A New Way to Form Three-Dimensional Microstructures by Electrochemical Etching of Silicon

• A new technique of bulk micromachining using anodic etching of (100)-oriented n-type silicon is presented. For particular conditions the transition regime between porous silicon formation and electropolishing enables the formation of high aspect ratio microtips which correspond to inverted macropore structures. This unusual property can be explained by the distortion of currant lines near the basis of formed structures. The distortion, which prevents the tip dissolution, is due to the electrical field in the space charge region at the silicon-electrolyte interface. The same property can be used to form three-dimensional microstructures. The position and shape of the structures can be defined by forming steps of a few microns depth, prior to the electrochemical etching. Then the etching parameters (HF concentration, light intensity, etching current density) are adjusted in order to electropolish the sample except where vertical walls are needed. This enables to form microstructures without a periodic pattern. The feasibility of this technique is demonstrated by forming 100 μm wide pores, free-standing beams as well as high aspect ratio micro-needles and micro-tubes.

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

Anodes

Current density

Electric currents

Electric distortion

Electric fields

Electric space charge

Electrochemistry

Electrolytes

Electrolytic polishing

Etching

Micromachining

Microstructure

Electrochemical etching

Semiconductor physics

Halvledarfysik

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