Micro-electromechanical system device, micro-electromechanical system accelerometer and forming method thereof

Abstract

A semiconductor oxide plate is formed on a recessed surface in a semiconductor matrix material layer. A plurality of comb structures are formed in the semiconductor matrix material layer. The plurality of comb structures include a pair of inner comb structures separated by a first semiconductor portion. An isotropic etching process is used to selectively remove a second semiconductor portion that laterally surrounds the first semiconductor portion relative to the plurality of comb structures. The semiconductor oxide plate, the pair of inner comb structures, and a patterned etching mask layer covering the plurality of comb structures protect the first semiconductor portion from an etchant of the isotropic etching process. A movable structure for a micro-electromechanical system device is formed, the movable structure including a combination of a first portion of the semiconductor matrix material layer and the pair of inner comb structures.

Description

Technical Field

[0001] The disclosed embodiments relate to a micro-electromechanical system device and a method for forming the same. Background Art

[0002] Micro-electromechanical system (MEMS) devices include devices made using semiconductor technology to form mechanical and electrical features. MEMS devices may include moving parts with micron or sub-micron dimensions and a mechanism for electrically coupling the moving parts to an electrical signal. The electrical signal may be an input signal that causes movement of the moving parts or an output signal generated by the movement of the moving parts. MEMS devices are useful devices that can be integrated with other devices (such as semiconductor devices) to act as sensors or actuators. Summary of the invention

[0003] The disclosed embodiment proposes a micro-electromechanical system device, characterized in that it includes: a movable structure located in a laterally restricted space, wherein the movable structure includes a central mass portion and a first movable comb structure, the first movable comb structure includes an inner comb shaft portion adhered to the first side wall of the central mass portion and a plurality of first movable comb finger-like members protruding laterally from the inner comb shaft portion, wherein: the central mass portion includes a portion of a first semiconductor material; a semiconductor oxide plate, comprising an oxide of the first semiconductor material, covering the entire bottom surface of the central mass portion; and the first movable comb structure includes a dielectric pad and a conductive filling material portion, the dielectric pad being physically exposed to a cavity within a substrate, the conductive filling material portion being located within the inner comb shaft portion and extending continuously into each of the plurality of first movable comb finger-like members and being laterally surrounded by the dielectric pad.

[0004] The disclosed embodiment provides a micro-electromechanical system accelerometer, characterized in that it includes: a movable structure located in a lateral restricted space, wherein the movable structure includes a central mass portion, a first movable comb structure and a second movable comb structure, the central mass portion includes a portion of a first semiconductor material, the first movable comb structure is fixed on a first side of the central mass portion, and the second movable comb structure is fixed on a second side of the central mass portion, wherein each of the first movable comb structure and the second movable comb structure includes a respective comb axis portion and a movable portion extending laterally from the respective comb axis portion. a plurality of movable comb fingers protruding from each group; a first fixed comb structure, fixed to the first side wall of the lateral confinement space and comprising a plurality of first fixed comb fingers, wherein the plurality of first fixed comb fingers are staggered with the plurality of movable comb fingers of each group of the first movable comb structure; a second fixed comb structure, fixed to the second side wall of the lateral confinement space and comprising a plurality of second fixed comb fingers, wherein the plurality of second fixed comb fingers are staggered with the plurality of second movable comb fingers; and a semiconductor oxide plate, comprising an oxide of the first semiconductor material and covering the entire bottom surface of the central mass portion.

[0005] The present disclosed embodiment proposes a method for forming a micro-electromechanical system device, which is characterized by comprising: forming a recessed surface by recessing an area of ​​a first horizontal surface of a semiconductor matrix material layer; forming a semiconductor oxide plate on the recessed surface; forming a plurality of comb structures extending from a second horizontal surface of the semiconductor matrix material layer toward the first horizontal surface, wherein the plurality of comb structures include a pair of inner comb structures and a pair of outer comb structures, the pair of inner comb structures are laterally spaced apart by a first portion of the semiconductor matrix material layer, and the pair of outer comb structures are staggered with the pair of inner comb structures; and using an isotropic etching process to selectively remove a second portion of the semiconductor matrix material layer that laterally surrounds the first portion of the semiconductor matrix material layer relative to the plurality of comb structures, wherein the semiconductor oxide plate, the pair of inner comb structures, and a patterned etching mask layer protect the first portion of the semiconductor matrix material layer from the etchant of the isotropic etching process, and the patterned etching mask layer is located on the second horizontal surface and covers the plurality of comb structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The various aspects of the present disclosure will be best understood by reading the following detailed description in conjunction with the accompanying drawings. It should be noted that, in accordance with standard practice in the industry, the various features are not drawn to scale. In fact, the size of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0007] Figure 1Ais a vertical cross-sectional view of an exemplary structure including a semiconductor matrix material layer after forming a recessed cavity according to an embodiment of the present disclosure.

[0008] Figure 1B It is along Figure 1A A horizontal cross-sectional view of an exemplary structure showing a horizontal plane BB'.

[0009] Figure 2 is a vertical cross-sectional view of an exemplary structure after forming a diffusion barrier spacer at the periphery of a recessed cavity according to an embodiment of the present disclosure.

[0010] Figure 3 is a vertical cross-sectional view of an exemplary structure after forming a semiconductor oxide plate according to an embodiment of the present disclosure.

[0011] Figure 4 is a vertical cross-sectional view of an exemplary structure after removal of a diffusion barrier spacer according to an embodiment of the present disclosure.

[0012] Figure 5A is a vertical cross-sectional view of an exemplary structure after bonding a semiconductor matrix material layer to a handle substrate according to an embodiment of the present disclosure.

[0013] Figure 5B It is along Figure 5A A horizontal cross-sectional view of an exemplary structure of the illustrated surface B-B'. The hinged vertical surface A-A' is Figure 5A The surface of the vertical section view shown.

[0014] Fig. 6A is a vertical cross-sectional view of an exemplary structure after forming comb trenches and moat trenches according to an embodiment of the present disclosure.

[0015] Figure 6B It is along Fig. 6A A horizontal cross-sectional view of an exemplary structure of the illustrated surface B-B'. The hinged vertical surface A-A' is Fig. 6A The surface of the vertical section view shown.

[0016] Fig. 7A is a vertical cross-sectional view of an exemplary structure after forming a comb structure and a wall structure according to an embodiment of the present disclosure.

[0017] Figure 7B It is along Fig. 7A A horizontal cross-sectional view of an exemplary structure of the illustrated surface B-B'. The hinged vertical surface A-A' is Fig. 7A The surface of the vertical section view shown.

[0018] Fig. 8Ais a vertical cross-sectional view of an exemplary structure after forming a metal material portion according to an embodiment of the present disclosure.

[0019] Figure 8B It is along Fig.11A A top view of an exemplary structure of the illustrated surface B-B'. The hinged vertical surface A-A' is Fig.11A The surface of the vertical section view shown.

[0020] Fig.9A is a vertical cross-sectional view of an exemplary structure after forming a patterned etch mask layer according to an embodiment of the present disclosure.

[0021] Fig. 9B yes Fig.9A A partial perspective top view of the exemplary structure shown. The hinged vertical plane A-A' is Fig.9A The surface of the vertical section view shown.

[0022] Fig. 10A is a vertical cross-sectional view of an exemplary structure after isotropically etching unmasked portions of a semiconductor matrix material layer selectively relative to a patterned etch mask layer, comb structures, moat trench fill structures, and semiconductor oxide plates according to an embodiment of the present disclosure.

[0023] Fig. 10B It is along Fig.9A A horizontal cross-sectional view of an exemplary structure of the illustrated surface B-B'. The hinged vertical surface A-A' is Fig.9A The surface of the vertical section view shown.

[0024] Fig.11A is a vertical cross-sectional view of an exemplary structure after removal of a patterned etch mask layer according to an embodiment of the present disclosure.

[0025] Fig. 11B It is along Fig.11A A top view of an exemplary structure of the illustrated surface B-B'. The hinged vertical surface A-A' is Fig.11A The surface of the vertical section view shown.

[0026] Fig.12 is a vertical cross-sectional view of an accelerometer formed by peeling off a handle substrate and singulating the exemplary structure into a plurality of accelerometers according to an embodiment of the present disclosure.

[0027] Fig.13 is a flow chart illustrating a set of processing steps that may be performed to form a MEMS device according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0028] The following disclosure provides many different embodiments or examples for implementing the different features of the provided subject matter. Specific examples of components and arrangements are set forth below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, the following description in which a first feature is formed "above" or "on" a second feature may include an embodiment in which the first feature and the second feature are formed to be in direct contact, and may also include an embodiment in which an additional feature may be formed between the first feature and the second feature so that the first feature and the second feature may not be in direct contact. In addition, the present disclosure may reuse reference numbers and / or letters in various examples. This repetition is for the purpose of brevity and clarity, rather than indicating the relationship between the various embodiments and / or configurations discussed in itself.

[0029] Additionally, for ease of description, spatially relative terms such as "beneath," "below," "lower," "above," "upper," etc. may be used herein to describe the relationship of one element or feature shown in a figure to another (other) element or feature. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or at other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

[0030] Many MEMS devices utilize precision detection masses to accurately measure physical parameters. For example, an accelerometer converts the displacement of a movable element into acceleration by, for example, measuring the capacitance change caused by the displacement of the movable element. The displacement of the movable element is proportional to the force applied to the movable element, which is proportional to the mass of the detection mass element within the movable element. Process variations in isotropic etching processes may cause changes in the mass of the detection mass element. Changes in the detection mass of the mass element may cause changes (i.e., inaccuracies) in the acceleration measurement. Therefore, a precision detection mass element with reduced mass variation may enhance precision measurements in some MEMS devices, which may be caused by the manufacturing process.

[0031] In general, embodiments of the present disclosure relate to microstructures including microelectromechanical systems (MEMS) devices. MEMS devices include a proof mass for measuring movement of an object to which the MEMS device is attached. For example, a MEMS device may include an accelerometer. Embodiments of the present disclosure may be used to form a high precision proof mass for a MEMS device.

[0032] Specifically, a semiconductor matrix material layer may be provided, the semiconductor matrix material layer comprising a semiconductor material and a semiconductor matrix layer, the semiconductor material to be subsequently patterned into a movable structure including a proof mass, the semiconductor matrix layer comprising a cavity, the movable structure may be confined within the cavity. A surface portion of the semiconductor matrix layer may be recessed in a vertical direction from a first horizontal surface to form a recessed cavity. A diffusion barrier spacer (e.g., a silicon nitride spacer) may be formed on a sidewall of the recessed cavity. An oxidation process may be performed to form a first semiconductor oxide plate on the recessed horizontal surface of the recessed cavity, and a second semiconductor oxide plate may be formed on an unrecessed portion of the first horizontal surface of the semiconductor matrix material layer. The diffusion barrier spacer may be selectively removed relative to the semiconductor oxide plate using an isotropic selective etching process. The second semiconductor oxide plate may be bonded to a handle substrate.

[0033] Comb grooves may be formed from the second horizontal surface of the semiconductor matrix material layer toward the first horizontal surface of the semiconductor matrix material layer. The comb grooves may include two pairs of staggered corresponding inner comb grooves and corresponding outer comb grooves. A first portion of the semiconductor matrix material layer that will be patterned into a proof mass (i.e., a center mass portion) may be located between the two inner comb grooves. The outer comb grooves may be connected by comb axis extension grooves. The outer comb grooves and comb axis extension grooves together surround all the inner comb grooves and define lateral boundaries for the cavity that will be formed laterally. The shared comb axis cavity portion may define the boundaries of the cavity, and the movable element that will be formed laterally is confined in the cavity. A dielectric liner layer and a conductive filling material may be deposited in the comb grooves, and the excess portions of the dielectric liner layer and the conductive filling material located above the horizontal plane including the top surface of the semiconductor matrix material layer may be removed by a planarization process. The remaining portion of the dielectric liner layer and the remaining portion of the conductive filling material in each comb groove comprises a comb structure. The comb structure includes an inner comb structure formed in the inner comb groove and an outer comb structure formed in the outer comb groove.

[0034] An etch mask layer (e.g., a photoresist layer) may be formed above the second horizontal surface of the semiconductor matrix material layer, and the etch mask layer may be patterned to provide openings in the region surrounded by the common comb axis portion of the outer comb structure. The openings may be formed in regions not overlying the comb structures, such that each comb structure is covered by the patterned etch mask layer. An isotropic etching process may be used to etch a second portion of the semiconductor matrix material layer located outside the comb structures and within the region surrounded by the common comb axis portion of the outer comb structures. During the isotropic etching process, the first semiconductor oxide plate, the inner comb structure, and the patterned etch mask layer protect the first portion of the semiconductor matrix material layer. Specifically, the first semiconductor oxide plate protects the first portion of the semiconductor matrix material layer that becomes the detection mass structure from below, and thus the first portion has a uniform thickness through a major portion thereof.

