 102.

[0065] Step S900: At least one signal lead-out structure 504 is formed on the second surface 102 of the first wafer 10, and each signal lead-out structure 504 is connected to the electrical connection structure 302 in the corresponding through hole 103.

[0066] In some embodiments, step S900 includes the following specific steps: Reference Figure 13 A dielectric layer 501 is formed. The dielectric layer 501 covers the second surface 102, and a second groove 5011 is formed on the dielectric layer 501. Each second groove 5011 corresponds to a through hole 103, and the electrical connection structure 302 in the corresponding through hole 103 is exposed in the second groove 5011. In some embodiments, the material of the dielectric layer 501 includes silicon oxide.

[0067] Reference Figure 14 A redistribution layer 502 is formed, which covers the dielectric layer 501 and the electrical connection structure 302 exposed in the second groove 5011.

[0068] Reference Figure 15 A passivation layer 503 is formed, which covers the redistribution layer 502. The passivation layer 503 has a plurality of openings 5031, through which the redistribution layer 502 is exposed. In some embodiments, the material of the passivation layer 503 includes silicon oxide.

[0069] Reference Figure 16Signal lead-out structures 504 are formed in the opening 5031 so that each signal lead-out structure 504 is electrically connected to the corresponding electrical connection structure 302 through the redistribution layer 502.

[0070] In some embodiments, the signal lead-out structure 504 includes a metal layer 5041 and solder balls 5042. The metal layer 5041 covers the redistribution layer 502 exposed in the opening 5031, and the solder balls 5042 are located on the metal layer 5041. At least one solder ball 5042 is formed above each opening 5031. In some embodiments, the solder ball 5042 is made of tin.

[0071] It is worth mentioning that, in this embodiment, the number of vias 103 can be set according to the number of electrical signals to be brought out from the second wafer 20 side. Figures 12 to 16 This diagram only shows a partial schematic of the formation process of the signal lead-out structure 504. The multiple signal lead-out structures 504 adjacent to a via 103 are shown for illustrative purposes only and do not represent that multiple solder balls 5042 correspond to the same via 103. In some embodiments, each signal lead-out structure 504 is electrically connected to an electrical connection structure 302 within a via 103, and one signal lead-out structure 504 cannot be electrically connected to conductive parts within multiple vias 103. When multiple vias 103 are provided, the electrical connection structure 302 within each via 103 is electrically connected to at least one corresponding signal lead-out structure 504 through a corresponding redistribution layer 502, and each signal lead-out structure 504 includes a metal layer 5041 and solder balls 5042 corresponding to that via 103.

[0072] In another method for forming a MEMS sensor disclosed in this application, the first surface 101 has at least one preset region 104. The preset region 104 corresponds to a movable part 3011, and in the thickness direction, the preset region 104 and the projection of the corresponding movable part 3011 on the first surface 101 at least partially overlap.

[0073] In this embodiment, the method for forming a MEMS sensor further includes: Reference Figure 17 and Figure 18 Before forming the first insulating layer 110 on the inner wall of the first surface 101 and the through hole 103 in step S300, a plurality of grooves 105 arranged at intervals are opened on the preset area 104; the first surface 101 is thermally oxidized so that the groove walls of the grooves 105 in the preset area 104 are oxidized and the grooves 105 are filled, thereby forming a continuous oxide layer 114 in the preset area 104.

[0074] In some embodiments, the width of the trench 105 ranges from 0.4 to 0.5 μm, and the depth of the trench 105 ranges from 10 to 15 μm.

[0075] The continuous oxide layer 114 facilitates the formation of a first groove 106 below the movable part 3011 during the subsequent release of the movable part 3011. As a result, the formed first groove 106 can provide more room for the movable part 3011 to move, reduce the risk of the movable part 3011 being attracted to the substrate 203 below, and help improve the reliability of the device operation.

[0076] Reference Figure 19 In step 300, the first insulating layer 110 formed covers the preset area 104. The first insulating layer 110 is made of the same material as the continuous oxide layer 114.

[0077] In this embodiment, the first insulating layer 110 and the second insulating layer 111 are also formed simultaneously. Specifically, after the continuous oxide layer 114 is formed, the first insulating layer 110 and the second insulating layer 111 are formed simultaneously by performing a thermal oxidation treatment on the side where the first surface 101 of the first wafer 10 is located. The first insulating layer 110, the second insulating layer 111, and the continuous oxide layer 114 are all silicon oxide.

