Oxygen gettering properties of boron film produced by diborane dc glow discharge

Abstract

Boron film coated on plasma facing walls has been utilized to reduce the oxygen impurity level by the gettering action. The boron film is also useful to reduce the hydrogen recycling. In this study, the boronization was conducted by a dc glow discharge with a mixture gas of diborane and helium both for a graphite and a stainless steel (SS) liners. After the boronization, the oxygen glow discharge was carried out to evaluate the gettered oxygen amount. The state of the oxygen in the surface was also examined. The gettered oxygen amount in the case of the graphite liner was about twice larger than that in the case of the SS liner. The oxygen was trapped in the depth range from the top surface to 100 nm or from the top surface to 20–30 nm in the case of graphite or SS, respectively. The oxygen was observed to be chemically bonded with the boron. After the oxygen discharge, the helium discharge was conducted to recover the oxygen gettering ability. After the helium discharge, the oxygen discharge was again carried out. The gettered oxygen amount in the case of graphite was comparable with that in the case of SS.