Patent Publication Number: US-2016240405-A1

Title: Stand alone anneal system for semiconductor wafers

Description:
BACKGROUND OF THE INVENTION 
     Micro-electronic circuits and other micro-scale devices are generally manufactured from a substrate or wafer, such as a silicon or other semiconductor material wafer. Multiple metal layers are applied onto the substrate to form micro-electronic or other micro-scale components or to provide electrical interconnects. These metal layers, typically copper, are plated onto the substrate, and form the components and interconnects in a sequence of photolithographic, plating, etching, polishing or other steps. 
     To achieve desired material properties, the substrate is typically put through an annealing process where the substrate is quickly heated, usually to about 200-500° C. and more typically to about 300-400° C. The substrate may be held at these temperatures for a relatively short time, e.g., 60-300 seconds. The substrate is then rapidly cooled, with the entire process usually taking only a few minutes. Annealing may be used to change the material properties of the layers on the substrate. It may also be used to activate dopants, drive dopants between films on the substrate, change film-to-film or film-to-substrate interfaces, densify deposited films, or to repair damage from ion implantation. 
     As feature sizes for microelectronic devices and interconnects become smaller, the allowable defect rate decreases substantially. Defects result from contaminant particles, so that reducing particle generating elements in the anneal chamber will reduce defects. The temperature uniformity of the wafer is another significant design factor as it affects the crystalline structure of copper or other materials on the wafer. Another consideration is serviceability. It is important to be able to recover or service a chamber as quickly and efficiently as possible. 
     Various annealing chambers have been used in the past. In single wafer processing equipment, these annealing chambers typically position the substrate between or on heating and cooling elements, to control the temperature profile of the substrate. However, achieving precise and repeatable temperature profiles can present engineering challenges. 
     In addition, certain materials, such as copper will rapidly oxidize when exposed to oxygen, at temperatures over about 70° C. If the copper or other material oxidizes, the substrate may no longer be useable, or the oxide layer must first be removed before further processing. These are both unacceptable options in efficient manufacturing. Accordingly, another design factor is to isolate the substrate from oxygen, when the substrate temperature is over about 70° C. Since oxygen is of course present in ambient air, avoiding oxidation of copper during annealing also can present engineering challenges. Improved annealing methods and apparatus are needed. 
     Pre-processing heat treatment has occasionally been performed via a single wafer pretreatment used for preheating a work piece before processing. At times post processing heat treatment has also been used. As process requirements have become more stringent, there has also been a general trend to shift to single wafer processing, which trend applies to thermal treatments too. Thermal treatments are typically performed in a very controlled environment, e.g., under vacuum conditions at temperatures between 300° C. and 1200° C. A typical post plating anneal process may operate for example at about 100° C. in forming gas (a mixture of H 2  and N 2 ) or 1-5 minutes at temperatures ranging between 175° C. and 300° C., for about 30 to 60 minutes. The longer, lower temperature process is typically done in a furnace whereas the shorter, higher temperature process is often done in an anneal chamber that is attached to a plating system in a so-called “on board anneal”. However, disadvantages remain with these systems and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an anneal module. 
         FIG. 2A  is a top view of the anneal module shown in  FIG. 1 . 
         FIG. 2B  is a section view taken along line  2 B- 2 B of  FIG. 2A . 
         FIG. 2C  is an enlarged detail view of the thermal choke shown in  FIG. 2B . 
         FIG. 3  is an exploded view of the anneal module shown in  FIGS. 1 and 2 . 
         FIG. 4  is an exploded top perspective view of the transfer mechanism shown in  FIG. 3 . 
         FIG. 5  is an exploded bottom perspective view of the transfer mechanism shown in  FIGS. 3 and 4 . 
         FIG. 6  is a section view of the transfer mechanism shown in  FIGS. 3-5 . 
         FIGS. 7 and 8  are alternative section views of the transfer mechanism. 
         FIG. 9  is a front and top perspective view of an anneal stack assembly holding multiple anneal modules. 
         FIG. 10  is a top view of the anneal stack assembly shown in  FIG. 9 . 
         FIG. 11  is a side view of the anneal stack assembly shown in  FIGS. 9-10 . 
