Abstract:
The invention provides a manufacturing method of a MEMS device, which includes: providing an integrated circuit device including a substrate and an electrical structure on the substrate, the electrical structure includes at least one sensing region and at least one first connection section; providing a structure layer, and forming at least one second connection section on the structure layer; bonding the at least one first connection section and the at least one second connection section; etching the structure layer for forming at least one movable structure, the movable structure being located at a position corresponding to a position of the sensing region, and the movable structure being connected to the at least one first connection section via the at least one second connection section; and thereafter, providing a cap to cover the movable structure and the sensing region, wherein the movable structure is not directly connected to the cap.

Description:
CROSS REFERENCE 
     The present invention claims priority to U.S. 61/868,418, filed on Aug. 21, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a manufacturing method of micro-electro-mechanical system (MEMS) device, especially a manufacturing method including: first providing a structure layer to connect a substrate, and afterward providing a cap to cover the structure layer and a portion of the substrate such that a movable structure is not connected to the cap for improving sensing stability, and a MEMS device made thereby. 
     2. Description of Related Art 
     MEMS devices are often used for sensing motion or pressure, such as acceleration sensors, gyroscopes, altitude sensors, etc. AMEMS device includes a micro-electro-mechanical device in cooperation with an integrated circuit. There are three approaches to integrate a micro-electro-mechanical device and an integrated circuit: two-chip solution, CMOS-MEMS solution, and wafer-level integration solution. 
       FIG. 1  shows a MEMS device  10  according to the two-chip solution. A micro-electro-mechanical device chip  11  and an integrated IC chip  12  are separately packaged into chips and wire-bonded for signal transmission (as illustrated by the solid dots in figure) . The two-chip solution has an advantage that the manufacturing process is simple, because the micro-electro-mechanical device chip  11  and the integrated circuit chip  12  are separately manufactured and packaged; however, the two-chip solution has a drawback that the separate packages require related pads and pins which increase the cost and consume a larger area. Further, the two-chip solution has another drawback that the wire bond may generate parasitic effects (such as parasitic capacitances formed by the pads), resulting in noises, and the parasitic effects may further influence other electrical behaviors of the MEMS device  10 . The problem is that the the parasitic capacitances and the change of these in operation can not be accurately predicted in the design stage for the micro-electro-mechanical device chip  11  and the integrated circuit  12 , and can not be accurately compensated in manufacturing the chips; therefore, the sensing performance of this solution is less accurate. 
       FIG. 2  shows a MEMS device  20  according to the CMOS-MEMS solution. A micro-electro-mechanical device  21  and an integrated circuit  22  are manufactured on one semiconductor wafer but located at different positions.  FIG. 2  shows an example that the micro-electro-mechanical device  21  and the integrated circuit  22  are located at two different regions on one same plane; there are other examples (not shown) wherein the micro-electro-mechanical device  21  and the integrated circuit  22  are processed in series. This solution has a drawback that the manufacturing process is more complicated because the micro-electro-mechanical device  21  and the integrated circuit  22  have different requirements. For example, the stack of metal interconnections and isolation layers in manufacturing the integrated circuit  22  may cause a structure distortion in the micro-electro-mechanical device  21  because of different thermal expansion coefficients of different layers, leading to non-ideality effect on signal distortion and large performance shift caused by temperature change. Because the micro-electro-mechanical device  21  and the integrated circuit are manufactured on a same wafer, the process of micro-electro-mechanical device  21  could limit the selection of the integrated circuit  22 . For example, the integrated circuit  22  could be improved by selecting more advance technology, but the micro-electro-mechanical device  21  does not. Thus, this type of integration cannot provide the state of art performance due to the different requirements regarding the mechanical and electrical characteristics. 
