Abstract:
A semiconductor wafer regenerating system is capable of easily and efficiently removing fabricating patterns formed on a semiconductor wafer to enable reuse of the semiconductor wafer. The system, which removes patterns of the semiconductor wafer in a dry manner by using blasting grit, includes a mesh conveyor, a grit blaster, a swinging element, a collecting element, a separating element, and a dust collector. The mesh conveyor transports the semiconductor wafer so that the patterns face upward. The grit blaster is installed above the mesh conveyor and has at least one blasting nozzle for blasting grits toward the semiconductor wafer to remove the patterns from the semiconductor wafer. The swinging element swings the blasting nozzle in a plane perpendicular to a transporting path of the semiconductor wafer along the mesh conveyor. The collecting element underneath the mesh conveyor collects pulverulent bodies including grits, chips, and dusts falling from the mesh conveyor. The separating element is connected to the collecting element to separate the grits and chips from the dusts. The dust collector is connected to the separating element to collect the dusts separated by the separating element.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a semiconductor wafer regenerating system and method and, more specifically, to a system and method for removing patterns formed on a semiconductor wafer to enable the reuse of the semiconductor wafer. 
   2. Description of Related Arts 
   Semiconductor integrated circuit (IC) chips being present in everyday electrical and electronic devices are created through a multiple-step sequence of photographic and chemical processing steps, during which electronic circuits are gradually created on a wafer made of pure semiconductor material. Reviewing the semiconductor device fabrication in more detail, extremely pure semiconductor material (e.g., silicon) is grown into mono-crystalline cylindrical ingots, and the ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very flat surface. Once the wafers are prepared, transistors are formed on the silicon water using various processing steps, e.g., chemical vapor deposition, etching, photolithography, and diffusion and/or ion implantation. After the various semiconductor devices have been created, they are interconnected to form the desired electrical circuits by metal interconnecting wires. 
   Considering the highly serialized nature of wafer processing, between the various processing steps, wafer tests are performed to verify that the wafer is still good and haven&#39;t been damaged by previous processing steps. If the number of die (i.e., a potential chip portion) on a wafer that measure as fails exceed a predetermined threshold, the wafer is discarded rather than invest in further processing. On the other hand, after the metal interconnections are completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. The device test is carried out using tiny probes, which marks bad chips with a drop of dye. In case that the yield which represents the proportion of devices on the wafer found to perform properly is high enough, the wafer is broken into individual dice, each of which is bonded on a lead frame and packaged. If, however, the yield is below a predetermined threshold, the wafer is discarded. 
   The discarded wafers which failed to pass the wafer test or device test retains circuit patterns and cannot be used for another purpose, and thus are typically crushed into pieces and scrapped under the ground. Such disposal of discarded wafers results in waste of expensive resources, wafer, and may bring about environment contamination. Accordingly, a method for recycling the discarded wafers is strongly needed. 
   Some attempts have been made for recycling the discarded wafers. For example, U.S. Pat. No. 6,706,636 issued 16 Mar. 2004 to Renesas Technology Corp. and entitled METHOD OF REGENERATING SEMICONDUCTOR WAFER discloses a method of regenerating a semiconductor wafer using mixed acids. According to this method, a wafer is polished and then immersed in mixed acids. Afterwards, a surface treatment is performed on the wafer to planarize the surface of the wafer, and then a high temperature annealing process is performed to ultimately obtain a regenerate wafer. However, the disclosed method may be inefficient in that not so few process steps are involved in the regenerating process, which makes this method time-consuming. Further, simply polishing and immersing the wafer in mixed acids cannot guarantee the complete removal of ion-implanted region showing physical characteristics different from that of pure silicon and trenches deeply formed into the surface. Besides, the use of several kinds of acids increases the cost for regenerating the wafer. 
   U.S. Patent Application Publication No. US2005/0092349 published 5 May 2005 and entitled METHOD OF RECLAIMING SILICON WAFERS discloses a method of regenerating a semiconductor wafer through consecutive steps of etching, polishing, and heat-treatment. Among the various steps, this attempt is focused on the heat-treatment of the wafer for 20 minutes-5 hours. As a result, this method may be much more time-consuming and inefficient. 
   As mentioned above, the conventional methods show low productivity in regenerating semiconductor wafers and are costly due to the use of a large quantity of chemicals and abrasives. Thus, the prior art wafer regenerating techniques provide little benefit from the economic point of view. 
   SUMMARY OF THE INVENTION 
   To solve the problems above, one object of the present invention to provide a semiconductor wafer regenerating system capable of easily and efficiently removing fabricated patterns formed on a semiconductor wafer to enable the reuse of the semiconductor wafer. 
   Another object of the present invention to provide a method for easily and efficiently removing fabricated patterns formed on a semiconductor wafer to enable the reuse of the semiconductor wafer. 
   The semiconductor wafer regenerating system for achieving one of the above objects removes patterns of semiconductor wafer in a dry manner by blasting grits onto a surface of the semiconductor wafer. 
