Abstract:
The disclosure is directed to a laser processing apparatus employing a polygon mirror, capable of processing an object efficiently. The apparatus is comprised of a laser generator for emitting a laser beam, a polygon mirror rotating at the axis and having a plurality of reflection planes which reflect the laser beam incident thereon from the laser generator, and a lens irradiating the laser beam on an object, e.g., a wafer, that is settled on a stage, after condensing the laser beam reflected from the polygon mirror. In applying the laser beam to the wafer in accordance with a rotation of the polygon mirror, the stage on which the wafer is settled moves to enhance a relative scanning speed of the laser beam, which enables an efficient cutout operation for the wafer. As it uses only the laser beam to cutout the wafer, there is no need to change any additional devices, which improves a processing speed and cutout efficiency. Further, it is available to control a cutout width and to prevent a recasting effect by which vapors generated from the wafer during the cutout process are deposited on cutout section of the wafer, resulting in accomplishing a wafer cutout process in highly fine and precise dimensions.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to a laser processing apparatus with a polygon mirror capable of processing an object by reflecting a laser beam on the polygon mirror.  
       BACKGROUND ART  
       [0002]     Since apparatuses using a laser beam have more advantage for cutting silicon wafers than other mechanical apparatuses, various studies about them have been advanced. One of the most advanced apparatus for cutting a wafer is an apparatus using a laser beam guided by ejected water from a high-pressure water jet nozzle.  
         [0003]     A wafer cutout apparatus employing the high-pressure water jet nozzle irradiates a laser beam on a wafer with ejecting water through a high-pressure jet nozzle. As the water jet nozzle is easily worn away due to the high pressure, the nozzle has to be changed periodically.  
         [0004]     The periodic change of the high-pressure jet nozzle causes inconveniences in conducting the wafer cutout process. It also results in lower productivity and higher manufacturing cost.  
         [0005]     Also, since it is difficult for a conventional wafer cutout apparatus to offer fine line width, there are problems in adopting the apparatus to high-precision process.  
         [0006]     Meanwhile a wafer cutout process using only a laser beam brings about a recasting effect which means vapors evaporated by a laser beam are deposited on cutout sides of wafer. It interrupts a wafer cutout process.  
       DISCLOSURE OF INVENTION  
       [0007]     To solve the aforementioned problems, an object of the present invention is to provide a laser processing apparatus with a polygon mirror, capable of processing an object such as a wafer precisely by preventing a recasting effect without changing any additional devices.  
         [0008]     In the embodiment of the invention, a laser processing apparatus with a polygon mirror is comprised of: a laser generator for emitting a laser beam; a polygon mirror constructed of a plurality of reflection planes that reflect the laser beam which is emitted from the laser generator, thereon while rotating on an axis; and a lens for condensing the laser beam which is reflected on the polygon mirror and irradiating the laser beam on the object. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIGS. 1A through 1C  are schematic diagrams illustrating conceptual features of a laser processing apparatus employing a polygon mirror in accordance with the present invention.  
         [0010]      FIG. 2  is a schematic diagram illustrating a conceptual feature of the laser processing apparatus employing the polygon mirror in accordance with the present invention.  
         [0011]      FIG. 3  is a diagram illustrating overlapping laser beams in accordance with the present invention.  
         [0012]      FIG. 4  is a diagram illustrating an exemplary embodiment of the laser processing apparatus with the polygon mirror in accordance with the present invention.  
         [0013]      FIG. 5  is a diagram illustrating another embodiment of the laser processing apparatus with the polygon mirror in accordance with the present invention.  
         [0014]      FIG. 6  is a flow chart explaining a procedure of processing an object in accordance with the present invention.  
         [0015]      FIG. 7  is a schematic diagram illustrating a configuration of wafer processing by the laser processing apparatus with the polygon mirror in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIGS. 1A through 1C  are schematic diagrams illustrating a conceptual feature of a laser processing apparatus employing a polygon mirror in accordance with the present invention.  
