Organosilane Monolayer Resists for Scanning Probe Lithography.

Abstract

We report the preparation of organosilane monolayers by means of chemical vapor deposition and scanning probe lithography (SPL) using these monolayers as resists. Two types of monolayers having different alkyl groups, that is, trimethylsilyl [(CH3)3Si-, TMS] and octadecylsilyl [CH3(CH2)17Si-, ODS] monolayers, were deposited on Si substrate from precursor molecules of hexamethyldisilazane [(CH3)3Si-NH-Si(CH3)3, ] and octadecyltrimethoxysilane [CH3(CH2)17Si(OCH3)3], respectively. The thicknesses of these monolayers as estimated by ellipsometry were 0.4 and 2.0nm, respectively, and, therefore, were concluded to be defined by their alkyl chain lengths. Using an atomic force microscope (AFM) with an electrically conductive probe, a Si sample deposited with a TMS or ODS monolayer was patterned by flowing current through the AFM-probe/sample junction. The pattern thus fabricated on the monolayer was transferred to the substrate Si by chemical etching in an aqueous solution of NH4F and H2O2. The etching proceeded area-selectively in the regions where the probe had passed, since, in these regions, the monolayer had been electrochemically degraded. The patterning was entirely accomplished through probe scanning without any need for further developing steps. The resist can thus be regarded as being self-developing. Both TMS and ODS successfully served as such SPL resists.