Stepwise mechanism and H2O-assisted hydrolysis in atomic layer deposition of SiO2 without a catalyst
- Guo-Yong Fang1, 2Email author,
- Li-Na Xu2,
- Lai-Guo Wang1,
- Yan-Qiang Cao1,
- Di Wu1 and
- Ai-Dong Li1Email author
https://doi.org/10.1186/s11671-014-0714-1
© Fang et al.; licensee Springer. 2015
Received: 12 November 2014
Accepted: 23 December 2014
Published: 18 February 2015
Abstract
Atomic layer deposition (ALD) is a powerful deposition technique for constructing uniform, conformal, and ultrathin films in microelectronics, photovoltaics, catalysis, energy storage, and conversion. The possible pathways for silicon dioxide (SiO2) ALD using silicon tetrachloride (SiCl4) and water (H2O) without a catalyst have been investigated by means of density functional theory calculations. The results show that the SiCl4 half-reaction is a rate-determining step of SiO2 ALD. It may proceed through a stepwise pathway, first forming a Si-O bond and then breaking Si-Cl/O-H bonds and forming a H-Cl bond. The H2O half-reaction may undergo hydrolysis and condensation processes, which are similar to conventional SiO2 chemical vapor deposition (CVD). In the H2O half-reaction, there are massive H2O molecules adsorbed on the surface, which can result in H2O-assisted hydrolysis of the Cl-terminated surface and accelerate the H2O half-reaction. These findings may be used to improve methods for the preparation of SiO2 ALD and H2O-based ALD of other oxides, such as Al2O3, TiO2, ZrO2, and HfO2.
Keywords
Background
Possible reaction mechanism of the full ALD cycle of SiO 2 using SiCl 4 and H 2 O. n represents ALD cycles.
Methods
SiO 2 (0001) surface (a) and cluster model Si 23 O 40 H 40 (b).
All the species in ALD SiO2 reactions were optimized using the M06-2X functional within the framework of DFT [11,12]. In order to gain a compromise between accuracy and computational cost, the 6-31G basis set was used for the fixed atoms of the substrate and the 6-31G(d,p) basis set was employed for other atoms on the surface. For each stationary point on the potential energy surface, a frequency calculation was carried out to determine if it is a minimum or a TS. All the transition states were verified by intrinsic reaction coordinates (IRC) calculations. Gibbs free energies of all species were estimated from the partition functions, and the enthalpy and entropy terms at 600 K. The energies reported here include zero-point energy (ZPE) corrections. We note that the solid surface lacks translational and rotational freedom, and the entropy of the surface only has a vibrational contribution. In other words, after being adsorbed onto the surface, the gas molecules lose translational and rotational momenta and produce new vibrational modes. All calculations in this work were performed with Gaussian 09 program [13].
Results and discussion
SiCl4 half-reaction: stepwise mechanism
Gibbs free energy profile of the SiCl 4 half-reaction of SiO 2 ALD. The inset shows the structures of four transition states, TS1A1, TS2A1, TS1A2, and TS2A2, two pentacoordinated intermediates, Im2A1 and Im1A2, and two products, PA1 and PA2.
Selected bond distances (in Å) of all species for SiCl 4 half-reaction
Species | Si-O | O-H | Si-Cl | H-Cl |
---|---|---|---|---|
Im1A1 | 2.01 | 1.03 | 2.11 | 2.62 |
TS1A1 | 1.83 | 1.08 | 2.24 | 2.83 |
Im2A1 | 1.79 | 1.13 | 2.24 | 3.21 |
TS2A1 | 1.77 | 1.02 | 2.94 | 2.01 |
Im3A1 | 1.62 | 4.86 | 4.88 | 1.29 |
PA1 | 2.95 | 0.97 | 2.05 | 3.81 |
TS1A2 | 2.10 | 1.00 | 2.11 | 2.95 |
Im1A2 | 1.83 | 1.02 | 2.27 | 2.76 |
TS2A2 | 1.79 | 1.14 | 2.50 | 1.65 |
Im2A2 | 1.62 | 3.44 | 4.02 | 1.29 |
H2O half-reaction: H2O-assisted hydrolysis
In conventional SiO2 CVD, SiCl4 and H2O are introduced into the reaction chamber simultaneously. Subsequent hydrolysis and condensation lead to the formation of SiO2. Although two reactants are separately introduced into the chamber, hydrolysis and condensation also occur in SiO2 ALD. In fact, the half-reaction between water and the Cl-terminated surface exchanges Cl and -OH ligands and changes Si-Cl* species into Si-OH* species. Due to this the possible reactions of the H2O half-reaction (B) may include the formation of silanol (-Si-OH) via the exchange of ligands between Cl and -OH (reactions B1, B2, B3, B4, and B5) and the formation of -O-Si-O- bridge bonds by removing H2O (reactions B6, B8, and B10) and HCl (reactions B7 and B9), similar to the hydrolysis (-Si-OH) and condensation (-O-Si-O-) processes of SiO2 CVD.
