Terraced Copper Growth Deposited Onto Teflon AF1600 by The Excimer Laser Irradiation of Cu(hfac)TMVS
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D. POPOVICI, K. PIYAKIS, E. SACHER and M. MEUNIER Groupe de recherche en physique et technologie des couches minces (GCM) and DIpartement de g6nie physique, Ecole Polytechnique, C. P. 6079, Succursale Centre-ville, Montr6al, Qu6bec, H3C3A7. ABSTRACT The laser chemical vapour deposition (LCVD) of the organometallic precursor Cu(hfac)TMVS (hexafluoroacetylacetonate)(trimethylvinylsilane) is used to grow copper films on a Teflon AFP1600 substrate. Exposure to excimer laser radiation at 248 nm results in a terraced copper growth. A simple model, based on interference effects in the Teflon and copper layers, is presented to account for this structure. INTRODUCTION We are studing the feasibility of constructing Cu/ fluoropolymer multilayer devices [1], in an effort to reduce both metal R and insulator C, a necessary condition in VLSI and GSI microelectronic applications [2-41. Copper films could be deposited by various methods but the use of UV radiation from the excimer laser to induce metallisation has the distinct advantage of being suitable for photolithographic patterning. This is due to the proportionality between the diffraction-limited resolution and the wavelength of the light used in the patterning process [7]; thus, smaller features can be more easily reproduced by projection or direct writing employing shorter wavelength radiation. Copper films have been successfully deposited by us from organometallic precursors onto TiN substrates by excimer laser chemical vapour deposition (LCVD) [5] and resistivities as low as 3.9 p4flcm have been obtained after one hour anneal at 4000C. Here, we consider the LCVD of copper from the Cu(I) precursor Cu(hfac)TMVS (Copper(I)(hexafluoroacetylacetonate) (trimethylvinylsilane)) on Teflon AF1600 substrates. In this paper, we present results on the constant terraced Cu structure deposited by LCVD on Teflon AF1600. Periodic structures (ripples) related to the photophysics of illumination and the growing film have been observed for a variety of organometallic precursors used for the metallisation of Si and SiO 2 substrates. Interference between the surface scattered wave and the incident beam produces a standing electromagnetic field at the surface; thus, the light intensity is modulated, leading to a variation in film thickness, forming ripples [8]. Their orientation is quite sensitive to the direction of the light polarisation and does not depend on the initial thickness of the substrate. The structure to be considered in this paper is fundamentally different; it is not related to the radiation polarisation and follows the initial configuration of the substrate thickness, forming terraces rather than sinusoidal ripples. A physical explanation and a simplified model are proposed to account for this type of growth. EXPERIMENTAL Teflon AF 1600, purchased from DuPont as a solution containing 6% solids, was diluted 50% in Sigma Fluorinert FC-77 and spun onto a cleaned Si wafer at 4000 rpm, giving a layer thickness of about 1 plm. The samples were then dried for 5 min at 25°C to remove
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