Patent Publication Number: US-2013233356-A1

Title: Process and apparatus for treating surfaces of wafer-shaped articles

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to processes and apparatus for treating surfaces of wafer-shaped articles, such as semiconductor wafers, wherein one or more treatment liquids are dispensed onto a surface of the wafer-shaped article. 
     2. Description of Related Art 
     Semiconductor wafers are subjected to various surface treatment processes such as etching, cleaning, polishing and material deposition. To accommodate such processes, a single wafer may be supported in relation to one or more treatment fluid nozzles by a chuck associated with a rotatable carrier, as is described for example in U.S. Pat. Nos. 4,903,717 and 5,513,668. 
     Alternatively, a chuck in the form of a ring rotor adapted to support a wafer may be located within a closed process chamber and driven without physical contact through an active magnetic bearing, as is described for example in International Publication No. WO 2007/101764 and U.S. Pat. No. 6,485,531. 
     In either type of device, process liquids are dispensed onto one or both major surfaces of the semiconductor wafer as it is being rotated by the chuck. Such process liquids may for example be strong oxidizing compositions such as mixtures of sulfuric acid and peroxide for cleaning surfaces of the semiconductor wafer. Such process liquids typically also include deionized water to rinse the wafer between processing steps, and the deionized water is commonly supplemented with isopropyl alcohol to reduce the surface tension of the rinse liquid on the wafer. 
     As the dimensions of the semiconductor devices formed on these wafers continue to decrease, new demands are made on the equipment for processing the wafers. Smaller device structures are more susceptible to “pattern collapse” when the surface tension of the rinse liquid or other processing liquid on the wafer is too great, a problem which arises from not only the reduced device dimensions but also from the typically higher aspect ratios that accompany smaller device structures. 
     These problems are exacerbated by the concurrent trend of increasing wafer diameter. Fabrication plants designed for semiconductor wafers of 200 mm diameter are increasingly giving way to those utilizing semiconductor wafers of 300 mm diameter, and a standard for the next generation of 450 mm wafers has already been developed. As the process liquids travel across larger wafer diameters, the potential increases for variations in the temperature and viscosity of the liquid as a function of distance from the point of dispensing, which can lead to inconsistent process performance. 
     Conventional wafer processing devices have included dispensing nozzles mounted on a swinging boom arm, so that the point of dispensing can be moved across the surface of the wafer, and have also included plural movable nozzles and showerheads as shown for example in U.S. Pat. Nos. 6,834,440 and 7,017,281 and U.S. Published Patent Appln. No. 2006/0086373. However, these approaches add mechanical complexity to the processing equipment, and, especially in the case of closed process chambers, the moving parts constitute a potential source of particle contamination. Furthermore, they do not necessarily afford sufficient control over the behavior and physical properties of the liquid across the wafer surface. 
     SUMMARY OF THE INVENTION 
     The present inventors have developed improved processes and apparatus for treating wafer-shaped articles, in which at least one array of stationary nozzles is arranged along the radius of a wafer-shaped article, with each of the nozzles being equipped with its own computer-controlled valve. 
     Thus, the invention in one aspect relates to an apparatus for processing wafer-shaped articles, comprising a rotary chuck adapted to hold a wafer shaped article of a predetermined diameter thereon and to rotate the wafer shaped article about an axis of rotation, and a liquid-dispensing device comprising an array of liquid-dispensing nozzles. The nozzles in a process position of the liquid-dispensing device open adjacent a major surface of a wafer shaped article positioned on the rotary chuck. The array of nozzles extends radially from an innermost nozzle positioned closest to the axis of rotation to an outermost nozzle positioned closest to a periphery of a wafer shaped article positioned on the rotary chuck. The liquid dispensing device further comprises an array of conduits with each of the conduits communicating with a corresponding one of the array of nozzles. Each of the conduits is equipped with a respective computer-controlled valve, such that a flow of liquid through each of the nozzles can be controlled independently of a flow of liquid through any others of the nozzles. The array of nozzles is mounted such that the nozzles when in the process position are not movable relative to one another in a direction perpendicular to the axis of rotation. 
     In preferred embodiments of the apparatus according to the present invention, the array of liquid-dispensing nozzles comprises at least three liquid dispensing nozzles, preferably 3-7 liquid-dispensing nozzles, more preferably 4-6 liquid-dispensing nozzles, and most preferably 5 liquid-dispensing nozzles. 
