Fabrication of Octagonal Structures Using Si (100) Wafers

Etch rate distribution of Si(100) wafers in KOH solution:

Etching from the (100) direction results in a structure with four stable planes (see red circles), resulting in a quadrilateral cross-section according to the rate distribution in the figure below. In order to construct an octagon, we need to find four sublevels of stable planes (see blue circle).

Layout design:

Guided by this idea, we designed a cross-shaped layout structure. By appropriately controlling the etching time, the four secondary stable surfaces and the four main stable surfaces appear simultaneously, thereby forming an octagonal cross-section (bottom hole).

Corrosion result:

The images below show the etched structure of the Si(100) wafer from the front and back, respectively.