A method for processing a substrate for forming TaC and TaCN films having good adhesion to Cu. The method includes disposing the substrate in a process chamber of a plasma enhanced atomic layer deposition (PEALD) system configured to perform a PEALD process, and depositing a TaC or TaCN film on the substrate using the PEALD process. The PEALD process includes (a) exposing the substrate to a first process material containing tantalum, (b) exposing the substrate to a second process material containing a plasma excited reducing agent, (c) repeating steps (a) (b) a predetermined number of times, (d) exposing the substrate to plasma excited Argon, and (e) repeating steps (c) and (d) until the TaC or TaCN film has a desired thickness. Preferably, purging of the process chamber is performed after one or more of the exposing steps.