Abstract:
A probe formed on a base table is detached from the base table without giving damage on the probe. The present invention provides a probe manufacturing method comprising the steps of forming on a sacrificial layer on a base table a recess exposing the sacrificial layer with a resist, depositing a probe material in the recess to form a probe and then removing the resist, leaving part of the sacrificial layer and removing the rest by an etching process, and detaching from the base table the probe held on the base table by the remaining part of the sacrificial layer. In the recess of the resist are formed a main body part corresponding to a flat surface shape of the probe and an auxiliary part continuing into the main body part. The probe is formed by deposition of the material at the main body part, and a holding portion is formed by deposition of the material at the auxiliary part. The auxiliary part is formed in a flat surface shape sufficient for a sacrificial layer part under the holding portion to remain when a sacrificial layer part under the probe is removed by the etching process. The probe is separated from the holding portion after the sacrificial layer part under the probe is removed and while the sacrificial layer part under the holding portion remains.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method for manufacturing a probe used in an electrical test of a device under test such as a semiconductor integrated circuit (hereinafter referred to as IC). 
         [0002]    A plurality of ICs formed on a semiconductor wafer generally undergo an electrical test before being separated into respective chips to determine whether or not they are manufactured in accordance with the specification. The electrical test of this kind can be performed by using a probe assembly comprising a probe board and a plurality of probes attached to the probe board (e.g., refer to Patent Documents 1 and 2). 
         [0003]    The probe of such a probe assembly is formed by using a silicon wafer as a base table, taking the flat form of the probe with a photosensitive photoresist on the base table by making use of a photolithographic technique, sequentially depositing metal materials in the recess on the base table formed by the resist to form the probe, and thereafter detaching the probe from the base table, as described in Patent Document 1. 
         [0004]    To detach the probe from the silicon base table, an etching technique is utilized. For prevention of damage on the probe caused by the etching and easy detachment of the probe, a sacrificial layer made of a metal material such as copper different from the probe material is formed on the base table, and the probe material is deposited on the sacrificial layer. Thus, by removing the sacrificial layer by means of, for example, wet etching with etchant, the probe can be detached from the silicon base table. 
         [0005]    However, when a plurality of micro probes formed collectively on the base table are soaked in the etchant until the sacrificial layer is completely removed, the plurality of micro probes may float on the etchant by the etching, in which case it is difficult to handle them. 
         [0006]    Accordingly, it is preferable to finish the etching process in a state where the minimum and proper amount of sacrificial layer is left between the silicon base table and the probe required to achieve easy detachment of the probe and to hold the probe on the silicon base table. 
         [0007]    After the etching process in which the proper amount of sacrificial layer is left, the probe can be detached by an external force with use of a tool such as a cutter knife or a spatula. However, if a large amount of sacrificial layer remains due to insufficiency of the etching process time, detachment of the probe attached to the silicon base table by the remaining large amount of sacrificial layer requires a strong force, and thus such a process may deform the probe. 
         [0008]    For these reasons, it has been necessary to keep observing the etching process for detachment of the probe from the base table for a relatively long time so that the etching process may be performed appropriately, and the manufacturing process has been complicated in some cases. Thus, a novel manufacturing method that enables time reduction and simplification of the probe manufacturing process has been desired. 
         [0009]    Patent Document 1: Japanese Patent Appln. Public Disclosure No. 2000-162241. Patent Document 2: International Publication WO2004/102207 Pamphlet. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a probe manufacturing method enabling relatively easy detachment of a probe from a base table, after a material for the probe is deposited on the base table, without causing damage to the probe formed by the deposition. 
         [0011]    A probe manufacturing method according to the present invention comprises the steps of forming on a sacrificial layer on a base table a recess exposing the sacrificial layer with a resist, depositing a probe material in the recess to form a probe and then removing the resist, leaving part of the sacrificial layer and removing the rest by an etching process, and detaching from the base table the probe held on the base table by the remaining part of the sacrificial layer, wherein in the recess of the resist are formed a main body part corresponding to a flat surface shape of the probe and an auxiliary part continuing into the main body part and formed in a flat surface shape sufficient for a sacrificial layer part under a holding portion made of the probe material deposited at the auxiliary part to remain when a sacrificial layer part under the probe made of the probe material deposited at the main body part is removed by the etching process, and after the probe material is deposited in the recess including the auxiliary part, the probe is separated from the holding portion after removing the sacrificial layer part under the probe completely and before removing the sacrificial layer part under the holding portion completely by the etching process. 
