Abstract:
Spin-coating apparatus for use in manufacturing a semiconductor device or the like and a method of operation of the apparatus prevent substrates from being positioned incorrectly in a process module of the apparatus. The spin-coating apparatus includes an image sensor that captures an image of the wafer in the process module, and a control unit that receives image data from the image sensor. The method includes loading a substrate onto a process module using an arm of a transfer device, capturing an image of the substrate using the image sensor, and comparing image data generated by the image sensor with a standard image data stored to determine an actual position of the substrate. If the substrate is incorrectly positioned, the operation of the arm of the transfer device is adjusted to compensate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to spin-coating apparatus for use in manufacturing a semiconductor device. More particularly, the present invention relates to a wafer transfer device which loads wafers into and unloads wafers from process modules in the apparatus.  
         [0003]     2. Description of the Related Art  
         [0004]     In general, a semiconductor device is manufactured by fabricating several circuits on a wafer. A typical one of such circuits is fabricated by forming a thin film on a wafer, coating the thin film with a layer of photoresist, transcribing an image corresponding to the circuit onto the layer of photoresist using a stepper, developing the layer of photoresist to pattern the layer, and etching the thin film using the patterned layer of photoresist as a mask.  
         [0005]     Spin-coating apparatus are used for creating a thin uniform layer of photoresist on the thin film. Although the details of spin-coating apparatus vary from manufacturer to manufacturer, most apparatus generally include a coating unit including a spin chuck for holding and rotating the wafer while the photoresist is applied to the wafer, a side rinsing unit for cleaning an edge of the wafer after the photoresist has been applied thereto, a baking unit for curing the wafer or photoresist before or after the side rinse, and a wafer transfer device for transferring the wafer between the respective units of the apparatus. The side rinse unit has a structure similar to that of the coating unit. The spin-coating apparatus also includes a loading station onto and from which a wafer cassette is loaded and unloaded, and an alignment device for aligning the wafers supplied from the wafer cassette.  
         [0006]      FIG. 1  is a perspective view of conventional spin-coating apparatus  100  for use in manufacturing a semiconductor device.  FIG. 2   a  shows a wafer transfer device of the spin-coating apparatus, and  FIGS. 2   b  and  2   c  show other process modules of the apparatus, respectively. A process of applying and developing the photoresist will now be described in detail with reference to  FIGS. 1 through 2   c.    
         [0007]     First, a wafer cassette  131  with wafers  170  stacked therein is loaded onto a wafer cassette loading station  130  by an automatic guided vehicle (AGV) or a manual guided vehicle. Next, a wafer  170  is removed from the wafer cassette  131  by an index arm  141  of an alignment device. The wafer  170  is loaded onto an alignment stage  140  of the device, and is then aligned by a mechanism, such as roller, such that a flat zone of the wafer or a notch in the wafer is oriented in a desired direction.  
         [0008]     The aligned wafer  170  is loaded into a baking unit  160  by one of the first and second main arms  151  and  152  of a wafer transfer device  150 . At this time, if a wafer  170  is already present in the baking unit  160 , the other of the first and second main arms  151  and  152  unloads the baked wafer from the baking unit  160 .  
         [0009]     The baked wafer  170  is transferred from the baking unit  160  to a coating unit  120 , as shown in  FIG. 2   c.  The coating unit  120  includes a spin chuck  121  for spinning the wafer  170  at a certain rotational speed. The wafer  170  is centered on the spin chuck  121  so that the photoresist will uniformly coat the entire surface of the wafer. The spin chuck  121  has a vacuum hole  122  through which a vacuum is created to adhere the wafer  170  to the chuck. At this time, if the wafer  170  is incorrectly loaded on the spin chuck  121 , i.e., is not centered relative to the spin chuck  121 , centrifugal force acting on the wafer may unseat the wafer  170  from the spin chuck  121 .  
         [0010]     Therefore, an operator should perform maintenance that prevents the wafer  170  from spinning off of the spin chuck  121 . Notwithstanding such preventive maintenance, the wafer  170  may still yet come off of the spin chuck  121  when the coating unit  120  has been running for a long time. In this case, the operator confirms an optimum state of the wafer transfer device  150  by performing several tests of the main arms  151  and  152 , and calibrates the wafer transfer device  150  accordingly to prevent the first and second main arms  151  and  152  from placing the wafer  170  incorrectly on the spin chuck  121 . (The optimum calibration of the wafer transfer device based on testing will be referred to hereinafter as the “teaching” of the main arms).  
