Wafer-level chip-scale packaging capacitive MEMS sensor

Abstract

The present disclosure relates to a wafer-level chip-scale packaging (WLCSP) microelectromechanical systems (MEMS) sensor, which exhibits both a high sensitivity for detecting a force load and a high dynamic range for capacitance variations. The disclosed WLCSP MEMS sensor includes a substrate structure, an electrode formed on the substrate structure, and a cap structure bonded to and over the substrate structure to provide a sealed cavity, within which the electrode is located. Herein, the cap structure includes a sensing pole vertically aligned with the electrode with an air gap in between. A bottom portion of the sensing pole is conductive and composes a capacitor with the electrode and the air gap in between. The sensing pole is capable of moving vertically based on a force load applied to the cap structure, which allows the capacitor to provide a variety of capacitances.

Description

WAFER-LEVEL CHIP-SCALE PACKAGING CAPACITIVE MEMS SENSORRelated Applications

[0001] This application claims the benefit of provisional patent application serial number 63 / 686,992, filed August 26, 2024, and provisional patent application serial number 63 / 744,991 , filed January 14, 2025, the disclosures of which are hereby incorporated herein by reference in their entireties.Field of the Disclosure

[0002] The present disclosure relates to a wafer-level chip-scale packaging (WLCSP) capacitive microelectromechanical systems (MEMS) sensor, which exhibits both a high sensitivity when detecting a force load and a high dynamic range for capacitance variations.Background

[0003] Wafer-level chip-scale packaging (WLCSP) refers to a technology for packaging an integrated circuit at a wafer level, which allows integration of devices using the smallest possible form factor without requiring extra packaging steps for the devices. Therefore, WLCSP technology offers high-density and small form-factor solutions for mobile or portable devices, such as mobile phones, smart watches, styluses, tablets, GPS navigation devices, and the like.

[0004] For the mobile or portable devices, microelectromechanical systems (MEMS) sensors have been increasingly widely used by virtue of their advantages of small size, low cost, and relatively simple manufacturing processes. Typically, a MEMS sensor includes a moveable microstructure that moves in response to an applied load such as a force, pressure, temperature, acceleration, magnetic field, or the like. Due to the movements of the microstructure, the MEMS sensor, in some applications, is configured to provide a variation in capacitance to indicate the applied load. There is a strong need for a cost-effective MEMS sensor design that utilizes the WLCSP technology and exhibits both a high sensitivity when detecting the applied load and a highdynamic range for capacitance variations. The present disclosure addresses such a need.Summary

[0005] The present disclosure relates to a wafer-level chip-scale packaging (WLCSP) microelectromechanical systems (MEMS) sensor, which exhibits both a high sensitivity to detect a force load and a high dynamic range for capacitance variations. The disclosed WLCSP MEMS sensor includes a substrate structure, an electrode formed on the substrate structure, and a cap structure bonded to and over the substrate structure to provide a sealed cavity, within which the electrode is located. Herein, the substrate structure includes a substrate body, a first via, and a second via, where the first via and the second via are separate from each other and extend vertically through the substrate body. The electrode is electrically connected to the first via within the substrate body. The cap structure includes a sensing pole, a peripheral edge surrounding the sensing pole, and a cap bridge connecting the peripheral edge to the sensing pole. The sensing pole and the peripheral edge extend vertically beyond the cap bridge to define a cap trench horizontally between the sensing pole and the peripheral edge and underneath the cap bridge. The sensing pole is vertically aligned with the electrode with an air gap in between, while the peripheral edge is bonded to the substrate structure and electrically connected to the second via. A bottom portion of the sensing pole is conductive and composes a capacitor with the electrode and the air gap in between. The sensing pole is capable of moving vertically due to bending of the cap bridge caused by a force load applied to the cap structure, which allows the capacitor to provide a variety of capacitances.

[0006] In one embodiment of the WLCSP MEMS sensor, the cap trench is continuous in a horizontal plane.

[0007] In one embodiment of the WLCSP MEMS sensor, in the horizontal plane, the cap trench includes an inner perimeter that has a circle, square, or cushion shape, and an outer perimeter that has a circle, square, or cushion shape.

[0008] According to one embodiment, the WLCSP MEMS sensor further includes a patterned isolation layer with an opening. Herein, the patterned isolation layer is formed on the substrate body, and the opening of the patterned isolation layer is aligned with the first via. The electrode is formed on and confined within the patterned isolation layer, so as to isolate the electrode from the substrate body. The electrode is electrically connected to the first via through the opening of the patterned isolation layer.

[0009] According to one embodiment, the WLCSP MEMS sensor further includes a dielectric layer, which at least extends over a top surface of the electrode, such that the air gap is vertically between the bottom portion of the sensing pole and the dielectric layer.

[0010] In one embodiment of the WLCSP MEMS sensor, the patterned isolation layer and the dielectric layer are formed of silicon dioxide.

[0011] According to one embodiment, the WLCSP MEMS sensor further includes a bonding layer. The peripheral edge of the cap structure is bonded to the substrate structure through the bonding layer. The bonding layer is in contact with the second via, and the cap structure is electrically connected to the second via through the bonding layer.

[0012] In one embodiment of the WLCSP MEMS sensor, the bonding layer is formed of one of gold-silicon, gold-germanium, gold-tin, gold-indium, aluminumsilicon, aluminum-germanium, silicon germanium, and copper-tin.

[0013] In one embodiment of the WLCSP MEMS sensor, the bonding layer is formed of gold, aluminum, or copper.

[0014] In one embodiment of the WLCSP MEMS sensor, the peripheral edge of the cap structure is directly bonded to the substrate structure. The cap structure is electrically connected to the second via.

[0015] In one embodiment of the WLCSP MEMS sensor, the substrate structure further includes a first isolation wall and a second isolation wall, each of which extends vertically through the substrate body. Herein, the first isolation wall and the second isolation wall surround the first via and the second via,respectively, such that the first isolation wall and the second isolation wall isolate the first via and the second via from the substrate body, respectively.

[0016] In one embodiment of the WLCSP MEMS sensor, the first isolation wall and the second isolation wall are formed of silicon dioxide, and the first via and the second via are formed of a metal material.

[0017] In one embodiment of the WLCSP MEMS sensor, the air gap vertically between the bottom portion of the sensing pole and the electrode has a height between 1 pm and 2 pm.

[0018] In one embodiment of the WLCSP MEMS sensor, the cap bridge has a thickness between 1 pm and 50 pm.

[0019] In one embodiment of the WLCSP MEMS sensor, a bottom surface of the peripheral edge extends vertically beyond a bottom surface of the sensing pole, and the substrate body of the substrate structure has a flat top surface, and the electrode is formed on the flat top surface.

[0020] In one embodiment of the WLCSP MEMS sensor, a bottom surface of the peripheral edge and a bottom surface of the sensing pole are coplanar, and the substrate body of the substrate structure has a substrate recess extending from a top surface of the substrate body into the substrate body. The electrode is formed within the substrate recess and on a bottom surface of the substrate recess. The first via extends vertically from the bottom surface of the substrate recess to a bottom surface of the substrate body.

[0021] According to one embodiment, the WLCSP MEMS sensor further includes a redistribution structure formed underneath the substrate structure. The redistribution structure at least includes a dielectric pattern formed directly underneath the substrate body, a first redistribution interconnection, and a second redistribution interconnection. The first redistribution interconnection is connected to the first via of the substrate structure and extends vertically through the dielectric pattern, while the second redistribution interconnection is connected to the second via of the substrate structure and extends vertically through the dielectric pattern.

[0022] According to one embodiment, the WLCSP MEMS sensor further includes a first bump structure and a second bump structure. Herein, the first bump structure and the second bump structure are formed underneath the redistribution structure. The first bump structure is electrically connected to the first redistribution interconnection, such that the electrode on the substrate structure is electrically connected to the first bump through the first via and the first redistribution interconnection. The second bump structure is electrically connected to the second redistribution interconnection, such that the cap structure on the substrate structure is electrically connected to the second bump through the second via and the second redistribution interconnection.

[0023] In one embodiment of the WLCSP MEMS sensor, the first bump structure and the second bump structure are solder bumps or metal pillars.

