Abstract:
Disclosed is a probing method comprising steps of moving a main chuck to align an object of inspection on the main chuck with probes of a probe card located over the main chuck, moving the main chuck toward the probe card, thereby bringing electrodes of the object of inspection into contact with the probes, overdriving the main chuck toward the probe card while measuring a load applied to the object of inspection by contact with the probes and controlling the movement of the main chuck in accordance with the measured load, and inspecting the electrical properties of the object of inspection by means of the probes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a Continuation-in-Part application of U.S. patent application Ser. No. 09/667,502, filed Sep. 22, 2000, the entire contents of which are incorporated herein by reference.  
         [0002]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-285139, filed Oct. 6, 1999, the entire contents of which are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    The present invention relates to a probing method and a probing apparatus, and more specifically, to a probing method and a probing apparatus with high reliability, in which a load applied to a main chuck carrying an object of inspection thereon by probes is measured when the main chuck is overdriven to the probes, so that a steady load can always be applied to the main chuck in accordance with the measured value.  
           [0004]    As shown in FIG. 8, a probing apparatus  10  for checking integrated circuits on a wafer for electrical properties, for example, is provided with a loading chamber  11 , probing chamber  12 , controller  13 , and display unit  14 . In the loading chamber  11 , wafers W stored in a cassette C are delivered one after another and transported to the probing chamber  12 . The probing chamber  12  adjoins the loading chamber  11 . Integrated circuits formed on each wafer W that is transported from the loading chamber  11  are inspected in the probing chamber  12 . The controller  13  controls the chambers  11  and  12 . The display unit  14  doubles as a control panel for operating the controller  13 .  
           [0005]    The loading chamber  11  is provided with a pair of tweezers  15  for use as a transportation mechanism for the wafers W. The tweezers  15  move back and forth in the horizontal direction and rotates forward and reversal, thereby delivering the wafers W in the cassette C one after another and transporting them into the probing chamber  12 . A sub-chuck  16  for pre-aligning each wafer W is provided near the tweezers  15 . As the sub-chuck  16  receives each wafer W from the tweezers  15  and rotates forward or reversal in a θ-direction, it pre-aligns the wafer W on the basis of its orientation flat.  
           [0006]    The probing chamber  12  is provided with a main chuck  17  that carries each wafer W thereon. The main chuck  17  is moved in X- and Y-directions by means of X- and Y-stages  18 ,  19 , respectively, and moved in Z- and θ-directions by means of built-in drive mechanisms. Alignment means  20  is provided in the probing chamber  12 . The alignment means  20  serves to align each wafer W with the probes. The alignment means  20  includes an alignment bridge  22  having first image-pickup means (e.g., a CCD camera)  21  for imaging the wafer W, a pair of guide rails  23  for guiding the bridge  22  in reciprocation in the Y-direction, and second image-pickup means (e.g., a CCD camera, not shown) attached to the main chuck  17 . A probe card is provided on the top surface of the probing chamber  12 . On the upper surface of the probe card, a test hed is connected electrically to the card by means of a connecting ring. A test signal from a tester  34  (see FIG. 1) is transmitted to the probe card via the test head and the connecting ring, and further transmitted from the probe card to the wafer W. The object of inspection is checked for electrical properties in accordance with the test signal.  
           [0007]    In inspecting the integrated circuits formed on each wafer W, the tweezers  15  takes out one of the wafers W from the cassette C. While the wafer W is being transported to the probing chamber  12 , it is pre-aligned on the sub-chuck  16 . Thereafter, the tweezers  15  deliver the wafer W to the main chuck  17  in the probing chamber  12 . The alignment bridge  22  moves to the center of the probe card. The main chuck  17  moves to the position under the first image-pickup means  21  of the bridge  22 , and the wafer on the chuck  17  is aligned with the probe card by means of the first image-pickup means  21  and the second image-pickup means. As the main chuck  17  moves in the X- and Y-directions, the wafer W is subjected to index feed. As the chuck  17  ascends in the Z-direction, the electrodes of the integrated circuits are brought into contact with probes. When the main chuck  17  is overdriven, the integrated circuits on the wafer W are checked for electrical properties with their electrodes electrically in contact with the probes.  
           [0008]    In the case of a wafer W with a diameter of 200 mm or less, as shown in FIG. 9A, the wafer W on the main chuck  17  ascends from the position indicated by a dashed line to the position indicated by a full line as the main chuck  17  is overdriven. As indicated by a full line in FIG. 9A, the wafer W rises in the Z-direction without substantially tilting from its horizontal position. As this is done, each probe  24 A of a probe card  24  is elastically raised from the position of the dashed line to the position of the full line of FIG. 9A. The tip of the probe  24 A moves from a starting point S to an ending point E, as indicated by a thick line. The plane distance covered by the tip that moves from the starting point S to the ending point E, as indicated by a hatched arrow in FIG. 9B, is within the area of an electrode pad P of each integrated circuit. Thus, the probes  24 A and the electrode pad P are brought electrically into contact with each other, whereupon the integrated circuit is inspected.  
