Abstract:
A plasma enhanced chemical vapor deposition (PECVD) system having an upper chamber for performing a plasma enhanced process, and a lower chamber having an access port for loading and unloading wafers to and from a wafer boat. The system includes apparatus for moving the wafer boat from the upper chamber to the lower chamber. The wafer boat includes susceptors for suspending wafers horizontally, spaced apart in a vertical stack. An RF plate is positioned in the boat above each wafer for generating an enhanced plasma. An RF connection is provided which allows RF energy to be transmitted to the RF plates while the wafer boat is rotated. Apparatus for automatic wafer loading and unloading is provided, including apparatus for lifting each wafer from its supporting susceptor and a robotic arm for unloading and loading the wafers.

Description:
This application claims the benefit of U.S. Provisional Application Ser. No. 60/071,571 filed Jan. 15, 1998, and is a continuation-inpart of copending U.S. Application Ser. No. 08/909,461 filed Aug. 11, 1997 (pending). 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to methods and apparatus for plasma enhanced chemical vapor deposition (PECVD) on wafers and plasma enhanced etching of wafers, and more particularly to a method and apparatus for transmitting RF energy to create a localized glow discharge over surfaces of wafers stacked vertically on a rotating wafer boat, and apparatus for robotically inserting and removing the wafers. 
     2. Brief Description of the Prior Art 
     There are a large number of plasma enhanced processes that are performed inside of enclosed chambers wherein the pressure, temperature, composition of gases and application of radio frequency (RF) power are controlled to (a) produce the desired thin film deposition of various materials onto substrates such as semiconductor wafers, flat panel displays and others, and (b) to remove various materials from such substrates via etching. For convenience, the term “wafer” as used in the following description of the prior art and in the disclosure of the present invention will be used with the understanding that the invention also applies to the manufacture of flat panel displays and other types of substrates or devices wherein plasma enhanced processes are employed. For example, silicon nitride is typically deposited via plasma enhanced chemical vapor deposition (PECVD) on top of metal layers on a semiconductor wafer. A main feature of PECVD processes is that they can be carried out at low substrate temperatures as described by S. Wolf and R. N. Tauber, “Silicon Processing for the VLSI Era”, Volume 1-Process Technology, Lattice Press, 1986, pp. 171-174. FIG. 1 shows a chamber  10  having a rotating susceptor  12  capable of holding a plurality of substrates. RF energy is applied to an upper electrode  14  to create an electric field causing a plasma (glow discharge) creating free electrons within the plasma region  16 . The electrons gain sufficient energy from the electric field so that when they collide with gas molecules, gas-phase dissociation and ionization of the reactant gases (e.g. silane and nitrogen) occurs. The energetic species are then adsorbed on the film surface. 
     FIG. 2 shows another prior art device including a single wafer PECVD chamber  18  wherein a wafer  20  is held stationary. There are a variety of single wafer PECVD chamber designs available in the marketplace. There are also a variety of commercially available multiple wafer chambers as described above wherein the wafers are all supported by a susceptor in a single horizontal plane. 
     The single wafer and horizontal multiple wafer PECVD chamber designs discussed above are problematic for numerous reasons. First, such single wafer designs suffer from relatively low throughput as only one wafer at a time can be processed. Further, the multiple wafer horizontal designs pose extreme difficulties in connection with the incorporation of automatic robotic wafer loading and unloading. Also, horizontal multiple wafer designs can process only a limited number of wafers before the chamber becomes so large in area as to become very difficult to maintain the necessary plasma uniformity and necessary gas flow control. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a PECVD chamber that can process multiple wafers in a uniform enhanced plasma environment. 
     It is a further object of the present invention to provide a PECVD chamber having facility for automatic robotic loading and unloading of wafers. 
     It is a still further object of the present invention to provide a PECVD chamber system including apparatus for transmitting RF energy to a rotating wafer boat having wafers held horizontally in a vertically spaced array, causing a glow discharge, and thereby enhanced plasma over a surface of each wafer. 
