Abstract:
Disclosed is a method for marking, by using a laser marker, a plurality of wafer dice divided by a wafer dicing process. The disclosed marking method for wafer dice comprises the steps of: setting a plurality of scan regions having a mutually overlapping portion on a wafer including the wafer dice; scanning the scan regions of the wafer a plurality of times by using a line scan camera; collecting position information of each of wafer dice located in regions in which the scan regions do not overlap; collecting, through image synthesis, position information of each of wafer dice located in regions in which the scan regions overlap; and marking, by using the laser marker, each of all the wafer dice of which the position information has been collected.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a marking method of wafer dies, and more particularly, to a method of marking wafer dies with a laser in which wafer dies which are divided after a wafer dicing process are marked with a laser after the position information is confirmed by using a line scan camera. 
       BACKGROUND ART 
       [0002]    According to conventional technologies, the following method has been used as a laser marking method of wafer dies. First, the back surface of a wafer in which wafer dies are integrated is made to have a desired thickness through backgrinding, and then, two wafer dies are selected as first and second reference wafer dies among wafer dies on the front surface of the wafer. By using the thus-selected first and second reference wafer dies, positions of all the rest wafer dies are identified and then, by using thus-identified position information, each wafer die is marked with a laser. Then, by dicing the wafer, the marked wafer dies are divided. However in this method, in the wafer dicing process fragments or chippings may be generated from the back surface of the wafer or the wafer may be damaged. 
         [0003]    There is a dicing before grinding (DBG) process as a method to solve this problem. In the DBG process, a wafer in which wafer dies are integrated is half-cut before grinding, and then backgrinding is performed to divide wafer dies. Then, a marking process for the thus-divided wafer dies is performed with a laser. However, as the divided wafer dies are located askew from the original positions on the wafer, it is difficult to mark the wafer dies on an accurate position of each of the divided wafer dies with the conventional marking method using the two wafer dies, namely, the first and second reference wafer dies, for marking the rest wafer dies. 
         [0004]    Meanwhile, a method of identifying position information of wafer dies by using a vision camera has been used according to conventional technologies. However, in this method, the vision camera photographs each wafer die individually to measure the position, and therefore the vision camera should perform the measuring job the same number of times as the number of the wafer dies. For example, if 1000 wafer dies are on a wafer, the vision camera should be used 1000 times to identify the position information of all wafer dies. Accordingly, it takes a long time. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
       [0005]    Provided is a method in which the position information of wafer dies which are divided in a dicing process is accurately measured and laser marking is performed by using a line scan camera. 
       Advantageous Effects of the Invention 
       [0006]    According to embodiments of the present invention, the shape and position information of wafer dies which are divided in a dicing process and arranged irregularly can be quickly collected by using a line scan camera. If a laser marking job is performed based on the thus-collected shape and position information of the wafer dies, marking can be accurately performed on a required location of each of the divided wafer dies. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  shows wafer dies arranged irregularly after a wafer is divided in a dicing process. 
           [0008]      FIG. 2  is a flowchart of a marking method of wafer dies according to an embodiment of the present invention. 
           [0009]      FIG. 3  illustrates a method of making the coordinate system of a line scan camera coincide with the coordinate system of a laser marker. 
           [0010]      FIGS. 4A through 4C  show a line scan camera scanning multiple times wafer dies on a wafer according to an embodiment of the present invention. 
           [0011]      FIG. 5  illustrates a method of collecting shape and position information of wafer dies in a scan area in which scan areas do not overlap. 
           [0012]      FIGS. 6A through 6D  illustrate a method of collecting shape information of wafer dies in a scan area in which scan areas overlap. 
       
    
    
     BEST MODE 
       [0013]    Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the drawings, like reference numerals refer to like elements throughout, and sizes or thicknesses of elements may be exaggerated for clarity of explanation. 
         [0014]      FIG. 1  shows a state in which a wafer W is divided in a dicing process. 
         [0015]    Referring to  FIG. 1 , if the wafer W attached on a fixing tape  30  is divided though the dicing process, at least some of a plurality of divided wafer dies  50  are made askew such that the plurality of divided wafer dies are irregularly arranged on the fixing tape  30 . 
