Abstract:
An apparatus for treating a disc-shaped article comprises a spin chuck and at least three individually controllable infrared heating elements. The infrared heating elements are mounted in a stationary manner with respect to rotation of said spin chuck. At least the transparent plate positioned between the infrared heating elements and the underside of a wafer is mounted for rotation with the spin chuck. Alternatively, the transparent plate is part of a housing that encloses the infrared heating elements and that rotates with the spin chuck as the heating elements are stationary relative thereto.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present disclosure is a divisional of U.S. patent application Ser. No. 13/894,950 (now U.S. Pat. No. 9,245,777) filed on May 15, 2013. The entire disclosure of the application referenced above is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an apparatus for liquid treatment of wafer-shaped articles, and to a heating system for use in such an apparatus. 
     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 distribution of the liquid may be assisted by the rotational motion imparted to the wafer. 
     Techniques for processing a surface of a disc-shaped article are typically used in the semiconductor industry on silicon wafers, for example of 300 mm or 450 mm diameter. However, such techniques may be applied for other plate-like articles such as compact discs, photo masks, reticles, magnetic discs or flat panel displays. When used in semiconductor industry they may also be applied for glass substrates (e.g. in silicon-on-insulator processes), III-V substrates (e.g. GaAs) or any other substrate or carrier used for producing integrated circuits. 
     When using heated process liquids, there is a problem in achieving temperature uniformity across the surface of the wafer, and the need to address that problem becomes more acute as wafer diameters increase. 
     In particular, as the wafer diameter increases, so too will the temperature differential between a liquid at the point where it is applied in a central region of the wafer and the same liquid after it has travelled radially outwardly to the periphery of the wafer. This results in varied etch rates as a function of the distance from the center of the wafer, and hence poor process uniformity. 
     Conventional approaches to alleviate this problem have included dispensing process liquid from movable arms, so-called “boom swing” dispensers; however, this involves an increase in the cost and complexity of the device as well as its operation. The problem can be addressed to some extent by increasing the flow of process liquid, and/or by dispensing a high temperature liquid such as deionized water on the opposite side of the wafer; however, these techniques result in higher consumption of process liquids. 
     U.S Patent Application Pub. No. 2013/0061873 describes improved apparatus equipped with an infrared heater for heating a wafer to enhance process uniformity. Although the devices of that patent application represent an improvement over conventional techniques, there remains a need to provide further enhanced process uniformity and equipment that is more robust and easier to maintain. 
     SUMMARY OF THE INVENTION 
     Thus, in one aspect, the present invention relates to an apparatus for treating a wafer-shaped article, comprising a spin chuck for holding a wafer-shaped article in a predetermined orientation wherein a lower surface of the wafer-shaped article is spaced a predetermined distance from an upper surface of the spin chuck. At least one infrared heater is mounted above the upper surface of the spin chuck and underlying a wafer-shaped article when mounted on the spin chuck, the at least one infrared heater being stationary in relation to rotation of the spin chuck. A plate that is transparent to infrared radiation emitted by the at least one infrared heater is mounted for rotation with the spin chuck and positioned between the at least one infrared heater and a wafer-shaped article when positioned on the spin chuck. 
     In preferred embodiments of the apparatus according to the present invention, the plate is part of a housing that surrounds the at least one infrared heater, the housing being mounted for rotation with the spin chuck. 
     In preferred embodiments of the apparatus according to the present invention, the housing comprises a lower shell surrounding the at least one infrared heater and positioned between the at least one infrared heater and the upper surface of the spin chuck, the lower shell having a reflective interior surface. 
     In preferred embodiments of the apparatus according to the present invention, the spin chuck comprises a rotatable chuck body surrounding a central stationary post, and the at least one infrared heater is mounted to an upper end of the central stationary post. 
     In preferred embodiments of the apparatus according to the present invention, the at least one infrared heater is part of a heating assembly comprising at least two, and preferably at least three, independently controllable infrared heating elements. 
     In preferred embodiments of the apparatus according to the present invention, the housing is centered on an axis of rotation of the spin chuck, and the spin chuck comprises a circular series of pins configured to contact an edge of a wafer-shaped article in a closed position, the pins passing through a corresponding series of openings formed in a periphery of the housing. 
     In preferred embodiments of the apparatus according to the present invention, each of the independently controllable heating elements comprises at least one curved portion. 
     In preferred embodiments of the apparatus according to the present invention, a lower shell surrounds the at least one infrared heater and is positioned between the at least one infrared heater and the upper surface of the spin chuck, the lower shell having a reflective interior surface and being stationary in relation to rotation of the spin chuck. 
     In another aspect, the present invention relates to an infrared heating assembly for use in an apparatus for treating a wafer-shaped article. The infrared heating assembly comprises a housing comprising an upper plate that is transparent to infrared radiation emitted by the infrared heating assembly, and a lower shell having a reflective interior surface. A plurality of infrared heating elements is mounted on a common frame positioned with the housing, the common frame comprising a connector portion projecting downwardly through a central opening in the lower shell. A rotary bearing is positioned outside of the connector portion and inside of the central opening, thereby to permit rotation of the housing relative to the common frame and the plurality of infrared heating elements. 
