Abstract:
For effecting a uniform temperature distribution in a wafer in a process chamber, a support apparatus for a wafer is disclosed, comprising support means for supporting the wafer, temperature homogenization means arranged peripherally regarding to the wafer to provide a uniform thermal environment for the wafer, temperature homogenization means consisting of a plurality of segments, at least one of the plurality of segments being movable with regard to the other segments to enable supply and removal of the wafer to and from support means. By the fact that the at least one segment is movable with regard to the other segments, it can be elevated when introducing the wafer and can then be lowered during a process step at the wafer such that temperature homogenization means provides a uniform thermal environment for the wafer. Thereby it is made sure that in material depositioning processes an even layer thickness (uniformity) on the wafer will be achieved.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention refers to a support apparatus for a wafer, which is mainly provided in a process chamber of a rapid thermal processing system.  
           [0003]    2. Description of Prior Art  
           [0004]    Wafer are thin flat disks out of a semiconductor crystal for the production of integrated circuits. For this purpose, certain material layers are disposed on the wafer surface in several process steps and then structured in several masking, etch and doping steps to generate the desired circuits. Some of the layers have to be subject to a so-called annealing process of the lattice structures afterwards. Such a treatment of material layers on the wafer surface is carried out in process chambers of RTP-systems, such as the SHS 2800 of Steag AST (now: Mattson). With RTP-systems, high temperature processes can be limited to a very short time span.  
           [0005]    [0005]FIG. 1 shows a schematic cross section view of a process chamber of the above mentioned RTP system. The actual process chamber (“tube”)  2 , consisting of quartz glass, for example, has an inlet for fluids on its right side. A front or press plate  6  is provided on the left side of the process chamber  2 , having an opening  8  leading to an interior  10  of process chamber  2 . Further, a chamber door  12  is provided serving for closing the opening  8  and thus the process chamber  2 . Specific lamps  14  are provided at the top and bottom sides of the process chamber  2 , enabling heating up of the chamber interior  10  or a wafer  22  in there, respectively, to process temperature in shortest possible time. A support apparatus  20  is provided in the chamber interior  10 , whereon a wafer  22  is supported via support elements provided therefore.  
           [0006]    As can be seen in FIG. 2, illustrating a top view of the wafer support apparatus  20 , wherein process chamber  2  and chamber door  12  are omitted, the wafer  22  is carried by support means  20  at three contact points  24 . Peripheral to wafer  22 , a temperature homogenization means is provided in form of a so-called slip guard ring  26  divided into two levels, consisting of four segments each.  
           [0007]    As can be seen best in the perspective view in FIG. 3, the upper level of the slip guard ring  26  has three segments on the side facing way from the front plate  6 , lying in one level, and one segment  27  on the side facing the front plate  6 , which is fixedly disposed in an elevated way to enable supply or delivery and removal of the wafer  22  from the wafer support apparatus or wafer tray  20 , respectively. As can further be seen in FIG. 3, the three segments  26  of the upper level facing away from the front plate  6  are on one level with wafer  22 . The four segments of the lower level are arranged in one level and are below the four segments of the upper level. Both the segments of the upper and lower levels are supported by support arms  28 , attached to a frame part  30  of support apparatus  20 . The totality of support means  20  (including support arms  28 ) and slip guard ring  26  is referred to as support apparatus (also wafer tray).  
           [0008]    In the following, the method for removal of the wafer from the wafer support means  20  will be discussed with reference to FIG. 1. As can be seen at the left portion of the figure, a wafer handling means  34 , a so-called end effector of a robot, is introduced with opended chamber door  12  into opening  8  into the process chamber interior  10  in the direction of arrow  32 . The end effector  34  will then be moved under the wafer  22  up to the end of arrow  32 , where a front portion of the end effector  34  is fixed to the wafer  22 , for example via a suction means (not shown). As soon as the area of the end effector  34  and the wafer  22  touch, a vacuum builds up, holding the wafer  22  at the end effector  34  when the robot is moving. Afterwards, the end effector  34  raises the wafer  22  by a small amount, so that it is in a position above the three segments of the upper level of the slip guard ring  26 , and finally moves the wafer  22  below the elevatedly disposed segment  27  in direction of arrow  36  through opening  8  out of the process chamber interior  10 . Thereupon, wafer  22  is usually inserted into a storage cassette (not shown) predetermined for that, to be taken out of it for a subsequent processing step. Inserting the wafer  22  proceeds in an analogous way in reverse order.  