         [0012]    In the probe manufacturing method according to the present invention, the holding portion is formed integrally with the probe to continue into it on the base table. When the sacrificial layer part under the probe is removed by the etching process, the sacrificial layer part under the holding portion is not removed at the same time. When the sacrificial layer part under the probe disappears, part of the sacrificial layer part under the holding portion remains. While the sacrificial layer part under the holding portion remains, the probe continuing into the holding portion is never disengaged from the base table. Thus, by separating the probe held to be distanced from the base table from the holding portion held on the base table during the period after the sacrificial layer part under the probe disappears by the etching process and until the sacrificial layer part under the holding portion disappears, the probe can be detached from the base table easily without giving the probe damage caused by excessive etching or an unnecessary detachment force. 
         [0013]    Also, by selecting the size or shape of the holding portion appropriately, an etching time period required for making the sacrificial layer part under the holding portion disappear after the sacrificial layer part under the probe disappears by the etching process can be sufficiently long. By doing so, since a relatively long allowable operation time period can be secured from the beginning to the end of the etching process for separation of the probe, strict management of the etching process time as in the conventional case is not needed. 
         [0014]    Prior to formation of the sacrificial layer on the base table, an adhesive layer for promotion of growth of the sacrificial layer may be formed on the base table. In the case where this adhesive layer is used, the holding portion is supported on the base table via the adhesive layer under the sacrificial layer exposed on the bottom of the recess. 
         [0015]    The resist may be formed by selective exposure and development of a resist layer made of a photosensitive photoresist material. 
         [0016]    As the base table, a silicon crystal substrate similar to a conventional one may be used. As the probe material, nickel or a nickel alloy may be used. Also, the sacrificial layer may be made of copper. In such a case, etchant consisting primarily of tetra amine copper chloride may be used as the etchant. Also, the adhesive layer may be made of nickel. 
         [0017]    With the aforementioned manufacturing method according to the present invention, an entirely plate-shaped probe comprising an attachment portion having an attachment end to a probe board, an arm portion extending in a lateral direction from the attachment portion, and a probe tip portion extending in a vertical direction from the arm portion and provided with a probe tip at its tip end may be formed. In such a case, the resist may have formed therein the recess so that the area of a flat surface shape of the auxiliary part is larger than the area of a flat surface shape of a part corresponding to the attachment portion in the recess. 
         [0018]    At the part corresponding to the attachment portion in the recess may be formed a hole forming portion to form an opening that promotes the etching process at the attachment portion. By the formation of the hole forming portion, removal of the sacrificial layer part under the attachment portion by the etching process is promoted. Thus, the sacrificial layer part under the probe can be removed reliably before the probe itself is substantially damaged by the etchant. 
         [0019]    In the recess may be provided a coupling part that is narrower than the auxiliary part and couples the auxiliary part with the main body part. In such a case, the auxiliary part continues into the main body part for the probe via the coupling part. 
         [0020]    The coupling part may be formed so as to continue into the part corresponding to the attachment portion in the recess at a portion except a part corresponding to the attachment end. 
         [0021]    It is preferable that the coupling part is formed so as to continue into the part corresponding to the attachment portion in the recess at its lateral side. 
         [0022]    Also, the coupling part may be formed so as to continue into a part corresponding to the probe tip portion in the recess at a portion except a part corresponding to the probe tip. 
         [0023]    It is preferable that the coupling part is formed so as to continue into the part corresponding to the probe tip portion in the recess at its lateral side. 
         [0024]    It is preferable that at the coupling part is formed a tapered portion to form a fragile portion at a coupling portion made of the probe material deposited at the coupling part. For separation of the probe from the holding portion, the coupling portion coupling them with each other can be broken off at its fragile portion. Thus, the separation can be done more easily. 
         [0025]    In the resist may be formed a plurality of the main body parts for probes so as to continue into one another via the shared auxiliary parts. 
         [0026]    According to the present invention, since the probe can be detached from the base table in a state where no sacrificial layer remains under the probe without the need for strict time management in the etching process of the sacrificial layer as in the conventional case as described above, the probe can be manufactured reliably and easily without causing damage to the probe itself as compared with the conventional case. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a bottom view showing a probe assembly according to the present invention. 
