Patent Publication Number: US-2007110895-A1

Title: Single side workpiece processing

Description:
This Application is a continuation-in-part of U.S. patent application Ser. No. 11/359,969, filed Feb. 21, 2006 and now pending, which is a continuation-in-part of U.S. patent application Ser. No. 11/075,099, filed Mar. 8, 2005 and now pending, and claiming priority to U.S. Provisional Patent Application No. 60/552,642. This application is also a continuation-in-part of U.S. patent application Ser. No. 11/172,162 filed Jun. 30, 2005 and now pending. This Application is also a continuation-in-part of U.S. patent application Ser. No. 11/288,770, filed Nov. 28, 2005 and now pending. These applications are incorporated herein by reference.  
      Remarkable progress made in microelectronic devices over the past several years has led to more useful yet less expensive electronic products of all types. It has also led to entirely new types of products. A major factor in the development of microelectronic devices has been the machines and methods used to manufacture them. Manufacturing of microelectronic devices requires extreme precision, extremely pure materials, and an extremely clean manufacturing environment. Even microscopic particles can cause defects and failures in devices. 
    
    
     BACKGROUND OF THE INVENTION  
      Microelectronic devices are typically manufactured on a front or device side of a semiconductor wafer. In general, no microelectronic devices are on the back side of the wafer. However, contaminants on the back side of the wafer, such as metal particles, residues, films, etc., if not removed, can result in damage to devices on the front side of the wafer. For example, certain metals used in the manufacturing process, such as copper, can migrate through the wafer, from the back side to the front side, where they can cause defects in the microelectronic devices. Processing the backside of the wafer is therefore important.  
      The back side of the wafer may be processed using existing techniques, to remove contaminants. These techniques involve applying process fluids onto the back side, usually while spinning the wafer. However, the process fluids may damage microelectronic devices if the process fluids contact the front side of the wafer. Therefore, during back side processing, or single side processing in general, the process fluids should ideally make minimal or no contact with the front side or opposite side of the wafer. As the process fluids include liquids, gases or vapors, and as the wafer is usually spinning when they are applied, this objective has largely not yet been reached with current wafer processing technology.  
      Wafer processing machines have used various designs to try to solve the problem of how to exclude process fluids from the front side while processing the back side. Some of these machines have used flows of inert gas to try to confine the process fluids only to the back side. Others have used gaskets, membranes, or other types of mechanical seals or barriers to keep the process fluids off of the top side of the wafer. However, in the machines using gas flow, some amounts of process fluids tend to still reach the top side of the wafer. In the machines using mechanical seals, the seal must physically touch the top side of the wafer. This physical touching may damage microelectronic devices. Consequently, use of seals or physical barriers can have serious disadvantages.  
      Physical contact with the wafer by seals, fingers, clamps or other sealing, holding or positioning elements, as often used in current processing machines, creates risk of contamination via particle generation or particle release. These types of elements can also disrupt the uniform flow of process fluids on the wafer, resulting in varying degrees of processing at different areas of the wafer. Accordingly, regardless of whether one side or both sides are processed, minimizing physical contact with wafer generally provides better results. On the other hand, the wafer must be properly positioned and secured in place during processing. Accordingly, better machines and methods are needed to provide single side wafer processing, and for processing generally with less physical contact with the wafer.  
     SUMMARY OF THE INVENTION  
      New processing machines and methods for solving these difficult wafer back side processing and physical wafer contact problems have now been invented. These machines and methods provide dramatic improvements in manufacturing microelectronic and similar devices. In one aspect of the invention, a circulating gas is provided on one side of the wafer. The circulating gas creates gas pressure and flow conditions that keep process fluids away from the front side, during processing of the back side of the wafer. Accordingly, the back side may be processed using a wide range of process chemicals, without risk of damage to microelectronic devices the front side.  
      The circulating flow of gas may also hold the wafer in place during processing, via gas pressure forces. The gas flow and pressure conditions created by the circulating gas can exert holding forces at the edges of the wafer, while applying relatively little or no forces towards the unsupported central area of the wafer. The wafer is accordingly held securely in place during processing, with minimal stress applied to the wafer. Physical contact with the wafer during processing of the front side or the back side, or both, is minimized. This reduces potential for contamination and increases wafer yield. As a result, more useable device chips may be produced from each wafer.  
