Rapid thermal nitridation of thin chromium films

Thin Cr films were nitrided during rapid thermal annealing for 3 min in NH3 between 500 and 850°C. Nitridation begins at 500°C and occurs in a layer-by-layer fashion, first forming Cr2N then CrN. At 550°C, Cr2N begins to nitride to CrN despite the existence of unreacted Cr, such that a CrN/Cr2N/Cr structure exists. At 650°C, no unreacted Cr remains and the layer consists of CrN on Cr2N; this configuration remains at 700°C although CrN grew at the expense of Cr2N. At 750°C, the reaction is complete, forming CrN. Oxygen accumulates in front of the growing nitrides until the temperature is high enough to allow redistribution. This occurs at lower temperatures in Cr2N than in CrN, which may be correlated to the enhanced oxidation resistance of CrN. Phase identification was performed by X-ray diffraction, composition determination by Rutherford backscattering spectrometry, and elemental profiling by secondary ion mass spectrometry. Ion beam resonances of the forms 16O(α,α)16O and 14N(α,α)14N provided additional elemental profiling. Vickers microhardness was measured and was observed to increase sharply once a surface nitride had formed, then remained nearly constant upon further annealing.