C-BN thin film formation in a hybrid rf-PLD technique

A hybrid radio frequency-pulsed laser deposition (r.f.-PLD) technique was used to deposit BN thin films on Si(100) and Si(111) substrates. Hexagonal boron nitride targets were ablated with excimer laser radiation (lambda = 248 nm, tau = 25 ns) in an N-2/Ar processing gas atmosphere. Additionally a radio frequency bias (v=13.56 Mhz, P=15-200 W) was capacitively coupled to the substrate, yielding an r.f glow discharge in the processing gas with formation of a d.c. bias voltage up to - 1500 V, resulting in bombardment of the substrate with processing gas ions. Langmuir single probe measurements revealed typical ion densities on the order of 10(15) m(-3). The c-BN content of the films as determined by FTIR-spectroscopy was up to 60% and depends strongly on the ion to-atom arrival ratio and therefore on the laser pulse repetition rate and fluence, as well as on the argon-to-nitrogen ratio in the processing gas atmosphere. Raman spectroscopy was used to characterize the crystallinity of the grown films. Most films adhered poorly to the substrate, indicating the presence of high internal stresses. The formation of the c-BN phase is discussed in the light of the currently available models for c-BN deposition. (C) 1997 Elsevier Science S.A.