Rapid atomic layer deposition (RALD) of SiO₂ thin films was achieved using trimethyl-aluminum and tris(tert-pentoxy)silanol (TPS) as the catalyst and Si precursor, respectively. A maximum growth rate as high as ∼28 nm/cycle was obtained by optimizing the catalyst layer density, whereas the previous reports showed lower values of 12 to 17 nm/cycle [Hausmann et al. Science2002, 298, 402-406; Burton et al. Chem. Mater. 2008, 20, 7031-7043]. When the growth temperature was increased from 140 to 230 °C, the growth rate was not much reduced and the TPS pulse time showing a saturated growth rate became rather longer. Si-CH₃, Si-OH, and Si-H bonds were not detected in infrared spectra from the RALD SiO₂ film grown at 230 °C. The film quality could be enhanced substantially by applying a higher growth temperature and an in situ post plasma treatment process.
Silicon oxide thin film grown at low temperatures (<300–500 °C) is essential for a range of applications in semiconductor devices. In this study, silicon oxide films were deposited at a substrate temperature of ∼300 °C by an atomic layer deposition (ALD) process using Bis(ethyl-methyl-amino)silane (BEMAS). BEMAS precursors adsorbed on the growing surface reacted with ozone but not with H2O. This suggests that the Si–H bonds in the BEMAS precursors adsorbed on the surface are robust and could be cleaved only by ozone. The reaction using BEMAS and ozone exhibited ALD saturation behavior. The dielectric constant of the ALD-SiO2 was measured to be ∼9, which is 2.3 times higher than that (∼3.9) of normal amorphous SiO2. This was attributed to the existence of the ∼10% OH species in the film.
It has not been an easy task to deposit SiN at low temperature by conventional plasma-enhanced atomic layer deposition (PE-ALD) since Si organic precursors generally have high activation energy for adsorption of the Si atoms on the Si-N networks. In this work, in order to achieve successful deposition of SiN film at low temperature, the plasma processing steps in the PE-ALD have been modified for easier activation of Si precursors. In this modification, the efficiency of chemisorption of Si precursor has been improved by additional plasma steps after purging of the Si precursor. As the result, the SiN films prepared by the modified PE-ALD processes demonstrated higher purity of Si and N atoms with unwanted impurities such as C and O having below 10 at. % and Si-rich films could be formed consequently. Also, a very high step coverage ratio of 97% was obtained. Furthermore, the process-optimized SiN film showed a permissible charge-trapping capability with a wide memory window of 3.1 V when a capacitor structure was fabricated and measured with an insertion of the SiN film as the charge-trap layer. The modified PE-ALD process using the activated Si precursor would be one of the most practical and promising solutions for SiN deposition with lower thermal budget and higher cost-effectiveness.
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