         [0017]     As shown in  FIGS. 1A through 1C , the laser processing apparatus is comprised of a polygon mirror  10  having a plurality of reflection planes and rotating at an axis  11 , and a telecentric f-theta lens  20  condensing laser beams reflected from the reflection planes thereon. The lens  20  is installed in parallel with a stage  30  on which a wafer  40  to be cut out is settled, in order to condense laser beams reflected from the reflection planes thereon. Thus, a laser beam condensed on the lens  20  is irradiated to the wafer in perpendicular, which enables the wafer  40  (e.g., a semiconductor wafer) to be processed (able to be cut out) in a predetermined shape.  
         [0018]     While the lens  20  may be composed of a couple groups of lenses, this embodiment uses a single lens in convenience on description.  
         [0019]      FIGS. 1A through 1C  illustrate the features that a laser beam reflected from the reflection plane  12  is applied to the wafer  40  being condensed through the lens  20  while the polygon mirror  10  is rotating in an anti-clockwise direction at the axis  11 .  
         [0020]     Referring to  FIG. 1A , laser beams are reflected from the beginning part of the reflection plane  12  in accordance with the rotation of the polygon mirror  10 , and then incident on a left end of the lens  20 . The reflected laser beams are condensed on the lens  20  and irradiated to a predetermined position S 1  of the wafer  40  in perpendicular.  
         [0021]     Referring to  FIG. 1B , when the polygon mirror  10  more advances its rotation to reflect the laser beams on a central part of the reflection plane  12 , the reflected laser beams are incident on a central position of the lens  20  and condensed on the lens  20 . The condensed laser beam on the lens  20  is irradiated on a predetermined position S 2  of the wafer  40  in perpendicular.  
         [0022]     Referring to  FIG. 1C , when the polygon mirror  10  further advances its rotation, more than the case of  FIG. 1B , to reflect the laser beams on a rear part of the reflection plane  12 , the reflected laser beams on the rear part are incident on a right end of the lens  20  and condensed on the lens  20 . The condensed laser beam on the lens  20  is irradiated on a predetermined position S 3  of the wafer  40  in perpendicular.  
         [0023]     As aforementioned throughout  FIGS. 1A  to  1 C, the laser beams are applied to the predetermined positions S 1  to S 3  on the wafer  40  in accordance with the anti-clockwise rotation of the polygon mirror  10 . The distance from S 1  to S 3  is regarded to as a scanning length S L  that means an interval to irradiate the wafer  40  by the reflection plane  12  along the rotation of the polygon mirror  10 . A reflection angle of the laser beam, which is formed by the beginning and rear parts of the reflection plane  12  is referred to as a scanning angle θ.  
         [0024]     Hereinafter, the theoretical feature of the present invention will be described in more detail.  
         [0025]      FIG. 2  illustrates a schematic configuration of the laser processing apparatus employing the polygon mirror in accordance with the present invention.  
         [0026]     Referring to  FIG. 2 , the polygon mirror  10  constructed with n-numbered reflection planes rotates in a constant speed at the axis  11  in an angular velocity of ω and a cycle period T. A laser beam incident thereon is reflected from the reflection plane  12  and irradiated on the wafer  40  through the lens  20 .  
         [0027]     In the polygon mirror  10  having the n-numbered reflection planes  12 , the scanning angle θ of the laser beam when one of the reflection planes  12  is rotating is summarized as the following Equation 1.  
                   θ   =     2   ⁢     (       α   2     -     α   1       )                     α   1     =     ϕ   +   ψ   -     π   2                     α   2     =     ϕ   +   ψ   -     π   2     +       2   ⁢           ⁢   π     n                     ∴           ⁢   θ     =       4   ⁢           ⁢   π     n                   [     Equation   ⁢           ⁢   1     ]             
 
         [0028]     From the Equation 1, it can be seen that the scanning angle θ is twice the central angle  
       (       2   ⁢   π     n     )       
 
 on the reflection plane  12  of the polygon mirror  10 . Therefore, the scanning length S L , that is a range of irradiation on the wafer  40  by the reflected laser beam applied from the reflection plane  12  of the polygon mirror  10 , is determined by a morphological characteristic of the lens  20 , as follows.  