       FIGS. 3 and 4  show a MEMS device  30  according to the wafer-level integration solution. The micro-electro-mechanical device and the integrated circuit are separately manufactured in different wafers and afterward bonded in wafer form, whereby a micro-electro-mechanical device  31  is stacked on an integrated circuit device  32 , and the stack structure of the micro-electro-mechanical device  31  and the integrated circuit device  32  is singulated from the stacked wafers and packaged into a MEMS device chip. As shown in  FIG. 3 , the micro-electro-mechanical device  31  and the integrated circuit device  32  have respectively finished their own manufacturing processes, wherein the micro-electro-mechanical device  31  includes a movable structure  312 , a cap  313 , and a connection section  314  for connecting the movable structure  312  and the cap  313  (the location of the connection section  314  is for illustrative purpose and not limited to the location as shown in figure). The integrated circuit device  32  includes a substrate  321 , a circuit layout (not shown), signal contacts  322  for connection to the micro-electro-mechanical device  31 , and a bond pad  323  for external communication. If necessary, a chamber  324  can be formed to provide a working space for the motion of the micro-electro-mechanical device  31 . In  FIG. 4 , the micro-electro-mechanical device  31  and the integrated circuit device  32  are bonded to each other, and the bond pad  323  can be exposed by etching the micro-electro-mechanical device  31  (related step not shown). 
     The prior art shown in  FIGS. 3-4  has the following drawback. To manufacture the micro-electro-mechanical device  31  in the semi-finished state as shown, the movable structure  312  which is suspending needs to be connected to a fixed part, so the movable structure  312  must be connected to the cap  313 . However, a pressure is laid on the cap  313  when the micro-electro-mechanical device  31  is bonded with the integrated circuit device  32 , and the molding step in the packaging process and the mounting step of the MEMS device on a circuit board will also cause the cap  313  to be stressed. Because the cap  313  is connected to the movable structure  312 , the stressed cap  313  will influence the structure and motion of the movable structure  312  to cause inaccuracy, and this inaccuracy cannot be predicted and compensated in the design stage or in the manufacturing process of the micro-electro-mechanical device  31  and the integrated circuit device  32 . 
     SUMMARY OF THE INVENTION 
     In one perspective, the present invention provides a manufacturing method of a MEMS device, including: providing an integrated circuit device including a substrate and an electrical structure on the substrate, wherein the electrical structure includes at least one sensing region and at least one first connection section; providing a structure layer, and forming at least one second connection section on the structure layer; bonding the at least one first connection section with the at least one second connection section; etching the structure layer to form at least one movable structure, the movable structure being located at a position corresponding to a position of the sensing region, and the movable structure being connected to the at least one first connection section via the at least one second connection section; and thereafter, providing a cap to cover the movable structure and the sensing region; wherein the movable structure is not directly connected to the cap. 
     In one embodiment of the present invention, the cap is connected to the electrical structure. In another embodiment, the cap is connected to a portion of the structure layer which is not the movable structure. 
     In one embodiment, the first connection section and the second connection section are bonded by eutectic bonding or fusion. 
     In one embodiment of the present invention, the step of forming at least one second connection section on the structure layer comprises: etching the structure layer to form at least one stand-off and coating an adhesive on the stand-off. 
     In one embodiment, the adhesive includes: aluminum, titanium, germanium, gold, a mixture of two or more of the above elements, or a compound containing one of the above elements. 
     In another embodiment, the movable structure is a membrane or a cantilever beam, or includes a proof mass and a spring connected to the proof mass. 
     In another embodiment, the manufacturing method further includes grinding the structure layer to reduce a thickness of the structure layer. 
     In one embodiment of the present invention, the manufacturing method further includes etching the cap to form a recess for forming a working space in the MEMS device. 
     In another perspective, the present invention provides a MEMS device made by one of the aforementioned methods, the MEMS device includes the integrated circuit device and a micro-electro-mechanical device, wherein the micro-electro-mechanical device includes the structure layer and the cap. 
     The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below, with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the prior art two-chip solution. 
         FIG. 2  shows the prior art CMOS-MEMS solution. 
         FIGS. 3-4  show the prior art wafer level integration solution. 
         FIGS. 5A-5F  show a manufacturing method of a MEMS device according to an embodiment of the present invention. 
         FIG. 6  shows a MEMS device according to an embodiment of the present invention. 
