Abstract:
Provided is a thermal type airflow volume meter improving measurement accuracy, a method for manufacturing the same, and an adhesive sheet for use therein, the adhesive sheet divided into at least two or more per adherend and having a thickness of approximately 0.1 mm or less is divided to correspond to a shape of the adherend and generates or increases adhesion or stickiness by external energy.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method for manufacturing a semiconductor device, and more specifically relates to a manufacturing method suitable for a thermal type airflow volume sensor installed in an air intake system of a car engine and appropriate for detecting an intake air volume of the engine, a thermal type airflow volume sensor, and an adhesive sheet for use therein. 
       BACKGROUND ART 
       [0002]    Conventionally, as an airflow volume sensor installed in an intake air passage of an internal combustion engine of a car or the like to measure an intake air volume, a thermal type sensor is becoming mainstream since the thermal type sensor can detect a mass airflow volume directly. 
         [0003]    Recently, an airflow volume sensor in which a film of a resistor and an insulating layer is deposited on a silicon substrate by means of a semiconductor micromachining technique, part of the silicon substrate is thereafter removed by a solvent represented by KOH or the like, and a thin film portion (a diaphragm) is formed attracts attention since the airflow volume sensor has quick responsiveness and can detect backflow, taking advantage of the quick responsiveness. Also, in recent years, for the purpose of reducing the number of parts of a substrate portion (a printed substrate, a ceramic substrate, or the like), the airflow volume sensor of a transfer mold package type is being considered, in which the airflow volume sensor is implemented on a lead frame, and in which an outer circumferential portion thereof is molded by a plastic. 
         [0004]    In a case in which a semiconductor circuit element such as an LSI and a microcomputer is molded, the circuit element and the lead frame are bonded with use of an adhesive sheet in many cases. In a general method for using the adhesive sheet, the adhesive sheet is stuck to a back surface side in a state of a semiconductor circuit wafer, and by cutting the adhesive sheet layer simultaneously at the time of dicing the wafer in a dicing process, the adhesive sheet is in a state of being stuck to an entire back surface of each semiconductor circuit chip. It is advantageous in that a process of printing a solvent as in a case of using a solvent-type adhesive can be omitted since the diced semiconductor circuit element can be implemented on the lead frame as it is. 
       CITATION LIST 
     Patent Literature 
       [0005]    PTL 1: Publication of JP 2001-85360 A 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    Meanwhile, the adhesive sheet is used for various applications. In a case in which the adhesive sheet is used for a semiconductor element, the adhesive sheet is used mainly for an integrated circuit chip provided with no backside process represented by an IC chip. A technique described in PTL 1 does not consider a problem specific to a case in which a physical quantity sensor produced by forming a diaphragm portion in a semiconductor element is bonded. The specific problem will be described below. 
         [0007]    In particular, in implementing on a support substrate a thermal type airflow volume sensor in which a thin film portion is formed in a semiconductor element, in a case in which an area of a back surface of the diaphragm portion is in an airtight state, air in the airtight area of the back surface of the diaphragm portion expands and contracts along with a temperature change and a pressure change, which causes a volume change. As a result, the diaphragm portion is deformed, and an error may occur at the time of detection of an airflow volume. To prevent the area of the back surface of the diaphragm portion from being airtight, it can be thought that the support substrate on which the semiconductor element is implemented is provided with a ventilation opening to let air outside, for example. However, since the semiconductor element having the diaphragm portion is bonded to the support substrate provided with the ventilation opening via the adhesive sheet to implement the semiconductor element on the support substrate, this adhesive sheet also needs to be provided with a ventilation opening. PTL 1 describes a method for sticking an adhesive tape to an arbitrary chip by forming a slit in the adhesive tape in advance. However, the method aims to peel the arbitrary chip at the time of processing a thin semiconductor wafer and does not assume sticking the adhesive sheet having the ventilation opening to the semiconductor element provided with the diaphragm portion. For this reason, in PTL 1, an area surrounded by the diaphragm portion formed in the semiconductor element and the adhesive sheet becomes in an airtight state, and an error may occur at the time of detecting the airflow volume. 
