Catalytically enhanced H2-free CVD of transition metals using commercially available precursors

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Abstract

The deposition of metals using thermal CVD in a hydrogen-free atmosphere was investigated starting from nontoxic metalorganic precursors. A remarkably simple process, which relies on the chemical reduction by alcohols, allows the deposition of high-quality films of a variety of metals and alloys. The growth characteristics of metal films are investigated as a function of temperature, and their performance is discussed in terms of electrical resistivity. Near-bulk resistivities were obtained for Ni, Co, Cu, and Ag, while Fe presents a 37-fold higher resistivity than the bulk because of the poor packing of crystallites. In this work, the deposition conditions for the growth of single-phase cubic or hexagonal nickel were determined.

Introduction

Metal thin films form a prominent part of modern technologies, since they are omnipresent in optic, magnetic and electronic devices. These extremely competitive and fast growing fields force the development toward device miniaturization, improved reliability and reduced costs. Although physical vapor deposition, electrochemical and electroless deposition techniques are widely used for metallization, chemical vapor deposition is expected to be the method of choice since it enables better conformal coverage.

However, the CVD of metals is still not widely applied, typical problems being hazardous precursors and/or byproducts, carbon contamination, long incubation times and the difficult control of the microstructure of the grown films. To overcome these limitations, novel metal precursors are investigated with the goal of enabling more advantageous surface reactions [1], [2], [3], [4], [5], [6], [7]. A second approach is proposed here, based on a more appropriate choice of the reduction strategy, which is of interest in combination with commercially available nontoxic metalorganic precursors. In fact, transition metals are used as catalysts to achieve a multitude of selective chemical reactions involving reduction–oxidation cycles [8], [9], [10], [11], [12], e.g. reforming, water–gas shift reaction and selective oxidation. Reproducing this type of reactions in a CVD reactor might be valuable in inducing the catalytically driven chemical reduction of the metal center. Alcohols are of particular interest in this context, since they tend to dissociate on the surface of transition metals forming adsorbed alkoxide intermediates and surface hydrogen [13], [14], [15]. The purpose of the present study is to prove the principle of the catalytically driven chemical reduction for the CVD of metals and alloys.

Section snippets

Experimental part

The deposition of metal films was performed in a cold-wall CVD reactor with stagnation point flow geometry as represented in Fig. 1. The flow of nitrogen gas was controlled using a mass flow controller, and the deposition pressure was measured and controlled using an electronic-valve system (MKS instruments). The CVD reactor was equipped with a home-built pulsed-spray evaporation part which enables a pulsed delivery of the precursor solution as a spray using a 4-pinholes injector with diameters

Results and discussions

The growth of metals was investigated in a hydrogen-free atmosphere using metalorganic precursors where the metal center is in a high oxidation state. Consequently, the use of inert solvents, such as, THF (tetrahydrofuran) and n-butyl acrylate did not allow the growth of metal films [17]. This is in agreement with previous reports indicating the non-occurrence of metal growth from metal acetylacetonates in the absence of hydrogen reduction [18], [19], [20]. However the growth of metal films was

Conclusion

The present contribution demonstrates the growth of metals and alloys starting from nontoxic metalorganic precursors without using hydrogen. This strategy relies on the selective reactivity of alcohols with transition metals to enable the growth of metal films starting from metal acetylacetonates or metal nitrates. The efficiency of this strategy was proven for the growth of Ni, Fe, Co, Cu, and Ag films and their corresponding alloys.

Acknowledgment

One of the authors (PAPK) wishes to acknowledge a Fellowship of the Alexander von Humboldt (AvH) Foundation for his postdoctoral stay in Germany.

References (30)

  • A. Grodzicki et al.

    Coord. Chem. Rev.

    (2005)
  • S.S. Bhoware et al.

    J. Mol. Catal., A Chem.

    (2006)
  • W. Shan et al.

    J. Catal.

    (2004)
  • J. Shen et al.

    J. Catal.

    (2006)
  • R. Zhang et al.

    Energy Convers. Manag.

    (2007)
  • Q. Liu et al.

    Catal. Today

    (2005)
  • M.M. Natile et al.

    J. Mol. Catal., A Chem.

    (2004)
  • X. Xu et al.

    Surf. Sci.

    (1992)
  • S.L. Roberson et al.

    Thin Solid Films

    (1998)
  • N.S. Borgharkar et al.

    Thin Solid Films

    (1998)
  • Y. Kajikawa et al.

    Appl. Surf. Sci.

    (2005)
  • S. Kim et al.

    Thin Solid Films

    (1998)
  • L.S. Hong et al.

    Appl. Surf. Sci.

    (2000)
  • H.A. Marzouk et al.

    Thin Solid Films

    (1994)
  • L. Gao et al.

    Microelectron. Eng.

    (2005)
  • Cited by (0)

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