           [0009]    In the case of a wafer W with a diameter of 300 mm, the wafer size is too large, and besides, the integrated circuits are hyperfine, and electrode pads are arranged at narrow pitches. The number of pins of the probe card is increased (e.g., to 2,000) correspondingly. A load from about 2,000 probes  24 A that acts on the main chuck  17  when the chuck is overdriven is as heavy as, for example, more than 10 kg to 20 kg. Accordingly, an unbalanced load that is generated when the wafer W is overdriven from the position indicated by a dashed line in FIG. 10A so that it touches the probes  24 A causes the rotating shaft (not shown) of the main chuck  17  to bend. In consequence, the wafer W is tilted for about 20 to 30 μm, for example, as indicated by a full line in FIG. 10A, and deflected outward from its original raised position. As this is done, the tip of each probe  24 A is elastically raised from the position indicated by the dashed line to the position indicated by the full line of FIG. 10A, and moves along a track (indicated by a thick line in FIG. 10A) that is longer than the one shown in FIG. 9A. Although the starting point S of the tip is situated in the same position as the one shown in FIG. 9A, the ending point E is located outside the area of the electrode pad P, as indicated by a hatched arrow in FIG. 10B. Thus, test signals cannot be transmitted from the probes  24 A to the electrode pads P, so that the reliability of the inspection is lowered.  
           [0010]    In Jpn. Pat. Appln. KOKAI Publication No. 11-30651, the inventor hereof proposed a probing method and a probing apparatus in which dislocation of probes attributable to contact load is corrected three-dimensionally. According to this technique, the probes estimate a distortion of a main chuck in the position where the probes are in contact with a wafer, in accordance with known data, such as information (outside diameter, material, etc.) on the main chuck, information (outside diameter, number of chips, etc.) on the wafer, and information (probe tip area, number of probes, etc.) on a probe card. Based on the estimated value, the position where the probes are in contact with the wafer is corrected three-dimensionally.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    According to the probing method and the probing apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 11-30651, a load (needle pressure) in the contact position of the probes is estimated in accordance with the contact position for overdrive operation and a given overdrive, the distortion of the main chuck is estimated according to the estimated load, and the contact position of the probes is three-dimensionally corrected in accordance with the estimated distortion. If the estimated load and an actual load are inconsistent, therefore, the three-dimensional correction of the contact position of the probes may possibly be wrong. Further, the conventional probing method and apparatus use a mechanism that obtains the given overdrive by driving the Z-axis. On the other hand, the distance between the probe tip and the wafer W changes due to deformation of the probe card with time or thermal expansion or contraction of the card during inspection. Since the overdrive of the main chuck is fixed, however, a constant contact load cannot be obtained.  
           [0012]    The object of the present invention is to solve the above problems.  
           [0013]    An object of the present invention is to bring probes and electrode pads of an object of inspection accurately into contact with one another under a steady load even if a probe card is deformed from various causes or expanded or contracted by any thermal effect.  
           [0014]    Another object of the of the invention is provide a probing method and a probing apparatus, in which probes and electrode pads of an object of inspection can be brought accurately into contact with one another if a main chuck is tilted by an unbalanced load during overdrive operation, so that high-accuracy inspection can be enjoyed.  
           [0015]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.  
           [0016]    In a first aspect of the present invention, there is provided a probing method comprising steps of: moving a main chuck to align an object of inspection on the main chuck with probes of a probe card located over the main chuck; moving the main chuck toward the probe card, thereby bringing electrodes of the object of inspection into contact with the probes; overdriving the main chuck toward the probe card while measuring a load applied to the object of inspection by contact with the probes and controlling the movement of the main chuck in accordance with the measured load; and inspecting electrical properties of the object of inspection by means of the probe.  
           [0017]    Preferably, in this probing method, the control of the movement of the main chuck is control of an overdrive based on the measured load, such that the load has a given value.  
           [0018]    Preferably, in this probing method, the control of the movement of the main chuck further includes steps of obtaining a distortion of the main chuck in accordance with the measured load and correcting at least one of dislocations between the object of inspection and the probe in X-, Y-, and θ-directions in accordance with the distortion.  
           [0019]    Preferably, in this probing method, the measurement of the load applied to the object of inspection by contact with the probes includes steps of locating a polishing mechanism right under the probes, the polishing mechanism including a polish plate to be used to polish the tip of the probes; moving the located polishing mechanism toward the probe card, thereby bringing the polish plate into contact with the probes; overdriving the polishing mechanism toward the probe card; and measuring a load applied to the polish plate by the probes by means of a pressure sensor attached to the polishing mechanism during the overdrive operation.  
           [0020]    In a second aspect of the present invention, there is provided a probing method comprising steps of: moving a main chuck in X-, Y-, and θ-directions to align an object of inspection on the main chuck with probes of a probe card located over the main chuck; moving the main chuck in a Z-direction, thereby bringing electrodes of the object of inspection into contact with the probes; overdriving the main chuck toward the probe card while measuring a load applied to the object of inspection by contact with the probes by means of a sensor and controlling the movement of the main chuck in accordance with the measured load; and inspecting electrical properties of the object of inspection by means of the probes.  
