FTIR study of copper agglomeration during atomic layer deposition of copper
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1155-C11-06
FTIR study of copper agglomeration during atomic layer deposition of copper Min Dai,1 Jinhee Kwon,2 Yves J. Chabal,2 Mathew D. Halls,3 and Roy G. Gordon4 1 Laboratoy for Surface Modification, Rutgers University, 136 Frelinghuysen Road, Piscataway, NJ 08854, U. S. A. 2 Department of Materials Science and Engineering, the University of Texas at Dallas, Richardson, TX 75080, U.S.A. 3 Materials Science Division, Accelrys Inc., San Diego, CA 92121, U.S.A. 4 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, U.S.A.
ABSTRACT The growth of of metallic copper by atomic layer deposition (ALD) using copper(I) di-secbutylacetamidinate ([Cu(sBu-amd)]2) and molecular hydrogen (H2) on SiO2/Si surfaces has been studied. The mechanisms for the initial surface reaction and chemical bonding evolutions with each ALD cycle are inferred from in situ Fourier transform infrared spectroscopy (FTIR) data. Spectroscopic evidence for Cu agglomeration on SiO2 is presented involving the intensity variations of the SiO2 LO/TO phonon modes after chemical reaction with the Cu precursor and after the H2 precursor cycle. These intensity variations are observed over the first 20 ALD cycles at 185oC. INTRODUCTION Atomic layer deposition (ALD) has recently received great interest with the need for new materials and thin-film deposition techniques for device scaling in integrated circuits (IC). The self-limiting growth mechanism of ALD is ideal for producing very thin, conformal films even on surfaces with high aspect ratios with control of the thickness and composition at the atomic level. As the industry heads toward the 22 nm node, the interest in metal ALD is growing, especially for copper interconnects. Cu is replacing aluminum as an interconnect material in ICs due to its lower resistivity (1.72×10−6Ω·cm vs. 2.82×10−6Ω·cm) and higher melting point (1083 o C vs. 659oC).1 For this application, a highly conformal and continuous copper seed layer is required before subsequent electrochemical deposition of copper film with high growth rate.2 ALD of non-noble metals, however, has had limited success 3, 4. One of the reasons for these difficulties is related to a lack of suitable precursors which satisfy stringent requirements for ALD. 5 In addition, the lack of understanding of growth mechanisms of metal ALD hinders the development of suitable precursors. ALD of Cu has been considered previously. Several copper (I) and copper (II) precursors were commonly used in the past, such as CuCl4, 6, Cu(II)-2,2,6,6 -tetramethyl-3,5-heptandionate [Cu(thd)2]7, 8, Cu(II)-1,1,1,5,5,5-hexafluoro-2,4 -pentanedionate [Cu(hfac)2] 9, 10, and Cu(II) acetylacetonate [Cu(acac)2] 11, 12, but all suffered from undesirable properties as ALD
precursors.13 For example, CuCl has very low vapor pressure, and the Cu film deposited by Cu(hfac)2 contains fluorine which reduces the Cu adhesion on the substrate. They all have very low reactivity with low growth rate, so that either high temperature (> 200oC), which is not well suited fo
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