         FIG. 12  is an enlarged front perspective view of the anneal stack assembly showing additional features. 
         FIG. 13  is a perspective view of the datum plate shown in  FIGS. 9 and 12 . 
         FIG. 14  is a front view of the module shown in  FIG. 1 . 
         FIG. 15  is front view of the datum plate shown in  FIG. 13 . 
         FIG. 16  is a view taken along line  16 - 16  of  FIG. 15 . 
         FIG. 17  is an enlarged view of one of the slots shown in  FIG. 16 . 
         FIG. 18  is a view taken along line  18 - 18  of  FIG. 17 . 
         FIG. 19  is a front view of a stand-alone anneal system. 
         FIG. 20  is a top view of the system of  FIG. 19 . 
         FIG. 21  is a left side view of the system of  FIG. 19 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     As shown in  FIGS. 1-3 , an anneal module  30  has a body  32  and a lid  40  forming a wafer or substrate chamber  34 . The body may be provided as a single cast or otherwise fabricated metal piece, to improve thermal conductivity. A hot plate  36  and a cold plate  38  are attached onto the floor  42  of the body  32 . As shown in dotted lines in  FIG. 1 , the body  32  may include cooling tubes  90  connected to a liquid coolant inlet  60  and a liquid coolant outlet  62 . The cooling tubes  90  may be tubes that are cast in place within the body  32 . Alternatively the body  32  may be formed of two or more attached sections with the cooling tubes  90  positioned in between sections. As shown in  FIG. 1  the coolant inlet  60  and outlet  62  may be located in a fitting recess  64  at the back end of the body  32 . In use liquid coolant pumped through the cooling tubes keep the surface temperature of the module  30  near ambient. The cooling tubes may be stainless steel to better resist corrosion. 
     The top surface of the hot plate  36  may be co-planar with the top surface of the cold plate  38 . As shown in  FIGS. 2B and 3  a pattern of bumps or risers  76  may be provided on the top surface of each of the plates to better provide uniform support to the wafer, which in turn provides for more uniform and consistent wafer temperature control. The risers  76  may be spheres attached to the top surface of the plate, to hold the wafer 0.2 to 1 mm up off of the plate. The cold plate  38  may be thermally bonded to the floor  42 . An electric resistive heater  58  is provided on the bottom side of the hot plate  36 , or within the hot plate  36 . 
     As shown in  FIGS. 2B and 2C , the hot plate  36  may be supported on a pedestal  66  attached to the floor  42  through a thermal choke  68  which provides only a thin annular ring of contact (e.g. 1-2 mm wide) between the hot plate  36  and the coolant chilled body  32 . In this design, as shown in  FIG. 2B , the hot plate  36  is spaced apart from the floor via an air or gas gap  88 , and contacts the body  32  only through the choke  68 . This allows the hot plate  36  to provide sufficient heat for a 500° C. wafer process temperature, without excessively heating the rest of the module  30 . Relatively more heat sensitive components of the module, such as seals, are not subjected to high heat. As shown in  FIG. 3 , the body  32  may have circular recesses  78  to accommodate the hot plate and the cold plate, with the circular recesses  78  adjoining or touching each other, or partially overlapping or intersecting. 
     As shown in  FIG. 2  an electronic servo control unit  44  and a heating control unit  46  may both be included within the anneal module  30  and attached to the body  32 . As shown in  FIG. 3 , the anneal module  30  may have a separate cover  50  over the electronic units  44  and  46 , and mounting brackets  48  and  52  for securing the module  30  in place in a higher level assembly as described below. Providing the electronic units  44  and  46  on the body  32  allows for a modular construction and testing of the modules  30 . In addition, the body provides conductive cooling of the electronic components, so that fans or convective heat sinks are not needed. 
     Also as shown in  FIG. 3 , a load/unload slot  74  is provided in the front end  72  of the anneal module  30 . Alignment bushings  54  and gas inlet/outlet ports  56  may also be located on the front end of the anneal module  30 . As shown in  FIG. 3 , the lid  40  includes a showerhead  80  for distributing purge gas above the hot plate  36 . The purge gas, which may be an inert gas, such as Nitrogen, or a forming gas, is supplied to the showerhead through a lid gas port  82  connected to a gas supply. 
     Turning now  FIGS. 3-5 , a transfer mechanism  70  provided in the anneal module  30  to move a wafer substrate from the cold plate  38 , which is acent to the load/unloslot  74 , to the hot plate  36 , and then back to theld plate  38 . The transfer mechanism  70  performs a lift, rotate (e.g., about ⅛ turn) and lower movement, to transfer a wafer from the cold plate  38  to the hot plate  36 , and vice versa. The transfer mechanism  70  also lifts the wafer to allow handoff of the wafer to a transfer robot. Various designs may be used for this purpose. In the example shown the transfer mechanism may include a coupler  106  in a coupler frame  104  on a base  100 . A lead screw  108  is driven by a rotate motor  114 , e.g., via a belt  130  turning a sprocket  132  on a lower end of the lead screw  108 . 
