Method of fabricating micro-electromechanical system microphone structure

A method of fabricating a micro-electromechanical system microphone structure is disclosed. First, a substrate defining a MEMS region and a logic region is provided, and a surface of the substrate has a dielectric layer thereon. Next, at least one metal interconnect layer is formed on the dielectric layer in the logic region, and at least one micro-machined metal mesh is simultaneously formed in the dielectric layer of the MEMS region. Therefore, the thickness of the MEMS microphone structure can be effectively reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro-electromechanical system (MEMS) microphone structure and a method of fabricating the same, and more particularly, to a method of fabricating a MEMS microphone structure and the MEMS microphone structure formed thereby so as to effectively reduce the thickness of the MEMS microphone structure.

2. Description of the Prior Art

MEMS microphone structures are modern technology, which coordinate electrical circuits and mechanics. The MEMS microphone structure presently can be made from general micro electronic technology, such as photolithography, vapor phase deposition, etching or LIGA, performed on the substrate, such as an insulating layer or other semiconductor. Recently, in order to coordinate the MEMS device and the complementary metal-oxide-semiconductor (CMOS) device into MEMS microphone structure, MEMS microphone structure is fabricated by using the same types of steps that are used to fabricate conventional analog and digital complementary metal oxide semiconductor (CMOS) circuits.

Referring toFIG. 1throughFIG. 3,FIG. 1throughFIG. 3are schematic diagrams illustrating a method of fabricating a MEMS microphone structure according to the prior art. As shown inFIG. 1, the method of fabricating the MEMS microphone structure10with multi-metal layers according to the prior art is as follows. First, a substrate12is provided, and the surface of the substrate12has a base sacrificial layer14and a first metal layer16. Then, the first metal layer16is patterned to form a first micro-machined metal mesh18. Next, as shown inFIG. 2, a first sacrificial layer20is deposited to cover the substrate12, and the surface of the first sacrificial layer20is planarized. Thereafter, a second metal layer22is formed on the first sacrificial layer20, and then, a second metal layer22is patterned to form a second micro-machined metal mesh. Next, a second sacrificial layer26is deposited to cover the substrate12, and the surface of the second sacrificial layer26is planarized. Then, a third metal layer28is formed on the second sacrificial layer26, and then, the third metal layer28is patterned to form a third micro-machined metal mesh. Next, a third sacrificial layer32covers the substrate12. Finally, as shown inFIG. 3, an isotropic dry etching process is utilized to remove the first sacrificial layer20, the second sacrificial layer26, the third sacrificial layer32and a part of the base sacrificial layer14among the first micro-machined metal mesh18, second micro-machined metal mesh and third micro-machined metal mesh, so that the first micro-machined metal mesh18, the second micro-machined metal mesh and the third micro-machined metal mesh are suspended above the substrate12so as to form a multilayer membrane. Next, a back side etching process is performed to etch through the substrate12so as to allow free movement of air molecules and vibrate the multilayer membrane. Therefore, the MEMS microphone structure10according to the prior art is formed.

As mentioned above, the micro-machined metal mesh according to the prior art is formed by using an Al process. The first metal layer, the second metal layer and the third metal layer composed of aluminum are respectively formed first, and then, a photoresist layer is coated thereon. Next, the photoresist layer is patterned, and then, the photoresist layer is used as a mask to etch the metal layers so as to form the micro-machined metal mesh. However, the height between the micro-machined metal mesh and the substrate depends on the thickness of the sacrificial layer, so that the thickness of the MEMS microphone structure is the total thickness of the sacrificial layers and the micro-machined metal meshes. The thickness of the MEMS device is limited. Therefore, in order to make the MEMS microphone structure have a smaller size or thickness, to improve the MEMS microphone structure and the method of fabricating the same is important.

SUMMARY OF THE INVENTION

It is therefore a primary objective of the present invention to provide a MEMS microphone structure and a method of fabricating the same, so that the thickness of the MEMS microphone structure can be effectively reduced.