      A wafer processing machine using circulating gas may have a bowl having one or more process fluid inlets for applying a process fluid onto a first side of a wafer. The machine has a head which can be positioned in engagement with the bowl during workpiece processing. Rotational gas flow is created in a rotor supported on the head. One way of creating the rotational gas flow is by releasing pressurized gas in the rotor in directions at or near tangent to direction of rotation. The rotational gas flow holds the wafer in place on or in the rotor, with minimal physical contact with the wafer. The fluid inlets apply one or more process fluids onto the first side of the wafer, while the wafer rotates with the rotor. In addition to holding the wafer in place, for single side processing, the rotational gas flow in the rotor can also be used to exclude process fluids from the second side of the wafer. The wafer is positioned on the rotor with a gap around the edge of the wafer. Some or all of the circulating gas provided into the rotor escapes out through the gap and around the edge of the wafer. This outflow of gas prevents any of the process fluids applied to the first side from reaching the second side. The invention resides as well in sub-combinations of the machines and methods described. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In the drawings, the same reference number indicates the same element, throughout the several views. Electrical wiring and gas and liquid plumbing lines are generally omitted from the drawings for clarity of illustration.  
       FIG. 1  is a section view showing principles of operation of the invention.  
       FIG. 1A  is a section view taken along line  1 A- 1 A of  FIG. 1 .  
       FIG. 1B  is a section view of an alternative design.  
       FIG. 2  is a top perspective view of a workpiece processor.  
       FIG. 3  is a side view of the processor shown in  FIG. 2 , in an open or load/unload position.  
       FIG. 4  is a section view taken along line  4 - 4  of  FIG. 2 .  
       FIG. 5  is a section view of the processor as shown in  FIG. 3 .  
       FIG. 6  is a top perspective view of the head shown in  FIGS. 2-5 , with the cover removed for illustration.  
       FIG. 7  is a top perspective view of the rotor shown in  FIGS. 4 and 5 .  
       FIG. 8  is a bottom perspective view of the rotor shown in  FIG. 7 .  
       FIG. 9  is a section view taken along line  9 - 9  of  FIG. 7 .  
       FIG. 10  is a bottom perspective view of an alternative rotor design.  
       FIG. 11  is a section view taken along line  11 - 11  of  FIG. 10   
       FIG. 12  is a perspective view of a workpiece processing system including several of the processors as shown in  FIGS. 2-9 .  
       FIG. 13  is a plan view of the system shown in  FIG. 12 .  
       FIG. 14  is a perspective view of components or subsystems shown in  FIG. 12 .  
       FIG. 15  is a perspective view of selected components and subsystems of an alternative processing system.  
       FIG. 16  is a perspective view of one of the processing assemblies shown in  FIG. 15 .  
       FIG. 17  is a section view taken along line  17 - 17  of  FIG. 16 .  
       FIG. 18  is a perspective view of the bowl shown in  FIGS. 16 and 17 .  
       FIG. 19  is a schematic diagram of an alternative processing system. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
      The invention is directed to apparatus and methods for processing a workpiece, such as a semiconductor wafer. The term workpiece, wafer, or semiconductor wafer means any flat media or article, including semiconductor wafers and other substrates or wafers, glass, mask, and optical or memory media, MEMS substrates, or any other workpiece having micro-electronic, micro-mechanical, or microelectro-mechanical devices.  
      Turning to  FIG. 1 , a processor  20  may perform single side processing. Single side processing means applying one or more process fluids to only one side (referred to here as the back side) of the wafer, and with the process fluid substantially excluded from contacting the second (front) side of the wafer. The process fluid may optionally also contact the bevel edge of the wafer. The process fluid may be a liquid, a gas or a vapor. In  FIG. 1 , the processor  20  includes a rotor  24  linked to a spin motor in a head  22 . Guide pins  25  may be provided around a perimeter of the rotor  24 , to help guide a wafer  100  into position. Gas nozzles or inlets  26  spray or jet out gas in a direction which creates a gas vortex flow in the rotor  24 . The arrows  23  in  FIGS. 1 and 1 A indicate the direction of gas flow. This gas flow creates a negative or lower pressure zone in the space above the wafer  100 . As a result, pressure forces may be used hold the wafer  100  onto the rotor  24 .  
      Referring to  FIG. 1 , the rotor  24  may be designed so that the only escape path for the gas is the annular opening between the edge of the wafer and the rotor. In this design, as the gas escapes or flows out of the rotor  24 , the gas substantially prevents the wafer  100  from touching the rotor  24 . The wafer is essentially be supported on, or held up by, a cushion of moving gas. The guide pins  25  may be provided to minimize or limit any side-to-side movement of the wafer in the rotor  24 .  
