Abstract:
A method of bonding a semiconductor chip, including step of photographing a surface of a semiconductor chip, on which an electrode is formed, and detecting a relative position of the electrode with respect to the semiconductor chip, a bonding step of making the electrode of the semiconductor chip to face a circuit pattern provided on a substrate, and bonding the electrode to the circuit pattern, a step of photographing the substrate on which the semiconductor chip is formed, and detecting a relative position of the semiconductor chip with respect to the substrate. Also included is a step of evaluating a bonding accuracy by calculating a relative position of the electrode with respect to the substrate from the relative position of the semiconductor chip with respect to the substrate and the relative position of the electrode with respect to the semiconductor chip.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor bonding method for bonding a semiconductor chip such as an IC to a substrate, in a face-down manner, and more specifically to a bonding method capable of detecting an error in terms of position, between an electrode of a semiconductor chip and a wiring line provided on a substrate, after a face-down bonding, by inspecting it from outside, and a device therefor. 
     As one of the methods for directly mounting and bonding a semiconductor chip such as an IC to a mount substrate such as a print wiring substrate, there is a method in which a surface in which the electrode (bump electrode) of a semiconductor chip is formed is made to face a substrate, and the electrode is directly bonded to the wiring pattern of the substrate. This method is generally called “face-down bonding” since the bonding operation is carried out while holding the surface of the semiconductor chip on which the electrode is formed facing downwards. 
     In the face-down bonding as above, the joint portion between the electrode and the circuit pattern is covered by the semiconductor chip, and therefore it is difficult to confirm if the bonding has been accurately carried out. 
     In order to detect whether or not bonding has been accurately carried out, that is, to inspect the accuracy of bonding, the method in which the status of the joint portion between the electrode and circuit pattern is physically observed so as to judge if the bonding is good or no good, is generally employed. 
     More specifically, there is a method in which a semiconductor device which has been subjected to the face-down bonding is sampled at a certain period, and the semiconductor chip is stripped off or cut from the substrate so as to inspect the joint portion of the electrode, and a method in which the joint portion between the electrode and the circuit pattern is examined from a rear side of the substrate transparently. 
     The method which involves stripping or cutting the semiconductor chip requires the transfer of a sampled semiconductor chip to a separate device, where the stripping and cutting is carried out, the entire system thereby becoming large in size. Further, the inspection cannot be conducted at real time during the bonding operation. 
     Further, with the transparent inspection method, it is not possible to obtain a clear image of the joint portion, and therefore an accurate inspection cannot be conducted. More specifically, for example, a ceramic substrate or glass substrate is used as the substrate, and particularly, in the case of the ceramic substrate, the amount of light transmission is very small. As a result, it is very difficult to confirm even the outline of a semiconductor chip, not to mention the joint portion between the electrode and circuit pattern. 
     Further, in the case where a semiconductor chip is face-down bonded to a glass substrate, it is difficult to obtain a clear image of the joint portion between the electrode and circuit pattern due to the state of the refraction of the glass substrate or the presence of the circuit pattern, although the outline of the semiconductor chip can be traced. 
     BRIEF SUMMARY OF THE INVENTION 
     Under these circumstances, the main object of the present invention is to provide a method of manufacturing a semiconductor device, which is capable of easily and accurately inspecting the bonding accuracy after a semiconductor chip is face-down bonded to a substrate. 
     Another object of the present invention is to provide a method of manufacturing a semiconductor device, capable of inspecting the alignment accuracy between a bump and a substrate by observation from outside without performing stripping or cutting of the device, after the face-down bonding. 
     In order to achieve the above-described objects, there is provided, according to the present invention, a method of bonding a semiconductor chip, comprising: 
     the step of photographing a surface of a semiconductor chip, on which an electrode is formed, and detecting a relative position of the electrode with respect to the semiconductor chip; 
     the bonding step of making the electrode of the semiconductor chip to face a circuit pattern provided on a substrate, and bonding the electrode to the circuit pattern; 
     the step of photographing the substrate on which the semiconductor chip is formed, and detecting a relative position of the semiconductor chip with respect to the substrate; and 
