Abstract:
The invention provides an electronic device package and fabrication method thereof. The electronic device package includes a sensor chip. An upper surface of the sensor chip comprises a sensing film. A covering plate having an opening structure covers the upper surface of the sensor chip. A cavity is between the covering plate and the sensor chip, corresponding to a position of the sensing film, where the cavity communicates with the opening structure. A spacer is between the covering plate and the sensor chip, surrounding the cavity. A pressure releasing region is between the spacer and the sensing film.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. application Ser. No. 12/652,715, filed Jan. 5, 2010, which claims the benefit of U.S. Provisional Application No. 61/204,367 filed Jan. 6, 2009, the entirety of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an electronics package, and in particular relates to an electronics package and a method for fabricating an electronics package using a wafer level package process. 
     Description of the Related Art 
     Micro electro-mechanical systems (MEMS) are micro-devices using semiconductor technology to integrate electronic and mechanical functions. MEMS products comprise accelerators, gyroscopes, pressure sensors, optical transmission devices, DLP (digital light processing) devices, ink printer heads and wireless network RF sensors. Currently, MEMS are applied in various products including tire pressure measurement systems, optical transmission networks, projectors, sensor networks, digital microphones, clock oscillators and game consoles. MEMS also play an important role in the development of research areas such as memory technology, biological chips, display technology and emerging energy. Pressure sensors are used for measuring a change in atmospheric pressure. Some pressure sensors applied in cars, for example, oil pressure gauges, are considered as being of very mature technology. However, pressure sensors, have the potential for new applications, such as in tire pressure gauges. Thus, an electronics package used in MEMSs and a method for fabricating the same are desired. 
     BRIEF SUMMARY OF THE INVENTION 
     An exemplary embodiment of a method for fabricating an electronic device package is provided. The method for fabricating an electronic device package, comprises: providing a wafer having an upper surface with a conductive electrode disposed thereon and a lower surface covering the upper surface of the wafer with a covering plate; covering the lower surface of the wafer with a passivation layer; forming conductive bumps on the passivation layer, electrically connected to the conductive electrodes; forming an opening structure on the covering plate, wherein the step of forming an opening structure is performed before the step of covering the upper surface of the wafer with the covering plate, or after the step of covering the lower surface of the wafer with the passivation layer and before the step of forming the conductive bumps. 
     An exemplary embodiment of an electronic device package is provided. The electronic device package, comprises: a sensor chip, wherein an upper surface of the sensor chip comprises a sensing film; a covering plate having an opening structure covering the sensor chip, wherein the covering plate and the sensor chip have a cavity therebetween, and the cavity is over a position corresponding to the sensing film, communicating with the opening structure; and a spacer between the covering plate and the sensor chip, surrounding the cavity, wherein the spacer and the sensing film have a pressure release region therebetween. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIGS. 1A-1I  are cross sections showing the steps for fabricating an electronic device package according to an embodiment of the invention. 
         FIGS. 2A-2E  are cross sections showing the steps for fabricating an electronic device package according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     A method for fabricating an electronic device package such as a pressure sensor is described. Embodiments of the electronic device packages of the invention may be applied to active or passive devices, or electronic components with digital or analog circuits, such as optoelectronic devices, micro electro mechanical systems (MEMS), micro fluidic systems, and physical sensors for detecting heat, light, or pressure. Particularly, a wafer level packaging (WSP) process may be applied to package semiconductor chips, such as image sensor devices, light-emitting diodes (LEDs), solar cells, RF circuits, accelerators, gyroscopes, micro actuators, surface acoustic wave devices, pressure sensors, or ink printer heads. 
     The wafer level packaging process herein mainly means that after the packaging process is accomplished during a wafer stage, a wafer with chips is cut to obtain separate independent packages. However, in an embodiment of the invention, separate independent chips may be redistributed overlying a supporting wafer and then be packaged, which may also be referred to as a wafer level packaging process. In addition, the wafer level packaging process may also be adapted to form electronic device packages of multi-layered integrated circuit devices by stacking a plurality of wafers having integrated circuits together. 
