Scanning capacitance microscopy for alkylsilane-monolayer-covered Si substrate patterned by scanning probe lithography

The surface and interfaces of Si substrates covered with an alkylsilane self-assembled monolayer (SAM) were locally modified using the probe tip of an atomic force microscope (AFM) as a minute electrode. The samples were prepared by coating oxide-covered p- and n-type Si substrates with an octadecylsilyl (ODS) SAM. The chemical and electrical properties of the modified regions were characterized by lateral force microscopy (LFM), Kelvin-probe force microscopy (KFM), and scanning capacitance microscopy (SCM). At a sample bias range higher than 6 V, the ODS-SAM was degraded and the probe-modified regions became more frictional, while there were no LFM contrasts on regions probe-scanned at a lower sample bias voltage. Nevertheless, the regions showed clear KFM and SCM contrasts. Such contrasts could not be ascribed to chemical changes in the ODS-SAM, but to charge trapping and deposition in the ODS-SAM and SiO2 layer. In addition, the charge trapping behavior was found to be different depending on carrier type of the Si substrates through the SCM characterization of the modified regions. The complementary use of KFM and SCM was crucial for the electrical characterization of organic-monolayer-covered semiconductor substrates.