     In preferred embodiments of the infrared heating assembly according to the present invention, each of the infrared heating elements is independently controllable and comprises at least one curved portion. 
     In preferred embodiments of the infrared heating assembly according to the present invention, the curved portions of adjacent infrared heating elements extend along concentric circles. 
     In preferred embodiments of the infrared heating assembly according to the present invention, the connector portion comprises a plurality of electrical connectors equal in number to the plurality of infrared heating elements, thereby to permit individual connection of each of the plurality of infrared heating elements to a controller for individually energizing each of the plurality of infrared heating elements. 
     In preferred embodiments of the infrared heating assembly according to the present invention, the housing is rotatable relative to the common frame and the plurality of infrared heating elements about an axis that is perpendicular to the upper plate. 
     In preferred embodiments of the infrared heating assembly according to the present invention, each of the infrared heating elements comprises at least one curved portion, and the at least one curved portion of each of the infrared heating elements extends along an arc of a circle whose center is offset from the axis. 
     In preferred embodiments of the infrared heating assembly according to the present invention, the housing comprises a circular series of peripheral openings to permit passage of gripping pins when the infrared heating assembly is mounted to a spin chuck. 
    
    
     
       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 exploded perspective view of an apparatus for treating disc-shaped articles according to an embodiment of the present invention; 
         FIG. 2  is top plan view of the embodiment of  FIG. 1 ; 
         FIG. 3  is an axial section through the chuck depicted in  FIGS. 1 and 2 , taken along the line III-III of  FIG. 2 ; 
         FIG. 4  is an enlarged view of the detail IV designated in  FIG. 3 ; 
         FIG. 5  is an enlarged view of the detail V designated in  FIG. 3 ; and 
         FIG. 6  is an axial sectional view similar to that of  FIG. 3 , of another embodiment of an apparatus for treating disc-shaped articles according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings,  FIGS. 1 and 2  depict an apparatus made up of two principal subassemblies, namely, a base spin chuck  10  and a modular infrared heating assembly  20 . The spin chuck  10  comprises a rotary main body  12  that is mounted for rotation about a stationary central hollow post  14 . This post  14  in turn comprises a central nozzle  18  for dispensing process liquid or gas onto the underside of a wafer when mounted on the spin chuck, as well a series of female electrical sockets  15  in a shoulder of the post  14 , which sockets receive corresponding male connectors (not shown) that depend downwardly from the heating assembly  20 , and which supply driving current to the IR heating lamps inside that assembly  20 . 
     The chuck body  12  has mounted therein a series of gripping pins  16 , which operate generally as described in the above-referenced U.S. Pat. No. 4,903,717, in that the pins  16  are driven in unison by a common ring gear between a radially outer open position and a radially inner closed position in which the upper ends of these pins engage the edge of a disc-shaped article to be treated. Chuck body  12  also includes smooth-walled bores  13  that receive corresponding positioning bosses (not shown) that depend downwardly from the heating assembly  20 , so as to aid in positioning and supporting the heating assembly  20  in its correct orientation relative to the chuck body  10 . 
     The heating assembly  20  in this embodiment is formed as a modular unit comprising a lower dished housing or shell  22  that contains the IR lamps  21 ,  23 ,  25 . A cover  24  is screwed onto the lower housing  22  by a series of peripheral screws  26 , which are six in number in this embodiment. Screws  26  alternate with six notches or openings  17  that pass entirely through the heating assembly  20  from top to bottom, and which permit passage of the gripping pins  16 . The broken line in  FIG. 1  designates the position of a wafer W when held by the apparatus, in which position the wafer is supported at its peripheral edge by the distal ends of the gripping pins  16  projecting upwardly through the through bores or notches  17 , with the underside of wafer W being spaced by a small defined gap from the cover  24 . 
     The cover  24  in this embodiment is a plate formed from a material that is transparent to the wavelengths of IR radiation emitted by the lamps  21 ,  23 ,  25 , and this plate  24  may be formed for example of sapphire or quartz glass, as is known to those skilled in this art. The plate  24  has a small central opening  19  formed therein, to permit passage of the upper end of dispensing nozzle  18 . 
     Within the housing of the heating assembly  20 , that is, inside the lower housing  22  and beneath the transparent plate  24 , there is mounted a set of three infrared heating lamps  21 ,  23 ,  25 , which are carried by a common frame  29  that also incorporates the associated electrical supply wiring (not shown). The assembly formed by frame  29  and lamps  21 ,  23 ,  25  in this embodiment is rigidly mounted to the stationary post  14 , whereas the housing formed of lower shell  22  and upper plate  24  is rigidly mounted to the rotary chuck body  12 . Therefore, the frame  29  and thus also the lamps  21 ,  23 ,  25  that it carries are mounted for rotation relative to the surrounding housing formed of components  22 ,  24 , as will be described in greater detail below. 