         FIG. 7  shows a MEMS device according to another embodiment of the present invention. 
         FIG. 8  shows a MEMS device according to yet another embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawings as referred to throughout the description of the present invention are for illustrative purpose only, but not drawn according to actual scale. The orientation wordings in the description such as: above, under, left, or right are for reference with respect to the drawings, but not for limiting the actual product made according to the present invention. 
       FIG. 6  shows a MEMS device  50  according to a perspective of the present invention. The MEMS device  50  includes a micro-electro-mechanical device  51  coupled with an integrated circuit device  52 . The micro-electro-mechanical device  51  includes a structure layer S and a cap  514 , wherein the structure layer S includes a connection region  511  connected to the cap  514 , at least one movable structure  512 , and at least one connection section  513  connected to the integrated circuit  52 . A working space  515  is formed between the structure layer S and the cap  514 ; the working space  515  can be a sealed space or a non-sealed space depending on the design of the MEMS device  50 . The integrated circuit device  52  includes a substrate  524  and an electrical structure  521  on the substrate  524  (the electrical structure  521  has insulation portions therein which is not shown in figure). The electrical structure  521  includes at least one sensing region  5211  and at least one connection section  5212 . The sensing region  5211  is located at a location corresponding to the movable structure  512  for sensing the motion of the movable structure to generate a sensing signal and transmitting the sensing signal to a circuit (not shown) in the integrated circuit device  52 . The connection section  5212  is for connecting to the corresponding connection section  513  of the micro-electro-mechanical device  51 . In this embodiment, the movable structure  512  for example can be but is not limited to a membrane or a cantilever beam. 
     In comparison with the prior art of  FIGS. 3 and 4 , the movable structure  512  in the MEMS device of the present invention is not directly connected to the cap  514 ; therefore, the motion of the movable structure  512  is not influenced by the cap  514  and the sensing result will not deviate, even though the cap  514  may need to receive high pressure or high temperature. That “the movable structure  512  is directly connected to the cap  514 ” means that the movable structure  512  is connected to the cap  514  via any component/portion of the micro-electro-mechanical device  51 ; that “the movable structure  512  is not directly connected to the cap  514 ” means that the movable structure  512  is not connected to the cap  514  via any component/portion of the micro-electro-mechanical device  51 , but the movable structure  512  can be indirectly connected to the cap  514  via the integrated circuit  52 . 
     In order for the movable structure  512  not to be directly connected to the cap  514 , the present invention discloses a different manufacturing method from the prior art of  FIGS. 3 and 4 .  FIGS. 5A-5F  show a manufacturing method of the MEMS  50  disclosed by the present invention. Referring to  FIG. 5A , the integrated circuit device  52  is manufactured on an integrated circuit wafer by a semiconductor process, wherein the integrated circuit device  52  includes the aforementioned substrate  524  and the electrical structure  521  on the substrate  524 . The electrical structure  521  includes at least one sensing region  5211  and at least one connection section  5212 . While the integrated circuit  52  is manufactured or at a different time, a structure layer S, and stand-offs S 1  are manufactured on one side of the structure layer S, by for example but not limited to etching. If the thickness of the structure layer S is too thick (for example, when the structure layer S is made of a silicon substrate), a grinding process can be performed to grind an opposite side (hereafter top surface) of the structure layer S to reduce the thickness. The grinding process can be performed later as an alternative. 
     Referring to  FIG. 5B , the stand-offs S 1  are coated with an adhesive S 3 . According to the present invention, the mechanical and electrical connections between the micro-electro-mechanical device  51  and the integrated circuit  52  are achieved by the bonding which includeseutectic bonding, solder bonding, thermocompression or fusion. For example, the bonding can be bonding which includes materials such as aluminum, titanium, germanium, gold, tin, or a mixture of two or more of the above elements, or a compound containing one of the above elements. However, the present invention is not limited to eutectic bonding; the connection can be achieved by other methods, such as by fusion. The stand-offs S 1  and adhesive S 3  together form the connection section  513  of the micro-electro-mechanical device  51 . 