The present invention provides a method of fabricating a MEMS microphone structure. First, a substrate is provided. The substrate defines a MEMS region and a logic region, and a surface of the substrate has a first dielectric layer and a first contact plug thereon. The first contact plug is located on the substrate in the logic region. Next, the first dielectric layer is etched to form at least one first meshed trench on the first dielectric layer in the MEMS region. Then, a metal layer is formed on the first dielectric layer and filled into the first meshed trench. Next, a patterned mask layer is formed on the metal layer in the logic region. Thereafter, a part of the metal layer uncovered with the patterned mask layer and outside the meshed trench is removed to simultaneously form at least one first metal interconnect layer on the first dielectric layer in the logic region and to form at least one first micro-machined metal mesh in the meshed trench of the MEMS region.

The present invention further provides a method of fabricating a MEMS microphone structure. First, a substrate is provided. The substrate defines a MEMS region and a logic region, and a surface of the substrate has a first dielectric layer thereon. Next, at least one circuit trench and at least one contact hole is formed in the first dielectric layer of the logic region. Then, at least one first meshed trench is formed in the first dielectric layer of the MEMS region. Then, a metal layer is formed on the first dielectric layer and filled into the circuit trench, the contact hole and the meshed trench. Finally, the metal layer outside the circuit trench, the contact hole and the meshed trench is removed to form a first metal interconnect structure in the circuit trench and the contact hole and to form a first micro-machined metal mesh in the meshed trench, wherein the first metal interconnect structure comprises at least one first lower contact plug and a first upper metal interconnect layer.

The present invention provides a MEMS microphone structure. The MEMS microphone structure comprises a substrate defining a logic region and a MEMS region, at least one dielectric layer disposed on the substrate of the logic region, at least one contact plug disposed in the dielectric layer of the logic region, at least one metal interconnect layer disposed on the dielectric layer, and at least one micro-machined metal mesh disposed on the dielectric layer in the MEMS region, and the height between an upper surface of the micro-machined metal mesh and the substrate and the height between a lower surface of the metal interconnect layer and the substrate being substantially the same.

The present invention further provides a MEMS microphone structure. The MEMS microphone structure comprises a substrate defining a logic region and a MEMS region, at least one dielectric layer disposed on the substrate of the logic region, at least one metal interconnect structure embedded in the dielectric layer, and at least one micro-machined metal mesh disposed in the MEMS region. The metal interconnect structure comprises at least one upper metal interconnect layer and at least one lower contact plug. The height between an upper surface of the micro-machined metal mesh and the substrate and the height between an upper surface of the upper metal interconnect layer and the substrate being substantially the same, and the height between a lower surface of the micro-machined metal mesh and the substrate and the height between a lower surface of the upper metal interconnect layer and the substrate being different.

The present invention utilizes a damascene process to form the micro-machined metal mesh in the MEMS region so as to reduce the thickness of the stacked micro-machined metal meshes, and reduce the thickness of the MEMS microphone structure.

DETAILED DESCRIPTION

ReferringFIG. 4throughFIG. 10,FIG. 4throughFIG. 10are schematic diagrams illustrating a method of fabricating a MEMS microphone structure according to a first embodiment of the present invention. As shown inFIG. 4, first, a substrate102, such as semiconductor substrate etc., is provided. The substrate102defines a MEMS region106and a logic region108, and a surface of the substrate102has a based dielectric layer104, a based metal interconnect layer112, a first dielectric layer110and at least one first contact plug thereon. In this embodiment, the based dielectric layer104is disposed on the substrate102, and the based metal interconnect layer112is disposed on the substrate102. The present invention is not limited to this condition, and the based metal interconnect layer can be embedded in the based dielectric layer. The first dielectric layer110covers the based metal interconnect layer112, and the first contact plug114is disposed in the first dielectric layer110and passing through the first dielectric layer110. The based dielectric layer104and the first dielectric layer110can be an Inter-Layer Dielectric (ILD) layer or any one of Inter-Metal Dielectric (IMD) layer of metal interconnect, and also can be single layer structure or multilayer structure. The material of the based dielectric layer104and the first dielectric layer110can comprise insulating material, such as silicon nitride and low-k.