       FIGS. 1A-1I  are cross sections showing the steps for fabricating an electronic device package  500   a  such as pressure sensor package according to an embodiment of the invention. As shown in  FIG. 1A , a wafer  3  having an upper surface  20  and a lower surface  30  is provided, wherein a plurality of cavities  5  is formed on the lower surface  30  of the wafer  3 , wherein the plurality of cavities  5  extend into the wafer  3 . The cavities  5  are sealed by a carrier substrate  1  bonded to the lower surface  30  of the wafer  3 . The carrier substrate  1  may comprise a glass substrate with a thickness of between about 300 μm and 500 μm, or preferably about 400 μm. In one embodiment, the wafer  3  may be formed of silicon or other materials having good thermal dissipation ability or a high thermal conductivity coefficient. The cavities  5  may be formed by etching the wafer  3  using a process such as a wet etching process. The wafer  3  may have a thickness of between about 100 μm and 200 μm, or preferably about 140 μm. In one embodiment, an adhesive such as epoxy may be used to bond the wafer  3  to the carrier substrate  1 . However, the invention is not limited to thereto. In one embodiment, a plurality of micro electro-mechanical devices comprising sensor chips is disposed on the wafer  3 . A sensor film  9 , for example, a piezoelectrical material film, is formed in the wafer  3  and adjacent to the upper surface  20  of the wafer  3  to measure the changes in the surrounding environment or fluids. The sensor film  9  is surrounded by a conductive electrode or a conductive pad  7 . As shown in  FIG. 1A , the conductive electrode  7  connects to the sensor film  9  to transfer sensing signals of the sensor film  9 . Alternatively, the sensor film  9  may be also formed on the upper surface  20  of the wafer  3 , connecting to the conductive electrode  7 . Also, the silicon wafer  3  and the conductive electrode  7  are separated by forming an insulating film (not shown), for example, forming a silicon oxide, silicon oxynitride or low dielectric constant material layer, therebetween. 
     As shown in  FIG. 1B , next, a packaging layer or a covering plate  13  may be formed on the upper surface  20  of the wafer  3 . In one embodiment, a spacer  11  or a dam may be formed between the covering plate  13  and the conductive electrode  7 , thereby forming a cavity  15  between the covering plate  13  and the sensor film  9 . The spacer  11  surrounds the cavity  15 . The covering plate  13  may comprise, for example, glass, quartz, opal or plastic. In this embodiment, the covering plate  13  is a silicon substrate. The covering plate  13  has an opening formed therein, for fluid to flow in and out of. The covering plate  13  may have a thickness of between about 500 μm and 800 μm, or preferably about 700 μm. The spacer  11  may comprise adhesive materials, for example, epoxy. Generally, the spacer  11  is on the conductive electrode  7 . 
     Next, a step of thinning down the carrier substrate  1  may be optionally performed. For example, a backside  10  of the glass substrate  1  is thinned down to a preferred thickness, for example, from 400 μm to 120 μm, by an etching, milling, grinding or polishing process. 
     Next, referring to  FIG. 1C , an opening  17  is formed at a position below a preferred scribe line or the conductive electrode  7 , through the carrier substrate  1  and deep into a portion of the wafer  3 . In one embodiment, a notching process may be performed by notch equipment. For example, a knife with a 60 degree cutting angle may cut the carrier substrate  1  and the wafer  3 , to form the channel notch  17 . 
     Next, as shown in  FIG. 1D , the wafer  3  is etched along the opening  17  to form an opening  19  with a wide lower portion and a narrow upper portion. For example, a silicon etching process is performed on the silicon wafer  3  to remove the wafer material on the sidewalls and a bottom of the opening, wherein the insulating layer between the conductive electrode  7  and the wafer  3  may serve as an etching stop layer in this step. 
     Referring to  FIG. 1E , an opening  21  with a wide upper portion (a portion in the carrier substrate  1 ) and a narrow lower portion (a portion in the wafer  3 ) is formed at a position of the opening  19 . A notching process may be performed by notch equipment to cut the carrier substrate  1 , wherein the knife used in the notching process has a wide width or a large cutting angle. For example, a knife with a cutting angle larger than about 60 degrees is selected. Preferably, a knife with the cutting angle between about 75 and 80 degrees is selected. Therefore, the opening  21  has a wide upper portion (a portion in the carrier substrate  1 ) and a tilted angle of the wide upper portion is larger than the lower portion (a portion in the wafer  3 ), thereby facilitating deposition of a conductive line. Additionally, sidewalls of the upper portion (a portion in the carrier substrate  1 ) and the lower portion (a portion in the wafer  3 ) of the opening  21  are connected together, thereby preventing voids from being generated while filling in the insulating layer  23  as shown in  FIG. 1F . 
