MEMS sensor with side port and method of fabricating same

A MEMS sensor package comprises a MEMS die that includes a substrate having a sensor formed thereon and a cap layer coupled to the substrate. The cap layer has a cavity overlying a substrate region at which the sensor resides. A port extends between the cavity and a side wall of the MEMS die and enables admittance of fluid into the cavity. Fabrication methodology entails providing a substrate structure having sensors formed thereon, providing a cap layer structure having inwardly extending cavities, and forming a channel between pairs of the cavities. The cap layer structure is coupled with the substrate structure and each channel is interposed between a pair of cavities. A singulation process produces a pair of sensor packages, each having a port formed by splitting the channel, where the port is exposed during singulation and extends between its respective cavity and side wall of the sensor package.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to microelectromechanical systems (MEMS) sensor packages. More specifically, the present invention relates to a MEMS sensor with a side wall port to provide a path for passage of an external fluid medium.

BACKGROUND OF THE INVENTION

Microelectromechanical systems (MEMS) devices are semiconductor devices with embedded mechanical components. MEMS devices include, for example, pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, micro fluidic devices, and so forth. MEMS devices are used in a variety of products such as automobile airbag systems, control applications in automobiles, navigation, display systems, inkjet cartridges, and so forth.

There are significant challenges to be surmounted in the packaging of MEMS devices due at least in part to the necessity for the MEMS devices to interact with the outside environment, the fragility of many types of MEMS devices, and severe cost constraints. Indeed, many MEMS device applications require smaller size and low cost packaging to meet aggressive cost targets.

DETAILED DESCRIPTION

As the uses for microelectromechanical systems (MEMS) devices continue to grow and diversify, increasing emphasis is being placed on smaller size and low cost packaging without sacrificing part performance. Embodiments entail a MEMS sensor package and a method of fabricating the MEMS sensor package. In particular, the MEMS sensor package is formed, through the execution of relatively simple methodology, to include a MEMS sensor on a substrate that is covered by a cap layer. The MEMS sensor resides in a cavity formed in the cap layer, and a port extends between the cavity and a side wall of one of the substrate and the cap layer. The pressure port formed in the side wall is exposed during a strip singulation operation of the methodology so that fluid, such as air, external to the cavity can be admitted into the cavity.

The instant disclosure is provided to explain in an enabling fashion the best modes, at the time of the application, of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.

Referring toFIG. 1,FIG. 1shows a side sectional view of a microelectromechanical systems (MEMS) sensor package20in accordance with an embodiment.FIG. 1and subsequentFIGS. 2-8are illustrated using various shading and/or hatching to distinguish the different elements of the MEMS sensor packages, as will be discussed below. These different elements within the structural layers may be produced utilizing current and upcoming micromachining techniques of depositing, patterning, etching, and so forth. It should be further understood that the use herein of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

MEMS sensor package20generally includes MEMS die22coupled to an application specific integrated circuit (ASIC), generally referred to herein as a semiconductor die24. Semiconductor die24, in turn, may be coupled to a mounting pad26of a carrier, referred to herein as a lead frame28. MEMS die22includes a substrate30and a cap layer32. In an embodiment, substrate30has a first inner surface34and a first outer surface36. Similarly, cap layer32has a second inner surface38and a second outer surface40. Second inner surface38of cap layer32is coupled to first inner surface34of substrate30. A MEMS sensor42is formed on first inner surface34of substrate30. More particularly, cap layer32includes a cavity44extending inwardly from second inner surface38and overlying a region46of first inner surface34of substrate30. MEMS sensor42resides in cavity44at region46of first inner surface34of substrate30.

One or both of substrate30and cap layer32includes a port48extending between cavity44and a side wall50of MEMS die22, where side wall50extends between first outer surface36of substrate30and second outer surface40of cap layer32. In the illustrated embodiment, port48is formed as a recess in second inner surface38of cap layer32. In other embodiments, port48may be formed as a recess in first inner surface34of substrate30. MEMS sensor42may be a pressure sensor having a pressure deformable diaphragm52disposed at region46of first inner surface34of substrate30. Port48is configured to admit a fluid, e.g., air, from an environment external to cavity44into cavity44. Since fluid can enter cavity44via port48, MEMS pressure sensor42having pressure deformable diaphragm52can detect an ambient pressure53, labeled P, of an environment external to MEMS sensor package20.