      Referring still to  FIG. 1 , the head  22  may be placed in or moved into alignment or engagement with a base or bowl  28 . Process fluids are applied onto the back side of the wafer from one or more nozzles or inlets  29  in the bowl  28 . During processing, the motor  84  spins the rotor  24 . The wafer  100  spins with the rotor  24 . Process fluids are applied to the back side of the wafer. In  FIG. 1 , the back side is the down facing side. The gas flow escaping from the rotor  24  acts as an isolation barrier for the front side of the wafer. As the gas is constantly flowing outwardly, no process fluid can move into the rotor  24  or contact the top side of the wafer. Consequently, highly effective single side wafer processing may be achieved.  
      Referring now to  FIG. 1  and  1 A, the gas flow is shown by the arrows  23 . The rotor is designed to create a rotational gas flow. Near the inlets  26  (adjacent to the perimeter of the rotor), gas flow velocity is relatively high, and gas pressure is correspondingly relatively low. Towards or at the center of the rotor, gas flow velocity is relatively lower, and gas pressure is correspondingly higher. Consequently, pressure forces holding the wafer in place on the rotor are highest near the wafer edges (where the negative gas pressure is highest) and are lowest towards the center. Towards or at the center of the rotor, gas flow velocity may be at or close to zero. Thus gas pressure in the inner area of the rotor will typically be only slightly negative, neutral, or even slightly positive. As a result, the edge areas of the wafer can be securely held against the rotor, with minimum forces acting on the center of the wafer. Bending stresses on the wafer may therefore be reduced.  
       FIG. 1B  shows a design where the rotor  24 B has a diameter larger than the wafer  100 . In this design, the wafer is entirely within the rotor  24 B. The rotor  24 B operates in the same way as the rotor in  FIGS. 1 and 1 A. However, the wafer is held away from the face of the rotor  24 B by standoffs or pins  27 . In this design, guide pins  25  are not needed, as the cylindrical side walls of the rotor prevent the wafer  100  from shifting excessively off center.  
      In each of the designs described here, the way that the gas escapes from the rotor may vary. In  FIG. 1 , gas escapes out through the annular opening between the edge of the wafer and the rotor. In the design shown in  FIG. 1B , the gas escapes out through the annular gap between the edge of the wafer and the cylindrical side walls of the rotor. However, other gas escape openings may be used, alone or in combination with the opening and gap shown in  FIGS. 1 and 1 B. For example, gas outlets  147  shown in dotted lines in  FIG. 1  may be provided in the rotor. The gas outlets  147  may be holes, slots, or other openings. The gas outlets  147  may be located anywhere on the rotor, and take any form which will facilitate the rotational gas flow described above.  
      With some processes and wafers, seals making physical contact with the wafer may be used. In these applications, a contact sealing element, such as a seal ring  149  shown in  FIG. 1 , may also be used to provide a physical seal between the rotor and wafer during processing. The negative pressure or vacuum conditions described above hold the edges of wafer securely against the seal ring  149 . Gas outlets  147  in the rotor provide an escape path for the gas flow. The positioning pins  25  can be omitted since the wafer is held in physical contact with the seal ring, largely preventing any shifting of the wafer during processing.  
       FIGS. 2-5  show an example of a processor  50  which may use the principles of operation described above relative to  FIG. 1 . However,  FIGS. 2-5  show various additional elements which are not essential to the invention. As shown in  FIGS. 2-5 , the processor  50  includes a head  80  and a bowl  78 . The bowl  78  may be supported on a mounting plate  70  which in turn may be attached to the deck  52 . As shown in  FIGS. 6 and 7 , a spin motor  84  may be supported on a base plate  88  of the head  80 , and covered by a head cover  82 . A rotor  92  is typically driven by the spin motor  84  and spins within the head  80 . However, the motor  84  can be omitted in favor of other techniques used to spin the rotor.  
      The head  80  is engageable with the bowl  78 . Specifically, for processing, the head  80  may be moved to a position adjacent to (but not contacting) the bowl  78 , or the head  80  may be physically contacting with the bowl  78 , or even sealed against the bowl  78 , as shown in  FIG. 4 .  
