Real-time control of AlN incorporation in epitaxial Hf 1 − xAl xN using high-flux, low-energy (10–40 eV) ion bombardment during reactive magnetron sputter deposition from a Hf 0.7Al 0.3 alloy target

Abstract

The AlN incorporation probability in single crystal Hf 1 − x Al x N(0 0 1) layers is controllably adjusted between ∼0% and 100% by varying the ion energy ( E i) incident at the growing film over a narrow range, 10–40 eV. The layers are grown on MgO(0 0 1) at 450 °C using ultrahigh vacuum magnetically unbalanced reactive magnetron sputtering from a Hf 0.7Al 0.3 alloy target in a 5%-N 2/Ar atmosphere at a total pressure of 20 mTorr (2.67 Pa). The ion to metal flux ratio incident at the growing film is constant at 8. Epitaxial film compositions vary from x = 0.30 with E i = 10 eV, to 0.27 with E i = 20 eV, 0.17 with E i = 30 eV, and ⩽0.002 with E i ⩾ 40 eV. Thus, the AlN incorporation probability decreases by greater than two orders of magnitude. This extraordinary range in real-time manipulation of film chemistry during deposition is due to the efficient resputtering of deposited Al atoms (27 amu) by Ar + ions (40 amu) neutralized and backscattered from heavy Hf atoms (178.5 amu) in the film. This provides a new reaction pathway to synthesize, at high deposition rates, compositionally complex heterostructures, multilayers, and superlattices with abrupt interfaces from a single alloy target by controllably switching E i. For multilayer and superlattice structures, the choice of E i value determines the layer composition and the switching periods control the individual layer thickness.