Abstract:
A wafer processing apparatus ( 10 ) has a grinder ( 80 ) for grinding the back surface ( 22 ) of a wafer ( 20 ) on whose front surface ( 21 ) a circuit pattern (C) has been formed, and a die attachment paste applicator ( 30 ) for applying die attachment paste on the entire back surface of the wafer ground by the grinder. With this arrangement, die attachment paste can be applied to a wafer in a short period of time without using a film. The die attachment paste applicator is either a spin-coater ( 30 A) that spin-coats die attachment paste supplied on the back surface of a wafer, or a screen-printing device ( 30 B) that screen-prints die attachment paste on the back surface of a wafer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a wafer processing method for applying a die attachment paste to the back surface of a wafer, and a wafer processing apparatus for executing such a method.  
         [0003]     2. Description of the Related Art  
         [0004]     In a semiconductor manufacturing process, a wafer on the front surface of which a predefined circuit pattern has been formed is diced and made into chips. Each IC chip obtained from the process is die-bonded onto a metal lead frame, tape substrate, or an organic hard substrate, etc., and built into a semiconductor device.  
         [0005]     Under Japanese Unexamined Patent Publication (Kokai) No. 2005-294535, when such IC chips are die-bonded, a die attachment film is stuck on the chip surface (the back surface) whereon a circuit pattern has not been formed. The die attachment film is an adhesive in a film form. After the wafer is divided into pieces by dicing, the IC chips are picked up. The IC chips are die-bonded to a metal lead frame or the like with the die attachment film that was applied to the back surfaces and serving as an adhesive.  
         [0006]     Wafers are becoming larger and larger, year by year in semiconductor manufacturing, and at the same time there is a trend toward making wafers increasingly thinner with a view to increasing packaging density. Today, thin wafers are obtained by grinding of their back surfaces. Then, it is desirable that the die attachment film placed between the IC chips formed as a result of dicing and the lead frame or the like be made thin to further reduce the thickness of the chips.  
         [0007]     However, there are technical limits to making die attachment film thin. Furthermore, the thinner the die attachment film is made, the more difficult it is to handle. Therefore, there is a possibility that a semiconductor manufacturing process may become more complicated as a result of die attachment film being made thin.  
         [0008]     Presently, a die attachment paste made of an adhesive paste is being applied instead of a die attachment film. However, as die attachment paste is supplied to the board by means of screen-printing or the like, and IC chips are mounted and stuck on top of the paste, it is necessary to supply the die attachment paste by screen-printing or the like to each board and the semiconductor manufacturing process becomes more complicated in such a case.  
         [0009]     The present invention, was conceived in view of the above problem and its objective is to provide a wafer processing method that makes it possible to apply a die attachment paste in a relatively period of short time without using a die attachment film, and a wafer processing apparatus for executing such a method.  
       SUMMARY OF THE INVENTION  
       [0010]     To realize the abovementioned objective, according to a first aspect of the invention, a wafer processing method comprises a grinding step for grinding a back surface of a wafer having on its front surface a circuit pattern, and a die attachment paste application step for applying a die attachment paste to the entirety of the ground, back surface of the wafer.  
         [0011]     In order words, in the first aspect, the die attachment paste is applied in one operation to the entirety of the ground back surface of the wafer. Therefore, the die attachment paste can be applied in a relatively short period of time without using a die attachment film.  
         [0012]     In a second aspect, the wafer processing method, as defined by the first aspect, further comprises the steps of sticking a dicing tape to the applied die attachment paste, dicing the wafer according to the circuit pattern.  
         [0013]     In other words, in the second aspect, the wafer is divided into individual chips, which can be mounted on a lead frame or the like.  
         [0014]     In a third aspect, as defined by the first or second aspect, the die attachment paste supplied to the back surface of the wafer in the die attachment paste application step in the first or second embodiment is spin-coated.  
         [0015]     In other words, in the third aspect, the die attachment paste can be applied at the required thickness, even in cases where the thickness of die attachment paste required is quite thin.  
         [0016]     In a fourth aspect, as defined by the first or second aspect, the die attachment paste is screen-printed on the back surface of the wafer in the die attachment paste application step as in the first or second aspect.  