     the step of evaluating a bonding accuracy by calculating a relative position of the electrode with respect to the substrate from the relative position of the semiconductor chip with respect to the substrate and the relative position of the electrode with respect to the semiconductor chip. 
     In connection with the above method, it is preferable that the step of detecting the relative position of the electrode with respect to the semiconductor chip, should include photographing of the semiconductor chip from a surface side on which the electrode is formed, and detecting a position of the electrode with reference to a predetermined location of the semiconductor chip; and the step of detecting the relative position of the semiconductor chip with respect to the substrate, should include photographing of the semiconductor chip mounted on the substrate, from a surface side on which the electrode is not formed, and detecting the relative position of the predetermined location of the semiconductor chip, with reference to an alignment mark formed on the substrate as a reference. 
     With the above-described structure, the position of the electrode is detected with reference to a predetermined location of the semiconductor chip in advance to the bonding, and the relative position of the predetermined location of the semiconductor chip, with respect to the substrate is detected after the bonding. In this manner, the position of the electrode with respect to the substrate can be obtained by calculation. Therefore, it becomes possible to inspect the bonding accuracy without stripping the semiconductor chip from the substrate or cutting it. 
     Further, it is preferable that the predetermined location should be an edge of the semiconductor chip, especially a corner edge thereof. With this structure, it becomes unnecessary to provide a mark on the semiconductor chip. 
     It should be noted that the evaluation of the bonding accuracy should be carried out by comparing the relative position of the electrode with respect to the substrate with a predetermined reference value, and the reference value should be set by performing the teaching operation. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a diagram showing an embodiment of the apparatus for manufacturing a semiconductor device, according to the present invention; 
     FIGS. 2A and 2B are schematic diagrams illustrating the operation of detecting a lateral surface of a semiconductor chip using the above apparatus; 
     FIGS. 3A and 3B are schematic diagrams illustrating the operation of detecting a gap between the lateral surface of a semiconductor chip and a reference mark, using the above apparatus; 
     FIG. 4 is a flowchart of a detection carried out by the apparatus; 
     FIG. 5 is a diagram illustrating the operation of detecting a lateral surface of a semiconductor chip; 
     FIG. 6 is a diagram showing how to pick up an image of a lateral surface of a semiconductor chip; 
     FIG. 7 is a diagram showing how to pick up an image of a reference pattern on a substrate; 
     FIG. 8 is a schematic diagram showing how to pick up an image of a reference pattern on a substrate; 
     FIG. 9 is a diagram showing the structure of an alternative version of the device of the present invention; and 
     FIG. 10 is a diagram showing a semiconductor device in which a semiconductor chip is face-down bonded. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the present invention will now be described with reference to accompanying drawings. 
     FIG. 1 is a diagram showing the entire structure of an apparatus for manufacturing a semiconductor device. 
     In this apparatus, as shown in FIG. 10, a semiconductor chip  13  such as IC, in which a bump electrode  15  is formed on its surface, is mounted on a substrate  11  on which a wiring pattern  11   a  is formed, in a face-down manner, and the bump electrode  15  is bonded to the wring pattern  11   a  (the face-down bonding). 
     As shown in FIG. 1, the apparatus includes a bonding tool  12  for adsorbing and holding a semiconductor chip  13  in a face-down state, that is, the bump electrode  15  is facing downwards, and a bonding stage  10  for holding a substrate  11  on which the semiconductor chip  13  is bonded. The bonding tool  12  moves in the direction indicated by the arrow (a) in the figure while adsorbing and holding the semiconductor chip  13 , so as to make the semiconductor chip  13  face the substrate  11 . 
     Further, on the downstream side of the passage (a) of the bonding tool  12 , a first recognition camera  14  for recognizing and picking up an image of the semiconductor chip  13  held by the bonding tool  12  is provided. The first recognition camera  14  has the function of picking up the image of the lower surface of the semiconductor chip  13  before bonding, that is, the bump electrode  15  of the semiconductor chip  13 , and outputting an image signal thereof. 
     On the lateral surface of the bonding tool  12 , a second recognition camera  16  which moves together with the bonding tool  12  as an integral body, is provided. The second recognition camera  16  has the function of picking up a reference pattern (denoted by reference numeral  28  in FIGS. 3A and 3B) formed on the substrate  11  before and after the semiconductor chip  13  is bonded onto the substrate  11 , and outputting an image signal thereof. 
