TWI477436B - Method for manufacturing a micro-electromechanical device - Google Patents

Description

Method of manufacturing a microelectromechanical device

The present invention is directed to a method of making a microelectromechanical device.

With the advancement of semiconductor process technology, the development of microelectromechanical systems (MEMS) has been promoted. In the manufacturing method of the conventional micromechanical system, the active component process and the microelectromechanical process are performed separately, and after the active component circuit and the microelectromechanical device are respectively completed, the two are integrated on the same substrate to complete the MEMS system. The above manufacturing method is also called "System In Package" (SIP).

Another conventional manufacturing method is to form a microelectromechanical structure after forming semiconductor elements such as a metal oxide semiconductor device (MOS) and a bipolar junction transistor (BJT) in an active device circuit, and then A wafer level MEMS is completed by performing a metallization process of the active device circuit. The wafer is then diced into wafers (Die) and finally wafer packaged.

Regardless of the manufacturing method described above, in the manufacturing process of a microelectromechanical device, a plasma etching method such as reactive ion etching (RIE) is generally employed to form a movable member or portion of the microelectromechanical device. However, the profile of the microelectromechanical device formed in the above manner is not ideal. In addition, when forming a movable member of a microelectromechanical device, it usually has to be completed by a grinding step. However, the grinding step is often accompanied by vibrations that cause some of the fine structures in the microelectromechanical device to be damaged.

Therefore, there is a need for a new manufacturing method that will improve the above problems.

It is an object of the present invention to provide a method of fabricating a microelectromechanical device that can ameliorate the above problems.

According to an embodiment of the invention, the method comprises the steps of: (a) forming a circuit layer on an upper surface of a substrate, wherein the circuit layer comprises a microstructure and an active component, and the microstructure is electrically connected to the active component; (b) forming a recess through the circuit layer and deep into the substrate such that one of the bottoms of the recess is lower than the upper surface of the substrate, wherein the recess surrounds a portion of the periphery of the microstructure; (c) a sacrificial layer is formed to fill the recess (d) arranging an upper cover over the circuit layer to cover the microstructure; (e) removing a portion of the substrate from a side of the lower surface of the substrate to expose the sacrificial layer; (f) removing the sacrificial layer To release the microstructure; and (g) to configure the cover below the substrate.

According to an embodiment of the invention, the circuit layer of step (a) further comprises a connection pad and a protective layer, wherein the connection pad is electrically connected to the active component, and the protection layer is located on an outer surface of the circuit layer and covers the connection pad. In an embodiment, after the step (g), the method further comprises: (h) removing a portion of the upper cover to expose a portion of the protective layer above the connection pad; and (g) removing a portion of the protective layer to expose Connection pad.

According to an embodiment of the invention, the active component of step (a) is a complementary metal oxide semiconductor component or a bipolar complementary metal oxide semiconductor component.

According to an embodiment of the invention, the vertical distance between the bottom of the step (b) and the upper surface is from about 5 μm to about 100 μm.

According to an embodiment of the invention, the sacrificial layer of step (c) is a polymer material and covers an upper surface of the microstructure.

According to an embodiment of the invention, step (e) comprises grinding the underlying surface of the substrate to expose the sacrificial layer.

According to an embodiment of the invention, step (e) comprises grinding the underlying surface of the substrate and etching the ground substrate by deep reactive ion etching to expose the sacrificial layer.

According to an embodiment of the invention, step (f) removes the sacrificial layer with an oxygen plasma.