[0035] A movable structure including a central mass portion, an inner comb structure, and an outer comb structure can be peeled off from a second semiconductor oxide plate. The volume into which the material of the semiconductor material layer can be etched forms a cavity that is laterally limited by a common comb axis portion of the outer comb structure. A semiconductor die including a suitable electrical contact structure for the comb structure can be bonded to a semiconductor matrix layer, which is the remaining portion of the semiconductor matrix material layer located outside the cavity. The semiconductor die can include a suitable contact structure that can electrically bias various portions of the comb structure in a configuration that provides a capacitor structure. The capacitor structure can be configured in any configuration that produces a change in capacitance when the movable structure moves relative to a fixed structure including an outer comb structure. The microstructure can include an accelerometer that can measure the acceleration of the system to which the microstructure is bonded. Various aspects of the embodiments of the present disclosure are further elaborated below.

[0036] Reference Figure 1A and Figure 1B , a semiconductor matrix material layer 10 is shown, and the semiconductor matrix material layer 10 may be provided as a planar structure, the planar structure including a first horizontal surface 101 located on a first side and a backside surface (i.e., a second horizontal surface) located on a second side, having a uniform thickness throughout the planar structure, but not necessarily limited thereto. The semiconductor matrix material layer 10 includes a first semiconductor material, which may be a single crystal semiconductor material or a polycrystalline semiconductor material. In one embodiment, the semiconductor matrix material layer 10 may include a single crystal semiconductor layer, such as a single crystal silicon layer. The uniform thickness of the semiconductor matrix material layer 10 may be in the range from 30 micrometers to 1 millimeter (mm), for example, from 100 micrometers to 600 micrometers. Although in Figure 1A and Figure 1B , the region used to form a single accelerometer is shown, however it should be understood that a two-dimensional array of accelerometers can be formed on a single wafer. Figure 1A and Figure 1B The pattern shown in FIG. 1 may be repeated in a two-dimensional array pattern over the semiconductor matrix material layer 10 .

[0037] A photoresist layer (not shown) may be applied over the first horizontal surface 101 of the semiconductor matrix material layer 10 and may be photolithographically patterned to form an opening having the approximate shape of a proof mass (also referred to as a central mass portion) to be subsequently formed. In one embodiment, the periphery of the opening in the photoresist layer may be laterally offset outwardly from the periphery of the proof mass to be subsequently formed by a lateral offset distance, which may, for example, be in the range of from 0.5 microns to 30 microns. Thus, the area of ​​the opening in the photoresist layer may have a larger area than the area of ​​the proof mass to be subsequently formed (A_PM). In a non-limiting illustrative example, the opening in the photoresist layer may have an elongated rounded rectangular shape with a longitudinal dimension in the range of from 300 microns to 6 mm and a lateral dimension in the range of from 30 microns to 600 microns, although smaller and larger dimensions may also be used.

[0038] The pattern of the opening in the photoresist layer can be transferred to the upper part of the semiconductor matrix material layer 10 by an etching process, and the etching process can include an anisotropic etching process or an isotropic etching process. A recessed cavity 13 recessed from the first horizontal surface 101 of the semiconductor matrix material layer 10 in the vertical direction can be formed. A recessed horizontal surface can be set at the bottom of the recessed cavity 13. The recessed depth of the recessed cavity 13 can be in the range of from 0.3 micron to 10 microns, for example from 0.6 micron to 5 microns, but a smaller recessed depth and a larger recessed depth can also be used. The recessed cavity 13 has a sidewall 13S, and the sidewall 13S connects the recessed bottom surface 13R of the recessed cavity 13 to the non-recessed portion of the first horizontal surface 101 of the semiconductor matrix material layer 10. The photoresist layer can be removed subsequently, for example, by ashing.

[0039] Reference Figure 2 , a diffusion barrier spacer 11 (also referred to as a blocking spacer) comprising a diffusion barrier material may be formed at the periphery of the recessed cavity 13. The diffusion barrier spacer 11 comprises a material that blocks the diffusion of oxygen through the diffusion barrier spacer 11. For example, the diffusion barrier spacer 11 may comprise silicon nitride and / or may consist essentially of silicon nitride. Other suitable materials are also within the contemplated scope of the present disclosure. In some embodiments, the blocking spacer 11 may be any material and is configured to protect the sidewalls 13S of the recessed cavity 13 from the subsequently formed semiconductor oxide plate ( Figure 3The diffusion barrier spacer 11 may be formed by conformally depositing a diffusion barrier material layer (e.g., a silicon nitride layer or a metal nitride layer including a metal nitride material (TaN, TiN, or WN)) on the recessed bottom surface 13R and sidewalls 13S of the recessed cavity 13 and on the non-recessed portion of the first horizontal surface 101 of the semiconductor matrix material layer 10. In other embodiments, the diffusion barrier spacer 11 may be formed by denaturing some portions of the semiconductor matrix material layer 10. The thickness of the diffusion barrier material layer may range from 30 nm to 200 nm, but smaller thicknesses and larger thicknesses may also be used. An anisotropic etching process may be performed to remove the horizontal portion of the diffusion barrier material layer deposited on the recessed bottom surface of the recessed cavity and on the non-recessed portion of the first horizontal surface 101 of the semiconductor matrix material layer 10. The remaining vertical portion of the diffusion barrier material layer constitutes the diffusion barrier spacer 11. In one embodiment, each sidewall 13S of the recessed cavity 13 may contact a corresponding outer sidewall of the diffusion barrier spacer 11. The diffusion barrier spacer 11 may have a generally tubular shape and may thus be topologically homeomorphic to a torus, i.e., may be continuously deformed into a torus without creating new pores or destroying pre-existing pores.

[0040] Reference Figure 3 , an oxidation process may be performed to convert physically exposed surface portions of the semiconductor matrix material layer 10 located at the bottom of the recessed cavity 13 and on the non-recessed portion of the semiconductor matrix material layer 10 into semiconductor oxide plates (12A, 12B). For example, a thermal oxidation process may be performed to convert physically exposed surface portions of the semiconductor matrix material layer 10 into semiconductor oxide material portions. The diffusion barrier spacer 11 prevents oxygen atoms from diffusing through the diffusion barrier spacer 11 to the semiconductor matrix material layer 10, thereby forming the sidewalls of the recessed cavity 13 during the oxidation process. The thermal oxidation process may employ a dry oxidation process, a wet oxidation process, or a rapid thermal oxidation process. For example, dry oxidation is a thermal oxidation process employing O2 as an oxidant. Wet oxidation is a thermal oxidation employing H2O as an oxidant. Rapid thermal oxidation is a thermal oxidation process employing a single wafer processing chamber and providing thermal oxidation at a high temperature.

[0041] A first semiconductor oxide plate 12A may be formed at the bottom of the recessed cavity 13 by converting an underlying surface portion of the semiconductor matrix material layer 10 into a dielectric semiconductor oxide material portion. A second semiconductor oxide plate 12B may be formed on the first horizontal surface 101 of the unrecessed portion of the semiconductor matrix material layer 10 by converting an underlying surface portion of the semiconductor matrix material layer 10 into an additional dielectric semiconductor oxide material portion. The thickness of the first and second semiconductor oxide plates (12A, 12B) may range from 50 nm to 500 nm, but lesser thicknesses and greater thicknesses may also be used. In one embodiment, if the semiconductor matrix material layer 10 includes any material other than silicon (e.g., a silicon-germanium alloy or a III-V compound semiconductor material), the first and second semiconductor oxide plates (12A, 12B) may include and / or may consist essentially of silicon oxide or an oxide of the semiconductor material of the semiconductor matrix material layer 10.

[0042] Reference Figure 4 , the diffusion barrier spacer 11 can be removed selectively relative to the material of the first and second semiconductor oxide plates (12A, 12B) and the material of the semiconductor matrix material layer 10. For example, if the diffusion barrier spacer 11 includes silicon nitride, a wet etching process using hot phosphoric acid can be performed to selectively remove the diffusion barrier spacer 11 relative to the material of the first and second semiconductor oxide plates (12A, 12B) and the material of the semiconductor matrix material layer 10. The semiconductor surface of the semiconductor matrix material layer 10 can be physically exposed at the sidewalls of the recessed cavity 13.

[0043] Reference Figure 5A and Figure 5B , the semiconductor matrix material layer 10 may be bonded to the handle substrate 20 through the second semiconductor oxide plate 12B. The handle substrate 20 may include a semiconductor substrate, a conductive substrate, a dielectric substrate, or a combination thereof. The handle substrate 20 may have a thickness sufficient to provide structural support during subsequent thinning of the semiconductor matrix material layer 10. For example, the thickness of the handle substrate 20 may range from 60 microns to 1 mm.

[0044] The horizontal top surface of the handle substrate 20 includes a material that can be bonded to the semiconductor oxide material of the second semiconductor oxide plate 12B. The second semiconductor oxide plate 12B can be attached to the handle substrate 20 by bonding the second semiconductor oxide plate 12B to the handle substrate 20. The second semiconductor oxide plate 12B can be bonded to the horizontal top surface of the handle substrate 20 using a suitable bonding method. For example, if the handle substrate 20 includes a semiconductor top surface, the handle substrate 20 can be bonded to the second semiconductor oxide plate 12B using semiconductor-to-oxide bonding (e.g., silicon-to-silicon oxide bonding). Alternatively, if the handle substrate 20 includes a semiconductor oxide top surface (e.g., silicon oxide top surface), the handle substrate 20 can be bonded to the second semiconductor oxide plate 12B using oxide-to-oxide bonding (e.g., silicon oxide-to-silicon oxide bonding). The semiconductor-to-oxide bonding or oxide-to-oxide bonding can be performed at an elevated temperature by an annealing process, and the elevated temperature can range from 200 degrees Celsius to 600 degrees Celsius.

[0045] The semiconductor matrix material layer 10 may then be thinned by grinding, polishing and / or etching the backside surface of the semiconductor matrix material layer 10 on the opposite side of the second semiconductor oxide plate 12B. The final step of the thinning process may include a polishing step to provide a horizontal plane surface on the backside (i.e., polished side) of the semiconductor matrix material layer 10. The polished backside surface of the semiconductor matrix material layer 10 is referred to herein as the second horizontal surface 102. The thickness t of the semiconductor matrix material layer 10 measured between the second horizontal surface 102 and the first horizontal surface 101 contacting the second semiconductor oxide plate 12B may be in the range of from 2 microns to 60 microns, for example from 4 microns to 30 microns, but smaller thicknesses and larger thicknesses may also be used. The lower limit of the thickness t of the semiconductor matrix material layer 10 may be imposed by the minimum capacitance requirement of the capacitor structure to be formed later, and the upper limit of the thickness t of the semiconductor matrix material layer 10 may be imposed by the process capability and economic feasibility of the etching process for forming the comb grooves through the semiconductor matrix material layer 10 later.

[0046] Reference Fig. 6A and Figure 6B, a photoresist layer 37 may be applied over the second horizontal surface 102 of the semiconductor matrix material layer 10 and the photoresist layer 37 may be photolithographically patterned to form openings through the photoresist layer 37. The pattern of the openings in the photoresist layer 37 may include two staggered comb patterns. Each staggered comb pattern may include an inner comb pattern (CPI1 or CPI2) and an outer comb pattern (CPO1 or CPO2). The first staggered comb pattern (CPI1, CPO1) includes a first inner comb pattern CPI1 and a first outer comb pattern CPO1. The second staggered comb pattern (CPI2, CPO2) includes a second inner comb pattern CPI2 and a second outer comb pattern CPO2.

