Alignment for masked ion beam lithography using ion-induced fluorescence

Abstract

We show that the bombardment of densified chemical vapor deposited SiO2 by hydrogen ions induces fluorescent defects. A proton dose of 6×1014 /cm2 saturates the fluorescence yield at approximately 0.6 photons/100 keV of absorbed proton energy. A beam rocking technique was used to obtain a fluorescence alignment signal corresponding to the registration of a stencil mask pattern with a corresponding SiO2 mark on a wafer. Simulation of an optimized alignment system implies that 50 nm (3σ) registration can be achieved with a 1 s settling time. This direct approach to alignment has the advantages of being simple, relatively insensitive to resist coating of the marks, and compatible with conventional integrated circuit processing.