3 years ago

Probing the Dielectric Properties of Ultrathin Al/Al2O3/Al Trilayers Fabricated Using in Situ Sputtering and Atomic Layer Deposition

Probing
the Dielectric Properties of Ultrathin Al/Al2O3/Al Trilayers Fabricated Using in Situ Sputtering
and Atomic Layer Deposition
Jagaran Acharya, Judy Wu, Bo Liu, Jamie Wilt
Dielectric properties of ultrathin Al2O3 (1.1–4.4 nm) in metal–insulator–metal (M–I–M) Al/Al2O3/Al trilayers fabricated in situ using an integrated sputtering and atomic layer deposition (ALD) system were investigated. An M–I interfacial layer (IL) formed during the pre-ALD sample transfer even under high vacuum has a profound effect on the dielectric properties of the Al2O3 with a significantly reduced dielectric constant (εr) of 0.5–3.3 as compared to the bulk εr ∼ 9.2. Moreover, the observed soft-type electric breakdown suggests defects in both the M–I interface and the Al2O3 film. By controlling the pre-ALD exposure to reduce the IL to a negligible level, a high εr up to 8.9 was obtained on the ALD Al2O3 films with thicknesses from 3.3 to 4.4 nm, corresponding to an effective oxide thickness (EOT) of ∼1.4–1.9 nm, respectively, which are comparable to the EOTs found in high-K dielectrics like HfO2 at 3–4 nm in thickness and further suggest that the ultrathin ALD Al2O3 produced in optimal conditions may provide a low-cost alternative gate dielectric for CMOS. While εr decreases at a smaller Al2O3 thickness, the hard-type dielectric breakdown at 32 MV/cm and in situ scanning tunneling spectroscopy revealed band gap ∼2.63 eV comparable to that of an epitaxial Al2O3 film. This suggests that the IL is unlikely a dominant reason for the reduced εr at the Al2O3 thickness of 1.1–2.2 nm but rather a consequence of the electron tunneling as confirmed in the transport measurement. This result demonstrates the critical importance in controlling the IL to achieving high-performance ultrathin dielectric in MIM structures.

Publisher URL: http://dx.doi.org/10.1021/acsami.7b16506

DOI: 10.1021/acsami.7b16506

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