Atomic insights into the oxygen incorporation in atomic layer deposited conductive nitrides and its mitigation by energetic ions

• Published in: Nanoscale Vol. 13; no. 22; pp. 192 - 199
• Main Authors: Karwal, Saurabh, Karasulu, Bora, Knoops, Harm C.M, Vandalon, Vincent, Kessels, Wilhelmus M.M, Creatore, Mariadriana
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.06.2021
• Subjects: Atomic layer epitaxy; Bonding; First principles; Impingement; Impurities; Material properties; Metal nitrides; Oxidation; Plasma; Radio frequency; Redox reactions; Substrates; Transition metals; Valence
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/d0nr08921d

Oxygen is often detected as impurity in metal and metal nitride films prepared by atomic layer deposition (ALD) and its presence has profound and adverse effects on the material properties. In this work, we present the case study of HfN x films prepared by plasma-assisted ALD by alternating exposures of CpHf(NMe 2 ) 3 and H 2 plasma. First, we identify the primary source of O contamination in the film. Specifically, we find that the extent of O incorporation in HfN x films is determined by the flux of background H 2 O/O 2 residual gases reaching the HfN x surface during the ALD process and leads to the formation of Hf-O bonds. Then, we report on the decrease in the concentration of Hf-O bonds in the film upon application of an external radiofrequency (rf) substrate bias during the H 2 plasma step. The experimental work is accompanied by first principles calculations to gain insights into the O incorporation and its mitigation upon the impingement of energetic ions on the surface. Specifically, we find that the dissociative binding of H 2 O on a bare HfN surface is highly favored, resulting in surface Hf-OH groups and concomitant increase in the oxidation state of Hf. We also show that energetic cations (H + , H 2 + and H 3 + ) lead to the dissociation of surface Hf-OH bonds, H 2 O formation, and its subsequent desorption from the surface. The latter is followed by reduction of the Hf oxidation state, presumably by H&z.rad; radicals. The atomic-level understanding obtained in this work on O incorporation and its abstraction are expected to be crucial to prevent O impurities in the HfN x films and contribute to the fabrication of other technologically relevant low resistivity ALD-grown transition metal nitride films. Oxygen incorporation from the residual H 2 O present in the reactor background is a long-standing issue in transition metal nitride films. Energetic ions can abstract H 2 O from surface and later radicals reduce the metal atom to +3 oxidation state.