DIAGNOSIS OF NMOS DRAM FUNCTIONAL PERFORMANCE AS AFFECTED BY A PICOSECOND DYE-LASER

A picosecond pulsed dye laser beam was at selected wavelengths successfully used to simulate heavy-ion single-event effects (SEEs) in negative channel metal-oxide semiconductor dynamic random access memories (NMOS DRAMs). A DRAM was used to develop the test technique because bit-mapping capability and previous heavy-ion upset data were available. Other investigators have used Nd:Yag lasers to correlate laser and heavy-ion data for devices characterized by prompt charge collection, which is controlled by charge carrier density in the immediate vicinity of a depletion region. However, the present analysis is the first to establish such a correlation for devices, such as the NMOS DRAM, where charge collection is dominated by long-range diffusion, which is controlled by carrier density at remote distances from a depletion region. In the latter case, penetration depth is an important parameter and is included in the present analysis. A single-pulse picosecond dye laser beam (1.5-mu-m dia.) focused onto a single cell component can upset a single memory cell. In addition, clusters of memory cell upsets (multiple errors) were observed when the laser energy was increased above the threshold energy. The multiple errors were analyzed as a function of the bias voltage and total energy of a single pulse. A diffusion model to distinguish the multiple upsets from the laser-induced charge agreed well with previously reported heavy ion data. This correlation is one more step toward the goal of using a picosecond dye laser for SEE investigations.