Intrinsic Stress in Porous Silicon Layers Formed by Anodization in HF Solution

Experiments about intrinsic stress in a porous silicon layer are described. After formation of a porous silicon layer compressive stress of 5 to 8>< 108 dyn/cm ' is generated. By heat-treatment, the stress is changed from compressive stress to tensile stress at about 300°C. This change is due to hydrogen bond dissociation, as shown by the decrease of the Si-H2 stretching band of the porous silicon layer. The generation mechanism and the change of the intrinsic stress can be explained by the effect of hydrogen bonds and the surface tension of micropores. Porous silicon is formed by the anodic reaction of a sili-con wafer in concentrated hydrofluoric acid (HF) solution below the critical current density.'2 Uhlir ' and Turner' reported the anodization of silicon in HF solution and observed a thin film formed on a silicon electrode surface. There have been a number of studies characterizing the properties of porous silicon layers as a function of dopant type and concentration, electrolyte, etching voltage, or current density.'&quot