     Meanwhile, FIG. 1 shows a main control unit  20  for controlling the entire manufacture apparatus. To a bus to which the main control unit  20  is connected, an input unit  22  for receiving image signals from the first and second recognition cameras  14  and  16 , an image memory  21  for storing image data input to the input unit  22 , a first detection unit  23  for generating alignment data used for the bonding operation, a second detection unit  25  for generating data used for inspecting the bonding accuracy, a register unit  24  in which a reference value set for inspecting the bonding accuracy is registered, an inspection unit  26  for inspecting the bonding accuracy, and an alarm unit  27  for generating a necessary alarm on the basis of the detection result obtained by the inspection unit  26 , are connected. 
     Of these members, the first detection unit  23  calculates alignment data necessary for carrying out the face-down bonding. More specifically, from the image memory  21 , the image of the semiconductor chip  13  (bump electrode  15 ) before bonding, which is picked up by the first recognition camera  13 , and the image of the reference pattern  28  before bonding, which is picked up by the second recognition camera  16 , are accessed. Then, the correction angle for the inclination of the semiconductor chip  13 , and the drive amount for the bonding tool  12 , which are necessary for aligning the semiconductor chip  13  with respect to the substrate  11 , are determined. 
     In the meantime, the second detection unit  25  outputs a signal indicating the relative position of the bump electrode  15  after executing the bonding, with respect to the reference pattern  28 , in order to evaluate the bonding accuracy. More specifically, from the image memory  21 , the image of the semiconductor chip  13  (bump electrode  15 ) before bonding, which is picked up by the first recognition camera  13 , and the images of the semiconductor chip  13  after the bonding and the reference pattern  28 , which are picked up by the second recognition camera  16 , are accessed. Then, the relative position of the bump electrode  15  with respect to the reference pattern  28  after bonding is detected. 
     The detection made by the second detection unit  25  will now be described in detail. 
     First, the second detection unit  25  detects the relative position of the bump electrode  15  with respect to the outline of the semiconductor chip  13 . FIGS. 2A and  2 B are conceptual diagrams illustrating the detection method used here. FIG. 2A shows an image of the semiconductor chip  13 , which is held in an ideal state, whereas FIG. 2B shows an image of the semiconductor chip  13  which is displaced (inclined and offset). 
     As shown in FIG. 2A, the relative position of the bump electrode  15  is obtained in the form of coordinates (X 1 , Y 1 ) with reference to the corner edge c of the semiconductor chip  13 . The coordinates (X 1 , Y 1 ) indicate a distance  1   1  from the corner edge c of the semiconductor chip  13  and the inclination θ 1  of the semiconductor chip  13 . 
     By contrast, in actual measurements, the relative position of the bump electrode  15  with respect to the semiconductor chip  13  is displaced, for example, as shown in FIG.  2 B. In such a case, the relative position of the bump electrode  15  is obtained in the form of coordinates (X 1 ′, Y 1 ′) taken with reference to the corner edge C of the semiconductor chip  13 . The coordinates (X 1 ′, Y 1 ′) indicate a distance  1   1′  from the corner edge c of the semiconductor chip  13  and the inclination θ 1′  of the semiconductor chip  13 . The difference between θ 1  and θ 1′  is an angle error which remains after the correction of the inclination of the semiconductor chip  13 , carried out on the basis of the detection result made by the first detection unit  23 , and the angle error is usually within ±2° 
     Next, the second detection unit  25  detects the relationship between the semiconductor chip  13  and the substrate  11  in terms of position, after the bonding. FIG. 3A shows an image of the semiconductor chip  13  and substrate  11  (reference pattern  28 ), when they are face-down bonded in an ideal state, whereas FIG. 3B shows an image of the semiconductor chip  13  and substrate  11  (reference pattern  28 ) after an actual bonding operation. 
     As shown in FIGS. 3A and 3B, the relationship between the semiconductor chip  13  and the substrate  11  in terms of position can be detected by obtaining the coordinates (X 2 , Y 2 ) or (X 2 ′, Y 2 ′) of the corner edge c of the semiconductor chip  13  with regard to the reference pattern  28  on the substrate  11  taken as the origin. The coordinates (X 2 , Y 2 ) and (X 2 ′, Y 2 ′) indicate, respectively, distances  12  and  12 ′ from the corner edge c to the reference pattern  28 , and inclinations θ 2  and θ 2′ . The difference between θ 1  and θ 1′  results due to the inclination error of the semiconductor chip  13  and the alignment error of the substrate  11 , caused by the bonding stage  10 , after bonding. 
     From the detection results illustrated in FIGS. 2A and 3A, the relative position (Xs, Ys) of the bump electrode  15  with respect to the reference pattern  28  in the case where an ideal face-down bonding is carried out, can be obtained as follows. 
     