           [0021]    Preferably, in this probing method, the sensor is located on at least one of the lower part of the main chuck and between an LM guide and an XY-stage on which the main chuck is set.  
           [0022]    Preferably, in this probing method, the control of the movement of the main chuck is control of an overdrive of the main chuck.  
           [0023]    Preferably, in this probing method, the control of the movement of the main chuck includes steps of obtaining a distortion of the main chuck in accordance with the measured load and correcting at least one of dislocations between the object of inspection and the probes in the X-, Y-, and θ-directions in accordance with the distortion.  
           [0024]    In a third aspect of the invention, there is provided a probing method in which a main chuck is moved in X-, Y-, and θ-directions to align an object of inspection on the main chuck with probes of a probe card located over the main chuck, the main chuck is moved in a Z-direction so that electrodes of the object of inspection are brought into contact with the probes, the main chuck is overdriven toward the probe card, and electrical properties of the object of inspection are inspected by means of the probes, the probing method comprising steps of: locating a polishing mechanism right under the probes, the polishing mechanism including a polish plate to be used to polish the tip of the probes; moving the located polishing mechanism toward the probe card, thereby bringing the polish plate into contact with the probes; overdriving the polishing mechanism toward the probe card; measuring a load applied to the polish plate by the probes by means of a pressure sensor during the overdrive operation; and controlling the movement of the main chuck in accordance with the measured load.  
           [0025]    Preferably, in this probing method, the sensor is set on the polishing mechanism.  
           [0026]    Preferably, in this probing method, the control of the movement of the main chuck is control of an overdrive of the main chuck.  
           [0027]    Preferably, this probing method comprises steps of obtaining a distortion of the main chuck in accordance with the measured load and correcting at least one of dislocations between the object of inspection and the probes in the X-, Y-, and θ-directions in accordance with the distortion.  
           [0028]    Preferably, in this probing method, the control of the overdrive of the main chuck includes steps of obtaining a distortion of the polish plate in accordance with the relation between the load applied to the polish plate and the distortion of the polish plate, and the load applied to the polish plate which is measured by means of the pressure sensor; obtaining the spring constant of the probes from the distortion and an overdrive of the polish plate; obtaining the spring constant of the main chuck in accordance with the spring constant of the probes and the relation between the load and a distortion of the main chuck; obtaining a load applied to the main chuck by the probes in accordance with the spring constant of the main chuck and the relation between the spring constant and the overdrive of the main chuck; and controlling the overdrive of the main chuck in accordance with the obtained load.  
           [0029]    Preferably, this probing method further comprises steps of obtaining a distortion of the main chuck in accordance with the load measured by means of the pressure sensor and correcting dislocations between the object of inspection and the probes in X- and Y-directions in accordance with the distortion.  
           [0030]    In a fourth aspect of the invention, there is provided a probing apparatus comprising: a main chuck carrying an object of inspection thereon; a probe card having a plurality of probes and located over the main chuck; a drive mechanism for moving the main chuck in X-, Y-, Z-, and θ-directions; a pressure sensor adapted to measure a load applied to the object of inspection by the probes when the drive mechanism moves the main chuck toward the probe card so that the object of inspection on the main chuck is brought into contact with probes; and a controller for controlling the movement of the main chuck in accordance with a position where the probes touch the object of inspection and the load measured by means of the pressure sensor.  
           [0031]    In a fifth aspect of the invention, there is provided a probing apparatus comprising: a main chuck carrying an object of inspection thereon; a probe card having a plurality of probes and located above the main chuck; a drive mechanism which moves the main chuck in X-, Y-, Z-, and θ-directions; a pressure sensor adapted to measure a load applied to the object of inspection by the probes, when the drive mechanism moves the main chuck toward the probe card to bring the object of inspection located on the main chuck into contact with probes; and a controller which obtains a distortion of the main chuck in accordance with a position where the probes contact the object of inspection and the load measured by means of the pressure sensor.  
           [0032]    Preferably, the controller of this probing apparatus controls an overdrive in accordance with the measured load so that the load has a given value.  
           [0033]    Preferably, the controller of this probing apparatus corrects at least one of dislocations between the object of inspection and the probes in the X-, Y-, and θ-directions in accordance with the distortion.  
           [0034]    In a sixth aspect of the invention, there is provided a probing apparatus comprising: a main chuck carrying an object of inspection thereon; a polishing mechanism having a polish plate and attached to the main chuck; a probe card having a plurality of probes and located above the main chuck; a drive mechanism which moves the main chuck in at least a Z-direction; a pressure sensor adapted to measure a load applied to the polish plate of the polishing mechanism attached to the main chuck by the probes, when the drive mechanism moves the main chuck toward the probe card to bring the polish plate into contact with the probes; and a controller which controls the drive mechanism and which obtains a load applied to a position where the probes contact the main chuck in accordance with the load measured by the pressure sensor.  