     Referring to  FIG. 1F , the insulating layer  23  is formed in the opening  21 . In one embodiment, the insulating layer  23  is formed on the backside  10  of the carrier substrate  1 , filling the opening  21 . Preferably, the insulating layer  23  may be made of epoxy, solder mask or other suitable insulating materials, such as insulating deposited layers including non-organic materials comprising silicon nitride, silicon oxinitride, metal oxide or combinations thereof, or organic materials comprising polyimide, BCB™, parylene, polynaphthalenes, fluorocarbons or acrylates. The insulation layer is preferably formed by a coating method such as spin coating, spray coating or curtain coating, or may be formed by any suitable method, such as a liquid phase deposition, physical vapor deposition, chemical vapor deposition, low pressure chemical vapor deposition, plasma enhanced chemical vapor deposition, rapid thermal chemical vapor deposition or atmospheric pressure chemical vapor deposition process. 
     Next, referring to  FIG. 1G , an opening  25 , extending deep into the spacer  11 , exposing the conductive electrodes  7 , is formed. The insulating layer  23  and the insulating layer between the conductive electrodes  7  and the wafer  3  and a portion of the spacer  11  are patterned to form the opening  25  (not shown) by methods such as a photolithography/etching process. Alternatively, a notching process is performed by notch equipment to cut the insulating layer  23  and the conductive electrodes  7  to a portion of the spacer  11 , thereby forming the opening  25  with exposed sides of the conductive electrode  7 . 
     Next, a conductive layer  27  is formed on an inner sidewall and a lower portion of the opening  25 , extended over a portion of the insulating layer  23  over the backside  10  of the carrier substrate  1 , wherein the conductive layer  27  may electrically connect to the conductive electrode  7 . In this embodiment, the conductive layer  27  electrically connects to sides of the conductive electrode  7 . Alternatively, the conductive layer  27  may electrically connect to a lower surface of the conductive electrode  7 . Generally, the conductive layer  27  may be a conductive material layer formed of Cu, Al, Ag, Ni or alloys thereof. The conductive material layer may be conformably formed on the backside  10  of the carrier substrate  1 , extending to a tiled side and the lower portion of the opening  25  by using, for example, an electroplating or sputtering process. Next, a photolithography/etching process is performed to pattern the conductive material layer, thereby forming the conductive layer  27 . 
     Next, as shown in  FIG. 1H , a passivation layer  29  is formed on the conductive layer  27 , covering the backside  10  of the carrier substrate  1  and filling the opening  25  after forming the conductive layer  27 . The passivation layer  29  may be, for example, a solder mask. In one embodiment, the passivation layer  29  may be patterned to form openings  31  exposing a portion of the conductive layer  27  after the passivation layer  29  is formed. 
     Next, referring to  FIG. 1I , before forming conductive bumps  33 , an opening  35  communicating with the cavity  15  is formed in the covering plate  13  and over a position corresponding to the sensing film  9 , wherein the opening  35  may comprise a single opening or a porous structure to communicate with an outside fluid. Next, the covering plate  13  is thinned down. In one embodiment, an area of the sensing film  9  to an area of the opening  35  is equal to a ratio preferably of between about 1 and 1.5, thereby stabilizing and protecting the covering plate  13  while not affecting the sensing film  9  when the sensing film  9  senses fluid flowing through the opening  35 . If the covering plate  13  is formed of silicon, the opening  35  can be formed by a dry etching process. Additionally, the spacer  11  and the sensing film  9  may further comprise a pressure release region  40  therebetween to prevent stress from transmitting from the covering plate  13  to the spacer  11 , which may affect detection of the sensing film  9 . For example, the spacer  11  and the sensing film may be horizontally separated by a default distance  40  larger than about 100 μm. Alternatively, one or more cavities may be formed on the silicon wafer horizontally between the spacer  11  and the sensing film  9  to prevent stress. Also, the cavities may be filled with buffer materials. Finally, conductive bumps  33  are formed on positions of the openings  31  to electrically connect to the conductive layer  27 . In one embodiment, a solder is filled in the opening by an electroplating or screen printing process. A solder re-flow process is performed to form the conductive bumps  33  such as solder balls or solder pastes. Next, the wafer  3  is cut along scribe lines SC to be divided into several individual pressure sensing chips, to complete the formation of the electronic device package  500   a.    
     In the aforementioned embodiments, the opening  35  of the covering plate  13  is exposed after the formation of the passivation layer  29 , thereby preventing the sensing film  9  from being contaminated during processes performed before exposure of the covering plate  13 . Also, the opening  35  is formed before the formation of the conductive bumps  33 , thereby preventing the conductive bumps  33  from being damaged due to processes performed up to the formation of the opening  35 . 
