Abstract:
A system is disclosed for evaluating relevant data across independent test sequences and providing a consumable output to give a tester an accurate account of the test data. A method for reporting the results of the test processes includes several steps. First, repair, trending, characterization, timing and engineering data for two separate test sequences are read. Next, the data is compared. Also, an analytical report of the test data comparisons is assembled and output.

Description:
This application is a continuation of U.S. Ser. No. 08/937,626, filed Sep. 26, 1997, now U.S. Pat. No. 6,070,131. 
    
    
     BACKGROUND 
     The present invention relates to systems for testing a manufacturing of an article, or the like, such as a memory device. In particular, the present invention relates to a system for evaluating and comparing data from two manufacturing tests performed during the manufacture of memory devices and then providing a consumable output to identify the relation between the data from the manufacturing tests. 
     Exercising a semiconductor-type memory device during manufacturing for testing purposes is known. Such exercising can include running all ones or zeros through the device and then recording the output, or running checkerboard patterns, digit stripes, double digit stripes, or other pattern mechanisms or ways of writing to a device, and comparing the actual output to an expected output for a given set of conditions such as supply and substrate voltage, or conditions with regard to timing, etc. 
     The results of such exercises are evaluated to provide information on the device and the testing process. Outputs of such tests are collected and a determination made as to whether the device had passed or failed. Data accumulated from the tests is logged, but each engineer or tester who wants to look at the data in order to make comparisons must go through the data by hand. If a change is to be made to the testing process, testers run a second sequence of tests on the device previously tested. Such test sequences could be used for, for example, to catch a new error mechanism or to eliminate a redundant test. To date, this evaluation has been done by hand. 
     Calculating repair solutions as a function of the testing process is also known. In the case of repair solutions, performed on a per die basis, this system was only feasible as long as the number of dice remained relatively small. As die sizes decreased, and as wafer sizes increased, thus increasing the number of dice, the number of repair solutions, increased geometrically. Consequently, the manual evaluation of data became overly burdensome. Even when the evaluation of test results became automated, the sheer amount of data that a test could provide prevented a thorough evaluation of all of the test results. For example, some manufacturers opted to analyze the data only after the tests were performed, and then only consider summaries of test data. 
     What is needed is a mechanism to evaluate all relevant data across independent test procedures and to provide a consumable output to give the tester an accurate account of the test results. In addition, what is needed is a way of present repair solutions which allow a facile comparison of different approach to generating the solutions. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system for evaluating relevant data across independent test sequences and providing a consumable output to give a tester an accurate account of the test data. A method for reporting the results of the test processes includes several steps. First, repair, trending, characterization, timing and engineering data for two separate test sequences are read. Next, the data is compared. Also, an analytical report of the test data comparisons is assembled and output. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a functional block diagram of a system constructed in accordance with the present invention. 
     FIG. 2 shows a process flow chart embodying features of the present invention. 
     FIG. 3 shows a detail of a feature of the flow chart of FIG.  2 . 
     FIG. 4 shows an example of an output in accordance with the process flow chart of FIGS. 9A-9B. 
     FIG. 5 shows an example of an output in accordance with the process flow chart of FIGS. 9A-9B. 
     FIG. 6 shows an example of an output in accordance with the process flow chart of FIGS. 9A-9B. 
     FIG. 7 shows an example of an output in accordance with the process flow chart of FIGS. 9A-9B. 
     FIG. 8 shows an example of an output in accordance with the process flow chart of FIGS. 9A-9B. 
     FIGS. 9A-9B show a particular example of the process flow chart shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a functional block diagram of a system  10  constructed in accordance with the present invention. System  10  includes a processing unit  12 , such as a computer, operably coupled to a testing device  14 , such as a memory tester, voltmeter, or the like. The testing device  14  is suitable for operating on a test subject matter  16  which may include a memory device, wafer, or die. The processing unit  12  is connected to an output mechanism  18  such as a printer, display, or the like. In operation, the testing device  14  accesses the test subject matter  16  in a predetermined manner and provides an input to the processing unit  12 . The processing unit  12  processes the data received from two separate tests on the subject matter  16  and then, through the output mechanism  18 , provides a consumable output to allow the tester to identify relationship between data sets. 
