Abstract:
A method for testing a semiconductor device is disclosed. The method comprises positioning a probe card comprising a plurality of probes above the semiconductor device and moving the probe card in a vertical direction towards the semiconductor device. The plurality of probes are moving in a vertical direction towards a plurality of electrical structures of the semiconductor device until each probe of the plurality of probes has made mechanical contact with a corresponding electrical structure of the plurality of electrical structures with a minimum quantity of force. The each probe of the plurality of probes absorbs a portion of vertical overdrive after contacting their corresponding electrical structures. The probe card absorbs any remaining vertical overdrive. The vertical overdrive is a continuing vertical movement of the plurality of probes after a first probe of the plurality of probes mechanically contacts a first corresponding electrical structure.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to the field of semiconductor device testing and more specifically to the field of probe cards for semiconductor testing. 
     BACKGROUND 
     Current electrical probe designs suffer from limitations in both design and manufacturing. Considerations include an increasing number of input/output channels, grounds, and power/electrical contact points and a decreasing array pitch size. Such limitations or concerns arise primarily because current probe designs require semiconductor solder pads or bumps to be mechanically engaged by a probe that continues travelling along a path substantially orthogonal to the surface of the semiconductor device even after initial contact to ensure a stable contact. This continuing travel is often called vertical overdrive and is used to ensure that each probe of a probe card contacts a corresponding contact point of the semiconductor device regardless of local or system variations (e.g., local non-planarity, semiconductor device tilting, and local height variations of pads). A prescribed amount of overdrive may be required (to meet a compliance requirement) to ensure that the probe card and its probes are able to absorb any of the local or device-wide variations to ensure that each probe has a stable contact with its target solder pad or bump. 
     With the grid array pitch size also becoming smaller, a space that may be used for an individual probe is also limited. It is extremely challenging to maintain an exact displacement while decreasing the size of a probe. This is because stresses to the probe may increase and exceed the probe material limits for yield strength and fatigue. For example, for a simple cantilever design, when a probe length is reduced by half, the maximum possible stress increases by a factor of four, for the same overdrive. 
     Reducing a required amount of overdrive is not a good option, given the above described local and device-wide variations. A long vertical probe may be a solution to address a large overdrive and high force requirement, but is not an ideal solution when considering signal integrity and cross talk requirements. Also, low probe resistance and high current carrying capacity may be requirements for the probe card. With limited space, a cross-section of the probe will also reduce, causing an increase in resistivity and reduction in current carrying capacity. 
     Other significant challenges pertain to manufacturing a probe with a sufficient overdrive capability to absorb local and device-wide variations. As the pitch between solder bumps or pads grows smaller, so does the real estate and the volume of space available for each individual probe. As the space allocated for each probe shrinks, it becomes increasingly difficult to construct a mechanical design that allows for large overdrives while maintaining stress levels at any point along the probe below the material maximum yield stress. 
     SUMMARY OF THE INVENTION 
     Embodiments of this present invention provide solutions to the challenges inherent in testing semiconductor devices with probe cards. In a method according to one embodiment of the present invention, a method for testing a semiconductor device is disclosed. The method comprises positioning a probe card comprising a plurality of probes above the semiconductor device and moving the probe card in a vertical direction towards the semiconductor device. The plurality of probes are moved in a vertical direction towards a plurality of electrical structures of the semiconductor device until each probe of the plurality of probes has made mechanical contact with a corresponding electrical structure of the plurality of electrical structures with a minimum quantity of force. The each probe of the plurality of probes absorbs a portion of vertical overdrive after contacting their corresponding electrical structures. The probe card absorbs any remaining vertical overdrive. The vertical overdrive is a continuing vertical movement of the plurality of probes after a first probe of the plurality of probes mechanically contacts a first corresponding electrical structure. 
     In an apparatus according to one embodiment of the present disclosure, an apparatus for electrically testing a semiconductor device is disclosed. The apparatus comprises a probe card comprising a plurality of probes. The probe card is operable to move a plurality of probes in a vertical direction towards a plurality of electrical structures of the semiconductor device until each probe of the plurality of probes has made mechanical contact with a corresponding electrical structure of the plurality of corresponding electrical structures with a minimum quantity of force. The each probe of the plurality of probes is operable to absorb a portion of vertical overdrive after contacting their corresponding electrical structures. The probe card is further operable to absorb any remaining vertical overdrive. The vertical overdrive is a continuing vertical movement of the plurality of probes after a first probe of the plurality of probes mechanically contacts a first corresponding electrical structure. 
     In a computer system according to one embodiment of the present invention, a computer-readable medium having computer-readable program code embodied therein for causing the computer system to perform a method for testing a semiconductor device is disclosed. The method comprises positioning a probe card comprising a plurality of probes above the semiconductor device and moving the probe card in a vertical direction towards the semiconductor device. The plurality of probes are moved in a vertical direction towards a plurality of electrical structures of the semiconductor device until each probe of the plurality of probes has made mechanical contact with a corresponding electrical structure of the plurality of electrical structures with a minimum quantity of force. The each probe of the plurality of probes absorbs a portion of vertical overdrive after contacting their corresponding electrical structures. The probe card absorbs any remaining vertical overdrive. The vertical overdrive is a continuing vertical movement of the plurality of probes after a first probe of the plurality of probes mechanically contacts a first corresponding electrical structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this present invention will be better understood from the following detailed description, taken in conjunction with the accompanying drawing figures in which like reference characters designate like elements and in which: 