[0047] Each inner comb pattern (CPI1 or CPI2) includes a respective comb axis pattern and a respective comb tooth pattern that can be adjacent to the respective comb axis pattern. Each comb axis pattern of the inner comb patterns (CPI1, CPI2) can extend laterally along the first horizontal direction hd1 with or without lateral undulation. Each outer comb pattern (CPO1 or CPO2) includes a respective comb axis pattern and a respective comb tooth pattern that can be adjacent to the respective comb axis pattern. Each comb axis pattern of the outer comb pattern (CPO1, CPO2) can extend laterally along the first horizontal direction hd1 with or without lateral undulation. The comb axis pattern within the outer comb pattern (CPO1, CPO2) can be adjacent to a comb axis extension pattern CSEP that extends laterally along a second horizontal direction hd2 that is perpendicular to the first horizontal direction hd1. Specifically, the end segment of each of the comb-axis patterns within the outer comb pattern (CPO1, CPO2) can be adjacent to the end segment of the comb-axis extension pattern CSEP, so that the group of comb-axis patterns within the outer comb pattern (CPO1, CPO2) and the comb-axis extension pattern CSEP together form a roughly rectangular shape, which defines the outer boundary of the cavity that will subsequently be formed in the semiconductor matrix material layer 10.

[0048] The two staggered comb patterns may be arranged so that the two inner comb patterns (CPI1, CPI2) are close to each other and the two outer comb patterns (CPO1, CPO2) are far away from each other. In other words, the lateral separation distance between the comb axis patterns of the two outer comb patterns (CPO1, CPO2) along the second horizontal direction hd2 is greater than the lateral separation distance between the comb axis patterns of the two inner comb patterns (CPI1, CPI2).

[0049] An elongated area masked by the photoresist layer 37 may be provided between the comb axis patterns of the two inner comb patterns (CPI1, CPI2), the elongated area including a region in which a detection mass (i.e., a central mass portion) will be subsequently patterned from the semiconductor matrix material layer 10. The opening in the photoresist layer 37 may include a detection mass barrier pattern PMBP located at a boundary of a region in which a detection mass will be subsequently formed. The comb axis patterns of the two inner comb patterns (CPI1, CPI2) may have an extended portion wrapped around the detection mass barrier pattern PMBP to provide an etchant constriction structure that prevents lateral etching of a portion of the semiconductor matrix material layer 10 located around the detection mass barrier pattern PMBP.

[0050] Each comb tooth pattern within the inner comb pattern (CPI1, CIP2) and the outer comb pattern (CPO1, CPO2) includes a plurality of comb tooth patterns parallel to each other. Each comb tooth pattern extends laterally away from the respective comb axis pattern along the common longitudinal direction of the comb tooth pattern. Each tooth pattern may be elongated along the longitudinal direction and may have a stem region having a substantially uniform width and being fitted to the respective comb axis pattern. Each tooth pattern may also have a tip segment having a width that gradually decreases with the distance from the respective comb axis pattern. The common longitudinal direction of the comb tooth pattern within the comb tooth pattern may be at an angle ranging from 1 degree to 10 degrees (e.g., from 2 degrees to 8 degrees) relative to the second horizontal direction hd2 to optimize the capacitance change of the capacitor structure that will be subsequently formed as a function of the displacement of the movable structure that will be subsequently formed. The tip segment of each comb tooth pattern may be advantageously used to increase the capacitance change during the displacement of the movable structure (i.e., the central mass portion) that will be subsequently formed.

[0051] For all the comb tooth patterns in the first inner comb pattern CPI1 and the first outer comb pattern CPO1, the comb tooth patterns of the first inner comb pattern CPI1 and the comb tooth patterns of the first outer comb pattern CPO1 may be staggered in parallel longitudinal directions. The staggered area may include the tip segment of the first inner comb pattern CPI1 and the comb tooth pattern of the first outer comb pattern CPO1. Similarly, for all the comb tooth patterns in the second inner comb pattern CPI2 and the second outer comb pattern CPO2, the comb tooth pattern of the second inner comb pattern CPI2 and the comb tooth pattern of the second outer comb pattern CPO2 may be staggered in parallel longitudinal directions. The staggered area may include the tip segment of the second inner comb pattern CPI2 and the comb tooth pattern of the second outer comb pattern CPO2. The longitudinal directions of the comb tooth patterns of the second inner comb pattern CPI2 and the comb tooth patterns of the second outer comb pattern CPO2 may be inclined in a direction opposite to the second horizontal direction hd2 relative to the longitudinal directions of the comb tooth patterns of the first inner comb pattern CPI1 and the comb tooth patterns of the first outer comb pattern CPO1. The overall pattern of openings in the photoresist layer 37 may have a mirror symmetry plane (MSP) extending along the first horizontal direction hd1 .

[0052] In one embodiment, in a top view, the region where the detection mass will be subsequently formed and the region of some portions of the comb axis patterns of the two inner comb patterns (CPI1, CPI2) extending along the first horizontal direction hd1 may be located between a pair of longitudinal side walls of the first semiconductor oxide plate 12A. Although the present disclosure is explained using an embodiment of an accelerometer, and the pattern of the openings in the photoresist layer 37 is optimized for forming an accelerometer, the method of the present disclosure may be used to form any microstructure including a movable structure including a detection mass (i.e., a movable center mass). In this way, the design of the openings in the photoresist layer 37 may be symmetrical or may not be symmetrical. In addition, although two sets of staggered patterns are used to explain the present disclosure, a single staggered pattern or three or more staggered patterns may be used to form a single staggered comb structure or three or more staggered comb structures of a microstructure, which may be a MEMS device. In general, the detection mass may be formed in an area defined by the periphery of the first semiconductor oxide plate 12A.

[0053] In addition, the pattern in the photoresist layer 37 may include a pattern of a region of the moat that laterally surrounds the comb tooth pattern of the first inner comb pattern CPI1 and the comb tooth pattern of the first outer comb pattern CPO1. For example, the pattern of the moat may include: a pattern of a proximal moat that laterally surrounds a region of the moat that laterally surrounds the comb tooth pattern of the first inner comb pattern CPI1 and the comb tooth pattern of the first outer comb pattern CPO1; a pattern of a middle moat that laterally surrounds the pattern of the proximal moat; a pattern of a distal moat that laterally surrounds the pattern of the middle moat; and a pattern of a suspension spring moat trench that connects a corresponding pair of segments of the pattern of the proximal moat with a pattern of a comb shaft portion.

[0054] An anisotropic etching process may be performed to transfer the pattern of the openings in the photoresist layer 37 through the upper portion of the semiconductor matrix material layer 10. The anisotropic etching process may be a reactive ion etching process that etches the unmasked portion of the matrix semiconductor material layer 10 and thereby replicates the pattern of the openings in the photoresist layer in the upper portion of the semiconductor matrix material layer 10. Comb grooves (31, 41, 51) are formed through the upper portion of the semiconductor matrix material layer 10. Each of the comb grooves extends from the second horizontal surface 102 of the semiconductor matrix material layer 10 toward the first horizontal surface 101 of the semiconductor matrix material layer 10. In one embodiment, the comb grooves (31, 41, 51) extend in the vertical direction to a horizontal plane including the top surface of the first semiconductor oxide plate 12A, i.e., a horizontal plane including the horizontal interface between the first semiconductor oxide plate 12A and the semiconductor matrix material layer 10. The anisotropic etching process may have an etching chemistry for selectively etching the semiconductor material of the semiconductor matrix material layer 10 relative to the material of the first semiconductor oxide plate 12A. For example, the anisotropic etching process may have an etching chemistry using HBr / NF3 / O2 / SF6.

[0055] Two staggered comb grooves may be formed, the two staggered comb grooves replicating the pattern of the two staggered comb patterns. Each staggered comb groove may include an inner comb groove 31 and an outer comb groove 41. The first staggered comb groove includes a first inner comb groove 311 and a first outer comb groove 411 located on one side of a mirror symmetry plane (MSP). The second staggered comb groove includes a second inner comb groove 312 and a second outer comb groove 412 located on the opposite side of the mirror symmetry plane (MSP).

[0056] Each inner comb groove 31 includes a respective comb groove shaft portion, which replicates the comb shaft pattern, and a respective comb groove tooth portion, which replicates the comb tooth pattern and is adjacent to the respective comb groove shaft portion. Each comb groove shaft portion of the inner comb groove 31 can extend laterally along the first horizontal direction hd1 with or without lateral undulation. Each outer comb groove 41 includes a respective comb groove shaft portion, which replicates the comb shaft pattern, and a respective comb groove tooth portion, which replicates the comb tooth pattern and is adjacent to the respective comb groove shaft portion. Each comb groove shaft portion of the outer comb groove 41 can extend laterally along the first horizontal direction hd1 with or without lateral undulation. The comb groove shaft portion in the outer comb groove 41 can be adjacent to the comb groove extension portion 43 extending laterally along the second horizontal direction hd2. Specifically, the end segment of each of the comb groove axis portions within the outer comb groove 41 can be adjacent to the end segment of the comb groove extension portion 43, so that the group of comb groove axis portions within the outer comb groove 41 and the comb groove extension portion 43 together form a roughly rectangular shape, which defines the outer boundary of the cavity that will subsequently be formed in the semiconductor matrix material layer 10.

[0057] The two staggered comb grooves (31, 41) may be arranged so that the two inner comb grooves (311, 312) are close to each other and the two outer comb grooves (411, 412) are far from each other. In other words, the lateral separation distance between the comb groove axis portions of the two outer comb grooves (411, 412) along the second horizontal direction hd2 is greater than the lateral separation distance between the comb groove axis portions of the two inner comb grooves (311, 312).

[0058] A first portion of the semiconductor matrix material layer 10 having a substantially elongated rectangular shape may be provided between the comb groove axis portions of the two inner comb grooves (311, 312), the first portion corresponding to a region from which a detection mass (i.e., a central mass portion) will be subsequently patterned. A detection mass barrier groove 51 may be formed below an opening in the photoresist layer 37, the opening comprising a detection mass barrier pattern (PMBP) located at a boundary of a region from which a detection mass will be subsequently formed. A pair of detection mass barrier grooves 51 may be laterally spaced apart along a first horizontal direction hd1. The comb groove axis portions of the two inner comb grooves (311, 312) may have an extension wrapped around the detection mass barrier groove 51 and may subsequently be used to form a structure for limiting lateral etching of the semiconductor matrix material layer 10 during a subsequent isotropic etching process.

[0059] Each comb groove tooth portion within the inner comb groove 31 and the outer comb groove 41 may include a plurality of comb groove tooth portions parallel to each other. Each comb groove tooth portion extends laterally away from the respective comb groove axis portion along the common longitudinal direction of the comb groove tooth portions. Each comb groove tooth portion may be elongated along the longitudinal direction and may have a stem region having a substantially uniform width and affixed to the respective comb groove axis portion, and each comb groove tooth portion may have a tip segment having a width that gradually decreases with the distance from the respective comb groove axis portion. The common longitudinal direction of the comb groove tooth portions within the comb groove tooth portion may be at an angle ranging from 1 degree to 10 degrees, for example from 2 degrees to 8 degrees. The tip segment of each comb groove tooth portion may be advantageously used to increase the change in capacitance during the displacement of the movable structure to be formed later.

[0060] For all the comb groove tooth portions in the first inner comb groove 311 and the first outer comb groove 411, the comb groove tooth portions of the first inner comb groove 311 and the comb groove tooth portions of the first outer comb groove 411 may be staggered in parallel longitudinal directions. The staggered region may include the tip section of the first inner comb groove 311 and the comb groove tooth portions of the first outer comb groove 411. Similarly, for all the comb groove tooth portions in the second inner comb groove 312 and the second outer comb groove 412, the comb groove tooth portions of the second inner comb groove 312 and the comb groove tooth portions of the second outer comb groove 412 may be staggered in parallel longitudinal directions. The staggered region may include the tip section of the second inner comb groove 312 and the comb groove tooth portions of the second outer comb groove 412. The longitudinal directions of the comb groove teeth of the second inner comb groove 312 and the comb groove teeth of the second outer comb groove 412 may be inclined in a direction opposite to the second horizontal direction hd2 relative to the longitudinal directions of the comb groove teeth of the first inner comb groove 311 and the comb groove teeth of the first outer comb groove 411. The overall pattern of the comb grooves (31, 41, 51) may have a mirror symmetry plane (MSP) extending along the first horizontal direction hd1.

[0061] In one embodiment, in a top view, the region where the proof mass will be formed laterally and the regions of some parts of the comb groove axis portions of the two inner comb grooves (311, 312) extending laterally along the first horizontal direction hd1 may be located between a pair of longitudinal side walls of the first semiconductor oxide plate 12A. The photoresist layer 37 may then be removed, for example, by ashing.

[0062] The moat grooves (81, 91, 96, 86) may laterally surround the area of ​​the inner comb groove 31 and the outer comb groove 41. For example, the moat grooves (81, 91, 96, 86) may include: a proximal moat groove 81 that laterally surrounds the inner comb groove 31 and the outer comb groove 41; an intermediate moat groove 91 that laterally surrounds the proximal moat groove 81; a distal moat groove 96 that laterally surrounds the intermediate moat groove 91; and a suspension spring moat groove 86 that connects a corresponding pair of segments of the proximal moat groove 81 and the comb groove shaft portions of the two outer comb grooves (411, 412).