           [0028]      FIG. 2  is a front view showing the probe assembly shown in  FIG. 1 . 
           [0029]      FIG. 3  is a partially enlarged front view of a probe of the probe assembly shown in  FIG. 1 . 
           [0030]      FIG. 4  is a perspective view showing a detachment process of the probe according to the present invention. 
           [0031]      FIGS. 5  ( a ) to  5  ( f ) are flow charts showing a probe manufacturing procedure according to the present invention. 
           [0032]      FIG. 6  is a plan view showing a resist pattern for obtaining the probe shown in  FIG. 4 . 
           [0033]      FIGS. 7  ( a ) and  7  ( b ) show details of an etching process, of which  FIG. 7  ( a ) is a plan view of a probe, a coupling portion, and a holding portion, and  FIG. 7  ( b ) is a front view thereof. 
           [0034]      FIG. 8  is a partially enlarged perspective view showing an example of the coupling portion shown in  FIG. 7 . 
           [0035]      FIG. 9  is a view similar to  FIG. 8  showing another example of a coupling portion according to the present invention. 
           [0036]      FIGS. 10  ( a ) and  10  ( b ) show a still further example of the present invention, of which  FIG. 10  ( a ) is a plan view of a coupling part of a resist pattern, and  FIG. 10  ( b ) is a perspective view of a coupling portion of a probe obtained by the resist pattern. 
           [0037]      FIGS. 11  ( a ) and  11  ( b ) show a still further example of the present invention, of which  FIG. 11  ( a ) is a plan view of a coupling part of a resist pattern, and  FIG. 11  ( b ) is a perspective view of a coupling portion of a probe obtained by the resist pattern. 
           [0038]      FIG. 12  is a view similar to  FIG. 6  showing a still further example of the present invention. 
           [0039]      FIG. 13  is a view similar to  FIG. 6  showing a still further example of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0040]    A probe assembly  10  according to the present invention comprises a generally round wiring board  12 , a probe board  14  attached to the center portion of a lower surface  12   a  of the wiring board and formed in a rectangular flat shape, and a plurality of probes  16  attached to one surface  14   a  of the probe board, as shown in  FIGS. 1 and 2 . Each probe  16  is fixed to each connection portion  18   a  of a corresponding conductive path  18  formed on one surface  14   a  of the probe board  14 , as shown in  FIG. 3 . The probe board  14  is fixed to the wiring board in a state where the other surface opposite one surface  14   a  on which the probes  16  are provided faces the lower surface  12   a  of the wiring board  12 . 
         [0041]    The wiring board  12  is an electrically insulated board into which not shown conductive paths are incorporated, as is conventionally well known. As shown in  FIG. 1 , at the rim portion on the upper surface of the wiring board  12  are provided a plurality of tester lands  20  that are connection ends to a not shown tester main body. Each probe  16  of the probe board  14  attached to the wiring board  12  is electrically connected to each corresponding tester land  20  via the corresponding conductive path  18  of the probe board  14  and the aforementioned corresponding conductive path in the wiring board  12 , in a similar manner as in a conventional case. Accordingly, each probe  16  is electrically connected to the aforementioned tester main body via the corresponding tester land  20 . 
         [0042]      FIG. 3  shows one example of the probe  16  according to the present invention. The probe  16  according to the present invention is formed in an entirely flat-plate shape. The probe  16  comprises an attachment portion  22  having an attachment end  22   a  to the connection portion  18   a  provided on the probe board  14 , an arm portion  24  extending in a lateral direction from the lower end of the attachment portion, and a probe tip portion  26  extending in a lateral direction or downward from the tip end of the arm portion, and a probe tip  26   a  is formed at the tip end of the probe tip portion. The attachment portion  22  is formed in an entirely rectangular flat surface shape having a height h and a width w. At the attachment portion  22 , a separation trace  22   b  from a coupling portion described later remains. 
