We show that complex patterns including three-dimensional structures, lines, curved features, and arrays can be machined in substrates in single-step processing without the need for rastering. High-aspect-ratio nanometer accurate features were machined in nickel using ultrashort voltage pulse electrochemical machining. Experiments were conducted with two different tool shapes. The first was a combination of rrectangles, squares, and a half circle; the second was a 2x2 array. The effect of pulse duration and electrolyte concentration on feature resolution was studied. Structures with 90 nm widths were made by applying 2 ns voltage pulses

Electrochemical micromachining (ECM) of p-type Si substrates is accomplished in HF-based solutions by applying nanosecond potential pulses between the substrate and a tungsten tool electrode. With sufficiently high potential pulses, the silicon potential locally reaches the electropolishing regime and microstructures may be machined. ECM precision is investigated as a function of pulse height, pulse duration, solution composition, and silicon doping level. Results show that micrometer precision may be obtained with highly doped substrates and that experimental data can be explained within a simple model, taking the charging time of the interface capacitance into account. In highly doped p-Si, well-defined microstructures can be realized without application of a mask on the surface. In addition, the isotropy of the process allows fabrication of structures not constrained by the crystal direction. In the case of low-doped material, ECM is only possible for very short pulses (<3 ns).

A maskless all-electrochemical method for the deposition of micro-and nanoscale Cu structures on p-Si is reported. The first step involves the electrochemical machining of p-type Si in HF by applying nanosecond voltage pulses between a tool and a Si electrode. This process generates a localized defect structure, which is successively utilized to achieve selective metal electrodeposition. The resolution of the process is limited mainly by the tool dimensions and by the time constants involved in electrochemical machining, which lead to a limited spread of the defect region on the Si surface. Copper isolated islands with 500 nm diameter have been grown by electrodeposition, with high selectivity. This process has the potential to become a preferred technique for the placement and growth of submicrometer metal islands on semiconductor surfaces.

All-Electrochemical Synthesis of Submicrometer Cu Structures on Electrochemically Machined p-Si Substrates. -Submicrometer features in highly doped p-Si substrates are produced by ultrashort voltage pulse electrochemical machining. The machined features function as a platform for the selective electrodeposition of Cu allowing for the maskless metallization of submicrometer regions of p-Si. Cu isolated islands with 500 nm diameter are grown by electrodeposition, with high selectivity. The process has the potential to become a preferred technique for the placement and growth of submicrometer metal islands on semiconductor surfaces. -(TRIMMER, A. L.; MAURER, J. J.; SCHUSTER, R.; ZANGARI, G.; HUDSON*, J. L.; Chem. Mater. 17 (2005) 26, 6755-6760; Dep. Chem. Eng., Univ. Va., Charlottesville, VA 22903, USA; Eng.) -W. Pewestorf 11-231

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