           [0035]    The probing apparatus provided based on the sixth aspect of the present invention preferably further includes the following (a).  
           [0036]    (a) The controller obtains a spring constant of the probe in accordance with the load measured by the pressure sensor, obtains a spring constant of the main chuck in accordance with a relation between the load and the distortion of the main chuck, and obtains the load applied to the position where the probes contact the main chuck in accordance with the spring constant of the probe and a relation between the spring constant and an overdrive of the main chuck.  
           [0037]    In a seventh aspect of the present invention, there is provided a probing method in which an object of inspection mounted on a main chuck is aligned with probes of a probe card located in a position facing the main chuck, the main chuck is relatively brought close to the probe card, an electrode of the object of inspection is brought into contact with the probes, the main chuck is overdriven toward the probe card, and electrical properties of the object of inspection are inspected by means of the probes, the probing method comprising the steps of:  
           [0038]    locating a table having a pressure sensor and attached to the main chuck in a position facing the probes;  
           [0039]    relatively moving the table with respect to the probe card;  
           [0040]    overdriving the table toward the probe card;  
           [0041]    measuring a load applied to the table by the probes by means of the pressure sensor during the overdrive operation; and  
           [0042]    controlling the movement of the main chuck in accordance with the measured load.  
           [0043]    The probing method provided in the seventh aspect of the present invention preferably further includes one of the following (b) to (h) or a combination of some of them.  
           [0044]    (b) A polishing mechanism which polishes tips of the probes is located on the table.  
           [0045]    (c) The control of the movement of the main chuck is control of an overdrive of the main chuck.  
           [0046]    (d) The control of the movement of the main chuck includes the steps of:  
           [0047]    obtaining a distortion of the main chuck in accordance with the measured load; and  
           [0048]    correcting a dislocation between the object of inspection and the probes in at least one of X-, Y-, and θ-directions in accordance with the distortion.  
           [0049]    (e) The control of the overdrive of the main chuck includes steps of:  
           [0050]    obtaining a distortion of the polish plate in accordance with the relation between the load applied to the polish plate and the distortion of the polish plate and the load applied to the polish plate measured by means of the pressure sensor;  
           [0051]    obtaining the spring constant of the probes from the distortion of the polish plate and an overdrive of the polish plate;  
           [0052]    obtaining the spring constant of the main chuck in accordance with the spring constant of the probes and the relation between the load and a distortion of the main chuck;  
           [0053]    obtaining a load applied to the main chuck by the probes in accordance with the spring constant of the main chuck and the relation between the spring constant and the overdrive of the main chuck; and  
           [0054]    controlling the overdrive of the main chuck in accordance with the obtained load.  
           [0055]    (f) A zero point detection plate which detects the contact of the probes is located on the table.  
           [0056]    (g) The zero point detection plate is a contact plate plated with gold.  
           [0057]    (h) The zero point detection plate is a dummy sheet to which probe traces are to be attached.  
           [0058]    In an eighth aspect of the present invention, there is provided a probing apparatus comprising:  
           [0059]    a main chuck carrying an object of inspection thereon;  
           [0060]    a table attached to the main chuck;  
           [0061]    a probe card having a plurality of probes and located in a position facing the main chuck;  
           [0062]    a drive mechanism which moves the main chuck in at least a Z-direction;  
           [0063]    a pressure sensor adapted to measure a load applied to the table attached to the main chuck by the probes, when the drive mechanism moves the main chuck toward the probe card to bring the table into contact with the probes; and  
           [0064]    a controller which controls the drive mechanism and which obtains a load applied to a position where the probes contact the main chuck in accordance with the load measured by the pressure sensor.  
           [0065]    The probing apparatus provided in the eighth aspect of the present invention preferably further includes the following (i).  