In addition, the logic region108between the based dielectric layer104and the substrate102can further has at least one transistor (not shown in figure), which is used to be a circuit-controlled device of the MEMS microphone structure. The transistor can be electrically connected to the based metal interconnect layer112through at least one based contact plug (not shown in figure). The transistor can be P-type, N-type or Complementary type Metal Oxide Semiconductor (MOS). Furthermore, the first dielectric layer110further has at least one lower electrode layer115thereon, and the lower electrode layer115is located in the MEMS region106. The material of the lower electrode layer115can be polysilicon or metal for being an electrode of MEMS microphone structure.

Next, as shown inFIG. 5, a first patterned mask layer116, such as a photoresist layer, is formed on the first dielectric layer110. The first patterned mask layer partially covers the first dielectric layer110in the MEMS region106and fully covers the first dielectric layer110in the logic region108. The area of the first dielectric layer exposed by the first patterned mask layer116in the MEMS region106has a same pattern as a pattern of a first layer in a required MEMS microphone structure.

Then, as shown inFIG. 6, the first patterned mask layer116is used as a mask, and an etching process, such as an anisotropic deep reactive-ion etching (DRIE) process for dry-etching, is performed to etch the first dielectric layer110uncovered with the first patterned mask layer116so as to form at least one meshed trench118on the first dielectric layer110in the MEMS region106. Then, the first patterned mask layer116used as the mask is removed. Next, a metal layer120is formed to cover the first dielectric layer110and fill the meshed trench118in the MEMS region106. After that, a second patterned mask layer122is formed on the metal layer120in the logic region108so as to define the required pattern of a first layer of the metal interconnect structure in logic region108. The second patterned mask layer122does not cover the metal layer120in the MEMS region106.

Next, as shown inFIG. 7, the second patterned mask layer122is used as a mask, and an etch back process is performed to remove a part of the metal layer uncovered with the second patterned mask layer122and outside the meshed trench118. At least one first metal interconnect layer124is therefore formed on the first dielectric layer110in the logic region108, and simultaneously, at least one first micro-machined metal mesh126is formed in the meshed trench118of the MEMS region106. It should be noted the first metal interconnect layer124and the first micro-machined metal mesh126of this embodiment are composed of the same metal layer120and formed in a same etching process. Therefore, the steps for individually fabricating the circuit device in the logic region and the microphone structure in the MEMS region according to the prior art can be effectively reduced. In addition, the material of the metal layer120can include conductive metal, such as aluminum or polycide etc., or metallic compound. The present invention is not limited to these materials, and the material of the metal layer is chosen according to the material used for etching.

Next, as shown inFIG. 8, a second dielectric layer128is formed to cover the first metal interconnect layer124, the first micro-machined metal mesh126and the first dielectric layer110, and at least one second contact plug130is formed in the second dielectric layer128of the logic region108. The second contact plug130is corresponding to the first metal interconnect layer124and passing through the second dielectric layer128. Then, the step of forming the first metal interconnect layer124and the first micro-machined metal mesh126is repeated to form a second metal interconnect layer132on the second dielectric layer128in the logic region108and to form a second micro-machined metal mesh134in the second dielectric layer128of the MEMS region106. Thereafter, a passivation layer136is formed to cover the second metal interconnect layer132, the second micro-machined metal mesh134and the second dielectric layer128. It should be noted that the present invention is not limited to fabricate only two metal interconnect layers or two micro-machined metal meshes. The present invention can only have one layer of the micro-machined metal mesh or the metal interconnect layer, and the numbers of the layers in the MEMS microphone structure can be chosen according to the design. After finishing fabricating the all metal interconnect layers and micro-machined metal meshes, the passivation layer136is then formed.

Finally, as shown inFIG. 9, after finishing all metal interconnect layer and the passivation layer136, a patterned mask (not shown in figure) is used to cover and protect the logic region108, and an etching process, such as an isotropic wet etching or vapor etching process, is performed to remove the first dielectric layer110surrounding the first micro-machined metal mesh126in the MEMS region106and the second dielectric layer128and the passivation layer136surrounding the second micro-machined metal mesh134. Therefore, the first micro-machined metal mesh126and the second micro-machined metal mesh134are suspended to be membranes of the MEMS microphone structure. Then, the patterned mask is removed.

