Abstract:
Methods of cutting a light-emitting device chip wafer by using a laser scribing process. The method includes: preparing a wafer that has a plurality of semiconductor chips on an upper surface of the wafer; attaching a first tape covering the semiconductor chips to the upper surface of the wafer; forming scribing lines to define each of the semiconductor chips on the wafer by irradiating a laser beam onto a lower surface of the wafer; attaching a second tape to the lower surface of the wafer; and breaking the wafer into a plurality of chips by applying a physical force to the wafer along the scribing lines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2011-0147417, filed on Dec. 30, 2011, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    The present disclosure relates to methods of cutting a light-emitting device chip wafer on which a plurality of light-emitting device chips are formed using laser scribing. 
         [0004]    2. Description of the Related Art 
         [0005]    Light-emitting device chips, e.g., light-emitting diodes (LEDs), are semiconductor devices that realize various light colors by configuring a light source through a PN junction of compound semiconductors. LEDs have a long lifespan, may be miniaturized and manufacture light, and may be driven at a low voltage due to high directionality. Also, LEDs are resilient to impact and vibration, do not require a preheating time and a complicated driving, and may be packaged in various types. Accordingly, LEDs may be applied for various purposes. 
         [0006]    When an LED is manufactured using a semiconductor manufacturing process, a plurality of light-emitting device chips are formed on a wafer to increase productivity. 
         [0007]    In order to separate the light-emitting device chips, the light-emitting device chips of the wafer are each cut. After the light-emitting device chips are separated by using a wafer cutting process, the characteristics of electrodes of each of the light-emitting device chips are inspected through contact with a multi-probe. 
         [0008]    In a related art, after attaching a protection tape on a side of the wafer, the wafer is cut by using a sawing blade, i.e., a rotating blade wheel, in a mechanical cutting process. However, the mechanical cutting process may contaminate the environment due to dust, generated during the mechanical cutting process. Also, a contact failure between electrodes and a multi-probe may occur due to a disorder of alignment of the separated light-emitting device chips on the protection tape. Thus, the contact failure may cause problems in the light-emitting device chips. 
       SUMMARY 
       [0009]    Disclosed are methods of cutting light-emitting device chip wafers to increase the productivity of a cutting process by separating the light-emitting device chips by using a laser scribing process and a breaking process. 
         [0010]    Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
         [0011]    According to an aspect of the exemplary embodiments, there is provided a method of cutting a wafer, the method including: preparing the wafer having a plurality of semiconductor chips on an upper surface of the wafer; attaching a first tape covering the semiconductor chips to the upper surface of the wafer; forming scribing lines to define each of the semiconductor chips on the wafer by irradiating a laser beam onto a lower surface of the wafer; attaching a second tape to the lower surface of the wafer; and breaking the wafer into a plurality of chips by applying a physical force to the wafer along the scribing lines. 
         [0012]    The semiconductor chips may be light-emitting device chips. 
         [0013]    The wafer may be a sapphire wafer through which the laser beam passes. 
         [0014]    The forming of the scribing lines may include irradiating the laser beam in a thickness direction, so that the laser beam is focused approximately in a middle position of the thickness of the wafer. 
         [0015]    The forming of the scribing lines may include forming the scribing lines in a lattice type, that is, in an X direction and a Y direction of the wafer, while moving an X-Y stage that supports the wafer in the X direction and the Y direction. 
         [0016]    The breaking of the wafer may include cutting the wafer by pressing the wafer along the scribing lines by using a break blade. 
         [0017]    According to a further aspect of the exemplary embodiments, there is provided a wafer, the wafer including a plurality of semiconductor chips on an upper surface of the wafer; a first tape, which covers the semiconductor chips and is attached to the upper surface of the wafer; and a second tape, which is attached to a lower surface of the wafer, wherein scribing lines are formed to define each of the semiconductor chips on the wafer. 
         [0018]    According to the exemplary embodiments, the failure rate of light-emitting device chips may be reduced by reducing particles generated from a cutting process. 