         FIG. 1A  illustrates an exemplary schematic cross-section of a semiconductor device under test with solder pads in accordance with an embodiment of the present invention; 
         FIG. 1B  illustrates an exemplary schematic cross-section of a semiconductor device under test with solder bumps in accordance with an embodiment of the present invention; 
         FIG. 2A  illustrates an exemplary schematic cross-section of a probe card with rigid probes in accordance with an embodiment of the present invention; 
         FIG. 2B  illustrates an exemplary schematic cross-section of a probe card with MEMS probes in accordance with an embodiment of the present invention; 
         FIG. 3A  illustrates an exemplary schematic cross-section of a probe card with rigid probes and a layer of secondary probes in accordance with an embodiment of the present invention; 
         FIG. 3B  illustrates an exemplary schematic cross-section of a probe card with MEMS probes and a layer of secondary probes in accordance with an embodiment of the present invention; 
         FIG. 4A  illustrates an exemplary schematic cross-section of the probe card with rigid probes of  FIG. 2A  mated with the semiconductor device under test with solder pads of  FIG. 1A  in accordance with an embodiment of the present invention; 
         FIG. 4B  illustrates an exemplary schematic cross-section of the probe card with rigid probes of  FIG. 2A  mated with the semiconductor device under test with solder bumps of  FIG. 1B  in accordance with an embodiment of the present invention; 
         FIG. 5A  illustrates an exemplary schematic cross-section of the probe card with MEMS probes of  FIG. 2B  mated with the semiconductor device under test with solder pads of  FIG. 1A  in accordance with an embodiment of the present invention; 
         FIG. 5B  illustrates an exemplary schematic cross-section of the probe card with secondary probes of  FIG. 2B  mated with the semiconductor device under test with solder bumps of  FIG. 1B  in accordance with an embodiment of the present invention; 
         FIG. 6A  illustrates an exemplary schematic cross-section of the probe card with rigid probes and a layer of secondary probes of  FIG. 3A  mated with the semiconductor device under test with solder pads of  FIG. 1A  in accordance with an embodiment of the present invention; 
         FIG. 6B  illustrates an exemplary schematic cross-section of the probe card with rigid probes and a layer of secondary probes of  FIG. 3A  mated with the semiconductor device under test with solder bumps of  FIG. 1B  in accordance with an embodiment of the present invention; 
         FIG. 7A  illustrates an exemplary schematic cross-section of the probe card with complaint probes and a layer of secondary probes of  FIG. 3B , mated with the semiconductor device under test with solder pads of  FIG. 1A  in accordance with an embodiment of the present invention; 
         FIG. 7B  illustrates an exemplary schematic cross-section of the probe card with compliant probes and a layer of secondary probes of  FIG. 3B  mated with the semiconductor device under test with solder bumps of  FIG. 1B  in accordance with an embodiment of the present invention; 
         FIG. 8  illustrates an exemplary schematic cross-section of a probe card with low overdrive probes and high overdrive probes in accordance with an embodiment of the present invention; 
         FIG. 9  illustrates an exemplary schematic cross-section of a probe card with low overdrive probes and high overdrive probes in accordance with an embodiment of the present invention; 
         FIG. 10  illustrates an exemplary schematic cross-section of a probe card with low overdrive probes and two layers of additional probes to provide high overdrive in accordance with an embodiment of the present invention; 
         FIG. 11  illustrates a flow diagram, illustrating the steps to a method in accordance with an embodiment of the present invention; 
         FIG. 12  illustrates an exemplary probe card with compliant probes, a layer of secondary probes, and a sonic scrubbing unit in accordance with an embodiment of the present invention; and 
         FIGS. 13A and 13B  illustrate an exemplary flexure design for a probe card, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of embodiments of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be recognized by one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the present invention. The drawings showing embodiments of the invention are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown exaggerated in the drawing Figures. Similarly, although the views in the drawings for the ease of description generally show similar orientations, this depiction in the Figures is arbitrary for the most part. Generally, the invention can be operated in any orientation. 
     Notation and Nomenclature: 
     Some portions of the detailed descriptions, which follow, are presented in terms of procedures, steps, logic blocks, processing, and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. A procedure, computer executed step, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present invention, discussions utilizing terms such as “processing” or “accessing” or “executing” or “storing” or “rendering” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories and other computer readable media into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. When a component appears in several embodiments, the use of the same reference numeral signifies that the component is the same component as illustrated in the original embodiment. 
     Embodiments of this present invention provide solutions to the increasing challenges inherent in manufacturing probes that are capable of absorbing a required amount of vertical overdrive to remain in compliance. As discussed herein, various embodiments dispense with large vertical probes with high overdrive absorbing capacities, in favor of splitting the required overdrive between a low overdrive probe and a high overdrive probe card. An exemplary low-overdrive micro electro-mechanical system (MEMS) probe may be used to absorb local height variations on the semiconductor wafer while still making effective contact at low overdrives. As discussed herein, such low-overdrive probes may be easily manufactured given that these probes address only local variations. The geometry of low-overdrive probes may also be kept small to provide good contact resistance, current carrying capability, and good signal integrity. As also discussed herein, any remaining overdrive may be absorbed through the use of a probe card with secondary probes such as: one or more spring interposers which may include POGO pin interposers, elastomeric interposers, etc. The two overdrive contributions added together provide ample margin for testing. 