MEMS die22further includes bond pads54on first inner surface34of substrate30, but external to cap layer32, and conductive traces56(shown inFIG. 5) interconnected between MEMS sensor42and bond pads54. Conductive traces56suitably electrically couple MEMS sensor42with bond pads54. Bond pads54may be utilized to electrically connect MEMS sensor42to bond pads58of semiconductor die24via electrically conductive interconnects, or bond wires60in this example. Semiconductor die24may include additional bond pads62that may be utilized to electrically connect semiconductor die24to external connection leads64of lead frame28via electrically conductive interconnects, or bond wires66in this example. Leads64provide input to and output from MEMS sensor package20, as known to those skilled in the art.

Referring now toFIGS. 2 and 3,FIG. 2shows a side sectional view of a structure70that includes a first intermediate sensor structure72and a second intermediate sensor structure74prior to singulation, andFIG. 3shows a side sectional view of structure70following singulation. First intermediate sensor structure72is laterally displaced from second intermediate sensor structure74within structure70. Additionally, each of first and second intermediate sensor structures72,74includes the structural components described in connection withFIG. 1. That is, each of first and second intermediate sensor structures72,74includes MEMS die22, semiconductor die24, lead frame28, and bond wires60,66all of which are covered in encapsulant68. Further description of MEMS die22, semiconductor die24, lead frame28, and bond wires60,66of first and second intermediate sensor structures72,74is not repeated herein for brevity.

In accordance with a particular embodiment, first and second intermediate sensor structures72,74of structure70are interconnected via inactive/unused material regions76of each of a cap layer structure78, a substrate structure80, a semiconductor die structure82, and a strip84of lead frames28. Structure70further includes a channel86interposed between cavity44of first intermediate sensor structure72and cavity44of second intermediate sensor structure74. Thus, cavity44of first intermediate sensor structure72and cavity44of second intermediate sensor structure74are in fluid communication with one another.

First intermediate sensor structure72is configured to be separated from second intermediate sensor structure74to produce a first MEMS sensor package, referred to herein as a first pressure sensor package20A (FIG. 3), and to produce a second MEMS sensor package, referred to herein as a second pressure sensor package20B (FIG. 3). That is, structure70may be sawn, diced, or otherwise singulated at inactive/unused material regions76bounded by dashed lines88in order to remove the material portion of structure70between dashed lines88.

Following singulation, each of first and second pressure sensor packages20A,20B includes the structural components described in connection withFIG. 1. That is, each of first and second sensor packages20A,20B includes MEMS die22, semiconductor die24, lead frame28, and bond wires60,66all of which are covered in encapsulant68. The letter “A” is used inFIG. 3to denote the elements of first pressure sensor package20A and the letter “B” is used herein to denote the elements of second pressure sensor package20B for clarity of description. It should be observed that the singulation process separates channel86into two remaining portions. Thus, a first port48A of first pressure sensor package20A is a first portion of channel86and a second port48B of second pressure sensor package20B is a second portion of channel86.

Referring toFIGS. 4 and 5,FIG. 4shows a side sectional view of a MEMS die structure89that is part of structure70(FIG. 2), andFIG. 5shows a top view of substrate structure80that may be used to form structure70. More particularly, MEMS die structure89ofFIG. 4includes cap layer structure78coupled with substrate structure80to form a pair of MEMS dies22. However, it should be observed thatFIG. 4does not include semiconductor dies24(FIG. 2) and lead frames28(FIG. 2).FIG. 5shows substrate structure80with cap layer structure78absent in order to reveal the features of substrate structure80.

In general, substrate structure80includes a bulk substrate88and a structural layer90fixed to a surface92of bulk substrate88. MEMS sensors42are formed on, or alternatively in, structural layer90. As shown, sets of bond pads54and conductive traces56are also formed on structural layer90. Substrate structure80is shown with only two MEMS sensors42for simplicity of illustration. It should be understood, however, that substrate structure80can include multiple MEMS sensors42arranged in pairs (as shown) in a high volume manufacturing configuration.

In accordance with an example embodiment, bulk substrate88has recesses94extending inwardly from surface92of bulk substrate88, and structural layer90is fixed to surface92of bulk substrate88surrounding recesses94. Material portions of structural layer90are removed surrounding each of MEMS sensors42to form cantilevered platform structures96at which each of MEMS sensors42reside. Thus, cantilevered platform structures96are formed in structural layer90and each extends over a respective one of recesses94.