         [0008]    An object of the present invention is to provide a thermal type airflow volume meter improving measurement accuracy, a method for manufacturing the same, and an adhesive sheet for use therein. 
       Solution to Problem 
       [0009]    To achieve the above object, an adhesive sheet of the present invention is divided into at least two or more per adherend and having a thickness of approximately 0.1 mm or less, the adhesive sheet is divided to correspond to a shape of the adherend, and adhesion or stickiness is generated or increased by external energy. 
       Advantageous Effects of Invention 
       [0010]    According to the present invention, a thermal type airflow volume meter improving measurement accuracy, a method for manufacturing the same, and an adhesive sheet for use therein can be provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIGS. 1( a ) to 1( d )  schematically illustrate slitting division of an adhesive sheet according to the present invention. 
           [0012]      FIGS. 2( a ) and 2( b )  schematically illustrate a semiconductor element provided with a thin film. 
           [0013]      FIGS. 3( a ) and 3( b )  schematically illustrate sticking of the adhesive sheet. 
           [0014]      FIG. 4  schematically illustrates the slitting division of the adhesive sheet according to the present invention. 
           [0015]      FIG. 5  schematically illustrates sticking of the adhesive sheet. 
           [0016]      FIG. 6  schematically illustrates dicing. 
           [0017]      FIG. 7  schematically illustrates pickup. 
           [0018]      FIG. 8  illustrates an embodiment of forming a ventilation hole in the adhesive sheet according to the present invention. 
           [0019]      FIGS. 9( a ) and 9( b )  illustrate an embodiment of a thermal type airflow volume sensor according to the present invention. 
           [0020]      FIGS. 10( a ) and 10( b )  illustrate an embodiment of the thermal type airflow volume sensor according to the present invention. 
           [0021]      FIG. 11  schematically illustrates molding. 
           [0022]      FIGS. 12( a ) and 12( b )  illustrate an embodiment of the thermal type airflow volume sensor according to the present invention. 
           [0023]      FIGS. 13( a ) and 13( b )  schematically illustrate molding. 
           [0024]      FIG. 14  is a cross-sectional view of the thermal type airflow volume sensor according to the present invention attached to an air intake duct. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0025]    A thermal type airflow volume sensor using a method for forming a ventilation opening of an adhesive sheet according to an embodiment of the present invention will hereinbelow be described. 
         [0026]    A method for forming a ventilation opening of an adhesive sheet will be described with reference to the drawings.  FIGS. 1( a ) to 1( d )  illustrate a slitting division method of an adhesive sheet. 
         [0027]      FIG. 1( a )  illustrates a state in which a sheet-adhesive-attaching dicing tape  101  before an adhesive sheet  102  is divided is stuck to a dicing ring  100 . At this time, at a part serving as a sticking surface between the dicing ring  100  and the sheet-adhesive-attaching dicing tape  101 , the dicing ring  100  may be stuck to a side of the adhesive sheet  102  as in  FIG. 1( b )  or to a side of the dicing tape  103  as in  FIG. 1( c ) . 
         [0028]      FIG. 1( d )  illustrates a state in which, in the state in  FIG. 1( a ) , slitting division has been performed to the adhesive sheet  102  by a dicing machine. As illustrated in  FIG. 1( d ) , dicing is performed at pitches of P 1  and P 3  and thereafter at pitches of P 2  and P 4  to leave the adhesive sheet  102  on the dicing tape  103 , and the adhesive sheet  102  can be divided at regular pitches with dimensions of Dx and Dy, for example. As for a dicing order at this time, the adhesive sheet  102  may be divided in an arbitrary cutting order. 
