Abstract:
A wafer probe station is equipped with an integrated environment control enclosure substantially surrounding a supporting surface for holding a test device, such enclosure limiting fluid communication between the interior and exterior of the enclosure and preferably also providing EMI shielding and a dark environment. The limited communication between the interior and exterior of the enclosure is kept substantially constant despite positioning movement of either the supporting surface or probes. The positioning mechanisms for the supporting surface and probes each are located at least partially outside of the enclosure.

Description:
This application is a continuation of U.S. patent application Ser. No. 10/068,728, filed Feb. 6, 2002, now U.S. Pat. No. 6,486,687, which is a continuation of U.S. patent application Ser. No. 09/886,353, filed Jun. 20, 2001, now U.S. Pat. No. 6,380,751, which is a continuation of U.S. patent application Ser. No. 08/790,969, filed Jan. 29, 1997, now U.S. Pat. No. 6,313,649, which is a continuation of U.S. patent application Ser. No. 08/641,029, filed Apr. 29, 1996, now U.S. Pat. No. 5,604,444, which is a continuation of U.S. patent application Ser. No. 08/417,982, filed Apr. 6, 1995, now U.S. Pat. No. 5,532,609, which is a division of U.S. patent application Ser. No. 08/245,581, filed May 18, 1994, now U.S. Pat. No. 5,434,512, which is a division of U.S. patent application Ser. No. 07/896,853 filed Jun. 11, 1992, now U.S. Pat. No. 5,345,170. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is directed to probe stations for making highly accurate measurements of high-speed, large scale integrated circuits at the wafer level, and of other electronic devices. More particularly, the invention relates to such a probe station having an environment control enclosure for limiting the communication of the wafer-supporting chuck and probes with outside influences such as electromagnetic interference (EMI), air, and/or light. 
     SUMMARY OF THE INVENTION 
     The probe station is equipped with an integrated environment control enclosure substantially surrounding a supporting surface for holding a test device, such enclosure limiting fluid communication between the interior and exterior of the enclosure and preferably also providing EMI shielding and a dark environment. The limited communication between the interior and exterior of the enclosure is kept substantially constant despite positioning movement of either the supporting surface or probes. The positioning mechanisms for the supporting surface and probes are each located at least partially outside of the enclosure so that mechanical movement of each of the positioning mechanisms outside of the enclosure causes proportional mechanical movement of the surface or probe. 
     According to another aspect of the invention, the environment control enclosure has an upper portion extending above the supporting surface and a side portion substantially surrounding the supporting surface, the supporting surface being movable laterally with respect to the top of the side portion. 
     According to another aspect of the invention, the environment control enclosure has an opening with a closable door for substituting different test devices on the supporting surface in a manner compatible with the positioning and environment control functions. 
     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a partial front view of an exemplary embodiment of a wafer probe station constructed in accordance with the present invention. 
     FIG. 2 is a top view of the wafer probe station of FIG.  1 . 
     FIG. 2A is a partial top view of the wafer probe station of FIG. 1 with the enclosure door shown partially open. 
     FIG. 3 is a partially sectional and partially schematic front view of the probe station of FIG.  1 . 
     FIG. 3A is an enlarged sectional view taken along line  3 A— 3 A of FIG.  3 . 
     FIG. 4 is a top view of the sealing assembly where the motorized positioning mechanism extends through the bottom of the enclosure. 
     FIG. 5A is an enlarged top detail view taken along line  5 A— 5 A of FIG.  1 . 
     FIG. 5B is an enlarged top sectional view taken along line  5 B— 5 B of FIG.  1 . 
     FIG. 6 is a partially schematic top detail view of the chuck assembly, taken along line  6 — 6  of FIG.  3 . 
     FIG. 7 is a partially sectional front view of the chuck assembly of FIG.  6 . 
     FIG. 8 is a partially sectional side view of a probe holder and probe. 
     FIG. 9 is a partially sectional bottom view taken along line  9 — 9  of FIG.  8 . 