Each of cantilevered platform structures96includes a platform98and an arm100extending from platform98. One end of arm100is fixed to platform98and the other end of arm100is fixed to bulk substrate88via an attachment of arm100to a portion of structural layer90fixed to surface92of bulk substrate88surrounding recess94. Thus, once the material portions of structural layer90are removed, openings102extend through structural layer90and partially surround cantilevered platform structures96. Accordingly, platforms98and arms100are suspended over recesses94, with an end of each of arms100being the sole attachment point of each of cantilevered platform structure96to the surrounding bulk substrate88. Although each of cantilevered platform structures96includes an arm100which forms a sole attachment point to the surrounding bulk substrate88, other configurations may include more than one attachment point to the surrounding bulk substrate.

The illustrated configuration yields MEMS sensors42each of which is formed on a cantilevered platform structure96that is suspended over a recess94. The cantilevered platform structure can achieve the benefits of improved package stress isolation and improved device performance, especially for pressure sensor configurations. However, it should be understood that alternative embodiments need not include that cantilevered platform structures overlying recesses. Instead, some embodiments may include MEMS sensors that are formed on a solid substrate (i.e., do not have recesses) and reside in cavities44, but still require porting to an external environment via port48(FIG. 1) in side wall50(FIG. 1).

Referring now toFIGS. 4 and 6,FIG. 6shows a bottom view of cap layer structure78that may be used to form structure70(FIG. 2). Cap layer78includes two cavities44and channel86extending inwardly from a surface104of cap layer structure78. Cap layer structure78is shown with only two cavities44formed therein to correspond with substrate structure80(FIG. 5) and for simplicity of illustration. It should be understood, however, that cap layer structure78can include multiple cavities44arranged in pairs with channels86extending between pairs of cavities44in a high volume manufacturing configuration.

In general, cap layer structure78may be coupled with substrate structure80via a bond material106, where bonding may be, for example, glass frit bonding, aluminum-germanium bonding, copper-to-copper bonding, or any other suitable bonding process and bonding material. Bond material106may be suitably located between cap layer structure78and substrate structure80outside of the boundaries of cavities44and channel86. In some embodiments, when cap layer structure78is coupled with substrate structure, material portions108overlie bond pads54. Thus, a saw-to-reveal process may be performed to expose bond pads54from cap layer structure78. That is, following coupling with substrate structure80, cap layer structure78may be sawn along saw lines (represented by dashed lines110) shown inFIG. 6to remove material portions108and thereby expose bond pads54. As such, bond material106may be limited to those regions between saw lines110so as not to come in contact with bond pads54. In other embodiments, bond material106may not be limited to the regions between saw lines110. As such, following a saw-to-reveal process, bond material106may be removed from bond pads54.

FIG. 7shows a side sectional view of a structure112that includes a first intermediate sensor structure114and a second intermediate sensor structure116prior to singulation in accordance with another embodiment. Structure112is similar to structure70(FIG. 2) described above. Thus, structure112includes cap layer structure78, substrate structure80, and strip84so that each of first and second intermediate sensor structures114,116includes MEMS die22, lead frame28, and bond wires60,66all of which are covered in encapsulant68. However, in lieu of semiconductor die structure82(FIG. 2), structure112is fabricated utilizing previously singulated semiconductor dies24that are suitably coupled to strip84. The resulting encapsulated structure112is singulated and channel86is split to expose the two ports48A,48B to the external environment, as discussed above.

FIG. 8shows a side sectional view of a structure118that includes a first intermediate sensor structure120and a second intermediate sensor structure122prior to singulation in accordance with another embodiment. Structure118is similar to structure70(FIG. 2). Thus, structure118includes cap layer structure78, semiconductor die structure82, strip84, and bond wires66all of which are covered in encapsulant68. However, in lieu of substrate structure80(FIG. 2), structure118is fabricated utilizing a substrate structure124that includes many of the elements described above including MEMS sensors42. However, substrate structure124includes electrically conductive interconnects in the form of electrically conductive vias126extending through a bulk substrate128of substrate structure in lieu of bond wires60(FIG. 2). Conductive vias126can thus form the electrical connections between MEMS sensors42and semiconductor dies24of semiconductor die structure82.

