In a TiN etching process using electron cyclotron resonance (ECR) plasma of BCl3 and Cl-2 gas mixture, the decline of TiN etch rate was observed after the erosion of the photoresist surface with the ECR plasma, but we could prevent the decline by the addition of N-2 to the etching gas mixture. Carbon was detected by x-ray photoelectron spectroscopy (XPS) on the TiN surface (on which there was no photoresist) etched in the reactor with the ECR plasma after the erosion of the photoresist. The TiN surface was contaminated by carbon in the reactor during the etching process. N-2 gas was added to reduce carbon contamination. In fact, after the photoresist was eroded with the N-2 added ECR plasma, carbon was hardly detected by the XPS on the sample surface etched in the reactor and the TiN etch rate did not decline. Therefore, we concluded that carbon contamination on the TiN surface originated from the erosion of the photoresist with the ECR plasma causing the decline of the TiN etch rate. The effect of N-2 addition must be attributed to the reaction between nitrogen radical in the N-2 added ECR plasma and carbon in the reactor.