Influence of diborane flow rate on the structure and stability of CVD boron nitride films

CVD boron nitride films have been deposited at 800 degrees Cdiborane, ammonia, and hydrogen gas mixtures, using different B2H6 flow rates. The effect of the [B2H6]/[NH3] ratio in the gas mixture on the structure, composition, and the stability of the layers in humid atmospheres has been studied. For low [B2H6]/[NH3] ratios (r less than or equal to 0.25), the deposition rate is low and some crystalline ordering in the deposit was detected. However, when ratios >0.25 are used, stable amorphous boron nitride films are deposited at deposition rates four times higher (160 nm min(-1)). The partially turbostratic boron nitride films, deposited at r I 0.25, are unstable in humid atmospheres (80% moisture). The evolution of the unstable films was followed by infrared spectroscopy. It is observed that the turbostratic component in the film is rapidly attacked by the water molecules present in the atmosphere, giving rise finally to boron enrichment in the films. After this stage, the attack rate becomes slower, due to the higher stability of the amorphous component in the films.