Method of forming barrier layer

1. 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 (H 3 PO 4 ), nitric acid (HNO 3 ), acetic acid (CH 3 COOH), and water (H 2 O), 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.

2. The method of claim 1 wherein the cleaning solution is a sulfuric acid (H 2 SO 4 ) solution.

3. The method of claim 1 wherein the examination procedure is performed for detecting the particles that influence electrical property.