         [0043]    In the example shown in the figure, at the arm portion  24 , a space  28  penetrating in a plate thickness direction of the probe  16  and extending in a longitudinal direction of the arm portion  24  is formed between the attachment portion  22  and the probe tip portion  26 . By this space  28 , the arm portion  24  is separated into a pair of arm portions  24   a ,  24   a  spaced from each other and arranged in parallel. In the example shown in the figure, one end of the space  28  reaches the attachment portion  22 . Also, at the attachment portion  22 , an opening  30  penetrating in the plate thickness direction of the probe  16  is formed. 
         [0044]    Although the space  28  may be eliminated, it is preferable to form the space  28  as shown in the figure and constitute the arm portion  24  by the arm portions  24   a ,  24   a  separated by the space for the purpose of applying appropriate elasticity to the arm portion  24  when the probe  16  is thrust to a device under test. 
         [0045]    Also, the opening  30  at the attachment portion  22  may be eliminated. However, it is preferable to appropriately form the opening  30  at the attachment portion  22  for the purpose of promoting removal of a sacrificial layer by an etching process in steps for manufacturing the probe  16  described later. 
         [0046]    The probe tip  26   a  of the probe  16  according to the present invention is thrust to an electrode of a device under test for an electrical test of the device under test such as an IC circuit using the aforementioned tester. At this moment, the probe tip  26   a  of the probe  16  is reliably connected to the aforementioned electrode with appropriate elasticity due to flexible deformation of both the arm portions  24   a ,  24   a.    
         [0047]    The probe  16  according to the present invention is formed integrally with a holding portion  36  coupled with the probe  16  via a coupling portion  34  on a base table such as a silicon crystal substrate  32  as shown in  FIG. 4 . In the example shown in  FIG. 4 , a plurality of probes  16  are formed on a single base table  32  in a state where each of them is integral with the coupling portion  34  and the holding portion  36 . As these plural probes  16  formed on the base table  32  are respectively detached from the base table  32  and are separated from the coupling portions  34 , the plurality of probes  16  are formed at a time. 
         [0048]    In the example shown in the figure, the holding portion  36  is formed in a rectangular flat surface shape having a height dimension h and a width dimension w approximately equivalent to the height dimension and the width dimension of the attachment portion  22 , respectively. The holding portion  36  is coupled with the probe  16  via the coupling portion  34  at the lateral side of the attachment portion  22  on the opposite side of a side where the arm portion  24  is provided. 
         [0049]    A preferred method for manufacturing these plural probes  16  at a time is described with reference to  FIG. 5 . For simplification of the explanation and drawings,  FIG. 5  shows a manufacturing process for a single probe  16  with which the coupling portion  34  and the holding portion  36  are formed integrally for descriptive purposes. 
         [0050]    In the manufacturing method according to the present invention, the silicon crystal substrate  32  whose surface has been mirror-finished by etching is prepared as a base table as shown in  FIG. 5  ( a ). 
         [0051]    Prior to growth of, e.g., a copper sacrificial layer on the silicon crystal substrate  32 , an adhesive layer  40  such as nickel is formed uniformly on the silicon crystal substrate or the base table  32  by, e.g., a sputtering technique to promote growth of the copper. On this adhesive layer  40  is suitably deposited the copper by, e.g., a sputtering technique. By the deposition of the copper, a sacrificial layer  42  is formed so as to have uniform quality and thickness dimension ( FIG. 5  ( b )). 
         [0052]    A photoresist material, which is a photosensitive material, is coated on the sacrificial layer  42  by, for example, a spin coat technique so as to have uniform thickness, and thus a photosensitive resist layer  44  is formed. This resist layer  44  is selectively exposed with use of a mask (not shown) and is thereafter developed ( FIG. 5  ( c )). This mask has a pattern corresponding to an entire flat surface shape containing the probe  16 , the coupling portion  34 , and the holding portion  36 . By transferring the pattern to the resist layer  44 , a resist  46  having a recess  46   a  formed in a flat surface shape corresponding to the generally flat surface shape of the probe  16  including the coupling portion  34  and the holding portion  36  is formed on the base table  32 . This resist or resist pattern  46  exposes the sacrificial layer  42  on the bottom surface of its recess  46   a.    
