Deep UV patterning of 3-amino-propyl-triethoxy-silane self-assembled molecular layers on alumina

Abstract

Organosilane molecular layers are widely used to modify surface functionality and for the immobilization and assembly of more complex nanostructures. Unlike alkanethiol layers, simple organosilanes have not been directly photopatterened with easily accessible optical wavelengths. In particular, 3-amino-propyl-triethoxy-silane (APTES) is commonly used for such purposes, and a direct means of patterning molecular layers of APTES would be of interest for a variety of applications. However, previous efforts to photopattern aminosilanes have been limited to vacuum ultraviolet (VUV) radiation at 172 nm. Here APTES layers were photopatterned on partially oxidized aluminum using 266 nm laser irradiation. APTES layers were grown on both oxidized Al and Si surfaces for patterning and reflection absorption infrared spectroscopy purposes. APTES on aluminum oxide, in contrast to silicon, retains ethoxy groups. These groups are eliminated by 266 nm laser irradiation providing insight into the photopatterning mechanism. Unlike 172 nm irradiation, the 266 nm wavelength retains the APTES backbone. Microscale patterning of APTES has been performed and the exposed samples were processed in a second organosilane, n-butyltrichlorosilane (BTS) or n-octadecyltrimethoxysilane (ODS), that enhances secondary-electron contrast compared to a patterned APTES sample. The authors found that BTS/APTES patterns exhibited contrast reversal compared to ODS/APTES structures. Direct patterning of organosilane films using deep-UV (rather than VUV or e-beam) exposure allows the use of coherent and continuous-wave sources and also prevents exposure of underlying resist layers when using the organosilane pattern as an in situ metrology standard for electron-beam lithography.