     The compliance for the probe card may come from macro secondary probes (e.g., elastomeric probes) or springs in various layers of the probe card. For example, suitable secondary probes may be bonded between a probe head and a substrate to act as an interposer as well as to provide compliance for the whole probe head. Another example may be to have suitable secondary probes, such as elastomeric springs, bonded between a fine pitch space transformer and a regular space transformer. As discussed herein, the use of one or more of these exemplary secondary probes as elastomeric interposers in a probe card may provide the necessary additional overdrive and force to the low-overdrive probes. 
     Size, spacing, and orientation of probe cards, probes, semiconductor devices, and electrical structures of the semiconductor devices illustrated in  FIGS. 1-12  have been exaggerated for the sake of clarity. Furthermore, while an exemplary semiconductor wafer may comprise thousands of electrical structures (e.g. components, solder runs, pads, bumps, etc.) and an exemplary probe card may comprise several layers and thousands of probes, for the sake of clarity, semiconductor wafers and probe cards discussed herein and illustrated in  FIGS. 1-12  are simplified such that only a limited quantity of solder pads or bumps are illustrated and a limited quantity of probes are illustrated. In one embodiment, an exemplary probe may comprise many hundreds or thousands of probes that are concentrated into one area to test a semiconductor device, such as a processor (e.g., a computer processor or smart phone processor) and each of these probes will need to be properly aligned with a target solder pad or bump on the semiconductor device. As discussed herein, such fine pitch requirements may be met through the use of MEMS probes. 
       FIG. 1A  illustrates an exemplary schematic cross-section of a semiconductor wafer under test  100  with solder pads  104 . As illustrated in  FIG. 1A , a semiconductor wafer  100  comprises a substrate  102  and a plurality of solder pads  104  (also referred to as electrical structures). As also illustrated in  FIG. 1A , the solder pads  104  may be of differing thicknesses, causing a varying local planarity or local height variation.  FIG. 1A  also illustrates that an exemplary tilt to the orientation of the semiconductor wafer  100  may cause a variation that affects the entire semiconductor wafer  100 . For the sake of clarity, an exaggerated tilt in the semiconductor wafer  100  due to an exaggerated non-planarity of the chuck  110  (used for holding and positioning the semiconductor wafer  100 ) is illustrated in  FIG. 1A . In one embodiment, the chuck  110  is a vacuum chuck. In one embodiment, such variations, also referred to as system variations, may be caused by the non-planarity of the chuck  110  and a thickness variation of the semiconductor wafer  100 . Tilt may also come from how a probe card is aligned to the semiconductor wafer  100 .  FIGS. 4A, 4B, 5A, 5B, 6A, 6B, 7A, and 7B , as discussed herein, also illustrate portions of semiconductor wafers and chucks with exaggerated tilts to demonstrate mating an exemplary probe card to a semiconductor wafer while overcoming tilt and/or non-planarity variations between the probe card, semiconductor wafer, and/or chuck. 
       FIG. 1B  illustrates an exemplary schematic cross-section of a semiconductor wafer under test  150  with solder bumps  154 . As illustrated in  FIG. 1B , the semiconductor wafer  150  comprises a substrate  152  and a plurality of solder bumps  154  (also referred to as electrical structures). As also illustrated in  FIG. 1B , the solder bumps  154  may also be of differing thicknesses, causing a varying local planarity or local height variation.  FIG. 1B  also illustrates an exemplary tilt (when mounted on chuck  110 ) as discussed above, introducing a system variation. 
     Overdrive Compliance while Meeting Fine Pitch Requirements: 
     When dealing with fine pitches (50 microns or less), it may be difficult to manufacture a vertical probe with the required accuracy to contact a target pad or bump that may be only 15-20 microns in size. Such small pitch requirements may be met with a probe card with MEMS probes. In one exemplary embodiment, MEMS probes may have 10 micron dimensional features. In one embodiment, MEMS probes have a spring-like structure that is very accurate in position, have an adequate amount of force to make good contact to the device under test, but do not have a lot of overdrive. A MEMS probe designed for providing a large overdrive may be too complex to fabricate and may not provide the force required to make good contact. 
     In one exemplary embodiment, a probe card may have probes that have a certain amount of spring-like ability to meet a compliance requirement (a proscribed quantity of force or overdrive to ensure a stable contact between a probe and a target solder pad). This spring-like ability must also be able to absorb any local variations in bump geometries in the semiconductor wafer being tested. Overdrive may be defined as a number of microns a spring is required to compress to ensure a compliance-meeting stable contact between a probe and a solder pad of a semiconductor device under test. 
     For example, a probe with a 25 micron overdrive requirement will need to compress at least 25 microns before a stable contact between itself and a target solder pad or bump is achieved. In addition to the minimum overdrive required for stable contact, there are also local and system planarity variations, as discussed herein, that will need to be absorbed. These variations need to be taken into account when determining a required amount of overdrive. An exemplary system planarity variation may be on the order of 20-25 microns. Therefore, there will need to be a minimum of 45-50 microns of overdrive (20-25 microns due to system variation and 25 microns for the probe) to meet compliance requirements and achieve a stable contact between the above exemplary probes and corresponding target solder pads/bumps. 
     However, with MEMS probes, which are well suitable for fine pitch applications, there may not be enough overdrive available to meet compliance requirements. As noted above, while an overdrive needed to meet compliance requirements due to system variation may be 20-25 microns and an overdrive need to meet overdrive compliance requirements of a MEMS probe may be 5-20, therefore, the MEMS probe may be unable to achieve the exemplary overall overdrive compliance requirement of a minimum of 25 microns or more. In other words, after meeting its own overdrive requirements, the MEMS probe may not have enough overdrive capacity left to meet the minimum amount of overdrive necessary to absorb the system variations. In other words, low overdrive MEMS probes may completely bottom out. Therefore, as noted above, the remaining microns of overdrive necessary to meet the compliance requirements to ensure stable contact between probes and target solder pads/bumps, across the whole wafer must be found somewhere else. 