         [0011]     Next, the first or second main arm  151  or  152  loads the wafer  170  into a side rinse unit  110  where photoresist is removed from the edge of the wafer  170 . At this time, the teaching of the first and second main arms  151  and  152  is relevant to the side rinse operation because the side rinse unit  110  also includes a spin chuck  121 .  
         [0012]     The rinsed wafer  170  is then again loaded into the baking unit  160  by one of the first and second main arms  151  and  152  to cure the photoresist on the wafer. After the baking process, the wafer  170  is again loaded onto the wafer cassette  131  by the first or second main arm  151  or  152 . The overall process described above is generally controlled by a control unit (not shown) of the spin-coating apparatus  100 .  
         [0013]     After all of the wafers  170  in the cassette  131  disposed at the wafer cassette loading station  130  have been processed as described above, the wafer cassette  131  is transferred from the wafer cassette loading station  130  to an exposing unit, such as stepper or scanner. Subsequently, each of the wafers  170  is removed from the cassette and loaded onto a stage of the exposing unit. Then, the photoresist layer the wafer  170  is then exposed to the image of a pattern of a photomask of the exposing unit, which pattern corresponds to the circuit pattern to be formed on the wafer.  
         [0014]     However, the conventional spin-coating apparatus  100  has the following problems.  
         [0015]     First, when the first and second main arms  151  and  152  are not placing the wafers  170  correctly on the spin chuck of the coating unit or side rinse unit, accidents occur. These accidents, resulting in scratches in or breakages of the wafer  170 , can not be prevented because the spin-coating apparatus  100  has no means to monitor the calibration of the arm(s)  151  and/or  152  of the transfer device  150 . The improper calibration of the arm or arms is only uncovered after the operation of the spin-coating apparatus  100  is stopped due to a process accident. Hence, the production yield of the conventional spin-coating apparatus is compromised by the inability of the apparatus to prevent such accidents from occurring.  
         [0016]     Second, the first and second main arms  151  and  152  are taught to position the wafers  170  on the spin-chuck of the coating unit  120  or side rinse unit  110  by a technician. Hence, the teaching of the first and/or second main arm is subject to human error. This also affects the productivity of the spin-coating apparatus.  
         [0017]     Finally, a technician must reside at the production line to manage the spin-coating apparatus, perform preventive maintenance and prevent production accidents due to the failure of the first and second main arms  151  and  152  to remain properly calibrated. Accordingly, the labor costs associated with running the conventional spin-coating apparatus are relatively high.  
       SUMMARY OF THE INVENTION  
       [0018]     Therefore, an object of the present invention is to provide spin-coating apparatus for manufacturing a semiconductor device and a method of operating the same, which prevent wafers or the like from being scratched or broken and thereby maximizing the yield of the apparatus.  
         [0019]     Another object of the present invention is to provide spin-coating apparatus for manufacturing a semiconductor device and a method of operating the same, wherein a main arm of a transfer device is taught to position substrates in a process module without human intervention thereby minimizing the likelihood of accidents and maximizing the yield of the apparatus.  
         [0020]     Still another object of the present invention is to provide spin-coating apparatus for manufacturing a semiconductor device and a method of operating the same, wherein the apparatus is interlocked when a process accident is in progress.  
         [0021]     According to one aspect of the present invention, a spin-coating apparatus comprises a plurality of process modules, a transfer device having at least one main arm for transferring substrates to the plurality of process modules, at least one image sensor for capturing images of substrates as the substrates are loaded onto the process module by the main arm, and a control unit operatively connected to the image sensor and the main arm. The control unit is electronically configured to compare image data generated by the image sensor with stored standard image data, to use the comparison to determine the position of the substrate at the time the substrate is loaded onto the process module, and to teach the main arm of the transfer device to position the substrate more accurately if necessary.  
         [0022]     Preferably, the process modules include a coating unit for coating an upper surface of the substrates with photoresist, a side rinsing for rinsing photoresist form the sides of the substrate, and a baking unit for baking the substrates coated with photoresist. The coating unit and the side rinsing unit each have a spin chuck. A respective image sensor is positioned relative to at least one such spin chuck in the apparatus to capture images of substrates after the substrates have been placed on the spin chuck by the main arm of the transfer device.  
