CRACKING BEHAVIOR OF XEROGEL SILICA FILMS ON SILICON SUBSTRATES

An analysis of the cracking behavior of sol-gel derived silica, ''xero gel,'' films on silicon substrates is presented. At the onset of film cracking, xerogel films on [100] Si substrates show a crosshatched cra ck pattern, while such films on [111] Si substrates show a random patt ern. This is explained by the fact that for an isotropic film the crit ical film thickness for cracking decreases for increasing substrate co mpliance. For a [100] Si wafer, the directions of highest compliance i n the plane of the wafer are in the [100] directions, which lead to cr acks in the film parallel to them. A [111] Si substrate is isotropic i n the plane of the wafer and, hence, there is no preferred direction f or film cracking. A random pattern is the result. (C) 1998 American In stitute of Physics. [S0003-6951(98)00346-5].