Enhancement-Mode Atomic Layer Deposited W-Doped In<sub>2</sub>O<sub>3</sub> Transistor at 55 nm Channel Length by Oxide Capping Layer with Improved Stability
Qing Lin, Nathaniel S. Safron, Donglai Zhong, Goutham Arutchelvan, Carlo Gilardi, Chanyoung Yoo, Jonathan Hartanto, Balreen Saini, Sheng-Chih Lai, Gregory Pitner, Gary Chen, Mi Chang, Yu-Ming Lin, Wilman Tsai, Paul C. McIntyre, Iuliana Radu
Abstract
Amorphous oxide semiconductor field-effect transistors (AOSFETs) exemplify the tradeoff between mobility, stability, and threshold voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\mathrm{V}_{\text{TH}})$</tex>. In this work, a new 5-axes AOSFET evaluation framework for backend-of-line (BEOL) integration is proposed, including (i) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\mathrm{D}}$</tex> extracted at a fixed over-drive beyond <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{TH}}$</tex> at 1 pA/um for performance, (ii) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\text{OFF}}$</tex>, (iii) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{TH}}$</tex>, (iv) subthreshold slope (SS) at 1V <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{DS}}$</tex> for off-state behaviors, and (v) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{TH}}$</tex> shift under positive bias stress for stability. To break the tradeoff between mobility and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{TH}}$</tex>, an oxide capping layer and post-capping anneal are used on back-gated W-doped <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{In}_{2}\mathrm{O}_{3}$</tex> (IWO) FETs. The oxide capping and anneal demonstrate stoichiometry-independent positive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{TH}}$</tex> shift on 1% and 2% IWO channel FETs by 0.85V and 0.4V, respectively, while mobility increases from 18.5 to 26 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{cm}^{2}\mathrm{V}^{-1}\mathrm{s}^{-1}$</tex> for 1% IWO. The contact resistance is also lowered from 2185 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Omega-\mu \mathrm{m}$</tex> to 967 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Omega-\mu \mathrm{m}$</tex>, enabling <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\text{ON}}$</tex> increase by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.42\times$</tex>. With the oxide capping and anneal, the stability under positive bias stress improves by 300 mV to -67 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{mV V}_{\text{TH}}$</tex> shift. An enhancement-mode 1% IWO FET is shown at 55 nm <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{L}_{\text{CH}}$</tex> with positive <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{TH}}=0.53\mathrm{V}$</tex>, low <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\text{OFF}}=160\ \text{pA}/\mu \mathrm{m}, \mathrm{I}_{\mathrm{D}}=192\ \mu \mathrm{A}/\mu \mathrm{m}$</tex> at 1E13 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> charge density, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\mathrm{D}}=50\mu \mathrm{A}/\mu \mathrm{m}$</tex> extracted at a fixed over-drive voltage beyond 1 pA/um at 1V <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{DS}}$</tex>.