[0063] Reference Fig. 7A and Figure 7B , a dielectric liner layer may be conformally formed on the physically exposed surface of the semiconductor matrix material layer 10 in the comb grooves (31, 41, 51), in the moat grooves (81, 91, 96, 86), and on the second horizontal surface 102 of the semiconductor matrix material layer 10. In one embodiment, the dielectric liner layer may be formed by an oxidation process that converts the physically exposed surface portion of the semiconductor matrix material layer 10 into a semiconductor oxide liner, such as a silicon oxide liner. Alternatively, the dielectric liner layer may be formed by conformally depositing a dielectric material such as silicon oxide, silicon nitride, a dielectric metal oxide such as aluminum oxide and / or hafnium oxide. The thickness of the dielectric liner layer may be in the range from 4 nm to 100 nm, such as from 6 nm to 20 nm. In general, the thickness of the dielectric liner layer may be optimized to maximize the capacitive coupling between the comb structures to be formed subsequently and to minimize the leakage current through the dielectric liner layer.

[0064] Subsequently, a conductive material may be deposited in the remaining volume of the comb trenches (31, 41, 51) and the moat trenches (81, 91, 96, 86) and on the horizontally extending portion of the dielectric liner layer overlying the second horizontal surface 102 of the semiconductor matrix material layer 10. The conductive material may include a doped semiconductor material or a metallic material. For example, the conductive material may include heavily doped polysilicon that may be p-doped or n-doped. The conductive material may fill the remaining volume of the comb trenches (31, 41, 51) and the moat trenches (81, 91, 96, 86).

[0065] A planarization process may be used to remove the excess portion of the conductive material and the horizontally extending portion of the dielectric liner layer located above the horizontal plane including the second horizontal surface 102 of the semiconductor matrix material layer 10. The planarization process may use chemical mechanical planarization (CMP) and / or a recess etch process. In an embodiment in which a recess etch process is used, the horizontally extending portion of the dielectric liner layer may be used as an endpoint measurement layer for a recess etch step that removes the conductive material overlying the horizontally extending portion of the dielectric liner. Subsequently, the horizontally extending portion of the dielectric liner may be removed by an isotropic etching step (e.g., a wet etching step using dilute hydrofluoric acid). In an embodiment in which a chemical mechanical planarization (CMP) process is used, the horizontally extending portion of the dielectric liner may be used as a planarization stop layer during polishing of the conductive material overlying the horizontally extending portion of the dielectric liner. Subsequently, the horizontally extending portion of the dielectric liner may be removed by an isotropic etching step (e.g., a wet etching step using dilute hydrofluoric acid).

[0066] The remaining portion of the dielectric liner layer includes dielectric liner (32, 42, 52, 82, 92, 87, 97). The dielectric liner (32, 42, 52, 82, 92, 87, 97) includes an inner dielectric liner 32 formed in a corresponding one of the inner comb trenches 31, an outer dielectric liner 42 formed in a corresponding one of the outer comb trenches 41, a barrier dielectric liner 52 formed in a corresponding one of the detection mass barrier trenches 51, and a moat dielectric liner (82, 92, 87, 97). The remaining portion of the conductive fill material includes a conductive fill material portion (34, 44, 54, 84, 94, 89, 99). The conductive filling material portions (34, 44, 54, 84, 94, 89, 99) include an inner conductive filling material portion 34 that can be formed in a corresponding one of the inner comb grooves 31, an outer conductive filling material portion 44 formed in a corresponding one of the outer comb grooves 41, a barrier conductive filling material portion 54 formed in a corresponding one of the detection quality barrier grooves 51, and a moat filling material portion (84, 94, 89, 99) formed in a corresponding one of the moat grooves (81, 91, 86, 96).

[0067] The combination of the remaining portion of the dielectric liner layer and the remaining portion of the conductive material comprises a comb structure (30, 40). Specifically, each combination of the inner dielectric liner 32 and the inner conductive filling material portion 34 comprises an inner comb structure 30, and each combination of the outer dielectric liner 42 and the outer conductive filling material portion 44 comprises an outer comb structure 40. A first staggered comb structure (301, 401) comprising a first inner comb structure 301 and a first outer comb structure 401 may be formed on one side of a mirror symmetry plane (MSP), and a second staggered comb structure (302, 402) comprising a second inner comb structure 302 and a second outer comb structure 402 may be formed on the opposite side of the mirror symmetry plane (MSP). A barrier structure 50 comprising a barrier dielectric liner 52 and a barrier conductive filling material portion 54 may be formed in each proof mass barrier trench 51.

[0068] The moat dielectric liner (82, 92, 87, 97) may include an inner dielectric liner 82 that may be formed in the proximal moat 81, an intermediate dielectric liner 92 that may be formed in the intermediate moat 91, an outer dielectric liner 97 that may be formed in the distal moat 96, and a suspension spring dielectric liner 87 that may be formed in the suspension spring moat 86. The moat filling material portion (84, 94, 89, 99) may include a proximal filling material portion 84 that may be formed in the proximal moat 81, an intermediate filling material portion 94 that may be formed in the intermediate moat 91, a distal filling material portion 99 that may be formed in the distal moat 96, and a suspension spring filling material portion 89 that may be formed in the suspension spring moat 86.

[0069] The combination of inner dielectric liner 82 and proximal filler material portion 84 constitutes proximal wall structure 80. The combination of middle dielectric liner 92 and middle filler material portion 94 constitutes middle wall structure 90. The combination of outer dielectric liner 97 and distal filler material portion 99 constitutes distal wall structure 95. Each combination of suspension spring dielectric liner 87 and suspension spring filler material portion 89 constitutes suspension wall structure 85.

[0070] In general, each of the comb structures (30, 40) may include a respective dielectric liner (32 or 42) and a respective conductive fill material portion (34 or 44). Each of the comb structures (30, 40) extends from a second horizontal surface 102 of the semiconductor matrix material layer 10 toward a first horizontal surface 101 of the semiconductor matrix material layer 10 located at an interface with the second semiconductor oxide plate 12B. Each dielectric liner (32, 42) may be a patterned portion of the dielectric liner layer, and each conductive fill material portion (34, 44) may be a remaining portion of the conductive fill material. In one embodiment, the comb structures (30, 40) include a pair of inner comb structures (301, 302) and a pair of outer comb structures (401, 402), the pair of inner comb structures (301, 302) being laterally spaced apart by a first portion of the semiconductor matrix material layer 10, the pair of outer comb structures (401, 402) being interlaced with the pair of inner comb structures (301, 302). The comb shaft portions of the outer comb structures (401, 402) extend along the first horizontal direction hd1 and then extend along the second horizontal direction hd2 to abut each other, thereby defining a substantially rectangular area that is completely surrounded laterally by the combined comb shaft portions of the outer comb structures (401, 402). In other words, the comb shaft portions of the outer comb structures (401, 402) can constitute a frame that laterally surrounds all tooth portions of the outer comb structures (401, 402) and the entire inner comb structure (301, 302).

[0071] Two staggered comb structures (30, 40) may be formed, the two staggered comb structures (30, 40) having a horizontal cross-sectional shape that replicates the pattern of the two staggered comb patterns. Each staggered comb structure (30, 40) may include an inner comb structure 30 and an outer comb structure 40. The first staggered comb structure includes a first inner comb structure 301 and a first outer comb structure 401 located on one side of a mirror symmetry plane (MSP). The second staggered comb structure includes a second inner comb structure 302 and a second outer comb structure 402 located on the opposite side of the mirror symmetry plane (MSP).

[0072] Each inner comb structure 30 includes a respective comb structure shaft portion, which replicates the comb shaft pattern, and a respective comb structure tooth portion, which replicates the comb tooth pattern and is adjacent to the respective comb structure shaft portion. Each comb structure shaft portion of the inner comb structure 30 can extend laterally along the first horizontal direction hd1 with or without lateral undulations. Each outer comb structure 40 includes a respective comb structure shaft portion, which replicates the comb shaft pattern, and a respective comb structure tooth portion, which replicates the comb tooth pattern and is adjacent to the respective comb structure shaft portion. Each comb structure shaft portion of the outer comb structure 40 can extend laterally along the first horizontal direction hd1 with or without lateral undulations. The comb structure shaft portion within the outer comb structure 40 can be adjacent to a comb structure extension portion 46 extending laterally along the second horizontal direction hd2. Specifically, the end segment of each of the comb structure axis portions within the outer comb structure 40 can be adjacent to the end segment of the comb structure extension portion 46, so that the group of comb structure axis portions within the outer comb structure 40 and the comb structure extension portion 46 together form a roughly rectangular shape, which defines the outer boundary of the cavity that will subsequently be formed in the semiconductor matrix material layer 10.

[0073] The two staggered comb structures (30, 40) may be arranged such that the two inner comb structures (301, 302) are close to each other and the two outer comb structures (401, 402) are far from each other. In other words, the lateral separation distance between the comb structure axis portions of the two outer comb structures (401, 402) along the second horizontal direction hd2 is greater than the lateral separation distance between the comb structure axis portions of the two inner comb structures (301, 302).

[0074] A first portion of the semiconductor matrix material layer 10 having a substantially elongated rectangular shape may be provided between the comb structure axis portions of the two inner comb structures (301, 302), the first portion corresponding to a region from which a proof mass (i.e., a central mass portion) may be subsequently patterned. A barrier structure 50 may be formed in the proof mass barrier trench 51. A pair of barrier structures 50 may be laterally spaced apart along a first horizontal direction hd1. The comb structure axis portions of the two inner comb structures (301, 302) may have an extension portion wrapped around the barrier structure 50 and subsequently used to form a structure for limiting lateral etching of the semiconductor matrix material layer 10 during a subsequent isotropic etching process.

[0075] Each comb structure tooth portion within the inner comb structure 30 and the outer comb structure 40 includes a plurality of comb structure tooth portions that may be parallel to each other. Each comb structure tooth portion extends laterally away from the respective comb structure shaft portion along the common longitudinal direction of the comb structure tooth portions. Each comb structure tooth portion may be elongated along the longitudinal direction and may have a stem region having a substantially uniform width and being fitted to the respective comb structure shaft portion, and each comb structure tooth portion may have a tip segment having a width that gradually decreases with the distance from the respective comb structure shaft portion. The common longitudinal direction of the comb structure tooth portions within the comb structure tooth portions may be at an angle ranging from 1 degree to 10 degrees, for example from 2 degrees to 8 degrees. The tip segment of each comb structure tooth portion may be advantageously used to increase the change in capacitance during the displacement of the movable structure that will be formed later.

[0076] For all comb structure tooth portions in the first inner comb structure 301 and the first outer comb structure 401, the comb structure tooth portions of the first inner comb structure 301 and the comb structure tooth portions of the first outer comb structure 401 may be staggered in parallel longitudinal directions. The staggered region may include the tip section of the first inner comb structure 301 and the comb structure tooth portions of the first outer comb structure 401. Similarly, for all comb structure tooth portions in the second inner comb structure 302 and the second outer comb structure 402, the comb structure tooth portions of the second inner comb structure 302 and the comb structure tooth portions of the second outer comb structure 402 may be staggered in parallel longitudinal directions. The staggered region may include the tip section of the second inner comb structure 302 and the comb structure tooth portions of the second outer comb structure 402. The longitudinal directions of the comb structure tooth portions of the second inner comb structure 302 and the comb structure tooth portions of the second outer comb structure 402 may be inclined relative to the longitudinal directions of the comb structure tooth portions of the first inner comb structure 301 and the comb structure tooth portions of the first outer comb structure 401 in a direction opposite to the second horizontal direction hd2. The overall pattern of the comb structures ( 30 , 40 ) and the barrier structure 50 may have a mirror symmetry plane (MSP) extending along the first horizontal direction hd1 .

[0077] Reference Fig. 8A and Figure 8B, a metal material portion (110, 120, 130) may be formed on the second horizontal surface 102 of the semiconductor matrix material layer 10 and on the comb structures (30, 40). For example, a patterned deposition mask (not shown) (e.g., a patterned photoresist layer) may be formed on the exemplary structure, and at least one metal material may be deposited by physical vapor deposition. The at least one metal material may include, for example, a metal liner material (e.g., TiN, TaN, or WN) and an under-bump metal material (e.g., Ni, Cr, Cu), and stacks thereof. The thickness of the at least one metal material may range from 100 nm to 2,000 nm, although smaller thicknesses and larger thicknesses may also be used. The patterned deposition mask and portions of the at least one metal material overlying the patterned deposition mask may be removed, for example, by a lift-off process.

