Abstract:
A method for loading a semiconductor wafer into a process unit comprises opening the process unit, inserting a wafer into the process unit, adjusting the position of the wafer in the process unit so that it is in a certain position in relation to markers, and inserting a camera into the process unit facing the markers. The camera acquires an image of the markers and of a part of the wafer, and displays on a display screen the image acquired. The position of the wafer is adjusted according to the position of the wafer in relation to the markers on the image displayed.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to the manufacture of integrated circuits on a semiconductor wafer and more particularly loading a semiconductor wafer into an oven. 
         [0003]    2. Description of the Related Art 
         [0004]    The ovens used for the manufacture of integrated circuits, and particularly to bake the layers of photo-sensitive resin, comprise several oven units, each comprising a process chamber provided to receive a semiconductor wafer to be processed. The chamber is closed by a cover movable between a high position in which the chamber is open for loading and unloading a wafer, and a low position for closing the chamber. The chamber comprises retractable pins for supporting a wafer, distributed on the periphery thereof and allowing the wafer to be moved between a high loading position and a low processing position. Loading and unloading a wafer in the oven is performed using a robotic arm which allows in particular a wafer to be introduced into the processing chamber at a very precise position. The wafers are positioned in the oven units in a clearly determined position so as to ensure that the wafer is subjected to a strictly homogeneous temperature rise in the oven unit. To that end, the robotic arm has three positions by oven unit, i.e., a high position to introduce a wafer into the oven unit, a median position to adjust the position of the wafer in the oven unit, and a low position in which it may go out of the oven without the wafer which is then supported by the pins. 
         [0005]    A learning phase is therefore provided to allow the control system of the robotic arm to memorize the exact position where the wafers are deposited in each oven unit. This learning phase is performed each time the arm looses a positioning marker or a wafer positioning defect is detected in an oven unit. The learning phase causes the manufacturing line to stop and includes the intervention of an operator who controls the move of the arm using a control panel to adjust the position of a wafer in an oven unit, until the wafer reaches the desired position. The operator then controls the memorization by the control system of the position of the arm for the oven unit where the wafer is located. The learning phase thus comprises memorizing the deposit position of a wafer in each oven unit. 
         [0006]    For wafer heat homogeneity and dimensions reasons, the process chamber of oven units used in the manufacture of integrated circuits has lower and lower dimensions to substantially reach the volume of the wafers to be processed. The result is that the slightest positioning defect of a wafer in an oven unit may cause the breakage of the wafer, particularly when closing the oven unit, and therefore the break of the manufacturing line for a relatively long duration to remove the pieces of broken wafer from the oven unit. For dimensions reasons too, the travel of the cover is very reduced, so that it is hard for an operator to see if the wafer is properly positioned inside the oven. 
         [0007]    One type of machine is a DNS SK-2000 commercialized by the company DAI NIPPON SCREEN. A machine of this type comprises 36 oven units located at a height of 2.20 m on average. Determining the deposit position of the wafers in oven units employs a scaffolding of a height around 1.30 m, on which the operator climbs to observe the position of the wafer in each oven unit, and handle the robotic arm by means of the control panel. Adjusting the position of a wafer in a unit takes around 10 to 15 minutes, i.e., 6 to 9 hours for the whole learning phase allowing the control system of the robotic arm to be set for all the units of a machine. This duration is considerably increased if a wafer is not positioned properly and breaks when closing the oven unit. 
         [0008]    To reduce the duration of the learning phase, it has been considered to use the positions of the oven units relative to each other to determine the deposit position of a wafer in each oven unit from a deposit position manually determined by an operator for an oven unit. It has proven that this solution is not reliable and leads to numerous wafer positioning errors in oven units. 
         [0009]    It is therefore desirable to reduce the duration of the learning phase and therefore make it easier to adjust the deposit position of a semiconductor wafer in an oven unit and be able to ensure that the wafer is properly positioned before closing the oven. 