     Referring now to  FIG. 2 , it can be seen that the wafer W is now supported by the ends of pins  16  projecting through the openings or notches  17  in the heating assembly  20 . The wafer W is centered on the heating assembly  20 , which in turn is centered on the axis of rotation of the underlying spin chuck. It will be appreciated that the spin chuck  10  is therefore designed to hold a wafer W of a specified diameter. In the embodiments described herein, that diameter is 300 mm, which is a common diameter of silicon wafer at present. However, the apparatus may of course be designed to hold disc-shaped articles of other diameters, such as 200 mm and 450 mm. 
     In the plan view of  FIG. 2  it can be seen that each of the three heating elements  21 ,  23 ,  25  in this embodiment is a continuous curved tubular element. Moreover, while these heating elements generally follow a circular arc, and while all three heating elements are preferably substantially concentric, the circles described by those heating elements are not in this embodiment concentric with the center of the heating assembly  20  and hence are not concentric with the axis of rotation of the spin chuck. 
     Consequently, in this embodiment, both the position and shape of the heating elements  21 ,  23 ,  25  is such that, as the wafer W is rotated by the chuck  10  relative to the stationary heating elements  21 ,  23 ,  25 , each heating element effectively “travels” radially relative to the rotating wafer W, in that each heating elements heats an annular region whose radial extent is significant greater than the cross-sectional diameter of the heating elements. 
     In  FIG. 3 , it can be seen that the frame  29  is supported within the housing  22 ,  24  by a suitable rotary bearing  33 , which permits the housing of the heating assembly  20  to rotate relative to the stationary post  14  with the frame  29  and lamps  21 ,  23 ,  25  being mounted in a stationary manner to the post  14 . The upwardly-facing surface of the lower housing part or shell  22  is preferably provided with a suitable IR reflective coating  31 , to aid in directing the IR radiation emitted by lamps  21 ,  23 ,  25 , upwardly through the transparent plate  24  and onto the downwardly facing surface of the wafer W. 
     The stationary post  14  is mounted onto the frame  32  of the apparatus, which in this embodiment also carries a stator  34 . Stator  34  in turn drives rotor  36 , which is attached to the body  12  of spin chuck  10 . Also visible in  FIG. 3  is the ring gear  11  mentioned above, which drives the gripping pins  16  in unison. 
       FIG. 4  shows an inlet  37  into the frame  29  and communicating with an outlet of the post  14 , which permits the interior of the heating assembly  20  to be purged for example with nitrogen gas. Also shown in  FIG. 4  is a conduit  35  that opens on a shoulder of the post  14 , and into the small gap  39  defined between the upper surface of the chuck body  12  and the lower surface of the housing shell  22 . Conduit  35  can be advantageously used to supply deionized water to the gap  39 , so as to cool the heating assembly  20  upon completion of a heating operation, as well as to regulate the temperature generated by the heating assembly during a heating operation. 
     Visible in  FIG. 5  is a gap  41  provided between the transparent cover  24  and the lower shell housing  22 , which permits nitrogen purge gas introduced into the housing to be exhausted outwardly therefrom. Similarly, gap  43  shown in  FIG. 5  permits the escape of the deionized water (or, if desired, nitrogen gas) that had been introduced into the gap  39  between the bottom of shell  22  and the upper surface of chuck body  12 . 
     In the alternative embodiment of  FIG. 6 , the transparent plate  24 ′ still rotates with the spin chuck  10 , and pins  16 ′ still pass upwardly through openings formed in the transparent plate  24 ′. However, the lower shell  22 ′ of this embodiment is now rigidly secured to the post  14  in a cantilever manner, along with the frame  29  and lamps  21 ,  23 ,  25 . This embodiment is otherwise as described above in connection with the preceding embodiment. 
     It is advantageous for the transparent plate  24 ,  24 ′ to rotate with the spin chuck  10  as in these embodiments, because any droplets of process liquid adhering to the transparent plate  24 ,  24 ′ will thereby be spun off. However, in a still further embodiment, the entire heating assembly may be mounted in a stationary manner on the post  14 , as is described for example in connection with the heating assembly disclosed in commonly-owned co-pending application U.S Patent Application Pub. No. 2013/0061873. 
     It is to be noted that the heating lamps in each of the preceding embodiments are preferably individually controllable. It is particularly preferred that each lamp can be not only switched on and off independently of the others, but also that the wattage to each lamp can be independently varied. This permits a variety of advantageous process control. 
     While the present invention has been described in connection with various preferred embodiments thereof, it is to be understood that those embodiments are provided merely to illustrate the invention, and should not be used as a pretext to limit the scope of protection conferred by the true scope and spirit of the appended claims.