Laser-controlled chemical etching of aluminum

Abstract
A new technique is described for high-spatial-resolution (<2-μm linewidth) etching of Al thin films. The process is based upon moderate local heating by a tightly focused Ar+ laser beam to activate an etching reaction in mixtures of phosphoric acid, nitric acid, and potassium dichromate. By chemically biasing the reaction near its passive/active transition, the laser can enhance the reaction rate by more than six orders of magnitude. The etching mechanism has been studied by etch-rate measurements, ellipsometry, and Auger spectroscopy, and is ascribed to a competition between the formation of soluble aluminum phosphates and insoluble aluminum oxides.

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