Abstract:
The present invention is directed to a high speed, spinning chuck for use in a semiconductor wafer inspection system. The chuck of the present disclosure is configured with a turbulence-reducing lip. Spinning of the chuck produces radial airflows proximal to a surface of the wafer and proximal to the bottom of the chuck. The turbulence-reducing lip of the chuck of the present disclosure directs the radial airflows off of the top surface of the wafer and the bottom surface of the chuck in a manner that minimizes the size of the low pressure zone formed between these radial airflows. The minimization of the low pressure zone reduces air turbulence about the periphery of the chuck and substrate, thereby reducing the possibility of contaminants in the system being directed onto the surface of the substrate by such air turbulence.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/522,569 entitled: Air Flow Management in a System With High Speed Spinning Chuck filed Aug. 11, 2011, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to spinning chucks used in conjunction with inspection systems, such as semiconductor wafer inspection systems, and more particularly to a high speed spinning chuck which may allow for air flow management when used with such inspection systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    As demand for ever-shrinking semiconductor devices continues to increase, so too will the demand for improved semiconductor device fabrication methodologies and semiconductor wafer inspection sensitivity. Due to the continued increase in complexity of modern integrated circuits, the tolerance for the presence of defects on a surface of a semiconductor wafer during and/or after fabrication continues to decrease. One class of defects that commonly negatively impact device fabrication and performance are contamination defects. One source of contamination defects results from the utilization of current wafer chucking systems. When spun at high rotational speeds, commonly implemented spinning wafer chucking systems, the top and bottom surfaces of the wafer/chuck assembly act as centrifugal pumps. This effect creates a layer of air on both the top and bottom surface that rapidly move from the centers (e.g., center of wafer) to the edges of the surfaces. The outward airflow, in turn, generates a low pressure zone at the centers of the top and bottom surfaces, when promotes the movement of more air into the center air from regions external to the wafer region. The air tending to flow into the low pressure zone may include various types of contaminants. The top and bottom layers of the pumped air meet generally off the chuck edge, and in a commonly implemented chuck combine at some distance away from the chuck, creating a low pressure zone between the two airflows. This low pressure zone is immediately filled with surrounding air, thereby generating a zone of air turbulence. This turbulence may bring contaminants from the downstream region (i.e., the below the chuck), which is generally not sufficiently clean. As a result of this turbulence, contaminants may be displaced from a region below the wafer and/or wafer chuck to a top surface of the wafer. The introduction of these contaminants onto the surface of a given semiconductor wafer have severe consequences on the performance of the semiconductor devices fabricated on wafer. As such, it is desirable to provide an improved rotating wafer chuck that acts to cure the turbulence, thereby reducing chuck rotation induced contamination in a semiconductor fabrication or inspection processes. 
       SUMMARY OF THE INVENTION 
       [0004]    Accordingly an embodiment of the invention is directed to a high speed, spinning chuck, including, but not limited to, a first surface, the first surface configured for supporting and retaining a substrate; and a second surface, the second surface being configured generally opposite the first surface, the second surface including at least one of: a sloped portion and a curved portion, the chuck configured for being connected to a driving mechanism, the driving mechanism configured for causing the chuck to rotate about a vertical axis, the vertical axis being perpendicular to the first surface, wherein the first surface of the chuck and the at least one of sloped portion and curved portion of the second surface of the chuck form a turbulence-reducing lip for: promoting a reduction in air turbulence proximal to the chuck when the chuck is rotating; and for promoting the reduction of a separation between a first radial airflow produced proximal to the substrate and a second radial airflow produced proximal to the second surface of the chuck when the chuck is rotating, thereby promoting reduced deposition of contaminants upon the substrate. 
         [0005]    A further embodiment of the present disclosure is directed to a semiconductor wafer inspection system, the system including, but not limited to, a vacuum chuck, the vacuum chuck configured for supporting and retaining the semiconductor wafer, the vacuum chuck configured for being connected to a shaft and motor, the vacuum chuck configured for being rotated via the shaft and motor; an inspection tool configured to optically inspect at least a portion of the semiconductor wafer supported and retained by the vacuum chuck, the inspection tool comprising: a laser light source, the laser light source configured for producing a beam of light, the beam of light illuminating an area on the semiconductor wafer; an imaging camera, the imaging camera configured to detect light emanating from the illuminated area on the semiconductor wafer; a set of optical elements configured for imaging the area on the semiconductor wafer illuminated by the beam of light onto an imaging portion of the camera, wherein the vacuum chuck includes a first surface and a second surface, the second surface being configured generally opposite the first surface, the first surface being configured for supporting the semiconductor wafer, the second surface including at least one of: a sloped portion and a curved portion, the first surface of the chuck and the at least one of sloped portion and curved portion of the second surface of the chuck forming a turbulence-reducing lip for: promoting a reduction in air turbulence proximal to the chuck when the chuck is rotating; and for promoting the reduction of a separation between a first radial airflow produced proximal to the substrate and a second radial airflow produced proximal to the second surface of the chuck when the chuck is rotating, thereby promoting reduced deposition of contaminants within the system upon the wafer. 
