Boring Deep Cylindrical Nanoholes in Silicon Using Silver Nanoparticles as a Catalyst.

ANNUAL REPORT OF OSAKA UNIVERSITY—Academic Achievement—2004-2005 We deposited silver nanoparticles on the surfaces of silicon wafers by electroless plating (Fig.A). Then we immersed the wafers in an aqueous solution containing hydrofluoric acid (HF) and hydrogen peroxide (H2O2). Since silver is a good catalyst for reduction of hydrogen peroxide, hydrogen peroxide in solution would be reduced by drawing electrons from silicon. This would lead to oxidative dissolution of silicon from the surface. This is what we expected. However, interestingly, the dissolution proceeded preferentially in the <100> directions at the silver/silicon interface, resulting in nanoholes in silicon. When the treatment was performed for 30 min, the depths of the nanoholes reached about 40 μm (Fig. B), and silver particles were observed at the bottoms of the holes (Fig.C). When the treatment was continued for 10 h, some of the silver particles penetrated through a 500-μm-thick silicon wafer, making through-wafer holes with diameters of about 100 nm. Such a boring process will be a useful method in the fields of nanotechnology and nanoscience. Boring Deep Cylindrical Nanoholes in Silicon Using Silver Nanoparticles as a Catalyst TSUJINO Kazuya and MATSUMURA Michio (Research Center for Solar Energy Chemistry)