           [0009]    If there is a wafer  22  in the interior  10  of process chamber  2 , chamber door  12  (see FIG. 1) is moved up to seal the process chamber interior  10 . After that, the processing procedure, for example depositing of a layer, will be started. As has been noted with reference to FIG. 3, the segment  27  of the upper level of the slip guard ring  26  facing the front plate  6  is disposed elevatedly regarding to the level where the wafer  22  and the other three segments of the lower level are disposed. Since the slip guard ring  26  serves to supply heat to wafer  22 , it can be seen that by a raised storage of the segment  27  in the area of the wafer  22  adjacent to this segment a temperature variation to the other areas of the wafer  22  occurs, which are adjacent to the three segments of the slip guard ring facing away from the front plate  6 . As a result, an uneven layer thickness occurs due to temperature variation in the area  23  of the wafer adjacent to segment  27 , for example in a process step of depositing a material layer on wafer  22 , such as is shown in FIG. 2.  
           [0010]    Especially with a plurality of process steps, this unevenness adds up to a no longer acceptable amount in the layer thickness on the side adjacent to segment  27 . Therefore it is, for example with photolitographic processes, no longer possible to focus this area  23  of the largest layer thickness deviation (“range deviation”) on the wafer, which leads to yield losses in area  23 .  
         SUMMARY OF THE INVENTION  
         [0011]    It is therefore the object of the present invention to provide a support apparatus for a wafer, especially for usage in a process chamber, where a uniform thermal environment i-s provided for the wafer.  
           [0012]    In accordance with a first aspect of the invention this object is achieved by a support apparatus for a wafer comprising a support means for supporting the wafer and a temperature homogenization means, disposed peripherally regarding the wafer to provide a uniform thermal environment for the wafer, the temperature homogenization means consisting of a plurality of segments, at least one of the plurality of segments being movable regarding to the other segments to enable supply and removal of the wafer to and from support means. In contrary to the prior art, where the segment of temperature homogenization means facing the front plate was disposed fixedly elevated to enable the supply and removal of the wafer to and from the support means, the inventive means allows that at least one segment of the plurality of segments of the temperature homogenization means is movable or riseable during supply and removal of the wafer to and from support means, and can be moved back, with the wafer inserted in support means, into a position where the temperature homogenization means can provide a uniform thermal environment to the wafer.  
           [0013]    According to an advantageous embodiment of the invention, the plurality of segments of the temperature homogenization means form one level, the at least one segment being movable regarding to the other segments from the level during supply and removal of the wafer. For providing an optimized uniform heat supply it is advantageous to arrange the plurality of segments of the temperature homogenization means in one level with the wafer. Further, the individual segments of the plurality of segments can be portions of a ring, forming together a ring-shaped temperature homogenization means, a so-called slip guard ring.  
           [0014]    According to another advantageous embodiment, the inventive support apparatus comprises a lifting or elevating means for moving the at least one segment of the temperature homogenization means. The lifting means can be built in form of a lifting or elevating fork, comprising a frame part with a portion where a plurality of support arms are provided that engage at predetermined locations of the at least one movable segment of the temperature homogenization means. Thereby it is possible, that projection portions are formed at the support arms, engaging predetermined recessions of the one movable segment of the temperature homogenization means. This lifting fork can then be activated by an electrical or mechanical means. Mechanical means can especially comprise a pneumatic liftinging cylinder and a pneumatic linear unit, respectively. Advantageously, support means of the inventive support apparatus is made of quartz glass.  
