Abstract:
An apparatus for testing semiconductor devices including probe tips for contacting input/output pads on the device attached to a probe membrane fixed to a package using a layer of elastomeric material. The elastomeric material and use of compliant bump probe tips effect a global planarization for improved electrical contact between the probe assembly and the input/output contacts on the device under test.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a division of application Ser. No. 08/858,107 filed May 19, 1997, now U.S. Pat. No. 6,028,437. 
     This application for patent is related to co-pending U.S. patent application Ser. No. 08/748,843, now U.S. Pat. No. 5,898,783, which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates in general to the testing of semiconductor devices, and in particular to a probe assembly for testing such devices. 
     BACKGROUND INFORMATION 
     In the course of fabricating semiconductor devices, it is necessary to perform test and burn in operations on the device. In order to carry out these operations, the device temporarily must be held in a test jig of some form in order to establish electrical contact between the input and output (input/output) pads on the device under test (“DUT”) and the test instrumentation. At the die level, this has previously been accomplished in the art by one of two means. One technique, “soft” Tape Automatic Bonding (“TAB”) requires making a temporary bond to the DUT input/output pads. This can give rise to considerable damage to the pads after removal. The second method for holding the DUT in a test assembly is to use a carrier in the form of a multichip module (“MCM”) with probe tips formed from hard metal bumps. The probe tips on the MCM are arranged in a pattern to exactly match the positions of the input/output pads on the DUT. The DUT is aligned with the probe tips by means of either a mechanical “alignment fence” or an optical technique. Because the probe tips are not sufficiently planarizing over the surface of the die, large forces are required in order to ensure good electrical contact with every input/output pad on the die. The hard metal probe tips may damage the pads. Furthermore, both of these techniques sometimes require that the DUT be mounted in a package using a temporary adhesive that can be complicated to remove. As a result, there is a need in the art for an improved test head assembly for the testing of semiconductor devices. 
     SUMMARY OF THE INVENTION 
     The foregoing need is satisfied by the present invention which includes a package having electrical contacts adaptable for connecting to device test instrumentation that also holds the DUT, and contains a compliant probe assembly referred to as the probe membrane. The package and probe membrane include features to effect global planarization of the interface between the DUT and the assembly of probe tips. The features that effect the necessary global planarization include one or more compliant bump probe tips, a compliant bonding material to mount the probe assembly in the package, and a compliant bonding layer for attaching the DUT to the package. 
     An advantage of the present invention is that a sufficient electrical connection between the compliant bump probe tips is made by the use of pressure applied to the outside of the package although, because of lack of global planarization, there may not be such sufficient connection at the location of one or more of the interfaces between the probe tip and the input/output pad at initial contact. Because compliant bump probe tips respond compliantly over a larger range of displacements than do metals, the pressure needed to effect global planarization is lower than with solid metal probe tips, thereby avoiding damage to the DUT. 
     Overdeformation of the compliant bump probe tips is prevented by another advantage of the present invention. One or more standoff structures are incorporated on the probe membrane. These have less height than the probe tips and have noncompliant properties. If excessive pressure is applied, the standoffs control the amount of deformation of the compliant bump probe tips, avoiding damage to both the compliant bump probe tips and the DUT. 
     An additional advantage of the present invention is the additional global planarization that is provided by the elastomeric bonding layer used to affix the probe membrane in the package. Because of the compressibility properties of the elastomeric material, deformations needed to adjust for nonplanarity and thereby effect global planarization are less than would be needed to achieve planarization in a “carrier” technique. 
     Another advantage of the present invention is further global planarization effected by the use of a layer of elastomeric material backing between the DUT and the package to attach it thereto. This elastomeric backing layer performs its global planarization function in the same way as the elastomeric bonding layer that affixes the probe membrane in the package. 
     The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a probe head assembly for testing and burn in of a semiconductor device in accordance with the present invention; 
     FIG. 2 illustrates a top view cross-section of a probe head assembly in accordance with the present invention; 
     FIG. 3 illustrates an apparatus for testing and burn in of a semiconductor device; 
     FIG. 4 illustrates a detail of a compliant bump probe tip; 
     FIG. 5 illustrates a plurality of semiconductor dies comprising a semiconductor wafer; 
     FIG. 6 illustrates an alternative embodiment of the present invention; 
     FIG. 7 illustrates a top view cross-section of an alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details concerning timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art. 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
     An invention which alleviates the problems associated with the present technology used in the testing and burn in of semiconductor dies will now be described in detail. Referring to FIG. 1, there is shown a probe head assembly  10 , in an elevation cross-sectional view, not to scale, in accordance with the present invention. 
     A device under test (“DUT”)  101 , which may be a die, is enclosed in the head assembly  10 , which is formed from a package  110  and probe membrane  120 . The package  110  is further formed from a package lid  111  and a package base  112 . The DUT  101  is mounted on the package lid  111  by a layer of bonding material  113 , which may be an elastomeric material. In one embodiment, the elastomeric material  113  offers some additional global planarization properties due to its compressibility properties. The package  110  may be a standard semiconductor package or any custom manufactured package. 