Such a structural configuration eliminates the need for bond wires between the MEMS sensor and the underlying semiconductor die which may reduce packaging size and complexity. The resulting encapsulated structure118is singulated and channel86is split to expose the two ports48A,48B to the external environment, as discussed above.

FIG. 9shows a side sectional view of a structure130that includes a first intermediate sensor structure132and a second intermediate sensor134structure prior to singulation in accordance with yet another embodiment. Structure130includes cap layer structure78and substrate structure124having electrically conductive vias126extending through it. Structure130further includes a semiconductor die structure136having electrically conductive vias138extending through it. Electrically conductive vias138are provided in lieu of bond wires66(FIG. 2) and lead frame28(FIG. 2) and enable input to and output from the resulting MEMS sensor packages.

Since conductive vias126are internal to substrate structure124and conductive vias138are internal to semiconductor die structure136, the resulting package need not be encapsulated in encapsulant68(FIG. 1). Furthermore, savings may be achieved in terms of the packaging complexity and overall size of the resulting MEMS sensor packages. The resulting structure130is singulated and channel86is split to expose the two ports48A,48B to the external environment, as discussed above.

Now referring toFIG. 10,FIG. 10shows a flowchart of a sensor package fabrication process140in accordance with another embodiment. The methodology entails fabrication of side oriented ports (for example, pressure ports) into the silicon that are exposed at strip singulation. Sensor package fabrication process140will be described in connection with the fabrication of two MEMS sensor packages20A,20B (FIG. 3) shown in detail inFIGS. 1-6for simplicity of illustration. However it should be apparent to those skilled in the art that the ensuing methodology may be executed to concurrently fabricate more than two MEMS sensor packages20in a high volume manufacturing environment. Additionally, it should be understood that sensor package fabrication process140may be adapted to produce any of the MEMS sensor package configurations alternatively described in connection withFIGS. 7-9above.

The ordering of process operations presented below in connection with sensor package fabrication process140should not be construed as limiting, but is instead provided as an example of a possible fabrication method that may be implemented. Furthermore, it will be understood by those skilled in the art that the following process operations may be executed in a different order than presented below.

Sensor package fabrication process140includes process blocks related to the fabrication of MEMS die structure89(FIG. 4) having MEMS sensors42formed therein. These process blocks are delineated by a larger dashed line box and include blocks142,144, and146. At block142of sensor package fabrication process140, substrate structure80is provided having MEMS sensors42formed thereon. At block144, cap layer structure78(FIGS. 4 and 6) is provided, with cavities44and channel86being formed in cap layer78. At block146, cap layer78is coupled to substrate structure80via bond material106to form MEMS die structure89. As mentioned previously, bonding may be performed using any other suitable bonding process and material.

At a block148, semiconductor die structure82containing semiconductor dies24may be coupled to strip84(FIG. 2) of lead frames28in some embodiments. Of course, in configurations that do not include a lead frame (e.g., structure130ofFIG. 9), block148need not be performed. At a block150, MEMS die structure89formed in accordance with process blocks142,144,146is coupled with semiconductor die structure82using, for example, a die attach adhesive.

At a block152, the electrically conductive interconnects may be formed. Referring toFIG. 2, bond wires60may be formed between substrate structure80and semiconductor die structure82. Additionally, bond wires66may be formed between semiconductor die structure82and external connection leads64of lead frames28. Referring toFIG. 8, in configurations that do not include bond wires60(e.g., structure118), the electrically conductive interconnects in the form of conductive vias126will be formed during fabrication of substrate structure124and the electrically conductive interconnects in the form of bond wires66will be formed after semiconductor die structure82is coupled to strip84of lead frames28. Referring now toFIG. 9, in still other configurations that do not include any bond wires60,66(e.g., structure130), the electrically conductive interconnects in the form of conductive vias126will be formed during fabrication of substrate structure124and the electrically conductive interconnects in the form of vias138will be formed during fabrication of semiconductor die structure136.

At a block154, strip84, semiconductor die structure82, substrate structure80, cap layer78, and bond wires60,66are encapsulated (i.e., covered) in encapsulant68. Referring toFIGS. 2, 7, and 8, the side oriented channel86that will become ports48A,48B following singulation is protected from encapsulant68. In configurations that do not include encapsulant68(e.g., structure130ofFIG. 9), block154need not be performed.

