Abstract:
A spin chuck in an apparatus for single wafer wet processing has structures at its periphery that, in combination with a supported wafer, form a series of annular nozzles that direct flowing gas from a chuck-facing surface of the wafer, around the edge of the wafer, and exhaust the gas away from the non-chuck-facing surface of the wafer, thereby preventing treatment fluid applied to the non-chuck-facing surface from contacting the edge region of the wafer. Retaining pins with enlarged heads engage the wafer edge and prevent it from being displaced upwardly when a high flow rate of gas is utilized.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a device and a process for liquid treatment of a surface of a wafer-shaped article. 
     2. Description of Related Art 
     Liquid treatment includes both wet etching and wet cleaning, wherein the surface area of a wafer to be treated is wetted with a treatment liquid and a layer of the wafer is thereby removed or impurities are thereby carried off. A device for liquid treatment is described in U.S. Pat. No. 4,903,717. In this device the wafer-shaped article is mounted on a spin chuck and treatment liquid is applied from above the chuck onto the surface of the wafer not facing the chuck. The distribution of the liquid may be assisted by the rotational motion of the wafer. Such rotational motion may also assist in removing the liquid from the surface of the wafer as the liquid is flung off laterally over the edge of the wafer. The &#39;717 patent discloses a chuck that flushes the chuck-facing surface of the wafer with a gas. In doing so, an annular nozzle is formed between the peripheral edge of the chuck and the peripheral edge of the main surface of the wafer facing the chuck. The flowing gas is exhausted from this annular nozzle and thereby limits the extent to which treatment liquid can flow onto the chuck-facing surface of the wafer; however, there is no provision for limiting treatment of the edge surfaces of the wafer while treating the upper main surface of the wafer. 
     U.S. Pat. No. 6,328,846 discloses guide elements on the periphery of a spin chuck that selectively engage the edge of a wafer supported by the chuck and thereby limit undesirable lateral motion of a wafer while it is being treated. Three or more pins in the shape of cylinders are disclosed as sufficient to limit the lateral motion of the wafer when spaced around the wafer and moved to engage the wafer&#39;s edge. The pins are disposed perpendicular to the main surface of the wafer and the chuck and extend above the chuck through bores. The pins extend above the edge of the wafer and move against the wafer after placement on the chuck. In the embodiment disclosed in the patent, the wafer floats above the chuck on a cushion of gas exhausted from the chuck. The gas flushes the surface of the wafer facing the chuck and is exhausted from the chuck at the peripheral edge of the wafer. 
     The &#39;846 patent discloses that treatment liquid can flow along the pins when engaged against the wafer&#39;s edge and treat the lower opposite main surface of the wafer, leading to so called pin marks on the wafer&#39;s edge and chuck-facing surface. To avoid this problem, the &#39;846 patent discloses a separate nozzle associated with each pin and localized at the pin structure to flush the pin area with a gas. The gas prevents the treatment liquid from flowing along the pin and treating the edge surfaces and chuck-facing surface of the wafer. 
     SUMMARY OF THE INVENTION 
     In certain processes, it is desirable to treat a main surface of the wafer while not treating the opposite main surface of the wafer and also not treating the edge surfaces of the wafer. In certain processes, it is furthermore desirable to prevent treatment of the edge surfaces of a wafer along the entire circumference of the wafer. It may also be desirable to limit the vertical displacement of the wafer during such treatment if using a gas at flow rates in excess of those necessary to create an equilibrium with the vacuum forces attracting the wafer to the chuck. In particular, for chucks that use gas flushing of the underside of a wafer to control liquid treatment applied to the top side of the wafer, such as disclosed in the &#39;717 and &#39;846 patents, it can be desirable to increase the flow of gas to affect the means by which the flowing gas controls or limits the treatment liquid. However, increasing the flow of gas in such chucks can lift the wafer away from the chuck if the wafer is not secured against such vertical movement. 
     One object of the invention is to limit treatment of the edge and downwardly-facing surfaces of a wafer during liquid treatment of an upwardly-facing surface of a wafer. The invention achieves this by guiding a flow of gas to generally follow the contours of a wafer&#39;s edge surfaces. The gas flushes the edge surfaces and thereby prevents processing liquid applied to an upper main surface of the wafer from treating an edge area of the wafer defined by the flowing gas. 