     The package  110  contains a probe membrane  120  consisting of a probe membrane head  121  on which are affixed probe tips  122 . The probe membrane  120  is larger than the DUT  101  so as not to interfere with electrical connections between the probe membrane  120  and the package  110 . In one embodiment, the membrane head  121  is fabricated of silicon in order to achieve an adequate thermal coefficient of expansion match between the DUT  101  and the probe membrane  120  over the range of operating temperatures of the invention. The probe tips  122  effect the electrical contact between the DUT  101  and the probe head assembly  10  by engaging pads  102  on the DUT  101 . In one embodiment, probe tips  122  are compliant bump probe tips, a probe tip with a refractory thin metal shell covering a polymer bump, which has compliancy properties that will allow multiple compressive cycles within the elastic limit of the material. Compliant bump technology is discussed in U.S. Pat. No. 5,508,228 which is incorporated herein by reference. 
     The array of probe tips  122  on the probe membrane head  121  is illustrated in the top view cross-section of FIG.  2 . The probe tips  122  are disposed on the probe membrane head  121  in an arrangement that mirrors the arrangement of input/output pads  102  (not shown) on the DUT  101  (not shown). Bond pads  124  corresponding to each of the probe tips  122  are disposed on the probe membrane head  121 ; electrical connection between a probe tip  122  and its corresponding bond pad  124  is effected by a conducting trace (not shown). The traces and bond pads  124  may be fabricated of aluminum. Bond pads  124  are electrically connected to corresponding package leads  114  by wire bonds  117 . Such wire bonding techniques are well known in the art. The package leads  114  provide the electrical connection, via interconnecting cable  201 , to the instrumentation  301  (see FIG. 3) for performing the test and burn in of the DUT  101 . Such instrumentation  301  also is well known in the art. 
     Compliant bump probe tips  122  permit a pressing force to be performed with little or no stressing of the DUT  101 , since the compliant bump probe tips  122  already in contact with pads  102  may be compressed slightly so that the other compliant bump probe tips  122  are able to eventually make contact with pads  102 . Thus, the bumps are compressed within the elastic limit of the material. 
     Also, fabricated on the probe membrane head  121  are standoffs  123  which serve to act as a controlled collapse stops when the head assembly  10  is in operation. These ensure that, in operation, the compliant bump probe tips  122  are not driven beyond their elastic limit. The standoffs  123  may be fabricated from metal or of a polymer material; the same polymer material from which the compliant bump probe tips  122  are formed is suitable. If the same polymer material is used, the standoffs  123  should each be larger in area than the compliant bump probe tips  122  so as to have limited compressibility compared to the compliant bump probe tips  122 . Forming the standoffs  123  from the same polymer material as the compliant bump probe tips has the advantage of probe membrane  120  fabrication simplicity. 
     Referring next to FIG. 4, an embodiment using compliant bump probe tips  122 , the thin metal shell  412  on the compliant bump  411  of the compliant bump probe tip  122  establishes the electrical connection between the compliant bump probe tip  122  and the electrically conducting traces. Also, the structure of the compliant bump probe tips  122  may be shaped to effect a “scrubbing” action as pressure is applied to make the probe membrane  120  to DUT  101  contact. This can effect an improved electrical contact between the DUT  101  and probe membrane  120  by “scrubbing” through the oxide coat that usually forms on the pads  102  on the DUT  101 . An optional layer of probe material  413  performs the scrubbing action. In a second embodiment, abrasive particles may be embedded, as just such a probe material, in the surface of the compliant bump probe tips  122  in order to effect better penetration of the oxide coat that typically forms on the DUT  101  pads  102 . 
     The probe membrane  120  is mounted in a recessed portion  115  of the package base  112  and fixed to the recessed portion  115  by a bonding material  116 . The height of the probe membrane  120  in the package  110  is controlled by the thickness of the bonding material  116 . The bonding material  116  may be an elastomeric material. This also serves to effect some global planarization of the DUT  101  when the probe head assembly  10  is in operation. 
     In operation, the package lid  111  with the DUT  101  affixed to it as illustrated in FIG. 1, is brought in contact with the probe membrane  120 . Alignment of the DUT  101  to the membrane  120  is accomplished using either optical alignment or mechanical alignment fence techniques; such techniques are known to one of ordinary skill in the art. In an embodiment using compliant bump probe tips  122 , the DUT  101  is brought in contact with the probe membrane  120  with sufficient pressure to compress the compliant bump probe tips  122 , and/or the elastomeric bonding materials  113 ,  116 , but not so much pressure as to compress the standoffs  123 . The package lid  111  is then held in place against the package base  112  by solder, mechanical clamp, or similar means (not shown), all of which are well understood by one of ordinary skill in the art. Test and burn in is then performed, followed by removal of the package lid  111 , and removal of the DUT  101  from the bonding layer  113 . The probe head assembly  10  is then ready for another test cycle. 
     Referring to FIG. 5, this same technique is extensible to an embodiment of a test head assembly  10  capable of testing a plurality of dies constituting each of the DUT  101  before the dies are cut from a wafer  500 . In such an embodiment, the probe membrane  120  has probe tips  122  affixed to the probe membrane head  121  in an array corresponding to the input/output pads  102  for each of the DUT  101 , here the dies comprising the wafer  500 . 
     In an alternative embodiment, illustrated in FIG. 6, probe tips  122  affixed to the probe membrane head  121  effect the electrical contact to the input/output pads  102  on the DUT  101  as well as the electrical contact to the package leads  114 . The electrical connection between a probe tip  122  in contact with an input/output pad  102  and the corresponding probe tip  122  forming the contact with the package lead is made through reroute leads  623 . This is further illustrated in FIG. 7 which depicts a top view cross section. 
     In another embodiment, the package may have a hinged package lid  111  (not shown) that automatically aligns the DUT  101  to the probe membrane  120 . 
     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.