[0024] In one embodiment of the WLCSP MEMS sensor, the cap structure is formed of doped silicon, the substrate body is formed of silicon, the first via and the second via are through-silicon vias, and the electrode is formed of a metal material or doped silicon.

[0025] According to one embodiment, a method of fabricating a WLCSP MEMS sensor starts with providing a substrate structure, which includes a substrate body, a first via, and a second via. The first via and the second via are separate from each other and extend vertically through the substrate body. Next, an electrode is deposited on the substrate structure, where the electrode is electrically connected to the first via within the substrate body. A cap structure, which includes a sensing pole, a peripheral edge, and a cap bridge, is also provided. Herein, the peripheral edge surrounds the sensing pole, the cap bridge connects the peripheral edge to the sensing pole, and the sensing pole and the peripheral edge extend vertically beyond the cap bridge to define a cap trench horizontally between the sensing pole and the peripheral edge and underneath the cap bridge. The cap structure is then bonded to the substrate structure to provide a sealed cavity, within which the electrode is located. The sensing pole is vertically aligned with the electrode with an air gap in between, while the peripheral edge is bonded to the substrate structure and electrically connected tothe second via. A bottom portion of the sensing pole is conductive and composes a capacitor with the electrode and the air gap in between. The sensing pole is capable of moving vertically due to bending of the cap bridge caused by a force load applied to the cap structure, which allows the capacitor to provide a variety of capacitances.

[0026] In one embodiment of the method, a bottom surface of the peripheral edge and a bottom surface of the sensing pole are coplanar. Providing the substrate structure starts with providing an initial substrate body with a substrate recess, which extends downward from a top surface of the initial substrate body into the initial substrate body and is located horizontally at an interior portion of the initial substrate body. The first via hole and the second via hole are formed to convert the initial substrate body into a substrate body. The first via hole is located in the interior portion of the substrate body and extends downward from a bottom surface of the substrate recess to a bottom surface of the substrate body, and the second via hole is located in a peripheral portion of the substrate body and extends downward from the top surface of the substrate body to the bottom surface of the substrate body. Next, the first via is formed in the first via hole, and the second via is formed in the second via hole. Herein, the electrode deposited on the substrate structure is formed within the substrate recess and on the bottom surface of the substrate recess and electrically connected to the first via.

[0027] In one embodiment of the method, the substrate body of the substrate structure has a flat top surface, and the electrode is formed on the flat top surface. Providing the cap structure starts with providing a cap body with a cap recess, which extends upward from a bottom surface of the cap body into the cap body and is located horizontally at an interior portion of the initial cap body. Next, the cap trench over the cap recess is formed to convert the cap body into the cap structure. Herein, the cap trench extends upward from a periphery of a top surface of the cap recess without penetrating. A first remaining portion of the cap body directly above the top surface of the cap recess and surrounded by the cap trench provides the sensing pole of the cap structure, a second remaining portion of the cap body directly above the cap trench provides the cap bridge of the capstructure, and a third remaining portion of the cap body surrounding the cap recess and the cap trench provides the peripheral edge of the cap structure. A bottom surface of the peripheral edge extends vertically beyond a bottom surface of the sensing pole.

[0028] In one embodiment of the method, the cap structure is bonded to the substrate structure by eutectic bonding, metal-to-metal thermal compression bonding, metal-to-metal diffusion bonding, or silicon fusion bonding.

[0029] In another aspect, any of the foregoing aspects individually or together, and / or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various features and elements as disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein.

[0030] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.Brief Description of the Drawing Figures

[0031] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0032] Figures 1 A-1 C illustrate an exemplary implementation of a wafer-level chip-scale packaging (WLCSP) microelectromechanical systems (MEMS) sensor according to some embodiments of the present disclosure.

[0033] Figure 2 illustrates an alternative implementation of the WLCSP MEMS sensor according to some embodiments of the present disclosure.

[0034] Figures 3A-3N illustrate an exemplary method of fabricating and packaging steps to provide the WLCSP MEMS sensor shown in Figure 1 C.

[0035] Figures 4A-4N illustrate an exemplary method of fabricating and packaging steps to provide the WLCSP MEMS sensor shown in Figure 2.

[0036] It will be understood that for clear illustrations, Figures 1 A-4N may not be drawn to scale.Detailed Description

[0037] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0038] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] It will be understood that when an element such as a layer, region, or substrate is referred to as being "on" or extending "onto" another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being "over" or extending "over" another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly over" or extending "directly over" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or"coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0040] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

[0041] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including" when used herein specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0043] Embodiments are described herein with reference to schematic illustrations of embodiments of the disclosure. As such, the actual dimensions of the layers and elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are expected. For example, a region illustrated or described assquare or rectangular can have rounded or curved features, and regions shown as straight lines may have some irregularity. Thus, the regions illustrated in the figures are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the disclosure. Additionally, sizes of structures or regions may be exaggerated relative to other structures or regions for illustrative purposes and, thus, are provided to illustrate the general structures of the present subject matter and may or may not be drawn to scale. Common elements between figures may be shown herein with common element numbers and may not be subsequently redescribed.

[0044] The present disclosure relates to a wafer-level chip-scale packaging (WLCSP) microelectromechanical systems (MEMS) sensor, which is configured to sense an applied force load (e.g., a user’s finger applying pressure) to dynamically change its capacitance. The disclosed WLCSP MEMS sensor is capable of achieving high sensitivity in detecting the applied force load and a high dynamic range for capacitance variations. Figures 1 A-1 C illustrate an exemplary implementation of a WLCSP MEMS sensor 10 according to some embodiments. Figure 1 A shows an isometric view of the WLCSP MEMS sensor 10, which includes a substrate structure 12 and a cap structure 14 bonded to and over the substrate structure 12. Figure 1 B shows a bottom view of the cap structure 14 of the WLCSP MEMS sensor 10. Figure 1 C shows a detailed cross- sectional view of the WLCSP MEMS sensor 10 along a dashed line A-A’ in Figure 1A.

[0045] Besides the substrate structure 12 and the cap structure 14, the WLCSP MEMS sensor 10 also includes an electrode 16 formed on the substrate structure 12 and covered by the cap structure 14, a redistribution structure 18 underneath the substrate structure 12, and a number of bump structures 20 underneath the redistribution structure 18. In detail, the substrate structure 12 includes a substrate body 22 and a number of vias 24 extending vertically through the substrate body 22. In some applications, the substrate body 22 may be formed of silicon, and the vias 24 accordingly are through-silicon vias (TSVs)and may be formed of a conductive material, such as copper, tungsten, or other metal materials. To prevent electrical leakage, each via 24 is isolated from the substrate body 22 by an isolation wall 26, which also extends vertically through the substrate body 22 and surrounds a corresponding via 24. Each isolation wall 26 may be formed of a dielectric material, such as silicon dioxide. For the purpose of this illustration, the substrate structure 12 includes two vias 24: a first via 24-1 located in an interior portion of the substrate body 22, and a second via 24-2 located in a peripheral portion of the substrate body 22, and includes two isolation walls 26: a first isolation wall 26-1 and a second isolation wall 26-2, accordingly. In different applications, the substrate structure 12 may include more vias 24 located in different portions of the substrate body 22.

[0046] The electrode 16 is formed over a top surface of the substrate body 22 through a patterned isolation layer 28 and at least covers and is electrically connected to one via 24 (e.g., the first via 24-1 ). Herein, the patterned isolation layer 28 has an opening 30 aligned with the first via 24-1 , and the electrode 16 is electrically connected to (e.g., in contact with) the first via 24-1 through the opening 30. The patterned isolation layer 28 is configured to prevent electrical leakage from the electrode 16 to the substrate body 22. The electrode 16 may be formed of a metal material (such as copper, tungsten, etc.) or doped polycrystalline silicon, and the patterned isolation layer 28 may be formed of silicon dioxide.

