Preferred orientation and film structure of TaN films deposited by reactive magnetron sputtering

Abstract

The structural evolution of tantalum nitride (TaN) films deposited by reactive rf magnetron sputtering were investigated in detail by using transmission electron microscopy (TEM) and x-ray diffractometry (XRD) for a wide range of thickness from 2 nm to 2 μm under various N2/Ar flow ratios from 0 to 20 vol % on both amorphous SiO2 (a-SiO2) and randomly oriented polycrystalline fcc TaN (poly-fcc-TaN) substrates. Although the films had various crystalline structures [including tetragonal Ta, bcc Ta(N), and fcc TaN] of different preferred orientation (PO) and had amorphous phases depending on deposition conditions, the formation mechanism of these structures was systematically explained by mapping them on 2D graphs of film thickness vs N2/Ar flow ratio. The texture map of films deposited on a-SiO2 substrates reflected both nucleation and growth stages, whereas that of films deposited on poly-fcc-TaN substrates reflected mainly the growth stage. Comparison of these two maps allowed the nucleation and growth processes to be separately discussed. For films deposited at 4 vol % N2/Ar ratio on a-SiO2 substrates, an amorphous phase initially appeared when the film thickness was 1.8–3.5 nm. When the film thickness was about 7 nm, nucleation occurred to form fcc TaN without any PO. When the thickness was about 100 nm, (111) PO appeared. Finally, when the thickness exceeded 200 nm, (200) PO dominated the film. Cross-sectional TEM micrographs revealed that evolutionary selection growth occurred when the film was 200-nm-thick to cause the PO change. (111) PO was preferred at relatively low (2–3 vol %) and high (⩾10 vol %) N2/Ar ratios, whereas (200) was preferred at medium N2/Ar ratio (4–7 vol %).