Analyzing device for saving semiconductor memory failures
First Claim
1. An analyzing device for saving memory failures, comprising:
- address generating means for sequentially generating column and row addresses in pairs;
a failure analysis memory, sequentially supplied with the result of a logical comparison for each memory cell of a memory under test, for storing a data "1" at an address thereof specified by one of said column and row address pairs when said result of comparison is a signal representing a disagreement between data supplied to said memory under test and data read out therefrom, said failure analysis memory performing a read modify write operation, said memory under test having spare lines which are used as substitutes for address lines which are determined to be failing;
an inhibit gate, supplied with said data "1" read out of said failure analysis memory, as an inhibit signal, and said result of the comparison for inhibiting said result of comparison from passing therethrough when a "1" is read out of said failure analysis memory and supplied thereto during said read modify write operation of said failure analysis memory, thereby inhibiting from passing therethrough a second and subsequent disagreement signals detected from the same memory cell of said memory under test;
a column address fail count memory, supplied, as an address, with the same column address as supplied to said failure analysis memory simultaneously therewith, for performing a read modify write operation each time said disagreement signal is applied thereto as an enable signal from said inhibit gate;
first arithmetic means for adding a "1" to data read out of said column address fail count memory during said read-modify-write operation thereof and providing the result of said addition to said column address fail count memory to be written thereinto as a count value during said read modify write operation, whereby a count value stored at each address of said column address fail count memory is updated in accordance with the number of defective cells on the corresponding column address line of said memory under test;
a row address fail count memory, supplied, as an address, with the same row address as supplied to said failure analysis memory simultaneously therewith, for performing a read modify write operation each time said disagreement signal is applied thereto as an enable signal from said inhibit gate;
second arithmetic means for adding a "1" to data read out of said row address fail count memory during said read-modify-write operation thereof and providing the result of said addition to said row address fail count memory to be written thereinto as a count value during said read modify write operation, whereby a count value stored at each address of said row address fail count memory is updated in accordance with the number of defective cells on the corresponding row address line of said memory under test;
fail counting means for counting the number of said enable signals outputted from said inhibit gate; and
control means for controlling operations of said failure analysis memory, said column address fail count memory, said row address fail count memory and said fail counting means as well as operating said failure analysis memory, said column address fail count memory, said row address fail count memory and said fail counting means simultaneously during a read modify write mode for completing the counting operation of defective cells concurrently with the end of the test for said memory under test.
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Abstract
A failure analysis of a semiconductor memory compares data written into and out of each cell of the semiconductor memory. When there is a disagreement, a "1" is written into a failure analysis memory. A disagreement signal is applied as a write command to column and row address fail count memories and is counted by a fail counter. The column address and row address fail count memories receive the column and row addresses, respectively. When the write command is applied to the column and row address fail count memories, the number of defective cells is read out of the memory addresses by a read modify write operation. A 1 is added by column and row adders to the number of defective cells read out, and the results are written into the column and row address fail count memories. The number of defective cells is read out of the column address fail count memory and compared with a number of row spare lines of the memory under test. When the former is greater than the latter, the column address is decided as a failing address line, is counted by a failing address line counter and is written into a failing address memory. The row address is sequentially changed, beginning with a 0, at each failing column address when a "1" is read out of the failure analysis memory. The contents of the memories are each rewritten by subtracting a 1 therefrom and the fail counter is decremented by one.
