Copper metalorganic chemical vapor deposition reactions of hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane and bis (hexafluoroacetylacetonate) Cu(II) adsorbed on titanium nitride

Abstract

Cu is receiving increasing attention as a replacement for Al in future Si ultra-large-scale integrated circuits due to its lower resistivity and potentially better reliability in terms of electromigration resistance and stress-induced voiding. Metalorganic chemical vapor deposition (MOCVD) of Cu offers the advantages of conformal coverage and selective growth. Whatever the means of deposition, a diffusion barrier and adhesion layer such as TiN is required. To understand the nucleation mechanisms of Cu film growth on TiN during MOCVD, we have studied the thermal decomposition of two metalorganic precursors, hexafluoroacetylacetonate Cu(I) vinyltrimethylsilane [CuI(hfac)(vtms)], and bis (hexafluoroacetylacetonate) Cu(II) [CuII(hfac)2] by x-ray photoelectron spectroscopy and temperature programmed desorption mass spectrometry in an ultrahigh vacuum (UHV) system. Experiments were carried out on polycrystalline air-exposed (i.e., oxidized) TiN and N2 ion beam sputter-cleaned TiN. These surfaces are representative of those found in the traditional stand-alone and newer integrated metallization processing sequences, respectively. Room temperature dosing of TiN with CuI(hfac)(vtms) is accompanied by rapid desorption of the vtms ligand, leaving chemisorbed CuI(hfac). This CuI(hfac) decomposes upon heating to form CO, CO2 and CF4 desorption products, leaving about 90% of the Cu on the surface, along with some F and C. CII(hfac)2 also dissociatively chemisorbs at room temperature to form CuI(hfac) and an adsorbate with the stoichiometry of hfac. Unlike CuI(hfac)(vtms), a Cu(hfac)-containing species desorbs upon heating above 75 °C. Near 200 °C this process ceases and decomposition (and possibly some intact desorption) of hfac takes place, leading to desorption of CO, CO2, and CF4. After desorption of all C-containing species, about 30% of the initially deposited Cu remains on the surface, along with a submonolayer coverage of F. Regardless of the precursor, Cu begins to diffuse into the TiN film, above 280 °C. The results of our studies offer insights into the different mechanisms that may play a role in the nucleation of MOCVD film growth and incorporation of impurities at the interface. Significantly, the disproportionation reaction that dominates the deposition of pure Cu from CuI(hfac)(vtms) at the higher pressures typical of MOCVD does not occur under UHV conditions.