The various embodiments described in this document relate in general to the field of semiconductor manufacturing, and more specifically to a micro electro mechanical system (MEMS) device and a manufacturing method thereof.
Electronic devices, such as commercial products (for example, True Wireless Stereo (TWS), wearable, phone, etc.), and higher-end products (for example, automotive), often include MEMS devices. MEMS devices such as inertia sensors, may, for example, be used to form accelerometers, gyroscopes and other types of sensors.
In recent years, technology for manufacturing MEMS devices having a three-dimensional structure in which a plurality of device die or device wafers are integrated in their thickness direction thereof has been developed primarily, for the purpose of further increasing the density of MEMS devices. When the plurality of Device Die involved at least 2 or more electrodes, eg. a Top wafer and a Bottom wafer, it is important to ensure all electrodes are grounded on the same potential. Without proper grounding, one of the electrodes will be electrically floating and induced unwanted charge accumulation within the electrodes. This phenomenon translates to higher resistance and larger parasitic capacitance for an electronic device, resulting in slower initiation response time and poorer signal to noise ratio (SNR).
Therefore, it is desired to provide a proper ground structure for MEMS devices.
According to one aspect of the present disclosure, a MEMS device is provided. The MEMS device includes a cap sheet defining a recess, and a device sheet bonded with the cap sheet and defining a functional cavity directly facing the recess. The cap sheet includes a substrate and a first metal layer, the substrate has a first surface facing the device sheet, the recess is defined on the first surface and the first metal layer is disposed on a portion of the first surface outside the recess. The device sheet includes a substrate, a structure layer and a second metal layer sequentially stacked, the structure layer includes a first portion, in which structures for achieving mechanical functionality are formed, located in the functional cavity and a second portion surrounding the first portion, and the second metal layer is located on the second portion. Each of the cap sheet and the device sheet includes at least one electrode, the cap sheet is bonded with the device sheet via the first metal layer and the second metal layer, and all electrodes are electrically connected via the first metal layer and the second metal layer bonded with each other. The cap sheet further includes a ground structure on the portion of the first surface outside the recess, and disposed along perimeter of a bonding area where the first metal layer located.
In some embodiments, the ground structure is disposed on both sides or either side of the bonding area.
In some embodiments, the bonding area is ring-shaped, and the ground structure is disposed along one or both of an outer side and an inner side of the bonding area.
In some embodiments, the ground structure is a complete loop trench, or is a single or multiple short trenches.
In some embodiments, the first metal layer covers the ground structure either fully or partially.
According to another aspect of the present disclosure, a method for manufacturing the MEMS device as described above is provided. The method includes forming the cap sheet, forming the device sheet, and bonding the cap sheet and the device sheet. Forming the cap sheet includes: providing a first substrate; forming an oxide layer on a first surface of the first substrate; patterning the oxide layer to form a grounding structure and to reserve targeted bonding area, the grounding structure being disposed along perimeter of the targeted bonding area; forming a first metal layer over the oxide layer at the target bonding area and in the grounding structure; and removing portions of the oxide layer and the first substrate to form the recess, so that the first metal layer and the grounding structure are disposed on the portion of the first surface outside the recess. Forming the device sheet includes: providing a second substrate; and forming the structure layer and the second metal layer on the second substrate, so that the structure layer includes a first portion, in which structures for achieving mechanical functionality are formed, located in the functional cavity and a second portion surrounding the first portion, and the second metal layer is located on the second portion. Bonding the cap sheet and the device sheet includes: performing a bonding process on the first metal layer and the second metal layer, so that the cap sheet is bonded with the device sheet via the first metal layer and the second metal layer, and all electrodes are electrically connected via the first metal layer and the second metal layer bonded with each other.
In some embodiments, patterning the oxide layer to form the grounding structure and to reserve the targeted bonding area includes disposing the ground structure on both sides or either side of the bonding area.
In some embodiments, patterning the oxide layer to form the grounding structure and to reserve the targeted bonding area includes disposing the targeted bonding area as ring-shaped, and disposing the ground structure along one or both of an outer side and an inner side of the targeted bonding area.
In some embodiments, patterning the oxide layer to form the grounding structure and to reserve the targeted bonding area includes disposing the ground structure as a complete loop trench, or as a single or multiple short trenches.
