Effects of Ar Ion Bombardment on a Formation of c-BN in IBED

Abstract

Cubic BN films were deposited on Si substrates by ion beam enhanced deposition (IBED) method, in which boron films were deposited at 2000Å/h by ion beam sputtering of a boron target, and an ion beam of argon and nitrogen was bombarded concurrently onto the growing film at an ion energy of 500eV and a current density of 100μA/cm². The effects of argon ion bombardment on the formation of c-BN were investigated by depositing BN films under several flow rate ratios of Ar to N₂ gases fed into the bombarding ion source. Infrared absorption spectra of the films changed with increasing Ar vol% from those of only sp² (region I: Ar 0-50vol%) to those of sp² and sp³ (region II: Ar 50-75vol%), and finally to those of only sp² again (region III: Ar 75-100vol%). Almost single phase film of c-BN was obtained at an Ar vol% of 75. XPS analyses showed that the nitrogen content in the BN film satisfied the stoichiometry of BN in regions I and II, but decreased in region III. Compressive stress in BN films was estimated by bending beam method. With increasing Ar vol%, compressive stress increased remarkably in region I and saturated at a high value of about -400kgf/mm² in regions II and III. These results show that both nitrogen and argon ion bombardments are necessary for the formation of c-BN, but their roles are different. Nitrogen should be supplied as active ions to form stoichiometric BN, while argon should be supplied with sufficient kinetic energy to make high temperature and high pressure state in atomic-scale by a thermal spike effect.