Abstract:
By constructing a universal test circuit on a tester chip, and stacking the tester chip in an IC package together with operational circuit chips to be tested, the problems inherent with external IC testing are reduced. The tester chip can be standardized across a number of different chip combinations and, if desired, pre-programmed during manufacturing for a particular package. The tester chip interfaces to other chips in the stack advantageously are standardized.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of prior U.S. patent application Ser. No. 12/147,918 to KASKOUN et al. entitled “INTEGRATED TESTER CHIP USING DIE PACKAGING TECHNOLOGIES” filed on Jun. 27, 2008. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to integrated circuit (IC) testing and more particularly to systems and methods for testing multi-tiered IC devices. 
     BACKGROUND 
     Typically, during the manufacturing process of an IC, testing (probing) is performed on the IC prior to the time the IC is mounted into a package. In some instances the probing is performed after the IC is mounted. However, in situations where multiple ICs are stacked into tiers, it is difficult to probe the ICs due to inaccessibility of test terminals on the outside of the stacked device. 
     The problem is compounded when a tier does not include a complete circuit. Thus, in situations where portions of a testable circuit are constructed on different tiers, it is not feasible to test the complete circuit until the dies are stacked into the final multi-tiered IC device (also referred to as a stacked IC device). Moreover, once stacked accessibility for test purposes may be limited. 
     One solution to this problem is to bring test leads to accessible locations on the periphery of the stacked device. This, however, in many situations is either not possible due to space constraints, signal propagation times, or simply because it is too expensive. Another problem is that the small size of stacked devices may require small electrical pads and through silicon vias (TSV), which may range in size to less than 10 microns, which in turn do not easily lend to testing with conventional probe tips (typically 25-50 microns). For testing, multiple probe tips usually must make contact at the same time, so even when each individual probe tip is small enough, a large number of probe tips becomes difficult to manage. 
     BRIEF SUMMARY 
     By constructing a universal test circuit on a die (or chip), and stacking the test die in the IC package together with other dies to be tested, the problems inherent with external IC testing are reduced. The tester chip would be standardized across a number of different chip combinations, and if desired, pre-programmed during manufacturing for a particular package. Standardization includes a standard input/output (I/O) configuration, as well as industry standard tester software programs. The standardization allows tester chips to test a wide variety of different products (chip combinations). 
     One advantage of such an arrangement is that it decouples tester chip development from the design or fabrication of the operational chip itself. Thus, a company could dedicate resources to working on the tester chip in a continuous mode, independent from a particular product. Consequently, the design of a tester chip would not necessarily need to keep pace with the design schedules for any particular product. 
     The foregoing has outlined, rather broadly, the features and technical advantages of the present invention in order that the detailed description 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 specific embodiments 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 teachings of the invention as set forth in the appended claims. The novel features, which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only, and is not intended as a definition of the limits of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows one configuration of an embodiment in which a tester chip is contained within an IC package; 
         FIGS. 2 and 3  show other configurations of different embodiments in which a tester chip is contained within an IC package; 
         FIGS. 4 and 5  show examples of chips manufactured as part of wafers according to embodiments of the invention; and 
         FIG. 6  shows one embodiment of a method of constructing an IC package. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows one configuration of an embodiment in which a tester chip is contained within IC package  10 . In the embodiment shown, IC tiers  101 ,  102 ,  103  are stacked to create a stacked IC device. This is only one example of how the tiers  101 ,  102 ,  103  can be assembled. Note that while three tiers are shown, the concepts discussed herein can be used with any number of tiers, including a single tier. 
     IC package  10  contains a tester chip in tier  101  electrically connected to one or more chips in tier  102  by contacts  110 . The tester chip is the only occupant of the tier (i.e.,  101 ) in the embodiment of  FIG. 1 . Vias  111  are shown constructed in chips in tier  102  to facilitate heat transfer and/or electrical connections among the tiers  101 ,  102 ,  103 . Not shown in tiers  101 ,  102 ,  103 , are active circuits and other elements formed in chips in the different tiers using standard IC processes all now well-known to those skilled in the art. Contact  130  can be used, for example, to make electrical contact with components outside IC package  10 . As will be discussed, a program control  12  optionally can be used to input testing programming control data to IC package  10  to control tester chip  101  to test one or more circuits on chips in tier  102  and/or tier  103 . 
     The tester chip in tier  101  may be a universal tester chip, meaning that it can be used to test various different circuits and/or circuit combinations. The ‘universal’ feature is enabled through a standard I/O configuration. In one embodiment, the I/O configuration includes only a few pins, such as a ground pin, a positive supply voltage pin, an input pin and an output pin. In another embodiment, the I/O configuration includes a ground pin, a positive supply voltage pin, and individual pins for each circuit block being tested (e.g., memory I/O tester pin, logic tester pin, RF tester pin, and analog tester pin, etc.). Each circuit block could have its own separate tester read out pin. In another embodiment, a single tester read out pin indicates results of the testing. In one embodiment, the results are simply whether a good or bad test result occurred. In alternate embodiments, detailed information about the test results is provided via the read out pin(s). 
     If desired, programming for testing a specific circuit can be built into the tester chip in tier  101  during manufacture, or the tester chip in tier  101  can be built with an ability to receive instructions (programming) at a later time. These instructions can be added to the tester chip in tier  101  before the tester chip is added to an IC package  10  in tier  101  or after. The instructions can be made permanent or temporary, and can be contained in a memory which is also placed into the IC package  10 . The memory containing the instructions could be part of the tester chip in tier  101  or added to the tester chip in tier  101  just prior to introducing the tester chip into tier  101  of a specific IC package  10 . 
