DOI: 10.1002/cvde.200606496 Full Paper Plasma Characterization of Oxygen-Tetramethylsilane Mixtures for the Plasma-Enhanced CVD of SiO x C y H z Thin Films** By Ángel Yanguas-Gil,* Ángel Barranco, José Cotrino, Pierangelo Gröning, and Agustín R. González-Elipe The plasma-enhanced (PE)CVD of SiO x C y H z thin films from O 2 /Ar/tetramethylsilane (TMS) mixtures, in a low-pressure microwave electron cyclotron resonant (ECR) plasma reactor, has been studied. The discharge has been analyzed by mass spectrometry (MS) and optical emission spectroscopy (OES) for varying amounts of oxygen in the gas mixture both in the presence and in the absence of argon. The films obtained have been characterized by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). It is found that the electron impact of the TMS molecules and their dissociative ion- ization play an important role in the deposition process. Si(OH) x (CH 3 ) 3–x species, produced by reactions between the Si(CH 3 ) 4 molecule and Si(CH 3 ) 3 + ion fragments with O and O 2 , have been identified as important reaction intermediates. Such species form in different proportions depending on the O 2 /TMS ratio in the gas mixture. It is proposed that their in- corporation onto the surface of the growing films accounts for the wide range of compositions achieved (ranging from SiO 2 to almost Si:C:H) and the high concentration of Si-C bonds experimentally detected in the SiO x C y H z thin films. Keywords: Mass spectrometry, Plasmas, SiO x C y H z , Thin films, TMS 1. Introduction During recent years plasma-deposited SiO x C y H z sili- cone-like thin films have attracted great interest because of their electronic, optoelectronic, and chemical properties. [1,2] Thus, for example, they are widely used in very large scale integration (VLSI) technology, [3,4] as anticorrosion protective layers, [5] hydrophobic coatings, [6] and passivation layers. [7] A common method of preparation of these thin films is PECVD. Typical precursors used in their synthesis are tetraethoxysilane (TEOS), hexamethyldisiloxane, TMS, and other silicon-based compounds with cyclic and aro- matic substituents. When SiO x C y H z thin films are used as low-k materials for the microelectronics industry and other applications, it is not only important that they present a very low dielectric constant, but also that they form conformal coatings that homogeneously cover strips and trenches, or any other kind of substrates with complex shapes. [8] This conformality is strongly dependent on the nature of the fragments coming from the plasma to form the growing film. [9] In this regard, knowledge of the plasma chemistry and the reaction path- ways involved in the deposition process are of paramount importance in understanding the properties of the films and in tailoring their characteristics and properties by changing the deposition parameters. TMS is an interesting precursor for plasma deposition of SiO x C y H z thin films that, even though it offers a series of advantages compared to other precursors, is not so widely reported in the literature. In fact, TMS is safer than silane and has a vapor pressure greater than that of other widely used precursors such as TEOS. [10] This means that heating of the experimental system to avoid wall condensation is not necessary. Moreover, due to its molecular structure, it is possible to obtain materials with compositions ranging from silicon carbide to silicon oxide. [11,12] Recently, the preparation of low-k SiO x C y H z thin films by PECVD from TMS mixtures has been reported by some authors. [13] Compared to other precursors, the plasma chemistry of TMS is not completely understood, particularly in oxygen/ TMS mixtures. The plasma chemistry of pure TMS in RF discharges has been studied using OES by Thomas et al. [14] and using MS by Jauberteau et al. [15] Fonseca et al. pre- sented Si NMR measurements of thin films obtained from 728 © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Vap. Deposition 2006, 12, 728–735 – [*] Dr. Á. Yanguas-Gil, [+] Dr. Á. Barranco, Prof. J. Cotrino, Prof. A. R. González-Elipe Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla) Avda. Américo Vespucio s/n., 41092 Sevilla (Spain) E-mail: angel.yanguas@icmse.csic.es Prof. J. Cotrino Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla, 41092 Sevilla (Spain) Prof. P. A. Gröning Swiss Federal Laboratories for Materials Testing and Research (EMPA), Nanotech Surfaces Laboratory Feuerwerkerstrasse 39, CH-3602 Thun (Switzerland) [+] Current address: Fakultät für Physik und Astronomie, Ruhr Universität Universitätstr. 150, 44780 Bochum (Germany) [**] We thank the Ministry of Science and Education of Spain for financial support (grants Nos. MAT2004-01558 and NAN2004-09317-C04-01).