In some embodiments, in performing a bonding process on the first metal layer and the second metal layer, the first metal layer is squeezed out to flow into the ground structure to make the first metal layer cover the ground structure either fully or partially.
The present embodiments are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references may indicate similar elements.
This specification discloses one or more embodiments that incorporate the features of this disclosure. The disclosed embodiment(s) merely exemplify the disclosure. The scope of the disclosure is not limited to the disclosed embodiment(s). The disclosure is defined by the claims appended hereto.
The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Terms used in embodiments of the present disclosure are for the purpose of describing specific embodiments only and are not intended to limit the present disclosure. Singular forms “an”, “said”, and “the” as used in embodiments of the present disclosure and in the appended claims are also intended to include a plurality of forms, unless the context clearly dictates otherwise.
It shall be understood that the term “and/or” used herein is merely an association relationship that describes an associated object, indicating that there can be three relationships. For example, the expression “A and/or B” may include three cases: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character “/” herein generally indicates that related objects are a kind of “or” relationship.
It is to be noted that the orientation words “up”, “down”, “left”, “right”, and the like described in the embodiments of the present disclosure are described from the angles shown in the drawings and should not be understood as limiting the embodiments of the present disclosure. Furthermore, in the context, it is to be understood that when a component is referred to as being connected “above/up” or “below/lower” of another component, the component can not only be directly connected to the “above/up” or “below/lower” of the another component, but can also be indirectly connected to the “above/up” or “below/lower” of the another component through a middle component.
Micro-electro-mechanical system (MEMS) devices refer to high-tech devices with a size of several millimeters or even smaller, and a size of an internal structure of this device is generally on the micron scale or even nanometer scale. The MEMS device may include a plurality of elements (e.g., movable elements) for achieving mechanical functionality. In addition, the MEMS devices may include MEMS acoustic sensors, MEMS pressure sensors, and MEMS inertial sensors, and so on. The MEMS inertial sensors generally include a MEMS accelerometer and a MEMS gyroscope.
The cap sheet 101 may include a substrate 111. In accordance with an embodiment, the substrate 111 of the cap sheet 101 may be formed of silicon. Alternatively, the substrate 111 of the cap sheet 101 may be formed of other semiconductor materials including silicon germanium (SiGe), silicon carbide and the like.
The substrate 111 has a first surface facing the device sheet 103. The cap sheet 101 defines a recess 102 on the first surface and includes a first metal layer 121 disposed on a portion of the first surface outside the recess 102.
The device sheet 103 may include a substrate 113. In accordance with an embodiment, the substrate 113 of the device sheet 103 may have similar materials as the substrate 111 of the cap sheet 101. However, the substrates of the cap sheet 101 and the device sheet 103 are not necessary to be the same material.
The device sheet 103 may further include a structure layer 123 and a second metal layer 133 sequentially stacked. The device sheet 103 defines a functional cavity 104 directly facing the recess 102. The structure layer 123 includes a first portion, in which structures for achieving mechanical functionality are formed, located in the functional cavity 104 and a second portion surrounding the first portion. The second metal layer 133 is located on the second portion.
Since the MEMS device needs to be operated in a sealed environment, the cap sheet 101 is bonded with the device sheet 103 via the first metal layer 121 and the second metal layer 133, so that the corresponding movable elements (or the structures for achieving mechanical functionality) of the MEMS device are sealed in the enclosed cavity 105 including the recess 102 and the functional cavity 104 defined by the cap sheet 101 and the device sheet 103.
For the sake of illustration, an area where the first metal layer 121 and the second metal layer 133 are located is called as a bonding area 106. The bonding area 106 may be in any morphologies as needed. For example, the bonding area 106 may be a bonding ring surrounding the enclosed cavity 105.
Each of the cap sheet 101 and the device sheet 103 includes at least one electrode. It is important to ensure all electrodes of the MEMS device are grounded on the same potential, because without proper grounding, one of the electrodes will be electrically floating and induced unwanted charge accumulation within the electrodes.
In order to provide proper grounding, the MEMS device includes a ground structure to electrically connect all electrodes. In some cases, an isolated island structure is created as a ground structure.