         [0016]    The wafer dies  50  arranged irregularly as shown in  FIG. 1  are generated through a following process. First, the wafer W on which the wafer dies  50  are integrated before the dividing is half cut, and then, a surface protection film (not shown) is coated on the wafer W to cover the wafer dies  50 . Then, backgrinding of the back surface of the wafer W is performed up to a cutting point such that the wafer W is divided into a plurality of wafer dies  50 . Here, the divided wafer dies  50  are irregularly arranged on the surface protection film as the positions of the divided wafer dies  50  are changed by the dicing process. 
         [0017]    Next, the fixing tape  30  for fixing the divided wafer dies  50  is attached on the back surface of the wafer  3 , and then the surface protection film is removed. Thus, when the wafer W is cut before a marking process is performed, the divided wafer dies are irregularly arranged. Accordingly, in order to perform laser marking accurately on a required location of each of the divided wafer dies  50 , the position information of the divided wafer dies  50  should be accurately collected in order to perform marking. 
         [0018]      FIG. 2  is a flowchart of a marking method of divided wafer dies according to an embodiment of the present invention. 
         [0019]    Referring to  FIG. 2 , firstly, a line scan camera  220  of  FIG. 3  and a laser marker  230  of  FIG. 3  are prepared, and then, the coordinate system in the line scan camera  220  and the coordinate system in the laser marker  230  are set to coincide with each other in operation  101 . As will be described below, the line scan camera  220  collects position information of each of the divided wafer dies  50 , and the thus-collected position information is input into the laser marker  230  to perform a marking process. As a prerequisite for this, it is necessary to make the coordinate system of the line scan camera  220  coincide with the coordinate system of the laser marker  230 . 
         [0020]      FIG. 3  illustrates a method of making the coordinate system of a line scan camera  220  coincide with the coordinate system of a laser marker  230 . Referring to  FIG. 3 , a transparent plate  210  with a shape corresponding to the wafer W is prepared and then, the line scan camera  220  is positioned above the transparent plate  210  and the laser marker  230  is positioned below the transparent plate  220 . Next, if the laser marker emits a beam on a predetermined position (for example, P 1 ) on the transparent plate, the line scan camera  220  recognizes the position P 1  on which the beam is emitted. In this process, the coordinate systems of the line scanner  220  and the laser marker  230  are made to coincide with each other. 
         [0021]    After the coordinate systems of the line scanner  220  and the laser marker  230  are made to coincide with each other, the shape and position information of each of the divided wafer dies  50  is obtained by using the line scan camera  220  in operation  102 . Here, the shape and position information of all the wafer dies irregularly arranged can be collected by the line scan camera  220  performing the scan process multiple times as will be described below. 
         [0022]    Then, the position information of the wafer dies  50  obtained through the line scan camera  220  is input to the laser marker  230  provided below the wafer W. According to the thus-input position information, the laser marker  230  performs a laser marking job on each of the divided wafer dies  230 . Here, according to the position information of the wafer dies  50  obtained through the line scan camera  220 , the laser marker  230  can accurately perform marking on a desired location of each of the wafer dies  50 . 
         [0023]    A process of obtaining shape and position information of each of the wafer dies  50  by using the line scan camera  220  will now be explained in detail. 
         [0024]      FIGS. 4A through 4C  show a process of a line scan camera scanning multiple times on a wafer W including wafer dies divided and arranged irregularly.  FIGS. 4A through 4C  illustrates the line scan camera  220  scanning three times as an example. For example, when the diameter of the wafer W is 300 mm, if a line scan camera  200  with a 120 mm scan field is used, the whole wafer can be scanned by performing the scan process approximately 3 times. 
         [0025]    First, a plurality of scan areas, that is, first, second and third scan areas S 1  through S 3 , are set on the wafer W including the wafer dies which are divided and arranged irregularly. Here, parts of the first through third scan areas S 1  through S 3  may overlap each other. Referring to  FIG. 4A , as the line scan camera  220  moves in a predetermined direction, the first scan area S 1  is scanned. The first scan area S 1  may include a first part of the wafer W (for example, the top part of the wafer W). 
         [0026]    Then, referring to  FIG. 4B , a second scan area S 2  is scanned with the line scan camera  220  moving in a predetermined direction. The second scan area S 2  may include a second part of the wafer W (for example, the middle part of the wafer W). Here, as a part of the second part of the wafer W overlaps the first part of the wafer W, a first overlapping area S 12  in which the first and second scan areas S 1  and S 2  overlap each other may be formed between the first and second scan areas S 1  and S 2 . 