[0078] Reference Figures 20 to 22 In this embodiment, the specific process of forming the initial device layer 117, the sensitive structure 301 and the electrical connection structure 302 can be referred to the foregoing embodiment, and will not be repeated here.

[0079] Reference Figure 23 In this embodiment, step S600 specifically includes the following steps: Remove a portion of the first insulating layer 110 and the continuous oxide layer 114 located in the preset region 104, and form a first groove 106 in the preset region 104 that is disposed opposite to the corresponding movable part 3011, so that a gap 116 is formed between the movable part 3011 and the first wafer 10. A portion of the first insulating layer 110 located below the fixing part 3012 is retained to form a support column 115 connected to the fixing part 3012.

[0080] In this embodiment, while forming the gap 116, a first groove 106 is formed on the first wafer 10. The first groove 106 can provide space for the displacement of the movable part 3011 in the direction perpendicular to the first surface 101, thereby enabling the formed MEMS sensor to detect movement in the direction perpendicular to the first surface 101.

[0081] In another method for forming a MEMS sensor disclosed in this application embodiment, the specific steps of step S300, which involves forming a first insulating layer 110 on the first surface 101, include: Reference Figure 24Before opening at least one through hole 103, a third insulating layer 112 is formed, which covers the first surface 101. A fourth insulating layer 113 is formed on the side of the third insulating layer 112 opposite to the first surface 101, and the fourth insulating layer 113 is made of a different material than the third insulating layer 112.

[0082] In some embodiments, the third insulating layer 112 is made of silicon oxide, and the fourth insulating layer 113 is made of silicon nitride.

[0083] Reference Figure 25 A first insulating layer 110 is formed on the side of the fourth insulating layer 113 opposite to the third insulating layer 112. The first insulating layer 110 is etched with the fourth insulating layer 113 as a stop layer to create at least one first notch 107 and a second notch 120 on the first insulating layer 110. The first notch 107 corresponds to the fixing portion 3012, and in the thickness direction, the projection of the first notch 107 overlaps with the projection of the corresponding fixing portion 3012. The projection of the through hole 103 is located within the projection range of the second notch 120.

[0084] By setting the fourth insulating layer 113 as a stop layer, on the one hand, excessive etching to the lower third insulating layer 112 can be avoided when etching the first insulating layer 110 to form the first notch 107 and the second notch 120, thereby improving the structural consistency of the first notch 107 and the second notch 120; on the other hand, it is also beneficial to control the depth and bottom morphology of the first notch 107 and the second notch 120.

[0085] Furthermore, the first notch 107 formed on the first insulating layer 110 facilitates the formation of a structure protruding toward the first wafer 10 on the lower side of the corresponding fixing part 3012 during the subsequent formation of the sensitive structure 301.

[0086] Reference Figures 28 to 31 The initial device layer 117 is also filled in the first notch 107 and the second notch 120. The specific steps of removing part of the first insulating layer 110 to form a gap 116 between the movable part 3011 and the first wafer 10 include: using the fourth insulating layer 113 as a stop layer, removing the first insulating layer 110 to form a gap 116 between the movable part 3011 and the first wafer 10; retaining the initial device layer 117 located in the first notch 107 to form a support post 115 connected to the fixed part 3012.

[0087] In other words, a first notch 107 exists below the area corresponding to the fixing part 3012. After the sensitive structure 301 is formed and released, the remaining part of the structure below the fixing part 3012 can form a support pillar 115 connected to the first wafer 10, thereby providing support for the sensitive structure 301. Thus, the fixing part 3012 in the sensitive structure 301 can be stably fixed relative to the first wafer 10, while the movable part 3011 can move within the corresponding space, which helps to ensure the working stability of the sensitive structure 301.

[0088] Reference Figure 26 In this embodiment, the through-hole 103 includes a fourth insulating layer 113 and a third insulating layer 112. (Refer to...) Figure 26 The specific steps of step S300, which involves forming a second insulating layer 111 on the inner wall of the through hole 103, include: Reference Figure 27 After opening at least one through hole 103, thermal oxidation is performed on the side where the first surface 101 of the first wafer 10 is located to form a second insulating layer 111 on the inner wall of the through hole 103.