     In preferred embodiments of the apparatus according to the present invention, the liquid dispensing device comprises a plurality of arrays of liquid-dispensing nozzles, wherein each of the arrays of liquid dispensing nozzles extends radially from an innermost nozzle positioned closest to the axis of rotation to an outermost nozzle positioned closest to a periphery of a wafer shaped article positioned on the rotary chuck. 
     In preferred embodiments of the apparatus according to the present invention, the liquid dispensing device comprises two to four arrays of liquid-dispensing nozzles, and preferably three arrays of liquid-dispensing nozzles. 
     In preferred embodiments of the apparatus according to the present invention, each of the arrays of liquid-dispensing nozzles is in communication with a respectively different liquid supply. 
     In preferred embodiments of the apparatus according to the present invention, the innermost nozzle of at least one array of liquid-dispensing nozzles opens on the axis of rotation so as to dispense liquid onto a center of a wafer-shaped article positioned on the rotary chuck. 
     In preferred embodiments of the apparatus according to the present invention, the apparatus includes a process chamber enclosing the rotary chuck, the process chamber comprising a cover, and wherein the liquid-dispensing device is mounted at least partially in the cover such that the liquid-dispensing nozzles extend into the chamber from the cover in a direction parallel to the axis of rotation. 
     In preferred embodiments of the apparatus according to the present invention, there is provided a central liquid supply nozzle separate from the liquid-dispensing device, the central liquid supply nozzle opening on the axis of rotation so as to dispense liquid onto a center of a wafer-shaped article positioned on the rotary chuck. 
     In preferred embodiments of the apparatus according to the present invention, each of the computer-controlled valves is positioned along its respective conduit at a distance from 5 mm-15 mm upstream of an opening of its respective liquid-dispensing nozzle. 
     In preferred embodiments of the apparatus according to the present invention, at least one of the liquid-dispensing nozzles has a dispensing opening whose diameter differs from a dispensing opening of at least one other of the liquid-dispensing nozzles. 
     In another aspect, the present invention relates to method for processing wafer-shaped articles, comprising positioning a wafer-shaped article on a rotary chuck, rotating the wafer shaped article about an axis of rotation, and dispensing a first liquid onto a surface of the wafer-shaped article through an array of liquid-dispensing nozzles. The array of nozzles extends radially from an innermost nozzle positioned closest to the axis of rotation to an outermost nozzle positioned closest to a periphery of the wafer shaped article. During the dispensing each of the array of nozzles is individually controlled by a respective computer-controlled valve, such that a flow of liquid through each of the nozzles during the dispensing is controlled independently of a flow of liquid through any others of the nozzles. The nozzles are stationary relative to one another throughout the dispensing. 
     In preferred embodiments of the method according to the present invention, the dispensing comprises dispensing a first liquid having a same composition through each of the nozzles within the array, with the computer-controlled valves being opened and closed sequentially from the innermost nozzle to the outermost nozzle. 
     In preferred embodiments of the method according to the present invention, the array of nozzles comprises at least three nozzles, and the dispensing comprises first dispensing the first liquid through the innermost nozzle simultaneously with an adjacent nozzle of the array, while the outermost nozzle remains closed, and subsequently dispensing the first liquid through the outermost nozzle simultaneously with an adjacent nozzle of the array, while the innermost nozzle remains closed. 
     In preferred embodiments of the method according to the present invention, the array of nozzles comprises at least three nozzles, and the dispensing comprises dispensing the first liquid through only one of the array of nozzles at any given time. 
