Fabrication of 2D-extruded fractal structures using repeated corner lithography and etching

We present a new wafer scale fabrication procedure for the creation of complex 2D-extruded geometries in silicon by a combination of repeated anisotropic etching of silicon and a 3D lithographic technique called corner lithography. Using corner lithography it is possible, by means of a nano-masking step, to select which corners are opened, depending on specific angles relative to the substrate normal. In this way complex 3D structures can be created in a repetitive manner. In this article we apply this procedure to the etching of trench like structures in a <;100> silicon wafer. Depending on which angles open in corner lithography, it is possible to etch just downward, downward and sideward, or a sequential combination of these two options. Examples of all three routes have been created on a micron/sub-micron scale. By depositing a conformal layer, the smallest hollow features will be auto-closed, thus forming buried channels. Continuing this deposition, automatically new closed channels will be formed with increasing diameter and wall thickness. These channel structures could find application in e.g. continuous flow microreactors.