                     S   L     =       f   ×   θ     =       4   ⁢           ⁢   π   ⁢           ⁢   f     n                     S   L     ⁢     :     ⁢           ⁢   Scanning   ⁢           ⁢   length               f   ⁢     :     ⁢           ⁢   Focal   ⁢           ⁢   distance                 θ   ⁢     :     ⁢           ⁢   Scanning   ⁢           ⁢   angle     ⁢                         [     Equation   ⁢           ⁢   2     ]             
 
         [0029]     According to Equation 2, a laser beam reflected from each of the reflection planes  12  of the polygon mirror  10  while the polygon mirror  10  is rotating is irradiated on the wafer  40  by the length of S L . In other words, the scanning length S L  of a laser beam irradiated on the wafer  40  in accordance with the rotation of the polygon mirror  10  is obtained from a product of the focal length ƒ and the scanning angle θ of the laser beam reflected from the reflection plane  12  of the polygon mirror  12 .  
         [0030]     By the way, as the polygon mirror  10  has the n-numbered reflection planes  12 , an n-times scanning with the scanning length S L  is available in every one cycle of rotation of the polygon mirror  10 . That is, a laser beam irradiated on the wafer  40  is applied to the wafer  40  by the scanning length S L , overlapping in the wafer  40  by the number of the reflection planes  12  of the polygon mirror  10  when the polygon mirror  10  rotates one time. A scanning frequency during a unit time interval (e.g., one second) may be obtained from the following Equation 3.  
               ⁢                   Scanning   ⁢           ⁢   frequency     =         ω   ⁢           ⁢   n       2   ⁢           ⁢   π       =     n   T                   ω   ⁢     :     ⁢           ⁢   Angular   ⁢           ⁢   velocity   ⁢           ⁢   of   ⁢           ⁢   the   ⁢           ⁢   polygon   ⁢           ⁢   mirror               T   ⁢     :     ⁢           ⁢   Cycle   ⁢           ⁢   period   ⁢           ⁢   of   ⁢           ⁢   the   ⁢           ⁢   polygon   ⁢           ⁢   mirror                 [     Equation   ⁢           ⁢   3     ]               
 
         [0031]     From Equation 3, in the condition with the n-numbered reflection planes  12  on the polygon mirror  10 , it is possible to adjust the scanning frequency by controlling the cycle period or the angular velocity of the polygon mirror  10 . In other words, the scanning length S L  is controllable in desired times of overlapping by varying the cycle period T or the angular velocity ω of the polygon mirror  10 .  
         [0032]     If the angular velocity ω of the polygon mirror  10  is constant, a relative wafer  40  scanning speed of the laser beam reflected from the polygon mirror  10  is enhanced by transferring the stage  30 , on which the wafer  40  is settled, toward the direction reverse to the rotating direction of the polygon mirror  10 . In other words, when the stage  30  is transferred to the direction reverse to the rotating direction of the polygon mirror  10 , a wafer  40  scanning speed of the laser beam S L  gets faster compared to the wafer  40  scanning speed of the laser beam when the stage  30  is standing without moving.  
         [0033]     Such overlaps with the scanning length S L , as illustrated in  FIG. 3 , progress along the direction reverse to the transfer direction of the stage  30  where the wafer  40  is settled. As a result, the wafer  40  on the stage  30  is scanned and cut out by the laser beam along the direction reverse to the transfer direction of the stage  30 . During this, the scanning lengths S L  continuously overlap from each other in a uniform range, in which the number of overlapping times may be adjustable by controlling the transfer speed of the stage  30 .  
         [0034]     Provided that a migration distance by the scanning length S L  is l along the transfer of the stage  30 , an overlapping degree N of the scanning length may be represented in S L /l.  
