Fabrication of silicon stencil masks with vitreous carbon ion-absorbing coatings

We show how to integrate a vitreous carbon ion-absorbing coating with current silicon stencil mask technology to create a mask for ion beam lithography with dramatically improved radiation resistance. The masks were formed by first sputtering a graphitic carbon film onto the nonplanar side of a patterned silicon stencil mask. The carbon film was subsequently vitrified by He+ ion implantation and patterned by O2 reactive ion etching using the silicon mask itself as an etching template. In the example reported herein, the thicknesses of the silicon mask and carbon film were 0.7 and 1.0 μm, respectively. Silicon mask openings as small as 80 nm were faithfully replicated in the carbon, making a 20:1 aspect ratio in the bilayer mask. The mean stress of these multilayer masks is extremely stable when lithography ions are stopped within the carbon layer: stress change is less than experimental error (0.5 MPa) for at least 500 000 proximity exposures. Compared to silicon stencil masks, which wrinkle after only 10...