Elsevier

Vacuum

Volume 81, Issue 7, 28 February 2007, Pages 920-927
Vacuum

Composite SiOx/hydrocarbon plasma polymer films prepared by RF magnetron sputtering of SiO2 and polyimide

https://doi.org/10.1016/j.vacuum.2006.10.013Get rights and content

Abstract

Preparation procedure and properties of composite SiOx/hydrocarbon plasma polymer films are described and discussed. The composite films have been prepared by RF sputtering in argon from two balanced magnetrons equipped with silica (SiO2) and polyimide (PI) targets. The films obtained reveal a wide range of properties which depend on the preparation conditions; primarily on the RF power delivered to the magnetrons. Morphology and composition of the composite films have been analysed by means of AFM, TEM, RBS/ERDA and FTIR. Wettability in terms of contact angle of water increases from 28 to 46 when the content of the SiOx component of the composite increases. Peculiar properties of the composite SiOx/hydrocarbon plasma polymer films are discussed with respect to their elemental composition and nature of chemical bonds created on the surface of the films. Finally, an attempt is made to express the amount of inorganic phase present in the organic matrix in terms of a filling factor.

Introduction

Composite films comprising a metal and plasma polymer have been investigated for several decades (For a review, see Refs. [1], [2], [3]). However, later the interest moved on to more complex composites such as the SiOx/fluorocarbon plasma polymer. These composite films were prepared by ion beam co-sputtering [4] and by plasma polymerization [5], [6] with the idea to apply them as protective coatings. The above-mentioned composite films were also deposited using an RF magnetron equipped with a composite SiO2/polytetrafluoroethylene (PTFE) target [7]. Recently, these films have been sputtered from two magnetrons equipped with PTFE and SiO2 targets, respectively [8]. At the same time composite films of SiOx/hydrocarbon plasma polymer, or, a-C:H prepared by plasma polymerization of hexamethyldisiloxane (HMDSO) and a hydrocarbon were investigated [9], [10]. Similar films have also been prepared by RF co-sputtering from two magnetrons equipped with SiO2 and polyethylene or polypropylene targets [11].

Polyimide-like films have been at the centre of attention for some time because of the prospect of their application in microelectronics owing to their low dielectric constant, high thermal stability, or, excellent anti-corrosion and wear resistant properties. Maggioni [12] focused on the preparation of these films by glow discharge vapour deposition polymerization (GDVDP) and Kinbara [13] prepared polyimide-based organic thin films by RF magnetron sputtering in an N2/CF working gas mixture using a polyimide (Kapton) target. Also hybrid nanocomposite films of silica (SiO2) in polyimide (PI) from 4,4-hexafluoroisopropylidene diphthalic anhydride (6FDA), 2,2-Bis (3-amino-4-hydroxyphenyl) hexafluoropropane (6FHP) and nonlinear optical (NLO) molecules were successfully fabricated by an in situ sol–gel process [14]. They were proposed to be used for a number of photonics applications including a doubled-frequency laser source, electro-optic modulation, optical signal processing and optical inter-connects.

In our study, we used RF co-sputtering in argon from two balanced planar magnetrons equipped with SiO2 and PI targets, respectively. In the following, we will simply denote these as SiOx/pPI reflecting that PI was used as the source material of the hydrocarbon plasma polymer component. The deposition process and basic characterization of these composite films are described below.

Section snippets

Experimental

Composite films were prepared by simultaneous RF sputtering of silica and PI targets from the two balanced magnetrons using argon as the working gas at a pressure of 5 Pa and a flow rate 7cm3 (STP)/min (see Table 1). The deposition arrangement (Fig. 1) consisted of two planar balanced magnetrons (marked as M1 and M2 in Fig. 1), 78 mm in diameter, placed next to each other with their centres 90 mm apart. SiO2 and PI (Fig. 2) targets in shapes of disks (marked as SiO2 and PI, respectively), both

Contact angle measurements

The dependence of static contact angle of water on the ratio of applied powers to the magnetrons is shown in Fig. 3. A decrease in static contact angle from 46 to 28 is observed with an increase in the power ratio PSiO2/PPI in the range from 0.1 to 6. The maximum contact angle is achieved at a higher concentration of pPI in the film at a power ratio of 0.1. The reported variation of a contact angle reflects changes in the amount of SiOx and hydrocarbon plasma polymer in the composite film.

Conclusions

Composite SiOx/hydrocarbon plasma polymer films prepared by radio frequency magnetron co-sputtering of PI and SiO2 possess a wide range of properties depending on the deposition parameters, in particular on the power ratio PSiO2/PPI of the powers delivered to the targets. Wettability in terms of contact angle of water reveals that with the decrease of SiOx content in the composite films (equivalent filling factor decreases from about 0.7 to 0.1) the static contact angle of water is increased in

Acknowledgements

This work is a part of the research plan MSM 0021620834 that is financed by the Ministry of Education and Sports of the Czech Republic.

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