Abstract:
A probe, comprising: a shank region having a top surface integrally connected to a bottom surface of a conical region; a pyramidal tip region having a base surface integrally connected to a top surface of the conical region; and wherein the base surface of the pyramidal tip region is contained within a perimeter of the top surface of the conical region. Also a method of fabricating the probe and a method of probing devices under test.

Description:
TECHNICAL FIELD 
     The present invention relates to the field of electrical probing; more specifically, it relates to electrical probes and methods of reconstructing electrical probes. 
     BACKGROUND 
     Electrical probes are used to make temporary electrical connections to integrated pads on circuits. During use the probes may become deformed, contaminated and or oxidized resulting in poor contact between the probe and the pad causing noisy and inaccurate electrical measurement results. Accordingly, there exists a need in the art to eliminate the deficiencies and limitations described hereinabove. 
     BRIEF SUMMARY 
     A first aspect of the present invention is a probe, comprising: a shank region having a top surface integrally connected to a bottom surface of a conical region; a pyramidal tip region having a base surface integrally connected to a top surface of the conical region; and wherein the base surface of the pyramidal tip region is contained within a perimeter of the top surface of the conical region. 
     A second aspect of the present invention is a method, comprising: providing a probe comprising a shank region having a top surface integrally connected to a bottom surface of a conical region, the conical region tapering to a point; ion milling a pyramidal tip region having a base and an apex into an upper portion of the conical region, the ion milling removing surface portions of the upper portion of the conical region and removing the point, the apex becoming a new point; and after the ion milling, a lower portion of the conical region remaining. 
     A third aspect of the present invention is a method, comprising: using a probe having a tapered probe tip having a point to electrically test a device under test by physically and electrically contacting the device under test with the point; after the testing, ion milling a pyramidal tip having a new point into the tapered probe tip; and after the ion milling, electrically testing the device under test or another device under test by physically and electrically contacting the device under test or the new device under test with the new point. 
     These and other aspects of the invention are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention are set forth in the appended claims. The invention itself, however, will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is an exemplary application of electrical probing using a wire probe; 
         FIG. 2  is a side view of a wire probe as initially supplied by a vender; 
         FIG. 3  is a side view of a wire probe supplied by a vender after use; 
         FIG. 4A  is a side view and  FIG. 4B  is a top view of a wire probe after a first reconstruction step according to embodiments of the present invention; 
         FIG. 5A  is a side view and  FIG. 5B  is a top view of a wire probe after a second reconstruction step according to embodiments of the present invention; 
         FIG. 6A  is a side view and  FIG. 6B  is a top view of a wire probe after a third reconstruction step according to embodiments of the present invention; 
         FIG. 7A  is a side view and  FIG. 7B  is a top view of a wire probe after a fourth reconstruction step according to embodiments of the present invention; 
         FIG. 8A  is a side view and  FIG. 8B  is a top view of a wire probe after a fifth reconstruction step according to embodiments of the present invention; 
         FIG. 9  is a top view of a wire probe after reconstruction according to embodiments of the present invention; 
         FIG. 10  is a side view of a wire probe after reconstruction according to embodiments of the present invention; 
         FIG. 11  is a schematic diagram of an exemplary focused ion beam tool; 
         FIG. 12  is a side view illustrating milling a new face on a the tip of a wire probe according to embodiments of the present invention; and 
         FIG. 13  is a flowchart illustrating a method for probing substrates according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments of the present invention reconstruct probes by ion milling a solid probe using a focused ion beam (FIB) tool in order to form a new probe tip and probe point. A pyramidal tip is defined as a solid figure with a polygonal base and triangular faces that meet at a common point. 
       FIG. 1  is an exemplary application of electrical probing using a wire probe. In  FIG. 1 , a probe manipulator  100  includes respective X, Y and Z stages  101 ,  102  and  103  and respective X, Y and Z micrometers  104 ,  105  and  106  which move a flexible wire  109 . An electrically conductive solid probe  110  is connected to wire  109  by a collet  115  allowing probe  115  to be removed. Probe  110  is electrically connected through wire  109  to a coaxial fitting  120  that allows connection to an electrical test apparatus. In  FIG. 1 , probe  110  is physically and electrically contacting an electrically conductive pad  124  on a semiconductor substrate  125  that may include, for example, wires and transistors that pad  125  is electrically connected to. Thus individual wires and transistors may be probed. 
