Suppressed boron-penetration through surface-nitrided ultrathin oxide films prepared by fluorination and subsequent exposure to atomic nitrogen

Several percent of nitrogen was incorporated only near the top surfaces of thermally grown oxides, by surface fluorination at room temperature followed by an atomic nitrogen treatment at 550degreesC. The dependences of the nitrogen content and the thickness of the nitrided layer on the process condition were studied by angle-resolved X-ray photoelectron spectroscopy. A model of the nitridation process was also proposed. MOS capacitors with boron-doped polycrystalline silicon gates were fabricated using the nitrided ultrathin oxide. From the capacitance-voltage measurements we confirmed that the nitrided oxide would more effectively prevent boron penetration in comparison with the conventional oxide films. The proposed technique is a unique process for obtaining high-quality ultrathin dielectrics.