         [0006]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The numerous advantages of the present invention may be better understood by those skilled in the art by reference to the accompanying figures in which: 
           [0008]      FIG. 1  is a schematic diagram of a wafer chuck, in accordance with an exemplary embodiment of the present disclosure; 
           [0009]      FIG. 2A  is a schematic diagram of a wafer chuck having a generally cylindrical shape in accordance with currently available embodiments, the chuck shown supporting a substrate and being connected to a driving mechanism for rotating the chuck, in accordance with an exemplary embodiment of the present disclosure; 
           [0010]      FIG. 2B  is a schematic diagram of a wafer chuck, in accordance with an exemplary embodiment of the present disclosure; 
           [0011]      FIG. 3  is a block diagram view of an inspection system equipped with a wafer chuck, in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention. Reference will now be made in detail to the subject matter disclosed, which is illustrated in the accompanying drawings. 
         [0013]    Referring generally to  FIGS. 1 through 3B , a wafer chucking apparatus  100  is described in accordance with the present invention. The present invention is directed to an improved wafer chuck  100  suitable for providing reduced contamination caused by air flow patterns generated by high wafer spinning speeds within an implementing system, such as a wafer inspection system. The present invention is further directed to an inspection system  300  equipped with the wafer chuck  100  suitable for providing improved accuracy and efficiency as a result of reduced air flow induced contamination. Since generally spinning of wafers is required to carry out an inspection process, the ability to provide a low contamination environment at high chuck/wafer spinning speeds may lead to an increase in inspection throughout. 
         [0014]      FIG. 1  illustrates a schematic view of a winged-shaped wafer chuck  100 , in accordance with one embodiment of the present invention. In one aspect of the invention, the wafer chuck  100  includes an airfoil structure  101  configured to provide reduced air turbulence around the perimeter of the wafer  102  during high speed spinning of the chuck  100  and wafer  102 . For example, the airfoil structure may include a winged-shaped airfoil structure suitable for reducing air turbulence about the perimeter of the wafer/chuck edges when spun at high speeds (e.g., up to 10,000 RPM), as shown in  FIG. 1 . The reduced air turbulence about the perimeter of the chuck  100 , in turn, aides in reducing contamination of an implementing environment (e.g., inspection system) by reducing the amount of contaminants “lifted” from the region below the chuck  100  and wafer  100  to the surface  103  of the wafer  102 . In a general sense, any airfoil structure capable of reducing the air turbulence about the perimeter of the wafer  102  and chuck  100  is suitable for implementation in the present invention. In one embodiment, the implemented airfoil structure  101  may include a solid machined portion (as shown in  FIG. 1 ), which includes a sloped region  116  and lip  118  positioned between the bottom-most portion of the chuck  100  and the top-most portion of the chuck  100 . In another embodiment, the implemented airfoil structure  101  may include one or more ring structures that may be attached to a currently existing chuck (e.g., chuck  202  in  FIG. 2A ). The attachable ring structure (not shown) may include features similar to the slope  116  and lip portions depicted in  FIG. 1 , thereby allowing a user to retrofit presently existing chucking systems with the contamination reducing ability of the present invention. 
         [0015]    In another aspect of the present invention, the wafer chuck  100  consists of a vacuum-based wafer chuck configured to secure a wafer  102  (e.g., semiconductor wafer) utilizing a supplied vacuum. In one embodiment, the vacuum chuck  100  may be configured as a generally circular bowl-shaped structure and may include a top surface  104  (e.g., a support surface) configured for supporting (e.g., holding) the wafer  102  in place. In an alternative embodiment, the wafer chuck  100  may include an edge handling wafer chuck (not shown). 