According to another embodiment of the present invention, a method of fabricating a microelectromechanical device includes the following steps. Forming a circuit layer on the upper surface of the substrate, the circuit layer comprising the characteristic structure and the microstructure; wherein the feature structure surrounds a portion of the periphery of the microstructure and penetrates the circuit layer, the feature structure comprises a dielectric structure penetrating the circuit layer and a metal structure penetrating circuit Layer and surround the dielectric structure. Next, the features are removed to expose the substrate; wherein removing the features comprises sequentially removing the dielectric structure by dry etching and wet etching to remove the metal structure. Then, a portion of the exposed substrate is removed to form a recess; the recess extends through the circuit layer and has a bottom portion that is lower than the upper surface of the substrate, the recess surrounding the perimeter of the microstructure. Subsequently, a sacrificial layer is formed to fill the recess, and an upper cover is disposed over the circuit layer to cover the microstructure. Next, a portion of the substrate is removed from the lower surface side of the substrate to expose the sacrificial layer. The sacrificial layer is then removed to release the microstructure and the cover is placed under the substrate.

Please refer to FIG. 1 , which is a top view of a microelectromechanical device according to an embodiment of the present invention. The microelectromechanical device can be applied to a microelectromechanical inertial sensing device such as an accelerometer or a gyroscope. FIG. 1 illustrates a microelectromechanical acceleration detector, but the manufacturing method disclosed in the present invention is applicable to other microelectromechanical devices, and is not limited to a microelectromechanical acceleration detector.

As shown in FIG. 1 , the MEMS acceleration detector 100 mainly includes a movable microstructure 110 , a semiconductor circuit 120 , a plurality of connection pads 130 , and a circuit layer 140 . The semiconductor circuit 120 is disposed substantially at the periphery of the movable microstructures 110. The connection pads 130 are typically configurable on the periphery of the semiconductor circuit 120.

The microstructure 110 is received in the through space 142 of the circuit layer 140 , and the microstructure includes a central portion 112 , at least one elastic support 114 , and at least one first electrode 116 . The elastic support member 114 connects the central portion 112 with the circuit layer 140 and causes the central portion 112 to assume a movable state. When an external force acts on the center portion 112, the center portion 112 can be displaced; when the external force disappears, the center portion 112 can return to the original position. The width of the elastic support 114 can be, for example, from about 0.5 μm to about 10 μm. The first electrode 116 extends outwardly from the central portion 112 into the through space 142. The width of the first electrode 116 may be, for example, from about 0.1 μm to about 10 μm.

The circuit layer 140 includes a second electrode 144 extending toward the through space 142 and forming a capacitance with the first electrode 116.

The semiconductor circuit 120 is electrically connected to the second electrode 144 and the first electrode 116 to measure the capacitance between the two electrodes 116 and 144 and convert the measured capacitance signal into a voltage or current signal. Semiconductor circuit 120 can include a complementary metal oxide semiconductor device. The semiconductor circuit 120 can be electrically connected to an external circuit (not shown) via the connection pad 130.

In operation, when the MEMS acceleration detector 100 is subjected to an acceleration, the distance between the second electrode 144 and the first electrode 116 changes, and the capacitance value therebetween changes. The semiconductor circuit 120 measures the amount of change in the capacitance value or the capacitance value to estimate the acceleration received by the MEMS acceleration detector 100.

The above described microelectromechanical acceleration detector 100 is merely an illustrative example to facilitate an understanding of the manufacturing methods disclosed herein, and the manufacturing methods disclosed herein may be used to fabricate other microelectromechanical devices. Furthermore, the embodiments disclosed in the following may be combined or substituted with each other in an advantageous manner, and other embodiments may be added to an embodiment without further description or description.

2 is a flow chart of a method 200 of fabricating a microelectromechanical device in accordance with an embodiment of the present invention. 3 to 16 are schematic cross-sectional views showing respective process stages in the manufacturing method of the embodiment of the present invention, which is roughly a schematic cross-sectional view of the line segment 3-3' in Fig. 1.

Step 210 is performed to form circuit layer 320 on the upper surface of substrate 310, as shown in FIG. Substrate 310 can be, for example, a germanium wafer or other substrate suitable for use in fabricating semiconductor components. Circuit layer 320 includes microstructures 330 and active components 322. The microstructure is electrically connected to the active component. The active component 322 can be, for example, a complementary metal oxide semiconductor device (CMOS) or a bipolar complementary metal oxide semiconductor device (BiCMOS).

