Maskless Wet Etching Silicon in Iodine-Supersaturated KOH Solution

Although maskless wet etching of silicon has been proposed for about two decades, it is not widely used as yet because of rough fast-etching planes etched in KOH-based etchants or lager ratio (r₃) between the etching rates of the fast-etching crystal plane and (001) planes etched in TMAH-based etchant. In this paper, the maskless wet etching characteristics of silicon in various etchants are experimental studied. It is found that the fast-etching planes etched in iodine-supersaturated KOH solution are smooth and the intersectant lines of (001) crystal planes and fast-etching planes are straight. The ratio between the etching rates of the fast-etching crystal planes and (001) planes etched in iodine-supersaturated KOH solution is smaller than that of other etchants. The deviation of r₃ in iodine-supersaturated KOH solution is also the smallest among all etchants. In addition, experiments demonstrate that iodine-supersaturated KOH solution has an extremely high stability and durability. All these characteristics prove it satisfies most demands of maskless etching silicon sensors and actuators.