[0047] The cap structure 14 includes a sensing pole 32, a peripheral edge 34 surrounding the sensing pole 32, and a cap bridge 36 connecting the peripheral edge 34 to the sensing pole 32. A top surface of the sensing pole 32, a top surface of the peripheral edge 34, and the top surface of the cap bridge 36 are coplanar. A combination of the top surface of the sensing pole 32 and the top surface of the cap bridge 36 provides a sensing area SA of the cap structure 14, herein and hereafter, SA refers to an area, where a force load is typically applied to the WLCSP MEMS sensor 10. The sensing pole 32 and the peripheral edge 34 extend vertically beyond a bottom surface of the cap bridge 36 to define a cap trench 38 underneath the cap bridge 36 and horizontally between the sensingpole 32 and the peripheral edge 34 (i.e. the cap trench 38 directly surrounds the sensing pole 32, and the peripheral edge 34 directly surrounds the cap trench 38). The sensing pole 32 is vertically aligned with the electrode 16 with an air gap 40 in between, while the peripheral edge 34 is bonded to a periphery of the top surface of the substrate body 22. The bonding of the cap structure 14 and the substrate structure 12 provides a sealed cavity 44, which is a combination of the cap trench 38, the air gap 40, and gaps horizontally surrounding the electrode 16.

[0048] The peripheral edge 34 may be connected to the periphery of the top surface of the substrate body 22 by eutectic bonding, metal-to-metal thermal compression bonding, metal-to-metal diffusion bonding, or silicon fusion bonding (more details are described in the following paragraphs). When the peripheral edge 34 is connected to the periphery of the top surface of the substrate body 22 by the eutectic bonding or the metal-to-metal (thermal compression / diffusion) bonding, there is a bonding layer 42 vertically between the peripheral edge 34 and the periphery of the top surface of the substrate body 22. The gaps surrounding the electrode 16 are horizontally between the bonding layer 42 and the electrode 16. The bonding layer 42 may be formed of a eutectic bonding layer, such as, but not limited to, gold-silicon, gold-germanium, gold-tin, goldindium, aluminum-silicon, aluminum-germanium, silicon germanium, or coppertin. In some applications, the bonding layer 42 may be formed of a metallic material such as gold, copper, aluminum etc. When the peripheral edge 34 is connected to the periphery of the top surface of the substrate body 22 by the silicon fusion bonding, the bonding layer 42 is omitted (not shown). The gaps surrounding the electrode 16 are horizontally between the peripheral edge 34 and the electrode 16.

[0049] For the purpose of this illustration, the sensing pole 32 is cylindrical. The cap trench 38 is continuous and, in a horizontal plane, has a circle shape in an inner perimeter and a cushion shape in an outer perimeter. A horizontal size of the sensing pole 32 is smaller than a horizontal size of the electrode 16 (i.e., the sensing pole 32 is horizontally confined in the electrode 16), while theelectrode 16 is confined in the outer perimeter of the cap trench 38 without touching the bonding layer 42 or the peripheral edge 34 of the cap structure 14. The peripheral edge 34 covers and is electrically connected to the second via 24- 2 (may be through the bonding layer 42). In different applications, the sensing pole 32 may have various shapes, such as a cube, a truncated cone, or any other appropriate shape. Correspondingly, the cap trench 38 may have an inner perimeter in the horizontal plane with a shape that varies accordingly, such as a square, a circle, a cushion, or any other appropriate shape. In addition, the cap trench 38 may have a different shape in the outer perimeter, like a square, a circle, or any other appropriate shape. The horizontal size of the sensing pole 32 may be larger than or equal to the horizontal size of the electrode 16. The peripheral edge 34 may cover and be electrically connected to more vias 24 through the bonding layer 42.

[0050] Herein, the entire cap structure 14 may be formed of doped silicon to provide conductivity, while the sensing pole 32, particularly a bottom portion of the sensing pole 32, may be further heavily doped to have a higher conductivity than the rest of the portions of the cap structure 14. In some applications, the bottom portion of the sensing pole 32 may be metalized (not shown). As such, the electrode16, the bottom portion of the sensing pole 32, and the air gap 40 in between form a capacitor 46. A capacitance of the capacitor 46 depends on an overlap area of the electrode 16 and the bottom portion of the sensing pole 32, a distance between the electrode 16 and the bottom portion of the sensing pole 32 (i.e. , a height of the air gap 40), and a permittivity of air.

[0051] The cap bridge 36 has a relatively low thickness between 1 pm and 50 pm and is configured to function as a spring that is deformed / bent in response to a force load applied to the sensing area SA of the cap structure 14. Due to the deformation and bending of the cap bridge 36, the sensing pole 32 connected to the cap bridge 36 moves towards the electrode 16 to change the distance between the electrode 16 and the bottom portion of the sensing pole 32 (i.e., the height of the air gap 40), so as to change the capacitance of the capacitor 46. With a different amount of the force load applied to the sensing area SA of thecap structure 14, the cap bridge 36 will have a different curvature, and the sensing pole 32 connected to the cap bridge will move towards the electrode 16 by a different amount. Therefore, the distance between the electrode16 and the bottom portion of the sensing pole 32 will vary, and the capacitance of the capacitor 46 will vary accordingly. If the overlap area of the electrode 16 and the bottom portion of the sensing pole 32 is relatively large, a small distance change may still lead to a relatively big change in capacitance.

[0052] In order to avoid electrical shorting between the electrode 16 and the sensing pole 32 (i.e. , the air gap 40 disappears) due to an excess force load, the electrode 16 is covered by a dielectric layer 48, which at least extends over a top surface of the electrode 16 and optionally covers sides of the electrode 16 and is connected with the patterned isolation layer 28. Therefore, when the excess force load occurs, the bottom portion of the sensing pole 32 will be in contact with the dielectric layer 48 rather than the electrode 16, and the capacitor 46 can still work properly.

[0053] When no force load is applied to the cap structure 14, a height H1 of the air gap 40 directly between the sensing pole 32 and the dielectric layer 48 above the electrode 16 may be 1 pm ~2 pm, which can be achieved by the sensing pole 32 being shorter than the peripheral edge 34 (i.e., a bottom surface of the peripheral edge 34 is vertically beyond a bottom surface of the sensing pole 32). The amount by which the sensing pole 32 is shorter than the peripheral edge 34 is based on a combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48 underneath the sensing pole 32 and optionally on a thickness of the bonding layer 42 between the peripheral edge 34 and the substrate structure 12.

[0054] The redistribution structure 18, which is formed underneath the substrate structure 12, includes a number of redistribution interconnections 50 and a dielectric pattern 52. Herein, each redistribution interconnection 50 is connected to a corresponding via 24 within the substrate body 22 and extends vertically through the dielectric pattern 52. The dielectric pattern 52 is formedunderneath the substrate structure 12 and surrounds each redistribution interconnection 50.

[0055] Furthermore, the bump structures 20, which allow for external connections of the WLCSP MEMS sensor 10, are formed at a bottom surface of the redistribution structure 18 and electrically coupled to the redistribution interconnections 50, respectively. The bump structures 20 are separate from each other. The redistribution interconnections 50 are configured to connect the bump structures 20 to the vias 24 of the substrate structure 12, respectively. For the purpose of this illustration, a first redistribution interconnection 50-1 is configured to connect a first bump structure 20-1 to the first via 24-1 , which is electrically connected to the electrode 16, while a second redistribution interconnection 50-2 is configured to connect a second bump structure 20-2 to the second via 24-2, which is electrically connected to the cap structure 14. The capacitor 46 provided by the WLCSP MEMS sensor 10 can be electrically connected into circuitry by adding different electrical voltages to the first and second bump structures 20-1 and 20-2. For a non-limiting example, a non-zero voltage is added to the first bump structure 20-1 / the electrode 16, while the second bump structure 20-2 / the cap structure 14 is grounded (i.e. , the sensing pole 32 is grounded). In different applications, the redistribution structure 18 may include more redistribution interconnections 50, and there will be correspondingly more bump structures 20. The redistribution interconnections 50 may be formed of copper or other suitable metals. The dielectric pattern 52 may be formed of benzocyclobutene (BCB), polyimide, or other dielectric materials. The bump structures 20 may be solder balls or metal (e.g., copper) pillars.