         [0023]     According to another aspect of the present invention, a method of operation of spin-coating apparatus comprises steps of: a) loading a substrate onto a process module using a main arm of a substrate transfer device, b) capturing an image of the substrate loaded on the process module, and comparing an data representing the image with stored standard image data to determine the position of the substrate, and c) adjusting the operation of the main arm to compensate for the extent to which the substrate has been incorrectly positioned on the process module.  
         [0024]     According to still another aspect of the present invention, the standard image data represents an ideal position of the substrate in the process module. Preferably, this ideal position corresponds to a position at which the substrate is centered on the spin chuck of a respective process module. The operation of the main arm is adjusted (taught) only when the determination reveals that the substrate has been placed on the process module by the main arm in a position that differs from the ideal position but is within certain tolerances of the ideal position. On the other hand, when the determination reveals that the substrate has been placed on the process module by the main arm in a position that differs from the ideal position and is outside certain tolerances of the ideal position, an interlock signal is output to lock down the spin-coating apparatus. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]     The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art from the following detailed description of the preferred embodiments thereof with reference to the attached drawings in which:  
         [0026]      FIG. 1  is a perspective view of conventional spin-coating apparatus for use in manufacturing a semiconductor device;  
         [0027]      FIG. 2   a  is a perspective view of a wafer alignment device of the conventional spin-coating apparatus;  
         [0028]      FIG. 2   b  is a perspective view of a wafer transfer unit of the conventional spin-coating apparatus;  
         [0029]      FIG. 2   c  is a perspective view a coating unit of the conventional spin-coating apparatus;  
         [0030]      FIG. 3  is a perspective view of spin-coating apparatus for use in manufacturing a semiconductor device according to the present invention;  
         [0031]      FIG. 4  is a perspective view of a coating unit and a wafer transfer device of the spin-coating apparatus shown in  FIG. 3 ; and  
         [0032]      FIG. 5  is a flowchart depicting a process of monitoring spin-coating apparatus to prevent process accidents from occurring according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings. Like reference numbers designate like elements throughout the drawings.  
         [0034]     Referring to  FIGS. 3 and 4 , the spin-coating apparatus  200  according to the present invention includes a wafer cassette loading station  230  for supporting a wafer cassette, an alignment device  240  having an index arm for removing a wafer  270  from a wafer cassette at the wafer cassette loading station  230  and for aligning the wafer, a coating unit  210  for coating a surface of the wafer  270  with photoresist, a side rinsing unit for removing photoresist from the edge of the wafer  270 , a baking unit  260  for curing the photoresist applied to the wafer  270 , a wafer transfer device  250  for transferring the wafer throughout the apparatus, and at least one image sensor  280  for taking a picture of the wafer  270  transferred by the wafer transfer device  250 .  
         [0035]     The wafer transfer device  250  has first and second arms  251  and  252  for loading and unloading wafers into and from the coating unit  210 , the side rinsing unit  220 , and the baking unit  260 . A respective image sensor  280  may be installed in the coating unit  210 , the side rinsing unit  220 , and/or the baking unit  260  for taking a picture of the wafer  270  as the wafer is loaded or unloaded by the first or second main arms  251  and  252 . The image sensor  280  may be a charge-coupled device, for example.  
         [0036]     The spin-coating apparatus  200  further includes a control unit for outputting control signals to control the coating unit  210 , the side rinsing unit  220 , the baking unit  260 , the wafer transfer  250 , and the first and second main arms  251  and  252 . The control unit is also connected to each image sensor  280  so as to receive data of the images sensed by each image sensor  280 . The control unit compares the data received from the image sensor(s)  280  with standard wafer image data stored in a memory of the control unit and, based on such a comparison, determines whether the wafer is being transferred in an optimal state. If the transferring of the wafer is not normal, an alarm is issued and the process is stopped. To this end, an audio or visual alarm-generating device is connected to the control unit.  
