Formation of self-aligned holes in an arbitrary pattern in silicon substrate

A self-aligning etch method for silicon substrates is presented. A hole pattern is defined on the front side of the silicon substrate while etching of the hole takes place from the back side through the application of a current from the front side of the silicon substrate to a cathode electrode in a solution of HF, HNO3, and H2O. As the etching proceeds, the etched pattern in the back side gradually becomes self-aligned with the front side pattern of the silicon substrate. Twenty five circular holes arranged in a 5×5 array are formed in a boron-doped (100) silicon substrate. The etch method provides control over hole dimensions which are 520 μm in diameter and spaced 520 μm apart. The self-aligning property of the etch method enables the formation of different shaped holes.