Gate Oxide Thinning Limit Influenced by Gate Materials

N-type poly Si has no serious influence on thin oxides down to about 30 Å. For a boron-doped poly-Si gate, however, current increase characterized by negative gate bias is found. For an Mo gate, gate oxide surface layer of about 20 Å next to the gate are deteriorated. By minimizing boron diffusion from a boron-doped poly-Si and Mo penetration during Mo gate formation, both gates will be of practical use for thin gate oxide down to near 30 Å.