Silicon wafers of n-type with different orientation and doping level were electrochemically etched in electrolytes containing HF acid with different concentration. A photocurrent was excited by illumination, which results in electronic holes formation, necessary in silicon dissolution. Independently from the Si orientation and doping level, increased HF concentration results in the increased current density under potentiodynamic dissolution conditions. At the initial increase of the current density a porous silicon formation takes place. The strongest increase of the current, up to a value of 15-20 mAcm to the -2 was observed with an increase of HF concentration up to 20% and 10% for the (111) and (100) orientation, respectively. This phenomenon was observed independently of the doping concentration. When the potential still increases, then current passes through maximum and the surface becomes flat owing to the changed electropolishing mechanism. In the case of (100) silicon wafer, immersed in 5% HF electrolyte, significant oscillations observed indicate point to oxide formation and its subsequent dissolution. On the other hand, very small oscillations take place in the case of (111) wafer orientation. Morphology of the wafers undergoes transformation from flat, through rough to electropolished.
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