Gibbs free energy profiles of the hydrolysis reactions of -O 2 SiCl 2 * , B1 and B2, in H 2 O half-reaction. The inset shows the structures of three transition states, TS1B1, TS1B2, and H2O-assisted-TS1B1, and two products, PB1 and PB2.
Gibbs free energy profiles of the hydrolysis reactions of -OSiCl 3 * , B3, B4, and B5, in H 2 O half-reaction. The inset shows the structures of seven transition states, TS1B3, TS2B3, TS1B4, TS2B4, TS1B5, TS2B5, and H2O-assisted-TS2B3, a pentacoordinated intermediate, H2O-assisted-Im2B3, and three products, PB3, PB4, and PB5.
Gibbs free energy profiles of H 2 O condensation reactions, B6, B8, and B10, in H 2 O half-reaction. The inset shows the structures of six transition states, TS1B6, TS2B6, TS1B8, TS2B8, TS1B10, and TS2B10.
The Gibbs free energy profiles of HCl condensation reactions, B7 and B9, in H 2 O half-reaction. The inset shows the structures of four transition states, TS1B7, TS2B7, TS1B9, and TS2B9.
When reviewing the full SiO2 ALD cycle, including reactions A1 to A2 and B1 to B10, we find that the free energy barrier for the H2O half-reaction is lower than that for SiCl4 half-reaction. The principal reason is that there are massive H2O molecules adsorbed on the surface, which result in H2O-assisted hydrolysis of -O2Si-Cl2 *, -O2SiOH-Cl*, -OSi-Cl3 *, -OSiOH-Cl2 *, and -OSi(OH)2-Cl* and accelerate the H2O half-reaction. Therefore, the SiCl4 half-reaction is the RDS of the full ALD cycle of SiO2 and controls the ALD growth of SiO2.
Conclusions
Through detailed DFT calculations, the possible reaction pathways of (A) SiCl4 half-reaction and (B) H2O half-reaction in SiO2 ALD without a catalyst have been investigated. The SiCl4 half-reaction is the RDS of SiO2 ALD. It may proceed through a stepwise pathway, first forming a Si-O bond and then breaking Si-Cl and O-H bonds and forming a H-Cl bond. The H2O half-reaction is a complicated process, including hydrolysis and condensation. In the H2O half-reaction, there are massive H2O molecules adsorbed on the surface, which can result in H2O-assisted hydrolysis of the Cl-terminated surface and accelerate the H2O half-reaction. These findings may be used in SiO2 ALD and H2O-based ALD of other oxides, such as Al2O3, TiO2, ZrO2, and HfO2.
Declarations
Acknowledgements
This work was supported by the National Natural Science Foundation of China (51202107), the State Key Program for Basic Research of China (2015CB921203 and 2011CB922104), the China Postdoctoral Science Foundation (2014 M551556), Open Project of National Laboratory of Solid State Microstructures (M27009), and Zhejiang Provincial Natural Science Foundation of China (LY13B030005). ADL is also grateful for the support of the Doctoral Fund of the Ministry of Education of China (20120091110049) and the Priority Academic Program Development (PAPD) in Jiangsu Province. We thank the High Performance Computing Center of Nanjing University for providing the computing resources.