      As shown in  FIGS. 4 and 5 , the bowl  78  has liquid spray nozzles or inlets  112 , for applying a process liquid onto the back or down facing surface of a workpiece  100  held in the head  80 . The nozzles or inlets  112  may be fixed in position on the sides or bottom surfaces of the bowl  78 . Alternatively, some or all of the nozzles  112  may be moving, e.g., on a swing arm. Combinations of fixed and moving nozzles  112  may also be used. Fixed or moving spray manifolds having multiple nozzles or inlets , may also be used in the bowl  78 . Gases or vapors may also be applied to the workpiece  100  via the nozzles  112 . A drain  114  collects spent process fluid for removal from the bowl  78 . One or more valves  116  may be associated with the drain  114 . Bowl stand-offs  110 , if used, are attached to the bowl and project upwardly from the bowl  78  towards the workpiece  100  on the head  80 . As shown in  FIG. 5 , the head  80  may be lifted vertically away from the bowl  78  by a head lifter (not shown) connected to the head by a head lifting arm  90 , shown in  FIG. 4 .  
       FIG. 6  shows the head  80  with the cover  82  and other components removed for illustration. Head gas supply lines  102  advantageously deliver gas or clean dry air to gas ports  96  passing through the base plate  88 , to provide a flow of gas between the base plate  88  and the rotor  92 . This flow of head gas or clean dry air helps to prevent migration of process liquids, vapors, or gases into the head  80 , thereby reducing corrosion of head components. A head ring  94  may be attached around the outside of the base plate  88 . An inflatable seal  98  may be provided in a groove in the head ring, to seal the head  80  against the bowl  78  during processing. The components shown in  FIG. 6  which are part of the head  80 , are supported by the head lifting arm  90 , and do not rotate.  
      Turning now to  FIGS. 7, 8  and  9 , in the example shown, the rotor  92  has a drive plate  130  attached to a shaft  124  at a hub  122 . The shaft  124  is keyed to the spin motor  84  in the head  80 . A chuck  132  is attached to the drive plate  130  by screws  128  or other fasteners. As shown in  FIGS. 8 and 9 , guide pins  134  extend out (or downwardly) from an outer rim  142  of the chuck  132 . The guide pins  134  may have a conical or tapered section  135 . As shown in  FIG. 9 , contact pins  154  project slightly from the chuck outer rim  142 . The contact pins  154  are shorter than the guide pins  134  and are positioned radially inside of the guide pins  134 .  
      Referring still to  FIG. 9 , the chuck  132  has a cylindrical side wall  138  joined, typically substantially perpendicularly, to a top or web plate  148 . An O-ring or other seal  144 , if used, seals the outer surface or perimeter of the chuck  132  against the drive plate  130 . The web or top plate section  148  of the chuck  132  is generally spaced apart from the drive plate  130  by a gap G (except at the fastener  128  attachment points).  
      A gas flow path generally designated  145  and indicated by the arrows in  FIGS. 7-9  extends through the rotor  92 . A supply of gas, such as nitrogen, or clean dry air, under pressure, connects from a supply line in the head  80 , through a labyrinth cap  126  (shown in  FIGS. 4, 5  and  7 ) attached to the motor housing and into an inlet line  86  extending through a sleeve  125  within the shaft  124 . The sleeve  125  is attached to the drive plate  130  and rotates within the cap  126   
      Gas provided to the head  80  flows (downwardly in the design shown) through the inlet line  86 , as shown in  FIG. 9 , radially outwardly in the gap G, as shown in  FIGS. 7 and 9 , to gas inlets  136 . The gas inlets  136 , located in the side wall  138  of the chuck  132  are positioned to jet or spray gas in a direction fully or at least partially tangent to the cylindrical side wall  138 . The inlets are oriented so that the gas direction is tangent to the sidewalls, or within 40, 30, 20 or 10 degrees of tangent. Multiple gas inlets  136 , for example, 3, 4, 5, 6, 7 or 8 gas inlets  136  are advantageously radially spaced apart and positioned in the side wall  138 , close to the top or web  148  of the chuck  132 . The number, shape, configuration, and location of the gas inlets  136  may of course be changed, as various designs may be used to create gas flow conditions which will cause the workpiece  100  to be held in place on the rotor  92 . The O-ring or seal  144  may be used to prevent gas from escaping from the gas flow path  145 , except through the gas inlets  136 .  
      The side walls  138  of outer rim  142  on the chuck plate  132  form a space generally designated  155  in the chuck  132  having a diameter D, and a depth or height H, as shown in  FIG. 9 . The dimension H is substantially uniform, except at the central area around the hub  122 .  