         [0035]     The migration distance l denotes a dimension by which the stage  30  with velocity v moves for a time until one of the reflection planes  12  completes to rotate, being summarized in the following Equation 4. The overlapping degree N is represented in Equation 5.  
             l   =       v     n   T       =         v   ⁢           ⁢   T     n     =       2   ⁢           ⁢   π   ⁢           ⁢   v       n   ⁢           ⁢   ω                   [     Equation   ⁢           ⁢   4     ]                 Overlapping   ⁢           ⁢   degree   ⁢           ⁢     (   N   )       =         S   L     l     =         4   ⁢           ⁢   π   ⁢           ⁢   f       v   ⁢           ⁢   T       =       2   ⁢           ⁢   ω   ⁢           ⁢   f     v                 [     Equation   ⁢           ⁢   5     ]             
 
         [0036]     By summarizing the aforementioned description, the angular velocity ω of the polygon mirror  10  with the overlapping degree N while the wafer  40  is cutting out in the velocity v results in Equation 6 as follows.  
             ω   =       N   ⁢           ⁢   v       2   ⁢           ⁢   f               [     Equation   ⁢           ⁢   6     ]             
 
         [0037]     As represented in Equation 6, the angular velocity is obtained by dividing a product of the overlapping degree N of the laser beam and the cutout velocity v with a double value of the focal length ƒ of the lens  20 , where the cutout velocity v corresponds to the transfer speed of the stage  30  settling the wafer  40  thereon.  
         [0038]     While this embodiment uses a polygon mirror shaped with eight reflection planes (i.e., n=8) in eight corners, other polygonal patterns may be available in modification under the scope of the present invention.  
         [0039]      FIG. 4  illustrates an exemplary embodiment of the laser processing apparatus with the polygon mirror in accordance with the present invention.  
         [0040]     Referring to  FIG. 4 , the laser processing apparatus with the polygon mirror according to the present invention is comprised of a controller  110  for conducting an overall operation, an input unit  120  for entering control parameters and control commands, a polygon mirror driver  130  for actuating the polygon mirror  10 , a laser generator  140  for emitting laser beams, a stage transfer unit  150  for transferring the stage  30 , on which the wafer  40  is settled, in a predetermined direction, a display unit  160  for informing the external users of current operating states, and a storage unit  170  for storing data relevant thereto.  
         [0041]     The polygon mirror driver  130  includes a plurality of the reflection plane  12 , being configured to make the polygon mirror  10 , which has multiple planes, rotate in a predetermined velocity at the axis  11 . The polygon mirror  10  uniformly rotates at the axis  11  in the predetermined velocity by means of a motor (not shown) under control of the controller  110 .  
         [0042]     The laser generator  140  is configured to emit the laser beams to process the wafer  40  as an object settled on the stage  30 , generating ultraviolet-ray laser beams under control of the controller  110  in this embodiment.  
         [0043]     The stage transfer unit  150  is configured to transfer the stage  30 , on which the wafer  40  as an object to be treated is settled, in a predetermined velocity.  
         [0044]     In the structure of the laser processing apparatus, laser beams emitted from the laser generator  140  are incident on the polygon mirror  10  under control of the controller  110 . The laser beams applied to the polygon mirror  10  are reflected toward the lens  20  from the reflection planes  12 , which are rotating by the polygon mirror driver  130 , within the range of the scanning angle θ. The laser beams reflected from the reflection planes  12  are condensed on the lens  20 , and the condensed laser beam is irradiated on the wafer  40  in perpendicular.  
         [0045]     The laser beam being irradiated on the wafer  40  while one of the reflection planes  12  of the polygon mirror  10  is rotating migrates by the scanning length S L  along the direction reverse to the transfer direction of the stage  30 .  
         [0046]      FIG. 5  illustrates another embodiment of the laser processing apparatus with the polygon mirror in accordance with the present invention.  