     Briefly, a preferred embodiment of the present invention includes a plasma enhanced chemical vapor deposition (PECVD) system having an upper chamber for performing a plasma enhanced process. and a lower chamber having an access port for loading and unloading wafers to and from a wafer boat. The system includes apparatus for moving the wafer boat from the upper chamber to the lower chamber. The wafer boat includes susceptors for suspending wafers horizontally, spaced apart in a vertical stack. An RF plate is positioned in the boat above each wafer for generating an enhanced plasma. A novel RF connection is provided, allowing the RF energy to be transmitted to the RF plates while the wafer boats are rotated. In addition, apparatus for automatic wafer loading and unloading is provided, including apparatus for lifting each wafer from its supporting susceptor, and a robotic arm for unloading and loading the wafers. 
    
    
     IN THE DRAWING 
     FIG. 1 shows a prior art rotating susceptor chamber; 
     FIG. 2 is a prior art chamber with a stationary wafer; 
     FIG. 3 illustrates a preferred embodiment of the present invention; 
     FIG. 4 is a top cross-sectional view of the upper chamber of the reactor of FIG. 3; 
     FIG. 5 shows a vertical cross-sectional view of the upper chamber; 
     FIG. 6 shows an alternate construction of an upper chamber constructed in the form of a bell jar; 
     FIG. 7 is an enlargened section C from FIG. 3 showing detail of the rotating RF input assembly; 
     FIG. 8 is a further enlargement of section D of FIG. 7, clarifying the detail of the rotating RF connection; 
     FIG. 9 is an enlargement of section E of FIG.  7 . showing the upper portion of the bottom RF shaft; 
     FIG. 10 shows further detail of the wafer boat; 
     FIG. 11 is an enlargened view of section F of FIG. 10; 
     FIG. 12 is an enlargened view of section G of FIG. 10 showing further detail of the wafer boat; 
     FIG. 13 is an enlargened view of section H of FIG. 10 showing the upper right hand portion of the boat; 
     FIG. 14 is an enlargened view of section G of FIG. 12, except showing a modified construction; 
     FIG. 15 shows the wafer boat in contact with the moveable plate; 
     FIG. 16 shows details of lifting wafers off of their susceptors for an embodiment wherein RF energy is applied to plates above the wafers; 
     FIG. 17 shows details of lifting wafers off of their susceptors for an embodiment wherein RF energy is applied to the susceptors; 
     FIG. 18 shows the boat in the fully down position; 
     FIG. 19 shows a top view of the boat showing a wafer being loaded on pins using a robotic arm; and 
     FIG. 20 is an enlargened view of section I of FIG. 3 showing further detail of the vertical motion mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 3 of the drawing, a preferred embodiment  22  of the PECVD chamber system of the present invention is shown. An enclosure  24  has an upper chamber  26  and a lower chamber  28 . The upper chamber has an optional radiant top heater  30 , and optional side heaters  32 . for use when the process requires temperatures above room temperature. A bottom heater (not shown) can also be attached, for example to plate  34  as described in U.S. patent application Ser. No. 08/909,461 entitled Mini-Batch Process Chamber, the contents of which are included herein by reference. 
     The wafer boat  36  includes susceptors for holding wafers horizontally, in a stacked, spaced apart array. The boat  36  includes a RF plate positioned above each wafer, for causing a glow discharge creating an enhanced plasma above each wafer. The wafer boat, in cooperation with other chamber system  22  apparatus, includes apparatus for automatically lifting each wafer from its susceptor for loading and unloading by a robotic arm when the boat is lowered into the lower chamber  28 . The boat  36  is supported on a rotatable shaft structure  38 , rotated by a rotation mechanism  40 . The RF energy is transmitted to the RF plate by way of a transmission line through the shaft structure. (RF refers to all types of RF power, including dual frequency RF and pulsed RF.) The transmission line is coupled to an RF connector  42  by way of a rotating contact joint  44 . The rotating contact  44  allows the RF energy to be transmitted while the boat  36  is rotated, a novel feature providing more uniform processing over a wafer surface. The vertical motion of the shaft  38  and boat  36  is accompanied by a lift mechanism  46 . Further details of the rotation mechanism  40  and lift mechanism  46  are included in U.S. Patent Ser. No. 08/090,461. A seal plate  48  prevents reactant gases from the upper chamber from passing into the lower chamber  28  during processing, and thereby minimizing unwanted deposition of material in the lower chamber. In order to assure minimal transfer of reactant gas from the upper chamber  26  to the lower chamber  28 , an inert gas at a low level positive pressure is injected into the lower chamber  28 . This operation, and the associated apparatus details of the movement of plate  48  when the boat is lowered into the lower chamber  28  are fully explained in U.S. patent application Ser. No. 08/909,461. The details of construction and operation of the present invention including the boat  36 , the rotating contact  44 , and the automatic loading and unloading mechanism will all be fully explained in the following text of the specification in reference to the various figures of the drawing. 
