Patent Publication Number: US-9835377-B2

Title: Support device for a plurality of wafers for a vertical oven

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry under 35 U.S.C. §371 of International Patent Application PCT/IB2013/001824, filed Aug. 20, 2013, designating the United States of America and published in English as International Patent Publication WO 2014/037777 A1 on Mar. 13, 2014, which claims the benefit under Article 8 of the Patent Cooperation Treaty and under 35 U.S.C. §119(e) to France Patent Application Serial No. 1202435, filed Sep. 10, 2012, the disclosure of each of which is hereby incorporated herein in its entirety by this reference. 
     TECHNICAL FIELD 
     The present invention concerns a support device for a plurality of wafers. 
     BACKGROUND 
     A known prior art support device for a plurality of wafers, shown in  FIGS. 1A and 1B , is a support device for a plurality of wafers, the support device  10  being adapted to be loaded into a heat treatment oven, the support device  10  having a central axis, the support device  10  including: 
     three uprights  30 ,  31  and  32  extending substantially parallel to the central axis, 
     a plurality of series of support members  35  spaced along the central axis, each series of support members  35  comprising three support members  40 ,  41  and  42  adapted to support one wafer W of the plurality of wafers and extending in different essentially longitudinal directions transverse to the central axis, each support member  40 ,  41  and  42  being mounted directly on a separate upright. 
     Accordingly, a heat treatment step consists in positioning a support device  10  containing a plurality of wafers W in a vertical heat treatment oven (not shown). Each series of support members  35  of the support device  10  includes three support members  40 ,  41  and  42 , the function of which is to hold a wafer W in a horizontal position.  FIG. 1B  shows the positioning of a wafer W relative to the support members  40 ,  41  and  42 . The support members are mounted directly on separate uprights  30 ,  31  and  32  and the disposition of the support members  40 ,  41  and  42  is adapted to ensure that a wafer W is held in a stable equilibrium position. Inside the vertical heat treatment oven, heating elements are disposed around a quartz tube into which the support device  10  is inserted. The wafers disposed horizontally in the support device  10  are heated radially by the heating elements. However, the support members  41  and  42  block some of the radiant flux during a heat treatment step and a locally heterogeneous temperature field is observed over the volume of the wafer W at the level of the support members  41  and  42 , as shown in  FIG. 2  (the shaded area symbolizing the flow of heat in the vicinity of the support member  41 ). 
     If the requirements in terms of homogeneous heat treatment are imperatives, such a temperature gradient is not acceptable. 
     Moreover, a homogeneous temperature of the wafers during a heat treatment step is required when depositing or forming thin layers of materials having a highly uniform thickness. 
     BRIEF SUMMARY 
     The present invention aims to remedy the aforementioned disadvantage and concerns a support device for a plurality of wafers, the support device being adapted to be loaded into a heat treatment oven, the support device having a central axis, the support device including: 
     three uprights extending substantially parallel to the central axis, 
     a plurality of series of support members spaced along the central axis, each series of support members comprising three support members adapted to support one wafer of the plurality of wafers and extending in different essentially longitudinal directions transverse to the central axis, each support member being mounted directly on a separate upright, the support device being remarkable in that the directions of the three support members of each series of support members are concurrent at a point on the central axis. 
     By central axis is meant the vertical axis of the support device when it is being used in a vertical heat treatment oven. A wafer intended to be supported by a series of support members has the central axis passing through its center when the wafer is positioned on the series of support members. 
     Accordingly, when the support device supports a plurality of wafers and is being used in a vertical oven, the directions concurrent at a point on the central axis of the three support members of each series of support members enable the radial radiant flux to propagate uniformly without blocking any of the flux. 
     In one embodiment, the support members of each series of support members are adapted to essentially form a point contact with the corresponding wafer. 
     Accordingly, holding the wafers so that there is essentially a point contact with the wafer making it possible to minimize the area of contact between the wafers and the support members. 
     Moreover, minimizing the area of contact between the wafers and the support members makes it possible to improve the radiant flux during a step of heat treatment of the wafers supported by the support device when it is being used in a vertical oven. 
     In one embodiment, the support members are distributed substantially uniformly along the central axis. 
     Accordingly, such a distribution enables much better equilibrium of the wafers. 