     FIG. 2 shows a process flow chart embodying features of the present invention. Specifically, FIG. 2 shows a general overview of the method of comparing the test data and providing a consumable output. To begin, at  20  all repair, trending, characterization, timing and engineering data are read for two separate testing processes of the subject matter. For example, datum specific to an individual die is related to that die using the lot, wafer, x-y die coordinates, and wafer size. Other data, such as probe time, are related only to the wafer. 
     The next step is, at  22 , to make comparisons of all the test data  22 . The comparison is subject to the specific data being compared. For example, a wafer probe time comparison would simply be a subtraction of the times. In the case of a repair solution, the comparison is done by matching the address of each solution with the other solutions to try to find a match. The number of matches and non matches are counted for use in calculating a correlation score. After the comparisons are complete, the next step is, at  24 , to present characterize the data compared at  22  in charts and forms. The last step of the illustrated process includes displaying, at  26 , the result of this characterization. 
     FIG. 3 shows one embodiment of a characterization which can be used in step  24  of FIG.  2 . Step  24  can include creating map overlays of the test data  28 , creating trend, characterization, engineering and timing difference tables  30 , creating a repair Venn diagram and calculating a correlation score percentage  32 , and creating a diagonal repair binning chart  34 . 
     In the case of repair solutions, for example, the comparison output is provided in three different formats to provide more extensive information about the correlation. First, a Venn diagram showing the set relationship between the two sets of solutions is presented, along with three scores for determining the successfulness of correlation. Calculation of the three scores is described in the context of FIG. 7 below. Second, a chart is provided to show how many repairs are made for each test within each testing process in order to help determine the failure relationship between tests. For example, if a test were to be removed, it would be possible to view a location of the repair solution, i.e. if there were 20 repair solutions at a given test during a first testing process and the given test was removed for a second testing process, 10 solutions may be indicated on the different test and the remaining 10 solutions might not be indicated at all. Finally, a list of all repair solution differences can be reported for each die. Other comparison information can be presented in the form of a map overlay produced through a program such as the VAX-based program “LMR”. 
     FIGS. 4-8 show comparison outputs in accordance with the present invention for a particular example set forth below. By way of background for the present example, final die testing reports that there is a 1% failure due to a test on a particular group of wafers. During probing of a wafer, a first test sequence labeled BASE STEP, is run with standard procedures and error data with respect to the wafer and its elements are recorded. After completion of the BASE STEP test sequence, the timing or voltage Vcc is adjusted in order to provide a more stringent test of the wafer. A second test sequence, labeled COMPARISON STEP or CORRELATION STEP, is run on the same subject matter and a second set of error data is recorded and calculated. Subsequently, the error solutions are compared, and matches and correlations between the first test and second test are identified as a usable output. 
     FIG. 4 shows an example of a characterization table labeled as an engineering register summary  40 . The values listed in the table represent values that are averages taken on samples of die across a wafer, e.g. five die per wafer, from data stored as part of each run of the test. A plurality of registers are listed in the first column  42 . Such tests are now known in the art involve measuring different timings and voltages, etc. The second column contains values obtained from a first test, i.e. the BASE test  44 . The third column contains values obtained from a second test, i.e. the COMPARISON test  16 . The fourth column, or delta column, represents the differences between these two tests within the register  48 . 
     FIG. 5 shows an example of a trending table which represent an average of all die  50 , as opposed to just samples of die as taken above. The first column again represents a plurality of registers  52 . The second column represents the values obtained from the first test sequence  54 . The third column represents values obtained from the second test sequence  56 . The last column represents the difference between the two values in a given register, or the delta  58 . 
     FIG. 6 shows an example of a repair summary  60 . The wafer-total statistics are output on the repair summary. The totals column  62  represents a particular set of data. The values for a given set are again set out in columns according to the first test  64 , the second test  66  and the delta  68 . 
     FIG. 7 shows an example of a Venn Diagram of repair solution statistics  70 . The sets represent data collected in a particular test. In the present example a first set  72  corresponds with the first test sequence, and a second set  74  corresponds with the second test sequence. Common solutions are indicated in the intersection of the sets  76 . The first test, or base step, unique solutions are indicated at  77 . A unique solution is one that was proposed in one test but not in the other. Unique solutions are indicated at  79 . 
