The application of ultrashort voltage pulses between a tool electrode and a workpiece in an electrochemical environment allows the three-dimensional machining of conducting materials with submicrometer precision. The principle is based on the finite time constant for double-layer charging, which varies linearly with the local separation between the electrodes. During nanosecond pulses, the electrochemical reactions are confined to electrode regions in close proximity. This technique was used for local etching of copper and silicon as well as for local copper deposition.

No abstract

Stainless Steel / Microstructures / Microfabrication / Electrochemistry / Short Voltage PulsesApplication of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel. In order to reach submicrometer precision and high processing speed, the formation of a passive layer on the workpiece surface during the machining process has to be prevented by proper choice of the electrolyte. Mixtures of concentrated hydrofluoric and hydrochloric acid are well suited in this respect and allow the automated machining of complicated three-dimensional microelements. The dependence of the machining precision on pulse duration and pulse amplitude was investigated in detail.

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).

The lateral extension of electrochemically induced surface modifications is usually determined by the macroscopic size of the electrodes and the diffusion length of the reacting species. To overcome this constraint, we conducted an electrochemical reaction far from equilibrium. We applied short voltage pulses (#100 ns, up to 64 V) to a scanning tunneling microscope tip while imaging a Au(111) surface in concentrated electrolytes. They lead either to hole formation by anodic dissolution of the Au or to cathodic deposition of Cu islands (in the Cu 21 containing electrolyte), both of nanometer extension. [S0031-9007(98)