         [0047]     Referring to  FIG. 5 , the laser processing apparatus with the polygon mirror, in accordance with another embodiment of the present invention, is basically comprised of a controller  110  for conducting an overall operation, an input unit  120  for entering control parameters and control commands, a polygon mirror driver  130  for actuating the polygon mirror  10 , a laser generator  140  for emitting laser beams, a stage transfer unit  150  for transferring the stage  30 , on which the wafer  40  is settled, in a predetermined direction, a display unit  160  for informing the external users of current operating states, and a storage unit  170  for storing data relevant thereto.  
         [0048]     These structures of  FIG. 5  are as same as those of  FIG. 4 . But, the laser processing apparatus with the polygon mirror in  FIG. 5  is further comprised of a beam expander  210  for enlarging diameters of pointing laser beams emitted from the laser generator  140  and then applying the enlarged laser beams to the polygon mirror  10 , and a beam transformer  220  for converting the laser beam, which is condensed on the lens  20  after being reflected from the polygon mirror  10 , into an elliptical pattern. At this time the beam transformer  220  may be easily implemented by employing a cylindrical lens.  
         [0049]     The enlarged laser beams incident on the polygon mirror  10  are reflected toward the lens  20  on the reflection planes  12  of the polygon mirror  10  within the range of the scanning angle θ. The laser beam reflected from the reflection planes  12  is condensed on the lens  20 , converted into an elliptical pattern by the beam transformer  220  in sectional view, and then irradiated on the wafer  40  in perpendicular.  
         [0050]     As the irradiated laser beam has elliptical sectional pattern, a long diameter of the elliptical section corresponds to a direction of cutout processing while a short diameter of the elliptical section corresponds to a width of cutout processing.  
         [0051]     When one of the reflection planes  12  is rotating on the axis  11 , the laser beam irradiated on the wafer  40  is shifted as the scanning length S L  along the direction reverse to the transfer direction of the stage  30 .  
         [0052]     Hereinafter, it will be described in detail about a procedure of processing an object (i.e., the wafer  40 ) by means of the laser processing apparatus with the polygon mirror shown in  FIG. 5 .  
         [0053]      FIG. 6  is a flow chart explaining a procedure of processing an object, in accordance with the present invention.  
         [0054]     Referring to  FIG. 6 , in order to process the wafer, i.e., to cut the wafer  40  out, first control parameters for a rotation velocity of the polygon mirror  10  and a transfer velocity of the stage  30  in the input unit  120  are established, in accordance with a type of the wafer  40  to be processed (step S 10 ). Such setting operations may be simply carried out by retrieving information menus from the storage unit  170  after registering the information, that has been preliminarily designed for wafer types and processing options (e.g., cutting, grooving, and so on), in the storage unit  170 .  
         [0055]     After completing the establishment for the control parameters, the controller  110  enables the polygon mirror driver  130  to rotate the polygon mirror  10  in a rotation velocity that has been predetermined at the step S 10  (step S 20 ), and also enables the stage transfer unit  150  to transfer the stage  30  in a predetermined velocity (step S 30 ). At this point the controller  110  makes the laser generator  140  emit the laser beam (step S 40 ).  
         [0056]     Then, the laser beam emitted from the laser generator  140  is incident on the polygon mirror  10  with being enlarged in its sectional diameter after passing through the beam expander  210 . The laser beam incident on the polygon mirror  10  is reflected from the reflection plane  12  of the polygon mirror  10  rotating at the axis  11 , toward the lens  20  within the range of the scanning angle θ.  
         [0057]     The lens  20  condenses the laser beam reflected from the polygon mirror  10 , and the condensed laser beam on the lens  20  is irradiated on the wafer  40  in perpendicular after being converted into an elliptical pattern in sectional view by the beam transformer  220 . The laser beam finally applied to the wafer  40  has a elliptical sectional pattern in which the long diameter accords to the cutout direction of the wafer  40 , i.e., a progressing direction of processing, which extends an irradiation range of the laser beam over the wafer  40  a time, while the short diameter corresponds to a cutout thickness, i.e., a cutout width of processing.  