[0056] In some applications, to achieve the air gap 40 between the sensing pole 32 and the electrode 16, the substrate body 22 may include a substrate recess 54 to accommodate the electrode 16, as illustrated in Figure 2. Herein, the substrate recess 54 extends downward from the top surface of the substrate body 22 into the substrate body 22 and is surrounded by the peripheral portion of the substrate body 22. Each via 24 still extends vertically through the substrate body 22. In this illustration, the first via 24-1 and the first isolation wall 26-1located in the interior portion of the substrate body 22 extend vertically from a bottom surface of the substrate body 22 to a bottom surface of the substrate recess 54, while the second via 24-2 and the second isolation wall 26-2 located in the peripheral portion of the substrate body 22 extend vertically from the bottom surface of the substrate body 22 to the top surface of the substrate body 22. The electrode 16 sits within the substrate recess 54 and is formed over the bottom surface of the substrate recess 54 through the patterned isolation layer 28. The electrode 16 is still electrically connected to the first via 24-1 through the opening 30 of the patterned isolation layer 28. In addition, the electrode 16 is still covered by the dielectric layer 48, which at least extends over the top surface of the electrode 16 and optionally covers the sides of the electrode 16 and is connected with the patterned isolation layer 28. In different applications, the substrate structure 12 may include more vias 24 extending vertically from the bottom surface of the substrate body 22 to the bottom surface of the substrate recess 54, and / or more vias 24 extending vertically from the bottom surface of the substrate body 22 to the top surface of the substrate body 22.

[0057] The cap structure 14 still includes the sensing pole 32 vertically aligned with the electrode 16 with the air gap 40 in between, the peripheral edge 34 bonded to the peripheral portion of the substrate body 22 (by the eutectic bonding, the metal-to-metal thermal compression bonding, the metal-to-metal diffusion bonding, or the silicon fusion bonding), and the cap bridge 36 connecting the peripheral edge 34 to the sensing pole 32. The sensing pole 32 and the peripheral edge 34 still extend vertically beyond the bottom surface of the cap bridge 36 to define the cap trench 38 underneath the cap bridge 36 and horizontally between the sensing pole 32 and the peripheral edge 34. The conductive bottom portion of the sensing pole 32, the aligned electrode16, and the air gap 40 in between still form the capacitor 46. The bonding of the cap structure 14 and the substrate structure 12 provides the sealed cavity 44, which is a combination of the cap trench 38, the air gap 40, and the substrate recess 54.

[0058] Herein, the sensing pole 32 and the peripheral edge 34 may have a same height (i.e., the bottom surface of the peripheral edge 34 and the bottom surface of the sensing pole 32 are at a same horizontal plane). To achieve the air gap 40 with a height of 1 pm ~2 pm directly between the sensing pole 32 and the dielectric layer 48 above the electrode 16 when no force load is applied to the cap structure 14, a depth of the substrate recess 54 needs to be carefully calculated. The depth of the substrate recess 54 is based on the combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48 underneath the sensing pole 32, and optionally on the thickness of the bonding layer 42 between the peripheral edge 34 and the substrate structure 12.

[0059] When a force load is applied to the cap structure 14, the cap bridge 36 of the cap structure 14 will be deform ed / bent, which will make the sensing pole 32 move towards the electrode 16 to change the distance between the sensing pole 32 and the dielectric layer 48 / the electrode16 (i.e., the height of the air gap 40). As such, the capacitance of the capacitor 46 (provided by the combination of the conductive bottom portion of the sensing pole 32, the aligned electrode 16, and the air gap 40) changes. With different amounts of the force load applied to the cap structure 14, the cap bridge 36 will have different curvatures, the distance between the bottom portion of the sensing pole 32 and the dielectric layer 48 / the electrode 16 will vary, and the capacitance of the capacitor 46 will therefore vary.

[0060] Figures 3A-3N provide an exemplary method of fabricating and packaging steps to provide the WLCSP MEMS sensor 10 shown in Figure 1 C. Although the exemplary steps are illustrated in a series, the exemplary steps are not necessarily order dependent. Some steps may be done in a different order than that presented. Further, processes within the scope of this disclosure may include fewer or more steps than those illustrated in Figures 3A-3N.

[0061] Initially, an initial substrate body 22IN is provided as illustrated in Figure 3A. The initial substrate body 22IN may be formed of silicon. Next, the substrate body 22 is converted from the initial substrate body 22IN by forming a number of via holes 56 extending vertically through the initial lid body 22IN, asillustrated in Figure 3B. The number and the locations of the via holes 56 may be determined based on the size and location of the electrode 16 subsequently formed on the substrate body 22 and / or the size and shape of the cap structure 14 subsequently bonded to the substrate body 22. For the purpose of this illustration, there are two via holes 56: a first via hole 56-1 located in the interior portion of the substrate body 22, and a second via hole 56-2 located in the peripheral portion of the substrate body 22. Each via hole 56 may have a cylindrical shape. In different applications, there might be more via holes 56 located in different portions of the substrate body 22, and each via hole 56 may have a different appropriate shape. The via holes 56 may be formed by a drilling process and / or a punching process.

[0062] The isolation walls 26 are then formed inside the via holes 56, respectively, as illustrated in Figure 3C. Each isolation wall 26 directly covers an entire interior surface of a corresponding via hole 56. The isolation walls 26 may be formed of a dielectric material, such as silicon dioxide, by a deposition process. After the isolation walls 26 are formed, each via hole 56 is filled with a conductive material (such as copper, tungsten, or other metal materials) to form one via 24 extending vertically through the substrate body 22 and to provide the substrate structure 12, as illustrated in Figure 3D. Herein, each via 24 is isolated from the substrate body 22 by a corresponding isolation wall 26. The first via 24- 1 and the first isolation wall 26-1 are located in the first via hole 56-1 , while the second via 24-2 and the second isolation wall 26-2 are located in the second via hole 56-2.

[0063] Subsequently, the patterned isolation layer 28 with the opening 30 is formed over the top surface of the substrate structure 12 / substrate body 22, as illustrated in Figure 3E. The patterned isolation layer 28 is disposed at a position where the first via 24-1 is exposed through the opening 30 of the patterned isolation layer 28. The patterned isolation layer 28 may be formed of a dielectric material, such as silicon dioxide, by a deposition process.

[0064] If the substrate structure 12 will be bonded to the cap structure 14 by the eutectic bonding in a subsequent step, the bonding layer 42 may be appliedon the top surface of the substrate structure 12 / substrate body 22, surrounding the patterned isolation layer 28 without contacting the patterned isolation layer 28, as illustrated in Figure 3F. The horizontal size and position of the bonding layer 42 on the top surface of the substrate body 22 corresponds to the size and shape of the peripheral edge 34 of the cap structure 14 subsequently bonded to the substrate structure 12. In this illustration, the bonding layer 42 is located at the periphery of the top surface of the substrate structure 12 / substrate body 22 and covers and contacts the second via 24-2. The bonding layer 42 may be formed of, but not limited to gold-silicon, gold-germanium, gold-tin, gold-indium, aluminum-silicon, aluminum-germanium, silicon germanium, or copper-tin by a deposition process. An applied amount of the bonding layer 42 needs to ensure reliable bonding between the substrate structure 12 and the cap structure 14 in a subsequent step.

[0065] If the substrate structure 12 will be bonded to the cap structure 14 by the metal-to-metal (thermal compression / diffusion) bonding in a subsequent step, a bottom bonding layer 42B may be applied on the top surface of the substrate structure 12 / substrate body 22, surrounding the patterned isolation layer 28 without contacting the patterned isolation layer 28. The bottom bonding layer 42B is a portion of the final bonding layer 42, and may be formed of, but not limited to gold, aluminum, or copper by a deposition process. If the substrate structure 12 will be bonded to the cap structure 14 by the silicon fusion bonding, there is no need to form the bonding layer 42. The top surface of the substrate structure 12 / substrate body 22 is cleaned and conditioned (not shown).