     In preferred embodiments of the method according to the present invention, a second liquid is dispensed through a further array of nozzles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects, features and advantages of the invention will become more apparent after reading the following detailed description of preferred embodiments of the invention, given with reference to the accompanying drawings, in which: 
         FIG. 1  is an explanatory perspective view of one embodiment of the apparatus according to the present invention; 
         FIG. 2  is an explanatory cross-sectional side view of a process chamber according to a second embodiment of the invention, with the interior cover shown in its first position; 
         FIG. 3  is an explanatory cross-sectional side view of a process chamber according to the second embodiment of the invention, with the interior cover shown in its second position; 
         FIGS. 4   a ,  4   b ,  4   c  and  4   d  are a sequential series of schematic illustrations showing one dispensing sequence according to an embodiment of the present invention; 
         FIGS. 5   a ,  5   b ,  5   c  and  5   d  are a sequential series of schematic illustrations showing another dispensing sequence according to an embodiment of the present invention; 
         FIG. 6  is an explanatory cross-sectional side view of a process chamber according to a third embodiment of the invention, with the interior and exterior covers shown in their first position; and 
         FIG. 7  is an explanatory cross-sectional side view of a process chamber according to the third embodiment of the invention, with the interior and exterior covers shown in their second position. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , shown therein is an apparatus for treating surfaces of wafer-shaped articles according to a first embodiment of the invention. The overall structure illustrated in  FIG. 1  is similar to the apparatus shown in FIGS. 2a-2f of commonly-owned U.S. Patent Application Pub. No. 2011/0253181 (corresponding to WO 2010/113089). In  FIG. 1 , the device  100  comprises a chamber defined by lower plate  165 , upper transparent cover  163 , and cylindrical wall  160  extending therebetween. The annular chuck  120  positioned within the chamber is levitated and rotated magnetically in cooperation with a stator surrounding the chamber and enclosed within stator housing  190 . 
     A lower dispensing tube  167  is led through the bottom plate  165  of the chamber. Reference numeral  181  denotes a first array of four radially arranged nozzles for supplying acid (e.g. hydrofluoric acid) to an upper surface of wafer W. Each of nozzles  181  passes through the transparent cover  163  and has an orifice at its lower end opening into the chamber. A second array  182  of four radially arranged nozzles supplies a basic liquid (e.g. ammonia with hydrogen peroxide SC 1 ). A third array  183  array of four radially arranged nozzles supplies deionized water. 
     Separately from the nozzle arrays  181 ,  182 ,  183 , a single central nozzle  184  supplies a fourth liquid (e.g. isopropyl alcohol). 
     The embodiment depicted in  FIG. 2  comprises an outer process chamber  1 , which is preferably made of aluminum coated with PFA (perfluoroalkoxy) resin. The chamber in this embodiment has a main cylindrical wall  10 , a lower part  12  and an upper part  15 . From upper part  15  there extends a narrower cylindrical wall  34 , which is closed by a lid  36 . 
     A rotary chuck  30  is disposed in the upper part of chamber  1 , and surrounded by the cylindrical wall  34 . Rotary chuck  30  rotatably supports a wafer W during use of the apparatus. The rotary chuck  30  incorporates a rotary drive comprising ring gear  38 , which engages and drives a plurality of eccentrically movable gripping members for selectively contacting and releasing the peripheral edge of a wafer W. 
     In this embodiment, the rotary chuck  30  is a ring rotor provided adjacent to the interior surface of the cylindrical wall  34 . A stator  32  is provided opposite the ring rotor adjacent the outer surface of the cylindrical wall  34 . The rotor  30  and stator  34  serve as a motor by which the ring rotor  30  (and thereby a supported wafer W) may be rotated through an active magnetic bearing. For example, the stator  34  can comprise a plurality of electromagnetic coils or windings that may be actively controlled to rotatably drive the rotary chuck  30  through corresponding permanent magnets provided on the rotor. Axial and radial bearing of the rotary chuck  30  may be accomplished also by active control of the stator or by permanent magnets. Thus, the rotary chuck  30  may be levitated and rotatably driven free from mechanical contact. Alternatively, the rotor may be held by a passive bearing where the magnets of the rotor are held by corresponding high-temperature-superconducting magnets (HTS-magnets) that are circumferentially arranged on an outer rotor outside the chamber. With this alternative embodiment each magnet of the ring rotor is pinned to its corresponding HTS-magnet of the outer rotor. Therefore the inner rotor makes the same movement as the outer rotor without being physically connected. 
     The lid  36  has a manifold  42  mounted on its exterior, which supplies a series of conduits  43 - 46  that traverse the lid  36  and terminate in respective nozzles  53 - 56  whose openings are adjacent the upper surface of wafer W. It will be noted that the wafer W in this embodiment hangs downwardly from the rotary chuck  30 , supported by the gripping members  40 , such that fluids supplied through nozzles  53 - 56  would impinge upon the upwardly facing surface of the wafer W. 
     Each conduit  43 - 46  is equipped with its own valve  47 , only one of which is labeled in  FIG. 2  for the sake of clarity. Valves  47  are individually computer controlled, as will be described in more detail hereinafter. 
