Interface investigations by infrared spectroscopy and X-ray reflectivity measurements of cubic boron nitride thin films

Abstract

Cubic boron nitride thin films were deposited by unbalanced r.f. magnetron sputtering of a hexagonal boron nitride target in a pure argon discharge in combination with r.f. argon ion bombardment. At a flux ratio of the argon ions relative to the film forming boron and nitrogen atoms of 20, and an argon ion energy of 87 eV, the total content of sp3-bonds of a 300 nm film amounts to 92.8%, according to infrared analysis. This film has a hexagonal interface between the silicon substrate and the cubic top layer which is estimated to be 15.6 nm on the basis of infrared spectroscopy as well as X-ray reflectivity. From the infrared investigations of the film thickness dependence it can be concluded that 72% of the sp2-bonds in the 300 nm c-BN film are formed in the hexagonal interface region, and only 18% between the cubic crystallites in the top layer. Consequently, the content of the cubic phase in the top layer amounts to 98.6%, which is in agreement with the density of 3.502 g/cm3 as determined by X-ray reflectivity measurements.