Abstract:
A blade assembly for a mechanical wafer handling system. The assembly includes an elongated planar member having a central region, wherein the central region has a first array of openings and a second array of openings, the openings of the first array being arranged substantially symmetrically to the openings of the second array on opposing sides of a central longitudinal axis extending along the length of the planar member and passing through a center point of the central region. The openings in the first array are arranged substantially symmetrically with respect to a perpendicular axis extending along the width of the elongated planar member and passing through a center point of the central region. The openings in the second array are also arranged substantially symmetrically with respect to the perpendicular axis. The assembly also includes a wrist with a wrist upper cap and a wrist lower cap. The wrist upper cap has a first and a second wing support on two opposing sides of the upper cap and a first non-supporting narrow ridge extending between the first and second wing supports. The wrist lower cap has a third and a fourth wing support on two opposing sides of the lower cap with a second non-supporting narrow ridge extending between the third and the fourth wing supports. The wrist upper cap is attached to a top surface of the planar member and the wrist lower cap is attached to a bottom surface of the planar member when the blade assembly is assembled.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to mechanical wafer handling systems for semiconductor processing equipment. 
     Mechanical wafer handling systems transport wafers from wafer carriers to processing chambers and vice versa. Various fabrication processes are carried out in processing chambers, including annealing, oxidation, nitridation, etching, and deposition. The wafer handling system might include a robot, an arm operated by the robot, and an implement at the end of the arm to hold the wafer. 
     Before processing, a wafer may be at room temperature, while in a wafer carrier. During processing, the temperature of a wafer may rise to 1200° C. or higher. Thus, a wafer may be extracted from the chamber while still hot, e.g. 550° C. to 750° C. or higher. Thus, the implement for holding the wafer needs to handle wafers of various temperatures, including hot wafers. 
     SUMMARY OF THE INVENTION 
     In general, in one aspect, the invention features a blade for a mechanical wafer handling system. An elongated planar member has a central region. A first array of openings and a second array of openings are provided within the central region. The openings of the first array are arranged substantially symmetrically to the openings of the second array on opposing sides of a central longitudinal axis extending along the length of the planar member and passing through a center point of the central region. The openings in the first array are arranged substantially symmetrically with respect to a perpendicular axis extending along the width of the elongated planar member and passing through a center point of the central region. The openings in the second array are also arranged substantially symmetrically with respect to the perpendicular axis. 
     Embodiments may include one or more of the following. The first array of openings and the second array of openings comprise two circular openings and two oval openings. One short end of the elongated planar member has a notch. The planar member has a peripheral opening positioned between the openings of the first and second arrays of openings and a second short end of the elongated planar member. Opposing short ends of the elongated planar member have ledges to support a wafer. The elongated planar member is made out of quartz. 
     In another aspect, the invention features a blade assembly for a mechanical wafer handling system. The assembly includes an elongated planar member with a central region. The central region has a first array of openings and a second array of openings. The openings of the first array are arranged substantially symmetrically to the openings of the second array on opposing sides of a central longitudinal axis extending along the length of the planar member and passing through a center point of the central region. The openings in the first array are arranged substantially symmetrically with respect to a perpendicular axis extending along the width of the elongated planar member and passing through a center point of the central region. The openings in the second array are also arranged substantially symmetrically with respect to the perpendicular axis. The assembly also includes a wrist upper cap having a first and a second wing support on two opposing sides of the upper cap and a first non-supporting narrow ridge extending between the first and second wing supports. Further, the assembly includes a wrist lower cap having a third and a fourth wing support on two opposing sides of the lower cap with a second non-supporting narrow ridge extending between the third and the fourth wing supports. The wrist upper cap is attached to a top surface of the planar member and the wrist lower cap is attached to a bottom surface of the planar member when the blade assembly is assembled. 
     Embodiments may also include one or more of the following. The elongated planar member and the first, second, third, and fourth wing supports have screw holes. The screw holes are arranged so that the screw holes in the planar member are aligned with the screw holes in the first, second, third, and fourth wing supports when the blade assembly is assembled. The first ridge and the second ridge are each less than ⅛ thick. The upper and the lower wrist caps are each made out of stainless steel. The upper and lower caps are each coated with anodized nickel. 