         [0037]     The coating unit  210 , the side rinsing unit  220 , and the baking unit  260  each constitute a process module of the spin-coating apparatus  200 . During the operation of the spin-coating apparatus  200  of the present invention, one of the main arms  251  and  252  of the wafer transfer device  250  unloads a processed wafer  270  from a process module as the other of the main arms  251  and  252  prepares to load another wafer  270  to be processed into the same process module. An example of this operation will be described with respect to the coating unit  260 , as shown in  FIG. 4 . Of course, the first and second main arms  251  and  252  move into and out of the side rinsing unit  220  and the baking unit  260  in a similar way.  
         [0038]     The coating unit  210  uniformly coat an upper surface of the wafer  270  with photoresist. More specifically, the coating unit  210  includes a photoresist supplier (not shown) that dispenses the photoresist onto the center of the wafer  270 , and a spin chuck  211  for rotating the wafer such that the photoresist is dispersed across the entire surface of the wafer. To this end, the spin chuck  211  has vacuum system, e.g. a vacuum pump, a platen defining a vacuum hole connected to the vacuum system, and a motor connected to the platen. A vacuum created by the vacuum system is applied through the vacuum hole to a wafer transferred to the platen by the first or second main arm  251  or  252 , whereby the wafer is adhered to the platen of the chuck. In this state, the platen is rotated by the motor connected thereto to rotate the wafer  270 .  
         [0039]     At this time, if the first or second main arm  251  or  252  has not centered the wafer  270  on the platen of the spin chuck  211 , the wafer  270  may be spun off of the spin chuck, or the photoresist may not uniformly coat the upper surface of the wafer  270 . More specifically, if the center of gravity of the wafer  270  is not positioned along the axis of rotation the spin chuck  270 , the wafer  211  may be spun off of the spin chuck  211  by the centrifugal force produced due to the rotation of the wafer  270 . Moreover, even if the centrifugal force is not great enough to unseat the wafer  270  from the spin chuck  211 , the photoresist will flows more prominently in one direction. As a result, the upper surface of the wafer is coated unevenly with the photoresist.  
         [0040]     However, according to the present invention, an image sensor  280  is disposed along the axis of rotation of the spin chuck  211  to take a picture of the wafer  270 . Accordingly, the control unit is able to determine whether the wafer  270  has been correctly transferred to the coating unit  210  by the first or second main arm  251  or  252 . That is, whether the main arm  251  or  252  has been properly calibrated or “taught” can be confirmed.  
         [0041]     As described above, the first and second main arms  251  and  252  are controlled based on images of the wafer taken by the image sensor  280 . However, the control unit may recalibrate the first and second main arms  251  and  252  using a plurality of photo sensors or limit switches (position sensors) that indicate the amount by which the first or second main arm  251  or  252  has been inserted into a process module, such as the coating unit  210 . In this case, the control unit conforms the recalibration of the transfer device  250  using signals output by the position sensors. In any case, a technician is notified of the failure of the first or second main arm to remain properly calibrated via an alarm.  
         [0042]     Now, a process of preventing wafers from being improperly positioned in the spin-coating apparatus according to the present invention will be described with reference to the flow chart of  FIG. 5 . First, the basic operation of the apparatus will now be described.  
         [0043]     A wafer cassette having wafers  270  stacked therein is loaded onto the wafer cassette loading station  230  by an automatic guided vehicle (AGV) or a manually guided vehicle. A wafer  270  is taken out of the wafer cassette by an index arm  241  of the alignment device  240 . The wafer  270  is then aligned by an aligning mechanism of the alignment device, such as roller, such that a flat zone of or notch in the wafer is oriented in a desired direction.  
         [0044]     The aligned wafer  270  is loaded into the baking unit  260  by one of the first and second main arms  251  and  252  of the wafer transfer  250 . At this time, if another wafer  270  is present in the baking unit  260 , the other of the first and second main arms  251  and  252  first unloads the wafer from the baking unit  260 .  
         [0045]     A wafer  270  unloaded from the baking unit  260  is transferred to the coating unit  210 , as shown in  FIG. 4 . Then, the wafer  270  is rotated and photoresist is dispensed onto a central region of the wafer  270 . At this time, If the wafer  270  is not placed correctly on the spin chuck  211 , i.e., is not centered relative to the axis of rotation of rotation of the spin chuck  211 , the centrifugal force acting on the wafer  270  is unbalanced. The faster the spin chuck rotates, the greater the centrifugal force. Therefore, the wafer  270  may be detached from the spin chuck  211  at high speeds. Even at lower speeds, the upper surface of the wafer is coated unevenly with the photoresist.  