In an embodiment, circuit layer 320 further includes feature structure 340 filled in region A. Feature structure 340 surrounds a portion of the perimeter of microstructure 330 and extends through circuit layer 320. In a subsequent step, feature structure 340 will be removed to form a portion of through space 142 depicted in FIG. In other words, the feature structure 340 is pre-filled in the area A to be subsequently removed.

Feature structure 340 includes a dielectric structure 342 and a metal structure 344. Dielectric structure 342 extends through circuit layer 320 and contacts underlying substrate 310. The dielectric structure 342 can be, for example, tantalum oxide or tantalum nitride, or a stack of tantalum oxide and tantalum nitride. Metal structure 344 also extends through circuit layer 320 and surrounds dielectric structure 342. In other words, the metal structure 344 is formed on the outer edge of the feature 340. In more detail, the metal structure 344 can comprise two portions 344a and 344b. The portion 344a of the metal structure physically connects the circuit layer 320 with the dielectric structure 342; the portion 344b of the metal structure physically connects the microstructure 330 with the dielectric structure 342.

In embodiments in which the circuit layer 320 described above includes features 340, the step of forming the circuit layer 320 includes forming a CMOS or BiCMOS process. In the standard process of CMOS components, it can include four metallization processes and two polysiliconization processes (2P4M process), and can also include five metallization processes and one polysiliconization process (5M1P process). Thus, in an embodiment, when CMOS component 322 is formed, feature 340 can be formed simultaneously by a suitable reticle design. For example, when forming a dielectric layer in CMOS device 322, dielectric structure 342 of feature structure 340 can be formed simultaneously. When the metal layer of CMOS element 322 is formed, portions of metal structure 344 in feature structure 340 can be formed simultaneously. When the metal is filled in the via of the CMOS device, a portion of the metal structure 344 can be formed simultaneously. Therefore, the feature structure 340 can be formed step by step while forming the CMOS element 322. In one embodiment, the metal filled in the via of the CMOS device is tungsten, and the metal layer of the CMOS device 322 is aluminum. Therefore, the metal structure 344 can be formed by stacking an aluminum layer and a tungsten layer. That is, the metal structure 344 is a multilayer structure and is composed of at least two metal materials.

In another embodiment, the circuit layer 320 may not include the feature structure 340, and the periphery of the microstructure 330 (such as the region A shown in FIG. 3) is filled with a dielectric material such as hafnium oxide or tantalum nitride instead of the feature structure.

In yet another embodiment, the circuit layer 320 can further include a connection pad 324 and a protective layer 326. The connection pad 324 is electrically connected to the active component 322. The protective layer 326 is located on the outer surface of the circuit layer 320 and covers the connection pads 324. The material of the protective layer 326 may be, for example, cerium oxide.

In step 220, a recess 312 is formed through the circuit layer 320 and into the substrate 310, as shown in FIG. The bottom 312b of the recess 312 is lower than the upper surface 310a of the substrate, and the recess 312 surrounds a portion of the perimeter of the microstructure 330. In a subsequent step, the groove 312 will form a through space 142 as depicted in FIG. Two embodiments of forming the recess 312 will be exemplarily described below.