[0066] After the patterned isolation layer 28 is formed, the electrode 16 is deposited over the substrate structure 12 through the patterned isolation layer 28, so that the electrode 16 can be in contact with the first via 24-1 through the opening of the patterned isolation layer 28, as illustrated in Figure 3G. The electrode 16 is confined within the patterned isolation layer 28 and is not in contact with the substrate body 22. In other words, the patterned isolation layer 28 isolates the electrode 16 from the substrate body 22 and allows the electrode 16 to be in contact with the first via 24-1 . The electrode 16 may be formed of ametal material (such as copper, tungsten, etc..) or doped polycrystalline silicon by a deposition process. In order to avoid electrical shorting related to the electrode 16 (i.e., electrical shorting between the electrode 16 and the sensing pole 32 as described above), the dielectric layer 48 is deposited to cover the electrode 16, as illustrated in Figure 3H. The dielectric layer 48 at least extends over the top surface of the electrode 16 and optionally covers the sides of the electrode 16 and is connected with the patterned isolation layer 28. If the bonding layer 42 / the bottom bonding layer 42B is present, the combination of the patterned isolation layer 28, the electrode 16 and the dielectric layer 48 may be surrounded by the bonding layer 42 / the bottom bonding layer 42B without contacting the bonding layer 42 / the bottom bonding layer 42B, and has a combined thickness greater than or less than the thickness of the bonding layer 42 / the bottom bonding layer 42B.

[0067] With reference to Figures 3I-3K, the cap structure 14 is provided according to some embodiments of the present disclosure. Although the processing steps are illustrated in a series, the processing steps are not necessarily order dependent. Some steps may be done in a different order than that presented. Further, the processing steps within the scope of this disclosure may include fewer or more steps than those illustrated in Figures 3I-3K. A cap body 58 is first provided, as illustrated in Figure 3I. The cap body 58 may be formed of doped silicon to provide conductivity.

[0068] Next, a cap recess 60 is formed at a bottom portion of the cap body 58, as illustrated in Figure 3J. The cap recess 60 extends upward from a bottom surface of the cap body 58 into the cap body 58. A horizontal location and size of the cap recess 60 may be determined based on the horizontal location and size of the electrode 16 on the substrate structure 12, respectively. The horizontal location of the cap recess 60 must be vertically matched with the electrode 16, and the horizontal size of the cap recess 60 must be greater than the electrode 16. Furthermore, a depth of the cap recess 60 in the cap structure 14 is determined based on the combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48 and optionally on the thickness of thebonding layer 42. A combination of the depth of the cap recess 60 and the thickness of the bonding layer 42 (if it exists) must be greater than the combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48. The cap recess 60 may be formed by a wet / dry etching process.

[0069] The cap trench 38 is then formed over the cap recess 60 to convert the cap body 58 with the cap recess 60 into the cap structure 14, as illustrated in Figure 3K. The cap trench 38 is formed by selectively removing a portion of the cap body 58 directly above the cap recess 60. The cap trench 38 is connected to the cap recess 60, is continuous in the horizontal plane (e.g., a closed loop), and extends upwards from a periphery of a top surface of the cap recess 60 without penetrating. The inner perimeter and the outer perimeter of the cap trench 38, in the horizontal plane, may each have a different shape, such as a circle, square, cushion, or any other appropriate shape. A first remaining portion of the original cap body 58 directly above the top surface of the cap recess 60 and surrounded by the cap trench 38 provides the sensing pole 32 of the cap structure 14. Since the horizontal positions of the cap recess 60 and the electrode 16 are matched, the sensing pole 32 directly above the cap recess 60 also matches the electrode 16 in horizontal positions. Due to the shape of the inner perimeter of the cap trench 38, the sensing pole 32 may have a different shape, such as a cylindrical shape, a cube, a truncated cone, or any other appropriate shape. A second remaining portion of the original cap body 58 directly above the cap trench 38 provides the cap bridge 36 of the cap structure 14. In addition, a third remaining portion of the original cap body 58 surrounding the cap recess 60 and the cap trench 38 provides the peripheral edge 34 of the cap structure 14. The sensing area SA of the cap structure 14 (i.e. , the combination of the top surface of the sensing pole 32 and the top surface of the cap bridge 36) may be defined by the location and horizontal size of the cap recess 60.

[0070] The cap bridge 36, which connects the sensing pole 32 and the peripheral edge 34 and covers the cap trench 38, has a thickness between 1 pm and 50 pm. The cap bridge 36 is configured to function as a spring that is deformed / bent in response to a force load applied to the sensing area SA of thecap structure 14. Because of the cap recess 60, the sensing pole 32 is shorter than the peripheral edge 34 (i.e. , the bottom surface of the peripheral edge 34 is vertically beyond the bottom surface of the sensing pole 32). Optionally, the bottom portion of the sensing pole 32 is further heavily doped or metalized to ensure conductivity (not shown).

[0071] In addition, if the cap structure 14 will be bonded to the substrate structure 12 by the metal-to-metal (thermal compression / diffusion) bonding in the subsequent step, the peripheral edge 34 may be metalized with a top bonding layer (not shown), which may be formed of (but not limited to) gold, aluminum, or copper corresponding to the bottom bonding layer 42B. This top bonding layer at the bottom surface of the peripheral edge 34 will also be a portion of the final bonding layer 42 (not shown).

[0072] Once the cap structure 14 and the substrate structure 12 are completed, and the electrode is deposited on the substrate structure 12, the cap structure 14 is bonded to the substrate structure 12, as illustrated in Figure 3L. The cap structure 14 is connected to the substrate structure 12 by the eutectic bonding, the metal-to-metal thermal compression bonding, the metal-to-metal diffusion bonding, or the silicon fusion bonding. The peripheral edge 34 of the cap structure 14 is connected to the periphery of the top surface of the substrate body 22 (possibly through the bonding layer 42) to provide the sealed cavity 44 between the substrate structure 12 and the cap structure 14. Herein, the sealed cavity 44 is formed by merging the cap trench 38, the cap recess 60, and gaps horizontally surrounding the electrode 16. In addition, the cap structure 14 is electrically connected to the second via 24-2 of the substrate structure 12 (possibly through the bonding layer 42).

[0073] The sensing pole 32 is vertically aligned with the electrode 16. Since the combination of the depth of the cap recess 60 and the thickness of the bonding layer 42 (if it exists) is greater than the combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48, the air gap 40 (without applied force load) exists vertically between the sensing pole 32 and the dielectric layer 48 above the electrode 16. The electrode 16, theconductive bottom portion of the sensing pole 32, and the air gap 40 in between form the capacitor 46. When a force load is applied to the sensing area SA of the cap structure 14, the cap bridge 36 deforms / bends in response to the force load applied to the cap structure 14 and causes the sensing pole 32 connected to the cap bridge 36 to move towards the electrode 16, which changes the distance between the electrode16 and the bottom portion of the sensing pole 32 (i.e. , change the height of the air gap 40), and thereby provides a certain capacitance of the capacitor 46. With a different amount of the force load applied to the sensing area SA of the cap structure 14, the cap bridge 36 will have a different curvature, and the sensing pole 32 connected to the cap bridge will move towards the electrode 16 by a different amount. Therefore, the distance between the electrode16 and the bottom portion of the sensing pole 32 will vary, and the capacitance of the capacitor 46 will vary accordingly. Herein, the dielectric layer 48 prevents electrical shorting between the electrode 16 and the sensing pole 32 (i.e., the air gap 40 disappears) due to an excess force load. When the excess force load occurs, the bottom portion of the sensing pole 32 will be in contact with the dielectric layer 48 rather than the electrode 16, and the capacitor 46 can still work properly.

[0074] Figure 3M shows that the redistribution structure 18 is formed underneath the substrate structure 12, which includes a number of the redistribution interconnections 50 and the dielectric pattern 52. Herein, the dielectric pattern 52 fully covers and is in contact with the bottom surface of the substrate body 22, and partially covers and is in contact with each via 24. The redistribution interconnections 50 are separate from each other, and each redistribution interconnection 50 extends vertically through the dielectric pattern 52 and is connected to a corresponding via 24. The redistribution interconnections 50 may be formed of copper or other suitable metals, while the dielectric pattern 52 may be formed of BCB, polyimide, or other dielectric materials.

