Light nitrogen implant for preparing thin-gate oxides

We have implanted nitrogen (N/sup +/) into Si substrates before growing thin thermal oxides, and discovered that light N/sup +/ doses of 5×10/sup 13/-5×10/sup 14//cm² reduced the oxidation rates by 20-30%. High-resolution TEMs and multiangle ellipsometry were used to study the oxides. The TEM reveals a highly uniform transition from the crystalline Si to the amorphous SiO₂. With a fixed index of refraction at 1.458 for the ellipsometry, the two measurements gave identical oxide thickness between 25 and 144 /spl Aring/, in contrast to the previously suggested 1.7 for oxides thinner than 100 /spl Aring/. In addition, the oxidation retardation was accompanied with an improvement of the oxide uniformity across the 6-in Si wafers. We also present results of n-channel MOSFETs with coded channel lengths varying from 0.2 μm to 3 μm. The implications of these findings in terms of VLSI technologies and oxidation chemistry are discussed.