         [0029]      FIGS. 2( a ) and 2( b )  illustrate a semiconductor element  122  provided with a thin film according to the first embodiment of the present invention.  FIG. 2( a )  is a plan view of the semiconductor element  122 , and  FIG. 2( b )  is a cross-sectional view of the semiconductor element  122 . As illustrated in  FIGS. 2 ( a ) and 2( b ) , in a flow volume detection element, a laminated structure film of an insulating film layer is formed on the semiconductor substrate  122  such as silicon, and a diaphragm  123  is formed by partially removing a back surface side of the semiconductor substrate  122  with use of potassium hydroxide or the like. 
         [0030]    Next, a method for sticking the adhesive sheet  102  to the semiconductor element  122  provided with the thin film  123  will be described with reference to  FIGS. 1( a ) to 3( b ) . The slitting pitches illustrated in  FIG. 1( d )  are made to correspond to chip pitches P 5  and P 6  of a semiconductor element wafer  200  illustrated in  FIG. 3( a )  to establish P 1 =P 2 =P 5  and P 3 =P 4 =P 6 . Also, the sheet-adhesive-attaching dicing tape  103  is stuck and bonded to the semiconductor element wafer  200  so that each area surrounded by the leaving dimensions Dx and Dy in  FIG. 1( d )  may fall in an opening area illustrated in  FIGS. 2( a )  and  2  ( b ). At this time, the dimensions Dx and Dy illustrated in  FIG. 1( d )  satisfy Dx&lt;opening dimension x and Dy&lt;opening dimension y. 
         [0031]    As a result, as illustrated in  FIG. 5 , a divided adhesive sheet (s)  201  is not bonded directly below the diaphragm  123  since the divided adhesive sheet (s)  201  does not contact the semiconductor element wafer there. In other words, slits produced by dicing are formed in an area in a cavity on a back surface side of the diaphragm  123 . 
         [0032]      FIG. 4  illustrates an overview of the slitting division of the adhesive sheet  102 . 
         [0033]    The adhesive sheet  102  is a mixture of a glue material softened and generating adhesion by application of heat, an initiator hardening a base material by application of heat, ultraviolet, light, or an electromagnetic wave, and a filler. By heating the adhesive sheet  102  in an attaching state to an adherend and applying pressure and ultrasound to the adhesive sheet  102  at the same time, the adhesive sheet  102  is bonded and hardened while the number of contact points with the adherend is increased. As for the glue material, by performing a dicing process in a state in which the glue material has no adhesion, digging resistance at the time of the process is reduced, and attachment of foreign matters is prevented. In a case in which heating of the adherend is restricted, the initiator is selected to harden the base material with the ultraviolet, the light, or the electromagnetic wave. The filler improves functions of the adhesive sheet  102 . For example, mixing silica particles enables strength of the adhesive sheet  102  after hardening to be increased, and mixing metal particles enables the adhesive sheet  102  to be conductive. 
         [0034]    In sticking the adhesive sheet  102 , in a case in which bubbles are confined between the semiconductor element  122  and the adhesive sheet  102  incorporated in a semiconductor device, for example, the semiconductor element  122  may be inclined by the bubbles thereby lowering the performance. Also, since the bubbles expand and contract due to a temperature change, the bubbles may cause fatigue of a connection part and lower durability of the semiconductor device. 
         [0035]    In the present invention, since the slits produced by dicing are formed in the area in the cavity on the back surface side of the diaphragm  123 , and the slits produced by dicing in the adhesive sheet  102  act as ventilation paths as illustrated in  FIG. 8 , the bubbles are hard to be caught in the bonding surface at the time of bonding, and gas generated from the adhesive sheet at the time of bonding is easy to be let out. 
         [0036]    Subsequently, as illustrated in  FIG. 6 , the semiconductor element wafer  200  is diced by dicing. The adhesive sheet  102  has higher digging resistance at the time of the dicing process than silicon and easily causes clogging of a dicing blade. Thus, the thickness of the adhesive sheet  102  is set to approximately 0.1 mm or less to prevent cracks on the back surface of the semiconductor element wafer  200  and burrs of the adhesive sheet  102  from being generated at the time of dicing. 
