Determining the interfacial toughness of low-k films on Si substrate by wedge indentation: Further studies

Abstract

This paper presents further studies to determine the interface toughness of low-k films (black diamond (BD) film) using wedge indentation experiments and analysis. In addition, the effects of film thickness on the delamination mode are studied and an analysis methodology is proposed. The curvature of the delamination crack front is measured and compared for the films with different thicknesses, and this information is used to determine the critical buckling stress and the delamination mode: i.e. with or without buckling. For a thinner film with a straight crack front, there is greater likelihood of buckling delamination, while for a thicker film with a curved crack front buckling is less likely. Combining these results with those from a previous study, it is shown that the wedge indentation test is capable of accurately measuring the interface toughness of low-k films, and a pop-in event in the load-penetration curve can be used as an early indication of interface crack initiation. It is also found that the resistances to the initiation and propagation of the interfacial cracks for the porous methylsilsesquioxane (MSQ) and non-porous BD films are significantly different; this could be due to the fact that in the porous MSQ film, molecular bridges might provide an additional mechanism to resist interfacial delamination cracks. © 2007 Acta Materialia Inc.