DECOMPOSITION OF HEXAFLUOROACETYLACETONATE CU(I) VINYLTRIMETHYLSILANE ON, AND DIFFUSION OF CU INTO SINGLE-CRYSTAL AND POLYCRYSTALLINE TITANIUM NITRIDE

Copper is a potential replacement for aluminum in future ultra large scale integrated (ULSI) circuits, due to its lower resistivity and better resistance to electromigration. Metal-organic chemical vapor deposition (MOCVD) of Cu offers advantages of conformal coverage and selective growth. We have studied the thermal decomposition of a Cu MOCVD precursor, hexafluoroacetylacetonate copper vinyltrimethylsilane (Cu(I)(hfac)(vtms)), on both air-oxidized and N2 ion beam sputter-annealed TiN single crystal (100) and polycrystalline surfaces. TiN is thought to be an effective barrier to the diffusion of Cu. Coverages and chemical bonding of C, O, F, and Cu were monitored by X-ray photoelectron spectroscopy (XPS). Dosing TiN with Cu(I)(hfac)(vtms) at 25-degrees-C results in chemisorption of Cu(I)(hfac) and desorption of vtms. On oxidized surfaces, little or no decomposition of CF3 groups is detected at room temperature, while on sputter-annealed polycrystalline and single crystal surfaces, a small amount of decomposition is indicated by a CF2 feature in the C(1s) XPS spectrum, and a low-binding energy fluoride in the F(1s) spectrum. Between 100-degrees-C and 250-degrees-C, Cu(I)(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 (confirmed by Rutherford backscattering spectroscopy), apparently enhanced by simultaneous diffusion of F. Decomposition of the hfac CF3 groups at elevated temperature is independent of the nature of the TiN surface (i.e. polycrystalline versus (100), or clean versus oxidized). However, Cu diffusion depends strongly on the surface preparation. The lowest temperatures at which Cu diffusion was observed are 250-degrees-C, 320-degrees-C, and 430-degrees-C, for oxidized polycrystalline, clean polycrystalline, and clean single crystal (100) TiN, respectively. Implications of these decomposition and diffusion processes for Cu MOCVD are discussed.