           [0066]    (i) The controller obtains a spring constant of the probe in accordance with the load measured by the pressure sensor, obtains a spring constant of the main chuck in accordance with a relation between the load and the distortion of the main chuck, and obtains the load applied to the position where the probes contact the main chuck in accordance with the spring constant of the probe and a relation between the spring constant and an overdrive of the main chuck. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0067]    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 given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
         [0068]    [0068]FIG. 1 is a side view showing the principal part of one embodiment of a probing apparatus according to the present invention;  
         [0069]    [0069]FIG. 2 is a block diagram showing the principal part of the probing apparatus shown in FIG. 1;  
         [0070]    [0070]FIG. 3 is a view illustrating the operation of the principal part of the probing apparatus shown in FIG. 2;  
         [0071]    [0071]FIG. 4 is a diagram for illustrating the operation of a wafer on a main chuck shown in FIG. 2 and a probe;  
         [0072]    [0072]FIGS. 5A and 5B illustrate the operation of the wafer and the probe shown in FIG. 4, in which FIG. 5A is a diagram for illustrating the respective behaviors of the wafer and the probe, and FIG. 5B is a diagram for illustrating the trace of the tip of the probe on an electrode pad;  
         [0073]    [0073]FIG. 6 is a side view showing another embodiment of the probing apparatus according to the invention;  
         [0074]    [0074]FIG. 7 is a block diagram showing the principal part of the probing apparatus shown in FIG. 6;  
         [0075]    [0075]FIG. 8 is a cutaway perspective view of a conventional probing apparatus;  
         [0076]    [0076]FIG. 9A is a partially enlarged conceptual diagram showing the relation between a main chuck and a probe established when the main chuck is overdriven under a single-pin probe card;  
         [0077]    [0077]FIG. 9B is a diagram for illustrating the relation between an electrode pad and the trace of the tip of the probe in the state shown in FIG. 9A;  
         [0078]    [0078]FIG. 10A is a partially enlarged conceptual diagram showing the relation between the main chuck and the probe established when the main chuck is overdriven under a multi-pin probe card;  
         [0079]    [0079]FIG. 10B is a diagram for illustrating the relation between the electrode pad and the trace of the tip of the probe in the state shown in FIG. 10A;  
         [0080]    [0080]FIG. 11A is a side view showing the principal part of other embodiment of a probing apparatus according the present invention; and  
         [0081]    [0081]FIG. 11B is a side view showing the principal part of other embodiment of a probing apparatus according the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0082]    A probing method and a probing apparatus according to the present invention can be used to check integrated circuits on a wafer for electrical properties. Alternatively, however, the invention may be applied to the inspection of the electrical properties of general electronic components such as LCD&#39;s.  
         [0083]    In order to explain the present invention more specifically and definitely, there will be described a case in which the invention is applied to the inspection of the electrical properties of integrated circuits formed on a wafer.  
         [0084]    The invention will be described in connection with embodiments shown in FIGS.  1  to  7 , in which like reference numerals refer to like or equivalent portions throughout the several views.  
         [0085]    A probing apparatus  10  according to an embodiment of the invention, like the probing apparatus shown in FIG. 8, may be provided with a loading chamber  11  and a probing chamber  12 . Alternatively, however, the loading chamber  11  and the probing chamber  12  may be arranged separately. The tweezers  15  and a sub-chuck  16  are arranged in the loading chamber  11 . Wafers W in a cassette C are transported one after another by means of the tweezers  15 . In this process of transportation, each wafer W can be pre-aligned by means of the sub-chuck  16 . A main chuck  17 , which is movable in Z- and θ-directions, X-stage  18 , Y-stage  19 , and alignment means  20  are arranged in the probing chamber  12 . As the main chuck  17  moves in X-, Y-, Z-, and θ-directions under the control of a controller  13 , it aligns the wafer W thereon with a probe card in conjunction with the alignment means  20 . After the alignment, the main chuck ascends in the Z-direction, whereupon integrated circuits formed on the wafer W are checked for electrical properties with their electrodes electrically in contact with a probe  24 A.  
         [0086]    According to the present embodiment, a pressure sensor (e.g., load cell)  31  is provided for the measurement of load. Although the pressure sensor  31  is located between the main chuck  17  and the X-table  18  in the arrangement shown in FIG. 1, the location of the sensor is not limited to this position. For example, the sensor  31  may be located between an X, Y-table and an LM guide  40  (FIG. 8). The pressure sensor  31  is used to measure load from the probe  24 A that acts on the wafer W on the main chuck  17 . As shown in FIG. 2, the sensor  31  is connected to the controller  13 . The controller serves to control the movement of the main chuck in accordance with a signal measured by means of the pressure sensor  31 . By this control, the overdrive can be adjusted so that the load from the probe  24 A that acts on the wafer W is constant. Alternatively, under this control, the distortion of the main chuck may be obtained from the measured load so that at least one of dislocations between the object of inspection and the probe in the X-, Y-, and θ-directions can be corrected in accordance with the distortion. The adjustment of the overdrive and correction of the dislocation between the object of inspection and the probe can be carried out in combination with each other.  
         [0087]    As shown in FIG. 2, the controller  13  can comprise first storage means  131  for storing data such as wafer information on the wafers W, card information on the probe card, etc., second storage means  132  for storing data such as control programs for the probing apparatus, main chuck information on the main chuck  17 , and a central processing unit (hereinafter referred to as a “CPU”)  133 . The CPU  133  can read the individual pieces of information stored in the first and second storage means  131  and  132  and carry out processes based on predetermined programs.  
         [0088]    The wafer information may include parameters such as the location of each chip, chip size, position of the center of gravity of the chip, number of electrode pads, pitches between the electrode pads, etc. The card information may include parameters such as the number of probe needles (number of pins), location of the probe needles, material and properties of the probe needles, etc. The main chuck information may include parameters such as the mechanical strength of the rotating shaft of the main chuck  17 , outside diameter and load-distortion data of the chuck  17 , etc. The load-distortion data may be defined as data that are indicative of load on a typical point on the upper surface of main chuck  17  and the relation between the load and the distortion of the chuck  17 . The CPU  133  includes the measured load (needle pressure) of the pressure sensor  31  and distortion processing means  133 A. The processing means  133 A obtains the distortion of the main chuck  17  for a probe contact position in an overdrive mode in accordance with the load-distortion data of the main chuck and the wafer information. The distortion processing means  133 A is used to obtain the distortion of the main chuck  17  in accordance with the measured load of the pressure sensor  31  for the contact position of the probe  24 A and the load-distortion data.  