Authors’ Affiliations
References
- Doering R, Nishi Y. Handbook of semiconductor manufacturing technology. 2nd ed. Boca Raton: CRC; 2007.View ArticleGoogle Scholar
- Pinna N, Knez M. Atomic layer deposition of nanostructured materials. New York: Wiley-VCH; 2011.View ArticleGoogle Scholar
- George SM, Sneh O, Dillon AC, Wise ML, Ott AW, Okada LA, et al. Atomic layer controlled deposition of SiO2 and Al2O3 using ABAB… binary reaction sequence chemistry. Appl Surf Sci. 1994;82–83:460–7.View ArticleGoogle Scholar
- Sneh O, Wise ML, Ott AW, Okada LA, George SM. Atomic layer growth of SiO2 on Si(100) using SiCl4 and H2O in a binary reaction sequence. Surf Sci. 1995;334:135–52.View ArticleGoogle Scholar
- George SM, Ott AW, Klaus JW. Surface chemistry for atomic layer growth. J Phys Chem. 1996;100:13121–31.View ArticleGoogle Scholar
- Klaus JW, Ott AW, Johnson JM, George SM. Atomic layer controlled growth of SiO2 films using binary reaction sequence chemistry. Appl Phys Lett. 1997;70:1092–4.View ArticleGoogle Scholar
- Kang JK, Musgrave CB. Mechanism of atomic layer deposition of SiO2 on the silicon (100)-2 × 1 surface using SiCl4 and H2O as precursors. J Appl Phys. 2002;91:3408–14.View ArticleGoogle Scholar
- Ritala M, Kukli K, Rahtu A, Räisänen PI, Leskelä M, Sajavaara T, et al. Atomic layer deposition of oxide thin films with metal alkoxides as oxygen sources. Science. 2000;288:319–21.View ArticleGoogle Scholar
- Hausmann D, Becker J, Wang S, Gordon RG. Rapid vapor deposition of highly conformal silica nanolaminates. Science. 2002;298:402–6.View ArticleGoogle Scholar
- Fang G, Ma J. Rapid atomic layer deposition of silica nanolaminates: synergistic catalysis of Lewis/Brønsted acid sites and interfacial interactions. Nanoscale. 2013;5:11856–69.View ArticleGoogle Scholar
- Zhao Y, Truhlar DG. Density functionals with broad applicability in chemistry. Acc Chem Res. 2008;41:157–67.View ArticleGoogle Scholar
- Zhao Y, Truhlar DG. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functional. Theor Chem Acc. 2008;120:215–41.View ArticleGoogle Scholar
- Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, et al. Gaussian 09. Revision B.02. Wallingford CT: Gaussian, Inc; 2009.Google Scholar
- Klaus JW, Sneh O, George SM. Growth of SiO2 at room temperature with the use of catalyzed sequential half reaction. Science. 1997;278:1934–6.View ArticleGoogle Scholar
- Klaus JW, Sneh O, Ott AW, George SM. Atomic layer deposition of SiO2 using catalyzed and uncatalyzed self-limiting surface reactions. Surf Rev Lett. 1999;6:435–48.View ArticleGoogle Scholar
- Klaus JW, George SM. Atomic layer deposition of SiO2 at room temperature using NH3-catalyzed sequential surface reactions. Surf Sci. 2000;447:81–90.View ArticleGoogle Scholar
- Klaus JW, George SM. SiO2 chemical vapor deposition at room temperature using SiCl4 and H2O with an NH3 catalyst. J Electrochem Soc. 2000;147:2658–64.View ArticleGoogle Scholar
- Ferguson JD, Smith ER, Weimer AW, George SM. ALD of SiO2 at room temperature using TEOS and H2O with NH3 as the catalyst. J Electrochem Soc. 2004;151:G528–35.View ArticleGoogle Scholar
- Du Y, Du X, George SM. SiO2 film growth at low temperatures by catalyzed atomic layer deposition in a viscous flow reactor. Thin Sol Film. 2005;491:43–53.View ArticleGoogle Scholar
- Du Y, Du X, George SM. Mechanism of pyridine-catalyzed SiO2 atomic layer deposition studied by Fourier transform infrared spectroscopy. J Phys Chem C. 2007;111:219–26.View ArticleGoogle Scholar
- Hatton B, Kitaev V, Perovic D, Ozin G, Aizenberg J. Low-temperature synthesis of nanoscale silica multilayers - atomic layer deposition in a test tube. J Mater Chem. 2010;20:6009–13.View ArticleGoogle Scholar
- Bachmann J, Zierold R, Chong YT, Hauert R, Sturm C, Schmidt-Grund R, et al. A practical, self-catalytic, atomic layer deposition of silicon dioxide. Angew Chem Int Ed. 2008;47:6177–9.View ArticleGoogle Scholar
