Nanochannels are widely used in biomedical applications such as DNA analysis and biomolecule detection. We report a study using sacrificial polymer and oxide to form three-dimensional (3D) nanochannels. Polymer nanostructures were patterned on Si substrates using optical lithography or nanoimprint lithography, followed by oxide deposition to form the sealed channels. A high-speed dry etching technique for removing the sacrificial polymer was developed using an O-2 plasma at high power, high pressure, and elevated temperature. This dry etching technique provides a fast lateral etch rate of 3.91 mu m/min for the polymer inside nanochannels, which is an order of magnitude higher than conventional reactive ion etching. High selectivity of 1200 was obtained between the lateral etch rate of polymer inside the nanochannels and the vertical etch rate of oxide. Etch rate dependence on pressure, temperature, and channel width were studied. It was found that the etch rate increases with pressure and temperature. To form multiple levels of nanochannels, the oxide covering the channels was planarized by a photoresist coating and etch-back process. After oxide planarization, the channel formation process is repeated and multiple levels of nanochannels can be stacked to build 3D nanostructures. A two-level channel structure was demonstrated. Interconnect openings between channels of adjacent levels were also demonstrated. With such technique, complex 3D system can be fabricated. Since oxide is transparent to visible light and the channels have hydrophilic surfaces, therefore such a 3D nanofluidic system is suitable for various biomedical studies. (c) 2006 American Vacuum Society.