Micromachining applications of selective anodization

Aimed at fabricating microstructures from single-crystal silicon, we have been studying selective anodization process as an application of anodization technology. Highly diffused p-type (p+) silicon layers, formed in a n-type single-crystal silicon, can be anodized selectively in hydrofluoric acid (HF) solution and then removed perfectly by etching in low concentration alkali solution, leaving a micromachined three-dimensional n-type silicon structure. This report discusses the anodization condition for making the selective p+/n-type silicon anodization feasible. Then it describes an accelerometer containing a piezoresistor gauge as the detector. This device was fabricated by applying the selective anodization to an ordinary bipolar semiconductor process. This small and high sensitivity accelerometer, which we could fabricate using the selective anodization, verified that the new process technology is effective for silicon micromachining. Finally, by citing advantages of the selective anodization process, such as: three-dimensional microstructure can be fabricated without back side lithography and deep machining in single-crystal silicon substrate can be performed quickly concurrently with surface machining, we indicate its potentiality as micromachining technology for silicon