Crack formation in TiN films deposited on Pa- n due to large thermal mismatch

Abstract

Advanced metallization requires stringent demands on the properties of dielectric materials and the respective conducting metals used. These include low dielectric constant, negligible water take up, chemical inertness, low temperature deposition, as well as compatibility with current integrated circuits manufacturing, low resistivity, and high electromigration resistance. To meet future integration requirements, Pa- n as the low κ-dielectric material and silver or copper as the low resistive metals are being studied. The issues of metal diffusion and adhesion are important for successful operation and long-term reliability. The diffusion barrier, titanium nitride has been well studied and is an accepted material in current industrial manufacturing. In this study, TiN was deposited using DC magnetron sputtering to minimize the thermal budget constrains associated with Pa- n. In situ four-point probe analysis was used to measure the resistivity of TiN and to elucidate the discontinuity in the films during thermal annealing. In situ X-ray analysis was performed to determine the coefficient of linear thermal expansion, which was then used to determine thermal stresses in TiN and Pa- n films. During the annealing, the hard and brittle TiN film did not comply with ductile Pa- n due to the thermal mismatch. This large tensile stress opposes the pre-existing compressive stress present upon deposition, and eventually exceeds the TiN fracture strength at approximately 150°C resulting in crack formation.