Tailoring of structure formation and phase composition in reactively sputtered zirconium oxide films using nitrogen as an additional reactive gas

Abstract

The structure of ZrO 2 films has been controlled during reactive sputtering in an argon/oxygen atmosphere by adding an amount of nitrogen gas to the process. Depending on the deposition conditions, amorphous, cubic, or monoclinic films have been obtained without any additional substrate heating. The resulting film structure is explained in terms of the control of fast negative oxygen ions generated at the target surface and accelerated toward the growing film. Furthermore, the nitrogen addition leads to a pronounced stabilization of the plasma discharge and fewer arcing events, while the incorporation of nitrogen atoms in the growing film is very small.

On the phase formation of sputtered hafnium oxide and oxynitride films

“…2 increases when the O 2 partial pressure is increased signifies an increase in the flux of O − species toward the growing film upon moving from a nonoxidized to an oxidized target. This, in turn, confirms the suggestion by Severin et al, 22 i.e., the operation in the transition zone allows for a suppression of the O − bombardment as compared to the operation in the oxidic sputtering mode. It is, therefore, evident that our experimental strategy that enables operation at different target working points ͑via the stabilization of the transition zone and variation in the O 2 partial pressure͒ and target voltages ͑via the implementation of HPPMS͒ facilitates growth of films at different conditions of energetic bombardment with respect to the flux the energy of the O − species.…”

“…In all deposition sets the p Ar / p O 2 ratio in the sputtering atmosphere was varied in order to grow films at different target working points ͑i.e., target coverage͒ of the stable transition zone ranging from a metallic to a fully oxidized target aiming to tune the flux of O − ions toward the film, as well as the atomic composition of the films. 22 The plasma chemistry and energetics at the various deposition conditions were studied by means of energyresolved mass spectrometry. A Pfeiffer Vacuum PPM 422 mass-energy analyzer equipped with a quadrupole mass spectrometer with an attached energy filter was employed to perform mass-to-charge measurements at constant energy, while ion energy distribution functions ͑IEDFs͒ were recorded at constant mass-to-charge ratios.…”

“…These films were O deficient ͑with respect to the nominal ZrO 2 stoichiometry͒ and contained up to 10 at. % N. 22 It was also reported 24 that the presence of N 2 in the sputtering atmosphere enabled the stabilization of the transition zone between the metallic and the compound ͑oxidic͒ sputtering mode. It is known 25 that during the reactive deposition of metal oxides the transition sputtering zone is commonly unstable and it is, in general, characterized by a lower degree of oxidation ͑coverage͒ of the target surface, as compared to the compound sputtering mode.…”

“…Ngaruiya et al 29 postulated and Mráz and Schneider 27 showed that these ions have implications for the structure evolution of transition metal oxides. Severin et al 22 suggested that the lower target coverage in the transition zone allows for a suppression of the O − flux toward the growing film and speculated that the latter is the reason for the growth of films with the c-ZrO 2 crystal structure. However, no experimental evi-dence for this suggestion has been presented so far.…”

“…21͒ could stabilize the cubic phase at room temperature, while the incorporation of Si facilitated the room temperature deposition of t-HfO 2 . 6,10 Recently, Severin et al 22 reported the growth of cubic ZrO 2 films 23 ͑ZrO 2 is isostructural with HfO 2 ͒ by reactive direct current magnetron sputtering ͑dcMS͒ from a Zr target in an Ar-O 2 -N 2 gas atmosphere. These films were O deficient ͑with respect to the nominal ZrO 2 stoichiometry͒ and contained up to 10 at.…”