Comparison of the Atomic Layer Deposition of Tantalum Oxide Thin Films Using Ta(N t Bu)(NEt 2 ) 3 , Ta(N t Bu)(NEt 2 ) 2 Cp, and H 2 O

• Published in: ACS applied materials & interfaces Vol. 9; no. 1; pp. 537 - 547
• Main Authors: Song, Seul Ji, Park, Taehyung, Yoon, Kyung Jean, Yoon, Jung Ho, Kwon, Dae Eun, Noh, Wontae, Lansalot-Matras, Clement, Gatineau, Satoko, Lee, Han-Koo, Gautam, Sanjeev, Cho, Deok-Yong, Lee, Sang Woon, Hwang, Cheol Seong
• Format: Journal Article
• Language: English
• Published: United States 11-01-2017
• Subjects: atomic layer deposition (ALD); Ta(NtBu)(NEt2)3 (TBTDET); resistive switching; Ta(NtBu)(NEt2)2Cp (TBDETCp); Ta2O5
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b11613

The growth characteristics of Ta
O
thin films by atomic layer deposition (ALD) were examined using Ta(N
Bu)(NEt
)
(TBTDET) and Ta(N
Bu)(NEt
)
Cp (TBDETCp) as Ta-precursors, where
Bu, Et, and Cp represent tert-butyl, ethyl, and cyclopentadienyl groups, respectively, along with water vapor as oxygen source. The grown Ta
O
films were amorphous with very smooth surface morphology for both the Ta-precursors. The saturated ALD growth rates of Ta
O
films were 0.77 Å cycle
at 250 °C and 0.67 Å cycle
at 300 °C using TBTDET and TBDETCp precursors, respectively. The thermal decomposition of the amido ligand (NEt
) limited the ALD process temperature below 275 °C for TBTDET precursor. However, the ALD temperature window could be extended up to 325 °C due to a strong Ta-Cp bond for the TBDETCp precursor. Because of the improved thermal stability of TBDETCp precursor, excellent nonuniformity of ∼2% in 200 mm wafer could be achieved with a step coverage of ∼90% in a deep hole structure (aspect ratio 5:1) which is promising for 3-dimensional architecture to form high density memories. Nonetheless, a rather high concentration (∼7 at. %) of carbon impurities was incorporated into the Ta
O
film using TBDETCp, which was possibly due to readsorption of dissociated ligands as small organic molecules in the growth of Ta
O
film by ALD. Despite the presence of high carbon concentration which might be an origin of large leakage current under electric fields, the Ta
O
film using TBDETCp showed a promising resistive switching performance with an endurance cycle as high as ∼17 500 for resistance switching random access memory application. The optical refractive index of the deposited Ta
O
films was 2.1-2.2 at 632.8 nm using both the Ta-precursors, and indirect optical band gap was estimated to be ∼4.1 eV for both the cases.