Chemical vapor deposition of cobalt using novel cobalt(I) precursors
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Ho G. Jang Division of Chemistry and Molecular Engineering, Korea University, Seoul, Korea (Received 26 July 2001; accepted 3 December 2001)
The deposition of cobalt thin films from cobalt hydride complexes, HCo[P(OR)3]4, where R ⳱ methyl, ethyl, i-propyl, and n-butyl, by a chemical vapor deposition method is reported. The new cobalt precursors deposited high-purity cobalt films at substrate temperatures as low as 300 °C without employing hydrogen. The deposited Co films showed smooth and dense surface morphology. The microstructure and growth rate of the deposited films depended on the reaction conditions such as substrate temperature and precursor feed. No gas phase reactions were observed during the deposition process.
Device scaling in silicon integrated circuits is leading toward the consideration of alternative materials or processing techniques, including a move from TiSi2 contacts to CoSi2.1,2 The main advantage of CoSi2 in scaling is that the formation of its low resistivity phase is relatively insensitive to line width and thickness so that its process window does not shrink as drastically as for TiSi2. Additionally, CoSi2 exhibits good thermal stability, chemical stability, and low resistivity. CoSi2 has also been used as a catalyst to grow carbon nanotubes (CNTs) in an effort to integrate CNTs into electronic devices.3–5 Although sputtering has been the commonly employed technique for metal deposition in the self-aligned silicide (salicide) process, the energetic ions in the sputtering process can potentially damage the substrate surface. Chemical vapor deposition (CVD) has been considered as an alternative method for growing metal films since it can deposit high-quality conformal films without substrate damage. A key element for the successful employment of CVD is securing a precursor with satisfactory properties. However, CVD of Co has been hampered due to the lack of a suitable precursor. The conventional Co precursors reported to date, such as cobalt carbonyl, Co2(CO)8; cobalt(II) acetylacetonate, Co(C 5 H 7 O 2 ) 2 ; cobalt(III) acetylacetonate, Co(C5H7O2)3; cobaltocene, Co(C5H5)2; and cyclopentadienylcobalt dicarbonyl, Co(C5H5)(CO)2,
a) b)
Address all correspondence to this author. On leave from Korea University. J. Mater. Res., Vol. 17, No. 2, Feb 2002
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have not demonstrated satisfactory properties to deposit Co films for the fabrication of device-quality CoSi2.6–8 Although Co2(CO)8 has been the most studied cobalt precursor, it exhibits serious drawbacks for depositing pure Co due to the existence of undesirable reaction pathways including polymerization reaction in the gas phase. In addition, its low thermal stability makes storage of the compound extremely difficult even under vacuum or inert atmosphere. Co(C5H7O2)2 and Co(C5H7O2)3 require high temperatures for vaporization and H2 reduction for the deposition of Co. Co(C5H5)2 and Co(C5H5)(CO)2, which deposit Co films under atmospheric pressure using H2 as a reducing agent, were report
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