Identification of Yield Limiting Defects in a 0.5 Micron, Shallow Trench Isolation Technology

During the development and qualification of a radiation-hardened, 0.5 μm shallow trench isolation technology, several yield-limiting defects were observed. The 256K (32K x 8) static-random access memories (SRAMs) used as a technology characterization vehicle had elevated power supply current during wafer probe testing. Many of the die sites were functional, but exhibited quiescent power supply current (I_DDQ) in excess of 100 μA, the present limit for this particular SRAM. Initial electrical analysis indicated that many of the die sites exhibited unstable I_DDQ that fluctuated rapidly. We refer to this condition as “jitter.” The I_DDQ jitter appeared to be independent of temperature and predominately associated with the larger 256K SRAMs and not as prevalent in the 16K SRAMs (on the same reticle set). The root cause of failure was found to be two major processing problems: salicide bridging and stress-induced dislocations in the silicon island.