Thereafter, the formation of the MEMS microphone structure is continued. As shown inFIG. 10, an elastic layer138is applied conformally to allow the vibrated membrane to have a better elasticity. The elastic layer138may comprise for example plastic rubber, Teflon, Pyralene (Trade name, a chemical compound of polychlorinated biphenyls), or polyamide. Then, a back side etching process is performed to etch through the substrate102in the MEMS region106to form a vent hole140so as to allow free movement of air molecules. Therefore, the micro-machined metal meshes can vibrate due to the acoustic wave from the outside or transfer the acoustic wave to the outside through vibrating itself. And, a MEMS microphone structure100according to the first embodiment of the present invention is finished. Furthermore, in this embodiment, the micro-machined metal meshes of the MEMS microphone structure are preferred as a membrane with a mesh structure, but the present invention is not limited to this. The layout structure of the micro-machined metal mesh can be adjusted depending on the required function of the MEMS microphone structure. It should be noted that the first micro-machined metal mesh126and the second micro-machined metal mesh134of this embodiment is suspended in the MEMS region106and held by the first dielectric layer110in the logic region108. In addition, the first micro-machined metal mesh126and the second micro-machined metal mesh134can respectively be further electrically connected to the first metal interconnect layer124and the second metal interconnect layer132in the logic region108, so that the first micro-machined metal mesh126and the second micro-machined metal mesh134can have a characteristic of electrical transportation.

As mentioned above, in this embodiment, the first metal interconnect layer124in the logic region108is made from the Al process, and the first micro-machined metal mesh126in the MEMS region106is made from a damascene-like process at the same time. The height between the upper surface of the first micro-machined metal mesh126and the substrate102and the height between the lower surface of the first metal interconnect layer124and the substrate102are substantially the same, and the height between the upper surface of the second micro-machined metal mesh134and the substrate102and the height between the lower surface of the second metal interconnect layer132and the substrate102are substantially the same. Therefore, the first micro-machined metal mesh126is lower than the first metal interconnect layer124, and the second micro-machined metal mesh134is lower than the second metal interconnect layer132, so that the stacked thickness in the MEMS region106can be effectively reduced. In addition, in this embodiment, the first metal interconnect layer124and the first micro-machined metal mesh126are composed of a same metal layer and simultaneously formed in a same etching process, and the second metal interconnect layer132and the second micro-machined metal mesh134are composed of a same metal layer and simultaneously formed in a same etching process, so that the cost of the required fabricating steps in individually fabricating the MEMS region106and the logic region108can be effectively reduced.

In addition, as shown inFIG. 10, the present invention further provides a MEMS microphone structure100fabricated by the abovementioned first embodiment. The MEMS microphone structure100includes a substrate102defining a MEMS region106and a logic region108, a based dielectric layer104, a based metal interconnect layer112, a first dielectric layer110, at least one first contact plug114, at least one first metal interconnect layer124, and a first micro-machined metal mesh126. The based dielectric layer104is disposed on the substrate102, and the based metal interconnect layer112is disposed on the based dielectric layer104. The first dielectric layer110partially covers the based dielectric layer104and the based metal interconnect layer112, and the first metal interconnect layer112is disposed on the first dielectric layer110. The first contact plug114is disposed in the first dielectric layer110and passing through the first dielectric layer110, and the first contact plug114connects the first metal interconnect layer124and the based interconnect layer112. The first micro-machined metal mesh126is held by the first dielectric layer110in the logic region108so as to be suspended in the MEMS region106, and the first micro-machined metal mesh126can be electrically connected to the first metal interconnect layer124. Therefore, control signals can be transported through the first metal interconnect layer124to the first micro-machined metal mesh126, and be transported to the outside by vibrating the first micro-machined metal mesh126. The height between an upper surface of the first micro-machined metal mesh126and the substrate102is substantially the same as or lower than the height between a lower surface of the first metal interconnect layer124and the substrate102. In addition, this embodiment is not limited to only have one micro-machined metal mesh or one metal interconnect layer. The MEMS microphone structure100can further comprises at least one second dielectric layer128disposed on the first dielectric layer110, at least one second metal interconnect layer132disposed on the second dielectric layer128, at least one second contact plug130connecting the first metal interconnect layer132and the second metal interconnect layer124, and at least one second micro-machined metal mesh134disposed in the MEMS region106.