           [0015]    According to another advantageous embodiment, the inventive support apparatus further comprises second temperature homogenization means arranged peripherally regarding to the wafer below the first temperature homogenization means. This second temperature homogenization means can therefore consist of a plurality of segments, like first temperature homogenization means. The segments of respective temperature homogenization means can thereby consist of silicon.  
           [0016]    According to another aspect, the present invention provides a process chamber for treating a wafer comprising a process area where a support apparatus for a wafer is provided, as defined above. Advantageously, the process chamber further comprises a chamber door for opening and closing the process chamber, the at least one moveable segment of temperature homogenization means of the support apparatus being moved depending on the opening state of the chamber door. This means, the moving of the one movable segment of temperature homogenization means, i.e. raising and lowering the segment, can-be controlled automatically in accordance with a door opening signal. Thereby it is possible, that with opened chamber door the at least one movable segment of the temperature homogenization means can be moved into a position where a wafer can be supplied to or removed from the support means, and is, with closed chamber door, moved into a position where temperature homogenization means surrounds the wafer evenly. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    Preferred embodiments of the present invention will be discussed in more detail with reference to the accompanying drawings. They show:  
         [0018]    [0018]FIG. 1 a cross sectional view of a process chamber arrangement of the prior art, taken along line A-A of FIG. 2;  
         [0019]    [0019]FIG. 2 a top view of a support apparatus arranged in a process chamber of the prior art, where, in contrary to FIG. 1, process chamber walls, heating means and heating elements, respectively, and chamber door are omitted;  
         [0020]    [0020]FIG. 3 a perspective view from the side and from the top of the support apparatus of the prior art shown in FIG. 2;  
         [0021]    [0021]FIG. 4 a perspective view from the side and from the top of support means of the inventive support apparatus;  
         [0022]    [0022]FIG. 5 a top view of a movable segment of temperature homogenization means of the inventive support apparatus;  
         [0023]    [0023]FIG. 6 a lifting fork for engagement with the movable segment shown in FIG. 5  
         [0024]    [0024]FIG. 7 a perspective view of a back side of a front plate of a RTP-system furnace where the inventive support apparatus is provided, the walls of the process chamber arranged around the support apparatus as well as heating means and chamber door being omitted; and  
         [0025]    [0025]FIG. 8 a front side of the front plate illustrated in FIG. 7 with the inventive support apparatus, wherein also the walls of the process chamber surrounding the support apparatus as well as heating means and chamber door are omitted. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]    For the illustration of an embodiment of the inventive support apparatus, reference is first made to FIG. 7, where the inventive support apparatus  100 , consisting mainly of support means (“wafer tray”)  120  and temperature homogenization means (“slip guard ring”)  122  is shown in an assembly representation.  
         [0027]    As it is shown in more detail in FIG. 4, support means  120  preferably consists of quartz glass and has an U-shaped frame  124  at whose portion shown on the right side in the Figure a strut  126  is provided. Further, on this portion illustrated at the right side, fixing elements  128  are provided, that are attached to the back side of the front plate of an RTP-system furnace at connecting portions  130 , as shown in FIGS. 7 and 8, to hold the support apparatus  100  in the process chamber (corresponding to FIG. 1, where the support apparatus of the prior art is shown in an inserted state).  
         [0028]    Support means  120  further has three support arms  132 , at whose side facing away from the frame portion  124  respective contact portions  134  are provided, on which a wafer  160  can be disposed via plugged-in pins, as it is shown in FIG. 7. Above that, the frame part  124  has support arrangements  136  having lower support arms with lower centering portions  140  and upper support arms  124  with upper centering portions  144 . The support arrangements  136  make it possible to attach the temperature homogenization means  122  (see FIG. 7) consisting of a ring of a lower level and an upper ring  146 , respectively, with segments  146   a - 146   d,  and a ring of a lower level and a lower ring  148 , respectively, with segments  148   a - 148   d  in an exact way with regard to position on support means  120 .  