         [0053]    The flat surface shape of the resist  46  is shown in  FIG. 6 . As apparent from comparison with  FIG. 4 , the recess  46   a  of the resist  46  has a main body part  116  for the probe  16  consisting of respective parts  122 ,  124   a ,  126  corresponding to the attachment portion  22 , the arm portion  24  (a pair of arm portions  24   a ), and the probe tip portion  26  of the probe  16  and a coupling part  134  and an auxiliary part  136  respectively corresponding to the coupling portion  34  and the holding portion  36 . Also, at the main body part  116  are formed respective hole forming portions  128  and  130  for the space  28  and the opening  30 . 
         [0054]    In the example shown in  FIG. 6 , the coupling part  134  coupling the main body part  116  with the auxiliary part  136  in the recess  46   a  is in a narrow flat surface shape having a much shorter width dimension w 2  than the height dimensions (h) of the main body part  116  and the auxiliary part  136 . Also, the coupling part  134  is in a tapered shape whose width dimension w 2  gradually decreases from the auxiliary part  136  toward the attachment part  122  of the main body part  116  corresponding to the attachment portion  22 . 
         [0055]    In the recess  46   a  of the resist  46  is deposited a conventionally well-known probe metal material  48  such as nickel, a nickel-phosphor alloy, rhodium, or tungsten by, e.g., electroforming (electroplating). By the deposition of the probe metal material  48  in the recess  46   a , the probe  16  shown in  FIG. 4  is formed on the sacrificial layer  42  of the base table  32  to be fixed to the sacrificial layer  42  together with the coupling portion  34  and the holding portion  36 . 
         [0056]    After deposition of the probe metal material  48  for the probe  16 , the coupling portion  34 , and the holding portion  36  on the sacrificial layer  42  for integral formation, the resist  46  is removed ( FIG. 5  ( d )). After removal of the resist  46 , in order to detach the probe  16  from the base table  32 , a wet etching process using etchant is performed for the purpose of removing a portion of the sacrificial layer  42  located under the probe  16 . By this wet etching process, a portion of the sacrificial layer  42  exposed from the probe  16 , the coupling portion  34 , and the holding portion  36  is firstly etched from its edges as shown in  FIG. 5  ( e ). 
         [0057]    By the ongoing etching process, the sacrificial layer  42  is etched as shown in  FIG. 5  ( f ). 
         [0058]    This etching process is explained in details with reference to  FIGS. 7  ( a ) and  7  ( b ). The aforementioned etching of the sacrificial layer  42  by etchant proceeds from the respective edges of the probe  16 , the coupling portion  34 , and the holding portion  36  toward the respective center portions. In the probe  16  formed on the sacrificial layer  42 , the shortest distance from the center to the edge of the attachment portion  22  is longer than those of the arm portion  24  and the probe tip portion  26 . Also, the holding portion  36  formed on the sacrificial layer  42  has a larger flat surface shape than that of the coupling portion  34  and is formed in approximately the same outer shape as that of the attachment portion  22 . However, at the attachment portion  22 , the opening  30  is formed, and the space  28  is extending. Thus, while the sacrificial layer  42  under the holding portion  36  is etched only from the outer edge toward the center of the holding portion, the sacrificial layer  42  under the attachment portion  22  is etched not only from the outer edge toward the center but also from the edges of the opening  28  and the space  28 . 
         [0059]    As a result, although the sacrificial layer  42  is removed at portions under the probe  16  and the coupling portion  34 , a sacrificial layer part  42   a  under the center of the holding portion  36  remains, as shown in  FIG. 7  ( b ). In this state, the probe  16  that needs to be separated from the base table  32  stays above the base table  32  as well as the coupling portion  34 , and the holding portion  36  coupled with the coupling portion  34  is fixed to the base table  32  via the remaining sacrificial layer part  42   a . Thus, since the probe  16  is held on the base table  32  via the holding portion  36 , the probe  16  is never disengaged from the base table  32 . 
         [0060]    Accordingly, as the etching process is finished in a state where this sacrificial layer part  42   a  remains, and the probe  16  is separated from the coupling portion  34 , the probe  16  can be detached from the base table  32  without a strong detachment force acting on the probe  16  as in a conventional case. To separate the probe  16  from the coupling portion  34 , by holding the probe  16  at its bottom with a tool such as tweezers, a spatula, or a knife, and holding this up entirely, one can break off the probe  16  at the narrowest part of the coupling portion  34 , that is, a fragile portion  34   a  formed at its end portion on the probe  16  side as shown in  FIG. 8 . Also, in a case where the probe metal material  48  is a magnetic material, a magnet can be used to handle the probe  16 . 
