Modeling and characterization of n⁺- and p⁺-polysilicon-gated ultra-thin oxides (21-26 angstroms)

The electrical characteristics of n+- and p+-polysilicon-gated ultra-thin-oxide capacitors (21-26 angstroms) were studied theoretically and experimentally in terms of oxide thickness determination, polysilicon depletion effect, boron penetration, and gate tunneling current. A scheme based on a fully quantum-mechanical model accurately extracts the oxide thickness to within 1 angstrom of the value measured by ellipsometry. N2O-grown oxides scaled down to 21 angstroms exhibit a high resistance to boron penetration with good thickness control. It is projected that thin oxides can be scaled down to 20 angstroms while still maintaining a sufficiently low chip standby power consumption (<0.1 W per chip) due to direct tunneling current. However, transconductance degradation due to polysilicon depletion effect becomes more severe for thinner oxides.