EFFECTS OF ACTIVE HYDROGEN ON THE STRESS-RELAXATION OF AMORPHOUS SINX-H FILMS

Amorphous SiNx:H (alpha-SiNx:H) films were deposited at 300 degrees C by plasma-enhanced chemical vapor deposition using SiH4-NH3-H-2 mixtures. The stress, vibrational absorption, buffered HF (BHF) etch rate, and breakdown strength were investigated as a function of the gas volume ratio [H-2]/[SiH4](=R(H)) and rf power. The [NH3]/[SiH4] ratio was maintained at 10, in which nitride films having a near-stoichiometric composition can be obtained. The measured stress for these films was intrinsic stress. It was suggested that the stress is relaxed by forming Si-NH-Si bonds instead of N-Si-3 bonds. An increase in both R(H) and rf power values was found to decrease the stress and BHF etch rate and increase the breakdown strength. A change in the bonding structure with increasing R(H) and rf power is examined in terms of a thermodynamic equilibrium reaction, and it was suggested that increased H-* radicals and/or H+ ions play an active role in relaxing the stress through the structural change.