Porosity effects on low-k dielectric film strength and interfacial adhesion

The elastic modulus and hardness of low k dielectric films rapidly decrease as porosity increases. By contrast, interfacial adhesion is relatively insensitive to porosity. Adhesion energy values measured by the four-point bend method are similar for porous and non-porous films. Additionally, interfacial adhesion is much stronger for polymer films than for organosiloxane films, regardless of porosity. E-beam treatments significantly improve the modulus and hardness of porous organosiloxane films, sacrificing only a slight increase in dielectric constant. Solid-state NMR and pore size measurements indicate that the improved mechanical properties result from a cross-linking mechanism rather than macroscopic densification. TOFSIMS results show that the increased dielectric constant results from carbon loss and an increase in silanol concentration. E-beam treatments, however, do not improve interfacial adhesion significantly.