Comparative Study of Tungsten Films Grown By Atomic Layer Deposition with Newly Synthesized Metalorganic and Halide Precursor
Authors: Sun Sangkyu , Lee Yujin , Seo Seunggi , Nam Taewook , Lee Hyunho , Yoon Hwi , Lee Sanghun , Kim Hyungjun 
Published: July 2021

For continuous scaling down of semiconductor devices, metal deposition has been developed as a plug filling process for interlayer connecting. Tungsten (W) has a wide range of industrial applications since it has a relatively good electrical conductivity and a high electromigration durability due to its high melting point of 3380 °C. [1] Among various techniques, atomic layer deposition (ALD) has been investigated to find the most feasible way to grow uniform, dense, conformal, and conductive W thin film to thicknesses of a few nanometers in more complicated structures, since its growth mechanism is entirely based on self-limited surface reaction. [2]

To date, several W precursors have been employed. Among them, the halide precursors have been widely used as precursors for metal deposition since it can fabricate a high-purity film compared to metal organic precursors. Tungsten hexafluoride (WF6) is the most widely reported halide-based precursor to date due to its simple structure and high reactivity. [3] However, the toxic by-product (HF) can provoke the interfacial Si consumptions and corrosion of devices. In this respect, in halide-based precursors, fluorine (F)-free tungsten precursors have recently received attention, but study on development of F-free tungsten precursor is still in its infancy. In contrast, the organic precursor is free from the formation of corrosive by-product. However, the carbon species derived from the organic ligand of the precursor can deteriorate film properties and device performance. [4] For this reason, studies for pure tungsten metal deposition with organic precursors have not been reported. Eventually, since the halide and organic precursors have their own strengths and weaknesses, there has been considerable controversy over the choice of precursors between the two groups.
In this work, we fundamentally investigated the growth characteristics, chemical composition, crystallinity of W films on SiO2 substrate using two newly synthesized precursors (tungsten pentachloride (WCl5) and ethylcyclopentadienyltungsten(Ⅴ) tricarbonyl hydride (HEtCpW(CO)3)). Ar/H2 plasma as the reactant was generated between the showerhead and the substrate during the reactant exposure by capacitively coupled plasma (CCP) with a radiofrequency (RF) of 13.56 MHz at 200 W. We used Commercial showerhead type ALD chamber which has 8-inch wafer capacity, and the precursors were contained in individual stainless-steel bubblers and evaporated at 135 and 55 °C, respectively, to obtain a sufficient vapor pressure. The delivery lines were heated to a temperature approximately 10–15 °C higher than that of the bubbler to prevent the condensation of the precursor. The microstructure of W film were analyzed using Grazing-incidence X-ray diffraction (GIXRD), the film density of W film was analyzed via X-ray reflectivity (XRR), and the resistivity was electrically measured via Four point probe (FPP) with semiconductor analyzer. Growth characteristics and film properties were significantly affected by ligands of precursors. In addition, the electrical properties, including resistivity depending on the ALD cycles, and conformality at trench were evaluated for potential application. These results provide fundamental and useful information, with respect to the selection of the suitable precursor, for practical implementation of device fabrication.

References

[1] M. Yang, A. A.I. Aarnink, J.Schmitz, and A.Y. Kovalgin, “Low-resistivity α-phase tungsten films grown by hot-wire assisted atomic layer deposition in high-aspect-ratio structures,” Thin Solid Films 646, (2018) pp. 199–208
[2] Leskelä, M. & Ritala, M. “Atomic layer deposition (ALD): From precursors to thin film structures,” Thin Solid Films 409 (2002) pp.138–146
[3] Elam, J. W., Nelson, C. E., Grubbs, R. K. & George, S. M. “Kinetics of the WF6 and Si2H6 surface reactions during tungsten atomic layer deposition,” Surf. Sci. 479, (2001) pp. 121–135
[4] Hirose, F., Watanabe, T., Shibata, A., Momiyama, K., Suzuki, T., Miya, H., “Tungsten deposition by metal-chloride-reduction chemical vapor deposition,” Electrochem. Solid-State Lett. 14, (2011) pp. 251–253

Figure 1