J. A. Shaw, C. H. McMahon, LSI Corporation, Fort Collins, CO; F. Beaudoin, IBM

Summary: A Dual Port SRAM Memory Built-in Self Test (MBIST) failure within an embedded Dual Port memory array was analyzed using Dynamic Laser Stimulation (DLS). This technique rapidly localized the failing area within the memory circuits. However from the MBIST results and the DLS localization signature it was not possible to identify with certainty if the failure was related to a write or read operation. In order to target specific sequences of the MBIST pattern during DLS, the laser output was modulated synchronously with the test pattern. To achieve this laser modulation an Electro-Optic Modulator (EOM) was used. Such a scheme allowed to stimulate only specific write or read operations of the MBIST pattern. The end result is a set of Time Resolved Dynamic Laser Stimulation (TR-DLS) maps obtained for each operation of the MBIST pattern. Those clearly identified that the read operation was failing and that the sense amp was the cause. The TR-DLS technique also provided different DLS signature between a Port AB read and a Port B read sequence.