     In preferred embodiments a plurality of annular nozzles serves to flush substantially the entire circumference of the wafer&#39;s edge. These annular nozzles define narrow and less narrow annular passages as measured from the surface of the wafer facing the structures through which gas flows around the edge of the wafer, and then away from the upper surface of the wafer. The preferred embodiments also include retaining pins with heads configured to limit the movement of the wafer in the vertical direction when the gas flow underneath the wafer is increased. 
     The disclosed embodiments are spin chucks that uses a flow of gas to support the wafer upon a gas cushion; however, the invention is also applicable to treating surfaces of other materials, for example glass masters and mother panels used in manufacturing optical disks and LCD display panels. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate preferred embodiments of the present invention and, together with the ensuing description, serve further to explain the invention. In the drawings: 
         FIG. 1  is a schematic perspective view of an apparatus for single wafer wet processing, including a spin chuck  1  comprising a ring  50  and carrying a wafer W; 
         FIG. 2  is a more detailed perspective view, partly in section, of the spin chuck of  FIG. 1 ; 
         FIG. 3  is an axial cross-section of the spin chuck of  FIG. 1 ; 
         FIG. 4  is an enlarged view of detail IV of  FIG. 3 ; 
         FIG. 5  is an enlarged view of detail V of  FIG. 3 ; 
         FIG. 6  is a view similar to  FIG. 2  at a different angular orientation of the spin chuck  1 ; 
         FIG. 7  is an enlarged view of detail VII of  FIG. 6 ; 
         FIG. 8  is an enlarged view of the detail VIII of  FIG. 7 ; and 
         FIG. 9  is a perspective view of a pin  56  as shown in  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1  wafer W is floats on a cushion of gas and is prevented from moving upward beyond a predetermined distance above the spin chuck  1  by pins that will be described hereinafter. Processing liquid is dispensed onto the wafer through dispenser  2 . As described in detail below, ring  50  is configured to prevent processing liquid from treating the wafer&#39;s underside or more than a predetermined amount of the wafer&#39;s edge surfaces. 
     As shown in  FIG. 2  the spin chuck  1  includes three base body elements: a lower part  10 , a middle part  20 , and an upper part  30 . The lower and middle base body elements are preferably secured together with screws, one of which is shown at  15 . 
     Ring  50  is mounted to the chuck by mounting screws  51 . The ring has openings to allow gripping pins  56  to extend through ring  50  and above the upper plane of the chuck. Six pockets  49  are formed into the ring so that an edge-contact-only gripper (e.g. as described in U.S. Pat. No. 5,762,391) can remove a wafer from the chuck or place a wafer onto the chuck. 
     Between the middle part  20  and the upper part  30  there is space  25  that can be filled with clean pressurized gas (e.g. nitrogen). Pressurized gas in space  25  flows through the three concentrically arranged arrays of nozzles: the inner nozzle array  32 , the middle nozzle array  33 , and the outer nozzle array  34 . The gas exhausted through the nozzles  32 ,  33 ,  34  provides a gas cushion, on which the wafer floats and may also assist in securing the wafer to the chuck via the Bernoulli principle. 
     In  FIG. 3 , between the lower part  10  and the middle part  20 , there is a space provided that accommodates a toothed gear ring  73 , which is connected to the lower base body element through the ball bearing  72 . With rod  71  the tooth gear  73  can be fixed when the chuck rotates by a few degrees so that the tooth gear  73  drives the pins  56  for opening. The tooth gear is held in a closed position by springs (not shown). 
       FIG. 4  depicts in detail the structures of upper base body  30  and ring  50  that route the gas exhausted from nozzles  32 ,  33 , and  34  from the chuck-facing surface of the wafer, around the edge portion of wafer, and away from the upper surface of the wafer. 
     The upper surface of the upper base body part  30  (the chuck surface facing the wafer) is conical in its peripheral region, and describes a cone whose apex is below the upper surface of the chuck. Thus, when a wafer W is positioned perpendicular to the axis of rotation of the chuck and at a predetermined distance of the chuck, the horizontal downwardly-facing periphery of the wafer and the conical periphery of the upper chuck surface will together define an annular nozzle  35  that narrows radially outwardly of the chuck and terminates in an annular opening of axial extent “a”. In the depicted embodiment the opening “a” is 0.3 mm. More generally, the opening “a” is preferably in the range of 0.1 mm to 1 mm, and more preferably in the range of 0.2 mm to 0.5 mm. 