         [0010]    In an embodiment, a method is provided for loading a semiconductor wafer into a process unit, comprising opening the process unit, inserting a wafer into the process unit, and adjusting the position of the wafer in the process unit so that it is in a certain position in relation to markers. According to one embodiment, the method comprises inserting a camera into the process unit facing the markers, the camera acquiring an image of the markers and of a part of the wafer, and displaying the image acquired on a display screen, adjusting the position of the wafer being performed according to the position of the wafer in relation to the markers on the image displayed. 
         [0011]    According to one embodiment, the markers are retractable pins supporting the edge of the wafer when the process unit is in open configuration. 
         [0012]    According to one embodiment, an image of each marker is acquired by a respective camera, the images acquired of all the markers being simultaneously displayed. 
         [0013]    According to one embodiment, the method comprises taking apart a part of a cover of the process unit and fixing as a replacement for the cover part, an acquisition module comprising the camera. 
         [0014]    According to one embodiment, the markers are enlightened during acquisition. 
         [0015]    According to one embodiment, the process unit is an oven unit. 
         [0016]    According to one embodiment, the method comprises monitoring the temperature in the oven unit during acquisition, and generating an alarm signal if the temperature measured exceeds a threshold value. 
         [0017]    According to one embodiment, the process unit is an oven unit belonging to a machine of DNS SK2000 type. 
         [0018]    In an embodiment, a learning method is also provided for the control of a robotic arm for loading and unloading semiconductor wafers in a machine comprising several wafer processing units, the method comprising, for each process unit, loading a wafer into the process unit by means of the robotic arm, adjusting the position of the wafer in the process unit by means of the robotic arm, and memorizing the position of the robotic arm for the process unit when the wafer has reached a desired position. According to one embodiment, loading and positioning the wafer in each process unit is performed in accordance with the method previously defined. 
         [0019]    In an embodiment, a device is also provided for helping positioning a semiconductor wafer into a process unit, configured to be introduced into a process unit, and comprising a camera configured to acquire an image of markers in relation to which the position of a semiconductor wafer is to be adjusted, and an image processing circuit for generating images which can be visualized on a display screen. 
         [0020]    According to one embodiment, the device comprises as many cameras as markers to be visualized in the process unit to perform the setting of the position of the wafer in the process unit. 
         [0021]    According to one embodiment, the image processing circuit is configured to simultaneously display the images acquired by all the cameras. 
         [0022]    According to one embodiment, the device is configured to be fixed to the process unit as a replacement for a cover part of the process unit. 
         [0023]    According to one embodiment, the device comprises one or two elements for lighting markers for each camera. 
         [0024]    According to one embodiment, the device comprises a circuit for monitoring the temperature in the oven unit, configured to generate an alarm signal if the temperature measured exceeds a threshold value. 
         [0025]    According to one embodiment, the device is configured to be mounted onto a cover part of a process unit. 
         [0026]    According to one embodiment, the process unit is an oven unit of a machine of DNS SK2000 type. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0027]    Some embodiments will be described hereinafter in relation with, but not limited to the appended figures wherein: 
           [0028]      FIG. 1  schematically shows in cross-section an oven unit in open configuration with a semiconductor wafer being inserted into the oven, 
           [0029]      FIG. 2  shows in top view a wafer on a support plate of oven unit, 
           [0030]      FIG. 3  schematically shows in cross-section an oven unit in closed configuration, with a semiconductor wafer inside, 
           [0031]      FIG. 4  schematically shows a device for helping setting the deposit position of a wafer in an oven unit, according to one embodiment, 
           [0032]      FIG. 5  is a schematic side view of an acquisition module of the setting helping device shown in  FIG. 4 , 
           [0033]      FIG. 6  schematically shows in front view the acquisition module shown in  FIG. 5 , 
           [0034]      FIG. 7  schematically shows in cross-section an oven unit equipped with the acquisition module, 
           [0035]      FIG. 8  shows a visualization screen displaying images supplied by the acquisition module. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]      FIG. 1  shows an oven unit  10  in an open configuration, for example of a machine of DNS SK-2000 type. The oven unit  10  comprises a lower part  11   a,  a cover  11   b  and a frame  15  fixed to the cover and forming lateral partitions of the oven unit. The lower part  11   a  of the oven unit houses a plate  12  to support a semiconductor wafer, and pins  13   a  to  13   f  perpendicular to the plate  12 , crossing the plate and having a higher face spreading out above the plate.  FIG. 1  also shows a semiconductor wafer  1  maintained by a robotic arm  19 , being inserted into the oven unit  10 . 