       
         Xs=X 1 +X 2   
       
     
     
       
         Ys=Y 1 +Y 2   
       
     
     These values Xs and Ys are registered as reference values S in the register unit  24  shown in FIG.  1 . 
     Further, from the detection results illustrated in FIGS. 2B and 3B, the relative position (Xs′, Ys′) of the bump electrode  15  with respect to the reference pattern  28  after an actual face-down bonding, can be obtained as follows (the relative position (Xs′, Ys′) will be called detection values hereinafter). 
     
       
         Xs′=X 1 ′+X 2 ′ 
       
     
     
       
         Ys′=Y 1 ′+Y 2 ′ 
       
     
     The inspection unit  26  shown in FIG. 1 has the function of comparing the difference between the reference values Xs and Ys and the detection values Xs′ and Xs′, with a predetermined threshold value H, and judging the case where the difference falls out of the threshold value H to be no good. The alarm unit  27  has the function of alarming the operator of the apparatus, as it operates when a case is judged by the inspection unit  26  to be no good. 
     Next, the operation of the face-down bonding apparatus will now be described with reference to the flowchart shown in FIG.  4 . 
     First, in order to register the reference values Xs and Ys for the judgment of an alignment error, an ideal face-down bonding operation is played back in Steps # 1  to # 4 , thus carrying out a teaching operation. 
     That is, a substrate  11  is placed on a bonding stage  10  at high accuracy. In the substrate  11 , the reference pattern  28 , and a circuit pattern  11   a  for bonding bump electrodes  15  are arranged in an ideal manner (FIG.  10 ). Further, on the distal end of the bonding tool  12 , the semiconductor chip  13  on which the bump electrodes  15  are arranged at ideal positions is held by adsorption in a face-down manner (FIG.  5 ). 
     First, in Step # 1 , the semiconductor chip  13  adsorbed by the bonding tool  12  is placed in the view field of the first recognition camera  14 , as shown in FIG.  5 . Then, the image of the lower surface of the semiconductor chip  13  is picked up from the below side of the semiconductor chip  13  as shown in FIG. 6, and thus it is possible to output an image signal shown in FIG.  2 A. The image data is stored in the image memory  21  via the input unit  22 . 
     Subsequently, the second detection unit  25  reads out the image data stored in the image memory  21 , and detects the coordinates (X 1 , Y 1 ) of the relative position of the bump electrode, from the image data as shown in FIG.  2 A. In this case, of electrodes (bump)  15 , the one which is located closest to the corner of the semiconductor chip  13  is detected as a representative. 
     After that, the bonding tool  12  is moved in the x-axial direction and the bonding stage  10  is moved in the y-axial direction, such as to make the semiconductor chip  13  face the upper surface of the substrate  11 . In this manner, the face-down bonding operation for the semiconductor chip  13  is carried out in an ideal alignment state (Step # 2 ). 
     After the bonding operation, the second recognition camera  16  is moved to a section above the substrate  11  on which the semiconductor chip  13  is mounted as shown in FIG.  7 . Then, the outline of the corner portion of the semiconductor chip  13  which has been bonded in Step # 2 , and the reference pattern  28  formed on the substrate  11  are photographed by the second recognition camera  16  as shown in FIG.  8 . The image data is stored in the image memory  21  via the input unit  22 . 
     Then, the second detection unit  25  reads out the image data stored in the image memory  21 . From this image data, the relationship between the semiconductor chip  13  ideally bonded and the reference pattern  28  on the substrate  11  in terms of position, is obtained in the form of coordinate (X 2 , Y 2 ) shown in FIG.  3 A. 
     Next, in Step # 4 , the reference value for the judgment of an alignment error is registered in the register unit  24 . That is, the second detection unit  25  detects the reference position (Xs, Ys) with respect to the reference pattern  28  of the bump electrode  15 , from the relative position (X 1 , Y 1 ) of the bump electrode  15  with respect to the corner edge c of the semiconductor chip  13  and the relative position (X 2 , Y 2 ) of the corner edge c of the semiconductor chip  13  with respect to the reference pattern  28 , on the basis of the equations: 
     