- Fang G, Chen S, Li A, Ma J. Surface pseudorotation in Lewis-base-catalyzed atomic layer deposition of SiO2: static transition state search and Born − Oppenheimer molecular dynamics simulation. J Phys Chem C. 2012;116:26436–48.View ArticleGoogle Scholar
- Fang GY, Xu LN, Cao YQ, Wang LG, Wu D, Li DL. Self-catalysis by aminosilanes and strong surface oxidation by O2 plasma in plasma-enhanced atomic layer deposition of high-quality SiO2. Chem Commun. 2015;51:1341–4.View ArticleGoogle Scholar
- Antonczak S, Ruiz-Lόpez MF, Rivail JL. Ab initio analysis of water-assisted reaction mechanisms in amide hydrolysis. J Am Chem Soc. 1994;116:3912–21.View ArticleGoogle Scholar
- Schmeer G, Sturm P. A quantum chemical approach to the water assisted neutral hydrolysis of ethyl acetate and its derivatives. Phys Chem Chem Phys. 1999;1:1025–30.View ArticleGoogle Scholar
- Tsuchida N, Satou H, Yamabe S. Reaction paths of the water-assisted solvolysis of N, N-dimethylformamide. J Phys Chem A. 2007;111:6296–303.View ArticleGoogle Scholar
- Gao JY, Zeng Y, Zhang CH, Xue Y. Theoretical studies on the water-assisted hydrolysis of N, N-dimethyl-N’-(2′,3′-dideoxy-3′-thiacytidine) formamidine with three water molecules. J Phys Chem A. 2009;113:325–31.View ArticleGoogle Scholar
- Bell RL, Truong TN. Primary and solvent kinetic isotope effects in the water-assisted tautomerization of formamidine: an ab initio direct dynamics study. J Phys Chem A. 1997;101:7802–8.View ArticleGoogle Scholar
- Gu J, Leszczynski J. A DFT study of the water-assisted intramolecular proton transfer in the tautomers of adenine. J Phys Chem A. 1999;103:2744–50.View ArticleGoogle Scholar
- Liu GX, Li ZS, Ding YH, Fu Q, Huang XR, Sun CC, et al. Water-assisted isomerization from linear propargylium (H2CCCH+) to cyclopropenylium(c-C3H3 +). J Phys Chem A. 2002;106:10415–22.View ArticleGoogle Scholar
- Balta B, Aviyente V. Solvent effects on glycine II. Water-assisted tautomerization. J Comput Chem. 2004;25:690–703.View ArticleGoogle Scholar
- Markova N, Enchev V, Timtcheva I. Oxo-hydroxy tautomerism of 5-fluorouracil: water-assisted proton transfer. J Phys Chem A. 2005;109:1981–8.View ArticleGoogle Scholar
- Michalkova A, Kosenkov D, Gorb L, Leszczynski J. Thermodynamics and kinetics of intramolecular water assisted proton transfer in Na+-1-methylcytosine water complexes. J Phys Chem B. 2008;112:8624–33.View ArticleGoogle Scholar
- Aplincourt P, Anglada JM. Theoretical studies of the isoprene ozonolysis under tropospheric conditions. 2. Unimolecular and water-assisted decomposition of the r-hydroxy hydroperoxides. J Phys Chem A. 2003;107:5812–20.View ArticleGoogle Scholar
- Jacobs G, Patterson PM, Graham UM, Crawford AC, Dozier A, Davis BH. Catalytic links among the water–gas shift, water-assisted formic acid decomposition, and methanol steam reforming reactions over Pt-promoted thoria. J Cat. 2005;235:79–91.View ArticleGoogle Scholar
- Huang J, Yeung CS, Ma J, Gayner ER, Phillips DL. A computational chemistry investigation of the mechanism of the water-assisted decomposition of trichloroethylene oxide. J Phys Chem A. 2014;118:1557–67.View ArticleGoogle Scholar
- Ouchi M, Yoda H, Terashima T, Sawamoto M. Aqueous metal-catalyzed living radical polymerization: highly active water-assisted catalysis. Polym J. 2012;44:51–8.View ArticleGoogle Scholar
- Thorat PB, Goswami SV, Jadhav WN, Bhusare SR. Water-assisted organocatalysis: an enantioselective green protocol for the henry reaction. Aust J Chem. 2013;66:661–6.View ArticleGoogle Scholar
- Mukhopadhyay AB, Musgrave CB, Sanz JF. Atomic layer deposition of hafnium oxide from hafnium chloride and water. J Am Chem Soc. 2008;130:11996–2006.View ArticleGoogle Scholar
Copyright
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.