[0075] Lastly, the bump structures 20 are formed at the bottom surface of the redistribution structure 18 to complete the WLCSP MEMS sensor 10, asillustrated in Figure 3N. The bump structures 20 are separate from each other, and each bump structure 20 is electrically coupled to a corresponding redistribution interconnection 50. As such, in this illustration, the electrode 16 is electrically connected to the first bump structure 20-1 through the first via 24-1 in the substrate structure 12 and the first redistribution interconnection 50-1 in the redistribution structure 18, while the cap structure 14 is electrically connected to the second bump structure 20-2 through the second via 24-2 in the substrate structure 12 and the second redistribution interconnection 50-2 in the redistribution structure 18. By adding different electrical voltages to the first and second bump structures 20-1 and 20-2, the capacitor 46 composed of the electrode 16 and the sensing pole 32 of the cap structure 14 can operate properly. For a non-limiting example, a non-zero voltage is added to the first bump structure 20-1 / the electrode 16, while the second bump structure 20-2 / the cap structure 14 is grounded (i.e., the sensing pole 32 is grounded).

[0076] Figures 4A-4N provide an alternative exemplary method of fabricating and packaging steps to provide the WLCSP MEMS sensor 10 shown in Figure 2. Although the exemplary steps are illustrated in a series, the exemplary steps are not necessarily order dependent. Some steps may be done in a different order than that presented. Further, processes within the scope of this disclosure may include fewer or more steps than those illustrated in Figures 4A-4N.

[0077] Initially, the initial substrate body 22IN is provided as illustrated in Figure 4A. The initial substrate body 22IN may be formed of silicon. Next, the substrate recess 54 is formed at a top portion of the initial substrate body 22IN, as illustrated in Figure 4B. The substrate recess 54 extends downwards from the top surface of the initial substrate body 22IN into the initial substrate body 22IN, and is located horizontally at the interior portion of the initial substrate body 22IN. Dimensions of the substrate recess 54 may be determined based on the size of the electrode 16, which is subsequently deposited within the substrate recess 54. The horizontal size of the substrate recess 54 must be greater than the horizontal size of the electrode 16. The substrate recess 54 may be formed by a wet / dry etching process.

[0078] A number of the via holes 56, each of which extends vertically through the initial substrate body 22IN, are then formed to convert the initial substrate body 22IN into the substrate body 22, as illustrated in Figure 4C. The number and the locations of the via holes 56 may be determined based on the horizontal size and location of the electrode 16 subsequently deposited within the substrate recess 54 and the size and shape of the cap structure 14 subsequently bonded to the substrate body 22. In this illustration, the first via hole 56-1 is located in the interior portion of the substrate body 22 and extends downward from the bottom surface of the substrate recess 54 to the bottom surface of the substrate body 22, while the second via hole 56-2 is located in the peripheral portion of the substrate body 22 and extends downward from the top surface of the substrate body 22 to the bottom surface of the substrate body 22. Each via hole 56 may have a cylindrical shape. In different applications, there might be more via holes 56 located in different portions of the substrate body 22, and each via hole 56 may have a different appropriate shape. The via holes 56 may be formed by a drilling process and / or a punching process.

[0079] Subsequently, the isolation walls 26 are formed inside the via holes 56, respectively, as illustrated in Figure 4D. Each isolation wall 26 directly covers the entire interior surface of a corresponding via hole 56. The isolation walls 26 may be formed of a dielectric material, such as silicon dioxide, by a deposition process. After the isolation walls 26 are formed, each via hole 56 is filled with a conductive material (such as copper, tungsten, or other metal materials) to form one via 24 extending vertically through the substrate body 22 and to provide the substrate structure 12, as illustrated in Figure 4E. Herein, each via 24 is isolated from the substrate body 22 by a corresponding isolation wall 26. In this illustration, the first via 24-1 and the first isolation wall 26-1 are located in the first via hole 56-1 and extend downwards from the bottom surface of the substrate recess 54 to the bottom surface of the substrate body 22. The second via 24-2 and the second isolation wall 26-2 are located in the second via hole 56-2 and extend downwards from the top surface of the substrate body 22 to the bottom surface of the substrate body 22.

[0080] The patterned isolation layer 28 with the opening 30 is then deposited on the bottom surface of the substrate recess 54, as illustrated in Figure 4F. The patterned isolation layer 28 is located such that the first via 24-1 is exposed through the opening 30 of the patterned isolation layer 28 at the bottom of the substrate recess 54. The patterned isolation layer 28 may be formed of a dielectric material, such as silicon dioxide, by a deposition process.

[0081] If the substrate structure 12 is bonded to the cap structure 14 by the eutectic bonding in a subsequent step, the bonding layer 42 may be applied on the periphery of the top surface of the substrate structure 12 / substrate body 22, surrounding the substrate recess 54 without extending into the substrate recess 54, as illustrated in Figure 4G. The horizontal size and position of the bonding layer 42 on the top surface of the substrate body 22 corresponds to the size and shape of the peripheral edge 34 of the cap structure 14 subsequently bonded to the substrate structure 12. In this illustration, the bonding layer 42 covers and contacts the second via 24-2. The bonding layer 42 may be formed of, but not limited to gold-silicon, gold-germanium, gold-tin, gold-indium, aluminum-silicon, aluminum-germanium, silicon germanium, or copper-tin by a deposition process. An applied amount of the bonding layer 42 needs to ensure reliable bonding between the substrate structure 12 and the cap structure 14 in a subsequent step.

[0082] If the substrate structure 12 is bonded to the cap structure 14 by the metal-to-metal (thermal compression / diffusion) bonding in a subsequent step, the bottom bonding layer 42B may be applied on the periphery of the top surface of the substrate structure 12 / substrate body 22, surrounding the substrate recess 54 without extending into the substrate recess 54. The bottom bonding layer 42B is a portion of the final bonding layer 42, and may be formed of, but not limited to gold, aluminum, or copper by a deposition process. If the substrate structure 12 is bonded to the cap structure 14 by the silicon fusion bonding, there is no need to form the bonding layer 42. The top surface of the substrate structure 12 / substrate body 22 is cleaned and conditioned (not shown).

[0083] After the patterned isolation layer 28 is formed, the electrode 16 is deposited within the substrate recess 54 and over the bottom surface of the substrate recess 54 through the patterned isolation layer 28, as illustrated in Figure 4H. Accordingly, the electrode 16 can be in contact with the first via 24-1 through the opening of the patterned isolation layer 28. The electrode 16 is confined within the patterned isolation layer 28 and is not in contact with any portion of the substrate body 22. In other words, the patterned isolation layer 28 isolates the electrode 16 from the substrate body 22 and allows the electrode 16 to be in contact with the first via 24-1 . The electrode 16 may be formed of a metal material (such as copper, tungsten, etc..) or doped polycrystalline silicon, by a deposition process.

[0084] In order to avoid electrical shorting related to the electrode 16 (i. e. , electrical shorting between the electrode 16 and the sensing pole 32 as described above), the dielectric layer 48 is deposited to cover the electrode 16, as illustrated in Figure 4I. The dielectric layer 48 at least extends over the top surface of the electrode 16 and optionally covers the sides of the electrode 16 and is connected with the patterned isolation layer 28. The combination of the patterned isolation layer 28, the electrode 16 and the dielectric layer 48 is horizontally confined within the substrate recess 54. If the bonding layer 42 / the bottom bonding layer 42B is present, the combination of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48 is surrounded by the bonding layer 42 / the bottom bonding layer 42B without contacting the bonding layer 42 / the bottom bonding layer 42B, and has a combined thickness greater than or less than the depth of the substrate recess 54. The depth of the substrate recess 54 needs to be carefully calculated. A combination of the depth of the substrate recess 54 and the thickness of the bonding layer 42 (if it exists) must be greater than the combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48.

