Surface condition effects of the inter-metal dielectrics on interconnect aluminum film properties

Surface quality and optical reflectivity of the hot-Al/Ti interconnecting metal layers show a strong dependence on the surface condition of the underlying inter-metal dielectric oxides (IMDs). When hot-Al/Ti films are deposited by a two-step method, a much lower (0002) Ti X-ray diffraction is obtained from the hydrophilic oxide substrates than from the hydrophobic ones. This Ti film crystalline structure affects (111) diffraction and surface roughness of the Al interconnecting films. An optimized RF pre-cleaning process prior to the Al/Ti deposition enhances the smoothness and hydrophobic surface property of the IMDs, as measured by atomic force microscopy and sessile drop contact angle method, and greatly improves aluminum surface quality. Etch yield of the interconnect lines is monitored at 0.4/0.4 μm bridge test patterns of 3.5 mega-bit arrays, and is greatly influenced by the surface condition of underlying IMDs.