         [0061]    While the sacrificial layer part  42   a  remains after the sacrificial layer  42  is removed under the probe  16  and the coupling portion  34 , the probe  16  can be detached from the base table  32  relatively easily without being disengaged. However, in order to keep etching of the probe  16  itself by etchant to a minimum, it is preferable that, after the sacrificial layer  42  under the probe  16  and the coupling portion  34  disappears, the probe  16  is broken off at the fragile portion  34   a  to separate it from the holding portion  36  promptly, and that the probe  16  is detached from the base table  32 . 
         [0062]    As for the aforementioned fragile portion  34   a  of the coupling portion  34 , the width dimension of the coupling portion  34  may be gradually decreased from one end on the holding portion  36  side to the other end on the attachment portion  22  side, and its thickness dimension may be gradually decreased, as shown in  FIG. 9 . This enables the break-off operation at the fragile portion  34   a  to be performed more easily. 
         [0063]    Also, a narrow neck portion  134   aa  may be formed at the coupling part  134  having a uniform width dimension as shown in  FIG. 10  ( a ), and a cross groove or step  50  intended for decrease of the thickness dimension may be formed at the coupling portion  34  as shown in  FIG. 10  ( b ). 
         [0064]    Further, only either sidewall  134   bb  of a pair of sidewalls of the coupling part  134  of the resist  46  may be tilted as seen on the plane so that the coupling part  134  is tapered as shown in  FIG. 11  ( a ), and the dimension of the coupling portion  34  may be gradually decreased in the plate thickness direction as shown in  FIG. 11  ( b ). 
         [0065]    In the foregoing description, the manufacturing method according to the present invention has been explained in the example in which a single auxiliary part  136  is formed per main body part  116  of the recess  46   a . Instead of this example, first and second auxiliary parts  136   a ,  136   b  may be formed per main body part  116  as shown in  FIG. 12 . 
         [0066]    The first auxiliary part  136   a  continues into the attachment part  122  of the recess  46   a  corresponding to the attachment portion  22  of the probe  16  via a coupling part  134   a  in a similar manner to that described above. Also, the second auxiliary part  136   b  continues into the part  126  corresponding to the probe tip portion  26  via a coupling part  134   b.    
         [0067]    By providing the first and second auxiliary parts  136   a  and  136   b , two holding portions formed at the auxiliary parts can hold the probe  16  on the base table  32  at the two points distanced from each other on the probe tip portion  26  side and on the attachment portion  22  side. 
         [0068]    In this holding state, the probe  16  can undergo heat treatment, and thus the strength of the probe  16  can be enhanced. In addition, a retroflexion force is introduced into the probe  16  by heating. However, since the probe  16  is supported on the base table  32  at the two points distanced from each other as described above, the probe  16  is prevented from being deformed. After this heat treatment, the probe  16  is separated form the first and second holding portions. 
         [0069]    As described above, in the example shown in  FIG. 12 , the probe  16  can be supported at the two points, and this two-point support restricts deformation of the probe  16  caused by the retroflexion. Thus, the example shown in  FIG. 12  is suitable in the case where the probe  16  undergoes heat treatment. 
         [0070]    Also, as shown in  FIG. 13 , each auxiliary part  136  may be shared by the adjacent main body parts  116  for the probes  16 . Each auxiliary part  136  continues into the part  122  of one main body part  116  via one coupling part  134   a  and continues into the part  126  of the other main body part  116  via the other coupling part  134   b.    
         [0071]    The aforementioned auxiliary part  136  of the recess  46   a  formed in the resist  46  does not need to be formed in the same flat surface shape as that of the part  122  of the main body part  116 . The shape and dimension of the auxiliary part  136  may be arbitrarily selected so as to form the holding portion  36  so that the sacrificial layer  42  remains under the holding portion  36  when the sacrificial layer  42  has been removed under the probe  16  with no residue by the etching process. 
         [0072]    Also, in the aforementioned examples, the probe tip is formed integrally with the probe tip portion  26 . However, the probe tip made of a hard metal material may be buried in the probe tip portion  26 . 
         [0073]    The present invention is not limited to the above embodiments but may be altered in various ways without departing from the spirit and scope of the present invention.