Low-k dielectric improves the switching speed by reducing the parasitic capacitance in integrated circuits. However it suffers the problem of copper diffusion. Forming gas (H2 + N2) plasma treatment on the surface of HSG-7000 low-k dielectric thin film has demonstrated to improve copper diffusion resistance. Two techniques using X-ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectroscopy (SIMS) have been used to examine the copper diffusion on this thin film. A thin layer of 10 nm with C-N bonds near the HSG-7000 surface were believed to be created by the plasma treatment and confirmed with XPS and SIMS and acts as barrier.