US Patent 9190293 Even tungsten etch for high aspect ratio trenches

Methods of evenly etching tungsten liners from high aspect ratio trenches are described. The methods include ion bombardment of a patterned substrate having high aspect ratio trenches. The ion bombardment includes fluorine-containing ions and the ion bombardment may be stopped before breaking through the horizontal liner portion outside the trenches but near the opening of the trenches. The methods then include a remote plasma etch using plasma effluents formed from a fluorine-containing precursor. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents react with the tungsten. The plasmas effluents react with exposed surfaces and remove tungsten from outside the trenches and on the sidewalls of the trenches. The plasma effluents pass through an ion suppression element positioned between the remote plasma and the substrate processing region.