[0089] Reference Figures 28 to 31 In this embodiment, the specific process of forming the initial device layer 117, the sensitive structure 301 and the electrical connection structure 302 can be referred to the foregoing embodiment, and will not be repeated here.

[0090] Reference Figure 31 In this embodiment, a gap 116 is formed between the movable part 3011 and the first wafer 10, between the movable part 3011 and the fourth insulating layer 113. The first insulating layer 110 is completely removed.

[0091] It should be noted that in this embodiment, the fourth insulating layer 113 is made of silicon nitride, and the initial device layer 117 is made of polysilicon. Because the opening of the via 103 has a stepped morphology, local uplift may occur at the opening of the via 103 during the formation of the initial device layer 117. Since silicon nitride and polysilicon have good stress matching properties, the risk of film cracking, peeling, or structural instability caused by the local uplift can be reduced. This helps to ensure the integrity of the initial device layer 117 and the subsequently formed electrical connection structure 302, and improves the structural stability and signal interconnect reliability of the device.

[0092] Reference Figure 16 This application also discloses a MEMS sensor, including: The first wafer 10 has a first surface 101 and a second surface 102 disposed opposite to each other along the thickness direction. At least one through hole 103 is formed on the first wafer 10, the through hole 103 penetrates the first surface 101 and the second surface 102, and the inner wall of the through hole 103 is covered with a second insulating layer 111. The second wafer 20 has metal wiring 201 laid on it; Independent sensing structures 301 and electrical connection structures 302 are located between the first wafer 10 and the second wafer 20. The sensing structure 301 includes a movable part 3011 and a fixed part 3012, with a gap 116 between the movable part 3011 and the first wafer 10. In the thickness direction, one side of the fixed part 3012 is fixedly connected to the first wafer 10, and at least one other side of the fixed part 3012 is fixedly connected to the second wafer 20. One end of the electrical connection structure 302 extends into the through hole 103 and is exposed on the second surface 102, while the other end is fixedly connected to the second wafer 20. At least one signal lead-out structure 504 is formed on the second surface 102 of the second wafer 20. Each signal lead-out structure 504 corresponds to a via 103 and is connected to the electrical connection structure 302 in the corresponding via 103.

[0093] In some embodiments, the material of the sensitive structure 301 and the electrical connection structure 302 both include polysilicon, and the material of the sensitive structure 301 and the electrical connection structure 302 are formed by the same polysilicon deposition process.

[0094] Reference Figure 23 In some embodiments, a first groove 106 is provided on the first surface 101, and in the thickness direction, the projection of the first groove 106 at least partially overlaps with the projection of a movable part 3011.

[0095] Reference Figure 31 In some embodiments, a support post 115 is provided between the fixing part 3012 and the first wafer 10. In some embodiments, it further includes: a third insulating layer 112 covering the first surface 101 and connected to the second insulating layer 111; a fourth insulating layer 113 covering the side of the third insulating layer 112 facing away from the first surface 101; wherein the third insulating layer 112 and the fourth insulating layer 113 are made of different materials, the through hole 103 also penetrates the third insulating layer 112 and the fourth insulating layer 113, and the fixing part 3012 has a support post 115 protruding on the side facing the first surface 101, and the support post 115 is fixedly connected to the fourth insulating layer 113.

[0096] It is worth noting that the MEMS sensors disclosed in this application are illustrated using inertial sensors as an example, but are not limited to inertial sensors. The technical solutions disclosed in this application are also applicable to other types of MEMS sensors, such as MEMS microphones and MEMS pressure sensors. For different types of MEMS sensors, their specific structural forms, sensitive units, and functional implementation methods can be adjusted according to actual application requirements, but as long as the technical concept of this application is adopted, they should fall within the protection scope of this application.

