Chemical dry etching of silicon nitride in F2/Ar remote plasmas

In this work, chemical dry etching process of the silicon nitride layers using the F2/Ar remote plasmas generated by a toroidal-type remote plasma source was investigated by varying the total (F2 + Ar) gas flow, the F2/(F2 + Ar) flow ratio, the etching temperature and the working pressure. Under the current experimental condition, the chemical etching rates of the silicon nitride were significantly enhanced with increasing the F2 gas flow rate and F2/(F2 + Ar) flow ratio. Observed tendency in the etch rate was consistent with the variations of the optical emission intensity of the F radicals in the afterglow region of the remote plasma source and of the concentration of the emitted SiF4 reaction by-product molecules. The substrate temperature was the most influential process parameter in determining the etching rates. The etching rates of the silicon nitride layers were increased by a factor of ≅ 50, 109, and 114 for the F2 gas flow ratios of 29, 50, and 68%, respectively, as the substrate temperature increases from 25 to 350 °C.