     As discussed herein, one solution is to use a global compliant probe card. When the probe card is driven to contact the device under test, the MEMS probes start to compress while the entire substrate holding the MEMS probes also compresses due to the presence of a matching spring body under the substrate which is designed with an appropriate spring constant. Thus there is an overdrive contribution from both the MEMS and the interposer springs underneath the substrate. While there is enough overdrive and force in the probes to absorb local variations and make good electrical contact, the larger overdrive capacity of the secondary probes in the probe card will provide the additional overdrive necessary to ensure there is a stable contact between probes and solder pads/bumps across the semiconductor wafer. In one embodiment, low overdrive MEMS probes can completely bottom out and then transfer the force to the secondary probes. Such a bottom out of MEMS probes may be seen in situations where a total MEMS probe count is small. 
     In one embodiment, due to system variations, some probes will be making contact with their target solder pads/bumps after an overdrive of 10 microns while the same probes at another location on the wafer will be making contact with their target solder pads/bumps after an overdrive of 20 microns due the system variation. 
     In one embodiment, as discussed herein, rather than low-overdrive probes, a probe card with an elastomeric interposer may comprise rigid probes with an infinite spring constant. Such an arrangement may be suitable when the necessary compliance is absorbed by an elastomeric interposer in the probe card and by the rigid probes penetrating and imbedding themselves into their respective solder bump (using a thick enough solder bump so that all of the remaining variation may be absorbed by the solder bump). But with fine pitches, care is taken to ensure that the local and system variations are minimized so that the elastomeric interposer of the probe card and the solder bumps are able to fully absorb the local and system variations and the probe overdrive necessary for compliance. In one embodiment, the overdrive of the probe card is sufficient to absorb the majority of the overdrive needed for compliance such that rigid probes will only slightly embed themselves into their respective fine pitch solder bumps. 
     Probe/Probe Card Combination Embodiments: 
       FIG. 2A  illustrates an exemplary schematic cross-section of a probe card  200  with rigid probes  206 . As illustrated in  FIG. 2A , the probe card  200  comprises a substrate  202 , an interposer and/or space transformer  204 , and a plurality of rigid probes  206 . As discussed herein, the probe card  200  illustrated in  FIG. 2A  does not provide any level of compliance because the probes  206  and probe card  200  are rigid and will not absorb any of the force when the probes  206  of the probe card  200  are applied to target solder pads. In other words, the probe card  200  of  FIG. 2A  is unable to apply a prescribed amount of vertical overdrive to ensure that the probes  206  of the probe card  200  are in stable contact with their corresponding target electrical structures because the probes  206  are rigid and unable to absorb any of the applied vertical overdrive. An exemplary interposer or space transformer  204  may be used to route a test signal from a larger pitch to a smaller pitch. 
       FIG. 2B  illustrates an exemplary schematic cross-section of a probe card  250  with compliant probes  256 . As illustrated in  FIG. 2B , the probe card  250  comprises a substrate  252 , an interposer and/or space transformer  254 , and a plurality of compliant probes  256 . As discussed herein, the probe card  250  illustrated in  FIG. 2B  provides a limited amount of compliance because the complaint probes  256  are able to absorb a quantity of vertical overdrive. In one embodiment, the compliant probes  256  are able to absorb 10 microns of vertical overdrive. In another embodiment, the compliant probes  256  are able to absorb 5 microns of vertical overdrive. In one embodiment, the compliant probes  256  are micro electro-mechanical system (MEMS) probes, which are able to absorb a limited amount of local height variations between the probes  256  and their corresponding target electrical structures on the device under test. 
       FIG. 3A  illustrates an exemplary schematic cross-section of a probe card  300  with rigid probes  306  and a layer of secondary probes  308  (e.g., elastomeric springs, etc.). As illustrated in  FIG. 3A , an exemplary probe card  300  comprises a substrate  302 , a layer of secondary probes  308  that may absorb a prescribed quantity of vertical overdrive, a space transformer  304 , and a plurality of rigid probes  306 . In one exemplary embodiment, the layer of secondary probes  308  is an elastomeric interposer layer. In one embodiment, the layer of secondary probes  308  comprises a plurality of springs  309  that function as interposers between the layers. As discussed herein, while the rigid probes  306  of the probe card  300  may not be able to absorb local planarity variations as they are unable to absorb vertical overdrive, the layer of secondary probes  308  within the probe card  300  is able to absorb a quantity of vertical overdrive such that a quantity of system variations are absorbed. 
       FIG. 3B  illustrates an exemplary schematic cross-section of a probe card  352  with compliant probes  356  and a layer of secondary probes  358  in accordance with an embodiment of the present invention. As illustrated in  FIG. 3B , an exemplary probe card  350  comprises a substrate  352 , a layer of secondary probes  358  that may absorb a prescribed quantity of vertical overdrive, a space transformer  354 , and a plurality of compliant probes  356 . In one exemplary embodiment, the layer of secondary probes  358  is an elastomeric interposer layer. In one embodiment, the layer of secondary probes  358  comprises a plurality of springs  359  that function as interposers between layers. As discussed herein, the compliant probes  356  are able to absorb an amount of local planarity variations when they are absorbing a quantity of vertical overdrive. In one embodiment, the compliant probes  356  are able to absorb vertical overdrive coming from local planarity differences. In another embodiment, the layer of secondary probes  358  is able to absorb a quantity of vertical overdrive, such that system variations are absorbed. 
     Example Test Scenarios with a Variety of Probe/Probe Card Arrangements: 
     The semiconductor wafers  100 ,  150 , and probe cards  200 ,  250 ,  300 ,  350  may be arranged into the following four scenarios illustrated in table 1 below. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Effective 
                 Effective 
                   
