About the origin and the mechanisms involved in the cracking of highly porous silicon layers under capillary stresses

The effects of the capillary stresses during the drying of p + -type porous silicon (PS) layers are reported. The cracking of the PS layers occurs for samples thicker than a critical thickness value h(c). Taking into account the elastic properties ofp + -type PS material, a simple model shows that h(c) varies as (1 - p)(3) and 1/gamma(LV)(2), where p is the porosity and gamma(LV) is the surface tension of the drying liquid. A good agreement with experimental results is observed. This study leads also to a very easy and simple method which increases the h(c) value by a factor of about 25 when using pentane as the drying liquid (instead of water).