Abstract
In this work, we report on the atomic layer deposition (ALD) of HfNx thin films by employing CpHf(NMe2)3 as the Hf(IV) precursor and Ar–H2 plasma in combination with external RF substrate biasing as the co-reactant. Following up on our previous results based on an H2 plasma and external RF substrate biasing, here we address the effect of ions with a larger mass and higher energy impinging on HfNx film surface during growth. We show that an increase in the average ion energy up to 304 eV leads to a very low electrical resistivity of 4.1 × 10–4 Ωcm. This resistivity value is achieved for films as thin as ~ 35 nm, and it is an order of magnitude lower than the resistivity reported in literature for HfNx films grown by either CVD or ALD, while being comparable to the resistivity of PVD-grown HfNx films. From the extensive thin film characterization, we conclude that the impinging ions during the film growth lead to the very low electrical resistivity of HfNx films by suppressing the oxygen incorporation and in-grain nano-porosity in the films.
Highlights
Conductive transition metal nitride (TMN) films find many applications in nano-electronics
We demonstrated that the application of an external RF substrate bias during the H2 plasma exposure and an increase in the timeaveraged substrate potential (|Vbias|) from 0 to 130 V resulted in a major decrease in electrical resistivity from 0.9 to 3.3 × 10–3 Ωcm [14]
The decrease in ρe was found to be correlated with a major increase in the fraction of Hf(III) oxidation state from 0.65 ± 0.02 to 0.82 ± 0.02 [13, 14]. These results demonstrated that the impingement of energetic ions during the film growth can significantly improve the chemical and associated electrical properties of H fNx thin films prepared by atomic layer deposition (ALD)
Summary
Conductive transition metal nitride (TMN) films find many applications in nano-electronics. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) studies were conducted using a JEOL ARM 200F operated at 200 kV in order to analyze: (1) the lateral grain sizes of thin HfNx films (t ≤ 10 nm), defined by the low atomic density grain boundary regions in the top-view images and (2) the microstructure and the nano-porosity of thick HfNx films (t > 30 nm), obtained from the crosssectional samples. These cross-sectional samples were prepared using a Focused Ion Beam (FIB), following a standard lift-out sample preparation procedure. In case of the H2 plasma sample, only EBID Pt/C and IBID Pt was used, as can be recognized from the TEM images below
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