       FIG. 2  is a side view of a wire probe as initially supplied by a vender. In  FIG. 2 , probe  110  comprises a shank  130  and a conical tip  135  that tapers to a point  140 . Probe  110  may be formed, for example, from tungsten, tungsten-rhenium, beryllium-copper or palladium alloy. 
       FIG. 3  is a side view of a wire probe supplied by a vender after use. In  FIG. 3 , probe  110  is shown after several touch downs on a test piece to illustrate how the extreme end of tip  135  may become bent. Also point  140  may become contaminated or oxidized. 
       FIG. 4A  is a side view and  FIG. 4B  is a top view of a wire probe after a first reconstruction step according to embodiments of the present invention. In  FIGS. 4A and 4B  a flat  145  has been ion milled, using for example, a focused ion beam on the extreme end of conical tip  135  thereby removing the bent end of point  135  of  FIG. 3 . This step is optional. 
       FIG. 5A  is a side view and  FIG. 5B  is a top view of a wire probe after a second reconstruction step according to embodiments of the present invention. In  FIGS. 5A and 5B  a first flat surface  150 A has been ion milled into conical tip  135 , using for example, a focused ion beam on the extreme end of conical tip  135  thereby removing any contamination and/or oxidation and exposing a clean new surface. Milling first flat surface  150 A does not require removing probe  110  from the ion milling machine/focused ion beam after milling flat  145  (See  FIG. 4A ), but merely repositioning the probe relative to the beam axis. See  FIGS. 11 and 12 . 
       FIG. 6A  is a side view and  FIG. 6B  is a top view of a wire probe after a third reconstruction step according to embodiments of the present invention. In  FIGS. 6A and 6B  a second flat surface  150 B opposite first flat surface  150 A has been ion milled into conical tip  135 , again using for example, a focused ion beam on the extreme end of conical tip  135  thereby removing any contamination and/or oxidation and exposing a second clean new surface. Milling second flat surface  150 B does not require removing probe  110  from the ion milling machine/focused ion beam after milling surface  150 A, but merely rotating the probe 180° relative to the beam axis. See  FIGS. 11 and 12 . 
       FIG. 7A  is a side view and  FIG. 7B  is a top view of a wire probe after a fourth reconstruction step according to embodiments of the present invention. In  FIGS. 7A and 7B  a third flat surface  150 C between and perpendicular to first and second flat surfaces  150 A and  150 B has been ion milled into conical tip  135 , again using for example, a focused ion beam on the extreme end of conical tip  135  thereby removing any contamination and/or oxidation and exposing a second clean new surface. Milling third flat surface  150 C does not require removing probe  110  from the ion milling machine/focused ion beam after milling surface  150 B, but merely rotating the probe 90° relative to the beam axis. See  FIGS. 11 and 12 . 
       FIG. 8A  is a side view and  FIG. 8B  is a top view of a wire probe after a fifth reconstruction step according to embodiments of the present invention. In  FIGS. 8A and 8B  a fourth flat surface  150 D between and perpendicular to first and second flat surfaces  150 A and  150 B has been ion milled into conical tip  135 , again using for example, a focused ion beam on the extreme end of conical tip  135  thereby removing any contamination and/or oxidation and exposing a second clean new surface. Milling fourth flat surface  150 D does not require removing probe  110  from the ion milling machine/focused ion beam after milling surface  150 C, but merely rotating the probe 180° relative to the beam axis. See  FIGS. 11 and 12 . After the fifth milling step, reconstructed probe  110 A, having a new square pyramidal tip  155  having a new point  160  has been formed. Point  160  is the apex of the pyramidal tip  155 . Remnants of old conical tip  135  remain between shank  140  and tip  155 . Alternatively, all of old conical tip  135  may (and even portions of shank  140 ) may be milled away so no surfaces of conical tip  135  remain. 
     The process described included, after milling flat  145  (see  FIG. 4A ), milling surface  150 A, rotating probe  110  180°, milling surface  150 B, rotating probe  110  90°, milling surface  150 C, rotating probe  110  180° and milling surface  150 D. Alternatively, the process may include, after milling flat  145  (see  FIG. 4A ), milling surface  150 A, rotating probe  110  90°, milling surface  150 C, rotating probe  110  90°, milling surface  150 B, rotating probe  110  90° and milling surface  150 D. 
