Improved diffusion barrier by stuffing the grain boundaries of TiN with a thin Al interlayer for Cu metallization

A laterally segregated diffusion barrier was investigated for Cu metallization. In this scheme, the intended final structure is composed of two different barrier materials; one is the parent barrier layer (TiN, in our case) and the other (Al2O3, in this case) is segregated laterally along the grain boundaries of the parent barrier layer. As a result, the fast diffusion paths, the so-called grain boundaries of the parent diffusion barrier, are effectively passivated. To realize this type of barrier experimentally, the TiN(5 nm)/Al(2 nm)/TiN(5 nm) structure was fabricated by sequential sputtering and compared with TiN(10 nm) as a diffusion barrier against Cu. The etch pit test results indicated that the barrier with the Al interlayer prevented Cu diffusion into the Si up to 650 °C, which is 250 °C higher than achieved by a TiN(10 nm) barrier.