ULTRA-THIN DIFFUSION-BARRIERS FOR CU INTERCONNECTIONS AT THE GIGABIT GENERATION AND BEYOND

The reliability of copper interconnection depends on the barrier effec tiveness of conductive or non-conductive layers to block any copper mo tion. The conductive barrier materials currently used in Al-based inte rconnections - Ti, TiN, W and nitrided W - have been investigated as b arrier against copper diffusion. The barrier thickness must be as thin as possible to achieve negligible barrier contribution to the total l ine resistance. Electrical tests C-V on MOS capacitors were performed to assess the rate of electrically active copper impurities transporte d through the barrier layer. The stability of a copper/barrier/oxide/s ilicon structure was studied under thermal stress with or without bias . For back-end process annealing performed under vacuum, the copper di ffusion was shown to be limited, and very thin barrier films were show n to be effective in preventing copper diffusion.