Study of the atomic models of three donorlike defects in silicon metal-oxide-semiconductor structures from their gate material and process dependencies

Abstract

The atomic models of the generation and annealing of three donorlike defects [the bulk compensating donor, the donorlike interface density-of-state (DOS) peak, and the positive turn-around charge] in silicon metal-oxide-semiconductor capacitors (MOSC) are investigated by studying their dependencies on the gate materials and process conditions. Starting thermal oxides used in this study include 1000 C dry oxides on 〈100〉 p-Si substrates and 750 C high-pressure steam oxides on 〈111〉 p-Si substrates. Gate materials include aluminum, gold, and LPCVD (low-pressure chemical-vapor-deposition) polycrystalline silicon (poly-Si) with several doping methods. The densities of these donors generated during avalanche electron injection in MOSC’s with boron in situ doped LPCVD poly-Si gates are smaller compared with those with aluminum gates. High temperature (>900 C) processes (diffusion or anneal) in dry inert gas after the poly-Si gate deposition inhibit the generation of all three donors. After the inhibition, the donor species can be reintroduced into the MOSC by replacing the poly-Si gate with metal gate using a wet etch process at room temperature, or by a post–aluminum-metallization anneal in water vapor at 400 C. All the experimental results are consistent with a proposed model based on hydrogen. This model consists of four steps: (1) The release of atomic hydrogen from SiO-H and Si-H in the bulk SiO2 and at the SiO2/Si interface, as well as from AlO-H and Al-H at the Al/SiO2 interface by ionizing radiation or energetic electrons or holes; (2) the migration of atomic hydrogen across the oxide, which involves multiple bond-breaking/diffusion/bond-forming processes; (3) the modification of the SiO2/Si interface which gives the buildup and reduction of the donorlike interface DOS peak and the positive turn-around charge; and (4) the formation of the electrically inactive B−H+ pair in the silicon surface space-charge layer.