Abstract:
A semiconductor chip, substrate employing plural bonding steps to ensure complete bonding particularly of peripheral edges. Embodiments include placing an adhesive layer on a chip mounting substrate positioned on a first supporting device, pressing a semiconductor chip against the chip mounting substrate to bond the semiconductor chip temporarily to the chip mounting substrate temporarily bonded chip on a second supporting device, and applying chip to straighten warpage and to bond the chip entirely to the chip mounting substrate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device, a method of producing the same, and semiconductor production equipment for carrying out the method. More specifically, the present invention relates to semiconductor production equipment for mounting a semiconductor chip on a die pad, and a method of operating the semiconductor production equipment. 
     2. Background Art 
       FIGS. 6A ,  6 B and  6 C are views of assistance in explaining a conventional method of bonding a semiconductor chip to a substrate for supporting the semiconductor chip. As shown in  FIG. 6A , in a semiconductor wafer  12 , a plurality of semiconductor chips  14  are formed. The semiconductor wafer  12  is diced into a plurality of semiconductor chips  14 . A collet  8  picks up one of the semiconductor chips  14  and carries the same to a die bonding apparatus, i.e., semiconductor production equipment. 
     As shown in  FIG. 6B , a lead frame  16  provided with a die pad  18  in its central part is mounted on a heating block  4 , i.e., a hot stage, of the die bonding apparatus. An adhesive layer  20  for bonding the semiconductor chip  14  to the die pad  18  is placed on the die pad  18 . The collet  8  presses the semiconductor chip  14  lightly against the die pad  18  to bond the semiconductor chip  14  to the die pad  18 . Then, the heating block  4  heats the die pad  18 , the adhesive layer  20  and the semiconductor chip  14  to enable the adhesive layer  20  to bond the semiconductor chip  14  to the die pad  18 . 
     SUMMARY OF THE INVENTION 
     Semiconductor devices have been progressively miniaturized and the thickness of semiconductor wafers has been reduced accordingly. Sometimes, the semiconductor chips formed by dicing the semiconductor wafer are warped by stress induced in surfaces thereof when circuits are formed thereon. The warped semiconductor chip  14  cannot be satisfactorily bonded to the die pad  18 . When the collet  8  having the shape of a thin rod applies pressure to the semiconductor chip  14  to bond the semiconductor chip  14  to the die pad  18 , the pressure is concentrated on the portion where the collet  8  presses the chip directly, i.e., a central part of the semiconductor chip  14  as shown in  FIG. 6B . Consequently, a peripheral part of the semiconductor chip  14  that receives a comparatively low pressure remains warped and are not bonded securely to the die pad  18  as shown in  FIG. 6C . 
     When the warped semiconductor chip  14  is bonded to the die pad  18  with its peripheral part spaced apart from the die pad  18  as shown in  FIG. 6C , the semiconductor device formed thus incompletely bonding the semiconductor chip  14  to the die pad  18  is connected electrically incompletely to an external circuit. Therefore, it is an object of the present invention to provide an apparatus and method capable of securely bonding a semiconductor chip to a substrate. 
     According to one aspect of the present invention, a Semiconductor production equipment for attaching a semiconductor chip to a semiconductor chip mounting substrate, comprises a chip mounting unit for mounting the semiconductor chip on and pressing the same against the semiconductor chip mounting substrate to bond the semiconductor chip temporarily to the semiconductor chip mounting substrate, and a chip pressing unit for pressing the semiconductor chip temporarily bonded to the semiconductor chip mounting substrate against the semiconductor chip mounting substrate. The chip mounting unit includes a first supporting device for supporting the semiconductor chip mounting substrate and the semiconductor chip thereon, and a holding device capable of holding the semiconductor chip, of carrying the semiconductor chip and pressing the semiconductor chip against the semiconductor chip mounting substrate to bond the semiconductor chip temporarily to the semiconductor chip mounting substrate. The chip pressing unit includes a second supporting device for supporting the semiconductor chip mounting substrate to which the semiconductor chip is bonded thereon, and a pressing device for pressing the semiconductor chip against the semiconductor chip mounting substrate. Accordingly, the semiconductor chip can be entirely and surely bonded to the mounting substrate. 