         [0089]    As shown in FIG. 2, input means (e.g., keyboard, etc.)  25  and the display unit  14  are connected to the controller  13 . Necessary data for various inspections, such as the wafer information and main chuck information, are input by means of the input means  25 . The input data are recognized by the display unit  14 . A drive mechanism  26  is connected to the controller  13 . The drive mechanism  26  serves to drive the main chuck  17 .  
         [0090]    The following is a description of the probing method and the operation of the probing apparatus. Before the wafers W are inspected, the wafer information and the card information are input by the input means  25 . The input data are recognized on a display screen. If the input data are correct, they are stored in the first storage means  131 . The wafers W in each cassette are fed into the probing apparatus  10 . After each wafer W is pre-aligned in the loading chamber, it is fed onto the main chuck  17  in the probing chamber. In the probing chamber, the wafer W is aligned with the probe  24 A by means of the alignment means. The electrical properties of each chip of the wafer W are successively inspected by means of the probe  24 A.  
         [0091]    In the inspection of each chip, the probing apparatus  10  is actuated in accordance with programs for the probing method of the invention read from the second storage means  132  by means of the CPU  133 . The first one of the integrated circuits on the wafer W to be measured is settled. The CPU  133  subjects the main chuck  17  to index feed, whereupon the integrated circuits on the wafer W are inspected in succession. In the inspection of each integrated circuit, the main chuck  17  is overdriven after it ascends to a position where the wafer W and the probe  24 A are in contact with each other. During the overdrive operation, the pressure sensor  31  measures load (needle pressure) between the probe  24 A and the wafer W. The overdrive is monitored in accordance with the measured load. When a preset load value is measured by means of the pressure sensor  31 , the controller  13  stops the operation of the drive mechanism  26 , thereby stopping the main chuck  17 , whereupon a fixed overdrive can be secured. The main chuck  17  tilts as it is subjected to an unbalanced load during the overdrive operation. FIG. 3 exaggeratedly shows the tilted state of the main chuck. In FIG. 3, arrows indicate a contact load and its reaction force, individually.  
         [0092]    In the conventional probing method, the overdrive is controlled by fixing the ascent of the main chuck  17  in the Z-direction. Accordingly, the position of the tip of the probe  24 A is vertically deviated from its reference position, due to thermal expansion of the probe card  24  that is caused when the wafer W is heated during the inspection, contraction of the card  24  that is caused when the wafer W is cooled, or deformation (exaggerated in FIG. 3) of the card  24  with time. Thus, the conventional probing method cannot secure an overdrive that matches the actual distance between the probe  24 A and the wafer W. In consequence, the contact load and the tip position fluctuate depending on the spot of contact of the probe, so that it is hard to effect steady inspection.  
         [0093]    According to the present embodiment, the pressure sensor measures the contact load (needle pressure) between the probe  24 A and the wafer W. Since the overdrive is controlled according to this measured load, steady inspection can be carried out under a constant contact load (needle pressure) without being influenced by any thermal effect or deformation of the probe card  24  with time.  
         [0094]    According to the present embodiment, the contact position of the probe  24 A can be corrected three-dimensionally during the overdrive operation. The method of the present embodiment, unlike a probing method proposed in Jpn. Pat. Appln. KOKAI Publication No. 9-306516, can three-dimensionally correct the contact position of the probe  24 A in accordance with the measured load from the probe  24 A that acts on the main chuck  17 . According to the method described in Jpn. Pat. Appln. KOKAI Publication No. 9-306516, the contact load produced by the probe is estimated, distortion of the main chuck  17  is obtained from the estimated value, and the contact position of the probe  24 A is three-dimensionally corrected in accordance with the distortion.  
         [0095]    As the wafer W, which is in contact with the probe  24 A in the position indicated by dashed line in FIG. 4, is overdriven to the position indicated by full line, it is subjected to an unbalanced load from the probe  24 A, and the main chuck  17  is tilted by the unbalanced load. In consequence, the wafer W tilts outward from its original position, and the a starting point S of the tip of the probe  24 A is urged to move in the direction indicated by arrow A in FIG. 4. According to the present embodiment, the distortion processing means  133 A obtains distortion for the load measured by means of the pressure sensor  31 , in accordance with the measured load and the load-distortion data. Based on this distortion, the movement of the main chuck  17  is corrected by means of the drive mechanism  26 , and the wafer W moves in the direction of arrow B in FIG. 4. Thus, the moving direction of the main chuck  17  is corrected according to the load measured by means of the pressure sensor  31 . Accordingly, the wafer W ascends as if it were kept horizontal, and the tip of the probe  24 A is vertically lifted upward, as indicated by arrow C. In consequence, the probe tip moves on a track that is hardly different from the track for the case where the wafer W is lifted horizontally (see FIG. 9). As shown in FIG. 5B, an ending point E of the tip remains in an electrode pad P. In consequence, the probe  24 A comes securely into contact with the given electrode pad P, so that the inspection of the integrated circuits can be carried out securely and steadily.  
