Graphenic carbon as etching mask: patterning with laser lithography and KOH etching

The wet anisotropic etching process is generally used in the field of micromachining (MEMS), particularly for commercial products such as accelerometers. Hard masks like oxide or nitride play a key role in the transfer of patterns to the substrate during the lithography process. This work reports on the use of polycrystalline graphenic carbon as an etch mask for wet chemical processing and outlines a simple method to create patterned structures on (100) silicon wafers. Graphenic carbon (GC) was deposited on the silicon substrate by chemical vapor deposition (CVD) using C₂H₄ as precursor. The desired pattern was written in the spin-coated negative photoresist using UV laser lithography. Different geometrical shapes were printed on the substrate with dimensions ranging from 10 to 50 micrometers. In the next stage, the O₂ plasma etched away the carbon from the area not covered by the photoresist, acting as an additional mask for this and the subsequent processing steps. Finally, the sample was immersed in the KOH bath saturated with isopropanol and the etching rate was evaluated for each crystal plane. Compared to the use of a sacrificial oxide mask, this technique is simpler and produces more reliable results.