   The system includes a mesh conveyor, a grit blaster, swinging means, collecting means, separating means, and a dust collector. The mesh conveyor transports the semiconductor wafer in a condition that the patterns are faced in an upward direction. The grit blaster is installed above the mesh conveyor and has at least one blasting nozzle for blasting grits toward the surface of the semiconductor wafers to remove the patterns from the semiconductor wafer. The swinging means swings the blasting nozzle in a plane perpendicular to a transporting path of the semiconductor wafer along the mesh conveyor. The collecting means is provided underneath the mesh conveyor and collects pulverulent bodies including grits, chips, and dusts falling from the mesh conveyor. The separating means is connected to the collecting means to separate the grits and chips from the dusts. The dust collector is connected to the separating means to collect the dusts separated by the separating means. 
   Preferably, the grits blasted onto the surface of the semiconductor wafer is recycled after separated by the separating means, which makes the overall process cost-effective. 
   Preferably, the semiconductor wafer is automatically fed onto the mesh conveyor by a de-stacker. 
   According to the semiconductor wafer regenerating method for achieving another one of the above objects, the semiconductor wafer is first baked so that moisture and a protective film coated on the semiconductor wafer is removed. Subsequently, the semiconductor wafer is put on a mesh conveyor and transported in a condition that the patterns are faced in an upward direction. While the semiconductor wafer is being transported on the mesh conveyor, grits are blasted onto the surface of the semiconductor wafer to remove the patterns from the semiconductor wafer by use of a grit blaster having at least one blasting nozzle. At this moment, the blasting nozzle swings across the transporting path of the wafer in order to facilitate uniform blasting. Afterwards, pulverulent bodies including grits, chips, and dusts falling from the mesh conveyor are collected under the mesh conveyor. The grits and chips are separated from the dusts to be recirculated to the grit blaster. 
   According to the present invention, it is possible to remove the circuit patterns formed in the semiconductor wafer in a simple, rapid, and efficient manner, thus regenerating the semiconductor wafer. The semiconductor wafer regenerated by the present invention can be used in applications which requires less planarity and purity of the wafer than the integrated circuits: e.g., the fabrication of solar cells or the like. Since the patterns of the silicon wafer is removed in a dry method of using a grit blasting technique, the present invention makes it possible to easily treat pulverulent bodies (P) such as chips and dusts produced in the pattern removal process. This allows the grits and chips to be reused, which makes the pattern removal process cost-effective. In addition, the silicon wafer can be supplied to the grit blaster in an automated fashion, which helps to increase the yield rate to a great extent. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a front elevational view of a semiconductor wafer regenerating system according to a preferred embodiment of the present invention; 
       FIG. 2  is a side elevational view of the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 3  is a cross-sectional view depicting a mesh conveyor, a grit blaster, a cleaning nozzle and a pulverulent body collecting unit employed in the semiconductor wafer regenerating shown in  FIG. 1 ; 
       FIG. 4  is a perspective view showing a mesh conveyor, a grit blaster, a cleaning nozzle and a swing arrangement employed in the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 5  is a side elevational view illustrating a mesh conveyor, a grit blaster and a swing arrangement employed in the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 6  is a block diagram showing a grit blaster employed in the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 7  is a cross-sectional view illustrating a grit supply device and a cyclone separator employed in the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 8  is a cross-sectional view showing a dust collector employed in the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 9  is a block diagram showing a controller employed in the semiconductor wafer regenerating system shown in  FIG. 1 ; 
       FIG. 10  is a perspective view showing a destacker employed in a semiconductor wafer regenerating system of the present invention; 
       FIG. 11  is a front elevational view showing the destacker shown in  FIG. 10 ; 
       FIG. 12  is a side elevational view showing the destacker shown in  FIG. 10 ; 
       FIG. 13  is a top view showing the destacker shown in  FIG. 10 ; 
       FIG. 14  is a block diagram illustrating a controller for use in the destacker shown in  FIG. 10 ; 
       FIG. 15  is a cross-sectional view illustrating an embodiment of a baking device employed in the semiconductor wafer regenerating system of the present invention; and 
       FIG. 16  is a flowchart for explaining a silicon wafer regenerating method in accordance with the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 and 2 , a semiconductor wafer regenerating system (referred to as “wafer regenerating system” hereinbelow) according to a preferred embodiment of the present invention includes a frame  10  above which is provided a mesh conveyor  20  for transferring silicon wafer  1 . Also, above the frame  10  are provided a blasting booth  60  and a cleaning booth  65  enclosing upper side and the lateral side of mesh conveyor  20  in a line. Inside the blasting booth  60  is provided a grit blaster which blasts grits along with compressed air onto the silicon wafer to remove patterns formed on the silicon wafer. Meanwhile, inside the cleaning booth  65  is provided a cleaning nozzle which blows off impurities remaining on the wafer surface using compressed air. 
   On the other hand, underneath the mesh conveyor  20  is provided a collecting unit  90  which collects grits bypassing the wafer, grits bounced by the wafer after colliding against the wafer to remove the patterns, scraps of grits (G)enerated by the collision against the wafer, pieces of insulation material and/or metal interconnections separated from the wafer, and shattered powder of wafer and grits. In this specification including the claims, a term “grits (G)” is used to generally refer to originally replenished grits, the grits bypassing the wafer, grits bounced by the wafer after colliding against the wafer to remove the patterns, and scraps of grits (G)enerated by the collision against the wafer. A term “chips (C)” is used to generally refer to pieces of insulation material and/or metal interconnections separated from the wafer. A term “dusts (D)” is used to refer to shattered powder of wafer and grits. In addition, a term “pulverulent bodies (P)” is used to refer the aggregate of the grits (G), chips (C), and dusts (D). 
