Abstract:
A wafer probing system, and a wafer-probing needle calibrating method using the same are provided. The system comprises a main support, a wafer chuck mounted on the main support, a needle chuck for contacting one of the plurality of needles. The needle chuck is comprised of a conductive signal line, and a shield line for shielding the signal line. Further, the system includes positioning means, for determining the position of the plurality of needles, moving means, for vertically moving the needle chuck, being coupled to the support, and means for horizontally moving the support based on the determined position of the plurality of needles. With the present invention system and method, signals applied to wafer probing needles can be accurately calibrated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wafer probing system, and more particularly, to a wafer probing system including wafer probing needles, and a method of calibrating timing of signals for the wafer probing system. 
     2. Description of the Related Art 
     Generally, a plurality of integrated circuit chips are formed on one wafer. Integrated circuit chips need to be electrically connected to testing equipment in order to measure the electrical performance thereof. Integrated circuit chips are too small to be directly connected to the testing equipment. Thus, a probing card having a plurality of needles is connected to the testing equipment, and the appropriate needles contact appropriate bonding pads of a particular integrated circuit chips on the wafer. This way, the electrical performance of the integrated circuit chips is measured. Here, the testing equipment is connected to the plurality of needles via one of a plurality of signal wires. Each signal wire must have the same signal delivery characteristics. However, in many cases, each signal wire has different signal delivery characteristics because the characteristics of signal wires can vary during the manufacturing thereof. Signals used in integrated circuit chips are so sensitive that if signal wires have different characteristics, signals output from the testing equipment reach the needles at different times via the signal wires. As a result, the electrical characteristics of integrated circuit chips cannot be accurately measured. Accordingly, in order to measure the electrical characteristics of integrated circuit chips accurately, the electrical characteristics of signal wires should be accurately measured. Then, the signals, which are applied from the testing equipment to the needles, can be controlled in accordance with the accurately measured electrical characteristics of signal wires. This is referred to as signal calibration. 
     Conventionally, however, all of the needles are made to come into electrical contact with the bonding pads of integrated circuit chips for the signal calibration, while a wafer is loaded on a wafer chuck in a wafer probing system. Therefore, the testing equipment cannot accurately calibrate the waveforms of signals which reach the needles. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a wafer probing system that contacts wafer probing needles, one at a time. 
     Another objective of the present invention is to provide a method of calibrating wafer-probing needles. With this method, signals applied to the wafer probing needles can be accurately calibrated. 
     Accordingly, to achieve the first objective, the present invention provides a wafer probing system including a probe card on which a plurality of needles are mounted. The system includes a main support, a wafer chuck mounted on the support, and a needle contact for individually contacting one of the plurality of needles. The needle contact is comprised of a conductive signal line, and a shield line for shielding the signal line. Further, the system includes positioning means, for determining the position of the plurality of needles, being mounted on the support, moving means, for vertically moving the needle contact, being coupled to the support, and means for horizontally moving the support based on the determined position of the plurality of needles. The needle contact includes a conductive signal line and a shield line for shielding the signal line. 
     Preferably, the moving means includes a needle contact support, a rail for vertically moving the needle contact support, a motor for moving the rail, and a needle contact controller for controlling the motor. 
     In another embodiment of the present invention, a wafer probing system includes a wafer chuck on which the wafer is loaded. The system also comprises a wafer chuck support including means for moving the wafer chuck horizontally and vertically. The wafer chuck support further includes a needle contact for contacting one of the plurality of needles. Also, means for determining the positions of the plurality of needles such as a camera is mounted on the wafer chuck support. In addition, a controller is provided for receiving data on the positions of the plurality of needles from said positioning means. The controller controls the motion of the needle contact and wafer chuck based on the position information data. 
     Preferably, the needle contact is lower than the wafer chuck, and the shield line is grounded. 
     To achieve the second objective, the present invention provides a method of calibrating the timing of signals that are applied to a plurality of needles for testing a wafer, using a wafer probing system including a probe card with the needles mounted thereon, a conductive needle contact for individually contacting one of the plurality of needles, means for moving the needle contact horizontally and vertically, a signal generator electrically connected to the probe card for generating a predetermined signal, and a measurer electrically connected to the needle contact for measuring wave form and timing of a signal. The method comprises (a) selecting a needle from the plurality of needles after determining the positions of the plurality of needles, and moving the needle contact to contact the selected needle, (b) applying a predetermined signal output from the signal generator, to the selected needle via the probe card, (c) measuring time of the signal received at the selected needle via the needle contact, and (d) based on said measuring, calibrating the timing of signals which are received at the needles, after repeating the steps (a), (b) and (c) for each needle. 
     Preferably, the positions of the needles in step (a) are ascertained using a camera. 
