Low Temperature Chemical Vapor Deposition of Hafnium Nitride−Boron Nitride Nanocomposite Films

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• 作者：Navneet Kumar ; Wontae Noh ; Scott R. Daly ; Gregory S. Girolami ; John R. Abelson
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：December 8, 2009
• 年：2009
• 卷：21
• 期：23
• 页码：5601-5606
• 全文大小：796K
• 年卷期：v.21,no.23(December 8, 2009)
• ISSN：1520-5002

文摘

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_yN_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, 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.