         [0019]    Also, because a tape that fixes the light-emitting device chips is attached onto both surfaces of a wafer, after cutting the wafer, the positions of the light-emitting device chips are fixed. Accordingly, characteristics of each of the light-emitting device chips may be inspected using a multi-probe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
           [0021]      FIG. 1  is a schematic cross-sectional view of an example of a light-emitting device chip according to an embodiment; 
           [0022]      FIGS. 2A-2D  are schematic cross-sectional views showing a method of cutting a wafer by using a laser scribing process, according to an embodiment; 
           [0023]      FIG. 3  is a perspective view of a wafer ring on which a wafer is mounted. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    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 the thicknesses or sizes of elements are exaggerated for convenience of explanation and clarity. It will be understood that when an element or layer is referred to as being “on” another element or layer, it can be directly or indirectly formed on the other element or layer. For example, intervening elements or layers may be present. 
         [0025]      FIG. 1  is a schematic cross-sectional view of an example of a light-emitting device chip according to an embodiment of the present invention. 
         [0026]    Referring to  FIG. 1 , a buffer layer  120  is formed on a substrate  110 . The substrate  110  may be a sapphire substrate  110 . The buffer layer  120  may be formed of In x Ga y Al z N, ZrB 2 , HfB 2 , ZrN, HfN, TiN, or AlN. An n-type nitride layer  130  is formed on the buffer layer  120 . The buffer layer  120  is formed to mitigate lattice misalignment between the n-type nitride layer  130  and the sapphire substrate  110 . The n-type nitride layer  130  may be formed of In x Ga y Al z N. The n-type nitride layer  130  may be formed as a single layer or a plurality of layers, compositions thereof vary. A portion of the n-type nitride layer  130  is exposed, and an n-type electrode pad  140  may be formed on the exposed portion of the n-type nitride layer  130 . A multiple quantum well active layer  150  and a p-type nitride layer  160  are sequentially formed on a portion of the first nitride layer  130 . A p-type electrode pad  170  is formed on the p-type nitride layer  160 . 
         [0027]    In  FIG. 1 , the light-emitting device chip  100  has a horizontal type electrode structure. However, the light-emitting device chip  100  according to the current embodiment is not limited. For example, the light-emitting device chip may have a vertical type electrode structure. 
         [0028]      FIGS. 2A through 2D  are schematic cross-sectional views showing a method of cutting a wafer by using a laser scribing process, according to an embodiment. 
         [0029]    Referring to  FIG. 2A , the wafer  210  has a plurality of semiconductor chips prepared on an upper surface  211 . The semiconductor chips may be light-emitting device chips  100 . The wafer  210  may be formed of sapphire, and the light-emitting device chips  100  may be GaN group light-emitting diodes formed on the wafer  210 . The light-emitting device chips  100  may be arranged in a matrix on the wafer  210 . For convenience, three light-emitting device chips  100  are depicted in  FIG. 2A . However, embodiments are not limited to three light-emitting device chips  100 . The light-emitting device chips  100  may also have various structures. As an example, the light-emitting device chips  100  may each include the horizontal light-emitting device chip  100  of  FIG. 1 . 
         [0030]    A first tape  220  may be attached above the upper surface  211  of the wafer  210  to cover the light-emitting device chips  100 . The first tape  220  fixes the wafer  210  in a laser scribing process and a cutting process. The first tape  220  is not specifically limited and may be any tape that provides adhesiveness. For example, the first tape  220  may be an ultraviolet tape (UV tape), or a thermosetting tape. The first tape  220  may be formed to have a thickness in a range from about 50 μm to about 200 μm. 
         [0031]    In  FIG. 2A , a gap between the light-emitting device chips  100  and the first tape  220  is shown to be very large. The first tape  220  is also shown to be separated from the upper surface  211  of the wafer  210 . However, in practice, the light-emitting device chips  100  formed on the wafer  210  may have a height of a few μm, and the first tape  220  may contact entire surfaces of the light-emitting device chips  100  and the upper surface  211  of the wafer  210 . 