         [0037]    Subsequently, when the diced semiconductor element  122  is picked up, the divided adhesive sheet (s)  201  is left on the dicing tape as illustrated in  FIG. 7 . Accordingly, on the back surface of the picked semiconductor element  122 , the divided adhesive sheets  102  are attached, and at a part of the semiconductor element  122  directly below the thin film portion, no adhesive sheet  102  exists, and a ventilation opening is formed, as illustrated in  FIG. 8 . 
         [0038]    Accordingly, for the process, an expensive system such as a laser processing machine is not required, and a dicing system for use in dicing into chips can be shared. Thus, a dedicated system can be dispensed with. 
         [0039]    Also, as a general method, forming a ventilation opening by processing a through hole into the dicing tape  103  with use of a puncher processing machine is considered. However, when the semiconductor wafer  200  provided with the thin film  123  is provided with the dicing tape  103  having the through hole and is diced, there is a fear that the thin film  123  may be damaged. Also, there is a fear of deformation around the hole and generation of process debris. Another conceivable method is processing a hole by means of laser. However, there is a fear of difficulty in coping with thickness variation of the adhesive sheet, thermal deformation and adhesion lowering around the hole, and generation of burn debris. 
         [0040]    Conversely, in the present method, the ventilation opening can be formed without opening a through hole in the dicing tape  103  at the time of forming the ventilation opening, and since the ventilation opening is formed with process accuracy of dicing, the ventilation opening can be provided to the semiconductor element  122  in the semiconductor wafer  200  at accurate pitches. Also, an influence of the thickness variation of the adhesive sheet  102  on the process accuracy is slight, and deformation and protrusion around the opening resulting from thickness fluctuation do not occur. In addition, cutting debris generated by the process can be removed easily by washing. 
         [0041]    Next, a thermal type airflow volume sensor using the method for forming a ventilation opening of the adhesive sheet  102  according to the present invention will be described with reference to  FIGS. 9( a )  to  11 .  FIGS. 9( a ) and 9( b )  illustrate a semiconductor element implementation structure according to an embodiment of the thermal type flow volume sensor.  FIG. 9( a )  is a cross-sectional view as seen from a side, and  FIG. 9( b )  is a surface view as seen from a top. 
         [0042]    As illustrated in  FIGS. 9( a ) and 9( b ) , in a flow volume detection element  15 , a laminated structure film  26  of an insulating film layer and a resistor layer is formed on a semiconductor substrate  20  such as silicon, and a diaphragm  25  is formed by partially removing a back surface side of the semiconductor substrate  20  with use of potassium hydroxide (KOH) or the like. On the diaphragm  25 , a heat generation resistor  21 , an upstream-side temperature measurement resistor  22 , and a downstream-side temperature measurement resistor  23  are formed. Also, an electrode pad  40  is formed on a surface of the semiconductor substrate  20  and is electrically connected to an outside of the semiconductor substrate  20  via a wire bonding  50  such as a gold wire. This flow volume detection element  15  is fixed on a lead frame  10  with the adhesive sheet  102 . 
         [0043]    The lead frame  10  is provided with a ventilation hole  11  for the purpose of ventilation of aback surface of the diaphragm. Further, a part of an area in which a diaphragm back surface opening end portion  24  and the ventilation hole  11  formed in the lead frame  10  correspond (that is, in  FIGS. 9( a ) and 9( b ) , the part is equivalent to an area of the reference sign  11 ) is provided with a ventilation hole  35  formed in the adhesive sheet  102 . 
         [0044]    Accordingly, in the structure illustrated in  FIGS. 9( a )  and  9  ( b ), the back surface of the diaphragm can communicate with external air via the two ventilation holes ( 11  and  35 ). 