   A cyclone separator  100 , which is connected to the collecting unit  90 , receives the pulverulent bodies (P) from the collecting unit  90  to centrifugally separate the grits (G) and chips (C) from the dusts (D). A dust collector  110 , which is connected to the cyclone separator  100 , collects the dusts exhausted from the cyclone separator  100 . 
   Referring to  FIG. 3 , the mesh conveyor  20  is comprised of a driving pulley  21 , a driven pulley  22 , a mesh belt  23 , and a motor  24 . The driving pulley  21  and the driven pulley  22  are provided in a spaced-apart relationship along a moving direction of the silicon wafer  1 . The mesh belt  23  is wound around the driving pulley  21  and the driven pulley  22 . The silicon wafers  1  are consecutively placed on the mesh belt  23  in such a manner that the patterns formed on the silicon wafers  1  face an upward direction. The mesh belt  23  is preferably made of a stainless wire and has mesh apertures having a size of, e.g., about 10-20 mm 2 . The motor (denoted by a reference numeral  24  in  FIG. 5 ) is mounted on one side of the frame  10  and can generate a driving force which is transferred to the driving pulley  21  through a belt transmission mechanism (denoted by a reference numeral  25  in  FIG. 5 ). The motor may be comprised of a geared motor that has an ability to transmit the driving force to the driving pulley  21  at a reduced ratio. 
   The blasting booth  60  has a first tunnel  61  through which the mesh conveyor  20  moves. Attached to the front side of the blasting booth  60  is a door  62  that can be opened for maintenance of the grit blasting nozzles  31 . The door  62  has a window  63  through which an operator can look into the first tunnel  61 . Just like the blasting booth  60 , the cleaning booth  65  has a second tunnel  66  through which the mesh conveyor  20  passes. The first tunnel  61  of the blasting booth  60  is aligned with and joined to the second tunnel  66  of the cleaning booth  65 . Attached to the front side of the cleaning booth  65  is a door  67  that can be opened for maintenance of the cleaning nozzle  32 . The door  67  has a window  68  through which an operator can look into the second tunnel  66 . 
   The upstream end of the mesh conveyor  20  is exposed to the outside of the blasting booth  60  to allow the silicon wafer  1  to be loaded into the blasting booth  60 . Also, the downstream end of the mesh conveyor  20  is exposed to the outside of the cleaning booth  65  to allow the silicon wafer  1  to be unloaded from the cleaning booth  65 . While the cleaning booth  65  is provided separately from the blasting booth  60  in the present embodiment, the cleaning booth  65  may be removed from the system by disposing the cleaning nozzle  32  at the downstream region within the first tunnel  61  of the blasting booth  60  and providing a partition wall into the first tunnel  61  to isolate the grit blaster  30  and the cleaning nozzle  32 , alternatively. 
   The grit blaster  30  includes a plurality of grit blasting nozzles  31 , a compressed air supply unit  40  and a grit supply unit  50 . The grit blasting nozzles  31  are disposed along a longitudinal direction of the mesh conveyor  20  so that they can blast the compressed air and the grits toward the surface of the silicon wafers  1  placed on and moved by the mesh belt  23  of the mesh conveyor  20 . 
   Referring to  FIG. 6 , the compressed air supply unit  40  includes an air compressor  41 , a reservoir  42 , an air drier  43 , and a plurality of air pipelines  44 . The air compressor  41  is provided in proximity to one side of the frame  10  and remains connected to the reservoir  42  which in turn is in communication with the air drier  43 . The compressed air generated by the air compressor  41  is stored in the reservoir  42  from which air is supplied to the air drier  43 . The air drier  43  serves to eliminate impurities such as moisture, oil, dusts and the like contained in the compressed air and also plays a role of controlling the flow rate of the compressed air. The air drier  43  may be comprised of an air control unit capable of eliminating the impurities contained in the compressed air and controlling the flow rate of the compressed air. The air drier  43  is connected to the grit blasting nozzles  31  through the air pipelines  44  so that the compressed air supplied from the air drier  43  can be blasted toward the surface of the silicon wafers  1  from the grit blasting nozzles  31 . 
   The cleaning nozzle  32  is connected to the air drier  43  via one of the air pipelines  44 . Although the cleaning nozzle  32  is one in number in the illustrated embodiment, the number of the cleaning nozzle  32  may be increased as occasions demand. 
   Referring to  FIG. 7 , the grit supply unit  50  includes a tank  51  for storing a large quantity of grits and a plurality of grit pipelines  52  for interconnecting the grit blasting nozzles  31  and the tank  51  to provide passageways through which the grits stored in the tank  51  are supplied to the grit blasting nozzles  31 . Examples of the grits available for use include particles of aluminum oxide, silicon carbide and ceramics, glass beads, steel balls, and chip separated from silicon wafers. Among these, the particles of aluminum oxide, silicon carbide and ceramics may have a grain size of, e.g., 10-80 μm. 