     An advantage of the blade is that its arrays of openings significantly reduce the thermal gradients which occur across the hot wafer when it is picked up by the blade. Further, the construction of the wrist assembly substantially reduces its points of contact with the blade, thereby reducing the heat sink effect of the wrist assembly. Finally, the ridges of the transition between the wrist assembly and the blade act as a barrier which prevents particles from reaching the wafer while it rests on the blade. 
     Further aspects, features, and advantages will be found in the following. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a mechanical wafer handling system; 
     FIG. 2 is a top view of blade being held by a wrist assembly; 
     FIG. 3 is a top view of a blade for a mechanical wafer handling system; 
     FIG. 4 is a cross-sectional view of an edge of the blade of FIG. 3; 
     FIG. 5 is a perspective view of the blade of FIG. 3; 
     FIG. 6 is a top view of a wrist upper cap; 
     FIGS. 6A and 7 are cross-sectional views of the wrist upper cap of FIG. 6; 
     FIG. 8 is a perspective view of the wrist upper cap of FIG. 7; 
     FIG. 9 is a top view of a wrist lower cap; 
     FIG.  9 A and FIG. 10 are cross-sectional views of the wrist lower cap of FIG. 9; and 
     FIG. 11 is a perspective view of the wrist lower cap of FIG.  8 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a cluster tool  10  which is typical of the type of system that utilizes a wafer handling robot system described herein. 
     The cluster tool  10  has loadlock chambers  12  and  14 . These chambers  12  and  14  hold wafer cassette(s)  15  in which wafers  16  are stored before and after processing. Loadlock chambers  12  and  14  are kept under vacuum while holding wafer cassette(s)  15  and constitute the only part of cluster tool  10  which is opened to the environment during normal operation. Cluster tool  10  also has a central transfer chamber  17  through which a wafer  16  travels when it is transferred between various stations. The wafer  16  is processed in a process chamber  18 , in which it may undergo any one of a several possible processes, such as oxidation, nitridation, anneal, deposition, or etch. After processing, the wafer is transferred to a cooldown chamber  20  before being returned to loadlock chamber  12  or  14 . If the wafer is hot after processing, in order to avoid contamination of the wafer and damage of cassette  15 , the wafer needs to be cooled before it can be placed in cassette  15 . For this reason, the wafer is cooled in cooldown chamber  20  after processing. A commercially available example of a cluster tool is the Applied Materials Centura platform (Applied Materials, 2881 Scott Boulevard, Santa Clara, Calif. 95050). 
     A robot system  21  transfers a wafer  16  both in and out of as well as between chambers  12 ,  14 ,  17 ,  18 , and  20 . Referring to FIGS. 1 and 2, robot system  21  includes two robot arms  22  and  23  and a blade  24 . Robot arms  22  and  23  each have elbow joints  25  and are pivoted on a central hub  27  to which they are attached at one end. Blade  24  is connected to the other ends of robot arms  22  and  23  by a wrist  26 . During wafer transfer, blade  24  supports the wafer  16 . The wafer  16  may be cold, e.g. coming out of loadlock chamber  12 , or it may be hot, e.g. after being processed in process chamber  18 . 
     As shown more clearly in FIGS. 2 and 3, blade  24  has a central region  28  with two arrays  30  and  32  of openings, with the openings arranged symmetrically in respect to each other. Wafer  16 , while being supported by blade  24 , would cover central region  28  and the edges of the wafer would overhang sides  29  and  31  of blade  24 . 
     Referring to FIG. 3, blade  24  is a substantially planar member with several openings. Array  30  includes openings  36  and  38 , which are elongated slots, located equidistantly from and on opposite sides of a central axis  34  extending along a length of blade  24 . Array  32  includes openings  40  and  42 , which are circular, located equidistantly from and on opposite sides of an axis  43  which is perpendicular to axis  34  and extending across a width of blade  24 . Openings  36 ,  38 ,  40 , and  42  are located and sized to reduce the thermal gradients which form across a hot wafer  16  when it is placed on a cold blade  24 . If the wafer  16  is hot, e.g. over 550° C., the cold blade  24  acts as a heat sink and will create thermal gradients across the wafer  16 . Peripheral parts of the wafer  16  which overhang blade  24  will not cool as fast as the parts of the wafer  16  directly above the blade  24 . The resulting thermal gradients will induce stress in the wafer  16  and, if large enough, that stress can cause the wafer  16  to break. Even if the stresses are not large enough to cause the wafer  16  to break, they may nonetheless induce the formation of slip dislocations in the wafer&#39;s crystal structure, thereby destroying individual devices on the wafer  16  and reducing the wafer&#39;s potential yield of functional devices. To counteract the formation of thermal gradients, blade  24  has openings  36 ,  38 ,  40 , and  42  specifically located and configured to reduce the heat loss at appropriate places on the hot wafer  16 . The portions of the wafer  16  proximate to openings  36 ,  38 ,  40 , and  42  tend to cool more slowly than the portions of the wafer  16  proximate to the material of blade  24 . This is because the material of blade  24  proximate to the wafer  16  acts as a heat sink, and the elimination of blade material reduces the heat sink effect in those areas in which it was eliminated. The particular arrangement and size of holes  36 ,  38 ,  40 , and  42  described herein was determined by using well-known thermal modeling tools and the objective was to significantly reduce thermal stresses without compromising the strength of the blade  24 . 
