| AVS 64th International Symposium & Exhibition | |
| Electronic Materials and Photonics Division | Tuesday Sessions |
| Session EM+SS-TuA |
| Session: | Surface and Interface Challenges in Semiconductor Materials and Devices |
| Presenter: | JongYoun Choi, University of California, San Diego |
| Authors: | J. Choi, University of California, San Diego C.F. Ahles, University of California, San Diego R. Hung, Applied Materials, Inc. N. Kim, Applied Materials, Inc. A.C. Kummel, University of California, San Diego |
| Correspondent: | Click to Email |
As MOSFETs size shrinks to <10 nm in a three dimensional structure (FinFET), electrical losses at the contacts must be minimized. Consequently, selective atomic layer deposition (ALD) of transition metal disilicides are of great interest due to their ability to minimize parasitic resistance and avoid lithograph onto a three dimensional structure. Selective ALD of metallic tungsten (W) via a fluorosilane elimination process have been demonstrated using WF6 and SiH4 or Si2H6.1,2 This selectivity was achieved by an inherently favorable reactivity of the precursors on hydrogen-terminated Si versus OH-terminated SiO2. In this W deposition process, SiH4 was used as a reducing agent for W while the reactions byproducts was SiF4. Here, we demonstrated that sub-stoichiometric silicide, MoSix (x=0.4 – 1.1), can also be selectively deposited on H-terminated Si (001) in preference to SiOx and SiN using MoF6 and Si2H6. X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical composition of MoSix ateach experimental step. It was observed that Si-H terminated silicon allowed single cycle nucleation of MoSix at the substrate temperature of 100-120°C in contrast to an inherent chemical passivation (non-reactivity) on SiOx and SiN surfaces. To enable formation near stoichiometric MoSix, excess amount of Si2H6 was dosed after 5 ALD cycles to incorporate more Si into the MoSix film while maintaining selectivity since the SiOx was unreactive to even high doses of Si2H6. This substrate-dependent selectivity was retained up to 5 - 10 ALD cycles. By applying a mixture gas of (H2+MoF6) instead of MoF6 dosing, (as previous shown by Kalanyan et al2), the inherent selectivity was greatly improved and the nucleation of MoSix was impeded up to at least 20 ALD cycles on SiN without perturbing MoSix deposition on silicon. The growth rate of MoSix on Si was ~0.8 Å/cycle; therefore, even 10 selective ALD cycles is sufficient for deposition of contacts. To confirm an in-situ selective deposition as well as the thickness of the film, MoSix was deposited on a sample patterned with Si and SiON and the cross-section of the patterned sample was quantified using transmission electron microscopy (TEM). The surface morphology and roughness were measured using ex-situ atomic force microscopy (AFM) and in-situ scanning tunneling microscopy (STM). MoSix on Si was conformal and atomically flat surface with root mean square (RMS) of 2.8 Å. Post-annealing in a ultra-high vacuum at 500°C for 3 mins further decreased the RMS roughness to 1.7 Å.
1. Thin Solid Films, 241, 374 (1994)
2. Chem. Mater., 28, 117-126 (2016)