Delamination of Cu and Ti thin films deposited by magnetron sputtering on Cu substrate: Analysis of reasons

Multilayer thin-film structures are widely used in microelectronic, optoelectronic and micro/nano- electromechanical devices. Mechanical properties and mechanical stresses are very critical for such devices. Structural stresses are composed of an intrinsic part resulting from growth defects and a thermal part caused by the mismatch of the thermal expansion coefficients of the different materials in the multilayer system and between coating and substrate. Excessive tensile stresses result in cracking of the film and/or substrate, and compressive stress can cause buckling. Determination and control of stress is an important scientific issue for both functional thin films and engineering coatings from the viewpoint of performance and integrity. In the present study the in situ stress measurements for thin films of Ti (300nm thick) and Cu (1000nm thick) sputtered on Cu substrates were performed using a method proposed in [6]. The stresses that occurred in the Ti film were tensile, stresses that occurred in the Cu film were compressive. The continuous measurements were performed both during the process of the deposition and after the magnetron cut off. The film delamination from a substrate occurred in both cases. The analysis of obtained curves (the specific force versus time) was performed. Analysis revealed that the arising stresses are not caused by any nonstationary heating process of the material surface. Local buckling due to interatomic binding weakening can lead to Cu film delamination. The major cause of Ti film delamination can be a microcracking due to substrate's thin surface layer yielding.