PLASMA-ETCHING WITH SELF-ASSEMBLED MONOLAYER MASKS FOR NANOSTRUCTURE FABRICATION

Self-assembled monolayers of octadecylthiol on GaAs and octadecylsilox anes on titanium, aluminum, and silicon have been used as electron bea m resists for plasma etching into the substrates. An electron cyclotro n resonance source was used to excite a low-pressure, high-density pla sma with low ion energy to achieve high selectivity with the thin mask ing layers. Patterning of monolayers on GaAs usually produced a negati ve tone, but etching of the metal surfaces resulted in positive tone p atterning. The maximum etch depth into the GaAs was similar to 100 nm using the negative tone process. Lines have been etched into Ti with l inewidths down to similar to 20 nm. The negative tone process can be e xplained by the cross linking of the monolayer under high-dose electro n beam exposure; however, the positive tone process must rely on contr ast either from different etching characteristics of the oxides or dif ferent structural arrangements of the different SAMs. (C) 1996 America n Vacuum Society.