                   
               
               
                   
                 spring 
                 spring 
               
               
                 Probe card 
                 constant of 
                 constant of 
                   
                 Applications 
               
               
                 configuration 
                 probes 
                 probe card 
                 Result 
                 Addressed 
               
               
                   
               
             
             
               
                 Rigid probe, 
                 Infinite 
                 Infinite 
                 Compliance 
                 Larger solder 
               
               
                 non compliant 
                   
                   
                 absorbed by 
                 bumps where the 
               
               
                 probe card 
                   
                   
                 solder bumps. 
                 probes penetrate 
               
               
                 system 
                   
                   
                   
                 into solder 
               
               
                 MEMS probe, 
                 N*K1s 
                 Infinite 
                 Low OD probe 
                 Larger/small 
               
               
                 non-compliant 
                   
                   
                 card, suitable for 
                 solder bumps, 
               
               
                 probe card 
                   
                   
                 probing dies with 
                 pads, without 
               
               
                 system 
                   
                   
                 little system 
                 much system 
               
               
                   
                   
                   
                 planarity 
                 planarity variation 
               
               
                   
                   
                   
                 variation 
               
               
                 Rigid probe, 
                 Infinite 
                 As designed 
                 Limits the max 
                 Local bump 
               
               
                 compliant 
                   
                   
                 force on the 
                 variation is 
               
               
                 probe card 
                   
                   
                 wafer. 
                 absorbed by 
               
               
                 system 
                   
                   
                   
                 solder bump 
               
               
                   
                   
                   
                   
                 penetration 
               
               
                 MEMS probe, 
                 N*K1s 
                 As designed 
                 Large overall OD, 
                 All applications 
               
               
                 compliant 
                   
                   
                 suitable for pads 
                 including fine 
               
               
                 probe card 
                   
                   
                 or bumps 
                 pitch 
               
               
                 system 
               
               
                   
