CVD of Thin Films of Copper and Cobalt from Different Precursors: Growth Kinetics and Microstructure
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CVD OF THIN FILMS OF COPPER AND COBALT FROM DIFFERENT PRECURSORS: GROWTH KINETICS AND MICROSTRUCTURE Anil Mane, K. Shalini, Anjana Devi, R. Lakshmi, M.S. Dharmaprakash, Mandar Paranjape, and S.A. Shivashankar, Materials Research Centre, Indian Institute of Science, Bangalore – 560 012, India ABSTRACT We have investigated the growth of thin films of Cu and Co by CVD using the β-diketonate complexes of the metals, viz., the respective acetylacetonates, dipivaloylmethanates, and ketocarboxylates. Film growth rate was measured as a function of CVD parameters such as substrate temperature and reactor pressure. Film microstructure was examined by optical microscopy, XRD, SEM, and STM. Electrical resistivity was measured as a function of temperature and film thickness. It was found that film microstructure is a function of the molecular structure of the precursor and of the other growth parameters. For example, Cu films from Cu(II) ethylacetoacetate comprise uniform, fine grains which result in bulk electrical conductivity at a thickness as small as 75nm. Though grown under nearly the same conditions, Cu films from Cu(II) dipivaloylmethanate are porous, with faceted, large crystallites. Cobalt films from Co(II) acetylacetonate are x-ray amorphous even at a deposition temperature of 450°C. It is possible, by choosing CVD parameters, to obtain metal films with microstructures appropriate to devices and to structures of very small dimensions. INTRODUCTION The requirements of VLSI metallization have led to extensive investigation of the CVD of copper and aluminium [1]. A number of new chemical precursors have been developed and used to optimize deposition conditions to suit VLSI fabrication, viz., reduced deposition temperature and enhanced deposition rate [1]. While the microstructure of the resulting films has been studied and reported [2], the link between film microstructure and the chemical structure of the CVD precursors does not appear to have been investigated and reported in detail. As CVD is a chemical process by definition, various process parameters such as reaction temperature, reactor pressure, the concentration of reactants, etc. affect film growth and film microstructure. One of the most important of these parameters would be the chemical nature of the CVD precursor. We have therefore studied the growth process and microstructure of copper and cobalt films prepared by CVD using different metalorganic complexes of the respective metals as precursors. The importance of the CVD of cobalt films [3-7] stems from their relevance to giant magnetoresistance (GMR) devices and from the possibility of exploring the magnetic behaviour of fine-grained metal films. The overall motivation of the work reported here has been to examine the prospect of tailoring the microstructure of metal films prepared by CVD for specific applications. EXPERIMENTAL The molecular structure of the metalorganic complexes of copper and cobalt used as CVD precursors is shown in Figure 1. Specifically, the copper complexes used were
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