Focused ion beam stimulated deposition of organic compounds

Abstract

The successful deposition of an opaque organic-based film for a clear defect photomask repair process has been reported. The process relies upon the polymerization of styrene stimulated by a focused ion beam, with subsequent cross-linking and ion implantation. Since that report, a class of compounds has been identified which are all suitable as precursors for film deposition with a focused ion beam. More importantly, this class of compounds defines the key chemical structures necessary for film deposition under focused ion beam conditions (high-current density/high-sputter yield). A necessary requirement for film formation is to supply the precursor to the substrate at a particle current density equivalent to that of the ion beam current density. This condition is not, however, a sufficient one: the chemistry which determines the bonding of the precursor to the substrate is the key to deposition. The combination of an aromatic ring with a pendant double or triply bonded substituent satisfies the chemical criteria. The incident molecules bond with high efficiency through the vinyl bond to radical sites created by ion bombardment. Subsequent ion bombardment at those sites cause the aromatic ring to open, leaving a highly reactive CnHn chain bonded to the surface. Vibrational excitation may cause fragmentation of this chain, but cross-linking will also occur, resulting in net deposition. The aromatic ring thus supplies a sufficient number of carbon atoms per incident precursor molecule to insure net deposition. Successful deposition has been obtained with styrene, phenylacetylene, indene, and benzofuran, all of which have a conjugated, unsaturated bond adjacent to an aromatic ring. No deposition, or net sputtering of the substrate was observed for the analogous class of molecules, benzene, toluene, ethylbenzene, and indane, all of which have an aromatic ring but lack the unsaturated pendant group necessary for efficient bonding to the surface.