      A central opening may be provided in the chuck plate  132  for alignment purposes. If used, the opening is closed via a plug  146  before the rotor  92  is put into use. Referring now to  FIGS. 8 and 9 , the guide pins  134  are positioned on a diameter DD slightly larger than the diameter of the workpiece  100  (which in turn is slightly larger than the diameter D of the cylindrical or disk-shaped space  155 ). Accordingly, with a workpiece placed into the rotor  92 , as shown in  FIG. 4 , there is only nominal radial or lateral clearance between the guide pins  134  and the edge of the workpiece.  
      Referring to  FIG. 3 , the processor  50  is in the up or open position for loading and unloading. In the design shown, the head lifting arm  90  lifts the head  82  up from the bowl  78 . A workpiece  100  is moved into a position between the head  82  and the bowl  78 , with the workpiece  100  generally aligned with the rotor  92 . The workpiece is then moved vertically upwardly, with the guide pins  134  around the outside edge of the workpiece. The workpiece at this point is at or above the plane P of the guide pins  134 , as shown in  FIG. 11 . These workpiece loading movements may be performed manually, or by a robot, as further described below.  
      Gas is then supplied to the gas flow path  145 . Referring momentarily to  FIG. 8 , due to the generally tangential orientation of the gas inlets  136  and the relatively high velocity of the gas flowing out of the inlets  136 , a rotational gas flow or vortex is created within the space  155 , between the workpiece and the top plate  148  of the chuck  132 . The gas flows in a circular pattern in the space  155 . The gas may then move out of the space by flowing around the edge of the workpiece  100  and into the bowl  78 . This creates a negative pressure or vacuum at the outer areas of the space  155 , causing the workpiece to lift up and off of the robot  44 . The negative pressure in the outer areas space  155  above the workpiece  100  holds the top surface of the workpiece against the contact pins  154 . This prevents the workpiece from rotating or shifting relative to the rotor  92 . The contact pin  154  may have a spherical end which essentially makes point contact with the wafer. Alternatively, the contact pin may have an end that makes contact over a very small area, e.g., over a diameter of 0.2-3 mm.  
      The normal force acting to hold the workpiece  100  against the contact pins  154  depends on the pressure difference created by the vortex gas flow, and the surface area of the workpiece on which the pressure acts. The normal force may be adjusted by controlling the gas flow. In general, the normal force will significantly exceed the weight of the workpiece, so that the workpiece remains held against the contact pins  154 , regardless of its orientation relative to gravity. The contact pins  154  which are the only surfaces supporting the workpiece, are generally positioned within 2-10, 4-8, or 5-7 mm of the edge of the workpiece.  
      The head lifter then lowers the head lifting arm  90  and the head  80 , with the head moving from the open position shown in  FIG. 5 , to the closed or processing position shown in  FIG. 4 . The seal  98 , if used, is inflated, creating a partial or full seal between the head  80  and the bowl  78 .  
      The only escape path for the gas in the space  155  is the small annular opening between the workpiece and the rim  142  of the chuck  132 . As gas escapes from the space  155 , it tends to prevent the workpiece  100  from touching the chuck  132 , or any part of the rotor  92  or processor  50 , except for the contact pins  154 . The workpiece  100  is otherwise essentially suspended within a flow of gas. The guide pins  134  act, if needed, to prevent the workpiece  100  from moving too far off center of the spin axis of the rotor  92 . Ordinarily though, the gas flow around the edges of the workpiece, and the normal force holding the workpiece against the contact pins  154 , will tend to keep the workpiece centered.  
      The spin motor  84  is turned on, spinning the rotor  92  and the workpiece  100 . In general, the gas flow vortex spins within the rotor in the same direction as the rotor spins. Process liquid is sprayed or jetted from the nozzles or inlets  112  onto the bottom or down facing surface of the spinning workpiece  100 . Process gases or vapors may also be used. Centrifugal force helps to distribute the process liquids over the entire bottom surface of the workpiece  100 . The gas flow via the flow path  145  in the rotor  92  helps to prevent any process liquids or gases from contacting the top surface of the workpiece  100 , as there is a constant flow of gas from the space above the workpiece to the space below the workpiece.  
      Following the application of process liquids and/or gases, the wafer may optionally be rinsed and/or dried, also while in the position shown in  FIG. 4 . When all processing within the processor  50  is completed, the workpiece  100  is unloaded following the reverse sequence of steps described above.  
