| AVS 65th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Monday Sessions |
| Session EM+AM+NS+PS-MoA |
| Session: | Atomic Layer Processing: Selective-Area Patterning (Assembly/Deposition/Etching) |
| Presenter: | Steven Wolf, University of California at San Diego |
| Authors: | S. Wolf, University of California at San Diego M. Breeden, University of California at San Diego M. Kavrik, University of California at San Diego D. Alvarez, RASIRC J. Spiegelman, RASIRC M. Naik, Applied Materials A.C. Kummel, University of California at San Diego |
| Correspondent: | Click to Email |
For device back end of line processing, there is a need to deposit conformal barrier layers on high aspect ratio 3D architectures via low-T ALD. Titanium nitride (TiN) and tantalum nitride (TaN) have been studied as diffusion barriers to WF6 during W metal fill and to Cu, as Cu can readily diffuse, causing device reliability issues. Organometallic-grown films are required when Cu is present to prevent etching, however, metal halide precursors are preferred for gate stack applications as films typically contain lower levels of carbon and oxygen contamination; this has been correlated with improved film conductivity. This work aims to deposit thermal ALD titanium nitride and tantalum nitride utilizing anhydrous N2H4 at lower temperatures than previously reported with NH3 while still maintaining good film properties.
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 400ºC. 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 150ºC.