         [0027]    Then, referring to  FIG. 4C , a third scan area S 3  is scanned by moving the line scan camera  220  in a predetermined direction. The third scan area S 3  may include a third part of the wafer W (for example, the bottom part of the wafer W). Here, as a part of the third part of the wafer W overlaps the second part of the wafer W, a second overlapping area S 23  in which the second and third scan areas S 2  and S 3  overlap each other may be formed between the second and third scan areas S 2  and S 3 . 
         [0028]    In the present embodiment, the line scan camera  220  performs the scan process on the wafer W multiple times and through this scan process, the shape and position information of the wafer dies arranged irregularly on the wafer W is obtained. Accordingly, the shape and position information of all wafer ties which are divided in the dicing process and arranged irregularly can be quickly collected using the line scan camera  220 . 
         [0029]    The process of obtaining shape and position information of all wafer dies according to the present embodiment includes, through the multiple scanning process describe above, a process of obtaining position information of the wafer dies  51  and  52  of  FIG. 5  which are in scan areas which do not overlap each other, in the first through scan areas S 1  through S 3 , and a process of obtaining the shape and position information of the wafer dies  61  of  FIG. 6A  which are in the first and second overlapping areas S 12  and S 23 . 
         [0030]    First,  FIG. 5  illustrates a method of collecting shape and position information of wafer dies  51  and  52  in a scan area which does not overlap other scan areas. In  FIG. 5 , the outlines of two wafer dies, first and second wafer dies  51  and  52 , which are arranged irregularly and reference points P 1  and P 2  are shown on an X-Y coordinate system. Referring to  FIG. 5 , as the line scan camera  220  moves and scans the wafer dies  50 , the shape of each of the wafer dies  50  is identified. In this process, the line scan camera  220  photographs each of the wafer dies  50  and then, through thus-captured images, the outline of each of the wafer dies  50  is expressed. Then, one of the vertices of each of the wafer dies  50  is selected as a reference point (for example, P 1  and P 2  of  FIG. 5 ). 
         [0031]    After the shape of each wafer die  50  is identified in this way, position information of each of the wafer dies  50  is collected in operation  103 . 
         [0032]    The position information of each of the divided wafer dies  50  can be collected by measuring the position of the reference point and tilt angle of each of the wafer dies  50 . 
         [0033]    In detail, the position information of a first wafer die  51  in  FIG. 5  may be the position of the reference point P 1  and tilt angle (θ 1 ) of the first wafer die  51 . 
         [0034]    The position of the reference point P 1  of the first wafer die  51  may be obtained by measuring the coordinate values (X 1 , Y 1 ) of the reference value P 1  in the X-Y coordinate system, and the tilt angle (θ 1 ) of the first wafer die  51  may be obtained from the external shape of the first wafer die  51  by measuring the angle of the first wafer die  51  leaning relative to the X-axis or Y-axis. 
         [0035]    The position of the reference point P 2  of the second wafer die  52  may be obtained by measuring the coordinate values (X 2 , Y 2 ) of the reference value P 2  in the X-Y coordinate system, and the tilt angle (θ 2 ) of the second wafer die  52  may be obtained from the external shape of the second wafer die  52  by measuring the angle of the second wafer die  52  leaning relative to the X-axis or Y-axis. If the line scan camera  220  thus scans the wafer dies  51  and  52  located in scan areas which do not overlap other scan areas, the position information of the wafer dies  51  and  52  (that is, the position of the reference point and tilt angle of each wafer die  51  and  52 ) can be obtained. 
         [0036]    Next,  FIGS. 6A through 6D  illustrate a method of collecting shape information of wafer dies  61  in an overlapping scan area S 12 . 
         [0037]      FIG. 6A  illustrates a wafer die  61  located in the first overlapping area S 12  in which the first and second scan areas S 1  and S 2  overlap each other. 
         [0038]    Referring to  FIG. 6A , if the line scan camera  220  scans the first scan area S 1 , an image of the shape of a part (for example, the middle part and top part) of the wafer die  61  may be obtained. If the line scan camera  220  scans the second scan area S 2 , an image of the shape of another part (for example, the middle part and bottom part) of the wafer die  61  may be obtained. Here, in the first overlapping area S 12  in which the first and second scan areas S 1  and S 2  overlap each other, images of the shape of a predetermined part (for example, the middle part) of the wafer die  61  may appear overlapping. The whole shape of the wafer die  61  located in this first overlapping area S 12  may be obtained by the following method. 