    
    
     DESCRIPTION OF THE INVENTION 
     General Arrangement of Probe Station 
     With reference to FIGS. 1,  2  and  3 , an exemplary embodiment of the probe station of the present invention comprises a base  10  (shown partially) which supports a platen  12  through a number of jacks  14   a ,  14   b ,  14   c ,  14   d  which selectively raise and lower the platen vertically relative to the base by a small increment (approximately one-tenth of an inch) for purposes to be described hereafter. Also supported by the base  10  of the probe station is a motorized positioner  16  having a rectangular plunger  18  which supports a movable chuck assembly  20  for supporting a wafer or other test device. The chuck assembly  20  passes freely through a large aperture  22  in the platen  12  which permits the chuck assembly to be moved independently of the platen by the positioner  16  along X, Y and Z axes, i.e. horizontally along two mutually-perpendicular axes X and Y, and vertically along the Z axis. Likewise, the platen  12 , when moved vertically by the jacks  14 , moves independently of the chuck assembly  20  and the positioner  16 . 
     Mounted atop the platen  12  are multiple individual probe positioners such as  24  (only one of which is shown), each having an extending member  26  to which is mounted a probe holder  28  which in turn supports a respective probe  30  for contacting wafers and other test devices mounted atop the chuck assembly  20 . The probe positioner  24  has micrometer adjustments  34 ,  36  and  38  for adjusting the position of the probe holder  28 , and thus the probe  30 , along the X, Y and Z axes respectively, relative to the chuck assembly  20 . The Z axis is exemplary of what is referred to herein loosely as the “axis of approach” between the probe holder  28  and the chuck assembly  20 , although directions of approach which are neither vertical nor linear, along which the probe tip and wafer or other test device are brought into contact with each other, are also intended to be included within the meaning of the term “axis of approach.” A further micrometer adjustment  40  adjustably tilts the probe holder  28  to adjust planarity of the probe with respect to the wafer or other test device supported by the chuck assembly  20 . As many as twelve individual probe positioners  24 , each supporting a respective probe, may be arranged on the platen  12  around the chuck assembly  20  so as to converge radially toward the chuck assembly similarly to the spokes of a wheel. With such an arrangement, each individual positioner  24  can independently adjust its respective probe in the X, Y and Z directions, while the jacks  14  can be actuated to raise or lower the platen  12  and thus all of the positioners  24  and their respective probes in unison. 
     An environment control enclosure is composed of an upper box portion  42  rigidly attached to the platen  12 , and a lower box portion  44  rigidly attached to the base  10 . Both portions are made of steel or other suitable electrically conductive material to provide EMI shielding. To accommodate the small vertical movement between the two box portions  42  and  44  when the jacks  14  are actuated to raise or lower the platen  12 , an electrically conductive resilient foam gasket  46 , preferably composed of silver or carbon-impregnated silicone, is interposed peripherally at their mating juncture at the front of the enclosure and between the lower portion  44  and the platen  12  so that an EMI, substantially hermetic, and light seal are all maintained despite relative vertical movement between the two box portions  42  and  44 . Even though the upper box portion  42  is rigidly attached to the platen  12 , a similar gasket  47  is preferably interposed between the portion  42  and the top of the platen to maximize sealing. 
     With reference to FIGS. 5A and 5B, the top of the upper box portion  42  comprises an octagonal steel box  48  having eight side panels such as  49   a  and  49   b  through which the extending members  26  of the respective probe positioners  24  can penetrate movably. Each panel comprises a hollow housing in which a respective sheet  50  of resilient foam, which may be similar to the above-identified gasket material, is placed. Slits such as  52  are partially cut vertically in the foam in alignment with slots  54  formed in the inner and outer surfaces of each panel housing, through which a respective extending member  26  of a respective probe positioner  24  can pass movably. The slitted foam permits X, Y and Z movement of the extending members  26  of each probe positioner, while maintaining the EMI, substantially hermetic, and light seal provided by the enclosure. In four of the panels, to enable a greater range of X and Y movement, the foam sheet  50  is sandwiched between a pair of steel plates  55  having slots  54  therein, such plates being slidable transversely within the panel housing through a range of movement encompassed by larger slots  56  in the inner and outer surfaces of the panel housing. 