         [0029]    As can be seen in FIG. 7, the upper  146  and lower ring  148  of temperature homogenization means  122  are divided into four segments each. Starting from the segment on the side of the ring facing the front plate  6 , the individual ring segments are to be designated with the letters a, b, c, d in the clockwise direction, even when some segments of the lower ring  148  can not be seen in the Figure. The individual segments  146   a  to  146   d  and  148   a  to  148   d  are preferably made of silicon.  
         [0030]    First, reference is made to the lower ring  148 , whose segments  148   a  to  148   d  are arranged in one level. As can be seen in FIG. 4, in connection with FIG. 7, the segment  148   c  facing away from the front plate  6  is supported by portions of the support arms  138  as well as by projection portions  147  of the support arms  132  and held in position by the lower centering portions  140 . The segments  148   b  and  148   d  are also supported by portions of the lower support arms  138  as well as by projection portions  149  of the support arms  132  and by projection portions  150  of the frame part  124  and held in position by the lower centering portions  140 . The segment  148   a  is supported by portions of the lower support arms  138  as well as by a support portion  152  of the strut  126  and held in position by respective lower centering portions  140 .  
         [0031]    Reference is now made to the upper ring  146 , whose segments  146   b  to  146   d  are supported in one level rigidly above the segments  148   b  to  148   d.  The segment  146   c  is thereby supported by portions of the support arms  142  as well as by a support portion  154  of the support arm  132  and held in position by respective upper centering portions  144 . The segments  146   b  and  146   d  are also supported by portions of the upper support arms  142  as well as by projections  156  at an upper strut  158  of a respective support arrangement  136  and held in position by respective upper centering portions  144 .  
         [0032]    In contrary to the prior art, the segment  146   a  facing the front plate  6  is not arranged rigidly above the level formed by segments  146   b  to  146   d,  to enable supply and removal of a wafer, respectively, to and from the support means  120 , respectively, but is movably arranged, as it is particularly illustrated by arrow  159  in FIG. 7.  
         [0033]    This movement of segment  146   a,  as well as the movement mechanism belonging to it will now be discussed. As it is shown in FIG. 7 by continuous lines, the movable segment  146   a  is in one level with the other segments  146  to  146   d  of the upper ring  146 , when a wafer  160  has been inserted into the inventive support apparatus  100  for treatment and processing, respectively,. More specifically, in this state the wafer  160  rests on the contact portions  134  of the plugged-in pins of the support arms  132  (see FIG. 4) and is surrounded along its periphery by rings  146  and  148  of temperature homogenization means  122 . To provide a thermal surrounding for wafer  160  that is as uniform as possible, all segments, including segment  146   a  of the upper ring  146 , are, in contrary to the prior art, in one level with regard to each other and are preferably in one level with wafer  160 . Below the wafer  160  is a so-called hotliner, i.e., a wafer with three bores, surrounded by the lower slip guard ring  148 .  
         [0034]    The slip guard rings  146 ,  148  serve for the prevention of thermal differences in the margin area of the so-called hotliner, upon which the actual product wafer  160  rests. Such thermal differences would occur without the slip guard rings  146 ,  148 , due to the so-called “photon box effect” and the edge effect. The so-called “photon box effect” occurs during the heat up procedure and causes the edges of the wafer to be hotter than its center. During the steady state the edge effect occurs, which means that the edges of the wafer are colder than its center.  
         [0035]    In contrary to the prior art, the rings  146  and  148  prevent that temperature variations or temperature deviations occur in wafer  160 , that would lead to an uneven layer thickness or a “range deviation”, especially in material depositioning steps, as it has been discussed with reference to FIG. 2 regarding to area  23 .  
