Various methods for selectively etching metal-containing materials (such as, for example, metal nitrides, which can include, for example, titanium nitride) relative to one or more of silicon, silicon dioxide, silicon nitride, and doped silicon oxides in high aspect ratio structures with high etch rates. The etching can utilize hydrogen peroxide in combination with ozone, ammonium hydroxide, tetra-methyl ammonium hydroxide, hydrochloric acid and/or a persulfate. The invention can also utilize ozone in combination with hydrogen peroxide, and/or in combination with one or more of ammonium hydroxide, tetra-methyl ammonium hydroxide and a persulfate. The invention can also utilize ozone, hydrogen peroxide and HCl, with or without persulfate. The invention can also utilize hydrogen peroxide and a phosphate, either alone, or in combination with a persulfate.