     Operation of IC package  10  is such that at some point in time, as will be discussed hereinafter, the tester chip in tier  101  is activated, either from an external stimulus, for example via contact  130  or program control  12 , to perform testing on some or all of the circuitry contained within IC package  10 . One or many test routines may be performed on all or some of the circuitry contained within IC package  10 . These test routines can be pre-programmed into the tester chip in tier  101  or may, as discussed, be contained in a separate memory. The instructions can be permanent or can last only for a period of time. 
     As discussed above, in some cases the operational circuitry that is being tested may be circuitry that partially resides on one tier and partially resides on one or more other tiers, all interconnected by contacts  110  and/or vias  111 . 
       FIG. 2  shows another configuration of an embodiment in which a tester chip  202  is contained within an IC package  20 . In this embodiment, tester chip  202  shares the same tier with chip  201  containing one or more operational circuits (not shown). A second tier contains operational chip  203 . 
       FIG. 3  shows another configuration of an embodiment in which tester chip  302  is contained within an IC package  30 . Operational chips, such as memory chip  304  along with another operational chip  303  (e.g., a processor, RF chip, etc.), share a tier with the tester chip  302 . Programming instructions could be contained within memory  304 . These instructions could be programmed into the memory either before the memory is positioned within the IC package  30  or thereafter. If the programming of the memory  304  occurs after the tester chip  302  is sealed within the IC package  30  then the test data can be supplied via contacts on the IC package  30  or via a wireless connection. This wireless connection can be, for example, RF, infrared, or any wireless protocol. The receiver for such wireless transmission can be built into one or more of the chips contained within the IC package  30 . Also contained in IC package  30  are operational chips  301  and  305 . 
       FIG. 4  shows an example of chips, such as operational chips  301  being manufactured as part of a wafer, such as wafer  40 . In some cases, a portion of each chip  301  can be tested while still part of the wafer. In other situations, such testing may not be feasible. 
       FIG. 5  shows wafer  50  on which are constructed dies of tester chip  302  which may be universal tester chips as discussed above. Each of these tester chips  302  is constructed the same regardless of which IC package the chip will actually become a part of. In one embodiment, each tester chip  302  can be identified as “belonging” to a particular IC package. In such a situation, if desired, the tester chip  302  can have loaded therein a test program unique to the identified IC package. In other situations, the tester chip  302  will be separated from the wafer  50  prior to any specific programming. In such a situation, as will be discussed, any desired unique programming will be added to the tester chip  302  at a later time. 
     It should be noted that while the tester chip  302  is shown as being constructed in conjunction with a wafer  50  of similar chips, the tester chip (or chips)  302  can be constructed on the same wafer  50  as the operational circuit chips  301 . 
       FIG. 6  shows one embodiment of a method  60  of constructing an IC package. Block  601  controls the selection of a die (or chip) that is to be incorporated into an IC package. The selected die can be pre-tested to the extent possible, but in many situations such pre-testing may not completely test the die for a variety of reasons. One of these reasons may be, as discussed, the fact that a complete operational circuit does not exist until two or more dies are stacked together in a stacked IC device and cooperatively interconnected, for example, in a timing path where a launching latch is on a different tier from a capturing latch in a pipeline stage. 
     Block  602  positions and interconnects the selected die into the IC package. Block  603  then determines if there are other dies to be added to the package. If so, the other dies are selected and positioned. When all the dies have been properly positioned, interconnected and/or stacked into the package, block  604  selects, positions, and interconnects a universal tester chip. Typically, the stacked IC device would be stacked tier by tier with operational and/or tester chips positioned on a tier and then another tier added. Thus, process  60 , or a portion thereof, can be repeated on a tier by tier basis if desired. 
     Block  605  determines if a test routine program should be loaded into the selected tester chip or into another memory that has been selected to be in the IC package. Such programming would convert the universal tester chip into a more specific tester chip arranged specifically to test the operational circuit chips in the IC package into which the tester chip is to be inserted. If so, then block  606  obtains and loads the proper test program. 
     Block  607  seals the stacked IC device within a self-contained package. Note that the tester chip, in one embodiment, may be sealed within the package and will remain within the package through the life of the package. In other embodiments, the tester chip is positioned in such a manner that it, or part of it, may be removed after testing. For example, if the tester chip were to be positioned on a top or bottom tier, then after testing the tier containing the tester chip could be removed if the test chip is the only chip on the tier, or only the test chip could be removed, if other chips exist on the tier. Removal is possible when the tester chip(s) were mounted at one end of the IC package. In one embodiment, the test chip is removable as a result of bonding with a temporary bond. In one example, a temporary bond is created by soldering the tester chip in place and then removing the tester chip by heating (de-soldering). Another example for a temporary bond uses Antistrophic conductive pastes with metal fillers. Yet another example includes a socketed connection. In a further example, the tester chip is aligned and held under pressure and heat during the testing operation and then removed after the testing operation. 
     Blocks  608  and  609  control the timing of the testing of the circuits under control of the associated tester chip in conjunction with any added programming. In some situations, external stimuli can be provided, as discussed above, to initiate and/or control the testing of the stacked IC device. 
     If testing is not to begin, as determined by blocks  608 , then block  610  determines if a test program or other stimulus is required. If not, testing is performed at a later time as controlled by block  612 . If block  610  determines that additional programs or stimuli are required then block  611  obtains the necessary programs and/or stimuli. Block  608  then again determines if it is time for testing to begin. 
     Note that process  60  shows that the tester chip is selected after the other chips are selected and positioned. This is but one embodiment and the tester chip can be selected at any time and positioned at any time in any desired tier of the IC device. 
     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. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.