Characteristics of TaSi_xN_y thin films as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices

摘要

Reactively sputtered TaSi_xN_y films have been investigated as gate electrodes for dual gate Si-complementary metal-oxide-semiconductor devices. The as-deposited TaSi_xN_y films were amorphous over a wide range of compositions. After annealing at 1000℃, Ta_(30)Si_(33)N_(37) film became crystalline, however Ta_(26)Si_(28)N_(52) film remained amorphous. The x-ray photoelectron spectroscopy shows a significant increase of Si-N bonding in the TaSi_xN_y films with increasing N content. The presence of Si-N bonds is attributed to cause the amorphous nature of the high N containing TaSi_xN_y films. The work functions of TaSi_xN_y films were extracted by capacitance-voltage analysis. The work function values for TaSi_xN_y films with varying N contents range from 4.26 to 4.35 eV after forming gas annealing at 400℃ for 30 min, suggesting that TaSi_xN_y films have work functions appropriate for n-type metal-oxide-semiconductor devices. However, it was observed, after 1000℃ anneals, that the work function of TaSi_xN_y films increased to ～4.8 eV. We believe that the mechanism that causes the work function to increase is the formation of a Ta-disilicide layer at the interface of the electrode and the dielectric. Current-voltage characteristics of the TaSi_xN_y gates showed lower gate leakage compared to the TaSi_x gates, due to the retarding formation of an interface layer in the TaSi_xN_y/SiO_2/p-Si structures.