| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+NS+EM-ThM |
| Session: | Thin Films: Growth and Characterization-II |
| Presenter: | C. Marichy, Universidade de Aveiro / CICECO, Portugal |
| Authors: | K. Bernal Ramos, University of Texas at Dallas G. Clavel, Université Montpellier 2, France C. Marichy, Universidade de Aveiro / CICECO, Portugal W. Cabrera, The University of Texas at Dallas N. Pinna, Universidade de Aveiro / CICECO, Portugal Y.J. Chabal, University of Texas at Dallas |
| Correspondent: | Click to Email |
Atomic layer deposition (ALD) is a unique technique for the deposition of conformal and homogenous thin films, by the use of successive self-limited surface reactions. Non-aqueous sol-gel routes are elegant approaches for the synthesis of metal oxide nanomaterials.1 High quality inorganic nanocrystals,1 ordered hybrid materials2 or ALD thin films3 can be obtained.
Our ALD approach makes use of metal alkoxides and carboxylic acids as metal and oxygen source, respectively.4 It is expected that the reaction of carboxylic acids with the surface alkoxide species leads to surface carboxylate species (eq. 1), in a second step an aprotic condensation reaction between surface carboxylate species and metal alkoxides leads to metal-oxide bond formation (eq. 2).
≡M-OR’ + RCOOH → ≡M-OOCR + R’OH
≡M-OOCR + M-OR’ → ≡M-O-M≡ + RCOOR’
Characterization of interface properties by in situ investigation of surface reaction mechanisms during deposition of high-k materials provides critical information for the development of semiconductor devices, where sharp interfaces and impurity free films are sought after.
In this work, in-situ IR spectroscopy is used to investigate the mechanisms for TiO2 growth using either acetic acid or O3 as oxygen source and titanium isopropoxide as metal source. It is believed to avoid intermediate OH group and to lead to sharp Si-high-k interfaces.
The IR results of the acetic acid process show clearly a ligand exchange leading to formation of acetates at the surface (vibrational bands at 1527 and 1440 cm-1)during the acetic acid pulse and then to their removal during the metal alkoxide pulse. These finding confirm the expected mechanism and demonstrate the absence of OH intermediate. However, the ligand exchange does not seem to be complete leading to accumulation of C impurities.
The in-situ study of O3 based ALD demonstrates similarities with the above process. Indeed, formation of formate, carboxylate or carbonate species are observed function of the O3 flow.5 The formation of surface carboxylic species upon reaction with O3 leads then to similar surface states as in the case of the reaction with carboxylic acids.4 The mechanism of both approaches and their similarities and differences will be discussed.
1. N. Pinna and M. Niederberger, Angew. Chem.-Int. Edit., 2008, 47, 5292-5304
2. N. Pinna, J. Mater. Chem., 2007, 17, 2769-2774
3. G. Clavel, E. Rauwel, M. G. Willinger and N. Pinna, J. Mater. Chem., 2009, 19, 454-462
4. E. Rauwel, G. Clavel, M. G. Willinger, P. Rauwel and N. Pinna, Angew. Chem.-Int. Edit., 2008, 47, 3592-3595
5. J. Kwon, M. Dai, M. D. Halls, E. Langereis, Y. J. Chabal and R. G. Gordon, J. Phys. Chem. C, 2009, 113, 654-660