   Referring to  FIGS. 4 and 5 , the silicon wafer regenerating system in accordance with the present invention further includes a swing arrangement  70  for swinging the grit blasting nozzles  31  into a direction perpendicular to the moving direction of the silicon wafers  1 . The swing arrangement  70  is comprised of a spindle  71 , a swing motor  72  and a linkage  80 . The spindle  71  extends in parallel with the moving direction of the silicon wafers  1 , the opposite ends of which are rotatably supported by a pair of bearings  73 . The bearings  73  are fixedly secured to the opposite sides of the blasting booth  60 . One end of the spindle  71  protrudes through the blasting booth  60 . A plurality of support bars  74  are attached to the spindle  71  in a spaced-apart relationship along the moving direction of the silicon wafers  1 . The grit blasting nozzles  31  are respectively affixed to the lower ends of the support bars  74 . The swing motor  72  is mounted on the outside of the blasting booth  60 . 
   The linkage  80  serves to convert and deliver the rotational force of the motor  72  to the spindle  71  in such a manner that the spindle  71  can be caused to swing. The linkage  80  is comprised of a disk  81 , a first link  83  and a second link  84 . The disk  81  is mounted to a shaft  72   a  of the motor  72  and has a guide groove  82  extending in a radial direction. The first link  83  is provided at one end with a screw  85  which in turn is slidably fitted into the guide groove  81 . One end of the second link  84  is joined to the other end of the first link  83  by a pivot pin  86  for rotation about the latter. The other end of the second link  84  is fixedly secured to an extremity of the spindle  71 . 
   The spindle  71  is caused to swing if the driving force of the motor  72  is transmitted to the spindle  71  through the disk  81 , the first link  83  and the second link  84 . As the spindle  72  is subjected to swinging movement, the grits blasted from the grit blasting nozzles  31  are initially hit on the center and then on the peripheral area of the silicon wafers  1 , thus assuring that the entire surface of the silicon wafer  1  is hit by the grits. Although the grit blasting nozzles  31  are arranged in two rows along the moving direction of the silicon wafers  1  in  FIGS. 4 and 5 , this is for the purpose of illustration and it would be possible to dispose the grit blasting nozzles  31  in a single row if desired. Furthermore, the grit blasting nozzles  31  may be mounted in such a fashion that they can make linear reciprocating movement in a direction across the moving direction of the silicon wafers  1 . In the meantime, if an operator loosens the screw  85  of the first link  83  and then displaces the same along the guide groove  82 , it becomes possible to place one end of the first link  83  at any position between the center and the peripheral edge of the disk  81 . The swinging angle of the spindle  71  becomes greater as one end of the first link  83  is placed farther away from the center, namely, closer to the peripheral edge, of the disk  81 . 
   Referring back to  FIG. 3 , the collecting unit  90  is comprised of a plurality of hoppers  91 , a first pulverulent body pipeline  92  and a second pulverulent body pipeline  93 . Each of the hoppers  91  has an inlet opening  91   a  lying adjacent to the underside of the mesh conveyor  20  and an outlet opening  91   b  connected to the first pulverulent body pipeline  92 . The first pulverulent body pipeline  92  is connected at its one end to the second pulverulent body pipeline  93  through which the pulverulent bodies (P) are discharged to the outside. Mounted on the top of the hoppers  91  is a first screen filter  94  that can filter out broken fragments of the silicon wafer  1 . A second screen filter  95  that can filter out the chips (C) greater in size than the grits (G) is provided at the upstream end portion of the second pulverulent body pipeline  93  in the vicinity of the first pulverulent body pipeline  92 . 
   Referring to  FIG. 7 , the cyclone separator  100  is provided with an upright housing  101  having a chamber  102 . The housing  101  has at its upper side wall an inlet opening  103  connected to the second pulverulent body pipeline  93  and at its bottom end an outlet opening  104  through which the chips (C) and the grits (G) are discharged. Connected to the top center of the housing  101  is an outlet pipe  105  through which the dusts (D) are exhausted from the chamber  102 . The outlet opening  104  of the housing  101  is connected to the tank  51  of the grit supply unit  50  through a grit return pipeline  53 . Although the housing  101  of the cyclone separator  100  and the tank  51  of the grit supply unit  50  are placed on the top of the blasting booth  60  in  FIGS. 1 and 2 , they may be detached from the blasting booth  60  and placed at other suitable positions, if desired. 
   Referring to  FIG. 8 , the dust collector  110  is provided with an upright housing  111  having a chamber  112 . The housing  111  has an inlet port  113  at its lower side wall portion and an outlet port  143  at its upper side wall portion. The inlet port  113  of the housing  111  is connected to the outlet pipe  105  of the cyclone separator  100  through a dust pipeline  115 . A partition  116  for dividing the chamber  112  into two compartments is provided at the upper portion of the chamber  112 . A plurality of apertures  116   a  that allow the air to pass are formed through the thickness of the partition  116 . A plurality of filters  118  for filtering the dusts are fitted to the apertures  116   a  of the partition  116 . Disposed at the lower part of the chamber  112  is a hopper  117  that helps the dusts to move downwards. 
   An air blower  119  is attached to the outlet port  114  of the housing  111 , which blower  119  serves to draw and discharge the air filtered by the filters  118 . The air blower  119  may be comprised of a typical vacuum pump. Disposed at the bottom of the housing  111  is a dust box  120  that collects the dusts (D)ropped through the hopper  117 . A first door  121  is attached to the upper side wall of the housing  111 , which door  121  can be opened for maintenance of the filters  118 . A second door  122  is attached to the lower side wall of the housing  111 , which door  122  can be opened when a need exists to draw out the dust box  120 . 
