Abstract:
Method for determining the location of a droplet of liquid placed on a surface of a semiconductor wafer. In one embodiment the method includes establishing first and second reference axes that intersect at a point and superimposing the point over the droplet on the semiconductor wafer surface. A first reference coordinate indicative of the position of the point along the first axis and a second reference coordinate indicative of the position of the point along the second axis are generated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a division of U.S. patent application Ser. No. 09/836,826 filed Apr. 17, 2001, which is continuation of U.S. patent application Ser. No. 09/316,233, filed May 21, 1999, now U.S. Pat. No. 6,242,271, issued Jun. 5, 2001, which is a division of U.S. patent application Ser. No. 08/979,894, filed Nov. 26, 1997, now U.S. Pat. No. 5,961,722, issued Oct. 5, 1999. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The subject invention relates generally to locating a reference point and, more particularly, to establishing reference coordinates for the location of a dried droplet of liquid on a semiconductor wafer for assessing the purity of the wafer surface.  
           [0003]    Integrated circuits are solid state devices in which electrical components and electrical connections between components are incorporated into a solid matrix by the strategic placement of various conducting, semiconducting and insulating materials. The development placement of various conducting, semiconducting and insulating materials. The development of the integrated circuit has led to the miniaturization of electronics by providing a strong matrix to support and protect fragile miniaturized components and connections and by facilitating the placement of the electrical components in close proximity. The integrated circuit has further served to increase the reliability of electronic devices by the elimination of moving parts and fragile electrical wiring and connections.  
           [0004]    Integrated circuits are typically mass produced by forming hundreds of circuits called “dice” on a semiconductor substrate known as a “wafer”. The circuits are formed by depositing a series of individual layers of predetermined materials on the wafer. The individual layers of the integrated circuit are produced by a series of manufacturing steps. The precise characteristics of the layers, such as composition, thickness, and surface quality uniquely determine the electronic properties and the performance of the integrated circuit.  
           [0005]    Successful fabrication of large scale integrated silicon circuits is dependent upon the purity of the wafer surfaces. The presence of metal contaminates such as iron, nickel, copper and zinc on the semiconductor surfaces can lead to defects during high temperature processing of the wafers because those contaminates can diffuse into the semiconductor material. In an effort to monitor the purity of the semiconductor surfaces, highly sensitive methods for analyzing surface purity have been developed.  
           [0006]    One method for determining the concentration of contamination on a silicon wafer is known as vapor phase decomposition or “VPD”. Such method involves supporting the wafer in a specially designed device known as a VPD reactor. A VPD reactor typically contains an acid-resistant beaker and platforms for supporting wafers within a chamber. The wafer platforms are typically water-cooled and the beakers are generally heated by a heat exchanger arrangement integrated into the bottom of the reactor.  
           [0007]    After the wafers are placed onto the wafer platform, a solution of hydrofluoric acid is added to a beaker. The hydrofluoric acid is heated within the beaker which causes it to vaporize within the chamber. The acid vapor permeates the chamber and dissolves the silicon oxide surface layer on the wafer. The wafer is cooled by the support platform which causes a thin film of moisture to condense on the wafer surface. The impurities on the surface of the wafer are contained in the moisture film.  
           [0008]    The wafer is then removed from the reactor and a predetermined amount of deionized water is then immediately pipetted on to the surface. This droplet is then moved over the entire surface area by gently tilting the wafer. During this process, the impurities are collected in the droplet. The droplet is then moved generally to the center of the wafer and the wafer is placed into a vacuum chamber wherein the droplet is dried on the wafer. After the droplet has been dried, its contents are analyzed by a process known as total reflection X-ray spectrometry (“TXRF”). The principle of TXRF is based on the detection of trace elements on the surface of an optically flat substrate by their characteristic X-rays excited by an incoming X-ray beam in total external reflection geometry. Through use of this process, the presence of iron, nickel, copper and zinc on the wafer surface can be detected.  
           [0009]    In the past, the location of the droplet of water on the wafer was approximated. Because the exact location of the droplet was unknown, accurate positioning of the TXRF machine relative to the water droplet was time consuming. Moreover, although some TXRF machines are capable of accepting coordinates of a point of interest relative to the machine head, prior methods lacked the capability of generating such coordinates for use by the X-ray machine.  
           [0010]    Thus, there is a need for an apparatus and method for generating reference coordinates for a position on a component such as a wafer that can be used to accurately orient a device such as an X-ray machine relative to the position.  
           [0011]    There is a further need for an apparatus having the above-mentioned attributes that is relatively inexpensive to manufacture.  
           [0012]    There is yet another need for an apparatus having the above-mentioned attributes that is relatively portable and easy to use.  
         SUMMARY OF THE INVENTION  
         [0013]    In accordance with a particularly preferred form of the present invention, there is provided an apparatus for establishing a reference coordinate for a point on a component. The invention preferably includes a component carriage that has coordinate indicia thereon. A locator plate is movably supported relative to the component support carriage. The locator plate is provided with reference indicia for registration with a point within the carriage and alignment with the coordinate indicia on the component carriage. The invention may further include a base to which the component carriage and locator plate are movably attached.  