               
             
          
         
       
     
     The exemplary probe card/probe combinations illustrated in  FIGS. 2A, 2B, 3A, and 3B , and compared in Table 1 follow the following assumptions: 
     1) A total force for a MEMS probe is N 1  with a spring constant of K1s. 
     2) A total force for a compliant probe card is N 2  with a spring constant of K2s. 
               An   ⁢           ⁢   overdrive   ⁢           ⁢   for   ⁢           ⁢   MEMS   ⁢           ⁢   probes     =           F     (       N   1     *   K   ⁢           ⁢   1   ⁢   s     )       .     
     ⁢   An     ⁢           ⁢   overdrive   ⁢           ⁢   for   ⁢           ⁢   a   ⁢           ⁢   compliant   ⁢           ⁢   probe   ⁢           ⁢   card     =           F     (       N   2     *   K   ⁢           ⁢   2   ⁢   s     )       .     
     ⁢   A     ⁢           ⁢   total   ⁢           ⁢   overdrive   ⁢           ⁢   for   ⁢           ⁢   a   ⁢           ⁢   MEMS   ⁢           ⁢   probe   ⁢     /     ⁢   compliant   ⁢           ⁢   probe   ⁢           ⁢   card   ⁢           ⁢   assemly     =       F     (       N   1     *   K   ⁢           ⁢   1   ⁢   s     )       +       F     (       N   2     *   K   ⁢           ⁢   2   ⁢   s     )       .                 
Therefore, if N 1 =10N 2 , and a same spring constant is used for both the MEMS probes and the compliant probe card, a 1 micron overdrive for the MEMS probes will correspond to a 10 micron overdrive for the compliant probe card. However, in various embodiments, the spring constants between the MEMS probes and the compliant probe cards may be different.
 
