Suppressing the memory state of floating gate transistors with repeated femtosecond laser backside irradiations

摘要

We demonstrate that infrared femtosecond laser pulses with intensity above the two-photon ioniza-tion threshold of crystalline silicon induce charge transport through the tunnel oxide in floating gate Metal-Oxide-Semiconductor transistor devices. With repeated irradiations of Flash memory cells, we show how the laser-produced free-electrons naturally redistribute on both sides of the tun-nel oxide until the electric field of the transistor is suppressed. This ability enables us to determine in a nondestructive, rapid and contactless way the flat band and the neutral threshold voltages of the tested device. The physical mechanisms including nonlinear ionization, quantum tunneling of free-carriers, and flattening of the band diagram are discussed for interpreting the experiments. The possibility to control the carriers in memory transistors with ultrashort pulses holds promises for fast and remote device analyses (reliability, security, and defectivity) and for considerable develop-ments in the growing field of ultrafast microelectronics.