We evaluated the silicon nitride (SiN) etching characteristics of Ar/O2/hydrofluorocarbon plasma. Ar/CH3F/O2 plasma achieved a high etching selectivity of SiN to SiO2 by increasing the oxygen flow rate. We also evaluated the dependence of SiN etching characteristics on SiN film density. A low-density film deposited at a low temperature of 200 °C (by plasma-enhanced CVD, PECVD) showed an 8–20% lower etching rate of SiN than a high-density film deposited at a high temperature of 780 °C (by low-pressure CVD, LPCVD) when we had a low RF bias of 30 W. This PECVD film might move the competitive balance to oxidation from fluorination, reducing the SiN etching rate. However, when we have a high RF bias of more than 50 W, the SiN etching rate is 2–15% higher in the PECVD film than in the LPCVD film. The etching rate of SiN at various densities depends on the balance between oxidation and ion bombardment.

The authors investigated the mechanisms of Si p+/n junction damage caused by N2/H2 plasma during organic implantation mask etching. The junction leakage current of a p+/n-well diode rose when the authors reduced the plasma-source power and increased the radio-frequency (RF) bias power, whereas it did not rise after they increased hydrogen ratio of the N2/H2 plasma gas. This indicates that ion energy and dose have a greater influence on junction damage than the density of hydrogen radicals does. Accordingly, the authors suggest that a high etching rate and low ion energy, which correspond to a high hydrogen ratio and low RF bias, are the best combination for low-damage organic block etching.