         [0016]    In another embodiment, the vacuum chuck  100  may be configured for having an air current drawn through it to create a vacuum for securing the wafer  102  to a support surface of the chuck  100 . In this regard, a wafer  102  placed on top of the vacuum chuck  100  will experience a pressure difference between the external environment and the evacuated volume of the vacuum chuck (not shown), thereby securing the wafer  102  on the support surface of the chuck  100 . For example, a vacuum may be applied to a bottom surface of the wafer  102  via a vacuum line (not shown) coupled to an external vacuum pump (not shown), whereby an inlet for the vacuum line is disposed on a bottom surface  108  (e.g., the surface opposite the support surface) of the chuck  100 . In this regard, a vacuum system may establish a vacuum, which acts to securely draw and hold the wafer  102  against the support surface of the chuck  100 . 
         [0017]    In another embodiment, the vacuum chuck  100  may be integrally supported by a shaft  114  (e.g., spindle). For example, the shaft  114  may be connected to a motor (e.g., spindle motor) (not shown). In this regard, the spindle motor may be configured to rotate the shaft  114 , thereby rotating the vacuum chuck  100  about an axis perpendicular to the support surface  104  (e.g., z-axis). For instance, the chuck  100  may be rotated at speeds greater than 1,000 revolutions per minute (rpm) (e.g., 1,000 to 10,000 rpm). 
         [0018]      FIGS. 2A and 2B  illustrate schematic views of both a commonly implemented wafer chuck  202  and the wafer chuck  100  of the present invention, respectively. Currently available vacuum chucks, such a the wafer chuck  202  illustrated in  FIG. 2A , are generally cylindrically-shaped, having a top surface support surface and a bottom surface connected via a cylindrically-shaped outer wall  204 , whereby the top and bottom surfaces of the chuck  202  form opposite ends of the cylinder. During a wafer inspection process of the wafer  102 , in settings where the cylindrical chuck  202  and wafer  102  are spun at a high rate of speed, radial airflows  206 ,  208  are created proximal to the top surface  103  of the wafer  102  and proximal to the bottom surface  108  of the cylindrical chuck  202 . It is recognized herein that the radial airflows  206 ,  208  generated at the opposing surfaces are caused by centrifugal air pumping resulting from the high spinning speed of the chuck  202 . In turn, the radial airflows  206 ,  208  at the wafer  102  surface  103  and the bottom surface  108  of the chuck  202  generate a large, low pressure zone  210  about the perimeter of the chuck  202  between the radial airflows  206 ,  208 . The low pressure zone  210 , in turn, leads to local air turbulence around the perimeter of the cylindrical chuck  202 . The air turbulence created around the perimeter of the cylindrical chuck  202  tends to cause lifting of contaminants  211  from a lower portion of an implementing system (e.g., inspection system  300 ) and may result in deposition of contaminants onto a surface of the wafer  102 . 
         [0019]    Referring now to  FIG. 2B , the vacuum chuck  100  of the present invention addresses the above-referenced shortfalls associated with currently available chucks  202  by minimizing air turbulence around the perimeter of the high speed spinning chuck  100 . The reduced air turbulence about the perimeter of the chuck  100 , in turn, promotes a low contamination environment in implementing systems, such as a wafer inspection system  300 . As shown in  FIG. 2B , the support surface  104  of the chuck  100  may be a generally planar surface suitable for receiving the wafer  102 . In alternative embodiments, the support surface  104  of the chuck  100  may include a recessed portion (e.g., concave portion). In a further aspect of the present invention, the bottom surface  108  of the chuck  100  may include (e.g., may form) a rounded or curved portion  116 , such that the curved portion  116  connects to (e.g., curves or slopes vertically upward to) the top surface  104  of the chuck  100 . In addition, the intersection of the sloped bottom surface  108  of the chuck  100  and the top surface  104  of the chuck  100  may form an outer structure, or lip  118  (e.g., turbulence reduction lip, radial airflow separation lip, and the like). The outer lip  118  may have a thickness ranging on the order of millimeters. For instance, the thickness of the outer lip  118  may be 1-2 mm. The winged structure  101  of the chuck  100  of the present invention allows for the more gradual combining of the radial airflows  206 ,  208  (as shown in  FIG. 2B ), which acts to promote the reduction of the low pressure zone between the radial airflows  206 ,  208  formed around the perimeter of the chuck  100 . The reduction of the low pressure zone, in turn, results in the reduction in air turbulence in the region proximal to the perimeter of the chuck  100 , thereby lessening the amount of contamination lifted from the region below the wafer  102 . As a result, the wafer  100  promotes a lower level of contamination in an implementing environment, such as a region of a wafer inspection system  300 . 