         [0037]      FIG. 2  shows the plate  12  of circular shape and a semiconductor wafer  1  maintained above the plate by the pins  13   a - 13   f . In  FIG. 2 , the pins  13   a - 13   f  are distributed in the oven unit so as to be able to support the wafer  1  by its periphery and to maintain it substantially parallel and centered above the plate  12 . To that end, each pin  13   a - 13   f  comprises a lug  14  formed on the higher face of the pin to prevent the wafer from laterally sliding and maintain it in a position substantially centered above the plate  12 . The pins allow the robotic arm  19  to maintain the wafer from below, to deposit it into the oven and to be removed from the oven after depositing the wafer onto the pins. 
         [0038]    The wafer conventionally has a circular shape, with scribe lines  5  allowing the chips  2  of substantially rectangular shape, on each of which an integrated circuit  3  may be formed, to be separated. 
         [0039]    In the example of  FIG. 2 , there are six pins  13   a - 13   f  which are positioned so as to be evenly distributed around a wafer  1  when the latter is centered in the oven unit  10 . 
         [0040]      FIG. 3  shows the oven unit  10  in closed configuration, the lower edge of the frame  15  being applied against the edge of the lower part  11   a  of the oven unit. During the closing of the oven unit, the pins  13   a - 13   f  completely retract into the plate  12  so that the wafer  1  is only supported by the plate  12 . 
         [0041]    The wafer may be deposited onto the pins  13   a - 13   f , precisely between the lugs  14 , in particular, to ensure a uniform temperature distribution during the process of the wafer  1  in the oven unit  10 . The accurate positioning of the wafer in the oven unit is also desirable due to the diameter of the pins which is relatively low to avoid the pins from affecting the uniformity of temperature distribution on the wafer during the process thereof. Indeed, if the wafer is not centered above the plate  12 , it may fall between the pins  13   a - 13   f  when the robotic arm  19  deposits it onto the pins and is removed from the oven unit. 
         [0042]      FIG. 4  schematically shows a device for helping setting the deposit position of a wafer in an oven unit, according to one embodiment. The setting helping device comprises an acquisition module  20  for acquiring the position of the wafer  1  in relation to each pin  13   a - 13   f , and an interface module INTM. The module INTM is configured to connect the acquisition module  20  to a computer  30  and supply to the acquisition module  20  the supply voltages for operating the acquisition module. The acquisition module  20  comprises one or more cameras  26  to acquire an image showing each pin and the position of the edge of the wafer  1  in relation to the pin. The interface module INTM comprises a power supply circuit PWC powering the module  20  and a video server VSRV connected to the cameras  26  and generating from the signals supplied by the cameras  26  images which can be used by the computer  30 . The images generated by the server VSRV are transmitted to the computer  30 . The computer  30 , for example of portable type, has a software adapted to the process and display of the images supplied by the server VSRV, and a screen  31  to display them. 
         [0043]      FIGS. 5 to 6  show the acquisition module  20 . The acquisition module  20  comprises a printed circuit board  21  on which the camera modules  22   a - 22   f,  each comprising a camera  26 , are mounted. Each module  22   a - 22   f  is associated to a lighting device comprising for example two light-emitting diodes  27 ,  28  ( FIG. 6 ) arranged on each side of the objective of the camera module. The diodes  27 ,  28  supply for example white light. 
