Abstract:
A wafer clamping tension measuring apparatus includes a base plate having a guide groove formed in an upper surface and a moving plate having a guide rail protruding from a lower surface and reciprocating with the guide groove. A tension gauge is fixed to an upper surface of the moving plate for measuring the tension of a wafer clamping elastic member confronting the tension gauge. A displacement restricting block is attached at one end of the base plate nearest to the wafer clamping elastic member to restrict the movement of the moving plate relative to the base plate when the moving plate is displaced towards the displacement restricting block.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for measuring wafer clamping tension, and more particularly, to an apparatus that can accurately measure and adjust the tension of an elastic member used in clamping the wafers, thereby preventing the clamped wafers from moving or dropping during a manufacturing process. 
     2. Description of the Related Art 
     In order to produce a highly-integrated, highly-functional semiconductor product, a variety of stringent operating conditions must be met during the intricate manufacturing process. Because of the minute dimensions and very small tolerances inherent in semiconductor manufacturing, one important requirement is the ability to firmly and accurately fix a plurality of wafers at predetermined positions while performing various semiconductor fabrication processes. 
     One conventional method of fixing wafers with an elastic member at a predetermined position is described in U.S. Pat. No. 5,350,427 (the &#39;427 patent), entitled “Wafer Retaining Platen Having Peripheral Clamp and Wafer Lifting Means.” The &#39;427 patent describes a protruding fence at one end of a platen at which wafers are to be fixed, a finger assembly formed at the opposing end of the platen for applying pressure with an elastic member to push the edge of the wafer toward the fence, and an operational unit installed at a lower portion of the finger assembly for selectively operating the finger assembly to load/unload the wafers, so that the finger assembly and fence can prevent the wafers from moving or dropping during processing. 
     However, in semiconductor manufacturing facilities where wafers are clamped by employing such an elastic member, repeated use of the elastic member can change the tensioning characteristics thereof, which in turn can cause the elastic members to fail to apply the requisite pressure to push the wafer toward the fence. As a result, the wafers may drop or move from the predetermined position to thereby cause a problem in the manufacturing process. 
     In an effort to solve this problem, present methods use a common commercial tension gauge in an effort to estimate and measure the elastic force used for clamping wafers. However, a problem exists in that such methods do not produce consistent results because the workers that use the tension gauge may measure the tension at different positions and apply different pressures during the readings. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an apparatus for measuring wafer clamping tension that provides consistent and accurate results for elastic member tension, regardless of which worker initiates the measurement. 
     To achieve this and other objects, the present invention provides a wafer clamping tension measuring apparatus, including a base plate having a guide groove formed in an upper surface and a moving plate having a guide rail protruding from a lower surface and reciprocating with the guide groove. A tension gauge is fixed to an upper surface of the moving plate for measuring the tension of a wafer clamping elastic member confronting the tension gauge. A displacement restricting block is attached at one end of the base plate to restrict the movement of the moving plate relative to the base plate when the moving plate is displaced towards the displacement restricting block. 
     Preferably, the base plate includes protrusions extending from a lower surface. The protrusions may be oriented so as to be aligned with holes on a wafer pedestal pad on which the base plate is placed. 
     The tension gauge includes a tension rod extending from the tension gauge, and a tension measuring block fixed to the other end of the tension gauge, such that the tension measuring block contacts the wafer clamping elastic member. The height of the tension measuring block from the surface can be adjusted. 