         [0017]     In other words, in the fourth aspect, the die attachment paste can be applied to the back surface of the wafer relatively easily and quickly.  
         [0018]     In a fifth aspect, as defined by the fourth aspect, the die attachment paste is applied except in the portions corresponding to channels formed when the wafer is diced in the screen-printing step.  
         [0019]     In other words, in the fifth aspect, it is possible when the wafer is diced using dicing blades, to prevent the dicing blades from becoming clogged with the die attachment paste, and their cutting capability from being reduced. Moreover, laser dicing can also be used since there is no need to cut the die attachment paste layer before or after the dicing.  
         [0020]     According to a sixth aspect, a wafer processing apparatus comprises a grinding means for grinding the back surface of the wafer having on its front surface a circuit pattern, and a die attachment paste application means for applying a die attachment paste on the entire back surface of the wafer ground by the grinding means.  
         [0021]     In other words, in the sixth aspect, the die attachment paste is applied in one operation to the entirety of the ground back surface of the wafer. Therefore, a die attachment paste can be applied in a relatively short period of time without using a die attachment film.  
         [0022]     If a seventh aspect, the wafer processing apparatus, as defined by the sixth aspect, comprises a dicing tape sticking means for sticking a dicing tape to the die attachment paste applied by the die attachment paste application means, and a dicing means for dicing the wafer according to the circuit pattern, in addition to the means provided in the sixth aspect.  
         [0023]     In other words, in the seventh aspect, the wafer is divided into individual chips that can be mounted on a lead frame or the like.  
         [0024]     In an eighth aspect, as defined by the sixth or seventh aspect, the die attachment paste application means in the sixth or seventh embodiment comprises a spin-coating means for spin-coating the die attachment paste supplied to the back surface of the wafer.  
         [0025]     In other words, in the eighth aspect, the die attachment paste can be applied at the required thickness, even in cases where the thickness of die attachment paste required is quite thin.  
         [0026]     In a ninth aspect, as defined by the sixth or seventh aspect, the die attachment paste application means in the sixth or seventh embodiment comprises a screen-printing means for screen-printing the die attachment paste to the back surface of the wafer.  
         [0027]     In other words, in the ninth aspect, the die attachment paste can be applied to the back surface of the wafer relatively easily and quickly.  
         [0028]     In a tenth aspect, as defined by the ninth aspect, the screen-printing means in the ninth embodiment applies the die attachment paste except on the portions corresponding to the channels formed when the wafer is diced.  
         [0029]     In other words, in the tenth aspect, it is possible, when the wafer is diced using dicing blades, to prevent the dicing blades from becoming clogged with the die attachment paste, and their cutting capability from being reduced. Moreover, laser dicing can also be used since there is no need to cut the die attachment paste layer before or after the dicing.  
         [0030]     The detailed explanation of the typical embodiments of the present invention, which are shown in the attached drawings, will surely serve to make clearer the above-mentioned and other objectives, characteristics and benefits of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]      FIG. 1  is a schematic plan view of a wafer processing apparatus according to the present invention  
         [0032]      FIG. 2   a  is a side view of a wafer that is supplied to the wafer processing apparatus.  
         [0033]      FIG. 2   b  is a side view of a wafer in a grinding condition.  
         [0034]      FIG. 2   c  is a side view of a wafer after grinding.  
         [0035]      FIG. 2   d  is a side view of a wafer whereon a die attachment paste film has been formed.  
         [0036]      FIG. 3  is a schematic diagram of a die attachment paste application unit in the first embodiment of the present invention.  
         [0037]      FIG. 4  is a schematic diagram of a die attachment paste application unit in the second embodiment of the present invention.  
         [0038]      FIG. 5   a  is a first explanatory view of a die attachment paste application unit according to the second embodiment of the present invention.  
         [0039]      FIG. 5   b  is a second explanatory view of a die attachment paste application unit, according to the second embodiment of the present invention.  
         [0040]      FIG. 5   c  is a third explanatory view of a die attachment paste application unit, according to the second embodiment of the present invention.  
         [0041]      FIG. 6   a  is a view showing a first screen used in the second embodiment of the present invention.  
         [0042]      FIG. 6   b  is a view showing a second screen used in the second embodiment of the present invention.  
