Low temperature chemical vapor deposition of hafnium nitride - Boron nitride nanocomposite films

Navneet Kumar, Wontae Noh, Scott R. Daly, Gregory S. Girolami, John R. Abelson

Research output: Contribution to journalArticle

Abstract

Nanocomposite HfNx-BN thin films are deposited by chemical vapor deposition at substrate temperatures of 350 - 800 °C using the single-source precursor hafnium borohydride, Hf(BH4)4,in combination with ammonia, NH3. Below 350 °C, the product is metallic HfB2 with essentially no incorporation of nitrogen. However, the presence of ammonia decreases the HfB2 deposition rate considerably; this growth suppression effect is attributed to blocking of reactive surface sites by adsorbed ammonia molecules. At substrate temperatures above 350 °C, film deposition occurs; however, the HfB2 phase is completely absent. The resulting film stoichiometry is HfByN 2.5; although the value of y is difficult to determine precisely, it is about unity. X-ray photoelectron spectroscopy (XPS) analysis detects Hf - N and B - N bonds but no Hf - B bonds; thus the films are nanocomposites that consist of a mixture of hafnium nitride, HfNx with x > 1 and boron nitride. The deposited films are X-ray amorphous and Raman inactive. Compared to HfB2 films grown under similar precursor pressure and substrate temperature, the HfNx-BN films are smoother and have a denser microstructure. The thermal activation energy for growth of HfNx/BN in the reaction-rate limted regime is ∼0.72 eV (70 kJ/mol), a value 0.3 eV larger than that for the growth of HfB2 from Hf(BH4) 4 alone. This difference in activation energy indicates that growth is governed by a different rate-limiting step; we interpret that the Hf(BH 4)4 precursor reacts with ammonia on the growth surface to generate species with Hf - N and B - N bonds, which subsequently lose H 2 and BHy to generate the nanocomposite. The HfN x/BN films have resistivities ∼ 10 ω • cm. Optical transmission and spectroscopic ellipsometry measurements indicate a bandgap of ∼ 2.6 eV.

Original languageEnglish (US)
Pages (from-to)5601-5606
Number of pages6
JournalChemistry of Materials
Volume21
Issue number23
DOIs
StatePublished - Dec 8 2009

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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