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Han, Jeong Hwan,Lee, Woongkyu,Jeon, Woojin,Lee, Sang Woon,Hwang, Cheol Seong,Ko, Changhee,Gatineau, Julien American Chemical Society 2012 Chemistry of materials Vol.24 No.24
<P>SrRuO<SUB>3</SUB> (SRO) film was deposited by sequential executions of atomic layer deposition of SrO and chemical vapor deposition of RuO<SUB>2</SUB> layers at a low growth temperature of 230 °C using Sr(<SUP><I>i</I></SUP>Pr<SUB>3</SUB>Cp)<SUB>2</SUB>, RuO<SUB>4</SUB> precursors, and O<SUB>2</SUB> gas. A wide range of Sr (Ru) concentration could be obtained by modulating the SrO/RuO<SUB>2</SUB> subcycle ratio, and a high growth rate of ∼2.0 nm/supercycle was achieved with the stoichiometric SRO composition. The as-deposited SRO film was amorphous, and crystallized SRO film was obtained by post deposition annealing in N<SUB>2</SUB> ambient at temperatures ranging from 600 to 700 °C. Crystallized SRO film was adopted as a seed layer for the in situ crystallization of ALD SrTiO<SUB>3</SUB> (STO) film for application to capacitors for next generation dynamic random access memory. Consequently, a crystalline STO film was grown on crystallized SRO in the as-deposited state, and the dielectric constant of the STO film was largely improved compared to that of the amorphous STO, from 12 to 44.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2012/cmatex.2012.24.issue-24/cm302470k/production/images/medium/cm-2012-02470k_0006.gif'></P>
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 American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.1
<P>The growth characteristics of Ta2O5 thin films by atomic layer deposition (ALD) were examined using Ta((NBu)-Bu-t)(NEt2)3 (TBTDET) and Ta((NBu)-Bu-t)(NEt2)(2)Cp (TBDETCp) as Ta-precursors, where tBu, Et, and Cp represent tert-butyl, ethyl, and cyclopentadienyl groups, respectively, along with water vapor as oxygen source. The grown Ta2O5 films were amorphous with very smooth surface morphology for both the Ta-precursors. The saturated ALD growth rates of Ta2O5 films were 0.77 angstrom cycle(-1) at 250 degrees C and 0.67 angstrom cycle(-1) at 300 degrees C using TBTDET and TBDETCp precursors, respectively. The thermal decomposition of the amido ligand (NEt2) limited the ALD process temperature below 275 degrees C for TBTDET precursor. However, the ALD temperature window could be extended up to 325 degrees C due to a strong Ta-Cp bond for the TBDETCp precursor. Because of the improved thermal stability of TBDETCp precursor, excellent nonuniformity of similar to 2% in 200 mm wafer could be achieved with a step coverage of similar to 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 (similar to 7 at. %) of carbon impurities was incorporated into the Ta2O5 film using TBDETCp, which was possibly due to readsorption of dissociated ligands as small organic molecules in the growth of Ta2O5 film by ALD. Despite the presence of high carbon concentration which might be an origin of large leakage current under electric fields, the Ta2O5 film using TBDETCp showed a promising resistive switching performance with an endurance cycle as high as similar to 17?500 for resistance switching random access memory application. The optical refractive index of the deposited Ta2O5 films was 2.1-2.2 at 632.8 nm using both the Ta-precursors, and indirect optical band gap was estimated to be similar to 4.1 eV for both the cases.</P>
Song, Seul Ji,Lee, Sang Woon,Kim, Gun Hwan,Seok, Jun Yeong,Yoon, Kyung Jean,Yoon, Jung Ho,Hwang, Cheol Seong,Gatineau, Julien,Ko, Changhee American Chemical Society 2012 Chemistry of materials Vol.24 No.24
<P>In this study, NiO thin films were deposited via a plasma-enhanced atomic layer deposition (PEALD) on metal (Pt, Ru, and W) substrates using a bis-methylcyclopentadienyl-nickel ([MeCp]<SUB>2</SUB>Ni) precursor followed by a reaction with plasma-enhanced oxygen gas. The ALD temperature regime of NiO films was defined between 150 and 250 °C, while substrate temperature higher than this region induced the thermal cracking of precursors. The saturated PEALD rates of NiO film on Pt, Ru, and W substrates were 0.48, 0.58, and 0.84 Å/cycle, respectively, even though it has been usually regarded that the substrate effect on the saturated ALD rate vanishes after covering the entire surface with the growing films. At the initial stage of film growth, the NiO film showed enhanced nucleation behavior on the W and Ru substrates, whereas it did not show enhanced growth behavior on the Pt substrate. X-ray photoelectron spectroscopy revealed that the surface of a NiO film, which is thick enough for the W substrate not to influence the analysis, contains WO<SUB>3</SUB> bonding states while the films grown on other metal substrates did not show any oxidation states of the substrate metal species. This could be due to the fact that the diatomic bond strength of W–O is stronger than that of Ni–O, which may induce the layer inversion during the ALD of NiO on the W substrate, and the surface W–O promotes the