Some prior art structures call for the bond wires to pass through a gel coating. The gel coating is prone to bubble formation and can cause flexing of the bond wires. Bubble formation and flexing of the bond wires can cause the parasitic capacitances between neighboring wires to change, thus adversely affecting the sensor offset. In accordance with the embodiments described herein, since bond wires60and bond wires66are encapsulated (FIGS. 2 and 6) in encapsulant68and/or through the use of conductive vias126(FIG. 7), the bond wires advantageously need not pass through the gel coating.

Following encapsulation block154, a process block156is performed. At block156, a singulation process (e.g., wet sawing, laser cutting, or the like) may be performed to separate the over molded structure into the individual first and second sensor packages20A,20B and to expose ports48A,48B. In cases in which the structure may be damaged by debris entering cavities44via ports48A,48B by conventional singulation techniques, singulation may be performed using a stealth dicing technique, by using a two step dicing operation to clear out any electrically conductive material produced by a first dicing operation prior to performing the second dicing operation, or any other technique which largely prevents or limits the entry of debris into cavities44via ports48A,48B.

Following block156, sensor package fabrication process140ends following the production of multiple MEMS sensor packages, each of which includes a side port extending between a cavity and a side wall of the sensor package. The side port is configured to admit a fluid, e.g., air, external to the cavity into the cavity. When the MEMS sensor package includes a pressure sensor, the pressure of the fluid entering the cavity can be suitably detected by the pressure sensor.

An embodiment of a MEMS sensor package comprises a MEMS die, said MEMS die comprising a substrate having a first inner surface and a first outer surface, a MEMS sensor formed on the first inner surface, and a cap layer having a second inner surface and a second outer surface. The second inner surface of the cap layer is coupled to the first inner surface of the substrate. The cap layer includes a cavity extending inwardly from the second inner surface and overlying a region of the first inner surface of the substrate. The MEMS sensor resides in the cavity at the region of the first inner surface of the substrate, and one of the substrate and the cap layer includes a port extending between the cavity and a side wall of the MEMS die, where the side wall extends between the first outer surface of the substrate and the second outer surface of the cap layer.

An embodiment of a method of making MEMS sensor packages comprises providing a substrate having a first inner surface and a second outer surface, the substrate including a first MEMS sensor at a first region of the first inner surface and a second MEMS sensor at a second region of the first inner surface, the second region being laterally displaced from the first region, and providing a cap layer having a second inner surface and a second outer surface, the cap layer including a first cavity and a second cavity laterally displaced from the first cavity, each of the first and second cavities extending inwardly from the second inner surface. A channel is formed extending inwardly from one of the first inner surface of the substrate and the second inner surface of the cap layer. The second inner surface of the cap layer is coupled to the first inner surface of the substrate such that the first cavity overlies the first region to form a first intermediate sensor structure, the second cavity overlies the second region to form a second intermediate sensor structure, and the channel is interposed between the first and second cavities such that the first and second cavities are in fluid communication with one another. The first intermediate sensor structure is separated from the second intermediate sensor structure to produce a first MEMS sensor package and a second MEMS sensor package.

An embodiment of a structure comprises a substrate having a first inner surface and a first outer surface, a MEMS pressure sensor formed on the first inner surface, a cap layer having a second inner surface and a second outer surface, and an encapsulant covering the substrate and the cap layer, wherein the second inner surface of the cap layer is coupled to the first inner surface of the substrate, the cap layer includes a cavity extending inwardly from the second inner surface and overlying a region of the first inner surface of the substrate, the MEMS pressure sensor resides in the cavity and includes a pressure deformable diaphragm disposed at the region of the first inner surface of the substrate, one of the substrate and the cap layer includes a port extending between the cavity and a side wall of the cap layer, the side wall extending between the first outer surface of the substrate and the second outer surface of the cap layer, and the encapsulant does not obstruct the port.

Thus, a MEMS sensor package is formed, through the execution of relatively simple methodology, to include a MEMS sensor on substrate that is covered by a cap layer. The MEMS sensor resides in a cavity formed in the cap layer, and a port extends between the cavity and a side wall of one of the substrate and the cap layer. The port, formed in the side wall, is exposed during a strip singulation operation of the methodology so that fluid, such as air, external to the cavity can be admitted into the cavity. Accordingly, the MEMS sensor may be a pressure sensor which is stress isolated and can be overmolded, and the pressure sensor is capable of sensing pressure from an environment external to the sensor via the port.