     The variety of probe cards illustrated in  FIGS. 2A, 2B, 3A, and 3B  are suitable for a variety of uses as illustrated in Table 1. For example, a rigid probe  206  paired with a non-compliant probe card  200 , as illustrated in Table 1 and  FIG. 2A , provides an infinite spring constant in both the probes  206  and the probe card  200  and therefore, any overdrive compliance must be absorbed by solder bumps (neither the probe nor the probe card have spring properties and would therefore have infinite spring constants and be unable to absorb any vertical overdrive). This first combination may be used with larger solder bumps where the rigid probes  206  may penetrate sufficiently into the solder bump to absorb the vertical overdrive when the overall overdrive compliance value is able to be absorbed by the solder bumps. 
     A MEMS probe  256  paired with a non-compliant probe card  250 , as illustrated in Table 1 and  FIG. 2B , provides a probe spring constant of N*K1s and an infinite spring constant in the probe card  250 . MEMS probes  256  paired with a non-compliant probe card  250  have a small amount of overdrive compliance capability and are suitable for probing both solder pads and solder bumps when there is little system variation. 
     A rigid probe  306  paired with a compliant probe card  300 , as illustrated in Table 1 and  FIG. 3A , provides an infinite probe spring constant and an “as designed” spring constant for the probe card  300 , where a spring constant for the probe card  300  may be selected for manufacture. In one embodiment, such a probe  306  and probe card  350  combination may limit a maximum force exerted on a device under test, but may not be suitable for probing solder or metal pads. As discussed herein, such a combination may be used to absorb local solder bump variations by solder bump penetration and absorb system level variations by the flexibility of the probe card  300 . 
     Lastly, a MEMS probe  356  paired with a compliant probe card  350 , as illustrated in Table 1 and  FIG. 3B , provides a probe constant of N*K1s and a probe card constant as designed, where a spring constant for the probe card  350  may be selected for manufacture. In one embodiment, a low-overdrive probe  356  and compliant probe card  350  may be used to provide a large overall overdrive and may be suitable for both solder bumps and solder pads. This combination may also be suitable for increasingly fine pitch sizes. In one embodiment, the MEMS probe  356  may absorb local compliance requirements (to deal with local variations) for solder pads/bumps while system variation may be absorbed by the flexibility in the probe card  350 . 
       FIG. 4A  illustrates an exemplary schematic cross-section of a probe card  200  with rigid probes  206 , mounted on a chuck  110  and mated with a semiconductor wafer  100  with solder pads  104 . As discussed herein, the variations illustrated are exaggerated for the sake of clarity. As illustrated in  FIG. 4A , because the probes  206  and probe card  200  have no compliant properties, there will be no overdrive absorption and the probes  206  may be driven into the solder pads  104  if the variation is too great. As illustrated in  FIG. 4A , the amount of overdrive required to ensure a stable contact across the probe card  200  may result in damaged solder pads  104  and damage the wafer if the amount of overdrive is too high. 
       FIG. 4B  illustrates an exemplary schematic cross-section of a probe card  200  with rigid probes  206 , mounted on a chuck  110  and mated with a semiconductor wafer  150  with solder bumps  154 . As discussed herein, the variations illustrated are exaggerated for the sake of clarity. As illustrated in  FIG. 4B , because the probes  206  and probe card  200  have no compliant properties, any overdrive absorption will be accomplished by the probes  206  penetrating into the solder bumps  154 . Therefore, if there is a planarity variation, the overdrive needed to accommodate the variations may be absorbed by penetrating the solder bumps  154 . 
       FIGS. 5A and 5B  illustrate an exemplary schematic cross-section of a probe card  250  with compliant probes  256 , mounted on chuck  110  and mated with a semiconductor wafer with either solder pads  104  or solder bumps  154 . As discussed herein, the variations illustrated are exaggerated for the sake of clarity. As illustrated in  FIGS. 5A and 5B , the compliance is absorbed by compliant probe  256 . In one embodiment, the compliant probes  256  are MEMS probes. With a compliant probe (e.g., a MEMS probe) and a non-compliant probe card, as illustrated in  FIGS. 5A and 5B , there is a small amount of overdrive compliance capability. So long as any system variation is minimized, the compliance-required amount of overdrive may be absorbed. 
       FIGS. 6A and 6B  illustrate an exemplary schematic cross-section of a probe card  300  with rigid probes  306 , mounted on a chuck  110  and mated with a semiconductor wafer with either solder pads  104  or solder bumps  154 . As discussed herein, the variations illustrated are exaggerated for the sake of clarity. As illustrated in  FIGS. 6A and 6B , a maximum force exerted on the semiconductor wafer is limited by a layer of secondary probes  308  in the probe card  300 . In one embodiment, as illustrated in  FIG. 6B , local solder bump variations may be absorbed by solder bump penetration. 
       FIGS. 7A and 7B  illustrate an exemplary schematic cross-section of a probe card  350  with compliant probes  356  and a layer of secondary probes  358 , mounted on a chuck  110  and mated with a semiconductor wafer with either solder pads  104  or solder bumps  106 . As discussed herein, the variations illustrated are exaggerated for the sake of clarity. In one embodiment, with a low overdrive MEMS probe  356  and a high overdrive probe card  300 , an overall large overdrive is provided. Such a combination may be useful in all applications; including fine pitch sizes in both solder pads and solder bumps. 
     Exemplary Embodiments: 
       FIG. 8  illustrates an exemplary schematic cross-section of a probe card  800  with compliant probes  812  and a layer of secondary probes  808 . As illustrated in  FIG. 8 , the probe card  800  comprises a substrate or PCB layer  802 , an interposer  804 , a space transformer  806 , a layer of fine pitch secondary probes  808 , a fine pitch space transformer  810 , and a plurality of compliant probes  812 . In one embodiment, the compliant probes  812  are MEMS probes. In one embodiment, the layer of fine pitch secondary probes  808  comprises a carbon nano tube interposer providing electrical connections as well as the desired additional compliance for the low-overdrive probes  812 . In one embodiment, the layer of fine pitch secondary probes  808  comprises elastomeric springs  809  that provide electrical connections and the desired additional overdrive compliance. 
     In one embodiment, the layer of fine pitch secondary probes  808  is permanently bonded between the fine pitch space transformer  810  and the space transformer  806 . In one embodiment, the fine pitch space transformer  810  and the space transformer  806  are permanently bonded  814  with the layer of fine pitch secondary probes  808  between them. The permanent bond  814  is an elastic bond with a very low spring constant as compared to a spring constant of the layer of fine pitch secondary probes  808 . By permanently binding the layers sandwiching the layer of fine pitch secondary probes  808 , the probe card  800  is able to share in system overdrive compliance. 
