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

We show how to integrate a vitreous carbon ion-absorbing coating with curre nt silicon stencil mask technology to create a mask for ion beam lithograph y with dramatically improved radiation resistance. The masks were formed by first sputtering a graphitic carbon film onto the nonplanar side of a patt erned silicon stencil mask. The carbon film was subsequently vitrified by H e+ ion implantation and patterned by O-2 reactive ion etching using the sil icon mask itself as an etching template. In the example reported herein, th e thicknesses of the silicon mask and carbon film were 0.7 and 1.0 mu m, re spectively. Silicon mask openings as small as 80 nm were faithfully replica ted 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 experiment al error (0.5 MPa) for at least 500000 proximity exposures. Compared to sil icon stencil masks, which wrinkle after only 100 exposures, these masks rep resent a breakthrough in nanostructure manufacturing. (C) 1998 American Vac uum Society. [S0734-211X(98)09106-9].