     A separate liquid manifold  62  supplies liquid to a single central nozzle  67 , via conduit  63 . Conduit  63  is equipped with its own computer-controlled valve  68 . 
     In case wafer  30  is a semiconductor wafer, for example of 300 mm or 450 mm diameter, the upwardly facing side of wafer W could be either the device side or the obverse side of the wafer W, which is determined by how the wafer is positioned on the rotary chuck  30 , which in turn is dictated by the particular process being performed within the chamber  1 . 
     Nozzles  53 - 56  and  67  may if desired be mounted for axial movement relative to one another and lid  36 ; however, they are preferably fixed, because movement in the axial direction would confer no particular advantage, and because such movement would constitute a potential source of particulate contamination interiorly of the chamber. 
     Similarly, nozzles  53 - 56  may be adjustable as to their radial position when lid  36  is removed from the apparatus  1 ; however, in their process position illustrated in  FIG. 2 , they are not movable in the radial direction relative to one another or relative to lid  36 . This stationary mounting similarly prevents particulate contamination of the chamber ambient. Moreover, owing to the nozzle configuration and individual valve arrangement according to the present invention, the need for the nozzles to move radially of the wafer W has been eliminated. Although the nozzles  53 - 56  in  FIG. 2  are disposed within the chamber  1 , it is also possible that the nozzles be positioned within the lid such that the orifices of the nozzles are flush with the inner surface of lid  36 . In that case the associated conduits  43 - 46  and valves  47  would be positioned outside of the chamber  1 , either within lid  36  or above it. 
     The apparatus of  FIG. 1  further comprises an interior cover  2 , which is movable relative to the process chamber  1 . Interior cover  2  is shown in  FIG. 1  in its first, or open, position, in which the rotary chuck  30  is in communication with the outer cylindrical wall  10  of chamber  1 . Cover  2  in this embodiment is generally cup-shaped, comprising a base  20  surrounded by an upstanding cylindrical wall  21 . Cover  2  furthermore comprises a hollow shaft  22  supporting the base  20 , and traversing the lower wall  14  of the chamber  1 . 
     Hollow shaft  22  is surrounded by a boss  12  formed in the main chamber  1 , and these elements are connected via a dynamic seal that permits the hollow shaft  22  to be displaced relative to the boss  12  while maintaining a gas-tight seal with the chamber  1 . 
     At the top of cylindrical wall  21  there is attached an annular deflector member  24 , which carries on its upwardly-facing surface a gasket  26 . Cover  2  preferably comprises a fluid medium inlet  28  traversing the base  20 , so that process fluids and rinsing liquid may be introduced into the chamber onto the downwardly facing surface of wafer W. 
     Cover  2  furthermore includes a process liquid discharge opening  23 , which opens into a discharge pipe  25 . Whereas pipe  25  is rigidly mounted to base  20  of cover  2 , it traverses the bottom wall  14  of chamber  1  via a dynamic seal  17  so that the pipe may slide axially relative to the bottom wall  14  while maintaining a gas-tight seal. An exhaust opening  16  traverses the wall  10  of chamber  1 , and is connected to a suitable exhaust conduit (not shown). 
     The position depicted in  FIG. 1  corresponds to loading or unloading of a wafer W. In particular, a wafer W can be loaded onto the rotary chuck  30  either by removing the lid  36 , or, more preferably, through a side door  33  in the chamber wall  10 . However, when the lid  36  is in position and when side door  33  has been closed, the chamber  1  is gas-tight and able to maintain a defined internal pressure. 
     In  FIG. 2 , the interior cover  2  has been moved to its second, or closed, position, which corresponds to processing of a wafer W. That is, after a wafer W is loaded onto rotary chuck  30 , the cover  2  is moved upwardly relative to chamber  1 , by a suitable motor (not shown) acting upon the hollow shaft  22 . The upward movement of the interior cover  2  continues until the deflector member  24  comes into contact with the interior surface of the upper part  15  of chamber  1 . In particular, the gasket  26  carried by deflector  24  seals against the underside of upper part  15 , whereas the gasket  18  carried by the upper part  15  seals against the upper surface of deflector  24 . 