      Interruption of the flow of gas to the rotor  92 , while the rotor is holding a workpiece  100 , could result in the workpiece  100  moving or falling out of the rotor  92 . To reduce the potential for damage in this event, bowl stand off posts  110  are positioned in the bowl  78  and extend up to a position about 10-15 millimeters below the workpiece  100  (when in the processing position) as shown in  FIG. 4 . In the event of a gas flow interruption, the workpiece will drop only a short distance and come to rest on the stand-off posts  110 .  
      After the gas moves out of the rotor  92 , it is drawn into a gas exhaust plenum  120  and then removed from the processor  50 . Depending on the specific processes to be run in the processor  50 , the chuck  132  and drive plate  130  may optionally be made of corrosion resistant materials, such as PVDF plastic materials or equivalents. The rotor  92  as described above, and the entire head  80 , may be used in virtually any centrifugal process where a process chemical, typically a liquid, is applied to one side only of a workpiece. While the processor  50  is shown in a vertical and upright position, it may also be used in other positions or orientations. Accordingly, the description here of top or bottom surfaces and up and down directions are provided to describe the examples shown in the drawings, and are not requirements or essential operating parameters.  
      In each of the embodiments described, the front or device side of the wafer may be facing towards or away from the rotor. For back side cleaning or processing, the wafer is placed into the rotor with device side facing the rotor. For front side cleaning or processing, the wafer is place into the rotor with the front side facing away from the rotor. The desired face up/face down orientation of the rotor may be achieved via robotic or manual handling. A separate inverting or wafer flipping station may also be used.  
      Generally, the gas provided to the rotor is inert, i.e., it does not significantly chemically react with the wafer. However, process chemical gases may be used in place of inert gases. Providing a process chemical gas to the rotor allows for chemically processing the side of the wafer facing the rotor, optionally while simultaneously processing the other side of the wafer with the same process chemical gas, or with a different process chemical gas or liquid.  
      As may be appreciated from the description above, the head  50  requires no moving parts for holding or securing the workpiece  100 . Since gas flow is used to hold the workpiece in place, the head  80  may have a relatively simple design. In addition, generally, chemically compatible plastic materials may be used for most components. This reduces the need for metal components, which can lead to contamination. There are also no obstructions or components over or shadowing the workpiece  100 . This allows distribution of process liquids onto the workpiece to be highly uniform, resulting in more consistent and uniform processing. The guide pins  134  only touch the edge of the workpiece. The contact pins  154  contact only very small areas of the front or top side of the workpiece  100 . Consequently, touching the workpiece  100  is minimized.  
       FIGS. 10 and 11  show an alternative rotor  160 . The rotor  160  is similar to the rotor  92 , except for the differences described below. As shown in  FIG. 10 , on one side, the rotor  160  has short guide pins  162 . The remaining guide pins  134  are full length guide pins, with the tip of the guide pin  134  extending by a dimension K beyond the rim  142  to the plane P. The full height guide pins  134  and workpiece holders  166  are spaced apart by dimensions greater than the diameter of the workpiece  100 . L-shape workpiece holders  166  are attached to the drive plate  130  and have a horizontal leg extending radially inwardly. The short guide pins  162  create a entrance pathway  164 , allowing a workpiece  100  to move laterally into the rotor  160  (in contrast to the vertical workpiece movement described above relative to the rotor shown in  FIGS. 7-9 . With lateral movement, the robot  44  can generally align the wafer  100  with the rotor  160 , and then move down to place the workpiece  100  on the holders  166 . The upfacing ends of each holder  166  preferably have a flat land area  168  for supporting the workpiece  100 . The robot  44  can then withdraw to perform other functions within the system  30  even if the processor having the rotor  160  is not active. Accordingly, a workpiece  100  may be placed into the rotor  160  even when no gas is flowing through the rotor  160 .  
      The rotor  160  shown in  FIG. 11 , in comparison to the rotor  92  shown in  FIG. 9 , is designed for handling smaller diameter workpieces. For example, the rotor  92  shown in  FIG. 9  is designed for 300 mm diameter workpieces, while the rotor  160  shown in  FIG. 11  is designed for 200 mm diameter workpieces. Of course, the rotor can be made in various other sizes as well for processing workpieces having other sizes.  