[0097] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0098] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0099] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0100] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A method for forming a MEMS sensor, characterized in that, include: A first wafer and a second wafer are provided, the first wafer having a first surface and a second surface disposed opposite to each other along the thickness direction, and the second wafer having metal wiring laid on it; At least one through hole is formed on the first surface, the through hole extending into the interior of the first wafer along the thickness direction, but not penetrating the first wafer; A first insulating layer is formed on the first surface, and a second insulating layer is formed on the inner wall of the through hole; An initial device layer is formed on the first insulating layer, and the initial device layer fills the via. The initial device layer is patterned to form independent sensitive structures and electrical connection structures, wherein the electrical connection structures are at least partially located within the vias, and the sensitive structures include movable parts and fixed parts; Remove a portion of the first insulating layer to create a gap between the movable part and the first wafer; Both the side of the sensitive structure facing away from the first surface and the side of the electrical connection structure facing away from the first surface are bonded to the second wafer, so that the sensitive structure and the electrical connection structure are electrically connected to the second wafer respectively. A portion of the first wafer is removed from the side containing the second surface to expose the electrical connection structure located in the via on the second surface; At least one signal lead-out structure is formed on the second surface of the first wafer, and each signal lead-out structure is connected to the electrical connection structure in the corresponding via.

2. The method for forming a MEMS sensor according to claim 1, characterized in that, The steps of forming a first insulating layer on the first surface and forming a second insulating layer on the inner wall of the through hole include: After creating at least one through-hole, the first side of the first wafer is thermally oxidized to form a first insulating layer on the first surface, and a second insulating layer is formed on the inner wall of the through-hole.

3. The method for forming a MEMS sensor according to claim 2, characterized in that, The first surface has at least one preset area, the preset area corresponding to one of the movable parts, and in the thickness direction, the preset area and the projection of the corresponding movable part on the first surface at least partially overlap; Before forming a first insulating layer on the first surface and the inner wall of the through hole, the method for forming the MEMS sensor further includes: Multiple grooves are opened at intervals in the preset area; The first surface is thermally oxidized to oxidize and fill the groove walls in the preset area, thereby forming a continuous oxide layer in the preset area.

4. The method for forming a MEMS sensor according to claim 3, characterized in that, The first insulating layer covers the preset area, and the first insulating layer is made of the same material as the continuous oxide layer.

5. The method for forming a MEMS sensor according to claim 4, characterized in that, The specific steps of removing a portion of the first insulating layer to create a gap between the movable part and the first wafer include: Remove a portion of the first insulating layer and the continuous oxide layer located in the preset region, and form a first groove in the preset region that is disposed opposite to the corresponding movable part, so that a gap is formed between the movable part and the first wafer; A portion of the first insulating layer located below the fixing part is retained to form a support column connected to the fixing part.

6. The method for forming a MEMS sensor according to claim 1, characterized in that, The specific steps of forming an initial device layer on the first insulating layer and filling the via with the initial device layer include: A polycrystalline silicon seed layer is formed, which covers the surface of the first insulating layer opposite to the first surface and the second insulating layer located in the through hole; Polycrystalline silicon is epitaxially grown on the polycrystalline silicon seed layer to form the initial device layer on the side of the first insulating layer opposite to the first surface, while the polycrystalline silicon fills the via.

7. The method for forming a MEMS sensor according to claim 1, characterized in that, The specific steps of removing a portion of the first insulating layer to create a gap between the movable part and the first wafer include: Remove a portion of the first insulating layer located below the movable part to create a gap between the movable part and the first wafer; A portion of the first insulating layer located below the fixing part is retained to form a support column connected to the fixing part.

8. The method for forming a MEMS sensor according to claim 1, characterized in that, The specific steps for forming the first insulating layer on the first surface include: Before opening at least one through hole, a third insulating layer is formed, the third insulating layer covering the first surface; A fourth insulating layer is formed on the side of the third insulating layer that is opposite to the first surface, and the fourth insulating layer is made of a different material than the third insulating layer; The first insulating layer is formed on the side of the fourth insulating layer that is opposite to the third insulating layer; The first insulating layer is etched with the fourth insulating layer as a stop layer to form at least one first notch and a second notch on the first insulating layer. The first notch corresponds to the fixing part. In the thickness direction, the projection of the first notch overlaps with the projection of the corresponding fixing part. The projection of the through hole is located within the projection range of the second notch.

9. The method for forming a MEMS sensor according to claim 8, characterized in that, The through hole extends through the fourth insulating layer and the third insulating layer, and the specific steps of forming a second insulating layer on the inner wall of the through hole include: After creating at least one through-hole, the first side of the first wafer is thermally oxidized to form the second insulating layer on the inner wall of the through-hole.