         [0032]      FIG. 3  is a perspective view of a wafer ring  215  on which the wafer  210  is mounted. The first tape  220  may be attached, in advance to the wafer ring  215 , where the upper surface  211  of the wafer  210  is attached. Lines C define each of the light-emitting device chips  100  and may be lines to be scribed. 
         [0033]    Referring to  FIG. 2B , the wafer  210  is disposed on an X-Y stage ( 217  in  FIG. 3 ). When the wafer ring  215  is used, the wafer ring  215  is mounted on the X-Y stage  217 . A driving device ( 219  in  FIG. 3 ) moves the X-Y stage  217  in two axes directions (X-Y axis). A description of the X-Y stage  217  is omitted. 
         [0034]    A laser apparatus  310  that irradiates a laser beam L is disposed on the X-Y stage  217 . While moving the X-Y stage  217  in the X direction and the Y direction step-by-step, scribing lines S, that define each of the light-emitting device chips  100 , are formed on the wafer  210  by irradiating the laser beam L onto a lower surface  212  of the wafer  210 . The wafer  210  may be a sapphire substrate through which a laser beam L may pass. The scribing lines S formed on the wafer  210  are formed in a lattice type to define the light-emitting device chips  100  formed in a matrix. The scribing lines S and the lines C in  FIG. 3  may be at a same position. 
         [0035]    The laser apparatus  310  for example, may be a fiber laser with a power in a range from about 0.25 W to about 0.4 W. The moving speed of the X-Y  217  stage may be approximately 400 mm/s. Cracks may be formed along the scribing lines S of the wafer  210  by irradiating a laser beam L so that the laser beam L is focused in the middle of the thickness of the wafer  210 . 
         [0036]    Referring to  FIG. 2C , a second tape  230  is attached on the lower surface  212  of the wafer  210 . The second tape  230  may be any tape that provides adhesiveness. For example, the second tape  230  may be a UV tape or a thermosetting tape having a thickness in a range from about 50 μm to about 200 μm. 
         [0037]    The attachment of the second tape  230  may be performed when the wafer  210  is mounted on the wafer ring  215  in a state that the wafer ring  215  is mounted on the X-Y stage  217 . 
         [0038]    Referring to  FIG. 2D , a breaking process for cutting the wafer  210  is performed on the scribing lines S of the wafer  210 . After aligning the lower surface  212  of the wafer  210  so that the scribing lines S are disposed between a pair of breaking blocks  242 , the upper surface  211  of the wafer  210  is pressed with respect to the scribing lines S by using a break blade  240 , such that the wafer  210  is cut along the scribing lines S formed on the wafer  210 . At this point, the light-emitting device chips  100  formed on the wafer  210  are also separated. The pair of breaking blocks  242  may be longer than the diameter of the wafers  210 . 
         [0039]    When the scribing operations are repeated while moving the X-Y stage  217 , the wafer  210  is separated into each of the light-emitting device chips  100 . In this process, the first tape  220  and the second tape  230  are not cut in the breaking process. Accordingly, the separated light-emitting device chips  100  are fixed. In other words, the positions of each of the light-emitting device chips  100  are fixed. 
         [0040]    Next, after removing the first tape  220 , that covers the light-emitting device chips  100 , characteristics of each of the light-emitting device chips  100  may be inspected using a multi-probe. In this process, a contact error between the multi-prober and the electrode pads of the light-emitting device chips  100  is reduced. Thus, the productivity for manufacturing the light-emitting device chips  100  may be increased. 
         [0041]    When a laser scribing process is used, instead of a mechanical cutting process, the failure of light-emitting device chips due to particles generated from the mechanical cutting process may be reduced. Also, because a tape that fixes the light-emitting device chips is attached onto both surfaces of a wafer, after cutting the wafer, the positions of the light-emitting device chips are fixed. Accordingly, characteristics of each of the light-emitting device chips may be inspected, by using a multi-probe without a contact failure between the light-emitting device chips and the multi-probe. Thus, productivity of manufacturing the light-emitting device chips may be increased. 
         [0042]    It should be understood that the exemplary embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.