INFLUENCE OF DIBORANE FLOW RATE ON THE STRUCTURE AND STABILITY OF CVDBORON-NITRIDE FILMS

CVD boron nitride films have been deposited at 800 degrees Cdiborane, ammonia, and hydrogen gas mixtures, using different B2H6 flow rates. T he effect of the [B2H6]/[NH3] ratio in the gas mixture on the structur e, composition, and the stability of the layers in humid atmospheres h as 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 amo rphous boron nitride films are deposited at deposition rates four time s higher (160 nm min(-1)). The partially turbostratic boron nitride fi lms, deposited at r I 0.25, are unstable in humid atmospheres (80% moi sture). The evolution of the unstable films was followed by infrared s pectroscopy. It is observed that the turbostratic component in the fil m is rapidly attacked by the water molecules present in the atmosphere , giving rise finally to boron enrichment in the films. After this sta ge, the attack rate becomes slower, due to the higher stability of the amorphous component in the films.