         [0043]      FIG. 6   c  is a view showing a wafer that has been screen-printed by means of the screens shown in  FIGS. 6   a  and  6   b.    
         [0044]      FIG. 7  is a side view of a wafer while it is being diced.  
         [0045]      FIG. 8  is a sectional side view for explaining laser dicing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0046]     The embodiments of the present invention will be explained below with reference to the attached drawings. In the drawings below, the same reference numerals have been used to designate identical members. The scale of these diagrams has been changed appropriately to facilitate understanding.  
         [0047]      FIG. 1  is a schematic plan view of a wafer processing apparatus according to the present invention. The wafer processing apparatus  10  shown in  FIG. 1  comprises a back-surface grinding unit  80  that grinds the back surface  22  of the wafer  20 , a die attachment paste application unit  30  that applies a die attachment paste to the wafer  20 , a UV-irradiating unit  40  that irradiates ultraviolet (UV) rays on the die attachment paste, and a dicing tape sticking unit  50  that sticks a dicing tape on the wafer  20 . Each of these units is controlled by a controller (not shown).  
         [0048]     Wafer cassettes  81 A and  81 B, which store therein a plurality of wafers  20 , are provided in the back--surface grinding unit  80 . As shown in  FIG. 2   a,  a plurality of circuit patterns C are pre-formed on the front surface  21  of the wafer  20  that is supplied to the back-surface grinding unit  80 , and a surface protection film  3  is stuck on to the front surface  21  to protect the circuit patterns C.  
         [0049]     With reference to  FIG. 1 , each of the wafers  20  are taken out from the wafer cassettes  81 A and  81 B by robot arms  82 A and  82 B. Then, the wafer  20  is held, with its back surface  22  facing upward, by suction portions  84  of a rotary stage  83 .  
         [0050]     As shown in  FIG. 2   b,  grinding parts  85 A and  85 B of the back-surface grinding unit  80  are operated to grind the back surfaces  22  of the wafers  20 . As a result of the grinding, as shown in  FIG. 2   c,  the thickness of the wafer  20  is reduced from the original wafer thickness LO to the after-grinding thickness LO′.  
         [0051]     After completion of the grinding of the wafer  20 , the wafer  20  is conveyed by a robot arm  39  from the back-surface grinding unit  80  to the die attachment paste application unit  30 . In the die attachment paste application unit  30 , a die attachment paste made of an adhesive paste material is applied to the ground back surface  22 , so that a die attachment paste film  24  is thereby formed (see  FIG. 2   d .)  
         [0052]      FIG. 3  is a schematic diagram of the die attachment paste application unit according to the first embodiment of the present invention. The die attachment paste application unit  30  shown in  FIG. 3  is a spin-coat type application unit  30 A. Note that the surface protection film  3  and the circuit patterns C have been omitted from  FIGS. 3, 4  and  8 .  
         [0053]     In the embodiment shown in  FIG. 3 , the die attachment paste application unit  30  comprises a holding table  33  that can be rotated by a motor  34 , and a dispenser  32  that dispenses die attachment paste.  
         [0054]     When the wafer  20  is held on the table  33  with its back surface  22  facing upward, a predefined amount of the die attachment paste is dispensed from the dispenser  32  onto the back surface  22  of the wafer  20 . Next, when the table  33  is rotated about its central axis by the motor  34 , the die attachment paste is scattered radially by centrifugal force toward the peripheral surface of the housing  31 . The die attachment paste film  24  is thereby formed on the back surface  22  of the wafer  20 . Then, the die attachment paste film  24  is subjected to a baking treatment.  
         [0055]     In this way, when the spin-coat type application unit  30 A is used, the die attachment paste can be applied in one operation to the entire back surface  22  of the wafer  20 . Consequently, it is possible to apply the die attachment paste in a relatively shorter period of time than compared to a case where it is applied on individual chips after dicing.  