   Although the dust collector  110  shown and described herein is an ascending flow type in which the air flows upwards from the inlet port  113  toward the outlet port  114 , it would be possible to change the dust collector  110  to a descending flow type wherein an inlet port is interchanged with an outlet port. Moreover, although the dust collector  110  shown and described herein is a dry type in which the dusts are filtered by the filters  118 , other types of dust collectors such as a wet type dust collector, an electric dust collector or the like may be used in place thereof if such need arises. 
   The dust collector  110  is provided with an air blaster  130  for injecting a compressed air toward the filters  118  to remove the dusts adhered thereto. The air blaster  130  is comprised of an air compressor  131  for generating the compressed air and a plurality of nozzles  133  connected to the air compressor  131  through an air pipeline  132  for injecting the compressed air toward the filters  118 . Alternatively, the nozzles  133  may be connected to the air drier  43  of the compressed air supply unit  40  through the air pipeline  132 , in which case the air compressor  131  can be eliminated. The air blaster  130  may be replaced with a well-known vibration generator of the type applying vibration to a filter to remove dusts stuck thereto. 
   Referring to  FIG. 9 , a controller  140  is provided to control the motor  24  of the mesh conveyor  20 , the air compressor  41  and the air drier  43  of the compressed air supply unit  40 , the swing motor  72  of the swing arrangement  70 , the air blower  119  of the dust collector  110 , and the air compressor  131  of the air blaster  130 . The controller  140  is preferably mounted to a side wall of the blasting booth  60 . 
   In the silicon wafer regenerating system in accordance with the present invention, it is preferable that the silicon wafers  1  are automatically placed on the mesh belt  23  one after another.  FIGS. 10 through 14  shows an embodiment of a distacker  200  being provided at the upstream side of the mesh conveyor  20  for consecutively loading the silicon wafers  1  one after another on the mesh conveyor  20 . The destacker  200  includes a frame  210 , a stacker  220 , a lifting arrangement  230 , a feeder  240 , a vacuum suction unit  250 , an air blaster  260 , a compressed air supply unit  270  and a controller  280 . The frame  210  includes a base  211  and first and second side frames  212  and  213  provided at the opposite sides of the base  211 . 
   As shown in  FIGS. 10 through 13 , the stacker  220  is mounted on the center of the base  211  for stacking a large number of silicon wafers  1  one atop above. The stacker  220  includes a plurality of support bars  222  extending vertically to define a stacking space  221  within which the silicon wafers  1  can be accommodated in multiple layers. As is apparent in  FIG. 13 , the support bars  222  are arranged along an imaginary circle at the rear half part of the stacking space  221  with respect to a horizontal center line  223  so that the silicon wafers  1  can be loaded from the front side of the stacking space  221 . A top fixture plate  224 , a bottom fixture plate  225  and an intermediate fixture plate  226  are secured to the top, bottom and intermediate portions of the support bars  222 . A plurality of reinforcing bars  227  for reinforcing the mechanical strength of the stacker  220  are affixed at their opposite ends to the bottom fixture plate  225  and the intermediate fixture plate  226 . 
   Just above the intermediate fixture plate  226 , a table  228  for carrying the silicon wafers  1  is fitted to the support bars  222  for sliding movement along the same. The top fixture plate  224  and the table  228  are respectively provided with a plurality of radially arranged positioning holes  224   a  and  228   a  through which a plurality of positioning bars  229  penetrate in a matching relationship with the diameters of the silicon wafers  1  to make contact with the periphery of the latter. The positioning bars  229  are capable of supporting the silicon wafers  1  of up to 300 mm in diameter. The radial positions of the positioning bars  229  can be changed so as to reliably support peripheral edges of the silicon wafers  1  of, e.g., 100 mm, 125 mm, 150 mm and 200 mm in diameter. 
   The lifting arrangement  230  serves to lift up into a standby position P 1  the uppermost silicon wafer  1 - 1  among the silicon wafers  1  that are stacked within the stacking space  221  of the stacker  220 . The lifting arrangement  230  is comprised of a first air cylinder  231  and a first linear motion guide  233 . The first air cylinder  231  includes a cylinder housing  231   a  placed upright at the center of the stacker  220 . The bottom end of the cylinder housing  231   a  is pivotally joined to the top surface of the base  211 . The first air cylinder  231  further includes a cylinder rod  231   b  whose top end is pivotally attached to the underside of the table  228 . The first linear motion guide  233  helps the table  228  to make a linear reciprocating movement. The first linear motion guide  233  is comprised of a pair of vertically extending guide rails  233   a  respectively mounted to the inner surfaces of the first and second side frames  212  and  213 , a pair of sliders  233   b  mating with the corresponding guide rails  233   a  for sliding movement therealong, and a pair of joints  233   c  interconnecting the respective sliders  233   b  and the table  228 . 
   Alternatively, the lifting arrangement  230  may be comprised of a servo motor for generating a driving force, a lead screw operatively connected to the servo motor for rotation with the servo motor, a ball bush threadedly engaged with the lead screw and fixedly secured to the table  228  for movement as a unit along the ball bush, and a linear motion guide that helps the table  228  to make a linear reciprocating movement in a vertical direction. Furthermore, the first linear motion guide  233  illustrated and describe herein may be comprised of a pair of vertically extending parallel guide bars mounted to the frame  210  and a pair of guide bushes combined with the guide bars for sliding movement and fixedly secured to the table  228 . 
