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 of p + -type PS material, a simple model shows that h_c varies as (1 - p)³ and 1/γ²_LV, where p is the porosity and γ_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).