     The present invention also relates to a support device for a plurality of wafers, the support device being adapted to be loaded into a heat treatment oven, the support device having a central axis, the support device including: 
     three uprights extending substantially parallel to the central axis, 
     a plurality of series of support members spaced along the central axis, each series of support members comprising three support members delimiting a central area, the three support members of the series of support members being adapted to support one wafer of the plurality of wafers in the central area, the central areas of all the series of support members defining a cylinder, the axis of which is the central axis, the three support members of each series extending in different essentially longitudinal directions transverse to the central axis, each support member being connected to a separate upright, each series of support members includes at least two connecting arms, each connecting arm being adapted to connect a support member to an upright, each connecting arm being contained within a peripheral area of the cylinder, the support device being remarkable in that the directions of the three support members of each series of support members are concurrent at a point on the central axis. 
     By peripheral area is meant the area adjacent the central cylinder and extending radially relative to the central cylinder. 
     Accordingly, when the support device supports a plurality of wafers and is being used in a vertical oven, the directions of the three support members of each series of support members concurrent at a point on the central axis enable the radial radiant flux to propagate uniformly. 
     The presence of the connecting arms makes it possible to decorrelate the distribution of the connecting members and the uprights. Thus, the function of a connecting arm is to offset the support member relative to the upright to which it is connected. This advantageously minimizes the overall size of the support device and thus enables use of the support device in a vertical oven of smaller volume. 
     The disposition of the connecting arms in the peripheral area makes it possible to avoid any disturbance or blocking of any of the radiant flux when the device is being used. The temperature distribution of the wafer during a heat treatment step in a vertical oven is therefore uniform. 
     In one embodiment, the support device comprises a cylinder portion and a peripheral area portion, the cylinder portion being the volume of the cylinder contained between two successive central areas along the central axis and the peripheral area portion extending radially relative to the cylinder portion, the connecting arms being disposed in the peripheral area portion. 
     By peripheral area portion is meant the area adjacent the cylinder portion and extending radially relative to the cylinder portion. 
     Accordingly, this disposition of the connecting arms advantageously prevents them from constituting an obstacle to the propagation of the radiant flux toward the wafers. 
     In one embodiment, the support members of each series of support members are adapted to essentially form a point contact with the corresponding wafer. 
     Accordingly, holding the wafers so that there is essentially a point contact with the wafer making it possible to minimize the area of contact between the wafers and the support members. 
     Moreover, minimizing the area of contact between the wafers and the support members makes it possible to improve the radiant flux during a step of heat treatment of the wafers supported by the support device when it is being used in a vertical oven. 
     In one embodiment, the uprights are disposed, in cross section, in an angular space around the central axis less than 180°. 
     In one embodiment, the support members of each series of support members are transversely distributed substantially uniformly along the central axis. 
     Accordingly, the uniform distribution of the support members around the central axis of the support members advantageously achieves complete radial symmetry of each series of support members. 
     Moreover, such a distribution enables much better equilibrium of the wafers. 
     The invention is advantageously completed by the following features separately or in any technically feasible combination: 
     the connecting arms are straight, 
     the connecting arms are curved. 
     The two embodiments presented above are linked to form a single inventive general concept consisting in the directions of the three support members of each series being concurrent at a point on the central axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features, aims and advantages of the invention will emerge from the following description, which is purely illustrative and is not limiting in the invention, and which should be read in conjunction with the accompanying drawings in which, in addition to  FIGS. 1A, 1B and 2  already discussed: 
         FIGS. 3A to 3C  are diagrams showing a support device in accordance with the invention; and 
         FIGS. 4A to 4C  are diagrams showing the support device in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     For the various embodiments, to simplify the description, the same references are used for elements that are identical or have the same function. 
     A support device  110  shown in  FIGS. 3A to 3C  is a device for supporting a plurality of wafers, the support device  110  being adapted to be loaded into a heat treatment oven, the support device  110  having a central axis, the support device  110  including: 
     three uprights  130 ,  131  and  132  extending substantially parallel to the central axis, 
     a plurality of series of support members  135  spaced along the central axis, each series of support members  135  comprising three support members  140 ,  141  and  142  adapted to support one wafer W of the plurality of wafers and extending in different essentially longitudinal directions transverse to the central axis, each support member  140 ,  141  and  142  being mounted directly on a separate upright  130 ,  131 ,  132  and the directions of the three support members  140 ,  141  and  142  of each series of support members  135  are concurrent at a point on the central axis. 
     The uprights  130 ,  131  and  132  are advantageously the same length and are parallel to the central axis of the support device  110 . 
     The uprights  131  and  132  have a lateral spacing at least equal to the diameter of the wafers that the support device  110  is adapted to support. This is to allow wafers W to pass between the uprights  131  and  132  in a horizontal position. 