     In another aspect of the present invention, in a semiconductor device producing method, a semiconductor chip mounting substrate provided with a predetermined adhesive layer is placed on a first supporting device included in a chip mounting unit and a semiconductor chip is mounted on the semiconductor chip mounting substrate in a chip mounting substrate feeding process. In a chip bonding process, a semiconductor chip is bonded temporarily to the semiconductor chip mounting substrate by pressing the semiconductor chip against the semiconductor chip mounting substrate. In a transfer process, the semiconductor chip mounting substrate is transferred to which the semiconductor chip is bonded temporarily by the chip bonding process from the first supporting device to a second supporting device. In a pressing process, the semiconductor chip is pressed firmly against the semiconductor chip mounting substrate to bond the semiconductor chip entirely to the semiconductor chip mounting substrate. Accordingly, the semiconductor chip can be entirely and surely bonded to the mounting substrate. 
     Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a die bonding apparatus, i.e., semiconductor production equipment, for carrying out a semiconductor device producing method in a first embodiment according to the present invention; 
         FIG. 2  is a flow chart of the die bonding method in the first embodiment according to the present invention; 
         FIGS. 3 to 5  are schematic views of assistance in explaining the die bonding method; 
         FIGS. 6A ,  6 B and  6 C are views of assistance in explaining a conventional method of bonding a semiconductor chip to a substrate for supporting the semiconductor chip. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described with reference to the accompanying drawings, in which the same or like parts are denoted by the same reference characters and the duplicate description thereof will be omitted. 
     First Embodiment 
       FIG. 1  is a schematic perspective view of a die bonding apparatus  100 , i.e., semiconductor production equipment, for carrying out a semiconductor device producing method in a first embodiment according to the present invention. 
     A plurality of semiconductor chips  14  are formed in a semiconductor wafer  12 . Each of the semiconductor chips is formed by dicing a semiconductor wafer  12 . 
     A lead frame  16  is a package for semiconductor devices. Die pad  18  is portion for mounting a semiconductor chip. The lead frame  16  is provided with the die pads  18 . Adhesive layers  20  are attached to the die pads  18 . The Adhesive layers  20  are used for bonding the semiconductor chips  14  to the die pads  18 , respectively. 
     A heating block  4  is a portion on which the semiconductor chips  14  and the die pads  18  are placed when the semiconductor chip  14  is bonded to the die pad  18 . The heating block  4  is internally provided with a cartridge heater, not shown. The heating block  4  heats the lead frame  16  and the semiconductor chip  14  mounted thereon to bond the semiconductor chip  14  to the die pad  18  of the lead frame  16 . 
     A collet  8  picks up one of the semiconductor chips  14  formed by dicing the semiconductor wafer  12  and carries the same onto the heating block  4 . The collet  8  presses the semiconductor chip  14  lightly against the die pad  18  to bond the semiconductor chip  14  to the die pad  18 . 
     A chip mounting unit  110  of the die bonding apparatus  100  comprises the heating block  4  and the collet  8 . The chip mounting unit  110  is a portion for pressing the semiconductor chip  14  against the die pad  18  of the lead frame  16  to bond the semiconductor chip  14  to the die pad  18 . 
     The heating block is a portion on which the die pad  18  and the semiconductor chip  14  bonded to the die pad  18  by the chip mounting unit  110  is placed. Rubber rings  3  are extended between rotating pulley  2  such that the upper and under sides thereof extend past the heating blocks  4  and  6  as shown in  FIG. 1 . The rubber rings  3  are moved by rotating the pulley  2  to transfer the lead frame  16  from the heating block  4  to the heating block  6 . The heating block  6  is internally provided with a cartridge heater, not shown, to heat the lead frame  16  and the semiconductor chip  14  when pressure is applied to the semiconductor chip  14 . 
