Steven Wolf1 Michael Breeden1 Mahmut Sami Kavrik1 Jun Hong Park1 Daniel Alvarez2 Mehul Naik3 Andrew Kummel1

1, University of California, San Diego, La Jolla, California, United States
2, Rasirc, San Diego, California, United States
3, Applied Materials, Sunnyvale, California, United States

Titanium nitride (TiN) has been extensively studied in semiconductor devices because of its ideal thermal, mechanical, and electrical properties. It has served as a diffusion barrier to WF6 during W metal fill [1]. Similarly, tantalum nitride (TaN) has been utilized as a diffusion barrier on SiOCH to Cu, as Cu can readily diffuse, causing device reliability issues [2]. ALD TiN and TaN films have previously been grown using a wide range of precursors including metal halides (i.e. TiCl4, TaF5) and metal organics (i.e. TDMAT, TBTDET), as well as nitrogen sources (thermal/plasma NH3, N2/H2). Metal halide precursors are preferred over organometallic grown films when there is no concern about substrate etching or damage; organometallic-grown films usually contain higher levels of carbon and oxygen contamination, which has been correlated with an increase in film resistivity [3].

In this study, low temperature thermal ALD TiNx from anhydrous N2H4 vs. NH3 and TiCl4 was performed on degreased and UHV annealed SiO2/Si substrates at temperatures of 300°C and 400°C. The deposited films were studied using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). TaNx films were grown at 150°C utilizing N2H4 and tris(diethylamido) (tertbutylimido)tantalum (TBTDET) and characterized similarly. In addition, the resistance of air-exposed ultra-thin films was measured using a 4-point probe technique. Resistivities were estimated from thicknesses obtained from cross-sectional scanning electron microscopy (SEM) images.

First, saturation dosing was performed to determine optimal half-cycle pulses of TiCl4 and N2H4. After TiNx ALD cycles, AFM imaging showed uniform deposition with sub-nanometer RMS surface roughness. The corrected and normalized XPS showed near stoichiometric Ti3N4 with low O and C and ~10% Cl. There was approximately 2x more O and C and 50% more Cl in NH3 grown films at 400°C. N2H4 films exhibited lower resistivities (359 vs. 555 µohm-cm), attributed to this lower contamination and likely better nucleation density. For TaNx films, XPS of 15 cycles ALD TaNx films resulted in 9% O and 4% C and had a Ta/N ratio of 4/5. Analysis on the Ta 4d peaks confirmed nucleation after the initial exposure of TBTDET (Si-O-Ta formation) based on the Ta 4d 5/2 peak BE of ~231.5 eV. A chemical shift to 229 eV was observed upon forming Ta-N bonds. Resistance measurements indicated insulating films consistent with the formation of Ta3N5. In summary, N2H4 grown TiNx films showed lower resistivities with fewer impurities. The anhydrous N2H4 chemistry was extended to an organometallic Ta precursor, in which nearly stoichiometric films were deposited with low contamination at a modest substrate temperature of 150°C.

[1] Sidhwa, A., et al. (2002). MRS Proceedings, 716.
[2] Chen, F., et al. (2006). Reliability Physics Symposium Proceedings, 44th Annual IEEE International.
[3] Musschoot, J., et al. (2009). Microelectronic Engineering 86.1: 72-77.