      The processors described above may be used in automated processing systems. An example of one processing system  30  is shown in  FIG. 12 . The processing system  30  generally has an enclosure  32 , a control/display  34 , and an input/output or docking station  36 . Wafers or workpieces within pods or boxes  38  (e.g., FOUPs) are removed from the boxes  38  at the input/output station  36  and processed within the system  30 .  
      Turning to  FIG. 13 , the processing system  30  preferably includes a frame  48  that supports an array of workpiece processors  50  on a deck  52  within the enclosure  32 . Facility or fab air inlets  42  are typically provided along with air filters, at the top of the system  30 . Each workpiece processor  50  may be configured to process workpieces, such as 200 or 300 mm diameter semiconductor wafers or similar workpieces, which may be provided within sealed boxes  38 , open cassettes, or other carriers or containers.  
      The frame  48  in  FIG. 13  is shown supporting ten workpiece processors  50 , but any desired number of processors  50  may be included. The frame  42  preferably includes one or more centrally located rails  46  between the processors  50 . One or more robots  44  can move on the rails  46  to load and unload workpieces into and out of the processors  50 .  
      Referring to  FIGS. 12-14 , in use, workpieces or wafers  100  are typically moved to the processing system  30  within containers  38  such as front opening unified pods (FOUPs) or similar closeable or sealable containers. Alternatively, open containers such as cassettes or other carriers may also be used. At the docking or input/output station  36 , the door or cover of the container  38 , if any, is removed, generally via a robotic or automated subsystem. The load port door or window in the enclosure  32 , if any, is opened. The robot  44  removes a workpiece  100  from a container  38  and carries it to one of the processors  20  or  50 . The workpiece  100  is then ready for loading into a processor. This sequence of steps, as well as the components or apparatus used in moving the workpiece  100  to the processor may of course vary, and are not essential to the invention. Rather, the sequence described above and as shown in  FIGS. 12-14  represents an example, for purposes of explanation.  
      Referring momentarily to  FIG. 5 . flow sensors in the head  80  may be used to verify the flow of gas, indicating to the controller  34  that the robot  44  may be safely withdrawn. The robot  44  moves down and away from the rotor  92 . Sensors on the robot  44  verify that the workpiece  100  is no longer on the robot  44 . The robot then retracts away from the processor  50 . The processor then operates as described above  
       FIGS. 15-18  show an additional alternative system  180 . The components and operation discussed above with reference to  FIG. 12  apply as well to the system  180  shown in  FIG. 15 . The system  180  shown in  FIG. 15  is similar to the system  30  shown in  FIGS. 12-14 . However, processor assemblies  182  are installed on the deck  52  within the enclosure  32 , instead of the processors  50 . As shown in  FIGS. 16 and 17 , one or more of the processor assemblies  182  includes a processor  184  which may be attached to a mounting plate  188 , and a lift/rotate unit  186 . The lift rotate unit  186  is attached to the head  80  through the head lifting arm  90 , in place of the head lifter used in the system  30  shown in  FIGS. 12-14 . In addition to lifting the head  80  vertically up and away from the bowl  78 , the lift/rotate unit  186  can also flip or rotate the head  80  into an upside down position.  
      As shown in  FIG. 16 , an air shield  190  is positioned on top of a rim  192  supported above the processor  184  on rim posts  194 . Electrical wiring runs through cable guides  198  which generally extend from near the top of the enclosure  32  to the mounting plate  188 . Referring to  FIGS. 16 and 17 , a drying process swing arm  196  is supported on and driven by a swing arm actuator  200  on the mounting plate  188 , and to one side of the processor  184 .  
      The head  80  shown in  FIG. 17  is similar or the same as the head  80  shown in  FIGS. 2-9  and described above. The head  80  shown in  FIG. 17  is engageable with a bowl  204 . The bowl  204  advantageously has a top section  210  having a cylindrical upper end  212 , a center section  208 , and a bottom plate  206 . The bowl  204  also has a reciprocating spray swing arm  220  driven by a actuator  222 . One or more spray or jet nozzles or inlets  218  are provided on the swing arm  220 . The bowl  204  is otherwise similar to the bowl  78  described above. The process chemicals applied by the nozzles or inlets in the bowl  78  or  204  may be liquid acid solutions, such as HF, HCL, nitric acid, or sulphuric acid. Alternatively, the process chemicals may include liquid solvents. The lift rotate unit  186  may position the head  80  at various vertical positions relative to the base.  