   The feeder  240  serves to unload the uppermost silicon wafer  1 - 1  among the silicon wafers  1  that are stacked within the stacking space  221  of the stacker  220 , and then to load the unloaded silicon wafer  1 - 1  onto the upstream side of the mesh conveyor  20 . The feeder  240  includes an arm  241 , a second air cylinder  242 , a carriage  243  and a second linear motion guide  244 . 
   The arm  241  is mounted to one of the first and second side frames  212  and  213 , namely, the second side frame  213  in the illustrated embodiment, to extend in a horizontal direction. The second air cylinder  242  is provided with a cylinder housing  242   a  lying above the arm  241  in a parallel relationship with respect thereto, the rear end of the cylinder housing  242   a  attached to the arm  241  for pivotal movement. The second air cylinder  242  is further provided with a cylinder rod  242   b , the distal end of which is pivotally attached to the carriage  243 . The second linear motion guide  244  is comprised of a guide rail  244   a  mounted to the top surface of the arm  241  and a slider  244   b  mating with the guide rail  244   a  for sliding movement therealong and attached to the carriage  243 . Alternatively, the second air cylinder  242  of the feeder  240  may be comprised of a servo motor capable of causing the carriage  243  to reciprocate along the arm  241 , a lead screw and a ball bush threadedly combined with the lead screw. 
   As shown in  FIGS. 11 and 12 , the vacuum suction unit  250  has a vacuum pad  251  attached to the underside of the carriage  243  and connected to a vacuum pump  252  for generating a suction force through an air pipeline  253 . As the first air cylinder  231  of the lifting arrangement  230  is operated to thereby extend the cylinder rod  231   b , the uppermost silicon wafer  1 - 1  comes closer to the vacuum pad  251  at the standby position. Under this condition, if the suction pump  252  creates a suction force, the uppermost silicon wafer  1 - 1  is sucked up into contact with the vacuum pad  251 . 
   As illustrated in  FIG. 11 , the air blaster  260  serves to inject a compressed air such that the uppermost silicon wafer  1 - 1  can be separated from the next silicon wafer  1 - 2  among the silicon wafers  1  stacked within the stacking space  221  of the stacker  220 . The air blaster  260  includes a plurality of nozzles  261  arranged in a vertical direction along one of the first and second side frames  212  and  213 , namely, the first side frame  212  in the illustrated embodiment. 
   Referring to  FIG. 14 , the compressed air supply unit  270  is mounted on the first side frame  212  to supply a compressed air to the second air cylinder  242  and the nozzles  261  of the air blaster  260 . Although not shown in the drawings, the compressed air supply unit  270  is comprised of an air compressor, an air controller and air pipelines. In place of the compressed air supply unit  270 , it would be possible for the destacker  200  to use the compressed air supply unit  40  of the grit blaster  30 . In this case, the air drier  43  of the compressed air supply unit  40  should be connected to the first air cylinder  231 , the second air cylinder  242  and the nozzles  261  of the destacker  200 . The controller  280  is mounted on the top of the first side frame  212  and controls operation of the vacuum pump  252  and the compressed air supply unit  270 . 
   The silicon wafer regenerating system of the present invention may further include a baking unit for removing moisture and a protective film coated on the silicon wafers.  FIG. 15  illustrates an embodiment of such a baking unit, which removes moisture and a protective film  3  from the surface of the silicon wafer  1 . The baking unit  300  shown in the drawing includes an oven  310 , a conveyor  320  and a heater  330 . The oven  310  has a drying chamber  311  and is provided with an inlet opening  312  and an outlet opening  313  formed at the opposite sides of the oven  310 . The conveyor  320  is provided in such a manner that the upstream and downstream extensions thereof are exposed from the oven  310  to the outside. The heater  330  is disposed at the upper part of the drying chamber  311  to heat the silicon wafers  1  moving with the belt  321  of the conveyor  320 . Alternatively, the heater  330  may be disposed under the belt  321  so that it can heat the silicon wafers  1  in a conduction or convection method. 
   Further, the baking unit  300  may be disposed at the upstream side of the mesh conveyor  20  or the destacker  200  or may be independently installed with respect to the mesh conveyor  20  or the destacker  200 . In addition, the conveyor  320  of the baking unit  300  may be disposed in an end-to-end relationship with the mesh conveyor  20 . The oven  310  of the baking unit  300  may be of a batch type, in which case the conveyor  320  can be eliminated in its entirety. 
   Now, mainly with reference to  FIG. 16 , description will be given to a silicon wafer regenerating method for removing patterns on the silicon wafers using the system described above. 
   Referring collectively to  FIGS. 15 and 16 , the silicon wafers  1  may be stained with moisture in the event that the moisture such as chemicals or water are left on the silicon wafers  1  discharged from a semiconductor manufacturing process. In such a case, the efficiency with which the patterns are removed from the silicon wafers  1  may be reduced due to the fact that the grits (G) blasted by the grit blasting nozzles  31  are adhered to the surface of the silicon wafers  1  and/or the fact that the silicon wafers  1  has a shock-absorbing property against the striking force of the grits (G). Moreover, the protective film  3  covered over the patterns  2  of the silicon wafers  1  has a shock-absorbing property against the striking force of the grits (G). 