     Referring to  FIG. 5C , the bonding can be performed after the connection sections  513  of the micro-electro-mechanical device  51  and the connection sections  5212  of the integrated circuit device  52  are disposed at corresponding positions. The aforementioned grinding process on the top surface St of the structure layer S for example can be performed in or after the step of  FIG. 5B  or  5 C. If necessary, the connection section  5212  can be cleaned in advance or coated with a coating such as TiN. 
     Referring to  FIG. 5D , a portion (regions S 2 ) of the structure layer S is removed for example by dry etching or wet etching, to form a least one movable structure  512  and a connection region  511  for connection to the cap  514 . 
     Referring to  FIG. 5E , a cap  514  is provided which has been etched to form a recess in order to provide the working space  515  in a later step. Referring to  FIG. 5F , the cap  514  is bonded to the connection region  511  to cover the movable structure  512  and the sensing region  5211 , thus completing the MEMS device  50 . The sensing region  5211  can sense the motion of the movable structure to generate the sensing signal. 
     The MEMS device according to the present invention is not limited to the structure as shown in  FIG. 6 . By simple modification of the manufacturing process as shown in  FIGS. 5A-5F , MEMS devices with different structures can be manufactured; for example, the MEMS device  500  of  FIG. 7  can be manufactured which is different from the MEMS device  50  of  FIG. 6  in that different etched regions S 2  are defined in the etching step of  FIG. 5D , and the cap  514  is bonded to the integrated circuit device  52  instead of the connection region  511  in the step of  FIG. 5F . 
       FIG. 8  shows a MEMS device  510  according to another embodiment of the present invention. The movable structures  512  of  FIGS. 6 and 7  include a membrane or a cantilever beam, while the movable structure  512  of  FIG. 8  includes a proof mass  512 A with at least one spring  512 B connected to the proof mass  512 A, and the sensing region  5211  is located in correspondence to the proof mass  512 A. The spring  512 B for example can have but not limited to a planar S-shape (referring to the enlarged top view below), and certainly can have any shape other than this planar S-shape. In  FIG. 8 , the proof mass  512 A is connected to the rest portion of the movable structure  512  via the spring  512 B, and the rest portion of the movable structure  512  is connected to the connection region  5212  via the connection section  513 . 
     The cap  514  can include one of the followings: silicon substrate, glass substrate, SiGe substrate, SiC substrate, GaAs substrate, or polymer substrate. The substrate  524  can include one of the followings: silicon substrate, glass substrate, SiGe substrate, SiC substrate, GaAs substrate, or a polymer substrate. The “polymer substrate” includes for example but not limited to PDMS substrate. 
     The advantages of the present invention at least include: in comparison with the prior art two-chip solution, the present invention has a smaller MEMS device size by eliminating the region of bond pads connecting micro-electro-mechanical device chip  11  and an integrated IC chip  12 , and the sensing performance of the present invention is not influenced by the wire-bond. In comparison with the prior art CMOS-MEMS solution, the manufacturing process of the present invention is less complicated; the stress during manufacturing the integrated circuit device will not cause distortion of the movable structure, while the steps of manufacturing the micro-electro-mechanical device will not damage the electrical structure of the integrated circuit device. In comparison with the wafer level integration solution, the MEMS device of the present invention has the same size as the prior art but a more accurate sensing performance than the prior art, because the sensing accuracy of the movable structure is not influenced when the cap is stressed. 
     The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention; for example, the stand-offs and the connection sections can be interchanged. That is, the stand-offs can be located on the integrated circuit device side and the connection sections can be located on micro-electro-mechanical device side. Besides, a component which does not affect the primary function of the devices can be inserted between two components shown to be in direct connection in the figures, or a step can be inserted between two sequential steps in the disclosed manufacturing method of the present invention. An embodiment or a claim of the present invention does not need to attain or include all the objectives, advantages or features described in the above. The abstract and the title are provided for assisting searches and not to be read as limitations to the scope of the present invention.