surface chemical reaction. This can result in the eventual increase of the saturated growth rate even in the ALD mode. The supply of oxygen to the adsorbing Ni-precursor by the reduction of a previously oxidized Ru substrate enhanced the initial growth rate of NiO film but this does not affect the steady-state growth rate on the Ru substrate. The small lattice mismatch between the NiO and Pt, as well as the identical crystal structure of the two materials results in the local epitaxial growth of NiO film on Pt substrate even though the growth temperature was only 250 °C. The NiO films on the W substrate showed reliable bipolar resistance switching in a wide temperature range (25–100 °C), which provides new opportunities for the next generation nonvolatile memory applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2012/cmatex.2012.24.issue-24/cm302182s/production/images/medium/cm-2012-02182s_0011.gif'></P>
Jung, Hanearl,Kim, Woo-Hee,Park, Bo-Eun,Woo, Whang Je,Oh, Il-Kwon,Lee, Su Jeong,Kim, Yun Cheol,Myoung, Jae-Min,Gatineau, Satoko,Dussarrat, Christian,Kim, Hyungjun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.2
<P>We report the effect of Y2O3 passivation by atomic layer deposition (ALD) using various oxidants, such as H2O, O-2 plasma, and O-3, on In-Ga-Zn-O thin-film transistors (IGZO TFTs). A large negative shift in the threshold voltage (V-th) was observed in the case of the TFT subjected to the H2O-ALD Y2O3 process; this shift was caused by a donor effect of negatively charged chemisorbed H2O molecules. In addition, degradation of the IGZO TFT device performance after the O-2 plasma-ALD Y2O3 process (field-effect mobility (mu) = 8.7 cm(2)/(V.s), subthreshold swing (SS) = 0.77 V/dec, and V-th = 3.7 V) was observed, which was attributed to plasma damage on the IGZO surface adversely affecting the stability of the TFT under light illumination. In contrast, the O-3-ALD Y2O3 process led to enhanced device stability under light illumination (Delta V-th = 1 V after 3 h of illumination) by passivating the subgap defect states in the IGZO surface region. In addition, TFTs with a thicker IGZO film (55 nm, which was the optimum thickness under the current investigation) showed more stable device performance than TFTs with a thinner IGZO film (30 nm) (Delta V-th = -0.4 V after 3 h of light illumination) by triggering the recombination of holes diffusing from the IGZO surface to the insulator-channel interface. Therefore, we envisioned that the O-3-ALD Y2O3 passivation layer suggested in this paper can improve the photostability of TFTs under light illumination.</P>
Lee, Sang Woon,Han, Jeong Hwan,Han, Sora,Lee, Woongkyu,Jang, Jae Hyuck,Seo, Minha,Kim, Seong Keun,Dussarrat, C.,Gatineau, J.,Min, Yo-Sep,Hwang, Cheol Seong American Chemical Society 2011 Chemistry of materials Vol.23 No.8
<P>The ever-shrinking dimensions of dynamic random access memory (DRAM) require a high quality dielectric film for capacitors with a sufficiently high growth-per-cycle (GPC) by atomic layer deposition (ALD). SrTiO<SUB>3</SUB> (STO) films are considered to be the appropriate dielectric films for DRAMs with the design rule of ∼20 nm, and previous studies showed that STO films grown by ALD have promising electrical performance. However, the ALD of STO films still suffers from much too slow GPC to be used in mass-production. Here, we accomplished a mass-production compatible ALD process of STO films using Ti(O-<SUP><I>i</I></SUP>Pr)<SUB>2</SUB>(tmhd)<SUB>2</SUB> as a Ti-precursor for TiO<SUB>2</SUB> layers and Sr(<SUP><I>i</I></SUP>Pr<SUB>3</SUB>Cp)<SUB>2</SUB> as a Sr-precursor for SrO layers. O<SUB>3</SUB> and H<SUB>2</SUB>O were used as the oxygen sources for the TiO<SUB>2</SUB> and SrO layers, respectively. A highly improved GPC of 0.107 nm/unit-cycle (0.428 nm/supercycle) for stoichiometric STO films was obtained at a deposition temperature of 370 °C, which is ∼7 times higher than previously reported. The origin of such high GPC values in this STO films could be explained by the partial decomposition of the precursors used and the strong tendency of water adsorption onto the SrO layer in comparison to the TiO<SUB>2</SUB> layer. The STO film grown in this study also showed an excellent step coverage (∼95%) when deposited inside a deep capacitor hole with an aspect ratio of 10. Owing to the high bulk dielectric constant (∼ 146) of the STO film, an equivalent oxide thickness of 0.57 nm was achieved with a STO film of 10 nm. In addition, the leakage current density was sufficiently low (3 × 10<SUP>−8</SUP> Acm<SUP>−2</SUP> at +0.8 V). This process is extremely promising for fabrication of the next generation DRAMs.</P><P>Conformal SrTiO<SUB>3</SUB> (STO) thin films were grown at 370 °C with a high growth-per-cycle (0.107 nm/unit-cycle) by atomic layer deposition. An equivalent oxide thickness of 0.57 nm was achived with a STO film of 10 nm.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2011/cmatex.2011.23.issue-8/cm2002572/production/images/medium/cm-2011-002572_0007.gif'></P>