Influence of Substrate Biasing on (Ba,Sr)TiO₃ Films Prepared by Electron Cyclotron Resonance Plasma Sputtering

Abstract

(Ba,Sr)TiO3 (BST) films were deposited by electron cyclotron resonance (ECR) plasma sputtering with mirror confinement. DC bias voltage was applied to Pt/Ti/SiO2/Si substrates during deposition to vary the intensity of bombardment of energetic ions and to modify film properties. BST films deposited on the substrates at floating potential (approximately +20 V) were found to be amorphous, while films deposited on +40 V-biased substrates were crystalline in spite of a low substrate temperature below 648 K. In addition, atomic diffusion, which causes deterioration in the electrical properties of the films, was hardly observed in the crystallized films deposited with +40 V bias perhaps due to the low substrate temperature. Plasma diagnoses revealed that application of a positive bias to the substrate reduced the energy of ion bombardment and increased the density of excited neutral particles, which was assumed to result in the promotion of chemical reactions during deposition and the crystallization of BST films at a low temperature.

Energy Distribution of Ions Incident onto a Dc-Biased Substrate in Electron Cyclotron Resonance Sputtering Plasma for SrTiO3Thin Film Preparation

“…Indeed, films deposited at V b ¼ À20 V were found to be amorphous from XRD patterns. 4,5) Thus, it is demonstrated that ions with E i > 60 eV (at V b < À20 V) markedly damage and make the deposited film amorphous. On the other hand, the substrate was not heated externally in the film preparation.…”

“…We have applied a mirror confinement electron cyclotron resonance (ECR) plasma sputtering method, which could enhance the crystallization of SrTiO 3 (STO) thin films on low-temperature substrates owing to the capability of obtaining high plasma density and highly excited neutral and/or ionized particles at a low pressure of 1-2 Â 10 À2 Pa. 4) In our previous results, 4,5) it was suggested that the crystallization of thin films was achieved by the suppression of the bombardment energy of ions to the substrate. However, the behavior of ions incident onto the substrate has not been clarified in detail in the form of ion energy distribution (IED), which plays an important role in the crystallization and morphology of thin films.…”