[0078] The remaining portion of the at least one metal material deposited on the inner comb structure 30 includes a movable metal plate 110. The remaining portion of the at least one metal material deposited on the outer comb structure 40 includes a fixed metal plate 120. The remaining portion of the at least one metal material deposited on the semiconductor matrix material layer 10 includes a spring structure 130, which may include an opening between an inner frame of the spring structure 130 and an outer frame of the spring structure 130. The spring structure 130 may have a suitable pattern to provide application of an electrical bias voltage to an opposing portion of the fixed comb structure 40.

[0079] Reference Fig.9A and Fig. 9B , an etch mask material layer 67 may be applied over the various metal material portions (110, 120, 130), and the etch mask material layer 67 may be photolithographically patterned to form openings through the etch mask material layer 67. The etch mask material layer 67 may include a photoresist material, or may include a hard mask material (e.g., silicon nitride, silicon oxide, or dielectric metal oxide). The etch mask material layer 67 may be patterned directly (if the etch mask material layer 67 includes a photoresist material), or the etch mask material layer 67 may be patterned by applying a photoresist layer over the etch mask material layer 67, patterning the photoresist layer, and transferring the pattern in the photoresist layer into the etch mask material layer using an anisotropic etching process.

[0080] The pattern of the openings in the patterned etch mask layer 67 may be selected so that a subset of the openings in the patterned etch mask layer 67 are formed within the boundaries defined by the comb shaft portion of the outer comb structure 40 and the comb structure extension portion 46. In addition, the pattern of the openings in the patterned etch mask layer 67 does not overlap with the area of ​​the comb structure (30, 40), the comb structure extension portion 46, the barrier structure 50, or a portion of the semiconductor matrix material layer 10 located between the intermediate wall structure 90 and the distal wall structure 95. The openings in the patterned etch mask layer 67 are located in the area where the metal material portion (110, 120, 130) is not present. The subset of the openings in the patterned etch mask layer 67 may overlie the area of ​​the gap between adjacent pairs of comb structure tooth portions. The subset of the openings in the patterned etch mask layer 67 may be formed between the barrier structure 50 and the comb structure extension portion 46. The openings in the patterned etch mask layer 67 do not exist in the first portion of the semiconductor matrix material layer 10 located between the pair of comb structure shaft portions of the inner comb structure 30 and the lateral extensions of the inner comb structure 30 and between the pair of barrier structures 50. A subset of the openings in the patterned etch mask layer 67 may be formed between the proximal wall structure 80 and the comb structure extension portion 46.

[0081] Reference Fig. 10A and Fig. 10B , a combination of anisotropic etching processes and isotropic etching processes or an isotropic etching process may be used to etch portions of the semiconductor matrix material layer 10 that are not masked by the patterned etch mask layer 67. In one embodiment, the anisotropic etching process may be formed to etch through the unmasked portions of the semiconductor matrix material layer 10. A deep trench may be formed below the opening in the patterned etch mask layer 67 to the depth of the first semiconductor oxide plate 12A.

[0082] Subsequently, an isotropic etching process using an isotropic etchant may be performed, the isotropic etching process selectively etching the semiconductor material of the semiconductor matrix material layer 10 relative to the dielectric material of the first and second semiconductor oxide plates (12A, 12B) and the dielectric material of the dielectric liner (32, 42, 52). A portion of the semiconductor matrix material layer 10 may be removed by the isotropic etching process. The removed portion of the semiconductor matrix material layer 10 includes a portion located within the lateral boundary defined by the comb structure axis portion within the outer comb structure 40, the comb structure extension portion 46, and the inner wall structure 80, and located outside the comb structure axis portion of the inner comb structure 30. The removed portion of the semiconductor matrix material layer 10 is referred to herein as a second portion of the semiconductor matrix material layer 10. In addition, a portion of the semiconductor matrix material layer 10 located between the intermediate wall structure 90 and the distal wall structure 95 is removed. The unetched portion of the semiconductor matrix material layer 10 that remains after the isotropic etching process and is located outside the distal wall structure 95 is referred to herein as the semiconductor matrix layer 10M. The unetched portion of the semiconductor matrix material layer 10 that remains after the isotropic etching process and is located between the proximal wall structure 80 and the intermediate wall structure 90 is referred to herein as the semiconductor frame 10F.

[0083] The isotropic etching process may use a wet etching process that selectively etches the semiconductor material of the semiconductor matrix material layer 10 relative to the material of the first and second semiconductor oxide plates (12A, 12B) and the material of the dielectric liner (32, 42, 52). In one embodiment, the wet etching process may use hot trimethyl-2hydroxyethyl ammonium hydroxide ("hot TMY") or tetramethyl ammonium hydroxide (TMAH). The duration of the isotropic etching process may be selected so that the etch front of the isotropic etching process reaches the entire area of ​​the portion of the top surface of the second semiconductor oxide plate 12B that is located within the area defined by the combination of the comb structure shaft portion within the outer comb structure 40, the comb structure extension portion 46, and the proximal wall structure 80. The comb structure extension portion 46 is attached to the semiconductor frame 10F through the spring wall structure 85 and the inner wall structure 80.

[0084] The movable structure includes the inner comb structures 30, the first portion of the semiconductor matrix material layer 10 located between the inner comb structures 30 and remaining unetched after the isotropic etching process, and the pair of barrier structures 50 attached to the first portion of the semiconductor matrix material layer 10 can be peeled off from the remaining unetched portion of the semiconductor matrix material layer 10 (which is referred to herein as the third portion), which is retained outside the combination of the comb structure shaft portion, the comb structure extension portion 46, and the proximal wall structure 80 within the outer comb structure 40. In one embodiment, when the isotropic etchant flows through the meandering channel defined by the extension of the comb structure shaft portion of the inner comb structure 30 and the extension of the barrier structure 50, the peripheral region of the first portion of the semiconductor matrix material layer 10 can be etched in parallel by the isotropic etchant.

[0085] The first portion of the semiconductor matrix material layer 10 includes a proof mass of a movable structure, which is referred to herein as a central mass portion 10A. The third portion of the semiconductor matrix material layer 10 is referred to herein as a semiconductor matrix layer 10M. The first and second semiconductor oxide plates (12A, 12B) and the dielectric liner (32, 42, 52) act as an etching barrier structure that defines the extent of a cavity 61 formed when the second portion of the semiconductor matrix material layer 10 is removed. The inner sidewalls of the comb structure shaft portion within the outer comb structure 40, the inner sidewalls of the comb structure extension portion 46, and the inner sidewalls of the proximal wall structure 80 can act as the outer lateral boundaries of the cavity 61. The sidewalls of the comb structure shaft portion of the inner comb structure 30 can act as the inner lateral boundaries of the cavity 61, which surrounds the first portion of the semiconductor matrix material layer 10 that is not etched by the isotropic etching process.

[0086] The volume of the recessed cavity 13 may be incorporated into the cavity 61. In embodiments where the handle substrate 20 comprises a semiconductor material such as silicon, the surface of the handle substrate 20 not covered by the second semiconductor oxide plate 12B may be isotropically recessed to form a void added to the cavity 61. The void may have an undercut portion located below the periphery of the second semiconductor oxide plate 12B. The isotropic etchant may laterally etch a portion of the semiconductor matrix material layer 10 located below the boundary formed by the comb structure shaft portion within the outer comb structure 40, the comb structure extension portion 46, and the proximal wall structure 80, and an undercut portion of the semiconductor matrix material layer 10 located outside the boundary.

[0087] In an alternative embodiment, the anisotropic etching process may be omitted and the isotropic etching process may be extended to etch through the second portion of the semiconductor matrix material layer 10 to form a cavity. In such an embodiment, the duration of the isotropic etching process may be extended to ensure that the etching front of the isotropic etching process reaches the entire area of ​​the portion of the top surface of the second semiconductor oxide plate 12B located within the area defined by the combination of the comb structure shaft portion within the outer comb structure 40, the comb structure extension portion 46, and the proximal wall structure 80.

[0088] In general, an isotropic etchant of an isotropic etching process may be applied through the openings in the patterned etching mask layer 67. The isotropic etchant etches the semiconductor material of the semiconductor matrix material layer 10 relative to the material of the semiconductor oxide plates (12A, 12B) and relative to the material of the comb structures (30, 40) in contact with the semiconductor matrix material layer 10, the material of the comb structures (30, 40) may be the material of the dielectric liner (32, 42). The isotropic etching process may be used to selectively remove a second portion of the semiconductor matrix material layer 10 that laterally surrounds the first portion of the semiconductor matrix material layer 10 relative to the comb structures (30, 40). The first semiconductor oxide plate 12A, the pair of inner comb structures 30, and the patterned etching mask layer 67 may protect the first portion of the semiconductor matrix material layer 10 from the etchant of the isotropic etching process, the patterned etching mask layer 67 being located on the second horizontal surface 102 of the semiconductor matrix material layer 10 and covering the comb structures 30.

[0089] The portion of the patterned etch mask layer 67 covering the first portion of the semiconductor matrix material layer 10 protects the front side surface of the first portion of the semiconductor matrix material layer 10 during the isotropic etching process. The first semiconductor oxide plate 12A protects the back side of the first portion of the semiconductor matrix material layer 10 during the isotropic etching process. Therefore, after the isotropic etching process, the center mass portion 10A as the first portion of the semiconductor matrix material layer 10 may have a uniform thickness between the first semiconductor oxide plate 12A and the interface with the patterned etch mask layer 67. In one embodiment, the center mass portion 10A may have a uniform thickness in the entire area laterally surrounded by the comb structure shaft portion of the inner comb structure 30 and the barrier structure 50.

[0090] The cavity 61 may be formed by removing the second portion of the semiconductor matrix material layer 10. The semiconductor matrix layer 10M including the unetched third portion of the semiconductor matrix material layer 10 laterally surrounds the cavity 61. The movable structure (10A, 30, 50) including the combination of the first portion of the semiconductor matrix material layer 10 and the pair of inner comb structures 30 may be peeled off from the semiconductor matrix layer 10M by an isotropic etching process.

[0091] The inner comb structure 30 is a component of the movable structure (10A, 30, 50) and is hereinafter referred to as the movable comb structure 30. The movable comb structure 30 includes a first movable comb structure 301 and a second movable comb structure 302. The comb structure tooth portion of the inner comb structure 30 includes movable comb fingers of the movable structure (10A, 30, 50).

[0092] The outer comb structure 40 is a fixed component and is therefore referred to hereinafter as a fixed comb structure 40. The fixed comb structure 40 comprises a first fixed comb structure 401 and a second fixed comb structure 402. The comb structure tooth portion of the fixed comb structure 40 comprises fixed comb fingers.

[0093] Reference Fig.11A and Fig. 11B , the patterned etching mask layer 67 can be removed, for example, by ashing. The metal material portion (110, 120, 130) is located on the top surface of the movable structure (10A, 30, 50), on the top surface of the fixed comb structure 40, on the top surface of the semiconductor frame 10F, and on the top surface of the semiconductor matrix layer 10M. The metal material portion (110, 120, 130) includes a movable metal plate 110 formed on the movable structure (10A, 30, 50), a fixed metal plate 120 formed on the fixed comb structure 40, and a spring structure 130 formed on the semiconductor frame 10F and the semiconductor matrix layer 10M and on the gap between the semiconductor frame 10F and the semiconductor matrix layer 10M. The spring structure 130 includes an opening located on the area of ​​the gap to provide elasticity.

[0094] Reference Fig.12 Each accelerometer 100 on the handle substrate 20 may be singulated, for example, by vacuum dicing. Subsequently, the handle substrate 20 may be stripped, for example, by removing the semiconductor oxide plates (12A, 12B). For example, wet etching using hydrofluoric acid may be performed to remove the semiconductor oxide plates (12A, 12B). Each accelerometer 100 may be electrically connected to a controller circuit or to a control unit using wiring harnesses, which may be attached to the spring structure 130 or to the fixed metal plate 120. The control circuit or the control unit may be configured to measure acceleration based on changes in the capacitance of the capacitor structure within the accelerometer 100.