     Atop the octagonal box  48 , a circular viewing aperture  58  is provided, having a recessed circular transparent sealing window  60  therein. A bracket  62  holds an apertured sliding shutter  64  to selectively permit or prevent the passage of light through the window. A stereoscope (not shown) connected to a CRT monitor can be placed above the window to provide a magnified display of the wafer or other test device and the probe tip for proper probe placement during set-up or operation. Alternatively, the window  60  can be removed and a microscope lens (not shown) surrounded by a foam gasket can be inserted through the viewing aperture  58  with the foam providing EMI, hermetic and light sealing. 
     The upper box portion  42  of the environment control enclosure also includes a hinged steel door  68  which pivots outwardly about the pivot axis of a hinge  70  as shown in FIG.  2 A. The hinge biases the door downwardly toward the top of the upper box portion  42  so that it forms a tight, overlapping, sliding peripheral seal  68   a  with the top of the upper box portion. When the door is open, and the chuck assembly  20  is moved by the positioner  16  beneath the door opening as shown in FIG. 2A, the chuck assembly is accessible for loading and unloading. 
     With reference to FIGS. 3 and 4, the sealing integrity of the enclosure is likewise maintained throughout positioning movements by the motorized positioner  16  due to the provision of a series of four sealing plates  72 ,  74 ,  76  and  78  stacked slidably atop one another. The sizes of the plates progress increasingly from the top to the bottom one, as do the respective sizes of the central apertures  72   a ,  74   a ,  76   a  and  78   a  formed in the respective plates  72 ,  74 ,  76  and  78 , and the aperture  79   a  formed in the bottom  44   a  of the lower box portion  44 . The central aperture  72   a  in the top plate  72  mates closely around the bearing housing  18   a  of the vertically-movable plunger  18 . The next plate in the downward progression, plate  74 , has an upwardly-projecting peripheral margin  74   b  which limits the extent to which the plate  72  can slide across the top of the plate  74 . The central aperture  74   a  in the plate  74  is of a size to permit the positioner  16  to move the plunger  18  and its bearing housing  18   a  transversely along the X and Y axes until the edge of the top plate  72  abuts against the margin  74   b  of the plate  74 . The size of the aperture  74   a  is, however, too small to be uncovered by the top plate  72  when such abutment occurs, and therefore a seal is maintained between the plates  72  and  74  regardless of the movement of the plunger  18  and its bearing housing along the X and Y axes. Further movement of the plunger  18  and bearing housing in the direction of abutment of the plate  72  with the margin  74   b  results in the sliding of the plate  74  toward the peripheral margin  76   b  of the next underlying plate  76 . Again, the central aperture  76   a  in the plate  76  is large enough to permit abutment of the plate  74  with the margin  76   b , but small enough to prevent the plate  74  from uncovering the aperture  76   a , thereby likewise maintaining the seal between the plates  74  and  76 . Still further movement of the plunger  18  and bearing housing in the same direction causes similar sliding of the plates  76  and  78  relative to their underlying plates into abutment with the margin  78   b  and the side of the box portion  44 , respectively, without the apertures  78   a  and  79   a  becoming uncovered. This combination of sliding plates and central apertures of progressively increasing size permits a full range of movement of the plunger  18  along the X and Y axes by the positioner  16 , while maintaining the enclosure in a sealed condition despite such positioning movement. The EMI sealing provided by this structure is effective even with respect to the electric motors of the positioner  16 , since they are located below the sliding plates. 
     Chuck Assembly 
     With particular reference to FIGS. 3,  6  and  7 , the chuck assembly  20  is of a unique modular construction usable either with or without an environment control enclosure. The plunger  18  supports an adjustment plate  79  which in turn supports first, second and third chuck assembly elements  80 ,  81  and  83 , respectively, positioned at progressively greater distances from the probe(s) along the axis of approach. Element  83  is a conductive rectangular stage or shield  83  which detachably mounts conductive elements  80  and  81  of circular shape. The element  80  has a planar upwardly-facing wafer-supporting surface  82  having an array of vertical apertures  84  therein. These apertures communicate with respective chambers separated by O-rings  88 , the chambers in turn being connected separately to different vacuum lines  90   a ,  90   b ,  90   c  (FIG. 6) communicating through separately-controlled vacuum valves (not shown) with a source of vacuum. The respective vacuum lines selectively connect the respective chambers and their apertures to the source of vacuum to hold the wafer, or alternatively isolate the apertures from the source of vacuum to release the wafer, in a conventional manner. The separate operability of the respective chambers and their corresponding apertures enables the chuck to hold wafers of different diameters. 