       FIG. 9  illustrates an exemplary schematic cross-section of a probe card  900  with compliant probes  912  and a layer of secondary probes  908 . As illustrated in  FIG. 9 , the probe card  900  comprises a substrate or PCB layer  902 , a layer of secondary probes  908 , a space transformer  904 , a fine pitch interposer  906 , a fine pitch space transformer  910 , and a plurality of fine pitch compliant probes  912 . In one embodiment, the compliant probes  912  are MEMS probes. In one embodiment, the layer of secondary probes  908  comprises a carbon nano tube interposer providing electrical connections as well as the desired additional compliance for the low-overdrive probes  912 . In one embodiment, the layer of secondary probes  908  comprises elastomeric springs  909  that provide electrical connections and the desired additional overdrive compliance. 
     In one embodiment, the layer of secondary probes  908  is permanently bonded between the substrate  902  and the space transformer  904 . In one embodiment, the substrate  902  and the space transformer  904  are permanently bonded  914  with the layer of secondary probes  908  between them. In one embodiment, the permanent bond  914  is an elastic bond with a very low spring constant as compared to a spring constant of the layer of secondary probes  908 . By permanently binding the layers sandwiching the layer of secondary probes  908 , the probe card  900  is able to share in system overdrive compliance. 
       FIG. 10  illustrates an exemplary schematic cross-section of a probe card  1000  with compliant probes  1012  and a plurality of layers of secondary probes  1006 A,  1006 B. As illustrated in  FIG. 10 , the probe card  1000  comprises a substrate or PCB layer  1002 , a layer of secondary probes  1006 A, a space transformer  1004 , a layer of fine pitch secondary probes  1006 B, a fine pitch space transformer  1010 , and a plurality of fine pitch compliant probes  1012 . In one embodiment, the compliant probes  1012  are MEMS probes. In one embodiment, the layer of secondary probes  1006 A and the layer of fine pitch secondary probes  1006 B comprise carbon nano tube interposers providing electrical connections as well as the desired additional compliance for the low-overdrive probes  912 . In one embodiment, the layer of secondary probes  1006 A and the layer of fine pitch secondary probes  1006 B comprise elastomeric springs  1007 A and  1007 B, respectively, that provide electrical connections and the desired additional overdrive compliance. 
     In one embodiment the layer of fine pitch secondary probes  1006 B has a greater quantity of elastomeric springs  1007 B to allow a finer variation across the surface of the semiconductor wafer under test as compared to the elastomeric springs  1007 A of the layer of secondary probes  1006 A. In one embodiment the probe card  1000  may comprise approximately 5000 MEMS probes  1012 , 500-1000 connections through the layer of fine pitch secondary probes  1006 B, and only approximately 400 connections through the larger pitch layer of secondary probes  1006 A. Some of the grounds and power lines are ganged together to allow the number of connections to be reduced. In one embodiment, the layer of fine pitch secondary probes  1006 B and the layer of secondary probes  1006 A, as illustrated in  FIG. 10  are similar to the layer of fine pitch secondary probes  808  and the layer of secondary probes  908  of  FIGS. 8 and 9 , respectively. 
     In one embodiment, a layer of secondary probes  1006 A is permanently bonded between a substrate  1002  and a space transformer  1004 . In one embodiment, a layer of fine pitch secondary probes  1006 B is permanently bonded between space transformer  1004  and fine pitch space transformer  1010 . In one embodiment, the fine pitch space transformer  1010  and the space transformer  1004  are permanently bonded  1014 B with the layer of fine pitch secondary probes  1006 B between them. In one embodiment, the space transformer  1004  and the substrate  1002  are permanently bonded  1014 A with the layer of secondary probes  1006 A between them. In one embodiment, the permanent bonds  1014 A,  1014 B, are elastic bonds having a very low spring constant as compared to a spring constant of the layer of secondary probes  1006 A, and the layer of fine pitch secondary probes  1006 B, respectively. 
       FIG. 11  illustrates the steps to a process for testing a semiconductor wafer by meeting an overdrive compliance requirement by absorbing the overdrive with an overall high overdrive capacity that is divided between complaint probes and one or more layers of secondary probes in a probe card. In step  1102  of  FIG. 11 , the probe card is positioned above a semiconductor wafer such that probes of the probe card are aligned above corresponding electrical structures of the semiconductor wafer. In one embodiment, the electrical structures may be solder pads or solder bumps. In step  1104  of  FIG. 11 , the probe card is moved in a Z-axis so that the probes of the probe card approach their corresponding electrical structures. In step  1104  of  FIG. 11 , the probe card continues moving until the probes of the probe card contact corresponding electrical structures with at least a minimum force to ensure a stable contact between probes and corresponding electrical structures. To ensure the stable contact between probes and electrical structures, an proscribed amount of overdrive is applied to the probes after physical contact with an electrical structure. Therefore, in one embodiment, a probe and probe card system has a sufficient overdrive capability to ensure that all probes are able to make mechanical contact with corresponding electrical structures and then apply further compliance-meeting overdrive to ensure a stable contact. 
       FIG. 12  illustrates an exemplary probe card  350  with complaint probes  356 , a layer of secondary probes  358 , and a sonic scrubbing unit  1202 . After the probes  356  have been mated with corresponding electrical structures as discussed herein, an exemplary sonic scrubber  1202  may be activated for a defined period of time (e.g., 10 ms) to induce a scrubbing motion to the probes  356  that facilitates an effective contact between the electrical structures of the semiconductor wafer under test and the probes  356  by breaking any existing oxide covering the electrical structures. In one embodiment, the sonic scrubber  1202  may comprise an ultrasonic or megasonic transducer in various layers of the probe card  350 . 
       FIGS. 13A and 13B  illustrate an exemplary flexure design. In one exemplary embodiment, probe card motion will be strictly in a Z direction without any lateral motion. The exemplary flexure may provide additional force to the interposer force without depending on a spring count or spring constant of the interposer. An exemplary embodiment may use an appropriate interconnect and use the flexure to provide additional controlled overdrive. 
     Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. It is intended that the invention shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.