Highly Conformal Amorphous W-Si-N Thin Films by Plasma-Enhanced Atomic Layer Deposition as a Diffusion Barrier for Cu Metallization

Abstract

Ternary and amorphous tungsten silicon nitride (W-Si-N) thin films were grown by atomic layer deposition (ALD) using a sequential supply of a new fluorine-free, silylamide-based W metallorganic precursor, bis(tert-butylimido)bis(bis(trimethylsilylamido))tungsten(VI) [W(NtBu)(2){N(SiMe3)(2)}(2)], and H-2 plasma at a substrate temperature of 300 degrees C. Here, W(NtBu)(2){N(SiMe3)(2)}(2) was prepared through a metathesis reaction of W(NtBu)(2)Cl-2(py)(2) (py = pyridine) with 2 equiv of LiN(SiMe3)2 [Li(btsa)]. The newly proposed ALD system exhibited typical ALD characteristics, such as self-limited film growth and linear dependency of the film growth on the number of ALD cycles, and showed a high growth rate of 0.072 nm/cycle on a thermally grown SiO2 substrate with a nearly zero incubation cycle. Such ideal ALD growth characteristics enabled excellent step coverage of ALD-grown W-Si-N film, similar to 100%, onto nanotrenches with a width of 25 nm and an aspect ratio similar to 4.5. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis confirmed that the incorporated Si and W were mostly bonded to N, as in Si-N and W-N chemical bonds. The film kept its amorphous nature until annealing at 800 degrees C, and crystallization happened at local areas after annealing at a very high temperature of 900 degrees C. An ultrathin (only similar to 4 nm thick) ALD-grown W-Si-N film effectively prevented diffusion of Cu into Si after annealing at a temperature up to 600 degrees C.