[0085] With reference to Figures 4J and 4K, the cap structure 14 is provided according to some embodiments of the present disclosure. A cap body 58 is firstly provided, as illustrated in Figure 4J. The cap body 58 may be formed ofdoped silicon to provide conductivity. Next, the cap trench 38 is formed by selectively removing a portion of the cap body 58 to convert the cap body 58 into the cap structure 14, as illustrated in Figure 4K. The cap trench 38 is continuous in the horizontal plane (e.g., a closed loop) and extends from a bottom surface of the original cap body 58 toward a top surface of the original cap body 58 without penetrating. A first remaining portion of the original cap body 58 surrounded by the cap trench 38 provides the sensing pole 32 of the cap structure 14. The inner perimeter of the cap trench 38 is a side surface of the sensing pole 32. A second remaining portion of the original cap body 58 directly above the cap trench 38 provides the cap bridge 36 of the cap structure 14. And a third remaining portion of the original cap body 58 surrounding the cap trench 38 provides the peripheral edge 34 of the cap structure 14. Herein, the horizontal size and position of the cap trench 38 is determined based on the horizontal location and size of the electrode 16. The cap trench 38 is shaped and located such that the sensing pole 32 is vertically aligned with the electrode 16 after the cap structure 14 is bonded to the substrate structure 12. The bottom surface of the sensing pole 32 may be smaller than, equal to or greater than a horizontal size of the electrode 16. In addition, the outer perimeter of the cap trench 38 may be vertically aligned with the substrate recess 54 after the cap structure 14 is bonded to the substrate structure 12.

[0086] The inner perimeter and the outer perimeter of the cap trench 38, in the horizontal plane, may each have a different shape, such as a circle, square, cushion, or any other appropriate shape. Due to the shape of the inner perimeter of the cap trench 38, the sensing pole 32 may have a different shape, such as a cylindrical shape, a cube, a truncated cone, or any other appropriate shape. The sensing area SA of the cap structure 14 is the combination of the top surface of the sensing pole 32 and the top surface of the cap bridge 36. The cap bridge 36, which connects the sensing pole 32 and the peripheral edge 34 and covers the cap trench 38, has a thickness between 1 pm and 50 pm. The cap bridge 36 is configured to function as a spring that is deformed / bent in response to a force load applied to the sensing area SA of the cap structure 14. Optionally, thebottom portion of the sensing pole 32 is further heavily doped or metalized to ensure conductivity (not shown).

[0087] In addition, if the cap structure 14 is bonded to the substrate structure 12 by the metal-to-metal (thermal compression / diffusion) bonding in the subsequent step, the peripheral edge 34 may be metalized with a top bonding layer (not shown), which may be formed of (but not limited to) gold, aluminum, or copper corresponding to the bottom bonding layer 42B. The top bonding layer at the bottom surface of the peripheral edge 34 will also be a portion of the final bonding layer 42 (not shown).

[0088] Once the cap structure 14 and the substrate structure 12 are completed, and the electrode is deposited on the substrate structure 12, the cap structure 14 is bonded to the substrate structure 12, as illustrated in Figure 4L. The cap structure 14 is connected to the substrate structure 12 by the eutectic bonding, the metal-to-metal thermal compression bonding, the metal-to-metal diffusion bonding, or the silicon fusion bonding. The peripheral edge 34 of the cap structure 14 is connected to the periphery of the top surface of the substrate body 22 (possibly through the bonding layer 42) to provide the sealed cavity 44 between the substrate structure 12 and the cap structure 14. Herein, the sealed cavity 44 is formed by merging the cap trench 38, the substrate recess 54, and gaps horizontally surrounding the electrode 16. In addition, the cap structure 14 is electrically connected to the second via 24-2 of the substrate structure 12 (possibly through the bonding layer 42).

[0089] The sensing pole 32 is vertically aligned with the electrode 16. Since the combination of the depth of the substrate recess 54 and the thickness of the bonding layer 42 (if it exists) is greater than the combined thickness of the patterned isolation layer 28, the electrode 16, and the dielectric layer 48, the air gap 40 (without applied force load) exists vertically between the sensing pole 32 and the dielectric layer 48 above the electrode 16. The electrode16, the conductive bottom portion of the sensing pole 32, and the air gap 40 in between form the capacitor 46. When a force load is applied to the sensing area SA of the cap structure 14, the cap bridge 36 deforms / bends in response to the force loadapplied to the cap structure 14 and causes the sensing pole 32 connected to the cap bridge 36 to move towards the electrode 16, which changes the distance between the electrode16 and the bottom portion of the sensing pole 32 (i.e., changes the height of the air gap 40), and thereby provides a certain capacitance of the capacitor 46. With a different amount of the force load applied to the sensing area SA of the cap structure 14, the cap bridge 36 will have a different curvature, and the sensing pole 32 connected to the cap bridge will move towards the electrode 16 by a different amount. Therefore, the distance between the electrode16 and the bottom portion of the sensing pole 32 will vary, and the capacitance of the capacitor 46 will vary accordingly. Herein, the dielectric layer 48 prevents electrical shorting between the electrode 16 and the sensing pole 32 (i.e., the air gap 40 disappears) due to an excess force load. When the excess force load occurs, the bottom portion of the sensing pole 32 will be in contact with the dielectric layer 48 rather than the electrode 16, and the capacitor 46 can still work properly.

[0090] Figure 4M shows that the redistribution structure 18 is formed underneath the substrate structure 12, which includes a number of the redistribution interconnections 50 and the dielectric pattern 52. Herein, the dielectric pattern 52 fully covers and is in contact with the bottom surface of the substrate body 22, and partially covers and is in contact with each via 24. The redistribution interconnections 50 are separate from each other, and each redistribution interconnection 50 extends vertically through the dielectric pattern 52 and is connected to a corresponding via 24. The redistribution interconnections 50 may be formed of copper or other suitable metals, while the dielectric pattern 52 may be formed of BCB, polyimide, or other dielectric materials.

[0091] Lastly, the bump structures 20 are formed at the bottom surface of the redistribution structure 18 to complete the WLCSP MEMS sensor 10, as illustrated in Figure 4N. The bump structures 20 are separate from each other, and each bump structure 20 is electrically coupled to a corresponding redistribution interconnection 50. As such, in this illustration, the electrode 16 iselectrically connected to the first bump structure 20-1 through the first via 24-1 in the substrate structure 12 and the first redistribution interconnection 50-1 in the redistribution structure 18, while the cap structure 14 is electrically connected to the second bump structure 20-2 through the second via 24-2 in the substrate structure 12 and the second redistribution interconnection 50-2 in the redistribution structure 18. By adding different electrical voltages to the first and second bump structures 20-1 and 20-2, the capacitor 46 composed of the electrode 16 and the sensing pole 32 of the cap structure 14 can operate properly. For a non-limiting example, a non-zero voltage is added to the first bump structure 20-1 / the electrode 16, while the second bump structure 20-2 / the cap structure 14 is grounded (i.e. , the sensing pole 32 is grounded).

[0092] It is contemplated that any of the foregoing aspects, and / or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various embodiments as disclosed herein may be combined with one or more other disclosed embodiments unless indicated to the contrary herein.

[0093] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

Claims

AMENDED CLAIMS received by the International Bureau on 23 January 2026 (23.01.2026)ClaimsWhat is claimed is:

1. A wafer-level chip-scale packaging (WLCSP) capacitive microelectromechanical systems (MEMS) sensor comprising:• a substrate structure having a substrate body, a first via, and a second via, wherein the substrate body is formed of silicon, and the first via and the second via are separate from each other and extend vertically through the substrate body;• an electrode formed on the substrate structure, wherein the electrode is [[and]] electrically connected to the first via within the substrate body, while electrically isolated from the substrate body; and• a cap structure bonded to and over the substrate structure to provide a sealed cavity, within which the electrode is located, wherein:• the cap structure includes a sensing pole, a peripheral edge surrounding the sensing pole, and a cap bridge connecting the peripheral edge to the sensing pole, wherein the sensing pole and the peripheral edge extend vertically beyond the cap bridge to define a cap trench horizontally between the sensing pole and the peripheral edge and underneath the cap bridge;• the sensing pole is vertically aligned with the electrode with an air gap in between, while the peripheral edge is bonded to the substrate structure and electrically connected to the second via, wherein a bottom portion of the sensing pole is conductive and composes a capacitor with the electrode and the air gap in between; and• the sensing pole is capable of moving vertically due to bending of the cap bridge caused by a force load applied to the cap structure, which allows the capacitor to provide a variety of capacitances.

2. The WLCSP MEMS sensor of claim 1 , wherein the cap trench is continuous in a horizontal plane.

3. The WLCSP MEMS sensor of claim 2, wherein, in the horizontal plane, the cap trench includes an inner perimeter having a circle, square, or cushion shape, and an outer perimeter having a circle, square, or cushion shape.

