Inhomogeneous strain states in sputter deposited tungsten thin films

Abstract

The results of an x-ray diffraction study of dc-magnetron sputtered tungsten thin films are reported. It is shown that the phase transformation from the β to α W can cause multilayered single-phase films where the layers have very different stress states even if the films are in the 500 nm thickness range.

Sputtering Targets and Thin Films for Integrated Circuits

“…At low sputtering pressure of 12 mTorr Ar ( Figure 5.29(a)), film was dense and without any columnar grains. Similar results were reported in relatively thin sputtered W films ( Figure 5.30) (p. 320) [81]. Spotted rings shown in the inset indicate presence of bcc α-W grains.…”

“…At this sputtering pressure, W film predominantly showed coarse bcc α-W grains and only few β-W grains were noticed. XRD patterns for W films of various thicknesses [81]. Similar results were reported in relatively thin sputtered W films ( Figure 5.30) (p. 320) [81].…”

“…Figure 5.27 shows XRD results from a number of sputtered W films of varying thickness values [81]. W film may have metastable A15 cubic β-W phase or equilibrium bcc α-W phase or a mixture of both phases.…”

Phase transformation of single crystal β-tungsten nanorods at elevated temperatures

“…1 shifted from the equilibrium position at 2h = 35.525-towards a smaller 2h angle at¨35.26-. This type of shift indicates the existence of a larger atomic plane spacing, and has been explained to originate from a compressive stress in the film [11][12][13]. The location of the h(200) peak for the as deposited W film (¨35.26-) corresponds to a lattice spacing of¨5.09 Å .…”

Dielectric barriers, pore sealing, and metallization

“…In addition, Ta films show peak shifts towards to smaller angles from the equilibrium position of a-Ta(110) at 2h = 38.47-. This kind of peak shift is usually due to the intrinsic compressive stress originating from the so-called ''atomic peening effect'' during sputter deposition [16]. Atomic peening occurs when the energetic sputter gas or depositing atoms penetrate into lattice planes, which causes the effective lattice spacing to increase and gives a smaller 2h angle in XRD.…”