     One end  44  of blade  24  has a notch  46 . An opposing end  48  of blade  24  has an opening  50 . Both notch  46  and opening  50  help reduce thermal gradients across a wafer  16  supported by blade  24  by reducing the thermal load of blade  24  on the wafer  16 . The dimensions of notch  46  and opening  50  are chosen so as to reduce the mass of blade  24  while not compromising its strength for transferring wafers. Further, when placed in position for processing, wafer  16  rests on three lift pins (not shown). Notch  46  is shaped and located so as to provide clearance to one of these three pins. Blade  24  is inserted between the other two pins, so that the parts of wafer  16  overhanging blade  24  are positioned above the other two pins. 
     Blade  24  is secured to wrist  26  with screws (not shown) at end  48 . End  48  has two wings  52  and  54  which are grasped by wrist  26 . Each wing  52  and  54  has a screw hole  56  and  58  for receiving the screws which attach blade  24  to wrist  26 . Two additional screw holes  60  and  62  for receiving additional screws to attach blade  24  to wrist  26  are located on blade  24  close to screw holes  56  and  58 . 
     Pins  64  and  66  are located on blade  24  near screw holes  60  and  62 . When blade  24  holds a wafer, pins  64  and  66  prevent the wafer from sliding out of position and accidentally touching wrist  26 , which is made out of metal and might contaminate the wafer  16 . 
     Blade  24  includes a narrow strip  67  which bridges wings  52  and  54 . Narrow strip  67  forms one side of opening  50 . The combination of narrow strip  67  and opening  50  provides stability to blade  24 , while reducing the thermal load on the wafer  16 . 
     Blade  24  has ledges  68  and  70  located on ends  44  and  48 . Referring also to FIG. 4 which shows a cross-section of ledge  68 , each ledge  68  and  70  includes three steps  72 ,  74 , and  76 , and  78 ,  80 , and  82 , respectively, following a contour of concentric circles. The wafer  16  rests on inner steps  76  and  78  during transport. Inner steps  76  and  78  reduce the wafer&#39;s contact with blade  24 . Middle steps  74  and  80  keep the wafer  16  in place by providing a stop to the wafer&#39;s  16  potential lateral movement. Outer steps  72  and  82  are used as a visual guide for centering the wafer  16  on the blade  24  during initial manual calibration of robot system  21 . 
     Opening  84  is located at an intersection of center axes  34  and  43  in central region  28  of blade  24 . Opening  84  is used for calibrating the positioning of the wrist  26  and blade  24  assembly in cluster tool  10 . More specifically, during the installation of cluster tool  10 , blade  24  is fully extended without a wafer into process chamber  18 . A rod (not shown) is lowered from the top of process chamber  18  and inserted through opening  84  to touch the bottom of process chamber  18 . The location of the rod is checked for alignment with the center of the bottom of process chamber  18 . If not properly aligned, the programming of robot system  21  is adjusted so as to accurately position the wafer  16  in process chamber  18 , i.e. robot system  21  is set to extend the precise distance necessary to place the wafer  16  in a center of process chamber  18 . 
     Blade  24  is made out of high purity quartz. Because it is made of the same elements as are typically found in the wafer  16  being processed, the possibility of contaminating the wafer  16  is reduced. Blade  24  is formed by machining with a laser in a laser milling machine. 
     Referring to FIG. 5, pins  64  and  66  project upwardly from blade  24 . Notch  86  is a centering slot which is an aid for assembling blade  24  and wrist  26 . 
