Plasma processing methods that provide for conformal etching of silicon nitride while also providing selectivity to another layer are described. In one embodiment, an etch is provided that utilizes gases which include fluorine, nitrogen, and oxygen, for example a gas mixture of SF6, N2 and O2 gases. Specifically, a plasma etch utilizing SF6, N2 and O2 gases at high pressure with no bias is provided. The process accelerates silicon nitride etching by chemical reactions of [NO]x molecules from the plasma and [N] atoms from silicon nitride film. The etch provides a conformal (isotropic) etch that is selective to other materials such as silicon and silicon oxides (for example, but not limited to, silicon dioxide).