Light nitrogen implant for preparing thin-gate oxides

We have implanted nitrogen (N+) into Si substrates before growing thin thermal oxides, and discovered that light N+ doses of 5 x 10(13)-5 x 10(14)/cm(2) reduced the oxidation rates by 20-30%. High-resolution TEM's 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 Angstrom, in contrast to the previously suggested 1.7 for oxides thinner than 100 Angstrom. 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 MOSFET's with coded channel lengths varying from 0.2 mu m to 3 mu m. The implications of these findings in terms of VLSI technologies and oxidation chemistry are discussed.