     In addition to the circular elements  80  and  81 , auxiliary chucks such as  92  and  94  are detachably mounted on the corners of the element  83  by screws (not shown) independently of the elements  80  and  81  for the purpose of supporting contact substrates and calibration substrates while a wafer or other test device is simultaneously supported by the element  80 . Each auxiliary chuck  92 ,  94  has its own separate upwardly-facing planar surface  100 ,  102  respectively, in parallel relationship to the surface  82  of the element  80 . Vacuum apertures  104  protrude through the surfaces  100  and  102  from communication with respective chambers within the body of each auxiliary chuck. Each of these chambers in turn communicates through a separate vacuum line and a separate independently-actuated vacuum valve (not shown) with a source of vacuum, each such valve selectively connecting or isolating the respective sets of apertures  104  with respect to the source of vacuum independently of the operation of the apertures  84  of the element  80 , so as to selectively hold or release a contact substrate or calibration substrate located on the respective surfaces  100  and  102  independently of the wafer or other test device. An optional metal shield  106  may protrude upwardly from the edges of the element  83  to surround the other elements  80 ,  81  and the auxiliary chucks  92 ,  94 . 
     All of the chuck assembly elements  80 ,  81  and  83 , as well as the additional chuck assembly element  79 , are electrically insulated from one another even though they are constructed of electrically conductive metal and interconnected detachably by metallic screws such as  96 . With reference to FIGS. 3 and 3A, the electrical insulation results from the fact that, in addition to the resilient dielectric O-rings  88 , dielectric spacers  85  and dielectric washers  86  are provided. These, coupled with the fact that the screws  96  pass through oversized apertures in the lower one of the two elements which each screw joins together thereby preventing electrical contact between the shank of the screw and the lower element, provide the desired insulation. As is apparent in FIG. 3, the dielectric spacers  85  extend over only minor portions of the opposing surface areas of the interconnected chuck assembly elements, thereby leaving air gaps between the opposing surfaces over major portions of their respective areas. Such air gaps minimize the dielectric constant in the spaces between the respective chuck assembly elements, thereby correspondingly minimizing the capacitance between them and the ability for electrical current to leak from one element to another. Preferably, the spacers and washers  85  and  86 , respectively, are constructed of a material having the lowest possible dielectric constant consistent with high dimensional stability and high volume resistivity. A suitable material for the spacers and washers is glass epoxy, or acetal homopolymer marketed under the trademark Delrin by E.I. DuPont. 
     With reference to FIGS. 6 and 7, the chuck assembly  20  also includes a pair of detachable electrical connector assemblies designated generally as  108  and  110 , each having at least two conductive connector elements  108   a ,  108   b  and  11   a ,  110   b , respectively, electrically insulated from each other, with the connector elements  108   b  and  110   b  preferably coaxially surrounding the connector elements  108   a  and  110   a  as guards therefor. If desired, the connector assemblies  108  and  110  can be triaxial in configuration so as to include respective outer shields  108   c ,  110   c  surrounding the respective connector elements  108   b  and  110   b , as shown in FIG.  7 . The outer shields  108   c  and  110   c  may, if desired, be connected electrically through a shielding box  112  and a connector supporting bracket  113  to the chuck assembly element  83 , although such electrical connection is optional particularly in view of the surrounding EMI shielding enclosure  42 ,  44 . In any case, the respective connector elements  108   a  and  110   a  are electrically connected in parallel to a connector plate  114  matingly and detachably connected along a curved contact surface  114   a  by screws  114   b  and  114   c  to the curved edge of the chuck assembly element  80 . Conversely, the connector elements  108   b  and  110   b  are connected in parallel to a connector plate  116  similarly matingly connected detachably to element  81 . The connector elements pass freely through a rectangular opening  112   a  in the box  112 , being electrically insulated from the box  112  and therefore from the element  83 , as well as being electrically insulated from each other. Set screws such as  118  detachably fasten the connector elements to the respective connector plates  114  and  116 . 
