Improvement of Surface Crystalline Quality of an Epitaxial (100)ZrN Film as a Bottom Electrode Diffusion Barrier for Ferroelectric Capacitors

Abstract

We fabricated the double epitaxial layers of Ir on barrier metal ZrN for Pb(ZrxTi1−x)O3 (PZT), using reactive sputtering. In order to remove the surface oxide layer of the ZrN film prior to depositing the Ir film, we used a new treatment method, in which the ZrN film is dipped into a 0.5% buffered HF solution for less than 30 seconds and then immediately dipped into a hydrazine (N2H4) monohydrate solution for 60 seconds. Also, in order to suppress the generation of twin boundaries and to improve crystalline quality, the ZrN film is deposited using a two-step method, which consists of an initial high temperature deposition step at 850s°C followed by a lower temperature step at 600°C. On the ZrN film prepared by these methods, we can obtain a mainly (110)-oriented epitaxial Ir film.

Epitaxial Growth of (001)ZrN Thin Films on (001)Si by Low Temperature Process

“…Although the obtained FWHM value (3.0 ) is somewhat larger than that of a 200nm-thick epitaxial ZrN film grown on a (001)MgO substrate at 450 C by pulsed laser deposition, 18) the value is comparable to that of a 100-nm-thick epitaxial ZrN film grown on a (001)Si at 850 C by rf reactive sputtering. 4) It is therefore expected that these ZrN films may be grown epitaxially.…”

“…ZrN films have attracted much attention for various applications such as diffusion barrier material used in Cu metallization technology for the production of Si-LSI devices, and the hard coating material of cutting tools, because of their high hardness, high thermal and chemical stabilities and low resistivity. [1][2][3] For example, Horita et al 4) recently reported the following. For an integrated ferroelectric random access memory (FeRAM) with a stacked capacitor cell structure, a direct electrical contact must be formed from the source of the transistor to the bottom of the capacitor via a conducting barrier layer which prevents reaction between the ferroelectric film and the Si substrate.…”

“…However, in order to obtain the epitaxial ZrN film, it has been generally recognized that fairly high substrate temperatures of approximately 600-900 C are required. [4][5][6] In addition, Barnett et al 6) reported that cracks were observed in the ZrN film prepared at a high substrate temperature, because the lattice misfit between ZrN and Si is 16% and the thermal expansion coefficient (7:24 Â 10 À6 / C) of ZrN is much larger than that (2:33 Â 10 À6 / C) of Si. Thus, it seems that a high substrate temperature is not suitable for the preparation of epitaxial ZrN films applicable to the diffusion barrier.…”