Adsorption and thermal decomposition of N₂H₄ and CH₃N₂H₃ on Si(111)7 × 7

The adsorption and thermal decomposition of N₂H₄ and CH₃N₂H₃ on Si(111)7 × 7 were investigated using XPS, UPS and HREELS in the 120-1350 K surface temperature range. Both molecules were partially dissociated into N₂H_x or CH₃N₂H_x (x=2, 3) species with the N-N bond parallel or nearly parallel to the surface as they adsorbed on the surface at 120 K, especially at lower dosages (e.g., < 0.2 L) and more so for N₂H₄ than CH₃N₂H₃. This was evidenced by the appearance of the Si-H vibration at 255 meV in the HREEL spectra and by the relatively larger FWHMs of the N_1s XPS and the n⁺, n^- molecular UPS peaks. When a ∼0.4 L N₂H₄ or CH₃N₂H₃ dosed sample was annealed to ∼500 K, significant desorption of the molecules occurred as well as further dissociation of the NH bonds. Above ∼600 K the NN bond began to break for both molecules. At ∼730 K, the CN bond dissociated to form CH_x on the surface in the case of CH₃N₂H₃. Further annealing of the sample caused complete cracking of the N-H and C-H bonds until Si₃N₄ or a mixture of Si-nitride and Si-carbide were formed for N₂H₄ or CH₃N₂H₃, respectively.