     Wrist  26  is made of a wrist upper cap  86  and a wrist lower cap  136 . Referring to FIGS. 6,  6 A,  7 , and  8 , wrist upper cap  86  is a roughly rectangular planar member with two curved corners  87  and  89  and one curved side  106 . Wrist upper cap  86  has two columns  88  and  90  positioned on stepped bases  92  and  94 , respectively, in a recessed center portion  96  of wrist upper cap  86 . When robot system  21  is assembled, an appropriately shaped end of robot arm  22  engages with column  88  and a similarly shaped end of robot arm  23  engages with column  90 . Recess  96  is defined by step  98  and rim  100 . Located in rim  100  and immediately adjacent to recess  96  are two screw holes  102  and  104 . Screws through these holes connect wrist upper cap  86  to wrist lower cap  136  (see FIGS. 9-11 for description of wrist lower cap  136 ). 
     Curved side  106  has two semi-circular indentations  108  and  110 . When blade  24  is secured to wrist  26 , pins  64  and  66  fit into indentations  110  and  108 , respectively. A portion of edge  106 , extending from and including indentations  108  and  110 , has an upwardly rising ridge  111 . When blade  24  is secured to wrist upper cap  86 , ridge  111  serves to block particles from reaching blade  24 , thus helping to prevent contamination of the wafer. Ridge  111  has a clearance of 0.002″ to 0.004″ from blade  24 . 
     Adjacent to indentations  108  and  110  are two wings  112  and  114 , respectively. Each wing  112  and  114  has a screw hole  116  and  118 , respectively. Near screw holes  116  and  118 , also located on rim  100 , are two additional screw holes,  120  and  122 . When blade  24  is secured to wrist  26 , screw hole  116  in wrist upper cap  86  aligns with screw hole  62  on blade  24  and screw hole  118  in wrist upper cap  86  aligns with screw hole  60  on blade  24 . Also, screw hole  120  in wrist upper cap  86  aligns with screw hole  58  in blade  24  and screw hole  122  in wrist upper cap  86  aligns with screw hole  56  in blade  24 . Four screws (not shown) attach wrist upper cap  86  to blade  24  through these holes. The screws go through wrist upper cap  86  and blade  24 , and screw into wrist lower cap  136 . 
     Referring to FIG. 7 which shows a cross-section of wrist upper cap  86 , cylinder  88  has a bore  124  at its center and two bores  126  and  128  near its outer perimeter. Bores  124 ,  126 , and  128  are screw holes to be used for attaching rotation bearings (not shown). Rotation bearings are necessary for attaching the wrist  26  and blade  24  assembly to robot arms  22  and  23 . Referring to FIG. 8, cylinder  90  has similarly located bores  130 ,  132 , and  134 . 
     Referring to FIGS. 9,  9 A,  10 , and  11 , wrist lower cap  136  has the same general shape as wrist upper cap  86  with two curved corners  138  and  140  and one curved side  142 . Wrist lower cap  136  also has two openings  144  and  146  in a recessed center portion  148 . Recess  148  is defined by step  150  and rim  152 . Located in rim  152  and immediately adjacent to recess  148  are two screw holes  154  and  156 . Screws (not shown) through these holes  154  and  156  connect wrist lower cap  136  to wrist upper cap  86 . 
     Wrist lower cap  136  has a curved edge  142 . Edge  142  has two indentations  158  and  160 . When blade  24  is secured to wrist  26 , pins  64  and  66  fit into indentations  158  and  160 . A portion of edge  142 , extending from and including indentations  158  and  160 , has a ridge  162 . When blade  24  is secured to wrist lower cap  86 , ridge  162  serves to block particles from reaching blade  24 , thus helping to prevent contamination of the wafer  16 . 
     Wrist lower cap  136  has two wings  164  and  166  adjacent to indentations  158  and  160 , respectively. Each wing  164  and  166  has a screw hole  168  and  170 , respectively. Near screw holes  168  and  170 , also located on rim  152 , are two additional screw holes,  172  and  174 . When blade  24  is secured to wrist  26 , screw hole  168  in lower wrist cap  136  aligns with screw hole  60  on blade  24  and screw hole  170  in wrist lower cap  136  aligns with screw hole  62  on blade  24 . Also, screw hole  172  in wrist lower cap  136  aligns with screw hole  56  in blade  24  and screw hole  174  in wrist lower cap  136  aligns with screw hole  58  in blade  24 . Thus, four screws (not shown) attach wrist lower cap  136  to blade  24 . 