     FIG. 4 is a top cross section of the upper chamber  26 , showing six side heater assemblies  32 . In operation, wafers  50  are rotated while gases enter the chamber  26  via a gas injection manifold  52  and are exhausted on the other side via an exhaust manifold  54 . FIG. 5 is a vertically cross sectioned view of the upper chamber  26  showing further detail of the tunable gas injection manifold  52  and the opposing tunable exhaust manifold  54  with the rotating wafer boat  36  in between. 
     FIG. 6 shows an alternate construction  56  for the upper chamber  26  of FIG. 3, where the upper portion is a simple bell jar  58  made of suitable material such as quartz or silicon carbide. Gas injection is accomplished via inlet tubes  60  and exhausted via exhaust tubes  62 . Optional radiant heaters or resistive heating elements can be arranged about the upper chamber  56  for processes above room temperature. 
     FIG. 7 shows the rotating RF input assembly  44  where the RF energy is introduced via connector  64  to a stationary bottom RF disk  66 . The RF is coupled to a lower RF shaft  68  via a metal thrust bearing  70 . The RF is then in turn connected to an upper RF shaft  72  via a threaded rod  74 . FIG. 8 is a section D blow up of the RF input assembly  44  showing an RF connector  64  which makes contact to a threaded rod  76  which in turn is threaded into the stationary bottom RF disk  78 . To avoid electrical contact with the lift carriage  80 . the threaded rod  76  is surrounded by an insulating tube  82  made from suitable insulating material such as ceramic or plastic. To keep the stationary bottom RF disk  78  from contacting the lift carriage  80 , an insulating disk  84  supports the bottom of RF disk  78  and an insulating tube  86  electrically isolates the sidewalls of RF disk  78 . The RF energy passes through a metal thrust bearing  88  first via bottom race  90 , then through the rotating balls  92  and finally to the upper race  94  which is in contact with bottom RF shaft  68 . The bottom RF shaft  68  is secured via insulating clamp ring  96  and bolts  98  to the bottom bellows disk  100  which has bellows  102  welded to its upper surface. A metal tube  104  which is a ground potential surrounds the bottom RF shaft  68  and is held in place via tube clamp  106  made from insulating material such as Delrin. To prevent electrical contact to the bottom RF shaft  68 , the bottom of metal tube  104  is isolated via insulating ring  108 . O-ring  110  in conjunction with metal washer  112  forms the vacuum seal between the metal tube  104  and the bottom bellows disk  100 . O-ring  112  forms the internal vacuum seal between the bottom RF shaft  68  and the metal tube  104 . This O-ring  112  also aligns the bottom RF shaft  68  to be parallel to the metal tube  104  and at the same time provides a small gap of about  0 . 05 ″ in between which prevents electrical contact and acts as a “dark space” which precludes the occurrence of a glow discharge or plasma within the gap. 
     FIG. 9, section E of FIG.  7 . shows the upper portion of bottom RF shaft  68 . An O-ring  114  further maintains the parallelism and the dark space gap between the bottom RF shaft  68  and the metal tube  104 . The upper RF shaft  72  is connected to the lower RF shaft  68  via wazzu threaded rod  74 . The space between the upper RF shaft  72  and the metal tube  104  is filled with insulating material to prevent the occurrence of a plasma. The insulating material is in the form of three concentric standard size quartz tubes  116 . The upper end of bellows  118  is welded to an upper bellows disk  120  and vacuum sealed to an outer rotation tube  122  via O-ring  124 . When the lift carriage  80  (FIG. 7) is in the up position, two or three rods  126  (only one shown for clarity) engage into holes  128  drilled into upper bellows disk  120  so that the rotational force is transmitted via the rods  126  to prevent contortion of the bellows  118 . Pulley  128  is affixed to the outer rotation tube  122  and drive belt  130  goes to a pulley on the rotation motor. Outer rotation tube  122  passes through a ferrofluidic rotary vacuum seal  132  and is held in place via tube clamp  134 . The ferrofluidic seal  132  is itself vacuum sealed to the feedthrough flange  136  via O-ring  138 . 