     The conical periphery of the upper base body part  30  is delimited by a convex cylindrical shoulder that confronts ring  50  and is separated therefrom by an annular gap or space  36  that is thus defined radially inwardly by that shoulder. The other bounds of space  36  are the concave cylindrical radially-inwardly facing surface of ring  50 , a lower portion of based body  30 , and, in use, the wafer. Gas is exhausted into this space from nozzle  35 . 
     A second annular nozzle is defined by the conical lip  37  formed on ring  50  together with the overlying wafer surface. In the embodiment shown, gas exiting nozzle  35  and passing through gap  36  must pass though the annular nozzle formed by lip  37  and the wafer, and substantially all gas exhausted from gap  36  passes through this annular nozzle. This second nozzle is formed by the differential distance between the lip  37  and the wafer W at its narrowest point and distances upstream from this point (i.e. in space or gap  36 ) where the distances between the chuck (i.e. the ring and base body  30 ) are greater. As depicted, the distance between the chuck and the wafer narrows in the direction of flow along the slanted portion of lip  37 . Also, more upstream distances between the chuck and the wafer in space  36  are greater than any such distance along the slanted portion of lip  37 . 
     A third annular nozzle is formed by shoulder  53  and the peripheral edge of wafer W that it confronts. Gas exhausted from the nozzle created by lip  37  and the wafer encounters annular space  52 . Space  52  includes distances from the wafer to the chuck (i.e. ring  50 ) greater than the narrowest distance from the wafer to the chuck at lip  37 . Also, distance “b” of the annular nozzle created by shoulder  53  represents a relative narrowing of the distance of the chuck to the wafer as compared to those in space  52 . The distance “b” is preferably 0.3 mm to 3 mm, and more preferably 0.5 mm to 2 mm. Gas is exhausted from the third nozzle in a manner that prevents treatment liquid from treating the wafer&#39;s edge surfaces. 
     The three annular nozzles depicted in  FIG. 4  are each formed by the combination of the chuck and the wafer. For each nozzle, the shape of the chuck is such that the more upstream portions of the nozzle define a relatively greater distance from the wafer than the distance from the water defined by more downstream portions of the nozzle. These differential distances correspond to differential volume areas through which gas flows. 
       FIG. 5  depicts the manner in which screws  51  secure ring  50  to upper base body  30 . Although the depicted embodiment provides for a ring  50 , alternative embodiments could integrate the structures necessary for creating the plurality of peripheral annular nozzles into the chuck base body. For example, ring  50  could be integrated into base element  30  and the lip  37 , shoulder  53 , and the annular space  52  between these could be integrated into base  30  rather than ring  50 . 
     Pins  56  have a specific shape at their upper end to limit the movement of the wafer in the axial direction during its treatment. The upper end of each pin  56  is mushroom-shaped or outwardly flared at head  59  (see  FIGS. 8 and 9 ). The ring  50  includes holes allowing the pin to pass through the ring and pivot through its eccentric range of motion (see  FIG. 8 ). In order to drain the hole provided for the pin an opening  55  is provided in the ring  50 . Tooth gear  73  drives the pins though complementary gear teeth (not shown) at the base  75  of the pins. The tooth gear  73  controls the opening and closing of the pins onto the wafer by rotating the pins. 
     In a typical processing of a wafer, when the wafer is loaded a gas flow is selected that allows the wafer to be supported above the chuck on a cushion without touching the chuck. This initial gas flow corresponds to that conventionally used in Bernoulli-type chucks, which is to say that the rate of flow is selected such that the upwardly directed force on the wafer approximately counterbalances the vacuum force created by the radially-outwardly accelerating gas flow. After the pins are closed and the wafer is confined against further upward displacement, the gas flow may be selectively increased, which increases the lifting force of the gas flow. However, the vertical lifting of the wafer from the chuck will be limited due to the pins. The pins are shaped with a head portion of increased diameter as compared to a body portion. By using such pins, the vertical movement of the wafer is limited and an increase in the rate of flow of gas increases the velocity of the gas through the series of annular nozzles, but not the distance of the wafer from the chuck. 
     The steps of a typical wafer processing according to the invention are described in the following table: 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                 spin 
                 etchant 
                   
