Adhesion between Cu and low-k films has been investigated. Low-k films deposited using a mixture of hexamethyldisilane(HMDS) and Para-xylene had a dielectric constant as low as 2.7, showing the thermally stable properties up to $400^{circ}C$. In this study, Ti glue layer, boron dopant, and $N_2$plasma treatment were used to improve adhesion property of between Cu and low-k films. Ti glue layer slightly improved adhesion property. After $N_2$plasma treatment, the adhesion property was significantly improved due to the increased roughness and the formation of new binding states between Ti and plasma-treated PPpX : HMDS. However, $300^{circ}C$ annealing of $N_2$plasma treated sample caused the diffusion of Cu into the PPpX : HMDS, degrading the low-k properties. In the case of Cu(B)/Ti/PPpX : HMDS, the adhesion was remarkably increased. This enhanced adhesion was attributed to formation of Ti-boride at the Cu-Ti interface. It is because the formed Ti-boride prevented the diffusion of Cu into the PPpX : HMDS and the Cu-Ti reaction at the Ti interface.