Cracking behavior of xerogel silica films on silicon substrates

An analysis of the cracking behavior of sol-gel derived silica, "xerogel," films on silicon substrates is presented. At the onset of film cracking, xerogel films on [100] Si substrates show a crosshatched crack pattern, while such films on [111] Si substrates show a random pattern. This is explained by the fact that for an isotropic film the critical film thickness for cracking decreases for increasing substrate compliance. For a [100] Si wafer, the directions of highest compliance in the plane of the wafer are in the [100] directions, which lead to cracks in the film parallel to them. A [111] Si substrate is isotropic in the plane of the wafer and, hence, there is no preferred direction for film cracking. A random pattern is the result. (C) 1998 American Institute of Physics. [S0003-6951(98)00346-5].