                   
               
               
                   
                   
                   
                 speed  
                 volume 
                 DI- 
                   
               
               
                   
                   
                 N2- 
                 of the  
                 flow 
                 water 
                   
               
               
                 Process 
                   
                 volume 
                 chuck 
                 (HF) 
                 20°- 
                 time 
               
               
                 Step 
                 Pins 
                 flow 
                 [rpm] 
                 20°-80° C. 
                 80° C. 
                 [s] 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 load 
                 open 
                 10 L/min 
                 0 
                 0 
                 0 
                 5 
               
               
                 2 after 
                 closed 
                 50-400  
                 100 
                 0 
                 0 
                 2 
               
               
                 pin  
                   
                 L/min 
                   
                   
                   
                   
               
               
                 close 
                   
                 (prefer- 
                   
                   
                   
                   
               
               
                   
                   
                 ably 
                   
                   
                   
                   
               
               
                   
                   
                 200-300) 
                   
                   
                   
                   
               
               
                 3 
                 closed 
                 50-400 
                 100-2000 
                 0.5-3.0 
                 0 
                 5-1000 
               
               
                 process 
                   
                 L/min 
                 (prefer- 
                 L/min 
                   
                 (prefer- 
               
               
                   
                   
                 (prefer- 
                 ably 
                   
                   
                 ably 
               
               
                   
                   
                 ably 
                 300- 
                   
                   
                 10-60) 
               
               
                   
                   
                 200-300) 
                 1500) 
                   
                   
                   
               
               
                 4 spin  
                 closed 
                 50-400  
                 500-2000 
                 0 
                 0 
                 2-30  
               
               
                 off 
                   
                 L/min 
                 (prefer- 
                   
                   
                 (prefer- 
               
               
                   
                   
                 (prefer- 
                 ably 
                   
                   
                 ably 
               
               
                   
                   
                 ably 
                 1000- 
                   
                   
                 5-10) 
               
               
                   
                   
                 200-300) 
                 1500) 
                   
                   
                   
               
               
                 5 pre 
                 closed 
                 10 L/min 
                 100-1500 
                 0 
                 0 
                 1 
               
               
                 wafer 
                   
                   
                 (prefer- 
                   
                   
                   
               
               
                 shift 
                   
                   
                 ably 
                   
                   
                   
               
               
                   
                   
                   
                 300-500) 
                   
                   
                   
               
               
                 6 wafer 
                 open 
                 10 L/min 
                 e.g. 
                 0 
                 0 
                 0.1 
               
               
                 shift 
                   
                   
                 100/500/ 
                   
                   
                   
               
               
                   
                   
                   
                 100 
                   
                   
                   
               
               
                   
                   
                   
                 500/100/ 
                   
                   
                   
               
               
                   
                   
                   
                 500 
                   
                   
                   
               
               
