Method of chemical mechanical polishing a semiconductor substrate

A method of polishing a substrate, comprising:

• providing the substrate, wherein the substrate has an exposed titanium nitride (TiN) feature and an exposed titanium (Ti) feature;
• providing a chemical mechanical polishing composition, comprising, as initial components:
• water;
• an oxidizing agent;
• a linear polyalkylenimine polymer;
• a colloidal silica abrasive having a positive surface charge;
• a carboxylic acid;
• a source of ferric ions;
• and,
• an optional pH adjusting agent;
• wherein the chemical mechanical polishing composition has a pH of 1 to 4;
• providing a chemical mechanical polishing pad, having a polishing surface;
• creating dynamic contact at an interface between the chemical mechanical polishing pad and the substrate;
• and
• dispensing the chemical mechanical polishing composition onto the polishing surface of the chemical mechanical polishing pad at or near the interface between the chemical mechanical polishing pad and the substrate;
• wherein at least some of the exposed titanium nitride (TiN) feature and at least some of the exposed titanium (Ti) feature are polished away from the substrate;
• and wherein the chemical mechanical polishing composition provided has a removal rate selectivity between the exposed titanium nitride (TiN) feature and the exposed titanium (Ti) feature is ≥100.