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

Copper is a potential replacement for aluminum in future ultra large s cale integrated (ULSI) circuits, due to its lower resistivity and bett er resistance to electromigration. Metal-organic chemical vapor deposi tion (MOCVD) of Cu offers advantages of conformal coverage and selecti ve growth. We have studied the thermal decomposition of a Cu MOCVD pre cursor, hexafluoroacetylacetonate copper vinyltrimethylsilane (Cu(I)(h fac)(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 spec troscopy (XPS). Dosing TiN with Cu(I)(hfac)(vtms) at 25-degrees-C resu lts in chemisorption of Cu(I)(hfac) and desorption of vtms. On oxidize d surfaces, little or no decomposition of CF3 groups is detected at ro om temperature, while on sputter-annealed polycrystalline and single c rystal 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 (c onfirmed by Rutherford backscattering spectroscopy), apparently enhanc ed by simultaneous diffusion of F. Decomposition of the hfac CF3 group s at elevated temperature is independent of the nature of the TiN surf ace (i.e. polycrystalline versus (100), or clean versus oxidized). How ever, Cu diffusion depends strongly on the surface preparation. The lo west temperatures at which Cu diffusion was observed are 250-degrees-C , 320-degrees-C, and 430-degrees-C, for oxidized polycrystalline, clea n polycrystalline, and clean single crystal (100) TiN, respectively. I mplications of these decomposition and diffusion processes for Cu MOCV D are discussed.