         [0046]     Now, a process of preventing such process failures or defects in the spin-coating apparatus according to the present invention will be described with reference to  FIG. 5 .  
         [0047]     First, as described above, the wafer  270  is positioned on the spin chuck  211  by the first or second main arm  251  or  252 . The wafer  270  positioned on the spin chuck  211  by the first or second main arm  251  or  252  is photographed by the image sensor  280  (S 100 ). To this end, the image sensor  280  may capture images constantly or at regular intervals under the command of the control unit.  
         [0048]     The control unit periodically checks the state in which the wafers  270  are being positioned by use of the image signals output from the image sensor  280 . The check is made once a certain number of wafers  270  have been placed on the spin chuck  211  or once the spin-coating apparatus  200  has been operating for a certain period of time (S 200 ). In either case, the control unit compares the image data generated by the image sensor  280  with standard wafer image data stored in a memory of the control unit. The wafer image data is representative of an ideal position of the wafer on the spin chuck  211 , e.g., a position at which the wafer is perfectly centered. Thus, the comparison reveals the actual position of the wafer  270 .  
         [0049]     Then, the control unit determines whether the positioning of the wafer by the first or second main arm  251  or  252  is off by an excessive amount, i.e., deviates from the ideal position by more than certain tolerances (S 300 ). If the wafer is not at the ideal position and has not been mis-positioned by an excessive amount, the control unit nonetheless teaches the first or second main arm  251  or  252  to more accurately position the wafer on the spin chuck of the coating unit (S 400 ). In this case, the control unit adjusts the operation of the main arm(s) by an appropriate “teaching” value, i.e., recalibrates the main arm(s). For example, the control unit adjusts the extent to which the arm is inserted into the coating unit  210  and confirms such an adjustment by detecting the position of the arm using an array of position sensors (for example, photo sensors or limit switches). The use of photo sensors or limit switches to sense the position of a mechanical element is known, per se, and thus, will not be described in more detail.  
         [0050]     If the position of the wafer on the spin chuck deviates from an ideal position by an excessive amount, e.g., if the wafer slides off of the spin chuck, the image data generated by the image sensor deviates significantly from the standard image data stored in the memory of the control unit. In this case, the control unit cannot adjust the first or second main arms  251  or  252  enough to compensate for its failure to position a wafer on the spin chuck accurately enough. Accordingly, the control unit outputs an interlock signal to the spin-coating apparatus  200  to stop the operation of the apparatus. Also, the control unit outputs a command to activate the alarm device and thereby signal an accident in progress (S 500 ).  
         [0051]     Next, a technician uncovers the cause of the accident, and performs corrective measures. Then, the spin-coating apparatus may be tested and reactivated (S 600 ). For example, the operator loads a test wafer or jig into the apparatus, whereby the spin chuck  211  the first or second main arm  251  or  252  loads the test wafer or jig onto the spin-chuck. The operation illustrated in  FIG. 5  is repeated using the test wafer or jig until the test indicates that the spin-coating apparatus is performing acceptably.  
         [0052]     According to the method of the present invention, the control unit automatically and periodically teaches the first main arm  251  and/or second main arm  252  to position the wafer  270  in a process module. Therefore, accidents associated with a failure of the arm(s) to remain calibrated are unlikely to occur, whereby the productivity of the spin-coating apparatus is maximized.  
         [0053]     Also the teaching of the first and second main arms  251  and  252  applies to the side rinse operation because the side rinsing unit  220  also includes a spin chuck.  
         [0054]     Still further, even when the control unit can not adjust the first main arm  251  and/or second main arm  252  to prevent an accident from occurring, the control unit generates an interlock signal and activates an alarm device. Thus, the spin-coating apparatus is shut down immediately to prevent subsequent wafers from being damaged. Moreover, the operator is notified that the spin-coating apparatus must be examined to uncover the cause of a significant malfunction.  
         [0055]     Finally, although the present invention has been described above in connection with the preferred embodiments thereof, the invention may be embodied differently. Accordingly, modifications of and changes to the disclosed embodiments are seen to be within the true spirit and scope of the invention as defined by the appended claims.