       
         Xs=X 1 +X 2   
       
     
     
       
         Ys=Y 1 +Y 2 ,  
       
     
     and thus obtained reference position is registered in the register unit  24 . 
     The above-described teaching operation is carried out for every one lot in the manufacture of products. 
     After the above operation, the actual bonding is started as illustrated by Steps # 5  to # 12 . 
     First, when the instruction of the start of the bonding is received in Step # 5 , an operation similar to that of Step # 1  is executed in Step # 6 . More specifically, the relative coordinates (X 1 ′, Y 1 ′) of the bump electrode  15  with respect to the corner edge c of the semiconductor chip  13  is obtained by the second detection unit  25  as can be seen in FIG.  2 B. 
     Subsequently, in Step # 7 , the first detection unit  23  reads out, from the memory  21 , the image picked up by the first recognition camera  14 , and the posture of the semiconductor chip  13  and the absolute coordinates thereof are thus detected. 
     In Step # 8 , the second recognition camera  16  is set to face the reference pattern  28  on the substrate  11  so as to pick up an image of the reference pattern  28 , and the image thus picked up is stored in the image memory  21 . The first detection unit  23  reads out the image thus picked up, and detects the posture of the reference pattern  28  and the absolute coordinates thereof. 
     Further, the main control unit  20  drives the bonding tool  12  on the basis of the results of the detection of the positions of the bump electrode  15  and the reference pattern  28  (Steps # 7  and # 8 ), so as to make the semiconductor chip  13  to face and be aligned with the substrate  11 . Then, the bonding tool  12  moves the semiconductor chip  13  down, and bond the chip onto the substrate  11  in a face-down manner (Step # 9 ). 
     After the chip is face-down-bonded, an operation similar to that of Step # 3  is carried out in Step # 10 . More specifically, the relative coordinates (X 2 ′, Y 2 ′) of the corner edge c of the semiconductor chip  13 , with respect to the reference pattern  28  are obtained by the second detection unit  25  as can be seen in FIG.  3 B. 
     Next, in Step # 11 , the reference values Xs and Ys, and the detection values Xs′ and Ys′ (Xs′=X 1 ′+X 2 ′, Ys′=Y 1 ′+Y 2 ′) are compared with each other by the inspection unit, so as to judge if the difference between these values exceeds the threshold value H, and then the operation moves on to Step # 12 . 
     In the case where the difference does not exceed the threshold value H, the face-down bonding of a next semiconductor chip  13  is executed continuously (Steps # 6  to # 11 ), whereas in the case where the difference exceeds the threshold value H, an alarm is generated from the alarm unit  27  in Step # 13 . 
     It should be noted that it is not necessary to perform the inspection (Steps # 6 ,  10 ,  11  and  12 ) for each and every bonding operation, but it suffices if it is carried out once in several times at random. 
     With the structure described above, the relative position of the bump electrode  15  and the relative position of the reference pattern  28  are obtained by taking the corner edge c of the semiconductor chip  13  as a reference. Therefore, it is possible to obtain the relative positions of the reference pattern  28  and the bump electrode  15  after the bonding. Thus, even after the bonding, the bonding accuracy can be evaluated without removing or cutting the semiconductor chip  13  from the substrate  11 . 
     In particular, since the corner edge c, which is located at the same position if viewed from above and below, is employed as the reference position used for obtaining the relative position, the reliability of the alignment is high. Alternatively, it is possible to use a mark provided at the same position if viewed from above and below. Further, even with marks which are located at different positions between the upper and lower surfaces, they can be used as the reference positions as long as the relationship between the relative positions of the upper and lower surfaces is maintained at high accuracy. 
     Lastly, the present invention is not limited to the above-described embodiment, but can be remodeled into a version which will be described. 
     For example, as shown in FIG. 9, it is possible that a beam splitter  30  is provided between the substrate  11  and the semiconductor chip  13 , and a recognition camera  31  is provided in its branching-off direction, so as to pick up the image of the semiconductor chip  13  by one camera, which is the recognition camera  31 . 
     Further, reference patterns  28  on the substrate  11  may be formed at positions symmetrical with respect to the semiconductor chip  13 , for example, as shown in FIG. 8, and it is possible to use one or both reference patterns  28  for carrying out the inspection. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.