Evidence of heteroepitaxial growth of copper on beta-tantalum

Abstract

Crystallographic orientations between thin-sputtered Cu film and β-Ta adhesion layer have been studied using high resolution electron microscopy and electron diffraction. Tetragonal β-Ta deposited on SiO2 has a strong texture with its closest packed plane (002) parallel to the film surface. On (002) β-Ta, the growth of (111) Cu is preferred. Even though more than 100 β-Ta grains are found under a single Cu grain, the Ta grains under a Cu grain have long range in-plane texture with [330] direction aligned parallel to the [220] direction of Cu. This orientational coincidence is explained by the heteroepitaxial relationship between the hexagonal close-packed atomic array in Cu (111) plane and the pseudohexagonal configuration of β-Ta atoms in (002) plane with a misfit strain of 7.6%.

X-ray characterization of oriented β-tantalum films

“…The thicknesses of the Ta films were estimated by XRR. While the density of the 70 nm Ta film was similar to the bulk density of Ta metal 3 ), the density values for 10 and 30 nm were lower than those reported in literature. This could be due to the increased presence of voids in the 10 and 30 nm films.…”

“…The results for the thickness and density of Ta are tabulated in Table 1. The thickness and density of this interface layer was found to be 1.9F0.2 nm and 10.5F0.5 g/ cm 3 , respectively. Prior to XPS analysis, the adventitious carbon and the native oxide layer on the surface of metal films were removed by Ar ion sputtering to expose the underlying clean surface.…”

“…The texture and grain structure of Cu films has been shown to affect the electromigration lifetime of Cu interconnects [2] with that of (111) oriented Cu about four times longer than that of (200) oriented Cu [2]. It has been shown that the growth of Cu(111) is preferred on hTa films oriented along (002) crystallographic planes [3].…”

Electrode and chemical reactions during electrodeposition of tantalum products in CsCl melt

“…Tantalum of this modification could be apparently prepared only in the presence on an electric field: by direct current magnetron sputtering [11] or using the electrodeposition from molten salts [12,13]. The structure of ␤-Ta was described in detail in our publication [14]:…”

The self-hosting structure of β-Ta

“…High temperature ($1000 K) and the presence of an electrical ®eld under reducing conditions allows the formation of -Ta by electrolytic crystalization on a cathode. Thin ®lms (up to 30 nm) of this phase used as an underlying layer for Cu metallization can also be obtained by dirrect current (d.c.) magnetron sputtering (Westwood, 1970;Kwon et al, 1997;Lee et al, 1999). -Ta was ®rst obtained by d.c. magnetron sputtering (Mills, 1966;Read & Altman, 1965) and later by electrodeposition from a molten uoride bath at 1073 K (Moseley & Seabrook, 1973).…”