Elsevier

Thin Solid Films

Volume 332, Issues 1–2, 2 November 1998, Pages 252-256
Thin Solid Films

Microstructural characterisation of carbonaceous dust generated during the deposition of diamond-like carbon coatings

https://doi.org/10.1016/S0040-6090(98)00993-6Get rights and content

Abstract

During plasma enhanced chemical vapour deposition (PECVD) of diamond-like carbon coatings, material is routinely deposited on the electrodes and chamber walls of the system. After prolonged deposition times, this material exfoliates, contributing to dusty plasmas and affecting the quality and microstructural properties of the films. We have generated such dust in a Plasma Technology DP800 radio frequency PECVD system, using a methane precursor at a variety of powers, pressures and electrode temperatures. A JEOL 2010 analytical electron microscope equipped with X-ray analysis (EDX) has confirmed that this dust is predominantly carbonaceous with negligible metal contamination from the chamber. JEOL 2000 FX and JEOL 4000 EX high resolution transmission electron microscopes (HRTEMs) have been used to investigate the morphology and microstructure of these dust particles for comparison with the amorphous diamond-like carbon films that are more typically produced using the apparatus. A significant number of the dust particles analysed revealed highly curved graphene layers and microcrystalline nano-particles more typically observed in the soot following the arc-discharge generation of fullerenes. This is in contrast to the amorphous nature of the carbon films deposited over shorter times on silicon and glass substrates, which rarely show any microcrystalline inclusions.

Introduction

Plasma enhanced chemical vapour deposition (PECVD) is routinely used as a means of depositing thin films of hydrogenated amorphous silicon (a-Si:H) [1] and hydrogenated amorphous carbon (a-C:H) [2]. These materials are finding applications as electronic devices, particularly in the case of silicon [3], and hard diamond-like coatings and passivation layers in the case of carbon [4], [5]. Presently work continues to apply both materials, and indeed their alloys (a-SiC), to large area opto-electronic devices such as solar cells, thin-film diode arrays, and field-emission cold cathodes for future flat-panel displays [6].

Although PECVD systems are capable of depositing large areas of uniform thin films on a variety of substrates, including polymers that must remain at relatively low temperatures, the technique can have the disadvantage of generating ‘dusty plasmas’ [7]. This problem is particularly acute when the PECVD system is used for prolonged lengths of time without a cleaning programme. The nucleation of dust particles, both in the plasma and on the electrodes, can lead to surface contamination, plasma instabilities through localised static charges, and poor quality films containing structural inhomogeneities [8], [9].

The problems of dusty plasmas in silicon-based systems, in which silane is routinely used as the precursor gas, has already been widely addressed by the established silicon industry [10]. However, because a-C:H has yet to become a commercially produced material with the associated quality-control and reproducibility constraints of an electronics industry, very little understanding of carbon-based dusty plasmas exists. Hence, both the physical and chemical nature of the dust produced has also received very little attention, and the conditions for their formation are not well characterised.

In this paper we begin an in-depth microstructural and morphological examination of PECVD generated carbonaceous dust, and compare it with the a-C:H films produced under similar conditions. It is interesting that although we believe this PECVD-generated dust has not been rigorously studied before, there is a wealth of information relating to carbonaceous dust and soot from other sources, including flames and carbon arcs [11], [12]. It was the latter, of course, that led to the fascination growth of fullerene science [13], and we will show that there exists some important parallels with PECVD generated dust and fullerene-related material.

Section snippets

Experimental

A Plasma Technology DP800 radio frequency PECVD system has been used to deposit a-C:H films on silicon and Corning glass substrates. In addition, after longer periods of deposition, dust has been collected from the upper electrode and chamber floor. The locations of the substrates and of the collected dust are illustrated in the schematic in Fig. 1. The conditions used to produce the dust discussed in this paper are summarised in Table 1.

A portion of each of these samples was ultrasonically

Results and discussion

Fig. 2illustrates an SEM image of the dust from sample 1 which we interpret as curled sheets of a-C:H, produced by excessive growth of carbon on the driven electrode. The growth rate of a carbon film on the lower electrode has been measured as approximately 3 Å/s. Hence, after 1800 s of deposition, layers in excess of 500 nm thickness would be expected. Similar films grown on silicon substrates on the driven electrode exhibit high compressive stresses, and so spawling of the material occurs at

Conclusion

We conclude that carbonaceous dust grown during film deposition in the RF-PECVD apparatus partially consists of aggregates of nanoparticles similar to the material deposited during the arc-discharge generation of fullerenes. Because of the continuous and controlled nature of the PECVD process, it is anticipated that the system may be optimised to yield large quantities of the dust and that the microstructure and morphology of the particles may be more finely tuned than is currently achievable

Acknowledgements

This work was supported by an EPSRC grant (GR/L09202). We acknowledge Dr J.L. Hutchison and Mr. R. Doole for their assistance while using the JEOL 2010 and JEOL 4000 EX(II) electron microscopes at the Department of Materials, University of Oxford, UK. We also thank Mrs. J. Cheetham for EDX analysis on the LEO Stereoscan 440i SEM at Corporate Technology Europe, Raychem Ltd., Swindon, and the Department of Physics for access to their Camspec M350 Spectrophotometer. Finally, Mr. Choon Hoe Lim is

References (22)

  • J.R. Fryer

    Carbon

    (1981)
  • M. Miki-Yoshida et al.

    Carbon

    (1994)
  • L.S.K. Pang et al.

    Carbon

    (1992)
  • R.A. Street, Hydrogenated Amorphous Silicon, Cambridge University Press, New York,...
  • P. Koidl

    Ch. Wild, B. Dischler, J. Wagner, M. Ramsteiner

    Mater. Sci. Forum

    (1989)
  • J.M. Shannon et al.

    Mater. Res. Soc. Symp. Proc.

    (1993)
  • G.A.J. Amaratunga et al.

    J. Appl. Phys.

    (1991)
  • K. Endo et al.

    Appl. Phys. Lett.

    (1997)
  • G.A.J. Amaratunga et al.

    Appl. Phys. Lett.

    (1996)
  • A. Garscadden

    Pure Appl. Chem.

    (1994)
  • H. Kawasaki et al.

    Jpn. J. Appl. Phys.

    (1994)
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