In a design shown in
In another design shown in
In some other cases, a ground structure is embedded within a bonding ring. In a design shown in
In some embodiments, a MEMS device includes a cap sheet and a device sheet. The cap sheet includes a substrate, a ground structure and a first metal layer, which is formed by depositing first metal material and patterning to form bonding ring structure at targeted bonding area, with the first metal material covering the ground structure either fully or partially. The ground structure is created along the peripheral of the bonding ring structure. The device sheet includes a substrate and a second metal layer, which is bonded with the first metal layer, so as to achieve a sealed environment, and provide proper grounding at the same time.
In the MEMS device as shown in
It should be noted that the grounding loop shown in
As described above, the ground structure may be created by pattern the oxide on silicon.
A structure layer 1123 and a second metal layer 1133 are sequentially stacked over the substrate 1113. A functional cavity 1104 is formed. The structure layer 1123 includes a first portion, in which structures for achieving mechanical functionality are formed, located in the functional cavity 1104 and a second portion surrounding the first portion. The second metal layer 1133 is located on the second portion.
After a cap sheet and a device sheet are fabricated, for example, the cap sheet shown in
It should be understood that the structure layer involved in the above embodiments may be any structure for achieving mechanical functionality of the MEMS device.
As can be seen, according to embodiments of the present disclosure, creating ground structure along the peripheral of the bonding ring structure allows maximal utilisation of the effective device area and cavity area. This facilitates the feasibility for optimal die size reduction. This is especially beneficial for 2 or more electrodes with grounding ability when bonded together as it ensures the whole device is connected at the same potential with minimal space wasted to create repeated ground structure for each electrode. Furthermore, having the ground structure along the outer/inner side of the bonding area allows excessive metal material that are squeezed out during the bonding process to flow into the ground trenches, and not flow towards the device active area or towards the neighbouring active die. In addition, with the ground structure created outside of the effective bonding area, there is no step height differences within the bonding area and the optimal bonding area is retained. This avoid creation of voids along bonding interface. Hence, ensuring the bonding quality and bonding strength is not compromised as shown in
The following will describe a method for manufacturing the MEMS device shown in
As illustrated in
At block 1402, a cap sheet is formed.
At block 1404, a device sheet is formed.
At block 1406, the cap sheet and the device sheet are bonded.
In some embodiments, the cap sheet is formed as follows. A substrate is provided. An oxide layer is formed on a surface of the substrate and patterned to form a grounding loop and to reserve target bonding area. A metal layer is formed over the oxide layer at the target bonding area and in the grounding loop. Portions of the oxide layer and the substrate are removed to define the recess. It shall be understood that the fabricating procedure of a cap sheet is similar to the procedure as illustrated in
In some embodiments, the device sheet is formed as follows. A substrate is provided. A structure layer and a second metal layer are sequentially stacked over the substrate. A functional cavity is formed. The structure layer includes a first portion, in which structures for achieving mechanical functionality are formed, located in the functional cavity and a second portion surrounding the first portion. The second metal layer is located on the second portion.
In some embodiments, the cap sheet is bonded with the device sheet via the first metal layer and the second metal layer, so that the corresponding movable elements (or the structures for achieving mechanical functionality) of the MEMS device are sealed in the enclosed cavity including the recess and the functional cavity defined by the cap sheet and the device sheet. The enclosed cavity provides a sealed environment in which the MEMS device needs to be operated.
It should be understood that the MEMS device is fabricated by completing above-mentioned operations in a vacuum environment, thereby drying moisture and/or organic gas in the functional cavity, so as to keep operating performance of the MEMS device at a stable level and improve the operating reliability of the MEMS device and prolong service life of the MEMS device.
This specification discloses one or more embodiments that incorporate the features of this disclosure. The disclosed embodiment(s) merely exemplify the present disclosure. The scope of the present disclosure is not limited to the disclosed embodiment(s). The present disclosure is defined by the claims appended hereto.
The terminology used in the description of the various described embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various described embodiments and the appended claims, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, 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.
The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the scope of the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen in order to best explain the principles underlying the claims and their practical applications, to thereby enable others skilled in the art to best use the embodiments with various modifications as are suited to the particular uses contemplated.