     The feedthrough flange  136  is sealed to the chamber bottom plate  138  via O-ring  140 . A fitting  142  leads to hole  144  so that inert gas may be injected to prevent process gases from entering the space between the metal tube  104  and the bottom plate  138  and the feedthrough flange  136 . 
     The details of construction of the wafer boat  36  will now be fully described in reference to FIGS. 10-17. 
     FIG. 10 shows the wafer boat  36 , wherein the upper end of metal tube  104  is connected to a boat bottom plate  146  via slitted flange  148  and secured in place to flange  148  via clamp ring  150 . Upper RF shaft  72  is connected to the bottom RF plate  152  via threaded rod  154 . A section F is shown in FIG. 11, enlarged for a more clear illustration of the following detail. To prevent electrical contact and/or the occurrence of a plasma, insulating tube  156  made from ceramic or other suitable material is inserted between the boat bottom plate  146  and the threaded rod  154 . Further isolation between the boat bottom plate  146  and the bottom RF plate  152  is provided by insulating disk  158 . To prevent a plasma from occurring in the space above the bottom RF plate  152 , a second insulating disk  160  is sandwiched between the bottom RF plate  152 , and a metal disk  162 . 
     FIG. 12 is an enlargement of the structure of section G of FIG.  10 . The wafer boat  36  is configured so that wafers  164  are at ground potential or electrically floating. The plasma is generated above the wafers  164  via RF plates  166 . Wafer susceptors  168  are held in place via threaded rod  170  and conductive spacers  172 ,  174 , and  176  made from suitable material such as metal or graphite. In the event that the wafer susceptors  168  are made of conductive material, the wafers  164  will be at ground potential. If the wafer susceptors  168  are made from insulating material, the wafers  164  will be floating. The rods  170  are threaded into the boat bottom plate  178  and metal band  180  surrounds the bottom RF plate  152  with insulating disks  158  and  160  holding the band slightly away from the bottom RF plate  152  to form a dark space gap  182 . Outer metal band  184  provides further structural support. The RF energy is transmitted up from the bottom RF plate  152  via threaded rod  186  which contacts the RF plates  166  via nuts  188 . To prevent the occurrence of a plasma around the threaded rod  186 , insulating tubes  190  surround the threaded rod  186 . The insulating tubes  190  are in turn surrounded by conductive tubes  192  which connect to ground potential via conductive shield disks  194  and conductive spacers  174  and  176  and the threaded rod  170 . 
     FIG. 13 is an enlargened view of Section H of FIG. 10, showing the upper right-hand portion of boat  36 . To prevent contact of the conductive shield disks  194  to the RF energized nuts  188 , insulating washers  196  are placed between them and insulating tubes  198  surround the nuts  188 . The conductive shield disks  194  are shaped along their inside diameters to capture the insulating tubes  198  and come to within a dark space distance to the RF plates  166 . To prevent the occurrence of plasma around the outside edge of RF plates  166 , a conductive band  200 , which is connected to ground potential via conductive shield disks  194 , is positioned around the entire periphery of RF plates  166 . Insulating plates  202  are positioned on top of RF plates  166  to prevent the occurrence of plasma above the RF plates  166 . During processing, grounded lift plates  204  rest upon the insulating plates  202 . The lift plates  204  function to lift the wafer during robotic loading and unloading as further described later herein. At the top of the boat  36 , the uppermost insulating plate  202  has a grounded conductive disk  206  resting on top of it. Positioned above the grounded conductive disk  206  is an insulating disk  208  which has holes  210  drilled through it near the periphery to capture the top end of RF threaded rod  186  and the nuts  188 . Before the nuts  188  are threaded onto the RF rod  186 , insulating washers  209  are placed into the holes  210 . On top of the nuts  188  are insulating disks  212 . A grounded conductive band  214  surrounds the periphery of disk  208  and a second grounded conductive disk  216  is positioned above the insulating disk  208  after which a nut  218  is threaded onto grounded threaded rod  170 . 
