Investigation of particle-induced timing sensitivity in one-megabit DRAMs

The understanding of failure mechanisms causing yield loss continues to be important when guaranteeing the reliability of a device to the customer. As vertical integration has increased and the horizontal geometries decreased in VLSI devices, the investigation of failure mechanisms has become increasingly more difficult. It has become necessary to incorporate more advanced equipment and techniques in the analysis of these failures. This investigation is an effort to understand the physical defect(s) related to a timing parameter sensitivity of a one megabit DRAM. These defects are primarily observed on repaired devices which have degraded such that they induce failures beyond the area of repair. This paper will provide an explanation of how the defect can effect the internal operation of the device and how this defect can degrade with time or be accelerated with reliability stressing. Advanced equipment such as a Focused Ion Beam system (FIB) and a Transmission Electron Microscope (TEM) were essential for precise milling, high magnification imaging, and elemental analysis capabilities. An advanced technique called SAXTEM (specific area TEM cross section) was also necessary in the analysis of the failure mechanism. Finally, corrective actions which will prevent the occurrence of this problem will be specified.