   In view of this, the baking unit  300  is first operated to get rid of the moisture and the protective film  3  from the silicon wafers  1  (S 10 ). For this purpose, the silicon wafers  1  are loaded onto the belt  321  of the conveyor  320 , at which time the silicon wafers  1  can be placed on the belt  321  of the conveyor  320  in multiple layers. The conveyor  320  is then operated to feed the silicon wafers  1  into the drying chamber  311  through the inlet opening  312  of the oven  310 , and the heater  330  is energized to heat the silicon wafers  1  and thus evaporate the moisture left on the silicon wafers  1 . The protective film  3  of the silicon wafers  1  can be removed by, for example, baking the silicon wafers  1  for about 20-30 minutes at a temperature of about 700-800° C. The silicon wafers  1  from which the moisture and the protective film have been removed are discharged from the drying chamber  311  through the outlet opening  313  of the oven  310  by the operation of the conveyor  320 . The grit blasting efficiency can be enhanced by removing the moisture and the protective film from the silicon wafers  1  through the baking process and thus making the silicon wafers  1  dry in this manner. 
   Referring to  FIGS. 1 ,  2  and  10  through  13 , the silicon wafers  1  are stacked one atop above within the stacking space  221  of the stacker  200  such that the patterns  2  of the silicon wafers  1  can face in an upward direction (S 11 ). In conformity with the size of the silicon wafers  1 , the positioning bars  229  are inserted through the positioning holes  224   a  and  228   a  of the top fixture plate  224  and the table  228  prior to stacking the silicon wafers  1 . This ensures that the silicon wafers  1  make contact with at their peripheral edges, and are aligned inside, the positioning bars  229 . Silicon wafers of 30 mm in diameter may be aligned in place by use of the support bars  222 , while removing the positioning bars  229 . 
   Next, the destacker  200  is operated to consecutively load the silicon wafers  1  one after another onto the upstream extension of the mesh belt  23  of the mesh conveyor  20  (S 12 ). If the first air cylinder  231  of the lifting arrangement  230  is actuated to extend the cylinder rod  231   b , the silicon wafers  1  are lifted up together with the table  228 . The rising movement of the table  228  is linearly guided by means of the slider  233   b  that makes sliding movement along the guide rails  233   a  of the first linear motion guide  233 . As the table  228  is lifted up in this manner, the uppermost silicon wafer  1 - 1  reaches the standby position P 1  and lies in proximity with the vacuum pad  251  of the vacuum suction unit  250 . The vacuum pump  262  is actuated to generate a suction force by which the uppermost silicon wafer  1 - 1  is sucked up to the vacuum pad  251 . The uppermost silicon wafer  1 - 1  is separated from the next silicon wafer  1 - 2  by the compressed air injected from the nozzles  261  of the air blaster  260 , as illustrated in  FIG. 11 . 
   Referring to  FIGS. 3 ,  4  and  12 , the second air cylinder  242  of the feeder  240  is operated to extend the cylinder rod  242   b  after the uppermost silicon wafer  1 - 1  has been sucked up by the vacuum pad  251  of the vacuum suction unit  250 . In response, the carriage  243  and the vacuum pad  251  are moved together toward the frontal end of the arm  241 . If the uppermost silicon wafer  1 - 1  carried by the vacuum pad  251  of the vacuum suction unit  250  arrives at above the mesh belt  23  of the mesh conveyor  20 , the vacuum pump  252  ceases to operate and generates no suction force. This allows the uppermost silicon wafer  1 - 1  to be detached from the vacuum pad  251  and then transferred to the mesh belt  23 . If the motor  24  of the mesh conveyor  20  begins to rotate under this state, the driving force of the motor  24  is transmitted to the driving pulley  21  through the belt transmission mechanism  25 , in response to which the mesh belt  23  wound around the driving pulley  21  and the driven pulley  22  begins to travel. As the mesh belt  23  travels, the uppermost silicon wafer  1 - 1  is transported from the upstream side to the downstream side. 
   In the meantime, after the uppermost silicon wafer  1 - 1  has been loaded onto the mesh conveyor  20  by the action of the feeder  240 , the cylinder rod  242   b  of the second air cylinder  242  is retracted to thereby return the carriage  243  and the vacuum pad  251  to their original position. As the vacuum pad  251  is returned back to the original position, the first air cylinder  231  is actuated again and performs the same operation as did with respect to the uppermost silicon wafer  1 - 1 . This allows the next silicon wafer  1 - 2  to be moved upwards and sucked up by the vacuum pad  251 . The next silicon wafer  1 - 2  is loaded onto the upstream side of the mesh conveyor  20  by the action of the feeder  240 . Alternatively, the silicon wafers  1  may be manually loaded onto the mesh conveyor  20  by the operator. 
   Referring to  FIGS. 3 ,  5  and  6 , the mesh conveyor  20  continues to operate and transports the silicon wafers  1  along the first tunnel  61  of the blasting booth  60  (S 13 ). The grits (G) are blasted toward the surfaces of the moving silicon wafers  1  to remove the defective patterns  2  of the silicon wafers  1  (S 14 ). In this process, the air compressor  41  of the compressed air supply unit  40  is operated to supply the compressed air to the grit blasting nozzles  31  which in turn blast the compressed air and the grits (G) toward the surfaces of the silicon wafers  1  transported by the mesh belt  23 . The grits (G) thus blasted strike and remove the patterns  2  of the silicon wafers  1 . 