         [0036]    To be able to remove wafer  160  from support apparatus  100  after a processing step via robot handling means or robot end effector  162 , it is necessary that the movable segment  146   a  is moved out of the level with the other segments  146   b  to  146   d,  and the wafer  160 , respectively. For that purpose, the segment  146   a  is positioned on a lifting fork  164 , preferably made of quartz glass, by which the segment  146   a  can carry out a movement according to arrow  159  perpendicular to the level of the ring  146  (in FIG. 7 upwards). As it is illustrated in more detail in FIG. 6, lifting fork  164  consists of a mainly U-shaped frame part  166 , at whose front portion three support arms  168  and at whose back portion at legs  167  respective mounting portions  170  are provided. The length of support arms  168  is dimensioned such that projection portions  172  provided on the end of support arms  168  facing away from the frame part  166  can engage with recessions  174  of the movable segment  146   a  as illustrated in a top view in FIG. 5. The mounting portions  170 , however are attached at lifting rams  176  of a lifting apparatus  178 .  
         [0037]    As can be seen best in FIG. 8, lifting apparatus  178  has a pneumatic linear unit  180 , which is disposed on the front plate  6  of the furnace of the RTP-system. It should be noted that instead of the pneumatic linear unit other mechanical or electrical drive means can be used as well. At the top of the pneumatic linear unit  180  a piston  182  protrudes, which is movable in the longitudinal direction of the pneumatic linear unit, i.e. upwards and downwards in the level of front plate  6 . A mainly U-shaped support part  184  is attached to this piston  182 , respective lifting rams  176  are attached at its upper leg portions  186 . Thereby, the respective lifting rams  176  are surrounded by a membrane bellows  188  across a certain distance, starting from the upper leg portions, to provide a sealed feed-through for the lifting ram  176 .  
         [0038]    In FIGS. 7 and 8, a lower position is illustrated by continuous lines, where all parts of lifting apparatus  178  including lifting ram  176  as well as lifting fork  164  are lowered such that the movable segment  146   a  is in one level with the other segments  146   b  to  146   d,  as it is requested during a processing step and a process step, respectively. The dash-dotted lines, however, show an upper state, where lifting means  178  including lifting ram  176  and lifting fork  164 , are risen such that the movable segment  146   a  is above the level of the upper ring  146  by a predetermined amount (in the practical embodiment about 8 mm). This state, corresponding essentially to the state shown in FIG. 1, makes it possible that a robot end effector  162  moves in the direction of arrow  190  in a position below wafer  160 , fixes it by sucking at its end portion, raises it slightly above the level of segments  146   b  to  146   d  and removes it from the process chamber through the opening  8  of the front plate. It should be noted that the legs  167  of the frame part  166  of the lifting fork  164  are spaced that far apart from each other that it is possible to move the wafer  160  between them for supply and removal, respectively.  
         [0039]    After removing the wafer  160 , a new wafer can be inserted by the robot end effector  162  in respective reverse order into the process chamber and the support apparatus  100  in it, respectively. Like in the process of removing the wafer  160 , when inserting the wafer the lifting apparatus  178  including the lifting ram  176  and lifting fork  164  is also in an upper position, to enable moving the wafer  160  into the upper ring  146  via the robot end effector  162 . After the wafer has been placed on the contact portions  134  of support means  120 , end effector  162  will be disengaged from the wafer and moves out of the process chamber in the direction of arrow  190 . To provide again a uniform and homogenous thermal environment for the wafer  160 , respectively, the lifting apparatus  178  including lifting  176  and lifting fork  164  is brought into a lower position, so that the movable segment  146   a  is lowered into a position where it is in one level with the other segments  146   b  to  146   d  and the wafer  160 . As soon as the chamber door  12  (see FIG. 1) closes process chamber  2 , treatment and processing, respectively, of the wafer can begin.  