In an embodiment in which the circuit layer 320 includes the features 340, a photoresist layer 350 is formed over the circuit layer 320 and the microstructures 330, as shown in FIG. 4A. The photoresist layer 350 has an opening 352 to expose the features 340. Next, the dielectric structure 342 is removed by a dry etching method such as reactive ion etching (RIE) as shown in FIG. 4B. Reactive ion etching only etches dielectric materials such as hafnium oxide and tantalum nitride without etching the metal material. During the reactive ion etching process, since the sidewalls of the microstructure 330 and the sidewalls of the circuit layer 320 are covered by the metal structure 344, the reactive ion etching does not damage or etch the sidewalls of the microstructure 330 and the circuit layer 320. The sidewalls of the microstructures 330 and circuit layers 320 maintain their original contoured appearance. Subsequently, the metal structure 344 is removed by wet etching as shown in FIG. 4C. After the metal structure 344 is removed, the opening B shown in FIG. 4C is formed in the circuit layer 320, and the substrate 310 in the opening B is exposed. The etchant employed in the wet etching has a high etching selectivity for the metal material and the oxide material (or nitride), for example, higher than 15:1 or higher than 20:1 or higher than 30:1 or higher. Therefore, when the metal structure 344 is removed, the original sidewall profile appearance of the microstructure 330 and the circuit layer 320 is hardly impaired. For example, the etchant contains sulfuric acid and hydrogen peroxide, and the weight ratio of sulfuric acid to hydrogen peroxide is about 2:1. Of course, other commercially available metal etchants are also suitable for use in the present invention. Finally, a portion of the exposed substrate 310 is removed by, for example, Deep Reactive Ion Etching (DRIE) to form a recess 312 as shown in FIG. In the above embodiment, the angle θ between the sidewall of the microstructure 330 and the upper surface of the substrate 310 may be from about 85 degrees to about 95 degrees. In addition, the sidewalls of the microstructures 330 on both sides of the gap d and the sidewalls of the circuit layer 320 are flat. Therefore, the performance and quality stability of the microelectromechanical device can be improved.

In embodiments in which circuit layer 320 does not include feature structure 340, region A of circuit layer 320 is a dielectric material. The dielectric material in the region A can be removed using the RIE, and the opening B shown in FIG. 4C is formed in the circuit layer 320. Next, a portion of the exposed substrate 310 is removed by, for example, Deep Reactive Ion Etching (DRIE) to form a recess 312 as shown in FIG.

In one embodiment, a vertical distance d between the bottom portion 312b and the upper surface 310a is from about 5 μm to about 100 μm, as shown in FIG.

In step 230, a sacrificial layer 360 is formed to fill the recess 312, as shown in FIG. The sacrificial layer can be made, for example, of a polymer material. For example, the sacrificial layer can be a photoresist material that is filled in the recess 312 after spin coating, drying, exposure, and development. The material of the sacrificial layer may be, for example, a phenol resin type photoresist, an acrylic type photoresist or other organic material. In an embodiment, the sacrificial layer 360 is filled in the recess 312 and covers the upper surface 332 of the microstructure 330.

In step 240, an upper cover 370 is disposed over the circuit layer 320 to cover the microstructures 330, as shown in FIG. The upper cover 370 is used to protect the finally formed microelectromechanical device, and the upper cover 370 can be made, for example, of a glass or tantalum substrate. In an embodiment, the upper cover 370 can be fixed above the circuit layer 320 by an adhesive layer 372.

In step 250, portions of the substrate 310 are removed from the side of the lower surface 310b of the substrate 310 to expose the sacrificial layer 360. Two ways of accomplishing this step are exemplarily described below.

In one embodiment, the lower surface 310b of the substrate 310 may be first ground to reduce the thickness of the substrate 310 to a certain thickness, as shown in FIG. 7A. For example, the thickness of the substrate 310 can be ground to about 150 [mu]m. Subsequently, the lower surface of the substrate 310 is etched by DRIE to form a recess 314 on the lower surface of the substrate 310. The depth of the recess 314 is sufficient to expose the sacrificial layer 360 as shown in Figure 7B.

In another embodiment, the lower surface of the substrate 310 is directly ground until the sacrificial layer is exposed. This embodiment does not use a DRIE process. As shown in Figure 7C.

