Engineering Band-Edge High-κ/Metal Gate n-MOSFETs with Cap Layers Containing Group IIA and IIIB Elements by Atomic Layer Deposition

Abstract

This paper presents studies performed in engineering high-κ metal gate stacks by using capping layers containing Group IIA and IIIB elements. Both high-κ gate dielectric (HfO 2 ) and capping materials, namely, the oxides of barium, lanthanum and yttrium are deposited by atomic layer deposition (ALD) to offer superior process control and flexibility. Position specific insertion of cap layers into the gate stack is studied and the device tradeoffs are highlighted. The magnitude of threshold voltage shift is correlated to the electronegativity of the cap layer species and its relative position in the gate stack. For a given cap position, BaO provides the maximum threshold voltage shift with the highest penalty in carrier mobility, followed by La 2 O 3 and Y 2 O 3 caps. Both lanthanum and barium incorporation into the high-κ gate stack provides a T inv scaling benefit. Ozone based ALD processes are shown to adversely impact T inv scaling due to the re-growth of the interface layer between the high-κ and the silicon substrate. This penalty is exacerbated in gate stacks with cap layers situated directly below the high-κ film. Significant improvements in T inv scaling are obtained by migrating to a water based ALD process.

Methodology of ALD HfO2 High-κ Gate Dielectric Optimization by Cyclic Depositions and Anneals

“…The choice of precursor and oxidant used in ALD is important in determining the end properties of the high-κ film. Water has been preferred over ozone as the oxidant used in ALD to suppress interface layer growth (2,3). There exist two main classifications among ALD hafnium precursors, namely, halide based and metal-organic (MO) based precursors.…”

“…The ALD used in this study consists of alternating pulses of a metal-organic precursor of hafnium, namely, tetrakis(ethylmethylamido)hafnium (TEMAH), with water as the oxidant. The process exhibits a steady-state growth-per-cycle of ~0.6 Å/cycle and ECS Transactions, 33 (3) 157-164 (2010) has been described in detail previously (2,3). Thermal anneals are inserted during the HfO 2 ALD cycles and are performed under vacuum in nitrogen at various temperatures and durations in the experiments.…”

Development of Lanthanide Precursors as Dopants for Advanced High-k Materials

“…Based on an extensive survey of thermodynamic and electrical property data on corresponding oxides and nitrides by Schlom et al (2) the rare earth oxides appear to offer the best potential of good interfacial stability with silicon and still maintain relatively high-κ with a suitable band gap. Some of the rare earth oxides such as La 2 O 3 and Y 2 O 3 have also found application in high-κ capping layer to tune the effective work function of a transistor (4).…”

(Invited) Radiation Hardness of SiGe and Ge-Based CMOS Technologies

“…To enable threshold voltage tuning the further implementation of metal gates (e.g. TaN or TiN) with an appropriate work function in combination with high-k capping layers is commonly applied [2][3][4][5].…”