Effect of catalyst shape and etchant composition on etching direction in metal-assisted chemical etching of silicon to fabricate 3D nanostructures.

Metal-assisted chemical etching (MaCE) of silicon in conjunction with shaped catalysts was used to fabricate 3D nanostructures such as sloping channels, cycloids, and spirals along with traditional vertical channels. The investigation used silver nanorods, nanodonuts along with electron beam lithography (EBL)-patterned gold nanodiscs, nanolines, squares, grids, and star-shaped catalysts to show how catalyst shape and line width directly influence etching direction. Feature sizes ranging from micrometers down to 25 nm were achieved with aspect ratios of at least 10:1 and wall roughness of 10 nm or less.