     An arm  150  of a hoop  142  is attached to the lead screw  108 , so that actuation of the rotation motor  114  causes the hoop  142  to rotate, to position the hoop  142  over either the cold plate  38  or the hot plate  36 . A ball spline  110  is linked to a lift motor  120  via a second belt  134  and sprockets  138  and  140 , as shown in  FIGS. 5-8 . Actuation of the lift motor  120  rotates the ball spline  110  which lifts or lowers a spline nut  116 , in turn lifting or lowering the hoop  142 . A shroud  112  is attached to the coupler  106  and may include a volume exchange channel  158 . The use of belts and pulleys provides a 180° gear box to minimize the height of the transfer mechanism  70 . The motors  114  and  120  may both be mounted to the base  100  which allows the transfer mechanism  70  to be assembled and pretested before being installed into the module  30 . 
     Referring momentarily back to  FIG. 4 , the hoop  142  has three or more inwardly projecting fingers  144 , with each finger  144  having a ledge  146  with a flat surface  148 . In use, as the hoop  142  is raised to lift a wafer off of the hot plate  36  or the cold plate  38 , the flat surfaces  148  contact the down facing side of the wafer. Clearance notches  84  may be provided in the hot plate and the cold plate to allow the hoop fingers  148  to move into vertical alignment with, or below, the top surface of the plate  36  or  38 . 
     The transfer mechanism  70  minimizes the number of moving or lubricated components in the module  30 . These components that are isolated from the process chamber  34  by outer housing  160 . An active exhaust system within the housing  160  draws process gas into the transfer mechanism  70 . This helps to prevent particles from entering the process chamber  34  where they can cause defects. As shown in  FIGS. 6 and 7 , this is achieved via an exhaust trench  156  in the base  100 , and via the volume exchange channel  158  located between the outer housing  160  and the base  100 . A top chamber  162  is formed between an upper shield  172  and the top of the outer housing  160 . A top gap  164  allows flow between the top chamber  162  and a bottom gap  168 . A bottom chamber  166  is formed between the base  100  and a lower shield  172 . As shown in  FIG. 6 , the bottom gap  168  connects into the bottom chamber  166 . Also as shown in  FIG. 6 , an exhaust port  170  in the base  100  connects into the bottom chamber  162 . 
     The volume exchange channel  158  minimizes any compression of gas in the transfer mechanism housing  160  that is caused by the movement of the components of within the housing. This avoids allowing the gas pressure within the housing  160  to rise above the gas pressure in the process chamber  34 , which could allow particles to flow from the transfer mechanism  70  into the process chamber  34  and contaminate the wafer. 
     Referring to  FIG. 2A , the radius of either plate  36  or  38 , or the radius of the recesses  78 , is shown as dimension RR. The hoop pivot axis shown as BB is spaced apart from the centerline CC of the plates or recesses by a dimension less than RR. This provides for a reduced volume process chamber  34  which reduces gas supply requirements, and also reduces the travel distance of the hoop, allowing for faster wafer movements and reduced particle generation potential. 
     Turning now to  FIGS. 9-12 , multiple anneal modules  30  may be placed into a stack assembly  200 , to allow multiple wafers to be annealed simultaneously, within a compact space. As shown in  FIGS. 9 and 11 , the stack assembly  200  may include a rack  202  divided into vertically stacked separate module slots or spaces  216 . A load/unload robot  206  may be provided at a front end  204  of the rack  202 . In the example shown the robot  206  includes a track or rail  208  attached to the rack  202 . A robot housing  210  having an end effector  212  is movable vertically along the rail  208 , so that the end effector may be moved into vertical alignment with a chamber door  214  at each of the module slots  216 . 
     As shown in  FIGS. 9 and 12 , an anneal module  30  may be placed into each of the module slots  216 , in the example shown, eight anneal modules  30  are vertically stacked in the stack assembly  200 . The body  32  of each anneal module  30  may be bolted onto a datum plate  222 . Gas inlet lines  218  and gas outlet or exhaust lines  220  may be connected to fittings on the datum plate  222 . Gas supplied through the datum plate  222  can be used to isolate the process chamber  34  from its environment, to better avoid contamination. Sealed interfaces between the datum plate  222  and the chamber body  32  maintain gas flow through the process chamber  34 . 
