Electron beam induced carbon deposition used as a negative resist for selective porous silicon formation

The present work describes direct porous silicon patterning based on electron-beam induced carbon deposition used as a mask against pore formation on Si. Under ideal conditions the C-deposits act as a negative resist to suppress completely and selectively the formation of light emitting porous Si at treated locations. Carbon patterns were written at different electron doses on p-type Si(1 0 0) surfaces. Subsequently by contamination writing in a scanning electron microscope the silicon surface was porosified by galvanostatic experiments in a 20% HF solution. The carbon masks as well as the etched surface were characterized by scanning electron microscopy and Raman spectroscopy. The selectivity of the technique depends on several factors such as the electron dose during masking and the electrochemical parameters. Under conditions typical for porous silicon formation, already a relatively low electron dose is sufficient to achieve the desired mask effect to produce patterned porous silicon structures.