Invited Paper TF-WeM8
Plasma-assisted Atomic Layer Deposition of SiN_x Films

Wednesday, December 14, 2016, 10:20 am, Room Makai

The introduction of 3-D device architectures in integrated circuits has created a need for atomic layer deposition (ALD) of highly conformal ultra-thin films. In particular, ALD of low-dielectric-constant, carbon-containing silicon nitride (SiC_xN_y) films at temperatures ≤400 °C is required. However, controlled incorporation of C atoms into SiN_x during ALD remains challenging. In this work, we report the C incorporation mechanism during two plasma-enhanced SiC_xN_yALD processes. The first ALD process consisted of three steps, Si₂Cl₆/thermal CH₃NH₂/N₂ plasma, while the second process consists of two steps, Si₂Cl₆/CH₃NH₂ plasma. In both ALD processes, we have determined the film composition, reactive sites, and adsorbed surface species using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. In addition, the growth per cycle (GPC) and refractive index were determined using in situ four-wavelength ellipsometry.

Our IR spectra show that in the first ALD process, the CH₃NH₂ thermally reacts with –SiCl_xsurface species created after the Si₂Cl₆ half-cycle to form -CH_xterminated surface amides. During the subsequent N₂ plasma half-cycle, in addition to nitridation of Si, a fraction of the surface CH_xgroups were incorporated into the SiC_xN_yfilm as -N=C=N- species, which appear as a strong vibrational mode at ~2170 cm^-1. The composition of the SiN_xfilms in the two-step ALD process was very similar, with C incorporated primarily as -N=C=N- groups created during the CH₃NH₂ plasma half-cycle. We find that during the exposure of the film to Si₂Cl₆ following an CH₃NH₂ plasma half-cycle, surface carbodiimides (-N=C=NH) react to nitriles (-NH-C≡N), while most of the surface is terminated with -SiCl_xspecies. The subsequent CH₃NH₂ plasma half-cycle, shows that the -NH-C≡N species formed during the Si₂Cl₆ half-cycle are removed, and the N=C=NH surface species are restored along with –NH_xgroups. For the Si₂Cl₆/CH₃NH₂ plasma ALD process, SiN_xfilms grown at 400 °C show a carbon content of ~4 at.% as measured through Rutherford backscattering spectroscopy combined with hydrogen forward scattering. Transmission electron microscopy shows a conformality of >95% for the SiC_xN_yfilms. The GPC for both processes was ~0.9 Å, with a refractive index of 1.95 and 1.86 for the N₂ plasma and CH₃NH₂ plasma ALD processes, respectively.