         [0040]    According to another embodiment of the present invention it is possible to control the movement and the activation of the lifting apparatus  178 , respectively, automatically depending on the position of the chamber door  12 . The lifting apparatus  178  is, for example, directed to take up an upper position where the movable segment  146   a  is above the level of segments  146   b  to  156   d,  when the chamber door is in a position where the opening of the front plate is not covered by it and the process chamber is opened, respectively. Consequently, the lifting apparatus  178  is directed to take up a lower position where the movable segment  146   a  is in one level with the other segments  146   b  to  146   d  of ring  146  when the chamber door  12  covers opening  8  and thus closes the process chamber to carry out a processing step and a process step, respectively, at a wafer  160 .  
         [0041]    This way it is automatically made sure that the segments of the respective rings  146  and  148  are in one level, respectively, to obtain the already described homogenization of the temperature distribution on the wafer.  
       REFERENCE NUMBER LIST  
       [0042]    [0042] 2  process chamber  
         [0043]    [0043] 4  inlet  
         [0044]    [0044] 6  front plate  
         [0045]    [0045] 8  opening  
         [0046]    [0046] 10  process chamber interior  
         [0047]    [0047] 12  chamber door  
         [0048]    [0048] 14  heating elements  
         [0049]    [0049] 20  support means  
         [0050]    [0050] 22  wafer  
         [0051]    [0051] 23  area of uneven layer thickness  
         [0052]    [0052] 24  contact points  
         [0053]    [0053] 26  heat transfer means/slip guard ring  
         [0054]    [0054] 27  fixed elevatedstored segment  
         [0055]    [0055] 28  support arms  
         [0056]    [0056] 30  frame part  
         [0057]    [0057] 32  arrow direction into  10   
         [0058]    [0058] 34  robot end effector  
         [0059]    [0059] 36  arrow direction out of  10   
         [0060]    [0060] 100  support apparatus  
         [0061]    [0061] 120  support means  
         [0062]    [0062] 122  heat transfer means/slip guard ring  
         [0063]    [0063] 124  O-shaped frame part of  120   
         [0064]    [0064] 126  strut for stabilizing  124   
         [0065]    [0065] 128  mounting end portion  
         [0066]    [0066] 130  connecting portions for attaching  128   
         [0067]    [0067] 132  support arms for  134   
         [0068]    [0068] 134  contact portions  
         [0069]    [0069] 136  support arrangements  
         [0070]    [0070] 138  lower support arms for  140   
         [0071]    [0071] 140  lower centering portions  
         [0072]    [0072] 142  upper support arms for  144   
         [0073]    [0073] 144  upper centering portions  
         [0074]    [0074] 146  upper ring  
         [0075]    [0075] 147  protection portions for  148   c    
         [0076]    [0076] 148  lower ring  
         [0077]    [0077] 149  projection portions for  148   b, d    
         [0078]    [0078] 150  projection portions at  124   
         [0079]    [0079] 152  support portion of  126   
         [0080]    [0080] 154  support portion of  132   
         [0081]    [0081] 156  projections at  158   
         [0082]    [0082] 158  upper strut of  136   
         [0083]    [0083] 159  arrow direction of the movement of  146   a    
         [0084]    [0084] 160  wafer  
         [0085]    [0085] 162  end effector  
         [0086]    [0086] 164  lifting fork  
         [0087]    [0087] 166  U-shaped frame part of  164   
         [0088]    [0088] 167  leg of  166   
         [0089]    [0089] 168  support arms to  166   
         [0090]    [0090] 170  mounting portions  
         [0091]    [0091] 172  projection portions of  168   
         [0092]    [0092] 174  recessions at  164   a    
         [0093]    [0093] 176  lifting ram  
         [0094]    [0094] 178  lifting apparatus  
         [0095]    [0095] 180  pneumatic linear unit  
         [0096]    [0096] 182  piston to  180   
         [0097]    [0097] 184  U-shaped support part  
         [0098]    [0098] 186  upper leg portions of  184   
         [0099]    [0099] 188  membrane bellows  
         [0100]    [0100] 190  arrow direction into/out of process chamber