Effects of active hydrogen on the stress relaxation of amorphous SiNx:H films

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Abstract
Amorphous SiNx:H (a‐SiNx:H) films were deposited at 300 °C by plasma‐enhanced chemical vapor deposition using SiH4–NH3–H2 mixtures. The stress, vibrational absorption, buffered HF (BHF) etch rate, and breakdown strength were investigated as a function of the gas volume ratio [H2]/[SiH4](=RH) 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—Si3 bonds. An increase in both RH 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 RH 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.