10. The method for forming a MEMS sensor according to claim 8, characterized in that, The initial device layer further fills the first and second gaps, and the specific steps of removing part of the first insulating layer to form a gap between the movable part and the first wafer include: Using the fourth insulating layer as a stop layer, the first insulating layer is removed to create a gap between the movable part and the first wafer; The initial device layer located within the first notch is retained, and the initial device layer located within the first notch forms a support column connected to the fixing part.

11. The method for forming a MEMS sensor according to claim 8, characterized in that, The fourth insulating layer is made of silicon nitride, and the initial device layer is made of polycrystalline silicon.

12. The method for forming a MEMS sensor according to claim 1, characterized in that, The second wafer has a first bonding layer deposited on the side facing the first wafer; the method for forming the MEMS sensor further includes: Before patterning the initial device layer, the side of the initial device layer opposite to the first insulating layer is etched to form a plurality of bonding bumps on the side of the initial device layer opposite to the first insulating layer. A second bonding layer is formed on the bonding protrusion; The step of bonding both the side of the sensitive structure away from the first surface and the side of the electrical connection structure away from the first surface to the second wafer includes: The first bonding layer and the second bonding layer are bonded together so that the sensitive structure and the electrical connection structure are electrically connected to the second wafer, respectively.

13. The method for forming a MEMS sensor according to claim 1, characterized in that, The specific steps of forming at least one signal lead-out structure on the second surface of the first wafer, and connecting each signal lead-out structure to the electrical connection structure in the corresponding via, include: A dielectric layer is formed, which covers the second surface. A second groove is formed on the dielectric layer, and each second groove corresponds to a through hole. The electrical connection structure corresponding to the through hole is exposed in the second groove. A redistribution layer is formed, which covers the dielectric layer and the electrical connection structure exposed in the second groove; A passivation layer is formed, which covers the redistribution layer. The passivation layer has multiple openings, and the redistribution layer is exposed in the openings. Signal lead-out structures are formed in the openings such that each signal lead-out structure is electrically connected to the corresponding electrical connection structure through the redistribution layer.

14. A MEMS sensor, characterized in that, include: A first wafer (10) has a first surface (101) and a second surface (102) arranged opposite to each other along the thickness direction. At least one through hole (103) is formed on the first wafer (10), the through hole (103) penetrates the first surface (101) and the second surface (102), and the inner wall of the through hole (103) is covered with a second insulating layer (111). The second wafer (20) has metal wiring (201) laid on it. Independent sensing structures (301) and electrical connection structures (302) are located between the first wafer (10) and the second wafer (20). The sensing structure (301) includes a movable part (3011) and a fixed part (3012). The movable part (3011) has a gap (116) with the first wafer (10). In the thickness direction, one side of the fixed part (3012) is fixedly connected to the first wafer (10), and at least one side of the fixed part (3012) is fixedly connected to the second wafer (20). One end of the electrical connection structure (302) extends into the through hole (103) and is exposed on the second surface (102), and the other end is fixedly connected to the second wafer (20). At least one signal lead-out structure (504) is formed on the second side (102) of the second wafer (20), and each signal lead-out structure (504) corresponds to one of the vias (103) and is connected to the electrical connection structure (302) in the corresponding via (103).

15. The MEMS sensor according to claim 14, characterized in that, The material of the sensitive structure (301) and the electrical connection structure (302) both include polycrystalline silicon, and the sensitive structure (301) and the electrical connection structure (302) are formed by the same polycrystalline silicon deposition process.

16. The MEMS sensor according to claim 14, characterized in that, A first groove (106) is provided on the first surface (101), and in the thickness direction, the projection of the first groove (106) at least partially overlaps with the projection of one of the movable parts (3011).

17. The MEMS sensor according to claim 14, characterized in that, Also includes: A third insulating layer (112) covers the first surface (101) and is connected to the second insulating layer (111); A fourth insulating layer (113) covers the side of the third insulating layer (112) that is away from the first surface (101); The third insulating layer (112) and the fourth insulating layer (113) are made of different materials. The through hole (103) also penetrates the third insulating layer (112) and the fourth insulating layer (113). The fixing part (3012) has a support column (115) protruding on the side facing the first surface (101). The support column (115) is fixedly connected to the fourth insulating layer (113).

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