         [0056]     As known, the lower the viscosity of the die attachment paste and the greater the rotation speed of the table  33 , the smaller the thickness of the die attachment paste film  24 . In other words, the thickness of the die attachment paste film  24  can be adjusted by changing the viscosity of the die attachment paste and/or the rotation speed of the table  33 . Moreover, when the spin-coat type application unit  30 A is utilized, the die attachment paste film  24  can be formed at the required thickness, even in cases where the thickness of the die attachment paste required is quite thin. For this reason, the spin-coat type application unit  30 A is particularly advantageous in cases where the thickness of the die attachment paste required is quite thin.  
         [0057]      FIG. 4  is a schematic diagram of the die attachment paste application unit according to the second embodiment of the present invention. The die attachment paste application unit  30  shown in  FIG. 4  is a screen-printing type application unit  30 B.  
         [0058]     As shown in  FIG. 4 , the movable squeegee  42  is arranged inside the frame body  41  so as to move along the inner walls of the frame body  41 . Moreover, the screen  44  having a hole  45  of a shape corresponding to the wafer  20 , is provided on the lower surface of the frame body  41 .  
         [0059]      FIGS. 5   a  to  5   c  are views for explaining the die attachment paste application unit according to the second embodiment of the present invention. First, as shown in  FIG. 5   a,  with its back surface  22  facing upward, the wafer  20  is held on the table  43 , and the squeegee  42  is placed on one side in the frame body  41 . Next, a predetermined amount of the die attachment paste  49  is supplied to one side of the squeegee  42 , directed to the direction of movement of the squeegee  42 .  
         [0060]     Next, as shown in  FIG. 5   b,  the squeegee  42  is made to move on the screen  44  toward the other side of the frame body  41 . As a result of this movement, the die attachment paste flows out from the hole  45  of the screen  44  and is applied little by little on the back surface  22  of the wafer  20 . When the squeegee  42  reaches the other side of the frame body  41 , the die attachment paste film  24  is formed on the back surface  22  of the wafer  20 . It should be evident that also in this embodiment, the die attachment paste can be applied in a relatively shorter period of time than compared to a case where it is applied on individual chips after dicing.  
         [0061]     In the second embodiment, it is desirable that the screen-printing process be carried out twice using the first screen  44   a  and the second screen  44   b.    FIG. 6   a  and  FIG. 6   b  respectively show the first screen and the second screen. Note that the arrows found in these diagrams indicate the direction of movement of the squeegee  42 .  
         [0062]     As can be seen from these diagrams, a plurality of elongated hole  45   a  that are substantially parallel to each other and evenly spaced apart are formed in the first screen  44   a.  These holes  45   a  are formed so that as a whole they correspond to the external diameter of the wafer  20 . A plurality of elongated holes  45   b  that are perpendicular to the holes  45   a  of the first screen  44   a  are formed in the second screen  44   b  similarly to the way the holes  45   a  are formed.  
         [0063]     The spaces between the plurality of holes  45   a  shown in  FIG. 6   a  and the spaces between the plurality of holes  45   b  shown in  FIG. 6   b  correspond substantially to the spaces between the circuit patterns C formed on the front surface  21  of the wafer  20 . Therefore, the spaces between the plurality of holes  45   a  and the spaces between the plurality of holes  45   b  respectively correspond to the plurality of channels formed during the dicing process mentioned below.  
         [0064]     When these screens  44   a  and  44   b  are used, the table  43  is rotated so that the spaces between the circuit patterns C and the spaces between the holes of the first screen  44   a  are made to coincide, using a near-infrared ray camera (not shown) and a positioning pattern previously formed on the front surface  21  of the wafer  20 . The screen-printing process of the first screen  44   a  is performed under the situation.  
         [0065]     Next, the table  43  is rotated approximately 90 degrees, and the spaces between the circuit pattern C and the spaces between the holes of the second screen  44   b  are made to coincide. After that, the screen-printing process of the second screen  44   b  is performed. As a result of this printing, as shown in  FIG. 6   c,  the die attachment paste is applied to the back surface  22  of the wafer  20 , except for the lattice-shaped parts. The lattice-shaped parts correspond to channels that are formed in the dicing process.  
         [0066]     With reference to  FIG. 1 , the wafer  20  on which the die attachment paste film  24  has been formed Is conveyed to the UV-irradiating unit  40 . In the UV-irradiating unit  40 , a predefined quantity of UV is irradiated to the die attachment paste film  24 . The die attachment paste film  24  thereby assumes the desired adhesion.  