[0095] Common Reference Figures 1A to 12According to various embodiments of the present disclosure, a micro-electromechanical system (MEMS) device is provided, the micro-electromechanical system (MEMS) device comprising: a movable structure (10A, 30, 50) located in a laterally restricted space and comprising a central mass portion 10A and a first movable comb structure 301, the first movable comb structure 301 comprising an inner comb shaft portion (i.e., a comb structure shaft portion of the first inner comb structure 301) attached to a first side wall of the central mass portion 10A and a first movable comb finger-shaped member (i.e., a comb structure tooth portion of the first inner comb structure 301) protruding from the comb shaft portion in a lateral direction. The central mass portion 10A comprises a portion of a first semiconductor material. A semiconductor oxide plate (e.g., a first semiconductor oxide plate 12A) comprising an oxide of the first semiconductor material covers the entire bottom surface of the central mass portion 10A. The first movable comb structure 301 includes a dielectric pad (e.g., an inner dielectric pad 32) and a conductive filling material portion (e.g., an inner conductive filling material portion 34), wherein the dielectric pad is physically exposed to a cavity within a laterally confined space, and the conductive filling material portion is located within the inner comb shaft portion and extends continuously into each of the first movable comb fingers and is laterally surrounded by the dielectric pad 32.

[0096] In one embodiment, the movable structure (10A, 30, 50) includes a second movable comb structure 302, which includes another inner comb shaft portion (i.e., the comb structure shaft portion of the second inner comb structure 302) attached to the second side wall of the central mass portion 10A and a second movable comb finger-like member protruding from the inner comb shaft portion in the lateral direction (i.e., the comb structure tooth portion of the second inner comb structure 302). In one embodiment, the semiconductor oxide plate 12A has a width greater than the lateral spacing between the inner comb shaft portion and the outer comb shaft portion. In one embodiment, the semiconductor oxide plate 12A contacts the bottom surface of the inner comb shaft portion and the bottom surface of the outer comb shaft portion.

[0097] In one embodiment, the lateral confinement space may be located within an opening in the semiconductor matrix layer 10M, the semiconductor matrix layer 10M comprising another portion of the first semiconductor material. In one embodiment, the first fixed comb structure 401 may be fixed to a first sidewall of the lateral confinement space and may include first fixed comb fingers (i.e., comb structure teeth portion of the first outer comb structure 401) interlaced with first movable comb fingers.

[0098] In one embodiment, the MEMS device of the present disclosure may include a MEMS accelerometer configured to measure the displacement of the movable structure (10A, 30, 50) relative to the first fixed comb structure 401 by sensing changes in the capacitance of a capacitor structure including the first movable comb structure 301 and the first fixed comb structure 401.

[0099] According to one aspect of the present disclosure, a microelectromechanical system (MEMS) accelerometer is provided, the microelectromechanical system (MEMS) accelerometer comprising a movable structure (10A, 30, 50) located in a laterally confined space. The movable structure (10A, 30, 50) may include a central mass portion 10A, a first movable comb structure 301, and a second movable comb structure 302, the central mass portion 10A comprising a portion of a first semiconductor material, the first movable comb structure 301 being fixed to a first side of the central mass portion 10A, and the second movable comb structure 302 being fixed to a second side of the central mass portion 10A. Each of the first movable comb structure 301 and the second movable comb structure 302 comprises a respective comb shaft portion and a respective set of movable comb fingers (i.e., comb structure tooth portions) protruding laterally from the respective comb shaft portion. The first fixed comb structure 401 is fixed to the first side wall of the lateral confinement space and includes first fixed comb fingers interlaced with first movable comb fingers (i.e., comb structure teeth of the first outer comb structure 401). The second fixed comb structure 402 is fixed to the second side wall of the lateral confinement space and includes second fixed comb fingers interlaced with second movable comb fingers (i.e., comb structure teeth of the second outer comb structure 402). A semiconductor oxide plate (e.g., first semiconductor oxide plate 12A) containing an oxide of a first semiconductor material covers the entire bottom surface of the central mass portion 10A.

[0100] In one embodiment, the first fixed comb structure 401 includes an additional dielectric liner (e.g., outer dielectric liner 42) and an additional conductive filling material portion (e.g., outer conductive filling material portion 44), the additional dielectric liner being physically exposed to the cavity within the lateral confinement space, the additional conductive filling material portion being located within a respective one of the first fixed comb fingers and being laterally surrounded by the additional dielectric liner 42. In one embodiment, each of the first movable comb structure 301, the second movable comb structure 302, the first fixed comb structure 401, and the second fixed comb structure 402 includes a respective dielectric liner (32, 34) and includes a respective conductive filling material portion (34, 44), the dielectric liner (32, 34) being physically exposed to the cavity within the lateral confinement space. In one embodiment, the conductive filling material portion (34, 44) may have a material composition different from the first semiconductor material of the central mass portion 10A and the semiconductor matrix layer 10M.

[0101] In one embodiment, the first semiconductor oxide plate 12A may have a width greater than the lateral spacing between the interface between the central mass portion 10A and the first movable comb structure 301 and the interface between the central mass portion 10A and the second movable comb structure 302. In one embodiment, the first semiconductor oxide plate 12A may have a lateral extent along the second horizontal direction hd2 greater than the combination of the central mass portion 10A and the two comb structure shaft portions of the inner comb structure 30 (which does not include the comb structure tooth portion of the inner comb structure 30). In this embodiment, the planar top surface of the peripheral portion of the first semiconductor oxide plate 12A may be physically exposed to the cavities 61 located between adjacent pairs of movable comb fingers in the first movable comb structure 301 and between adjacent pairs of movable comb fingers in the second movable comb structure 302.

[0102] In one embodiment, the top surface of the center mass portion 10A and the top surface of each conductive fill material portion (34, 44, 54) can be physically exposed to the cavity 61 within the laterally confined space. The entire top surface of the center mass portion 10A (which faces the semiconductor die 70) can be located in a horizontal plane. The entire bottom surface of the center mass portion 10A (which contacts the first semiconductor oxide plate 12A) can be located in another horizontal plane. In one embodiment, the thickness of the center mass portion 10A can be uniform.

[0103] In one embodiment, the MEMS device of the present disclosure may include a MEMS accelerometer. The combination of the movable structure (10A, 30, 50) and the semiconductor matrix layer 10M may be attached to a semiconductor structure (e.g., a semiconductor die 70), the semiconductor structure including a semiconductor substrate 72, a field effect transistor (including a subset of semiconductor devices 74) located on the semiconductor substrate 72, and a metal interconnect structure formed in a dielectric material layer 76. The field effect transistor may include a circuit as follows: the circuit is configured to measure the displacement of the movable structure (10A, 30, 50) relative to the pair of fixed comb structures 40 and the semiconductor matrix layer 10M by sensing the change in the capacitance of the capacitor structure including the pair of movable comb structures 30 and the pair of fixed comb structures 40.

[0104] In one embodiment, the MEMS device of the present disclosure may include a capacitor structure, which includes two subsets of conductive filling material portions (e.g., outer conductive filling material portions 44) of the first fixed comb structure 401 and / or the second fixed comb structure 402 as a first conductive node and a second conductive node. In one embodiment, the first conductive node of the capacitor structure may be formed by electrically connecting a first subset of the outer conductive filling material portions 44 located in the pair of outer comb structures (i.e., fixed comb structures 40), and the second conductive node of the capacitor structure may be formed by electrically connecting a second subset of the outer conductive filling material portions 44 located in the pair of outer comb structures 40. In one embodiment, the outer conductive filling material portions 44 in the first subset and the outer conductive filling material portions 44 in the second subset may alternate in each outer comb structure 40. In an illustrative example, the external conductive filling material portions 44 within each of the external comb structures (i.e., the fixed comb structure 40) can be sequentially numbered using positive integers starting from 1, and a group of odd-numbered external conductive filling material portions 44 can be connected to the first conductive node of the capacitor structure, and a group of even-numbered external conductive filling material portions 44 can be connected to the second conductive node of the capacitor structure.

[0105] According to another aspect of the present disclosure, a microelectromechanical system (MEMS) accelerometer is provided, the MEMS device may include a movable structure (10A, 30, 50) located in a lateral confinement space. The movable structure may include a central mass portion 10A, a first movable comb structure 301, and a second movable comb structure 302, the central mass portion 10A includes a portion of a first semiconductor material, the first movable comb structure 301 is fixed to a first side of the central mass portion, and the second movable comb structure 302 is fixed to a second side of the central mass portion 10A, wherein each of the first movable comb structure 301 and the second movable comb structure 302 includes a respective comb shaft portion and a respective set of movable comb fingers protruding from the respective comb shaft portion in a lateral direction. The MEMS device may also include a first fixed comb structure 401, the first fixed comb structure 401 is fixed to a first sidewall of the lateral confinement space and includes first fixed comb fingers interlaced with the respective set of movable comb fingers of the first movable comb structure 301. The MEMS device may further include a second fixed comb structure 402 fixed to the second sidewall of the lateral confinement space and including second fixed comb fingers interlaced with second movable comb fingers. The MEMS device may further include a semiconductor oxide plate 12A including an oxide of the first semiconductor material 10 and covering the entire bottom surface of the central mass portion 10A.

[0106] In general, the MEMS accelerometer of the present disclosure may be configured to measure the displacement of the movable structure (10A, 30, 50) relative to the first fixed comb structure 401 and / or the second fixed comb structure 402 by sensing the change in capacitance of a capacitor structure including at least the first movable comb structure 401 and the first fixed comb structure 402. The capacitor structure may include the first movable comb structure 301, the second movable comb structure 302, the first fixed comb structure 401, and the second fixed comb structure 402.

[0107] Reference Fig.13 , flow chart 1300 shows a set of processing steps that can be performed to form a MEMS device according to an embodiment of the present disclosure. At step 1310, a recessed surface can be formed by recessing a region of a first horizontal surface 101 of a semiconductor matrix material layer 10. At step 1320, a semiconductor oxide plate (e.g., a first semiconductor oxide plate 12A) can be formed on the recessed surface. At step 1330, a comb structure (30, 40) can be formed in the semiconductor matrix material layer 10 extending from a second horizontal surface 102 of the semiconductor matrix material layer 10 toward the first horizontal surface 101 of the semiconductor matrix material layer 10. The comb structure (30, 40) includes a pair of inner comb structures 30 and a pair of outer comb structures 40, the pair of inner comb structures 30 being laterally spaced apart by a first portion of the semiconductor matrix material layer 10, the pair of outer comb structures 40 being interlaced with the pair of inner comb structures. At step 1340, an isotropic etching process may be used to selectively remove a second portion of the semiconductor matrix material layer 10 that laterally surrounds the first portion of the semiconductor matrix material layer 10 relative to the comb structures (30, 40). The semiconductor oxide plate 12A, the pair of inner comb structures 30, and the patterned etch mask layer 67 protect the first portion of the semiconductor matrix material layer 10 from the etchant of the isotropic etching process, the patterned etch mask layer 67 being located on the second horizontal surface 102 and covering the comb structures (30, 40). At step 1350, a semiconductor die 70 may be attached to the semiconductor matrix material layer 10M, and the handle substrate 20 may be thinned to provide an enclosure material layer 120. The bonded assembly may be diced to provide discrete MEMS devices including respective accelerometers 100.

[0108] Therefore, according to another aspect of the present disclosure, a method of forming a micro-electromechanical system (MEMS) accelerometer is provided, and the method of forming a MEMS device may include an operation of forming a recessed surface 13 by recessing a region of a first horizontal surface 101 of a semiconductor matrix material layer 10. The method may also include an operation of forming a semiconductor oxide plate 12A on the recessed surface 13. The method may include an operation of forming a comb structure (301, 302) extending from a second horizontal surface 102 of the semiconductor matrix material layer 10 toward the first horizontal surface 101, wherein the comb structure includes a pair of inner comb structures (301, 302) and a pair of outer comb structures 401, 402, the pair of inner comb structures (301, 302) being spaced apart laterally by a first portion of the semiconductor matrix material layer, and the pair of outer comb structures 401, 402 being staggered with the pair of inner comb structures (301, 302). The method also includes an operation of selectively removing a second portion of the semiconductor matrix material layer 10 that laterally surrounds the first portion of the semiconductor matrix material layer relative to the comb structure (301, 302, 401, 402) using an isotropic etching process, wherein the semiconductor oxide plate 12A, the pair of inner comb structures 301, 302, and a patterned etching mask layer protect the first portion 10A of the semiconductor matrix material layer 10 from the etchant of the isotropic etching process, and the patterned etching mask layer is located on the second horizontal surface 102 and covers the comb structure.