         [0045]    Next, a mold structure in which the structure in  FIGS. 9 ( a )  and  9  ( b ) is sealed by a plastic by means of transfer mold will be described with reference to  FIGS. 10( a ) and 10( b ) . An outer circumferential portion of the structure in  FIGS. 9( a ) and 9( b )  is sealed by a mold plastic  60 , and an opening  61  is formed on a side of a front surface of the diaphragm  25  for the purpose of partially exposing the diaphragm  25  from the mold plastic  60 . Also, an opening  62  is formed on a side of a back surface of the ventilation hole  11  formed in the lead frame  10  for the purpose of ventilation. By doing so, even in a case in which the flow volume detection element  15  and the lead frame  10  are sealed by the mold plastic  60 , the back surface of the diaphragm  25  communicates with external air and can prevent an airtight state. 
         [0046]    Next, a method for manufacturing the mold structure described with reference to  FIGS. 10( a ) and 10( b )  (hereinbelow referred to as “the transfer mold package”) will be described with reference to  FIG. 11 . When the transfer mold package in which the flow volume detection element  15  is molded by the mold plastic  60  detects a flow volume, the diaphragm  25  detecting the airflow volume must partially be exposed from the mold plastic  60  to a medium to be measured. As a method for achieving this, the lead frame  10  implementing the flow volume detection element  15  is interposed between a lower mold  80  and an upper mold  81 . At this time, an inlet  82  for pouring the mold plastic is provided in either the lower mold  80  or the upper mold  81 . Also, to partially expose the diaphragm  25 , a structure in which an insert die  83 , which is a separate mold from the upper mold  81 , is inserted in the upper mold  81 , is employed, and this insert die  83  receives load from an upper portion to be brought into close contact with a surface of the flow volume detection element  15 . Also, the lower mold  80  is provided with a projection portion to prevent the mold plastic  60  from flowing into the ventilation hole  11  formed in the lead frame  10 , and this projection portion and the lead frame  10  are brought into close contact with each other at an area containing the ventilation hole  11 . When the plastic is poured from the inlet  82  in this state, the mold structure semiconductor package illustrated in  FIGS. 10( a ) and 10( b )  can be manufactured. 
       Second Embodiment 
       [0047]    A second embodiment of the thermal type airflow volume sensor using the method for forming a ventilation opening of the adhesive sheet  102  according to the present invention described in the first embodiment will hereinbelow be described. 
         [0048]      FIGS. 12( a ) and 12( b )  illustrate a semiconductor element implementation structure before the thermal type flow volume sensor is molded.  FIG. 12 ( a )  is a cross-sectional view as seen from a side, and  FIG. 12( b )  is a surface view as seen from a top. 
         [0049]    As illustrated in  FIGS. 12( a ) and 12( b ) , what is different from the first embodiment is a support substrate  70 , which is a separate part, intervening between the semiconductor substrate  20  and the lead frame  10 . Also, in the second embodiment, the lead frame  10  is provided with no ventilation hole. 
         [0050]    As an advantage of such a structure, this structure is effective in a case in which the semiconductor substrate  20  is attached to another support member on an entire surface thereof, and in which the opening  62  formed on the side of the back surface of the ventilation hole  11  formed in the lead frame  10  for the purpose of ventilation illustrated in  FIGS. 10( a ) and 10( b )  is closed in an airtight state. As illustrated in  FIGS. 12( a ) and 12( b ) , the support substrate  70 , which is the separate part, intervenes, a ventilation hole  71  is formed in the cavity area formed on the side of the back surface of the diaphragm  25 , another ventilation hole  72  for circulating air to the side of the semiconductor substrate  20  is formed, the respective ventilation holes  71  and  72  communicate with each other via a groove  73 , and air can thus be circulated to the side of the semiconductor substrate  20 . 