         [0058]     During the procedure, as the polygon mirror  10  rotates with a constant speed, a plurality of the laser beam irradiated on the wafer  40  are overlapped in predetermined times by a plurality of the scanning length S L  over the wafer  40 .  
         [0059]     In addition, as the stage  30  settling the wafer  40  thereon is transferred in the direction reverse to the rotation direction of the polygon mirror  10 , a relative speed of irradiation with the scanning length by the laser beam on the wafer  40  becomes faster which makes the wafer cutout process efficient (step S 50 ).  
         [0060]     On the other hand, the laser beam emitted from the laser generator  140  is directly irradiated on the wafer  40  when it skips the steps of the beam expander  210  and the beam transformer  220 .  
         [0061]      FIG. 7  illustrates a configuration of processing the wafer  40  by the laser processing apparatus with the polygon mirror in accordance with the present invention.  
         [0062]     As aforementioned, the laser beam enlarged with its sectional diameter after passing through the beam expander  210  is incident on the polygon mirror  10 . The laser beam incident on the polygon mirror  10  is reflected within the range of the scanning angle θ toward the lens  20  on the reflection plane  12  of the polygon mirror  10  that is rotating. The lens  20  condenses the laser beam. The laser beam condensed on the lens  20  is shaped into a sectional elliptical pattern by the beam transformer  220  and then irradiated on the wafer  40 .  
         [0063]     During this, as the laser beam irradiated on the wafer  40  has the sectional elliptical pattern, the long diameter of the ellipse is associated with a progressing direction on the wafer  40  by the laser beam while the short diameter of the ellipse is associated with a cutout width on the wafer  40  by the laser beam.  
         [0064]     As illustrated in  FIG. 7 , the elliptical laser beam irradiated on the wafer  40  is progressing along the direction of its long diameter, accompanying with the cutout width by its short diameter. In other words, the cutout width  41  of the wafer  40  is adjustable by controlling the short diameter of the elliptical section of the laser beam, which is established by the beam transformer  220 .  
         [0065]     During the irradiation on the wafer  40  by the laser beam, evaporation may be occurred at places on which the laser beam is irradiated. However, the progressing direction of the laser beam is reverse to the transfer direction of the wafer  40 , as aforementioned, so that the relative scanning speed of the laser beam becomes faster and the long diameter of the laser beam is arranged to the processing direction (i.e., the cutout direction). As a result, a cutout section  42  has a slope throughout the cutout process, by which vapors escaping from the wafer material due to the irradiation of the laser beam are easily discharged without depositing on the cutout plane  42  during the process.  
         [0066]     Moreover, since the rapid overlapping with the laser beam along the processing direction makes the cutout portion of the wafer  40  be swiftly evaporated, the wafer processing is carried out easily without such as a recasting effect for which vapors from the wafer material are deposited on the cutout wall  43  of the wafer  40 .  
         [0067]     Although the aforementioned, embodiments is exemplarily describes as being applicable to processing a semiconductor wafer, the present invention is also available to processing other substrates or boards such as plastics, metals, and so on.  
         [0068]     As described above, the laser processing apparatus with the polygon mirror in accordance with the present invention needs not any change of additional devices because a laser beam is enough to perform the cutout process, which enables the process to be rapidly carried out in easy and efficiency. Furthermore, since the present invention provides an efficient technique to able to control the cutout width by adjusting the short diameter of the elliptical laser beam and to prevent a recasting effect that causes vapors escaping from an object to be cut out, it is advantageous to processing a wafer in highly precise operations, as well as normal objects.  
         [0069]     Although the present invention has been described in connection with the embodiment of the present invention illustrated in the accompanying drawings, it is not limited thereto. It will be apparent to those skilled in the art that various substitution, modifications and changes may be thereto without departing from the scope and spirit of the invention.