Optimization of gate dopant concentration and microstructure for improved electrical and reliability characteristics of ultrathin oxides and N2O oxynitrides

We study the effects of gate dopant species (boron, arsenic, or phosphorous) concentration (1×1019 cm−3–1×1021 cm−3) and microstructure (as-deposited amorphous or polycrystalline silicon gate) on the electrical and reliability characteristics of ultrathin oxides and N2O oxynitrides (60 Å). In order to minimize polysilicon depletion, a high gate dopant concentration is desirable. However, for devices with BF2 doped gates, it is found that because of boron penetration through the thin gate oxide, device characteristics degrade as the gate doping concentration increases, thus an intermediate gate doping must be chosen. In contrast, samples with arsenic and phosphorous doped gates show no degradation as the doping level increases. Optimization of gate microstructure for N2O and O2 dielectrics is also discussed.