It should be noted the present invention is not limited to the fabricating method according to the abovementioned embodiment, and the steps for fabricating the metal interconnect layer and the contact plug in the method of fabricating the MEMS microphone structure of the present invention also can be different. For convenience, like elements are denoted by like numerals, and the like steps are not detailed redundantly. Referring toFIG. 11throughFIG. 15,FIG. 11throughFIG. 15are schematic diagrams illustrating a method of fabricating a MEMS microphone structure according to a second embodiment of the present invention. As shown inFIG. 11, compared with the first embodiment, this embodiment provides a substrate102, which has a first dielectric layer110thereon, and there are no contact plug in the first dielectric layer110before forming the MEMS microphone structure of this embodiment.

Thereafter, as shown inFIG. 12, different from the first embodiment, this embodiment performs a dual damascene process, such as a via-first dual damascene process, a trench-first dual damascene process, a partial via-first dual damascene process and etc., for the first dielectric layer110in the logic region108so as to form at least one circuit trench202and at least one contact hole204in the first dielectric layer110of the logic region108and form the meshed trench118in the first dielectric layer110of the MEMS region106. It should be noted that the meshed trench118can be formed by two stage etching process in dual damascene process. For this reason, when the dual damascene process is via-first dual damascene process, the meshed trench118and the circuit trench202are formed in a same etching process. When the dual damascene process is trench-first dual damascene process, the meshed trench118and the contact hole204are formed in a same etching process. When the dual damascene process is partial via-first dual damascene process, the meshed trench118, the contact hole204and the circuit trench202are formed in a same etching process. The present invention is not limited that the meshed trench118should be formed with the contact hole204and the circuit trench202in a same etching process, and the meshed trench118also can be formed before or after the dual damascene process.

Then, as shown inFIG. 13, a metal layer120is formed on the substrate102to cover the first dielectric layer110and fill the circuit trench202, the contact hole204and the meshed trench118. Next, the metal layer120outside the circuit trench202, the contact hole204and the meshed trench118is removed to form a first metal interconnect structure206in the circuit trench202and the contact hole204and form a first micro-machined metal mesh126. Compared with the first embodiment, the first metal interconnect structure206includes at least one first upper metal interconnect layer208and at least one lower contact plug210, which are composed of a same metal layer and formed in a same step. The first upper metal interconnect layer208and the first lower contact plug210construct a dual damascene structure, and the first micro-machined metal mesh126is a single damascene structure. In addition, the step for removing the metal layer120is a planarization process, which can includes a chemical mechanical polishing (CMP) process, an etching process or a combination thereof. The material constituting the metal layer120can include Cu, Al, alloy, polycide, W, Ti, TiN, Ta, TaN or a combination thereof, and the material of the metal layer120is mainly determined according to the method for removing the metal layer120. The metal layers for filling the meshed trench118, the circuit trench202and the contact hole204in the present invention also can be different metal layers. This means a metal layer can be filled into the meshed trench118, and the other metal layer can be filled into the circuit trench202and the contact hole204, so that the material of the first metal interconnect structure206can be different from the material of the first micro-machined metal mesh126.

Next, as shown inFIG. 14, a second dielectric layer128is formed to cover the first metal interconnect structure206, the first micro-machined metal mesh126and the first dielectric layer110. Then, the step of this embodiment for forming the first metal interconnect structure206and the first micro-machined metal mesh126is repeated to form a second metal interconnect layer212embedded in the second dielectric layer128of the logic region108and to form a second micro-machined metal mesh134in the second dielectric layer128of the MEMS region106. Thereafter, a passivation layer136is formed to cover the second metal interconnect structure212, the second micro-machined metal mesh134and the second dielectric layer128. It should be noted that the present invention is not limited to fabricate only two metal interconnect layers or two micro-machined metal meshes. The present invention can only have one layer of the micro-machined metal mesh or the metal interconnect layer, and the numbers of the layers in the MEMS microphone structure can be chosen according to the design. After finishing fabricating the all metal interconnect layers and micro-machined metal meshes, the passivation layer136is then formed.