     In another embodiment, the present invention provides a method for measuring a wafer clamping tension, wherein the base plate of the wafer clamping tension measuring apparatus is fixed relative to the wafer clamping elastic member, and then a moving plate that reciprocates relative to the base plate is pushed towards the wafer clamping elastic member. A tension gauge attached to the moving member measures and displays the tension value. Displacement of the moving plate is accurately determined and standardized through repeated procedures by a displacement restricting block attached to one end of the base plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objects and advantages of the present invention will become more readily apparent from the detailed description of the preferred embodiments, with reference to the accompanying drawings, in which: 
     FIG. 1 is a partially cut-away, perspective view illustrating a spinning disc of an ion implantation unit equipped with a wafer clamping tension measuring apparatus in accordance with the present invention; 
     FIG. 2 is a cross-sectional view illustrating a relationship among a spinning disc, a wafer loading/unloading unit, and a wafer clamping finger unit; 
     FIG. 3 is an exploded perspective view illustrating an apparatus for measuring the tension of a wafer clamping finger unit of the spinning disc shown in FIGS. 1 and 2; 
     FIG. 4 is a perspective view illustrating the back side of the moving plate shown in FIG. 3; 
     FIG. 5 is an partial exploded perspective view illustrating the structure of a tension measuring apparatus and a spinning disc in accordance with the present invention; 
     FIG. 6 is a cross-sectional view illustrating a state of a tension measuring apparatus just before measuring the tension of a finger of a wafer clamping finger unit in accordance with the present invention; and 
     FIG. 7 is a cross-sectional view illustrating a state of a tension measuring apparatus just after measuring the tension of a finger of a wafer clamping finger unit in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a partially cut-away, perspective view illustrating a spinning disc of an ion implantation unit equipped with a wafer clamping tension measuring apparatus in accordance with the present invention. In this embodiment, the spinning disc assembly  800  supports wafers  1  during an ion implantation process. In addition to supporting and precisely positioning the wafers during the ion implantation process, the spinning disc assembly rotates the wafers at a predetermined speed to achieve uniformity of ion implantation. Note that while the present embodiment is described with reference to an ion implantation unit, the principles of the present invention are not limited thereto, and may be applied to any wafer manufacturing process. 
     The spinning disc assembly  800  includes spinning disc  100 , wafer pedestal  200 , wafer loading/unloading unit  300 , wafer clamping finger unit  400 , spinning disc turning unit (not shown) and spinning disc rotating unit (not shown). 
     The spinning disc  100  is shaped like a large circular plate and includes a turning unit or shaft connected to a rotating unit (not shown) installed at the center of the rotation of the spinning disc  100  for turning the spinning disc  100  during the ion implanting process, for example, at the speed of about 1000 RPM or more. 
     At least one or more wafer pedestals  200  are circularly arranged at positions that are equidistant from the center of the spinning disc  100  and are firmly fixed to the upper surface of the spinning disk  100 . The wafer pedestals  200  are formed in the shape of a circular plate and directly contact the lower surface of the wafers  1 . The wafer pedestals  200  include an accommodating pad  210  and finger groove  220 . The wafer accommodating pad  210  is formed in the shape of a circular plate with is its lower surface being firmly fixed to the upper surface of the disc  100  and its top surface being rubber coated. 
     An upwardly protruding, arcuate shaped fence  230  is installed along part of the circumferential edge of the wafer accommodating pad  210 , and the finger groove  220  is formed across from the fence  230 . When a finger  410  of a wafer clamping finger unit  400  (described further below) is inserted into the finger groove  220 , the wafer  1  is pressed against the fence  230 . 
     As shown in FIG. 1, when the wafer  1  is to be loaded or unloaded by a partially shown wafer transfer unit  2 , it is difficult for the wafer transfer unit  2  to directly load the wafer onto the wafer pedestals  200 . Therefore, a wafer loading/unloading unit  300  is positioned below the lower surface of the spinning disc  100 . 
     The wafer loading/unloading unit  300  includes: a loading/unloading elevator  310  that moves vertically; wafer loading/unloading pins  321 ,  322 ,  323  projecting from the loading/unloading elevator  310 ; wafer detection sensor  324  for sensing wafers  1 ; and a finger operating unit  325 . The three wafer loading/unloading pins  321 ,  322 ,  323  are oriented in a triangular configuration, and the wafer detection sensor  324  is positioned at the center of the wafer loading/unloading elevator  310 . The wafer loading/unloading pin  323  formed closest to the aforementioned finger groove  220  includes a finger operating unit  325  for operating the finger  410  of the wafer clamping finger unit  400  which will be described below in detail. The finger operating unit  325  further includes a spring  325   b  inserted into the wafer loading/unloading pin  323 , and a ring-shaped hitching plate  325   a  formed at the top of the spring  325   b.    
