Structure, mechanical properties, and fracture behavior of organosilicate glass thin films

Organosilicate glass (OSG) thin films with low permittivity made by means of plasma enhanced chemical vapor deposition are the inter-metal insulator in advanced integrated circuits. These materials are employed to reduce the interconnect delay and power consumption associated with the inter-line capacitance. However the implementation of OSG is hampered by its poor mechanical properties and susceptibility to stress-corrosion cracking. In this work, we present a study of the structure evolution of OSG under various processing conditions, as well as the impact of structure and environment on the mechanical properties and fracture behavior. We will show that the composition and structure of OSG can be finely tuned by changing the parameters during film deposition or post-treatments. Adding carbon content in the film lowers the density and reduces the dielectric constant, accompanied by a decrease of the network connectivity. Ultraviolet-cure is very effective in crosslinking and stabilizing the network structure without causing significant increase in permittivity. With the assist of a structure model, we determined the infrared absorption inverse cross-sections that may be used to analyze infrared spectra of other OSG films. The mechanical properties of OSG are very sensitive to the network structure. Both the mean connectivity number and networking bond density correlate well with mechanical properties. The comparison of cohesive and adhesion energies reveals that plasma treatments substantially enhance the adhesion. However, the enhancement diminishes when the films are exposed to reactive environments. Our study shows that the adhesion energy at given crack velocity changes linearly with the logarithm of the water partial pressure in ambient, or with pH value in aqueous environment. On the other hand, water degrades the electrical property and adhesion when absorbed. We found that the water diffusion in OSG film stacks is very fast, reversible under mild annealing; and the activation energy is low (∼0.27 eV), consistent with an interfacial diffusion process. These findings can be applied to assess the reliability of OSG-containing thin film structures in microelectronics.