     A heating tool  10  applies heat and pressure to the semiconductor chip  14 . The heating tool  10  has a surface area greater than that of the semiconductor chip  14  to apply pressure all over the semiconductor chip  14  at a time. The heating tool  10  presses the semiconductor chip  14  so that the entire contact surface of the semiconductor chip  14  including that of a warped peripheral part of the semiconductor chip  14  is bonded to the die pad  18 . The heating tool  10  is internally provided with a cartridge heater, not shown, to apply both pressure and heat to the semiconductor chip  14 . 
     A chip pressing unit  120  of the die bonding apparatus  100  comprises the heating block  6  and the heating tool  10 . The chip pressing unit  120  straightens a warped peripheral part, which cannot be satisfactorily bonded to the die pad  18 , of the semiconductor chip, so that the semiconductor chip  14  can be entirely bonded to the die pad  18 . The die bonding apparatus  100  comprises the chip mounting unit  110  and the chip pressing unit  120 . 
     A die-bonding method of bonding the semiconductor chip  14  to the die pad  14  by the die bonding apparatus  100  will be described.  FIG. 2  is a flow chart of the die bonding method, and  FIGS. 3 to 5  are schematic views of assistance in explaining the die bonding method. 
     Referring to  FIG. 2 , a lead frame  16  is fed to the die bonding apparatus  100  in step S 1 . Adhesive layers  20  are formed on die pads  18 , on which semiconductor chips  14  are mounted, of the lead frame  16 . The lead frame  16  is moved onto the heating block  4  of the chip mounting unit  110  of the die bonding apparatus  100 . 
     In step S 2 , semiconductor chips  14  are carried. A semiconductor wafer  12  is divided into a plurality of semiconductor chips  14  by dicing as shown in  FIG. 3 . The collet  8  picks up the semiconductor chip  14  and carries the same onto the die pad  18  of the lead frame  16 , located on the heating block  4 . 
     Then, in step S 3 , the semiconductor chip  14  is bonded to the die pad  18 . The collet  8  presses the semiconductor chip  14  carried onto the die pad  18  in step S 2  lightly against the die pad  18  as shown in  FIG. 4A . At this time, the heating block  4  heated by the cartridge heater heats the adhesive layer  20  to bond the semiconductor chip  14  to the die pad  18 . 
     Sometimes, a peripheral part of the semiconductor chip  14  is warped by stress induced in a surface provided with a circuit of the semiconductor chip  14  because the semiconductor wafer  12  is thin, and the collet  8  having the shape of a thin rod applies pressure to a central part of the semiconductor chip  14  in step S 3 . Therefore, only the central part of the semiconductor chip  14  is bonded to the die pad  18  and a peripheral part of the semiconductor chip  14  remains warping away from the die pad  18  as shown in  FIG. 4B . 
     Then, in step s 4 , the lead frame  16  supporting the semiconductor chips  14  each having only the central part bonded to the die pad  18  is transferred from the chip mounting unit  110  to the heating block  6  of the chip pressing unit  120 . Since the rubber rings  3  are extended past the heating block  4  of the chip mounting unit  110  and the heating block  6  of the chip pressing unit  120 , the rotating Pulley  2  are rotated to move the rubber rings  3  so as to carry the lead frame  16  from the chip mounting unit  110  to the chip pressing unit  120 . 
     A pressing operation is executed in step S 5 . As shown in  FIGS. 5A and 5B , the heating tool  10  applies pressure to the semiconductor chip  14  temporarily bonded to the die pad  18  of the lead frame  16  placed on the heating block  6  to depress the semiconductor chip  14  entirely. At the same time, the heating block  6  and the heating tool  10  heated by the cartridge heaters apply heat through the semiconductor chip  14  and the die pad  18  to the adhesive layer  20  to bond the semiconductor chip  14  securely to the die pad  18 . Consequently, the warped semiconductor chip  14  is straightened and the semiconductor chip  14  can be bonded properly to the die pad  18  as shown in  FIG. 5C . 
     In this embodiment, the semiconductor chip  14  is temporarily bonded to the die pad  18 , the warped peripheral part of semiconductor chip  14  is straightened, and then the semiconductor chip  14  is bonded to the die pad  18 . Thus, the semiconductor chip  14  including a warped peripheral part of the semiconductor chip  14  can be surely entirely bonded to the die pad  18 . 
