Paper TF+AS+EL+PS-ThM13
Realization of Shifts in Threshold Voltage and Subthreshold Swing in Atomic Layer Deposited Zinc Oxide As Channel Layer through in-situ Half-Cycle Analysis

Thursday, October 25, 2018, 12:00 pm, Room 102A

Thin film process monitoring of atomic layer deposition (ALD) has been adopted as the versatile technique to identify both chemical and physical properties of ALD films. Their in-situ characterization technique includes mostly Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and quartz crystal microbalance analysis. ^[1–3] However, currently there are no reports on monitoring the results of sub-nm device physics even if we are already in the era of beyond 10 nm node semiconductor processes. Moreover, even if there are a few initial studies, demonstrating in-situ electrical characterization with ALD, it requires device packaging, which ultimately limits the flexibility to be further characterized. ^[4]

In this current work, we have developed an ultra-high vacuum (UHV) cluster tool equipped with thermal processing, plasma surface treatment, thin film deposition, and electrical characterization which can be performed in-situ (Figure 1). With this feasibility, we demonstrate the deposition of semiconducting zinc oxide (ZnO) in inverted-coplanar structured thin film transistors (TFT). Diethylzinc (DEZ) and water (H₂O) is used as ALD precursors at 100°C. DEZ and H₂O half-cycle analysis is carried out to monitor the interface states of ZnO/dielectric (Figure 2). Initially, 45 ALD cycles of ZnO have shown switching behavior with an on/off ratio of ~10² in vacuum. Subsequent ALD cycle shifts the threshold voltage (V_th). V_th shifts associated with each ALD cycle are assumed to be attributed to the changes in interface trap density as a result of interface state passivation in ZnO during its growth, especially passivating fixed oxide charges (Q_ox). To understand interface states of ZnO and the bulk of oxide better, further analysis of shift of subthreshold swing (SS) is demonstrated. Since shifts in SS best represents changes in interface trap density, ^[5] it is worthwhile to note the changes in SS in metal-oxide-semiconductor transistors.

This work was supported by the Creative Materials Discovery Program on Creative Multilevel Research Center (2015M3D1A1068061) through the National Research Foundation(NRF) of Korea funded by the Ministry of Science, ICT & Future Planning.

[1] D. N. Goldstein et al., J. Phys. Chem. C.112, 19530, 2008.

[2] M. D. Groner et al., Chem. Mater.16, 639, 2004.

[3] C. L. Hinkle et al., Appl. Phys. Lett.91, 1, 2007.

[4] S. Jandhyala et al., ACS Nano.6, 2722, 2012.