     As shown in  FIGS. 12-16 , the modules  30  may be attached to the datum plate  222  via bolts passing through mounting holes  225  in the datum plate, with pins on the back side of the datum plate used to more precisely position the modules  30  on the datum plate. Gas seals on the gas ports  56  on the front of the module  30  seal against the back surface of the datum plate. The datum plate is sufficiently rigid (e.g., a 3-12 or 4-10 mm thick metal plate) to securely support and position the modules. The number of connections between anneal module  30  and the stack assembly  200  is reduced to allow quick removal and service of the anneal modules  30  from the stack assembly  200 . A service rack  250  may be attached onto the back end of the rack  202 , for holding an anneal module  30  during servicing. 
     As shown in  FIGS. 13-16 , each module slot or position  216 , a plate slot  240  in the datum plate  222  aligns with the load slot  74  in the front end of the module  30 . An exhaust plenum  224  may be provided in the datum plate  222  at each module position  216 . The exhaust plenum  224  may be drilled into the datum plate  222 , from one side of the plate, with the exhaust plenum adjacent and parallel to an upper or lower edge of each plate slot  240 . The exhaust plenum is aligned with the plate slot  240  to exhaust gas from the process chamber  34 , via the exhaust lines  220 . 
     As shown in  FIGS. 15-18 , this may be achieved via exhaust slot segments  242  extending from the exhaust plenum  224  to the plate slot  240 , at each module position  216 . The exhaust slot segments may be cut through the down facing surface  244  of each plate slot  240 , for example by positioning a circular blade cutting tool or mill, having a diameter nominally smaller than the slot height HH in  FIG. 15 , and then moving the cutter up to create arcuate opening leading into the exhaust plenum, as shown in  FIGS. 17 and 18 . 
     In use the exhaust slot segments  242  lead into the exhaust plenum  224  which may be connected to a vacuum source. When the module door  214  is closed during processing, gaps may exist around the door  214 , so that the module  30  is not sealed. The vacuum drawn through the exhaust slot segments  242  at each plate slot  240  largely prevents ambient air from entering into the module  30 . When the door is open, during load and unload, gas flows out of the module  30  through the module slot  74  and the plate slot  240 , if the interior of the module is maintained at a gas pressure higher than ambient. The size of the exhaust slot segments  242  may vary along the length of the plate slot  240 , with the slot segments  242  further upstream from the vacuum source larger than the slot segments  242  closer to the vacuum source, to provide a substantially uniform draw or gas intake across the length of the plate slot  240 . For example, the slot segments closer to the vacuum source, i.e., closer to the top of  FIG. 15 , may be 1 mm wide and 20-40 mm long, with the slot segments closer to the bottom of  FIG. 15  made wider or longer. 
     As shown in  FIG. 14 , the number of gas ports  56  provided may vary depending on the specific anneal process performed by the module  30 . For example, two helium gas ports  56  may be used, to separately provide helium to the hot plate  36  and to the cold plate  38 . One or more other inert gas ports  56  may be used to supply nitrogen into the module. An additional gas port  56  may supply hydrogen, to that a forming gas may be used within the module. Separate gas supply and exhaust ports may also be routed directly to the transfer mechanism, to better reduce potential for contamination. 
     The anneal module  30  may be used with or without the stack assembly  200 . When used in the stack assembly  200 , the robot  206  is actuated to carry a wafer  300  on the end effector  212  into alignment with one of the anneal modules  30  in the stack assembly  200 . The chamber door  214  is opened. The robot  206  advances the end effector  212  and the wafer  300  into the process chamber  34  and sets the wafer down onto the hoop  142  of the transfer mechanism  70 . Typically at this step the hoop  142  is in a raised up above the cold plate  38 , so that the end effector  212  moves down and sets the wafer  300  onto the ledges  146  of the hoop  142 . Alternatively, if the hoop is in a down position, then the wafer  300  may be set down directly onto the cold plate  38 . 