46 Citations
14 Claims
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1. An analyzing device for saving memory failures, comprising:
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address generating means for sequentially generating column and row addresses in pairs; a failure analysis memory, sequentially supplied with the result of a logical comparison for each memory cell of a memory under test, for storing a data "1" at an address thereof specified by one of said column and row address pairs when said result of comparison is a signal representing a disagreement between data supplied to said memory under test and data read out therefrom, said failure analysis memory performing a read modify write operation, said memory under test having spare lines which are used as substitutes for address lines which are determined to be failing; an inhibit gate, supplied with said data "1" read out of said failure analysis memory, as an inhibit signal, and said result of the comparison for inhibiting said result of comparison from passing therethrough when a "1" is read out of said failure analysis memory and supplied thereto during said read modify write operation of said failure analysis memory, thereby inhibiting from passing therethrough a second and subsequent disagreement signals detected from the same memory cell of said memory under test; a column address fail count memory, supplied, as an address, with the same column address as supplied to said failure analysis memory simultaneously therewith, for performing a read modify write operation each time said disagreement signal is applied thereto as an enable signal from said inhibit gate; first arithmetic means for adding a "1" to data read out of said column address fail count memory during said read-modify-write operation thereof and providing the result of said addition to said column address fail count memory to be written thereinto as a count value during said read modify write operation, whereby a count value stored at each address of said column address fail count memory is updated in accordance with the number of defective cells on the corresponding column address line of said memory under test; a row address fail count memory, supplied, as an address, with the same row address as supplied to said failure analysis memory simultaneously therewith, for performing a read modify write operation each time said disagreement signal is applied thereto as an enable signal from said inhibit gate; second arithmetic means for adding a "1" to data read out of said row address fail count memory during said read-modify-write operation thereof and providing the result of said addition to said row address fail count memory to be written thereinto as a count value during said read modify write operation, whereby a count value stored at each address of said row address fail count memory is updated in accordance with the number of defective cells on the corresponding row address line of said memory under test; fail counting means for counting the number of said enable signals outputted from said inhibit gate; and control means for controlling operations of said failure analysis memory, said column address fail count memory, said row address fail count memory and said fail counting means as well as operating said failure analysis memory, said column address fail count memory, said row address fail count memory and said fail counting means simultaneously during a read modify write mode for completing the counting operation of defective cells concurrently with the end of the test for said memory under test. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An analyzing device for saving memory failures, comprising:
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address generating means for sequentially generating column and row addresses in pairs; a failure analysis memory supplied with the result of a logical comparison for each memory cell of a memory under test specified by each of said column and row address pairs supplied thereto, for storing data "1" at an address thereof specified by one of said column and row address pairs when said result of the comparison is a signal representing a disagreement between data supplied to said memory under test and data read out therefrom, said memory under test having spare lines which are used as substitutes for address lines which are determined to be failing; memory read out means for sequentially reading out the results of the logical comparison stored in said failure analysis memory by applying said column and row address pairs from said address generating means to said failure analysis memory after said failure analysis memory has stored all the results of the logical comparison; a column address fail count memory, supplied, as an address, with the same column address as supplied to said failure analysis memory for read out thereof simultaneously therewith, for performing a read modify write operation each time a "1" read out of said failure analysis memory is applied thereto as an enable signal; first arithmetic means for adding a "1" to data read out of said column address fail count memory during said read-modify-write operation thereof and providing the result of said addition to said column address fail count memory to be written thereinto as a count value during said read modify write operation, whereby a count value stored at each address of said column address fail count memory is updated in accordance with the number of defective cells on the corresponding column address line of said memory under test; a row address fail count memory, supplied, as an address, with the same row address as supplied to said failure analysis memory for read out thereof simultaneously therewith, for performing a read modify write operation each time a "1" read out of said failure analysis memory is applied thereto as an enable signal; second arithmetic means for adding a "1" to data read out from said row address fail count memory during said read-modify-write operation thereof and providing the result of said addition to said row address fail count memory to be written thereinto as a count value during said read modify write operation, whereby a count value stored at each address of said row address fail count memory is updated in accordance with the number of defective cells on the corresponding row address line of said memory under test; fail counting means for counting the number of said enable signals read out from said failure analysis memory; and control means for controlling operations of said failure analysis memory, said column address fail count memory, said row address fail count memory and said fail counting means as well as operating said column address fail count memory, said row address fail count memory and said fail counting means simultaneously in a read modify write mode so that the number of defective cells on the row address lines and the total number of defective cells can be counted at the same time by only one scanning of said failure analysis memory. - View Dependent Claims (9, 10, 11, 12, 13, 14)
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Specification