Study of the cracking of highly porous p+ type silicon during drying

The origin of the cracking of highly porous silicon layers during drying is investigated. Optical and scanning electron microscopy observation allow us to observe the cracking occurrence, In situ x-ray diffraction experiments, under controlled vapor pressure of pentane, reveal that large capillary stresses occur at a vapor pressure P* during the controlled drying. These stresses lead to the cracking of the highly porous layer, which occurs for samples thicker than a critical thickness h(c). Taking into account the mechanical properties of the material, a model based on energy balance is presented. This model predicts a layer thickness h(c) of cracking occurrence, showing that h(c) varies as (1-p)(3)/gamma(LV)(2) (where gamma(LV) is the surface tension of the drying liquid and p is the porosity). This model is in good agreement with experimental data obtained with two liquids, water, and pentane, which have very different surface tension and also for two different porosities. (C) 1996 American Institute of Physics.