     With the wafer  300  now held by the hoop  142 , the transfer mechanism is actuated to rotate the hoop by about a ⅛ turn, moving the wafer  300  over the hot plate  36 . In some methods, the heater  58  may operate continuously with the hot plate  36  correspondingly staying at a desired steady state temperature. In other methods the heater  58  may be cycled, or turned on only upon imminent delivery of a wafer. The transfer mechanism  70  lowers the hoop  142  so that the bottom surface of the wafer comes to rest on the risers  76  on the top surface of the hot plate  36 . Gas is cycled through the chamber  34  with the gas pressure within the chamber remaining positive relative to ambient. This helps to exclude oxygen and contaminant particles from the chamber  34 . 
     The wafer  300  may remain on the hot plate  36  for a specific dwell time. The transfer mechanism  70  is then again actuated to lift the wafer  300  up off of the hot plate and rotate the hoop  142  back to the initial position over the cold plate  38 . The transfer mechanism  70  then lowers the wafer onto the cold plate  38 , with the wafer supported on the risers  76  on the top surface of the cold plate  38 . Chilled liquid is pumped through the cooling tubes  90  to cool the cold plate and the base  32 . After the wafer is sufficiently cooled, the wafer may be lifted up off of the cold plate via the hoop  142  for handoff back to the robot  206 . The chamber door  214  is opened and the end effector  212  extended into the chamber  34 , below the hoop  142 . The end effector  212  may then be lifted, or the hoop  142  lowered, to complete the handoff. The robot  206  then moves the annealed wafer  300  to a subsequent station, and may proceed to deliver another wafer to the anneal chamber  30  for processing. 
     The module  30  may be designed to provide oxygen levels of less than  100  ppm when the door  214  is closed during processing. Gas flow in the chamber  34  may be optimized to sweep across the whole chamber. The showerhead  80  may have gas ports optimized in spacing and orifice size to enhance wafer temperature uniformity. The exhaust plenum  224  may be located just behind the door  214  at the farthest point from the hot plate  36  and the gas is exhausted through a series of slots across the chamber entrance. The slot size may be optimized to ensure even gas flow across the chamber. The flow and internal chamber geometry can be designed to minimize the time required to evacuate any oxygen in the chamber either at startup or after transfer robot handoff. For example the chamber volume is minimized and deep corners or pockets that may take longer to purge are eliminated. The flow exit paths are restricted to slightly pressurize the chamber above atmospheric pressure to avoid oxygen infiltration into the chamber whether the door is opened or closed. 
     Turning now to  FIGS. 19-21  show a high throughput anneal processing system  260  that is not a furnace, and is not attached to, or part of, a plating or other processing apparatus. The system  260  includes a system robot  268  within an enclosure  262 . The robot  268  may move laterally on a horizontal track  270  within the enclosure  262 . 
     Docking stations  264  are provided on a front wall of the enclosure  262 , with the docking stations design to accept, or to dock with, wafer containers  266  such as so-called front opening unified pods, of FOUPS. A controller  280  may be provided on the enclosure to provide a user interface and to allow for local control, if desired, of some or all of the operations of the system  260 . Referring again momentarily to  FIG. 9 , a buffer station  272  may be provided at the lower end of the rack  202 , to provide temporary storage of wafers. A notch aligner  276  may also optionally be provided in the rack  202 . The stack assembly  200  of anneal modules  30  as described above may be positioned off to one side of the enclosure to better facilitate loading and unloading of the modules by the robot  268 .  FIG. 20  shows a design with the stack assembly  200  on the left side. In this case, other apparatus may be located on the right side of the enclosure, such as a metrology station. 
     In use, containers  266  are docked and opened at the docking stations  264 . The system robot  268  removes a wafer  300  from a container and places the wafer into the buffer station  272 . Referring to  FIG. 9 , the rack robot  206  then picks up the wafer at the buffer station  272  and places the wafer into one of the anneal modules  30 , as described above. After annealing, the wafer is returned to the container using the reverse sequence. The buffer station  272  may be provided as an assembly of vertically stacked shelves, with each shelf adapted to hold a single wafer in a horizontal orientation. Some designs may use more than one buffer station. 
     The system  260  may be characterized as a stand-alone anneal system as it is not associated with a plating system or an anneal furnace, and it can operate independently of any other apparatus. The system  260  may have a minimal footprint, with the enclosure for example having a width and a height of 2 to 2.4 meters and a depth of 1 to 1.6 meters Table AA below shows typical operating parameters of the system  260 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE AA 
               