       FIGS. 2A-2E  are cross sections showing the steps for fabricating an electronic device package  500   b  such as pressure sensor package according to another embodiment of the invention. As shown in  FIG. 2A , a wafer  3  having an upper surface  20  and a lower surface  30  is provided, wherein a plurality of cavities  5  is formed on the lower surface  30  of the wafer  3 , extending into the wafer  3 . The cavities  5  are sealed by a carrier substrate  1  bonded to the lower surface  30  of the wafer  3 . The carrier substrate  1  may comprise a glass substrate with a thickness of between about 300 μm and 500 μm, or preferably about 400 μm. In one embodiment, the wafer  3  may be formed of silicon or other materials having good thermal dissipation ability or a high thermal conductivity coefficient. The cavities  5  may be formed by etching the wafer  3  using methods such as a wet etching process. The wafer  3  may have a thickness of between about 100 μm and 200 μm, or preferably about 140 μm. In one embodiment, an adhesive such as epoxy may be used to bond the wafer  3  to the carrier substrate  1 . However, the invention is not limited to thereto. In one embodiment, a plurality of micro electro-mechanical devices comprising sensor chips is disposed on the wafer  3 . A sensor film  9 , for example, a piezoelectrical material film, covers the upper surface  20  of the wafer  3  to sense changes in the surrounding environment or fluids. The sensor film  9  is surrounded by an electrode or a conductive pad  7  to transfer sensing signals of the sensor film  9 . Also, the silicon wafer  3  and the conductive electrode  7  are separated by forming an insulating film (not shown), for example, forming a silicon oxide, silicon oxynitride or low dielectric constant material layer, therebetween. 
     As shown in  FIG. 2B , next, a packaging layer or a covering plate  53  may be formed on the upper surface  20  of the wafer  3 . In one embodiment, a spacer  11  may be formed between the covering plate  53  and the conductive electrode  7 , thereby forming a cavity  55 . The spacer  11  surrounds the cavity  55 . The covering plate  53  may comprise, for example, glass, quartz, opal or plastic. In this embodiment, the covering plate  53  is a silicon substrate. The covering plate  53  has an opening formed therein, for fluid to flow in and out of. The covering plate  53  may have a thickness of between about 200 μm and 400 μm, or preferably about 300 μm. The spacer  11  may comprise adhesive materials, for example, epoxy. Generally, the spacer  11  is on the conductive electrode  7 . An opening  65  may be pre-formed in the covering plate  53  and sealed by pasting a sealing layer  67 , such as an adhesive tape, to the opening  65 . Next, the covering plate  53  is attached to the upper surface of the wafer  3  so that the cavity  55  may communicate the opening  65 , wherein the opening  65  may be a single opening or a porous structure. 
     Next, a step of thinning down the carrier substrate  1  may be optionally performed. For example, a backside  10  of the glass substrate  1  is thinned down to a preferred thickness, for example, from 400 μm to 120 μm, by an etching, milling, grinding or polishing process. 
     Next, referring to  FIG. 2C , an opening  17  is formed at a position below the preferred scribe line or conductive electrode  7 , through the carrier substrate  1 , extending deep into the wafer  3 . In one embodiment, a notching process may be performed by notch equipment. For example, a knife with a 60 degree cutting angle may cut the carrier substrate  1  and the wafer  3 , to form the channel notch  17 . Next, the wafer  3  is etched along the opening  17  to form an opening  19  with a wide lower portion. For example, a silicon etching process is performed on the silicon wafer  3  to remove the wafer material on the sidewalls and a bottom of the opening, wherein the insulating layer between the conductive electrode  7  and the wafer  3  may serve as an etching stop layer in this step. 
     Referring to  FIG. 2D , an opening  21  with a wide upper portion is formed at a position of the opening  19 . A notching process may be performed by notch equipment to cut the carrier substrate  1 , wherein the knife used in the notching process has a wide width or a large cutting angle. For example, a knife with the cutting angle larger than about 60 degrees is selected. Preferably, a knife with the cutting angle between about 75 and 80 degrees is selected. Therefore, the opening  21  has a wide upper portion (a portion in the carrier substrate  1 ) and a tilted angle of the upper portion is larger than the lower portion (a portion in the wafer  3 ), thereby facilitating conductive line deposition. Additionally, sidewalls of the upper portion (a portion in the carrier substrate  1 ) and the lower portion (a portion in the wafer  3 ) of the opening  21  are connected together, thereby preventing voids from being generated while filling the insulating layer  23 . Next, the insulating layer  23  is formed in the opening  21 . In one embodiment, the insulating layer  23  is formed on the lower surface of the carrier substrate  1 , filling the opening  21 . Preferably, the insulating layer  23  may be epoxy, solder mask or other suitable insulating materials, such as insulating deposited layers including non-organic materials comprising silicon nitride, silicon oxinitride, metal oxide or combinations thereof, or organic materials comprising polyimide, BCB™, parylene, polynaphthalenes, fluorocarbons or acrylates. The insulation layer is preferably formed by a coating method such as spin coating spray coating or curtain coating, or may be formed by any suitable method, such as, a liquid phase deposition, physical vapor deposition, chemical vapor deposition, low pressure chemical vapor deposition, plasma enhanced chemical vapor deposition, rapid thermal chemical vapor deposition or atmospheric pressure chemical vapor deposition process. 