     In this specification, a chip mounting substrate thereon is a substrate which supports a semiconductor chip thereon in a semiconductor device, and different types of packages of semiconductor devices use different chip mounting substrates, respectively. In this embodiment, the package is the lead frame  16  and hence the die pad  18  is the chip mounting substrate. However, packages and chip mounting substrates other than the lead frame  16  and the die pad  18  may be employed. 
     A holding device in the present invention is, for example, the collet  8  employed in this embodiment. The holding device may be any device other than the collet  8 , provided that the device is capable of carrying a semiconductor chip and placing the same on a mounting member. 
     A first supporting device of a chip mounting unit and a second supporting device of a chip pressing unit according to the present invention correspond to, for example, the heating block  4  and the heating block  6 , respectively, of the die bonding apparatus in this embodiment. The respective supporting devices of the chip mounting unit and the chip pressing unit are not limited thereto and may be any devices capable of supporting the semiconductor chip and the mounting substrate thereon when bonding the semiconductor chip to the mounting substrate. 
     The heating blocks  4  and  6  are interconnected by the rubber rings  3  which carry the lead frame  16  having the die pads  18  to which the semiconductor chips  14  are bonded in the chip mounting unit  110 . The chip mounting unit  110  and the chip pressing unit  120  may be completely separate units, and the lead frame  16  may be held and transferred from the heating block  4  to the heating block  6  by a carrying mechanism capable of gripping the lead frame  16 . 
     Heating devices according to the present invention, for example, correspond to the cartridge heaters incorporated into the heating blocks  4  and  6 . The heating devices are not limited to the cartridge heaters and may be any suitable heating devices capable of heating the heating blocks  4  and  6 . Although both the heating blocks  4  and  6  are provided with the heating devices in this embodiment, heating blocks not provided with any heating devices may be used. 
     A pressing device according to the present invention is, for example, the heating tool  10  in this embodiment. The surface area of the heating tool  10  in this embodiment is greater than that of the semiconductor chip to straighten the warped peripheral part of the semiconductor chip by a single pressing operation. The pressing device does not necessarily need to be formed in such a shape and may be formed in any suitable shape provided that the pressing device is capable of straightening a warped peripheral part of a semiconductor chip. 
     The die bonding apparatus  100  used by this embodiment is provided with the single heating tool  10 . The die bonding apparatus  100  may be provided with a plurality of heating tools to straighten a plurality of warped semiconductor chips simultaneously. 
     A heating device of the chip pressing unit according to the present invention, for example, corresponds to the cartridge heater incorporated into the heating tool  10 . However, the heating device of the chip pressing unit is not limited to the cartridge heater, and the heating tool  10  does not necessarily need to be provided with the heating device. 
     A mounting substrate feeding process according to the present invention is executed, for example, in step S 1  of this embodiment. A chip bonding process according to the present invention is executed, for example, in steps S 2  and S 3 . A workpiece transfer operation according to the present invention is executed, for example, in step s 4 . A pressing process according to the present invention is executed, for example, in step S 5 . A method according to the present invention is not limited to the foregoing method including steps S 1  to S 5 . 
     Although the lead frame  16  having the die pads  18  respectively provided with the adhesive layers  20  is fed onto the heating block  4  in step S 1  in this embodiment, step S 1  is not limited thereto; the adhesive layers  20  may be formed on the die pads  18  after mounting the lead frame  16  on the heating block  4 . An additional heating block may be disposed on the path of the rubber rings  3 , the adhesive layers  20  may be formed on the die pads  18  on the additional heating block, and then the lead frame  16  may be carried to the heating block  4  by the rubber rings  3 . 
     The feature and advantage of the present invention as described above may be summarized as follow. 
     According to the present invention, the semiconductor chip is mounted on and bonded temporarily to the mounting substrate, the warped part of the semiconductor chip is straightened, and then the semiconductor chip is bonded completely to the mounting substrate. Accordingly, the semiconductor chip can be entirely and surely bonded to the mounting substrate. 
     Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may by practiced otherwise than as specifically described. 
     The entire disclosure of a Japanese Patent Application No. 2001-290713, filed on Sep. 25, 2001 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.