[0109] In various embodiments, a proof mass including a central mass portion 10A may be provided from a first portion of a semiconductor matrix material layer 10, which proof mass may have a uniform thickness due to the presence of a semiconductor oxide plate 12A at the bottom surface of the first portion of the semiconductor matrix material layer 10 and due to the presence of a patterned etch mask layer 67 at the top surface of the first portion of the semiconductor matrix material layer 10. Thus, random etching of the bottom surface of the proof mass present in prior art methods may be completely avoided, and the central mass portion 10A may have a well-defined mass, which may be determined with high precision by the pattern of the movable comb structure 30. The displacement of the movable comb structure 30 is proportional to the inertial force applied to the movable structure (10A, 30, 50), which is proportional to the product of the mass of the movable structure (10A, 30, 50) and the acceleration of the movable structure (10A, 30, 50). Since the mass of the central mass portion 10A can be determined with high precision, the mass of the movable structure (10A, 30, 50) can be determined with high precision. Therefore, the measurement of the change in capacitance of the capacitor comprising at least one of the movable structure (10A, 30, 50) and the fixed comb structure 40 can provide an accurate measurement of the acceleration of the movable structure (10A, 30, 50), and thus provide an accurate measurement of the object to which the MEMS device is attached. The high-precision measurement of acceleration can enhance the accuracy of velocity calculations and travel distance calculations and the accuracy of the estimation of the force on the object to which the accelerometer is attached.

[0110] The accelerometer 100 of the present disclosure may be used in various applications to measure acceleration and / or rotation of any object, such as a mobile device, an optical device, or a vehicle. In the example shown, the accelerometer 100 may be used as an actuator in an optical image stabilization system.

[0111] The disclosed embodiment proposes a micro-electromechanical system device, characterized in that it includes: a movable structure located in a laterally restricted space, wherein the movable structure includes a central mass portion and a first movable comb structure, the first movable comb structure includes an inner comb shaft portion adhered to the first side wall of the central mass portion and a plurality of first movable comb finger-like members protruding laterally from the inner comb shaft portion, wherein: the central mass portion includes a portion of a first semiconductor material; a semiconductor oxide plate, comprising an oxide of the first semiconductor material, covering the entire bottom surface of the central mass portion; and the first movable comb structure includes a dielectric pad and a conductive filling material portion, the dielectric pad being physically exposed to a cavity within a substrate, the conductive filling material portion being located within the inner comb shaft portion and extending continuously into each of the plurality of first movable comb finger-like members and being laterally surrounded by the dielectric pad.

[0112] In some embodiments, the movable structure comprises a second movable comb structure comprising another inner comb shaft portion attached to a second side wall of the central mass portion and a plurality of second movable comb fingers protruding laterally from the inner comb shaft portion.

[0113] In some embodiments, the width of the semiconductor oxide plate is greater than the lateral spacing between the inner comb axis portion and the outer comb axis portion.

[0114] In some embodiments, the semiconductor oxide plate contacts a bottom surface of the inner comb shaft portion and a bottom surface of the outer comb shaft portion.

[0115] In some embodiments, the lateral confinement space is located within an opening in a semiconductor matrix layer, the semiconductor matrix layer comprising another portion of the first semiconductor material.

[0116] In some embodiments, the micro-electromechanical system device further includes a first fixed comb structure, which is fixed to the first side wall of the lateral restriction space and includes a plurality of first fixed comb fingers, and the plurality of first fixed comb fingers are staggered with the plurality of first movable comb fingers.

[0117] In some embodiments, the first fixed comb structure includes an additional dielectric pad and an additional conductive filling material portion, wherein the additional dielectric pad is physically exposed to the cavity within the laterally confined space, and the additional conductive filling material portion is located within a corresponding one of the first fixed comb fingers and is laterally surrounded by the additional dielectric pad.

[0118] In some embodiments, the MEMS device includes a MEMS accelerometer configured to measure a displacement of the movable structure relative to the first fixed comb structure by sensing a change in capacitance, wherein the capacitor structure includes the first movable comb structure and the first fixed comb structure.

[0119] In some embodiments, a top surface of the central mass portion and a top surface of the conductive fill material portion are physically exposed to the cavity; and the entire top surface of the central mass portion is located in a horizontal plane.

[0120] The disclosed embodiment provides a micro-electromechanical system accelerometer, characterized in that it includes: a movable structure located in a lateral restricted space, wherein the movable structure includes a central mass portion, a first movable comb structure and a second movable comb structure, the central mass portion includes a portion of a first semiconductor material, the first movable comb structure is fixed on a first side of the central mass portion, and the second movable comb structure is fixed on a second side of the central mass portion, wherein each of the first movable comb structure and the second movable comb structure includes a respective comb axis portion and a movable portion extending laterally from the respective comb axis portion. a plurality of movable comb fingers protruding from each group; a first fixed comb structure, fixed to the first side wall of the lateral confinement space and comprising a plurality of first fixed comb fingers, wherein the plurality of first fixed comb fingers are staggered with the plurality of movable comb fingers of each group of the first movable comb structure; a second fixed comb structure, fixed to the second side wall of the lateral confinement space and comprising a plurality of second fixed comb fingers, wherein the plurality of second fixed comb fingers are staggered with the plurality of second movable comb fingers; and a semiconductor oxide plate, comprising an oxide of the first semiconductor material and covering the entire bottom surface of the central mass portion.

[0121] In some embodiments, each of the first movable comb structure, the second movable comb structure, the first fixed comb structure and the second fixed comb structure includes a respective dielectric liner and includes a respective conductive filling material portion, and the dielectric liner is physically exposed to the cavity within the lateral confinement space.

[0122] In some embodiments, the microelectromechanical system accelerometer is configured to measure the displacement of the movable structure relative to the first fixed comb structure and the second fixed comb structure by sensing changes in the capacitance of a capacitor structure, wherein the capacitor structure includes the first movable comb structure, the second movable comb structure, the first fixed comb structure, and the second fixed comb structure.

[0123] In some embodiments, a width of the semiconductor oxide plate is greater than a lateral spacing between an interface between the central mass portion and the first movable comb structure and an interface between the central mass portion and the second movable comb structure.

[0124] In some embodiments, a peripheral portion of the semiconductor oxide plate is physically exposed to the cavity, the cavity is located between adjacent pairs of movable comb fingers in the first movable comb structure and between adjacent pairs of movable comb fingers in the second movable comb structure; the lateral confinement space is located within an opening in a semiconductor matrix layer, the semiconductor matrix includes another portion of the first semiconductor material; and each of the first movable comb structure, the second movable comb structure, the first fixed comb structure and the second fixed comb structure includes a respective conductive filling material portion, the conductive filling material portion having a material composition different from that of the first semiconductor material.

[0125] The present disclosed embodiment proposes a method for forming a micro-electromechanical system device, which is characterized by comprising: forming a recessed surface by recessing an area of ​​a first horizontal surface of a semiconductor matrix material layer; forming a semiconductor oxide plate on the recessed surface; forming a plurality of comb structures extending from a second horizontal surface of the semiconductor matrix material layer toward the first horizontal surface, wherein the plurality of comb structures include a pair of inner comb structures and a pair of outer comb structures, the pair of inner comb structures are laterally spaced apart by a first portion of the semiconductor matrix material layer, and the pair of outer comb structures are staggered with the pair of inner comb structures; and using an isotropic etching process to selectively remove a second portion of the semiconductor matrix material layer that laterally surrounds the first portion of the semiconductor matrix material layer relative to the plurality of comb structures, wherein the semiconductor oxide plate, the pair of inner comb structures, and a patterned etching mask layer protect the first portion of the semiconductor matrix material layer from the etchant of the isotropic etching process, and the patterned etching mask layer is located on the second horizontal surface and covers the plurality of comb structures.

[0126] In some embodiments, a cavity is formed by removing the second portion of the semiconductor matrix material layer; a semiconductor matrix layer, including a third portion of the semiconductor matrix material layer, laterally surrounding the cavity; and a movable structure, including a combination of the first portion of the semiconductor matrix material layer and the pair of inner comb structures, is peeled off from the semiconductor matrix layer.

[0127] In some embodiments, forming the plurality of comb structures comprises: forming a plurality of comb grooves in the semiconductor matrix material layer, wherein each of the plurality of comb grooves extends from the second horizontal surface of the semiconductor matrix material layer toward the first horizontal surface of the semiconductor matrix material layer; and forming the plurality of comb structures within the plurality of comb grooves, wherein each of the plurality of comb structures comprises a respective dielectric liner and a respective conductive filling material portion.

[0128] In some embodiments, the method of forming a micro-electromechanical system device further includes: forming a dielectric liner layer on the physically exposed surfaces of the plurality of comb grooves; after forming the dielectric liner layer, depositing a conductive filling material in the remaining volume of the plurality of comb grooves; and removing some portions of the conductive filling material from the outside of the plurality of comb grooves, wherein each of the plurality of dielectric liners includes the remaining portion of the dielectric liner layer, and each of the conductive filling material portions includes the remaining portion of the plurality of conductive filling materials.

[0129] In some embodiments, the MEMS device includes a MEMS accelerometer; and the combination of the movable structure and the semiconductor matrix layer is bonded to a semiconductor structure, the semiconductor structure including a semiconductor substrate, a plurality of field effect transistors located on the semiconductor substrate, and a plurality of metal interconnect structures formed in a plurality of dielectric material layers, wherein the plurality of field effect transistors include the following circuit: the circuit is configured to measure the displacement of the movable structure relative to the pair of outer comb structures and the semiconductor matrix layer by sensing changes in the capacitance of a capacitor structure, the capacitor structure including the pair of inner comb structures and the pair of outer comb structures.

[0130] In some embodiments, the method for forming a micro-electromechanical system device further includes: forming an additional semiconductor oxide plate on the first horizontal surface of the semiconductor matrix material layer; before forming the multiple comb grooves, attaching the additional semiconductor oxide plate to an operating substrate, wherein a lateral confinement space is formed between the semiconductor oxide plate and the operating substrate; forming the patterned etch mask layer on the second horizontal surface of the semiconductor matrix material layer by applying an etch mask material layer and forming multiple openings through the etch mask material layer, wherein the multiple openings are formed in multiple areas that do not overlap with the areas of the multiple comb structures; and applying an isotropic etchant of the isotropic etching process through the openings in the patterned etch mask layer, wherein the isotropic etchant selectively etches the material of the semiconductor matrix material layer relative to the material of the semiconductor oxide plate and the material of the additional semiconductor oxide plate and relative to the material of the multiple comb structures in contact with the semiconductor matrix material layer.

[0131] The features of several embodiments are summarized above so that those skilled in the art can better understand the various aspects of the present disclosure. Those skilled in the art will understand that they can easily use the present disclosure as a basis for designing or modifying other processes and structures to implement the same purposes and / or achieve the same advantages as the embodiments described herein. Those skilled in the art will also recognize that these equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they can make various changes, substitutions and modifications to the present disclosure without departing from the spirit and scope of the present disclosure.