         [0096]    According to the present embodiment, as described above, the load that is produced as the probe  24 A touches the wafer W is measured by means of the pressure sensor  31  when the main chuck  17  is overdriven under the control of the controller  13 . The overdrive of the main chuck  17  or the position of the wafer W relative to the position of the probe is corrected according to the measured load. If the probe card  24  is deformed by any thermal effect or use, therefore, the probe  24 A can touch the wafer W under a constant needle pressure. Alternatively, the probe  24 A can steadily touch a given position on the wafer W. In consequence, highly reliable inspection can be carried out.  
         [0097]    If the diameter of the wafer W and the number of pins of the probe card  24  are increased, moreover, the main chuck  17  is tilted by the unbalanced load during the overdrive operation. However, the pressure sensor  31  can measure the unbalanced load, and the contact position of the probe  24 A can be corrected according to the measured load and the load-distortion data of the main chuck  17 . In consequence, the position of the main chuck can be highly accurately corrected without being influenced by deformation that is attributable to heat from the probe card  24  or use. As shown in FIG. 5B, the probe  24 A can be securely brought into electrical contact with the electrode pad P of each integrated circuit in any spot on the wafer W, so that high-reliability inspection can be carried out securely.  
         [0098]    [0098]FIGS. 6 and 7 show another embodiment of the present invention. According to the present embodiment, as shown in FIG. 6, a support arm  32  extends horizontally from a straight trunk portion of a main chuck  17 . The arm  32  is provided with a polishing mechanism  33  for polishing a probe  24 A. The mechanism  33  includes a polish plate  33 A for polishing the probe  24 A and a support block  33 B for supporting the polish plate  33 A. The polishing mechanism  33  overdrives the main chuck  17  to bring the probe  24 A into contact with the polish plate  33 A, thereby polishing the probe  24 A. A pressure sensor  31 A (e.g., load cell) is located between the support arm  32  and the support block  33 B. The sensor  31 A measures load that is applied to the polish plate  33 A during overdrive operation. The relation between the measured load and a distortion of the polishing mechanism  33 , like the load-distortion data of the main chuck  17 , is measured in advance and loaded as load-distortion data of the polishing mechanism  33  in second storage means  132 .  
         [0099]    Still another embodiment of the present invention will be described with reference to FIG. 11A. As shown in FIG. 11A, when the probe  24 A directly contacts the surface of a table  33 ′, a contact pressure can be transmitted to the pressure sensor. In this structure, a contact member does not have to be disposed on the table  33 ′.  
         [0100]    Still another embodiment of the present invention will be described with reference to FIG. 11A. As shown in FIG. 11A, a support arm  32  extends horizontally from a straight trunk portion of a main chuck  17 . Instead of the polish plate  33 A, a table  33 ′ is disposed on the support arm  32  via a support block  33 B. The table  33 ′ can be provided with a pressure sensor  31 A (e.g., load cell). As shown in FIG. 11A, the pressure sensor  31 A can be disposed under the table  33 ′, but may also be disposed in an upper or intermediate portion of the table, or in the support arm  32 . In short, the pressure sensor  31 A may also be disposed in any position or mode as long as the contact pressure from the probe  24 A can be detected.  
         [0101]    In the embodiment, a contact pressure at a time when the probe  24 A contacts the table  33 ′ can be detected by the pressure sensor  31 A.  
         [0102]    Further another embodiment of the present invention will be described with reference to FIG. 11B. In FIG. 11B, a contact member  33 A′ capable of correctly transmitting the contact pressure at the time of the contact with the probe  24 A to the pressure sensor  31 A is disposed on the table  33 ′. As the contact member  33 A′, the polish plate  33 A, a contact plate  33 A′, or a dummy sheet  33 A″ may be used.  
         [0103]    The contact plate  33 A′ is, for example, a plate plated with gold, and is used for detecting electric conduction between the probe  24 A and the plate to detect a position (height) where the probe  24 A contacts the plate.  
         [0104]    The dummy sheet  33 A″ is a sheet for observing probe traces formed on the dummy sheet  33 A″, when the probe  24 A contacts the dummy sheet  33 A″. When the probe traces formed on the dummy sheet  33 A″ are observed, a contact state of the probe  24 A can be inspected.  
         [0105]    An operation of the embodiment using the auxiliary table  33 ′ shown in FIGS. 11A and 11B is similar to that of the embodiment shown in FIG. 6.  