         [0020]    In an alternative embodiment, an airfoil structure consisting of a wing-shaped ring (when viewing edge on) (not shown) may be selectably attached to a standard chuck  202 . In this regard, a ring structure which incorporates the curvature, slop, and lip features described previously herein may be attached to a surface of a stand chuck  202 , such as a cylindrical shaped chuck. It is anticipated that the advantages of the winged-structure evident in the chuck  100  of the present invention will be applicable to a wing-shaped ring attachment suitable for retrofitting currently existing vacuum-based wafer chucks  202 . 
         [0021]    In an additional alternative embodiment, airfoil structure may include a stationary airfoil structure (not shown) positioned proximate to the top surface of a standard chuck (e.g., chuck  202 ). The stationary airfoil structure may act to disrupt the air flow pattern, as described previously herein, thereby reducing the amount of contaminants displaced from a region below the chuck and wafer assembly to the surface of the wafer  102 . 
         [0022]      FIGS. 3A and 3B  illustrate high-level block diagram views of inspection systems  300  equipped with the low contamination winged-shaped wafer chuck  100 , in accordance with embodiments of the present invention. In a general sense, the wafer inspection system  300  of the present invention may include the winged-shaped wafer chuck  100  previously described herein, at least one light source  302  (e.g., a laser) configured to illuminate an area on the surface of the wafer  102 , and a detector, or camera  304 , such as a CCD or TDI based detector, or a photomultiplier detector, suitable for detecting light reflected or scattered from the area illuminated by the light source. In addition, the inspection system  300  may include a set of optical elements (e.g., illumination optics, collection optics, and the like) configured for directing (and focusing) illumination from the light source  302  onto the surface of the wafer  102  and, in turn, directing illumination from the surface of the wafer  102  to the imaging portion of the camera  304  of the inspection system  300 . For instance, the set of optical elements may include, but is not limited to, primary imaging lens suitable for imaging the illuminated area on the semiconductor wafer onto a collection region of the camera. Further, the imaging camera  304  may be communicatively coupled to an image processing computer which may identify and store imagery data acquired from the camera  304 . 
         [0023]    The inspection system  300  of the present invention may be configured as any inspection system known in the art. For example, as shown in  FIG. 3A , the inspection system  300  of the present invention may be configured as a bright field (BF) inspection system. Alternatively, as shown in  FIG. 3B , the inspection system  300  may be configured as a dark field (DF) inspection system. Applicant notes that the optical configurations depicted in  FIGS. 3A and 3B  are provided merely for illustrative purposes and should not be interpreted as limiting. In a general sense, the inspection system  300  of the present invention may include any set of imaging and optical elements suitable for imaging the surface of the wafer  102 . Examples of currently available wafer inspection tools are described in detail in U.S. Pat. No. 7,092,082, U.S. Pat. No. 6,702,302, U.S. Pat. No. 6,621,570 and U.S. Pat. No. 5,805,278, which are each herein incorporated by reference. 
         [0024]    In a further aspect of the present disclosure, the vacuum chuck  100 , wafer  102 , light source  302 , imaging camera  304  and various optical elements of the inspection system  300  may be contained within a pressurized enclosure (e.g., an inspection chamber) (not shown) of the system  300 . The inspection chamber may be maintained, by vacuum pump(s), at a vacuum pressure level suitable for processing of the wafer  102 . 
         [0025]    Those skilled in the art will recognize that it is common within the art to describe devices and/or processes in the fashion set forth herein, and thereafter use engineering practices to integrate such described devices and/or processes into data processing systems. That is, at least a portion of the devices and/or processes described herein can be integrated into a data processing system via a reasonable amount of experimentation. Those having skill in the art will recognize that a typical data processing system generally includes one or more of a system unit housing, a video display device, a memory such as volatile and non-volatile memory, processors such as microprocessors and digital signal processors, computational entities such as operating systems, drivers, graphical user interfaces, and applications programs, one or more interaction devices, such as a touch pad or screen, and/or control systems including feedback loops and control motors (e.g., feedback for sensing position and/or velocity; control motors for moving and/or adjusting components and/or quantities). A typical data processing system may be implemented utilizing any suitable commercially available components, such as those typically found in data computing/communication and/or network computing/communication systems. 
         [0026]    While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. 
         [0027]    Although particular embodiments of this invention have been illustrated, it is apparent that various modifications and embodiments of the invention may be made by those skilled in the art without departing from the scope and spirit of the foregoing disclosure. Accordingly, the scope of the invention should be limited only by the claims appended hereto. It is believed that the present disclosure and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory, and it is the intention of the following claims to encompass and include such changes.