     FIG. 14 is an enlargened view of section G of FIG. 12, except showing a modified construction for boat  36  where the wafer susceptor  168  is powered with RF energy as opposed to the configuration of FIG. 13 where plate  166  above the wafer was RF energized. In this case, the energized susceptor  168  is connected to the RF rod  186  via nuts  188 . The bottom of the susceptor is insulated to prevent a plasma on the bottom side by insulating disk  218  which rests upon grounded conductive disk  220  and which has through holes drilled therein to capture nuts  188 . The thickness of insulating disk  218  is such to allow only a small dark space gap  222  between the grounded conductive disk  220  and the nut  188 . Insulating washers  224  have a thickness of approximately 0.04″ to 0.07″ and hold the dark space grounded disks  226  above the susceptor to leave a small enough gap  228  as to preclude a plasma from occurring in this region. Surrounding the periphery of susceptor  168  is a grounded conductive band  230  with spacing  232  in between such as to preclude a plasma around the periphery of susceptor  168 . Spacers  234  keep grounded lifting disks  236  at the desired spacing above the wafers  164  top surface. The top of this type of boat  236  has construction similar to that of FIG. 13 to insulate and preclude a plasma from occurring anywhere except in the desired region of wafers  164 . 
     The following describes an apparatus for automatic robotic loading and unloading of wafers  164  into and out of boat  36 . As shown in FIGS. 12 and 14, wafers  164  are resting on top of susceptors  168  when the boat  36  is in the up position within the upper chamber  26  of the reactor  22 , as shown in FIG.  3 . As the boat  36  is lowered down into the load/unload lower chamber  28  of the reactor  22 , lift rods  238  come in contact with the movable plate  48  as shown in FIG.  15 . The plate  48  is supported by three rods  240  of which only one is shown in FIGS. 3 and 15 for clarity. The rods  240  are made movable and vacuum sealed via three vertical motion mechanisms  242  shown in FIG.  3 . (See U.S. patent application Ser. No. 08/909,461 for details of the mechanisms  242 ). The mechanisms  242  may be motorized or effected with constant upward force via the combination of the force of the bellows counteracted by the force of a downward pulling constant force spring. Once the lift rods  238  contact plate  48 , continued downward motion of boat  36  causes the rods  238  to move upwards relative to the rest of boat  36  causing lift plates  244  to move up, which in turn causes the lift pins  246  to move upwards lifting wafers  164  off of the susceptors  168  as shown in more detail in FIG. 16 for the case of where the RF energy is applied during processing on plates above the wafers  164  and in FIG. 17 for the case where the RF energy is applied to the susceptors  168 . The lift plates  244  are vertically spaced apart via spacers  248  (FIGS. 16 &amp; 17) at a predetermined distance. FIG. 16 shows that the upward motion of lift plates  244  stops relative to the rest of the boat  36  when the lift plates  244  come in contact with the bottom of the susceptors  168 . In FIG. 17 the lift plates  244  stop moving upward when the lift plates  244  come in contact with the grounded disk  250 . 
     FIG. 18 shows the boat  36  in the fully down position. Wafers  164  are then loaded onto the pins  246  and unloaded from the pins  246  via a robotic arm which in FIG. 18 would be moving in a plane perpendicular to the paper on which the figure is drawn. FIG. 19 shows a top view of boat  36  showing the wafer  164  being loaded onto the pins  246  via the robotic arm&#39;s end effector  248 . The robotic arm&#39;s “Z” motion allows it to position the wafer  164  above the pins  246  and then the arm lowers to rest the wafers onto the pins  246 . Once the end effector  248  is below the plane of the wafer  164 , the end effector  248  is pulled out of the reactor via the robotic arm. The wafers  164  can be loaded one at a time through a slit valve or all at once via a multiple level end effector which passes through a larger rectangular valve in the wall of the reactor  22 . 
     FIG. 20 shows apparatus in Section I referenced to FIG. 3, including the vertical motion mechanism  242 . More detail on the mechanism is provided in U.S. patent application Ser. No. 08/909.461. 
     Although the present invention has been described above in terms of a specific embodiment, it is anticipated that alterations and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all such alterations and modifications as fall within the true spirit and scope of the invention.