4. The WLCSP MEMS sensor of claim 1 further comprising a patterned isolation layer with an opening, wherein:• the patterned isolation layer is formed on the substrate body, wherein the opening is aligned with the first via;• the electrode is formed on and confined within the patterned isolation layer, so as to isolate the electrode from the substrate body; and• the electrode is electrically connected to the first via through the opening of the patterned isolation layer.

5. The WLCSP MEMS sensor of claim 4 further comprising a dielectric layer, which at least extends over a top surface of the electrode, wherein the air gap is vertically between the bottom portion of the sensing pole and the dielectric layer.

6. The WLCSP MEMS sensor of claim 5, wherein the patterned isolation layer and the dielectric layer are formed of silicon dioxide.

7. The WLCSP MEMS sensor of claim 1 further comprising a bonding layer, wherein:• the peripheral edge of the cap structure is bonded to the substrate structure through the bonding layer; and• the bonding layer is in contact with the second via, and the cap structure is electrically connected to the second via through the bonding layer.

8. The WLCSP MEMS sensor of claim 7, wherein the bonding layer is formed of one of gold-silicon, gold-germanium, gold-tin, gold-indium, aluminum-silicon, aluminum- germanium, silicon germanium, and copper-tin.

9. The WLCSP MEMS sensor of claim 7, wherein the bonding layer is formed of gold, aluminum, or copper.

10. The WLCSP MEMS sensor of claim 1 , wherein:• the peripheral edge of the cap structure is directly bonded to the substrate structure; and• the cap structure is electrically connected to the second via.

11. The WLCSP MEMS sensor of claim 1 , wherein the substrate structure further comprises a first isolation wall and a second isolation wall, wherein:• the first isolation wall and the second isolation wall extend vertically through the substrate body and surround the first via and the second via, respectively, such that the first isolation wall and the second isolation wall isolate the first via and the second via from the substrate body, respectively.

12. The WLCSP MEMS sensor of claim 11 , wherein:• the first isolation wall and the second isolation wall are formed of silicon dioxide; and the first via and the second via are formed of a metal material.

13. The WLCSP MEMS sensor of claim 1 , wherein the air gap has a height between 1 μm and 2 μm.

14. The WLCSP MEMS sensor of claim 1 , wherein the cap bridge has a thickness between 1 pm and 50 pm.

15. The WLCSP MEMS sensor of claim 1 , wherein:• a bottom surface of the peripheral edge extends vertically beyond a bottom surface of the sensing pole; and• the substrate body of the substrate structure has a flat top surface, and the electrode is formed on the flat top surface.

16. The WLCSP MEMS sensor of claim 1 , wherein:• a bottom surface of the peripheral edge and a bottom surface of the sensing pole are coplanar;• the substrate body of the substrate structure has a substrate recess extending from a top surface of the substrate body into the substrate body;• the electrode is formed within the substrate recess and on a bottom surface of the substrate recess; and• the first via extends vertically from the bottom surface of the substrate recess to a bottom surface of the substrate body.

17. The WLCSP MEMS sensor of claim 1 further comprising a redistribution structure formed underneath the substrate structure, wherein:• the redistribution structure at least includes a dielectric pattern formed directly underneath the substrate body, a first redistribution interconnection, and a second redistribution interconnection; the first redistribution interconnection is connected to the first via of the substrate structure and extends vertically through the dielectric pattern; and the second redistribution interconnection is connected to the second via of the substrate structure and extends vertically through the dielectric pattern.

18. The WLCSP MEMS sensor of claim 17 further comprising a first bump structure and a second bump structure, wherein:• the first bump structure and the second bump structure are formed underneath the redistribution structure;• the first bump structure is electrically connected to the first redistribution interconnection, such that the electrode on the substrate structure is electrically connected to the first bump through the first via and the first redistribution interconnection; and• the second bump structure is electrically connected to the second redistribution interconnection, such that the cap structure on the substrate structure is electrically connected to the second bump through the second via and the second redistribution interconnection.

19. The WLCSP MEMS sensor of claim 18, wherein the first bump structure and the second bump structure are solder bumps or metal pillars.

20. The WLCSP MEMS sensor of claim 1 , wherein:• the cap structure is formed of doped silicon;• the first via and the second via are through-silicon vias; and• the electrode is formed of a metal material or doped silicon.

21. A method of fabricating a wafer-level chip-scale packaging (WLCSP) capacitive microelectromechanical systems (MEMS) sensor comprising:• providing a substrate structure, which includes a substrate body, a first via, and a second via, wherein the substrate body is formed of silicon, and the first via and the second via are separate from each other and extend vertically through the substrate body;• depositing an electrode on the substrate structure, wherein the electrode is electrically connected to the first via within the substrate body, while electrically isolated from the substrate body;• providing a cap structure, which includes a sensing pole, a peripheral edge surrounding the sensing pole, and a cap bridge connecting the peripheral edge tothe sensing pole, wherein the sensing pole and the peripheral edge extend vertically beyond the cap bridge to define a cap trench horizontally between the sensing pole and the peripheral edge and underneath the cap bridge; and• bonding the cap structure to the substrate structure to provide a sealed cavity, within which the electrode is located, wherein:• the sensing pole is vertically aligned with the electrode with an air gap in between, while the peripheral edge is bonded to the substrate structure and electrically connected to the second via;• a bottom portion of the sensing pole is conductive and composes a capacitor with the electrode and the air gap in between; and• the sensing pole is capable of moving vertically due to bending of the cap bridge caused by a force load applied to the cap structure, which allows the capacitor to provide a variety of capacitances.

22. The method of claim 21 , wherein:• a bottom surface of the peripheral edge and a bottom surface of the sensing pole are coplanar; and• providing the substrate structure comprises:• providing an initial substrate body with a substrate recess, which extends downward from a top surface of the initial substrate body into the initial substrate body and is located horizontally at an interior portion of the initial substrate body;• forming the first via hole and the second via hole to convert the initial substrate body into a substrate body, wherein the first via hole is located in the interior portion of the substrate body and extends downward from a bottom surface of the substrate recess to a bottom surface of the substrate body, and the second via hole is located in a peripheral portion of the substrate body and extends downward from the top surface of the substrate body to the bottom surface of the substrate body; and• forming the first via in the first via hole and the second via in the second via hole, wherein the electrode deposited on the substrate structure is formedwithin the substrate recess and on the bottom surface of the substrate recess to be electrically connected to the first via.

23. The method of claim 21 , wherein:• the substrate body of the substrate structure has a flat top surface, and the electrode is formed on the flat top surface; and• providing the cap structure comprises:• providing a cap body with a cap recess, which extends upward from a bottom surface of the cap body into the cap body and is located horizontally at an interior portion of the cap body; and• forming the cap trench over the cap recess to convert the cap body into the cap structure, wherein the cap trench extends upward from a periphery of a top surface of the cap recess without penetrating, wherein:• a first remaining portion of the cap body directly above the top surface of the cap recess and surrounded by the cap trench provides the sensing pole of the cap structure, a second remaining portion of the cap body directly above the cap trench provides the cap bridge of the cap structure, and a third remaining portion of the cap body surrounding the cap recess and the cap trench provides the peripheral edge of the cap structure; and• a bottom surface of the peripheral edge extends vertically beyond a bottom surface of the sensing pole.

24. The method of claim 21 , wherein the cap structure is bonded to the substrate structure by eutectic bonding, metal-to-metal thermal compression bonding, metal-to- metal diffusion bonding, or silicon fusion bonding.STATEMENT UNDER ARTICLE 19(1)Applicant has submitted amendments under Article 19 PCT for the above- referenced application.Applicant has amended original claims 1, 20, and 21.Original claim 1 has been amended to clarify that the claimed substrate body is formed of silicon, thereby distinguishing it from a dielectric or insulating layer. Additionally, claim 1 further clarifies that the claimed electrode over the substrate structure is electrically connected only to the first via within the substrate body, while remaining electrically isolated from the silicon substrate body. Accordingly, the claimed electrode differs from an electrode formed directly on a dielectric or insulating layer.Original claim 20 has been amended to remove the feature that “the substrate body is formed of silicon. ”Original claim 21 has been amended to include similar features to claim 1.

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