     Next, still referring to  FIG. 2D , an opening  25 , exposing the conductive electrode  7  is formed. The insulating layer  23  and the insulating layer between the electrodes and the wafer are patterned to form the opening  25  (not shown) by a method such as a photolithography/etching process. Alternatively, a notching process is performed by notch equipment to cut the insulating layer  23  and the conductive electrodes  7  to a portion of the spacer  11 , thereby forming the opening  25 , exposing the sides of the conductive electrode  7 . 
     Next, a conductive layer  27  is formed on an inner sidewall and a lower portion of the opening  25 , extending over the insulating layer over the lower surface of the carrier substrate  1 , wherein the conductive layer  27  may electrically connect to the conductive electrodes  7 . In this embodiment, the conductive layer  27  electrically connects to sides of the conductive electrode  7 . Alternatively, the conductive layer  27  may electrically connect to a lower surface of the conductive electrode  7 . Generally, the conductive layer  27  may be a conductive material layer formed of Cu, Al, Ag, Ni or alloys thereof. The conductive material layer may be conformably formed on the backside of the carrier substrate  1 , extending to a tiled side and the lower portion of the opening  25  by using, for example, by an electroplating or sputtering process. Next, a photolithography/etching process is performed to pattern the conductive material layer, thereby forming the conductive layer  27 . 
     Next, as shown in  FIG. 2E , a passivation layer  29  is formed on the conductive layer  27 , covering the backside  10  of the carrier substrate  1  and filling the opening  25  after the conductive layer  27  is formed. The passivation layer  29  may be, for example, a solder mask. In one embodiment, the passivation layer  29  may be patterned to form openings  31  exposing a portion of the conductive layer  27  after the passivation layer  29  is formed. 
     Next, conductive bumps  33  are formed on positions of the openings  31  to electrically connect to the conductive layers  27 . In one embodiment, a solder is filled into the opening by an electroplating or screen printing process. A solder re-flow process is performed to form the conductive bumps such as solder balls or solder pastes. After forming the conductive bumps, the adhesive tape  67  is removed to expose the opening  65 , which is in the covering plate  13  and over a position corresponding to the sensing film  9 , communicating with the cavity  55 , wherein the opening may comprise a single opening or a porous structure to communicate with outside fluids. In one embodiment, an area of the sensing film  9  to an area of the opening  65  is equal to a ratio preferably of between about 1 and 1.5, thereby stabilizing and protecting the covering plate  53  while not affecting the sensing film  9  when the sensing film  9  senses fluid flows through the opening  65 . Additionally, the spacer  11  and the sensing film  9  may further comprise a pressure release region  40  therebetween to prevent stress from transmitting from the covering plate  13  to the spacer  11 , affecting the detection of the sensing film  9 . For example, the spacer  11  and the sensing film may be horizontally separated by a default distance  40  such as a default distance larger than about 100 μm. Alternatively, one or more cavities may be formed on the silicon wafer horizontally between the spacer  11  and the sensing film  9  to prevent stress. Also, the cavities may be filled with buffer materials. Finally, the sealing layer  67  such as adhesive tape is torn, and the wafer is cut along scribe lines SC to divide the wafer into several individual pressure sensing chips, thus completing formation of the electronic device package  500   b.    
     In the aforementioned embodiments, the opening  65  is firstly formed in the covering plate  53  and sealed by a sealing layer  67  such as an adhesive tape and then the covering plate  53  is attached to the wafer  3 , thereby preventing the sensing film  9  from contamination during the fabricating process. 
     The exemplary embodiments of the electronic device package  500   a  pr  500   b  of the invention are fabricated by a wafer level package process. Therefore, the package may have a smaller size. Additionally, in the electronic device package, conductive layers or conductive bumps rather than bond wires are used to electrically connect to the electrodes of the semiconductor chip. Therefore, package size is further reduced. 
     While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.