         [0051]    It is to be noted that, although a structure in which the groove  73  is formed in the support substrate  70  serving as the separate part is employed in the description with reference to  FIGS. 12( a ) and 12( b ) , a similar effect can be obtained in a case of forming the groove  73  in the lead frame  10 . 
         [0052]    Also in the structure illustrated in  FIGS. 12 ( a )  and  12  ( b ), since the ventilation hole  35  is formed in the adhesive sheet  102  in which the area of the diaphragm  25  and the area of the ventilation hole  71  formed in the support substrate  70  correspond, the area of the diaphragm  25  and the ventilation hole  72  for circulating air to the side of the semiconductor substrate can communicate with each other entirely. 
         [0053]    Also, a mold structure in which the structure in  FIGS. 12 ( a )  and  12  ( b ) is sealed by a plastic by means of transfer mold will be described with reference to  FIGS. 13 ( a )  and  13  ( b ). The mold structure is different from that in  FIGS. 10 ( a )  and  10  ( b ) in that the ventilation hole  72  formed in the support substrate  70  is not covered with the transfer mold plastic, either. This enables communication with external air via the ventilation hole  72 . 
         [0054]    Also, an effect of providing the ventilation hole  72  in a separate position, not on the back surface of the element, will be described with reference to  FIG. 14 .  FIG. 14  illustrates the thermal type airflow volume sensor implementing the transfer mold package illustrated in  FIGS. 13 ( a )  and  13  ( b ), attached to an air intake duct  5 . As illustrated in  FIG. 14 , an end of each connector terminal  8  extends to a circuit chamber  16  and is electrically connected to a semiconductor package  2  in the circuit chamber  16 , and the other end extends to a fitting portion of a connector portion  12  and is electrically connected to an external terminal. 
         [0055]    A housing  3  is provided with a communication hole  9  causing the circuit chamber  16  and the fitting portion of the connector portion  12  to communicate with each other. Due to the communication hole  9 , the circuit chamber  16  communicates with an outside of the air intake duct to prevent the circuit chamber  16  from being in an airtight state. 
         [0056]    Here, the ventilation hole  72  formed in the support substrate  70  is ventilated to the different space  16  (circuit chamber) from a bypass passage  6  taking intake air. The bypass passage  6  and the circuit chamber  16  are separated to prevent communication. Also, since the circuit chamber  16  communicates with external air via the ventilation hole  9  formed in the housing  3 , airtightness of the back surface of the diaphragm can be avoided. Further, since the bypass passage  6  and the circuit chamber  16  are separated, the ventilation hole  72  formed in the support substrate  70  is not clogged by wastes such as oil and carbon flowing in the bypass passage  6 , and reliability is thus improved. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           10  lead frame (substrate support member) 
           11  ventilation hole formed in lead frame 
           15  flow volume detection element 
           20  semiconductor substrate 
           21  heat generation resistor 
           22  upstream-side temperature measurement resistor 
           23  downstream-side temperature measurement resistor 
           24  diaphragm back surface opening end portion 
           25  diaphragm 
           26  laminated structure film of insulating film layer and resistor layer 
           27  semiconductor element back surface outer circumferential portion 
           28  minimum dimension from diaphragm back surface opening end to semiconductor element back surface outer circumferential portion 
           30  adhesive sheet 
           35  ventilation hole formed in adhesive sheet 
           60  mold plastic 
           61  mold opening formed on side of front surface 
           62  mold opening formed on side of back surface 
           70  substrate support member 
           71  ventilation hole formed in substrate support member 
           72  ventilation hole formed in substrate support member 
           73  groove causing ventilation holes ( 71  and  72 ) to communicate with each other 
           102  adhesive sheet 
           103  dicing tape 
           122  semiconductor element (semiconductor substrate) 
           123  thin film (diaphragm) 
           124  opening area 
           200  semiconductor element wafer 
           201  divided adhesive sheet (s) 
           202  slit E by dicing 
           203  slit F by dicing 
           210  diced semiconductor element 
           220  pickup nozzle