Tunneling leakage in Ge preamorphized shallow junctions

CMOS shallow junctions with depths less than 0.2 μm were fabricated using Ge preamorphization and rapid thermal annealing. A low bulk generation current (<1 nA/cm²) for both poly-gated and Al gated diodes was obtained by placing the extended end-of-range defects inside the heavily doped junction. However, gated diode characterization shows a large tunneling current component in addition to the bulk generation current when the surface is accumulated by the gate. By comparing preamorphized with nonpreamorphized junctions for both poly-gated and Al gated diodes, it is concluded that the tunneling effect is due to the presence of the midgap states within or near the depletion region at the surface of the junction edge. These midgap states are a result of the crystal damage associated with Ge preamorphization. PISCES simulations of this tunneling current show good agreement with the experimental results, which show that gate-induced drain leakage in n⁺ poly-gate PMOS devices at high drain voltages is strongly dependent on removal of junction implantation damage