Wedge indentation studies of low-k films at inert, water and ambient environments

Wedge indentation experiments are performed to study the time-dependent fracture behavior of silica-based low-k films, namely BlackDiamond® (BD) film and methysilsesquoxane (MSQ) film, both on Si substrate. Two wedge indentation tests, load-holding and varying-loading-rates tests, are performed in this study. It is found that the chemical structure of the low-k films greatly influences the crack growth during the load-holding and varying-loading-rates tests. For the MSQ/Si system, continuously increasing indentation load to above the critical load (>2 mN) is required for crack growth; while for the BD/Si system, spending excessive period of time at below the critical load (<7.5 mN) is leading to the initiation and propagation of interface and film cracks. The wedge indentation tests on BD/Si system at ambient environment show that time-to-failure decreases exponentially with holding load, and a linear relation exists between loading rate and the onset of time-dependent fracture. Supplying the indentation site with a water droplet, the time-to-failure reduces by at least one order of magnitude. Time-dependent fracture is also found to persist under inert environment.