Comparison of the Atomic Layer Deposition of Tantalum Oxide Thin Films Using Ta(NtBu)(NEt2)3, Ta(NtBu)(NEt2)2Cp, and H2O
文摘
The growth characteristics of Tab>2b>Ob>5b> thin films by atomic layer deposition (ALD) were examined using Ta(Np>tp>Bu)(NEtb>2b>)b>3b> (TBTDET) and Ta(Np>tp>Bu)(NEtb>2b>)b>2b>Cp (TBDETCp) as Ta-precursors, where p>tp>Bu, Et, and Cp represent tert-butyl, ethyl, and cyclopentadienyl groups, respectively, along with water vapor as oxygen source. The grown Tab>2b>Ob>5b> films were amorphous with very smooth surface morphology for both the Ta-precursors. The saturated ALD growth rates of Tab>2b>Ob>5b> films were 0.77 Å cyclep>–1p> at 250 °C and 0.67 Å cyclep>–1p> at 300 °C using TBTDET and TBDETCp precursors, respectively. The thermal decomposition of the amido ligand (NEtb>2b>) 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 Tab>2b>Ob>5b> film using TBDETCp, which was possibly due to readsorption of dissociated ligands as small organic molecules in the growth of Tab>2b>Ob>5b> film by ALD. Despite the presence of high carbon concentration which might be an origin of large leakage current under electric fields, the Tab>2b>Ob>5b> 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 Tab>2b>Ob>5b> 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.