Influence of direct laser writing with femtosecond pulses on electrochemical etching of n-type low conductivity (>1,000Ωcm) silicon is demonstrated. It has been shown that thermal 1-µm-thick SiO2 layer on silicon surface can be used as a protective layer in the electrochemical etching process. It has been found that laser ablation changes not only the surface morphology and structure of silicon samples but also the character of their anodic etching in aqueous solution of hydrofluoric acid. Formation of microvoids and caverns of irregular shape has been observed at the laser-ablated sites. It is proposed that the change of silicon conductivity from n- to p-type takes place at the laser fabricated regions. Processes of Si anodic oxidation and electrochemical etching are discussed.
Journal of Solid State Electrochemistry,
Vol. 14, no. 5 (May 2010), pp. 797-802