     FIG. 8 shows an example of a diagonal table which indicates the location of repair solutions for two successive tests  80 . The vertical axis represents solutions obtained in the first test  81 . The horizontal axis represents solutions obtained in the second test  82 . The values obtained in group  83  represent the location of solutions. The values in group  84  represent unmatched repairs. With this diagram, one skilled in the art can determine a particular fail mechanism that cannot typically be detected with merely a “pass” or “fail” output based on results after testing is completed. 
     A tester analyzing the outputs  40 ,  50 ,  60 ,  70 ,  80  of the present example after the above-described modification can determine several pieces of information. In the hypothetical example set forth, the tester may expect to see the number of repair solutions for a given test to increase for the second test sequence. Additionally, the tester can expect to capture the same amount of repair solutions for the first test sequence as for the second test sequence. Therefore, the tester can confirm this hypothesis with an examination that the first test sequence has a minimal number of unique repair solutions from that of the second test sequence. Additionally, for other tests, the tester may verify that the differences between the first test and the second test are minimal to ensure that the test procedures were performed similarly under similar conditions so as to add validity to the test comparisons. 
     Once such information is analyzed, the tester can determine how to proceed. For example, if the particular test failed by about 1% for the second test sequence with a more stringent timing adjustment or voltage adjustment, then it can be determined that the proper test modification has been found with the second test sequence. Thus, the second test sequence can be used with a certain level of confidence that the 1% final die failure will be reduced. If, however, the particular test did not fail by 1%, the tester can adjust the test parameter, e.g. timing or voltage, again until noting about a 1% additional solution repair count (for a given test) increase relative to the first test. 
     Additional uses of the present invention are contemplated. Among these include an example where a probe card replacement is made for a probe machine, and the functionality of the probe machine must again be confirmed. A comparison of repair solutions pre-replacement against. post-replacement can be determined with a diagonal table  80  such as that indicated in FIG.  8 . Test personnel can check the table for common repair solution converts between “before” and “after” probe card replacement tests of a common wafer. Additionally, the tester can consult the trend tables  40 ,  50 , and Venn diagrams  80  for additional information. If a discrepancy is discovered, for example, the “new” probe card can be replaced or repaired. 
     Similarly, the above method can be used to test changes to the test sequence. For example, if a particular test is removed from the second test sequence, the data can be analyzed to determine to where the repair solution has moved to a different bin. In other words, the second test sequence can be used to determine if the remaining tests capture the errors previously captured by the eliminated test. Finally, if a bad device is discovered on the back end, the device can be run through a sequence of different front end tests and identify which test or tests capture the error and might be available for additions to the production test flow. 
     FIGS. 9A-9B show a flow chart setting out in more detail the steps shown in FIG. 2, and is described with reference to the outputs shown in FIGS. 4-8. The first step includes an initialization of the system processes  110 . The system requests a user input such as lot, wafer or wafers, step, and output formatting  112 . The system then checks to see if the user input is valid  114 , and if not, returns to step  112 . 
     The first test sequence is performed  120 . Step  122  is to accumulate repair data from input selections. Step  124  is to accumulate lot, wafer and die level binning data. Step  126  is to accumulate trending, characterization, timing and engineering data. Subsequently, the second test sequence is performed  130 . Step  132  is to accumulate repair data from input selections. Step  134  is to accumulate lot, wafer and die level binning data. Step  136  is to accumulate trending, characterization, timing and engineering data. 
     Next, a sequence of calculations and comparisons are performed on the collected results from the two test sequences  140 . Repair difference data are calculated  142 . Die, wafer and lot level binning differences are calculated  144 . Repair statistics are calculated  146 . Also, trending, characterization, and other register data are calculated  148 . 
     Subsequently, outputs are created  150 . Creating the outputs includes creating map overlays  151 , creating register difference tables  152 , creating Venn diagrams  153 , creating diagonal repair/binning charts  154 , and creating binning summaries  155 . Finally, as illustrated, output data is formatted and written  160 . 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.