     Wrist upper cap  86  and wrist lower cap  136  are made out of nickel-plated anodized steel, a corrosion-resistant material. 
     When wrist  26  is assembled, cylinders  88  and  90  of wrist upper cap  86  fit into openings  144  and  146  of wrist lower cap  136 . The wrist upper cap  86  and the wrist lower cap  136  contact the blade  24  only with the wing supports  112 ,  114 ,  164 , and  166 . Thus, contact with the blade  24  is minimized, thereby reducing the heat-sinking effect of the wrist  26 . 
     In the illustrated embodiment, blade  24  is designed to transport 8-inch wafers. As indicated in FIG. 3, blade  24  has a width W 1  of 3.8 inches and a length L 1  of 8.42 inches. Openings  36  and  38  each have a length L 2  of 2.5 inches and a width W 2  of 0.5 inches, with rounded ends with a radius R 1  of 0.25 inches. Openings  40  and  42  are circles with a radius R 2  of 0.65 inches. A center of each opening  40  and  42  is a distance D 1  of 0.840 inches from center line  43 . Notch  46  is a rectangular cut-out, with a length L 3  of 1.070 inches and a width W 3  of 1.500 inches. Opening  50  is rectangular, with a length L 4  of 1.080 inches and a width W 4  of 1.500 inches. Narrow strip  67  has a width W 5  of 0.170 inches. Center hole  84  has a radius R 3  of 0.063 inches. 
     As illustrated in FIG. 4, the outside edge of step  72  is formed at a radius R 4  of 4.15 inches. The inside edge of step  72  is a portion of a circle with a diameter D 2  of 8.118 inches. Step  72  has a height H 1  of 0.007±0.002 inches. The inside edge of step  74  is a portion of a circle with a diameter D 3  of 7.892 inches. Step  74  has a height H 2  of 0.014±0.002 inches. The inside edge of step  76  is a portion of a circle with a diameter D 4  of 7.40 inches. Step  76  has a height H 3  of 0.015±0.003 inches. Blade  24  at end  44  has a total thickness T 1  of 0.120 inches. 
     As shown in FIG. 6, wrist upper cap  86  has indentations  108  and  110  which have a ridge  111  with an outside radius R 5  of 0.160 inches and an inside radius R 6  of 0.140 inches. Curved side  106  has a ridge  111  with an outside radius R 7  of 4.130 inches and an inside radius R 8  of 4.110 inches. 
     As shown in FIG. 9, wrist lower cap  136  has indentations  158  and  160  which have a ridge  162  with an outside radius R 9  of 0.160 inches and an inside radius R 10  of 0.140 inches. Along curved side  142 , ridge  162  has an outside radius R 11  of 4.130 inches and an inside radius R 12  of 4.110 inches. Ridge  162  has a height H 4  of 0.050 inches. 
     Although arrays  30  and  32  in FIG. 3 were described as each including two identical openings, one can also view the same arrangement of openings as being two arrays arranged symmetrically to each other on both sides of a central axis extending along the length of the blade. In the latter case, the first array would include opening  36  and the upper halves of openings  40  and  42 , and the second array would include opening  38  and the lower halves of openings  40  and  42 . In addition, embodiments could include various arrays of openings arranged substantially symmetrically on both sides of a central axis of a blade. The degree of symmetry required is such as is necessary to significantly reduce thermal gradients across the wafer to prevent breakage of the wafer or formation of dislocations due to thermal stresses. 
     Optimal configurations, sizes, and locations of these openings can be determined through the use of well-known thermal modelling techniques. The object of such thermal modelling is to size and locate arrays of openings so as to reduce thermal gradients across a wafer resting on a blade to the extent necessary to avoid damage-causing stresses. Such modelling typically takes into account the heat sinking effect of the material constituting the blade, the size of the wafer to be held, and the dimensions of the blade. In addition, consideration may be given to the effect of reflective surfaces above and below a wafer in the chamber in which the blade will be used. Because of the symmetry of the wafer and the general symmetry of the blade, the openings will generally be arranged substantially symmetrically over the blade. However, strict symmetry of the actual holes is not required although the thermal loading impact by the blade needs to be generally symmetrical to reduce thermal gradients sufficiently. 
     Other embodiments are within the following claims.