In the prior art, when the lower surface of the substrate is ground, vibration is often accompanied, and the fine structure in the microstructure is damaged by vibration. For example, the elastic support member 114 or the electrodes 116, 144 shown in Fig. 1 are typically only about 0.1 μm to about 10 μm wide and are easily damaged by vibration. In the embodiment of the present invention, after the recess 312 is formed, the sacrificial layer 360 is filled in the recess 312, which can effectively prevent the microstructure from being damaged by vibration. In addition, filling the sacrificial layer 360 in the recess 312 also prevents the adhesive layer 372 or other contaminants from entering the recess 312 when step 240 is performed. Thus, according to an embodiment of the present invention, the yield of the microelectromechanical device can be effectively improved.

In step 260, the sacrificial layer 360 is removed to release the microstructures 330 as shown in Figures 8A and 8B. Fig. 8A corresponds to the embodiment of Fig. 7B, and Fig. 8B corresponds to the embodiment of Fig. 7C. In an embodiment, the sacrificial layer 360 may be removed using an oxygen plasma. In other embodiments, other chemical solvents may be utilized to remove the sacrificial layer 360. In other words, the method of removing the sacrificial layer 360 can be changed or adjusted depending on the material properties or process requirements of the sacrificial layer 360. As used herein, "releasing microstructure" means causing a microelectromechanical device to produce a structure or component that is relatively movable. In particular, after the sacrificial layer 360 is removed, the microstructures 330 can be displaced relative to the circuit layer 320.

In step 270, the lower cover 380 is disposed below the substrate 310 to form the microelectromechanical device 300 as shown in FIGS. 9A and 9B (the 9A and 9B drawings correspond to the embodiments of FIGS. 8A and 8B, respectively). The lower cover 380 and the upper cover 370 form a closed space C surrounding the microstructures 330. The microstructures 330 can be relatively displaced in the enclosed space C to cause the microelectromechanical device to produce a predetermined function. The upper cover 370 and the lower cover 380 serve to protect the microstructures 330 while preventing contaminants from entering the enclosed space C. The material of the lower cover 380 may be the same as or different from the upper cover 370. In an embodiment, the lower cover 380 can be fixed under the substrate 310 by an adhesive layer 382.

The MEMS device 300 can be electrically connected to an external circuit or system by various connection methods. The manner in which the MEMS device is connected to an external circuit or system is generally related to the package form of the MEMS device. The following is an example of a Quad Flat Non-leaded Package (QFN) to illustrate how a microelectromechanical device can be connected to an external circuit. It should be understood by those skilled in the art that other forms of connection are also applicable to the present invention, and thus the present invention is not limited to the methods or steps disclosed herein.

In an embodiment, after step 270, a portion of the upper cover 370 is removed to expose the protective layer 326 located above the connection pad 326, as shown in FIGS. 10A and 10B (the 10A and 10B drawings respectively correspond to the 9A and The implementation of Figure 9B). This step can be accomplished by laser cutting or mechanical cutting, which is well known to those skilled in the art. Subsequently, the exposed portion of the protective layer 326 can be removed by, for example, an RIE process, and the connection pads 324 under the protective layer 326 are exposed as shown in FIGS. 11A and 11B. The exposed connection pads 324 can serve as a connection point for the microelectromechanical device to external circuitry.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention, and the present invention can be modified and modified without departing from the spirit and scope of the present invention. The scope is subject to the definition of the scope of the patent application attached.

100. . . MEMS acceleration detector

110. . . microstructure

112. . . Central department

114. . . Elastic support

116. . . First electrode

120. . . Semiconductor circuit

130. . . Connection pad

140. . . Substrate

142. . . Through space

144. . . Second electrode

200. . . method

210, 220, 230, 240, 250, 260, 270. . . step

300. . . Microelectromechanical device

310. . . Substrate

310a. . . Upper surface

310b. . . lower surface

312. . . Groove

312b. . . bottom

314. . . Depression

320. . . Circuit layer

322. . . Active component

324. . . Connection pad

326. . . The protective layer

330. . . microstructure

332. . . Upper surface

340. . . Feature structure

342. . . Dielectric structure

344. . . Metal structure

350. . . Photoresist layer

352. . . Opening

360. . . Sacrificial layer

370. . . Upper cover

372. . . Adhesive layer

380. . . Lower cover

382. . . Adhesive layer

A. . . region

B. . . Opening

C. . . Closed space

d. . . distance

θ. . . Angle

1 is a top view of a microelectromechanical device according to an embodiment of the present invention.

