Developing a Local Characterization Procedure to Study the Dielectric Properties of HfO2 on MoS2

Abstract

The semiconductor industry will eventually run up against the limits of silicon field-effect transistors. Ultrathin transition metal dichalcogenides (TMDs) are promising candidates to enable continued scaling of microelectronics, beyond the limits of silicon. This will require methods to integrate TMDs with high-performance dielectric materials. Hafnium oxide (HfO2), a well-studied high-k dielectric, is a promising candidate for integration with TMDs in novel transistor technology. There is not yet an established process for this integration due to challenges arising from the dissimlar chemistry of TMD surfaces and ALD oxides. We use Atomic Force Microscopy (AFM) to study the integration of HfO2 grown by Plasma-Enhanced ALD with the 2D TMD MoS2 through charge diffusion measurements, a form of local defect characterization. We have developed a procedure for these measurements in which we inject charge into the exposed oxide surface using the AFM tip, and then use Kelvin Probe Force Microscopy (KPFM) to measure changes in surface potential over time as the injected charge leaks through the thin oxide layer. This procedure was developed with careful consideration of how the measurement environment impacts these electrical measurements. This approach enables quantitative comparison of dielectric performance of oxides on the nanoscale, akin to industry-established methods of wafer-scale oxide integrity testing, which will inform our evaluation of the integration between HfO2 and MoS2.