Low temperature ZrB 2 remote plasma enhanced chemical vapor deposition

Abstract

Deposition of zirconium diboride films on Zircaloy-4 substrates at 733 K over 20 cm is carried out by remote plasma enhanced chemical vapor deposition (RPECVD). Different post-discharge compositions (Ar–H 2, Ar–H 2–BCl 3 and Ar–BCl 3) are tested in several process configurations. Experiments performed by thermal CVD and RPECVD with Ar–H 2 post-discharge show that the deposition of ZrB 2 films on oxidized Zircaloy-4 is impossible at temperature lower than 853 K. Ar–H 2–BCl 3 post-discharges do not give to adherent films on oxidized Zircaloy-4 at a temperature lower than 753K. It is shown that ZrB 2 thin films can be synthesized by using flowing Ar–BCl 3 microwave post-discharges. Chlorine must etch the zirconia protective layer before zirconium diboride is synthesized. Therefore, the control of thickness of this zirconia layer by a previous oxidation treatment gives homogeneous deposition. The structure of the films has been determined to be nanograins of ZrB 2 dispersed in an amorphous solid solution of boron and zirconium oxides. The origin of the boron species incorporated in the ZrB 2 films is attributed to the eching of the quartz tube by chlorine.