               
                   
                   
               
               
                   
                 Parameter 
                 System capabilities 
               
               
                   
                   
               
             
            
               
                   
                 Wafer Temperature Range 
                 250° C.-500° C. 
               
            
           
           
               
               
               
               
            
               
                   
                 Operating Pressure 
                 780  
                 Torr 
               
               
                   
                 WIW temp uniformity 
                 ±5°  
                 C. 
               
               
                   
                 (° C., range) 
                   
                   
               
               
                   
                 Ramp Up Rate (temp range 
                 15°  
                 C./sec 
               
               
                   
                 200° C.-500° C.) 
                   
                   
               
               
                   
                 Ramp down Rate (temp range 
                 15°  
                 C./sec 
               
               
                   
                 200° C.-500° C.) 
                   
                   
               
               
                   
                 Wafer Edge Exclusion 
                 2  
                 mm 
               
               
                   
                 Ambient Control 
                 &lt;10  
                 ppm O2 
               
            
           
           
               
               
               
            
               
                   
                 (Process chamber/transfer 
                   
               
               
                   
                 chamber/SWLL) 
                   
               
               
                   
                 Metal Contamination  
                 &lt;2e10 (all metals using TXRF) 
               
               
                   
                 (wafer frontside and backside) 
                   
               
               
                   
                 Particles 
                 ≦5 added ( &gt;0.035 μm) at  
               
               
                   
                   
                 2 mm EE 
               
               
                   
                   
                 ≦1 adder at 0.035 um per  
               
               
                   
                   
                 wafer pass, 98% of the time,  
               
               
                   
                   
                 after 4 sigma filtering 
               
            
           
           
               
               
               
               
            
               
                   
                 Throughput 
                 180  
                 WPH 
               
               
                   
                   
               
            
           
         
       
     
     Thus, novel apparatus and methods have been shown and described. Various changes and modifications may be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims and their equivalents.