2 is a flow chart showing a method of manufacturing a microelectromechanical device according to an embodiment of the present invention.

3 to 11B are schematic cross-sectional views showing respective process stages in the method of fabricating a microelectromechanical device of the present invention.

200. . . method

210, 220, 230, 240, 250, 260, 270. . . step

Claims (10)

A method of fabricating a microelectromechanical device, comprising: (a) forming a circuit layer on an upper surface of a substrate, wherein the circuit layer comprises a microstructure and an active component, and the microstructure is electrically connected to the active component; (b) forming a recess extending through the circuit layer and into the substrate such that a bottom of the recess is lower than an upper surface of the substrate, wherein the recess surrounds a portion of the perimeter of the microstructure; (c) forming a sacrificial layer is filled in the recess; (d) an upper cover is disposed over the circuit layer to cover the microstructure; (e) a portion of the substrate is removed from a side of the lower surface of the substrate to Exposing the sacrificial layer; (f) removing the sacrificial layer to release the microstructure; and (g) disposing the cover under the substrate, the lower cover and the upper cover forming a closed space surrounding the microstructure. The method of claim 1, wherein the circuit layer of the step (a) further comprises a connection pad and a protective layer, wherein the connection pad is electrically connected to the active component, and the protective layer is located on an outer surface of the circuit layer And covering the connection pad. The method of claim 2, after the step (g), further comprising: (h) removing a portion of the upper cover to expose a portion of the protective layer above the connection pad; (i) removing the portion of the protective layer to expose the connection pad. The method of claim 1, wherein the active component of step (a) is a complementary metal oxide semiconductor device or a bipolar complementary metal oxide semiconductor device. The method of claim 1, wherein a vertical distance between the bottom of the step (b) and the upper surface is from about 5 μm to about 100 μm. The method of claim 1, wherein the sacrificial layer of the step (c) is a polymer material and covers an upper surface of the microstructure. The method of claim 1, wherein the step (e) comprises: grinding a lower surface of the substrate to expose the sacrificial layer. The method of claim 1, wherein the step (e) comprises: grinding the lower surface of the substrate; and etching the ground substrate by deep reactive ion etching to expose the sacrificial layer. The method of claim 1, wherein the step (f) removes the sacrificial layer with an oxygen plasma. A method of fabricating a microelectromechanical device, comprising: Forming a circuit layer on an upper surface of a substrate, the circuit layer comprising a feature structure and a microstructure, wherein the feature structure surrounds a portion of the periphery of the microstructure and penetrates the circuit layer, wherein the feature structure comprises: a dielectric structure extending through the circuit layer; and a metal structure extending through the circuit layer and surrounding the dielectric structure; removing the feature to expose the substrate, wherein removing the feature comprises sequentially etching dry Removing the metal structure in addition to the dielectric structure and wet etching; removing a portion of the exposed substrate to form a recess, wherein the recess extends through the circuit layer and has a bottom lower than the substrate a surface, and the groove surrounds the portion of the periphery of the microstructure; a sacrificial layer is formed in the recess; an upper cover is disposed over the circuit layer to cover the microstructure; and a lower surface of the substrate is Removing a portion of the substrate to expose the sacrificial layer; removing the sacrificial layer to release the microstructure; and disposing a cover under the substrate, the lower cover and the upper cover forming a closure The microstructure around the room.