     Either coaxial or, as shown, triaxial cables  118  and  120  form portions of the respective detachable electrical connector assemblies  108  and  110 , as do their respective triaxial detachable connectors  122  and  124  which penetrate a wall of the lower portion  44  of the environment control enclosure so that the outer shields of the triaxial connectors  122 ,  124  are electrically connected to the enclosure. Further triaxial cables  122   a ,  124   a  are detachably connectable to the connectors  122  and  124  from suitable test equipment such as a Hewlett-Packard 4142B modular DC source/monitor or a Hewlett-Packard 4284A precision LCR meter, depending upon the test application. If the cables  118  and  120  are merely coaxial cables or other types of cables having only two conductors, one conductor interconnects the inner (signal) connector element of a respective connector  122  or  124  with a respective connector element  108   a  or  110   a , while the other conductor connects the intermediate (guard) connector element of a respective connector  122  or  124  with a respective connector element  108   b ,  110   b.    
     In any case, the detachable connector assemblies  108 ,  110 , due to their interconnections with the two connector plates  114 ,  116 , provide immediately ready-to-use signal and guard connections to the chuck assembly elements  80  and  81 , respectively, as well as ready-to-use guarded Kelvin connections thereto. For applications requiring only guarding of the chuck assembly, as for example the measurement of low-current leakage from a test device through the element  80 , it is necessary only that the operator connect a single guarded cable  122   a  from a test instrument such as a Hewlett-Packard 4142B modular DC source/monitor to the detachable connector  122  so that a signal line is provided to the chuck assembly element  80  through the connector element  108   a  and connector plate  114 , and a guard line is provided to the element  81  through the connector element  108   b  and connector plate  116 . Alternatively, if a Kelvin connection to the chuck assembly is desired for low-voltage measurements, such as those needed for measurements of low capacitance, the operator need merely attach a pair of cables  122   a  and  124   a  to the respective connectors  122 ,  124  from a suitable test instrument such as a Hewlett-Packard 4284A precision LCR meter, thereby providing both source and measurement lines to the element  80  through the connector elements  108   a  and  110   a  and connector plate  114 , and guarding lines to the element  81  through the connector elements  108   b  and  110   b  and connector plate  116 . 
     Probe Assembly 
     With reference to FIGS. 5B,  8  and  9 , respective individually movable probes  30  comprising pairs of probe elements  30   a  are supported by respective probe holders  28  which in turn are supported by respective extending portions  26  of different probe positioners such as  24 . Atop each probe positioner  24  is a shield box  126  having a pair of triaxial connectors  128 ,  130  mounted thereon with respective triaxial cables  132  entering each triaxial connector from a suitable test instrument as mentioned previously. Each triaxial connector includes a respective inner connector element  128   a ,  130   a , an intermediate connector element  128   b ,  130   b , and an outer connector element  128   c ,  130   c  in concentric arrangement. Each outer connector element  128   c ,  130   c  terminates by connection with the shield box  126 . Conversely, the inner connector elements  128   a ,  130   a , and the intermediate connector elements  128   b ,  130   b , are connected respectively to the inner and outer conductors of a pair of coaxial cables  134 ,  136  which therefore are guarded cables. Each cable  134 ,  136  terminates through a respective coaxial connector  138 ,  140  with a respective probe element  30   a  having a center conductor  142  surrounded by a guard  144 . In order to provide adequate shielding for the coaxial cables  134 ,  136 , especially in the region outside of the octagonal box  48 , an electrically-conductive shield tube  146  is provided around the cables  134 ,  136  and electrically connected through the shield box  126  with the outer connector element  128   c ,  130   c  of the respective triaxial connectors  128 ,  130 . The shield tube  146  passes through the same slit in the foam  50  as does the underlying extending member  26  of the probe positioner  24 . Thus, each individually movable probe  30  has not only its own separate individually movable probe holder  28  but also its own individually movable shield  146  for its guarded coaxial cables, which shield is movable in unison with the probe holder independently of the movement of any other probe holder by any other positioning mechanism  24 . This feature is particularly advantageous because such individually movable probes are normally not equipped for both shielded and guarded connections, which deficiency is solved by the described structure. Accordingly, the probes  30  are capable of being used with the same guarding and Kelvin connection techniques in a ready-to-use manner as is the chuck assembly  20 , consistently with full shielding despite the individual positioning capability of each probe  30 . 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.