         [0044]    The number of camera modules  22   a - 22   f  may be provided equal to the number of pins  13   a - 13   f  of the oven unit. Thus, in the example of  FIGS. 2 and 6 , the acquisition module  20  comprises six camera modules  22   a - 22   f , each comprising a camera  26 , distributed on the board  21  so as to be able to supply images of each pin  13   a - 13   f.    
         [0045]    The acquisition module  20  may also comprise a module for monitoring the temperature comprising a temperature sensor  29  and an audio signal transmitter  24 , and a circuit for processing the signal supplied by the sensor  29  to trigger the transmission of an audio signal if the temperature measured by the sensor exceeds a certain threshold value. The whole consisting of the sensor  29 , the transmitter  24  and the processing circuit is for example mounted on a board  23 . Thus, if the acquisition module  20  is placed in a too hot oven that may damage the cameras  26  in particular, an audio signal is emitted. It may also be provided to send an alarm signal to the interface module INTM which may then emit an audio signal if the temperature measured by the sensor  29  exceeds the threshold value. 
         [0046]      FIG. 7  shows an oven unit  10  in open configuration, a wafer  1  being maintained on the pins  13   a - 13   f  by the robotic arm  19 . The acquisition module  20  is associated to the oven unit  10 , by being fixed to the frame  15  previously separated from the cover  11   b.  To that end, the board  21  has a shape and dimensions adapted to those of the frame  15 , the camera modules  22   a - 22   f  being fit into the frame  15  and positioned so that each may supply an image of a pin  13   a - 13   f.    
         [0047]    In an embodiment, the cameras  26  of the modules  22   a - 22   f  are cameras with fixed focal distance and without focusing setting. The modules  22   a - 22   f  are then mounted above the board  21  using spacers  22  which height is adjusted so that the images of the pins  13   a - 13   f  supplied by the cameras are clear. 
         [0048]    In another embodiment, the cameras  26  of the modules  22   a - 22   f  are of autofocus type, and adjust the clearness of the image so that the higher surface of each pin  13   a - 13   f  is clear in the images supplied. In this case, the spacers  22  may not be required. 
         [0049]      FIG. 8  shows a composite image  40  displayed by the computer  30 . The composite image  40  comprises an image of a pin  41   a - 41   f  supplied by each camera module  22   a - 22   f . Each image of pin  41   a - 41   f  shows the edge of the wafer  1 , one of the pins  13   a - 13   f  and the lug  14  formed on the pin. The operator may thus visualize the precise position of the edge of the wafer  1  in relation to each pin  13   a - 13   f  and particularly in relation to the lug  14  of each pin, and control the robotic arm  19  so as to position the wafer  1  in a precise position in relation to each pin, so that the edge of the wafer is at a same distance from each lug  14 . To that end, the image processing software installed in the computer  30  may be configured to allow one or more images of pins  41   a - 41   f  previously selected by the operator to be magnified. When the wafer  1  is properly positioned in relation to the pins  13   a - 13   f , the operator can control the memorization of the position of the robotic arm  19 . 
         [0050]    The cameras  26  may be equipped with a zoom controlled by the image processing software, so as to be able to adjust the size of the portion of image  41   a - 41   f  of each pin. 
         [0051]    It will be clear to those skilled in the art that the present disclosure is susceptible of various other embodiments and applications. In particular, the disclosure does not only apply to ovens, or to a particular type of oven unit, or to an oven unit comprising a particular number of pins, but to any process unit wherein it is desirable for the wafer to be precisely positioned. In addition, other markers than pins may be used to evaluate the position of the wafer in the oven unit. 
         [0052]    It is not required either that the number of camera modules corresponds to the number of pins. It may thus be provided that each camera module supplies an image of several pins. If the dimensions of the oven unit make it possible, the acquisition module may comprise only one camera module supplying a complete image of the wafer  1  and therefore of the pins distributed at the periphery of the wafer. 
         [0053]    These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.