Depending on the required application, there are multiple strategies for etching pores in silicon, for example, wet etching , metal assisted chemical etching , electrochemical etching and dry etching techniques such as reactive ion etching (RIE). Reactive ion etching (RIE) is a dry etching process which is compatible with complementary metal-oxide-semiconductor (CMOS) methods used in the semiconductor industry. RIE is often used to remove silicon from substrates in situations where metal contamination from wet etching is undesirable or in situations where wet etching would not give the required directionality. RIE uses a reactive gas that reacts with the silicon to form volatile species which are pumped away, thereby removing silicon. This reaction is quasi-isotropic since the removal of silicon typically happens in all directions almost equally. Since isotropy is undesirable when creating high aspect ratio structures such as nanopores, or trenches, an extra step is needed to make the etch process anisotropic.