Electrochemical Micromachining of p-Type Silicon

Abstract

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).

Simulation of Anisotropic Chemical Etching of Single Crystalline Silicon using Cellular-Automata

“…The step value of 0.32 nm is identical with the thickness of one layer. This result agrees the experimental observation (8) . The etching depth against time plot of the (110) plane is almost linear as shown in Fig.9.…”

Electrochemical Microstructuring with Short Voltage Pulses

“…As a consequence for the machining of stainless steel, highly corrosive electrolytes like HCl/HF mixtures have to be applied, thus keeping the passivation layer presumably very thin due to chemical etching. [23,24] Similarly, the machining of highly doped silicon is possible in the presence of HF, which dissolves silicon oxides formed during the electrochemical reaction. [23,24] In cases of transpassive dissolution in the presence of a thick oxide layer, for example, upon machining stainless steel in H 2 SO 4 , the application of short pulses does not suffice to confine electrochemical reactions and additional means, such as partial insulation of the electrodes, have to be applied for local confinement of the electrode reactions.…”

3D patterning of silicon by contact etching with anodically biased nanoporous gold electrodes

“…They used nanosecond pulses to confine the EC reactions to electrode regions in close proximity. This technique allowed holes and trenches to be etched with the tip of a tungsten wire (2 µm) in HF under anodic bias of Si vs. tungsten [2]. The machining precision (~10 µm) and process speed were, however, not suitable for the design of submicrometer structures in low doped Si.…”