     In a particularly advantageous manner, the uprights  130 ,  131  and  132  are equidistant from the central axis. 
     The series of support members  135  are spaced along the central axis. Each series of support members  135  is adapted to support one wafer W in a horizontal position when the support device  110  is being used. 
     Each series of support members  135  comprises three support members  140 ,  141  and  142 . The support members  140 ,  141  and  142  of each series of support members  135  are mounted directly on the uprights  130 ,  131  and  132 , respectively. 
     The support members  140 ,  141  and  142  of a series of support members  135  are disposed so as to support one wafer W essentially horizontally in a stable equilibrium position. 
     The support members  140 ,  141 ,  142  extend in different directions, the directions being concurrent at a point on the central axis. 
     In a particularly advantageous manner, as shown in  FIG. 3C , the support members  140 ,  141  and  142  of each series of support members  135  are adapted to essentially make a point contact with the corresponding wafer W. The angle between a support member and a perpendicular to the upright on which it is mounted is preferably less than 5°. 
     The support members  140 ,  141  and  142  are advantageously distributed substantially uniformly along the central axis. 
     The present invention also relates to another support device. 
     A support device  210  shown in  FIGS. 4A-4C  is a support device for a plurality of wafers, the support device  210  being adapted to be loaded into a heat treatment oven, the support device  210  having a central axis, the support device  210  including: 
     three uprights  230 ,  231  and  232  extending substantially parallel to the central axis, 
     a plurality of series of support members  235  spaced along the central axis, each series of support members  235  comprising three support members  240 ,  241  and  242  delimiting a central area ZC, the three support members  240 ,  241  and  242  of the series of support members  235  being adapted to support one wafer W from the plurality of wafers in the central area ZC, the central areas ZC of all the series of support members  235  defining a cylinder CC the axis of which is the central axis, the three support members  240 ,  241  and  242  of each series of support members  235  extending in different essentially longitudinal directions transverse to the central axis, each of the support members  240 ,  241  and  242  being connected to a separate upright, each series of support members  235  includes at least two connecting arms  250 , each connecting arm  250  being adapted to connect a support member to an upright, each connecting arm  250  being contained within a peripheral area of the cylinder CC, and the directions of the three support members  240 ,  241  and  242  of each series of support members are concurrent at a point on the central axis. 
     The uprights  230 ,  231  and  232  are advantageously the same length and are parallel to the central axis of the support device  210 . 
     In a particularly advantageous manner, the uprights  230 ,  231  and  232  are equidistant from the central axis. 
     The series of support members  235  are spaced along the central axis. Each series of support members  235  is adapted to support one wafer W in a horizontal position when the support device  210  is being used. 
     Each series of support members  235  comprises three support members  240 ,  241  and  242 . 
     The support members  240 ,  241  and  242  of a series of support members  235  are disposed so as to support one wafer W substantially horizontally in a stable equilibrium position in a central area ZC corresponding to the area occupied by a wafer W. The central area ZC defines a cylinder CC centered on the central axis. At least two of the support members  240 ,  241  and  242  of each series of support members  235  are connected to the uprights  230 ,  231  and  232 , respectively, of the different connecting arms  250 . The connecting arms  250  are disposed in a peripheral area ZP of the central cylinder CC. 
     The support members  240 ,  241  and  242  extend in different directions, the directions being concurrent at a point on the central axis. 
     In a particularly advantageous manner, the support device  210  comprises a cylinder portion PC and a peripheral area portion PP, the cylinder portion PC being the volume of the cylinder CC contained between two successive central areas ZC along the central axis and the peripheral area portion PP extending radially relative to the cylinder portion PC, the connecting arms  250  being disposed in the peripheral area portion PP. 
     The support members  240 ,  241  and  242  of each series of support members  235  are advantageously adapted to essentially form a point contact with the corresponding wafer. 
     The uprights  230 ,  231  and  232  are advantageously disposed, in cross section, in an angular space around the central axis less than 180°. 
     The support members  240 ,  241  and  242  of each series of support members  235  are advantageously transversely distributed substantially uniformly along the central axis. 
     The connecting arms are advantageously straight or curved. 
     The execution of a step of heat treatment of wafers disposed in a support device in accordance with the invention, the device being inserted into a vertical oven, enables greater uniformity of the wafers to be obtained. This result is valid for a support device whether it is equipped with connecting arms or not. 
     Thus, the invention makes it possible to limit blocking of any of the radiant flux by the support members, thus enabling the uniformity of the heat treatment of the wafers to be improved.