         [0039]    First, as shown in  FIG. 6A , a reference line L which is a reference for image synthesis is set in order to obtain the whole shape of the wafer die  61  located in the first overlapping area S 1 . Next, as shown in  FIG. 6B , a first image  61 A based on the reference line L is extracted from an image of the shape of the part of the wafer die  61  obtained in the scanning of the first scan area S 1 . Then, as shown in  FIG. 6C , a second image  61 B based on the reference line L is extracted from an image of the shape of the part of the wafer die  61  obtained in the scanning of the second scan area S 2 . Finally, as shown in  FIG. 6D , if the extracted first and second images  61 A and  61 B are synthesized, the whole shape of the wafer die  61  located in the first overlapping area S 12  can be identified. Here, the shape of the wafer dies may be identified by expressing the outline of each of the wafer dies  61  through the images obtained by synthesizing the first and second images  61 A and  61 B. 
         [0040]    After the shape of each of the wafer dies  61  located in the first overlapping area S 12  is identified through this process, the position information of the wafer die  61  may be obtained by measuring the position of the reference point and tilt angle of the wafer die  61  in the X-Y coordinate system. The method of identifying the position information of the wafer die  61  is explained above in detail with reference to  FIG. 5  and the explanation will be omitted here. Meanwhile, a case in which the scan process is performed three times is explained above, but the number of times of scanning may vary greatly according to the size of a wafer W or the scan field of the line scan camera  220 . 
         [0041]    As described above, the position information of the wafer dies  51  and  52  located in a non-overlapping area among the scan areas S 1  through S 3  may be obtained by the method shown in  FIG. 5 , and the shape and position information of the wafer dies  61  located in the overlapping areas S 12  and S 23  among the scan areas S 1  through S 3  may be obtained by using the method shown in  FIGS. 6A through 6D  and the method shown in  FIG. 5 . Accordingly, in the present embodiment, the shape and position information of all wafer dies divided on a wafer can be obtained through multiple scan processes using the line scan camera  220 . According to the thus-obtained position information of all wafer dies, the laser marker  230  of  FIG. 3  can perform accurate marking on a required location of each wafer die. 
         [0042]    While one or more embodiments of the present invention have been described with reference to the figures, they should be considered in a descriptive sense only, and it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein. 
       MODE OF THE INVENTION 
       [0043]    According to an aspect of the present invention, provided is a marking method of a plurality of wafer dies which are divided by a wafer dicing process, with a laser marker, the method including: setting a plurality of scan areas on the wafer including the wafer dies in which some of the scan areas overlap each other; performing a plurality of scan processes for scanning the scan areas on the wafer by using a line scan camera; collecting position information of each wafer die located on areas where the scan areas do not overlap; collecting through image synthesis position information of each wafer die located on areas where the scan areas overlap; and with the laser marker performing marking of each of the wafer dies whose position information is collected. 
         [0044]    The wafer dies may be arranged irregularly. 
         [0045]    The method may further include making the coordinate system of the line scan camera coincide with the coordinate system of the laser marker. 
         [0046]    The collecting of position information of each wafer die located on areas where the scan areas do not overlap may include: identifying the shape of each of the wafer dies; and collecting the position information of the wafer dies by using the identified shape information of the wafer dies. 
         [0047]    The identifying of the shape of each wafer die may be pedalled by photographing the wafer dies with the line scan camera and expressing through the photographed image the outline of each of the wafer dies. 
         [0048]    The collecting of the position information of each wafer die may be performed by measuring the position of a reference point and the tilt angle of each of the wafer dies. 
         [0049]    The collecting of position information of each wafer die located on areas where the scan areas overlap may include: identifying the shape of each of the wafer dies; and collecting the position information of the wafer dies by using the identified shape information of the wafer dies. 
         [0050]    The identifying of the shape of each of the wafer dies may include: extracting a first image from partial images of the wafer dies which are captured by scanning any one scan area of two scan areas which overlap each other partially; extracting a second image from partial images of the wafer dies which are captured by scanning the other scan area of the two scan areas which overlap each other partially; and identifying the shape of each of the wafer dies by synthesizing the first image and the second image. 
         [0051]    The shape of each wafer die may be identified by expressing the outline of each of the wafer dies with the images in which the first and second images are synthesized. 
         [0052]    The marking of each of the wafer dies may be performed by the laser marker performing marking of each of the wafer dies according to the position information of each of the wafer dies.