      Referring to  FIGS. 4 and 17 , the processor assemblies  50  and  182  are shown in an upright orientation, with the arrow U pointing vertically up (i.e., opposite to the direction of gravity). The arrow U is also shown as co-axial with the rotor spin axis. A joggle or angle section  302  extends between the cylindrical upper end  212  of the top section  210  of the bowl  204 , and a cylindrical lower shield  304 . The cylindrical upper end  212  and the cylindrical lower shield  304  may be generally vertical or near vertical surfaces. The angle section  302  connecting them is oriented at an angle of about 20-70° or 30-60° or 40-50° degrees from vertical. The lower end of the angle section  302  (where the angle section  302  joins the lower shield  304 ) is generally near or at the same vertical position as the top of the exhaust plenum  120 . The lower end of the lower shield  304  is spaced slightly apart from angle section  304 , providing an annular gas flow passageway  305 .  
      With the edge of the spinning wafer generally aligned vertically with the angle section  302 , liquid flung off the wafer  100  tends to be deflected downwardly, towards the bottom of the bowl  204 . This reduces back splattering onto the wafer. The annular lip exhaust channel or plenum  120  is positioned around the lower shield  304 . Gas exhaust pipe connections  306 , generally located on opposite sides of the bowl, lead into the exhaust channel  120 . A slight vacuum may be applied to the pipe connections, inducing gas flow from the bowl, through the passageway  305  to the exhaust channel  120  and then out of the processor via the pipe connections  306 . Typical gas flow through the processor ranges from about 60-200, 100-170 or 120-150 liters per minute.  
      The head  80  of the processor  184  operates in the same way as the head  80  described above relative to  FIGS. 2-9 . The nozzles or inlets  218  on the swing arm  220  apply process liquids onto the bottom surface of a workpiece  100 . Fixed nozzles or inlets may also be used, with or without the swing arm nozzles. When this processing is complete, the lift/rotate unit  186  lifts the head  80  up and rotates the head into an upfacing position, i.e., the down facing surface of the wafer in the processing position shown in  FIG. 17 , is moved into an upfacing position. While the rotor  92  is rotating, the drying process swing arm  196  applies drying fluids onto the workpiece  100 . The drying process swing arm  196  begins at or near the center of the workpiece and moves radially outwardly towards the edge of the workpiece, to dry the workpiece as described in U.S. patent application Ser. No. 11/075,099, incorporated herein by reference. The openings in the shield  190  help to diffuse and/or control downward air flow through the processor assembly  182 .  
      Referring to  FIG. 18 , an optical end point detector  310  may be provided on the swing arm  220 . The end point detector may use elements or steps as described in U.S. patent application Ser. No. 11/288,770, incorporated herein by reference. The controller may include software to integrate the signal provided from the moving end point detector  310 . This may shorten the process time and improve yield by reducing over etching.  
      The drying process swing arm  196  typically applies deionized water (DI) along with nitrogen and a solvent, such as isopropyl alcohol vapor, as the arm sweeps across the upfacing surface of the workpiece. A similar process could alternatively be performed by the swing arm  220  in the bowl  204 . Other process liquids or gases including ozone gas, or ozone dissolved and/or entrained in a liquid, such as DI, may also be applied via fixed or moving nozzles or inlets in the bowl  78  or  204 .  
      While the head is inverted or upfacing, gas flow through the rotor  92  continues, thereby holding the workpiece  100  against the contact pins  154 . Similarly, the workpiece  100  is held onto the rotor  92  while the head  80  pivots from the downfacing position shown in  FIG. 17  to the upfacing position by the normal force holding the workpiece against the contact pins  154 .  
       FIG. 19  shows an alternative system design  230  having processors or processor assemblies  50  or  182  arranged in an arc  234 , or other array or pattern, rather than the linear columns shown in  FIGS. 12 and 15 . Workpieces  100  may be moved into and out of the processors  50  or  182  by a single robot  232 . While automated or robotic systems  30  and  180  have been shown and described, the head  80  and rotors  92  and  160  may be used in various other systems including manually operated and/or single processor machines.  
      The terms cylindrical, round, or circular also include multi-segmented shapes. The term engaged or engagement includes actual physical contact, as well as adjacent positioning allowing cooperation between the elements without physical contact between them. The term vortex or gas flow vortex means a flow of gas having a generally circular characteristic, and includes helical, spiral, and similar flows. The plural, as used here, includes the singular as well, and vice-versa. The terms attached to or supported on include both direct and indirect connections or interactions. Novel systems and methods have been shown and described. Various changes, substitutions and uses of equivalents may of course 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.