       FIG. 9  is a top view of a wire probe after reconstruction according to embodiments of the present invention. In  FIG. 9 , shank  140  has a diameter of D 1 , the base of square pyramidal tip  155  has four sides (surfaces  150 A,  150 B,  150 C and  150 D) of nominal base length W 1  and a point  160  having a diameter D 2 . Regions  161 ,  162 ,  163  and  164  of the top surface of conical tip  135  are exposed and not covered by pyramidal tip  155 . The vertexes of perimeter of the base of pyramidal tip  155  (there are four vertexes) touch the circular perimeter  166  of the top surface of conical tip  135 . In one example, D 1  is between about 10 microns and about 15 microns. In one example, W 1  is between about 6 microns and about 7 microns. Note, in one example, the lengths of the sides may independently vary by as much as plus or minus 0.5 microns from W 1 . In one example, D 2  is between about 0.15 microns and about 0.35 microns. 
       FIG. 10  is a side view of a wire probe after reconstruction according to embodiments of the present invention. In  FIG. 10 , length of pyramidal tip  155  is L 1  and the length of un-milled conical tip  135  (if any) plus the length of pyramidal tip  155  is L 2 , where L 1  is between about 15 microns and about 25 microns and L 2  is between about 35 microns and about 45 microns. The angle of the sidewall of conical section  135  relative to a plane containing a diameter of shank  140  is A 1  and angle of the sidewalls of pyramidal section  155  relative to a plane containing a diameter of shank  140  is A 2 . In one example, A 1  is between about 62° and about 82°. In one example A 2  is between about 69° and about 89°. In one example, A 1  is different from A 2 . In one example, A 1  is about equal to A 2 . In one example, A 1  is greater than A 2 . 
     Alternatively to square or four-sided pyramidal tips (as illustrated in  FIG. 9 ), the method of reconstructing probes can produce triangular or three-sided pyramidal tip or more generally N-sided pyramidal tips where N is an integer between 3 and 8. Referring back to  FIG. 9 , the base is illustrated as a square inscribed as inscribed in a circle. Alternatively the corners of the base of pyramidal tip  155  (or the corners of the base of an N-sided pyramidal tip) may be “moved in” away from the perimeter  166  so they do not touch the perimeter  166  in which case A 2  may be greater than A 1  if so desired. 
       FIG. 11  is a schematic diagram of an exemplary focused ion beam tool. In  FIG. 11  a focused ion beam tool  200  includes an extractor  205  which is a source of gallium ions, a beam aperture  210 , a first focusing lens  215 , a beam blanker  220 , a blanking aperture  225 , a multi-pole deflection aperture  230  and a second focusing lens  235  which cooperate to shape and direct a heavy metal ion beam  240  (in this example gallium) along a central axis  245  to a stage  250 . Beam  240  and stage  250  are contained within a vacuum. 
       FIG. 12  is a side view illustrating milling a new face on a tip of a wire probe according to embodiments of the present invention. In  FIG. 12 , probe  110  is placed on a stage at angle A 2  to a ion beam  240  (i.e. Ga) and either the stage moved relative to beam in a direction  255  so a surface  150  is milled that is perpendicular to the beam axis  245  (see  FIG. 11 ) and parallel to direction  255  or the beam scanned. After milling of surface  150 X, probe  260  is rotated 360/N degrees along the longitudinal axis  260  of probe  110  to mill the next surface, where N is the number of surfaces to be milled to produce an N sided pyramidal tip. 
       FIG. 13  is a flowchart illustrating a method for probing substrates according to embodiments of the present invention. In step  275 , a substrate or device under test (DUT) is probed using a wire probe. In step  280 , the probe tip is inspected for contamination, oxidation or physical deformation or other damage such a broken point. In step  280 , if the probe is not defective, the method loops to step  275  where additional probing of the same or another substrate or DUT occurs. If in step  280 , the probe is found to be defective (i.e., is contaminated, oxidized, deformed or broken) the method proceeds to step  290  where the probe is reconstructed using ion milling according to the embodiments of the present invention. The method then loops to step  275  where additional probing of the same or another substrate or DUT occurs. The probe may be reconstructed at least two times. 
     Thus the embodiments of the present invention provide a method of reconstructing electrical probes to provide new sharp and clean probe tips. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.