   The pulverulent bodies (P) are dislodged from the surfaces of the silicon wafers  1  whose patterns  2  have been removed (S 15 ). In this process, the silicon wafers  1  whose patterns  2  have been removed in the first tunnel  61  of the blasting booth  50  is transferred to the second tunnel  61  of the cleaning booth  65  by the operation of the mesh conveyor  20 . A compressed air is injected from the cleaning nozzle  32  that remains connected to one of the air pipelines  44  of the compressed air supply unit  40 . The pulverulent bodies (P) are dislodged from the surfaces of the silicon wafers  1  by the compressed air. The silicon wafers  1  from which the pulverulent bodies (P) have been dislodged are moved past the second tunnel  61  of the cleaning booth  65  toward the downstream side of the mesh conveyor  20  at which the silicon wafers  1  are unloaded from the mesh conveyor  20 . The silicon wafers  1  whose defective patterns  2  were removed in this manner may be used as a silicon wafer for, e.g., solar cells. 
   As illustrated in  FIG. 3 , the pulverulent bodies (P) inclusive of the wafer chips (C), the dusts (D) and the grits (G) dropped from the mesh belt  23  of the mesh conveyor  20  are collected in the first pulverulent body pipeline  92  via the hoppers  91  (S 16 ). The silicon wafers  1  may be fractured into fragments B in the process of removing the patterns  2  by the grit blasting operation. The fragments B of the silicon wafers  1  cannot pass the mesh belt  23  for their most parts. Some fragments B having a small size are dropped through the mesh belt  23  and filtered out by means of the first screen filter  94 . This prevents the first pulverulent body pipeline  92  from being clogged with the fragments B. 
   Referring to  FIGS. 1 and 7 , the pulverulent bodies (P) collected in the first pulverulent body pipeline  92  of the collecting unit  90  is supplied to the cyclone separator  100  where the dusts (D) are separated from the chips D and the grits (G) (S 17 ). More specifically, the air blower  119  of the dust collector  110  is operated to generate a vacuum pressure by which the pulverulent bodies (P) collected in the first pulverulent body pipeline  92  are supplied to the cyclone separator  100  through the second pulverulent body pipeline  93 . The second screen filter  95  provided between the first pulverulent body pipeline  92  and the second pulverulent body pipeline  93  filters out the chips (C) whose particle size is greater than 80 μm, for instance. Filtering out the chips (C) of a great size at the upstream side of the second pulverulent body pipeline  93  ensures that the second pulverulent body pipeline  93 , the grit blasting nozzles  31  and the grit pipeline  52  are prevented from any unwanted clogging. The pulverulent bodies (P) introduced into the chamber  102  through the inlet opening  103  of the housing  101  are sorted under the action of a swirling air stream. The chips (C) and the grits (G) having a particle size of, e.g., no smaller than 10 μm, impact on the internal surface of the housing  101  and then discharged through the outlet opening  104 , whereas the dusts (D) having a particle size of smaller than 10 μm are borne by the swirling air stream and then exhausted through the outlet pipe  105 . 
   The chips (C) and the grits (G) discharged from the chamber  102  of the cyclone separator  100  are recovered into the tank  51  of the grit supply unit  50  (S 18 ). Specifically, the air compressor  41  is operated to supply a compressed air to the grit blasting nozzles  31  through the air pipelines  44 . As the compressed air is injected from the grit blasting nozzles  31 , a vacuum pressure is developed in the grit pipelines  52  connected to the grit blasting nozzles  31 . Under the action of the vacuum pressure, the chips (C) and the grits (G) discharged from the chamber  102  of the cyclone separator  100  are recovered into the tank  51  through the grit return pipeline  53 . The chips (C) and the grits (G) thus recovered are recirculated through the grit blasting nozzles  31  of the grit blaster  30 . 
   Referring to  FIGS. 1 and 8 , the dusts (D) exhausted through the outlet pipe  105  of the cyclone separator  100  are removed by filtering (S 19 ). Specifically, if the air blower  119  of the dust collector  110  is operated to generate a vacuum pressure, the dusts (D) exhausted through the outlet pip  105  of the cyclone separator  100  are supplied to the chamber  112  through the dust pipeline  115  and the inlet opening  113  and then filtered out by means of the filters  118 . In the event that the filters  118  are clogged by the dusts (D), the air compressor  131  of the air blaster  130  is operated to generate a compressed air which in turn is supplied to the nozzle  133  through the air pipeline  132 . The dusts (D) adhered to the filters  118  are detached by the compressed air injected from the nozzles  133 . The dusts (D) are then discharged through the outlet opening  114  and collected in the dust box  120 . 
   Although the present invention has been described in detail above, it should be understood that the foregoing description is illustrative and not restrictive. For example, even though the above description was presented in viewpoint of wafers made of silicon, the present invention may be used to regenerate wafers made of another kinds of semiconductor material such as gallium arsenide and the other compound semiconductor. Thus, those of ordinary skill in the art will appreciate that many obvious modifications can be made to the invention without departing from its spirit or essential characteristics. We claim all modifications and variation coming within the spirit and scope of the following claims.