     Therefore, in accordance with the present invention, signals applied to wafer probing needles can be accurately calibrated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a schematic cross-sectional side view of a wafer probing system according to a first embodiment of the present invention; 
     FIGS. 2A and 2B are a schematic plan view and a schematic side view, respectively, of the wafer chuck support and the apparatuses for controlling the wafer chuck support shown in FIG. 1; 
     FIG. 3 is a magnified view of the needle contact shown in FIG. 1; 
     FIGS. 4A and 4B are cross-sectional views of one of the needles of FIG. 1 which contacts a wafer loaded on a wafer chuck, and which contacts a needle contact, respectively; and 
     FIG. 5 is a waveform diagram of signals which are applied to needles; 
     FIG. 6 is for illustrating a method of measuring the time at which signals reach needles; 
     FIG. 7 is a schematic cross-sectional side view of a wafer probing system according to a second embodiment of the present invention; and 
     FIG. 8 is a flowchart illustrating a method of calibrating wafer probing needles according to a preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The attached drawings for illustrating a preferred embodiment of the present invention, and the contents written on the attached drawings must be referred to in order to gain a sufficient understanding of the merits of the present invention, the operation thereof, and the objects accomplished by the operation of the present invention. 
     Hereinafter, the present invention will be described in detail by explaining a preferred embodiment of the present invention with reference to the attached drawings. Like reference numerals in the drawings denote the same members. 
     Referring to FIG. 1, a wafer probing system according to a first embodiment of the present invention includes a main body  105 , a probe card  111 , a wafer chuck  121 , a wafer chuck support  131 , a sub-chuck  141 , and a camera  151 . A wafer  181  is loaded on the wafer chuck  121 . A plurality of integrated circuit chips are formed on the wafer  181 . FIGS. 2A and 2B show an apparatus for controlling the wafer chuck support  131 . In detail, the wafer chuck support  131  is positioned on X-axis rails  211  and  212  and rides along the X-axis rails  211  and  212 . The X-axis rail  211  is screw-shaped. The X-axis rails  211  and  212  are horizontally fixed by rail supports  221  and  222 . A step motor  231  is installed on the rail support  222 , and rotates the X-axis rail  211 . As the X-axis rail  211  rotates, the wafer chuck support  131  moves in the direction of the X axis. The rail supports  221  and  222  are positioned on Y-axis rails  241  and  242 , and moved in the direction of the Y-axis thereby. A step motor  251  is installed on one end of the Y-axis rail  241 . The step motor  251  rotates the Y-axis rail  241 , and the rail supports  221  and  222  move in the direction of the Y-axis with rotation of the Y-axis rail  241 . A controller  261  is connected to the step motors  231  and  251 , and drives the same. The controller  261  and the rail supports  221  and  222  are installed on a main support  271 . The main support  271  can be moved up and down by a motor (not shown). The direction of movement of the wafer chuck support  131  and the rail supports  221  and  222  may vary depending on the structure and characteristics of the wafer probing system  101  of FIG.  1 . 
     The probe card  111  of FIG. 1 is placed on the wafer chuck  121 . A plurality ofneedles  161  (see FIG. 1) are installed on the probe card  111 . The plurality of needles  161  contact the bonding pads of an integrated circuit chip. The camera  151  is mounted on the wafer chuck support  131 , and views the needles  161  mounted on the probe card  111  and transmits a photographic image or other x-y positional information to the controller  261 . The controller  261  analyzes the photographic image and locates the positions of the needles  161  to accurately contact the wafer  181  or the sub chuck  141  with the needles  161 . The camera  151  is mounted on the wafer chuck support  131 , such that it moves in every direction along with the wafer chuck  121 . 
     The sub-chuck  141  includes a needle contact  171  and moving means  173 ,  175 ,  177  and  179  as shown in FIG.  1 . The needle contact  171  is shown in detail in FIG.  3 . The needle contact  171  includes a signal line  311  and a shield line  321  which surrounds the signal line  311 . The shield line  321  is grounded. The shield line  321  is stripped at one end to expose the signal line  311  to enable it to contact one of the needles  161 . This structure also prevents the signal line  311  from contacting another adjacent needles when the signal line  311  contacts the needle  161 . The diameter L 1  of the signal line  311  is smaller than the distance between needles  161 . The diameter L 1  is set to be similar to the length of one side of a bonding pad of an integrated circuit chip. The lengths of the four sides of a bonding pad of the integrated circuit chip are generally the same. Thus, as the bonding pad size of the integrated circuit chip decreases, the diameter of the signal line  311  becomes smaller accordingly. The height of the needle contact  171  is set to be lower than the wafer chuck  121  to prevent the needle contact  171  from being damaged by the probe card  111  while a wafer is being tested. 
     The moving means  173 ,  175 ,  177  and  179  (See FIG. 1) may take the form of a needle contact support  173 , a vertical rail  175 , a needle contact controller  177 , and a motor  179 . The needle contact  171  is mounted on the needle contact support  173 . The needle contact support  173  is connected to the vertical rail  175 , and moves up and down with rotation of the vertical rail  175 . A motor  179 , for example, a step motor, is attached to the vertical rail  175 , and rotates the vertical rail  175 . The motor  179  is controlled by the needle contact controller  177 . The needle contact controller  177  can be included in the controller  261  of FIG.  2 . 
