Method of forming barrier layer

A method of forming a barrier layer comprising:

• (a) providing a substrate having a cobalt silicide and a plug hole exposing the cobalt silicide;
• (b) performing a chemical vapor deposition (CVD) process for forming a Ti/TiN film, functioning as the barrier layer, onto the cobalt silicide and inner walls of the plug hole;
• (c) performing an examination procedure, and if particles are detected in the barrier layer, then performing step (d);
• and
• (d) performing a rework procedure comprising:
• performing a wet etching process to remove the barrier layer, the wet etching process being implemented with an acid solution comprising phosphoric acid (H3PO4), nitric acid (HNO3), acetic acid (CH3COOH), and water (H2O), wherein the ratio of phosphoric acid, nitric acid, acetic acid, and water in the acid solution is between (38–41):(1–1.5):(1.8–2.1):(2.8–3.2);
• scrubbing the substrate with a scrubber machine for removing the particles;
• rinsing the substrate with a cleaning solution;
• and
• performing another CVD process for forming another Ti/TiN film onto the cobalt silicide and the inner walls of the plug hole.