Light-controlled, electrochemical, anisotropic etching of silicon

The process of electrochemical silicon etching in alkaline solutions was found to depend on the illumination. Experiments in 30% KOH revealed that on p-type silicon light shifts the passivation potential towards more positive values, whereas on n-type samples this shift is in the negative direction. As a consequence, etching can be initiated by light on p-type silicon when a potential slightly above etch stop is chosen. Similarly, etching currently in progress can be stopped by light on n samples when a potential slightly below etch stop is chosen. These effects are expected to open up new possibilities for micromachining, such as light-controlled etching of n-Si membranes or light-induced anisotropy effects in p-Si.<>