     When the interior cover  2  reaches its second position as depicted in  FIG. 2 , there is thus created a second chamber  48  within the closed process chamber  1 . Inner chamber  48  is moreover sealed in a gas tight manner from the remainder of the chamber  1 . 
     During processing of a wafer, processing fluids may be directed through nozzles  53 - 56 ,  67  and/or  28  to a rotating wafer W in order to perform various processes, such as etching, cleaning, rinsing, and any other desired surface treatment of the wafer undergoing processing. 
     For example, in  FIGS. 4   a - 4   d , the valves  47  of nozzles  53 - 56  are controlled so as to effect a radial sweeping motion of the dispensed liquid across the upper surface of the wafer, as might be achieved with a conventional boom arm, but without the disadvantages associated with a moving nozzle assembly. In  FIG. 4   a , the valve  47  associated with the radially innermost nozzle  56  is open, whereas the valves  47  associated with nozzles  53 - 55  are closed. Liquid is therefore dispensed only through nozzle  56 . After a predetermined interval, which may be as short as a few milliseconds or as long as a few seconds, the valve  47  for nozzle  56  is closed and the valve  47  for the next adjacent nozzle  55  is almost instantaneously opened, as shown in  FIG. 4   b . The process is repeated by closing nozzle  55  after a predetermined interval and opening nozzle  54 , as shown in  FIG. 4   c . Next, the radially outermost or peripheral nozzle  53  is opened and nozzle  54  is closed, as shown in  FIG. 4   d.    
     The sequence may be repeated in the reverse order to cause “scanning” of the dispensed liquid from the periphery toward the center of the wafer. 
     An alternative sequence of opening and closing the valves  47  is illustrated in  FIGS. 5   a - 5   d , from which it can be seen that the nozzles  53 - 56  are opened and closed in pairs. That is, the valves  47  for the radially innermost nozzle  56  and the next adjacent nozzles are opened together, as shown in  FIG. 5   a , while the valves  47  for nozzles  53  and  54  remain closed. Next, the valve for nozzle  56  is closed simultaneously with opening the valve for nozzle  54 , while the valve for nozzle  55  remains open ( FIG. 5   b ). The process is repeated so as to open nozzles  53  and  54  ( FIG. 5   c ), whereafter, if desired, the sequence can be reversed as illustrated in  FIG. 5   d , which is actually the same valve state as in  FIG. 5   b . This alternative sequence permits “scanning” the wafer surface while contacting a relatively larger area of the wafer at any given time. 
     The foregoing examples make plain to those skilled in the art that the apparatus and methods according to the present invention permit a wide range of tuning of liquid flows to particular process requirements. That is, by suitable selection of the number of nozzles in the or each array, the diameters of the nozzle orifices, which may the same or different, the duration of valve opening for each nozzle and the extent of overlap, if any, in the opening times of adjacent nozzles, it is possible to achieve a more homogeneous etch result than with conventional devices and techniques. That is, for example, the etch speed (expressed in nm/min or Angstrom/min) may be more nearly the same in the center of the wafer as it is near the edge. 
       FIGS. 7 and 8  show a third embodiment of the present invention, in which the chamber design of the first embodiment is adapted for use with a spin chuck in which a wafer W is mounted on an upper side of a chuck that is rotated through the action of a motor on a central shaft. 
     In particular, wafer W is loaded onto spin chuck  80  when interior cover  2  is in the loading/unloading position depicted in  FIG. 7 , and wafer W is secured in the predetermined orientation relative to chuck  80  by gripping members  82 . The chuck  80  is accessed by removal of cover  86 , which is movable both vertically and horizontally by translation and rotation of the lid about the hydraulic shaft  84  of motor  88 , as shown by the arrow in  FIG. 7 . 
     Lid  86  is then rotated back to its position overlying the wafer, and lowered so as to seal the outer chamber, as shown in  FIG. 7 . Interior cover  2  is then moved to its second position, as shown in  FIG. 7  and as described above in connection with the second embodiment, to define the inner chamber  48 . 
     In this embodiment, it will be seen that spin chuck  80  is also vertically moveable relative to the interior cover  2 , so that it can be raised to an optimum processing position within the chamber  48 . Spin chuck  80  is then rotated by a motor (not shown) acting upon shaft  85 . 
     Alternatively, the lid  86  may be kept open during the liquid supply. In such a case the lid  86  may be replaced by a media arm carrying the array of the plurality of nozzles.