Laser-induced formation of porous silicon

Abstract

The mechanism of photoelectrochemical porous silicon formation in fluoride solutions under laser illumination and dark conditions has been investigated. Experiments were performed in a PTFE cell with a plastic window to allow the laser path to be horizontal and the silicon electrode to be in a vertical position inside the cell. Dark and illuminated anodic and cathodic current-voltage (I-V) curves were both measured in real time by chopping the laser beam. N-type wafers of resistivities 0.001 to 22 Ω · cm have been investigated for various conditions of illumination intensity and polarization. We focused our attention on relatively low illumination intensities ∼ 10-5-10-8 W/mm2 and high HF concentration. By measuring the dissolution rate and the photogenerated current we estimated that the main reaction path requires two holes for each Si atom as: S i + 2 H F + 2 h+ over(→, h v) S i F2 + 2 H+. The utilization of this technique for direct projection printing of porous Si images of 10 μm resolution was demonstrated. © 1995 Elsevier Science B.V. All rights reserved.