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Uniform Growth of Sub-5-Nanometer High‑κ Dielectrics on MoS2 Using Plasma-Enhanced Atomic Layer Deposition

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posted on 2017-06-27, 00:13 authored by Katherine M. Price, Kirstin E. Schauble, Felicia A. McGuire, Damon B. Farmer, Aaron D. Franklin
Regardless of the application, MoS2 requires encapsulation or passivation with a high-quality dielectric, whether as an integral aspect of the device (as with top-gated field-effect transistors (FETs)) or for protection from ambient conditions. However, the chemically inert surface of MoS2 prevents uniform growth of a dielectric film using atomic layer deposition (ALD)the most controlled synthesis technique. In this work, we show that a plasma-enhanced ALD (PEALD) process, compared to traditional thermal ALD, substantially improves nucleation on MoS2 without hampering its electrical performance, and enables uniform growth of high-κ dielectrics to sub-5 nm thicknesses. Substrate-gated MoS2 FETs were studied before/after ALD and PEALD of Al2O3 and HfO2, indicating the impact of various growth conditions on MoS2 properties, with PEALD of HfO2 proving to be most favorable. Top-gated FETs with high-κ films as thin as ∼3.5 nm yielded robust performance with low leakage current and strong gate control. Mechanisms for the dramatic nucleation improvement and impact of PEALD on the MoS2 crystal structure were explored by X-ray photoelectron spectroscopy (XPS). In addition to providing a detailed analysis of the benefits of PEALD versus ALD on MoS2, this work reveals a straightforward approach for realizing ultrathin films of device-quality high-κ dielectrics on 2D crystals without the use of additional nucleation layers or damage to the electrical performance.

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