     FIG. 4A shows the wafer  181  in contact with the needles  161 , and FIG. 4B shows the needle contact  171  in contact with the needles  161 . As shown in FIGS. 4A and 4B, in order to test the wafer  181  loaded on the wafer chuck  121 , the wafer chuck support  131  horizontally moves to align the wafer chuck  121  with the probe card  111 . Then the wafer chuck support  131  is lifted to contact the bonding pads of a selected integrated circuit chip with the needles  161 . 
     On the other hand, in order to contact the needle contact  171  with one of the needles  161 , the wafer chuck support  131  horizontally moves to align the needle contact  171  with the probe card  111 . Then the needle contact support  173  is lifted to contact the needle contact  171 , i.e., signal line  311  with one of the needles  161 . The signal line  311  contacts the needles  161 , one at a time. 
     When signals are applied from testing equipment  611  of FIG. 6 to needles  161  to test an integrated circuit chip, the signals must reach the needles  161  at the same time. However, signals, e.g., AO through A 3 , may reach the needles  161  at different times as shown in FIG.  5 . As a result, the testing equipment  611  of FIG. 6 cannot accurately test the electrical characteristics of an integrated circuit chip. Accordingly, in order to accurately test the electrical characteristics of an integrated circuit chip, the signals AO through A 3  must be controlled so that they can simultaneously reach the needles  161 . That is, each of the signals AO through A 3  is calibrated to reach the needles  161  at the same time by slightly delaying the signals AO, A 2  and A 3  with respect to the signal AI which is output from the testing equipment  611  of FIG.  6  and is the last signal to reach the needles  161 . 
     In order to calibrate signals applied to the needles  161 , the testing equipment  611  is electrically connected to the wafer probing system  101  as shown in FIG.  6 . The testing equipment  611  includes a signal generator  621  and a measurer  631 . The signal generator  621  is electrically connected to the probe card  111 , and the measurer  631  is electrically connected to the needle contact  171 . First, the needle contact  171  is lifted to contact one of the needles  161 . At this stage, the signal generator  621  applies a signal to one of the needles  161  via probe card  111 . Then, the measurer  631  receives the signal via needle contact  171 . The measurer  631  measures the time period from the point (in time) the signal is output from the signal generator  621  to the point (in time) it reaches the measurer  631 . Using the same method, the measurer  631  measures the time period for each one of the needles  161  mounted on the probe card  111 . The testing equipment  611  compares these time periods, and calibrates the signals based on the last signal to arrive at the measurer  631  or the corresponding one of needles  161 . 
     FIG. 7 is a schematic cross-sectional side view of a wafer probing system according to a second embodiment of the present invention. Particularly, the needle contact  171  is installed on the wafer chuck support  131 . The wafer chuck support  131  and a fixing device, i.e., a main support  271  of FIG. 2B move in every direction to contact the needle contact  171  with the needles  161 . Thus, the moving means  173 ,  175  and  177  shown in FIG. 1 are not required. Other operations are the same as those described in FIG.  1 . 
     FIG. 8 is a flowchart illustrating one example of a method of calibrating waferprobing needles according to a preferred embodiment of the present invention. A method of calibrating signals, which reach the wafer probing needles shown in FIG. 1, will now be described with reference to FIG.  8 . 
     First, in needle contact step  811 , accurate positioning of the plurality of needles  161  can be achieved using the camera  151 . One of the plurality of needles  161  is selected, and the wafer chuck support  131  and the needle contact  171  are moved to contact the signal line  311  of the needle contact  171  (see FIG. 3) with the selected one of the needles using position information of the needles  161  obtained through the camera  151 . 
     Next, in a signal-applying step  821 , the signal generator  621  outputs a predetermined signal and transmits the predetermined signal to the probe card  111 . Then, the predetermined signal is transmitted to the selected needle via an internal circuit of the probe card  111 . 
     After this, in a signal measuring step  831 , the measurer  631  measures the time period of a signal transmitted via the needle contact  311  which contacts the selected needle using the method as described above. 
     Next, in a signal calibrating step  841 , the needle contact  171  is horizontally moved to contact the other needle, and applies a signal to the other needle and measures the time period for the signal using the method as described above. 
     In this method, signals are applied to each and every one of the needles  161 . The applied signals are compared and analyzed using the data on the time period obtained by the measurer  631 . As a result, the signals can be calibrated based on the last signal having the longest time period. When necessary, the voltage and current of signals which are applied to the needles  161  can be measured and controlled. 
     When integrated circuit chips on a wafer are tested with calibrated signals, the electrical characteristics of the integrated circuit chips can be accurately tested. 
     According to the present invention, as described above, signals applied to needles  161  can be calibrated by contacting a needle contact  171 , i.e. signal line  311 , to each and every one of the needles  161  mounted on the wafer probe card  111 . This way, the waveform of a signal output from each of the needles  161  and the calibration state of each of theneedles  161 , and a current and voltage flowing through each of the needles  161  can be determined. This allows the electrical characteristics of an integrated circuit chip to be accurately measured. 
     Although the invention has been described with reference to particular embodiments, it will be apparent to one of ordinary skill in the art that modifications of the described embodiment may be made without departing from the spirit and scope of the invention.