         [0067]     Next, the wafer  20  is conveyed to the dicing tape sticking unit  50 , and the dicing tape  29  is stuck on the die attachment paste film  24  of the wafer  20  according to a known technique. Next, the surface protection film  3  that is stuck on the top surface  21  of the wafer  20  is peeled off using a known technique, and then the wafer  20  is conveyed to the dicing unit  60  and diced.  
         [0068]      FIG. 7  is a side view of the wafer  20  as it is being diced. In the dicing unit  60 , the wafer  20  is cut by the part of the dicing tape  29  by the dicing blade  61 .  
         [0069]     In the second embodiment, the dicing blade  61  cuts the wafer  20  by moving along the lattice-shaped parts (see  FIG. 6   c ) on which the die attachment paste film  24  has not been formed. Consequently, the channels  65  formed by the dicing blade  61  correspond substantially to the aforementioned lattice-shaped parts. Due to the foregoing, the dicing blade  61  hardly cuts the die attachment paste film  24 . Therefore, in the second embodiment, it is possible to prevent the dicing blade  61  from becoming clogged with the die attachment paste film  24 , and the cutting ability of the dicing blade  61  from being reduced.  
         [0070]     While the channels (grooves)  65  are formed by the dicing blade  61  according to  FIG. 7 , the channels  65  may be formed in other ways. Moreover, it is also possible to form the channels  65  by means of a laser dicing device.  
         [0071]      FIG. 8  is a sectional side view for explaining laser dicing. In  FIG. 8 , the laser V from a laser source (not shown) is irradiated through a condensing lens  75  onto the front surface  21  of the wafer  20  under conditions where multiple photon absorption occurs. At this point, the light gathering point  74  is set to fall inside the wafer  20  rather close to the front surface  21 . A modified area  74  is thereby formed in the vicinity of the light gathering point  74 . Next, when the laser V and the condensing lens  75  are moved in accordance with the arrow X 3 , a band-like modified area  76  is formed inside the wafer  20 .  
         [0072]     In the laser dicing process, the laser V is made to pass through the wafer  20  and cause multiple photon absorption to occur inside the wafer. A modified area is thus formed. Consequently, the laser V is hardly absorbed by the front surface  21  of the wafer  20 , and as a result, the front surface  21  of the wafer  20  does not melt, and cracks that deviate from the lines planned to be cut or the like do not occur on the top surface of the wafer.  
         [0073]     As the modified area  76  is formed rather close to the front surface  21 , when the modified area  76  breaks naturally in the thickness direction toward the front surface  21 , the channels  65  corresponding to the width of the laser V are formed. As mentioned above, when the die attachment paste is applied, except for the lattice-shaped parts, there is no need to cut off the die attachment paste layer before or after the dicing, and consequently a laser dicing system can be utilized in the dicing unit  60 .  
         [0074]     The wafer  20  is diced and divided into individual chips by the dicing operation shown in  FIG. 7  or  FIG. 8 . Next, the dicing tape  29  is expanded by means of a known technique, and, each chip is picked up from the dicing tape  29 . The die attachment paste films  24 , which serve as an adhesive on the bottom surfaces of the chips, the chips can then be die-bonded on to a lead frame or the like.  
         [0075]     In this way, according to the present invention, the die attachment paste application unit  30  is arranged between the back-surface grinding unit  80  for the wafer  20  and the dicing unit  60 . The invention provides for the die attachment paste to be applied in one operation on the entire ground back surface  22  of the wafer  20  in the die attachment paste application unit  30 . For this reason, it is possible to apply die attachment paste in a shorter period of time than compared to a case where die attachment paste is separately applied to the individual chips after dicing.  
         [0076]     Note that in the die attachment paste application unit  30 , die attachment paste may be applied on the back surface  22  of the wafer  20  using a technique other than spin-coating or screen-printing, such as a so-called ink-jet method. It should be understood that such cases also fall within the scope of the present invention.  
         [0077]     The present invention as been explained using representative embodiments, however it should be understood that a person skilled in the relevant art could execute the abovementioned change and various other modifications, omissions or additions, without deviating from the scope of the present invention.