[0132] [Explanation of Symbols]

[0133] 10: Semiconductor matrix material layer / first semiconductor material

[0134] 10A: Central mass section / movable structure / part 1

[0135] 10F: Semiconductor frame

[0136] 10M: Semiconductor matrix layer

[0137] 11: Diffusion Barrier Spacers / Blocking Spacers

[0138] 12A: Plate / semiconductor oxide plate / first semiconductor oxide plate

[0139] 12B: Plate / semiconductor oxide plate / second semiconductor oxide plate

[0140] 13: Concave cavity

[0141] 13R: Concave bottom surface

[0142] 13S: Sidewall

[0143] 20: Operation substrate

[0144] 30: Comb structure / internal comb structure / movable structure / movable comb structure

[0145] 31: Comb groove / internal comb groove

[0146] 32: Dielectric liner / internal dielectric liner

[0147] 34: Conductive filling material part / internal conductive filling material part

[0148] 37: Photoresist layer

[0149] 40: Comb structure / external comb structure / fixed comb structure

[0150] 41: Comb groove / External comb groove

[0151] 42: Dielectric liner / external dielectric liner

[0152] 43: Comb groove extension

[0153] 44: Conductive filling material part / external conductive filling material part

[0154] 46: Comb structure extension

[0155] 50: Barrier structure / movable structure

[0156] 51: Comb groove / detection quality barrier groove

[0157] 52: Dielectric liner / barrier dielectric liner

[0158] 54: Conductive filling material part / barrier conductive filling material part

[0159] 61: Cavity

[0160] 67: Etching mask material layer

[0161] 70: Semiconductor die

[0162] 72: Semiconductor substrate

[0163] 74: Semiconductor devices

[0164] 76: Dielectric material layer

[0165] 80: Proximal wall structure / inner wall structure

[0166] 81: Trench / Proximal Trench

[0167] 82: Dielectric liner / trench dielectric liner / internal dielectric liner

[0168] 84: Conductive filling material part / trench filling material part / proximal filling material part

[0169] 85: Suspended wall structure / spring wall structure

[0170] 86: Trench groove / suspension spring trench groove

[0171] 87: Dielectric gasket / trench dielectric gasket / suspension spring dielectric gasket

[0172] 89: Conductive filling material part / trench filling material part / suspension spring filling material part

[0173] 90: Middle wall structure

[0174] 91: Trench / Middle Trench

[0175] 92: Dielectric liner / trench dielectric liner / intermediate dielectric liner

[0176] 94: Conductive filling material part / trench filling material part / intermediate filling material part

[0177] 95: Distal wall structure

[0178] 96: Trench / Distant Trench

[0179] 97: Dielectric liner / trench dielectric liner / external dielectric liner

[0180] 99: Conductive filling material part / trench filling material part / distal end filling material part

[0181] 100: Accelerometer

[0182] 101: First horizontal surface

[0183] 102: Second horizontal surface

[0184] 110: Metal material parts / removable metal plates

[0185] 120: Metal material part / fixed metal plate / surrounding material layer

[0186] 130: Metal material part / spring structure

[0187] 301: first inner comb structure / comb structure / inner comb structure / first movable comb structure

[0188] 302: Second inner comb structure / comb structure / inner comb structure / second movable comb structure

[0189] 401: first outer comb structure / comb structure / outer comb structure / first fixed comb structure

[0190] 402: Second outer comb structure / comb structure / outer comb structure / second fixed comb structure

[0191] 311: First inner comb groove / inner comb groove

[0192] 312: Second inner comb groove / inner comb groove

[0193] 411: First outer comb groove / outer comb groove

[0194] 412: Second outer comb groove / outer comb groove

[0195] 1300: Flowchart

[0196] 1310, 1320, 1330, 1340, 1350: Steps

[0197] A–A': Hinged vertical surface

[0198] A_PM: Region

[0199] B–B': Horizontal plane / plane

[0200] CPI1: Inner Comb Pattern / Comb Pattern / First Inner Comb Pattern

[0201] CPI2: Inner comb pattern / Comb pattern / Second inner comb pattern

[0202] CPO1: Outer comb pattern / Comb pattern / First outer comb pattern

[0203] CPO2: Outer comb pattern / Comb pattern / Second outer comb pattern

[0204] CSEP: Comb Extension Pattern

[0205] hd1: first horizontal direction

[0206] hd2: second horizontal direction

[0207] MSP: Mirror Symmetry Plane

[0208] PMBP: Detection of mass barrier patterns

[0209] t: thickness

Claims

1. A micro-electromechanical system device, characterized in that include: A movable structure located in the lateral restricted space, wherein the movable structure comprises a central mass portion and a first movable comb structure, wherein the first movable comb structure comprises an inner comb shaft portion attached to a first side wall of the central mass portion and a plurality of first movable comb fingers protruding from the inner comb shaft portion in a lateral direction, wherein: The central mass portion includes a portion of a first semiconductor material; a semiconductor oxide plate comprising an oxide of the first semiconductor material covering the entire bottom surface of the central mass portion; and The first movable comb structure includes a dielectric liner and a conductive filling material portion, wherein the dielectric liner is physically exposed to the cavity within the matrix, and the conductive filling material portion is located within the inner comb shaft portion and extends continuously into each of the plurality of first movable comb fingers and is laterally surrounded by the dielectric liner.

2. The micro-electromechanical system device according to claim 1, wherein the movable structure includes a second movable comb structure, the second movable comb structure including another inner comb shaft portion attached to the second side wall of the central mass portion and a plurality of second movable comb fingers protruding from the inner comb shaft portion in a lateral direction. 3 . The MEMS device according to claim 2 , wherein a width of the semiconductor oxide plate is greater than a lateral spacing between the inner comb-axis portion and the outer comb-axis portion. 4 . The MEMS device according to claim 2 , wherein the semiconductor oxide plate contacts a bottom surface of the inner comb-shaft portion and a bottom surface of the outer comb-shaft portion. 5 . The MEMS device of claim 1 , wherein the lateral confinement space is located within an opening in a semiconductor matrix layer, the semiconductor matrix layer comprising another portion of the first semiconductor material.

6. The MEMS device according to claim 1 further includes a first fixed comb structure, which is fixed to the first side wall of the lateral restriction space and includes a plurality of first fixed comb fingers, and the plurality of first fixed comb fingers are staggered with the plurality of first movable comb fingers.

7. A micro-electromechanical system device according to claim 6, wherein the first fixed comb structure includes an additional dielectric pad and an additional conductive filling material portion, wherein the additional dielectric pad is physically exposed to the cavity within the laterally confined space, and the additional conductive filling material portion is located within a corresponding one of the first fixed comb fingers and is laterally surrounded by the additional dielectric pad.

8. The MEMS device of claim 6, wherein the MEMS device comprises a MEMS accelerometer, the MEMS accelerometer being configured to measure the displacement of the movable structure relative to the first fixed comb structure by sensing a change in capacitance, the capacitor structure comprising the first movable comb structure and the first fixed comb structure.

9. The MEMS device of claim 1, wherein a top surface of the central mass portion and a top surface of the conductive filling material portion are physically exposed to the cavity; and the entire top surface of the central mass portion is located in a horizontal plane.

10. A micro-electromechanical system accelerometer, characterized in that include: a movable structure located in the laterally confined space, wherein the movable structure comprises a central mass portion, a first movable comb structure and a second movable comb structure, the central mass portion comprising a portion of a first semiconductor material, the first movable comb structure being fixed on a first side of the central mass portion, the second movable comb structure being fixed on a second side of the central mass portion, wherein each of the first movable comb structure and the second movable comb structure comprises a respective comb shaft portion and respective groups of a plurality of movable comb fingers protruding laterally from the respective comb shaft portion; a first fixed comb structure fixed to a first side wall of the lateral confining space and comprising a plurality of first fixed comb fingers interlaced with the plurality of movable comb fingers of each group of the first movable comb structure; a second fixed comb structure fixed to a second side wall of the lateral confining space and comprising a plurality of second fixed comb fingers, the plurality of second fixed comb fingers being interlaced with the plurality of movable comb fingers of the respective groups of the second movable comb structure; as well as a semiconductor oxide plate comprising an oxide of the first semiconductor material and covering the entire bottom surface of the central mass portion, The first and second movable comb structures respectively include a dielectric pad and a conductive filling material portion, wherein the dielectric pad is physically exposed to the cavity within the substrate, and the conductive filling material portion is located within the respective comb shaft portion and extends continuously into each of the plurality of movable comb fingers in each group and is laterally surrounded by the dielectric pad.

11. A micro-electromechanical system accelerometer according to claim 10, wherein each of the first movable comb structure, the second movable comb structure, the first fixed comb structure and the second fixed comb structure includes a respective dielectric pad and includes a respective conductive filling material portion, and the dielectric pad is physically exposed to the cavity within the lateral confinement space.

12. The MEMS accelerometer of claim 11 , wherein the MEMS accelerometer is configured to measure the displacement of the movable structure relative to the first fixed comb structure and the second fixed comb structure by sensing changes in capacitance of a capacitor structure, wherein the capacitor structure comprises the first movable comb structure, the second movable comb structure, the first fixed comb structure, and the second fixed comb structure.

13. The MEMS accelerometer of claim 11, wherein a width of the semiconductor oxide plate is greater than a lateral spacing between an interface between the central mass portion and the first movable comb structure and an interface between the central mass portion and the second movable comb structure.

14. A micro-electromechanical system accelerometer according to claim 11, wherein a peripheral portion of the semiconductor oxide plate is physically exposed to the cavity, the cavity is located between adjacent pairs of movable comb fingers in the first movable comb structure and between adjacent pairs of movable comb fingers in the second movable comb structure; the lateral confinement space is located in an opening in a semiconductor matrix layer, the semiconductor matrix includes another portion of the first semiconductor material; and each of the first movable comb structure, the second movable comb structure, the first fixed comb structure and the second fixed comb structure includes a respective conductive filling material portion, the conductive filling material portion having a material composition different from that of the first semiconductor material.

15. A method for forming a micro-electromechanical system device, characterized in that include: forming a recessed surface by recessing a region of the first horizontal surface of the layer of semiconductor matrix material; forming a semiconductor oxide plate on the recessed surface; forming a plurality of comb structures extending from a second horizontal surface of the semiconductor matrix material layer toward the first horizontal surface, wherein the plurality of comb structures include a pair of inner comb structures and a pair of outer comb structures, the pair of inner comb structures being laterally spaced apart by a first portion of the semiconductor matrix material layer, the pair of outer comb structures being interleaved with the pair of inner comb structures; as well as removing a second portion of the semiconductor matrix material layer laterally surrounding the first portion of the semiconductor matrix material layer selectively relative to the plurality of comb structures using an isotropic etching process, wherein the semiconductor oxide plate, the pair of inner comb structures, and a patterned etch mask layer protect the first portion of the semiconductor matrix material layer from an etchant of the isotropic etching process, the patterned etch mask layer being located on the second horizontal surface and covering the plurality of comb structures, The forming of the plurality of comb structures comprises: forming a plurality of comb grooves in the semiconductor matrix material layer, forming the plurality of comb structures in the plurality of comb grooves, wherein each of the plurality of comb structures comprises a respective dielectric liner and a respective conductive filling material portion, the dielectric liner being physically exposed to the cavity in the matrix, the conductive filling material portion being located in the pair of inner comb structures and the pair of outer comb structures and extending continuously, and being laterally surrounded by the dielectric liner.

16. The method for forming a micro-electromechanical system device according to claim 15, wherein: forming the cavity by removing the second portion of the semiconductor matrix material layer; a semiconductor matrix layer, including a third portion of the semiconductor matrix material layer, laterally surrounding the cavity; as well as A movable structure, comprising the first portion of the semiconductor matrix material layer in combination with the pair of inner comb structures, is peeled off from the semiconductor matrix layer. 17 . The method for forming a MEMS device according to claim 16 , wherein each of the plurality of comb grooves extends from the second horizontal surface of the semiconductor matrix material layer toward the first horizontal surface of the semiconductor matrix material layer.

18. The method for forming a MEMS device according to claim 17, further comprising: forming a dielectric liner layer on the physically exposed surfaces of the plurality of comb grooves; After forming the dielectric liner layer, depositing a conductive filling material in the remaining volume of the plurality of comb trenches; as well as removing portions of the conductive filling material from outside the plurality of comb grooves, Each of the dielectric liners includes a remaining portion of the dielectric liner layer, and each of the conductive filling material portions includes a remaining portion of the plurality of conductive filling materials.

19. The method for forming a MEMS device according to claim 16, wherein The MEMS device comprises a MEMS accelerometer; and The combination of the movable structure and the semiconductor matrix layer is bonded to a semiconductor structure, the semiconductor structure comprising a semiconductor substrate, a plurality of field effect transistors located on the semiconductor substrate, and a plurality of metal interconnect structures formed in a plurality of dielectric material layers, wherein the plurality of field effect transistors include the following circuit: the circuit is configured to measure the displacement of the movable structure relative to the pair of outer comb structures and the semiconductor matrix layer by sensing changes in the capacitance of a capacitor structure, the capacitor structure comprising the pair of inner comb structures and the pair of outer comb structures.

20. The method for forming a MEMS device according to claim 17, further comprising: forming an additional semiconductor oxide plate on said first horizontal surface of said layer of semiconductor matrix material; Before forming the plurality of comb grooves, attaching the additional semiconductor oxide plate to a handle substrate, wherein a lateral confinement space is formed between the semiconductor oxide plate and the handle substrate; forming the patterned etch mask layer on the second horizontal surface of the semiconductor matrix material layer by applying an etch mask material layer and forming a plurality of openings through the etch mask material layer, wherein the plurality of openings are formed in a plurality of regions that do not overlap with regions of the plurality of comb structures; as well as An isotropic etchant of the isotropic etching process is applied through the openings in the patterned etch mask layer, wherein the isotropic etchant selectively etches the material of the semiconductor matrix material layer relative to the material of the semiconductor oxide plate and the material of the additional semiconductor oxide plate and relative to the material of the plurality of comb structures in contact with the semiconductor matrix material layer.

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