Journal article
Low Temperature Chemical Vapor Deposition of Hafnium Nitride−Boron Nitride Nanocomposite Films
Chemistry of materials, Vol.21(23), pp.5601-5606
12/08/2009
DOI: 10.1021/cm901774v
Abstract
Nanocomposite HfN x -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 HfB y N2.5; 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, HfN x 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 HfN x -BN films are smoother and have a denser microstructure. The thermal activation energy for growth of HfN x /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(BH4)4 precursor reacts with ammonia on the growth surface to generate species with Hf−N and B−N bonds, which subsequently lose H2 and BH y 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.
Details
- Title: Subtitle
- Low Temperature Chemical Vapor Deposition of Hafnium Nitride−Boron Nitride Nanocomposite Films
- Creators
- Navneet KumarWontae NohScott R DalyGregory S GirolamiJohn R Abelson
- Resource Type
- Journal article
- Publication Details
- Chemistry of materials, Vol.21(23), pp.5601-5606
- Publisher
- American Chemical Society
- DOI
- 10.1021/cm901774v
- ISSN
- 0897-4756
- eISSN
- 1520-5002
- Language
- English
- Date published
- 12/08/2009
- Academic Unit
- Chemistry
- Record Identifier
- 9983985933302771
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