Then, as shown inFIG. 15, after finishing all metal interconnect layer and the passivation layer136, the first dielectric layer110surrounding the first micro-machined metal mesh126in the MEMS region106and the second dielectric layer128and the passivation layer136surrounding the second micro-machined metal mesh134are removed. Therefore, the first micro-machined metal mesh126and the second micro-machined metal mesh134are suspended to be membranes of the MEMS microphone structure200. Thereafter, the following processes of this embodiment are the same as theFIG. 10of the first embodiment, and the following processes of this embodiment will not be detailed redundantly. It should be noted that the step for forming the meshed trench118and the step for forming the circuit trench202and the contact hole204are performed in a same dual damascene process, and the meshed trench118, the circuit trench202and the contact hole204are filled with a same metal layer in the following process. Therefore, the cost of the required fabricating steps in individually fabricating the MEMS region106and the logic region108can be effectively reduced.

In addition, as shown inFIG. 15, the present invention further provides a MEMS microphone structure200fabricated by the abovementioned method according to the second embodiment. The MEMS microphone structure200includes a substrate102defining a MEMS region106and a logic region108, a based dielectric layer104, a based metal interconnect layer112, a first dielectric layer110, a first metal interconnect structure206, and a first micro-machined metal mesh126. The based dielectric layer104is disposed on the substrate102, and the based metal interconnect layer112is disposed on the based dielectric layer104. The first dielectric layer110partially covers the based dielectric layer104and the based metal interconnect layer112, and the first metal interconnect structure206is embedded in the first dielectric layer110. The first metal interconnect structure206includes at least one first upper metal interconnect layer208and at least one first lower contact plug210, and the first lower contact plug210is electrically connected to the based metal interconnect layer112and the first upper metal interconnect layer208. The first micro-machined metal mesh126is held by the first dielectric layer110so as to be suspended in the MEMS region106. The differences of this embodiment from the MEMS microphone structure of the first embodiment are that the height between the upper surface of the first micro-machined metal mesh126and the substrate102is substantially the same as the height between the upper surface of the first metal interconnect structure206and the substrate102, and the height between the lower surface of the first micro-machined metal mesh126and the substrate102is different from the height between the first lower contact hole210and the substrate102. This also means the thicknesses of the first micro-machined metal mesh126and the first upper metal interconnect layer208are different. In addition, this embodiment is not limited to only have one micro-machined metal mesh or one metal interconnect structure. The MEMS microphone structure200can further comprises at least one second dielectric layer128disposed on the first dielectric layer110, at least one second metal interconnect structure212disposed in the second dielectric layer128and at least one second micro-machined metal mesh134disposed in the MEMS region106. The second metal interconnect structure212includes at least one second upper metal interconnect layer214and at least one lower contact plug216.

It should be noted that the present invention can further combine the methods of the first embodiment and the second embodiment to form the MEMS microphone structure including the first embodiment and the second embodiment. Referring toFIG. 16andFIG. 17,FIG. 16andFIG. 17are schematic diagrams illustrating cross-sections of a MEMS microphone structure combining the first embodiment and the second embodiment of the present invention. As shown inFIG. 16, a MEMS microphone structure300can utilize the method of the first embodiment to form a first micro-machined metal mesh302and a first metal interconnect layer304on the first dielectric layer110in the logic region108. Then, the method of the second embodiment can be utilized to form a second micro-machined metal mesh306on the first micro-machined metal mesh302and the first metal interconnect layer304and a second metal interconnect structure308disposed in the second dielectric layer128. The present invention is not limited to the abovementioned combination of the first embodiment and the second embodiment, and the present invention can adjust the order and repeated time of the first embodiment and the second embodiment according to the requirements. In addition, as shown inFIG. 17, a method of fabricating a MEMS microphone structure400of the present invention also can selectively utilize a dual damascene process in the MEMS region106to form a plurality of contact plugs406between the first micro-machined metal mesh402and the second micro-machined metal mesh404so as to help the connections between the micro-machined metal meshes. The mechanical quality and the synchronous resonance of the micro-machined metal mesh are enhanced.

In summary, the present invention utilize the damascene-like process, the damascene process or the dual damascene process to form the micro-machined metal mesh in the MEMS region, and simultaneously, the present invention further integrates the Al process, the plug process or the dual damascene process to form the metal interconnect structure in the logic region so as to effectively reduce the thickness of the MEMS microphone structure and greatly simplify the process of the integrated MEMS microphone structure.