         [0106]    As shown in FIG. 7, a controller  13  according to the present embodiment comprises first spring constant calculating means  133 B, second spring constant calculating means  133 C, and generated load calculating means  133 D. Based on the load measured by means of the pressure sensor  31 A, the first spring constant calculating means  133 B obtains a spring constant KP of the probe  24 A. Based on the relation between the load and distortion of the main chuck  17 , the second spring constant calculating means  133 C obtains a spring constant KC of the chuck  17 . Based on the relation between the spring constant KP of the probe  24 A, the spring constant KC of the main chuck  17 , and an overdrive OD of the chuck  17 , the generated load calculating means  133 D obtains a generated load GC in the position of contact between the probe  24 A and the chuck  17 . Based on the measured load from the pressure sensor  31 A and the load-distortion data of the polishing mechanism  33 , as mentioned before, the controller  13  can obtain a distortion of the main chuck  17  during inspection with high accuracy.  
         [0107]    More specifically, the polish plate  33 A is brought into contact with the probe  24 A when a given overdrive (X) is attained. The pressure sensor  31 A measures a load (G) at that time. An overdrive that then affects the probe  24 A is obtained as (B−X) from the relation between the aforesaid overdrive (X) and a distortion (B) for the load (G) of the load-distortion data of the polishing mechanism  33  loaded in the second storage means  132 . Further, the first spring constant calculating means  133 B obtains the spring constant KP of the probe  24 A according to Equation (1) as follows:  
           KP=G /( B−X )  (1)  
         [0108]    The second spring constant calculating means  133 C obtains the spring constant KC of the main chuck  17  from the relation between load-distortion data loaded in a main chuck information storage unit. The generated load calculating means  133 D obtains the overdrive OD of the main chuck  17  according to Equation (2), and the then generated load GC can be obtained according to Equation (3) as follows:  
           OD=ODP+ODC,   (2)  
           GC=KP*ODP=KC*ODC,   3)  
         [0109]    where ODP is an overdrive on the probe  24 A and ODC is an overdrive on the main chuck  17 .  
         [0110]    As seen from Equations (2) and (3), the overdrive OD and the generated load GC on the main chuck  17  have the relation given by Equation (4) as follows:  
           GC =[( KP*KC )/( KP+KC )]* OD,   (4)  
         [0111]    where the spring constants KP and KC are known amounts.  
         [0112]    Equation (4) is stored in a main chuck information storage unit  132 A of the controller  13 . During the inspection of the wafer W, as mentioned before, a CPU  133  can obtain the generated load GC on the main chuck  17  from the overdrive OD of the chuck  17 , and besides, the load GC generated according to the overdrive OD for each moment can be monitored in order. Steady inspection can be securely carried out by controlling the movement of the main chuck so that the overdrive is constant in accordance with the generated load GC.  
         [0113]    If a probe card  24  is deformed with time, according to the present embodiment, a load reflective of the deformation of the probe card  24  can be monitored even during the inspection of the wafer W, since the generated load GC that reflects the deformation is measured. Probe cards  24  of the same type are distorted somewhat differently and cannot be guaranteed exactly the same shape. Even in this case, the load GC from the probe  24 A that is applied to the polish plate  33 A in the polishing mechanism  33  is measured, so that the load on the main chuck  17  that is reflective of the shape of each probe card  24  can be monitored.  
         [0114]    If an unbalanced load is applied to the main chuck  17  during the inspection of the wafer W, according to the present embodiment, the load on the chuck  17  can be monitored in the aforesaid manner. Thus, the accuracy of three-dimensional correction of the probe  24 A can be improved, and the probe  24 A can be securely brought into contact with an electrode pad P. In consequence, functions and effects similar to those of the foregoing embodiment can be enjoyed.  
         [0115]    The present invention is not limited to the embodiments described above. According to the above description, the pressure sensor  31  is located between the main chuck  17  and the X-stage  18 , for example. However, the pressure sensor may be set in any place that allows the load on the chuck  17  to be measured. The same applies to the pressure sensor on the polishing mechanism. After all, the probing method and the probing apparatus of the present invention comprehend any of probing methods and probing apparatuses in which load (needle pressure) from a probe that is applied to a main chuck is monitored during the inspection of wafers, the overdrive of the main chuck is controlled in accordance with the monitored load, and the position of contact of the probe is corrected three-dimensionally.  
         [0116]    The present embodiment includes a mechanism for measuring the contact pressure applied from the probe  24 A using the polish plate  33 A of the polishing mechanism  33 , but any other mechanism may also be used, as long as the contact pressure from the probe  24 A can be transmitted to the pressure sensor. For example, the contact plate  33 A′ or dummy sheet  33 A″ disposed on the table may also be used in the mechanism. A mechanism which allows the probe  24 A to contact the surface of the table itself may also be used.  
         [0117]    According to the present invention, as described herein, the probe can be brought accurately into contact with the electrode pad of the object of inspection even if the probe card is deformed from various causes or expanded or contracted by any thermal effect. If the main chuck is tilted by an unbalanced load during overdrive operation, moreover, the probe can accurately touch the electrode pad of the object of inspection, so that high-accuracy inspection can be enjoyed.  
         [0118]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.