           [0014]    The present invention provides solutions to the aforementioned problems associated with prior locator methods and apparatuses and, in particular, with those methods and apparatus employed in connection with the evaluation of surface contaminates on silicon wafers. The subject invention is also relatively inexpensive to manufacture, is easy to use and is portable. Those of ordinary skill in the art will readily appreciate that these and other details, features and advantages will become further apparent as the following detailed description of the preferred embodiments proceeds. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In the accompanying Figures, there are shown present preferred embodiments of the invention wherein like reference numerals are employed to designate like parts and wherein:  
         [0016]    [0016]FIG. 1 is an isometric view of a preferred location device of the present invention;  
         [0017]    [0017]FIG. 2 is an isometric view of the location device of FIG. 1, supporting a silicon wafer thereon;  
         [0018]    [0018]FIG. 3 is a plan view of the location device of FIG. 2; and  
         [0019]    [0019]FIG. 4 is a side elevational view of the location device depicted in FIGS. 2 and 3. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to the drawings for the purposes of illustrating the present preferred embodiments of the invention only and not for the purposes of limiting the same, FIGS.  1 - 4  show a preferred location device  10  for supporting a component such as a silicon wafer  12  thereon. Although the subject invention is particularly well-suited for use in connection with silicon semiconductor wafers, the skilled artisan will readily appreciate that the subject invention could be easily adapted for use in connection with a variety of other types of articles and components without departing from the spirit and scope of the present invention.  
         [0021]    As can be seen in FIGS. 1 and 2, the location device  10  preferably comprises a base  16  that movably supports a component or wafer carriage  40  and a transparent locator plate  60 . In a preferred form, the base  16  includes two side members  18  fabricated from stainless steel or other suitable material. A pair of spaced rods  20  are attached to the side members  18  and extend therebetween. As will be discussed in further detail below, rods  20  define a first plane along which the component carriage  40  can be selectively positioned. The linear directions in which the component carriage  40  can move within the first plane are defined by a first linear axis “X-X”.  
         [0022]    Each side member  18  has a longitudinally extending notch  24  for receiving a corresponding lateral rod  26 . Lateral rods  26  serve to movably support the locator plate  60  along a second plane that is preferably above and parallel to the first plane. The directions in which the locator plate  60  can move within the second plane are defined by a second linear axis “Y-Y” that is perpendicular to the “X-X” axis in a manner that will be discussed in further detail below.  
         [0023]    Component carriage  40 , in a preferred form, comprises a base plate  41 , two side members  42  and an end member  44 . The base plate  41  and end member  44  are preferably attached to the side members  42  by screws such that the side members  42  are supported in spaced relation to each other. In this embodiment, the side members  42  are notched to laterally support a component such as a silicon wafer  12  thereon. See FIG. 2. In a preferred embodiment, commercially available bearings are installed in corresponding bores  45  provided through the side members  42  as shown in FIGS. 1 and 2. The skilled artisan will appreciate that the bearings  46  have a bore  48  therethrough for slidably receiving a corresponding rod to slidably support the component carriage  40  between the side members  18 .  
         [0024]    Also in a preferred embodiment, a support frame assembly  62  is provided to movably support the transparent locator plate  60  on the base  16 . Preferably, locator plate  60  is fabricated from tempered glass. However, other transparent material could be successfully employed.  
         [0025]    Frame assembly  62  preferably comprises a pair of end members  64  and a pair of side members  66  that are interconnected by screws (not shown) in a shape that is complementary to the shape of the locator plate  60 . The side members  66  are preferably “L”-shaped for receiving a corresponding edge of the locator plate  60  as shown in FIGS. 1 and 2. Attached to each corner of the frame assembly  62  are bearing blocks  70 . Each bearing block  70  is preferably fabricated from stainless steel or other suitable material and has a bearing  72  installed therein. Each bearing  72  has a bore  74  for slidably receiving a corresponding rod  26  therethrough. Those of ordinary skill in the art will appreciate that the bearing blocks  70 , in cooperation with the rods  26  serve to movably support the frame assembly  62  and locator plate  60  for selective travel along axis “Y-Y”. Referencing indicia  80 , preferably in the form of crossed lines ( 82 ,  84 ) is provided on the locator plate  60  which can be used to reference a specific point or location on the wafer. Reference scales  86  containing coordinate indicia  81  (preferably numerical in nature) are also preferably attached to at least one side member  42  and the end member  44  of the component carriage  40 . Such referencing coordinate indicia  81  are arranged on the end member  44  and the side member  42  to lie along intersecting axes “A-A” and “B-B”, respectively. See FIGS. 2 and 3.  
         [0026]    Use of the subject invention  10  in connection with locating a specific reference point such as the location of a water droplet on a wafer  12  will now be described. After the water droplet has been dried on the wafer  12 , the wafer  12  is placed onto the wafer carriage  40  of the subject invention. The carriage  40  and/or the locator plate  60  are moved as necessary along the “X-X” and “Y-Y” axes, respectively to bring the point where the lines ( 82 ,  84 ) cross into registration with the water droplet. After the point where the crossed lines ( 82 ,  84 ) intersect is brought into registration with the water droplet, X and Y coordinates for the droplet location are established wherein the reference lines ( 82 ,  84 ) intersect the coordinate indicia on the scales mounted to the side member  42  and end member  44  of the component carriage  40 .  
         [0027]    Those of ordinary skill in the art will appreciate that such coordinates can be used in conjunction with known control systems to locate a piece of equipment, such as an X-ray machine relative to the water droplet. The skilled artisan will further appreciate that the positioning of the component carriage  40  and the locator plate  60  relative to the base structure  16  can be automatically established by utilizing, for example, by positioning apparatuses such as lead screws/ball screws and stepper motor arrangements. Also, commercially available sensor arrangements could be employed to detect the final position of the carriage, the locator plate and referencing indicia thereon and such data could be incorporated into a control system for controlling the position of other machinery components relative thereto.  
         [0028]    Thus, from the foregoing discussion, it is apparent that the present invention provides significant improvements over prior methods for locating a point of interest on a component such as a silicon wafer. The subject invention also provides the advantages of being readily portable and easy to use and cost-effective to manufacture. Those of ordinary skill in the art will appreciate that various changes in the details, materials and arrangement of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by the skilled artisan within the principle and scope of the invention as expressed in the appended claims.