Copper CVD Reactions of Cu(I)(hfae)(vtms) Adsorbed on TiN
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COPPER CVD REACTIONS OF Cu(I)(hfac)(vtms) ADSORBED ON TiN K.V. Guinn*, V.M. Donnelly*, M.E. Gross*, F.A. Baiocchi*, I. Petrov**, J.E. Greene** *AT&T Bell Laboratories, 600 Mountain Ave., Murray Hill, NJ 07974 "**MaterialScience Dept., University of Illinois, Urbana, IL 61801 ABSTRACT We have studied the thermal decomposition of a Cu MOCVD precursor, hexafluoroacetylacetonate copper vinyltrimethylsilane (Cul(hfac)(vtms)), on both air-oxidized and N2 ion beam sputter-annealed single crystal (100) and polycrystalline TiN surfaces. Dosing TiN with CuI(hfac)(vtms) at 25"C results in chemisorption of CuI(hfac) and desorption of vtms. On oxidized surfaces, little or no decomposition of CF 3 groups is detected at room temperature, while on sputter-annealed polycrystalline and single crystal surfaces, a small amount of decomposition is indicated by a CF 2 feature in the C(ls) X-ray photoelectron spectroscopy (XPS) spectrum, and a low-binding energy fluoride in the F(ls) spectrum. Between 100 and 250"C, CuI(hfac) decomposes to evolve gaseous products and leaves Cu, F, and C on the surface. Further heating leads to diffusion of Cu into the TiN, apparently enhanced by simultaneous diffusion of F. Decomposition of the hfac CF 3 groups at elevated temperature is independent of the nature of the TiN surface (i.e. polycrystalline vs. (100), or clean vs. oxidized). However, Cu diffusion depends strongly on the surface preparation. The onset of Cu diffusion into oxidized polycrystalline, clean polycrystalline, and clean single crystal (100) TiN occurs at 250, 320, and 430"C, respectively. INTRODUCTION
Cu is currently being evaluated as a replacement for Al in future generations of ultra-large scale integrated (ULSI) Si circuits because of its higher electrical conductivity and higher resistance to electromigration and stress-induced voiding. 1-4 Cu does, however, have some drawbacks. The rapid diffusion of Cu into Si, where it forms deep level traps, and through SiO 2 requires the use of a diffusion barrier completely surrounding the Cu. 5 A protective capping layer is also required to prevent corrosion on exposure to air. Several recent studies have demonstrated good diffusion barrier properties for TiN, 6 -8 which has the added advantage of already being in use in ULSI devices for other purposes. MOCVD of Cu is of particular interest because of its recently demonstrated ability to achieve selective deposition and conformal coverage over uneven circuit topography. In this study, we focus on one of a class of CuI precursors, Cul(hfac)(vtms), that have been shown to deposit Cu cleanly at low temperatures (100-250"C) by a disproportionation mechanism, as shown in reaction (1).9-12 Cu'(hfac)(vtms)(g) -> Cu0 + Cul"(hfac)2(g) + 2vtms(g)
(1)
The mechanism responsible for nucleation, however, may differ significantly from that responsible for steady-state growth and may lead to incorporation of contaminants at the Cu/substrate interface that affect the device reliability. We have previously studied the mechanisms of decomposition of Cul
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