Improvement of Rough Interface Between Barrier/Seed Layer and Porous Ultralow k Film for 28nm Technological Node and Beyond

With critical dimension of device scaled down to 28 nm technological node and beyond, porous ultralow k (PULK) film as an insulator is used in Cu interconnects to further reduce resistance-capacitance (RC) delay. The integration of the PULK film faces more severe challenges due to the presence of porosity. Plasma treatments and wet cleaning processes have been considered to be critical steps to impact the PULK film properties. In this paper, the effects of the various plasma treatments and wet cleaning processes on the PULK films were investigated. Results indicated that NH
₃
, N
₂
, and CHF
₃
plasma treatments resulted in the formation of a thin and densified layer on the surface of the PULK films, which prevented TaN/Ta barrier diffusing inside the pores to avoid forming rough interface. In addition, specific EKC520 product + dilute hydrofluoric acid (DHF) were used to clean the PULK film treated by the CHF
₃
plasma, and the rough interface was observed after the barrier deposition. Moreover, the specific EKC520 product was used to clean the PULK film treated by the N
₂
plasma, and there was smooth interface after the barrier deposition. However, the DHF chemical could remove the thin and densified layer from the surface of the PULK film to cause the re-exposure of pores. During barrier deposition, the TaN barrier diffused inside pores resulting in the formation of the rough interface.