Abstract:The interaction between urea and tetrabutylammonium acetate was investigated in dimethylformamide/ dimethyl sulfoxide solutions using 1 H and 15 N NMR. The chemical-shift behavior of the urea protons is consistent with a urea-acetate hydrogen-bonded complex involving both carboxylate oxygens and the urea hydrogens trans to the carbonyl oxygen with K assoc ) 120 ( 10. Line shape analysis of the temperature-dependent 1 H NMR spectra show that ∆G q for rotation about the C-N bond of urea changes only slightly from 11.0 ( 0.1 to 11.2 ( 0.1 kcal/mol on 1:1 molar addition of tetrabutylammonium acetate to a dilute solution of urea. A parallel investigation of the interaction of thiourea with tetrabutylammonium acetate gave a binding constant, K assoc ) 90 ( 10. The ∆G q for rotation about the C-N bond of thiourea was found to increase from 13.5 ( 0.1 to 14.0 ( 0.1 kcal/mol on 1:1 addition of tetrabutylammonium acetate to a dilute solution of thiourea in dimethylformamide/dimethyl sulfoxide. Measurements were also made of the self-association of several ureas and of ∆G q for rotation about both C(O)-N bonds of 1,1-dimethylurea.

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Results are presented from a systematic study of the composition, texture, and electrical properties of titanium nitride (TiN) films and their performance as diffusion barrier in multilevel interconnect schemes of ultralarge scale integration (ULSI) computer chip device structures. The films were grown by low temperature (<450°C) inorganic chemical vapor deposition using titanium tetraiodide as source precursor and ammonia and hydrogen as co-reactants. The TiN films were nitrogen-rich., with iodine concentrations below 2 atom percent, displayed resistivities in the range 100 to 150 p.ul cm depending on thickness, and exhibited excellent step coverage with better than 90% conformality in both nominal 0.45 p.m, 3:1 aspect ratio and 0.25 p.m, 4:1 aspect ratio contact structures. A comparison of the properties of chemical vapor deposited (CVD) TiN with equivalent physical vapor deposited (PVD) TiN showed that reactivity with Al-0.5 a/o Cu alloys was equivalent in both cases. In particular a 10% increase in the Al-Cu/TiN stack sheet resistance was observed for both types of TiN after a 450°C, 30 mm sinter. Similarly, the characteristics of CVD tungsten and reflow plug fills were identical on both types of TiN films. However, barrier performance for CVD TiN in aluminum and tungsten plug technologies was superior to that of PVD TiN, as evidenced by lower contact diode leakage for CVD TiN in comparison with PVD TiN films of equal thickness. This improved barrier performance could be attributed to a combination of factors, which include the nitrogen-rich composition, higher density, and enhanced conformality of the CVD TiN phase in comparison with the PVD TiN. In view of the superior step coverage and diffusion barrier characteristics, the low temperature inorganic CVD route to TiN seems to provide an adequate replacement for conventional PVD TiN in emerging ULSI metallization interconnect schemes. InfroductionTitanium nitride (TiN) is a commonly used material in current integrated circuit (IC) technologies.1 Its applications range from diffusion barrier and glue layer at the contact/via level to diffusion barrier and antireflection coating in the interconnect stack.2 Such applications are made possible by the desirable properties of TiN, including its refractory nature at elevated temperature, excellent mechanical, chemical, and thermal inertness, and good resistance to corrosion. These properties allow TiN to withstand the repeated thermal cycles use in multilevel metallization of IC devices, and make its continued use in emerging subquarter micron device technologies highly desirable. However, the suitability of TiN for such applications is only possible if it is deposited with good conformality in subquarter micron features, leading to void-free plug formation, reduced junction leakage, and low contact/via resistance. This requirement is further complicated by a strong push to reduce barrier thickness, as device size shrinks, to provide the cross section of aluminum or copper conductor required for optimum device perf...