                 7  
                 closed 
                 50-400  
                 100-2000 
                 0.5-3.0 
                 0 
                 5-1000 
               
               
                 etching 
                   
                 L/min 
                 (prefer- 
                 L/min 
                   
                 (prefer- 
               
               
                 process 
                   
                 (prefer- 
                 ably 
                   
                   
                 ably 
               
               
                   
                   
                 ably 
                 300- 
                   
                   
                 10-60) 
               
               
                   
                   
                 200-300) 
                 1500) 
                   
                   
                   
               
               
                 8  
                 closed 
                 50-400  
                 100-2000 
                 0 
                 0.5- 
                 5-60  
               
               
                 rinsing 
                   
                 L/min 
                 (prefer- 
                   
                 3.0  
                 (prefer- 
               
               
                   
                   
                 (prefer- 
                 ably 
                   
                 L/min 
                 ably 
               
               
                   
                   
                 ably 
                 300- 
                   
                   
                 15-25) 
               
               
                   
                   
                 200-300) 
                 1500) 
                   
                   
                   
               
               
                 9  
                 closed 
                 50-400  
                 500-2000 
                 0 
                 0 
                 5-60  
               
               
                 spin 
                   
                 L/min 
                 (prefer- 
                   
                   
                 (prefer- 
               
               
                 dry 
                   
                 (prefer- 
                 ably 
                   
                   
                 ably 
               
               
                   
                   
                 ably 
                 1000- 
                   
                   
                 15-25) 
               
               
                   
                   
                 200-300) 
                 1500) 
                   
                   
                   
               
               
                 10 
                 open 
                 50-400  
                 0 
                 0 
                 0 
                 5 
               
               
                 unload 
                   
                 L/min 
                   
                   
                   
                   
               
               
                   
                   
                 (prefer- 
                   
                   
                   
                   
               
               
                   
                   
                 ably 
                   
                   
                   
                   
               
               
                   
                   
                 100-200) 
               
               
                   
               
             
          
         
       
     
     The wafer shift at step  6  is desirable because the wafer edge will be treated differently at the pocket areas  49  and at the areas near the pins  56 . In order to achieve a more evenly processed wafer edge the wafer is preferably shifted by some degrees with respect to the chuck. Depending on the direction of the rotation whether clockwise or counter-clockwise the chuck speed will be reduced or increased for example by a tenth of a second. Because of the moment of inertia of the tooth gear  73  the tooth gear will rotate some degrees relative to the chuck base body and thus the pins will be opened. When the pins are open the wafer will rotate relative to the chuck due to its moment of inertia. Thereafter the wafer is automatically secured by the pins again, but at a somewhat twisted position. 
     It will therefore be understood that the ring profile depicted in  FIG. 4  (and, optionally, also gap  36 ) may be interrupted by other structures such as the pins  56  and the pockets  49 . The ring profile as depicted in  FIG. 4  nevertheless preferably extends over a majority of the circumference of the upper surface of the chuck body, and furthermore preferably extends uninterrupted over multiple arcuate ranges spanning from 15° to 20° of the full 360° circumference of the upper surface of the chuck body. 
     The foregoing description and the illustrative embodiments of the present invention have been described in detail with respect to a particular embodiment. It should be understood, however, that the foregoing description of the present invention is exemplary only, and that the scope of the present invention is to be limited only to the claims as properly construed. 
     For chucks that support the wafer with a gas cushion, and/or for chucks securing the wafer with the Bernoulli effect, the same gas medium used for supporting the wafer and/or used to regulate the Bernoulli effect may be directed through the plurality of edge-region annular nozzles according to the invention. For such chucks, each annular nozzle is disposed peripheral to an area where the gas cushion is formed between the chuck and the wafer. 
     Although the depicted embodiment provides that the same gas flow assists in supporting the wafer and, additionally, is utilized to prevent treatment fluid from reaching the wafer&#39;s edge surfaces according to the invention, it is not necessary that the present invention be implemented on a chuck utilizing such a gas cushion.