     In order to get the wafer loading/unloading unit  300  to load or unload the wafers  1  to or from the wafer pedestals  200 , through-holes  250 ,  110  are formed in the spinning disc  160  and the wafer pedestals  200  at locations corresponding to the wafer loading/unloading pins  321 ,  322 ,  323  (through holes  250 ) and the wafer detection sensor  324  (through holes  110 ). 
     Now the wafer clamping finger unit  400 , and its interaction with the wafer loading/unloading unit  300 , will be described with reference to FIG.  2 . The wafer clamping finger unit  400  comprises an L-shaped finger  410  and is connected to the spinning disc  100  via a plate spring  420 . The finger  410  includes a finger tip  415  that projects through the spinning disc  100  through the finger groove  220 , and a finger operating part  417  positioned below the spinning disc  100 . 
     The finger operating part  417  of the finger  410  also includes a concave groove or through-hole at its distal end (shown more clearly in FIG.  1 ), which is where the wafer loading/unloading pin  323  of the wafer loading/unloading unit  300  interacts with the finger operating unit  325  to lift the finger operating part  417  up by an angle of θ 1 , and in turn tilts the finger tip  415  by an angle of θ 2 . 
     As a result, when the wafers are loaded onto the pedestals  200 , the finger tip  415  moves to an area where it does not disturb the loading of the wafers by moving the wafer loading/unloading unit  300  upwards. After the wafer is loaded on the wafer pedestal  200 , the wafer loading/unloading unit  300  moves downward so that the finger tip  415  is pressed against the circumference of the wafers toward the fence  230  to fix the wafers  1  at the predetermined positions. 
     FIG. 3 is an exploded perspective view illustrating a tension measuring apparatus  500  for measuring the tension of the wafer clamping finger unit  400  described above. The measuring apparatus  500  includes a standard base plate  510 , moving plate  520 , tension gauge  530 , measuring tip  540 , and displacement restricting block  550 . 
     More specifically, the standard base plate  510  is a flat, rectangular shaped plate with beveled corners (that is, a hexahedral shape). Fixing protruders  515  are formed at the lower surface of the standard base plate  510  (see also FIG. 4) to stabilize and fix the standard base plate  510 . The fixing protruders  515  are oriented so that they are aligned with, and can be inserted, into through-holes  250  of the spinning disc  100  and wafer pedestals  200  as shown in FIG.  5 . The fixing protruders  515  ensure the standard base plate  510  is placed in the same standard measuring position at all times. 
     Referring back to FIG. 3, one pair of guide rail grooves  516  are formed at the opposite side of the fixing protruder  515  of the standard base plate  510  with a predetermined distance therebetween, with the guide rails  516  extending from one edge of the standard base plate  510  to the other in a longitudinal direction. Note that the guide rails  516  extend in the same direction as the movement of the finger tip  415  described above. Preferably, the cross-section of the guide rail groove  516  has a dovetail shape, similar to an I-beam configuration, to correspond to a similar shaped guide rail  522  of the moving plate  520 , which when coupled with the rail groove  516 , can reciprocate linearly without vertical separation. 
     The moving plate  520  has the same hexahedral shape as the standard base plate  510 . The guide rails  522  formed at the lower surface of the moving plate  520  are inserted to the guide rail grooves  516  of the standard base plate  510 . At least one or more screw holes  524  are formed in the moving plate  520 . 
