Influence of ultra-low ethylene partial pressure on microstructural and compositional evolution of sputter-deposited Zr-C thin films

Abstract

Zr-C thin films are grown on single-crystalline MgO(001) substrates via ultra-high vacuum dc magnetron sputtering of Zr target in 10 mTorr Ar-C2H4 gas mixtures with ethylene partial pressures (p C 2 H 4) between 2 × 10-7 Torr and 2 × 10-4 Torr at substrate temperature Ts = 923 K and using p C 2 H 4 = 2 × 10-6 Torr at 723 K ≤ Ts ≤ 1123 K. The as-deposited layer microstructure and composition are determined using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. We find that the layers sputter-deposited at Ts = 923 K using the lowest p C 2 H 4 = 2 × 10-7 Torr are polycrystalline, close-packed hexagonal structured Zr:C solid solutions. At higher p C 2 H 4 = 2 × 10-6 Torr and 2 × 10-5 Torr, we obtain films composed of freecarbon (C) and NaCl-structured ZrCx, x  1. The amount of C increases 104% with tenfold increase in p C 2 H 4 from 2 × 10-6 Torr to 2 × 10-5 Torr. At the highest p C 2 H 4 = 2 × 10-4 Torr, the layers are X-ray amorphous with ~ 49 at.% C. Films grown at 723 K ≤ Ts ≤ 1123 K using constant p C 2 H 4 = 2 × 10-6 Torr exhibit qualitatively similar microstructures, irrespective of Ts, composed of dense columnar ZrCx grains surrounded by C and corrugated surfaces. Our results suggest that the compositional and microstructural evolution of Zr-C films during reactive 2 sputter-deposition of Zr is highly sensitive to ethylene partial pressure, with as little as 0.02% of the total pressure sufficient at Ts ≥ 723 K to obtain ZrCx films.