Origin of the Hydrogen/Deuterium (H/D) isotope effect of hot-electron degradation of MOS devices

In order to verify Van de Walle and Jackson's theory on the isotope effect of the Si-H/D bonds resistant to hot-electron excitation [Appl. Phys. Lett., 69, 2441 (1996)], we measured the Si-H, Si-D, and other vibrational modes in oxidized silicon wafers annealed in hydrogen and deuterium using Fourier Transform Infrared (FTIR) spectrometry. Our PTIR data suggest that the frequency for the Si-D bending mode at the SiO₂/Si interface is 490 cm ^-1. Our experimental data support Van de Walle and Jackson's theory with some modification. Their theory is correct for the experiments of breaking Si-H/D bonds using scanning tunneling microscope (STM) where no oxide is involved. In the SiO₂/Si case, the de-excitation of the Si-D bond may be due to the energy coupling from the Si-D bending mode to two vibrational modes; i.e., the Si-O TO mode and the Si-Si TO phonon mode. Van de Walle and Jackson only pointed out coupling to the Si-Si TO phonon mode. The strongest coupling might happen between the Si-D mode and the Si-O TO mode. Therefore, the oxide may play a crucial role in energy dissipation of the Si-D bond in metal-oxide-semiconductor (MOS) devices.