     A tension gauge  530  is installed on the moving plate  520  for measuring the tension of the wafer clamping finger unit  400 . The tension gauge  530  is firmly fastened to the moving plate  520  by means of a screw  526  inserted into the fastening hole  524 . The tension gauge  530  includes a tension rod  532  to actually measure the tension. Preferably, the tension gauge  530  includes functional buttons  534  (e.g., a reset or initialization button, maximum value button, etc.) and a display window  536  to display the tension value. The tension rod  532  has a male screw portion at one end, and is inserted though a longitudinal hole  544  in the tension measuring block  540  for coupling using nut  546 . The tension measuring block  540  confronts the finger tip  415  in order to measure the tension as determined by the displacement of the tension measuring block  540 . The longitudinal hole  544  is formed such that there can be some vertical movement of the tension rod  532  inside is the hole  544 . In other words, the circumference of the longitudinal hole  544  is greater than the circumference of the tension rod  532 . This enables the tension measuring block  540  to be positioned at a designated height such that the bottom surface of the tension measuring block  540  does not contact the upper rubber surface of the wafer pedestals  200 , after which the nut  546  is tightened. This prevents damage to the wafer pedestals  200 , and provides an accurate measurement since the tension measuring block  540  can move freely. 
     Note that a 0.1 mm change in displacement (e.g., 5 mm to 5.1 mm) of the tension measuring block  540  pushing on the finger tip  415  may actually be a rather large change in tension value. However, it is impossible for a worker to confirm visually or through experience that the tension measuring block  540  is pushed by a predetermined length of displacement, for instance, 4.9 mm, 5 mm or 5.1 mm. Therefore, a displacement restricting block  550  is additionally installed at the end  517  of the standard plate  510  for restricting the movement of the moving plate  520 . The displacement restricting block  550  makes it possible for any worker to press the finger tip  415  with the tension measuring apparatus  500  by a predetermined length of displacement, so that the worker can accurately measure the tension of the wafer clamping finger unit  400 . Even if the diameter of the wafers  1  is changed, the displacement restricting block  550  can be replaced with another one having a different diameter to fit the wafer accommodating pad  210 . This would not change the positions of the wafer loading/unloading pins. 
     FIGS. 5 through 7 illustrate a method for measuring the tension of the wafer clamping finger unit  400  with the tension measuring apparatus  500  of the present invention. First, fixing protruders  515  formed at the bottom surface of the standard base plate  510  of the tension measuring apparatus  500  are aligned and inserted into the through-holes  250  formed at the upper surface of the wafer accommodating pad  210  of the wafer pedestals  200 , so that the tension measuring apparatus  500  is fixed in a standard position for measurement. 
     Then, the nut  546  fixing the tension measuring block  540  of the tension measuring apparatus  500  is released to enable a gap gauge of approximately 0.3 mm in thickness between the top surface of the wafer accommodating pad  210  and the bottom surface of the tension measuring block  540  while the tension measuring block  540  is left movable. Then, the nut  546  is tightened to fix the tension measuring block  540 . Accordingly, a predetermined gap is formed between the wafer accommodating pad  210  and the tension-measuring block  540  to ensure accurate measurement and prevent the tension measuring block  540  from scratching the upper surface of the wafer accommodating pad  210 . 
     A worker then initializes the measuring process such that the tension gauge  530  is set to zero, and the moving plate  520  is moved toward the finger tip  415  until the moving plate contacts the displacement restricting block  550  as shown in FIG.  6  and FIG.  7 . Accordingly, the tension of the wafer clamping finger unit  400  can be accurately measured by the tension gauge  530 . Tension readings outside the limits will enable the workers to readjust and set the proper limits before the wafer manufacturing process continues. 
     As described above, one advantage of the tension measuring apparatus of the present invention is that the finger pressing force needed for clamping wafers can always be measured accurately with only a simple manipulation, regardless of the worker carrying out the measurement procedure. 
     While the present invention was described in detail referring to the attached embodiments, various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the present invention as set forth in the appended claims.