Deposition of Thin Films of SiO_xC_yH in a Surfatron Microwave Plasma Reactor with Hexamethyldisiloxane as Precursor

Abstract

Thin films of SiO x C y H have been prepared by plasma enhanced (PE)CVD in a surface-wave, microwave reactor. The films were deposited in direct mode by using hexamethyldisiloxane (HMDSO) as the precursor, and mixtures of oxygen/argon as the plasma gas. Analysis of the plasma by optical emission spectroscopy (OES) showed that, under reaction conditions, the molecules of the precursor are not greatly fragmented in the plasma. This suggests that polymerization occurs after adsorption of the precursor species on the surface of the growing films. The chemical structure and composition of the films were examined by Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). A strong correlation is found between the composition and bonding structure of the thin films and the oxygen:HMDSO ratio in the plasma gas. Raising the oxygen concentration leads to an increase in the growth rate and to the removal of the organic groups from the films that, for O 2 :HMDSO ratios greater than 0.8, reach a composition close to silicon dioxide. It has been shown that the Auger parameter of silicon determined by XPS depends on the composition of the films (e.g., 1714.5 for O 2 :HMDSO = 0, and 1712.3 for O 2 :HMDSO = 0.75). It is shown that this parameter can be taken as a measurement of the polarizability of the films. It is concluded that surfatron launchers are a versatile set-up for an efficient control of the composition and properties of thin films of SiO x C y H prepared by PECVD.

Low‐Temperature PECVD of Transparent SiOxCyHz Thin Films

“…Irrespective of the synthesis conditions, the more intense signal was centered at 1070-1080 cm -1 and mainly ascribed to Si-O-Si stretching (see below for further details). [6,13,17,22,26] Accordingly, peaks located at ≈840 and ≈450 cm -1 were mainly related to…”

“…In fact, besides requiring the use of oxidizing reagents such as O 2 or N 2 O, the above compound has a high toxicity and reactivity. [17,18] Moreover, in the obtained films, poor conformal step coverage, and the formation of powders and defects that are detrimental to their functional utilization, have been observed. [1,13,19] In order to overcome such limitations, alternative precursors have been employed, including tetramethylsilane and similar halogenated derivatives, as well as esamethyldisilazane, esamethyldisiloxane (HMDSO), tetramethoxy-(TMOS) and tetraethoxysilane (TEOS).…”

“…[1,13,19] In order to overcome such limitations, alternative precursors have been employed, including tetramethylsilane and similar halogenated derivatives, as well as esamethyldisilazane, esamethyldisiloxane (HMDSO), tetramethoxy-(TMOS) and tetraethoxysilane (TEOS). [1,2,6,[13][14][15]17,20,21] Among these compounds, alkoxysilanes, besides allowing easy manipulation and offering an appreciable volatility, also contain pre-formed Si-O bonds which, under suitable preparative conditions, can be readily incorporated in the growing films thus allowing the exclusion of oxidizing agents from the reaction atmosphere. This aspect is important in the deposition of SiO x C y H z as a protective coating for metallic substrates, in order to prevent undesired chemical modifications of the growth surface.…”

“…[10] On this basis, PECVD represents a preferred choice among the various liquid-and vapor-phase routes, thanks to the low temperature deposition of such materials at appreciable growth rates, and the possibility of obtaining homogeneous coatings and also sharp interfaces on complexly shaped substrates. [4,5,10,[12][13][14][15][16][17] Nevertheless, conventional processes involving the use of SiH 4 as a precursor suffer from several disadvantages. In fact, besides requiring the use of oxidizing reagents such as O 2 or N 2 O, the above compound has a high toxicity and reactivity.…”

Plasma Characterization of Oxygen‐Tetramethylsilane Mixtures for the Plasma‐Enhanced CVD of SiOxCyHz Thin Films

“…In general, very low intensities of the dissociated species H and O, as compared with the results of other authors using silicon precursors, were recorded. [29,30] In the case of the plasma of pure TMS, the spectrum was characterized by a continuous profile from 250 to 500 nm associated with the H 2 molecule. [29] In addition, the lines of the Balmer series of H, and the CH bands located at 314 and 390 nm, [14] were also detected.…”